アークプラズマ法によって調製した高分散担持金属触媒の局所構造解析 日隈 聡士1,2・池上 啓太1,2・町田 正人1,2 （熊本大学1・京都大学ESICB2）

Arc-plasma (AP) preparation = Directly deposition

Ingot

precious

metal

Powder

Water-soluble

salt

Supported

catalyst

Loss

Loss

Loss

anode

condenser

Arc power supply

cathode

catalyst support

Ingot precious

metal

Plasma

insulator

trigger

electrode

trigger power

supply

stirring

mechanism

Al2O3

CeO2

ZrO2

AlPO4 Ingot

precious metal

Rh, Pd, Pt

(1) enhanced catalyst

activation,

selectivity

and lifetime

(2) a highly dispersed

active species

(3) reduced energy

requirements

(4) shortened

preparation time

C.-j. Liu et al., Catal. Today

72, 173 (2002).

Conventional

catalyst preparation

(Impregnation)

= Multistage process

0

20

40

60

80

100

0 100 200 300

0

20

40

60

80

100

0 100 200 300

Catalytic activity for CO

oxidation over Rh/AlPO4

S. Hinokuma et al., Top. Catal., 52, 2108 (2009).

S. Hinokuma et al., Catal. Today, 175, 593 (2011).

S. Hinokuma et al., Bull. Chem. Soc. Jpn, in press.

AP av. b : 2.4±1.1 nm

imp av. a : 6.4 ±5.5 nm

Temperature/ ̊C

CO

convers

ion

/ %

0 61 2 3 4 5

5

10

15

0

20

Distance / Å

FT

magnitude / a

.u.

AP

imp

1/8

1/16 Rh foil

Rh2O3

Rh-O

Rh-O-P

Rh-Rh

Rh-O-Rh

EXAFS of Rh/AlPO4

(Rh K-edge) a

a Interval of k-space to r-space of FT is 3.0-13.8 Å–1.

b Average size of Rh nanoparticles on AlPO4.

Introduction

Unsupported Rh nanoparticles prepared by arc-plasma process

In this work Experimental

previous research

arc-plasma gun

(APG: Fe)

vacuum

(TMP/RP)

Preparation condition arc-plasma gun

(APG: Pd or Cu)

container

(Al2O3, CeO2)

Synchronous (syn) pulse

syn

asyn (aged) (fresh)

900 ˚C, 25 h,

10% H2O/air

◇ Supports : Al2O3 , CeO2

◇ Cathodes : Fe and M (M=Pd, Cu)

◇ Pressure : 1.0×10-3 Pa

◇ Discharge voltage: 125 V

◇ Condenser capacity: 360 μF

Fe-M/Al2O3 or CeO2

Experimental setup of dual arc-plasma Characterization

◆ XRD ◆ XRF ◆ XPS

◆ Specific surface areas (SBET) ◆ FT-IR

◆ Metal dispersion (CO chemisorption) ◆ HRTEM

◆ CO oxidation catalytic activity test

(0.1% CO, 1.25%O2, He balance, W/F=5.0×10-4 g･min･cm-3)

◆ XAFS (BL9C, NW10A, KEK)

PF-AR

ring

X-ray

Proposal No. 2012G749

Light source: Bending magnet, Double-crystal monochromator: Si(111) or (311)

support

Dual-mode

arc-plasma

metal metal bimetal

1. to clarify effects of synchronous and asynchronous pulse deposition

2. to evaluate a local structure and catalytic performance

3. to compare with catalytic properties of wet-impregnation (imp) catalysts

Plasma

Results and Discussion

2 nm2 nm

2 7 Energy / keV

asyn

2 7 Energy / keV

0

10

20

30

40

50

60

0 1 2 3 4 5

av. : 2.3

±0.7 nm

Fra

cti

on

/ %

Particle size / nm

0

10

20

30

40

50

60

0 1 2 3 4 5

av. : 2.3

±0.7 nm syn

TEM images and EDX spectra of Fe-Pd

Fe: 67wt% Pd: 33wt% Fe: 100wt%

Pd: 0wt%

Fra

cti

on

/ %

Particle size / nm

0

10

20

30

40

0 1 2 3 4 5

1/3

Distance / Å

FT

magnitude / a

.u.

syn

asyn

PdO

Pd foil

Pd-Fe

Pd-O Pd-O-Pd

Pd-Pd

Pd K-edge EXAFS and fitting parameters

1.2wt% Fe-1.0wt% Pd/Al2O3(fresh)

shell CNa

(±0.2)

r/Åb

(±0.03)

σ2/10–2 Å2c

(±0.05) R/%

syn Pd-O 2.7 2.01 0.45 2.0

Pd-Fe 0.5 2.70 0.65

Pd-Pd 0.8 2.73 0.59

asyn Pd-O 2.7 2.01 0.27 2.5

Pd-Pd 0.6 2.71 0.59

PdO Pd-O 4.0 2.02 0.27 0.5

Pd-O-Pd 4.0 3.05 0.52

Pd-O-Pd 8.0 3.43 0.55

Pd foil Pd-Pd 12.0 2.74 0.59 0.1

Interval of k-space to r-space of FT is 3.0-16.0 Å–1. aCoordination number. bInteratomic distance. cDebye-Waller factor.

Catalytic properties of CeO2-supported catalysts

CeO2

Fe-Pd

syn

CeO2

Pd

CeO2

Fe

asyn

S. Hinokuma et al., Catal. Today, 201, 92 (2013).

CO/Pda

/ %

SBET

/ m2・g-1

Pd0b

/ %

Fe-Pd (fresh)

syn

Fe-Pd (fresh)

asyn

167 57 36

166 74 51

T10c

/ C

105

98

a Determined by pulsed CO chemisorption at 50 C. Reduction by H2 at 200 C. b Determined by Fe2p and Pd3d XPS. c Temperature at which CO conversion reached to 10%

Fe0b

/ %

65

77

0.22

0.25

Pd

/ wt%

Fe

/ wt%

0.31

0.43

5 nm

Fe AP Cu AP Fe-Cu syn

5 nm 5 nm

Particle size / nm

Fra

cti

on

/ %

0

10

20

30

40

50

60

70

0 1 2 3 4 5 0

10

20

30

40

50

60

70

0 1 2 3 4 5 Particle size / nm

Fra

cti

on

/ %

Particle size / nm

Fra

cti

on

/ %

0

10

20

30

40

50

60

70

0 1 2 3 4 5

2.9±0.7 nm 2.7±0.7 nm 2.8±0.7 nm

TEM images and size distributions

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

7100 7110 7120 7130 7140

Energy / eV

imp (aged)

imp (fresh)

AP (aged)

AP (fresh)

FeO

Fe foil

Fe2O3

Cu K-edge EXAFS Fe K-edge XANES

2.4wt% Fe-3.1wt% Cu/Al2O3

0

10

20

30

40

50

60

70

80

0 1 2 3 4 5

1/3

AP (fresh)

imp (fresh)

AP (aged)

imp (aged)

Distance / Å

FT

magnitude / a

.u.

Cu foil

CuO

Cu-O

Cu-O

Cu2O

CuFeO2 2

Cu-O-Fe

Cu-O-Cu

Cu-Cu

Cu-O-Cu

Cu-O-Cu

Cu-O

Shell CN a

(±0.2)

r/Å b

(±0.03)

σ2/10–2 Å2 c

(±0.05) R/%

AP (fresh) Cu-O (CuFeO2) 0.60 1.83 0.10 0.1

Cu-O (CuO) 2.60 1.95 0.26

AP (aged) Cu-O (CuFeO2) 0.50 1.81 0.19 0.01

Cu-O (CuO) 3.40 1.95 0.55

imp (fresh) Cu-O (CuO) 3.20 1.94 0.60 0.5

imp (aged) Cu-O (CuO) 3.10 1.95 0.60 0.7

Cu foil Cu-Cu 12.00 2.54 0.95 0.4

Cu2O Cu-O 2.00 1.84 0.46 3.9

CuO Cu-O 4.00 1.96 0.52 1.9

CuFeO2 Cu-O 2.00 1.83 0.58 2.2

Interval of k-space to r-space of FT is 2.0-15.0 Å–1. aCoordination number. bInteratomic distance. cDebye-Waller factor. CuFeO2

Cu(I)

Fe(II)

1.785

~1.825Å

X-ray absorption spectra (XAFS) of Al2O3-supported catalysts

Catalytic activity over CeO2-supported catalysts CO adsorption (in situ FT-IR at 50 ˚C) The amount of CO adsorption on Cu

Fe

/ wt%

Cu

/ wt% Cu+/Cu

COads

/ μmol・g-1 CO/Cu CO/Cu+

0.20 - AP (aged) - 0.3 - -

- 0.15 AP (aged) 0.89 5.7 0.24 0.27

0.18 0.11 AP (aged) 0.79 10.7 0.62 0.79

0.17 0.11 imp (aged) 0.66 1.9 0.11 0.17

- 0.13 imp (aged) 0.84 3.7 0.18 0.21

Conclusions

0

20

40

60

80

100

0 100 200 300 400

0

20

40

60

80

100

0 100 200 300 400

0

20

40

60

80

100

0 100 200 300 400

CO

co

nvers

ion

/ %

aged

fresh aged

fresh

aged

fresh

Fe AP Fe-Cu AP

Cu AP

20

40

60

80

100

0 100 200 300 400

CO

co

nvers

ion

/ %

0

20

40

60

80

100

Temperature / ̊C

aged

600 ̊C Fe-Cu imp

0 100 200 300 400

Temperature / ̊C

0.4% Pt/Al2O3

imp (aged)

SBET / m2・g-1

fresh

aged

Fe-Cu

AP

169

6

0.1% CO, 1.25% O2,

He balance. 10 ˚C·min−1,

W/F=5.0×10⁻4 g·min·cm−3.

200020502100215022002250

Fe-Cu/CeO2 syn (aged) Cu/CeO2 AP (aged) Fe/CeO2 AP (aged)

2250 2200 2150 2100 2050 2000 2250 2200 2150 2100 2050 2000 2250 2200 2150 2100 2050 2000

Wavenumber / cm-1

O2

He

CO

0.05 0.01

Absorb

ance / a

.u.

O

C

Cu

0.05

本研究は文部科学省の委託（元素戦略プロジェクトおよび元素戦略拠点形成型プロジェクト）を受けて実施した。

パルス放電を同期した多元系AP法によって平均粒子径2～3 nmの均一なFe-PdおよびFe-Cuナノ粒子を調製し、大型研究施設（KEK, PF）を利用して局所構造を測定した。

XAFS測定によって、AP法により調製したFe-Pd触媒ではFe3Pd1、Fe-Cu触媒ではデラフォサイト型CuFeO2に類似の局所構造を有する表面化合物が生成していることが明らかになった。

高分散の複合金属ナノ粒子の形成によって、活性な低酸化状態の金属が安定化した。これが要因となって、単独金属および湿式含浸法で調製した触媒より高いCO酸化活性を示した。

CO吸着量およびin situ FT-IR測定から、Fe-Cu/CeO2のCO吸着サイトは低酸化状態のCuである。熱処理によるCeO2のシンタリングにも関わらず、CuFeO2は高分散状態を保持することが分かった。

10 nm

Rh2.2 A = d111(Rh)

002

111

[110]