Complementary mechanistic properties of Fe- and Mn-doped aluminophosphates in the catalytic aerobic oxidation of hydrocarbons

A comparative computational study of the reaction mechanisms for hydrocarbon oxidations catalysed by Mn- and Fe-doped nanoporous aluminophosphates shows distinctive features for each transition metal depending on its electronic configuration. Preactivation of Mn catalysts is easier due to the higher stability of Mn-II, but its oxidation during propagation requires activation barriers. In contrast, preactivation of Fe is more difficult and avoids a direct Fe reduction because of the low stability of FeII. FeII is only produced at the end of the propagation cycle, favoured by an energetic compensation caused by the simultaneous exothermic oxidation of an alcohol molecule. Fe-catalysed propagation is kinetically favoured since it requires lower activation barriers, and is further assisted by higher adsorption energies of the reactants and lower desorption energies of the products on the active site. The mechanistic information gained can be used for the rational design of improved oxidation catalysts.