Activation of CuO/ZnO/Al2O3 water-gas shift catalysts with hydrogen

GINES, MJL; APESTEGUIA C.R.

LATIN AMERICAN APPLIED RESEARCH

Año: 1995 vol. 25 p. 215 - 221

0327-0793

The CuO reduction in Cu/Zn/Al mixed oxides employed in the low-temperature CO-shift reaction was investigated. Three sets of samples with different Cu/Zn and (Cu+Zn)/Al ratios were prepared by coprecipitation. The mixed oxides contained CuO, ZnO, ZnAl2O4 and Al2O3; the relative proportion of these phases depended on both the chemical composition and the calcination temperature. The reduction kinetics was studied by thermogravimetry in the 170-300°C range using a 5%H2/N2 gaseous mixture. The general patterns of reductograms indicated that the reduction of CuO to metallic copper proceeds in a one-step process. Results were interpreted in terms of the unreacted shrinking core model by assuming that reduction was controlled by reaction at the metal/metal oxide interface. Samples characterization by temperature programmed reduction (TPR) technique showed that CuO reduces in a single peak at ca. 260°C. In agreement with model predictions, the peak width increased and the peak maximum shifted to higher temperatures when the initial CuO crystallite size was increased. The apparent activation energy, Ea, was determined from TPR profiles and by considering a first order reaction with respect to reactant concentrations; values of Ea between 67-75 kJ/mol were found. The effect of the reduction temperature on the resulting Cuo crystallite size was also studied. Although initial copper sintering was noted at about 275°C, severe loss of the metallic dispersion took place only after 300°C.