Behaviors of acetylene adsorption and benzene desorption over hollow sphere MCM-22 catalyst for aromatization

초록

A hollow sphere-type MCM-22 zeolite (HS-MCM-22) was synthesized via a hard-template method using alumina-coated carbon spheres (CS-Al). The distributed alumina seeds embedded on the surface of CS-Al are believed to play a role of anchoring sites to aluminosilicate crystallites and to stabilize the tetrahedral structure. The distinctive leaf-like structure of MWW-type zeolites makes them suitable for preparing hierarchical macroporous structures. This approach yielded a robust hierarchical morphology and promoted the effective incorporation of aluminum into the zeolite framework, minimizing the formation of extra-framework aluminum. These crucial structural properties were retained in the final H-form zeolite catalyst even after ion exchange and calcination. The intrinsic advantages of HS-MCM-22 for acetylene aromatization were investigated using acetylene adsorption in-situ FT-IR spectroscopy and benzene-TPD. The in-situ FT-IR results revealed that HS-MCM-22 favored the formation of aromatic intermediates over coke precursors. Furthermore, benzene-TPD revealed that the lower activation energy for the desorption of a representative product benzene was observed in HS-MCM-22. This enhanced desorption rate of the product is crucial to suppress secondary and side reactions, leading to catalyst deactivation and coke formation. These catalytic advantages are attributed to the higher density of Brønsted acid sites and the shorter diffusion length inherent in the hollow sphere macroporous architecture. Consequently, the rationally designed catalyst exhibits significantly improved activity and stability in aromatization reactions. © 2025 Elsevier B.V.

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