The Brønsted–Evans–Polanyi relation and the volcano curve in heterogeneous catalysis

A number of elementary reactions at metal surfaces show a linear Brønsted–Evans–Polanyi relation between the activation energy and the reaction energy, and reactions belonging to the same class even follow the same relation. We investigate the implications of this finding on the kinetics of surface-catalyzed chemical processes. We focus in particular on the variation in the activity from one metal to the next. By analyzing a number of simple microkinetic models we show that the reaction rate under given reaction conditions shows a maximum as a function of the dissociative adsorption energy of the key reactant, and that for most conditions this maximum is in the same range of reaction energies. We also provide a database of chemisorption energies calculated using density-functional theory for a number of simple gas molecules on 13 different transition metals. An important part of the analysis consists of developing a general framework for analyzing the maximum rate. We use these concepts to rationalize trends in the catalytic activity of a number of metals for the methanation process.