助剂对Ru/C催化剂的表面性质及氨合成催化性能的影响

A series of alkaline- or/and alkaline-earth-promoted, carbon-supported ruthenium catalysts have been prepared N2 physisorption, CO chemisorption and X-ray diffraction were carried out to investigate the effect of promoter on the surface area, pore size distribution and ruthenium dispersion of catalysts. The activities of the series catalyst for ammonia synthesis were measured under the reaction condition 430 ℃, 10.0 MPa and 10 000 h－1. It has been found that the effectiveness of alkaline- or alkaline-earth-promoter is roughly related to the basicity of alkaline metal hydroxide or alkaline-earth metal oxide. For the single-promoted Ru/C catalyst, cesium and barium proved to be most effective in the alkaline and alkaline-earth promoter. Barium-promoted Ru/C catalyst was more effective in ammonia synthesis than cesium-promoted Ru/C catalyst. Barium was suggested to have a stronger interaction with the Ru surface than cesium. For the double-promoted Ru/C catalyst, the activity of the catalyst was affected remarkably by the method of preparation. Barium and cesium promoter in 4w% Ru-Ba-Cs/C were impregnated by two steps method, barium was impregnated first, after reducing treatment at 400 ℃, cesium was impregnated again. The catalyst of 4w% Ru-Cs-Ba/C was prepared from impregnating cesium first barium later by two step impregnation. The catalyst of 4w% Ru-(Ba+Cs)/C was prepared from co-impregnation the mix aqueous solution of barium and cesium by one step method. The result showed that the activity of 4w% Ru-Ba-Cs/C was higher obviously not only than 4w% Ru-(Ba+Cs)/C, but also than 4w% Ru-Cs-Ba/C. 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.