期刊
APPLIED CATALYSIS B-ENVIRONMENTAL
卷 127, 期 -, 页码 68-76出版社
ELSEVIER SCIENCE BV
DOI: 10.1016/j.apcatb.2012.08.001
关键词
Radioactive isotope; Cobalt; Zeolite; EXAFS; SEM
资金
- Basic Science Research Program through the National Research Foundation of Korea (NRF)
- Ministry of Education, Science and Technology [2010-0023824]
- NAP (National Agenda Project) of the Korea Research Council of Fundamental Science Technology
- Ministry of Educational Science and Technology of the Korean Government
- Pohang University of Science and Technology (POSTECH)
- National Research Foundation of Korea [2010-0023824] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
This study investigated thermal stabilization of Co2+-exchanged zeolite X (Co-X) using scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), and leaching tests. From SEM-EDX analysis, cobalt was dispersed randomly at <= 600 degrees C, suggesting its presence as an extraframework cation in exchange sites. At >= 800 degrees C, cobalt was locally concentrated with Al on the vitreous surface. Consistent with such observations, XRD data indicated that Co-X maintained the zeolite framework at <= 600 degrees C, and that it became vitrified and transformed to nepheline (NaAlSiO4(s)) and cobalt aluminate (CoAl2O4(s)) at >= 800 degrees C. Cobalt-K edge XAS was subjected to both X-ray absorption near-edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS) analyses. In XANES spectra, the pre-edge peaks and edge-shoulders, characteristic of 4-fold coordinated cobalt (e.g., CoAl2O4(s)), were not evident at <= 600 degrees C, but such features were strong at >= 800 degrees C. The EXAFS spectra of Co-X at <= 600 degrees C lacked in the coordination shells beyond the first Co-O shell. In contrast, Co-X at >= 800 degrees C showed the EXAFS spectra similar to CoAl2O4(s). Taken together, cobalt was likely present as 6-fold coordinated Co2+ in exchange sites at <= 600 degrees C and mainly incorporated into a non-exchangeable CoAl2O4-like phase in both vitreous and crystalline forms at 800 degrees C. In agreement with this proposition, leaching tests with concentrated CaCl2 solutions supported the greater stability of cobalt at >800 degrees C. (C) 2012 Elsevier B.V. All rights reserved.
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