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2013 04-10 fabrication of complex model oxides

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Philip R. Davies
Philip R. Davies

The document describes the fabrication and characterization of molybdenum oxide films supported on iron oxide (111) single crystal surfaces as model oxide catalysts. Molybdenum oxide was deposited on iron oxide using a hot filament metal oxide deposition technique in oxygen gas and then annealed. X-ray photoelectron spectroscopy showed the molybdenum existed as Mo6+ and the surface concentration of molybdenum increased with higher annealing temperatures. Scanning tunneling microscopy images revealed the formation of triangular molybdenum oxide clusters on the iron oxide surface that became larger and more ordered at higher annealing temperatures.

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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
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
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
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
Surface Science & Catalysis Cardiff Catalysis Institute From Figs 5 & 9. Mo = 3.7 1014 cm-2 (4x4) (b) (a) Faraday Discussion 162: Anchored Nanoparticles 10-12th April 2013 5
Surface Science & Catalysis Cardiff Catalysis Institute Mo = 4.5 1014 cm-2 From Figs 6 & 8. (b) (a) (2x2) (4x4) Faraday Discussion 162: Anchored Nanoparticles 10-12th April 2013 6
Surface Science & Catalysis Cardiff Catalysis Institute Mo = 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
Surface Science & Catalysis Cardiff Catalysis Institute Mo = 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 IronCmolybdate Thin Films. Surface Science 605 (2011) 1550 (2323)R30 Faraday Discussion 162: Anchored Nanoparticles 10-12th April 2013 8
Surface Science & Catalysis Cardiff Catalysis Institute (a) (b) (a) Side view of Fe3O4(111) Top view of FeCMo oxide model. Blue = O Orange = Fe. The triangle and unit cell are indicated to compare with (33)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 IronCmolybdate Thin Films. Surface Science 605 (2011) 1550 Faraday Discussion 162: Anchored Nanoparticles 10-12th April 2013 9
Surface Science & Catalysis Cardiff Catalysis Institute Paper Figures Faraday Discussion 162: Anchored Nanoparticles 10-12th April 2013 10
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
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
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
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
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
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
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
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
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

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2013 04-10 fabrication of complex model oxides

  • 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. Mo = 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 Mo = 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 Mo = 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 Mo = 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 IronCmolybdate Thin Films. Surface Science 605 (2011) 1550 (2323)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 FeCMo oxide model. Blue = O Orange = Fe. The triangle and unit cell are indicated to compare with (33)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 IronCmolybdate 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