PHYSICOCHEMICAL PROPERTIES AND CATALYTIC ACTIVITIES OF THE SPINEL SERIES MNXFE3-XO4 TOWARDS PEROXIDE DECOMPOSITION

Samples of the spinel series, MnxFe3-xO4 (O less than or equal to x less than or equal to 3), have been synthesized by the hydroxide coprecipitation technique and characterised by chemical analysis; XRD and SEM techniques, and measurements of their BET specific surface areas, saturation magnetisations and electrical resistivities. The specimens with values of x less than or equal to 1.5 are single-phase cubic spinels and those with x > 1.5 are two-phase cubic and tetragonal spinels. The relative catalytic activities of the specimens towards the decomposition of H2O2 in both alkaline and neutral media, measured on the basis of the energies of activation, a microstructure-independent parameter, and the rate constants normalised to unit BET surface area, a microstructure normalised parameter, follow the order, (given as values of x) 1.45 > 2.5 approximate to 2.0 > 1.0 > 1.2 > 0.8 > 0.5. All the MnxFe3-xO4 prepared specimens are potential substitutes for CoFe2O4, the high-performance catalyst for the decomposition of H2O2; the specimen with x = 1.45 is the most powerful and is significantly more active than CoFe,O,. The activity appears to depend on the availability and efficacy of redox conversion of Mn-II centres in the sublattices of the MnxFe3-xO4 catalysts.