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

点击翻译按钮获取中文摘要

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