Synthesis And Performances Investigation Of Catalyst In Direct Synthesis Of Ammonia From Methane And Nitrogen At Atmospheric Pressure

Ammonia is not only a mainstay of the chemical industry, but also an important position in national economy.The traditional ammonia was synthesized in high temperature ?500??, high pressure ?15?30 MPa?,which is need large energy consumption in reaction process, strict operation conditionsand complexequipment. Therefore the future research direction of synthetic ammonia is to developed a new catalyst, which is suitable for low pressure and low energy consumption.In this work,ammonia isdirectly synthesis from the feed gas of methaneand nitrogen atatmospheric pressure and a series of catalystsused forthe reaction were prepared by the fractional wetness impregnation method. We examined the different catalyst supports, differentcatalysts promoters,different active componentsand the influence ofloading amount, loading sequence and reaction temperaturefor the performance of catalysts.The catalysts were characterized byhydrogen temperature programmed ?H₂-TPR?,X-ray diffraction ?XRD?,N₂ isothermal adsorption stripping ?BET?,scanning electron microscope ?SEM? and thermogravimetric ?TG?,etc.The main research results are as follows:?1? The different catalyst supports were characterized by BET,SEM,etc.Theexperimental results show that after dealing with the 30% HNO₃ of theactivated carbon, the surface impurities isreducedand specific surface area is increased.The cocoanut shell carbon has the most uniformpore distribution with outstanding increase of average pore volume.It has an advantage for dispersion of components andpromoters.?2? We investigated the the influence of different catalyst supports anddifferent catalysts promoters.The experimental results prove that at atmospheric pressure,700?, V_CH4/V_N2 =2/1,flow rate of 50ml/min,iron catalystsof different supports, the coconut shell activated carbon displayed a higher catalytic activity than SiO₂,?-Al₂O₃, and columnar carbon.5%Fe/ cocoanut-char can achieve the most favorable synthetic ammoniarate of 3.46×10-7mol·g^-1·s^-1.Through the promoter selection experiments such as Zr, Ce,Kand Ba, we found thatthe synthetic ammonia rate of the K promoted iron catalyst is thehighest, and the Ba promoted iron catalyst is the second.?3? The potassium promoted iron catalystwere characterized by XRD,XPS.The results show that the new phase KNO₂ and KFeO₂ were formed by iron and KNO₃.3%K-5%Fe/ cocoanut-char can achieve the most favorable synthetic ammoniarate of 1.03×10-6mol·g^-1·s^-1, which is 83.4times higher than current literature.?4? Weinvestigated the promoting effect of barium on the performance of iron/cocoanut-char catalyst.When the calcination temperature is 400 ?,calcinations time is 4h,the reaction temperature is 800?, V_CH4/ V_N2=2/1, the maximum synthetic ammoniarate rate of 5%Fe-7%Ba/cocoanut-charcatalyst is 2.86×10-5mol·g^-1·s^-1.?5? We explored the the reaction mechanism of the direct synthesis of ammonia from methane and nitrogen at atmospheric pressure. The first step is methane decompose into hydrogen and carbon,the second step is hydrogen and nitrogen synthesize to ammonia at atmospheric pressure. The products were characterized by SEM. It shows that filamentous carbon exist in catalyst. The long time integration of filamentous carbon influenced the physical and chemical structure and coverdthe active site of catalyst, in which way it declined the catalyst activity.