synthesis of off-type zeolite in a quasi non aqueous medium: structure directing role of p-dioxane...

Microporous and Mesoporous Materials 29 (1999) 405–412

Synthesis of OFF-type zeolite in a quasi non aqueous medium:structure directing role of p-dioxane and alkaline cations

A. Matijasic, J. Patarin *Laboratoire de Materiaux Mineraux, ENSCMu, Universite de Haute Alsace, UPRES-A 7016, 3 rue Alfred Werner,

F-68093 Mulhouse Cedex, France

Received 25 September 1998; received in revised form 7 December 1998; accepted 8 December 1998

Abstract

Syntheses were performed at 150°C with the starting composition 10 SiO2:1 Al2O3:a Na2O:b A2O:c p-dioxane:dH2O where A represents an alkaline cation (K, Rb, Cs and Li). In the presence of potassium a pure OFF-type zeoliteis obtained for a Na/K molar ratio equal to 2, independently of the p-dioxane content. The OFF-type solids werecharacterized by XRD, SEM 29Si and 27Al MAS NMR spectroscopy. Using 13C CP MAS NMR spectroscopy,thermal and chemical analysis, one molecule of p-dioxane was found per unit cell; it is probably trapped in thegmelinite cage (1 cage per unit cell ) as a complex with sodium. Indeed, in the absence of sodium, an LTL-type zeolitefree of p-dioxane crystallizes. Concerning the other alkaline cations (Rb, Cs and Li), an OFF-type material wasobtained with rubidium, cesium directs the synthesis toward analcime, whereas no real structure-directing effect wasobserved for lithium. Indeed, in the latter case, a mixture of GIS-, MAZ-, MOR- or SOD-type zeolites was obtained.© 1999 Elsevier Science B.V. All rights reserved.

Keywords: OFF-type zeolite; Quasi non-aqueous medium; Structure-directing agent; Synthesis

1. Introduction and therefore the interaction capacity with thereacting species, leading to a modification of thecrystallization process. In fact, the crystallizationHydrothermal treatment (water as solvent) isdepends on the hydrogen-bonding capacity, thethe classical route for the synthesis of zeolites [1].viscosity and the basicity of the solvent as well asHowever, in recent years several zeolites and zeo-on the starting chemical composition [6 ]. Anlites-like materials have also been obtained fromincrease in viscosity of the solvent leads to annon-aqueous or quasi non-aqueous mixtures. Thisincrease in crystallization time. This is because thewas the case, for instance, for sodalite [2],rate of crystal growth is directly proportional tosilicalite-1 [3], ZSM-39 [3], ZSM-48 [3] or omegathe diffusion constant for mass transfer, which is[4] but also for aluminophosphates such as JDF-20inversely proportional to the viscosity. Organic[5]. The use of such non-aqueous media leads tosolvents can be classified in four categories basednew crystallization pathways. The addition ofon their ability to form hydrogen bonds [7]: high,organic solvents changes the viscosity of the mediahigh-medium, low-medium and non-hydrogen-bonding. In the first group, i.e. high hydrogen-* Corresponding author. Tel.: +33 3 8942 7020;bonding capacity, the solvent prevents the frame-Fax: +33 3 8942 8730;

E-mail address: [email protected] (J. Patarin) work units from interacting with the template

1387-1811/99/$ – see front matter © 1999 Elsevier Science B.V. All rights reserved.PII: S1387-1811 ( 99 ) 00009-8

406 A. Matijasic, J. Patarin / Microporous and Mesoporous Materials 29 (1999) 405–412

because the dissolution of silica is hindered and no The sources of alkaline cations were KOH(Prolabo, 86% KOH ), Rb2O (Ventron, 99%),crystalline product is obtained. For high–medium

and low–medium hydrogen-bonding solvents, the LiOH · H2O (Fluka, 99%) and CsOH · H2O(Aldrich, 99%).interactions are easier; they are for this reason more

efficient in synthesis. Finally, in the case of non-hydrogen-bonding solvents, the silica particles 2.2. Synthesis procedureaggregate and form a dense silica network.

In some cases the organic solvent can influence The samples were obtained by solvothermalthe chemical composition of the material obtained synthesis at 150°C. The molar composition ofand plays a structure-directing role besides its the starting mixture was 10 SiO2:1 Al2O3:asolvating role. Thus, a pure silica sodalite has been Na2O:b A2O:c p-dioxane:d H2O, with a+b=2.5synthesized in the presence of ethylene glycol [2] and A representing K, Rb, Cs or Li. c and d arewhich was found to be trapped inside the sodalite expressed as wt.% with c+d=100. The totalcages of the structure. amount of solvent, on a mass basis, was equal to

Recently, MAZ-type zeolite was prepared using 200 mol of water.glycerol [8] or p-dioxane [4] as the main solvent The starting mixture was prepared by dissolvingwith no other organic species. In an aqueous NaOH and the source of alkaline cation in watermedium such a zeolite was prepared in the presence under stirring. Then p-dioxane was added and theof sodium and tetramethylammonium (TMA+) sodium aluminate. Finally, the silica source wascations [9], the latter being located inside the rapidly introduced into the thoroughly stirred solu-gmelinite cages of the structure. It seems that for tion. For a high organic content (>60 wt.%) fumedthe MAZ-type zeolite synthesized in the presence silica was used, whereas for a low organic contentof p-dioxane, the cyclic ether is also trapped in the (<60 wt.%) silica sol was employed.same cages probably forming a complex with After aging for 24 h under magnetic stirring,sodium thus mimicking the role of TMA+ [10]. the gels were transferred into PTFE-lined stainless

It is well known that in the aqueous system steel autoclaves. The crystallization was carriedSiO2–Al2O3–H2O–K2O, the presence of potassium out at 150°C under static conditions. After 6 dayscations leads to the formation of KFI-, LTL- and the products were recovered, washed with distilledOFF-type zeolites. Recently, the latter phase was water until neutral pH and then dried at 60°Calso obtained by Yang et al. [11] using glycerol as overnight.solvent and in the presence of potassium. In the As an example, for sample A (Table 1) 0.64 gpresent work, the influence of the nature of the of NaOH and 0.34 g of KOH was mixed withalkaline cation (mainly potassium) was studied for 3.6 g of water. Then 23 g of p-dioxane and 1.36 galuminosilicate gels prepared in the presence of of sodium aluminate were successively added. Atvarious amounts of p-dioxane. The products last 4.96 g of Ludox AS-40 were introducedobtained were characterized by several techniques under stirring.such as XRD, TG/DSC, elemental analysis, SEM In some cases, particularly for p-dioxane-richand solid-state NMR spectroscopy. mixtures, a phase separation was observed leading

to two liquid phases.

2. Experimental2.3. Thermal analysis

2.1. ReactantsPrior to analysis, the solids were kept in a wet

atmosphere over a saturated aqueous solution ofThe reactants were p-dioxane (Aldrich, 99.8%),sodium aluminate (Carlo Erba, 56% Al2O3, 37% NH4Cl (P/P0=0.85) for 24 h to set the hydration

state. Differential scanning calorimetry (DSC) andNa2O), sodium hydroxide (Fluka p.a.). Twodifferent types of silica sources were employed; thermogravimetric (TG) analyses were performed

on a Setaram TG DSC 111 microanalyser. Thefumed silica (Zeosil, 9.7% H2O) or a silica sol(Ludox AS-40, 40% SiO2, 60% H2O). samples were heated under air at 6°C min−1.

407A. Matijasic, J. Patarin / Microporous and Mesoporous Materials 29 (1999) 405–412

Table 1Typical synthesis conditions and products obtained in the presence of p-dioxane. 10 SiO2:1 Al2O3:a Na2O:b K2O:c p-dioxane:d H2O, a+b=2.5, c and d are expressed as wt.% with c+d=100

Sample Molar reaction mixture composition Solvent (wt.%) Products

a Na2O b K2O c p-dioxane d H2O

A 2.15 0.35 85 15 OFFB 1.87 0.62 85 15 OFFC 0 2.5 85 15 LTLDa 3.34 1.11 10 90 OFFE 1.67 0.83 85 15 OFFF 0 2.5 10 90 LTLG 1.67 0.83 10 90 OFFH 1.87 0.62 35 65 OFF+ imp.bI 1.87 0.62 60 40 OFF

a For this sample the OH−/Si molar ratio was equal to 0.9 as in Ref. [10].b Impurity, not identified.

Table 22.4. Powder X-ray diffractionRecording conditions of the MAS and CP MAS NMR spectra

The powder X-ray diffraction patterns were 29Si 27Al 13Cobtained on a STOE STADI-P diffractometer equ-

Chemical shift standard TMS Al(H2O)3+6 TMSipped with a curved germanium (111) primaryFrequency (MHz) 59.63 104.26 75.47monochromator and a linear position-sensitiveRecycle time (s) 2 1 8

detector using Cu Ka1 radiation. The unit cell Pulse width (10−6 s) 4 0.7 6.5parameters were refined using the STOE software Contact time (10−3 s) – – 1

Spinning rate (Hz) 4100 10000 3600program package, silicon being used as an internalNumber of scans 440 65 1200standard.

2.5. Chemical analysis relation [12] was used to determine the Si/Al ratio:

The analysis of Si and Al was performed byatomic absorption spectroscopy. The amount of Si

Al=

∑n=04

IT1

Si(nAl )+IT2

Si(nAl )

∑n=04

0.25n[IT1

Si(nAl )+IT2

Si(nAl )]water and organic species of the as-made materialswas determined by thermogravimetry. Carbonanalysis was also performed by coulometric deter-

where ITi

Si(nAl ) are the intensities of the resonancemination after calcination of the samples at 1050°Clines resulting from silicon atoms occupyingunder air.Ti-type tetrahedral sites (i=1 or 2) and having n

aluminum nearest neighbors (n=0, 1, 2, 3 or 4).2.6. 29Si, 27Al and 13C solid-state magic anglespinning (MAS) NMR spectroscopy

3. Results and discussionThe 29Si MAS and 13C CP MAS NMR spectrawere recorded on a Bruker MSL 300 and the 27Al 3.1. Synthesis, crystal morphology and chemicalMAS spectra on a Bruker DSX 400 spectrometer; compositionthe recording conditions are given in Table 2.

As the OFF-type structure shows two distinct In Table 1 the typical synthesis examples arereported using a mixture of potassium and sodiumcrystallographic sites, T1 and T2, the following


as alkaline cations in the presence of various i.e., 85 wt.%, and assuming that the crystallizationprocess occurs in the aqueous phase, the alkalinityamounts of p-dioxane and for a OH−/Si molar

ratio equal to 0.5. A better representation of the of the latter (minor phase compared with theorganic phase) is probably higher than would beresults obtained is given in Figure 1.

From Fig. 1 and Table 1 it is clear that at a expected in the absence of phase separation, thusleading (in the presence of sodium (Na/K>0)) tohigh p-dioxane content (85 wt.%) and in the pres-

ence of Na and whatever the Na/K molar ratio, a the formation of OFF-type zeolite. In contrast, fora low organic content (10 wt.%), the alkalinity ofpure OFF-type material is obtained (samples A,

B, E). However, in the absence of Na an LTL- the aqueous phase is comparatively low, favoringthe formation of materials such as mordenite,type material crystallizes independent of the p-

dioxane content in the starting mixture (samples which is known to crystallize at a relatively lowalkalinity. This is confirmed by the fact that anC and F). For low Na/K molar ratios, the use of

p-dioxane as a structure-directing agent (10 wt.%) OFF-type material is obtained (sample D, Table 1)at higher alkalinity (OH−/Si=0.9) even at a lowleads to offretite (sample G). When the sodium

content increases, a mixture of MOR-, GIS- and p-dioxane content (10 wt.%) [10].As an example, the XRD pattern of the OFF-OFF-type zeolites is observed. For intermediate

concentrations of the cyclic ether in the starting type sample A is given in Fig. 2. This pattern canbe unambiguously indexed in the hexagonal sym-gel, the results obtained depend on the Na/K ratio.

A potassium-rich mixture (Na/K≤3) leads to metry with the unit-cell parameters a=b=13.265(1) A, c=7.550(1) A.offretite (samples H and I ), whereas, as previously

reported [4], an MAZ-type zeolite appears as The fact that the crystallization process occursin the aqueous phase is confirmed by the compari-by-product for sodium-rich gels (Na/K#6). Even

if the phase separation process was only observed son of the scanning electron micrographs of theoffretite samples prepared at high (85 wt.%, samplein some cases (see Section 2), the results seem to

show that this phenomenon occurs systematically A, Fig. 3a) and low (10 wt.%, sample G, Fig. 3b)p-dioxane content. At 10 wt.% p-dioxane, isolatedwhen the p-dioxane content in the gel is too high.

Under these conditions (high p-dioxane contents), crystals were obtained with a morphology similarto that of samples prepared by hydrothermal syn-thesis, i.e. hexagonal rod-like with a size rangingfrom 8 to 15 mm. However, at 85 wt.% p-dioxane,the crystals display a similar morphology (hexago-nal prisms) but are mainly aggregated. Such aggre-

Fig. 1. Type of products obtained as a function of the Na/Kstarting molar ratio and the solvent composition (the majority

Fig. 2. Powder XRD pattern of the OFF-type sample Aphase is underlined and the reference of the sample is indicatedin parentheses). (Cu Ka1).


Table 3Influence of the nature of the alkaline cations on the productsobtained for syntheses performed in the presence of tetramethyl-ammonium cations [13] and p-dioxane (this work) respectively

TMA+ [13] p-dioxane (this work)

TMA+, K+�OFF p-dioxane, K+�LTLTMA+, K+, Na+�OFF, p-dioxane, K+, Na+:

MAZ p-dioxane>60 wt.%�OFFp-dioxane<60 wt.%�OFF(Na/K≤3) or OFF+MAZ(Na/K>3)

TMA+, Na+�MAZ p-dioxane, Na+�MAZ [4,10]

a pure MAZ-type zeolite crystallizes, whereas, inthe presence of potassium, a pure OFF-type mate-rial is obtained. When both sodium and potassiumcations are present, the final product correspondsto a mixture of OFF- and MAZ-type materials.Concerning the syntheses performed in the pres-ence of p-dioxane as solvent ( p-dioxane>60 wt.%), it appears clearly that the key-point for forming offretite is the simultaneouspresence of potassium cations and the sodium/p-dioxane pair (see Table 3), the latter structuringthe MAZ-type [4,10] as well as the OFF-typezeolites. Both structures are characterized by thepresence of gmelinite cages (one per unit cell ). Inthe case of the MAZ-type phase, Zones [10] sug-gested that a sodium/p-dioxane complex might beincorporated in these cages, thus mimicking the

(a)

(b)

Fig. 3. Scanning electron micrographs of OFF-type samples: (a) role of the tetramethylammonium (TMA+) cationsample A; (b) sample G. in hydrothermal synthesis.

The chemical analysis (Table 4) performed onpure offretite samples shows undoubtedly the pres-gates are typical of crystals growing in a very

concentrated medium, which is the case for ence of p-dioxane in the as-synthesized materials.This is also confirmed by thermal analysis (seesamples A, B and E.

A major point for the synthesis of OFF-type below). Whatever the Na/K molar ratio, aboutone molecule of p-dioxane per unit cell is presentzeolite with p-dioxane as main solvent (85 wt.%)

is that sodium is needed besides potassium in the in the OFF-type samples, which is in goodagreement with the location of the organic speciesstarting mixtures. Indeed, as was seen above, in

the absence of sodium (Na/K molar ratio equal in the gmelinite cages (one per unit cell ).Nevertheless, whatever the p-dioxane content into 0), an LTL-type zeolite free of p-dioxane crystal-

lizes (sample C, Table 1). The structure-directing the starting mixture, the sodium content in theas-synthesized materials is relatively high and, ineffect of the alkaline cation (Na+, K+) in TMA-

containing aqueous aluminosilicate gels was all cases, higher than would be expected if thesodium cations were present only as sodium/p-studied by Breck [13], and the main results are

summarized in Table 3. In the presence of sodium, dioxane complexes.


Table 4Chemical composition (wt.%) of the as-synthesized OFF-type samples

Sample Si Al K Na H2O Organic species Si/Al molar ratio p-Dioxane/unit cell

TGa CAb NMRc CAb

A 25.2 7.4 3.4 6.4 11.0 4.0 3.6 2.9 3.4 1B 24.6 7.5 5.6 4.2 11.2 3.8 3.2 3.0 3.3 1

a Determined by thermogravimetric analysis.b Determined by chemical analysis.c Determined by 29Si MAS NMR spectroscopy.

The results obtained show that an organic resolution of the peaks, the signal due toSi(0Al )T

2

is not observed, thus leading to anmedium does not affect the Si/Al molar ratio ofthe zeolitic samples. The latter, close to 3.4, is underestimation of the Si/Al ratio (Table 4) as

determined from the relation given in the experi-quite similar to that obtained for materials pre-pared in aqueous medium with TMA as template mental section. This phenomenon of underestima-

tion has been reported previously in the literature[14].[16 ].

The 27Al NMR spectrum of the as-synthesized3.2. 29Si, 27Al and 13C solid-state NMRspectroscopy OFF-material (sample A), reported in Fig. 5, dis-

plays one main component at 57.5 ppm corre-sponding to aluminum in a four-fold coordination.The 29Si NMR spectrum (Fig. 4) of sample A

is relatively noisy and consists of three peaks A very small component at 10 ppm, which isprobably due to traces of amorphous material, iswith the chemical shifts −97.9, −102.9 and

−106.9 ppm, respectively. According to also observed. The latter component disappearsafter calcination and only one signal is observedEngelhardt and Michel [12], and Occelli et al. [15]

these three components can be assigned to in the spectrum of the calcined and fully rehydratedsample (Fig. 5b).Si(3Al )T

2

+Si(2Al )T1

, Si(2Al )T2

+Si(1Al )T1

andSi(1Al )T

2

+Si(0Al )T1

groups. Because of the low The 13C CP MAS NMR spectrum of theas-synthesized OFF-type zeolite (Fig. 6) consistsof a single but relatively broad resonance at68.7 ppm (reference TMS). Such a chemical shiftis in good agreement with that determined by 13Cliquid NMR spectroscopy for the p-dioxane mole-cule. The broadness of this signal might be due tothe interactions of p-dioxane with sodium cations,reinforcing the hypothesis of the presence of asodium/p-dioxane complex in the OFF-typematerials.

3.3. Thermal analysis

The DSC and TG curves of the as-synthesizedsample A performed under air are given in Fig. 7.Two steps of weight losses are observed on theTG curve, at 200 and 450°C, respectively. The first

Fig. 4. 29Si MAS NMR spectrum of the OFF-type sample A. one (10.9 wt.%) corresponds to the removal of


Fig. 7. Thermal analysis of the OFF-type sample A performedunder air: (a) TG; (b) DSC.

adsorbed water and leads to an endothermic peakon the DSC curve. The second weight loss (7 wt.%)which corresponds to an exothermic peak, with amaximum at 450°C on the DSC curve, is due tothe decomposition of the organic species occludedin the structure.

3.4. Synthesis from p-dioxane-containingaluminosilicate gels in the presence of other alkalinecations (Na, Rb; Na, Cs; Na, Li)

Fig. 5. 27Al MAS NMR spectra of the OFF-type sample A: (a)as synthesized; (b) calcined. The different results obtained are summarized

in Table 5. In the presence of rubidium and for aNa/Rb molar ratio in the starting mixture close to3, a pure OFF-type material is obtained whateverthe p-dioxane content. For a higher ratio

Table 5Synthesis from p-dioxane-containing aluminosilicate gels in thepresence of other alkaline cations (Na, Rb; Na, Cs; Na, Li),10 SiO2:1 Al2O3:a Na2O:b A2O:c p-dioxane:d H2O, a+b=2.5,c and d are expressed as wt.% with c+d=100

A Na/A molar Product formed versus p-dioxane contentratio

c=10 wt.% c=85 wt.%

Rb 6 OFF + MAZ OFF + MAZ (e)3 OFF OFF

Cs 6 MAZa+ ANA ANA + MAZ3 ANA+ MAZ ANA

Li 6 MOR + GIS MAZ + SOD2 MOR + MAZ Not identified

Fig. 6. 13C CP MAS NMR spectrum of the OFF-type sample A. a The underlined phases are the majority phases.


(Na/Rb=6), similar results are observed; never- was also studied. An OFF-type material wasobtained with rubidium, while cesium directs thetheless, mazzite co-crystallizes a at low p-dioxane

content. Such a result was expected since the synthesis toward analcime. No real structure-directing effect was observed for lithium, a mixtureaffinity of the OFF-type structure for the rubidium

cation is well documented in the literature [10,11]. of GIS-, MAZ-, MOR- or SOD-type zeolites beingobtained.The presence of cesium cations in the p-dioxane-

containing aluminosilicate gels seems to favor theformation of ANA-type zeolite. The structure-directing effect increases with the Cs content, a Acknowledgementpure ANA-type phase being obtained for a Na/Csmolar ratio close to 3. The authors would like to thank Dr. H. Kessler

for fruitful discussions.In the case of lithium, no specific structure-directing effect is observed whatever the organiccontent and the Na/Li molar ratio. Indeed, amixture of GIS-, MAZ-, MOR- or SOD-type Referenceszeolites was obtained.

[1] R.M Barrer, Hydrothermal Chemistry in Zeolites, Aca-demic Press, London, 1982.

[2] D.M. Bibby, N.I. Baxter, D. Grant-Taylor, L.M. Parker,Zeolite Synthesis, M.L. Occelli, H.E. Robinson (Eds.),

4. Conclusion ACS Symp. Ser. 398 (1989) 209.[3] Q.S. Huo, S.H. Feng, R.R. Xue, J. Chem. Soc., Chem.

Commun. (1988) 1486.The synthesis of zeolite materials in p-dioxane[4] B. De Witte, J. Patarin, J.L. Guth, T. Cholley, Micro-media was investigated. For the composition 10

porous Mater. 10 (1997) 247.SiO2:1 Al2O3:a Na2O:b A2O:c p-dioxane:d H2O,[5] Q. Huo, R. Xu, S. Li, Z. Ma, J.M. Thomas, R.H. Jones,

where A represents an alkaline cation ( K, Rb, Cs A.M. Chippindale, J. Chem. Soc., Chem. Commun.and Li), the products obtained depend strongly (1992) 875.

[6 ] S. Nadimi, S. Olivier, A. Kuperman, A. Lough, G.A. Ozin,on the nature of the alkaline cation. In the presenceJ.M. Garces, M.M. Olken, P. Rudolf, in: Zeolites andof potassium and for a Na/K molar ratio lowerRelated Microporous Materials: State of the Art, J.than 3, a pure OFF-type zeolite was obtainedWeitkamp, H.G. Karge, H. Pfeifer, W. Holderich

whatever the p-dioxane content. Nevertheless, in (Eds.), Studies in Surface Science and Catalysis Vol. 84,the absence of sodium cations (Na/K#0), a pure Part A, Elsevier, Amsterdam, 1994, p. 93.

[7] R.E. Morris, S.J. Weigel, Chem. Soc. Rev. 26 (1997) 309.LTL-type phase free of p-dioxane crystallizes. As[8] S. Yang, N.P. Evmiridis, in: Zeolite and Related Micro-was previously reported for the synthesis of MAZ-

porous Materials, J. Weitkamp, H.G. Karge, H. Pfeifer,type zeolite [4], the key-point for the synthesis ofW. Holderich (Eds.), Studies in Surface Science and Catal-

an OFF-type material performed in a p-dioxane ysis Vol. 84, Part A , Elsevier, Amsterdam, 1994, p. 155.medium seems to be the formation of a sodium/p- [9] R. Aiello, R.M. Barrer, J. Chem. Soc. A (1970) 1470.

[10] S.I. Zones, in: M.L. Occelli, H. Kessler (Eds.), Synthesisdioxane complex, which acts as a template for theof Porous Materials, Zeolites, Clays and Nanostructures,gmelinite cages of the structure, thus mimickingDekker, New York, 1996, p. 93.the role of the tetramethylammonium (TMA+)

[11] S. Yang, N.P. Evmiridis, Microporous Mater. 6 (1996) 19.cations in the hydrothermal synthesis. Indeed, one [12] G. Engelhardt, D. Michel, High Resolution Solid Statep-dioxane molecule per unit cell, probably located NMR of Silicates and Zeolites, Wiley, Chichester, 1987.

[13] D.W. Breck, Zeolite Molecular Sieves, Wiley, New York,in the gmelinite cages (1 per unit cell ), was found1974.in the as-synthesized sample. Moreover, the results

[14] R. Aiello, R.M. Barrer, J.A. Davies, I.S. Kerr, Trans. Fara-seem to show that the crystallization process occursday Soc. 66 (1970) 1610.

essentially in the aqueous phase. [15] M.L. Occelli, G.P. Ritz, P.S. Iyer, R.D. Walker, B.C.The presence of other cations such as rubidium, Gerstein, Zeolites 9 (1989) 104.

[16 ] J.H. Raeder, Zeolites 4 (1984) 311.cesium and lithium, in such an organic medium,

synthesis of off-type zeolite in a quasi non aqueous medium: structure directing role of p-dioxane...

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