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We present the use of the redox active MIL‐100(Fe) metal‐organic framework (MOF) as a catalyst for the oxidation of 5‐hydroxymethyl furfural (HMF) into 2,5‐furan dicarboxylic acid (FDCA) in water. The MOF is synthesised in water alone under mild hydrothermal conditions and 1H NMR is used to analyse the products of HMF oxidation. The MOF in combination with the co‐catalyst TEMPO provides a total selectivity of desired products of 74 % with a maximum FDCA yield of 57 % seen after 24 hours at only 70 °C. The catalyst is recycled ten times with no loss in activity and no evidence of a reduction in the crystallinity of the MOF. [ABSTRACT FROM AUTHOR]

Metal organic framework UiO‐66 is studied as an adaptable heterogeneous catalyst for glucose conversion. UiO‐66 was modified by; i) partial linker substitution, ii) particle size modulation and iii) linker defects. We studied the effect of crystallinity and functional groups on the glucose conversion and product yields. The main products are: i) fructose from the isomerisation of glucose, ii) mannose from the epimerisation of glucose and iii) 5‐hydroxymethyl furfural from the dehydration of fructose. We found that defective and nano crystalline UiO‐66 catalyst performs best for isomerisation. When 50 % of the linkers of UiO‐66 are replaced by a sulfonate‐containing linker, the catalyst shows higher isomerisation activity than other UiO‐66 catalysts. Naphthalene‐dicarboxylate linkers were introduced to induce hydrophobicity and this catalyst further increased isomerisation activity showing 31 % fructose selectivity. Finally, the promising catalysts were tested in a flow reactor and a bifunctional mixed linker catalyst possessing both hydrophobic and acidic functional groups is shown to be stable in a time‐on‐stream study. [ABSTRACT FROM AUTHOR]

Abstract: Heterogeneous catalysts are desired for the conversion of glucose, the most abundant sugar in renewable biomass, but presently their synthesis requires highly toxic chemicals with long synthesis times. We report the conversion of glucose into fructose and 5‐hydroxymethylfurfural on a heterogeneous catalyst that is stable and selective and operates in the most environmentally benign solvent, water. We used a bifunctional solid with Lewis and Brønsted acid sites by partially replacing the organic linker of the zirconium organic framework UiO‐66 with 2‐monosulfo‐benzene‐1,4‐dicarboxylate. This catalyst showed high product selectivity (90 %) to 5‐hydroxymethylfurfural and fructose at 140 °C in water after a reaction time of 3 h. It was recyclable and showed only a minor loss in activity after the third recycle, offering a realistic solution for the bottleneck glucose isomerization reaction for scale‐up and industrial application of biomass utilization. [ABSTRACT FROM AUTHOR]

A complementary computational and experimental study of the reactivity of Lewis acidic CrCl2, CuCl2 and FeCl2 catalysts towards glucose activation in dialkylimidazolium chloride ionic liquids is performed. The selective dehydration of glucose to 5-hydroxymethylfurfural (HMF) proceeds through the intermediate formation of fructose. Although chromium(II) and copper(II) chlorides are able to dehydrate fructose with high HMF selectivity, reasonable HMF yields from glucose are only obtained with CrCl2 as the catalyst. Glucose conversion by CuCl2 is not selective, while FeCl2 catalyst does not activate sugar molecules. These differences in reactivity are rationalized on the basis of in situ X-ray absorption spectroscopy measurements and the results of density functional theory calculations. The reactivity in glucose dehydration and HMF selectivity are determined by the behavior of the ionic liquid-mediated Lewis acid catalysts towards the initial activation of the sugar molecules. The formation of a coordination complex between the Lewis acidic Cr2+ center and glucose directs glucose transformation into fructose. For Cu2+ the direct coordination of sugar to the copper(II) chloride complex is unfavorable. Glucose deprotonation by a mobile Cl− ligand in the CuCl42− complex initiates the nonselective conversion. In the course of the reaction the Cu2+ ions are reduced to Cu+. Both paths are prohibited for the FeCl2 catalyst. [ABSTRACT FROM AUTHOR]

Stabilization of the CrCl active phase in a thin layer of an ionic liquid covalently grafted to mesoporous silica results in a highly selective catalyst for the dehydration of glucose to 5-hydroxymethylfurfural (HMF) in an aqueous medium. Glucose dehydration in water by using the CrCl-Im-SBA-15 catalyst leads to a 50 % HMF selectivity that can be further increased to up to 70 % by modifying the solvent system. [ABSTRACT FROM AUTHOR]

The cover page of the journal "ChemCatChem" is presented.