Lignin is an aromatic polymer that constitutes over 30 wt% of lignocellulosic biomass and is the most important source of renewable aromatics in nature. The global paper industry generates more than 130 million tons of Kraft lignin annually. Depolymerization of Kraft lignin to value-added monomers can significantly enhance the profitability of biorefinery. However, the method is impeded by the severe condensation of Kraft lignin during the pulping process, which forms robust C-C bonds and results in low monomer yields. In this study, we present a stepwise approach for producing valuable aromatic monomers from Kraft lignin through cleavage of both C-O and C-C bonds. The approach initiated with complete cleavage of C-O bonds between lignin units within Kraft lignin through alcoholysis in isopropanol, resulting in a monomer yield of 8.9%. Subsequently, the selective cleavage of methylene linkages present in the residual dimers and oligomers was achieved with commercial MCM-41 zeolite in the same pot, proceeding with an additional monomer yield of 4.0%, thereby increasing the total monomer yield by 45%. This work provides an avenue for increasing the depolymerization efficiency of Kraft lignin.

In this article, we address the transition of the Kolbe electrolysis of valeric acid (VA) to n-octane as an exemplary electrosynthesis process from a batch reaction to a continuous, self-regulated process. Based on a systematic assessment of chemical boundary conditions and sustainability aspects, we propose a continuous electrosynthesis including a simple product separation and electrolyte recirculation, as well as an online-pH-controlled VA feeding. We demonstrate how essential performance parameters such as product selectivity (S) and coulombic efficiency (CE) are significantly improved by the transition from batch to a continuous process. Thus, the continuous and pH-controlled electrolysis of a 1M valeric acid, starting pH 6.0, allowed a constantly high selectivity of around 47% and an average Coulomb efficiency about 52% throughout the entire experimental duration. Under otherwise identical conditions, the conventional batch operation suffered from lower and strongly decreasing performance values (Sn-octane, 60min= 10.4%, Sn-octane, 240min= 1.3%; CEn-octane, 60min=7.1%, CEn-octane, 240min= 0.5%). At the same time, electrolyte recirculation significantly reduces wastes and limits the use of electrolyte components.

From Waste to Anode Material: Hard carbons are produced from waste biomass (spent coffee grounds, sunflower seed shells and rose stems) by two methods: direct pyrolysis and by combined hydrothermal carbonization and pyrolysis. Electrochemical performance of as-obtained hard carbons using hydrothermal carbonization combined with pyrolysis is improved with up to 76 % ICE and 280 mAh g⁻¹ at C/5.

Abstract

Over the last years, hard carbon (HC) has been the most promising anode material for sodium-ion batteries due to its low voltage plateau, low cost and sustainability. In this study, biomass waste (spent coffee grounds, sunflower seed shells and rose stems) was investigated as potential material for hard carbon preparation combining a two-step method consisting of on hydrothermal carbonization (HTC), to remove the inorganic impurities and increase the carbon content, and a subsequent pyrolysis process. The use of HTC as pretreatment prior to pyrolysis improves the specific capacity in all the materials compared to the ones directly pyrolyzed by more than 100 % at high C-rates. The obtained capacity ranging between 210 and 280 mAh g⁻¹ at C/15 is similar to the values reported in literature for biomass-based hard carbons. Overall, HC obtained from sunflower seed shell performs better than that obtained from the other precursors with an initial Coulombic efficiency (ICE) of 76 % and capacities of 120 mAh g⁻¹ during 1000 cycles at C with a high capacity retention of 86–93 %.

To be or not to be burnt: that's the question. Read more about kraft lignin: the potential, the chemistry of how it is formed, and stateof-the-art applications in both fuels and materials. A technoeconomic discussions discloses two important economic incentives to recover lignin from pulp production.

Abstract

Kraft lignin, a by-product from the production of pulp, is currently incinerated in the recovery boiler during the chemical recovery cycle, generating valuable bioenergy and recycling inorganic chemicals to the pulping process operation. Removing lignin from the black liquor or its gasification lowers the recovery boiler load enabling increased pulp production. During the past ten years, lignin separation technologies have emerged and the interest of the research community to valorize this underutilized resource has been invigorated. The aim of this Review is to give (1) a dedicated overview of the kraft process with a focus on the lignin, (2) an overview of applications that are being developed, and (3) a techno-economic and life cycle asseeements of value chains from black liquor to different products. Overall, it is anticipated that this effort will inspire further work for developing and using kraft lignin as a commodity raw material for new applications undeniably promoting pivotal global sustainability concerns.

The enantioselective C−H arylation of aryl bromides herein developed afforded 30 enantioenriched products with high yields and enantioselectivities. By exploiting the “release and catch” mechanism of recoverable SP-NHC-Pd^II catalyst, in combination with BozPhos as a broadly applicable chiral ligand, good performances have been obtained across different substrates containing methyl, cyclopropyl and aryl C−H bonds.

Abstract

We herein report a general and efficient enantioselective C−H arylation of aryl bromides based on the use of BozPhos as the bisphosphine ligand and SP-NHC-Pd^II as recoverable heterogeneous catalyst. By exploiting the “release and catch” mechanism of action of the catalytic system, we used BozPhos as a broadly applicable chiral ligand, furnishing high enantioselectivities across all types of examined substrates containing methyl, cyclopropyl and aryl C−H bonds. For each reaction, the reaction scope was investigated, giving rise to 30 enantioenriched products, obtained with high yields and enantioselectivities, and minimal palladium leaching. The developed catalytic system provides a more sustainable solution compared to homogeneous systems for the synthesis of high added-value chiral products through recycling of the precious metal.

The 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide ([EMI][FSI]) and, especially, N-trimethyl-N-butylammonium bis(fluorosulfonyl)imide ([N₁₁₁₄][FSI]) have shown very good compatibility towards hard carbon electrode with excellent cycling behavior, which represents one of the best results obtained for hard carbon electrodes in ionic liquid electrolytes, exceeding even that exhibited in organic electrolytes, making them rather appealing for the realization of safe, reliable and highly performing Na-ion cells.

Abstract

Hard carbons (HC) from natural biowaste have been investigated as anodes for sodium-ion batteries in electrolytes based on 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide ([EMI][FSI]) and N-trimethyl-N-butylammonium bis(fluorosulfonyl)imide ([N1114][FSI]) ionic liquids. The Na⁺ intercalation process has been analyzed by cyclic voltammetry tests, performed at different scan rates for hundreds of cycles, in combination with impedance spectroscopy measurements to decouple bulk and interfacial resistances of the cells. The Na⁺ diffusion coefficient in the HC host has been also evaluated via the Randles-Sevcik equation. Battery performance of HC anodes in the ionic liquid electrolytes has been evaluated in galvanostatic charge/discharge cycles at room temperature. The evolution of the SEI (solid electrochemical interface) layer grown on the HC surface has been carried out by Raman spectroscopy. Overall the sodiation process of the HC host is highly reversible and reproducible. In particular, a capacity retention exceeding 98 % of the initial value has been recorded in[N1114][FSI] electrolytes after more than 1500 cycles with a coulombic efficiency above 99 %, largely beyond standard carbonate-based electrolytes. Raman, transport properties and impedance confirms that ILs disclose the formation of SEI layers with superior ability to support the reversible Na+ intercalation with the possible minor contributions from the EMI+cation.

This paper reports a new sustainable protocol for the microwave-assisted catalytic conversion of levulinic acid into N-substituted pyrrolidones over tailor-made mono (Pd, Au) or bimetallic (PdAu) catalysts supported on either highly mesoporous silica (HMS) or titania-doped HMS, exploiting the advantages of dielectric heating. MW-assisted reductive aminations of levulinic acid with several amines were first optimized in batch mode under hydrogen pressure (5 bar) in solvent-free conditions. Good-to-excellent yields were recorded at 150 °C in 90 min over the PdTiHMS and PdAuTiHMS, that proved recyclable and almost completely stable after six reaction cycles. Aiming to scale-up this protocol, a MW-assisted flow reactor was used in combination with different green solvents. Cyclopentyl methyl ether (CPME) provided a 99% yield of N-(4-methoxyphenyl) pyrrolidin-2-one at 150 °C over PdTiHMS. The described MW-assisted flow synthesis proves to be a safe procedure suitable for further industrial applications, while averting the use of toxic organic solvents.

Vanadium redox flow battery (VRFB) electrodes face challenges related to their long-term operation. We investigated different electrode treatments mimicking the aging processes during operation, including thermal activation, aging, soaking, and storing. Several characterization techniques were used to deepen the understanding of the treatment of carbon felts. Synchrotron X-ray imaging, electrochemical impedance spectroscopy (EIS) with the distribution of relaxation times analysis, and dynamic vapor sorption (DVS) revealed differences between the wettability of felts. The bulk saturation after electrolyte injection into the carbon felts significantly differed from 8% to 96%. DVS revealed differences in the sorption/desorption behavior of carbon felt ranging from a slight change of 0.8 wt% to over 100 wt%. Additionally, the interactions between the water vapor and the sample change from type V to type H2. After treatment, morphology changes were observed by atomic force microscopy and scanning electron microscopy. Cyclic voltammetry and EIS were used to probe the electrochemical performance, revealing different catalytic activities and transport-related impedances for the treated samples. These investigations are crucial for understanding the effects of treatments on the performance and optimizing materials for long-term operation.

Alcohols are used as accessible and safe C-alkylation agents to produce α-functionalized nitriles or oxindoles and 2-quinolinones via borrowing hydrogen strategy mediated by a [Mg₄Al-LDH]-supported silver nanoparticle catalyst. Combination of a suitable basic LDH support together with homogeneously distributed silver metallic centers are the key elements for the success of the protocol.

Abstract

An efficient heterogeneous silver-catalyzed α-alkylation of nitriles and oxindoles using alcohols via borrowing hydrogen strategy has been developed for the first time. The active nanostructured material, namely [Ag/Mg₄Al-LDH], composed by silver nanoparticles (3-4 nm average particle size) homogeneously stabilized onto a [Mg₄Al-LDH] support with suitable Brønsted basic properties, constitutes a stable catalyst for the sustainable building of novel C−C bonds from alcohols and C-nucleophiles. By applying this catalyst, a broad range of α-functionalized nitriles and oxindoles has been accessed with good to excellent isolated yields and without the addition of external bases. Moreover, the novel silver nanocatalyst has also demonstrated its successful application to the cyclization of N-[2-(hydroxymethyl)phenyl]-2-phenylacetamides to afford 3-arylquinolin-2(1H)-ones, through a one-pot dehydrogenation and intramolecular α-alkylation. Control experiments, kinetic studies, and characterization data of a variety of [Ag/LDH]-type materials confirmed the silver role in the dehydrogenation and hydrogenation steps, while [Mg₄Al-LDH] matrix is able to catalyze condensation. Interestingly, these studies suggest as key point for the successful activity of [Ag/Mg₄Al-LDH], in comparison with other [Ag/LDH]-type nanocatalysts, the suitable acid-base properties of this material.

Combining electrosynthesis with thermocatalysis: A strategy for efficient conversion of propane to high value-added C₃ oxygenated products is developed by coupling the electrosynthesis of H₂O₂ on oxygen-doped carbon electrocatalyst for 2e⁻ oxygen reduction reaction with thermocatalysis of propane oxidation over MIL-53 (Al, Fe) active sites in the proton exchange membrane fuel cell.

Abstract

Electrochemical conversion of alkanes to high value-added oxygenated products under a mild condition is of significance. Herein, we effectively couple the electrocatalysis of H₂O₂ with the thermo-catalysis of propane oxidation in the cathode of proton exchange membrane fuel cell. Specifically, H₂O₂ is in-situ generated on the nitric acid-treated carbon black (C-acid) via 2e⁻ process of oxygen reduction reaction, and then transports to the Fe active sites of MIL-53 (Al, Fe) metal–organic frameworks for propane oxidation. Based on this strategy, the space-time yield of C₃ oxygenated products of propane oxidation reaches 2.65 μmol h⁻¹ cm⁻², which represents a new benchmark for electrochemical alkane oxidation in the fuel-cell-type electrolyzer. This study highlights the importance of multifunctional composite catalysts in the field of electrosynthesis.