The influence of surface structure on the catalytic activity of cerium promoted copper oxide catalysts on alumina : oxidation of carbon monoxide and methane

X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) have been used to characterize a series of Cu/Ce/Al2O3 catalysts. Catalysts were prepared by incipient wetness impregnation using metal nitrate and alkoxide precursors. Catalyst loadings were held constant at 12 wt% CuO and 5.1 wt% CeO2. Mixed oxide catalysts were prepared by impregnation of cerium first, followed by copper. The information obtained from surface and bulk characterization has been correlated with CO and CH4 oxidation activity of the catalysts. Cu/Al2O3 catalysts prepared using Cu(II) nitrate (CuN) and Cu(II) ethoxide (CuA) precursors consist of a mixture of copper surface phase and crystalline CuO. The CuA catalyst shows higher dispersion, less crystalline CuO phase, and lower oxidation activity for CO and CH4 than the CuN catalyst. For Cu/Ce/Al2O3 catalysts, Ce has little effect on the dispersion and crystallinity of the copper species. However, Cu impregnation decreases the Ce dispersion and increases the amount of crystalline CeO2 present in the catalysts, particularly in Ce modified alumina prepared using cerium alkoxide precursor (CeA). Cerium addition dramatically increases the CO oxidation activity, however, it has little effect on CH4 oxidation.