ATOMIC PROCESSES IN THE THERMAL-DESTRUCTION OF ZEOLITES AS INVESTIGATED BY MOLECULAR-DYNAMICS AND COMPUTER-GRAPHICS

The destruction processes of various zeolites, such as a silicalite wi th the ZSM-5 structure (SiO2-MFI), Cu-ZSM-5, and a silicalite with the faujasite structure (SiO2-FAU), with increasing temperature were inve stigated by using molecular dynamics and computer graphics methods. Th e mobility of atoms in SiO2-MFI was increased and the framework became unstable, as the temperature was increased. Finally the framework was destroyed to an amorphous phase. Increasing the Al content led to a d ecrease in the heat-resistance in Cu-ZSM-5. The change in the Si-O, Al -O, and Cu-Al distances as well as the change in the pairs of Si-O bon ds are discussed to clarify the mechanism of Cu-ZSM-5 destruction. The destruction process of SiO2-FAU was also investigated in order to und erstand the effect of framework structure, and it was suggested that t he presence of the 4-membered ring provides one of the reasons for the inferior heat-resistance of SiO2-FAU to that of SiO2-MFI.