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-1(CO)(2) species supported on an Al2O3 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 CO2 formation. An infrared band at 2344 cm(-1) is produced by photochemically generated CO2 species which are then adsorbed on the Al2O3 Support Infrared band assignments are supported by a photochemical O-2 activation experiment using doubly isotopically labeled Rh-I((CO)-C-13-O-18)(2) species. This work demonstrates a low-temperature route for the oxidation of CO on catalyst sites using ultraviolet light as an energy source.