Thermal desorption and infrared studies of butylamine adsorbed on SiO2, Al2O3 and CaO

Abstract

The adsorption of n-butylamine on SiO₂, γ-Al₂O₃ and CaO at the solid/vapour interface has been studied by infrared spectroscopy and temperature-programmed desorption(t.p.d.) The infrared spectroscopic results show that adsorption of n-butylamine on SiO₂ leads to the formation of hydrogen bonds between surface hydroxy groups and amine molecules. Adsorption on γ-Al₂O₃ and CaO involves coordinative interactions between amine molecules and Lewis-acidic surface sites (Al³⁺ and Ca²⁺ cations), but hydrogen bonding also occurs. In the t.p.d. spectra one (SiO₂) or two (Al₂O₃, CaO) strong maxima appear caused by the desorption of n-butylamine and butyronitrile, respectively. Desorption of unchanged butylamine at low temperatures can be attributed to amine molecules hydrogen-bonded to surface hydroxy groups of the oxides. However, there are some phenomena which indicate the possibility that molecules coordinatively bonded to weak Lewis-acidic surface centres contribute to this maximum. On the other hand, only butylamine molecules coordinatively bonded to strong Lewis-acidic centres are dehydrogenated and desorb as butyronitrile at higher temperatures.