The conversion of glucose into fructose is widespread in the food industry for the production of the sweetener high-fructose corn syrup, and has also emerged in the field of renewable energy as a path to degrading biomass into fuel or other valuable chemicals. Enzymatic catalysts are typically used for this isomerization, but their lifetime is limited, they require pre-purified substrates, and only work under specific conditions (neutral pH and around 333 K). To remedy these limitations, research is now focusing on chemical catalysts. Basic catalysts have shown promising activity, but are not practical as glucose and fructose easily decompose in alkaline solutions.

Now, Mark Davis and colleagues from the California Institute of Technology have prepared an efficient inorganic, heterogeneous catalyst by incorporating tin centres into a microporous zeolite with large pores (Beta)1. Much lower or no conversion was observed when tin was inserted into an ordered mesoporous silica or a medium-pore zeolite, respectively, showing that the catalyst's activity greatly depends on the size of the pores. The tin–Beta heterogeneous catalyst was efficient even under high glucose concentrations (up to 45%), reusable over three cycles, and remained active after subsequently undergoing a typical zeolite regeneration process (involving calcination at 813 K).

Its activity in acidic aqueous solutions also makes the tin-containing zeolite promising for one-pot processes, as demonstrated with the degradation of starch into fructose, coupling hydrolysis and isomerization steps. The isomerization mechanism remains to be elucidated, but the researchers suggest that it occurs through the formation of a five-membered ring involving the tin centre, followed by an intramolecular hydrogen transfer.