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.

High CO-Tolerant Ru-Based Catalysts by Constructing an Oxide Blocking Layer.

CO poisoning of Pt-group metal catalysts is a long-standing problem, particularly for hydrogen oxidation reaction in proton exchange membrane fuel cells. Here, we report a catalyst of Ru oxide-coated Ru supported on TiO2 (Ru@RuO2/TiO2), which can tolerate 1-3% CO, enhanced by about 2 orders of magnitude over the classic PtRu/C catalyst, for hydrogen electrooxidation in a rotating disk electrode test. This catalyst can work stably in 1% CO/H2 for 50 h. About 20% of active sites can survive even in a pure CO environment. The high CO tolerance is not via a traditional bifunctional mechanism, i.e., oxide promoting CO oxidation, but rather via hydrous metal oxide shell blocking CO adsorption. An ab initio molecular dynamics (AIMD) simulation indicates that water confined in grain boundaries of the Ru oxide layer and Ru surface can suppress the diffusion and adsorption of CO. This oxide blocking layer approach opens a promising avenue for the design of high CO-tolerant electrocatalysts for fuel cells.