Interpreting the Operando XANES of Surface-Supported Subnanometer Clusters: When Fluxionality, Oxidation State, and Size Effect Fight

0524177 - ÚFCH JH 2021 RIV US eng J - Článek v odborném periodiku
Zandkarimi, B. - Sun, G. - Halder, A. - Seifert, S. - Vajda, Štefan - Sautet, P. - Alexandrova, A. N.
Interpreting the Operando XANES of Surface-Supported Subnanometer Clusters: When Fluxionality, Oxidation State, and Size Effect Fight.
Journal of Physical Chemistry C. Roč. 124, č. 18 (2020), s. 10057-10066. ISSN 1932-7447. E-ISSN 1932-7455
GRANT EU: European Commission(XE) 810310
Institucionální podpora: RVO:61388955
Klíčová slova: X-ray absorption near edge structure * nanoclusters * spectroscopy
Obor OECD: Physical chemistry
Impakt faktor: 4.126, rok: 2020
Způsob publikování: Omezený přístup

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.
Trvalý link: http://hdl.handle.net/11104/0308545