Cage effects control the mechanism of methane hydroxylation in zeolites

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

doi:10.1126/science.abd5803

Cited by 82 publications

(73 citation statements)

References 38 publications

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“…241−243 Snyder et al speculated that cavity size must be playing a crucial role to decide reactivity. 244 The α-Fe(IV)O sites in *BEA are constituted of a large 12-membered ring (12MR) of SiO 4 tetrahedra, while in CHA α-Fe(IV)O, it is encased in a cagelike pore environment. Despite the similar cage dimension, the entrance to α-Fe(IV)O sites in CHA are controlled by an 8MR.…”

Section: Characterization Of Sacsmentioning

confidence: 99%

Single Atom Catalysts for Selective Methane Oxidation to Oxygenates

Kumar

Al‐Attas

et al. 2022

ACS Nano

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Direct conversion of methane (CH 4 ) to C 1−2 liquid oxygenates is a captivating approach to lock carbons in transportable value-added chemicals, while reducing global warming. Existing approaches utilizing the transformation of CH 4 to liquid fuel via tandemized steam methane reforming and the Fischer−Tropsch synthesis are energy and capital intensive. Chemocatalytic partial oxidation of methane remains challenging due to the negligible electron affinity, poor C−H bond polarizability, and high activation energy barrier. Transition-metal and stoichiometric catalysts utilizing harsh oxidants and reaction conditions perform poorly with randomized product distribution. Paradoxically, the catalysts which are active enough to break C−H also promote overoxidation, resulting in CO 2 generation and reduced carbon balance. Developing catalysts which can break C−H bonds of methane to selectively make useful chemicals at mild conditions is vital to commercialization. Single atom catalysts (SACs) with specifically coordinated metal centers on active support have displayed intrigued reactivity and selectivity for methane oxidation. SACs can significantly reduce the activation energy due to induced electrostatic polarization of the C−H bond to facilitate the accelerated reaction rate at the low reaction temperature. The distinct metal−support interaction can stabilize the intermediate and prevent the overoxidation of the reaction products. The present review accounts for recent progress in the field of SACs for the selective oxidation of CH 4 to C 1−2 oxygenates. The chemical nature of catalytic sites, effects of metal−support interaction, and stabilization of intermediate species on catalysts to minimize overoxidation are thoroughly discussed with a forward-looking perspective to improve the catalytic performance.

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Section: Characterization Of Sacsmentioning

confidence: 99%

Single Atom Catalysts for Selective Methane Oxidation to Oxygenates

Kumar

Al‐Attas

et al. 2022

ACS Nano

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“…Small-pore iron zeolites are known to have attractive properties for catalysis . In selective catalytic reduction (SCR), the small pores prevent the clustering of Cu and Fe active sites and aluminum. − In methane activation with α-O, the restricted windows in CHA enable catalytic turnover . However, the restricted pore hinders the dispersion of iron during catalyst preparation and favors the formation of inactive Fe oxide clusters. , Here we introduce iron during hydrothermal synthesis (“one-pot synthesis”).…”

Section: Introductionmentioning

confidence: 99%

“…14−16 In methane activation with α-O, the restricted windows in CHA enable catalytic turnover. 17 However, the restricted pore hinders the dispersion of iron during catalyst preparation and favors the formation of inactive Fe oxide clusters. 11,18 Here we introduce iron during hydrothermal synthesis ("one-pot synthesis").…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2021

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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).

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“…This directing of radical rebound is similar to that seen in enzymes that perform HAA and can be used to efficiently produce CH 3 OH without deactivation of the catalyst, the focus of section 5 (Figure 1H). 32 These second-sphere effects will be explored in-depth in this review; however, a complete understanding of these requires understanding the first coordination sphere of the metal sites of interest. Thus, we begin the review with an overview of how the relevant metallozeolites are synthesized, how metals bind to the lattice, and how active sites are formed and spectroscopically identified.…”

Section: Second-sphere Effects In Bioinorganic Chemistrymentioning

confidence: 99%

Second-Sphere Lattice Effects in Copper and Iron Zeolite Catalysis

et al. 2022

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Transition-metal-exchanged zeolites perform remarkable chemical reactions from low-temperature methane to methanol oxidation to selective reduction of NOx pollutants. As with metalloenzymes, metallozeolites have impressive reactivities that are controlled in part by interactions outside the immediate coordination sphere. These second-sphere effects include activating a metal site through enforcing an "entatic" state, controlling binding and access to the metal site with pockets and channels, and directing radical rebound vs cage escape. This review explores these effects with emphasis placed on but not limited to the selective oxidation of methane to methanol with a focus on copper and iron active sites, although other transitionmetal-ion zeolite reactions are also explored. While the actual active-site geometric and electronic structures are different in the copper and iron metallozeolites compared to the metalloenzymes, their second-sphere interactions with the lattice or the protein environments are found to have strong parallels that contribute to their high activity and selectivity.

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Cage effects control the mechanism of methane hydroxylation in zeolites

Cited by 82 publications

References 38 publications

Single Atom Catalysts for Selective Methane Oxidation to Oxygenates

Single Atom Catalysts for Selective Methane Oxidation to Oxygenates

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

Second-Sphere Lattice Effects in Copper and Iron Zeolite Catalysis

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