H-1-NMR CHEMICAL-SHIFTS OF AMMONIA, METHANOL, AND WATER-MOLECULES INTERACTING WITH BRONSTED ACID SITES OF ZEOLITE CATALYSTS - AB-INITIO CALCULATIONS

The theoretically predicted H-1 shift of ammonia adsorbed on a zeolite cluster which containes two complete coordination spheres of O and Si around the central aluminum is 6.8 ppm. It corresponds well to the data observed for a single adsorbed NH4+ ion. The calculated H-1 chemical shifts of the two possible structure types, the neutral and the ion-pair complex, of a single adsorbed methanol molecule are 5.7 and 15.3 ppm, respectively. For complexes with a single water molecule these values are 4.5 and 12.7 ppm, respectively. Additional calculations on the ion-pair complex with a second adsorbed neutral methanol or water molecule indicate the formation of an oxonium species only for higher loadings on the Bronsted sites.