1 d. bazin l’interaction agrégat métallique - molécule au cœur des processus physicochimiques...

1

D. Bazin

L’interaction Agrégat métallique - Molécule au cœur des processus physicochimiques

environnementaux

Laboratoire de Physique de la Matière CondenséeLaboratoire mixte de l’école Polytechnique et du CNRS (UMR 7643)

3 Novembre 2005

2

Objectiv of the lecture

Cluster BehaviourAdsorption Mode

II

3

PLANI. X-ray Absorption Spectroscopy

II. Interaction between nanometer scale metallic cluster & NO

4

I.1 X-ray Absorption Spectroscopy

x(E) log

SI0 I1E

1s

2s

2p1/2

2p3/2

Sayers, D. A., Lytle F. W. and Stern E. A., Advances in X-ray Analysis, (Ed. Plenum, New-York, 13, 1970).

0

0,5

1

1,5

2

2,5

11400 11600 11800 12000 12200 12400

Absorption

Energy (eV)

Pt, LIII

I

5

I.1 The associated formula

Electronic termsfj(k), j(k),

Structural termsNj , Rj , j.

(k) =j Nj/kRj

2 fj(k)exp(-Rj/)exp(-2j2k2)sin(2kRj +j(k))

-0,3

-0,2

-0,1

0

0,1

0,2

0,3

2 4 6 8 10 12 14 16

k(Å-1)

Pt, LIII

edge

0

0,5

1

1,5

2

2,5

11400 11600 11800 12000 12200 12400

Absorption

Energy (eV)

Pt, LIII

Modulus of the Fourier Transform or

Pseudo radial distribution function

R(Å)-a

N

Pt

( )R Å 2 3 4 5 6

I

6

I.2 Nanometer scale metallic cluster & Xas

• D. Bazin, D. Sayers, J. Rehr, Comparison between Xas, Awaxs, Asaxs & Dafs applied to nanometer scale metallic clusters. J. Phys. Chem. B 101, 11040 (1997).• D. Bazin, D. Sayers, J. Rehr, C. Mottet Numerical simulation of the Pt LIII edge white line relative to nanometer scale clusters, J. of Phys. Chem. B 101, 5332 (1997).• D. Bazin, J. Rehr, Limits and advantages of X-ray absorption near edge structure for nanometer scale metallic clusters. J. Phys. Chem. B 107, 12398 (2003).

0

5

10

15

20

25

0 1 2 3 4 5 6 7

N1N2N3N4

Diameter (nm)

I

7

I.3 Some examples



R(Å)-a

N

Pt

( )R Å 2 3 4 5 6

Cl

Pt

Impregnation

0 1 2 3 4 5 6R(Å)

_ H2PtCl

6

.. Pt/Y-SiO2

_ PtO2

Modules de T.F. (u.a.)

Pt, LIII

Pt PtPtPt

PtPt Pt

Reduction

0 1 2 3 4 5 6

Modules de la T.F. (u.a.)

... Pt/Y-SiO2

R(Å)

__ PtO2

_ Pt métal

1%wt Pt/oxide• Xas studies of bimetallic Pt-Re(Rh)/Al2O3 catalysts in the

first stages of preparation.D. Bazin et al., J. of Cat. 110, 209 (1988).• Bimetallic reforming catalysts : Xas of the particle

growing process during the reduction.D. Bazin et al., J. Cat. 123, 86 (1990).• In situ high temperature and high pressure Exafs

studies of Pt/ Al2O3 catalysts : Part I.N. S. Guyot-Sionnest et al., Cat. Let 8, 283 (1991).• In situ high temperature and high pressure Exafs

studies of Pt/ Al2O3 catalysts : Part II.N. S. Guyot-Sionnest et al., Cat. Let 8, 297 (1991).• Investigation of dispersion and localisation of Pt species

in mazzite using Exafs.A. Khodakov et al. J. of Phys. Chem. 101, 766 (1996).• In situ study by Xas of the sulfuration of industrial

catalysts : the Pt & PtRe/Al2O3 system.A. Bensaddik et al., Applied Cat. A 162, 171, (1997).• Xas of electronic state correlations during the reduction

of the bimetallic PtRe/Al2O3 system.D. Bazin et al., J. of Synchrotron Radiation 6, 465, 1999.• Influence of the H2S/H2 ratio and the temperature on the

local order of Pd atoms in the case of a highly dispersed multimetallic catalyst : Pd-Ni-Mo/Al2O3.

D. Bazin et al., J. de Physique IV, 12-6, 379, (2002).• Structure & size of bimetallic PtPd clusters in an

hydrotreatment catalyst.D. Bazin et al., Accepted in Oil & Gas Science and

Technology – Rev. IFP

Reforming …Pt, PtPd, PtRh, PtMo,PtSn,PtRe, PtIr,Fischer–Tropsch, Co, CoPt, CoPd, CoRu,

I

Calcination

0 1 2 3 4 5 6

_ H2PtCl

6

_ PtO2

.. Pt/Y-SiO2

Modules de la T.F. (u.a.)

R(Å)

O

O

PtO

O

8

I.4 Nanometer scale metallic cluster & R.S.

I

2 3 4 5 6

N=2057

N=147

N=1415

111

200 220

311

222

N=923

N=561

N=309

N=55

N=13

k(Å-1)

Intensity (a.u.)

• Real time in situ Xanes approach to characterise electronic state of nanometer scale entities D. Bazin, L. Guczi, J. Lynch, Rec. Res. Dev. Phys. Chem. 4, 259, 2000.• Soft X-ray absorption spectroscopy and heterogeneous catalysis. D. Bazin, L. Guczi, App. Cat. A 213/2, 147, 2001.

• Comparison between Xas & Awaxs applied to monometallic clusters. D. Bazin, D. Sayers, Jpn J. Appl. Phys. 32-2, 249, 1993.• Comparison between Xas & Awaxs applied to bimetallic clusters. D. Bazin, D. Sayers, Jpn J. Appl. Phys. 32-2, 252, 1993.• AWAXS in heterogeneous catalysis D. Bazin, L. Guczi, J. Lynch, App. Cat. A 226, 87, 2002.

• New opportunities to understand heterogeneous catalysis processes through S.R. studies and theoretical calculations of density of states : The case of nanometer scale bimetallic particles D. Bazin, C. Mottet, G. Treglia, Applied Catalysis A (1-2), 47-54, 2000.• New trends in heterogeneous catalysis processes on metallic clusters from S.R. & theoretical studies D. Bazin, C. Mottet, G. Treglia, J. Lynch, Applied Surf. Sci. 164, 140, 2000.

J.D. Grunwaldt et al., J. of Cat. 213,291 (2003) L. Drozdova et al. J. Phys. Chem. B 106,2240 (2002)

9

II. Catalyse DeNOx

II.1 IntroductionII.2 Behaviours of the metallic clusters Ex : NO/PtII.3 NO adsorption on metallic surfaceII.4 NO adsorption on metalic clusters (Ru & Pt)II.5 Remarks from Prof. J. Friedel II.6 Other experimental results Ir,Rh,Cu,Pt,PdII.7 Discussion : Support, Preparation, Cluster size, Temp.II.8 Some explanationsII.9 Mechanisms Pt,Cu,Rh,Ru,IrII.10 CO on metallic surface II.11 A bridge between surface science and nanoscience : Implications in heterogeneous catalysis : How to select a catalyst

LMSPC

II

10

Alumina

Ceria

Pt/Rh

II.1 Introduction

The Goal : To obtain CO2 and N2 from CO and NOx

LMSPC

II

11

Pt, Rh, CeO2, Al2O3

Pt :CO+1/2O2 __>CO2 & HC + O2 __> CO2 + H2O

Rh NO+CO__>1/2 N2+CO2 &NO+H2 __>1/2N2+H2O

CeO2 :

Oxygen (Ce3+ ____> Ce4+)Al2O3 : High specific surface (>200m2/g)

PtRh

LMSPC

II

A detailed study of the metallic function of bimetallic PtRh post combustion catalyst by Xas, Met : correlation with their catalytic activity, D. Bazin et al., J. de Phys. IV, C2 - 841, 1997.

NO reaction over nanometer scale Pt clusters deposited on -Al2O3

S. Schneider et al., App. Cat. A 189, 139, 1999.

Analyse par Exafs d'agrégats de platine de taille nanométrique soumis à différents gaz réactifsS. Schneider et al., J. de Phys. IV, Pr10, 299, 2000.

An Exafs study of the interaction of different reactant gases over nanometer scale Pt clusters deposited on -Al2O3.

S. Schneider et al., Cat. Let. 71,155, 2001.

12

II.2 Behaviours of the metallic clusters Ex : NO/Pt

Initial state

II

D. Bazin, L. Guczi, , Recent Res. Dev. Phys. Chem. 3, 387, 1999.D. Bazin, C. Mottet, G. Treglia, J. Lynch, Applied Surf. Sci. 164, 140, 2000.

13

NO/Pt Experimental data



R(Å)-a

N

Pt

( )R Å 2 3 4 5 6

Initial state

14

II.3 NO adsorption on metallic surface

G. Broden et al. Surf. Sci. 59, 593 (1976).

Ability of transition metal surface to dissociate the NO molecule from G. Broden et al.

Sc Ti V Cr Mn Fe Co Ni CuY Zr Nb Mo Tc Ru Rh Pd AgLu Hf Ta W Re Os Ir Pt Au

Metals which are associated with a molecular chemisorption are in red style, the others give rise to a dissociative chemisorption.

In particularly, in the case of NO, we can distinguish metals for which there is dissociative chemisorption and

those for which molecular chemisorption occurs.

II

15

W. A. Brown , D. A King. J. Phys. Chem. B, 104, 2581 ( 2000).

The melting points are a direct measure of the cohesive energies of the elements. The higher the metal cohesive energy, the greater is the propensity for NO dissociation.

More recently, W. A. Brown and D. A. King suggest a correlation between the propensity for dissociation of the NO monomer at low

coverage and the melting points of the transition metals.

II

16

II.4 NO adsorption on metalic clusters (Ru & Pt)

In the case of Ru, the adsorption of NO leads to break up the metallic cluster T. Hashimoto et al., Physica B 208& 209, 683 (1995).

Ru

NO adsorption induces a sintering of the Pt clusters deposited on-Al2O3 .P. Lööf et al., J. Catal. 144 (1993) 60.S. Schneider et al., App. Cat. 189, 139 (1999).

PtInitial state

II

17

Correlation adsorption mode & cluster behaviour ?

D. Bazin, Topics in Catalysis 18(1), 79, 2002.

II

18

II.5 Remarks from Prof. J. Friedel

II

0

500

1000

1500

2000

2500

3000

3500

4000

10 20 30 40 50 60 70 80 90

3d4d

5d

Melting Point °C

Atomic Number

Pt

Au

Ir

Os

Re

W

Ta

Hf

Lu

Ag

Pd

Rh

Ru

Mo

Nb

Zr

Y

Zn

Cu

Ni

Mn

Cr

Na + O

a

Fragmentation processof the metallic cluster

NOa

Sintering process of the metallic cluster

19

II.6 Other experimental results Ir,Rh,Cu,Pt, Pd

At 500°C, almost all NO in contact with Ir0 was decomposed to N2 and oxidized Ir0 to IrO2 .C. Wögerbauer, et al. J. of Catalysis, 205, 157-167 (2002).

0

500

1000

1500

2000

2500

3000

3500

4000

10 20 30 40 50 60 70 80 90

3d4d

5d

Melting Point °C

Atomic Number

Pt

Au

Ir

Os

Re

W

Ta

Hf

Lu

Ag

Pd

Rh

Ru

Mo

Nb

Zr

Y

Zn

Cu

Ni

Mn

Cr

Na + O

a


NOa


II

20

II.6 Other experimental results Ir,Rh,Cu,Pt, Pd

Examination of the effects of the individual gases showed that NO alone disperses Rh over the SiO

2

K. R. Krause et al. J. of Catalysis, 140 (1993) 424.

• In the initial state, the environment of Rh atoms is NRhRh

= 8 @ 2.68Å. After

exposure to 4%NO/He at 313K for 5 s, NRhRh

has significantly decreased

(NRhRh

=2). Note the presence of N (NRhN

[email protected]Å) & O (NRhO

=2 @2.05Å).

T. Campbell et al. Chem. Comm. 304-305 (2002)

Surface studies of supported model catalystsSurface Science Reports 31 (1998) 231-325Claude R. Henry

II

21

II.6 Other experimental results Ir,Rh, Cu, Pt, Pd

The adsorption and reaction of NO on Cu clusters deposited on a 5 Å thick Al2O3 film shows strong similarities to its behaviour on Cu single crystals. The STM results show that the Cu clusters grow according to the Volmer-Weber mechanism.

Nitric oxide reduction by Cu nanoclusters supported on thin Al2O3 films J. of Catalysis, Volume 22 ( 2004) 204.S. Haq, A. Carew and R. Raval

0

500

1000

1500

2000

2500

3000

3500

4000

10 20 30 40 50 60 70 80 90

3d4d

5d

Melting Point °C

Atomic Number

Pt

Au

Ir

Os

Re

W

Ta

Hf

Lu

Ag

Pd

Rh

Ru

Mo

Nb

Zr

Y

Zn

Cu

Ni

Mn

Cr

Na + O

a


NOa


II

22

II.6 Other experimental results Ir,Rh, Cu, Pt, Pd

X. Wang et al. Cat.Today 96 (2004) 11-20.

0

500

1000

1500

2000

2500

3000

3500

4000

10 20 30 40 50 60 70 80 90

3d4d

5d

Melting Point °C

Atomic Number

Pt

Au

Ir

Os

Re

W

Ta

Hf

Lu

Ag

Pd

Rh

Ru

Mo

Nb

Zr

Y

Zn

Cu

Ni

Mn

Cr

Na + O

a


NOa


II

23

II.6 Other experimental results Ir,Rh,Cu,Pt,Pd

In Xafs of the Pd/MgO catalyst indicates that neither Pd oxidation nor particle sintering occurs during heating in flowing 1%/NO/He to 300°C.

0

500

1000

1500

2000

2500

3000

3500

4000

10 20 30 40 50 60 70 80 90

3d4d

5d

Melting Point °C

Atomic Number

Pt

Au

Ir

Os

Re

W

Ta

Hf

Lu

Ag

Pd

Rh

Ru

Mo

Nb

Zr

Y

Zn

Cu

Ni

Mn

Cr

Na + O

a


NOa

Sintering process of the metallic clusterPd(111)

Pd(110)

Pd(100)

II

24

II.7 Discussion

Combining Solid State Physics Concepts & X-Ray Absorption Spectroscopy to understand heterogeneous catalysis, D. Bazin, D. Sayers, J. Lynch, L. Guczi, G. Treglia, C. Mottet

II

Discussion

•Nature of the support• Preparation procedure

• Cluster size• Temperature

25

II.7 Discussion : Support, Preparation, Cluster size, Temp.

Ru/-Al2O3Ir/

Rh/-Al2O3, ZrO2, CeO2

Cu/Al2O3 Pt/ SiO2, Al2O3

Support

Ru3(CO)12

Precursor

IrCl3(H2O)3, Ir(NH3)xCl3(H2O)y

RhCl(CO)2/-Al2O3

H2PtCl6 Pt(NH3)4(OH)2

Cu : Evaporation

II

26

II.7 Discussion : Support, Preparation, Temp., Cluster size

Effect on the NO adsorption mode

Rh NO adsorbs molecularly on Rh at low temperatures and dissociatively at higher temperatures. On Rh[100], molecular NO dominates upon adsorption at 100K, but heating leads to N2 and O2 production in TPD, suggesting dissociation.

Ni molecular adsorption takes place on Ni at low temperature and at higher temperatures both molecular and dissociative adsorption are observed.

II

27

II.7 Discussion : Support, Preparation, Temp., Cluster size

II

0

5

10

15

20

25

0

10

20

30

40

50

60

70

0,20,30,40,50,60,70,80,91

N1N2N3N4

Diamètre (Å)

Dispersion

28

Preliminary conclusion

Discussion

• Nature of the support• Preparation procedure

• Cluster size• Temperature

• Pressure• Cluster morphology

0

500

1000

1500

2000

2500

3000

3500

4000

10 20 30 40 50 60 70 80 90

3d4d

5d

Melting Point °C

Atomic Number

Pt

Au

Ir

Os

Re

W

Ta

Hf

Lu

Ag

Pd

Rh

Ru

Mo

Nb

Zr

Y

Zn

Cu

Ni

Mn

Cr

Na + O

a


NOa


II

29

II.8 Some explanations : Cohesion energy

[a] A. Khoutami, PhD thesis, Paris XI University (1993).[b] F. Baletto et al., Phys. Rev. Let. 84, 5544 (2000).[c] R. A. Guirado-Lopez, PhD thesis, Paris XI University (1999).

As it can be seen, a significant decrease of the cohesive energy, around 30%, is observed independently the nature of the metal and the morphology of the cluster [a-c].

2

3

4

5

6

7

0 500 1000 1500

Pt IcosahedraPt CubooctahedraPd IcosahedraPd CubooctahedraRu IcosahedraRu CubooctahedraRh Cubooctahedra

Cohesion Energy (eV)

Nb of atoms in the cluster

Ru ECoh

=4.28eV

Pd ECoh

=3.91eV

Pt ECoh

=5.86eV

Rh ECoh

=3.03eV

How change the Brown diagram when we consider not metallic surface but metallic cluster ?

II

30

II.8 Some explanations : Validity of the straight line

these adsorption energies are more important for metals which are at the middle of the transition series, metals for which we observed here a dissociative adsorption.

/ Eads(N)/ + / Eads(O)/ > Edis(NO) + /Eads(NO)/

Dissociative chemisorption is the most stable situation 0

500

1000

1500

2000

2500

3000

3500

4000

10 20 30 40 50 60 70 80 90

3d4d

5d

Melting Point °C

Atomic Number

Pt

Au

Ir

Os

Re

W

Ta

Hf

Lu

Ag

Pd

Rh

Ru

Mo

Nb

Zr

Y

Zn

Cu

Ni

Mn

Cr

Na + O

a


NOa


II

31

II.9 Mechanisms Pt,Cu,Rh,Ru,Ir

High coverage regime

Initial state

II

High temperatureMobility & Decompostion of the nitrosyl species

0

500

1000

1500

2000

2500

3000

3500

4000

10 20 30 40 50 60 70 80 90

3d4d

5d

Melting Point °C

Atomic Number

Pt

Au

Ir

Os

Re

W

Ta

Hf

Lu

Ag

Pd

Rh

Ru

Mo

Nb

Zr

Y

Zn

Cu

Ni

Mn

Cr

Na + O

a


NOa


32

Initial state

II

N2 desorption

II.9 Mechanisms Pt,Cu,Rh,Ru,Ir

0

500

1000

1500

2000

2500

3000

3500

4000

10 20 30 40 50 60 70 80 90

3d4d

5d

Melting Point °C

Atomic Number

Pt

Au

Ir

Os

Re

W

Ta

Hf

Lu

Ag

Pd

Rh

Ru

Mo

Nb

Zr

Y

Zn

Cu

Ni

Mn

Cr

Na + O

a


NOa


High temperatureDecomposition process

33

Other molecules


O2 : 5.12 eV, N

2O : 4.4 eV

II

NO : 6.50 eV

/ Eads(N)/ + / Eads(O)/ > Edis(NO) + /Eads(NO)/

N2: 9.76 eV Sc Ti V Cr Mn Fe Co Ni Cu

Y Zr Nb Mo Tc Ru Rh Pd AgLu Hf Ta W Re Os Ir Pt Au

0

500

1000

1500

2000

2500

3000

3500

4000

10 20 30 40 50 60 70 80 90

3d4d

5d

Melting Point °C

Atomic Number

Pt

Au

Ir

Os

Re

W

Ta

Hf

Lu

Ag

Pd

Rh

Ru

Mo

Nb

Zr

Y

Zn

Cu

Ni

Mn

Cr

Na + O

a


NOa


34

II.10 CO on metallic surface

R.B. Anderson ”The fischer-Tropsch Synthesis”, Chap 4, Academic press, New York, 1984

In particularly, in the case of CO, we can distinguish metals for which there is dissociative chemisorption and those for

which molecular chemisorption occurs.

T=20°C T=200°C-300°C

Ability of transition metal surface to dissociate the CO molecule from R.B. Anderson


Dissociativ Non-Dissociativ

II

CO: 11.09 eV

35

II.10 Behaviours of the metallic cluster

Initial state

II

High coverage

High Temperature

On Pt clusters, A. Berko et al. [1] found that CO adsorption induces a significant increase in the initial size of the Pt nanoparticles of 1–2 nm even at room temperature. This agglomeration preceded by disruption of the smaller Pt nanoclusters at lower CO pressures is explained by CO-assisted Ostwald ripening, in which the mass transport proceeds via surface carbonyl intermediates. Similar results have been obtained in the case of Ru [2], Rh[3,4], Cu[5] and Pd [6,7]. [1] A. Berko et al. Surface Science 566568, 337 (2004).[2] T. Mizushima et al. J. Phys. Chem. 94, 4980 (1990).[3] H. F. J. Van't Blik et al. J. Phys. Chem. 87, 2264 (1983).[4] A. Suzuki et al. Angew. Chem. Int. Ed., 42, 4795 (2003).[5] X. Wang et al. J. Phys. Chem. B 2004, 108, 13667.[6] S. L. Anderson et al. J. Phys. Chem., 95, 6603(1991)[7] W. Vogel et al. J. Phys. Chem. B 102, 1750 (1998).

For all these metals, we are in the case of a non dissociative adsorption mode and it seems that the structural evolution of the nanometer scale metallic atoms follows the same scheme. Based on all these experimental facts, we can suppose that CO adsorption leads to a disruption of metal-metal atoms and to the formation of Metal-(CO)n species. Then, metallic clusters can be observed and as supposed in the case of Pt, mass transport proceeds via surface carbonyl intermediates. This general schema is quite close to the

one proposed in the case of NO adsorption process.

36

II.10 Behaviours of the metallic cluster

Initial state

II

Boudouard reaction2CO --> Cads+CO2

What happens if we consider metals which displays a dissociative adsorption mode? A beginning of the answer is given by the study performed by O. Ducreux et al. [1] on the Co/Al2O3 system. Through in situ X-ray diffraction experiments, the formation of a carbide is pointed out.

[1]O. Ducreux, PhD Thesis, University Paris VI, 1999.

37

II.11 A bridge between surface science and nanoscience

0

500

1000

1500

2000

2500

3000

3500

4000

10 20 30 40 50 60 70 80 90

3d4d

5d

Melting Point °C

Atomic Number

Pt

Au

Ir

Os

Re

W

Ta

Hf

Lu

Ag

Pd

Rh

Ru

Mo

Nb

Zr

Y

Zn

Cu

Ni

Mn

Cr

Na + O

a


NOa


Cluster BehaviourAdsorption Mode

II

38

II.11a the metal-support interaction ?

• As we have seen the relationship we have proposed between the adsorption mode of NO and the behaviour of the metallic cluster seems to be independant of the nature of the support, except for Pd. • For this metal, a great difference exists between MgO and CeO2. We have linked this dependency to the position of the metal versus the line which separates the two adsorption modes. • If this assumption is correct, such dependency is not so significant for other metals such Rh or Pt.

the metal-support interaction ?

0

500

1000

1500

2000

2500

3000

3500

4000

10 20 30 40 50 60 70 80 90

3d4d

5d

Melting Point °C

Atomic Number

Pt

Au

Ir

Os

Re

W

Ta

Hf

Lu

Ag

Pd

Rh

Ru

Mo

Nb

Zr

Y

Zn

Cu

Ni

Mn

Cr

Na + O

a


NOa


II

39

II.11b NO on monometallic cluster

For metals above the stability line, NO adsorption leads to the formation of a metal oxide. Thus, the catalytic activity tends to decrease.

0

500

1000

1500

2000

2500

3000

3500

4000

10 20 30 40 50 60 70 80 90

3d4d

5d

Melting Point °C

Atomic Number

Pt

Au

Ir

Os

Re

W

Ta

Hf

Lu

Ag

Pd

Rh

Ru

Mo

Nb

Zr

Y

Zn

Cu

Ni

Mn

Cr

Na + O

a


NOa


Catalytic activity of metallic clusters ?

For metals below the line, large metallic clusters are finally generated and evolution of the catalytic activity will follow these structural modifications.

II

NO

N2

t

40

II.11c Bimetallic systems

This simple model leads to a complete rejection of some bimetallic systems. For example, if we consider a RhRu bimetallic cluster, the NO adsorption process conducts to the formation of a metal oxide i.e. the dissociation of NO will stop.

0

500

1000

1500

2000

2500

3000

3500

4000

10 20 30 40 50 60 70 80 90

3d4d

5d

Melting Point °C

Atomic Number

Pt

Au

Ir

Os

Re

W

Ta

Hf

Lu

Ag

Pd

Rh

Ru

Mo

Nb

Zr

Y

Zn

Cu

Ni

Mn

Cr

Na + O

a


NOa


Al2O3CeO2

At the opposite, if we consider a PtCu bimetallic system, the NO adsorption will lead to some large clusters.

•A guideline for the choice of bimetallic systems is to add to Pt (or Cu) a second metal such Rh, Ru or Ir. If we consider the CeO2 support, the

PtPd bimetallic seems to be acceptable while the PtPd bimetallic system supported on alumina has to be rejected.

II

NO

N2

t

41

II.11d a mixture of NO+O2

For metals above the stability line, NO adsorption leads to the formation of a metal oxide. The presence of O2 will not change significantly this simple scheme. For these metals, it is necessary to add to a NO+O2 mixing, a reductor agent in order to retablish the metallic state of the atoms.

Thus, the presence of NO allowed the Pt particles to conserve a metallic character. In this case, we can probably play with the relative concentration of the two gases NO and O2 to keep a metallic state.

II

42

II.12 Conclusion & Perspectives

D. Bazin, (2003) Solid State Physics and Synchrotron Radiation Techniques to Understand Heterogeneous Catalysis in nanotechnology, Ed. G.A. Somorjai, S. Hermans, B. Zhou.D. Bazin, J. Lynch, M. Ramos-Fernandez, X-ray absorption spectroscopy and Anomalous Wide Angle X-ray Scattering Two basic tools in heterogeneous catalysis, Oil & Gas Science and Technology – Rev. IFP, 58 (2003), No. 6, pp. 667-683

• Nature of the support• Preparation procedure• Cluster size• Temperature

0

500

1000

1500

2000

2500

3000

3500

4000

10 20 30 40 50 60 70 80 90

3d4d

5d

Melting Point °C

Atomic Number

Pt

Au

Ir

Os

Re

W

Ta

Hf

Lu

Ag

Pd

Rh

Ru

Mo

Nb

Zr

Y

Zn

Cu

Ni

Mn

Cr

Na + O

a


NOa


Séminaires

7 Avril 2005 : Modélisation de l’interaction entre le monoxyde d’azote et un agrégat métallique de dimension nanométrique, Centre de Recherche en Matière Condensée et Nanosciences, Marseille, France11 Avril 2005 : L’interaction Agrégat métallique - Molécule au cœur des processus physico-chimiques environnementaux, Laboratoire de Chimie Théorique, Ivry sur Seine, France20 Avril 2005 : L’interaction Agrégat métallique - Molécule au cœur des processus physico-chimiques environnementaux, Groupe de Physique des solides (GPS), Paris, France

II

43

II.13 Remarks from Prof. J. Friedel

44

II.12 Conclusion & Perspectives

Structural Characterization @ the atomic scale

Catalytic Activity

1 d. bazin l’interaction agrégat métallique - molécule au cœur des processus physicochimiques...

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