The stability of H-ZSM-5, an active catalyst of hydration reaction of cyclohexene in the liquid phase, was studied under the hydrothermal conditions. The acidity and the activity were decreased with the passage of time at the higher temperature than 100-degrees-C. Al-27-NMR spectra of deactivated H-ZSM-5 showed the increase in the nonframework aluminum. From investigating the reactivation method of the deactivated catalyst, we were able to regenerate both original levels of acidity and hydration reaction activity by treating them with the dilute alkali aqueous solution at 80-degrees-C for 1 h and with the ion exchange with the nitric acid solution. The detailed change of the amount of H+, aluminum cation and aluminum hydroxide in the catalyst followed by repeated deactivation and reactivation were determined, the following facts became clear from the above results: (1) With H-ZSM-5 deactivating, H+ and aluminum cation decreased with dealumination from the framework, and the aluminum hydroxide increased. (2) While the catalyst reactivating, the elution and the rearrangement of nonframework aluminum took place at the same time. (3) By repeated deactivation and reactivation, the acidity and the activity was held the original value after the regeneration.
