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 NH3
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 and synchrotron characterization techniques coupled with DFT calculations allow us to gain molecular-level insight into various active PNA species. This provides a pathway to PNA materials with impressive performance under industrially relevant conditions.
The authors gratefully acknowledge the US Department of Energy (DOE), Energy Efficiency and Renewable Energy, Vehicle Technologies Office for the support of this work. The research described in this paper was performed in the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the DOEâs Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL). PNNL is operated for the US DOE by Battelle.