Synthesis of microporous titanosilicate ETS-10 from TiCl3 and TiO2: a comprehensive study

Microporous and Mesoporous Materials 23 (1998) 253–263

Synthesis of microporous titanosilicate ETS-10 from TiCl3and TiO2: a comprehensive study

Joao Rocha a, Artur Ferreira a, Zhi Lin a, Michael W. Anderson b,*a Department of Chemistry, University of Aveiro, 3810 Aveiro, Portugal

b Department of Chemistry, UMIST, PO Box 88, Manchester, M60 1QD, UK

Received 14 October 1997; accepted 25 February 1998

Abstract

A comprehensive study of the hydrothermal synthesis conditions which afford pure and highly crystalline samplesof microporous titanosilicate ETS-10 from TiCl3 and crystalline TiO2 (anatase) is reported. The following parametershave been studied: fluoride ions, temperature, pH of the parent gel, sodium and potassium cations, H2O/Si and Si/Timolar ratios, seeds and time. The best ETS-10 samples are obtained after only ~15 h (TiCl3) and 24 h (anatase)hours of synthesis at 230°C and pH#10.5 with a Si/Ti molar ratio of 5–6. By carefully selecting the titanium sourcesand synthesis parameters, it is possible to obtain crystallites with sizes ranging from ~0.5 mm (anatase route) to~25 mm (TiCl3 route). The latter are the largest ETS-10 crystals reported so far. The first step in the TiCl3 synthesisis the formation of a silica–titania gel which then transforms into ETS-10. The rate-limiting step of the TiO2 route isthe slow dissolution of anatase followed by condensation with silicate species which are more readily available insolution. Good-quality ETS-10 is easily prepared in the presence of Na+ and K+, without the addition of fluorideions. If K+ is absent, the synthesis becomes a difficult task and seems to be possible only in the presence of fluorideand under strict control of other synthesis parameters. When the precursor is TiCl3, seeding with good-quality ETS-10is important, but this is not so when anatase is used. © 1998 Elsevier Science B.V. All rights reserved.

Keywords: ETS–10; Microporous; Synthesis; Titanosilicate

1. Introduction nel system whose minimum diameter is defined by12-ring apertures. The disorder arises from struc-tural faulting along planes parallel to the 12-ringETS-10 is a novel large-pore titanosilicate withchannel directions, and it is possible to describea framework consisting of ‘‘TiO2’’ rods which runthe structure in terms of an intergrowth of twoin two orthogonal directions, surrounded by tetra-ordered polymorphs with tetragonal and mono-hedral silicate units [1,2]. The pore structure con-clinic symmetry, respectively. Since ETS-10 con-sists of 12-rings, seven-rings, five-rings and three-tains corner-sharing TiO6 octahedra and corner-rings and has a three-dimensional large-pore chan-sharing SiO4 tetrahedra, for every framework tita-

* Corresponding author. Fax: +44 161 2367677. nium there is an associated charge of −2. This

1387-1811/98/$19.00 © 1998 Elsevier Science B.V. All rights reserved.PII: S1387-1811 ( 98 ) 00120-6

254 J. Rocha et al. / Microporous and Mesoporous Materials 23 (1998) 253–263

charge is compensated by extra-framework cat- at preparing highly pure and crystalline ETS-10samples containing crystallites with a wide rangeions, usually Na+ and K+.

The synthesis of ETS-10 was first reported by of sizes. In particular, we have made considerableefforts in order to increase the size of the particlesKuznicki in 1989 [3]. The Ti source was TiCl3.

Using a slight modification of this method, highly (usually <10 mm), and succeed in preparing thelargest (~25 mm) ETS-10 crystals reported so far.pure and crystalline ETS-10, suitable for structural

studies, was obtained by Anderson and Rocha and When characterising the precursors and the pro-ducts of the ETS-10 synthesis, two techniques areco-workers [1,2]. Later, others prepared ETS-10

with a range of template molecules [4–6 ]. of paramount importance, i.e. powder X-raydiffraction ( XRD) and 29Si solid-state magic-angleSivasanker and co-workers [7] improved a pre-

viously proposed method [8] based on TiCl4, and spinning (MAS) NMR. The latter in particular isquite useful since it allows the detection and esti-reported the synthesis of pure and crystalline

ETS-10 within 16 h. Liu and Thomas [9] showed mation of any siliceous amorphous phases present.In addition, by examining a very large number ofthat the crystalline forms of TiO2, anatase and

rutile can be used as adequate sources of titanium samples, we have found that the resolution of the29Si MAS NMR spectra provides the best meansin the synthesis of ETS-10. Although the early

syntheses of ETS-10 were carried out in the pres- of ascertaining the crystallinity of ETS-10 samples.For example, only the very best materials giveence of fluoride ions, a recent patent discloses a

process which is free of halide-containing reac- spectra showing well-resolved peaks at −95.8 and−96.5 ppm and at ~−94.1 ppm (see Fig. 1).tants [10].

In this paper, we report a comprehensive study Several papers discuss 1H, 23Na and 29Si MASNMR spectra of ETS-10 [1,2,11]. All the materialsof the synthesis of ETS-10 using two of the most

useful titanium sources, i.e. TiCl3 and crystalline reported in this paper have been studied by powderXRD and 29Si MAS NMR.TiO2 in the form of anatase. Specifically, we aim

2. Experimental

2.1. Typical titanium trichloride synthesis

Sodium silicate aqueous solution (20.0 g,8 w/w% Na2O, 27 w/w% SiO2, BDH) were mixedwith 15.4 g distilled water, 2.47 g sodium hydrox-ide (pro analysis, EKA Nobel ), 2.33 g sodiumchloride (Panreac) and 3.63 g potassium chloride(Panreac). When used, fluoride was introduced asKF (Aldrich). This mixture was stirred thoroughlyuntil a solution is obtained. Titanium trichloride(10.7 g) aqueous solution (1.9 M in 2.0 M HCl,Aldrich) were then added with stirring, and ahomogeneous gel formed. ETS-10 seeds (0.1 g)were added to this gel. The pH of the parent gelwas 10.6. Static crystallisation was carried out inTeflon-lined autoclaves at 230°C for 24 h. Theproducts were washed with distilled waterFig. 1. 29Si MAS NMR spectra of ETS-10 prepared from

TiCl3 and TiO2 (anatase) precursors. (~500 cm3, two slurries) filtered and dried

255J. Rocha et al. / Microporous and Mesoporous Materials 23 (1998) 253–263

2.2. Typical anatase synthesis

Sodium silicate aqueous solution (20.0 g,8 w/w% Na2O, 27 w/w% SiO2, BDH) were mixedwith 20.0 g distilled water, 6.90 g sodium chloride(Panreac) and 1.30 g potassium chloride(Panreac). When used, fluoride was introduced asKF (Aldrich). This mixture was stirred thoroughlyuntil a solution was obtained. 1.30 g anatase(Merck) were then slowly added with stirring. Theinitial synthesis pH was 10.4. Static crystallisationwas carried out in Teflon-lined autoclaves at 230°Cfor 24 h. The products were washed with distilledwater (~500 cm3, two slurries), filtered anddried overnight at 110°C. The gel compositionwas 5.2Na2O:0.5K2O:TiO2:5.5SiO2:113H2O. Bulkchemical analysis by X-ray fluorescence gives forthe final ETS-10 material a composition close to(Na1.5,K0.5)TiSi5O13. No significant amounts ofchloride were found in the syntheses products.Synthesis yields (based on Ti) were in excess of90%. The 29Si MAS NMR spectrum, powder XRDpattern and the SEM image (crystal sizes in therange 0.5–0.6 mm) of this sample are shown inFig. 2. Powder XRD patterns of of ETS-10 prepared fromFigs. 1–3a and b, respectively. Powder XRDTiCl3 and TiO2 (anatase) precursors. Asterisks depict the reflec-

tion given by anatase. revealed that ETS-10 prepared in this way con-tained a small amount of anatase (3–5 w/w%).

Powder XRD data were collected on a Rigakudiffractometer using Cu Ka radiation filtered byNi. Scanning electron microscope (SEM) imagesovernight at 110°C. The gel compositionwere recorded on a Hitachi S-4100 microscope.was 4.7Na2O:1.5K2O:TiO2:5.5SiO2:122H2O. Bulk

29Si MAS NMR spectra were recorded atchemical analysis by X-ray fluorescence gives for79.49 MHz (9.4 T) on a Bruker MSL 400P spec-the final ETS-10 material a composition close totrometer using 40° pulses, spinning rates of(Na1.5,K0.5)TiSi5O13. No significant amounts of5.0–5.5 kHz and 50 s recycle delays. When tryingchloride were found in the syntheses products.to quantify the amount of quartz or amorphousSynthesis yields (based on Ti) were in excess ofsilica present in the samples, spectra were also95%. The 29Si MAS NMR spectrum, the powderrecorded with a long recycle delay (usually 120 s).XRD pattern, and the SEM image (crystal sizeChemical shifts are quoted in ppm from TMS.~5 mm) of this sample are shown in Figs. 1, 2 andMany materials were routinely characterised by3c, respectively.energy-dispersive absorption of X-rays of singleThe synthesis of large (up to ~25 mm, Fig. 3d)crystals and bulk chemical analysis, 23Na MASETS-10 crystals was carried out using a similarNMR, Fourier transform infrared, Raman andprocedure, with the following differences: (1) nodiffuse-reflectance ultraviolet spectroscopies, andseeds were added (b) the synthesis time was longer,by thermogravimetric analysis and differentiali.e. −~60 h, and (c) a lower (Na+K)/Si molarscanning calorimetry, but these data will not beratio was used. The gel composition was

3.4Na2O:1.5K2O:TiO2:5.5SiO2:125H2O. presented here.


(a) (b)

(c) (d)

Fig. 3. SEM images of ETS-10 prepared from (a, b) TiO2 (anatase) and (c, d) TiCl3 precursors. (b) is simply an expansion of (a).The large crystals in (d) were obtained using a slight modification of the usual TiCl3 synthesis (see text).

3. Results and discussion crystalline ETS-10 was only obtained when nofluoride was used. The presence of fluoride favoursthe cocrystallisation of other phases, particularly3.1. Fluoride ionAM-3. [12] In summary, the synthesis of ETS-10from titanium trichloride does not seem to require3.1.1. Titanium trichloride synthesis

The gel composition used was 4.7Na2O: the use of fluoride ions.1.5K2O:TiO2:5.5SiO2:122H2O. The F−/Ti molarratio was varied between 0 and 3. The initial pH 3.1.2. Anatase synthesis

The gel composition used was 5.0Na2O:was 10.6, the temperature 230°C and the synthesistime two days. When the synthesis was carried out 1.3K2O:TiO2:6.0SiO2:122H2O. The F−/Ti molar

ratio was varied between 0 and 4. The initial pHwith ETS-10 seeds, the presence of fluoride ionsdid not improve the crystallinity or the purity of was 10.6, the temperature 230°C and the synthesis

time 30 h. No seeding was used. The presence ofthe final material. In contrast, the 29Si MAS NMRpeaks were slightly sharper when no fluoride ions fluoride ions had no effect on the crystallinity and

purity of the final ETS-10 material. Indeed, thewere used. If no seeds were added, pure and


29Si MAS NMR spectra display a similar reso- temperatures (and times) were 175°C (72 h) and230°C (24 h). At pH 10.3 and 175°C, ETS-10 waslution for all the F−/Ti ratios studied and the

powder XRD patterns are rather similar. The heavily contaminated with anatase (>50 w/w%)and quartz (~10 w/w%), while at 230°C highlyETS-10 samples prepared by this method may

contain a small amount of anatase which does not crystalline ETS-10 was obtained, with only a verysmall (<3 w/w%) amount of quartz. At pH 10.8decrease when fluoride ions are used. Thus, our

work shows that ETS-10 can be prepared from and 175°C poorly crystalline ETS-10 materialswere contaminated with a large (>50 w/w%)anatase without the addition of fluoride ions to

the parent gel. This is contrast with previous amount of unreacted anatase. At 230°C less ana-tase was present, but large amounts of ETS-4studies which have found that when anatase is

used the synthesis of ETS-10 does require fluo- (~40 w/w%) [3] and AM=3 (~30 w/w%) [12]cocrystallised with ETS-10. When anatase was theride. [9]titaneous precursor, the best ETS-10 samples wereobtained at 230°C and pH 10.3.

Comparing the syntheses from titanium trichlo-3.2. Temperatureride and anatase, at pH 10.3 and 175°C, it is foundthat the former yields ETS-10 contaminated with3.2.1. Titanium trichloride synthesis

The gel composition used was 4.7Na2O: amorphous silica and titania while the latteraffords ETS-10 contaminated with quartz and0.86K2O:TiO2:6.0SiO2:122H2O. Three initial pH

values were used, i.e. 10.3, 10.4 and 10.5. The anatase. This suggests that in the TiCl3 route thefirst step is the formation of a silica–titania gelsynthesis temperatures (and times) were 175°C

(120 h), 200°C (36 h) and 230°C (24 h). In this which then transforms into ETS-10. In the TiO2route, the important step is the dissolution ofrange of conditions, ETS-10 was always obtained,

but its quality varied. At pH 10.3 and 175°C, anatase followed by condensation with the silicatespecies which are more readily available inETS-10 contained a considerable amount of amor-

phous siliceous material. In addition, the powder solution.XRD pattern displayed a broad reflection at 21.5°2h given by an unknown impurity. At 200°C thispeak almost disappeared and the sample did not 3.3. pH of the parent gelseem to contain any significant amount of amor-phous material. At 230°C ETS-10 was contami- 3.3.1. Titanium trichloride synthesis

The gel composition used was 4.8Na2O:nated with only a small (<5 w/w%) amount ofquartz (not shown). At pH 10.4, all temperatures 1.1K2O:TiO2:5.5SiO2:122H2O. The synthesis tem-

perature was 230°C and the time 48 h. ETS-10afforded good-quality ETS-10 with a very small(<3 w/w %) amount of quartz. The 29Si MAS seeds were used. The pH was varied in the range

9.8–11.7. Below pH 9.8, only amorphous materialsNMR peaks were slightly sharper at higher synthe-sis temperatures (230°C), indicating that the crys- were obtained. At pH<10.0 the synthesis materials

contained mainly AM-1. Between pH 10.0 andtallinity of ETS-10 improved. The best ETS-10samples were obtained at pH 10.5. At 175°C the 10.7, and particularly at pH 10.5±0.2, good-qual-

ity ETS-10 was obtained. Above pH 10.7, ETS-4material was contaminated with a very small(<3 w/w%) amount of AM-1. [12] At 200 and was the main product.230°C the samples were pure.

3.3.2. Anatase synthesisThe gel composition used was 5.5Na2O:3.2.2. Anatase synthesis

The gel composition used was 4.6Na2O: 0.5K2O:TiO2:5.5SiO2:122H2O. The synthesis tem-perature was 230°C and the time 36 h. The pH1.5K2O:TiO2:5.6SiO2:130H2O. The F−/Ti molar

ratio was varied between 0 and 4. Two initial pH was varied in the range 2.5–12.0. No seeding wasused. At pH<9.4 the products were anatase andvalues, i.e. 10.3 and 10.8, were used. The synthesis


amorphous silica. At pH 9.8±0.4 some ETS-10 four times the usual amount. The gel compositionwas 5.2Na2O:TiO2:5.9SiO2:121H2O.formed, together with a large amount (>50 w/w%)

of quartz. Some anatase was still present. AtpH 10.4±0.2, highly crystalline and pure ETS-10

3.4.2. Anatase synthesiswas obtained. Between pH 10.6 and 11.0 the syn-

The gel composition used was 6(Na,K)2O:thesis yielded a mixture of ETS-10, ETS-4 and

TiO2:5.8SiO2:120H2O. The synthesis temperatureAM-3. Above pH 11.0, ETS-4 was the main

was 230°C and the time 36 h. The initial pH wasproduct.

10.4±0.2. Seeding was not used. Other synthesisconditions were used in selected experiments.When no potassium ions were used, the synthesisproducts were quartz and anatase. Up to about

3.4. Sodium and potassium cations %K=4% only a small amount of poorly crystallineETS-10 was obtained, contaminated with AM-3

3.4.1. Titanium trichloride synthesisand small amounts of anatase and quartz. In the

The gel composition used was 6(Na,K )2O:range 5%<%K<60%, particularly at 15±6%,

TiO2:5.5SiO2:122H2O. The potassium molar frac-very good quality ETS-10 was obtained. Above

tion is given as %K=[K2O/(Na2O+K2O)]×100. %K=60%, AM-2 formed and was the main pro-The synthesis temperature was 230°C and the time

duct at %K>80%.48 h. The initial pH was 10.5±0.2. ETS-10 seedswere used. Other synthesis conditions were usedin selected experiments. For 0%<%K<4%, no

3.5. H2O/Si molar ratio

ETS-10 was obtained, the products being AM-1and AM-3 in relative amounts which depend on

3.5.1. Titanium trichloride synthesisthe temperature and synthesis time. AM-1 formed

The gel composition used was 5.2Na2O:first, and was later converted to AM-3. For

1.3K2O:TiO2:5.5SiO2:99–550H2O. The H2O/Si4%<%K<14%, the materials contained ETS-10

molar ratio was thus varied from 18 to 100. Thecontaminated with AM-1 and AM-3. In this %K

synthesis temperature was 230°C and the timerange, the synthesis was very sensitive to pH and

60 h. The initial pH was 10.6. No seeds were used.to the presence of impurities which might act as

ETS-10 was always obtained, but the most crystal-seeds (very clean autoclaves must be used). If

line and pure samples were obtained atETS-10 seeds of excellent quality are used and the

H2O/Si#20. When this ratio was increased, thepH is 10.6, good-quality ETS-10 can be obtained

crystallinity decreased and small amounts of ETS-4with %K=12±2%. The very best ETS-10 samples

and AM-2 also formed. The habit of the crystalliteswere obtained rapidly (18–36 h) when

changed slightly with the H2O/Si ratio.14%<%K<30%. Above %K=30%, and up to60%, pure ETS-10 was obtained, but it was slightlyless crystalline. Crystallinity can, however, be 3.5.2. Anatase synthesis

The gel composition used was 5.8Na2O:improved if longer reaction times are used. When%K>60%, ETS-10 was contaminated with AM-2, 0.6K2O:TiO2:5.6SiO2:45–336H2O. The H2O/Si

molar ratio was thus varied from 8 to 60. Thewhich became the major phase above %K>80%.Using the gel composition and synthesis condi- synthesis temperature was 230°C and the time

36 h. The initial pH was 10.4. No seeds were used.tions given above, it was not possible to prepareETS-10 only with sodium cations. We have been At very low H2O/Si ratios (i.e. about 8),

only anatase and quartz crystallised. Whenable to do so using the following slight modifica-tion of the synthesis procedure given in Section 2: H2O/Si=8–13, ETS-10 was obtained, contami-

nated with some anatase. The best samples were(1) sodium fluoride (Aldrich) was added to theparent gel, which (2) is much richer in silicon, and prepared at H2O/Si#22. Above this value and up

to 55, good-quality ETS-10 was always obtained.(3) extensive seeding was used (~0.4 g), about


Fig. 4. Crystallinity of ETS-10, prepared from anatase (squares)and TiCl3 (circles), with increasing synthesis time.

Fig. 6. Selected 29Si MAS NMR spectra of the solid phasesobtained in the synthesis of ETS-10 from TiCl3. The diamonddepicts the resonance given by the AM-3 impurity.

3.6. Si/Ti molar ratio

3.6.1. Titanium trichloride synthesisThe gel composition used was 4.3Na2O:

0.8K2O:TiO2:4.0–7.0SiO2:120H2O. The synthesistemperature was 230°C and the time 48 h. Theinitial pH was 10.4. ETS-10 seeds were used. Si/Tiratios between 4.0 and about 5.0 yielded ETS-10

Fig. 5. Selected powder XRD patterns of the solid phasescontaminated with phases which were richer inobtained in the synthesis of ETS-10 from TiCl3. Diamondstitanium, usually ETS-4 and AM-1. Good-qualitydepict the reflections given by the AM-3 impurity.ETS-10 was obtained for Si/Ti ratios in the range5.0 and ~5.9. Above Si/Ti=6.0, increasingAt higher H2O/Si ratios, a small amount of quartz

and anatase formed together with ETS-10. The amounts of quartz formed. This was not unex-pected in view of the 5(Si):1(Ti) stoichiometrycrystallite habit did not seem to change much with

the H2O/Si ratio. of ETS-10.


(a) (b)

(c) (d)

Fig. 7. SEM images of the solid phases obtained in the synthesis of ETS-10 from TiCl3. The synthesis times are (a) 6, (b) 9 and (d)14.5 h. (c) is an expansion of (b).

3.6.2. Anatase synthesis 3.7. SeedsThe gel composition used was 4.5Na2O:

1.0K2O:TiO2:3–20SiO2:120H2O. The synthesis 3.7.1. Titanium trichloride synthesisThe gel composition used was 5.0Na2O:temperature was 230°C and the time 42 h. The

initial pH was 10.4. No seeds were used. Si/Ti 1.0K2O:TiO2:5.5SiO2:120H2O. The synthesis tem-perature was 230°C and the time 48 h. The initialratios between 3.0 and about 5.0 yielded ETS-10

contaminated with phases which were richer in pH was 10.5. The amount of seeds used was alwaysbetween 1 and 3 w/w% (by reference to SiO2 intitanium, usually ETS-4 and AM-3. Good-quality

ETS-10 was obtained for Si/Ti ratios in the range the parent gel ). It is important to stress that inthese studies, virgin Teflon liners and autoclaves5.0 and 6.0. ETS-10 was, however, always obtained

above Si/Ti=6.0, although the materials contained were used. However, we have found that routinesynthesis of ETS-10 can be performed in Teflonincreasing amounts of quartz.


liners thoroughly cleaned with HF and distilled sis, the materials contained a significant amountof AM-3.water. When no seeds were used the product was

usually ETS-10, with very small (<3 w/w%)amounts of ETS-4 and AM-1. Seeding with good- 3.8.2. Anatase synthesis

The gel composition used was 5.2Na2O:quality ETS-10 afforded pure ETS-10. If ETS-4seeds were used, ETS-10 with a small (3–5 w/w%) 0.8K2O:TiO2:5.5SiO2:122H2O. The synthesis tem-

perature was 230°C and the initial pH was 10.4.amount of ETS-4 was obtained. Seeding withAM-1 yielded only AM-1. This shows the impor- The best ETS-10 was obtained at ~24 h of synthe-

sis, after which the crystallinity decreased slightlytance of removing even very small amounts ofAM-1 from the synthesis system. Thus, ETS-10 and AM-3 began to crystallise. Powder XRD

(Fig. 8) revealed that the precursor materials con-seeds contaminated with AM-1 cannot be used.As already discussed, extensive seeding with tained an amorphous phase and undissolved ana-

tase. 29Si MAS NMR (Fig. 9) showed that theETS-10 crystals seems to be necessary when pre-paring ETS-10 only with sodium. siliceous amorphous phase contained Qn (n=1–4)

environments (silicon connected to n silicons viabridging oxygens), Q3 being predominant. After3.7.2. Anatase synthesis

Using the same gel composition and the condi- 5 h of synthesis, a small amount of poorly crystal-tions given for the TiCl3 route, it was found thatseeding seems to have little or no effect on anatasesynthesis.

3.8. Time

A single parent gel was prepared and portionsof it were reacted in different autoclaves. Thesyntheses were quenched in ice after given times.The materials were filtered and dried at 40°C for12 h. The degree of crystallinity was ascertainedby summing the intensity of the powder XRDreflections at 20.05, 24.60, 25.75 and 27.10° 2h andnormalising them to the corresponding sumobtained with a sample reacted for 24 h.

3.8.1. Titanium trichloride synthesisThe gel composition used was 4.9Na2O:

1.1K2O:TiO2:5.4SiO2:120H2O. The synthesis tem-perature was 230°C and the initial pH was 10.5.The most crystalline ETS-10 was obtained after14.5–24 h of synthesis (Fig. 4). Probably due topartial dissolution of the material, longer timesresulted in a material which was slightly less crys-talline. Powder XRD (Fig. 5) and 29Si MAS NMR(Fig. 6) data indicated that the starting precursormaterials were amorphous. After 6 h of synthesis,some ETS-10 began to crystallize. SEM (Fig. 7)

Fig. 8. Selected powder XRD patterns of the solid phasesshows that the crystals grew from ~2.3 mm after obtained in the synthesis of ETS-10 from TiO2 (anatase).6 h to ~5.5 mm after 14.5 h. No further growth Diamonds and asterisks depict the reflections given by the

AM-3 impurity and by unreacted anatase, respectively.was observed after this time. After 72 h of synthe-


Since it is relatively inexpensive, the latter is a veryconvenient titanium source. Moreover, by carefullyselecting the titanium precursors and synthesisparameters it is possible to obtain crystallites withsizes ranging from ~0.5 mm (anatase route) to~25 mm (TiCl3 route). The synthesis of ETS-10depends on a large number of other synthesisparameters (which we have optimised), namelytemperature, pH of the parent gel, sodium andpotassium cations, H2O/Si and Si/Ti molar ratios,seeds and time. In the absence of K+ it is difficultto prepare good-quality ETS-10. This synthesisseems to be possible only in the presence of fluorideions and under strict control of other synthesisparameters. Although the detailed ETS-10 synthe-sis mechanisms were not the main object of thispaper, we have found that (1) the first step in theTiCl3 route is the formation of a silica–titania gelwhich then transforms into ETS-10, and (2) therate-limiting step of the TiO2 route is the slowdissolution of anatase followed by condensationwith silicate species which are more readily avail-able in solution.

AcknowledgementFig. 9. Selected 29Si MAS NMR spectra of the solid phasesobtained in the synthesis of ETS-10 from TiCl3. Diamonds We would like to thank the Europeandepict the resonance given by the AM-3 impurity. Commission through Joule II for funding of A.F.,

and JNICT, PRAXIS XXI and PRODEP forgeneral funding.

line ETS-10 was formed. A large amount of ana-tase was still present in the products. From 5 to24 h of synthesis, anatase dissolved, and simulta-neously the populations of the Q2 and Q2 environ- Referencesments decreased. The broad Q3 and Q4 peakstransformed into sharp ETS-10 resonances. The [1] M.W. Anderson, O. Terasaki, T. Ohsuna, A. Phillippou,

S.P. Mackay, A. Ferreira, J. Rocha, S. Lidin, Nature 367rate-limiting step in the synthesis of ETS-10 from(1994) 347.anatase is therefore the slow dissolution of anatase.

[2] M.W. Anderson, O. Terasaki, T. Ohsuna, P.J.O. Malley,A. Phillippou, S.P. Mackay, A. Ferreira, J. Rocha, S.Lidin, Philos. Mag. B 71 (1995) 813.

[3] S.M. Kuznicki, US Patent 4 853 202, 1989.[4] V. Valtchev, S. Mintova, Zeolites 14 (1994) 697.4. Conclusions[5] V. Valtchev, J. Chem. Soc., Chem. Commun. (1994) 261.[6 ] T.Kr. Das, A.J. Chandwadkar, A.P. Budhkar, S.

Pure and highly crystalline ETS-10 can be read- Sivasanker, Microporous Mater. 5 (1996) 401.ily prepared from different titanium precursors, [7] T.Kr. Das, A.J. Chandwadkar, S. Sivasanker, Chem.

Commun. (1996) 1105.particularly TiCl3 and crystalline TiO2 (anatase).


[8] S.M. Kuznicki, K.A. Thrush, F.M. Allen, S.M. Levine, [9] X. Liu, J.K. Thomas, Chem. Commun. (1996) 1435.[10] P.W. Blosser, S.M. Kuznicki, US Patent 5 453 263, 1995.M.M. Hamil, D.T. Hayhurst, M. Mansour, in: M.L.

Occelli, H. Robson (Eds.), Synthesis of Microporous [11] X. Yang, P.W. Blosser, Zeolites 17 (1996) 237.[12] Z. Lin, J. Rocha, A. Ferreira, A.P. Esculcas, A. Philippou,Materials, Molecular Sieves, vol. I, Van Nostrand

Reinhold, New York, 1992, p. 426. M.W. Anderson, J. Phys. Chem. B 101 (1997) 7114.

Synthesis of microporous titanosilicate ETS-10 from TiCl3 and TiO2: a comprehensive study

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Transcript of Synthesis of microporous titanosilicate ETS-10 from TiCl3 and TiO2: a comprehensive study