Effects of CeO2-doping on surface and catalytic properties of CuO/Al2O3 solids

The effects of doping of CuO/Al2O3 solids with CeO2 on their surface and catalytic properties were investigated using nitrogen adsorption measurements at −196°C and oxidation of CO by O2 at 100–175°C. The dopant concentrations were varied between on 0.75–4.5 mol% CeO2 and the amount of copper was fixed at 16.7 mol% CuO. Pure and variously doped solids were prepared by wet impregnation method using finely-powdered Al(OH)3 and solutions containing different amounts of cerium nitrate. The impregnated solid samples were dried at 100°C and calcined at 400°C. The obtained solids were treated with solutions containing fixed amounts of copper nitrate, drying then calcination at 300, 500 and 700°C. The results showed that the doping process resulted in a measurable increase in the BET-surface area of the treated solids. The maximum increase in the SBET attained 51, 22.5 and 5% for the solids precalcined at 300, 500 and 700°C, respectively. The doping process brought about a considerable increase in the catalytic activity of the treated catalysts. Furthermore, the catalytic activity of pure solids decreased considerably (about 60%) by increasing the precalcination temperature from 300 to 700°C. On the other hand, the catalytic activity of doped samples remained almost unchanged or increased slightly (about 22%) upon increasing the temperature of heat treatment from 300 to 700°C. The maximum increase in the catalytic activity, expressed as reaction rate constant per unit surface area measured at 125°C attained 27, 150 and 422% for the catalysts doped with 3 mol% CeO2 and precalcined at 300, 500, and 700°C, respectively. The doping process did not modify the activation energy of the catalyzed reaction i.e. doping of CuO/Al2O3 solids with CeO2 followed by heating at 300–700°C did not alter the mechanism of the catalytic reaction but increased the concentration of catalytically active constituents taking part in the catalytic process without changing their energetic nature.