Comparative study of the structure of protective oxide layers on the surface of macrocrystalline iron and a promoted catalyst of synthesis of ammonia by absorption and conversion M�ssbauer spectroscopy

Abstract

1. The protective layer of microcrystalline iron consists of crystallites of hematite magnetically ordered at 20‡C and ∿0.1 Μm in size, and the phase composition of the surface and bulk of the sample is qualitatively the same in all conditions of oxidation. 2. The passivating film of the promoted catalyst of synthesis of ammonia is formed from small clusters of iron oxide with an effective size of 0.005–0.01 Μm; the composition of the surface and bulk of the stabilized catalyst is qualitatively different. 3. The role of the defects in the promoted catalyst in the mechanism of formation of oxide clusters was discussed.