Controllably Confined ZnO on USY Zeolites (USY@ZnO/Al₂O₃) as Efficient Lewis Acid Catalysts for Baeyer–Villiger Oxidation

A ZnAl-LDHs (layered double hydroxides) phase was readily formed on the surface of a USY zeolite through a distinctive in situ growth method that benefitted from the interaction of the added Zn source and aluminum species extracted from the Al-rich USY zeolite crystals. The migration of aluminum and simultaneous interaction with the external Zn source took place in one pot to form a ZnAl-LDHs phase coated on the surface of the USY crystals. Upon calcination, the ZnAl-LDHs phase was transformed into a ZnO/Al₂O₃ composite that was still firmly anchored on the USY zeolite, without sacrificing the core–shell structure. The resultant USY@ZnO/Al₂O₃ materials gave rise to unique Lewis acidity and hierarchical porosity, which endowed the catalyst with promising performance in the Baeyer–Villiger oxidation of ketones with H₂O₂ or bulky tert-butyl hydroxide as an oxidant.