Photoredox Cascade Catalyst for Efficient Hydrogen Production with Biomass Photoreforming

Biomass photoreforming is a promising method to provide both a clean energy resource in the form of hydrogen (H₂ ) and valuable chemicals as the results of water reduction and biomass oxidation. To overcome the poor contact between heterogeneous photocatalysts and biomass substrates, we fabricated a new photoredox cascade catalyst by combining a homogeneous catalyst, 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO), and a heterogeneous dual-dye sensitized photocatalyst (DDSP) composed of two Ru(II)-polypyridine photosensitizers (RuP⁶ and RuCP⁶ ) and Pt-loaded TiO₂ nanoparticles. During blue-light irradiation (λ=460±15 nm; 80 mW), the DDSP photocatalytically reduced aqueous protons to form H₂ and simultaneously oxidized TEMPO^• radicals to generate catalytically active TEMPO⁺ . It oxidized biomass substrates (water-soluble glycerol and insoluble cellulose) to regenerate TEMPO^• . In the presence of N-methyl imidazole as a proton transfer mediator, the photocatalytic H₂ production activities for glycerol and cellulose reforming reached 2670 and 1590 μmol H₂ (g_TiO2 )^-1  h^-1 , respectively, which were comparable to those of state-of-the-art heterogeneous photocatalysts.