The optimal heterogeneous catalyst for an acid-base reaction

Abstract

I show that experimental Turn Over Frequencies published by Wachs et al. for acid-base and redox reactions of isopropyl-alcohol and methanol catalyzed by solid binary oxides can be organized into seven distinct volcano curves when described by a metal–oxygen bond strength EMO computed by DFT for the oxide unit-cell. Similarly to previously shown, the optimal EMO is interpreted as proportional to the gas phase enthalpy change of the reaction, now augmented by the enthalpic balance of proton exchanges occurring in adsorbed phase, i.e. the difference of Proton Affinities of the reactant and surface hydroxyls. The oxides surface proton affinities (SPA) are thus indirectly determined for the optimal descriptors EMO. The relationship SPA = f(EMO) is found to follow exactly the Shustorovich UBI-QEP version of the Bond Order Conservation Principle for Morse Potentials. The DFT descriptor EMO provides therefore a quantitative scale for oxides SPA, useful to predict the optimal catalysts for other acid-base or redox reactions catalyzed by oxides. An example of application is shown. Finally, a first extension of the theory to molecular catalysis is demonstrated.