Preparation of a coprecipitated Cu/ZnO catalyst for the methanal synthesis from CO2 -: effects of the calcination and reduction conditions on the catalytic performance

Cu/ZnO catalysts having a Cu:Zn molar ratio of 50:50 were prepared from hydroxycarbonate precursors, such as aurichalcite and zincian-malachite. CuO crystallite size of the calcined catalysts obtained from aurichalcite greatly depended on the heating rate for the calcination Very small crystallites of CuO were formed at low heating rates. On the other hand, no effect of the heating rate on the CuO crystallites was observed for the catalysts obtained from zincian-malachite. The calcined catalyst containing the very small crystallites of CuO was reduced under various conditions. The catalysts prepared were then subjected to the methanol synthesis from CO2. Activity and selectivity of the catalysts depended on the procedure for the reduction and the reductant. The most active and selective catalyst was obtained by the reduction with methanol at 443 K for 17 h. It was suggested that the high activity and selectivity resulted from the high dispersion of Cu and the preferential emergence of flat surface Cu sites. (C) 2001 Elsevier Science B.V. All rights reserved.