Temperature-programmed reduction and temperature-programmed desorption studies of CuO/ZrO2 catalysts

Copper/zirconia 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, α1, α2 and β) might be attributed to highly dispersed copper oxide species. These have different environment and interaction with the surface oxygen vacancies of the ZrO2 support. The other two TPR peaks of CuO/ZrO2 might be the reduction of bulk-like copper oxide. When calcination temperature was higher than 650°C, α, β-peak species were gradually transformed into the bulk CuO (γ-peak) with increasing calcination temperature. The CO-TPR curve of CuO/ZrO2 had four reduction peaks. Three peaks below 360°C 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 α-peak were predominant contributors to the catalytic activity of CuO/ZrO2 catalysts, while excess copper forms bulk CuO particles contributing little to the catalytic activity.