A study on synthesis of ultrafine perovskite-type oxide catalyst LaCoO_{3} via mesoporous silica templating

Abstract

Perovskite-type oxide LaCoO_{3} as a substitute of noble metal catalysts has high potential for their use in various oxidations. There are some classical methods commonly used for the synthesis of perovskite-type oxide such as solid-state method and co-precipitation method, etc. These methods require high calcination temperature (>900℃) for forming perovskite structure and hence yield perovskite-type oxides with low surface area (<2 m^{2}/g) due to sintering. A new synthesis route combining the citrate sol-gel method and the mesoporous silicas (MCM-41 and MCM-48) as templates was investigated to produce ultrafine LaCoO_{3}. Ultrafine LaCoO3 obtained by the new synthesis method was characterized with XRD, N2-adsorption/desorption, and EDX, configuring the single crystallite structures of perovskite. Ultrafine LaCoO_{3} obtained by silica templates removal showed the crystallite size of 18nm and the surface area of 140 m^{2}/g. The small crystallite size was caused by forming the perovskite-type oxides of La and Co precursors inside mesopores of silica template. The ultrafine LaCoO_{3} was applied as a catalyst for total oxidation of toluene. Catalytic performance of ultrafine LaCoO_{3} was compared with those of traditional LaCoO_{3} (by co-precipitation or citric acid method) and LaCoO_{3} with silica templates. The ultrafine LaCoO_{3} catalyst was the most active due to remarkably high surface area(140 m^{2}/g). The ultrafine LaCoO_{3} catalyst by the new synthesis route has improved surface area and catalytic activity compared with traditional LaCoO_{3}.