Kotaro Miyazaki

Preparation and structure of a single Au atom on the TiO2(110) surface: control of the Au–metal oxide surface interaction

Three-dimensional Au structures on bare and organic-compound-modified TiO2(110) surfaces were interrogated by Au L3-edge polarization dependent total reflection fluorescence X-ray absorption fine structure (PTRF-XAFS) spectroscopy. On the bare TiO2(110) surface, icosahedral Au55 nanoclusters were the main product found. When the surfaces were modified with ortho or meso mercaptobenzoic acid (o-MBA or m-MBA), Au was atomically dispersed. Sulfur atoms in the o- and m- MBA formed strong covalent bonds with Au to produce stable Au-MBA (o- and m- forms) surface complexes. On the other hand, only oxygen atoms on the surface did not make a strong enough interaction to stabilize the Au species. We discuss how the Au species formed on the modified TiO2(110) surface and the possibility to control the Au structure by the surface modification method.

Fine tuning and orientation control of surface Cu complexes on TiO2(110) premodified with mercapto compounds: the effect of different mercapto group positions

Three-dimensional structures of vacuum-deposited Cu species formed on TiO2(110) surfaces premodified with three mercaptobenzoic acid (MBA) isomers were studied using polarization-dependent total reflection fluorescence X-ray absorption fine structure (PTRF-XAFS). We explored the possibility of fine tuning and orientation control of the surface Cu structures, including their coordination and configuration against the surface, according to the different mercapto group positions of the three MBA isomers (o-, m-, and p-MBA). Almost linear S-Cu-O (lattice O of TiO2) surface compounds were formed on the three MBA-modified TiO2(110) surfaces; however, the orientation of the Cu species on the o- and m-MBA-modified TiO2(110) surfaces (40-45° inclined from the surface normal) was different from that on the p-MBA-modified TiO2(110) surface (60° from the surface normal). This work suggests that the selection of a different MBA isomer for premodification of a single crystal TiO2(110) surface enables fine tuning and orientation control of surface Cu complexes.

Combined in situ analysis of Ni2P/MCM-41 under hydrodesulfurization conditions ? Simultaneous observation of QXAFS and FTIR ?

Supported Ni2P catalysts are efficient for the hydrodesulfurization (HDS) of liquid fuels. In situ extended x-ray absorption fine-structure (EXAFS) analysis of the Ni2P catalyst under realistic HDS conditions revealed the formation of Ni-S bonds in the catalyst system. In order to identify the origin of these bonds, a quick x-ray absorption fine structure (QXAFS) system was set up, which enabled measurement of one Ni K-edge EXAFS spectrum in 10 sec. In addition, a Fourier transform infrared (FTIR) unit was incorporated to the QXAFS system, which allowed simultaneous measurements of XAFS and IR spectra on the same sample. The catalyst (12.2 wt% Ni2P/MCM-41) was activated under H2 at 723 K to regenerate an active phosphide phase. After activation, a reaction gas mixture (thiophene/He/H2 = 0.1/1.9/98, at a total flow rate of 102 ml/min) was introduced. Under the reaction conditions, there was a change in the pre-edge area of XANES, which corresponded to the evolution of Ni-S bonds in EXAFS. The simultaneous measurements of XANES and IR revealed that this Ni-S could be attributed to the formation of a Ni phosphosulfide species rather than bonding between Ni and S of adsorbed thiophene. The combined in situ techniques proved to be an effective tool for the characterization of working catalysts.