Temperature-programmed reduction and temperature-programmed desorption studies of CuOrZrO2 catalysts

Copperrzirconia catalysts were prepared by an impregnation method. The reducibility and characteristics of the supported copper oxide catalysts with various copper loadings were revealed and determined by H2-TPR, CO-TPR, XRD and O2-TPD, respectively. Five H2-TPR peaks could be observed. In conjunction with the observations by X-ray diffraction XRD., three temperature-programmed reduction TPR.peaks with lower peak temperatures namely, a1, a2and b.might be attributed to highly dispersed copper oxide species. These have different environment and interaction with the surface oxygen vacancies of the ZrO2support. The other two TPR peaks of CuOrZrO2might be the reduction of bulk-like copper oxide. When calcination temperature was higher than 6508C, a, b-peak species were gradually transformed into the bulk CuO g-peak.with increasing calcination temperature. The CO-TPR curve of CuOrZrO2 had four reduction peaks. Three peaks below 3608C on the CO-TPR curves corresponded to five peaks on the H2-TPR curves. The O2-TPD analyses showed that lattice oxygen from the highly dispersed copper oxide was desorped more easily than that from the bulk CuO. The reducibility and the desorptibility of lattice oxygen from the highly dispersed copper oxide species located on the ZrO2, which increased with CuO loading, may be related to the catalytic activity. The copper oxide species corresponding to a-peak were predominant contributors to the catalytic activity of CuOrZrO2 catalysts, while excess copper forms bulk CuO particles contributing little to the catalytic activity. q1999 Published by Elsevier Science B.V. All rights reserved.