水滑石类复合氧化物的制备及其催化性能研究

采用低饱和共沉淀法制备TMgAL—LDHs、ZnAI—LDHs、CuMgAI—LDHs等几种水滑石结构化合物．研究了pH值和原料比对MgAI—LDHs、ZnAI—LDHs和CuMgAl-LDHs结构的影响．并以这些类水滑石为前驱体得到了MgAI、ZnAI、CuMgAl三种复合氧化物催化剂．研究结果表明：当pH〉9时，对MgAl-LDHs结构的影响较小；当Zn／Al-3时．形成的ZnAl—LDHs结晶度最好；在Cu2＋／Mg2＋=0．25条件下，M2＋／M3＋=2．0时形成的CuMgAl—LDHs结晶度和品形最好；在M2＋／M3＋-3条件下，随着Cu2＋／Mg2＋比的增大．层间距加大．Mg—Al、Zn—A、Cu—Mg—Al三种复合氧化物对逆水煤气变换反应的热稳定性均较好，Cu的引入大幅度的提高催化活性，特别是低温活性的提高尤为明显．

SYNTHESIS OF HYDROTALCITE-LIKE COMPOSITE OXIDES AND THEIR CATALYTIC PERFORMANCE

Hydrotalcite-like compounds （LDHs） of MgAI,ZnA1 and CuMgA1 are synthesized by way of low saturation copreeipitation. The effects of pH and the ratio of starting materials on the structure of MgAl-LDHs, ZnAl-LDHs and CuMgAl-LDHs are studied. These hydrotalcite-like compounds are used as precursors and three kinds of catalysts, namely MgAl, ZnAl and CuMgAl composite oxides,are prepared by calcination. Results show that the structure of MgAl-LDH is less affected when pH〉9 ;when Zn/Al=3.0,the crystallization of ZnAl-LDHs is perfect ;and when Cu2＋/ Mg2＋ =0.25 and M2＋/M3＋-= 2 ,the crystallization structure and crystallinity of CuMgAl-LDHs appear to be the best. And, when M2＋/M3＋= 3,he interlayer-spacing gets enhanced with the increase of Cu2＋/ Mg2＋. It is proved that the MgAl,ZnAl and CuMgAl composite oxide catalysts all exhibit fairly good thermal stability with the reverse water-gas shift reaction. Moreover,the Cu substitution of the assynthesized CuMgAl hydrotalcite-like compounds makes the catalytic activity, especially the lowtemperature activity,get improved to a great extent.