The difference c M,M>C OPQ -Ω M,e#C OPQ appears as an important ingredient in the model expressions for both = ?:#$â< ()((* and = ?IJK#<9C# ()((* models. Indeed, both targets are proportional to the absolute difference |c M,M>C OPQ -Ω M,e#C OPQ | in eqs. 5 and 6. Thus, the production of value-added olefins and oxygenate correlates with the change in surface RAE oxidation state that occurs from UHV to reaction conditions. This can be associated to the response of the catalyst to the environment and to the formation, on selective catalysts, of a surface termination layer that has different properties compared to the bulk phase.