Three-dimensional structure analyses of Cu species dispersed on TiO2(110) surfaces studied by polarization-dependent total-reflection fluorescence X-ray absorption fine structure (PTRF-XAFS)

Three-dimensional analysis of structures for dispersed Cu species on a TiO2(110) surface has been performed by a polarization-dependent total-reflection fluorescence X-ray absorption fine structure (PTRF-XAFS) technique. The dispersed Cu species were prepared by a chemical reaction between Cu(DPM)(2) and a TiO2(110) surface and reduced with H-2. The Cu(DPM)(2) dissociatively adsorbed on the 2-fold site of bridging oxygen atoms of the TiO2(110) surface to form a Cu(DPM)(O-)(2) species. Subsequent reduction of the Cu species with H-2 at 363 K produced Cu-3 trimers that were bound to the bridging oxygen atoms with the trimer plane inclined at about 30degrees from the TiO2(110) normal. There were direct Cu-O bonds at the Cu-3 trimer/TiO2(110) interface in addition to Cu-Cu bonds. Further reduction at 473 K produced three-dimensional prismatic small Cu-6 clusters by vertical growth in the [110] direction of the Cu fee lattice. Orientations of the Cu-3 triangle and Cu-6 prism clusters may be regulated by the interaction between the Cu atoms and the bridging oxygen atoms on the anisotropic TiO2(110) surface.