Atomic processes in the thermal destruction of zeolites as investigated by molecular dynamics and computer graphics

Abstract

The destruction processes of various zeolites, such as a silicalite with the ZSM-5 structure (SiO 2-MFI), Cu-ZSM-5, and a silicalite with the faujasite structure (SiO 2-FAU), with increasing temperature were investigated by using molecular dynamics and computer graphics methods. The mobility of atoms in SiO 2-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 decrease 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 bonds are discussed to clarify the mechanism of Cu-ZSM-5 destruction. The destruction process of SiO 2-FAU was also investigated in order to understand the effect of framework structure, and it was suggested that the presence of the 4-membered ring provides one of the reasons for the inferior heat-resistance of SiO 2-FAU to that of SiO 2-MFI.