Distinction between surface and bulk oxidation of Cu through N2O decomposition

A Cu metal surface was evaluated by a novel technique combining temperature -programmed reduction (TPR) measurement with N2O oxidation. The technique c onsists of three steps: the usual TPR measurement, the oxidation of the Cu surface by N2O, and the subsequent TPR measurement. The surface Cu oxidized by N2O was determined as a ratio of the peak area of the second TPR profil e to that of the first one. It was found that bulk oxidation gradually proc eeds after surface oxidation even at 30 degreesC. After the surface oxidati on, the Cu2O produced by N2O oxidation varied with N2O exposure time (t) an d had a linear correlation with ta at temperatures below 100 degreesC. The linear correlation in the parabolic plot proves that bulk oxidation proceed s through the diffusion process, and the Y-intercept corresponds to the sur face oxidation. Both the dispersion and the Cu metal surface area of the sa mple were calculated from the intercept in the parabolic plot for the Cu2O produced by N2O oxidation. In addition, we found that a very large Cu metal surface area, as high as 32 m(2) g(cat)(-1), was created on a Cu-MgO catal yst through a citrate process using a molten mixture of copper nitrate, mag nesium nitrate, and citric acid. (C) 2000 Academic Press.