Solid acid catalysed formation of ethyl levulinate and ethyl glucopyranoside from mono- and disaccharides

Lignin-Derived Ternary Polymeric Carbon as a Green Catalyst for Ethyl Levulinate Upgrading from Fructose

Currently, the utilization of lignocellulose mainly focuses on the conversion of polysaccharide components to value-added chemicals, such as ethyl levulinate (EL). Lignin is an important component of lignocellulosic biomass that is often neglected. Herein, ternary polymeric carbon (TPC–S) was synthesized by polymerization of mixed monomers (4-methylphenol, 4-ethylphenol, and 4-propylphenol) derived from lignin and subsequent sulfonation, which was used as a heterogeneous catalyst for the transformation of fructose to EL. Through a series of characterization methods, it was illustrated that the prepared catalyst had a layered porous structure. The calculated carbon layer spacing is 0.413 nm, and the average pore size is 5.1 nm. This structure greatly increases the specific surface area (165.2 m2/g) of the catalyst, which makes it possible to introduce more –SO3H species in the process of sulfonation, thus furnishing EL with increased yield. The effects of reaction temperature, time, catalyst dosage, and fructose initial concentration on the production of EL were investigated. It was found that 70.3% EL yield was detected at 130 °C for 10 h. In addition, the catalyst had good stability and could obtain 65.6% yield of EL in the fourth cycle. The obtained catalyst has the advantages of low cost, easy preparation, and high catalytic efficiency, which is expected to achieve efficient utilization of lignin and provide a potential solution for the future production of EL.

Advances in the Catalytic Reductive Amination of Furfural to Furfural Amine: The Momentous Role of Active Metal Sites

One-pot synthesis of sustainable primary amines by catalytic reductive amination of bio-based carbonyl compounds with NH₃ and H₂ is emerging as a promising and robust approach. The primary amines, especially furfuryl amine (FUA) derived from furfural (FUR), with a wide range of applications from pharmaceuticals to agrochemicals, have attracted much attention due to their versatility. This Review is majorly comprised of two segments on the reductive amination of FUR to FUA, one with precious (Ru, Pd, Rh) and the other with non-precious (Co, Ni) metals on different supports and in various solvent systems in the presence of NH₃ and H₂ . The active metal sites generated on multiple supports are accentuated with experimental evidence based on CO-diffuse reflectance infrared Fourier-transform spectroscopy, H₂ temperature-programmed reduction, X-ray photoelectron spectroscopy, and calorimetry. Moreover, this Review comprehensively describes the role of acidic and basic support for the metal on the yield of FUA. Overall, this Review provides an insight into how to design and develop an efficiently robust catalyst for the selective reductive amination of a broad spectrum of carbonyl compounds to corresponding amines.

Direct Alcoholysis of Carbohydrate Precursors and Real Cellulosic Biomasses to Alkyl Levulinates: A Critical Review

Alkyl levulinates (ALs) represent outstanding bio-fuels and strategic bio-products within the context of the marketing of levulinic acid derivatives. However, their synthesis by acid-catalyzed esterification of pure levulinic acid, or by acid-catalyzed alcoholysis of furfuryl alcohol, although relatively simple, is still economically disadvantageous, due to the high costs of the pure precursors. The direct one-pot alcoholysis of model C6 carbohydrates and raw biomass represents an alternative approach for the one-step synthesis of ALs. In order to promote the market for these bio-products and, concurrently, the immediate development of new applications, it is necessary to speed up the intensification of their production processes, and this important achievement is onlypossible by using low-cost or, even better, waste biomasses, as starting feedstocks. This review provides an overview of the most recent and promising advances on the one-pot production of ALs from model C6 carbohydrates and real biomasses, in the presence of homogeneous or heterogeneous acid catalysts. The use of model C6 carbohydrates allows for the identification of the best obtainable ALs yields, resulting in being strategic for the development of new smart catalysts, whose chemical properties must be properly tuned, taking into account the involved reaction mechanism. On the other hand, the transition to the real biomass now represents a necessary choice for allowing the next ALs production on a larger scale. The improvement of the available synthetic strategies, the use of raw materials and the development of new applications for ALs will contribute to develop more intensified, greener, and sustainable processes.

Current Approaches to Alkyl Levulinates via Efficient Valorization of Biomass Derivatives

Biomass is a potential non-food, carbon-neutral, and abundant resource, which can be used as an alternative to fossil fuels during the sustainable preparation of various platform chemicals. Alkyl levulinates (ALs) have found widespread application as flavorings, plasticizing agents, and fuel additives, as well as synthetic precursors to various building blocks. Several processes have been investigated to transform biomass and its derivatives into ALs, which mainly include: (i) direct esterification of levulinic acid (LA) with alkyl alcohols and (ii) alcoholysis reactions of renewable biomass feedstocks and their derivatives, including furfuryl alcohol (FAL), chloromethyl furfural (CMF), and saccharides. This review focuses on illustrating the effects of the biomass pretreatment step, catalyst texture, possible mechanisms, acidities, and intermediates on the synthesis of ALs from sustainable resources covering a wide range of intermediates, including diethyl ether (DEE), 4,5,5-triethoxypentan-2-one (TEP), ethoxymethylfuran (EMF), ethyl-D-fructofuranoside (EDFF), and ethyl-D-glucopyranoside (EDGP).

Rapid Depolymerization of Decrystallized Cellulose to Soluble Products via Ethanolysis under Mild Conditions

Efficient cellulose depolymerization is a major bottleneck for economical production of second-generation biofuels. In this work, crystalline cellulose was subjected to sequential ball milling and ethanolysis as a mild and selective depolymerization approach. Ball milling and ethanolysis resulted in 38±1 % cellulose conversion, with 24 % ethyl-glucopyranoside as the main identified and quantified product and negligible side reaction of the ethanol solvent to form diethyl ether. In comparison, ethanolysis of the original cellulose resulted in only 3±1 % conversion. Additional soluble products from cellulose ethanolysis included carbohydrate isomers and oligomers, differing from the products obtained from hydrolysis. X-ray diffraction and nuclear magnetic resonance spectroscopy revealed increased crystallinity post-reaction, retarding further depolymerization. Hot liquid water extracted soluble oligomers from the ethanolyzed cellulose, suggesting formation of a nanoscale barrier of crystalline cellulose that traps soluble products during ethanolysis. Use of cellulose-swelling co-solvents and repeated mechanical decrystallization both proved effective at increasing cellulose conversion and soluble product yields. Repeated ball milling and ethanolysis resulted in 62±1 % cellulose conversion. Ethanolysis of decrystallized cellulose has potential for rapid (<2 h) de-polymerization at mild conditions.

Study of a recycling reaction system for catalytic transformation of biomass-based carbohydrates via acidic-polar biphasic conditions

Ethyl levulinate was easily produced via one-pot conversion of sucrose under a reusable biphasic system over an active/stable acid catalyst.

Niobium pentoxide nanomaterials with distorted structures as efficient acid catalysts

Niobium pentoxides are promising acid catalysts for the conversion of biomass into fuels and chemicals. Developing new synthesis routes is essential for designing niobium pentoxide catalysts with improved activity for specific practical processes. Here we show a synthesis approach in acetophenone, which produces nanostructured niobium pentoxides with varying structure and acidity that act as efficient acid catalysts. The oxides have orthorhombic structures with different extents of distortions and coordinatively unsaturated metal atoms. A strong dependence is observed between the type and strength of the acid sites and specific structural motifs. Ultrasmall niobium pentoxide nanoparticles, which have strong Brønsted acidity, as well as Lewis acidity, give product yields of 96% (3 h, 140 °C, 100% conversion), 85% (3 h, 140 °C, 86% conversion), and 100% (3 h, 110 °C, 100% conversion) in the reactions of furfuryl alcohol, 5-(hydroxymethyl)furfural, and α-angelica lactone with ethanol, respectively.

Synthesis of Biomass-Derived Ethers for Use as Fuels and Lubricants

Ethers synthesized from biomass-derived compounds have exceptional properties as fuels, lubricants, and specialty chemicals and can serve as replacements for petroleum-derived products. Recent efforts have identified heterogeneous catalysts for the selective synthesis of ethers from alcohols, aldehydes, ketones, furans, esters, olefins, carboxylic acids, and other molecules derived from biomass. This Review highlights the scope of etherification reactions and provides insights into the choice of catalysts and reaction conditions best suited for producing targeted ethers from the available starting materials. First, the properties of ethers for specific applications and the methods by which synthons for ether synthesis can be obtained from biomass are discussed. Then the progress that has been made on the synthesis of ethers via the following methods is summarized: direct etherification of alcohols; reductive etherification of alcohols with aldehydes or ketones; etherification of furanic compounds, esters, and carboxylic acids; and the addition of alcohols to olefins. Next, the mechanisms of these reactions and catalyst properties required to promote them are discussed, with the goal of understanding how reaction conditions can be tuned to optimize catalyst activity and selectivity towards desired ethers. The Review closes by examining the tradeoffs between catalyst selectivity, activity, stability, and reaction conditions required to achieve the most economically and environmentally favorable routes to biomass-derived ethers.

Catalytic Upgrading of Biomass-Derived Sugars with Acidic Nanoporous Materials: Structural Role in Carbon-Chain Length Variation

Shifting from petroleum-based resources to inedible biomass for the production of valuable chemicals and fuels is one of the significant aspects in sustainable chemistry for realizing the sustainable development of our society. Various renowned biobased platform molecules, such as 5-hydroxymethylfurfural, furfural, levulinic acid, and lactic acid, are successfully accessible from the transformation of biobased sugars. To achieve the specific reaction routes, heterogeneous nanoporous acidic materials have served as promising catalysts for the conversion of bio-sugars in the past decade. This Review summarizes advances in various nanoporous acidic materials for bio-sugar conversion, in which the number of carbon atoms is variable and controllable with the assistance of the switchable structure of nanoporous materials. The major focus of this Review is on possible reaction pathways/mechanisms and the relationships between catalyst structure and catalytic performance. Moreover, representative examples of catalytic upgrading of biobased platform molecules to biochemicals and fuels through selective C-C cleavage and coupling strategies over nanoporous acidic materials are also discussed.

One pot conversion of glucose to ethyl levulinate over a porous hydrothermal acid catalyst in green solvents

The one-pot conversion of glucose to ethyl levulinate over an acid-functionalised hydrothermal catalyst (derived from glucose) provides high initial yields up to 37 mol%, comparable to the homogeneous H₂SO₄ catalyst, whilst catalyst performance is strongly influenced by green solvent choice.

One-pot conversion of glucose to ethyl levulinate over an acid-functionalised hydrothermal carbon gives high initial yields up to 37 mol% (comparable to H₂SO₄) with catalyst performance strongly influenced by green solvent choice.

Upgrading of Carbohydrates to the Biofuel Candidate 5-Ethoxymethylfurfural (EMF)

5-Ethoxymethylfurfural (EMF), one of the significant platform molecular derivatives, is regarded as a promising biofuel and additive for diesel, owing to its high energy density (8.7 kWh·L−1). Several catalytic materials have been developed for the synthesis of EMF derived from different feedstocks under relatively mild reaction conditions. Although a great quantity of research has been conducted over the past decades, the unsatisfactory production selectivity mostly limited to the range 50%–70%, and the classic fructose used as the substrate restricted its application for fuel manufacture in large scale. To address these production improvements, this review pays attention to evaluate the activity of various catalysts (e.g., mineral salts, zeolites, heteropolyacid-based hybrids, sulfonic acid-functionalized materials, and ionic liquids), providing potential research directions for the design of novel catalysts for the achievement of further improved EMF yields.

Levulinic Acid Biorefineries: New Challenges for Efficient Utilization of Biomass

Levulinic acid is a sustainable platform molecule that can be upgraded to valuable chemicals and fuel additives. This article focuses on the catalytic upgrading of levulinic acid into various chemicals such as levulinate esters, δ-aminolevulinic acid, succinic acid, diphenolic acid, γ-valerolactone, and γ-valerolactone derivatives such valeric esters, 5-nonanone, α-methylene-γ valerolactone, and other various molecular-weight alkanes (C9 and C18-C27 olefins).

Efficient conversion of furfuryl alcohol to ethyl levulinate with sulfonic acid-functionalized MIL-101(Cr)

MIL-101(Cr)–SO₃H with highly dispersed Brønsted acid sites was efficient and robust for the ethanolysis of furfuryl alcohol to ethyl levulinate.

Effective conversion of biomass-derived ethyl levulinate into γ-valerolactone over commercial zeolite supported Pt catalysts

Selective hydrogenation of biomass-derived ethyl levulinate into γ-valerolactone over commercial zeolite supported catalysts was performed, and high yield was obtained.

Xylose isomerization with zeolites in a two-step alcohol-water process

Isomerization of xylose to xylulose was efficiently catalyzed by large-pore zeolites in a two-step methanol-water process that enhanced the product yield significantly. The reaction pathway involves xylose isomerization to xylulose, which, in part, subsequently reacts with methanol to form methyl xyluloside (step 1) followed by hydrolysis after water addition to form additional xylulose (step 2). NMR spectroscopy studies performed with (13) C-labeled xylose confirmed the proposed reaction pathway. The most active catalyst examined was zeolite Y, which proved more active than zeolite beta, ZSM-5, and mordenite. The yield of xylulose obtained over H-USY (Si/Al=6) after 1 h of reaction at 100 °C was 39%. After water hydrolysis in the second reaction step, the yield increased to 47%. Results obtained from pyridine adsorption studies confirm that H-USY (6) is a catalyst that combines Brønsted and Lewis acid sites, and isomerizes xylose in alcohol media to form xylulose at low temperature. The applied zeolites are commercially available; do not contain any auxiliary tetravalent metals, for example, tin, titanium, or zirconium; isomerize xylose efficiently; are easy to regenerate; and are prone to recycling.