QUANTUM CALCULATIONS OF BRONSTED ACIDITY AND H-1-NMR CHEMICAL-SHIFT IN ZEOLITES

Ab initio SCF-GIAO evaluation of proton shielding constants was perfor med on two classes of cluster models, consisting of eight tetrahedra a nd two tetrahedra, to study the dependence of Bronsted acidity and H-1 NMR chemical shift on Si/Al ratio, Si-O-Al angle and metal incorporat ion (B and Ga) in zeolites. Linear correlations between H-1 NMR chemic al shift and acidity parameters were obtained. The consistency between calculated and experimental results confirms that SCF-GIAO calculatio n is a valuable method for predicting H-1 NMR chemical shift and also the acid strength of zeolites.