Scientists Track Ultrafast Formation of Catalyst with X-ray Laser

First-of-its-kind measurements provide insights on reactions that could one day turn sunlight and water into fuels.

The benchmark catalyst Fe(CO)5 is irradiated with ultraviolet light, causing it to lose one of its five carbon monoxide groups. — Image courtesy of Helmholtz Zentrum Berlin/SciStyle, Thomas Splettstößer

The Science

At the SLAC National Accelerator Laboratory, an international team has – for the first time – precisely tracked the surprisingly rapid process by which light rearranges the outermost electrons of a metal compound known as Fe(CO)₅ and turns it into an active catalyst – a substance that promotes chemical reactions. The results come from using resonant inelastic x-ray scattering at SLAC, which also provides information about the chemical dynamics of the catalyst.

The Impact

The new x-ray spectroscopy technique allows scientists to investigate how light rearranges the outermost electrons of a compound in a few hundred femtoseconds, or quadrillionths of a second. Learning these details could help scientists predict and control the quick, early steps in reactions to turn sunlight and water into fuel as well as master the chemistry required to produce other renewable fuels.

Summary

The proper methods to interrogate the electronic states of transition metal complexes, such as the iron-based Fe(CO)5, during a reaction have been lacking. Recently, a team of researchers from the United States and Europe employed a technique designed to alleviate this problem. This research group used resonant inelastic x-ray scattering (RIXS) at the SLAC National Accelerator Laboratory to probe the frontier or outermost orbitals of Fe(CO)₅ with atomic-level and femtosecond resolution. In this work, the researchers used femtosecond duration x-ray laser pulses generated by the Linac Coherent Light Source to follow Fe-CO bond dissociation in the metal complex and the resulting catalyst formation. The measurement is the first of its kind, showing the potential for using multi-dimensional x-ray spectroscopy to probe chemical dynamics and better understand how catalysts function. Data acquired through this technique has already addressed a long-standing question in the photochemistry of the catalyst Fe(CO)₄ by demonstrating that triplet and singlet reaction pathways occur in parallel even on the sub-picosecond timescale. The use of RIXS should be applicable to a variety of research fields, especially those looking to gain information on structural dynamics in ultrafast processes.

Contact

Kelly Gaffney
PULSE Institute
SLAC National Accelerator Laboratory and Stanford University
[email protected]

Funding

This work was supported by the Volkswagen Stiftung (M.B.), the Swedish Research Council (M.O.), the Carl Tryggers Foundation (M.O.), the Magnus Bergvall Foundation (M.O.), the Collaborative Research Centers SFB755 and SFB1073 (I.R., S.G.,W.Q., M.S. and S.T.), and the Helmholtz Virtual Institute Dynamic Pathways in Multidimensional Landscapes. W.Z., R.W.H. and K.J.G. acknowledge support through the AMOS program within the Chemical Sciences, Geosciences, and Biosciences Division of the Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy (DOE). Portions of this research were performed on the Soft X-ray Materials Science (SXR) Instrument at the Linac Coherent Light Source (LCLS), a division of SLAC National Accelerator Laboratory and an Office of Science user facility operated by Stanford University for DOE. The SXR Instrument is funded by a consortium whose membership includes the LCLS, Stanford University through the Stanford Institute for Materials Energy Sciences (SIMES), Lawrence Berkeley National Laboratory (LBNL), the University of Hamburg through the BMBF priority program FSP 301, and the Center for Free Electron Laser Science (CFEL).

Publications

P. Wernet, K. Kunnus, I. Josefsson, I. Rajkovic, W. Quevedo, M. Beye, S. Schreck, S. Grübel, M. Scholz, D. Nordlund, W. Zhang, R. W. Hartsock, W. F. Schlotter, J. J. Turner, B. Kennedy, F. Hennies, F. M. F. de Groot, K. J. Gaffney, S. Techert, M. Odelius, and A. Föhlisch, “Orbital-specific mapping of the ligand exchange dynamics of Fe(CO)5 in solution.” Nature 520, 78-81 (2015). [DOI: 10.1038/nature14296]