Photochemical on-demand production of hydrogen peroxide in a modular flow reactor†

Hydrogen peroxide (H₂O₂) is a valuable green oxidant with a wide range of applications. Furthermore, it is recognized as a possible future energy carrier achieving safer operation, storage and transportation. The photochemical production of H₂O₂ serves as a promising alternative to the waste- and energy-intensive anthraquinone process. Following green and sustainable chemistry principles, we demonstrated a sustainable photocatalyst utilizing earth-abundant iron and biobased sources only. These iron oxide nanoparticles (FeO_x NPs) facilitated effective H₂O₂ production under batch conditions. Here, through the design of a modular photo-flow reactor, we achieved continuous and enhanced production of H₂O₂ by minimizing Fenton degradation. After detailed investigation of Fenton chemistry, we designed a reactor tailored to optimize the performance of our catalyst system. Optimal reaction conditions balancing production and energy efficiencies allowed a remarkable increase in production of >14× and productivity by >3× when compared to batch conditions. The produced H₂O₂ was concentrated to 0.02 wt% via rotary evaporation, approaching commercially relevant concentrations. The reactor design also allowed other chemical transformations, such as photoclick chemistry, as well as the processing of biomass waste into valuable products.