FISCHER-TROPSCH SYNTHESIS CATALYST, AND PROCESS FOR

PRODUCING HYDROCARBONS USING THE SAME This invention relates to a process for activating a Fischer-Tropsch synthesis catalyst.

In particular, the invention relates to a process comprising a carbon monoxide reduction step followed thereafter by a separate hydrogen reduction step for producing an activated Fischer-Tropsch synthesis catalyst which exhibits improved selectivity for C ₅₊

hydrocarbons in subsequent Fischer-Tropsch reactions.

The conversion of synthesis gas into hydrocarbons by the Fischer-Tropsch process has been known for many years. The growing importance of alternative energy sources has seen renewed interest in the Fischer-Tropsch process as one of the more attractive direct and environmentally acceptable routes to high quality transportation fuels.

Many metals, for example cobalt, nickel, iron, molybdenum, tungsten, thorium, ruthenium, rhenium and platinum are known to be catalytically active, either alone or in combination, in the conversion of synthesis gas into hydrocarbons and oxygenated derivatives thereof. Of the aforesaid metals, cobalt, nickel and iron have been studied most extensively. Generally, the metals are used in combination with a support material, of which an example is titanium dioxide (titania).

In the preparation of cobalt-containing Fischer-Tropsch catalysts, a solid support is typically impregnated with a cobalt-containing compound, which may for instance be an organometallic or inorganic compound (e.g. Co(N0 ₃ )2.6H ₂ 0), by contacting with a solution of the compound. The particular form of cobalt-containing compound is generally selected for its ability to form a cobalt oxide (for instance, CoO, Co ₂ 0 ₃ or Co ₃ 0 ₄ ) following a subsequent calcination/oxidation step. Following generation of the supported cobalt oxide, a reduction step is necessary in order to form the pure cobalt metal as the active catalytic species. Thus, the reduction step is also commonly referred to as an activation step.

Various different methods of either activating a fresh Fischer-Tropsch catalyst or regenerating a used Fischer-Tropsch catalyst have been proposed. Historically, supported cobalt oxide catalyst precursors were reduced by means of hydrogen at elevated

temperature, before being transferred under inert conditions to the reactor. Typically, reduction in the presence of hydrogen is conducted at above 300 °C. For example, WO 03/035257 and WO 06/075216 disclose a two-step reduction of a Fischer-Tropsch catalyst precursor with hydrogen, wherein the final reduction stage is conducted with pure hydrogen gas at a temperature of from 300 °C to 600 °C.

US 4,626,552 also proposes a pretreatment of the catalyst with hydrogen gas mixed with a minor proportion of carbon monoxide. DE 977498 describes the pretreatment of a catalyst comprising a Group VIII metal, preferably iron, with a carbon monoxide containing gas.

US 8,557,879 describes a process for producing an activated Fischer-Tropsch synthesis catalyst having improved initial catalyst activity comprising a hydrogen reduction step at a temperature of from 300 °C to 600 °C, preferably followed by a separate carbon monoxide reduction step at a temperature of from 200 °C to 400 °C.

US 5,585,316 describes a method for the pretreatment of a cobalt-containing catalyst with a gas containing carbon monoxide and less than 30 vol.% hydrogen, preferably no hydrogen. This method is reported to afford improvements in selectivity for C ₅ + hydrocarbons in subsequent Fischer-Tropsch reactions over conventional pretreatment processes employing a hydrogen reduction at elevated temperatures of, for instance, 320 °C (Comparative Example 2).

There remains a need for a process for producing an activated Fischer-Tropsch synthesis catalyst which exhibits improved selectivity for C ₅₊ hydrocarbons, and preferably also catalytic activity, in subsequent Fischer-Tropsch reactions, which hydrocarbons are of most value for preparing fuel compositions.

It has now surprisingly been found that a reductively activated cobalt-containing Fischer-Tropsch catalyst, exhibiting improved selectivity for C ₅₊ hydrocarbons, as well as improved catalytic activity in at least some embodiments, in subsequent Fischer-Tropsch reactions may be prepared by a process comprising two distinct reduction steps. In particular, the activation process comprises a first carbon monoxide reduction of a cobalt- containing Fischer-Tropsch catalyst precursor, followed by a separate hydrogen reduction step, resulting in a limited degree (or extent) of reduction of a titanium dioxide supported cobalt catalyst, (commensurately a lessened extent of reduction of the catalyst when it is subsequently exposed to the feed).

The present invention thus provides a process for the production of a reductively activated cobalt-containing Fischer-Tropsch catalyst supported on a support material comprising titanium oxide, said process comprising i) a carbon monoxide reduction step comprising contacting a cobalt-containing Fischer-Tropsch catalyst with a gaseous stream comprising carbon monoxide and less than 10 vol.% hydrogen based on the volume of carbon monoxide; followed by ii) a hydrogen reduction step comprising contacting the product of the carbon monoxide reduction step i) with a gaseous stream comprising hydrogen and less than 10 vol.% carbon monoxide based on the volume of hydrogen such that the reductively activated cobalt-containing Fisher-Tropsch catalyst comprises from 30% to 95% metallic cobalt by weight of cobalt.

The order of the reduction steps has been found to be key to the present invention.

When the cobalt-containing catalyst undergoes a first reduction with carbon monoxide, it has been found that a subsequent, separate hydrogen reduction step generally improves selectivity for C ₅₊ hydrocarbons in subsequent Fischer-Tropsch reactions, beyond that which is achievable by either a carbon monoxide reduction or hydrogen reduction alone. In at least some embodiments, the catalytic activity of the reductively activated cobalt- containing catalyst prepared in accordance with the process of the invention is also improved over those processes comprising either a carbon monoxide reduction or hydrogen reduction alone. Furthermore, the temperature of the subsequent hydrogen reduction step appears to have a more than additive affect upon C ₅₊ hydrocarbon selectivity in subsequent Fischer-Tropsch reactions and while it may be in the range of from 100 °C to 500 °C, or 200 °C to 350 °C, the temperature of the subsequent hydrogen reduction step is therefore advantageously in the range of from 200 °C to 300 °C, preferably 220 °C to 280 °C, most preferably 230 °C to 260 °C (or 230 °C to 250 °C), for example 240 °C. As used herein, temperatures may refer to feed temperatures, applied temperatures and/or catalyst bed temperatures.

These preferred embodiments of the process of the present invention are thus further unexpected since conventional processes for activation of a Fischer-Tropsch synthesis catalyst which include a hydrogen reduction step are typically conducted at temperatures exceeding 300 °C. Meanwhile, in terms of selectivity for C ₅ + hydrocarbons in subsequent Fischer-Tropsch reactions, according to the prior art (for instance, US

5,585,316) a single carbon monoxide reduction step is favored. The carbon monoxide reduction step i) of the process of the present invention comprises contacting a cobalt-containing Fischer- Tropsch catalyst with a gaseous stream comprising carbon monoxide and less than 10 vol.% hydrogen based on the volume of carbon monoxide. The gaseous stream comprising carbon monoxide used in step i) of the process of the invention may, in addition to carbon monoxide, comprise inert diluent gases such as argon, helium, nitrogen, hydrocarbons such as methane, and/or water vapour. For the avoidance of any doubt, the upper limit of hydrogen which may be present in the carbon monoxide-containing gaseous stream as reported herein is relative only to the volume of carbon monoxide in the gaseous stream, and not relative to the combined volume of carbon monoxide and any inert diluents.

Preferably, the carbon monoxide containing gaseous stream comprises from 5 to 50 vol.% of carbon monoxide with the balance comprising inert diluents, more preferably the carbon monoxide containing gaseous stream comprises from 15 to 35 vol.% of carbon monoxide, and the balance comprising inert diluents. Still more preferably, the carbon monoxide containing gaseous stream comprises from 20 to 30 vol.% carbon monoxide, and the balance comprising inert diluents. In other embodiments, the carbon monoxide containing gaseous stream comprises up to 80 vol.%, up to 90 vol.% or even up to 95 vol.%) carbon monoxide.

Preferably, the carbon monoxide-containing gaseous stream comprises less than 5 vol.% hydrogen based on the volume of carbon monoxide, more preferably less than 2 vol.%, yet more preferably less than 1 vol.%. Most preferably, the carbon monoxide- containing gaseous stream comprises substantially no hydrogen.

Suitably, the temperature at which the carbon monoxide reduction is performed is from 100 °C to 500 °C, preferably 200 °C to 350 °C. For example, the temperature at which the carbon monoxide reduction is performed may be from 120 °C to 350 °C, from 150 °C to 280 °C, from 160 °C to 240 °C or from 170 °C to 200 °C. The carbon monoxide reduction step may be carried out at any desired pressure, for instance from 10 to 5500 kPa, preferably from 20 to 3000 kPa, more preferably from 50 to 1000 kPa, and even more preferably from 100 to 800 kPa. More preferably, the carbon monoxide reduction step is performed at atmospheric pressure.

The carbon monoxide-containing gas is suitably passed over the catalyst bed at a gas hourly space velocity (GHSV) in the range from 100 to 10000 h ^"1 (gas volumes converted to standard temperature and pressure), preferably from 250 to 5000 h ^" , such as from 250 to 3000 h ^"1 and more preferably from 250 to 2500 h ^"1 (or 250 to 2000 h ^"1 ), for example 1000 h ^"1 .

Suitably, the carbon monoxide reduction step is conducted over a period of at least 30 minutes, preferably over a period of from 1 to 24 hours, more preferably over a period of from 2 to 18 hours, most preferably over a period of from 3 to 12 hours. These durations particularly apply in combination with the exemplified temperature ranges above.

The carbon monoxide reduction step, in addition to leading to at least partial reduction of the oxidic cobalt of the catalyst precursor, is thought to lead to the formation of coke deposits on the catalyst, thus potentially blocking active sites thereby affecting catalyst selectivity and activity. However, this coking may be removed upon a subsequent treatment with hydrogen.

Thus, reversing the order of the carbon monoxide and hydrogen reduction steps is considered to be detrimental to at least the C ₅₊ hydrocarbon selectivity of the resulting reductively activated catalyst. This is because of the propensity for the carbon monoxide reduction to lead to coke deposition, which cannot be ameliorated without a subsequent hydrogen reduction step. Moreover, it is believed that the hydrogen reduction step performed on a catalyst material which has been exposed to coking in accordance with the present invention produces a superior activated catalyst compared to one which is prepared following a hydrogen reduction of an un-coked catalyst.

In step ii) of the reductive activation process of the present invention, the product of the carbon monoxide reduction step i) is subjected to a hydrogen reduction comprising contacting with a gaseous stream comprising hydrogen and less than 10 vol.% carbon monoxide based on the volume of hydrogen.

For the avoidance of doubt, hydrogen referred to herein as a component of the hydrogen containing gaseous stream corresponds to molecular hydrogen (H ₂ gas).

The gaseous stream comprising hydrogen used in step ii) of the process of the invention may, in addition to hydrogen, comprise inert diluent gases such as argon, helium, nitrogen and/or water vapour. For the avoidance of any doubt, the upper limit of carbon monoxide which may be present in the hydrogen-containing gaseous stream as reported herein is relative only to the volume of hydrogen in the gaseous stream, and not relative to the combined volume of hydrogen and any inert diluents.

Preferably, the hydrogen containing gaseous stream comprises from 5 to 60 vol.% of hydrogen with the balance comprising inert diluents, more preferably the hydrogen containing gaseous stream comprises from 15 to 50 vol.% of hydrogen, and the balance comprising inert diluents. Still more preferably, the hydrogen containing gaseous stream comprises from 25 to 40 vol.% hydrogen, and the balance comprising inert diluents. In other embodiments, the hydrogen containing gaseous stream comprises up to 80 vol.%, up to 90 vol.% or even up to 95 vol.% hydrogen. In some embodiments, the hydrogen containing gaseous stream consists essentially of hydrogen in the absence of diluents.

Preferably, the hydrogen-containing gaseous stream comprises less than 5 vol.% carbon monoxide based on the volume of hydrogen, more preferably less than 2 vol.%, yet more preferably less than 1 vol.%. Most preferably, the hydrogen-containing gaseous stream comprises substantially no carbon monoxide.

The hydrogen reduction step is typically carried out at a temperature of from 100 °C to 500 °C, or 200 °C to 350 °C but is preferably at a temperature of from 200 °C to 300 °C, preferably 220 °C to 280 °C, most preferably 230 °C to 250 °C, for example 240 °C. The hydrogen reduction step may be carried out at any desired pressure, for instance from from 10 to 5500 kPa, preferably from 20 to 3000 kPa, more preferably from 50 to 1000 kPa, and even more preferably from 100 to 800 kPa. More preferably, the hydrogen reduction step is carried out at atmospheric pressure.

The hydrogen-containing gas is suitably passed over the catalyst bed at a gas hourly space velocity (GHSV) in the range from 100 to 10000 h ^"1 (gas volumes converted to standard temperature and pressure), preferably from 250 to 5000 h ^"1 , such as from 250 to 3000 h ^"1 and more preferably from 250 to 2500 h ^"1 (or 250 to 2000 h ^"1 ), for example 1000 h ^"1 .

Suitably, the hydrogen reduction step is conducted over a period of at least 30 minutes, preferably over a period of from 1 to 48 hours, more preferably over a period of from 6 to 36 hours, most preferably over a period of from 8 to 18 hours. These durations particularly apply in combination with the exemplified temperature ranges above.

Without being bound to any particular theory, it is thought that the two stage reduction may lead to the formation of an enhanced level of available active cobalt metal, or otherwise favourable distribution of available active cobalt metal over the catalyst surface, giving rise to the superior C ₅₊ hydrocarbon selectivity in subsequent Fischer- Tropsch reactions. The level of reduction and/or distribution of active cobalt metal species is also believed to be dictated largely by the temperature of the subsequent hydrogen reduction step, which is preferably from 200 °C to 300 °C, indicating that the temperature of this reduction influences the nature of the surface reactions favorably. Notably, hydrogen only reductions conducted outside the above range of temperature gave inferior results in terms of C ₅₊ hydrocarbon selectivity in subsequent Fischer-Tropsch reactions while within the preferred ranges of the present invention, it .

At least prior to reductive activation, the cobalt-containing catalyst referred to herein comprises a reducible cobalt species which may upon reduction be converted to cobalt metal, i.e. the predominant catalytic species. In particular, the cobalt-containing catalyst preferably at least partially comprises cobalt in the form of an oxide, for example CoO, Co ₂ 0 ₃ and/or Co ₃ 0 ₄ , at least prior to reductive activation.

The cobalt-containing catalyst for reductive activation in accordance with the method of the invention may be a freshly prepared catalyst material. Alternatively, the cobalt-containing catalyst may be obtained from a cobalt-containing material which has previously been used for catalyzing a Fischer-Tropsch reaction. If necessary, the cobalt- containing material which has previously been used for catalyzing a Fischer-Tropsch reaction is subjected to a passivation step, so as to convert at least a part of the cobalt contained in the material into the oxide form.

Generally, the cobalt-containing material which has previously been used in a Fischer-Tropsch reaction may be passivated by treating at elevated temperature with a gas containing molecular oxygen, such as air, prior to reductive activation in accordance with the present invention. Such passivation desirably increases the proportion of oxidic cobalt in the cobalt-containing material which has been previously used in a Fischer-Tropsch reaction. The elevated temperature for this passivation is usually in the range of from 100 °C to 500 °C, preferably 120 °C to 250 °C. The treatment may be carried out at any desired pressure, atmospheric pressure being preferred.

The optimum treatment time will depend upon the history of the cobalt- containing material, on the oxygen content of the gas used and on the treatment conditions. The treatment time should in general be of sufficient length to remove any carbonaceous residues present on the cobalt containing material, and is thus especially useful with a cobalt-containing material which has previously been used in Fischer-Tropsch reactions. Treatment times of at least 30 minutes, preferably from 1 to 48 hours, are preferred.

The reductive activation process according to the present invention may therefore be used as an activation for a fresh cobalt-containing catalyst, or it can be used as part of a regeneration sequence for a cobalt-containing material which has already been used in a Fischer-Tropsch reaction. In either case, the treatment leads to improved performance in subsequent Fischer-Tropsch reactions. Such an improvement is not seen with conventional activation or regeneration treatments such as a single reduction step with hydrogen at elevated temperature, or a single reduction step with carbon monoxide.

Thus, in further aspects, the present invention also provides a use of a cobalt- containing Fischer-Tropsch catalyst prepared by a process described herein for increasing selectivity towards C _{5 +} hydrocarbons, and preferably also catalytic activity, in a Fischer- Tropsch reaction, and the catalyst itself. As this use and this catalyst are associated with the process for the production of a reductively activated cobalt-containing Fischer-Tropsch catalyst as herein described, any features of the process for the production of a reductively activated cobalt-containing Fischer-Tropsch catalyst are applicable to these aspects, either individually or in any combination.

The cobalt-containing Fischer-Tropsch catalyst is supported on a support material comprising titanium dioxide. For example, the support material may be a titanium dioxide support material or may consist of titanium dioxide.

The cobalt-containing Fischer-Tropsch catalyst may be prepared by any suitable method of which the skilled person is aware. For example, it may be prepared by impregnation, precipitation or gelation. A suitable Fischer-Tropsch catalyst may also be prepared by mulling or kneading the support material with either of a soluble or insoluble cobalt compound, before extruding, drying and calcining the product.

A suitable impregnation method, for example, comprises impregnating a support material with a compound of cobalt which is thermally decomposable to the oxide form. Any suitable impregnation technique including the incipient wetness technique or the excess solution technique, both of which are well-known in the art, may be employed. The incipient wetness technique is so-called because it requires that the volume of

impregnating solution be predetermined so as to provide the minimum volume of solution necessary to just wet the entire surface of the support, with no excess liquid. The excess solution technique as the name implies, requires an excess of the impregnating solution, the solvent being thereafter removed, usually by evaporation.

The impregnation solution may suitably be either an aqueous solution or a nonaqueous, organic solution of the thermally decomposable cobalt compound. Suitable non- aqueous organic solvents include, for example, alcohols, ketones, liquid paraffinic hydrocarbons and ethers. Alternatively, aqueous organic solutions, for example an aqueous alcoholic solution, of the thermally decomposable cobalt compound may be employed.

Suitable soluble compounds include for example the nitrate, acetate or

acetylacetonate, preferably the nitrate, of cobalt. It is preferred to avoid the use of the halides because these have been found to be detrimental.

Impregnation may be conducted with a support material which is in a powder, granular or pelletized form. Alternatively, impregnation may be conducted with a support material which is in the form of a shaped extrudate.

A suitable precipitation method for producing the cobalt-containing catalyst comprises, for example, the steps of: (1) precipitating at a temperature in the range from 0 °C to 100 °C cobalt in the form of an insoluble thermally decomposable compound thereof using a precipitant comprising ammonium hydroxide, ammonium carbonate, ammonium bicarbonate, a tetraalkylammonium hydroxide or an organic amine, and (2) recovering the precipitate obtained in step (1).

In contrast to impregnation methods, any soluble salt of cobalt may be employed.

Suitable salts include, for example, carboxylates, chlorides and nitrates. It is preferred to use aqueous solutions of the cobalt salt(s), although aqueous alcoholic solutions for example may be employed if desired.

As regards the precipitant, in addition to ammonium carbonate, ammonium bicarbonate and ammonium hydroxide, tetraalkylammonium hydroxides and organic amines may also be used. The alkyl group of the tetraalkylammonium hydroxide may suitably be a Ci to C ₄ alkyl group. A suitable organic amine is cyclohexylamine.

Experiments have shown that the use of alkali metal precipitants lead to very much inferior catalysts. It is therefore preferred to avoid the presence of alkali metals in the catalyst composition. Compositions free from alkali metal may suitably be produced using as the precipitant either ammonium carbonate or ammonium bicarbonate, even more preferably ammonium bicarbonate. Ammonium carbonate may suitably be used in a commercially available form, which comprises a mixture of ammonium bicarbonate and ammonium carbamate. Instead of using a pre-formed carbonate or bicarbonate it is possible to use the precursors of these salts, for example a soluble salt and carbon dioxide.

Irrespective of the method for preparing the cobalt-containing material, it is usually necessary to convert the cobalt-containing material into a catalyst comprising cobalt in the oxide form, for subsequent reductive activation in accordance with the present invention. Calcination may be used to afford a catalyst comprising cobalt in the oxide form by, for instance, causing thermal-decomposition of a thermally decomposable compound of cobalt formed previously. Calcination may be performed by any method known to those of skill in the art, for instance in a fluidized bed or rotary kiln at a temperature suitably in the range from 200 °C to 700 °C. In some embodiments, calcination may be conducted as part of an integrated process also comprising the reductive activation and performed in the same reactor.

The amount of cobalt compound present in the cobalt-containing catalyst is not particularly limited. According to some embodiments of the present invention, the catalyst comprises from 5% to 40%, preferably from 5% to 35%, more preferably from 10% to 30% and more preferably from 15% to 25%, cobalt, or cobalt compound, by weight of the catalyst. Alternatively, the amount of cobalt compound present in the cobalt-containing catalyst may be from 5% to 30%, preferably from 5%» to 25% and more preferably from 10% to 20% cobalt, or cobalt compound, by weight of the catalyst.

The cobalt-containing catalyst may additionally comprise one or more promoters, which may promote reduction of an oxide of cobalt to cobalt metal, preferably at lower temperatures. Preferably, the one or more promoters is selected from the list consisting of ruthenium, palladium, platinum, rhodium, rhenium, manganese, chromium, nickel, iron, molybdenum, boron tungsten, zirconium, gallium, thorium, lanthanum, cerium and mixtures thereof.

The promoter is typically used in a cobalt to promoter atomic ratio of up to 250:1 and more preferably up to 125: 1, still more preferably up to 25:1, and most preferably 10:1. A promoted catalyst may be prepared by a variety of methods including

impregnation, precipitation or gelation.

The promoter may be added at one or more of the catalyst preparation stages including: during precipitation as a soluble compound; precipitation by incipient wetness impregnation; or following calcination of the cobalt comprising precipitate.

The cobalt-containing catalyst may also be a composition additionally comprising titanium dioxide, as described, for instance, in US7851404. Such a composition is preferably made by the preferred process described therein.

The reductive activation process of the present invention is preferably carried out batch wise in a fixed bed reactor. In at least some embodiments, the reductive activation process of the present invention is conducted in the same reactor as the subsequent Fischer- Tropsch synthesis reaction.

The carbon monoxide-containing gaseous stream and/or the hydrogen-containing gaseous stream may be separately fed into the reactor in the gas-phase, or alternatively as a condensed phase which vaporizes within the reactor so that it contacts the solid catalyst in the gas-phase. The process of the present invention may optionally comprise a plurality of reactors arranged in series, such that any composition removed from the first reactor is fed to a second reactor, and composition removed from the second reactor is fed to a third reactor and so on.

Thus, in one embodiment, the cobalt-containing catalyst may be contacted with the carbon monoxide gaseous stream in one reactor before the product of that reduction is transferred to a second reactor for contacting with the hydrogen gaseous stream. In an alternative embodiment, both reduction steps i) and ii) according to the process of the present invention are conducted in the same reactor.

Advantageously, the reductively-activated catalyst produced by the process of the present invention comprises from 35% to 90% metallic cobalt by weight of cobalt, preferably from 40% to 85% (or 50% to 85%) metallic cobalt by weight of cobalt, such as from 70% to 80%> metallic cobalt by weight of cobalt. Within these preferred ranges, the selectivity/activity is surprisingly further improved. As used herein, the general term "cobalt" includes cobalt either in metallic (elemental) form or as part of a cobalt compound (i.e. referring to the total cobalt present), so for example where the catalyst is referred to as "comprising cobalt", it is intended to mean that the catalyst comprises metallic/elemental cobalt and/or at least one cobalt compound. Commensurately, the mass of cobalt includes the total mass of cobalt atoms and ions present, i.e. ignoring any other ions in any cobalt compounds. As used herein, the more specific terms "metallic cobalt" or "elemental cobalt" mean cobalt in an oxidation state of zero, i.e. Co .

The percentage metallic cobalt by weight of cobalt (herein interchangeable with the degree of reduction) of the catalyst according to the present invention when used in a Fischer-Tropsch synthesis applies to the catalyst initially, which refers to process startup, i.e. the point in time at which the catalyst is first contacted with the feed. Accordingly, the percentage metallic cobalt by weight of cobalt applies to the catalyst immediately prior to, and/or substantially at the time of, introducing the feed to the catalyst to produce hydrocarbons, or may additionally or alternatively refer to the degree of reduction achieved by a reduction step, especially if such a reduction step is carried out in situ. Notably, it is thus recognised that exposing the catalyst to a Fischer-Tropsch feed at elevated

temperature may further impact the degree of reduction, for example to a level outside the claimed range, such as complete reduction. However, even if further reduction of the catalyst occurs upon, or following exposure to the feed, it has been found that the benefits of the present invention remain, and this is specifically included within the scope of the present invention.

As used herein, the degree of reduction may be measured using temperature programmed reduction (TPR). TPR is a technique for the characterisation of solid materials in which a catalyst (e.g. cobalt(II,III) oxide) is subjected to a programmed temperature increase while a reducing gas is passed over the sample. The effluent gas may be analysed by a thermal conductivity detector (TCD) or mass spectrometer (MS) to determine the decrease in reductant gas concentration or evolution of other species, such as water.

In order to determine the degree of reduction herein, a standard data set is produced by drying a sample and conducting TPR through to 100% reduction of the cobalt atoms present in the catalyst (e.g. corresponding to 100% reduction of Co ₃ 0 ₄ to Co ⁰ ). The standard data may thus be obtained in situ (i.e. within the TPR unit) by initially exposing the sample to a drying step including contacting the sample with argon gas at a GHSV of 1800 h ^"1 , ramping the temperature from 20°C to 120°C at a rate of 5°C/min then dwelling at 120°C for 15 min before cooling back to 20°C also under argon gas. The TPR itself may be performed utilising 4% H ₂ gas (in Argon), at a gas hourly space velocity (GHSV) of 3800 h ^"1 and ramping the temperature from 20°C to 800°C at a rate of 5°C/min. Sample data is generally produced by conducting the drying step as above, followed by the reduction step desired (for example 10 hours under 100% hydrogen gas at 240, 260, 280 or 300°C at a GHSV of 1800 h ^"1 ) and then conducting TPR through to 100% reduction. The sample data may thus be obtained in situ (i.e. within the TPR unit) by initially exposing the sample to a drying step including contacting the sample with argon gas at a GHSV of 1800 h ^"1 , ramping the temperature from 20°C to 120°C at a rate of 5°C/min then dwelling at

120°C for 15 min before cooling back to 20°C also under argon gas. For the reduction step itself, 100%) H ₂ gas may be utilised, also at a GHSV of 1800 h ^"1 and the temperature ramped from 20°C to 150°C at a rate of 2°C/min followed by slower ramping from 150°C to the desired reduction temperature at a rate of 1 °C/min before dwelling at the desired reduction temperature for 10 hours and cooling to 20°C under argon gas. The TPR itself is then conducted as described above. Utilising a TCD, a graph of thermal conductivity against temperature may be produced, with the conductivity approaching a baseline value at complete reduction. Comparison of the area under the TCD graph (relative to the baseline) obtained in the sample TPR data against the corresponding area of the standard TPR data allows the calculation of the relative amount of hydrogen consumed during prereduction between the sample and standard data. In practice, this involves subtracting the integrated area under the TCD graph obtained for the sample data from the area under the TCD graph for the standard data, then expressing the resultant value as a percentage of the integrated area from the standard data. Expressed as an equation, this is:

[Area of standard TPR data]— [Area of sample TPR data]

%H2 consumed = 100 x

[Area of standard TPR data]

Equation 1 : Method of calculating relative hydrogen consumption using TPR data TPR is an advantageous technique to utilise for determining degree of reduction because the technical measurements on a sample are made following the reduction step. Accordingly, while the % H ₂ consumed is calculated via the formula above, the data obtained is applicable even if another reducing gas (for example, carbon monoxide) has been used, merely being expressed as the equivalent % H ₂ consumed and enabling the stoichiometry from hydrogen reduction to be used in calculating the degree of reduction i.e. the percentage of cobalt atoms present as Co ⁰ . This is a preferred approach because determining simply the percentage ¾ consumed may correspond to a different relative amount of Co ⁰ produced by reduction for different catalysts, but Co ⁰ is understood to be the catalytically active species so in the context of the present invention it is desirable to understand the actual amount of Co ⁰ produced by reduction.

The complete reduction of cobalt oxide (Co ₃ 0 ₄ ) is a two-step process (firstly the reduction to cobalt(II) oxide, also known as cobaltous oxide, and then the reduction of cobalt(II) oxide to metallic cobalt) as shown by the chemical equations below:

Co ₃ 0 ₄ + ¾→ 3CoO + H ₂ 0

CoO + H ₂ → Co ⁰ + H ₂ 0

Equations 2 and 3: Step-wise reduction of cobalt(II,III) oxide to metallic cobalt

The overall reduction may alternatively be represented as a single stoichiometric equation:

Co ₃ 0 ₄ + 4H ₂ → 3CoO + H ₂ 0 + 3H ₂ → 3Co ^u + 4¾0 Equation 4: Overall reduction of cobalt(II,III) oxide to metallic cobalt

Accordingly, in the first step, 1 equivalent of H ₂ is consumed without producing any metallic cobalt, while in the second, 3 equivalents are consumed. In total, therefore, complete reduction requires 4 equivalents of H ₂ to reduce the 3 equivalents Co to Co ⁰ . However, the first step is believed to be much faster than the second so herein is assumed to proceed to completion before any formation of Co ⁰ occurs. The amount of hydrogen required to produce the metallic cobalt is thus higher per mole of metallic cobalt when the degree of reduction is lower, and tends towards the stoichiometric ratio of 4 moles of ¾ for every 3 moles of Co as 100% reduction is approached.

Taking this into account, the degree of reduction achieved in the sample may be calculated using the formula below:

4 [Area of sample TPR data]

% Degree of Reduction = 100 * (1 -

3 [Area of standard TPR data] Equation 5: Calculation of degree of reduction from TPR data.

More generally, for a reduction having stoichiometry whereby x equivalents of H ₂ are required before the rate determining step of the reduction, and y equivalents of H ₂ are required during and after the rate determining step, the degree of reduction may be calculated using the formula below:

(x + y} [Area of sample TPR data]

% Degree of Reduction = 100 * (1 - -— — - — H : =-¾

y [Area of standard TPR data] ^J

Equation 6: General Calculation of degree of reduction from TPR data

Using TPR as described above, the degree of reduction may thus be determined for a catalyst that has been reduced ex situ, e.g. following any period in storage, transport or other intermediate steps that may occur before the catalyst is used to produce

hydrocarbons, in order to be assured that the amount of cobalt metal present by weight of cobalt remains within the range of the present invention. If not, additional measures may be taken in order to achieve the required degree of reduction, for example additional reduction in situ or avoiding exposing the catalyst to an oxidising atmosphere during storage and transport. Such avoidance of oxidising atmospheres may be achieved by packing the catalyst in an inert (e.g. nitrogen) atmosphere, packing the catalyst in a reducing atmosphere (e.g. 5% H ₂ , 95% nitrogen by volume), passivating by creating a thin, protective oxide layer on the surface of the catalyst, or wax-coating the catalyst for storage and transport.

The reductively activated cobalt-containing catalyst formed following the process according to the present invention is useful in the heterogeneously catalysed production of hydrocarbons from a feed comprising a mixture of carbon monoxide gas and hydrogen gas (e.g. syngas) by Fischer-Tropsch synthesis, for example in the production of a diesel or aviation fuel or precursor thereof. Fischer-Tropsch synthesis of hydrocarbons from syngas may be represented by Equation 7: mCO + ( _2m+ i ₎ H ₂ → _m H ₂ 0 + C _m H _2m +2 Equation 7 As discussed hereinbefore, the process of the present invention has been

surprisingly found to afford a reductively activated cobalt-containing Fischer-Tropsch catalyst exhibiting high C ₅₊ hydrocarbon selectivity, which hydrocarbon distribution desirably encompasses C ₅ to C ₉ gasoline and C10-C20 diesel fractions. Furthermore, at least in some embodiments, the catalytic activity has also been found to be superior.

In accordance with an embodiment of the invention, the process comprises an additional step iii) of performing a Fischer-Tropsch synthesis reaction for forming hydrocarbons, said additional step comprising contacting the reductively activated cobalt- containing Fischer-Tropsch catalyst obtained in step ii) with a feed comprising a mixture of carbon monoxide and hydrogen gases, preferably in the form of a synthesis gas mixture (syngas).

The reductively activated cobalt-containing Fischer-Tropsch catalyst obtained in step ii) may be transferred to a different reactor for contacting with a mixture of carbon monoxide and hydrogen gases as part of the Fischer-Tropsch reaction according to step iii). Alternatively, both steps ii) and iii) may be conducted in the same reactor.

In another aspect, the present invention also provides a process for the conversion of a mixture of hydrogen and carbon monoxide, preferably in the form of a synthesis gas mixture, to hydrocarbons, which process comprises contacting a mixture of hydrogen and carbon monoxide with a reductively activated catalyst composition as hereinbefore described. The present invention also provides a product (preferably a fuel) comprising hydrocarbons obtained from such a process. As this process and product are associated with the process for the production of a reductively activated cobalt-containing Fischer- Tropsch catalyst as herein described, any features of the process for the production of a reductively activated cobalt-containing Fischer-Tropsch catalyst are applicable to these aspects, either individually or in any combination.

In the Fischer-Tropsch reactions described above, the volume ratio of hydrogen to carbon monoxide (H ₂ :CO) in the gaseous reactant mixture (e.g. in the feed and/or at the reactor inlet) is preferably in the range of from 0.5 : 1 to 5 : 1, more preferably from 1 : 1 to 3 : 1, and most preferably 1.6 : 1 to 2.2 : 1. The gaseous reactant stream may also comprise other gaseous components, such as nitrogen, carbon dioxide, water, methane and other saturated and/or unsaturated light hydrocarbons, each preferably being present at a concentration of less than 30% by volume. The temperature of the Fischer-Tropsch reaction is preferably in the range from 100 to 400 °C, more preferably from 150 to 350 °C, and most preferably from 150 to 250 °C. The pressure is preferably in the range from 1 to 100 bar (from 0.1 to 10 MPa), more preferably from 5 to 75 bar (from 0.5 to 7.5 MPa), and most preferably from 10 to 50 bar (from 1.0 to 5.0 MPa).

The gaseous reactants for the Fischer-Tropsch reaction may be fed into the reactor either separately or pre-mixed (e.g. as in the case of syngas). They may initially all contact the solid catalyst at the same portion of the solid catalyst, or they may be added at different positions of the solid catalyst. The initial point of contact of the one or more reactants with the solid catalyst is the point at which all the reactants initially contact each other in the gas-phase and in the presence of the solid catalyst. Preferably, the one or more gaseous reactants flow co-currently over the solid catalyst.

The gaseous reactant mixture used for the Fischer-Tropsch reaction may also comprise recycled materials extracted from elsewhere in the process, such as unreacted reactants separated from reduction steps i) and ii) according to the process of the invention.

The mixture of hydrogen and carbon monoxide is suitably passed over the catalyst bed at a gas hourly space velocity (GHSV) in the range from 100 to 10000 h ^"1 (gas volumes converted to standard temperature and pressure), preferably from 250 to 5000 h ^"1 , such as from 250 to 3000 h ^"1 and more preferably from 250 to 2000 h ^"1 .

As is well known in the art, synthesis gas, which is preferably used for the Fischer- Tropsch reaction, principally comprises carbon monoxide and hydrogen and possibly also minor amounts of carbon dioxide, nitrogen and other inert gases depending upon its origin and degree of purity. Methods of preparing synthesis gas are established in the art and usually involve the partial oxidation of a carbonaceous substance, e.g. coal. Alternatively, synthesis gas may be prepared, for example by the catalytic steam reforming of methane. The ratio of carbon monoxide to hydrogen present in the synthesis gas may be altered appropriately by the addition of either carbon monoxide or hydrogen, or may be adjusted by the so-called shift reaction well known to those skilled in the art.

The Fischer-Tropsch reaction is preferably carried out continuously in a fixed bed, fluidised bed or slurry phase reactor. When using the reductively activated cobalt- containing Fischer-Tropsch catalyst in a fixed bed process the particle size should be of such shape and dimension that an acceptable pressure drop over the catalyst bed is achieved. A person skilled in the art is able to determine the particle dimension optimal for use in such fixed bed reactors. Particles of the desired shape and dimension may be obtained by extrusion of a slurry to which optionally extrusion aids and/or binders may be added.

The invention will now be further illustrated by the following Examples. In the Examples CO conversion is defined as moles of CO used/moles of CO fed x 100 and carbon selectivity as moles of CO attributed to a particular product/moles of CO converted x 100. Unless otherwise stated, temperatures referred to in the Examples are applied temperatures and not catalyst/bed temperatures. Examples

Example 1

Catalyst Preparation

Cobalt oxide supported on titanium dioxide was manufactured as a catalyst by impregnating titanium dioxide powder with an aqueous solution of cobalt nitrate hexahydrate, followed by extrusion of the formed paste, and then drying and calcining to yield catalyst extrudates with a cobalt loading of 10% by weight of catalyst and a manganese loading of 1% by weight of catalyst.

Example 2

Reductive Activation - CO reduction followed by H? reduction

10 mL (1250 to 3000 μηι) of the catalyst prepared in Example 1 is charged into a microreactor. As part of a drying phase, nitrogen is introduced at GHSV - 950 h ^"1 and the temperature raised from room temperature to 180 °C at 20 °C. h ^"1 and the temperature maintained for 12 hours, before the reactor is cooled at 20 °C. h ^"1 to 1 10 °C. The gaseous supply is then switched to a mixture of carbon monoxide (25 vol.%) and nitrogen (75 vol.%) and introduced into the reactor at GHSV = 1000 h ^"1 before the temperature raised to 250 °C at 8 °C. hr ^"1 and maintained for 3 hours. The reactor is then cooled at 20 °C. h ^"1 to 110 °C. The carbon monoxide/nitrogen supply is then switched off and a mixture of hydrogen (50 vol.%) and nitrogen (50 vol.%) subsequently introduced at GHSV = 1000 h ^"1 before the temperature raised to 240 °C at 4 °C. h ^"1 and maintained for 16 hours, after which the reactor is cooled to 150 °C over the course of 1 h. The pressure is maintained at 7 bar.g (700 kPa.g) throughout.

Example 3 (Comparative) Reductive Activation - H? Only

10 mL (1250 to 3000μηι) of the catalyst prepared in Example 1 is charged into a microreactor. As part of a drying phase, nitrogen is introduced at GHSV = 950 h ^"1 and the temperature raised from room temperature to 180 °C at 20 °C. h ^"1 and the temperature maintained for 12 hours, before the reactor is cooled at 20 °C. h ^"1 to 110 °C. The reactor is heated to a temperature of 150 °C and the gaseous supply switched to a mixture of hydrogen (50 vol.%) and nitrogen (50 vol.%) and introduced into the reactor at GHSV = 1100 h ^"1 before the temperature raised to 240 °C at 4 °C. hr ^"1 and maintained for 32 hours, after which the reactor is cooled to 150 °C over the course of 1 h. The pressure is maintained at 7 bar.g (700 kPa.g) throughout.

Example 4 (Comparative)

Reductive Activation - CO Only

10 mL (1250 to 3000μηι) of the catalyst prepared in Example 1 is charged into a microreactor. As part of a drying phase, nitrogen is introduced at GHSV = 950 h ^"1 , the temperature raised from room temperature to 180 °C at 20 °C. h ^"1 and the temperature maintained for 12 hours, before the reactor is cooled at 20 °C. h ^"1 to 110 °C. The reactor is heated to a temperature of 250 °C and the gaseous supply switched to carbon monoxide (100 vol.%) and introduced into the reactor at GHSV = 1000 h ^"1 . The temperature of the reactor is maintained at 250 °C for 3 hours, after which the reactor is cooled to 150 °C over the course of 1 h. The pressure is maintained at 7 bar.g (700 kPa.g) throughout.

Example 5

Fischer-Tropsch synthesis reactions

The treated catalysts from Examples 2 to 4 are each exposed to Fischer-Tropsch reaction conditions in the same microreactor where respective pre-treatments are conducted. The same start-up procedure is used for each of the pre-treated catalysts. The gaseous supply is switched to a mixture of hydrogen (52.71 vol.%), carbon monoxide (29.28 vol.%) and nitrogen (18.00 vol.%), which is introduced into the reactor at GHSV = 2500 h ^"1 . Temperature is then increased from 150 °C to 160 °C at 60 °C. h ^"1 and maintained for 15 minutes. Temperature is then increased to 180 °C at 10 °C. h ^"1 and maintained for 15 minutes. Temperature is then increased to 190 °C at 5 °C. h ^"1 and maintained for 15 minutes. Finally, temperature is ramped so as to give approximately 65 % CO conversion in the Fischer-Tropsch synthesis reaction. The pressure in the reactor is maintained at 32 bar.g (3.2 MPa.g) throughout the start-up procedure and over the course of Fischer-Tropsch synthesis.

The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as "40 mm" is intended to mean "about 40 mm."

Every document cited herein, including any cross referenced or related patent or application, is hereby incorporated herein by reference in its entirety unless expressly excluded or otherwise limited. The citation of any document is not an admission that it is prior art with respect to any invention disclosed or claimed herein or that it alone, or in any combination with any other reference or references, teaches, suggests or discloses any such invention. Further, to the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern.

While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope and spirit of this invention.