Table 2.

Summary and Characteristics of Upgrading Strategies for Lignin-Derived Monomers

Upgrading Process	Target Products	Product Value	C-H-O Ratio	Catalyst	Note
Chemocatalytic	Alkanes and cyclohexanes	Low-value, mid-range fuel additive	High H/C, low O/C	Noble metals (Ru, Rh, Pd, Pt), Ni-based catalyst, H3PO4, acetic acid, acidic IL, HZSM-5, HBEA	Monomers are ring opened and products are fully deoxygenated
	Aromatic hydrocarbons	Low value, mid-range fuel additive	Low H/C, low O/C	Co-Mo, NiMo, MoO3, FeMoP, Ru/TiO2, PdFe/C, PtCo/C	Operated at gas phase, high temperature, and low H2 pressure (<1 bar) for CO hydrogenation. Products are fully deoxygenated
	Cyclohexanols	As feed for synthesis of high-value monomers (e.g., adipic acid and polyester building blocks)	High H/C, high O/C	Ni/CeO2, Ni/SiO2–Al2O3, RANEYs Ni, CoNx/C,Ru/ZrO2–La(OH)3, Ru–MnOx/C, and Ru/C + MgO	Operated in liquid phase, partial HDO, demethoxylation, and aromatic ring hydrogenation
	Phenols	As feed for synthesis of high-value monomers (e.g., terephthalic acid, ethylene, propylene, and phenol)	Low H/C, high O/C	Nobel metal, base metal,	Selective demethoxylation
Biological	Vanillin, medium-chain-length polyhydroxyalkanoates, muconic acid	Precursor to adipic acid, terephthalic acid, pyridine dicarboxylic acids, and fatty acids			Close to theoretical yields obtained from representative components such as p-coumarate, ferulate, and benzoate