Solid-solid interaction in CuO-ZnO/Al2O3 system under varying conditions

A series of pure and Li2O-doped CuO-ZnO/Al2O3 mixed solids was prepared by wet impregnation of finely powdered Al(OH)(3) with Zn(NO3)(2) and Cu(NO3)(2) solutions. The doped solids were treated with LiNO3 solution prior to treatment with zinc and copper nitrate solutions. The amount of zinc oxide varied between 0.0 and 7.7 wt,% and that of copper oxide between 15 and 16.3 wt.%. The solid-solid interactions between the different constituents were investigated using TG, DTG and DTA of uncalcined solids and XRD of the solids calcined at 400-1000 degrees C. The results revealed that Al(OH)(3) undergoes dehydroxylation in different steps starting from 206 degrees C and the removal of last traces of OH groups strongly bound to Al2O3 lattice occurs at 396-496 degrees C. Copper and zinc nitrates decompose simultaneously at 165-216 degrees C, forming the corresponding oxides. The produced CuO interacts readily with Al2O3, producing CuAl2O4 at temperatures starting from 600 degrees C and the completion of this reaction, yielding well-crystallized CuAl2O4 phase, requires heating at 1000 degrees C. Zinc oxide hinders the CuAl2O4 formation at 600 degrees C and enhances this reaction at 800 degrees C. The hindering and enhancing effects depended on the amount of zinc oxide present. Furthermore, zinc oxide hinders the crystallization of alumina into cl-corundum phase by heating at 1000 degrees C. Li2O-doping catalyzes the crystallization of copper oxide phase by heating the supported oxides at 600 degrees C and suppresses the solid-solid interactions between CuO and Al2O3 yielding CuAl2O4 by heating at 800 degrees C. (C) 1998 Elsevier Science B.V.