IMX Seminar Series - X-ray Spectroscopy Techniques Probing Active Species in Homogeneous Catalysis

Detailed information on the structural and electronic properties of a catalyst or material and how they change during reaction is required to understand their reaction mechanism and performance. An experimental technique that can provide structural as well as electronic analysis and that can be applied in situ/operando and in a time-resolved mode, is X-ray spectroscopy. Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy is powerful in determining the local structure of compounds including amorphous materials and solutions, since long-range order is not required. Combined X-ray Absorption and X-ray Emission spectroscopy (XAS and XES resp.) provides detailed insights in the electronic properties of a material. Detailed information about the materials in their dynamic chemical active environment can thus be obtained and structure/electronic – performance relationships and reaction mechanisms derived. Developments in XAS using new instrumentation and data acquisition methods while selecting specific X-ray energies provide this more detailed electronic information [1]. High energy resolution XAS, XES and Resonant Inelastic X-ray Scattering (RIXS) provide very detailed electronic information on the systems under investigation. The secondary spectrometer design also opens up lab-based spectrometer designs as will be demonstrated [2].
Over the last years, different approaches have been reported to allow operando time resolved XAS on catalytic systems, mostly solid-gas. Our group has also developed stopped-flow methodologies allowing simultaneous time-resolved UV–Vis/XAS experimentation on liquid systems down to the millisecond (ms) time resolution [3]. Low X-ray energy systems (light elements) or for low concentrated systems, longer XAS data acquisition times in fluorescence detection are required and therefore a stopped flow freeze-quench procedure has been developed [4]. Pushing the time-resolution has been achieved by synchronizing the synchrotron bunches with an optical laser in order to perform fast pump-probe experiments [6] or applying modulation excitation methodologies, which can isolate active from spectator species [6].
The methodologies and instrumentation have been developed and applied to a wealth of materials science, for homogeneous and heterogeneous catalysis to batteries and fuel cells as well as art objects. This lecture will focus on homogeneous catalysis, providing insights in active/activated catalyst species and reaction mechanisms. A range of complementary spectroscopic techniques have for example been applied to different selective ethene oligomerisation catalysts, i.e. industrially applied chromium-based ones [4] as well as novel iron and nickel-based systems [7]. Solving the complicated puzzles of data, revealing active and inactive catalyst intermediates as a function of time and process conditions, has led to design concepts for novel catalysts in the field.

1.         See for example: Angew. Chem. Int. Ed. 45 (2006) 4651-4654; J. Phys. Chem. B 110 (2006) 16162-16164; Angew. Chem. Int. Ed. 47 (2008) 9260-9264; Catal. Today 145 (2009) 300-306; J. Phys. Chem. C 117 (2013) 23286–23294; Chem. Phys. Chem. 8 (2014) 1569–1572; J. Phys. Chem. C 119 (2015) 2419–2426.
2.         Coord. Chem. Rev. 423 (2020), 213466 (28 p.).
3.         Organometallics 29 (2010) 3085–3097.
4.         J. Catal. 285 (2011) 247–258; ACS Catalysis 4 (2014) 4201; Catal. Sci. Techn. 6 (2016) 6237; ACS Catal. 9 (2018) 1197-1210; Chem. Cat. Chem. 12 (2020), 881-892; Cat. Sci. Tech. 10 (2020), 6212-6222.
5.         J. Phys. Chem. B 117 (2013) 7381–7387; Photochem. Photobiol. Sci. 17 (2018) 896-902.
6.         manuscript in preparation.
7.         Phys. Chem. Chem. Phys. 21 (2019) 14638-14645; RSC Advances 10 (2020) 729-738; Organometallics 39 (2020), 3480-3489.
Bio: Moniek Tromp finished her MSc in Chemistry, with specialisations in spectroscopy and catalysis, at the University of Utrecht (Nld) in 2000. She then obtained a PhD from the same university, in the fields of homogeneous catalysis and time-resolved X-ray absorption spectroscopy with Profs. Koningsberger and van Koten.  After finishing with distinction (‘cum laude’, greatest honours possible) in 2004, she moved to the University of Southampton (UK) for a Post-Doctoral Research fellowship in the fields of heterogeneous catalysis and spectroscopy. In 2007, she was awarded an EPSRC Advanced Research Fellowship to start her own independent academic career (and became lecturer). She moved to Germany in 2010, where she took up a position as professor in Catalyst Characterisation at the Technical University Munich. In 2014, she decided to come back to the Netherlands, working at the University of Amsterdam. From July 2018 she has taken up the Chair of Materials Chemistry at the Zernike Institute at the University of Groningen.
She has been awarded prestigious fellowships/awards like the EPSRC Advanced Research Fellowship, NWO VIDI and the NWO Athena prize. She is active in numerous science advisory and review panels of large research facilities and universities internationally, part of a European Science Strategy team for large facilities, has published close to 100 papers in high profile journals and given over 80 invited lectures worldwide.
She is chair of the Dutch Catalysis Society (of the KNCV). She is co-chair of the organizing committee of the annual conference on Catalysis (NCCC) in The Netherlands. Gender and diversity are important for her and she has been active as Gender Equality Officer (D) and is now developing programs for primary school on science and engineering as well as gender bias issues. From April 2019, she has taken up a board position at the National Network for Female Professors (LNVH). She is a board member of the Dutch Science Association NWO (division ENW) since May 2019.
Her research focusses on the development and application of operando spectroscopy techniques in catalysis and materials research, incl. fuel cells, batteries, photochemistry, as well as arts, with a focus on X-ray spectroscopy techniques. Novel (time resolved) X-ray absorption and emission spectroscopy methods have been developed as tools in catalysis and energy material (battery and fuel cell) research. This includes the development of the required operando instrumentation and cells, as well as data analysis and theoretical methods. Application of the techniques to fundamentally or industrially interesting catalytic processes and materials has been pursued, providing unprecedented insights in properties and mechanisms.