Selective catalytic cracking of n-hexane to olefins over SSZ-54 fabricated by facile and novel dual templating method

Abstract

A detailed study of the preparation of SSZ-54, an intergrowth of MTT and TON frameworks using a novel mixture of two templates; isopropyl amine (IPA) and 1,6-hexane diamine (DAH), was carried out. The characterization of the products done using X-ray diffraction (XRD), scanning electron microscopy (SEM) and aberration-corrected scanning transmission electron microscopy (Cs-corrected STEM) unveil assemblies of needles with spans of about 1 µm and 20–30 nm in thickness typical of structures of both MTT and TON frameworks, confirms the formation of SSZ-54. The amount of the structure directing agents, synthesis time and temperature were pivotal in the synthesis of SSZ-54 zeolite. Furthermore, we observed that the higher molecular weighted molecule (DAH) has more influence on the control of the metamorphosis of the SSZ-54 phase. To the best of our knowledge, this is the first application of intergrowth SSZ-54 in the production of light olefins especially propylene from the cracking of n-hexane. Although, initial activity of SSZ-54 is not the best among the three frameworks, its activity, nevertheless, is more stable as compared with its component frameworks (MTT and TON). Also, SSZ-54 zeolite showed high and stable olefin yield than both component frameworks irrespective of SiO2/Al2O3 (Si/Al2) ratio. The shape selective property of SZZ-54 zeolite to mainly olefins owing to its unique innate pore structure was demonstrated as the selectivity to BTX on SSZ-54 was minimized to ca. 1% over 10 h time-on-stream.