4-hydroxyvaleric Acid Research Articles

Algal biomass-based zero-waste biorefinery for producing optically pure (R)-γ-valerolactone and carbonaceous electrodes applicable for energy storage devices

Mankind is facing a severe climate crisis caused by fossil fuel-derived CO2 emissions. Although biorefineries utilizing biomass have been considered the best option for carbon-neutrality, most biorefinery-derived products have not yet been promising for economic feasibility; various strategies have been developed to increase economic competitiveness, and zero-waste biorefineries are challenging options. Herein, we aim to develop an algal biomass-based zero-waste biorefinery for producing enantioselective (R)-γ-valerolactone ((R)-GVL) and carbonaceous electrodes applicable for Li-ion batteries (LiBs). Various algal biomasses were hydrothermally oxidized to produce levulinic acid (LA) as an intermediate for producing (R)-GVL, resulting that Gracilaria verrucosa was selected as feedstock. For the hydroxylation of G. verrucosa-derived LA to 4-hydroxyvaleric acid (4-HV), 3-hydroxybutyrate dehydrogenase (HBDH) was explored through genome mining and further engineered. The engineered HBDH successfully converted G. verrucosa-derived LA to 4-HV, which was subsequently lactonized under acidic conditions, resulting in optically pure (R)-GVL. To our knowledge, this is the first report of the production of an algal biomass-derived enantioselective (R)-GVL with a perfect enantiomeric excess (>99.99 %) that can be used as a precursor for more valuable biopharmaceuticals and bioplastics than biofuels. Furthermore, residual G. verrucosa after hydrothermal oxidation was used as a carbonaceous anode material for LIBs for the first time; hard carbon anodes, which were prepared through simple heat treatment (800 ℃, 3 h, argon atmosphere), exhibit good capacities of 231, 191, 133, 108, 97 and 86 mAh/g at 0.05, 0.1, 0.5, 1, 1.5, and 2 A/g, respectively. The results discussed herein can provide insights into zero-waste biorefineries applicable for diverse industrial fields (e.g., biopolymer, biopharmaceutical and energy storage) and contribute to the construction of closed-carbon-loops for coping with climate change.

Enhancing translation efficiency and exploring constraints in high-level 4-hydroxyvaleric acid production from levulinic acid in Escherichia coli

Enhancing translation efficiency and exploring constraints in high-level 4-hydroxyvaleric acid production from levulinic acid in Escherichia coli

Establishment of efficient 5-hydroxyvaleric acid production system by regenerating alpha-ketoglutaric acid and its application in poly(5-hydroxyvaleric acid) production

5-hydroxyvaleric acid (5-HV) is a versatile C5 intermediate of bio-based high-value chemical synthesis pathways. However, 5-HV production faces a few shortcomings involving the supply of cofactors, especially α-ketoglutaric acid (α-KG). Herein, we established a two-cell biotransformation system by introducing L-glutamate oxidase (GOX) to regenerate α-KG. Additionally, the catalase KatE was adapted to inhibit α-KG degradation by the H2O2 produced during GOX reaction. We searched for the best combination of genes and vectors and optimized the biotransformation conditions to maximize GOX effectiveness. Under the optimized conditions, 5-HV pathway with GOX showed 1.60-fold higher productivity than that of without GOX, showing 11.3 g/L titer. Further, the two-cell system with GOX and KatE was expanded to produce poly(5-hydroxyvaleric acid) (P(5HV)), and it reached at 412 mg/L of P(5HV) production and 20.5% PHA contents when using the biotransformation supernatant. Thus, the two-cell biotransformation system with GOX can potentially give the practical and economic alternative of 5-HV production using bio-based methods. We also propose direct utilization of 5-HV from bioconversion for P(5HV) production.

Mechanism of CO2 in promoting the hydrogenation of levulinic acid to γ-valerolactone catalyzed by RuCl3 in aqueous solution.

A Ru-containing complex shows good catalytic performance toward the hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) with the assistance of organic base ligands (OBLs) and CO2. Herein, we report the competitive mechanisms for the hydrogenation of LA to GVL, 4-oxopentanal (OT), and 2-methyltetrahydro-2,5-furandiol (MFD) with HCOOH or H2 as the H source catalyzed by RuCl3 in aqueous solution at the M06/def2-TZVP, 6-311++G(d,p) theoretical level. Kinetically, the hydrodehydration of LA to GVL is predominant, with OT and MFD as side products. With HCOOH as the H source, initially, the OBL (triethylamine, pyridine, or triphenylphosphine) is responsible for capturing H+ from HCOOH, leading to HCOO- and [HL]+. Next, the Ru3+ site is in charge of sieving H- from HCOO-, yielding [RuH]2+ hydride and CO2. Alternatively, with H2 as the H source, the OBL stimulates the heterolysis of H-H bond with the aid of Ru3+ active species, producing [RuH]2+ and [HL]+. Toward the [RuH]2+ formation, H2 as the H source exhibits higher activity than HCOOH as the H source in the presence of an OBL. Thereafter, H- in [RuH]2+ gets transferred to the unsaturated C site of ketone carbonyl in LA. Afterwards, the Ru3+ active species is capable of cleaving the C-OH bond in 4-hydroxyvaleric acid, yielding [RuOH]2+ hydroxide and GVL. Subsequently, CO2 promotes Ru-OH bond cleavage in [RuOH]2+, forming HCO3- and regenerating the Ru3+-active species owing to its Lewis acidity. Lastly, between the resultant HCO3- and [HL]+, a neutralization reaction occurs, generating H2O, CO2, and OBLs. Thus, the present study provides insights into the promotive roles of additives such as CO2 and OBLs in Ru-catalyzed hydrogenation.

Mild Hydrogenation of 2-Furoic Acid by Pt Nanoparticles Dispersed in a Hierarchical ZSM-5 Zeolite.

Hydrogenation of biobased compounds can add value to platform molecules obtained from biomass refining. Herein, we explore the hydrogenation of 2-furoic acid (2-furancarboxylic acid, FCA), a derivative of furfural, with H2 generated in situ by NaBH4 hydrolysis at ambient conditions. Nearly complete conversion of FCA was obtained with tetrahydrofuroic acid (THFA) and 5-hydroxyvaleric acid (5-HVA) as the only two reaction products over Pt nanoparticles supported on hierarchical ZSM-5. Small Pt nanoparticles (2 to 3 nm) were stabilized by ZSM-5 nanosheets. At an optimized Pt loading, the Pt nanoparticles can catalyze the hydrolysis of NaBH4 and the subsequent hydrogenation of FCA with the assistance of Brønsted acid sites. Nanostructuring ZSM-5 into nanosheets and its acidity contributes to the stability of the dispersed Pt nanoparticles. Deactivation due to NaBO2 deposition on the Pt particles can be countered by a simple washing treatment. Overall, this approach shows the promise of mild hydrogenation of biobased feedstock coupled with NaBH4 hydrolysis.

Complementation of reducing power for 5-hydroxyvaleric acid and 1,5-pentanediol production via glucose dehydrogenase in Escherichia coli whole-cell system

One of the key intermediates, 5-hydroxyvaleric acid (5-HV), is used in the synthesis of polyhydroxyalkanoate monomer, δ-valerolactone, 1,5-pentanediol (1,5-PDO), and many other substances. Due to global environmental problems, eco-friendly bio-based synthesis of various platform chemicals and key intermediates are socially required, but few previous studies on 5-HV biosynthesis have been conducted. To establish a sustainable bioprocess for 5-HV production, we introduced gabT encoding 4-aminobutyrate aminotransferase and yqhD encoding alcohol dehydrogenase to produce 5-HV from 5-aminovaleric acid (5-AVA), through glutarate semialdehyde in Escherichia coli whole-cell reaction. As, high reducing power is required to produce high concentrations of 5-HV, we newly introduced glucose dehydrogenase (GDH) for NADPH regeneration system from Bacillus subtilis 168. By applying GDH with D-glucose and optimizing the parameters, 5-HV conversion rate from 5-AVA increased from 47% (w/o GDH) to 82% when using 200 mM (23.4 g/L) of 5-AVA. Also, it reached 56% conversion in 2 h, showing 56 mM/h (6.547 g/L/h) productivity from 200 mM 5-AVA, finally reaching 350 mM (41 g/L) and 14.6 mM/h (1.708 g/L/h) productivity at 24 h when 1 M (117.15 g/L) 5-AVA was used. When the whole-cell system with GDH was expanded to produce 1,5-PDO, its production was also increased 5-fold. Considering that 5-HV and 1,5-PDO production depends heavily on the reducing power of the cells, we successfully achieved a significant increase in 5-HV and 1,5-PDO production using GDH.

Metabolic engineering of Escherichia coli for the efficient production of 5-hydroxyvaleric acid

There is increasing industrial demand for five-carbon platform chemicals, particularly 5-hydroxyvaleric acid (5-HV), a widely used building block for the synthesis of polyesters and polyurethanes. Here, we developed an efficient 5-HV microbial producer by systems metabolic engineering of Escherichia coli W3110. To derive 5-HV, Pseudomonas putidal-lysine monooxygenase (davB) and 5-aminovaleramide amidohydrolase (davA), E. coli 4-aminobutyrate aminotransferase (gabT), and different aldehyde reductase genes were introduced to E. coli W3110 to convert l-lysine hydrochloride to the target product. Three aldehyde reductases, including YajO from P. putida and YahK and YqhD from E. coli, were examined, revealing that the overexpression of aldehyde reductases was critical for 5-HV production and YajO was first reported for efficient production of 5-HV. The E. coli 5-aminovalerate exporter encoded by gabP and E. coli lysine-specific permease encoded by lysP were expressed to further enhance 5-HV production. In addition, a hok/sok toxin/antitoxin system based on the E. coli XL1-Blue genome was inserted to the dual-vector system to decrease plasmid loss. Finally, 5.59 g/L of 5-HV with a yield of 0.96 mol/mol (5-HV/l-lysine hydrochloride) by shake flask cultivation of the engineered E. coli W3110 and 35.6 g/L of 5-HV with a yield of 0.92 mol/mol (5-HV/l-lysine hydrochloride) by fed fermentation were achieved respectively. The developed metabolic engineering strategies provide a basis for the efficient and sustainable bio-based production of 5-HV.

Bimetallic Ni-Zn@OMC catalyst for selective hydrogenation of levulinic acid to γ-valerolactone in water

Hydrogenation of levulinic acid to γ-valerolactone is one of the important reactions for conversion of biomass into renewable fuels and chemicals. Ni-Zn non-noble bimetallic catalysts supported on ordered mesoporous carbon (Ni-Zn@OMC) were prepared by one-pot solvent evaporation induced self-assembly (EISA) method and used for hydrogenation of levulinic acid to γ-valerolactone (GVL) in water. A GVL yield of 93% was obtained over bimetallic Ni1-Zn1@OMC catalyst at 180 °C in 90 min reaction time, with a turnover frequency (TOF) of 686.4 h−1. Compared with Ni@OMC, the incorporation of Zn metal leads to the formation of Ni-Zn alloy and high dispersion of Ni particle on the catalyst surface. NiO sites on the catalysts lowered competitive adsorption between H2 and levulinic acid on Ni0 sites, as well as the Ni-Zn alloy is beneficial to the activation of carbonyl group in levulinic acid, and they synergistically promote the hydrogenation of levulinic acid to 4-hydroxyvaleric acid (4-HVA). Zn content in the catalyst influences both the activity of Lewis acid sites and the ratio of Lewis acid to Brønsted acid sites, and the active sites of Niδ–Znδ+ can facilitates the weakening and cleavage of C-O in 4-HVA, both of them are beneficial to the dehydration of 4-HVA to GVL.

Multienzymatic conversion of monosaccharides from birch biomass after pretreatment

This study presents proof-of-concept validation of a multi enzymatic biocatalytic system, capable of producing monosaccharides from a birch biomass pretreated liquor with simultaneous cofactor regeneration. To improve the stability of the proposed biocatalyst, co-immobilization of NAD + -dependent xylose dehydrogenases, glucose dehydrogenase, and NADH-dependent 3-hydroxybutyrate dehydrogenase was performed on mesoporous silica SBA-15. The results of the physicochemical analysis confirmed the effectiveness of enzymes deposition on the support material and changes in the surface area and porous structure of silica before and after the process. Process conditions in which the three-enzymes system allowed to achieve the highest efficiency of the conducted reactions were optimized at 20 °C, pH 7, 90 min of process duration, 400 mM of levulinic acid addition and ratio of NAD + :NADH 1:5. Results from this study demonstrate excellent xylonic acid, gluconic acid and 4-hydroxyvaleric acid production at conversion rate of 98.7%, 95.6% and 99.2%, respectively. In addition, the high stability and reusability of the developed biocatalytic system was confirmed based on tests in ten successive catalytic cycles and the storage time of 10 days at 4 °C. At the end of the tests, co-immobilized enzymes were capable of catalyzing the process with >70% efficiency. The presented data confirmed the effectiveness of co-immobilization, improvement of enzyme properties including their high reusability, as well as indicated the application potential of the proposed multienzymatic system in the conversion of components of pretreated biomass solutions. • Three types of dehydrogenases have been successfully co-immobilized using silica SBA-15. • Monosaccharides from the birch biomass pretreated liquor were effectively converted. • Addition of levulinic acid ensured the creation of a cofactor regeneration system. • The production of three organic acids was carried out with over 95% of efficiency. • Co-immobilized enzymes retained 70% of acids productivity after 10 catalytic cycles.

A novel strategy for the application of levulinic acid with simultaneous NAD+ regeneration and membrane separation of products

In this study, we present the concept of co-immobilization of 3-hydroxybutyrate dehydrogenase with xylose dehydrogenase or glucose dehydrogenase on the XN45 nanofiltration membrane for application in the bioconversion of levulinic acid as well as xylose or glucose with simultaneous cofactor regeneration. During the research, changes in the properties of the membrane were defined before and after the co-immobilization of enzymes and the effectiveness of this process was confirmed. Using produced multifunctional systems, the efficiencies of 4-hydroxyvaleric acid, xylonic acid or gluconic acid production were over 98 %. The highest yields of acids production were obtained for systems with substrate ratio 1:1, enzyme ratio 1:1 and cofactor ratio 1:1, irrespectively of the enzyme used. Additionally, the co-immobilization of enzymes made it possible to carry out ten successive catalytic cycles and storage of the biocatalyst for 10 days without a significant decrease in the efficiencies of the processes, all acids were synthetized with over 50 % of productivity. The presented results confirm the effective protein co-immobilization, improvement of their stability and the possibility of their reuse, as well as the effective cofactor regeneration. Therefore the developed two enzymatic systems might be promising in application in the conversion of biomass components.

Substrate-inducible and antibiotic-free high-level 4-hydroxyvaleric acid production in engineered Escherichia coli

In this study, we developed a levulinic acid (LA)-inducible and antibiotic-free plasmid system mediated by HpdR/P hpdH and infA-complementation to produce 4-hydroxyvaleric acid (4-HV) from LA in an engineered Escherichia coli strain. The system was efficiently induced by the addition of the LA substrate and resulted in tight dose-dependent control and fine-tuning of gene expression. By engineering the 5′ untranslated region (UTR) of hpdR mRNA, the gene expression of green fluorescent protein (GFP) increased by at least two-fold under the hpdH promoter. Furthermore, by evaluating the robustness and plasmid stability of the proposed system, the engineered strain, IRV750f, expressing the engineered 3-hydroxybutyrate dehydrogenase (3HBDH∗) and formate dehydrogenase (CbFDH), produced 82 g/L of 4-HV from LA, with a productivity of 3.4 g/L/h and molar conversion of 92% in the fed-batch cultivation (5 L fermenter) without the addition of antibiotics or external inducers. Overall, the reported system was highly beneficial for the large-scale and cost-effective microbial production of value-added products and bulk chemicals from the renewable substrate, LA.

Corn stover hydrolysate and levulinic acid: Mixed substrates for short-chain polyhydroxyalkanoate production

The plastic disposal problem has been augmented over the years due to the surge in utilization of single-use plastics, the indiscriminate discarding of plastics, and space limitations associated with landfill sites. Therefore, in this study the biodegradable, biorenewable, and biocompatible plastic substitutes, poly(hydroxyalkanoate) (PHA) biopolymers were synthesized from low-value and high-volume corn stover in combination with levulinic acid (LevA). Acid hydrolysis liberated the fermentable sugars from the cellulosic and hemicellulosic fractions of the corn stover. This hydrolysate was used as a feedstock in combination with LevA to produce a terpolyester composed of 3-hydroxybutyric acid (3-HB), 3-hydroxyvaleric acid (3-HV), and 4-hydroxyvaleric acid (4-HV) by the bacterium Azohydromonas lata, and a copolymer of 3-HB and 3-HV by the bacterium Burkholderia sacchari. Detoxification of the hydrolysate through ‘overliming’ was necessary to induce bacterial growth and PHA production in A. lata, while B. sacchari was able to utilize the hydrolysate without detoxification achieving a maximum PHA titer of 1.2 g PHA/L. The inclusion of higher LevA in the medium affected the monomeric composition of the copolymers produced by B. sacchari resulting in a 3-HB:3-HV ratio of 39:61 when grown in the presence of 0.4% (w/v) LevA. In contrast, the monomeric compositions were relatively unaffected by the LevA media concentration for the PHA biopolymers produced by A. lata. The results of this study should help reduce the overall costs to synthesize bacterially derived PHA biopolymers and increase their applicability, thus reducing our dependence on recalcitrant petroleum-based plastics.

Metabolic Engineering of Escherichia coli for Production of Polyhydroxyalkanoates with Hydroxyvaleric Acid Derived from Levulinic Acid.

Polyhydroxyalkanoates (PHAs) are emerging as alternatives to plastics by replacing fossil fuels with renewable raw substrates. Herein, we present the construction of engineered Escherichia coli strains to produce short-chain-length PHAs (scl-PHAs), including the monomers 4-hydroxyvalerate (4HV) and 3-hydroxyvalerate (3HV) produced from levulinic acid (LA). First, an E. coli strain expressing genes (lvaEDABC) from the LA metabolic pathway of Pseudomonas putida KT2440 was constructed to generate 4HV-CoA and 3HV-CoA. Second, both PhaAB enzymes from Cupriavidus necator H16 were expressed to supply 3-hydroxybutyrate (3HB)-CoA from acetyl-CoA. Finally, PHA synthase (PhaCCv) from Chromobacterium violaceum was introduced for the subsequent polymerization of these three monomers. The resulting E. coli strains produced four PHAs (w/w% of dry cell weight): 9.1 wt% P(4HV), 1.7 wt% P(3HV-co-4HV), 24.2 wt% P(3HB-co-4HV), and 35.6 wt% P(3HB-co-3HV-co-4HV).

Correction: Tuning the selectivity of electrochemical levulinic acid reduction to 4-hydroxyvaleric acid: a monomer for biocompatible and biodegradable plastics

Correction for ‘Tuning the selectivity of electrochemical levulinic acid reduction to 4-hydroxyvaleric acid: a monomer for biocompatible and biodegradable plastics’ by Francisco W. S. Lucas et al., Green Chem., 2021, 23, 9154–9164, DOI: 10.1039/D1GC02826J.

Electrochemical Valorization of Biomass-Derived Feedstocks: Levullinic Acid to 4-Hydroxyvaleric Acid

Fossil fuel-based sources of energy are being gradually replaced by renewable electricity (such as solar, wind, etc), while there is a rising interest in biomass as a sustainable platform to produce fuels and other carbon-based chemicals.1,2 Electrochemistry is thus an attractive approach for the valorization of biomass-derived feedstocks. This approach has shown some advantages compared to traditional thermal- or bio-based chemical conversion such as the amenability to operate directly on aqueous biomass hydrolysate streams, and operability near ambient conditions, which also facilitates distributed scale production.2 This work discusses the electrochemical conversion of levulinic acid (LA) to 4-hydroxyvaleric acid (HVA). HVA is a versatile compound that can be used as a monomer for the production of biodegradable and biocompatible polyesters, in addition to diverse commodities and fine chemicals.3,4 It is projected that the biopolymers industry will reach a global market size of USD 27.9 billion by 2025.5 While prior work has demonstrated that LA can be electrochemically converted into valeric acid (VA) and γ-valerolactone (GVL), among other compounds,2, HVA has only previously been fund as a trace-level intermediate of LA electrochemical reduction into GVL.Here, we show a maximum HVA production rate higher than 40 g L-1 h-1 (i.e., 200 kg L-1 m-2 h-1) at 100% selectivity, and conversion and faradaic efficiency of 81%, while complete LA conversion could also be achieved under lower rates. Our characterization indicates this can further be optimized by reactor design (particularly the mass transport properties) and electrolyte engineering. Though evaluation of different pHs, aqueous supporting electrolytes, temperature, electrode potential, stirring rates, and initial concentration of LA we also elaborate on mechanistic underpinnings of the reaction selectivity, proposing that the formation of VA and GVL is through surface-mediated reactions, while HVA is formed via an outer sphere electron transfer (OSET) route (Fig.1). References (1) npj Clim. Atmos. Sci. 2019, 2 (1), 35.(2) ACS Energy Lett. 2021, 1205–1270. https://doi.org/10.1021/acsenergylett.0c02692.(3) . J. Biotechnol. 2015, 210, 38–43.(4) J. Agric. Food Chem. 2019, 67 (9), 2540–2546.(5) Global Bioplastics & Biopolymers Market Outlook 2020-2025 https://www.globenewswire.com/news-release/2020/04/17/2017839/0/en/Global-Bioplastics-Biopolymers-Market-Outlook-2020-2025.html (accessed April 22, 2021). Figure 1

Stability of gamma-valerolactone under pulping conditions as a basis for process optimization and chemical recovery

This study focuses on the investigation of the extent of the γ-valerolactone (GVL) hydrolysis forming an equilibrium with 4-hydroxyvaleric acid (4-HVA) in aqueous solutions over a wide pH range. The hydrolysis of a 50 wt% GVL solution to 4-HVA (3.5 mol%) was observed only at elevated temperatures. The addition of sulfuric acid (0.2 × 10–5 wt% to 6 wt%) at elevated temperatures (150–180 °C) and reaction times between 30 and 180 min caused the formation of 4 mol% 4-HVA. However, with decreasing acidity, the 4-HVA remained constant at about 3 mol%. The hydrolysis reactions in alkaline conditions were conducted at a constant time (30 min) and temperature (180 °C) with the variation of the NaOH concentration (0.2 × 10–6 wt% to 7 wt%). The addition of less than 0.2 wt% of NaOH resulted in the formation of less than 4 mol% of sodium 4-hydroxyvalerate. A maximum amount of 21 mol% of 4-HVA was observed in a 7 wt% NaOH solution. The degree of decomposition after treatment was determined by NMR analysis. To verify the GVL stability under practical conditions, Betula pendula sawdust was fractionated in 50 wt% GVL with and without the addition of H2SO4 or NaOH at 180 °C and a treatment time of 120 min. The spent liquor was analyzed and a 4-HVA content of 5.6 mol% in a high acidic (20 kg H2SO4/t wood) and 6.0 mol% in an alkaline (192 kg NaOH/t wood) environment have been determined.

Chemoenzymatic valorization of agricultural wastes into 4-hydroxyvaleric acid via levulinic acid

Given that (i) levulinic acid (LA) is one of the most significant platform chemicals derived from biomass and (ii) 4-hydroxyvaleric acid (4-HV) is a potential LA derivative, the aim of this study is to achieve chemoenzymatic valorization of LA, which was obtained from agricultural wastes, to 4-HV. The thermochemical process utilized agricultural wastes (i.e., rice straw and corncob) as feedstocks and successfully produced LA, ranging from 25.1 to 65.4 mM. Additionally, formate was co-produced and used as a hydrogen source for the enzymatic hydrogenation of LA. Finally, engineered 3-hydroxybutyrate dehydrogenase from Alcaligenes faecalis (eHBDH) was applicable for catalyzing the conversion of agricultural wastes-driven LA, resulting in a maximum concentration of 11.32 mM 4-HV with a conversion rate of 48.2%. To the best of our knowledge, this is the first report describing the production of 4-HV from actual biomass, and the results might provide insights into the valorization of agricultural wastes.

Fermentative High-Level Production of 5-Hydroxyvaleric Acid by Metabolically Engineered Corynebacterium glutamicum

We report metabolic engineering of Corynebacterium glutamicum (C. glutamicum) for high-level production of 5-hydroxyvaleric acid (5-HV), an important C5 platform chemical covering a wide range of i...

Tuning the selectivity of electrochemical levulinic acid reduction to 4-hydroxyvaleric acid: a monomer for biocompatible and biodegradable plastics

Levulinic acid (LA) is a biomass-derived feedstock; herein, we present an efficient electrochemical method for converting LA into 4-hydroxyvaleric acid, a valuable monomer for bio-polyesters, as well as γ-valerolactone (a green fuel/solvent).

Hydrogenolysis of tetrahydrofuran-2-carboxylic acid over tungsten-modified rhodium catalyst

Catalysts for reduction of tetrahydrofuran-2-carboxylic acid (THFCA), which can be synthesized from furfural via oxidation and hydrogenation, were explored among the combinations of noble metal and reducible metal oxide supported on SiO2. Rh-WOx/SiO2 catalysts showed activity in C-O hydrogenolysis at 2-position of THFCA (to δ-valerolactone and 5-hydroxyvaleric acid) and higher yield ratio of these C-O hydrogenolysis products to carboxylic acid hydrogenation products than other bimetallic catalysts. The activity of Rh-WOx/SiO2 catalysts was highest at W/Rh = 0.25 mol/mol. XRD, TPR, CO adsorption and XAFS characterizations showed that the Rh-WOx/SiO2 (W/Rh = 0.25) catalyst contained Rh metal particles with surface modification with isolated W2+ oxide species. The mechanism that hydride-like species formed on Rh atom attacks the C atom at the α-position (2-position) of adsorbed carboxylate on W atom is proposed based on the similar kinetics and similar catalyst structure to Rh-MOx/SiO2 (M = Re, Mo) which is known to be active in THFA hydrogenolysis to 1,5-pentanediol.