The Interaction Between NO and CO on Rh Loaded CeOX(111)
Journal of Catalysis, 195 (2000) 169.
The co-adsorption of and reactions between NO and CO on ceria supported Rh model catalysts have been studied by soft x-ray photoelectron spectroscopy (SXPS) and temperature programmed desorption spectroscopy (TPD). The gases were adsorbed sequentially on the sample. If either gas was first adsorbed to saturation, the other gas could not be adsorbed on the surface. The gases could be co-adsorbed by making sub-saturation doses.
If the ceria is fully oxidized, the only significant interaction observed between co-adsorbed NO and CO was the formation of gas phase CO2 through the reaction of CO with the O from dissociated NO. This is similar to what is observed on Rh single crystals [1].
If the ceria is highly reduced, only N2 and CO desorb. However, a number of new species are formed on the Rh particles as revealed by SXPS. The reaction pathway for NO and CO co-adsorbed on Rh / CeOX is shown schematically at right. NO and CO are co-adsorbed molecularly at 200 K. The the sample is heated, the NO dissociates. The oxygen diffuses to the oxide leaving N and CO on the Rh. These species combine to form isocyanate, NCO. As the sample is heated further the isocyanate decomposes releasing CO and forming cyanide, CN, on the Rh. More complex carbon-nitrogen species, CXNY, are formed at higher temperatures. Eventually these species decompose above 700 K. The N recombines to form N2 and the C reacts with the ceria to form CO.
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