Geometric and compositional properties of size- and shape-selective nanocatalysts often change in working (<i>operando</i>) conditions. Extended X-ray absorption fine structure (EXAFS) spectroscopy has been a method of choice to study mono- and bimetallic nanoparticles for four decades. EXAFS abilities to measure the coordination numbers, however, are impaired by the decreased spatial resolution and increased number of artifacts at the conditions of operando catalysis experiments, i.e., high temperature and pressure. Furthermore, the data analysis methods commonly require additional time, from several minutes to days, until the 3D structure is obtained. In this talk I will review new methods of data analysis and modeling of nm-scale nanoparticles and sub-nm clusters that extend beyond conventional fitting of experimental EXAFS spectra. Our new approach is based on Supervised Machine Learning that finds "hidden" correlation between the features space of the X-ray absorption coefficient values in the near edge (XANES) spectrum and the structural descriptors affecting them. As a proof of principle, the same coordination numbers that were previously obtained by multiple scattering analysis of EXAFS spectra over several hours of data analysis, were obtained by the SML-XANES method in less than a second per spectrum. Because XANES features are less impaired by temperature, and because good quality XANES spectra can be measured for much lower weight loading than EXAFS, this method is ideal for operando and high throughput experiments. As one example of such use, a structure of the catalyst can be analyzed on the fly, and its sintering or fragmentation can be observed during the reaction and thus, potentially, reversed by changing reaction regimes. Another example is the ability to improve this method by increasing the spectral contrast in XANES features by using high energy resolution methods available at high flux beamlines at new synchrotrons.

Toward “on the fly” analysis of reactive sites from their X-ray absorption spectra

255th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.