Characterization of crystalline and amorphous phases during the synthesis of (TPA, M)-ZSM-5 zeolites (M = Li, Na, K)

Abstract

The crystallization kinetics, the composition of the various phases and the physical state of the different components are examined during the crystallization of ZSM-5 zeolite via the combined physico-chemical techniques of PIGE, EDX, atomic absorption, X.p.s., thermal analysis (TG-DTA), 29Si, 27Al, 13C, 7Li and 23Na n.m.r. A nucleation process on the gel/liquid interface and crystal growth through liquid phase transportation is evidenced. In our synthesis conditions, rather large amounts of SiOR defect groups (R = H, M or tetrapropylammonium) are present in the final crystalline phases, even at high Al contents [2–3 Al per unit cell (u.c.)]. 7Li- and 23Na-n.m.r. data indicate that in the beginning of the synthesis the small alkali cations are incorporated into the zeolitic channels as hydrated counterions to (Si—O—Al)– negative charges and later as less hydrated counterions to SiO– defect groups.