论文部分内容阅读
以传统的浸渍法,在不同焙烧温度下制备了用于CO氧化反应的Co3O4/SiO2催化剂.通过激光拉曼光谱(Raman)、X射线光电子能谱(XPS)、X射线衍射(XRD)、程序升温还原(TPR)和X射线吸收精细结构谱(XAFS)表征了该系列催化剂的结构.存所有的催化剂中,XRD和Raman光谱都只检测到了Co3O4晶相的存在.与Co3O4体相相比,XPS结果表明在200℃焙烧的(Co3O4(200)/SiO2)催化剂中Co3O4表面上存在着过量的Co^2+.与XPS的结果一致,TPR结果表明Co3O4(200)/SiO2催化剂中Co3O4表面上存在氧缺陷,并且XAFS结果也表明Co3O4(200)/SiO2催化剂中Co3O4具有更多的Co^2+.提高焙烧温度使得过量的Co^2+进一步氧化为Co^3+,同时降低了表面氰缺陷浓度,从而得到计量比的Co3O4/SiO2催化剂.存所有的负载催化剂中,Co3O4(200)/SiO2催化剂表现出了最好的CO氧化健化性能,表明过量CO2+和表面氧缺陷的存在能够促进Co3O4催化CO氧化反应的活性.“,”Co3O4/SiO2 catalysts for CO oxidation were prepared by conventional incipient wetness impregnation followed by calcination at various temperatures. Their structures were char- acterized with X-ray diffraction (XRD), laser Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR) and X-ray absorption fine structure (XAFS) spectroscopy. Both XRD and Raman spectroscopy only detect the existence of Co3O4 crystallites in all catalysts. However, XPS results indicate that excess Co2+ ions are present on the surface of Co3O4 in Co3O4(200)/Si02 as compared with bulk Co3O4. Meanwhile, TPR results suggest the presence of surface oxygen vacancies on Co3O4 in Co3O4(200)/SiO2, and XAFS results demonstrate that Co3O4 in Co3O4(200)/SIO2 contains excess Co2+. Increasing calcination temperature results in oxidation of excess Co2+ and the decrease of the concentration of surface oxygen vacancies, consequently the for- mation of stoichiometric Co3O4 on supported catalysts. Among all Co3O4/SiO2 catalysts, Co3O4(200)/SiO2 exhibits the best catalytic performance towards CO oxidation, demonstrating that excess Co2+ and surface oxygen vacancies can enhance the catalytic activity of Co3O4 towards CO oxidation. These results nicely demonstrate the effect of calcination temperature on the structure and catalytic performance towards CO oxidation of silicasupported Co3O4 catalysts and highlight the important role of surface oxygen vacancies on Co3O4.