Catalysis Reviews-Science and Engineering, Vol.57, No.4, 436-477, 2015
The Bronsted-Evans-Polanyi Correlations in Oxidation Catalysis
The experimental BrOnsted-Evans-Polanyi (BEP) correlations in the field of oxidation catalysis, describing both the liquid-phase reactions on metal complexes and especially the gas-phase oxidations on metal oxides including the O-2 isotopic exchange, were analyzed. It was shown that the rate of deep oxidations on metal oxides is determined by two thermodynamic parameters of a catalytic system: the heat of oxygen adsorption, Q(O2), and the heat of reaction, Q(r), which constitute a unified BEP descriptive parameter Q(uni) = (Q(r) - Q(O2)). The correlations based on the energy of chemical bonds that are cleaved or formed in the course of reaction are more limited and less predictive. Special attention was paid to the numerical value of the BrOnsted coefficient . It was found that for all oxidations, in both the liquid and gas phases, approximate to 0.5. Using the unified BEP descriptor Q(uni) with = 0.5, a universal correlation was plotted describing the rates of all reactions over all catalysts under consideration. An idea of considering the kinetic compensation effect as a part of an extended BEP correlation is suggested. One may think that this long-debated phenomenon may relate primarily to mechanistic features of the reaction rather than to the nature of catalyst. In conclusion, difficult questions arising from analysis of the BEP correlations are summarized.
Keywords:Bronsted-Evans-Polanyi relationship;Oxidation catalysis;Deep oxidation;Hydrogen atom transfer;Hydrogen abstraction;Isotopic exchange of O-2;N-2;H-2;Bronsted coefficient;Heat of oxygen adsorption;Compensation effect