Effect of Steam Dealumination on H–Y Acidity and 2-Methylpentane Cracking Activity

Abstract

The relationship between 2-methylpentane cracking activity and the acid properties ofH–Y (acidic Y zeolite), H–USY (acidic ultrastable Yzeolite), steamed H–USY, and (H,NH4)–USY ((H,NH4)– ultrastable Yzeolite) was investigated. The acid strengthdistributions of these samples were determined by microcalorimetry of NH3adsorption, and thetypes of acid sites by FTIR spectroscopy. It was found that even for an H–Y sample of a highdegree of crystallinity, its cracking activity per unit catalyst weight was 35 times lower than thatof H–USY. With further steaming of H–USY, the cracking activity decreased, although theactivity per strong Brønsted site remained essentially constant. Interestingly, although thestrongly acidic Lewis acid sites were covered by NH3in (H,NH4)–USY, the catalyst had the sameactivity as H–USY. Also, the heat of NH3adsorption on (H,NH4)–USY did not exceed 130 kJ/mol. Thus, it was concluded that strong Lewis acid sites were not active for hydrocarboncracking, and that 2-methylpentane cracking did not require Brønsted sites with a high heat ofNH3adsorption. H–USY, with both Brønsted and Lewis sites, had a heterogeneous acid strengthdistribution, whereas zeolites containing only Brønsted sites had a homogeneous acid strength.