Synthesis design and structure of a multipore zeolite with interconnected 12- and 10-MR channels

A new molecular sieve, ITQ-38, containing interconnected large and medium pores in its structure has been synthesized. The rational combination of dicationic piperidine-derivative molecules as organic structure directing agents (OSDAs) with germanium and boron atoms in alkaline media has allowed the synthesis of ITQ-38 zeolite. High-resolution transmission electron microscopy (HRTEM) has been used to elucidate the framework topology of ITQ-38, revealing the presence of domains of perfect ITQ-38 crystals as well as very small areas containing nanosized ITQ-38/ITQ-22 intergrowths. The structure of ITQ-38 is highly related to ITQ-22 and the recently described polymorph C of ITQ-39 zeolite. It shares a common building layer with ITQ-22 and contains the same building unit as the polymorph C of ITQ-39. All three structures present similar framework density, 16.1 T atoms/1000 ?(3).     

Synthesis and crystal structure of As-synthesized and calcined pure silica zeolite ITQ-12

The small-pore pure silica zeolite ITQ-12 has been synthesized with fumed silica as the silica source in the presence of 1,3,4-trimethylimidazolium hydroxide and hydrofluoric acid under hydrothermal conditions at 448 K. Rietveld refinement using synchrotron X-ray diffraction data of the calcined ITQ-12 product taken at 298 K confirms the proposed topology, framework type code ITW, which can be described by a monoclinic unit cell [Si(24)O(48)] having Cm symmetry. Unit cell parameters are a = 10.3360(4), b = 15.0177(6), and c = 8.8639(4) A, beta = 105.356(3) degrees, and cell volume V = 1326.76(9) A(3). For as-synthesized ITQ-12, the occluded fluoride anion is located inside the double four-membered ring, while the flat 1,3,4-trimethylimidazolium cation lies on the equatorial plane of the slit-shaped [4(4)5(4)6(4)8(4)] cage, with its longest dimension in the [010] direction. The monoclinic unit cell |(C(6)N(2)H(11))(+)(2)F(-)(2)|[Si(24)O(48)], having Cm symmetry, has parameters a = 10.4478(3), b = 14.9854(4), and c = 8.8366(3) A, beta = 105.935(2) degrees, and cell volume V = 1330.34(7) A(3) at 298 K. Cooperative structure-directing effects during the crystallization of ITQ-12 are discussed in terms of the structure of the as-made material.     

Synthesis and Structure Determination of SCM-15: A 3D Large Pore Zeolite with Interconnected Straight 12×12×10-Ring Channels

A new germanosilicate zeolite named SCM-15 (Sinopec Composite Material No. 15), the first zeolite containing a 3-dimensional (3D) channel system with interconnected 12-, 12-, and 10-ring channels (pore sizes: 6.1×7.2, 6.1×7.4, and 5.2×5.9 Å), has been synthesized using neutral 4-pyrrolidinopyridine as organic structure-directing agents (OSDAs). Its structure has been determined by combining single-crystal electron diffraction (SCED) and synchrotron powder X-ray diffraction (SPXD) data. The unique open framework structure of SCM-15 is related to that of FOS-5 ( BEC ), ITQ-7 ( ISV ), PKU-16 ( POS ), ITQ-26 ( IWS ), ITQ-21, Beta polymorph B, and SU-78B, since all these framework structures can be constructed from similar chains which are connected through shared 4-ring or double 4-ring (d4r) units. Based on this relation, six topologically reasonable 3D large or extra-large pore hypothetical zeolites are predicted.     

Synthesis of a new zeolite structure ITQ-24, with intersecting 10- and 12-membered ring pores

A new 10- and 12-membered ring zeolite, named ITQ-24, has been synthesized, and its structure has been solved. It has been found that this zeolite structure is topologically identical to that proposed for the hypothetical polymorph C of the SSZ-33/SSZ-26/CIT-1 family. This new zeolite has been achieved by using a rational approach of introducing Ge in the framework that has a directing effect toward zeolite structures with double-four-membered rings as secondary building units. Notoriously, active catalytic centers, such as Ti and Al, have been incorporated into this new zeolite, demonstrating that it is catalytically active for alkylation of aromatics.     

A new aluminosilicate molecular sieve with a system of pores between those of ZSM-5 and beta zeolite

A new aluminosilicate zeolite (ITQ-39) has been synthesized. This is an extensively faulted structure with very small domains that makes the structure elucidation very difficult. However, a combination of adsorption spectroscopy and reactivity studies with selected probe molecules suggests that the pore structure of ITQ-39 is related to that of Beta zeolite, with a three-directional channel system with large pores (12-MR), but with an effective pore diameter between those of Beta and ZSM-5, or a three-directional channel system with interconnected large (12-MR) and medium pores (10-MR). The pore topology of ITQ-39 is very attractive for catalysis and shows excellent results for the preparation of cumene by alkylation of benzene, while it can be a promising additive for FCC.     

Synthesis and structure of the bidimensional zeolite ITQ-32 with small and large pores

A new bidimensional zeolite containing 8R and 12R pores, denoted as ITQ-32, has been synthesized and its structure solved from powder X-ray diffraction data. This zeolite presents a relatively large pore volume (0.16 cm3/g) and pore apertures of 3.5 x 4.3 A and can be prepared as a nearly pure silica zeolite and as aluminosilicate. In the latest case, acidic properties are developed.     

Propene adsorption sites in zeolite ITQ-12: a combined synchrotron X-ray and neutron diffraction study

The adsorption site of propene in the small-pore, pure silica zeolite [Si24O48]-ITW-ITQ-12 has been characterized via Rietveld refinement of the crystal structure of propene-loaded ITQ-12 on the basis of synchrotron X-ray and neutron diffraction data taken at 298 K. The structure can be described with a monoclinic unit cell having Cm symmetry and unit cell parameters a = 10.436 angstroms, b = 15.018 angstroms, c = 8.855 angstroms, beta = 105.74 degrees, and volume = 1335.9 angstroms3. Four-fold disordered adsorption sites that are nearly equivalent relative to the cage's 2/m pseudosymmetry are located near the center of each ellipsoidally shaped [4(4)5(4)6(4)8(4)] cage. At this site, the adsorbed propene molecule lies on a plane close and approximately parallel to the equatorial plane of the cage and is aligned with its methylene group pointing toward the pore's eight-ring window. The refined propene concentration, 1.8 per unit cell content, is close to one propene molecule per [4(4)5(4)6(4)8(4)] cage and the amount observed in adsorption experiments at 298 K and 1 atm propene partial pressure.     

Photochemical generation of electrons and holes in germanium-containing ITQ-17 zeolite

Laser flash photolysis of germanium-containing ITQ-17 zeolite (Ge/ITQ-17, a single polymorph of beta zeolite) at 266 nm generates a transient spectrum decaying in the sub-millisecond time scale that is compatible with the formation of two transient species. The shorter lived transient (tau approximately 45 micros under nitrogen) has been assigned to trapped electrons due to the characteristic spectroscopic absorption (single band at 480 nm) and its quenching by typical electron scavengers such as N(2)O and CH(2)Cl(2). The second longer lived transient (lambda(max) = 500, 540, and 600 nm; tau approximately 390 micros) is not quenched by O(2) or electron scavengers, but it is quenched by methanol as hole scavenger and has been assigned to positive holes. Also there is a remarkable similarity of the transient spectrum of the Ge/ITQ-17 with the optical spectrum reported previously for electron-hole pairs in ZSM-5 zeolite. Under the same irradiation conditions, photoejection of electrons and photogeneration of positive holes has not been observed for conventional aluminosilicate zeolites, all-silica zeolites, or GeO(2)-impregnated zeolites. Therefore this photochemical behavior has been ascribed to the presence of framework germanium atoms opening the way for photoresponsive zeolites. The ability of Ge/ITQ-17 to generate photochemically electrons and holes has been confirmed by adsorbing naphthalene and propyl viologen sulfonate as electron donor and acceptor, respectively, and observing the generation of the corresponding radical ions.     

Synthesis of ITQ-2 zeolite under static conditions and its properties

Zeolite ITQ-2 can be synthesized by swelling the layers of MCM-22 precursor. It has a single delami-nated structure of MWW with thickness of 2.5 nm. It shows disordered properties in long range and ordered in short range, which is a promising catalytic ma…     

Pyrene covalently anchored on a large external surface area zeolite as a selective heterogeneous sensor for iodide

Pyrene as a fluorophore has been covalently anchored on a delaminated ITQ-2 zeolite having a large external surface area (730 m2 g-1) and the resulting solid found to have a selective response as a heterogeneous sensor for I- in the presence of other halides.     

Al-ITQ-13分子筛的快速合成及表征

通过设计首次提出针对ITQ-13分子筛晶化促进剂的合成策略,ITQ-13分子筛.通过X射线粉末衍射(XRD)、扫描电子显微镜(SEM)、N2吸附、原位红外(FTIR)及固体核磁(27Al NMR)等测试手段对ITQ-13分子筛的物化性能进行了表征,考察了晶化过程中结晶度的变化,得出了晶化过程的动力学参数,对晶化机理进行了探讨.结果表明:快速合成法与传统方法合成的ITQ-13分子筛具有相似的物化性能,并且可以合成含有更多骨架铝的ITQ-13分子筛;NO3-的加入通过极化憎水基团,加速SiOSi物质结合,降低ITQ-13分子筛的成核活化能以及生长活化能,从而可以提高晶化速率,缩短晶化时间至11 h.     

Structures and reaction mechanisms of cumene formation via benzene alkylation with propylene in a newly synthesized ITQ-24 zeolite: an embedded ONIOM study

The cumene formation via benzene alkylation with propylene on the new three-dimensional nanoporous catalyst, ITQ-24 zeolite, has been investigated by using the ONIOM2(B3LYP/6-31G(d,p):UFF) method. Both consecutive and associative reaction pathways are examined. The contributions of the short-range van der Waals interactions, which are explicitly included in the ONIOM2 model, and an additional long-range electrostatic potential from the extended zeolite framework to the energy profile are taken into consideration. It is found that benzene alkylation with propylene in the ITQ-24 zeolite prefers to occur through the consecutive reaction mechanism. The benzene alkylation step is the reaction rate-determining step with an estimated activation energy of 35.70 kcal/mol, comparable with an experimental report in beta-zeolite of 34.9 kcal/mol. The electrostatic potential from the extended zeolite framework shows a much more significant contribution to the transition state selectivity than the van der Waals interactions.     

P-derived organic cations as structure-directing agents: synthesis of a high-silica zeolite (ITQ-27) with a two-dimensional 12-ring channel system

Recently, efforts have been made to synthesize large-pore, multidimensional zeolite frameworks as a basis for new catalysts to improve various hydrocarbon conversions. A new aluminosilicate zeolite, ITQ-27, has been prepared using the phosphorus-containing structure-directing agent, dimethyldiphenylphosphonium. Its crystal structure was determined in its calcined form by direct methods (FOCUS) on synchrotron powder diffraction data (lambda = 0.8702 A) after the unit cell and space group were determined from tilt electron diffraction experiments on individual microcrystals. The material crystallizes in space group Fmmm, where a = 27.7508(5) A, b = 25.2969(7) A, and c = 13.7923(4) A. The final model, refined by Rietveld methods, comprises seven unique T-sites forming a framework with straight 12-MR channels that are connected by 14-MR openings between them. (Corresponding 12-ring pore dimension is 6.94 A x 6.20 A.) Since access from one 14-MR opening to the next is through the 12-MR channel, the structure is best described as a two-dimensional, 12-MR framework.     

Study on hexane adsorption in zeolite ITQ-29 by molecular simulation

Adsorption isotherms and isosteric heat of adsorption of n-hexane in zeolite ITQ-29 were simulated using the Configurational Bias Monte Carlo (CBMC) technique in the grand-canonical (μ VT) ensemble and compared with experimental results published by Gribov et al. and obtained by IR spectroscopy where the fractional loadings of n-hexane in ITQ-29 are presented in units from integral intensities of the absorption bands [u.a.]. In this work we present the simulation loadings of n-hexane in ITQ-29 converted to fractional coverages and compared to the experimental results. The simulations were performed using a united atom force field. In addition, we calculated equilibrium adsorption isotherms of ethane and propane in ITQ-29 in excellent agreement with published experiments. This force field successfully reproduces adsorption properties of linear alkanes in cation-free LTA zeolite and is suitable for fast and accurate adsorption data predictions.     

Correction: Direct synthesis of the organic and Ge free Al containing BOG zeolite (ITQ-47) and its application for transformation of biomass derived molecules

Aluminosilicate boggsite (Si/Al-BOG) has been hydrothermally synthesized without adding organic structure-directing agents (OSDAs) in the synthesis gel using the borosilicogermanium ITQ-47 (Si/B-ITQ-47) zeolite as seeds. The introduction of the costly and environmentally less benign phosphazene organic structure-directing agent is not required to grow the zeolite. Physicochemical characterization experiments show that Si/Al-BOG has good crystallinity, high surface area, tetrahedral Al³⁺ species, and acid sites. In order to test the catalytic performance of the zeolite, the synthesis of l,l-lactide from l-lactic acid was performed. Si/Al-BOG exhibits 88.2% conversion of l-lactic acid and 83.8% l,l-lactide selectivity, which are better than those of other zeolites studied up to now.

Aluminosilicate boggsite (Si/Al-BOG) has been hydrothermally synthesized without adding organic structure-directing agents (OSDAs) in the synthesis gel using the borosilicogermanium ITQ-47 (Si/B-ITQ-47) zeolite as seeds.     

MCM-22和ITQ-2分子筛负载型催化剂加氢裂化性能的对比研究

 以MCM-22和ITQ-2分子筛为载体, WNi为活性组分,制得两种负载型催化剂,考察了两种催化剂的加氢裂化性能,并通过N2吸附、氨程序升温脱附和原位红外光谱对催化剂进行了表征. 减压瓦斯油加氢裂化反应结果表明, WNi/ITQ-2的加氢裂化活性高于WNi/MCM-22, 并且前者的反应温度相对较低. WNi/ITQ-2具有高催化活性是因为ITQ-2分子筛具有空旷的次级结构和较多的可接近的酸性位; 中油选择性高是因为空旷的次级结构使裂化产物快速离开酸性位而避免了二次裂化.     

Evidence for through-framework electron transfer in intrazeolite photochemistry. Case of Ru(bpy)3(2+) and methylviologen in novel delaminated ITQ-2 zeolite

A sample of novel delaminated zeolite ITQ-2 containing Ru(bpy)3(2+) on the external cups and MV2+ included in the independent and not connected channels has been prepared; emission and time-resolved laser flash photolysis has shown unambigously that photoinduced electron transfer from Ru(bpy)3(2+) to MV2+ occurs through the zeolite framework.     

Esterification of Oleic Acid to Produce Biodiesel over 12-Tungstophosphoric Acid Anchored Two-dimensional Zeolite

Biodiesel has emerged as a non-toxic, biodegradable, and renewable fuel substitute that can be readily produced via the esterification reaction of free fatty acids. The present work explores the potential of 12-tungstophosphoric acid(TPA) anchored two-dimensional(2D) ITQ-2 zeolite(TPA/ITQ-2) as heterogeneous acid catalysts for biodiesel production. TPA/ITQ-2 material was prepared by swelling, delamination, and subsequent wetness incipient impregnation approach. The prepared catalysts were comprehensively characterized by powder X-ray diffraction, N₂ adsorption/desorption, temperature-programmed desorption of ammonia, flou-rier transform infrared spectroscopy, and transmission electron microscopy. The catalytic activity of TPA/ITQ-2 for biodiesel production was evaluated by the esterification reaction of oleate acid with methanol. Process parameters, such as reactant molar ratio and TPA loading were optimized. Due to the superior mass transfer and adequate stable acid sites, 2D TPA/ITQ-2 showed a higher catalytic activity and a better recyclable stability than the 3D and layered TPA/zeolites. This work will provide new opportunities for the design of 2D zeolite-based acid catalysts for biodiesel production.     

SSZ-39分子筛的合成及应用进展

近年来,小孔八元环SSZ-39分子筛因具有特殊的孔道结构和物理化学性质,在小分子择形催化反应中展现出相对优异的催化活性、抗积碳性和水热稳定性.本文概述了SSZ-39分子筛的合成历程,包括不同种类有机模板剂的使用、特定硅源铝源的选择以及凝胶组成的调控等;简要总结了SSZ-39分子筛在甲醇制低碳烯烃、氮氧化物的选择性催化还...     

Formation and Properties of Losod,a New Sodium Zeolite

Losod, a new type of crystalline hydrated sodium aluminosilicate, Na₁₂Al₁₂Si₁₂O₄₈ · q H₂O, has been prepared from reaction mixtures containing bulky quaternary alkylammonium ions, particularly azonia-spiro[4.4]nonane, besides sodium ions. Losod crystallizes from batches with a low sodium content (Na/Al ≤ 1 and Si/Al ≈? 1). The quaternary ammonium hydroxide primarily serves as a source of hydroxide ions and is not incorporated into the zeolite crystals. These bulky bases provide a useful means for controlling the alkalinity of the system independently of the concentration of the necessary cations built into the zeolite. The crystals of Losod are hexagonal (a = 12.91 and c = 10.54 Å) and the proposed framework structure shows a polytypic relationship to sodalite and cancrinite. Losod has reversible sorption and ion exchange properties typical of a small-pore zeolite and in essential agreement with the proposed structure.