María J. Díaz-Cabañas

A large-cavity zeolite with wide pore windows and potential as an oil refining catalyst

Crude oil is an important feedstock for the petrochemical industry and the dominant energy source driving the world economy, but known oil reserves will cover demand for no more than 50 years at the current rate of consumption. This situation calls for more efficient strategies for converting crude oil into fuel and petrochemical products. At present, more than 40% of oil conversion is achieved using catalysts based on faujasite; this zeolite requires extensive post-synthesis treatment to produce an ultrastable form, and has a large cavity accessible through four 0.74-nm-wide windows and thus limits the access of oil molecules to the catalytically active sites. The use of zeolites with better accessibility to their active sites should result in improved catalyst efficiency. To date, two zeolites with effective pore diameters exceeding that of faujasite have been reported, but their one-dimensional pore topology excludes use in oil refining. Similarly, zeolites with large pores and a three-dimensional pore topology have been reported, but in all these materials the pore openings are smaller than in faujasite. Here we report the synthesis of ITQ-21, a zeolite with a three-dimensional pore network containing 1.18-nm-wide cavities, each of which is accessible through six circular and 0.74-nm-wide windows. As expected for a zeolite with this structure, ITQ-21 exhibits high catalytic activity and selectivity for valuable products in preliminary oil refining tests.

The ITQ-37 mesoporous chiral zeolite

The synthesis of crystalline molecular sieves with pore dimensions that fill the gap between microporous and mesoporous materials is a matter of fundamental and industrial interest. The preparation of zeolitic materials with extralarge pores and chiral frameworks would permit many new applications. Two important steps in this direction include the synthesis of ITQ-33, a stable zeolite with 18 × 10 × 10 ring windows, and the synthesis of SU-32, which has an intrinsically chiral zeolite structure and where each crystal exhibits only one handedness. Here we present a germanosilicate zeolite (ITQ-37) with extralarge 30-ring windows. Its structure was determined by combining selected area electron diffraction (SAED) and powder X-ray diffraction (PXRD) in a charge-flipping algorithm. The framework follows the SrSi2 (srs) minimal net and forms two unique cavities, each of which is connected to three other cavities to form a gyroidal channel system. These cavities comprise the enantiomorphous srs net of the framework. ITQ-37 is the first chiral zeolite with one single gyroidal channel. It has the lowest framework density (10.3 T atoms per 1,000 Å3) of all existing 4-coordinated crystalline oxide frameworks, and the pore volume of the corresponding silica polymorph would be 0.38 cm3 g-1.

High-throughput synthesis and catalytic properties of a molecular sieve with 18- and 10- member rings

Crystalline molecular sieves with large pores and high adsorption capacities have many potential applications. Of these materials, zeolites are of particular interest owing to their stability in a wide range of experimental conditions. An aluminophosphate with very large circular channels5 containing 18 oxygen atoms (18-ring channels) has been synthesized, but in the search for large-pore zeolites, most of the materials which have been synthesized up to now contain only 14-ring channels; the synthesis of zeolites with larger ring structures has been believed to be hindered by the low Si-O-Si bond angles available. A silicogaloaluminate (ECR-34) with unidirectional 18-ring channels was recently reported, but exhibited low micropore volume, thus rendering the material less attractive for catalytic applications. Here we report the structure and catalytic activity of the silicogermanate zeolite ITQ-33; this material exhibits straight large pore channels with circular openings of 18-rings along the c axis interconnected by a bidirectional system of 10-ring channels, yielding a structure with very large micropore volume. The conditions for synthesis are easily accessible, but are not typical, and were identified using high-throughput techniques.

Synthesis and Structure Determination of the Hierarchical Meso-Microporous Zeolite ITQ-43

A zeolite with microporous channels (6 to 7 angstrom diameter) and mesoporous channels (~2-nanometer diameter) was made. The formation of mesopores in microporous zeolites is generally performed by postsynthesis acid, basic, and steam treatments. The hierarchical pore systems thus formed allow better adsorption, diffusion, and reactivity of these materials. By combining organic and inorganic structure-directing agents and high-throughput methodologies, we were able to synthesize a zeolite with a hierarchical system of micropores and mesopores, with channel openings delimited by 28 tetrahedral atoms. Its complex crystalline structure was solved with the use of automated diffraction tomography.

ITQ-15: The first ultralarge pore zeolite with a bi-directional pore system formed by intersecting 14- and 12-ring channels, and its catalytic implications

The pore topology of ITQ-15 zeolite consists of an ultra-large 14-ring channel that is intersected perpendicularly by a 12-ring pore; acid sites have been introduced in its framework and this unique structure shows advantages over unidirectional ultralarge pore zeolites for diffusing and reacting large molecules.

The Synthesis of an Extra-Large-Pore Zeolite with Double Three-Ring Building Units and a Low Framework Density†

Zeolites are crystalline inorganic solids formed by TO4 tetrahedra (T=Si, P, Al, Ge, etc.) with a well-defined system of regular pores having diameters up to about 2 nm. The possibility of tuning pore dimensions and framework compositions have made zeolites the most successful materials for applications in gas adsorption and separation and for catalysis. Their uses have been further expanded to microelectronics for preparing materials with low values of the high-frequency dielectric constant or manufacturing encapsulated light-emitting devices (LEDs), to medicine for diagnostic treatments and controlled drug delivery, or for release of semiotics for controlling insect populations in agricultural uses. Those applications often require structures with low framework densities, large internal volumes, and preferentially, extra-large pores. However, up to now, the number of known zeolites with a low framework density (FD 12) is almost negligible, and the number with extra-large pores ( 18-R) is also extremely small. Computational methods can predict a large number of thermodynamically feasible new structures, and they can stimulate and inspire the discovery of new structures. For example, Foster and Treacy have used a symmetry-constrained intersite bond searching method and have generated more than two million structures. With that methodology, the authors predicted a series of thermodynamically feasible extra-large-pore zeolites. Deem et al. have also modeled relatively large number of low density zeolites and were able to show that the low-energy and low-density materials also tend to have desirably large rings. Among the zeolite structures with extra large pores predicted by Foster and Treacy, there is one with 18 10 10-R pore topology that could be of particular interest for catalysis, as it combines an extra-large pore (18-R) for molecular accessibility with connected 10-R pores that can introduce shape-selectivity effects. Recently, the predicted zeolite was synthesized and named ITQ-33. This zeolite has 3-R and D4R units in the structure, and was at the time the silicate-based zeolite with the lowest framework density (12.3.T/1000 ). The pore topology of this extra-large-pore zeolite presented quite unique and interesting catalytic properties: The pore accessibility to large molecules through the 18-R was combined with shape selectivity in the 10-R pores for the primary products formed. In the same data base, Foster and Treacy also predicted an extra-large-pore zeolite that was closely related to ITQ-33 (Zeolite reference 191_4_1985). In that new structure, the 10-R pores of ITQ-33 were expanded to 12-R pores connecting the larger perpendicular 18-R channels. The result was a zeolite with 18 12 12 pore topology instead of the 18 10 10 for ITQ-33. In particular, along with D4R units, the new zeolite contains D3R units that have never been seen in synthesized zeolites, which could be related to geometric strains introduced in the framework owing to the formation of D3R based on silicon. In any case, the pore expansion with the 18 12 12-R pore system in the new zeolite should result in a decrease of the framework density from 12.3 in the case of ITQ-33 to 10.9 T atoms/1000 . Herein, we show that the zeolite containing D3R that was predicted above can be successfully synthesized (ITQ-44) as a silicogermanate by combining a relatively inexpensive, rigid and bulky organic structure-directing agent (SDA) with the directing effect of germanium. Furthermore, we show that in ITQ-44, germanium locates preferentially in D3R (with 50% Ge occupancy), followed by D4R (with 37% Ge occupancy). ITQ-44 was synthesized using (2’-(R),6’-(S))-2’,6’-dimethylspiro[isoindole-2,1’-piperidin-1’-ium] as the SDA (Supporting Information, Figure S1). The synthesis of ITQ-44 was carried out in fluoride media using high-throughput (HT) synthesis techniques, which involve the use of a 15-well multiautoclave. The XRD pattern of a calcined ITQ-44 sample (Figure 1) was collected (as described in the Supporting Information), and the crystal structure was solved using the program FOCUS. The agreement between the observed and calculated XRD patterns are shown in Figure 1; it certainly confirms that this structure corresponds to that of the pure silica polymorph of this material predicted by Foster and Treacy (reference number 191_4_19854). The structure of ITQ-44 is closely related to the previously described zeolite ITQ-33 (Figure 2). It also comprises a building unit formed by a [346] cage with two additional [*] J. Jiang, Dr. J. L. Jorda, Dr. M. J. Diaz-Cabanas, Prof. A. Corma Instituto de Tecnologia Quimica (UPV-CSIC) Universidad Politecnica de Valencia Consejo Superior de Investigaciones Cientificas Av. de los Naranjos s/n, 46022 Valencia (Spain) Fax: (+34)96-387-7809 E-mail: acorma@itq.upv.es

A zeolitic structure (ITQ-34) with connected 9- and 10-ring channels obtained with phosphonium cations as structure directing agents.

Zeolites are materials with a large applied interest. Here we present ITQ-34 a new zeolitic material, obtained combining the use of the highly stable tetraalkylphosphonium cations as structure directing agents with the incorporation of Ge atoms in the structure.

Synthesis of micro- and mesoporous molecular sieves at room temperature and neutral pH catalyzed by functional analogues of silicatein

By using functional mimics of the protein silicatein alpha together with organic structure directing agents, it was possible to produce different mesoporous and microporous molecular sieves at room temperature and neutral pH.

Biomimetic synthesis of microporous and mesoporous materials at room temperature and neutral pH, with application in electronics, controlled release of chemicals, and catalysis

Micro- and mesoporous materials molecular sieves have been synthesized at neutral pH and room temperature using a mimic of “silicatein” for mobilizing the silica. This methodology allows preparing molecular sieves materials in where less stable molecules can be encapsulated, leading to a final material with potential applications in electronics (conducting polymers) or for controlled release of chemicals (pheromones). Furthermore, the framework flexibility of the obtained materials allows introducing transition metals in tetrahedral coordination within the silicate in larger amounts than in zeolites, while preserving the activity and selectivity of the metals for selective oxidation reactions.

Hydrocracking catalysts based on the new large-pore ITQ-21 zeolite for maximizing diesel products

Abstract Hydrocracking catalysts based on the new large-pore ITQ-21 zeolite show a higher selectivity to diesel-range products at high conversions as compared with USY and Beta based catalysts. The results are explained considering the particular topology of ITQ-21, which favors the diffusion of the intermediate diesel products decreasing their recracking into lighter compounds. A benefit in both activity and selectivity to middle distillates in ITQ-21 based catalysts has been observed when the metal function (NiMo) is first impregnated on γ-Al 2 O 3 and then physically mixed with the zeolite as compared to a catalyst prepared by impregnating the metal precursors on a physical mixture of γ-Al 2 O 3 and ITQ-21.