Effects of Acid Sites on Thin MCM‐22 Zeolite Catalysts and Their Catalytic Applications for Acetylene Aromatization

Abstract

Two types of thin zeolite MCM‐22 catalysts were prepared by using a carbon sphere template. By applying different calcination methods, a hollow sphere‐type MCM‐22 catalyst (HS‐MCM‐22) and a nanosheet‐type MCM‐22 catalyst (NS‐MCM‐22) were synthesized. Those catalysts were tested and evaluated for acetylene aromatization to see the effects of thin structures. The two types of thin catalysts were found to have higher amounts of acid sites than those of the conventional MCM‐22 catalyst. It was found that the extremely short diffusion length not only enhanced the aromatic yield, but also suppressed the formation of graphitic coke. Notably, the diffusion length of NS‐MCM‐22 was found to be at least 15 times shorter than that of conventional MCM‐22, leading to an 11% and 18% increase in benzene yield, respectively. The thin structure seemed to help the produced aromatics efficiently desorb before they were further converted into carbon precursors and coke. According to the thermogravimetric analysis, the carbon species in the spent thin catalysts were found less graphitic than that of the conventional MCM‐22 catalyst. Because of this, the thin MCM‐22 catalysts were believed to show higher coke removal capability. Especially, the coke removal rate of NS‐MCM‐22 was estimated over 90% despite the severe carbon deposition during the reaction.