Guaiacol Hydrogenation in Methanesulfonic Acid Using a Stirred Slurry Electrocatalytic Reactor: Mass Transport and Reaction Kinetics Aspects

The electrocatalytic reduction of guaiacol, a lignin model compound, is investigated in a stirred slurry electrocatalytic reactor (SSER) under mild conditions (1 atm, 30–60 °C). Methanesulfonic acid (MSA) is used as an electrolyte due to its eco-friendly properties along with comparable ionic conductivity to the mineral acids (e.g., sulfuric acid and perchloric acid). Mass transport and kinetic aspects are investigated combining the experimental results obtained under either galvanostatic or potentiostatic control with reaction network kinetic models. The reactant mass transport rate to the catalyst particle surface, together with the collision rates among catalyst particles and the current collector, respectively, has a significant effect on guaiacol conversion and Faradaic efficiency. Therefore, optimum stirring is necessary to ensure good electric contact in the catalyst bed slurry to achieve substantial electrocatalytic hydrogenation (ECH) reaction rates. In the absence of mass transfer limitation, reaction network kinetic modeling based on the Langmuir–Hinshelwood mechanism was performed and validated by the experimental data. Rate constants and activation energies were calculated, and it was found that phenol hydrogenation was the fastest reaction, while 2-methoxycyclohexanol demethoxylation was the slowest in the overall guaiacol ECH network. Furthermore, we show that the SSER can be operated at industrially relevant cathode superficial current densities (>100 mA cm^–2), thereby, opening new and practical possibilities for the sustainable valorization of biomass-derived compounds.