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