Synthesis of the Small Pore Silicoaluminophosphate STA-6 by Using

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Synthesis of the Small Pore Silicoaluminophosphate STA‑6 by Using Supramolecular Self-Assembled Organic Structure Directing Agents Raquel Martínez-Franco, Á ngel Cantín, Manuel Moliner,* and Avelino Corma* Instituto de Tecnología Química, Universidad Politécnica de Valencia - Consejo Superior de Investigaciones Científicas (UPV-CSIC), Valencia 46022, Spain ABSTRACT: By means of organic structure directing agents (OSDA) formed by bulky paired quinolinium derived molecules, obtained by self-assembled monomers, it has been possible to synthesize for the first time the pure silicoaluminophosphate form of the small pore STA-6 zeotype. This synthesis method allows obtaining samples with very well dispersed framework silicon atoms, opening the possibility for its use in catalysis.

1.-. INTRODUCTION Recently, small pore molecular sieves containing large cavities have received significant attention as efficient catalysts for methanol to olefins (MTO), selective catalytic reduction (SCR) of NOx, as well as for gas separation applications.1 These important applications have motivated the synthesis of small pore zeolites with new pore topologies,2 different crystallite size,3 and different chemical compositions. Among them, we can include silicoaluminates, silicoaluminophosphates [SAPOs], or metalloaluminophosphates [MeAlPOs],4 with the adequate heteroatom distribution.5 The optimized small pore zeolites show improved physicochemical properties, such as higher acidities, good hydrothermal stabilities, catalytic activities, and interesting gas separation properties.6 Most of the methodologies reported in the literature for the synthesis of small pore zeolites with large cavities are based on the use of bulky and cyclic organic structure directing agents (OSDAs).1 The choice of these OSDAs seems reasonable in order to fill the large cavities, with the relationship observed between the properties of the OSDA and the size/shape of the cavity being remarkable.7 A very interesting example of the excellent host−guest fitting between the OSDA and the zeolitic cavity can be found for the small pore metalloaluminophosphate STA-6 zeotype (the IZA code of this material is SAS).8 STA-6 is a small pore zeotype with a monodimensional channel system connected by large cavities (see Figure 1). In this case, different bulky macrocyclic polyamines, such as 1,4,8,11-tetraazacyclotetradecane (cyclam), 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (tmtact), and 1,4,7,10,13,16-hexamethyl-1,4,7,10,13,16-hexaazacyclooctadecane (hmhaco), show the adequate shape/size to selectively template the SAS cavity, proceeding as very efficient OSDAs for this material.2e,8,9 © 2014 American Chemical Society

Figure 1. Structure of the STA-6 zeotype.

The incorporation of different elements in the framework has a significant effect on the acid properties and thermal stability of these AlPO-related materials.10 It is broadly described in the literature that if the Si atoms are isolated within the structure, the SAPO form will show higher acidity and thermal stability than other MeAlPO forms of the same zeotype.11 If this was so, it should be of interest to synthesize the STA-6 zeotype in their silicoaluminophosphate form. Unfortunately, this synthesis remained elusive,12 and some attempts to synthesize the silicoaluminophosphate form of STA-6 using the abovedescribed azamacrocyles resulted in a mixture of phases.12 Several years ago, Corma et al. introduced a new concept for the preparation of bulky OSDAs based on the supra-molecular self-assembling of aromatic molecules.13 In this case, two Received: February 28, 2014 Revised: July 8, 2014 Published: July 10, 2014 4346

dx.doi.org/10.1021/cm5005483 | Chem. Mater. 2014, 26, 4346−4353

Chemistry of Materials

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temperature was held for 8 h under flowing air; and third, the samples were cooled to room temperature under flowing N2. 2.2.-. Characterization. Powder X-ray diffraction (PXRD) measurements were performed with a multisample Philips X’Pert diffractometer equipped with a graphite monochromator, operating at 45 kV and 40 mA, and usig Cu Kα radiation (λ = 0.1542 nm). The chemical analyses were carried out in a Varian 715-ES ICPOptical Emission spectrometer, after solid dissolution in HNO3/HCl/ HF aqueous solution. The organic content of the as-made materials was determined by elemental analysis performed with a SCHN FISONS elemental analyzer. Thermogravimetrical analysis was performed using a Mettler Toledo thermo-balance. The morphology of the samples was studied by scanning electron microscopy (SEM) using a JEOL JSM-6300 microscope. MAS NMR spectra were recorded at room temperature with a Bruker AV 400 spectrometer. 29Si NMR spectra were recorded with a spinning rate of 5 kHz at 79.459 MHz with a 55° pulse length of 3.5 μs and repetition time of 180 s. 27Al MAS NMR spectra were recorded at 104.2 MHz with a spinning rate of 10 kHz and a 9° pulse length of 0.5 μs with a 1 s repetition time. Solid-state 31P NMR spectra were recorded at 161.9 MHz with a spinning rate of 10 kHz, a π/2 pulse of 5 μs with 20 s repetition time. 13C MAS NMR cross-polarization (CP) spectrum was recorded at a sample spinning rate of 5 kHz. 29Si, 27Al, 31 P, and 13C chemical shifts were referenced to tetramethylsilane, Al3+(H2O)6, 85% H3PO4, and adamantane, respectively. UV−vis spectra were obtained with a PerkinElmer (Lambda 19) spectrometer equipped with an integrating sphere with BaSO4 as reference. Steady-state photoluminescence measurements were performed in a Photon Technology International (PTI) 220B spectrofluorimeter having a Xe arc lamp light excitation and Czerny-Turner monochromator, coupled to a photomultiplier. The solid samples were pressed between two windows Suprasil quartz cuvettes with a path length of 0.01 mm and placed at a 45° angle to both the excitation and emission monochromators. All measurements were carried out at room temperature. Textural properties were determined by N2 adsorption isotherms measured at 77 K with a Micromeritics ASAP 2020.

aromatic quinolinium-derived molecules are able to form a bulky paired-OSDA through π−π interactions (see Figure 2b),

Figure 2. (A) Quinolinium-derived molecule (MTPQ) used as OSDA. (B) Paired-OSDAs through self-assembling π−π stacking interactions.

which perfectly fits the spherical large cavities of LTA zeolite. The self-assembling methodology allowed the control of the chemical composition of the LTA zeolite, obtaining high-silica and even the pure silica polymorph in the presence of fluoride anions.13 The maximization of the volume/charge ratio and the allocation of the positive charges in this paired-OSDA are the main reasons for the excellent control of the chemical composition in the LTA preparation. The self-assembling methodology has been shown later to also work for other zeolite structures.14 We thought that an OSDA formed by the molecular selfassembling of two smaller counter parts could be used, instead of the large macrocycles, to efficiently synthesize the SAPO polymorph of STA-6 zeolite. This silicoaluminophosphate, as it happens in the case of the chabazite SAPO-34,1 could be an efficient catalyst for the SCR of NOx or MTO reactions. We will show here that by means of the self-assembled quinolinium-derived molecules, it has been possible to synthesize for the first time the pure phase of the SAPO polymorph of STA-6. With this synthesis method, it is possible to achieve an excellent framework Si distribution, avoiding the formation of silicon-rich domains. New AlPO-based materials with large cavities in their structure could be prepared by using paired aromatic OSDAs in the near future.

3.-. RESULTS AND DISCUSSION The quinolinium-derived MTPQ organic molecule (see Figure 2a) was selected as potential OSDA to direct the synthesis of small pore AlPO-related materials with large cavities. The selection was based on the fact that this organic molecule, when self-assembling, is a very efficient OSDA to direct the synthesis of the high-silica and pure silica form of the small pore LTA zeolite, named ITQ-29.13 It is important to note that this is the unique report described in the literature where bulky selfassembled OSDAs direct the crystallization of small pore zeolites with large cavities, and its use opens the door to the synthesis of small pore AlPO-related materials with large cavities. An experimental program was designed to study the effect of relevant synthesis variables for the preparation of AlPO-related materials, using MTPQ as OSDA (see Table 1). The preparation of neutral AlPOs [Si/(Al+P) = 0] or acidic

2.-. EXPERIMENTAL SECTION 2.1.-. Synthesis. -. OSDA Synthesis. Ten grams of the commercial amine Julolidine (97 wt %, Aldrich) was dissolved in 100 mL of CHCl3. 24.5 g of methyl iodide was added to the above solution, and the reaction mixture was stirred at room temperature for 3 days. The resulting ammonium salt was collected by filtration, washed exhaustively with ether and dried at room temperature (yield ∼85%). For preparing the corresponding hydroxide form, 8.52 g of cation in the iodide form was dissolved in water, and 27 g of resin Dower SBR was added and maintained under agitation overnight. The solution was filtered, and the hydroxide form of the organic cation (4-methyl2,3,6,7-tetrahydro-1H,5H-pyrido [3.2.1-ij] quinolinium, MTPQ, see Figure 2a) was obtained. -. Zeotype Synthesis. To synthesize the AlPO-related materials, we added the required amount of orthophosphoric acid (85 wt %, Aldrich) to the aqueous solution of the hydroxide form of the OSDA. The alumina source (75 wt %, Condea) was then introduced, keeping the gel under stirring for 5 min. Finally, the silica source (Ludox AS40, 40 wt %, Aldrich) was introduced into the synthesis gel, leaving this under stirring for 30 min. The gel was transferred to a Teflon-lined stainless steel autoclave with a free volume of 3 mL, and heated at 150 °C under static conditions for 5 days. Crystalline products were filtered and washed with abundant water, and dried at 100 °C overnight. The samples were calcined in a tube furnace following the next temperature program: first, the samples were heated to 600 °C using a 1 °C/min ramp under flowing N2; second, this elevated

Table 1. Experimental Design for the Synthesis of AlPORelated Materials Using MTPQ as OSDA at 150°C for 5 Days under Static Conditions

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variable

values

MTPQ/(Al+P) H2O/(Al+P) P/Al [Si/(Al+P)]

0.3, 0.5 10, 50 1, 0.9, 0.8 [0, 0.1, 0.2, respectively]



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Figure 3. Phase diagram achieved using the quinolinium-derived MTPQ OSDA at 150 °C for 5 days under static conditions.

Figure 4. PXRD patterns of the different STA-6 materials in their silicoaluminophosphate form obtained using the quinolinium-derived MTPQ OSDA.

SAPOs [Si/(Al+P) = 0.1, 0.2] was attempted by varying the amount of the OSDA in the synthesis gels [MTPQ/(Al+P) = 0.3, 0.5] and their concentration [H2O/(Al+P) = 10, 50] at 150 °C for 5 days. Under those synthesis conditions, STA-6 and an unstable lamellar material were obtained (see Figure 3). The crystallization of pure STA-6 materials using MTPQ as OSDA was favored in their silicoaluminophosphate form working with large amounts of OSDA, and in concentrated gels (see SAS-1 and SAS-2 in Figure 3). On the other hand, an unknown dense phase competes with STA-6 when the gels are highly diluted. When low amounts of OSDA are present in concentrated gels, an unstable lamellar material is preferentially formed. Figure 4 shows the PXRD patterns of the two silicoaluminophosphate STA-6 materials, SAS-1 and SAS-2, clearly

revealing the high crystallinity of these samples and the absence of other crystalline impurities. This is an important point because it is the first description of the pure silicoaluminophophate form of STA-6 reported in the literature. Previous attempts using azamacrocycles led to the formation of mixtures of STA-6 and SAPO-43 (GIS-type SAPO).12 The nature and stability of the quinolinium-derived MTPQ organic molecules acting as OSDA have been studied using different characterization techniques. Comparison of the solid 13 C MAS NMR spectra of the as-prepared SAS-1 and SAS-2 materials (see SAS-1 and SAS-2 in Figure 5) with the liquid 13C NMR spectrum of an aqueous solution of MTPQ (see OSDA in Figure 5), indicates that most of the organic molecules occluded within STA-6 zeotypes remain stable after the hydrothermal crystallization. This high stability of the organic molecules is also shown by the elemental analysis of the as4348



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Figure 5. 13C MAS NMR spectra of the as-prepared STA-6 materials and liquid 13C NMR of the OSDA. Spinning sidebands are highlighted by asterisks.

prepared SAS-1 solid, where the C/N molar ratio is close to 12, revealing that almost 90% of the MTPQ molecules remain intact (see Table 2). Interestingly, the number of MTPQ molecules per SAS cavity can be easily calculated from the thermogravimetric analysis (TGA) of the as-prepared solids (see SAS-1 in Figure 6) and the structural information on the SAS framework (each unit cell has two cavities and it is composed by 32 T atoms). The number of MTPQ molecules per cavity for SAS-1 is 1.8. This value would indicate that most of the MTPQ molecules should act as paired-OSDAs for the crystallization of the STA-6. Corma et al. described that MTPQ molecules can act as paired-OSDA molecules due to their supramolecular selfassembling through π- π interaction of the aromatic rings.13 When that occurs, an intense shift of the emission band toward higher wavelengths in the fluorescence spectrum due to these π−π interactions occurs.13 To prove if this self-assembling also takes place in the as-synthesized SAPO materials, the samples were studied by fluorescence. First, a highly diluted (5 × 10−4 M) aqueous solution in where MTPQ was expected to be mostly present as monomers, and a very concentrated MTPQ solution (3 M) that should favor the formation of dimers, were prepared as a reference for the spectroscopic study. Notice that, this concentrated aqueous solution presents the same organic concentration as in the SAS-1 and SAS-2 gels. The photoluminescence study of both MTPQ aqueous solutions was performed at the excitation wavelength of 265 nm, because the UV−vis spectrum of MTPQ in aqueous solution shows a band with its maximum centered at 265 nm (see Figure 7). As can be observed in Figure 8, the fluorescence emission spectra of the diluted solution shows a main fluorescence band centered at 300 nm (Figure 8a), whereas the concentrated solution shows a broad fluorescence band ranging from 400 to 440 nm (Figure 8b). This intense shift of the emission band toward higher wavelengths and the absence

Figure 6. Thermogravimetric analysis of as-prepared STA-6 materials.

Figure 7. UV−vis spectrum of the quinolinium-derived MTPQ OSDA in aqueous solutions.

of the 300 nm band corresponding to single MTPQ molecules in the concentrated aqueous solution, reveal that MTPQ molecules at the concentration present in the synthesis gel, are forming self-assembled dimers through π−π interactions. The fluorescence emission spectrum of the as-prepared SAS-2 also shows a broad fluorescence band ranging from 400 to 440 nm, as was observed with the concentrated aqueous solution (see

Table 2. Chemical and Elemental Analysis of the STA-6 Zeotypes Achieved Using the Quinolinium-Derived MTPQ OSDA

a

sample

Sia

Pa

Ala

Si/TO2b

wt % N

wt % C

(C/N)real

OSDA/cavity

SAS-1 SAS-2 SAS-3 SAS-4

0.21 0.10 0.11 0.07

0.28 0.37 0.35 0.40

0.51 0.53 0.54 0.52

0.21 0.10 0.11 0.07

1.71 N.Dc N.D 1.70

16.99 N.D N.D 17.03

11.6 N.D N.D 11.8

∼1.8 N.D N.D ∼1.7

Normalized mole fractions. bT = Si + P + Al. cN.D.: Nondetermined. 4349



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the absence of the band centered at 302 nm corresponding to monomeric species, confirming the sole presence of selfassembled MTPQ molecules. Note that under these lower excitation wavelengths (λex = 255 and 260 nm), it should be possible to distinguish the monomeric species if they were present in the sample (see fluorescence emission spectra of the MTPQ aqueous solution at 5 × 10−4 M in Figure 9a). SEM images of SAS-1 and SAS-2 silicoaluminophosphates show differences in crystal shape (see Figure 10a, b, respectively). SAS-2 presents well-shaped tetragonal crystals of ∼4 × 1 × 1 μm (see Figure 10b), whereas SAS-1 also shows similar tetragonal crystals but mixed with very small particles of another phase (Figure 10a). This impurity seems to be an amorphous phase due to the absence of additional diffraction peaks in the PXRD pattern of SAS-1, and its very low particle size and irregular morphology. The as-prepared SAS-1 and SAS-2 materials have been studied by 27Al, 31P, and 29Si MAS solid NMR spectroscopy to obtain chemical information on the local atomic environments. 31 P MAS NMR spectra show the presence of two bands centered at −28 and −33 ppm, indicating the presence of two types of tetrahedral phosphorus species (see Figure 11). This observation is in clear agreement with the two different crystallographic positions reported for P in the structure solution of STA-6.8 27Al MAS NMR spectra of the as-prepared SAS-1 and SAS-2 show a broad band at 40 ppm, which corresponds to Al in tetrahedral environments in the framework, whereas the signal at 6 ppm could be assigned to five-coordinated aluminum in the framework or extra-framework Al atoms (see Figure 12).15 However, the presence of extra-framework Al atoms could be considered almost negligible because the Al mole fractions in the final solids are close to the expected values (∼0.5, see Table 2), precluding the large presence of octahedral Al2O3 environments (note that physical mixtures of Al2O3 and the crystalline silicoaluminophosphate STA-6 necessarily would result in Al mole fractions

Figure 8. Photoluminescence spectra (λex = 265 nm) of (a) diluted aqueous solution of MTPQ at 5 × 10−4 M, (b) concentrated aqueous solution of MTPQ at 3 M, and (c) as-prepared SAS-2 material.

Figure 8c). This result would confirm that supramolecular selfassembling of the MTPQ molecules through π−π interactions in the STA-6 cavities may occur. Nevertheless, the fluorescence emission spectrum of the as-prepared SAS-2 material shows a clear increase of the signal at wavelengths below 300 nm (see Figure 8c). This increase could be attributed to the direct emission signal that comes from the fixed excitation wavelength of the lamp (λex = 265 nm), and not to the presence of monomeric organic species (see the absence of any band centered at 302 nm in Figure 8c). Nevertheless, to rule out the presence of monomeric species in the as-prepared silicoaluminophosphate form of the STA-6 material, the fluorescence emission spectrum of the solid has also been studied at lower excitation wavelengths (λex = 255 and 260 nm), to force the reduction of the intensity of the direct emission band in the region where the monomer signal would appear (∼300 nm). As can be seen in Figure 9b, all the achieved emission spectra show

Figure 9. Photoluminescence spectra (λex = 255, 260, and 265 nm) of (A) diluted aqueous solution of MTPQ at 5 × 10−4 M, (B) as-prepared SAS-2 material. 4350



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Figure 10. SEM images of the different silicoaluminophosphate STA-6 zeotypes: (a) SAS-1, (b) SAS-2, (c) SAS-3, and (d) SAS-4.

Figure 11. Solid materials.

31

P MAS NMR spectra of the as-prepared STA-6 Figure 12. Solid materials.

significantly higher than 0.5). Similar signals centered at 6 ppm have been assigned in the literature to framework aluminum atoms coordinated to the OSDAs, or even water molecules.16 29 Si MAS NMR spectrum of the SAS-1 material shows two clear bands centered at −95 and −110 ppm, corresponding to isolated Si atoms [silicon tetrahedron that has no silicon neighbors and form Si(4Al) environments] and highly enriched silicon areas [also named “silicon islands”, which form Si(4Si) environments], respectively (see SAS-1 in Figure 13). The Si(4Al) type environment results by the isomorphic substitution of a P5+ atom in the zeolitic framework by a Si4+ atom. This selective isomorphic substitution will create a negative charge in the inorganic framework that could be balanced by a proton after calcination, and consequently, can generate a Brönsted acid site. On the other hand, the substitution of a

27

Al MAS NMR spectra of the as-prepared STA-6

large area of consecutive P5+ and Al3+ atoms by Si4+ atoms will form the “silicon islands” that have Brönsted acidity, only at the border of those Si islands. As observed in Figure 13, the signal of the silicon-rich area is more intense than the isolated Si atoms for the SAS-1 zeotype, and this would indicate that most of the silicon species are preferentially forming Si-rich areas in the framework. However, the mixture of crystal morphologies observed in the SEM image of SAS-1 material points out that this highly polymerized silicon regions would be mainly in segregated amorphous particles (see Figure 10a). In contrast, 29 Si MAS NMR spectrum shows a higher proportion of silicon as isolated Si(4Al) species than in Si-rich domains for the SAS4351



Figure 13. Solid materials.

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charge distribution in the as-prepared SAS-4 reveals that the positive charges introduced by the MTPQ organic molecules (∼0.10 MTPQ/TO2, calculated from TGA, see Figure 6) are only slightly higher than the negative charges that would be created in the framework by the presence of isolated Si(4Al) species (∼0.07 Si/TO2, see Table 2). This result suggests that supramolecular self-assembled MTPQ molecules not only shows a remarkable capacity to direct the crystallization of small pore zeotypes with large cavities, but it may also allow directing the presence of isolated Si species when introduced in the adequate amount in the synthesis gel. This is only a hypothesis, and more examples describing this effect will be required, but it seems that the steady allocation of the positive charges of the paired-OSDA dimers when filling the zeotype cavities could be a plausible reason for the isolated distribution of Si atoms in framework positions. Importantly, the crystalline structure of the silicoaluminophosphate form of STA-6 remains intact after being calcined in air at 600 °C for 8 h to remove the occluded organic moieties, as reveals the PXRD pattern of the calcined SAS-4 material (see Figure 4). In addition, N2 adsorption at 77 K on the calcined SAS-4 material shows a characteristic “Type I” adsorption isotherm of microporous solids (see Figure 14), giving a

29

Si MAS NMR spectra of the as-prepared STA-6

2 sample (see Figure 13). In this case, the SEM image of the SAS-2 does not reveal the presence of segregated amorphous particles, and therefore, the Si-rich domains in this sample must be placed in the zeolitic framework. The reduction of the Si content in the synthesis gel, from a Si/(Al+P) ratio of 0.2 to 0.1, avoids the formation of the segregated amorphous phase, and increases the amount of isolated Si(4Al) species in the framework of STA-6 materials (see SAS-1 and SAS-2 in Figures 10 and 13). If the synthesis conditions of SAS-1 and SAS-2 are further analyzed, it can be observed that the amount of Si introduced in the gels is much higher than that required for the single isomorphic substitution of P with Si (P/Al + Si/Al > 1). That means that there is an excess of the Si species, and this could explain the large presence of silicon-rich domains in both SAS-1 and SAS-2 materials. To attempt the preparation of this small pore silicoaluminophosphate with a more uniform Si-distribution within the zeolitic crystals, the silicon content has been adjusted in the synthesis gels to fix the theoretical uniform isomorphic heteroatom substitution (P/Al + Si/Al = 1). Therefore, the SAS-3 experiment has been performed under a Si/Al ratio of 0.2 and a P/Al ratio of 0.8, while the SAS-4 experiment has been performed under 0.1 and 0.9, respectively (see Figure 3). Under these syntheses conditions highly crystalline STA-6 materials are also obtained in their silicoaluminophosphate form (see PXRD patterns of SAS-3 and SAS-4 in Figure 4). SAS-3 and SAS-4 materials present well-shaped tetragonal crystals of ∼4 × 1 × 1 μm, indicating also the absence of amorphous phase impurities (see SEM images c and d in Figure 10, respectively). The desired Si(4Al) species are notably increased versus the undesired Si-rich domains in SAS-3 and SAS-4 (see the main band at −95 ppm in the 29Si MAS NMR spectra of these samples in Figure 13). Particularly, the silicoaluminophosphate SAS-4 shows the single presence of the band at −95 ppm in the 29 Si MAS NMR spectrum, indicating the unique arrangement of Si atoms as isolated Si(4Al) environments (see SAS-4 in Figure 13). The OSDA molecules remain intact in the as-prepared SAS-4 sample, as indicated by 13C MAS NMR spectroscopy, thermogravimetric, and elemental analyses in Figures 5 and 6 and Table 2, respectively. Interestingly, a detailed study of the

Figure 14. N2 adsorption isotherm of the calcined SAS-4 material.

micropore area of 245 m2/g and a micropore volume of 0.12 cm3/g (Table 3). It is important to note that this micropore Table 3. Textural Properties Calculated from N2 Adsorption Isotherms sample SAS4_Calc

BET surface area (m2/g)

micropore area (m2/g)

micropore volume (cm3/g)

299

245

0.12

volume is comparable to the one previously reported by Wright et al. for the Mg-containing aluminophosphate STA-6 material.8 However, a micropore volume of 0.25 cm3/g has been reported in the literature for the pure silica counterpart of the SAS structure, SSZ-73.17 This higher micropore volume observed for the SSZ-73 zeolite compared to STA-6 does not necessarily mean that STA-6 is being damaged during the calcination process. Indeed, the presence of few pore obstructions, as for instance structural defects, could reduce the measured pore volume of one-dimensional zeolites.18 In this sense, it is wellknown that the synthesis of pure silica zeolites in fluoride media allows the crystallization of defect-free crystals, as it is the case of SSZ-73,17 resulting in a higher measured micropore volume. 4352



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Parker, J. E.; Brandani, S.; Wright, P. A. J. Am. Chem. Soc. 2012, 134, 17628. (7) (a) Lobo, R. F.; Zones, S. I.; Davis, M. E. J. Inclusion Phenom. Mol. Recognit. Chem. 1995, 21, 47. (b) Moliner, M.; Rey, F.; Corma, A. Angew. Chem., Int. Ed. 2013, 52, 13880. (8) Patinec, V.; Wright, P. A.; Lightfoot, P.; Aitken, R. A.; Cox, P. A. J. Chem. Soc., Dalton Trans. 1999, 3909. (9) Wheatley, P. S.; Morris, R. E. J. Solid State Chem. 2002, 167, 267. (10) Yu, J.; Xu, R. Chem. Soc. Rev. 2006, 35, 593. (11) Lourenço, J. P.; Ribeiro, M. F.; Borges, C.; Rocha, J.; Onida, B.; Garrone, E.; Gabelica, Z. Microporous Mesoporous Mater. 2000, 38, 267. (12) García, R.; Philp, E. F.; Slawin, A. M. Z.; Wright, P. A.; Cox, P. A. J. Mater. Chem. 2001, 11, 1421. (13) Corma, A.; Rey, F.; Rius, J.; Sabater, M. J.; Valencia, S. Nature 2004, 431, 287. (14) (a) Gomez-Hortiguela, L.; Lopez-Arbeloa, F.; Cora, F.; PerezPariente, J. J. Am. Chem. Soc. 2008, 130, 13274. (b) Gomez-Hortiguela, L.; Hamad, S.; Lopez-Arbeloa, F.; Pinar, A. B.; Perez-Pariente, J.; Cora, F. J. Am. Chem. Soc. 2009, 131, 16509. (15) Castro, M.; Warrender, S. J.; Wright, P. A.; Apperley, D. C.; Belmabkhout, Y.; Pirngruber, G.; Min, H. K.; Park, M. B.; Hong, S. B. J. Phys. Chem. C 2009, 113, 15731. (16) (a) Fyfe, C. A.; Wong-Moon, K. C.; Huang, Y.; Grondey, H. Microporous Mater. 1995, 5, 29. (b) Chen, T. H.; Wouters, B. H.; Grobet, P. J. Colloids and Surfaces A: Physicochem. Eng. Aspects. 1999, 158, 145. (17) Wragg, D. S.; Morris, R.; Burton, A. W.; Zones, S. I.; Ong, K.; Lee, G. Chem. Mater. 2007, 19, 3924. (18) Coulomb, J. P.; Floquet, N. Stud. Surf. Sci. Catal. 2008, 174B, 913.

The application of the silicoaluminophosphate form of STA6 on different catalytic and separation processes is currently under investigation.

4. CONCLUSIONS Rationalized bulky supramolecular self-assembled aromatic molecules have been applied for the first time to the synthesis of small pore AlPO-related zeotypes with large cavities as OSDAs. This methodology has allowed the first description of the pure silicoaluminophosphate form of the STA-6 zeotype. The unique supramolecular paired nature of the organic molecules through π−π interactions of the aromatic rings has been demonstrated by photoluminescence for the STA-6 synthesis. Moreover, these bulky MTPQ-paired molecules allow controlling the Si distribution and, consequently, the Brönsted acid sites within the STA-6 crystals. This description allows envisioning the synthesis of new small pore AlPO-related materials with large cavities, which could show unique properties for new catalytic or separation processes.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work has been supported by the Spanish Government through Consolider Ingenio 2010-Multicat, the “SEVERO OCHOA PROGRAM”, MAT2012-37160 and, Intramural201480I015. Manuel Moliner also acknowledges to “Subprograma Ramon y Cajal” for the contract RYC-2011-08972.

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REFERENCES

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