DEUTERIUM NMR CHARACTERIZATION OF BRONSTED ACID SITES AND SILANOL SPECIES IN ZEOLITES

Solid-state deuterium NMR has been used to characterize Bronsted acid sites and nonacidic silanol species in D-Y, D-mordenite, and D-ZSM-5 z eolites. Bronsted acid deuterons may be static, with quadrupole coupli ng constants (QCC) near 240 kHz and asymmetries (eta) of 0. These acid ic deuterons may also be motionally averaged to give QCC = 120 kHz and eta = 1, consistent with jumping between two oxygen sp(3) orbitals. T hese results indicate that the acid deuteron does not remain fixed in the Al-O-Si plane. Isolated silanol species display a narrow, axially symmetric powder pattern, consistent with an Si-O-D bond angle of 116 degrees. Most of the silanol species are more densely packed, and the variety of hydrogen-bonded positions possible results in a Gaussian pe ak about 56 kHz wide. Deuterium NMR shows promise as a technique for c haracterizing both acidic and nonacidic hydroxyl groups in zeolites.