Stoichiometric active site modification observed by alkali ion titrations of Sn-Beta

Elliot, Samuel Gilbert; Tosi, Irène; Meier, Sebastián; Martínez-Espín, Juan S.; Tolborg, Søren; Taarning, Esben

doi:10.1039/c9cy01189g

Cited by 12 publications

(16 citation statements)

References 39 publications

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“…Previous studies have shown how the addition of small quantities of alkali salts can improve the selectivity of certain Sn-Beta catalysts toward retro-aldol fragmentation. 12 , 21 , 22 , 30 , 55 It has been proposed that the effect of alkali salts arises from their ability to exchange protons present in the active site environment, thereby minimizing the partial Brønsted acidity of Sn-Beta materials and favoring the retro-aldol fragmentation pathway. 21 , 55 However, the susceptibility of different preparations of Sn-Beta catalysts for the alkali effect in continuous flow has not yet been evaluated.…”

Section: Resultsmentioning

confidence: 99%

High-Productivity Continuous Conversion of Glucose to α-Hydroxy Esters over Postsynthetic and Hydrothermal Sn-Beta Catalysts

Botti

Navar

Tolborg

et al. 2022

ACS Sustainable Chem. Eng.

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The retro-aldol fragmentation of glucose is a complex reaction of industrial relevance, which provides a potentially sustainable route for the production of α-hydroxyester compounds of relevance to the green polymer industry, such as methyl lactate and methyl vinyl glycolate. Although the zeolite catalyst, Sn-Beta, has shown itself to be a promising catalyst for this process, important information concerning the stability of the catalyst during continuous operation is not yet known, and improvements to its yield of retro-aldol products are also essential. Here, we perform detailed spectroscopic studies of a selection of Sn-Beta catalysts and evaluate their performances for the retro-aldol fragmentation of glucose under continuous processing conditions, with the dual aims of developing new structure–activity–lifetime relationships for the reaction and maximizing the productivity and selectivity of the process. Kinetic studies are performed under both established reaction conditions and in the presence of additional promoters, including water and alkali salts. Generally, this study demonstrates that the reaction conditions and choice of catalyst cannot be optimized in isolation, since each catalyst explored in this study responds differently to each particular process perturbation. However, by evaluating each type of the Sn-Beta catalyst under each set of reaction conditions, we reveal that postsynthetic Sn-Beta catalysts exhibit the best levels of performance when activity, selectivity, and stability are taken into account. Specifically, the best levels of performance are obtained with a postsynthetic Sn-Beta catalyst that is preactivated in a flow of methanol prior to reaction, which provides α-hydroxyester yields over 90% at the early stages of continuous operation and operates at high yield and selectivity for over 60 h on stream. Space–time-yields over two orders of magnitude higher than any previously reported for this reaction are achieved, setting a new benchmark in terms of the retro-aldol fragmentation of glucose.

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Section: Resultsmentioning

confidence: 99%

High-Productivity Continuous Conversion of Glucose to α-Hydroxy Esters over Postsynthetic and Hydrothermal Sn-Beta Catalysts

Botti

Navar

Tolborg

et al. 2022

ACS Sustainable Chem. Eng.

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“…This phenomenon seems to be related to a saturation effect of the tin catalytic sites with K + ions, blocking the access of the monosaccharide substrates to Sn sites and thus reducing the catalytic efficiency of the materials in retro-aldol condensation transformations. 35 …”

Section: Resultsmentioning

confidence: 99%

Efficient Conversion of Glucose to Methyl Lactate with Sn-USY: Retro-aldol Activity Promotion by Controlled Ion Exchange

Jimenez-Martin

Orozco-Saumell

Hernando

et al. 2022

ACS Sustainable Chem. Eng.

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Sn-USY materials have been prepared through an optimized post-synthetic catalytic metalation procedure. These zeolites displayed, upon ion exchange with alkaline metals, an outstanding activity in the direct transformation of glucose into methyl lactate, yielding more than 70% of the starting glucose as the target product, and an overall combined retro-aldol condensation product yield above 95% in a short reaction time (<4 h). This outstanding catalytic performance is ascribed to the neutralization of Brønsted acid sites, the consequent depression of side reactions, and a higher population of tin open sites in the ion-exchanged Sn-USY zeolites. Reusability tests evidenced some loss of catalytic activity, partially caused by the closing of tin sites, although the use of small amounts of water in the reaction media demonstrated that this deactivation mechanism can be, at least, partially alleviated.

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“…MCM-48, instead, is typically prepared in mixtures rich in sodium or potassium, which remain on the surface of the material . For the isomerization of glucose, it is well-known that the presence of these cations affects the reaction mechanism. ,,, To highlight the presence of the cation, the materials were named K + /Sn-MCM-48. Note that this is a typical MCM-48 and has not undergone any modification (except for the introduction of Sn).…”

Section: Resultsmentioning

confidence: 99%

Isomerization and Epimerization of Glucose Catalyzed by Sn-Containing Mesoporous Silica

Lorenti

Scolari

Cabral

et al. 2021

Ind. Eng. Chem. Res.

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Herein, we propose methodologies for the direct syntheses of Sn-containing MCM-41, SBA-16, MCM-48 with tin loadings between 1.5 and 4.5%. The catalysts were active in the isomerization of glucose to fructose, and the sample containing 3.0% of Sn showed the highest selectivity. Compared to the other structures, Sn-MCM-48 displayed a lower selectivity to fructose and a higher one to mannose, which is due to the presence of K+ remaining from the synthesis gel. Interestingly, the TOFFru is similar for Sn-MCM-41(3.0%) and K+/Sn-MCM-48(3.0). For K+/Sn-MCM-48(3.0%), the TOFMan and TOFFru were comparable. The presence does not affect the rate of fructose formation, but it promotes side reactions that involve glucose epimerization to mannose and, more importantly, the decomposition of glucose to unidentified products. Indeed, the ratio (TOFFru+TOFMan)/TOFGlu was 0.79, 0.37, and 0.81 for Sn-MCM-41, K+/Sn-MCM-48, and Sn-SBA-16(3.0%). The lowest TOF for fructose formation was observed for Sn-SBA-16(3.0%), which can be attributed to the high contribution of Sn in high coordination and extra framework tin oxide. For the direct conversion of glucose to HMF, Sn-MCM-41(3.0%), K+/Sn-MCM-48(3.0%), and Sn-SBA-16(3.0%) were combined with HCl, reaching selectivities of 77, 73, and 67%, respectively. These results are comparable or superior to those previously reported.

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Stoichiometric active site modification observed by alkali ion titrations of Sn-Beta

Abstract: Titrations and functional assays are combined to gain insight into the stoichiometric correlations for alkali ions and the tin active sites in Sn-Beta, and show that three different states with distinct catalytic properties exist.

Cited by 12 publications

References 39 publications

High-Productivity Continuous Conversion of Glucose to α-Hydroxy Esters over Postsynthetic and Hydrothermal Sn-Beta Catalysts

High-Productivity Continuous Conversion of Glucose to α-Hydroxy Esters over Postsynthetic and Hydrothermal Sn-Beta Catalysts

Efficient Conversion of Glucose to Methyl Lactate with Sn-USY: Retro-aldol Activity Promotion by Controlled Ion Exchange

Isomerization and Epimerization of Glucose Catalyzed by Sn-Containing Mesoporous Silica

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