and 10000 cm -1 , respectively. First, we carried out MM MD simulation of both the zeolites (pure siliceous) at 300 K to equilibrate the structures using the GULP package. In the equilibrated zeolite structure, one of the Si atoms is replaced by an Al atom in the preferred tetrahedral site and a proton was added to one of the O atoms in the AlO 4 tetrahedra as explained in the earlier. A methane molecule was also added into the system, and the entire system was equilibrated by QM/MM MD simulations at 300 K.