论文部分内容阅读
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（dimerordinitrosyl）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.
The adsorption of H2 and NO on γ-Mo2N was studied by TPD-MS method. The results of H2-TPD alone show that there are three H2 desorption peaks at 443K, 573K and 723K when H2 is adsorbed at 673K, indicating that there are three different H2 adsorption sites on γ-Mo2N. NO-TPD results showed that there are three desorption peaks (383K, 493K, 543K) after NO adsorption, which correspond to the three different NO adsorption sites on γ-Mo2N: low, medium and high energy adsorption sites. NO can be dissociated as well as adsorbed on γ-Mo2N in the form of NO dimerordinitrosyl, which produce a large amount of N 2 and a small amount of N 2 O during the desorption process. The TPD results of γ-Mo2N under different processing conditions show that NO is the coordinatively unsaturated center of MO adsorbed on γ-Mo2N. These adsorption centers can both pass the reduction catalyst and pass the vacuum passivation at 773K γ-Mo2N, the results of co-adsorption of H2 and NO show that the desorption of H2 and NO are greatly reduced after the pre-adsorption of H2 and NO, and only two desorption peaks appear.The NO only appear at 363K and 493K The two desorption peaks indicate that the pre-adsorbed hydrogen occupies a strong adsorption site for NO, and NO is very hard to replace so that NO can only be adsorbed on lower energy adsorption sites; while H2 only appears at 523K and 723K Desorption peak, with the generation of N2 and H2O along with the desorption of H2, suggesting that NO may form a composite phase MoHx (NO) y with pre-adsorbed hydrogen on γ-Mo2N, which decomposes to H2 upon desorption. N2 and H2O.