Study On Propylene Epoxidation By O₂ Over CuO_x And CuO_x/carbon Nanotube Catalysts

Propylene oxide(PO)is a very important raw material for the organic chemical industry.Currently,PO is produced by the chlorohydrin and Halcon processes in industry.While the chlorohydrin process causes environmental problems,Halcon processes produces equal amount of by-products.Oxygen as an oxidant to produce propylene oxide for the epoxidation of propylene has attracted widespread attention due to its high atomic utilization,environmental friendliness,and low price.It is also one of the most challenging reactions in the field of selective oxidation.In this thesis,an unsupported nano CuOx catalyst was prepared by a liquid-phase reduction method,and the influence of pretreatment temperature on the epoxidation of propylene was investigated in N2 atmosphere.The results show that the epoxidation activity is highest when the pretreatment temperature is 300 ?.The selectivity to PO reached 30%at a C3H6 conversion of 0.13%,when the reaction temperature is 150 ?.The XRD patterns showed that CuOx is composed of Cu and Cu2O at different pretreatment temperatures in N2 atmosphere and their relative contents almost remained unchanged.With the increasement of pretreatment temperature under N2 atmosphere,the particle size of CuOx gradually increases.The best activity for propylene epoxidation was achieved at the CuOx particle size of 41 nm,indicating that the particle size of CuOx is an important factor affecting the epoxidation of propylene by oxygen.The modifier of NaCl and KAc is not conducive to the formation of propylene oxide.The epoxidation activity for CuOx/CNT catalysts synthesized by deposition-precipitation method is obviously higher than impregnation method.Different pretreatment atmospheres and different pretreatment temperatures will affect the activity of propylene epoxidation.The highest yield of propylene oxide was achieved at 350 ? under N2 atmosphere.The selectivity to PO reached 30%at a C3H6 conversion of 0.13%,when the reaction temperature is 220 ?.The acidification and alkalization of carbon nanotubes severely inhibit the production of propylene oxide.TEM showed that most of copper species on CuOx/CNT3 synthesized by deposition-precipitation method are present in the carbon nanotubes.Different pretreatment atmospheres and different pretreatment temperatures hardly affect the morphology and size of copper species.The copper species on CuOx/CNT3 gradually changed from CuO to Cu2O and Cu due to the reduction role of carbon nanotubes with the increasement of pretreatment temperature in N2 atmosphere.The catalyst only contains Cu2O at the pretreatment temperature of 350 ?.We believe that the monovalent Cu2O species in the catalyst has the highest activity of propylene epoxidation,and is most beneficial to the production of propylene oxide.