Polymer-packed bed reactors enhance photocatalytic efficiency by utilizing multiple light reflections in heterogeneous photocatalysis

Efficient light utilization is a central challenge in flow photochemistry, which strongly influences catalytic performance. Here, we improve photocatalytic performance by controlling the optical properties of packing materials in the packed-bed flow reactor. Synthetic polymer particles were selected as reactor packings because their size and refractive index can be readily tuned. A Ru(bpy)₃ photocatalyst was covalently immobilized on polymer particle surfaces and mixed with catalyst-free co-packing particles, poly(methyl methacrylate) or poly(styrene), possessing different refractive indices. The mixtures were packed into columns and evaluated in the blue-light-driven oxidation of 9,10-diphenylanthracene. By systematically varying particle size, refractive index of packings and solvent, we clarified how the optical properties govern multiple light reflection and photoreaction kinetics by experiments, modelling, and theoretical simulation. The optimized reactor design enhanced photocatalytic performance and showcased successful synthesis of juglone, demonstrating a practical strategy for advancing sustainable photochemical processes.