Surface spectroscopic studies of model supported-metal catalysts

Abstract

A new surface science approach to the study of supported-metal catalysts will be described. Thin oxide films (~100 Å) of SiO2, Al2O3, or MgO supported on a refractory metal substrate (e.g., Mo or W) have been prepared by depositing the oxide metal precursor in a background of oxygen (ca. l×l0-5 Torr) [1]. The thin-film catalysts facilitate investigation by an array of surface techniques, many of which are precluded when applied to the corresponding bulk oxide [1,2]. In particular, the oxide films have been characterized by AES, ELS, HREELS, XPS, UPS, ISS, IRAS, and TD spectroscopies and shown to have essentially identical electronic and vibrational properties of the corresponding bulk oxides. These studies indicate then that these films can serve as convenient models for oxide catalysts or metal supports. Metal thin films (e.g., Cu, Pd, Ni) have subsequently been deposited onto the oxide films and the properties of the metal/oxide system then studied with the above array of surface techniques [3]. By properly defining the metal thin film thickness, metal particles of varying sizes can be synthesized with dispersions from a few nanometers to tens of nanometers.