OBSERVATION OF BRONSTED ACID SITES OF D-Y ZEOLITE WITH DEUTERIUM NMR

Solid-state deuterium NMR has been used to detect Bronsted acid sites and non-acidic silanols in D-exchanged zeolites. The quadrupolar coupling constant for Bronsted sites in D-Y zeolite is 234 +/- 2 kHz, and the sites are axially symmetric. This reduction by 1/4 from the water O-D coupling constant is indicative of the acidic character of the O-D bond. The acid deuterons are immobile at room temperature on a millisecond timescale. Effects of reversible adsorption of ammonia are readily monitored through changes in peaks corresponding to O-D and O--NH3D+ species.