DETERMINATION OF THE DISPERSION AND SURFACE OXIDATION-STATES OF SUPPORTED CU CATALYSTS

A combination of CO adsorption at 300 K, which provides irreversible a dsorption on Cu+1 sites, and oxygen adsorption via N2O dissociation at 363 K, which counts surface Cu-0 atoms, was used to obtain values for the dispersion of Cu on SiO2, Al2O3, TiO2 ZrO2, diamond powder, and g raphitized carbon fibers. The crystallite sizes obtained from these es timates were compared to those obtained from TEM and XRD measurements and were found to be in very good agreement. DRIFT spectra of CO adsor bed on these catalysts were obtained at subambient temperatures as wel l as at 300 K, and the various amounts of Cu-0, Cu+l, and Cu+2 at the surface were detected by respective peaks in the regions of 2110 cm(-1 ) and lower, 2110-2140 cm(-1), and 2145 cm(-1) and above. Spectra obta ined at 173 K were especially useful because irreversible CO adsorptio n 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 wer e obtained for Cu dispersed on SiO2, Al2O3, and diamond: Cu-0--4.7 kca l/mole; Cu+1--11.7 kcal/mole; and Cu+2--5.3 kcal/mole. (C) 1998 Academ ic Press.