Hydrogenolysis of Lignin-Derived Aromatic Ethers over Heterogeneous Catalysts

Abstract

Global temperature has risen >1 °C since the preindustrial era, resulting in well-documented adverse climate impacts including extreme weather (floods, droughts, storms, and heat waves), a rise in sea level accompanying melting polar and glacial ice, and disrupted crop growth. These changes are closely correlated with anthropogenic greenhouse gas emissions, predominantly arising from the combustion of nonrenewable fossil fuels. Lignin derived from lignocellulose is the second most abundant biopolymer on Earth, and a rich source of renewable aromatic hydrocarbons to replace those currently obtained from fossil resources. Lignin depolymerization by cleavage of C–O and C–C linkages in the biopolymer can be achieved by direct pyrolysis or catalytic transformations, involving oxidation, hydrolysis, or hydrogenolysis reactions. Hydrogenolysis, in which H2 gas (or in-situ generated reactive H species) is supplied to lignin under relatively mild conditions, has attracted significant attention. This Perspective summarizes recent progress in the development of heterogeneous catalysts for the cleavage of C–O linkages in lignin-derived aromatic ethers by hydrogenolysis: it encompasses strategies using H2, hydrogen transfer, and photocatalysis for aromatic monomers production, and the determination of structure–activity relationships and underlying reaction mechanisms.

Catalytic Conversion of Lignin to Liquid Fuels with an Improved H/Ceff Value over Bimetallic NiMo-MOF-Derived Catalysts

“…When isopropanol was utilized as the solvent in the reaction, 2-phenoxy-1-phenylethan-1-ol was completely converted and the yields of ethylcyclohexane (95%) and cyclohexanol (92%) reached the maximum. Secondary alcohols provided higher activity, with isopropanol being the most effective, whereas primary alcohols (methanol and ethanol) poisoned catalysis through some absorption of the alkoxy anions . The same result was confirmed in our previous research. − In comparison, other solvents were employed in the reaction.…”

Selective Catalytic Transfer Hydrogenation of Lignin to Alkyl Guaiacols Over NiMo/Al‐MCM‐41

“…A feasible alternative strategy is catalytic transfer hydrogenation (CTH), [6] in which an internal hydrogen donor provides a reactive source of hydrogen in liquid phase. [7] For example, Guan et al reported the CTH of an α-O-4 model compound 4-(benzyloxy)phenol and lignin extracted from bioconverted rice straw over Pt/HNbWO 6 /CNTs catalyst using isopropanol as the solvent and in-situ hydrogen donor. [8] Light alcohols (methanol, ethanol, and isopropanol) are the most common solvents for CTH due to their ability to solvate/ disperse lignin degradation products and donate hydrogen atoms, [8,9] thereby conferring excellent CTH performance.…”

“…Unfortunately, the requirement for high pressures of gaseous hydrogen during lignin HDO imposes significant reactor cost and safety constraints and requires a source of sustainable (green) H 2 . A feasible alternative strategy is catalytic transfer hydrogenation (CTH), [6] in which an internal hydrogen donor provides a reactive source of hydrogen in liquid phase [7] . For example, Guan et al.…”

Catalytic Stereoselective Conversion of Biomass-Derived 4′-Methoxypropiophenone to Trans-Anethole with a Bifunctional and Recyclable Hf-Based Polymeric Nanocatalyst

“…The catalytic transfer hydrogenation (CTH) or MPV refers to the addition of hydrogen molecules to the unsaturated groups of organic compounds in the presence of a solid catalyst [26][27][28], which does not require external hydrogen or special catalytic hydrogenation equipment and is easy to operate, occupying a certain position in organic synthesis [29][30][31]. Therefore, the CTH reaction is recognized as a versatile method for upgrading bio-based carbonyl compounds [32][33][34][35].…”