Determination of the Dispersion and Surface Oxidation States of Supported Cu Catalysts

A combination of CO adsorption at 300 K, which provides irreversible adsorption on Cu+1sites, and oxygen adsorption via N2O dissociation at 363 K, which counts surface Cu0atoms, was used to obtain values for the dispersion of Cu on SiO2, Al2O3, TiO2, ZrO2, diamond powder, and graphitized carbon fibers. The crystallite sizes obtained from these estimates were compared to those obtained from TEM and XRD measurements and were found to be in very good agreement. DRIFT spectra of CO adsorbed on these catalysts were obtained at subambient temperatures as well as at 300 K, and the various amounts of Cu0, Cu+1, and Cu+2at the surface were detected by respective peaks in the regions of 2110 cm−1and lower, 2110–2140 cm−1, and 2145 cm−1and above. Spectra obtained at 173 K were especially useful because irreversible CO adsorption occurred on all three sites, thus allowing the removal of gas-phase CO and clarifying the spectra of adsorbed CO. Heats of adsorption for CO were determined from the variation in the intensity of the Kubelka–Munk function versus temperature, and the following average values were obtained for Cu dispersed on SiO2, Al2O3, and diamond: Cu0—4.7 kcal/mole; Cu+1—11.7 kcal/mole; and Cu+2—5.3 kcal/mole.