Preparation, structural and catalytic properties of B-site ordered perovskite-type oxides

钙钛矿型氧化物是一类非常重要的催化剂等功能材料。然而，关于有序排列B位阳离子的所谓双钙钛矿和三钙钛矿的报道却很少。本研究对B位有序双钙钛矿和三钙钛矿进行了系统的合成和结构表征。研究了它们的催化活性与有序结构的关系。合成了Ba-W、Sr-W和La-Ti基双钙钛矿结构，并用Rietveld方法对其晶体结构进行了精炼。研究了高氧化条件下(O2/C3H8=19.5)双钙钛矿系列催化剂上丙烷的氧化反应。催化剂的催化活性明显依赖于B^&lt；2+和gt；阳离子。含3d过渡金属离子的双钙钛矿催化剂对C_3H8氧化反应具有较高的催化活性，而含有IIA和IIB的双钙钛矿催化剂对C_3H8氧化反应具有较高的催化活性更多的UP金属阳离子的活性较差。在所研究的每一系列化合物中，共化合物的活性最高。催化剂活性与B^&lt；2+和Gt；O生成热的关系呈火山型依赖关系，强烈表明该反应是通过氧化还原机理进行的。当使用BaCoO_3、WO_3以及它们的混合物时，在900℃时，在还原BaCoO_3相上沉积的金属Co上证实了碳纤维的形成。在1000℃时，由于金属Co的团聚，碳纤维的生成量减少。另一方面，在1000℃时，双钙钛矿Ba2CoWO6上形成的碳纤维的形貌及其温度依赖性与其他样品不同，这可能是由于双钙钛矿的形成提高了还原耐受性，金属Co的分散性更高。La_2ZnTiO_6选择性地产生一氧化碳，这与在TiO_2上选择性地生产H_2形成了鲜明对比。

Perovskite-type oxides are very important compounds as functional materials such as catalysts. However, there are few reports on so-called double and triple perovskites which have ordered arrangement of B-site cations. In this study, systematic synthesis and structural characterization of B-site-ordered double and triple perovskites were carried out. Their catalytic activity was investigated in relation to the ordered structure.Ba-W, Sr-W and La-Ti based double perovskites were synthesized and their crystal structures were refined by Rietveld method. Accordingly, B-site ordered and disordered structures were able to evaluate successfully.The oxidation of propane in highly oxidizing condition (O_2/C_3H_8=19.5) was investigated over systematic series of double perovskites. The catalytic activity depended significantly on the B^<2+> cations. The double perovskites containing 3d transition metal ions showed high activity for C_3H_8 oxidation reaction, while those containing IIA and IIB gro … More up metal cations were poor in activity. The Co-compounds were most active in every series investigated. The relation between the catalytic activity and the heat of B^<2+>O formation displayed volcano-shaped dependence, strongly suggesting that the reaction proceeds by the redox mechanism.Ba-Co-W based oxides were applied to the reaction of carbon fiber formation. When BaCoO_3, WO_3 and the mixture of them were used, carbon fiber formation was confirmed on metal Co deposited on the reduced BaCoO_3 phase at 900 ℃. In the case of 1000 ℃, the amount of carbon fiber formation decreased due to agglomeration of metallic Co. On the other hand, morphology and its temperature dependency of carbon fiber formed on double perovskite Ba_2CoWO_6 was different from those on other samples at 1000 ℃, probably due to the improvement of reduction tolerance by the formation of double perovskite and the higher dispersion of metallic Co.La_2ZnTiO_6 was prepared and its photocatalytic properties (methanol decomposition) were evaluated. Carbon monoxide was selectively produced with La_2ZnTiO_6, which was in quite contrast to selective production of H_2 over TiO_2. Less