Mechanistic Investigation On The Catalytic Oxidation Of CO Over Heterodinuclear Tantalum-nickel Monoxide Carbonyl Complexes

With the rapid economic development,the toxic CO derived from the automobile exhaust and petrochemical industry increases gradually,leading to serious environmental pollution.Catalytic oxidation of CO to CO₂ is one of the key technologies in controlling vehicle exhaust emission and purification of gas streams.The research on catalytic CO oxidation can contribute to the fundamental understanding of many aspects of the catalytic activation mechanism over transition metal oxides and surface catalysts.Extensive condensed-phase research has been devoted to the detection of the active site the catalytic CO oxidation,while the gas-phase spectroscopic studies of metal oxide clusters provide a molecular-level understanding of the catalytic mechanisms.Recently,the reactions of CO with various heteronuclear transition metal oxide clusters were extensively investigated to understand many facets of the transition metal oxide clusters,including the composition of clusters,charge state,the support,and the active atomic oxygen species.However,the role of coadsorbed CO ligands has rarely been taken into consideration during the CO oxidation progress.In this thesis,CO adsorption and catalytic oxidation over heterodinuclear tantalum-nickel monoxide complexes have been studied.First,using photoelectron velocity-map imaging spectroscopy experiment combined with density functional theory calculations,we have characterized the continuous CO adsorption on the heterodinuclear tantalum-nickel monoxide.For the series of NiTa O（CO）_n^-（n=5-8）,all of the CO ligands are terminally bonded to the Ta ONi core at n≤7.Thereinto,theμ²-O-bent structure is the most beneficial for NiTa O（CO）₅^-,and then bothμ²-O-bent andμ²-O-linear structures are degenerated in energy for NiTa O（CO）₆^-,then theμ²-O-linear structure is the most favorable one for NiTa O（CO）₇^-,but theη²-CO₂-tagged structure is the most energetically competitive configuration for NiTa O（CO）₈^-,indicating that CO oxidation occurs at n=8.The calculations suggest that both Langmuir-Hinshelwood（LH）-type and Eley-Rideal（ER）-type mechanisms become energetically favorable for the CO oxidation reaction on the NiTa O（CO）₈^-complex.Furthermore,in order to further realize the complete catalytic cycle reaction,although it has not been confirmed experimentally at present,we have made a theoretical prediction.Density functional theory（DFT）has been used to investigate the CO₂ desorption of NiTa O（CO）₈^-complex and the re-oxidization of NiTa O（CO）_n^-heterodinuclear carbonyl complex,respectively.It is found that the desorption of CO₂ molecule from NiTa O（CO）₈^-complex can generate NiTa（CO）₇^-,which can be further oxidized by one O₂ molecule to simultaneously release one CO₂ molecule and NiTa O（CO）₆^-complex,i.e.the regeneration of tantalum-nickel monoxide carbonyl complexes catalyst.The special electronic structure of the complex NiTa（CO）₇^-has been studied by various bonding analysis methods.The results show that there exists 3c×2e electron-sharing chemical bond between Ta-C-Ni,and both Ta and Ni atoms have reached coordination saturation,satisfying the 18-electron rule.In summary,the consecutive CO chemisorption has promoted the CO oxidation reaction over tantalum-nickel monoxide,revealing the CO ligand self-promoted mechanism for the CO oxidation reaction.Moreover,the regeneration of NiTa O（CO）₆^-indicates that the tantalum-nickel monoxide carbonyl complex is a potential catalyst for CO oxidation.The mechanism of ligand-mediated reactivity has important significance of application in heterogeneous catalysis and offers a theoretical foundation for the rational design and development of efficient catalysts.