Dr. Olga Safonova
5232 Villigen PSI
Olga Safonova is a senior scientist at the Paul Scherrer Institute. She received her degree in chemistry and completed her PhD thesis in inorganic chemistry at Lomonosov Moscow State University in Russia studying the mechanism of operation of gas sensors based on semiconductor oxides. Then she moved to France, where she was a postdoc and became a staff scientist at the European Synchrotron Radiation Facility performing research in the field of heterogeneous catalysis using X-ray absorption and diffraction methods. Since 2010, she is a senior scientist at the Paul Scherrer Institute in the Operando spectroscopy group shared between the Energy and Environment and the Photon Science Divisions.
Olga Safonova participates in the management and operation of SuperXAS beamline at the Swiss Light Source. She currently supervises three PhD students funded by the Swiss National Science foundation upon two project:“Uncovering dynamic structure of active sites in selective oxidation catalysts using time-resolved X-ray absorption spectroscopy” and “Tailored CO2 hydrogenation catalysts for selective methanol synthesis via structure-Activity Relationship across Time and Length Scale.”
Safonova’s scientific interests are focused on understanding of the structure-activity relationships in heterogeneous catalysts involving metal and oxide nanoparticles and cationic species on oxide surfaces. Research of Olga Safonova uses new development of time-resolved spectroscopic methods to access the structure and reactivity of active sites in heterogeneous catalysts on the atomic scale. Her main expertise lies between chemical kinetics and in situ/operando X-ray absorption and emission spectroscopy (XAS and XES) techniques based on hard X-rays. She currently leads research projects on fundamental understanding of CO oxidation and CO2 hydrogenation processes at the metal-support interfaces and selective alcohol oxidation reaction on supported vanadia-oxo species.
Elucidating the Oxygen Activation Mechanism on Ceria-Supported Copper-Oxo Species Using Time-Resolved X-ray Absorption Spectroscopy , Olga V. Safonova, Alexander Guda, Yury Rusalev, René Kopelent, Grigory Smolentsev, Wey Yang Teoh, Jeroen A. van Bokhoven and Maarten Nachtegaal, ACS Catalysis volume 10, Article number: 4692 (2020). Rational design of better catalysts requires precise knowledge about the structure of active sites and their reactivity during catalytic cycle. However, for majority of catalytic systems and processes such information remains elusive due to large structural heterogeneity of catalytic material and various limitations of experimental and theoretical methods. Here, element specific operando spectroscopy helped us to gain such knowledge for copper-ceria system, which finds application in exhaust and sustainable energy catalysts. For this study, we have chosen the material with well-defined structure consisting of finely dispersed copper-oxo species (predominantly dimers) stabilized on ceria surface. Using times-resolved X-ray absorption spectroscopy we observed that oxidation states of copper and cerium atoms forming active sites change in concert allowing efficient catalytic oxidation of carbon monoxide below 100 oC. The developed methodology can be applied in future for more complex catalytic systems and processes to clarify complex structure-activity relationships.
Isolated Zr Surface Sites on Silica Promote Hydrogenation of CO2 to CH3OH in Supported Cu Catalysts , Erwin Lam, Kim Larmier, Patrick Wolf, Shohei Tada, Olga V. Safonova and Christophe Copéret, J. Am. Chem. Soc. volume 140, Article number: 10530 (2018). Copper nanoparticles supported on zirconia or related supported oxides show promising activity and selectivity for the hydrogenation of CO2 to methanol. However, the role of the support remains controversial. In order to understand the role of the support and in particular of the Zr surface species at a molecular level, a surface organometallic chemistry approach has been used to tailor a silica support containing isolated Zr(IV) surface sites, on which copper nanoparticles (∼3 nm) are generated. Ex situ and in situ X-ray absorption spectroscopy reveals that the Zr sites on silica remain isolated and in their +4 oxidation state, while ex situ solid-state nuclear magnetic resonance spectroscopy and catalytic performances show that similar mechanisms are involved with the single-site support and ZrO2. These observations imply that Zr(IV) surface sites at the periphery of Cu particles are responsible for promoting methanol formation on Cu–Zr-based catalysts and provide a guideline to develop selective methanol synthesis catalysts.
Fluorescence-detected XAS with sub-second time resolution reveals new details about the redox activity of Pt/CeO2 catalyst , Alexander A. Guda, Aram L. Bugaev, Rene Kopelent, Luca Braglia, Alexander V. Soldatov, Maarten Nachtegaal, Olga V. Safonova and Grigory Smolentsev, J. Synchrotron Rad. volume 25, Articlenumber: 989 (2018). A setup for fluorescence-detected X-ray absorption spectroscopy (XAS) with sub-second time resolution has been developed. This technique allows chemical speciation of low-concentrated materials embedded in highly absorbing matrices, which cannot be studied using transmission XAS. The new time-resolved XAS setup can be applied to various systems, capable of reproducible cycling between different states triggered by gas atmosphere, light, temperature, etc. It opens up new perspectives for mechanistic studies on automotive catalysts, selective oxidation catalysts and photocatalysts.
X-ray emission spectroscopy: highly sensitive techniques for time-resolved probing of cerium reactivity under catalytic conditions Rene Kopelent, Jeroen A. van Bokhoven, Maarten Nachtegaal, Jakub Szlachetko and Olga V. Safonova, Phys. Chem. Chem. Phys. volume 18, Article number: 32486 (2016). Oxygen storage materials such as ceria are used in many catalytic applications because they can reversibly bind and release oxygen. Tools are needed to observe and quantify this activity which involves a change in the cerium oxidation state and to understand the involvement of cerium in catalytic processes. In this paper, we evaluate the sensitivity of high-resolution X-ray emission-based methods for the in situ time-resolved quantification of small concentrations of Ce3+ in ceria-based materials. We demonstrate that resonant X-ray emission spectroscopy (RXES) at optimal excitation energy is more sensitive than high energy resolution off-resonant spectroscopy (HEROS) and non-resonant X-ray emission spectroscopy (non-resonant XES) and that it can track the reactivity of less than 0.3% of cerium atoms in a 1% Pt/CeO2 catalyst in a plug-flow reactor with sub-second time resolution. These results demonstrate that X-ray emission-based methods can be used as very sensitive tools and provide new insights into dynamic changes of the oxidation state in reducible oxides in a variety of applications.
Catalytically Active and Spectator Ce3+ in Ceria‐Supported Metal Catalysts René Kopelent, Jeroen A. van Bokhoven, Jakub Szlachetko, Jacinta Edebeli, Cristina Paun, Maarten Nachtegaal, Olga V. Safonova Angew. Chem. Int. Ed. Volume 54, Article number:8728 (2015) Identification of active species and the rate‐determining reaction steps are crucial for optimizing the performance of catalysts. We demonstrated that active Ce3+ species in a ceria‐supported platinum catalyst during CO oxidation are short‐lived and therefore cannot be observed under steady‐state conditions. Using time‐resolved resonant X‐ray emission spectroscopy, we quantitatively correlated the initial rate of Ce3+ formation under transient conditions to the overall rate of CO oxidation under steady‐state conditions and showed that ceria reduction is a kinetically relevant step in CO oxidation, whereas a fraction of Ce3+ was present as spectators. This approach can be applied to various catalytic processes involving oxygen‐storage materials and reducible oxides to distinguish between redox and non redox catalytic mechanisms.