Theoretical And Spectroscopic Evidence Of The Dynamic Nature Of Copper Active Sites In Cu-Cha Catalysts Under Selective Catalytic Reduction (Nh3-Scr-Nox) Conditions

The dynamic nature of the copper cations acting as active sites for selective catalytic reduction of nitrogen oxides with ammonia is investigated using a combined theoretical and spectroscopic approach. Ab initio molecular dynamics simulations of Cu-CHA catalysts in contact with reactants and intermediates at realistic operating conditions show that only ammonia is able to release Cu+ and Cu2+ cations from their positions coordinated to the zeolite framework, forming mobile Cu+(NH3)(2) and Cu2+(NH3)(4) complexes that migrate to the center of the cavity. Herein, we give evidence that such mobilization of copper cations modifies the vibrational fingerprint in the 800-1000 cm(-1) region of the IR spectra. Bands associated with the lattice asymmetric T-O-T vibrations are perturbed by the presence of coordinated cations, and allow one to experimentally follow the dynamic reorganization of the active sites at operating conditions.