Page 97 - Principles of Catalyst Development
P. 97

84                                                       CHAPTER  5
            faster into understanding the principles of catalyst design.  If nothing more,
            the organization leads to a disciplined identification of critical features and
            structure  of background  material.  Often,  missing  pieces  in  the  puzzle  of
            data suggest  areas for further research.
                Discussion  on  process  development  in  Chapter  3  emphasized  the
            importance  of defining  the  process  need  and  identifying  the  objectives  to
            be achieved.  If these caIl  for  diffusional  or mechanical  modifications, then
            the design wiIl involve changes in preparation and formulation that optimize
            the  particle size,  pore structure, and strength.  In cases where resistance to
            deactivation must be improved, the solution is found through incorporation
            of chemical  or structural  promoters, or perhaps by  changing the shape  of
            pores.  Improvements in  regeneration call for the  incorporation of combus-
            tion additives.
                In  all  these  situations,  catalyst  design  is  essentially  modification  of
            existing catalyst composition and structure. The procedure may be difficult
            but  is  a  fairly  straightforward  application  of  many  principles  discussed
            earlier. However, when an entirely new composition is  required, the catalyst
            designer  is  faced  with  selecting suitable  materials  for  further  testing.  The
            ease  with  which  this  is  done  depends  on  available  research  data.  In  the
            event  that  no  proven  process  technology  exists  as  a  guideline,  then  the
            search  must  turn  toward  totally  novel  and  untried  materials.  A  suitable
            active  component  must  be  found.  Other  factors  such  as  optimal
            activity,  selectivity,  lifetime,  and  formulation  are  subjects  for  future
            development.
                A  target  reaction  is  essential.  This  is  easiest  with  chemical  processes
            since the critical reaction is  easily identified. With petroleum and other fuel
            processes, so many reactions exist that some degree of lumping into reaction
            types,  perhaps with  model  compounds, is  necessary.
                We  now follow the original strategy of Dowden. (149) The distinct steps
            in  the  method are shown  in  Fig.  5.1.  These are as  follows:

                1.  Stoichiometric analysis.
                2.  Thermodynamic analysis.
               3.  Proposed molecular mechanism.
               4.  Proposed surface mechanism.
                5.  Reaction  path identification.
               6.  Necessary catalyst properties.
               7.  Search for  appropriate materials.
               8.  Proposed catalyst(s).

               Each  of these  steps  is  demonstrated  with  an  example,  selected  more
           for pedagogical purposes than  practicality.
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