Microporous and Mesoporous Materials 150 (2012) 7–13

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Microporous and Mesoporous Materials

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Simple, efficient syntheses of zeolite ZSM-11 (MEL) at temperatures below 100 �Cusing very dense gels

C.A. Fyfe a,⇑, Z.S. Lin a, C. Tong a, R.J. Darton b,⇑a Chemistry Department, University of British Columbia, 2036 Main Mall, Vancouver, British Columbia, Canada V6T 1Z1b School of Physical and Geographical Sciences, Keele University, Keele, Staffordshire ST5 5BG, UK

a r t i c l e i n f o a b s t r a c t

Article history:Received 15 July 2011Received in revised form 12 September2011Accepted 14 September 2011Available online 20 September 2011

Keywords:High-silica zeolitesLow-temperature synthesisDense gelsMEL

1387-1811/$ - see front matter � 2011 Elsevier Inc. Adoi:10.1016/j.micromeso.2011.09.021

⇑ Corresponding authors.E-mail addresses: fyfe@chem.ubc.ca (C.A. Fyfe),

(R.J. Darton).

The synthesis of pure phase ZSM-11 (MEL) at temperatures below 100 �C has been achieved using extre-mely dense gels with minimal water contents. Both hydroxide and fluoride routes were investigatedusing N,N-diethyl-3,5-dimethylpiperidinium and 2,2-diethoxyethyltrimethylammonium based tem-plates. Highly crystalline materials were successfully synthesised within relatively short reaction timesusing a wide range of reaction conditions. The syntheses are shown to be not as efficient as the relatedZSM-5 (MFI) materials, suggesting that the structure directing power of the template molecules is criticalfor low temperature reactions.

� 2011 Elsevier Inc. All rights reserved.

1. Introduction terized. The two syntheses differ mainly in the quaternary ammo-

There are obvious advantages in performing hydrothermal syn-theses below 100 �C and this is possible and efficient for a numberof low-silica zeolites such as zeolites A, X, and Y [1–3]. In the caseof high silica zeolites, a number of researchers have studied theZSM-5 system [4–13] even to the stage of industrially relevant pro-cesses [14–18]. However, these reactions were limited by longreaction times or the use of seeding, stirring or high template to sil-ica ratios. No successful studies of other high-silica zeolites usingreaction temperatures below 100 �C have been reported.

In previous work [19] we reported on various syntheses of thezeolite ZSM-5 (MFI) at temperatures below 100 �C using verydense synthesis gels. These syntheses were very efficient, neededonly very simple apparatus and worked in both high pH and fluo-ride media and with a variety of silica sources. The motivation be-hind these studies was to see if the expected lowering of reactionrates at lower temperatures could be compensated for by the high-er concentrations of reactive species in extremely dense synthesisgels where the water to silicon ratios were between 3 and 8.

The general idea behind these experiments should be applicableto other high silica zeolite syntheses and we presently report theresults of a similar investigation of zeolite ZSM-11, structure typeMEL [20], that is very closely related to zeolite ZSM-5, structuretype (MFI) [21], but has been much less well studied and charac-

ll rights reserved.

r.j.darton@chem.keele.ac.uk

nium ion templates used, tetrabutyl ammonium and tetrapropylammonium, respectively. While ZSM-5 and its variants are verywidely used both as high volume industrial catalysts as well asin a myriad of high value niche applications and as host frameworkfor various intercalated active species [22], ZSM-11 has not seensuch development. It was realized after the framework structurewas established that the original tetrabutyl ammonium-templatedsyntheses yielded materials that were, to greater or lesser degrees,intergrowths containing ZSM-5 [23].

More recently, other templates for the synthesis of ZSM-11 havebeen introduced by Nakagawa [24] and Zones and co-workers[25–28] and by Piccione and Davis [29] and it has been shown thatthese templates yield the phase-pure MEL framework, free of anyMFI-type intergrowths.

In the present paper, we present our findings from an investiga-tion of the synthesis of zeolite ZSM-11 (MEL) system, carried out at90 �C using very dense synthesis gels with minimal water contents.It should be noted that these syntheses of MEL presently reportedenjoy the same advantages of simplicity, efficiency, low cost andthe use of simple inexpensive equipment as did the previous MFIexperiments [19].

2. Experimental

2.1. Materials

All materials used were from commercial sources: fumed silica(<1% water), Sigma S-2128; colloidal silica, Ludox (30%) HS-30 Du

8 C.A. Fyfe et al. / Microporous and Mesoporous Materials 150 (2012) 7–13

Pont, Ludox (40%) HS-40 and Ludox (50%) Sigma TM-50; alumin-ium sulphate, Fisher; tetrapropylammonium hydroxide, Aldrich;tetrapropylammonium bromide, Acros Organics; sodium hydrox-ide, ammonium fluoride, Fisher; tetrabutylammonium bromide,Aldrich; tetrabutylammonium hydroxide, Aldrich.

N,N-Diethyl-3,5-dimethylpiperidinium iodide (DECDMPI) (I)was synthesized from 3,5-dimethylpiperidine (Aldrich) and iodo-ethane (Aldrich) and 2,2-diethoxyethyltrimethylammonium iodide(DEOTAI) (II) from 2,2-diethoxy-N,N-ethyldimethylethylamine(Aldrich) and methyl iodide (Aldrich), as previously described[24,29]. The two templates were converted to their hydroxideforms by successive exchanges with excess basic ion exchange re-sin (Amberlite A-26(OH), Aldrich) in aqueous solution. The hydrox-ide concentration was determined by titration against standardHCl and the solution concentrated appropriately for use in thesyntheses.

(I) (II)

2.2. Syntheses

Appropriate amounts of SiO2 (fumed silica or Ludox) and tem-plate as the hydroxide, iodide or bromide were added together ina suitable reaction vessel, as described below, and sodium hydrox-ide, ammonium fluoride and distilled water added as required forthe different syntheses. The components were thoroughly mixedby hand until the mixture was homogeneous, the resulting reac-tion mixtures ranging from dry powders to gels to liquids inappearance. The vessel was then sealed and heated at 90 �C in anoven. There was no obvious decomposition of either template un-der these conditions and it was found that the syntheses weremore reproducible if as large a fraction as possible of the internalvolume was filled with the reactant mixture.

In contrast to the MFI syntheses previously studied [19] where30 ml Nalgene polypropylene bottles sufficed, because the reactionsin the present work were slower, the slow loss of water from theseover extended periods became important. Fluorinated ethylene pro-pylene (FEP) and perfluoralkoxy polymer resin (PFA) bottles werefound to seal better and were preferable to polypropylene for thepresent work. In addition, some reaction mixtures were sealed in25 ml glass ampoules or in conventional Teflon-lined stainless steelautoclaves to eliminate water loss completely. All reactions werecarried out at 90 �C under static conditions in a conventional oven.

After the required time, the reaction was quenched and the sam-ples subsequently treated by two cycles of dilution with water andisolation of the solid products by centrifugation at 3500–4500 rpmfor up to 1 h before being dried at 90 �C. To qualitatively probe thereaction profiles, some reactions were monitored by taking samplesat different times to ascertain when crystallization took place.Based on these, more quantitative data were obtained from a seriesof identical reactions quenched after different reaction times.

2.3. Analyses

Electron microscopy experiments were performed on a HitachiS-2300 system using graphite as conductive coating. Powder

X-ray diffraction patterns were obtained from Bruker D8 Advanceand Discover diffractometers using a flat disc sample holder and1.0 mm capillary samples respectively. Solid state NMR measure-ments were performed using a Bruker Avance 400 spectrometeroperating at frequencies of 400.13, 376.55, 104.267, 100.622 and79.494 MHz for 1H, 19F, 27Al, 13C and 29Si respectively, using Brukerprobes with either 7 or 4 mm MAS rotors. 29Si chemical shifts werereferenced to tetramethylsilane (TMS) with Q8M8 (the octamerSi8O12[OSi(CH3)3]8) as external secondary reference, 19F shifts toCFCl3 using octadecasil as external secondary reference (d =�38.2 ppm), 27Al shifts to 1 M aluminium nitrate aqueous solutionas external reference and 13C chemical shifts to TMS with adaman-tane as an external secondary reference. Further experimental de-tails are given in the figure captions.

3. Results and discussion

Both high pH and fluoride syntheses were investigated for bothDECDMP and DEOTA templates. A full range of reaction conditionswere studied, using both fumed silica and Ludox solutions as silicasources and hydroxide, iodide and bromide forms of the templates.In some cases, specific reaction mixtures were investigated in moredetail in order to optimize the reaction times.

For ease of presentation, these data are presented separately. Ingeneral terms, the reactions are slower and less forgiving andreproducible than the analogous syntheses of MFI using the tetra-propylammonium ion described previously. It was also necessaryto increase the water contents of the dense gels somewhat in orderto obtain reasonably homogeneous mixtures due to the lower sol-ubility of the organic templates.

3.1. Previous high pH syntheses at high temperatures using DECDMPtemplate

The most quantitative data on the reactions of the DECDMPtemplate come from the original Nakagawa patent [24] wherethe examples presented were carried out at moderate tempera-tures (150–170 �C) and had reaction times mostly in the range of7–21 days and H2O:SiO2 ratios of between 20 and 50, althoughno yields were given for these reactions. The example closest tothe present work was the synthesis of the completely siliceousframework using fumed silica which was carried out at 160 �C witha H2O:SiO2 ratio of 38.5 and took only 3 days. However, seedingwas used in this example. Subsequent papers on this and relatedpyrrolidinium ion-based templates [25–28] focused primarily onattempting to elucidate the factors important in the templatingprocess and to identify the frameworks formed, but provide noquantitative measures (yields, reaction times) of the relative effi-ciencies of the different synthesis procedures.

3.2. DECDMP hydroxide syntheses

Our initial synthesis used a dense gel of composition(1.0SiO2:0.18DECDMPOH:0.1NaOH:13.46H2O) formed by thor-oughly hand-mixing 1.0 g of fumed silica in a 30 ml polypropylenebottle with 3.0 g of 1.0 M DECDMPOH template solution and 1.66 gof 1.0 M NaOH. This produced a high yield of phase-pure MEL in7 days at 90 �C. However, subsequent repeat syntheses were muchless reproducible and all had longer reaction times. Lack of repro-ducibility emerged as a general characteristic of syntheses usingthis template and more systematic studies were carried out.

In a synthesis using a slightly less than stoichiometric amountof template, 1.0 g of fumed silica was mixed by hand with 3.0 gof 0.43 M DECDMPOH solution and 1.66 g of 1.0 M NaOH yieldinga homogeneous gel with the oxide formula; 1.0SiO2:0.075DEC-

Fig. 2. 29Si NMR spectra of MEL produced using DECDMPOH/NaOH and fumedsilica. (a) Single pulse NMR spectrum of as-synthesized sample; 1754 scans, 60 sdelay, 50 Hz linebroadening. (b) CPMAS spectrum of as-synthesized sample; 16,152scans, 5 s delay, 7.0 ms contact time, 1.0 Hz linebroadening. (c) Single pulse NMRspectrum of sample calcined at 350/500 �C; 984 scans, 60 s delay, 0.0 Hz linebro-adening. (d) CPMAS spectrum of sample calcined at 350/500 �C; 10478 scans, 10 sdelay, 7.0 ms contact time, 50 Hz linebroadening. (e) Single pulse NMR spectrum ofsample calcined at 350/500/600 �C; 1208 scans, 60 s delay, 0.0 Hz linebroadening.

C.A. Fyfe et al. / Microporous and Mesoporous Materials 150 (2012) 7–13 9

DMP+:0.17OH�:14.4H2O. Reaction at 90 �C produced MEL in40 days, crystallization taking place in 36–40 days, yield 0.53 g.

The reaction was found to be sensitive to the water content:increasing it by adding 1.0 g distilled water to give an H2O:SiO2 ra-tio of 17.8:1 increased the reaction time to between 50 and 58 daysin duplicate experiments. Yields were between 0.5 and 0.6 g.

The XRD patterns of all the samples are identical, as are the SEMimages, and typical examples are shown in Fig. 1a and b. The XRDpatterns indicate the materials are all very highly crystalline with asingle sharp reflection at 45.2� 2h, characteristic of the MEL struc-ture and clearly show the weak reflection at 18.7� 2h, indicative ofphase pure MEL material [23]. The SEM images show the crystalsto be very well defined, approximately cubic and with dimensionsof ca. 5 � 7 lm.

13C and 29Si solid state NMR spectra were obtained to character-ize the general structural perfection of the as-synthesized materi-als. The 13C CP MAS spectrum (not shown) indicated that thetemplate was intact, with chemical shift values close to those ob-served in solution. Fig. 2 shows both single pulse and CP MAS29Si spectra. The single pulse spectrum used a 60 s delay and isan approximate measure of the different Q3 (SiOH) and Q4 siliconlocal co-ordinations. It shows a relatively large Q3 signal, 30% ofthe total intensity, suggesting that the framework is imperfectlyformed in detail. However, the Q3 signal is much smaller relativeto the Q4 in the CP MAS spectrum. In amorphous silica, it is known[30] that the Q3 SiOH resonance is greatly enhanced relative to theQ4 at the short contact time used here, suggesting that the tem-plate protons are the most important source of silicon magnetiza-tion for these MEL materials. In turn, this indicates that thetemplate is in intimate contact with the framework silicons in acompact structure with the atoms in positions very close to thoseof the calcined framework.

Further information comes from the 29Si spectra shown in Fig. 2of samples at various stages of calcination produced from the samesample whose data are shown in the previous figures. After a firstcalcination at 350 �C for 3 h followed by 18 h at 500 �C, there is adrastic change in the spectrum. The single pulse spectrum nowshows only a small Q3 signal but very intense Q4 resonances, whilethe CP MAS spectrum shows only broad and weak Q3 and Q4 res-onances. Taken together, these indicate that the template has beencleanly removed and the CP magnetization probably arises fromprotons in residual SiOH groups. A second treatment at 600 �Cfor 18 h further reduces the Q3 signal so that it is not easily obser-vable in the single pulse experiment at all while the sharpness ofthe Q4 resonances increases, some five chemical shift resolved sig-nals now being clearly observable. This indicates that the frame-work is perfectly intact, intergrowth free and that the healing ofSiOH defect sites is very efficient during the simple calcination pro-cesses. Such observations have not been previously reported andthe resolution of the final spectrum is quite close to that of the best

Fig. 1. (a) Powder XRD pattern and (b) SEM image (magnification 100

sample reported in the literature that shows 11 closely spaced butresolved signals out of the 12 expected [31,32] for the emptyframework at room temperature. However, that sample had beenextensively steam-treated at elevated temperatures and less crys-talline material removed by digestion with hydroxide. The qualityof the current samples could probably also be improved further bysteaming. Calcination at 800 �C destroys the framework, producingamorphous material.

The chemical shift resolution of these spectra of the calcinedmaterials not only indicates efficient healing of the framework pro-ducing very highly crystalline material, but they also provide avery sensitive test of the phase purity of this material, complemen-tary to the information from X-ray diffraction, as the presence ofeven small amounts of MFI intergrowth destroys the perfectionof the local ordering, resulting in the calcined material showing asingle broad featureless absorption characteristic of a calcinedsample of phase-impure MEL containing MFI intergrowths pre-pared using tetrabutylammonium ion template at 90 �C with anoxide formula of 1SiO2:0.07NBu4

+:0.07OH�:10.8H2O.

0�) of MEL produced using DECDMPOH/NaOH and fumed silica.

10 C.A. Fyfe et al. / Microporous and Mesoporous Materials 150 (2012) 7–13

To reduce the reaction time further, the DECDMP template con-centration was increased by using a 1 M solution of the templatehydroxide. Reaction at 90 �C of gels of identical composition(1.0SiO2:0.18DECDMP+:0.28OH�:16.7 H2O) yielded 0.6 and 1.0 gof product after 28 and 37 days, respectively, reducing the reactiontime somewhat, although the template to silicon ratio is nowgreater than stoichiometric. The materials are of similar qualityto those described above, produced at a lower template concentra-tion. For comparison, a similar reaction mixture at 150 �C yielded0.63 g MEL in 14 days.

Seeding the above reaction at 90 �C with calcined, phase-pureMEL increased the yield to 0.91 g, but the reaction time was stilllong at 35 days.

3.3. DECDMP halide plus hydroxide syntheses

Mixing 1 g fumed silica with 0.4 g DECDMPI (approximately stoi-chiometric), 2 g 1 M NaOH and 3.0 g H2O by hand gave a gel (oxidecomposition 1.0SiO2:0.08DECDMP+:0.12OH�:16.5H2O) which re-acted at 90 �C to give 0.75 g MEL after 12 days. In a series of exper-iments with this gel composition, near quantitative yields werereliably obtained in less than 34 days, crystallization taking placebetween 17 and 34 days for the slowest reactions. The XRD, SEMand NMR data from a representative sample are shown in Fig. 3and indicate that the MEL produced is again highly crystalline,phase-pure and has a well defined morphology, again cubic withapproximate dimensions 4 � 4 � 6 lm. Calcination again yielded

Fig. 3. (a) Powder XRD pattern. (b) SEM image (magnification 1000�) of MEL producsynthesized sample; 7016 scans, 10 s delay time,100 Hz linebroadening. (d) CPMAS speclinebroadening. (e) Single pulse NMR spectrum of sample calcined at 350/500 �C; 2342

material whose 29Si spectra showed considerable resolution and lit-tle Q3 intensity, again indicative of phase-pure material.

Doubling the amount of template to 0.8 g (1.0SiO2:0.16DEC-DMP+:0.12OH�:16.5H2O) substantially reduced the reaction time,near quantitative yields now being obtained in �21 days. Reducingthe water content while keeping the other reactants constant at1.0 g fumed silica, 0.8 g DECDMPI and 2.0 g 1 M NaOH had little ef-fect on the reaction time for H2O/Si ratios of 16.5 and 21.4, butreducing it to H2O/Si = 8.25 decreased the time to 14–21 days,within the general range reported for reactions at 160, 170 �C.These were the most reproducible and efficient of the reactionswith fumed silica under very basic conditions.

Kinetic curves generated from the XRD intensities of the majorreflections of a series of identical syntheses quenched after differ-ent reaction times were obtained for several different reactioncompositions. They all showed the expected behavior with an ini-tiation period and then a relatively sharp growth curve, followedby slower growth to the limiting product yield.

3.4. DECDMP halide reactions with Ludox

Interestingly, it was found that Ludox as a silicon source gavemuch more reproducible reactions. Near quantitative yields wereobtained in 21 days or less in a series of reactions from oxide gelsof oxide composition (1.0SiO2:0.08DECDMP+:0.12OH�:9.81H2O)made with Ludox 30% as the silicon source and with minimal wateradded other than that present in the colloidal silica.

ed using DECDMPI/NaOH and fumed silica. (c) Single pulse NMR spectrum of as-trum of as-synthesized sample; 5602 scans, 3 s delay time, 7 ms contact time, 50 Hzscans, 30 s delay time, 0.0 Hz linebroadening.

C.A. Fyfe et al. / Microporous and Mesoporous Materials 150 (2012) 7–13 11

Increasing the template concentration twofold had little effecton the rate of the reaction. Only phase pure MEL was obtainedwhen glass ampules were used, while a small Magadiite impuritywas also present when Teflon bottles were used. The reasons forthis are unclear at present, but may be due to the slight loss ofwater from the Telfon bottle reactions over time. Surprisingly,seeding increased the reaction time to 28–32 days but still gave al-most quantitative yields.

3.5. Introduction of aluminium

It was possible to introduce aluminium using aluminium sul-phate and seeding the reaction for both fumed silica and 30% Lu-dox, but the reaction times are longer at 70 and 30–54 days,respectively. 27Al MAS NMR spectra show a single resonance at�47 ppm, indicating that it is tetrahedral and incorporated intothe framework.

3.6. Mixed template syntheses

Although the tetrabutylammonium ion templated synthesis de-scribed earlier gave intergrown material, it was, however, fasterthan those using DECDMP template, giving quantitative yields in13–18 days and syntheses using a mixture of the two templateswere investigated in the hope that they would have the attractivefeatures of both. Unfortunately, although the reaction times wereeven shorter (3–14 days), only intergrown MEL/MFI type materialswere obtained.

3.7. Fluoride syntheses using DECDMPI template and NH4F

Synthesis mixtures of 1.0 g fumed silica, 0.4 g DECDMPI, 3.0 gH2O and 1.5 g NH4F (oxide composition 1.0SiO2:0.08DEC-DMP+:2.43F�:10.1H2O) gave between 0.6 and 0.7 g of product,identified as phase-pure MEL by XRD, in reaction times between

Fig. 4. (a) Powder XRD pattern, (b) SEM image (magnification 3000�) of MEL produce(magnification 1000�) of MEL produced using DECDMPI/ NH4F with seeding.

30 and 60 days. For comparison, reaction of the same gel composi-tion, but at 150 �C gave 0.8 g product in 12 days.

These results were disappointing, but it was found that in thissynthesis method, seeding had a huge effect, on both yield andreaction time. Thus, multiple syntheses using gels of exactly theoxide composition above, but seeded with 0.05 g calcined MELgave near quantitative yields of material in between 7 and 20 days.

Substituting 30% Ludox as the silica source giving a reaction mix-ture with a lower water content (oxide composition 1.0SiO2:0.08DECDMP+:2.44F�:7.78H2O), while still seeding, gave 0.76 g productin less than 13 days.

All of the samples described above show very similar XRD andSEM patterns, of which typical examples are shown in Fig. 4a–d.The XRD results indicate both phase purity and a high degree ofcrystallinity. The crystals are well defined, but now have a nee-dle-shaped morphology in contrast to those from the high pH syn-theses and are considerably larger as expected for fluoride basedsyntheses.

The 29Si spectra of all these samples (Fig. 5) confirm the perfec-tion of the frameworks, the Q3 resonance being much smaller thanthose of samples from the corresponding high pH syntheses andthere is a small broad resonance at �155 ppm, consistent with fivecoordinate silicon with a covalently bonded fluorine [33]. The lowrelative intensity of the signal for the five coordinate Si is similar tothat observed for fluoride containing ZSM-5 (F-MFI) at low tem-peratures and the lack of a doublet splitting and the broadeningcould suggest that there is some degree of initial exchange takingplace as seen in other fluoride containing higher silica zeolites[34]. Calcination yields a spectrum with clear chemical shift reso-lution, confirming the perfection of the samples.

The 19F fast spinning MAS spectrum shows two isotropic peakswith associated spinning sidebands similar to the correspondingspectrum of F-MFI as well as a broad background signal from theprobe. The major signal at -64 ppm is in the general range observedfor fluorine covalently bonded to silicon, confirming this structuralunit. The presence of a second signal at -75 ppm is similar to the

d using DECDMPI/NH4F without seeding, (c) powder XRD pattern, (d) SEM image

Fig. 5. NMR spectra of MEL produced using DECDMPI/ NH4F with seeding (a) 29SiCPMAS spectrum of as-synthesized sample; 11,660 scans, 5 s delay, 7.0 ms contacttime,100 Hz linebroadening, (b) 29Si single pulse NMR spectrum of sample calcinedat 350/500 �C; 6412 scans, 10 s delay, 0.0 Hz linebroadening, (c) fast spinning 19Fsingle pulse NMR spectrum of as-synthesized sample; vR = 12.0 kHz, 2082 scans,200.0 Hz linebroadening.

12 C.A. Fyfe et al. / Microporous and Mesoporous Materials 150 (2012) 7–13

situation in F-MFI, but has a higher relative intensity. It is not pos-sible to deduce its local environment from the data presentlyavailable.

3.8. High pH syntheses using DEOTA template

The basic gel composition used by Piccione and Davis [29] was1.0SiO2:0.60DEOTAOH:24.7H2O with the silica source being LudoxHS-30 or AS-40 (DuPont). Of note are the relatively high water con-tents and the large excess of template, about five times the stoichi-ometric quantity. The reaction temperature was 135 �C, abovewhich template decomposition was reported while amorphous orlayered materials were reported at lower temperatures. With Lu-dox silica alone, the reaction time was quite long (41 days) andthe yield very low (15%). Addition of Na+, K+ ions increased therates and improved the yields. Interestingly, the use of 24% cal-cined MFI as part of the silica source greatly increased the yieldsfor similar reaction times. Finally, combining this with the additionof Na+, K+ ions gave high yields after 22 days of reaction.

3.9. High pH syntheses using DEOTA at 90 �C

One gram of fumed silica was mixed with 3.4 g of 0.37 M DEO-TAOH and 1 g of distilled water, oxide formula 1.0SiO2:0.08DEO-TA+:13.9H2O. The mixture was sealed in a small glass ampouleand placed in an oven at 90 �C. After 90 days there was a clear sep-aration of solid material from supernatant liquid. The solid was iso-lated by centrifugation (0.34 g) and washed and identified as veryhigh quality, phase-pure MEL from its powder XRD pattern and themorphology was approximately cubic. The 29Si spectrum of the cal-cined material (not shown) shows clear chemical shift resolutionas described above for the corresponding materials made with

DECDMP+ as template, confirming the phase purity. However, thereaction time is even longer than for those syntheses.

Various attempts were made to shorten the synthesis time,including seeding, the use of Ludox and using DEOTAI and sodiumhydroxide. Reproducibility was a major problem and in the lattersystem this was compounded by the formation of magadiite asco-product. For example, in one of the best syntheses, reaction of1.0 g fumed silica with 1.04 g of DEOTAI, 2.0 g of 1.0 M NaOHand 3.0 g of distilled water gave 0.90 g of phase-pure MEL in26 days, crystallization taking place between 12 and 26 days. How-ever, a duplicate reaction but with seeding yielded MEL with mag-adiite as major co-product in 25 days. Reducing the added water inthe original reaction to 1.0 g yielded only magadiite after�120 days. It is possible that progress could be made by usingpotassium hydroxide, but this avenue was not pursued due tothe very long reaction times and high variability of the experi-ments to this point. Fluoride syntheses were also unsuccessful.

4. Conclusions

It is clear from the results that low temperature syntheses ofhigh silica zeolites are not limited to the case of MFI/TPA+ origi-nally reported and that pure phase MEL can be synthesised at90 �C with both DECDMP and DEOTA templates as reported earlierfor reactions at higher temperature. Syntheses of both MEL andMFI at 90 �C show similar characteristics to more traditional highertemperature syntheses. MFI reactions are, however, significantlymore efficient in terms of both reaction time and reproducibilityindicating that the structure directing power of the template mol-ecules is critical to both syntheses. This suggests that structuredirecting templates that are highly efficient and selective at hightemperatures are likely to be the best candidates for lower temper-ature syntheses and further work to address this is currently inprogress.

Acknowledgements

The authors would like to acknowledge the financial support ofthe Natural Sciences and Engineering Research Council (NSERC) ofCanada in the form of Discovery and Major Equipment grants(C.A.F.) and the award of a Summer Studentship (C.T.). They wouldalso like to acknowledge the assistance of Dr. P. Sidhu in obtainingthe initial NMR spectra and Ms. Anita Lam and Ms. Mary Mager inobtaining the powder XRD and SEM data, respectively.

Appendix A. Supplementary data

Supplementary data associated with this article can be found, inthe online version, at doi:10.1016/j.micromeso.2011.09.021.

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