Sn-Beta zeolite derived from a precursor synthesized via an organotemplate-free route as efficient Lewis acid catalyst

Abstract

Sn-containing Beta zeolite (Sn-Beta) is an effective solid Lewis acid catalyst useful for a large number of redox reactions. However, it is still a challenging task to prepare Sn-Beta without the usage of organic structure directing agents (OSDAs) and/or fluoride. Considering synthesis cost and the consumption of energy as well as environmental problems, in this study, hierarchical Sn-Beta is successfully prepared via post-synthesis method by incorporating Sn ions into silanol nests of dealuminated Beta zeolite which is synthesized through an OSDA- and fluoride-free route. Prior to deep dealumination, the OSDA-free aluminosilicate Beta is steamed at a mild temperature for a short time (823 K, 30 min), which allows for the effectively stabilizing the Beta framework structure. Then Sn ions are tetrahedrally incorporated into the Beta framework at 773 K under vapor condition via the reaction between the Sn ions and silanol defects derived from the steaming and subsequent acid treatment. The Sn-Beta zeolite thus obtained exhibits better catalytic performances than conventional Sn-Beta-F in the conversion of dihydroxyacetone to ethyl lactate (yield, 89.1% vs. 74.3%) and Baeyer-Villiger oxidation of 2-adamantanone (conversion, 72.3% vs. 58.6%, using H2O2 as the oxidant). The enhanced catalytic performance is predominantly contributed by hierarchical pore channels and the smaller particle size, which greatly enhance mass transfer and lower the apparent reaction activation energy.