Hydrogenation of Furfural over Biomass-Based Electron-Deficient Co-NC Nanotube Catalyst

The conversion of furfural to furfuryl alcohol is one of the most significant reactions from industrial-scale produced biomass platform molecules to value-added chemicals. In this work, biomass-based chitosan was used as both a carbon source and nitrogen source to synthesize nitrogen-doped carbon. With the addition of cobalt, the optimized 7.5Co-NC-900 catalyst had the largest surface area and the graphite nanotube structure with the least defects. It was employed for the hydrogenation of furfural to furfuryl alcohol and reached a nearly full conversion and an equivalent yield at 130 °C in 4 MPa initial H2. The structure-function relationship study indicated that the N could interact with the neighbor Co in this catalyst and formed an electron-deficient Co center which was in favor of the adsorption of furfural in the nanotube and had high catalytic activity. The interactions between Co and N stabilized the catalyst so that it could remain stable in five runs of catalytic reactions.

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.

MOF-derived Ru@ZIF-8 catalyst with the extremely low metal Ru loading for selective hydrogenolysis of C–O bonds in lignin model compounds under mild conditions

A MOF-derived Ru@ZIF-8 catalyst with extremely low Ru loading effectively cleaved the C–O bonds of lignin model compounds under mild conditions.

Lignin-Derived Syringol and Acetosyringone from Palm Bunch Using Heterogeneous Oxidative Depolymerization over Mixed Metal Oxide Catalysts under Microwave Heating

Biomass valorization to building block chemicals in food and pharmaceutical industries has tremendously gained attention. To produce monophenolic compounds from palm empty fruit bunch (EFB), EFB was subjected to alkaline hydrothermal extraction using NaOH or K2CO3 as a promotor. Subsequently, EFB-derived lignin was subjected to an oxidative depolymerization using Cu(II) and Fe(III) mixed metal oxides catalyst supported on γ-Al2O3 or SiO2 as the catalyst in the presence of hydrogen peroxide. The highest percentage of total phenolic compounds of 63.87 wt% was obtained from microwave-induced oxidative degradation of K2CO3 extracted lignin catalyzed by Cu-Fe/SiO2 catalyst. Main products from the aforementioned condition included 27.29 wt% of 2,4-di-tert-butylphenol, 19.21 wt% of syringol, 9.36 wt% of acetosyringone, 3.69 wt% of acetovanillone, 2.16 wt% of syringaldehyde, and 2.16 wt% of vanillin. Although the total phenolic compound from Cu-Fe/Al2O3 catalyst was lower (49.52 wt%) compared with that from Cu-Fe/SiO2 catalyst (63.87 wt%), Cu-Fe/Al2O3 catalyst provided the greater selectivity of main two value-added products, syringol and acetosyrigone, at 54.64% and 23.65%, respectively (78.29% total selectivity of two products) from the NaOH extracted lignin. The findings suggested a promising method for syringol and acetosyringone production from the oxidative heterogeneous lignin depolymerization under low power intensity microwave heating within a short reaction time of 30 min.

Ru-gC3N4 Catalyzed Hydrodebenzylation of Benzyl Protected Alcohol and Acid Groups Using Sodium Hypophosphite as a Hydrogen Source

A straightforward process for hydrodebenzylation of benzyl protected acid and alcohol derivatives to the corresponding acids and alcohols using sodium hypophosphite in the presence of Ru-GCN catalyst is reported. The developed Ru-GCN catalyst is cost effective compared to other noble metal-based catalysts and has been explored to exhibit excellent activity for catalytic hydrodebenzylation reactions under moderate reaction conditions. The non-corrosive sodium hypophosphite has been found as a better hydrogen donor compared to alkali metal formats in presence of Ru-GCN catalyst. The stated catalyst was characterized using several spectrometric and material characterization methods such as PXRD, IR, SEM, TEM, XPS, and TGA. The Ru-GCN catalyst corroborated good reusability and stability for multiple cycles. The catalyst preparation is facile and the developed process is simple and safe as it avoids use of high hydrogen pressure. The developed protocol can also be replicated on industrial scale on account of excellent recyclability and retained activity after multiple cycles and makes the process sustainable. Gram scale reaction was performed to verify the industrial potential of reported catalyst.

α-Oxidation of banana lignin with atmospheric oxygen catalyzed by Co3O4

Banana lignin was subjected to oxidation, converting alpha hydroxyl to carbonyl. In this process, atmospheric oxygen acted as an oxidizing agent, CO₃O₄ as a catalyst under mild conditions of temperature and pressure.

Effect of cobalt on titania, ceria and zirconia oxide supported catalysts on the oxidative depolymerization of prot and alkali lignin

The production of phenolics by oxidative depolymerization of prot lignin and alkali lignin were studied in the presence of cobalt impregnated TiO₂, CeO₂ and ZrO₂ catalysts at 140 °C for 1 h. Maximum bio-oil yield of 78.0 and 60.2 wt% were observed with Co/CeO₂ catalyst for prot lignin and alkali lignin, respectively. The characterizations of the bio-oils were carried out using GC-MS, FTIR, and ¹H NMR. The GC-MS compounds have been classified into four categories (G, H, S-type and others). The depolymerization of prot lignin showed a mixture of G, H and S type phenolic monomers. Interestingly, higher selectivity of acetosyringone (47.1%) was obtained in the presence of Co/TiO₂ catalyst with prot lignin. The depolymerization of alkali lignin exhibited only G-type phenolic monomers production, and was effectively produced 67.4% (G-type monomer) in the presence of Co/ZrO₂ catalyst.

Hydrogenolysis of lignin-derived aryl ethers to monomers over a MOF-derived Ni/N–C catalyst

A highly efficient Ni/N–C catalyst was synthesized by facile pyrolysis of a Ni-MOF, and its catalytic hydrogenolysis performance towards C–O bonds in lignin was evaluated in detail using diphenyl ether (DPE) as a model compound.

Efficient hydrogenolysis of aryl ethers over Ce-MOF supported Pd NPs under mild conditions: mechanistic insight using density functional theoretical calculations

The significant Pd⁰ content and optimum bonding of the reactant & product (higher adsorption energy of benzyl phenyl ether and lower desorption energy for phenol) are responsible for the exceptional catalytic activity of Pd/Ce-MOF.

Advances in lignin valorization towards bio-based chemicals and fuels: Lignin biorefinery

Lignin is one of the most promising renewable sources for aromatic hydrocarbons, while effective depolymerization towards its constituent monomers is a particular challenge because of the structural complexity and stability. Intensive research efforts have been directed towards exploiting effective valorization of lignin for the production of bio-based platform chemicals and fuels. The present contribution aims to provide a critical review of key advances in the identification of exact lignin structure subjected to various fractionation technologies and demonstrate the key roles of lignin structures in depolymerization for unique functionalized products. Various technologies (e.g., thermocatalytic approaches, photocatalytic conversion, and mechanochemical depolymerization) are reviewed and evaluated in terms of feasibility and potential for further upgrading. Overall, advances in pristine lignin structure analysis and conversion technologies can facilitate recovery and subsequent utilization of lignin towards tailored commodity chemicals and fungible fuels.

Lignin Valorizations with Ni Catalysts for Renewable Chemicals and Fuels Productions

Energy and fuels derived from biomass pose lesser impact on the environmental carbon footprint than those derived from fossil fuels. In order for the biomass-to-energy and biomass-to-chemicals processes to play their important role in the loop of the circular economy, highly active, selective, and stable catalysts and the related efficient chemical processes are urgently needed. Lignin is the most thermal stable fraction of biomass and a particularly important resource for the production of chemicals and fuels. This mini review mainly focuses on lignin valorizations for renewable chemicals and fuels production and summarizes the recent interest in the lignin valorization over Ni and relevant bimetallic metal catalysts on various supports. Particular attention will be paid to those strategies to convert lignin to chemicals and fuels components, such as pyrolysis, hydrodeoxygenation, and hydrogenolysis. The review is written in a simple and elaborated way in order to draw chemists and engineers’ attention to Ni-based catalysts in lignin valorizations and guide them in designing innovative catalytic materials based on the lignin conversion reaction.