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Hindawi Publishing CorporationJournal of ChemistryVolume 2013 Article ID 781595 10 pageshttpdxdoiorg1011552013781595
Research ArticleSize Control of Iron Oxide Nanoparticles UsingReverse Microemulsion Method Morphology Reductionand Catalytic Activity in CO Hydrogenation
Mohammad Reza Housaindokht and Ali Nakhaei Pour
Department of Chemistry Ferdowsi University of Mashhad PO Box 9177948974 Mashhad Iran
Correspondence should be addressed to Ali Nakhaei Pour nakhaeipourayahoocom
Received 8 May 2013 Revised 15 August 2013 Accepted 6 September 2013
Academic Editor Mohamed Afzal Pasha
Copyright copy 2013 M R Housaindokht and A Nakhaei Pour This is an open access article distributed under the CreativeCommons Attribution License which permits unrestricted use distribution and reproduction in any medium provided theoriginal work is properly cited
Iron oxide nanoparticles were prepared by microemulsion method and evaluated in Fischer-Tropsch synthesis The precipitationprocess was performed in a single-phase microemulsion operating region Different HLB values of surfactant were prepared bymixing of sodium dodecyl sulfate (SDS) and Triton X-100 Transmission electron microscopy (TEM) surface area pore volumeaverage pore diameter pore size distribution and XRD patterns were used to analyze size distribution shape and structureof precipitated hematite nanoparticles Furthermore temperature programmed reduction (TPR) and catalytic activity in COhydrogenation were implemented to assess the performance of the samples It was found that methane and CO
2selectivity and
also the syngas conversion increased as the HLB value of surfactant decreased In addition the selectivity to heavy hydrocarbonsand chain growth probability (120572) decreased by decreasing the catalyst crystal size
1 Introduction
Nanoscale materials exhibited novel properties includingquantum size effect on photochemistry nonlinear opticalproperties of semiconductor and new catalytic properties ofmetallic nanoparticles [1] Therefore synthesis of nanopar-ticles is of a great interest field during the past few yearsAs compared to their bulk counterparts nanoparticles oftenhave superior or even new catalytic properties following fromtheir nanometer size [2] Hence the size of the nanoparticlesis pivotal in determining the catalytic properties and under-standing how size may affect the catalytic properties remainsa central goal in nanocatalysis research [3]
Many methods have been reported for preparation ofnanoparticles [2 3] Preparation of metallic nanoparticlesusing microemulsion has been well established [4ndash7] Dueto the specific structure of the microemulsion system it wasexpected as a suitable environment for producing small metalnanoparticles with narrow size distribution A microemul-sion is defined as a system of water oil and amphiphile(surfactant) [4ndash7] In some respects microemulsions can
be considered as small-scale versions of emulsions that isdroplet type dispersions either of oil-in-water (ow) or ofwater-in-oil (wo) with a size range in the order of 5minus50 nmin drop radius In the hydrophilic interior of these droplets acertain amount of water-solublematerial can be dissolved forexample transitionmetal salts that then serve as precursor(s)for the final metal particles As for simple aqueous systemsmicroemulsion formation is dependent on surfactant typeand structure A surfactant substance reduces the surfacetension of a liquid in which it is dissolved [4ndash7] Hydrophilic-lipophilic balance (HLB) is an important concept whichrelates the molecular structure to the interfacial packingand film curvature It is generally expressed as an empiricalequation based on the relative proportions of hydrophobicand hydrophilic groups within the molecule If the structureof the surfactantmolecule is designed precisely the surfactantfilmmay spontaneously adopt a natural radius of curvature ofthe interface which has a direction and magnitude withoutany need for an energy input [4ndash7]
Recent studies revealed structure sensitive properties ofmany catalytic reactions like CO hydrogenation process in
2 Journal of Chemistry
Fischer-Tropsch synthesis (FTS) [8ndash12] Murzin reportedthat FTS reactions on the supported cobalt based catalystsshow many sensitivities to the catalyst particle size [13 14]Moreover many new results showed that nanosized ironparticles play an essential role to achieve high FTS activity [8ndash12] Iron-based catalysts are preferred for utilizing synthesisgas derived from coal or biomass because of the excellentactivity for the water-gas-shift reaction which allows usinga synthesis gas with a low H
2CO ratio directly without an
upstream shift-step [15 16] In our previous works we triedto show structure sensitivity of unsupported iron catalysts[10 11 17]
In this the present work feasibility of iron nanoparticleformation in the microemulsion systems with different HLBvalues was investigated Moreover effects of HLB values onthe particle size were investigated Then catalyst character-ization and catalytic FTS reaction are examined at differentparticle sizes
2 Experimental
21 Catalyst Preparation Fe-Cu nanoparticles were preparedby coprecipitation in a water-in-oil microemulsion [11ndash15] The precipitation was performed in the single-phasemicroemulsion operating region For this purpose a watersolution of metal precursor Fe(NO
3)3-9H2O (Fluka puriss
pa ACS 98ndash100) and Cu(NO3)2-4H2O (Fluka purum
pa gt 97) were added to a mixture of an oil phase(Chloroform Aldrich gt99) and mixed surfactants containTriton X-100 and SDS The HLB values of Triton X-100 andSDS are 134 and 40 respectively Besides 1-butanol as acosurfactant was added to system in order to obtain a propermicroemulsion
For preparation of various sizes of hematite nanoparticlesreverse microemulsions were prepared with different HLBvalues through varying the weight ratio of Triton X-100 andSDS For a quaternary system of surfactant (119878 g) oil (119874 g)alcohol (119860 g) and water (119882 g) the following symbols weredefined 120572 represents the mass fraction of oil in water plus oil120572 = 119874(119882 + 119874) 120573 the mass ratio of surfactant in the wholesystem 120573 = 119878(119882 + 119874 + 119878 + 119860) and 120576 the mass fraction ofalcohol in the whole system 120576 = 119860(119882 + 119874 + 119878 + 119860) [4ndash7]In the prepared microemulsion system the parameters are120572 = 062 120573 = 003 and 120576 = 028 After stirring well andstabilizing for 24 h a transparentmixturewas obtainedThenhydrazine was added to reducemetal precursorThe resultingmixture was decanted overnight The solid was recoveredby centrifuging and then washing thoroughly with distilledwater and ethanol for several times Lanthanum promoterwas added by wet impregnation method with La(NO
3)3
precursor on its optimal value after treatment in air asdescribed previously [10ndash12 17]The promoted catalysts weredried at 383K for 16 h and calcined at 723K for 3 h in air Thecatalyst compositions were designated in terms of the atomicratios as 100Fe564Cu2La
22 Catalyst Characterization Elemental analysis was per-formed to determine the composition of the elements in
the bulk of catalysts The surface area was calculated fromthe Brunauer-Emmett-Teller (BET) equation and pore vol-ume average pore diameter and pore size distribution ofthe catalysts were determined by N
2physisorption using a
micromeritics ASAP 2010 automated system A 05 g catalystsample was degassed in the micromeritics ASAP 2010 at100∘C for 1 h and then at 573K for 2 h prior to analysis Theanalysis was done using N
2adsorption at 77K Both the pore
volume and the average pore diameter were calculated byBarrett-Joyner-Hallender (BJH)method from the adsorptionisothermAssuming that the Fe
2O3particles are spherical the
corresponding particle size (119889BET) can be estimated as [18]
119889BET =6
120588119860
(1)
where 120588 is the true density of Fe2O3 that is 524 gcm3 and
119860 is the specific surface area of samplesThe XRD spectrum of the catalysts was collected by an
X-ray diffractometer Philips PW1840 X-ray diffractometerusing monochromatized CuK
120572radiation (40 kV 40mA)
and a step scan mode at a scan rate of 002∘ (2120579) per secondfrom 10ndash80∘ XRD peak identification was recognized bycomparison to the JCPDS database software The averagecrystallite size of samples 119889XRD can be estimated from XRDpatterns by applying full-width half-maximum (FWHM) ofcharacteristic peak (104) Fe
2O3located at 2120579 = 333∘ peak to
Scherrer equation
119889XRD =09120582
FWHMcos 120579 (2)
where 120582 is the X-ray wavelength (15406 A in this study) and120579 is the diffraction angle for the (104) plane
Temperature programmed reduction (TPR) measure-ments of the calcined catalysts were recorded by using aMicromeritics TPD-TPR 2900 system The catalyst samples(50mg) were purged with argon at 473 for 30min and cooledto 323K The samples were heated from 350 to 1100K at arate of 10 Kmin under flow of 51 hydrogen in argon gasmixture The consumption of hydrogen was monitored by athermal conductivity detector (TCD)
The morphology of prepared catalysts was observed witha transmission electron microscope (TEM LEO 912 ABGermany) An appropriate amount of Fe
2O3suspension
directly taken from the reaction solution was dropped ontothe carbon-coated copper grids for TEM observation Theaverage particle size (119889TEM) and particle size distributionwere determined by TEM images considering more than 100particles
23 Catalytic Performance The catalysts were tested in afixed-bed microreactor A detailed description of the exper-imental setup and procedures has been provided elsewhere[15 16] The catalyst samples (30 g catalyst diluted with 12 gquartz 100ndash180 120583m) were activated by a 5 (vv) H
2N2
gas mixture with space velocity of 151 nl sdot hminus1 sdot gFeminus1 at
01MPa by increasing temperature from ambient to 673Kat 5 Kmin then maintained for one hour and subsequently
Journal of Chemistry 3
20 30 40 50 60 70
Inte
nsity
(a)
(b)
(c)
(d)
2120579
012
104
110
113
024
116
018
214
300
Figure 1 X-ray diffraction patterns of the prepared catalysts aftercalcinations ((a) HLB = 139 (b) HLB = 237 (c) HLB = 312 and (d)HLB = 40)
reduced to 543K The pretreatment was followed by thesynthesis gas stream with H
2CO = 1 and space velocity
of 307 nl sdot hminus1 sdot gFeminus1 for 24 h in 01Mpa and 543K After
catalyst pretreatment synthesis gas was feed to the reactorat 563K 17 bar (H
2CO)feed = 1 and a space velocity of
49 nl sdot hminus1 sdot gFeminus1
The products were analyzed by means of three gas chro-matographs a Shimadzu 4C gas chromatograph equippedwith two subsequent connected packed columns Porapak Qand Molecular Sieve 5A and a thermal conductivity detector(TCD) with Ar as carrier gas for hydrogen analyzing AVarian CP 3800 with a chromosorb column and a thermalconductivity detector (TCD) were used for CO CO
2 CH4
and other noncondensable gases A Varian CP 3800 with aPetrocolDH100 fused silica capillary column and a flame ion-ization detector (FID) were used for organic liquid productsso that a complete product distribution could be provided
3 Results and Discussion
31 Catalyst Characterization Nanostructure iron catalystswere characterized by X-ray diffraction (XRD) measurementafter calcinations (Figure 1) As shown in Figure 1 XRDpatterns of samples very close to the ones with cubic hematitestructured Fe
2O3crystal in JCPDS database The character-
istic peaks corresponding to (012) (104) (110) (113) (024)(116) (018) (214) and (300) planes are located at 2120579 = 243333 358 408 496 541 576 641 and 656∘ respectivelyDiffraction data indicates that the presence of lanthanumand copper and also subsequent treatment by dried airdo not affect the hematite crystalline phases in differentcatalyst preparation methods This shows that the formed
Table 1 Average particle size determined by TEM BET and XRDtechniques
HLB dBET (nm) dXRD (nm) dTEM (nm)139 168 154 14237 203 188 17312 221 206 2140 263 248 24
Table 2 Textural properties of prepared catalysts
HLB BET surface area(m2g)
Average pore size(nm)a
Pore volume(cm3g)a
139 682 162 014237 564 196 016312 518 223 01940 435 259 021aThese values were calculated by BJH method from desorption isotherm
hematite structure remains stable during subsequent aqueousimpregnation and thermal treatment It was also shown inFigure 1 that the microemulsion system only modules thephysical properties of reactionmediumwithout changing thereaction paths and arrangements of crystal structure Thecharacteristic peak at 2120579 = 333∘ which corresponds to thehematite 104 plane was used to calculate the average metalparticle size by the Scherrer equation The calculated valuesof 119889XRD of the samples are listed in Table 1
Textural properties and pore size distributions of the freshiron-based catalysts are shown in Table 2 and Figures 2 and 3respectively N
2adsorption-desorption isotherms of catalysts
are presented in Figure 3 As shown in this Figure theprepared catalysts show type IV of Brunauerrsquos classificationisothermswithH
1-type hysteresis loop at the relative pressure
of 1198751198750= 08ndash095 This hysteresis loop is characterized as
hexagonal mesoporous materials with cylindrical channels[19]
The pore size distributions of the catalysts which werecalculated by Barrett-Joyner-Halenda (BJH) method foradsorption step are presented in Figure 3 and Table 2 Sinceall pore size values are fairly close to the dimension ofparticles it deduces that the measured pore size is mainlycaused by the inter particle voids
The TEM photographs for the prepared samples aredemonstrated in Figure 4 and Table 1 and also the particlesize distribution determined by TEM images are shown inFigure 5 The average particle size (119889TEM) and particle sizedistribution were obtained from TEM images by consideringmore than 100 particles As shown in Figures 4 and 5 theaverage range of particle size and particle size distributionincreases as HLB value increases
The particle size of samples which were determined byXRD BET and TEM techniques are summarized in Table 1Particle sizes which were estimated by different techniquesprovide different physical explanation The particle sizeobtained from XRD pattern (119889XRD) indicates the average
4 Journal of Chemistry
0
100
50
150
00 05 10Relative pressure (PP0)
Volu
me a
dsor
bed
(cm
3g
STP
)
(a)
0
100
50
00 05 10
Relative pressure (PP0)
Volu
me a
dsor
bed
(cm
3g
STP
)
(b)
0
100
50
150
00 05 10Relative pressure (PP0)
Volu
me a
dsor
bed
(cm
3g
STP
)
(c)
0
100
50
00 05 10
Relative pressure (PP0)
Volu
me a
dsor
bed
(cm
3g
STP
)
(d)
Figure 2 N2adsorption-desorption hysteresis at 77 K of prepared catalysts after calcinations ((a) HLB = 139 (b) HLB = 237 (c) HLB = 312
and (d) HLB = 40)
00
02
04
1 10 100Pore diameter (nm)
(cm
3n
mg
STP
)Ad
sorp
tiondV
dlo
g(D
)
(a)
00
02
04
1 10 100Pore diameter (nm)
(cm
3n
mg
STP
)Ad
sorp
tiondV
dlo
g(D
)
(b)
00
02
1 10 100Pore diameter (nm)
(cm
3n
mg
STP
)Ad
sorp
tiondV
dlo
g(D
)
(c)
00
02
1 10 100Pore diameter (nm)
(cm
3n
mg
STP
)Ad
sorp
tiondV
dlo
g(D
)
(d)
Figure 3 Adsorption BJH pore size distribution of prepared catalysts after calcinations ((a) HLB = 139 (b) HLB = 237 (c) HLB = 312 and(d) HLB = 40)
Journal of Chemistry 5
10nm
(a)
10nm
(b)
(c)
20nm
(d)
Figure 4 TEM image of prepared catalysts after calcinations ((a) HLB = 139 (b) HLB = 237 (c) HLB = 312 and (d) HLB = 40)
crystallite size of particles The 119889BET value is calculated fromsurface area which is measured by nitrogen adsorption-desorption assuming that the particles are spherical andnonporous The 119889XRD and 119889BET possess the cumulative andcomprehensive information on particle size although theyare derived indirectly However the 119889TEM value is a directevidence of average particle size of Fe
2O3suspension and thus
in this work it has been used for further calculationsAs shown in Table 1 the particle size is increased and the
particle size distribution becomes wider with the increase ofHLB value In fact nanoparticles are formed in the internalstructure of the microemulsion which is determined bythe HLB value of surfactant The results show that the sizeof different droplets determines the hematite particle sizedepending on the HLB value of surfactant
The effects of the iron particle size on the reductionbehavior of the catalysts were measured by H
2-TPR The
profiles of H2-TPR are presented in Figure 6 As shown in
Figure 6 all catalysts present two main reduction peaks atabout 700 and 900K in the H
2-TPR profiles It has been
postulated that the first stage corresponds to the reductions
of 120572-Fe2O3to magnetite (Fe
3O4) and CuO to Cu whereas
the second stage corresponds to the subsequent reduction ofFe3O4to metallic iron (120572-Fe) [15 16] It is also found that the
first stage can be further separated into two peaks the firstpeak corresponds to the reduction of the solid solution ofCuO and part of 120572-Fe
2O3to Cu and Fe
3O4 and the second
small peak is ascribed to the reduction of the residual 120572-Fe2O3to Fe3O4 The presence of Cu in iron catalyst reduces
120572-Fe2O3to Fe3O4at lower temperature rather than Cu-
free samples As CuO reduces Cu crystallites nucleate andprovide H
2dissociation sites which in turn lead to reactive
hydrogen species capable of reducing iron oxides at relativelylow temperatures [8 9]
The TPR profiles in Figure 6 clearly show that the firstreduction peaks of the catalysts shift to the lower temperaturewith the decrease of the iron particle sizeTheprobable reasonis higher interaction between iron and copper oxides inhomogeneous phase of the catalyst prepared via microemul-sion system This suggests that the microemulsion techniquepromotes the dispersion of Cu promoter which subsequentlyenhances the effect of Cu promoter improves the reduction
6 Journal of Chemistry
000
020
040
060Re
lativ
e fre
quen
cy
Size range (nm)
5ndash10
10ndash1
5
15ndash2
0
20ndash2
5
25ndash3
0
lt30
(a)
000
020
040
060
Rela
tive f
requ
ency
Size range (nm)
5ndash10
10ndash1
5
15ndash2
0
20ndash2
5
25ndash3
0
lt30
(b)
000
020
040
Rela
tive f
requ
ency
Size range (nm)
5ndash10
10ndash1
5
15ndash2
0
20ndash2
5
25ndash3
0
lt30
(c)
Size range (nm)
000
020
040
Rela
tive f
requ
ency
5ndash10
10ndash1
5
15ndash2
0
20ndash2
5
25ndash3
0
lt30
(d)
Figure 5 Relative particle size distribution of prepared catalysts after calcinations ((a) HLB = 139 (b) HLB = 237 (c) HLB = 312 (d)HLB = 40)
of the 120572-Fe2O3 and decreases the reduction temperature for
first peak in H2-TPR profile
The amount of the consumed H2during different reduc-
tion stages which is obtained from integrating the area of thecorresponding reduction peak is summarized in Table 3 Theoverall H
2consumption [molH
2molM(Fe +Cu)] of the first
reduction peaks can be assigned to the reduction of CuO andalso the reduction of 120572-Fe
2O3to Cu and Fe
3O4 respectively
In the first stage of reduction CuO and Fe2O3reacted with
hydrogen based on the following reactions
3Fe2O3+H2997888rarr 2Fe
3O4+H2O
(
molH2
mol Fe= 0166 for complete reduction)
(3)
CuO +H2997888rarr Cu +H
2O
(
molH2
molCu= 1 for complete reduction)
(4)
The peaks at 851 K (molH2mol Fe) correspond to the reduc-
tion of Fe3O4to Fe as below
Fe3O4+ 4H2997888rarr 3Fe + 4H
2O
(
mol H2
mol Fe= 133 for complete reduction)
(5)
The peaks at higher temperature (above 900K)may be due tothe reduction of FeO to Fe and the H
2consumptions which
are consistent with theoretical valuesAs shown in Figure 6 and Table 3 smaller crystal size of
the catalyst has also influence on the reduction of Fe3O4to
Journal of Chemistry 7
450 550 650 750 850 950 1050 1150Temperature (K)
H2
upta
ke
(a)
(b)
(c)
(d)
Figure 6 TPR profiles of prepared catalysts after calcinations ((a)HLB = 139 (b) HLB = 237 (c) HLB = 312 and (d) HLB = 40)
0
05
1
15
2
25
3
35
4
45
0 2 4 6 8 10 12 14 16 18
OlP
a rat
io
Carbon number
HLB = 139HLB = 237
HLB = 312HLB = 40
Figure 7 Olefin-to-paraffin ratio in products after 35 h time-on-stream reaction conditions 583 K 17 bar (H
2CO)feed = 1 and
space velocity of 49 nl sdot hminus1 sdot gFeminus1 ((a) HLB = 139 (b) HLB = 237
(c) HLB = 312 and (d) HLB = 40)
120572-Fe as well as first reduction step The results show that theamount of the catalyst reduction increased with decreasingthe catalyst crystal size
32 Catalytic Activity The effect of the catalyst particle sizeon catalyst activity product selectivity and hydrocarbondistribution at the same time-on stream is listed in Table 4It was found that the CO and H
2conversion was increased
while the HLB value of surfactant decreased It is also shownin this table that the methane and CO
2selectivity increased
while the catalyst particle size decreased Moreover higherhydrocarbon selectivity and chain growth probability (120572)decreased when the crystal size decreased
Olefin-to-paraffin ratio in products and olefin and paraf-fin production rates after 35 h time-on-stream are shown inFigures 7 and 8 As listed in Table 4 and shown in Figures 7and 8 olefin selectivity is decreased by reduction of the HLBvalue of the surfactant (catalyst particle size decreased) Alsoas shown in Figures 7 and 8 olefin selectivity decreases withincreasing the olefins carbon number
The catalytic properties of nanoparticles depend on thesize of catalysts active site Thus different sizes of nanopar-ticles have different catalytic activity and selectivity Thedynamic surface restructuring of nanoparticles should alsodepend on their size that is smaller nanoparticles havehigher surface energies For the heterogeneous catalyticreactions adsorption equilibrium constant of feed increasedwith decreasing the particle size [13 14] By increasing theadsorption equilibrium constant of hydrogen and carbonmonoxide on surface of iron catalysts in small particles thecatalyst reduction and FTS reaction increased Also higheractivity of the iron catalyst with lower particle size (Table 4)may be related to the reduction ability of the catalysts thatincreased with the particle size (Figure 6 and Table 3)
It is postulated that 1-alkenes are primary products ofthe FTS reaction over iron-based catalyst and may be trans-formed to paraffin by hydrogenation as a secondary reaction[20 21] Secondary reactions occur when primary productsdesorbed from a site and then interact with another catalyticsite before leaving the catalyst particles Secondary reactionscan influence the type and molecular weight of the hydro-carbon products Hydrogenation of 1-alkenes to paraffin isthe most famous secondary reaction in FT synthesis Thusthe extent of secondary reactions can also be observed fromthe dependency of the 119874
119899119875119899ratio or olefin content on chain
length The ratio of olefins to paraffins depends on catalysttype structure and the reaction conditions Slow removalof reactive products (eg 120572-olefins) due to the reductionof diffusion coefficients with increasing chain length caninfluence the FTS reaction rate and selectivity The resultspresented in Table 4 show that the olefinparaffin ratios aredecreased with increasing catalyst particle size
Van der Laan and Beenackers emphasized the solubilityimpact (vapor-liquid equilibrium) over diffusion as the maincontributor on secondary reactions [21] As shown in Table 4the secondary reactions are increased (119874119875 decreased) inthe lower iron particle size because of some difficulties ofolefin diffusion in nanoparticles with narrow pores On theother hand the steric hindrance can limit the competitiveadsorption of bigger molecules on smaller crystal sizesThus increasing the adsorption equilibrium constant bydecreasing iron particle size is more for hydrogen than thatof carbon monoxide [8ndash12] Higher hydrogen concentrationson smaller particles enhance the hydrogenation of olefinTheresults presented in Figures 7 and 8 and Table 4 show thatthe olefinparaffin ratios are decreased with increasing thecatalyst particle size of the samples
Anderson-Schultz-Floury (ASF) distribution of FTSproducts on catalysts is presented in Figure 9 Product
8 Journal of Chemistry
00
05
10
15
20
25
30
35
40
0 4 8 12 16Carbon number
HLB = 139
(mm
ole
(gca
tmiddoth))
(a)
00
05
10
15
20
25
30
35
0 4 8 12 16
Carbon number
HLB = 237
(mm
ole
(gca
tmiddoth))
(b)
00
05
10
15
20
25
30
0 4 8 12 16
Carbon number
Para
Ol
HLB = 312
(mm
ole
(gca
tmiddoth))
(c)
00
05
10
15
20
25
0 4 8 12 16Carbon number
Para
Ol
HLB = 40(m
mol
e(g
catmiddoth
))
(d)
Figure 8 Olefin and paraffin production rates after 35 h time-on-stream and reaction conditions 583 K 17 bar (H2CO)feed = 1 space
velocity of 49 nl sdot hminus1 sdot gFeminus1 ((a) HLB = 139 (b) HLB = 237 (c) HLB = 312 and (d) HLB = 40)
Table 3 Quantitative results of H2 consumption for catalysts in H2-TPRa
HLB Peak (K) H2 consumption Reductionmol H2mol Mb mol H2mol Fe
139 533 0171 93850 124
237 558 0163 87851 116
312 608 0154 84842 112
40 640 0142 79852 106
aThe H2 consumption was measured from the area under the corresponding peakbM = Fe + Cu
Journal of Chemistry 9
Table 4 Catalysts activity and products selectivity after 35 h time-on-stream
HLB XCOa HCb OPc
120572d CO2 ()e Products selectivity
CH4 C2ndashC4 C5ndashC12 C12+
40 672 213 11 083 313 137 417 350 96312 715 222 10 08 322 146 476 315 63237 752 228 10 078 331 156 532 274 38139 775 235 09 075 345 176 575 228 21Reaction conditions 563K 17Mpa and H2CO = 1 and space velocity = 49 nl sdot hminus1 sdot gFe
minus1aCarbon monoxide conversion (mol)bHydrocarbon production gCH2gFes (times10
5) and CH4 freecOlefin to paraffin ratiodChain growth probabilityeCO2 selectivity selectivity to oxygenates was negligible (lt20) in all cases
0
00
5 10 15 20 25 30 35
Carbon number
minus120
minus100
minus80
minus60
minus40
minus20
lnX
i
HLB = 139HLB = 237
HLB = 312HLB = 40
Figure 9 Overall products distributions on catalysts after 35 h time-on-stream reaction conditions 583 K 17 bar (H
2CO)feed = 1 space
velocity of 49 nl sdot hminus1 sdot gFeminus1 ((a) HLB = 139 (b) HLB = 237 (c)
HLB = 312 and (d) HLB = 40)
distribution shows a slight shift to the lower molecularweight hydrocarbons by decreasing the HLB value of thesurfactant The trend lines are plotted to determine the chaingrowth probability 120572 As listed in Table 4 the chain growthprobabilities were 083 08 078 and 075 for 40 312 237and 139 HLB value of surfactant respectively This confirmsthe higher molecular weight hydrocarbons production usinghigher HLB value of surfactant in preparation of catalystAs mentioned in the previous section higher HLB value ofsurfactant produced higher particle size of catalysts
Figure 9 and Table 4 also show the effects of the catalystparticle size on the selectivity of Fischer-Tropsch synthesisproducts Comparison of the product distributions of thecatalysts clearly shows that the product distribution shiftto the lower molecular weight hydrocarbons by decreasingthe HLB value of the surfactant (or decreasing the catalystparticle size)
The most accepted mechanism for FTS reaction is C1
insertion which leads to the carbide theory [21] These C1
species have various hydrogenation degrees as follows COHCO HCOH CH and CH
2 Literature results [19 20] have
discussed that light hydrocarbons are built up by monomersthat exhibited higher degree of hydrogenation that is CH
2
Obviously heavy hydrocarbons are built up due tomonomersexcept CH
2species with lower degree of hydrogenation
With increasing the hydrogen concentration on the surfaceof the catalyst the concentration of C
1monomers with
higher degree of hydrogenation are increased Increasing theconcentration of hydrogen on the surface of the catalysts as aresult of reduction of the catalyst particle size increases theconcentration of C
1monomers and ultimately leads to the
higher selectivity to the lower hydrocarbons being enhanced
4 Conclusion
Nanosized iron oxide particles have been successfully synthe-sized by reverse microemulsion with different HLB valuesThe iron oxide particle size and particle size distribution areincreased by decreasing of HLB values It was found that theCO and H
2conversion is increased as the HLB value of the
surfactant is reduced Also the methane and CO2selectivity
is increased at the same time as the catalyst particle size isdecreased In addition higher hydrocarbon selectivity andchain growth probability (120572) show a descending trend incarbon number when the crystal size decreases
Acknowledgment
Financial support of the Ferdowsi University of MashhadIran (P153691-8985) is gratefully acknowledged
References
[1] A T Bell ldquoThe impact of nanoscience on heterogeneouscatalysisrdquo Science vol 299 no 5613 pp 1688ndash1691 2003
[2] J Y Ying ldquoDesign and synthesis of nanostructured catalystsrdquoChemical Engineering Science vol 61 no 5 pp 1540ndash1548 2006
[3] X Zhou W Xu G Liu D Panda and P Chen ldquoSize depen-dent catalytic activity and dynamics of gold nanoparticles at
10 Journal of Chemistry
the single-molecule levelrdquo Journal of the American ChemicalSociety vol 132 no 1 pp 138ndash146 2010
[4] P Kumar and K L MittalHandbook of Microemulsions Scienceand Technology Marcel Dekker New York NY USA 1999
[5] S Eriksson U Nylen S Rojas andM Boutonnet ldquoPreparationof catalysts from microemulsions and their applications inheterogeneous catalysisrdquoApplied Catalysis A vol 265 no 2 pp207ndash219 2004
[6] I Capek ldquoPreparation of metal nanoparticles in water-in-oil (wo) microemulsionsrdquo Advances in Colloid and InterfaceScience vol 110 no 1-2 pp 49ndash74 2004
[7] G Guo Y Sun Z Wang and H Guo ldquoPreparation of hydrox-yapatite nanoparticles by reverse microemulsionrdquo CeramicsInternational vol 31 no 6 pp 869ndash872 2005
[8] T Herranz S Rojas F J Perez-Alonso M Ojeda P Terrerosand J L G Fierro ldquoHydrogenation of carbon oxides overpromoted Fe-Mn catalysts prepared by the microemulsionmethodologyrdquo Applied Catalysis A vol 311 pp 66ndash75 2006
[9] A Sarkar D Seth A K Dozier J K Neathery H H Hamdehand BHDavis ldquoFischer-Tropsch synthesismorphology phasetransformation and particle size growth of nano-scale particlesrdquoCatalysis Letters vol 117 no 1-2 pp 1ndash17 2007
[10] A Nakhaei Pour S Taghipoor M Shekarriz S M K Shahriand Y Zamani ldquoFischer-tropsch synthesis with FeCuLaSiO
2
nano-structured catalystrdquo Journal of Nanoscience andNanotech-nology vol 9 no 7 pp 4425ndash4429 2009
[11] A Nakhaei Pour M R Housaindokht S F Tayyari and JZarkesh ldquoFischer-Tropsch synthesis by nano-structured ironcatalystrdquo Journal of Natural Gas Chemistry vol 19 no 3 pp284ndash292 2010
[12] A Nakhaei Pour M R Housaindokht S F Tayyari and JZarkesh ldquoEffect of nano-particle size on product distributionand kinetic parameters of FeCuLa catalyst in Fischer-Tropschsynthesisrdquo Journal of Natural Gas Chemistry vol 19 no 2 pp107ndash116 2010
[13] D Y Murzin ldquoSize-dependent heterogeneous catalytic kinet-icsrdquo Journal ofMolecular Catalysis A vol 315 no 2 pp 226ndash2302010
[14] D Y Murzin ldquoThermodynamic analysis of nanoparticle sizeeffect on catalytic kineticsrdquo Chemical Engineering Science vol64 no 5 pp 1046ndash1052 2009
[15] ANakhaei Pour SMK ShahriH R Bozorgzadeh Y ZamaniA Tavasoli and M A Marvast ldquoEffect of Mg La and Capromoters on the structure and catalytic behavior of iron-basedcatalysts in Fischer-Tropsch synthesisrdquo Applied Catalysis A vol348 no 2 pp 201ndash208 2008
[16] A Nakhaei Pour Y Zamani A Tavasoli S M K Shahri andS A Taheri ldquoStudy on products distribution of iron and iron-zeolite catalysts in Fischer-Tropsch synthesisrdquo Fuel vol 87 no10-11 pp 2004ndash2012 2008
[17] A Nakhaei Pour M R Housaindokht S F Tayyari J Zarkeshand M R Alaei ldquoDeactivation studies of Fischer-Tropschsynthesis on nano-structured iron catalystrdquo Journal ofMolecularCatalysis A vol 330 no 1-2 pp 112ndash120 2010
[18] H I Chen and H Y Chang ldquoHomogeneous precipitation ofcerium dioxide nanoparticles in alcoholwater mixed solventsrdquoColloids and Surfaces A vol 242 pp 61ndash69 2004
[19] A Ramirez and L Sierra ldquoSimulation of nitrogen sorptionprocesses in materials with cylindrical mesopores hysteresisas a thermodynamic and connectivity phenomenonrdquo ChemicalEngineering Science vol 61 no 13 pp 4233ndash4241 2006
[20] M E Dry ldquoThe Fischer-Tropsch synthesisrdquo inCatalysis Scienceand Technology J R Anderson and M Boudart Eds SpringerNew York NY USA 1981
[21] G P van der Laan and A A C M Beenackers ldquoKinetics andselectivity of the Fischer-Tropsch synthesis a literature reviewrdquoCatalysis Reviews Science and Engineering vol 41 no 3-4 pp255ndash318 1999
Submit your manuscripts athttpwwwhindawicom
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CatalystsJournal of
2 Journal of Chemistry
Fischer-Tropsch synthesis (FTS) [8ndash12] Murzin reportedthat FTS reactions on the supported cobalt based catalystsshow many sensitivities to the catalyst particle size [13 14]Moreover many new results showed that nanosized ironparticles play an essential role to achieve high FTS activity [8ndash12] Iron-based catalysts are preferred for utilizing synthesisgas derived from coal or biomass because of the excellentactivity for the water-gas-shift reaction which allows usinga synthesis gas with a low H
2CO ratio directly without an
upstream shift-step [15 16] In our previous works we triedto show structure sensitivity of unsupported iron catalysts[10 11 17]
In this the present work feasibility of iron nanoparticleformation in the microemulsion systems with different HLBvalues was investigated Moreover effects of HLB values onthe particle size were investigated Then catalyst character-ization and catalytic FTS reaction are examined at differentparticle sizes
2 Experimental
21 Catalyst Preparation Fe-Cu nanoparticles were preparedby coprecipitation in a water-in-oil microemulsion [11ndash15] The precipitation was performed in the single-phasemicroemulsion operating region For this purpose a watersolution of metal precursor Fe(NO
3)3-9H2O (Fluka puriss
pa ACS 98ndash100) and Cu(NO3)2-4H2O (Fluka purum
pa gt 97) were added to a mixture of an oil phase(Chloroform Aldrich gt99) and mixed surfactants containTriton X-100 and SDS The HLB values of Triton X-100 andSDS are 134 and 40 respectively Besides 1-butanol as acosurfactant was added to system in order to obtain a propermicroemulsion
For preparation of various sizes of hematite nanoparticlesreverse microemulsions were prepared with different HLBvalues through varying the weight ratio of Triton X-100 andSDS For a quaternary system of surfactant (119878 g) oil (119874 g)alcohol (119860 g) and water (119882 g) the following symbols weredefined 120572 represents the mass fraction of oil in water plus oil120572 = 119874(119882 + 119874) 120573 the mass ratio of surfactant in the wholesystem 120573 = 119878(119882 + 119874 + 119878 + 119860) and 120576 the mass fraction ofalcohol in the whole system 120576 = 119860(119882 + 119874 + 119878 + 119860) [4ndash7]In the prepared microemulsion system the parameters are120572 = 062 120573 = 003 and 120576 = 028 After stirring well andstabilizing for 24 h a transparentmixturewas obtainedThenhydrazine was added to reducemetal precursorThe resultingmixture was decanted overnight The solid was recoveredby centrifuging and then washing thoroughly with distilledwater and ethanol for several times Lanthanum promoterwas added by wet impregnation method with La(NO
3)3
precursor on its optimal value after treatment in air asdescribed previously [10ndash12 17]The promoted catalysts weredried at 383K for 16 h and calcined at 723K for 3 h in air Thecatalyst compositions were designated in terms of the atomicratios as 100Fe564Cu2La
22 Catalyst Characterization Elemental analysis was per-formed to determine the composition of the elements in
the bulk of catalysts The surface area was calculated fromthe Brunauer-Emmett-Teller (BET) equation and pore vol-ume average pore diameter and pore size distribution ofthe catalysts were determined by N
2physisorption using a
micromeritics ASAP 2010 automated system A 05 g catalystsample was degassed in the micromeritics ASAP 2010 at100∘C for 1 h and then at 573K for 2 h prior to analysis Theanalysis was done using N
2adsorption at 77K Both the pore
volume and the average pore diameter were calculated byBarrett-Joyner-Hallender (BJH)method from the adsorptionisothermAssuming that the Fe
2O3particles are spherical the
corresponding particle size (119889BET) can be estimated as [18]
119889BET =6
120588119860
(1)
where 120588 is the true density of Fe2O3 that is 524 gcm3 and
119860 is the specific surface area of samplesThe XRD spectrum of the catalysts was collected by an
X-ray diffractometer Philips PW1840 X-ray diffractometerusing monochromatized CuK
120572radiation (40 kV 40mA)
and a step scan mode at a scan rate of 002∘ (2120579) per secondfrom 10ndash80∘ XRD peak identification was recognized bycomparison to the JCPDS database software The averagecrystallite size of samples 119889XRD can be estimated from XRDpatterns by applying full-width half-maximum (FWHM) ofcharacteristic peak (104) Fe
2O3located at 2120579 = 333∘ peak to
Scherrer equation
119889XRD =09120582
FWHMcos 120579 (2)
where 120582 is the X-ray wavelength (15406 A in this study) and120579 is the diffraction angle for the (104) plane
Temperature programmed reduction (TPR) measure-ments of the calcined catalysts were recorded by using aMicromeritics TPD-TPR 2900 system The catalyst samples(50mg) were purged with argon at 473 for 30min and cooledto 323K The samples were heated from 350 to 1100K at arate of 10 Kmin under flow of 51 hydrogen in argon gasmixture The consumption of hydrogen was monitored by athermal conductivity detector (TCD)
The morphology of prepared catalysts was observed witha transmission electron microscope (TEM LEO 912 ABGermany) An appropriate amount of Fe
2O3suspension
directly taken from the reaction solution was dropped ontothe carbon-coated copper grids for TEM observation Theaverage particle size (119889TEM) and particle size distributionwere determined by TEM images considering more than 100particles
23 Catalytic Performance The catalysts were tested in afixed-bed microreactor A detailed description of the exper-imental setup and procedures has been provided elsewhere[15 16] The catalyst samples (30 g catalyst diluted with 12 gquartz 100ndash180 120583m) were activated by a 5 (vv) H
2N2
gas mixture with space velocity of 151 nl sdot hminus1 sdot gFeminus1 at
01MPa by increasing temperature from ambient to 673Kat 5 Kmin then maintained for one hour and subsequently
Journal of Chemistry 3
20 30 40 50 60 70
Inte
nsity
(a)
(b)
(c)
(d)
2120579
012
104
110
113
024
116
018
214
300
Figure 1 X-ray diffraction patterns of the prepared catalysts aftercalcinations ((a) HLB = 139 (b) HLB = 237 (c) HLB = 312 and (d)HLB = 40)
reduced to 543K The pretreatment was followed by thesynthesis gas stream with H
2CO = 1 and space velocity
of 307 nl sdot hminus1 sdot gFeminus1 for 24 h in 01Mpa and 543K After
catalyst pretreatment synthesis gas was feed to the reactorat 563K 17 bar (H
2CO)feed = 1 and a space velocity of
49 nl sdot hminus1 sdot gFeminus1
The products were analyzed by means of three gas chro-matographs a Shimadzu 4C gas chromatograph equippedwith two subsequent connected packed columns Porapak Qand Molecular Sieve 5A and a thermal conductivity detector(TCD) with Ar as carrier gas for hydrogen analyzing AVarian CP 3800 with a chromosorb column and a thermalconductivity detector (TCD) were used for CO CO
2 CH4
and other noncondensable gases A Varian CP 3800 with aPetrocolDH100 fused silica capillary column and a flame ion-ization detector (FID) were used for organic liquid productsso that a complete product distribution could be provided
3 Results and Discussion
31 Catalyst Characterization Nanostructure iron catalystswere characterized by X-ray diffraction (XRD) measurementafter calcinations (Figure 1) As shown in Figure 1 XRDpatterns of samples very close to the ones with cubic hematitestructured Fe
2O3crystal in JCPDS database The character-
istic peaks corresponding to (012) (104) (110) (113) (024)(116) (018) (214) and (300) planes are located at 2120579 = 243333 358 408 496 541 576 641 and 656∘ respectivelyDiffraction data indicates that the presence of lanthanumand copper and also subsequent treatment by dried airdo not affect the hematite crystalline phases in differentcatalyst preparation methods This shows that the formed
Table 1 Average particle size determined by TEM BET and XRDtechniques
HLB dBET (nm) dXRD (nm) dTEM (nm)139 168 154 14237 203 188 17312 221 206 2140 263 248 24
Table 2 Textural properties of prepared catalysts
HLB BET surface area(m2g)
Average pore size(nm)a
Pore volume(cm3g)a
139 682 162 014237 564 196 016312 518 223 01940 435 259 021aThese values were calculated by BJH method from desorption isotherm
hematite structure remains stable during subsequent aqueousimpregnation and thermal treatment It was also shown inFigure 1 that the microemulsion system only modules thephysical properties of reactionmediumwithout changing thereaction paths and arrangements of crystal structure Thecharacteristic peak at 2120579 = 333∘ which corresponds to thehematite 104 plane was used to calculate the average metalparticle size by the Scherrer equation The calculated valuesof 119889XRD of the samples are listed in Table 1
Textural properties and pore size distributions of the freshiron-based catalysts are shown in Table 2 and Figures 2 and 3respectively N
2adsorption-desorption isotherms of catalysts
are presented in Figure 3 As shown in this Figure theprepared catalysts show type IV of Brunauerrsquos classificationisothermswithH
1-type hysteresis loop at the relative pressure
of 1198751198750= 08ndash095 This hysteresis loop is characterized as
hexagonal mesoporous materials with cylindrical channels[19]
The pore size distributions of the catalysts which werecalculated by Barrett-Joyner-Halenda (BJH) method foradsorption step are presented in Figure 3 and Table 2 Sinceall pore size values are fairly close to the dimension ofparticles it deduces that the measured pore size is mainlycaused by the inter particle voids
The TEM photographs for the prepared samples aredemonstrated in Figure 4 and Table 1 and also the particlesize distribution determined by TEM images are shown inFigure 5 The average particle size (119889TEM) and particle sizedistribution were obtained from TEM images by consideringmore than 100 particles As shown in Figures 4 and 5 theaverage range of particle size and particle size distributionincreases as HLB value increases
The particle size of samples which were determined byXRD BET and TEM techniques are summarized in Table 1Particle sizes which were estimated by different techniquesprovide different physical explanation The particle sizeobtained from XRD pattern (119889XRD) indicates the average
4 Journal of Chemistry
0
100
50
150
00 05 10Relative pressure (PP0)
Volu
me a
dsor
bed
(cm
3g
STP
)
(a)
0
100
50
00 05 10
Relative pressure (PP0)
Volu
me a
dsor
bed
(cm
3g
STP
)
(b)
0
100
50
150
00 05 10Relative pressure (PP0)
Volu
me a
dsor
bed
(cm
3g
STP
)
(c)
0
100
50
00 05 10
Relative pressure (PP0)
Volu
me a
dsor
bed
(cm
3g
STP
)
(d)
Figure 2 N2adsorption-desorption hysteresis at 77 K of prepared catalysts after calcinations ((a) HLB = 139 (b) HLB = 237 (c) HLB = 312
and (d) HLB = 40)
00
02
04
1 10 100Pore diameter (nm)
(cm
3n
mg
STP
)Ad
sorp
tiondV
dlo
g(D
)
(a)
00
02
04
1 10 100Pore diameter (nm)
(cm
3n
mg
STP
)Ad
sorp
tiondV
dlo
g(D
)
(b)
00
02
1 10 100Pore diameter (nm)
(cm
3n
mg
STP
)Ad
sorp
tiondV
dlo
g(D
)
(c)
00
02
1 10 100Pore diameter (nm)
(cm
3n
mg
STP
)Ad
sorp
tiondV
dlo
g(D
)
(d)
Figure 3 Adsorption BJH pore size distribution of prepared catalysts after calcinations ((a) HLB = 139 (b) HLB = 237 (c) HLB = 312 and(d) HLB = 40)
Journal of Chemistry 5
10nm
(a)
10nm
(b)
(c)
20nm
(d)
Figure 4 TEM image of prepared catalysts after calcinations ((a) HLB = 139 (b) HLB = 237 (c) HLB = 312 and (d) HLB = 40)
crystallite size of particles The 119889BET value is calculated fromsurface area which is measured by nitrogen adsorption-desorption assuming that the particles are spherical andnonporous The 119889XRD and 119889BET possess the cumulative andcomprehensive information on particle size although theyare derived indirectly However the 119889TEM value is a directevidence of average particle size of Fe
2O3suspension and thus
in this work it has been used for further calculationsAs shown in Table 1 the particle size is increased and the
particle size distribution becomes wider with the increase ofHLB value In fact nanoparticles are formed in the internalstructure of the microemulsion which is determined bythe HLB value of surfactant The results show that the sizeof different droplets determines the hematite particle sizedepending on the HLB value of surfactant
The effects of the iron particle size on the reductionbehavior of the catalysts were measured by H
2-TPR The
profiles of H2-TPR are presented in Figure 6 As shown in
Figure 6 all catalysts present two main reduction peaks atabout 700 and 900K in the H
2-TPR profiles It has been
postulated that the first stage corresponds to the reductions
of 120572-Fe2O3to magnetite (Fe
3O4) and CuO to Cu whereas
the second stage corresponds to the subsequent reduction ofFe3O4to metallic iron (120572-Fe) [15 16] It is also found that the
first stage can be further separated into two peaks the firstpeak corresponds to the reduction of the solid solution ofCuO and part of 120572-Fe
2O3to Cu and Fe
3O4 and the second
small peak is ascribed to the reduction of the residual 120572-Fe2O3to Fe3O4 The presence of Cu in iron catalyst reduces
120572-Fe2O3to Fe3O4at lower temperature rather than Cu-
free samples As CuO reduces Cu crystallites nucleate andprovide H
2dissociation sites which in turn lead to reactive
hydrogen species capable of reducing iron oxides at relativelylow temperatures [8 9]
The TPR profiles in Figure 6 clearly show that the firstreduction peaks of the catalysts shift to the lower temperaturewith the decrease of the iron particle sizeTheprobable reasonis higher interaction between iron and copper oxides inhomogeneous phase of the catalyst prepared via microemul-sion system This suggests that the microemulsion techniquepromotes the dispersion of Cu promoter which subsequentlyenhances the effect of Cu promoter improves the reduction
6 Journal of Chemistry
000
020
040
060Re
lativ
e fre
quen
cy
Size range (nm)
5ndash10
10ndash1
5
15ndash2
0
20ndash2
5
25ndash3
0
lt30
(a)
000
020
040
060
Rela
tive f
requ
ency
Size range (nm)
5ndash10
10ndash1
5
15ndash2
0
20ndash2
5
25ndash3
0
lt30
(b)
000
020
040
Rela
tive f
requ
ency
Size range (nm)
5ndash10
10ndash1
5
15ndash2
0
20ndash2
5
25ndash3
0
lt30
(c)
Size range (nm)
000
020
040
Rela
tive f
requ
ency
5ndash10
10ndash1
5
15ndash2
0
20ndash2
5
25ndash3
0
lt30
(d)
Figure 5 Relative particle size distribution of prepared catalysts after calcinations ((a) HLB = 139 (b) HLB = 237 (c) HLB = 312 (d)HLB = 40)
of the 120572-Fe2O3 and decreases the reduction temperature for
first peak in H2-TPR profile
The amount of the consumed H2during different reduc-
tion stages which is obtained from integrating the area of thecorresponding reduction peak is summarized in Table 3 Theoverall H
2consumption [molH
2molM(Fe +Cu)] of the first
reduction peaks can be assigned to the reduction of CuO andalso the reduction of 120572-Fe
2O3to Cu and Fe
3O4 respectively
In the first stage of reduction CuO and Fe2O3reacted with
hydrogen based on the following reactions
3Fe2O3+H2997888rarr 2Fe
3O4+H2O
(
molH2
mol Fe= 0166 for complete reduction)
(3)
CuO +H2997888rarr Cu +H
2O
(
molH2
molCu= 1 for complete reduction)
(4)
The peaks at 851 K (molH2mol Fe) correspond to the reduc-
tion of Fe3O4to Fe as below
Fe3O4+ 4H2997888rarr 3Fe + 4H
2O
(
mol H2
mol Fe= 133 for complete reduction)
(5)
The peaks at higher temperature (above 900K)may be due tothe reduction of FeO to Fe and the H
2consumptions which
are consistent with theoretical valuesAs shown in Figure 6 and Table 3 smaller crystal size of
the catalyst has also influence on the reduction of Fe3O4to
Journal of Chemistry 7
450 550 650 750 850 950 1050 1150Temperature (K)
H2
upta
ke
(a)
(b)
(c)
(d)
Figure 6 TPR profiles of prepared catalysts after calcinations ((a)HLB = 139 (b) HLB = 237 (c) HLB = 312 and (d) HLB = 40)
0
05
1
15
2
25
3
35
4
45
0 2 4 6 8 10 12 14 16 18
OlP
a rat
io
Carbon number
HLB = 139HLB = 237
HLB = 312HLB = 40
Figure 7 Olefin-to-paraffin ratio in products after 35 h time-on-stream reaction conditions 583 K 17 bar (H
2CO)feed = 1 and
space velocity of 49 nl sdot hminus1 sdot gFeminus1 ((a) HLB = 139 (b) HLB = 237
(c) HLB = 312 and (d) HLB = 40)
120572-Fe as well as first reduction step The results show that theamount of the catalyst reduction increased with decreasingthe catalyst crystal size
32 Catalytic Activity The effect of the catalyst particle sizeon catalyst activity product selectivity and hydrocarbondistribution at the same time-on stream is listed in Table 4It was found that the CO and H
2conversion was increased
while the HLB value of surfactant decreased It is also shownin this table that the methane and CO
2selectivity increased
while the catalyst particle size decreased Moreover higherhydrocarbon selectivity and chain growth probability (120572)decreased when the crystal size decreased
Olefin-to-paraffin ratio in products and olefin and paraf-fin production rates after 35 h time-on-stream are shown inFigures 7 and 8 As listed in Table 4 and shown in Figures 7and 8 olefin selectivity is decreased by reduction of the HLBvalue of the surfactant (catalyst particle size decreased) Alsoas shown in Figures 7 and 8 olefin selectivity decreases withincreasing the olefins carbon number
The catalytic properties of nanoparticles depend on thesize of catalysts active site Thus different sizes of nanopar-ticles have different catalytic activity and selectivity Thedynamic surface restructuring of nanoparticles should alsodepend on their size that is smaller nanoparticles havehigher surface energies For the heterogeneous catalyticreactions adsorption equilibrium constant of feed increasedwith decreasing the particle size [13 14] By increasing theadsorption equilibrium constant of hydrogen and carbonmonoxide on surface of iron catalysts in small particles thecatalyst reduction and FTS reaction increased Also higheractivity of the iron catalyst with lower particle size (Table 4)may be related to the reduction ability of the catalysts thatincreased with the particle size (Figure 6 and Table 3)
It is postulated that 1-alkenes are primary products ofthe FTS reaction over iron-based catalyst and may be trans-formed to paraffin by hydrogenation as a secondary reaction[20 21] Secondary reactions occur when primary productsdesorbed from a site and then interact with another catalyticsite before leaving the catalyst particles Secondary reactionscan influence the type and molecular weight of the hydro-carbon products Hydrogenation of 1-alkenes to paraffin isthe most famous secondary reaction in FT synthesis Thusthe extent of secondary reactions can also be observed fromthe dependency of the 119874
119899119875119899ratio or olefin content on chain
length The ratio of olefins to paraffins depends on catalysttype structure and the reaction conditions Slow removalof reactive products (eg 120572-olefins) due to the reductionof diffusion coefficients with increasing chain length caninfluence the FTS reaction rate and selectivity The resultspresented in Table 4 show that the olefinparaffin ratios aredecreased with increasing catalyst particle size
Van der Laan and Beenackers emphasized the solubilityimpact (vapor-liquid equilibrium) over diffusion as the maincontributor on secondary reactions [21] As shown in Table 4the secondary reactions are increased (119874119875 decreased) inthe lower iron particle size because of some difficulties ofolefin diffusion in nanoparticles with narrow pores On theother hand the steric hindrance can limit the competitiveadsorption of bigger molecules on smaller crystal sizesThus increasing the adsorption equilibrium constant bydecreasing iron particle size is more for hydrogen than thatof carbon monoxide [8ndash12] Higher hydrogen concentrationson smaller particles enhance the hydrogenation of olefinTheresults presented in Figures 7 and 8 and Table 4 show thatthe olefinparaffin ratios are decreased with increasing thecatalyst particle size of the samples
Anderson-Schultz-Floury (ASF) distribution of FTSproducts on catalysts is presented in Figure 9 Product
8 Journal of Chemistry
00
05
10
15
20
25
30
35
40
0 4 8 12 16Carbon number
HLB = 139
(mm
ole
(gca
tmiddoth))
(a)
00
05
10
15
20
25
30
35
0 4 8 12 16
Carbon number
HLB = 237
(mm
ole
(gca
tmiddoth))
(b)
00
05
10
15
20
25
30
0 4 8 12 16
Carbon number
Para
Ol
HLB = 312
(mm
ole
(gca
tmiddoth))
(c)
00
05
10
15
20
25
0 4 8 12 16Carbon number
Para
Ol
HLB = 40(m
mol
e(g
catmiddoth
))
(d)
Figure 8 Olefin and paraffin production rates after 35 h time-on-stream and reaction conditions 583 K 17 bar (H2CO)feed = 1 space
velocity of 49 nl sdot hminus1 sdot gFeminus1 ((a) HLB = 139 (b) HLB = 237 (c) HLB = 312 and (d) HLB = 40)
Table 3 Quantitative results of H2 consumption for catalysts in H2-TPRa
HLB Peak (K) H2 consumption Reductionmol H2mol Mb mol H2mol Fe
139 533 0171 93850 124
237 558 0163 87851 116
312 608 0154 84842 112
40 640 0142 79852 106
aThe H2 consumption was measured from the area under the corresponding peakbM = Fe + Cu
Journal of Chemistry 9
Table 4 Catalysts activity and products selectivity after 35 h time-on-stream
HLB XCOa HCb OPc
120572d CO2 ()e Products selectivity
CH4 C2ndashC4 C5ndashC12 C12+
40 672 213 11 083 313 137 417 350 96312 715 222 10 08 322 146 476 315 63237 752 228 10 078 331 156 532 274 38139 775 235 09 075 345 176 575 228 21Reaction conditions 563K 17Mpa and H2CO = 1 and space velocity = 49 nl sdot hminus1 sdot gFe
minus1aCarbon monoxide conversion (mol)bHydrocarbon production gCH2gFes (times10
5) and CH4 freecOlefin to paraffin ratiodChain growth probabilityeCO2 selectivity selectivity to oxygenates was negligible (lt20) in all cases
0
00
5 10 15 20 25 30 35
Carbon number
minus120
minus100
minus80
minus60
minus40
minus20
lnX
i
HLB = 139HLB = 237
HLB = 312HLB = 40
Figure 9 Overall products distributions on catalysts after 35 h time-on-stream reaction conditions 583 K 17 bar (H
2CO)feed = 1 space
velocity of 49 nl sdot hminus1 sdot gFeminus1 ((a) HLB = 139 (b) HLB = 237 (c)
HLB = 312 and (d) HLB = 40)
distribution shows a slight shift to the lower molecularweight hydrocarbons by decreasing the HLB value of thesurfactant The trend lines are plotted to determine the chaingrowth probability 120572 As listed in Table 4 the chain growthprobabilities were 083 08 078 and 075 for 40 312 237and 139 HLB value of surfactant respectively This confirmsthe higher molecular weight hydrocarbons production usinghigher HLB value of surfactant in preparation of catalystAs mentioned in the previous section higher HLB value ofsurfactant produced higher particle size of catalysts
Figure 9 and Table 4 also show the effects of the catalystparticle size on the selectivity of Fischer-Tropsch synthesisproducts Comparison of the product distributions of thecatalysts clearly shows that the product distribution shiftto the lower molecular weight hydrocarbons by decreasingthe HLB value of the surfactant (or decreasing the catalystparticle size)
The most accepted mechanism for FTS reaction is C1
insertion which leads to the carbide theory [21] These C1
species have various hydrogenation degrees as follows COHCO HCOH CH and CH
2 Literature results [19 20] have
discussed that light hydrocarbons are built up by monomersthat exhibited higher degree of hydrogenation that is CH
2
Obviously heavy hydrocarbons are built up due tomonomersexcept CH
2species with lower degree of hydrogenation
With increasing the hydrogen concentration on the surfaceof the catalyst the concentration of C
1monomers with
higher degree of hydrogenation are increased Increasing theconcentration of hydrogen on the surface of the catalysts as aresult of reduction of the catalyst particle size increases theconcentration of C
1monomers and ultimately leads to the
higher selectivity to the lower hydrocarbons being enhanced
4 Conclusion
Nanosized iron oxide particles have been successfully synthe-sized by reverse microemulsion with different HLB valuesThe iron oxide particle size and particle size distribution areincreased by decreasing of HLB values It was found that theCO and H
2conversion is increased as the HLB value of the
surfactant is reduced Also the methane and CO2selectivity
is increased at the same time as the catalyst particle size isdecreased In addition higher hydrocarbon selectivity andchain growth probability (120572) show a descending trend incarbon number when the crystal size decreases
Acknowledgment
Financial support of the Ferdowsi University of MashhadIran (P153691-8985) is gratefully acknowledged
References
[1] A T Bell ldquoThe impact of nanoscience on heterogeneouscatalysisrdquo Science vol 299 no 5613 pp 1688ndash1691 2003
[2] J Y Ying ldquoDesign and synthesis of nanostructured catalystsrdquoChemical Engineering Science vol 61 no 5 pp 1540ndash1548 2006
[3] X Zhou W Xu G Liu D Panda and P Chen ldquoSize depen-dent catalytic activity and dynamics of gold nanoparticles at
10 Journal of Chemistry
the single-molecule levelrdquo Journal of the American ChemicalSociety vol 132 no 1 pp 138ndash146 2010
[4] P Kumar and K L MittalHandbook of Microemulsions Scienceand Technology Marcel Dekker New York NY USA 1999
[5] S Eriksson U Nylen S Rojas andM Boutonnet ldquoPreparationof catalysts from microemulsions and their applications inheterogeneous catalysisrdquoApplied Catalysis A vol 265 no 2 pp207ndash219 2004
[6] I Capek ldquoPreparation of metal nanoparticles in water-in-oil (wo) microemulsionsrdquo Advances in Colloid and InterfaceScience vol 110 no 1-2 pp 49ndash74 2004
[7] G Guo Y Sun Z Wang and H Guo ldquoPreparation of hydrox-yapatite nanoparticles by reverse microemulsionrdquo CeramicsInternational vol 31 no 6 pp 869ndash872 2005
[8] T Herranz S Rojas F J Perez-Alonso M Ojeda P Terrerosand J L G Fierro ldquoHydrogenation of carbon oxides overpromoted Fe-Mn catalysts prepared by the microemulsionmethodologyrdquo Applied Catalysis A vol 311 pp 66ndash75 2006
[9] A Sarkar D Seth A K Dozier J K Neathery H H Hamdehand BHDavis ldquoFischer-Tropsch synthesismorphology phasetransformation and particle size growth of nano-scale particlesrdquoCatalysis Letters vol 117 no 1-2 pp 1ndash17 2007
[10] A Nakhaei Pour S Taghipoor M Shekarriz S M K Shahriand Y Zamani ldquoFischer-tropsch synthesis with FeCuLaSiO
2
nano-structured catalystrdquo Journal of Nanoscience andNanotech-nology vol 9 no 7 pp 4425ndash4429 2009
[11] A Nakhaei Pour M R Housaindokht S F Tayyari and JZarkesh ldquoFischer-Tropsch synthesis by nano-structured ironcatalystrdquo Journal of Natural Gas Chemistry vol 19 no 3 pp284ndash292 2010
[12] A Nakhaei Pour M R Housaindokht S F Tayyari and JZarkesh ldquoEffect of nano-particle size on product distributionand kinetic parameters of FeCuLa catalyst in Fischer-Tropschsynthesisrdquo Journal of Natural Gas Chemistry vol 19 no 2 pp107ndash116 2010
[13] D Y Murzin ldquoSize-dependent heterogeneous catalytic kinet-icsrdquo Journal ofMolecular Catalysis A vol 315 no 2 pp 226ndash2302010
[14] D Y Murzin ldquoThermodynamic analysis of nanoparticle sizeeffect on catalytic kineticsrdquo Chemical Engineering Science vol64 no 5 pp 1046ndash1052 2009
[15] ANakhaei Pour SMK ShahriH R Bozorgzadeh Y ZamaniA Tavasoli and M A Marvast ldquoEffect of Mg La and Capromoters on the structure and catalytic behavior of iron-basedcatalysts in Fischer-Tropsch synthesisrdquo Applied Catalysis A vol348 no 2 pp 201ndash208 2008
[16] A Nakhaei Pour Y Zamani A Tavasoli S M K Shahri andS A Taheri ldquoStudy on products distribution of iron and iron-zeolite catalysts in Fischer-Tropsch synthesisrdquo Fuel vol 87 no10-11 pp 2004ndash2012 2008
[17] A Nakhaei Pour M R Housaindokht S F Tayyari J Zarkeshand M R Alaei ldquoDeactivation studies of Fischer-Tropschsynthesis on nano-structured iron catalystrdquo Journal ofMolecularCatalysis A vol 330 no 1-2 pp 112ndash120 2010
[18] H I Chen and H Y Chang ldquoHomogeneous precipitation ofcerium dioxide nanoparticles in alcoholwater mixed solventsrdquoColloids and Surfaces A vol 242 pp 61ndash69 2004
[19] A Ramirez and L Sierra ldquoSimulation of nitrogen sorptionprocesses in materials with cylindrical mesopores hysteresisas a thermodynamic and connectivity phenomenonrdquo ChemicalEngineering Science vol 61 no 13 pp 4233ndash4241 2006
[20] M E Dry ldquoThe Fischer-Tropsch synthesisrdquo inCatalysis Scienceand Technology J R Anderson and M Boudart Eds SpringerNew York NY USA 1981
[21] G P van der Laan and A A C M Beenackers ldquoKinetics andselectivity of the Fischer-Tropsch synthesis a literature reviewrdquoCatalysis Reviews Science and Engineering vol 41 no 3-4 pp255ndash318 1999
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
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Quantum Chemistry
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Organic Chemistry International
ElectrochemistryInternational Journal of
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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
Journal of Chemistry 3
20 30 40 50 60 70
Inte
nsity
(a)
(b)
(c)
(d)
2120579
012
104
110
113
024
116
018
214
300
Figure 1 X-ray diffraction patterns of the prepared catalysts aftercalcinations ((a) HLB = 139 (b) HLB = 237 (c) HLB = 312 and (d)HLB = 40)
reduced to 543K The pretreatment was followed by thesynthesis gas stream with H
2CO = 1 and space velocity
of 307 nl sdot hminus1 sdot gFeminus1 for 24 h in 01Mpa and 543K After
catalyst pretreatment synthesis gas was feed to the reactorat 563K 17 bar (H
2CO)feed = 1 and a space velocity of
49 nl sdot hminus1 sdot gFeminus1
The products were analyzed by means of three gas chro-matographs a Shimadzu 4C gas chromatograph equippedwith two subsequent connected packed columns Porapak Qand Molecular Sieve 5A and a thermal conductivity detector(TCD) with Ar as carrier gas for hydrogen analyzing AVarian CP 3800 with a chromosorb column and a thermalconductivity detector (TCD) were used for CO CO
2 CH4
and other noncondensable gases A Varian CP 3800 with aPetrocolDH100 fused silica capillary column and a flame ion-ization detector (FID) were used for organic liquid productsso that a complete product distribution could be provided
3 Results and Discussion
31 Catalyst Characterization Nanostructure iron catalystswere characterized by X-ray diffraction (XRD) measurementafter calcinations (Figure 1) As shown in Figure 1 XRDpatterns of samples very close to the ones with cubic hematitestructured Fe
2O3crystal in JCPDS database The character-
istic peaks corresponding to (012) (104) (110) (113) (024)(116) (018) (214) and (300) planes are located at 2120579 = 243333 358 408 496 541 576 641 and 656∘ respectivelyDiffraction data indicates that the presence of lanthanumand copper and also subsequent treatment by dried airdo not affect the hematite crystalline phases in differentcatalyst preparation methods This shows that the formed
Table 1 Average particle size determined by TEM BET and XRDtechniques
HLB dBET (nm) dXRD (nm) dTEM (nm)139 168 154 14237 203 188 17312 221 206 2140 263 248 24
Table 2 Textural properties of prepared catalysts
HLB BET surface area(m2g)
Average pore size(nm)a
Pore volume(cm3g)a
139 682 162 014237 564 196 016312 518 223 01940 435 259 021aThese values were calculated by BJH method from desorption isotherm
hematite structure remains stable during subsequent aqueousimpregnation and thermal treatment It was also shown inFigure 1 that the microemulsion system only modules thephysical properties of reactionmediumwithout changing thereaction paths and arrangements of crystal structure Thecharacteristic peak at 2120579 = 333∘ which corresponds to thehematite 104 plane was used to calculate the average metalparticle size by the Scherrer equation The calculated valuesof 119889XRD of the samples are listed in Table 1
Textural properties and pore size distributions of the freshiron-based catalysts are shown in Table 2 and Figures 2 and 3respectively N
2adsorption-desorption isotherms of catalysts
are presented in Figure 3 As shown in this Figure theprepared catalysts show type IV of Brunauerrsquos classificationisothermswithH
1-type hysteresis loop at the relative pressure
of 1198751198750= 08ndash095 This hysteresis loop is characterized as
hexagonal mesoporous materials with cylindrical channels[19]
The pore size distributions of the catalysts which werecalculated by Barrett-Joyner-Halenda (BJH) method foradsorption step are presented in Figure 3 and Table 2 Sinceall pore size values are fairly close to the dimension ofparticles it deduces that the measured pore size is mainlycaused by the inter particle voids
The TEM photographs for the prepared samples aredemonstrated in Figure 4 and Table 1 and also the particlesize distribution determined by TEM images are shown inFigure 5 The average particle size (119889TEM) and particle sizedistribution were obtained from TEM images by consideringmore than 100 particles As shown in Figures 4 and 5 theaverage range of particle size and particle size distributionincreases as HLB value increases
The particle size of samples which were determined byXRD BET and TEM techniques are summarized in Table 1Particle sizes which were estimated by different techniquesprovide different physical explanation The particle sizeobtained from XRD pattern (119889XRD) indicates the average
4 Journal of Chemistry
0
100
50
150
00 05 10Relative pressure (PP0)
Volu
me a
dsor
bed
(cm
3g
STP
)
(a)
0
100
50
00 05 10
Relative pressure (PP0)
Volu
me a
dsor
bed
(cm
3g
STP
)
(b)
0
100
50
150
00 05 10Relative pressure (PP0)
Volu
me a
dsor
bed
(cm
3g
STP
)
(c)
0
100
50
00 05 10
Relative pressure (PP0)
Volu
me a
dsor
bed
(cm
3g
STP
)
(d)
Figure 2 N2adsorption-desorption hysteresis at 77 K of prepared catalysts after calcinations ((a) HLB = 139 (b) HLB = 237 (c) HLB = 312
and (d) HLB = 40)
00
02
04
1 10 100Pore diameter (nm)
(cm
3n
mg
STP
)Ad
sorp
tiondV
dlo
g(D
)
(a)
00
02
04
1 10 100Pore diameter (nm)
(cm
3n
mg
STP
)Ad
sorp
tiondV
dlo
g(D
)
(b)
00
02
1 10 100Pore diameter (nm)
(cm
3n
mg
STP
)Ad
sorp
tiondV
dlo
g(D
)
(c)
00
02
1 10 100Pore diameter (nm)
(cm
3n
mg
STP
)Ad
sorp
tiondV
dlo
g(D
)
(d)
Figure 3 Adsorption BJH pore size distribution of prepared catalysts after calcinations ((a) HLB = 139 (b) HLB = 237 (c) HLB = 312 and(d) HLB = 40)
Journal of Chemistry 5
10nm
(a)
10nm
(b)
(c)
20nm
(d)
Figure 4 TEM image of prepared catalysts after calcinations ((a) HLB = 139 (b) HLB = 237 (c) HLB = 312 and (d) HLB = 40)
crystallite size of particles The 119889BET value is calculated fromsurface area which is measured by nitrogen adsorption-desorption assuming that the particles are spherical andnonporous The 119889XRD and 119889BET possess the cumulative andcomprehensive information on particle size although theyare derived indirectly However the 119889TEM value is a directevidence of average particle size of Fe
2O3suspension and thus
in this work it has been used for further calculationsAs shown in Table 1 the particle size is increased and the
particle size distribution becomes wider with the increase ofHLB value In fact nanoparticles are formed in the internalstructure of the microemulsion which is determined bythe HLB value of surfactant The results show that the sizeof different droplets determines the hematite particle sizedepending on the HLB value of surfactant
The effects of the iron particle size on the reductionbehavior of the catalysts were measured by H
2-TPR The
profiles of H2-TPR are presented in Figure 6 As shown in
Figure 6 all catalysts present two main reduction peaks atabout 700 and 900K in the H
2-TPR profiles It has been
postulated that the first stage corresponds to the reductions
of 120572-Fe2O3to magnetite (Fe
3O4) and CuO to Cu whereas
the second stage corresponds to the subsequent reduction ofFe3O4to metallic iron (120572-Fe) [15 16] It is also found that the
first stage can be further separated into two peaks the firstpeak corresponds to the reduction of the solid solution ofCuO and part of 120572-Fe
2O3to Cu and Fe
3O4 and the second
small peak is ascribed to the reduction of the residual 120572-Fe2O3to Fe3O4 The presence of Cu in iron catalyst reduces
120572-Fe2O3to Fe3O4at lower temperature rather than Cu-
free samples As CuO reduces Cu crystallites nucleate andprovide H
2dissociation sites which in turn lead to reactive
hydrogen species capable of reducing iron oxides at relativelylow temperatures [8 9]
The TPR profiles in Figure 6 clearly show that the firstreduction peaks of the catalysts shift to the lower temperaturewith the decrease of the iron particle sizeTheprobable reasonis higher interaction between iron and copper oxides inhomogeneous phase of the catalyst prepared via microemul-sion system This suggests that the microemulsion techniquepromotes the dispersion of Cu promoter which subsequentlyenhances the effect of Cu promoter improves the reduction
6 Journal of Chemistry
000
020
040
060Re
lativ
e fre
quen
cy
Size range (nm)
5ndash10
10ndash1
5
15ndash2
0
20ndash2
5
25ndash3
0
lt30
(a)
000
020
040
060
Rela
tive f
requ
ency
Size range (nm)
5ndash10
10ndash1
5
15ndash2
0
20ndash2
5
25ndash3
0
lt30
(b)
000
020
040
Rela
tive f
requ
ency
Size range (nm)
5ndash10
10ndash1
5
15ndash2
0
20ndash2
5
25ndash3
0
lt30
(c)
Size range (nm)
000
020
040
Rela
tive f
requ
ency
5ndash10
10ndash1
5
15ndash2
0
20ndash2
5
25ndash3
0
lt30
(d)
Figure 5 Relative particle size distribution of prepared catalysts after calcinations ((a) HLB = 139 (b) HLB = 237 (c) HLB = 312 (d)HLB = 40)
of the 120572-Fe2O3 and decreases the reduction temperature for
first peak in H2-TPR profile
The amount of the consumed H2during different reduc-
tion stages which is obtained from integrating the area of thecorresponding reduction peak is summarized in Table 3 Theoverall H
2consumption [molH
2molM(Fe +Cu)] of the first
reduction peaks can be assigned to the reduction of CuO andalso the reduction of 120572-Fe
2O3to Cu and Fe
3O4 respectively
In the first stage of reduction CuO and Fe2O3reacted with
hydrogen based on the following reactions
3Fe2O3+H2997888rarr 2Fe
3O4+H2O
(
molH2
mol Fe= 0166 for complete reduction)
(3)
CuO +H2997888rarr Cu +H
2O
(
molH2
molCu= 1 for complete reduction)
(4)
The peaks at 851 K (molH2mol Fe) correspond to the reduc-
tion of Fe3O4to Fe as below
Fe3O4+ 4H2997888rarr 3Fe + 4H
2O
(
mol H2
mol Fe= 133 for complete reduction)
(5)
The peaks at higher temperature (above 900K)may be due tothe reduction of FeO to Fe and the H
2consumptions which
are consistent with theoretical valuesAs shown in Figure 6 and Table 3 smaller crystal size of
the catalyst has also influence on the reduction of Fe3O4to
Journal of Chemistry 7
450 550 650 750 850 950 1050 1150Temperature (K)
H2
upta
ke
(a)
(b)
(c)
(d)
Figure 6 TPR profiles of prepared catalysts after calcinations ((a)HLB = 139 (b) HLB = 237 (c) HLB = 312 and (d) HLB = 40)
0
05
1
15
2
25
3
35
4
45
0 2 4 6 8 10 12 14 16 18
OlP
a rat
io
Carbon number
HLB = 139HLB = 237
HLB = 312HLB = 40
Figure 7 Olefin-to-paraffin ratio in products after 35 h time-on-stream reaction conditions 583 K 17 bar (H
2CO)feed = 1 and
space velocity of 49 nl sdot hminus1 sdot gFeminus1 ((a) HLB = 139 (b) HLB = 237
(c) HLB = 312 and (d) HLB = 40)
120572-Fe as well as first reduction step The results show that theamount of the catalyst reduction increased with decreasingthe catalyst crystal size
32 Catalytic Activity The effect of the catalyst particle sizeon catalyst activity product selectivity and hydrocarbondistribution at the same time-on stream is listed in Table 4It was found that the CO and H
2conversion was increased
while the HLB value of surfactant decreased It is also shownin this table that the methane and CO
2selectivity increased
while the catalyst particle size decreased Moreover higherhydrocarbon selectivity and chain growth probability (120572)decreased when the crystal size decreased
Olefin-to-paraffin ratio in products and olefin and paraf-fin production rates after 35 h time-on-stream are shown inFigures 7 and 8 As listed in Table 4 and shown in Figures 7and 8 olefin selectivity is decreased by reduction of the HLBvalue of the surfactant (catalyst particle size decreased) Alsoas shown in Figures 7 and 8 olefin selectivity decreases withincreasing the olefins carbon number
The catalytic properties of nanoparticles depend on thesize of catalysts active site Thus different sizes of nanopar-ticles have different catalytic activity and selectivity Thedynamic surface restructuring of nanoparticles should alsodepend on their size that is smaller nanoparticles havehigher surface energies For the heterogeneous catalyticreactions adsorption equilibrium constant of feed increasedwith decreasing the particle size [13 14] By increasing theadsorption equilibrium constant of hydrogen and carbonmonoxide on surface of iron catalysts in small particles thecatalyst reduction and FTS reaction increased Also higheractivity of the iron catalyst with lower particle size (Table 4)may be related to the reduction ability of the catalysts thatincreased with the particle size (Figure 6 and Table 3)
It is postulated that 1-alkenes are primary products ofthe FTS reaction over iron-based catalyst and may be trans-formed to paraffin by hydrogenation as a secondary reaction[20 21] Secondary reactions occur when primary productsdesorbed from a site and then interact with another catalyticsite before leaving the catalyst particles Secondary reactionscan influence the type and molecular weight of the hydro-carbon products Hydrogenation of 1-alkenes to paraffin isthe most famous secondary reaction in FT synthesis Thusthe extent of secondary reactions can also be observed fromthe dependency of the 119874
119899119875119899ratio or olefin content on chain
length The ratio of olefins to paraffins depends on catalysttype structure and the reaction conditions Slow removalof reactive products (eg 120572-olefins) due to the reductionof diffusion coefficients with increasing chain length caninfluence the FTS reaction rate and selectivity The resultspresented in Table 4 show that the olefinparaffin ratios aredecreased with increasing catalyst particle size
Van der Laan and Beenackers emphasized the solubilityimpact (vapor-liquid equilibrium) over diffusion as the maincontributor on secondary reactions [21] As shown in Table 4the secondary reactions are increased (119874119875 decreased) inthe lower iron particle size because of some difficulties ofolefin diffusion in nanoparticles with narrow pores On theother hand the steric hindrance can limit the competitiveadsorption of bigger molecules on smaller crystal sizesThus increasing the adsorption equilibrium constant bydecreasing iron particle size is more for hydrogen than thatof carbon monoxide [8ndash12] Higher hydrogen concentrationson smaller particles enhance the hydrogenation of olefinTheresults presented in Figures 7 and 8 and Table 4 show thatthe olefinparaffin ratios are decreased with increasing thecatalyst particle size of the samples
Anderson-Schultz-Floury (ASF) distribution of FTSproducts on catalysts is presented in Figure 9 Product
8 Journal of Chemistry
00
05
10
15
20
25
30
35
40
0 4 8 12 16Carbon number
HLB = 139
(mm
ole
(gca
tmiddoth))
(a)
00
05
10
15
20
25
30
35
0 4 8 12 16
Carbon number
HLB = 237
(mm
ole
(gca
tmiddoth))
(b)
00
05
10
15
20
25
30
0 4 8 12 16
Carbon number
Para
Ol
HLB = 312
(mm
ole
(gca
tmiddoth))
(c)
00
05
10
15
20
25
0 4 8 12 16Carbon number
Para
Ol
HLB = 40(m
mol
e(g
catmiddoth
))
(d)
Figure 8 Olefin and paraffin production rates after 35 h time-on-stream and reaction conditions 583 K 17 bar (H2CO)feed = 1 space
velocity of 49 nl sdot hminus1 sdot gFeminus1 ((a) HLB = 139 (b) HLB = 237 (c) HLB = 312 and (d) HLB = 40)
Table 3 Quantitative results of H2 consumption for catalysts in H2-TPRa
HLB Peak (K) H2 consumption Reductionmol H2mol Mb mol H2mol Fe
139 533 0171 93850 124
237 558 0163 87851 116
312 608 0154 84842 112
40 640 0142 79852 106
aThe H2 consumption was measured from the area under the corresponding peakbM = Fe + Cu
Journal of Chemistry 9
Table 4 Catalysts activity and products selectivity after 35 h time-on-stream
HLB XCOa HCb OPc
120572d CO2 ()e Products selectivity
CH4 C2ndashC4 C5ndashC12 C12+
40 672 213 11 083 313 137 417 350 96312 715 222 10 08 322 146 476 315 63237 752 228 10 078 331 156 532 274 38139 775 235 09 075 345 176 575 228 21Reaction conditions 563K 17Mpa and H2CO = 1 and space velocity = 49 nl sdot hminus1 sdot gFe
minus1aCarbon monoxide conversion (mol)bHydrocarbon production gCH2gFes (times10
5) and CH4 freecOlefin to paraffin ratiodChain growth probabilityeCO2 selectivity selectivity to oxygenates was negligible (lt20) in all cases
0
00
5 10 15 20 25 30 35
Carbon number
minus120
minus100
minus80
minus60
minus40
minus20
lnX
i
HLB = 139HLB = 237
HLB = 312HLB = 40
Figure 9 Overall products distributions on catalysts after 35 h time-on-stream reaction conditions 583 K 17 bar (H
2CO)feed = 1 space
velocity of 49 nl sdot hminus1 sdot gFeminus1 ((a) HLB = 139 (b) HLB = 237 (c)
HLB = 312 and (d) HLB = 40)
distribution shows a slight shift to the lower molecularweight hydrocarbons by decreasing the HLB value of thesurfactant The trend lines are plotted to determine the chaingrowth probability 120572 As listed in Table 4 the chain growthprobabilities were 083 08 078 and 075 for 40 312 237and 139 HLB value of surfactant respectively This confirmsthe higher molecular weight hydrocarbons production usinghigher HLB value of surfactant in preparation of catalystAs mentioned in the previous section higher HLB value ofsurfactant produced higher particle size of catalysts
Figure 9 and Table 4 also show the effects of the catalystparticle size on the selectivity of Fischer-Tropsch synthesisproducts Comparison of the product distributions of thecatalysts clearly shows that the product distribution shiftto the lower molecular weight hydrocarbons by decreasingthe HLB value of the surfactant (or decreasing the catalystparticle size)
The most accepted mechanism for FTS reaction is C1
insertion which leads to the carbide theory [21] These C1
species have various hydrogenation degrees as follows COHCO HCOH CH and CH
2 Literature results [19 20] have
discussed that light hydrocarbons are built up by monomersthat exhibited higher degree of hydrogenation that is CH
2
Obviously heavy hydrocarbons are built up due tomonomersexcept CH
2species with lower degree of hydrogenation
With increasing the hydrogen concentration on the surfaceof the catalyst the concentration of C
1monomers with
higher degree of hydrogenation are increased Increasing theconcentration of hydrogen on the surface of the catalysts as aresult of reduction of the catalyst particle size increases theconcentration of C
1monomers and ultimately leads to the
higher selectivity to the lower hydrocarbons being enhanced
4 Conclusion
Nanosized iron oxide particles have been successfully synthe-sized by reverse microemulsion with different HLB valuesThe iron oxide particle size and particle size distribution areincreased by decreasing of HLB values It was found that theCO and H
2conversion is increased as the HLB value of the
surfactant is reduced Also the methane and CO2selectivity
is increased at the same time as the catalyst particle size isdecreased In addition higher hydrocarbon selectivity andchain growth probability (120572) show a descending trend incarbon number when the crystal size decreases
Acknowledgment
Financial support of the Ferdowsi University of MashhadIran (P153691-8985) is gratefully acknowledged
References
[1] A T Bell ldquoThe impact of nanoscience on heterogeneouscatalysisrdquo Science vol 299 no 5613 pp 1688ndash1691 2003
[2] J Y Ying ldquoDesign and synthesis of nanostructured catalystsrdquoChemical Engineering Science vol 61 no 5 pp 1540ndash1548 2006
[3] X Zhou W Xu G Liu D Panda and P Chen ldquoSize depen-dent catalytic activity and dynamics of gold nanoparticles at
10 Journal of Chemistry
the single-molecule levelrdquo Journal of the American ChemicalSociety vol 132 no 1 pp 138ndash146 2010
[4] P Kumar and K L MittalHandbook of Microemulsions Scienceand Technology Marcel Dekker New York NY USA 1999
[5] S Eriksson U Nylen S Rojas andM Boutonnet ldquoPreparationof catalysts from microemulsions and their applications inheterogeneous catalysisrdquoApplied Catalysis A vol 265 no 2 pp207ndash219 2004
[6] I Capek ldquoPreparation of metal nanoparticles in water-in-oil (wo) microemulsionsrdquo Advances in Colloid and InterfaceScience vol 110 no 1-2 pp 49ndash74 2004
[7] G Guo Y Sun Z Wang and H Guo ldquoPreparation of hydrox-yapatite nanoparticles by reverse microemulsionrdquo CeramicsInternational vol 31 no 6 pp 869ndash872 2005
[8] T Herranz S Rojas F J Perez-Alonso M Ojeda P Terrerosand J L G Fierro ldquoHydrogenation of carbon oxides overpromoted Fe-Mn catalysts prepared by the microemulsionmethodologyrdquo Applied Catalysis A vol 311 pp 66ndash75 2006
[9] A Sarkar D Seth A K Dozier J K Neathery H H Hamdehand BHDavis ldquoFischer-Tropsch synthesismorphology phasetransformation and particle size growth of nano-scale particlesrdquoCatalysis Letters vol 117 no 1-2 pp 1ndash17 2007
[10] A Nakhaei Pour S Taghipoor M Shekarriz S M K Shahriand Y Zamani ldquoFischer-tropsch synthesis with FeCuLaSiO
2
nano-structured catalystrdquo Journal of Nanoscience andNanotech-nology vol 9 no 7 pp 4425ndash4429 2009
[11] A Nakhaei Pour M R Housaindokht S F Tayyari and JZarkesh ldquoFischer-Tropsch synthesis by nano-structured ironcatalystrdquo Journal of Natural Gas Chemistry vol 19 no 3 pp284ndash292 2010
[12] A Nakhaei Pour M R Housaindokht S F Tayyari and JZarkesh ldquoEffect of nano-particle size on product distributionand kinetic parameters of FeCuLa catalyst in Fischer-Tropschsynthesisrdquo Journal of Natural Gas Chemistry vol 19 no 2 pp107ndash116 2010
[13] D Y Murzin ldquoSize-dependent heterogeneous catalytic kinet-icsrdquo Journal ofMolecular Catalysis A vol 315 no 2 pp 226ndash2302010
[14] D Y Murzin ldquoThermodynamic analysis of nanoparticle sizeeffect on catalytic kineticsrdquo Chemical Engineering Science vol64 no 5 pp 1046ndash1052 2009
[15] ANakhaei Pour SMK ShahriH R Bozorgzadeh Y ZamaniA Tavasoli and M A Marvast ldquoEffect of Mg La and Capromoters on the structure and catalytic behavior of iron-basedcatalysts in Fischer-Tropsch synthesisrdquo Applied Catalysis A vol348 no 2 pp 201ndash208 2008
[16] A Nakhaei Pour Y Zamani A Tavasoli S M K Shahri andS A Taheri ldquoStudy on products distribution of iron and iron-zeolite catalysts in Fischer-Tropsch synthesisrdquo Fuel vol 87 no10-11 pp 2004ndash2012 2008
[17] A Nakhaei Pour M R Housaindokht S F Tayyari J Zarkeshand M R Alaei ldquoDeactivation studies of Fischer-Tropschsynthesis on nano-structured iron catalystrdquo Journal ofMolecularCatalysis A vol 330 no 1-2 pp 112ndash120 2010
[18] H I Chen and H Y Chang ldquoHomogeneous precipitation ofcerium dioxide nanoparticles in alcoholwater mixed solventsrdquoColloids and Surfaces A vol 242 pp 61ndash69 2004
[19] A Ramirez and L Sierra ldquoSimulation of nitrogen sorptionprocesses in materials with cylindrical mesopores hysteresisas a thermodynamic and connectivity phenomenonrdquo ChemicalEngineering Science vol 61 no 13 pp 4233ndash4241 2006
[20] M E Dry ldquoThe Fischer-Tropsch synthesisrdquo inCatalysis Scienceand Technology J R Anderson and M Boudart Eds SpringerNew York NY USA 1981
[21] G P van der Laan and A A C M Beenackers ldquoKinetics andselectivity of the Fischer-Tropsch synthesis a literature reviewrdquoCatalysis Reviews Science and Engineering vol 41 no 3-4 pp255ndash318 1999
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
4 Journal of Chemistry
0
100
50
150
00 05 10Relative pressure (PP0)
Volu
me a
dsor
bed
(cm
3g
STP
)
(a)
0
100
50
00 05 10
Relative pressure (PP0)
Volu
me a
dsor
bed
(cm
3g
STP
)
(b)
0
100
50
150
00 05 10Relative pressure (PP0)
Volu
me a
dsor
bed
(cm
3g
STP
)
(c)
0
100
50
00 05 10
Relative pressure (PP0)
Volu
me a
dsor
bed
(cm
3g
STP
)
(d)
Figure 2 N2adsorption-desorption hysteresis at 77 K of prepared catalysts after calcinations ((a) HLB = 139 (b) HLB = 237 (c) HLB = 312
and (d) HLB = 40)
00
02
04
1 10 100Pore diameter (nm)
(cm
3n
mg
STP
)Ad
sorp
tiondV
dlo
g(D
)
(a)
00
02
04
1 10 100Pore diameter (nm)
(cm
3n
mg
STP
)Ad
sorp
tiondV
dlo
g(D
)
(b)
00
02
1 10 100Pore diameter (nm)
(cm
3n
mg
STP
)Ad
sorp
tiondV
dlo
g(D
)
(c)
00
02
1 10 100Pore diameter (nm)
(cm
3n
mg
STP
)Ad
sorp
tiondV
dlo
g(D
)
(d)
Figure 3 Adsorption BJH pore size distribution of prepared catalysts after calcinations ((a) HLB = 139 (b) HLB = 237 (c) HLB = 312 and(d) HLB = 40)
Journal of Chemistry 5
10nm
(a)
10nm
(b)
(c)
20nm
(d)
Figure 4 TEM image of prepared catalysts after calcinations ((a) HLB = 139 (b) HLB = 237 (c) HLB = 312 and (d) HLB = 40)
crystallite size of particles The 119889BET value is calculated fromsurface area which is measured by nitrogen adsorption-desorption assuming that the particles are spherical andnonporous The 119889XRD and 119889BET possess the cumulative andcomprehensive information on particle size although theyare derived indirectly However the 119889TEM value is a directevidence of average particle size of Fe
2O3suspension and thus
in this work it has been used for further calculationsAs shown in Table 1 the particle size is increased and the
particle size distribution becomes wider with the increase ofHLB value In fact nanoparticles are formed in the internalstructure of the microemulsion which is determined bythe HLB value of surfactant The results show that the sizeof different droplets determines the hematite particle sizedepending on the HLB value of surfactant
The effects of the iron particle size on the reductionbehavior of the catalysts were measured by H
2-TPR The
profiles of H2-TPR are presented in Figure 6 As shown in
Figure 6 all catalysts present two main reduction peaks atabout 700 and 900K in the H
2-TPR profiles It has been
postulated that the first stage corresponds to the reductions
of 120572-Fe2O3to magnetite (Fe
3O4) and CuO to Cu whereas
the second stage corresponds to the subsequent reduction ofFe3O4to metallic iron (120572-Fe) [15 16] It is also found that the
first stage can be further separated into two peaks the firstpeak corresponds to the reduction of the solid solution ofCuO and part of 120572-Fe
2O3to Cu and Fe
3O4 and the second
small peak is ascribed to the reduction of the residual 120572-Fe2O3to Fe3O4 The presence of Cu in iron catalyst reduces
120572-Fe2O3to Fe3O4at lower temperature rather than Cu-
free samples As CuO reduces Cu crystallites nucleate andprovide H
2dissociation sites which in turn lead to reactive
hydrogen species capable of reducing iron oxides at relativelylow temperatures [8 9]
The TPR profiles in Figure 6 clearly show that the firstreduction peaks of the catalysts shift to the lower temperaturewith the decrease of the iron particle sizeTheprobable reasonis higher interaction between iron and copper oxides inhomogeneous phase of the catalyst prepared via microemul-sion system This suggests that the microemulsion techniquepromotes the dispersion of Cu promoter which subsequentlyenhances the effect of Cu promoter improves the reduction
6 Journal of Chemistry
000
020
040
060Re
lativ
e fre
quen
cy
Size range (nm)
5ndash10
10ndash1
5
15ndash2
0
20ndash2
5
25ndash3
0
lt30
(a)
000
020
040
060
Rela
tive f
requ
ency
Size range (nm)
5ndash10
10ndash1
5
15ndash2
0
20ndash2
5
25ndash3
0
lt30
(b)
000
020
040
Rela
tive f
requ
ency
Size range (nm)
5ndash10
10ndash1
5
15ndash2
0
20ndash2
5
25ndash3
0
lt30
(c)
Size range (nm)
000
020
040
Rela
tive f
requ
ency
5ndash10
10ndash1
5
15ndash2
0
20ndash2
5
25ndash3
0
lt30
(d)
Figure 5 Relative particle size distribution of prepared catalysts after calcinations ((a) HLB = 139 (b) HLB = 237 (c) HLB = 312 (d)HLB = 40)
of the 120572-Fe2O3 and decreases the reduction temperature for
first peak in H2-TPR profile
The amount of the consumed H2during different reduc-
tion stages which is obtained from integrating the area of thecorresponding reduction peak is summarized in Table 3 Theoverall H
2consumption [molH
2molM(Fe +Cu)] of the first
reduction peaks can be assigned to the reduction of CuO andalso the reduction of 120572-Fe
2O3to Cu and Fe
3O4 respectively
In the first stage of reduction CuO and Fe2O3reacted with
hydrogen based on the following reactions
3Fe2O3+H2997888rarr 2Fe
3O4+H2O
(
molH2
mol Fe= 0166 for complete reduction)
(3)
CuO +H2997888rarr Cu +H
2O
(
molH2
molCu= 1 for complete reduction)
(4)
The peaks at 851 K (molH2mol Fe) correspond to the reduc-
tion of Fe3O4to Fe as below
Fe3O4+ 4H2997888rarr 3Fe + 4H
2O
(
mol H2
mol Fe= 133 for complete reduction)
(5)
The peaks at higher temperature (above 900K)may be due tothe reduction of FeO to Fe and the H
2consumptions which
are consistent with theoretical valuesAs shown in Figure 6 and Table 3 smaller crystal size of
the catalyst has also influence on the reduction of Fe3O4to
Journal of Chemistry 7
450 550 650 750 850 950 1050 1150Temperature (K)
H2
upta
ke
(a)
(b)
(c)
(d)
Figure 6 TPR profiles of prepared catalysts after calcinations ((a)HLB = 139 (b) HLB = 237 (c) HLB = 312 and (d) HLB = 40)
0
05
1
15
2
25
3
35
4
45
0 2 4 6 8 10 12 14 16 18
OlP
a rat
io
Carbon number
HLB = 139HLB = 237
HLB = 312HLB = 40
Figure 7 Olefin-to-paraffin ratio in products after 35 h time-on-stream reaction conditions 583 K 17 bar (H
2CO)feed = 1 and
space velocity of 49 nl sdot hminus1 sdot gFeminus1 ((a) HLB = 139 (b) HLB = 237
(c) HLB = 312 and (d) HLB = 40)
120572-Fe as well as first reduction step The results show that theamount of the catalyst reduction increased with decreasingthe catalyst crystal size
32 Catalytic Activity The effect of the catalyst particle sizeon catalyst activity product selectivity and hydrocarbondistribution at the same time-on stream is listed in Table 4It was found that the CO and H
2conversion was increased
while the HLB value of surfactant decreased It is also shownin this table that the methane and CO
2selectivity increased
while the catalyst particle size decreased Moreover higherhydrocarbon selectivity and chain growth probability (120572)decreased when the crystal size decreased
Olefin-to-paraffin ratio in products and olefin and paraf-fin production rates after 35 h time-on-stream are shown inFigures 7 and 8 As listed in Table 4 and shown in Figures 7and 8 olefin selectivity is decreased by reduction of the HLBvalue of the surfactant (catalyst particle size decreased) Alsoas shown in Figures 7 and 8 olefin selectivity decreases withincreasing the olefins carbon number
The catalytic properties of nanoparticles depend on thesize of catalysts active site Thus different sizes of nanopar-ticles have different catalytic activity and selectivity Thedynamic surface restructuring of nanoparticles should alsodepend on their size that is smaller nanoparticles havehigher surface energies For the heterogeneous catalyticreactions adsorption equilibrium constant of feed increasedwith decreasing the particle size [13 14] By increasing theadsorption equilibrium constant of hydrogen and carbonmonoxide on surface of iron catalysts in small particles thecatalyst reduction and FTS reaction increased Also higheractivity of the iron catalyst with lower particle size (Table 4)may be related to the reduction ability of the catalysts thatincreased with the particle size (Figure 6 and Table 3)
It is postulated that 1-alkenes are primary products ofthe FTS reaction over iron-based catalyst and may be trans-formed to paraffin by hydrogenation as a secondary reaction[20 21] Secondary reactions occur when primary productsdesorbed from a site and then interact with another catalyticsite before leaving the catalyst particles Secondary reactionscan influence the type and molecular weight of the hydro-carbon products Hydrogenation of 1-alkenes to paraffin isthe most famous secondary reaction in FT synthesis Thusthe extent of secondary reactions can also be observed fromthe dependency of the 119874
119899119875119899ratio or olefin content on chain
length The ratio of olefins to paraffins depends on catalysttype structure and the reaction conditions Slow removalof reactive products (eg 120572-olefins) due to the reductionof diffusion coefficients with increasing chain length caninfluence the FTS reaction rate and selectivity The resultspresented in Table 4 show that the olefinparaffin ratios aredecreased with increasing catalyst particle size
Van der Laan and Beenackers emphasized the solubilityimpact (vapor-liquid equilibrium) over diffusion as the maincontributor on secondary reactions [21] As shown in Table 4the secondary reactions are increased (119874119875 decreased) inthe lower iron particle size because of some difficulties ofolefin diffusion in nanoparticles with narrow pores On theother hand the steric hindrance can limit the competitiveadsorption of bigger molecules on smaller crystal sizesThus increasing the adsorption equilibrium constant bydecreasing iron particle size is more for hydrogen than thatof carbon monoxide [8ndash12] Higher hydrogen concentrationson smaller particles enhance the hydrogenation of olefinTheresults presented in Figures 7 and 8 and Table 4 show thatthe olefinparaffin ratios are decreased with increasing thecatalyst particle size of the samples
Anderson-Schultz-Floury (ASF) distribution of FTSproducts on catalysts is presented in Figure 9 Product
8 Journal of Chemistry
00
05
10
15
20
25
30
35
40
0 4 8 12 16Carbon number
HLB = 139
(mm
ole
(gca
tmiddoth))
(a)
00
05
10
15
20
25
30
35
0 4 8 12 16
Carbon number
HLB = 237
(mm
ole
(gca
tmiddoth))
(b)
00
05
10
15
20
25
30
0 4 8 12 16
Carbon number
Para
Ol
HLB = 312
(mm
ole
(gca
tmiddoth))
(c)
00
05
10
15
20
25
0 4 8 12 16Carbon number
Para
Ol
HLB = 40(m
mol
e(g
catmiddoth
))
(d)
Figure 8 Olefin and paraffin production rates after 35 h time-on-stream and reaction conditions 583 K 17 bar (H2CO)feed = 1 space
velocity of 49 nl sdot hminus1 sdot gFeminus1 ((a) HLB = 139 (b) HLB = 237 (c) HLB = 312 and (d) HLB = 40)
Table 3 Quantitative results of H2 consumption for catalysts in H2-TPRa
HLB Peak (K) H2 consumption Reductionmol H2mol Mb mol H2mol Fe
139 533 0171 93850 124
237 558 0163 87851 116
312 608 0154 84842 112
40 640 0142 79852 106
aThe H2 consumption was measured from the area under the corresponding peakbM = Fe + Cu
Journal of Chemistry 9
Table 4 Catalysts activity and products selectivity after 35 h time-on-stream
HLB XCOa HCb OPc
120572d CO2 ()e Products selectivity
CH4 C2ndashC4 C5ndashC12 C12+
40 672 213 11 083 313 137 417 350 96312 715 222 10 08 322 146 476 315 63237 752 228 10 078 331 156 532 274 38139 775 235 09 075 345 176 575 228 21Reaction conditions 563K 17Mpa and H2CO = 1 and space velocity = 49 nl sdot hminus1 sdot gFe
minus1aCarbon monoxide conversion (mol)bHydrocarbon production gCH2gFes (times10
5) and CH4 freecOlefin to paraffin ratiodChain growth probabilityeCO2 selectivity selectivity to oxygenates was negligible (lt20) in all cases
0
00
5 10 15 20 25 30 35
Carbon number
minus120
minus100
minus80
minus60
minus40
minus20
lnX
i
HLB = 139HLB = 237
HLB = 312HLB = 40
Figure 9 Overall products distributions on catalysts after 35 h time-on-stream reaction conditions 583 K 17 bar (H
2CO)feed = 1 space
velocity of 49 nl sdot hminus1 sdot gFeminus1 ((a) HLB = 139 (b) HLB = 237 (c)
HLB = 312 and (d) HLB = 40)
distribution shows a slight shift to the lower molecularweight hydrocarbons by decreasing the HLB value of thesurfactant The trend lines are plotted to determine the chaingrowth probability 120572 As listed in Table 4 the chain growthprobabilities were 083 08 078 and 075 for 40 312 237and 139 HLB value of surfactant respectively This confirmsthe higher molecular weight hydrocarbons production usinghigher HLB value of surfactant in preparation of catalystAs mentioned in the previous section higher HLB value ofsurfactant produced higher particle size of catalysts
Figure 9 and Table 4 also show the effects of the catalystparticle size on the selectivity of Fischer-Tropsch synthesisproducts Comparison of the product distributions of thecatalysts clearly shows that the product distribution shiftto the lower molecular weight hydrocarbons by decreasingthe HLB value of the surfactant (or decreasing the catalystparticle size)
The most accepted mechanism for FTS reaction is C1
insertion which leads to the carbide theory [21] These C1
species have various hydrogenation degrees as follows COHCO HCOH CH and CH
2 Literature results [19 20] have
discussed that light hydrocarbons are built up by monomersthat exhibited higher degree of hydrogenation that is CH
2
Obviously heavy hydrocarbons are built up due tomonomersexcept CH
2species with lower degree of hydrogenation
With increasing the hydrogen concentration on the surfaceof the catalyst the concentration of C
1monomers with
higher degree of hydrogenation are increased Increasing theconcentration of hydrogen on the surface of the catalysts as aresult of reduction of the catalyst particle size increases theconcentration of C
1monomers and ultimately leads to the
higher selectivity to the lower hydrocarbons being enhanced
4 Conclusion
Nanosized iron oxide particles have been successfully synthe-sized by reverse microemulsion with different HLB valuesThe iron oxide particle size and particle size distribution areincreased by decreasing of HLB values It was found that theCO and H
2conversion is increased as the HLB value of the
surfactant is reduced Also the methane and CO2selectivity
is increased at the same time as the catalyst particle size isdecreased In addition higher hydrocarbon selectivity andchain growth probability (120572) show a descending trend incarbon number when the crystal size decreases
Acknowledgment
Financial support of the Ferdowsi University of MashhadIran (P153691-8985) is gratefully acknowledged
References
[1] A T Bell ldquoThe impact of nanoscience on heterogeneouscatalysisrdquo Science vol 299 no 5613 pp 1688ndash1691 2003
[2] J Y Ying ldquoDesign and synthesis of nanostructured catalystsrdquoChemical Engineering Science vol 61 no 5 pp 1540ndash1548 2006
[3] X Zhou W Xu G Liu D Panda and P Chen ldquoSize depen-dent catalytic activity and dynamics of gold nanoparticles at
10 Journal of Chemistry
the single-molecule levelrdquo Journal of the American ChemicalSociety vol 132 no 1 pp 138ndash146 2010
[4] P Kumar and K L MittalHandbook of Microemulsions Scienceand Technology Marcel Dekker New York NY USA 1999
[5] S Eriksson U Nylen S Rojas andM Boutonnet ldquoPreparationof catalysts from microemulsions and their applications inheterogeneous catalysisrdquoApplied Catalysis A vol 265 no 2 pp207ndash219 2004
[6] I Capek ldquoPreparation of metal nanoparticles in water-in-oil (wo) microemulsionsrdquo Advances in Colloid and InterfaceScience vol 110 no 1-2 pp 49ndash74 2004
[7] G Guo Y Sun Z Wang and H Guo ldquoPreparation of hydrox-yapatite nanoparticles by reverse microemulsionrdquo CeramicsInternational vol 31 no 6 pp 869ndash872 2005
[8] T Herranz S Rojas F J Perez-Alonso M Ojeda P Terrerosand J L G Fierro ldquoHydrogenation of carbon oxides overpromoted Fe-Mn catalysts prepared by the microemulsionmethodologyrdquo Applied Catalysis A vol 311 pp 66ndash75 2006
[9] A Sarkar D Seth A K Dozier J K Neathery H H Hamdehand BHDavis ldquoFischer-Tropsch synthesismorphology phasetransformation and particle size growth of nano-scale particlesrdquoCatalysis Letters vol 117 no 1-2 pp 1ndash17 2007
[10] A Nakhaei Pour S Taghipoor M Shekarriz S M K Shahriand Y Zamani ldquoFischer-tropsch synthesis with FeCuLaSiO
2
nano-structured catalystrdquo Journal of Nanoscience andNanotech-nology vol 9 no 7 pp 4425ndash4429 2009
[11] A Nakhaei Pour M R Housaindokht S F Tayyari and JZarkesh ldquoFischer-Tropsch synthesis by nano-structured ironcatalystrdquo Journal of Natural Gas Chemistry vol 19 no 3 pp284ndash292 2010
[12] A Nakhaei Pour M R Housaindokht S F Tayyari and JZarkesh ldquoEffect of nano-particle size on product distributionand kinetic parameters of FeCuLa catalyst in Fischer-Tropschsynthesisrdquo Journal of Natural Gas Chemistry vol 19 no 2 pp107ndash116 2010
[13] D Y Murzin ldquoSize-dependent heterogeneous catalytic kinet-icsrdquo Journal ofMolecular Catalysis A vol 315 no 2 pp 226ndash2302010
[14] D Y Murzin ldquoThermodynamic analysis of nanoparticle sizeeffect on catalytic kineticsrdquo Chemical Engineering Science vol64 no 5 pp 1046ndash1052 2009
[15] ANakhaei Pour SMK ShahriH R Bozorgzadeh Y ZamaniA Tavasoli and M A Marvast ldquoEffect of Mg La and Capromoters on the structure and catalytic behavior of iron-basedcatalysts in Fischer-Tropsch synthesisrdquo Applied Catalysis A vol348 no 2 pp 201ndash208 2008
[16] A Nakhaei Pour Y Zamani A Tavasoli S M K Shahri andS A Taheri ldquoStudy on products distribution of iron and iron-zeolite catalysts in Fischer-Tropsch synthesisrdquo Fuel vol 87 no10-11 pp 2004ndash2012 2008
[17] A Nakhaei Pour M R Housaindokht S F Tayyari J Zarkeshand M R Alaei ldquoDeactivation studies of Fischer-Tropschsynthesis on nano-structured iron catalystrdquo Journal ofMolecularCatalysis A vol 330 no 1-2 pp 112ndash120 2010
[18] H I Chen and H Y Chang ldquoHomogeneous precipitation ofcerium dioxide nanoparticles in alcoholwater mixed solventsrdquoColloids and Surfaces A vol 242 pp 61ndash69 2004
[19] A Ramirez and L Sierra ldquoSimulation of nitrogen sorptionprocesses in materials with cylindrical mesopores hysteresisas a thermodynamic and connectivity phenomenonrdquo ChemicalEngineering Science vol 61 no 13 pp 4233ndash4241 2006
[20] M E Dry ldquoThe Fischer-Tropsch synthesisrdquo inCatalysis Scienceand Technology J R Anderson and M Boudart Eds SpringerNew York NY USA 1981
[21] G P van der Laan and A A C M Beenackers ldquoKinetics andselectivity of the Fischer-Tropsch synthesis a literature reviewrdquoCatalysis Reviews Science and Engineering vol 41 no 3-4 pp255ndash318 1999
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
Journal of Chemistry 5
10nm
(a)
10nm
(b)
(c)
20nm
(d)
Figure 4 TEM image of prepared catalysts after calcinations ((a) HLB = 139 (b) HLB = 237 (c) HLB = 312 and (d) HLB = 40)
crystallite size of particles The 119889BET value is calculated fromsurface area which is measured by nitrogen adsorption-desorption assuming that the particles are spherical andnonporous The 119889XRD and 119889BET possess the cumulative andcomprehensive information on particle size although theyare derived indirectly However the 119889TEM value is a directevidence of average particle size of Fe
2O3suspension and thus
in this work it has been used for further calculationsAs shown in Table 1 the particle size is increased and the
particle size distribution becomes wider with the increase ofHLB value In fact nanoparticles are formed in the internalstructure of the microemulsion which is determined bythe HLB value of surfactant The results show that the sizeof different droplets determines the hematite particle sizedepending on the HLB value of surfactant
The effects of the iron particle size on the reductionbehavior of the catalysts were measured by H
2-TPR The
profiles of H2-TPR are presented in Figure 6 As shown in
Figure 6 all catalysts present two main reduction peaks atabout 700 and 900K in the H
2-TPR profiles It has been
postulated that the first stage corresponds to the reductions
of 120572-Fe2O3to magnetite (Fe
3O4) and CuO to Cu whereas
the second stage corresponds to the subsequent reduction ofFe3O4to metallic iron (120572-Fe) [15 16] It is also found that the
first stage can be further separated into two peaks the firstpeak corresponds to the reduction of the solid solution ofCuO and part of 120572-Fe
2O3to Cu and Fe
3O4 and the second
small peak is ascribed to the reduction of the residual 120572-Fe2O3to Fe3O4 The presence of Cu in iron catalyst reduces
120572-Fe2O3to Fe3O4at lower temperature rather than Cu-
free samples As CuO reduces Cu crystallites nucleate andprovide H
2dissociation sites which in turn lead to reactive
hydrogen species capable of reducing iron oxides at relativelylow temperatures [8 9]
The TPR profiles in Figure 6 clearly show that the firstreduction peaks of the catalysts shift to the lower temperaturewith the decrease of the iron particle sizeTheprobable reasonis higher interaction between iron and copper oxides inhomogeneous phase of the catalyst prepared via microemul-sion system This suggests that the microemulsion techniquepromotes the dispersion of Cu promoter which subsequentlyenhances the effect of Cu promoter improves the reduction
6 Journal of Chemistry
000
020
040
060Re
lativ
e fre
quen
cy
Size range (nm)
5ndash10
10ndash1
5
15ndash2
0
20ndash2
5
25ndash3
0
lt30
(a)
000
020
040
060
Rela
tive f
requ
ency
Size range (nm)
5ndash10
10ndash1
5
15ndash2
0
20ndash2
5
25ndash3
0
lt30
(b)
000
020
040
Rela
tive f
requ
ency
Size range (nm)
5ndash10
10ndash1
5
15ndash2
0
20ndash2
5
25ndash3
0
lt30
(c)
Size range (nm)
000
020
040
Rela
tive f
requ
ency
5ndash10
10ndash1
5
15ndash2
0
20ndash2
5
25ndash3
0
lt30
(d)
Figure 5 Relative particle size distribution of prepared catalysts after calcinations ((a) HLB = 139 (b) HLB = 237 (c) HLB = 312 (d)HLB = 40)
of the 120572-Fe2O3 and decreases the reduction temperature for
first peak in H2-TPR profile
The amount of the consumed H2during different reduc-
tion stages which is obtained from integrating the area of thecorresponding reduction peak is summarized in Table 3 Theoverall H
2consumption [molH
2molM(Fe +Cu)] of the first
reduction peaks can be assigned to the reduction of CuO andalso the reduction of 120572-Fe
2O3to Cu and Fe
3O4 respectively
In the first stage of reduction CuO and Fe2O3reacted with
hydrogen based on the following reactions
3Fe2O3+H2997888rarr 2Fe
3O4+H2O
(
molH2
mol Fe= 0166 for complete reduction)
(3)
CuO +H2997888rarr Cu +H
2O
(
molH2
molCu= 1 for complete reduction)
(4)
The peaks at 851 K (molH2mol Fe) correspond to the reduc-
tion of Fe3O4to Fe as below
Fe3O4+ 4H2997888rarr 3Fe + 4H
2O
(
mol H2
mol Fe= 133 for complete reduction)
(5)
The peaks at higher temperature (above 900K)may be due tothe reduction of FeO to Fe and the H
2consumptions which
are consistent with theoretical valuesAs shown in Figure 6 and Table 3 smaller crystal size of
the catalyst has also influence on the reduction of Fe3O4to
Journal of Chemistry 7
450 550 650 750 850 950 1050 1150Temperature (K)
H2
upta
ke
(a)
(b)
(c)
(d)
Figure 6 TPR profiles of prepared catalysts after calcinations ((a)HLB = 139 (b) HLB = 237 (c) HLB = 312 and (d) HLB = 40)
0
05
1
15
2
25
3
35
4
45
0 2 4 6 8 10 12 14 16 18
OlP
a rat
io
Carbon number
HLB = 139HLB = 237
HLB = 312HLB = 40
Figure 7 Olefin-to-paraffin ratio in products after 35 h time-on-stream reaction conditions 583 K 17 bar (H
2CO)feed = 1 and
space velocity of 49 nl sdot hminus1 sdot gFeminus1 ((a) HLB = 139 (b) HLB = 237
(c) HLB = 312 and (d) HLB = 40)
120572-Fe as well as first reduction step The results show that theamount of the catalyst reduction increased with decreasingthe catalyst crystal size
32 Catalytic Activity The effect of the catalyst particle sizeon catalyst activity product selectivity and hydrocarbondistribution at the same time-on stream is listed in Table 4It was found that the CO and H
2conversion was increased
while the HLB value of surfactant decreased It is also shownin this table that the methane and CO
2selectivity increased
while the catalyst particle size decreased Moreover higherhydrocarbon selectivity and chain growth probability (120572)decreased when the crystal size decreased
Olefin-to-paraffin ratio in products and olefin and paraf-fin production rates after 35 h time-on-stream are shown inFigures 7 and 8 As listed in Table 4 and shown in Figures 7and 8 olefin selectivity is decreased by reduction of the HLBvalue of the surfactant (catalyst particle size decreased) Alsoas shown in Figures 7 and 8 olefin selectivity decreases withincreasing the olefins carbon number
The catalytic properties of nanoparticles depend on thesize of catalysts active site Thus different sizes of nanopar-ticles have different catalytic activity and selectivity Thedynamic surface restructuring of nanoparticles should alsodepend on their size that is smaller nanoparticles havehigher surface energies For the heterogeneous catalyticreactions adsorption equilibrium constant of feed increasedwith decreasing the particle size [13 14] By increasing theadsorption equilibrium constant of hydrogen and carbonmonoxide on surface of iron catalysts in small particles thecatalyst reduction and FTS reaction increased Also higheractivity of the iron catalyst with lower particle size (Table 4)may be related to the reduction ability of the catalysts thatincreased with the particle size (Figure 6 and Table 3)
It is postulated that 1-alkenes are primary products ofthe FTS reaction over iron-based catalyst and may be trans-formed to paraffin by hydrogenation as a secondary reaction[20 21] Secondary reactions occur when primary productsdesorbed from a site and then interact with another catalyticsite before leaving the catalyst particles Secondary reactionscan influence the type and molecular weight of the hydro-carbon products Hydrogenation of 1-alkenes to paraffin isthe most famous secondary reaction in FT synthesis Thusthe extent of secondary reactions can also be observed fromthe dependency of the 119874
119899119875119899ratio or olefin content on chain
length The ratio of olefins to paraffins depends on catalysttype structure and the reaction conditions Slow removalof reactive products (eg 120572-olefins) due to the reductionof diffusion coefficients with increasing chain length caninfluence the FTS reaction rate and selectivity The resultspresented in Table 4 show that the olefinparaffin ratios aredecreased with increasing catalyst particle size
Van der Laan and Beenackers emphasized the solubilityimpact (vapor-liquid equilibrium) over diffusion as the maincontributor on secondary reactions [21] As shown in Table 4the secondary reactions are increased (119874119875 decreased) inthe lower iron particle size because of some difficulties ofolefin diffusion in nanoparticles with narrow pores On theother hand the steric hindrance can limit the competitiveadsorption of bigger molecules on smaller crystal sizesThus increasing the adsorption equilibrium constant bydecreasing iron particle size is more for hydrogen than thatof carbon monoxide [8ndash12] Higher hydrogen concentrationson smaller particles enhance the hydrogenation of olefinTheresults presented in Figures 7 and 8 and Table 4 show thatthe olefinparaffin ratios are decreased with increasing thecatalyst particle size of the samples
Anderson-Schultz-Floury (ASF) distribution of FTSproducts on catalysts is presented in Figure 9 Product
8 Journal of Chemistry
00
05
10
15
20
25
30
35
40
0 4 8 12 16Carbon number
HLB = 139
(mm
ole
(gca
tmiddoth))
(a)
00
05
10
15
20
25
30
35
0 4 8 12 16
Carbon number
HLB = 237
(mm
ole
(gca
tmiddoth))
(b)
00
05
10
15
20
25
30
0 4 8 12 16
Carbon number
Para
Ol
HLB = 312
(mm
ole
(gca
tmiddoth))
(c)
00
05
10
15
20
25
0 4 8 12 16Carbon number
Para
Ol
HLB = 40(m
mol
e(g
catmiddoth
))
(d)
Figure 8 Olefin and paraffin production rates after 35 h time-on-stream and reaction conditions 583 K 17 bar (H2CO)feed = 1 space
velocity of 49 nl sdot hminus1 sdot gFeminus1 ((a) HLB = 139 (b) HLB = 237 (c) HLB = 312 and (d) HLB = 40)
Table 3 Quantitative results of H2 consumption for catalysts in H2-TPRa
HLB Peak (K) H2 consumption Reductionmol H2mol Mb mol H2mol Fe
139 533 0171 93850 124
237 558 0163 87851 116
312 608 0154 84842 112
40 640 0142 79852 106
aThe H2 consumption was measured from the area under the corresponding peakbM = Fe + Cu
Journal of Chemistry 9
Table 4 Catalysts activity and products selectivity after 35 h time-on-stream
HLB XCOa HCb OPc
120572d CO2 ()e Products selectivity
CH4 C2ndashC4 C5ndashC12 C12+
40 672 213 11 083 313 137 417 350 96312 715 222 10 08 322 146 476 315 63237 752 228 10 078 331 156 532 274 38139 775 235 09 075 345 176 575 228 21Reaction conditions 563K 17Mpa and H2CO = 1 and space velocity = 49 nl sdot hminus1 sdot gFe
minus1aCarbon monoxide conversion (mol)bHydrocarbon production gCH2gFes (times10
5) and CH4 freecOlefin to paraffin ratiodChain growth probabilityeCO2 selectivity selectivity to oxygenates was negligible (lt20) in all cases
0
00
5 10 15 20 25 30 35
Carbon number
minus120
minus100
minus80
minus60
minus40
minus20
lnX
i
HLB = 139HLB = 237
HLB = 312HLB = 40
Figure 9 Overall products distributions on catalysts after 35 h time-on-stream reaction conditions 583 K 17 bar (H
2CO)feed = 1 space
velocity of 49 nl sdot hminus1 sdot gFeminus1 ((a) HLB = 139 (b) HLB = 237 (c)
HLB = 312 and (d) HLB = 40)
distribution shows a slight shift to the lower molecularweight hydrocarbons by decreasing the HLB value of thesurfactant The trend lines are plotted to determine the chaingrowth probability 120572 As listed in Table 4 the chain growthprobabilities were 083 08 078 and 075 for 40 312 237and 139 HLB value of surfactant respectively This confirmsthe higher molecular weight hydrocarbons production usinghigher HLB value of surfactant in preparation of catalystAs mentioned in the previous section higher HLB value ofsurfactant produced higher particle size of catalysts
Figure 9 and Table 4 also show the effects of the catalystparticle size on the selectivity of Fischer-Tropsch synthesisproducts Comparison of the product distributions of thecatalysts clearly shows that the product distribution shiftto the lower molecular weight hydrocarbons by decreasingthe HLB value of the surfactant (or decreasing the catalystparticle size)
The most accepted mechanism for FTS reaction is C1
insertion which leads to the carbide theory [21] These C1
species have various hydrogenation degrees as follows COHCO HCOH CH and CH
2 Literature results [19 20] have
discussed that light hydrocarbons are built up by monomersthat exhibited higher degree of hydrogenation that is CH
2
Obviously heavy hydrocarbons are built up due tomonomersexcept CH
2species with lower degree of hydrogenation
With increasing the hydrogen concentration on the surfaceof the catalyst the concentration of C
1monomers with
higher degree of hydrogenation are increased Increasing theconcentration of hydrogen on the surface of the catalysts as aresult of reduction of the catalyst particle size increases theconcentration of C
1monomers and ultimately leads to the
higher selectivity to the lower hydrocarbons being enhanced
4 Conclusion
Nanosized iron oxide particles have been successfully synthe-sized by reverse microemulsion with different HLB valuesThe iron oxide particle size and particle size distribution areincreased by decreasing of HLB values It was found that theCO and H
2conversion is increased as the HLB value of the
surfactant is reduced Also the methane and CO2selectivity
is increased at the same time as the catalyst particle size isdecreased In addition higher hydrocarbon selectivity andchain growth probability (120572) show a descending trend incarbon number when the crystal size decreases
Acknowledgment
Financial support of the Ferdowsi University of MashhadIran (P153691-8985) is gratefully acknowledged
References
[1] A T Bell ldquoThe impact of nanoscience on heterogeneouscatalysisrdquo Science vol 299 no 5613 pp 1688ndash1691 2003
[2] J Y Ying ldquoDesign and synthesis of nanostructured catalystsrdquoChemical Engineering Science vol 61 no 5 pp 1540ndash1548 2006
[3] X Zhou W Xu G Liu D Panda and P Chen ldquoSize depen-dent catalytic activity and dynamics of gold nanoparticles at
10 Journal of Chemistry
the single-molecule levelrdquo Journal of the American ChemicalSociety vol 132 no 1 pp 138ndash146 2010
[4] P Kumar and K L MittalHandbook of Microemulsions Scienceand Technology Marcel Dekker New York NY USA 1999
[5] S Eriksson U Nylen S Rojas andM Boutonnet ldquoPreparationof catalysts from microemulsions and their applications inheterogeneous catalysisrdquoApplied Catalysis A vol 265 no 2 pp207ndash219 2004
[6] I Capek ldquoPreparation of metal nanoparticles in water-in-oil (wo) microemulsionsrdquo Advances in Colloid and InterfaceScience vol 110 no 1-2 pp 49ndash74 2004
[7] G Guo Y Sun Z Wang and H Guo ldquoPreparation of hydrox-yapatite nanoparticles by reverse microemulsionrdquo CeramicsInternational vol 31 no 6 pp 869ndash872 2005
[8] T Herranz S Rojas F J Perez-Alonso M Ojeda P Terrerosand J L G Fierro ldquoHydrogenation of carbon oxides overpromoted Fe-Mn catalysts prepared by the microemulsionmethodologyrdquo Applied Catalysis A vol 311 pp 66ndash75 2006
[9] A Sarkar D Seth A K Dozier J K Neathery H H Hamdehand BHDavis ldquoFischer-Tropsch synthesismorphology phasetransformation and particle size growth of nano-scale particlesrdquoCatalysis Letters vol 117 no 1-2 pp 1ndash17 2007
[10] A Nakhaei Pour S Taghipoor M Shekarriz S M K Shahriand Y Zamani ldquoFischer-tropsch synthesis with FeCuLaSiO
2
nano-structured catalystrdquo Journal of Nanoscience andNanotech-nology vol 9 no 7 pp 4425ndash4429 2009
[11] A Nakhaei Pour M R Housaindokht S F Tayyari and JZarkesh ldquoFischer-Tropsch synthesis by nano-structured ironcatalystrdquo Journal of Natural Gas Chemistry vol 19 no 3 pp284ndash292 2010
[12] A Nakhaei Pour M R Housaindokht S F Tayyari and JZarkesh ldquoEffect of nano-particle size on product distributionand kinetic parameters of FeCuLa catalyst in Fischer-Tropschsynthesisrdquo Journal of Natural Gas Chemistry vol 19 no 2 pp107ndash116 2010
[13] D Y Murzin ldquoSize-dependent heterogeneous catalytic kinet-icsrdquo Journal ofMolecular Catalysis A vol 315 no 2 pp 226ndash2302010
[14] D Y Murzin ldquoThermodynamic analysis of nanoparticle sizeeffect on catalytic kineticsrdquo Chemical Engineering Science vol64 no 5 pp 1046ndash1052 2009
[15] ANakhaei Pour SMK ShahriH R Bozorgzadeh Y ZamaniA Tavasoli and M A Marvast ldquoEffect of Mg La and Capromoters on the structure and catalytic behavior of iron-basedcatalysts in Fischer-Tropsch synthesisrdquo Applied Catalysis A vol348 no 2 pp 201ndash208 2008
[16] A Nakhaei Pour Y Zamani A Tavasoli S M K Shahri andS A Taheri ldquoStudy on products distribution of iron and iron-zeolite catalysts in Fischer-Tropsch synthesisrdquo Fuel vol 87 no10-11 pp 2004ndash2012 2008
[17] A Nakhaei Pour M R Housaindokht S F Tayyari J Zarkeshand M R Alaei ldquoDeactivation studies of Fischer-Tropschsynthesis on nano-structured iron catalystrdquo Journal ofMolecularCatalysis A vol 330 no 1-2 pp 112ndash120 2010
[18] H I Chen and H Y Chang ldquoHomogeneous precipitation ofcerium dioxide nanoparticles in alcoholwater mixed solventsrdquoColloids and Surfaces A vol 242 pp 61ndash69 2004
[19] A Ramirez and L Sierra ldquoSimulation of nitrogen sorptionprocesses in materials with cylindrical mesopores hysteresisas a thermodynamic and connectivity phenomenonrdquo ChemicalEngineering Science vol 61 no 13 pp 4233ndash4241 2006
[20] M E Dry ldquoThe Fischer-Tropsch synthesisrdquo inCatalysis Scienceand Technology J R Anderson and M Boudart Eds SpringerNew York NY USA 1981
[21] G P van der Laan and A A C M Beenackers ldquoKinetics andselectivity of the Fischer-Tropsch synthesis a literature reviewrdquoCatalysis Reviews Science and Engineering vol 41 no 3-4 pp255ndash318 1999
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
6 Journal of Chemistry
000
020
040
060Re
lativ
e fre
quen
cy
Size range (nm)
5ndash10
10ndash1
5
15ndash2
0
20ndash2
5
25ndash3
0
lt30
(a)
000
020
040
060
Rela
tive f
requ
ency
Size range (nm)
5ndash10
10ndash1
5
15ndash2
0
20ndash2
5
25ndash3
0
lt30
(b)
000
020
040
Rela
tive f
requ
ency
Size range (nm)
5ndash10
10ndash1
5
15ndash2
0
20ndash2
5
25ndash3
0
lt30
(c)
Size range (nm)
000
020
040
Rela
tive f
requ
ency
5ndash10
10ndash1
5
15ndash2
0
20ndash2
5
25ndash3
0
lt30
(d)
Figure 5 Relative particle size distribution of prepared catalysts after calcinations ((a) HLB = 139 (b) HLB = 237 (c) HLB = 312 (d)HLB = 40)
of the 120572-Fe2O3 and decreases the reduction temperature for
first peak in H2-TPR profile
The amount of the consumed H2during different reduc-
tion stages which is obtained from integrating the area of thecorresponding reduction peak is summarized in Table 3 Theoverall H
2consumption [molH
2molM(Fe +Cu)] of the first
reduction peaks can be assigned to the reduction of CuO andalso the reduction of 120572-Fe
2O3to Cu and Fe
3O4 respectively
In the first stage of reduction CuO and Fe2O3reacted with
hydrogen based on the following reactions
3Fe2O3+H2997888rarr 2Fe
3O4+H2O
(
molH2
mol Fe= 0166 for complete reduction)
(3)
CuO +H2997888rarr Cu +H
2O
(
molH2
molCu= 1 for complete reduction)
(4)
The peaks at 851 K (molH2mol Fe) correspond to the reduc-
tion of Fe3O4to Fe as below
Fe3O4+ 4H2997888rarr 3Fe + 4H
2O
(
mol H2
mol Fe= 133 for complete reduction)
(5)
The peaks at higher temperature (above 900K)may be due tothe reduction of FeO to Fe and the H
2consumptions which
are consistent with theoretical valuesAs shown in Figure 6 and Table 3 smaller crystal size of
the catalyst has also influence on the reduction of Fe3O4to
Journal of Chemistry 7
450 550 650 750 850 950 1050 1150Temperature (K)
H2
upta
ke
(a)
(b)
(c)
(d)
Figure 6 TPR profiles of prepared catalysts after calcinations ((a)HLB = 139 (b) HLB = 237 (c) HLB = 312 and (d) HLB = 40)
0
05
1
15
2
25
3
35
4
45
0 2 4 6 8 10 12 14 16 18
OlP
a rat
io
Carbon number
HLB = 139HLB = 237
HLB = 312HLB = 40
Figure 7 Olefin-to-paraffin ratio in products after 35 h time-on-stream reaction conditions 583 K 17 bar (H
2CO)feed = 1 and
space velocity of 49 nl sdot hminus1 sdot gFeminus1 ((a) HLB = 139 (b) HLB = 237
(c) HLB = 312 and (d) HLB = 40)
120572-Fe as well as first reduction step The results show that theamount of the catalyst reduction increased with decreasingthe catalyst crystal size
32 Catalytic Activity The effect of the catalyst particle sizeon catalyst activity product selectivity and hydrocarbondistribution at the same time-on stream is listed in Table 4It was found that the CO and H
2conversion was increased
while the HLB value of surfactant decreased It is also shownin this table that the methane and CO
2selectivity increased
while the catalyst particle size decreased Moreover higherhydrocarbon selectivity and chain growth probability (120572)decreased when the crystal size decreased
Olefin-to-paraffin ratio in products and olefin and paraf-fin production rates after 35 h time-on-stream are shown inFigures 7 and 8 As listed in Table 4 and shown in Figures 7and 8 olefin selectivity is decreased by reduction of the HLBvalue of the surfactant (catalyst particle size decreased) Alsoas shown in Figures 7 and 8 olefin selectivity decreases withincreasing the olefins carbon number
The catalytic properties of nanoparticles depend on thesize of catalysts active site Thus different sizes of nanopar-ticles have different catalytic activity and selectivity Thedynamic surface restructuring of nanoparticles should alsodepend on their size that is smaller nanoparticles havehigher surface energies For the heterogeneous catalyticreactions adsorption equilibrium constant of feed increasedwith decreasing the particle size [13 14] By increasing theadsorption equilibrium constant of hydrogen and carbonmonoxide on surface of iron catalysts in small particles thecatalyst reduction and FTS reaction increased Also higheractivity of the iron catalyst with lower particle size (Table 4)may be related to the reduction ability of the catalysts thatincreased with the particle size (Figure 6 and Table 3)
It is postulated that 1-alkenes are primary products ofthe FTS reaction over iron-based catalyst and may be trans-formed to paraffin by hydrogenation as a secondary reaction[20 21] Secondary reactions occur when primary productsdesorbed from a site and then interact with another catalyticsite before leaving the catalyst particles Secondary reactionscan influence the type and molecular weight of the hydro-carbon products Hydrogenation of 1-alkenes to paraffin isthe most famous secondary reaction in FT synthesis Thusthe extent of secondary reactions can also be observed fromthe dependency of the 119874
119899119875119899ratio or olefin content on chain
length The ratio of olefins to paraffins depends on catalysttype structure and the reaction conditions Slow removalof reactive products (eg 120572-olefins) due to the reductionof diffusion coefficients with increasing chain length caninfluence the FTS reaction rate and selectivity The resultspresented in Table 4 show that the olefinparaffin ratios aredecreased with increasing catalyst particle size
Van der Laan and Beenackers emphasized the solubilityimpact (vapor-liquid equilibrium) over diffusion as the maincontributor on secondary reactions [21] As shown in Table 4the secondary reactions are increased (119874119875 decreased) inthe lower iron particle size because of some difficulties ofolefin diffusion in nanoparticles with narrow pores On theother hand the steric hindrance can limit the competitiveadsorption of bigger molecules on smaller crystal sizesThus increasing the adsorption equilibrium constant bydecreasing iron particle size is more for hydrogen than thatof carbon monoxide [8ndash12] Higher hydrogen concentrationson smaller particles enhance the hydrogenation of olefinTheresults presented in Figures 7 and 8 and Table 4 show thatthe olefinparaffin ratios are decreased with increasing thecatalyst particle size of the samples
Anderson-Schultz-Floury (ASF) distribution of FTSproducts on catalysts is presented in Figure 9 Product
8 Journal of Chemistry
00
05
10
15
20
25
30
35
40
0 4 8 12 16Carbon number
HLB = 139
(mm
ole
(gca
tmiddoth))
(a)
00
05
10
15
20
25
30
35
0 4 8 12 16
Carbon number
HLB = 237
(mm
ole
(gca
tmiddoth))
(b)
00
05
10
15
20
25
30
0 4 8 12 16
Carbon number
Para
Ol
HLB = 312
(mm
ole
(gca
tmiddoth))
(c)
00
05
10
15
20
25
0 4 8 12 16Carbon number
Para
Ol
HLB = 40(m
mol
e(g
catmiddoth
))
(d)
Figure 8 Olefin and paraffin production rates after 35 h time-on-stream and reaction conditions 583 K 17 bar (H2CO)feed = 1 space
velocity of 49 nl sdot hminus1 sdot gFeminus1 ((a) HLB = 139 (b) HLB = 237 (c) HLB = 312 and (d) HLB = 40)
Table 3 Quantitative results of H2 consumption for catalysts in H2-TPRa
HLB Peak (K) H2 consumption Reductionmol H2mol Mb mol H2mol Fe
139 533 0171 93850 124
237 558 0163 87851 116
312 608 0154 84842 112
40 640 0142 79852 106
aThe H2 consumption was measured from the area under the corresponding peakbM = Fe + Cu
Journal of Chemistry 9
Table 4 Catalysts activity and products selectivity after 35 h time-on-stream
HLB XCOa HCb OPc
120572d CO2 ()e Products selectivity
CH4 C2ndashC4 C5ndashC12 C12+
40 672 213 11 083 313 137 417 350 96312 715 222 10 08 322 146 476 315 63237 752 228 10 078 331 156 532 274 38139 775 235 09 075 345 176 575 228 21Reaction conditions 563K 17Mpa and H2CO = 1 and space velocity = 49 nl sdot hminus1 sdot gFe
minus1aCarbon monoxide conversion (mol)bHydrocarbon production gCH2gFes (times10
5) and CH4 freecOlefin to paraffin ratiodChain growth probabilityeCO2 selectivity selectivity to oxygenates was negligible (lt20) in all cases
0
00
5 10 15 20 25 30 35
Carbon number
minus120
minus100
minus80
minus60
minus40
minus20
lnX
i
HLB = 139HLB = 237
HLB = 312HLB = 40
Figure 9 Overall products distributions on catalysts after 35 h time-on-stream reaction conditions 583 K 17 bar (H
2CO)feed = 1 space
velocity of 49 nl sdot hminus1 sdot gFeminus1 ((a) HLB = 139 (b) HLB = 237 (c)
HLB = 312 and (d) HLB = 40)
distribution shows a slight shift to the lower molecularweight hydrocarbons by decreasing the HLB value of thesurfactant The trend lines are plotted to determine the chaingrowth probability 120572 As listed in Table 4 the chain growthprobabilities were 083 08 078 and 075 for 40 312 237and 139 HLB value of surfactant respectively This confirmsthe higher molecular weight hydrocarbons production usinghigher HLB value of surfactant in preparation of catalystAs mentioned in the previous section higher HLB value ofsurfactant produced higher particle size of catalysts
Figure 9 and Table 4 also show the effects of the catalystparticle size on the selectivity of Fischer-Tropsch synthesisproducts Comparison of the product distributions of thecatalysts clearly shows that the product distribution shiftto the lower molecular weight hydrocarbons by decreasingthe HLB value of the surfactant (or decreasing the catalystparticle size)
The most accepted mechanism for FTS reaction is C1
insertion which leads to the carbide theory [21] These C1
species have various hydrogenation degrees as follows COHCO HCOH CH and CH
2 Literature results [19 20] have
discussed that light hydrocarbons are built up by monomersthat exhibited higher degree of hydrogenation that is CH
2
Obviously heavy hydrocarbons are built up due tomonomersexcept CH
2species with lower degree of hydrogenation
With increasing the hydrogen concentration on the surfaceof the catalyst the concentration of C
1monomers with
higher degree of hydrogenation are increased Increasing theconcentration of hydrogen on the surface of the catalysts as aresult of reduction of the catalyst particle size increases theconcentration of C
1monomers and ultimately leads to the
higher selectivity to the lower hydrocarbons being enhanced
4 Conclusion
Nanosized iron oxide particles have been successfully synthe-sized by reverse microemulsion with different HLB valuesThe iron oxide particle size and particle size distribution areincreased by decreasing of HLB values It was found that theCO and H
2conversion is increased as the HLB value of the
surfactant is reduced Also the methane and CO2selectivity
is increased at the same time as the catalyst particle size isdecreased In addition higher hydrocarbon selectivity andchain growth probability (120572) show a descending trend incarbon number when the crystal size decreases
Acknowledgment
Financial support of the Ferdowsi University of MashhadIran (P153691-8985) is gratefully acknowledged
References
[1] A T Bell ldquoThe impact of nanoscience on heterogeneouscatalysisrdquo Science vol 299 no 5613 pp 1688ndash1691 2003
[2] J Y Ying ldquoDesign and synthesis of nanostructured catalystsrdquoChemical Engineering Science vol 61 no 5 pp 1540ndash1548 2006
[3] X Zhou W Xu G Liu D Panda and P Chen ldquoSize depen-dent catalytic activity and dynamics of gold nanoparticles at
10 Journal of Chemistry
the single-molecule levelrdquo Journal of the American ChemicalSociety vol 132 no 1 pp 138ndash146 2010
[4] P Kumar and K L MittalHandbook of Microemulsions Scienceand Technology Marcel Dekker New York NY USA 1999
[5] S Eriksson U Nylen S Rojas andM Boutonnet ldquoPreparationof catalysts from microemulsions and their applications inheterogeneous catalysisrdquoApplied Catalysis A vol 265 no 2 pp207ndash219 2004
[6] I Capek ldquoPreparation of metal nanoparticles in water-in-oil (wo) microemulsionsrdquo Advances in Colloid and InterfaceScience vol 110 no 1-2 pp 49ndash74 2004
[7] G Guo Y Sun Z Wang and H Guo ldquoPreparation of hydrox-yapatite nanoparticles by reverse microemulsionrdquo CeramicsInternational vol 31 no 6 pp 869ndash872 2005
[8] T Herranz S Rojas F J Perez-Alonso M Ojeda P Terrerosand J L G Fierro ldquoHydrogenation of carbon oxides overpromoted Fe-Mn catalysts prepared by the microemulsionmethodologyrdquo Applied Catalysis A vol 311 pp 66ndash75 2006
[9] A Sarkar D Seth A K Dozier J K Neathery H H Hamdehand BHDavis ldquoFischer-Tropsch synthesismorphology phasetransformation and particle size growth of nano-scale particlesrdquoCatalysis Letters vol 117 no 1-2 pp 1ndash17 2007
[10] A Nakhaei Pour S Taghipoor M Shekarriz S M K Shahriand Y Zamani ldquoFischer-tropsch synthesis with FeCuLaSiO
2
nano-structured catalystrdquo Journal of Nanoscience andNanotech-nology vol 9 no 7 pp 4425ndash4429 2009
[11] A Nakhaei Pour M R Housaindokht S F Tayyari and JZarkesh ldquoFischer-Tropsch synthesis by nano-structured ironcatalystrdquo Journal of Natural Gas Chemistry vol 19 no 3 pp284ndash292 2010
[12] A Nakhaei Pour M R Housaindokht S F Tayyari and JZarkesh ldquoEffect of nano-particle size on product distributionand kinetic parameters of FeCuLa catalyst in Fischer-Tropschsynthesisrdquo Journal of Natural Gas Chemistry vol 19 no 2 pp107ndash116 2010
[13] D Y Murzin ldquoSize-dependent heterogeneous catalytic kinet-icsrdquo Journal ofMolecular Catalysis A vol 315 no 2 pp 226ndash2302010
[14] D Y Murzin ldquoThermodynamic analysis of nanoparticle sizeeffect on catalytic kineticsrdquo Chemical Engineering Science vol64 no 5 pp 1046ndash1052 2009
[15] ANakhaei Pour SMK ShahriH R Bozorgzadeh Y ZamaniA Tavasoli and M A Marvast ldquoEffect of Mg La and Capromoters on the structure and catalytic behavior of iron-basedcatalysts in Fischer-Tropsch synthesisrdquo Applied Catalysis A vol348 no 2 pp 201ndash208 2008
[16] A Nakhaei Pour Y Zamani A Tavasoli S M K Shahri andS A Taheri ldquoStudy on products distribution of iron and iron-zeolite catalysts in Fischer-Tropsch synthesisrdquo Fuel vol 87 no10-11 pp 2004ndash2012 2008
[17] A Nakhaei Pour M R Housaindokht S F Tayyari J Zarkeshand M R Alaei ldquoDeactivation studies of Fischer-Tropschsynthesis on nano-structured iron catalystrdquo Journal ofMolecularCatalysis A vol 330 no 1-2 pp 112ndash120 2010
[18] H I Chen and H Y Chang ldquoHomogeneous precipitation ofcerium dioxide nanoparticles in alcoholwater mixed solventsrdquoColloids and Surfaces A vol 242 pp 61ndash69 2004
[19] A Ramirez and L Sierra ldquoSimulation of nitrogen sorptionprocesses in materials with cylindrical mesopores hysteresisas a thermodynamic and connectivity phenomenonrdquo ChemicalEngineering Science vol 61 no 13 pp 4233ndash4241 2006
[20] M E Dry ldquoThe Fischer-Tropsch synthesisrdquo inCatalysis Scienceand Technology J R Anderson and M Boudart Eds SpringerNew York NY USA 1981
[21] G P van der Laan and A A C M Beenackers ldquoKinetics andselectivity of the Fischer-Tropsch synthesis a literature reviewrdquoCatalysis Reviews Science and Engineering vol 41 no 3-4 pp255ndash318 1999
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
Journal of Chemistry 7
450 550 650 750 850 950 1050 1150Temperature (K)
H2
upta
ke
(a)
(b)
(c)
(d)
Figure 6 TPR profiles of prepared catalysts after calcinations ((a)HLB = 139 (b) HLB = 237 (c) HLB = 312 and (d) HLB = 40)
0
05
1
15
2
25
3
35
4
45
0 2 4 6 8 10 12 14 16 18
OlP
a rat
io
Carbon number
HLB = 139HLB = 237
HLB = 312HLB = 40
Figure 7 Olefin-to-paraffin ratio in products after 35 h time-on-stream reaction conditions 583 K 17 bar (H
2CO)feed = 1 and
space velocity of 49 nl sdot hminus1 sdot gFeminus1 ((a) HLB = 139 (b) HLB = 237
(c) HLB = 312 and (d) HLB = 40)
120572-Fe as well as first reduction step The results show that theamount of the catalyst reduction increased with decreasingthe catalyst crystal size
32 Catalytic Activity The effect of the catalyst particle sizeon catalyst activity product selectivity and hydrocarbondistribution at the same time-on stream is listed in Table 4It was found that the CO and H
2conversion was increased
while the HLB value of surfactant decreased It is also shownin this table that the methane and CO
2selectivity increased
while the catalyst particle size decreased Moreover higherhydrocarbon selectivity and chain growth probability (120572)decreased when the crystal size decreased
Olefin-to-paraffin ratio in products and olefin and paraf-fin production rates after 35 h time-on-stream are shown inFigures 7 and 8 As listed in Table 4 and shown in Figures 7and 8 olefin selectivity is decreased by reduction of the HLBvalue of the surfactant (catalyst particle size decreased) Alsoas shown in Figures 7 and 8 olefin selectivity decreases withincreasing the olefins carbon number
The catalytic properties of nanoparticles depend on thesize of catalysts active site Thus different sizes of nanopar-ticles have different catalytic activity and selectivity Thedynamic surface restructuring of nanoparticles should alsodepend on their size that is smaller nanoparticles havehigher surface energies For the heterogeneous catalyticreactions adsorption equilibrium constant of feed increasedwith decreasing the particle size [13 14] By increasing theadsorption equilibrium constant of hydrogen and carbonmonoxide on surface of iron catalysts in small particles thecatalyst reduction and FTS reaction increased Also higheractivity of the iron catalyst with lower particle size (Table 4)may be related to the reduction ability of the catalysts thatincreased with the particle size (Figure 6 and Table 3)
It is postulated that 1-alkenes are primary products ofthe FTS reaction over iron-based catalyst and may be trans-formed to paraffin by hydrogenation as a secondary reaction[20 21] Secondary reactions occur when primary productsdesorbed from a site and then interact with another catalyticsite before leaving the catalyst particles Secondary reactionscan influence the type and molecular weight of the hydro-carbon products Hydrogenation of 1-alkenes to paraffin isthe most famous secondary reaction in FT synthesis Thusthe extent of secondary reactions can also be observed fromthe dependency of the 119874
119899119875119899ratio or olefin content on chain
length The ratio of olefins to paraffins depends on catalysttype structure and the reaction conditions Slow removalof reactive products (eg 120572-olefins) due to the reductionof diffusion coefficients with increasing chain length caninfluence the FTS reaction rate and selectivity The resultspresented in Table 4 show that the olefinparaffin ratios aredecreased with increasing catalyst particle size
Van der Laan and Beenackers emphasized the solubilityimpact (vapor-liquid equilibrium) over diffusion as the maincontributor on secondary reactions [21] As shown in Table 4the secondary reactions are increased (119874119875 decreased) inthe lower iron particle size because of some difficulties ofolefin diffusion in nanoparticles with narrow pores On theother hand the steric hindrance can limit the competitiveadsorption of bigger molecules on smaller crystal sizesThus increasing the adsorption equilibrium constant bydecreasing iron particle size is more for hydrogen than thatof carbon monoxide [8ndash12] Higher hydrogen concentrationson smaller particles enhance the hydrogenation of olefinTheresults presented in Figures 7 and 8 and Table 4 show thatthe olefinparaffin ratios are decreased with increasing thecatalyst particle size of the samples
Anderson-Schultz-Floury (ASF) distribution of FTSproducts on catalysts is presented in Figure 9 Product
8 Journal of Chemistry
00
05
10
15
20
25
30
35
40
0 4 8 12 16Carbon number
HLB = 139
(mm
ole
(gca
tmiddoth))
(a)
00
05
10
15
20
25
30
35
0 4 8 12 16
Carbon number
HLB = 237
(mm
ole
(gca
tmiddoth))
(b)
00
05
10
15
20
25
30
0 4 8 12 16
Carbon number
Para
Ol
HLB = 312
(mm
ole
(gca
tmiddoth))
(c)
00
05
10
15
20
25
0 4 8 12 16Carbon number
Para
Ol
HLB = 40(m
mol
e(g
catmiddoth
))
(d)
Figure 8 Olefin and paraffin production rates after 35 h time-on-stream and reaction conditions 583 K 17 bar (H2CO)feed = 1 space
velocity of 49 nl sdot hminus1 sdot gFeminus1 ((a) HLB = 139 (b) HLB = 237 (c) HLB = 312 and (d) HLB = 40)
Table 3 Quantitative results of H2 consumption for catalysts in H2-TPRa
HLB Peak (K) H2 consumption Reductionmol H2mol Mb mol H2mol Fe
139 533 0171 93850 124
237 558 0163 87851 116
312 608 0154 84842 112
40 640 0142 79852 106
aThe H2 consumption was measured from the area under the corresponding peakbM = Fe + Cu
Journal of Chemistry 9
Table 4 Catalysts activity and products selectivity after 35 h time-on-stream
HLB XCOa HCb OPc
120572d CO2 ()e Products selectivity
CH4 C2ndashC4 C5ndashC12 C12+
40 672 213 11 083 313 137 417 350 96312 715 222 10 08 322 146 476 315 63237 752 228 10 078 331 156 532 274 38139 775 235 09 075 345 176 575 228 21Reaction conditions 563K 17Mpa and H2CO = 1 and space velocity = 49 nl sdot hminus1 sdot gFe
minus1aCarbon monoxide conversion (mol)bHydrocarbon production gCH2gFes (times10
5) and CH4 freecOlefin to paraffin ratiodChain growth probabilityeCO2 selectivity selectivity to oxygenates was negligible (lt20) in all cases
0
00
5 10 15 20 25 30 35
Carbon number
minus120
minus100
minus80
minus60
minus40
minus20
lnX
i
HLB = 139HLB = 237
HLB = 312HLB = 40
Figure 9 Overall products distributions on catalysts after 35 h time-on-stream reaction conditions 583 K 17 bar (H
2CO)feed = 1 space
velocity of 49 nl sdot hminus1 sdot gFeminus1 ((a) HLB = 139 (b) HLB = 237 (c)
HLB = 312 and (d) HLB = 40)
distribution shows a slight shift to the lower molecularweight hydrocarbons by decreasing the HLB value of thesurfactant The trend lines are plotted to determine the chaingrowth probability 120572 As listed in Table 4 the chain growthprobabilities were 083 08 078 and 075 for 40 312 237and 139 HLB value of surfactant respectively This confirmsthe higher molecular weight hydrocarbons production usinghigher HLB value of surfactant in preparation of catalystAs mentioned in the previous section higher HLB value ofsurfactant produced higher particle size of catalysts
Figure 9 and Table 4 also show the effects of the catalystparticle size on the selectivity of Fischer-Tropsch synthesisproducts Comparison of the product distributions of thecatalysts clearly shows that the product distribution shiftto the lower molecular weight hydrocarbons by decreasingthe HLB value of the surfactant (or decreasing the catalystparticle size)
The most accepted mechanism for FTS reaction is C1
insertion which leads to the carbide theory [21] These C1
species have various hydrogenation degrees as follows COHCO HCOH CH and CH
2 Literature results [19 20] have
discussed that light hydrocarbons are built up by monomersthat exhibited higher degree of hydrogenation that is CH
2
Obviously heavy hydrocarbons are built up due tomonomersexcept CH
2species with lower degree of hydrogenation
With increasing the hydrogen concentration on the surfaceof the catalyst the concentration of C
1monomers with
higher degree of hydrogenation are increased Increasing theconcentration of hydrogen on the surface of the catalysts as aresult of reduction of the catalyst particle size increases theconcentration of C
1monomers and ultimately leads to the
higher selectivity to the lower hydrocarbons being enhanced
4 Conclusion
Nanosized iron oxide particles have been successfully synthe-sized by reverse microemulsion with different HLB valuesThe iron oxide particle size and particle size distribution areincreased by decreasing of HLB values It was found that theCO and H
2conversion is increased as the HLB value of the
surfactant is reduced Also the methane and CO2selectivity
is increased at the same time as the catalyst particle size isdecreased In addition higher hydrocarbon selectivity andchain growth probability (120572) show a descending trend incarbon number when the crystal size decreases
Acknowledgment
Financial support of the Ferdowsi University of MashhadIran (P153691-8985) is gratefully acknowledged
References
[1] A T Bell ldquoThe impact of nanoscience on heterogeneouscatalysisrdquo Science vol 299 no 5613 pp 1688ndash1691 2003
[2] J Y Ying ldquoDesign and synthesis of nanostructured catalystsrdquoChemical Engineering Science vol 61 no 5 pp 1540ndash1548 2006
[3] X Zhou W Xu G Liu D Panda and P Chen ldquoSize depen-dent catalytic activity and dynamics of gold nanoparticles at
10 Journal of Chemistry
the single-molecule levelrdquo Journal of the American ChemicalSociety vol 132 no 1 pp 138ndash146 2010
[4] P Kumar and K L MittalHandbook of Microemulsions Scienceand Technology Marcel Dekker New York NY USA 1999
[5] S Eriksson U Nylen S Rojas andM Boutonnet ldquoPreparationof catalysts from microemulsions and their applications inheterogeneous catalysisrdquoApplied Catalysis A vol 265 no 2 pp207ndash219 2004
[6] I Capek ldquoPreparation of metal nanoparticles in water-in-oil (wo) microemulsionsrdquo Advances in Colloid and InterfaceScience vol 110 no 1-2 pp 49ndash74 2004
[7] G Guo Y Sun Z Wang and H Guo ldquoPreparation of hydrox-yapatite nanoparticles by reverse microemulsionrdquo CeramicsInternational vol 31 no 6 pp 869ndash872 2005
[8] T Herranz S Rojas F J Perez-Alonso M Ojeda P Terrerosand J L G Fierro ldquoHydrogenation of carbon oxides overpromoted Fe-Mn catalysts prepared by the microemulsionmethodologyrdquo Applied Catalysis A vol 311 pp 66ndash75 2006
[9] A Sarkar D Seth A K Dozier J K Neathery H H Hamdehand BHDavis ldquoFischer-Tropsch synthesismorphology phasetransformation and particle size growth of nano-scale particlesrdquoCatalysis Letters vol 117 no 1-2 pp 1ndash17 2007
[10] A Nakhaei Pour S Taghipoor M Shekarriz S M K Shahriand Y Zamani ldquoFischer-tropsch synthesis with FeCuLaSiO
2
nano-structured catalystrdquo Journal of Nanoscience andNanotech-nology vol 9 no 7 pp 4425ndash4429 2009
[11] A Nakhaei Pour M R Housaindokht S F Tayyari and JZarkesh ldquoFischer-Tropsch synthesis by nano-structured ironcatalystrdquo Journal of Natural Gas Chemistry vol 19 no 3 pp284ndash292 2010
[12] A Nakhaei Pour M R Housaindokht S F Tayyari and JZarkesh ldquoEffect of nano-particle size on product distributionand kinetic parameters of FeCuLa catalyst in Fischer-Tropschsynthesisrdquo Journal of Natural Gas Chemistry vol 19 no 2 pp107ndash116 2010
[13] D Y Murzin ldquoSize-dependent heterogeneous catalytic kinet-icsrdquo Journal ofMolecular Catalysis A vol 315 no 2 pp 226ndash2302010
[14] D Y Murzin ldquoThermodynamic analysis of nanoparticle sizeeffect on catalytic kineticsrdquo Chemical Engineering Science vol64 no 5 pp 1046ndash1052 2009
[15] ANakhaei Pour SMK ShahriH R Bozorgzadeh Y ZamaniA Tavasoli and M A Marvast ldquoEffect of Mg La and Capromoters on the structure and catalytic behavior of iron-basedcatalysts in Fischer-Tropsch synthesisrdquo Applied Catalysis A vol348 no 2 pp 201ndash208 2008
[16] A Nakhaei Pour Y Zamani A Tavasoli S M K Shahri andS A Taheri ldquoStudy on products distribution of iron and iron-zeolite catalysts in Fischer-Tropsch synthesisrdquo Fuel vol 87 no10-11 pp 2004ndash2012 2008
[17] A Nakhaei Pour M R Housaindokht S F Tayyari J Zarkeshand M R Alaei ldquoDeactivation studies of Fischer-Tropschsynthesis on nano-structured iron catalystrdquo Journal ofMolecularCatalysis A vol 330 no 1-2 pp 112ndash120 2010
[18] H I Chen and H Y Chang ldquoHomogeneous precipitation ofcerium dioxide nanoparticles in alcoholwater mixed solventsrdquoColloids and Surfaces A vol 242 pp 61ndash69 2004
[19] A Ramirez and L Sierra ldquoSimulation of nitrogen sorptionprocesses in materials with cylindrical mesopores hysteresisas a thermodynamic and connectivity phenomenonrdquo ChemicalEngineering Science vol 61 no 13 pp 4233ndash4241 2006
[20] M E Dry ldquoThe Fischer-Tropsch synthesisrdquo inCatalysis Scienceand Technology J R Anderson and M Boudart Eds SpringerNew York NY USA 1981
[21] G P van der Laan and A A C M Beenackers ldquoKinetics andselectivity of the Fischer-Tropsch synthesis a literature reviewrdquoCatalysis Reviews Science and Engineering vol 41 no 3-4 pp255ndash318 1999
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
8 Journal of Chemistry
00
05
10
15
20
25
30
35
40
0 4 8 12 16Carbon number
HLB = 139
(mm
ole
(gca
tmiddoth))
(a)
00
05
10
15
20
25
30
35
0 4 8 12 16
Carbon number
HLB = 237
(mm
ole
(gca
tmiddoth))
(b)
00
05
10
15
20
25
30
0 4 8 12 16
Carbon number
Para
Ol
HLB = 312
(mm
ole
(gca
tmiddoth))
(c)
00
05
10
15
20
25
0 4 8 12 16Carbon number
Para
Ol
HLB = 40(m
mol
e(g
catmiddoth
))
(d)
Figure 8 Olefin and paraffin production rates after 35 h time-on-stream and reaction conditions 583 K 17 bar (H2CO)feed = 1 space
velocity of 49 nl sdot hminus1 sdot gFeminus1 ((a) HLB = 139 (b) HLB = 237 (c) HLB = 312 and (d) HLB = 40)
Table 3 Quantitative results of H2 consumption for catalysts in H2-TPRa
HLB Peak (K) H2 consumption Reductionmol H2mol Mb mol H2mol Fe
139 533 0171 93850 124
237 558 0163 87851 116
312 608 0154 84842 112
40 640 0142 79852 106
aThe H2 consumption was measured from the area under the corresponding peakbM = Fe + Cu
Journal of Chemistry 9
Table 4 Catalysts activity and products selectivity after 35 h time-on-stream
HLB XCOa HCb OPc
120572d CO2 ()e Products selectivity
CH4 C2ndashC4 C5ndashC12 C12+
40 672 213 11 083 313 137 417 350 96312 715 222 10 08 322 146 476 315 63237 752 228 10 078 331 156 532 274 38139 775 235 09 075 345 176 575 228 21Reaction conditions 563K 17Mpa and H2CO = 1 and space velocity = 49 nl sdot hminus1 sdot gFe
minus1aCarbon monoxide conversion (mol)bHydrocarbon production gCH2gFes (times10
5) and CH4 freecOlefin to paraffin ratiodChain growth probabilityeCO2 selectivity selectivity to oxygenates was negligible (lt20) in all cases
0
00
5 10 15 20 25 30 35
Carbon number
minus120
minus100
minus80
minus60
minus40
minus20
lnX
i
HLB = 139HLB = 237
HLB = 312HLB = 40
Figure 9 Overall products distributions on catalysts after 35 h time-on-stream reaction conditions 583 K 17 bar (H
2CO)feed = 1 space
velocity of 49 nl sdot hminus1 sdot gFeminus1 ((a) HLB = 139 (b) HLB = 237 (c)
HLB = 312 and (d) HLB = 40)
distribution shows a slight shift to the lower molecularweight hydrocarbons by decreasing the HLB value of thesurfactant The trend lines are plotted to determine the chaingrowth probability 120572 As listed in Table 4 the chain growthprobabilities were 083 08 078 and 075 for 40 312 237and 139 HLB value of surfactant respectively This confirmsthe higher molecular weight hydrocarbons production usinghigher HLB value of surfactant in preparation of catalystAs mentioned in the previous section higher HLB value ofsurfactant produced higher particle size of catalysts
Figure 9 and Table 4 also show the effects of the catalystparticle size on the selectivity of Fischer-Tropsch synthesisproducts Comparison of the product distributions of thecatalysts clearly shows that the product distribution shiftto the lower molecular weight hydrocarbons by decreasingthe HLB value of the surfactant (or decreasing the catalystparticle size)
The most accepted mechanism for FTS reaction is C1
insertion which leads to the carbide theory [21] These C1
species have various hydrogenation degrees as follows COHCO HCOH CH and CH
2 Literature results [19 20] have
discussed that light hydrocarbons are built up by monomersthat exhibited higher degree of hydrogenation that is CH
2
Obviously heavy hydrocarbons are built up due tomonomersexcept CH
2species with lower degree of hydrogenation
With increasing the hydrogen concentration on the surfaceof the catalyst the concentration of C
1monomers with
higher degree of hydrogenation are increased Increasing theconcentration of hydrogen on the surface of the catalysts as aresult of reduction of the catalyst particle size increases theconcentration of C
1monomers and ultimately leads to the
higher selectivity to the lower hydrocarbons being enhanced
4 Conclusion
Nanosized iron oxide particles have been successfully synthe-sized by reverse microemulsion with different HLB valuesThe iron oxide particle size and particle size distribution areincreased by decreasing of HLB values It was found that theCO and H
2conversion is increased as the HLB value of the
surfactant is reduced Also the methane and CO2selectivity
is increased at the same time as the catalyst particle size isdecreased In addition higher hydrocarbon selectivity andchain growth probability (120572) show a descending trend incarbon number when the crystal size decreases
Acknowledgment
Financial support of the Ferdowsi University of MashhadIran (P153691-8985) is gratefully acknowledged
References
[1] A T Bell ldquoThe impact of nanoscience on heterogeneouscatalysisrdquo Science vol 299 no 5613 pp 1688ndash1691 2003
[2] J Y Ying ldquoDesign and synthesis of nanostructured catalystsrdquoChemical Engineering Science vol 61 no 5 pp 1540ndash1548 2006
[3] X Zhou W Xu G Liu D Panda and P Chen ldquoSize depen-dent catalytic activity and dynamics of gold nanoparticles at
10 Journal of Chemistry
the single-molecule levelrdquo Journal of the American ChemicalSociety vol 132 no 1 pp 138ndash146 2010
[4] P Kumar and K L MittalHandbook of Microemulsions Scienceand Technology Marcel Dekker New York NY USA 1999
[5] S Eriksson U Nylen S Rojas andM Boutonnet ldquoPreparationof catalysts from microemulsions and their applications inheterogeneous catalysisrdquoApplied Catalysis A vol 265 no 2 pp207ndash219 2004
[6] I Capek ldquoPreparation of metal nanoparticles in water-in-oil (wo) microemulsionsrdquo Advances in Colloid and InterfaceScience vol 110 no 1-2 pp 49ndash74 2004
[7] G Guo Y Sun Z Wang and H Guo ldquoPreparation of hydrox-yapatite nanoparticles by reverse microemulsionrdquo CeramicsInternational vol 31 no 6 pp 869ndash872 2005
[8] T Herranz S Rojas F J Perez-Alonso M Ojeda P Terrerosand J L G Fierro ldquoHydrogenation of carbon oxides overpromoted Fe-Mn catalysts prepared by the microemulsionmethodologyrdquo Applied Catalysis A vol 311 pp 66ndash75 2006
[9] A Sarkar D Seth A K Dozier J K Neathery H H Hamdehand BHDavis ldquoFischer-Tropsch synthesismorphology phasetransformation and particle size growth of nano-scale particlesrdquoCatalysis Letters vol 117 no 1-2 pp 1ndash17 2007
[10] A Nakhaei Pour S Taghipoor M Shekarriz S M K Shahriand Y Zamani ldquoFischer-tropsch synthesis with FeCuLaSiO
2
nano-structured catalystrdquo Journal of Nanoscience andNanotech-nology vol 9 no 7 pp 4425ndash4429 2009
[11] A Nakhaei Pour M R Housaindokht S F Tayyari and JZarkesh ldquoFischer-Tropsch synthesis by nano-structured ironcatalystrdquo Journal of Natural Gas Chemistry vol 19 no 3 pp284ndash292 2010
[12] A Nakhaei Pour M R Housaindokht S F Tayyari and JZarkesh ldquoEffect of nano-particle size on product distributionand kinetic parameters of FeCuLa catalyst in Fischer-Tropschsynthesisrdquo Journal of Natural Gas Chemistry vol 19 no 2 pp107ndash116 2010
[13] D Y Murzin ldquoSize-dependent heterogeneous catalytic kinet-icsrdquo Journal ofMolecular Catalysis A vol 315 no 2 pp 226ndash2302010
[14] D Y Murzin ldquoThermodynamic analysis of nanoparticle sizeeffect on catalytic kineticsrdquo Chemical Engineering Science vol64 no 5 pp 1046ndash1052 2009
[15] ANakhaei Pour SMK ShahriH R Bozorgzadeh Y ZamaniA Tavasoli and M A Marvast ldquoEffect of Mg La and Capromoters on the structure and catalytic behavior of iron-basedcatalysts in Fischer-Tropsch synthesisrdquo Applied Catalysis A vol348 no 2 pp 201ndash208 2008
[16] A Nakhaei Pour Y Zamani A Tavasoli S M K Shahri andS A Taheri ldquoStudy on products distribution of iron and iron-zeolite catalysts in Fischer-Tropsch synthesisrdquo Fuel vol 87 no10-11 pp 2004ndash2012 2008
[17] A Nakhaei Pour M R Housaindokht S F Tayyari J Zarkeshand M R Alaei ldquoDeactivation studies of Fischer-Tropschsynthesis on nano-structured iron catalystrdquo Journal ofMolecularCatalysis A vol 330 no 1-2 pp 112ndash120 2010
[18] H I Chen and H Y Chang ldquoHomogeneous precipitation ofcerium dioxide nanoparticles in alcoholwater mixed solventsrdquoColloids and Surfaces A vol 242 pp 61ndash69 2004
[19] A Ramirez and L Sierra ldquoSimulation of nitrogen sorptionprocesses in materials with cylindrical mesopores hysteresisas a thermodynamic and connectivity phenomenonrdquo ChemicalEngineering Science vol 61 no 13 pp 4233ndash4241 2006
[20] M E Dry ldquoThe Fischer-Tropsch synthesisrdquo inCatalysis Scienceand Technology J R Anderson and M Boudart Eds SpringerNew York NY USA 1981
[21] G P van der Laan and A A C M Beenackers ldquoKinetics andselectivity of the Fischer-Tropsch synthesis a literature reviewrdquoCatalysis Reviews Science and Engineering vol 41 no 3-4 pp255ndash318 1999
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
Journal of Chemistry 9
Table 4 Catalysts activity and products selectivity after 35 h time-on-stream
HLB XCOa HCb OPc
120572d CO2 ()e Products selectivity
CH4 C2ndashC4 C5ndashC12 C12+
40 672 213 11 083 313 137 417 350 96312 715 222 10 08 322 146 476 315 63237 752 228 10 078 331 156 532 274 38139 775 235 09 075 345 176 575 228 21Reaction conditions 563K 17Mpa and H2CO = 1 and space velocity = 49 nl sdot hminus1 sdot gFe
minus1aCarbon monoxide conversion (mol)bHydrocarbon production gCH2gFes (times10
5) and CH4 freecOlefin to paraffin ratiodChain growth probabilityeCO2 selectivity selectivity to oxygenates was negligible (lt20) in all cases
0
00
5 10 15 20 25 30 35
Carbon number
minus120
minus100
minus80
minus60
minus40
minus20
lnX
i
HLB = 139HLB = 237
HLB = 312HLB = 40
Figure 9 Overall products distributions on catalysts after 35 h time-on-stream reaction conditions 583 K 17 bar (H
2CO)feed = 1 space
velocity of 49 nl sdot hminus1 sdot gFeminus1 ((a) HLB = 139 (b) HLB = 237 (c)
HLB = 312 and (d) HLB = 40)
distribution shows a slight shift to the lower molecularweight hydrocarbons by decreasing the HLB value of thesurfactant The trend lines are plotted to determine the chaingrowth probability 120572 As listed in Table 4 the chain growthprobabilities were 083 08 078 and 075 for 40 312 237and 139 HLB value of surfactant respectively This confirmsthe higher molecular weight hydrocarbons production usinghigher HLB value of surfactant in preparation of catalystAs mentioned in the previous section higher HLB value ofsurfactant produced higher particle size of catalysts
Figure 9 and Table 4 also show the effects of the catalystparticle size on the selectivity of Fischer-Tropsch synthesisproducts Comparison of the product distributions of thecatalysts clearly shows that the product distribution shiftto the lower molecular weight hydrocarbons by decreasingthe HLB value of the surfactant (or decreasing the catalystparticle size)
The most accepted mechanism for FTS reaction is C1
insertion which leads to the carbide theory [21] These C1
species have various hydrogenation degrees as follows COHCO HCOH CH and CH
2 Literature results [19 20] have
discussed that light hydrocarbons are built up by monomersthat exhibited higher degree of hydrogenation that is CH
2
Obviously heavy hydrocarbons are built up due tomonomersexcept CH
2species with lower degree of hydrogenation
With increasing the hydrogen concentration on the surfaceof the catalyst the concentration of C
1monomers with
higher degree of hydrogenation are increased Increasing theconcentration of hydrogen on the surface of the catalysts as aresult of reduction of the catalyst particle size increases theconcentration of C
1monomers and ultimately leads to the
higher selectivity to the lower hydrocarbons being enhanced
4 Conclusion
Nanosized iron oxide particles have been successfully synthe-sized by reverse microemulsion with different HLB valuesThe iron oxide particle size and particle size distribution areincreased by decreasing of HLB values It was found that theCO and H
2conversion is increased as the HLB value of the
surfactant is reduced Also the methane and CO2selectivity
is increased at the same time as the catalyst particle size isdecreased In addition higher hydrocarbon selectivity andchain growth probability (120572) show a descending trend incarbon number when the crystal size decreases
Acknowledgment
Financial support of the Ferdowsi University of MashhadIran (P153691-8985) is gratefully acknowledged
References
[1] A T Bell ldquoThe impact of nanoscience on heterogeneouscatalysisrdquo Science vol 299 no 5613 pp 1688ndash1691 2003
[2] J Y Ying ldquoDesign and synthesis of nanostructured catalystsrdquoChemical Engineering Science vol 61 no 5 pp 1540ndash1548 2006
[3] X Zhou W Xu G Liu D Panda and P Chen ldquoSize depen-dent catalytic activity and dynamics of gold nanoparticles at
10 Journal of Chemistry
the single-molecule levelrdquo Journal of the American ChemicalSociety vol 132 no 1 pp 138ndash146 2010
[4] P Kumar and K L MittalHandbook of Microemulsions Scienceand Technology Marcel Dekker New York NY USA 1999
[5] S Eriksson U Nylen S Rojas andM Boutonnet ldquoPreparationof catalysts from microemulsions and their applications inheterogeneous catalysisrdquoApplied Catalysis A vol 265 no 2 pp207ndash219 2004
[6] I Capek ldquoPreparation of metal nanoparticles in water-in-oil (wo) microemulsionsrdquo Advances in Colloid and InterfaceScience vol 110 no 1-2 pp 49ndash74 2004
[7] G Guo Y Sun Z Wang and H Guo ldquoPreparation of hydrox-yapatite nanoparticles by reverse microemulsionrdquo CeramicsInternational vol 31 no 6 pp 869ndash872 2005
[8] T Herranz S Rojas F J Perez-Alonso M Ojeda P Terrerosand J L G Fierro ldquoHydrogenation of carbon oxides overpromoted Fe-Mn catalysts prepared by the microemulsionmethodologyrdquo Applied Catalysis A vol 311 pp 66ndash75 2006
[9] A Sarkar D Seth A K Dozier J K Neathery H H Hamdehand BHDavis ldquoFischer-Tropsch synthesismorphology phasetransformation and particle size growth of nano-scale particlesrdquoCatalysis Letters vol 117 no 1-2 pp 1ndash17 2007
[10] A Nakhaei Pour S Taghipoor M Shekarriz S M K Shahriand Y Zamani ldquoFischer-tropsch synthesis with FeCuLaSiO
2
nano-structured catalystrdquo Journal of Nanoscience andNanotech-nology vol 9 no 7 pp 4425ndash4429 2009
[11] A Nakhaei Pour M R Housaindokht S F Tayyari and JZarkesh ldquoFischer-Tropsch synthesis by nano-structured ironcatalystrdquo Journal of Natural Gas Chemistry vol 19 no 3 pp284ndash292 2010
[12] A Nakhaei Pour M R Housaindokht S F Tayyari and JZarkesh ldquoEffect of nano-particle size on product distributionand kinetic parameters of FeCuLa catalyst in Fischer-Tropschsynthesisrdquo Journal of Natural Gas Chemistry vol 19 no 2 pp107ndash116 2010
[13] D Y Murzin ldquoSize-dependent heterogeneous catalytic kinet-icsrdquo Journal ofMolecular Catalysis A vol 315 no 2 pp 226ndash2302010
[14] D Y Murzin ldquoThermodynamic analysis of nanoparticle sizeeffect on catalytic kineticsrdquo Chemical Engineering Science vol64 no 5 pp 1046ndash1052 2009
[15] ANakhaei Pour SMK ShahriH R Bozorgzadeh Y ZamaniA Tavasoli and M A Marvast ldquoEffect of Mg La and Capromoters on the structure and catalytic behavior of iron-basedcatalysts in Fischer-Tropsch synthesisrdquo Applied Catalysis A vol348 no 2 pp 201ndash208 2008
[16] A Nakhaei Pour Y Zamani A Tavasoli S M K Shahri andS A Taheri ldquoStudy on products distribution of iron and iron-zeolite catalysts in Fischer-Tropsch synthesisrdquo Fuel vol 87 no10-11 pp 2004ndash2012 2008
[17] A Nakhaei Pour M R Housaindokht S F Tayyari J Zarkeshand M R Alaei ldquoDeactivation studies of Fischer-Tropschsynthesis on nano-structured iron catalystrdquo Journal ofMolecularCatalysis A vol 330 no 1-2 pp 112ndash120 2010
[18] H I Chen and H Y Chang ldquoHomogeneous precipitation ofcerium dioxide nanoparticles in alcoholwater mixed solventsrdquoColloids and Surfaces A vol 242 pp 61ndash69 2004
[19] A Ramirez and L Sierra ldquoSimulation of nitrogen sorptionprocesses in materials with cylindrical mesopores hysteresisas a thermodynamic and connectivity phenomenonrdquo ChemicalEngineering Science vol 61 no 13 pp 4233ndash4241 2006
[20] M E Dry ldquoThe Fischer-Tropsch synthesisrdquo inCatalysis Scienceand Technology J R Anderson and M Boudart Eds SpringerNew York NY USA 1981
[21] G P van der Laan and A A C M Beenackers ldquoKinetics andselectivity of the Fischer-Tropsch synthesis a literature reviewrdquoCatalysis Reviews Science and Engineering vol 41 no 3-4 pp255ndash318 1999
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
10 Journal of Chemistry
the single-molecule levelrdquo Journal of the American ChemicalSociety vol 132 no 1 pp 138ndash146 2010
[4] P Kumar and K L MittalHandbook of Microemulsions Scienceand Technology Marcel Dekker New York NY USA 1999
[5] S Eriksson U Nylen S Rojas andM Boutonnet ldquoPreparationof catalysts from microemulsions and their applications inheterogeneous catalysisrdquoApplied Catalysis A vol 265 no 2 pp207ndash219 2004
[6] I Capek ldquoPreparation of metal nanoparticles in water-in-oil (wo) microemulsionsrdquo Advances in Colloid and InterfaceScience vol 110 no 1-2 pp 49ndash74 2004
[7] G Guo Y Sun Z Wang and H Guo ldquoPreparation of hydrox-yapatite nanoparticles by reverse microemulsionrdquo CeramicsInternational vol 31 no 6 pp 869ndash872 2005
[8] T Herranz S Rojas F J Perez-Alonso M Ojeda P Terrerosand J L G Fierro ldquoHydrogenation of carbon oxides overpromoted Fe-Mn catalysts prepared by the microemulsionmethodologyrdquo Applied Catalysis A vol 311 pp 66ndash75 2006
[9] A Sarkar D Seth A K Dozier J K Neathery H H Hamdehand BHDavis ldquoFischer-Tropsch synthesismorphology phasetransformation and particle size growth of nano-scale particlesrdquoCatalysis Letters vol 117 no 1-2 pp 1ndash17 2007
[10] A Nakhaei Pour S Taghipoor M Shekarriz S M K Shahriand Y Zamani ldquoFischer-tropsch synthesis with FeCuLaSiO
2
nano-structured catalystrdquo Journal of Nanoscience andNanotech-nology vol 9 no 7 pp 4425ndash4429 2009
[11] A Nakhaei Pour M R Housaindokht S F Tayyari and JZarkesh ldquoFischer-Tropsch synthesis by nano-structured ironcatalystrdquo Journal of Natural Gas Chemistry vol 19 no 3 pp284ndash292 2010
[12] A Nakhaei Pour M R Housaindokht S F Tayyari and JZarkesh ldquoEffect of nano-particle size on product distributionand kinetic parameters of FeCuLa catalyst in Fischer-Tropschsynthesisrdquo Journal of Natural Gas Chemistry vol 19 no 2 pp107ndash116 2010
[13] D Y Murzin ldquoSize-dependent heterogeneous catalytic kinet-icsrdquo Journal ofMolecular Catalysis A vol 315 no 2 pp 226ndash2302010
[14] D Y Murzin ldquoThermodynamic analysis of nanoparticle sizeeffect on catalytic kineticsrdquo Chemical Engineering Science vol64 no 5 pp 1046ndash1052 2009
[15] ANakhaei Pour SMK ShahriH R Bozorgzadeh Y ZamaniA Tavasoli and M A Marvast ldquoEffect of Mg La and Capromoters on the structure and catalytic behavior of iron-basedcatalysts in Fischer-Tropsch synthesisrdquo Applied Catalysis A vol348 no 2 pp 201ndash208 2008
[16] A Nakhaei Pour Y Zamani A Tavasoli S M K Shahri andS A Taheri ldquoStudy on products distribution of iron and iron-zeolite catalysts in Fischer-Tropsch synthesisrdquo Fuel vol 87 no10-11 pp 2004ndash2012 2008
[17] A Nakhaei Pour M R Housaindokht S F Tayyari J Zarkeshand M R Alaei ldquoDeactivation studies of Fischer-Tropschsynthesis on nano-structured iron catalystrdquo Journal ofMolecularCatalysis A vol 330 no 1-2 pp 112ndash120 2010
[18] H I Chen and H Y Chang ldquoHomogeneous precipitation ofcerium dioxide nanoparticles in alcoholwater mixed solventsrdquoColloids and Surfaces A vol 242 pp 61ndash69 2004
[19] A Ramirez and L Sierra ldquoSimulation of nitrogen sorptionprocesses in materials with cylindrical mesopores hysteresisas a thermodynamic and connectivity phenomenonrdquo ChemicalEngineering Science vol 61 no 13 pp 4233ndash4241 2006
[20] M E Dry ldquoThe Fischer-Tropsch synthesisrdquo inCatalysis Scienceand Technology J R Anderson and M Boudart Eds SpringerNew York NY USA 1981
[21] G P van der Laan and A A C M Beenackers ldquoKinetics andselectivity of the Fischer-Tropsch synthesis a literature reviewrdquoCatalysis Reviews Science and Engineering vol 41 no 3-4 pp255ndash318 1999
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of