柠檬酸对Ru/AC氨合成催化剂结构和活性的影响

使用柠檬酸(CA)修饰石墨化活性炭(AC)和钌以改善Ru/AC催化剂中钌粒子的尺寸分布和催化剂的活性, 并通过透射电镜(TEM)、热重分析(TGA)、CO化学吸附和N2物理吸附等方法研究了柠檬酸对AC和Ru/AC催化剂织构、钌的分散度和催化剂的活性等性质的影响. 结果表明, 负载的柠檬酸优先吸附于活性炭微孔, 少量柠檬酸即可大幅度降低活性炭的比表面积, 增加活性炭表面含氧官能团的数量, 改善了钌粒子分布. 最佳负载顺序是柠檬酸和氯化钌依次负载. 在活性炭中添加适量的柠檬酸对催化剂的低温活性有显著影响. 柠檬酸处理后的Ru/AC催化剂活性最大提高幅度为21.4%.

Influence of Citric Acid on Structures and Catalytic Activities of Ru/AC Catalysts for Ammonia Synthesis

Citric acid (CA) was used to modify graphitic activated carbon (AC) to improve the ruthenium distribution and the catalytic activity of Ru/AC catalyst. The influence of CA on the texture of AC and Ru/AC, Ru dispersion and catalytic activity were investigated. Transmission electron microscopy (TEM), thermogravimetric analysis (TGA), CO pulse chemisorption and N2 physisorption indicated that minor amounts of citric acid significantly decreased the surface area of AC and increased the content of oxygen-containing functional groups on the surface of AC. This is the result of preferential adsorption of CA in AC micropores which improves the particle distribution of Ru. The optimal loading sequence is CA followed by RuCl3. A suitable content of CA in Ru/AC catalysts has a remarkable influence on the activities of Ru/AC catalysts at low reaction temperature. The greatest increase of activity was 21.4% for the Ru/AC catalysts treated with CA.