Promoting effect of CO on low-temperature NOx adsorption over Pd/CeO2 catalyst

Passive NOx adsorbers (PNA) adsorb NOx at low temperatures and release NOx at high temperatures, at which downstream catalytic systems, such as selective catalytic reduction catalysts, operate efficiently and can remove NOx. Pd/CeO2 is a promising catalyst for PNA applications. In this study, the promoting effect of CO on the NOx adsorption ability of Pd/CeO2 at low temperatures was investigated. The amount of NOx adsorbed significantly increased when CO was added to the feed gas. Specifically, during the first 10 min, the amount of adsorbed NOx increased more than six times in the presence of CO. A mechanism for the promoting effect of CO on low-temperature NOx adsorption was suggested by considering the decreased CO oxidation ability with increasing amount of NOx adsorbed over Pd/CeO2. The model proposes that NOx was readily adsorbed by the oxygen vacancies of CeO2 adjacent to the Pd particles, which were generated during CO oxidation, resulting in an in-crease in NOx adsorption. A better understanding of the CO and NO interactions would contribute to the development of ceria-based PNA materials.