2, University of Hamburg, Hamburg, , Germany
3, ESRF, The European Synchrotron, Grenoble, , France
4, Universite de Toulon, Marseille, , France
Tracking structural changes down to the atomic level in a catalyst under operando conditions is crucial to gain a fundamental insight into the catalytic process . We report on structural changes in a pre-selected single platinum (Pt) nanoparticle epitaxially grown on a (100)-oriented strontium titanate (STO) single crystal as observed by in-situ coherent X-ray diffraction imaging (CXDI) during catalytic CO oxidation at near ambient pressure and elevated temperature.
(111)-oriented Pt nanoparticles were grown on the STO substrate by e-beam evaporation. Scanning electron microscopy (SEM) was used to pre-select an isolated Pt nanoparticle that was marked in its vicinity by Pt-containing nano-crystalline markers using electron-beam induced deposition (E-BID). The in-situ catalytic CXDI experiment was conducted at the beamline ID01 at ESRF in Grenoble, France, using an X-ray energy of 8.5 keV and focusing Fresnel zone plates . The hierarchical position markers and a transfer and positioning protocol developed in the framework of the European user platform Nanoscience Foundries Fine Analysis (NFFA Europe)  permitted us to re-localize the pre-selected Pt nanoparticle. CXDI signals of the Pt(111) Bragg peak were collected in a gas flow of 20 ml/min and a pressure of 50 mbar in inert Ar and in a stoichiometric 2:1 mixture of CO and O2.
The facet signals around the Pt(111) Bragg peak in Ar at room temperature showed that the Pt nanoparticle surface was facetted. Alterations in the facet signals at elevated temperature and in a catalytic CO/O2 atmosphere indicate that applying these conditions induced structural changes in the Pt nanoparticle. These are evident by reconstructing the CXDI data and comparing the resulting real space particle in the different environments. In particular, we discuss the observed particle shape-changes, atomic displacements and a dislocation inside the Pt nanoparticle also in respect to complementary molecular dynamics simulations of the Pt nanoparticle under the applied catalytic CO oxidation conditions.
 U. Hejral, P. Mueller, O. Balmes, D. Pontoni, A. Stierle, Tracking the Shape-Dependent Sintering of Platinum-Rhodium Model Catalysts under Operando Conditions, Nature Communications 7, 10964 (2016) http://www.nature.com/articles/ncomms10964
 M. I. Richard, M. H. Zoellner, G. A. Chahine, P. Zaumseil, G. Capellini, M. Haeberlen, P. Storck, T. U. Schulli, T. Schroeder, Structural Mapping of Functional Ge Layers Grown on Graded SiGe Buffers for sub-10 nm CMOS Applications Using Advanced X-ray Nanodiffraction, ACS Appl. Mater. Interfaces 7, 26696 (2015). http://pubs.acs.org/doi/10.1021/acsami.5b08645
 EU H2020 framework programme for research and innovation under grant agreement n. 654360. http://www.nffa.eu/