Control of RhI(CO)₂ Formation on Rh/Al₂O₃ Catalysts by Complexation of Surface −OH Groups Using NH₃

It has been shown that the isolated −OH groups present on a Rh/Al 2 O 3 catalyst form a weak H-bonded complex by exposure to gas-phase NH 3 at 298 K. This reversible complex suppresses the tendency for isolated −OH groups to participate in the oxidation of metallic Rh, forming Rh I (CO) 2 /Al 2 O 3 species in the presence of a CO atmosphere. There is no IR spectroscopic evidence for the formation of NH 4 + during surface complexation. However, evidence for NH 2 formation at Lewis base sites on Al 2 O 3 is found.