Insights into the Electrochemical Hydrogenation Reaction Mechanisms of Aromatic Compounds Mixtures over Bimetallic PtRu Catalyst

Efficient and selective electrochemical hydrogenation (ECH) of organic compounds is crucial for global sustainability; offering both chemical feedstock circularity and routes to generate synthetic fuels, reducing fossil fuel reliance. This study focuses on ECH of benzoic acid (BA), phenol (P), and guaiacol (G), commonly appearing as mixtures in potential oils for upgrade. The impact of various conditions on the hydrogenation process was elucidated using a carbon-supported PtRu catalyst; assessing initial concentrations/mixtures, temperatures, and current densities. Phenol ECH exhibited the most favourable outcome, achieving an 83.17% conversion rate and 60% Faradaic Efficiency (FE). When mixtures (BA + P, BA + G, P + G, and BA + P + G) were evaluated, revealing that BA + P yielded the highest conversion rate (64.19%) and FE (74%). This outcome suggests a potential synergistic effect between benzoic acid and phenol. Additionally, regardless of experimental parameters, BA selectivity for cyclohexane carboxylic acid (CCA) remained consistently at 100%. Density functional theory (DFT) calculations provided insight into molecular/catalyst interactions, highlighting the stability of parallel positioning the BA molecule on the cathode surface compared to perpendicular placement (-1.12 eV vs. 0.58 eV), this offers a plausible explanation for the observed high selectivity towards CCA. These findings provide a foundation for future developments in ECH of real pyrolysis oil.