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Ethanethiol Decomposition Pathways on MoS2(0001) Susan L. Peterson† and Kirk H. Schulz* Department of Chemical Engineering, Michigan Technological University, 1400 Townsend Drive, Houghton, Michigan 49931 Received April 3, 1995. In Final Form: August 24, 1995X The reactivity of thiophene (C4H4S) and ethanethiol (CH3CH2SH) has been studied with TDS on the MoS2(0001) surface. No catalytic activity was detected for thiophene adsorption on MoS2(0001); however, ethanethiol decomposed into ethylene and hydrogen sulfide on the same surface. Ethanethiol is hypothesized to dissociatively adsorb as a thioethoxy surface species, which undergoes hydride elimination to give ethylene. Hydrogen sulfide is formed via hydrogen combination with lattice or adsorbed sulfur. Ethanethiol is thought to adsorb at catalytically active defect sites on the MoS2 basal plane, which are most likely coordinately unsaturated Mo+VI cations. The proposed mechanism is analgous to those observed between thiols and molybdenum/cobalt/sulfur (Cp2Mo2Co2S3(CO)4) clusters. The difference in reactivity between the thiol and aromatic organosulfur compound on MoS2 is thought to occur because of the difference in the C-S bond strengths in thiophene and ethanethiol.
1. Introduction Molybdenum disulfide (MoS2) is an important catalytic material with a variety of different applications as a hydrogenation catalyst1 and as the major component in hydrodesulfurization catalysts.2-5 The use of MoS2 as the catalytically active component for desulfurization has been well-documented and established.2-5 The majority of the work on the catalytic properties of MoS2 has focused on desulfurization mechanisms and surface chemistry, particularly of industrially significant aromatic organosulfur compounds. The study of desulfurization catalytic processes involves (1) the type and structure of the catalyst material, (2) the nature of the organosulfur compound being desulfurized, and (3) the nature of the adsorbed hydrogen. Each of these processes requires separate and independent study for a complete understanding of the reaction mechanisms involved in desulfurization catalysis. Thiophene is the de facto standard molecule used to test desulfurization catalysts, and thus, the majority of mechanistic studies have concentrated on thiophene desulfurization mechanisms. As might be expected, the resultant surface chemistry and mechanisms are complicated due to the relatively large size of the molecule. Our approach has been to study the surface chemistry and intermediate species occurring during the reaction of smaller organosulfur molecules such as alkanethiols, sulfides, and dithiols. We anticipate that these investigations will allow us to identify and characterize the surface chemistry of different types of organosulfur intermediates and thus to gain some insight into the types of surface chemistry which might occur during the decomposition of larger organosulfur molecules of industrial significance. Most surface chemistry studies of organosulfur molecules have focused on alkanethiol behavior on singlecrystal metal surfaces. These studies have prevalently examined methanethiol (CH3SH) on a variety of metal † Current address: Eveready Battery Corp., Westlake, OH 44145. * To whom correspondence should be addressed. X Abstract published in Advance ACS Abstracts, February 1, 1996.
(1) Polz, J.; Zeilinger, H.; Mu¨ller, B.; Kno¨zinger, H. J. Catal. 1989, 120, 22. (2) Prins, R.; DeBeer, V. J. H.; Somorjai, G. A. Catal. Rev. Sci. Eng. 1989, 31 1. (3) Furimsky, E. Catal. Rev. Sci. Eng. 1983, 25, 421. (4) Grange, P. Catal. Rev. Sci. Eng. 1980, 21, 135. (5) Ratnasamy, P.; Sivasanker, S. Catal. Rev. Sci. Eng. 1980, 22, 401.
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surfaces including Ni(100),6-9 Cu(100),10 Pt(111) and (2×2)-S-Pt(111),11 Ni(111),7 Fe(100) and c(2×2)S-Fe(100),12 Cu(111),8,13 Pt(111),14 and Ni(110).15 However, Roberts and Friend,16-20 Parker and Gellman,6 and Huntley21 have examined the surface chemistry of higher thiols (C2 and above). For most of these studies, the significant intermediate following methanethiol adsorption was a thiomethoxy (CH3S-) species, which normally formed at low temperatures (
