Selective production of lactitol from lactose using the Lewis acid site of MOF catalysts without exogenous hydrogen

Abstract

Lactose is found in the residue obtained from the separation of high value-added proteins from whey and can be used to solve the problem of waste generated by the agri-food industry through upgrading lactose into more valuable derivatives, such as lactitol. However, the production of lactitol is usually under high pressure and requires the exogenous addition of H₂ using nickel-, palladium-, and ruthenium-based catalysts. Consequently, lactitol has a high production cost. In this study, a Fe-based metal–organic framework with Lewis acid sites (MIL-101(Fe)) has been constructed to convert lactose into lactitol. The production of lactitol using MIL-101(Fe) did not require high pressure and the exogenous addition of H₂. The MIL-101(Fe) exhibited a high lactose conversion of 97.66% and a remarkable selectivity of 99.99% lactitol in the conversion of lactose to lactitol. Our mechanistic findings suggest that the Lewis acid site of MIL-101(Fe) activates C₍₁₎–O₍₅₎ in the glucose portion of lactose, while DMSO interacts with Fe–OH, allowing H˙ from water cleavage to transfer it to the etheric-oxygen of the glucopyranose ring, leading to the cleavage of C₍₁₎–O₍₅₎ to open the ring and convert lactose to lactitol. Furthermore, MIL-101(Fe) exhibited good stability and reusability with no significant loss in its catalytic activity observed after five consecutive cycles.