高等学校化学学报 ›› 1982, Vol. 3 ›› Issue (2): 162-168.

• 论文 • 上一篇    下一篇

碱金属助催合成氨铁催化剂的研究(Ⅴ)——氯离子的效应

忻新泉, 朱龙根, 孟庆金, 张雪琴, 吴沛成, 戴安邦   

  1. 南京大学配位化学研究所
  • 收稿日期:1981-01-30 出版日期:1982-04-24 发布日期:1982-04-24

STUDIES ON ALKALI METAL PROMOTED IRON CATALYST FOR AMMONIA SYNTHESIS (V)——EFFECT OF CHLORIDE ION

Xin Xinquan, Zhu Longgen, Meng Qingjin, Zhang Xueqin, Wu Peicheng, Dai Anbang   

  1. Coordination Chemistry Research Insititute, Nanjing University, Nanjing
  • Received:1981-01-30 Online:1982-04-24 Published:1982-04-24

摘要: 本文指出,氯离子是碱金属助催的合成氨催化剂Fe-AC(活性炭)-K(金属钾)体系的毒物。通过对含氯催化刑的活性测试,配合气相色谱、穆斯堡尔谱以及X-射线衍射图的研究,所得实验結果指出,KCl使催化剂中毒的机制是氯离子引起了高分散的小颗粒α-Fe的聚结,本文还讨论了氯离子对Fe体系和Ru体系催化剂的不同影响,归之于Fe系合成氨催化剂的结构敏感性。

Abstract: This report points out that chloride ion is a poison for iron catalyst of ammonia synthesis promoted by alkali metal. Results of the experiment on adding KCl to the system Fe-AC (active carbon)-Kshowed a very marked decrease in catalytic activity (Fig. la), while the addition of KCl to the system, Ru-AC-K, activity decreases much less (Fig. lb), indicating that chloride ion is a poison for iron catalyst but has little effect on ruthenum catalyst for ammonia synthesis.Gas chromotographic study on Fe2(C2O4) S-AC and Fe2(C2O4)3-KCl-AC systems showed that in hydrogen atmosphere the decomposition of the iron salt took place at different temperatures. In the system that contained KCl, the decomposition products COand CO3 appeared at a higher temperature (Fig. 2a, 2b). In hydrogen atmosphere, the reduction of FeOfrom pure Fe2(C3O4)3 crystals was almost completed at 300-420℃, but FeOof the Fe2(C3O4)3-AC system was reduced only slightly even at 500℃. Under the same condition, FeOfrom the Fe2(C3O4)3-AC-KCl system was reduced much more as indicated by the amount of water evolved (Fig. 2c). It was therfore postulated that the presence of KCl lowered the degree of dispersion of FeO and made it more easily reduced to form large particles of a-iron of low or no catalytic activity.X-ray diffraction study of the catalysts by the powder method revealed that the product of the decomposition of Fe2(C3O4)3-KCl-ACgave the characteristic spectrum of a-iron(Fig. 3) while that of Fe2(C3O4)3-ACgave no spectrum. It was also found, by comparing the Mossbauer spectra of the two systems, that in the catalyst from Fe2(C2O4)3-KCl-ACsystem the spectral lines of the fine particulate a-iron in paramagnetic region which corresponded to high catalytic activity disappeared.In conclusion, it is considered probable that the poisonous effect of chloride ion is due to the agglomeration of the superfine particles of a-iron which are the active centers of the catalyst for ammonia synthesis and ruthenum catalyst is much less sensitive to this agglomeration effect.