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Lignocellulosic biomass, a cheap and plentiful resource, could play a key role in the production of sustainable chemicals. The simple sugars contained in the renewable lignocellulosic biomass can be converted into commercially valuable products such as 5-hydroxymethyl furfural (HMF). A platform molecule, HMF can be transformed into numerous chemical products with potential applications in a wide variety of industries. Of the hexoses contained in the lignocellulosic biomass, the successful production of HMF from glucose has been a challenge. Various heterogeneous catalysts have been proposed over the last decade, ranging from zeolites to metal organic frameworks. The reaction conditions vary in the reports in the literature, which makes it difficult to compare catalysts reported in different studies. In addition, the slight variations in the synthesis of the same material in different laboratories may affect the activity results, because the selectivity towards desired products in this transformation strongly depends on the nature of the active sites. This poses another difficulty for the comparison of different reports. Furthermore, over the last decade the new catalytic systems proposed have increased profoundly. In this article, we summarize the heterogeneous catalysts: Metal Organic Frameworks (MOFs), zeolites and conventional supported catalysts, that have been reported in the recent literature and provide an overview of the observed catalytic activity, in order to provide a comparison. [ABSTRACT FROM AUTHOR]

Herein, Zeolitic imidazolate framework-8 (ZIF-8) is considered as an easy and cheap to prepare alternative catalyst for the isomerization of glucose and production of 5-hydroxymethyl furfural (HMF). For the synthesis of the ZIF-8 catalysts two preparation methods were evaluated, being room temperature and hydrothermal synthesis at 140 °C. Of these, the hydrothermal synthesis method yields a material with exceptionally high surface area (1967 m2·g−1). As a catalyst, the ZIF-8 materials generated excellent fructose yields. Specifically, ZIF-8 prepared by hydrothermal synthesis yielded a fructose selectivity of 65% with a glucose conversion of 24% at 100 °C in aqueous reaction medium. However, this selectivity dropped dramatically when the reactions were repeated at higher temperatures (~140 °C). Interestingly, greater quantities of mannose were produced at higher temperatures too. The lack of strong Brønsted acidity in both ZIF-8 materials resulted in poor HMF yields. In order to improve HMF yields, reactions were performed at a lower pH of 1.0. At 140 °C the lower pH was found to drive the reaction towards HMF and double its yield. Despite the excellent performance of ZIF-8 catalysts in batch reactions, their activity did not translate well to the flow reactor over a continuous run of 8 h, which was operating with a residence time of 6 min. The activity of ZIF-8 halved in the flow reactor at 100 °C in ~3 h, which implies that the catalyst's stability was not maintained in the long run. [ABSTRACT FROM AUTHOR]

The metal–organic framework MIL-101(Cr) is known as a solid–acid catalyst for the solution conversion of biomass-derived glucose to 5-hydroxymethyl furfural (5-HMF). We study the substitution of Cr3+ by Fe3+ and Sc3+ in the MIL-101 structure in order to prepare more environmentally benign catalysts. MIL-101(Fe) can be prepared, and the inclusion of Sc is possible at low levels (10% of Fe replaced). On extended synthesis times the polymorphic MIL-88B structure instead forms.Increasing the amount of Sc also only yields MIL-88B, even at short crystallisation times. The MIL-88B structure is unstable under hydrothermal conditions, but in dimethylsulfoxide solvent, it provides 5-HMF from glucose as the major product. The optimum material is a bimetallic (Fe,Sc) form of MIL-88B, which provides ~70% conversion of glucose with 35% selectivity towards 5-HMF after 3 hours at 140 °C: this offers high conversion compared to other heterogeneous catalysts reported in the same solvent. [ABSTRACT FROM AUTHOR]

Utilisation of lignocellulosic agricultural waste biomass could provide a carbon net zero alternative for production of valuable chemicals. However, the progress is hindered because there's no catalyst to carry out a selective and efficient conversion process. In this study a new promising catalyst for this challenging conversion is reported. It is prepared by sulfonation of activated carbon followed by the impregnation of tin (Sn). The catalyst has been characterized by NH 3 -TPD, FTIR, XRF and N 2 physisorption. The catalyst was tested at 120 °C for the conversion of model carbohydrate mixtures prepared in the laboratory and real biomass mixtures of apple fruit biomass waste. The catalytic performance for the conversion of a model carbohydrate mixture resulted in a 5-hydroxymethylfurfural (5-HMF) yield of 30% in 80 min. On the other hand, catalytic testing of real apple pomace biomass showed a 5-HMF yield of 24% in 80 min. The Sn catalyst was also shown to maintain the 5-HMF yield in recycle experiments using a model carbohydrate mixture. Conversely, stability was lower when the Sn catalyst was tested in real apple pomace mixture, which is likely due to the presence of other impurities. • Low temperature (120 °C) conversion of carbohydrates rich agricultural apple fruit waste to 5-HMF. • Cheap and easy method for the preparation of tin doped sulfonated carbon catalysts. • Characterization revealed that the Sn-Fn-Ac catalyst contained both Lewis and Brønsted acidity. • Sn-Fn-AC showed for glucose, fructose and sucrose mixtures 30% 5-HMF yield at conversion of 60%. • Catalytic conversion of carbohydrate mixtures from biomass yielded 24% of 5-HMF respectively. [ABSTRACT FROM AUTHOR]

• Gallium and Tin can be doped in zeolite Y framework successfully. • Ga has similar activity to Sn in the reaction of glucose conversion to HMF. • Ga zeolite Y catalyst can be recycled and regenerated in DMSO. • Ga-Y zeolite gives fructose yield of 5% at 17 % glucose conversion and Sn-Y zeolite gives 17 % yield at 36 % conversion. This study demonstrates the use of gallium and tin modified Y zeolites as catalysts for the conversion of glucose into fructose, mannose and 5-Hydroxymethyl furfural. These catalysts can be synthesised via a simple and scalable procedure that uses commercially available Y zeolite. The catalysts were characterised by various techniques including elemental analysis, electron microscopy, nitrogen physisorption, X-ray diffraction, X-ray photoelectron spectroscopy, ultraviolet-visible spectroscopy, solid state nuclear magnetic resonance spectroscopy and X-ray absorption near edge spectroscopy. It is found that tin containing Y zeolite generate a glucose conversion of 36 % and total product yield of 17 % in water. Meanwhile, gallium containing Y zeolite shows an HMF yield of 33 % when reactions were conducted in DMSO. The recyclability of tin and gallium containing Y zeolites were studied in DMSO and the activities of both materials were shown to remain stable. Furthermore, the spent catalysts can be regenerated via calcination in air. [ABSTRACT FROM AUTHOR]