High Value-added Chemicals Research Articles

Continuous flow versatile conversion of furfural to valuable end products catalyzed by commercial Pd/C

The conversion of furfural has gained significant attention in recent years due to its potential for transforming this basic chemical into a wide range of valuable end products, such as alcohols, amines, acids, and biopolymers. This contribution aims to demonstrate the versatility and potential of continuous flow processes combined with commercial Pd/C catalysts for converting furfural into high value-added chemicals, including furfuryl alcohol, tetrahydrofurfuryl alcohol, and furfurylimine. By optimizing reaction conditions, high product yields (60–90%) were achieved, marking the first literature example of continuous flow conversion of furfural into diverse products, such as alcohols and imines. This work advances the production of high-value products using propanol as a hydrogen donor, with high yields and selectivity, employing commercial catalysts in a scalable continuous process.

Targeted valorization of waste polycarbonate into bisphenol A dimethyl ether

The chemical recycling of waste polycarbonate (PC) plastic to produce high value-added chemicals represents a sustainable and economical approach to its management. Facile methods that utilize the unique structure of the bisphenol A (BPA) unit are expected to be more low-carbon and cost-effective. However, there are few established routes for converting BPA into valuable derivatives while preserving its structure. In this work, we developed a new pathway for the targeted valorization of PC waste into a multifunctional value-added chemical, bisphenol A dimethyl ether (BPAME). Using ionic liquids as catalysts, low-toxicity and environmentally friendly dimethyl carbonate (DMC) as a methyl source, and N-methylpyrrolidone as a co-solvent, we successfully achieved 100 % depolymerization of PC and an impressive 99 % yield of BPAME under mild conditions (150 °C, 6 h). Kinetic studies indicated that the methylation of BPA is the rate-determining step. Moreover, this innovative pathway not only transformed commercial PC waste into BPAME with exceptional selectivity (99 %) and high yield (≥92 %), but also facilitated the efficient methylation of aromatic phenols and amines. This valorization strategy for PC waste disposal offers a promising option for industrial applications.

Triazine- and amino-functionalized poly(ionic liquid) heterogeneous catalyst for efficient CO2 conversion under mild conditions

The efficient conversion of atmospheric CO2 into high value-added chemicals remains a persistent challenge. In this study, a novel strategy for the fabrication of triazine- and amino-functionalized poly(ionic liquid)s (PILs) was reported. By virtue of the rich nitrogen species, the newly-developed PILs possessed great potential in CO2 conversion to produce high-value chemicals. The systematic investigation illustrated that rich-nitrogen PILs could promote the cycloaddition reaction of CO2 and epoxides through the intramolecular synergy of multiple active sites. Excellent conversion and selectivity were achieved under the mild conditions without any co-catalysts and solvents. In addition, PIL heterogeneous catalysts could be easily recovered and reused at least several times without obvious loss in activity. The density functional theory calculation demonstrated that the superior catalytic activity of rich nitrogen PILs was attributed to the synergistic effect of hydrogen bond donor and triazine ring in the catalytic process. Our finding thus presents a versatile platform for fabricating multi-functional heterogeneous catalysts for efficient CO2 conversion.

Silica gel supported Cu nanoparticles for selective reductive etherification of furfural into isopropyl furfuryl ether

Furfural (FF) is one of the important platform molecules of biomass, which can be obtained by hydrolysis from lignocellulose and can produce many high value-added chemicals. In this study, a new 4.5 wt% Cu-supported silica gel (SG) catalyst with dual functions of metal and acid site was prepared by acid-base adsorption impregnation method. Isopropyl furfuryl ether (IPFE) with 80.4 % yield was obtained by one-pot reductive etherification of FF in 2-propanol at 150 °C under 2 MPa H2. The characterization of the catalyst proved that the Cu synthesized by this method was well dispersed, and the average size of Cu NPs was 3.34 nm. The reduction of FF to IPFE in a one-pot reaction system is deduced as follows: the existence of a hydrogenation-etherification pathway (main path) and an acetalization-hydrogenolysis pathway. The study in this paper provides a reference for the development of non-noble metal hydroetherification catalysts.

Ultrathin B:NiCoOx-modified BiVO4 photoanode with abundant oxygen vacancies for photoelectrochemical glycerol conversion coupled with hydrogen production

Photoelectrochemical (PEC) conversion of glycerol (GLY) into high value-added chemicals coupled with clean hydrogen production can be achieved over a BiVO4-based PEC cell, but the low photocurrent density and poor photostability of the most BiVO4 photoanodes limit the PEC performance and sustainable application of solar resources. Herein, we construct a high-efficiency stable photoanode by decorating an amorphous ultrathin B-activation NiCoOx (B:NiCoOx) nanolayer with abundant oxygen vacancies (Ov) on the BiVO4 photoanode via a simple immersing process. We demonstrate the optimized B:NiCoOx/BiVO4 photoanode in the PEC GLY oxidation yields a high photocurrent density of 6.05 mA cm−2 at 1.23 VRHE, a formic acid (FA) production rate of 360.3 mmol m−2 h−1, a dihydroxyacetone (DHA) production rate of 228.4 mmol m−2 h−1, with simultaneously hydrogen production at the cathode. An intermittent 60-h PEC GLY oxidation assay results indicates the superb durability of the B:NiCoOx/BiVO4 photoanode. The outstanding PEC performance is predominantly ascribed to the amorphous ultrathin structure of the B:NiCoOx nanolayer (∼ 2 nm) and the abundant Ov, which effectually accelerates the photogenerated holes transport/extraction and offers more catalytic active sites for the PEC GLY oxidation. Moreover, the free state and adsorbed state •OH radicals originated from active oxygen are deduced to be responsible for the oxidation of GLY to FA and GLY to DHA. This study develops a sustainable BiVO4-based catalyst with high activity and photostability for the PEC GLY oxidation and hydrogen production.

Efficient adsorption and selective separation of high value-added chemicals from simulated expired energy drinks by metal-organic frameworks

Expired energy drinks contain a certain amount of high-value chemicals, such as caffeine, that possess biological activity. The recovery and recycling of these valuable chemicals plays a crucial role in promoting the achievement of carbon emission reduction goals. In this work, 11 kinds of water-stable MOFs with different pore channel structure were synthesized and used for the first time to adsorb caffeine, nicotinic acid, or taurine from water. It has been found that the size effect of the topological structure of MOF adsorbents is the fundamental factor governing their adsorption performance. The optimized adsorbent UiO-67 exhibits excellent adsorption performance for caffeine and nicotinic acid, with respective adsorption capacities of 830 mg/g and 583 mg/g. The investigated MOF has a very low adsorption capacity for taurine (48 mg/g); therefore, selective separation of caffeine/taurine and nicotinic acid/taurine was achieved. The adsorption process can be accurately described by both the Langmuir model and pseudo-second-order model. Adsorption mechanism reveals that the main driving forces of the adsorption process are π-π interaction between UiO-67 and CN in caffeine, as well as hydrogen bonding interactions between the N atom of caffeine’s two CO groups and μ-OH of UiO-67.

Construction of dendritic mesoporous SiO2 supported Cu catalyst for hydrodeoxidation of lignin derivatives

Chemoselective hydrodeoxygenation (HDO) of lignin derivatives is of great importance in converting biomass into high value-added chemicals. Herein, we report a simple hydrothermal pathway to fabricate a highly active, chemically selective, and reusable catalyst (Cu/DMSN) by loading copper clusters on “dendritic” mesoporous silica nanospheres. Cu/DMSN exhibits exceptional catalytic activity (conversion > 99 %, selectivity > 99 %) in the HDO of vanillin toward 2-methoxy-4-methylphenol under mild conditions (140 °C, 0.5 MPa, 3 h), along with good scalability and a wide range of substrates. The excellent catalytic performance can be owed to the combination of suitable acid site and more exposed metal site. This study provides a new strategy for designing supported metal catalysts for hydrodeoxidation of biomass and its derivatives.

Tailoring the local catalytic microenvironment of metal centers NH2 groups to enhance the CO2RR performance of Ni based catalysts

Efficient catalytic reduction of the main greenhouse gas CO2 into high value-added chemicals is an important measure to alleviate the greenhouse effect and energy depletion. Metal nitrogen (M-N4) macrocyclic complexes have attracted increasing attention in the field of electrocatalytic CO2 reduction (CO2RR) due to the precise adjustment of the catalytic active site according to the requirements and the flexible modification of the external ligand structure. Nevertheless, the poor activity and low selectivity of reduction products restrict their widespread application in electrocatalytic CO2RR. Herein, a combination of nanoscale and molecular level method has been developed to construct easily obtainable 4NH2-NiPc/NH2-CNT hybrid material, in which amino groups are connected to provide electrons toward the central Ni-N4 site to promote the electrocatalytic CO2RR catalytic activity. As a result, the catalyst 4NH2-NiPc/NH2-CNT mainly produces CO in the electrocatalytic CO2RR, which exhibits a Faradaic efficiency of CO (FECO) higher than 92 % within a wide overpotential range of −0.70 to −0.95 V vs. RHE, and provides excellent stability with a current density of 12 mA cm−2 at −0.80 V vs. RHE. In addition, 4NH2-NiPc/NH2-CNT reaches its maximum FECO value of 96 % at −0.8 V vs. RHE, which is approximately 3.1 times that of the original unmodified NiPc/CNT, demonstrating excellent promotion of electrochemical performance. Similarly, compared to NiPc/CNT without amino modification, the current density of 4NH2-NiPc/NH2-CNT exceeds it by more than twice. The research results indicate that promoting role of electron substituted amino groups in catalysis dispersion and electronic environment coordination. This study proposes a promising strategy of introducing amino groups into molecular catalysts and hybridizing with carbon nanotube to enhance the electrocatalytic conversion of CO2 to deep reduction products.

Emergence of meta-methylbenzyl alcohol in novel pathway of ethanol with methacrolein catalyzed by hydroxyapatite

Bioethanol, a renewable resource, can be converted into high value-added chemicals. Methylbenzyl alcohol in its ortho- and para-isomers has been successfully synthesized from ethanol upgrading over metal-modified hydroxyapatite (HAP). However, meta-methylbenzyl alcohol (3-MB-OH), a particularly valuable fine chemical, has yet to be produced from ethanol. Herein, we present a novel reaction pathway for the selective synthesis of 3-MB-OH over HAP by co-feeding ethanol with methacrolein. Notably, the selectivity of 3-MB-OH reached up to 36.2 % in our tests. Experiments using intermediates as reactants proved that the introduction of methacrolein definitively led to the production of 3-MB-OH, which was also confirmed by in-situ diffuse reflectance infrared Fourier-transform spectroscopy. Moreover, we inferred the co-conversion reaction pathway of ethanol and methacrolein. Density functional theory calculations indicated that ethanol preferentially underwent Meerwein-Ponndorf-Verley hydrogen transfer with methacrolein, resulting in acetaldehyde formation and subsequently promoting the synthesis of aromatic compounds.

Dynamically Regulating Homologous Recombination Enables Precise Genome Editing in Ogataea polymorpha.

Methylotrophic yeast Ogataea polymorpha has become a promising cell factory due to its efficient utilization of methanol to produce high value-added chemicals. However, the low homologous recombination (HR) efficiency in O. polymorpha greatly hinders extensive metabolic engineering for industrial applications. Overexpression of HR-related genes successfully improved HR efficiency, which however brought cellular stress and reduced chemical production due to constitutive expression of the HR-related gene. Here, we engineered an HR repair pathway using the dynamically regulated gene ScRAD51 under the control of the l-rhamnose-induced promoter PLRA3 based on the previously constructed CRISPR-Cas9 system in O. polymorpha. Under the optimal inducible conditions, the appropriate expression level of ScRAD51 achieved up to 60% of HR rates without any detectable influence on cell growth in methanol, which was 10-fold higher than that of the wild-type strain. While adopting as the chassis strain for bioproductions, the dynamically regulated recombination system had 50% higher titers of fatty alcohols than that static regulation system. Therefore, this study provided a feasible platform in O. polymorpha for convenient genetic manipulation without perturbing cellular fitness.

Efficient cleavage of C-C bond in lignin adopting Z-scheme heterojunction photocatalyst by g-C3N4/CQDs/WO3

It is a practical approach to overcome the shortage of energy and environmental pollution simultaneously if obtaining useful products from biomass through chemical decomposition. Photocatalytic depolymerization of lignin to generate high value-added chemicals has received extensive attention for decades. The low yield of aromatic monomers is still one of the urgent problems to be solved. Selective breakage of Cα-Cβ bonds in lignin is of importance to improve the yield of aromatic monomers. Herein, Z-scheme heterojunction g-C3N4/CQDs/WO3 was constructed by combining graphite-like carbon nitride (g-C3N4), tungsten oxide (WO3) with carbon quantum dots (CQDs) to break the C-C bond selectively in β-O-4 model compounds. Both the efficiencies of substrate conversion and selectivity of C-C bond cleavage reached to 99 %. As a result, the total yield of benzaldehyde and benzoic acid attained to 83.92 %. Furthermore, the photocatalyst has satisfactory effect on depolymerization of four types of lignin, while the heterojunction can validly reduce the recombination rate of photogenerated carriers. Additionally, CQDs broadens the light absorption range and enhances the mobility of photogenerated carriers. Consequently, this study provides a feasible idea for highly selective cleavage of lignin C-C bonds through heterojunction engineering.

Unusual Long-Term Stability of Enzymatic Bioelectrocatalysis in Organic Solvents

Organic solvent tolerant enzymes are of tremendous importance for the pharmaceutical industry in search of high added-value chemicals. However, enzymes exhibit usually weak long-term activity and stability in various media. Here, we report a general strategy allowing stabilizing and keeping enzymes active in biphasic systems upon immobilization on an electrode surface. It consists in the combination of an engineered solvent-tolerant enzyme, combined with fine-tuned osmium-based redox polymers where the concentration of osmium complex has been specifically tuned to minimize its deswelling associated with the use of porous gold electrodes. This approach is validated with bilirubin oxidase as a model system. This copper enzyme is able to oxidize a wide range of substrates, combined with the reduction of O2 to water. While all other enzymatic systems irreversibly lose their activity and stability in the presence of 7.5 M methanol or below, this optimized enzymatic system stays functional in 12.5 M methanol with no loss in current density. It exhibits a half-life of more than 8 days, which is unprecedented in the literature. We show that this electrode can also operate in DMSO, dioxane, acetonitrile and acetone, thus opening up a very wide variety of applications in the field of bioelectrocatalysis and bioelectrosynthesis. Figure: Example of a long-term stability experiment for a mediated bilirubin oxidase biocathode in 12.5 M methanol. Black curve: immobilized on a bare gold electrode; red curve: immobilized on a 11/2 layers porous gold electrode. Experiments performed at +0.1V vs. Ag/AgCl. The total loading was fixed at 600 µg.cm-2 for both experiments. Figure 1

Determination and analysis of 4-hydroxyphenylacetamide solubility in different solvents by Hansen solubility parameters, solvent effect and thermodynamic properties

4-Hydroxyphenylacetamide (HPAD) is commonly used in the synthesis of high value-added chemicals in the fields of medicine, food and agriculture, such as atenolol, p-hydroxyphenylacetic acid, L-phenylalanine and D-phenylalanine. HPAD relies on chemical synthesis, involving multi-step reactions and multiple chemical catalysts. It is crucial to select appropriate organic solvent to improve yield and purity. In this work, the solubility of HPAD in 12 pure solvents (water, acetonitrile, methanol, ethanol, n-propanol, isopropanol, n-butanol, n-hexane, n-heptane, methyl acetate, ethyl acetate, n-butyl acetate) and 3 binary solvents (n-hexane + methanol, acetonitrile + methanol, n-heptane + methanol) was investigated in the range of 278.15–323.15 K. The solubility of HPAD in the selected solvents was positively correlated with the temperature. Hansen solubility parameters were used to study the dissolution behavior of HPAD. Then, the solvent effect was analyzed by KAT-LSER model, and it was found that the hydrogen bond acidity and nonspecific dipolarity/polarizability of solvents favored the dissolution of HPAD. Moreover, the modified Apelblat model (MA model), λh model, CNIBS/R-K model (CNK model), Jouyban-Acree model (JA model), and SUN model were used to fit and analyze experimental data. The results showed that the MA model and the CNK model were the best models for single and binary solvents, respectively. Finally, van’t Hoff analysis showed that the dissolution of HPAD in the selected solvents was an endothermic and entropic driven process. This work provided reference data for the separation, purification and crystallization of HPAD, and had certain guiding significance for its industrial production and application.

Exploring industrial lignocellulosic waste: Sources, types, and potential as high-value molecules

Lignocellulosic biomass has a promising role in a circular bioeconomy and may be used to produce valuable molecules for green chemistry. Lignocellulosic biomass, such as food waste, agricultural waste, wood, paper or cardboard, corresponded to 15.7% of all waste produced in Europe in 2020, and has a high potential as a secondary raw material for industrial processes. This review first presents industrial lignocellulosic waste sources, in terms of their composition, quantities and types of lignocellulosic residues. Secondly, the possible high added-value chemicals obtained from transformation of lignocellulosic waste are detailed, as well as their potential for applications in the food industry, biomedical, energy or chemistry sectors, including as sources of polyphenols, enzymes, bioplastic precursors or biofuels. In a third part, various available transformation treatments, such as physical treatments with ultrasound or heat, chemical treatments with acids or bases, and biological treatments with enzymes or microorganisms, are presented. The last part discusses the perspectives of the use of lignocellulosic waste and the fact that decreasing the cost of transformation is one of the major issues for improving the use of lignocellulosic biomass in a circular economy and green chemistry approach, since it is currently often more expensive than petroleum-based counterparts.

Engineering a versatile yeast platform for sesquiterpene production from glucose or methanol.

Natural sesquiterpene are valuable compounds with diverse applications in industries, such as cosmetics and energy. Microbial synthesis offers a promising way for sesquiterpene production. Methanol, can be synthesized from CO2 and solar energy, serves as a sustainable carbon source. However, it is still a challenge to utilize methanol for the synthesis of value-added compounds. Pichia pastoris (syn. Komagataella phaffii), known for its efficient utilization of glucose and methanol, has been widely used in protein synthesis. With advancements in technology, P. pastoris is gradually engineered for chemicals production. Here, we successfully achieved the synthesis of α-bisabolene in P. pastoris with dual carbon sources by expressing the α-bisabolene synthase gene under constitutive promoters. We systematically analyzed the effects of different steps in the mevalonate (MVA) pathway when methanol or glucose was used as the carbon source. Our finding revealed that the sesquiterpene synthase module significantly increased the production when methanol was used. While the metabolic modules MK and PMK greatly improved carbon source utilization, cell growth, and titer when glucose was used. Additionally, we demonstrated the synthesis of β-farnesene from dual carbon source by replacing the α-bisabolene synthase with a β-farnesene synthase. This study establishes a platform strain that is capable to synthesize sesquiterpene from different carbon sources in P. pastoris. Moreover, it paves the way for the development of P. pastoris as a high-efficiency microbial cell factory for producing various chemicals, and lays foundation for large-scale synthesis of high value-added chemicals efficiently from methanol in P. pastoris.

Bimetallic Single Atom/Nanoparticle Ensemble for Efficient Photochemical Cascade Synthesis of Ethylene from Methane.

Light-driven photoredox catalysis presents a promising approach for the activation and conversion of methane (CH4) into high value-added chemicals under ambient conditions. However, the high C-H bond dissociation energy of CH4 and the absence of well-defined C-H activation sites on catalysts significantly limit the highly efficient conversion of CH4 toward multicarbon (C2+) hydrocarbons, particularly ethylene (C2H4). Herein, we demonstrate a bimetallic design of Ag nanoparticles (NPs) and Pd single atoms (SAs) on ZnO for the cascade conversion of CH4 into C2H4 with the highest production rate compared with previous works. Mechanistic studies reveal that the synergistic effect of Ag NPs and Pd SAs, upon effecting key bond-breaking and -forming events, lowers the overall energy barrier of the activation process of both CH4 and the resulting C2H6, constituting a truly synergistic catalytic system to facilitate the C2H4 generation. This work offers a novel perspective on the advancement of photocatalytic directional CH4 conversion toward high value-added C2+ hydrocarbons through the subtle design of bimetallic cascade catalyst strategy.

Efficient C(sp3)-H Bond Oxidation on Perovskite Quantum Dots Based on Ce-Oxygen Affinity.

Perovskite quantum dots (QDs) have shown attractive prospects in the field of visible photocatalysis, especially in the synthesis of high value-added chemicals. However, under aerobic conditions, the stable operation of QD catalysts has been limited by the reactive oxygen species (ROS) generated by photoexcitation, especially superoxide species O2⋅-. Here, we propose a strategy of Ce3+ doping in perovskite QDs to guide superoxide species for photocatalytic oxidation reactions. In C(sp3)-H bond oxidation of hydrocarbons, superoxide species were rapidly generated and efficiently utilized on the surface of perovskite QDs, which achieves the stable operation of the catalytic system and obtains a high product conversion rate (15.3 mmol/g/h for benzaldehydes). The mechanism studies show that the strong Ce-oxygen affinity accelerates the relaxation process of photoinduced exciton transfer to superoxide species and inhibits the radiative recombination pathway. This work provides a new idea of utilizing oxygen species on perovskite surface and broadens the design strategy of high-performance QD photocatalysts.

S-scheme TiO2/Bi2WO6 heterojunction for enhanced photocatalytic selective oxidation of toluene

Selective activation of saturated C–H bonds in hydrocarbons, such as the activation of the C–H bond in toluene, is an effective method for the production of high value-added chemicals. However, improving the C–H bond activation of toluene remains a challenge. In this study, S-scheme TiO2/Bi2WO6 composites were synthesized by loading TiO2 nanoparticles on Bi2WO6 flakes using a simple hydrothermal method. The physical and chemical properties of the prepared materials were characterized using X-Ray Diffraction (XRD), Fourier Transform Infrared Spectoscopy (FT-IR), Scanning Electronic Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS) and other characterization methods. Selective oxidation of toluene to benzaldehyde under visible light irradiation using air as an oxidizing agent. When the molar ratio of TiO2 and Bi2WO6 was 0.20, the composites exhibited excellent photocatalytic performance with a benzaldehyde production rate of 1725.41 μmol g−1 h−1, which was 2.31 and 1.91 times higher than that of TiO2 and Bi2WO6, respectively. This excellent performance is attributed to the formation of heterojunction structure by the loaded TiO2 nanoparticles, which improves the separation efficiency of photogenerated carriers and thus enhances its photocatalytic performance. In addition, the active substances involved in the photocatalytic reaction were identified by free radical trapping experiments as ·O2− and h+. Finally, the photocatalytic mechanism of S-scheme TiO2/Bi2WO6 composites was proposed by energy band structure analysis and radical trapping experiments. This study provides a simple design pathway for the construction of visible-light responsive bismuth tungstate-based heterojunction photocatalysts and some ideas for the development of new and efficient photocatalytic toluene selective oxidation catalysts.

Catalyst and base-free, direct oxidation of chitin to lactic acid with hydrogen peroxide

In recent years, the research on the conversion of chitin to high value-added chemicals has attracted more and more attention. At present, the method of preparing lactic acid from chitin mostly uses strong base or catalyst. The reaction system under alkaline condition not only corrodes the container but also easily harms the human body. Herein, a simple and effective method to convert chitin to organic acids in catalyst and base-free conditions is developed. The use of H2O2 only can efficiently convert chitin to organic acids in the absence of bases and catalysts. Under the optimal conditions of 30 mg chitin, 2.1 mL water, 0.9 mL H2O2 at 230 °C for 1.5 h, the lactic acid yield of chitin can reach 58.2 % and the total organic acid yield can reach 84.0 %. This work provides an efficient method for the resource utilization of chitin biomass.

Photochemical Aerobic Upcycling of Polystyrene Plastics via Synergistic Indirect HAT Catalysis.

Plastic pollution constitutes an evergrowing urgent environmental problem, since overaccumulation of plastic waste, arising from the immense increase of the production of disposable plastic products, overcame planet's capacity to properly handle them. Chemical upcycling of polystyrene constitutes a convenient method for the conversion of plastic waste into high-added value chemicals, suggesting an attractive perspective in dealing with the environmental crisis. We demonstrate herein a novel, easy-to-perform organocatalytic photoinduced aerobic protocol, which proceeds via synergistic indirect hydrogen atom transfer (HAT) catalysis under LED 390 nm Kessil lamps as the irradiation source. The developed method employs a BrCH2CN-thioxanthone photocatalytic system and was successfully applied to a variety of everyday-life plastic products, leading to the isolation of benzoic acid after simple base-acid work up in yields varying from 23-49 %, while a large-scale experiment was successfully performed, suggesting that the photocatalytic step is susceptible to industrial application.