Mathematical modeling of oscillating CO oxidation on Pt-group metals at near atmospheric pressure: Activity of metallic and oxidized surfaces

This article is a theoretical and numerical analysis of experimental results concerning the oscillatory and steady-state behavior during CO oxidation on Pd(100) and Pt(110) catalysts in continuous flow and batch reactors at near atmospheric pressure conditions. In the literature there is disagreement about which mechanism describes the reaction of CO oxidation. Some authors suggested that the oxidized phase is more active than the metallic phase with chemisorbed oxygen and that the Mars-van Krevelen mechanism and not the traditional Langmuir-Hinshelwood mechanism is required to describe the catalytic reaction. To study this disagreement in data interpretation, we apply a slight modification of a well-known kinetic model suggested by Sales, Turner, and Maple, which is based on the Langinuir-Hinshelwood mechanism. We show that in a high-activity state the calculated concentration of the oxide can exceed 0.9 ML. However, this does not mean that the oxide phase is more active than the metallic phase, because oxide-free sites of the partially oxidized catalyst may be responsible for the observed reaction rate. Available experimental results, including oscillatory behavior, can be explained on the basis of the Langmuir-Hinshelwood mechanism. We conclude that there is no need to introduce the Mars van Krevelen mechanism to model CO oxidation on Pt-group metals.