Effect Of The Preparing Method Of The Supporter And Catalyst On The Characters Of The Activated Carbon Supported Ruthenium Catalyst For Ammonia Synthesis

The preparing methods and conditions of the supporter and catalyst were studied elementary and the effect of these methods and conditions on the characters of the ruthenium catalyst was researched too in this paper. N₂ physical adsorption,CO chemisorption,X-ray Diffraction (XRD) et al were carried out to characterize the properties of the supports and ruthenium catalysts. The ammonia synthesis activities were also measured in high pressure minisize catalyst reaction system. The results showed that the surface character of the activated carbon has a direct effect on the ruthenium dispersion and the activity of the ruthenium catalyst. It was found that the thermal modification of the activated carbon between 1800℃to 1900℃can bring about different degrees of grafitization ,but the surface area and porosity decrease dramatically and it's unsuitable to be the support of the Ru/AC catalyst. Oxidation treatment partially recovers the surface area and porosity. The optimum condition of oxidation treatment is oxidation 10h at 500℃in the gas flow (5%O₂,95%N₂).The activated carbon treated with the above conditions can improve the ruthenium dispersion and the activity of the ruthenium catalyst in a great extent. At the same time, we discovered ruthenium dispersion directs ration on the activity of the ruthenium catalyst. The load of the ruthenium and promoters ,the species and the preparing methods of the promoters are all affecting the ruthenium dispersion and affection the activity of the ruthenium catalysts in a further. Ruthenium dispersion decreases with the increasing of the promoter and ruthenium load. For the single-promoted catalysts, the ruthenium dispersion of Ru-Ba/AC catalyst is lower than Ru-K/AC catalys. For the double-promoted catalysts the method of ruthenium first loading,barium second loading and potassium last loading is better than other preparing method to improve the ruthenium dispersion. The reduction temperature has a great effect on the ruthenium dispersion for Ru/AC catalysts. With the increasing of the reduction temperature, the ruthenium disperson decreased gradually. When the reduction temperature exceeds 450℃, the ruthenium dispersion decreased seriously and the ruthenium size increased obviously. So ,the reduction temperature of Ru/AC catalysts shouldn't exceed 450℃.. The characters of the Ru/AC catalysts will be improved when the surfactants are added into the solution of the ruthenium salt. The molecular weight of the surfactants affects the adsorption of surfactants on the surface of the activated carbon. The great of the molecular weight , the less of the adsorption on the activated carbon. The surface tension of the ruthenium salt solution can be adjusted by adding the surfactants. The surface tension of the ruthenium salt solution affects the ruthenium dispersion .The ruthenium dispersion is contrary to the surface tension of the ruthenium salt solution. The lower of the surface tension, the higher of the ruthenium dispersion. The viscosity of the ruthenium salt solution treated by the surfactants affects the dry time of ruthenium catalysts. The great of the viscosity ,the longer of the dry time. Besides, using surfactants treating ruthenium salt solution can improve the activity and heat resistance of the ruthenium catalysts.