Platinum-oxide species formed by oxidation of platinum crystallites supported on alumina

Pt/Al2O3 samples of different platinum loadings are prepared by impregnating gamma-Al2O3 with PtCl4 solution. Reduced Pt/Al2O3 samples are oxidized by dioxygen to examine the variation of Pt-O-x (platinum-oxide) species with the oxidation temperature. Four different Pt-O-x species are characterized according to their reduction temperature (T-r) found in the temperature-programmed reduction (TPR) experiments. They are assigned as surface platinum oxide (T-r = -25 degrees C), PtO (T-r = 50 degrees C), PtO2 (T-r = 100 degrees C) and PtAl2O4 (T-r = 220 degrees C), respectively, mainly according to their N-o/N-Pt stoichiometry found in the TPR and their desorption kinetics found in the technique of temperature-programmed desorption (TPD). These four species alternate as the dominant Pt-O-x products on Pt/Al2O3 samples when the oxidation temperature is raised to 25 degrees C, 300 degrees C, 500 degrees C and 600 degrees C, respectively.