Abstract
AbstractThe 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
Pressing environmental and societal concerns are driving researchers to develop new processes with minimised reliance on fossil resources.[1]
Our preliminary experiments revealed that amongst a range of analogous Lewis acidic silicate zeolites—each of which was prepared by fluoride-media hydrothermal synthesis (SI Figure S1)—Sn-BEA was the best performing catalyst for GI during batch operation in methanol (MeOH), which was chosen as solvent as it maximises catalyst stability and facilitates downstream processing (Table 1).[9a,b] Other Lewis acidic silicates were either much less active (Ti-BEA, Zr-BEA), or inactive (Hf-BEA), for GI
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 94 %, for over 100 hours on stream
Summary
The isomerisation of glucose to fructose (GI) is a key step towards converting glucose (the most abundant fraction of lignocellulose) into a variety of commercially relevant chemicals, including furanics, levulinates and unsaturated hydroxyesters.[3] enzymes catalyse GI to single pass fructose yields of up to 42 %,[4] development of a solid (heterogeneous) catalyst capable of performing this reaction would be an important step forward, both by improving operational flexibility (temperature, pH, feed purity)[5] and facilitating process intensification.[6] To date, it has become generally appreciated that tin (Sn) containing zeolites ( Sn-BEA) possess the greatest potential for chemocatalytic GI.[7] Zeolites are crystalline, microporous silicates, which in the case of Sn-BEA is a three-dimensional silicate containing dilute amounts of Lewis acidic SnIV atoms within its lattice.[8] the high activity of Sn-BEA for GI has received widespread attention, several negative aspects of its performance are less appreciated, such as its poor stability in the polar solvents required for biomass conversion,[9] and its tendency to catalyse a variety of competitive and/or degradation reactions at operational conditions.[10] The latter is especially problematic, as it wastes a precious resource[1b] and negatively impacts process economics. Productivity isomerisation to be achieved without the undesirable side reactions that plague existing chemo-catalysts
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