Temperature-programmed desorption of CO and NO over γ-Mo2N

The temperature-programmed desorption-mass spectroscopy technique has been used to characterize the desorption behaviors of adsorbed CO and NO on gamma-Mo2N. It has been found that adsorbed CO is desorbed with a prominent peak at 383 K and a shoulder at 423 K, without evidence of any decomposition. This suggests that the aggressive adsorption of molybdenum toward CO has been modified considerably by nitridation to resemble the properties of the Group WI metals. After synthesis there is some NH3 left on the Mo2N sample, which decomposes upon heating and the hydrogen liberated helps reduce the sample to certain extents, according to the conditions employed. Reducing the sample with hydrogen at high temperatures can produce coordinatively unsaturated sites of Mo whose number and nature are important to the interaction between the sample and CO and NO. Three types of active sites on the reduced Mo2N to adsorb NO with low, medium, and high adsorption energies have been found, from which NO is desorbed at 393, 503, and 543 K, respectively. In addition to NO, N-2 and N2O were detected as desorption products, which suggests that adsorbed NO undergoes decomposition and disproportionation reactions under appropriate conditions. The results of NO adsorbed on H-2-preadsorbed Mo2N show that the adsorption and reaction of NO on the sample is very much affected by preadsorbed hydrogen dosed at 673 K. The reactions between the reversely migrated hydrogen and the other surface species have also been discussed. (C) 1998 Academic Press.