Characterization of defects in dealuminated faujasite

A NaY zeolite was dealuminated with SiCl 4 vapor. Subsequent acid washing of this sample gave a dealuminated Y (DAY) that had an aluminum content of 120 ppm. Both i.r. spectroscopy and 29 Si n.m.r. techniques (Bloch Decay and cross-polarization) detected several different types of SiOH present in the DAY. Additionally, n.m.r. determined that a small fraction of the sample contained amorphous Si(OSi) 4 groups. Steaming of the DAY at 800 K resulted in a partial removal of both the SiOH groups and the amorphous material, neither of which could be detected by n.m.r. after steaming at 973 K. The defect sites were shown to react with trimethylsilylchloride. We detect at least three different types of SiOH defects, and none of them can be associated with residual framework aluminum.