Decomposition of CH3NH2 on Pt and Rh: rate oscillations and surface intermediates

The adsorption and decomposition of CH 3 NH 2 have been studied on Pt(111), Rh(111), and on polycrystalline wires with characterization by TPD, XPS, AES, and steady-state reactivity measurements. HCN, C 2 N 2 , and H 2 are the exclusive products on Pt while ∼ 15 % N 2 is produced on Rh. The dominant surface species on the surface upon heating CH 3 NH 2 is therefore CN which is stable to 1100K on Pt and to 800K on Rh. On an electrically heated Pt wire in a 1 torr reactor, this reaction exhibits self-sustaining rate oscillations over a wide range of temperatures and reactant pressures. These oscillations are quite reproducible with frequencies up to 8 Hz and temperature amplitudes up to 400K. A model incorporating all known rate parameters from low pressure experiments has been shown to fit the observed data semiquantitatively assuming a simple unimolecular reaction which is blocked by adsorbed CN at low temperatures.