Dealumination-controlled strategy mediates Ti–Y zeolite with cooperative active sites for selective oxidations

Abstract

Plentiful heteroatom-containing zeolites as versatile redox catalysts have been successfully post-synthesized via the top-down methodology, where the starting aluminosilicate zeolites are normally expected to be highly dealuminated to maximize the amounts of silanol nests and occasionally to evade the detrimental effect of framework Al ions on the catalytic performance. Herein, our proposed dealumination-controlled strategy for the synthesis of hierarchical Ti–Y zeolite breaks through this concept. Framework-substituted Ti and tri-coordinated Al species were afforded from the interaction of Ti ions with dealumination-derived silanol nests and from the process of acid treatment, respectively. Structure–function relationships revealed that Lewis acid sites were the catalytically active centres of Ti–Y zeolite in oxidative desulfurization with hydrogen peroxide as the oxidant, which came from the cooperative effect of dual active sites containing framework-substituted Ti and tri-coordinated Al species. The amounts of Lewis acid sites demonstrated a volcanic-type trend as the acid-treatment time increases. The reusability, regeneration ability, deactivation mechanism were also systematically investigated in oxidative desulfurization. Thus the Ti–Y zeolite catalyst was also effective for Baeyer–Villiger oxidation of 2-adamantanone. This work discloses the effectiveness of preparing an efficient Ti–Y zeolite catalyst with cooperative dual active sites via a dealumination-controlled strategy, which bears potential application for constructing other heteroatom-containing FAU-type zeolites with Lewis acid property.