Solvent-Activated Hafnium-Containing Zeolites Enable Selective and Continuous Glucose–Fructose Isomerisation

The isomerisation of glucose to fructose is a critical step towards manufacturing petroleum‐free chemicals from lignocellulosic biomass. Herein we show that Hf‐containing zeolites are unique catalysts for this reaction, enabling true thermodynamic equilibrium to be achieved in a single step during intensified continuous operation, which no chemical or biological catalyst has yet been able to achieve. Unprecedented single‐pass yields of 58 % are observed at a fructose selectivity of 94 %, and continuous operation for over 100 hours is demonstrated. The unexpected performance of the catalyst is realised following a period of activation within the reactor, during which time interaction with the solvent generates a state of activity that is absent in the synthesised catalyst. Mechanistic studies by X‐ray absorption spectroscopy, chemisorption FTIR, operando UV/Vis and 1H–13C HSQC NMR spectroscopy indicate that activity arises from isolated HfIV atoms with monofunctional acidic properties.