Kinetics of Nanoparticle Catalysis from First Principles

Doctoral thesis, 2019

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.