Homogenous Meets Heterogenous and Electro‐Catalysis: Iron‐Nitrogen Molecular Complexes within Carbon Materials for Catalytic Applications

Abstract

High activity, selectivity and recyclability are crucial parameters in the design of performant catalysts. Furthermore, depletion of platinum‐group metals (PGM) drives further research towards highly available metal‐based catalysts. In this framework, iron‐based active sites supported on nitrogen‐doped carbon materials (Fe/N@C) have been explored to tackle important applications in organic chemistry, for both oxidation and reduction of C−O/C−N bonds, as well as in electrocatalysis for energy applications. This versatile reactivity makes them ideal substitutes to PGM‐based catalysts, being based on abundant elements. Despite important advances in material science and characterisation techniques allowing the analysis of heterogeneous/electro‐ catalysts at the atomic scale, the nature of the catalytically active sites in Fe/N@C remains elusive. Most recent theoretical studies point at individual FeNx single sites as the origin of the catalytic activity. Although their identification is still challenging with current technology, establishing their real nature will foster further research on these PGM‐free and redox‐polyvalent catalysts. In this review, we provide an overview of their applications in both thermal and electrochemical processes. Throughout the review, we highlight the different characterisation techniques employed to gain insight into the catalyst's active sites.

Transition metal-based catalysts for the electrochemical CO2reduction: from atoms and molecules to nanostructured materials

“…are potential competitive coordination sites for the metal or may act themselves as metal-free catalytic sites for CO 2 RR, changing neutrality, altering charge and spin densities and promoting thermodynamic stability. 296,[303][304][305] Furthermore, aggregation phenomena should be considered in the investigation of SACs. Indeed, SACs tend to aggregate into clusters or NPs during the catalytic process or storage due to their thermodynamic instability, high surface free energies and low coordination.…”

Iron/N-doped graphene nano-structured catalysts for general cyclopropanation of olefins

“…17,18 So far, they have been mainly used in reduction/oxidation reactions and no application in other advanced organic transformations has been reported. 19 Clearly, the discovery of new reactivity for iron-based heterogeneous catalysts will give new impetus for 3d-metal catalysis in general, and probably facilitate their actual implementation in industry (Scheme 1).…”

Mesoporous Carbons from Polysaccharides and Their Use in Li-O2 Batteries

“…In addition, the activation of the carbon and, therefore, the formation of micropores can be achieved by physical (e.g., CO 2 , steam) or chemical (e.g., KOH) methods [ 11 , 12 ]. Different applications were found in catalysis, working both as a catalyst (carbocatalysis [ 13 ]) and as supporting material during the catalytic electrochemical reactions (e.g., Oxygen Reduction Reaction (ORR) [ 14 , 15 ], Carbon Dioxide Reduction Reaction (CO 2 RR) [ 16 ]). Furthermore, high conductivity carbonaceous materials have been investigated for energy storage applications using carbon as electrodes in systems such as super-capacitors, fuel cells, or rechargeable batteries (Li-ion [ 17 ], Na-ion [ 18 ], Li-S [ 19 ], and Li-air [ 20 ]).…”