Simple Quaternary Ammonium Cations-Templated Syntheses of Extra

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Simple Quaternary Ammonium Cations-Templated Syntheses of Extra-Large Pore Germanosilicate Zeolites Risheng Bai,† Qiming Sun,† Ning Wang,† Yongcun Zou,† Guanqi Guo,† Sara Iborra,‡ Avelino Corma,‡ and Jihong Yu*,† †

State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012, People’s Republic of China ‡ Instituto de Tecnología Químicia, UPV-CSIC, Universidad Politénica de Valencia, Avda. de los Naranjos, s/n, Valencia 46022, Spain S Supporting Information *

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(TPAOH), and tetrabutylammonium hydroxide (TBAOH), were used as the sole organic template, the maximum opening windows of the obtained zeolite frameworks is no more than 12-rings, such as zeolites MFI,25 *BEA,26 SZR,27 and MEL,28 etc. Herein, with a series of the simple quaternary ammonium hydroxide TEAOH (∼8 Å), TPAOH (∼9 Å), and TBAOH (∼10 Å)29 as the sole organic template, we have for the first time successfully synthesized the extra-large pore germanosilicate zeolites ITQ-33 (18R × 10R × 10R), ITQ-44 (18R × 12R × 12R), and NUD-1 (18R × 12R × 10R) by introducing germanium and fluoride anions in the concentrated-gel synthesis system. Importantly, the extra-large pores in zeolites could facilitate the high-efficient catalytic conversion of bulky organic molecules. ITQ-33,14 ITQ-44,18 and NUD-121 zeolites have an identical structure building unit (SBU) [32.43.69], forming a twodimensional layer with 18-rings. And the different connection styles via 3-Rs and/or D3Rs between the neighboring twodimensional building layers give rise to the formation of the three different zeolite topologies. Corma and co-workers used the mixed templates of hexamethonium bromide and hexamethonium hydroxide, a flexible template, in synthesizing ITQ-33, and with (2′-(R),6′-(S))-2′,6′-dimethylspiro[isoindole-2,1′-piperidin-1′-ium] as the organic template, they synthesized ITQ-44 zeolite. Du and co-workers synthesized NUD-1 zeolite, using 1-methyl-3-(4-methyl-benzyl) imidazolium or 1-methyl-3-(naphthalen-2-ylmethyl)imidazolium as the organic template via supramolecular aggregates of aromaticcontaining cations. Notice that, these bulky, rigid, and welldesigned organic molecules need to be presynthesized when applied for synthesizing extra-large pore zeolites. Figure 1 shows the phase diagram in the F−-containing concentrated gel systems in the presence of TEAOH, TPAOH, and TBAOH. ITQ-33 zeolite can be synthesized with TBAOH as the template, ITQ-44 zeolite can be obtained with TEAOH or TPAOH as the template, and NUD-1 zeolite can be prepared with TPAOH or TBAOH as the template. These assynthesized samples are named as TBA-ITQ-33, TEA-ITQ-44, TPA-ITQ-44, TPA-NUD-1, and TBA-NUD-1, respectively. Using TEAOH as the template, with a low water content

eolites are a class of inorganic microporous crystalline materials formed by TO4 (T = Si, Ge, Al, P, etc.) tetrahedral units with uniform pores and regular channels.1,2 They are of great importance in ion-exchange, adsorption, and catalysis, because of the unique porous structures, high surface areas, moderate acidities, and excellent thermal stabilities.3,4 However, the narrow pore openings of zeolites strongly hinder the transportation of bulky molecules, and thus restrict the performance of zeolites in the catalytic conversion of large molecules.5,6 Such a problem can be solved by the utilization of mesoporous materials or hierarchical zeolites.7−9 However, the hydrothermal stability and acidity of the mesoporous materials are not as sufficient as those of the crystalline zeolites;10 on the other hand, using the combined templates of surfactant molecules and organic cations in synthesizing hierarchical zeolites usually generates impurity phases composed of zeolite crystals and amorphous mesoporous materials instead of the hierarchical zeolites.11 To overcome these problems, great efforts have been made to synthesize zeolites with extra-large pores (T > 12), and so far much progress has been achieved, for instance, the successful preparation of VPI-5 (VFI, 18-R),12 UTD-1 (DON, 14-R),13 ITQ-33 (ITT, 18-R),14 ITQ-37 (-ITV, 30-R),15 ITQ-40 (-IRY, 16-R),16 ITQ-43 (28-R),17 ITQ-44 (IRR, 18-R),18 ITQ-51 (IFO, 16-R),19 and ITQ-54 (-IFU, 20R),20 etc. Very recently, the successful synthesis of a new germanosilicate zeolite, named NUD-1, possessing 18-ring channels, further enriches the extra-large pore zeolite family.21 Significantly, the extra-large pore zeolites are promising in cracking heavy oils.14 Using rational designed templates, with characteristics of bulky size, appropriate rigidity and proper C/ N ratio, etc., is one of the key strategies for synthesizing the extra-large pore zeolites possessing novel zeolite topologies.22 However, the complicated synthesis procedure, expensive cost, and sometimes high toxicity involved in synthesizing these templates may limit the large-scale industrial applications of the extra-large pore zeolites. Notably, Strohmaier and co-workers used tetraethylammonium (TEA) cations together with alkali metal as templates successfully prepared ECR-34 (ETR), containing 18-ring channel systems,23 Lin and co-workers synthesized PKU-12 (-CLO, 20-R) using diisopropylethylmethylammonium as the template that was prepared from N,Ndiisopropylethylamine and the highly toxic methyl iodide.24 However, when the simple, cheap, and commercially available quaternary ammonium bases, such as tetraethylammonium hydroxide (TEAOH), tetrapropylammonium hydroxide © XXXX American Chemical Society

Received: August 1, 2016 Revised: September 3, 2016

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DOI: 10.1021/acs.chemmater.6b03179 Chem. Mater. XXXX, XXX, XXX−XXX

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Figure 1. Phase diagram in F−-containing concentrated gel systems in the presence of tetraethylammonium hydroxide (TEAOH), tetrapropylammonium hydroxide (TPAOH), and tetrabutylammonium hydroxide (TBAOH).

compositions of the as-synthesized zeolite samples are calculated on the basis of ICP analyses, thermogravimetric analyses, and CHN elemental analyses, as well as crystallographic data of the corresponding zeolite structures (Table S1).14,18,21 The solid-state 13C MAS NMR measurements and CHN elemental analyses suggest that all these three templates remain intact in the resultant zeolite structures (Figure S2). The 19F MAS NMR measurements of the TEA-ITQ-44, TPA-ITQ-44, TPA-NUD-1, TBA-ITQ-33, and TBA-NUD-1 samples all give resonance bands ranging from −9 to −13 ppm, attributed to the F− in D4Rs (Figure S3).18,21 Their 29Si MAS NMR spectra show signals between −100 and −112 ppm, owing to the tetrahedral framework silicon (Figure S4). Thermogravimetric analyses indicate that the series of simple organic template molecules start to decompose at about 250 °C (Figure S5). The templates in ITQ-33 and NUD-1 can be successfully removed by calcination in air at 550 °C for 6 h, with the framework structures remained as confirmed by XRD analysis (Figure S6). N2 adsorption−desorption measurements were performed at 77 K to investigate the porosity of the TPANUD-1, TBA-NUD-1, and TBA-ITQ-33 samples. As shown in Figure 3, the nitrogen adsorption−desorption isotherms of the

(H2O/T = 1−3, T = Si+Ge), and a relative high Si/Ge ratio (Si/Ge = 1−4), we synthesized BEC zeolite, but if increasing the germanium content (Si/Ge = 0.25−1), together with the incorporation of aluminum (Al/T = 0.05−0.25), the extra-large pore zeolite ITQ-44 was obtained. When changing the template from TEAOH to TPAOH, the extra-large pore zeolite NUD-1 was synthesized with low water content (H2O/T = 1) and relative high Si/Ge ratio (Si/Ge = 1−4) in the gel, while increasing the germanium content (Si/Ge = 0.25), ITQ-44 zeolite can be prepared. With TBAOH, we could synthesize ITQ-33 zeolite with a high water content (H2O/T = 3) in the gel and NUD-1 zeolite with a low water content (H2O/T = 1) in the gel. Powder X-ray diffraction (PXRD) was used to investigate the crystallinity and phase purity of the as-synthesized samples. The XRD patterns of the five as-synthesized zeolites are consistent with the corresponding simulated XRD patterns of ITQ-33, ITQ-44, and NUD-1 (Figure 2). TEM images show the morphological characteristics of the as-synthesized zeolites (Figure S1). All these samples are of nanosized dimensions, particularly the TPA-NUD-1 possesses a sheet-like morphology, with dimension ranging from 10 to 25 nm. The molar

Figure 2. XRD patterns of the as-synthesized TEA-ITQ-44, TPA-ITQ44, TPA-NUD-1, TBA-ITQ-33, and TBA-NUD-1 samples and the simulated XRD patterns of ITQ-33, ITQ-44, and NUD-1.

Figure 3. N2 adsorption−desorption isotherms of the as-synthesized TPA-NUD-1 (red), TBA-NUD-1 (blue), and TBA-ITQ-33 (pink). B

DOI: 10.1021/acs.chemmater.6b03179 Chem. Mater. XXXX, XXX, XXX−XXX

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active sites for the bulky reactants, thus leading to the superior performance of the TPA-NUD-1 catalyst. It is expected that the easily synthesized NUD-1 catalyst with extra-large pore systems, appropriate acidity, and high thermal stability can be used in more catalytic reactions involving bulky molecules. In summary, extra-large pore germanosilicate zeolites ITQ33, ITQ-44, and NUD-1 have been for the first time successfully synthesized by using a series of simple, cheap, and commercially available quaternary ammonium hydroxides, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide, as the organic templates. Thanks to the small crystallite size, the suitable acidity, and most importantly, the extra-large 18-ring channel system, the Al-containing NUD-1 catalyst shows good catalytic performance for the acetalization reactions involving bulky organic molecules. The utilization of simple quaternary ammonium cations as templates opens new possibilities for the synthesis of extra-large zeolites and paves the way for achieving industrial application of the extra-large pore zeolites. However, it should be pointed out that the high content of Ge and F in the as-synthesized zeolites is also more problematic than the template and is likely to prevent further consideration for large-scale applications until adequately resolved.

three calcined samples show a rapid N2 uptake at low relative pressure (P/P0 < 0.1), characteristic of the microporous structure of the zeolites. There exist large hysteresis loops at the high relative pressure (0.8 < P/P0 < 0.99) in NUD-1 samples, coming from the capillary condensation in the mesopores formed by the aggregation of the nanosized crystallites.30 Notably, the BET surface area of the calcined TPA-NUD-1 sample is 686 m2/g, which is higher than that of the reported one (646 m2/g).21 The detailed surface area and pore volume data are listed in Table S2. Incorporating the aluminum atoms into the framework can endow the zeolite with Brønsted acidity. The 27Al MAS NMR spectrum of the calcined Al-containing TPA-NUD-1 sample ((Si+Ge)/Al = 3.13) shows two peaks at +51 and −2 ppm, corresponding to the tetrahedral framework aluminum atoms and octahedral extra-framework aluminum atoms, respectively (Figure S7).14 As confirmed by the NH3 temperatureprogrammed desorption measurements, the induction of tetrahedral Al atoms increases the acidity of the sample (Figure S8). The Al-containing TPA-NUD-1 was used as a catalyst in the condensation of benzaldehyde with 2- hydroxyacetophenone that involves bulky reactants and products. The conversion of 2-hydroxyacetophenone is as high as 91% with a selectivity to the main product, Flavanone, higher than 99%, which is comparable to the reported mesoporous ZSM-5 single crystals (90.8%), and much higher than other hierarchical zeolites as well as the aluminum oxide and aluminum hydroxide catalysts (Table 1 and Table S3). The Al-containing TPA-NUD-1 was

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The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.chemmater.6b03179. Experimental details, 13C-MAS NMR spectra, 19F-MAS NMR spectra, 29Si-MAS NMR spectra, TG curves, XRD patterns of the calcined samples, 27Al-MAS NMR spectra, NH3-TPD, compositional analysis, porous properties, and catalytic reaction data (PDF)

Table 1. Catalytic Activity in Converting Bulky Substrates over Different Catalysts

samples

Si/Al ratio

conversion (%)a

note

TPA-NUD-1 multilamellar ZSM-5 nanosheet unilamellar ZSM-5 nanosheet ZSM-5-Mc ZSM-5-OMd nano-BEAe Beta-MSf

3.13b 48 53 39 41 11 11

91 48 76 45.7 90.8 53.8 56.3

this work ref 7 ref 7 ref 8 ref 8 ref 9 ref 9

ASSOCIATED CONTENT

S Supporting Information *

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AUTHOR INFORMATION

Corresponding Author

*J. Yu. E-mail: [email protected]. Author Contributions

The paper was written through contributions of all authors. All authors have given approval to the final version of the paper. Funding

The research is funded by the National Natural Science Foundation of China (Grant No. 21320102001) and the State Basic Research Project of China (Grant No. 2014CB931802).

a The conversion was calculated on the 2-hydroxyacetophenone. bThis value was the molar ratio of (Si+Ge)/Al. cZSM-5 containing disordered mesopores (ZSM-5-M). dZeolite ZSM-5 single crystals with b-axis-aligned mesopores (ZSM-5-OM). eSurfactant-derived mesoporous zeolite Beta (nano-BEA). fMesoporous single-crystalline zeolite Beta (Beta-MS). All reactions were carried out under the same conditions.

Notes

The authors declare no competing financial interest.

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REFERENCES

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also used as a catalyst for the reaction of carbonyl compound (heptanal, 2-phenylpropanal, or diphenylacetaldehyde) with trimethylorthoformate, and the conversion of the TPA-NUD-1 catalyst is higher than that of the conventional ZSM-5, tested under the same reaction conditions. With increasing of the reactant molecular size, the corresponding conversion of ZSM5 is significantly decreased compared to that of TPA-NUD-1 (Table S4). During the catalytic reaction, the extra-large pores in the nanosized NUD-1 catalyst could offer more accessible C

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DOI: 10.1021/acs.chemmater.6b03179 Chem. Mater. XXXX, XXX, XXX−XXX