Development of the CON-type Aluminosilicate Zeolite and Its Catalytic Application for the MTO Reaction

The <b>CON</b>-type aluminosilicate zeolites, which consist of a three-dimensional pore system with 12-, 12-, and 10-membered ring pores have been prepared by postsynthesis and the newly developed direct-synthesis methods. We first found that the <b>CON</b>-type aluminosilicate zeolites exhibited a higher catalytic performance in the methanol to olefins (MTO) reaction in terms of duration and propene selectivity than the <b>MFI</b> and *<b>BEA</b>-type aluminosilicate zeolites. They exhibited high propene selectivity, low ethene selectivity, and a very long catalytic life compared to Beta and ZSM-5; the selectivity for C3–C4 olefins reached 80%. Interestingly, the <b>CON</b>-type aluminosilicate zeolite synthesized by the direct-synthesis method showed a much longer catalytic lifetime than the one obtained by the postsynthesis method. The ²⁷Al MAS and ²⁷Al MQMAS NMR spectra suggest that there is a significant difference in the state of tetrahedrally coordinated Al species between the directly and postsynthesized zeolites, leading to the marked difference in the catalytic performance

Intramolecular H/D Exchange of Ethanol Catalyzed by Acidic OH Groups on H‑ZSM‑5 Zeolite

IR observation of ethanol adsorption clarified the presence of the apparent intramolecular isotope exchange from CD₃CH₂OH to CHD₂CH₂OD on acidic OH groups of H-ZSM-5 zeolite. This reaction did not proceed with CD₃OH nor CH₃CD₂OH, implying that the β-hydrogen of alcohol had interaction with the lattice oxygen adjacent to Al and that the reaction was mediated by isotope exchange of CD₃ groups of ethanol and OH groups on zeolite

Control of the Al Distribution in the Framework of ZSM‑5 Zeolite and Its Evaluation by Solid-State NMR Technique and Catalytic Properties

The effects of the organic structure-directing agents (OSDAs) and Na cations for the synthesis of ZSM-5 on the location of Al atom in the framework as well as the acidic and catalytic properties were investigated. To achieve these purposes, ZSM-5 zeolites were synthesized by using four kinds of OSDAs including tetrapropylammonium hydroxide cations, dipropylamine, cyclohexylamine, and hexamethylenimine with or without Na cations. In situ FT-IR spectroscopy using CO as probe molecule was applied to the evaluation of the acid property of the ZSM-5 zeolites. The location of Al atoms was examined by high resolution ²⁷Al MAS and MQMAS NMR techniques. The constraint index (CI) has also been used to estimate the distribution of acid sites in the micropores. The location of acid sites was investigated based on the difference in the transition-state shape-selectivity through the cracking of <i>n</i>-hexane and 3-methylpentane. Furthermore, the cracking of various types of paraffins and the conversion of aromatic compounds were conducted to clarify the acid site distributions

Determination of Acid Site Location in Dealuminated MCM-68 by ²⁷Al MQMAS NMR and FT-IR Spectroscopy with Probe Molecules

A series of MCM-68 zeolites with different Si/Al ratios were prepared by treatment with nitric acid and compared with beta zeolites. Speciation of aluminum and location of acid sites changed depending on the Si/Al ratio. The location of Brønsted acid sites in MCM-68 samples was able to be classified by FT-IR measurements with pyridine and 2,6-di-<i>tert</i>-butylpyridine as probe molecules, and the number of Brønsted acid sites was quantified according to the locations. For high-aluminum MCM-68, Brønsted acid sites were broadly distributed in both the 12-ring channel and 10-ring windows as well as inside the supercage. The Brønsted acid sites in the 12-ring channel were easily removed by the acid treatment, and consequently, high-silica MCM-68 had Brønsted acid sites predominantly in the 10-ring windows and inside the supercage. ²⁷Al MQMAS NMR spectra of high-silica MCM-68 showed two specific peaks assignable to T6 and T7 sites, which did not face the 12-ring channel, forming the Brønsted acid sites highly tolerant to the acid treatment. MCM-68 catalysts showed better catalytic performance in dehydration of sorbitol than beta, mordenite, and ZSM-5. Large void spaces at the intersection of 12- and 10-ring channels and inside the supercage for MCM-68 made it easy to take bulky transition states in the dehydration of sorbitol, resulting in its high catalytic performance

Insights into the Topotactic Conversion Process from Layered Silicate RUB-36 to FER-type Zeolite by Layer Reassembly

Layered RUB-36 and PREFER (lamellar precursor of ferrierite) are the precursors of CDO and FER-type zeolites, respectively. Both are composed of the same ferrierite (FER) layer building blocks. Topotactic conversion from RUB-36 to pure silica zeolite ZSM-35 has been demonstrated in the presence of a surfactant cetyltrimethylammonium hydroxide (CTAOH). The transformation mechanism of this process was revealed, for the first time, by the detailed investigations of powder X-ray diffraction (XRD), scanning electron microscopy (SEM), thermal analysis, and one- and two-dimensional (2-D) solid-state magic-angle spinning nuclear magnetic resonance (MAS NMR) as well as theoretical simulations. During swelling at room temperature, cetyltrimethylammonium cations (CTA⁺) replacing the original template were intercalated into FER layers to expand the interlayer distance remarkably and consequently to destroy the strong hydrogen-bonding interactions between the layers. 2-D ¹H–²⁹Si heteronuclear correlation (HETCOR) NMR indicates that the surfactant polar heads approximate the FER layers in swollen RUB-36. After deswelling, only a small amount of CTA⁺ cations with long tails lay in the void space between the FER layers. The Monte Carlo simulations on the deswollen RUB-36 further elucidate the occlusion of CTA⁺ cations in the pre-10 member ring of the layered ferrierite precursor, which may act as the structure-directing agent for the formation of FER-structured zeolite. The FER layer reassembly from the alteration of CTA⁺ conformation at the interlayers is of key importance to the topotactic transformation of RUB-36 to FER-type zeolite by the dehydration-condensation reaction. This may open up more applications in the lamellar zeolite system by the layer restacking approach

Interlayer Expansion of the Hydrous Layer Silicate RUB-36 to a Functionalized, Microporous Framework Silicate: Crystal Structure Analysis and Physical and Chemical Characterization

The hydrous layer silicate RUB-36, (C₆H₁₆N)₄ [H₄Si₃₆O₇₆], has been used for an interlayer expansion reaction with dichlorodimethylsilane to interconnect neighboring ferrierite-type layers to a three-dimensional framework silicate. The linker group (−O–Si­(CH₃)₂–O−) still has the two methyl groups in the as-synthesized form (material name COE-3 [Si₂₀O₃₈(CH₃)₄] for the silicate framework) rendering hydrophobic properties. The interlayer expanded zeolite, IEZ, is thermally stable and can be calcined at 550 °C to yield a hydrophilic material COE-4 [Si₂₀O₃₈(OH)₄]. ²⁹Si solid state MAS NMR experiments confirm the insertion of the linker group and the methyl and hydroxyl substitution in the as-made and calcined form, respectively. The BET surface area is 238 m²/g for COE-3 and 350 m²/g for COE-4. COE-3 and COE-4 crystallize in space group <i>Pm</i> with <i>a</i> = 12.2503(3) Å, <i>b</i> = 13.9752(2) Å, <i>c</i> = 7.3850(1) Å, and β = 107.33(1)° and <i>a</i> = 12.16985(4) Å, <i>b</i> = 13.95066(3) Å, <i>c</i> = 7.37058(2) Å, and β = 107.30(1)°, respectively. Rietveld crystal structure refinement of the PXRD pattern of COE-3 and COE-4 reveal the expanded, two-dimensional 10-ring pore system including the linker group as homogeneous structural property of the materials