5 minute presentation to Faraday discussion 162

1. Surface Science &
Catalysis Cardiff Catalysis Institute
Fabrication of complex model oxide catalysts:
Mo oxide supported on Fe3O4(111)
Chanut Bamroongwongdee, Michael Bowker, Albert F.
Carley, Philip R. Davies, Robert J. Davies
and Dyfan Edwards.
Faraday Discussion 162: Anchored Nanoparticles 10-12th April 2013 1

2. Surface Science &
Catalysis Cardiff Catalysis Institute
Model iron molybdate catalysts
Hot Filament Metal Oxide Deposition (HFMOD)
of molybdenum oxide films
8x10-6 mbar O2(g) Annealed
Mo(s) 1x10-7 mbar
O2(g)
873 K
Mo3O9+, Mo4O12+
Fe3O4(111)
Crystal
Faraday Discussion 162: Anchored Nanoparticles 10-12th April 2013 2

3. Surface Science &
Catalysis Cardiff Catalysis Institute
Fe3O4 (111): sputtered & annealed in 1 10-7 mbar O2(g), 873K
From Fig 2.
(2x2)
11.8 nm
40 nm
Faraday Discussion 162: Anchored Nanoparticles 10-12th April 2013 3

4. Surface Science &
Catalysis Cardiff Catalysis Institute
XP spectra of Mo(3d)
Ag(111)
From Fig 4. Fe3O4(111)
Mo4+ - Mo6+
Mo6+
231.3
232.4
Surface
concentration
of Mo
6.2 × 1014 cm-2
4.5 × 1014 cm-2
3.7 × 1014 cm-2
Faraday Discussion 162: Anchored Nanoparticles 10-12th April 2013 4

5. Surface Science &
Catalysis Cardiff Catalysis Institute
From Figs 5 & 9. σMo = 3.7 1014 cm-2
(4x4)
(b)
(a)
Faraday Discussion 162: Anchored Nanoparticles 10-12th April 2013 5

6. Surface Science &
Catalysis Cardiff Catalysis Institute
σMo = 4.5 1014 cm-2
From Figs 6 & 8.
(b)
(a)
(2x2)
(4x4)
Faraday Discussion 162: Anchored Nanoparticles 10-12th April 2013 6

7. Surface Science &
Catalysis Cardiff Catalysis Institute
σMo = 6.2 1014 cm-2
Annealed at 873 K
From Figs 7 & 8.
7nm
Mo3O9
(2x2) ?
0.6 nm x 0.6 nm structure
4.5 to 5nm
Fe3O4 ?
2 to 2.5nm
1.2 nm x 1.2 nm
200 nm Mo3O9
0.6 nm x 0.6 nm
(2x2) structure
Fe3O4
80 nm
Faraday Discussion 162: Anchored Nanoparticles 10-12th April 2013 7

8. Surface Science &
Catalysis Cardiff Catalysis Institute
σMo = 1 1015 cm-2
From Fig 9. Annealed at 973 K
1.06 nm
50 nm
1 ML Mo/Fe3O4/Pt(111) annealed in
21.2 nm 10−6 mbar O2 at 900 K for 5 min
Uhlrich et al. “Preparation and
Characterization of Iron–molybdate Thin
Films.” Surface Science 605 (2011) 1550
(2√3×2√3)R30
Faraday Discussion 162: Anchored Nanoparticles 10-12th April 2013 8

9. Surface Science &
Catalysis Cardiff Catalysis Institute
(a)
(b)
(a) Side view of Fe3O4(111) Top view of Fe–Mo oxide model.
Blue = O Orange = Fe. The triangle and unit cell are indicated to
compare with (√3×√3)R30° structure observed
(b) Side view of Fe2Mo3O8 (0001) by STM
Blue = O Orange = Fe, Red = Mo Red and orange atoms represent Mo atoms I
different layers
Uhlrich et al. “Preparation and Characterization of Iron–molybdate Thin Films.”
Surface Science 605 (2011) 1550
Faraday Discussion 162: Anchored Nanoparticles 10-12th April 2013 9

10. Surface Science &
Catalysis Cardiff Catalysis Institute
Paper Figures
Faraday Discussion 162: Anchored Nanoparticles 10-12th April 2013 10

11. Surface Science &
Catalysis Cardiff Catalysis Institute
Figure 1: MoOx film thickness as a function of the deposition time, determined
from the Mo(3d) XPS signal. Filament current: 3.8 A; oxygen
pressure: 8.0 10-6 mbar.
Faraday Discussion 162: Anchored Nanoparticles 10-12th April 2013 11

12. Surface Science &
Catalysis Cardiff Catalysis Institute
Figure 2:
STM images from the clean
Fe3O4 (111) surface after
sputtering and annealing in
1 10-7 mbar of oxygen at 873
K. (a) Large-scale image in
which one can clearly
observe individual terraces,
separated by single height
steps (~0.5 nm). (b)-(d)
Higher magnification views
showing complex nature of
the surface. Line profiles are
identified with Roman
numerals and drawn in (e)
and (f). (Vb = -1.0 V, It = 0.465
nA)
Faraday Discussion 162: Anchored Nanoparticles 10-12th April 2013 12

13. Surface Science &
Catalysis Cardiff Catalysis Institute
Figure 3: LEED pattern recorded from the Fe3O4 (111) single crystal surface
(a) Clean surface at 70 eV after annealing in oxygen pressure of 10-
7 mbar for 30 min at 873 K. (b) After deposition of MoO for 50
x
minutes and annealing to 973 K for 30 minutes in in oxygen
pressure of 10-7 mbar.
(a) (b)
Faraday Discussion 162: Anchored Nanoparticles 10-12th April 2013 13

14. Surface Science &
Catalysis Cardiff Catalysis Institute
XP spectra of Mo(3d)
Ag(111)
From Fig 4. Fe3O4(111)
Mo4+ - Mo6+
Mo6+
231.3
232.4
Surface
concentration
of Mo
6.2 × 1014 cm-2
4.5 × 1014 cm-2
3.7 × 1014 cm-2
Faraday Discussion 162: Anchored Nanoparticles 10-12th April 2013 14

15. Surface Science &
Catalysis Cardiff Catalysis Institute
Figure 5:
STM image after
exposure of a clean
Fe3O4 (111) single crystal
surface to molybdenum
oxide followed by
annealing in oxygen at
10-7 mbar. Total Mo
concentration calculated
from Mo(3d) XP spectra
= 3.7 1014 cm-2. Profile
(i) shows the 0.6 nm
periodicity of the
underlying surface;
profiles (ii) and (iii) show
the 0.15 nm height of the
adsorbed features and
the 1.2 nm periodicity of
the islands. ). (Vb = -1.0
V, It = 0.465 nA
Faraday Discussion 162: Anchored Nanoparticles 10-12th April 2013 15

16. Surface Science &
Catalysis Cardiff Catalysis Institute
Figure 6:
STM image after exposure
of a clean Fe3O4 (111) single
crystal surface to
molybdenum oxide followed
by annealing in oxygen at
10-7 mbar. Total Mo
concentration calculated
from Mo(3d) XP spectra =
4.5 1014 cm-2. Profile (i)
shows the typical 0.3 nm
step height; profiles (ii) and
(iii) show the 0.6 nm and
0.12 nm periodicity of the
underlying structures)
Faraday Discussion 162: Anchored Nanoparticles 10-12th April 2013 16

17. Surface Science &
Catalysis Cardiff Catalysis Institute
Figure 7:
STM images of Fe3O4 (111) with a total
Mo concentration calculated from
Mo(3d) XP spectra of 6.2 1014 cm-2.
(a) & (b) STM of MoOx overlayer after
annealing in oxygen at 873 K. (c) & (d)
after further annealing at 973 K. Profile
(i) shows the typical 0.3 nm step height;
profiles (ii) and (iii) show the 0.6 nm
and 0.12 nm periodicity of the
underlying structures).
Faraday Discussion 162: Anchored Nanoparticles 10-12th April 2013 17

18. Surface Science &
Catalysis Cardiff Catalysis Institute
Figure 8: LEIS spectra of an iron
oxide surface exposed to
a hot Mo filament and
after subsequent
annealing (a) clean, (b)
following Mo
exposure, and after
annealing at (c) 473 K, (d)
573 K, (e) 673 K, (f) 873
K, (g) 973 K
Faraday Discussion 162: Anchored Nanoparticles 10-12th April 2013 18

19. Surface Science &
Catalysis Cardiff Catalysis Institute
Figure 9: Schematic model of the cyclic (MoO3)3 trimers adsorbed on the A-
Termination21 of a Fe3O4(111) surface. The (MoO3)3 clusters are shown having
the plane of the rings located on top of the capping oxygens. The hexagonal
surface unit cell of Fe3O4(111) is indicated. The van der Waals contour of the
(MoO3)3 clusters is based on dimensions calculated by Jang & Goddard.27
Faraday Discussion 162: Anchored Nanoparticles 10-12th April 2013 19