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

Recently developed NMR methods reveal that the acid sites of zeolite B eta are complex. Variable-temperature H-1 and H-1{Al-27} spin echo dou ble-resonance magic scale spinning measurements showed that the proton s 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 n arrow resonance at 4.1 ppm and a broader resonance at 5.5 ppm. C-13 sh ifts of adsorbed acetonitrile and acetone suggest a Bronsted acid stre ngth intermediate between zeolites HZSM-5 and HY, as well as possible complexation with an unusual aluminum site associated with the framewo rk that was observed by Al-27 NMR.