Transport properties of ammonia in a series of Na+-faujasite zeolites as studied by 2H NMR technique

The molecular motion of ammonia has been investigated in Na+-faujasite zeolites with various Si/Al ratios from 1.2 to 3.4. 2H NMR spectra show fast isotropic reorientation of the ammonia at room temperature, which indicates the jump of the molecule from one adsorption site to another. A fast rotation around its three-fold axis is observed with decreasing temperature. The correlation time and activation energy values have been determined and reveal a significant decrease in ammonia mobility, with decreasing Si/Al ratio, that has been correlated with the negative charge of the framework oxygen atoms.