Kinetics and mechanism of iridium (III) catalysed oxidation of tellurium (IV) by cerium (IV) in sulfuric acid medium

The kinetics and mechanism of iridium (III) catalysed oxidation of tellurium (IV) by cerium (IV) have been studied in sulfuric acid medium. The reaction is first order in [Ir (III)] as well as in [Ce (IV)] and fractional order (0.23) in [Te (IV)]. Increase in [H3O+] accelerates the rate while that in ionic strength or [HSO4-] retards. Ce (III), one of the products, inhibits while the other, Te (VI), has negligible effect on the rate. The reaction is supposed to proceed via the formation of a complex between Te (IV) and Ir (III) which in turn reacts with active Ce (IV) species in a reversible step. A rate law, consistent with the observed kinetic data, has been derived basing on the proposed mechanism. (author)