Effect of Chlorine on the Properties of Ru/Al₂O₃

Abstract

Ru/Al 2 O 3 catalysts with different chlorine contents were prepared using RuCl 3 as the precursor. Different HCl concentrations in the impregnation solution or different treatments after impregnation were used. The catalysts were characterized by temperature-programmed reduction, X-ray photoelectron spectroscopy, and hydrogen chemisorption. They were tested in the selective hydrogenation of benzene to cyclohexene in a stirred tank reactor at 373 K and 3 MPa hydrogen pressure. It was found that different electronic states of Ru appear according to the chlorine content on Ru/Al 2 O 3 . The electronic state of Ru influences the selectivity to cyclohexene. The results seem to support that the most electron-deficient Ru species may adsorb cyclohexene more weakly. When cyclohexene is more weakly adsorbed, it could be more easily desorbed by avoiding its further hydrogenation to cyclohexane, thus increasing selectivity.