Infrared study on the interaction of CO with alumina-supported rhodium

Abstract

The interaction of CO with alumina-supported Rh has been investigated by infrared spectroscopy at 85–573 K. The oxidative disruption of Rh crystallites occurred at temperatures as low as 150 K. Desorption and readsorption of CO at low temperature demonstrated that there is a stable Rh⁺(CO)₂ species which releases CO only at 573 K. The desorption of CO from Rh⁺ is mainly reductive but a certain fraction of Rh⁺ escapes reduction even during desorption at high temperatures, 473–573 K. The reductive agglomeration of Rh⁺ induced by CO occurs at 473 K. At 573 K the process is almost irreversible, which means that such large crystallites are produced that they cannot be disintegrated and oxidized again to Rh⁺ by CO and OH groups at room temperature. Hydrogen adsorbed on Rh_x greatly retards the oxidative disruption process at low temperature which is attributed to the formation of Rh carbonyl hydride.