Selective Conversion of Propane by Electrothermal Catalysis in Proton Exchange Membrane Fuel Cell.

Electrochemical conversion of alkanes to high value-added oxygenated products under a mild condition is of significance. Herein, we effectively couple the electrocatalysis of H2 O2 with the thermo-catalysis of propane oxidation in the cathode of proton exchange membrane fuel cell. Specifically, H2 O2 is in-situ generated on the nitric acid-treated carbon black (C-acid) via 2e- process of oxygen reduction reaction, and then transports to the Fe active sites of MIL-53 (Al, Fe) metal-organic frameworks for propane oxidation. Based on this strategy, the space-time yield of C3 oxygenated products of propane oxidation reaches 2.65 µmol h-1 cm-2 , which represents a new benchmark for electrochemical alkane oxidation in the fuel-cell-type electrolyzer. This study highlights the importance of multifunctional composite catalysts in the field of electrosynthesis.

Reaction Mechanism and Selectivity Tuning of Propene Oxidation at the Electrochemical Interface.

Electrochemical conversion of propene is a promising technique for manufacturing commodity chemicals by using renewable electricity. To achieve this goal, we still need to develop high-performance electrocatalysts for propene electrooxidation, which highly relies on understanding the reaction mechanism at the molecular level. Although the propene oxidation mechanism has been well investigated at the solid/gas interface under thermocatalytic conditions, it still remains elusive at the solid/liquid interface under an electrochemical environment. Here, we report the mechanistic studies of propene electrooxidation on PdO/C and Pd/C catalysts, considering that the Pd-based catalyst is one of the most promising electrocatalytic systems. By electrochemical in situ attenuated total reflection Fourier transform infrared spectroscopy, a distinct reaction pathway was observed compared with conventional thermocatalysis, emphasizing that propene can be dehydrogenated at a potential higher than 0.80 V, and strongly adsorb via µ-C═CHCH3 and µ3-η2-C═CHCH3 configuration on PdO and Pd, respectively. The µ-C═CHCH3 is via bridge bonds on adjacent Pd and O atoms on PdO, and it can be further oxidized by directly taking surface oxygen from PdO, verified by the H218O isotope-edited experiment. A high surface oxygen content on PdO/C results in a 3 times higher turnover frequency than that on Pd/C for converting propene into propene glycol. This finding highlights the different reaction pathways under an electrochemical environment, which sheds light on designing next-generation electrocatalysts for propene electrooxidation.