Density Functional Theory Study On The Mechanism Of Styrene Epoxidation Catalyzed By Modified FeCo Prussian Blue Analogues

Prussian blue analogues(PBAs)have attracted lots of attention from catalytic researchers for their flexibility in structures and properties.While the study of catalytic reaction mechanism of PBAs is rare.It still has many arguments that how ligands,metal centers and interstitial ions affect the adsorption and catalysis.Based on these,with the method of density functional theory(DFT),this paper made the styrene epoxidation as pattern reaction to probe the catalytic reaction mechanism of FeCo Prussian blue analogues(FeCo PBA).And the influence of amide ligands,metal centers and interstitial ions(Rb~+?Cs~+)on catalytic reaction were also discussed.The main contents include:1.Four slab models were built based on optimized cell structure of FeCo PBA,which represent the Fe or Co metal center on(111)and(110)surfaces.The catalytic mechanism was probed based on the slab models.The results show that the catalyst mechanism could have two stages.In the first stage,the oxidant tert-butanol peroxide(TBHP)was adsorbed on metal centers,and then decomposed in to an absorbed atomic oxygen and a tert-butanol which desorbed from surface subsequently.In the second stage,styrene reacted with the adsorbed oxygen atom to generate styrene oxide,and then catalyst returned to the original state with styrene oxide desorbed.Comprehensively considering the energies of each adsorption states and transition states,energy barriers on metal centers and adsorption strength,we found that Fe centers exhibit a higher catalytic activity than Co centers,for Fe centers have a lower energy barrier and moderate adsorption strength.Through the analysis of electronic structure,it shows that the electron transfer occurred exceed between metal center and the absorbate,the coordinated cyanides participated in the electron transfer.Therefore,the catalytic activity of metal centers was affected by the types of metals,nitrogen or carbon coordination of cyanide and surfaces of FeCo PBA.2.The catalytic effect of amide ligand modified FeCo PBA on styrene epoxidation had been studied.To discuss the modification that nitrogen or oxygen atom coordination of formamide(FM),N-methylformamide(NMF)and N,N-dimethylformamide(DMF),four kinds of slab models which named Fe(N-coordination),Co(N-coordination),Fe(O-coordination)and Co(O-coordination)were built for each amides.The analysis on the coordination properties of amide on metal center shows that the modified Co centers were more stable than that of Fe centers,and the surface with O coordination were more stable than that with N coordination.The analysis of the energy barriers on each metal centers shows that the catalysis activity was affected by the types of amides,amide coordination and metal center at the same time.Among these three amides,DMF modified FeCo PBA has the best catalytic activity.3.Based on the optimized cell structures of RbFeCo PBA and CsFeCo PBA,four kinds of slab models were built,which named(111)-Fe,(111)-Co,(110)-Fe and(110)-Co.The results show that the types of interstitial ions will affect the cell structure of FeCo PBA.As the radius of alkali metal increase,the lattice constant expands slightly,the bond length of Fe-N,Co-C,C?N and the deformation of(111)and(110)surface increase,while the band gap decreases.After considering the relative energy of each adsorption states and transition states,we found that the change trend of relative energy on RbFeCo PBA and CsFeCo PBA were similar with KFeCo PBA.With the discuss of energy barrier,it shows that Fe centers have better activity than Co centers.Through the analysis of electronic structure,we found that changing the interstitial ions will affect the electronic structure of FeCo PBA,thus indirectly affecting the interaction between metal center and reactant.