Infrared study of ammonia and nitric oxide adsorption on silica-supported iron catalysts

Abstract

Infrared spectra are reported of ammonia, nitrogen and nitric oxide adsorbed on Fe/SiO₂ with and without the addition of K₂O promoter. Ammonia is coordinatively bound to the iron surface at ambient temperature and at high temperature decomposes to give adsorbed dinitrogen with an infrared band at 2180 cm^–1. Dinitrogen was more strongly adsorbed on Fe/SiO₂ containing K₂O than on Fe/SiO₂ alone. Nitric oxide adsorbs at Fe⁰ and cationic Feⁿ⁺ sites on iron the latter being generated by the dissociative adsorption of NO. Hydrogen reacts with adsorbed NO to form ammonia and water and promotes Feⁿ⁺—NO surface species at the expense of Feⁿ⁺—NO. NO displaces CO from iron, giving CO₂(g) and NCO(ads) as products. The effects of K₂O on the reactions between NO and H₂ or CO have been studied. The kinetics of ammonia decomposition over Fe/SiO₂ at 683–823 K are briefly reported.