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

本研究采用反向均匀沉淀法制备了几种混合金属氧化物。RHP方法的优越性得到证明，通过表征所获得的氧化物和催化性能。一些重要的结果如下所示。（1）在大量的碱性溶液（氨水）中滴加La和Mn的混合酸性溶液（硝酸盐），过氧化氢相的形成温度降低200℃以上。（2）在碱性溶液中加入烷基铵离子（R_4N^+;R=Me、Et和Pr），使LaMnO_3的比表面积增大。金属氢氧化物前驱体的粒径随烷基基团的疏水性（C数）而减小，其顺序为无>Me>Et> Pr。（3）RHP-P（孔内RHP;将碱性溶液和酸性溶液按与孔体积相同的体积依次吸附到氧化铝载体的介孔中）。用RHP-P法制备的氧化铝负载LaMnO_3和LaFeO_3催化剂的活性高于传统浸渍法制备的负载LaMnO_3和LaFeO_3催化剂，这是因为负载LaMnO_3和LaFeO_3的氧化铝载体孔中钙钛矿氧化物颗粒的聚集和晶粒长大受到抑制。(4)In与<1-x>常规共沉淀法相比，RHP法合成的CeZrxO_2颗粒的组成均匀性和比表面积均有所提高。（5）LaMn_<1-x0.8>Cu_（0.2）O_3是一种很有前途的富氢气氛中CO选择氧化材料。制备方法和焙烧条件对催化剂的性能有很大影响。RHP制备结合750℃焙烧得到的催化剂活性最高，特别是在150℃的较低温度范围内，因为这样制备的催化剂具有更好的结晶度和更高的比表面积。

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.