A theoretical study on the complete dehydrogenation of methanol on Pd (100) surface

Density functional theory (DFT) method was employed to investigate the adsorption and decomposition mechanisms of CH ₃ OH on Pd (100) surface. Different kinds of possible adsorption modes of relevant intermediates on the surface were identified. It was found that CH ₃ OH and CH ₂ OH prefers to adsorb on the top site, CH ₃ O, CHOH and CO occupy preferentially on the bridge site, while CH ₂ O, CHO, COH and H species adsorb on the hollow site. The adsorption energies of all species exhibit the following trend: CH ₃ OH < CH ₂ O < CH ₃ O < CO < CH ₂ OH < H < CHO < CHOH < COH. Subsequently, four possible dissociation pathways of CH ₃ OH via initial O-H and C-H bond scissions were proposed and studied systematically. The transition states, energy barriers and reaction energies were calculated to explore the dehydrogenation mechanisms of CH ₃ OH on Pd (100) surface. It was indicated that the scission of C-H bond is more favorable for CH ₃ OH and CH ₂ OH and the H-O bond cleavage is easier for CHOH. The path 2 (CH ₃ OH-CH ₂ OH-CHOH-CHO-CO) is the most possible dehydrogenation pathway, where the highest energy barrier of CH ₃ OH dissociation makes it to be the rate-determining step of the whole dehydrogenation reaction.