Modeling Ammonia and Water Co-Adsorption in CuI-SSZ-13 Zeolite Using DFT Calculations

Cu-SSZ-13 efficiently catalyzes the selective catalytic reduction (SCR) of NO by NH3 but the structure of the active site and, particularly, the redox state of the copper (+I or +II) is still debated. This paper focuses on the possible contribution of CuI species using quantum chemistry of adsorption and co-adsorption of NH3 and H2O on CuI species. The calculations show that CuI clearly migrates upon adsorption of NH3 and H2O. All the CuI complexes sit in the cage containing the 8 MR and interact with the zeolite framework through several H-bonds. In the experimental temperature and pressure domain of SCR conditions, calculated phase diagrams show that a coordination number of two is predicted for the co-adsorption of NH3 and H2O on CuI. Finally, the calculated phase diagrams of CuI-SSZ-13 are discussed together with those of CuII-SSZ-13 and recent experimental characterizations, providing a wider picture of the real catalyst in SCR conditions.