X-ray absorption near edge structure (XANES) spectroscopy is widely used for operando catalyst characterization. We show that, for highly fluxional supported nanoclusters, the customary extraction of the oxidation state of the metal from the XANES data by fitting to the bulk standards is highly questionable. The XANES signatures as well as the apparent oxidation state for such clusters arise from a complex combination of many factors, and not only from the chemical composition in reaction conditions (e.g., oxygen content in oxidizing atmosphere). The thermally accessible isomerization and population of several structurally distinct cluster forms, cluster-support interaction, and intrinsic size effects all impact the metal oxidation state and XANES signal. We demonstrate this on copper oxide clusters with different compositions, Cu4Ox(x = 2-5) and Cu5Oy (y = 3, 5), deposited on amorphous alumina and ultrananocrystalline diamond, for which we computed the XANES spectra and compare the results to the experiment. We show in addition that fitting the experimental spectrum to calculated spectra of supported clusters can, in contrast, provide good agreement and insight into the spectrum-composition-structure relation. Experimental XANES interpreted using the proposed fitting scheme shows the partial reduction of Cu oxide clusters at rising temperatures, and pinpoints the specific stoichiometries that dominate in the ensemble of cluster states as the temperature changes.
Zandkarimi, Borna, Sun, Geng, Halder, Avik, et al., "Interpreting the Operando XANES of Surface-Supported Subnanometer Clusters: When Fluxionality, Oxidation State, and Size Effect Fight.," Journal of Physical Chemistry. C 124, no. 18 (2020), https://doi.org/10.1021/acs.jpcc.0c02823
@article{osti_1765980,
author = {Zandkarimi, Borna and Sun, Geng and Halder, Avik and Seifert, Soenke and Vajda, Stefan and Sautet, Philippe and Alexandrova, Anastassia N.},
title = {Interpreting the Operando XANES of Surface-Supported Subnanometer Clusters: When Fluxionality, Oxidation State, and Size Effect Fight.},
annote = {X-ray absorption near edge structure (XANES) spectroscopy is widely used for operando catalyst characterization. We show that, for highly fluxional supported nanoclusters, the customary extraction of the oxidation state of the metal from the XANES data by fitting to the bulk standards is highly questionable. The XANES signatures as well as the apparent oxidation state for such clusters arise from a complex combination of many factors, and not only from the chemical composition in reaction conditions (e.g., oxygen content in oxidizing atmosphere). The thermally accessible isomerization and population of several structurally distinct cluster forms, cluster-support interaction, and intrinsic size effects all impact the metal oxidation state and XANES signal. We demonstrate this on copper oxide clusters with different compositions, Cu4Ox(x = 2-5) and Cu5Oy (y = 3, 5), deposited on amorphous alumina and ultrananocrystalline diamond, for which we computed the XANES spectra and compare the results to the experiment. We show in addition that fitting the experimental spectrum to calculated spectra of supported clusters can, in contrast, provide good agreement and insight into the spectrum-composition-structure relation. Experimental XANES interpreted using the proposed fitting scheme shows the partial reduction of Cu oxide clusters at rising temperatures, and pinpoints the specific stoichiometries that dominate in the ensemble of cluster states as the temperature changes.},
doi = {10.1021/acs.jpcc.0c02823},
url = {https://www.osti.gov/biblio/1765980},
journal = {Journal of Physical Chemistry. C},
issn = {ISSN 1932-7447},
number = {18},
volume = {124},
place = {United States},
year = {2020},
month = {05}}
USDOE Office of Science - Office of Basic Energy Sciences - Materials Sciences and Engineering Division; European Union - Horizon 2020 Research and Innovation Programme; USDOE Office of Science - Office of Basic Energy Sciences - Scientific User Facilities Division; USDOE Office of Science - Office of Basic Energy Sciences
DOE Contract Number:
AC02-06CH11357
OSTI ID:
1765980
Journal Information:
Journal of Physical Chemistry. C, Journal Name: Journal of Physical Chemistry. C Journal Issue: 18 Vol. 124; ISSN 1932-7447
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 649, Issue 1https://doi.org/10.1016/j.nima.2010.12.172