Effect of ZnO on surface and catalytic properties of CuO/Al2O3 system

The effects of ZnO on solid-solid interactions, surface and catalytic properties of CuO/Al2O3 solids were investigated using XRD, nitrogen adsorption at -196 degrees C and oxidation of CO by O-2 at 125-175 degrees C. The nominal composition of pure mixed solids was 0.25 CuO : Al2O3 and the amounts of ZnO were varied between 0.83 and 7.7 wt%. Pure and zinc oxide-treated solid were subjected to thermal treatment at 600 degrees C. The results showed that ZnO inhibited the formation of CuAl2O4 and decreased the degree of crystallinity of CuO phase to an extent proportional to its amount present. The presence of ZnO led to pore widening and resulted in an increase of 23% and 28% of S-BET and V-P of treated solids, respectively. The addition of ZnO decreased the catalytic activity of CuO/ZnO solids but much increased their stability. The activity of pure CuO/Al2O3 decreased progressively by regeneration while that of ZnO-containing solids increased monotonically by regeneration to attain a high constant value after the fourth regeneration. The values of reaction rate constant k measured at 150 degrees C on the regenerated catalysts were 2.2 and 22.2x10(-3) min(-1) for pure sample and that treated with 1.96% ZnO, respectively. ZnO-treatment did not modify the mechanism of catalytic oxidation of CO with O-2 but changed the concentration of catalytically active constituents (surface copper oxide crystallites).