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Liquid fuel, such as 2,5‐dimethylfuran (DMF), from biomass, is an efficient, potential alternative to fossil‐based fuels due to its exceptional properties, including lower volatility, a remarkable octane number, heightened energy density, and immiscibility with water. DMF can be the starting substrate for producing bio‐based p‐xylene through the Diels‐Alder reaction with ethylene to produce biobased polyethylene terephthalate (PET). This review, thus, discusses the catalytic role of various precious and non‐precious metals on different supports, such as carbon, metal‐oxide, zeolite, and hydrotalcite, for the production of DMF via catalytic hydrodeoxygenation (HDO) of 5‐hydroxymethylfurfural (HMF) based on the previously reported literature. Various characteristic properties of the employed catalytic materials, such as particle size, metal‐support and substrate interaction, surface area, porosity, and acidic and basic sites, are delineated, playing a crucial role in the HDO of HMF to DMF. The influence of various reaction parameters, such as hydrogen atmosphere, solvents‐ including hydrogen donor solvents‐ and temperature are also discussed. [ABSTRACT FROM AUTHOR]

Sulfonated carbons and commercial Amberlyst 15 and 45 served as model catalysts to explore the impact of the ratio between stronger and weaker acid sites (NS/NW) on 5‐hydroxymethylfurfural (HMF) and furfural production from fructose and xylose. Catalysts with varying structural and surface properties, and consequently different NS/NW ratios, were prepared from diverse templated mesoporous carbons and distinct sulfonation methods. HMF or furfural yields exhibited an exponential correlation with the NS/NW ratio. However, the catalytic activity per site (TON) displayed a volcano‐like plot, reaching a maximum between NS/NW=2–4. Consequently, our findings suggest the involvement of both strong (sulfonic acid) and weak acid (surface carboxylic acid, alcohol, and phenol groups) sites in monosaccharide dehydration mechanisms. These insights may guide the development of novel catalysts. [ABSTRACT FROM AUTHOR]

The selective oxidation of 5‐(Hydroxymethyl)furfural (HMF) to 2,5‐Furandicarboxylic acid (FDCA) is highly attractive for the production of renewable monomers as substitute for fossil‐based monomers. To achieve a sustainable synthesis, we report on advances for a base‐free approach, reducing waste from the process, using air as oxidant and heterogeneous catalysts. Various Carbon‐based supports, which can be bio‐sourced and cost‐efficient, for Pt particles were investigated as they allow for an easy reuse and at the end‐of‐life Pt can be recycled to enable a closed cycle. Commercially available supports with varying properties, which might replace the base, were studied with Pt particles of similar size and loading. Significant differences in the catalytic activity were observed, which were correlated with the O‐functionalities and graphitization degree of the supports derived from Raman spectroscopy, temperature‐programmed desorption, and X‐ray photoelectron spectroscopy. An activated carbon (Norit ROX) rich in quinone/pyrone‐type groups and a carbon black‐based catalyst with graphene‐layers pushed the efficiency with enhanced FDCA‐yields enabling the complete substitution of the homogeneous base. This allows to circumvent the base in this process which together with high selectivity, air as oxidant, a reusable catalyst, and the use of bio‐based feedstock contributes to the sustainability of the production of renewable monomers. [ABSTRACT FROM AUTHOR]

A novel catalytic strategy involving protective chemistry is presented for the selective production of 5‐formylfuran‐2‐carboxylic acid (FFCA) and furan‐2,5‐dicarboxylic acid (FDCA) from concentrated 5‐hydroxymethylfurfural (HMF) solutions. By protecting the reactive formyl group of HMF by acetalization with 1,3‐propanediol (PDO), degradation and premature oxidation of HMF is suppressed. A hydroxyapatite‐supported Au catalyst can selectively oxidize HMF‐acetal in a 10 wt % solution to FFCA‐acetal in 94 % yield in 2 hours at 373 K under 0.5 MPa of O2. Deprotection of FFCA‐acetal by mineral acids affords FFCA in 98 % yield and recovers nearly all PDO. FFCA in a 20 wt % solution can be oxidized to FDCA in 95 % yield under similar reaction conditions. The presented chemistry contributes to the development of novel manufacturing routes of prospective biobased monomer precursors using protecting agents. [ABSTRACT FROM AUTHOR]

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]

Defective D‐CeO2@N/C@TiO2 nanospheres, each comprising a spherical CeO2 core coated with shells of N‐doped carbon and TiO2, were successfully synthesized then evaluated for the aerobic oxidation of 5‐hydroxymethylfurfural (HMF) to 5‐hydroxymethyl‐2‐furancarboxylic acid (HMFCA). Detailed catalyst characterization studies using XRD, SEM, TEM, TG‐DTA, XPS, N2 physisorption confirmed the hierarchical core‐shell structure of the D‐CeO2@N/C@TiO2 nanospheres, with the defective surface structures created through a thermal hydrogenation process using NaBH4 promoting HMF conversion. The effect of various reaction parameters, including the reaction time, temperature, oxygen pressure, type of alkali co‐reactant and the amount of catalyst, on HMF oxidation to HMFCA over the D‐CeO2@N/C@TiO2 nanospheres were studied. Under the optimized reaction conditions (temperature 80 °C, reaction time 30 min, O2 pressure 1 MPa), a high HMF conversion of 87.8 % and a remarkable HMFCA selectivity of 100 % were obtained. In addition, the D‐CeO2@N/C@TiO2 nanosphere catalyst showed great stability over four consecutive HMF oxidation tests, implying good catalyst stability. Experimental findings were used to develop a plausible reaction mechanism for the selective oxidation of HMF on the D‐CeO2@N/C@TiO2 nanospheres. [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]

Efficient oxidation of 5‐hydroxymethylfurfural (HMF) to corresponding furanic products represents an important research focus of biomass valorization, recent research on polyoxometalates (POMs)‐catalyzed aerobic oxidation of HMF usually requires high temperature and sometimes high O2/air pressure. In this work, we report a mild and green approach to photocatalytically transform HMF into various furanic products using atmospheric oxygen as oxidant and POMs as photocatalysts. The influence of different POMs, light sources, and additives were systematically investigated by various experimental and spectroscopic results. Under minimally optimized conditions, 88.0 % HMF can be efficiently photooxidized with as high as 70.2 % furanic yield by TBA‐W10 catalyst after 2 h irradiation of 365 nm UV light when coupling with TEMPO and Na2CO3 as additives. Finally, detailed mechanistic pathways of HMF photooxidation have been proposed to illustrate the transformation of HMF to various furanic products. This work provides some insightful guidelines for photooxidation of biomass‐derived platform chemicals to value‐added products under efficient, mild, and green conditions, exhibiting potential practical applications in the future. [ABSTRACT FROM AUTHOR]

The selective hydroconversion of 5‐hydroxymethylfurfural (HMF) to biofuels is currently highly sought‐for. While the literature has demonstrated that this reaction is possible on promoted Ni catalysts, we show here that a monometallic, non‐promoted Ni/SBA‐15 catalyst, prepared by incipient wetness impregnation, can convert HMF to 2,5‐dimethylfuran (DMF) and to 2,5‐dimethyltetrahydrofuran (DMTHF) at 180 °C, in a consecutive way. Through a control over reaction time, high yields to DMF (71 %, at conversion of 93 %) or DMTHF (97 %, at conversion of 100 %) can be achieved. Kinetic modelling suggests a preferential route to DMF via 5‐methylfurfural (MFFR) as intermediate, though the route via 2,5‐bis(hydroxylmethyl)furan (BHMF) is also present. The favored route in the experimental conditions involves the hydrogenolysis of the hydroxyl group of HMF as first step, followed by the hydrogenation of the aldehyde function, to methylfurfuryl alcohol (MFOL). It is suggested a higher reaction rate of hydrogenation or hydrogenolysis of the side group is linked to the presence of a methyl group in the molecule. No hydrogenation of the furan ring is detected on the intermediates. [ABSTRACT FROM AUTHOR]

Within the last decade, interest in using biphasic systems for producing furans from biomass has grown significantly. Biphasic systems continuously extract furans into the organic phase, which prevents degradation reactions and potentially allows for easier separations of the products. Several heterogeneous catalyst types, including zeolites, ion exchange resins, niobium‐based, and others, have been used with various organic solvents to increase furan yields from sugar dehydration reactions. In this minireview, we summarized the use of heterogeneous catalysts in biphasic systems for furfural and 5‐hydroxymethylfurfural production from the past five years, highlighting trends in chemical and physical properties that effect catalytic activity. Additionally, the selection of an organic solvent for a biphasic system is extremely important and we review and discuss properties of the most commonly used organic solvents. Reviewing biomass media: There is a significant amount of research available on the topic of furan production from sugars and biomass in biphasic solvent systems. Herein, we present trends in heterogeneous catalyst properties and solvent selection that emerged from papers published within the last five years. [ABSTRACT FROM AUTHOR]

Abstract: Catalytic transformation of biomass‐derived compounds to different platform chemicals and liquid fuel is a prominent way to reduce the global dependence on fossil resources. In past few decades, biomass‐derived furans such as 2‐furfuraldehyde (furfural) and 5‐hydroxymethyl‐2‐furfural (HMF) have received outstanding attention because of their wide applications in the production of various industrially important value‐added chemicals and fuel components. Various catalytic systems and methodologies have been extensively explored for the transformation of these furans to a wide range of products including open ring diketones, ketoacids, alcohols and long chain alkanes. This Review is aimed to provide an extensive overview of the recent developments of several high‐performing heterogeneous catalysts for the catalytic upgradation of the key biomass‐derived furans (furfural and HMF) to value‐added chemicals. Moreover, the role of these catalysts in the catalytic transformations including hydrogenation, decarbonylation, oxidation, hydrogenolysis and ring opening reactions, and the mechanistic pathways are also highlighted in this Review. [ABSTRACT FROM AUTHOR]

Nanosized phosphated TiO2 catalysts with different phosphate contents were synthesized and tested for the conversion of glucose to 5-hydroxymethylfurfural. The resulting materials were characterized by using N2-adsorption, XRD, inductively coupled plasma atomic emission spectroscopy, X-ray spectroscopy, TEM, temperature-programmed desorption of ammonia, and FTIR spectroscopy of pyridine adsorption techniques to determine their structural, bulk, surface, and acid properties. We found that TiO2 nanoparticles catalyzed this reaction under mild conditions in a water-butanol biphasic system. The incorporation of phosphorus into the TiO2 framework remarkably enhances the target product selectivity, which is ascribed to increased surface area, enhanced acidity, as well as thermal stability resulting from the TiOP bond formation. Under optimal reaction conditions, phosphated TiO2 was found to exhibit excellent catalytic performance, which resulted in 97 % glucose conversion and 81 % HMF yield after 3 h of reaction at 175 °C. More importantly, the catalyst showed good stability and could be reused for several reaction cycles. [ABSTRACT FROM AUTHOR]

More information can be found in the Research Article by E. J. M. Hensen, K. Nakajima and co-workers. Keywords: biomass; FDCA; heterogeneous catalysis; HMF; protection strategy EN biomass FDCA heterogeneous catalysis HMF protection strategy 1 1 1 08/23/22 20220819 NES 220819 B The Front Cover b presents the stepwise oxidation of concentrated 5-hydroxymethylfurfural (HMF), protected as its acetal with 1,3-propanediol, to selectively produce the biobased monomers 5-formylfurancarboxylic acid (FFCA) and 2,5-furandicarboxylic acid (FDCA). The weakly-acidic nature of the support prevents premature deprotection and overoxidation of the produced FFCA, still protected as its 1,3-propanediol acetal. [Extracted from the article]