Decomposition of CH₃NH₂ on Pt(111)

The adsorption and decomposition of CH₃NH₂ on Pt(111) have been studied using TPD and AES. The major species observed following adsorption at 300 K are C₂N₂, H₂ and HCN with N₂ and CH₄ being only a few percent of these species. No CH₃NH₂ desorbs following 300 K adsorption. HCN desorbs as two major peaks at 480 and 520 K while C₂N₂ desorbs as several peaks between 700 and 1200 K. Hydrogen desorbs as a peak at ≈420 K from H atom recombination and two peaks at 480 and 520 K from H_xCN decomposition. Desorption from the saturated surface produces approximately 4 times more C₂N₂ than HCN. No carbon residues are left on the surface after heating to 1300 K. Adsorption of CH₃NH₂ at 100 K produces a monolayer CH₃NH₂ desorption peak at 230 K and a multilayer, at 135 K. More HCN and less C₂N₂ form with adsorption at 100 K than at 300 K. Annealing the 100 K adlayer increases the C₂N₂/HCN ratio. These results indicate that HCN is formed only from H_xCN products rather than from H+CN bimolecular reaction as confirmed by hydrogen titration experiments At lower coverages C₂N₂ desorbs with second-order kinetics, suggesting that this product is formed by combination of adsorbed CN species. These results indicate that CH₃NH₂ dehydrogenates totally by 600 K and that no C-N bonds are broken on this surface. Onece H₂ desorbs to leave CN on the surface, the dimer C₂N₂ is the only gaseous product which can form, and this occurs avove 1000 K.