Influence of Extra-Framework Aluminum Species on the Catalytic Properties of Acidic USY Zeolite in (Hydro)cracking Reactions

Extra-framework aluminum (EFAl) species are known to alter the acidic nature of zeolites and therefore their catalytic properties. Although it has been reported that the formation of such species leads to a change in the concentration and strength of acidity, the influence of those on hydrocracking warrants further exploration. To investigate these concepts, faujasite zeolite (ultrastable Y, USY) samples with various SiO₂/Al₂O₃ ratios were steamed at different conditions until they showed similar hydrocracking activity to the reference USY sample. The steaming process results in zeolite samples with similar catalytic activity and selectivity but different levels of EFAl. Hexane cracking tests and pentylamine adsorption followed by two-dimensional ¹H–²⁷Al heteronuclear nuclear magnetic resonance spectroscopy show that samples with a high number of EFAl sites have a larger number of those species in close proximity to the Brønsted acid site (BAS). After the extensive characterization, we concluded that the catalytic activity and product selectivity in hydrocracking is unrelated to both Brønsted acid strength and EFAl species near BAS, leaving the number of BAS as the main activity descriptor.