Promotion of the hydrogen peroxide decomposition activity of manganese oxide catalysts

Abstract

Pure (MnO x ), mixed (A y Mn 1− y O x ) and composite ((A,B) y Mn 1− y O x ) manganese oxide based catalysts were prepared, where A is either Ni II, Cu II, Bi III or Ce IV, A and B are various combinations of them, and y=0.4. Subsequently, they were characterized for the crystalline bulk structure by X-ray powder diffractometry, the electron availability by magnetic susceptibility measurements, the surface area by BET-analysis of nitrogen adsorption isotherms, and the surface chemical composition and oxidation state by X-ray photoelectron spectroscopy. The H 2O 2 decomposition activity was determined by oxygen-gasometry of the reaction kinetics at 20–35°C. Results thus obtained have helped to conclude that (i) the mixed and composite catalysts are generally more active than the pure catalyst, and (ii) of the mixed and composite catalysts, those assuming mixed bulk phases with the host oxide are relatively more active. The optimal catalytic surface has been found to be that exposing ionic sites of different oxidation states and residing on a crystalline bulk of ca. 50% electron availability. These properties were found to be accomplished by surfaces of NiMnO x , on which the H 2O 2 decomposition required a much lower activation energy (11.6 kJ mol −1) as compared to that (77.1 kJ mol −1) necessary for the reaction on the pure catalyst (MnO x ).