Valorization of humin as a glucose derivative to fabricate a porous carbon catalyst for esterification and hydroxyalkylation/alkylation

A challenge of today's industry is to transform low-value side products into more value-added materials. The acid-catalyzed conversion of hemi(cellulose) to platform chemicals in green chemical/fuel production and biorefinery yields large formation of insoluble byproduct called humin. Herein, humin obtained from dehydration of glucose was transformed into a novel class of effective carbonaceous solid acid catalyst for the first time via low-temperature pyrolysis followed by sulfonation. A range of preparation conditions were investigated, and the structure-function relationships of the resulting catalysts were also discussed based on the analysis of structure and composition. Comparing with the glucose-derived carbon catalyst, the humin-derived catalyst has substantially larger surface area and higher SO₃H density, which enable it to display higher catalytic activity and efficiency not only in esterification of levulinic acid and n-butanol (yield = 95.0%, 373 K), but also in hydroxyalkylation/alkylation of 2-methylfuran and furfural (yield = 64.2%, 323 K). Additionally, the catalyst could be repeatedly employed for at least four cycles without obvious deactivation, exhibiting good reusability. This work provides a green method to convert humin byproduct into economic and eco-friendly solid acid catalyst and may contribute to a holistic approach for biomass utilization.

Recent advances in zeolite-encapsulated metal catalysts: A suitable catalyst design for catalytic biomass conversion

Metal clusters and nanoparticles, which have been used to tune the acidity of zeolite support, are beneficial for promoting the catalytic performance of various reaction processes, including biomass conversion. However, catalytic instabilities resulting from metal coalescence, sintering and leaching are major problems that need to be resolved. Therefore, metal encapsulation within the zeolite structure has been proposed as a feasible solution for this issue, particularly for biomass conversions that require high temperatures. In this current review, recent developments in metal confinement techniques are described along with experimental examples of biomass upgrading reactions. The present and future perspectives of zeolite-encapsulated metal catalysts in biomass conversions are also given.

CNN pincer ruthenium complexes for efficient transfer hydrogenation of biomass-derived carbonyl compounds

The ligand HCNNOMe (6-(4-methoxyphenyl)-2-aminomethylpyridine) is easily prepared from the commercially available 6-(4-methoxyphenyl)pyridine-2-carbaldehyde by the reaction of hydroxylamine and hydrogenation (H2, 1 atm) with Pd/C. The pincer complexes cis-[RuCl(CNNOMe)(PPh3)2] (1) and [RuCl(CNNOMe)(PP)] (PP = dppb, 2; and dppf, 3) are synthesized from [RuCl2(PPh3)3], HCNNOMe and PP (for 2 and 3) in 2-propanol with NEt3 at reflux and are isolated in 85-93% yield. Carbonylation of 1 (CO, 1 atm) gives [RuCl(CNNOMe)(CO)(PPh3)] (4) (79% yield) which cleanly reacts with Na[BArf4] and PCy3, affording the cationic trans-[Ru(CNNOMe)(CO)(PCy3)(PPh3)][BArf4] (5) (92% yield). These robust pincer complexes display remarkably high catalytic activity in the transfer hydrogenation (TH) of lignocellulosic biomass carbonyl compounds, using 2-propanol at reflux in a basic medium (NaOiPr or K2CO3). Thus, furfural, 5-(hydroxymethyl)furfural and Cyrene are reduced to the corresponding alcohols with 2 and 3, at S/C in the range of 10 000-100 000, within minutes or hours (TOF up to 1 500 000 h-1). The monocarbonyl complex 5 was found to be extremely active in the TH of cinnamaldehyde, vanillin derivatives and ethyl levulinate at S/C in the range of 10 000-50 000. Vanillyl alcohol is also obtained by the TH of vanillin with 5 (S/C = 500) in 2-propanol in the presence of K2CO3.

Convenient synthesis of cobalt nanoparticles for the hydrogenation of quinolines in water

Easily accessible cobalt nanoparticles are prepared by hydrolysis of NaBH₄ in the presence of inexpensive Co(ii) salts.

Selective dihydroxylation of methyl oleate to methyl-9,10-dihydroxystearate in the presence of a recyclable tungsten based catalyst and hydrogen peroxide

Synthesis of methyl-9,10-dihydroxystearate with high yield (99%) from methyl oleate in the presence of hydrogen peroxide and tungsten based catalyst.

High-Yield 5-Hydroxymethylfurfural Synthesis from Crude Sugar Beet Juice in a Biphasic Microreactor

5-Hydroxymethylfurfural (HMF) is an important biobased platform chemical obtainable in high selectivity by the hydrolysis of fructose (FRC). However, FRC is expensive, making the production of HMF at a competitive market price highly challenging. Here, it is shown that sugar beet thick juice, a crude, sucrose-rich intermediate in sugar refining, is an excellent feedstock for HMF synthesis. Unprecedented high selectivities and yields of >90 % for HMF were achieved in a biphasic reactor setup at 150 °C using salted diluted thick juice with H2 SO4 as catalyst and 2-methyltetrahydrofuran as a bioderived extraction solvent. The conversion of glucose, obtained by sucrose inversion, could be limited to <10 mol %, allowing its recovery for further use. Interestingly, purified sucrose led to significantly lower HMF selectivity and yields, showing advantages from both an economic and chemical selectivity perspective. This opens new avenues for more cost-effective HMF production.

2,2'-Dipyridylamines: more than just sister members of the bipyridine family. Applications and achievements in homogeneous catalysis and photoluminescent materials

2,2'-Dipyridylamines (dpa) and related compounds belong to the family of polydentate nitrogen ligands. More than a century has passed since their first report but new complexes and applications have been emerging in recent years owing to the versatility of dpa-based architectures. This review aims to present and highlight the main achievements attained with dpa-containing metal complexes in the domains of homogeneous catalysis and luminescent materials.

Bio-based building blocks from 5-hydroxymethylfurfural via 1-hydroxyhexane-2,5-dione as intermediate

The limits to the supply of fossil resources and their ever increasing use forces us to think about future scenarios for fuels and chemicals. The platform chemical 5-hydroxymethyl-furfural (HMF) can be obtained from biomass in good yield and has the potential to be converted in just a few steps into a multitude of interesting products. Over the last 20 years, the conversion of HMF to 1-hydroxyhexane-2,5-dione (HHD) has been studied by several groups. It is possible to convert HMF into HHD by hydrogenation/hydrolytic ring opening reaction in aqueous phase using various heterogeneous and homogeneous catalysts. This review addresses both the state of the art of HHD synthesis, including mechanistic aspects of its formation, as well as the recent progress in the application of HHD as a building block for many useful chemicals including pyrroles, cyclopentanone derivatives and triols.

Catalytic Cleavage of Ether Bond in a Lignin Model Compound over Carbon-Supported Noble Metal Catalysts in Supercritical Ethanol

Decomposition of lignin-related model compound (benzyl phenyl ether, BPE) to phenol and toluene was performed over carbon-supported noble metal (Ru, Pd, and Pt) catalysts in supercritical ethanol without supply of hydrogen. Phenol and toluene as target products were produced by the hydrogenolysis of BPE. The conversion of BPE was higher than 95% over all carbon-supported noble metal catalysts at 270 ° for 4 h. The 5 wt% Pd/C demonstrated the highest yield (ca. 59.3%) of the target products and enhanced conversion rates and reactivity more significantly than other catalysts. In the case of Ru/C, BPE was significantly transformed to other unidentified byproducts, more so than other catalysts. The Pt/C catalyst produced the highest number of byproducts such as alkylated phenols and gas-phase products, indicating that the catalyst promotes secondary reactions during the decomposition of BPE. In addition, a model reaction using phenol as a reactant was conducted to check the secondary reactions of phenol such as alkylation or hydrogenation in supercritical ethanol. The product distribution when phenol was used as a reactant was mostly consistent with BPE as a reactant. Based on the results, plausible reaction pathways were proposed.

Tin modified Nb2O5 as an efficient solid acid catalyst for the catalytic conversion of triose sugars to lactic acid

Edge-sharing octahedral niobium oxides were used efficiently for the conversion of trioses to lactic acid under hydrothermal conditions.

Synthesis of 5-hydroxymethyl furfural from cellulose via a two-step process in polar aprotic solvent

The synthesis of 5-hydroxymethyl furfural (HMF) from cellulose via a two-step process was investigated. To optimize reaction conditions, the separate conversion of cellulose and glucose was first performed in tetrahydrofuran (THF) and N, N-dimethylformamide (DMF) via a one-step process using hosphotungstic acid (PHA) as catalyst. The direct conversion of cellulose to HMF was then performed via the two-step process. The first step and the second step were carried out in THF and the mixture solvent composed of THF/DMF, respectively. Cellulose was converted to HMF and glucose in the first step in THF. Both of cellulose and the as-formed glucose were then converted to HMF in the second step. The conversion of cellulose to HMF and glucose were significantly improved by the two-step process, and the total yield of HMF and glucose was elevated from 52.1 to 97.0%. A possible mechanism for the formation of HMF from cellulose via the two-step process was also proposed.

Recent progress in homogeneous Lewis acid catalysts for the transformation of hemicellulose and cellulose into valuable chemicals, fuels, and nanocellulose

The evolution from petroleum-based products to the bio-based era by using renewable resources is one of the main research challenges in the coming years. Lignocellulosic biomass, consisting of inedible plant material, has emerged as a potential alternative for the production of biofuels, biochemicals, and nanocellulose-based advanced materials. The lignocellulosic biomass, which consists mainly of carbohydrate-based polysaccharides (hemicellulose and cellulose), is a green intermediate for the synthesis of bio-based products. In recent years, the re-engineering of biomass into a variety of commodity chemicals and liquid fuels by using Lewis acid catalysts has attracted much attention. Much research has been focused on developing new chemical strategies for the valorization of different biomass components. Homogeneous Lewis acid catalysts seem to be one of the most promising catalysts due to their astonishing features such as being less corrosive to equipment and being friendlier to the environment, as well as having the ability to disrupt the bonding system effectively and having high selectivity. Thus, these catalysts have emerged as important tools for the highly selective transformation of biomass components into valuable chemicals and fuels. This review provides an insightful overview of the most important recent developments in homogeneous Lewis acid catalysis toward the production and upgrading of biomass. The chemical valorization of the main components of lignocellulosic biomass (hemicellulose and cellulose), the reaction conditions, and process mechanisms are reviewed.

Alternatives for Chemical and Biochemical Lignin Valorization: Hot Topics from a Bibliometric Analysis of the Research Published During the 2000–2016 Period

A complete bibliometric analysis of the Scopus database was performed to identify the research trends related to lignin valorization from 2000 to 2016. The results from this analysis revealed an exponentially increasing number of publications and a high relevance of interdisciplinary collaboration. The simultaneous valorization of the three main components of lignocellulosic biomass (cellulose, hemicellulose, and lignin) has been revealed as a key aspect and optimal pretreatment is required for the subsequent lignin valorization. Research covers the determination of the lignin structure, isolation, and characterization; depolymerization by thermal and thermochemical methods; chemical, biochemical and biological conversion of depolymerized lignin; and lignin applications. Most methods for lignin depolymerization are focused on the selective cleavage of the β-O-4 linkage. Although many depolymerization methods have been developed, depolymerization with sodium hydroxide is the dominant process at industrial scale. Oxidative conversion of lignin is the most used method for the chemical lignin upgrading. Lignin uses can be classified according to its structure into lignin-derived aromatic compounds, lignin-derived carbon materials and lignin-derived polymeric materials. There are many advances in all approaches, but lignin-derived polymeric materials appear as a promising option.

Cleave and couple: toward fully sustainable catalytic conversion of lignocellulose to value added building blocks and fuels

The structural complexity of lignocellulose offers unique opportunities for the development of entirely new, energy efficient and waste-free pathways in order to obtain valuable bio-based building blocks. Such sustainable catalytic methods - specifically tailored to address the efficient conversion of abundant renewable starting materials - are necessary to successfully compete, in the future, with fossil-based multi-step processes. In this contribution we give a summary of recent developments in this field and describe our "cleave and couple" strategy, where "cleave" refers to the catalytic deconstruction of lignocellulose to aromatic and aliphatic alcohol intermediates, and "couple" involves the development of novel, sustainable transformations for the formation of C-C and C-N bonds in order to obtain a range of attractive products from lignocellulose.

Selective Coupling of Bioderived Aliphatic Alcohols with Acetone Using Hydrotalcite Derived Mg-Al Porous Metal Oxide and Raney Nickel

Fermentation of sugars to the so-called ABE mixture delivers a three component mixture of shorter chain oxygenates: acetone, n-butanol and ethanol. In order to convert these into liquid transportation fuels that are analogous to the currently used fossil energy carriers, novel catalytic chain elongation methods involving C-C bond formation are desired. Herein we report on a simple, non-noble-metal-based method for the highly selective coupling of 1-butanol and acetone into high molecular weight (C7-C11) ketones, as well as ABE mixtures into (C5-C11) ketones using the solid base Mg-Al-PMO in combination with small amount of Raney nickel. Upon hydrodeoxygenation, these ketones are converted to fuel range alkanes with excellent carbon utilization (up to 89%) using Earth abundant metal containing catalysis.

Bright Side of Lignin Depolymerization: Toward New Platform Chemicals

Lignin, a major component of lignocellulose, is the largest source of aromatic building blocks on the planet and harbors great potential to serve as starting material for the production of biobased products. Despite the initial challenges associated with the robust and irregular structure of lignin, the valorization of this intriguing aromatic biopolymer has come a long way: recently, many creative strategies emerged that deliver defined products via catalytic or biocatalytic depolymerization in good yields. The purpose of this review is to provide insight into these novel approaches and the potential application of such emerging new structures for the synthesis of biobased polymers or pharmacologically active molecules. Existing strategies for functionalization or defunctionalization of lignin-based compounds are also summarized. Following the whole value chain from raw lignocellulose through depolymerization to application whenever possible, specific lignin-based compounds emerge that could be in the future considered as potential lignin-derived platform chemicals.

Cyclopentanone Derivatives from 5-Hydroxymethylfurfural via 1-Hydroxyhexane-2,5-dione as Intermediate

An efficient strategy for the conversion of biomass derived 5-hydroxymethylfurfural (HMF) into 2-hydroxy-3-methylcyclopent-2-enone (MCP) by an intramolecular aldol condensation of 1-hydroxyhexane-2,5-dione (HHD) has been developed. Further transformations of MCP towards the diol, enol acetate, levulinic acid and N-heterocyclic compounds are also reported.