Page 89 - Principles of Catalyst Development
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76                                                        CHAPTER  4
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                                SOLID              TRUNCATED
                             TETRAHEDRON           OCTAHEDRON













                                  FACE  OF  CUBIC  ARRAY
                                OF  TRUNCATED OCTAHEDRA
                                Figure 4.21.  Zeolite  building blocks.

                Third, ions introduced into cavities through ion exchange have separate
           activities of their own. Opportunities for dual functional catalysis involving
           acidity  with  other  activities  are  greatly  facilitated.(57)  These  three  factors
           have  made  zeolites  a  powerful  addition  to  the  arsenal  of  catalytic
           materials.( 135,136)
               Zeolites are built from basic units consisting of four oxygen ions packed
           like spheres (Fig.  4.21).  Interstices between the oxygen  ions are  filled  with
             3
           A1 +  and  Si +  ions  in  the  ratio  x: y.  By  joining  these  tetrahedra  together
                      4
           through  apical  oxygen  atoms,  a  truncated  octahedron  "sodalite"  unit  is
           produced.  With  this  as  a  building  block,  a  vast  number of structures  can
           be  produced.  For  example,  by  joining  them  through  the  four-membered
           faces  in  a  cubic array, the structure in  Fig.  4.21  results.  When two of these














                                          0.42  nm
                              Figure 4.22.  Structure  of type  A  zeolite.
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