Quantitative Electron Microscopy Studies of Metal Nanoparticle Catalysts: Nanostructure, Support Interaction and Ageing Effects
Doktorsavhandling, 2017

Heterogeneous catalysis plays a major role in modern society, for example in chemical production, sustainable energy production and emission control technologies. Metal nanoparticles (NPs) supported on oxide materials are frequent catalytic systems in this field. Although used and investigated for decades, open questions about the structure of supported catalysts and correlation with their catalytic properties remain. Some of these questions involve the three-dimensional structures of the catalysts, which become increasingly accessible by modern characterisation techniques, as well as the nanoscale structures down to the atomic level. In this work, we focused on both of these aspects. We developed a specimen preparation method to reveal the three-dimensional structures of supported NP catalysts using transmission electron microscopy (TEM). We also refined the imaging of the catalysts’ structures in the size range of a few nanometres down to individual atoms by using high-resolution dark-field scanning TEM (STEM) imaging, reaching a precision of 2 pm. Structural aspects that were investigated included sintering (e.g. coalescence) of NPs in realistic catalysts at different temperatures and in different gas atmospheres, as well as sintering of NPs on model systems to investigate the effect of support surface corrugation. We used the developed specimen preparation method to study the three-dimensional distribution of NPs on the oxide support in a realistic catalyst as a function of ageing temperature. The structural properties were correlated to the catalytic activity, which was evaluated using a continuous flow reactor and simulations. The interaction at the interface between NPs and different support materials was studied by STEM imaging. The high spatial precision of 2 pm enabled the measurement of strain distributions within supported NPs and at external interfaces. This work has given new insights into the detailed three-dimensional nanoscale structure of some of the most commonly used supported catalysts and improved the understanding of the relation between their structural properties and catalytic activity. The observation of interfacial strain indicates the possibility to tailor the catalytic activity by tuning the NP-support interaction.

CO oxidation

strain

ageing

specimen preparation

scanning electron microscopy (SEM)

FIB/SEM

supported nanoparticle catalyst

transmission electron microscopy (TEM)

particle size distribution (PSD)

platinum

Kollektorn, MC2, Kemivägen 9
Opponent: Dr. Sarah Haigh, School of Materials, The University of Manchester

Författare

Torben Nilsson Pingel

Chalmers, Fysik, Eva Olsson Group

The effect gas composition during thermal aging on the dispersion and NO oxidation activity over Pt/Al2O3 catalysts

Applied Catalysis B: Environmental,; Vol. 129(2013)p. 517-527

Artikel i vetenskaplig tidskrift

Pt Nanoparticle Sintering and Redispersion on a Heterogeneous Nanostructured Support

Journal of Physical Chemistry C,; Vol. 120(2016)p. 14918-14925

Artikel i vetenskaplig tidskrift

Nilsson Pingel, T., Jørgensen, M., Yankovich, A. B., Grönbeck, H., Olsson, E., Influence of Strain Patterns on Catalytic Activity of Supported Nanoparticles

Catalysis is one of the most important technologies in modern society. Estimations show that catalysis contributes to products that constitute approximately 35 % of the global gross domestic product. A catalyst increases the rate of a chemical reaction and favours a particular product. Catalysis saves tremendous amounts of energy during the production of fuels, industrial products, fertilisers, food and pharmaceuticals. Catalysts also directly benefit our health by cleaning toxic exhaust gases from power plants, ships and motor vehicles. Many catalysts rely on small metal particles with diameters of a few nanometres (one nanometre is one millionth of a millimetre, and there is not room for more than ten atoms in a row along a nanometre).

In this thesis, we investigated the three-dimensional structure of catalysts on the nanoscale and obtained new insights about how variations on the atomic scale impact their catalytic properties. In order to reach these conclusions, we used electron microscopy to study the metal nanoparticles. These microscopes use electrons instead of light, reaching a resolution more than a thousand times higher than the best conventional light microscopes and allowing us to image individual atoms and their positions with high precision.

The results that we obtained improve the understanding of complex catalyst systems and indicate ways to tailor their nanoscale structure in order to enhance their performance and establish a more efficient use of material resources. The development of better catalysts is a critical challenge on the way to a sustainable society, which relies on green energy, efficient processes and reduced air pollution.

Styrkeområden

Nanovetenskap och nanoteknik

Materialvetenskap

Ämneskategorier

Fysik

Kemi

ISBN

978-91-7597-623-5

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4304

Utgivare

Chalmers tekniska högskola

Kollektorn, MC2, Kemivägen 9

Opponent: Dr. Sarah Haigh, School of Materials, The University of Manchester

Mer information

Skapat

2017-08-20