COADSORPTION OF AMMONIA AND METHANOL ON H-ZEOLITES AND ALKALINE-EXCHANGED ZEOLITES

The interactions of methanol and ammonia on H-zeolites (H-Z) and alkal ine-exchanged zeolites (Na-Z) have been investigated using Hartree-Foc k (HF) and density functional theory (DFT) approaches. Full optimizati on of all clusters and their complexes has been optimized at B3LYP/6-3 1G and HF/6-31G* theoretical levels. The reaction mechanism of coadso rption of methanol and ammonia on H-Z is that the ammonia is found to bound to the Bronsted acid site of H-Z, yielding ammonium cation, whic h in turn operates as an active site for methanol. The result of coads orption processes indicates that the stronger base ammonia is preferen tially bonded to the Bronsted acid sites of H-Z, while methanol is int eracted with the Lewis acid of Na-Z. Our findings are in excellent agr eement with very recently reported data (Kogelbauer, A., Grundling, G. , Lercher, J.A., J. Phys. Chem. 100 (1996) 1852-1837). (C) 1997 Elsevi er Science B.V.