| Abstract: A series of CuO/CeO2-Al2O3 catalysts were prepared by chemisorption-hydrolysis method. The techniques of XANES, EXAFS, XRD and H2-TPR were employed for the structural characterization of the catalysts. The effect of calcination temperature on the fine structures, the dispersion and the existing state of the copper species was investigated carefully. The characterization results reveal that the copper species in the sample calcined at 500 ℃ mainly exist as highly dispersed CuO crystallites, which weakly interact with the support Al2O3 and the promoter CeO2. When the calcination temperature is elevated to 650 ℃, three kinds of copper species are detected, namely the small crystallites CuO, the amorphous CuO-CeO2 interacting phase and the Cu-Al surface spinel phase. At higher calcination temperature of 800 ℃, CeO2 is obviously sintered, and the interaction between copper species and Al2O3 is remarkably promoted, leading to the diffusion of partial octahedrally coordinated Cu2+ into tetrahedral sites. The results of the activity evaluation show that the catalyst calcined at 650 ℃ is the most active one for CO oxidation. In this catalyst, Cu and CeO2 effectively interact with each other, and a part of Cu2+ ions have diffused into the lattice of CeO2, leading to the lengthening of Cu-O bond and easier activation of it during the CO oxidation process by forming the -Cu2+-O-Ce4+- linkage. However, after calcination at 800 ℃, the interaction between Cu and Al2O3 is prominently enhanced, and most Cu species transform into bulk spinel phase, which possesses shorter Cu-O bond length than CuO and Cu-Ce interaction phases. Additionally, the CeO2 phase is seriously sintered at this temperature. All of these make the remarkable decrease of the oxidation activity of the catalyst. |
