Location of organic bases and identification of Brønsted acid sites in zeolites by 14N solid state NMR

Abstract

Solid state ¹⁴N NMR spectra of R₄N⁺ ions in zeolites, like ZK-4 and ZSM-20, are easily detected due to high tetrahedral symmetry at the ¹⁴N site; spectral perturbations due to ¹⁴N quadrupolar interactions distinguish TMA⁺(TMA⁺= tetramethylammonium) ion environments in α- and β-cages of ZK-4 and a lone TEA⁺(TEA⁺= tetraethylammonium) environment in ZSM-20 and it is further shown that solid state ¹⁴N NMR spectroscopy offers a convenient method to detect the presence of Brønsted acidic sites in zeolites.