Methane dissociation and syngas formation on Ru, Os, Rh, Ir, Pd, Pt, Cu, Ag, and Au: A theoretical study

A theoretical study of methane dissociation and syngas formation on a number of transition metals M (M = Ru, Os, Rh, Ir, Pd, Pt, Cu, Ag, Au) is presented. The metal surface is simulated by a M-10 cluster model. Reaction energies for the steps involved are determined. The activation energies have been estimated using the analytic BOCMP formula. The dissociation energy is shown to be an important factor determining the catalytic activity of the metal. The order of the calculated total dissociation energies (CH4,s, --> C-s + 4H(s)) is consistent with the order of methane conversions over the metals. In the presence of adsorbed oxygen, oxygen at metal on-top sites promotes methane dehydrogenation; oxygen at hollow sites promotes methane dehydrogenation on Pt, Cu, Ag, and Au, but shows no such effect on the other transition metals. The difference in the H-2 selectivities can be associated with the difference in the stabilities of OH on the metals. For CHx couplings, the trend in the calculated combination energies is in agreement with experimental observation. (C) 1999 Academic Press.