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