Johan Gustafson

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Catalysis Studied on the Atomic Level
Johan Gustafson Department of Synchrotron
Radiation Research
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Outline

• Introduction
• Experimental Methods
• Some Results

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What is a catalyst?

• A catalyst fastens up a process that would take
  place anyway, without self being processed.

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Motivation

• Catalysis has for a long time been widely used in
  chemical industry, and thus also studied a lot on
  a macroscopic level.
• What happens is hidden in a black box.
• In order to develop better and/or cheaper
  catalysts we need a deeper knowledge of what
  really goes on inside the box.

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Surfaces

• If the reactants adsorb on a surface the local
  concentration of molecules is increased
  drastically and it is easier to find a molecule
  or atom to react with.
• Often dissociation is a part of the wanted
  reaction and this often occurs during adsorption.
• Help the reactants to meet and lower possible
  barriers

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Experimental methods

• Under as clean situation as possible let us study
  the adsorption properties of our molecules on the
  surfaces of interest.
• If all molecules that hit the surface will adsorb
  it takes 1 ns to grow 1 monolayer
• Ultra High Vacuum
• 10-13 atm ? 10 000 s 3 h
• Expose the surface to a controlled amount of
  molecules that may adsorb.

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Experimental methodsto find what the surface
looks like

• LEED Low Energy Electron Diffraction

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Experimental methodsto find what is on the
surface

• Photoemission Spectroscopy (PES)

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Experimental methodsto find what the surface
looks like

• High resolution core level photoemission

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Experimental methodsto find what the surface
looks like

• High resolution core level photoemission

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Experimental methodsto find what the surface
looks like

• STM Scanning Tunnelling Microscopy

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Adsorption on Rh(111)O2 - dissociates to three
fold hollow
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Adsorption on Rh(111)CO - dissociates to on-top
sites
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Adsorption on Rh(111)O2 and CO can adsorb and
meet
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Adsorption on Rh(111)After reaction CO2 can
leave the surface
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Other things that change the catalytic properties

• Mobility on the surface
• Defects
• Steps
• Kinks
• Area

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Stepped surface Rh(553)
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Rh(553) oxygen
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Oxidation
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Results - oxidation of Rh(100)
aRh2.7 Å aoxide3.1 Å
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Results - oxidation of Rh(100)
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Results - oxidation of Rh(100)
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Summary

• The catalytic properties of most known catalysts
  have been studied deeply, but not the explanation
  of what really happens.
• We are trying to get knowledge about catalysis on
  an atomic level using simple model systems.
• By changing the model systems we are trying to
  reach more realistic situations.