Effect of lanthanum on the activity and thermal stability of copper-cobalt oxide catalysts supported on alumina

La-modified alumina-supported copper oxide and cobalt oxide catalysts were investigated. The catalyst samples were prepared by impregnation of supports (gamma-Al2O3 or La-Modified gamma-Al2O3) with a mixed aqueous solution of Cu and Co nitrates. The samples were characterized by ICP analysis, X-ray powder diffraction (XRD) and BET method. The catalytic reduction of NO by CO and the catalytic oxidation of CO and C6H6 by O-2 were carried out over non-modified and La-modified catalysts. The modification of gamma-Al2O3 support with La at a loading below 3 wt. % has a positive effect on the catalytic performance of supported Cu-Co oxide catalysts. Lanthanum plays a stabilizing role on the specific surface area of the carriers and Cu-Co oxide catalysts; the addition of La suppresses the a-transformation of the alumina support and its interaction with the active Cu-Co oxide phase to produce aluminates. The modification of the support with La prevents the intercalation of Cu ions into the gamma-Al2O3 during The impregnation with Cu-Co nitrates. Thus, the active Cu-Co oxide spinel supported on La/Al2O3 has a higher Co:Cu ratio, which is close to that in the stoichiometric CuCo2O4 spinel. La-modified catalysts have higher activity in the NO+CO, CO+O-2 and C6H6+O-2 reactions, compared to the non-modified catalysts. Incorporation of La into the support does not change the energy level of catalytically active sites but rather increases the number of these sites.