Kinetics of gas adsorption on gold nanoparticles in ...

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Kinetics of gas adsorption on gold nanoparticles in catalysts, real-time monitored by plasmon resonance investigation

Nanoscale Physics Research Laboratory

Ben Van Duppen, Sébastien Royer, Florentin Haese, YBInstitute for NanoSciences in Paris – CNRS – UPMC- Paris VI

Catherine Louis, Laurent Delannoy, Sandra CasaleLaboratory for Reactivity of Surfaces – CNRS – UPMC- Paris VI

Ruth Chantry, Ziyou Li Nanoscale Physics Research Laboratory, Univ. Birmingham

Ruben G. Barrera Institute of Physics, Univ. Nacional Autonoma de Mexico, Mexico

Oliver Merchiers Centre de Recherche Paul Pascal, Univ. Bordeaux

Financial supports :French National Agency for Research (ANR-07-NANO-024-01 ; ANR-09-NANO-003)COST Action MP0903 NanoalloysConsejo Nacional de Ciencia y Tecnologia (Mexico) (No. 82073 )Direccion General de Asuntos del Personal Academico, UNAM, Mexico (PAPIIT 111710)

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Overview

1. Introduction• Surface vs. bulk in nanoparticles• Localized surface plasmon resonance in a metal NP• Au NP - based catalysts for CO oxidation

2. Size and shape of active Au NPs : abberration-corrected TEM

3. Oxygen / Au NPs interaction• Charge transfer ?• Two-step kinetics• Active vs. non active catalysts

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170

670

1500

surface N

67 %2502 nm

34 %19904 nm

22 %67006 nm

Surface/total

Ratio total N Diameter

Number of 4 nm diameter NPs in 1 g of Au : 1018

Specific surface ~ 100 m2

Metallic nanocristals

Au NPs

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1.7 nm

1.8 nm

1.3 nm


A.S. Barnard,

octahedra

truncated octahedra

truncated cube

cuboctahedra

icosahedra

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1.7 nm

1.8 nm

1.3 nm


A.S. Barnard,

octahedra

truncated octahedra

truncated cube

cuboctahedra

icosahedra

Yoshida, Haruta et al, Science 2012

L. Delannoy, R. Chantry, Z. Li, Y. Borensztein, C. Louis, to be published

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Overview

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Color effects in gold particles : plasmon resonance

Teapot in ruby glass, Kunckel,

v. 1680

F. Kim et al, J. Am. Chem. Soc. 124, 14316 (2002)

Lycurgus cup (4th century, Rome), British Museum

I. Freestone et al, Gold Bull. 40, 270 (2007)

Lightened from outside

Lightened from inside

absorption around 540 nm: green red colour

0

1

2

3

400 450 500 550 600 650 700Wavelength of light (nm)

pola

rizab

ility

Im()

in glass

in airAbs

orpt

ion

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E

induced dipoleEp o

m

Plasmon resonance in a metal sphere

Effect of the embedding mediumEffect of the shape of the particle (ellipsoid)Effect of the substrateEffect of adsorbed species

02)( m

Plasmon = collective oscillation of the surface conduction electrons induced by

an oscillating applied electric field

Plasmon resonance for :

dielectric function of the embedding medium

Polarizability :m

m3

2R4

dielectric function of the metal

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0

1

2

3


Abs

orpt

ion

light reference, then sample

detector


detector

integrating sphere

PVA colloid Au NPs on Al2O3

10 nm10 nm

PVA colloid Au NPs on TiO2

Absorption of the powder alone

Au colloids on TiO2

on Al2O3

B. Van Duppen, L. Delannoy, YB, unpublished

510 nm

isolated Au sphere

Plasmon resonance of gold spheres on an oxide powder

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0

1

2

3


Abs

orpt

ion


detector


detector

integrating sphere


10 nm10 nm

PVA colloid Au NPs on TiO2

Absorption of the powder alone

Au colloids on TiO2

on Al2O3

B. Van Duppen, L. Delannoy, YB, unpublished

510 nm

isolated Au sphere

Plasmon resonance of gold spheres on an oxide powder

02 mAu

Plasmon resonance :

.subsm 121

crude approximation to get an idea

74.2

2

32

TiO

OAl

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Overview

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Gold was considered inactive till the 80'

In 1987 Haruta* showed that Au NPs are active for the CO oxidation

Keypoints:

• size < 5 nm

• active at room temperature

• supported on reducible oxide:

TiO2 > CeO2 > Al2O3

22 COO21CO

M. Haruta, Chem. Record 3 (2003) 75.

0° C

160° C

Gold-nanoparticle-based catalyst for oxidation reactions

* Masatake Haruta et al. Chem. Lett. 1987, 2, 405

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Pt-Rh (0.2-0.3 wt %)

Washcoat of alumina-ceria

Honey-comb monolithCordierite (MgO, Al2O3, SiO2)

engine Pt-Rh (0.2-0.3 wt %)

Washcoat of alumina-ceria

Honey-comb monolithCordierite (MgO, Al2O3, SiO2)

engine

1. Fundamental interest: what is the mechanism ?

2. Applications

• CO oxidation in catalytic exhausts

• Purification of hydrogen for fuel cells

80% of vehicle pollution comes from the engine cold-start

anode: H2 oxidation

cathode: O2 reduction

Methanol reforming:CH3OH + H2O 3 H2 + CO2 + (CO)

Problem of poisoning of the Pt anode by CO

Gold-nanoparticle-based catalyst for CO oxidation

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Some issues :

What is the size of the more active particles ? Is there a minimal size ? What shape ? 3D ou 2D ?

Electronic microscopy and reactivity

Does oxygen adsorb on Au NPs ? Is there any charge transfer ? Optical studies (plasmon resonance)

What are the active sites (adsorption / dissociation of O2) ? Optical studies and reactivity

2.

1.

3.

Gold-nanoparticle-based catalyst for CO oxidation

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Overview

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M. Haruta, Chem. Record 3 (2003) 75.

0° C

160° C

22 COO21CO

* Masatake Haruta et al. Chem. Lett. 1987, 2, 405

MC Saint Lager et al, J. Phys Chem. 115, 4673 (2011)

Gold-nanoparticle-based catalyst for oxidation reactions

Gold was considered inactive till the 80'

In 1987 Haruta* showed that Au NPs are active for the CO oxidation

Keypoints:

• size < 5 nm

• active at room temperature

• supported on reducible oxide:

TiO2 > CeO2 > Al2O3

• maximum activity around 2-3 nm (?)

still under discussion

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Difficulties : The actual samples display size and shape distributions

The very small nanoparticles (< 1 nm) are not easily visualisable

Some minority NPs can provide the activity of a catalyst

Aberration-corrected High-angle annular darkfield (HAADF)

scanning transmission electron microscopy (STEM)

Size and shape of the active Au nanoparticles

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Herzing, Hutchings et al, Science 321, 1331 (2008)

« High catalytic activity for carbon monoxide oxidation is correlated with the presence of bilayer clusters that are ~ 0.5 nanometer in diameter and contain only ~ 10 gold atoms. »

Aberration-corrected scanning transmission electron microscopy

bilayer clusters

individual atoms

Chen-Goodman, Science 2004,Chem. Soc. Rev., 2008, 37, 1860

"These studies have shown that a bilayer Au structure is a critical feature for catalytically active Au nanoparticles, along with low coordinated Au sites, support-to-particle charge transfer effects, and quantum size effects."

...in agreement with previous results on model catalysts

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Herzing, Hutchings et al, Science 321, 1331 (2008)

« High catalytic activity for carbon monoxide oxidation is correlated with the presence of bilayer clusters that are ~ 0.5 nanometer in diameter and contain only ~ 10 gold atoms. »

Aberration-corrected scanning transmission electron microscopy Size and shape of the active Au nanoparticles

bilayer clusters

individual atoms

Liu, Schuth et al, Angew. Chem. Int. Ed. 49, 5771 (2010)

« For the current catalyst, gold nanoclusters have diameters larger than 1 nm and bilayer structures and/or diameters of about 0.5 nm are not mandatory to achieve the high activity. »

...in disagreement with other recent measurements...

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Au / TiO2 : Deposition-Precipitation with Urea

Thermal treatment in hydrogen (300 °C) very small Au° particles ( 1-5 nm )Thermal treatment in air (500 °C) small Au° particles ( 2-6 nm )

drying

RT/vacuum

thermal

treatm

ent

water

washings

HAuCl4 + TiO2 (or Al2O3) + urea (CO(NH2)2)

H2O/80°C

Au0

R. Zanella, L. Delannoy, C. Louis, Appl. Catal. A 291, 62 (2005)

complex with Au3+


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Au / TiO2 reduced 300°C Au / TiO2 calcined 500°C

activityextremely active majority : 2-4 nm

very active majority : 2-5 nm

3.56 +/- 0.9 nm3.20 +/- 1.4 nm

1-2 2-3 3-4 4-5 5-6 6-7 (nm) 1-2 2-3 3-4 4-5 5-6 6-7 (nm)


L. Delannoy, R. Chantry, S. Casale, C. Louis, Ziyou Li, Y. Borensztein, Phys. Chem. Chem. Phys. 15, 3473 (2013)

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Au / TiO2 calcined 500°CAberration-corrected High-angle annular dark field (HAADF) STEM

detachment of a sub-nanometer cluster through electron beam effects



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Au / TiO2 calcined 500°CAberration-corrected High-angle annular dark field (HAADF) STEM

detachment of a sub-nanometer cluster through electron beam effects

Main conclusions about the active Au NPsfor the oxidation of CO

1. The active Au particles on TiO2 are 3D (truncated octahedron)

2. Their size is 1.5 - 3 nm

3. Bigger particles are not or very few active4. Active Au/TiO2 catalysts don't have clusters < 1 nm, nor bilayer clusters



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Overview

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Near Ambient Pressure XPS (Berkeley)

0.2 Torr O2

UHV

« Adsorbed O2 and O2- may play a key role in supplying reactive oxygen »

« Au NPs supported on TiO2 do not donate or accept additional charge when the sample is exposed to O2 »

Evaporated Au NPs / TiO2(110)

"Model" catalyst

10 nmNaitabdi, Prévot, Bernard, Borensztein, 2011, unpublished

(under 10-4 torr O2)

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Near Ambient Pressure XPS (Berkeley)

0.2 Torr O2

UHV

« Adsorbed O2 and O2- may play a key role in supplying reactive oxygen »

« Au NPs supported on TiO2 do not donate or accept additional charge when the sample is exposed to O2 »

Evaporated Au NPs / TiO2(110)

"Model" catalyst1. Model catalyst: Au NPs evaporated on TiO2(110)

2. Low pressure of O2 (0.2 Torr)

10 nmNaitabdi, Prévot, Bernard, Borensztein, 2011, unpublished

(under 10-4 torr O2)

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Au / TiO2 : Deposition-Precipitation with UreaVery Active

Thermal treatment in hydrogen (300 °C) very small flat Au° particles ( 1-5 nm )Thermal treatment in air (500 °C) small flat Au° particles ( 2-6 nm )

drying

RT/vacuum

thermal

treatm

ent

water

washings

HAuCl4 + TiO2 (or Al2O3) + urea (CO(NH2)2)

H2O/80°C

Au0

complex with Au3+

Au colloids (PVA) / Al2O3Poorly Active

round "big" Au° particles ( 4 - 6 nm )


"Real" catalysts : chemical Au NPs dispersed on oxide powder

Thermal treatment small and flatter particles (1 - 5 nm)

2 nm

AuPVA

AuPVA

Au colloid

Au colloid

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0

1

2

400 500 600 700 800

Abso

rptio

n

Wavelength of light (nm)

Oxygen adsorption on Au NPs ? Charge transfer ?

Operando investigation on Au colloids on Al2O3: switch from H2 to O2

• Better controlled Au NPs: 4 - 6 nm spherical colloids

• Al2O3 not reducible (i.e. no effect expected with O2)

If oxygen adsorbs on Au NPs, we expect a modification of the plasmon resonance

experiment

calculation for spheres


+ oxide powder

+ calcination in air at 500 °

Plasmon resonance

10 nm

Decrease of the electron density

Red shift of the plasmon resonance

Au colloid

Au colloid

AuPVA

AuPVA

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Monitoring the optical response changes with gases

2

22

H

HO

R

RR

RR

DDR:

Comparison between

- a reducing gas (H2)

- and an oxidant one (O2)

Differential Diffuse Reflectance

gas flow

Devoted cell for in-situ study

under O2

to the spectrometer

under H2

UV-vis light

under O2under O2

to the spectrometer

under H2

UV-vis light

to the time-resolved spectrometer

visiblelight

under H2 under O2


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Monitoring the optical response changes with gases

2

22

H

HO

R

RR

RR

DDR:

Comparison between

- a reducing gas (H2)

- and an oxidant one (O2)

Differential Diffuse Reflectance

gas flow

Devoted cell for in-situ study

under O2

to the spectrometer

under H2

UV-vis light

under O2under O2

to the spectrometer

under H2

UV-vis light

to the time-resolved spectrometer

visiblelight

under H2 under O2


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2

22

H

HO

R

RR

RR

Differential DiffuseReflectance (DDR)

surface plasmon absorption of Au / Al2O3

The DDR spectrum appears as a derivative of the plasmon resonance

( mainly due to a red shift )

H2 O2

Borensztein, Delannoy, Barrera, Louis, J. Phys. Chem. C114, 9008 (2010) ;Eur. Phys. J. D 63, 235 (2011)


Inactive catalyst : Au colloids / Al2O3

increasing time of exposure to O2

Au colloid

Au colloid

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Reversibility

H2 O2 O2 H2increasing amount of O2 increasing

amount of H2

-0.1

-0.08

-0.06

-0.04

-0.02

0

0.02

0 100 200 300 400 500Time (s)

kinetics

intro O2

intro H2

cell isolated with O2


Au colloid

Au colloid

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0.0075 ~ 50 electrons

0.03 e / surf. atom

0.0265~ 180 electrons

0.1 e / surf. atom

charge transfer N/N

experiment

calculation

-0.12

-0.1

-0.08

-0.06

-0.04

-0.02

0

0.02

0.04

400 500 600 700 800wavelength (nm)

DD

R

Charge transfer from Au to oxygen

Borensztein, Delannoy, Barrera, Louis, J. Phys. Chem. C114, 9008 (2010) Eur. Phys. J. D 63, 235 (2011)

21

p21

o

2mod

pNN1

meNN

eV9m

eNo

2

p

)()i(

1)( bi1

2p


6 nm

6700 atoms

1500 surface atoms

- -

Au colloid

Au colloid

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Overview

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2

22

H

HO

R

RR

RR

H2 O2

T = 22 °C T = 90 °C

- a larger amount of oxygen is adsorbed on Au at larger temperature- the adsorption is faster- two-step process

increasing amount of O2

Kinetics:

-0.18

-0.14

-0.1

-0.06

-0.02

0.02

30 80 130 180 230 280Time (s)

-0.18

-0.14

-0.1

-0.06

-0.02

0.02

30 80 130 180 230 280Time (s)

Oxygen adsorption on Au NPs ? Charge transfer ?Effect of temperature

Au colloid

Au colloid

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-0.2

-0.1

0

460 480 500 520 540 560 580 600Time (sec)

-0.16

-0.12

-0.08

-0.04

0

40 60 80 100 120 140 160 180Time (sec)

Kinetic effects : 2-step processT = 90 °C

-0.16

-0.12

-0.08

-0.04

0

40 60 80 100 120 140 160 180Time (sec)

O2 introduction H2 introduction

Time (sec) Time (sec)

Au colloid

Au colloid

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-0.2

-0.1

0

460 480 500 520 540 560 580 600Time (sec)

-0.16

-0.12

-0.08

-0.04

0

40 60 80 100 120 140 160 180Time (sec)

T = 90 °C

-0.16

-0.12

-0.08

-0.04

0

40 60 80 100 120 140 160 180Time (sec)

O2O2

tentative picture of the O2 adsorption


H2 purging

very reactive sites( perimeter, edge or corner sites )

Kinetic effects : 2-step processAu

colloidAu

colloid

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O2

Hammer, Molina, PRL 2003, PRB 2004Au-MgO interface

Active sites ?

"We propose that under operational conditions, Au particles will have such atomic oxygen at the metal/oxide interface perimeter forming a nano-scale Au-oxide.

It is oxygen from this part of the system that is responsible for the CO oxidation reaction. "

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-0.2

-0.1

0

460 480 500 520 540 560 580 600Time (sec)

-0.16

-0.12

-0.08

-0.04

0

40 60 80 100 120 140 160 180Time (sec)

T = 90 °C

-0.16

-0.12

-0.08

-0.04

0

40 60 80 100 120 140 160 180Time (sec)

O2O2

H2H2H2H2



H2 purging

very reactive sites( perimeter, edge or corner sites )


colloidAu

colloid

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-0.16

-0.12

-0.08

-0.04

0

40 60 80 100 120 140 160 180Time (sec)


-0.2

-0.1

0

460 480 500 520 540 560 580 600Time (sec)

T = 90 °C

tentative picture of the O2 desorption

H2H2H2 H2H2

H2 introduction

O2purging

O2 introduction


colloidAu

colloid

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Conclusions

1. In "usual" catalysts, the active Au particles are 3D, 1-3 nm large

2. Oxygen adsorbs on Au NPs and induces a charge transfer, visible by a reversible shift of the surface plasmon resonance

3. A long-wavelength resonance is present for the highly catalytic Au / TiO2:

• Extremely sensitive to oxygen• Is it related to specific sites (perimeter?) on which O2 would adsorb

easily, and for a nanoscale oxide ?

Perspectives1. Better understand the origin of the long wavelength resonance2. Role of the support (TiO2 , Al2O3...)3. Environnemental XPS4. Vibrational methods : IR , SFG, SERS5. Local studies of Au NPs under reactive gas by use of Environmental STM

We combined electron microscopy, reactivity measurements, plasmon resonance studies, for investigating Au-based catalysts

Is this the key-point for the reactivity ?

Kinetics of gas adsorption on gold nanoparticles in ...

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