STRUCTURAL AND SURFACE-PROPERTIES OF CUO-ZNO-CR2O3 CATALYSTS AND THEIR RELATIONSHIP WITH SELECTIVITY TO HIGHER ALCOHOL SYNTHESIS

A series of copper-zinc-chromium catalysts of different compositions and calcination temperatures has been prepared, characterized by several techniques (BET specific surface area, XRD, gravimetric TPR, TPD-CO, and XPS), and tested under high alcohol synthesis (HAS) conditions. CO hydrogenation was carried out at reaction temperatures of 523-598 K and 50 bar total pressure. The influence of catalyst composition, calcination temperature, and surface characteristics on the HAS selectivity was studied. The optimum HAS yields were found in the low Cr content region, but chromium was needed. Although chromium oxide does not seem to be involved in the catalytic site, its presence in the catalyst composition is essential, owing to the larger specific surfaces and catalyst stability obtained at the highest reaction temperatures. For low Cr content composition, the temperature-programmed reduction (TPR) profiles were shifted to higher temperatures and simultaneously larger CO2 amounts were found in the temperature-programmed desorption profiles of adsorbed CO (TPD-CO). Photoelectron spectra (XPS) revealed that the oxidation state of copper is Cu2+ in the calcined catalysts and Cu-0 in the reduced ones; Cu+ was only stabilized in a CuCr2O4 spinel in the Cr-rich catalysts. These features derived from catalyst characterization are discussed in the framework of the catalytic behaviour for HAS synthesis. (C) 1995 Academic Press, Inc.