High spatial resolution studies of ceria and ceria based catalysts by aberration corrected Environmental Transmission Electron Microscopy
Résumé
High spatial resolution studies of ceria and ceria based catalysts by aberration corrected Environmental Transmission Electron Microscopy
F.J. Cadete Santos Aires1, T. Epicier2, M. Bugnet2, M. Aouine1, Z.Wu3, A. Gänzler4, G. Ferré1, M. Casapu4, J.D. Grunwaldt4, S. Loridant1, C. Geantet1, P. Vernoux1, L. Massin1, P. Gélin1
1 Université de Lyon, UCBL Lyon 1, IRCELYON UMR 5256 CNRS, 2 Avenue Albert Einstein, 69626
– Villeurbanne Cedex, France.
2 Université de Lyon, INSA-Lyon, UCBL Lyon 1, MATEIS UMR 5510 CNRS, 7 Avenue Jean Capelle, 69626 – Villeurbanne Cedex, France.
3 Chemical Science Division, Center for Nanophase Materials Science, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
4 Institute for Chemical Technology and Polymer Chemistry (ITCP), Karlsruhe Institute of Technology (KIT), Engesserstraße 20, 76131 Karlsruhe, Germany.
Ceria (CeO2) is a rather versatile material extensively used in catalysis (as a catalyst or as a catalyst support) due to its redox properties and oxygen mobility capabilities. Despite exhaustive literature on its structural and chemical properties, in depth atomic scale surface analysis in environmental (realistic) conditions is lacking. This is essential to gain crucial, and otherwise unavailable, insight into the surface reactivity mechanisms driving the catalytic performance (activity, selectivity, stability, active sites and species, …). The advent of environmental transmission electron microscopes (ETEM) equipped with
advanced accessories such as an aberration corrector and a high speed camera opened these perspectives. It is now possible to follow in situ (variable P and T), almost in real-time and at subnanometer resolution the evolution of the morphology, the structure and the chemistry of the supported nanoparticles, of the support and of their interface. In particular, the termination of the surfaces, the mobility of the surface atoms, the local chemical composition and the redox state can be analysed down to the atomic level in most favourable cases.
Here we present dynamic in situ studies dealing with issues directly related with the surface termination and mobility of ceria and with the evolution of metallic species supported on ceria for different catalytic
applications:
(i) Atomic scale study of the surface mobility of CeO2 nanocubes under gaseous environments;
(ii) Tuning in situ the noble metal dispersion in Pt/CeO2 diesel oxidation catalysts;
(iii) Evolution of Ir/CeO2 catalysts during methane steam reforming.
The studies were performed within the Ly-EtTEM (Lyon Environmental and tomographic Transmission Electron Microscope), a 80-300 kV TITAN objective lens Cs-corrected Environmental TEM from FEI, equipped with a GATAN high resolution Imaging Filter (GIF), a SDD XMaxN EDX spectrometer (Oxford Instruments) and a high-speed CCD Gatan OneViewTM camera, in varying pressure and temperature conditions using a Wildfire sample holder and SiNx nanochips from DENS Solutions.
The authors are thankful for funding from INSA Lyon through a BQR project THERMOS, from the IMUST project at University of Lyon and IFPen (Solaize, F), from the German Federal Ministry for Economic Affairs and Energy (BMWi: 19U15014B) as well as from the DFG (High-Output Catalyst Development Platform, INST 121384/16-1), from the French National Research Agency for financial support of the ORCA and 3DCLEAN projects 14-CE22-0011-02 and 15-CE09-0009-0 respectively) and from the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division. The electron microscopy work presented here was performed on a FEI Titan ETEM at the Centre Lyon–St-Etienne de Microscopie (www.clym.fr).