Effects of Alloyed Metal on the Catalysis Activity of Pt for Ethanol Partial Oxidation: Adsorption and Dehydrogenation on Pt(3)M (M=Pt, Ru, Sn, Re, Rh, and Pd)

The adsorption and dehydrogenation reactions of ethanol over bimetallic clusters, Pt(3)M (M = Pt, Ru, Sn, Re, Rh, and Pd), have been extensively investigated with density functional theory. Both the α-hydrogen and hydroxyl adsorptions on Pt as well as on the alloyed transition metal M sites of PtM were considered as initial reaction steps. The adsorptions of ethanol on Pt and M sites of some PtM via the α-hydrogen were well established. Although the α-hydrogen adsorption on Pt site is weaker than the hydroxyl, the potential energy profiles show that the dehydrogenation via the α-hydrogen path has much lower energy barrier than that via the hydroxyl path. Generally for the α-hydrogen path the adsorption is a rate-determining-step because of rather low dehydrogenation barrier for the α-hydrogen adsorption complex (thermodynamic control), while the hydroxyl path is determined by its dehydrogenation step (kinetic control). The effects of alloyed metal on the catalysis activity of Pt for ethanol partial oxidation, including adsorption energy, energy barrier, electronic structure, and eventually rate constant were discussed. Among all of the alloyed metals only Sn enhances the rate constant of the dehydrogenation via the α-hydrogen path on the Pt site of Pt(3)Sn as compared with Pt alone, which interprets why the PtSn is the most active to the oxidation of ethanol.