USY zeolites with tunable mesoporosity designed by controlling framework Fe content and their catalytic cracking properties

Abstract

Tunable mesoporosity was successfully generated by introducing Fe cations into the framework of NaY as starting points, and then by sequential ammonium ion exchange and steaming deferrization–dealumination treatment. Accordingly, the pore diameter and volume of mesopores depended on the content of framework Fe. The zeolite products were characterized by a complementary combination of X-ray diffraction (XRD), N2 physisorption, TEM, DSC, Py-IR, and 27Al MAS NMR. The results show that the mesopore volumes of the Fe-induced mesoporous ultra-stable Y (USYFe) zeolites, which prepared via sequential deferrization-dealumination by steaming, are all higher than 0.21 cm3 g−1 with an additional thermal stability. The highest one reaches 0.23 cm3 g−1, over 53% of enhancement compared to USY (0.15 cm3 g−1) without deteriorating acidity. Furthermore, the most probable mesopore distributions can be finely tuned, typically in the range of 9–17 nm. In addition, it is found that large mesopores (8–50 nm) are surprisingly boosted with the increase in the Fe content used for the preparation of USYFe samples. In the catalytic cracking of adsorbate molecule of 1,3,5-triisopropylbenzene, the mesopores-enriched zeolites exhibit higher activity and lower deactivation tendency than USY with time on stream. The results demonstrated that the mesoporous material originating from the modification of zeolite with the pre-set Fe sites aided the diffusion into and out of the micropores via mesopores, and thus produced a positive influence on the catalytic performance.