The strong metal–support
interaction (SMSI) effect plays
a central role in catalysis by decreasing the catalytic activity or
even improving it in some specific cases. In spite of the intense
research, a detailed description of the SMSI effect in CeO2-based catalysts is still missing. In this work, Cu
x
Ni1–x
/CeO2 (0
< x < 1) nanoparticles were exposed to a reduction
treatment in a H2 atmosphere followed by an oxidation treatment
in a CO2 atmosphere, both at 500 °C, and studied by
using state-of-the-art techniques (in situ time-resolved X-ray absorption
near edge structure (XANES) and near ambient pressure X-ray photoelectron
spectroscopy (NAP-XPS)). It was observed the migration of Cu (Ni)
atoms toward the surface of Cu–Ni bimetallic nanoparticles
during reduction (oxidation) treatments. The core–shell-like
structure is dependent on the Cu/Ni ratio. It was observed the existence
of a capping layer from the support (CeO2–x
) surrounding the metallic nanoparticles after reduction treatment
(characteristic of the SMSI effect) in some specific cases, depending
on the Cu/Ni ratio as well. The surface of the nanoparticles presenting
the SMSI effect is recovered to the initial state after exposure to
the CO2 atmosphere. Moreover, the nature of the SMSI effect
was elucidated. The capping layer interacts with the Cu and Ni atoms
via Ce 3d10 O 2p6 Ce 4f0 and Ce 3d10 O 2p6 Ce 4f1 initial states, depending
on the case studied. As a consequence of the SMSI effect, the Cu atoms
of the nanoparticles reduce at lower temperature than similar nanoparticles
that do not present the SMSI effect. Therefore, the decrease in reduction
temperature is directly related to the interaction between the CeO2–x
capping layer and Cu and Ni atoms.
The development of thermally stable
nanoparticles is of utmost
importance for applications like catalysis. In particular, Cu nanoparticles
supported on metal oxides are easily deactivated under thermal treatments
at low temperatures by sintering of the Cu nanoparticles. The formation
of thermally stable nanoparticles is typically obtained with secondary
drawbacks. In this study, an alternative method for avoiding sintering
of Cu nanoparticles is proposed. The method is based on the impregnation
of dithiol molecules at the metal oxide support before supporting
the Cu nanoparticles. The dithiol molecules are able to avoid the
Cu nanoparticle diffusion, thus decreasing the coalescence rate. Furthermore,
the Cu nanoparticles are not poisoned during thermal treatments. A
simple model is proposed and numerically studied to estimate the minimal
concentration of dithiol necessary to avoid sintering of the nanoparticles.
The method is not complex, and there is no interference on the original
Cu nanoparticles properties. It opens possibilities for widening the
lifespan of metal nanoparticles supported on metal oxides.
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