A Nanoscale Model Catalyst Preparation: Solution Deposition of Phosphine-Stabilized Gold Clusters onto a Planar TiO2(110) Support

Agglomeration of noble metal particles has been a long-standing obstacle in the preparation of planar, finely dispersed, metal cluster−oxide support model catalyst systems. A solution deposition method was devised. Six-atom gold clusters, in the form of [Au6(PPh3)6][BF4]2 (Au6L6), were deposited onto a TiO2(110) single crystal after an acetone pretreatment of the substrate and examined with scanning tunneling microscopy (STM), high-resolution electron energy loss spectroscopy (HREELS), and X-ray photoelectron spectroscopy (XPS). STM revealed single-unit entities of clusters ca. 1 nm in height, corresponding to the six-atom Au center with the triphenyl phosphine ligands attached. As a check on the success of the homogeneous dispersion, electron-stimulated desorption (ESD) was performed, irradiating the TiO2(110) surface with a 0.12 C cm-2 electron beam flux followed by STM, HREELS, and XPS. Evidence for ligand removal was shown by a pronounced reduction in height in the STM, a disappearance of the aromatic...