Catalytic oxidation of carbon monoxide on non-doped and zinc oxide-doped nickel-alumina catalysts

Alumina-supported NiO catalysts, promoted with 0.14-3 wt.% ZnO, were prepared by impregnation and then calcined at 400, 600, and 800 degreesC for 4 and 40 h. The phase analysis, surface and catalytic properties were investigated by using XRD technique, nitrogen adsorption at -196 degreesC, and oxidation of CO by O-2 at 200-300 degreesC, respectively. The results obtained reveal that ZnO doping of Ni/Al mixed oxides followed by calcination at 400 or 600 degreesC for 4 h brought about slight increase in their specific surface area, which decreased progressively by increasing the calcination temperature of doped solids to 800 'C for 4 and 40 h. CO oxidation activity over NiO/Al2O3 mixed solids increased by treatment with ZnO followed by heating at 400 or 600 'C for 4 h, and then decreased by increasing the calcination temperature to 800 'C for 4 and 40 h. The maximum increase in the catalytic reaction rate constant per unit surface area measured at 250 degreesC ((k) over bar (250 degreesC)) due to doping with 3 wt.% ZnO attained 78 and 217% for the catalysts calcined at 400 and 600 degreesC for 4 h, respectively, while the maximum decrease in (k) over bar (300 degreesC) over 3 wt.% ZnO-doped solids attained 21 and 31% for the catalyst samples calcined at 800 degreesC for 4 and 40 h, respectively. The doping process did not change the mechanism of the catalytic reaction but modified the concentration of catalytically active constituents without changing their energetic nature. (C) 2003 Published by Elsevier Science B.V.