Toward Value-Added Dicarboxylic Acids from Biomass Derivatives via Thermocatalytic Conversion

5-Hydroxymethylfurfural and its Downstream Chemicals: A Review of Catalytic Routes

Biomass assumes an increasingly vital role in the realm of renewable energy and sustainable development due to its abundant availability, renewability, and minimal environmental impact. Within this context, 5-hydroxymethylfurfural (HMF), derived from sugar dehydration, stands out as a critical bio-derived product. It serves as a pivotal multifunctional platform compound, integral in synthesizing various vital chemicals, including furan-based polymers, fine chemicals, and biofuels. The high reactivity of HMF, attributed to its highly active aldehyde, hydroxyl, and furan ring, underscores the challenge of selectively regulating its conversion to obtain the desired products. This review highlights the research progress on efficient catalytic systems for HMF synthesis, oxidation, reduction, and etherification. Additionally, it outlines the techno-economic analysis (TEA) and prospective research directions for the production of furan-based chemicals. Despite significant progress in catalysis research, and certain process routes demonstrating substantial economics, with key indicators surpassing petroleum-based products, a gap persists between fundamental research and large-scale industrialization. This is due to the lack of comprehensive engineering research on bio-based chemicals, making the commercialization process a distant goal. These findings provide valuable insights for further development of this field.

A comprehensive review of recent advances in the applications and biosynthesis of oxalic acid from bio-derived substrates

Organic acids are important compounds with numerous applications in different industries. This work presents a comprehensive review of the biological synthesis of oxalic acid, an important organic acid with many industrial applications. Due to its important applications in pharmaceuticals, textiles, metal recovery, and chemical and metallurgical industries, the global demand for oxalic acid has increased. As a result, there is an increasing need to develop more environmentally friendly and economically attractive alternatives to chemical synthesis methods, which has led to an increased focus on microbial fermentation processes. This review discusses the specific strategies for microbial production of oxalic acid, focusing on the benefits of using bio-derived substrates to improve the economics of the process and promote a circular economy in comparison with chemical synthesis. This review provides a comprehensive analysis of the various fermentation methods, fermenting microorganisms, and the biochemistry of oxalic acid production. It also highlights key sustainability challenges and considerations related to oxalic acid biosynthesis, providing important direction for further research. By providing and critically analyzing the most recent information in the literature, this review serves as a comprehensive resource for understanding the biosynthesis of oxalic acid, addressing critical research gaps, and future advances in the field.

Mechanism of Electrocatalytic H2 Evolution, Carbonyl Hydrogenation, and Carbon-Carbon Coupling on Cu

Aqueous-phase electrocatalytic hydrogenation of benzaldehyde on Cu leads not only to benzyl alcohol (the carbonyl hydrogenation product), but Cu also catalyzes carbon-carbon coupling to hydrobenzoin. In the absence of an organic substrate, H2 evolution proceeds via the Volmer-Tafel mechanism on Cu/C, with the Tafel step being rate-determining. In the presence of benzaldehyde, the catalyst surface is primarily covered with the organic substrate, while H* coverage is low. Mechanistically, the first H addition to the carbonyl O of an adsorbed benzaldehyde molecule leads to a surface-bound hydroxy intermediate. The hydroxy intermediate then undergoes a second and rate-determining H addition to its α-C to form benzyl alcohol. The H additions occur predominantly via the proton-coupled electron transfer mechanism. In a parallel reaction, the radical α-C of the hydroxy intermediate attacks the electrophilic carbonyl C of a physisorbed benzaldehyde molecule to form the C-C bond, which is rate-determining. The C-C coupling is accompanied by the protonation of the formed alkoxy radical intermediate, coupled with electron transfer from the surface of Cu, to form hydrobenzoin.

Synergistic Interaction between Ruthenium Catalysts and Grafted Niobium on SBA-15 for 2,5-Furandicarboxylic Acid Production Using 5-Hydroxymethylfurfural

This study entailed the synthesis of Ru nanocatalyst decorated on Nb-grafted SBA-15. A Nb-grafted SBA-15 support with varying Nb contents was utilized as a support for the Ru nanoparticles. The effect of Nb grafting on the immobilized Ru nanoparticle catalyst was systematically investigated, and its catalytic performance in the synthesis of furandicarboxylic acid using 5-hydroxymethylfurfural under base-free reaction conditions was evaluated. The results indicate the increased productivity of the Ru@Nb-grafted SBA-15 catalyst with a yield exceeding 95%, representing a significant advancement in catalysis. This study also affords insights into the complex relationship between the catalytic activity and selectivity and its unique surface attributes. Moreover, acidic sites were created, and the electron density within the active sites was modulated by monomeric Nb oxide species on the SBA-15. Additionally, the role of high-electron-density Ru atoms in facilitating the efficient adsorption and activation of the reactant, resulting in enhanced catalytic efficacy, was highlighted.

Production of 2,5-Furandicarboxylic Acid Methyl Esters from Pectin-Based Aldaric Acid: from Laboratory to Bench Scale

2,5-Furandicarboxylic acid (FDCA) is one of the most attractive emerging renewable monomers, which has gained interest especially in polyester applications, such as the production of polyethylene furanoate (PEF). Recently, the attention has shifted towards FDCA esters due to their better solubility as well as the easier purification and polymerisation compared to FDCA. In our previous work, we reported the synthesis of FDCA butyl esters by dehydration of aldaric acids as stable intermediates. Here, we present the synthesis of FDCA methyl esters in high yields from pectin-based galactaric acid using a solid acid catalyst. The process enables high substrate concentrations (up to 20 wt %) giving up to 50 mol % FDCA methyl esters with total furancarboxylates yields of up to 90 mol %. The synthesis was successfully scaled up from gram-scale to kilogram-scale in batch reactors showing the feasibility of the process. The stability of the catalyst was tested in re-use experiments. Purification of the crude product by vacuum distillation and precipitation gave furan-2,5-dimethylcarboxylate with a 98 % purity.

Sustainable application of rice-waste for fuels and valuable chemicals-a mini review

The global annual production of rice is over 750 million tons, and generates a huge amount of biomass waste, such as straw, husk, and bran, making rice waste an ideal feedstock for biomass conversion industries. This review focuses on the current progress in the transformation of rice waste into valuable products, including biochar, (liquid and gaseous) biofuels, valuable chemicals (sugars, furan derivatives, organic acids, and aromatic hydrocarbons), and carbon/silicon-based catalysts and catalyst supports. The challenges and future prospectives are highlighted to guide future studies in rice waste valorization for sustainable production of fuels and chemicals.

Lignocellulose Conversion via Catalytic Transformations Yields Methoxyterephthalic Acid Directly from Sawdust

Poly(ethylene terephthalate) polyester represents the most common class of thermoplastic polymers widely used in the textile, bottling, and packaging industries. Terephthalic acid and ethylene glycol, both of petrochemical origin, are polymerized to yield the polyester. However, an earlier report suggests that polymerization of methoxyterephthalic acid with ethylene glycol provides a methoxy-polyester with similar properties. Currently, there are no established biobased synthetic routes toward the methoxyterephthalic acid monomer. Here, we show a viable route to the dicarboxylic acid from various tree species involving three catalytic steps. We demonstrate that sawdust can be converted to valuable aryl nitrile intermediates through hydrogenolysis, followed by an efficient fluorosulfation-catalytic cyanation sequence (>90%) and then converted to methoxyterephthalic acid by hydrolysis and oxidation. A preliminary polymerization result indicates a methoxy-polyester with acceptable thermal properties.

Highly Selective Transformation of Biomass Derivatives to Valuable Chemicals by Single-Atom Photocatalyst Ni/TiO2

Selective CC cleavage of the biomass derivative glycerol under mild conditions is recognized as a promising yet challenging synthesis route to produce value-added chemicals. Here, a highly selective catalyst for the transformation of glycerol to the high-value product glycolaldehyde is presented, which is composed of nickel single atoms confined to the surface of titanium dioxide. Driven by light, the catalyst operates under ambient conditions using air as a green oxidant. The optimized catalyst shows a selectivity of over 60% to glycolaldehyde, resulting in 1058 µmol g_Cat ^-1  h^-1 production rate, and ≈3 times higher turnover number than NiO_x -nanoparticle-decorated TiO₂ photocatalyst. Diverse operando and in situ spectroscopies unveil the unique function of the Ni single atom, which can significantly promote oxygen adsorption, work as an electron sink, and accelerate the production of superoxide radicals, thereby improving the selectivity toward glycolaldehyde over other by-products.

Polymers without Petrochemicals: Sustainable Routes to Conventional Monomers

Access to a wide range of plastic materials has been rationalized by the increased demand from growing populations and the development of high-throughput production systems. Plastic materials at low costs with reliable properties have been utilized in many everyday products. Multibillion-dollar companies are established around these plastic materials, and each polymer takes years to optimize, secure intellectual property, comply with the regulatory bodies such as the Registration, Evaluation, Authorisation and Restriction of Chemicals and the Environmental Protection Agency and develop consumer confidence. Therefore, developing a fully sustainable new plastic material with even a slightly different chemical structure is a costly and long process. Hence, the production of the common plastic materials with exactly the same chemical structures that does not require any new registration processes better reflects the reality of how to address the critical future of sustainable plastics. In this review, we have highlighted the very recent examples on the synthesis of common monomers using chemicals from sustainable feedstocks that can be used as a like-for-like substitute to prepare conventional petrochemical-free thermoplastics.

p-Xylene Oxidation to Terephthalic Acid: New Trends

Large-scale terephthalic acid production from the oxidation of p-xylene is an especially important process in the polyester industry, as it is mainly used in polyethylene terephthalate (PET) manufacturing, a polymer that is widely used in fibers, films, and plastic products. This review presents and discusses catalytic advances and new trends in terephthalic acid production (since 2014), innovations in terephthalic acid purification processes, and simulations of reactors and reaction mechanisms.

Advances in Selective Electrochemical Oxidation of 5-Hydroxymethylfurfural to Produce High-Value Chemicals

The conversion of biomass is a favorable alternative to the fossil energy route to solve the energy crisis and environmental pollution. As one of the most versatile platform compounds, 5-hydroxymethylfural (HMF) can be transformed to various value-added chemicals via electrolysis combining with renewable energy. Here, the recent advances in electrochemical oxidation of HMF, from reaction mechanism to reactor design are reviewed. First, the reaction mechanism and pathway are summarized systematically. Second, the parameters easy to be ignored are emphasized and discussed. Then, the electrocatalysts are reviewed comprehensively for different products and the reactors are introduced. Finally, future efforts on exploring reaction mechanism, electrocatalysts, and reactor are prospected. This review provides a deeper understanding of mechanism for electrochemical oxidation of HMF, the design of electrocatalyst and reactor, which is expected to promote the economical and efficient electrochemical conversion of biomass for industrial applications.

Combined conversion of lignocellulosic biomass into high-value products with ultrasonic cavitation and photocatalytic produced reactive oxygen species - A review

The production of high-value products from lignocellulosic biomass is carried out through the selective scission of crosslinked CC/CO bonds. Nowadays, several techniques are applied to optimize biomass conversion into desired products with high yields. Photocatalytic technology has been proven to be a valuable tool for valorizing biomass at mild conditions. The photoproduced reactive oxygen species (ROSs) can initiate the scission of crosslinked bonds and form radical intermediates. However, the low mass transfer of the photocatalytic process could limit the production of a high yield of products. The incorporation of ultrasonic cavitation in the photocatalytic system provides an exceptional condition to boost the fragmentation and transformation of biomass into the desired products within a lesser reaction time. This review critically discusses the main factors governing the application of photocatalysis for biomass valorization and tricks to boost the selectivity for enhancing the yield of desired products. Synergistic effects obtained through the combination of sonolysis and photocatalysis were discussed in depth. Under ultrasonic vibration, hot spots could be produced on the surface of the photocatalysts, improving the mass transfer through the jet phenomenon. In addition, shock waves can assist the dissolution and mixing of biomass particles.

Critical Assessment of the Sustainability of Deep Eutectic Solvents: A Case Study on Six Choline Chloride-Based Mixtures

An outline of the advantages, in terms of sustainability, of Deep Eutectic Solvents (DESs) is provided, by analyzing some of the most popular DESs, obtained by the combination of choline chloride, as a hydrogen bond acceptor, and six hydrogen bond donors. The analysis is articulated into four main issues related to sustainability, which are recurrently mentioned in the literature, but are often taken for granted without any further critical elaboration, as the prominent green features of DESs: their low toxicity, good biodegradability, renewable sourcing, and low cost. This contribution is intended to provide a more tangible, evidence-based evaluation of the actual green credentials of the considered DESs, to reinforce or question their supposed sustainability, also in mutual comparison with one another.

Targeting Valuable Chemical Commodities: Hydrazine-mediated Diels-Alder Aromatization of Biobased Furfurals

A hydrazine-mediated approach towards renewable aromatics production via Diels-Alder aromatization of readily available, biobased furfurals was explored as alterative to the more classical approaches that rely on reactive but uneconomical reduced dienes (e. g., 2,5-dimethylfuran). To enable cycloaddition chemistry with these otherwise unreactive formyl furans, substrate activation by N,N-dimethyl hydrazone formation was investigated. The choice of the reaction partner was key to the success of the transformation, and in this respect acrylic acid showed the most promising results in the synthesis of aromatics. This strategy allowed for selectivities up to 60 % for a complex transformation consisting of Diels-Alder cycloaddition, oxabridge opening, decarboxylation, and dehydration. Exploration of the furfural scope yielded generic structure-reactivity-stability relationships. The proposed methodology enabled the redox-efficient, operationally simple, and mild synthesis of renewable (p-disubstituted) aromatics of commercial importance under remarkably mild conditions.

High Bio-Content Thermoplastic Polyurethanes from Azelaic Acid

To realize the commercialization of sustainable materials, new polymers must be generated and systematically evaluated for material characteristics and end-of-life treatment. Polyester polyols made from renewable monomers have found limited adoption in thermoplastic polyurethane (TPU) applications, and their broad adoption in manufacturing may be possible with a more detailed understanding of their structure and properties. To this end, we prepared a series of bio-based crystalline and amorphous polyester polyols utilizing azelaic acid and varying branched or non-branched diols. The prepared polyols showed viscosities in the range of 504–781 cP at 70 °C, with resulting TPUs that displayed excellent thermal and mechanical properties. TPUs prepared from crystalline azelate polyester polyol exhibited excellent mechanical properties compared to TPUs prepared from amorphous polyols. These were used to demonstrate prototype products, such as watch bands and cup-shaped forms. Importantly, the prepared TPUs had up to 85% bio-carbon content. Studies such as these will be important for the development of renewable materials that display mechanical properties suitable for commercially viable, sustainable products.

Selective Conversion of HMF into 3-Hydroxymethylcyclopentylamine through a One-Pot Cascade Process in Aqueous Phase over Bimetallic NiCo Nanoparticles as Catalyst

5-hydroxymethylfurfural (HMF) has been successfully valorized into 3-hydroxymethylcyclopentylamine through a one-pot cascade process in aqueous phase by coupling the hydrogenative ring-rearrangement of HMF into 3-hydroxymethylcyclopentanone (HCPN) with a subsequent reductive amination with ammonia. Mono- (Ni@C, Co@C) and bimetallic (NiCo@C) nanoparticles with different Ni/Co ratios partially covered by a thin carbon layer were prepared and characterized. Results showed that a NiCo catalyst, (molar ratio Ni/Co=1, Ni_0.5 Co_0.5 @C), displayed excellent performance in the hydrogenative ring-rearrangement of HMF into HCPN (>90 % yield). The high selectivity of the catalyst was attributed to the formation of NiCo alloy structures as hydrogenating sites that limited competitive reactions such as the hydrogenation of furan ring and the over-reduction of the formed HPCN. The subsequent reductive amination of HPCN with aqueous ammonia was performed giving the target cyclopentylaminoalcohol in 97 % yield. Moreover, the catalyst exhibited high stability maintaining its activity and selectivity for repeated reaction cycles.

Recent Advances in Reductive Upgrading of 5-Hydroxymethylfurfural via Heterogeneous Thermocatalysis

The catalytic conversion of 5-hydroxymethylfufural (HMF), one of the vital platform chemicals in biomass upgrading, holds great promise for producing highly valuable chemicals through sustainable routes, thereby alleviating the dependence on fossil feedstocks and reducing CO₂ emissions. The reductive upgrading (hydrogenation, hydrogenolysis, ring-opening, ring-rearrangement, amination, etc.) of HMF has exhibited great potential to produce monomers, liquid fuel additives, and other valuable chemicals. Thermocatalytic conversion has a significant advantage over photocatalysis and electrocatalysis in productivity. In this Review, the recent achievements of thermo-reductive transformation of HMF to various chemicals using heterogeneous catalytic systems are presented, including the catalytic systems (catalyst and solvent), reaction conditions, (reaction temperature, pressure, etc.), and reaction mechanisms. The current challenges and future opportunities are discussed as well, aiming at guiding the catalyst design and practical scalable productions.

Recent Advances in the Catalytic Hydroconversion of 5-Hydroxymethylfurfural to Valuable Diols

Biomass, a globally available resource, is a promising alternative feedstock for fossil fuels, especially considering the current energy crisis and pollution. Biomass-derived diols, such as 2,5-bis(hydroxymethyl)furan, 2,5-bis(hydroxymethyl)-tetrahydrofuran, and 1,6-hexanediol, are a significant class of monomers in the polyester industry. Therefore, the catalytic conversion of biomass to valuable diols has received extensive research attention in the field of biomass conversion and is a crucial factor in determining the development of the polyester industry. 5-Hydroxymethylfurfural (HMF) is an important biomass-derived compound with a C6-furanic framework. The hydroconversion of HMF into diols has the advantages of being simple to operate, inexpensive, environmentally friendly, safe, and reliable. Therefore, in the field of diol synthesis, this method is regarded as a promising approach with significant industrialization potential. This review summarizes recent advances in diol formation, discusses the roles of catalysts in the hydroconversion process, highlights the reaction mechanisms associated with the specificities of each active center, and provides an outlook on the challenges and opportunities associated with the research on biomass-derived diol synthesis.

Strong Metal Phosphide-Phosphate Support Interaction for Enhanced Non-Noble Metal Catalysis

Strong metal-support interaction (SMSI) is crucial for supported catalysts in heterogeneous catalysis. Here is the first report on strong metal phosphide-phosphate support interaction (SMPSI). The key to SMPSI is the activation of P species on the support, which leads to simultaneous generation of metal phosphide nanoparticles (NPs) and core-shell nanostructures formed by support migration onto the NPs. The encapsulation state of metal phosphide and charge transfer are identical to those of classical SMSIs and can be optimally regulated. Furthermore, the strong interactions of Co₂ P_L /MnP-3 not only significantly enhance the anti-oxidation and anti-acid capability of non-noble metal but also exhibit excellent catalytic activity and stability toward hydrogenating a wide range of compounds into value-added fine chemicals with 100% selectivity, which is even better than Pd/C and Pt/C. The SMPSI construction can be generally extended to other systems such as Ni₂ P_L /Mn₃ (PO₄ )₂ , Co₂ P_L /LaPO₄ , and CoP_L /CePO₄ . This study provides a new approach for the rational design of advanced non-noble metal catalysts and introduce a novel paradigm for the strong interaction between NPs and support.

Molybdenum carbide anchored on glucose-derived carbon (β-Mo2C@C) as a bifunctional catalyst for conversion of fructose to 2,5-diformylfuran

Molybdenum carbide anchored on glucose-derived carbon (β-Mo2C@C) has been successfully synthesized and applied as a bifunctional catalyst for one-pot conversion of fructose to DFF.

Dehydration of fructose to 5-hydroxymethylfurfural over a mesoporous sulfonated high-crosslinked polymer in different solvents

SHCP was active and stable for dehydration of fructose to 5-HMF in DIO/H2O as H2O depressed oligomerization of 5-HMF.

Enantioselective Reductive Oligomerization of Carbon Dioxide into l-Erythrulose via a Chemoenzymatic Catalysis

A cell-free enantioselective transformation of the carbon atom of CO₂ has never been reported. In the urgent context of transforming CO₂ into products of high value, the enantiocontrolled synthesis of chiral compounds from CO₂ would be highly desirable. Using an original hybrid chemoenzymatic catalytic process, we report herein the reductive oligomerization of CO₂ into C₃ (dihydroxyacetone, DHA) and C₄ (l-erythrulose) carbohydrates, with perfect enantioselectivity of the latter chiral product. This was achieved with the key intermediacy of formaldehyde. CO₂ is first reduced selectively by 4e^- by an iron-catalyzed hydroboration reaction, leading to the isolation and complete characterization of a new bis(boryl)acetal compound derived from dimesitylborane. In an aqueous buffer solution at 30 °C, this compound readily releases formaldehyde, which is then involved in selective enzymatic transformations, giving rise either (i) to DHA using a formolase (FLS) catalysis or (ii) to l-erythrulose with a cascade reaction combining FLS and d-fructose-6-phosphate aldolase (FSA) A129S variant. Finally, the nature of the synthesized products is noteworthy, since carbohydrates are of high interest for the chemical and pharmaceutical industries. The present results prove that the cell-free de novo synthesis of carbohydrates from CO₂ as a sustainable carbon source is a possible alternative pathway in addition to the intensely studied biomass extraction and de novo syntheses from fossil resources.

Synthesis and characterization of an α-MoO3 nanobelt catalyst and its application in one-step conversion of fructose to 2,5-diformylfuran

α-MoO3 nanobelts have been successfully synthesized and applied as a bifunctional catalyst for one-step conversion of fructose to DFF under atmospheric air.

Critical practices in conducting electrochemical conversion of 5-hydroxymethylfurfural

This work systematically studied the effects of various experimental parameters on the catalytic activity and product yield of HMF conversion and affords a rigorous assessment protocol for conducting electrochemical conversion of HMF.