Development of Betaine-Based Sustainable Catalysts for Green Conversion of Carbohydrates and Biomass into 5-Hydroxymethylfurfural

Photocatalytic conversion of sugars to 5-hydroxymethylfurfural using aluminium(III) and fulvic acid

5-hydroxymethylfurfural (HMF) is a valuable and essential platform chemical for establishing a sustainable, eco-friendly fine-chemical and pharmaceutical industry based on biomass. The cost-effective production of HMF from abundant C6 sugars requires mild reaction temperatures and efficient catalysts from naturally abundant materials. Herein, we report how fulvic acid forms complexes with Al³⁺ ions that exhibit solar absorption and photocatalytic activity for glucose conversion to HMF in one-pot reaction, in good yield (~60%) and at moderate temperatures (80 °C). When using representative components of fulvic acid, catechol and pyrogallol as ligands, 70 and 67% HMF yields are achieved, respectively, at 70 °C. Al³⁺ ions are not recognised as effective photocatalysts; however, complexing them with fulvic acid components as light antennas can create new functionality. This mechanism offers prospects for new green photocatalytic systems to synthesise a range of substances that have not previously been considered.

Electroreductive CO coupling of benzaldehyde over SACs Au-NiMn2O4 spinel synergetic composites

Electroreductive CO coupling provides a prospective strategy for biomass derivative upgrading via reducing the number of oxygen-containing functional groups and increasing their molecular weight. However, exploring superior electrocatalysts with effective reactivity and high selectivity for target products are still a challenge. In this work, single atom Au surface derived NiMn₂O₄ (SACs Au-NiMn₂O₄) spinel synergetic composites were fabricated by a versatile adsorption-deposition method and applied in electroreductive self-coupling of benzaldehyde to dibenzyl ether. The SACs Au-NiMn₂O₄ spinel synergetic composites enhanced electroreductive coupling of benzaldehyde, significantly improved the yield and selectivity of dibenzyl ether. Systematic characterizations and density functional theory calculation revealed that atomically dispersed Au occupied surface Ni²⁺ vacancies, which played a dominated role in CO coupling of benzaldehyde. Detailed calculation results showed that benzaldehyde preferred to adsorb on Ni octa-hedral sites of NiMn₂O₄ spinel synergetic structure, single atom Au surficial derivation over NiMn₂O₄ further reduced the adsorption energy (E_ads) of benzaldehyde on SACs Au-NiMn₂O₄, thus the CO coupling of benzaldehyde to dibenzyl ether was promoted. Moreover, single atom Au surficial derivation lowered the energy barrier of rate-determining step, facilitated the formation of dibenzyl ether species. Our work also paves an avenue for rational design single atom materials using spinel as support.

Probing the effects of fructose concentration on the evolution of humins during fructose dehydration

A universal understanding on the concentration-aggravated evolution of humins during fructose dehydration has been demonstrated, wherein difructose anhydrides act as the key intermediates for both 5-hydroxymethylfurfural and humin formations.

Earth-abundant 3d-transition-metal catalysts for lignocellulosic biomass conversion

Transformation of biomass to chemicals and fuels is a long-term goal in both science and industry. However, high cost is one of the major obstacles to the industrialization of this sustainable technology. Thus, developing catalysts with high activity and low-cost is of great importance for biomass conversion. The last two decades have witnessed the increasing achievement of the use of earth-abundant 3d-transition-metals in catalysis due to their low-cost, high efficiency and excellent stability. Here, we aim to review the fast development and recent advances of 3d-metal-based catalysts including Cu, Fe, Co, Ni and Mn in lignocellulosic biomass conversion. Moreover, present research trends and invigorating perspectives on future development are given.

Catalytic Conversion of Biomass to Furanic Derivatives with Deep Eutectic Solvents

Biomass is the only renewable organic carbon resource in nature, and the transformation of abundant biomass into various chemicals has received immense spotlight. As a novel generation of designer solvents, deep eutectic solvents (DESs) have been widely used in biorefinery due to their excellent properties including low cost, easy preparation, and biodegradability. Although there have been some reports summarizing the performance of DESs for the transformation of biomass into various chemicals, few Reviews illuminate the relationship between the functional structure of DESs and catalytic conversion of biomass. Hence, this Minireview comprehensively summarizes the effects of the types of functional groups in DESs on catalytic conversion of biomass into furanic derivatives, such as carboxylic acid-based hydrogen-bond donors (HBDs), carbohydrate-based HBDs, polyalcohol-based HBDs, amine/amide-based HBDs, spatial structure of HBDs, and various hydrogen-bond acceptors (HBAs). It also further summarizes the effects of adding different additives into the DESs on the synthesis of high value-added chemicals, including water, liquid inorganic acids, Lewis acids, heteropoly acids, and typical solid acids. Moreover, current challenges and prospects for the application of DESs in biomass conversion are provided.

Green Process for 5-(Chloromethyl)furfural Production from Biomass in Three-Constituent Deep Eutectic Solvent

5-(Chloromethyl)furfural (CMF), a versatile bio-platform molecule, was first synthesized in a three-constituent deep eutectic solvent (3c-DES) including choline chloride, AlCl₃  ⋅ 6H₂ O, and oxalic acid. In particular, 3c-DES was conducive for the production of CMF from glucose and provided a CMF yield of 70 % at 120 °C within 30 min. In addition, CMF yields reached up to 86, 80, 30, 29, and 35 % from fructose, sucrose, cellulose, bamboo, and bamboo pulp, respectively. This study opens new avenues for the preparation of CMF.

Deep eutectic solvents as non-traditionally multifunctional media for the desulfurization process of fuel oil

Deep eutectic solvents (DESs) have been intensively pursued in the field of separation processes, catalytic reactions, polymers, nanomaterial science, and sensing technologies due to their unique features such as the low cost of components, ease of preparation, tunable physicochemical properties, negligible vapor pressure, non-toxicity, renewability, and biodegradability in the recent decade. Considering these appealing merits, DESs are widely used as extraction agents, solvents and/or catalysts in the desulfurization process since 2013. This review is focused on summarizing the physicochemical properties of DESs (i.e., freezing point, density, viscosity, ionic conductivity, acidity, hydrophilicity/hydrophobicity, polarity, surface tension, and diffusion) to some extent, and their significant advances in applications related to desulfurization processes such as extraction desulfurization, extraction-oxidation desulfurization, and biomimetic desulfurization. In particular, we systematically compile very recent works concerning the selective aerobic oxidation desulfurization (AODS) under extremely mild conditions (60 °C and ambient pressure) via a biomimetic approach coupling DESs with polyoxometallates (POMs). In this system, DESs act as multifunctional roles such as extraction agents, solvents, and catalysts, while POMs serve as electron transfer mediators. This strategy is inspirational since biomimetic or bioinspired catalysis is the "Holy Grail" of oxidation catalysis, which overcomes the difficulty of O2 activation via introducing electron transfer mediators into this system. It not only can be used for AODS, but also paves a novel way for oxidation catalysis, such as the selective oxyfunctionalization of hydrocarbon. Eventually, the conclusion, current challenges, and future opportunities are discussed. The aim is to provide necessary guidance for precisely designing tailor-made DESs, and to inspire chemists to use DESs as a powerful platform in the field of catalysis science.

LiCl-promoted-dehydration of fructose-based carbohydrates into 5-hydroxymethylfurfural in isopropanol

The carbohydrate-derived 5-hydroxymethylfurfural (HMF) is one of the most versatile intermediate chemicals, and is promising to bridge the growing gap between the supply and demand of energy and chemicals. Developing a low-cost catalytic system will be helpful to the production of HMF in industry. Herein, the commercially available lithium chloride (LiCl) and isopropanol (i-PrOH) are used to construct a cost-effective and low-toxic system, viz., LiCl/i-PrOH, for the preparation of HMF from fructose-based carbohydrates, achieving ∼80% of HMF yield under the optimum conditions. The excellent promotion effect of LiCl on fructose conversion in i-PrOH could be attributed to the synergistic effect of LiCl with i-PrOH through the LiCl-promoted and i-PrOH-aided dehydration process, and the co-operation of LiCl and i-PrOH for stabilizing the as-formed HMF by hydrogen/coordination bonds, giving a low activation energy of 68.68 kJ mol-1 with a pre-exponential factor value of 1.2 × 104 min-1. The LiCl/i-PrOH system is a substrate-tolerant and scalable catalytic system, fructose (scaled up 10 times), sucrose, and inulin also give 73.6%, 30.3%, and 70.3% HMF yield, respectively. Moreover, this system could be reused 8 times without significant loss of activity. The readily available and low-toxic LiCl, the sustainable solvent (i-PrOH), the renewable starting materials, and the mild reaction conditions make this system promising and sustainable for the industrial production of HMF in future.

Keggin-type Heteropolyacids-Catalyzed Selective Hydrothermal Oxidation of Microalgae for Low Nitrogen Biofuel Production

Hydrothermal liquefaction (HTL) of microalgae for biofuel production is suffering from low bio-oil yield and high heteroatomic compositions owing to their low efficiency and selectivity to hydrolysis of cellular compounds. Hereby we report Keggin-type (Mo-V-P) heteropolyacids (HPAs)-catalyzed HTL of microalgae for efficient low-nitrogen biocrude production. The increases of reaction temperature, reaction time, and vanadium substitution degrees of HPAs are favorable to biocrude yield initially, whereas a significant decrease of biocrude yield is observed owing to the enhanced oxidation of carbohydrates above the optimum reaction conditions. The maximum biocrude yield of HPAs-catalyzed HTL of microalgae is 29.95 % at reaction temperature of 300 °C, reaction time of 2 h, and 5 wt% of HPA-4, which is about 19.66 % higher than that of control with 71.17 % less N-containing compounds, including 1,3-propanediamine, 1-pentanamine, and 2, 2'-heptamethylene-di-2-imidazoline than that of control. This work reveals that HPAs with Brønsted acidity and reversible redox properties are capable of both enhancing biocrude production via catalyzing the hydrolysis of cellular compounds and reducing their nitrogen content through avoiding the Maillard reactions between the intermediates of hydrolysis of carbohydrates and proteins. HPAs-catalyzed HTL is an efficient strategy to produce low N-containing biofuels, possibly paving the way of their direct use in modern motors.

Synthesis of MCM-41-Supported Metal Catalysts in Deep Eutectic Solvent for the Conversion of Carbohydrates into 5-Hydroxymethylfurfural

A series of MCM-41 supported metal catalysts (denoted M/D41) were prepared by using the deep eutectic solvent (DES)-mediated ionothermal synthesis strategy. Al/D41 was found to have excellent performance in the conversion of carbohydrates into 5-hydroxymethylfurfural (HMF). Furthermore, the production of HMF from glucose could be performed at high concentrations in choline chloride aqueous solution (CAS; 32 wt %, relative to the reaction phase) and as a result, CAS is a more promising solvent than water and DES for HMF production.