Fe-exchanged zeolites are known to be catalytically active for various reactions, for example, N2O decomposition, methane to methanol oxidation, selective catalytic reduction of NOx, etc. In spite of great efforts spent on understanding these catalytic mechanisms over Fe-zeolites, identification of available Fe species and their siting preference, even under ex situ conditions, is still under debate. The difficulty of site identification lies in (1) potential coexistence of Fe with different nuclearities, ranging from monomeric cations to oligomeric Fe complexes and Fe oxides, (2) coexistence of Fe with oxidation states (Fe2+ and Fe3+) and (3) uncertainties in interpretations of experimental characterization results.<br/><br/>Here we present a theoretical approach to determine Fe siting preference in Fe-SSZ-13 zeolite using density functional theory (DFT) and ab Initio molecular dynamics (AIMD). Relative stabilities of exchanged Fe monomers in isolation and dimers ligated by arbitrary combinations of O and OH ligands at isolated Al and different paired Al sites are determined by construction of reactions that interconvert these species. AIMD and time-dependent DFT are combined to compute ensemble-averaged UV-visible spectra of Fe3+ species. We show that both Fe2+ and Fe3+ have strong tendency to form hydroxo-bridged dimers at paired Al sites, and OH-ligated Fe3+ monomer and dimers have qualitatively similar computed UV-visible spectra, suggesting previous UV-vis based assignments of isolated Fe3+ cation preference may need to be revisited.<br/><br/>

Determination of siting preference of exchanged Fe ions in Fe-SSZ-13 zeolite through density functional theory and ab Initio molecular dynamics

254th National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.