Isomorphous Incorporation of Tin Ions into Germanosilicate Framework Assisted by Local Structural Rearrangement

Abstract

The crystalline structure of UTL zeolite experienced an unusual orientated collapse and reconstruction within an extremely narrow time window during the structural stabilization process by nitric acid treatment at elevated temperature. Taking full advantage of this unique structural change, extra-large-pore Sn-UTL zeolites were postsynthesized via the reaction between the SnCl 4 molecules and the silanols in the hydroxyl nests, which occurred concomitantly with the removal of Ge and/or Si species from the dense layer. The original UTL topology was restored thereafter, leading to a Sn-incorporated analogue. The usage of the most seriously collapsed intermediate structure, which was captured by timing during the precisely controlled acid treatment, was vital for achieving Sn-UTL zeolites with a larger amount of isolated Sn species effectively incorporated. With tetrahedrally coordinated Sn ions in the highly stabilized UTL topology consisting of intersecting 12- and 14-membered ring (MR) pore channels, Sn-UTL showed promising catalytic performance in the Meerwein–Pondorf–Verley reaction as well as in the Baeyer–Villiger oxidation reactions of ketones using H 2 O 2 or even bulky tert -butyl hydroperoxide (TBHP) as an oxidant.