19 April 2019 Lars G.M. Pettersson


Speaker: Lars G.M. Pettersson, Stockholm University
Catalysis in Real Time Using X-ray Lasers and DFT
Date: April 19, 2019 (Friday)
Time: 11:00
Cookie & Tea: SCI 103, 10:45
Place: SCI 103
web: https://physics-seminars.ku.edu.tr/

I will describe how the unique temporal and spectral characteristics of X-ray free-electron lasers (XFEL) can be utilized to follow chemical transformations in heterogeneous catalysis in real time and how DFT calculations contribute to the analysis of the data. The systematic study of CO oxidation on Ru(0001) will be highlighted, initiated either using a femtosecond pulse from an optical laser  [1] or by activating only the oxygen atoms using atom-selective core-excitation [2]. We find that CO is promoted into an entropy-controlled precursor state prior to desorbing when the surface is heated in the absence of oxygen [3], whereas in the presence of oxygen, CO desorbs directly into the gas phase [4]. We monitor the activation of atomic oxygen explicitly by the reduced split between bonding and antibonding orbitals as the oxygen comes out of the strongly bound hollow position. Applying these novel XFEL techniques to the full oxidation reaction resulted in the surprising observation of a significant fraction of the reactants at the transition state through the electronic signature of the new bond formation [1]. We furthermore follow hydrogenation of CO on Ru and elucidate the different catalytic pathways in real time. The experiments are combined with DFT calculations of reaction paths and X-ray spectroscopic signals for a more complete and detailed analysis.
[1] Öström et al., Probing the Transition State Region in Catalytic CO Oxidation on Ru, Science 347, 978 (2015)
[2] Schreck et al., Atom-Specific Activation in Catalytic CO Oxidation, J. Chem. Phys. 149, 234707 (2018)
[3] Dell’Angela et al., Real-Time Observation of Surface Bond Breaking with an X-ray Laser, Science 339, 1302 (2013)
[4] Xin et al., Strong Influence of Coadsorbate Interaction on CO Desorption Dynamics, Phys. Rev. Lett. 114, 156101 (2015)
[5] LaRue et al., Real-Time Elucidation of Catalytic Pathways in CO Hydrogenation on Ru, J. Phys. Chem. Lett. 8, 3820 (2017)

Short Bio: https://www.su.se/english/profiles/lgm-1.186601