Adsorption and Dissociation of Methanol on Pd(111), Pd/Au(111) and Pd/Rh(111) Surfaces

The adsorption and dissociation behaviors of methanol on Pd(111), Pd/Au(111) and Pd/Rh(111) surfaces were studied using a periodical slab model and the PW91 generalized gradient approximation (GGA) within the framework of first-principles calculations based on density functional theory (DFT). The adsorption energy and geometric parameters for the three surfaces showed that methanol is preferentially adsorbed onto the top-Pd sites and that the adsorption energy of methanol on these surfaces decreases in the order Pd/Au(111) > Pd/Rh(111) > Pd(111). After adsorption, the C-O, C-H and 0-H bonds in methanol adsorbed onto these surfaces are elongated and the vibrational stretching frequency of the O-H bond is obviously redshifted. Furthermore, the first step for the possible dissociation pathway for methanol on these surfaces was calculated. Our results indicate that the O-H bond in methanol decomposes producing methoxy and a hydrogen atom, with the Pd/Au(111) surface exhibiting the smallest dissociation barrier.