Current Advances in the Sustainable Conversion of 5-Hydroxymethylfurfural into 2,5-Furandicarboxylic Acid

Pulcherrimin: a bio-derived iron chelate catalyst for base-free oxidation of 5-hydroxymethylfurfural to furandicarboxylic acid

This study explores the green and sustainable catalytic properties of pulcherrimin, a naturally occurring iron chelate, for the base-free oxidation of 5-hydroxymethylfurfural (5-HMF) to high-value products such as 2,5-furandicarboxylic acid (FDCA), a vital precursor for renewable bioplastics. Pulcherrimin, derived from Metschnikowia pulcherrima, selectively oxidised 5-HMF to 5,5-diformylfuran (DFF) at 100 °C, while at 120 °C, the oxidation proceeded efficiently to FDCA with a conversion of 73.3 ± 1.1%, and FDCA selectivity of 89.0 ± 1.9% under mild, base-free conditions. Adding a mild base enhanced overall conversion but diverted the reaction pathway towards 5-hydroxymethyl-2-furancarboxylic acid (HMFCA), reducing the FDCA yield. The reusability of the pulcherrimin catalyst was tested over five reaction cycles, retaining a conversion activity of 59.1% and FDCA selectivity of 39.8%. These findings establish pulcherrimin as a promising, water-tolerant biocatalyst with potential environmental advantages, such as base-free operation and simplified product recovery, contributing to greener catalytic processes. Eliminating a homogenous base co-catalyst makes the process greener by avoiding the need for subsequent neutralisation steps while reducing environmental and economic costs.

Mechanistic Insights into the Aerobic Oxidation of 2,5-Bis(hydroxymethyl)furfural to 2,5-Furandicarboxylic Acid on Pd Catalysts

2,5-Furandicarboxylic acid (FDCA) is one of the top selected value-added chemicals, which can be obtained by the aerobic oxidation of 2,5-bis(hydroxymethyl)furfural (BHMF) over a Pd-based catalyst. However, the elucidation of the reaction mechanism was hindered by its rapid kinetics. Herein, employing the density functional theory (DFT) calculations, we delve into the detailed reaction pathways of the BHMF oxidation into FDCA over Pd(111) and PdHx(111) identifying the rate-determining steps. The results demonstrated that 2,5-diformylfuran (DFF) and 5-formyl-2-furancarboxylic acid (FFCA) are the important intermediates, while the oxidation of FFCA is the rate-limiting step with the energy barrier of 0.68 and 0.51 eV on Pd(111) and PdH1/4(111), respectively. By comparison of the d-band center of Pd(111) and PdHx(111) surfaces and the overall energy barrier of this reaction over these two surfaces, it makes clear that the occupation of H atoms in the Pd bulk changes the surface electronic structures and enhances the binding energy of BHMF with the PdHx surface, which consequently speeds up the conversion of BHMF into FDCA. Water plays a crucial role in facilitating the activation of O2 via the H-transfer by constructing a hydrogen-bonding chain with the O2 and OH*. The activation of molecular oxygen experiences enhancement through the synergy of OH* and H2O, resulting in the production of actomic oxygen (O*). Both O* and OH* actively participate in the BHMF oxidation, where O* improved the activation toward initial critical reaction pathways on Pd(111) while OH* exhibited its pronounced impact on the latter two key processes on both Pd(111) and PdH1/4(111). This study will contribute to well understanding the oxidation mechanism of BHMF into FDCA over Pd-based catalysts and establish a theoretical framework for the potential development of an effective catalyst.

Nitrogen-doped graphene supported single-atom catalysts for efficient electrocatalytic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid: a density functional theory study

Electrocatalytic oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) is a promising alternative for oxygen evolution reactions. The search for efficient catalysts has been attracting increasing scientific attention. This work explores the performance of nitrogen-doped graphene-supported single-atom catalysts (M-NC SACs) for the reaction. Hydroxide was found to compete with HMF for the adsorption site on early transition metal SACs. Electronic structure analysis showed that only the electron density of the functional group directly bonded to the metal site is significantly perturbed upon adsorption. Two reaction free energies were identified as descriptors for constructing the activity volcano. Scaling relation analysis elucidated the general mechanism of the reaction including the trend for the activation of the aldehyde and alcohol groups of HMF, the potential-limiting steps, and the preferred reaction pathways. In general, the reaction is limited by an aldehyde/alcohol oxidation step in the scenarios of weak/strong adsorption regardless of the reaction pathways. Nine promising candidate catalysts were proposed, including Mn, Sc, Co, Cd, Ru, Y, Cr, Fe, and Zn SACs with limiting potentials not exceeding 0.51 V. This work provides valuable insights into the electrocatalytic oxidation mechanism of HMF to FDCA on M-NC SACs and proposes candidate catalysts to guide future research.

Non-Noble Metal Catalysts for Electrooxidation of 5-Hydroxymethylfurfural

2,5-Furandicarboxylic acid (FDCA) is a class of valuable biomass-based platform compounds. The creation of FDCA involves the catalytic oxidation of 5-hydroxymethylfurfural (HMF). As a novel catalytic method, electrocatalysis has been utilized in the 5-hydroxymethylfurfural oxidation reaction (HMFOR). Common noble metal catalysts show catalytic activity, which is limited by price and reaction conditions. Non-noble metal catalyst is known for its environmental friendliness, affordability and high efficiency. The development of energy efficient non-noble metal catalysts plays a crucial role in enhancing the HMFOR process. It can greatly upgrade the demand of industrial production, and has important research significance for electrocatalytic oxidation of HMF. In this paper, the reaction mechanism of HMF undergoes electrocatalytic oxidation to produce FDCA are elaborately summarized. There are two reaction pathways and two oxidation mechanisms of HMFOR discussed deeply. In addition, the speculation on the response of the electrode potential to HMFOR is presented in this paper. The main non-noble metal electrocatalysts currently used are classified and summarized by targeting metal element species. Finally, the paper focus on the mechanistic effects of non-noble metal catalysts in the reaction, and provide the present prospects and challenges in the electrocatalytic oxidation reaction of HMF.

A New Platform Molecule from Gluconolactone? Access to Furanics, Rare Sugars, β-Ketoamides and Amino Furanones

Gluconolactone serves as a readily available and inexpensive starting material for synthesizing the potential platform chemical (Z)-3-deoxy-1,2 : 5,6-di-O-isopropylidene-D-erythro-hex-3-enolactone in two steps. In this work, the selective elimination of triacetone gluconolactone was optimized. The resulting product is a versatile molecule, capable of being transformed into various compound classes in one or a few steps, i. e. potentially a new biomass-based platform chemical. This study demonstrates how it can be transformed into furanics, rare sugars, β-ketoamides, and amino furanones.

Catalytic conversion of biomass-derived 5-hydroxymethylfurfural to 5-hydroxymethyl-2-furancarboxylic acid using novel cobalt-based MOF in the presence of deep eutectic solvents

The oxidation of 5-HMF to HMFCA is an important yet complex process, as it generates high-value chemical intermediates. Achieving this transformation efficiently requires the development of non-precious, highly active catalysts derived from renewable biomass sources. In this work, we introduce UoM-1 (UoM, University of Mazandaran), a novel cobalt-based metal-organic framework (Co-MOF) synthesized using a simple one-step ultrasonic irradiation method. The synthesis employed the ligand 4,4'-((1E,1'E)-((5-carboxy-1,3-phenylene)bis(azaneylylidene))bis (methaneylylidene))dibenzoic acid (H3bdda). A comprehensive suite of analytical techniques, including FT-IR, EDX, ICP, XRD, TEM, DLS, FESEM, and BET-BJH, was used to confirm the structural integrity of the synthesized material. The catalytic performance of UoM-1 was investigated for the selective conversion of HMF to HMFCA, demonstrating its effectiveness as a low-cost, accessible catalyst. To promote a more sustainable and environmentally friendly approach, the oxidation reactions were performed in deep eutectic solvents, which offer a green, low-energy alternative to traditional solvents. This study shows that the UoM-1 catalyst not only provides an economical solution but also aligns with modern green chemistry principles, making it a highly promising candidate for future catalytic applications.

Co@NC Chainmail Nanowires for Thermo- and Electrocatalytic Oxidation of 2,5-Bis(hydroxymethyl)furan to 2,5-Furandicarboxylic Acid

2,5-Furandicarboxylic acid (FDCA) has emerged as an important bio-based furanic compound, which has broad application prospects in renewable energy and materials, especially in the preparation of polyethylene 2,5-furandicarboxylate (PEF). While the conventional synthesis of FDCA involves oxidation of 5-hydroxymethylfurfural (HMF) as a substitute, the thermal and chemical instability of HMF due to its aldehyde group poses challenges. A more favorable alternative is the utilization of 2,5-bis(hydroxymethyl)furan (BHMF), a non-aldehyde and more stable precursor. This study pioneeringly reports nitrogen-doped-carbon encapsulated cobalt (Co@NC) chainmail nanowires for the thermal and electrocatalytic oxidation of BHMF to FDCA. The Co@NC/NF achieved a 97.9 % conversion of BHMF with a 93.3 % yield of FDCA at 1.475 V vs. RHE, whereas thermal catalysis only obtained 14.9 % FDCA yield after 10 hours. Kinetic studies indicated that the large electrochemically active surface area and excellent kinetic parameters contribute its superior electrochemical performance. Mechanistic analysis revealed that the migration of inner electrons to the exterior modified the electronic properties of the carbon layer, thereby facilitating the oxidation of BHMF. Furthermore, the in-situ generation of high-valent cobalt species markedly accelerated the BHMF oxidation. This research underscores the potential of carbon-encapsulated metal chainmail catalysts in thermal and electrochemical biomass conversion.

The Use of 5-Hydroxymethylfurfural (5-HMF) in Multi-Component Hantzsch Dihydropyridine Synthesis

The renewable 5-hydroxymethylfurfural (5-HMF) has gained a wide interest from the chemistry community as a valuable biobased platform opening the way to many applications. Despite an impressive number of publications reporting either its preparation or its functionalization, its direct use in fine chemistry, and especially in multi-component reaction (MCR), is less reported. Here, we report a complete study of the use of 5-HMF in the Hantzsch dihydropyridines synthesis. The strategy was applied to a scope of β-dicarbonyl molecules (including β-ketoesters and 1,3-diketones) in a 3-component procedure leading to a series of symmetrical 1,4-dihydropyridines derived from 5-HMF in excellent yields. The study was extended to the 4-component protocol using one equivalent of a β-ketoester and one equivalent of 5,5-dimethyl-1,3-cyclohexanedione (dimedone), which efficiently provided the corresponding unsymmetrical dihydropyridines.

Preparation of carbon-supported ruthenium spinel oxide catalyst and application thereof in the oxidation of 5-hydroxymethylfurfural

Trivalent ruthenium (Ru) can catalyse the oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA). However, the structure of Ru itself is unstable and is prone to aggregation and oxidation, leading to a decrease in catalytic activity. Therefore, it is necessary to prepare a stable, reliable, Ru-based catalyst. Based on the catalytic properties of trivalent Ru, a stable spinel structure with zinc ferrite was designed and loaded onto different carbon supports to prepare a homogeneous and stable Ru-based catalyst. The structure and physico-chemical properties were characterized through scanning electron microscopy, X-ray diffraction, transmission electron microscopy and other techniques, and the catalyst was applied to the oxidation of HMF for the preparation of FDCA. The results show that the prepared magnetic activated carbon-supported Ru-based catalyst has a concentrated particle size distribution in the range of 5-8 nm, with a loading amount of 3.61 at%. It exhibits strong soft magnetism, which is beneficial for Ru loading. Additionally, it can be reused in the oxidation of HMF to prepare FDCA over 10 cycles, with the product yield remaining essentially unchanged. The catalyst prepared in this study is characterized by recyclability and structural stability, making it promising for practical applications.

Ecotoxicological assessment of biomass-derived furan platform chemicals using aquatic and terrestrial bioassays

An environmental toxicological assessment of fourteen furanic compounds serving as valuable building blocks produced from biomass was performed. The molecules selected included well studied compounds serving as control examples to compare the toxicity exerted against a variety of highly novel furans which have been additionally targeted as potential or current alternatives to biofuels, building blocks and polymer monomers. The impact of the furan platform chemicals targeted on widely applied ecotoxicity model organisms was determined employing the marine bioluminescent bacterium Aliivibrio fischeri and the freshwater green microalgae Raphidocelis subcapitata, while their ecotoxicity effects on plants were assessed using dicotyledonous plants Sinapis alba and Lepidium sativum. Regarding the specific endpoints evaluated, the furans tested were slightly toxic or practically nontoxic for A. fischeri following 5 and 15 min of exposure. Moreover, most of the building blocks did not affect the growth of L. sativum and S. alba at 150 mg L-1 for 72 h of exposure. Specifically, 9 and 11 out of the 14 furan platform chemicals tested were non-effective or stimulant for L. sativum and S. alba respectively. Given that furans comprise common inhibitors in biorefinery fermentations, the growth inhibition of the specific building blocks was studied using the industrial workhorse yeast Saccharomyces cerevisiae, demonstrating insignificant inhibition on eukaryotic cell growth following 6, 12 and 16 h of exposure at a concentration of 500 mg L-1. The study provides baseline information to unravel the ecotoxic effects and to confirm the green aspects of a range of versatile biobased platform molecules.

Enhancing Low-Potential Electrosynthesis of 2,5-Furandicarboxylic Acid on Monolithic CuO by Constructing Oxygen Vacancies

Electrosynthesis of 2,5-furandicarboxylic acid (FDCA) from the biomass-derived 5-hydroxymethylfurfural (HMF) is one of the most potential means to produce a bioplastic monomer. Copper oxide (CuO) catalyst shows promising prospects due to its high surface activity, conductivity, and stability, but relatively poor capability of oxygen evolution; however, the weak adsorption of substrates and the lack of facile synthetic strategies largely restrict its practical application. Here, a novel facile in situ method, alternate cycle voltammetry (denoted as c) and potentiostatic electrolysis (denoted as p), was proposed to prepare a monolithic cpc-CuO/Cu-foam electrocatalyst. Along with the increment of CuO and its surficial oxygen vacancies (OV), the FDCA yield, productivity, and Faradaic efficiency can reach up to ∼98.5%, ∼0.2 mmol/cm2, and ∼94.5% under low potential of 1.404 VRHE. Such an efficient electrosynthesis system can be easily scaled up to afford pure FDCA powders. In a combinatory analysis via electron paramagnetic resonance spectroscopy, H2 temperature-programmed reduction, open circuit potential, infrared spectroscopy, zeta potential, electrochemical measurement, and theoretical calculation, we found that the CuO was the active phase and OV generated on CuO surface can dramatically enhance the adsorption of *HMF and *OH (* denotes an active site), accounting for its superior FDCA production. This work offers an excellent paradigm for enhancing biomass valorization on CuO catalysts by constructing surficial defects.

Oxygen Vacancy-Induced Metal-Support Interactions in AuPd/ZrO2 Catalysts for Boosting 5-Hydroxymethylfurfural Oxidation

The construction of strong metal-support interactions in oxide-supported noble metal nanocatalysts has been considered an emerging and efficient way in improving catalytic performance in biomass-upgrading reactions. Herein, a citric acid (CA)-assisted synthesized ZrO2 layer with improved oxygen vacancy (Ov) concentrations on a natural clay mineral of halloysite nanotubes (HNTs) was designed. Moreover, AuxPdy/ZrO2@HNTs-zCA catalysts were prepared by loading AuPd bimetal and employed for aerobic oxidation of the lignocellulosic biomass-derived 5-hydroxymethylfurfural (HMF) platform to the bioplastic monomer 2,5-furandicarboxylic acid (FDCA) with water as the solvent. The results of catalytic experiments revealed that the Au3Pd1/ZrO2@HNTs-1.0CA catalyst exhibited excellent catalytic activity at 0.5 MPa O2, with a satisfactory FDCA yield of 99.5% and outstanding FDCA formation rate of 1057.9 mmol·g-1·h-1. The improved Ov concentration in the ZrO2 support enhanced the adsorption and activation ability of the catalyst for O2, and a higher Lewis acid concentration provided a stronger adsorption ability of the catalyst for reaction substrates. Besides, the synergistic effect of AuPd bimetallic nanoparticles steered the tandem oxidation of aldehyde and alcohol groups in HMF and accelerated the rate-determining step. More importantly, the relationship between the Ov concentration and catalytic performance also demonstrated that the enhanced catalytic activity for HMF oxidation was mainly attributed to the active interface of AuPd-ZrOx. This work offers fresh insights into rationally designing oxygen vacancy-driven strong interactions between the oxide support and noble nanoparticles for the catalytic upgrade of biomass platform chemicals.

Chemoselective Lipase-Catalyzed Synthesis of Amido Derivatives from 5-Hydroxymethylfurfurylamine

The acylations of furfurylamine and 5-hydroxymethylfurfurylamine (HMFA) have been studied finding immobilized Candida antarctica lipase B (CALB) as an ideal biocatalyst. CALB was used immobilized on two different supports (Novozyme 435 and EziG-CALB), with the polymer-coated controlled porosity glass carrier material from EnginZyme being an excellent carrier to yield an active and stable enzymatic preparation for the acylation of the primary amine group. The amount of the acyl donor in the reaction was a key factor to achieve the mono- and chemoselective N-protection of HMFA with large excess of ethyl acetate leading to the formation of the N,O-diacetylated product. Thus, a series of 16 nonactivated esters were used to selectively modify the amine group of HMFA, obtaining 9 hydroxy amides under mild reaction conditions and with quantitative yields through chromatography-free transformations. The influence of substrate concentration was studied, resulting in complete conversions in all cases after 22 h (100-1000 mM). Excellent results were observed at 100 and 200 mM of HMFA, while higher concentrations led to longer reaction times and, to some extent, the formation of the diacetylated product (up to 7% after 22 h at 1 M). After this optimization, a metric analysis was performed to confirm the high sustainability of the presented process (E-factor of 1.1 excluding solvents) upon intensification of the biotransformation to 1 g at 200 mM HMFA concentration. The possibility of obtaining orthogonally protected HMFA-derived amido esters has been achieved through a clean and sequential one-pot process using EziG-CALB, which involved the use of ethyl methoxy acetate as the nonactivated ester for N-acylation and the activated vinyl acetate for O-protection.

Cell-free enzyme cascades - application and transition from development to industrial implementation

In the vision to realize a circular economy aiming for net carbon neutrality or even negativity, cell-free bioconversion of sustainable and renewable resources emerged as a promising strategy. The potential of in vitro systems is enormous, delivering technological, ecological, and ethical added values. Innovative concepts arose in cell-free enzymatic conversions to reduce process waste production and preserve fossil resources, as well as to redirect and assimilate released industrial pollutions back into the production cycle again. However, the great challenge in the near future will be the jump from a concept to an industrial application. The transition process in industrial implementation also requires economic aspects such as productivity, scalability, and cost-effectiveness. Here, we briefly review the latest proof-of-concept cascades using carbon dioxide and other C1 or lignocellulose-derived chemicals as blueprints to efficiently recycle greenhouse gases, as well as cutting-edge technologies to maturate these concepts to industrial pilot plants.