AL-27 AND SI-29 MAS NMR-STUDY OF ZEOLITE MCM-22

Zeolite MCM-22 was studied by Al-27 and Si-29 NMR with magic angle spi nning (MAS). Bloch-decay and cross-polarization spectra were compared and assigned for as-synthesized and calcined samples with various Al c ontent. The interpretation was assisted by Al-27 quadrupole nutation N MR, It was found that the average Si-O-Si angles corresponding to ineq uivalent framework tetrahedral sites vary from 138 degrees to 163 degr ees. The as-synthesized and calcined materials both contain two kinds of framework tetrahedral Al, but the calcined zeolite also contains tw o kinds of extraframework octahedral Al. Such results can be interpret ed on the basis of the MCM-22 structure proposed by Leonowicz et al. ( Science 1994, 264, 1910). However, the detailed assignment of the Si(O Al) peaks is still open to discussion.