Effects of Alkali and Alkaline Earth Cocations on Cu/SSZ-13 NH3-SCR Catalysts

Feng  Gao, PNNL

Zeolite-based selective catalytic reduction (SCR) catalysts, most notably Cu/SSZ-13, have received intensive research interest since they meet the requirements for commercialization as part of diesel engine exhaust aftertreatment catalytic systems. Despite the high activity and remarkable hydrothermal stability for the current-generation Cu/SSZ-13 SCR catalysts, there is still plenty of room for improvement. Notably, the need for high activities at low reaction temperatures requires rather high Cu ion-exchange levels; however, during hydrothermal aging Cu ions in these highly loaded catalysts tend to agglomerate to generate CuOx clusters that are active in side reactions, and even to promote decomposition of the Chabazite structure.  However, maintaining low Cu ion-exchange levels without sacrificing low-temperature activity and hydrothermal stability is challenging. Moreover, at low exchange levels, excessive NH3 storage occurs that may lead to potential NH3 slip. We show in this presentation that these issues are solved by introducing alkali or alkaline earth cocations in Cu/SSZ-13. Cu/SSZ-13 catalysts with low Cu loadings and alkali/alkaline earth cocations display excellent low-temperature activities, hydrothermal stability and high-temperature SCR selectivities after aging.

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