The selective catalytic reduction (SCR) with ammonia is increasingly used to treat NOx produced in the exhaust of fuel-efficient lean-burn engines.  The ascent of this technology has largely been enabled by the discovery of Cu-SSZ-13 zeolite catalysts that exhibit high activity over a wide temperature range.  The origins of this catalytic activity and even the nature of the catalytically active sites remains largely unknown.  Here we apply a first-principles thermodynamics approach based on supercell density functional theory to compare the stability of various states of Cu under the wet and oxidizing conditions that prevail during SCR.  We find, consistent with experimental observation, that the stable Cu oxidation state is related to the ratio of NO2 to NO, and that the Cu oxidation states are connected with the incorporation of extralattice adsorbates, in particular H2 and OH.  We consider the implications for the overall catalytic performance of the exchanged zeolites.

First-principles thermodynamics of active sites in Cu-SSZ-13 NO<sub>x</sub> reduction catalysts

243rd National Meeting (2012)

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First-principles thermodynamics of active sites in Cu-SSZ-13 NOx reduction catalysts

First-principles thermodynamics of active sites in Cu-SSZ-13 NO_x reduction catalysts