High specific activity and cost effectiveness of single-atom catalysts hold practical value for water gas shift (WGS) reaction toward hydrogen energy. We reported the preparation and characterization of Ir single atoms supported on FeO(x) (Ir1/FeO(x)) catalysts, the activity of which is 1 order of magnitude higher than its cluster or nanoparticle counterparts and is even higher than those of the most active Au- or Pt-based catalysts. Extensive studies reveal that the single atoms accounted for ∼70% of the total activity of catalysts containing single atoms, subnano clusters, and nanoparticles, thus serving as the most important active sites. The Ir single atoms seem to greatly enhance the reducibility of the FeO(x) support and generation of oxygen vacancies, leading to the excellent performance of the Ir1/FeO(x) single-atom catalyst. The results have broad implications on designing supported metal catalysts with better performance and lower cost.

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.

With the right support: A Ir/Fe(OH)x catalyst was designed. The Fe(OH)x support stabilizes the metal catalyst used for the oxidation of carbon monoxide. The catalyst was highly active for the oxidation of carbon monoxide in the presence of excess hydrogen at room temperature and showed a wide temperature range for the total conversion of CO (see picture).