Electrocatalytic Hydrogenation of Lignin-Derived Phenol into Alkanes by Using Platinum Supported on Graphite

Abstract

In this work, electrocatalytic hydrogenation (ECH) of phenol to cyclohexane and cyclohexanol was studied. Experiments were run in a H-type cell with a Pt sheet as anode. The cathode material and structure were found to have a large effect on the ECH of phenol. Among the cathodes studied, the 1.5% Pt supported on graphite gave the highest product yield and current efficiency. Temperature was another important variable, the yield of cyclohexane increased from 44.1% at 20°C to 63.7% at 60°C, but then dropped back to 50.3% at 80°C. Effects of electrolyte composition on ECH of phenol were also investigated. The yield of cyclohexane was highest when 0.2 mol/L HClO 4 as electrolyte. Variable current studies in the range of 10-90 mA showed an increase in product yields with increasing current from 10-30 mA, but yields decreased when current above 70 mA. The suitable starting concentration of phenol was 50 mmol/L.

Selective Electrohydrogenation of Toluene to Methylcyclohexane Using Carbon-Supported Non-Platinum Electrocatalysts in the Hydrogen Storage System

“…10). Similar reaction scheme has been proposed for the electrohydrogenation of acetophenone, benzophenone, phenol and xylene …”

Electrochemical Lignin Conversion

“…[137][138][139][140][141] Formally, electrocatalytic hydrogenolysis consists of integrating the reduction of protons [Eq. (13)] and the hydrogenation of organic compounds at the cathode, [142] while at the anode, O 2 [Eq. (14)] is formed, or other oxidation reactions occur.…”

“…17] and the concerted reductive H 2 production [Heyrovsky steps; Eqs. (18) and (19)] [142,143] Many reports of the thermal catalytic hydrogenolysis of lignin demonstrate good selectivity and excellent conversion, but often utilize either elevated temperatures (180-270°C) or pressures (10-77 bar), or both, and require hydrogen gas to achieve these transformations. [144,145] Due to ease of operation and environmental friendliness, electrocatalytic hydrogenolysis holds great potential in lignin depolymerization.…”

“…In electrocatalytic hydrogenolysis, chemisorbed hydrogen (H)M is generated in situ on the electrocatalyst surface by electroreduction of water at a low overpotential and reacts with the adsorbed lignin ( Figure 21). [138,142,143] Hydrogenation is usually accompanied by hydrogenolysis during electro-reduction of lignin. Hydrogenolysis processes can cleave CÀ O single bonds through attack by chemisorbed hydrogen, while hydrogenation is associated with addition of chemisorbed hydrogen to aromatic rings after hydrogenolysis of ether linkages (Figure 22).…”

“…[170] To circumvent this, efforts have focused on using electrocatalytic hydrogenation as a mild process to upgrade ligninderived bio-oil compounds such as phenol, 4-phenoxyphenol, syringol, and guaiacol using hydrogen and heterogeneous catalysts to form chemicals and fuels. [141,142,169,[171][172][173] For the effects of various reaction parameters (temperature, applied potential/current, initial concentration of reactants, electrolyte pH, and catalyst nature) on electrochemical upgrading of ligninoil compounds, one can refer to a review by Carneiro and Nikolla. [174] Figure 25 depicts an electrocatalytic hydrogenation cell for upgrading lignin-oil compounds, highlighting the electrode material, electrolyte, and catalyst.…”