Preparation Of Composite Metal Oxide Catalyst And Research On Its Catalytic Oxidation Performance

Selective oxidation of alcohols to the corresponding aldehydes(ketones)has been regarded as one of the most basic organic reactions,since its products are widely used in the manufacture of spice,agricultural chemicals and other fine chemicals.Nitrile is an important industrial intermediate,which is widely used in synthesis of different polymers.The catalytic oxidation of Baeyer-Villiger(BV)type of ketones is an attractive and valuable reaction on the industrial view,and the products of esters are widely used in food and cosmetic industries.Currently,the production technology mainly uses the traditional production method,which is risk and has serious pollution,high material and energy consumption.It is highly desirable to find environmentally friendly,safe,cheap,recyclable,highly active and selective catalysts,so that the aforementioned reactions can be carried out in a moderate condition.In this paper,a series of composite metal oxide catalysts were prepared by co-impregnation method,which were used in the alcohols,amines,and BV oxidation as mentioned above.The main contents of this paper are as follows:(1)Two kinds of ternary metal complex oxides(Ru-Mn-Ce and Ru-Co-Ce)were fabricated by co-precipitation method for the selective oxidation of alcohols to the corresponding aldehydes(ketones)under aerobic condition.Interestingly,the calcination temperature had a negative effect on the catalytic activity of Ru-Mn-Ce catalyst,whereas it was beneficial to the Ru-Co-Ce catalyst.A series of characterization,including X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),Fourier transform infrared spectroscopy(FT-IR),electron paramagnetic resonance(EPR),temperature programmed reduction(TPR),transmission electron microscope(TEM)and scanning electron microscope(SEM),were employed for two materials to prove the two effects.The results indicated that the interaction between RuOx and Mn-Ce compound oxides was weakened in Ru-Mn-Ce catalyst,but the interaction between RuOx and Co-Ce composite oxides enhanced in Ru-Co-Ce catalyst after roasting.The content of surface active oxygen species reduced and the migration of oxygen was restricted in Ru-Mn-Ce catalyst after roasting,whereas calcination had opposite effect on Ru-Co-Ce catalyst.(2)A series of Mn-Ce composite oxides and corresponding MnOx,CeO2 were synthesized by co-precipitation method,and have been used in catalytic oxidation of primary amines to corresponding nitriles.When the mole ratio of Mn/Ce is 2:1(denoted as Mn0.67Ce0.33Os),the favorable selectivity and the best conversions were obtained for the catalytic oxidation of heterocyclic,benzylic,and aliphatic primary amines.The related characterization shows that the favorable catalytic performance should be assigned to the Mn0.67Ce0.33Os solid solution was formed with manganese ions doped into the CeO2 lattice,it reduces the formation energy of the oxygen vacancies and increases the mobility of the reactive oxygen species from the bulk to the surface.(3)Catalytic Baeyer-Villiger(BV)type oxidations of ketones to corresponding esters based on O2/aldehyde oxidation system were performed using mesoporous Mn-Ce and Mn-Co mixed oxides prepared by co-impregnation method.When the mole ratio of Mn/Ce is 1:2(denoted as Mn0.33Ce0.67Os),the favorable selectivity and the best conversions were obtained through investigating the effect of Mn/Ce molar ratio on the structure and catalytic properties of the catalyst.Interestingly,Mn0.33Co0.67Os(Mn/Co is 1:2)catalyst lost its catalytic activity in this BV reaction.In order to explain this interesting phenomenon,Mn0.33Co0.67Os catalyst and various Mn-Ce composite oxides were characterized by BET,XRD,SEM,TEM,DR-UV-vis,XPS,and H2-TPR techniques.The results exhibited that Mno.33Ce0.67Os sample has great potential in the BV oxidation due to the large numer of surface reactive oxygen species and the high concentration of Ce3+.Additionally,Mn and Co species on the surface of Mn0.33Co0.67Os material are almost in the form of Mn2+ and Co3+,it is known that Mn2+ can be served as a potential antioxidant and inhibit the activity of reactive oxygen species,while Co3+ ions could inhibit the formation of oxygen vacancies and prevent the release of active oxygen species,thus the presence of Co3+and Mn2+ scavenge the catalytic activity of Mn0.33Co0.67Os sample in BV oxidation.