【作者】 刘广臻；

【导师】 郑晓玲；

【作者基本信息】 福州大学 ， 无机化学， 2004， 硕士

【摘要】 本文以RuCl3·3H2O为活性前体、碱金属及碱土金属的硝酸盐为助剂制备负载型活性炭载钌氨合成催化剂。采用元素分析、N2物理吸附、CO化学吸附、X－射线粉末衍射等表征手段，详细考察了载体、钌活性组分、助剂及催化剂的制备方法对氨合成催化性能的影响。同时在接近工业生产条件下对所制备的催化剂的使用条件进行了探讨。结果显示，具有较高的纯度、较大的比表面、合适孔体积分布的活性炭载体能够对钌金属充分的分散，制备出高活性的催化剂；活性炭在惰性气体保护下经1800 ℃高温热处理及随后10 % O2/N2限量氧气的氧化扩孔处理能够使炭载体既具有良好的导电性和较高的纯度，又具有合适的孔结构来分散金属钌，因而能使钌催化剂的活性得到明显提高。较低的还原脱氯温度不能有效消除RuCl3/TCOX中残余氯离子的影响，但过高的脱氯温度却使炭载体发生明显的甲烷化甚至钌粒子烧结，最佳的脱氯温度为400～450 ℃；综合考虑性价比，优化的活性金属负载量为4～6 wt%。助剂的促进作用大体上与化合物的碱性大小相一致，钡、铯分别是碱土金属和碱金属化合物中最有效的助剂，钡比铯具有更强的促进作用。助剂只有与钌粒子发生有效接触后才能对催化剂产生较大促进作用；对于单助剂钌催化剂，钡、铯助剂的最佳加入量分别是Ba/Ru摩尔比为5，Cs/Ru摩尔比为10，铯比钡所需添加量较大的原因源于它们在催化剂中的分布状态不同；催化剂在明显高于助剂前体发生分解的温度下活化能使其产生更多的活性位。但过高的活化温度使钌粒子发生烧结，导致催化剂的活性明显下降。碱金属和碱土金属盐类促进的催化剂的活化温度分别以470 ℃和500 ℃为宜。采用先钡后铯分步浸渍制备的双助剂钌催化剂的活性明显高于钡、铯共浸渍钌催化剂和先铯后钡分步浸渍钌催化剂。在钡铯双助剂钌催化剂中，铯助剂主要分布在钌与载体的界面发挥电子助剂作用；而钡助剂主要分布在钌粒子表面，在发挥电子助剂作用的同时，也有可能起结构助剂作用。在425 ℃、13.0 MPa反应条件下，钌催化剂的活性比熔铁型催化剂提高了26～30 %。更多还原

【Abstract】 A serial of alkali- and/or alkali-earth-promoted, carbon-supported Ru catalysts for ammonia synthesis have been prepared by impregnation from acetone solutions of RuCl3·3H2O precursor. The article investigated the effect of support, Ru precursor, promoter and preparation process on catalytic properties of ruthenium catalyst for ammonia synthesis by means of various characterization methods performed by N2 physical adsorption, CO chemisorption and X－ray diffraction. Meanwhile, the application condition of Ru catalyst was investigated under near industrial reaction condition.It was suggested that activated carbon with higher purities, higher surface area and fitting pore size distribution as a support might disperse ruthenium and promoter sufficiently in Ru catalyst, which would manufacture high activity ruthenium for ammonia synthesis. The ammonia synthesis activity of Ru catalyst was greatly improved by using the activated carbon as support which was heated at 1800 ℃ in an inert atmosphere followed by moderate oxidizing treatment in 10 % O2/N2, which can make carbon support with better conductivity, higher purities and fitting pore structure for dispersing metal Ru.Reductive dechlorination of RuCl3/TCOX at lower temperature cannot remove negative-effected chlorine, but the methanation of carbon support is induced at extremely high dechlorination temperature and even lead to the sintering of Ru particles in catalyst. Activity results showed that a moderate dechlorination condition of 400～450 ℃ is advisable. Moreover, optimal ruthenium loading is 4～6 wt% when the ratio of performance and price of catalyst is considered. Promoting role of promoter is in line with electronegativity of compounds. <WP=5>Barium and cesium proved to be most effective in the alkaline-earth metal or alkaline metal promoter accordingly. But Barium-promoted Ru catalyst is more effective in ammonia synthesis than cesium-promoted Ru catalyst. The promoters can play a much promoting role for ruthenium catalysts, only when part of promoters contact with ruthenium effectively. The optimal promoter loading of Barium-promoted Ru catalyst or Cesium-promoted Ru catalyst is (Ba/Ru) mol = 5, (Cs/Ru) mol = 10 respectively. The reason why much more Cesium is needed than Barium for promoted-ruthenium catalysts is attributed to their different morphological models. The needed hydrogenolysis temperature of catalysts is higher than decompose temperature of promoter precursor, which can produce much more activity sites in Ru catalyst. However, the extremely high hydrogenolysis temperature can lead to the sintering of Ru particles in catalyst and the decreasing of Ru catalyst. The hydrogenolysis temperature of alkaline metal promoted catalyst or alkaline metal promoted catalyst is ought to be controlled at 470 ℃, 500 ℃ respectively.The activity of 4 wt% Ru-Ba-Cs/TCOX is higher obviously not only than 4 wt% Ru- (Ba+Cs)/TCOX, but also than 4 wt% Ru-Cs-Ba/TCOX. The barium promoters distribute uniformly on the ruthenium surface while the Cesium promoters mainly distribute at the C/Ru contact points to act as effective promoter. The Cesium promoter is considered to precede via electron transfer from the alkali to the active metal surface and barium promotion acts as a structural and/or electronic promoter. The catalytic activity of the supported Ru catalyst is 26～30 % higher than that of Fe catalyst under 425 ℃、13.0 MPa reaction condition.更多还原