Adsorption and decomposition of H 2NCHO, D 2NCHO, N 2H 4, and NH 3 on Rh(111)

Abstract

The adsorption and decomposition of H 2NCHO, D 2NCHO, N 2H 4, and NH 3 on Rh(111) have been examined using TPD. Adsorption of H 2NCHO on Rh(111) at 100 K produces four major desorption products: CO, H 2, N 2, and NH 3. The absence of any CN bond retention demonstrates that CO bond formation is favored over CN bond formation on Rh(111). At low coverage N 2 is the primary nitrogen containing product, but near saturation up to ∼ 25% NH 3 is formed. Hydrogen desorption has a peak from the recombination of H adatoms and a reaction limited peak at ∼ 450 K. The decomposition of D 2NCHO showed that the reaction-limited H 2 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 NH 3 decomposition. Ammonia desorption from H 2NCHO was reaction-limited and appeared to be formed from the scavenging of H adatoms by a NH 2 surface species. Adsorption of N 2H 4 on Rh(111) at 100 K gave rise to three major desorption products: N 2, H 2, and NH 3. N 2 desorption has a peak at ∼ 700 K formed by the recombination of N adatoms at ∼ 700 K and also a low-temperature N 2 peak at ∼ 270 K which was due to the decomposition of a N 2H y ( y ⩽ 3) species not involving the scission of the NN bond. H 2 desorption from N 2H 4 results from the recombination of H adatoms and the decomposition of NH. NH 3 desorption from N 2H 4 has a peak corresponding with the NH 3 peak from H 2NCHO and a second peak caused by the direct intramolecular decomposition of N 2H 4.