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CuO x /ZrO2 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 H2 and O2. 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 CuII species were in a distorted octahedral configuration, and in samples heated in dry O2 at 773 K, in a square-pyramidal configuration. Water vapor adsorption transformed the latter species into distorted octahedral complexes. In all samples, heating in O2 at 773 K anchored copper to the zirconia surface. All copper was present as CuII. Evacuation of these samples at 773 K caused no copper reduction, whereas heating with H2 above 450 K reversibly reduced CuII 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 CuII to CuI 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 O2 at 773 K, CO adsorption at RT yielded CuI−CO and carbonates. Volumetric CO adsorption combined with FTIR showed that copper was highly dispersed on the ZrO2 surface up to 2.5 atoms nm-2.

A commercial Na-MOR was exchanged to various extents with cobalt. The sodium and cobalt contents were determined by atomic absorption. Samples were characterized by UV−vis and by FTIR. The FTIR results with CO show that Co-MOR heated in O2 at 793 K and evacuated at the same temperature contained isolated Co2+ (86 to 100% of cobalt detected by CO adsorption at RT) and [Co−O−Co]2+. After exposure of samples to CO at RT, FTIR showed that only a minute fraction of [Co−O−Co]2+ underwent reduction yielding [(CO) n Co+−Co+(CO) n ], with n = 2 or 3, and CO2. After exposure to CO at increasing temperature up to 623 K, the subsequent adsorption of CO at RT yielded increasing amounts of [(CO) n Co+−Co+(CO) n ] and CO2. Whereas isolated Co2+ did not undergo reduction, Co2+ in [Co−O−Co]2+ reduced to Co+. On evacuation at RT, [(CO)3Co+−Co+(CO)3] completely and reversibly transformed into [(CO)2Co+−Co+(CO)2]. On evacuation at increasing temperature, [(CO)2Co+−Co+(CO)2] progressively disappeared and transformed into a stable bridged species, [Co+(CO)Co+], and [(CO)Co+−Co+(CO)]. As the total cobalt content in Co-MOR samples increases, the [Co−O−Co]2+ amount increases exponentially. Hence, we infer that the [Co−O−Co]2+ species is not the active site for NO abatement with CH4 in the presence of O2.

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