Supports
As
much research, work and care is involved in developing appropriate supports
as in developing the catalyst itself. In some cases the correct support is what
makes all the difference to the viability of a process.
A catalyst support should allow the catalyst to be highly dispersed on the
surface of the support. The support needs to be stable under reaction conditions,
and under the conditions needed for regeneration. It must not be affected
by any solvents used, or by the reactants or products.
oil refining catalysts, showing the variety of shapes used
Some
of the supports used are:
- Silica/alumina
- clays
- zeolites
- carbon-graphite,
- carbon black,
- activated charcoal
- titanium oxide
Important physical properties of a support include:
- surface area
- pore volume
- particle size
- shape
- good mechanical properties (so that it allows repeated recycling).
The photographs give some idea of the variety of catalyst forms developed
for different reaction systems.
Different
catalyst shapes and sizes
honeycomb
ceramic structure
for a fixed bed reactor (right) and a catalytic converter (above)
A
variety of supports developed for use in
Fuel
cells (below)
The
layer structure of montmorillonite
Surface areas of different supports
| Support material |
Surface area m2/g |
| silica gel |
300-600 |
| alumina |
100-300 |
| montmorillonites
(clay) |
50-300 |
| zeolites |
300-600 |
| charcoals |
300-1000 |
The
pore structure of a
zeolite (right)
New zeolites are being designed with larger pores and catalysts attached
to the internal surfaces (below)
This
is an area of active research and development. These two photographs show the
experimental development of carbon nanotubes as potential supports for metal
catalysts
