WO1998035910A1

WO1998035910A1 - Metal molecular sieve catalysts

Info

Publication number: WO1998035910A1
Application number: PCT/EP1998/000765
Authority: WO
Inventors: Jihad Dakka; Georges Marie Karel Mathys
Original assignee: Exxon Chemical Patents Inc.
Priority date: 1997-02-14
Filing date: 1998-02-11
Publication date: 1998-08-20
Also published as: GB9703093D0

Abstract

The present invention relates to metal and in particular titanium isomorphous substituted molecular sieve catalysts and to their manufacture. A particularly important feature of the process of their manufacture is that templating agents which are relatively impure in relation to alkali metal cations may be used.

Description

Metal Molecular Sieve Catalysts

The present invention relates to metal containing molecular sieve catalysts in particular titanium molecular sieve catalysts and in particular to a method of manufacture of such catalysts

Titanium containing molecular sieve catalysts are well known Examples of such catalysts are the titanium containing silicalite catalysts based on a crystalline synthetic material comprising silicon and titanium oxides and which are characterised by an infra red absorption band at around 950 cm^{" '}' to 960 cm^{- 1} and typically are of the general formula xTiO2(1 -x)SiO2

where < is from 0 0001 to 0 10 preferably 0 1 to 4 These catalysts known as TS-1 ana TS-2 are typically prepared in the absence of aluminium from a mixture containing a source of silicon oxide a source of titanium oxide a nitrogenated organic base and water Various specific processes for the preparation of titanium silica te catalysts are described in for example Belgian Patent 886812 EP 0190609 A US 3329481 US4410501 US 4666692 US4701428 EP 031 1983 EP 0376453 M G Cleπci et al Journal of Catalysis 129. 159-167 (1991 ), M A Ugina et al Applied Catalysis A General. 124 391 -408 (1995) A J H P van der Pol et al Applied Catalysis A 92 93 (1992) J A Martens, et al Applied Catalysis A 99 71 (1993 ^* A Thangaraj, et al Zeolites 12 943 ( 1992) M Padovan Stud Surf Sci Cat 63 431 (1991 ) D P Serrano et al Microoorous Materials 4 273-282 (1995), GB 2071071 EP 0226258) J Catal 130 M 991 ) pages 1 -8 More recently aluminium containing titanium silicalites have been reported as well for example in EP 0293950 and in Zeolites 12 (1992) 135-137 In this case the catalysts exhibit both oxidizing and acidic catalytic activities In EP 0230949 the treatment of TS-1 catalyst with neutralizing agents (e g alkaline compounds is reported) The examples given in the patent show that TS-1 catalyst treated with alkaline compounds give better yields of epoxides and lower amounts of by-products when they are used as catalysts for the epoxidation of olefins by H2O2 It is suggested that the applied treatments have a neutralizing effect on the catalyst's acidity, and thus prevent the catalyst to initiate undesirable side reactions

Recently the synthesis of a titanium containing zeolite isomorphous to zeolite Beta has also been reported (J Chem Soc Chem Comm 1992 (8) 589-590) In

CONFIRMATION C0PV the described synthesis method low concentrations of aluminium (Si/AI = 192) are used for the preparation of the synthesis mixture Like TS-1 and TS-2 the titanium containing zeolite Beta is characterised by an IR absorption at ± 960 cm^{- -}' Further methods of sytnthesis have been described for example in WO94/02245 J Chem Soc Chem Commun 8, 589-590, 1992 (low concentrations of aluminium are present in the synthesis mixture) WO95/03249 WO95/03250 A Corma et al J Chem Soc Chem Commun page 1635 ( 1995) M A Camblor et al , Applied Catalysis A General 133 L185-L189, ( 1995) US5474754 M A Camblor et aj, Zeolites 202 to 210, (1991 )

Typical synthesis mixtures yielding Ti-Beta zeolite after hydrothermal treatment have an initial molar composition within the following ranges

Sι0₂(1 ) T1O2 (0 0001 to 0 10 preferaby 0 04) AI2O3 (0 005 to 0 100) H2O (10 to 100), and TEAOH (0 1 to 1 )

Advantageously the Ti plus Si Al molar ratio is within the range of from 10 to 200 1 Hydrogen peroxide is advantageously present in the synthesis mixture although it may decompose before or during hydrothermal treatment, preferably in a proportion of 10 to 200 moles H2O2 per mole of TEOT when that is used as the source of titanium

A further example of a titanium containing zeolite is Ti MCM-41 Various methods for the manufactute of this catalyst are described in for example in A Corma et al , J Chem Soc Chem Commun, page 1635, (1995), A Corma, et al J Chem Soc Chem Commun , page 147 (1994), and T Blasco et al , J Catalysis 156, 65-74, (1995)

According to the state-of-the-art understanding of TS-1 and Tι-MCM-41 synthesis the presence of alkali ions must be avoided during the hydrolysis of the Ti and Si sources in order to prevent the formation of T1O2 This is explicitly taught in for example US 4 410 501 , US 5,401 486 and EP 631983-AI and other open published litterature such as for example A J H P van de Pol, Applied Catalysis A92, (1992), 93, A Tuel, Applied Catalysis A, 1 10 (1994) 137, and more recently in M A Ugina et al Applied Catalysis A General, 124, 391 -408, and P Serrano, et al Microporous Materials, 4, 273-282, (1995) This control is required according to the prior art irrespective of the nature of the hydrolysis and other synthesis parameters Recently M A Camblor et al , Applied Catalysis A General 133 L185-L189 ( 1995), and US5474754 have disclosed methods of preparing titanium containing zeolites which are able to utilise smaller amounts of expensive templating agents but the requirement is still observed that the templating agents should be free of alkali metal cations Providing templates whicn have 'ow levels of alkali metal cations is a costly operation The use of such templates is a significant cost in the production of titanium containing zeolites

We have now discovered a process for the production of catalytically active metal containing molecular sieves and in particular titanium containing molecular sieves such as for example TS-1 or TS-2 which differs from the known processes for preparing such molecular sieves The process of the present invention provides a metal e g titanium, isomorphous substituted molecular sieve which is free of unwanted impurities In the case of a titanium molecular sieve it is free of significant quantities of polymeric T1O2 species as detected by UVΛ/is spectroscopy even though the synthesis uses templating agents which hitherto have not been used due to T1O2 formation

Accordingly the present invention provides a method for the synthesis of a metal isomorphous substituted molecular sieve which method comprises

a) forming a co-precipitate or co-gel comprising metal oxide in the absence of alkali metal and

b) crystallising the co-precipitate or co-gel in the presence of an organic templating agent to form a the a metal isomorphous substituted molecular sieve

wherein the level of alkali metal within the organic structure directing agent is at least 50 ppm

The metal may be any metal which may be incorporated in the framework of a molecular sieve and includes for example titanium and chromium The process of the present invention is applicable to any synthesis of a metal containing molecular sieve which is normally sensitive to the presence of alkali metal in the template during syntheses of the molecular sieve Preferably the metal is titanium and the metal oxide is si ca/titania In the process of the present invention it has been found that the use of an intermediate silica titania co-precipitate or co-gel in the synthesis of zeolite isomorphous substituted molecular sieves enables the use of impure templating agents In particular it is possible to use templating agents which contain relatively high levels of alkali metal species such as Na+ and K+ cations This is particularly advantageous as the normal practice in the synthesis of molecular sieve materials using organic templating agents is to ensure as far as possible the total absence of alkali metal cations Typically the levels of sodium are 20 ppm or less and the levels of potassium are 5 ppm or less In the present invention therefore the templating agents do not have to be alkali metal free and may have 20ppm or higher levels of sodium and/or 5 ppm or higher levels of potassium Preferably the sodium and/or potassium levels are greater than 50 ppm, preferably greater than 1 00 ppm and most preferably greater than 1 30 ppm The levels may be greater than 500 ppm

A number of titanium isomorphous substituted molecular sieves may be prepared by this method Which molecular sieve is produced will depend on the templating agent used and the presence of other precursors for the particular zeolite desired It is envisaged that the process will be particularly suitable for the production of titanium isomorphous substituted si calite molecular sieves such as beta and MCM-41 molecular sieves

The co-precipitate or co-gel may be made by any of the known processes in the art As example suitable co-precipitates and co-gels may be made according to EP 031 1 983 which describes the synthesis of a co-precipitate, WO95/03249 WO95/03250 and sol-gel methods as disclosed in M A Ugina, et al Applied Catalysis A General 124 391 -408 P Serrano, et al Microporous Materials 4 273-282 and M A Camblor et al Applied Catalysis A General 133 L185- L189 ( 1995)

The desired titanium isomorphous substituted molecular sieve may be derived from the co-precipitate or the co-gel using organic templating agents containing high levels of alkali metal cations via either the hydrothermal crystallization of a liquid gel produced by the complete dissolution of either a co-precipitate or a co- gel, by the formation of a liquid gel with incomplete dissolution of the co-gel or co- precipitate or by incipient wetness impregnation of the co-precipitate or co-gel as described in M A Camblor et al Applied Catalysis A General, 133 L185-L189 (1995) and US5474754

TS-1 may be made by the following process The silica titania co-precipitate may be formed by mixing any suitable silica source together with a source of titanium to form a co-solution which may then be subject to the appropriate conditions for co- precipitation In a preferred embodiment the silica source such as for example tetra ethyl ortho silicate (TEOS) is hydrolysed in an acid environment preferably a nitric acid environment followed by addition of a solution of a titanate such as for example tetrapropyl ortho titanate (TPOTi) in a suitable solvent such as for example isopropanoi The titanate is not hydroiysed before mixing with the silica source The silica source solution is free of alkali metal ions such as K+ or Na+ and is either neutral (pH=7) or is acidic (pH< 7) This careful control of the hydrolysis environment ensures that there are no significant amounts of polymeric T1O2 species formed in the co-solution and in the resulting co-precipitate The silica source solution and the titania source solution are free of organic templating agents

Once the co-solution is produced the silica titania may be co-precipitated by removal of water and the solvent used to prepare the co-solution The water ana solvent mav oe removed by evaporation at ambient temperatures or may be removed by heating or by supercritical CO2 We have found that heating to a temperature in the range of room temperature to 200°C is particularly suitable preferably it is in the range 80 to 120°C

The silica titania co-precipitate may then be used for the production of titanium isomorpnous substituted molecular sieves such as sιlιcalιte-1 by dissolution in an appropriate templating agent e g tetra propyl ammonium hydroxide (TPAOH) The resultant solution may then optionally be seeded with colloidal molecular sieve such as colloidal silicalite which may be prepared according to the procedure described in for example WO93/08125 the disclosure of which is incorporated by reference Once seeded the titanium containing molecular sieve e g sιlιcalιte-1 may be obtained by crystallisation whilst stirring at an appropriate temperature and over an appropriate period of time For example we found 1 to 30 days preferably 1 to 10 days and most preferably is at least 3 days at 50 to 200 C preferably 130 to 180"C to be particularly suitable for the formation of isomorphous titanium sιlιca te-1

The crystallised product obtained may be removed from the crystallisation medium by filtration and the washed

Templat'ng agent may be used in the formation of the co-precipitate or co-gel In this aspect the templating agent will need to be substantially free of alkali metal cations Typical templating agents include for example TEAOH TPAOH TMAOH and dibenzyldimethyl ammonium hydroxide

The titanium containing catalysts of the present invention are useful catalysts particularly for hydrocarbon oxidation The direct oxidation of saturates to introduce functional groups such as ketoπes and alcohols using a heterogeneous catalyst system would be extremely attractive especially if there is high conversions and selectivity for either alcohol or ketone or even if conversion is low there is relatively high selectivity for one of the products

The titanium isomorphous substituted molecular sieve catalysts of the present invention and in particular titanium sιlιcalιte-1 have been found to be an active oxidation catalyst especially for reactions involving hydrogen peroxide as oxidant The new catalysts may also be effective with organic hydroperoxide oxidants

When aqueous hydrogen peroxide is used the solution contains from 10-100 preferably 10 to 70 wt % hydrogen peroxide for example diluted hydrogen peroxide (30 to 40% by weight in water) It is also preferred that a polar solvent be present when aqueous hydrogen peroxide is used to increase the solubility of the organic compound in the H202 aqueous phase Examples of suitable solvents include acetone and methanol

The oxidising agent may be an organic hydroperoxide examples of suitable organic hydroperoxides include di-isopropyl benzene monohydroperoxide, cumene hydroperoxide tert butyl hydroperoxide cyclohexylhydroperoxide ethylbenzene hydroperoxide tert amyl hydroperoxide tetra ne hydroperoxide and the compound containing the saturated organic group is liquid or in the dense phase at the conditions used for the reaction When the oxidant is a an organic hydroperoxide then tertiary butyl hydroperoxide is particularly beneficial since the tertiary butyl alcohol produced can readily be converted to the valuable isobutylene molecule The preferred oxidising agent is hydrogen peroxide

It is possible to oxidise saturated aliphatic compounds including aliphatic substituents of aliphatic/aromatic compounds by the process of the invention The saturated groups which may be oxidised by the process of this invention include long or short branched or linear alkanes containing 3 or more, preferably 3 to 30 more preferably 3 to 12 carbon atoms cyclic alkanes and mono- and poly- alkyl aromatics in which at least one of the alkyl groups contain at least two preferably at least three more preferably 3 to 18 most preferably 3 to 12 carbon atoms and mono- and poly-alkyl cyclic alkanes The process of the invention is equally applicable to the epoxidation of olefins dienes, the production of ether glycols diols the oxidation of alcohols or ketones, aldehydes to acids and the hydroxylation of aromatics We have surprisingly found that by the selection of appropriate conditions saturated groups may be oxidised with high selectivity to alcohols and ketones under relatively mild conditions One particularly useful application is in the oxidation of linear and branched paraffins to secondary alcohols and ketones The process is especially useful in the lower carbon numoer range to enable use of low-cost propane and butane feedstock in the manufacture of isopropanol alcohol, acetone, secondary butyl alcohol and methyl ethyi ketone The aliphatic substituent may be a part of a totally aliphatic compound an aryl compound (alkyl aromatic) or an alkylnaphthene compound Furthermore said compound may contain other functional groups providing they do not prevent the desired oxidation reaction taking place

The reactivity sequence for the aliphatic compounds slows down from tertiary to secondary and to primary compounds

Particular advantages of the present invention are that the process uses mild temperature and pressure conditions and the conversion and yield are high and by-product formation is small In particular the oxidant conversion is high The optimum reaction temperature is between 50 and 150°C preferably about 100°C when using hydrogen peroxide The oxidation reaction may be in the liquid or dense phase or in the gaseous phase preferably the reactions are in the liquid phase

The reaction can be carried out at room temperature but higher reaction rates may be involved at higher temperatures, for example under reflux conditions Through increase of the pressure either due to the autogeneous pressure created by the heated reactants or by use of a pressurised reactor still higher temperatures can be reached Use of higher pressures in the range of 1 to 100 bars (105 to 107Pa) can increase the conversion and selectivity of the reaction

The oxidation reaction can be carried out under batch conditions or in a fixed bed and the use of the heterogeneous catalyst enables a continuous reaction in system The catalyst is stable under the reaction conditions and can be totally recovered and reused The oxidation process of the present invention is preferably carried out in the presence of a solvent Choice of solvent is important since it should dissolve the organic phase and the aqueous phase when hydrogen peroxide is used which is generally present due to the use of aqueous hydrogen peroxide as the oxidising agent where organic hydroperoxides are used suitable organic solvents should be used Polar compounds are preferred which are inert under reaction conditions and examples of preferred solvents are alcohols, ketones and ethers, with a number of carbon atoms which is not too high, preferably less than or equal to 6 Methanol or tertiary butanol is the most preferred of the alcohols, acetone and butanone are the most preferred of the ketones The amount of solvent may influence the reaction product and the conversion, the choice of solvent and the amount depending on the material to be oxidised We have found for example, that when oxidising normal hexane with aqueous hydrogen peroxide yields are improveα when the ratio of acetone to hexane is in the range 1 1 to 4 1 The solvent improves the miscibility of the hydrocarbon phase and the aqueous phase which is generally present due to the use of aqueous hydrogen peroxide as the oxidising agent If, however, the peroxide is supplied as a solution such as tertiary butyl hydroperoxide which is frequently dissolved in ditertiary butyl peroxide and the substrate is soluble in the solvent then no additional solvent is required

The invention will be described with further details including a preparation of the catalyst and several examples of oxidation reactions

EXAMPLE 1

TS-1 (Euro Cat ) was made following the Enichem procedure (U S patent 4 410 501 )

The composition ratio Si Ti OH H2O 1 0 03 0 43 30

25 8 g of TEOS was transfered to a Teflon beaker and vigorously stirred, 0 8 ml of TEOT was carefully dripped into this TEOS, whilst nitrogen was flushed over it to prevent carbon dioxide absorption The temperature was raised to 35°C and the reactants were mixed homogeneously for half an hour Then the mixture was cooled to 0°C 53 3 g of a 20 % aqueuos solution of TPAOH (low levels of alkali metal) was added very slowly into the mixture of TEOS and TEOT After addition of all TPAOH the mixture was heated in about one hour to a temperature in the range 80 - 90°C The mixture was kept for 3 to 5 h at this temperature Distilled water was added to increase the volume of the mixture to its original value of about 0 085 I The hydrothermal synthesis was done at 175° C for 3 days

The catalyst was characterized by XRD UV-Vis, IR ICP and its catalytic performance in n-heptane oxidation with 30% H2O2 The catalytic test results are summarized in Table 1

TEOS = Tetra Ethyl ortho Silicate

TEOT = Tetra Ethyl ortho Titanate

TPAOH = Tetra Propylammonium Hydroxide

Example 2

TS - 1 made by using Grace coprecipitated T1O2- S1O2 ( European patent 031 1983)

32.6 g T1O2 - S1O2 Grace (T1O2 4 3% 0.52 mol 50 micron) was dissolved in 158 3 g aqueous TPAOH 40% (containing 26 ppm K⁺ 630 ppm Na+) Then 183 46 g H2O was added at once The reaction mixture was charged into Teflon- lined autoclave and heated to 175°C under stirring 350 rpm for 2 days After cooling the material was centπfuged and washed with water several times The calcination was done at 550° C for 16 h in an air flow The catalyst was characterized by XRD to indicate a solid highly crystaline titanium zeolite and ICP to indiate the presence of high levels of titanium Its catalytic perfomance in n- heptane oxidation with 30% H2O2 was evaluated

The catalytic test shows the following results (Table 1 )

Example 3

TS-1 was synthesized using a freshly prepared silica -titania coprecipitate The silica-titania coprecipitate was made by hydrolizing TEOS and TEOT in a 0 05M HNO3 solution The resulting clear solution was heated at 100°C under stirring until a white solid material formed This material was then dried overnight at 120°C to remove the remaining water and alcohol The coprecipetate was found to be amorphous by X-ray powder diffraction Typical procedure is as follows 300g TEOS ( 1 44 mol) was added slowly to 1460 g 0 05M HNO3 (7 26 g HNO3 65%) 16.22g TEOT(0 048 mol) was disolved in 162g isopropanol and was added dropwise to the silicen solution (addition time 5h) Si Ti ratio 30 1

Example 4

23 g T1O2/S1O2 (freshly made following example 3) was dissolved in 1 16 8 g TPAOH 40% (26 ppm K+ 630 ppm Na⁺), then 1 12 H₂0 was added The TS-1 mixture was charged into Teflon-lined autoclave and heated at 175° C under stirring conditions for 5 days The mixture was cooled centπfuged and washed with water several times The solid material was dried at 120°C overnight, then calcined at 550° C for 16 h in air The catalyst was characterized by XRD UV- VIS, ICP and its catalytic performance in n-heptane oxidation with 30 % H2O2

The catalytic test shows the following results (table 1 )

Example 5

The composition ratio Si TI HO^" Q⁺ H2O 1 0 03 0 132 0 09 27

35 g T1O2-S1O2 was dissolved in a solution of 26 6 g TPAOH 40 %, 269 g H2O 0 1 g NaOH subsequently 5 g of colloidal seed which are 0 16 wt %, was added to the mixture The mixture was charged into Teflon-lined autoclave, then it was stirred at 350 rpm and heated to 180°C for 3 days The mixture was cooled, centπfuged and washed with water several times The solid material was dried at 120° C overnight and calcined at 550°C for 16 h in air

The catalyst was characterized by XRD and its catalytic performance The catalytic test results are summarized in table I

Example 6

Molar ratio Si Ti HO^" Q⁺ H₂0 1 0 03 0 57 0 51 30

27 g T1O2-S1O2 was added to solution of 1 14 2 g TPAOH 40 % 174 g H 0, O 13 g NaOH subsequently 5 g colloidal seed, which are 0 16 wt %, was added The mixture was stirred for 2 h, then transfered to Teflon-lined autoclave The hydrothermal synthesis was done at180° C for 3 days under stirring conditions (350 ppm) The mixture was cooled, centπfuged and washed with water several times The solid material was dried at 120° C overnight and calcined at 550° C for 16 h The catalyst was characterized by XRD and its catalytic performance. The catalytic oxidation results are summarized in table 1

Example 7

The composition molar ratio Si Ti HO^" Q⁺ H2O 1 0 03 0 05 0 023 31

31 g T1O2-S1O2 was added to a solution of 1 1 678 g TPAOH 40 % 0 088 g NaOH 272 g water subsequently 5 g colloidal seed, which are 0 16 w % was added Then the mixture was charged into Teflon-lined autoclave stirred at 350 rpm and heated to 160°C for 3 days After cooling the mixture was centrifuged and washed with water several times The solid material was dried at 120°C overnight and calcineα at 550°C for 16 h The solid material was characterized by XRD and its catalytic performance The catalytic oxidation results are summarized in table I

Example 8

The composition molar ratio Si Ti HO^" Q⁺ H2O I 0 03 0 05 0 023 31

31 g T1O2-S1O2 was added to a solution of 1 1 678 g TPABr , 0 088 g NaOH, 272 g water subsequently 5 g colloidal seed which are 0 16 wt % was added Then the mixture was charged into Teflon-lined autoclave, stirred at 350 rpm and heated to 160°C for 3 days After cooling the mixture was centrifuged and washed with water several times The solid material was dried at 120°C overnight and calcined at 550°C for 16 h The catalytic test in n -heptane oxidation gives the following results Table 1

Example 9

22 7 g T1O2-S1O2 was dissolved in a solution of 73 588 g NH4OH 25 % 8 67 g TPABr 1 51 75 g H2O, subsequently 5 g colloidal seed which are 0 16 wt %, was added The mixture was charged intoTefion-lined autodave, which was heated to 175°C for 5 days The hydrothermal synthesis was performed under stirring conditions The mixture was cooled centrifuged and washed with water several times The solid material was dried at 120°C overnight and calcined at 550°C for 16 h The solid material was characterized by XRD and its catalytic performance which shows the following results(table I) Oxidation Examples

The catalyst were tested in n-heptane oxidation with aqueous H2O2 30 % The reaction conditions are 20 4 g n-heptane (0 204 mol) 44 4 g H2O2 30 % (0 39 mole), 1 g catalyst 71 1 g acetone 100° C, under magnetic stirring The results are summarized in the following table

Table 1

^*The catalyst was treated with a solution of H2SO4 as described in the following procedure 3 g calcined catalyst was stirred with 1 M H2SO4 overnight at room temperature The mixture was centrifuged and washed with water several times till pH 7 was obtained The solid material was dried at 120° C overnight

As Table 1 shows, our synthes.s' method (Examples 2, and 3/4) in the presence of Na⁺ or even with deliberatly added Na⁺ (Examples 5 6,7,8) give a catalyst which does not contain anatase at all as verified by UV-VIS and this are very active in oxidation of hydrocarbons with H2O2

Claims

1 A method for the synthesis of a metal isomorphous substituted molecular sieve which method comprises

2 A method as claimed in claim 1 wherein the metal is titanium and the metal oxide comprises silica titania

3 A method as claimed in claim 2 wherein the titanium isomorphous molecular sieve is a titanium si calite

4 A method as claimed in any of claims 2 to 3 wherein the titanium isomorphous molecular sieve comprises at least 1 mole % of Ti

5 A method as claimed in any of claims 2 to 4 which further comprises

(a) dissolving a co-precipitate or co-gel or silica titania , which is substantially free of polymeric T1O2 and alkali metal cations in a solvent to form a gel,

(b) seeding the resultant gel with colloidal molecular sieve seeds to form a crystallisation mixture

(c) allowing the titanium isomorphous substituted molecular sieve to crystallise from the crystallisation mixture, and

(d) separating the crystallised molecular sieve from the crystallisation mixture

A method as claimed in any of claims 1 to 4 wherein the organic templating agent is a tetraalkyl ammonium hydroxide or halide A method as claimed in any of claims 2 to 5 wherein the silica titania coprecipitate is made by the process of any of claims 8 to 13

A method for manufacturing a silica titania co-precipitate which is substantially free of alkali metal cations which method comprises,

(a) preparing a titania source solution substantially free of alkali metal cations and which comprises an organometallic titanium precursor which is not hydrolysed,

(b) preparing a silica source solution substantially free of alkali metal cations which solution comprises the hydrolysis product of an organometallic silica precursor and wherein the solution is at pH 7 or less,

(c) addition of solution (a) to solution (b) to produce a co-solution, and

(d) removing the solution solvent and any water from the co-solution to provide a co-precipitate which is substantially free of alkali metal cations

A method as claimed in claim 8 wherein the organometallic titanium precursor is a titanate A method as claimed in either claim 8 or claim 9 wherein the co-precipitate is formed from an alcoholic co-solution

A method as claimed in any of claims 8 to 10 wherein the co-solution is heated in the range 70°C to 250°C

A method as claimed in any of claims 8 to 1 1 wherein the silica source solution has a pH of less than 7

A method as claimed in any of claims 8 to 12 wherein the silica source solution is acidified with a mineral acid

A method as claimed in claim 13 wherein the mineral acid is nitric acid

A method for the oxidation of an aliphatic hydrocarbon or an alkylaromatic hydrocarbon to an alcohol which method comprises oxidising the hydrocarbon in the presence of a titanium sιlιcalιte-1 isomorphous substituted molecular sieve as prepared by example ?

A method as claimed in claim 15 wherein the oxidation is undertaken in the presence of hydrogen peroxide.

17 A method as claimed in either of claims 15 or 16 wherein the hydrocarbon is a saturated aliphatic hydrocarbon.

18. A titanium isomorphous substituted molecular sieve obtainable by the process of any one of claims 2 to 14.