Molecular mechanisms for initial step of methanol dehydrogenation on metal surface

The initial step of methanol dehydrogenation on M(111) (MCu, Pd and PdZn) surfaces is investigated based on the GGA-PW91 functions and periodic slab models in the framework of the first principles. To determine the preferred reaction pathway on M(111) surfaces, the transition states, reaction energies and energy barriers are quantified for the OH and CH cleavage pathways at the initial step of methanol dehydrogenation. The surface energy and the density of states (DOSs) for the methanol molecule over the M(111) surfaces are compared and analyzed to explain the initial hydrogen abstraction process of methanol molecule. The results indicate that the OH bond cleavage resulting in the co-adsorbed methoxyl and hydrogen atom is preferred on Cu(111) and PdZn(111) surfaces, while the CH bond cleavage with the formation of co-adsorbed hydroxymethyl and hydrogen atom is adapted on the Pd(111) surface. On the PdZn(111) surface, the methanol molecule possesses a higher surface energy than other two slabs. The behaviors of methanol dehydrogenation on M(111) surfaces are influenced by the d-electron structures of M(111). The initial hydrogen abstraction pathways of methanol molecule on the Cu(111) surface and the PdZn(111) surfaces are identical due to the similar d-electron structure near the Fermi level.