Copper oxide-platinum/alumina catalysts for volatile organic compound and carbon monoxide oxidation:: Synergetic effect of cerium and lanthanum

gamma -Alumina alone or modified with 3 mol% additive (La, Ce, or a mixture of both), on which Pt (0.5 mol%), copper oxide (10 mol% Cu), and CuO-Pt were supported, was characterized and tested for the oxidation of a mixture Of CO, C2H4, and CH4 in excess oxygen. Catalysts were also subjected to various thermal treatments. Due to its dispersed form, La was more effective than Ce in restraining the formation of corundum and copper aluminate. La-Ce solid solution led to an increase of cerium dispersion and a higher reducibility of ceria. Copper dissolved into the cerium lattice, in CuO/Ce-Al2O3, which, after thermal treatments at 1000 degreesC, produced smaller amounts of copper aluminate and lower particle size than on CuO/Al2O3. Besides the presence of surface Cu2+ species dispersed on alumina, on CuO/Ce-Al2O3 temperature-programmed reduction evidenced some Cu2+ interacting with ceria. The interaction between Cu and Ce led to stabilization of reduced copper and an enhancement of copper reducibility, thus leading to a substantial increase of CO oxidation for CuO/Ce-Al2O3 catalyst. The oxidation ability of Pt for CO and C2H4 was improved by the presence of CuO due to an increase of the Pt dispersion and decrease of the Pt particle size. For the oxidation of CH4 the activities of CuO and CuO-Pt were similar and superior to that of Pt, with or without additives. The presence of Ce decreased the oxidation activity of the CuO-Pt catalyst due to oxidation of Pt. However, a synergetic effect between La and Ce in the CuO-Pt/LaCe-Al2O3 catalyst led to more reduced Pt metal and ceria and a well-dispersed Pt with smaller particle size. This resulted in a highly active and thermally stable CuO-Pt/La-Ce-Al2O3 catalyst for oxidation reactions of model reactants. (C) 2001 Academic Press.