Abstract
The effects of different carriers (SiO 2, MgO, Al 2O 3, and MgO) on the formation and stability of isocyanate complexes in the NO + CO reaction on a platinum catalyst were investigated. The method used was infrared spectroscopy combined with mass spectrometry. Isocyanate formed with great ease on Pt TiO 2 , whereas its formation on the other catalysts, particularly on Pt SiO 2 , was much slower. The supports markedly influenced the location of the band due to isocyanate: It appeared at 2210 cm −1 on Pt TiO 2 , 2241 cm −1 on Pt MgO , 2272 cm −1 on Pt Al 2O 3 , and 2318 cm −1 on Pt SiO 2 . The stability of the isocyanate depended sensitively on the support. Whereas it decomposed very rapidly on Pt TiO 2 even at 300 °C, it was extremely stable on Pt SiO 2 . This latter behavior is in harmony with the high stability of the SiNCO species. The results led to the conclusion that the isocyanate complex is located on the support which basically determines its properties. It was assumed that either the isocyanate formed on the Pt migrated to the acceptor sites of the support, or the nitrogen atoms formed in the dissociation on the Pt migrated to the support and reacted with gaseous or adsorbed CO yielding isocyanate species. The phenomenon observed forms a special case of the spillover.
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