Fischer−Tropsch Synthesis: Comparison of Performances of Iron and Cobalt Catalysts

Fischer-Tropsch Synthesis: Comparison of Performances of Iron and CobaltCatalysts

Burtron H. Davis*

Center for Applied Energy Research, UniVersity of Kentucky, 2540 Research Park DriVe,Lexington, Kentucky 40511

Biomass represents a source of syngas that can be further processed to hydrocarbon fuels. This paper examinesthe Fischer-Tropsch technology for the biomass-to-clean fuels scenario. A comparison of the activities,selectivities, and lifetimes of iron and cobalt catalysts for Fischer-Tropsch synthesis is made. For the moresevere conditions, iron is the more active catalyst, whereas a cobalt catalyst may be more active at low-severity conditions. In spite of many reports, there are still considerable differences in defining catalyst activity.The selectivity for methane likewise shows a wide range of reported results. Under the proper conditions,both catalysts are capable of operating for 6 months or more.

Introduction

Synthesis of hydrocarbon fuels from synthesis gas derivedfrom coal or natural gas by the Fischer-Tropsch option is awell-established commercial process. As the “biorefinery”concept, i.e., biomass to fuels, gains momentum, the Fischer-Tropsch synthesis (FTS) needs to be considered from thebiomass feedstock point of view. Many catalysts have beenutilized for studies of the Fischer-Tropsch synthesis. Forexample, supported ruthenium catalysts have been widelyutilized for mechanism studies, and while these results haveacademic interest, the commercial Fischer-Tropsch synthesisplants have utilized either iron or cobalt catalysts. Thus, thispaper will review the iron and cobalt systems.

The H2/CO ratio of the syngas generated from a specificfeedstock, say, a particular coal, may vary widely dependingupon the gasifier used. For example, a H2/CO ratio of nearly2.0 may be obtained from coal using a Sasol-Lurgi gasifier,but the ratio may be∼0.7 using a GE (formerly Texaco) gasifier.While the ratio obtained may be varied somewhat by the amountof CO2 or steam added with the carbonaceous feed, the C/Hratio of the feedstock will also impact the H2/CO ratio of thesyngas. The high oxygen content of most biomass materialsleads to the conversion of a large fraction of the carbon to CO2

and a syngas with a low (1 or less) H2/CO ratio.Once the syngas is generated and the H2/CO ratio is defined,

the same amount of hydrogen must be generated to producethe hydrocarbon fuel with a general formula of CH2+n, wheren is usually in the 0.1-0.2 range. The difference in the C/Hratio in the syngas and in the product defines the amount ofcarbon that must be converted to CO2 to generate the requiredamount of hydrogen by the water gas shift (WGS) reaction. Ifthe cobalt catalyst is selected for the FTS, then a WGS unitmust be installed after the gasifier and before the FT reactor.On the other hand, because the iron catalyst has WGS activity,the two reactions, WGS and FTS, may be carried out in thesame reactor. Thus, either catalyst system can be used with thesyngas derived from biomass, and a similar amount of carbonmust be converted to CO2 to generate the hydrogen that isneeded to produce the hydrocarbons.

In general, one is interested in the comparison of activity,selectivity, and lifetime of a catalyst under conditions appropriate

for commercial operation. At first glance, this should be an easytask. However, in practice, it is a very demanding task to makea useful comparison. Three reactor types have been utilized forFTS in many laboratory studies and at the commercial scale:fixed-bed, fluidized circulating and fixed-bed, and liquid slurry-phase reactors. In general, these reactors utilize differenttemperatures and different catalyst sizes. The optimum selectiv-ity of two catalysts usually will not occur for the same reactionconditions. In addition, the catalytic activity and selectivity maynot be constant with CO conversion levels, and this is not alwaystaken into account. In the following, we make an attempt tomake a valid comparison of some of the synthesis propertiesof iron and cobalt FTS catalysts.

Comparison of Catalytic Activity

There are a number of ways to compare the activity of acatalyst: measure of the activity per site (turnover number(TON)), conversion/(g of catalyst), conversion/(volume of cata-lyst), conversion/(unit of active catalytic component), and con-version/(surface area). For the cobalt catalyst, the situation isclear. A measure of the number of surface cobalt atoms can beobtained directly from the amount of hydrogen or carbon mon-oxide that is adsorbed on the reduced catalyst. Thus, a measureof the number of cobalt surface atoms and the CO convertedby these catalysts allows one to obtain the CO conversion/(surface cobalt). When such a plot is made, almost all cobaltcatalysts exhibit a constant activity per surface cobalt; that is,a plot of the CO conversion versus the cobalt dispersion is linear(Figure 1).1 The only exception reported to date for this is theRu promoted cobalt catalyst in some limited situations. SinceRu is a FT catalyst, it may contribute to the synthesis as wellas the cobalt, even though its intended function is as a promoter.

There appears, contrary to the conclusion one may reach fromthe data in Figure 1, to be room for debate when selecting thebest cobalt catalyst. On the basis of turnover data, cobaltsupported on titania appears to be the superior catalyst (Figure2).2 However, if we make a comparison from another study,we conclude that silica supported cobalt is the more activecatalyst (Figure 3).3 Comparing results from a third studyindicates that the alumina supported cobalt catalyst has thesuperior activity (Figure 4).4 The conclusion one reaches incomparing the data in Figures 1-4 is that, while it may be easyto measure the number of active sites in cobalt catalysts, thereis a considerable variation in the effects introduced by the

* Phone: (859) 257-0253. Fax: (859) 257-0302. E-mail: [email protected].

8938 Ind. Eng. Chem. Res.2007,46, 8938-8945

10.1021/ie0712434 CCC: $37.00 © 2007 American Chemical SocietyPublished on Web 11/28/2007

support. Presumably a factor in the differences in the data inFigures 2-4 is the variation in the conversion levels and in theconditions utilized in the studies.

The situation for the iron catalyst cannot be defined in thesimple manner as was done above for the cobalt catalyst. First,the active iron catalyst is a mixture that may contain ironcarbides, iron oxides, and even metallic iron.5 For this catalystmixture, the active species has not been defined. For example,there are claims that Fe3O4 is active, while there are other claimsthat it is the carbide phases, and not Fe3O4, that have catalyticactivity. No direct measure of catalytic sites is available for ironcatalysts. Thus, a reliable measure of the TON for iron catalystsis not possible today.

The rate of conversion of CO with an iron catalyst dependsupon the total CO conversion level; that is, the CO conversionis not linear over the total conversion range (Figure 5).6

Furthermore, the H2/CO ratio in the reactor depends upon theCO conversion level (Figure 5). This causes the productivity

of an iron catalyst to be strongly dependent upon the COconversion level (Figure 6). The reason for this is that the watergas shift (WGS) reaction that competes with the Fischer-Tropsch synthesis (FTS) becomes more important at higher COconversion levels (Figure 7).

It is difficult to obtain literature data for the rate of COconversion with a cobalt catalyst as the space velocity is varied.One comparison of iron and cobalt catalysts has been providedby van Berge and Everson.7 At the higher space velocities, theiron catalyst is more active, but at the lower space velocities(higher conversion), the cobalt catalyst becomes more active.

Figure 1. Effect of cobalt dispersion, support, and alloying on FTS Co-time yields ((mol of CO converted)/((total g)(atom of Co)(s))) (from ref1).

Figure 2. Turnover number (TON) for unsupported and supported cobaltcatalysts (plotted from data in ref 2).

Figure 3. Effect of support on activity of Co/Zr catalysts in a fixed-bedreactor (from ref 3).

Figure 4. Comparison of relative activity of Co supported on titania, silica,and alumina (from ref 4).

Figure 5. Variation of hydrogen (0) and CO (O) conversion and the H2/CO ratio (]) in the exit gas with flow rate (from ref 6).

Ind. Eng. Chem. Res., Vol. 46, No. 26, 20078939

The comparison in Figure 87 shows that the iron catalyst is moreproductive at the more severe conditions (i.e., at higher spacevelocities and at higher reactor pressures).

Common practice frequently is the factor that determines theexpression used for catalytic activity. Today, the activity foran iron catalyst is usually expressed on the basis of 1 g of iron,while for the cobalt catalyst, this is usually reported on the basisof 1 g of catalyst. For the use of the catalyst, the productivityper reactor volume is the important consideration. The expres-sion of the activity as indicated above can be used once thereactor type, the catalyst loading, and the operating conditionsare defined. For mechanistic considerations, all of the methodsfall short of providing a preferred expression of catalytic activity.

Reactor Productivity

It is difficult to obtain productivity data for catalysts utilizedin a slurry reactor that is operated under commercial conditions.

Kolbel8 reported that a large pilot plant (60 m3) could produce0.47-0.94 (g of hydrocarbon)/(g of catalyst)/h; however, themaximum productivity during the operation of the pilot plantwas 0.44 (g of hydrocarbon)/(g of catalyst)/h. The slurry reactorutilized by Sasol is 5 m diameter and 22 m tall. Assuming thatonly 2/3 of the total volume is filled with slurry and, thus,available for synthesis, the reactor volume containing catalystis ∼290 m3. The output from the plant is 2 500 bbl/day; if oneassumes a density of the product of 1 g/cm3, the output is∼16 600 kg/h. This corresponds to a productivity of∼58 kg/h/m3. If the reactor contains 2 wt % catalyst in the slurry, theproductivity would be∼2.9 g/(g of Fe)/h; on the other hand, ifthe catalyst loading is 20 wt %, the productivity would be 0.3(g of hydrocarbon)/(g of Fe)/h. While the productivity from theoperation of the U.S. DOE La Porte plant is not currentlyavailable to the public, the run conditions are available. Theslurry concentration was to be in the range of 24-25 wt %catalyst, and when operating at 250-260°C and 710 psig (48.3atm), the reactor productivity goal was 150 (g of hydrocarbon)/L/h. If one assumes a density for the slurry of 1.25 kg/L, onecalculates a productivity of 0.5 (g of hydrocarbon)/(g ofcatalyst)/h. Koros9 reports productivities in the range of 450-750 (volume of CO converted)/(volume of catalyst)/h whenoperating with a cobalt-titania catalyst in a 6 in. diameter slurrybubble column reactor at space velocities of 2800-3600 h-1.This should correspond to a productivity in the range of 0.28-0.47 (g of hydrocarbon)/cm3/h. If the catalyst density is 1 g/cm3,the maximum productivity is∼0.5 (g of hydrocarbon)/(g ofcatalyst)/h; on the other hand, if the density is 2.7 g/cm3,10 themaximum productivity is∼0.19 g/(g of catalyst)/h. Consideringthese four examples, and realizing that they involve estimatesthat may not correspond to the actual situation, it appears thatthese larger units are operated in a manner such that the ultimateproductivity of the catalyst is not realized. It therefore appearsthat engineering advances for the operation of the slurry bubblecolumn reactor and in the catalyst formulation provide op-portunities to realize significant advances in productivity.

Selectivity

The production of methane should be related to the distribu-tion of other carbon-number products if the Anderson-Schulz-Flory distribution is followed. This is the case with much ofthe data compiled by Kuo11 (Figure 9). However, prior to theMobil data that was reported by Kuo, Ko¨lbel’s data that wasgenerated in Germany in the 1950s was the standard for slurry-

Figure 6. Productivity of precipitated iron catalyst operated at 270°C fordifferent Cu contents (ref 6).

Figure 7. Reaction rate for FTS (0, O) and WGS (2) versus space velocity(from ref 6).

Figure 8. Productivity comparison between the iron catalyst (240°C) andthe cobalt catalyst 220°C) (from ref 7).

Figure 9. Reactor wax yield versus methane yield (modified figure fromref 11).

8940 Ind. Eng. Chem. Res., Vol. 46, No. 26, 2007

phase reactor considerations, e.g., ref 12. As can be seen bythe data point in Figure 9 representing Ko¨lbel and Ralek’s result,the methane and/or wax production is much lower than thatobtained by other workers. In agreement with the Mobil data,we find that the methane plus ethane selectivity increases asthe CO conversion increases above∼75% for the low-alphairon catalyst (Figure 10). A major reason for the increase in themethane production at higher CO conversion is that theconcentration of water has increased so that the WGS reactionoccurs at about the same rate as the FTS; thus, there is anincrease in the H2/CO ratio (Figure 5 for H2/CO inlet ) 0.7).While the general shape of the curve will be the same whenoperating with a high-alpha iron catalyst, the fraction of methaneproduced is much lower (ca. 1-3% at low CO conversion).

The situation for methane is not as clear-cut when oneconsiders the cobalt catalyst. Yates and Satterfield,13 using acobalt catalyst that was intended to reproduce a Ruhrchemiecatalyst in a continuous stirred tank reactor (CSTR), found thatmethane corresponded to an increasing fraction of the hydro-carbons as the CO conversion increased (low space velocity,Figure 11). On the other hand, data obtained while operatingwith a cobalt-titania catalyst in a fixed-bed reactor show thatthe methane fraction of hydrocarbons decreases with increasingCO conversion (Figure 12).14 This result is consistent with amechanism with the alkenes produced at lower conversion levels

(i.e., at the top of the reactor) being reincorporated into products,as claimed by Iglesia,15 thereby reducing the fraction of theproducts that are derived from the C1 surface species andreducing the fraction of methane in the products. In a thirdexample,16 the fraction of methane that is produced remainsconstant with increasing CO conversion (Figure 13). Thus, atthe present time, it does not appear that one can make a validassessment for the selectivity for methane production at variousCO conversion levels for the cobalt catalyst.

WGS activity in the catalyst may, or may not, be a desirablefeature of the catalyst. If one is to operate with a synthesis gasas is derived from coal (H2/CO) 0.5-1.0), one needs to obtainwater gas shift within the FT reactor or to operate in a hydrogendeficient mode that will limit CO conversion, or to conductWGS in a unit located upstream of the reactor. On the otherhand, if the syngas is obtained from natural gas, the H2/COratio may be 2 or greater; in this case, one wants to limit theextent of water gas shift. In the case of a cobalt catalyst, theCO2 production that results from WGS that is shown in Figure12 is typical. Thus, WGS only occurs to a measurable extentwith a cobalt catalyst as the CO conversion is∼80% or greater.With the iron catalyst, WGS always occurs but becomes moreimportant as the CO conversion increases. Thus, the iron catalystappears to be the choice when the synthesis gas is derived fromcoal. For syngas derived from natural gas, the cobalt catalyst isusually preferred; iron would be considered in this case onlywhen the CO2 that is produced could be recycled to the gasifier.

The product distribution of the total hydrocarbons is usuallyconsidered to follow an Anderson-Schulz-Flory distribution.

Figure 10. Methane plus ethane selectivity versus CO conversion(unpublished CAER data).

Figure 11. Effect of space velocity on product yield. The C10+ yield isgreater at higher space velocities. Data at 240°C, 0.79 MPa, and (H2/CO)in) 2 (from ref 13).

Figure 12. Co-Re versus Ru selectivity (from ref 14).

Figure 13. Contact time-C1 and C2 selectivity correlation (from ref 16).


Thus, when the log(mole fraction) of each product is plottedversus the carbon number, a straight line should be produced;the slope of this line can be related to the probability of chaintermination (â) relative to the chain growth (R). In this instance,whenR ) 0, methane is the only product. AsR increases, thefraction of heavier products increases, and asR approaches avalue of 1.0, the product approaches a high-molecular polyeth-ylene product. In many situations, the product distribution doesnot follow this simple, ideal distribution.

The selectivity for the heavier products is an importantconsideration. Data that are typical of earlier work are shownin the figure reproduced from a recent study by Sasol workers(Figure 14).17 While the general perception is that a cobaltcatalyst produces heavier products than an iron catalyst, the datain Figure 14 show that this is not the case. Our data are ingeneral agreement with the data generated by the Sasol workers(Figure 14). For the iron-based catalyst, the pressure can bevaried over a wide range without having a significant impactupon the product distribution (Figure 15). In agreement withmuch previous work, the product distribution changes to heavierproducts over a wide range of pressures, approaching that ofthe high-alpha iron catalyst at pressures greater than 40 atm(Figure 16).

With the iron catalyst, the product distribution can be variedover a wide range merely by varying the potassium content.Thus, alpha ranges from∼0.72 for low potassium catalyst to∼0.95 for high potassium containing iron catalysts. While thealkali content does impact the activity of the iron catalyst, thereis a much more dramatic effect for the cobalt catalyst. Dataobtained at atmospheric pressure with a cobalt catalyst indicate

Figure 14. Chain growth probabilityR2 as a function of reactor pressureat constant superficial velocity ((b), CAER result on iron catalyst under175 psig; (2), CAER result on cobalt catalyst under 175 psig) (modificationof figure from ref 17).

Figure 15. Mass % product distribution as a function of reactor pressureat constant superficial velocity for the iron slurry-phase catalyst (from ref17).

Figure 16. Mass % product distribution as a function of reactor pressureat constant superficial velocity for the cobalt catalyst (from ref 17).

Figure 17. Alpha versus K/Co ratio (from ref 18).

Figure 18. % CO conversion versus K/Co ratio (from ref 18).

Figure 19. Dependence of activity change for an iron catalyst with theamount of alkali promoter (data from ref 5).


that the alpha value increases from∼0.75 for a catalyst thatdoes not contain potassium to approach 0.9 for a catalystcontaining 0.04 K/Co (Figure 17).18 At the same time, there isa linear decline in activity with increasing K/Co ratio so that aslittle as 0.04 wt % potassium will result in about a 5-folddecrease in catalyst activity (Figure 18). The impact of thepromoter on the activity of an iron catalyst appears to dependupon operating temperature. Potassium appears to be an activitypromoter when operating at high temperatures using a low-alphairon catalyst (Figure 19).5 However, when operating at a lower(200°C) temperature, the alkali appears to be acting as a catalystpoison. Unfortunately, these data for the iron catalyst onlyprovide the alkali content in relative concentrations.

Impact of Diffusion

Workers at Exxon have produced a significant amount ofliterature relating product selectivity to the physical propertiesof the catalyst and to the number and distribution of thecatalytically active cobalt sites.15,19-24 The workers at the formerGulf Oil obtained results for cobalt supported on three sizes ofsupport particles25 and found that the amount of methane

increased with increasing particle size of the catalyst (Figures20 and 21). They also reported results that indicate the reactionwas diffusion controlled. This type of selectivity that dependsupon both the physical and chemical characteristics of thesample has been quantified, and it is observed that the catalystcan be modified so that a minimum of methane and a maximumof C5+ products can be produced (Figure 22). Thus, in Figure22a, the C5+ product selectivity increases, which is claimed tobe because of olefin reincorporation, reaches a maximum, andthen decreases as diffusion limitations become dominant. Theopposite is observed for methane production (Figure 22b), whereolefin reincorporation causes a decrease in the amount ofmethane formed, attains a minimum, and then increases as themore rapid diffusion of hydrogen effectively increases the H2/CO ratio in the interior of the catalyst pellet and, hence, therate of formation of methane.

In a slurry reactor, the size of the catalyst pellet is so smallthat one would not anticipate diffusion to provide an impactupon conversion or selectivity. However, as more activecatalysts become available, this may not be the case. The datafor the fraction of 1-alkene in the alkene component of each

Figure 20. Methane selectivity versus catalyst particle size (data from ref 25).

Figure 21. C5+ product selectivity for three particle size catalysts in fixed-bed reactor ((b), 185 °C, H2/CO ) 2; (2), 195 °C, H2/CO ) 2; (0), 195 °C,H2/CO ) 1.5) (data from ref 25).


carbon number decreases with increasing carbon number for asupported iron catalyst compared to that of an unsupportedcatalyst. In this instance, the unsupported catalyst (1) waspresent in 1-3 µm particles, whereas in the supported catalyst,the particle size ranged from 25 to 250µm. Thus, it appearsthat, even for these small particle sizes, diffusional limitationsmay be encountered for the rapid reactions. For the fraction ofalkenes of each carbon number, a plot similar to that of Figure23 was obtained, again providing evidence that diffusionlimitations may be encountered even in the particle sizes thatare common for slurry bubble column reactors.

Catalyst Life

Two factors, at least, impact the useful life of a catalyst. Onefactor is the physical properties such as catalyst attrition, waxaccumulation within the catalyst pellet, pressure drop acrossthe bed, etc.; these properties limit catalyst life because of theoperating conditions and physical properties of the catalyst. Theother factor is the loss of catalyst sites through poisoning and/or fouling. It has been shown in experiments lasting 3500 h ormore that both cobalt and iron catalysts decline in laboratorysettings at a rate of<1% of unit activity per week of operationfor cobalt (Figure 24)26 and for iron (Figure 25). Lifetimes forcatalysts in commercial operations are difficult to obtain. Sasolworkers have indicated that they replace their iron catalystsbecause of physical changes in the catalyst or to attrition andnot due to the loss of catalyst sites due to poisoning and/orfouling. Shell has indicated that they expect their supportedcobalt catalyst to have a lifetime of five or more years in theirfixed-bed reactor operations. Thus, it appears that catalystlifetime is not a major issue for operation in today’s commercial

plant. Obviously, higher catalyst activity is always desirablefrom a productivity viewpoint, and as more active catalysts aredeveloped, deactivation of the catalyst may become an issue.

Conclusions

In summary, it is concluded that iron catalyst may be as activeand, at more severe conditions of pressure and space velocity,even have a higher activity than a cobalt catalyst. The selectivityproperties of an iron catalyst may be varied over a wide rangeby the use of promoters. In contrast, the use of promoters witha cobalt catalyst to control selectivity has, to date, been limited,and the elements that may alter selectivity appear to have avery detrimental impact on the catalytic activity. Cobalt catalystsexhibit two distinct advantages for some applications. The lack

Figure 22. (a, b) Effect of structural parameters (ø) on FTS selectivity. Diffusion-enhanced readsorption (---) and diffusion-inhibited chain growth (s)simulations and experimental data ((b), dispersion/support effects; (2), pellet size variations; (O) eggshell thickness variations; (a) C5+ selectivity; (b) CH4

selectivity [473 K, 2000 kPa, H2/CO ) 2.1, 55-65% CO conversion] (ø values from eq 2 withrp andRo in m andθCo in surface Co atoms m-2) (ref 22).

Figure 23. 1-Alkene/total alkene versus carbon number ((b), 100Fe/6.0Cu/8.1K/250SiO2; ([), 100Fe/6.0Cu/8.1K/250Al2O3; (2), 100Fe/6.0Cu/8.0K/260MgAl2O4; (1), precipitated 100Fe/3.1Cu/8.1K/5.0SiO2) (unpublishedCAER results).

Figure 24. Bulk activity maintenance for extended slurry reactor test ofcatalyst L at baseline conditions (260°C, 2.07 MPa, CO/H2 ) 1.0, and SV) 2.0 nL/h per g of catalyst) (from ref 26).

Figure 25. Deactivation of an iron catalyst (unpublished CAER data).


of water gas shift activity allows one to reject the oxygen inCO as water rather than CO2 so that the carbon efficiency ofthe cobalt catalyst is almost twice that of the iron catalyst,especially when operating at high conversion levels. If theprocess is operated at∼30% conversion, the iron catalyst rejectsa significant fraction of the oxygen as water so that theadvantage of cobalt, while still present, is not as great. Thesecond advantage of the cobalt catalyst is that it can be addedto a support that can provide robustness that the iron catalystdoes not have in the unsupported state. Catalyst robustnessbecomes an important, and perhaps a deciding, factor for slurrybubble column reactors where the ability to remove wax fromthe reactor will determine the success of the operation.

Acknowledgment

This work was supported by U.S. DOE contract numberDE-FC26-98FT40308 and the Commonwealth of Kentucky.

Literature Cited

(1) Iglesia, E.; Reyes, S. C.; Madon, R. J.; Soled, S. L. Selectivity controland catalyst design in the Fischer-Tropsch synthesis: Sites, pellets, andreactors.AdV. Catal. 1993, 39, 221.

(2) Bartholomew, C. H.; Pannell, R. B.; Butler, J. L. Support andcrystallite size effects in carbon monoxide hydrogenation on nickel.J. Catal.1980, 65, 335.

(3) Withers, H.P., Jr.; Eliezer, K. F.; Mitchell, J. W. Slurry-phase Fischer-Tropsch and kinetic studies over supported cobalt carbonyl derived catalysts.Ind. Eng. Chem. Res.1990, 29, 1807.

(4) Singleton, A. E. Advances make gas-to-liquids process competitivefor remote locations.Oil Gas J.1997, 95, 68.

(5) Dry, M. E. The Fischer-Tropsch synthesis; Catalysis: Science andTechnology; Anderson, J. R., Boudart, M., Eds.; Springer-Verlag: Berlin,1981; Vol. 1, p 159.

(6) Xu, L.; Bao, S.; O’Brien, R. J.; Raje, A.; Davis, B. H. Don’t ruleout iron catalysts for Fischer-Tropsch synthesis.CHEMTECH1998, 28,47.

(7) van Berge, P. J.; Everson, R. C. Natural Gas Conversion IV. InStudies in Surface Science and Catalysis; de Pontes, M., Espinoza, R. L.,Nicolaides, C. P., Scholz, J. H., Currell, M. S., Eds.; Elsevier: Amsterdam,1997; Vol. 107, p 207.

(8) Kolbel, H.Chemische Technologie. Band 3: Organische TechnologieI; Carl Hansen Verlag: Mu¨nchen, Germany, 1959; p 439.

(9) Koros, R. M. U.S. Patent 5,384,336, Jan 24, 1995.

(10) Behrmann, W. C., et al. U. S. Patent 5,545,674, Aug 13, 1996.(11) Kuo, J. C. W. Two-stage process for conversion of synthesis gas

to high quality transportation fuels; Final Report DOE/PC/60019-9; DOE:Washington, DC, Oct 1985.

(12) Kolbel, H.; Ralek, M. The Fischer-Tropsch synthesis in the liquidphase.Catal. ReV.sSci. Eng.1980, 21, 225.

(13) Yates, I. C.; Satterfield, C. N. Hydrocarbon selectivity from cobaltFischer-Tropsch catalysts.Energy Fuels1992, 6, 308.

(14) U.S. Patent, 4,568,663, Feb. 4, 1986.(15) Iglesia, E. Design, synthesis and use of cobalt-based Fischer-

Tropsch synthesis catalysts.Appl. Catal., A1997, 161, 59.(16) Hurlbut, R. S.; Puskas, I.; Schumacher, D. J. Fine details on the

selectivity and kinetics of the Fischer-Tropsch synthesis over cobaltcatalysts by combination of quantitative gas chromatography and modeling.Energy Fuels1996, 10, 537.

(17) Van Berge, P. J.; Everson, R. C. Cobalt as an alternative Fischer-Tropsch catalyst to iron for the production of middle distillates.Stud. Surf.Sci. Catal.1997, 107 (Natural Gas Conversion IV), 207-212.

(18) U.S. Patent 4,880,763, Nov 14, 1989.(19) Iglesia, E.; Soled, S. L.; Fiato, R. A.; Via, G. H. Bimetallic synergy

in cobalt-ruthenium Fischer-Tropsch synthesis catalysts.J. Catal. 1993,143, 345.

(20) Madon, R. J.; Iglesia, E.; Reyes, S. C. Non-Flory productdistributions in Fischer-Tropsch synthesis catalyzed by ruthenium, cobaltand iron.ACS Symp. Ser.1993, 517, 383.

(21) Iglesia, E.; Soled, S. L.; Fiato, R. A. Fischer-Tropsch synthesison cobalt and ruthenium. Metal dispersion and support effects on reactionrate and selectivity.J. Catal.1992, 137, 212.

(22) Iglesia, E.; Reyes, S. C.; Soled, S. L. InComputer-Aided Designof Catalysts and Reactors; Becker, E. R., Pereira, C. J., Eds.; Marcel Dekker,Inc.: New York, 1992.

(23) Iglesia, E.; Soled, S. L.; Baumgartner, J. E.; Reyes, S. C. Synthesisand catalytic properties of eggshell cobalt catalysts for the Fischer-Tropschsynthesis.Top. Catal.1995, 2, 17.

(24) Iglesia, E.; Reyes, S. C.; Madon, R. J.; Soled, S. L. Selectivitycontrol and catalyst design in the Fischer-Tropsch synthesis: sites, pelletsand reactors.AdV. Catal. 1993, 39, 221.

(25) Beuther, H.; Kobylinski, T. P.; Kibby, C. E.; Pannell, R. B. SouthAfrica Patent 855317, July 15, 1985.

(26) Withers, H. P., Jr.; Eliezer, K. F.; Mitchell, J. W. Slurry-phaseFischer-Tropsch synthesis and kinetic studies over supported cobaltcarbonyl derived catalysts.Ind. Eng. Chem. Res.1990, 29, 1807.

ReceiVed for reView September 13, 2007ReVised manuscript receiVed October 26, 2007

AcceptedOctober 26, 2007

IE0712434


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Fischer−Tropsch Synthesis: Comparison of Performances of Iron and Cobalt Catalysts