Predominant effect of zeolite topology on hydrocracking pathways of 9,10-dihydrophenanthrene

The aim of this study is to reveal the topological effects of three industry-friendly zeolites of H-ZSM-5, H-USY, and H-Beta in 9,10-dihydrophenanthrene(9,10-DHP) hydrocracking under a mild reaction condition in a batch reactor. In which, there different zeolitic catalysts that vary in acidity and crystal size were used and a variety of hydrocracking products were detected, with distinct product distribution patterns observed. The precise product analysis has allowed for well-founded speculation on the hydrocracking pathways. The hydroconversion of 9,10-DHP is initiated through two primary routes: one involving bimolecular hydrogen transfer and the other characterized by monomolecular protolytic attack on the central rings. The key finding is that the relative influence of these two hydrocracking pathways is predominantly governed by the pore topological structure of the zeolites, though enhancing the acid density and reducing the crystal size have positive effect on inhibiting hydrogen transfer. It is noteworthy that the monomolecular protolytic attack is significantly more pronounced in zeolites with smaller pores compared to those with larger pores. Indeed, it is due to this pivotal factor that the predominant products formed over H-USY are mono-, di-, and tri-aromatics, whereas the product distribution over H-ZSM-5 is notably different, comprising over 90% of low-carbon alkanes and cycloalkanes. The reaction on H-Beta reflects the enhanced formation of benzene and lighter alkanes associated with both small- and large-pore structures facilitating ring-opening and dealkylation reactions. Furthermore, the H-ZSM-5 catalyst demonstrates a high conversion rate with a significantly lower level of carbon deposition compared to other 12 MR zeolites.