Characterization of NH3/Fe catalytic systems by laser Raman spectroscopy

Abstract Laser Raman spectra of species adsorbed on doubly promoted fused iron catalysts were obtained under static and flowing atmospheres of NH3 and 1 N 2 3 H 2 . 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 FeH stretch due to H(a); 1940 and 2040 cm−1 for the NN stretch due to N2(a); 1090 cm−1 for the FeN stretch due to N(a); 895 cm−1 for the FeN stretch due to NH(a); 500 cm−1 for the FeN stretch due to NH2(a); 465 and 410 cm−1 for the FeN stretch due to N2(a); and 140 cm−1 for the FeN 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: .