Advances in the synthesis, characterisation, and mechanistic understanding of active sites in Fe-zeolites for redox catalysts

Bols, Max L.; Rhoda, Hannah M.; Snyder, B.; Solomon, Edward I.; Pierloot, Kristine; Schoonheydt, Robert A.; Sels, Bert F.

doi:10.1039/d0dt01857k

Cited by 22 publications

(17 citation statements)

References 92 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…These bare Fe(II)-ions were proposed as active sites for N 2 O decomposition 65 as well as partial oxidation of methane to methanol with N 2 O. 46,66,67 To summarize, our results on sulfur-free species are consistent with the two previous studies on Fe-SSZ-13. 29,30 Some differences in results could be due to the use of different functionals in the calculations, as well as the environmental conditions modeled.…”

Section: Introductionsupporting

confidence: 91%

See 1 more Smart Citation

First-Principles Calculations of Condition-Dependent Cu/Fe Speciation in Sulfur-Poisoned Cu- and Fe-SSZ-13 Catalysts

et al. 2021

View full text Add to dashboard Cite

A combination of first-principles thermodynamics and density functional theory (DFT) was applied for the prediction of sulfur-poisoned monomeric Cu/Fe species formed in the SSZ-13 catalyst framework under selective catalytic reduction (SCR)-relevant conditions in the presence of sulfur dioxide, ammonia, oxygen, and water. Differences in fresh and sulfurpoisoned species were found for Cu-and Fe-SSZ-13 catalysts containing one Al (1Al sites) or two Al (2Al sites) in 6-membered rings (6MRs) or 8membered rings (8MRs). The impact of ammonia concentration during lowand high-temperature sulfur-poisoning on Cu-and Fe-speciation was also investigated. SCR-relevant concentrations of ammonia in the gas mixture led to the formation of ammonium sulfates over copper in 2Al and 1Al sites of Cu-SSZ-13, while bisulfate and sulfuric acid species were predicted at these copper sites either in the absence of ammonia or at negligible concentrations of ammonia during low-and high-temperature poisoning. The absence of ammonia in the gas mixture led to the formation of iron-bisulfates at 2Al sites of Fe-SSZ-13 during lowtemperature poisoning, while the formation of ammonium sulfates was favorable under SCR-relevant conditions. In contrast to the facile formation of ammonium sulfates at copper sites of Cu-SSZ-13, only ammonium-free iron-sulfates formed at 1Al sites in Fe-SSZ-13 under realistic operational conditions. The regeneration of 2Al sites of Cu-SSZ-13 was predicted to occur at higher temperatures compared to 2Al sites in Fe-SSZ-13, whereas the opposite was predicted for 1Al sites. The analysis of fresh and regenerated Cu/Fe species was carried out as well. These theoretical results on model catalysts provide a first step in the understanding of sulfur-poisoning in Fe-SSZ-13 catalysts, supporting further experimental investigations to improve NH 3 -SCR catalysts for meeting future emission standards.

show abstract

Section: Introductionsupporting

confidence: 91%

“…observed Fe 2+ sites after activation of Fe-CHA in He at 900 °C. These bare Fe(II)-ions were proposed as active sites for N 2 O decomposition as well as partial oxidation of methane to methanol with N 2 O. ,, …”

Section: Resultsmentioning

confidence: 99%

First-Principles Calculations of Condition-Dependent Cu/Fe Speciation in Sulfur-Poisoned Cu- and Fe-SSZ-13 Catalysts

et al. 2021

View full text Add to dashboard Cite

show abstract

“…The study of Fe-zeolite catalysts has been obstructed by the complex mixture of iron species derived from the chemistry of Fe in solution and on the zeolite surface and by ambiguity in the assignment of spectroscopic features. , Over the past 5 years, the structure and spectroscopy of the α-Fe(II) active site have been described, ,, and we can now reinterpret findings from past Fe zeolite studies on α-Fe(II) formation to arrive at a consistent model. In doing so, we will maintain the original definition of α-Fe(II) sites by Panov et al: Fe capable of forming an active oxygen that oxidizes benzene (and methane) at room temperature. , …”

Section: Discussionmentioning

confidence: 92%

“…For every Al(III) T atom, the lattice carries a negative charge that must be balanced by exchangeable cations. Zeolites exchanged with cationic iron are useful redox catalysts and attract attention for their stabilization of the α-Fe(II)/α-O sites. − These are well-known as the active sites for room temperature partial oxidation of methane to methanol and benzene to phenol and are likely also involved in selective catalytic reduction (SCR) of NO X and catalytic N 2 O decomposition. − On the Fe-*BEA zeolite, the α-Fe(II)/α-O active sites are formed in six membered ring (6MR) motifs of the zeolite framework with two Al(III) T atoms (Al FW ) at opposite sides of the 6MR . How these α-Fe(II) sites are formed from their precursors remains unclear.…”

Section: Introductionmentioning

confidence: 99%

Selective Formation of α-Fe(II) Sites on Fe-Zeolites through One-Pot Synthesis

et al. 2021

Self Cite

View full text Add to dashboard Cite

α-Fe(II) active sites in iron zeolites catalyze N2O decomposition and form highly reactive α-O that selectively oxidizes unreactive hydrocarbons, such as methane. How these α-Fe(II) sites are formed remains unclear. Here different methods of iron introduction into zeolites are compared to derive the limiting factors of Fe speciation to α-Fe(II). Postsynthetic iron introduction procedures on small pore zeolites suffer from limited iron diffusion and dispersion leading to iron oxides. In contrast, by introducing Fe(III) in the hydrothermal synthesis mixture of the zeolite (one-pot synthesis) and the right treatment, crystalline CHA can be prepared with >1.6 wt % Fe, of which >70% is α-Fe(II). The effect of iron on the crystallization is investigated, and the intermediate Fe species are tracked using UV–vis-NIR, FT-IR, and Mössbauer spectroscopy. These data are supplemented with online mass spectrometry in each step, with reactivity tests in α-O formation and with methanol yields in stoichiometric methane activation at room temperature and pressure. We recover up to 134 μmol methanol per gram in a single cycle through H2O/CH3CN extraction and 183 μmol/g through steam desorption, a record yield for iron zeolites. A general scheme is proposed for iron speciation in zeolites through the steps of drying, calcination, and activation. The formation of two cohorts of α-Fe(II) is discovered, one before and one after high temperature activation. We propose the latter cohort depends on the reshuffling of aluminum in the zeolite lattice to accommodate thermodynamically favored α-Fe(II).

show abstract

“…Zeolites embedding transition metal ions are receiving considerable attention owing to their unique catalytic properties, notably in environmental catalysis [97][98][99]. However, in terms of computational modeling, the presence of TMI site in a material presents numerous challenges related to the variability of the metal oxidation states, the possible existence of multiple spin states, the significant interplay between electronic and geometric degrees of freedom, and the strong electron correlation effects affecting the electronic structure of the TMI (d electrons) and the metal-ligand interaction [100][101][102].…”

Section: Transition Metal Ions: the Challenge For Electronic Structure Calculation And Interpretationmentioning

confidence: 99%

Zeolites at the Molecular Level: What Can Be Learned from Molecular Modeling

et al. 2021

View full text Add to dashboard Cite

show abstract

Advances in the synthesis, characterisation, and mechanistic understanding of active sites in Fe-zeolites for redox catalysts

Abstract: Strategies for further research and developments on active sites in Fe-zeolites for redox catalysis.

Cited by 22 publications

References 92 publications

First-Principles Calculations of Condition-Dependent Cu/Fe Speciation in Sulfur-Poisoned Cu- and Fe-SSZ-13 Catalysts

First-Principles Calculations of Condition-Dependent Cu/Fe Speciation in Sulfur-Poisoned Cu- and Fe-SSZ-13 Catalysts

Selective Formation of α-Fe(II) Sites on Fe-Zeolites through One-Pot Synthesis

Zeolites at the Molecular Level: What Can Be Learned from Molecular Modeling

Contact Info

Product

Resources

About