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

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 ∼ 25% NH3 is formed. Hydrogen desorption has a peak from the recombination of H adatoms and a reaction limited peak at ∼ 450 K. The decomposition of D2NCHO 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 ∼ 700 K formed by the recombination of N adatoms at ∼ 700 K and also a low-temperature N2 peak at ∼ 270 K which was due to the decomposition of a N2Hy (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.