SURFACE PROPERTIES AND REDUCTION KINETICS OF CuO-ZnO CATALYSTS

CuO-ZnO catalysts have been extensively used by chemical industry for a long time and several papers have appeared in the literature dealing with the structure and surface characterization of these mixed oxides. However, only few works have been devoted to the reduction of copper component. Since these catalysts are used in the reduced state, it appears interesting to obtain more details on the phenomena involved in the reduction process. CuO-ZnO catalysts with differenl Cu/Zn ratios were prepared by drying and calcination of well defined mixed hydroxycarbonate precursors. All catalysts were characterized by XRD, XPS, DTA and TGA techniques. According to the lliterature, calcined samples appeared as well interdispersed mixed oxides with homogeneous composition and high surface area (about 70 m2/g).As observed by XPS, samples with low Zn content showed an electric contact between ZnO and CuO particles. The samples were reduced by hydrogen and the kinetics of the process was studied by detecting the consumption of hydrogen as a function of time at different pressures and temperatures. The results were interpreted by means of a kinetic model based on the following assumptions : dissociative adsorption of hydrogen on ZnO and Cu° species and associative adsorption on Cu2+, nucleation of Cu° or Cu1+, reduction of Cu2+ and Cu1+ at solid interfaces. The model appears to correctly account for the effect of ZnO and gives results in quite good agreement with experimental data both for the hydrogen consumption and the distribution of the different copper species during the reduction process.