Selective production of phenolic monomers via high efficient lignin depolymerization with a carbon based nickel-iron-molybdenum carbide catalyst under mild conditions

Production of vanillin via oxidation depolymerization of lignin over Fe- and Mn-modified TS-1 zeolites

Converting lignin into specific aromatic chemicals for utilization through depolymerization of lignin is an effective way to achieve high-value applications. There are many depolymerization methods that can do this, but there are problems such as harsh reaction conditions, low depolymerization efficiency and uncontrollable target products that need to be solved. This study reports a novel system for the oxidative depolymerization of alkali lignin using Fe- and Mn- modified TS-1 as a catalyst to assist in the highly selective production of vanillin. We also proposed a possible reaction pathway for the oxidative depolymerization of alkali lignin to produce vanillin catalyzed by Fe-Mn/TS-1 catalyst. The catalytic effects of TS-1, Fe/TS-1, and Fe-Mn/TS-1 catalysts on the oxidative depolymerization of lignin to produce phenolic monomers and vanillin were investigated. The results show that the modified catalysts can effectively improve the efficiency of linkage bond breaking in lignin, especially the β-O-4 bond, in which the inter-band transitions of Fe and Mn play an important role. The synergistic effect of the bimetallic-loaded catalyst (Fe-Mn/TS-1) could catalyze the oxidative depolymerization of lignin more efficiently than the monometallic-loaded catalyst (Fe/TS-1). This lignin oxidative depolymerization system produced 40.59 wt% bio-oil including 12.24 wt% phenolic monomers and 16.17 wt% re-lignin after the addition of Fe-Mn/TS-1 catalyst, owning the highest phenolic monomer yield. Surprisingly, this lignin oxidative depolymerization system exhibited high yield for vanillin (8.36 wt%) production. These results demonstrated that the Fe-Mn/TS-1 catalytic system has potential to produce vanillin from lignin under mild conditions.

Review of the application of bimetallic catalysts coupled with internal hydrogen donor for catalytic hydrogenolysis of lignin to produce phenolic fine chemicals

Lignocellulosic biomass contains lignin, an aromatic and oxygenated substance and a potential method for lignin utilization is achieved through catalytic conversion into useful phenolic and aromatic monomers. The application of monometallic catalysts for lignin hydrogenolysis reaction remains one of the major reasons for the underutilization of lignin to produce valuable chemicals. Monometallic catalysts have many limitations such as limited catalytic sites for interacting with different lignin linkages, poor catalytic activity, low lignin conversion, and low product selectivity. It is due to lack of synergy with other metallic catalysts that can enhance the catalytic activity, stability, selectivity, and overall catalytic performance. To overcome these limitations, works on the application of bimetallic catalysts that can offer higher activity, selectivity, and stability have been initiated. In this review, cutting-edge insights into the catalytic hydrogenolysis of lignin, focusing on the production of phenolic and aromatic monomers using bimetallic catalysts within an internal hydrogen donor solvent are discussed. The contribution of this work lies in a critical discussion of recent reported findings, in-depth analyses of reaction mechanisms, optimal conditions, and emerging trends in lignin catalytic hydrogenolysis. The specific effects of catalytic active components on the reaction outcomes are also explored. Additionally, this review extends beyond current knowledge, offering forward-looking suggestions for utilizing lignin as a raw material in the production of valuable products across various industrial processes. This work not only consolidates existing knowledge but also introduces novel perspectives, paving the way for future advancements in lignin utilization and catalytic processes.

Study on the catalytic hydrodeoxygenation of lignin dimers: Adsorption properties and linkages cleavage

Production of mono-phenols through hydrodeoxygenation is one of the most promising routes for value-added lignin valorization. However, the adsorption characteristic of key intermediates and hydrodeoxygenation mechanism of key linkages in lignin have received inadequate attentions. In this paper, experiments combined with density functional theory calculations were done to explore the adsorption and catalytic HDO mechanism of lignin dimers. It was found that NiFe(111)-Mo2C(001) had a better ability on linkages activation, and showed stronger adsorption on CO containing intermediates, which was favor for further hydrodeoxygenation. Moreover, the calculation results certificated the cleavage of β-O-4 was prior to the hydrodeoxygenation of CO, and the hydrodeoxygenation of β-O-4 included a H· addition to O atom before the C-O cleavage. Finally, the elementary reactions energy barriers were efficiently reduced by NiFe(111)-Mo2C(001) catalyst during the hydrodeoxygenation reactions, which elucidated the superior performance of NiFe catalyst. This work provides a theoretical basis on efficient lignin utilization.

Ni-Fe Cocatalysts on Magnesium Silicate Supports for the Depolymerization of Kraft Lignin

This research aimed to synthesize magnesium silicate (MgSiO₃) used as a support for Ni-Fe cocatalysts in the depolymerization of kraft lignin. Magnesium silicate was prepared by a hydrothermal method, followed by metal solution impregnation to obtain lignin depolymerization catalysts. The catalytic efficiency of kraft lignin depolymerization to valued phenolic compounds was studied by varying the ratios of Ni and Fe on the MgSiO₃ support. Moreover, other factors such as temperature, reaction time, and catalyst recycling affected both the quality and quantity of the products studied. The results illustrated that the catalyst 10Ni10Fe/MS produced all lignin depolymerization products with the highest yield (14.29 wt %) using reaction conditions of 300 °C and 1 h. In addition, the main products were found to be catechol (11.38 wt %), guaiacol (1.51 wt %), and phenol (0.79 wt %). More importantly, the 10Ni10Fe/MS catalyst showed good reusability even after two recycling processes, and the obtained phenol and guaiacol were found to be 0.63 and 1.01 wt %, respectively.

Reductive Catalytic Fractionation of Abies Wood into Bioliquids and Cellulose with Hydrogen in an Ethanol Medium over NiCuMo/SiO2 Catalyst

Noble metal-based catalysts are widely used to intensify the processes of reductive fractionation of lignocellulose biomass. In the present investigation, we proposed for the first time using the inexpensive NiCuMo/SiO2 catalyst to replace Ru-, Pt-, and Pd-containing catalysts in the process of reductive fractionation of abies wood into bioliquids and cellulose products. The optimal conditions of abies wood hydrogenation were selected to provide the effective depolymerization of wood lignin (250 °C, 3 h, initial H2 pressure 4 MPa). The composition and structure of the liquid and solid products of wood hydrogenation were established. The NiCuMo/SiO2 catalyst increases the yield of bioliquids (from 36 to 42 wt%) and the content of alkyl derivatives of methoxyphenols, predominantly 4-propylguaiacol and 4-propanolguaiacol. A decrease in the molecular mass and polydispersity (from 1870 and 3.01 to 1370 Da and 2.66, respectively) of the liquid products and a threefold increase (from 9.7 to 36.8 wt%) in the contents of monomer and dimer phenol compounds were observed in the presence of the catalyst. The solid product of catalytic hydrogenation of abies wood contains up to 73.2 wt% of cellulose. The composition and structure of the solid product were established using IRS, XRD, elemental and chemical analysis. The data obtained show that the catalyst NiCuMo/SiO2 can successfully replace noble metal catalysts in the process of abies wood reductive fractionation into bioliquids and cellulose.

Nature-inspired pretreatment of lignocellulose - Perspective and development

As sustainability gains increasing importance in addition to cost-effectiveness as a criterion for evaluating engineering systems and practices, biological processes for lignocellulose pretreatment have attracted growing attention. Biological systems such as white and brown rot fungi and wood-consuming insects offer fascinating examples of processes and systems built by nature to effectively deconstruct plant cell walls under environmentally benign and energy-conservative environments. Research in the last decade has resulted in new knowledge that advanced the understanding of these systems, provided additional insights into these systems' functional mechanisms, and demonstrated various applications of these processes. The new knowledge and insights enable the adoption of a nature-inspired strategy aiming at developing technologies that are informed by the biological systems but superior to them by overcoming the inherent weakness of the natural systems. This review discusses the nature-inspired perspective and summarizes related advancements, including the evolution from biological systems to nature-inspired processes, the features of biological pretreatment mechanisms, the development of nature-inspired pretreatment processes, and future perspective. This work aims to highlight a different strategy in the research and development of novel lignocellulose pretreatment processes and offer some food for thought.

Cobalt catalysts (Co–N–C) for C–O bond cleavage in lignin-derived aryl ethers and lignin

The transformation of lignin into value-added chemicals represents one of the relevant approaches for sustainable development.

Hydrogenolysis of Lignin and C–O Linkages Containing Lignin-Related Compounds over an Amorphous CoRuP/SiO2 Catalyst

Efficient depolymerization of C–O linkages is essential for converting lignin into fuels and higher value-added chemicals. In this work, CoRuP/SiO2, an amorphous Ru-Co phosphide composite, was fabricated for the efficient hydrogenolysis of ether linkages. The 4–O–5 and α–O–4 linkages containing lignin-related compounds, such as diphenyl ether, benzyl phenyl ether, 3-methyl diphenyl ether, and dibenzyl ether, are selected as representatives of linkages in lignin. Under mild conditions, Ru-containing metallic phosphides have high-performance for the catalytic depolymerization of C–O linkages. Compared with other catalysts, CoRuP/SiO2 shows an outstanding selectivity for benzene and excellent efficiency in depolymerizing diphenyl ethers, yielding only a small amount of by-products. Furthermore, the total acidity shows a linear relationship with the hydrogenolysis reactivity in cleaving aromatic ether bonds. The mechanisms for the catalytic hydrogenolysis of 4–O–5 and α–O–4 bonds over CoRuP/SiO2 are proposed. Moreover, two-dimensional heteronuclear single quantum coherence nuclear magnetic resonance spectroscopic analysis demonstrates that CoRuP/SiO2 could effectively depolymerize C–O bonds of lignin. These dominant hydrogenolysis products from lignin have excellent potential in the production of high value-added drugs or pharmaceutical intermediates. The hydrogenolysis of lignin can be a highly efficient alternative to the existing method of lignin utilization.

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.

Review on the preparation of fuels and chemicals based on lignin

Lignin is by far the most abundant natural renewable aromatic polymer in nature, and its reserves are second only to cellulose. In addition to the rich carbon content, the structure of lignin contains functional groups such as benzene rings, methoxyl groups, and phenolic hydroxyl groups. Lignin degradation has become one of the high value, high quality and high efficiency methods to convert lignin, which is of great significance to alleviating the current energy shortage and environmental crisis. This article introduces the hydrolysis methods of lignin in acidic, alkaline, ionic liquids and supercritical fluids, reviews the heating rate, the source of lignin species and the effects of heating rate on the pyrolysis of lignin, and briefly describes the metal catalysis, oxidation methods such as electrochemical degradation and photocatalytic oxidation, and degradation reduction methods using hydrogen and hydrogen supply reagents. The lignin degradation methods for the preparation of fuels and chemicals are systematically summarized. The advantages and disadvantages of different methods, the selectivity under different conditions and the degradation efficiency of different catalytic combination systems are compared. In this paper, a new approach to improve the degradation efficiency is envisioned in order to contribute to the efficient utilization and high value conversion of lignin.

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.

An efficient way to synthesize biomass-based molybdenum carbide catalyst via pyrolysis carbonization and its application for lignin catalytic pyrolysis

In this study, a simple and rapid method was proposed to synthesize orthorhombic α-Mo₂C as catalyst for lignin catalytic pyrolysis. Biomass in-situ pyrolysis products were used as the carbon source and supporter, the carbonization of Mo precursor was realized under rapid heating. Experimental results show that Pine-Mo₂C catalyst can achieve lignin pyrolysis vapor bond breaking and deoxidation under normal pressure, and the yield of monocyclic aromatic hydrocarbons is 13.26 wt%, of which aromatic hydrocarbons with side chain account for 74%. The side chain aliphatic hydrocarbons of lignin are effectively retained, and hydrogen consumption is minimized. The characterization of catalyst and experiments of guaiacol, 2-phenoxy-1-phenylethanol and 4,4'-biphenol shows that efficient deoxidation is due to targeted attack of catalyst on C-O. Therefore, Pine-Mo₂C shows excellent activity in promoting direct bond breaking deoxidation of lignin.

Mild depolymerization of the sinocalamus oldhami alkali lignin to phenolic monomer with base and activated carbon supported nickel-tungsten carbide catalyst composite system

In this study, the sinocalamus oldhami alkali lignin was depolymerized into phenolic products in a combined system by using the composite alkali and Ni-W₂C/activated carbon (AC) as catalysts. FT-IR, GPC, TG, 2D-HSQC and GC-MS were used to analyze the composition, structure and distribution of degradation products, and the synergistic effect of metal and alkali catalysts on the depolymerization of lignin was also studied. The results showed that Ni-W₂C/AC and composite alkali could effectively improve the catalytic degradation efficiency of lignin under mild conditions, 94.4% of lignin was converted and 17.18% of phenolic monomers were obtained under 260 °C for 5 h. In this composite system, the synergism of the basic sites, the metal active sites and the Lewis acid sites could promote the cleavage of C-O bonds in the lignin molecule and lower the char formation during the base-catalyzed solvolysis. Phenolic monomers were mainly composed of phenol, 2-methyl-phenol and p-cresol etc.

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.