Effects of Alloyed Metal on the Catalysis Activity of Pt for Ethanol Partial Oxidation: Adsorption and Dehydrogenation on Pt3M (M = Pt, Ru, Sn, Re, Rh, and Pd)

The adsorption and dehydrogenation reactions of ethanol over bimetallic dusters Pt3M (M = Pt, Ru, Sn, Re, Rh, and Pd) have been extensively investigated with density functional theory: Both the alpha-hydrogen and 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 dusters through the a-hydrogen were well established. Although the alpha-, hydrogen adsorption on the Pt site is weaker than the hydroxyl adsorption, the potential energy profiles show that the dehydrogenation by the a-hydrogen path has much lower energy barrier than that by the hydroxyl path. Generally, for the a- hydrogen path, the adsorption is a rate-determining-step because of the rather low,H dehydrogenation barrier for the a-hydrogen adsorption complex (thermodynamic control), whereas the hydroxyl path is determined by its dehydrogenation step (kinetic control). The effects of alloyed metal On the catalytic activity of Pt for ethanol partial oxidation including adsorption energy, energy barrier,eletronic structure, and eventually rate constant, are discussed Among all of the alloyed metals investigated, only Sn was found to enhance the rate constant of the dehydrogenation by the a-hydrogen path on the Pt site of Pt3Sn as compared with that on Pt alone which explains why PtSn is the most active catalyst for the oxidation of ethanol.