Photogeneration of Hydrogen from Glycerol and Other Oxygenates Using Molecular Photocatalysts and In Situ Produced Nanoparticulate Cocatalysts

This work describes a photocatalytic process using the oxidation of biorenewable alcohols as the electron/proton source for the photogeneration of hydrogen. The approach utilizes a molecular iridium photosensitizer (PS), an in situ synthesized Pd-containing colloid catalyst, and a redox shuttle (RS). By virtue of the high-throughput photoreactor utilized in this work, rapid reaction parameter screening for five donor species (oxalic acid, benzyl alcohol, isopropanol, ethanol, and glycerol) was undertaken, resulting in the identification of reaction conditions conducive to the formation of hydrogen from all species. Using these newly identified reaction conditions, screening was undertaken for 96 uniquely structured iridium organometallic complexes as photocatalysts and for a set of structurally diverse RSs. The top-performing PS resulted in catalytic turnover numbers (TONs) of 81 for glycerol (quantum yield (Φ) = 0.73%), 100 for isopropanol (Φ = 1.21%), 133 for ethanol (Φ = 0.91%), and 159 for oxalic acid (Φ = 1.44%). The wealth of data on the inner workings of these light-driven alcohol-reforming reactions was supplemented with nanoparticle characterization of select candidates by transmission electron microscopy and X-ray photoelectron spectroscopy, and identification and quantification of the alcohols’ oxidation products was undertaken via 1H NMR.