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Herbaceous plants-derived hydroxycinnamic units can serve as unique monomers to construct recyclable and controllable copolyesters via biomass RCF, one-pot derivatization, and copolymerization.

Bio-oils are an important part of the future energy composition. This review primarily focuses on model compounds, catalysts, and equipment involved in the hydrodeoxygenation (HDO) of bio-oils. Initially, this article reviews the basic physicochemical properties of bio-oils and introduces different upgrading methods. Among them, HDO can effectively facilitate calorific value and improve the acidity and viscosity of bio-oils. Secondly, the basic HDO reaction pathways and proposed catalytic mechanism of various model compounds are summarized to understand the catalytic behavior and structure–performance relationship of the HDO reaction. Subsequently, we review different catalysts used in actual HDO of bio-oils, some of which lead to excellent stability and improved HDO reactivity. Finally, progress in the development of HDO equipment, including fixed bed and ebullated bed reactors in the pilot stage, is reviewed. This review aims to summarize progress in the utilization of the HDO process and provides useful insights for the efficient practical application of bio-oils.

The excessive use of petroleum-based non-biodegradable plastic products has resulted in severe environmental pollution and ecological problems, which has stimulated the development of biodegradable and renewable alternative materials. Lignin, as the most abundant aromatic polymer with great biodegradability and biocompatibility, exhibits enormous potential for preparing various functional and sustainable materials as alternatives to plastics. Recently, lignin-derived biodegradable films have received extensive attention in both fundamental research and practical applications, and many significant achievements have been made in this field. Herein, the latest progress in the preparation and advanced applications of lignin-derived biodegradable film materials is summarized from a sustainability point of view. An introduction to the structural and chemical characteristics of lignin is presented first, and then the designs and advances of construction systems are reviewed based on the building matrixes, including lignocellulose, natural macromolecules, biodegradable synthetic copolymers, and other cutting-edge materials. In this review, the tailored applications of these film materials are mainly focused on sensors and responsive materials, energy storage systems, packaging, and biomedical materials. Finally, the main challenges of lignin-derived biodegradable film materials are presented, and potential development directions for sustainable and eco-friendly lignin-derived film materials are also proposed.

The search for efficient and selective routes for the disassembly of C-lignin and G/S lignin coexisting in Euphorbiaceae seed coats is of great interest and importance, because a plentiful supply of C-lignin can serve as a green carbon feedstock for the production of catechols in a selective manner. Herein, we investigated a series of pretreatment methods for the disassembly of C and G/S lignins in Jatropha seed coats, and extraction by dilute HCl in dioxane was established as the optimized process. This protocol enabled the almost complete segregation of the two types of lignins in Jatropha seeds, and can be generalized to other Euphorbiaceae plants (candlenut, tung, and castor) containing both C and G/S lignins. Characterization by NMR spectroscopic analyses revealed that the isolated lignin samples were mostly composed of benzodioxane units. The disassembled C-lignin samples can produce a single catechylpropanol product (selectivity up to 97%) through Pd/C-catalyzed hydrogenolysis, and are superior to the feedstocks containing C and G/S lignins in terms of catalytic activity and selectivity.

Biodegradable materials are increasingly imperative in modern society owing to their eco-friendly character, but their high cost and limited properties restrict their applications. In this study, lignin-based (30–50 wt%) biodegradable composites with superior performances were successfully prepared by incorporating lignin into the poly(butylene adipate-co-terephthalate) (PBAT) matrix. In order to improve the compatibility, lignin was efficiently modified by a green esterification reaction under microwave-assisted solvent-free conditions. Comprehensive characterization revealed that modified lignin had fewer inter-unit linkages, increased molecular weights, lower Tg and enhanced hydrophobicity. Moreover, the prepared modified lignin/PBAT composites reinforced with maleic anhydride (MAH) exhibited controllable improvements in mechanical properties and exhibited excellent UV-shielding properties, and their elongation at break, even with 40 wt% lignin, increased by 500% compared to that of unmodified counterparts. The ideal dispersion and compatibility of the modified lignin in the matrix facilitated the mechanical properties of composites, as revealed by morphological and thermal analysis. Importantly, molecular dynamics (MD) simulation unprecedentedly confirmed that the modification of lignin distinctly strengthened molecular interaction and compatibility of the matrices, enhancing the mechanical performance of the composites. This work presents a green and feasible route to produce cost-efficient biodegradable materials with controlled mechanical and UV-shielding properties for packaging application.

Reductive catalytic fractionation (RCF) of lignocellulosic biomass, that is depolymerization of the native lignin component into well-defined monomeric phenols in the first step, offers an opportunity to utilize entire biomass components. Herein, we report that Ni@ZIF-8 can serve as a chemodivergent catalyst in RCF of eucalyptus sawdust, thus selectively producing phenolic compounds having either a propyl or propanol end-chain under different reaction conditions. In both cases, high yields of lignin monomers and a high degree of delignification were achieved, next to well-preserved carbohydrate pulp suitable for further processing. A mechanistic study using model compounds indicated that the dehydroxylation at the γ-position of the β-O-4 structure may be involved in the selectivity-controlling step.

Lignin is the most abundant renewable resource for production of bio-aromatic chemicals. However, the catalytic depolymerisation of lignin into phenolic monomers is still challenging due to its intrinsic heterogeneity. Herein, we report that Ni/AC can serve as an efficient and stable catalyst in the hydrogenolysis of biorefinery corncob lignin into low-molecular-weight aromatics. This catalyst showed high activity towards reductive fragmentation of hydroxycinnamic esters and β-O-4 linkages through scission by reaction with hydrogen to cleave C–O bonds. Under optimal conditions, this catalytic system produced 31% selectivity towards unsaturated substituents containing coumarate and ferulate derivatives, which afforded mono-aromatic phenols (up to 12.1 wt%) derived from hydroxycinnamic acid moieties (8.1 wt%) and β-O-4 units (2.7 wt%), respectively. The use of non-precious metals to develop highly efficient heterogeneous catalysts makes this approach of great interest in the production of aromatic phenols for the valorisation of industrial lignin.

A fundamental understanding of lignin solubilization offers structural information that would benefit a variety of value added applications. Small angle neutron scattering (SANS) and nuclear magnetic resonance (NMR) spectroscopy were used to study correlations between the functional groups/substructures and solution structures of lignin in DMSO-d6 and 0.1 N NaOD. Three types of alkaline lignins (Sigma-Aldrich kraft lignin, poplar wood kraft lignin, and corncob soda lignin), exhibiting different degrees of aggregation in 0.4 wt% solutions, were investigated to identify the major intermolecular interactions that cause lignin aggregation. Intermolecular hydrogen bonding, non-covalent π–π interactions between phenyl rings, lignin chain conformation and the degree of branching were discussed. Different operating forces for lignin solubilization and aggregation were found in DMSO-d6 and NaOD solutions.

A new family of protic NHC Ru complexes ligated with a phosphine-tethered imidazole moiety were prepared, which can act as excellent catalysts for acceptorless dehydrogenation of secondary alcohols and dehydrogenative coupling of primary and secondary alcohols, thus leading to the formation of a variety of carbonyl compounds with release of H2.

The efficient and selective ortho-alkylation of N,N-dimethyl anilines via C–H addition to alkenes was achieved for the first time using a cationic half-sandwich yttrium catalyst. This protocol constitutes a straightforward and atom-economical route for the synthesis of a new family of tertiary aniline derivatives with branched alkyl substituents, which are otherwise difficult to obtain. DFT calculation studies suggest that the interaction between the yttrium atom and the NMe2 group plays an important role and the intramolecular C–H activation through a σ-bond metathesis pathway is the rate-determining step, which is consistent with the experimental KIE observations.

Rhodium(III)-catalyzed direct functionalization of C-H bonds under oxidative conditions leading to C-C, C-N, and C-O bond formation is reviewed. Various arene substrates bearing nitrogen and oxygen directing groups are covered in their coupling with unsaturated partners such as alkenes and alkynes. The facile construction of C-E (E = C, N, S, or O) bonds makes Rh(III) catalysis an attractive step-economic approach to value-added molecules from readily available starting materials. Comparisons and contrasts between rhodium(III) and palladium(II)-catalyzed oxidative coupling are made. The remarkable diversity of structures accessible is demonstrated with various recent examples, with a proposed mechanism for each transformation being briefly summarized (critical review, 138 references).

[RhCp*Cl(2)](2) can catalyze the oxidative coupling of secondary isonicotinamides with activated olefins using Cu(OAc)(2) as an oxidant. The selectivity can be controlled by the solvent. In MeCN, the mono-olefination and two-fold oxidation reaction is the major pathway, while in THF this reaction gave mostly diolefination products. In both cases, the coupled products contain an exocyclic C=C bond.