1 Institute of Isotopes, Budapest, Hungary; 2 Research Institute for Technical Physics and Materials Science, Budapest Hungary; 3 Chemical 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 dependency modelling the structure dependency Krisztina Frey Krisztina Frey 1 , Gábor Pető , Gábor Pető 2 , , Viacheslav Iablokov Viacheslav Iablokov 3 , Norbert , Norbert Kruse Kruse 3 and László Guczi and László Guczi 1
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1 Institute of Isotopes, Budapest, Hungary; 2 Research Institute for Technical Physics and Materials Science, Budapest Hungary; 3 Chemical Physics of Materials,
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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).
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.
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