The Preparation Of Perovskite Catalyst And Its Catalytic Performance For CO Oxidation

Carbon monoxide, CO, originated from the combustion of fossil fuels andvehicular e_xhaust, not only affects human health but also caused severe environmentalpollution. The catalytic oxidation of carbon monoxide is a relatively simple surfacereaction which is important for the control of toxic automotive emission. The catalystsgenerally used for the elimination of automobile e_xhaust are supported noble metalssuch as Pt, Pd, Ru and Au which show high activity and long-life time. However, theirhigh prices and easily poisoned property restrict their industrial applications. However,the perovskite-type catalysts which are highly active for CO oxidation may be used asan alternative.As is well known, the good performance for CO oxidation of perovskite catalystsof formula ABO₃is related to its specific surface area, redox ability and its crystalstructure. Perovskite mixed oxides have been e_xtensively studied due to its physicaland chemical properties, good thermal stability and oxygen storage capacity. However,the perovskite mixed oxides prepared via conventional synthesis routes haverelatively low specific surface areas and pore volume. Its applications were limited.It is known that ordered mesoporous silica material, SBA-15, is a good catalystssupport due to their large surface area, uniform pore size and high hydrothermalstability.In this paper,30%La_1-xCe_xCoO₃/SBA-15（x=0.05-0.25）catalysts wereprepared by a hydrothermal method. The crystal structure, particle size, surface area,pore size distribution and pore volume after La was substituted with Ce wereinvestigated. The following conclusions are obtained:Lanthanum nitrate, Cobalt nitrate, Cerium nitrate and citric acid were used asraw materials for the preparation of30%La_1-xCe_xCoO₃/SBA-15（x=0.05-0.25）perovskite catalysts. It was found that Ce doping improved the catalytic performancefor CO oxidation. The catalyst with x=0.2showed the highest activity. It was alsofound that the specific surface area is not the only factors influencing the activity, butthe structural defects of perovskite and the metal valence states are also importantcontributors.The catalysts, La_1-xAg_xMnO₃（x=0.1-0.3）, have been prepared by Ureacombustion method. It has been reported that catalytic performance of catalystsprepared by different methods varied due to their different physical and chemical properties. Catalyst preparation by urea combustion method has a number ofadvantages including low synthesis temperature, short reaction time and high purityproducts. The crystal structure, particle size, surface area have been studied after Agwas substituted for La in the catalysts. The following conclusions are obtained:The perovskite catalysts La_1-xAg_xMnO₃（x=0.1-0.3）prepared by the ureacombustion method showed good activity after Ag was substituted for La for COoxidation reaction. The catalyst x=0.2showed the highest activity. It can be e_xplainedthat doping Ag enhanced the catalytic performance of CO oxidation reaction andpromoted the reduction of Mn.The catalysts prepared were characterized by XRD, N₂adsorption-desorption,transmission electron microscopy （TEM）， hydrogen temperature programmedreduction （H₂-TPR）. Further, the catalysts activity was evaluated for CO oxidation.