Nanostructured, mesoporous Au/TiO(2) model catalysts - structure, stability and catalytic properties.

Aiming at model systems with close-to-realistic transport properties, we have prepared and studied planar Au/TiO(2) thin-film model catalysts consisting of a thin mesoporous TiO(2) film of 200-400 nm thickness with Au nanoparticles, with a mean particle size of ~2 nm diameter, homogeneously distributed therein. The systems were prepared by spin-coating of a mesoporous TiO(2) film from solutions of ethanolic titanium tetraisopropoxide and Pluronic P123 on planar Si(100) substrates, calcination at 350 °C and subsequent Au loading by a deposition-precipitation procedure, followed by a final calcination step for catalyst activation. The structural and chemical properties of these model systems were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N(2) adsorption, inductively coupled plasma ionization spectroscopy (ICP-OES) and X-ray photoelectron spectroscopy (XPS). The catalytic properties were evaluated through the oxidation of CO as a test reaction, and reactivities were measured directly above the film with a scanning mass spectrometer. We can demonstrate that the thin-film model catalysts closely resemble dispersed Au/TiO(2) supported catalysts in their characteristic structural and catalytic properties, and hence can be considered as suitable for catalytic model studies. The linear increase of the catalytic activity with film thickness indicates that transport limitations inside the Au/TiO(2) film catalyst are negligible, i.e., below the detection limit.