Shushi Suzuki

Study of pyridine and its derivatives adsorbed on a TiO2(110)–(1×1)surface by means of STM, TDS, XPS and MD calculation in relation to surface acid[ndash ]base interaction

Pyridine, benzene, 2,6-dimethylpyridine (2,6-DMP), and m-xylene molecules adsorbed on a TiO2(110)–(1×1) surface have been characterized by scanning tunneling microscopy, thermal desorption spectroscopy, X-ray photoelectron spectroscopy, and molecular dynamics calculation to explore the structural features of acid–base interaction, which is relevant to acid–base catalysis of metal oxides. Individual pyridine and 2,6-DMP admolecules were successfully visualized by STM at room temperature. Those probe molecules were only weakly adsorbed on the surface and desorbed near room temperature. The absence of chemical bonds between the nitrogen atoms of adsorbed pyridine and 2,6-DMP and the Ti4+ atoms exposed to the surface was suggested, despite the presence of enough space for bonding on the Ti4+ atoms at the surface.

Compositional control of AuPt nanoparticles synthesized in ionic liquids by the sputter deposition technique

Bimetallic alloy nanoparticles (NPs) are attractive materials for exploring advanced functions to reduce consumption of resources and energy. AuPt alloy NPs are of special interest for their potential applications to fuel cells, because of the reduction of CO poisoning on Pt. Here, we report the synthesis of AuPt alloy NPs by sputter deposition into (N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl) amide (TMPA-TFSA). Transmission electron microscopy (TEM), X-ray fluorescent spectroscopy (XRF) and X-ray diffraction (XRD) measurements showed that changes in particle diameters and compositions of AuPt bimetallic NPs, were controllable by choosing initial compositions of metal targets for the sputter deposition. By cyclic voltammetry measurements, the detection of an anodic peak corresponding to the methanol oxidation reaction on the AuPt NPs demonstrated the presence of an AuPt alloy phase in the NPs.

STM visualization of site-specific adsorption of pyridine on TiO2(110)

Pyridine molecules adsorbed on a TiO2(110)-(1 x 1) surface were visualized by scanning tunneling microscopy (STM). Direct evidence of coordination-controlled adsorption on a metal oxide surface is reported for the first time. A pyridine molecule was more strongly adsorbed on a four-fold coordinated Ti atom exposed at single-atom-height step edges than on the five-fold coordinated Ti site over the perfect (110) terrace. Furthermore, the activity of the four-fold coordinated Ti sites at step edges was strongly dependent on the orientation of the step in azimuth. Sequential imaging of the pyridine-exposed surface revealed that terrace-adsorbed molecules were transformed to step-bonded species and vice versa even at room temperature.

The selective adsorption and kinetic behaviour of molecules on TiO2(110) observed by STM and NC-AFM

In the present paper we report a kinetic aspect of molecules on terraces and steps of a TiO2(110)-(1×1) surface as observed by scanning probe microscopy, which may be relevant to oxide catalysis. When the TiO2 surface, heated at 400–450 K, was exposed to a formic acid ambient of 1–2×10-6 Pa, small particles were formed on terraces. Post-reaction STM observation revealed that the particle formation was strongly suppressed in the vicinity of single-atom height steps. The suppressive effect of the steps ranged 2.4 nm into the terrace. Formate ions (a possible reaction intermediate) were imaged in-situ during formic acid exposure at the reaction temperature. The local density of the formates and hence the product distribution, which were very low near the steps, were simulated by a model. The particles produced were suggested to be carbonates, CO32- on the bridging oxygen atoms of the TiO2(110) surface.

Identification of individual 4-methylpyridine molecules physisorbed and chemisorbed on TiO2(110)-(1 x 1) surface by STM

We succeeded in identifying geometries of 4-methylpyridine (4-MP) molecules adsorbed on a TiO2(110)-(1 x 1) surface based on sequential STM imaging. Characteristics in mobility, topographic height, and location allowed us to distinguish three adsorption states at room temperature: a chemisorbed state with the upright geometry (A1), a flat-lying state localized at specific sites (A2), and a flat-lying physisorbed state mobile over the surface (B). The concentration of A1 and A2 species was restricted at an order of 0.01 ML. The A2 state was related to the adsorption at oxygen vacancies resident on the vacuum-annealed surface. The present study demonstrates the promising ability of STM to identify the adsorption geometry of small probe molecules, 4-methylpyridine in the present case, and to provide atom-level information on the origin of acidic property of oxide surfaces.

The condensation reaction of pyridine on TiO2(110): STM observation in the presence of the reactant atmosphere

Abstract The thermally activated reaction of pyridine was studied by STM on a TiO 2 (110)–(1×1) surface. The unexpected condensation of weakly physisorbed pyridine was found. The formation and growth of the product particles were monitored in-situ on the surface heated at reaction temperatures (300–400 K) in the presence of pyridine atmosphere. A physisorbed pyridine molecule was activated at 350 K to form an intermediate, probably a partially dehydrogenated or chemisorbed state of pyridine. The intermediates aggregated into larger particles of nm size. A gas-phase or physisorbed pyridine molecule is also directly involved in the particle growth reaction.

A scanning tunneling microscopy observation of (√3x√3)R30° reconstructed Ni2P(0001)

A Ni2P(0001) single crystal surface has been studied in the framework of model catalysis with a low temperature scanning tunneling microscope (STM) under ultrahigh vacuum (UHV). We observed a previously unreported (√3×√3) R30° reconstruction and successfully recorded its atomically-resolved STM images. Two types of atomic arrangements have been found for this (√3×√3) R30° structure depending on annealing conditions during preparation. One shows a filled and the other one an empty network of polygons. Upon annealing to 940 K, only the latter empty type of structure has been observed.

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.

Structures and dynamic behavior of catalyst model surfaces characterized by modern physical techniques

This paper reports the visualization of mobile pyridine on the terraces and site-specific adsorption of pyridine on the particular step sites on a TiO2(110)-(1×1) surface by scanning tunneling microscopy (STM), the anisotropic structure and reactivity of molybdenum oxides dispersed on TiO2(110)-(1×1) characterized by polarization-dependent total-reflection fluorescence x-ray absorption fine structure (PTRF-EXAFS), and the energy dispersive and real-time images of Au mesh on Si(111) recorded by a new x-ray photoemission electron miscroscopy (XPEEM).

Polarization-Dependent EXAFS Measurements of an α-Molybdenum Trioxide Single Crystal

We observed the polarization-dependent XAFS of an α-MoO3 single crystal. Polarization-dependent XANES spectra change with the polarization direction and the 1s → 4d pre-edge peak is shown to be a good indicator for the Mo=O (double bond oxygen) bond direction. The three Mo–O bond lengths at 0.175, 0.195 and 0.223 nm can clearly be distinguished in the Fourier transforms of polarization-dependent EXAFS spectra. Curve-fitting analysis was carried out on a powder MoO3 spectrum based on the phase shift and amplitude functions derived from the polarization-dependent EXAFS spectra.