Iron Loading Effects in Fe/SSZ-13 NH₃-SCR Catalysts: Nature of the Fe Ions and Structure–Function Relationships

Abstract

Using a traditional aqueous solution ion exchange method under a protecting atmosphere of N2, a series of Fe/SSZ-13 catalysts with various Fe loadings were synthesized. UV–vis, EPR, and Mössbauer spectroscopic methods, coupled with temperature-programmed reduction and desorption techniques, were used to probe the nature of the Fe sites. The major Fe species are extraframework Fe­(III) species: [Fe­(OH)2]+ (monomeric) and [HO–Fe–O–Fe–OH]2+ (dimeric). Larger oligomers with unknown nuclearity, poorly crystallized Fe oxide particles, together with isolated Fe2+ ions, are minor Fe-containing moieties. Reaction rate and Fe loading correlations, and temperature and Fe loading effects on SCR selectivities, suggest that isolated Fe3+ ions are the active sites for low-temperature standard SCR, and dimeric sites provide the majority of reactivity at higher temperatures. For NO oxidation, dimeric sites are the active centers. NH3 oxidation, on the other hand, is catalyzed by sites with higher nuclearity.

Catalytic performance of MnFeSi composite in selective oxidation of styrene, ethylbenzene and benzyl alcohol

“…It is worth noting that the another signal with g = 6 is frequently observed in axially distorted sites of Fe species [31], but the uncertainties in this assignment are likely due to the board feature of the spectra. Thereby, EPR spectra are clearly similar, suggesting comparable distributions as Fe 3+ species visible by EPR for samples tested in different reactions.…”

Fe‐Containing Zeolites for NH3‐SCR of NOx: Effect of Structure, Synthesis Procedure, and Chemical Composition on Catalytic Performance and Stability

“…In general, the introduction of these metals allows treatment of exhaust gases at different temperatures . Copper‐containing zeolites give better SCR performance at low‐to‐medium temperatures (below 400 °C), whereas iron‐containing zeolites provide better SCR performance at high temperatures with improved selectivity (above 400 °C) …”

Zeolitic Materials for DeNOx Selective Catalytic Reduction

“…summarized the progress till 2013 focusing on the advantages of Cu‐SSZ‐13 (especially for the much enhanced hydrothermal stability) and the research achievements of active centers . Only one year later, Fe‐SSZ‐13 was also reported, which shows higher activity at the elevated temperature (Figure b) ,,. The advance in Cu/Fe‐SSZ‐13 was reviewed by Beale et al.…”