Dynamic behaviour of triethylamine molecules adsorbed in aluminophosphate (AlPO4-5) and silicoaluminophosphate (SAPO-5) molecular sieves

Abstract

¹ H NMR spectra, second moments of line and spin–lattice relaxation times were measured for triethylamine (TEA) adsorbed in aluminophosphate (AlPO₄-5) and silicoaluminophosphate (SAPO-5) molecular sieves in the temperature range 90 K to room temperature. Two modes of motions, molecular reorientations about the pseudo-C₃ axis and the isotropic rotation were observed in both systems. The fact that the former motion in SAPO-5 is hindered more than in AlPO₄-5 was attributed to the hydrogen-bond formation between Brönsted acid sites and lone-pair electrons in TEA. This difference in interaction was shown to be the origin of the distribution of the motional correlation time (τ) in SAPO-5 less than in AlPO₄-5 in which the presence of molecular C₃ axes in micropores oriented more randomly than in SAPO-5 result in a marked τ distribution.