Synthesis and Catalytic Performance of Hierarchical Ultrastable Y-Type Zeolite with Ubstantially Increasing Acid Sites

Ultrastable Y-type (USY) zeolite catalysts with high acid content and high hydrothermal stability (USY-c-w) were obtained by crystallizing an industrial USY-zeolite in a traditional hydrothermal system with the help of a surfactant cetyltrimethylammonium bromide (CTABr). The physicochemical properties of as-synthesized USY-zeolite samples were analyzed by X -ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), solid-state NMR, N-2 adsorption-desorption, ammonia temperature programmed desorption (NH3-TPD), FT-IR, and pyridine infrared spectroscopy (Py-IR). Catalytic cracking of 1,3,5-triisopropylbenzene (TIPB) was selected as a probe reaction to investigate the catalytic performance of as-synthesized catalysts and compare it with that of the industrial USY-zeolite. The results exhibited that after hydrothermal re-crystallization, the framework of USY-zeolite suffered from a partial reformation. Desilicication by steam or alkali treatment results in the formation of a large number of silanol nests, which reacts with Al species resulting from the non-framework aluminum in the USY-zeolite and then promotes the formation of the"new"framework Al. This offers as-synthesized sample with a less Si/Al ratio (n(Si)/ n(Al)) and with increasing acid sites. The increased Al content in the zeolite framework was confirmed by the results of XRD, FT-IR, X-ray energy dispersive spectrum (EDS), and NMR. For example, the framework Si/Al ratio decreased from 10 (industrial USY-zeolite) to 3.0 (USY-045-07C). The NH3-TPD experiment and Py-IR provided direct evidence supporting the increased acidity in as-synthesized catalysts. Moreover, the results obtained by the N2 adsorption-desorption experiment, SEM, and TEM also showed that abundant mesopores were also introduced into as-synthesized samples with more weak acid sites along with more medium-strong acid ones. During the catalytic cracking of TIPB, as-synthesized USY-c-w showed more excellent catalytic performance with higher conversion of TIPB than the reference sample.