Density Functional Theory Study On Oxidation Of CO Catalyzed By Doped Aluminum, Platinum Clusters And Molybdenum Carbonyl Compounds

Recently,the transition metal alloy clusters have elicited extensive attention in CO oxidation reaction due to the special optical properties,catalytic activity and magnetic properties.Researches find that doped clusters have more high catalytic activity and low cost than pure clusters.Therefore,in line with the principle of high-efficient and low-cost,we investigate the Al-Pt alloy clusters catalyzing CO oxidation reaction.Although the related studies of Al-Pt alloy clusters showed that Al₁₂Pt cluster has a good catalytic activity for catalyzing CO oxidation reaction,as the change of clusters size,some effect of the catalytic properties of the cluster will be alter.So,in this chapter we will investigate the Al_nPt?n=1-11?clusters catalyzing CO oxidation reaction using density functional theory?DFT?calculation.Based on the research of structures of Al_nPt?n=1-11?clusters and the adsorption behavior of small molecules CO,O₂ on clusters surface,we find that doped Pt atom can influence the geometric of Al_nPt cluster.The symmetry of the clusters has been changed.And the active sites in Al_nPt clusterswould be first occupied by the coming O₂ rather than CO,in view of its more negative adsorption energy than those of CO.At the same time,in order to clarify the reaction mechanism,the reaction pathway for CO oxidation on Al_nPt clusters has been described by Langmuir-Hinshelwood?LH?reaction in our calculation.It is shown that mixing two different metals?Al and Pt?can have beneficial effects on the catalytic activity and the Al₁₁Pt cluster is proposed as the best effective nanocatalyst.Water-gas-shift?WGS?reaction?H₂O+CO?H₂+CO₂?is an important industrial reaction in aspect of hydrogen fuel cells and industrial applications,especially for steam reforming of methanol,ammonia synthesis and conversion of syngas into a variety of chemicals.WGS reaction can remove the side product CO and regenerates H₂ in the process of the production of hydrogen fuel.Currently,for WGS catalysts,many studies have calculated the reaction on metal surface,metallic nanoparticles,metallic nanoparticles supported on oxide surface aiming to finding a new and efficient kind of catalysts.Comparison the catalytic activity of those WGS reaction catalysts,the transition metal carbonyl catalysts can not only effectively catalyze the WGS reaction continues but also easy to be prepared.Therefore,the mechanisms of WGS reaction catalyzed by Mo?CO?₆ and Mo₂?CO?₁₀ have been studied.Four different reaction mechanisms of the WGSR catalyzed by mononuclear Mo?CO?₆ in the gas and methanol solution are discussed,in order to find the optimal reation pathways and appropriate reaction conditions.The results shows that the OHdesorption from the Mo?CO?₆ is very energy demanding in Torrentmechanism,which makes the Torrent mechanism unlikely to proceed.However,following Barrows mechanism the key intermediate is not present which has been observed in experimental,although the mechanistic pathways avoid the OH-desorption step.At the same time,the Rozanska and Zhang mechanism revised the reaction mechanism proposed by Torrent.In our work,the Zhang mechanism is demonstrated to be feasible not only in gas phase but also in solvent.And the mechanism involves these steps,which correspond to Mo?CO?₆+OH^-?Mo?CO?₅?COOH?^-?Mo?CO?₅H^-+H₂O?Mo?CO?₄H₂?COOH?^-?Mo?CO?₄?COOH?^-+CO?Mo?CO?₅?COOH?^-.The possibility of metal-metal cooperativity in improving the yield of the water-gas shift reaction has been investigation.Binuclear complexes Mo₂?CO?₁₀ catalyst has been designed as the catalysts for the WGSR.The calculations indicate that the binuclear Mo₂?CO?₁₀ has lower barriers and higher TOF in comparison to the mononuclear Mo?CO?₆.Mo₂?CO?₁₀ is thus the promising candidate for improved WGSR catalysts.