Insight into tri-coordinated aluminum dependent catalytic properties of dealuminated Y zeolites in oxidative desulfurization

Abstract

Aluminosilicate zeolite as a versatile material is of great importance for industrial catalysis, whose noumenal Brønsted and Lewis acid sites generally determine the activity, selectivity, and even stability during the catalytic reactions. Unlike well-studied Brønsted acid sites for acid-catalyzed reactions, the pending question about the effectiveness and role of Lewis acid sites derived from framework-associated and/or extra-framework aluminum in selective oxidation reactions remains unanswered. Herein, tri-coordinated Al was rationally constructed via precisely tailoring acid-treatment time for ultra-stable Y zeolite, which was associated with Lewis acidity. This Lewis acid sites rather than extra-framework related Lewis acid sites were confirmed to be the catalytic active sites for oxidative desulfurization with hydrogen peroxide as oxidant. Additionally, the Al evolution mechanism and physicochemical properties for dealumination-derived samples were systematically investigated via series of techniques. The most possible tri-coordinated Al micro-structure with Lewis acidity was verified by density functional theory calculations. More importantly, the superoxide and hydroxyl radical were both the active oxygen species during the catalytic reactions. This work discloses the decisive effectiveness of framework-associated Al species with Lewis acidity in zeolites to oxidative desulfurization and paves a straightforward way for rationally designing Lewis acidic Al-zeolite catalysts.