期刊
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY
卷 36, 期 17, 页码 10834-10844出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.ijhydene.2011.05.187
关键词
Metal-organic framework; Exposed metal; Cobalt; Isomorphic substitution; Band gap; Hydrogen adsorption
资金
- Comunidad de Madrid
- Spanish Ministry of Science and Innovation [MAT-2009-13569]
- SOLGEMAC Project through the Programme of Activities between Research Groups [S2009/ENE-1617]
- CICYT [CTQ2009-11934]
Simultaneous incorporation of Zn and Co ions into MOF-74 during the crystallization process has been studied, covering the whole Zn/Co concentration range (0-100% Co). The characterization techniques used, including X-ray diffraction, DR-UV-visible spectroscopy, N-2 adsorption isotherms and thermogravimetric analysis, strongly evidence the successful incorporation of both cations into the material framework, producing the crystallization of MOF-74 with 100% Co and MOF-74 with 100% Zn starting from Zn-free and Co-free initial mixtures, respectively, under the same conditions. H-2, CH4 and CO2 uptakes of MOF-74 type materials generally increase with framework Co content at any pressure, suggesting a relevant role of cobalt in the adsorption process. As expected, the comparison between the gas adsorption behavior of Co-substituted MOF-5 and Co-containing MOF-74 materials shows that exposed metal sites play a key role in MOF performance in adsorption. On the other hand, the good agreement between the evolution of the experimental band gap values as a function of the Co content and the computational-based predictions found in the literature further supports the coexistence of Zn2+ and Co2+ ions forming the MOF-74 metal clusters. Finally, we found that variations of both isosteric heat of hydrogen adsorption and band gap energy with the metal cluster composition show a parallel trend, although it is not systematic in the whole range of Zn/Co ratio. Indeed, a minimum band gap energy value and a maximum isosteric heat of H-2 adsorption value were found to appear simultaneously for Co-rich samples still having some Zn rather than for all-Co samples. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
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