Al-Sn bimetallic ZSM-5: Acidity regulation and excellent performance in cracking n-hexane for production of light olefins

Abstract

ZSM-5 zeolite is extensively employed for hydrocarbons cracking to generate light olefins, and its acidity is closely related to the activity and product distribution. In this work, Al-Sn bimetallic ZSM-5 was prepared via a “one-pot” route. Characterizations, including XRD, UV–Vis, XPS, revealed that Sn species were mainly embedded into the zeolite framework as tetrahedral Sn (IV). Moreover, the Sn atoms promoted the formation of Lewis acid sites and reduced the Brønsted acid amount, which effectively inhibited occurrence of side reactions (e.g., aromatization, hydrogen transfer) and improved the selectivity of light olefins in n-hexane cracking. Light olefins yield over HZ5[100,200] (Si/Al = 100, Si/Sn = 200) reached 33.4% due to the appropriate acid property, in comparison with only 15.4% for HZ5[50,∞] (Si/Al = 50, Si/Sn = ∞) containing system. Through optimization of reaction conditions, better catalytic performance (n-hexane conversion of 91.6% and light olefins yield of 37.6%) was obtained over HZ5[100,200] under 575 °C with WHSV of 2 h⁻¹.