Introduction

In recent years there have been considerable academic and industrial research efforts carried out in the field of zeolite catalysis. There are 34 known natural zeolites and about 100 zeolites which do not have natural counterparts have been synthesized. Of this large number of zeolites, only a few have found commercial application: they are mostly synthetic zeolites and synthetic-analog natural zeolites. Since zeolites were first used in petroleum processing in the 1960s, zeolite catalysis has undergone rapid and dynamic advances. A zeolite has been defined by Smith as a “crystalline aluminosilicate with a tetrahedral framework structure enclosing cavities occupied by cations and water molecules, both of which have enough freedom of movement to permit cation exchange and reversible dehydration”. However, because of the unique intercrystalline pore-channel systems and the excellent maintenance of catalyst activity of the new organic cation containing zeolites, applications in the organic chemical process industry are increasing.