Catalytic Hydrogenolysis by Atomically Dispersed Iron Sites Embedded in Chemically and Redox Non-innocent N-Doped Carbon
Zhicheng Luo, Li Li, Vy T. Nguyen, Uddhav Kanbur, Yuting Li, Jie Zhang, Renfeng Nie, Abhranil Biswas, Sergey L. Bud’ko, Jin‐Su Oh, Lin Zhou, Wenyu Huang, Aaron D. Sadow, Bin Wang, Susannah L. Scott, Long Qi
Abstract
Atomically dispersed first-row transition metals embedded in nitrogen-doped carbon materials (M–N–C) show promising performance in catalytic hydrogenation but are less well-studied for reactions with more complex mechanisms, such as hydrogenolysis. Their ability to catalyze selective C–O bond cleavage of oxygenated hydrocarbons such as aryl alcohols and ethers is enhanced with the participation of ligands directly bound to the metal ion as well as longer-range contributions from the support. In this article, we describe how Fe–N–C catalysts with well-defined local structures for the Fe sites catalyze C–O bond hydrogenolysis. The reaction is facilitated by the N–C support. According to spectroscopic analyses, the as-synthesized catalysts contain mostly pentacoordinated Fe III sites, with four in-plane nitrogen donor ligands and one axial hydroxyl ligand. In the presence of 20 bar of H 2 at 170–230 °C, the hydroxyl ligand is lost when N 4 Fe III OH is reduced to N 4 Fe II, assisted by the H 2 chemisorbed on the support. When an alcohol binds to the tetracoordinated Fe II sites, homolytic cleavage of the O–H bond is accompanied by reoxidation to Fe III and H atom transfer to the support. The role of the N–C support in catalytic hydrogenolysis is analogous to the behavior of chemically and redox-non-innocent ligands in molecular catalysts based on first-row transition metal ions and enhances the ability of M–N–Cs to achieve the types of multistep activations of strong bonds needed to upgrade renewable and recycled feedstocks.