Deconstruction of biomass into lignin oil and platform chemicals over heteropoly acids with carbon-supported palladium as a hybrid catalyst under mild conditions

Efficient conversion of lignin fractions in lignocellulose using multifunctional polyoxometalate catalysts

The efficient catalytic conversion of lignin represents a critical challenge in biomass valorization, primarily due to the inherent difficulty in selectively depolymerizing lignin while maintaining the structural integrity of cellulose and hemicellulose. Herein, we present an innovative approach involving the synthesis of ionic liquid polyoxometalate (IL-POM) catalysts, which integrate both redox-active and Lewis acid sites, and are further modified with a choline chloride monomer. Among the synthesized catalysts, ChH4PMo11Al0.5V0.5O40 demonstrated exceptional catalytic performance, achieving an aromatic compound yield of 16.35 % under optimized conditions. Comprehensive characterization of the catalyst revealed that its catalytic efficacy is intrinsically linked to its acidity profile, with the synergistic interplay between Brønsted and Lewis acids facilitating the cleavage of CC and CO bonds. Notably, the incorporation of choline chloride was found to be pivotal in ensuring the catalyst's recyclability. This study underscores the potential of multifunctional IL-POM catalysts in advancing biomass valorization, providing a promising pathway to bridge the gap between homogeneous and heterogeneous catalysis for sustainable biomass conversion.

Selective oxidative depolymerization of lignin into aromatic monomers using a palladium-doped polyoxometalate catalyst

The depolymerization of lignin via selective cleavage of β-O-4 linkages is hindered by the tendency of Cα-OH groups to form benzyl carbocations, leading to condensation side reactions. Although pretreatment strategies to block Cα-OH have been widely studied, methods for efficient oxidative depolymerization remain limited. Herein, we propose a polyoxometalate (POM)-based catalytic approach under mild conditions (150 °C, 1 MPa O₂) to address this challenge. A series of metal-doped POM catalysts were synthesized, among which Pd/CsPMA exhibited optimal performance. Through condition optimization (180 min reaction, lignin-to-catalyst mass ratio of 1:1), an aromatic monomer yield of 11.01 wt% was achieved. The main product yield was 81.9 % of the total lignin yield. Investigations using lignin model compounds indicated that Pd/CsPMA promotes selective oxidation of Cα-OH groups, suggesting a synergistic mechanism between palladium and the POM framework. Furthermore, Pd/CsPMA maintained stable catalytic performance over five consecutive cycles without significant deactivation. This work demonstrates the potential of rationally designed POM catalysts for lignin valorization and provides insights into suppressing condensation during biomass conversion.

Hydrogen-transfer strategy in lignin refinery: Towards sustainable and versatile value-added biochemicals

Lignin, the most prevalent natural source of polyphenols on Earth, offers substantial possibilities for the conversion into aromatic compounds, which is critical for attaining sustainability and carbon neutrality. The hydrogen-transfer method has garnered significant interest owing to its environmental compatibility and economic viability. The efficacy of this approach is contingent upon the careful selection of catalytic and hydrogen-donating systems that decisively affect the yield and selectivity of the monomeric products resulting from lignin degradation. This paper highlights the hydrogen-transfer technique in lignin refinery, with a specific focus on the influence of hydrogen donors on the depolymerization pathways of lignin. It delineates the correlation between the structure and activity of catalytic hydrogen-transfer arrangements and the gamut of lignin-derived biochemicals, utilizing data from lignin model compounds, separated lignin, and lignocellulosic biomass. Additionally, the paper delves into the advantages and future directions of employing the hydrogen-transfer approach for lignin conversion. In essence, this concept investigation illuminates the efficacy of the hydrogen-transfer paradigm in lignin valorization, offering key insights and strategic directives to maximize lignin's value sustainably.

Sulfonated P-W modified nitrogen-containing carbon-based solid acid catalysts for one-pot conversion of cellulose to ethyl levulinate under water-ethanol medium

Converting cellulose (Cel) into ethyl levulinate (EL) is one of the promising strategies for supplying liquid fuels. In this paper, the prepared sulfonated P-W-modified N-containing carbon-based solid acid catalyst (PWNCS), in which the Polyaniline (PANI) was employed as N and C precursors, successfully converted Cel into EL under the water-ethanol medium. The characterization results demonstrated that a tiny addition of P increased the Brønsted acid sites (BAS) content and defective WO3 provided the Lewis acid sites (LAS), meanwhile, the sulfonation process did not change the fundamental structure but introduced the sulfonic groups to dramatically increase the acidic content. Therefore, under optimized reaction conditions, PWNCS realized about 100% Cel conversion and 71.61% of EL yield, furthermore, the selectivity of EL reached 89.14%. In addition, the effect of water on the reaction pathway of Cel to EL over PWNCS was proposed. The addition of water generally resulted in the hydration of defective WO3 to reduce the LAS and increase BAS, which significantly inhibited the side reactions of retro-aldol condensation (RAC) and subsequent etherification reactions during Cel conversion and then improved the selectivity of EL.

Characteristics of dissolved organic matter (DOM) in Chinese farmland soils under different climate zone types: A molecular perspective

Interactions between dissolved organic matter (DOM) and surrounding environments are highly complex. Understanding DOM at the molecular level can contribute to the management of soil pollution and safeguarding agricultural fields. Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) has enabled a molecular-level understanding of DOM. Accordingly, in this study, we investigated soil samples from 27 different regions of mainland China with various soil types and climatic characteristics. Based on the geographical features of the four typical climatic zones in mainland China (temperate monsoon, temperate continental, subtropical monsoon, and Qinghai-Tibet Plateau climates), we employed high-resolution mass spectrometry to determine the molecular diversity of DOM under different climatic conditions. The results indicated that lignin and tannin-like substances were the most active categories of DOM in the soils. Collectively, the composition and unsaturation of DOM molecules are influenced by sunlight, precipitation, temperature, and human activity. All climatic regions contained a substantial number of characteristic molecules, with CHO and CHON constituting over 80%, and DOM containing nitrogen and sulfur was relatively more abundant in the monsoon regions. The complex composition of DOM incorporates various active functional groups, such as -NO2 and -ONO2. Furthermore, soil DOM in the monsoon regions showed higher unsaturation and facilitated various (bio) biochemical reactions in the soil.

Advances in Heterogeneous Catalysts for Lignin Hydrogenolysis

Lignin is the main component of lignocellulose and the largest source of aromatic substances on the earth. Biofuel and bio-chemicals derived from lignin can reduce the use of petroleum products. Current advances in lignin catalysis conversion have facilitated many of progress, but understanding the principles of catalyst design is critical to moving the field forward. In this review, the factors affecting the catalysts (including the type of active metal, metal particle size, acidity, pore size, the nature of the oxide supports, and the synergistic effect of the metals) are systematically reviewed based on the three most commonly used supports (carbon, oxides, and zeolites) in lignin hydrogenolysis. The catalytic performance (selectivity and yield of products) is evaluated, and the emerging catalytic mechanisms are introduced to better understand the catalyst design guidelines. Finally, based on the progress of existing studies, future directions for catalyst design in the field of lignin depolymerization are proposed.

Bimetallic polyoxometalates catalysts for efficient lignin depolymerization: Unlocking valuable aromatic compounds from renewable feedstock

Lignin, a complex and abundant polymer present in lignocellulosic biomass, holds immense potential as a renewable source for the production of valuable aromatic compounds. However, the efficient depolymerization of lignin into these compounds remains a formidable challenge. Here, we present a promising solution by harnessing polyoxometalates (POMs) catalysts, which exhibit improved catalytic performance and selectivity. We synthesized a series of NixCoy@POMs catalysts (POMs: CsPW or CsPMo) and explored their application in the depolymerization of pine lignin, aiming to investigate the influence of different metal species and doping ratios of POMs on catalytic performance. Through meticulous optimization of reaction conditions, we achieved significant yields of valuable aromatic compounds, including methyl vanillate, vanillin, and 4-hydroxy-3-methoxyacetophenone. Furthermore, the Ni0.75Co0.75@CsPMo catalyst demonstrated exceptional efficacy in catalyzing the cracking process of C-C and/or C-O bonds in a β-O-4 dimer model compound. Notably, our catalyst exhibited outstanding stability over five cycles, underscoring its suitability as an effective heterogeneous catalyst for cyclic lignin depolymerization. This study sheds light on the potential of POMs-based catalysts for advancing lignin valorization and offers new avenues for sustainable biomass conversion into valuable chemicals.

Direct and efficient conversion of cellulose to levulinic acid catalyzed by carbon foam-supported heteropolyacid with Brønsted-Lewis dual-acidic sites

This study aimed to produce bio-based levulinic acid (LA) via direct and efficient conversion of cellulose catalyzed by a sustainable solid acid. A carbon foam (CF)-supported aluminotungstic acid (HAlW/CF) catalyst with Brønsted-Lewis dual-acidic sites was creatively engineered by a hydrothermal impregnation method. The activity of the HAlW/CF catalyst was determined via the hydrolysis and conversion of cellulose to prepare LA in aqueous system. The cooperative effect of Brønsted and Lewis acids in HAlW/CF resulted in high cellulose conversion (89.4%) and LA yield (60.9%) at 180 °C for 4 h, which were greater than the combined catalytic efficiencies of single HAlW and CF under the same conditions. The HAlW/CF catalyst in block form exhibited superior catalytic activity, facile separation from reaction system, and favorable reusability. This work offers novel perspectives for the development of recyclable dual-acidic catalysts to achieve one-pot catalytic conversion of biomass to value-added chemicals.

Lignin valorization: Status, challenges and opportunities

As an abundant aromatic biopolymer, lignin has the potential to produce various chemicals, biofuels of interest through biorefinery activities and is expected to benefit the future circular economy. However, lignin valorization is hindered by a series of constraints such as heterogeneous polymeric nature, intrinsic recalcitrance, strong smell, dark colour, challenges in lignocelluloses fractionation and the presence of high bond dissociation enthalpies in its functional groups etc. Nowadays, industrial lignin is mostly combusted for electricity production and the recycling of inorganic compounds involved in the pulping process. Given the research and development on lignin valorization in recent years, important applications such as lignin-based hydrogels, surfactants, three-dimensional printing materials, electrodes and production of fine chemicals have been systematically reviewed. Finally, this review highlights the main constraints affecting industrial lignin valorization, possible solutions and future perspectives, in the light of its abundance and its potential applications reported in the scientific literature.

Highly efficient Ni–NiO/carbon nanotubes catalysts for the selective transfer hydrogenation of 5-hydroxymethylfurfural to 2,5-bis(hydroxymethyl)furan

Ni–NiO/CNTs showed an excellent activity towards the catalytic transfer hydrogenation of 5-hydroxymethylfurfural to 2,5-bis(hydroxymethyl)furan.