Kinetic studies on the formation of zeolite ZSM-5

Abstract

Zeolite ZSM-5 was synthesized from sodium tetrapropylammonium aluminosilicate gels and tetrapropylammonium silicate gel. Effects of varying the ratio SiO,/AI,O, and alkalinity in the starting gels and the reaction temperature were studied. The alkalinity was found to affect the rate of nucleation more than the rate of crystal growth. An optimum alkalinity exists in the synthesis of ZSM-5; the optimum value is closely related to the value of SiO,jAl,O, ratio in the batch composition. The apparent activation energies for nucleation and crystal growth are 38 and 46 kJ mot-', respectively, for the aluminium-free silicate system and 25 and 29 kJ mot-', respectively, for the aluminosilicate system with SiO,/Al,O, = 70. The results are consistent with a complicated solution mechanism of crystallization.A newly synthesized zeolite known as ZSM-5 has interesting applications in fuel and petrochemical processing.l? ZSM-5 possesses a unique channel structure with an aperture of ca. 6 A and an unusually high silica ~o n t e n t . ~ These properties contribute to the excellent shape selectivity and steam and heat stability of ZSM-5.4 This paper reports a study of the mechanism of the formation of ZSM-5. The effects of temperature and alkalinity on the syntheses were investigated by measuring the rates of nucleation and crystal growth for selected batch compositions at various temperatures. Detailed kinetic studies on the growth and Aand near-faujasite zeolites have been reported by K e ~r , ~ Ciric,6 Lechert7 and Culfaz and Sand.H Some of their techniques have been followed in this work.

Effect of Sublimation Treatment on the Catalytic Performance of MFI Catalysts in Pyridine and 3‐Picoline Synthesis

“…These absorptions bands have been assigned to the external asymmetric stretching, internal asymmetric stretching, external symmetric stretching and the bending modes of the Si(Al)O 4 tetrahedra, respectively [16]. A characteristic band at 550 cm -1 due to the asymmetric stretching mode in double-ring blocks is observed in each of the samples [17,18], which confirms that all the samples have the MFI structure. The absorbance ratio of the bands at 550 and 450 cm -1 has been taken as a measure of IR to determine the relative crystallinity [16,18,19].…”

Catalytic behaviors of bifunctional Fe-HZSM-5 catalyst in Fischer–Tropsch synthesis

“…It has postulated that the first stage corresponded to reductions of Fe 2 O 3 to Fe 3 O 4 and CuO to Cu. The second stage corresponds to the subsequent reductions of Fe 3 O 4 to a metallic iron (Chao et al, 1981). The physically mixed Fe/HZSM-5 with binder showed a similar reduction manner with the iron catalyst but the amount of consumed hydrogen in Fe/HZSM-5 TPR profile with a binder was decreased.…”

Catalytic oxidation of pyridine on the supported copper catalysts in the presence of excess oxygen

“…Zeolite beta with a Si/Al ratio of 20 was synthesized according to the procedure reported elsewhere [10]. Zeolite ZSM-5 with a Si/Al ratio of 15 was synthesized hydrothermally at 170 • C using tetrapropylammonium hydroxide (TPAOH) as the structure-directing agent [11,12]. The mesoporous MCM-41 with a Si/Al ratio of 20 was hydrothermally synthesized at 100 • C using C 16 TMABr as a template [13,14].…”