MTW

MTW

[Ga] ZSM-12

Si(93), Ga(7)

Contributed by Susan Lambert

Verified by K. Reddy and by M. Mertens

Type Material Na₂[Ga₂Si₂₆O₅₆] : 4 H₂O

Method S. L Lambert [1]

Batch Composition 4.5 Na₂O : Ga₂O₃ : 52.4 SiO₂ : 13.7 TEMA Br : 867 H₂O (TEMA = triethylmethylammonium)

Source Materials

deionized water
sodium hydroxide (Mallinkrodt dry pellets,> 98.5% NaOH)
gallium oxide (Alfa, 99.99%)
triethylmethylammonium bromide (TEMA Br) (Fluka, purum)
silica sol (Dupont Ludox AS-40, 40% Si0₂)^a

Batch Preparation (for 13 g dry product)

(1) [21.72 g NaOH + 37.04 g water + 11.37 g Ga₂O₃], heat in a closed pressure vessel (Teflon-lined Parr acid digestion bomb) at 110¡C for 23 hours
(2) [4.65 g of solution (1) + 29.22 g water + 10.78 g TEMA Br], stir until dissolved
(3) [(2) + (31.47 g silica sol + 11.63 g H₂O)], add diluted silica sol to (2) with stirring using an eye dropper over course of 15 min. Batch pH 13-14 ^b

Crystallization

Vessel: two Teflon-lined Parr acid digestion bombs (125 mL)
Time: 20 days ^c
Temperature: 150¡C
Agitation: none

Product Recovery

(1) Supernatant liquid pH 12.5
(2) Filter and wash with 600 mL distilled water
(3) Dry at l00⁰C
(4) Yield: 13.64 g white solids (12.25 g volatile free), 91% recovery on SiO₂or 87% on Ga₂O₃

Product Characterization

XRD: MTW framework by comparison to ZSM- 12 crystallinity reference, best is [Al] MTN.
Minor impurity: cristobalite; no other phases present
Elemental Analyses (volatile-free): 93.4% SiO₂, 5.35% Ga₂O₃, 0.62% Na₂O, 0.14%Al₂O₃.
Loss on ignition at 900^¡C: 10.17% ^dMolar Composition: 0.35 Na₂O : 0.05 A1₂O₃ : Ga₂O₃: 54.4 SiO₂: 22 H₂O ^e
Click here to view XRD pattern

Reference

[1] S. L Lambert in Proceedings of the 9th international Zeolite Conference, R. von Ballmoos, J. B. Higgins, M. M. J. Treacy (eds.), Butterworth-Heinemann, London, 1993, P. 223

Notes

a. Dupontâs Ludox HS-40 is an acceptable substitute.

b. pH values were measured with ColorpHast pH indicator paper (range 5-10 or 7.5-14, from E. M. Science, Gibbstown, NJ, USA)

c. Crystallinity vs. (Al) ZSM-12 reference: 70% after 16 days, 88% after 18 days, 90% after 20 days. The crystallization proceeds more rapidly as the amount of gallium in the synthesis batch is reduced.

d. Template burnout occurs at 460⁰C in air.

e. By ²⁹Si MAS NMR, Si/(Ga + Al) = 14; excess SiO₂by elemental analysis is attributed to amorphous silica. ^7lGa static NMR one symmetrical Ga line at 158.5 ppm
(ref. Ga(N0₃)₃).