Study on Thermal Desorption of Aromatic Guest Molecules Adsorbed in Zeolites

Abstract

Thermal desorption for an aromatic guest molecule of phenanthrene adsorbed in Y and X zeolites exchanged with cations such as Na+, Tl+ and K+ has been studied successfully by means of TG-DTA and temperature programmed desorption (TPD)-MS. The thermal desorption of phenanthrene from the zeolites took place at temperatures between 300°C and 800°C. The temperature of thermal desorption depended critically on the cations in the order of the temperature of Na+<Tl+<K+. On the contrary, the activation energy for the desorption of phenanthrene estimated in terms of the Ozawa method, was almost the same for the three cation-exchanged Y zeolites with the approximate values of 120 kJ mol-1. On the other hand, the activation energy for the desorption of phenanthrene from the cation-exchanged X zeolites was the larger than that obtained from the Y zeolites, and was estimated as approximately 140 kJ mol-1. It is concluded that the activation energy for the desorption of phenanthrene from the zeolites does not directly correlate with the charge-compensating cation in the zeolites and depends strongly on the framework structures of the zeolites.