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fractional selectivity

in catalysis
The term selectivity(S) is used to describe the relative rates of two or more competing reactions on a catalyst. Such competition includes cases of different reactants undergoing simultaneous reactions or of a single reactant taking part in two or more reactions. For the latter case, S may be defined in two ways. The first of these defines a fractional selectivity, S F, for each product by the equation
S F = ξ i ∑ ξ i
The second defines relative selectivities, S R, for each pair of products by
S R = ξ i ξ j
In each case, ξ i and ξ j are the rates of increase of the extent of reactionsi and j respectively, i.e.
ξ i = d ξ i d t
ξ j = d ξ j d t,
where ξ i and ξ j are the extents of reactions i and j respectively.
PAC, 1976, 46, 71 (Manual of Symbols and Terminology for Physicochemical Quantities and Units - Appendix II. Definitions, Terminology and Symbols in Colloid and Surface Chemistry. Part II: Heterogeneous Catalysis) on page 81
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IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8.
Last update: 2014-02-24; version: 2.3.3.
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