A density functional theory study of methanol dehydrogenation on the PtPd3(111) surface

Abstract

Platinum (Pt)-based catalyst has been widely used as the catalyst in direct methanol fuel cells. This study aimed at determining the favorable pathway for methanol (CH3OH) dehydrogenation on the PtPd3(111) surface through the periodic density functional theory (DFT) calculation. The calculation evaluated the stable adsorption configurations of the possible intermediates produced from the successive dehydrogenation of methanol through C–H and O–H bond scission. The results showed that CH3OH, CH2OH, CH3O and CHO preferred to locate at the top site, COH, CO and H preferred to adsorb on the face centered cubic (fcc) site, while CH2O and CHOH would choose the bridge site. Both CH3OH and CH2O were bonded weakly on the PtPd3(111) surface due to their closed-shell electronic configurations. The other intermediate species were interacted strongly with the surface. The energy barriers in four possible pathways via initial breakage of O–H or C–H bond were calculated. By comparing the energy changes in the potential energy surface, the initial O–H scission of CH3OH as the most favorable reaction pathway was determined. The activation barrier by this pathway was only 0.955 eV. The dehydrogenation mechanism from CH3OH to CO via breaking O–H bond was derived as CH3OH → CH3O → CH2O → CHO → CO. The first dissociation step, CH3OH into CH3O and H was identified as the rate-limiting step. The theoretical results indicated that the proposed pathway for methanol dehydrogenation on PtPd3(111) surface was energetically favorable, and verified that the PtPd3 catalyst with Pt monolayer is a good candidate for methanol dissociation.