Assessment of BEP relations for hierarchical modeoing of surface chemical kinetics

A first principles assessment of semi-empirical relations to predict chemical reactivity at different catalyst surfaces has been performed by means of periodic plane-wave Density Functional Theory (DFT) calculations. Semi-empirical methods are directly employed in the application of hierarchical multiscale methodology for the development of structure-dependent microkinetic models in heterogeneous catalysis. Thus, a rigorous assessment of their validity is a crucial requirement. In this work, Brønsted-Evans-Polanyi (BEP)-type correlation has been assessed by the analysis of different dissociation reactions. This relation is a useful tool to make a first estimation of the activation energy as a function of thermochemical parameters. The dissociation of CH, CH2, CO, CO2 and COOH molecule have been investigated on six different metals Ag, Cu, Ni, Pd, Pt and Rh and three low index surfaces (100), (110) and (111). The analysis has been performed according to a theory-to-theory comparison using periodic DFT with PBE ultrasoft exchange correlation functionals has been employed in the calculation of the activation energy of the Minimum-Energy-Path (MEP) for the investigated reactions. This analysis has shown the nature of the transition state (TS) to markedly affect the BEP relation. It has been observed that BEP relation can correlate well the activation energy of diatomic and triatomic dissociation reaction. This is due to the fact that the nature of the TS is similar on the whole range of conditions herein considered. COOH dissociation, instead, has shown significant differences in the nature of the TS among the different metal structures. As a result, on one side, BEP relation is no longer able to correlate the activation energies on the whole range of conditions, but only on the limited range of structures where the nature of the TS is similar. Thus, the nature of the TS is a crucial information for the application of BEP relations.