Atomically dispersed metal catalysts or single-atom catalysts have recently emerged as a new frontier in the field of catalysis. They exhibit extreme atom efficiency and unusual catalytic activity and selectivity, which are hard to be attained with nanoparticle-based concentional catalysts. In this talk, we present metallomacrocyclic compound-driven syntheses of carbon supported atomically dispersed metal (M–N/C) catalysts toward selective small molecule conversion reactions, including oxygen reduction reaction reaction (ORR), CO₂ reduction reaction (CO2RR), and chlorine evolution reaction (CER) [1-5]. The M–N/C catalysts provide unique catalytic selectivity in these reactions. For the ORR, tuning of metal type can direct the reaction pathway with Fe–N/C catalyzing the ORR via the four-electron (4e^–) reduction to generate water (H₂O) [1,2] whereas Co–N/C exhibiting preferred 2e^– pathway to produce hydrogen peroxide (H₂O₂) [3,4]. In the CO2RR, Ni–N/C selectively reduces CO₂ to CO while suppressing parasitic hydrogen evolution reaction [5]. For the CER, Pt–N/C catalyst is capable of catalyzing the CER with very high selectivity approaching 100% without competitive oxygen evolution reaction, even under low concentration of Cl^– and neutral electrolyte, where OER is favored [6,7]. In contrast, traditional mixed metal oxide catalysts show substantially low CER selectivity. For the selective ORR and CER, in situ X-ray absorption spectroscopy combined with other spectroscopic techniques and density functional theory calculations have played a pivotal role in identifying the active sites and uncovering reaction kinetics and mechanisms.

References

1. J. Sa et al., J. Am. Chem. Soc. 138, 15046 (2016).
2. Woo et al., Chem. Mater. 30, 6684 (2018).
3. Ko et al., Nature Commun. 10, 5123 (2019).
4. Ko et al., Nature Catal. Accepted for Publication (2021).
5. J. Sa et al., ACS Catal. 10, 10920 (2020).
6. Lim et al., Nature Commun. 11, 412 (2020).
7. Lim et al., ACS Catal. 11, 12232 (2021).