Catalysts supports

1. A method for preparing a silica-modified catalyst support comprising:

(i) applying an alkyl silicate of formula Si(OR) 4 , where R is a C1-C4 alkyl group to the surface of a porous support material in an amount to produce a silica content of the silica-modified catalyst support, expressed as Si, in the range 0.25 to 15 % by weight,

(ii) drying the resulting silicate-modified support,

(iii) treating the silicate-modified support with water to force hydrolysis of the alkyl silicate on the support and to cause cross-linking to form a silicate material having a greater molecular mass and reduced volatility than the alkyl silicate,

(iv) drying the resulting water-treated support, and

(v) calcining the dried material to form the silica-modified catalyst support.

2. A method according to claim 1 , wherein the porous support comprises alumina, titania, or zirconia.

3. A method according to claim 1 , wherein the porous support comprises a transition alumina or hydrated alumina.

4. A method according to claim 1 , wherein the porous support is a spray-dried powder with an average particle size in the range 1 to 200 micrometres.

5. A method according to claim 1 , wherein the porous support is a pellet, extrudate, or granule with a particle size in the range 1 to 25 mm.

6. A method according to claim 1 , wherein the surfaces of the porous support are pre-activated prior to application of the alkyl silicate by treating the porous support with an acidic wash solution and drying the acid-washed support.

7. A method according to claim 1 , wherein the alkyl silicate is tetraethyl-orthosilicate (TEOS).

8. A method according to claim 1 , wherein the silica content of the silica-modified catalyst support , expressed as Si, is in the range 1 to 10% by weight.

9. A method according to claim 1 , wherein the alkyl silicate is applied as a solution in an alcohol.

10. A method according to claim 9 , wherein the volume of the alkyl silicate solution is less than or equal to the pore volume of the porous support material.

11. A method according to claim 1 , wherein the silicate-modified support is dried at a temperature in the range 30-150° C. prior to the treatment with water.

12. A method according to claim 1 , wherein the water treatment comprises immersing or slurrying the silicate-modified support in water.

13. A method according to claim 11 , wherein the water treatment comprises applying a volume of liquid water to the dried silicate-modified support, said volume of water being equal to or less than the pore volume of the dried silicate-modified support.

14. A method according to claim 1 , wherein the water-treated support is dried for a period at ambient pressure or under vacuum.

15. A method according to claim 1 , wherein the water treated support is dried at a temperature in the range 30-150° C.

16. A method according to claim 1 , wherein the water-treated support is dried under a vacuum of 1-10 mm Hg.

17. A method according to claim 1 , wherein the calcination step is performed by heating the dried support to a temperature in the range 500-950° C. for between 0.5 and 8 hours.

18. A method according to claim 1 , wherein the silica content of the calcined catalyst support is ≧90% wt of that derivable from the amount of alkyl silicate applied to the porous support.

19. A method of preparing a catalyst comprising the step of applying a catalytically active material to a silica-modified catalyst support prepared according to the method of claim 1 .

20. A method according to claim 19 , wherein the catalytically active material comprises cobalt.

21. A method according to claim 1 , wherein the water-treated support is dried for a first period at ambient pressure and then a second period under vacuum.

22. A method according to claim 1 , wherein the calcination step is performed by heating the dried support to a temperature in the range 820-900° C., for between 0.5 and 8 hours.