Preparation Of Copper-based Catalysts For Epoxidation Of Propylene To Propylene Oxide With Molecular Oxygen

Propylene oxide is derived from propylene.The traditional production process of propylene oxide suffers from environmental pollution and low economic benefits.Therefore,direct epoxidation of propylene has been gradually studied frequently.Among them,the direct epoxidation with molecular oxygen(O2)as the sole oxidant is environmentally friendly with high atom efficiency and low cost,being considered to be the most ideal propylene epoxidation route.The crucial problem of this route is the preparation of catalysts.Although there are many reports about different types of copper-based catalysts for propylene epoxidation,high propylene conversion and high PO selectivity can not be achieved simultaneously.Besides,catalyst deactivation,and unclear reaction mechanism are still main problems.In the first work,supported copper oxide catalysts(CuO/LaCoO3)and doped catalysts(LaCoxCu1-xO3-δ)based on LaCoO3 perovskites were prepared by the citric acid complexation method,and they were characterized by physical and chemical characterizations.It is proved that the formula of copper-doped perovskites samples can be defined as LaCoxCu1-xO3-δ with a doubleB-site,without the formation of free CuOx under low amount of copper doping.It effectively avoids the agglomeration of CuOx.After being modified by NaCl,it is found that the doped samples can achieve a higher propylene conversion(11.96%),with a PO selectivity of 10.84%.Subsequent characterizations and theoretical calculation results confirm that the doping of Cu increases the electrophilicity of adsorbed oxygen species of LaCoO3,as well as establishes a strong interaction between Cu with Co.O2-TPD and calculation results imply that the weakly adsorbed oxygen on catalysts may benefit the desorption of PO and prevent the total oxidation of PO.The above conclusions exemplify the possibility of propylene epoxidation using perovskites materials.The reaction mechanism based on this catalyst is proposed.In the second work,a series of hollow copper-based samples were successfully prepared by hydrothermal method using DMF as the reducing agent.In addition,other Cu2O materials with different shapes and sizes were prepared by different methods as a comparison.The catalytic performance of all samples were tested.The catalytic performance of the hollow Cu2O catalyst for propylene epoxidation is significantly better than other Cu2O samples prepared by other methods.Hollow Cu2O samples can achieve a PO selectivity of 43.07%with a propylene conversion of 2.86%at a lower temperature(180℃).Relevant characterizations(TPR,TPD,XPS,AES,etc.)were executed to confirm a higher specific surface area over hollow Cu2O materials.It is speculated that above results implied sufficient active sites for the propylene epoxidation under O2 and propylene over Cu2O catalysts which is conducive to propylene epoxidation.O2-TPD results indicate that more oxygen species can be used at a lower temperature.Moreover,a similar result to LaCoxCu1-xO3-δ samples is also deduced:Weak physically adsorbed oxygen over Cu2O samples may be beneficial to the desorption of PO.This work manifests the possibility of propylene epoxidation employing hollow Cu2O materials.