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Graphical abstract Highlights • Hydrogenolysis of HMF to DMF reaction catalyzed by various catalytic systems was reviewed. • Pathways to produce DMF were determined by different catalysts and reaction conditions. • Some noble metal-based catalysts showed good catalytic performance, but needed strict reaction conditions. • Highly active and good recyclable catalysts are needed for DMF production from HMF hydrogenolysis. Abstract 2, 5-dimethylfuran (DMF), which is synthesized through catalytic hydrogenolysis of 5-hydroxymethylfurfural (HMF), is one of the most promising liquid biofuels for transportation because of its high energy density, high boiling point, and water insolubility. In recent years, studies of the hydrogenolysis of HMF to DMF have attracted increasing attention, with numerous novel catalytic systems and significant research achievements being reported as a result. Thus, in this review, we focus on hydrogenolysis of HMF into DMF through various catalytic systems, and systemically summarize the latest advances and progress on this reaction from the perspective of catalysts, including noble and non-noble metal-based catalysts. Moreover, the reaction mechanisms for different catalysts, the limitations and problems in current research, and potential research trends are discussed in this review. [ABSTRACT FROM AUTHOR]

Abstract: Low melting systems consisting of ammonium salts and highly concentrated fructose were used for the conversion of fructose into 5-hydroxymethylfurfural (HMF). Not only acting as solvents, at sufficiently high temperatures, the ammonium salts themselves could also catalyse the dehydration of fructose to HMF. Among those salts, tetraethyl ammonium chloride (TEAC) was found to be the most efficient solvent-catalyst, demonstrated by its ability to achieve 81.3% HMF yield with 33.3wt% fructose concentration at 120°C. 79.2% HMF yield was obtained with 50wt% fructose concentration in the TEAC/fructose system using 5mol% NaHSO4·H2O as a co-catalyst. A semi continuous biphasic system of TEAC/fructose/NaHSO4·H2O melt using tetrahydrofuran (THF) to recover HMF was proposed and demonstrated in a laboratory scale process operating at 120°C. The impurities in the HMF recovered, involving TEAC and NaHSO4·H2O, were determined using 1H NMR, elemental analysis and ICP-OES. [Copyright &y& Elsevier]

[Display omitted] • Humins by-product was employed as carrier to prepare NbO x -based solid catalysts. • The preparation methodology induces structural modifications of the humins carrier. • NbO x is merely homogeneously distributed on the humins-derived carrier. • A high yield to HMF requires a catalyst with an optimum base/acid sites ratio. • In biphasic TBP/water system the yield to HMF reached 96 %, at 180 °C and after 8 h. Highly dispersed supported NbOx species were prepared via a deposition precipitation-carbonization (DPC)-like method. As precursors for niobium species and carrier ammonium niobate(V) oxalate hydrate and humins were used. Characterization of the resulted catalysts indicated bi-functional acid-base niobium species anchored onto a highly hydrophobic graphite-like carbon structure. These catalysts were investigated in the one-pot conversion of glucose to 5-hydroxymethylfurfural (HMF) in a biphasic system consisting of a mixture of a 20 wt% NaCl aqueous solution phase and an organic extracting phase (methyl-isobutyl-ketone (MIBK), 2-tert-butylphenol (TBP) or 2-sec-butylphenol (SBP)). The optimization conditions afforded the highest yield to HMF (96 %) for the GHNb1.2 catalyst (with 2.5 wt%Nb), the base/acid sites ratio of 1.76, in biphasic TBP/water system, at 180 °C after 8 h. [ABSTRACT FROM AUTHOR]