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時間分解測定の過去と現在,そしてOperando XAFS法による触媒構造のその場観察と触媒作用機構に関する研究
朝倉清高
北海道大学触媒科学研究所
2Institute for Catalysis, Hokkaido University
Department of Fundamental ResearchCatalyst Surface Research Division (K.Asakura
Catalysis Theory Research Division(J.HasegawaCatalytic Transformation Research Division(A.Fukuoka
Catalyst Material Research Division(K.ShimizuPhotocatalysis Research Division (B.Ohtani
Molecular Catalyst Research Division(T.TakahashiMacromolecular Science Research Division (T.Nakano
Department of Practical ApplicationResearch and Development Division(M.Nishida
Founded in 1943 by Prof. Juro Horiuchias Institute for Catalysis
AndRemodel in 1989 to Catalysis Research Center(CRC)
reorganized in 2015 to Institute for Catalysis (ICAT )8 Professors. 8 Associate Professors, 8 Assistant Professors
Director :Kiyotaka AsakuraVice Director : Junya Hasegawa Speical Professors.
Prof. E.NegishiProf. A.Suzuki
Joint Usage and Research Center in Catalysis Field in Japan
Mission
Catalysis is a material to accelerate chemical reactions.
Exhaustion gas Medicals
Fuel Plastic
Haruta and Akita et alo.
Abe and Ohtani
Water splitting
Fuel cellTakeguchi
3
refrigerator
Pt ctalyst
Fukuoka
Shimizu
ppm O3 decomposes the cell membrane!!
Shen Ye
Biomass
Hasegawa
X-ray Absorption Fine StructureFine structure appearing around X-ray absorption edge
extending upto about 1000eV
m / a
rb. units
24500240002350023000Photon energy/ eV
EXAFS (40-1000 eV)XANES
m = ln ( I0 / I )
I0 I
X-ra
y ab
sorp
tion
edge
XANES(X-ray Absorption Near Edge Structure)EXAFS(Extended X-ray Absorption Fine Structure)
x-ray
outgoing electron and incoming electron interfere with each other
Outgoing and incoming electrons have a wavelength (or wave number
X-ray Absorbing atomX-ray scatteringatom
Lytle, F. W.; Via, G. H.; Sinfelt, J. HJ.Chem.Phys. 1977, 67, 3831.
Y. Iwasawa, K. Asakura, H. Ishii and H. Kuroda, Dynamic Behavior of Active Sites of a SiO2-attached Mo(VI)-dimer Catalyst during Ethanol Oxidation Observed by means of EXAFS. Z.Phys.Chem. N. F. 144,105-115(1985).
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XAFSの特徴
対象が結晶に限定されない.
ガス中,反応中測定が可能である.
時空間分解実験が可能である.
低濃度での測定が可能である.
空間,時間,エネルギー分解測定の高度化が進んでいる.
5XAFSの特徴
対象が結晶に限定されない.
ガス中,反応中測定が可能である.
時空間分解実験が可能である.
低濃度での測定が可能である.
空間,時間,エネルギー分解測定の高度化が進んでいる.
6
Mo dimer
固定化触媒
金属錯体を表面水酸基と反応させる.
Tailored catalyst, fixed catalyst, attached catalystYermakov, Gates, Iwasawa,Ichikawa…..
Mo dimer Active for metathesis, alcohol oxidation, hydrogengation
Mo2(C3H5)4 + OHー → Mo dimer
7In lab XAFS
In lab system.1980 ころ 岩澤康裕先生,黒田晴雄先生と共同研究を
開始, Mo2/Al2O3 Mo-Moの観測(Chem.Lett)
1981.12-1982.3Mo2/SiO2-〔0〕(純粋),SiO2- [30](Na含量大)を開始
Mo-Mo結合なし.
8
Sato, Y.; Iwasawa, Y.; Kuroda, H., EXAFS STUDY OF HIGHLY ACTIVE Mo 2 CATALYST. Chem. Lett. 1982, 11 (7), 1101-1104.
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日本初のX線放射光施設が運転開始Photon Factory(PF) in June in 1982-2005. BL10B
PFが1982年6-7月に運転開始
9
BL10B
Mo Dimer 反応中を見るZ.Phys. Chem. 1985:Catal Today 1989.
10
SiO2-30
SiO2-O
1%Naを含む
Operando XAFS
Operando 測定.Operando=Working
in situ は空気に触れずにという意味合いが強いが,Operando は 実際に働いている最中に限定する.
In operandoは誤りです.
1.Weckhuysen, B. M., Operando spectroscopy: fundamental and technical aspects of spectroscopy of catalysts under working conditions. Phys ChemChem Phys 2003, 5 (20), vi-vi.
11 より 実際に近づけるためには?High pressure in situ測定
12
高圧下におけるXAFS
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高圧下での酸素の吸着
13
Asakura, K.; Iwasawa, Y., Extended X-ray Absorption Fine Structure Studies on the Structure Change of the Al2O3-attached [CoII]4 Catalyst during a CO Oxidation Reaction. J.Phys.Chem. 1989, 93, 4213-4218.
Ni2P 脱硫触媒へのIn situ EXAFSの応用 2001-2007
In situ EXAFS is a powerful tool. The hydrodesulfurization reactions are often carried out in the presence of oil
under high-pressure and high temperature conditions.
油から脱硫反応を起こしている最中を測定する.
油はX線を吸収し、熱を伝える.窓と炉を離すことが不可能
14
S Hydrodesulfurizationreaction
Ni2P/SiO2
Oyama, S. T.; Wang, X.; Requejo, F. G.; Sato, T.; Yoshimura, Y., Hydrodesulfurization of petroleum feedstocks with a new type of nonsulfidehydrotreating catalyst. J.Catal 2002, 209, 1.
高温高圧に耐える窓材は?
15
Demands are “window materials must stand for high pressure and high temperature at the same time”.
Capillary cellsBut curved window causes thickness effects
Diamond, Be and Al Flat windows.Expensive (diamond) or toxic (Be) Diamond, Be and Al are chemically and thermally not so stable.
Demands are “window materials must stand for high pressure and high temperature at the same time”.– Capillary cells
• But curved window causes thickness effects
– Diamond, Be and Al Flat windows.• Expensive (diamond) or toxic (Be) • Diamond, Be and Al are chemically and thermally not so
stable.
Al windowN. Weiher et.al., J. Synchrotron Rad. 12 (2005) 675.
G. Sankar, and J. M. Thomas, Topics.in Catal. 8, 1 (1999).
J. D. Grunwaldt, et al. Rev. Sci. Instrum. 76, (5), 054104 (2005).
16Cubic BN 2番目に硬い物質
cBN
Cubic BN is Second hardest materialTensile strength = 1078.7 MPa
Diamond=2000 Mpa;Be=260 MPaPreviously cBN was made using binders and stregths was reduced. Recently direct formation of cBN without binders by directly conversion at high pressure (7.7 GPa ) and high temperature(2400 K).
(Sumitomo Electro Engineering Co. Dr. Sumiya)It is thermally stable upto 1273 K and chemically also stable.
600 μmの厚みで十分な透過性と30気圧の耐久性
Sumiya, H.; Uesaka, N., High purity cBNpolycrystalline its high pressure synthesis and its fieature. New Diamond 1999, 15 (4), 14.
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Catalysis Research Center Hokkaido University 17
A cell drawing .
Cross section
SUS3153.5 kg
Volt
Fixed screw hole
Cartridge heater
C- BN
sample
Catalysis Research Center Hokkaido University 18
Photographs of the cell1
XANES of Ni2P under reaction conditions.
c(k) oscillations of Ni K-edge XANES for Ni2P on SiO2 before (a) and during the HDS reaction 10 h and 24 h after the introduction of oil (b) and (c), respectively. The Ni2P was reduced at 723 K and cooled to room temperature. The HDS was carried out at 3 MPa and 613 K.
19
8300 8350 8400 8450 85000.0
0.5
1.0
1.5
(c)
(a)
(b)
t
Energy /eV
Before reaction
10 h
24 h
1.Kawai, T.; Chun, W. J.; Bando, K. K.; Oyama, S. T.; Sumiya, H.; Asakura, K., A high-temperature and high -pressure liquid flow cell to measure operando XAFS spectra under the hydrodesulfurization reaction. Rev.Sci.Instrum 2005.2.Kawai, T.; Bando, K. K.; Lee, Y. K.; Oyama, S. T.; Chun, W. J.; Asakura, K., EXAFS measurements of a working catalyst in the liquid phase: An in situ study of a Ni2P hydrodesulfurizationcatalyst. J.Cat. 2006, 241, 20-24.3.T.Kawai; S. Sato, K. K. B., W.-J.Chun, S.T.Oyama,Y.-K.Lee ; K.Asakura, Active Phase of Ni2P Observed by an Operando XAFS. In TOCAT2006, Tokyo, 2006.
30気圧613K モデル油中のXAFS20 wt% tetralin, 77 wt% tetradecane, and 3 wt% DBT,80cc /min H2
EXAFS of Ni2P under reaction conditions.
c(k) oscillations of Ni K-edge EXAFS for Ni2P on SiO2 before (a)druing the HDS reaction 10 h after the introduction of oil (b).
20
Ni2P structure のあらわな変化がない.反応中安定である.
2 4 6 8 10 12-0.1
0.0
0.1
0.2
b)
a)
(k)
k / A-1
Before reaction
10 h
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In situ XAFS of Ni2P in the reaction.J. Cat. 2006, 241, 20-24.Rev. Sci. Instrum. 2008, 79,014101
21
2 4 6 8 10 12-0.1
0.0
0.1
0.2
b)
a)
(k)
k / A-1
Before reaction
Working conditions
4 6 8 10-0.004
-0.002
0.000
0.002
0.004
(k)
k / 10 nm-1
Ni-S
Ni-S=0.227 nm
Difference spectrum.
Ni2P bulk structure is stable.
Small change (probably in surface) occurs.
チオフェン脱硫反応(1気圧)の脱硫反応 22
NiP
NiP
P
PNi
S PNi
P
NiP
P
PNi
P
• CF results of Ni-SR=0.227 nm; CN=0.1.
• Judging from the ratio of surface Ni to the bulk ~0.5 S/Nisurf=0.2
• Little reaction temperature dependence
c (k)
0.00
0.02
0.04
0.06
0.08
0.10
0.12
k / 10 nm-13 104 5 6 7 8 9
Ni – S (FEFF)CN = 0.1, R = 0.227 nm,
HDS at 513 K
HDS at 553 K
HDS at 593 K
Simulated XAFS based on Ni-S bond
/0.1
But what is Ni-S for?
Ni-S is a spectator ?
Ni-S is a poison ?
Ni-S is included in an active site?
23
We carried out the simultaneous measurements of in situ quick XAFS,IR, and product analysis.
XAFS,IR,反応生成物分析同時測定
1. Bando, K. K.; Koike, Y.; Kawai, T.; Tateno, G.; Oyama, S. T.; Inada, Y.; Nomura, M.; Asakura, K., Quick X-ray absorption fine structure studies on the activation process of Ni2P supported on K-USY. J. Phys. Chem. C 2011, 115 (15), 7466-.
2. Bando, K. K.; Wada, T.; Miyamoto, T.; Miyazaki, K.; Takakusagi, S.; Koike, Y.; Inada, Y.; Nomura, M.; Yamaguchi, A.; Gott, T.; Ted Oyama, S.; Asakura, K., Combined in situ QXAFS and FTIR analysis of a Ni phosphide catalyst under hydrodesulfurizationconditions. J Catal 2012, 286 (0), 165-.
3. Wada, T.; Bando, K. K.; Miyamoto, T.; Takakusagi, S.; Oyama, S. T.; Asakura, K., Operando QEXAFS studies of Ni2P during thiophene hydrodesulfurization: Direct observation of Ni-S bond formation under reaction conditions J.Synchrotro.Rad. 2012, 19 (2), 205-209.
4. Wada, T.; Bando, K. K.; Oyama, S. T.; Miyamoto, T.; Takakusagi, S.; Asakura, K., Operando Observation of Ni2P Structural Changes During Catalytic Reaction: Effect of H2S Pretreatment. Chem. Lett. 2012, 41, 1238-1240.
24
X-rayInfraredThermocouple
Gas injection bulb
Heater
Sample : Ni2P/MCM-4135 mg, 15 mm Φ disk
45 deg tilted against Xray and IR.
Sample
C4H4S + 2H2 → C4H8SC4H8S + H2 → H2S + C4H8
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XANES, IR and MS changes during 513 KBando, K. K.;et al J Catal 2012, 286 (0), 165.
25
HDSreaction starts
XAFSNi-S
Infrared
XANES, IR and MS changes during 513 KBando, K. K.;et al J Catal 2012, 286 (0), 165.
26
HDS reaction starts
Ⅲ : STEADY STATE
Ⅰ : Ni-S FORMATION
Ⅱ : H2S & THTproduction
THT=TetrahydrofuranXAFSNi-S
Reaction mechanismsBando, K. K.;et al J Catal 2012, 286 (0), 165.
27
NiPS Formation processes
Ⅰ : Ni-S Formation
同時測定による反応機構提案Bando, K. K.;et al J Catal 2012, 286 (0), 165.
28
2012/Oct/24ICEAN2012
Hydorgenation processes C-S bond cleavage
C-S bond cleavage
H2S
2H2
NiPS Formation processes
Ⅱ : REACTION
THT
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もっと早く 反応を止めずにはかる
高速XAFSと分散XAFS
29
特徴 msの測定が可能比較的機構が簡単で蛍光法を併用し低農度が可能サンプルの均一性の要求が小さい
特徴 μsの測定が可能特別なセットアップと白色X線が必要蛍光法を併用し低農度が可能サンプルの均一性の要求が小さい
分散型XAFSKaminaga, U.; Matsushita, T.; Kohra, K., A Dispersive Method of Measuring Extended X-Ray Absorption Fine Structure. Jpn. J. Appl. Phys. 1981, 20 (5), L355.;Nomura, M.; Asakura, K.; Kaminaga, U.; Matsushita, T.; Kohra, K.; Kuroda, H., EXAFS spectroscopy of some iron (III) compounds by use of dispersive-type in-laboratory X-ray spectrometer. Bull. Chem. Soc. Jpn. 1982, 55 (12), 3911-3914.
実験室
30
FeCl3 6H2O
Fe(ClO4)3 6H2O
FeCl3
AsI3 構造無水塩化鉄(FeCl3)
封入管球30kV-20 mA
分散型XAFS@NW2A, Photon Factory(in the cortesy of Dr. Uemura, Prof Nomura and Prof Inada PF. )
A pink beam is dispersed by a polychrometer, which is a bent Si crystal.→ X-ray with several hundreds of eV can be obtained by using position sensitive
detector.→ A XAFS spectrum can be obtained simultaneously.→ The minimum time resolution of the DXAFS system at Photon Factory is 2 ms.
Typical time resolution for in situ XAFS experiments is between several tens and hundreds of milliseconds.
qp
Setup of DXAFS
x-ray
polychrometer
cell
detector(PDA)
Focal point
gas
PDA: 1024 ch, 25 mm/chpolychrometer: Si(111): R = 1500, 2000 or 3000 mm, Si(311): R = 1500 mm, Si(511): R = 800 mm in situ cell: sus, 230 ml
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33
11560 1160011520
Energy / eV
1.0
0.9
0.8
0.7
11560 11600E/ eV
mt
Ptの水素吸着脱着をmsオーダで測定
Hydrogen reaction on Ptnanocluster
A(d empty state)
B(Pt-Hbondforation)
8
Oxidation Reduction1.0
0.8
0.6
0.4
0.2
0.0
1086420
1.0
0.8
0.6
0.4
0.2
0.0
1086420
B
A
t / st / s
Ratio
of s
pecie
s
900 ms
H
R Pt-Pt =0.254 nmO
2010/8/25Summer Challenge in KEK 2
A.Suzuki, to be published
A.Suzuki, Y.Inada, M.Nomura, K.Asakura
もっともっと早くPump Probe XAFS
Sample: 0.6 mM WO3 suspensionpump laser: 400 nm 270 mJ/cm2@945 HzX-ray pulse width: 100 ps(FWHM)
J. Synchrotron Radiat. 2007, 14, 313.J. Synchrotron Radiat. 2009, 16, 110.
2p→5d
可視光応答型光触媒
R. Abe, et. al. J. Am. Chem. Soc. 2008, 130, 7780-7781
Honda-Fujishima effect
WO3
TaON
Photoexcited State of WO3 : LIII XANES at PF-ARSingle bunch operation
k = 0.5(1) ns -1
The excited state decayed in 10 ns.→It was successfully fitted with a single exponential function.
1. Uemura, Y.; Uehara, H.; Niwa, Y.; Nozawa, S.; Sato, T.; Adachi, S.; Ohtani, B.; Takakusagi, S.; Asakura, K., In Situ Picosecond Xafs Study of an Excited State of Tungsten Oxide. Chem. Lett. 2014, 43 977-979.
Pump probe XAFS at SACLA(X線自由電子レーザ;XFEL)Experiments at SACLA
SPring-8
SACLA~30 fs
~50 fs
Sample: 4 mM WO3 suspensionpump laser: 520 mJ/cm2@15 HzX-ray pulse width: 30 fs(FWHM)Time resolution: 500 fs
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光吸収過程におけるWO3の超高速XAFS
peak A : Edge shift due to formation of W5+ < 1 pspeak C : decrease of absorption from eg orbitals ~ 200 ps
Three distinct peaks were found in the differential spectra.
peak B which was not found in the previous experiments was observed.
Uemura, Y., et al., Dynamics of Photoelectrons and Structural Changes of Tungsten Trioxide Observed by Femtosecond Transient Xafs. Angew. Chem.Int.Ed in press
何が起こったのか? What happens? 38
Monoclinic(stable at room temperature)
Orthorhombic(stable at higher temperature}
WO3
WO2
還元とエッジシフト
Dバンドフィッリング
構造変化
Keisuke Hatada2015
Peak A
0 200 400 600
5.2
5.4
5.6
5.8
6.0
Whi
te li
ne a
rea
ratio
time /ps
Change of state after the photoabsorption
Fig. 4 A proposed scheme for the photoexcitation process of WO3.
Total white line
W(5+)W(5+)
W(6 +)
WO3*
WO3**
Angewandte ChemieUemura, Y., et al., Dynamics of Photoelectrons and Structural Changes of Tungsten Trioxide Observed by Femtosecond Transient Xafs. Angew. Chem.Int.Ed in press
触媒そのものをはかる 集光とイメージング
KB mirror, Capillary tube
40
Tada, M. et al. [small mu ]-XAFS of a single particle of a practical NiOx/Ce2Zr2Oy catalyst. Phys Chem Chem Phys 13, 14910-14913, doi:10.1039/c1cp20895k (2011).
Fresh DegradadedCT
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Micro XAFS センサーの例41
GAS LEAKAGE ALERT
1 Wada, T. et al. Degradation mechanism of a high-performance real micro gas sensor, as determined by spatially resolved XAFS. Phys ChemChem Phys, doi:10.1039/c6cp00065g (2016).2 Wada, T. et al. Improvement of a Real Gas-Sensor for the Origin of Methane Selectivity Degradation by µ-XAFS Investigation. Nano-Micro Lett. 7, 255-260, doi:10.1007/s40820-015-0035-7 (2015).
蛍光検出=低濃度が可能.42
透過XAFSではみたい原子以外の吸収で、原子が隠される.
みたい原子からその元素特有の蛍光X線をだす.
1.5
2.0
2.5
3.0
3.5
11500 12000 12500 13000
t / a
rb. u
nit
Energy / eV
a) 4mmol/L H AuCl4 aq.
b) 6 m A u foil
蛍光検出と透過法 希薄であること・薄膜であること
43
0
5000
10000
15000
20000
700 800 900 1000 1100 1200
a) D irectb) +Filterc) +Filter+Slit
Coun
t
M C A C h#
↓ A u L
G a K ↓
↓ G a K
Elastic scattering↓
11800 12000 12200 12400 12600
t / a
rb. u
nit
Energy /eV
a) Lytle detector
b) Ge-SSD
Lytle 検出器 SSD
積分型 パルスカウント透過法 >0.5wt%Lytle 100 ppmSSD
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High resolution XAFS 45
High resolution
Conventional
Pt nanoparticles with different environment.
O2
CO
Experimental
Theory
M edge energy resolution
2p23d10 5d9 2p13d105d10 2p23d95d10W w
46
In-situ 発光分光計測(In courtesy of Uruga, Skizawa,Iwasawa) 47
In-situ燃料電池セル
発光分光XAFS用
湾曲アナライザ結晶
発光分光XAFS用
2次元X線検出器
X線
イオンチェンバー
In-situ 発光分光計測システム概念図
発光分光計測試料から発生するPt Lα蛍光X線をアナライザ結晶で分光することにより、高エネルギー分解XANES(High-energy resolution XANES, HR-XANES)を計測試料から発生するPt L3端近傍の散乱X線をアナライザ結晶で分光することにより、共鳴非弾性X線散乱(Resonant inelastic X-ray scattering, RIXS)を計測両計測データに対して理論計算を行うことにより、 Pt触媒粒子表面の吸着原子種を同定
http://www.pieter-glatzel.de/XASXES.html
2.5
2.0
1.5
1.0
0.5
0.011600115801156011540
Energy (eV)
XANES HR-XANES
HR-XANES
11.570
11.565
11.560
Inci
dent
ene
rgy
(keV
)
1050
transfer energy (eV)
RIXS
Energy resolutiona few eV
In-situ RIXS 電位依存性
理論計算による吸着元素種の解明を開始
0.0 V
0.5 V 1.0 V
0.4 V
11.570
11.565
11.560
Inci
dent
ene
rgy
(keV
)
1050
transfer energy (eV)
0
5
0
1050
1050
0.8 V
In courtesy of Uruga, Skizawa,Iwasawa
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MARX-RAMAN
1. XAFSは元素選択的 結合に敏感だったら
2. 結合に敏感な方法は?MARPE(Multi Atom Resonance Photo Emission). (A. Kay, C.S. Fadley, Multiatom resonant photoemission: a method for determining near-neighbor atomic entities and bonding. Science. 281,679(1998). )
3. X-ray Raman: 炭素のK-edge XAFSを硬いX線で見る。
4. 組み合わせるともしかして、PtについたCをみえるかも。あるいはTaについたNが見えるかも
49
(K. Tohji, Y. Udagawa, Physical Review B 1987, 36, 9410-9412. )
MARX-RAMAN(Multi atom resonance X-ray Raman)の原理(こじつけ)
50
MARX-Raman
Resonant X-ray Raman
Experimental setup51
MARX-RAMAN of TaN.
Confidential!!
52
Bond specific spectroscopy
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触媒研究にXAFSは欠かせない.
XAFSーーーOperando法 現場を見る。同時測定で組み合わせ情報
高感度で見る。(1013 cm-3)高速で見る。(fs-second)imaging(10 nm-1 mm)
働いている触媒その物を見る。
触媒の舞台と反応物を同時に測定、相関を見ながら
より深い理解
53Acknolwedgment
Late Haruo Kuroda(Univ. Tokyo)Yasuhiro Iwasawa(ECU)Masaharu Nomura(KEK)Takashi Fujikawa(Chiba U)S. Ted Oyama(Univ. Tokyo)K.K.Bando (AIST)T.Kawai(HU)Wang-Jae Chun(ICU)Satoru Takaksuagi(HU)Hiroko Ariga(HU)Takahiro Wada(TMDU)Yohei Uemura(IMS)Daiki Kido(HU)B.Ohtani, J.Hasegawa(HU)T.Uruga and O.Sekizawa(SP8)T.Katayama,Makina Yabashi(RIKEN)Y.Niwa, Y.Nitani, H.Abe, M.Kimura(PF)
54
FundsCREST 1997-2002原子レベル触媒NEDO 2002-2004 脱硫触媒開発科研費S 2004-2010 脱硫触媒のオ
ペランド解析
NEDO 2008- 燃料電池
Structure of α-MoO3 single crystal
2010/08/06
第1回 XAFS夏の学校 55
Mo O
[001]
[010]
[100]
0.233
0.167
*scale:nm
Every parameters are opitimized?
5 x 4=20 parameters
Ar 5.1 119Ak
DE=1400 eV!!
What should we do???
2010/08/06
第1回 XAFS夏の学校 56
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2017/6/11
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Single crystal work
Topics in Catalysis Vol. 18, Nos. 1–2, January 2002 125
Polarization-dependent EXAFS measurements of an α-molybdenumtrioxide single crystal
K. Ijima, Y. Ohminami, S. Suzuki and K. Asakura ∗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 powderMoO3 spectrum based on the phase shift and amplitude functions derived from the polarization-dependent EXAFS spectra.
2010/08/06
第1回 XAFS夏の学校 572010/Apr/15
58
偏光依存性
X線の電場ベクトルに対し基板の向きを変化させることでEXAFSから三次元情報を得る
EXPERIMENTAL
MoO3 single crystals were prepared by a flux method with Na2CO3 (a mole ratio of 0.78 and 0.22 )
Heated up to appropriate temperature as shown below
Washed with HNO3
0 20 40 60 80 100 120200
300
700
800
900
1000
MoO3
Tem
pera
ture
/ K
t / hour
2010/08/06
第1回 XAFS夏の学校 59
MoO3 XANES
19950 20000 20050 20100
=
907560
3045
0 15
EDCA B
Abso
rban
ce /
arb.
units
Energy /eV
[100]
[001]
19950 20000 20050 20100-1.0-0.50.00.51.01.52.02.5 EDCB
A
Abso
rban
ce /
arb.
uni
ts
E / eV
PowderMoO3 Crystal
Correlation between A andMo=O bond direction.
2010/08/06
第1回 XAFS夏の学校 60
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Fourier transformation of MoO3 single crystal.
Powder and Single crystal
0 1 2 3 4 5 6
9075
604530150 =
Am
plitu
de /
arb.
uni
ts
r / 0.1 nm
0 1 2 3 4 5 60
2
4
6
8
FT /
arb.
uni
ts
r / 0.1 nm
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第1回 XAFS夏の学校 61
Fourier transformation of MoO3 single crystal.
Powder and Single crystal
0 1 2 3 4 5 6
9075
604530150 =
Am
plitu
de /
arb.
uni
ts
r / 0.1 nm
0 1 2 3 4 5 60
2
4
6
8
FT /
arb.
uni
ts
r / 0.1 nm
2010/08/06
第1回 XAFS夏の学校 62
XAFS Fourier transformation.
0 1 2 3 4 5 60
5
10
15 Mo-O
Mo---O
Mo=O
Mo-O-Mo-O
[100] 45 [001] powder
FT /
arb.
uni
ts
r / 0.1 nm
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第1回 XAFS夏の学校 63
Powder sample analysis2010/08/06
第1回 XAFS夏の学校 64
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2010/08/06
第1回 XAFS夏の学校 65
Am
plitude
/ a
rb. units
6543210r / 0.1 nm
30 K
70 K
110 K
210 K
300 K
(a)
Am
plit
ude /
arb
. units
6543210r / 0.1 nm
300 K
200 K
110 K
70 K
30 K
(b)
Temperature dependent experiments2010/08/06
第1回 XAFS夏の学校 66
Equation of Motion (EM)A. V. Poiarkova and J. J. Rehr により提案
Physical Review B, Vol. 59, No. 2 (1999) 948-957
運動方程式を解いて、状態密度を出してDW因子を見積もる
分子に近い系に対しても対応ができる。
計算に必要なデータはForce constantのみ。
MoO3のForce constantはRaman分光法より得られる。
2010/08/06
第1回 XAFS夏の学校 67
EM法検討の流れ
feff.inp: a-MoO3結晶構造情報よりspring.inp: Raman 分光法より
force constantを求める
Fourier Transformation
Fourier Filtering
Inversed FT
Fourier Transformation
Fourier Filtering
Inversed FT
Raw data
E0決定と波数への変換
BG除去と規格化
FEFF 8.01
比較
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第1回 XAFS夏の学校 68
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[100]
[100][001]
Force constant
Bond distance Force constants (nm) (N/m)0.167 791.50.173 4660.195 1710.225 800.233 80
0.233
0.167
[001]
[010]
[100]
M.A. Py et al.,Physica 105B(1981) 370-374
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第1回 XAFS夏の学校 69
Results of [001] direction
Am
plitud
e /
arb.
uni
ts
6543210
r / 0.1 nm
30 K
70 K
110 K
210 K
300 K
[001]
測定結果をうまく再現
k3(k
)
1210864
k / 10 nm-1
30 K
70 K
110 K
210 K
300 K
observed calculatedMo-O 0.195nm
2010/08/06
第1回 XAFS夏の学校 70
Results of [100] direction
[100]Mo-O 0.173, 0.225nm
Am
plitud
e /
arb.
uni
ts
6543210
r / 0.1 nm
300 K
200 K
110 K
70 K
30 K
測定結果をうまく再現
k3(k
)
1210864
k / 10 nm-1
observed calculated
300 K
200 K
110 K
30 K
70 K
2010/08/06
第1回 XAFS夏の学校 71
?
Approaches to improve the discrepancies
assumed that the discrepancies are due to the asymmetrical Mo-O bond lengths (0.173, 0.225 nm) in the [100] direction– EM
• underestimated or overestimated force constants– not improved
– FEFF• muffin-tin theory: uniformed mean-free-path term
– mean-free-path depends on bond length» inelastic amplitude reduction factors is correlated to
mean-free-path term » finely adjusted S02 applied to the calculation
2010/08/06
第1回 XAFS夏の学校 72
2
/22
0
)(2sin)(
)(
22
kr
kkreekFN
k
ii
rkii
s
i
-
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Improved calculation of the Fourier Filtered EXAFS of the [100] direction
Finely adjusted inelastic amplitude reduction factors improved the discrepancies remarkably.
k3(k
)
1210864
k / 10 nm-1
300 K
200 K
110 K
30 K
70 K
observed calculated
2010/08/06
第1回 XAFS夏の学校 73
Powder MoO3 simulated by FEFF+DW+IEMP
-4
-2
0
2
4
k3(k
)
121086
k / 10 nm-1
observed curve fit
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第1回 XAFS夏の学校 74
Conclusion
Debye-Waller factors for a-MoO3 (010) single crystal were successfully estimated by the EM method.
The calculations agreed with the experiments. But, minor discrepancies were found in the [100] direction.
Finely adjusted inelastic amplitude reduction factors for each Mo-O bond improved the discrepancies successfully.
Our results suggest that a priori Debye-Waller factors calculated by the EM method using the force constants derived from Raman spectroscopy can reduce curve-fitting parameters even in highly distorted systems.
2010/08/06
第1回 XAFS夏の学校 75
How many parameters do we need to fit the MoO3. N--- unknown. 5 R---unknown 5Sigma estimated from r 0E_0 one common E_0 1Total 11 parameters Dk=10Å-1
2010/08/06
第1回 XAFS夏の学校 76
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2017/6/11
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How many parameters do we need to fit the MoOx. N--- unknown. 3 R---unknown 3Sigma estimated from r 0E_0 one common E_0 1
Total 7 Dk=5 3-8 A-1 !!
2010/08/06
第1回 XAFS夏の学校 77
If no body knows the vibration frequency
F. D. Hardcastle and I. E. WachsJournal of Raman Spectroscopy, Vol. 21(1990) 683-691
2010/08/06
第1回 XAFS夏の学校 78
Total coordination number and distance has relation. BROWN’s Bond valence
j
iji B
RRV 0exp
R0=190.7 ppm B=37ppm
MoO3 V=6.006
2010/08/06
第1回 XAFS夏の学校 79
1: Sum up the close bond
Anyway we fit the data by assuming structure = close bond is the same bond
It is not necessarily corresponding to real structure. Compare the samples and discuss the difference.
2010/08/06
第1回 XAFS夏の学校 80
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2017/6/11
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2:New methods
Model distribution functions. 1 E. D. Crozier, J. J. Rehrand R. Ingalls, in EXAFS, XANES and SEXAFS, eds.
Koningsberger, D. C.; Prins, R., 1988.
Bayesian method1 H. J. Krappeand H. H. Rossner, Physical Review B, 6618, 4303(2002).
Reverse Monte Carlo1. S. J. Gurmanand R. L. McGreevy, J.Phys.Cond.Matter, 2, 9463(1990).
2010/08/06
第1回 XAFS夏の学校 81
Conclusions
How to determine the parameters is yet unresolved problems.
Further work must be necessary.
2010/08/06
第1回 XAFS夏の学校 82
Polarization dependent83
3 dimensional information can be obtained using polarization
dependece
)
Parallel to the surface Parpendicular to the surface
)(cos3)( 2 kk iiTotal-Reflection and Fluorescence Mode
84
They make us possible to detect very small amount on single crystal surface
19 elements SSD
Total-Reflection modeX-ray
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PTRF-XAFS=Polarization dependent total reflection fluorescence XAFS
85
E: electric vector
parallel bondperpendicular bond
E
E
Amplitude of XAFS 2cos3
θX-ray
X-ray absorbing atom
Scattering atom
Electric vector
XAFS can give three dimensional structure of highly dispersed system
4 6 8
-0.1
0.0
0.1
k / 10 nm-1
k(k
)
(a)
-0.1
0.0
0.1
FT
4 6 8k / 10 nm
-1
4 6 8
-0.1
0.0
0.1
k / 10 nm-1
k(k
)(c)
FT
Cu(2)Cu(1)
O(p)O(b)
Ti(6)
Ti(5)
Y. Tanizawa, J.Phys.Chem., 107 (2003) 12917.
Photon Factory BL9A
Mo dimer on TIO2(110)86
Mo+ TiO2(110) Oxidation at 773 K
超純水
Na +, Ca2+
MoO42-
Oxidation at 773 K
Mo dimerMo monomer or dimer attahed tosupport surface.
Chun, W. J., Asakura, K. & Iwasawa, Y. (1996). Appl.Surf.Sci. 100 &101, 143-146.Chun, W. J., Shirai, M., Tomishige, K., Asakura, K. & Iwasawa, Y. (1996). J.Mol.Catal. 107, 55-65.
Asakura, K., Chun, W. J., Shirai, M., Tomishige, K. & Iwasawa, Y. (1997). J.Phys.Chem. 101, 5549-5556.Chun, W. J., Asakura, K. & Iwasawa, Y. (1997). J.de Phys. 7-C2, 921-922.Chun, W. J., Asakura, K. & Iwasawa, Y. (1998). Chem. Phys. Lett. 288, 868-872.
Na dependence of(Mo/Si =1*10-4 ) Mo structure. Chun, W. J.; Asakura, K.; Ishii, H.; Liu, T.; Iwasawa, Y., The effect of ppm-level Na Impurity on the structure of SiO2-supported Mo catalysts prepared in a clean room. Topics in Catal. 2002, 20, 89-95.
87
5 * 10-85 *10-6 1 *10-42*10-4
SiO2
MoO3MoO3+Na2Mo2O7Na2MoO4+Na2Mo2O7
MoO3
5 *10-6 5 *10-45 *10-8 5 *10-10
Na/Si
5*10-6 Na affects the structure
Weber, R. S., Effect of local structure on the UV-Visible absorption edges of MoO3 clusters and supported MoO3. J.Catal. 1995, 151, 470.
Acknowledgement
Prof. W.-J. Chun (ICU)Prof. K.Ijima (Univ. Yamanashi)Prof. S.Suzuki (Univ. Osaka)Prof. Y.Ominami (Hitachi)
2010/08/06
第1回 XAFS夏の学校 88