Search

Sodium lignosulfonate (LS) was valorized to low molecular weight (Mw) fractions by combining solvothermal (SF) and catalytic hydrogenolysis/hydrogenation fragmentation (SHF) in a continuous flow system. This was achieved in either alcohol/H2O (EtOH/H2O or MeOH/H2O) or H2O as a solvent and Ni on nitrogen-doped carbon as a catalyst. The tunability according to the temperature of both SF and catalytic SHF of LS has been separately investigated at 150 °C, 200 °C, and 250 °C. In SF, the minimal Mw was 2994 g mol−1 at 250 °C with a dispersity (Đ) of 5.3 using MeOH/H2O. In catalytic SHF using MeOH/H2O, extremely low Mw was found (433 mg gLS−1) with a Đ of 1.2 combined with 34 mg gLS−1. The monomer yield was improved to 42 mg gLS−1 using dual catalytic beds. These results provide direct evidence that lignin is an unstable polymer at elevated temperatures and could be efficiently deconstructed under hydrothermal conditions with and without a catalyst. [ABSTRACT FROM AUTHOR]

The abundant carbohydrate fructose is converted into two biofuel molecules, namely 2,5-dimethylfuran (DMF) and ethyl levulinate (EL) in a simple cascade flow reactor. With an overall yield of 85% (38.5% of 2,5-dimethylfuran and 47% of ethyl levulinate), the main remainder is unconverted fructose. The two column flow reactor set-up enables the adjustment of temperatures and reaction times in such a way that the reactive intermediate hydroxymethylfurfural (5-HMF) is generated in optimal yields and converted into the stable DMF immediately. The process is so simple and fast (＜20 min) that economic and sustainable production of these fuels and platform chemicals can be envisioned. A remaining minor char formation is regarded to be the major problem which has to be addressed by catalyst development. [ABSTRACT FROM AUTHOR]

Ionic liquids were prepared via hydrothermal decarboxylation of zwitterionic imidazolium compounds derived from amino acids and carbohydrate related dicarbonyl compounds. Two of these ionic liquids were used successfully as solvents in the Heck reaction and for the dissolution of cellulose. [ABSTRACT FROM AUTHOR]

Cross-coupling reactions play a vital role in modern organic synthesis, enabling the construction of necessary C–C or C–(het)atom bonds for synthetic transformations. Although C(sp2)–C and C(sp2)–N cross-coupling reactions have received significant attention, recent advancements have also highlighted the significance of C(sp2)–S cross-coupling reactions. These reactions lead to the synthesis of valuable compounds, including pharmaceuticals and materials. In a recent report, we introduced Adaptive Dynamic Homogeneous Catalysis (AD-HoC) as an efficient method for C(sp2)–S cross-coupling reactions. This method operates without the need for any ligands, base, or additional additives, relying solely on essential parameters. In this report, we discuss the use of mesoporous graphitic carbon nitride (mpg-CN) as an all-organic heterogeneous photocatalyst in such transformations. The versatility and robustness of the reaction are showcased with fifty synthetic examples, achieving up to a 98% yield. The use of mpg-CN as a catalyst additionally enables the easy recovery of the photocatalyst from the reaction mixture and facilitates the sequential execution of multiple cross-coupling reactions with consistent yields of the desired products using a simple setup. This approach is a significant advancement in the field, both in terms of operational simplicity and environmental impact, traits that we all envision for sustainability. [ABSTRACT FROM AUTHOR]

This article reviews a variety of literature-reported lignin isolation procedures that bring partly minor but important changes in the produced extracts. Five lignins were produced or acquired from various sources and characterized based on their thermal properties, molecular weights, chemical structures, as well as elemental compositions, which were all found to depend on their extraction methods. These extracts were then used to produce 5 different nanolignins using 2 similar facile solvent shifting methods with the difference being an alteration in pH. The nanolignins were characterized after the solvent shifting accounting for differences in pH. Nanolignins generated via only solvent exchange exhibited diameters ranging from 58 nm to 95 nm, while nanolignins precipitated using a solvent shifting method along with a shift in pH exhibited diameters ranging from 10 nm to 34 nm and dissimilar morphology, size, and surface charge. Those differences highlight the control options for nanolignin preparetion on the colloidal length scale. Understanding how different lignins can be used to generate nanolignins is mandatory for unlocking the possibilities of nanolignin for functional material applications. These nanolignins can be applied in construction, medical, and/or agricultural industries as renewable, biodegradable alternatives to existing polymer dispersions. [ABSTRACT FROM AUTHOR]

A novel method based on the use of reactive eutectic media for the extraction of cellulose nanocrystals and their functionalization with positively charged functional groups in a one-step procedure is presented. With its ability to form strong hydrogen bonds, the eutectic medium serves as a cellulose-solubilizing agent, while the presence of a Leuckart reagent provides the reactivity toward the reductive amination of carbonyl groups in the cellulose chains. In the proposed method, amorphous cellulose domains are partially dissolved by undergoing aminolysis, resulting in the formation of water-dispersible nanocellulose products with high crystallinity. [ABSTRACT FROM AUTHOR]

In this paper, we propose a new approach for valorization of monosaccharides derived from biomass into value added chemicals in a green and economically efficient manner by forming eutectic medium exclusively between reactants. Eutectic mixtures are emerging as an advantageous alternative to ionic liquids and have already found broad applications in biomass treatment; however they are preferably used only as low vapor pressure solvents. Increasing interest in eutectic solvents originates from their flexibility to adjust their properties to different biorefinery needs by simple variation of the compositions of eutectic mixtures. In this work, we made a first attempt to use a low molecular weight component, ammonium formate, to significantly change the physical properties of the eutectic mixtures and simultaneously increase their chemical reactivity. Using this approach, we valorised simple monosaccharides by turning them into fructopyrazines with high yields in their eutectic mixtures with ammonium formate. The research revealed a high sensitivity of the product yields to the temperature of the reaction and composition of the eutectic medium, as well as an important role of formate anions in product stabilization. [ABSTRACT FROM AUTHOR]

Herein, we report the use of reactive eutectic media from ammonium formate and monosaccharides to synthesize poly(hydroxyalkyl)pyrazines via microwave irradiation. This enabled unprecedented fast rates as well as better atom economy compared to previous methods. We investigated the influence of water on the reaction yield as well as the physical properties of the eutectic media and could thereby drastically reduce the viscosity, while preserving high reaction yields. The results were consistent for different monosaccharides, using fructose, glucose, rhamnose and fucose as reactants. Furthermore, the major reaction products were separated, chemically analyzed and tested for their antimicrobial activity via high-throughput screening. [ABSTRACT FROM AUTHOR]

The hydrothermal synthesis of nitrogen-doped monolithic carbon aerogels derived from sustainable precursors (i.e.d-glucose and ovalbumin) is presented. The protein acts as nitrogen donor and surface stabilizing agent in this saccharide hydrothermal carbonization, to generate high surface area aerogels (＞240 m2g−1) composed of functional continuous large diameter mesopores with excellent hierarchical transport architecture. Post-carbonization treatment controls surface chemistry (e.g. C or N condensation), facilitating tuneable physicochemical properties on a unique continuous 3D carbonaceous pore structure. This highly flexible synthesis lays the basis for the development of a new generation of sustainable (heteroatom-doped) porous carbon aerogels suitable for a range of high value applications. [ABSTRACT FROM AUTHOR]

The hydrothermal synthesis of nitrogen-doped monolithic carbon aerogels derived from sustainable precursors (i.e.d-glucose and ovalbumin) is presented. The protein acts as nitrogen donor and surface stabilizing agent in this saccharide hydrothermal carbonization, to generate high surface area aerogels (>240 m2g−1) composed of functional continuous large diameter mesopores with excellent hierarchical transport architecture. Post-carbonization treatment controls surface chemistry (e.g.C or N condensation), facilitating tuneable physicochemical properties on a unique continuous 3D carbonaceous pore structure. This highly flexible synthesis lays the basis for the development of a new generation of sustainable (heteroatom-doped) porous carbon aerogels suitable for a range of high value applications. [ABSTRACT FROM AUTHOR]

We report the synthesis of 1,4-dicarbonyl compounds and substituted alkenes (Mizoroki–Heck type coupling) starting from secondary and tertiary alkyl halides and vinyl acetate or styrene derivatives using visible-light photocatalysis. The protocol uses mesoporous graphitic carbon nitride (mpg-CN) as a heterogeneous organic semiconductor photocatalyst and Ni(II) salts as Lewis acid catalysts. Detailed post-characterization of the heterogeneous material has been carried out to support the proposed catalytic cycle. Apart from high functional-group tolerance, mild reaction conditions, scalability as well as easy recovery and reuse of the mpg-CN photocatalyst provide a practical solution to these widespread transformations in terms of sustainability and efficiency and this methodology is recommended for applications in academic and industrial synthesis. [ABSTRACT FROM AUTHOR]

The continuous flow synthesis of p-xylene (pXL) via Diels–Alder cycloaddition of lignocellulosic biomass-derivable 2,5-dimethylfuran (DMF) and acrylic acid (AA) was performed over different type of zeolites, i.e. Beta, ZSM-5 and Y. Among the tested zeolites, Beta zeolite showed an optimum catalytic performance in pXL synthesis from DMF and AA. In this context, Beta zeolite with a Si/Al molar ratio of 150 which is abbreviated as Beta(150), resulted in complete DMF conversion with a pXL yield of 83% and by-product 2,5-dimethylbenzoic acid (DMBA) with a yield of 17%, at 473 K in 10.1 min residence time (τ), with excess AA (0.7 M). This high catalytic activity is attributed to the high specific surface area of 1180 m2 g−1 with a three-dimensional porous architecture with a pore diameter of 6.6 × 6.7 Å and an acid site density above 40 μmol g−1. The utilized Beta(150) showed a very stable performance up to 10 h time on stream with minor deactivation after 8 h of TOS, while the pXL yield remained above 70%. The original catalytic performance of Beta(150) in the conversion of DMF to pXL was restored by applying a regeneration step for the spent catalyst, which is simple in continuous flow reactors. Finally, this sustainable continuous flow process enables an efficient and selective pXL production from DMF and AA as a dienophile at lower reaction temperature (473 K) and shorter residence time (τ = 10.1 min) in comparison to a batch fashion. [ABSTRACT FROM AUTHOR]

Electrochemical reduction of CO2 provides a way to generate base chemicals from an abundant C1-source under mild conditions, whilst at the same time mitigating CO2 emissions. In this work, a novel class of tailorable, porous electrocatalysts for this process is proposed. Covalent triazine frameworks (CTFs) are grown in situ onto functionalized multiwalled carbon nanotubes. Hydroxyl groups decorating the surface of the multiwalled carbon nanotubes facilitate intimate contact between the carbon nanotubes and CTF, thus promoting efficient electron transfer. The novel hybrid materials generate CO with a faradaic efficiency up to 81% at an overpotential of 380 mV. The selectivity of the electrocatalysts could be linked to the amount of nitrogen present within the framework. [ABSTRACT FROM AUTHOR]

Hydrogenation reactions in water at elevated temperatures are challenging for heterogeneous catalysts. Thus, we present a simple, cheap, scalable, and sustainable approach for synthesizing an efficient and stable Ni catalyst supported on highly porous nitrogen-doped carbon (NDC) in pellet form. The performance of this catalyst was evaluated in the aqueous-phase hydrogenation of lignocellulosic biomass-derived compounds, i.e., glucose (Glu), xylose (Xyl), and vanillin (V), using a continuous-flow system. The as-prepared 35 wt% Ni on NDC catalyst exhibited a high catalytic performance in all three aqueous-phase hydrogenation reactions, i.e., the conversion of Glu, Xyl, and V was 96.3 mol%, 85 mol%, and 100 mol% and the yield of sorbitol (Sor), xylitol (Xyt), and 2-methoxy-4-methylphenol (MMP) was 82 mol%, 62 mol%, and 100 mol%, respectively. This high activity was attributed to the high specific surface area of NDC and mainly to the heterojunction effects stabilizing and adjusting the homogenously and highly dispersed Ni nanoparticles (ANi = 20 m2 g−1) on the surface of NDC. Changing the electron density in the nickel nanoparticles allows the high performance of the catalyst for a long time on stream (40 h) with minimized Ni leaching and without the loss in catalytic performance. [ABSTRACT FROM AUTHOR]

Fully renewable pyridinium ionic liquids were synthesised via the hydrothermal decarboxylation of pyridinium zwitterions derived from furfural and amino acids in flow. The functionality of the resulting ionic liquid (IL) can be tuned by choice of different amino acids as well as different natural carboxylic acids as the counterions. A representative member of this new class of ionic liquids was successfully used for the synthesis of ionogels and as a solvent for the Heck coupling. [ABSTRACT FROM AUTHOR]

Mesoporous graphitic carbon nitride (mpg-C3N4) has been developed as a non-metal, heterogeneous photocatalyst for the selective oxidation of sulfides to sulfoxides with O2 at room temperature. Especially, the combination of mpg-C3N4 and aldehydes was a highly active system under visible-light irradiation. For example, mpg-C3N4/isobutyraldehyde catalytic oxidation of methyl phenyl sulfide afforded 97% conversion with 98% selectivity for the methyl phenyl sulfoxide in 4 h. Moreover, the mpg-C3N4 can be easily recovered by filtration and then reused at least four times without losing activity. By exploring the electron spin resonance and some comparative experiments, a catalytic mechanism of this oxidation was provided. Finally, the system also works well in the oxidation of a number of sulfides, including sulfides bearing various groups, and phenyl disulfide. The use of a metal-free heterogeneous catalyst and visible light energy, along with the mild reaction conditions makes this oxidation reaction an environmentally benign and energy-saving chemical process. [ABSTRACT FROM AUTHOR]

A one-pot, hydrothermal synthesis of nitrogen and sulfur dual doped carbon aerogels is presented, derived from our previously published hydrothermal carbonization approach. Two co-monomers, S-(2-thienyl)-l-cysteine (TC) and 2-thienyl carboxaldehyde (TCA), were used for sulfur incorporation, giving rise to distinct morphologies and varying doping levels of sulfur. Nitrogen-doping levels of 5 wt% and sulfur-doping levels of 1 wt% (using TCA) to 4 wt% (using TC) were obtained. A secondary pyrolysis step was used to further tune the carbon aerogel conductivity and heteroatom binding states. By comparing solely nitrogen-doped with nitrogen- and sulfur-doped carbon aerogels, it was observed that the presence of sulfur improves the overall electrocatalytic activity of the carbon material in both basic and acidic media. This study of the synergistic effect of combined sulfur- and nitrogen-doping in the catalysis of the “oxygen reduction reaction” (ORR) is expected to be significant to future research concerning the improvement of heterogeneous, metal-free, carbon-based catalysts. [ABSTRACT FROM AUTHOR]

In terms of broadening the potential application range of carbon based materials, heteroatom doping provides a useful tool to moderate their physical and chemical properties. While nitrogen doped carbons have been extensively researched, the reports for sulfur, and especially nitrogen/sulfur dual-doped materials is far less exhaustive. We present a one-pot synthesis of dual nitrogen/sulfur doped materials which is based on sustainable carbohydrate and amino acid precursors and enables tailoring of the final material's physicochemical properties. The addition of cysteine gives rise to pending sulfur functionalities, while addition of thienyl-cysteine results in structurally bound sulfur within the carbonaceous framework. Post pyrolysis offers an additional tool for controlling the material stability and results in microporosity as well as superior conductivity relative to undoped carbon microspheres from glucose. Nitrogen doping levels of about 4 wt% and sulfur doping levels of 3 wt% to 12 wt% could be achieved. The samples were, amongst other methods, characterized by XPS, 13C MAS solid state NMR and both N2 and CO2 sorption isotherms. Since this is the first report on heteroatom doped, sulfur containing carbon materials obtained via hydrothermal carbonization, we anticipate our work to be a starting point for more sophisticated studies concerning the role of sulfur (and nitrogen) on the physicochemical properties of hydrothermal carbon. [ABSTRACT FROM AUTHOR]