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. Hafnium zeolites are shown to catalyse glucose–fructose isomerisation to thermodynamic equilibrium during continuous operation, which no chemical catalyst has yet been able to achieve. Fructose yields of 58 % are observed at a selectivity of 94 %. Structure–activity relationships are developed with X‐ray absorption spectroscopy, chemisorption FTIR, operando UV/Vis and HSQC NMR spectroscopy.