title: Tracking the shape-dependent sintering of platinum-rhodium model catalysts under operando conditions.
abstract: Nanoparticle sintering during catalytic reactions is a major cause for catalyst deactivation. Understanding its atomic-scale processes and finding strategies to reduce it is of paramount scientific and economic interest. Here, we report on the composition-dependent three-dimensional restructuring of epitaxial platinum-rhodium alloy nanoparticles on alumina during carbon monoxide oxidation at 550 K and near-atmospheric pressures employing in situ high-energy grazing incidence x-ray diffraction, online mass spectrometry and a combinatorial sample design. For platinum-rich particles our results disclose a dramatic reaction-induced height increase, accompanied by a corresponding reduction of the total particle surface coverage. We find this restructuring to be progressively reduced for particles with increasing rhodium composition. We explain our observations by a carbon monoxide oxidation promoted non-classical Ostwald ripening process during which smaller particles are destabilized by the heat of reaction. Its driving force lies in the initial particle shape which features for platinum-rich particles a kinetically stabilized, low aspect ratio.
authors.affiliation: Deutsches Elektronen-Synchrotron (DESY), NanoLab, Notkestrasse 85, D-22607 Hamburg, Germany.|Universität Hamburg, Fachbereich Physik, Jungiusstraße 9, 20355 Hamburg, Germany.|Universität Siegen, Fachbereich Physik, Walter-Flex-Straße 3, 57072 Siegen, Germany.
authors.forename: Uta
authors.initials: U
authors.lastname: Hejral
authors.affiliation: Deutsches Elektronen-Synchrotron (DESY), NanoLab, Notkestrasse 85, D-22607 Hamburg, Germany.|Universität Hamburg, Fachbereich Physik, Jungiusstraße 9, 20355 Hamburg, Germany.|Universität Siegen, Fachbereich Physik, Walter-Flex-Straße 3, 57072 Siegen, Germany.
authors.forename: Patrick
authors.initials: P
authors.lastname: Müller
authors.affiliation: MAX IV Laboratory, Fotongatan 2, 22594 Lund, Sweden.|ESRF - The European Synchrotron, Radiation Facility, 71 Avenue des Martyrs, 38043 Grenoble, France.
authors.forename: Olivier
authors.initials: O
authors.lastname: Balmes
authors.affiliation: ESRF - The European Synchrotron, Radiation Facility, 71 Avenue des Martyrs, 38043 Grenoble, France.
authors.forename: Diego
authors.initials: D
authors.lastname: Pontoni
authors.affiliation: Deutsches Elektronen-Synchrotron (DESY), NanoLab, Notkestrasse 85, D-22607 Hamburg, Germany.|Universität Hamburg, Fachbereich Physik, Jungiusstraße 9, 20355 Hamburg, Germany.|Universität Siegen, Fachbereich Physik, Walter-Flex-Straße 3, 57072 Siegen, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Stierle