Chemical and physical properties of small-pore Cu-zeolite catalysts for the selective catalytic reduction of NOx with NH3: Implications for the reaction mechanism

Charles  Peden, Pacific Northwest National Laboratory

Selective catalytic reduction (SCR) of NOx with ammonia using metal-exchanged zeolites is now being commercialized on diesel vehicles. In particular, small-pore zeolites with a chabazite (CHA) structure are being used due to their high activities and selectivities, their hydrothermal stability, and their minimal deactivation in the presence of unburned hydrocarbons. We recently published the first open-literature paper describing the comparative performance of a Cu-CHA (SSZ-13) catalyst relative to Cu-beta and Cu-ZSM-5 for the SCR of NOx with NH3, particularly focusing on the activity and N2 selectivity. In this presentation, we will describe results of more recent studies that address a number of additional aspects of these catalysts including the effects of NO/NO2 ratio and Cu loading on performance, as well as structural studies that are aimed at understanding the relative performance of these materials. The implications of these results for the NH3 SCR reaction mechanisms will also be discussed.

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