Photo: Evgeniy Redekop from University of Oslo and Niclas Johansson, Samuli Urpelainen, Esko Kokkonen from MAX IV
Many of our everyday materials originate from industrial processes that involve chemical reactions. Most of these reactions would be very slow or require a lot of energy if it wasn’t for catalysts. A catalyst is a substance that when added to the process, increases the reaction rate without being consumed itself and may for example come in the form of metallic nanoparticles. The catalytic converter of our cars contains nanoparticles which can convert highly toxic carbon monoxide in the exhaust to carbon dioxide and water. Another example involving metal nanoparticles is the so-called water-gas shift reaction where carbon monoxide reacts with water to form carbon dioxide and hydrogen, an important step in the production of ammonia or renewable hydrocarbons.
The atomic scale structure of the nanoparticle surfaces and sometimes also the material on which they are attached, the so-called support, play an essential role in determining how efficient they are as catalysts. It can be studied with X-ray Photoelectron Spectroscopy (XPS), a method available at the beamline HIPPIE. When an X-ray beam shines on a material, it will cause electrons to be emitted from the surface. The electrons will have a specific energy that correlates to the chemical content and atomic-scale structure of the surface from which they originate. The structure of the surface will change depending on the composition and pressure of the gasses surrounding it. At HIPPIE, it is possible to perform measurements at pressures close to the conditions where a real catalyst would operate, so-called ambient pressure XPS (AP-XPS).
An ongoing collaboration with a team from the University of Oslo aims to combine AP-XPS setup with Temporal Analysis of Products (TAP), a method for analysing the composition of gasses before and after reacting with the catalyst. An experimental setup for measuring the dynamics of the gas phase and the structure of the surface at the same time will be an important step towards correlating surface structure and reaction efficiency. Another similar set-up is also being developed at beamline SPECIES, which do not have X-rays from the MAX IV accelerators yet but work with a smaller external source of X-rays, a so-called lab source.
At HIPPIE, we can study how our gas flow system works together with the AP-XPS setup and the high-quality X-ray light available there and at SPECIES. Since the beamline is not in regular user operation and still works with a lab X-ray source, there is time to be a bit more creative, so it’s a great combination, says Evgeniy Redekop, researcher at the Centre for Materials Science and Nanotechnology Chemistry at the University of Oslo.
The experimental setup will be used by the team to for example study and design new materials within the area of so-called metal-organic frameworks, which are a highly customizable type of material with a large surface area which is very promising for catalysis. Another focus of the group is to move towards studying catalysts closer to the real industrial conditions by performing measurements on the more complex metal nanoparticles as opposed to the larger polished surfaces otherwise often used in catalysis research.
We’re looking forward to taking advantage of the high time- and energy resolution available at MAX IV and we hope to be able to build an experimental setup where we can manipulate and study the gas composition over the catalyst at the same timescale to follow the chemical reactions taking place, says Redekop.
The TAPXPS project is supported by the Norwegian Research Council and the European Regional Development Fund.