![]() Cracking over hierarchical zeolites with nanocrystal sizes larger than about 50 nm took place under transition-limiting conditions, whereas the reaction over hierarchical zeolites with nanocrystal sizes of 15 or 30 nm proceeded under reaction control conditions. The reaction rate was first order with respect to the n-heptane concentration. The crystal size affected the textual properties of the catalysts but not the acidic properties of the catalysts. The effect of the crystal size on the catalytic cracking of n-heptane was investigated and the Thiele modulus and effectiveness factor were used to determine the reaction rate-limiting step. ![]() Hierarchical ZSM-5 zeolite aggregates with different sizes of nanocrystals were synthesized using different amounts of the mesoporogen 3-aminopropyltriethoxysilane. We also proposed a related model accordingly. The improved selectivity of both ethylene and propylene was then ascribed to the decreased diffusion resistance caused by the presence of secondary porosity, comparing with traditional ZSM-5. Additionally, the crystal size distribution of the hierarchical samples ranging from 250 to 330 nm did not influence the diffusion rate of light olefins. The results revealed that the dual functions of APTES and increasing amount of TPAOH favored for forming higher intercrystalline mesopore volume in the hierarchical ZSM-5 zeolites while maintained the micropores. Chemical and textural properties of samples were characterized by X-ray diffraction (XRD), N2 adsorption-desorption, scanning electronic microscopy (SEM), transmission electronic microscopy (TEM), inductively coupled plasma atomic emission spectroscopy (ICP-OES) and NH3 temperature programmed desorption (NH3-TPD). ![]() To investigate the effect of pore structure on catalytic cracking of n-heptane, hierarchical ZSM-5 zeolites with unchanged acidity were prepared by hydrothermal synthesis with organosilane ((3-aminopropyl) triethoxysilane, APTES) and tetrapropylammonium hydroxide (TPAOH) as double templates.
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