Activation of NH4+-Type ZSM-5 via DBD Plasma for Regulating Al Species Coordination and Enhancing Light Olefins Production in n-Hexane Cracking

The metal coordination state and the corresponding acid property of zeolite closely relate to its catalytic performance. In this study, DBD-plasma (dielectric barrier discharge-plasma), a low-temperature and energy-efficient external activation method, was proposed to activate the NH4+-type ZSM-5 zeolite and to regulate the Al coordination. It was found that DBD treatment could efficiently decompose NH4+ species at 115 °C, far below that required for calcination (550 °C). Characterizations, including X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), 27Al magic angle spinning nuclear magnetic resonance (27Al MAS NMR), and pyridine-adsorption infrared spectroscopy (Py-IR), revealed that DBD-plasma treatment could inhibit zeolite framework destruction and retain more framework Al and mesoporous structure, thus improving the stability and enhancing the amount of medium-strong Brønsted acid sites. In n-hexane cracking, DBD-activated zeolite exhibited improved conversion and C2–C4 olefin selectivity due to the enhanced monomolecular cracking pathway induced by increased Brønsted acidity, while reducing aromatics and coke formation by suppressing side reactions. This paper presents an alternative method that is more energy-efficient, highly effective, and capable of regulating the metal coordination and acidity of ZSM-5 zeolite.