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

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 1 H-13 C HSQC NMR spectroscopy indicate that activity arises from isolated Hf IV atoms with monofunctional acidic properties.

Tailoring Lewis/Brønsted acid properties of MOF nodes via hydrothermal and solvothermal synthesis: simple approach with exceptional catalytic implications

“…In both MOF samples, Hf 4+ is the main oxidation state due to the position of the rst derivative at $9563 eV, 50,51 corroborating the results obtained in the XPS analysis. The intense whiteline (related to the 2p 3/2 / 5d electronic transition) of the MOFs is similar to that of other Hfbased materials, 50 which is stronger in the Hf-MOF-808_DMF followed by the Hf-MOF-808_H 2 O sample. EXAFS data (see Table S3 and Fig.…”

Mechanistic Studies of Continuous Glucose Upgrading over Lewis Acidic Silicates by Operando UV–Vis and HSQC NMR

“…Kinetic data generated during these experiments are shown in Figure 6, right. In line with our recent studies, the reaction effluent generated during the continuous conversion of glucose over Hf-Beta 30 only contained detectable quantities of glucose, fructose and mannose, with no loss of carbon balance observed. At the reaction conditions measured, the total yield of selective (GI) products when using Hf-Beta was 30 %.…”

“…We also note that Hf-Beta was first activated in a flow of methanol for 20 h prior to reaction, which we recently demonstrated to be important for activity to be observed during low temperature GI. 30 Whilst the operando UV-Vis spectra generated during glucose upgrading at 110°C with Sn-Beta consisted of absorbances at  440 ,  330 and  360 , the spectra from Hf-Beta did not show any absorbance at  440 (Figure 6, left). Moreover, although the overall intensity of the spectrum was lower in the 330-380 nm region, this was clearly due to the absence of any major absorbance at  360 , as highlighted by the differential spectrum.…”

“…Firstly, operando UV-Vis was performed on a sample of Hf-containing zeolite Beta, which we recently demonstrated to be able to selective catalyse GI to thermodynamic equilibrium without initiating non-selective pathways. 30 We note that the basic characterisation of this material was recently published in reference 30. Figure 6 shows the operando UV-Vis spectrum generated by the catalytic conversion of glucose over Hf-Beta at 110 °C (Si/Hf molar ratio of 200), alongside the operando UV-Vis spectrum from the 10Sn-Beta SSI catalysed reaction at otherwise identical conditions.…”

Catalytically active Rh species stabilized by zirconium and hafnium on zeolites

“…indicates that Hf/S-1 exhibits absorption bands at 200 nm and 220-260 nm, which are ascribed to the isolated Hf(IV) and HfO x clusters, respectively. [39][40][41] The Rh/S-1 sample shows absorption bands at 260 nm and 320 nm, ascribed to the Rh-O charge transfer and the 1 A 1g → 1 T 1g transition, respectively. 42 Thus, the absorption bands of RhHf/S-1 at 200 nm and 260 nm can be the superposition of two different bands (Fig.…”