Theoretical and Spectroscopic Evidence of the Dynamic Nature of Copper Active Sites in Cu-CHA Catalysts under Selective Catalytic Reduction (NH₃-SCR-NO_x) Conditions.

ABSTRACT: 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.

SUBMITTER: Millan R 

PROVIDER: S-EPMC7720274 | biostudies-literature | 2020 Dec

REPOSITORIES: biostudies-literature