Study on a novel Zn-containing HZSM-5 catalyst for ethylene aromatization

Abstract

The Zn-modified HZSM-5 catalyst has been predominantly utilized in the aromatization reaction of light olefins, a crucial step in the conversion of coal-based methanol to aromatics (MTA). Nonetheless, the catalyst encounters a challenge wherein Zn species undergo migration, transformation, and subsequent loss, ultimately resulting in irreversible deactivation. To address this concern, we have developed a stable catalyst, ZnAl_1.5O/HZSM-5, which incorporates both spinel-structured ZnAl₂O₄ and ZnO species in HZSM-5 zeolite. The results demonstrate that the ZnAl_1.5O/HZSM-5 catalyst, with ZnO content of 0.69 wt.%, exhibits exceptional catalytic performance characterized by a significantly higher aromatization selectivity of 67.8 %, remarkable stability spanning 174.5 h, and a substantially lower Zn loss rate of 0.15 wt.%/h, when compared to other Zn-based catalysts. Despite the absence of aromatization catalytic activity in the pure spinel sample (ZnAl₂O₄-pure), it effectively aids in improving the dispersion of ZnO and facilitates reversible migration, which promotes ethylene aromatization (ETA) and enhances catalytic stability. Furthermore, the migration and capture mechanisms of Zn on the ZnAl_1.5O/HZSM-5 catalyst are also discussed.