Ru-based Catatlysts Supported On Oxides For Ammonia Synthesis

Ammonia and the products of ammonia are important in agriculture, plastic, medicine, detonator, metallurgy, environment, fester and so on. Since we first got ammonia from disperse Fe in 1904, the country of the world have not stopped studying and developing on ammonia synthesis. Carbon supported ruthenium-based catalysts easy get methanion and that cause a great drop of the activity under the operating condition. So we need others steady supports.magnesia and alumina are known for stabilization, high mechanism intension and easy figuration, in this article we use magnesia and alumina as the supports, RuCl₃·nH₂O as the precursor, K and Ba as the promoters, the ruthenium-based catalysts are prepared which use one promoter or two promoters. Their ammonia synthesis activities are evaluated under 2.0 MPa or 5.0 MPa and the Ru-based catalysts are characterized, we get those results:In those four catalysts of Ru/MgO, K-Ru/MgO, Ba-Ru/MgO and K-Ba-Ru/MgO, the activity of alkali-promoted K-Ru/MgO is the best, the activity is 552.7 mL NH₃ h^-1 g^-1_cat under 2.0 MPa and the activity is 1111.4 mL NH₃h^-1 g^-1_cat under 5.0 MPa. In those four catalysts of Ru/Al₂O₃, K-Ru/Al₂O₃, Ba-Ru/Al₂O₃ and K-Ba-Ru/Al₂O₃, when the synthesis pressure is 2.0 MPa, the activity of K-Ru/Al₂O₃ that is 680.6 mL NH₃ h^-1 g^-1_cat is the best; When the synthesis pressure is 5.0 MPa, the activity of K-Ba-Ru/Al₂O₃ that is 822.4 mL NH₃ h^-1 g^-1_cat is the best.By compared with the ammonia synthesis activities of Ru-based catalysts, we get those results, for Ru/MgO-based catalysts, when the pressure is improved form 2.0 MPa to 5.0 MPa, the activities of those four catalysts improve double times. For Ru/Al₂O₃-based catalysts, improving pressure is not always good to improve the activities, thereinto the activity of K-Ru/Al₂O₃ is just discrepancy 77.6 mL NH₃ h^-1 g^-1_cat in two kinds pressure, but the activity of K-Ba-Ru/Al₂O₃ improve markedly when the pressure is improved. This shows that even if the support is the same Al₂O₃ or oxide, the effect of pressure on their activities is not always the same. The activities of those four catalysts which are loaded on MgO get change when the reaction temperature and pressure have changed, it is showed that for Ru/MgO-based catalysts, whether addition promoters, addition which kind promoter should be decided by the desired operation temperatures and pressure.