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

Copper/zirconia catalysts were prepared by an impregnation method. The redu cibility and characteristics of the supported copper oxide catalysts with v arious copper loadings were revealed and determined by H-2-TPR, CO-TPR, XRD and O-2-TPD, respectively. Five H-2-TPR peaks could be observed. In conjun ction with the observations by X-ray diffraction (XRD), three temperature-p rogrammed reduction (TPR) peaks with lower peak temperatures (namely, alpha (1), alpha(2) and beta) might be attributed to highly dispersed copper oxid e species. These have different environment and interaction with the surfac e 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 tempera ture was higher than 650 degrees C, alpha, beta-peak species were gradually transformed into the bulk CuO (gamma-peak) with increasing calcination tem perature. The CO-TPR curve of CuO/ZrO2 had four reduction peaks. Three peak s below 360 degrees C on the CO-TPR curves corresponded to five peaks on th e H-2-TPR curves. The O-2-TPD analyses showed that lattice oxygen from the highly dispersed copper oxide was desorped more easily than that from the b ulk 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 oxi de species corresponding to alpha-peak were predominant contributors to the catalytic activity of CuO/ZrO2 catalysts, while excess copper forms bulk C uO particles contributing little to the catalytic activity. (C) 1999 Publis hed by Elsevier Science B.V. All rights reserved.