Metal clusters on ultrathin oxide films: model catalysts for surface science studies

Characterization and reaction kinetics studies have been performed over a variety of planar model supported catalysts prepared by the vapor deposition of catalytically interesting metals onto ultrathin oxide films on refractory metal single crystal substrates in ultrahigh vacuum. These unique systems feature many of the advantages for fundamental study associated with single crystals, while addressing important issues for supported catalysts, such as the intrinsic effects of particle size and the role of the support. The oxide thin films have been shown to roughly mimic the chemical and physical properties of the bulk analogs, and yet they are electrically conductive via defects and tunnelling to the single crystal substrate. This renders them amenable to the various charged particle spectroscopies that comprise the core of modern surface science; also, because they are flat as well conductive, they are suitable for scanning–tunnelling and atomic force microscopy. Characterization studies carried out over these models focusing on structural, electronic, and chemical properties as a function of particle size have been related to parallel studies of relevant catalytic reactions, providing fundamental insight into these processes at the atomic level. The select group of experiments presented here provides a broad illustration of the versatility and utility of these materials for elucidating the properties of small, supported metal particles and for simulating catalysis over ‘real world’ high surface area supported catalysts. q 1998 Elsevier Science B.V.