13CNMR of methane in anAlPO4−11molecular sieve: Exchange effects and shielding anisotropy

Abstract

${}^{13}\mathrm{C}$ NMR spectra of ${}^{13}{\mathrm{CH}}_{4}$ in an ${\mathrm{AlPO}}_{4}\ensuremath{-}11$ molecular sieve reveal exchange effects between adsorbed and nonadsorbed methane gas. An application of pulsed field gradients is introduced to decrease nonadsorbed and exchanging gas signals in order to extract the chemical shift anisotropy line shape of the adsorbed gas. The resulting ${}^{13}\mathrm{C}$ shielding anisotropy of methane is compared to existing value for methane in related SAPO-11 material. Less anisotropic shielding is observed in ${\mathrm{AlPO}}_{4}\ensuremath{-}11,$ most likely due to the lack of charge-compensating cations.