Theoretical Study Of Coordination Environment Modification Of Cobalt And Copper Single-atom And Their Catalytic Performance In Organic Reaction

Compared to homogeneous and inhomogeneous catalysts,metal single-atom catalysts have the advantages of near 100%atomic utilization,homogeneous active sites,and unsaturated coordination of active centers.Since the catalytic activity of single-atom catalysts is related to the coordination environment,researchers typically focus on the precise design of the local coordination structure of single-atom catalysts to improve catalytic activity and selectivity.Up to now,environment modulation strategies for singleatom catalysts are commonly applied in activation reactions of small molecules(e.g.CO2,O2,etc.),and there are few studies of coordination environment modulation and catalytic mechanisms for poly-atomic organic molecules in organocatalytic reactions.Due to the complexity of organic molecular systems,it’s necessary to consider thermodynamic and kinetic aspects in the coordination environments construction of single-atom catalysts.Thesis,we construct single-atom catalysts with specific coordination environments for nitrobenzene hydrogenation and benzene oxidation reactions,and analyze the catalystsubstrate interaction mechanism at the electronic structure level.The research work in this paper is divided into three parts.(1)We systematically investigated the stability of Co single atom catalyst,and its application in the reaction of nitrobenzene hydrogenation to aniline.The transition state calculations revealed that a single Co atom split from the Co6 cluster anchored to the defect of N4 requiring to overcome an energy barrier of 1.33 eV and to release the energy of 3.87 eV to reach a stable state,coordination with N-atom to form CoN4 atomic interface,while the Co single atom transformed from Co nanoparticles are less prone to agglomeration due to the high thermodynamic energy of transformation into particles.In the nitrobenzene hydrogenation reaction,the rate-determining step energy barrier on the surface of Co single atom catalyst is 0.95 eV,which is much lower than the Co cluster energy barrier(1.61 eV),which can be attributed to the suitable adsorption energy of the reactants and intermediates on Co single atom catalyst.The experimentally synthesized Co monoatomic catalyst were further verified our calculations by experimental tests.(2)We constructed Co single atom catalyst(CoN3P1 and CoN3S1)by doping strategy with high efficiency in catalyzing the hydrogenation of nitrobenzene to aniline.By calculating the reaction energy and reaction energy barriers of different reaction paths for the nitrobenzene hydrogenation to aniline,we found the optimal reaction pathway for the reaction catalyzed on the Co single atom catalyst is:C6H5NO2→C6H5NOOH→C6H5NO→C6H5NOH→QH5NHOH→C6H5NH→C6H5NH2,and the P-doping effectively reduces the energy barrier,thereby promoting the aniline formation.(3)We designed an efficient Cu single-atom catalyst with a CuN2B1 atomic interface for the reaction of benzene oxidation to phenol.Theoretical calculation studies showed that the introduction of B atom in the CuN2B1 atomic interface changed the electronic structure of the Cu single atom and weakened the adsorption of the key intermediate compared with the CuN3 atomic interface,thus reducing the energy barrier for the formation of*O from 1.12 eV to 0.87 eV.In addition,a Cu single-atom catalyst with a CuN2B1 atomic interface was experimentally synthesized and achieved good activity.This work provides meaningful theoretical implications for the design of single-atom catalysts in organocatalytic systems.