Preparation,Modification Of Ferrite Spinel Catalyst And Its Catalytic Performance For Oxidative Dehydrogenation Of N-Butene To Butadiene

Oxidative dehydrogenation of n-butene is a promising process for the production of butadiene,for which the key is to develop catalysts with high activity,high selectivity and good stability.In this paper,a series of modified ferrite spinel catalysts were prepared by different methods and applied in the oxidative dehydrogenation of n-butene to butadiene.The effects of catalyst surface properties,crystal structures and oxygen species properties on its oxidative dehydrogenation performance of n-butene to butadiene were investigated.The Mg,P co-doped ferrite spinel catalysts were prepared by reverse mode co-precipitation method and calcined at 800°C.The catalysts were characterized by means of BET,XRD,NH₃-TPD,H₂-TPR and evaluated in oxidative dehydrogenation of n-butene to butadiene,studying the effect of doping of Mg and P on the oxidative dehydrogenation performance of n-butene over ferrite spinel catalysts.Results show that the doping of Mg can reduce the relative content ofα-Fe₂O₃phase in ferrite spinel catalyst to increase its oxidative dehydrogenation performance of n-butene;the doping of P can further reduce the relative content ofα-Fe₂O₃phase in ferrite spinel catalyst,increase the activity and content of oxygen species of selective oxidation,maintain a higher surface acidity and inhibit the unfavorable reduction of Fe³⁺to Fe²⁺.The catalyst with Fe:Mg:Zn:P=32:15:1:0.02（molar ratio）has the highest oxidative dehydrogenation activity of n-butene,which can steadily catalyze the oxidative dehydrogenation of n-butene to butadiene for 50 h under the conditions of400℃,n-butene:O₂:H₂O=1:0.75:14（volume flow）,and GHSV_1-butene=300 h^-1.The conversion of n-butene,selectivity and yield of butadiene decreased slightly,and finally 80.7%of n-butene conversion,90.6%of butadiene selectivity and 73.2%of butadiene yield were obtained.A series of ferrite spinel catalysts were prepared by sol-gel method with surfactant modification,and their physical and chemical properties were characterized by BET,XRD,NH₃-TPD,H₂-TPR.The effects of the type and amount of surfactant and the doped Mg on the oxidative dehydrogenation performance of n-butene over Zn Fe₂O₄catalysts were also investigated.Results show that the addition of surfactant improved the oxidative dehydrogenation activity of Zn Fe₂O₄catalyst,and olyethylene glycol（PEG-6000）exhibits the best performance;the addition of PEG-6000 can modify the crystal structure and increase the amount of surface weak acid of catalyst.The addition of PEG-6000 and Mg will improve the reactivity and number of oxygen species of selective oxidation.The catalyst with 0.2 g PEG-6000 and 50%molar fraction of Mg in the divalent metal obtained the highest n-butene conversion,butadiene selectivity and yield,being 76.6%,89.1%and 68.2%,respectively.