Ru/Ba-ZrO2催化剂的制备及其氨合成性能研究
收稿日期: 2012-10-11
网络出版日期: 2012-12-18
基金资助
项目受国家科技支撑计划(No. 2007BAE08B02)和中石油科技创新基金(No. 2010D-5006-0502)资助.
Preparation of Ru/Ba-ZrO2 Catalyst and Its Performance for Ammonia Synthesis
Received date: 2012-10-11
Online published: 2012-12-18
Supported by
Project supported by the National Key Technology Research and Development Program (No. 2007BAE08B02) and Innovation Fund of China Petroleum Corporation (No. 2010D-5006-0502).
分别采用柠檬酸络合法、改性共沉淀法和湿浸渍法制备了掺Ba纳米ZrO2材料, 负载Ru后用于催化氨合成反应. 采用X射线衍射、CO2程序升温脱附(CO2-TPD)、N2物理低温吸附、H2程序升温还原技术(H2-TPR)、扫描电镜(SEM)、透射电镜(TEM)、X射线光电子能谱(XPS)和CO化学吸附对载体材料和催化剂进行了表征. 结果表明, 不同方法制备载体的物相结构和织构性能均有明显差别, 负载Ru后催化剂的氨合成性能差别也较大. 其中, 以柠檬酸络合法制备的载体材料中Ba以BaZrO3的形式存在, 钙钛矿型BaZrO3具有较强的供电子能力, 电子可以通过Ru与载体间强相互作用传递到Ru表面, 有效地促进N≡N的断裂, 使催化剂的低温活性显著提高. 在425℃, 3 MPa, 空速为10000 h-1条件下, 出口氨浓度为5.72%. 其氨合成活性分别是改性共沉淀法和湿浸渍法制备催化剂的3.8倍和14.3倍.
王自庆 , 陈赓 , 林建新 , 王榕 , 魏可镁 . Ru/Ba-ZrO2催化剂的制备及其氨合成性能研究[J]. 化学学报, 2013 , 71(02) : 205 -212 . DOI: 10.6023/A12090725
The Ba-doped ZrO2 materials were prepared by three methods and used as support for Ru catalysts for ammonia synthesis, i.e., citric acid sol-gel method (SG), modified co-precipitation (CP) and impregnation method (IP). The certain amount of analytical-grade Zr(NO3)4·5H2O and Ba(NO3)2 were dissolved in deionized water to form a transparent mixed nitrate solution. The citric acid was slowly added into the mixture to form a transparent solution and then heated to 80℃ under vigorous stirring until all the water evaporated and a viscous material was obtained. After calcination at 750℃ for 5 h and a puffy white powder was obtained. This was BZ-SG. The solution of NH3·H2O and K2C2O4·H2O was added dropwise to the mixture solution of Zr(NO3)4·5H2O and Ba(NO3)2 with vigorous stirring, and the obtained white suspension was aged at 60℃ for 60 min. The resulting precipitate was centrifuged and washed with distilled water for several times, and then calcined at 750℃ for 5 h. The obtained white solid was named as BZ-CP. The Zr(OH)4 was prepared by adding the KOH into the Zr(NO3)4·5H2O solution. Then the obtained Zr(OH)4 was baked at 300℃ for 3 h and impregnated with aqueous solution of Ba(NO3)2. After dried at 85℃ for 12 h, the sample was heated at 750℃ for 5 h and obtained the BZ-IP sample. Ruthenium catalysts were prepared by impregnating the supports directly with K2RuO4 solution. After reduction with ethyl alcohol, then was dried at 120℃ for 12 h. The samples with 4 wt% Ru were labeled as RBZ-X (X=SG, CP and IP). The molar ratio of Ba to Zr in all the samples is 1:9. The composites materials and catalysts were characterized by X-ray diffraction (XRD), temperature programmed reduction of H2 (H2-TPR), temperature programmed desorption of CO2 (CO2-TPD), N2 adsorption- desorption isotherms, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and CO chemisorption. The results displayed that the RBZ-SG catalyst showed the highest activity for ammonia synthesis compared to those of RBZ-CP and RBZ-IP. The optimum ammonia concentration over RBZ-SG catalyst is 5.72% under the conditions of 3 MPa, 10000 h-1 and 425℃. This activity is 3.8 and 14.3 times of that of RBZ-CP and RBZ-IP, respectively. Such high activity is mainly resulted from the presence of BaZrO3, which has high electron-donating ability. Mobile electrons would be transferred from BaZrO3 to the Ru metal surface by means of the strong metal-support interaction existed between Ru and reduction BaZrO3, which can facilitate the cleavage of N≡N and enhance the activity for ammonia synthesis sufficiently.
Key words： preparation method; barium; zirconium; ruthenium catalysts; ammonia synthesis
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