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1Institute of Isotopes, Budapest, Hungary;2Research Institute for Technical Physics and Materials
Science, Budapest Hungary;3Chemical Physics of Materials, ULB, Brussels, Belgium
Gold and silver catalysts for abatement of Gold and silver catalysts for abatement of environmentally harmful materials: environmentally harmful materials:
modelling the structure dependencymodelling the structure dependency
Gold and silver catalysts for abatement of Gold and silver catalysts for abatement of environmentally harmful materials: environmentally harmful materials:
modelling the structure dependencymodelling the structure dependency
Krisztina FreyKrisztina Frey11, Gábor Pető, Gábor Pető22, , Viacheslav IablokovViacheslav Iablokov33, Norbert , Norbert
KruseKruse33 and László Guczi and László Guczi11
Krisztina FreyKrisztina Frey11, Gábor Pető, Gábor Pető22, , Viacheslav IablokovViacheslav Iablokov33, Norbert , Norbert
KruseKruse33 and László Guczi and László Guczi11
INTRODUCTIONINTRODUCTIONINTRODUCTIONINTRODUCTION
Automotive exhaust contains high concentrations of NOx, CO and
hydrocarbons, which are harmful to human health.
All commercial solutions (Three Way Catalysis, Selective Catalytic
Reduction, Storage, etc.) are based on platinum, palladium and
rhodium metal.
The present work is aimed at exploring the The present work is aimed at exploring the
potential of a new generation of potential of a new generation of
catalysts, based on catalysts, based on gold gold and and silversilver, to , to
replace the more expensive platinum and replace the more expensive platinum and
rhodium metals.rhodium metals.
GOAL of the present workGOAL of the present workGOAL of the present workGOAL of the present work
Provide sound understanding of the intrinsic properties of silver Provide sound understanding of the intrinsic properties of silver
and gold based model catalysts:and gold based model catalysts:
1.1. Compare activities CO oxidation between silver and gold Compare activities CO oxidation between silver and gold
supported catalysts.supported catalysts.
2.2. Study gold particles and gold films either in presence or Study gold particles and gold films either in presence or
absence of metal-oxide supports (TiOabsence of metal-oxide supports (TiO22 and FeO and FeOxx). What is the ). What is the
effect of metal-oxides?effect of metal-oxides?
3.3. Demonstrate the CO oxidation activity in sandwiched layers of Demonstrate the CO oxidation activity in sandwiched layers of
gold/metal-oxide systems („inversed” system). gold/metal-oxide systems („inversed” system).
4.4. Use high resolution microscopy (AFM) and spectroscopy (SIMS, Use high resolution microscopy (AFM) and spectroscopy (SIMS,
XPS) to characterize the morphology of the used layered XPS) to characterize the morphology of the used layered
catalysts. catalysts.
Justification of the ApproachJustification of the ApproachJustification of the ApproachJustification of the Approach
Unique electronic and Unique electronic and morphologicalmorphological properties properties may developmay develop when dimensions when dimensions reach the nanoscale.reach the nanoscale.
These changes These changes may alter the chemay alter the chemical reactivitymical reactivity..
Develop an understanding Develop an understanding of of the key features the key features ofof nanoscale nanoscale materials is a first step towards the materials is a first step towards the control and design of highly selective catalysts at control and design of highly selective catalysts at otherwiseotherwise optimum catalytic activity. optimum catalytic activity.
Ag/TiOAg/TiO22
Sample preparationSample preparation
Ag/TiOAg/TiO22
Sample preparationSample preparation
Ag(COO)Ag(COO)22 →→ Ag + 2 CO Ag + 2 CO22
Ag/TiO2 catalysts have been prepared via oxalate co-precipitationoxalate co-precipitation of AgNO3 and Ti(OCH(CH3)2)4 as precursors than TPO (temperature-programmed oxidation). Ag loadings in the catalysts were 2, 4, 7 and 10% (w/w).
0 2000 4000 6000 8000 10000Time (s)
Par
tial p
ress
ure
(a.u
.)
O2
CO2
CO
300
400
500
600
700
800
Tem
perature (K)
Temperature
10% Ag/TiO2
0 2000 4000 6000 8000 10000Time (s)
Par
tial p
ress
ure
(a.u
.)
O2
CO2
CO
300
400
500
600
700
800
Tem
perature (K)
Temperature
2% Ag/TiO2
TPOTPO
Ag/TiOAg/TiO22
Sample characterizationSample characterization
Ag/TiOAg/TiO22
Sample characterizationSample characterization
(HR)TEM(HR)TEM4%Ag/TiO4%Ag/TiO22 10%Ag/TiO10%Ag/TiO22
Ag
0 1000 2000 30000
500
1000
1500
CO
2 fo
rmed
, m
ol/g
cat
reaction time, s
2%Ag/TiO2
7%Ag/TiO2
10%Ag/TiO2
In circulate system: In circulate system: 9 mbar CO and9 mbar CO and 9 mbar 9 mbar O O22 and 162 mbar He and 162 mbar He at 313 Kat 313 K
Ag/TiOAg/TiO22
CO oxidation in circulate system CO oxidation in circulate system
Ag/TiOAg/TiO22
CO oxidation in circulate system CO oxidation in circulate system
EEaa=13-25 kJ/mol=13-25 kJ/mol
Ag/TiOAg/TiO22
CO oxidation in flow systemCO oxidation in flow system
Ag/TiOAg/TiO22
CO oxidation in flow systemCO oxidation in flow system
CO+OCO+O22 mixture of 2% each, using Ar as diluent with a flow mixture of 2% each, using Ar as diluent with a flow
rate of 50 ml/minrate of 50 ml/min..
300 350 400 450 500 5500
20
40
60
80
100
10% Ag 2% Ag 7% Ag
CO
con
vers
ion
(%
)
Temperature (K)
Au/SiOAu/SiO22/Si(100) catalysts/Si(100) catalystsAu/SiOAu/SiO22/Si(100) catalysts/Si(100) catalysts
CharacterizationCharacterizationCharacterizationCharacterization
TEMTEM particle size.
AFM AFM particle size and surface roughness.
SEM SEM scanning electron microscopy.
SIMS,SIMS, XPSXPS surface composition.
XPS, UPSXPS, UPS electron structure.
CO oxidationCO oxidation catalytic activity.
Effect examination:
Characterization:
The samples were treated in 200 The samples were treated in 200 mbarmbar H H22 at 573 K for at 573 K for
1 h, then at 803 K CO oxidation was performed in an all 1 h, then at 803 K CO oxidation was performed in an all
glass made circulation reactor connected to a QMS. A glass made circulation reactor connected to a QMS. A
mixture of mixture of 9 9 mbar CO + mbar CO + 1818 mbar O mbar O22 + 15 + 1533 mbar He was mbar He was
used. The initial rate of COused. The initial rate of CO22 formation was related to the formation was related to the
geometrical surface of the wafer (cc. 0.5 cmgeometrical surface of the wafer (cc. 0.5 cm22). ).
CO oxidationCO oxidationCO oxidationCO oxidation
Au/SiOAu/SiO22/Si(100)/Si(100)
Sample preparationSample preparation
Au/SiOAu/SiO22/Si(100)/Si(100)
Sample preparationSample preparation
Si SiO2 Au
Implantation(40 keV, 1015 atom/cm2)
Evaporation
hAu= 10 nm
hAu= 80 nm
Modelling „inverse” Modelling „inverse” FeOFeOxx/Au and TiO/Au and TiO22/Au system/Au system
Modelling „inverse” Modelling „inverse” FeOFeOxx/Au and TiO/Au and TiO22/Au system/Au system
80 nm Au film/SiO2/Si(100) Au nanoparticles/SiO2/Si(100)
Si Au FeOx, TiO2
Laser ablation (PLD)
SiO2
0 500 1000 1500 2000 2500 30000
5
10
15
20
25
30
35
CO
2 fo
rmed
, m
ol/c
m2
reaction time, s
FeOx/Au nanoparticles/SiO
2/Si(100)
FeOx/Au layer/SiO
2/Si(100)
FeOx/SiO
2/Si(100)
FeOFeOxx/Au/SiO/Au/SiO22/Si(100)/Si(100)
CO oxidationCO oxidation
FeOFeOxx/Au/SiO/Au/SiO22/Si(100)/Si(100)
CO oxidationCO oxidation
In circulate system: In circulate system: 9 mbar CO9 mbar CO, 18 mbar, 18 mbar O O22 and 162 mbar He and 162 mbar He at 803 K at 803 K
CO oxidationCO oxidationCO oxidationCO oxidation
Au nanoparticles
0,00E+00
5,00E-03
1,00E-02
1,50E-02
2,00E-02
2,50E-02
1 2 3 4samples
r o/
mo
l cm
-2s
-1
SiO2/Si(100)
Au/SiO2/Si(100)
FeOx/Au/SiO2/Si(100)
FeOx/SiO2/Si(100)
80 nm Au film
0,00E+00
5,00E-03
1,00E-02
1,50E-02
2,00E-02
2,50E-02
1 2 3 4samples
r o/
mol
.cm
-2.s
-1
SiO2/Si(100)
Au/SiO2/Si(100)
FeOx/Au/SiO2/Si(100)
FeOx/SiO2/Si(100)
FeOFeOxx/Au/SiO/Au/SiO22/Si(100)/Si(100)
CO oxidationCO oxidation
FeOFeOxx/Au/SiO/Au/SiO22/Si(100)/Si(100)
CO oxidationCO oxidation
CO oxidationCO oxidationCO oxidationCO oxidationTiOTiO22/Au/SiO/Au/SiO22/Si(100)/Si(100)
CO oxidationCO oxidation
TiOTiO22/Au/SiO/Au/SiO22/Si(100)/Si(100)
CO oxidationCO oxidation
0 1000 2000 3000 40000
20
40
60
80
CO
2 fo
rmed
, m
ol/
cm2
reaction time, s
TiO2/SiO
2/Si(100)
TiO2/8 nm Au layer/SiO
2/Si(100)
8 nm Au layer/SiO2/Si(100)
Au nanoparticles on SiOAu nanoparticles on SiO22/Si(100)/Si(100)Au nanoparticles on SiOAu nanoparticles on SiO22/Si(100)/Si(100)
AFMAFM
80 nm Au film/SiO80 nm Au film/SiO22/Si(100): AFM/Si(100): AFM80 nm Au film/SiO80 nm Au film/SiO22/Si(100): AFM/Si(100): AFM
80 82 84 86 88 90
Inte
ns
ity
a.u
.
Binding energy, eV
80 nm film Au/SiO2/Si(100)
10 nm implanted Au/SiO2/Si(100)
x10
Au characterizationAu characterizationBulk or nanoBulk or nano??
Au characterizationAu characterizationBulk or nanoBulk or nano??
Au 4f XPS Au 4f XPS
bulk
nanonano
Si 2p XPS Si 2p XPS Si 2p XPS Si 2p XPS
Au nanoparticles
80 nm Au film covered
uncovereduncovered
96 98 100 102 104 106 108 110
Inte
nsi
ty, a
.u.
Binding energy, eV
FeOFeOxx/Au/SiO/Au/SiO22/Si(100)/Si(100)FeOFeOxx/Au/SiO/Au/SiO22/Si(100)/Si(100)
196,5 197,0 197,5
MS
sig
na
l, a
.u.
mass (m/z)
Au/SiO2/Si(100)
Fe/Au/SiO2/Si(100)
80 nm Au film/SiO2/Si(100)
Au nanoparticles/SiO2/Si(100)SIMSSIMS
SEMSEM
OOn the surface of Fen the surface of Fe22OO33 covered covered Au/SiOAu/SiO22/Si(100) /Si(100) (Au nanoparticles (Au nanoparticles
& 80 nm thick Au& 80 nm thick Au film film)) no goldno gold was detected was detected..
705710715720725730735
Binding energy, eV
Inte
nsi
ty,
a.u
.
1
2
aFe 2p
Fe3+
Fe2+satellite
526528530532534536
Binding energy, eV
1
2
bO 1s
O2-
O=C
OH
XPS spectra of XPS spectra of FeOFeOxx/Au layer/SiO/Au layer/SiO22/Si(100)/Si(100)
XPS spectra of XPS spectra of FeOFeOxx/Au layer/SiO/Au layer/SiO22/Si(100)/Si(100)
FeFe22OO33 (Fe (Fe3+3+) and FeO (Fe) and FeO (Fe2+2+))
Effect of temperature used in CO Effect of temperature used in CO oxidation on the surface: cracks ?oxidation on the surface: cracks ?Effect of temperature used in CO Effect of temperature used in CO
oxidation on the surface: cracks ?oxidation on the surface: cracks ?
nano Au
FeOx/nano Au
80 nm Au
FeOx/80 nm Au
SEM SEM after 5 min reactionafter 5 min reaction
0.1 m
0.1 m
0.1 m
0.1 m
Core level binding energy is shifted to higher value when gold film was Core level binding energy is shifted to higher value when gold film was transferred into gold nanoparticles.transferred into gold nanoparticles.
When When anan “inverse” “inverse” Au/FeOAu/FeOxx iis fabricated bys fabricated by FeO FeOxx deposition onto deposition onto either either
Au nanoparticles/SiOAu nanoparticles/SiO22/Si(100) or 80 nm /Si(100) or 80 nm Au film/Au film/SiOSiO22/Si(100) reference /Si(100) reference
samplesample,, the the catalytic activity in the CO oxidation is enhanced compared catalytic activity in the CO oxidation is enhanced compared to to both both Au/SiOAu/SiO22/Si(100) and FeO/Si(100) and FeOxx/SiO/SiO22/Si(100). /Si(100).
The activity enhancement is larger for nano-type Au/FeOThe activity enhancement is larger for nano-type Au/FeOxx than for bulk- than for bulk-
type Au/FeOtype Au/FeOxx co-operation. The gold effect co-operation. The gold effect isis indirect, indirect, becausebecause Au Au is is not not
exposed to the surface exposed to the surface and it and it modifies the catalytically working FeOmodifies the catalytically working FeOxx..
The activity of theThe activity of the TiOTiO22/SiO/SiO22/Si(100) was higher than that of /Si(100) was higher than that of
TiOTiO22/Au/SiO/Au/SiO22/Si(100), which indicated an inhibiting effect of gold layer/Si(100), which indicated an inhibiting effect of gold layer
underneath the TiOunderneath the TiO22 overlayer. overlayer.
Ag/TiOAg/TiO22 catalysts with different Ag loadings (2, 4, 7 and 10% (w/w)) the catalysts with different Ag loadings (2, 4, 7 and 10% (w/w)) the
best conversion performance was obtained in a CO/Obest conversion performance was obtained in a CO/O22=1:1 mixture over =1:1 mixture over
10% Ag/TiO10% Ag/TiO22 for which the temperature of 50% CO conversion was for which the temperature of 50% CO conversion was
TT5050=333 K =333 K
We can conclude thatWe can conclude that
Thank you for your attention!Thank you for your attention!
Au Au nanoparticles nanoparticles on SiOon SiO22/Si(100):/Si(100):
before and after CO oxidationbefore and after CO oxidation
Au Au nanoparticles nanoparticles on SiOon SiO22/Si(100):/Si(100):
before and after CO oxidationbefore and after CO oxidation
beforebefore afterafter
J. Am. Chem. Soc., 125(14), 4332-4337 (2003)
1 6 1 2 8 4 0
8 0 0 0
1 0 0 0 0
1 2 0 0 0
1 4 0 0 0
1 6 0 0 0
1 8 0 0 0
Inte
nsi
ty (C
ount
s)
Binding Energy (eV)
After CO oxidationAfter CO oxidationAfter CO oxidationAfter CO oxidation
BULK!!!BULK!!!
10 nm implanted Au/SiO2/Si(100) XPS spectrum
1h catalytic reaction!
J. Am. Chem. Soc., 125(14), 4332-4337 (2003)
The aggregated Au particles shows „bulk type” electron structures.
FeOFeOxx/Au/SiO/Au/SiO22/Si(100)/Si(100)
Is FeOIs FeOxx porous? porous?
FeOFeOxx/Au/SiO/Au/SiO22/Si(100)/Si(100)
Is FeOIs FeOxx porous? porous?
0 500 1000 1500 20000
5
10
15
20
25
30
CO
2, m
ol/
cm
2
reaction time,s
10 nm FeO10 nm FeOxx/Au/SiO/Au/SiO22/Si(100)/Si(100)
40 nm FeO40 nm FeOxx/Au/SiO/Au/SiO22/Si(100)/Si(100)
40 nm FeOx/SiO2/Si(100)
In case of thick FeOIn case of thick FeOxx layer no effect of underlying gold on the catalytic activity layer no effect of underlying gold on the catalytic activity
of FeOof FeOxx..
AFM picture afterAFM picture after 5 min. reaction5 min. reaction
AFM picture afterAFM picture after 5 min. reaction5 min. reaction