Synthesis and characterization of GaZSM-5 with different Si/Ga molar ratio and its catalytic performance in the MTH reaction

GaZSM-5 molecular sieve catalysts with different Si/Ga molar ratios were prepared with hydrothermal synthesis method followed by acid exchange and pelletization. The catalyst samples were characterized using XRD, SEM, FT-IR, XPS, ICP, low temperature N₂ physical adsorption and desorption, NH₃-TPD and Py-FTIR. The catalytic performance in the reaction of methanol to hydrocarbons was evaluated in a fixed bed reactor system. The results indicated that there were two kinds of gallium species, i. e. Ga in the framework Ga and Ga₂O₃ species on the crystal surface. The catalysts synthesized from SiO₂/Ga₂O₃ (60/1) gel with modest acidity (0.62 mmol NH₃/g and the ratio of B/L 4.88) and large mesopore volume of 0.51 cm³/g had the best catalytic stability. Under the same reaction conditions, the lifetime of GaZSM-5 catalyst was 456 h. The acid strength of GaZSM-5 was weaker than that of AlZSM-5, which could inhibit the coke formation. The intercrystalline mesopores of the nano GaZSM-5 crystal improved the diffusion property as well the catalyst stability. The GaZSM-5 lifetime was prolonged by 120 h.