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Figure 10.18
(a) Atom map of a single Ag@Pd nanoparticle core-shell structure with
sharp interface (Ag
¼
gray dots; Pd
¼
yellow spheres). (b) Slice through a
1 : 1 Ag : Pd ratio showing a shell thickness of one to two atomic layers.
(Adapted by permission from Macmillan Publishers Ltd: Nature Nano-
technology, ref. 113, copyright (2011)).
suggests that the electronic modification of Pd due to underlying Ag has a
rather short range. This discovery is a breakthrough in the understanding of
atomically precise tailored catalysts.
.
10.3.3.2.2 CoCuMn Used in Fischer-Tropsch Reaction. CoCuMn nano-
particles have been used during catalytic CO hydrogenation in order to
produce long-chain terminal alcohols. The synthesis of the core-shell
structure of the catalyst has been achieved using the co-precipitation of
Co-, Cu- and Mn-oxalates followed by thermal decomposition. Details of
the synthesis can be found elsewhere.
121,122
An intimate mixing of the
metals seems to be the key to improving the selective formation of long-
chain hydrocarbons with terminal functionalization. APT has been used to
demonstrate the presence of a metallic phase with the three metals being
present in the same particles.
118
A passivated catalyst powder sample has been conditioned to form a
nanosized tip using the CVD-FIB method. The 3D reconstruction of a 10 nm
thick slice through a single grain of catalyst is presented in Figure 10.19a
where Co atoms are represented as blue spheres, Cu as orange spheres, Mn
as green spheres and O as white spheres. A core-shell chemical structure can
be observed with major amounts of Co forming the core, with all three
elements present in a Cu-dominated shell of about 2 nm thickness. An en-
larged view is presented Figure 10.19b showing the distribution of oxygen
throughout the core-shell interface. Only small amounts of oxygen are
detected, proving the presence of a largely metallic CoCuMn phase.
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