CHEMISTRY OF OLEFINS AT METAL-OXIDE SURFACES - A TOOL FOR SURFACE SCIENCE INVESTIGATION OF OXIDE CATALYSTS

The results of IR investigations of the adsorption of simple olefins (ethylene, propylene and isobutene) on a number of metal oxide catalysts are summarized. The spectroscopic features of molecularly adsorbed species interacting with the surface via H-bonding, via sigma-type electron donation over d0 cations and via sigma-type donation with pi-type back donation on d-electron-containing cations are briefly discussed. Evidence for surface reactivities including: i) oxidative breaking of the C = C bond; ii) hydroxylation of the C = C bond giving alkoxides; iii) proton induced cationic polymerization; iv) proton abstraction at the allylic position giving anionic allyl species; v) hydrogen abstraction at the allylic position giving radical-like allyl species; vi) adsorption with hydrogen transposition giving metal alkylidene species; is also discussed on particular surfaces.