Experimental optimization and process modelling of the selective electrochemical hydrogenation of phenol to cyclohexanol using a non-noble metal catalyst

Electrochemical hydrogenation (ECH) enables upgrading aqueous phenolic streams to cyclohexanol at room temperature and ambient pressure without the need for external hydrogen and noble metal catalysts. Screening of non-noble materials (Ni-, Fe-, and Cu-based) using a Na 2 SO 4 electrolyte identified Raney nickel (RNi) as the sole catalyst achieving selectivity to cyclohexanol ( S cyclohexanol ) as the only detected liquid-phase product. A catalyst-free control showed no measurable product formation, supporting that electrogenerated hydrogen is utilized via heterogeneous hydrogenation on suspended RNi. It was observed that hydrogen availability was not limiting in the potential range of −1.2 to −1.9 V vs. Ag/AgCl, but increasing catalyst loading only modestly increases cyclohexanol formation. In contrast, the operating conditions are decisive. Lowering pH and decreasing Na 2 SO 4 concentration markedly increase Coulombic efficiency ( CE ) and cyclohexanol yield ( Y cyclohexanol ), reaching CE = 43.9% and Y cyclohexanol = 22% in 1 mM Na 2 SO 4 after 24 h with >90% carbon balance and an energy demand of 3.6 kWh mol −1 cyclohexanol. Kinetic analysis yields apparent first-order kinetics of phenol conversion ( k_ app = 0.0164 h −1 , R 2 = 0.984). A fed-batch flowsheet model coupling a water electrolyser to the ECH reactor was validated against the experimental concentration–time profiles. The model identifies electrolyser capacity (i.e., H 2 generation rate) as the primary lever for increasing throughput at fixed current-density constraints, rather than a limitation of intrinsic reaction selectivity. • Electrochemical hydrogenation converts phenol to cyclohexanol without H 2 or noble metals. • Raney nickel achieves 100% selectivity to cyclohexanol as sole liquid product. • Optimized pH and Na 2 SO 4 concentration yield 43.9% Coulombic efficiency. • Modelled process throughput is governed by electrolyser H 2 generation capacity.