ELECTRON-PARAMAGNETIC RESONANCE STUDY OF THE INTERACTIONS OF OXYGEN WITH SILVER TITANIA

A 2% Ag/TiO2 catalyst has been prepared by the impregnation method. Hydrogen reduction and oxygen adsorption treatments of this sample were studied by electron paramagnetic resonance (EPR) spectroscopy. Signals from Ag(o) (g = 2.001, DELTA-H = 12 G), Ag2+ (g perpendicular-to 2.032, g parallel-to = 2.293, A perpendicular-to = 32 G), O2- (g1 = 2.035, g2 = 2.015, g3 = 2.003), and Ti3+ (g almost-equal-to 1.97) were observed. The intensity of these peaks varied with the temperature of hydrogen reduction and the time of oxygen adsorption. Ag(o) and O2- signals were maximized in a sample reduced at 473 K. Severe reduction at higher temperatures caused sintering to the supported silver crystallites and consequently, a diminution of the Ag(o) signal. Ti3+ was generated by hydrogen spillover through silver. This species may be destroyed by appropriate calcinations. Two kinds of Ti3+ signal (a and b) were observed. The signal a (probably from TiOOH) was generated on the spillover but changed to signal b (probably from Ti2O3) on evacuation at T > 573 K. The O2- signal was observed after reduced Ag/TiO2 samples were partially oxidized by gaseous oxygen. The site of O2- adsorption is at the interface of Ag crystallites with TiO2.