Akane Suzuki

Design of catalytic sites at oxide surfaces by metal-complex attaching and molecular imprinting techniques

This paper attempts to summarize our recent studies on the chemical design and characterization of catalytic sites at oxide surfaces such as Nb monomer, dimer and monolayer on SiO2, Rh dimers on SiO2 ,T iO 2 ,A l 2O3, and MgO, and Au nanoparticles on TiO2(1 1 0), prepared by using suitable metal-complex precursors in a molecular scale. The paper also reports performances of new molecular imprinting catalysts, SiO2 overlayers/-Al2O3 and Rh–SiO2 overlayers/SiO2, designed by surface molecular imprinting techniques.

Energy-dispersive XAFS study on the decarbonylation process of Mo(CO)6 in NaY zeolite

The temperature-programmed decarbonylation process of Mo(CO)6 in NaY zeolite was studied by means of a time-resolved energy-dispersive XAFS method. The XANES analysis demonstrated that the decarbonylation proceeded by two successive steps via a stable intermediate which existed between 440 and 490 K. The curve fitting analysis of the EXAFS data revealed that the intermediate was a molybdenum monomer subcarbonyl species Mo(CO)3(OL)3 coordinated by three CO ligands and three oxygen atoms of zeolite framework (OL). Molybdenum dimer subcarbonyl species were not observed. This study demonstrated that the DXAFS technique is a powerful method to study the dynamic behavior of the Mo carbonyl species during decarbonylation process.

Time-Resolved Dispersive XAFS Instrument at NW2A Beamline of PF-AR

The configuration and performance of the time‐resolved dispersive XAFS (DXAFS) instrument, which has been constructed at the NW2A beamline of PF‐AR (KEK), are presented. The DXAFS instrument is mainly composed of a polychromator part, a position control part for sample, and a linear detector part. The Bragg‐ and Laue‐type polychromator crystal (Si(111) or Si(311)) is bent using the holder with fixed bending radius, in which the thermostated water is circulated to prevent the temperature change of crystal due to the heat load. The photodiode array (PDA) with and without phosphor screen is used as the linear X‐ray detector, and the minimum exposure time is 2 ms for the 1024‐element PDA. The phosphor screen on the PDA detector prevents the damage of the chip especially for high energy X‐rays but the existence reduces the energy resolution because of the scattering of the visible light converted on the phosphor. The DXAFS instrument was applied to the mechanistic study of the reduction processes of Cu support...

DXAFS study on the decarbonylation process of Mo(CO)6 in NaY supercages

The decarbonylation process of Mo(CO)6 in the NaY supercages was studied by means of a time resolved dispersive XAFS method during temperature programmed decarbonylation. XANES analysis demonstrated that the decarbonylation proceeded through two steps and that a stable intermediate existed between 440-490 K. The curve fitting analysis revealed that the intermediate was a molybdenum monomer subcarbonyl species coordinated by three CO ligands and three oxygen atoms of zeolite framework. Molybdenum dimer subcarbonyl species were not observed. This study demonstrated that DXAFS technique is a powerful method to study the dynamic behaviour of the Mo carbonyl species during decarbonylation process.

Time‐Resolved DXAFS Study of Adsorption and Release of Hydrogen on Pt/MCM‐41

We have clarified the adsorption and release mechanism of hydrogen to/from Pt clusters on an MCM‐41 surface by using the XAFS technique. After reduction, the icosahedral Pt13 cluster of r(Pt‐Pt) =0.273 nm is formed. In contrast, a very small oxidized metal particle of r(Pt‐Pt) = 0.254 nm is formed after the oxidation. We have measured time‐resolved energy dispersive XAFS in order to clarify the adsorption and release mechanism of hydrogen to/from Pt clusters on an MCM‐41 surface. Although the reduction process can be explained as the sum of the initial and the final species, a third species should be considered in the oxidation process.

ジルコニウムを含むメソポーラスシリカZr-MCM-41の調製, キャラクタリゼーションおよび触媒特性

Zirconium--containing mesoporous silicas, Zr-MCM-41, were synthesized by two different methods. They were characterized by XRD, TEM, nitrogen adsorption and EXAFS and applied to the reaction for the peroxidative bromination of phenol red. In one method, we prepared Zr-MCM-41 by hydrolysis and condensation for the mixture of tetraethoxysilane (TEOS) and zirconium tetra-n-propoxide (ZTNP) in aqueous cetyltrimetylammonium bromide solution. EXAFS analysis revealed that zirconium species in this Zr-MCM-41 aggregated each other and formed the bonds of Zr-O-Zr. This catalyst had a low catalytic activity for the peroxidative bromination of phenol red. In the other method, ethanolic zirconium chloride solution and pure silica MCM-41 were used for impregnation. Zirconium species in this Zr-MCM-41 were highly dispersed as shown in the result of EXAFS analysis. This catalyst exhibited a high catalytic activity for the peroxidative bromination of phenol red. Zirconium species aggregated each other by calcination at 573 K, which caused reduction of catalytic activity.