FUNDAMENTALS OF GAS-SURFACE INTERACTIONS ON METAL-OXIDES

In an attempt to understand the fundamental ways in which Molecules in teract with metal-oxide surfaces, chemisorption has been studied on si ngle-crystal oxide samples. Chemisorption behavior is determined both by the electronic configuration of surface cations and by the geometri c structure of the surface. Stoichiometric, well ordered oxide surface s are, for the most part, relatively unreactive (although striking exc eptions exist). However, point defects, which consist predominantly of oxygen vacancies, significantly change the surface electronic structu re on most oxides and are the active sites for many types of chemisorp tion. The interaction between 02 and transition-metal-oxide surfaces i s determined primarily by cation electronic structure, while the disso ciation of H2O seems to be promoted by particular structural features at defect sites and is less sensitive to electronic structure. For org anic molecule chemisorption, a general feature of oxide surfaces is th e rather facile breaking of C-H bonds, but not of C-C bonds; this is i mportant in selective oxidation catalysis.