Study On Olefins Epoxidation Catalyzed By Metal Carbon Nitrogen Materials

Epoxy compounds are important intermediates of organic synthesis,which are widely applied in pharmaceutical,fine chemical and other fields.Cyclohexene oxide is a kind of odorous colorless or light yellow liquid,which is the main raw material of pesticide insecticides,surfactant and rubber auxiliary,and it also can be used in synthetic resin,adhesive and so on.Traditionally,epoxidation processes were carried out with stoichiometric oxidants,such as halogen or peracid.However,those methods have the defects of environmental pollution,equipment corrosion,complex process and low efficiency,etc.;With the development of the epoxy strategy,these directly oxidations are being discouraged in favor of catalytic processes.Oxygen is the most clean and inexpensive oxygen source,but in industry,except ethylene,other epoxy compounds are difficult to obtained by directly oxidizing corresponding olefins thorugh oxygen.Therefore,it is of great significance to develop an efficient,stable and cyclic heterogeneous catalyst which can achieve olefins epoxidation by directly using of oxygen under mild conditions with high conversion and selectivity.In this paper,various metal carbon-nitrogen materials including Ti-g-C₃N₄,Co-g-C₃N₄,Fe-g-C₃N₄,Cu-g-C₃N₄,CuNPs/g-C₃N₄,etc.were prepared by impregnation calcination method.and among which,Ti-g-C₃N₄ as one of the new materials was characterized characteristed by TEM,SEM,XRD,XPS,BET,FT-IR and EPR in detail.It was found that Ti-g-C₃N₄ has better catalytic activity than other metal carbon-nitrogen materials in the cyclohexene epoxidation experiment.And after adjusting a series of reaction conditions,the optimal condition is determined as Ti-g-C₃N₄-1 used as catalyst,oxygen used as oxygen source,acetonitrile used as solvent and isobutyraldehyde used as sacrificial agent,for 8 hours reaction,the conversion of cyclohexene is up to 97%and the selectivity of cyclohexene is up to 95%.Moreover,the material has good catalytic activity for some other olefin substrates and has excellent recycling performance.Combined with the characterization results and related literature reports,it is found that the activity of the catalyst may be derived from the unique ability of the trivalent titanium species in Ti-g-C₃N₄ material to activate oxygen,and the possible reaction mechanism is given accordingly.Moreover,a new photocatalytic epoxidation system of olefins has been successfully developed using Cu/g-C₃N₄ as catalyst,the system is convenient,economical and has good reaction efficiency.Finally,in order to expand the application of the catalyst,the catalytic effect of Ti-g-C₃N₄ on the liquid phase selective oxidation of ethylbenzene was studied,and.the mechanism of the reaction of selective oxidation of aromatic side chains catalyzed by Co-N-C was discussed in detail;With a series of control experiments and related characterization results,the active species in the catalyst was determined,which provided theoretical support for the wider application of this material in the field of catalysis.