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 a t 400-1000 degrees C. The solid-solid interactions between the different co nstituents of the prepared solids were studied using XRD analysis of differ ent calcined solids. The surface characteristics of various calcined adsorb ents were investigated using nitrogen adsorption at -196 degrees C and thei r catalytic activities were determined using CO-oxidation by O-2 at tempera tures ranged between 125 degrees C and 200 degrees C. The results showed that CuO interacts with Al2O3 to produce copper aluminat e at greater than or equal to 600 degrees C and the completion of this reac tion requires heating at 1000 degrees C. ZnO hinders the formation of CuAl2 O4 at 600 degrees C while stimulates its production at 800 degrees C. The t reatment of CuO/Al2O3 solids with different amounts of ZnO increases their specific surface area and total pore volume and hinders their sintering (th e activation energy of sintering increases from 30 to 58 kJ mol(-1) in pres ence of 7.71 wt% ZnO). This treatment resulted in a progressive decrease in the catalytic activities of the investigated solids but increased their ca talytic durability. Zinc and copper oxides present did not modify the mecha nism of the catalyzed reaction but changed the concentration of catalytical ly active constituents (surface CuO crystallites) without changing their en ergetic nature. (C) 1999 Elsevier Science B.V. All rights reserved.