WO2010106146A1

WO2010106146A1 - Manufacture process for titanium dioxide materials with high surface areas and high thermal stability

Info

Publication number: WO2010106146A1
Application number: PCT/EP2010/053555
Authority: WO
Inventors: Alexandra Seeber; Cornelia Roeger; Alexander Traut; Roman Zieba; Iris Schneider
Original assignee: Basf Se
Priority date: 2009-03-20
Filing date: 2010-03-18
Publication date: 2010-09-23

Abstract

The present invention relates to a process for the preparation of particles comprising at least one transition metal oxide and silicon dioxide, comprising at least the following steps: (A) Contacting at least one precursor of the at least one transition metal oxide and at least one non-ionic surfactant comprising silicon in at least one non-aqueous organic solvent, to obtain a reaction mixture and (B) Drying the reaction mixture obtained in step (A) to obtain particles comprising the at least one transition metal oxide and silicon dioxide. (C) Calcination of the particles obtained from step (B) of the process according to the present invention at a temperature of 200 to 800°C in an oxygen comprising atmosphere. The preferred transition metal oxide is titanium dioxide.

Description

Manufacture process for titanium dioxide materials with high surface areas and high thermal stability

Description

The present invention relates to a process for the preparation of particles comprising at least one transition metal oxide and silicon dioxide, comprising at least the following steps: (A) contacting at least one precursor of the at least one transition metal oxide and at least one non-ionic surfactant comprising silicon in at least one non-aqueous organic solvent, to obtain a reaction mixture and (B) drying the reaction mixture obtained in step (A) to obtain particles comprising the at least one transition metal oxide and silicon dioxide. The present invention further relates to the use of TiCI₄ and/or Ti(O¹Pr)₄ in the preparation of particles comprising TiO₂ and SiO₂ and to a particle comprising at least one transition metal oxide and silicon dioxide.

Processes for the preparation of such particles, comprising for example titanium dioxide and silicon dioxide, have already been reported in the prior art.

EP 0 668 100 A1 discloses a process for preparing a silica-titania catalyst by adding an acidic solution containing a silicon compound such as sodium silicate and a titanium compound such as titanium sulphate dissolved therein to a solution of a compound such as ammoniumbicarbonate to bring about co-precipitation, in which the acidic solution is a highly concentrated nitric acid-acidic or sulphuric acid-acidic solution. EP 0 668 100 A1 does not disclose that silicon comprising surfactants may be used as structure directing agent. In addition, the process according to this document is conducted in an aqueous acidic solution.

US 3,887,494 discloses a method for preparing a composition comprising silica and titanium, convertible to a catalyst suitable for olefin polymerisation by the addition of chromium and the process performable therewith, wherein the preparation involves the addition of an alkali metal silicate to an acid containing a titanium compound and recovering a dry gel for use as catalyst upon the addition of chromium. The process according to US 3,887,494 is conducted in an aqueous medium. In addition, the use of non-ionic silicon surfactants is not disclosed.

EP 0 826 410 A2 discloses a catalyst for purifying exhaust gases, which is capable of maintaining the catalytic property and purification performance against particulates, HC, CO and NOx over a long period of time. The catalyst has a catalyst substrate and a heat-resistant inorganic oxide layer containing catalytic components, which is pro- vided on the catalyst substrate. This layer contains silica-doped titania in anatase modification having a structure that 3 to 35% by weight of silica is finely dispersed between and retained by anatase titania particles which is an oxide obtained in the state where a silicon-containing compound and titanium containing compound are mixed in the molecular state. Examples of the titanium comprising compound is titania sol, and an example of the silica comprising compound is silica sol. EP 0 826 410 A2 does not dis- close the process for the preparation of mixed oxides in non-aqueous organic solvents. In addition, the use of non-ionic surfactants comprising silicon is not disclosed in this document.

JP 2002-348380 A discloses titanium oxide silica composites and a method for the preparation of these composites. In order to obtain titanium oxide silica composites according to this document, titanium oxide organopolysiloxane hybrid granular material is treated in a mixture of water and chloride-isopropyl alcohol. This granular material is heat-treated to obtain porous titanium oxide silica composites having a BET specific surface area of about 100 m²/g. JP 2002-348380 A does not disclose a process for the preparation of titanium dioxide materials doped with silicon dioxide, wherein this process is conducted in a non-aqueous organic solvent in the presence of non-ionic surfactants comprising silicon.

WO 2006/058254 A1 discloses a process for the preparation of mesoporous metal ox- ides. In detail, the mesoporous oxides of titanium, zirconium or hafnium are disclosed. A solvent for the process according to WO 2006/058254 A1 can be chosen from aqueous or organic solvents. In addition, emulsifiers can be added to the reaction mixture, for example glyceryl stearate, polyethyleneglycol-100 stearate etc.

JP 2003-073585 A relates to a fluid for titania film formation, a method for forming a titania film and the titania film itself. In the fluid according to this document, an organic substance is mixed with the anatase crystal/amorphous mixing titania sol solution containing an amorphous type titania, an anatase type crystal titania, or its precursor. The organic substances, which can be added, can be chosen from polyalkylene oxide, like polyethylene oxide, polypropylene oxide and further polyethers. In addition, compounds comprising siloxane bonds represented by polydimethylsiloxane can be used. The method according to JP 2003-073585 A is conducted in an aqueous solvent.

Xu et al., Adv. Mater. 2002, 14 No. 15, pages 1064 to 1068 disclose a method for the preparation of oxide monoliths and films with unusual long range highly ordered lamellar structures. These lamellar metal oxide (Tiθ₂ and Zrθ₂) monoliths and films are prepared by a sol-gel method, wherein a mixture of metal alkoxide, cationic silicon surfactant, water and HCI in ethanol is used. Xu et al. do not disclose particles which are obtained from a non-aqueous organic solution. The problem with the processes according to the prior art is that calcination often leads to polystructured or dense or collapsed materials with low surface areas. In addition, the mechanism of formation is kinetically controlled, reproducibility of the synthetic procedure can present problems in the production of high quality mesoporous materials. In addition, mesoporous titanium dioxide materials which are obtained by the methods according to the prior art often show a low thermal stability of both the mesoporous structure and the anatase modification of titanium dioxide. After heating the materials of the prior art to high temperatures, the BET surface area often dramatically decreases in addition to an at least gradual structural phase change to the inactive rutil modification. In addition the removal of surfactants which are commonly used as structure directing agents in the preparation of TiC>₂ particles is often difficult.

It is therefore an object of the present invention to develop transition metal oxide particles with a high BET surface area, high crystallinity, small particle size and improved temperature stability. In addition, a process for the preparation of these particles should be provided.

These objects are solved by the process for the preparation of particles comprising at least one transition metal oxide and silicon dioxide, comprising at least the following steps:

(A) contacting at least one precursor of the at least one transition metal oxide and at least one non-ionic surfactant comprising silicon and at least one non-aqueous organic solvent, to obtain a reaction mixture and

(B) drying the reaction mixture obtained in step (A) to obtain particles comprising the at least one transition metal oxide and silicon dioxide.

These objects are further solved by particles obtained from this process and by the use of TiCI₄ and/or Ti(O¹Pr)₄ in the preparation of particles comprising titanium dioxide and silicon dioxide.

The process according to the present invention gives rise to particles comprising at least one transition metal oxide and silicon dioxide.

In general, any transition metal known to a person having ordinary skill in the art can be used in order to obtain the particles according to the present invention. In a preferred embodiment, the at least one transition metal oxide is chosen from the group consisting of TiO₂, ZrO₂, ZnO, VO_x, NbO_x, MoO_x, WO₃, HfO₂ and mixtures thereof. In a very preferred embodiment, the present invention relates to a process, wherein the transition metal oxide is titanium dioxide (TiO₂).

The present invention therefore further relates to the process as mentioned above, wherein the transition metal oxide is titanium dioxide (TiO₂).

In a particularly preferred case, titanium dioxide is predominantly present in its anatase modification. In a further preferred embodiment, titanium dioxide is present in the anatase modification in an amount of at least 50%, more preferred at least 60%, particu- larly preferred at least 70% based on the total amount of titanium dioxide in each case.

In addition to the at least one transition metal oxide, the particles which are prepared by the process according to the present invention further comprise silicon dioxide. In general, the particles which are prepared by the process according to the present in- vention comprise silicon dioxide in an amount of 0.1 to 30 % by weight, preferably 1 to 20 % by weight, and particularly preferred 3 to 12 % by weight.

The single steps of the process according to the present invention are described in the following in detail.

Step (A):

Step (A) of the process according to the present invention comprises contacting at least one precursor of the at least one transition metal oxide and at least one non-ionic surfactant comprising silicon in at least one non-aqueous organic solvent, to obtain a reaction mixture.

In general, all precursors of the at least one transition metal oxide can be used in step (A) of the process according to the present invention, which are known to a person skilled in the art to be convertible to at least one transition metal oxide. Examples of suitable precursors of the at least one transition metal oxide are compounds comprising the corresponding metal cation in addition to a suitable anion. Suitable anions are for example chosen from the group consisting of halides, for example chloride, bromide, sulphates, phosphates, carbonates, anions of carboxylic acids, alcoxides, for example methoxide, ethoxide, propoxides, for example n-propoxide, iso-propoxide, butoxides, for example n-butoxide, iso-butoxide, tert.-butoxide and mixtures thereof. Particularly preferred precursors are halides, especially chlorides and/or alkoxides, especially iso-propoxides, of the corresponding transition metal. In the preferred case that titanium dioxide is the at least one transition metal oxide, preferred precursors are chosen from the group consisting of titanium tetrachloride (TiCI₄), titanium tetra- alkoxides, for example titanium tetra isopropoxide, and/or mixtures thereof. The use of a combination of at least one halide and at least one alkoxide as precursor of the at least one transition metal oxide gives rise to the advantage that a nonaqueous organic solvent can be used, instead of water as solvent according to the prior art. The use of non-aqueous organic solvents makes it possible that the solvent is in general easily removed from the reaction mixture obtained in step (A) of the process according to the present invention. A further advantage of the use of a non-aqueous (< 1 % H₂O) organic solvent is that no water molecules are present that may accelerate the hydrolysis process or be trapped within the hydrolyzed metal oxide framework, and may disturb the formation of the desired highly ordered structures.

In a particularly preferred embodiment, a mixture of at least two different precursor compounds of the at least one transition metal oxide is used in step (A) of the process according to the present invention. Preferred mixtures of at least two different precur- sors are for example at least one halide and at least one alkoxide, especially preferred a mixture of the chloride and the isopropoxide of the corresponding transition metal. These two components of the mixture of precursors can be used in any suitable ratio, for example in a weight ratio of halide : alkoxide of 10:1 to 1 :10.

Based on this, in the particularly preferred case of titanium dioxide as the at least one transition metal oxide, a very preferred mixture of suitable precursor compounds is titanium tetrachloride (TiCI₄) and titanium tetra-isopropoxide (Ti(O¹Pr)₄). In this especially preferred mixture titanium tetrachloride and titanium tetra-isopropoxide can be used in any ratio, preferably in a weight ratio of TiCI₄ to Ti(O¹Pr)₄ of 10:0.1 to 0.1 :10, particularly preferred between 6:1 to 1 :6.

Contacting according to step (A) of the process according to the present invention is conducted in at least one non-aqueous organic solvent.

In the sense of the present invention non-aqueous means that essentially less than 1 % water is present in the organic solvent at the start of the reaction and that any water introduced to the reaction mixture after the mixing of the precursors of at least one transition metal oxides with the at least one non-ionic surfactant comprising silicon in at least one non-aqueous organic solvent is less than 30% by weight of the entire reaction mixture, preferably less than 20% by weight and particularly preferred less than 10% by weight, in each case in respect of the whole reaction mixture. The amount of water present in the reaction mixture can be acquired by titration according to the known Karl-Fischer method.

The non-aqueous organic solvent which is used in step (A) of the process according to the present invention, can be any organic solvent, which is able to dissolve or at least to disperse the reaction components, particularly the at least one precursor of the at least one transition metal oxide and the at least one non-ionic surfactant.

In a preferred embodiment of the process according to the present invention, the at least one organic solvent can be chosen from the group consisting of alcohols, esters, ethers, aliphatic hydrocarbons, aromatic hydrocarbons, amines, ketones, diketones, nitrated or chlorinated hydrocarbons and mixtures thereof. In a particularly preferred embodiment of the process according to the present invention, the organic solvent comprises an alcohol and/or a cyclic ether.

Suitable alcohols can be chosen from aliphatic alcohols having 1 to 10 carbon atoms, like methanol, ethanol, propanols, like n-propanol, iso-propanol, butanols, like n- butanol, iso-butanol, tert-butanol and mixtures thereof.

Suitable ethers can be chosen from cyclic or acyclic ethers. Examples of suitable acyclic ethers are dialkyl ethers for example chosen from the group consisting of dimethyl ether, diethyl ether, methyl-tert. -butyl ether and mixtures thereof. Examples of suitable cyclic ethers can be chosen from the group consisting of tetrahydrofurane (THF), 1 ,2-dioxane, 1 ,3-dioxane and 1 ,4-dioxane and mixtures thereof.

Suitable ketones or diketones can be chosen from the group consisting of acetone, acetoacetate, 2-propanone, 2-butanone, benzophenone, diacetyl, acetylacetone, hex- ane-2,5-dione and mixtures thereof.

In a very preferred embodiment of the process according to the present invention, an alcohol, for example ethanol, or a mixture of at least two non-aqueous organic solvents is used, for example a mixture of at least one alcohol and at least one ether. Suitable alcohols and ethers are mentioned above. Ethanol or a mixture of ethanol and THF is particularly preferred. The volume ratio of the at least two organic solvents, in the case where a mixture is used, can be any volume ratio which gives rise to a mixture that is able to dissolve or at least to disperse the reaction components. Preferably, the volume ratio of at least two solvents is from 1 :10 to 10:1 , preferably from 1 :5 to 5:1 , for example 1 :2 to 2:1.

The at least one non-ionic surfactant comprising silicon can in general be chosen from silicon comprising non-ionic surfactants known to a person having ordinary skill in the art. Suitable compounds are described, for example, in Wang et al., Journal of Colloids and Interface Science 242, 337 to 345 (2001 ) and Wang et al., Journal of Colloids and Interface Science 256, 331 to 340 (2002). An overview of syntheses and structures of common silicone surfactants is given in Silicone surfactants, Randal M. Hill, Surfactant science series, Volume 86, 1999, Ed.: Arthur T. Hubbard. Silicone comprising non-ionic surfactants, comprising polyoxyalkylene polyether groups are preferred, for example made of at least one alkylene oxide, for example chosen from the group consisting of ethylene oxide, propylene oxide, butylene oxide and mix- tures thereof. In addition to these polyoxyalkylene polyether building blocks, silicon comprising building blocks, for example -SiR¹R²-O-moieties, in which R¹ and R² can be identical or different, and can be chosen from d^o-alkyl radicals and/or polyoxyalkylene polyether building blocks as mentioned above, are present in the surfactants according to the present invention.

Polyoxyalkylene polyether building blocks and silicon comprising moieties are in general connected via hydrolytically unstable -Si-O-C- and/or hydrolytically stable -Si-C- groups. The Si-C linkage is usually made by a Pt-catalysed hydrosilylating addition of an Si-H function in the polysiloxane to a terminal olefinic bond in the substituent poly- ether. The Si-O-C linkage can be made by esterification of chloropolysiloxanes with hydroxyl-functionalized polyether.

The arrangement of these different blocks within the surfactant can be random or block-wise, linear or branched. Molecular weight of silicon comprising non-ionic surfac- tants is in general 500 to 50000 g/mol, preferably 1000 to 20000 g/mol.

Depending on the number of siloxane units, the number of branching points of the silicone and the number of connection points to the polyoxyalkylene polyether building blocks can be varied.

In a preferred embodiment of the present invention, non-ionic surfactants comprising silicon, which are used in the process according to the present invention are chosen from silicon-polyoxy alkylene polyether copolymers, for example according to formulae (1 ), (2), (3) and (4) and mixtures thereof

(3)

wherein (4) is a cyclic compound and R¹, R², x and y have the following meanings:

R¹ independently of each other, radical chosen from Ci-C₂o-alkyl, Ci-C₂₅-alicyclic, Ci-C₂5-aryl, Ci-C₂5-alkaryl, Ci-C₂₅-aralkyl.

R² independently of each other a polyoxyalkylene polyether radical of formula (5) -(CH₂)_a-(OCH₂CH₂)_b[OCH₂CH(CH₃)]c[OCH₂CH(CH₂CH₃)]d-R⁴ (5),

wherein a, b, c, d, and R⁴ have the following meanings: a integer of 0 to 6, preferably 0 to 4, for example 0, 1 , 2, 3 or 4, most preferably 3 b integer of O to 100, preferably 5 to 50, for example 6, 7, 8, 9, 10, 1 1 , 12, 13,

14 or 15, c integer of 0 to 50, preferably 0 to 25, for example 0, 1 , 2, 3, 4, 5, 6, 7, 8, 9,

10, d integer of 0 to 20, preferably 0 to 10, for example 0, 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, wherein b+c+d ≥ 1 ,

R⁴ chosen from the group consisting of functional groups like NH₂, NH, OH, OR⁵, wherein R⁵ is Ci-Cio-alkyl, preferably methyl and/or ethyl, C₅-Ci₆-aryl, C₅-Ci6-alkaryl, preferably benzyl, Ci-C₂₀-alkoyl, aroyl, preferably benzoyl, wherein arrangement of polyoxyalkylene polyether units may be block-wise, alternating or randomly, x integer of 0 to 200, preferably 0 to 100, y integer of 1 to 50, preferably 1 to 30.

In a preferred embodiment of the process according to the present invention, the at least one silicon comprising non-ionic surfactant is chosen from the group consisting of silicon-polyoxy alkylene polyether copolymers according to formulae (1 ), (2) or (3).

In a more preferred embodiment of the process according to the present invention, the at least one silicon comprising non-ionic surfactant is chosen from the group consisting of silicon-polyoxy alkylene polyether copolymers according to formulae (1 ) or (2). In a more preferred embodiment of the process according to the present invention, the at least one silicon comprising non-ionic surfactant is chosen from the group consisting of silicon-polyoxy alkylene polyether copolymers according to formulae (1 ) or (2) wherein R¹ is methyl, a is 3, b is an integer of 0 to 100, preferably 5 to 50, for example 6, 7, 8, 9, 10, 1 1 , 12, 13, 14 or 15, c is an integer of 0 to 50, preferably 0 to 25, for example 0, 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, d is an integer of 0 to 20, preferably 0 to 10, for example 0, 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, wherein b+c+d ≥ 1 , R⁴ is chosen from OH and OR⁵, wherein R⁵ is methyl, wherein arrangement of polyoxyalkylene polyether units may be block-wise, alternating or randomly, x is an integer of 0 to 200, preferably 0 to 100, and y is an integer of 1 to 50, preferably 1 to 30.

In a very preferred embodiment of the process according to the present invention, the at least one silicon comprising non-ionic surfactant is chosen from the group consisting of silicon-polyoxy alkylene polyether copolymers according to formulae (1 ) or (2) wherein R¹ is methyl, a is 3, b is an integer of 0 to 100, preferably 5 to 50, for example 6, 7, 8, 9, 10, 1 1 , 12, 13, 14 or 15, c is an integer of 0 to 50, preferably 0 to 25, for example 0, 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, d equals 0, R⁴ is OH, wherein arrangement of polyoxyalkylene polyether units may be block-wise, alternating or randomly, x is an integer of 0 to 200, preferably 0 to 100, and y is an integer of 1 to 50, preferably 1 to 30.

In a very preferred embodiment of the process according to the present invention, the at least one silicon comprising non-ionic surfactant is chosen from the group consisting of silicon-polyoxy alkylene polyether copolymers according to formula (2) wherein R¹ is methyl, a is 3, b is an integer of 5 to 50, preferably 5 to 30, for example 5, 6, 7, 8, 9, 10, 1 1 , 12, 13, 14 or 15, c is an integer of 0 to 50, preferably 0 to 25, for example 0, 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, d equals 0, R⁴ is OH, wherein arrangement of polyoxyalkylene polyether units may be block-wise, alternating or randomly, x is an integer of 3 to 200, preferably 3 to 100, more preferably 3 to 50, more preferably 10 to 30 and most preferred 15 to 25.

In a very preferred embodiment of the process according to the present invention, the at least one silicon comprising non-ionic surfactant is chosen from the group consisting of silicon-polyoxy alkylene polyether copolymers according to formula (1 ), wherein R¹ is methyl, a is 3, b is an integer of 1 to 30, preferably 1 to 20, for example 8, 9, 10, 11 , 12 c is an integer of 0 to 5, preferably 0-2, d equals 0, R⁴ is OH, wherein arrangement of polyoxyalkylene polyether units may be block-wise, alternating or randomly, x is an integer of 1 to 50, preferably 15 to 30, for example 20, 21 , 22, 23, 24, 25, 26, 27, 28, 29, and y is an integer of 1 to 50, preferably 1 to 20, for example 5, 6, 7, 8, 9, 10, 11 , 12, 13, 14, 15. In a very preferred embodiment of the process according to the present invention, the at least one silicon comprising non-ionic surfactant is chosen from the group consisting of silicon-polyoxy alkylene polyether copolymers according to formula (1 ), wherein R¹ is methyl, a is 3, b is an integer of 1 to 50, preferably 5 to 30, for example 8, 9, 10, 1 1 , 12, 13, 14, 15, 16, 17, 18, 19, c is an integer of 0 to 50, preferably 0 to 25, more preferably 1 to 15, for example 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, d equals 0, R⁴ is OH, wherein arrangement of polyoxyalkylene polyether units may be block-wise, alternating or randomly, preferably block-wise, x is an integer of 1 to 100, preferably 30 to 80, more preferably 50 to 70, for example 55, 56, 57, 58, 59, 60, 61 , 62, 63, 64, 65, and y is an integer of 1 to 50, preferably 1 to 20, for example 5, 6, 7, 8, 9, 10, 11 , 12, 13, 14, 15.

In a very preferred embodiment of the process according to the present invention, the at least one silicon comprising non-ionic surfactant is chosen from the group consisting of silicon-polyoxy alkylene polyether copolymers according to formula (1 ), wherein R¹ is methyl, a is 3, b is an integer of 1 to 50, preferably 10 to 30, for example 18, 19, 20, 21 , 22, 23, 24, 25, c is an integer of 0 to 50, preferably 0 to 25, more preferably 1 to 10, for example 5, 6, 7, 8, 9, 10, d equals 0, R⁴ is OH, wherein arrangement of polyoxyalkylene polyether units may be block-wise, alternating or randomly, preferably block- wise, x is an integer of 1 to 50, preferably 20 to 40, for example 25, 26, 27, 28, 29, 30, 31 , 32, 33, 34, and y is an integer of 1 to 50, preferably 1 to 20, for example 5, 6, 7, 8,

9, 10.

In a very preferred embodiment of the process according to the present invention, the at least one silicon comprising non-ionic surfactant is chosen from the group consisting of silicon-polyoxy alkylene polyether copolymers according to formula (1 ), wherein R¹ is methyl, a is 3, b is an integer of 1 to 50, preferably 1 to 20, for example 5, 6, 7, 8, 9, 10, 1 1 , 12, 13, 14, 15, c is an integer of 0 to 50, preferably 20 to 40, for example 24, 25, 26, 27, 28, 29, 30, 31 , 32, 33, 34, d equals 0, R⁴ is OH, wherein arrangement of polyoxyalkylene polyether units may be block-wise, alternating or randomly, x is an integer of 1 to 30, preferably 1 to 10, for example 1 , 2, 3, 4, 5, 6, 7, and y is an integer of 1 to

10, preferably 1 to 5, for example 1 , 2, 3.

In a very preferred embodiment of the process according to the present invention, the at least one silicon comprising non-ionic surfactant is chosen from the group consisting of compounds (6), (7), (8), (9) or (10)

(Tegostab B8642, Evonik), wherein the arrangement of polyoxyalkylene polyether units of (8) is block-wise,

(Silstab 2000, Siltech Corporation), and

(Silstab 3000, Siltech Corporation) and mixtures thereof.

Contacting in step (A) of the process according to the present invention can be conducted in all manners known to the skilled artisan. In a preferred embodiment, the reaction components, being the at least one precursor of the at least one transition metal oxide, the at least one non-ionic surfactant comprising silicon and the at least one nonaqueous organic solvent can be added subsequently into a suitable reactor. Suitable reactors are known to the skilled artisan, for example laboratory equipment like flasks, beakers, etc. In an industrial scale, suitable reactors can be used, which are operated continuously or discontinuously. For reasons of efficiency, a continuous process is preferred.

In a preferred embodiment, the at least one precursor of the at least one transition metal oxide is added to the dispersed polymer either dispersed in an organic solvent or neat. In a very preferred embodiment, the at least one precursor of the at least one transition metal oxide is added neat, e.g. that it is not dissolved or dispersed in any solvent, to a solution of the at least one non-ionic surfactant comprising silicon in at least one non-aqueous organic solvent.

Based on the whole reaction mixture which is obtained after the addition of the reaction components, at least one precursor of the at least one transition metal oxide is present in an amount of 1 to 50% by weight, preferably 5 to 40% by weight, particularly preferred in an amount of 10 to 38% by weight, based on the whole reaction mixture in each case.

The at least one non-ionic surfactant comprising silicon is present in an amount of 0.1 to 30% by weight, preferably 1.0 to 25% by weight, particularly preferred in an amount of 2 to 20% by weight, based on the whole reaction mixture in each case. After contacting the reaction components, the reaction mixture obtained is stirred for a period long enough to obtain the desired particles in high yield, for example 1 minute to 24 hours, preferably 10 minutes to 10 hours, particularly preferred 30 minutes to 6 hours, for example 2 hours.

Stirring of the reaction mixture can be conducted by any method known to a person having ordinary skill in the art, for example blade stirrer, stirrer bar, overhead stirrer, milling (ball milling), mechanical agitation.

Step (A) of the process according to the present invention can be conducted at any temperature, at which the reaction mixture is in the liquid or dispersed phase. For example, a reaction temperature of 0 to 80⁰C, particularly preferably 10 to 40⁰C, for example room temperature, is suitable. Step (A) of the process according to the present invention, can be conducted at any pressure, at which the reaction mixture is in the liquid or dispersed phase. For example, a pressure of 0.5 to 10 bar (absolute), preferably 0.8 to 5 bar (absolute), particularly preferably 0.9 to 2 bar (absolute), for example atmospheric pressure, is suitable.

At the end of step (A) of the process according to the present invention, a reaction mixture is obtained, which is preferably a homogenous reaction mixture.

Step (B):

Step (B) of the process according to the present invention comprises drying the reaction mixture obtained in step (A) to obtain particles comprising the at least one transition metal oxide and silicon dioxide.

Step (B) of the process according to the present invention can be conducted by all methods that are known to the person having ordinary skill in the art, for example spray-drying, spontaneous evaporation in an open vessel, evaporation by application of direct or indirect heat or evaporation under reduced pressure (for example in a rotary evaporator or on a Schlenk line).

In a preferred embodiment, step (B) is conducted by evaporating the at least one nonaqueous organic solvent at a temperature depending on the organic solvent and the method of evaporation. For example, in the case where the non-aqueous organic solvent is ethanol and the evaporation method is the application of heat to an open vessel, step (B) is conducted at temperatures of 25 to 60°C, preferably 30 to 50⁰C, for example 40°C. In a preferred embodiment, the particles which are obtained after removing of the non-aqueous organic solvent can further be dried at a higher temperature depending on the organic solvent. For example, in the case where the non-aqueous organic sol- vent is ethanol and the drying step is carried out in a drying cabinet, step (B) is conducted at temperatures for example 60 to 120⁰C, preferably 70 to 100⁰C, and particularly preferred 70 to 90°C.

Drying according to step (B) of the process according to the present invention can be conducted for a period which is long enough to obtain dry particles, meaning that no solvent is left. Suitable periods of time depend upon the amount and choice of organic solvent involved and are generally 10 minutes to two days, particularly preferred 30 minutes to 20 hours, for the first drying step, and 30 minutes to 12 hours, preferably 1 to 8 hours, for the second drying step at higher temperature, as mentioned above.

After step (B), the particles comprising at least one transition metal oxide and silicon dioxide are obtained. In general, the primary size of these particles lies at 1 to 40 nm, preferably 3 to 30 nm, even without any further heat treatment.

In order to obtain further improved particles, step (C) can optionally be conducted after step (B):

(C) Calcination of the particles obtained from step (B) of the process according to the present invention at a temperature of 200 to 800⁰C in an oxygen comprising atmosphere.

Calcination according to step (C) of the present invention can be conducted in any reactor suitable for a calcination reaction, for example laboratory furnace, shaft furnace, multiple hearth furnace, drying oven, microwave oven, cabinet ovens, batch ovens, tunnel ovens, horizontal or vertical conveyor ovens, tray type ovens, fluidized bed reactor or rotary kiln.

In general, the calcination temperature can be chosen from 200 to 800°C, preferably 280 to 600°C. In a preferred embodiment, more than one different temperature are used in step (C) depending on the polyethersiloxane used as structure directing agent, wherein in a particularly preferred embodiment, calcination is firstly conducted at a lower temperature of for example 200 to 400⁰C, followed by a second calcination step at a higher temperature of for example 400 to 700°C.

Calcination according to step (C) of the present invention can be conducted for a period of time depending on the amount of sample to be calcined and the initial concentration of polyethersiloxane, generally one to 24 hours, preferably 2 to 12 hours. In the case, wherein two different calcination temperatures are used, the first calcination step can be conducted at a lower temperature for a period of time of 15 minutes to five hours, preferably 1 to 3 hours, followed by the second calcination step at a higher temperature for a period of time of 1 to 12 hours.

In general, any atmosphere comprising oxygen known to the skilled artisan can be used and different atmospheres can be used for the different calcination steps described above. For example, one or more of these atmospheres can be nitrogen, oxygen, air or an artificial ("oxygen poor" or "oxygen rich") atmosphere comprising oxygen, nitrogen and/or other inert gases. In a preferred embodiment, the atmosphere comprising oxygen in step (C) of the process according to the present invention is air or an oxygen poor atmosphere.

After step (C) of the process according to the present invention, particles comprising at least one transition metal oxide and silicon dioxide are obtained.

The primary size (diameter) of these particles is in general 0.01 to 40 nm, preferably 0,01 to 30 nm, particularly preferred 0,01 to 15 nm, for example 0,01 to 10 nm, calculated using diffraction data from XRD-measurements and confirmed by transmission electron microscopic analysis. In a particular embodiment more than 70% of all particles lie in the specified range, preferred more than 80% and particularly preferred more than 90%.

The process according to the present invention gives rise to particles as mentioned above, having a high BET surface area. The BET surface area of the particles obtained from the process according to the present invention is higher than 150 m²/g, preferably higher than 200 m²/g. The BET surface area of the particles obtained from the process according to the present invention is in general lower than 600 m²/g.

The pore size of the material obtained from the process according to the present invention is in general 0.5 to 25 nm, preferably 1 to 20 nm, particularly preferably 2 to 10 nm.

The amount of silicon dioxide which is present in the particles according to the present invention is in general 1 to 20 % by weight, preferably 3 to 12 % by weight, in each case based on the whole particle.

In general in the particles obtained from the process according to the present invention, SiC>₂ is present within the pores of the high surface area TiC>₂ material, preferably small SiO₂-particles are present on the pore walls of TiO₂. The presence of SiO₂ at the pore walls Of TiO₂ gives rise to an improved heat stability of these particles, because the anatase modification Of TiO₂ is less easily transferred into the less active rutil modifica- tion; this is a known effect. The present invention further relates to a particle comprising at least one transition metal oxide and silicon dioxide, obtainable, preferably obtained, by the process according to the present invention. In a preferred embodiment the present invention relates to a particle as mentioned above, wherein the size (diameter) of the primary particle de- termined by XRD method for calculating crystallite size is 1 to 40 nm, the BET surface area of the particle measured according to DIN standard 66131 is higher than 200 m²/g and the pore size of the particle calculated using the BHJ method for adsorption is 1 to 6 nm. Preferred embodiments of these particles are mentioned above.

In addition, the present invention relates to the use of at least one halide, preferably at least one chloride, or at least one alkoxide, preferably at least one iso-propoxide, or a mixture of the two, and of at least one transition metal, in a process for the preparation of particles comprising at least one transition metal oxide and silicon dioxide in the presence of at least one non-ionic surfactant comprising silicon, in a non-aqueous or- ganic solvent, preferably the use of a mixture of titanium tetrachloride (TiCI₄) and titanium tetraisopropoxide Ti(O¹Pr)₄ in the preparation of particles comprising titanium dioxide (TiO₂) and silicon dioxide (SiO₂). Preferred embodiments of the use of this specific mixture have been mentioned above.

The present invention further relates to a mixture comprising the particle according to the present invention and at least one other transition metal oxide, activating agent and/or catalytic material, for example the oxides of the elements of Groups III to XII or metallic nanoparticles for example of platinum, palladium, silver or gold.

The present invention further relates to the use of the particles according to the present invention as a catalyst or as a catalyst carrier material.

In order to obtain further improved activity in applications as catalysts or catalyst carriers, step (D) can optionally be conducted after step (C):

(D) Impregnation, coating, doping or mixing in any other known method with at least one other transition metal oxide, activating agent or catalytic material at temperatures of from 20 ⁰C to 800 ⁰C.

The present invention further relates to a process for the preparation of a powder film, wherein particles according to the present invention are applied to a substrate such as glass, plastics, textiles, ceramics or metal. The particles obtained from the process according to the present invention can be suspended into transparent or non- transparent solutions with aqueous or non-aqueous solvents with or without the aid of stabilizing acids, bases or surfactants. The suspensions are introduced to the substrate surface by methods generally known to a person having ordinary skill in the art. The present invention further relates to a process for the preparation of a coating of at least one transition metal oxide and silicon oxide, wherein a mixture comprising at least one precursor of the at least one transition metal oxide and at least one non-ionic sur- factant comprising silicon in at least one non-aqueous organic solvent is applied to a substrate. This mixture is the same mixture that is described above, in respect of step (A) of the process for the preparation of particles. Preferred embodiments are mentioned above. In a very preferred embodiment of this process, the at last one precursor of at least one transition metal oxide is a combination of titanium tetra-chloride (TiCI₄) and titanium tetra-isopropoxide (Ti(O¹Pr)₄). Application of the mixture to the substrate is preferably conducted by dip- or spin-coating. These methods are in general known to a person having ordinary skill in the art.

The present invention is further illustrated by the following examples:

Examples

1. General synthesis:

Examples 1 to 30 are prepared by mixing TiCI₄ with Ti(iPrO)₄ in amounts as shown in table 1 , and adding this mixture to a stirred ethanolic or mixed ethanol/THF solution containing the respective surfactant. The volume ratio of ethanol and THF is shown in table 1. The reaction mixture is stirred for 2h at room temperature and is then dried for 16 h at 40 ⁰C and then for 6 h at 80 ⁰C. The powder formed upon drying is then cal- cined in air. Calcination temperatures and times are detailed in table 1.

(6)

Surfactant 2 = Tegostab B8642, Evonik

(8) wherein the arrangement of polyoxyalkylene polyether units of (8) is block-wise, Surfactant 3 =

Surfactant 4 = Silstab 2000, Siltech Corporation

Surfactant 5 = Silstab 3000, Siltech Corporation

(10) 2. Material Characterization

BET and N₂-adsorption measurements are carried out according to DI N standard 66131 . The pore diameter is calculated using the BHJ method for adsorption. The modification of the crystalline TiO₂ and the primary particle size are determined by use of XRD (Powder Diffraction). The Si- and Ti-concentrations are determined by elemental analysis and are given in weight percent.

The photocatalytic activity is determined via the rate of degradation of the chlorinated hydrocarbon dichloroacetic acid (DCA) in suspension. The total reaction time of the degradation experiments for determining the rate of degradation of DCA in aqueous solution is 24 hours. The UV-light intensity is 1 mW/cm². The pH-value of the suspension is set to 3 with sodium hydroxide. The temperature of the reaction vessel is 20 to 30⁰C. The concentration of DCA is 20 mmol/L and the concentration of the photocata- lyst is 3 g/L. The degradation rate (ppm/h) is determined by measurement of the pH- value before and after 24h irradiation. Degradation rates are normalized to the weight Of TiO₂ in the sample.

Blank tests are carried out to degrade DCA under irradiation using the method de- scribed above in the presence of a commercially available standard photocatalyst (De- gussa P25, ,,blank 1 "), comprising no silicon dioxide, as well as to degrade DCA under irradiation without the presence of a photocatalyst ("blank 2").

Material characterization data including DCA degradation rates can be found in Table 2:

Table 2

Information from the data sheets accompanying the material.

3. Thermal Stability Tests

The thermal stability of the mesoporous, SiO₂-stabilized materials was tested by heating the sample to given temperatures over 10h and measurement of the BET surface area and pore size (via nitrogen adsorption), particle size via XRD analysis, and photo- catalytic activity according to the DCA-degradation test described above. Comparative Example 1 (DT52, Millennium Chemicals), being anatase TiC>₂ with WO3 dopant (BET surface area 78-98 m²/g, information from Millennium Inorganic Chemicals website) and Comparative Example 2 (DT58, Millennium Chemicals), being anatase TiC>₂ with SiC>₂ and WO3 dopants (BET surface area 95-125 m²/g, information from Millennium Inorganic Chemicals website) were also treated in the same manner. The results are given in Table 3:

Table 3

4. Water compatibility tests

Water present in the mixture containing the titanium dioxide precursors causes a rapid formation of hydrated titanium species, which leads to polystructured or dense or collapsed materials with low surface areas with low reproducibility. The water compatibility of the synthesis to produce mesoporous, SiO₂-stabilized metal oxide materials was tested by the addition of water during the synthesis in the following synthetic method: Examples 31 to 38 are prepared by mixing 0.6 g TiCI₄ with 2.5 g Ti(¹PrO)₄, and adding this mixture to a stirred 20 mL ethanolic solution containing 2.0 g of surfactant 1. Distilled water is added to the reaction mixture in amounts shown in table 4. The reaction mixture is stirred for 2 h at room temperature and is then dried for 16 h at 40 ⁰C and then for 6 h at 80 ⁰C. The powder formed upon drying is then calcined in air for 2 h at 300 ⁰C and then 5 h at 450 ⁰C.

Measurement of the BET surface area and pore size (via nitrogen adsorption) and the photocatalytic activity according to the DCA-degradation test described above was used as an indictator of the water compatibility of the synthesis.

Table 4

Claims

1. Process for the preparation of particles comprising at least one transition metal oxide and silicon dioxide, comprising at least the following steps:

(A) Contacting at least one precursor of the at least one transition metal oxide and at least one non-ionic surfactant comprising silicon in at least one nonaqueous organic solvent, to obtain a reaction mixture and

(B) Drying the reaction mixture obtained in step (A) to obtain particles compris- ing the at least one transition metal oxide and silicon dioxide.

2. Process according to claim 1 , wherein the transition metal oxide is TiC>₂.

3. Process according to claim 1 or 2, wherein the organic solvent is chosen from the group consisting of alcohols, esters, ethers, aliphatic hydrocarbons, aromatic hydrocarbons, amines, ketones, diketones, nitrated or chlorinated hydrocarbons and mixtures thereof.

4. Process according to any of claims 1 to 3, wherein TiCI₄ and/or Ti(O¹Pr)₄ is used as precursor of the at least one transition metal oxide.

5. Process according to any of claims 1 to 4, wherein the organic solvent comprises an alcohol and/or a cyclic ether.

6. Particle comprising at least one transition metal oxide and silicon dioxide, obtainable by the process according to any of claims 1 to 5.

7. Particle according to claim 6, wherein the size (diameter) of the primary particle determined from XRD data is 0.1 to 40 nm, the BET surface area of the particle measured according to DIN standard 66131 is higher than 200 m²/g and the pore size of the particle calculated using the BHJ method for adsorption is 1 to 6 nm.

8. Use of at least one halide, preferably at least one chloride, or at least one alkox- ide, preferably at least one iso-propoxide, or a mixture of the two, and of at least one transition metal, in a process for the preparation of particles comprising at least one transition metal oxide and silicon dioxide in the presence of at least one non-ionic surfactant comprising silicon, in a non-aqueous organic solvent.

9. Mixture comprising the particle according to claim 6 or 7, at least one other transi- tion metal oxide, activating agent and/or catalytic material.

10. Use of the particles according to claim 6 or 7 as a catalyst or as a catalyst carrier material.

1 1. Process for the preparation of a powder film, wherein particles according to claim 6 or 7 are applied in suspension to a substrate.

12. Process for the preparation of a coating of at least one transition metal oxide and silicon oxide, wherein a mixture comprising at least one precursor of the at least one transition metal oxide and at least one non-ionic surfactant comprising silicon in at least one non-aqueous organic solvent is applied to a substrate.