Hydrogenolysis of adsorbed methylthiolate on the Pt(111) surface

Abstract

A combination of temperature programmed reaction experiments and fluorescence yield near edge spectroscopy (FYNES) has been used to characterize hydrogen induced C-S bond activation in adsorbed methylthiolate on the Pt(111) surface. The low temperature methane peak observed at 310 K during temperature programmed decomposition of methanethiol clearly involves reaction with adsorbed hydrogen since deuterium incorporation is observed in the presence of coadsorbed deuterium. Some multiple deuteration is observed suggesting that a mixture of carbon containing species may be involved in the hydrogenolysis process. In situ FYNES above the carbon K edge has been used to characterize the kinetics of this hydrogenolysis process in more detail. Transient FYNES measurements were used to characterize changes in the total carbon concentration during the hydrogenolysis reaction. In situ temperature programmed reaction experiments performed in 0.02 Torr of hydrogen clearly indicate that hydrogenolysis begins near 290 K and all carbon containing species are removed by 360 K. In situ isothermal kinetic studies indicate that the hydrogenolysis reaction is first order in adsorbed thiolate coverage and approximately half order in hydrogen pressure. The apparent activation energy for the hydrogenolysis reaction is 18 kcal/mol in the presence of 0.02 Torr of gaseous hydrogen. This activation energy represents a lower bound for the hydrogenolysis activation energy since the apparent heat includes the heat of adsorption for hydrogen. These direct kinetic measurements of this hydrogenolysis reaction under reactive gaseous environments highlight the role that in situ methods can play in characterizing surface reaction processes.