Dynamic structural changes of perovskite-supported metal catalysts during cyclic redox treatments and effect on catalytic CO oxidation

Abstract

CaTiO 3 -and BaTiO 3 -supported Ag and Pt catalysts were subjected to cyclic oxidation and reduction treatments and their surface structures were investigated using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The CO oxidation reactions over the Ag and Pt catalysts showed that the oxidized Ag/oxide catalysts performed better in CO oxidation than the reduced ones did, whereas the reduced Pt/oxide catalysts had higher CO oxidation activity than that after oxidation treatment. The XRD and XPS measurements revealed that the oxidation treatment helped to improve the dispersion of Ag nanoparticles, but their metallic state was retained, which enhanced CO oxidation. In contrast, the surfaces of the Pt nanoparticles were dominated by PtO 2 after the oxidation treatment, which lowered the CO oxidation activity compared with that of the reduced Pt catalyst. 研究了钛酸钡和钛酸钙担载的Ag和Pt纳米催化剂的表面结构随氧化-还原处理过程的动态变化及其对CO完全氧化反应性能的影响. 发现氧化物担载的Ag催化剂在氧化处理后其催化活性较还原处理的高; X射线衍射(XRD)和X射线光电子能谱(XPS)表征结果表明, 氧化处理能够提高载体表面Ag颗粒的分散度, 而还原处理导致Ag颗粒的聚集, 从而降低了催化氧化CO反应的活性. 氧化-还原处理改变了担载Ag纳米粒子的尺寸并影响其CO氧化反应活性. 与此相反, 氧化物担载的Pt催化剂在还原处理后所表现出的CO氧化反应活性较氧化处理的高; 对比研究发现, 氧化和还原处理后Pt纳米粒子的尺寸基本相同, 但是氧化处理的样品中Pt表面物种以氧化态为主, 而还原处理后Pt表面物种主要为金属态. Pt纳米粒子表面化学状态随氧化-还原处理的调变是导致表面催化活性差异的主要原因. Perovskite-supported Ag and Pt catalysts show reversible structural changes and oxidation catalysis performance during cyclic oxidation and reduction treatments. Supported Ag catalysts show better performance after oxidation treatment, whereas supported Pt catalysts have enhanced activity after reduction treatment.