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

An effective model for describing NO_x adsorption and desorption on a PtPd/CeO₂-ZrO₂ passive NO_x adsorber is presented. The kinetic parameters are evaluated from the available experimental data obtained during NO_x adsorption/desorption experiments including CO₂ and H₂O in the feed, performed at 80, 120 and 160 °C both in the presence and in the absence of reducing agents (CO or C₂H₄). The model describes the temperature dependence of the NO_x adsorption rate and capacity, the impact of CO, and dynamics of the NO_x desorption events. The model predicts formation of nitrites, nitrates, and additional storage enabled in the presence of CO. Thermal decomposition of the stored NO_x 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 NO_x 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.