WO2010049715A1

WO2010049715A1 - Cobalt catalyst precursor

Info

Publication number: WO2010049715A1
Application number: PCT/GB2009/051290
Authority: WO
Inventors: Peter Richard Ellis
Original assignee: Johnson Matthey Plc
Priority date: 2008-10-30
Filing date: 2009-10-01
Publication date: 2010-05-06
Also published as: CN102202787A; AU2009309421A1; BRPI0919649A2; GB0819849D0

Abstract

A catalyst precursor is described comprising 5 to 50 % by weight of one or more oxidic cobalt compounds selected from CoO, CoO(OH) and Co3O4 and 0.05 to 10 % by weight of one or more reduction promoter selected from metals or compounds of Ru, Pt, Cu, Rh, Pd, Ir, Ag and Bi, supported on an inert support selected from alpha alumina, a metal-aluminate, silica, titania, zirconia, zinc oxide, silicon carbide, carbon or mixtures thereof, wherein the cobalt is in a highly reducible form such that at least 75 % of the cobalt is reducible by a reducing gas stream at temperatures ≤ 24O °C.

Description

Cobalt Catalyst Precursor

This invention relates to cobalt catalysts and in particular cobalt catalysts suitable for the

Fischer-Tropsch synthesis of hydrocarbons.

Cobalt catalysts suitable for use in the Fischer Tropsch process for synthesising hydrocarbons are generally subjected to pre-reduction and encapsulation in a suitable material prior to installation in the Fischer-Tropsch reactor. This is because the reduction processes typically are operated at temperatures > 25O⁰C, and in particular >300°C, which are challenging for the fixed bed or slurry phase reactors used. Furthermore reduction is typically performed using hydrogen gas streams, and the gas streams available for in-situ reduction generally comprise synthesis gas mixtures containing carbon monoxide. Whereas in-situ reduction of cobalt Fischer-Tropsch catalysts is a desired aim, heretofore such processes have not been commercially used.

We have found a specific combination of inert support and additive that allows effective cobalt reduction at low temperatures.

Accordingly the invention provides a catalyst precursor comprising 5 to 50% by weight of one or more oxidic cobalt compounds selected from CoO, CoO(OH) and Co₃O₄and 0.05 to 10% by weight of one or more reduction promoters selected from metals or compounds of Ru, Pt, Cu, Rh, Pd, Ir, Ag and Bi, supported on an inert support selected from alpha alumina, a metal- aluminate, silica, titania, zirconia, zinc oxide, silicon carbide, carbon or mixtures thereof, wherein the cobalt is in a highly reducible form such that at least 75% of the cobalt is reducible by a reducing gas stream at temperatures < 24O⁰C. Hence, in the catalyst according to the present invention, the cobalt is present in a highly reducible form so that the oxidic cobalt compound may be effectively reduced by a reducing gas stream at temperatures < 24O⁰C. By "effectively reduced" we mean that the degree of reduction, i.e. the amount of cobalt reduced is >75% wt, preferably >85% wt, more preferably >90% wt of the Co present in the catalyst precursor.

Such low temperature reduction offers the opportunity for commercially attractive in-situ reduction thereby removing the need for pre-reduced, encapsulated catalysts that can be difficult to manufacture and transport.

Accordingly the invention further provides a process for activating a catalyst comprising placing the above catalyst precursor in a Fischer-Tropsch reactor and passing a reducing gas mixture over the catalyst precursor for a period of time to reduce cobalt present therein to elemental form, wherein the temperature of the reducing gas mixture throughout the activation step is < 24O⁰C. The invention further provides a process for the Fischer-Tropsch synthesis of hydrocarbons comprising the step of passing a gas mixture comprising hydrogen and carbon monoxide over a catalyst in a Fischer-Tropsch reactor wherein the catalyst has been activated by passing a reducing gas mixture at a temperature of < 24O⁰C over the above catalyst precursor in the Fischer Tropsch reactor,.

The cobalt content of the catalyst precursor is in the range 5 to 50% by weight, preferably 10 to 35% by weight, most preferably 12 to 30% by weight. The additive or promoter content of the catalyst precursor is in the range 0.05 to 10% by weight, preferably 0.1 to 5% wt, most preferably 0.1 to 2% by weight . The total amount of additive or promoter in the catalyst precursor is preferably < 10% by weight. The metal contents may be determined using known methods such as ICP AES or ICP OES.

In the present invention preferably all of the cobalt is in reducible form, i.e. preferably <5% by weight, more preferably <1 % by weight, most preferably < 0.05% by weight and especially none of the cobalt is in the form of a cobalt-support mixed oxide such as cobalt aluminate. The reducible cobalt is present as one or more of CoO, CoO(OH) and Co₃O₄. Preferably substantially all of the reducible cobalt is present as Co₃O₄.

At least 75%, preferably at least 85%, more preferably at least 90% of the cobalt is reducible, i.e. the degree of reduction (DOR) is preferably >75%, more preferably >85%, especially >90%. A temperature-programmed reduction (TPR) method for estimating DOR may be used as follows:

1. Steadily increase the sample temperature to the desired temperature (≤240°C) at 10°C/min, hold at that temperature for ten hours (TPR1 ).

2. Without cooling back to room temperature, increase the sample temperature to 1000⁰C at 10°C/min and hold at 1000⁰C for ten minutes. (TPR2). This gives complete reduction of all cobalt.

3. Integrate the hydrogen uptakes from TPRs 1 and 2. The ratio TPR1/(TPR1 + TPR2) is the degree of reduction (expressed as %).

The reduction promoter in the present invention is selected from one or more compounds or metals of Ru, Pt, Cu, Rh, Pd, Ir, Ag and Bi, preferably one or more of Ru, Pt and Cu, more preferably Ru.

The inert support in the present invention is one that is inert to the cobalt, i.e. does not readily form mixed oxides of cobalt, such as cobalt aluminate spinels. The inert support is selected from alpha alumina, a metal-aluminate, silica, titania, zirconia, zinc oxide, silicon carbide, carbon or mixtures thereof. The support and hence the resulting catalyst precursor may be in the form of a powder having a surface-weighted mean diameter D[3,2] in the range 1 to 200 microns. The term surface- weighted mean diameter D[3,2], otherwise termed the Sauter mean diameter, is defined by M. Alderliesten in the paper "A Nomenclature for Mean Particle Diameters"; Anal. Proc, vol 21 , May 1984, pages 167-172, and is calculated from the particle size analysis, which may conveniently be effected by laser diffraction for example using a Malvern Mastersizer. Agglomerates of such powders having particle sizes in the range 200 microns to 1 mm may also be used as the support. Alternatively the support and hence the resulting catalyst precursor may be in the form of shaped units such as pellets, extrudates or granules typically having particle sizes in the range 1-25 mm and an aspect ratio of less than 2. (By particle size we mean the smallest particle dimension such as width, length or diameter). Alternatively the support may be in the form of a monolith, e.g. a honeycomb, or a cellular material such as an open foam structure. The inert support may also be in the form of a wash-coat on a ceramic, metal, carbon or polymer substrate. Such catalysts advantageously offer in-situ reduction in micro GTL equipment.

Carbon supports, such as activated carbons, high surface area graphites, carbon nanofibres, and fullerenes in powder, pellet or granular form and having suitable porosities, e.g. above 0.1 ml/g may be used as supports for the present invention. Such supports are preferably not used in methods where air calcination is employed because of oxidation of the support. Preferably catalyst precursors comprising carbon supports are produced where the gas stream to which the carbon is exposed during calcination contains preferably <1 %, more preferably < 0.1 %, oxygen by volume, e.g. oxygen free nitrogen, helium or argon.

The support may be a silica support. Silica supports may be formed from natural sources, e.g. as kieselguhr, may be a pyrogenic or fumed silica or may be a synthetic, e.g. precipitated silica or silica gel. Structured mesoporous silicas, such as SBA-15 may be used as a support. Precipitated silicas are preferred. The silica may be in the form of a powder or a shaped material, e.g. as extruded, pelleted or granulated silica pieces. Suitable powdered silicas typically have particles of surface weighted mean diameter D[3,2] in the range 3 to 100 μm. Shaped silicas may have a variety of shapes and particle sizes, depending upon the mould or die used in their manufacture. For example the particles may have a cross-sectional shape which is circular, lobed or other shape and a length from about 1 to greater than 10 mm. The BET surface area of suitable powdered or granular silicas is generally in the range 10 - 500 m²/g, preferably 100 - 400 m²gΛ The pore volume is generally between about 0.1 and 4 ml/g, preferably 0.2 - 2 ml/g and the mean pore diameter is preferably in the range from 0.4 to about 30 nm. If desired, the silica may be mixed with another metal oxide, such as titania or zirconia. The silica may alternatively be present as a coating on a shaped unit, which is preferably of alumina typically as a coating of 0.5 to 5 monolayers of silica upon the underlying support. The support may be a titania support. Titania supports are preferably synthetic, e.g. precipitated titanias. The titania may optionally comprise e.g. up to 20% by weight of another refractory oxide material, typically silica, alumina or zirconia. The titania may alternatively be present as a coating on a support which is preferably of silica or alumina, for example as a coating of 0.5 to 5 monolayers of titania upon the underlying alumina or silica support. The BET surface area of suitable titania is generally in the range 10 - 500 m²/g, preferably 100 to 400 m²/g. The pore volume of the titania is preferably between about 0.1 and 4 ml/g, more preferably 0.2 to 2 ml/g and the mean pore diameter is preferably in the range from 2 to about 30 nm.

Similarly zirconia supports maybe synthetic, e.g. precipitated zirconias. The zirconia may again optionally comprise e.g. up to 20% by weight of another refractory oxide material, typically silica, alumina or titania. Alternatively the zirconia may be stabilised e.g. an yttria- or ceria- stabilised zirconia. The zirconia may alternatively be present as a coating on a support, which is preferably of silica or alumina, for example as a coating of 0.5 to 5 monolayers of zirconia upon the underlying alumina or silica support. The support may be a metal aluminate, for example a calcium aluminate.

In one embodiment the inert support is alpha-alumina. The alpha alumina may be obtained commercially or made by heating transition aluminas, e.g. gamma-alumina, to temperatures in the range 1000-1500⁰C, preferably >1200°C. The alpha alumina is preferably reasonably pure with an alkali content < 100ppm, preferably < 50 ppm and substantially no metal aluminate spinel present. The BET surface area is preferably < 50m²/g. A suitable alpha alumina powder generally has a surface-weighted mean diameter D[3,2] in the range 1 to 200 μm. In certain applications such as for catalysts intended for use in slurry reactions, it is advantageous to use very fine particles which are, on average, preferably less than 20 μm, e.g. 10 μm or less. For other applications e.g. as a catalyst for reactions carried out in a fluidised bed, it may be desirable to use larger particle sizes, preferably in the range 50 to 150 μm. The alumina support material may be in the form of a spray dried powder or formed into shaped units such as spheres, pellets, cylinders, rings, or multi-holed pellets, which may be multi-lobed or fluted, e.g. of cloverleaf cross-section, or in the form of extrudates known to those skilled in the art. The alpha alumina support may be advantageously chosen for high filterability and attrition resistance.

Alpha-alumina supported cobalt Fischer-Tropsch catalysts are known. WO 02/47816 describes cobalt catalysts on an alpha alumina or alpha alumina-containing support. The list of possible promoters given includes Re, Pt, Ir or Rh. However, reduction of the catalyst precursors was performed at 250-400⁰C, preferably 300-400⁰C. Metal-aluminate supports such as nickel aluminate, lithium aluminate or calcium aluminate supports may also be used in the present invention. These supports have the advantage of being unable to readily interact with the cobalt oxides formed thereon.

The catalyst precursors may be prepared using known methods. For example the catalysts may be prepared using impregnation methods, precipitation methods or deposition precipitation methods, or a combination of these, generally followed by a drying step to remove any solvents and a calcination step to effect conversion of the cobalt and additive or promoter compounds to their respective oxides. The cobalt and promoter may be uniformly distributed within the support or may be in the form of an eggshell on its surface.

Deposition precipitation methods and impregnation methods are preferred.

Deposition precipitation methods whereby cobalt ammine carbonate solutions are heated to deposit cobalt compounds onto supports are known. For example, suitable methods for preparing alumina-, silica- and titania-supported catalysts using cobalt ammine carbonate solutions are described in US 5874381 , WO 01/62381 , WO 01/87480, WO 04/28687 and WO 05/107942. In general, cobalt compounds may be deposited onto the inert support by either

(a) impregnating the support with an aqueous cobalt ammine carbonate solution, separating the impregnated support from any excess solution, and then heating the impregnated support to a temperature in the range 60-110⁰C, in air or in the presence of a suitable oxidant or,

(b) heating a slurry of support in cobalt ammine carbonate solution to a temperature in the range 60-11O⁰C in air or in the presence of a suitable oxidant.

The first method is particularly suitable when preparing catalysts on shaped supports such as extrudates or pellets, whereas the second method is particularly suitable for powder supports.

In impregnation methods, a suitable soluble metal compounds, for example the metal nitrate or acetate may be impregnated onto a support material from an aqueous or non-aqueous solution, e.g. ethanol, which may include other materials, and then dried to remove the solvent or solvents. One or more soluble metal compounds may be present in the solution. One or more impregnation steps may be performed, with or without intervening drying and/or calcination steps, to increase metal loading or provide sequential layers of different metal compounds. Impregnation may be performed using any of the methods known to those skilled in the art of catalyst manufacture, but preferably is by way of a so-called 'dry' or 'incipient- wetness' impregnation as this minimises the quantity of solvent used and to be removed in drying. Incipient wetness impregnation comprises mixing the support material with only sufficient solution to fill the pores of the support. Impregnation methods for producing cobalt catalysts generally comprise combining a catalyst support with a solution of cobalt nitrate, e.g. cobalt (II) nitrate hexahydrate at a suitable concentration. Whereas a number of solvents may be used such as water, alcohols, ketones or mixtures of these, preferably the support has been impregnated using aqueous solutions of cobalt nitrate.

The reduction promoter may also be included in the catalyst precursor by impregnation, using suitable soluble compounds such as the nitrate chloride, acetate, or mixtures of these. The additive or promoter may be included in the catalyst precursor before or after the cobalt, or at the same time by combining the cobalt and additive or promoter compounds in the same impregnating solution. The amount of cobalt and additive or promoter compound in solution, or the amount of inert support may be varied to achieve the desired metal loadings. Single or multiple impregnations may be performed to achieve the desired cobalt and additive or promoter levels in the catalyst precursor. In a preferred embodiment, the catalyst precursor is made by co-impregnating an inert support with a solution of ruthenium acetate and cobalt nitrate.

If desired, the catalyst precursor may be dried to remove solvent prior to calcination. The drying step may be performed at 20-120⁰C, preferably 95-11O⁰C, in air or under an inert gas such as nitrogen, or in a vacuum oven.

The catalyst precursor may then be heated in air to effect conversion of the cobalt and additive or promoter compounds to their respective oxides. The calcination temperature is preferably in the range 250 to 500⁰C. The calcination time is preferably < 24, more preferably < 16, most preferably < 8, especially < 6 hours. As an alternative to calcination in air, the dried catalyst precursor may be heated under an inert gas containing <5 % volume oxygen such as nitrogen or argon, which may include nitric oxide or nitrous oxide at a concentration in the range 0.001 to 15% by volume. We have found that calcination of supported nitrate materials under nitric oxide or nitrous oxide leads to improved cobalt dispersion and hence higher cobalt surface areas following reduction than similar air-calcined catalyst precursors.

The drying and/or calcination steps may be carried out batch-wise or continuously, depending on the availability of process equipment and/or scale of operation. In a preferred embodiment, the method for making a catalyst precursor comprises the steps of

(a) calcining a transition alumina such as gamma alumina at a temperature in the range 1000-1500⁰C to form an alpha alumina,

(b) co-impregnating the alpha alumina with a solution comprising ruthenium and cobalt compounds, at least one of said compounds being a nitrate,

(c) drying and calcining the impregnated alumina, said calcination step being performed in air or in an inert gas having <5 % volume oxygen and including nitric oxide or nitrous oxide at a concentration in the range 0.001 to 15% by volume, and (d) optionally repeating steps (b) and (c).

If desired, the catalyst precursor may in addition to cobalt and one or more of Ru, Pt, Cu, Rh, Pd, Ir, Ag and Bi, further comprise one or more suitable additives useful in Fischer-Tropsch catalysis. For example, the catalysts may comprise one or more additives that alter the physical properties and/or promoters that effect the reducibility or activity or selectivity of the catalysts. Suitable additives are selected from compounds of metals selected from molybdenum (Mo), iron (Fe), manganese (Mn), titanium (Ti), zirconium (Zr), lanthanum (La), cerium (Ce), chromium (Cr), magnesium (Mg) or zinc (Zn). The additives may be incorporated into the catalyst precursor by use of suitable compounds such as acids, metal salts, e.g. metal nitrates or metal acetates, or suitable metal-organic compounds, such as metal alkoxides or metal acetylacetonates. Typical amounts of the additives are 0.1 - 10% metal by weight on catalyst precursor. If desired, the compounds of the additional additives may be added in suitable amounts to the cobalt solution. Alternatively, they may be combined with the catalyst precursor before or after drying or calcination.

To render the catalyst precursor catalytically active for Fischer-Tropsch reaction, at least a portion of the cobalt oxide may be reduced to the metal. Reducing gas streams that may be used include hydrogen- and/or carbon monoxide-containing gases. Reduction is preferably performed using hydrogen-containing gasses at elevated temperature. In the present invention the temperature of the reducing gas stream, and hence the catalyst precursor, during the entire reduction stage is < 24O⁰C, preferably < 23O⁰C, more preferably < 225⁰C. The minimum reduction temperature is preferably 9O⁰C, more preferably 100°C, although higher temperatures may speed up reduction and a particularly preferred reduction temperature range is 180-240°C.

Before the reduction step, the catalyst precursor may, if desired, be formed into shaped units suitable for the process for which the catalyst is intended, using methods known to those skilled in the art.

In the present invention the catalysts are desirably reduced in-situ, i.e. in the reactor in which they are to be used. Fischer Tropsch reactors take a variety of forms including fixed bed reactors in which a gas stream comprising carbon monoxide and hydrogen is passed through one or more beds of a particulate or monolithic catalyst, including catalyst supported on a wash-coated ceramic or metal substrate; and slurry phase reactors in which a gas stream comprising hydrogen and carbon monoxide is passed through a slurry of particulate catalyst in a suitable liquid medium. Such reactors include the well-known slurry bubble column reactors (SBCR's). The reduction, also termed activation, may be performed by passing a reducing gas stream such as hydrogen, synthesis gas (a gas mixture comprising hydrogen, carbon monoxide and/or carbon dioxide) or a mixture of hydrogen and/or carbon monoxide with nitrogen or other inert gas over the oxidic composition at elevated temperature, for example by passing the hydrogen- containing gas over the catalyst precursor at temperatures in the range 140-240⁰C, preferably 160-220⁰C for between 1 and 16 hours, preferably 1 - 8 hours. Preferably the reducing gas stream comprises hydrogen at >25% vol, more preferably >50% vol, most preferably >75%, especially >90% vol hydrogen. However, in the present invention, it may also be possible to effectively reduce the catalyst precursor using a synthesis gas mixture containing less hydrogen. This may be particularly useful where the catalyst is to be activated in-situ.

Preferably at least 90% of the reducible cobalt is reduced at < 24O⁰C. The cobalt surface areas of the reduced catalysts may be determined by H₂ chemisorption using known methods.

Reduction may be performed at ambient pressure or increased pressure, i.e. the pressure of the reducing gas may suitably be from 1-50, preferably 1-20, more preferably 1-10 bar abs. Higher pressures >10 bar abs may be more appropriate where the reduction is performed in- situ.

The gas-hourly-space velocity (GHSV) for the reducing gas stream may be in the range 100- 25000hr^"1, preferably 1000 - 15000hr^"1.

Where the catalyst is to be used in a SBCR, it may be preferable to disperse the catalyst precursor in a suitable liquid medium such as a molten hydrocarbon wax, e.g. a C6 to C40 hydrocarbon mixture, and pass the reducing gas stream through the resulting slurry. The solids content of such a slurry is preferably in the range 1 to 50% w/v, more preferably from 3 to 40% w/v, most preferably from 5 to 35 % w/v.

The catalysts may be used for the Fischer-Tropsch synthesis of hydrocarbons.

The Fischer-Tropsch synthesis of hydrocarbons with cobalt catalysts is well established. The Fischer-Tropsch synthesis converts a mixture of carbon monoxide and hydrogen to hydrocarbons. The mixture of carbon monoxide and hydrogen is typically a synthesis gas having a hydrogen: carbon monoxide ratio in the range 1.6-3.0:1 , preferably 1.7 - 2.5:1. The reaction may be performed in a continuous or batch process using one or more stirred slurry- phase reactors, bubble-column reactors, loop reactors or fluidised bed reactors. The process may be operated at pressures in the range 0.1-10Mpa and temperatures in the range 150- 35O⁰C. The gas-hourly-space velocity (GHSV) for continuous operation is in the range 100- 25000hrΛ A preferred operating range is 1000-15000hr Λ The invention will now be further described by reference to the following Examples and by reference to Figures 1 to 5, which depict temperature-programmed reduction (TPR) plots for Ru-, Pt- and Cu-promoted catalysts that may be used according to the invention, in comparison with an un-promoted catalyst.

Example 1 : Preparation of alpha-alumina-supported catalyst precursors

A gamma alumina (HP 14-150 available from Sasol Condea) was subjected to calcination in air at a temperature of 1400°C for sufficient time to convert it to alpha alumina.

(i) Examples 1(a) - (c) were prepared by a co-impregnation method. An impregnation solution was prepared by dissolving 5% wt ruthenium acetate in acetic acid and cobalt nitrate hexahydrate in demineralised water. The alpha alumina was treated with the solution by the dry impregnation method, dried at 105°C for 3 hours and calcined by heating to 400°C at 2°C/min, and holding at this temperature for 1 hour. The procedure was then repeated on the calcined material. The resulting catalyst precursor had a cobalt content of 17.8% by weight and a ruthenium content of 0.21 % by weight.

Catalyst precursors were made in the same way using copper (II) nitrate and platinum nitrate to achieve a cobalt content of about 18% wt and reduction promoter level of about 1 % wt on the calcined material. (A Co content of about 18% wt in a catalyst precursor corresponds to a Co content of about 20% in a reduced catalyst assuming all the Co is reduced).

Comparative catalyst precursor materials containing about 18% wt Co and no promoter, or differing amounts of gold, lanthanum and rhenium were also prepared using the same co- impregnation method.

(ii) Example 1 (d) was prepared by a sequential impregnation method: The alpha alumina was treated with a solution of cobalt nitrate hexahydrate by dry the impregnation method, dried at 105°C for 3 hours and calcined by heating to 400°C at 2°C/min, and holding at this temperature for 1 hour. This procedure was then repeated on the calcined material. The resulting alpha- alumina-supported cobalt oxide precursor was promoted by impregnation with 5% wt ruthenium acetate in acetic acid and then drying at 105⁰C for 3 hours. The resulting Ru-promoted catalyst precursor was not calcined. The analysis of the catalyst precursors gave the following;

BET surface areas were measured for the catalyst precursor 1(a), the uncoated alpha alumina and the comparative catalyst precursors. The results were as follows:

The ruthenium promoted catalyst gave the highest surface area result, followed by the Re- promoted catalyst.

Temperature-programmed reduction (TPR) experiments can be useful in predicting the behaviour of catalysts during reduction in situ. Thermal conductivity measurements were made on a sample exposed to hydrogen over time with increasing temperature using an AMI-200 instrument available from Altamira Instruments. The TPR experiments were run using 70- 80mg of catalyst precursor in a quartz tube held in place by quartz wool plugs. The catalyst precursor was heated to 1000⁰C from ambient at a rate of 10°C/min under a flow of 30ml/min of 10% H₂/Ar, and then held at 1000⁰C for ten minutes.

Figures 1 - 4 depict Examples 1(a)-(d) respectively and show the thermal conductivity changes associated with the reduction of of Co₃O₄ to CoO and then CoO to Co metal as the temperature is increased and with time. The figures show the copper, ruthenium and platinum containing catalysts to be reduced below 300°C and well below that of the corresponding un-promoted catalyst. The rhenium and lanthanum catalyst precursors were reduced at higher temperatures than the un-promoted catalyst precursor under these conditions. The results were as follows;

A series of two-step TPR experiments were performed as above, except that in the first step the catalyst was heated to 22O⁰C at 10°C/min, and held for 10 hours, then in the second step heated to 1000⁰C at 10°C/min and held for 10 minutes. By comparing the two experiments, the degree of reduction at 22O⁰C can then be calculated.

A further comparative example was done using a catalyst prepared on the gamma alumina using the co-impregnation method described above. The gamma alumina used was HP14- 150. The resulting Co content of the precursor was 16.4% and the Ru content, 0.77%. The results were as follows;

It can be seen that the degree of reduction obtained with the Ru or Pt catalyst is better than the copper catalyst or the catalyst prepared using gamma alumina.

Example 2: Preparation of silica-supported catalyst precursors

(i) Co-impregnation method. An impregnation solution was prepared by dissolving 5% wt ruthenium acetate in acetic acid and cobalt nitrate hexahydrate in demineralised water. The powdered silica (a precipitated silica with BET surface area of 342m²/g and a pore diameter of 6.6 nm) was treated with the solution by the dry impregnation method, dried at 105⁰C for 3 hours and calcined by heating to 400⁰C at 2°C/min, and holding at this temperature for 1 hour. A single impregnation was used. The resulting catalyst precursor had an estimated cobalt content of 18% by weight and an estimated ruthenium content of 1% by weight.

A platinum-promoted catalyst was prepared using the same method except that platinum nitrate was used,to obtain a catalyst precursor having an estimated cobalt content of 18% wt and an estimated Pt content of 1 % wt.

TPR experiments were performed according to the method described in Example 1. The TPR plot of the silica-supported Ru-promoted Co catalyst is depicted in Figure 5, along with that of a comparable un-promoted catalyst precursor and clearly shows the lower reduction temperature for the catalyst precursors of the invention. On silica, the performance of Pt as a reduction promoter is similar to that of Ru. The results are given below.

A two-step TPR experiment was also performed according to the method described in Example 1 and showed a degree of reduction of 86% for the Ru-promoted catalyst precursor.

Example 3: In situ reduction tests and FT Reactivity

The catalyst precursor of Example 1(a) was used for the Fischer-Tropsch synthesis of hydrocarbons in a laboratory-scale tubular reactor. About 0.1 g of catalyst precursor mixed with SiC was placed in bed (ca. 4 mm ID by 50 mm depth) and reduced by passing a reducing gas stream through the bed using three different regimes; a) reduction at 21O⁰C for 7 hours under hydrogen gas, b) reduction at 21O⁰C for 7 hours under a synthesis gas comprising hydrogen and carbon monoxide at a ratio of 2:1 and, c) for comparison, reduction at 38O⁰C for 7 hours under hydrogen gas.

Following the reduction step, the samples were cooled to 100°C, the flow for (a) and (c) changed to the synthesis gas and the pressure increased to 20 barg. The temperature was then increased at 1°C/min to 21O⁰C and the Fischer-Tropsch reaction monitored over 120 hrs. The space velocity during reduction was 14400hr^"1 and this was maintained until 30 hrs at which point it was reduced to 3600hr^"1. The activity and selectivity of the catalyst to CH₄, C2- C4 and C5+ hydrocarbons were measured using known Gas Chromatography (GC) techniques. The results at 40 hrs, 100 hrs and 120 hrs for the catalyst reduced according to the different regimes are given below. 40hrs at Fischer-Tropsch conditions

The results show that the activity relative to the precursor reduced at 38O⁰C is maintained and that the selectivity of the catalysts reduced under hydrogen or syngas is comparable.

Claims

Claims.

1. A catalyst precursor comprising 5 to 50% by weight of one or more oxidic cobalt compounds selected from CoO, CoO(OH) and Co₃O₄ and 0.05 to 10% by weight of one or more reduction promoter selected from metals or compounds of Ru, Pt, Cu, Rh, Pd, Ir, Ag and Bi, supported on an inert support selected from alpha alumina, a metal- aluminate, silica, titania, zirconia, zinc oxide, silicon carbide, carbon or mixtures thereof, wherein the cobalt is in a highly reducible form such that at least 75% of the cobalt is reducible by a reducing gas stream at temperatures < 24O⁰C.

2. A catalyst precursor according to claim 1 wherein the reduction promoter is a compound or metal of Ru, Pt or Cu.

3. A catalyst precursor according to claim 2 wherein the reduction promoter is Ru or an oxide of Ru.

4. A catalyst precursor according to any one of claims 1 to 3 wherein the inert support is alpha alumina.

5. A catalyst precursor according to any one of claims 1 to 4 further comprising one or more additives selected from compounds of metals selected from molybdenum (Mo), iron (Fe), manganese (Mn), titanium (Ti), zirconium (Zr), lanthanum (La), cerium (Ce), chromium (Cr), magnesium (Mg) or zinc (Zn).

6. A catalyst precursor according to any one of claims 1 to 5 wherein the catalyst precursor is a powder with a surface-weighted mean diameter D[3,2] in the range 1 to 200 μm.

7. A catalyst precursor according to any one of claims 1 to 6 wherein the catalyst precursor is a powder with a surface-weighted mean diameter D[3,2] on average, in the range from 1 to 20 μm.

8. A catalyst precursor according to any one of claims 1 to 5 wherein the support and hence the resulting catalyst precursor is in the form of a shaped unit having a particle size in the range 1-25 mm and an aspect ratio of less than 2.

9. A catalyst precursor according to any one of claims 1 to 5 wherein the support is in the form of a wash-coat on a ceramic, metal, carbon or polymer substrate.

10. A process for activating a catalyst comprising placing a catalyst precursor according to any one of claims 1 to 9 in a Fischer-Tropsch reactor and passing a reducing gas mixture over the catalyst precursor for a period of time to reduce cobalt present therein to elemental form, wherein the temperature of the reducing gas mixture throughout the activation step is < 24O⁰C.

11. A process according to claim 10 wherein at least 90% of the reducible cobalt is reduced at < 24O⁰C.

12. A process according to claim 10 or claim 11 wherein the Fischer Tropsch reactor is a fixed bed reactor or a slurry phase reactor.

13. A process according to any one of claims 10 to 12 wherein the reducing gas mixture is hydrogen, synthesis gas or a mixture of hydrogen and/or carbon monoxide with nitrogen or other inert gas.

14. A process according to claim 13 wherein the reducing gas mixture comprises >90% vol hydrogen.

15. A process according to claim 13 wherein the reducing gas mixture comprises a synthesis gas mixture.

16. A process according to any one of claims 10 to 15 wherein the reducing gas mixture is passed over the catalyst precursor at temperatures in the range 140-240°C for between 1 and 16 hours.

17. A process for the Fischer-Tropsch synthesis of hydrocarbons by passing a gas mixture comprising hydrogen and carbon monoxide over a catalyst in a Fischer-Tropsch reactor that has been activated according to the process of any one of claims 10 to 16

18. A process according to claim 17 wherein the mixture of carbon monoxide and hydrogen is a synthesis gas having a hydrogen: carbon monoxide ratio in the range 1.6-3.0:1

19. A process according to claim 17 or claim 18 wherein the reaction is operated at pressures in the range 0.1-10Mpa and temperatures in the range 150-350⁰C.

20. A process according to any one of claims 17 to 19 wherein the Fischer Tropsch reactor is a fixed bed reactor or a slurry phase reactor.