MODIFICATION OF SURFACE STRUCTURE BY SPILLOVER SPECIES: CONSEQUENCES IN THE REACTION OF SOLIDS AND CATALYSIS

Abstract

Transition metals can dissociate hydrogen to a surface mobile species called spillover hydrogen ( H so ). Similarly, oxides like α- Sb 2 O 4, BiPO 4, Bi 2 O 3 (donors) can dissociate molecular oxygen to a mobile surface species ( O so ). These metals or oxides are conveniently called donors. This article reviews effects which are due to spillover species when reacting with the surface of a solid distinct from the donors: (i) acceleration of the nucleation steps in the reduction of oxides, (ii) control of the nature of active sites on sulfides (e.g., MoS 2), and (iii) control of the adequate oxido-reduction state of the surface of the oxides active in selective oxidation. Atomic interpretations of the surface reactions explaining these effects will be given. It will be shown that all these phenomena are caused by the special reactivity of spillover species. Fundamental questions which could be solved by surface science approaches will be outlined.