Search

Your search keyword '"Kido, Daiki"' showing total 47 results
Start Over Author "Kido, Daiki"
47 results on '"Kido, Daiki"'

2. Metastable structure of photoexcited WO$_{3}$ determined by the pump--probe extended X-ray absorption fine structure spectroscopy and constrained thorough search analysis

Author

Kido, Daiki, Uehara, Hiromitsu, Takakusagi, Satoru, Hasegawa, Jun-ya, Asakura, Kiyotaka, Uemura, Yohei, Wakisaka, Yuki, Koide, Akihiro, Yokoyama, Toshihiko, Niwa, Yasuhiro, Nozawa, Shunsuke, Ichiyanagi, Kohei, Fukaya, Ryo, Adachi, Shin-ichi, Jenkins, Harry, and Sato, Tokushi more...

Subjects
Condensed Matter - Materials Science
Abstract

We have determined the local structure of photoexcited metastable WO$_3$ created 150 ps after 400 nm laser irradiation by the pulse pump--probe L$_3$-edge extended X-ray absorption fine structure spectroscopy and the constrained thorough search analysis. We have found a highly distorted octahedral local structure with one of the shortest W=O bonds being further shortened to 1.66 \AA while the other five bonds were elongated even though theoretical calculations predicted the reverse change. We discuss this contradiction and propose a possible structure for the metastable state., Comment: 9 pages, 3 figures with SI more...

Published
2022

Catalog

Books, media, physical & digital resources
See catalog results

6. In situ Study on Structure of a Diluted Pt/HOPG Model Catalyst System Prepared by the Two-phase Liquid Reduction Method Using a Novel BCLA/HERFD+BI-XAFS Method

Author

Dong, Kaiyue, primary, Hu, Bing, additional, Rashid, Md Harun Al, additional, Lu, Bang, additional, Miyabayashi, Keiko, additional, Higashi, Kotaro, additional, Uruga, Tomoya, additional, Iwasawa, Yasuhiro, additional, Kido, Daiki, additional, Takakusagi, Satoru, additional, and Asakura, Kiyotaka, additional more...

Published
2024
Full Text
View/download PDF

9. The Effect of Structural Change during the Activation Process on the Catalysis of In/SiO2 Nonoxidative Coupling of Methane: An Operando XAFS Study

Author

Wada, Takahiro, primary, Kashaboina, Upendar, additional, Nishikawa, Yuta, additional, Wakisaka, Yuki, additional, Bao, Deling, additional, Takakusagi, Satoru, additional, Inami, Yuta, additional, Kuriyama, Fumiya, additional, Dipu, Arnoldus Lambertus, additional, Ogihara, Hitoshi, additional, Iguchi, Shoji, additional, Yamanaka, Ichiro, additional, Kido, Daiki, additional, Kimura, Masao, additional, Uo, Motohiro, additional, and Asakura, Kiyotaka, additional more...

Published
2023
Full Text
View/download PDF

10. The Effect of Structural Change during the Activation Process on the Catalysis of In/SiO2 Nonoxidative Coupling of Methane : An Operando XAFS Study

Author

Wada, Takahiro, Kashaboina, Upendar, Nishikawa, Yuta, Wakisaka, Yuki, Bao, Deling, Takakusagi, Satoru, Inami, Yuta, Kuriyama, Fumiya, Dipu, Arnoldus Lambertus, Ogihara, Hitoshi, Iguchi, Shoji, Yamanaka, Ichiro, Kido, Daiki, Kimura, Masao, Uo, Motohiro, Asakura, Kiyotaka, Wada, Takahiro, Kashaboina, Upendar, Nishikawa, Yuta, Wakisaka, Yuki, Bao, Deling, Takakusagi, Satoru, Inami, Yuta, Kuriyama, Fumiya, Dipu, Arnoldus Lambertus, Ogihara, Hitoshi, Iguchi, Shoji, Yamanaka, Ichiro, Kido, Daiki, Kimura, Masao, Uo, Motohiro, and Asakura, Kiyotaka more...

Abstract

A SiO2-supported indium catalyst (In/SiO2) has shown high performance for the nonoxidative coupling of CH4 (NOCM). Previous operando X-ray absorption fine structure (XAFS) studies revealed that the In/SiO2 catalyst undergoes dynamic structural changes during the activation process under flowing CH4, such as melting, new bond formation, and regeneration of the metallic form. To understand the effect of these dynamic changes, especially the formation of new bonds, on the catalytic properties, we examined the structures of an In/SiO2 catalyst during the activation process under various gas flows (CH4, H-2, and He) using operando XAFS. Fresh In/SiO2 catalysts are composed of metallic In particles covered with InOx. All of the samples melted at 430 K. In the XAFS spectrum of the sample under the He flow, peaks associated with the In-O bonds on the surface became visible at similar to 800 K. In was partially evaporated at 1100 K because of the formation of volatile In2O. When the gas was switched from He to CH4, the In/SiO2 was reduced to liquid-metal In. By contrast, in the In/SiO2 under the H-2 flow, the In-O bonds were removed at similar to 600 K. In the spectra of In/SiO2 under the CH4 flow, an In-X peak appeared at 800 K and then increased in intensity as the temperature was increased to 1100 K; this latter peak-increasing process was not observed under the He flow. The In-X peak was assigned to either In-CH3 formed via the reaction with CH4 or to In-O of surviving InOx species. The In-X peaks completely disappeared at 1100 K, and the catalyst became active toward the NOCM. Under all three gas-flow conditions, the liquid-metal In served as the active site during the reaction. The remarkable activity and long lifetime of the active site stem from the exceptional mobility and flexibility of the In atoms within the liquid metal. more...

Published
2023

11. Automatic Collection and Visualization of the Models Given by Thorough Search Analysis and Its Application to the MoO3 EXAFS Analysis

Author

Kido, Daiki, Wada, Takahiro, Asakura, Kiyotaka, Kido, Daiki, Wada, Takahiro, and Asakura, Kiyotaka

Abstract

The thorough search (TS) method was introduced to solve the problems in a conventional extended X-ray absorption fine structure analysis method. The TS method gives all possible and rational structures (structure candidates) which can reproduce the experimental data well in the parameter space. However, it still has difficulties how to decide the number of structure candidates without discretion and visualize the parameter sets with dimensions of more than 3. In this paper, we have applied the K-means method and principal component analysis and discussed its merits and drawbacks. more...

Published
2023

16. Metastable Structure of Photoexcited WO3 Determined by the Pump-probe Extended X-ray Absorption Fine Structure Spectroscopy and Constrained Thorough Search Analysis

Author

Kido, Daiki, primary, Uemura, Yohei, additional, Wakisaka, Yuki, additional, Koide, Akihiro, additional, Uehara, Hiromitsu, additional, Niwa, Yasuhiro, additional, Nozawa, Shunsuke, additional, Ichiyanagi, Kohei, additional, Fukaya, Ryo, additional, Adachi, Shin-ichi, additional, Sato, Tokushi, additional, Jenkins, Harry, additional, Yokoyama, Toshihiko, additional, Takakusagi, Satoru, additional, Hasegawa, Jun-ya, additional, and Asakura, Kiyotaka, additional more...

Published
2022
Full Text
View/download PDF

17. The Effect of Structural Change during the Activation Process on the Catalysis of In/SiO2Nonoxidative Coupling of Methane: An OperandoXAFS Study

Author

Wada, Takahiro, Kashaboina, Upendar, Nishikawa, Yuta, Wakisaka, Yuki, Bao, Deling, Takakusagi, Satoru, Inami, Yuta, Kuriyama, Fumiya, Dipu, Arnoldus Lambertus, Ogihara, Hitoshi, Iguchi, Shoji, Yamanaka, Ichiro, Kido, Daiki, Kimura, Masao, Uo, Motohiro, and Asakura, Kiyotaka more...

Abstract

A SiO2-supported indium catalyst (In/SiO2) has shown high performance for the nonoxidative coupling of CH4(NOCM). Previous operandoX-ray absorption fine structure (XAFS) studies revealed that the In/SiO2catalyst undergoes dynamic structural changes during the activation process under flowing CH4, such as melting, new bond formation, and regeneration of the metallic form. To understand the effect of these dynamic changes, especially the formation of new bonds, on the catalytic properties, we examined the structures of an In/SiO2catalyst during the activation process under various gas flows (CH4, H2, and He) using operandoXAFS. Fresh In/SiO2catalysts are composed of metallic In particles covered with InOx. All of the samples melted at 430 K. In the XAFS spectrum of the sample under the He flow, peaks associated with the In–O bonds on the surface became visible at ∼800 K. In was partially evaporated at 1100 K because of the formation of volatile In2O. When the gas was switched from He to CH4, the In/SiO2was reduced to liquid-metal In. By contrast, in the In/SiO2under the H2flow, the In–O bonds were removed at ∼600 K. In the spectra of In/SiO2under the CH4flow, an In–Xpeak appeared at 800 K and then increased in intensity as the temperature was increased to 1100 K; this latter peak-increasing process was not observed under the He flow. The In–Xpeak was assigned to either In–CH3formed via the reaction with CH4or to In–O of surviving InOxspecies. The In–Xpeaks completely disappeared at 1100 K, and the catalyst became active toward the NOCM. Under all three gas-flow conditions, the liquid-metal In served as the active site during the reaction. The remarkable activity and long lifetime of the active site stem from the exceptional mobility and flexibility of the In atoms within the liquid metal. more...

Published
2023
Full Text
View/download PDF

19. Photoinduced anisotropic distortion as the electron trapping site of tungsten trioxide by ultrafast W L-1-edge X-ray absorption spectroscopy with full potential multiple scattering calculations

Author

Koide, Akihiro, Uemura, Yohei, Kido, Daiki, Wakisaka, Yuki, Takakusagi, Satoru, Ohtani, Bunsho, Niwa, Yasuhiro, Nozawa, Shunsuke, Ichiyanagi, Kohei, Fukaya, Ryo, Adachi, Shin-ichi, Katayama, Tetsuo, Togashi, Tadashi, Owada, Shigeki, Yabashi, Makina, Yamamoto, Yusaku, Katayama, Misaki, Hatada, Keisuke, Yokoyama, Toshihiko, and Asakura, Kiyotaka more...

Abstract

Understanding the excited state of photocatalysts is significant to improve their activity for water splitting reaction. X-ray absorption fine structure (XAFS) spectroscopy in X-ray free electron lasers (XFEL) is a powerful method to address dynamic changes in electronic states and structures of photocatalysts in the excited state in ultrafast short time scales. The ultrafast atomic-scale local structural change in photoexcited WO3 was observed by W L-1 edge XAFS spectroscopy using an XFEL. An anisotropic local distortion around the W atom could reproduce well the spectral features at a delay time of 100 ps after photoexcitation based on full potential multiple scattering calculations. The distortion involved the movement of W to shrink the shortest W-O bonds and elongate the longest one. The movement of the W atom could be explained by the filling of the d(xy) and d(zx) orbitals, which were originally located at the bottom of the conduction band with photoexcited electrons. more...

Published
2020

22. Visualization of four‐dimensional X‐ray absorption fine structure data using a virtual reality system.

Author

Igarashi, Haruo, Kido, Daiki, Ishii, Yutaka, Niwa, Yasuhiro, Okamoto, Atsushi, and Kimura, Masao

Subjects
*VIRTUAL reality, *GEOMETRIC analysis, *MAGNETITE, *SERPENTINE, *ABSORPTION
Abstract

X‐ray spectromicroscopy is extensively utilized for nondestructive mapping of chemical states in materials. However, understanding and analyzing the geometric and topological aspects of such data pose challenges due to their representation in 4D space, encompassing (x, y, z) coordinates along with the energy (E) axis and often extending to 5D space with the inclusion of time (t) or reaction degree. In this study, we addressed this challenge by developing a new approach and introducing a device named `4D‐XASView', specifically designed for visualizing X‐ray absorption fine structures (XAFS) data in 4D (comprising 3D space and energy), through a multi‐projection system, within the virtual reality (VR) environment. As a test case for the new system, X‐ray spectromicroscopy measurements were conducted on a specimen prepared from serpentinized harzburgite sourced from the upper mantle section of the Oman ophiolite. Our 4D‐XASView facilitates the visualization and analysis of the geometric and topological aspects of the data using VR goggles, enabling detailed exploration of microstructures via rotation and zooming functionalities. This capability allows us to extract XAFS spectral data by selecting specific positions and regions, thereby aiding in the identification of `trigger sites' (magnetite in serpentine), which are characteristic locations within materials that substantially influence the macroscopic propagation of reactions. Our methodology establishes a new platform for analyzing 4D or 5D XAFS data that has applicability potential in various other multidimensional datasets, including microstructures coupled with spectroscopy and diffraction data. [ABSTRACT FROM AUTHOR] more...

Published
2024
Full Text
View/download PDF

23. Extracting the local electronic states of Pt polycrystalline films surface under electrochemical conditions using polarization-dependent total reflection fluorescence x-ray absorption near edge structure spectroscopy

Author

Wakisaka, Yuki, primary, Uehara, Hiromitsu, additional, Yuan, Qiuyi, additional, Kido, Daiki, additional, Wada, Takahiro, additional, Uo, Motohiro, additional, Uemura, Yohei, additional, Yokoyama, Toshihiko, additional, Kamei, Yutaro, additional, Kuroda, Seiichi, additional, Ohira, Akihiro, additional, Takakusagi, Satoru, additional, and Asakura, Kiyotaka, additional more...

Published
2020
Full Text
View/download PDF

24. Bent crystal Laue analyser combined with total reflection fluorescence X-ray absorption fine structure (BCLA + TRF-XAFS) and its application to surface studies

Author

Wakisaka, Yuki, primary, Hu, Bing, additional, Kido, Daiki, additional, Al Rashid, Md. Harun, additional, Chen, Wenhan, additional, Dong, Kaiyue, additional, Wada, Takahiro, additional, Bharate, Bapurao, additional, Yuan, Quiyi, additional, Mukai, Shingo, additional, Takeichi, Yasuo, additional, Takakusagi, Satoru, additional, and Asakura, Kiyotaka, additional more...

Published
2020
Full Text
View/download PDF

27. Evidence for Multi-Atom Resonance X-ray Raman Spectroscopy : An in situ Low Z-element and Bond-specific X-ray Spectroscopy

Author

Sirisit, Natee, Kido, Daiki, Wakisaka, Yuki, Ariga-Miwa, Hiroko, Takakusagi, Satoru, Asakura, Kiyotaka, Sekizawa, Oki, Sakata, Tomohiro, Uruga, Tomoya, and Iwasawa, Yasuhiro

Subjects
X-ray absorption fine structure, Synchrotron radiation, XAFS, Multi-atom resonance, In situ
Abstract

We have shown a possibility of multi-atom resonant X-ray Raman (MARX-Raman) spectroscopy by measuring the N K-edge loss spectrum of TaN at Ta L3-edge and C K-edge loss spectrum of Er(C5H5)3 at Er L1-edge. When the excitation X-ray energy was tuned to the Ta L3-edge and inelastic scattering spectra were recorded around 400 eV loss corresponding to the N K-edge Raman region, we found a clear enhancement of emission spectrum. The same enhancement was observed in C K-edge Raman region in Er(C5H5)3. These experimental results have indicated the possibility of MARX-Raman phenomenon which may lead to a new in situ and bond-speci_c XAFS spectroscopy for low Z elements. more...

Published
2018

28. Metastable Structure of Photoexcited WO3Determined by the Pump-probe Extended X-ray Absorption Fine Structure Spectroscopy and Constrained Thorough Search Analysis

Author

Kido, Daiki, Uemura, Yohei, Wakisaka, Yuki, Koide, Akihiro, Uehara, Hiromitsu, Niwa, Yasuhiro, Nozawa, Shunsuke, Ichiyanagi, Kohei, Fukaya, Ryo, Adachi, Shin-ichi, Sato, Tokushi, Jenkins, Harry, Yokoyama, Toshihiko, Takakusagi, Satoru, Hasegawa, Jun-ya, and Asakura, Kiyotaka more...

Abstract

The local structure of WO3photocatalyst in the photoexcited metastable state created 150 ps after laser irradiation have been determined by pump-probe L3-edge EXAFS and constrained thorough search analysis. A highly distorted octahedral local structure was found where one of the shortest W-O bonds was further shortened to 1.66 Å while the other five bonds were rather elongated even though theoretical calculations predicted the reverse change. We discuss this contradiction and propose a possible structure for the metastable state.The local structure of WO3photocatalyst in the photoexcited metastable state created 150 ps after laser irradiation has been determined by pump-probe EXAFS and constrained thorough search analysis. A highly distorted octahedral local structure was found, especially one of the shortest W-O was further shortened. We discuss contradiction with theoretical calculation and propose a possible structure for the metastable state. more...

Published
2022
Full Text
View/download PDF

29. Thorough Search Analysis of Extended X-ray Absorption Fine Structure Data for Complex Molecules and Nanomaterials Applications

Author

Kido, Daiki, Uemura, Yohei, Ariga-Miwa, Hiroko, Takakusagi, Satoru, Asakura, Kiyotaka, Kido, Daiki, Uemura, Yohei, Ariga-Miwa, Hiroko, Takakusagi, Satoru, and Asakura, Kiyotaka

Abstract

Extended X-ray absorption fine structure (EXAFS) plays an important role in the surface science and nanotechnology to characterize the non-crystalline materials using the curve fitting (CF) analysis. However, the CF has problems such as correlation between the structural parameters, the dependence on initial parameters, and the limitation of degree of freedom when EXAFS is applied to the complex system. In this paper, we propose a thorough search (TS) method to solve these problems. We analyzed EXAFS data for molybdenum oxide (alpha-MoO3) using the TS method. MO3 possesses a well-defined but complex local structure in which a central molybdenum (Mo) atom is surrounded by six oxygen (0) atoms. In CF analysis, the correlations of these six Mo-O bonds make it very difficult to derive reliable structural parameters from EXAFS data. In the TS analysis, the structural parameters regarded as a point (P) were surveyed thoroughly over a certain range. The goodness of fit was evaluated by R-factor. All P with R-factors less than a certain value were accepted. The accepted points P made a domain in which it was assumed that all points P in the domain should occur with equal probability and consequently their averages were used as representative structural parameters. If multiple independent domains were obtained, they were all regarded as possible candidates and the TS analysis provided possible structural parameters. The feasibility and advantages of the TS method were compared with the CF analysis and the micro reverse Monte Carlo method. more...

Published
2020

31. Photoinduced anisotropic distortion as the electron trapping site of tungsten trioxide by ultrafast W L1-edge X-ray absorption spectroscopy with full potential multiple scattering calculations

Author

Koide, Akihiro, primary, Uemura, Yohei, additional, Kido, Daiki, additional, Wakisaka, Yuki, additional, Takakusagi, Satoru, additional, Ohtani, Bunsho, additional, Niwa, Yasuhiro, additional, Nozawa, Shunsuke, additional, Ichiyanagi, Kohei, additional, Fukaya, Ryo, additional, Adachi, Shin-ichi, additional, Katayama, Tetsuo, additional, Togashi, Tadashi, additional, Owada, Shigeki, additional, Yabashi, Makina, additional, Yamamoto, Yusaku, additional, Katayama, Misaki, additional, Hatada, Keisuke, additional, Yokoyama, Toshihiko, additional, and Asakura, Kiyotaka, additional more...

Published
2020
Full Text
View/download PDF

33. Development of Surface Fluorescence X‐Ray Absorption Fine Structure Spectroscopy Using a Laue‐Type Monochromator

Author

Wakisaka, Yuki, Kido, Daiki, Uehara, Hiromitsu, Yuan, Qiuyi, Feiten, Felix E., Mukai, Shingo, 1000030359484, Takakusagi, Satoru, Uemura, Yohei, Yokoyama, Toshihiko, Wada, Takahiro, Uo, Motohiro, Sekizawa, Oki, Uruga, Tomoya, Iwasawa, Yasuhiro, 1000060175164, Asakura, Kiyotaka, Wakisaka, Yuki, Kido, Daiki, Uehara, Hiromitsu, Yuan, Qiuyi, Feiten, Felix E., Mukai, Shingo, 1000030359484, Takakusagi, Satoru, Uemura, Yohei, Yokoyama, Toshihiko, Wada, Takahiro, Uo, Motohiro, Sekizawa, Oki, Uruga, Tomoya, Iwasawa, Yasuhiro, 1000060175164, and Asakura, Kiyotaka more...

Abstract

Surface fluorescence X-ray absorption fine structure (XAFS) spectroscopy using a Laue-type monochromator has been developed to acquire structural information about metals with a very low concentrate on a flat highly oriented pyrolytic graphite (HOPG) surface in the presence of electrolytes. Generally, surface fluorescence XAFS spectroscopy is hindered by strong scattering from the bulk, which often chokes the pulse counting detector. In this work, we show that a bent crystal Laue analyzer (BCLA) can efficiently remove the scattered X-rays from the bulk even in the presence of solution. We applied the technique to submonolayer (similar to 10(14) atoms cm(-2)) Pt on HOPG and successfully obtained high signal/noise in situ XAFS data in combination with back-illuminated fluorescence XAFS (BI-FXAFS) spectroscopy. This technique allows in situ XAFS measurements of flat electrode surfaces to be performed in the presence of electrolytes. more...

Published
2019

35. Development of Surface Fluorescence X‐Ray Absorption Fine Structure Spectroscopy Using a Laue‐Type Monochromator

Author

Wakisaka, Yuki, primary, Kido, Daiki, additional, Uehara, Hiromitsu, additional, Yuan, Qiuyi, additional, Feiten, Felix E., additional, Mukai, Shingo, additional, Takakusagi, Satoru, additional, Uemura, Yohei, additional, Yokoyama, Toshihiko, additional, Wada, Takahiro, additional, Uo, Motohiro, additional, Sekizawa, Oki, additional, Uruga, Tomoya, additional, Iwasawa, Yasuhiro, additional, and Asakura, Kiyotaka, additional more...

Published
2018
Full Text
View/download PDF

36. A Demonstration of Pt L3-Edge EXAFS Free from Au L3-Edge Using Log–Spiral Bent Crystal Laue Analyzers

Author

Wakisaka, Yuki, primary, Kido, Daiki, additional, Uehara, Hiromitsu, additional, Yuan, Qiuyi, additional, Takakusagi, Satoru, additional, Uemura, Yohei, additional, Yokoyama, Toshihiko, additional, Wada, Takahiro, additional, Uo, Motohiro, additional, Sakata, Tomohiro, additional, Sekizawa, Oki, additional, Uruga, Tomoya, additional, Iwasawa, Yasuhiro, additional, and Asakura, Kiyotaka, additional more...

Published
2018
Full Text
View/download PDF

37. A Demonstration of Pt L-3-Edge EXAFS Free from Au L-3-Edge Using Log-Spiral Bent Crystal Laue Analyzers

Author

Wakisaka, Yuki, Kido, Daiki, Uehara, Hiromitsu, Yuan, Qiuyi, Takakusagi, Satoru, Uemura, Yohei, Yokoyama, Toshihiko, Wada, Takahiro, Uo, Motohiro, Sakata, Tomohiro, Sekizawa, Oki, Uruga, Tomoya, Iwasawa, Yasuhiro, Asakura, Kiyotaka, Wakisaka, Yuki, Kido, Daiki, Uehara, Hiromitsu, Yuan, Qiuyi, Takakusagi, Satoru, Uemura, Yohei, Yokoyama, Toshihiko, Wada, Takahiro, Uo, Motohiro, Sakata, Tomohiro, Sekizawa, Oki, Uruga, Tomoya, Iwasawa, Yasuhiro, and Asakura, Kiyotaka more...

Abstract

Pt-Au nanostructures are important and well-studied fuel cell catalysts for their promising catalytic performance. However, a detailed quantitative local structure analysis, using extended X-ray absorption fine structure (EXAFS) spectroscopy, have been inhibited by interference between Pt and Au L-3-edges. In this paper, Pt L-3-edge XAFS analysis, free of Au L-3 edge, is demonstrated for a Pt-Au reference sample using a low-cost log-spiral bent crystal Laue analyzer (BCLA). This method facilitates the EXAFS structural analysis of Pt-Au catalysts, which are important to improve fuel cell catalysts. more...

Published
2018

38. Photoinduced anisotropic distortion as the electron trapping site of tungsten trioxide by ultrafast W L1-edge X-ray absorption spectroscopy with full potential multiple scattering calculations.

Author

Koide, Akihiro, Uemura, Yohei, Kido, Daiki, Wakisaka, Yuki, Takakusagi, Satoru, Ohtani, Bunsho, Niwa, Yasuhiro, Nozawa, Shunsuke, Ichiyanagi, Kohei, Fukaya, Ryo, Adachi, Shin-ichi, Katayama, Tetsuo, Togashi, Tadashi, Owada, Shigeki, Yabashi, Makina, Yamamoto, Yusaku, Katayama, Misaki, Hatada, Keisuke, Yokoyama, Toshihiko, and Asakura, Kiyotaka more...

Abstract

Understanding the excited state of photocatalysts is significant to improve their activity for water splitting reaction. X-ray absorption fine structure (XAFS) spectroscopy in X-ray free electron lasers (XFEL) is a powerful method to address dynamic changes in electronic states and structures of photocatalysts in the excited state in ultrafast short time scales. The ultrafast atomic-scale local structural change in photoexcited WO3 was observed by W L1 edge XAFS spectroscopy using an XFEL. An anisotropic local distortion around the W atom could reproduce well the spectral features at a delay time of 100 ps after photoexcitation based on full potential multiple scattering calculations. The distortion involved the movement of W to shrink the shortest W–O bonds and elongate the longest one. The movement of the W atom could be explained by the filling of the dxy and dzx orbitals, which were originally located at the bottom of the conduction band with photoexcited electrons. [ABSTRACT FROM AUTHOR] more...

Published
2020
Full Text
View/download PDF

39. Capturing local structure modulations of photoexcited BiVO4 by ultrafast transient XAFS

Author

Uemura, Yohei, primary, Kido, Daiki, additional, Koide, Akihiro, additional, Wakisaka, Yuki, additional, Niwa, Yasuhiro, additional, Nozawa, Shunsuke, additional, Ichiyanagi, Kohei, additional, Fukaya, Ryo, additional, Adachi, Shin-ichi, additional, Katayama, Tetsuo, additional, Togashi, Tadashi, additional, Owada, Shigeki, additional, Yabashi, Makina, additional, Hatada, Keisuke, additional, Iwase, Akihide, additional, Kudo, Akihiko, additional, Takakusagi, Satoru, additional, Yokoyama, Toshihiko, additional, and Asakura, Kiyotaka, additional more...

Published
2017
Full Text
View/download PDF

41. Approach to Highly Sensitive XAFS by Means of Bent Crystal Laue Analyzers

Author

WAKISAKA, Yuki, primary, IWASAKI, Yuya, additional, UEHARA, Hiromitsu, additional, MUKAI, Shingo, additional, KIDO, Daiki, additional, TAKAKUSAGI, Satoru, additional, UEMURA, Yohei, additional, WADA, Takahiro, additional, YUAN, Qiuyi, additional, SEKIZAWA, Oki, additional, URUGA, Tomoya, additional, IWASAWA, Yasuhiro, additional, and ASAKURA, Kiyotaka, additional more...

Published
2017
Full Text
View/download PDF

42. Dynamics of Photoelectrons and Structural Changes of Tungsten Trioxide Observed by Femtosecond Transient XAFS

Author

Uemura, Yohei, Kido, Daiki, Wakisaka, Yuki, Uehara, Hiromitsu, Ohba, Tadashi, Niwa, Yasuhiro, Nozawa, Shunsuke, Sato, Tokushi, Ichiyanagi, Kohei, Fukaya, Ryo, Adachi, Shin-ichi, Katayama, Tetsuo, Togashi, Tadashi, Owada, Sigeki, Ogawa, Kanade, Yabashi, Makina, Hatada, Keisuke, 1000030359484, Takakusagi, Satoru, Yokoyama, Toshihiko, 1000080176924, Ohtani, Bunsho, 1000060175164, Asakura, Kiyotaka, Uemura, Yohei, Kido, Daiki, Wakisaka, Yuki, Uehara, Hiromitsu, Ohba, Tadashi, Niwa, Yasuhiro, Nozawa, Shunsuke, Sato, Tokushi, Ichiyanagi, Kohei, Fukaya, Ryo, Adachi, Shin-ichi, Katayama, Tetsuo, Togashi, Tadashi, Owada, Sigeki, Ogawa, Kanade, Yabashi, Makina, Hatada, Keisuke, 1000030359484, Takakusagi, Satoru, Yokoyama, Toshihiko, 1000080176924, Ohtani, Bunsho, 1000060175164, and Asakura, Kiyotaka more...

Abstract

The dynamics of the local electronic and geometric structures of WO3 following photoexcitation were studied by femtosecond time-resolved X-ray absorption fine structure (XAFS) spectroscopy using an X-ray free electron laser (XFEL). We found that the electronic state was the first to change followed by the local structure, which was affected within 200 ps of photoexcitation. more...

Published
2016

43. Can amine ligands atomically disperse Cu atoms on TiO2(110)? Cu deposition on TiO2(110) premodified with o-anthranilic acid

Author

Kim, Cho Rong, Maeda, Honoka, Lu, Bang, Nakamura, Yuto, Lin, Yunli, Wakisaka, Yuki, Kido, Daiki, Asakura, Kiyotaka, and Takakusagi, Satoru

Abstract

The three-dimensional (3D) structure of evaporated Cu atoms on a TiO2(110) surface premodified with o-anthranilic acid (o-AA) was examined using polarization-dependent total reflection fluorescence X-ray absorption fine structure (PTRF-XAFS) to elucidate the effect of the premodification on the Cu dispersion over the TiO2(110) surface. Cu was found to be atomically dispersed with the formation of N–Cu–O bonds (where the N is provided by the o-AA and the O is present in the TiO2lattice) on the surface, and the factors for controlling the atomic dispersion are discussed.Graphical AbstractThe three-dimensional structure of evaporated Cu atoms on a TiO2(110) surface premodified with o-anthranilic acid (o-AA) was examined using PTRF-XAFS spectroscopy to elucidate the effect of the premodification on the Cu dispersion over the TiO2(110) surface. Atomically dispersed Cu was formed on the surface with the formation of N–Cu–O bonds, and the factors for controlling the atomic dispersion are discussed. more...

Published
2024
Full Text
View/download PDF

44. What Is the Active Structure for High-Temperature Direct Dehydrogenative Conversion of Methane by the Supported NiP Catalysts-An in SituXAFS Study

Author

Wang, Qing, Iguchi, Shoji, Yamanaka, Ichiro, Ohta, Jin, Wada, Takahiro, Uo, Motohiro, Kido, Daiki, Kimura, Masao, and Asakura, Kiyotaka

Abstract

SiO2-supported NiP catalysts exhibit high activity for the direct dehydrogenative conversion of methane (DCM) to hydrocarbons, such as ethylene, ethane, acetylene, and propylene, at 1173 K. To investigate the real active structure of the SiO2-supported NiP catalysts at high temperature, in situX-ray absorption fine structure (XAFS) experiments were conducted under the DCM reaction conditions. XAFS results showed that all of the SiO2-supported NiP catalysts with atomic ratios of Ni/P = 1:1, 1:2, 1:3, and 1:4 mainly showed a similar Ni2P structure. The Ni2P structure was stable under the DCM reaction conditions. The high stability of the Ni2P structure ensured robust catalysis for DCM. The high catalytic performance of Ni2P was discussed. more...

Published
2024
Full Text
View/download PDF

45. Dynamics of Photoelectrons and Structural Changes of Tungsten Trioxide Observed by Femtosecond Transient XAFS

Author

Uemura, Yohei, primary, Kido, Daiki, additional, Wakisaka, Yuki, additional, Uehara, Hiromitsu, additional, Ohba, Tadashi, additional, Niwa, Yasuhiro, additional, Nozawa, Shunsuke, additional, Sato, Tokushi, additional, Ichiyanagi, Kohei, additional, Fukaya, Ryo, additional, Adachi, Shin‐ichi, additional, Katayama, Tetsuo, additional, Togashi, Tadashi, additional, Owada, Sigeki, additional, Ogawa, Kanade, additional, Yabashi, Makina, additional, Hatada, Keisuke, additional, Takakusagi, Satoru, additional, Yokoyama, Toshihiko, additional, Ohtani, Bunsho, additional, and Asakura, Kiyotaka, additional more...

Published
2015
Full Text
View/download PDF

46. Capturing local structure modulations of photoexcited BiVO4 by ultrafast transient XAFS.

Author

Uemura, Yohei, Kido, Daiki, Koide, Akihiro, Wakisaka, Yuki, Niwa, Yasuhiro, Nozawa, Shunsuke, Ichiyanagi, Kohei, Fukaya, Ryo, Adachi, Shin-ichi, Katayama, Tetsuo, Togashi, Tadashi, Owada, Shigeki, Yabashi, Makina, Hatada, Keisuke, Iwase, Akihide, Kudo, Akihiko, Takakusagi, Satoru, Yokoyama, Toshihiko, and Asakura, Kiyotaka more...

Subjects
*BISMUTH compounds, *PHOTOEXCITATION, *X-ray absorption spectra
Abstract

Ultrafast excitation of photocatalytically active BiVO4 was characterized by femto- and picosecond transient X-ray absorption fine structure spectroscopy. An initial photoexcited state (<500 fs) changed to a metastable state accompanied by a structural change with a time constant of ∼14 ps. The structural change might stabilize holes on oxygen atoms since the interaction between Bi and O increases. [ABSTRACT FROM AUTHOR] more...

Published
2017
Full Text
View/download PDF

47. Development of OperandoPolarization-Dependent Total-Reflection Fluorescence X-ray Absorption Fine Structure Technique for Three-Dimensional Structure Determination of Active Metal Species on a Model Catalyst Surface under Working Conditions

Author

Lu, Bang, Kido, Daiki, Sato, Yuta, Xu, Haoran, Chun, Wang-Jae, Asakura, Kiyotaka, and Takakusagi, Satoru

Abstract

A novel operandoX-ray absorption fine structure (XAFS) technique was developed that we have called the operandopolarization-dependent total reflection fluorescence (PTRF)-XAFS technique, which can provide information on the valence state (XANES) and three-dimensional (3D) structure (EXAFS) of active metal species dispersed on a well-defined single-crystal surface during catalytic reactions. A new compact vacuum chamber, termed an operandoPTRF-XAFS cell, was designed with an internal volume of 216 cm3for PTRF-XAFS measurements of deposited metal species at high temperatures (<800 K) in the presence of reactant gases (up to atmospheric pressure). Product gas analysis in the cell can be simultaneously conducted with a quadrupole mass spectrometer (QMS) during the PTRF-XAFS measurements. The developed operandoPTRF-XAFS technique was applied to a Pt/α-Al2O3(0001) model catalyst during the CO oxidation reaction. Pt clusters that favor an icosahedral Pt55structure were formed on the α-Al2O3(0001) surface after Pt deposition at room temperature, while they were converted to larger cuboctahedral clusters (Pt147) under the CO oxidation reaction at 493 K. The turnover frequency (TOF) of the CO oxidation activity at 493 K was also estimated to be 0.06 s–1from simultaneous QMS and XAFS measurements. Thus, operandoPTRF-XAFS has enabled the relationship between the 3D structure of a metal species on a well-defined oxide surface and its catalytic activity to be determined. more...

Published
2021
Full Text
View/download PDF