物理化学学报 >> 1996, Vol. 12 >> Issue (12): 1084-1089.doi: 10.3866/PKU.WHXB19961207

研究论文 上一篇    下一篇

γ-Mo2N催化剂上H2及NO吸附性质的TPD-MS研究

杨树武,纪纯新,徐江,阎卫宏,张耀军,应品良,辛勤   

  1. 大连化学物理研究所,催化基础国家重点实验室,大连 116023
  • 收稿日期:1996-06-14 修回日期:1996-08-28 发布日期:1996-12-15
  • 通讯作者: 辛勤

TPD-MS Study of H2 and NO Adsorption Properties of γ-Mo2N

Yang Shu-Wu,Ji-Chun-Xin,Xu Jiang,Yan Wei-Hong,Zhang Yao-Jun,Ying Pin-Liang,Xin Qin   

  1. State Key Laboratory of Catalysis,Dalian Institute of Chemical Physics,CAS,Dalian 116023
  • Received:1996-06-14 Revised:1996-08-28 Published:1996-12-15
  • Contact: Xin Qin

摘要:

采用TPD-MS方法研究了H2及NO在γ-Mo2N上的吸附状况.单独的H2-TPD结果表明,当H2在673K吸附时,在443K、573K及723K得到了三个H2脱附峰,表明γ-Mo2N上有三种不同能量的H2吸附位.NO-TPD结果表明,NO吸附后亦有三个脱附峰(383K、493K、543K),对应着γ-Mo2N上三种不同能量的NO吸附位:低、中、高能吸附位.NO既可以以解离状态,又可以以一种NO三聚态(dimer or dinitrosyl)的形式吸附在γ-Mo2N上,这些吸附物种在脱附过程中产生大量的N2及少量的N2O. 对比NO吸附在不同处理条件的γ-Mo2N上的TPD结果可知,NO是吸附在γ-Mo2N上的MO的配位不饱和中心上,这些吸附中心既可通过还原催化剂,又可通过在773K抽空钝化态的γ-Mo2N而产生,H2和NO共吸附的结果表明,预吸附H2再吸附NO后,H2和NO的脱附量均大大减少,且只有两个脱附峰出现. NO只在363K及493K出现两个脱附峰,表明预吸附氢占据了NO的强吸附位,且NO很难取代它,从而使NO只能吸附在能量较低的吸附位上;而H2只在523K及723K出现两个脱附峰,且伴随着H2的脱出有N2和H2O的产生,表明在γ-Mo2N上NO可能与预吸附氢形成了一种复合相MoHx(NO)y,它在脱附时分解为H2、N2及H2O.

关键词: γMo2N, 催化剂, 程序升温托付技术(TPD), NO, 吸附, 活性位

Abstract:

TPD-MS technique has been used to characterize the H2 and NO adsorption properties of γ-Mo2N. Three categories of adsorbed H2 can be well distinguished when H2 was adsorbed at 673K. Mo coordinatively unsaturated sites (cus), on which NO can be adsorbed, can be produced by either reducing or evacuating the passivated Mo2N at elevated temperature. A comparison of NO adsorbed on evacuated, reduced and H2 preadsorbed Mo2N revealed that there were three categories of active sites on reduced Mo2N surface that adsorbed No: low, medium and high energy sites on which NO was desorbed with peak maxima at 383, 493 and 543K respectively. NO can be adsorbed in both a dissociative and a dimer or dinitrosyl state. The results of NO adsorbed on H2 preadsorbed Mo2N showed that NO can only be adsorbed on low and medium energy sites when hydrogen preadsorbed at 673K. NO cannot displace the most strongly adsorbed hydrogen. It is also suggested that NO can form some stable complexes with the adsorbed hydrogen. The complexes can only be desorbed at temperatures at which hydrogen can be desorbed, and the desorbed complexes decompose to N2, H2O and H2.

Key words: γMo2N, Catalyst, Temperature-programmed desorption(TPD), NO, Adsorption, Active sites