Sustainable oxidation catalysis supported by light: Fe-poly (heptazine imide) as a heterogeneous single-atom photocatalyst

Fe-N-C materials, when prepared as single-atom catalysts (SAC), display excellent activities in oxidation reactions. The systematic investigation of the iron coordination mode revealed that Fe-N4C catalysts are the most active for C-H bond oxidation. However, many of these catalysts are synthesized through pyrolysis, which is characterized by a lack of control and structures with heterogeneous composition, rarely presenting only atomically dispersed Fe-N-C as active sites. Herein, an alternative, reliable and easily reproducible method to obtain highly active Fe SACs (atomically dispersed) with Fe-N4 sites is presented, which is based on ion exchange of sodium from high crystalline sodium poly(heptazine imide) (Na-PHI) by other ions. The obtained catalyst can photocatalytically oxidize C-H bonds selectively toward ketones using only dioxygen. Detailed mechanism investigations indicate that the active species in the C-H bond oxidation are highly valent Fe(IV)/Fe(V)-oxo species, which are further activated by the holes generated at the PHI support under light irradiation.

Automated summary

This study presents an alternative method for the preparation of highly active Fe single-atom catalysts (SACs) with Fe-N4 sites, which exhibit high selectivity in the oxidation of C-H bonds. The catalyst obtained through ion exchange can effectively oxidize C-H bonds to ketones under light irradiation.