Crystallite Size and Structure Sensitivity

Considerable efforts have been made over the years to discover if specific activity (and, where relevant, selectivity) are dependent on the size of the metal crystallites in a supported catalyst, which might be anticipated for several reasons. With use of regular shapes, such as the cubo-octahedron, as crystallite models the fractions of surface atoms with various co-ordination numbers can be calculated as a function of crystaUite size and show marked variation in the size range below The statistics of surface atoms and 

Takasu and A. M. Bradshaw in Chemical Physics of Solids and their Surfaces , ed., M. W. Roberts and J. M. Thomas (Specialist Periodical Reports), The Chemical Society, London, 1978, Vol. 7, p. 59. 

Therefore, it seems timely to survey recent studies where well characterized series of catalysts have been used with appropriate ranges of crystallite size, sometimes catalysts with ultra-dispersed metals, and generally prepared and used with an appreciation of the possible intmsion of adventitious factors, e.g., chloride residues, storage time, or conversion levels. 

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