@inproceedings{01J9V89RH6DN5F29Q90QVBGRRY,
  abstract     = {{The development of MEXAS (Modulation Excitation X-ray Absorption Spectroscopy) opened
up a wealth of possibilities to study the surface of catalysts at a high level of detail, while operating
under reaction conditions.1 Since the modulation excitation technique is quite new, its
experimental design is still subject of study.2 Maximizing the amount of information derived from
this complex technique necessitates advanced data analysis. The application of PSD (PhaseSensitive Detection) was already a big step forward in analysing MEXAS data, even giving
access to kinetic information.2 To further enhance the spectral interpretation, simulation
techniques are required. This is where DFT (Density Functional Theory) calculations come in.
When applying MCR-ALS (Multivariate Curve Resolution with Alternating Least Squares) data
analysis on an experimental MEXAS dataset, one obtains the spectra of a number of ‘pure’
components.3 To characterize these pure components based on their spectra, EXAFS modelling
is used. This gives a lot of information about the bulk properties of the catalyst. However, catalysis
researchers are also interested in the chemistry occurring at the surface. The presence of
adsorbates will impact the XAS spectra of surface elements and as a result, details about these
adsorbates can be found in the MEXAS data. To extract this information, a detour via DFT is
needed. Based on the bulk properties of the pure components and chemical intuition, VASP
(Vienna Ab-initio Software Package) can be used to construct an atom scale structure of the
catalyst surface.
4
It should be stressed that this structure comprises both catalyst and
adsorbates. Using the FDMNES (Finite Difference Method Near-Edge Spectrum) software, the
XANES (X-ray Absorption Near Edge Structure) spectrum of this structure can be estimated.
5
If
the predicted spectrum matches the spectrum of the pure component, the proposed VASPstructure is likely similar to the real structure. In this way, one has indirectly obtained information
about the surface chemistry from the modulation experiments.
The proposed methodology, combining MEXAS with DFT, is in a conceptual phase and as
such presents challenges. One is the fact that the errors from MCR-ALS, VASP and FDMNES
all add up to the final product. Another lies in the question whether the FDMNES software is
sensitive enough to predict the subtle differences, occurring during a MEXAS experiment.
However, if this methodology proves functional, it provides a unique approach to simultaneously
validate DFT calculation outcomes and analyse MEXAS results on a deeper level. All of this,
while remaining at the surface ...}},
  author       = {{Lips, Servaas and Xie, Yufei and De Coster, Valentijn and Poelman, Hilde and Sabbe, Maarten and Galvita, Vladimir}},
  booktitle    = {{18th SOLEIL Users' Meeting (SUM2024), Abstracts}},
  language     = {{eng}},
  location     = {{Saint-Aubin, France}},
  pages        = {{1}},
  title        = {{Modulation excitation XAS : how to go deeper, while remaining at the surface?}},
  url          = {{https://www.synchrotron-soleil.fr/en/events/sum2024#:~:text=In%20the%20afternoon%20of%20January,tutorial%20will%20be%20communicated%20later.}},
  year         = {{2024}},
}