| 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. |
