NITRIC-OXIDE ADSORPTION AND NITRIC-OXIDE CARBON-MONOXIDE INTERACTION ON RU/ZNO CATALYST

The adsorption of NO and the interaction of NO-CO mixtures on Ru/ZnO has been studied by FTIR and mass spectroscopic experiments. NO is adsorbed initially on Ru0 and Ru2+ surface sites present on the reduced catalyst; however, a slow NO dissociation process leads to NO species adsorbed on more oxidized Ru3+ sites and to NO−2 species adsorbed on the support. CO reacts at 423-573 K with the NO species dissociated on the Ru sites giving isocyanate and carbonate species spilled over to the support and resistant to decomposition up to 573 K, whereas CO is adsorbed on Ru0 and Ru2+ sites. The formation of large amounts of CO2 and N2 has been shown by mass spectroscopic experiments to occur only at T ≥ 473 K. The opposite reaction of NO interacting with preadsorbed CO leads to CO displacement producing NO and CO species on oxidized Ru and carboxylates or carbonates on the ZnO phase. In this case, with NO predominating in the NO-CO mixture, higher quantities of N2O, N2, and CO2 are formed already at room temperature, whereas isocyanate species are formed in small quantities also at higher temperatures. The mass spectral and FTIR results confirm previous literature data showing that the isocyanates compete with the production of N2 and CO2 during the NO-CO reaction on supported metal catalysts. © 1993 Academic Press, Inc.