MTT

ZSM-23

Si(97), Al(3)

Contributed by Stefan Ernst

Verified by R Ravishankar and by Wha-Seung Ahn

Type Material Na[AlSi23O48] wH2O (w » 4)

Method S. Ernst, R Kumar, J. Weitkamp [1]

Batch Composition 20.6Na2O : Al2O3: 100SiO2 : 4610H2O: 46.2Pyrr: 18.8 H2SO4

Source Materials

demineralized water
sodium hydroxide, reagent grade (Riedel-de Haen)
pyrogenic silica (Cab-o-Sil M5 ) a
pyrrolidine (Pyrr), (Fluka)
aluminum sulfate (Al2(SO4)3. 18H2O, Fluka)
sulfuric acid (96 wt% H2SO4, Fluka)

Batch Preparation (for 14 g product) b

(1) [195.8 g water + 4.40 g sodium hydroxide], mix until dissolved
(2) [(1) + 16.5 g silica], add silica to solution (1) over the course of ~5 minutes under continuous stirring
(3) [24.4 g water + 8.81 g pyrrolidine + 1.79 g aluminum sulfate], mix until dissolved
(4) [(2) + (3)], add solution (3) to solution (2) with good mixing
(5) [(4) + 4.33 g sulfuric acid], add acid dropwise with stirring; final gel pH = 12.6

Crystallization

Vessel: stainless steel autoclave (300 mL) c
Temperature: 180¡C
Time: 50 hours
Agitation: autoclaves are rotated ~30/minutes

Product Recovery

(1) Cool and filter
(2) Wash extensively with demineralized water
(3) Dry at 100¼C for 16 hours
(4) Yield: approx. 14 g

Product Characterization

XRD: MTT (only crystalline phase), competing phases: MFI (contaminated autoclave)
cristobalite (occasional overheating, or pH too high)
Elemental Analysis: SiO2/Al2O3 = 78 (AFS/ICP) d
Crystal Size and Habit: bundles of needles e

Click here to view XRD pattern

Reference

[1] S. Ernst, R Kumar, J. Weitkamp, in Zeolite Synthesis, Am. Chem. Soc. Symposium Series 398, M. Occelli, H. Robson (eds.), 1989, pp 560-573

Notes

a. Cab-O-Sil M5 must be used; other silica sources, such as silica sol or sodium silicate, lead to different products.

b. The synthesis has been successfully scaled up to a 5 liter autoclave (stirring rate:
120/minutes, yield: 250 g).

c. The crystallization vessels have to be cleaned very thoroughly in order to avoid seeding effects from residual crystallites of ZSM-5, for example.

d. With pyrrolidine as template, the molar ratio can be varied between 70 and 150.

e. Platelet-like ~1 um can be synthesized using C7diquat [(CH3)3N-(CH2)7-N(CH3)3]Br2 as template. [1]