(264b) Tin-Containing Zeolites Are Highly Active Catalysts for the Isomerization of Glucose in Water

The isomerization of glucose into fructose is a large-scale reaction for the production of high-fructose corn syrup and, recently, is being considered as an intermediate step in the possible route of biomass to fuels and chemicals. Although the isomerization of glucose to fructose can be performed under mild conditions using either biological or chemical catalysts, the preferred industrial isomerization method involves the use of an immobilized enzyme (xylose isomerase) at 333 K, that generates an equilibrium mixture of 42% (w/w) fructose, 50% (w/w) glucose, and 8% (w/w) other saccharides. Here, it is shown that a large pore zeolite that contains tin (Sn-Beta) is able to isomerize glucose to fructose in aqueous media with high activity and selectivity. Specifically, a 10 wt% glucose solution containing a catalytic amount of Sn-Beta (1:50 Sn:glucose molar ratio) gives product yields of approximately 46% (w/w) glucose, 31% (w/w) fructose, and 9% (w/w) mannose after 30 and 12 minutes of reaction at 383 K and 413 K, respectively. This reactivity is achieved also when a 45 wt% glucose solution is used. The properties of the large pore zeolite greatly influence the reaction behavior as the reaction does not proceed with a medium pore zeolite, and the isomerization activity is considerably lower when the metal centers are incorporated in ordered mesoporous silica (MCM-41). The Sn-Beta catalyst can be used for multiple cycles, and the reaction stops when the solid is removed, clearly indicating that the catalysis is occurring heterogeneously. Most importantly, the Sn-Beta catalyst is able to perform the isomerization reaction in highly acidic, aqueous environments with equivalent activity and product distribution as in media without added acid. This enables Sn-Beta to couple isomerizations with other acid-catalyzed reactions, including hydrolysis/isomerization or isomerization/dehydration reaction sequences, including starch to fructose and glucose to 5-hydroxymethylfurfural (HMF).