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

H-1 NMR spectra, second moments of line and spin-lattice relaxation times w ere measured for triethylamine (TEA) adsorbed in aluminophosphate (AlPO4-5) and silicoaluminophosphate (SAPO-5) molecular sieves in the temperature ra nge 90 K to room temperature. Two modes of motions, molecular reorientation s about the pseudo-C-3 axis and the isotropic rotation were observed in bot h 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 Bronsted a cid sites and lone-pair electrons in TEA. This difference in interaction wa s shown to be the origin of the distribution of the motional correlation ti me (tau) in SAPO-5 less than in AlPO4-5 in which the presence of molecular C-3 axes in micropores oriented more randomly than in SAPO-5 result in a ma rked tau distribution.