Abstract
The isomerization of 1,3‐dihydroxyactone and d‐glucose over Sn‐Beta zeolite was investigated by in situ 13C NMR spectroscopy. The conversion rate at room temperature is higher when the zeolite is dehydrated before exposure to the aqueous sugar solution. Mass transfer limitations in the zeolite micropores were excluded by comparing Sn‐Beta samples with different crystal sizes. Periodic density functional theory (DFT) calculations show that sugar and water molecules compete for adsorption on the active framework Sn centers. Careful solvent selection may thus increase the rate of sugar isomerization. Consistent with this prediction, batch catalytic experiments show that the use of a co‐solvent, such as tetrahydrofuran, that strongly interacts with the Sn centers suppresses glucose isomerization. On the other hand, the use of ethanol as cosolvent results in significantly higher isomerization activity in comparison with pure water because of decreased competition with glucose adsorption on zeolitic Sn sites.
Highlights
The isomerization of 1,3-dihydroxyactone and d-glucose over Sn-Beta zeolite was investigated by in situ 13C NMR spectroscopy
Isomerization of glucose into fructose is important for two reasons: 1) catalyzed by glucose isomerase, this reversible reaction is used at the industrial scale to produce high-fructose corn syrup; 2) in addition, the aldose-ketose isomerization is at the center of the attention of the scientific community in the context of biomass valorization into fuels and chemicals, as fructose can be readily dehydrated in high yield to 5-hydroxymethylfurfural, a prospective platform molecule.[1,2,3,4]
SnBeta can isomerize hexoses, pentoses, and trioses by intramolecular hydride and carbon shift reactions in various solvents.[8,10,11,12]. Another platform molecule is lactic acid, which can be obtained from fructose via retro-aldol condensation[13,14] and hydride shift reactions involving 1,3-dihydroxyacetone and glyceraldehyde as intermediates (Scheme 1)
Summary
The isomerization of 1,3-dihydroxyactone and d-glucose over Sn-Beta zeolite was investigated by in situ 13C NMR spectroscopy. The use of ethanol as cosolvent results in significantly higher isomerization activity in comparison with pure water because of decreased competition with glucose adsorption on zeolitic Sn sites.
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