Experimental

✓ Model system: Ag/NaY ✓ Ion-exchange of NaY with AgNO3 at 150°C✓ Reduction in H2 at 150°C

Results

Figure 3: 2D-TEM images of Ag/NaY at a tilt angle of 0° (a) and –71° (b). Silver particles are 10-40 nm.

Figure 4: Threeorthogonal slicesthrough thereconstruction ofAg/NaY showinga silver particleon the outsideof the zeolite (a)and a silverparticle insidethe zeolite (b).

Figure 5: Volume rendering of Ag/NaY showing 10-40 nm silver particles (pink) on the zeolite (green).On the blue plane a shadow projection is visible. a, external surface; white arrow indicates the shadowof a silver particle inside the zeolite, b, crosscut showing silver particles both on the inside and theoutside of the zeolite.

Conclusions

✓ 3D-TEM is a very promising new technique for the characterization of catalysts✓ Unequivocal determination of location of metal particles on/in zeolites✓ Nanometer scale resolution in three dimensions

Future plans

✓ Enhancement of resolution✓ Incorporation of EDAX-data in 3D-TEM✓ Other materials (e.g. mesopores in zeolites)

References

[1] J. Frank, Electron Tomography, 1992, Plenum, New York.[2] A.J. Koster et al., Automatic Electron Tomography, 23, 176-188 (1993).[3] A.J. Koster, et al., J. Struct. Biol., 120, 276-308 (1997).

Department of Inorganic Chemistry and Catalysis, Debye Institute, Utrecht University, Sorbonnelaan 16, 3584 CA Utrecht, The Netherlands,E-mail: A.H.Janssen@chem.uu.nl*Department of Molecular Cell Biology,Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands

Three-dimensional TransmissionElectron Microscopy (3D-TEM) forthe Characterization of ZeoliteSupported Metal CatalystsA.H. Janssen, A.J. Koster*, U. Ziese*, A.J. Verkleij*,J. de Graaf, and K.P. de Jong

AV-dienst Chemie, Faculteit Scheikunde UU. januari 2000

Introduction

Many solid catalysts are three-dimensional nano-structured materials. Especially zeolitesand some mesoporous materials are well known for their well-defined three-dimensionalstructures. Characterization, however, is often only two-dimensional. ✓ Scanning Tunneling Microscopy (STM) and Atomic Force Microscopy (AFM) can provide

a surface image of a material with atomic resolution.✓ Transmission Electron Microscopy (TEM) does give high-resolution information of a

sample, but the three-dimensional information is projected into a 2D image. ✓ Scanning Electron Microscopy (SEM) can provide a high-resolution image of a surface

in three dimensions (topography), but the material below the surface is not imaged.

Objective

Use electron tomography (3D-TEM) for the characterization of nano-structured materialsin three dimensions with nanometer scale resolution.

3D-TEM: Setup

A transmission electron microscope is controlled by a computer for automatedtomographic data acquisition. From the datasets a 3D reconstruction is calculated withUNIX based programs.

Figure 1: 3D-TEM Setup.

3D-TEM: Data acquisition

The sample is tilted in the microscope from ca. +70° to –70° with 1 degree increment.Every degree the computer:✓ changes tilt angle✓ adjusts the defocus✓ corrects for the image shift✓ takes an imageIn total ca. 140 images are taken from one and the same sample/crystallite

3D-TEM: Reconstruction

A 2D-FT (Fourier Transform) of a 2D-projection at a particular tilt angle is acentral slice in the 3D-FT of the object.Many images thus fill up the 3DFourier Space. After alignment of theimages the 3D reconstruction iscalculated by an inverse FourierTransform of the 3D Fourier Space(see Figure 2).

The final resolution d of thereconstruction depends on thenumber of images N and the thicknessof the sample T according to:

d = π * (T/N)

Figure 2: From a stack of 2D projections a 3D FourierTransform (FT) is obtained. Inverse FT results in a 3Dreconstruction of the object.

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