Molecular Sieve Zeolites

Abstract

A special class of porous hydrous aluminosilicates, some of which occur as minerals in nature and some others can be synthesized in the laboratory, has assumed great importance in the field of chemical technology during the last decade. These are known as molecular sieve zeolites. The structural elements characterizing such materials can conveniently be visualized in terms of conceptual linkages and building units of their aluminosilicate frameworks; they have been reviewed and a structural classification scheme has been proposed. The non-framework cations required for charge compensation can conveniently be exchanged to yield structures with pore dimensions permitting, on dehydration, size-and-shape grading and fractionation of gas or liquid mixtures on molecular scale. The useful properties of the as-synthesized and treated forms, like sorption, sieving, etc have been reviewed in the perspective of their technological applications. Intrinsic catalytic activity of some treated variants has been reviewed in some detail because of their extensive application to the petrochemical industry.