Synthesis of tin-silicalite molecular sieves with MEL structure and their catalytic activity in oxidation reactions

Mal, Nawal Kishor; Ramaswamy, V.; Ganapathy, S.; Ramaswamy, A.V.

doi:10.1016/0926-860x(95)00021-6

Cited by 86 publications

(12 citation statements)

References 8 publications

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“…The signal centred at around δ =−695 ppm (Figure a) can be attributed to intra‐framework Sn IV connected to four Si atoms by oxygen bridges or partially hydrated Sn species with an extended coordination shell . The presence of significant amount of SnO 2 was not detected, since such extra‐framework Sn IV species in an octahedral coordination would yield a signal similar to that of pure SnO 2 nanoparticles (Figure b) . However, if we consider the broad linewidth of the signal shown in Figure a, the presence of a minor amount of extra‐framework SnO 2 cannot be excluded completely.…”

Section: Resultsmentioning

confidence: 96%

High‐Yield Synthesis of Ethyl Lactate with Mesoporous Tin Silicate Catalysts Prepared by an Aerosol‐Assisted Sol–Gel Process

et al. 2017

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An aerosol‐assisted sol–gel method is used to prepare mesoporous tin silicate catalysts that exhibit a record activity in the synthesis of ethyl lactate from dihydroxyacetone and ethanol. The method is based on the formation of an aerosol from a solution of precursors and surfactant. During the fast drying of the droplets, the surfactant self‐assembles and the Sn‐silica matrix is formed by polycondensation reactions. After calcination, the resulting material is composed of a true tin‐silicon mixed oxide in the form of spherical microparticles with calibrated mesopores of 5–6 nm. Sn species are incorporated in the silica network, mainly in the form of single sites. This makes these catalysts highly active for the targeted reaction, as shown by record turnover numbers. The catalyst is recyclable and truly heterogeneous as it can be reused for several cycles and it does not leach.

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Section: Resultsmentioning

confidence: 96%

High‐Yield Synthesis of Ethyl Lactate with Mesoporous Tin Silicate Catalysts Prepared by an Aerosol‐Assisted Sol–Gel Process

et al. 2017

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“…6 Unfortunately, the high cost of isotopic enrichment drastically hinders high-throughput screening, routine analysis, or analysis of low-yield syntheses with NMR. DNP addresses these challenges by transferring the larger polarization of electron spins, such as those found in stable exogenous radical compounds, to nuclear spins through irradiation with high-frequency microwaves.…”

mentioning

confidence: 99%

“…Although framework Sn incorporation can be quantitatively verified with 119 Sn ( I = 1/2, natural abundance = 8.6%) magic angle spinning (MAS) NMR, the coupled effects of low natural abundance of the 119 Sn isotope, low intrinsic NMR sensitivity, and low Sn loadings in the sample make NMR analysis impractical without 119 Sn isotopic enrichment. 6 Unfortunately, the high cost of isotopic enrichment drastically hinders high-throughput screening, routine analysis, or analysis of low-yield syntheses with NMR. DNP addresses these challenges by transferring the larger polarization of electron spins, such as those found in stable exogenous radical compounds, to nuclear spins through irradiation with high-frequency microwaves.…”

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confidence: 99%

Dynamic Nuclear Polarization NMR Enables the Analysis of Sn-Beta Zeolite Prepared with Natural Abundance ¹¹⁹Sn Precursors

Gunther¹,

Michaelis²,

et al. 2014

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The catalytic activity of tin-containing zeolites, such as Sn-Beta, is critically dependent on the successful incorporation of the tin metal center into the zeolite framework. However, synchrotron-based techniques or solid-state nuclear magnetic resonance (ssNMR) of samples enriched with 119Sn isotopes are the only reliable methods to verify framework incorporation. This work demonstrates, for the first time, the use of dynamic nuclear polarization (DNP) NMR for characterizing zeolites containing ∼2 wt % of natural abundance Sn without the need for 119Sn isotopic enrichment. The biradicals TOTAPOL, bTbK, bCTbK, and SPIROPOL functioned effectively as polarizing sources, and the solvent enabled proper transfer of spin polarization from the radical’s unpaired electrons to the target nuclei. Using bCTbK led to an enhancement (ε) of 75, allowing the characterization of natural-abundance 119Sn-Beta with excellent signal-to-noise ratios in <24 h. Without DNP, no 119Sn resonances were detected after 10 days of continuous analysis.

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“…Direct detection techniques, namely, 119 Sn magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, are used to determine the local coordination of framework heteroatoms and qualitatively assess the extent of extraframework metal oxide species (MO x ) present on a given sample. Although framework Sn incorporation can be quantitatively verified with 119 Sn MAS NMR spectroscopy, the coupled effects of low natural abundance of the 119 Sn isotope (natural abundance = 8.6%) and low Sn loadings in zeolitic samples (often <1 mol %) make such NMR analyses impractical without costly isotopic enrichment . To address these limitations, dynamic nuclear polarization (DNP) MAS NMR methods have been developed for zeolites containing ∼2 wt % natural abundance 119 Sn (Figure ).…”

Section: Spectroscopic Methods To Probe Lewis Acidic Active Sitesmentioning

confidence: 99%

“…Although framework Sn incorporation can be quantitatively verified with 119 Sn MAS NMR spectroscopy, the coupled effects of low natural abundance of the 119 Sn isotope (natural abundance = 8.6%) and low Sn loadings in zeolitic samples (often <1 mol %) make such NMR analyses impractical without costly isotopic enrichment. 19 To address these limitations, dynamic nuclear polarization (DNP) MAS NMR methods have been developed for zeolites containing ∼2 wt % natural abundance 119 Sn (Figure 2). 20,21 In this approach, high-powered microwaves irradiate a zeolite sample treated with an exogenous biradical polarizing agent and a glassing agent (e.g., 1,1,2,2tetrachloroethane).…”

Section: Spectroscopic Methods To Probe Lewis Acidic Active Sitesmentioning

confidence: 99%

Tailoring Distinct Reactive Environments in Lewis Acid Zeolites for Liquid Phase Catalysis

2021

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Metrics & MoreArticle Recommendations CONSPECTUS: Lewis acidic zeolites are microporous crystalline materials that offer promise as catalysts for the activation and conversion of biomassderived precursors in the liquid phase due to their unique water tolerance and synthetic versatility. The active site environment in zeolite catalysts is multifaceted in nature and is composed of a primary catalytic binding site, the secondary pore structure that confines such binding sites, and occluded solvent and reactant molecules that interact with adsorbed species. Moreover, Lewis acidic heteroatoms can adopt structurally diverse coordination that selectively catalyze different classes of chemical transformations and can be difficult to control synthetically or characterize spectroscopically. Thus, precise mechanistic interpretation of liquid-phase zeolite catalysis necessitates the development of synthetic, spectroscopic, and kinetic methods that can decouple such complex active site structures and probe the interactions that occur between confined active sites, solvent and reactant molecules, and adsorbed intermediates and transition states.In this Account, we describe the development and application of synthetic, spectroscopic, and kinetic methods to investigate chemically distinct Lewis acid zeolite environments in siliceous zeolites for liquid-phase catalysis. Identification of unique Lewis acidic active site structures relied on the development of direct and indirect solid-state nuclear magnetic resonance (NMR) methods that probe the number and connectivity of framework Lewis acid sites for a diverse range of metal heteroatoms. Such methods enabled the quantitative comparison of catalytic turnover rates, on a per active site basis, measured on different catalysts in order to establish structure−function relationships between active site structure and reactivity. Rigorous normalization of turnover rate further permits comparison of catalytic turnover rates across materials of varying topology, metal heteroatom identity, solvent, and framework polarity to extract salient thermodynamic descriptors of catalysis through kinetic probes. Ex situ interrogation of alcohols adsorbed within hydrophobic and hydrophilic Sn-containing zeolites revealed that hydrophobic voids induce structural order on confined alcohol hydrogen-bonding networks, which give rise to enhanced turnover rates of liquid-phase transfer hydrogenation catalysis. This acceleration of turnover rates arises because ordered alcohol networks occluded within the pores of hydrophobic zeolites stabilize adsorbed transfer hydrogenation intermediates and transition states to a greater extent than liquidlike solvent networks observed in hydrophilic zeolites. The effects of confined solvent molecules can also influence catalysis, independent of framework polarity, due to differences in solvent polarity and substituent effects, which alter turnover rates via changes in how different solvent molecules interact with adsorbed intermediates and transition states. These observ...

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Synthesis of tin-silicalite molecular sieves with MEL structure and their catalytic activity in oxidation reactions

Cited by 86 publications

References 8 publications

High‐Yield Synthesis of Ethyl Lactate with Mesoporous Tin Silicate Catalysts Prepared by an Aerosol‐Assisted Sol–Gel Process

High‐Yield Synthesis of Ethyl Lactate with Mesoporous Tin Silicate Catalysts Prepared by an Aerosol‐Assisted Sol–Gel Process

Dynamic Nuclear Polarization NMR Enables the Analysis of Sn-Beta Zeolite Prepared with Natural Abundance ¹¹⁹Sn Precursors

Tailoring Distinct Reactive Environments in Lewis Acid Zeolites for Liquid Phase Catalysis

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Synthesis of tin-silicalite molecular sieves with MEL structure and their catalytic activity in oxidation reactions

Cited by 86 publications

References 8 publications

High‐Yield Synthesis of Ethyl Lactate with Mesoporous Tin Silicate Catalysts Prepared by an Aerosol‐Assisted Sol–Gel Process

High‐Yield Synthesis of Ethyl Lactate with Mesoporous Tin Silicate Catalysts Prepared by an Aerosol‐Assisted Sol–Gel Process

Dynamic Nuclear Polarization NMR Enables the Analysis of Sn-Beta Zeolite Prepared with Natural Abundance 119Sn Precursors

Tailoring Distinct Reactive Environments in Lewis Acid Zeolites for Liquid Phase Catalysis

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Dynamic Nuclear Polarization NMR Enables the Analysis of Sn-Beta Zeolite Prepared with Natural Abundance ¹¹⁹Sn Precursors