Examining the Linearity of Transition State Scaling Relations

Abstract

The dissociation of strong bonds in molecules shows large variations in the geometric structure of the transition state depending on the reactivity of the surface. It is therefore remarkable that the transition state energy can be accurately described through linear relations such as the Bronsted-Evans–Polanyi relations. Linear scaling relations for adsorbates with fixed structure can be understood in terms of bond order conservation but such arguments should not apply to transition states where the geometric structure varies. We have investigated how to relate the concepts from linear adsorption energy scaling to transition state energies. We expect that strong deviations from linearity only occur for very early or very late transition states. According to the Sabatier principle, the rate-limiting step of the best catalysts is not expected to be in either of these regions. Our results therefore support the use of linear transition state scaling relations for the optimization of catalysts.