沉淀剂种类对Ru/CeO2氨合成催化剂结构和性能的影响

采用6种沉淀剂通过共沉淀法制备了6种Ru/CeO2氨合成催化剂, 考察了沉淀剂种类对其氨合成性能的影响. 通过X射线衍射、N2吸附-脱附、X射线荧光光谱和H2程序升温还原等表征手段, 对不同沉淀剂影响Ru/CeO2催化剂氨合成性能的原因进行探讨. 结果表明: 采用(NH4)2CO3和NH4HCO3制备的催化剂样品具有较好的氨合成活性, 其中NH4HCO3为最佳沉淀剂, 所制备的催化剂在450 ℃, 10 MPa , 10000 h－1测试条件下, 出口氨浓度为14.46%. 而采用KHCO3, KOH, K2CO3沉淀剂制备的样品的氨合成活性相对较低. 沉淀剂种类不仅明显地影响钌离子和铈离子的共沉淀, 而且会影响载体二氧化铈表面氧的还原. 由NH4HCO3沉淀剂制备的Ru/CeO2催化剂的高活性归因于钌负载量增大、钌粒子分散度提高以及二氧化铈表面氧易还原三者相互作用的结果.

Effect of Precipitants on Structure and Catalytic Activity of Ru/CeO2 Catalysts for Ammonia Synthesis

Ru/CeO2 catalysts were prepared by the co-precipitation method using six precipitants, K2CO3, NH3•H2O, (NH4)2CO3, KOH, NH4HCO3 and KHCO3, used for the ammonia synthesis and characterized by N2 adsorption-desorption, X-ray fluorescence spectroscopy, X-ray diffraction and H2 temperature-pro- grammed reduction to explore the cause resulting in their significant difference of catalytic activity. The ammonia synthesis activity of Ru/CeO2 catalyst prepared using NH4HCO3 as the precipitant was 14.46% at 10 MPa, 10000 h－1, 450 ℃, which was higher than those obtained by other precipitants. The samples prepared using the rest four precipitants presented lower activity for ammonia synthesis. The type of precipitant not only significantly affects the coprecipitation of ruthenium and cerium ions, but also affects the reduction of the surface oxygen. The high catalytic activity of Ru/CeO2 catalyst prepared using NH4HCO3 can be attributed to the synergism among the increase in ruthenium loading, the higher dispersion of ruthenium particles, and the easier reduction of surface oxygen of the support.