Surface and bulk changes in iron nitride catalysts in H sub 2 /CO mixtures
- Purdue Univ., West Lafayette, IN (USA)
Preparation of the {zeta}, {epsilon}, and {gamma}{prime}-iron nitride phases was confirmed by Moessbauer spectroscopy, X-ray diffraction, and quantitative mass spectrometry of NH{sub 3} evolved during decomposition. Computer fitting of the {epsilon}-nitride Moessbauer spectra with a distribution of hyperfine fields shows the conversion of iron with two nitrogen nearest neighbors (Fe 2nn) to Fe 3nn as the nitrogen content increases. The dynamic response of the nitrides to H{sub 2}/CO mixtures at reaction temperatures was followed by constant-velocity Moessbuaer spectroscopy and transient mass spectrometry. The rapid decomposition of the iron nitrides in H{sub 2} at 523 K occurs with surface reaction as the rate-limiting step, initially. At lower temperatures or after significant nitride decomposition, the data are best fit with a shrinking core model. For reaction at 473 K, the Moessbauer effect identified an {alpha}-Fe shell, a {zeta}-Fe{sub 2}N core, and an {epsilon}-Fe{sub x}N transition region. Surprisingly, loss of the pure nitride phase is barely retarded for H{sub 2}/CO mixtures compared to H{sub 2} alone at 523 K. Mass spectrometric studies show that the freshly prepared nitride has a substantial hydrogen inventory, equivalent to a monolayer of NH{sub 3} for {zeta}-Fe{sub 2}N. On exposure to synthesis gas, the nitride catalysts produce no methane until one to two monolayers of N have been removed, but carbon is deposited on the catalysts by the Boudouard reaction. Mass spectral measurements show no evidence for active nitrogen on the surface after the synthesis reaction has been established. Both Moessbauer spectroscopy and mass spectral measurement confirm, however, that following the initial loss of nitrogen, bulk carbonitrides form which lose their nitrogen very slowly as the reaction proceeds. 28 refs.
- DOE Contract Number:
- FG22-82PC50804
- OSTI ID:
- 6854977
- Journal Information:
- Journal of Catalysis; (USA), Journal Name: Journal of Catalysis; (USA) Vol. 113:1; ISSN 0021-9517; ISSN JCTLA
- Country of Publication:
- United States
- Language:
- English
Similar Records
CO + H/sub 2/ reaction over nitrogen-modified iron catalysts. Final technical report, August 1, 1982-December 31, 1985
CO + H/sub 2/ reaction over nitrogen-modified iron catalysts. Quarterly technical progress report, October 1, 1983-December 30, 1983. [Denitriding of iron nitrides in both hydrogen and helium]
Related Subjects
010408* -- Coal
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ALKANES
AMMONIA
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CATALYSTS
CHALCOGENIDES
CHEMICAL PREPARATION
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
COHERENT SCATTERING
DECOMPOSITION
DIFFRACTION
ELEMENTS
EQUATIONS
FISCHER-TROPSCH SYNTHESIS
FLUIDS
GASES
HIGH TEMPERATURE
HYDRIDES
HYDROCARBONS
HYDROGEN
HYDROGEN COMPOUNDS
HYDROGENATION
IRON COMPOUNDS
IRON NITRIDES
KINETIC EQUATIONS
KINETICS
MASS SPECTROSCOPY
MATHEMATICAL MODELS
METHANATION
METHANE
MOESSBAUER EFFECT
MONITORING
NITRIDES
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
NONMETALS
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PNICTIDES
REACTION KINETICS
SCATTERING
SPECTROSCOPY
SURFACE PROPERTIES
SYNTHESIS
SYNTHESIS GAS
TRANSITION ELEMENT COMPOUNDS
X-RAY DIFFRACTION