Ammonia synthesis over cobalt catalysts doped with cerium and barium. Effect of the ceria loading
Ammonia synthesis over cobalt catalysts doped with cerium and barium. Effect of the ceria loading
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DOI：
10.1016/j.apcata.2012.08.028
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发表时间：
2012-11-28
影响因子：
5.5
通讯作者：
Rarog-Pilecka, Wioletta
中科院分区：
文献类型：
--
作者：
Karolewska, Magdalena;Truszkiewicz, Elzbieta;Rarog-Pilecka, Wioletta
研究了CeO_2负载量对合成氨钴催化剂活性和热稳定性的影响。Co3O4+CeO2混合物中CeO2的浓度从0到29wt%，而Ba2的含量是恒定的，与Co3O4的相对含量为13wt%。在标准条件下(p=6.3 Mpa，T=400℃，H-2：N-2=3：1)的流动微分反应器中进行了NH3合成的动力学测量。在NH3合成动力学测试的基础上，对所制得的材料进行了表征研究--N-2物理吸附、XRPD、H-2化学吸附、TPR-TG/DTG-MS和SEM-EDS。结果表明，CeO_2起着结构促进剂的作用，在焙烧过程中阻碍了Co3O4的烧结，在反应条件下稳定了Co的表面积。此外，CeO2似乎稳定了金属钴的hcp相，从而使钴催化剂具有更高的活性。结果表明，CeO2含量为11.5wt%的共促进钴催化剂(符号Co/Ce(11.5)/Ba)比常规熔铁催化剂(KmI，H.Topsoe)具有更高的NH3合成活性。Co/Ce(11.5)/Ba催化剂具有很好的抗过热性能。在600℃下热处理160h(3H(2)：n-2=30.01/h，p=0.1 Mpa)，其NH3合成活性仅下降几个百分点。(C)2012爱思唯尔B.V.保留所有权利。
The effect of ceria loading on the activity and thermal stability of a cobalt catalyst for ammonia synthesis has been studied. The concentration of CeO2 in the Co3O4 + CeO2 mixtures ranged from 0 to 29 wt%, whereas the barium content was constant and equaled 13 wt% in relation to Co3O4. Kinetic measurements in NH3 synthesis were carried out in a flow differential reactor operating under standard conditions (p = 6.3 MPa, T= 400 degrees C, H-2:N-2 =3:1). The kinetic measurements of NH3 synthesis were supplemented with the characterization studies of the obtained materials - N-2 physisorption, XRPD, H-2 chemisorption, TPR-TG/DTG-MS and SEM-EDS. It has been found that ceria plays the role of a structural promoter; it hinders the sintering of Co3O4 during calcination and stabilizes the surface area of Co under reaction conditions. Moreover, it seems that ceria stabilizes the hcp phase of metallic cobalt, which results in a higher activity of the cobalt catalysts. The co-promoted cobalt catalyst containing 11.5 wt% of CeO2 (symbol Co/Ce(11.5)/Ba) was shown to be more active in NH3 synthesis than the conventional fused iron catalyst (KM I, H. Topsoe). Moreover, the catalyst Co/Ce(11.5)/Ba is very resistant to overheating. Heat treatment at 600 degrees C for 160h (3H(2):N-2 =30.01/h, p =0.1 MPa) results in a decrease of its activity in NH3 synthesis by only a few percent. (C) 2012 Elsevier B.V. All rights reserved.