Effective Model of NOx Adsorption and Desorption on PtPd/CeO2-ZrO2 Passive NOx Adsorber

An effective model for describing NOx adsorption and desorption on a PtPd/CeO2-ZrO2 passive NOx adsorber is presented. The kinetic parameters are evaluated from the available experimental data obtained during NOx adsorption/desorption experiments including CO2 and H2O in the feed, performed at 80, 120 and 160 degrees C both in the presence and in the absence of reducing agents (CO or C2H4 ). The model describes the temperature dependence of the NOx adsorption rate and capacity, the impact of CO, and dynamics of the NOx desorption events. The model predicts formation of nitrites, nitrates, and additional storage enabled in the presence of CO. Thermal decomposition of the stored NOx species results in two main desorption peaks. Nitrites are desorbed at lower temperatures while nitrates are thermally more stable. The evolution of nitrite and nitrate species in the model corresponds with the measured DRIFTS spectra of the catalyst surface. The presence of CO significantly improves the rate of NOx adsorption and storage efficiency at low temperatures, most probably due to reduction of oxidic Pt and Pd nanoparticles. The developed model captures well the observed trends and can be utilized for simulations of PNA performance under real operating conditions.