Effect of n-Butanol Cofeeding on the Methanol to Aromatics Conversion over Ga-Modified Nano H-ZSM-5 and Its Mechanistic Interpretation

Ga-modified nano H-ZSM-5 zeolites with different Ga contents were prepared and applied as methanol-to-aromatics (MTA) catalysts. The Ga introduction can strongly increase the selectivity to aromatics but also decrease the catalyst lifetime simultaneously. Upon the cofeeding of n-butanol with methanol, a significant prolongation of the catalyst lifetime from 18 to ca. 50 h can be achieved. According to several spectroscopic results, e.g., TGA, GC–MS, in situ UV/vis, and solid-state MAS NMR spectroscopy, the addition of n-butanol during the MTA conversion shows no impact on the deactivation mechanism but can influence the dual-cycle mechanism. Namely, n-butanol preferentially adsorbs on Brønsted acid sites over methanol, followed by dehydration into n-butene. The formed n-butene can directly participate in the olefin-based cycle and, therefore, significantly alter the proportions of the dual-cycle mechanism. These results provide mechanistic insights into the roles of n-butanol cofeeding in the MTA conversion and exemplify a simple but efficient strategy to prolonged the catalyst lifetime, which is crucial to the industrial application.