A Nanoscale Model Catalyst Preparation:Solution Deposition of Phosphine-Stabilized Gold Clusters onto a Planar TiO_2(110)Support

摘要

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 [Au_6(PPh_3)_6] [BF_4]_2(Au_6L_6), were deposited onto a TiO_2(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 TiO_2(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 v(C-H) intensity at ca. 3000 cm~(-1) in the HREEL spectra, and a +0.4 eV shift in the XPS Au 4f_(7/2), core level.