Page 82 - Visions of the Future Chemistry and Life Science

Chemistry on the inside 71

taining materials have been prepared by three different routes. These mate-
rials are capable of the fast and efficient catalysis of several reactions with
excellent selectivity. Activity is greater than that found with the tradi-
tional amine-containing silicas, as is the stability of the catalyst, allowing
more product to be prepared with a given amount of catalyst. The increased
amount of amine groups which can be attached to the MTS materials gives
them even more of an advantage over the traditional catalysts. Initial
results on a catalyst with both amine and phenyl (non-polar) groups indi-
cate a substantial rate increase over the simple amine-only material. The
reasons for this are not yet understood, but may be due to improved trans-
port of reagents and products onto and off the surface. Many important
reactions can be carried out with such solid bases, and their uses in chem-
istry will increase. In particular, many reactions which either do not gen-
erate any side products or only generate water (condensation reactions) are
amenable to catalysis using these materials. Early work on such systems
indicates that the future for these materials is very rosy.
Sulphur-containing materials have been found to be excellent adsor-
bents for heavy metals. The sulphur atom is known to complex strongly to
heavy metal ions, with gold and mercury being two particularly interest-
ing examples. The higher amounts of sulphur which can be attached to the
MTS materials means that their capacity for binding these metals, and
removing them from e.g. drinking water, is much greater than that
achieved with traditional materials.
Solid acids can also be prepared from these materials by transforma-
tion of the sulphur group to the sulphonic acid, very closely related to sul-
phuric acid, one of the most commonly used acids industrially. The
material can be easily recovered and easily handled; since the acidity
resides within pores, it cannot come into contact with living tissue.
Important transformations, such as the formation of synthetic lubricants
and intermediates for fragrances, have already been reported using these
materials. The scope for such materials in future is enormous.
More sophisticated materials have been made by attachment of tran-
sition metal complexes to the surface. These materials are designed to
enhance the fundamental activity of the metal ion, by providing it with an
environment tailored to make it as active as possible, and to aid in its
recovery afterwards. The heterogenisation of such (normally homogene-
ous) complexes has attracted a lot of attention, since the heterogeneous
equivalents can be much more easily separated and recycled than the