WO2007065794A2

WO2007065794A2 - A zeolite family built from a framework building layer

Info

Publication number: WO2007065794A2
Application number: PCT/EP2006/068778
Authority: WO
Inventors: Zou Xiaodong; Tang Liqiu
Original assignee: Hovmoller, Sven
Priority date: 2005-12-06
Filing date: 2006-11-22
Publication date: 2007-06-14
Also published as: WO2007065794A3

Abstract

The present invention is a structure comprising, a basic zeolite framework building layer. The zeolite framework building layer is built of tetrahedra formed by oxygen atoms where a T-atom is at the center of each tetrahedron. The TO4 tetrahedra are connected through their vertices to form a layer that contains 4-, 5- and 12-rings. A ring is defined by the number of T-atoms forming the rings. The layer can be described as chains of alternating 4- and 5-rings of TO4 tetrahedra. The neighboring 5-rings in each chain are pointing in opposite directions and further connect to the 5-rings from another chain through vertex-sharing of oxygen atoms to form a layer containing 12-rings. The unconnected oxygen in the tetrahedra can be either pointing up or down with respect to the layer.

Description

A ZEOLITE FAMILY BUILT FROM A FRAMEWORK BUILDING LAYER

DESCRIPTION

TECHNICAL FIELD

The invention concerns a family of microporous crystalline materials of zeolitic structure.

BACKGROUND OF THE INVENTION

The term "zeolite" is generally used for microporous crystalline materials based on silicon and aluminum, but it is recognized in the art that silicon and aluminum may be replaced by other elements in whole or in part, in particular germanium, boron, gallium, phosphor, iron, and/or titanium. The term "zeolite" has been broadened and materials with a similar framework structure but prepared in different chemical compositions are termed as "zeolite".

Each zeolite framework type is distinguished by a crystal structure with an ordered pore system, and is characterized by a unique X-ray diffraction pattern. Thus, the crystal structure defines cavities and pores that are characteristic of the different species. The cavities and pore sizes are normally defined as the number of T-atoms forming the rings of the channels. The adsorptive and catalytic properties of zeolites are determined by their chemical compositions, the dimensions of their pores and cavities and their pore structures.

Because of their unique sieving characteristics, as well as their catalytic properties, zeolites are especially useful in applications such as hydrocarbon conversion, gas drying and separation. Although many different zeolites have been discovered, there is a continuing need for zeolites with new structures and desirable properties.

Zeolites with intersecting 12- and 8-ring have been widely used in the many chemical processes as described by the following patents: US6822129, concerns the method of converting aromatic compounds; US6831184, US2003100780, WO2004089854 and CA2453330, relate to a process for the isomerization of unsaturated fatty acids with a catalyst to branched fatty acids; US2003191330 and US2004204598, describe the skeletal isomerization of alkyl esters and derivatives; US2004262200, shows desulfurization with octane enhancement. US2004158103, relates to cyclohexane oxidation catalysts; US6165428, and EP1094881, demonstrate process for the removal of metal carbonyl from a gaseous stream.

During the last decade, the utilizations of pure enantiomers in biology have increased exponentially, implying their economic importance.

Zeolites with chiral channels are considered to be extremely useful as chiral solid catalysts, zeolite beta shows very good catalytic properties for the production of substantially enantiomerically pure products, as demonstrated by US5997840. Among the 174 known zeolites, only two of them, zeolite beta and CZP, contain chiral channels. Zeolite beta has been well investigated and widely used in many chemical processes. Whereas, zeolite CZP, due to its highly distorted 12-ring channels, has seldom been used so far.

Many known zeolites are built from the same periodic building units. For example both MFI and MEL are built from a pentasil building unit and they belong to the pentasil family.

DESCRIPTION OF THE INVENTION

The present invention is a structure comprising, a basic zeolite framework building layer. The zeolite framework building layer is built of tetrahedra formed by oxygen atoms where a T-atom is at the center of each tetrahedron. The TO₄ tetrahedra are connected through their vertices to form a layer that contains 4-, 5- and 12-rings. A ring is defined by the number of T-atoms forming the rings. The layer can be described as chains of alternating 4- and 5-rings of TO₄ tetrahedra. The neighboring 5-rings in each chain are pointing in opposite directions and further connect to the 5-rings from another chain through vertex-sharing of oxygen atoms to form a layer containing 12-rings. The unconnected oxygen in the tetrahedra can be either pointing up or down with respect to the layer.

The T atoms are Si and/or Ge, appearing alone or together in the same structure. They can be replaced in whole or in part by other elements such as for example Al, Ga, P, B, Fe, Ti, Co, Sn, Zn or other transition metals, or combinations thereof. Several such elements can be present in the same framework.

The framework oxygen can be also partly replaced by, for example F, Cl, or OH^".

The framework building layers can be packed in different ways to form different 3D framework structures.

The framework building layers can be packed in such a way that the adjacent layers are related by a center of symmetry and connected through vertex-sharing of the oxygen atoms as in SU-15. Or, the framework building layers can be packed so that the adjacent layers are rotated by about 60° and connected through vertex-sharing of the oxygen atoms as in SU-32. The 3D framework structures can be also packed in other ways, for example with some of the layers related by a center of symmetry as in SU-15 and other layers related by rotations similar to that in SU-32. The neighboring layers may be also related by other symmetries, for example mirror planes perpendicular or parallel to the layer, or a combination of all these symmetries. The framework building layers with the same orientations or rotated by each other may be stacked to form 3D framework structures, either in an ordered manner to form an end-member of the family or in a disordered way to form a disordered member of the family. Different combinations of the ways of stacking may result in different framework structures, but they all belong to the same family of zeolites of this invention.

SU- 15 is the first zeolite with intersecting 12 and 9-ring channels. The intersecting channels make the diffusion of small molecules and ions feasible in all three dimensions. The 12-ring channels are elliptical which is also usual in zeolites.

SU-32 is the first chiral zeolite with helical channels that are defined by 10-ring windows.

The synthesis of SU- 15 and SU-32 can be done in many different ways. One way of synthesizing SU- 15 and SU32 is under hydro-/solvo-thermal conditions using diisopropylamine (DIPA) as a structure directing agent.

The unique channel systems of the zeolites built from the basic framework building layer give these zeolites great potential for applications in sorption, separation and catalysis, especially enantioselective sorption, separation and catalysis.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 shows the framework building layer forming SU- 15 and SU-32. In fig l(a) the structure is represented as balls and sticks and in fig l(b) as TO4 tetrahedra. The 4-, 5- and 12- rings are marked in fig l(b).

In figure 2, the framework building layers are packed into a structure, SU-15. The layers are packed in such a way that the adjacent layers are related by a center of symmetry and connected through vertex-sharing of the oxygen atoms. SU-15 contains intersecting elliptical 12-ring and 9-ring channels. The 12-ring channels can be heavily distorted and the free dimensions of the channels have a range of 3 - 11 A, for example 4.1 A x 9.7 A. The 9-ring channels have free dimensions in the range between 3 - 6A, for example 4.3 A x 4.8 A.

The framework structure of SU-15 is represented by TO4 tetrahedra where the small circles are oxygen and the T atoms are at the centers of the tetrahedra. The two different shades of the tetrahedra represent two framework building layers. The two layers are connected through the 4-rings by vertex-sharing of oxygen atoms. The coordination system (a, b, c) is shown in the figure and a unit cell is marked with whole drawn lines.

In figure 3, the framework building layers are packed into a structure, SU-32. Two adjacent layers rotated by 60° to each other and connected through vertex-sharing of the oxygen atoms are represented (a) by TO4 tetrahedra and (b) by T-T connections. There are six such layers in each unit cell.

U-32 is crystalline and contains 8-ring channels and helical channels with 10-ring windows.

The structure of SU-32 is chiral, all the helical channels have the same handedness and are connected through the 8-ring windows, see fig. 3(c). The 8-ring channels are perpendicular to the helical channels and intersecting the helical channels along three different directions. The free-dimensions of the 10-ring windows are in the range of 3 - 7 A, for example 5.0 x 5.5 A, and those of the 8-ring channels are in the range of 2.5 - 6 A, for example 3.0 x 4.7 A.

The framework structure of SU-32 viewed perpendicular to the layers and represented (c) by

TO4 tetrahedra and (d) by T-T connections. The helical channels are shown in (d). Only the T atoms are shown in (b) and (d).

Each layer can be rotated either clockwise or anticlockwise, so that the helical channels are either left-handed or right-handed. The 3D structure of SU-32 is chiral and can be prepared in a pure enantiomorph form.

Both SU- 15 and SU-32 are built from the same framework building layer, where the neighboring layers are related by a center of symmetry in SU- 15 and by a rotation of 60° in

SU-32, see fig. 4. The framework layers can be also packed in other ways, for example with some of the layers related by a center of symmetry as in SU- 15 and other layers related by rotations similar to that in SU-32. The neighboring layers may be also related by other symmetries, for example mirror planes perpendicular or parallel to the layer, or a combination of all these symmetries.

The framework building layers with the same orientations or rotated by each other may be stacked to form 3D framework structures, either in an ordered manner to form an end-member of the family or in a disordered way to form a disordered member of the family. Different combinations of the ways of stacking may result in different framework structures, but they all belong to the same family of zeolite structure.

In fig. 4(a) a building layer present in both SU- 15 and SU-32, it is formed by the 4-1 units, which are pointed up and down alternatively in the αό-plane. Two possible unit cell choices are marked. In fig 3(b) a structure model of SU- 15 shows the building layers packed along the c-axis and related by a center of symmetry in the centre of the unit cell. In fig 4(c), a structure model of SU-32 shows the building layers packed along the c-axis, the layer down is rotating by -60° or 60° with respect to the layer above, so the D4Rs are formed. This packing results in either 65 or 61 screw axis along c-axis, which corresponds to the two enantiomorphs of SU-32. SU- 15 and SU-32 often coexist in the same products but as separate crystals, figure 5. The crystal structures of SU- 15 and SU-32 were determined by single crystal X-ray diffraction.

In figure 5 is shown the experimental and simulated XRD patterns of SU- 15 and SU-32 * peak from GeO₂. The experimental XRD patterns were collected using a synchrotron radiation, with a wavelength of 1.2A.

Figure 6 shows SEM images of SU- 15 (a,b) and SU-32 (c,d).

The synthesis of SU- 15 and SU-32 can be done in many different ways. One way of synthesizing SU- 15 and SU32 is under hydro-/solvo-thermal conditions using diisopropylamine (DIPA) as a structure directing agent. A typical synthesis procedure can be: GeO₂ is added to a solution formed by a mixture of H₂O and diispropylamine (DIPA) under continuous stirring. Then tetraethyl orthosilicate Si(OC₂Hs)₄ (TEOS) is dropped slowly into the solution and a mixture is obtained. Finally HF (40 wt%) is added to the mixture. The molar ratio Of GeO₂ : Si(OC₂Hj)₄ : DIPA : H₂O : HF is 1.0 : 0.8 : 79.3 : 27.7: 5.8-22.4. The final mixture is sealed in a Teflon-lined autoclave and heated at 170°C for 7 days under autogeneous pressure. The obtained product is washed first with water, then with ethanol, and finally dried at room temperature.

Claims

1. A structure comprising, a basic zeolite framework building layer characterized by that the layer contains chains of alternating 4-and 5- rings Of TO₄ tetrahedra, and said chains are further connected to form a framework building layer containing 4-, 5-, and 12- rings and wherein unconnected oxygen in the tetrahedra can either be pointing up or down.

2. A structure in accordance with claim 1, characterized by that the T atoms are Si and/or Ge.

3. A structure in accordance with claim 1, characterized by that the T atoms are Si, Ge, Al, Ga, P, B, Fe, Ti, Zn, Co, Sn or other transition metals, or combinations thereof.

4. A structure in accordance with claim 1, 2 or 3, characterized by that the framework oxygen is partly replaced by F, Cl, or OH^".

5. A structure in accordance with claim 1, 2, 3 or 4, characterized by that framework building layers are packed to form 3D framework structures.

6. A structure in accordance with claim 5, characterized by that the framework building layers are packed with some of the layers related by a center of symmetry and other layers related by rotations.

7. A structure in accordance with claim 5, characterized by that neighboring framework building layers are related by mirror planes perpendicular or parallel to an adjacent layer, or a combination of such symmetries.

8. A structure according to claim 5, characterized by that the framework building layers having same orientations or rotated by each other are stacked to form 3D framework structures, either in an ordered manner to form an end-member of a family or in a disordered way to form a disordered member of a family.

9. A structure in accordance with claim 5, characterized by that a SU- 15 zeolite structure have intersecting 12 and 9-ring channels, thereby making diffusion of small molecules and ions feasible in all three dimensions.

10. A structure in accordance with claim 9, characterized by that the 12-ring channels are elliptical.

11. A structure in accordance with claim 5, characterized by a SU-32 zeolite structure have intersecting 10- and 8-ring channels, thereby enabling diffusion of small molecules and ions in all three dimensions.

12. A structure in accordance with claim 11, characterized by helical channels with only one handededness defined by 10-ring windows are present, leading to a chiral zeolite.

3. A structure in accordance with claim 12, characterized by the helical channels can be lefthanded or righthanded.