The Surface Composition of CuOx/ZrO2 Catalysts as Determined by FTIR, XPS, ESR Spectroscopies and Volumetric CO Adsorption

CuO x /ZrO 2 samples prepared by adsorption from copper solutions or by impregnation were characterized by means of FTIR, XPS, ESR, DRS, volumetric CO adsorption, and redox cycles with H 2 and O 2 . In samples prepared by adsorption, the maximum copper uptake corresponded to an extended plateau at 2.5 atoms nm -2 . In as-prepared samples, isolated Cu II species were in a distorted octahedral configuration, and in samples heated in dry O 2 at 773 K, in a square-pyramidal configuration. Water vapor adsorption transformed the latter species into distorted octahedral complexes. In all samples, heating in O 2 at 773 K anchored copper to the zirconia surface. All copper was present as Cu II . Evacuation of these samples at 773 K caused no copper reduction, whereas heating with H 2 above 450 K reversibly reduced Cu II to metal copper. Evacuation of as-prepared samples differed according to how samples were prepared. In particular, evacuation of samples prepared from Cu−acetylacetonate or Cu−acetate reduced Cu II to Cu I at 473 K and to copper metal at higher temperature. Evacuation reduced copper because acetylacetonates and acetates underwent oxidation during desorption. Evacuation up to 773 K of samples prepared from Cu−nitrate caused no copper reduction. In samples heated in O 2 at 773 K, CO adsorption at RT yielded Cu I −CO and carbonates. Volumetric CO adsorption combined with FTIR showed that copper was highly dispersed on the ZrO 2 surface up to 2.5 atoms nm -2 .