Electrocatalytic Upgrading of Phenolic Compounds Observed after Lignin Pyrolysis

Lignin valorization is increasingly important as biomass fractionation approaches achieve higher technology readiness levels. One approach to upgrade lignin first involves its deconstruction by fast pyrolysis to create a lignin-derived bio-oil. The phenolics-rich liquid product is a promising feedstock for electrocatalytic hydrogenation, as aromatics can be deoxygenated and saturated by hydrogen chemisorbed on catalytic cathodes, mitigating the product's corrosivity and raising its energy content. By integrating biomass fractionation with pyrolytic deconstruction and electrocatalytic upgrading, lignin can be valorized to fuels and chemicals that significantly enhance the profitability of biorefineries. In this study, model compounds representing lignin bio-oil components were subjected to electrocatalytic hydrogenation (ECH) at mild temperatures using ruthenium on activated carbon cloth. Phenol, guaiacol, syringol, and several related alkyl phenols and aryl methyl ethers were studied. In addition to hydrogenation, C–O and C–C hydrogenolysis were observed. Conversion of the alkyl phenols decreased with increasing alkyl chain length. Similarly, for alkyl-substituted guaiacols, conversion decreased as alkyl chain length increased, and selectivity shifted away from demethoxylation, favoring alkyl-substituted 2-methoxycyclohexanol. Increasing substrate concentration improved the Faradaic efficiency up to a plateau at higher concentrations. By mapping out electrocatalytic conditions and reactivities of lignin-relevant substrates, this work further opens the door to the promise of biomass upgrading to fuels and chemicals via the pyrolysis–electrocatalysis pathway.