Toluene Formation from Coadsorbed Methanethiol and Benzenethiol on Nickel Surfaces

Abstract

Carbon−carbon bond formation resulting in cross-coupling has been demonstrated for coadsorbed benzenethiol and methanethiol on the Ni(111) and Ni(100) surfaces. Toluene formation indicates that desulfurized C6 and C1 intermediates are formed by direct interaction with the Ni surface rather than by hydrogen addition to the C−S bond. Coupling occurs in the same temperature range as hydrogenation of the C6 and C1 intermediates to form benzene and methane. Thus, competition between hydrogenation and cross-coupling plays an important role in controlling reaction selectivity. As surface hydrogen increases, the yield of toluene falls. Reduction of surface hydrogen by reaction with coadsorbed oxygen enhances toluene formation. The effect of coadsorbed hydrogen is larger on the Ni(111) surface where large amounts of coadsorbed hydrogen remain on the surface above the reaction temperatures. On both surfaces the toluene yield increases rapidly for coadsorbed reactant coverages above half saturation, indicating toluene formation is not limited exclusively by stoichiometries but also by kinetic factors. Methyl mobility appears to play a key role in determining toluene yields. The complex dependence of toluene yield on the surface concentrations of both the methanethiol and benzenethiol is consistent with a radical mechanism where both kinetic and stoichiometric factors play a role in determining yields. Toluene formation in the 300 K range appears to be related to the reaction of phenyl and methyl, while toluene formed at higher temperature appears to be associated with hydrogenation of a more extensively dehydrogenated intermediate.

Toluene Formation from Coadsorbed Methanethiol and Benzenethiol on Nickel Surfaces

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Abstract

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