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Nanoparticle Interfaces Studied Using Environmental TEM and Atomic Scale Modelling

Liu, Pei; Madsen, Jacob; Schiøtz, Jakob; Wagner, Jakob Birkedal; Hansen, Thomas Willum

Publication date:2016

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Citation (APA):Liu, P., Madsen, J., Schiøtz, J., Wagner, J. B., & Hansen, T. W. (2016). Nanoparticle Interfaces Studied UsingEnvironmental TEM and Atomic Scale Modelling. Poster session presented at 16th International Congress onCatalysis, Beijing, China.

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4 %- 4 %

Strain

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Nanoparticle Interfaces Studied Using

Environmental TEM and Atomic Scale Modelling Pei Liu*1, Jacob Madsen2, Jakob Schiøtz2, Jakob B. Wagner1 and Thomas W. Hansen1.1 Center for Electron Nanoscopy, Technical University of Denmark, Kgs. Lyngby, 2800, Denmark2 Department of Physics, Technical University of Denmark, Kgs. Lyngby, 2800, Denmark

Supported heterogeneous catalysts play an essential role in areas such as automotive exhaust abatement, energy storage/conversion and

sustainable production of chemicals. In order to gain insight into properties such as activity and stability of these materials, catalysts must be studied

in situ in reactive environments. Only a few experimental techniques allow for investigation of the materials at a local scale with atomic resolution

while exposing samples to gases and elevated temperatures. Recent advances in high-resolution environmental transmission electron microscopy

(ETEM) have shown that the atomic configuration at surfaces and interfaces of a metal nanoparticle is a function of its surroundings [1]. Similarly, the

dynamics and hence stability of the catalyst are important parameters which can be studied using in situ microscopy [2].

Motivation and background

AcknowledgementsWe kindly acknowledge the support of the The Danish Council for Independent Research | Technology and Production Sciences (FTP).

Furthermore, the A. P. Møller and Chastine Mc-Kinney Møller Foundation is gratefully acknowledged for their contribution to the

establishment of the Center for Electron Nanoscopy in the Technical University of Denmark.

email: peiliu@cen.dtu.dk

References[1] H. Yoshida, Y. Kuwauchi, J.R. Jinschek, K. Sun, S. Tanaka, M. Kohyama, S. Shimada, M. Haruta, S. Takeda, Science

335, 317-319 (2012).

[2] T.W. Hansen, A.T. DeLaRiva, S.R. Challa, A.K. Datye, Accounts of Chemical Research 46, 1720-1730 (2013).

In order to study the influence of the environment on catalytic nanoparticles, model systems

consisting of Au/CeO2, Pt/CeO2, Au/TiO2, and Pt/TiO2 were prepared using a physical method

(sputter coating). For the preliminary in situ experiments low gas pressures at room temperature

were used.

ETEM experiments

1) Sputter coat prepared

Au/TiO2, exposed to

0.45 mbar CO dose rate:

4.27E+4 e-/Ųs.

2) FFT of Au particle and

TiO2 respectively,

Au(-1-11)||TiO2 (1-10).

3) Snap shots from an

image sequence, arrows

indicate the three top most

layers of the particle.

4) The number of atomic

columns in each layer of

the particle as seen in

image 3), the trend

indicates that the dynamics

is a fluctuating

phenomenon.

1)

3)

2)

4)

2)

Surface atom diffusion

Particle wiggling

1) Angle between Au(11-1) and CeO2(200) vesus time. 2) FFT of Au particle and TiO2 respectively,

Au(11-1)||CeO2(200); 3) two snap shots from an image sequence of Au/CeO2 (sputter coating

prepared) exposed to 0.017 mbar O2, dose rate: 4.54E+4 e-/Ųs .

34s 104s

1)

2)

3)

Supported nanoparticles are dynamic displaying both atomic scale diffusion and collective motion

of the entire particle. We can observe both of these phenomenons in situ with ETEM.

Precise information of what happens at the support interface is

not directly available from experiment. We are developing

theoretical models specifically for metal/oxide interfaces

relevant for catalytic systems. Three qualitatively different

examples are shown below.

Modelling support interfaces

4.3 %

- 4.3 %

Str

ain

Comparison between a free Pt nanoparticle and a similar

particle supported on anatase TiO2. The small lattice mismatch

of 3.4 % modifies the overall strain distribution.

7 %- 7 %

Strain

Pt nanoparticle supported on cubic ZrO2. The particle is unable

to adapt to the large lattice mismatch of 24 %, leading to a

disorganized strain distribution.

Cu nanoparticle supported on alumina. The strain distribution of

the bottom atomic layer of the particle reveals a dislocation

network at the interface.

Coherent interface

Semi coherent interface

Incoherent interface