Abstract
ZSM-5 (Zeolite Socony Mobil-5, patented by Mobil oil company in 1975) is a high silica zeolite with a MFI framework structure (Mobil Five) characterized by the formula |(Na x(H 2O) 16|[Al xSi 96−xO 192], where x < 27 (International Zeolite Association-IZA). It is composed of pentasil units which are linked to form pentasil chains connected via oxygen bridges to form corrugated sheets with 10-ring holes (Fig. 1). Oxygen bridges between these sheets result in a 3-dimensional system with straight 10-ring channels parallel to the corrugations (along y) and sinusoidal 10-ring channels perpendicular to the sheets (along x). The MFI 3D framework, consisting of straight and zigzag channels, is a rather complex zeolite framework type. The structure is orthorhombic (space group Pnma) at high temperatures, but a phase transition to the monoclinic space group occurs on cooling below the transition temperature, i.e., between 300 and 350 K. Because the pore openings are 10-rings (straight channels have...