Hydrogenation of carbon monoxide on Mo(100) single crystals and polycrystalline foils

Abstract

The hydrogenation of carbon monoxide over (100)-oriented single crystals and polycrystalline molybdenum catalysts produces primarily methane, ethene, and propene. The rates of formation of all products were found to be the same for both the (100) single crystals and polycrystalline foils suggesting that the reaction is structure insensitive. The dependence of the rate of formation of methane on reactant pressure was found to be rCH4 = KPCO+0.32 ± 0.05PH21.0 ± 0.1 The unusual positive CO pressure dependence points to a mechanism of methanation that is different from that on other transition metal methanation catalysts (Fe, Ru, Ni) although the activation energy for the reaction is similar, 24 kcal/mol. Addition of K to the surface, at coverages of less than 0.3 ML, increased the overall rate of reaction and enhanced the olefin-to-paraffin ratio. The addition of S to the surface decreases the rate of hydrogenation but, for coverages up to ~0.25 ML, increases the ratio of ethene to methane by a factor of as much as 5.