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 impacts on the deactivation process, 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 in 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.