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
Metallic nanocristals
A.S. Barnard,
octahedra
truncated octahedra
truncated cube
cuboctahedra
icosahedra
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1.7 nm
1.8 nm
1.3 nm
Metallic nanocristals
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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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
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
400 500 600 700 800 900 1Wavelength of light (nm)
Abs
orpt
ion
light reference, then sample
detector
light reference, then sample
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
400 500 600 700 800 900 1Wavelength of light (nm)
Abs
orpt
ion
light reference, then sample
detector
light reference, then sample
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
02 mAu
Plasmon resonance :
.subsm 121
crude approximation to get an idea
74.2
2
32
TiO
OAl
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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
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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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
Overview
- 16 -
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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Size and shape of the active Au nanoparticles
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+
Size and shape of the active Au nanoparticles
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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)
Size and shape of the active Au nanoparticles
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
Size and shape of the active Au nanoparticles
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
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
Size and shape of the active Au nanoparticles
L. Delannoy, R. Chantry, S. Casale, C. Louis, Ziyou Li, Y. Borensztein, Phys. Chem. Chem. Phys. 15, 3473 (2013)
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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
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 )
PVA colloid Au NPs on Al2O3
"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
PVA colloid Au NPs on Al2O3
+ 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
Oxygen adsorption on Au NPs ? Charge transfer ?
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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
Oxygen adsorption on Au NPs ? Charge transfer ?
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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)
Oxygen adsorption on Au NPs ? Charge transfer ?
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
Oxygen adsorption on Au NPs ? Charge transfer ?
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
Oxygen adsorption on Au NPs ? Charge transfer ?
6 nm
6700 atoms
1500 surface atoms
- -
Au colloid
Au colloid
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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
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
O2 introduction H2 introduction
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
tentative picture of the O2 adsorption
O2 introduction H2 introduction
H2 purging
very reactive sites( perimeter, edge or corner sites )
Kinetic effects : 2-step processAu
colloidAu
colloid
- 40 -
-0.16
-0.12
-0.08
-0.04
0
40 60 80 100 120 140 160 180Time (sec)
tentative picture of the O2 adsorption
-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
Kinetic effects : 2-step processAu
colloidAu
colloid
- 41 -
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 ?
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