Improving Tandem Epoxidation Efficiency via Hydrogel Confinement Effect towards Photoelectrochemical Propylene Oxide...

Propylene oxide (PO) is among the world's most abundantly produced commodity chemicals, but it suffers from an energy-intensive and highly polluting industrial production route. In this work, we present a tandem photoelectrochemical (PEC) PO production system involving water oxidation to H₂O₂ via a BiVO₄ photoanode and subsequent propylene epoxidation by titanium silicalite-1 (TS-1) catalyst-loaded hydrogel using in situ-generated H₂O₂. The hydrogel encapsulated on the BiVO₄ photoanode surface provides a confined space to enhance H₂O₂ enrichment, as well as propylene transport, thereby reinforcing the epoxidation kinetics with conversion efficiencies of 94.06% for H₂O₂ and 75.55% for propylene. With the assistance of solar energy, the PO productivity per unit of electricity can reach 6.10 mol·cm^-2·kWh^-1, which is the lowest electricity consumption for existing alkene epoxidation technology. For industrial scalability, a multi-pass light absorption configuration is designed for decimeter-sized reactor to address the issue of a plunge in solar to chemical (STC) efficiency arising from the scale-up of the photoanode, achieving the optimum light harvesting efficiency of 98.21% and STC efficiency of 5.57% which is comparable to its 1 cm² counterpart (86% retention). The continuous PO productivity in flowing electrolyte can reach 1.74 mmol·h^-1 with a steady selectivity of 91.05% under AM 1.5G illumination. Finally, a techno-economic analysis is provided to offer targets that need to be met for economically compelling industrial implementation.