Physicochemical Surface and Catalytic Properties of the Na2O-doped CuO–ZnO/Al2O3 System

Abstract

In order to investigate the effect of Na2O doping (0.75–4.5 mol%) on metal oxide-support interactions, the surface and catalytic properties of the CuO–ZnO/Al2O3 system have been studied using XRD, nitrogen adsorption at -196°C and the catalytic oxidation of CO by O2 at 150–200°C. Pure and doped mixed oxide solid samples were prepared via the wet impregnation method using Al(OH)3, NaNO3. Zn(NO3)2 and Cu(NO3)2 solutions, followed by drying and calcination at 600°C and 700°C.The nominal composition of the solids thus prepared was 0.25CuO:0.06ZnO: Al2O3. The results obtained showed that Na2O doping followed by heating in air at 600°C leads to enhanced crystallization of the CuO crystallites to an extent proportional to the amount of dopant present, while doping followed by heating in air at 700°C hinders the solid–solid interactions between CuO andA12O3, and leads to the production of CuAl2O4. The specific surface area was found to increase progressively as a function of the dopant concentration for the solid calcined at 700°C. The catalytic activity was also found to increase progressively on increasing the amount of dopant added. The maximum increase in the catalytic activity measured at 150, 175 and 200°C over solids calcined at 700°C was 114, 102 and 82%. respectively. The doping process did not modify the mechanism of the catalyzed reaction but rather increased the concentration of catalytically active constituents (surface CuO crystallites) involved in the chemisorption and catalysis of the CO oxidation reaction without affecting their energetic nature.