Production of the NH radical from the catalytic decomposition of NH₃ on polycrystalline Pt and Fe surfaces at high temperatures

Decomposition of NH₃ on polycrystalline platinum at temperatures >1200 K was found to result in desorption of the NH radical into the gas phase. The gaseous NH radical was detected by means of the laser-induced fluorescence technique. The desorption process is one of several possible steps involving the surface-adsorbed NH radical. NH₂ was not observed to desorb from the catalyst at all temperatures studied. The measured activation energy for NH desorption is 66 ± 3 kcal/mol and appears to be independent of NH₃ or H₂ gas phase concentration over the range studied. Addition of H₂ to NH₃ enhances the yield of NH desorbed; however, addition of D₂ to NH₃ enhances the desorption yield of both ND and NH. A mechanism for NH₃ decomposition is proposed to account for these observations and the results of other studies. A similar but brief study of NH₃ decomposition on polycrystalline Fe surfaces was also made. Similarly NH, but not NH₂, was found to desorb from the Fe surface above 1000 K.