Abstract
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.
Highlights
Its unique performance is maintained even at elevated temperature (
Hf-containing zeolites are shown to be unique catalysts for glucose-fructose isomersation, enabling unprecedented single pass yields of 58% to be achieved at a fructose selectivity of RESEARCH ARTICLE 94%, for over 100 hours on stream
Spectroscopic studies by X-ray Absorption Spectroscopy (XAS), chemisorption FTIR, operando UV-Vis and 1H-13 C HSQC NMR suggest the activity of Hf-BEA arises from the presence of isolated Hf(IV) atoms with monofunctional Lewis acidic properties
Summary
204 15 converted, from 33.6 % to 66.2 %. Fitting of the EXAFS data (Table 2) revealed two clear first shell Hf-O paths in the catalyst samples, compared to a single Hf-O path in monoclinic HfO2 that was fitted to represent the 7 very similar Hf-O paths seen in monoclinic HfO2.21 The first Hf-O path in all the catalyst samples was found at 2.00 Å, and possessed a coordination number of 4 These values are in excellent agreement to those we determined for Sn-BEA during previous XAS studies,20a and this path can be attributed to Hf atoms present in the BEA framework. Separation of the product mixture by reduced pressure distillation revealed that the isolated product formed at 140 °C was a white, crystalline solid, confirming the absence of Maillard browning processes even during high temperature operation with Hf-BEA (SI Figure S10)
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