The catalytic activity of metal-exchanged zeolites for nitrogen oxide (NOx) reduction in the literature, as measured by the turnover of individual metal atoms, is not constant but generally increases with metal loading. The occupation of specific zeolite environments by metal atoms is also a fuunction of the metal loading, suggesting that the metal-zeolite coordination environment influences the observed catalytic activity. Here, first principles calculations were applied to examine the adsorption of several molecules relevant to de-NOx catalysis for two metal-zeolite environments. For a given adsorbate, the preference for cobalt in the ferrierite B environment over the G environment ranges from negligible to approximately 40 kJ/mol. Two primary characteristics were identified that account for the variable preferential adsorption. First, calculations revealed that cobalt in the B environment is more coordinatively unsaturated than cobalt in the G environment. The second characteristic arises from the adsorbate-induced strain on the local zeolite environments, which is generally larger for the G environment. Additional effects are discussed for molecules capable of forming secondary hydrogen bonds with the zeolite and/or highly polar molecules such as water.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films
- Materials Chemistry