The Preparation And Characterization Of The Ruthenium Catalysts Supported On Active Carbon For Ammonia Synthesis

An active carbon which is suitable to support metal ruthenium catalyst was pretreated by several methods, the pretreated active carbon was used as the supports to prepare a series of ruthenium catalysts. Elemental analysis, N2-physisorption and CO chemisorption were carried out to characterize the properties of supports and ruthenium catalysts. The ammonia synthesis activities were also measured. Much attention was paid to study the effect of supports, the reducing conditions of RuCl3 and promoter on the catalytic properties of ruthenium catalyst for ammonia synthesis.The result shows that the ammonia synthesis activity of Ru/AC catalyst was directly related to the properties of activated carbon. The resource of carbon is the main influencing factor which determines the texture and components of active carbon. The high purity, high surface area, large pore volume and proper pore structure of active carbon as a support for ruthenium catalyst usually lead to high catalytic activity for ammonia synthesis. The thermal treatment of active carbon leads to partially graphitized and improves the stability and conductivity of carbon support, but greatly decreases the surface area and pore volume simultaneously which can be partially restored by oxidative treatment. It is found that high surface area is the main reason leading to high Ru dispersion, the porous structure of supports is important to high catalytic activity, Ruthenium catalysts supported on the active carbon with 20% weight lost exhibited the highest activity for ammonia synthesis. The H2-treatment aided by ruthenium and microwave treatment of active carbon can reform functional groups and eliminate the impurity on the carbon surface which result in improving the ruthenium metal dispersion and ammonia synthesis activity of ruthenium catalysts supported on it.Ruthenium metal derived from RuCl3·3H2O and promoters derived from nitrate were impregnated on thermally modified active carbon, Effects of dechlorination and hydrogenolysis temperature on ruthenium dispersion and ammonia synthesis activity were studied. results show that based on such a support, dechlorination temperature shows a little impact on ruthenium sizes, but affects the catalytic activity obviously. The reason leading to high acivity may be the extent of dechlorinating. The alkali metals potassium and cesium seem to be more sensitive to the Ru dispersion than barium. The selectivity of various promoters on hydrogenolysis temperature may relate to their existing state and their thermal resistence ability proved with the changes of ruthenium dispersion.