Development of new and facile method to synthesize better mixed metal oxide catalysts

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In this study, several kinds of mixed metal oxides were prepared by reverse homogeneous precipitation(RHP) method. The superiority of the RHP method was demonstrated by characterization of obtained oxides and catalytic properties. Some of important results were shown below.(1)Perovskite phase formation temperature decreased more than 200℃ when the mixed acidic solution(ex.La and Mn nitrates) was added dropwise to a large amount of the basic solution(ex.aq.ammonia).(2)Addition of alkyl ammonium ion(R_4N^+;R=Me,Et and Pr) into basic solution resulted in enlargement of the specific surface area of LaMnO_3. Particle size of metal hydroxide precursor decreased depending on hydrophobicity(C numher) of alkyl group in the order of none>Me>Et>Pr.(3)RHP-P(RHP in pore ; basic solution and acidic solution was absorbed into the mesopores of the alumina support successively just as same volume as pore volume) was carried out. Catalytic activity of alumina supported LaMnO_3 and LaFeO_3 prepared by the RHP-P method were higher than that of conventionally impregnated one because the aggregation and grain growth of perovskite oxide particle was suppressed in the pores of alumina support.(4)In the synthesis of Ce_<1-x>Zr_xO_2, the RHP synthesis also resulted in an increase in the homogeneity of composition of each particle and specific surface area as compared with the normal coprecipitation method.(5)LaMn_<1-x0.8>Cu_<0.2O_3 was revealed to be the promising material for CO preferential oxidation in hydrogen rich gas. Catalytic properties were strongly depended on preparation method and calcination conditions. The RHP preparation combined with 750℃ calcination gave the most active catalyst especially at lower temperature range of 150℃ because the catalyst thus prepared had both better crystallinity and higher surface area.