Investigating Nano-structured Catalysts at the Atomic scale by Field Ion Microscopy and Atom Probe Tomography - Atomically-Precise Methods for Synthesis of Solid Catalysts - page 290

well as the synergies between the bulk and the surface. In the early devel-
opment of atom probe, the analysis was limited to a narrow field of view,
restricting the discussion to different crystallographic orientations. More
recently, the development of the laser-pulsed LEAP has increased the po-
tential to analyze fragile or complex samples such as those containing
nanoparticles, as well as widening the size of the analysis regions and the
collection rates. These new features have opened a global investigation of
changes occurring at the surface and in the bulk of catalytic samples, with
atomic spatial resolution. Dedicated environmental cells have been de-
veloped to avoid contamination during the sample transfers between re-
action and analysis chamber. As in FIM studies, different alloys show
different response towards similar treatment, including segregation of one
metal at the surface by chemically driven surface enrichment, formation of
core-shell structures, as well as formation of separate active phases in the
form of nano-islands. These features are highly dependent on the com-
position of the alloy, the temperature and duration of treatments, the
crystallographic orientation, and the presence of surface or bulk defects. As
an example, the behavior of a ternary alloy cannot be predicted from that of
its respective binary alloys. A systematic study has to be undertaken for each
alloy composition. The next step towards the understanding of catalytic be-
havior lies in the study of applied formulation of catalysts. In that case, the
tip sample becomes the support for the deposition of catalyst particles.
Supported on carbon, dispersed in colloidal solution, or even powders of
catalytic nanoparticles have been successfully analyzed by APT revealing
core-shell structures and mixed metallic phases. APT can also be used as a
quality control tool, which could serves as feedback to adjust and improve
the synthesis of nanoparticles at the atomic scale.
Looking forward, a new generation of ambient-pressure atom probes is
also being developed. Tools of this nature will provide the highest impact
studies to address the complexities of catalytic systems/particle upon ex-
posure to reactive environments.

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Acknowledgements
C.B. thanks the Fonds de la Recherche Scientifique (F.R.S.-FNRS) for fi-
nancial support (PhD grant). The Wallonia-Brussels Federation is gratefully
acknowledged for supporting this research (Action de Recherches Con-
cert´es n1 AUWB 2010-2015/ULB15), as well as the Foundation Wiener-
Anspach. C.B. and T.V.d.B. also thank Professors Yannick De Decker and
Norbert Kruse for fruitful discussions. P.A.J.B. acknowledges financial sup-
port from the UK Engineering and Physical Sciences Research Council
(EPSRC, grant EP/077664/1) and from The Queen's College Oxford. Provision
of samples and support

from Johnson Matthey plc is also gratefully

acknowledged.