Effect of crystal size of ZSM-11 zeolite on the catalytic performance and reaction route in methanol to olefins

Abstract

ZSM-11 zeolite is a promising catalyst for methanol to olefins (MTO); however, its low catalytic stability limits its realistic application. Herein, various ZSM-11 zeolites with different particle sizes were synthesized. The particle size of ZSM-11 has a significant influence on the formation and evolution of reaction intermediates, thereby determining its catalytic performance in MTO. Notably, S-ZSM-11, with a smaller particle size (approximately 400 nm), showed remarkable propene selectivity and catalytic lifetime as high as 42.6% and 243 h, respectively. These values were significantly higher than those observed with larger particle sizes (> 1 µm). The results obtained from gas chromatograph (GC)-MS, 13C MAS NMR, and various isotope-labeling experiments indicated that reduction of crystal size, accompanied by the generation of more intracrystalline mesopores, inhibits the aromatic intermediates formation and decreases the aromatic-based cycle contribution. In contrast, the alkene-based cycle is relatively enhanced, resulting in higher yields of propene and C3+ alkenes. Moreover, ethene is mainly produced via the paring route due to the limitation of alkyl side-chain growth of methylbenzenes.Highlights: various ZSM-11 zeolites with different particle sizes were synthesized by the hydrothermal method. S-ZSM-11, with a particle size of approximately 400 nm, shows superior catalytic performance in methanol to olefins. The propene selectivity and catalytic lifetime reach as high as 42.6% and 243 h, respectively. Decrease of crystal size inhibits the formation of aromatic species and decreases the aromatic-based cycle contribution. Ethene is mainly produced via the paring route.