IR study of TiO-2-based gas-sensor materials: effect of ruthenium on the oxidation of NH3, (CH3)3N and NO

1994 
Abstract The adsorption and oxidation of ammonia, trimethylamine and and nitric oxide on Ru/TiO 2 and TiO 2 have been studied by FTIR spectroscopy. On both the samples ammonia and trimethylamine are adsorbed at room temperature molecularly on the surface Ti 4+ sites. By heating ammonia at T >473 K, wate and hydroxyls are produced. The oxidation at 473 K of the trimethylamine on both the samples leads to the formation of dimethylformamide and water, the oxidation at T >573 K on pure TiO 2 leaves residual NH and Ch x groups; on Ru/TiO 2 a complete oxidation occurs, leading to nitrosyl species adsrobed on Ru ions and nitrate species and water on titania. No adsorbs molecularly on oxidized Ru/TiO 2 samples, with formation of Ru 3+ -No surface complexes; on the contrary it does not adsorb at all as such on pure TiO 2 . On both the samples, nitrate species on titania are produced by interaction with dry air. The complex of data presented in the paper indicates that the presence of the Ru as a metallic activator allows a more complete oxidation of the studied molecules, justifying the higher sensitivity.
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