Schlögl, R.

Su, D.

Wang, D.

English

MPG.PuRe

1 von 2011th Scientific Conference &12th Annual General Meetingof the ELECTRON MICROSCOPY SOCIETY OF MALAYSIAJohore Bahru 17 December 2002Transmission Electron MicroscopyInvestigation on Defect Structuresof Molybdenum OxidesDangsheng SuDi WangRobert SchlöglFritz Haber Institute ofthe Max Planck SocietyBerlin2 von 20 Why I come here ?      born in China.    Ph.D in Austriawork in Germany     look like Malay3 von 20Reduction/Oxidation of Mo OxidesShort range order  defect structure forms molybdenium suboxide ?Visualisation and detection by means of HREM and electron diffraction ?u XAS studies on reduction/oxidation of MoO3-xPresence of edge-shared octahedra with short Mo-Mo distance in MoO3-x (T. Ressler, etc., J. Catalysis (2000) 191, 75)u XRD and XAS studies on reduction of MoO3T<698K    MoO3+H2                       MoO2+H2OT>698K    3MoO3+MoO2                      Mo4O11Mo4O11+3H2                     4MoO2+3H2ONo Crystalline intermediates is formed(T. Ressler, etc., J. Phys. Chem. B (2000) 104, 6360)4 von 20Homologous series of Mo suboxidesu MonO3n-2 (17£ n £25)    Mo18O52 , ¼  derived from MoO3 (layered structure)u MonO3n-1 (n<10)    Mo8O23 , ¼  derived from ReO3-type structureShear StructuresOther structuresu Mo4O11 , u Mo5O14 , ¼5 von 20abc xyzcbbacaStructure Model of MoO3Space group: PbnmStructure type: Orthorhombica=3.92 Åb=13.94 Åc=3.66 Å6 von 20Structure Model of MoO2Space group: P21/cStructure type: Monoclinica=5.61 Åb=4.86 Åc=5.63 Åb=120.9°7 von 201/2 aM+1/2 cM1/2 aM - 1/6 bMPrinciples of Shear Operation8 von 20Structure Model of Mo18O52Space group: p-1Structure type: triclinica=8.15 Åb=11.89 Åc=21.23 Åa=102.7°b=67.8°g= 110.0° abc9 von 20Simulated EDP and HREM images of Mo18O52 on [100] projection 24.4 73.3 97.7 146.6Sample Thickness(Å)EDPHREM ImageDefocus: -400 ÅDefocus: -600 Å10 von 20EDP and HREM of Mo18O522 nm 2 nm11 von 20a(1 0 2)RcStructural Principles of Mo8O23Space group: P2/aStructure type: Monoclinica=16.8 Åb=4.04 Åc=13.4 Åb=106.5 °12 von 2020.2 60.6 101.0 141.4Sample Thickness(Å)EDPHREM ImageDefocus: -400 ÅDefocus: -600 ÅSimulated EDP and HREM images of Mo8O23 on [010] projection 13 von 20EDP and HREM of Mo8O232 nm 2 nm14 von 20Structure Model of Mo4O11Space group: P21/aStructure type: Monoclinica=24.54 Åb=5.44 Åc=6.70 Åb=94.3°ca15 von 20Simulated EDP and HREM images of Mo4O11on [010] projectionSample Thickness(Å)EDPHREM ImageDefocus: -400 ÅDefocus: -600 Å21.76 65.27 108.78 152.2916 von 20EDP and HREM of Mo4O1110 nm17 von 20Structure Model of Mo5O14Space group: P4/mbmStructure type: tetragonala=45.99 Åb=45.99 Åc=3.94 Å18 von 20Simulated EDP and HREM images of Mo5O14on [001] projectionSample Thickness(Å)EDPThickness: 50 ÅHREM ImageDefocus: -400 ÅDefocus: -600 Å19.7 59.1 137.898.419 von 20 Summary      Crystallographic shearing is  important in understanding       the oxygen diffusion and phase transition mechanism of      transition metal oxides in catalytic reactions.    CS plane produces well defined satellite spots in    electron diffraction pattern             Application of TEM    in the investigation of the reaction mechanism in solid    state chemistryHREM, supported by image simulation, allows the visualization of the CS structures at nanometer scale             Opens the possibility for the in-situ HREM investigation of real catalyticreaction at atomic scale. 

Transmission Electron Microscopy Investigation on Defect Structures of Molybdenum Oxides

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