Chemistry of Silica-Supported Cobalt Catalysts Prepared by Cation Adsorption. 2. Neoformation of Cobalt Phyllosilicate

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• 作者：Raquel Trujillano ; Jean-Franois Lambert ; Catherine Louis
• 刊名：Journal of Physical Chemistry C
• 出版年：2008
• 出版时间：November 27, 2008
• 年：2008
• 卷：112
• 期：47
• 页码：18551-18558
• 全文大小：298K
• 年卷期：v.112,no.47(November 27, 2008)
• ISSN：1932-7455

文摘

The goal of this study was to determine whether it was possible to avoid the formation of cobalt silicate during the preparation of silica-supported Co catalysts since this too-stable cobalt phase is detrimental to catalyst activity. The strategy was to use the strong chelating ligand ethanediamine (en) to complex Co cations, then to adsorb them on silica, and to determine whether an optimal en:Co ratio could be found to avoid the formation of cobalt silicate. In a previous paper (Trujillano, R.; Villain, F.; Louis, C.; Lambert, J. F. J. Phys. Chem. C 2007, 111, 7152), which explored short contact times between Co complex solutions and silica (15 min and 2 h), it was found that cobalt ethanediamine adsorbed very quickly on silica. In the present paper, a longer contact time (7 days) was explored. XRD, UV−visible−near IR, and FT-IR characterization showed that after the fast phenomenon of cation adsorption, a second slow chemical phenomenon occurs, leading to the formation of cobalt phyllosilicate. The amount depended on the en:Co ratio, the silica surface area, and the atmosphere under which the suspension was maintained. Formation of cobalt phyllosilicate was avoided when the en:Co ratio = 3 or when preparations were performed under air bubbling in the solution, i.e., when Co(II) was oxidized into Co(III).