Direct Electrocatalytic\nPropylene Epoxidation on PdO<sub><i>x</i></sub> and PtO<sub><i>x</i></sub>

The direct electrocatalytic epoxidation of propylene\ninto propylene\noxide (PO) is a promising sustainable approach in comparison to current\nindustrial methods for propylene oxidation. However, the yield rates\nand selectivities of this reaction are too low for industrial requirements.\nTherefore, it is important to understand the reaction mechanisms for\nrational catalyst design. In this regard, two noble metal oxides,\nPtO<sub><i>x</i></sub> and PdO<sub><i>x</i></sub>, are considered in this work for investigating the electrooxidation\nof propylene into PO. PO is measured in situ via an electrochemical\nmass spectrometry instrument to overcome the ex situ detection challenges\ncaused by the PO being unstable in aqueous media. In this way, PO\ncould be measured before undergoing hydrolysis or other possible transformations.\nThe selectivity toward PO reaches the maximum at 1.3 V vs RHE on PdO<sub><i>x</i></sub>, whereas on PtO<sub><i>x</i></sub>, the vertex occurs at 1.6 V vs RHE. Moreover, the activity trends\nof PO production indicate that on PdO<sub><i>x</i></sub>, the rate-determining step for the epoxidation is different whether\none is more anodic or more cathodic than 1.3 V vs RHE, while it remains\nthe same in the 1.0–1.6 V vs RHE potential window on PtO<sub><i>x</i></sub>.