Solid State NMR Characterization of Sn-Beta Zeolites that Catalyze Glucose Isomerization and Epimerization

Tin-containing zeotypes, particularly Sn-BEA, are promising heterogeneous catalysts for a number of important industrially relevant reactions. However, the direct hydrothermal synthesis of these materials requires unfavourably long times, which is an obstacle for their industrial application. In the present study we show that up to 4-fold reduction of the crystallization time can be achieved by the decreasing of the H2O/SiO2 ratio in the synthesis gel from 7.5 to 5.6. The crystallization kinetics has been studied for five series of gels containing 1.0 SiO2 : 0.27 TEA2O : x SnO2 : 0.54 HF : y H2O, for which y was fixed to 5.6, 6.8 and 7.7 at x = 0.005 and to 5.6 and 6.8 at x = 0.010. The crystallization time was varied within 0.5 -60 days. The intermediate and final products obtained were investigated using XRD, FTIR, XRF, SEM, UV-Vis, MAS NMR spectroscopy and nitrogen adsorption-desorption techniques. The products obtained with lower water content are shown to have the same structure, textural properties and morphology as materials synthesized with higher water content.Although the size of the crystals is found to decrease with water content in the gel, it does not affect the Sn coordination and environment as confirmed by 119 Sn MAS NMR.

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“…-436 was also reported previously 37 but was not assigned. The quantitative analysis of the spectra in Fig.…”

Section: Characterization Of Sn-sitesmentioning

confidence: 57%

Accelerated synthesis of Sn-BEA in fluoride media: effect of H₂O content in the gel

et al. 2016

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“…Davis and coworkers already observed differences in the relative ratios of the resonances in the 119 Sn‐NMR spectra between two batches of Sn‐ β prepared following the same recipe. [28a] This effect is even more pronounced comparing hydrothermal Sn‐ β samples prepared following similar, but different synthesis protocols in different research groups ( Fig. ).…”

Section: Resultsmentioning

confidence: 95%

“…[7a][20a][21b][21c][28] Upon dehydration, these resonances shift downfield and appear in the range of −420 to −465 ppm. [7a][17b][28] Davis and coworkers differentiated between open and closed sites by cross polarization (CP) experiments on dehydrated Sn‐ β and found that the signals at around −425 ppm and −445 ppm correspond to defect‐open and closed sites, respectively. [20a] Saturating Sn‐ β with ammonia and evacuating at 120 °C allowed correlation of the −425 ppm resonance in 119 Sn‐NMR with the Sn site giving rise to the C≡N vibration at 2316 cm −1 in CD 3 CN IR spectra.…”

Section: Introductionmentioning

confidence: 99%

Identifying Sn Site Heterogeneities Prevalent Among Sn‐Beta Zeolites

Wolf

Liao

Ong

et al. 2016

Helvetica Chimica Acta

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In recent years, various protocols on preparing Lewis acidic Sn‐β zeolite hydrothermally and postsynthetically have been reported. However, very little is known about the effects of different synthesis protocols on the Sn(IV) speciation in the final material. Even the effects of individual synthesis parameters within a certain preparation method have not been studied systematically. Here, we demonstrate that hydrothermally synthesized Sn‐β zeolites prepared via very similar recipes show significantly different 119Sn‐NMR spectra, suggesting different Sn site speciation. Among postsynthetically prepared Sn‐β zeolites, less variation in the resulting 119Sn‐NMR spectra have been observed, indicating a more reproducible synthesis procedure compared to hydrothermal synthesis in fluoride media. This work highlights the importance of 119Sn‐NMR measurements to elucidate the precise local geometry of the Sn heteroatoms in Sn‐β, and the need to quantify the number of reactive Sn sites on each sample that participate in a given catalytic reaction, in order to accurately compare materials prepared by different routes.

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“…Thus, to better understand the changes that occur to the Sn sites of the zeolite during operation, 119 Sn MAS NMR experiments were performed. [37][38] In line with recent developments, spectra were recorded by Carr-Purcell-Meiboom-Gill (CPMG) echo-train acquisition methods, as exemplified by the Ivanova group. 39,40 Due to the signal enhancements made possibly by CPMG methods, spectra could be recorded on materials containing naturally abundant quantities of Sn.…”

Section: Resultsmentioning

confidence: 99%

Active Site Hydration Governs the Stability of Sn-Beta during Continuous Glucose Conversion

2018

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The stability of Sn-Beta for the continuous upgrading of hexoses is improved dramatically upon the addition of small amounts of water to the methanol/sugar reaction feed, despite water itself being an unfavourable solvent. Herein, the molecular level origin of this effect is investigated. Spectroscopic studies of the catalytic materials pre-, post-and during operation, with operando UV-Vis, 119 Sn CPMG MAS NMR, DRIFTS-MS, TGA, TPD/O-MS and porosimetry, are coupled to additional kinetic studies, to generate detailed structure-activity-lifetime relationships. In doing so, we find that the addition of water influences two particular processesfouling and active site modification. However, mitigating the second is the most crucial role of water. Indeed, in the absence of water, the loss of Sn-OH and Si-OH sites occurs. Notably, these changes in active site hydration correlate to deactivation and reactivation of the system. The consequences of these findings, both for mechanistic understanding of the system in addition to the design of alternative regeneration methods, are also discussed.

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Solid State NMR Characterization of Sn-Beta Zeolites that Catalyze Glucose Isomerization and Epimerization

Cited by 40 publications

References 20 publications

Accelerated synthesis of Sn-BEA in fluoride media: effect of H₂O content in the gel

Accelerated synthesis of Sn-BEA in fluoride media: effect of H₂O content in the gel

Identifying Sn Site Heterogeneities Prevalent Among Sn‐Beta Zeolites

Active Site Hydration Governs the Stability of Sn-Beta during Continuous Glucose Conversion

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Solid State NMR Characterization of Sn-Beta Zeolites that Catalyze Glucose Isomerization and Epimerization

Cited by 40 publications

References 20 publications

Accelerated synthesis of Sn-BEA in fluoride media: effect of H2O content in the gel

Accelerated synthesis of Sn-BEA in fluoride media: effect of H2O content in the gel

Identifying Sn Site Heterogeneities Prevalent Among Sn‐Beta Zeolites

Active Site Hydration Governs the Stability of Sn-Beta during Continuous Glucose Conversion

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Product

Resources

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Accelerated synthesis of Sn-BEA in fluoride media: effect of H₂O content in the gel

Accelerated synthesis of Sn-BEA in fluoride media: effect of H₂O content in the gel