Research On The Preparation Of Carbon-Supported Ruthenium Catalyst And Its Catalytic Performance For Ammonia Synthesis

Many kinds of activated carbon from different raw materials were used as support to prepare ruthenium catalyst. Elemental analysis, physisorption, chemisorption, temperature-program reduction, X-ray diffraction and scan electron microscope were carried out to characterize the properties of activated carbon support and ruthenium catalyst. The ammonia synthesis activities for a series of ruthenium catalyst were measured at a high temperature and under a high pressure. Particular attention was paid to the effect of support, promoter, preparation process and reaction condition on the metal dispersion and catalytic properties of ruthenium catalyst for ammonia synthesis.The result was shown that, for the same raw material, the high purities, high surface area, large pore volume and fitting pore size distribution of activated carbon might disperse ruthenium and promoter sufficiently, which activated carbon as support would manufacture high activity of ruthenium catalyst for ammonia synthesis. The different raw material of activated carbon as support would greatly influence the catalytic properties of ruthenium catalyst for ammonia synthesis.The thermal treatment of activated carbon could eliminate carbon impurities, bring about different degrees of graphitization, and improve the resistance of the carbon support to undergo methanation under ammonia synthesis conditions, but the surface area and porosity decreased dramatically. Oxidative treatment partially recovered the surface area and porosity. The higher the thermal treatment temperature, the greater the stability of the carbon support, and the more difficult the recovery of the surface area and porosity becomes. The ammonia synthesis activity of Ru catalyst was greatly improved by using theactivated carbon as support which was heated at 1900 in an inert atmosphere and then subjected to an oxidation treatment.The microwave treatment of activated carbon could also eliminate carbonimpurities, improve the stability of activated carbon support under the ammonia synthesis condition, at the same time, the surface area and porosity of activated carbon wouldn't decrease obviously. With the microwave-treated carbon as the support, the catalysts could not only give a higher Ru dispersion, but also protect the ruthenium particle from sintering, when the catalysts were reduced at a higher temperature.A series of precursor were used as promoter to prepare the single-promoted or double-promoted Ru/C catalyst. For the single-promoted Ru/C catalyst, barium and cesium proved to be most effective in the alkaline-earth metal or alkaline metal promoter. Barium-promoted Ru/C catalyst was more effective in ammonia synthesis than cesium-promoted Ru/C catalyst. For the double-promoted Ru/C catalyst, because barium and cesium competed adsorption during the process of preparing the double-promoted Ru/C catalyst, that would influence the surface distribution of barium and cesium promoter and ammonia synthesis activity of the Ru/C catalyst. The activity of 4 wt% Ru-Ba-Cs/C was higher obviously not only than 4 wt% Ru-(Ba+Cs)/C, but also than 4 wt% Ru-Cs-Ba/C. Barium and cesium promoter in 4 wt% Ru-Ba-Cs/C were impregnated by two steps method, barium was impregnated first, after reducing treatment at 400癈, cesium was impregnated again.The preparation process and the feasible or limited application condition of Ru catalyst were investigated. The result showed that the catalytic reaction of Ru catalyst for ammonia synthesis was carried out below 500 . It is important of improving the stability of carbon support by heading treatment. Compare the performance of Ru catalyst with Fe catalyst. It was found that the ammonia synthesis activity of Ru catalyst is higher than that of Fe catalyst at a lower temperature and under a middle pressure. The catalytic performance would further increase by Ru catalyst in tandem with Fe catalyst.