Journal
JOURNAL OF SOLID STATE CHEMISTRY
Volume 182, Issue 9, Pages 2385-2391Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.jssc.2009.06.030
Keywords
Ammonia synthesis; Iron catalyst; Fe1-xO; In situ X-ray diffraction
Funding
- National Nature Science Foundation of China (NSFC) [20473074, 20376075]
- Science-Technology Planning Project of Zhejiang Province [2007F70039]
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The temperature-programmed reduction process of two types of industrial ammonia-synthesis catalysts, A110 and ZA-5, which are, respectively, based on Fe3O4 and Fe1-xO 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 Fe3O4- and Fe1-xO-based ammonia-synthesis catalysts is proposed, and the origins for the activity difference has been also discussed. (C) 2009 Elsevier Inc. All rights reserved.
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