Synthesis of Novel Titanosilicate Catalysts by Simultaneous

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Synthesis of Novel Titanosilicate Catalysts by Simultaneous Isomorphous Substitution and Interlayer Expansion of Zeolitic Layered Silicates Boting Yang, Jin-Gang Jiang, Kun Zhang, and Peng Wu Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.6b00750 • Publication Date (Web): 11 Jul 2016 Downloaded from http://pubs.acs.org on July 11, 2016

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Chemistry of Materials

Synthesis of Novel Titanosilicate Catalysts by Simultaneous Isomorphous Substitution and Interlayer Expansion of Zeolitic Layered Silicates

Boting Yang†,‡, Jin-Gang Jiang†, Kun Zhang†, Peng Wu*,†

†Shanghai Key Laboratory of Green Chemistry and Chemical Processes, School of Chemistry and Molecular Engineering, East China Normal University, North Zhongshan Road 3663, Shanghai 200062, China ‡Department of Chemistry and Biology, Beihua University, Jilin 132013, China E-mail: [email protected] Tel/Fax: 86-21-62232292

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Abstract A facile and cheap method for the post-synthesis of large-pore titanosilicates from layered zeolitic silicate precursors is presented, in which isomorphous substitution of Ti for Si and interlayer expansion with mobile Si debris are realized simultaneously using aqueous H2TiF6 solution at room temperature. This versatile and convenient one-pot post-synthesis was used to construct several different 3D interlayer-expanded zeolite (IEZ) structures with tetrahedrally coordinated Ti incorporated into the framework without the use of external silane. The structural transformation and the incorporation of Ti in the preparation of IEZ-Ti-PLS-3 were monitored using Rietveld refinement and NMR studies. Furthermore, IEZ-Ti-PLS-3 exhibited unique catalytic properties in the epoxidation of alkenes with hydrogen peroxide, and was active not only for linear alkenes but also for bulky cyclic alkenes.

KEYWORDS: metallosilicates, interlayer expansion, post-synthesis, isomorphous substitution, alkene epoxidation

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INTRODUCTION Zeolites with tunable framework compositions, valuable crystalline structures, and

discrete micropores of molecular dimensions have been widely applied in catalysis, adsorption/separation, and ion exchange.1 However, in order to improve the ability of these materials to process bulky molecules, zeolites with catalytic or adsorbent properties that contain larger micropores constructed from 10 (or more)-membered rings (MRs) are needed in order to maximize diffusion into the micropore channels.2,3 The most effective method for this purpose is direct hydrothermal synthesis. The preparation of larger-pore zeolites can be realized with the use of new organic structure-directing agents (OSDAs),4-6 and/or crystallization-supporting metal ions like Ge, which are able to construct the double 4-membered ring (D4R) building units rarely formed by Si or Al alone.7,8 Alternatively, structural modification of known zeolites, for example by introducing random mesopores into microporous zeolite crystals by dealumination or desilication, has also been widely investigated.9,10 However, this kind of treatment is of limited utility, especially for the rigid 3D structures constructed by hydrothermal synthesis. Layered zeolites are a unique microporous material composed of rigid zeolitic lamellae. In contrast to traditional 3D zeolites, layered zeolites originate from zeolitic precursors consisting of lamellar sheets of unit cell thickness. Furthermore, they exhibit structural diversity and are capable of being modified.11,12 Various zeolitic topologies, including MWW,13 FER,14,15 CDO,15-17 NSI,18 SOD,19,20 RWR,21 RRO,22

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MFI,23 AFO,24 MTF,25 CAS,26 RTH,27 and PCR,28 are known to have corresponding lamellar precursors. Recently, Ge-zeolites in which the layers are held together by D4Rs have been shown to be potential sources of layered materials as their D4R planes are easily hydrolyzed.28 The weak interlayer bonds of layered zeolites impart flexibility in the third dimension with regard to the distance and spatial arrangements of up-and-down nanosheets. Hence, the zeolitic precursors can be structurally modified

by

several

approaches,

such

as

pillaring,29

delamination,30,31

intercalation,29,32 and silylation,3 generating a large number of new zeolite structures. These modified materials exhibit catalytic activity in various areas, including petrochemistry, oxidation reactions, fine chemical synthesis, and organometallics.11 In terms of interlayer expansion, we have previously reported a useful silylation strategy for converting 2D precursors into novel 3D zeolites with high crystallinity by inserting monomeric silane (diethoxydimethylsilane) into the interlayer spaces,3 producing a series of interlayer expanded zeolitic (IEZ) materials. Subsequently, other interlayer expanded structures, including IEZ-FER,33 IEZ-RRO,34 IEZ-CDO,35,36 and IEZ-NSI,37 have been post-constructed using this method. However, the method requires high-temperature hydrothermal treatment in concentrated acid media, and these harsh conditions can cause leaching of the active sites in the precursors and also lead to handling difficulties in material preparation.38,39 Moreover, the method requires expensive organosilane sources, further limiting its practical application. Therefore, new methods for expanding zeolite porosity and inducing active sites

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under mild conditions are required. Here, we propose a versatile method that achieves interlayer expansion and Ti insertion into a zeolite framework simultaneously by post-modifying lamellar silicates with H2TiF6 at low temperature. As illustrated in Scheme 1, the OSDA species are partially extracted in acidic media, allowing H2TiF6 molecules to freely enter the interlayers. Some of the Si species are then removed as a result of the corrosion of silicate layers by H2TiF6 treatment, leaving hydroxyl-nest type defect sites in the framework. The mobile Si species may migrate into the interlayer spaces to interact with the terminal silanols on the layer surface, forming new Si-O-Si linkages via dehydroxylation. Concurrently, Ti species generated from the hydrolysis of H2TiF6, are inserted into the hydroxyl nests, giving rise to new large-pore titanosilicates containing isolated tetrahedral Ti ions.

EXPERIMENTAL SECTION Synthesis of Zeolitic Lamellar Precursors. PLS-3, the lamellar precursor of FER

topology zeolite, was synthesized through hydrothermal treatment of protonated kanemite using tetraethylammonium hydroxide (TEAOH) as the OSDA, according to literature procedures.15 In a typical synthesis, H-kanemite, NaOH, deionized water, and TEAOH (25 wt% aqueous solution) were mixed using magnetic stirring. The molar composition of the starting mixture was 1.0 SiO2:0.2 TEA+:0.04 NaOH:6.5 H2O. The synthetic gel was transferred to a Teflon-lined autoclave and heated to 443 K for 24 h under static conditions. PLS-4, the lamellar precursor of CDO topology

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zeolite, was synthesized under the same conditions as PLS-3,15 except that TEAOH was substituted with diethyldimethylammonium hydroxide (DEDMAOH, 25 wt% aqueous solution). MCM-47, the lamellar precursor of CDO topology zeolite, was synthesized using tetramethylene bis(N-methylpyrrolidinium) dibromide as the OSDA.17 The product of the lamellar precursor was obtained by crystallizing the gel with a composition of 1.0 SiO2:0.12 OSDA:0.30 NaOH:40 H2O, at 443 K for 6 d under static conditions. RUB-39, the lamellar precursor of RRO topology zeolite, was synthesized using dimethyldipropylammonium hydroxide solution as the OSDA according to the literature,22 using a typical gel composition of 1.0 SiO2:0.5 OSDA:(8–12) H2O. The gel was crystallized in a Teflon-lined autoclave at 423 K for 30 d under static conditions. All crystalline products were collected by filtration, washed repeatedly with deionized water, and then dried at 373 K overnight to obtain the lamellar precursors. A portion of the precursor was calcined in air at 823 K for 10 h to burn off the occluded organic species and obtain the corresponding zeolites with 3D structures. Ti-MWW,40 TS-1,41 Ti-MOR,42 and Ti-Beta43 were synthesized directly following the procedures described in literatures as control samples. H2TiF6 Treatment of Lamellar Precursors. The zeolite precursors were post-treated in H2TiF6 solution under mild conditions, in which the mixture had a composition of 1.0 SiO2:(0.033–0.2) Ti4+:0.4 H+:1.2 F-:83.33 H2O. Taking the treatment of PLS-3 precursor as an example, 1.2 g PLS-3 precursor, 0.95 g H2TiF6 (60

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wt% aqueous solution), and 30 g H2O were charged into a Teflon beaker and stirred at 308 K for 5 h. The solid product was then separated from the solution by filtration, and washed with plenty of deionized water. The amount of H2TiF6 used was adjusted to vary the Si/Ti molar ratio of treatment mixture over the range of 5–30. For the treatments in which the Si/Ti ratio was higher than 5, HCl and NH4F were added to compensate the H+ and F- contents, making the composition the same as that given above. The resultant titanosilicates were calcined in a muffle furnace at 823 K for 6 h, resulting in interlayer expanded zeolites denoted IEZ-Ti-PLS-3-n, where n represents the Si/Ti ratio used in preparation. The other lamellar precursors were treated in H2TiF6 solution similarly, except for MCM-47, which was treated at the higher temperature of 353 K. As a control experiment, PLS-3 was also treated in a solution without Ti4+ but with the same H+ and F- concentrations as the usual H2TiF6 system. This gave rise to an interlayer-expanded silicate denoted IEZ-Si-PLS-3. Characterization Methods. Powder X-ray diffraction (XRD) patterns were measured on a Rigaku Ultima IV X-ray diffractometer using CuKα radiation (λ = 1.5405 Å) to check the structure and crystallinity of the products. Synchrotron radiation XRD analysis was employed to determine the structure of the interlayer-expanded IEZ-Si-PLS-3 by Rietveld refinement. The data were collected on synchrotron beam line 14B at the Shanghai Synchrotron Radiation Facility (SSRF). To improve accuracy, the sample was continuously rotated in a 0.5 mm glass capillary. The wavelength of the incident monochromatic X-ray was 1.2438 Å. Based on the

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indexed powder pattern, a structure model for IEZ-Si-PLS-3 was derived by adapting that of the lamellar precursor PLS-3, and energy minimized using high-level density functional theory (DFT) calculations. The DFT calculations were performed with the quantum mechanical code Dmol3 to optimize the structure. The exchange correlation function was expressed by the generalized gradient corrected (GGA) functional with Perdew-Burke-Ernzerh of parametrization.44 Subsequently, the coordinates of the optimized tetrahedral network were used as starting parameters for the Rietveld refinement of the XRD data, using the Reflex powder refinement module in the Materials Studio suite of programs.45 The details of the diffraction experiments and the fractional coordinates obtained from the Rietveld measurement are summarized in Table 1 and Table S1-S3. The adsorption isotherms were measured by N2 adsorption at 77 K on a BELSORP-MAX instrument equipped with a precise sensor for low-pressure measurement. The samples were activated at 573 K under vacuum for at least 10 h. The specific surface areas were calculated by the Brunauer-Emmett-Teller method. The vapor phase adsorption isotherms of water, hexane, and benzene on the products were obtained at 25 °C on a BELSORP-MAX instrument. The samples were activated at 573 K under vacuum for at least 10 h. The pore size distribution was calculated by the Horvath-Kawazoe method based on the data collected by Ar adsorption at 87 K on a Micromeritics ASAP 2020 instrument. UV-visible diffuse reflection spectra were recorded on a Perkin-Elmer Lambda 35 spectrophotometer over the range of 190–500 nm at an interval of 2 nm. The IR spectra were collected on

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a Nicolet Nexus 670 FT-IR spectrometer in absorbance mode at a spectral resolution of 2 cm-1 using the KBr technique (3 wt% wafer). 29Si and 13C solid-state MAS NMR spectra were recorded on a VARIAN VNMRS-400WB spectrometer under one-pulse conditions.

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Si NMR spectra were acquired with a 7.5 mm T3HX probe at 79.43

MHz and a spinning rate of 3 kHz. The chemical shifts were referred to 2,2-dimethyl-2-silapentane-5-sulfonic acid sodium salt ((CH3)3Si(CH2)3SO3Na).

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C

NMR spectra were recorded with a 7.5 mm T3HX probe at 100.54 MHz and a spinning rate of 5 kHz. Thermogravimetric analysis (TGA) was carried out on a METTLER TOLEDO TGA/SDTA 851e, with the measurement temperature being increased from 298 to 1073 K at a rate of 10 K min-1. The C, N, and H contents were determined with a Carlo Erba1106 elemental analyzer. The Ti content was determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) on a Thermo IRIS Intrepid II XSP atomic emission spectrometer after dissolving the samples in HF solution. Scanning electron microscopy (SEM) was performed on a Hitachi S-4800 microscope. Catalytic Reactions. The catalytic tests were performed in a 50-mL flask equipped with a condenser and immersed in a thermal bath. The reaction mixture typically contained 10 mmol of alkene (1-pentene or 1-hexene) or cycloalkane (C5–C12), 10 mmol of H2O2 (30 wt%), 50 mg of catalyst, and 7.8 g solvent. The mixture was stirred vigorously at 333 K for 2 h. The reaction mixture was then subjected to GC analysis (Shimadzu GC-14B) to determine the conversion and product selectivity. The

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products were identified with GC-MS (Agilent-6890GC/5973MS).

RESULTS AND DISCUSSION Post Treatment of Lamellar Precursors. Different lamellar precursors of zeolitic

silicates (PLS-3, PLS-4, MCM-47, and RUB-39) were treated in H2TiF6 solution to prepare highly crystalline titanosilicates with enlarged pores. The XRD patterns shown in Figure 1 illustrate the structural changes after the lamellar precursors were directly calcined or treated with H2TiF6 and further calcined. The precursors exhibit characteristic diffractions in the low-angle region due to the layered structures (Figure 1a). Direct calcination in air burns off the OSDA species between the layers and causes interlayer condensation, converting the 2D lamellar structures into their corresponding 3D crystalline structures with FER, RRO, and CDO topologies. This procedure results in a high-angle shift of the layer-related diffractions (Figure 1b), characterizing typical topotactic transformations for layered materials. The direct calcination results in ordered 3D crystalline structures but narrowed interlayer distances. For example, the d spacing of the [200] plane decreases from 23.48 to 18.72 Å in the case of PLS-3. In contrast, when the precursors are treated in H2TiF6 solution at 308 K for 5 h and further calcined at 823 K for 6 h, the resultant materials present layer-related XRD diffractions in a lower angle region than that of the normal 3D zeolites obtained by the direct calcination of the precursors (Figure 1c). This indicates the occurrence of interlayer expansion between the layers, even in the absence of any external Si sources. The H2TiF6 treatment-derived materials possess

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well-resolved diffraction patterns, indicating high crystallinity. The physicochemical properties of all these materials are summarized in Table 2. Based on the d spacing of typical layer-related planes, the H2TiF6 treatment expands the interlayer entrance by 2.3 - 2.5 Å compared to that achieved by the direct calcination of the precursors. The H2TiF6-treated samples also show a higher specific surface area due to the enlargement of the interlayer pore windows. The amount of Ti incorporated under otherwise identical conditions depends on the zeolite structure, which varies over a wide Si/Ti molar ratio range of 39–166. This is mainly caused by the distinctions in layer structures and, in particular, the initial interlayer entrance. To achieve an interlayer-expanded structure, the removal of interlayer occluded OSDA species must match well with the pillaring by Si species. For the structural expansion of MCM-47, a higher H2TiF6 treatment temperature (353 K) than that used to prepare the others (308 K) is required. To clarify the reaction mechanism, we monitored the treatment process in detail, taking the preparation of PLS-3 as a representative example. Further Characterization of IEZ-Ti-PLS-3. A series of IEZ-Ti-PLS-3 samples with different Ti contents were prepared by varying the amount of H2TiF6 in post-treatment. The samples were prepared by treating the PLS-3 precursor with aqueous H2TiF6 solution at various Si/Ti ratios under mild temperature conditions (for IEZ-Si-PLS-3, the treatment was performed in the absence of Ti using a HCl/NH4F mixture). The XRD investigation indicated that the interlayer expanded structure is

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constructed over a wide Si/Ti ratio range (5–∞) in solution (Figure 2). Table 3 summarizes the textural properties and Si/Ti ratios of the IEZ-Ti-PLS-3 products. Along with an increasing Si/Ti ratio in the preparative mixture, the Ti content of the resulting products decreases. To exclude the influence of Ti4+ ions on the interlayer silylation process, a control experiment was conducted in the absence of any Ti species, i.e., treating the PLS-3 precursor in HCl and NH4F solution while keeping the H+ and F- contents the same as those used in the preparation of IEZ-Ti-PLS-3-5 with Si/Ti = 5. The interlayer expanded structure forms readily without Ti4+ ions (Figure 2e), which indicates that pillaring by Si occurs predominantly, even in the complete absence of Ti. The presence of F- may raise health and safety concerns; however, it is critical to induce bi-functional modifications (as illustrated in Scheme 1), isomorphous substitution of Ti4+ for Si4+, and Si pillaring-assisted interlayer expansion. Consequently, we tried to reduce the amount of F- by replacing H2TiF6 with a combination of Ti(SO4)2 and NH4F. The results indicate that IEZ-Ti-PLS-3 is readily obtained when the amount of F- added is reduced by 80 % by using Ti(SO4)2 and NH4F, and Ti4+ loading at the same level as that using H2TiF6 treatment was achieved. XPS investigation indicates that the washed and calcined IEZ-PLS-3 possesses 1.5 wt% surface F- content. Further work on the influence of F- is necessary to address the issues concerning the practical usability of F systems, as well as F-related catalysis. This will be reported in future communications.

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We also investigated the weight loss caused by Si dissolution during H2TiF6 treatment by comparing the weights of calcined PLS-3 and calcined H2TiF6-treated PLS-3 prepared from equal weights of the same as-made PLS-3. The weight loss caused by H2TiF6 treatment is about 13.1 %. The SEM images verify that H2TiF6 treatment does not bring about morphology changes or amorphization (Figure S1). Both calcined PLS-3 and IEZ-Ti-PLS-5 are highly crystalline materials with small, rod-like crystals of ca. 100–200 nm in size. The 13C NMR spectra qualitatively prove that the OSDA TEA+ is not decomposed during H2TiF6 treatment (Figure 3), but 50–60 wt% of it is extracted, as indicated by quantitative TGA (Figure 4). The TGA curves show a weight loss of ca. 3–5 % before 373 K, which is caused by desorption of water molecules. Subsequently, a rapid weight loss of 8–10 % for IEZ-Ti-PLS-3-n samples and 20 % for the PLS-3 precursor are observed. This indicates that 50-60 % of the organic molecules are removed from the lamellar precursor PLS-3 by H2TiF6 treatment, which is different from that observed for the silylation treatment reported previously.46 The CHN elemental analysis gives consistent results (Table S4). The C/N ratio given by CHN elemental analysis is ca. 8, which is the theoretical C/N molar ratio for TEA+, indicating that the OSDA does not decompose during H2TiF6 treatment (Figure 3). This is further confirmed by the

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C NMR results. We calculated the amount of organic molecules

contained in the layered silicate according to the value for N obtained in elemental analysis, and nearly 60 wt % of the organic molecules are removed from the

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interlayers of PLS-3 by H2TiF6 treatment. Removal of organic species from the interlayer opens the space to accommodate Si species to form new Si-O-Si linkages with terminal silanols, and to allow the isomorphous substitution of Ti4+ to occur inside the zeolite channels. 29

Si MAS NMR spectroscopy was used to obtain information regarding the silanols

during post-treatment (Figure 5 and Table S5). The PLS-3 precursor presents resonances at -97–106 ppm (9.3 %) and -106–116 ppm (91.7 %), which are assigned to the Q3 and Q4 groups, respectively.33,39,47 Upon calcination, the Q3 resonance decreases in intensity significantly (1.24 %) as a result of interlayer dehydroxylation. H2TiF6 treatment leads to a new resonance at -91.07 ppm (Figure 5c), which is attributed to the Q2 groups. The relative peak area for Q2 decreases from 4.47 % for the as-made sample to 1.08 % for calcined IEZ-Ti-PLS-3-5 (Table S5, entries 2 and 3) and the relative peak area of Q3 increases at the expense of Q2. A similar phenomenon was observed in the silylation of PREFER, owing to two 5-MR units forming in the interlayer.33 Thus, the above phenomenon imply the presence of Si(OH)2(OSi)2 moieties pillaring the FER layers of PLS-3, similarly to that reported for PREFER. The increase in the Q3 signal at the expense of that for Q2 indicates that the two neighboring Q2 pillars may be partially condensed to form Si-O-Si bonds. Meanwhile, the intensity of the Q3 resonance does not decrease correspondingly, which is different from the result observed for the silylation case.3,33 This is most probably caused by two factors: Firstly, the removal of OSDA species that form SiO-···TEA+

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interactions results in more exposed silanols; secondly, corrosion by HF generates hydroxyl nests, leading to SiOH groups. Ar adsorption is a useful technique for obtaining the precise window sizes of micropores.48 The pore size distribution is centered at 3.2 Å for PLS-3 and 5.1 Å for IEZ-Ti-PLS-3 (Figure 6). The enlargement of the average pore size by 1.9 Å strongly indicates the formation of an interlayer expanded structure. From the adsorption isotherms using different vapor molecules (Figure 7), it is apparent that IEZ-Ti-PLS-3 has larger pores and pore volumes than PLS-3, as the former shows higher adsorption capacities for both small adsorbate molecules, i.e., H2O or hexane, and bulky molecules, i.e., benzene. Moreover, IEZ-Ti-PLS-3-5 exhibits a distinctly high adsorption of water (Figure 7A), implying that it is highly hydrophilic. This is in agreement with the

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Si NMR characterization, as the (Q2 + Q3)/Q4 ratio for

IEZ-Ti-PLS-3 is much higher than that of PLS-3-cal (Table S5). UV-Vis spectroscopy is a sensitive method that can be used to detect the coordination states of transition metal ions in zeolites, particularly in the case of Ti-, Sn-, or Zr-containing metallosilicates.49 The UV-Vis spectra of IEZ-Ti-PLS-3-n samples with different Ti loadings all present a main absorption band at 215 nm (Figure 8), which is characteristic of tetrahedrally coordinated Ti species in the framework. Meanwhile, a weak band at 260 nm is also observed for the IEZ-Ti-PLS-3-n samples prepared with higher Ti loadings (see b, c, and d). This implies the presence of a small quantity of hexa-coordinated extra-framework Ti

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species. Upon decreasing the Si/Ti ratio used in preparation, the 215 nm band increases in intensity, indicating that Ti4+ ions are incorporated mostly inside the framework. Meanwhile, the IR spectra show a characteristic band at ca. 960 cm-1 (Figure 9), which is regarded as the fingerprint for framework Ti species.42 This result further confirms that H2TiF6 treatment leads to effective incorporation of tetrahedrally coordinated Ti species into the framework. Thus, the H2TiF6 treatment effectively generates isolated tetrahedral Ti species through isomorphous substitution. Structure Analysis of IEZ-Si-PLS-3. For simplicity, the structure simulation was performed on siliceous IEZ-Si-PLS-3 free of Ti species. This is appropriate because the organic residue in as-made IEZ-Si-PLS-3 would affect the accuracy of the model, and refinement of the calcined material is enough to explain the structure. Additionally, we have to use the calcined material as the catalyst. Thus, we only provide structure refinement of IEZ-Si-PLS-3 after calcination (see Figure 10). The space group is IM11 (No. 8), we constructed the interlayer expanded structure using P1 as the space group and then optimized it. IM11 (No. 8) is the space group given by Material Studio after optimization, and its serial number is 8. The lattice parameters b and c of calcined IEZ-Si-PLS-3 resemble those of calcined PLS-3 (a = 18.721 Å, b = 13.987 Å, c = 7.415 Å) very closely, but the a parameter is significantly larger. The bc-planes in PLS-3 are parallel to the layers and are preserved in IEZ-Si-PLS-3. Thus, combined with analysis of the

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Si NMR data, a structural model was built for the

as-made IEZ-Si-PLS-3 based on the collection of FER sheets expanded by Q2 units,

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and for IEZ-Si-PLS-3, neighboring Q2 groups bond to form two adjacent 5-MRs, which is analogous to the formation of IEZ-FER prepared by silylation.33 The resulting material has 12 × 10-MR pore openings. For the refinement of the interlayer expanded structure, we have to take the silanol groups of the pillaring silicon into consideration. We considered a situation in which all silanol groups sit on opposite sides of the two 5-MRs, which agrees with the observed HREM images along the [010] zone more closely, according to the previous literature report.33 The atom labeling scheme is provided in Figure S2. According to the refined structure, IEZ-Si-PLS-3 has a unit cell composition of Si37O79H2 in the IM11 space group (Table 1 and S1-S3). The final results of the Rietveld analyses were Rwp = 7.89 %, Rp = 22.64 % and Rwp (w/o bck) = 7.83 %, indicating that the simulated powder pattern agrees well with the experimental one. Catalytic Properties IEZ-Ti-PLS-3. Table 4 compares the catalytic activities of different titanosilicates for the epoxidation of small alkenes. These titanosilcates have very similar Ti contents (except for Ti-MOR). Ti-MWW and TS-1 show higher activities than IEZ-Ti-PLS-3, but Ti-MOR and Ti-Beta are less active. Thus, Ti-MWW and TS-1 possess more efficient active sites for catalyzing small alkenes, but have less intrinsic activity. IEZ-Ti-PLS-3 appears to be a relatively active catalyst for selective epoxidation on the basis of the specific activity per Ti site, i.e., the turnover number (TON), and apparent alkene conversions. When increasing the substrate size to that of bulky cycloalkenes, Ti-MWW and

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TS-1 lose their catalytic superiority due to steric restrictions. It is worth highlighting that in the epoxidation of cyclohexene, IEZ-Ti-PLS-3 shows higher activity and oxide selectivity than the other materials (Table 5). The superiority of IEZ-Ti-PLS-3 to Ti-Beta with 3D 12-MR channels may be ascribed to its higher hydrophobicity. However, the change in TON with increasing cycloalkene molecular size (from C6 to C12) is similar for IEZ-Ti-PLS-3, Ti-MWW, TS-1, and Ti-MOR (Figure 11), but is different for Ti-Beta, which shows the maximum TON for cycloheptene, implying that the pore size of IEZ-Ti-PLS-3 is slightly smaller than that of *BEA. These results suggest that IEZ-Ti-PLS-3-5 has a pore size between the sizes of Ti-Beta and TS-1, which represent 12-MR and 10-MR zeolites, respectively. This is also in accord with the 12 × 10-MR structure of IEZ-Ti-PLS-3-5, as determined above.

CONCLUSIONS A facile and cheap method based on H2TiF6 treatment for post-synthesizing large

pore titanosilicates without using any external silane agents was proven to be useful. The one-pot preparation procedure involves the isomorphous substitution of Ti for Si and interlayer expansion by mobile Si debris. This strategy may possibly be extended to the preparation of other metallosilicates.

ASSOCIATED CONTENT

Supporting Information Available The Supporting Information is available free of charge via the Internet at http://pubs.acs.org.

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Figure S1 shows SEM images of calcined PLS-3 and IEZ-Ti-PLS-3-5. Figure S2 shows the atom labeling scheme of calcined IEZ-Si-PLS-3. Table S1 gives the final fractional coordinates with site occupancy factors for IEZ-Si-PLS-3 after Rietveld analysis. Table S2 and Table S3 show the interatomic distances and angles. Table S4 shown the organic-species content of the PLS-3 precursor and the as-made IEZ-Ti-PLS-3-n given by elemental and TG analysis. Table S5 shows relative intensity ratios of Q2, Q3, and Q4 resonances estimated by deconvolution of 29Si MAS NMR Spectra.

AUTHOR INFORMATION

Corresponding Author *E-mail: [email protected] Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS

The authors gratefully acknowledge the financial supports from NSFC of China (21533002, 21403069, 21573074), Programs Foundation of Ministry of Education (2012007613000), and Shanghai Synchrotron Radiation Facility (j13sr0021).

REFERENCES

(1) Čejka, J.; Wichterlova, B. Acid Catalyzed Synthesis of Mono and Dialkyl Benzenes over Zeolites: Active Sites, Zeolite Topology, and Reaction Mechanisms. Catal. Rev. 2002, 44, 375-421.

19



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(2) Davis, M. E. Ordered Porous Materials for Emerging Applications. Nature 2002, 417, 813-821. (3) Wu, P.; Ruan, J.; Wang, L.; Wu, L.; Wang, Y.; Liu, Y.; Fan, W.; He, M.; Terasaki, T.; Tatsumi, T. Methodology for Synthesizing Crystalline Metallosilicates with Expanded Pore Windows through Molecular Alkoxysilylation of Zeolitic Lamellar Precursors. J. Am. Chem. Soc. 2008, 130, 8178-8187. (4) Camblor, M. A.; Barrett, P. A.; Diaz-Cabanas, M. J.; Villaescusa, L. A.; Puche, M.; Boix, T.; Perez, E.; Koller, H. High Silica Zeolites with Three-Dimensional Systems of Large Pore Channels. Micropor. Mesopor. Mater. 2001, 48, 11-22. (5) Song, J.; Gies, H. Zeolites Synthesis in the System N(CH3)(C2H5)3F-SiO2-H2O. Stud. Surf. Sci. Catal. 2004, 154A, 295-300. (6) Zones, S. I.; Darton, R. J.; Morris, R.; Hwang, S. J. Studies on the Role of Fluoride Ion vs Reaction Concentration in Zeolite Synthesis. J. Phys. Chem. B 2005, 109, 652-661. (7) Sastre, G.; Corma, A. Predicting Structural Feasibility of Silica and Germania Zeolites. J. Phys. Chem. C 2010, 114, 1667-1673. (8) Castañeda, R.; Corma, A.; Fornés, V.; Rey, F.; Rius, J. Synthesis of a New Zeolite Structure ITQ-24, with Intersecting 10-and 12-Membered Ring Pores. J. Am. Chem. Soc. 2003, 125, 7820-7821. (9) Rachwalik, R.; Olejniczak, Z.; Jiao, J. Isomerization of α-pinene over Dealuminated Ferrierite-Type Zeolites. J Catal. 2007, 252, 161-170.

20


Page 20 of 46

Page 21 of 46

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(10) Verboekend, D.; Pérez-ramírez, J. Design of Hierarchical Zeolite Catalysts by Desilication. Catal Sci Technol. 2011, 1, 879-890. (11) Roth, W. J.; Nachtigall, P.; Morris, R. E. Two-dimensional Zeolites: Current Status and Perspectives. Chem. Rev. 2014, 114, 4807-4837. (12) Roth, W. J.; Čejka, J. Two-dimensional Zeolites: Dream or Reality. Catal. Sci. Technol 2011, 1, 43-53. (13) Leonowicz, M. E.; Lawton, J. A.; Lawton, S. L.; Rubin, M. K. MCM-22: A Molecular Sieve with Two Independent Multidimensional Channel Systems. Science 1994, 264, 1910-1913. (14) Schreyeck, L.; Caullet, P. H.; Mougenel, J. C.; Guth, J. L.; Marler, B. PREFER: A New Layered (Alumino) Silicate Precursor of FER-type Zeolite. Micropor. Mater. 1996, 6, 259-271. (15) Ikeda, T.; Kayamori, S.; Mizukami, F. Synthesis and Crystal Structure of Layered Silicate PLS-3 and PLS-4 as A Topotactic Zeolite Precursor. J. Mater. Chem. 2009, 19, 5518-5525. (16) Ikeda, T.; Akiyama, Y.; Oumi, Y.; Kawai, A.; Mizukami, F. The Topotactic Conversion of A Novel Layered Silicate into A New Framework Zeolite. Angew. Chem. Int. Ed. 2004, 43, 4892-4896. (17) Burton, A.; Accardi, R. J.; Lobo, R. F. MCM-47: A Highly Crystalline Silicate Composed of Hydrogen-Bonded Ferrierite Layers. Chem. Mater. 2002, 12, 2936-2942.

21



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 46

(18) Zanarrdi, S.; Alberti, A.; Cruciani, G.; Corma, A.; Forne´s, V.; Brunelli, M. Crystal Structure Determination of Zeolite Nu-6 (2) and Its Layered Precursor Nu-6 (1). Angew. Chem. Int. Ed. 2004, 43, 4933-4937. (19) Oberhagemann, U.; Bayat, P.; Marler, B.; Gies, H.; Rius, J. A Layer Silicate: Synthesis

and

Structure

of

the

Zeolite

Precursor

RUB-15-[N(CH3)4]8[Si24O52(OH)4]•20H2O. Angew. Chem. Int. Ed. 1996, 35, 2869-2872. (20) Moteki, T.; Chaikittisilp, W.; Shimojima, A.; Okubo, T. Silica Sodalite without Occluded Organic Matters by Topotactic Conversion of Lamellar Precursor. J. Am. Chem. Soc. 2008, 130, 15780-15781. (21) Marler, B.; Ströter, N.; Gies, H. The Structure of the New Pure Silica Zeolite RUB-24, Si32O64, Obtained by Topotactic Condensation of the Intercalated Layer Silicate RUB-18. Micropor. Mesopor. Mater. 2005, 83, 201-211. (22) Wang, Y. X.; Gies, H.; Marler, B. Synthesis and Crystal Structure of Zeolite RUB-41 Obtained as Calcination Product of A Layered Precursor: A Systematic Approach to A New Synthesis Route. Chem. Mater. 2005, 17, 43-49. (23) Choi, M.; Na, K.; Kim, J.; Sakamoto, Y.; Terasaki, O.; Ryoo, R. Stable Single-Unit-Cell Nanosheets of Zeolite MFI as Active and Long-Lived Catalysts. Nature 2009, 461, 246-249.

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Page 23 of 46

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(24) Wheatley, P. S.; Morris, R. E. Calcination of A Layered Aluminofluorophosphate Precursor to Form the Zeolitic AFO Framework. J. Mater. Chem. 2006, 16, 1035-1037. (25) Rojas, A.; Camblor, M. A. HPM-2, the Layered Precursor to Zeolite MTF. Chem. Mater. 2014, 26, 1161-1169. (26) Marler, B.; Camblor, M. A.; Gies, H. The Disordered Structure of Silica Zeolite EU-20b, Obtained by Topotactic Condensation of the Piperazinium Containing Layer Silicate EU-19. Micropor. Mesopor. Mater. 2006, 90, 87-101. (27) Schmidt, J. E.; Xie, D.; Davis, M. E. Synthesis of the RTH-type Layer: the First Small-pore, Two Dimensional Layered Zeolite Precursor. Chem. Sci. 2015, 6, 5955-5963. (28) Roth, W. J.; Nachtigall, P.; Morris, R. E. A Family of Zeolites with Controlled Pore Size Prepared Using A Top-Down Method. Nat. Chem. 2013, 5, 628-633. (29) Roth, W. J.; Kresge, C. T.; Vartuli, J. C.; Leonowicz, M. E.; Fung, A. S.; McCullen, S. B. Stud. Surf. Sci. and Catal. 1995, 94, 301-308. (30) Corma, A.; Fornes, V.; Pergher, S. B.; Maesen, T. L. M.; Buglass, J. G. Delaminated Zeolite Precursors as Selective Acidic Catalysts. Nature 1998, 393, 353-356. (31) Corma, A.; Diaz, U.; Fornés, V.; Guil, J.M.; Martínez-Triguero, J.; Creyghton, E.J. Characterization and Catalytic Activity of MCM-22 and MCM-56 Compared with ITQ-2. J. Catal. 2000, 191, 218-224.

23



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(32) Maheswari, S.; Jordan, E.; Kumar, S.; Bates, F. S.; Penn, R. L.; Shantz, D. F.; Tsapatsis, M. Layer Structure Preservation during Swelling, Pillaring, and Exfoliation of A Zeolite Precursor. J. Am. Chem. Soc. 2008, 130, 1507-1516. (33) Ruan, J.; Wu, P.; Slater, B.; Zhao, Z.; Wu, L.; Terasaki, O. Structural Characterization of Interlayer Expanded Zeolite Prepared from Ferrierite Lamellar Precursor. Chem. Mater. 2009, 21, 2904-2911. (34) Gies, H.; Müller, U.; Yilmaz, B.; Tatsumi, T.; Xie, B.; Xiao, F. S.; Bao, X. H.; Zhang, W. P.; Vos, D. D. Interlayer Expansion of the Layered Zeolite Precursor RUB-39: A Universal Method to Synthesize Functionalized Microporous Silicates. Chem. Mater. 2011, 23, 2545-2554. (35) Xiao, F. S.; Xie, B.; Zhang, H. Y.; Wang, L.; Meng, X. J.; Zhang, W. P.; Bao, X. H.; Yilmaz, B.; Müller, U.; Gies, H.; Imai, H.; Tatsumi, T.; Vos, D. D. Interlayer-Expanded Microporous Titanosilicate Catalysts with Functionalized Hydroxyl Groups. ChemCatChem 2011, 3, 1442-1446. (36) Gies, H.; Müller, U.; Yilmaz, B.; Feyen, M.; Tatsumi, T.; Imai, H.; Zhang, H. Y.; Xie, B.; Xiao, F. S.; Bao, X. H.; Zhang, W. P.; Baerdemaeker, T. D.; Vos, D. D. Interlayer Expansion of the Hydrous Layer Silicate RUB-36 to A Functionalized, Microporous Framework Silicate: Crystal Structure Analysis and Physical and Chemical Characterization. Chem. Mater. 2012, 24, 1536-1545.

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Page 25 of 46

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(37) Jiang, J. G.; Jia, L. L.; Yang, B. T.; Xu, H.; Wu, P. Preparation of Interlayer-Expanded Zeolite from Lamellar Precursor Nu-6(1) by Silylation. Chem. Mater. 2013, 25, 4710-4718. (38) Yilmaz, B.; Müller, U.; Feyen, M.; Zhang, H. Y.; Xiao, F. S.; Baerdemaeker, T. D.; Tijsebaert, B.; Jacobs. P.; Vos, D. D.; Zhang, W. P.; Bao, X. H.; Imai, H.; Tatsumih, T.; Gies, H. New Zeolite Al-COE-4: Reaching Highly Shape-Selective Catalytic Performance through Interlayer Expansion. Chem. Commum. 2012, 48, 11549-11551. (39) Inagakia, S.; Tatsumi, T. Vapor-Phase Silylation for the Construction of Monomeric Silica Puncheons in the Interlayer Micropores of Al-MWW Layered Precursor. Chem. Commun. 2009, 18, 2583-2585. (40) Wu, P.; Tatsumi, T.; Komatsu, T.; Yashima, T. A Novel Titanosilicate with MWW Structure. I. Hydrothermal Synthesis, Elimination of Extraframework Titanium, and Characterizations. J. Phys. Chem. B 2001, 105, 2897-2905. (41) Bellussi, G.; Gigutto, M. S. Chapter 19 Metal Ions Associated to Molecular Sieve Frameworks as Catalytic Sites for Selective Oxidation Reactions. Stud. Surf. Sci. Catal. 2001, 137, 911-955. (42) Wu, P.; Komatsu, T.; Yashima, T. Characterization of Titanium Species Incorporated into Dealuminated Mordenites by Means of IR Spectroscopy and 18

O-exchange Technique. J. Phys. Chem. 1996, 100, 10316-10322.

(43) Blasco, T.; Camblor, M. A.; Corma, A.; Perez-Pariente, J. The State of Ti in Titanoaluminosilicates Isomorphous with Zeolite Beta. J. Am. Chem. Soc. 1993, 115,

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11806-11813. (44) Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865. (45) Materials Studio Release Notes v.6.1; Accelrys Software: San Diego, CA, 2012. (46) Ikeda, T.; Kayamori, S.; Oumi, Y.; Mizukami, F. Structure Analysis of Si-Atom Pillared Lamellar Silicates Having Micropore Structure by Powder X-ray Diffraction. J. Phys. Chem. C 2010, 114, 3466-3476. (47) Inagaki, S.; Yokoi, T.; Kubota, Y.; Tatsumi, T. Unique Adsorption Properties of Organic–Inorganic Hybrid Zeolite IEZ-1 with Imethylsilylene Moieties. Chem. Commun. 2007, 48, 5188-5190. (48) Moliner, M.; Corma, A. Synthesis of Expanded Titanosilicate MWW-Related Materials from A Pure Silica Precursor. Chem. Mater. 2012, 24, 4371-4375. (49) Li, P.; Liu, G. Q.; Wu, H. H.; Liu, Y. M.; Jiang, J. G.; Wu, P. Postsynthesis and Selective Oxidation Properties of Nanosized Sn-Beta Zeolite. J. Phys. Chem. C 2011, 115, 3663-3670. Figure captions Scheme 1. Strategy for synthesizing large-pore titanosilicates from zeolitic lamellar precursors through H2TiF6-assisted one-pot Ti insertion and interlayer pillaring by Si species. Figure 1. XRD patterns of (a) the lamellar precursor of zeolitic silicate, (b) the 3D crystalline zeolite formed by direct calcination of the precursor, and (c) the new IEZ-titanosilicate prepared by H2TiF6 treatment and further calcination.

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Figure 2. XRD patterns of (a) as-made PLS-3, (b) IEZ-Ti-PLS-3-5, (c) IEZ-Ti-PLS-3-10, (d) IEZ-Ti-PLS-3-20, (e) IEZ-Ti-PLS-3-30, and (f) IEZ-Si-PLS-3. The products were in calcined form. Figure 3. 13C NMR spectra of (a) the PLS-3 precursor and (b) the as-made IEZ-Ti-PLS-3-5. Figure 4. TGA curves of (a) PLS-3 and as-made samples of (b) IEZ-Ti-PLS-3-5, (c) IEZ-Ti-PLS-3-10, (d) IEZ-Ti-PLS-3-20, and (e) IEZ-Ti-PLS-3-30. Figure 5.

29

Si NMR spectra of (a) as-made PLS-3, (b) calcined PLS-3, (c) as-made

IEZ-Ti-PLS-3-5, and (d) calcined IEZ-Ti-PLS-3. Figure 6. Pore size distribution of (a) PLS-3 and (b) IEZ-Ti-PLS-3-5 obtained by Ar adsorption. Figure 7. Vapor adsorption isotherms of the calcined samples of (■) PLS-3 and (●) IEZ-Ti-PLS-3-5. Figure 8. UV-Vis spectra of (a) IEZ-Ti-PLS-3-30, (b) IEZ-Ti-PLS-3-20, (c) IEZ-Ti-PLS-3-10, and (d) IEZ-Ti-PLS-3-5. Figure 9. FT-IR spectra of (a) calcined PLS-3, (b) IEZ-Ti-PLS-3-30, (c) IEZ-Ti-PLS-3-20, (d) IEZ-Ti-PLS-3-10, and (e) IEZ-Ti-PLS-3-5. Figure 10. Rietveld refinement of the PXRD data for IEZ-Si-PLS-3. Experimental (red) and calculated (black) XRD patterns, as well as the difference profile, are shown (blue). The short tick marks (green) below the patterns give the positions of the Bragg reflections. The insets show the refined structure view along the [001] and [010] directions, indicating 12-MR and 10-MR channels. Figure 11. The turnover number (TON) for the epoxidation of cycloalkenes with 6–12 carbon

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atoms over various titanosilicate catalysts. For reaction conditions, see Table 5.

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Table 1. Experimental Parameters for Structure Analysis of Calcined IEZ-Si-PLS-3. Parameter

Value /remark

Sample Unite cell composition Condition of data collection Diffractometer Sample holder Wavelength 2θ range Step size Number of points Total no. of reflections FWHM [deg] Peak profile Profile parameters Structural parameters Lattice parameters a b c α [deg] β [deg] γ [deg] Number of atoms Space group Rwp Rwp (w/o bck) Rp

IEZ-Si-PLS-3 Si37O79H2 Room temperature data collection SSRFBL14B1 Capillary 1.2438Å 3–48o 0.013o (2θ) 3461 380 0.162 (2θ = 21.40o) Thompson-Cox-Hastings 9 179 23.6095(36) Å 14.0547(22) Å 7.4675(28) Å 90 90 90 118 IM11 (No. 8) 7.89 % 7.83 % 22.64 %

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Table 2. Physicochemical Properties of Lamellar Precursors, Directly Calcined Samples and Interlayer Expanded Zeolites. Surface area (m2 g-1)

d Spacing (Å)

Original zeolite

hkla

precursor

3Db

H2TiF6-treatedc

3Db

H2TiF6-treatedc

PLS-4

020

10.87

9.18

11.79

303

331

166

MCM-47

020

11.25

9.16

11.51

312

410

65

a

e

RUB-39

010

10.72

8.72

11.04

-

PLS-3

200

11.74

9.36

11.87

379

b

-

e

459

Si/Tid

-e 41

Representative layered structure-related plane. Three-dimensional zeolites obtained by direct calcination of the precursors. c New IEZ-titanosilicate prepared by H2TiF6 treatment and further calcination. d Molar ratio given by ICP. e Not determined.

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Table 3. Surface Area (SBET)a, Total Pore Volume (Vtotal)b and Si/Ti ratiosc of calcined PLS-3 and IEZ-Ti-PLS-3-n. Sample

SBET (m2 g-1)

Si/Ti ratio in product

Vtotal (mL g-1)

Calcined PLS-3 ∞ 379 0.27 IEZ-Ti-PLS-3-5 41 459 0.29 IEZ-Ti -PLS-3-10 55 404 0.27 IEZ-Ti -PLS-3-20 64 438 0.28 IEZ-Ti -PLS-3-30 86 425 0.28 a Specific surface area given by N2 adsorption at 77 K and estimated by the Brunauer-Emmett-Teller (BET) method. b Calculated from the adsorption capacity at P/P0 = 0.9. c Determined by ICP.

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Table 4. Catalytic Activity of Different Catalysts in the Oxidation of Small Molecule Alkenes.a Sample

Si/Ti

Ti-MWW Ti-Beta IEZ-Ti-PLS-3-5 TS-1 Ti-MOR b

42 36 39 40 155

1-Pentene

1-Hexene

Cyclopentene

Conv. (%)

TON

Conv. (%)

TON

Conv. (%)

TON

57.5 6.7 21.0 25.4 5.3

290 36 98 122 25

42.5 5.5 15.4 21.0 0.4

214 30 72 101 2

24.9 13.0 35.1 52.8 4.4

125 70 164 253 20

a

Reaction conditions: catalyst, 0.05 g; acetonitrile, 7.8 g; alkane, 10 mmol; H2O2 (31 % aqueous solution), 10 mmol; 333 K, 2 h. b 0.2 g catalyst was used while keeping other conditions identical.

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Table 5. Catalytic Activity of Different Catalysts in the Oxidation of Cyclohexene.a Sample

Si/Ti

Conv. (%)

Ti-MWW Ti-Beta IEZ-Ti-PLS-3-5 TS-1 Ti-MOR b

42 36 39 40 155

6.5 9.1 15.2 3.2 3.4

Sel. (%) Epoxide

Others c

39.0 47 52.3 41.7 43.5

61.0 53 47.7 58.3 54.9

a

Reaction conditions: catalyst, 0.05 g; acetonitrile, 7.8 g; alkane, 10 mmol; H2O2 (31 % aqueous solution), 10 mmol; 333 K, 2 h. b 0.2 g catalyst was used while keeping other conditions identical. c By-products of cyclohexanediol, 2-cyclohexen-1-ol and 2-cyclohexen-1-one.

33


o o Ti o o

o o Si o o

Isomorphous substitution

Lamellar Precursor of Zeolitic Silicate

OSDA

H2TiF6

OH

HO OH

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 34 of 46

HO


Si species

Interlayer pillaring by Si

Calcination

Interlayer-Expanded Ti-Zeolite

Scheme 1. Strategy for synthesizing large-pore titanosilicates from zeolitic lamellar precursors through H2TiF6-assisted one-pot Ti insertion and interlayer pillaring by Si species.

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010

RUB-39

c b a

5

10

15

20

25

30

200

PLS-3 c b a 5

10

15

20

25

30

020

MCM-47

c b a

5

10

15

20

25

30

020

PLS-4

c b a

5

10

15

20

25

30

2 Theta (Cu Kα)

Figure 1. XRD patterns of (a) the lamellar precursor of zeolitic silicate, (b) the 3D crystalline zeolite formed by direct calcination of the precursor, and (c) the new IEZ-titanosilicate prepared by H2TiF6 treatment and further calcination.

35



e

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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d c b a 5

10

15

20

25

30

35

2Theta (degree)

Figure 2. XRD patterns of (a) as-made PLS-3, (b) IEZ-Ti-PLS-3-5, (c) IEZ-Ti-PLS-3-10, (d) IEZ-Ti-PLS-3-20, (e) IEZ-Ti-PLS-3-30, and (f) IEZ-Si-PLS-3. The products were in calcined form.

36


Page 37 of 46

2

+

1

N

C2

C1

Intensty (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


b

a

80

60 40 20 0 Chemical shift (ppm)

Figure 3. 13C NMR spectra of (a) the PLS-3 precursor and (b) the as-made IEZ-Ti-PLS-3-5.

37



100

95

Weight Weightloss loss(%) (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 38 of 46

b

90

d

c e

85

a

80

100 200 300 400 500 600 700 800 o o Temperature ( (C)C) Temperature

Figure 4. TGA curves of (a) PLS-3 and as-made samples of (b) IEZ-Ti-PLS-3-5, (c) IEZ-Ti-PLS-3-10, (d) IEZ-Ti-PLS-3-20, and (e) IEZ-Ti-PLS-3-30.

38


Page 39 of 46

Q4

×5

3

Q

Intensity (a.u.)

Q2

d

×5

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


c ×5

b

a

-80

-90

-100

-110

-120

-130

Chemical shift shift (ppm) (ppm) Chemical

Figure 5. 29Si NMR spectra of (a) as-made PLS-3, (b) calcined PLS-3, (c) as-made IEZ-Ti-PLS-3-5, and (d) calcined IEZ-Ti-PLS-3.

39



5.1 Å

dv/dw (cm3 g-1 Å-1)

3.2 Å

b

a

3

4

5

6

?

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 40 of 46

7

8

Pore width ((Å) )

Figure 6. Pore size distribution of (a) PLS-3 and (b) IEZ-Ti-PLS-3-5 obtained by Ar adsorption.

40


Volume adsorbed (cm 3 g -1)


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60



Page 41 of 46

400 H2O

300 b 200 100 a 0 0.0 0.2 0.4 0.6 0.8 1.0 P/P0 100

80

Hexane

60 b 40 20 a 0 0.0 0.2 0.4 0.6 0.8 1.0 P/P0 100

80

Benzene

60 b

40 20

a 0 0.0 0.2 0.4 0.6 0.8 1.0 P/P0

Figure 7. Vapor adsorption isotherms of the calcined samples of (■) PLS-3 and (●) IEZ-Ti-PLS-3-5.

41



4 215 Absorbance (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 42 of 46

3 2

260 d c b a

1 0 200

250 300 350 Wavelength (nm)

400

Figure 8. UV-Vis spectra of (a) IEZ-Ti-PLS-3-30, (b) IEZ-Ti-PLS-3-20, (c) IEZ-Ti-PLS-3-10, and (d) IEZ-Ti-PLS-3-5.

42


Page 43 of 46

963 1.5 Absorbance (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1.0 e d c b a

0.5

0.0 1400 1200 1000 800 600 -1 Wavenumber (cm ) Figure 9. FT-IR spectra of (a) calcined PLS-3, (b) IEZ-Ti-PLS-3-30, (c) IEZ-Ti-PLS-3-20, (d) IEZ-Ti-PLS-3-10, and (e) IEZ-Ti-PLS-3-5.

43


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Intensity (a.u.)


[001]

10

20

[010]

30

40

2 Theta (degree)

Figure 10. Rietveld refinement of the PXRD data for IEZ-Si-PLS-3. Experimental (red) and calculated (black) XRD patterns, as well as the difference profile, are shown (blue). The short tick marks (green) below the patterns give the positions of the Bragg reflections. The insets show the refined structure view along the [001] and [010] directions, indicating 12-MR and 10-MR channels.

44


Page 44 of 46

Page 45 of 46

75

Ti-MWW IEZ-Ti-PLS-3-5 TS-1 Ti-MOR Ti-Beta

50 TON

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


25

0 C6

C7

C8

C12

Figure 11. The turnover number (TON) for the epoxidation of cycloalkenes with 6–12 carbon atoms over various titanosilicate catalysts. For reaction conditions, see Table 5.

45



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

TOC

46


Page 46 of 46

Synthesis of Novel Titanosilicate Catalysts by Simultaneous

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