XPS CHARACTERIZATION OF GAMMA-RAY INDUCED CHEMISORPTION OF OXYGEN IN LANTHANUM MANGANATE (LAMNO3)

Catalysis of mixed oxide LaMnO3 was studied for the decomposition of h ydrogen peroxide (H2O2). The catalyst was gamma-irradiated in open pet ri dishes, vacuum, dry oxygen and moist oxygen. LaMnO3 irradiated in m oist oxygen showed highest catalytic activity. X-ray photoelectron spe ctroscopic (XPS) studies were carried out to investigate the surface m odifications occurred during gamma-irradiation of LaMnO3. No significa nt change in the surface was noticed in LaMnO3 irradiated in vacuum an d dry oxygen. However, LaMnO3 irradiated in moist oxygen and in open p etri dishes showed the reduction of transition metal (MN(3+) to Mn2+) which in turn leads to the formation of chemisorbed superoxide ions (O -2(-)) and surface carbonate species (CO32-). The latter processes dec reases the electrical conductivity by trapping the charge carriers. Th e hydrated electron generated by the radiolysis of moisture reduces th e transition metal, A qualitative molecular orbital model has been pro posed for the chemisorption of O-2(-) on the reduced transition metal centers (Mn2+).