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 ca talytic properties were investigated using nitrogen adsorption measurements at - 196 degreesC and oxidation of CO by O-2 at 100-175 degreesC. The dopa nt 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 sol utions containing different amounts of cerium nitrate. The impregnated soli d samples were dried at 100 degreesC and calcined at 400 degreesC. The obta ined solids were treated with solutions containing fixed amounts of copper nitrate, drying then calcination at 300, 500 and 700 degreesC. 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 S-BET atta ined 51, 22.5 and 5% for the solids precalcined at 300, 500 and 700 degrees C, respectively. The doping process brought about a considerable increase i n the catalytic activity of the treated catalysts. Furthermore, the catalyt ic activity of pure solids decreased considerably (about 60%) by increasing the precalcination temperature from 300 to 700 degreesC. On the other hand , the catalytic activity of doped samples remained almost unchanged or incr eased slightly (about 22%) upon increasing the temperature of heat treatmen t from 300 to 700 degreesC. The maximum increase in the catalytic activity, expressed as reaction rate constant per unit surface area measured at 125 degreesC attained 27, 150 and 422% for the catalysts doped with 3 mol% CeO2 and precalcined at 300, 500, and 700 degreesC, respectively. The doping pr ocess did not modify the activation energy of the catalyzed reaction i.e. d oping of CuO/Al2O3, solids with CeO2 followed by heating at 300-700 degrees C did not alter the mechanism of the catalytic reaction but increased the c oncentration of catalytically active constituents taking part in the cataly tic process without changing their energetic nature. (C) 2001 Elsevier Scie nce B.V. All rights reserved.