Microporous and Mesoporous Materials 150 (2012) 7–13
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Simple, efficient syntheses of zeolite ZSM-11 (MEL) at temperatures below 100 °C using very dense gels C.A. Fyfe a,⇑, Z.S. Lin a, C. Tong a, R.J. Darton b,⇑ a b
Chemistry Department, University of British Columbia, 2036 Main Mall, Vancouver, British Columbia, Canada V6T 1Z1 School of Physical and Geographical Sciences, Keele University, Keele, Staffordshire ST5 5BG, UK
a r t i c l e
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Article history: Received 15 July 2011 Received in revised form 12 September 2011 Accepted 14 September 2011 Available online 20 September 2011 Keywords: High-silica zeolites Low-temperature synthesis Dense gels MEL
a b s t r a c t The synthesis of pure phase ZSM-11 (MEL) at temperatures below 100 °C has been achieved using extremely dense gels with minimal water contents. Both hydroxide and fluoride routes were investigated using N,N-diethyl-3,5-dimethylpiperidinium and 2,2-diethoxyethyltrimethylammonium based templates. Highly crystalline materials were successfully synthesised within relatively short reaction times using a wide range of reaction conditions. The syntheses are shown to be not as efficient as the related ZSM-5 (MFI) materials, suggesting that the structure directing power of the template molecules is critical for low temperature reactions. Ó 2011 Elsevier Inc. All rights reserved.
1. Introduction There are obvious advantages in performing hydrothermal syntheses below 100 °C and this is possible and efficient for a number of low-silica zeolites such as zeolites A, X, and Y [1–3]. In the case of high silica zeolites, a number of researchers have studied the ZSM-5 system [4–13] even to the stage of industrially relevant processes [14–18]. However, these reactions were limited by long reaction times or the use of seeding, stirring or high template to silica ratios. No successful studies of other high-silica zeolites using reaction temperatures below 100 °C have been reported. In previous work [19] we reported on various syntheses of the zeolite ZSM-5 (MFI) at temperatures below 100 °C using very dense synthesis gels. These syntheses were very efficient, needed only very simple apparatus and worked in both high pH and fluoride media and with a variety of silica sources. The motivation behind these studies was to see if the expected lowering of reaction rates at lower temperatures could be compensated for by the higher concentrations of reactive species in extremely dense synthesis gels where the water to silicon ratios were between 3 and 8. The general idea behind these experiments should be applicable to other high silica zeolite syntheses and we presently report the results of a similar investigation of zeolite ZSM-11, structure type MEL [20], that is very closely related to zeolite ZSM-5, structure type (MFI) [21], but has been much less well studied and charac-
terized. The two syntheses differ mainly in the quaternary ammonium ion templates used, tetrabutyl ammonium and tetrapropyl ammonium, respectively. While ZSM-5 and its variants are very widely used both as high volume industrial catalysts as well as in a myriad of high value niche applications and as host framework for various intercalated active species [22], ZSM-11 has not seen such development. It was realized after the framework structure was established that the original tetrabutyl ammonium-templated syntheses yielded materials that were, to greater or lesser degrees, intergrowths containing ZSM-5 [23]. More recently, other templates for the synthesis of ZSM-11 have been introduced by Nakagawa [24] and Zones and co-workers [25–28] and by Piccione and Davis [29] and it has been shown that these templates yield the phase-pure MEL framework, free of any MFI-type intergrowths. In the present paper, we present our findings from an investigation of the synthesis of zeolite ZSM-11 (MEL) system, carried out at 90 °C using very dense synthesis gels with minimal water contents. It should be noted that these syntheses of MEL presently reported enjoy the same advantages of simplicity, efficiency, low cost and the use of simple inexpensive equipment as did the previous MFI experiments [19]. 2. Experimental 2.1. Materials
⇑ Corresponding authors. E-mail addresses:
[email protected] (C.A. Fyfe),
[email protected] (R.J. Darton). 1387-1811/$ - see front matter Ó 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.micromeso.2011.09.021
All materials used were from commercial sources: fumed silica (
