Water‐Promoted Hydrocarbon Activation Catalyzed by Binuclear Gallium Sites in ZSM‐5 Zeolite

Hensen, Emiel J. M.; Pidko, Evgeny A.; Rane, Neelesh; Santen, Rutger A. van

doi:10.1002/ange.200702463

Cited by 9 publications

(6 citation statements)

References 20 publications

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“…The addition of Ga in excess of this saturation stoichiometry leads to Ga 3+ structures in oxidized Ga/H-MFI with condensed Ga−O−Ga linkages that do not appear to be ion-exchanged at cation-exchange sites. Our data are therefore not consistent with the presence of binuclear [Ga 2 O 2 ] 2+ cations at Ga/Al ratios >0.3, as proposed by Hensen et al 17 We suggest instead that the addition of Ga at levels higher than Ga/Al ratios of 0.3 leads to the formation of weakly bound [Ga(OH) 2 ] + cations at residual cation-exchange sites associated with isolated framework Al atoms. In the presence of trace levels of H 2 O during calcination, these structures may deanchor via reaction of [Ga(OH) 2 ] + with H 2 O to form a Brønsted acid O−H group and mobile Ga(OH) 3 species, which may undergo subsequent condensation to form neutral, GaO x oligomers with structures that may resemble the Ga 4 O 4 complexes proposed by Faro et al 75 As noted above, Ga− O−Ga linkages in these structures are detectable by wavelet 8, as the molar consumption rate of H 2 per gram of catalyst (Figure 8a) and as the molar formation rate of H 2 O per gram of catalyst (Figure 8b).…”

Section: Acs Catalysiscontrasting

confidence: 99%

“…In the second-coordination shell, however, isolated Ga 3+ cations are expected to be proximate to framework Al or Si atoms only. On the other hand, Ga 3+ centers in multinuclear cationic Ga 3+ species such as the [Ga 2 O 2 ] 2+ structures proposed by Hensen et al, 17 or in neutral GaO x species, are expected to be proximate to extraframework Ga 3+ atoms, via Ga−O−Ga linkages. Evidence for [Ga(OH) 2 ] + −H + cation pairs at Ga/Al ratios ≤0.3 and for the formation of GaO x species at Ga/Al ratios >0.3 was obtained by wavelet analyses of the EXAFS spectra.…”

Section: Acs Catalysismentioning

confidence: 99%

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Characterization of Isolated Ga³⁺ Cations in Ga/H-MFI Prepared by Vapor-Phase Exchange of H-MFI Zeolite with GaCl₃

et al. 2018

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Ga/H-MFI was prepared by vapor-phase reaction of GaCl 3 with Brønsted acid O−H groups in dehydrated H-MFI zeolite. The resulting [GaCl 2 ] + cations in the as-exchanged zeolite are treated in H 2 at 823 K to stoichiometrically remove Cl ligands and form [GaH 2 ] + cations. Subsequent oxidation in O 2 and characterization by IR spectroscopy and NH 3 -temperature-programmed desorption (TPD) suggests that, for Ga/Al ratios ≤0.3, Ga 3+ exists predominantly as [Ga(OH) 2 ] + −H + cation pairs and to a lesser degree as [Ga(OH)] 2+ cations at low Ga/Al ratios (∼0.1); while both species are associated with proximate cationexchange sites, calculated free energies of formation suggest that [Ga(OH)] 2+ cations are more stable on cation-exchange sites associated with NNN (next-nearest neighbor) framework Al atoms than on those associated with NNNN (next-next-nearest neighbor) framework Al atoms. Ga K-edge X-ray Absorption Near Edge Spectroscopy (XANES) measurements indicate that, under oxidizing conditions and for all Ga/Al ratios, all Ga species are in the +3 oxidation state and are tetrahedrally coordinated to 4 O atoms. Fourier analysis of Ga K-edge Extended Xray Absorption Fine Structure (EXAFS) data supports the conclusion that Ga 3+ is present predominantly as [Ga(OH) 2 ] + cations (or [Ga(OH) 2 ] + −H + cation pairs). For Ga/Al ratios ≤0.3, wavelet analysis of EXAFS data provide evidence for backscattering from nearest neighboring O atoms and from next-nearest neighboring framework Al atoms. For Ga/Al > 0.3, backscattering from next-nearest neighboring Ga atoms is also evident, characteristic of GaO x species. Upon reduction in H 2 , the oxidized Ga 3+ species produce [Ga(OH)H] + −H + cation pairs, [GaH 2 ] + −H + cation pairs, and [GaH] 2+ cations. Computed phase diagrams indicate that the thermodynamic stability of the reduced Ga 3+ species depends sensitively on temperature, Al−Al interatomic distance, and H 2 and H 2 O partial pressures. For Ga/Al ratios ≤0.2, it is concluded that [GaH 2 ] + −H + cation pairs and [GaH] 2+cations are the predominant species present in Ga/H-MFI reduced above 673 K in 10 5 Pa H 2 and in the absence of water vapor.

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Section: Acs Catalysiscontrasting

confidence: 99%

Section: Acs Catalysismentioning

confidence: 99%

Characterization of Isolated Ga³⁺ Cations in Ga/H-MFI Prepared by Vapor-Phase Exchange of H-MFI Zeolite with GaCl₃

et al. 2018

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“…[30] Alkane dehydrogenation over Cr/Al 2 O 3 or Ga/Zn-zeolite were also proposed to occur through CÀH activation and the formation of metal-alkyl surface species as key intermediates. [29,31] We have described the formation of isolated Cr II and Cr III dinuclear surface species by a molecular approach. The welldefined Cr II sites are not efficient olefin-polymerization catalysts, but Cr III sites do polymerize ethylene.…”

Section: Methodsmentioning

confidence: 99%

Polymerization of Ethylene by Silica‐Supported Dinuclear Cr^III Sites through an Initiation Step Involving CH Bond Activation

et al. 2014

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The insertion of an olefin into a preformed metal-carbon bond is a common mechanism for transition-metal-catalyzed olefin polymerization. However, in one important industrial catalyst, the Phillips catalyst, a metal-carbon bond is not present in the precatalyst. The Phillips catalyst, CrO3 dispersed on silica, polymerizes ethylene without an activator. Despite 60 years of intensive research, the active sites and the way the first CrC bond is formed remain unknown. We synthesized well-defined dinuclear Cr(II) and Cr(III) sites on silica. Whereas the Cr(II) material was a poor polymerization catalyst, the Cr(III) material was active. Poisoning studies showed that about 65 % of the Cr(III) sites were active, a far higher proportion than typically observed for the Phillips catalyst. Examination of the spent catalyst and isotope labeling experiments showed the formation of a Si-(μ-OH)-Cr(III) species, consistent with an initiation mechanism involving the heterolytic activation of ethylene at Cr(III) O bonds.

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“…At present, in zeolite-supported Ga-based catalysts, the effect of Ga species properties on catalytic performance has been extensively investigated [67]. Taking the form of Ga species in +3 valence as an example, the possible active species are deemed to be 2+ , Ga + and/or GaO x clusters [68][69][70][71][72][73][74]. A variety of oxygenated gallium species, such as monomer [GaO] + or dimer [Ga 2 O 2 ] 2+ are also reported [68].…”

Section: Basic Information About Ga Speciesmentioning

confidence: 99%

Recent Progress of Ga-Based Catalysts for Catalytic Conversion of Light Alkanes

Li¹,

Fu²,

Zhang³

et al. 2022

Catalysts

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The efficient and clean conversion of light alkanes is a research hotspot in the petrochemical industry, and the development of effective and eco-friendly non-noble metal-based catalysts is a key factor in this field. Among them, gallium is a metal component with good catalytic performance, which has been extensively used for light alkanes conversion. Herein, we critically summarize recent developments in the preparation of gallium-based catalysts and their applications in the catalytic conversion of light alkanes. First, we briefly describe the different routes of light alkane conversion. Following that, the remarkable preparation methods for gallium-based catalysts are discussed, with their state-of-the-art application in light alkane conversion. It should be noticed that the directional preparation of specific Ga species, strengthening metal-support interactions to anchor Ga species, and the application of new kinds of methods for Ga-based catalysts preparation are at the leading edge. Finally, the review provides some current limitations and future perspectives for the development of gallium-based catalysts. Recently, different kinds of Ga species were reported to be active in alkane conversion, and how to separate them with advanced in situ and ex situ characterizations is still a problem that needs to be solved. We believe that this review can provide base information for the preparation and application of Ga-based catalysts in the current stage. With these summarizations, this review can inspire new research directions of gallium-based catalysts in the catalysis conversion of light alkanes with ameliorated performances.

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Water‐Promoted Hydrocarbon Activation Catalyzed by Binuclear Gallium Sites in ZSM‐5 Zeolite

Cited by 9 publications

References 20 publications

Characterization of Isolated Ga³⁺ Cations in Ga/H-MFI Prepared by Vapor-Phase Exchange of H-MFI Zeolite with GaCl₃

Characterization of Isolated Ga³⁺ Cations in Ga/H-MFI Prepared by Vapor-Phase Exchange of H-MFI Zeolite with GaCl₃

Polymerization of Ethylene by Silica‐Supported Dinuclear Cr^III Sites through an Initiation Step Involving CH Bond Activation

Recent Progress of Ga-Based Catalysts for Catalytic Conversion of Light Alkanes

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Water‐Promoted Hydrocarbon Activation Catalyzed by Binuclear Gallium Sites in ZSM‐5 Zeolite

Cited by 9 publications

References 20 publications

Characterization of Isolated Ga3+ Cations in Ga/H-MFI Prepared by Vapor-Phase Exchange of H-MFI Zeolite with GaCl3

Characterization of Isolated Ga3+ Cations in Ga/H-MFI Prepared by Vapor-Phase Exchange of H-MFI Zeolite with GaCl3

Polymerization of Ethylene by Silica‐Supported Dinuclear CrIII Sites through an Initiation Step Involving CH Bond Activation

Recent Progress of Ga-Based Catalysts for Catalytic Conversion of Light Alkanes

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Characterization of Isolated Ga³⁺ Cations in Ga/H-MFI Prepared by Vapor-Phase Exchange of H-MFI Zeolite with GaCl₃

Characterization of Isolated Ga³⁺ Cations in Ga/H-MFI Prepared by Vapor-Phase Exchange of H-MFI Zeolite with GaCl₃

Polymerization of Ethylene by Silica‐Supported Dinuclear Cr^III Sites through an Initiation Step Involving CH Bond Activation