ITMI20091292A1 - NANOPOROSO FUNCTIONAL MATERIAL FOR APPLICATION IN "GAS STORAGE - Google Patents

Description

FUNCTIONAL NANOPOROUS MATERIAL FOR APPLICATION

IN GAS STORAGE

DESCRIPTION

The present invention relates to the development of new hybrid organic / inorganic nanoporous materials with improved gas adsorption properties and, in particular, effective for hydrogen storage applications. These porous materials include aromatic organic groups both integrated and anchored to the wall of the structure.

Hydrogen is considered the most promising alternative fuel due to its high energy content, its clean combustion and its natural integration with renewable energy sources. However, its use in the transport sector requires the development of a practical and safe storage system. Unlike in the case of static storage, where the volume and mass of the tank are not a factor of concern, the storage of large quantities of hydrogen in a car - in which the volume, mass and heat exchange are of primary importance - represents a formidable scientific and technological challenge. Many studies have dealt with the use of hydrogen as a fuel and its storage in various solid-state materials and in high-pressure or cryogenic tanks. Among the new materials, microporous crystalline solids comprising metallic building blocks and organic bridging ligands, known as metal-organic frameworks (MOFs), are perhaps the most promising candidates for physisection. However, these materials are considered to be relatively expensive; moreover they are in most cases sensitive to atmospheric agents and in particular to humidity and therefore require to be handled in a special way. From numerous works on different types of materials for the physical storage of hydrogen, some important structural characteristics can be derived that help to increase the storage capacity, such as: a) high surface area (the highest possible), b) pore size of excellent accessibility (in the range of 10-15 Å), c) aromaticity (the presence of aromatic groups increases the storage of hydrogen), d) point charges, e) metal sites with an incomplete bond order.

Taking into consideration these important parameters we have developed a new synthesis methodology for the preparation of new porous materials based on hybrid organ silicates that meet the above requirements. In particular we have developed new functionalized aromatic mesoporous periodic organosilic (Periodic Mesoporous Organosilica, PMO) suitable for storing large quantities of hydrogen.

PMOs are a category of porous hybrid organic-inorganic mesoporous materials first introduced in 1999. These materials were prepared by hydrolysis and condensation reactions from alkoxysilane precursors with bridges consisting of organic molecules of the type (R'O) 3Si- R-Si (R'O) 3 long known in sol-gel chemistry. PMOs were synthesized using the same structure-directed procedure as for pure mesoporous silica materials, incorporating suitable bis-silylated organo-silica precursor surfactants described above. This procedure leads to the obtainment of porous mesostructured materials in which the organic bridges are integral components of the silica-based lattice, are characterized by a system of periodically organized pores and a very narrow distribution of the pore radii.

Inagaki et al (US patent 6248686B1; 2001) described a hybrid ordered mesoporous material (organic / inorganic) and its synthesis methods. The variety of the material is very wide compared to:

- Inorganic groups (mainly Si oxides but also many other metal oxides such as Zr Ti Nb Ta W Sn Hf Al V B Mn Co Ni Ga Be Y La Pb)

- Organometallic compounds

- Surfactants: C8-C18 but also aromatic rings and sulfonyl groups and others (very wide variety)

- Pore size (1-30 nm)

- Surface area (> 700 m <2> / g)

- Lattice parameter (at least 1 nm)

The preferred metal is Si, the preferred organic ligands are linear chains or phenylene or amino or their mixtures, the preferred surfactant is alkyltrimethylammonium.

The synthesis method is described with many variations. They indicate the control parameters for the structure (radius and shapes of the pores, crystal structure, stability). Ozin et al (US patent 6,960,551 B2, Nov.1, 2005) have described a similar type of materials functionalized with sulfonyl groups (-SO -3) and their potential use as solid acids in heterogeneous catalysis. The present invention refers to an aromatic functionalized mesoporous hybrid material and to a method for obtaining functionalization for improving the adsorption properties of hydrogen. These materials show a significant increase in hydrogen storage capacity compared with known hybrid mesoporous solids. The invention refers to a porous organic-inorganic material containing aromatic organic groups inside the pore wall and / or inside the pores, characterized in that it comprises a polymer consisting of units derived from an M1 monomer or monomers M1 and M2 having the structural formula:

M1 = (OR) 3Me-A-Me (OR) 3

M1 M2 = [(OR) 3Me-A-Me (OR) 3] x- [(OR) 3Me-B] (1-x)

in which:

- Me is a metal chosen from silicon, germanium, tin and boron;

- R is independently a saturated or unsaturated monovalent aliphatic group;

- A and B are aromatic groups chosen independently, the same or different;

- 0 <x≤ 1;

this material having a pore size from 0.5 to 5 nm and a specific surface area ≥ 200 m <2> / g.

Preferably the metal atom Me is silicon. The aromatic groups A and B are preferably phenylene and bi-phenylene.

Figures 1-23 illustrate the properties of the materials according to the invention as well as of comparison materials.

The porous organic-inorganic material according to the invention is obtained by polymerizing a monomer or a mixture of monomers having the structural formula M1 or M1 and M2 above.

Polymerization takes place in the presence of a surfactant species under controlled pH conditions. The surfactant species can be cationic, anionic or nonionic with chains of different lengths. Preferably the surfactant species is an alkylpyridinium or alkyltrimethylammonium bromide having 8-18 carbon atoms in the alkyl chain.

Unlike known organosilicate solids, the method of the invention provides microporous and non-mesoporous materials and this leads, in combination with a high aromatic content, to a significant increase in the hydrogen storage capacity. The isosteric adsorption heat measured in representative material (see Figure 18) is ~ 7kJ / mol and represents the highest value in this class of compounds, comparable to that of the best metal-organic microporous crystal lattices (MOF's).

The structure can be controlled using surfactants with chains of different length and composition, obtaining a crystalline order of the pores ranging from hexagonal 2D to cubic Pm-3n or disordered systems. In each case, it has been found that the symmetry of the pores has a minimal effect on the hydrogen storage capacity.

A key aspect of the invention is the formation of solids with a high surface area (> 200 m2 / g), small pore size (<5.0 nm) and a high content of aromatic organic groups. The synthesis of these materials was obtained with condensable alkoxysilanes functionalized with aromatic groups in controlled hydrolysis reactions in the presence of suitable surfactants. Preferably, the alkoxysilane that forms the wall of the structure contains two silicon atoms bonded with a biphenyl-like bridging organic group (see silane 2 described below). The internal surface of the pore can be functionalized with other aromatic groups such as phenyls. In this case, the functionalized solid has a small pore size (<2.0 nm).

The functionalization methods concern the inclusion of active groups such as metal atoms, organic groups or sulfonyl groups by integrating them into the structure and / or its surface.

A mixed occupation of the metal atom site in the structure is obtained by partially replacing the Si atoms in the Me site of monomers (OR) 3Me-A-Me (OR) 3.

An increase in the aromatic character of the structure can be obtained by varying the organic fraction of the monomer by including aromatic rings (A) (phenylene, bi-phenylene and the like).

The addition of surface organic groups is achieved by grafting using (OR) 3Me-A precursors such as X-SiO3-z (OH) z groups with z = 0, 1, 2 and X = phenyl, diphenyl, pyridine, thiol or sulfonyl and the like.

Point charges and molecular bonding sites on the surface are obtained by impregnation with alkali metals such as Li, Na, K and the like, transition metals such as Ti, V, Fe, Co, Ni, Pd, Mn and their oxides, alkaline earth metals such as Mg, Ca, Be and their oxides.

The functionalization process conforms to the specific gas to be stored and the operating conditions of storage. The described material is preferably used for the adsorption of hydrogen, methane, carbon dioxide and similar light gases. By way of example, the reversible adsorption of hydrogen at a pressure below 100 bar and temperatures between 77K and 350K, is increased by means of (1) grafting methods (see Figures 11 and 17); (2) increase in the organic content of organ silica walls via synthesis under basic conditions (see Figures 14 and 8 (a)) and decrease in the content of aromatic rings under acidic conditions (see Figure 8 (b)); (3) use of pyridinium halides as the polar head of the surfactant molecule (see Figure 23); (4) partial replacement of the metallic Si atom with Al atoms in the monomer precursor (see Figure 22).

Typical examples of condensable aromatic organo-alkoxysilanes M1 used in different combinations for the development of new nano-porous materials for hydrogen storage are represented by the formulas below:

Typical surfactant molecules used to make up the cast for the development of porous structures are represented by the formulas below:

(S1)

(S2)

The pore size in each solid was determined from the corresponding isothermal nitrogen and argon adsorption curves acquired at 77K by applying established methods such as BJH and NLDFT.

DETAILS OF PHYSICAL MEASUREMENTS:

X-ray diffraction of powders: X-ray diffraction spectra of powders were obtained with a Rigaku D / MAX-2000H rotating anode diffractometer (CuKα radiation) equipped with a secondary pyrolytic graphite monochromator operated at 40 kV and 178 mA. In all cases, data was collected between 0.8 and 60 degrees (2theta), with a scan speed of 0.15 degrees / min and step size of 0.01 degrees.

Thermogravimetric analyzes (TGA) were performed using a TA SDT Q 600 analysis system. A 20 mg sample was placed in an alumina crucible and heated to 600 <o> C under argon flow with a heating rate of 5 <o> C / min.

Infrared Spectroscopy: ATR-IR spectra were recorded on a Thermo-Electron Nicolet 6700 FT-IR optical spectrometer with DTGS KBr.

Raman spectroscopy: Raman spectra were obtained at room temperature using a Raman Nicolet Almega XR spectrometer with a 473 nm blue laser (25% laser power of 15mW). The beam was focused on the sample by a confocal microscope using 10x objective lenses.

Gas adsorption measurements: Low pressure (up to 1 bar) adsorption / desorption measurements of nitrogen, argon and hydrogen were performed on a Quantachrome Autosorb 1-MP instrument equipped with multiple oil-free pressure transducers for highly accurate and an oil-free vacuum system. Ultra-high purity grades of N2 (99.999%), Ar (99.999%), He (99.999%), and H2 (99.999) were used for all adsorption measurements. Before analysis, all the samples were degassed at 150 ° C under dynamic vacuum for 12 hours up to an outlet gas flow rate of less than 2 mTorr / min. The sample and the tube were re-weighed after evacuation to obtain the precise mass of the evacuated sample. Eventually the tube was transferred to the opening for the analysis of the gas adsorption tool. To record the argon adsorption isotherm at 77 K, the saturation pressure was set at 200 torr. The same procedure was used for the high pressure adsorption measurement in which the instrument used is DeltaE f-PcT 80-200.

Porous organosilica materials were prepared under basic or acidic conditions. A general description of synthesis strategies includes the following.

A unit quantity of S1 or S2 surfactant is dissolved in distilled water and sodium hydroxide (basic conditions) or hydrochloric acid (36% weight, acid conditions) at 60-70 ° C. A unit amount of organo-alkoxysilane (1) or (2) or (4) or (1) and (3) or (1) and (5) or (2) and (3) or (2) and (5) it is then added drop by drop to the above solution at room temperature. The mixture is ultrasonically treated for 10–60 min and stirred for 3–48 h at room temperature. The precipitate obtained was filtered and washed repeatedly with distilled water to obtain the raw material. The surfactant was initially removed by solvent extraction using HCl in ethanol. Samples with partially exchanged metal content were prepared by immersing the porous material prepared using the organo-alkoxysilanes (4) or (1) and (5) or (2) and (5) under stirring in a 1N ethanol solution of appropriate metal halide (metal = Li, Na, K, Ti, Fe, Co, Ni, Pd, Mn, Mg, Ca, Be, etc) and the suspension was refluxed overnight at 20-90 <o> C. The cation exchange was completed by three cycles of reflux and centrifugation with the appropriate solutions. Finally the samples were washed with ethanol and dried at room temperature.

EXAMPLES

Example 1

Synthesis of porous organosilica materials using the condensable aromatic organ-alkoxysilane (1) and the surfactant S1 (CnPyBr, n = 12, 14, 16, 18 and 20) in acidic conditions.

In a typical synthesis, 0.4 g of C16PyBr was dissolved in 53.2 g of distilled water and 23.1ml of hydrochloric acid (36% by weight). The silane (1) (1.0 g) was then added to the above solution and the mixture was stirred for 1h at 273 K followed by further stirring for ~ 24h at 318K. The obtained white precipitate was filtered and washed repeatedly with distilled water to obtain the raw material. The surfactant was initially removed by solvent extraction using HCl in ethanol (3ml HCl 36% by weight in 50ml EtOH). Eventually the material was heated to 573 K for 2h in air. Following exactly the same synthesis protocol we synthesized materials using surfactants with chains of different lengths. The molar ratio is given in Table 1 below.

Table 1. Experimental parameters used in the synthesis of organ silica materials.

Representative X-ray powder diffraction spectra are shown in Figures 1 and 2. Nitrogen adsorption isotherms corresponding to 77K are shown in Figures 3 and 4. A representative thermogravimetric analysis (TGA) curve of a raw organosilica material and the corresponding solid from which the surfactant was removed are shown in Figure 5.

A representative Raman spectrum showing the presence of aromatic rings in porous materials is shown in Figure 6.

The hydrogen adsorption isotherms at 77K and up to a pressure of 1bar of the solids above are shown in Figure 7. A representative high pressure isotherm is shown in Figure 8 (b - solid circle curve) for the surfactant C16Py.

Example 2

Synthesis of porous organosilica materials using the condensable aromatic organ-alkoxysilane (1) and (3) and the surfactant S1 (CnPyBr, n = 12, 14, 16, 18 and 20) in acidic conditions.

In a typical synthesis, 0.4 g of C16PyBr was dissolved in 53.2 g of distilled water and 23.1ml of hydrochloric acid (36% by weight). Silane (1) (0.8 g) and silane (3) (0.12 g) (the molar ratio of silane (1) to (3) was 80:20) were then added to the above solution and the mixture was was stirred for 1h at 273K followed by further stirring for ~ 24h at 318K. The obtained white precipitate was filtered and washed repeatedly with distilled water to obtain the raw material. The surfactant was then removed initially by solvent extraction using HCl in ethanol (3ml HCl 36% by weight in 50ml EtOH). Eventually the material was heated to 573 K for 2h in air. Following exactly the same synthesis protocol we synthesized materials using surfactants with chains of different lengths.

A representative X-ray powder diffraction spectrum is shown in Figure 9. The nitrogen adsorption isotherm corresponding to 77K is shown in Figure 10.

Hydrogen adsorption isotherms at 77K and up to a pressure of 1bar are shown in Figure 11.

Example 3

Synthesis of porous organosilica materials using the condensable aromatic organ-alkoxysilane (2) and the surfactant S1 (CnPyBr, n = 12, 14, 16, 18 and 20) in acidic conditions.

In a typical synthesis, 0.4 g of C16PyBr was dissolved in 53.2 g of distilled water and 23.1ml of hydrochloric acid (36% w.). The silane (2) (1.18 g) was then added to the above solution and the mixture was stirred for 1h at 273K followed by further stirring for ~ 24h at 318K. The obtained white precipitate was filtered and washed repeatedly with distilled water to obtain the raw material. The surfactant was then removed initially by solvent extraction using HCl in ethanol (3ml HCl 36% by weight in 50ml EtOH). Eventually the material was heated to 573 K for 2h in air. Following exactly the same synthesis protocol we synthesized materials using surfactants with chains of different lengths.

A representative X-ray powder diffraction spectrum is shown in Figure 12. The nitrogen adsorption isotherm corresponding to 77K is shown in Figure 13.

A representative isotherm of hydrogen adsorption at 77K and up to a pressure of 1bar is shown in Figure 14. In order to illustrate the effects of the aromatic ring content of the alkoxysilane a comparison of high isotherms is shown in Figure 8 (b). pressure at 77K while keeping the other parameters fixed.

Example 4

Synthesis of porous organosilica materials using the condensable aromatic organ-alkoxysilane (2) and (3) and the surfactant S1 (CnPyBr, n = 12, 14, 16, 18 and 20) in acidic conditions.

In a typical synthesis, 0.8 g of C16PyBr was dissolved in 106.4 g of distilled water and 46.1 ml of hydrochloric acid (36% by weight). Silane (2) (1,914 g) and silane (3) (0.24 g) were then added to the above solution and the mixture was stirred for 1h at 273K followed by further stirring for ~ 24h at 318K. The obtained white precipitate was filtered and washed repeatedly with distilled water to obtain the raw material. The surfactant was then removed initially by solvent extraction using HCl in ethanol (3ml HCl 36% by weight in 50ml EtOH). Eventually the material was heated to 573 K for 2h in air. Following exactly the same synthesis protocol we synthesized materials using surfactants with chains of different lengths.

A representative X-ray powder diffraction spectrum is shown in Figure 15. The nitrogen adsorption isotherm corresponding to 77K is shown in Figure 16.

A representative isotherm of hydrogen adsorption at 77K and up to a pressure of 1bar is shown in Figure 17.

A comparison of the experimentally calculated isosteric heat of hydrogen adsorption in benzenesilica and organosilica-containing biphenyl is shown in Figure 18.

Example 5

Synthesis of porous organosilica materials using the condensable aromatic organ-alkoxysilane (2) and the S2 surfactant (CnBr, n = 10, 12, 14, 16 and 18) in basic conditions. In a typical synthesis, 1.26 g of C18Br was dissolved in 59.4 g of distilled water and 5.06 ml of sodium hydroxide (6M aqueous solution) at 50-60 ° C. The silane (2) (1.2 ml) was then added to the above solution drop by drop at room temperature. The mixture was then treated with ultrasound for 20 min and stirred for 20h at room temperature and finally the solution was kept at 95 ° C for 20h in static conditions. The obtained white precipitate was filtered and washed repeatedly with distilled water to obtain the raw material. The surfactant was then removed initially by solvent extraction using HCl in ethanol (9 g HCl 36% by weight in 250ml EtOH per 1 g of raw material).

A representative X-ray powder diffraction spectrum is shown in Figure 19. The nitrogen adsorption isotherm corresponding to 77K is shown in Figure 20.

A representative infrared (IR) spectrum showing the presence of aromatic rings in porous materials is shown in Figure 21.

A representative isotherm of high pressure adsorption is shown in Figure 8 (a - solid circle curve) for a short chain surfactant. The effects of the replacement of the metal atom in the organometallic precursors are shown in Figure 22 for high pressure adsorption isotherms: a partial replacement of the Si atoms with Al atoms causes an increase in hydrogen adsorption.

Example 6

Synthesis of porous organosilica materials using condensable aromatic organo-alkoxysilane (1) and (3) and surfactant S2 (CnBr, n = 16) (CnBr, n = 10, 12, 14, 16 and 18) under basic conditions .

In a typical synthesis, 2.18 g of C16Br were dissolved in 47.5 g of distilled water and 4.1 ml of sodium hydroxide (6M aqueous solution) at 50-60 ° C. The silane (2) (2.44 ml) and the silane (3) (0.15 ml) (the molar ratio of silane (1) to (3) was 95: 5) were then added to the above solution dropwise to room temperature. The mixture was then treated with ultrasound for 20 min and stirred for 20h at room temperature and finally the solution was kept at 95 ° C for 20h in static conditions. The obtained white precipitate was filtered and washed repeatedly with distilled water to obtain the raw material. The surfactant was then removed initially by solvent extraction using HCl in ethanol (9 g HCl 36% by weight in 250ml EtOH for each 1 g of raw material).

Example 7

Synthesis of porous organosilica materials doped with metals using the condensable aromatic organoalkoxysilane (4) and the surfactant S2 (CnBr, n = 10, 12, 14, 16 and 18) in basic conditions.

In a typical synthesis, 1.26 g of C18Br was dissolved in 59.4 g of distilled water and 5.06 ml of sodium hydroxide (6M aqueous solution) at 50-60 ° C. The silane (4) (1.2 ml) was then added to the above solution drop by drop at room temperature. The mixture was then treated with ultrasound for 20 min and stirred for 20h at room temperature and finally the solution was kept at 95 ° C for 20h in static conditions. The obtained white precipitate was filtered and washed repeatedly with distilled water to obtain the raw material. The surfactant was then removed initially by solvent extraction using HCl in ethanol (9 g HCl 36% by weight in 250ml EtOH per 1 g of raw material). Samples with exchanged metals were prepared by immersing the porous material under stirring in a 1N ethanol solution of the appropriate metal halide (metal = Li, Na, K, Ti, Fe, Co, Ni, Pd, Mn, Mg, Ca, Be , etc) and the suspension was refluxed overnight at 60-70 <o> C. The cation exchange was completed by refluxing and centrifuging three times with appropriate solutions. Finally the samples were washed and dried at room temperature.

Example 8

Synthesis of metal-doped porous organosilica materials using condensable aromatic organoalkoxysilane (1) and (5) and surfactant S2 (CnBr, n = 16) (CnBr, n = 10, 12, 14, 16 and 18) under conditions basic.

In a typical synthesis, 2.18 g of C16Br were dissolved in 47.5 g of distilled water and 4.1 ml of sodium hydroxide (6M aqueous solution) at 50-60 ° C. Silane (2) (2.44 ml) and silane (5) (0.15 ml) (the molar ratio of silane (1) to (5) was 95: 5) were then added to the above solution dropwise to room temperature. The mixture was then treated with ultrasound for 20 min and stirred for 20h at room temperature and finally the solution was kept at 95 ° C for 20h in static conditions. The obtained white precipitate was filtered and washed repeatedly with distilled water to obtain the raw material. The surfactant was then removed initially by solvent extraction using HCl in ethanol (9 g HCl 36% by weight in 250ml EtOH per 1 g of raw material). Samples with exchanged metals were prepared by immersing the porous material under stirring in a 1N ethanol solution of the appropriate metal halide (metal = Li, Na, K, Ti, Fe, Co, Ni, Pd, Mn, Mg, Ca, Be , etc) and the suspension was refluxed overnight at 60-70 <o> C. The cation exchange was completed by refluxing and centrifuging three times with appropriate solutions. Finally the samples were washed and dried at room temperature.

Claims (13)

CLAIMS 1. Porous organic-inorganic material containing aromatic organic groups within the pore wall and / or within the pores; characterized in that it comprises a polymer consisting of units derived from an M1 monomer or from M1 and M2 monomers having the structural formula: M1 = (OR) 3Me-A-Me (OR) 3 M1 M2 = [(OR) 3Me-A-Me (OR) 3] x- [(OR) 3Me-B] (1-x) in which: - Me is a metal chosen from silicon, germanium, tin and boron; - R is independently a saturated or unsaturated monovalent aliphatic group; - A and B are aromatic groups chosen independently, the same or different; - 0 <x≤ 1; said material having a pore size from 0.5 to 5 nm and a specific surface area ≥ 200 m2 / g. 2. Material according to claim 1, wherein x = 1 and wherein A is an aromatic group containing at least two phenylene rings, selected from biphenyl, naphthalene, anthracene, pyrene. 3. Material according to claim 1 wherein x is between 0.01 and 0.99 and wherein A and B are an aromatic group containing at least one phenylene ring, selected from phenyl, biphenyl, naphthalene, anthracene, pyrene. 4. Material according to claim 1, wherein x = 1 and A is an aromatic group containing at least two phenylene rings, selected from biphenyl, naphthalene, anthracene, pyrene and wherein A comprises one or more organic functional groups selected from the thiol groups , sulfonic, sulfone, carboxyl, amino. 5. Material according to claim 1, wherein x is comprised between 0.01 and 0.99 and wherein A and B are aromatic groups comprising at least one phenylene ring selected from phenyl, biphenyl, naphthalene, anthracene, pyrene and wherein A comprises one or more organic functional groups selected from the thiol, sulphonic, carboxyl, amino groups and the like. 6. Material according to claim 4 or 5 doped with a metal selected from the group consisting of Li, Na, K, Ti, V, Fe, Co, Ni, Pd, Mn, Mg, Ca, Be and their oxides. 7. A material according to claims 1 or 6 wherein the pores are arranged in long-range ordered or disordered structures. 8. Material according to claims 1 or 6 wherein the pores are arranged in hexagonal, cubic or lamellar ordered structures. 9. Material according to any of claims 1-6 exhibiting hydrogen storage capacity of at least 0.4 wt% at 77K and 1 bar pressure. 10. A material according to any one of claims 1-6 showing an isosteric hydrogen adsorption heat of at least 4 kJ / mol. 11. Process for the production of a porous material according to any one of claims 1-6, characterized in that it comprises the polycondensation step of the monomer M1 or M1 and M2 in the presence of a surfactant. 12. Process according to claim 11, wherein said surfactant is an alkylpyridinium halide or an alkyltrimethylammonium halide; and in which the alkyl has the formula CH3 (CH2) nin which n = 9, 11, 13, 15, 17 and 19; and in which the halide is a bromide or chloride anion. 13. Process according to claim 12 in which the polycondensation step takes place in an acidic or basic environment.