Synergetic Catalysis Of Magnetic Single-atom Catalysts Confined In G-C₃N₄/CeO₂（111） Heterojunction For CO Oxidization

In recent years,researchers have reduced the size of transition metal（TM）nanoparticles,especially noble metal nanoparticles,to atomic clusters and even“single atom”scales dispersively deposited on suitable substrates.Such highly dispersed single-atom systems are called“Single-atom Catalysts”（SAC）,which has become an attractive star in the field of catalysis.Magnetic single-atom catalysts（MSAC）,due to the intrinsic spin degree of freedom,are of particular importance relative to other conventional SAC for applications in various catalytic processes,especially in those cases that spin-triplet O₂ involved.However,the bottleneck issue in this field is the clustering of the SAC during the processes.Here using first-principles calculations we predict that Mn atoms can be readily confined in the interface of the porous g-C₃N₄/CeO₂（111）heterostructure,forming high-performance MSAC for O₂ activation and thus CO oxidization.Such a recipe is also demonstrated to be valid for V-and Nb-MSACs,which is expected to be constructive in fabrication of highly efficient MSACs for various important chemical processes wherein spin-selection matters.The contents of this thesis are as follows:We first briefly introduce the geometric structure of g-C₃N₄/CeO₂（111）heterostructure.It is verified that Mn atoms prefer to respectively dispersed in different pores of the heterostructure,termed“1+1+1”configuration.Furthermore,the verified kinetic（diffusion barrier）and thermodynamic stability（molecular dynamics）convincingly prove that the present porous g-C₃N₄/CeO₂（111）heterostructure can serve as an ideal harboring substrate to confine and stabilize magnetic Mn single atom.Our results show that Mn-MSAC is highly efficient for spin-triplet O₂ activation and CO oxidation via a delicate synergetic mechanism of charge transfer,mainly provided by the p-block g-C₃N₄overlayer mediated by the d-block Mn active site,spin selection,mainly preserved through active participation of the f-block Ceatoms and/or g-C₃N₄polarized by the confined d-block magnetic Mn-SA sites.Our calculations demonstrate that both the Eley-Rideal（ER）or tri-molecular Eley-Rideal（TER）mechanisms only need to overcome a fairly low reaction barrier（～0.1 e V）to release CO₂ molecules.To confirm the general validity of the present central findings,almost all the 3d-,4d-,and 5d-TMs have been screened.We focus on the catalytic activities of the TM@g-C₃N₄/CeO₂（111）where TM atoms are stably confined in the interface forming single-atom catalytic centers（1+1+1）.Taking V and Nb as examples,our results demonstrate that both V₁@g-C₃N₄/CeO₂（111）and Nb₁@g-C₃N₄/CeO₂（111）also exhibit the features of the MSACs as established in Mn₁@g-C₃N₄/CeO₂（111）for O₂ activation and CO oxidation.i.e.,synergetic charge transfer and spin accommodation.Specially,we emphasize that the reaction barriers calculated here of CO oxidation for the present TM₁@g-C₃N₄/CeO₂（111）MSACs are significantly lower than those obtained for some typical nonmagnetic and low spin-state single-atomic scale noble metal catalysts experimentally fabricated.