The document provides an overview of Hajo Freund's research on modeling heterogeneous catalysts at the atomic level. It discusses four conceptual studies: (1) investigating the active sites at metal-oxide interfaces in supported nanoparticle systems using scanning tunneling microscopy, (2) modeling amorphous silica supports through thin film preparation, characterization, and scanning probe microscopy, (3) examining adsorption and chemical reactions in confined spaces using infrared absorption spectroscopy, and (4) understanding the influence of morphology on reactivity through carbon dioxide activation studies. The research aims to develop molecular-scale models of heterogeneous catalysts through advanced surface science techniques.

1. Models for Heterogeneous Catalysts:
Complex Materials at the Atomic Level
Hajo Freund
Fritz Haber Institute of the Max Planck Society
Program
 Introduction
 4 conceptual studies :
nanoparticles/ amorphous silica/confined space
strong metal support interaction

2. Introduction: Catalysis
Activation Energy
Energy
without
Catalyst
With Catalyst
E*
∆E

3. Introduction: Catalysis at the Atomic Scale
The Active Center
Heterogeneous
Catalysis
Homogeneous
Catalysis
Enzymatic
Catalysis

4. Ammonia Synthesis
Technical Plant
Fritz Haber
1868 -1934
Nobel Price 1918World Production: 160 Mio t/a

5. Surface Science Models
Energy Profile
G. Ertl, Catal.Rev.Sci.Eng. 21(1980), 201
Gerhard Ertl
b. 1936
Nobel Price 2007
Fe(111)

6. Mustertext
Heterogeneous Catalysis
J. Sauer, H.-J. Freund; Catal Lett 145, 109 (2015)

7. Thin Oxide Film Systems
Scenarios
H.-J. Freund; Perspective J. Amer.Chem.Soc. 138, 8985 (2016)

8. Thin Oxide Film Systems
Area 1
Identification of the
Active Site at the Metal-Oxide
Interface
in supported nanoparticle systems

9. STM
Imaging Nano-Particles at the Rim
Thanks to Markus Heyde
and Shamil Shaikhutdinov
W.-D. Schneider, M. Heyde, HJF, Chem.Eur.J. accepted
(111) facet
(100) facet
(a) b(b)
K. H. Hansen et al.
Phys. Rev. Lett. 83, 4120 (1999)

10. Thin versus Thick Oxide Films
Density functional calculations
D. Ricci, A. Bongiorno, G. Pacchioni , U. Landmann, Phys. Rev. Lett. 97, 036106 (2006)

11. STM – MgO(001)/Ag(001)
Au nanoparticles on MgO thin films
Images: 30x30 nm², It=10 pA, US=+500 mV.
3 ML MgO(001)
anneal to 210 K anneal to 300 K
8 ML MgO(001)
M. Sterrer, T. Risse, M. Heyde, H.P. Rust, HJF, Phys. Rev. Lett. 96, 206103 (2007)

12. Au on MgO / Ag(001)
Low Temperature STM
Au18 Cluster
• Experimental
signature
X. Lin, N.Nilius, HJF, M. Walter, P. Frondelius, K. Honkola, H.Häkkinen, Phys. Rev. Lett., 102, 206801 (2009)
4-

13. Au on MgO / Ag(001)
Low Temperature STM
Harmonic oscillator model: Eigenstates
1S
2S
3S
1P
2P
1P
2P
1D
2D
1D
2D
1F
1G 1G
1F
Energy
Angular momentum quantum number
0 1 2 3-4 -3 -1
Au18
-4
Au14
-2
Au8
-2
-2 4

14. Properties of perimeter atoms
Au islands on MgO/Ag(001) films
5 K – STM
10 × 10 nm2
Parameterized
DFT-approach
StructureModel
Theory: Pekka Koskinen, Hannu Häkkinen, Nanoscience Center, University of Jyväskylä
X. Lin, N.Nilius, M.Sterrer, P. Koskinen, H. Häkkinen, HJF , Phys. Rev. B81, 153406 (2010)

15. Properties of perimeter atoms
Au islands on MgO/Ag(001) films
STM conductance imaging (10 × 10 nm2)
X. Lin, N.Nilius, M.Sterrer, P. Koskinen, H. Häkkinen, HJF, Phys. Rev. B81, 153406 (2010)

16. Vibrations at Surfaces
1 internal vibrational mode
3 frustrated translational modes
2 frustrated rotations
Individual CO Molecule on a Surface
N. V. Richardson and N. Sheppard, Vibrational Spectroscopy of Molecules on Surfaces, in Plenum Press, 1987, Ed. J. T. Yates, T. E. Madey

17. CO adsorption on planar islands
Au on MgO/Ag(001) films
45 mV, 10 × 10 nm2 -45 mV
Contrast in d2I/dV2 images relates to inelastic transport channels
Maximum signal at ±45 mV suggests excitation of CO hindered rotation
Au island
CO
MgO
+45 mV
Second derivative images
X. Lin, B. Yang, M. Brown, M. Sterrer, T. Risse, N. Nilius, et al. HJF;J. Amer. Chem. Soc. 132 7745 (2010)

18. Model Catalysts
Isophorone at the Rim
Ch. Stiehler, F. Calaza, W.-D. Schneider, N. Nilius, H.-J. Freund, Phys. Rev. Lett. 115, 0368041 (2015)
C9H14O

19. Model Catalysts
Physisorption vs. Chemisorption
Ch. Stiehler, F. Calaza, W.-D. Schneider, N. Nilius, H.-J. Freund, Phys. Rev. Lett.115, 0368041 (2015)

20. Influence of 2D3D Morphology on Reactvity
Carbon Dioxide Activation

21. Carbon Dioxide Activation
Electron Attachment
Energetics
CO2
-: - 0.6 eV,
(CO2)2
-: + 0.9 eV
H.-J. Freund, M.W. Roberts, Surf.Sci. Rep. 25, 225 (1996)
A. Stamatovic, K. Stephan, T.D. Märk; Int. J. Mass Spectr. 63 37 (1985)
R.N. Compton, P.W. Reinhardt, C.D. Cooper; J. Chem. Phys. 63, 3821 (1975)
(CO2)2 + e-  (CO2)2
-
A.R. Rossi and K.D. Jordan, J. Chem. Phys. 70 (1979) 4422

22. Model Catalysts
Carbon Dioxide Activation
0.3V 0.3VN=182 N=190
0 1 2 3 4
0.0
0.5
1.0
1.5
2.0 Pristine Cluster
Cluster with Molecules
FittedPeakPositionsU[V]
Quantum number n
0 1 2 3 4
0.0
0.1
0.2
0.3
0.4
Quantum number n
m*
Cl+mol = 0.7 m*
Cl
∆U = UCl+mol – Uprist
F. Calaza, C. Stiehler, Y. Fujimori, M.Sterrer, S. Beeg, M. Ruiz-Oses, N. Nilius, M. Heyde, T. Parviainen, K. Honkala, H. Häkkinen, H.-J. Freund;
Angew. Chem.Int. Ed. 54,12484 (2015); Ch. Stiehler, F. Calaza, W.-D. Schneider, N. Nilius, H.-J. Freund, Phys. Rev. Lett.115, 0368041 (2015)

23. Carbon Dioxide Activation
Isotopic Labeling in IRAS Spectra
1100 1200 1300 1400 1500 1600
13
CO2
/ 2ML MgO
C
18
O2
/ 2ML Mg
18
O
CO2
/ 2ML Mg
18
O
Absorbance/a.u.
wavenumber / cm
-1
1259
1275
1295
CO2
/ 2ML MgO
0.0004
F. Calaza, C. Stiehler, Y. Fujimori, M.Sterrer, S. Beeg, M. Ruiz-Oses, N. Nilius, M. Heyde, T. Parviainen, K. Honkala, H. Häkkinen, H.-J. Freund;
Angew. Chem. Int. Ed. 54,12484 (2015)

24. IRAS
2 ML MgO(001)/Ag(001) samples recorded after a saturation dose of CO2 at 223 K. Au was deposited at 100 K and
the samples subsequently annealed to the indicated temperature prior to CO2 adsorption.
Carbon Dioxide Activation
C.P. O´Brien, K.-H. Dostert, M. Hollerer, C. Stiehler, F. Calaza, S. Schauermann, S. Shaikhutdinov,, M. Sterrer, HJF, Farad. Disc. 188, 309 (2016)

25. Carbon Dioxide Activation
STM
STM images of (a) Au deposited on 2 ML MgO(001)/Ag(001) at 77 K, and subsequent annealing to 343 K (b), 400 K
(c) and 500 K (d). All images were taken at 77 K.
(a)‐(c) 25 nm  25 nm; (d) 50 nm  50 nm. Ubias = +(0.5‐0.75) V. It = 30 pA. The inset show height
C.P. O´Brien, K.-H. Dostert, M. Hollerer, C. Stiehler, F. Calaza, S. Schauermann, S. Shaikhutdinov,, M. Sterrer, HJF, Farad. Disc. 188, 309 (2016)

26. Model Catalyst Concepts
Dispersed Metal Catalyst Models: Dopants
Metal particles
Metal single crystal
Oxide film
Dopants

27. Mo-donors and the tip influence
Mo-doped CaO films on Mo(001)
Filled
25 ML CaO grown on Mo(001) (5050 nm2, 4.5 V)
Topo-graphic and dI/dV image of charging rings.
Adsorption of an O2 suppresses(118 nm2, 2.5eV)
STM images of 25 ML CaO annealed to the given temperatures (3030 nm2, 2.6 V)
On 50 ML thick films, the diameter is larger due to the bad dielectric screening (30x30 nm2, 4.4.eV)
Y. Cui, N. Nilius , H.-J. Freund, S. Prada, L. Giordano, G. Pacchioni, Phys.Rev. B 88, 205421 ( 2013)

28. Mo-donors and the tip influence
Mo-doped CaO films on Mo(001)
Filled
Y. Cui, S. Tosoni, W.-D. Schneider, G. Pacchioni, N. Nilius , H.-J. Freund, Phys. Rev. Lett. 114, 016804 (2015)

29. Growth behavior of gold
Mo-doped CaO films on Mo(001)
Pristine
CaO film
60 ML plus
0.8 ML Au
Mo-doped
CaO film
60 ML plus
2% Mo
0.8 ML Au
4040 nm2
 Crossover from 3D to 2D growth behavior for Au after Mo doping
 2D Au islands display stripe pattern due to Moiré structure with CaO surface
 3D growth is restored after co-doping with Li
(X. Shao, N. Nilius, HJF; JACS 134, 2432 (2012))
X. Shao, S. Prada, L. Giordano, G. Pacchioni, N. Nilius, H.-J. Freund , Angew.Chem. Int. Ed. 50, 11525 (2011)

30. Internal Structure of the Au Islands
Mo-doped CaO films on Mo(001)
Moiré pattern in pseudo 3D representation: 25ML thick CaO Film, Mo doped
Vs=4.0 V; 15 pA. Left: 40x40 nm; right: 11x11nm

31. Thin Oxide Film Systems
Area 2
Modeling
amorphous silica supports

32. Film Preparation and Characterization
Correlation between Structure and IR Spectra
B. Yang, R. Wlodarczyk, M. Sierka, J. Sauer et al., Phys. Chem. Chem. Phys. 14 (2012) 11344

33. Film Structure and Scattering
Crystalline and Vitreous Silica Films
B. Yang, R. Wlodarczyk, M. Sierka, J. Sauer et al., Phys. Chem. Chem. Phys. 14 (2012) 11344
C. Buechner, L. Lichtenstein, X. Yu, A. Boscoboinik, B. Yang
, R. Wlodarczyk, M. Heyde. S. Shaikhutdinov, J. Sauer, H.-J. Freund; Chem. Eur. J. 20, 1 (2014)

34. Scanning Probe: nc-AFM vs. STM
Chemical Sensivity
L. Lichtenstein, M. Heyde, H.-J. Freund, J. Phys. Chem. C
116 (2012) 20426
all images:
3.5 x 3.5 nm²

35. Scanning Probe: nc-AFM vs. STM
Simultaneous Imaging of Si and O
L. Lichtenstein, M. Heyde, H.-J. Freund, J. Phys. Chem. C 116 (2012) 20426

36. Crystal-Glass Transition
Silica Interface - Atomic Model
L. Lichtenstein, M. Heyde, H.-J. Freund,
Phys. Rev. Lett. 109 (2012) 106101
STM, 12.3 x 7.0 nm², VS = 2 V, IT = 100 pA

37. liquidAFM Setup
2D Silica on Ru(0001)
K. M. Burson, L. Gura, C. Büchner, B. Kell, M. Heyde, H.-J. Freund
 Film production in UHV
 Rapid transfer to liquid (<45s)
 Pure water / NaCl solution
 High-frequency cantilevers
fair = 1.0-1.3 MHz
fwater = 400 - 475 kHz
 Amplitude modulation mode

38. liquidAFM versus LT-UHV-ncAFM-STM
2D Silica on Ru(0001)
K. M. Burson, L. Gura, C. Büchner, B. Kell, M. Heyde, H.-J. F. ;Appl. Phys. Lett. 108, 201602 (2016)

39. Substrate Changed – Structure Retained
2D Silica Transfer
C. Büchner, Z.-J. Wang, K. M. Burson, M.-G. Willinger, M. Heyde, R. Schlögl, H.-J. Freund, ACS Nano 10 ,7982 (2016)

40. Thin Oxide Film Systems
Area 3
3
Investigating adsorption and
chemical reactions in
confined space

41. Chemistry in Confined Space
Crystalline-Vitreous Interface in 2D Silica
X. Yu, E. Emmez, Q Pan, B. Yang, S. Pomp, W.E. Kaden, M. Sterrer, S. Shaikhutdinov, HJF, I. Goikoetxea, R. Wlodarczyk, J. Sauer,
Phys. Chem. Chem. Phys.,18,3755 (2016)
IRA spectra measured in 2 × 10−6 mbar CO (a−g)
and 10−5 mbar CO (h) at the indicated temperatures.
Each spectrum takes 12 s. Total: 6-min exposure.

42. Experimental Setup
SMART
R. Fink et al. J. Elec. Spec. Rel. Phen. 84, 231 (1997)
Sample
e- gun
Mirror
Transfer
optics
Energy filter
Projector Screen
X-rays
• Energy resolution: 180 meV
• Lateral resolution: 2.6 nm (LEEM), 18 nm (XPEEM)
• Temperature range: 100 ÷ 2000 K;
• Pressure range: 10-11 ÷ 10-5 mbar;
• Photon range: 80 ÷ 1500 eV
• surface sensitive
• temporal evolution
• multi-method: microscopy-diffraction-spectroscopy
SMART: Spectro-microscope with
aberration correction for many relevant techniques

43. Chemistry in confined space
Intercalation using a vitreous SiO2 bilayer
CO intercalation

44. Thin Oxide Film Systems
Area 4
Modeling
Strong Metal Support Interaction

45. History and Evidences
Strong Metal Support Interaction (SMSI)
A.K.Datye, D.J. Smith, Langmuir 1988, 4, 827-830
Short History of SMSI:
F. Solymosi in Cat. Rev. 1, 233-255 (1968)
1957 G.M. Schwab et al.: Electronic properties of the
support are important.
1961 Z.G, Szabo, F. Solymosi: Concrete examples of
Ni on various supports of doped oxides
1978 S.J. Tauster et al.: Reduction of metal
supresses chemisorption through electronic
interaction
1983 J. Dumesic et al./ G. Haller et al. Migration
of support species onto the particle
1984 J.M. Hermann: Transport measurements to infer
electronic interaction
F. Solymosi J. Catal. „Letter to the Editor“ 94, 581 (1985)
The term SMSI as it is used today is,
indeed, somewhat missleading!

46. Pt/Fe3O4(111): SMSI Effect
Morphology and Structure
CO TPD
Fe3O4(111)
FeO(111)
Pt
100 nm x 100 nm
80 nm x 80 nm
Wadh = 3.8 ± 0.1 J/m2
(~3.1 J/m2 for Pd/Al2O3, Fe3O4)
Encapsulation of Pt particles by a FeO(111) film
at elevated temperatures driven by high adhesion energy.
Qin et al., J. Phys. Chem. C 112 (2008) 10209; Qin et al., J. Phys. C 21 (2009) 134019

47. FeO(111)/Pt(111)
Structure
Deposition ~1 ML Fe in UHV
Oxidation @ 1000 K in 10-6 mbar O2
Lattice mismatch ~10%: 2.78 Å (Pt) vs 3.11 Å (FeO)
Vurens et al., Surf. Sci. 201 (1988) 129; 268(1992) 170;
Galloway et al., Surf. Sci. 298 (1993) 127;
Kim et al., Surf. Sci. 416 (1998) 68;
Ritter et al., Phys. Rev. B 57 (1998) 7240
150 nm x 150 nm

48. CO Oxidation on FeO(111)/Pt(111)
Reactivity
Batch reactor: 40 mbar CO + 20 mbar O2 balanced by He
Ultrathin FeO(111) film is much more active than
Pt(111) and nm-thick Fe3O4(111) films.
Sun et al., J. Catal. 266 (2009) 359

49. FeO(111)/Pt(111) Reconstruction
Density Functional Theory and STM
See also Grönbeck et al., JACS (2009) for
2 ML MgO(100)/Ag(100).
EPR evidence for O2
- species!
(Risse et al. Angew.Chem. (2011))
Charge transfer + Structural flexibility
Y.-N. Sun, L. Giordano, J. Goniakowski, M. Lewandowski, Z.-H. Qin, C. Noguera, S. Shaikhutdinov, G. Pacchioni, HJF, Angew. Chem. 122, 4520 (2010)

50. High Angle Annular Dark Field (HAADF)-STEM Images
Strong Metal Support Interaction
The nature of the interface between support and particle!
Pt(111)
Fe3O4(111)
Pt
M. Willinger*, W. Zhang, O. Bondarchuk, S. Shaikhutdinov*, H.-J. Freund, R. Schlögl ; Angew. Chem.Int.Ed. 53, 5998 (2014)

51. EELS and STEM
Strong Metal Support Interaction
How does the material migrate ?
M. Willinger*, W. Zhang, O. Bondarchuk, S. Shaikhutdinov*, H.-J. Freund, R. Schlögl; Angew. Chem. Int.Ed. 53, 5998 (2014)

52. High Resolution TEM
Strong Metal Support Interaction
M. Willinger*, W. Zhang, O. Bondarchuk, S. Shaikhutdinov*, H.-J. Freund, R. Schlögl; Angew. Chem.Int.Ed. 53, 5998 (2014)
FeO(111)

53. Summary
Models for Heterogeneous Catalysts:
Complex Materials at the Atomic Level
 The rim of a supported nanoparticle may be identified
as the active site for a chemical reaction
 An amorphous silca film may prepared and characterized
at the atomic level. Transferability to other substrates is possible.
 Underneath a silica film reactions in confined space may be studied
and interesting spatio-temporal phenomena may be observed.
 Strong Metal Support Interaction may be studied via thin oxide films
and its transformation under reaction conditions may be modelled.

54. T H A N K S
Collaborations
R. Schloegl / FHI
C. Campbell / U Washington
J. C. Hemminger / UC Irvine
C. Henry / Luminy
M.-P. Pileni / Paris
M. Bowker / Cardiff
T. Oyama / Virginia, Tokyo
M. Schmal / Rio de Janeiro
H. Niehus / HU Berlin
P. Stair / Northwestern
H. Gao / Beijing
F. Zaera / UC Riverside
K. Hermann / Berlin
M. Wilde / Tokyo
K. Fukutani / Tokyo
K. Asakura / Sapporo
E. Bauer, A. Pavlovska / Arizona
C. Friend, R. Madix/ Harvard
W. Huang / Hefei
E. Giamello / Turino
M. Asscher / Jerusalem

55. Thanks
The Department