Characterization of catalytic materials containing zeolites using n-hexane cracking reaction.

摘要

ZSM-5 zeolites precursors were synthesized by hydrothermal crystallization method from aluminosilicate gels in the presence of organic templates:---tetrapropyl ammonium bromide, and diethanolamine at temperatures of 175°C under autogeneous pressure. The materials were characterized by powder X-ray diffraction, Infrared spectroscopy, and benzene adsorption. The course of crystallization was followed by examining the X-ray diffraction pattern of the calcined samples and the optical density ratio of the bands at 550cm-1 and 450cm -1 in the mid IR region of the structure spectra as a function of crystallization time. For a well crystalline material, the optical density ratio is 0.70; this ratio was found to be less if amorphous silica is present in zeolite.;The X-ray, IR and n-hexane cracking activity data suggests that these zeolite precursors are microcrystalline solid material in amorphous matrix with structures similar to that of ZSM-5. The infrared spectroscopy results were correlated with other structural data obtained by X-ray diffraction, adsorption measurements, and also with the results of catalytic test.;The catalytic activity of the samples has been evaluated for the n-hexane cracking in tubular fixed bed reactor at the temperature range of 300°C to 500°C. The Cracking Mechanism Ratio (CMR) calculated reveals that the n-hexane cracking reaction over the catalyst tested proceeds predominantly via protolytic route and catalytic activity of the TPABr-mediated samples increases with crystallinity. Apparent activation energies are remarkably similar in spite of differences in relative level of activity.