Coordination Number Dependent Catalytic Activity of Single-Atom Cobalt Catalysts for Fenton-Like Reaction

Single-atom catalysts (SACs) are widely investigated in Fenton-like reactions for environmental remediation, wherein their catalytic performance can be further improved by coordination structure modulation, but the relevant report is rare. Herein, a series of atomically dispersed cobalt catalysts with diverse coordination numbers (denoted as Co-N-x, x represents nitrogen coordination number) are synthesized and their peroxymonosulfate (PMS) conversion performance is explored. The catalytic specific activity of Co-N-x is found to be dependent on coordination number of single atomic Co sites, where the lowest-coordinated Co-N-2 catalyst exhibits the highest specific activity in PMS activation, followed by under-coordinated Co-N-3 and normal Co-N-4. Experimental and theoretical results reveal that reducing coordination number can increase the electron density of single Co atom in Co-N-x, which governs the Fenton-like performance of Co-N-x catalysts. Specifically, the entire Co-pyridinic N-C motif serves as active centers for PMS conversion, where the single Co atom, and pyridinic N-bonded C atoms along with nitrogen vacancy neighboring the unsaturated Co-pyridinic N-2 moiety account for PMS reduction and oxidation toward radical and singlet oxygen (O-1(2)) generation, respectively. These findings provide a useful avenue to coordination number regulation of SACs for environmental applications.

Automated summary

In this study, a series of atomically dispersed cobalt catalysts with different coordination numbers were synthesized and their performance in peroxymonosulfate (PMS) conversion was explored. The results showed that the catalytic specific activity of the catalysts depended on the coordination number of single Co atom, with the lowest-coordinated Co-N-2 catalyst exhibiting the highest specific activity. It was found that reducing the coordination number increased the electron density of the single Co atom, which governed the Fenton-like performance of the catalysts. Additionally, the entire Co-pyridinic N-C motif was identified as the active center for PMS conversion, with the single Co atom, pyridinic N-bonded C atoms, and nitrogen vacancy neighboring the unsaturated Co-pyridinic N-2 moiety contributing to PMS reduction and oxidation.