A ruthenium and palladium bimetallic system superior to a rhodium co-catalyst for TiO2-photocatalyzed ring hydrogenation of aniline to cyclohexylamine

Article abstract of DOI:10.1016/j.jcat.2020.05.035

Cyclohexylamine (CHA) is used as an important raw material in chemical industries. Since the production of CHA requires a high temperature and excess amounts of hydrogen gas (H₂) and ammonia, the development of a simple reaction operated under milder conditions using a safe compound is indispensable for achieving sustainable chemistry. A highly selective ring hydrogenation of aniline (AN) to CHA over a titanium(IV) oxide photocatalyst having a co-catalyst in water at room temperature, in which oxalic acid was used as the hydrogen source in place of H₂, is described in this paper. Among TiO₂ photocatalysts having co-catalysts, Rh-TiO₂ showed high activity for CHA production, while Pd-TiO₂ and Ru-TiO₂ showed negligible activity. When a bimetallic photocatalyst, Ru/Pd-TiO₂, was used, the yield was larger than that when Rh-TiO₂ was used. Metal particles loaded on TiO₂ were observed by using TEM, and electronic states of Ru and Pd were evaluated by using XPS. Interactions among metal, AN and CHA were investigated through adsorption experiments. Based on the results, active sites for AN hydrogenation are discussed.