采用普通浸渍法(CI)、超声-包覆法(UC)和超声-静电吸附法(UEA)制备了Ru/Ba-MgO氨合成催化剂,并运用高分辨透射电镜、场发射扫描电镜、X射线粉末衍射、N_2的物理吸附、H_2脉冲化学吸附及程序升温还原等手段对催化剂进行了表征.结果表明,在UEA样品中,Ba以静电吸附形式均匀地掺入MgO载体中,因而不仅极大地改善了载体表面形貌,而且有效地控制了Ru晶粒大小,其平均粒径在2～3nm.该样品中,BaCO_3起始分解温度较低,低温BaCO_3含量较高,因而还原性能较佳.在10MPa,10000h~(-1)和425℃条件下,UEA法制得的Ru基催化剂上氨合成反应速率达到60.42mmol/(g·h),分别是CI法和UC法的1.9和1.1倍.
Three Ru-based catalysts for ammonia synthesis were prepared by the conventional impregnation method (CI), ultrasound-coating method (UC), and ultrasound electrostatic adsorption (UEA). The physical and chemical properties of the supports and catalysts were characterized by high-resolution transmission electron microscopy, scanning electron microscopy, X-ray powder diffraction, N_2 physical adsorption, H_2 pulse chemical adsorption, and temperature-programmed reduction (TPR). The results showed that Ba was uniformly dispersed on the surface of the MgO support through its electrostatic adsorption in the catalyst prepared by UEA, which not only greatly improved the surface morphology of the support but also effectively controlled the size of Ru particles within the range 2-3 nm. TPR results also showed that the Ru-based catalyst prepared by UEA contained more BaCO_3 species that decomposed at low temperature and therefore gave a better reduction property. The highest catalytic activity for ammonia synthesis was obtained on the Ru-based catalyst prepared by UEA with a reaction rate of 60.42mmol/(g·h)for ammonia synthesis under the conditions of 10 Mpa,10000 h~(-1) ,and 425℃,which is 1.9 and 1.1 times that of Ru-based catalysts prepared by CI and UC, respectively.
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