Model materials and in-situ/operando studies for industrially important chemical processes

 Professor Anja Olafsen Sjåstad, Department of Chemistry, University of Oslo

In this talk, some of our recent work on the preparation of model materials and their use in operando studies connected to the ammonia oxidation step for nitrogen based fertilizer production, the Fischer-Tropsch process, and NOx abatement will be discussed.

The main challenge in providing a suited model catalyst is to achieve an appropriate nanostructure (with a specific particle size, chemical composition, element distribution and atomic arrangement) that contains the key ingredients of the real catalyst, and at the same time provides a material that is suited for the analysis probe in question.  I.e., geometrically we require 3D-powders and 2D-surfaces that are thermally and chemically stable during the experiment, likewise that the material can withstand a high-energy electron (or X-ray) beam, that it is sufficiently conductive and maintains the appropriate chemical state during the investigation. Ideally, all such performance studies of heterogeneous catalysts should be done at real process conditions with respect to reaction temperature, process pressure and linear gas velocity. Fortunately, there is a tremendous development of operando instrumentation working at relevant process conditions. Examples are Near Ambient Pressure X-ray Photoelectron Spectroscopy (NAP-XPS), operando sub-Ångström (Å) resolution Transmission Electron Microscopy (TEM) and High Pressure Reactor Scanning Tunnelling Microscope (HP Reactor STM), along with rapid developments in computational materials science

Relevant references

1. “Mechanism of grain reconstruction of Pd and Pd/Ni wires during Pt–catchment”, A. S. Fjellvåg, P. Jørgensen, D. Waller, D. S. Wragg, M. Di Michiel, A. O. Sjåstad, Materiala, 21, 101359, 2022.
2. “Structural disorder and antiferromagnetism in LaNi_1–xPt_xO₃”,  A. S. Fjellvåg, Ø. Fjellvåg, Y, Breard, A. O. Sjåstad, J. Solid State Chem., 299, 122181, 2021.
3. “How surface species drives product distribution during ammonia oxidation: An STM and operando APXPS study”, O. Ivashenko, N. Johansson, C. Pettersen, M. Jensen, J. Zheng, J. Schnadt, A.O. Olafsen; ACS Catalysis, 11, 8261, 2021.
4. “Controlled Alloying of Pt-Rh Nanoparticles by the Polyol Approach”, S. Bundli, P. Dhak. A.E. Gunnæs, P. D. Nguyen, H. Fjellvåg, A. O. Sjåstad, J. Alloys and Compounds,  779, 879, 2019.
5. “Roadmap for Modeling RhPt/Pt(111) Catalytic Surfaces for Intermediate-Temperature Ammonia Oxidation", J. Zheng, O. Ivashenko, H. Fjellvåg, I. Groot, A. O. Sjåstad, J. Phys. Chem. C, 122(46), 26430, 2018.
6. “The nucleation, alloying, and stability of Co-Re bimetallic nanoparticles on Al₂O₃/NiAl(110)”, R. V. Mom, O. Ivashenko, J. W. M. Frenken, I. M. N. Groot, A. O. Sjåstad, J. Phys. Chem. C 122, 8967, 2018.
7. “In situ TEM observation of the Boudouard reaction: multi-layered graphene formation from CO on cobalt nanoparticles at atmospheric pressure”, M. Bremmer, E. Zacharaki, A. O. Sjåstad, V. Navarro, J. Frenken, P. Kooyman, Faraday Discussions, 197, 337, 2017.
8. “From colloidal monodisperse nickel nanoparticles to well-defined Ni/Al₂O₃ model systems”, E. Zacharaki, P. Beato, R. R Tiruvalam, K. J. Andersson, H. Fjellvåg, A. Olafsen Sjåstad, Langmuir, 33, 9836, 2017.
9. “Structural arrangement in close-packed cobalt polytypes”, W. A. Slawinski, E. Zacharaki, H. Fjellvåg, A. Olafsen Sjåstad, Crystal Growth& Design, 18, 2318, 2017.