Abstract
Abstract An attempt is made to show that a coherent picture of electronic aspects of adsorption and surface reactions, including heterogeneous catalysis, is developing. It originates from an increased understanding of the adsorbate-induced electron structure and potential-energy surfaces of adsorbates derived from self-consistent Kohn-Sham-scheme calculations. For instance, the weakening or breaking of molecular bonds on metal surfaces get their explanation in terms of the lowering (raising), broadening, and filling (emptying) of molecular affinity (ionization) levels, occurring for molecules on the surface. Theoretical results for H2 on Mg(0001) are used to illustrate this point. The range of applicability of the picture has recently been extended considerably by results in the so-called Effective-Medium theory and similar schemes. Potential-energy surfaces of atoms and molecules on transition-metal surfaces can thereby be relatively simply calculated with a practically useful accuracy, and the role of the d-electrons can be understood. Trends in chemisorption properties along the transition-metal series can be explained. The qualitative picture can be used to analyse key features of potential-energy surfaces for surface reactions, in particular adsorption/desorption reactions. In this way the variations of reaction rates along the transition-metal series, variations between different faces of the same substrate, and the roles of defects, like steps, promoters and poisons, can be understood. The conclusions will be illustrated for the ammonia synthesis and the methanation reaction, model reactions in heterogeneous catalysis.
Published Version
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