Study of Sm2O3-doped CeO2/Al2O3-supported copper catalyst for CO oxidation

Samaria-doped ceria (SDC) and SDC/gamma-alumina-supported copper catalysts were prepared by a co-impregnation method. Temperature-programmed reduction (TPR) analysis and X-ray diffraction were employed for catalyst characteri zation. The activities of CO oxidation over these catalysts were measured a nd compared. It was found that significant enhancement of catalytic activit y was achieved for copper supported on SDC, leading to a precious metal-lik e catalytic behavior. Catalytic activity is governed by oxygen vacancies of SDC and interfacial active centers formed, not by the dispersion and BET s urface area offered by gamma-Al2O3. Thus, SDC-supported Cu exhibits higher activity for CO oxidation than that of SDC/gamma-alumina-supported Cu. For Cu/SDC catalysts, the composition of samaria in SDC at which the maximum of CO oxidation activity occurs corresponds well with the maximum of the oc-p eak area of TPR. The optimum CO activity is due to the maximum number of th e interfacial active centers. The surface oxygen ions of the SDC and SDC/ga mma-Al2O3 supports can be removed by hydrogen, which is associated with the reduction of ceria. These oxygen ions have been judged to be the surface c apping oxygen ions, which coordinate beside the surface oxygen vacancies of SDC. The activity decline which resulted from excess samaria over the opti mal composition of 5 mol% Sm2O3 in SDC can be attributed to the segregation of samaria. (C) 2000 Elsevier Science B.V. All rights reserved.