Selective catalytic reduction (SCR) of NOx with ammonia using metal-exchanged molecular sieves with a Chabazite (CHA) structure has recently been commercialized on diesel vehicles. Catalysts with outstanding SCR performance (activity, hydrothermal stability, etc.) include the aluminosilicate zeolite, SSZ-13, and the silico-alumino-phosphate, SAPO-34, with ion-exchanged Cu. Apart from the commercial success, detailed catalyst structures, reaction mechanisms, and structure-activity relationships are still lacking. In this presentation, we will describe results of recent studies of these Cu-CHA materials that address a number of aspects of the reactivity of these catalysts, as well as structural studies that account for the relative performance of these materials. Understanding the location and the chemical environment of the catalytically active Cu ions, as well as the adsorbed species present on (in) the catalyst under practical operation conditions are critical in developing a viable reaction mechanism. Transmission FITR of adsorbed probe molecules and DRIFT spectroscopy under quasi operando conditions were used to determine the adsorption properties of these materials, as well as to follow the fate of adsorbed NH3 upon its exposure to oxidizing gases of different composition, respectively.  We also use a number of characterization methods including electron paramagnetic resonance (EPR) spectroscopy, a technique ideally suited for studying Cu2+ exchanged zeolites, to study hydrated Cu-SSZ-13 catalysts at various Cu loadings in order to gain further insights into their locations. Finally, NH3-SCR and NH3 oxidation kinetics are investigated over these catalysts at high space velocity conditions for the development of structure-activity relationships. The implications of these results for understanding the NH3 SCR reaction mechanisms will also be discussed.

Mechanism of the selective catalytic reduction of NOx with NH<sub>3</sub> over Cu-CHA-based catalysts

247th National Meeting (2014)

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Mechanism of the selective catalytic reduction of NOx with NH3 over Cu-CHA-based catalysts

Mechanism of the selective catalytic reduction of NOx with NH₃ over Cu-CHA-based catalysts