Effect of Pt and Ru-based catalysts on the electrochemical hydrodeoxygenation of phenol to cyclohexane†

Electrochemical hydrodeoxygenation (EC-HDO) is a promising method for upgrading biomass derived oxygenates into biofuels at near ambient conditions without the need for external hydrogen (H₂). Although the EC-HDO approach has many advantages over conventional thermochemical hydrodeoxygenation (HDO) methods, the selective production of fully deoxygenated hydrocarbons remains a key challenge. In this study we explore the EC-HDO of phenol as a bio-oil-derived model compound using carbon supported metal electrocatalysts in a custom-made divided electrochemical batch cell. We demonstrated EC-HDO of phenol to cyclohexane and investigated the effect of multiple variables, including catalyst type, and cathodic potential to determine their influence on reaction rate, selectivity, and faradaic efficiency (FE). The results obtained show that lab-synthesized, bi-metallic PtRu–C catalyst results in the highest specific EC-HDO rate of 5.05 mol_cyclohexane h⁻¹ g_metal⁻¹ in comparison to 4.65 mol_cyclohexane h⁻¹ g_metal⁻¹ and 0.35 mol_cyclohexane h⁻¹ g_metal⁻¹, measured using mono-metallic Pt–C and Ru–C catalysts, respectively. In addition, the labPtRu–C electrocatalyst achieved >30% selectivity towards cyclohexane while the monometallic Pt and Ru only achieved 25 and 11%, respectively. Operando Raman spectroscopy demonstrated strong evidence for ketone reaction intermediates.