Effects of Li 2O doping on surface and catalytic properties of CuO–ZnO/Al 2O 3 system

Abstract

The effect of Li 2O doping (0.375–4.5 mol.%) on surface and catalytic properties of CuO–ZnO/Al 2O 3 was investigated using nitrogen adsorption at −196°C and catalytic oxidation of CO by O 2 at 150–200°C. Pure and doped solids were subjected to thermal treatment at 600–800°C prior to surface and catalytic measurements. The results showed that Li 2O doping caused measurable increases in the specific surface area (23–45%) and in the total pore volume (24–43%) for the adsorbents preheated in air at 600–700°C. If the doping process was carried out at 600°C, it resulted in a considerable decrease (52%) in the catalytic activity, measured at 175°C. A rise in calcination temperature of the doped solid specimens (4.5 mol.% Li 2O) to 700 and 800°C brought about marked increases of 125% and 186%, respectively, in the catalytic activity measured at 175°C. This discrepancy is discussed in terms of the effect of Li 2O doping in decreasing the dispersity of CuO crystallites of the solids calcined at 600°C and the role of Li 2O in hindering CuAl 2O 4 formation upon calcination at 700 and 800°C. The decrease in the degree of dispersion of CuO crystallites due to doping at 600°C is normally followed by a decrease in the catalytic activity while the suppression or hindrance of CuAl 2O 4 formation might be followed by an increase in the catalytic activity. The doping process carried out at 600–800°C did not modify the concentration of catalytically active constituents involved in chemisorption and catalysis of the CO oxidation reaction.