Ruthenium and palladium bimetallic nanoparticles achieving functional parity with a rhodium cocatalyst for TiO2-photocatalyzed ring hydrogenation of benzoic acid

Abstract

Our previous study showed that a rhodium (Rh) cocatalyst is indispensable for ring hydrogenation of benzoic acid over a titanium(IV) oxide (TiO₂) photocatalyst. In this study, we explored ring hydrogenation under an Rh-free condition by using two kinds of cocatalyst that were inactive for this reaction when used solely. Cyclohexanecarboxylic acid as the ring hydrogenation product was successfully obtained when ruthenium (Ru) and palladium (Pd) were simultaneously loaded on TiO₂, indicating that this bimetallic system can be used in place of an Rh cocatalyst in ring hydrogenation. The state and distribution of Ru and Pd in particles loaded on TiO₂ were investigated by transmission electron microscopy, X-ray photon spectroscopy, and X-ray absorption near edge structure analysis. The functions of Ru and Pd as cocatalysts are discussed on the basis of results of characterization and activity tests. The effects of different contents of Ru and Pd in Ru–Pd/TiO₂ prepared by a two-step photodeposition method on catalytic activity and the features of the reaction system were investigated in detail.