Tin-containing zeolites are highly active catalysts for the isomerization of glucose in water

Abstract

The isomerization of glucose into fructose is a large-scale reaction for the prodn. of high-fructose corn syrup (HFCS; reaction performed by enzyme catalysts), and recently, is being considered as an intermediate step in the possible route of biomass to fuels and chems. Here, we show that a large pore zeolite that contains tin (Sn-Beta) is able to isomerize glucose to fructose in aq. media with high activity and selectivity. For example, a 10 wt% glucose soln. contg. a catalytic amt. of Sn-Beta (1:50 Sn:glucose molar ratio) gives product yields of approx. 46% (wt./wt.) glucose, 31% (wt./wt.) fructose, and 9% (wt./wt.) mannose after 30 and 12 min of reaction at 383 K and 413 K, resp. 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. Addnl., the Sn-Beta catalyst is able to perform the isomerization reaction in highly acidic, aq. environments with equiv. 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 (starch to fructose and glucose to 5- hydroxymethylfurfural (HMF) demonstrated here). Details of the catalyst prepn. and reaction mechanism will be presented as well as discussions on how this new catalyst system could be integrated into larger reaction networks.