Dynamically Reversible Interconversion of Molecular Catalysts for Efficient Electrooxidation of Propylene into Propylene Glycol

For the electrooxidation of propylene into 1,2-propylene glycol (PG), the process involves two key steps of the generation of *OH and the transfer of *OH to the C═C bond in propylene. The strong *OH binding energy (E_B(*OH)) favors the dissociation of H₂O into *OH, whereas the transfer of *OH to propylene will be impeded. The scaling relationship of the E_B(*OH) plays a key role in affecting the catalytic performance toward propylene electrooxidation. Herein, we adopt an immobilized Ag pyrazole molecular catalyst (denoted as AgPz) as the electrocatalyst. The pyrrolic N-H in AgPz could undergo deprotonation to form pyrrolic N (denoted as AgPz-H_vac), which can be protonated reversibly. During propylene electrooxidation, the strong E_B(*OH) on AgPz favors the dissociation of H₂O into *OH. Subsequently, the AgPz transforms into AgPz-H_vac that possesses weak E_B(*OH), benefiting to the further combination of *OH and propylene. The dynamically reversible interconversion between AgPz and AgPz-H_vac accompanied by changeable E_B(*OH) breaks the scaling relationship, thus greatly lowering the reaction barrier. At 2.0 V versus Ag/AgCl electrode, AgPz achieves a remarkable yield rate of 288.9 mmol_PG g_cat^-1 h^-1, which is more than one order of magnitude higher than the highest value ever reported.