Spectroscopic Identification of the α-Fe/α-O Active Site in Fe-CHA Zeolite for the Low-Temperature Activation of the Methane C–H Bond

Bols, Max L.; Hallaert, Simon D.; Snyder, B.; Devos, Julien; Plessers, Dieter; Rhoda, Hannah M.; Dusselier, Michiel; Schoonheydt, Robert A.; Pierloot, Kristine; Solomon, Edward I.; Sels, Bert F.

doi:10.1021/jacs.8b05877

Cited by 93 publications

(145 citation statements)

References 57 publications

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“…29 Si MAS NMR was recorded after 4-s 90 degree pulse under a sample spinning rate of 8 kHz and referenced to externally tetramethylsilane (TMS). Solid-state 27 Al MAS NMR was measured at spinning rate of 13 kHz and referenced to 1 M aq. aluminum nitrate.…”

Section: Cobalt Cation Exchangementioning

confidence: 99%

“…Fe,H-SSZ-13 materials were prepared according to the strategy used by Bols and co-workers. [26][27] Iron was introduced into dried H-CHA by diffusion impregnation in a solution of Fe(acac) 3 in toluene (25 mL/g zeolite) for 24h. The concentration of Fe(acac) 3 in toluene is approximately 7.6 mM.…”

Section: Sample Treatment For Methane Partial Oxidation (Mpo)mentioning

confidence: 99%

“…Bols et al hinted to the importance of Al-distribution for methane partial oxidation (MPO) on Fe-exchanged SSZ-13 materials. 27 A sample of each synthesis type (amorphous sources Am*-3 vs. IZC-2) was subjected to an identical MPO procedure. Although both samples are open SSZ-13 zeolites with similar physico-chemical properties, they take up iron to a different extent: Am*-3 exchanges 0.06 Fe/Al, compared to 0.17 Fe/Al for IZC-2.…”

Section: Methane Partial Oxidation On Ssz-13 From Differentmentioning

confidence: 99%

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Synthesis–Structure–Activity Relations in Fe-CHA for C–H Activation: Control of Al Distribution by Interzeolite Conversion

et al. 2019

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The search for structurally relevant Alarrangements in zeolites is an important endeavor for single site catalysis. Little is known about the mechanisms and zeolite dynamics during synthesis that are responsible for creating those Al-ensembles. Here, new synthetic strategies for creating Al-hosts in small-pore zeolites suitable for divalent cation catalysis are uncovered, leading to a mechanistic proposal for Al-organization during crystallization. As such, unique synthesis-structure-activity relations are demonstrated for the partial oxidation of methane on Fe-exchanged CHA-zeolites. With modified interzeolite conversions, the divalent cation capacity of the resulting high Si SSZ-13 zeolites (Si/Al ~ 35) can be reproducibly controlled in a range between 0.04 and 0.34 Co 2+ /Al. This capacity is a proxy for the distribution of framework aluminum in pairs and correlates with the methanol production per Al when these zeolites host the -Fe II redox active site. The uncovered IZC synthesis-structure relations paint an Al-distribution hypothesis, where incongruent dissolution of the starting USY zeolite and fast synthesis kinetics with atypical growth modes allow assembling specific Alarrangements, resulting in a high divalent cation capacity. Prolonged synthesis times and high temperatures overcome the energetic barriers for T-atom reshuffling favoring Al-isolation. These mechanisms and the relations uncovered in this work will guide the search for relevant Al-ensembles in a range of zeolite catalysts where controlling the environment for a single active site is crucial.

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Section: Cobalt Cation Exchangementioning

confidence: 99%

Section: Sample Treatment For Methane Partial Oxidation (Mpo)mentioning

confidence: 99%

Section: Methane Partial Oxidation On Ssz-13 From Differentmentioning

confidence: 99%

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Synthesis–Structure–Activity Relations in Fe-CHA for C–H Activation: Control of Al Distribution by Interzeolite Conversion

et al. 2019

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“…The formation of the α-oxygen in Fe-zeolites and the successive selective oxidation of methane to methanol was firstly reported by Panov et al 1 . The structure of [Fe = O] 2+ is suggested to be balanced by the negative charges of two AlO 4 − tetrahedra located in the ring of the zeolite framework which creates an extra-framework cationic site for divalent cations 2,3 and only recently has been experimentally confirmed by Snyder et al for Fe-BEA* 4 and Bols et al for Fe-SSZ-13 5 . The selective oxidation of methane by N 2 O is connected with several obstacles.…”

mentioning

confidence: 99%

Low-temperature selective oxidation of methane over distant binuclear cationic centers in zeolites

et al. 2019

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Highly active oxygen capable to selectively oxidize methane to methanol at low temperature can be prepared in transition-metal cation exchanged zeolites. Here we show that the αoxygen stabilized by the negative charges of two framework aluminum atoms can be prepared by the dissociation of nitrous oxide over distant binuclear cation structures (M(II)…M (II), M = cobalt, nickel, and iron) accommodated in two adjacent 6-rings forming cationic sites in the ferrierite zeolite. This α-oxygen species is analogous to that known only for iron exchanged zeolites. In contrast to divalent iron cations, only binuclear divalent cobalt cationic structures and not isolated divalent cobalt cations are active. Created methoxy moieties are easily protonated to yield methanol, formaldehyde, and formic acid which are desorbed to the gas phase without the aid of water vapor while previous studies showed that highly stable methoxy groups were formed on isolated iron cations in iron exchanged ZSM-5 zeolites.

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“…Bols et al. applied in situ 57 Fe Mössbauer spectroscopy to a Fe‐CHA catalyst synthesized by diffusion impregnation to identify the active site for methane hydroxylation to methanol . The room temperature Mössbauer spectrum of Fe‐CHA after reduction in He at 1173 K possesses a single doublet (IS=0.93 mm/s, QS=0.63 mm/s), indicating the existence of a single Fe 2+ site.…”

Section: In Situ Investigations Of Reaction and Deactivation Mechanismsmentioning

confidence: 99%

Characterization of Metal‐zeolite Composite Catalysts: Determining the Environment of the Active Phase

et al. 2020

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Metal‐zeolite composite catalysts are attracting increased attention due to their unique multifunctional properties. However, it is challenging to identify the physicochemical environment of the active phase, which is essential to improve our understanding of the structure‐performance relationships of such complex catalysts. In this work, commonly available analytical techniques (FTIR, TEM, XRD, etc.) and state‐of‐the‐art user instrumentation (XAS, SANS, e‐TEM, etc.) are reviewed with respect to their applications at different stages of the catalyst lifetime, from early nucleation, to the reaction mechanism and deactivation. Each technique is discussed in detail with examples to provide suggestions and guidelines for choosing the characterization technique(s) that are most appropriate for determining the desired structure‐property relationships of metal‐zeolite composite catalysts. Understanding the most appropriate applications of characterization techniques promotes development of novel synthesis methodologies, and in turn, applications for designing active, selective and stable multifunctional metal‐zeolite composite catalysts.

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Spectroscopic Identification of the α-Fe/α-O Active Site in Fe-CHA Zeolite for the Low-Temperature Activation of the Methane C–H Bond

Cited by 93 publications

References 57 publications

Synthesis–Structure–Activity Relations in Fe-CHA for C–H Activation: Control of Al Distribution by Interzeolite Conversion

Synthesis–Structure–Activity Relations in Fe-CHA for C–H Activation: Control of Al Distribution by Interzeolite Conversion

Low-temperature selective oxidation of methane over distant binuclear cationic centers in zeolites

Characterization of Metal‐zeolite Composite Catalysts: Determining the Environment of the Active Phase

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