DNL Successfully Confines FeN4 Structure in the Matrix of Graphene Nanosheets

Recently, on the basis of their previous studies towards two-dimensional catalytic materials and nano confined catalysis, Assoc. Prof. Dehui Deng and Prof. Xinhe Bao etc. from DNL and SKLC, they have successfully confined FeN4 structure in the matrix of graphene nanosheets, and for the first time observed the atomic structure of the FeN4 centers in graphene nanosheets by multiple high resolution probe techniques. The obtained confined structure can efficiently stabilize the coordinatively unsaturated (CUS) single iron sites, achieving a high activity and stability in the direct catalytic oxidation of benzene to phenol at room temperature and even 0 oC. This work was published in Science Advances (Sci. Adv. 2015, 1(11): e1500462) in the recent.

Previous researches show that CUS iron sites can exhibit higher catalytic activity for some reactions even than precious metals. For example, in cytochrome P-450 and methane monooxygenase in organism, the organic ligands and proteins confine these CUS iron sites, making them highly active and stable. In heterogeneous catalysis, however, preparation of the analogous CUS iron sites in supported catalysts with robust structures and high activity remains an attractive challenge. Early in 1960s, scientists had tried using organic macrocycles with FeN4 centers supported on carbon materials for the catalytic activation of oxygen in fuel cells and heterogeneous catalysis. However, supported FeN4 macrocycles on substrates often tend to aggregate during catalytic reactions because of the weak interactions between these macrocycles and substrates. On the other hand, it is also a great challenge to characterize or directly observe the atomic structure of the FeN4 center due to its complicated structure on carbon materials.

DNL Successfully Confines FeN4 Structure in the Matrix of Graphene Nanosheets(Photo by Ying Shi and Xiaoqi Chen)

During the past five years, this research group has achieved a highly dispersed single FeN4 center with CUS Fe sites confined in a graphene matrix using N atoms as “anchors” via high-energy ball milling of iron phthalocyanine and graphene nanosheets under controllable conditions. In collaborations with Prof. Litao Sun’s group (SEU-FEI Nano-Pico Center, Southeast University), Prof. Jianqi Li’s group (Institute of Physics, CAS), Canadian Light Source, Shanghai Synchrotron Radiation Facility and Prof. Junhu Wang (Mossbauer Effect Data Center, DICP) etc., they, for the first time, directly observed the atomic structure of the FeN4 centers in graphene nanosheets. Further DFT calculations indicate that FeN4 centers are well stabilized by the graphene matrix, and H2O2 molecule can be easily dissociated on the confined iron site by forming O=FeN4=O centers. The activation barriers of oxidation of benzene to phenol on these centers are quite moderate for reactions to proceed at room temperature and even at 0 °C. These findings pave the way toward the design of highly efficient nonprecious catalysts for catalytic oxidation reactions at low temperature.

This work was supported by the National Natural Science Foundation of China, the Strategic Priority Research Program of the Chinese Academy of Sciences, and Collaborative Innovation Center of Chemistry for Energy Materials of the Ministries of Education (2011iChEM). (by Ying Shi and Xiaoqi Chen).

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