Interaction of methyl-, ethyl- and n-propyl-amines with metal films of iron, nickel, palladium and aluminium

Abstract

Adsorption and decomposition of methyl-, ethyl- and n-propyl-amines on metal films of Fe, Ni, Pd and Al have been investigated in the temperature range 193–500 K. Chemisorption of the amines took place on the films at 193 K without noticeable decomposition. The chemisorption at this temperature occurred probably at the amino group with the hydrocarbon chain being oriented randomly on the surface. The pre-adsorbed oxygen or deuterium enhanced the subsequent chemisorption of the amine on the film at 193 K. All the amines are chemisorbed dissociatively on the films above 300 K with the rupture of the N—H bonds. The proposed dominant pathway involved the decomposition of the amine to form RNH and RN adsorbed species and hydrogen adatoms on the surface. Hydrogen remained the only gaseous product at all experimental temperatures. At any temperature in the range 400–500 K, the total gas pressure remained constant as a consequence of the evolution of one hydrogen molecule for each amine molecule adsorbed. Exchange of deuterium with the hydrogen of the adsorbed amine molecules was only detectable at temperatures greater than 300 K. The rate of amine adsorption dependend directly on its pressure, and the kinetic data revealed the operation of a compensation effect throughout the interaction of the amines with Fe, Ni and Pd films. Adsorption of the amines on Al and oxidized Fe films took place with constant energies of activation regardless of the type of amine used. Al showed a higher, and oxidized Fe a lower, activity for amine adsorption than the transition metal films Fe, Ni and Pd. The tendencies of the amines for adsorption and decomposition on the latter three metals followed the order: MeNH₂ > EtNH₂ > n-PrNH₂.