A spatially integrated electrochemical–thermal tandem reaction for continuous mild synthesis of propylene oxide†

An electrochemical–thermal tandem reaction system was designed in this work and enabled the highly efficient synthesis of propylene oxide (PO) at 1 atm without the use of H₂O₂. The electrochemical part produced OOH⁻ through a 2e⁻ oxygen reduction reaction, which migrated and distributed in the full space of a chamber filled with a mixture of solid electrolyte particles and modified TS-1 (m-TS-1) catalysts. Mediated by the relay of OOH⁻ and protic solvent methanol, full space tandem reactions were achieved with a high PO selectivity of 95.2% and a productivity of 319.75 mmol g_ecat⁻¹ h⁻¹. A mechanistic study revealed that the m-TS-1 catalysts accepted the migrated OOH⁻ and formed a Ti-OOH intermediate, which played a key role in relaying the tandem reactions for an efficient propylene epoxidation reaction. Techno-economic analysis and life-cycle assessment revealed favorable figures for the proposed process compared to the conventional process.