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Contribution

X-ray structural analysis

Study of Phase Transformation of Iron Containing Catalyst in Ethylene-Ammonia Mixture Decomposition Reaction

Speakers

  • Dr. Alexander SHMAKOV

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Co-authors

Content

Nitrogen doped carbon nanomaterials (N-CNM) currently attract a lot of interest due to their special physical, chemical and functional properties [1]. Nitrogen doped carbon nanotubes (N-CNT) look most investigated in details. It is generally recognized that N-CNT growth proceeds over iron containing catalysts with mixture of hydrocarbons and ammonia, as well as organic compounds, as a source of carbon and nitrogen. So the aim of this work is the study of the transformation of iron containing catalyst phase composition during the reaction of N-CNT growth in ethylene-ammonia mixture. The reaction of ethylene-ammonia decomposition over iron containing catalyst leads to formation of bamboo-like N-CNT with nitrogen content up to 7 at. %. Pure ethylene decomposition over the same catalyst gives CNT with coaxial cylindrical graphite layers packing. To explain the difference of CNT morphology the investigation was carried out by means of Ex Situ and In Situ X-ray diffraction. According to Ex Situ XRD data the initial sample of catalyst consists of two phases – metal iron and iron-alumina spinel Fe[Fe,Al]2O4. The preliminary reduction of the catalyst at hydrogen flow at 650-700°C makes the iron content increased that was demonstrated by In Situ experiments. Under consequent exposure of reduced catalyst to ethylene-ammonia mixture at 650°C the spinel phase almost disappears and iron carbide phase arises. In contrast, the phase composition of catalyst doesn’t changes while the reaction with pure ethylene. However, at 700°C the catalyst demonstrates similar behavior under both pure ethylene and ethylene-ammonia mixture.

[1] G. Ćirić-Marjanović, I. Pašti, S. Mentus // Progress in Material Science. 2015. 69. P. 61.