Conversion of methanol to light olefins over nanosized [Fe,Al]ZSM-5 zeolites: Influence of Fe incorporated into the framework on the acidity and catalytic performance

摘要

Nanosized ZSM-5 zeolites (NZ5(x) series) with different SiO2/Al2O3 ratios as well as samples isomorphously substituted by Fe ([Fe,AI]NZ5(x) series) with various SiO2/(Al2O3+Fe2O3.) ratios were synthesized by an in situ seed-induced hydrothermal method. The structure, morphology, textural and acidity of catalysts were characterized via XRD, SEM, Al-27 and Si-29 MAS NMR, UV-vis spectroscopy, XPS, N-2 physical adsorption, NH3-TPD and Py-IR. The catalytic performance was assessed by methanol-to-olefins (MTO) reaction and the effect of the textural and acidity of the two series of samples on the catalytic performance was also investigated. The results showed that the catalyst acidity is closely related to the product selectivity in the MTO reaction. Compared with NZ5(x), the [Fe,AI]NZ5(x) samples with smaller particle size, weaker acid strength and fewer Bronsted acid sites displayed a higher selectivity towards C-2 similar to C-4 light olefins. Highest selectivity of 82.7% for C-2 similar to C-4 light olefins and lowest coke amount of 0.71% after reaction for 50 h was obtained for the [Fe,Al]NZ5(300) catalyst due to the appropriate acidity and improved diffusion properties.