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 °C for 4 and 40 h. The phase analysis, surface and catalytic properties were investigated by using XRD technique, nitrogen adsorption at −196 °C, and oxidation of CO by O2 at 200–300 °C, respectively. The results obtained reveal that ZnO doping of Ni/Al mixed oxides followed by calcination at 400 or 600 °C 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 °C (k̄250 °C) due to doping with 3 wt.% ZnO attained 78 and 217% for the catalysts calcined at 400 and 600 °C for 4 h, respectively, while the maximum decrease in k̄300 °C over 3 wt.% ZnO-doped solids attained 21 and 31% for the catalyst samples calcined at 800 °C 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.