Improving PNA performance by understanding the chemistry and hydrothermal stability of Pd-loaded zeolites with different framework structures

Janos  Szanyi, Pacific Northwest National Laboratory

Improving PNA performance by understanding the chemistry and hydrothermal stability of Pd-loaded zeolites with different framework structures

Konstantin Khivantsev, Libor Kovarik, Nicholas Jaegers, Feng Gao, Yong Wang and János Szanyi*

Passive NOx adsorbers (PNA) are designed to eliminate NOx release at cold start from the exhaust gas stream of internal combustion engines [1].  Among the large number of adsorbers tested Pd-loaded zeolites exhibit the most promising NOx uptake and release properties.  In fact, a ~2wt% Pd/SSZ-13 prepared by our modified incipient wetness impregnation (IWI) method has achieved 100% NOx removal for about 3 min at 373 K, and complete NOx release at T<673 K [2].  In this contribution we are going to focus on two key aspect of Pd/zeolite PNA materials: 1. our current understanding of the PNA chemistry for small and large pore zeolites and 2. the effect of crystallite size on the hydrothermal stability of the PNA materials in Pd/BEA zeolites.  These studies involve NOx uptake/release measurements, spectroscopy (FTIR and NMR) and microscopy (TEM) investigations.  The results of these studies reveal a common NOx uptake/release chemistry for all the zeolites studies.  The combined spectroscopy/microscopy investigations help to understand the changes in the zeolite-based PNA materials during high temperature hydrothermal aging, and provide some guidance how to minimize the performance decline during these processes.

[1] Chen, H.-Y.; Collier, J. E.; Liu, D.; Mantarosie, L.; Duran-Martin, D.; Novak, V.; Rajaram, R.; Thompsett, D., Catal. Lett. 2016, 146, 1706-1711.

[2] K. Khivantsev, N. R. Jaegers, L. Kovarik, J. C. Hanson, F. F. Tao, Y. Tang, X. Zhang, I. Z. Koleva, H. A. Aleksandrov, G. N. Vayssilov, Y. Wang, F. Gao, J. Szanyi, Angew. Chem. Int. Ed., 2018, doi:10.1002/anie.201809343.