Mesoporous carbon-containing MoS2 materials formed from the in situ decomposition of tetraalkylammonium thiomolybdates

Mesoporous carbon-containing MoS2 materials formed from thein situ decomposition of tetraalkylammonium thiomolybdates

Gabriel Alonsoa,b, Gilles Berhaultc,*, Francisco Paraguaya, Eric Riverad,Sergio Fuentese, Russell R. Chianellib

aCentro de Investigacion en Materiales Avanzados, Miguel de Cervantes # 120,

Chihuahua C.P. 31109, Chih., MexicobMaterials Research Technology Institute, University of Texas at El Paso, 500 W. University Av.,

El Paso, TX 79968-0685, USAcLaboratoire de Catalyse en Chimie Organique, UMR 6503 CNRS, Universite de Poitiers,

40 Avenue du Recteur Pineau, 86022 Poitiers Cedex, FrancedFısica Aplicada y Tecnologıa Avanzada, Instituto de Fısica, Universidad Nacional Autonoma de Mexico,

A.P. 1-1010, Queretaro 76000, MexicoeDepartamento de Catalisis, Centro de Ciencias de la Materia Condensada (CCMC), UNAM,

Apartado Postal 2681, 22830 Ensenada, B.C., Mexico

Received 30 October 2002; received in revised form 15 January 2003; accepted 28 February 2003

Abstract

Molybdenum disulfide with unique mesoporous structure was synthesized from tetraalkylammonium

thiometallate precursors in situ decomposed in a batch reactor in the presence of dibenzothiophene (DBT).

The precursors used in this study were tetraalkylammonium thiomolybdates with alkyl groups ranging from

propyl to octyl. Molybdenum disulfide thus prepared presents high surface area (from 255 up to 329 m2/g), high

content of carbon (C/Mo ¼ 2:7–4.0) and type IV nitrogen adsorption–desorption isotherms when decomposed

from tetrahexyl-, tetraheptyl- or tetraoctylammonium thiomolybdates. The as-formed materials are poorly

crystallized with a very weak intensity of the (0 0 2) peak of the 2H–MoS2 structure. Such diffraction patterns are

characteristic of exfoliated samples. Characterization by TEM shows a disordered layered structure with no long

range order for the MoS2 catalysts. Therefore, the nature of the alkyl group in the precursor affects both the

surface area and the pore size distribution of the final MoS2 catalysts with a progressive morphological

modification up to a mesoporous organization.

# 2003 Elsevier Science Ltd. All rights reserved.

Keywords: A. Layered compounds; B. Chemical synthesis; C. Electron microscopy; C. X-ray diffraction

Materials Research Bulletin 38 (2003) 1045–1055

* Corresponding author. Tel.: þ33-549-45-39-51; fax: þ33-549-45-38-99.

E-mail address: [email protected] (G. Berhault).

0025-5408/03/$ – see front matter # 2003 Elsevier Science Ltd. All rights reserved.

doi:10.1016/S0025-5408(03)00066-7

1. Introduction

Transition metal dichalcogenides form a very important group of materials exhibiting a number ofinteresting properties as photoactive materials [1], solid-state lubricants [2,3], cathode materials forhigh-energy density batteries [4], and catalysts for hydrotreating applications [5,6]. Transition metalsulfides (TMS) such as MoS2, WS2, TaS2 and TiS2 are anisotropic layered materials. In themolybdenum disulfide structure, each Mo ion is surrounded by three sulfur anions in a trigonalprismatic arrangement resulting in a sandwich layered configuration with only weak van der Waalsinteraction between the layers. Therefore, these sulfide solids are widely used as host materials forintercalated compounds giving rise to interesting conductive properties [7,8]. Molybdenum disulfide-based solids are also particularly useful in the petroleum industry as hydrodesulfurization (HDS)catalysts [5,9] in order to prevent emissions of atmospheric pollutants since sulfur present in crude oil isdirectly responsible for the production of sulfur oxides by combustion of fuels.

MoS2- and WS2-based materials have been prepared by different methods, including directsulfidation of oxides [10], comaceration [11], or homogeneous sulfide precipitation [12]. However,using these preparation methods, the catalytic properties of the as-obtained MoS2 and WS2 catalysts arereported to depend strongly on the H2/H2S activation procedure necessary to get the active phase[11,12]. Moreover, large variations in surface area have also been observed for MoS2 and WS2

catalysts, from a few to several tens of squared meters per gram [13,14].Thiosalt decomposition [15] is an interesting alternative preparation process for chalcogenides

providing a good control of the MoS2 stoichiometry. These thiosalts have already sulfur bound to themetal atoms in a tetrahedral coordination and their decomposition undergoes a topotactic reactionwhereby the c-axis of sulfide remains the same as in the precursor. Starting from tetraalkylammoniumthiosalts, the decomposition of these precursors generates carbon-containing MoS2 and WS2 catalystswith high surface area and with interesting catalytic properties [16,17]. Such solids contain certainamounts of carbon, and are described with the general formula MoS2�yCz, where 0:01 < y < 0:5 and0:01 < z < 3:0 [18].

The aim of this work was to obtain MoS2 catalysts with a unique amorphous structure and with an internaldistribution of mesopores. Therefore, herein is reported the use of tetraalkylammonium thiomolybdateprecursors decomposed in a hydrocarbon solution containing a sulfur-containing organic reactant,dibenzothiophene (DBT), and pressurized with hydrogen at 623 K. This method of decomposition isexpected to achieve a bulk MoS2 structure with high surface area. This in situ preparation differs stronglyfrom the ex situ decomposition (simple thermal decomposition of the precursor under H2/H2S) for whichlow surface area solids are obtained [19]. These MoS2 catalysts were characterized using X-ray diffraction(XRD), transmission electron microscopy (TEM), and nitrogen adsorption at 77 K using the BET isothermfor surface area measurement and the BJH method for pore size distribution.

2. Experimental

2.1. Precursor preparation

The ammonium tetrathiomolybdate (ATM, (NH4)2MoS4) compound was prepared following methodsreported elsewhere [20,21]. Tetraalkylammonium thiomolybdate precursors were synthesized at room

1046 G. Alonso et al. / Materials Research Bulletin 38 (2003) 1045–1055

temperature using an aqueous solution of ATM and quaternary ammonium halides [(R4N)Br, whereR ¼ propyl, pentyl, hexyl, heptyl and octyl] with yields approximately 80%. The tetraalkylammoniumtetrathiomolybdate salts are referred as TProATM, TPenATM, THexATM, THepATM and TOctATMwhen the following alkyl groups are used, respectively: propyl, pentyl, hexyl, heptyl, and octyl.

2.1.1. Synthesis of [(C3H7)4N]2MoS4 (TProATM)

(NH4)2MoS4 (2.0 g, 7.7 mmol) was dissolved in water (20 ml). This solution was added to anaqueous solution (50 ml) of tetrapropylammonium bromide (4.1 g, 15.4 mmol). The resulting solutionwas stirred at room temperature for 10 min and then kept undisturbed overnight, precipitating redcrystals of [(C3H7)4N]2MoS4.

2.1.2. Synthesis of [(C5H11)4N]2MoS4 (TPenATM)(NH4)2MoS4 (2.0 g, 7.7 mmol) was dissolved in water (20 ml). This solution was added to an

aqueous solution (100 ml) of tetrapentylammonium bromide (5.8 g, 15.4 mmol). The resulting solutionwas stirred at room temperature for 10 min and then kept undisturbed overnight, precipitating redcrystals of [(C5H11)4N]2MoS4.

2.1.3. Synthesis of [(C6H13)4N]2MoS4 (THexATM)(NH4)2MoS4 (2.0 g, 7.7 mmol) was dissolved in water (20 ml). This solution was added to an

aqueous solution (300 ml) of tetrahexylammonium bromide (6.7 g, 15.4 mmol). The resulting solutionwas stirred at room temperature for 10 min and then kept undisturbed overnight, precipitating redcrystals of [(C6H13)4N]2MoS4.

2.1.4. Synthesis of [(C7H15)4N]2MoS4 (THepATM)

(NH4)2MoS4 (1.0 g, 3.8 mmol) was dissolved in water (20 ml). This solution was added to a solutionof tetraheptylammonium bromide (3.7 g, 7.6 mmol) in a mixture of methanol/water (100/300 ml). Theresulting solution was stirred at room temperature and red solid of [(C7H15)4N]2MoS4 immediatelyprecipitates.

2.1.5. Synthesis of [(C8H17)4N]2MoS4 (TOctATM)(NH4)2MoS4 (1.0 g, 3.8 mmol) was dissolved in water (20 ml). This solution was added to a solution

of tetraoctylammonium bromide (4.1 g, 7.6 mmol) in a mixture of methanol/water (100/300 ml). Theresulting solution was stirred at room temperature and red solid of [(C8H17)4N]2MoS4 immediatelyprecipitates.

2.2. Preparation of the MoS2 catalysts

The appropriate amount of precursor to yield 1 g of MoS2 (1.6 g for ATM, 3.7 g for TProATM, 5.1 gfor TPenATM, 5.8 g for THexATM, 6.5 g for THepATM, and 7.7 g for TOctATM) was prepared intablet form by uniaxial pressing and were crushed in a mortar before placing it inside a Parr model 4522high pressure batch reactor. A solution of 5 vol.% of DBT in decaline (150 ml) was then added to theprecursors. The reactor was then pressurized to 3.1 MPa with hydrogen and heated to 623 K during 5 hat a rate of 10 K/min. The samples were separated from the organic mixture by filtration, then washedwith isopropanol to remove residual hydrocarbons and dried at room temperature.

G. Alonso et al. / Materials Research Bulletin 38 (2003) 1045–1055 1047

2.3. Catalyst characterization

Specific surface area was determined with a quantachrome AUTOSORB-1 model by nitrogenadsorption at 77 K using the BET isotherm. The pore distribution was obtained from the desorptionbranch of the isotherm following the BJH method. Samples were degassed under flowing argon at473 K for 2 h before nitrogen adsorption. The mean standard deviation for surface area measurementswas estimated about 2%.

C and S contents were determined using a total combustion analyzer CE Instruments NA2100. S/Moratios were corrected by comparison to a reference compound: a highly crystallized MoS2 sample witha S/Mo ratio of 2.00.

XRD studies were performed using a Phillips X Pert MPD diffractometer, equipped with a curvedgraphite monochromator, using Cu Ka radiation (l ¼ 1:54056 A) and operating at 43 kV and 30 mA.

Transmission electron micrographs were obtained in a side entry CM-200 analytical transmissionelectron microscope (TEM) operating at 200 kV. Particle size distribution was determined by countingabout 600 particles on 10 different pictures. The average particle size was calculated according to thefirst moment of the distribution:

Pni¼1niLiPn

i¼1ni

;

with L representing the length of a MoS2 slab as determined directly on pictures corresponding to thediagonal of a slab, n is the number of particles measured in a size range of index i.

3. Results

3.1. Elemental analysis

The S/Mo and C/Mo atomic ratios are reported in Table 1. A nearly constant S/Mo stoichiometricvalue of 2.0 is observed for all catalysts obtained by the decomposition of the tetraalkylammoniumsalts, while, for the ATM-made catalyst, a lower S/Mo ratio is found (1.7). High amounts of carbon aredetected after the in situ decomposition of the tetraalkylammonium thiomolybdate salts in the presenceof DBT while, once again, for the ATM-made catalyst, a low C/Mo ratio (0.5) is found. Strong

Table 1

Specific surface areas, total pore volume and elemental analysis of Mo, S, and C atomic ratios for in situ prepared

molybdenum sulfide catalysts

MoS2 catalysts from Specific surface area (m2/g) Total pore volume (cm3/g) Elemental analysis

S/Mo C/Mo

ATM 60 0.092 1.7 0.5

TProATM 61 0.175 2.0 3.5

TPenATM 329 0.247 2.0 2.7

THexATM 255 0.429 2.0 3.7

THepATM 267 0.472 2.0 4.0

TOctATM 278 0.546 2.0 4.5


variations in the C/Mo ratio (2.7–4.5) are observed when starting from tetraalkylammoniumthiomolybdate precursors. However, the final amount of carbon could be partly correlated to the sizeof the alkyl group. A slight increase (from 3.5 to 4.5) in the C/Mo ratio is detected when increasing thealkyl size length with the noticeable exception of TPenATM.

3.2. Surface area and pore size distribution

The size of the alkyl group in the precursor compound has an important effect on the surface area andthe total pore volume of the MoS2-based catalysts (cf. Table 1). The length of the organic chain has adirect impact on the total pore volume of the materials since it increases from 0.092 cm3/g for ATM to0.546 cm3/g for TOctATM. As observed in Fig. 1, ATM- and TProATM-made catalysts exhibit a type Iisotherm with a very small hysteresis upon desorption whereas, for TPenATM-, THexATM-,THepATM- and TOctATM-made catalysts, the adsorption–desorption curves correspond to type IVisotherms with a desorption step characteristic of mesoporous materials above the relative pressure of0.4 (0.3 for TPenATM).

For MoS2 solids formed from ATM and TProATM, a very poorly developed porous system isobserved with a surface area of only 60 m2/g. Very low values of N2 adsorption were observed for bothcatalysts formed from ATM and TProATM particularly at low P/P0 values. Their structure appearsessentially non-porous with a quite low proportion of micropores. However, as revealed by theirdifferent isotherm profiles, the higher pore volume of TProATM is related to the formation of very largemesopores while the low P/P0 region appears similar between these solids.

The TPenATM-made catalyst is an interesting intermediate situation. While this solid presents thehighest surface area (329 m2/g), it shows only a moderate pore volume (0.247 cm3/g) indicating thatmicroporosity contributes to a large extent to its high surface area. Indeed, this solid has the highestnitrogen adsorption values at low relative pressures (P/P0).

Fig. 1. Adsorption–desorption isotherms for MoS2 catalysts formed by in situ decomposition of the different thiomolybdate

precursors.


For the MoS2 catalysts based on the decomposition of THex-, THep- and TOctATM precursors, theincrease of the size of the alkyl group from hexyl to octyl hardly changes the BET values (255–278 m2/g) while the total pore volume increases. This result suggests the development of a mesoporousorganization at the expense of the proportion of micropores when increasing alkyl size length. Thehysteresis loops shown by all these materials suggest that cylindrical pores are open at both ends.

Fig. 2 shows the desorption BJH pore size distributions. Results about TProATM-derived sampleshave not been reported since only a very broad pore size distribution is obtained. The MoS2 catalystsformed from THex-, THep- and TOctATM precursors present narrow pore size distributions rangingfrom 30 to 50 A. The mean pore size value for TPenATM is once again an intermediate situation with a

Fig. 2. BJH pore size distribution of MoS2 catalysts formed by in situ decomposition of the different thiomolybdate

precursors.

Fig. 3. XRD patterns of MoS2 catalysts formed by in situ decomposition of the different thiomolybdate precursors.


maximum at 29 A but with a profile suggesting a bimodal porous distribution with another maximum inthe microporous region.

3.3. X-ray diffraction

XRD patterns of the final MoS2 catalysts formed from the different tetraalkylammoniumthiomolybdate precursors are reported in Fig. 3. These diffractograms are in agreement with thosereported for the poorly crystalline MoS2 structure [22]. The (0 0 2) diffraction peak (2Y ¼ 14�) is welldefined for MoS2 catalysts made from ATM and TProATM precursors while a very weak (0 0 2) peak isobserved for the series from TPenATM- to TOctATM-made catalysts. Accordingly, the layer stackingalong the c direction is strongly reduced when going from the ATM- and TProATM-derived catalysts to

Fig. 4. Transmission electron micrographs of MoS2 catalysts prepared from (A) TProATM, (B) TPenATM, (C) THexATM,

(D) THepATM and (E) TOctATM.


the THexATM-, THepATM-, and TOctATM-derived ones. This result suggests a possible exfoliatingeffect when large amounts of carbon are generated during the in situ decomposition of the thiosalts.

3.4. Transmission electron microscopy

Bright field micrographs of the five MoS2 catalysts are shown in Fig. 4A–E. TEM pictures revealfringes characteristic of the layered MoS2 phase. Fig. 4A presents a micrograph of a MoS2 sampleformed from the in situ decomposition of the TProATM precursor in the presence of DBT. Even ifMoS2 fringes appear relatively stacked, their organization is largely disordered. The progressiveincrease of the alkyl size length in the precursor resulting in a higher carbon amount is accompanied bythe appearance of a higher proportion of destacked layers with ‘‘fluffy’’ areas due to the amorphouscarbon phase [23]. These results are in agreement with the observation by XRD of an exfoliation

Fig. 5. Particle length statistical distribution of MoS2 catalysts obtained by in situ decomposition of the following

thiomolybdate precursors: (A) TProATM, (B) TPenATM, (C) THexATM, (D) THepATM, and (E) TOctATM.


process when increasing the length of the organic chain. The statistical distribution of the particle slablength was determined by processing images by Image-Pro software version 4.1 [24]. As reported inFig. 5, the slab length of fringes for all materials is comprised between 1 and 15 nm with a maximumbetween 4 and 8 nm. For MoS2 formed from THepATM, the length of layers appears surprisinglyhigher reaching values up to 40 nm with a mean average slab length of 14.9 nm. This results seemsdoubtful since TEM micrographs of this solid presents large ‘‘fluffy’’ zones which could produceartifacts when calculating the average slab length, only the largest slabs being visible.

4. Discussion

MoS2 catalysts were prepared from the in situ decomposition of tetraalkylammonium thiomolybdateprecursors. This preparation method is carried out in an organic solution (decalin) at 450 psi and 623 Kand leads to very high surface area solids (from 60 to 329 m2/g). The presence of alkyl fragments in theinitial thiomolybdate precursor clearly contributes to increase the surface area. The nature of carbonpresent on this catalyst is complex. While a low C/Mo ratio (0.5) is observed for the ATM-derivedcatalyst, a high increase in carbon content was obtained for catalysts formed by in situ alkylammoniumthiomolybdates decomposition. Therefore, the main part of carbon comes from the decomposition ofalkyl fragments of the precursors. In ATM-derived catalysts, the unique source of carbon is the organicmedia and is mainly coke. In tetraalkylammonium thiomolybdate-derived catalysts, carbon comes fromthe organic media and from the alkyl fragments. In that case, this latter form of carbon can substitutesome sulfur atoms during the reduction of MoS4

2� into MoS2 leading to carbide-like entities [18].Surface carbide-like species could also result from the formation of a stabilized active phase during theHDS reaction [23]. Finally, excess amorphous carbon can be formed from the decomposition of thealkyl fragments leading to ‘‘fluffy’’ zones in TEM micrographs. Even if a strong increase in surfacearea is observed when the organic chain increases from propyl to pentyl groups, for MoS2 catalystsformed from precursors containing hexyl to octyl groups, lower (but still high) surface areas areobserved. This situation differs markedly from the evolution of the total pore volume which shows acontinuous increase for MoS2 catalysts formed from ATM to TOctATM. These results suggest aprogressive modification of the morphology of the MoS2 catalysts shifting from a non-porous structure to amesoporous structure. This is in fact confirmed by the gradual evolution of the BJH pore size distributionof these solids as reported in Fig. 2. While for the MoS2 catalyst formed from ATM, no real uniformed sizedistribution could be detected, narrowing and shifting to diameters corresponding to mesopores (40 A) areobserved when increasing the organic chain in the precursor from propyl to octyl groups. Nitrogenadsorption results demonstrate this progressive formation of characteristic type IV isotherms. While theMoS2 catalyst formed from TProATM presents a type I isotherm profile and MoS2 derived from TPenATMan intermediate situation with only a small hysteresis, MoS2 catalysts formed from THexATM,THepATM, or TOctATM exhibit type IV isotherms with well-developed hysteresis loops.

The formation of type IV isotherms was extensively studied by Everett who gave possibleexplanations to the existence of large and wide hysteresis loops in nitrogen adsorption studies [25] for alarge series of different solids. More particularly, for amorphous materials, Mayagoitia et al. [26,27]have correlated type IV hysteresis loops with the presence of an extensively interconnected porousnetwork of mesoporous cavities and connecting channels. In the MoS2 materials studied here,mesoporous cavities are directly related to the use of tetraalkylammonium thiomolybdates as


precursors. Indeed, accumulation of gases is coming from the decomposition of the tetraalkylammo-nium part of the precursor producing complex reaction steps as revealed in a previous TGA-DTA study[28]. Channels could then be created probably during the escape of such gases to the exterior. Such aporous network in amorphous MoS2 materials may be considered equivalent to the porous structure ofmolecular sieves. Moreover, according to XRD results (see Fig. 3), THexATM, THepATM andTOctATM-made catalysts demonstrate large morphological modifications compared to ATM andTProATM-made catalysts. Indeed, as revealed by the disappearance of the (0 0 2) peak, the layeredstructure is less stacked for MoS2 catalysts formed from THexATM, THepATM or TOctATM than forMoS2 catalysts derived from ATM and TProATM precursors. One may suggest that during thedecomposition process, the organic tetraalkylammonium fragment has first participated in anintercalation process which afterwards leads to exfoliated MoS2 layers after decomposition of theorganic fragment. Such a process has been recently reported by Vanchura et al. [29]. This progressiveexfoliation of the MoS2 layers is clearly visible in the TEM micrographs which also reveals a highertendency to disordered morphologies when increasing the alkyl size length. Particle size length iscentered on values ranging from 5 to 7 nm. This situation should also be related to a previous study byAfanasiev et al. [30] showing that the addition of a surfactant, like cetyltrimethylammonium bromide toan aqueous solution of ATM leads to the precipitation of a tetraalkylammonium thiomolybdate which issubsequently reduced to a high surface area MoS2 structure with only single layers. In this case, the roleof the organic molecule was of scaffolding and preventing the agglomeration of layered sulfide fringes.Moreover, this formation of highly disordered destacked layers was already observed in a previousstudy about the interaction of organosulfides with unsupported molybdenum disulfide [23] and shouldbe considered as a general situation when carbon interacts with TMS.

Due to such properties, the high surface area MoS2 catalysts reported in this work may also be called‘‘amorphous mesoporous sulfides.’’

5. Conclusions

MoS2-based catalysts were prepared by decomposition of different tetraalkylammonium thiomo-lybdate precursors (with alkyl ¼ propyl, pentyl, hexyl, heptyl and octyl groups). The solids obtainedusing this procedure present interesting morphological properties with high surface area, characteristictype IV isotherms, narrow pore size distribution and very dispersed crystallites with low-stacked layers.This new type of sulfide materials could be named ‘‘amorphous mesoporous sulfide’’ catalysts.

Acknowledgements

The authors appreciate the valuable technical assistance of C. Ornelas, W. Antunez and A. Reyes.This work was financially supported by Conacyt project J31397-U; FIES-98-27-III.

References

[1] A. Ennaoui, S. Fiechter, W. Jaegermann, H.J. Tributsch, J. Electrochem. Soc. 133 (1986) 97.

[2] F.L. Clauss, Solid Lubricants and Self-Lubricating Solids, Academic Press, New York, London, 1974.


[3] E. Stoffels, W.W. Stoffels, G. Ceccone, R. Hasnaoui, H. Keune, G. Wahl, F. Rossi, J. Appl. Phys. 86 (1999) 3442.

[4] J. Rouxel, R.A. Bree, Annu. Rev. Mater. Sci. 16 (1986) 137.

[5] O. Weisser, S. Landa, Sulfide Catalysts: Their Properties and Applications, Pergamon Press, New York, 1973.

[6] M.D. Curtis, J. Schwank, L. Thompson, P.D. Williams, O. Baralt, Prepr. Am. Chem. Soc., Div. Fuel Chem. 31 (1986) 44.

[7] A.V. Powell, L. Kosidowski, A. McDowall, J. Mater. Chem. 11 (2001) 1086.

[8] E. Benavente, M.A. Santa Ana, F. Mendizabal, G. Gonzalez, Coord. Chem. Rev. 224 (2002) 87.

[9] H. Topsøe, B.S. Clausen, F.E. Massoth, Hydrotreating Catalysis, in: J.R. Anderson, M. Boudart (Eds.), Catalysis, Science

and Technology, vol. 11, Springer-Verlag, Berlin, 1996.

[10] P. Arnoldy, J.A.M. van den Heijkant, G.D. de Bok, J.A. Moulijn, J. Catal. 92 (1985) 35.

[11] G. Hagenbach, P. Courty, B. Delmon, J. Catal. 31 (1973) 264.

[12] R. Candia, B.S. Clausen, H. Topsøe, J. Catal. 77 (1982) 564.

[13] R. Frety, M. Breysse, M. Lacroix, M. Vrinat, Bull. Soc. Chim. Belg. 93 (1984) 663.

[14] K. Ramanathan, S. Weller, J. Catal. 95 (1985) 249.

[15] M. Zdrazil, Catal. Today 3 (1988) 269.

[16] A.J. Jacobson, R.R. Chianelli, T.A. Pecoraro, U.S. Patent 4,650,563 (1987).

[17] T.A. Pecoraro, R.R. Chianelli, U.S. Patent 4,528,089 (1985).

[18] G. Alonso, M. Del Valle, J. Cruz-Reyes, A. Licea-Claverie, V. Petranovskii, S. Fuentes, Catal. Lett. 52 (1998) 55.

[19] G. Alonso, M. Del Valle, J. Cruz-Reyes, S. Fuentes, in: Proceedings of the American Institute of Physics Conference on

Surfaces, Vacuum and Their Applications, vol. 378, Springer-Verlag, New York, 1996, p. 552.

[20] S. Fuentes, G. Diaz, F. Pedraza, H. Rojas, N. Rosas, J. Catal. 113 (1988) 535.

[21] K. Inamura, R. Prins, J. Catal. 147 (1994) 515.

[22] H.W. Wang, P. Sheldon, G.E. Thompson, G.C. Wood, J. Mater. Sci. 32 (1997) 497.

[23] G. Berhault, A. Mehta, A. Pavel, J. Yang, L. Rendon, M.J. Yacaman, L. Cota, A. Duarte, R.R. Chianelli, J. Catal. 198

(2001) 9.

[24] Image-Pro Plus version 4.1 for WindowsTM manufactured by MediaCybernetics.

[25] D.H. Everett, in: E.A. Flood (Ed.), The Solid–Gas Interface, vol. 2, Marcel Dekker, New York, 1967, p. 1055.

[26] V. Mayagoitia, F. Rojas, I. Kornhauser, J. Chem Soc., Faraday Trans. I 84 (1988) 785.

[27] V. Mayagoitia, B. Gilot, F. Rojas, I. Kornhauser, J. Chem Soc., Faraday Trans. I 84 (1988) 801.

[28] G. Alonso, G. Berhault, R.R. Chianelli, Inorg. Chim. Acta 316 (2001) 105.

[29] B.A. Vanchura, P. He, V. Antochshuk, M. Jaroniec, A. Ferryman, D. Barbash, J.E. Fulghum, S.D. Huang, J. Am. Chem.

Soc. 124 (2002) 12090.

[30] P. Afanasiev, G.-F. Xia, G. Berhault, B. Jouguet, M. Lacroix, Chem. Mater. 11 (1999) 3216.


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Mesoporous carbon-containing MoS2 materials formed from the in situ decomposition of tetraalkylammonium thiomolybdates