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.

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.

Catalytic Transfer Hydrogenolysis Reactions for Lignin Valorization to Fuels and Chemicals

Lignocellulosic biomass is an abundant renewable source of chemicals and fuels. Lignin, one of biomass main structural components being widely available as by-product in the pulp and paper industry and in the process of second generation bioethanol, can provide phenolic and aromatic compounds that can be utilized for the manufacture of a wide variety of polymers, fuels, and other high added value products. The effective depolymerisation of lignin into its primary building blocks remains a challenge with regard to conversion degree and monomers selectivity and stability. This review article focuses on the state of the art in the liquid phase reductive depolymerisation of lignin under relatively mild conditions via catalytic hydrogenolysis/hydrogenation reactions, discussing the effect of lignin type/origin, hydrogen donor solvents, and related transfer hydrogenation or reforming pathways, catalysts, and reaction conditions.

Solvothermal Conversion of Lignosulfonate Assisted by Ni Catalyst: Investigation of the Role of Ethanol and Ethylene Glycol as Solvents

In this study, reductive solvolysis of lignosulfonate using Ni-based catalysts in ethylene glycol (EG) and ethanol (EtOH) at 250 °C was investigated. The liquefied fractions, regarded as oil, were carefully analyzed using size-exclusion chromatography (SEC) and gas chromatography–mass spectrometry with flame ionization detection (GC-MS-FID). The oil yields from catalytic conversion in EtOH and EG were similar, being 31 and 32 wt.%, respectively. The oil fractions from depolymerization in EtOH had lower molecular weight compared to the oil products in EG, indicating a higher degree of degradation of liquefied products in EtOH. On the other hand, EG showed superior activity in inhibiting condensation reactions; 16 and 46 wt.% tetrahydrofuran (THF) soluble and THF insoluble solid fractions were obtained from conversion in EtOH, while those numbers in EG were 45 and 23 wt.%, respectively. The Ni-based catalyst was introduced to provide active sites for hydrogenation of lignosulfonate fragments released into the solvent. The presence of NiS in the spent catalyst, formed from reaction between Ni and sulfur in the lignosulfonate, was confirmed. The sulfur content in the oil obtained in EtOH was 0.38 wt.%, which in comparison to lignosulfonate with 3.1 wt.% sulfur, indicated a high level of desulfurization.

Study on the cleavage of alkyl-O-aryl bonds by in situ generated hydroxyl radicals on an ORR cathode

˙OH selectively attacks the active sites opposite to phenolic hydroxyl groups and leads to bond-cleavage of ether bonds.