MULTINUCLEAR NMR-STUDIES REVEAL A COMPLEX ACID FUNCTION FOR ZEOLITE-BETA

Recently developed NMR methods reveal that the acid sites of zeolite Beta are complex. Variable-temperature H-1 and H-1{Al-27} spin echo double-resonance magic scale spinning measurements showed that the protons associated with aluminum gave a narrow resonance at 4.5 ppm at 123 K, but upon warming to 298 K, this intensity was redistributed into a narrow resonance at 4.1 ppm and a broader resonance at 5.5 ppm. C-13 shifts of adsorbed acetonitrile and acetone suggest a Bronsted acid strength intermediate between zeolites HZSM-5 and HY, as well as possible complexation with an unusual aluminum site associated with the framework that was observed by Al-27 NMR.