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Free keywords:
Atoms; Catalyst activity; Ion exchange; Iron compounds; Ketones; Photooxidation; Sodium, Benzene oxidation; C-H bond oxidations; Coordination modes; Oxidation catalysis; Oxidation reactions; Poly (heptazine imide); Single-atom catalyse; Single-atoms; Synthesised; ]+ catalyst, Catalysis
Abstract:
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. © 2021 Elsevier B.V.
