Exploring the impact of synthetic strategies on catalytic cracking in hierarchical beta zeolites via hydrothermal desilication and organosilane-templated synthesis

Hierarchical zeolites can be synthesized by different strategies (e.g.top-down or bottom-up), resulting in the creation of mesoporosity with different configurations (inter-crystalline or intra-crystalline) in addition to unique properties that are often characteristic of the specific synthetic route. In this work, hierarchical beta zeolites with similar Si/Al ratios are obtained by a top-down hydrothermal desilication and a bottom-up organosilane-templated synthesis using both commercial and custom designed organosilanes. It is identified that the typically destructive nature of desilication can be offset by inducing recrystallization under hydrothermal conditions, while the organosilane soft-template route shows a disruptive effect where microporosity needs be sacrificed in order to obtain additional mesoporosity, a feature that is commonly associated with the top-down approach. The distinctive structural and porous features of these zeolites are presented, and their catalytic performances evaluated by the cracking of cumene and 1,3,5-triisopropylbenzene. The effect of mesopore configuration on catalytic activity and the merits (or lack thereof) of mesoporosity in improving catalytic performances will be discussed. The catalytic results demonstrate that a combination of intracrystalline mesoporosity and high crystallinity are necessary to achieve optimal performance for hydrocarbon cracking.