钙钛矿型复合氧化物用于汽车尾气催化净化的研究进展(二)

综述了钙钛矿型汽车催化剂的研究进展.和过渡金属简单氧化物相比,钙钛矿型复合氧化物(ABO3)在热稳定性、化学稳定性和结构稳定性方面具有一定的优越性,因而表现出更高的催化活性.钙钛矿型催化剂的合成方法影响到催化剂的物理化学性能,如结构、形貌、粒度、比表面及催化活性等.大量的注意力集中在如何提高这类催化剂的比表面上.将纳米技术应用于钙钛矿型化合物的制备,不仅提高了催化剂的比表面,更重要的是改善了这类催化剂的催化活性.某些制备技术可以有效地防止催化剂与载体的反应, 从而延长了催化剂的使用寿命.真对不同的制备方法,研制出了相应的负载方法.在许多情况下,制备方法和负载技术组成了一个完整的体系.催化机理是一项颇具挑战性的课题.事实上,钙钛矿型催化剂在汽车尾气净化过程中的作用机制还没有得到彻底理解.在催化机理研究中,还原氧化模型已被人们普遍接受.反应物和产物分子的吸附和解吸以及催化剂结构中的氧离子空位,是许多动力学模型的重要因素.

Advances on research of perovskite catalyst for purification of motor-vehicle's exhaust (part 2)

The present article is the continuation of the previous one entitled Part I, which aims to finish the retrospection and commentary on the up-to-date advances in the research of motor-vehicle's exhaust catalyst with perovskite being the main structure. As is known, compared with the simple transition metal ones, various pertovskite-type mixed oxides (ABO_3) enjoy the advantages of higher thermal, chemical and structural stability, and well-advanced catalytic activity. The synthetic routes have an essential effect on the physical-chemical properties, such as structure, morphology, grain size, specific surface area, catalytic activity and so on. So far as we know, great attention has been paid to improving the specific surface areas. The introduction of nanometer technique into the preparation of perovskite-type oxides not only contributes to the extension of the specific surface area, but also helps to enhance the catalytic activity simultaneously, which proves to be of greater significance. Some novel preparations prevent the catalysts from reacting with the supports, and thus extend the catalyst service life. According to the preparations, many loading processes have been developed, which, in many cases, along with the preparation, forms a system. In the last decades, the catalytic mechanism of perovskite-type oxides has been an issue of challenge. In fact, the kinetics of the catalytic reactions is far from being well understood. In many mechanisms, redox model, which was proposed by Mars and van Krevelen, has been adopted, and the adsorption and desorption of the reactants or products, and the oxygen ion vacancies actually play an important role.