The Study On Controllable Modulation Of Transition Metal-nitrogen Sites And Their Applications

Single-atom materials with a single structure and adjustable surrounding coordination environment of the central atom build a bridge between theoretical and experimental research,which provides an ideal platform for understanding the structure-activity relationship at the atomic level.In the past decade,single-atom materials with unique and superior application properties have gradually become one of the materials that have attracted much attention in the fields of energy conversion devices and organic synthesis.Herein,copper,iron,and cobaltbased single-atom nitrogen-doped carbon materials were prepared by host-guest method.The nitrogen coordination environment of the central metal atom was adjusted and the metal singleatom material with saturated and unsaturated coordination was obtained by controlling the pyrolysis temperature.On this basis,the application of transition metal single-atom nitrogendoped carbon materials in organic synthesis were explored,and the action mechanism of materials in the reaction process was studied using the styrene epoxidation as a model.The specific contents are as follows:(1)A series of single-atom nitrogen-doped carbon materials such as copper,iron,and cobalt were prepared.The morphology,physical and chemical properties,and microstructure of the materials were systematically studied by basic characterization such as SEM,TEM,nitrogen adsorption,XRD,Raman,XPS,and ICP,as well as advanced technologies such as HAADFSTEM and XAFS.The results show that the properties of the synthesized materials are similar except for the metal core atoms.In addition,it is found that the coordination environment changes with the processing temperature.Through precise control of temperature,a series of single-atom materials can be obtained with saturated and unsaturated coordination structures,which provides an ideal solution for the study of structure-activity relationship.(2)The reaction process model was constructed,and combined with first-principles calculations,the high performance of unsaturated coordination single-atom cobalt-based materials in styrene epoxidation was accurately predicted.At cobalt sites,the energy barrier of C=C epoxidation is lower than that of direct oxidation,while C=C is more prone to direct oxidation at iron site,copper site.In addition,due to the asymmetry of the charge density of the central atom under the unsaturated coordination,the energy of the intermediate reaction process can be effectively reduced and the occurrence of the reaction can be promoted.The results of the real reaction tests are consistent with the calculated results,in which the catalytic activity of the unsaturated coordinated single-atom cobalt-based material reaches the highest level reported so far,showing its great potential for industrial application.