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Co-immobilization of a Rh complex and a tertiary amine on the same silica surface enhances the hydrosilylation reaction of olefins. In our previous study, the silica-supported Rh complex-tertiary amine catalyst (SiO2/Rh-NEt2) showed higher activity than a silica-supported Rh complex (SiO2/Rh) alone. Herein, the influence of the amine on the local structure of the Rh complex was evaluated by DNP-enhanced solid-state 15N NMR spectroscopy and Rh K-edge XAFS measured at 20 K. The amine distorts the structure of the cyclooctadiene (COD) ligand in the Rh complex immobilized on the silica surface. The reactivity of the COD ligand with hydrosilane was confirmed by the in situ FTIR spectra, and it was found that the presence of an amine facilitates COD dissociation from the Rh center. This phenomenon accelerates the ligand exchange process in Rh-catalyzed hydrosilylation.

Organic molecular layers with viologen moieties as electron transfer mediators were constructed on hydrogen-terminated Si(111) surfaces, and metal catalysts for multielectron transfer reactions were incorporated into the molecular layers by immersing the viologen-modified Si(111) electrodes in aqueous solutions containing various metal complexes (K2PdCl4, NaAuCl4, and K2PtCl4). Significant enhancements were achieved for CO2 reduction at the Au-modified Si(111) electrode and for both hydrogen evolution reaction (HER) and CO2 reduction at the Pd-modified Si(111) electrode. X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) analysis showed that Au complexes were spontaneously reduced to metal nanoparticles during the metal insertion, and therefore, actual catalysts for CO2 reduction at the Au-modified Si(111) electrode were Au metal nanoparticles. In contrast, Pd complexes were inserted into the molecular layers and partly reduced during HER and CO2 reduction. Pd complexes and ...

Ni and Pt structures evaporated onto a TiO2(110) surface premodified with ortho-mercaptobenzoic acid (o-MBA) were studied using polarization-dependent total reflection fluorescence X-ray absorption fine structure analysis to determine the effects of the premodification on the dispersion of the metal atoms over the TiO2(110) surface. Ni was found to be atomically dispersed with the formation of S–Ni–O bonds (where the S is provided by the o-MBA and the O is present in the TiO2 lattice) on the surface. In contrast, Pt underwent aggregation to form small clusters. The varying behavior of these metals on the o-MBA-modified TiO2(110) surface is discussed based on the energy difference between sulfur–metal–oxygen and metal–metal bond formations, and we propose a new indicator for single metal dispersion on the TiO2(110) surface.

The structure of Au clusters on the TiO2(110) surface and the cluster-substrate interaction were investigated by polarization-dependent total reflection fluorescence X-ray absorption fine structure (PTRF-XAFS). The TiO2(110) (1 × 1) and (1 × 2) surfaces were compared in terms of substrate structural effects on Au cluster structure. We could not find evidence for the direct Au-substrate bonding and observed that the substrate morphology did not significantly affect the size and structure of Au clusters. Finally, we precisely determined that the Au clusters favored a geometry with icosahedral Au55 symmetry. We discuss the possible interaction mechanism between Au and TiO2(110) that leads to these results.

The effects upon the photophysical and photocatalytic properties of the codoping of rhodium and antimony in rutile-type TiO2 were investigated. TiO2 codoped with rhodium and antimony (TiO2:Rh/Sb) had an absorption band in the visible light region. Its energy gap was 2.1 eV. The TiO2:Rh/Sb powder showed photocatalytic activity for the oxidation of water to form O2 in the presence of Ag+ ions as an electron acceptor under visible light irradiation (λ > 440 nm), whereas TiO2 doped with only rhodium showed no activity. The photocatalytic activity strongly depended on the amount and ratio of the Sb/Rh dopant. Electron spin resonance, diffuse reflection spectroscopy, and X-ray absorption near-edge structure analyses revealed that the doped rhodium exists in a trivalent oxidation state in the active photocatalyst. The photocatalytic activity was decreased remarkably even by a small amount of Rh4+ ions. Antimony played an important role in suppressing the formation of Rh4+ ions by charge compensation. Thus, it ha...