WO2003064322A1

WO2003064322A1 - Silica materials with meso- and macropores

Info

Publication number: WO2003064322A1
Application number: PCT/GB2003/000327
Authority: WO
Inventors: John Leonello Casci; Gordon Joseph Tregellaf Tiddy; Michael William Anderson; Tapas Sen; Chrystelle Celine Egger
Original assignee: Imperial Chemical Industries Plc
Priority date: 2002-01-29
Filing date: 2003-01-28
Publication date: 2003-08-07
Also published as: GB0201951D0

Abstract

A process is described for preparing a silica material having an interconnected macro-porous structure and a mesoporous wall structure comprising the steps of; (i) preparing a template of spheres of removable material, said spheres having a diameter greater than 50 nm; (ii) coating said template with a silica-forming soluting comprising at least one hydrolysable silicon compound, water, a first surfactant selected from a polyalkylene oxide compound, quaternary ammonium or C10-C18 alkyl amine compound and a second alcohol co-surfactant to form a coated template, and (iii) removing the removable material from the coated template. The second alcohol co-surfactant provides means to determine the ordering of the mesoporous wall structure. The silica material may be either particulate or monolith in form.

Description

SI ICA MATERIALS WITH MESO- AND MACROPORES

Silica Materials

This invention relates to silica materials and in particular to silica materials having an interconnected macroporous structure and mesoporous wall structure.

The IUPAC definition of porous materials distinguishes materials on the basis of pore size:

Microporous < 2 nm (20 A)

Mesoporous ≥ 2 nm; ≤ 50 nm

Macroporous > 50 nm

Microporous materials such as zeolites and related molecular sieve materials have been the subject of intensive industrial and academic research for 5 decades prompted by their extensive use as catalysts, adsorbents and ion-exchange materials. In part, their attraction (and properties) relies upon their 3-dimensional crystal structures, which enclose channels of constant dimensions.

It is a well-known problem that as the porosity dimension changes from microporosity to mesoporosity and macroporosity, the ability to prepare crystalline materials with a regular ordered pore structure declines markedly. By the term ordered we mean a regular repeating geometrical arrangement. However, in recent years there have been advances in the preparation of new porous materials with a range of compositions and topologies.

Mobil (and workers in Japan) published, in 1992, the class of mesoporous materials with regular ordered pore systems often referred to as M41S or MCM's (Mobil Composition of Matter), with perhaps the best known example being MCM-41. The advance in the design of such new framework topologies was largely due to the use of single quaternary ammonium compounds or amines as templates around which the material was formed. M41 S material may comprise a silica or aluminosilicate composition having geometrical, e.g. hexagonal or cubic, arrays of pores in the range 1.5 - 10 nm depending upon the template employed in its synthesis.

While the development of such ordered mesoporous materials has proved industrially useful, macroporous materials potentially have a broader range of applications such as catalytic materials and supports, separation and adsorbent media, biomaterials, chromatographic materials as well as optical and electronic applications.

Consequently, a number of workers, notably Stein, Stucky, Mann and Zhao, have turned their attention to the difficulty of producing useful macroporous materials, in particular macroporous materials having high interconnectivity between the macro- pores. The formation of macropores is beyond the limit of molecular templating or molecular assemblies such as micelles. Rather, a physical templating approach using colloidal spheres or oil droplets or vesicles or foams has been used. One known approach is to use polystyrene spheres formed by emulsion polymerisation tech- niques (e.g. see Stein et al, Science, 24th July 1998, 538). The polystyrene spheres are first formed into a template by slow sedimentation onto a membrane or by cen- trifugation. Treatment of the template with a hydrolysable compound such as a metal alkoxide or alkylsilicate in air, often as an alcoholic solution, ie a methanolic or etha- nolic solution, followed by removal of the template by thermal decomposition or sol- vent extraction produces a macroporous silica material. As will be generally understood, the term "spheres" is used to cover a range of materials whose shape is approximately spherical such that oblated or slightly flattened spheres are also included in this definition as are slightly elliptical shapes. Thus the spheres need not have a perfectly circular cross-section but may be flattened or slightly elliptical. As a guide the ratio of the minimum dimension (diameter) to the maximum dimension (diameter) should be not less than 0.75.

Addition of quaternary ammonium compounds (e.g. cetyltrimethylammonium hydroxide and tetrapropylammonium hydroxide) to the silica-forming solution, in a technique that has become known as dual templating, has provided mesoporous wall structures within the macroporous framework. This method has been used to prepare Si, Ti, Zr, Al, W, Fe, Sb and Zr-Y oxide materials (e.g. see Stein et al, Chem. Mater., 1999, 11, 795; Microporous and Mesoporous Materials, 2001, 44-45, 227). Alternatively macro-mesoporous silica materials have been prepared from complex surface- functionalised polymer latices treated with amphilic surfactant (see Antonietti et al, Adv. Mater., 1998, 10 (2), 154), and preformed zeolite nanoparticles and polyionic macromolecules adsorbed onto latex beads (see Mann et al, Chem. Mater., 2000, 12, 2832). However, the materials prepared by these methods have poorly defined wall structures with disordered meso-porosity and no crystalline domains. In wholly mesoporous materials, e.g. MCM's, the generation of ordered mesoporous structures has successfully been achieved by use of tri-block copolymers of ethylene- oxide and propylene-oxide. In particular tri-block copolymers, such as those available under the trade marks PLURONIC™ F127 (EO₁₀βPOtoEO₁₀β) and PLURONIC™ 123 (EO₂₀PO₇₀EO₂₀) in which EO = ethylene oxide and PO = propylene oxide, have been used. (PLURONIC is a trade mark of BASF Aktiengesellschaft.) (See for example, Stucky et al, Science, 23rd January 1998, 279, 548; J. An. Chem. Soc, 1998, 120, 6024; and Langmuir, 2000, 16, 8291). Tri-block copolymers appear also to introduce a level of microporosity within the walls of mesopores (see Davidson et al, J. Am. Chem. Soc, 2000, 122, 11925). Co-surfactants have been used to augment the tri-block copolymers (see Pine et al, Langmuir, 2000, 16, 5304). The co- surfactants used were alcohols (butanol, pentanol and hexanol), which were found to affect the size of the mesopores and/or wall thickness in a hexagonal mesoporous structure.

In spite of the success in controlling the mesoporosity in such mesoporous materials, attempts at producing a particulate or monolithic materials having an ordered crystalline mesoporous wall structure within an ordered macroporous framework have not succeeded. Rather only thin coatings having ordered mesoporosity around a macroporous framework have been described. For example, Stucky et al (Science, 18th December 1998, 282, 2244) produced patterned macro-mesoporous silica, titania and niobia films from polydimethylsiloxane moulds in a two-stage process where a polystyrene dispersion was first applied to the mould to generate an ordered macroporous template, followed by the oxide-forming solution which in this case contained amphilic triblock copolymer surfactants. It was found that the ordering of the mesopores could be determined by the choice of the surfactant; when PLURONIC™ F127 tri-block copolymer was used, a cubic mesophase resulted, whereas a hexagonal mesophase was obtained when PLURONIC™ 123 tri-block copolymer was used. This method is not however useful for the production of particulate materials. Attempts at producing a particulate material using polystyrene latex spheres sedi- mented or pressed into pellets and treated with a silica-forming solution having an amphilic tri-block copolymer surfactant in place of the quaternary ammonium compound, produced an ordered meso-structure but without significant interconnectivity between the macropores (see Zhao et al, Chem. Lett., 2000, 378). Kaliaguine et al (Microporous and Mesoporous Materials, 2001, 44-45, 241) prepared a macro- structured MCM-48 material (i.e. having cubic-structure mesopores) by simple addi- tion of macro-sized polystyrene latex beads to a silica-forming solution containing cetyltrimethylammonium chloride/hydroxide, but the materials had poor interconnec- tivity between the macropores and the mesopores were small (9-10 nm).

We have found surprisingly that in the generation of particulate silica materials hav- ing an interconnected macroporous structure and a mesoporous wall structure, the addition of alcohol co-surfactants to the silica-forming solution provides means to control the ordering of the mesoporosity in the wall structure.

Accordingly the invention provides a process for preparation of a silica material having an interconnected macroporous structure and a mesoporous wall structure com- prising the steps of; (i) preparing a template of spheres of removable material, said spheres having a diameter greater than 50 nm; (ii) coating said template with a silica- forming solution comprising at least one hydrolysable silicon compound, water, a first surfactant selected from a polyalkylene oxide compound, quaternary ammonium compound or C10-C18 alkyl amine and a second alcohol co-surfactant; and (iii) re- moving the removable material from the coated template.

The invention further provides a silica material prepared according to such a process.

According to another aspect of the invention, a silica material in the form of a particulate material or in the form of a monolith and having an interconnected macroporous structure and an ordered mesoporous wall structure.

In the present invention, the spheres of removable material may be spheres of a thermally decomposable or solvent-soluble material, colloidal material or oil droplets. Preferred materials are polystyrene latex spheres formed by emulsion polymerisation techniques using styrene monomer, optionally with other co-monomers. To obtain useful macroporous materials the spheres should have a diameter >50nm. The spheres may be monodispersed, i.e. all of similar size, or may be bi-, tri- or poly- dispersed, i.e. many sizes (each of which is > 50 nm). For example monodispersed polystyrene spheres in the range 50 nm to 12000 nm, preferably 50 nm to 3000 nm may be used. As mentioned above, the spheres need not have a perfectly circular cross-section but may be flattened or slightly elliptical. As a guide the ratio of the minimum dimension (diameter) to the maximum dimension (diameter) should be not less than 0.75 The spheres are formed into a template. The spheres provide macroporosity and by forming a template, where the spheres touch, windows between adjacent macro- pores are created in the resulting silica material. The template may be formed by slow sedimentation of a dispersion of the spheres e.g. on a porous material, or by accelerated sedimentation, e.g. by centrifugation. The template may be dried under ambient or elevated temperatures (e.g. about 60oC). The resultant template may be, depending upon the method chosen for its formation, a shaped block, i.e. a monolith, or a particulate material and if desired, a monolith may be crushed to provide a particulate or powdery material. In one embodiment, the template is in the form of a monolith which may be formed, for example, by centrifugation of a polystyrene latex dispersion, followed by drying.

The template is coated with a silica-forming solution. The coating may be applied by spraying, brushing or pouring the solution onto or over the template or by complete immersion of the template in the solution for a period of time. The thickness of the coating may be varied depending upon for example, the permeability of the template, i.e. the ability of the silica-forming solution to penetrate between the spheres, and the viscosity of the silica-forming solution. Separation of the coated template from the silica-forming solution may, depending upon the coating method, be accomplished by filtration, decantation or other physical separation techniques known to those skilled in the art.

Alternatively the template may be dispersed within the silica-forming solution without subsequent separation of the template from the silica-forming solution.

The coating process may be performed under ambient air or under dried air or other dry gas, e.g. nitrogen. The temperature is typically about ambient temperature (ca 20°C) but may be higher depending upon e.g. the reactivity of the silica-forming species within the silica-forming solution. The resulting coated template may be dried under ambient or elevated temperatures (e.g. about 60°C) before removal of the spheres of removable material and surfactants.

Removal of the spheres of removable material and the surfactants may be accom- pushed for example by solvent dissolution of the spheres or by thermal decomposition of the spheres or by a combination of both techniques. Solvent dissolution of the spheres may be accomplished by treatment of the coated template with suitable solvents in which the spheres are soluble. Suitable solvents include hydrocarbons, chlorinated hydrocarbons, aromatic hydrocarbons, ethers and acetonitrile. For example, where the spheres are polystyrene-based, suitable solvents include toluene or xylene. Solvent dissolution may be carried out at ambient temperature or higher depending upon the solvent, the material being dissolved and the structural stability of the resulting silica material. The treatment may be by spraying, brushing or pouring the solvent onto or over the coated template or by complete immersion of the coated template in solvent for a period of time or by soxhlet extraction. Preferably the solvent treatment is by immersion of the coated template in a solvent for a period of time up to e.g. 24 hours. Where non-polar solvents such as hydrocarbons and aromatic hydrocarbons are used to remove the spheres, surfactants such as quaternary ammonium compounds present from the silica-forming solution may not be completely removed. In such cases it is preferable that the resultant silica material is further treated with a polar solvent, optionally containing an acid. For example to remove residues of cetyltrimethylammonium bromide (CTAB), a 1 -molar aqueous hy- drochloric acid-ethanol solution may be used. Alcohols such as ethanol may remove C10-C18 amines. Surfactant extraction may be done at ambient temperature or higher, depending upon the solvent, the surfactant being removed and the structural stability of the silica material. In the above example, removal of the CTAB may be accomplished by stirring a suspension of the silica material in the acidic methanol at 70°C for 24 hours or by soxhlet extraction. The resulting silica material may then be dried, e.g. at 50°C for 12 hours.

As an alternative to solvent extraction, the spheres of removable material and surfactant may be removed by calcining the coated template to affect their thermal decomposition. By the term calcining we mean heating of the coated template to a ten- perature above the thermal decomposition temperatures of the spheres and the surfactants whereby the spheres and surfactants are converted substantially completely to gaseous materials. Generally this temperature is greater than 300°C. The heating may be performed under air or other oxidising gas. For example, with a polystyrene sphere template coated with a silica-forming solution containing an amphilic block copolymer surfactant, thermal decomposition of the template and surfactant may be achieved by heating in air to above 400°C, preferably between 400 and 550^°C for greater than 4 hours, preferably between 4 and 8 hours.

As an alternative to dissolution or thermal decomposition of the spheres and surfactant residues, other techniques for removal may be used e.g. raising the coated tern- plate to a temperature where the sphere material is molten and removing the spheres as a liquid, or chemical transformation of the spheres and/or surfactant into a removable form by reacting them with chemical reagents that e.g. effect their solubility.

The silica-forming solution of the present invention comprises at least one hydroly- sable silicon compound, water, a first surfactant selected from a polyalkylene oxide compound, quaternary ammonium compound or C10-C18 alkyl amine and a second alcohol co-surfactant. The hydrolysable silicon compound is a silicon compound containing at least one halide or alkoxide group bonded to the silicon atom. Whereas silicon halide compounds such as SiCI4 may be used, preferably the hydrolysable silicon compound is an alkyl silicate, and most preferably a tetraalkylsilicate. Tetraal- kylsilicates have the general formula Si(OR)4 in which R represents an alkyl group or substituted alkyl group, which may be the same or different, having between 1 and 4 carbon atoms. Alkyl silicates useful for the present invention include tetramethylor- thosilicate, tetraethylorthosilicate and tetrapropylorthosilicate and mixtures of these.

In addition to an alkylsilicate, the silica-forming solution may include in part, an or- ganofunctional silane according to the general formula:

(Y)aSi((CH2)cX)b

in which:

a = 3 or 2, b = 1 or 2 and a + b = 4, and c = 1 to 8 or c = 0 to 8;

Y = halogen (CI or Br) or alkoxy group having 1 to 4 carbon atoms; and

when c = 1 to 8, X is a functional group selected from hydrogen, halide, hydroxyl, carbonyl, carboxyl, anhydride, carbene, methacryl, epoxide, vinyl, nitrile, amine, imine, amide and imide; and

when c = 0 to 8, X is a substituted phenyl moiety, preferably a 3- or 4substituted phenyl moiety, wherein the substituting groups are selected from the list comprising halide, hydroxyl, carbonyl, carboxyl, methacryl, epoxide, vinyl, nitrile, amine, imine, amide and imide which may be may be bonded to the phenyl ring directly or through an alkyl or alkoxy (C1-C4) linking group.

Organofunctional silanes useful for the present invention include vinyltrimethoxy si- lane, vinyltriethoxysilane, dichlorodivinylsilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, [3-(methacryloyloxy)-propyl]trimethoxysilane, [3-[tri(eth- oxy/methoxy)silyl]propyl]urea, 3-glycidoxy-propyltrimethoxysilane, 4-(triethoxysilyl)- butyroitrile, 3-(triethoxysilyl)propionitrile, butyltrichlorosilane, dodecyltrichlorosilane, octadecyltrimethoxysilane, octyltrimethoxysilane, octyltriethoxysilane, 4-aminopheny- Itrimethoxysilane and 4-(2-chloroethyl)phenyltrimethoxysilane. Mixtures of organo- functional silanes having different functional groups may be used.

Where an organofunctional silane is present in the silica-forming solution, it is present in an amount that provides up to 20 mol% silicon, based on the total silicon present in the silica-forming solution.

The silica-forming solution preferably contains a solvent to moderate the rate of hydrolysis of the hydrolysable silicon compound and provide the silica-forming solution with a suitable viscosity and storage stability for treatment of the template. Suitable solvents include polar solvents such as ethers and alcohols. Particularly suitable solvents include methanol and ethanol.

The silica-forming solution contains water that reacts with the hydrolysable silicon compounds to generate a silica material. The silica-forming solution may be pH neutral or acidic. Preferably the solution has an acidic pH and most preferably has a pH < 2. This may be achieved by addition of an acid, for example, hydrochloric acid or an organic acid, e.g. acetic acid.

The silica-forming solution contains a first surfactant species to provide mesopores and if desired, micropores in the resulting silica material. The first surfactant is selected from polyalkylene oxide compounds, quaternary ammonium compounds or C10-C18 alkyl amines. The polyalkylene oxide compounds are typically amphilic block copolymer materials containing segments of propylene oxide (hydrophobic) and ethylene oxide (hydrophilic). Suitable polyalkylene oxide compounds are tri- block copolymers, e.g. PLURONIC™ F127 (EO₁₀ePO₇oEO₁₀6) tri-block copolymer and PLURONIC™ 123 (EO₂₀PO₇oEO₂o) tri-block copolymer and mixtures of these. The quaternary ammonium compounds are quaternary ammonium salts or hydroxides e.g. of general formula [P_MNJ+IZ]- in which R may be the same or different and is al- kyl or substituted alkyl (C1-C30), and Z is preferably CI, Br, or OH. Quaternary ammonium compounds wherein the nitrogen atom forms part of a ring structure may also be used. Suitable quaternary ammonium compounds are tetrapropylammonium hydroxide, tetrapropylammonium chloride, tetrabutylammonium hydroxide, benzyl- trimethylammonium hydroxide, benzylcetyldimethylammonium chloride, benzyl- trimethylammonium hydroxide, benzyltrimethylammonium chloride, cetyltrimethyl ammonium hydroxide, cetyltrimethylammonium bromide, cetyltrimethylammonium chloride and mixtures of these. Suitable amines are amines having greater than 10 carbon atoms in their structure, preferably C10-C18 alkyl amines and most preferably C12-C18 alkyl amines such as n-dodecylamine or n-octadecylamine or mixtures of these.

The silica-forming solution contains a second alcohol co-surfactant that directs the order of the mesoporosity. The alcohol is a branched or unbranched alcohol having between 3 and 20 carbon atoms and preferably between 3 and 10 carbon atoms. The alcohol may be mono-, di, tri- or poly-hydroxylic, may be substituted or unsubsti- tuted and may contain heteroatoms selected from N or S. Suitable alcohols include thioalcohols, aminoalcohols, linear alcohols having between 3 and 10 carbon atoms, diols and triols. Preferred alcohols are linear alcohols having between 3 and 10 car- bon atoms. Suitable linear alcohols include n-propanol, n-butanol, n-pentanol and n- hexanol.

Other additives may be added to the silica-forming solution if desired to effect the properties of the resulting silica material. For example additives may be added to increase the pore size of the mesopores e.g. 1 ,3,5-trimethyl benzene. Without wish- ing to be bound by any theory, it is believed that such additives increase the pore size by swelling the surfactant micelles.

The silica-forming solution preferably comprises components in the following molar ratios;

Hydrolysable silicon compounds (Si) 1.0

Water 0.5 - 10

First Surfactant 0.002 - 0.010

Second Co-surfactant 0.01 - 0.50

In a first embodiment, the hydrolysable silicon compound is tetramethylorthosilicate

(TMOS), the first surfactant is PLURONIC™ F127 tri-block copolymer or PLU- RONIC™ P123 tri-block copolymer and the second co-surfactant is pentanol. In a preferred first embodiment the silica-forming solution has the following composition by weight; TMOS 44.9 wt%; water 34.3 wt%; PLURONIC™ F127 tri-block copolymer or PLURONIC™ P123 tri-block copolymer 11.8 wt%; and pentanol 8.8 wt%. A pH of about 1 is achieved by addition of 0.2 wt% aqueous HCI to the silica-forming solution.

In a second embodiment, the hydrolysable silicon compound is tetramethylorthosili- cate (TMOS), the first surfactant is PLURONIO^M P123 tri-block copolymer and the co-surfactant is butanol. In a preferred second embodiment, the silica-forming solution has the following composition by weight; TMOS 48.2 wt%; water 37.0 wt%; PLURONIC™ P123 tri-block copolymer 12.7wt %; and butanol 1.92 wt%. A pH of about 1 is achieved by addition of 0.18 wt% aqueous HCI to the silica-forming solution.

Thus the invention further provides a silica material having an interconnected macroporous structure and a mesoporous wall structure prepared according to the steps comprising; (i) preparing a template of spheres of removable material, said spheres having a diameter greater than 50 nm; (ii) coating said template with a silica-forming solution comprising at least one hydrolysable silicon compound, water, a first surfactant selected from a polyalkylene oxide compound, quaternary ammonium compound or C10-C18 alkyl amine and a second alcohol co-surfactant to form a coated template, and (iii) removing the removable material from the coated template

The silica materials of the present invention are preferably particulate or monolithic in form depending upon the nature of the template and the method of coating of the template by the silica-forming solution, and have an ordered mesoporous wall structure. Thus the invention further provides a silica material in the form of a particulate material or in the form of a monolith having an interconnected macroporous structure and an ordered mesoporous wall structure.

Depending upon the combination of first and second surfactant used, the mesoporous wall structure of the silica material may contain mesopores in an ordered hexagonal arrangement or an ordered cubic arrangement. The silica material may, as a result of the surfactants, advantageously additionally contain mesopores, resulting a silica material containing macropores, mesopores and micropores.

In further embodiments, the silica material may contain Al, Ti, Zr, Nb, Ta, Sn, V, Cr, Fe, Ca, Mg atoms within the silica material. The sources of the atoms may be metal- alkoxides or carboxylates added to the silica-forming solution. The atoms may provide e.g. catalytically active sites. Alternatively, the silica material of the present invention may be subjected to further treatment with compounds, e.g. metal containing compounds, in order to form catalytic materials.

The invention will be further illustrated by reference to the drawings and the following Examples. In the drawings:

Figure 1 is a transmission electron micrograph (TEM) of the silica material of the comparative example described below using a scale of approximately 1 cm = 75 nm;

Figure 2 is a TEM of the silica material of Example 2 described below using a scale of approximately 1 cm = 100 nm; and

Figures 3 and 4 are TEMs of the silica material of Example 6a described below using scales of approximately 1 cm = 200 nm and 1 cm = 100 nm, respectively.

Example 1 : Preparation of polystyrene sphere templates

Non-crossed linked, mono-dispersed polystyrene spheres were synthesised using an emulsifier-free polymerisation technique according to the literature (Holland et al, Chem. Mater., 1999, 11 , 795). Styrene (105 ml, Fluka, >99% purity) was washed in a separating funnel five times with 100 ml of 0.1 M NaOH (BDH, 99% purity) then five times with 100 ml deionised water to remove stabiliser. A five necked, 2000 ml round bottom flask fitted with electrically-driven stirrer, water condenser, thermometer, sep- tum and N₂ supply was filled with a specific amount of deionised water and heated to 70°C using an isomantle, before adding 100 ml of washed styrene. In a separate 100 ml beaker, potassium persulfate initiator (Sigma, 99% purity) was dissolved in 50 ml water and heated to 70°C. The persulfate solution was added to the reaction vessel containing the mixture of deionised water and washed styrene at 70°C and the whole mixture was stirred at a specific stirring speed for 28 hr. The temperature was kept at 70°C during the reaction duration. The final reaction mixture was milky white. A sample was collected by syringe for particle size distribution analysis. The remaining colloidal solution of polystyrene spheres was cooled and stored at 4^°C.

Monoliths were prepared as follows; 35 ml of suspension in a 50 ml centrifuge tube were centrifuged at 4000-5000 rpm for 60 minutes. The supernatant was decanted off and the resulting monolith dried at 60oC for 4-5 hours. Table 1 detailsthe reac- tion conditions used to produce two batches of polystyrene spheres having different average sizes and Table 2 contains the analytical results of the spheres and monoliths derived from them.

Table 1. Synthesis of polystyrene latex spheres.

Table 2. Properties of polystyrene spheres & monoliths.

*The PLS-A monolith was prepared from a commercial polystyrene latex dispersion supplied by Interfacial Dynamics Corp., USA

Comparative Example: Preparation of silica material - No use of co-surfactant

0.9 g of tri-block copolymer PLURONIC™ P123 tri-block copolymer was mixed at room temperature (ca 20^°C) with 15g ethanol solvent, 0.4 g of 0.1 (M) HCI solution and 0.5 g of deionised water in a polypropylene beaker. The mixture was stirred for 10 minutes before addition of 2.08 g of tetraethylorthosilicate (TEOS). The ethanol solvent to TEOS molar ratio = 32.6:1. The mixture was stirred for 30 minutes at room temperature. 2.0 g of polystyrene monolith PLS-A was dipped into the TEOS solution for 1 hr at room temperature before separation by filtration. The coated monolith after filtration (no washing) was placed in an oven and heated at 1°C/minute from ambient to 480°C and calcined at 480°C for 10 hr in the presence of air. 10% wt solid remained after calcination.

Example 2: Preparation of silica material 2 -use of cosurfactant.

4.06 g of 0.475(M) HCI were diluted by 9.71 g deionised water in a polypropylene beaker at room temperature. 18.16 g of tetramethylorthosilicate (TMOS, Aldrich, purity 99%) was added to the acidic solution. The tetramethylorthosilicate vigorously reacted with acidic solution and the temperature of the mixture increased to 60^° C. The mixture was stirred for 15 minutes during which time the solution temperature decreased to 30°C. In a separate polypropylene beaker 4.76 g of tri-block copolymer, PLURONIC™ F127 (Sigma) was mixed at room temperature with 3.40 g n-pentanol (Aldrich, purity 99%). The TMOS solution was added to the surfactants solution to create the silica-forming solution and stirred for 5 minutes before addition to the combined solutions of 4.0 g of polystyrene template, PS-B1. The whole mixture was stirred for a further 15 minutes at room temperature before separation of the coated template from the solution by filtration. The coated template was dried at 60C before heating at 1°C/minute to 500"C and being calcined at 500°C for 10 hrs in the presence of air to effect decomposition of the surfactants and polystyrene spheres. 14% wt solid remained after calcination.

Example 3: Preparation of silica material 3.

The method of Example 2 was repeated replacing the surfactant PLURONIC™ F127 tri-block copolymer with PLURONIC™ P123 tri-block copolymer at the same weight addition. 13% wt solid remained after calcination.

Example 4: Preparation of silica material 4.

The method of Example 2 was followed using a reduced wt% of second alcohol co- surfactant and a different polystyrene sphere monolith. 2.02 g 0.475(M) HCI solution was diluted by 4.96 g of deionised water in a polypropylene beaker at room temperature. 9.06 g of TMOS was added to the acidic solution. Addition of TMOS increased the temperature of the solution to nearly 60°C. The mixture was stirred for 15 minutes at room temperature. In a separate beaker, 2.38 g PLURONIC™ P123 tri-block copolymer was mixed with 0.36 g of n-butanol (BDH, 99% purity). The TMOS solution was added to the surfactants solution to create the silica-forming solution and stirred for 10 minutes until the mixture became homogeneous. 2.0 g of polystyrene monolith (PS-B4) was added to the silica-forming solution and stirred for another 15 minutes. The solution started to thicken while stirring. The drying and calcination procedures were same as Example 2. 12% wt solid remained after calcination.

Example 5: Preparation of silica material 5.

The method of Example 2 was followed replacing the PLURONIC™ F127 tri-block copolymer with PLURONIC™ P123 tri-block copolymer, n-pentanol with n-butanol and polystyrene spheres PS-B1 with PS-B4, each at the same corresponding wt% addition.

Example 6: Preparation of silica materials 6a and 6b.

The method of Example 2 was followed using n-butanol instead of n-pentanol as co- surfactant and PS-B4 template material instead of PS-B1, each at the same corresponding wt% addition. Silica material 6a was calcined for 10 hours in air at 550^°C instead of 500°C and 14 wt% solid remained. In the case of silica material 6b, as an alternative to calcination, the polystyrene spheres were removed by treatment with toluene (sigma, >99% purity) for 1day at about 27°C. The toluene-extracted Sample 6b was then calcined at 450^°C for 12 hours in air (Sample 6b-ι).

The silica materials were characterised by different physicochemical methods as follows;

Method Characteristics Measured

Powder X-ray diffraction (XRD) Crystallinity

Scanning electron microscopy (SEM) Macroporosity & interconnectivity. Size of surface pores and windows between pores and thickness of walls

Transmission electron microscopy (TEM) Interconnectivity and mesoporosity

(order). Size of internal pores and windows

N2 Adsorption BET and t-plot surface area (SA), size

(d) and volume (V) of mesopores (mp) and micropores (mi)

Hg Porosimetry Size and volume of macropores The synthesis and characterisation of the silica materials are provided in Tables 3 to 5 and figures 1 to 4.

In Figure 1 the walls 10 of the macropores 12 appear to possess mesopores with no apparent order, whereas in Figure3 2, 3 and 4, the walls 14, 16 and 18 show a dis- tinct ordering of the mesopores.

The materials of the present invention were highly ordered in the macro-scale range. All materials contain macropores (primary pores in the order of 300 nm to 900 nm) with connectivity through windows (secondary pores in the order of 70 to 140 nm). The mesopores (tertiary in the order of 2 to 10 nm) were present over all the materi- als with order depending on surfactant combinations. In the materials of the present invention microporosity (quaternary pore in the order of few A) in between ordered mesopores was measured and is believed to have resulted from use of the tri-block copolymers as first surfactant. In comparison, the comparative example showed disordered mesoporosity and no microporosity.

Using PLURONIC™ F127 tri-block copolymer and n-butanol as co-surfactant, the macroporous silica (material 6a) had a mesoporous wall structure with an ordered cubic arrangement of mesopores (see Figures 3 and 4), whereas using PLURONIC™ F127 tri-block copolymer and n-pentanol (material 2), an ordered hexagonal arrangement of mesopores was obtained (see Figure 2). Conversely, using PLU- RONIC™ P123 tri-block copolymer and n-butanol as co-surfactant, the macroporous silicas (materials 4 and 5) had mesoporous walls with ordered hexagonal arrangements of mesopores.

Applicant's Reference TEC 51023

-16-

Table 3. Synthesis of hierarchically ordered silica materials by using colloidal spheres as templates.

Table 4. XRD, SEM and TEM Characterization of hierarchically ordered silica materials.

Table 5. Hg porosimetry and N2 adsorption characterization of hierarchically ordered silica materials.

Where 'SA' = surface area, 'V = volume, 'mi' = micropores and 'mp' = mesopores.

Claims

Claims.

1. A process for preparation of a silica material having an interconnected macroporous structure and a mesoporous wall structure comprising the steps of; (i) preparing a template of spheres of removable material, said spheres having a diameter greater than 50 nm; (ii) coating said template with a silica-forming solution comprising at least one hydrolysable silicon compound, water, a first surfactant selected from a polyalkylene oxide compound, quaternary ammonium compound or C10-C18 alkyl amine and a second alcohol co-surfactant to form a coated template; and (iii) removing the removable material from the coated tem- plate.

2. A process according to claim 1 wherein the template of spheres is particulate or in the form of a monolith.

3. A process according to claim 1 or claim 2 wherein the spheres of removable material are spheres of a thermally decomposable or solvent-soluble material.

4. A process according to any one of claims 1 to 3 wherein the hydrolysable silicon compound is an alkyl silicate.

5. A process according to any one of claims 1 to 3 wherein the hydrolysable silicon compound comprises an alkyl silicate and an organofunctional silane, said or- ganofunctional silane present in an amount that provides up to 20 mol% silicon, based on the total silicon present in the silica-forming solution.

6. A process according to any one of claims 1 to 5 wherein the polyalkylene oxide compound is an amphilic block copolymer material containing segments of pro- pylene oxide and ethylene oxide.

7. A process according to any one of claims 1 to 5 wherein the quaternary ammo- nium compound is a quaternary ammonium salt or hydroxide of general formula

[R₄N]⁺[Z]^" in which R may be the same or different and is alkyl or substituted alkyl (C1-C30), and Z is CI, Br, or OH, or a quaternary ammonium compound wherein the nitrogen atom forms part of a ring structure.

8. A process according to any one of claims 1 to 7 wherein the second alcohol co- surfactant is a branched or unbranched alcohol having between 3 and 20 carbon atoms selected from the list comprising substituted or unsubstituted mono-, di, tri- or poly-hydroxylic alcohols and alcohols containing N or S heteroatoms.

9. A silica material having an interconnected macroporous structure and a mesoporous wall structure prepared according to the steps comprising; (i) pre- paring a template of spheres of removable material, said spheres having a diameter greater than 50 nm; (ii) coating said template with a silica-forming solution comprising at least one hydrolysable silicon compound, water, a first surfactant selected from a polyalkylene oxide compound, quaternary ammonium compound or C10-C18 alkyl amine and a second alcohol co-surfactant to form a coated template, and (Hi) removing the removable material from the coated template.

10. A silica material in the form of a particulate material or in the form of a monolith having an interconnected macroporous structure and an ordered mesoporous wall structure.

11. A material according to claim 9 or claim 10 wherein the silica material contains Al, Ti, Zr, Nb, Ta, Sn, V, Cr, Fe, Ca, Mg atoms within the silica material.

12. A material according to any one of claims 9 to 11 wherein the silica material is subjected to further treatment with compounds in order to form a catalytic material.