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

Hydrodeoxygenation of Isoeugenol-Derived Model Compound over Carbon-Supported Pt and Pt-SnS Catalysts for the Production of Sustainable Jet Fuel

This study focuses on the sustainable production of bio-jet fuel through the catalytic hydrodeoxygenation (HDO) of isoeugenol (IE). Sucrose-based activated carbon supported bimetallic Platinum-Tin metal sulphides (PtO-SnS/AC) catalyst was prepared for HDO process. Physicochemical properties of catalysts with different spraying synthesis methods (in situ and ex situ metal doping) and Pt loading (0.1-1.0 %) were further investigated. The PtO-SnS/AC catalysts were characterised using various techniques such as X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), field-emission scanning electron microscopy (FESEM) and thermogravimetric analysis (TGA). Both HRTEM and FESEM results show the successful preparation of a spherical nanoparticles doped over activated carbon, and Pt was dispersed on the outer shell of the particles. The catalytic HDO of IE was evaluated in a batch system and showed a high yield and conversion as follows: IE conversion of 100 %, liquid-phase mass balance of 95.92 %, dihydroeugenol (DH) conversion of 99.32 %, propylcyclohexane (PCH) yield of 88.94 % and 2-methoxy-4-propylcyclohexanol (HYD) yield of 76.19 %. Moreover, the PtO-SnS/AC catalyst exhibited high reusability with low metal leaching and high coke resistance for 10 cycles. The catalyst was evaluated in a continuous flow reactor for 100 h at different reaction temperatures, and interestingly, the catalyst showed low deactivation with a high half-time.

Mechanocatalytic Hydrogenolysis of the Lignin Model Dimer Benzyl Phenyl Ether over Supported Palladium Catalysts

This work demonstrates the mechanocatalytic hydrogenolysis of the ether bond in the lignin model compound benzyl phenyl ether (BPE) and hardwood lignin isolated by hydrolysis with supercritical water. Pd catalysts with 4 wt % loading on Al2O3 and SiO2 supports achieve 100% conversion of BPE with a toluene production rate of (2.6-2.9) × 10-5 mol·min-1. The formation of palladium hydrides under H2 gas flow contributes to an increase in the turnover frequency by a factor of up to 300 compared to Ni on silica-alumina. While a near-quantitative toluene yield is obtained, some of the phenolic products remain adsorbed on the catalyst.

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.

Sustainable production of catechol derivatives from waste tung nutshell C/G-type lignin via heterogeneous Cu-NC catalytic oxidation

The sustainable production of catechol derivatives is a challenging task. Catechyl (C) and guaiacyl (G) lignins coexisting in waste tung nutshells are promising feedstocks to form valuable catechol derivatives, but the depolymerization of C/G lignin typically involves a catalytic reductive process that cannot produce these oxidized aromatic chemicals. Herein, we demonstrated that the sustainable production of catechol derivative aldehydes and acids from C/G lignin could be achieved through a heterogeneous copper-catalyzed oxidative process. Under optimized conditions, the Cu-NC-800 catalyst affords a 43.5 mg g-1 yield (8.9 wt%, based on Klason lignin) of aromatic aldehydes (protocatechuic aldehyde, vanillin) and acids (protocatechuic acid, vanillic acid). XRD and XPS analyses showed that CuO and Cu2O may be the active species during the heterogeneous oxidation of the Cu-NC-800 catalyst. This study opens new opportunities for the sustainable production of catechol derivatives from C/G-type lignin.

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.

Reductive catalytic fractionation as a novel pretreatment/lignin-first approach for lignocellulosic biomass valorization: A review

Presently, the use of lignocellulosic biomass is mainly focused on creating pulp/paper, energy, sugars and bioethanol from the holocellulose component, leaving behind lignin to be discarded or burned as waste despite of its highest aromatic carbon and energy content (22-29 KJ/g). During the pulping process, lignin undergoes significant structural changes to yield technical lignin. For a circular bioeconomy, there is an urgent need to enhance the use of native lignin for generating more valuable products. Over the last few years, a new method called 'lignin-first', or 'reductive catalytic fractionation' (RCF), has been devised to achieve selective phenolic monomers under mild reaction conditions. This involves deconstructing lignin before capitalizing on carbohydrates. The objective of this study is to record the recent developments of the 'lignin-first' process. This review also underlines the contribution of RCF biorefinery towards achieving sustainable development goals (SDGs) and concludes with an overview of challenges and upcoming opportunities.

Lignin to value-added products: Research updates and prospects

Due to the urgent need for renewable and clean energy, the efficient use of lignin is of wide interest. A comprehensive understanding of the mechanisms of lignin depolymerization and the generation of high-value products will contribute to the global control of the formation of efficient lignin utilization. This review explores the lignin value-adding process and discusses the link between lignin functional groups and value-added products. Mechanisms and characteristics of lignin depolymerization methods are presented, and challenges and prospects for future research are highlighted.

Catalytic Hydrogenolysis of Lignin: The Influence of Minor Units and Saccharides

The precise elucidation of native lignin structures plays a vital role for the development of "lignin first" strategies such as reductive catalytic fractionation. The structure of lignin and composition of the starting material has a major impact on the product yield and distribution. Here, the differences in structure of lignin from birch, pine, reed, and walnut shell were investigated by combining detailed analysis of the whole cell wall material, residual enzyme lignin, and milled wood lignin. The results of the 2D heteronuclear single quantum coherence NMR analysis could be correlated to the product from Ru/C-catalyzed hydrogenolysis if monomeric products from ferulate and p-coumaryl and its analogous units were also appropriately considered. Notably, residual polysaccharide constituents seemed to influence the selectivity towards hydroxy-containing monomers. The results reinforced the importance of adequate structural characterization and compositional analysis of the starting materials as well as distinct (dis)advantages of specific types of structural characterization and isolation methods for guiding valorization potential of different biomass feedstocks.

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

In this work, near-complete conversion of lignocellulosic biomass and high products yields were achieved through catalytic transfer hydrogenolysis (CTH) in isopropanol using a heteropoly acid SiW₁₂ synergistic with Pd/C catalyst at a relatively mild condition. The performances of various heteropoly acids and catalytic conditions were extensively examined. The results confirmed that SiW₁₂ exhibited the highest activity on disrupting C-C linkages and C-O linkages than H₂WO₄, PW₁₂, and PMo₁₂. 34.91 wt% and 43.55 wt% monophenols were achieved for hydrogenolysis of bagasse and eucalyptus, respectively, at their optimal temperature for 5 h. Characterization studies on the lignin oil revealed that the notable structural changes were observed including the breaking of the side chain alkyl-aryl ether bonds and glycosidic bonds, while methoxyl groups were retained. Additionally, particle size of feedstock also has significant impact on the distribution and yields of the monophenols.