Synthesis Of LaSrCo_XFe_2-XO₆ Double Perovskites And Study On Their Catalytic Epoxidation Of Olefin

Epoxy compounds are important fine chemicals,which have been widely used in pharmaceuticals,fragrances and polymers.The direction of green development for epoxidation of olefins to Epoxy compounds is promoted by solid catalyst with oxygen as the oxidant.It is well known that,construction of abundant oxygen defects over solid catalysts is the key pathway to attain this goal.As a new type of functional material,perovskite（ABO₃）has important application prospects in the fields of catalysis and environmental protection.The A and B sites in the perovskite can be flexibly incorporated by heterogeneous atoms,which lead to form abundant oxygen defect sites and could be used as potential olefin epoxidation catalysts.In this thesis,the A and B sites can be flexibly incorporated by heterogeneous atoms to synthesize La Sr Co _XFe_2-XO₆（LSCF-X,X=1,1.2,1.4,1.6 and 1.8）double calcium by the sol-gel method（Sol-Gel）Titanium ore,using Sr/Fe to modulate the micro-coordination environment of LSCF-X to obtain abundant oxygen defects,and its catalytic performance for olefin epoxidation was studied.And the detail characterization of the LSCF catalysts was performed by XRD,BET,SEM,TEM,FT-IR,XPS,UV-Vis/NIR,and Mott-Schottky.Using styrene and cyclohexene as the model epoxidation reaction,the process and mechanism of the reaction were analyzed,and the following main results were obtained.（1）A series of LSCF-X catalysts were synthesized.The results show that Sr and Fe are successfully incorporated into LSCF-X,and LSCF-X still maintains the crystal structure of ABO₃;photoelectric performance analysis shows that LSCF-X has a strong absorption peak in the ultraviolet and visible range,and its conduction band The potential energy is-0.37e V,and the forbidden band width is 1.521e V,which is conducive to the activation and conversion of O₂ to·O₂^—.（2）The highly efficient epoxidation of styrene was realized by using LSCF-1.6 as photothermal catalyst and oxygen as an oxidant.The results showed that under the reaction conditions of 365 nm,100℃ and 16 m L/min O₂ bubbling,as high as 99.9%conversion of styrene and 87.8%selectivity of styrene oxide were obtained over LSCF-1.6 catalyst.Free radical capture experiments show that,singlet oxygen（¹O₂）is the key oxygen-active species for epoxidation of styrene.Mechanism studies have shown that the catalyst and DMF are complexed,light-excited to generate hot electrons and holes,O₂ is adsorbed on the catalyst and the generated hot electrons interact to form super oxygen species（·O₂^—）,and the holes and super oxygen species react to form singlet oxygen,which promotes the high-efficiency epoxidation of styrene is achieved.（3）The LSCF-1 catalyst is used to achieve high-efficiency oxidation of cyclohexene under the action of oxygen as an oxidant and a photothermal field.The results showed that under the conditions of 365 nm,60℃ and 16 m L/min O₂ bubbling,the selectivity of La Sr Co Fe O₆ catalyst for cyclohexene epoxidation reached 64.3%.In addition to the higher selectivity of cyclohexane epoxy,La Sr Co Fe O₆ also exhibits a higher conversion rate of cyclohexene（62.0%）under mild reaction conditions.