The Preparation And Study Of The Ruthenium Catalyst For Ammonia Synthesis

Many kinds of activated carbon and alumina were used as the supports to prepare a series of ruthenium catalysts. Physical adsorption, chemical adsorption, elemental analysis, scanning electron microscope were carried out to characterize the properties of supports and ruthenium catalysts. The ammonia synthesis activities were also measured. It has attracted much attention to study the effect of supports, promoter, and preparation process and reaction condition on the catalytic properties of ruthenium catalyst for ammonia synthesis.When activated carbon was used as support to prepare the ruthenium catalyst, it was found that the ammonia synthesis activity of Ru/AC catalyst was directly related to the properties of activated carbon. The ruthenium catalyst supported by the special activated carbon, which had high purity, high surface area, large pore volume and proper pore structure, usually had high catalytic properties for ammonia synthesis. A series of alkaline and alkaline-earth metal were used as promoter to prepare the single-promoted or double-promoted. For the single-promoted Ru/AC catalyst, it was confirmed that alkaline-earth metal are more effective in ammonia synthesis than alkaline metal promoter. For the double-promoted catalyst, it was more active when the promoters were impregnated step by step than that the promoters were co-impregnated. For Ru/AC catalyst, Ru loading affected the catalytic activity obviously. With the Ru loading increased, the activity of catalyst also increased, but the dispersion of the Ru decreased reversely. The optimal Ru loading was 4 wt%. In order to avoid sintering of the Ru particle and the methanation of the carbonsupport, the ruthenium catalyst should be reduced at a relative low temperature.Under the reaction condition similar with the industrial application, the effects of the reaction temperature, pressure and GHSV on the ruthenium catalyst were also investigated. The result showed that the Ru catalyst had relatively high catalytic properties at a low temperature and under a middle pressure. The enhancement of reaction temperature could weaken a strong adsorption of hydrogen in high pressure and would be beneficial to improve the activity of the ruthenium catalyst for ammonia synthesis.Ruthenium catalyst supported on alumina was also studied. The result showed that Ru dispersion of catalyst was not completely determined by surface area of the support, the large pore volume and fitting pore size were the main factors of affecting the Ru dispersion. Barium and cesium nitrate were proved to be effective promoter for Ru/Al2O3 catalyst. If used to modify the Al2O3 support, Sm(NO3)3 would be more effective than being the promoter singly.