Zeolite T (Linde type T) is a crystalline aluminosilicate with hexagonal symmetry. Its typical formula is 0.3Na 2O-0.7K 2O-Al 2O 3-6.9SiO 2-7.2H 2O. It corresponds to a disordered intergrowth of erionite and offretite structures in which the more open offretite (12-ring main channels parallel to the c-axis and 8-ring sub-channels normal to the c-axis with pore sizes of 0.67 × 0.68 nm and 0.36 × 0.49 nm, respectively) (Fig. 1) is interspersed at intervals with the tighter erionite units (8-ring channels parallel to the c-axis with pore size of 0.36 × 0.51 nm) (Spivey et al. 1992). The framework structures of offretite and erionite are closely related, and the synthesized zeolite T is mainly composed of the offretite phase with only small amounts of erionite sheets. Due to the specific position of single erionite unit cells at the end of the large pore of offretite, erionite controls the diffusion path by forcing the molecules to pass through the small 8-rings erionite rings. Pure erionite...