Thermal desorption and infrared studies of primary aliphatic amines adsorbed on haematite (α-Fe2O3)

Abstract

The adsorption of n-octadecylamine on α-Fe₂O₃ at the solid/liquid interface, and of n-butylamine at the solid/liquid and solid/vapour interfaces has been studied by infrared spectroscopy. To obtain further information about the nature of desorbing products, temperature-programmed desorption experiments were made with n-butylamine–α-Fe₂O₃ absorbates. No difference could be detected by i.r. spectroscopy between the nature of adsorbates formed under the various mentioned conditions. Adsorption of n-octadecylamine and n-butylamine on α-Fe₂O₃ mainly involves coordinative interactions between amine and Lewis-acidic surface sites (Fe³⁺ cations). Furthermore, hydrogen bonds are formed between surface hydroxy groups and adsorbed amine molecules. n-Butylamine adsorbed on α-Fe₂O₃ gave four different desorption peaks (I–IV) which are formed by n-butylamine (I: 423 K), butyronitrile (II: 530 K), CO₂(III: 630 K) and H₂O (IV: 713 K). Desorption of CO₂ and H₂O is caused by the oxidation of amine molecules strongly adsorbed on two different types of coordination sites.