Infrared study of ammonia–carbon monoxide reactions on silica-supported iron catalysts

Abstract

Infrared spectroscopy has been used to study the reactions of carbon monoxide and ammonia over Fe/SiO₂ catalysts at ca. 298–723 K. Adatoms of nitrogen resulting from the dissociative adsorption of ammonia reacted with CO to form surface isocyanate on iron at 298–523 K. At high temperatures spillover of isocyanate to the silica surface occurred. An accompanying decomposition reaction led to the appearance of intense infrared bands at 2120 and 2055 cm^–1, which are ascribed to surface cyano complexes of iron. Hydrogen cyanide was adsorbed on iron at ca. 298 K as FeCNH. At 573 K complete oxidation of bulk iron occurred, giving bulk cyanide and surface isocyanate groups on the silica support. Subsequent standing at ca. 293 K in vacuum led to the formation of HCN polymerisation products.