Metal-Dependent Control of Methoxy Retention versus Cleavage in Electrocatalytic Hydrogenation of Lignin-Derived Aromatics

Electrochemical hydrogenation of lignin-derived aromatics offers a route to biomass upgrading, but controlling methoxy retention versus cleavage remains challenging. Here, we compare carbon-supported Rh, Pt, Ru, and Pd catalysts for guaiacol conversion under identical conditions. Rh/C and Pt/C are the most active catalysts but favor sharply different pathways: Rh/C promotes methoxy-retaining ring hydrogenation, whereas Pt/C preferentially forms demethoxylated products. Time-resolved profiles, intermediate-feeding experiments, and initial-rate analysis indicate that this selectivity difference emerges predominantly during early reaction branching. The apparent activation free energies of methoxy retention and demethoxylation are closely matched on Rh/C (91.1 and 91.8 kJ mol–1, respectively), but favor demethoxylation on Pt/C (91.1 and 89.2 kJ mol–1, respectively). Calculations on model surfaces suggest that metal-dependent interactions with adsorbed guaiacol facilitate access to different bond-activation pathways, providing a possible molecular basis for the observed kinetic preference. The Rh/Pt selectivity contrast persists across the investigated potentials and temperatures and extends to four additional lignin-derived aromatics as a broader difference in functional-group retention and cleavage. These results link metal-dependent early pathway partitioning to control over oxygen retention in electrochemical biomass upgrading.