Page 135 - Principles of Catalyst Development
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CATALYST PREPARATION 123
6.6.3. Metal Gauze
Platinum and silver gauze are used in ammonia and ml~thanol oxidation
to nitric oxide and formaldehyde, respectively. The gauze consists of fine
wire mesh of 0.5 mm diameter, supported as layers within the reactor.
Activation that "pits" the metal wire is necessary to enhance the active
83
surface area.o )
6.6.4. Honeycombed Monolith
The introduction of automobile exhaust catalysts in lthe United States
and elsewhere has produced a major market for platinum-type oxidation
and reduction systems. (184) An innovative consequence of this industry has
been the development of ceramic honeycombed monoliths as catalyst
supports. These structures contain long, parallel channels ofless than 0.1 mm
in diameter, with about 50 channels per square centimeter. The monolith
is composed of cordierite (2MgO . 2A1 20) . 5Si0 2 ) and is manufactured by
extrusion. (185) A wash coat of stabilized alumina is administered prior to
deposition of the active metal, either by adsorption or impregnation
methods.
These structures have high mechanical strength, good thermal stability,
and produce low pressure drop. Applications other than automobile exhaust
clean-up will no doubt be forthcoming.
6.7. COMMERCIAL MANUFACTURE OF CATALYSTS
A current list of commercial catalyst manufacturers is given in Appendix
7. These companies account for over three billion dollars worth of sales
annually.o86) They contribute skills, expertise, and know-how that are
unique and often the key to successful manufacturing. The business is highly
competitive and secretive. Very little is available in the' open literature
concerning specific technology as practiced· by these manufacturers.
Nevertheless, it is important to consider their methods and problems, their
expectations and limitations. If these factors are addressed early in catalyst
development, then not only are impractical paths avoided but designers
may find useful guidance from past experiences.
With the exception of particle formulations, catalyst manufacturing
follows the same paths already considered in this chapter, except on a larger
scale. In the laboratory, it is sufficient to make small batc:hes-a hundred
grams or a kilogram at the most. Even quantities this small often pose
difficult quality control and manipulation problems. When the development