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Abstract Details
XAS Evidence of Silica-Interactions with Supported Transition Metal Chlorides
| Speaker | Eric Deguns (UC Santa Barbara) |
| Full Author List | E.W. Deguns (1), G.D. Meitzner (2), S.L. Scott (1), (none) (0), (none) (0), (none) (0), (none) (0), (none) (0), (none) (0), (none) (0) |
| Affiliations | 1. Departments of Chemistry and Chemical Engineering, University of California, Santa Barbara, CA, USA,
2. Materials Research and Technology Institute, University of Texas, El Paso, TX, USA,
3. (none),
4. (none),
5. (none),
6. (none),
7. (none),
8. (none),
9. (none),
10. (none) |
| Category | Materials Science |
| Abstract |
The vapor-phase deposition of transition metal halides onto silica can be used to make precursors to catalytically active materials for epoxidation, partial reduction and polymerization. We have previously explored the mass balanced reactions of TiCl4 and VOCl3 with hydroxyl-terminated silica to give stoichiometries as follows:
TiCl4 + ≡SiOH → ≡SiOTiCl3 + HCl
VOCl3 + ≡SiOH → ≡SiOVOCl2 + HCl
Metal loading and HCl yield is 1:1, irrespective of the type and concentration of the silica hydroxyls.
XAS is the only method which allows us to directly probe the interactions of the metal with the support. XAS evidence shows that silica hydroxyls act differently towards the two complexes: Highly spaced hydroxyls yield isolated ≡SiOTiCl3 and ≡SiOVOCl2 fragments, while paired hydroxyls give rise to dimeric (TiCl3)2(μ-OSi≡)2 sites. The supported vanadium complexes do not dimerize. The effect of cryogenic cooling to aid in detection of dimeric species, featuring M-O-M moieties, will be highlighted.
Unexpected interactions of chlorine ligands with the silica support gives rise to asymmetric chlorine distances, evident in EXAFS model refinements. These interactions are consistent with the varying ligand reactivity of the complexes.
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