Dynamically Reversible Interconversion of Molecular Catalysts for Efficient Electrooxidation of Propylene into Propylene Glycol
Jingwen Ke, Mingfang Chi, Jiankang Zhao, Yan Liu, Ruyang Wang, Kaiyuan Fan, Yuxuan Zhou, Zhikai Xi, Xiangdong Kong, Hongliang Li, Jie Zeng, Zhigang Geng
Abstract
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 H 2 O 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 H 2 O 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.