A Review on C-C Coupling-Based Framework for Targeted Synthesis of Sustainable Aviation Fuels from Lignocellulose

Abstract

Lignocellulosic biomass is regarded as an important renewable carbon resource for sustainable aviation fuels owing to its abundance, broad availability and limited competition with food production. Nevertheless, platform molecules derived from cellulose, hemicellulose and lignin are commonly characterized by insufficient carbon numbers, high oxygen contents and low effective hydrogen-to-carbon ratios, resulting in a pronounced molecular gap between lignocellulose-derived intermediates and qualified C8-C16 aviation fuel hydrocarbons. Therefore, the construction of an appropriate carbon skeleton through C-C bond formation before deoxygenation becomes a central issue in the targeted synthesis of lignocellulose-derived sustainable aviation fuel. Representative C-C coupling reactions cover aldol condensation, alkylation and hydroxyalkylation, Diels-Alder cycloaddition, photocatalytic cycloaddition, cyclopropanation, oligomerization and carbon rearrangement. These reactions enable diverse skeleton construction modes, including chain growth, aryl-alkyl connection, ring formation, high-strain motif introduction, polycyclic condensation and framework reorganization. Different C-C coupling reactions involve distinct activation modes and bond-forming processes. The functional groups, electron density distribution, steric hindrance and ring strain of the reactants collectively determine nucleophile-electrophile matching, cycloaddition orientation or rearrangement pathways, thereby influencing the selective formation of target skeletons and their subsequent evolution. Meanwhile, acid-base properties of catalysts and catalytic microenvironments further regulate side reaction suppression and product distribution. Hydrodeoxygenation is then positioned as a post-coupling refining step that converts oxygenated carbon frameworks into target hydrocarbon fuels, where oxygen removal must be balanced with the preservation of the constructed skeleton. Finally, the effects of branching, cycloalkane formation, polycyclic frameworks and limited aromatic retention on density, low-temperature fluidity and volumetric energy density are briefly summarized. This C-C coupling-oriented molecular engineering framework links platform molecule recognition, coupling pathway selection, catalyst design and fuel property regulation, thereby providing a skeleton-centered perspective for the rational design of lignocellulose-derived sustainable aviation fuel.