Mechanism of ozone decomposition on a manganese oxide catalyst. 2. Steady-state and transient kinetic studies

This paper presents an in-depth study of the mechanism of ozone decomposition on a manganese oxide catalyst as studied by in situ Raman spectroscopy and kinetic measurements. In the companion paper, the reaction intermediate was identified to be a peroxide species by:using isotopic substitution and ab initio calculations. To ascertain the role of the intermediate in the catalytic reaction, we investigated its steady-state and transient kinetics, as well as the steady-state kinetics of the overall decomposition reaction, at temperatures from 281 to 340 K and ozone partial pressures from 4.7 Pa to 2.1 kPa; The steady-state and transient kinetics were found to be well-represented by a two-step sequence consisting of (i) adsorption of ozone to form the peroxide species, and (ii) desorption of molecular oxygen. The surface was found to be nonuniform, with activation energies that varied linearly with amount of surface coverage. At zero surface coverage the activation energy for ozone adsorption was 6.2 kJ mol(-1); that for molecular Oxygen desorption was 69.0 kJ mol(-1). The steady-state surface coverages derived from the transient results are in excellent agreement with those measured at steady-state conditions, and the transient desorption kinetics are well-described by the kinetic parameters obtained from the steady-state data, indicating that the proposed:reaction sequence accurately describes the mechanism of decomposition.