Tin oxide surfaces. Part 8.—Infrared study of the mechanism of formation of a surface isocyanate species on SnO2· 0·55 CuO during catalysis of the oxidation of carbon monoxide by nitric oxide

Abstract

An experimental study has been carried out on the mechanism of formation of a surface isocyanate species on the mixed oxide catalyst SnO₂· 0·55 CuO during the initial stages of catalysis of the CO + NO reaction at ≈470 K. Using infrared spectroscopy, the isotopic shifts of the 2189 cm^–1 pseudo-antisymmetric stretching vibration have been measured for ¹³C, ¹⁵N and ¹⁸O substitution. The oxygen atom of the surface isocyanate has been shown to originate from NO rather than CO as was previously assumed. This observation has been interpreted in terms of a mechanism involving initial dissociative chemisorption of CO followed by the formation of a fulminate via reaction of NO with the surface carbon atom and subsequent rapid isomerisation to the isocyanate: [graphic omitted].