Model for NOx storage/reduction in the presence of CO2 on a Pt–Ba/γ-Al2O3 catalyst

We have constructed a global reaction kinetic model to better understand and describe the NOx storage/reduction process in the presence of CO2. Experiments were performed in a packed-bed reactor with a Pt–Ba/γ-Al2O3 powder catalyst (1 wt% Pt and 30 wt% Ba) with different lean/rich cycle timings. The model is based on a multiple storage sites mechanism and considers that fast NOx storage occurs at surface barium sites, as determined by the reaction kinetics. Slow NOx storage occurs at the semi-bulk and bulk barium sites, where diffusion plays a major role. It is assumed that surface, bulk, and semi-bulk sites differ not only in physical appearance, but also in chemical reactivity. The distribution of these sites is obtained from 9-h lean-phase and 15-h rich-phase cycling experiments and thermogravimetric analysis of fresh catalyst. The model adequately describes the NO and NO2 breakthrough profiles during 9 h of lean exposure, as well as the subsequent release and reduction of the stored NOx. Furthermore, the model is also capable of simulating transient reactor experiments with 240-s lean-cycle and 60-s rich-cycle timings.