Morphology Control And Catalytic Performance Of Bismuth Molybdenum-based Nanosheet Catalysts For Oxidative Dehydrogenation Of 1-Butene

1,3-Butadiene is an important chemical raw materials,which is a necessary monomer for synthetic rubber,synthetic resins and other important industrial products.With the continuous development of China's economy,the demand for 1,3-butadiene is increasing year by year.There are two main methods for production of 1,3-butadiene.One is to extract 1,3-butadiene from a mixed C4 hydrocarbons byproduct of naphtha cracking reactor,the other one is from oxidative dehydrogenation of C4 hydrocarbons byproduct of coal chemical industry.Extraction method is the main source of 1,3-butadiene at present,but largely dependent on oil.The dehydrogenation of 1-butene to 1,3-butadiene can not only break the dependence on oil but also make more efficient use of surplus C4 resources.The key to oxidative dehydrogenation of 1-butene to 1,3-butadiene is the highly efficient catalysts.This thesis aims to improve the activity of BiMo based catalyst by the Morphology control.Bismuth molybdate nanosheet catalysts were prepared by one-step hydrothermal method in this work.The effect of hydrothermal synthesis conditions on the morphology and activity of the bismuth molybdate nanosheet was investigated.On this basis,the oxygen mobility and reaction performance of Ce-doped bismuth molybdate nanosheet catalyst were futher analyzed.The effect of different pH value of hydrothermal precutsors on the morphology and activity of bismuth molybdate nanosheet catalyst was investigated.Bismuth molybdate catalyst synthesized at different pH value(pH=1,3,5,7)of hydrothermal precursor are all nanosheet structure.The physical properties of bismuth molybdate nanosheet were characterized by XRD,SEM and nitrogen adsorption.The result showed that the crystallinity of bismuth molybdate nanosheet increased with the increase of the pH value of hydrothermal precursors.The results of oxidative dehydrogenation of 1-butene showed that bismuth molybdate nanosheet catalyst which synthesized at pH=3 had the best activity.The oxygen mobility of the catalyst was studied by XPS.The result showed that the activity of catalyst was positively correlated with the oxygen mobility.The effect of different step of oxygen flow cycle on catalyst performance were studies by 1-butene-TPD and TPRO.The results showed that the key factor of catalyst activity is the ability of selective oxidation of 1-butene rather than the re-oxidation ability of the catalyst.The effect of different content of cerium doping on the morphology and properties of bismuth molybdate nanosheet catalysts were investigated.The morphology of cerium-doped bismuth molybdate nanosheet was characterized by XRD,TEM and nitrogen adsorption.The result showed that the doping of cerium made the bismuth molybdate nanosheet smaller and thinner,and the BET surface area of the catalyst greatly increased.The effect of different content of cerium doping on activity and oxygen mobility of catalyst were studies by oxidative dehydrogenation of 1-butene reaction and XPS.The result showed that the activity of cerium-doped bismuth molybdate nanosheet catalyst varies volcanically with the increase of cerium content.Bi2MoCe0.05 shows the best oxygen mobility and activity.