Metal nanoclusters supported on metal oxide thin films: bridging the materials gap

Characterization and reactivity studies were performed on model catalysts comprised of metal clusters supported on metal oxide thin films. The thin films are prepared by vaporizing the parent metal onto a refractory metal substrate in an O-2 environment. The oxide films are sufficiently conductive via defects and tunneling to the substrate that the use of charged particle spectroscopies does not lead to any adverse charging effects. Numerous characterization techniques demonstrated that both spectroscopically and chemically these thin films are comparable to the analogous bulk metal oxides. Model supported catalysts were subsequently prepared by vapor-depositing catalytically-interesting metals onto these thin film oxide supports. This deposition method realizes tight control over cluster size and, therefore, represents an ideal approach to studying size-dependent chemical and physical properties. Reactivity studies established the validity of the supported systems as models of conventional catalysts. Furthermore, the use of these model catalysts provides a bridge between fundamental studies of single crystal reactivities and applied studies of high-surface-area catalyst activities.