Stannate-catalysed glucose-fructose isomerisation in alcohols

摘要

Isomerisation of glucose to fructose is a crucial step in the valorisation of biomass-derived carbohydrates to renewable chemicals, polymers, and fuels. Glucose isomerisation is base-catalysed but superior catalytic activity can be obtained with Lewis acidic materials such as Sn-beta zeolite, where partially hydrolysed framework Sn-sites, Sn-(OH)x, are considered the catalytically active sites. Alkali-metal stannate salts (MxSnO3·3H2O) contain a similar type of Sn-(OH)x sites in the form of [Sn(OH)6]2-complex anions. In this work, we report the use of M2SnO3·3H2O (M = Na, K) as effective catalysts for glucose-fructose iso-merisation in alcohols. Isotope-labelling experiments and kinetic studies demonstrated that the iso-merisation with Na2SnO3·3H2O proceeded in methanol by base-catalysis via a proton-transfer mechanism with a low activation energy (63.5 ± 7.0 kJ mol~(-1)). This allowed the stannate to facilitate a higher fructose yield and a higher fructose selectivity than Sn-beta within a shorter reaction time at a lower reaction temperature. Furthermore, in isopropanol and higher alcohols where the stannates are insoluble the reaction proceeded heterogeneously, thus suggesting the catalytic system to be a green and viable alternative to other soluble catalyst systems.