A breakthrough in the electrooxidation of propylene

Professor, University of Science and Technology of China (USTC). A research group led by Geng Zhigang designed a molecular catalyst that can undergo dynamic reversible interconversion for the electrooxidation of propylene to 1,2-propylene glycol. This work was published Journal of the American Chemical Society.

1,2-Propylene glycol (PG) is an important chemical substance. Traditional production of PG involves the hydrolysis of propylene oxide to propylene oxide and the hydrolysis of propylene oxide to PG. In this process, highly polluting chlorine is used as oxidant and high temperature or acid condition is required for hydrolysis of propylene oxide.

In contrast, the one-step electrooxidation of propylene to 1,2-propanediol simplifies the production process but avoids the use of chlorine gas and uses water as the oxygen source, reducing pollution and energy costs.

In the electrooxidation of propylene to PG, the formation of *OH and coupling of *OH to propylene are the two main steps. Strong adsorption of the catalyst to *OH favors the dissociation of H₂O to *OH, weak absorption favors *OH and propylene coupling. Such a process results in a scaling dependence of the binding energy of *OH on the catalysts, which severely limits the catalytic performance for propylene electrooxidation.

Researchers have designed an Ag pyrazole molecular catalyst (AgPz) with a dynamically reversible interconversion system. Due to the hydrogen bonding between pyrrolic NH and *OH, AgPz with pyrrolic NH structure has strong adsorption to *OH, which promotes dissociation of water to form *OH. The pyrrolic NH structure undergoes deprotonation, which creates H vacancies and leads to the loss of hydrogen bonds. AgPz with H vacancy systems has a weak adsorption to *OH, which accelerates the coupling of *OH and propylene.

Then, the H vacancy recombines with hydrogen, reforming AgPz with a pyrrolic NH structure. The dynamic interconversion leads to a variable binding energy of *OH to AgPz, which breaks the scaling relationship and enhances the electrooxidation of propylene.

Performance Evaluation At 2.0 V and working potential against Ag/AgCl electrode, the yield rates of PG using AgPz as catalyst reached 288.9 mmol g._Cat^-1 M^-1This is more than one order of magnitude higher than the previous high rate.