Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
10244694 | Journal of Catalysis | 2005 | 8 Pages |
Abstract
Two types of Lewis acid sites are shown to exist in Sn-beta zeolite: partially hydrolysed framework tin centers (SiO)3SnOH (sites A) and fully framework coordinated tin atoms Sn(SiO)4 (sites B). ONIOM and DFT calculations for adsorbed acetonitrile, which is a probe molecule for Lewis acid sites, show that acetonitrile coordinates more strongly to partially hydrolysed framework Sn (sites A) in Sn-beta zeolite than to nonhydrolysed framework Sn (sites B). The corresponding IR bands associated with the ν(CN) stretching vibration were also calculated. Adsorption-desorption experiments of deuterated acetonitrile on Sn-beta give two IR bands at 2316 and 2308 cmâ1 with IR shifts of 43 and 51 cmâ1 with respect to gas-phase acetonitrile. These values are in excellent agreement with theoretical calculations, making it possible then to associate the Lewis sites related to 2316 and 2308 cmâ1 with partially hydrolysed and nonhydrolysed framework Sn sites, respectively. Catalytic results confirm that partially hydrolysed Sn (sites A) is much more active than fully framework-integrated Sn (sites B) for Baeyer-Villiger oxidation of cyclic ketones. Finally, the ratio between these two types of sites could be influenced by postsynthesis treatments.
Related Topics
Physical Sciences and Engineering
Chemical Engineering
Catalysis
Authors
Mercedes Boronat, Patricia Concepción, Avelino Corma, Michael Renz, Susana Valencia,