Dispersion and surface states of copper catalysts by temperature-programmed-reduction of oxidized surfaces (s-TPR)

Surface and sub-surface oxidation of dispersed copper phase by N2O adsorptive decomposition at controlled temperature followed by H2 temperature programmed reduction of the Cu2O surface layers formed (s-TPR) was performed on siliceous supported catalysts (ca. 6 wt.% Cu). The combined analysis permitted to measure the copper dispersion and to identify different surface copper species. Copper dispersion parameters were calculated from the H2-uptakes in the back-titration of the oxygen atoms fixed on the Cu particles by the s-TPR analysis. S-shaped curves were obtained plotting the H2 uptakes vs. N2O oxidation temperature, the change of slope could indicate the beginning of copper deep oxidation, ca. 70°C, that continued up to bulk oxidation at higher temperatures. Extrapolation of the H2-uptake to “zero-temperature” allowed calculating the “true” copper dispersion (DCu*) and related parameters. In addition, s-TPR provided qualitative and quantitative reduction profiles of the copper surface species. Besides Cu2O, formed by N2O oxidation of Cu(0) particles, copper species strongly interacting with support were clearly individuated as a function of the support nature.