Page 103 - Principles of Catalyst Development
P. 103

90                                                        CHAPTER  5
           5.2.6.  Necessary Catalyst Properties

                This  step  is  merely  a  redefinition  of the  surface  mechanism  in  terms
           of properties  helpful  in  the  search  for  appropriate  materials.  The  catalyst
           must  have

                1.  Oxygen adsorption sites, leading to dissociation and immobile oxy-
                  gen  species.
               2.  Mild dehydrogenation sites that give CH 3  from CH 4  and remove H
                  from  the  intermediate.
               3.  Adjacent sites  in  order to  facilitate  the  final  dehydrogenation step.

           5.2.7.  Search for  Appropriate Materials

               The  requirement  for  mild  dehydrogenation  and  low  oxidation  elimi-
           nates  most  metals,  focusing  the  search  upon  oxides.  Figure  5.4  shows  a
           typical pattern of activity for dehydrogenation. (45)  High activity is  centered
           around ions with d and  d configurations. Mild dehydrogenation is found
                            4
                                   6
           in oxides containing ions such as Cu 2 +,  Ni 2 +,  Fe H ,  Mn2t, y3+, y5+, and Ti4+.
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                                              Co  0   CuO    ZnO
                                                3  4
                           Figure 5.4.  Dehydrogenation  patterns  in  oxides.
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