The best identified model for oxygenate yield = ?IJK#<9C# ()((* , shown in eq. 6 (Table ), depends on the surface RAE content under dry feed (L M,@"J OPQ ), the surface RAE oxidation state of the spent catalyst under UHV (c M,M>C OPQ ), the surface RAE oxidation state under dry feed (c M,@"J OPQ ), and on the relative amount of carbon assigned to C-C on the activated sample under UHV (ê 9BC DoD ). These parameters correlate with the availability of surface redox-active species, the surface redox activity and the importance of specific surface sites where reactants, reaction intermediates, or products might adsorb. The -4 ?IJ values increase from ethane to propane and n-butane oxidation (Fig. ).