Synthesis of gallium-containing ZSM-5 zeolites by the seed-induced method and catalytic performance of GaZSM-5 and AlZSM-5 during the conversion of methanol to olefins

Abstract Ga isomorphically substituted HZSM-5 and AlZSM-5 with different Si/Ga and Si/Al ratios were synthesized by a seed-induced hydrothermal in situ synthesis. This strategy significantly reduced organic templates in the synthesis process. Various techniques, including XRD, SEM, TEM, XRF, NMR, N2-sorption and H2-TPR, were used in the analogy of the Ga-containing ZSM-5 zeolites and AlZSM-5. The acidities were evaluated by NH3-TPD, Py-IR and acetonitrile-TPD in detail. The Bronsted acidity of GaZSM-5 was introduced by the framework incorporation of Ga atom, which led to a lower intrinsic acid strength than incorporation of Al atom. The effect of gallium incorporation into the MFI zeolite on the catalytic lifetime and the product distribution in methanol-to-olefins (MTO) was also investigated. GaZSM-5 showed a higher amount of Lewis acid sites than did AlZSM-5. More strong acid sites, Bronsted acid sites and a higher B/L ratio have been observed for the AlZSM-5 sample, which is related to the high olefin selectivity of AlZSM-5. ZSM-5 showed higher selectivity of C2H4 and C3H6 than GaZSM-5 samples at reaction temperature of 320 °C, a space velocity of 20 h−1 and reaction time of 8 h. The selectivity of C2H4 and C3H6 over the ZSM-5 samples reached 57%.