Basic Study on Design of Complex Oxide Catalysts of Two Components

本研究的目的是为复合氧化物催化剂的设计提供依据。我们采用钙钛矿型氧化物作为复合氧化物，以甲烷的氧化为实验反应。主要研究结果如下：1.探讨了复合氧化物的制备方法与其催化活性的关系。碱性中心是Ce基钙钛矿型氧化物上甲烷氧化的活性中心。随着氧化固相反应温度的升高，碱性中心的数量增加。Li取代BaCeO_3和LaCeO_3的A位金属离子，提高了催化剂的氧化活性。对于LaCeO_3，活性随Li取代比的增加而增加，表明Li取代形成的氧空位起着重要的作用。C_2生成物的活性变化与CO_2生成物的活性变化是平行的。含Ce的钙钛矿型氧化物具有很高的活性。在氧化物中，Ce的一部分被还原为三价，表面有大量的锶碳酸盐。认为氧化物的高活性是由于O~+离子和/或氧空位所致。氧在300-500ﾟ℃脱附，源于晶格氧，在甲烷氧化过程中也起着重要作用。催化活性与氧离子和金属离子键长的变化没有明显的关系。

The aim of this research was to obtain criteria for design of complex oxide catalysts. We employed perovskite-type oxide as a complex oxide, and oxidation of methane as a test reaction. Obtained results are followings :1. Relation between the preparation method of complex oxides and their catalytic activity was discussed for SrCeO_3. The basic sites are the active ones for methane oxidation over Ce-based perovskite-type oxides. The number of the basic sites increases with the temperature of the solid-state reaction of oxides.2. Substitution of Li for A-site metal ion of BaCeO_3 and LaCeO_3 caused an increase of activity of oxidation. For LaCeO_3, activity increased with the ratio of Li substitution, which suggested that Oxygen vacancies formed by Li substitution play an important role. The activity change of C_2 formation paralleled that of CO_2 formation.3. perovskite-type oxides containing Ce were very active. In the oxides, a part of Ce contained was reduced to trivalence, and there were a plenty of carbonate of Sr on the surface. It was suggested high activity of the oxides are due to O^- ions and/or oxygen vacancies. Oxygen desorbed at 300-500 ^ﾟC, which stems from the lattice oxygen, also plays an important role in methane oxidation.4. The catalytic activities did not show a clear relationship with the change of bonding length between an oxygen ion and a metal ion.