Dynamic oxygen storage modeling in a three-way catalyst for natural gas engines: A dual-site and shrinking-core diffusion approach

Abstract

A dual-site oxygen storage model was developed to predict the dynamic oxygen storage on a Pd/Rh/CeZrOx TWC catalyst. Two oxygen storage sites (surface and sub-surface) were used to describe two distinct regimes of the oxygen storage process. A shrinking core diffusion model was applied on the sub-surface site to predict slow oxygen storage and depletion. It is found that water gas shift and steam reforming reactions play significant roles in determining the oxygen storage capacity (OSC) and they were included in the model. A methodology of OSC measurement was designed to quantify the OSC with distinct reductants over a temperature window of 250°C to 650°C for model development. The amount of OSC with different reductants were compared. The reducibility of the reductants on OSC decreased in the order of H2>CO>CH4. The amount of OSC showed a slight temperature dependency when using H2, followed by CO and CH4 in the temperature from 250°C to 450°C. However, similar amount of OSC was observed when the temperature was above 450°C regardless of the reductants. With the dual-site OSC model, the dynamic oxygen storage capacities with various reductants could be correctly predicted.