Chemistry of Silica-Supported Cobalt Catalysts Prepared by Cation Adsorption. 1. Initial Localized Adsorption of Cobalt Precursors
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- 作者：Raquel Trujillano ; Franç ; oise Villain ; Catherine Louis ; Jean-Franç ; ois Lambert
- 刊名：Journal of Physical Chemistry C
- 出版年：2007
- 出版时间：May 17, 2007
- 年：2007
- 卷：111
- 期：19
- 页码：7152 - 7164
- 全文大小：244K
- 年卷期：v.111,no.19(May 17, 2007)
- ISSN：1932-7455
文摘
The speciation of cobalt ethanediamine (en) complexes [Co(en)x(H2O)6-2x]2+ (x = 1, 2, and 3) in aqueoussolution changes when a silica support is introduced into the solution ((en/Co = 1), (en/Co = 2), and (en/Co= 3) preparations). The pH-buffering effect of the silica support causes speciation shifts, especially for theprecursor complex [Co(en)2(H2O)2]2+ in solution, which transform into [Co(en)1(H2O)4]2+, as the main species.Once adsorbed on silica and after drying (25 and 100 
C), UV-visible and XAS characterization show that,for the (en/Co = 1) and (en/Co = 2) preparations, the Co(en)1 complexes form dimers bonded to silicathrough one silanol group per Co ([(SiO)(en)(H2O)2CoII]2(
-O)). For the (en/Co = 3) preparation, the adsorbedCo(II) complexes are monomeric and contain two ethanediamine ligands. Upon drying at 100 C, residualwater molecules in the coordination sphere of adsorbed Co(II) complexes may be lost reversibly, causing theestablishment of an octahedral/tetrahedral coordination equilibrium. Upon calcination at 450 C, theethanediamine ligands are eliminated. The monomeric complex in (en/Co = 3) probably becomes graftedonto silica through two bonds ((SiO)2CoII(OH2)4), while the dimer initially formed in (en/Co = 1) and (en/Co= 2) mostly gives rise to species reminiscent of Co silicate germs.
C), UV-visible and XAS characterization show that,for the (en/Co = 1) and (en/Co = 2) preparations, the Co(en)1 complexes form dimers bonded to silicathrough one silanol group per Co ([(SiO)(en)(H2O)2CoII]2(-O)). For the (en/Co = 3) preparation, the adsorbedCo(II) complexes are monomeric and contain two ethanediamine ligands. Upon drying at 100 C, residualwater molecules in the coordination sphere of adsorbed Co(II) complexes may be lost reversibly, causing theestablishment of an octahedral/tetrahedral coordination equilibrium. Upon calcination at 450 C, theethanediamine ligands are eliminated. The monomeric complex in (en/Co = 3) probably becomes graftedonto silica through two bonds ((SiO)2CoII(OH2)4), while the dimer initially formed in (en/Co = 1) and (en/Co= 2) mostly gives rise to species reminiscent of Co silicate germs.