Kinetics of Nanoparticle Catalysis from First Principles
Doktorsavhandling, 2019

Modern society depends heavily on heterogeneous catalysis, which creates strong economical and environmental incentives to improve catalyst efficiency. Heterogeneous catalysts are often realized as metal nanoparticles (NPs) supported on oxide surfaces, and catalysts are traditionally developed by trial and error approaches. However, rational catalyst design can be enabled by understanding reactions on the atomic scale. Presently, computational power has matured sufficiently to obtain atomic scale insights into reaction kinetics, directly from first-principles kinetic simulations.

This thesis develops the methodologies of first-principles kinetic simulations over NPs. Multiple factors affect modeling of reactions over NPs, such as reaction energy landscapes and entropy changes during reaction. This makes it important to investigate different methodological choices, within kinetic modeling.

Herein, Complete Potential Energy Sampling (CPES) is introduced as a method to calculate adsorbate entropy. CPES directly samples the adsorbate potential energy landscape, which allows for systematic improvements over approximate models within mean-field kinetics. CPES is tested on CO-oxidation over Pt(111), where it improves agreement with experimental references. Furthermore, CPES is applied to enable accurate description of molecular entropy in zeolites.

Reaction energy landscapes on NPs are challenging to calculate as NPs contain multiple different sites. Thus, NPs are commonly approximated using extended surfaces as model systems. In this thesis, the challenge of mapping out NP reaction energy landscapes is solved pragmatically using scaling relations. Kinetic Monte Carlo simulations are used to investigate the kinetics for CO-oxidation over Pt and selective acetylene hydrogenation over Pd/Cu single-atom alloys. It is found that kinetic couplings between the NP-sites govern the kinetics. The kinetic couplings influence how turnover frequency and selectivity depend on particle size, shape, and strain. Thus, the energetics of isolated sites and extended surface models are found to have limited value as descriptors for NP catalysis.

Density functional Theory

Mean field approximation

Acetylene hydrogenation

Kinetic Monte Carlo

CO oxidation

Entropy

Methane oxidation

Heterogeneous catalysis

Kinetic modeling

Nanoparticles

PJ lecture hall, Fysikgården 2B, Fysik Origo.
Opponent: Prof. Michail Stamatakis, University College London, United Kingdom.

Författare

Mikkel Jørgensen

Chalmers, Fysik, Kemisk fysik

Adsorbate Entropies with Complete Potential Energy Sampling in Microkinetic Modeling

Journal of Physical Chemistry C,; Vol. 121(2017)p. 7199-7207

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Monte Carlo Potential Energy Sampling for Molecular Entropy in Zeolites

Journal of Physical Chemistry C,; Vol. 122(2018)p. 20351-20357

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MonteCoffee: A programmable kinetic Monte Carlo framework

Journal of Chemical Physics,; Vol. 149(2018)

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First-Principles Microkinetic Modeling of Methane Oxidation over Pd(100) and Pd(111)

ACS Catalysis,; Vol. 6(2016)p. 6730-6738

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Connection between macroscopic kinetic measurables and the degree of rate control

Catalysis Science and Technology,; Vol. 7(2017)p. 4034-4040

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Scaling Relations and Kinetic Monte Carlo Simulations To Bridge the Materials Gap in Heterogeneous Catalysis

ACS Catalysis,; Vol. 7(2017)p. 5054-5061

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The Site‐Assembly Determines Catalytic Activity of Nanoparticles

Angewandte Chemie - International Edition,; Vol. 57(2018)p. 5086-5089

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Strain affects CO oxidation on metallic nanoparticles non-linearly

Topics in Catalysis,; (2019)

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Influence of atomic site-specific strain on catalytic activity of supported nanoparticles

Nature Communications,; Vol. 9(2018)

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Jørgensen, M. and Grönbeck, H. - Selective acetylene hydrogenation over single-atom alloy nanoparticles by kinetic Monte Carlo

Understanding reactions on nanoparticles can save energy and provide cleaner air.
This might seem like a bold statement at first; but did you know that nanoparticles are used in about 90% of the chemical industry, and are the main actors in cleaning exhaust from cars?

The technological devices used for automotive exhaust treatment are called catalysts. Catalysts are composed of nanoparticles that transform toxic gases, such as CO, into less harmful chemicals such as CO2 . Such a transformation takes place on the surface of the nanoparticle, which has been researched for over a 100 years. Catalysts are often composed of scarce metals, such as platinum, palladium, and gold; and even small improvements in efficiency can have huge impacts on a global scale. Despite the efforts to understand what characterizes an efficient catalyst, the technology is often developed by trial and error. This is partly because catalyst-nanoparticles are smaller than the wavelength of visible light and can only be seen using electron microscopes. Therefore, understanding how chemical reactions proceed over nanoparticles is an achievement that can have tremendous consequences for gobal pollution control and chemical technology.

Today, computers are so powerful that it is possible to perform computer experiments solely on the screen. Computer simulations have the advantage that we directly can address causes and effects. Such insights may help answer the tough question: How do we arrange and combine the atoms in nanoparticles to design a cheap, efficient, and sustainable catalyst? In this thesis, I delve into developing and performing computer simulations to understand chemical reactions on the surface of nanoparticles. The computer simulations are performed over simple, yet, realistic nanoparticles, as they appear in an electron microscope. I give examples of methods developed to perform the computer simulations, the information we can extract from them, and how the simulations relate to real experiments.

The simulations revealed that the chemistry of the individual atoms that make up the nanoparticle is quite different from the chemistry of the combined system. That is, the system behaves differently than the sum of its parts. This information helped finding interesting relations between catalytic efficiency/effectiveness and particle shape and size. While the methods and results in this thesis helps understanding chemical reactions on nanoparticles, more investigations are required to disentangle the complex chemistry of nanoparticle catalysis. Ultimately, we may be able to design a sustainable future, atom by atom.

Styrkeområden

Nanovetenskap och nanoteknik

Ämneskategorier

Fysikalisk kemi

Materialkemi

Teoretisk kemi

Nanoteknik

Den kondenserade materiens fysik

Infrastruktur

C3SE (Chalmers Centre for Computational Science and Engineering)

ISBN

978-91-7597-872-7

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4553

Utgivare

Chalmers tekniska högskola

PJ lecture hall, Fysikgården 2B, Fysik Origo.

Opponent: Prof. Michail Stamatakis, University College London, United Kingdom.

Mer information

Senast uppdaterat

2019-03-05