Influence of composition of reaction mixture NO + CO + O/sub 2/ on catalytic properties and surface states of supported noble metals. III. Rh/. gamma. -Al/sub 2/O/sub 3/. Comparison of results from studies of platinum, palladium, and rhodium catalysts

IR spectroscopy has been used to investigate the interaction of mixtures of NO + CO + O/sub 2/ on Rh/..gamma..-Al/sub 2/O/sub 3/, for comparison with previous results on palladium and platinum catalysts. The adsorption of NO and CO as probe molecules was used in evaluating the state of the active component. On the rhodium catalyst, in contrast to Pt/..gamma..-Al/sub 2/O/sub 3/ and Pd/..gamma..-Al/sub 2/O/sub 3/, not only carbonyl and nitrosyl complexes were detected, but also dicarbonyl, dinitrosyl, and mixed complexes. Analysis has been made of the required formation conditions and the behavior of isocyanate complexes localized on the support and on the active component. The higher efficiency of the rhodium catalysts is explained by the possibility of a reaction proceeding through mixed complexes.