| EXAFS Studies of Perrhenate and SnMe4-promoted Perrhenate on Silica, Silica-Alumina, and Alumina |
| Abstract ID | MAT-21 |
| Presenter | Ming-Yung
Lee |
| Presentation Type | Poster
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| Full Author List | M.-Y. Lee (1) , B. Vicente (1) , A. W. Moses (1) , S. L. Scott (1)
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| Affiliations | (1) University of California, Santa Barbara
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| Category | Materials Science |
| Abstract | Perrhenate supported on both silica-alumina and alumina are heterogeneous catalysts for olefin metathesis. When promoted with SnMe 4, these catalysts become tolerant to functionalized olefins. EXAFS studies of perrhenate and tetramethyltin individually grafted on different supports, such as silica, silica-alumina, and alumina, were conducted in order to obtain the local structure around Re and Sn sites on different supports. Ammonium perrhenate and (CH3)3SiOReO3 were used as model compounds for the different perrhenate-modified supports. Interactions between the perrhenate and Lewis-acidic aluminum sites are seen on both silica-alumina and alumina. These interactions result in a distortion of the perrhenate away from tetrahedral geometry and are believed to be responsible for the catalytic activity, since supported perrhenate on silica, which is inactive for olefin metathesis, retains the tetrahedral environment of unsupported perrhenate. Before Me4Sn is added on the perrhenate modified support, we also attempted to study how to maximize the uniformity of the methyltin sites via controlled vapor-phase grafting, in order to establish the nature of the sites present prior to assembling the multicomponent catalytic system. EXAFS studies combine with the results of 1H and 13C solid-state NMR spectra indicate that the SnMe4 loading, the reaction temperature and the evacuation time all affect the distribution of methyltin sites. Higher reaction temperatures and longer evacuation times favor the formation of Me2Sn(IV) sites on the support. |
| Footnotes | |
| Funding Acknowledgement | DOE, NSF IREE, NSF CENTC
Cathy Knotts, Dr. Sam Webb, Dr. Erik Nelson, Dr. Allyson Aranda, Dr. Corwin Booth, Dr. Serena George, and Dr. Jeroen van Bokhoven (ETH-Zurich)
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