Toward Rational Synthesis and Molecular Level Understanding of Pd/Zeolite Passive NOx Adsorbers (PNA)
Konstantin Khivantsev, Institute for Integrated Catalysis, Pacific Northwest National Laboratory
Removal of criteria pollutant NOx species from diesel engine exhaust is a challenge for current lean NOx control technologies. Substantial decrease in the amount of released NOx has been achieved by the successful development and commercialization of NH3 selective catalytic reduction (SCR) technology. SCR catalysts rely on ammonia supply from urea transformation > 180 °C. Furthermore, they perform effectively at temperature > 250 °C. During cold start, most of NOx emissions escape into the atmosphere. To address this issue, Passive NOx adsorber (PNA) materials, capable of storing NOx at low temperature and releasing it > 200 °C, are being developed. Herein, we focus specifically on Pd/Zeolite PNA materials. We systematically study structure-storage performance relationships for a wide range of Pd/Zeolite materials and determine the important factors that govern their PNA activity and response to hydrothermal aging. Advanced spectroscopic, imaging and synchrotron characterization techniques coupled with DFT calculations allow us to gain molecular-level insight into various active PNA species under varying gas environments. This provides a direct route to PNA materials with impressive performance under industrially relevant conditions.