Mechanistic Studies Into The Methanol Oxidative Dehydrogenation On Pt-group Metals

Pure Pt and Pt alloy species have good catalysis effect on Direct Methanol Fuel Cell?DMFC?.In this paper,we have studied two different Pt alloy catalyst systems:PtRu alloy reaction system and Pt Pd alloy reaction system.With the related theory and experimental researches,we have studied the reaction mechanism of methanol on PtRu and Pt Pd alloy surface based on the density functional theory?DFT?and periodic slab model system,and have analysis the related properties.On PtRu?111?surface,we found:?1?Ru atoms is the dominant role on PtRu alloy surface.The Oxidative dehydrogenation of methanol and water activation process take place mainly around the Ru atoms.?2?The reaction path for methanol on PtRu?111?surface is non-CO path:First,the methanol dehydrogenates and generates CHO,namely CH₃OH?CH₃O?CH₂O?CHO;then water activate and generate oxygenated intermediate OH;CHO will react with OH and generate CHOOH;finally CHOOH dehydrogenize successively and generate the final product CO₂.?3?The water activation on PtRu?111?surface is more easily than that on Pt?111?surface.Under the same theoretical level,the energy barrier on PtRu?111?surface is 0.91 e V and on Pt?111?surface is 1.20 e V.By the analysis of contribution factors for energy barrier,we found product of OH in the translation state interact intensively with the PtRu alloy surface.This is the primary reason for the easy activation of water on PtRu surface.By the study on Pt Pd surface,we found:?1?Pt atom is the dominant role for the intermediates adsorbing and reacting on Pt Pd alloy surface,which indicates that Pt is the activation center on Pt Pd?111?surface.?2?The methanol reaction starts with the C-H activation,and the reaction path is CO path.The methanol first dehydrogenize successively and generate CO;then CO react with oxygenated intermediate OH and generate acid intermediate COOH;finally the COOH decompose and generate CO₂,which follow by:CH₃OH?CH₂OH?CHOH?CHO?CO,CO+OH?COOH?CO₂.?3?The water activation is also more easy on Pt Pd?111?surface?0.89 e V?than on Pt?111?surface?1.10 e V?.By analyzing the energy barrier contribution factors,we found the deformation energy of the substrate is relatively small,and OH interact intensively with Pt Pd alloy surface in the translation state.