Treating of catalyst carrier, fischer-tropsch catalysts and method of preparation thereof

Abstract

A method for the preparation of a modified catalyst support comprising: (a) treating a bare catalyst support material with an aqueous solution or dispersion of one or more titanium metal sources and one or more carboxylic acids; and (b) drying the treated support, and (c) optionally calcining the treated support. Also provided are catalyst support materials obtainable by the methods, and catalysts prepared from such supports.

Claims

1. A method for the preparation of a modified catalyst support comprising: a. treating a bare catalyst support material with an acidic aqueous solution or dispersion to form the modified support, the acidic aqueous solution or dispersion comprising: one or more titanium metal sources; and one or more carboxylic acids; b. drying the modified support; and c. calcining the modified support, wherein at least a portion of the one or more carboxylic acids is partially decomposed on the modified catalyst support during at least one of the drying and the calcining of the modified support, and the modified support comprises from about 11% to about 30% by weight TiO.sub.2.

2. The method of claim 1, wherein the method of treating is impregnating.

3. The method of claim 1, wherein the titanium metal source is titanium (IV) bis(ammoniumlactato)dihydroxide.

4. The method of claim 1, wherein the one or more carboxylic acids comprises citric acid.

5. The method of claim 1, wherein the one or more carboxylic acids comprises lactic acid.

6. The method of claim 1, wherein the bare catalyst support material is a refractory oxide.

7. The method of claim 6, wherein the refractory oxide is silica.

8. The method of claim 1, wherein the modified catalyst support is a modified Fischer-Tropsch catalyst support.

9. The method of claim 1 wherein the modified catalyst support is treated to form a catalyst precursor, the method further comprising: d. depositing a solution or suspension comprising at least one catalyst metal precursor and a complexing/reducing agent onto the modified catalyst support to form the catalyst precursor; e. optionally drying the catalyst precursor; and f. calcining the catalyst precursor.

10. The method of claim 9, wherein the catalyst metal precursor is a cobalt-containing precursor.

11. The method of claim 10, wherein the cobalt-containing precursor is cobalt nitrate.

12. The method of claim 9, wherein the complexing/reducing agent is one or more polar organic solvents.

13. The method of claim 12, wherein the polar organic solvent is one or more carboxylic acids.

14. The method of claim 13, wherein the carboxylic acid comprises citric acid.

15. The method of claim 9, wherein the calcination is carried out in an oxygen-containing atmosphere.

16. The method of claim 1, wherein the one or more carboxylic acids are present in the acidic aqueous solution or dispersion in an amount of about 5% w/v to about 20% w/v.

17. The method of claim 1, wherein a pH of the acidic aqueous solution or dispersion is from about 3.0 to about 3.5.

18. The method of claim 1, wherein the bare catalyst support material is in the form of a structured shape.

19. The method of claim 1, wherein the bare catalyst support material is in the form of pellets.

20. The method of claim 1, wherein the bare catalyst support material is in the form of a powder.

Description

DETAILED DESCRIPTION

(1) The present invention is now described, by way of illustration only, with reference to the accompanying drawings, in which:

(2) FIG. 1 shows the comparative FTS performance of a catalyst comprising a modified catalyst support prepared using an aqueous method (support B, shown by the squares) and one prepared using an alkoxide method (comparative support A, shown by crosses), showing the % CO conversion against the time on stream in days.

(3) FIG. 2 shows the TGA/DSC profiles for a comparative modified catalyst support C. The TGA/DCS profile for comparative modified catalyst support C (1105-13-016-1) which exhibits a single isotherm at 265 C. indicating a one-step decomposition is shown by dashed lines. The solid lines shows the profile when the modified catalyst support C (1106-15-016-1) was subjected to prolonged calcinations (at 250 C.).

(4) FIG. 3 shows the TGA/DSC profiles for a modified catalyst support D of the present invention (1104-05-016-2 and 1105-18-016-2).

(5) FIG. 4 shows the MS profiles for the unique mass fragments for NO.sub.x taken in conjunction with the TGA/DSC profiles of FIGS. 2 and 3.

(6) FIG. 5 shows the MS profiles for the unique mass fragments for CO/CO.sub.2 taken in conjunction with the TGA/DSC profiles of FIGS. 2 and 3.

(7) FIG. 6 shows the powder X-ray diffraction patterns for catalyst precursors prepared from modified catalyst supports C (lower pattern) and D (upper pattern).

(8) FIG. 7 shows the comparative FTS performance of catalysts comprising a modified catalyst support prepared using an aqueous method comprising citric acid (plotted with squares, 1106-14-016-2) and one prepared using an aqueous method without citric acid (plotted as diamonds, 1106-21-016-4), showing % CO conversion against time on stream in days.

(9) FIG. 8 shows the comparative TGA/DSC profiles for a catalyst precursor comprising a modified catalyst support prepared by calcining at 100 C. (solid lines), 250 C. (dashed lines) and 360 C. (long dash with dots lines).

(10) FIG. 9 (a) shows the MS profiles for the unique mass fragments for NO.sub.x taken in conjunction with the TGA/DSC profile of FIG. 8 for a support dried at 100 C.; (b) shows the MS profiles for the unique mass fragments for NO.sub.x taken in conjunction with the TGA/DSC profile of FIG. 8 for a support calcined at 250 C.

(11) FIG. 10 (a) shows the MS profiles for the unique mass fragments for CO/CO.sub.2 taken in conjunction with the TGA/DSC profile of FIG. 8 for a support dried at 100 C.; (b) shows the MS profiles for the unique mass fragments for CO/CO.sub.2 taken in conjunction with the TGA/DSC profile of FIG. 8 for a support calcined at 250 C.

(12) FIG. 11 shows the comparative FTS performance of a catalyst comprising a modified catalyst support prepared using an aqueous method but calcined at 100 C. (1104-06-016-6); calcined at 250 C. (1105-18-016-4); and calcined at 360 C. (1105-18-016-2); and one prepared using an alkoxide method (1011-25-016-4).

(13) The invention is further illustrated by the following examples. It will be appreciated that the examples are for illustrative purposes only and are not intended to limit the invention as described above. Modification of detail may be made without departing from the scope of the invention.

EXAMPLES

Example 1

(OCN11-027)

(14) A comparison between a catalyst comprising a titania-modified silica support manufactured using an alkoxide method and a catalyst comprising a titania-modified silica support manufactured using the aqueous method of the present invention was carried out.

(15) Synthesis of Modified Catalyst Support Using Alkoxide Method (Comparative Support A)

(16) Silica bare catalyst support material (Grace Davison, SG432 180 to 300 m particle size) was dried at 100 C. for 2 hours and allowed to cool to room temperature before impregnation. The impregnation solution was made by mixing 58.7 g of titanium isopropoxide with 60 ml of isopropanol, giving a solution volume of approximately 120 ml. 84 g of silica (weight determined after drying) was impregnated by spraying with the impregnation solution. Following impregnation, the modified catalyst support was dried at a temperature that increased at a ramp rate of 2 C./min up to 100 C. The temperature was held at 100 C. for 10 hours.

(17) The resulting catalyst support A had TiO.sub.2 present as titanium alkoxide bound to silica surface. The amount is equivalent to 16% TiO.sub.2 on silica support. (Conversion to titania occurs during subsequent calcination.)

(18) Synthesis of Modified Catalyst Support Using Aqueous Method of Present Invention (Support B)

(19) Silica bare catalyst support material (Grace Davison SG432/LC150, 180 to 300 m sieve particle size range) was dried at 100 C. for 2 hours and allowed to cool to room temperature before impregnation. The impregnation solution was made by dissolving 25 g of citric acid in minimum water at 40 to 45 C. and cooling down to less than 30 C. The citric acid solution was then added to 118 g (97 ml) of titanium (IV) bis(ammonium lactate)dihydroxide solution (TALH) and made up to the required volume of impregnation, which was about 130 to 135 ml, with water. 84 g of silica (weight determined after drying) was impregnated by spraying with the impregnation solution. Following impregnation, the modified catalyst support was dried at a temperature that increased at a ramp rate of 2 C./min up to 100 C. The temperature was held at 100 C. for 5 hours. The modified support catalyst was subsequently calcined by increasing the temperature to 250 C. using a ramp rate of 2 C./min and holding the temperature at 250 C. for 5 hours. The yield of the modified catalyst support B after drying and calcining was about 120 g. The modified catalyst support B was dark brown in colour.

(20) The resulting catalyst support B was a 16% TiO.sub.2 on silica support, incompletely calcined from the titanium alkoxide complex. Calcination is completed occurs during the calcination after cobalt nitrate impregnation.

(21) Synthesis of Catalysts

(22) Catalyst A

(23) 15 g of citric acid monohydrate (Sigma Aldrich, ACS Reagent) was dissolved in water. To the clear solution was added 106 g of cobalt nitrate hexahydrate (Sigma Aldrich, 98% purity) and then the solution was heated to 40 to 45 C. until the salt dissolved. The minimum required water was used to obtain a clear solution. 0.19 g of perrhenic acid (Sigma Aldrich, 70 wt % solution in water, 99.99% purity) was added to the cobalt nitrate and citric acid solution and was mixed well. The resulting solution was cooled to room temperature (less than 30 C.) and made up with water to 85 to 88 ml.

(24) A first impregnation of catalyst support A was carried out by using 20.9 ml of the solution to impregnate 20 g of the modified catalyst support A. The modified catalyst support A was then dried at a temperature that increased at a ramp rate of 2 C./min up to 100 C. The temperature was held at 100 C. for 5 hours. The modified support catalyst was subsequently calcined by increasing the temperature to 250 C. using a ramp rate of 2 C./min and holding the temperature at 250 C. for 3 hours.

(25) A second impregnation step was carried out by using 20.7 ml of the solution to impregnate the modified catalyst support A obtained from the first impregnation step (27.20 g). The modified catalyst support was then dried at a temperature that increased at a ramp rate of 2 C./min up to 100 C. The temperature was held at 100 C. for 5 hours.

(26) The modified support catalyst was subsequently calcined by increasing the temperature to 250 C. using a ramp rate of 2 C./min and holding the temperature at 250 C. for 3 hours.

(27) A third impregnation step was carried out by using 21.2 ml of the solution to impregnate the modified catalyst support A obtained from the second impregnation step (34.40 g). The modified catalyst support was then dried at a temperature that increased at a ramp rate of 2 C./min up to 100 C. The temperature was held at 100 C. for 5 hours. The modified support catalyst was subsequently calcined by increasing the temperature to 250 C. using a ramp rate of 2 C./min and holding the temperature at 250 C. for 3 hours.

(28) A fourth impregnation step was carried out by using 22.2 ml of the solution to impregnate the modified catalyst support A obtained from the third impregnation step (41.60 g). The modified catalyst support was then dried at a temperature that increased at a ramp rate of 2 C./min up to 100 C. The temperature was held at 100 C. for 5 hours. The modified support catalyst was subsequently calcined by increasing the temperature to 250 C. using a ramp rate of 2 C./min and holding the temperature at 250 C. for 3 hours.

(29) The four impregnation steps are summarised in Table 1.

(30) TABLE-US-00001 TABLE 1 Co(NO.sub.3).sub.26H.sub.2O (g) Citic Solution Support (Purity Co(NO.sub.3).sub.26H.sub.2O Co.sub.3O.sub.4 Co acid Perrhenic % Re H.sub.2O volume Mass % Step wt (g) 98%) (g) (g) (g) (g) acid (g) (g) (ml) (ml) (g) Co 1 20 26.53 26 7.17 5.26 3.75 0.0480 0.05 min. 20.9 27.2 19.4 2 27.2 26.53 26 7.17 5.26 3.75 0.0480 0.05 min. 20.7 34.4 30.6 3 34.4 26.53 26 7.17 5.26 3.75 0.0480 0.05 min. 21.2 41.6 38.0 4 41.6 26.53 26 7.17 5.26 3.75 0.0480 0.05 min. 22.2 48. 43.2 Total 106.12 15.01 0.19 0.20 85.01

(31) A promoter addition step was then carried out using 20 g of the catalyst precursor obtained after the four impregnation steps. 0.06 g of tetraammine platinum hydroxide (Alfa Aesar, 9.3% Pt w/w) was added to 9 ml water to make a dilute solution and this solution was used to further impregnate the catalyst precursor. After impregnation, the catalyst was then dried at a temperature that increased at a ramp rate of 2 C./min up to 100 C. The temperature was held at 100 C. for 5 hours. The catalyst was subsequently calcined by increasing the temperature to 250 C. using a ramp rate of 2 C./min and holding the temperature at 250 C. for 3 hours.

(32) The resulting catalyst A had 0.03% Pt and is suitable for use as, for example, a Fischer-Tropsch catalyst.

(33) Catalyst B

(34) g of cobalt nitrate hexahydrate (Sigma Aldrich, 98% purity) was dissolved in water and then the solution was heated to 40 to 45 C. until the salt dissolved completely. The minimum required water was used to obtain a clear solution. 0.048 g of perrhenic acid (Sigma Aldrich, 70 wt % solution in water, 99.99% purity) was added to the cobalt nitrate solution and mixed well. The resulting solution was cooled to room temperature (less than 30 C.) and made up with water to 19 ml.

(35) A first impregnation of catalyst support B was carried out by using 19 ml of the cobalt nitrate/perrhenic acid solution to impregnate 20 g of the modified catalyst support B. The resulting modified catalyst support B was then dried at a temperature that increased at a ramp rate of 2 C./min up to 100 C. The temperature was held at 100 C. for 5 hours. The modified support catalyst was subsequently calcined by increasing the temperature to 200 C. using a ramp rate of 2 C./min and holding the temperature at 200 C. for 3 hours, followed by further increasing the temperature to 250 C. using a ramp rate of 2 C./min and holding the temperature at 250 C. for 1 hour.

(36) 12 g of citric acid monohydrate (Sigma Aldrich, ACS Reagent) was dissolved in water. To the clear solution was added 81.4 g of cobalt nitrate hexahydrate (Sigma Aldrich, 98% purity) and then the solution was heated to 40 to 45 C. until the salt dissolved. The minimum required water was used to obtain a clear solution. 0.14 g of perrhenic acid (Sigma Aldrich, 70 wt % solution in water, 99.99% purity) was added to the cobalt nitrate and citric acid solution and was mixed well. The resulting stock solution was cooled to room temperature (less than 30 C.) and made up with water to 66 to 67 ml.

(37) A second impregnation step was carried out by using about 22 ml of the stock solution to impregnate the modified catalyst support B obtained from the first impregnation step (27.20 g). The modified catalyst support was then dried at a temperature that increased at a ramp rate of 2 C./min up to 100 C. The temperature was held at 100 C. for 5 hours. The modified support catalyst was subsequently calcined by increasing the temperature to 250 C. using a ramp rate of 2 C./min and holding the temperature at 250 C. for 3 hours.

(38) A third impregnation step was carried out by using about 22 ml of the stock solution to impregnate the modified catalyst support B obtained from the second impregnation step (34.40 g). The modified catalyst support was then dried at a temperature that increased at a ramp rate of 2 C./min up to 100 C. The temperature was held at 100 C. for 5 hours. The modified support catalyst was subsequently calcined by increasing the temperature to 250 C. using a ramp rate of 2 C./min and holding the temperature at 250 C. for 3 hours.

(39) A fourth impregnation step was carried out by using about 22 ml of the stock solution to impregnate the modified catalyst support B obtained from the third impregnation step (41.60 g). The modified catalyst support was then dried at a temperature that increased at a ramp rate of 2 C./min up to 100 C. The temperature was held at 100 C. for 5 hours. The modified support catalyst was subsequently calcined by increasing the temperature 20 to 250 C. using a ramp rate of 2 C./min and holding the temperature at 250 C. for 3 hours.

(40) The four impregnation steps are summarised in Table 2. The total value in Table 2 relates to the total of steps 2 to 4 only.

(41) TABLE-US-00002 TABLE 2 Co(NO.sub.3).sub.26H.sub.2O (g) Citic Solution Support (Purity Co(NO.sub.3).sub.26H.sub.2O Co.sub.3O.sub.4 Co acid Perrhenic % Re H.sub.2O volume Mass % Step wt (g) 98%) (g) (g) (g) (g) acid (g) (g) (ml) (ml) (g) Co 1 20 24.49 24 6.62 4.86 0.00 0.0480 0.05 min. 19 26.6 18.2 2 27.2 27.14 26.6 7.33 5.38 3.84 0.0480 0.05 min. 22 34.5 29.7 3 34.4 27.14 26.6 7.33 5.38 3.84 0.0480 0.05 min. 22 41.7 37.4 4 41.6 27.14 26.6 7.33 5.38 3.84 0.0480 0.05 min. 22 48.9 42.9 Total 81.43 11.52 0.14 0.20 66.38 2-4

(42) A promoter addition step was then carried out using 20 g of the catalyst precursor obtained after the four impregnation steps. 0.06 g of tetraammine platinum hydroxide (Alfa Aesar, 9.3% Pt w/w) was added to 9 ml water to make a dilute solution and this solution was used to further impregnate the catalyst precursor. After impregnation, the catalyst was then dried at a temperature that increased at a ramp rate of 2 C./min up to 100 C. The temperature was held at 100 C. for 5 hours. The catalyst was subsequently calcined by increasing the temperature to 250 C. using a ramp rate of 2 C./min and holding the temperature at 250 C. for 3 hours.

(43) The resulting catalyst had 0.03% Pt and is suitable for use as, for example, a Fischer-Tropsch catalyst.

(44) Comparison

(45) The catalysts comprising modified catalyst supports A and B were then screened and the % CO conversion was measured over a number of days on stream. FIG. 1 shows that the performance of the catalyst comprising modified catalyst support B (i.e. the support according to the present invention) provides a higher % CO conversion compared to the catalyst comprising comparative modified catalyst support A. In other words, the catalyst comprising the support of the present invention remained more active over the screening period.

(46) Furthermore, a linear fit of the data in FIG. 1 showed that the deactivation rate of modified catalyst support B was lower than comparative modified catalyst support A. This indicates that modified catalyst support B was more stable than comparative modified catalyst support A.

Example 2

The Effect of the Carboxylic Acid on Supports (OCIN11-032)

(47) A comparison between a modified catalyst support which was modified using an aqueous solution comprising a carboxylic acid (i.e. the method of the present invention, support D) and one which was modified using an aqueous solution which did not comprise a carboxylic acid was carried out as follows (i.e. a comparative method, support C).

(48) Synthesis of Modified Catalyst Support Using Comparative Aqueous Method (Support C)

(49) Silica bare catalyst support material (Grace Davison SG432/LC150, 180 to 300 m) was dried at 100 C. for 2 hours and allowed to cool to room temperature before impregnation. The impregnation solution was made by adding water to 118 g (97 ml) of titanium (IV) bis(ammonium lactate)dihydroxide solution (TALH) to make the required volume for impregnation, which was about 130 to 135 ml. 84 g of silica was impregnated by spraying with the impregnation solution. Following impregnation, the modified catalyst support was dried at a temperature that increased at a ramp rate of 2 C./min up to 100 C. The temperature was held at 100 C. for 5 hours. The modified support catalyst was subsequently calcined by increasing the temperature to 250 C. using a ramp rate of 2 C./min and holding the temperature at 250 C. for 5 hours. The yield of the modified catalyst support C after drying and calcining was about 120 g. The modified catalyst support C was dark brown in colour.

(50) The resulting modified catalyst support C was a 16% TiO.sub.2 on silica support.

(51) Synthesis of Modified Catalyst Support Using Aqueous Method of Invention (Support D)

(52) Silica bare catalyst support material (Grace Davison SG432/LC150, 180 to 300 m) was dried at 100 C. for 2 hours and allowed to cool to room temperature before impregnation. The impregnation solution was made by dissolving 25 g of citric acid in minimum water at 40 to 45 C. and cooling down to less than 30 C. The citric acid solution was then added to 118 g (97 ml) of titanium (IV) bis(ammonium lactate)dihydroxide solution (TALH) and made up to the required volume of impregnation, which was about 130 to 135 ml, with water. 84 g of silica was impregnated by spraying with the impregnation solution. Following impregnation, the modified catalyst support was dried at a temperature that increased at a ramp rate of 2 C./min up to 100 C. The temperature was held at 100 C. for 5 hours. The modified support catalyst was subsequently calcined by increasing the temperature to 250 C. using a ramp rate of 2 C./min and holding the temperature at 250 C. for 5 hours. The yield of the modified catalyst support D after drying and calcining was about 120 g. The modified catalyst support D was dark brown in colour.

(53) The resulting modified catalyst support D was a 16% TiO.sub.2 on silica support.

(54) Comparison

(55) Comparative modified catalyst support C was compared to modified catalyst support D of the present invention. TGA/DSC (Thermogravimetry/Differential scanning calorimetry) was carried out on modified catalyst supports C and D. Simultaneous differential scanning colorimetry and thermogravimetric analysis of the support and catalyst precursors were carried out in a flow of air using TA thermal analyser. The sample loading was typically 20 to 30 mg. The sample was heated up to 600 C. at a ramp rate of 1 C./min.

(56) FIG. 2 shows the TGA/DCS profile for comparative modified catalyst support C (1105-13-016-1) which exhibits a single isotherm at 265 C. indicating a one-step decomposition. Modified catalyst support C was then subjected to prolonged calcinations (at 250 C.) but no further exotherm was observed under TGA/DCS analysis (1106-15-016-1). After prolonged calcinations at 250 C., the sample retained some amorphous carbon/coke (CHN analysis data shows 4.0% C and 0.5% N for the sample after calcination at 250 C.) that decomposes at a higher temperature and no exotherm was observed for this step.

(57) In contrast, FIG. 3 shows the TGS/DCS profile for modified catalyst support D (1104-05-016-2) of the present invention which exhibits two separate isotherms indicating a two-step decomposition. The high temperature decomposition in FIG. 3 (1105-18-016-2) corresponds to decomposition after prolonged calcinations (at 250 C.). This shows that the presence of citric acid is stabilising the titanium species leading to a high temperature decomposition step which is not present in comparative modified catalyst support C.

(58) The evolved gases during thermal decomposition were analysed using Micromeritics 2920 AutochemII equipment with an on line mass spectrometer (MS). Temperature programmed oxidation (TPO) experiments were carried out using 5% O.sub.2 in helium. About 100 to 150 mg of catalyst precursor sample was loaded in a U-shaped quartz microreactor and purged with helium for 2 minutes. Thermal decomposition of the support or catalyst precursor was done using 5% O.sub.2/He at a programmed heating rate of 5 C./min up to 800 C. The gas flow rate was maintained at 50 ml/min. The evolved gases were monitored by analysing the outlet gases using an on line MS for all possible mass fragments. FIG. 4 and FIG. 5 show the unique mass fragments for NO and CO/CO.sub.2 respectively. These data also show that the citric acid (CA) is stabilising the titanium species.

(59) These results show that modified catalyst support D is more stable than comparative modified catalyst support C.

(60) X-ray diffraction data of catalyst precursors made from modified catalyst supports C and D (post-calcination, pre-activation) are shown in FIG. 6. The diffraction patterns of the catalyst precursors were collected at room temperature on a fully automated Siemens D5000 theta/theta powder diffractometer using Cu K radiation. Each sample was ground thoroughly before loading into a spinner carousel in air. Data were collected over the range 10-80 2, with a step size of 0.05 and a step length of 12 s.

(61) It is clear from these diffraction patterns that the crystal structure of the catalyst precursor made from modified support D is different from that made from modified support C. A sharp peak at 26.7 is present in the catalyst precursor made from support C. This peak may be modelled as the (110) rutile titania reflection. The sharpness of the peak at 26.7 indicates that this phase is not nanocrystalline. This data suggests that when citric acid is present with the aqueous titania precursor (support D) the titania phase is amorphous, but when the aqueous titania precursor is used without citric acid (support C) the titania phase is crystalline and not nanoparticulate.

Example 3

The Effect of the Carboxylic Acid on Deactivation Rate of Catalysts (OCIN11-032)

(62) Fischer-Tropsch catalysts were prepared using modified catalyst supports C and D discussed in Example 2.

(63) Catalyst C was made in the same way as catalyst A described in Example 1, except that modified catalyst support C was used in place of modified catalyst support A.

(64) Catalyst D was made in the same way as catalyst B described in Example 1, except that modified catalyst support D was used in place of modified catalyst support B.

(65) The catalysts C and D were each tested for Fischer-Tropsch synthesis performance. The catalyst (0.129 ml) diluted with SiC (2.184 ml) was loaded in a Spider reactor (L/D 31 cm) and reduced using pure hydrogen at 400 C. for 120 minutes at Gas Hourly Space Velocity (GHSV)=15 000 per hour. The temperature was increased from room temperature to 400 C. at 1 C./min. After the reduction, the reactor was cooled to 165 C. and the gas was switched from hydrogen to synthesis gas. The operating conditions were kept constant for 1 hour. The pressure was then increased to 20 bar at the flow rate of the reaction and held for 1 hour. The temperature was then increased from 165 C. to 190 C. at a ramp rate of 4 C./hour, from 190 to 210 C. (GHSV=12 400 per hour) at 2 C./hour and then kept at 210 C. (GHSV=12 400 per hour) for about 120 hours.

(66) The liquid products from the reaction were trapped in hot and cold knock-out pots and the gas products were injected on line to a Clarus 600 gas chromatograph. Hydrogen, carbon monoxide and nitrogen were detected with a thermal conductivity detector and hydrocarbons (from C.sub.1 to C.sub.4) with a flame ionization detector. Conversion and product selectivity were calculated by using nitrogen as a tracer and employing a carbon mass balance.

(67) The results are shown in FIG. 7. Linear fits to the data in FIG. 7 show that the catalyst (1106-14-016-2) prepared using a modified catalyst support in which citric acid had been present during the titania modification step (i.e. modified catalyst support D) displayed a lower deactivation rate compared to one (1106-21-016-4) prepared without citric acid (i.e. comparative modified catalyst support C).

Example 4

The Effect of Calcination on Stability of Catalysts (OCIN11-035)

(68) A comparison between a catalyst precursor comprising a modified catalyst support that has not been calcined (support E), a modified catalyst that has been calcined at 250 C. (support F), and a modified catalyst support that has been calcined at 350 C. (support G) was carried out as follows.

(69) Synthesis of Modified Catalyst Support E.

(70) Silica bare catalyst support material (Grace Davison SG432/LC150, 180 to 300 m) was dried at 100 C. for 2 hours and allowed to cool to room temperature before impregnation. The impregnation solution was made by adding water to 118 g (97 ml) of titanium (IV) bis(ammonium lactate)dihydroxide solution (TALH) to make it up to the required volume for impregnation, which was about 130 to 135 ml. 84 g of silica was impregnated by spraying with the impregnation solution. Following impregnation, the modified catalyst support was dried at a temperature that increased at a ramp rate of 2 C./min up to 100 C. The temperature was held at 100 C. for 10 hours. The resulting modified catalyst support E was a 16% TiO.sub.2 on silica support.

(71) Synthesis of Modified Catalyst Support F.

(72) Silica bare catalyst support material (Grace Davison SG432/LC150, 180 to 300 m) was dried at 100 C. for 2 hours and allowed to cool to room temperature before impregnation. The impregnation solution was made by adding water to 118 g (97 ml) of titanium (IV) bis(ammonium lactate)dihydroxide solution (TALH) to make it up to the required volume for impregnation, which was about 130 to 135 ml. 84 g of silica was impregnated by spraying with the impregnation solution. Following impregnation, the modified catalyst support was dried at a temperature that increased at a ramp rate of 2 C./min up to 100 C. The temperature was held at 100 C. for 5 hours. The modified support catalyst was subsequently calcined by increasing the temperature to 250 C. using a ramp rate of 2 C./min and holding the temperature at 250 C. for 5 hours. The yield of the modified catalyst support F after drying and calcining was about 120 g. The modified catalyst support F was dark brown in colour.

(73) The resulting catalyst support F was a 16% TiO.sub.2 on silica support.

(74) Synthesis of Modified Catalyst Support G.

(75) Silica bare catalyst support material (Grace Davison SG432/LC150, 180 to 300 m) was dried at 100 C. for 2 hours and allowed to cool to room temperature before impregnation. The impregnation solution was made by adding water to 118 g (97 ml) of titanium (IV) bis(ammonium lactate)dihydroxide solution (TALH) to make it up to the required volume for impregnation, which was about 130 to 135 ml. 84 g of silica was impregnated by spraying with the impregnation solution. Following impregnation, the modified catalyst support was dried at a temperature that increased at a ramp rate of 2 C./min up to 100 C. The temperature was held at 100 C. for 5 hours. The modified support catalyst was subsequently calcined by increasing the temperature to 250 C. using a ramp rate of 2 C./min and holding the temperature at 250 C. for 5 hours, followed by further increasing the temperature to 360 C. using a ramp rate of 2 C./min and holding the temperature at 360 C. for 5 hours. The resulting catalyst support G was a 16% TiO.sub.2 on silica support.

(76) These modified supports were used to form Fischer-Tropsch catalyst precursors E, F and G in the way as used to make the catalyst B in Example 1 using modified catalyst supports E, F and G, respectively, instead of modified catalyst support B. A promotion step (with platinum) was performed in all the catalyst preparations.

(77) Results

(78) FIG. 8 shows the TGA/DSC profile (obtained in the same way as described in Example 2) of catalyst precursors E, F and G. The decomposition of catalyst precursor E of the present invention (following drying at 100 C.) occurred in two steps, both being exothermic. In contrast, the decomposition of comparative catalyst precursor F (following calcination at 250 C.) occurred in a single step within a broad temperature range. This shows that the presence of a calcining step at 250 C. stabilises the titanium species on the support.

(79) Catalyst precursor G exhibited a single low temperature endothermic decomposition peak following complete decomposition of TALH at 360 C. This shows that the calcining temperature used in making the modified catalyst support G is high enough to convert TALH to TiO.sub.2.

(80) CHN analysis of catalyst precursors E, F and G was performed and the results are shown in Table 3.

(81) TABLE-US-00003 TABLE 3 Calcination temperature ( C.) 100 250 360 % C 13.17 6.93 0.25 % H 1.69 0.24 <0.1 % N 2.12 1.31 <0.1

(82) The evolved gases during thermal decomposition for catalyst precursor E and catalyst precursor F were analysed using Micromeritics AutochemII equipment with an on line MS, as described in Example 2. FIG. 9 and FIG. 10 show the unique mass fragments for CO/CO.sub.2 and NO respectively. These data confirm that calcining at 250 C. compared to 360 C. stabilises the titanium species leading to more stable catalyst precursor materials. Both figures show E (support used is calcined at 100 C.) and F (support used is calcined at 250 C.). FIG. 9 shows the presence of NOx in the evolved exit gas mixture due to the decomposition of the cobalt nitrate in the precursor. FIG. 10 shows the presence of CO/CO.sub.2 in the same exit gas and that is coming from the TALH.

(83) These results show that catalyst precursor F of the present invention is more stable than comparative catalyst precursors E and G.

Example 5

(84) The active catalyst formed from catalyst precursors E, F and G described in Example 4 were tested for Fischer-Tropsch synthesis performance, as described in Example 3 and compared to an active catalyst comprising a modified catalyst support prepared using an alkoxide method. The results are shown in FIG. 11. FIG. 11 shows that the catalyst formed from catalyst precursor F provides a higher % CO conversion compared to the catalysts comprising a catalyst support calcined at 100 C. or at 360 C., or comprising a catalyst support modified using an alkoxide method. In other words, the catalyst of the present invention remained more active over the screening period.

(85) Furthermore, a linear fit of the data in FIG. 11 showed that the deactivation rate of the catalyst formed from catalyst precursor F was lower than for the catalyst precursors E and G or for the comparative catalyst comprising a catalyst support modified using an alkoxide method.

(86) This shows the effect of calcination temperature of the support after titanium-modification. The more carbon there is on the support, the more stable the catalyst will be. However, the nature of the carbonaceous species and the heat evolved during the decomposition of cobalt precursor are also important. After the modified support was calcined at 360 C., the catalyst is less stable.