Model Hydrodesulfurization Reactions: Saturated C4S Molecules on Mo(110)

Article abstract of DOI:10.1021/ja00283a011

The reactions of tetrathiophene and 1-butanethiol on Mo(110) have been investigated by using temperature-programmed reaction spectroscopy, isotopic exchange reactions, and Auger electron spectroscopy.At low exposures, tetrahydrothiophene decomposes below 400 K to gaseous dihydrogen and surface carbon sulfur.Higher tetrathiophene exposures also result in reaction limited formation of butane and butene at 350 and 380 K, respectively.Preadsorption of a saturation coverage of hydrogen or deuterium atoms decreases the temperature at which butane is formed by 50 K and increases the yield of butane by a factor of approximately 6 at reaction saturation.The butene formation peak is unaffected by the presence of excess surface hydrogen.Reversible desorption of molecularly bound tetrahydrothiophene from the Mo(110) surface is observed at 310 K.In the absence of preadsorbed hydrogen, approximately 25percent of the tetrahydrothiophene that reacts forms hydrocarbons, as measured by Auger electron spectroscopy.An irreversibly bound hydrocarbon fragment is present on the surface which decomposes at 565 K to produce gaseous dihydrogen.The butane, butene, and dihydrogen incorporate surface deuterium.The proposed mechanism for this rection is initial hydrogenation of one of the α-carbon atoms with accompanying C-S bond scission.Hydrogenation of the resulting intermediate at the α-carbon yields butane.Alternatively, elimination of a hydrogen atom bonded to a carbon located β to sulfur in the partially hydrogenated intermediate results in 1-butene formation.The reaction of 1-butanethiol was investigated to test the mechanism since 1-butanethiol will yield the intermediate proposed for tetrahydrothiophene reaction if S-H bond scission is the first step in the reaction of 1-butanethiol.The reaction of 1-butanethiol is, in fact, analogous to the reaction of tetrathiophene.Molecular hydrogen, butane, and butene are produced in the same temperature regime as for the tetrahydrothiophene reaction on Mo(110), with butane and butene formation occuring at 305 and 355 K, respectively.There is an order of magnitude greater hydrocarbon yield from reaction of 1-butanethiol, compared to tetrahydrothiophene.At most one surface deuterium atom is incorporated into the butane produced during 1-butanethiol decomposition, while no surface deuterium atom is incorporated into the butene produced.These results further support the proposed mechanism.