Chemistry Reference
In-Depth Information
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Figure 7.11 ALD for catalysis: (a) Introducing catalytic sites on the pore walls.
(b) Introducing catalytic nanoparticles on the pore walls. (c) and (d)
Tuning the pore size of the support prior to the introduction of catalytic
sites (c) or nanoparticles (d). (e) Stabilizing catalytic nanoparticles with
an ALD over-layer. The coating is dense on the oxide support material; a
porous layer is formed on top of the metal nanoparticles.
stage of these processes, ALD can be used for the conformal deposition of
catalytic noble metal particles with the desired size and composition.
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Alternatively, nanoparticles can also be formed by the controlled break-up of
an ALD-deposited layer through calcination.
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Besides, for the deposition of the catalytically active material, ALD can be
used to modify the support material prior to the introduction of the active
species or particles. In Figures 7.11c and d, the atomic level thickness con-
trol of ALD is exploited to precisely tune the pore size of the support ma-
terial.
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In this way, the selectivity of the catalyst can be tailored to the
specific application.
In Figure 7.11e, a thin oxide coating is applied on top of the catalytic metal
nanoparticles to stabilize them.
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The over-layer is dense and continuous
on the oxide support, while it contains some porosity on top of the metallic
particles (formed during the ALD process or induced by thermal treatment).
In this way, an ultra-thin ALD coating can act as a physical barrier to prevent
migration and sintering of the particles while keeping the surface of the
active nanoparticles accessible for the chemical species that are to be cata-
lytically converted.
In the following sections, examples are provided for the different ALD
approaches depicted in the schematic picture. Section 7.2 briefly reviews a
selection of catalysis-related ALD papers, while Section 7.3 elaborates on two
.
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