2017/6/11 xafsxafs法...2017/6/11 3 日本初のx線放射光施設が運転開始 photon...

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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．

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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

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高圧下におけるXAFS

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高圧下での酸素の吸着

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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？

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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).

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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

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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.

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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.

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HDSreaction starts

XAFSNi-S

Infrared

XANES, IR and MS changes during 513 KBando, K. K.;et al J Catal 2012, 286 (0), 165.

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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.

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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.

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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

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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???

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15

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.

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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

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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.

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16

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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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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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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Powder sample analysis2010/08/06


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17

2010/08/06


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


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。

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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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[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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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

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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

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?

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

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2

/22

0

)(2sin)(

)(

22

kr

kkreekFN

k

ii

rkii

s

i

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19

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

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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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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.

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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

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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 !!

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If no body knows the vibration frequency

F. D. Hardcastle and I. E. WachsJournal of Raman Spectroscopy, Vol. 21(1990) 683-691

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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


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.

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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).

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Conclusions

How to determine the parameters is yet unresolved problems.

Further work must be necessary.

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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

2017/6/11

22

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


2017/6/11 xafsxafs法...2017/6/11 3 日本初のx線放射光施設が運転開始 photon...

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