The dynamic character of the active centers has made it difficult to unravel the reaction path for NH3-assisted selective catalytic reduction (SCR) of nitrogen oxides over Cu-functionalized Chabazite (Cu-CHA). In this work, we have used density functional theory calculations to explore reaction mechanisms for low-temperature NH3-SCR. The desired reaction is found to proceed in a multi-site fashion over ammonia-solvated Cu cations Cu(NH3)2+ and Bronsted acid sites. The activation of oxygen and the formation of the key intermediates HONO and H2NNO occur on the Cu-sites, whereas the Bronsted acid sites facilitate the decomposition of HONO and H2NNO to N2 and H2O. The Cu- and Bronsted acid sites are found to be important also for the competing reaction where instead N2O is formed. Density functional theory-based calculations of reactions in Cu-CHA poses some general challenges including the shallow potential energy surfaces, effects of Al-distribution and the limitations of exchange-correlation functionals. Some of these challenges will also be discussed in the presentation.

First principles studies of NH3-SCR over Cu-CHA

ACS Spring Meeting 2021

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