Characterization of NH₃ Fe catalytic systems by laser Raman spectroscopy

Laser Raman spectra of species adsorbed on doubly promoted fused iron catalysts were obtained under static and flowing atmospheres of NH₃ and 1N₂ 3H₂. The spectra provided new information about the nature of the surface species involved in iron-hydrogen, iron-nitrogen, and nitrogen-nitrogen bonding. Assignment of the Raman bands included: 1951 and 1902 cm^-1 for the FeH stretch due to H(a); 1940 and 2040 cm^-1 for the NN stretch due to N₂(a); 1090 cm^-1 for the FeN stretch due to N(a); 895 cm^-1 for the FeN stretch due to NH(a); 500 cm^-1 for the FeN stretch due to NH₂(a); 465 and 410 cm^-1 for the FeN stretch due to N₂(a); and 140 cm^-1 for the FeN stretch due to NH₃(a). In situ studies and studies performed at room temperature indicated that dehydrogenation of NH₃(a) to NH(a) or N(a) did not occur extensively for catalysts which had been reduced by H₂ or for catalysts which were actually functioning for NH₃ decomposition. N₂(a) and H(a) were the dominant chemisorbed species on the surface of the functioning catalyst. The Raman results were consistent with an associative mechanism for ammonia synthesis or decomposition: {A figure is presented}.