Structural and Kinetic Changes to Small-Pore Cu-Zeolites After Hydrothermal Treatment and NOx SCR with Ammonia
Rajamani Gounder, Purdue University
Molecular sieves of the chabazite topology (SSZ-13, SAPO-34) are viable as practical selective NOx reduction catalysts in diesel engine exhaust aftertreatment because of their excellent hydrothermal stability and resistance to hydrocarbon poisoning. Research and commercial interests have focused on alternate formulations of CHA zeolites and alternative small-pore (eight-membered ring) molecular sieve frameworks as potential catalysts for NOx selective catalytic reduction (SCR) with ammonia. Here, we discuss the results of a comparative study of three different 8-MR zeolites of the CHA (SSZ-13), AEI (SSZ-39) and RTH (SSZ-50) topologies. These three zeolites are treated according to standard hydrothermal aging protocols before and after Cu exchange, characterized using a range of spectroscopic and titration techniques, and assessed for catalytic performance in low temperature NOx SCR with NH3 (473 K). The systematic approach employed in this study compares the different zeolite frameworks on an equivalent basis and provides evidence for different structural and kinetic changes to each zeolite framework after hydrothermal aging and exposure to NOx SCR conditions.