CO elimination through
oxidation over highly active and cost-effective
catalysts is a way forward for many processes of industrial and environmental
importance. In this study, doped CeO
2
with transition metals
(TM = Cu, Co, Mn, Fe, Ni, Zr, and Zn) at a level of 20 at. % was tested
for CO oxidation. The oxides were prepared using microwave-assisted
sol–gel synthesis to improve catalyst’s performance
for the reaction of interest. The effect of heteroatoms on the physicochemical
properties (structure, morphology, porosity, and reducibility) of
the binary oxides M–Ce–O was meticulously investigated
and correlated to their CO oxidation activity. It was found that the
catalytic activity (per gram basis or TOF, s
–1
)
follows the order Cu–Ce–O > Ce–Co–O
>
Ni–Ce–O > Mn–Ce–O > Fe–Ce–O
> Ce–Zn–O > CeO
2
. Participation of
mobile
lattice oxygen species in the CO/O
2
reaction does occur,
the extent of which is heteroatom-dependent. For that, state-of-the-art
transient isotopic
18
O-labeled experiments involving
16
O/
18
O exchange followed by step-gas CO/Ar or CO/O
2
/Ar switches were used to quantify the contribution of lattice
oxygen to the reaction. SSITKA-DRIFTS studies probed the formation
of carbonates while validating the Mars–van Krevelen (MvK)
mechanism. Scanning transmission electron microscopy-high-angle annular
dark field imaging coupled with energy-dispersive spectroscopy proved
that the elemental composition of dopants in the individual nanoparticle
of ceria is less than their composition at a larger scale, allowing
the assessment of the doping efficacy. Despite the similar structural
features of the catalysts, a clear difference in the O
lattice
mobility was also found as well as its participation (as expressed
with the α descriptor) in the reaction, following the order
α
Cu
> α
Co
> α
Mn
>
α
Zn
. Kinetic studies showed that it is rather the
pre-exponential (entropic) factor and not the lowering of activation
energy that justifies the order of activity of the solids. DFT calculations
showed that the adsorption of CO on the Cu-doped CeO
2
surface
is more favorable (−16.63 eV), followed by Co, Mn, Zn (−14.46,
−4.90, and −4.24 eV, respectively), and pure CeO
2
(−0.63 eV). Also, copper compensates almost three
times more charge (0.37
e
−
) compared
to Co and Mn, ca. 0.13
e
−
and 0.10
e
−
, respectively, corroborating for its
tendency to be reduced. Surface analysis (X-ray photoelectron spectroscopy),
apart from the oxidation state of the elements, revealed a heteroatom–ceria
surface interaction (O
a
species) of different extents and
of d...
