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
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