endo- to exo-Isomerization of dicyclopentadiene over zeolites Original Research Article

The endo- to exo-isomerization of dicyclopentadiene was performed in liquid phase using acidic zeolites. Among the zeolites tested, the activity order is Hβ > HY > HUSY > HZSM-5 ≈ H-mordenite. Beta and Y-type zeolites exhibit higher activity because of their large three-dimensional channels. Surface passivation of Hβ confirms that the reaction proceeds in the inner channels. TG measurements verify that HY is deactivated very quickly because the strong acidity induces serious coke formation, but this phenomenon is much less over beta zeolites. Evaluation on Hβ with different SiO2/Al2O3 ratios indicates that both the weak Lewis acid concentration and isomerization activity of zeolites monotonically decrease with the SiO2/Al2O3 ratio. Thus a weak acid, especially a weak Lewis acid, of Hβ is responsible for the isomerization reaction. Calcination at 500 °C provides the highest activity due to complete removal of template residues, generation of large amounts of weak Lewis acid, and good crystal structure. The Hβ concentration was also studied: the optimal value is 15 wt%. Zeolites deactivated due to coke deposition can be regenerated by calcination in air flow at 500 °C, and there was no obvious activity loss after four times’ regeneration.