Page 101 - Principles of Catalyst Development
P. 101

88                                                       CHAPTER  5

            selectivity.  Searching  further,  the  analysis  shows  a  possible  alternative
            reaction


                                                                          (5.2)

            involving  only  oxygen  insertion  and  dehydrogenation.  This  may  proceed
            directly or involve a  combination of the next  reaction,  with CH]OH as an
            intermediate  that  decomposes  via  the  last  reaction.  At  this  point,  one
           possibility  is  to focus  upon  equation  (5.2)  as  the  target.


           5.2.3.  Proposed  Molecular Mechanism
                The  purpose  of this  step  is  to  visualize  the  molecular events.  In  this
           case, the path is fairly simple, as shown in  Fig. 5.2. However, other examples
           may  have  any  number of proposed  molecular mechanisms,  with  each one
           a  starting  point  for  an  analysis  to  follow.  Some  discretion  is  needed  to
           differentiate  among competing possibilities.



           5.2.4.  Proposed Surface Mechanism
               This  is  the  point  where  prior  experience  of the  designer  and  some
           knowledge of existing surface chemistry is invaluable. Obviously the surface
           mechanism  is  just a guess,  but it  should be as  informed as  possible. There
           will be many possible surface schemes, each one leading to possible catalysts.
           If time  permits, a  number of these could be investigated. Otherwise, some
           priorities  must  be  assigned,  based  on  as  much  information  as  possible.
           Exercises  of this  type,  although  speculative,  often  have side benefits  since



                                          --- ....
                                        /'
                                      (  '"     "  \
                                      I   CH 0H  ,
                                            3
                                      \          I
                    G //'----/~
                       8                             9@







                             Figure 5.2.  Proposed  molecular mechanism.
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