Kinetic analysis of a generalized catalytic selective oxidation reaction

A kinetic model is presented for a generalized catalytic selective oxidation reaction in which lattice oxygen is the proximate source of oxygen. The model takes into account the effects on the overall kinetics due to finite residence time of intermediates on the surface, diffusional rate of lattice oxygen, and overall stoichiometry of the reaction. It is shown that except under the condition when adsorption of the hydrocarbon reactant is the slow step, the rate expression derived from this model differs from that obtained with a model in which these effects are neglected. One important consequence of the model is that the rate of consumption of hydrocarbon can be changed if the selectivity of the reaction is changed, even when reoxidation of the catalyst is the rate-limiting step. In such a circumstance, the rate might show an order dependence in oxygen partial pressure, the apparent activation energy reflects that of reoxidation and the temperature dependence of the selectivity, and the apparent preexponential factor is also influenced by the stoichiometry of the reaction. The implications of these to the interpretation of substituent effects and deuterium kinetic isotope effects are discussed.