Page 62 - Principles of Catalyst Development
P. 62

CATALYTIC  MATERIALS


            What  They Are







            It  has  been  said  that  everything  is  a  catalyst  for  something.  Although
            profound, the  statement  is  not very  useful  unless  materials  are  organized
            into  groups  with  common  properties,  explained  with  theories  or  models,
            and systematized into patterns from which new catalysts may be predicted.
            In  this  chapter we  examine  common  types  of catalytic materials,  current
            theories  underlining  their  mode  of action,  and  activity  patterns  useful  in
            design. Much of this is brief by necessity, but the interested reader will find
            sufficient  references  for  further  study.  For the  casual  reader,  this  chapter
            illustrates  the  complex background in  catalysis and testifies  to the  current
            attempts to  lift  catalysis from  an  "art" to  a  "science."





           4.1.  TYPES  OF  CATALYTIC  MATERIALS

                Catalytic  materials  fall  into well-defined  categories.  Although  we  use
            broader classifications than those given in  Chapter 1,  the motivation is  the
           same-to group according to common types  of activity and to explain the
            catalytic behavior on the basis of common properties.
               Table  4.1  is  a  list  of catalytic  materials  with  examples.  The  state  of
           each  catalyst is  a  consequence of process demands,  e.g.,  for  high  activity,
           or degree of interaction with other components. Classification by electrical
           conductivity, as  metals, semiconductors, and insulators, remains a satisfac-
           tory  method  in  treating  the  theoretical  background  and behavior patterns
           of these  widely differing materials.
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