Activation of O₂ on a Photochemically Generated RhI Site on an Al₂O₃ Surface:  Low-Temperature O₂ Dissociation and CO Oxidation

The ultraviolet (3.8-eV) photolysis of atomically dispersed Rh I (CO) 2 species supported on an Al 2 O 3 surface in the presence of O 2 at 174 K has been studied by transmission infrared spectroscopy (FTIR). Dioxygen is activated on photochemically generated Rh I (CO) sites to produce oxidized rhodium carbonyl species and carbon dioxide. A new infrared band in the C−O stretching region is observed at 2156 cm - 1 and assigned to Rh IV (CO)(O) 2 species. A second C−O infrared band is observed at 2122 cm - 1 and is assigned to Rh II (CO)O species. The Rh IV (CO)(O) 2 species is a precursor to CO 2 formation. An infrared band at 2344 cm - 1 is produced by photochemically generated CO 2 species which are then adsorbed on the Al 2 O 3 support. Infrared band assignments are supported by a photochemical O 2 activation experiment using doubly isotopically labeled Rh I ( 13 C 18 O) 2 species. This work demonstrates a low-temperature route for the oxidation of CO on catalyst sites using ultraviolet light as an energy source.