Abstract: Nano HZSM-5 crystal was synthesized directly by microwave-assisted hydrothermal route.The obtained products were characterized by XRD, FT-IR, SEM, BET and NH3-TPD techniques, and the effect of various crystallization temperatures and time on the crystal properties of HZSM-5 were investigated.The results indicate that crystallization temperature and time has significant impact on the micromorphology, crystal size and dispersibility of the synthesized products.HZSM-5 crystals with regular morphology are hard to form at lower crystallization temperature or shorter crystallization time.As crystallization temperature increases, the synthetic sample gradually changes into spherical grains, the grain size increases and the degree of dispersion improved.When the crystallization temperature increases to 180 ℃, the grain size became larger and the specific surface area decreases slightly.With the extension of the crystallization time, the micropores, mesopores, specific surface area and pore volume of the samples increases.When the crystallization time was further prolonged, the possible shrinkage of the micropores in the crystal and the growth of the grains made the pore volume and specific surface area of the sample decrease.The HZSM-5 molecular sieve crystals with spherical crystal size about 60 nm and excellent dispersibility was synthesized at 160 ℃ for 1.5 h by microwave hydrothermal route, and the obtained HZSM-5 possessed distinct physicochemical properties including high specific surface area of 398.45 m2·g-1, pore volume of 0.63 cm3·g-1, average pore diameter of 6.27 nm and the weak acidity on the surface of crystal.

Key words: Nano HZSM-5 crystal was synthesized directly by microwave-assisted hydrothermal route.The obtained products were characterized by XRD, FT-IR, SEM, BET and NH3-TPD techniques, and the effect of various crystallization temperatures and time on the crystal properties of HZSM-5 were investigated.The results indicate that crystallization temperature and time has significant impact on the micromorphology, crystal size and dispersibility of the synthesized products.HZSM-5 crystals with regular morphology are hard to form at lower crystallization temperature or shorter crystallization time.As crystallization temperature increases, the synthetic sample gradually changes into spherical grains, the grain size increases and the degree of dispersion improved.When the crystallization temperature increases to 180 ℃, the grain size became larger and the specific surface area decreases slightly.With the extension of the crystallization time, the micropores, mesopores, specific surface area and pore volume of the samples increases.When the crystallization time was further prolonged, the possible shrinkage of the micropores in the crystal and the growth of the grains made the pore volume and specific surface area of the sample decrease.The HZSM-5 molecular sieve crystals with spherical crystal size about 60 nm and excellent dispersibility was synthesized at 160 ℃ for 1.5 h by microwave hydrothermal route, and the obtained HZSM-5 possessed distinct physicochemical properties including high specific surface area of 398.45 m2·g-1, pore volume of 0.63 cm3·g-1, average pore diameter of 6.27 nm and the weak acidity on the surface of crystal.