Universiteit Leiden

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Lecture

Mini symposium

  • Dr. Jeppe Lauritsen (Aarhus University)
  • Prof. Dr. Katharina Al Shamery (Carl von Ossietzky University)
Date
Thursday 29 June 2017
Time
Location
Gorlaeus Building
Einsteinweg 55
2333 CC Leiden
Room
DM0.13

Dr. Jeppe Lauritsen: Atom-resolved Scanning Probe Microscopy Studies of Metal-Oxide and Metal-Sulfide Catalyst Nanostructures

Development of new catalysts is seen as a crucial element for securing energy resources and for better protection of the environment. However, progress in the fundamental understanding of catalysts is often lacking and, furthermore, the detailed control of materials on the nanoscale is of essence. We pursue the goal of understanding catalytic processes by focusing on what happens on the atomic-level. Scanning Probe Microscopies (SPMs) are particularly strong techniques in this regard, since they allow us to resolve surfaces and nanoparticles atomically and sometimes directly inspect the intermediate stages of a chemical reaction. We have successfully used the scanning tunneling microscope (STM) to investigate models of catalysts. The so-called hydrodesulfurization catalyst is a very important catalyst used in oil refineries worldwide for upgrading crude oil and removing sulfur impurities to prevent pollution (acid rain). The catalyst mainly consists of so-called single-layer MoS2 nanoparticles, and we can reveal in atom-resolved STM images how S-containing molecules representative of the oil interact and react on the surface of the MoS2 nanoparticles [1]. We also investigate novel metal-oxide nanostructures [2] from earth-abundant transition metals (Co, Ni), which are promising replacements of typical expensive noble metals for catalytic water splitting for hydrogen production. I will show how we can follow the first steps of this reaction in STM movies, by in-situ monitoring water dissociation and subsequent hydrogen diffusion.

References

  1. Bruix A, Füchtbauer HG, Tuxen AK, Walton AS, Andersen M, Porsgaard S, et al. In Situ detection of active edge sites in Single-Layer MoS2 catalysts. ACS Nano 2015, 9: 9322-9330.
  2. Fester J, García-Melchor M, Walton AS, Bajdich M, Li Z, Lammich L, et al. Edge reactivity and water-assisted dissociation on cobalt oxide nanoislands. Nature Communications 2017, 8: 14169.

Prof. Dr. Katharina Al Shamery: Titania

TiO2 is an interesting material for heterogeneous catalysis as it is nontoxic, earth abundant and low priced and thus has been widely studied also in view of its interesting photocatalytic properties.[1-6] Recently attention has been drawn towards the role of defect states like bridging oxygen vacancies as well as Ti +III interstitials with respect to their role in the catalytic activity. Particularly interesting is that the Ti +III interstitials start to be mobile around 300 K and are able to diffuse from deeper parts of the bulk towards the surface.[6]  Reaction pathways may change with increasing bulk defect density as will be outlined for model studies on benzaldehyde and methanol on rutile TiO2 (110) in absence or presence of atomic or molecular oxygen.[5] Low temperature partial oxidation to formaldehyde as well as high temperature C-C-coupling can be observed. Investigations using temperature programmed desorption spectroscopy (TPD) and Fourier-transformation polarized infrared reflection-absorption spectroscopy (FT-IRRAS) under UHV-conditions will be presented.

 

References

  1. U. Diebold, Surf. Sci. Rep., 2003, 48, 53-229.
  2. C. Pang, R. Lindsay, G. Thornton, Chem. Rev., 2013, 113, 3887-3948.
  3. M. Henderson, S. Otero-Tapia, M. Castro, Faraday Discuss., 1999, 114, 313-329.
  4. N. Petrik, M. Henderson, G. Kimmel, J. Phys. Chem. C, 2015, 119, 12262-12272.
  5. P. Clawin, C. Friend, K. Al-Shamery, Chem. Eur. J., 2014, 20, 7665-7669.
  6. E. Lira, S. Wendt, P. Huo et al., J. Am. Chem. Soc., 2011, 133, 6529-6532.
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