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Abstract

One goal of surface science studies is to unravel the changes in electronic and geometric structure a molecule experiences when bound to a substrate surface. In spite of the vast knowledge on molecular adsorbates on solid surfaces there are only very few examples where detailed and rather complete experimental information on the geometric and electronic structure has been collected. One example is the CO(2xl)p2mg/Ni(llO) system and we shall discuss this case to exemplify the power of electron spectroscopic studies in this respect. In light of the question "How do surface science studies contribute relevant information to mechanistic problems in catalysis?" we discuss the interaction of molecules with single crystal surfaces of metal and oxide surfaces as monitored with HREELS, IDS, ARUPS, XPS, and NEXAFS. We shall discuss the bonding of N₂ to a Fe(lll) surface as the prototype system for a small molecule on a metal surface. This system is of some importance with respect to ammonia synthesis. In connection with methanol synthesis from CO and H₂ the question of the role of CO₂ in the leading step of the mechanism has turned up. We consider systems where
CO₂ is known to chemisorb and discuss possible consequences for the above catalytic reaction. As an example for a rather complex reaction we shall discuss results for benzene on Os(OOOl) where we find interesting intermediate species on the way from molecular adsorption to complete dissociation. The overwhelming majority of catalytic reactions takes place on oxide surfaces. Molecular adsorbates on various oxides and their bonding towards the oxide surfaces are discussed and compared with metal surfaces. We consider NiO(lOO) and Cr₂0₃(lll) surfaces interacting with small molecules such as CO, NO, NO₂ and CO₂.