Sn-Modified NaY Zeolite Catalysts Prepared by Post-Synthesis Methods for Baeyer–Villiger Oxidation

The Sn–NaY zeolite catalysts, Sn–NaY-gas and Sn–NaY-liq, were prepared by two-step post-synthesis methods, through hydrothermal dealumination and the post-incorporation of Sn species using chemical vapor deposition and impregnation separately. The Sn-ion incorporation and the physicochemical properties of the catalysts were characterized by various techniques. The amount of Sn species that were incorporated into the zeolite framework depended closely on the Sn introduction method. Sn–NaY-gas was found to have more Lewis-acid tetracoordinated Sn sites, which led to a better catalytic performance in the Baeyer–Villiger oxidation of cyclohexanone. The higher Sn loadings in the Sn–NaY-liq (3.4%) resulted in many inactive amorphous extra-framework Sn species, which also caused partial blockage of the zeolite pores and led to a loss in catalytic efficiency. Therefore, chemical vapor deposition could be used to form more active Lewis acidic Sn sites.