In situ X-ray diffraction study of reduction processes of Fe{sub 3}O{sub 4}- and Fe{sub 1-x}O-based ammonia-synthesis catalysts

Journal Article · Tue Sep 15 00:00:00 EDT 2009 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2009.06.030· OSTI ID:21370568

Huazhang, Liu; Zongjian, Liu; Xiaonian, Li ^[1]

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1. College of Chemical Engineering and Materials Science, Zhejiang University of Technology, Hangzhou 310014 (China)

The temperature-programmed reduction process of two types of industrial ammonia-synthesis catalysts, A110 and ZA-5, which are, respectively, based on Fe{sub 3}O{sub 4} and Fe{sub 1-x}O precursors, were studied by in situ X-ray power diffraction (XRD). It has been found that the ZA-5 has lower reduction temperature and faster reduction rate, and its active phase alpha-Fe possesses a higher value of lattice microstrain than A110. The simulation based on Rietveld refinement has also shown that the shape of alpha-Fe grain of ZA-5 has a mixed shape of cube and sphere with more exposing (111) and (211) planes, while that of A110 looks like a concave cube with more exposing (110) planes. Based on the results obtained, a growth model of alpha-Fe during the reduction of Fe{sub 3}O{sub 4}- and Fe{sub 1-x}O-based ammonia-synthesis catalysts is proposed, and the origins for the activity difference has been also discussed. - Graphical Abstract: A proposed growth model of active phase alpha-Fe during reduction. Due to H{sub 2} diffusing easily into the pores, reduction starts on outside and inside surface simultaneously to form 'microcrystalline film', and the particles shrink during reduction which results in breaking of the aggregated oxide particle.

• OSTI ID: 21370568
• Journal Information: Journal of Solid State Chemistry, Journal Name: Journal of Solid State Chemistry Journal Issue: 9 Vol. 182; ISSN 0022-4596; ISSN JSSCBI
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
AMMONIA
CATALYSTS
CHALCOGENIDES
CHEMICAL REACTIONS
COHERENT SCATTERING
DIFFRACTION
ELEMENTS
HYDRIDES
HYDROGEN COMPOUNDS
IRON
IRON COMPOUNDS
IRON OXIDES
IRON-ALPHA
METALS
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
OXIDES
OXYGEN COMPOUNDS
REDUCTION
SCATTERING
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
X-RAY DIFFRACTION