Effects of Manganese Doping into Nickel Hydroxides for the Electrochemical Conversion of KA Oil

Selective oxidative cleavage of C(OH)–C or C(O)–C bonds in cyclohexanol and cyclohexanone (KA oil) to produce adipic acid (AA), a monomer for the synthesis of nylon-66, is of significant importance for the petrochemical industry. Herein, we report an electrochemical method to improve the efficiency for upgrading KA oil into AA. Free-standing electrodes consisting of hydroxides (Ni(OH)2 and Mn-doped Ni(OH)2) supported by carbon paper were fabricated via an in situ electrodeposition process and further examined for KA oil conversion. The morphology and structures of the samples were characterized by field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy. The electrochemical performance of the samples was studied by cyclic voltammetry, linear sweep voltammetry, and electrochemical impedance spectroscopy. The products of KA oil oxidation were analyzed by high-performance liquid chromatography. The introduction of manganese into nickel hydroxides enhanced the catalytic performance in terms of activity and product selectivity. Specifically, the optimal sample exhibited a current density of 50 mA mg–1 and selectivity of 46.8%, which are superior to those of pure nickel hydroxides. Such enhancement was attributed to the electronic interaction of manganese with nickel hydroxides, thereby modifying the adsorption of the substrates. Interestingly, the introduction of Mn into nickel hydroxides had negligible effects in the oxygen evolution reaction. The effects of critical parameters including substrate composition, reaction temperatures, KOH concentrations, and electrolysis time on the conversion of KA oil were investigated.