Dr. Adam Hugh Clark

Adam Clark is a tenure track scientist at the Paul Scherrer Institute. With a bachelors degree in Physics from the University of Nottingham, masters and PhD degrees in Molecular Modelling and Materials Science from University College London chiefly studying the redox properties of nanocatalysts using synchrotron scattering and spectroscopic techniques. Subsequently he moved to Paul Scherrer Institute as a postdoc and later became a tenure track scientist based within the Operando Spectroscopy group performing research in the field of heterogeneous catalysis using primarily X-ray absorption methods. 

Adam Clark participates in the management and operation of SuperXAS beamline at the Swiss Light Source. In addition to this he is responsible for the development of processing and analysis software for the treatment of quick-scanning X-ray absorption spectroscopy from the SuperXAS beamline. Whilst also leading the development of highly time resolved fluorescence detected X-ray absorption spectroscopy. 

Adam's scientific research is currently focused on the investigation of ceria based materials towards semi-hydrogenation catalysis. His main expertise is in the application of highly time-resolved X-ray absorption spectroscopy. During the course of his research developing and enhancing the abilities of time resolved X-ray absorption spectroscopy methods allows for new structure-activity relationships in heterogeneous catalysts to be uncovered. Bringing the enhanced sensitivity of modulation-excitation spectroscopy methods to an array of new applications such as in heterogeneous catalysis and now more widely in electrochemistry.

For an extensive overview we kindly refer you to our publication repository DORA

ProQEXAFS: a highly optimized parallelized rapid processing software for QEXAFS data. Clark, A. H., Imbao, J., Frahm, R., & Nachtegaal, M. Journal of Synchrotron Radiation, 27, 551-557 (2020). 

The high temporal resolution in data acquisition, possible in the quick-scanning EXAFS (QEXAFS) mode of operation, provides new challenges in efficient data processing methods. Here a new approach is developed that combines an easy to use interactive graphical interface with highly optimized and fully parallelized Python-based routines for extracting, normalizing and interpolating oversampled time-resolved XAS spectra from a raw binary stream of data acquired during operando QEXAFS studies. The programs developed are freely available via a Github repository.

Fluorescence-detected quick-scanning X-ray absorption spectroscopy. Clark, A. H., Steiger, P., Bornmann, B., Hitz, S., Frahm, R., Ferri, D., & Nachtegaal, M. Journal of Synchrotron Radiation, 27 (2020) .

Time-resolved X-ray absorption spectroscopy (XAS) offers the possibility to monitor the state of materials during chemical reactions. While this technique has been established for transmission measurements for a number of years, XAS measurements in fluorescence mode are challenging because of limitations in signal collection as well as detectors. Nevertheless, measurements in fluorescence mode are often the only option to study complex materials containing heavy matrices or in samples where the element of interest is in low concentration. Here, it has been demonstrated that high-quality quick-scanning full extended X-ray absorption fine-structure data can be readily obtained with sub-second time resolution in fluorescence mode, even for highly diluted samples. It has also been demonstrated that in challenging samples, where transmission measurements are not feasible, quick fluorescence can yield significant insight in reaction kinetics. By studying the fast high-temperature oxidation of a reduced LaFe_0.8Ni_0.8O₃ perovskite type, an example where the perovskite matrix elements prevent measurements in fluorescence, it is shown that it is now possible to follow the state of Ni in situ at a 3 s time resolution.

Functional role of Fe-doping in Co-based perovskite oxide catalysts for oxygen evolution reaction.  Kim, B. J., Fabbri, E., Abbott, D. F., Cheng, X., Clark, A. H., Nachtegaal, M., … Schmidt, T. J. Journal of the American Chemical Society, 141(13), 5231-5240 (2019).

Perovskite oxides have been at the forefront among catalysts for the oxygen evolution reaction (OER) in alkaline media offering a higher degree of freedom in cation arrangement. Several highly OER active Co-based perovskites have been known to show extraordinary activities and stabilities when the B-site is partially occupied by Fe. At the current stage, the role of Fe in enhancing the OER activity and stability is still unclear. In order to elucidate the roles of Co and Fe in the OER mechanism of cubic perovskites, two prospective perovskite oxides, La_0.2Sr_0.8Co_1-xFe_xO_3-δ and Ba_0.5Sr_0.5Co_1-xFe_xO_3-δ with x = 0 and 0.2, were prepared by flame spray synthesis as nanoparticles. This study highlights the importance of Fe in order to achieve high OER activity and stability by drawing relations between their physicochemical and electrochemical properties. Ex situ and operando X-ray absorption spectroscopy (XAS) was used to study the local electronic and geometric structure under oxygen evolving conditions. In parallel, density function theory computational studies were conducted to provide theoretical insights into our findings. Our findings show that the incorporation of Fe into Co-based perovskite oxides alters intrinsic properties rendering efficient OER activity and prolonged stability.

Elucidating the mechanism of heterogeneous Wacker oxidation over Pd-Cu/zeolite Y by transient XAS. Imbao, J., van Bokhoven, J. A., Clark, A., & Nachtegaal, M.  Nature Communications, 11, 1118 (9 pp.) (2020).

The heterogenization of Wacker catalysts using chloride-free systems can potentially be a good alternative for the commercial homogeneous Wacker oxidation of ethylene, which utilizes excessive aqueous chloride solvents. However, the mechanism of the heterogeneous system has not been clarified, preventing the rational design of better catalysts. Here, we report a transient X-ray absorption spectroscopic (XAS) investigation of the heterogeneous Wacker oxidation over Pd-Cu/zeolite Y coupled with kinetic studies and chemometric analysis. Insight is obtained by operando quickXAS allowing the quantitative determination of rates and thereby revealing a rapid redox reaction involving copper. Our work demonstrates that copper is not only the site of oxygen activation, but is also involved in the formation of undesired carbon dioxide. Without detecting the presence of Cu(0) and Pd(I), our results suggest that two one-electron transfers to two Cu(II) ions to reoxidize Pd(0) is at work in this heterogeneous Wacker catalyst

Nanostructuring unlocks high performance of platinum single-atom catalysts for stable vinyl chloride production. Kaiser, S. K., Fako, E., Manzocchi, G., Krumeich, F., Hauert, R., Clark, A. H., … Pérez-Ramírez, J.  Nature Catalysis, 3(4), 376-385  (2020). 

The worldwide replacement of the toxic mercuric chloride catalyst in vinyl chloride manufacture via acetylene hydrochlorination is slowed by the limited durability of alternative catalytic systems at high space velocities. Here, we demonstrate that platinum single atoms on carbon carriers are substantially more stable (up to 1,073 K) than their gold counterparts (up to 473 K), enabling facile and scalable preparation and precise tuning of their coordination environment by simple temperature control. By combining kinetic analysis, advanced characterization, and density functional theory, we assess how the Pt species determines the catalytic performance and thereby identify Pt(_II)-Cl as the active site, being three times more active than Pt nanoparticles. We show that Pt single atoms exhibit outstanding stability in acetylene hydrochlorination and surpass the space-time yields of their gold-based analogues after 25 h time-on-stream, qualifying them as a candidate for sustainable vinyl chloride production.