Challenges and Opportunities for Applications of Advanced X-ray Spectroscopy in Catalysis Research

Abstract

X-ray spectroscopy has had a significant and continually growing impact on catalysis research for nearly 50 years. In particular, the ability to obtain element selective electronic and geometric structural information via the X-ray absorption (XAS) edge and extended X-ray absorption fine structure regions, respectively, has been a major asset for catalysis research. In the last two decades, the development of dedicated synchrotron-based X-ray emission spectrometers has greatly expanded the range of possible experiments, enabling both nonresonant and resonant Xray emission spectroscopy experiments that can provide greater selectivity and more detailed electronic and structural information. Herein, we briefly review the range of hard X-ray photon-in, photon-out experiments that are presently possible, and highlight their recent applications in catalysis research. We also discuss the ongoing need for conventional XAS applications, either in standalone applications or in combination with more advanced approaches. The open opportunities and ongoing challenges for applying these methods, and ultimately for analyzing and interpreting the data, are also discussed.

Investigating ultrafast structural dynamics using high repetition rate x-ray FEL radiation at European XFEL

“…The use of XES was crucial to obtain this spin excitation lifetime information which is not accessible through optical spectroscopy. These results demonstrate the importance of ultrafast time-resolved x-ray techniques to further develop our understanding of photo-active molecules for their application as energy converters, catalysts or sensors [5].…”

“…4 Perspectives of future scientific challenges to be addressed by European XFEL Hard x-ray FEL experiments are presently converging from a phase of exploratory experiments, during which new methods and techniques were developed and tested on prototypical or highly standard sample systems, to a phase focused on targeted scientific applications and their requirements. Examples of such areas are SFX for drug discovery [48] or chemical crystallography [49], water research [50], or systematic studies of photo-catalysts [5]. These application areas are supported by several scientific instruments around the globe and all instruments at European XFEL assign significant fractions of their user time to them.…”

Operando Elucidation of Electrocatalytic and Redox Mechanisms on a 2D Metal Organic Framework Catalyst for Efficient Electrosynthesis of Hydrogen Peroxide in Neutral Media

“…Additionally, LCA reveals that the primary speciation in an O 2 -saturated environment is HAB red and further reaches 100% HAB red at potentials ≤0.2 V vs RHE. The initially high fraction of HAB red in the O 2 -saturated XANES is strange and could suggest some limitation of Ni K-edge XANES as an oxidation state probe 56 in such a complex chemical environment.…”

Speciation of Nanocatalysts Using X-ray Absorption Spectroscopy Assisted by Machine Learning

“…X-ray absorption fine structure (XAFS) spectroscopy has been a premier method for investigating nanoparticle catalysts in reaction conditions, and its advantages and limitations have been discussed multiple times, including recent reviews. − In this Perspective, we will summarize existing and emerging strategies for solving the complexity of nanoparticles by relying, primarily, on the recently developed XAFS-based methods assisted by using machine learning approaches. A relatively recent contribution to the XAFS data analysis, machine learning has rapidly gained attention after the first reports that demonstrated its utility for “inverting” the X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) data and mapping the XANES and EXAFS spectra on various structural descriptors of nanoparticles, ,− clusters, − and SACs .…”