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

摘要

The effects of doping of CuO/Al2O3 solids with CeO2 on their surface and catalytic properties were investigated using nitrogen adsorption measurements at - 196 degreesC and oxidation of CO by O-2 at 100-175 degreesC. 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 degreesC and calcined at 400 degreesC. The obtained 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 attained 51, 22.5 and 5% for the solids precalcined at 300, 500 and 700 degreesC, 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 degreesC. 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 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 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 degreesC 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. (C) 2001 Elsevier Science B.V. All rights reserved. [References: 38]