Deterioration Behavior of H-ZSM--5 and H-Mordenite under Hydrothermal Condition

Abstract

To investigate the origin of deterioration of H-ZSM-5 and H-mordenite, the active catalysts of reactions in the aqueous solution, such as cyclohexene hydration and trioxane sythetic reaction from formalin, the stability of both zeolites was studied under the hydrothermal conditions in the presence of only water at 130 °C.
The results showed the decreasing of the catalytic activity of trioxane synthetic reaction on the both zeolites.
The origins of deterioration of the activity were investigated by the change of the amount of acid and the hydrophobic nature determined by means of the adsorption method of aqueous 1-propanol solution.
On H-ZSM-5, the amount of acid was decreased by dealumination from the framework under the hydrothermal conditions at 130 °C, but the hydrophobic nature was not changed. It may be concluded that the decreasing of the activity was chiefly caused by reducing the amount of acid.
Dealumination of H-mordenite under the hydrothermal conditions was large at SiO₂/Al₂O₃ ratio of 57and very small at 90. However, the amount of acid in the pore within 12-membered oxygen rings, the ac-ti ve site, increased in the both mordenites. But the hydrophobic nature of two mordenites largely reduced. We may, therefore, reasonably conclude that the lowering of the hydrophobic nature was responsible for decreasing the activity of mordenite.