Through periodic density functional
theory (DFT) calculations we have investigated the catalytic mechanism
of CO oxidation on an Ir1/FeO
x
single-atom catalyst (SAC). The rate-determining step in the catalytic
cycle of CO oxidation is shown to be the formation of the second CO2 between the adsorbed CO on the surface of Ir1/FeO
x
and the dissociated O atom from gas phase.
Comparing with Pt1/FeO
x
catalyst,
the reaction activation barrier for CO oxidation is higher by 0.62
eV and the adsorption energy for CO molecule is larger by 0.69 eV
on Ir1/FeO
x
. These results
reveal that Ir1/FeO
x
catalyst
has a lower activity for CO oxidation than Pt1/FeO
x
, which is consistent with our experimental
results. The results can help to understand the fundamental mechanism
of monodispersed surface atoms and to design highly active single-atom
catalysts.
Herein, we report a theoretical and experimental study of the water‐gas shift (WGS) reaction on Ir1/FeOx single‐atom catalysts. Water dissociates to OH* on the Ir1 single atom and H* on the first‐neighbour O atom bonded with a Fe site. The adsorbed CO on Ir1 reacts with another adjacent O atom to produce CO2, yielding an oxygen vacancy (Ovac). Then, the formation of H2 becomes feasible due to migration of H from adsorbed OH* toward Ir1 and its subsequent reaction with another H*. The interaction of Ir1 and the second‐neighbouring Fe species demonstrates a new WGS pathway featured by electron transfer at the active site from Fe3+−O⋅⋅⋅Ir2+−Ovac to Fe2+−Ovac⋅⋅⋅Ir3+−O with the involvement of Ovac. The redox mechanism for WGS reaction through a dual metal active site (DMAS) is different from the conventional associative mechanism with the formation of formate or carboxyl intermediates. The proposed new reaction mechanism is corroborated by the experimental results with Ir1/FeOx for sequential production of CO2 and H2.
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