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.