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 numbe r of transition metals M (M = Ru, Os, Rh, Ir, Pd, Pt, Cu, Ag, Au) is presen ted. The metal surface is simulated by a M-10 cluster model. Reaction energ ies for the steps involved are determined. The activation energies have bee n estimated using the analytic BOCMP formula. The dissociation energy is sh own to be an important factor determining the catalytic activity of the met al. The order of the calculated total dissociation energies (CH4,s, --> C-s + 4H(s)) is consistent with the order of methane conversions over the meta ls. In the presence of adsorbed oxygen, oxygen at metal on-top sites promot es methane dehydrogenation; oxygen at hollow sites promotes methane dehydro genation on Pt, Cu, Ag, and Au, but shows no such effect on the other trans ition metals. The difference in the H-2 selectivities can be associated wit h the difference in the stabilities of OH on the metals. For CHx couplings, the trend in the calculated combination energies is in agreement with expe rimental observation. (C) 1999 Academic Press.