Nickel nanoparticles inlaid in lignin-derived carbon as high effective catalyst for lignin depolymerization

Heterogeneously Catalyzed Reductive Depolymerization of Lignin to Value-Added Chemicals

Lignin is an abundant renewable source of aromatics, but its complex heterogeneous structure poses challenges for its depolymerization and valorization. Heterogeneously catalyzed reductive depolymerization (HCRD) has emerged as a promising approach, utilizing heterogeneous catalysts to facilitate selective bond cleavage in lignin and hydrogen transfer to stabilize the products under mild conditions. This review provides a comprehensive understanding of the hydrogen transfer mechanisms in HCRD, involving different hydrogen sources, including molecular hydrogen, alcohols, formic acid, etc., and the native hydrogen donor groups in lignin. The interaction between hydrogen sources and catalyst design is explored, emphasizing how catalyst characteristics must align with specific hydrogen transfer pathways to optimize efficiency and selectivity. Precious metal-based and non-precious metal-based catalysts are examined, highlighting advances that enhance hydrogen activation and transfer. Comparative analyses of hydrogen sources reveal distinct advantages and limitations. The significance of HCRD in lignin valorization and the development of integrated biorefineries is underscored, emphasizing its potential to contribute to a sustainable bioeconomy through improved process integration and economic viability.

Bimetallic nickel‑cobalt sulfide derived from lignin-MOFs hybrid as a high-efficiency heterogeneous catalyst for hydrogenolysis of lignin dimers

Lignin represents a significant source of aromatic hydrocarbons in the natural world. The production of high-value chemicals from lignin has the great potential to effectively address the issue of fossil energy scarcity. In this study, complex sulfides of nickel‑cobalt bimetallic catalysts were prepared via hydrothermal synthesis and subsequently employed in the catalytic hydrogenolysis of CO bonds present in lignin. A series of complex sulfides Ni3S2/Co3S4-CSn-x-T derived from lignin-MOF (n = 0.5, 1, 1.5 and 2; x = 2, 4 and 6; T = 400, 500, 600 and 700 °C), were prepared under different conditions and subsequently employed in the catalytic hydrogenolysis of lignin model compounds. The optimal catalyst Ni3S2/Co3S4-CS1-4-500 exhibited the highest conversion rate of benzyl phenyl ether (BPE) (about 97.3 %), and the yields of toluene and phenol produced were 49.5 % and 43.6 %, respectively with isopropanol as the reaction solvent and no external H2. The introduction of element sulfur in catalysts could effectively inhibit the further hydrogenation of generated aromatic chemicals. The catalysts were well characterized, and the results demonstrated that the catalysts exhibited high catalytic activity with an increased loading of active components. This study provided some novel findings for the construction of biomass-based catalysts and the production lignin-derived aromatic chemicals.

Activity and product distribution in Ni-Co and Ni-Cu catalyst-mediated lignin depolymerization into phenolic substances with isopropanol H-donating solvent

Lignin, a vital renewable biopolymer, serves as the Earth's primary source of aromatics and carbon. Its depolymerization presents significant potential for producing phenolic fine chemicals. This study assesses promoted Ni-based bimetallic catalysts (Ni-Co/C and Ni-Cu/C) supported on activated carbon in isopropanol for lignin depolymerization, compared to monometallic counterparts. BET, SEM, EDX, and XPS analyses highlight their physicochemical properties and promotional effects, enhancing hydrogenolysis activity and hydrogen transformation. Reaction parameter exploration elucidates the influence on lignin depolymerization, with cobalt and copper as promoters notably increasing conversion and monomer yield. Ni-Co/C exhibits the highest lignin conversion (94.2%) and maximum monomer yield (53.1 wt%) under specified conditions, with lower activation energy (36.1 kJ/mol) and higher turnover frequency (31.6 h-1) compared to Ni/C. FT-IR, GPC, GC-FID, and GC-MS analyses confirm effective depolymerization, identifying 20 monomer products. Proposed reaction mechanisms underscore the potential of Ni-based bimetallic catalysts for lignin valorization, offering insights into developing efficient catalytic systems for lignin hydrogenolysis. This research enhances understanding and facilitates the development of selective catalytic processes for lignin valorization.

Advances in lignin-based biosorbents for sustainable wastewater treatment

The heavy metals, pesticides and dyes in agriculture and industry caused serious water pollution have increased the urgency for the advancement of biomass-based adsorbents due to their merits of low cost, high efficiency, and environmental sustainability. Thus, this review systematically examines the recent progress of lignin-based adsorbents dedicated to wastewater purification. Commencing with a succinct exposition on the intricate structure and prevalent forms of lignin, the review proceeds to expound rational design strategies tailored for lignin-based adsorbents coupled with adsorption mechanisms and regeneration methods. Emphasis is placed on the potential industrial applications of lignin-based adsorbents, accentuating their capacity for recovery and direct utilization post-use. The future challenges and outlooks associated with lignin-based adsorbents are discussed to provide novel perspectives for the development of high-performance and sustainable biosorbents, facilitating the effective removal of pollutants and the value-added utilization of resources in a sustainable manner.

Impact of Temperature an Order of Magnitude Larger Than Electrical Potential in Lignin Electrolysis with Nickel

Lignin, a major component of plant biomass, is a promising sustainable alternative carbon-based feedstock to petroleum as a source of valuable aromatic compounds such as vanillin. However, lignin upgrading reactions are poorly understood due to its complex and variable molecular structure. This work focuses on electrocatalytic lignin upgrading, which is efficient and sustainable at moderate temperatures and pressures and does not require stoichiometric reagents. We used a meta-analysis of published lignin conversion and product yield data to define the operating range, to select the catalyst, and then performed electrocatalytic experiments. We quantified the impact of temperature and electrical potential on the formation rate of valuable products (vanillic acid, acetovanillone, guaiacol, vanillin, and syringaldehyde). We found that increasing temperature increases their formation rate by an order of magnitude more than increasing electrical potential. For example, increasing temperature from 21 to 180 °C increases the vanillin formation rate by +16.5 mg⋅L-1 ⋅h-1 ±1.7 mg⋅L-1 ⋅h-1 , while increasing electrical potential from 0 to 2 V increases the vanillin formation rate by -0.6 mg⋅L-1 ⋅h-1 ±1.4 mg⋅L-1 ⋅h-1 .

Fabrication modulation of lignin-derived carbon nanosphere supported Pd nanoparticle via lignin fractionation for improved catalytic performance in vanillin hydrodeoxygenation

Nano-lignin presents great potential in advanced carbon materials preparation since it integrates the advantages of nanomaterials as well the preferable properties of lignin (e.g. high carbon content and highly aromatic structure). Herein, lignin-derived carbon nanosphere supported Pd catalysts (Pd@LCNS) were prepared via a two-step carbonization of Pd2+ adsorbed lignin nanospheres (LNS) and applied in vanillin hydrodeoxygenation. The effect lignin heterogeneity on the synthesis of Pd@LCNS as well as its catalytic performance was further investigated through the synthesis of Pd@LCNS using three lignin fractions with different molecular weight. The results showed that the three Pd@LCNSs exhibited significant differences in the morphology of both carbon support and Pd nanoparticles. Pd@LCNS-3 prepared from high molecular weight lignin fraction (L-3) presented stable carbon nanosphere support with the smallest particle size (∼150 nm) and the highest Pd loading amount (3.78 %) with the smallest Pd NPs size (∼1.6 nm). Therefore, Pd@LCNS-3 displayed superior catalytic activity for vanillin hydrodeoxygenation (99.34 % of vanillin conversion and 99.47 % of 2-methoxy-4-methylphenol selectivity) at 90 °C without H2. Consequently, this work provides a sustainable strategy to prepare uniformly dispersed lignin-based carbon-supported Pd catalyst using high molecular weight lignin as the feedstock and further demonstrate its superior applicability in the selective transfer hydrogenation of vanillin.

Catalytic hydrothermal liquefaction of alkali lignin for monophenols production over homologous biochar-supported copper catalysts in water

Constructing an advanced catalytic system for the purposeful liquefaction of lignin into chemicals has presented a significant prospect for sustainable development. In this work, the catalytic process of mesoporous homologous biochar (HBC) derived from alkali lignin supported copper catalysts (Cu/HBC) was reported for catalytic liquefaction of alkali lignin to monophenols. The characterization results revealed HBC promoted the formation of metal-support strong interaction and the generation of oxygen vacancies, enhancing the acid sites of Cu/HBC. Under the optimal conditions (0.2 g alkali lignin, 280 °C, 0.05 g Cu/HBC, 6 h, 18 mL water), the monophenol yield reached 75.01 ± 0.76 mg/g, and the bio-oil yield was 57.98 ± 1.76%. The copious mesopores, high surface area, and rich acidic sites were responsible for the high activity of Cu/HBC, which significantly outperformed the controlled catalysts, such as HBC, commercial activated carbon (AC), and reported Ni/AC, Ni/MCM-41, etc. In four consecutive runs, the catalytic performance of Cu/HBC was only reduced by 3.65% per cycle. Interestingly, catechol was selectively produced with Cu/HBC, which provided an effective strategy for the conversion of G/S-type lignin to catechyl phenolics (C-type). These findings indicate that the Cu/HBC will be a promising substitution of noble metal-supported catalysts for conversion biomass into high value-added phenolics.

The Physicochemical Characteristics and Heavy Metal Retention Capability of Black Liquor Lignin-Based Biochars

Due to its high carbon content, lignin, particularly for lignin-containing solid waste, is considered an excellent raw material for the preparation of carbon materials like biochar. To produce high-quality lignin-based biochar (LGBCs), lignin extracted from black liquor was employed to prepare biochar at various pyrolysis temperatures (300~600 °C). The physicochemical properties of LGBCs were assessed using scanning electron microscopy, N2 adsorption/desorption, Fourier transform infrared spectroscopy, Raman spectroscopy, and X-ray diffraction. Furthermore, the adsorption capability and potential mechanism of LGBCs in removing Cd(II) were investigated as well. The results indicate that LGBCs produced at higher pyrolysis temperatures exhibit rougher surfaces and more developed pore structures, which facilitate the exposure of numerous active adsorption sites. The adsorption of Cd(II) by LGBCs generally follows the order of LG-300C < LG-400C < LG-500C < LG-600C. According to the Langmuir adsorption isotherm model, the theoretical maximum adsorption capacity of LG-600C for Cd(II) is calculated to be 18.54 mg/g. Adsorption mechanism analysis reveals that the complexation interaction, dependent on the surface functional groups, plays a crucial role in the adsorption of Cd(II) by LGBCs prepared at higher pyrolysis temperatures. This study demonstrates that, by controlling the pyrolysis temperature during biochar preparation, high-quality lignin-based biochar can be readily obtained.

Lignin-coordinated highly dispersed PdZn alloy nanocluster supported on N-doped nanolayer carbon and its application in hexavalent chromium detoxification

As a renewable and low-cost biomacromolecule with high aromaticity and carbon content, lignin is a promising raw material for preparation of versatile carbon materials. Herein, we present a facile one-pot approach to prepare PdZn alloy nanocluster catalysts supported on N-doped lignin-derived nanolayer carbon through facile pyrolysis of melamine-mixed lignin-Pd-Zn complex. The dispersion of the PdZn alloy nanoclusters could be effectively modulated by varying the addition of melamine and the molar ratio of Pd and Zn salts. PdZn alloy nanocluster catalysts (Pd-Zn₂₉@N₁₀C) with ultra-small particle size (about 0.47 nm) were prepared when 10 times of melamine (relative to lignin weight) was added and the molar ratio of Pd and Zn salts was 1:29. Thereby, the catalyst presented superior catalytic activity for reduction of Cr(VI) to harmfulless Cr(III), significantly better than the two references Zn@N₁₀C (without Pd addition) and Pd-Zn₂₉@C (without N doping), as well as the commercial Pd/C. In addition, thanks to the strong anchoring of the PdZn alloy on the N-doped nanolayer support, the Pd-Zn₂₉@N₁₀C catalysts also exhibited good reusability. Consequently, the current study provides a straightforward and feasible method for producing highly dispersed PdZn alloy nanoclusters by lignin coordination, and further demonstrates its excellent applicability in hexavalent chromium reduction.

Emerging Modification Technologies of Lignin-based Activated Carbon toward Advanced Applications

Lignin-based activated carbon (LAC) is a promising high-quality functional material due to high surface area, abundant porous structure, and various functional groups. Modification is the most important step to functionalize LAC by altering its porous and chemical properties. This Review summarizes the state-of-the-art modification technologies of LAC toward advanced applications. Promising modification approaches are reviewed to display their effects on the preparation of LAC. The multiscale changes in the porosity and the surface chemistry of LAC are fully discussed. Advanced applications are then introduced to show the potential of LAC for supercapacitor electrode, catalyst support, hydrogen storage, and carbon dioxide capture. Finally, the mechanistic structure-function relationships of LAC are elaborated. These results highlight that modification technologies play a special role in altering the properties and defining the functionalities of LAC, which could be a promising porous carbon material toward industrial applications.

Synchronous catalytic depolymerization of alkaline lignin to monophenols with in situ-converted hierarchical zeolite for bio-polyurethane production

Catalytic depolymerization of lignin to high-value chemicals is crucial to the comprehensive achievement of sustainable and economic concerns. Herein, we propose a green, practical, and economic strategy for the synchronous catalytic depolymerization of lignin based on in situ conversion of geopolymer precursor to hierarchical zeolite, using water as a mild solvent and without external H₂, additives, co-catalysts or co-solvents. The in situ-converted hierarchical analcime (ANA) zeolite outperformed previously reported representative catalysts, such as PTA/MCM-41 and CuAlMgO_x in lignin depolymerization with a high monophenol yield (95.61 ± 7.89 mg/g). The synergetic effect of the micro-mesoporous structure and enhanced acidic sites of the ANA played a vital role in regulating the monomer composition and the yield of monophenols. The obtained monophenols are rich in -OH groups and can be utilized as a substitute for petroleum resources, such as ethylene glycol or glycerin for the synthesis of bio-polyurethane foams (bio-PUFs). This work expands the scope of using biomass in a sustainable manner to make high-value chemicals and biomaterials.

Carbon-Based Nanocatalysts (CnCs) for Biomass Valorization and Hazardous Organics Remediation

The continuous increase of the demand in merchandise and fuels augments the need of modern approaches for the mass-production of renewable chemicals derived from abundant feedstocks, like biomass, as well as for the water and soil remediation pollution resulting from the anthropogenic discharge of organic compounds. Towards these directions and within the concept of circular (bio)economy, the development of efficient and sustainable catalytic processes is of paramount importance. Within this context, the design of novel catalysts play a key role, with carbon-based nanocatalysts (CnCs) representing one of the most promising class of materials. In this review, a wide range of CnCs utilized for biomass valorization towards valuable chemicals production, and for environmental remediation applications are summarized and discussed. Emphasis is given in particular on the catalytic production of 5-hydroxymethylfurfural (5-HMF) from cellulose or starch-rich food waste, the hydrogenolysis of lignin towards high bio-oil yields enriched predominately in alkyl and oxygenated phenolic monomers, the photocatalytic, sonocatalytic or sonophotocatalytic selective partial oxidation of 5-HMF to 2,5-diformylfuran (DFF) and the decomposition of organic pollutants in aqueous matrixes. The carbonaceous materials were utilized as stand-alone catalysts or as supports of (nano)metals are various types of activated micro/mesoporous carbons, graphene/graphite and the chemically modified counterparts like graphite oxide and reduced graphite oxide, carbon nanotubes, carbon quantum dots, graphitic carbon nitride, and fullerenes.

Wood-Sourced Polymers as Support for Catalysis by Group 10 Transition Metals

Despite providing interesting solutions to reduce the number of synthetic steps, to decrease energy consumption or to generate less waste, therefore contributing to a more sustainable way of producing important chemicals, the expansion of the use of homogeneous catalysis in industrial processes is hampered by several drawbacks. One of the most important is the difficulty to recycle the noble metals generating potential high costs and pollution of the synthesized products by metal traces detrimental to their applications. Supporting the metals on abundant and cheap biosourced polymers has recently appeared as an almost ideal solution: They are much easier to recover from the reaction medium and usually maintain high catalytic activity. The present bibliographical review focuses on the development of catalysts based on group 10 transition metals (nickel, palladium, platinum) supported on biopolymers obtained from wood, such as cellulose, hemicellulose, lignin, and their derivatives. The applications of these catalysts in organic synthesis or depollution are also addressed in this review with examples of C-C couplings, oxidation, or hydrogenation reactions.

Hydrodeoxygenation of Xylose Isopropylidene Ketal Over Pd/HBEA Catalyst for the Production of Green Fuels

1,2:3,5-Di-O-isopropylidene-α-D-xylofuranose (DX) is a major component of a new bio-crude: a viscous oil presenting petroleum-friendly properties produced by the ketalization of sugarcane bagasse. This article studies DX HDO (hydrodeoxygenation) over a Pd/HBEA catalyst in a batch reactor at 250°C. The effects of hydrogen pressure from 10 to 40 bar, catalyst/DX ratio from ½ to 2, and reaction time 0–24 h were investigated. A range of conditions for complete hydrodeoxygenated DX into alkanes with a Pd/HBEA catalyst was found. In these conditions, a low coke yield with water as the principal deoxygenated product was obtained. Further, higher amounts of alkanes containing seven or more carbons (A₇₊) were favored at 30 bar of hydrogen pressure, Cat/DX ratio = 2, and short reaction time. Products analysis that accompanied the above variations during reaction time led to general insights into reaction pathways. First, in the presence of DX, an effective n-hexane conversion was not observed on experiments of low catalyst/DX ratio (½) or in the initial period of high Cat/DX ratio, suggesting DX is much more successful than n-hexane to compete for active sites. Then, the formation of a pool of oxygenated compounds, such as furans, ketones, and carboxylic acids, along with lighter and heavier alkanes was observed. Hence, the aforementioned oxygenates may undergo reactions, such as aldol condensation with subsequent hydrodeoxygenation reaction, generating heavier alkanes.

Advances in Versatile Nanoscale Catalyst for the Reductive Catalytic Fractionation of Lignin

In the past five years, biomass-derived biofuels and biochemicals were widely studied both in academia and industry as promising alternatives to petroleum. In this Review, the latest progress of the synthesis and fabrication of porous nanocatalysts that are used in catalytic transformations involving hydrogenolysis of lignin is reviewed in terms of their textural properties, catalytic activities, and stabilities. A particular emphasis is made with regard to the catalyst design for the hydrogenolysis of lignin and/or lignin model compounds. Furthermore, the effects of different supports on the lignin hydrogenolysis/hydrogenation are discussed in detail. Finally, the challenges and future opportunities of lignin hydrogenolysis over nanomaterial-supported catalysts are also presented.

Theoretical insight into the deoxygenation molecular mechanism of butyric acid catalyzed by a Ni12P6 cluster

For the deoxygenation of butyric acid catalyzed by Ni12P6 cluster, decreasing temperature is beneficial to butyraldehyde, n-butyl alcohol, and n-butane formation, and increasing temperature is preferable to propylene, propane, and butylene formation.

A critical review of the production and advanced utilization of biochar via selective pyrolysis of lignocellulosic biomass

Biochar is a carbon-rich product obtained from the thermo-chemical conversion of biomass. Studying the evolution properties of biochar by in-situ modification or post-modification is of great significance for improving the utilisation value of lignocellulosic biomass. In this paper, the production methods of biochar are reviewed. The effects of the biomass feedstock characteristics, production processes, reaction conditions (temperature, heating rate, etc.) as well as in-situ activation, heteroatomic doping, and functional group modification on the physical and chemical properties of biochar are compared. Based on its unique physicochemical properties, recent research advances with respect to the use of biochar in pollutant adsorbents, catalysts, and energy storage are reviewed. The relationship between biochar structure and its application are also revealed. It is suggested that a more effective control of biochar structure and its corresponding properties should be further investigated to develop a variety of biochar for targeted applications.

Catalytic hydrotreatment of kraft lignin into aromatic alcohols over nickel-rhenium supported on niobium oxide catalyst

Direct hydrogenolysis of Kraft lignin was catalyzed over a series of supported Ni or Re catalysts in ethanol solvent. The best results showed that the oil yield of 96.70 wt% was obtained with less char formation at 330 °C for 3 h over 5Ni-5Re/Nb₂O₅ catalyst. Product analysis demonstrated that the monomer yield of 35.41 wt% was given under mild condition, and low-molecular-weight aromatic alcohols were the main component in the liquid products. Ethanol was found to be more effective in H₂ production and facilitated the transformation of phenolic monomers to aromatic chemicals. The results confirmed that the optimal 5Ni-5Re/Nb₂O₅ catalyst had superior oxophilicity and appropriate acid sites, which improved the ability to directly remove the methoxyl and hydroxyl groups of lignin-derived phenolic compounds without aromatic ring hydrogenation. In addition, the temperature, time and solvent effects on the lignin depolymerization were also investigated.