Modelling of oxygen storage in automotive catalysts

Abstract

The designers of catalytic converters have found that the use of cerium oxide in the washcoat formulation, to store and release oxygen, gives higher conversion efficiencies in three-way catalysts. It has also been shown that oscillating the air-fuel ratio around λ = 1, which effectively oscillates the oxygen concentration, is a useful method of using this oxygen storage capability. This paper describes a detailed mathematical model for oxygen storage, which forms an important part of a complete kinetic model of a three-way automotive catalyst. This model consists of two interdependent submodels: one for the oxidation process and a second for the reduction process. In this study, O2 and NO were used as oxidizing agents and CO, C3H6 and C3H8 were used as reducing agents. The structure and equations of the model are presented and discussed in detail. Some validation work has also been carried out on a purpose-built miniature catalyst test rig. The purpose of this work was to provide the important kinetic factors for the reaction equations. The result of this analysis is included and compared with other published data.