Bare Simon R, Kelly Shelly D, Sinkler Wharton, Low John J, Modica Frank S, Valencia Susana, Corma Avelino, Nemeth Laszlo T
UOP LLC, Des Plaines, Illinois 60016, EXAFS Analysis, Bolingbrook, Illinois 60440, USA.
J Am Chem Soc. 2005 Sep 21;127(37):12924-32. doi: 10.1021/ja052543k.
The Sn silicate zeolite, Sn-beta, has been shown to be an efficient, selective heterogeneous catalyst for Baeyer-Villiger oxidations. Using primarily a multishell fit to extended X-ray absorption fine structure (EXAFS) data, we show that the Sn does not randomly insert into the beta-zeolite structure but rather occupies identical, specific, crystallographic sites. These sites are the T5/T6 sites in the six-membered rings. Moreover, the Sn is substituted in pairs on opposite sides of these six-membered rings. We believe that it is the specific, uniform crystallographic location of the Sn in the beta crystal structure that leads to sites with uniform catalytic activity, and consequently to the high chemical selectivity demonstrated for this catalyst. This manifests itself in the almost enzyme-like selectivity of this catalyst in Baeyer-Villiger oxidations. This uniform site distribution of the Sn suggests that there is likely a symbiotic relationship between the structure-directing agent in the zeolite synthesis and the Sn heteroatoms during the framework formation.
锡硅酸盐沸石Sn-β已被证明是一种用于拜耳-维利格氧化反应的高效、选择性非均相催化剂。主要通过对扩展X射线吸收精细结构（EXAFS）数据进行多壳层拟合，我们发现锡并非随机插入β沸石结构中，而是占据相同的特定晶体学位置。这些位置是六元环中的T5/T6位点。此外，锡在这些六元环的相对两侧成对取代。我们认为，正是β晶体结构中锡的特定、均匀晶体学位置导致了具有均匀催化活性的位点，从而使该催化剂表现出高化学选择性。这在该催化剂在拜耳-维利格氧化反应中几乎类似酶的选择性中得以体现。锡的这种均匀位点分布表明，在沸石合成过程中，结构导向剂与锡杂原子在骨架形成过程中可能存在共生关系。
