Physicochemical surface and catalytic properties of CuO-ZnO/Al2O3 system

A series of CuO-ZnO/Al2O3 solids were prepared by wet impregnation using Al(OH)(3) solid and zinc and copper nitrate solutions. The amounts of copper and zinc oxides were varied between 10.3 and 16.0 wt% CuO and between 0.83 and 7.71 wt% ZnO. The prepared solids were subjected to thermal treatment at 400-1000 degrees C. The solid-solid interactions between the different constituents of the prepared solids were studied using XRD analysis of different calcined solids. The surface characteristics of various calcined adsorbents were investigated using nitrogen adsorption at -196 degrees C and their catalytic activities were determined using CO-oxidation by O-2 at temperatures ranged between 125 degrees C and 200 degrees C. The results showed that CuO interacts with Al2O3 to produce copper aluminate at greater than or equal to 600 degrees C and the completion of this reaction requires heating at 1000 degrees C. ZnO hinders the formation of CuAl2O4 at 600 degrees C while stimulates its production at 800 degrees C. The treatment of CuO/Al2O3 solids with different amounts of ZnO increases their specific surface area and total pore volume and hinders their sintering (the activation energy of sintering increases from 30 to 58 kJ mol(-1) in presence of 7.71 wt% ZnO). This treatment resulted in a progressive decrease in the catalytic activities of the investigated solids but increased their catalytic durability. Zinc and copper oxides present did not modify the mechanism of the catalyzed reaction but changed the concentration of catalytically active constituents (surface CuO crystallites) without changing their energetic nature. (C) 1999 Elsevier Science B.V. All rights reserved.