Abstract: On the basis of the experimental investigation of 2-methylpentane cracking over USHY zeolite catalyst, we established a quantitative description to the mechanism of isomerization in 2-methylpentane catalytic cracking, by carefully examining the reactions of C₆⁺ carbenium ions in this reaction system. We find that at 400 ℃, hexyl carbenium ions undergo hydride addition from the feed 10 times faster than proton release to the Brфnsted base. This makes the isomerization of the feed a much faster reaction than the production of C₆ olefins. We also find that proton release from a C₆⁺ ion to the Brфnsted base requires a higher activation energy than a hydride transfer from the feed to the same ions. At high temperatures, isomerization is therefore reduced with respect to olefins production. The full picture of individual C₆⁺ ion structures and fates is presented, and the reaction pathways are quantified, giving an important insight into the causes underlying cracking selectivity.

Key words: 2-Methylpentane, Carbenium ion, Isomerization, Reaction mechanism