A First-principles Study Of The Structures And Catalytic Activity Of Noble Metal/perovskite Catalyst

Automobiles’ exhaust gas is one of the main sources of air-pollution. Developing exhaust catalysts technology is a major measure to reduce diesel engine exhaust emission. Recently, welldispersed noble metal on perovskite support is expected to show better catalytic ability. Therefore, we explore the mechanism of Ptn/CaTiO3 interfacial activity of NO oxidation and the origin of active O atom in CO oxidation on Pd/LaCoO3 surface.Since the oxidation of NO to NO2 is the important step for reducing NO in lean burn exhaust gas, we study the catalytic oxidation of NO on metal-support interface based on a Pt4/CaTiO3 model and find the effort of interface site. Initially, we optimize to obtain the stable CaO(001) surface and TiO2(001) surface. Then, the effects of cluster size Ptn(n = 4, 5, 6) on the support was evaluated by analyzing interface electronic character and binding energies. Subsequently, the adsorption and dissociation of O2 on Pt4/CaTiO3 were investigated to find out the activation barrier and the most favorable sites for active dissociated O atoms. After producing active O atoms, the catalytic reaction process of NO+1/2O2â†'NO2 on Pt4 and the interface were compared to evaluate the Pt4/CaTiO3 interfacial effect. Finally, we mapped out the energy landscape of NO2 desorption and found that it is an important and rate-limiting step to refresh the Pt4/ CaTiO3 catalyst in the whole NO oxidation process.It has been studied that LaCoO3 exhibited higher catalytic activity toward CO oxidation among perovskites and Sr-doped LaCoO3 could enhance the activity. In our study, by doping Pd atom in LaCoO3 surface, we attempt to discovery the effect of Pd-doping on CO oxidation and find the origin of active oxygen atom. CoO2(1-12) surface is selected as substrate in O2-rich environment due to its low formation energy. It is found that Co-OPd bridge site of the first-layer Pd-doped surface is the most stable adsorption site by comparing Pd-deposition and Pd-doping structures. When CO moved from Pd-Top adsorption site to Co-O bridge site, it binds with the lattice O and C atom to form O-C-O bent structure. The oxidation process is exothermic reaction with 0.70 eV and the formed CO2 desorbs from surface with the activation barrier less than 0.10 eV. The results indicate that the Pd-doping to substitute the first-layer Co could increase the lattice oxygen activity for CO oxidation and CO2 desorption by leaving one O-vacancy. The O-vacancy could be filled by one O atom of free O2, which creates a new active O atom to oxidize another CO with the activation barrier of 1.70 eV. Therefore, it can be drawn such a conclusion that the key factor of influencing CO oxidation is the origin of active O atom, while the subsequent CO2 desorption form surface occurs easily and readily refreshes Pd/LaCoO3 surface.