Preparation Technics Of Co/C Ammonia Synthetic Catalysts And Performance In The Rotating Magnetic Field.

In this thesis, attempts have been made to devise a new catalytic material that is highly active and less inhibited by the ammonia product than conventional iron and also considerably cheaper than ruthenium. According to the function relationship between ammonia synthesis rate and N-M binding energy, cobalt was selected as the metal active phase component, and barium as a promoter precursor for the catalyst optimization. All the catalysts were characterized by physical adsorption, X-ray diffraction (XRD), transmission electron microscope (TEM), acidometer (pH meter), Energy Dispersive X-ray Detector (EDS). The effects of preparation procedure, carbon support pretreatment and promoter composition on physical and chemical performance were observed, and evalated their catalytic activities in the rotating magnetic field.The influence of preparation technique on the catalytic activities of cobalt catalysts in the rotating magnetic field was examined. Un-promoted and promoted Co/C material pretreatment (reduction in H2 and passivation, subsequent calcination step) was prepared by the impregnation method in ultrasonic field. The results have showed that ultrasound assistance during the impregnation process can short time impregnation, prevents the Co(NO3)3 maceration extract forming micelle and thus favors the metal particles thinning. Ultrasound stabilizes the average size of cobalt crystallites, avianizes the grains agglomerating, openings up pore canal of active phase and increases the metal dispersion. Additionally, it can increase specific surface area and micro-pore volume, and also make the distribution of loading ingredient uniform. Thus, adsorption and activation abilities of nitrogen and hydrogen boost up on the surface of Co-based catalysts. For un-promoted Co/C (reduction-passivation-calcination) material, it is likely to formed cobalt oxide from fine Co crystallites on contact of the post-reaction material with air. Redispersion of Co particles on support possibly induced by reduction–oxidation pretreatment due to the stronger interaction of cobalt oxide with oxygenated amorphous carbon. And the test results revealed that the catalytic activity of un-promoted Co/AC material (reduction- passivation-oxidation step) prepared with ultrasound assistance was proved to be higher. The rresults showed that the activity of Ba-CoR+P+C/C was as the 15 % high as the Ba-CoR+P/C catalyst。The effect of different treatments of active carbon on the catalytic activities of cobalt- based catalysts in the rotating magnetic field. Experimental results show the H2-treatment at 900℃for 24 h was effective to eliminate the electron-withdrawing impurities from raw carbon, its surface area and porosity almost keep unchanged, but the resulted carbon had not distinctively been graphitized at this extremely high temperature. The carbon, reduced in H2 at 900℃, and treated with nitric acid-ammonia, increased the number of mesopore and porosity volume, especially, the surface area by 14 %. Treatment of carbon increased hydrophilicity, make for active ingredients adsorption and dispersion improvement. The results displayed applying the carbon treated with HNO3-NH3 after reduction to the support of ammonia synthetic catalyst, its activity was proved to be the highest with 7.15μmol·s-1g-1, that of Co catalyst over raw catbon is higher by 15 %. Furthermore, the stability of cobalt-doping carbon catalyst was distinctly improved.The impacts of the different promoters on the catalytic activities of cobalt- based catalysts in the rotating magnetic field. The promoting effect is found to be inversely proportional to the electronegativity of the alkali metal and alkaline-earth metals. Ba is the most effective promoter for Co/C system ammonia synthetic catalyst, and the promoter are in the order, Ce > La > K. For single promoter, when the loading of metal Co is 8 %, the optimal atom ratio of Ba/Co, Ce/Co, La/Co, K/Co is 0.8, 0.45,0.4,0.6, respectively. Beyond the values, productivity of ammonia formation levelled off. Futher, the reaction rate on the double promoted Co catalysts was found to be higher than single promoted one.The effect of the rotating magnetic field on the catalytic activities of cobalt- based catalysts. The rotating magnetic field may bring about magnetization of metal Co particles, and improve adsorption ability of mixed gas and catalytic activity. Additionally, magnetic field can remove association reaction of hydrogen bond, play an auxiliary effemect on enhancent of relation rate. Accordingly, the required time that ammonia synthesis rate reached the climax was shorted. The rotating magnetic field expedites falling off of reaction products from the surface of catalyst, enhance relation rate and conversion.The results showed that the rate of ammonia formation may increase 2 % under the rotating magnetic intensity applied 30 potential , the conditions of the mixed flow of 45 ml/min(V N2:V H2=1:3), 440℃and normal pressure.