(461a) Exploring the Nature of Active Sites in Cu-Exchanged SSZ-13 Under Realistic Conditions Conference: AIChE Annual MeetingYear: 2015Proceeding: 2015 AIChE Annual MeetingGroup: Catalysis and Reaction Engineering DivisionSession: Computational Catalysis IV Time: Wednesday, November 11, 2015 - 8:30am-8:50am Authors: Göltl, F., UW Madison Love, A., Sautet, P., University of California Los Angeles Hermans, I., University of Wisconsin-Madison Cu exchanged SSZ-13 is one of the most promising catalysts in the selective catalytic reduction of NOx using ammonia. However, the true nature of the active sites under realistic conditions (i.e. finite temperature and presence of water) is still not fully understood. In this work we explore these effects using ab-initio molecular dynamics calculations and thermodynamic analysis. A key technique in understanding the chemical activity of transition metal centers in zeolites is infrared spectroscopy of adsorbed tracer molecules. In this work we model vibrational spectra of CO adsorbed to Cu(I) sites and NO adsorbed to Cu(II) sites in SSZ-13 using molecular dynamics calculations. For both cases finite temperature induces a movement of the cation. For NO, changes in the Cu-N-O angle lead to additional accessible local minima. A combination of those two phenomena leads to complex multi-peak vibrational spectra for one molecule adsorbed to one active site, which then allows a clear assignment of experiment and the identification of the distribution of active sites present in realistic systems. Linking this distribution to experimental activity measurements furthermore allows the identification of active and inactive species for the given reaction. Under realistic conditions also water is present, which leads to a reconstruction of the active sites. We use thermodynamic analysis to imitate realistic conditions. Interestingly not all active sites reconstruct similarly, i.e. not the same amount of water molecules are adsorbed to them under the same conditions. This allows closely reproducing experimentally observed Cu-O vibrations and their variation with hydration. The results in this work suggest that under reaction conditions Cu cations are hydrated and finite temperature leads to regular changes of coordination. We expect that these two effects lead to significant changes for reaction paths and barriers, which explains the experimentally observed catalytic behavior.