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Catalysis and Catalysts - TEM and SEM Principles of Electron Microscopy (EM)  Resolution strongly dependent of wavelength: –electron microscope: about.

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Presentation on theme: "Catalysis and Catalysts - TEM and SEM Principles of Electron Microscopy (EM)  Resolution strongly dependent of wavelength: –electron microscope: about."— Presentation transcript:

1 Catalysis and Catalysts - TEM and SEM Principles of Electron Microscopy (EM)  Resolution strongly dependent of wavelength: –electron microscope: about 0.2 nm –optical microscope: about 500 nm  Image formed due to different lateral absorption of the beam –heavy atoms darkest –light atoms high transmissions  Electron microscopes often equipped with instrumentation for elemental analysis –EDAX (Energy Dispersive Analysis of X-rays)  Two techniques: –Transmission Electron Microscopy (TEM) –Scanning Electron Microscopy (SEM)

2 Catalysis and Catalysts - TEM and SEM Transmission Electron Microscopy (TEM) Similarity of Optical and Electron Microscope Optical Electron Electron gun Condenser lenses Objective lens Projector lens Sample Intermediate image Final image Essential difference: wavelength of electrons: 3.7  nm at 100 keV wavelength of light: nm Consequently: resolution of electron microscope higher Anode

3 Catalysis and Catalysts - TEM and SEM TEM image of MoS 2 /Al 2 O 3 MoS 2 slabs

4 Catalysis and Catalysts - TEM and SEM Scanning Electron Microscopy (SEM) Cathode Anode Magnetic lens Sample & Detector Monitor Magnetic lens  Sample scanned by electron beam  Reflected (“backscattered”) electrons are measured  Advantage: –simple interpretation –user-friendly  Disadvantage: –low resolution (compared to TEM)

5 Catalysis and Catalysts - TEM and SEM SEM Image of Zeolite ZSM-5 Elongated Cubic

6 Catalysis and Catalysts - TEM and SEM Example SEM/TEM  Au/TiO 2 –impregnationno activity –precipitationactivity  Au/TS-1 –TS-1 preparation affects activity 1a: silica as source 1b: TEOS (tetra-ethyl-ortho-silicate)

7 Catalysis and Catalysts - TEM and SEM Example: Au/TiO 2 Catalyst Impregnation versus Precipitation SEM image of inactive Au/TiO 2 catalyst prepared by impregnation TEM image of active Au/TiO 2 catalyst prepared by precipitation 100 nm Au particle 500 nm Au particle nm

8 Catalysis and Catalysts - TEM and SEM Effect of Ti-Silicalite Preparation - SEM SEM image of TS-1a synthesized from Aerosil SiO 2 Crystallisation: 5 days at 453 K SEM image of TS-1b synthesized from TEOS Crystallisation: 1 day at 443 K Totally inactive after Au precipitation Good catalyst after Au precipitation

9 Catalysis and Catalysts - TEM and SEM TEM image of TS-1a synthesized from Aerosil SiO 2 TEM image of TS-1b synthesized from TEOS Au inactiveactive Effect of Ti-Silicalite Preparation - TEM

10 Catalysis and Catalysts - TEM and SEM Conclusions  Au particle size of 3-10 nm necessary for epoxidation activity  TS-1 morphology affects activity: small crystallites needed to establish Au-TiO 2 contact

11 Catalysis and Catalysts - TEM and SEM Summary of Electron Microscopy  direct information on particle size distributions of catalysts  user friendly  atomic resolution  usually combined with EDAX


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