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 le ss than or equal to 3), have been synthesized by the hydroxide copreci pitation technique and characterised by chemical analysis; XRD and SEM techniques, and measurements of their BET specific surface areas, sat uration magnetisations and electrical resistivities. The specimens wit h 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. Th e relative catalytic activities of the specimens towards the decomposi tion 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 micros tructure 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 MnxFe 3-xO4 prepared specimens are potential substitutes for CoFe2O4, the hi gh-performance catalyst for the decomposition of H2O2; the specimen wi th x = 1.45 is the most powerful and is significantly more active than CoFe,O,. The activity appears to depend on the availability and effic acy of redox conversion of Mn-II centres in the sublattices of the Mnx Fe3-xO4 catalysts.