Adsorption and decomposition of H2NCHO, D2NCHO, N2H4, and NH3 on Rh(111)

Article abstract of DOI:10.1016/0039-6028(91)90785-Q

The adsorption and decomposition of H₂NCHO, D₂NCHO, N₂H₄, and NH₃ on Rh(111) have been examined using TPD. Adsorption of H₂NCHO on Rh(111) at 100 K produces four major desorption products: CO, H₂, N₂, and NH₃. The absence of any CN bond retention demonstrates that CO bond formation is favored over CN bond formation on Rh(111). At low coverage N₂ is the primary nitrogen-containing product, but near saturation up to approximately 25% NH₃ is formed. Hydrogen desorption has a peak from the recombination of H adatoms and a reaction-limited peak at approximately 450 K. The decomposition of D₂ NCHO showed that the reaction-limited H₂ comes from the amino group, and mass balances support the assignment of the reacting species as NH. The stability of NH suggests that NH decomposition may be a limiting factor in NH₃ decomposition. Ammonia desorption from H₂NCHO was reaction-limited and appeared to be formed from the scavenging of H adatoms by a NH₂ surface species. Adsorption of N₂H₄ on Rh(111) at 100 K gave rise to three major desorption products: N₂, H₂, and NH₃. N₂ desorption has a peak at approximately 700 K formed by the recombination of N adatoms at approximately 700 K and also a low-temperature N₂ peak at approximately 270 K, which was due to the decomposition of a N₂H_y (y ≤ 3) species not involving the scission of the N-N bond. H₂ desorption from N₂H₄ results from the recombination of H adatoms and the decomposition of NH. NH₃ desorption from N₂H₄ has a peak corresponding with the NH₃ peak from H₂NCHO and a second peak caused by the direct intramolecular decomposition of N₂H₄.