TEMPERATURE-PROGRAMMED REACTION OF METHYLAMINE ON THE NI(100) SURFACE

The adsorption and temperature-programmed reaction of methylamine on the Ni{100} surface is investigated. Irreversible decomposition of methylamine predominates at very low exposures in which the C-N bond scission is favored over dehydrogenation to form ammonia. At slightly higher exposures, nondissociative adsorption takes place. A new adsorption state of methylamine, in which the chemisorbed methylamine molecule is hydrogen bonded to nitrogen residues on the surface, is found which has a binding energy of about 19 kcal/mol. Desorption of methylamine from this new state occurs at a temperature close to that from an oxygen-precovered Ni{100} surface and is dependent on the predosage of oxygen. Hydrogen bonding between the chemisorbed methylamine and the residual nitrogen present on the surface also results in an increase in the decomposition rate. A further increase in methylamine exposure results in molecular adsorption to form the first and the second chemisorption states as well as a third state thought to be due to multiple layers of weakly adsorbed methylamine. In addition, several adsorption states for ammonia produced from decomposition of methylamine on Ni{100} are also identified. More than 90% of the ammonia initially produced at very low methylamine exposures are hydrogen bonded to surface nitrogen residues. The trend of the reactivity of methylamine on transition metals across the Periodic Table is also discussed.