What makes copper-exchanged SSZ-13 zeolite efficient at cleaning car exhaust gases?

Recently, the outstanding properties of Cu-SSZ-13 (a zeolite in the chabazite structure) for the selective catalytic reduction of nitrous oxides were discovered. However, the true nature of the active site is still not answered satisfactorily. In this work, we identify the active site for the given reaction from first-principles simulations of the total energy of Cu(II) ions in various positions in combination with previously published catalytic activity as a function of the copper exchange level. This attribution is confirmed by the simulation of vibrational properties of CO adsorbed to the reduced Cu(I) species. The relation between energetic considerations, vibrational calculations, and experiment allows a clear statement about the distribution of active sites in the catalyst. We furthermore discuss the structural properties of the active site leading to the high stability under reaction conditions over a large temperature range. The insights from this work allow a more targeted catalyst design and represent a step toward an industrial application of copper-exchanged zeolites in cleaning car exhaust gases.