Postsynthesis and Selective Oxidation Properties of Nanosized Sn-Beta Zeolite

Abstract

Nanosized Beta zeolites were postsynthetically modi-fied through the solid−gas reaction of highly dealuminated Beta zeolite with SnCl4 vapor at elevated temperatures. The incorporation mechanism of Sn ions and the physicochemical properties of resultant Sn-Beta-PS were characterized by various techniques. Its catalytic performance in Baeyer−Villiger oxidation was compared with the micrometer-sized Sn-Beta-F hydrothermally synthesized by conventional fluoride method. The Sn species were inserted into the framework via the reaction of the SnCl4 molecules with the silanols in the hydroxyl nests that were created by dealumination and thus occupied predominately the tetrahedral coordination sites. The Sn content gained by postsynthesis reached up to 6.2 wt %, corresponding to a Si/Sn ratio of ca. 35. The isolated Sn species exhibited Lewis acidity useful for the Baeyer−Villiger oxidation of ketones. Containing higher Sn contents and more importantly proposing less diffusion limitations to the substrates with a large molecular dimension, nanosized Sn-Beta-PS was superior to Sn-Beta-F in the selective oxidation of 2-adamantanone with hydrogen peroxide.