CATALYST SUPPORT AND CATALYST FOR

FISCHER-TROPSCH SYNTHESIS

FIELD OF THE INVENTION

The present invention relates to a method of preparing a support comprising aluminate for a catalyst and to a method of preparing an aluminate supported catalyst. The invention also relates to the support comprising aluminate per se and to the aluminate supported catalyst per se as well as to the use of the catalyst in Fischer- Tropsch Synthesis of hydrocarbons. BACKGROUND

Conversion of natural gas to liquid hydrocarbons ("Gas To Liquids" or "GTL" process) is based on a 3 step procedure consisting of: 1 ) synthesis gas production; 2) synthesis gas conversion by Fischer-Tropsch (FT) synthesis; and 3) upgrading of FT products (wax and naphtha/distillates) to final products.

The Fischer-Tropsch reaction for conversion of synthesis gas, a mixture of CO and hydrogen, and possibly inert components such as C0 ₂ , nitrogen and methane, is commercially operated over catalysts containing the active metals Fe or Co. Iron catalysts are best suited for synthesis gas with low H ₂ /CO ratios (< 1 .2), e.g. from coal or other heavy hydrocarbon feedstock, where this ratio is considerably lower than the consumption ratio of the FT-reaction (2.0 - 2.1 ). The present invention is primarily concerned with Co-based catalysts, in particular, supported Co-based catalysts. A variety of products can be made by the FT reaction, but from supported cobalt, the primary product is long-chain hydrocarbons that can be further upgraded to products like diesel fuel and petrochemical naphtha. Byproducts can include olefins and oxygenates. One of the most important properties of a FT catalyst is its selectivity to producing longer hydrocarbons (i.e. its C ₅₊ selectively). The other key FT catalyst properties are its resistance towards deactivation and its activity.

To achieve sufficient catalytic activity in a FT synthesis, it is conventional to disperse the active metal such as Co on a catalyst carrier, often referred to as a support. In this way, a larger portion of the active metal is exposed as surface atoms where the reaction can take place. Suitable support materials include titania, silica and alumina, but other oxides and mixtures of oxides have also been employed. Commonly used supports in FT synthesis are often based on alumina. In general, the active metal, e.g. Co, is impregnated into the alumina support using a salt solution of the active metal. Optionally, a promoter can be added, and rhenium is a wellknown promoter for cobalt Fischer-Tropsch catalysts. Other promoters besides rhenium, specifically platinum, iridium or ruthenium, can be employed. It is also possible to add a stabiliser such as lanthanum oxide or a mixture of oxides of the lanthanides or other compounds which are difficult to reduce. A number of other promoters have also been described in the literature

Typically the impregnated support is then dried and calcined. Finally the active metal is activated by a reduction step, typically by treating the catalyst with a reducing gas.

Modifying agents can be used to treat supports before or after impregnation of the catalytically active metal. W099/42214, WO02/07883, WO03/012008, US6875720 and US7365040, for example, each disclose modification of a FT synthesis support with an agent to reduce the dissolution of the catalyst and/or its support in an aqueous environment. These documents all focus on the use of tetra-ethoxysilane (TEOS) as modifying agent. More recently WO2012/107844 describes the use of tungsten (W) instead of silicon based agents on the basis that tungsten is also effective at high calcination temperatures. US 5,356,845 discloses reactivation of a nickel on alumina catalyst by oxidation and then acid treatment of the supported catalyst.

WO2006/106357 discloses a method for the preparation of precipitated metal oxide catalyst supports, e.g. alumina supports, containing reduced levels of contaminants. Precipitated metal oxide supports are prepared by adding a base, often a Group 1 A or 2A metal hydroxide, to a metal salt solution such as aluminium sulphate, chloride or nitrate solution. The oxidic materials are subsequently separated, washed with water, dried and calcined. Contaminants such as metals from the base, however, are often present in undesirably high amounts. Most commonly sodium (Na) from sodium hydroxide is present.

WO2006/106357 teaches that the precipitated metal oxide catalyst support such as alumina may be washed with water and/or acid and/or base solutions to reduce the contaminants, such as Group 1 A or 2A metals, to provide more pure supports. Thus in the method of WO2006/106357 a precipitated metal oxide support is prepared then washed with acid, water and/or base. This removes, for example, the sodium left over as a contaminant in the support. The support is then dried and calcined. Example 5 of WO2006/106357 describes testing of the washed catalyst supports, once converted into catalysts, in Fischer-Tropsch synthesis. The results show that whilst catalyst activity is increased, that C ₅₊ selectivity is decreased. Contrary to the teaching of WO2006/106357, WO2005/072866 discloses a method of producing an aluminate-supported catalyst wherein a metal is added. The method comprises the following steps:

a first impregnation step in which an initial alumina support is impregnated with a source of a 2-valent metal capable of forming a spinel compound with alumina;

a first calcination step in which the impregnated alumina support is calcined at a temperature of at least 550 ^e C to produce a modified alumina support;

a second impregnation step in which the modified alumina support is impregnated with a source of catalytically active metal; and

a second calcination step in which the impregnated modified support is calcined at a temperature of at least 150 ^e C.

This is then followed by a reduction step to activate the cobalt.

The purpose of the first impregnation step, wherein a 2-valent metal is incorporated into the alumina support, is to improve the attrition resistance of the support. This is particularly important for supports that are ultimately used in FT synthesis carried out in a fluidised bed or slurry type reactor. The data in table 2 of WO2005/072866, which is partially reproduced below, clearly shows that the presence of a 2-valent metal in an aluminate support improves the attrition resistance of the support.

WO2005/072866 also teaches, however, that the use of divalent metals such as Mg and Ni to increase support strength does have a significant disadvantage. This is that catalytic activity is greatly reduced, particularly when Mg is used as the metal to improve support strength. Furthermore the use of Mg also tends to reduce C ₅₊ selectivity. This is clear from the data in table 3 of WO2005/072866 which is partially reproduced below. Modified alumina support Catalyst Relative Relative C ₅₊ [metal impregnated impregnation activity selectivity wt%/calcination temperature °C] (wt%/wt%)

— /1 140 20 Co/0.5 Re 0.75 0.988

— /1 140 12 Co/1 Re 0.66 1.007

5Mg/1 140 12 Co/0.5 Re 0.48 0.979

10Mg/1 140 12 Co/0.5 Re 0.38 0.952

3ΝΪ/1 140 12 Co/0.5 Re 0.66 0.991

This result correlates with the finding that catalysts on magnesium aluminates are known to give lower FT synthesis activity than the corresponding catalysts on nickel aluminates. The Journal of Catalysis, 284, (201 1 ), p 9-22, for example, describes a study wherein it was found that magnesium had a loading dependent negative effect on both activity and selectivity. Also Journal of Catalysis 279 (201 1 ), pp 163-173) deals with the negative effect of alkali and alkaline earth elements in FTS cobalt catalysts, including magnesium.

The teaching in the prior art is therefore somewhat contradictory. WO2006/106357 teaches that metal cations such as Na ⁺ , Ca ²⁺ and Mg ²⁺ introduced into a support during the precipitation reaction to prepare the base support itself (e.g. alumina) should be removed by, e.g. acid, washing. In contrast WO2005/072866 advocates introducing a divalent metal such as Mg ²⁺ or Ni ²⁺ into an alumina support to improve its attrition resistance. Both of WO2006/106357 and WO2005/072866 teach, however, that an effect of their processing (i.e. acid washing and addition of Mg ²⁺ respectively) is to decrease the C ₅₊ selectivity of FT catalysts prepared from the supports.

SUMMARY OF INVENTION

Viewed from a first aspect the present invention provides a method of preparing an aluminate support for a catalyst comprising:

(i) impregnating an alumina support with a divalent metal to produce an impregnated alumina support;

(ii) calcining said impregnated alumina support to produce a support comprising aluminate; and (iii) washing said support comprising aluminate with an acid to remove divalent metal not incorporated into the aluminate.

Viewed from a further aspect the present invention provides a method of preparing a catalyst comprising:

(i) preparing an aluminate support as hereinbefore defined; and

(ii) impregnating said aluminate support with a catalytically active metal to produce said catalyst.

Viewed from a further aspect the present invention provides an aluminate support obtainable by a method as hereinbefore defined.

Viewed from a further aspect the present invention provides a support for a catalyst comprising divalent metal aluminate and alumina, wherein said support comprises substantially no divalent metal of the type used to form the divalent metal aluminate that is a not a part of the aluminate.

Viewed from a further aspect the present invention provides use of a support as hereinbefore defined in the preparation of a catalyst.

Viewed from a further aspect the present invention provides a catalyst obtainable by a method as hereinbefore defined.

Viewed from a further aspect the present invention provides a catalyst comprising:

70-90 %wt divalent metal aluminate and alumina;

5-30 %wt catalytically active metal; and

0-3 %wt catalyst promoter,

wherein said catalyst comprises substantially no divalent metal of the type used to form the divalent metal aluminate that is a not a part of the aluminate.

Viewed from a further aspect the present invention provides use of a catalyst as hereinbefore defined in Fischer-Tropsch Synthesis.

Viewed from a further aspect the present invention provides a process for the production of hydrocarbons comprising subjecting H ₂ and C0 ₂ gases to a Fischer- Tropsch synthesis reaction in a reactor in the presence of a catalyst as hereinbefore defined.

Viewed from a further aspect the present invention provides a Fischer-Tropsch synthesis reaction comprising mixing H ₂ and C0 ₂ gases with a catalyst as hereinbefore defined. DEFINITIONS As used herein the term "alumina" refers to aluminium oxide, Al ₂ 0 ₃ . Alumina occurs in a number of forms including alpha and gamma. The term encompasses all of the different crystalline forms possible.

As used herein the term "aluminate" refers to a compound comprising an ionic lattice comprising aluminium cations, cations of a metal other than aluminium and oxygen anions. An example of a preferred aluminate is a spinel. The mineral spinel has the chemical formula MgAI ₂ 0 ₄ in which the oxygen atoms are in a ccp (cubic close packing) array. One-eighth of tetrahedral holes are occupied by Mg ²⁺ ions and one-half of octahedral holes are occupied by Al ³⁺ This structure, or the so-called inverse-spinel structure, is adopted by many other mixed-metal oxides, notably by substituting the divalent metal ion. In the present context the term spinel encompasses both of spinel and inverse spinel, as well as disordered spinels and solid solutions with the incorporated oxides. Metal ions that are not part of the aluminate, i.e. that do not constitute its lattice, may be in solid solution therein. Generally the metal ions in solid solution are present in the interstices of the lattice.

As used herein the term "support" refers to a material on which a catalyst can be dispersed. The purpose of the support is to increase the surface area of catalyst exposed. Often supports are in the form of particles. In some cases the support also enhances the effectiveness of the catalyst.

As used herein the term "impregnating" refers to the process of incorporating a species, e.g. metal ion, into the structure of a support. Typically the process involves exposing the support (e.g. by immersion) to a solution comprising the species to be impregnated therein.

As used herein the term "washing" refers to the process of contacting a support with a liquid, e.g. solution, under conditions that result in the removal of species that do form part of the ionic lattices (e.g. aluminate and/or alumina) forming the support. Washing, for example, preferably removes any divalent metal cations that are present in solid solution in the lattice. Usually the support is separated from the liquid used in the washing step in a follow up step.

As used herein the term "calcining" refers to a process of heating a support in the presence of air to cause a physiochemical change such as a thermal decomposition, phase transition, or removal of a volatile fraction.

As used herein the term "drying" refers to a process of heating a support to substantially remove the liquids therefrom. As used herein the terms "surface area", "pore volume" and "pore diameter" refer to surface area, pore volume and pore diameter as measured by the BET method using the nitrogen desorption isotherm and a TRISTAR3000 instrument from Micromeretics. The values reported herein are the BET surface area, the BJH desorption cumulative pore volume between 17 and 3000 A diameter and the BJH desorption average pore diameter (4V/A).

As used herein the term "attrition" refers to a measure of the tendency of a support to break up or disintegrate. The term "attrition resistance" refers to the ability of a support to resist disintegration. The values reported herein are determined by a modified version of ASTM D5757 as described in the examples herein. The attrition values reported are the level of support that breaks up under the test conditions. Lower values are therefore preferred over larger values.

As used herein the term "water absorbtivity" refers to a measure of the capacity of a support to absorb water wherein water is successively added to a given volume of support until water is visually released from the pores of the support.

As used herein the term "catalyst promoter" refers to a substance that increases the catalytic activity of the catalyst but is not itself a catalyst.

As used herein the term "catalyst stabiliser" refers to a substance that increases the stability of the catalyst. The stabiliser, for instance, may increase the resistance of the catalyst to deactivation.

DESCRIPTION OF INVENTION

The present invention provides a method of preparing an aluminate support for a catalyst comprising impregnating an alumina support with a divalent metal to produce an impregnated alumina support. The alumina support preferably comprises γ- alumina. Still more preferably the alumina support comprises 85-100 %wt γ-alumina and more preferably 95-99.5 %wt γ-alumina. Particularly preferably the alumina support consists essentially of, e.g. consists of, γ-alumina. Another form of alumina that may be present in small amounts is a-alumina.

The surface area of the alumina support is preferably 50 to 500 m ² /g, more preferably 100 and 300 m ² /g and still more preferably 150 and 200 m ² /g. The pore volume of the alumina support is preferably greater than 0.2 cm ³ /g, more preferably greater than 0.4 cm ³ /g and still more preferably greater than 0.5 cm ³ /g. Particularly preferably the pore volume of the alumina support is 0.2 to 1 .0 cm ³ /g and more preferably 0.5 to 0.8 cm ³ /g. The average pore diameter of the alumina support is preferably 50 to 200 nm and more preferably 70 to 150 nm. The attrition of the alumina support is preferably 1 to 10 g/50 g at 5 hour and more preferably 1 to 5 g/50 g at 5 hour.

Preferably the alumina support is in the form of substantially spherical particles. Particularly preferably the average diameter of the alumina support particles is 30 to 150 μιη and more preferably 50 to 130 μιη. Preferably at least 60 %, more preferably at least 70 % and still more preferably at least 80 % of the alumina support particles have a diameter of 30 to 150 μιη and more preferably 50 to 130 μιη.

Suitable alumina supports can be prepared according to conventional techniques in the art. For instance suitable alumina supports can be prepared by precipitation. Alternatively alumina supports may be prepared by spray-drying of an appropriate solution of aluminium salt in order to obtain essentially spherical particles of appropriate size. Suitable alumina supports are also commercially available, e.g. from Sasol GmbH of Hamburg, Germany.

Optionally the starting material alumina support is washed with an acid, base and/or water. This removes any contaminants introduced into the support during its preparation. This is the process described in WO2006/106357.

Optionally the starting material alumina support is calcined at a high temperature to give the appropriate crystal size and pore structure. Preferably calcination is carried out at 300 to 800 °C and more preferably 400 to 700 °C. Preferably, however, the starting material aluminate support is not calcined.

Typical properties of suitable alumina support materials are shown in the table below.

In the method of the present invention the alumina support is impregnated with a divalent metal. Preferably the divalent metal is capable of forming a spinel phase with alumina upon calcination. Preferably the divalent metal is selected from cobalt, zinc, magnesium, manganese, nickel or iron. Still more preferably the metal is selected from zinc, magnesium, manganese, nickel or iron and yet more preferably magnesium or nickel and especially preferably magnesium. Magnesium provides supports having the highest levels of attrition resistance. The amount of divalent metal present in the aluminate support following impregnation, drying and calcination is preferably 5 to 35 %wt, more preferably 7 to 30 %wt and still more preferably 8 to 25 %wt. When the divalent metal is magnesium, the amount of divalent metal present in the aluminate support is particularly preferably 6 to 12 %wt, e.g. about 8 to 10 %wt. When the divalent metal is nickel, the amount of divalent metal present in the aluminate support is particularly preferably 10 to 25 %wt, e.g. about 20 %wt.

Preferably the alumina support is impregnated with a divalent metal by contacting the alumina support with a solution of a metal salt of the divalent metal. Alternatively impregnation of the alumina support with the divalent metal may take place simultaneously with production of the alumina or alumina precursor and/or forming of the alumina particles.

Preferably impregnation with divalent metal is carried out by a technique selected from pore filling or "incipient wetness", spraying (e.g. spraying continuously such as in a screw impregnator), impregnation from slurry with surplus liquid and chemical vapour deposition. Preferably, however, the impregnation is carried out by incipient wetness. In this method the solution of divalent metal is mixed with the dry support until the pores are filled. Suitable metal salts include nitrates, chlorides, hydroxides and carbonates. Preferably the alumina support is contacted with a volume of solution that is 0.9 to 2.0 and more preferably 1 .1 to 1 .6 times the total pore volume of the support. Preferably the alumina support is contacted with the solution of a metal salt for 0 to 2 hours and more preferably 0 to 1 hours. Typically the impregnation will be carried out at room temperature (i.e. 25 °C). The whole or part of the impregnation system may be heated moderately to avoid crystallization in the impregnation fluid.

In preferred methods of the invention the impregnated alumina support is dried. Preferably drying is carried out at a temperature in the range 80 to 160 °C and preferably 1 10 to 150 °C. Preferably drying is carried out for 0.1 to 10 hours and more preferably 0.5 to 4 hours, e.g. in a rotary dryer or in a continuously agitated dryer.

In preferred methods of the invention the impregnated and dried alumina support is calcined to produce an aluminate support. Preferably this calcination step is carried out at a temperature of 800 to 1300 °C and more preferably 900 to 1250 °C. Preferably calcination is carried out for 2 to 20 hours and more preferably 5 to 16 hours. Preferably calcination is carried out in a stationary kiln. Alternatively calcination is carried out for 0.2 to 2 hours in a continuous rotary furnace. The calcination step converts the impregnated alumina support into aluminate, preferably in the spinel form, and a smaller amount of a-alumina.

As tabulated above, incorporation of a divalent metal salt into the alumina followed by drying and calcination and further impregnation with cobalt to produce an FT-catalyst is expected to give a catalyst with reduced activity. Now we have surprisingly found that washing with an acidic solution prevents this negative effect. In the method of the present invention the aluminate support is washed with an acid. Preferably the pH of the acid is less than 4, more preferably less than 3 and still more preferably less than 2. Preferably the pKa of the acid is less than 6, more preferably less than 5 and still more preferably less than 4. Particularly preferably the acid completely dissociates in water. Relatively strong acids are preferred.

The acid may be inorganic or organic. Representative examples of preferred inorganic acids include nitric acid, hydrochloric acid, phosphoric acid, boric acid, hydrobromic acid, hydroiodic acid and perchloric acid. Nitric acid and hydrochloric acid are preferred. Preferred organic acids comprise at least one carboxylic acid group (i.e. COOH). Representative examples of preferred organic acids include formic acid, acetic acid, ethanoic acid, propionic acid, chloroacetic acid, fluoroacetic acid, trifluoroacetic acid, trifluoroethanoic acid, benzoic acid, oxalic acid, citric acid, ascorbic acid, malonic acid and succinic acid. Preferred organic and inorganic acids do not comprise sulfur because sulfur is a catalyst poison.

In preferred methods of the invention the acid is an aqueous solution. Preferably the concentration of the acid is in the range 0.0001 to 1 M, more preferably 0.01 to 0.5 M and still more preferably about 0.1 M. Preferably the volume (liters) :weight (kilogram) ratio of acid to support used in the washing step of the method of the present invention is 2:1 to 100:1 , more preferably 10:1 to 40:1 .

Preferably the aluminate support is washed with acid by agitating it in a solution of the acid. Washing may, for example, in the laboratory be carried out in a rotavapor or in a PARR autoclave reactor. At a larger scale the acid wash can be carried out in a stirred tank, either batch wise or in a continuous or semi-continuous fashion. Preferably the temperature during washing is 20 to 150 °C and more preferably 50 to 100 °C. Preferably washing is carried out for 0.1 to 10 hours and more preferably 0.5 to 3 hours.

The effect of the acid washing is surprising. Without wishing to be bound by theory, it may be that it removes any divalent metal (M) that is not incorporated into the aluminate lattice of the support. This is the divalent metal ions provided by the impregnation step that upon calcination can be transformed to the oxide MO. The removal of presumably harmful MO oxide is surprising as can be seen from the theoretical formula of the calcined aluminate support, M ₍₁ . _X) AI(2 ₊ 2 3x)0 ₄ , with 0<x<1 , meaning that the stoichiometry of the calcined aluminate support has an excess of alumina compared to divalent metal oxide for giving a pure spinel with formula MAI ₂ 0 ₄ . Indeed this stoichiometric excess of alumina is seen in a number of the prepared aluminate supports in that they contain a-alumina. Therefore, no harmful MO oxide is in the outset expected to be present, particularly as the calcination is carried out at high temperatures at reaction times that should be adequate for ion transport and equilibration toward the thermodynamic stable structure. Still it appears that some MO remains present and adversely influences the catalytic performance. Therefore, the acid washing step of the method of the present invention may remove divalent metal used in impregnation that is not incorporated into the aluminate lattice during calcination. This metal may be removed as metal ions per se or as metal oxide. In preferred methods of the invention some aluminium is also removed during the washing step. The aluminium may be aluminium that does not form part of the aluminate structure (e.g. aluminium from alumina) or it may be from the aluminate structure.

The method of the present invention may further comprise washing the aluminate support with further washes, e.g. further acid washes as herein described as well as washing with water. Optionally the aluminate support is dried.

Preferably the acid washed aluminate support comprises at least 60 %wt aluminate, preferably at least 80 %wt and more preferably at least 90% aluminate based on the total weight of the support. Preferably the aluminate is a spinel, i.e. of the formula M ²⁺ AI ₂ ³⁺ 0 ₄ ^2" , where M is the divalent metal, or a solid solution with a formula approaching the spinel formula and the balance is made up of alumina (expected to be in the form of a-alumina). Particularly preferred acid washed aluminate supports further comprise a-alumina, e.g. 0-10 %wt α-alumina and more preferably 1 -5 %wt a- alumina.

Preferably the acid washed aluminate support comprises substantially no divalent metal from impregnation that is not a part of the aluminate lattice. Preferably the acid washed aluminate support comprises 0 to 5 %wt, more preferably 0 to 2.5 %wt and still more preferably 0 to 1 %wt divalent metal that is not incorporated into the aluminate lattice, based on the total weight of the support. The surface area of the acid washed aluminate support is preferably 10 to 100 m ² /g, more preferably 15 and 80 m ² /g and still more preferably 20 and 60 m ² /g. The pore volume of the acid washed aluminate support is preferably greater than 0.10 cm ³ /g, more preferably greater than 0.15 cm ³ /g and still more preferably greater than 0.20 cm ³ /g. Particularly preferably the pore volume of the acid washed aluminate support is 0.15 to 0.40 cm ³ /g and more preferably 0.20 to 0.30 cm ³ /g. The attrition of the acid washed aluminate support is preferably less than 2.5 g/50 g at 5 hour and more preferably less than 1 .5 g/50 g at 5 hour.

The method of the present invention also relates to a method of preparing a catalyst. The method comprises preparing an aluminate support as hereinbefore defined. Preferred features of the method of preparing the support are also preferred features of the method of preparing the catalyst. The method of preparing a catalyst comprises the further step of impregnating the aluminate support with a catalytically active metal to produce the catalyst.

Preferably the catalytically active metal is selected from cobalt and iron but is more preferably cobalt. Preferably the catalytically active metal is provided in the form of a solution, e.g. aqueous solution, of metal salt. Representative examples of metal salts include cobalt nitrate, cobalt acetate, cobalt halide, cobalt carbonyl, cobalt oxalate and cobalt phosphate. The amount of catalytically active metal present in the catalyst is preferably 5 to 25 %wt, more preferably 8 to 20 %wt and still more preferably 10 to 16 %wt. Preferably the volume of solution of catalytically active metal is 0.9 to 3 times and more preferably 1 .1 to 2.0 times the pore volume of the aluminate support.

Preferably impregnation with catalytically active metal is carried out by contacting the aluminate support with a solution of a catalytically active metal salt. Preferably the impregnation is carried out by a technique selected from pore filling or "incipient wetness", impregnation from slurry with surplus liquid and chemical vapour deposition. Preferably, however, the impregnation is carried out by incipient wetness. In this method a solution of catalytically active metal is mixed with a dry support until the pores are filled. The definition of the end point of this method may vary somewhat from laboratory to laboratory so that an impregnated catalyst could have a completely dry appearance or a sticky snow-like appearance. However, in no instances are there are any free flowing liquid present.

Further preferred methods of the present invention further comprise impregnating the aluminate support with a catalyst promoter. Preferably the catalyst promoter is selected from platinum, iridium or rhenium but is preferably rhenium. Preferably the catalyst promoter is provided in the form of a solution, e.g. aqueous solution, of a catalyst promoter or catalyst promoter salt. Representative examples of suitable catalyst promoters and catalyst promoter salts include perrhenic acid, ammonium perrhenate, rhenium halide and rhenium carbonyl. The amount of catalyst promoter present in the catalyst is preferably 0.05 to 3 %wt, more preferably 0.1 to 1 %wt and still more preferably 0.15 to 0.6 %wt.

Preferably impregnation with catalyst promoter is carried out by contacting the aluminate support with a solution of catalyst promoter or catalyst promoter salt. This may be carried out simultaneously or separately to impregnation with catalytically active metal. Preferably, however, impregnation is carried out simultaneously, i.e. by co-impregnation.

Further preferred methods of the present invention comprise impregnating the aluminate support with a catalyst stabiliser. Preferably the catalyst stabiliser is a lanthanum oxide or a mixture of rare earth oxides comprising lanthanum. Preferably the catalyst stabiliser is provided in the form of a solution, e.g. aqueous solution, of a catalyst stabiliser or catalyst stabiliser salt. The stabiliser can also be adding during preparation of the alumina support. Suitable lanthanum oxide solutions are well known in the art. Preferably impregnation with catalyst stabiliser is carried out by contacting the aluminate support with a solution of catalyst stabilser or catalyst stabiliser salt.

Impregnation is preferably in one step, but multiple steps can also be employed, e.g. from a mixed aqueous solution of appropriate metal salts, e.g. cobalt nitrate and perrhenic acid or alternatively ammonium perrhenate. Optionally lanthanum oxide may also be used.

In preferred methods of the invention the impregnated catalyst is dried. Preferably drying is carried out at 80-120 °C. Preferably drying is carried out for 0.1 to 10 hours, preferably for 0.5 to 4 hours. This drying removes water from the catalyst pores. In preferred methods of the invention the impregnated catalyst is calcined. Preferably calcination is at 200-450 C, e.g. at 300 C. Preferably calcination is carried out for 0.5 to 16 hours. Longer times will be needed for stationary kilns compared to continuous rotary calciners.

In further preferred methods of the invention the catalyst of the present invention is activated. Preferably activation is carried out by reducing a substantial portion of the catalytically active metal present therein to metal. Preferably reduction is carried out by treating the catalyst material with a reducing gas, e.g. hydrogen and/or carbon monoxide, optionally mixed with an inert gas such as noble gases or steam. Preferably the reduction is carried out at a temperature of 250 to 500 °C and more preferably 300 to 450 °C. If a fluidised bed reactor is used for activation, it may be convenient to use a recycle of (part of) the reductive gas and a slight atmospheric total overpressure in order to achieve a suitable gas flow. It is also possible to use elevated total pressures, eg. up to 8 bar or higher, or even the Fischer-Tropsch reactor pressure.

In preferred methods of the invention the surface area of the catalyst is preferably 10 to 100 m ² /g, more preferably 15 and 80 m ² /g and still more preferably 20 and 60 m ² /g. The pore volume of the catalyst is preferably greater than 0.10 cm ³ /g, more preferably greater than 0.15 cm ³ /g and still more preferably greater than 0.20 cm ³ /g. Particularly preferably the pore volume of the catalyst is 0.15 to 0.40 cm ³ /g and more preferably 0.20 to 0.30 cnrVg. The attrition of the catalyst is preferably less than 2.5 g/50 g at 5 hour and more preferably less than 1 .5 g/50 g at 5 hour.

In preferred methods of the present invention the resulting catalyst is a Fischer- Tropsch Synthesis catalyst. Particularly preferably the catalyst comprises:

75-90 %wt divalent metal aluminate and alumina;

5-25 %wt catalytically active metal; and

0.1 -1 .0 %wt catalyst promoter; wherein

the catalyst comprises substantially no divalent metal of the type used to form the aluminate that is a not a part of the aluminate.

Still more preferably the catalyst comprises:

85-90 % wt divalent metal aluminate and alumina;

10-15 %wt catalytically active metal;

0.15-0.8 %wt catalyst promoter; and

0-2.5 %wt divalent metal of the type used to form the aluminate that is a not a part of the aluminate.

Preferably the catalyst comprises 0-10 %wt a-alumina and more preferably 1 -5 %wt a-alumina.

The present invention also relates to aluminate supports and to catalysts obtainable by the methods described herein.

The aluminate support preferably comprises magnesium. The surface area of the aluminate support is preferably 10 to 100 m ² /g, more preferably 15 and 80 m ² /g and still more preferably 30 and 60 m ² /g. The pore volume of the aluminate support is preferably greater than 0.10 cm ³ /g, more preferably greater than 0.15 cm ³ /g and still more preferably greater than 0.20 cm ³ /g. Particularly preferably the pore volume of the aluminate support is 0.15 to 0.40 cm ³ /g and more preferably 0.20 to 0.30 cm ³ /g. The attrition of the aluminate support is preferably less than 2.5 g/50 g at 5 hour and more preferably less than 1 .5 g/50 g at 5 hour.

Particularly preferably the aluminate support comprises divalent metal aluminate and alumina, and substantially no divalent metal of the type used to form the divalent metal aluminate that is a not a part of the aluminate. Preferably the aluminate support comprises 0 to 5 %wt, more preferably 0 to 2.5 %wt and still more preferably 0 to 1 %wt divalent metal of the type used to form the divalent metal aluminate that is a not a part of the aluminate, based on the total weight of the support. Particularly preferably the aluminate support consists essentially of (e.g. consists of) divalent metal aluminate and alumina. Preferably the aluminate support comprises a-alumina, e.g. 0- 10 %wt a-alumina and more preferably 1 -5 %wt a-alumina.

Further preferred features of the modified support are as set out above in relation to the method.

The catalyst preferably comprises magnesium. The catalyst preferably also comprises cobalt and optionally rhenium.

The surface area of the catalyst is preferably 10 to 100 m ² /g, more preferably

15 and 80 m ² /g and still more preferably 20 and 60 m ² /g. The pore volume of the catalyst is preferably greater than 0.10 cm ³ /g, more preferably greater than 0.15 cm ³ /g and still more preferably greater than 0.20 cm ³ /g. Particularly preferably the pore volume of the catalyst is 0.15 to 0.40 cnrVg and more preferably 0.20 to 0.30 cnrVg.

The attrition of the catalyst is preferably less than 2.5 g/50 g at 5 hour and more preferably less than 1 .5 g/50 g at 5 hour.

Particularly preferably the catalyst comprises:

75-90 %wt divalent metal aluminate and alumina;

5-25 %wt catalytically active metal; and

0.1 -1 .0 %wt catalyst promoter,

wherein the catalyst comprises substantially no divalent metal of the type used to form the aluminate that is a not a part of the aluminate.

Preferably the catalyst comprises 0 to 5 %wt, more preferably 0 to 2.5 %wt and still more preferably 0 to 1 %wt divalent metal of the type used to form the aluminate that is a not a part of the aluminate. Still more preferably the catalyst consists essentially of (e.g. consists of):

75-90 %wt divalent metal aluminate and alumina;

5-25 %wt catalytically active metal; and 0.1 -1 .0 %wt catalyst promoter.

Preferably the catalyst comprises 0-10 %wt a-alumina and more preferably 1 -5 %wt a-alumina.

Further preferred features of the catalyst are as described above in relation to the methods of the invention.

The present invention further relates to use of the catalyst hereinbefore described in Fischer-Tropsch Synthesis and to a process for the production of hydrocarbons comprising subjecting H ₂ and C0 ₂ gases to a Fischer-Tropsch synthesis reaction in a reactor in the presence of a catalyst as hereinbefore described. In preferred uses and methods the Fischer-Tropsch reaction is carried out in a slurry bubble column reactor. In particularly preferred uses and methods the H ₂ and CO are supplied to a slurry in the reactor, the slurry comprising the catalyst in suspension in a liquid including the reaction products of the H ₂ and CO, the catalyst being maintained in suspension in the slurry at least partly by the motion of the gas supplied to the slurry.

In further preferred methods of Fischer-Tropsch Synthesis the reaction is a three-phase reaction in which the reactants are gaseous, the product is at least partially liquid and the catalyst is solid. Preferably the reaction temperature is 190-250 °C and more preferably 200-230 °C. Preferably the reaction pressure is 10-60 bar and more preferably 15 to 30 bar. Preferably the H ₂ /CO ratio of the gases supplied to the Fischer-Tropsch synthesis reactor is in the range 1 .1 to 2.2 and more preferably 1 .5 to 1 .95. Preferably the superficial gas velocity in the reactor is in the range 5 to 60 cm/s and more preferably 20 to 40 cm/s.

In particularly preferred methods of the present invention the product of the Fischer-Tropsch synthesis reaction is subsequently subjected to post- processing, e.g. post-processing selected from de-waxing, hydro-isomerisation, hydro-cracking and combinations thereof.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 a shows the hydrocarbon formation rate (g/g,h) for Co/Re Ni-aluminate supported catalysts with different amounts of Mg (ppm);

Figure 1 b shows the C ₅₊ (%) selectivity for Co/Re Ni-aluminate supported catalysts with different amounts of Mg (ppm);

Figure 2a shows the hydrocarbon formation rate (g/g,h) for Co/Re Mg-aluminate supported catalysts versus the amount of Mg (ppm) removed from the support by acid wash; Figure 2b shows the C ₅₊ (%) selectivity for Co/Re Mg-aluminate supported catalysts versus the amount of Mg (ppm) removed from the support by acid wash; and

Figure 3 shows the end-pH after HCI treatment of aluminates with different BET surface areas (m ² /g).

EXAMPLES

Materials

• Aluminate support with nominal loading of 18-20 wt% nickel (Ni) was prepared as described in WO 2005/072866. Aluminate supports with different surface area and pore volume were made by varying the severity of the high temperature calcination, higher severity giving lower surface area and pore volume.

• Aluminate supports with nominal loading of 10 wt % magnesium (Mg) was prepared as described in WO2005/072866. Aluminate supports with different surface area and pore volume were made by varying the severity of the high temperature calcination, higher severity giving lower surface area and pore volume.

• Aluminate support with Zn, loading 5%ZnO, and containing detrimental amounts of activity suppressing elements such as Ca and Mg were prepared as described in WO2012/020210

• Nitric acid and hydrochloric acid were obtained from Merck and J.T baker, respectively.

• Co(ll) nitrate hexahydrate was obtained from Acros Organics.

· Perrhenic acid (HRe04) 75-80% solution was obtained from Alfa Aesar.

• Drying was carried out in a Termaks drying oven with forced convection.

• Calcination was carried in an Entech chamber furnace with air supply 100ml/min. Testing

• Attrition testing was conducted with a modified version of ASTM D5757 wherein the modified equipment consists of two main parts, one air feeding system and one reactor where the attrition takes place. Compressed air passes through a pressure regulator (5 bar) to a moisture chamber where the air is moistened to approximately 30 % relative moisture. This is done to avoid static electricity in the system. The amount of air is then adjusted in a mass flow controller. The humid air then enters the reactor through a sieve tray where the holes have a diameter of 0.4 mm. Because of these holes, the gas reaches sonic velocity, which causes the "wear and tear" on the particles in the reactor. The reactor has an internal diameter of 35.6 mm (1 .4 inches) and a length of 71 1 mm (28 inches) and the pressure is approximately 1 .8 bar. After passing through the reactor, the velocity is lowered in a separation chamber which has an internal diameter of 1 12 mm (4.4 inches) and a length of 305 mm (12 inches). There is a conical connection 203 mm long (8 inches) between the reactor and the separation chamber. Particles > 40 μιη will fall back down into the reactor, while smaller particles < 40 μιη (fines) will enter a Soxhlet-filter through a u-formed tubing, connected to the separation chamber via a conical connection 106 mm long (4 inches). A vibrator is mounted on the separation chamber, to loosen any particles on the inside walls. 50 g of powder or catalyst, sieved to > 40 μιη before testing, is loaded to the reactor, and the reactor is connected to the separation chamber. The air is turned on, and the fines produced in the reactor and collected in the Soxhlet filter are weighed every 15 minutes during the first 2 hours, and every 30 minutes during the next 3 hours. A normal run lasts 5 hours and the amount of fines produced is plotted against time. The results presented herein are the total amount of fines produced from 50g in 5 hours. Surface area (m ² /g) was measured by TRISTAR3000 from Micromeritics Pore volume (%) was measured by TRISTAR3000 from Micromeritics

Pore diameter (nm) was measured by TRISTAR3000 from Micromeritics All of the catalyst testing was performed in a fixed bed laboratory unit with four parallel fixed-bed reactors connected to a gas chromatograph (GC) equipped with flame ionization and thermal conductivity detectors (FID and TCD). Approximately 1 g of catalyst particles in a size fraction between 53 and 90 microns was mixed with 20 g of inert SiC. Reduction was performed in situ at 350 °C for 16 h in hydrogen before a mixture of hydrogen and CO at a ratio of 2:1 was added. After 20 h on stream at 210°C and 20 bar total pressure, the space velocity was adjusted to give an estimated conversion level of CO between 45 and 50% after 70 h. It is very important to perform selectivity, as well as activity, comparisons at the same level of conversion, as the level of steam generated in the reaction has a profound influence on the catalyst performance. • rCH (g/g,h), C ₅₊ selectivity (%), and C0 ₂ (%) were calculated based on analysis with GC described above. The level of C0 ₂ is an indicator of the presence of impurities in the catalyst, i.e. the higher the level of C0 ₂ , the higher the level of impurities.

Support preparation - Treatment with acid

Treatment of the supports with acid was done by exposing the support to 0.1 M acid in a PARR autoclave reactor or in a rotavapor. The acids used were 0.1 M nitric acid (HN0 ₃ ) and 0.1 M hydrochloric acid (HCI). Unless otherwise specified, the temperature was held at 90°C for 1 or 2 hours. In the PARR autoclave system, a 450 ml reactor and 500 rpm stirring was used. In the rotavapor system, the stirring used was 150 rpm, and round flasks of 500 or 1000 ml was used depending on the amount of support treated. Different volume:weight ratios of acid:support were investigated. Catalyst preparation

The catalysts were prepared by one-step incipient wetness co-impregnation of supports with aqueous solutions of cobalt nitrate hexahydrate and perrhenic acid. The freshly prepared catalysts were dried for 3 h at a temperature of 1 10°C. During drying, the catalysts were stirred every 15 min during the first hour and every 30 min during the next two hours. After impregnation and drying, the samples were calcined at 300 °C for 16 h.

Series A (comparative) - 12%Co/0.3%Re catalysts were post-impregnated with Mg- nitrate by incipient wetness. Different amounts of Mg were impreganted onto the catalyst. This afforded catalysts with 12 wt% Co, 0.3 wt% Re and different amounts of Mg after drying, calcination and reduction. The freshly prepared catalysts were dried for 3 h at 1 10 C before calcination at 300 °C for 16h.

Series B - 10% Mg-alumina support was calcined at 1080 C The calcined aluminate support, untreated and treated at different ratios of acid:support, was impregnated with Co-nitrate and HRe0 ₄ by incipient wetness. This afforded catalysts with 12 wt% Co and 0.5 wt% Re after drying, calcination and reduction. The freshly prepared catalysts were dried for 3 h at 1 10°C before calcination at 300 °C for 16h. Series C - Mg-alumina support was calcined at 1080 °C and Ni-alumina support was calcined at 1 100 and 1 120 °C to give different calcined aluminate supports. These calcined aluminate supports, untreated and treated at different ratios of acid:support were impregnated with Co-nitrate and HRe0 ₄ by incipient wetness to give catalysts with nominal amounts of 12 wt% cobalt (Co) and 0.5 wt% rhenium (Re) after drying, calcination and reduction. The freshly prepared catalysts were dried for 3 h at 1 10 °C before calcination at 300 °C for 16h.

Series D - Zn-alumina support containing detrimental amounts of activity suppressing elements including Ca and Mg, untreated and treated with acid, were impregnated with Co-nitrate and HRe0 ₄ by incipient wetness. This afforded catalysts with either 20 or 12 wt% Co and 0.5 wt% Re after drying, calcination and reduction. The freshly prepared catalysts were dried for 3 h at 1 10 °C before calcination at 300 °C for 16h. EXAMPLE 1 : Mg-aluminate support

In table 1 below the characterization data of untreated and acid treated Mg- aluminate supports is given.

Table 1 : Characterization data of Mg-aluminates that are untreated or treated with acid

Substrate treated Treatment Attrition Surface Pore

(%) area volume

(m ₂ /g) (%)

Alumina None 10 170 0.70

Mg-aluminate None 0.3 20 0.12 calcined 1140°C

Mg-aluminate None 0.5 34 0.20 calcined 1110°C

Mg-aluminate None 0.6 51 0.28 calcined 1080°C

Mg-aluminate 5:1 0.1M HN0 ₃ 90°C, PARR 1.4 49 0.28 calcined 1080°C 20:1 0.1M HC1 90°C, rotavapor 1.9 51 The attrition data show that magnesium is an excellent divalent compound for strengthening alumina supports and that temperatures in the range 1080 to 1 140 °C all give excellent support strength without losing too much pore volume. The data further shows that after treating the Mg-aluminate support with acid the strength is still high.

EXAMPLE 2: Ni-aluminate support

In table 2 below the characterization data of untreated and acid treated Ni- aluminate supports are given.

Table 2: Characterization data of Ni-aluminates that are untreated and treated with acid

The data show that for this divalent compound, the improved strength of the support is largely retained after acid treatment. Specifically even though the acid treatment reduces the strength of the support slightly, the strength is still clearly much better than for the base alumina support.

EXAMPLE 3 (Comparative): Co/Re catalyst post-impregnated with magnesium

The Fischer-Tropsch synthesis performance of the catalysts in series A described above is given in table 3 below and shown graphically in figure 1 . The catalysts comprised 12%Co and 0.3%Re on a Ni-aluminate (No. 3) support and were post-impregnated with different amounts of magnesium as shown in the table. No acid treatment was carried out.

Table 3.

Treatment rCH (g/g,h) C5+ selectivity (%) C02 (%) None 0.537 83.1 0.16

H20 0.489 81.2 0.16

400 ppmw Mg 0.433 82.2 0.20

1000 ppmw Mg 0.379 81.5 0.19

2000 ppmw Mg 0.333 81.1 0.22

It is clear that activity decreases with increasing magnesium amount. Addition of 1000-2000 ppm Mg decreases the activity to the level of Co- Re catalyst on Mg- aluminate shown later in table 4. This is consistent with the results obtained in example 4 below.

EXAMPLE 4: Mg-aluminate treated at different acid (HCI) to support ratios

The Fischer-Tropsch synthesis performance of the catalysts in series B described above is given in table 4 below and shown in Figure 2. The catalysts were untreated and acid treated Mg-aluminate impregnated with 12 % Co and 0.5 % Re. All acid treatments were with 0.1 M HCI at 90°C. Different (volume:weight) HCI:support ratios were used as shown in table 4 below. The amount of Mg and Al removed by the acid treatment is shown in columns 2 and 3 of the table.

Table 4

HCI: substrate ppm Mg ppm Al rHC C ₅₊ C0 ₂ ratio (v/w) removed removed (g g,h) selectivity selectivity

(%) (%)

No treatment 0.346 83.8 0.18

0.327 83.3 0.21

5:1 1600 2200 0.374 84.8 0.17

2200 3000 0.410 85.6 0.15

10:1 n.a. n.a. 0.424 86.8 0.13

20:1 3000 14700 0.401 85.6 0.15

0.473 87.2 0.13

0.398 85.9 0.18 It is clear that treatment of Mg-aluminate support with acid improves the performance of the catalysts made thereon. Not only is the activity increased, but surprisingly the selectivity to C ₅₊ is also strongly enhanced, also seen in figure 2. The results further show that a certain level/amount of acid is necessary to achieve the improvement in catalytic performance. The level of Mg and Al dissolved increases as the amount of acid is increased.

EXAMPLE 5: Ni-and Mg-aluminates treated at HCksupport ratio of 20:1

The Fischer-Tropsch synthesis performance of the catalysts of series C described above is given in table 5 below. The catalysts were untreated and acid treated Mg- and Ni-aluminates impregnated with 12% Co and 0.5% Re or 12% Co and 0.3% Re, respectively as shown. The Mg-aluminate used was calcined at 1080°C. The Ni-aluminate was calcined at different temperatures to give surface areas as showed in table 2. All acid treatments were done with 0.1 M acid, with an acid:support (v:w) ratio of 20:1 and at 90 °C unless otherwise specified. As a comparison, a 12 %Co/0.5 %Re catalyst on a Mg-aluminate support was treated with acid after impregnation of the catalyst.

Table 5

Substrate treated Treatment rHC C ₅₊ C0 ₂

(g/g,h) selectivity selectivity

(%) (%)

Mg-aluminate None 0.346 83.8 0.18

0.327 83.3 0.21

HN0 ₃ 0.400 85.9 0.14

HNO ₃ , 150°C 0.449 86.2 0.14

HC1 0.473 87.2 0.13

0.398 85.9 0.18

12%Co/0.5 Re on Mg-aluminate calc. HC1, 5:1 0.228 80.4 0.23

1080°C

Ni-aluminate 1 None 0.457 86.0 0.12

HC1 0.573 88.7 0.10 Ni-aluminate 2 None

HC1 0.669 87.8 0.09

The same effect as shown in table 4 is obtained on different aluminate supports. Again it is clear that treating aluminates with diluted acid before impregnation of Co and Re improves the catalysts performance, especially the selectivity to C ₅₊ . Post-treatment of catalysts on the same supports after cobalt and rhenium impregnation has a negative effect on catalyst performance.

It is further seen that the effect of acid treatment on Ni-aluminate 2 is larger than on Ni-aluminate 1 . Based on surface areas given in table 2, this is believed to be caused by the presence of more oxides receptive for the acids dissolution effect in Ni- aluminate 2 with higher surface area. Said another way, the aluminate with less surface area, Ni-aluminate 1 , is more inert and thereby more stable toward the acids effect. This statement is supported by a lower end-pH of 1 .8 after treatment of aluminate 1 compared to end-pH of 2.4 for aluminate 2, the end-pH being the pH at which the pH levels out during the treatment. For Mg-aluminate the end-pH is 3.9-4.0. This is shown in figure 3.

EXAMPLE 6: Treatment of aluminate supports containing detrimental amounts of activity suppressing elements

The Fischer-Tropsch synthesis performance of the catalysts of series D is given in table 6. The catalysts comprise Zn-aluminate with Mg and Ca impurities, treated with HCI prior to impregnation of 12% cobalt and 0.5% Re respectively

Table 6

Substrate Treatment rHC (g/g,h) C ₅₊ C0 ₂

selectivity selectivity

(%) (%)

Zn-aluminate None 0.305 82.8 0.27

Zn-aluminate 0.1M HCI 0.436 85.6 0.14

20: 1, 90°C It is clear that the method is not only applicable to aluminate supports modified with elements such as Mg known to have a negative impact on Fischer-Tropsch synthesis, but also for other support materials with high levels of impurities such as Ca. The results shown in tables 1 -6 and Figures 1 -3 clearly demonstrate that acid treatment of divalent metal aluminate supports improves their performance in Fischer- Tropsch Synthesis. The method is especially well suited for magnesium aluminate supports wherein the magnesium strengthens the attrition resistance in slurry Fischer- Tropsch Synthesis. Surprisingly the acid treatment increases the C ₅₊ selectivity of the catalyst in Fischer-Tropsch Synthesis as well as activity.