WO2018138512A1

WO2018138512A1 - Catalyst suitable for methanol synthesis

Info

Publication number: WO2018138512A1
Application number: PCT/GB2018/050227
Authority: WO
Inventors: Michael Bowker; James Hayward
Original assignee: University College Cardiff Consultants Ltd
Priority date: 2017-01-27
Filing date: 2018-01-26
Publication date: 2018-08-02
Also published as: GB201701382D0

Abstract

A catalyst precursor and a catalyst comprising separate double hydroxide layers of a or derived from a hydrotalcite structure comprising copper, zinc and aluminium, methods for making said catalyst precursor and catalyst, and the use of said catalyst in a method for synthesising methanol.

Description

CATALYST SUITABLE FOR METHANOL SYNTHESIS TECHNICAL FIELD The present invention relates generally to catalyst precursors and catalysts suitable for use in the synthesis of methanol. The catalyst precursors and catalysts comprise separate double hydroxide layers of a or derived from a hydrotalcite structure comprising copper, zinc and aluminium. The present invention further relates to methods of making the catalyst precursors and catalysts and the use of the catalyst for the synthesis of methanol.

BACKGROUND

Methanol has a number of applications including in the production of other chemicals (e.g. formaldehyde, acetic acid and synthesis gas), as a fuel, as denaturant for ethanol, as a solvent (e.g. in antifreeze) and as a carbon food source (e.g. for denitrifying bacteria, for example in wastewater plants). Methanol is increasingly finding application as a form of energy carrier since it is easier to store than hydrogen and burns cleaner than fossil fuels. Further, since methanol is miscible with water and is biodegradable, it is unlikely to accumulate in groundwater, surface water, air or soil.

Methanol synthesis is an established industrial process and involves the reaction of carbon monoxide, carbon dioxide and hydrogen in the presence of a catalyst. The standard industrial catalyst used in methanol synthesis comprises Cu/ZnO/AI₂0₃ and is formed from carbonate-based malachite structures, which have needle-like morphology.

It is desirable to provide alternative and/or improved catalysts and catalyst precursors suitable for use in methanol synthesis. It is further desirable to provide alternative and/or improved methods for making catalysts and catalyst precursors suitable for use in methanol synthesis.

SUMMARY In accordance with a first aspect, there is provided a method for making a catalyst precursor, the method comprising making separate double hydroxide layers of a hydrotalcite structure comprising copper, zinc and aluminium. In certain embodiments, the method comprises making a hydrotalcite structure comprising copper, zinc and aluminium by precipitation. In certain embodiments, the method comprises treating a hydrotalcite structure comprising copper, zinc and aluminium with a water-miscible organic solvent.

In accordance with a second aspect, there is provided a method for making a catalyst precursor, the method comprising making a hydrotalcite material comprising copper, zinc and aluminium by precipitation and treating the hydrotalcite material comprising copper, zinc and aluminium with a solvent. The solvent treatment may, for example, occur subsequently to the precipitation. The solvent treatment may, for example, occur simultaneously to the precipitation.

In accordance with a third aspect, there is provided a method for making a catalyst, the method comprising making a catalyst precursor by a method of any aspect or embodiment of the present invention and calcining said catalyst precursor. In certain embodiments, the method further comprises reducing the catalyst precursor.

In accordance with a fourth aspect, there is provided a catalyst precursor obtained by or obtainable by a method of any aspect or embodiment of the present invention.

In accordance with a fifth aspect, there is provided a catalyst obtained by or obtainable by a method of any aspect or embodiment of the present invention. In accordance with a sixth aspect, there is provided a catalyst precursor comprising separate double hydroxide layers of a hydrotalcite structure comprising copper, zinc and aluminium.

In accordance with a seventh aspect, there is provided a catalyst comprising separate double hydroxide layers comprising copper, zinc and aluminium. The double hydroxide layers may, for example, be derived from a hydrotalcite structure.

In accordance with a eighth aspect, there is provided a use of the catalyst or catalyst precursor of any aspect or embodiment of the present invention for the synthesis of methanol. Certain embodiments or aspects of the present invention may provide one or more of the following advantages:

• increased specific surface area;

· increased copper surface area;

• smaller copper particles;

• increased catalytic activity;

• increased selectivity for methanol production;

• reduced temperature during catalyst production;

· reduced energy consumption during catalyst production;

• increased pH during catalyst production.

The details, examples and preferences provided in relation to any particular one or more of the stated aspects of the present invention apply equally to all aspects of the present invention. Any combination of the embodiments, examples and preferences described herein in all possible variations thereof is encompassed by the present invention unless otherwise indicated herein, or otherwise clearly contradicted by context. BRIEF DESCRIPTION OF THE FIGURES

Figure 1 . is a schematic representation of the structure of a single (separate) double hydroxide layer of a hydrotalcite structure comprising copper, zinc and aluminium. Figure 2. is transmission electron microscopy photographs of (A) the malachite material formed by the method described in Example 2 (after calcination), (B) a hydrotalcite material formed by the co-precipitation and solvent treatment method described in Example 2 prior to calcination, (C) a catalyst hydrotalcite material formed by the co- precipitation and solvent treatment method described in Example 2 after calcination but before reduction, and (D) a hydrotalcite material formed by the co-precipitation and solvent treatment method described in Example 2 after calcination and reduction.

Figure 3 shows the X-ray diffraction pattern of the malachite material formed by the method described in Example 2 and the hydrotalcite material formed by the co- precipitation and solvent treatment method described in Example 2, both prior to calcining. Figure 4 shows the malachite material formed by the method described in Example 2 and the hydrotalcite material formed by the co-precipitation and solvent treatment method described in Example 2, both after calcining but before reduction.

Figure 5 shows the hydrotalcite material formed by the co-precipitation and solvent treatment method described in Example 2, after calcining and reduction.

DETAILED DESCRIPTION

The present invention is based, at least in part, on the surprising finding that a product comprising separated double hydroxide layers of a hydrotalcite structure comprising copper, zinc and aluminium have a high surface area and high catalytic activity for methanol synthesis. In certain embodiments, the surface area and/or catalytic activity of the product is higher than that of the industrial catalyst that is currently used for methanol synthesis, namely catalysts formed from Cu/ZnO/AI₂0₃ malachite materials.

Method for Making a Catalyst Precursor Therefore, provided herein is a method for making a catalyst precursor. In certain embodiments, the method comprises making separate double hydroxide layers of a hydrotalcite structure comprising copper, zinc and aluminium. In certain embodiments, the method comprises making a hydrotalcite structure comprising copper, zinc and aluminium by precipitation and separating the double hydroxide layers of the hydrotalcite structure comprising copper, zinc and aluminium by treatment with solvent. The treatment with solvent may occur simultaneously with the precipitation or may occur after the precipitation.

The term "hydrotalcite structure comprising copper, zinc and aluminium" refers to a material or compound that includes (but is not limited to) copper, zinc and aluminium, and has the hydrotalcite layered double hydroxide crystal structure. The compound comprises layers of intermixed Cu(OH)₆, Zn(OH)₆ and AI(OH)₆ octahedra ("hydroxide layers"), two of which are held together with counterions (X^n~) such as C0₃ ^2" to form "double hydroxide layers", and has a general formula of (Cu,Zn)₆AI₂X2/n(OH) i6. In certain embodiments, the counterions of the compound comprise, consist essentially of or consist of carbonate (C0₃ ² ) counterions. Thus, in certain embodiments, the compound has a general formula of (Cu,Zn)₆AI₂C03(OI-l) i 6. The hydrotalcite structure comprising copper, zinc and aluminium also includes water, which holds multiple layers of the double hydroxide layers together by hydrogen bonding. The general structure of a single double hydroxide layer is shown in Figure 1 , where the small dark spheres represent hydroxyl groups, the larger grey spheres represent metal atoms (e.g. copper, zinc and aluminium) and the spheres labelled A represent counterions.

The term "separate" or "separated" in relation to the double hydroxide layers of a hydrotalcite structure comprising copper, zinc and aluminium, thus means that the double hydroxide layers of the hydrotalcite are discrete and distinct units that would not aggregate or agglomerate upon drying (where the precursor is in solution or suspension) or are not aggregated or agglomerated where the precursor is in solid form. For example, the term "separate" or "separated" in relation to the double hydroxide layers of a hydrotalcite structure comprising copper, zinc and aluminium may mean that hydrotalcite structure is in the form of 2D rather than 3D sheets. For example, the term "separate or "separated" in relation to the double hydroxide layers of a hydrotalcite structure comprising copper, zinc and aluminium may mean that there is no water between the double hydroxide layers. This could, for example, be measured by heating the catalyst precursor and analysing the gas produced by mass spectrometry or on-line IR spectroscopy.

For the avoidance of doubt, the term "separate" or "separated" in relation to the double hydroxide layers of the hydrotalcite structure comprising copper, zinc and aluminium does not mean that the two "hydroxide layers", which each comprise intermixed Cu(OH)₆, Zn(OH)₆ and AI(OH)₆ octahedra and are held together by a counterion to from a single "double hydroxide layer", are discrete and distinct units that would not aggregate or agglomerate upon drying. Prior to any calcination step, the counterion remains in the material, holding the "double hydroxide layers" together. After a calcination step, the counterion is decomposed and the two hydroxide layers may or may not aggregate.

In certain embodiments, the catalyst precursor may be in solution or suspension and the layers of double hydroxide may be separated by an organic solvent (have organic solvent interspersed between the double hydroxide layers). In certain embodiments, the catalyst precursor may have been filtered and/or dried to form a solid catalyst precursor. The solid catalyst precursor may also comprise layers of double hydroxide that are separated by molecules of organic solvent (have organic solvent interspersed between the double hydroxide layers).

The term "catalyst precursor" used herein refers to any non-calcined material. The term "catalyst" used herein refers to any calcined material. The term "catalyst" as used herein may refer to a reduced or non-reduced material. It would be understood by a person of ordinary skill in the art that it may be necessary to reduce the catalyst to form elemental copper prior to use.

The copper, zinc and aluminium may each be present in the form of ions in the catalyst precursor and catalyst. In the catalyst precursor, some or all of the copper, zinc and/or aluminium may each individually be in the form of a metal hydroxide, such as M(OH)₆ where M is copper, zinc or aluminium.

In the catalyst, the copper, zinc and/or aluminium may each individually be in the form of a metal oxide, such as M_xO_y where M is copper, zinc or aluminium. For example, in a (calcined) catalyst, some or all of the copper, zinc and/or aluminium may each individually be in the form of a metal oxide, such as M_xO_y where M is copper, zinc or aluminium. For example, in a reduced catalyst, some or all of the copper, zinc and/or aluminium may each individually be in the form of a metal oxide, such as M_xO_y where M is copper, zinc or aluminium. For example, in a reduced catalyst, some or all of the copper may be in the form of elemental copper. For example, in a reduced catalyst, some of the zinc may be in the form of elemental zinc.

When in reduced form, the catalyst comprises at least some particles of elemental copper. In certain embodiments, at least about 90 wt% of the copper in the catalyst is in the form of elemental copper particles, for example at least about 92 wt% or at least about 94 wt% or at least about 95 wt% or at least about 96 wt% or at least about 98 wt% or at least about 99 wt%. In certain embodiments, 100 wt% of the copper in the catalyst is in the form of elemental copper particles.

In certain embodiments, the method comprises separating double hydroxide layers of a hydrotalcite structure comprising copper, zinc and aluminium. For example, in certain embodiments, the method comprises providing a hydrotalcite structure comprising copper, zinc and aluminium (wherein the double hydroxide layers are not separate and would aggregate or agglomerate upon drying) and then separating the double hydroxide layers of the hydrotalcite structure.

In other embodiments, the method comprises making a hydrotalcite structure comprising copper, zinc and aluminium, and separating the double hydroxide layers of the hydrotalcite structure. In certain embodiments, making the hydrotalcite structure and separating the layers of the hydrotalcite structure occurs sequentially. In other embodiments, making the hydrotalcite structure and separating the layers of the hydrotalcite structure occurs simultaneously. In the simultaneous method, a hydrotalcite structure where the layers are not separate (a structure where the layers would aggregate or agglomerate upon drying) may not be formed. For example, in the simultaneous method, the separated layers of the hydrotalcite structure (layers that would not aggregate upon drying) may be formed directly.

In certain embodiments, the method comprises making a hydrotalcite structure comprising copper, zinc and aluminium, for example the separate double hydroxide layers of the hydrotalcite structure comprising copper, zinc and aluminium, by precipitation (co-precipitation).

The precipitation process may, for example, comprise adding a hydroxide salt to a one or more of copper, zinc and aluminium precursors. For example, the precipitation process may comprise adding an hydroxide salt, for example a hydroxide salt solution, to a solution comprising one or more of copper, zinc and aluminium precursors. For example, the precipitation process may comprise adding hydroxide salt, for example a hydroxide salt solution, to a solution comprising a mixture of copper, zinc and aluminium precursors. The solution of copper, zinc and/or aluminium precursors may, for example, be an aqueous solution. Where the precipitation process comprises adding a hydroxide salt to one or two of copper, zinc and aluminium precursors, the process further comprises adding the remaining precursors to the mixture of copper, zinc and/or aluminium precursor and hydroxide salt, for example simultaneously or sequentially. The hydroxide salt may, for example, be a metal hydroxide or non-metal hydroxide. The metal hydroxide may, for example, be one or more alkali metal hydroxides, one or more alkali earth metal hydroxides or combinations thereof. Preferably, the metal hydroxide is one or more alkali metal hydroxides. The non-metal hydroxide may, for example, be ammonium hydroxide. Preferably, the hydroxide salt is sodium hydroxide, potassium hydroxide, ammonium hydroxide or a combination of one or more thereof. The present invention may herein be described in terms of sodium hydroxide. However, the invention should not be construed as being limited as such.

Copper, zinc and aluminium precursors are compounds respectively providing a source of copper, zinc and aluminium. The copper, zinc and aluminium precursors may, for example, each respectively be a copper, zinc or aluminium salt. For example, all of the copper, zinc and aluminium precursors may respectively be copper, zinc and aluminium salts. For example, each of the copper, zinc and aluminium precursors may individually be a nitrate, acetate (acetylacetone if preparation is in ethanol/acetone), formate, sulphate, bromide or chloride. For example, all of the copper, zinc and aluminium precursors may be a nitrate, acetate (acetylacetone if preparation is in ethanol/acetone), formate, sulphate, bromide or chloride. The copper, zinc and aluminium precursors may, for example, all comprise the same anion. For example, the copper zinc and aluminium precursors may all be nitrates or may all be acetates or may all be acetylacetones or may all be formates or may all be sulphates or may all be bromides or may all be chlorides. The copper, zinc and aluminium precursors may, for example, comprise different anions. Hereinafter, the present invention may be described in terms of nitrates (copper nitrate and/or zinc nitrate and/or aluminium nitrate). However, the invention should not be construed as being limited as such. The method may, for example, comprise adding an additional metal salt to the metal hydroxide and/or copper, zinc and aluminium precursors. This may, for example, provide a source of counterions for the hydrotalcite structure. The additional metal salt may, for example, be added to the hydroxide salt before combination with the copper, zinc and/or aluminium precursors. The additional salt may, for example, be added to the copper, zinc and/or aluminium precursors before combination with the hydroxide salt. The additional salt may, for example, be added to a mixture of hydroxide salt and copper, zinc and/or aluminium precursors.

The additional salt may, for example, be a metal salt or non-metal salt. For example, the additional salt may be a carbonate, sulphate, chloride, nitrate, oxalate, acetate or combination thereof. Preferably, the metal or non-metal salt is a carbonate. The metal may, for example, be one or more alkali metals. Hereinafter, the present invention may be described in terms of sodium carbonate. However, the invention should not be construed as being limited as such. Preferably, the hydroxide salt(s) and any additional salt(s) are combined with the metal (copper, zinc and aluminium) precursors at approximately the same time. Preferably, the hydroxide salt(s) and any additional salt(s) are combined with a mixture of the metal (copper, zinc and aluminium) precursors. For example, the copper precursor(s), zinc precursor(s), aluminium precursor(s), hydroxide salt(s) and any additional salt(s) may all be combined within 1 minute of each other.

In certain embodiments, the hydroxide salt and additional salt (e.g. carbonate) are used in amounts having a ratio equal to or greater than about 1 :1 . For example, the hydroxide salt and additional salt (e.g. carbonate) may be used in amounts having a ratio equal to or greater than about 5:1 or equal to or greater than about 6:1 or equal to or greater than about 7:1 or equal to or greater than about 8:1 or equal to or greater than about 9:1 or equal to or greater than about 10:1 or equal to or greater than about 1 1 :1 or equal to or greater than about 12:1 or equal to or greater than about 13:1 or equal to or greater than about 14:1 or equal to or greater than about 15:1 . For example, the hydroxide salt and additional salt (e.g. carbonate) may be used in a ratio up to about 20:1 or up to about 19:1 or up to about 18:1 or up to about 17:1 or up to about 16:1 or up to about 15:1 . For example, the hydroxide salt and additional salt (e.g. carbonate) may be used in a ratio ranging from about 5:1 to about 20:1 . This may, for example, assist in preventing formation of carbonate-rich phases, such as malachite which is used to form the industrial catalyst used in current industrial processes for methanol synthesis.

In certain embodiments, the copper and zinc precursors are used in amounts having a ratio equal to or greater than about 1 :5. For example, the copper and zinc precursors may be used in amounts having a ratio equal to or greater than about 1 :2 or equal to or greater than about 1 :3 or equal to or greater than about 1 :2 or equal to or greater than about 1 :1 . For example, the copper and zinc precursors may be used in a ratio up to about 5:1 or up to about 4:1 or up to about 3:1 . For example, the copper and zinc precursors may be used in a ratio ranging from about 1 :5 to about 5:1 or from about 1 :3 to about 3:1 or from about 1 :2 to about 2:1 . For example, the copper and zinc precursors may be used in a ratio ranging from about 1 :1 to about 3:1 or from about 2:1 to about 3:1 . The ratio of copper to zinc in the catalyst precursor and catalyst products may therefore be within these ranges.

In certain embodiments, the zinc and aluminium precursors are used in amounts having a ratio equal to or greater than about 1 :2. For example, the zinc and aluminium precursors may be used in amounts having a ratio equal to or greater than about 1 :1 or equal to or greater than about 2:1 . For example, the zinc and aluminium precursors may be used in amounts having a ratio up to about 5:1 or up to about 5:2. For example, the zinc and aluminium precursors may be used in a ratio ranging from about 1 :2 to about 5:2 or from about 1 :1 to about 3:4. The ratio of zinc to aluminium in the catalyst precursor and catalyst products may therefore be within these ranges.

In certain embodiments, the copper and aluminium precursors are used in amounts having a ratio equal to or greater than about 1 :2. For example, the copper and aluminium precursors may be used in amounts having a ratio equal to or greater than about 1 :1 or equal to or greater than about 2:1 . For example, the copper and aluminium precursors are used in amounts having a ratio up to about 5:1 or up to about 5:2. For example, the zinc and aluminium precursors may be used in a ratio ranging from about 1 :2 to about 5:2. For example, the zinc and aluminium precursors may be used in a ratio ranging from about 1 :2 to about 9:4. The ratio of copper to aluminium in the catalyst precursor and catalyst products may therefore be within these ranges.

The method may be carried out under any conditions suitable to form the hydrotalcite structure comprising copper, zinc and aluminium.

In certain embodiments, the method is carried out at a pH ranging from about 6 to about 10. For example, the method may be carried out at a pH ranging from about 6.5 to about 10. For example, the method may be carried out at a pH ranging from about 6.5 to about 9.5 or from about 7 to about 9.

In certain embodiments, the method is carried out at a pH ranging from about 7 to about 9. For example, the method may be carried out at a pH ranging from about 7.25 to about 8.75 or from about 7.5 to about 8.5 or from about 7.75 to about 8.25. For example, the method may be carried out at a pH of about 8. When measuring pH, it would be known to a person of ordinary skill in the art to use a probe appropriate and calibrated for the medium that is being tested (e.g. aqueous or organic solvent-based). In certain embodiments, the method is carried out at a temperature ranging from about 20°C to about 70°C. For example, the method may be carried out at a temperature ranging from about 20°C to about 65°C or from about 20°C to about 60°C or from about 20°C to about 55°C or from about 20°C to about 50°C or from about 20°C to about 45°C or from about 20°C to about 40°C or from about 20°C to about 35°C or from about 20°C to about 30°C. For example, the method may be carried out at a temperature ranging from about 21 °C to about 29°C or from about 22°C to about 28°C or from about 23°C to about 27°C or from about 24°C to about 26°C. For example, the method may be carried out at a temperature of about 25°C. In certain embodiments, the double hydroxide layers of the hydrotalcite structure comprising copper, zinc and aluminium are separated by treatment with an organic solvent. Treatment with an organic solvent may, for example, refer to contacting the hydrotalcite material comprising copper, zinc and aluminium with the organic solvent, for example mixing and/or stirring the hydrotalcite material comprising copper, zinc and aluminium with the organic solvent. In certain embodiments, the treatment with organic solvent occurs at the same time as precipitation of the hydrotalcite structure comprising copper, zinc and aluminium. Treatment with an organic solvent may thus, for example, refer to contacting, for example mixing and/or stirring, a mixture of copper precursor, zinc precursor, aluminium precursor, hydroxide salt and any (optional) other salt with the organic solvent.

In certain embodiments, the treatment with organic solvent occurs sequentially to the formation of the hydrotalcite material comprising copper, zinc and aluminium. Where the treatment with organic solvent is performed after the formation of the hydrotalcite structure comprising copper, zinc and aluminium (e.g. after precipitation process), the hydrotalcite structure (e.g. the precipitate) may, for example, be filtered and/or washed with solvent prior to the organic solvent treatment. Any method of filtration known to those skilled in the art or disclosed herein may be used. Any solvent known to those of ordinary skill in the art, for example any organic solvent such as ethanol, may be used for the washing step. Alternatively, a solution or suspension including the hydrotalcite material (e.g. the precipitate) may be directly contacted (e.g. mixed with) the organic solvent (after the precipitation process has completed).

Where the treatment with organic solvent is performed simultaneously with the formation of the hydrotalcite structure comprising copper, zinc and aluminium (e.g. simultaneously with precipitation process), the copper, zinc and aluminium precursors, hydroxide salt and organic solvent are all contacted at approximately the same time, for example within about 5 minutes or about 4 minutes or about 3 minutes or about 2 minutes or about 1 minute of each other. For example, the organic solvent may be mixed with the copper precursor, zinc precursor and/or aluminium precursor prior to mixing the precursors with the hydroxide salt. For example, the copper, zinc and/or aluminium precursors may be dissolved in the organic solvent and may not be dissolved in water. Alternatively or additionally, the organic solvent may be mixed with the hydroxide salt prior to mixing with the precursors. Alternatively or additionally, the organic solvent may be mixed with the additional metal salt described herein prior to mixing with the precursors and/or hydroxide salt.

Preferably, the organic solvent is a water-miscible organic solvent. By "water-miscible" it is meant that the organic solvent can be mixed with an equal volume of the mixture of copper precursor, zinc precursor, aluminium precursor, hydroxide salt and any (optional) other salt without forming separate phases. In certain embodiments, the water-miscible organic solvent is a polar organic solvent. In certain embodiments, the water-miscible organic solvent is acetone, acetaldehyde, acetonitrile, butanediol, butoxyethanol, diethanolamine, diethylenetriamine, dimethylformamide, dimethoxyethane, dimethyl sulfoxide, 1 ,4-dioxane, ethanol, ethylamine, ethylene glycol, furfuryl alcohol, glycerol, methanol, methyl diethanolamine, methyl isocyanide, 1 - propanol, 1 ,3-propanediol, 1 ,5-pentanediol, 2-propanol, propylene glycol, pyridine, tetrahydrofuran, triethylene glycol, or combinations thereof. In certain embodiments, the water-miscible organic solvent is acetone and/or ethanol and/or methanol.

In certain embodiments, the organic solvent is used in an amount of about 10 to about 100 ml per gram of filtered or filterable material. The term "filterable material" refers to the material that would form if a solution or suspension was filtered. For example, the organic solvent may be used in an amount of about 20 to about 90 ml per gram of filtered or filterable material or in an amount of about 30 to about 80 ml per gram of filtered or filterable material or in an amount of about 40 to about 70 ml per gram of filtered or filterable material or in an amount of about 40 to about 60 ml per gram of filtered or filterable material.

The treatment with organic solvent may, for example, occur at any temperature below the boiling point of the solvent. For example, the treatment with organic solvent may occur at a temperature ranging from about 15°C to about 30°C. For example, the treatment may occur at a temperature ranging from about 16°C to about 29°C or from about 17°C to about 28°C or from about 18°C to about 27°C or from about 19°C to about 26°C or from about 20°C to about 25°C or from about 21 °C to about 24°C. Where the treatment with organic solvent occurs simultaneously with making the separate double hydroxide layers of hydrotalcite structure, the solvent treatment occurs at the same temperature as the making the separate double hydroxide layers of hydrotalcite structure. In certain embodiments, the separate double hydroxide layers of hydrotalcite structure comprising copper, zinc and aluminium may be filtered to form a solid catalyst precursor. For example, after filtering the catalyst precursor may have a solid content equal to or greater than about 95 wt%. For example, after filtering the catalyst precursor may have a solid content equal to or greater than about 96 wt% or equal to or greater than about 97 wt% or equal to or greater than about 98 wt%.

Filtration may, for example, be carried out by any suitable method known to those skilled in the art. For example, filtration may be carried out by hot filtration, cold filtration, vacuum filtration, centrifugation or any combination thereof. Preferably, filtration is carried out by vacuum filtration, for example using a water pump.

In certain embodiments, the separate layers of hydrotalcite structure are dried to form a solid catalyst precursor. In certain embodiments, the separate layers of hydrotalcite structure are dried after filtration to form a solid catalyst precursor. For example, after drying, the catalyst precursor may have a solid content equal to or greater than about 97 wt% or equal to or greater than about 98 wt% or equal to or greater than about 99 wt% or equal to or greater than about 99.5 wt%.

Drying may, for example, be carried out by any suitable method known to those skilled in the art. For example, drying may be carried out in an oven at a temperature above the boiling point of the organic solvent. For example, drying may be carried out in an oven at a temperature equal to or greater than about 80°C. For example, drying may be carried out at a temperature equal to or greater than about 85°C or equal to or greater than about 90°C or equal to or greater than about 95°C or equal to or greater than about 100°C or equal to or greater than about 105°C or equal to or greater than about 1 10°C.

Drying may, for example, be carried out for a period of time ranging from about 30 minutes to about 24 hours. For example, drying may be carried out for a period of time ranging from about 1 hour to about 24 hours, for example from about 1 hour to about 16 hours, for example from about 1 hour to about 8 hours.

Method for Making a Catalyst

There is further provided herein a method for making a catalyst suitable for use in the synthesis of methanol. The method comprises making a catalyst precursor by any aspect or embodiment disclosed herein and calcining the catalyst precursor to form a catalyst. The calcined catalyst may, for example, be reduced to form a catalyst comprising copper particles. The reduction may, for example, occur after the calcination or may occur concurrently with the calcination.

Calcination refers to a process in which the catalyst precursor is heated to a temperature sufficient to effect the removal of solvents in the crystal structure and to bring about the decomposition of volatile species in the presence of air or oxygen. In certain embodiments, calcination is carried out at a temperature equal to or greater than about 200°C. For example, calcination may be carried out at a temperature equal to or greater than about 210°C or equal to or greater than about 220°C or equal to or greater than about 230°C or equal to or greater than about 240°C or equal to or greater than about 250°C or equal to or greater than about 260°C or equal to or greater than about 270°C or equal to or greater than about 280°C or equal to or greater than about 290°C or equal to or greater than about 300°C. For example, calcination may be carried out at a temperature up to about 600°C.

Calcination may, for example, be carried out for a period of time ranging from about 30 minutes to about 24 hours. For example, calcination may be carried out for a period of time ranging from about 1 hour to about 16 hours or from about 1 hour to about 8 hours or from about 1 hour to about 4 hours or from about 1 hour to about 2 hours.

The reduction may be carried out by any process known to those skilled in the art in order to form a catalyst comprising copper particles. In certain embodiments, the reduction is carried out by heating the catalyst precursor in the presence of a reducing agent.

In certain embodiments, the reducing agent is selected from hydrogen, carbon monoxide, methanol, and combinations thereof. For example, the reducing agent may be used in a mixture with an inert gas such as argon, helium or nitrogen.

In certain embodiments, the reduction is carried out at a temperature equal to or greater than about 150°C. For example, the reduction may be carried out at a temperature equal to or greater than about 160°C or equal to or greater than about 170°C or equal to or greater than about 180°C or equal to or greater than about 190°C or equal to or greater than about 200°C or equal to or greater than about 210°C or equal to or greater than about 220°C. For example, the reduction may be carried out at a temperature up to about 300°C or up to about 290°C or up to about 280°C or up to about 270°C or up to about 260°C or up to about 250°C. For example, the reduction may be carried out at a temperature ranging from about 200°C to about 250°C, for example from about 220°C to about 230°C.

In certain embodiments, the reduction process is carried out for a period of time ranging from about 30 minutes to about 24 hours or from about 1 hour to about 24 hours or from about 1 hour to about 16 hours or from about 1 hour to about 8 hours.

Catalyst Precursor There is further provided herein a catalyst precursor obtained by or obtainable by a method according to any aspect or embodiment disclosed herein. There is further provided herein a catalyst precursor comprising separate double hydroxide layers of a hydrotalcite structure comprising copper, zinc and aluminium. The double hydroxide layers of a hydrotalcite structure may, for example, be separated by solvent molecules. The term "separate double hydroxide layers of a hydrotalcite structure comprising copper, zinc and aluminium" has the same meaning as discussed above, namely that the double hydroxide layers are discrete and distinct units that would not aggregate or agglomerate upon drying (where the precursor is in solution or suspension) or are not aggregated or agglomerated where the precursor is in solid form. Where the catalyst precursor is in solid form, separate sheets of the hydrotalcite structure can be seen using transmission electron microscopy.

The catalyst precursor may, for example, be a solution or suspension (for example before any of the filtration and/or drying steps disclosed herein are performed). The catalyst precursor may, for example, be a solid (for example, after any of the filtration and/or drying steps disclosed herein are performed). Thus, in certain embodiments, the catalyst precursor has a solids content equal to or greater than about 95 wt%. For example, the catalyst precursor may have a solids content equal to or greater than about 96 wt% or equal to or greater than about 97 wt% or equal to or greater than about 98 wt% or equal to or greater than about 99 wt%.

The catalyst precursor may, for example, comprise copper, zinc and/or aluminium each in the form of ions. For example, the catalyst precursor may comprise copper in the form of copper ions. The catalyst precursor may, for example, comprise copper, zinc and/or aluminium each in the form of the metal hydroxide. For example, the catalyst precursor may comprise copper in the form of copper hydroxide. The ratios of copper, zinc and aluminium in the catalyst precursor may, for example, be as described above. In certain embodiments, the catalyst precursor does not comprise magnesium.

Further characterisation of structural features of catalyst precursor can be performed using X-Ray diffraction (XRD) and Transmission Electron Microscopy (TEM). XRD analysis of the catalyst precursor may show a peak pattern consistent with a substituted hydrotalcite structure. For example, the catalyst precursor may have diffraction peaks at about 10.0° - 12.0°, about 22.0° - 24.0°, about 33.0° - 35.0° and/or about 58.0° - 61 .0°. For example, the catalyst precursor may have diffraction peaks at about 10.5° - 1 1 .5°, about 22.5° - 23.5°, about 33.5° - 34.5° and/or about 58.5° - 60.5°. For example, the catalyst precursor may have diffraction peaks at about 1 1 .20 ° - 1 1 .30 ° , about 23.05° - 23.1 °5, about 33.95° - 34.05° and/or about 59.90° - 60.¾(For example, the catalyst precursor may have diffraction peaks at about 1 1 .25° , about 23.1 ° , about 34.0° , and/or about 59.95° . These diffraction peaks may, for example, correspond to the (003), (006), (012) and a combination of (1 10) and (1 13) crystal planes of hydrotalcite.

The catalyst precursor may, for example, have an X-Ray diffraction pattern substantially the same as that shown in Figure 3(A).

TEM of the catalyst precursors may, for example, show discrete sheets of material. For example, the discrete sheets of material may be of the order of about 50 nm to about 150 nm in diameter, for example about 60 nm to about 140 nm in diameter, for example about 70 nm to about 130 nm in diameter, for example about 80 nm to about 120 nm in diameter, for example about 90 nm to about 1 10 nm in diameter, for example about 100 nm in diameter. For example, the discrete sheets of material may be in the order of 5 nm to about 15 nm in thickness, for example from about 6 nm to about 14 nm in thickness, for example from about 7 nm to about 13 nm in thickness, for example from about 8 nm to about 12 nm in thickness, for example from about 9 nm to about 1 1 nm in thickness, for example about 10 nm in thickness. The diameter and/or thickness are both measured between the further points where the sheets are not uniform in diameter and/or thickness.

The catalyst precursor may, for example, have a specific surface area equal to or greater than about 100 m²/g. For example, the catalyst precursor may have a specific surface area equal to or greater than about 1 10 m²/g or equal to or greater than about 120 m²/g or equal to or greater than about 130 m²/g or equal to or greater than about

140 m²/g or equal to or greater than about 150 m²/g or equal to or greater than about

160 m²/g or equal to or greater than about 170 m²/g or equal to or greater than about

180 m²/g or equal to or greater than about 190 m²/g or equal to or greater than about

200 m²/g or equal to or greater than about 210 m²/g or equal to or greater than about 220 m²/g or equal to or greater than about 230 m²/g or equal to or greater than about

240 m²/g or equal to or greater than about 250 m²/g or equal to or greater than about

260 m²/g or equal to or greater than about 270 m²/g or equal to or greater than about

280 m²/g or equal to or greater than about 290 m²/g or equal to or greater than about

300 m²/g. The catalyst precursor may, for example, have a specific surface area up to about 500 m²/g. For example, the catalyst precursor may have a specific surface area up to about 450 m²/g or up to about 400 m²/g or up to about 350 m²/g. For example, the catalyst precursor may have a specific surface area ranging from about 100 m²/g to about 500 m²/g or from about 200 m²/g to about 400 m²/g.

Unless otherwise stated, specific surface area is measured by according to the BET method by the quantity of nitrogen adsorbed on the surface of said particles so to as to form a monomolecular layer completely covering said surface (measurement according to the BET method, AFNOR standard X1 1 -621 and 622 or ISO 9277).

Catalyst There is further provided herein a catalyst obtained by or obtainable by a method according to any aspect or embodiment disclosed herein. There is further provided herein a catalyst comprising separate oxide layers (or wafers) comprising copper, zinc and aluminium. The catalyst may, for example, comprise an amorphous mixture comprising copper, zinc and aluminium. The catalyst may, for example, be derived from a hydrotalcite structure comprising copper, zinc and aluminium.

The term "separate oxide layers comprising copper, zinc and aluminium" has a corresponding meaning as discussed above in relation to the term "separate double hydroxide layers of a hydrotalcite structure", namely that the oxide layers (that are each separated by counterions in the normal hydrotalcite crystal structure) are discrete and distinct units that are not aggregated or agglomerated.

The catalyst has undergone calcination. The catalyst may or may not have undergone reduction.

In certain embodiments, the catalyst is a solid. For example, the catalyst may have a solids content equal to or greater than about 98 wt% or equal to or greater than about 99 wt% or equal to or greater than about 99.5 wt%. The catalyst may, for example, comprise copper, zinc and/or aluminium in the form of copper oxide, zinc oxide and/or aluminium oxide respectively. For example, in the non- reduced form, the catalyst may comprise copper in the form of copper oxide. For example, in the reduced form, the catalyst may comprise zinc and aluminium in the form of zinc oxide and aluminium oxide respectively. In certain embodiments, the catalyst does not comprise magnesium.

When in reduced form, the catalyst comprises particles of elemental copper. For example, the catalyst may comprise copper nanoparticles. For example, the catalyst may comprise copper nanoparticles that have an average diameter of less than about 10 nm. For example, the catalyst may comprise copper nanoparticles that have an average diameter of less than about 9 nm or less than about 8 nm or less than about 7 nm or less than about 6 nm or less than about 5 nm. For example, the catalyst may comprise copper nanoparticles that have an average diameter of about 4 nm. For example, the catalyst may comprise copper nanoparticles that have an average diameter of at least about 1 nm.

The average size of the copper particles is measured using X-ray diffraction and the Scherrer equation. Further characterisation of structural features of the catalyst (after calcination and before reduction or after reduction) can be performed using X-Ray diffraction (XRD) and Transmission Electron Microscopy (TEM).

XRD of the calcined (but not reduced) material may, for example, show a peak pattern consistent with copper (II) oxide (CuO). For example, the XRD of the calcined (but not reduced) material may have a diffraction peak centred at about 35° to about 38°, for example a single broad diffraction peak at about 35° to about 38°. This is consistent with the (002), (-1 1 1 ), (1 1 1 ) and (200) crystal planes of CuO. Should the material be calcined at temperatures of 600+ °C the peaks will sharpen and resolve as the particles sinter and increase in size. When this occurs, diffraction peaks may, for example, be evident at about 35.5°, about 35.6°, about 38.8° and/or about 38.9°. For example, the diffraction peaks may be evident at about 35.45°, about 35.56°, about 38.75° and/or about 38.92°. This may, for example, be consistent with the (002), (-1 1 1 ), (1 1 1 ) and (200) peaks respectively. The catalyst may, for example, have an X-Ray diffraction pattern substantially the same as that shown in Figure 3(B) after calcination but before reduction.

TEM of the calcined (but not reduced) material may, for example, show discrete sheets of material. For example, the discrete sheets of material may be of the order of about 50 nm to about 150 nm in diameter, for example about 60 nm to about 140 nm in diameter, for example about 70 nm to about 130 nm in diameter, for example about 80 nm to about 120 nm in diameter, for example about 90 nm to about 1 10 nm in diameter, for example about 100 nm in diameter. For example, the discrete sheets of material may be in the order of 5 nm to about 15 nm in thickness, for example from about 6 nm to about 14 nm in thickness, for example from about 7 nm to about 13 nm in thickness, for example from about 8 nm to about 12 nm in thickness, for example from about 9 nm to about 1 1 nm in thickness, for example about 10 nm in thickness. The diameter and/or thickness are both measured between the further points where the sheets are not uniform in diameter and/or thickness.

XRD of the reduced material may, for example, show a peak pattern consistent with elemental copper combined with zinc oxide. For example, the catalyst may have diffraction peaks at about 42.0° - 44.0° and/or about 49.0° - 52.0°. For example, the catalyst may have diffraction peaks at about 42.5° - 43.5° and/or about 49.5° - 51 .5°. For example, the catalyst may have diffraction peaks at about 43.0° - 43.5° and/or about 50.0° - 51 .0°, for example at about 43.0° - 43.5° and/or about 50.5° - 51 .0°. For example, the catalyst may have diffraction peaks at about 43.20° - 43.40° and/or about 50.70 ° - 50.80°. For example, the catalyst may have diffraction peaks at about 43.25° and about 50.73 °. This may, for example, correspond to the (1 1 1 ) and (200) crystal planes of elemental copper.

The catalyst may, for example, have an X-Ray diffraction pattern substantially the same as that shown in Figure 3(C) after calcination and reduction.

TEM of the reduced material will show discrete sheets of material. For example, the discrete sheets of material may have diameters of about 30 nm to about 150 nm, for example about 40 nm to about 140 nm, for example from about 50 nm to about 130 nm, for example from about 60 nm to about 120 nm, for example from about 70 nm to about 1 10 nm, for example from about 80 nm to about 100 nm. The discrete sheets of material may be decorated with small particles, for example having a size of less than about 15 nm, for example less than about 14 nm or less than about 13 nm or less than about 12 nm or less than about 1 1 nm or less than about 10 nm, which are believed to be copper. The catalyst may, for example, have a specific surface area equal to or greater than about 100 m²/g. For example, the catalyst may have a specific surface area equal to or greater than about 1 10 m²/g or equal to or greater than about 120 m²/g or equal to or greater than about 130 m²/g or equal to or greater than about 140 m²/g or equal to or greater than about 150 m²/g or equal to or greater than about 160 m²/g or equal to or greater than about 170 m²/g or equal to or greater than about 180 m²/g or equal to or greater than about 190 m²/g or equal to or greater than about 200 m²/g or equal to or greater than about 210 m²/g or equal to or greater than about 220 m²/g or equal to or greater than about 230 m²/g or equal to or greater than about 240 m²/g or equal to or greater than about 250 m²/g or equal to or greater than about 300 m²/g.

The catalyst may, for example, have a specific surface area up to about 500 m²/g. For example, the catalyst may have a specific surface area up to about 450 m²/g or up to about 400 m²/g or up to about 350 m²/g or up to about 300 m²/g or up to about 250 m²/g.

For example, the catalyst may have a specific surface area ranging from about 100 m²/g to about 300 m²/g or form about 150 m²/g to about 250 m²/g.

The catalyst in reduced form may, for example, have a copper surface area equal to or greater than about 30 m²/g. For example, the catalyst in reduced form may have a copper surface area equal to or greater than about 35 m²/g or equal to or greater than about 40 m²/g or equal to or greater than about 45 m²/g or equal to or greater than about 50 m²/g. For example, the catalyst in reduced from may have a copper surface area up to about 80 m²/g or up to about 75 m²/g or up to about 70 m²/g or up to about 65 m²/g or up to about 60 m²/g.

Unless otherwise stated, copper surface area is measured by the decomposition of N₂0 on copper at 65°C to give N₂ and Cu₂0. The amount of N₂ produced is assumed to be equivalent to half a monolayer coverage of oxygen, and the surface density of Cu is assumed to be 1 .47 x 10¹⁹ atoms rrr². Uses of the Catalyst Precursor and Catalyst

There is also provided herein the various uses of the catalyst precursors and catalysts disclosed herein and made by the methods disclosed herein.

In certain embodiments, the catalyst precursors disclosed herein can be used to make a catalyst, for example can be used to make a catalyst that is active for the synthesis of methanol or dimethyl ether and/or is active for the water-gas shift reaction. In certain embodiments, the catalysts disclosed herein can be used in a method of synthesizing methanol. For example, the catalysts disclosed herein may be used in a method synthesizing methanol from a mixture of carbon monoxide, hydrogen, carbon dioxide and/or hydrogen. In certain embodiments, the synthesis gas is made from any solid biomass, including, for example, agricultural, city and industrial waste. In certain embodiments, synthesis gas is made from gas and liquid sources such as methane or glycerol. In certain embodiments propane-1 ,2,3-triol (glycerol) (e.g. a by-product from the production of biodiesel from animal fats and vegetable oils) is used to produce the synthesis gas. In certain embodiments, the carbon dioxide is waste carbon dioxide.

In certain embodiments, the method for synthesizing methanol is carried out in a fixed bed reactor. In certain embodiments, the method for synthesizing methanol is carried out at a temperature ranging from about 200°C to about 300°C. For example, the method of synthesizing methanol may be carried out at a temperature ranging from about 210°C to about 290°C or from about 220°C to about 280°C or from about 230°C to about 270°C or from about 240°C to about 260°C. For example, the method of synthesizing methanol may be carried out at a temperature of about 250°C. This may refer to the temperature of the reaction container and/or the temperature of the catalyst bed.

In certain embodiments, the method for synthesizing methanol may be carried out at a pressure ranging from about 100 kPa to about 10,000 kPa. For example, the method for synthesizing methanol may be carried out at a pressure ranging from about 500 kPa to about 9000 kPa or from about 1000 kPa to about 8000 kPa or from about 1500 kPa to about 7000 kPa or from about 2000 kPa to about 6000 kPa or from about 3000 kPa to about 5000 kPa.

The invention will now be described in detail by way of reference only to the following non-liming examples.

EXAMPLES

Example 1

Hydrotalcite layered double hydroxide structures of general formula (M)6AI₂C03(OH) i6, wherein M is either Mg, Zn or Cu were made by coprecipitation of metal salts using a Toledo Metrohm autotitrator, followed by a solvent delamination treatment. Copper nitrate hemipentahydrate (Cu(N0₃)₂-2.5H₂0) or zinc nitrate hexahydrate (Zn(N0₃)₂-6H₂0) or magnesium nitrate hexahydrate (Mg(N0₃)₂-6H₂0) plus aluminium nitrate nonahydrate (AI(N0₃)₂-9H₂0) were dissolved in deionised water to create a solution with a total molar concentration of 0.25 M, with concentrations of 0.1875 M for the (M) salt and 0.0625 M of aluminium nitrate. Additionally, a base solution was created by dissolving sodium hydroxide (NaOH) and sodium carbonate (Na₂C0₃) in deionised water to give concentrations of 0.5 M NaOH and 0.05 M Na₂C0₃.

A small aliquot (20 cm³) of the mixed metal solution was added to the reaction vessel, which was maintained at a temperature of 25°C, and stirred continuously. The amount of liquid was chosen such that it was sufficient to cover the pH probe. This initial aliquot was brought to pH 8 by the addition of the base solution until the target pH was reached.

Subsequently, the mixed metal solution was added to the vessel at a rate of 5 cm³/min with continuous stirring. Concurrently, base solution was added at a sufficient rate to ensure that the reaction mixture maintained a constant pH of 8. Once all of the mixed metal solution was added, the pH was monitored and controlled for a further 10 mins to ensure complete precipitation of the material. This precipitate was filtered under suction and washed with an amount of water equal to twice the volume of the mixed metal solution used in the precipitation (i.e. 400 cm³ for a reaction involving 200 cm³ of mixed metal solution) to remove excess sodium salts. This material was then washed with an amount of ethanol or acetone equal to twice the amount of water used in the previous step. This wet cake was added to an amount of acetone or ethanol equal to the volume of the mixed metal solution used in the precipitation and stirred for 1 hour.

This re-dispersed material was then filtered under suction and dried at 1 10 °C for 16 hours. The material was then calcined at 300 °C (thermal ramp rate of 5 °C/min) in static air for 2 hours.

It was found that it was not possible to make a hydrotalcite material when M was copper.

The specific surface areas of the zinc and magnesium samples were measured by BET as described above. It was found that when M was magnesium, the material had a specific surface area of about 350 m²/g. When M was zinc, the material had a specific surface area of about 90 m²/g.

Example 2

A catalyst precursor was made by coprecipitation of metal salts using a Toledo Metrohm autotitrator, followed by a solvent delamination treatment. Copper nitrate hemipentahydrate (Cu(N0₃)₂-2.5H₂0), zinc nitrate hexahydrate (Zn(N0₃)₂-6H₂0) and aluminium nitrate nonahydrate (AI(N0₃)₂-9H₂0) were dissolved in deionised water to create a mixed metal solution with a total molar concentration of 0.25 M. Additionally, a base solution was created by dissolving sodium hydroxide (NaOH) and sodium carbonate (Na₂C0₃) in deionised water to give concentrations of 0.5 M NaOH and 0.05 M Na₂C0₃. A small aliquot (20 cm³) of the mixed metal solution was added to the reaction vessel, which was maintained at a temperature of 25°C, and stirred continuously. The amount of liquid was chosen such that it was sufficient to cover the pH probe. This initial aliquot was brought to pH 8 by the addition of the base solution until the target pH was reached. Subsequently, the mixed metal solution was added to the vessel at a rate of 5 cm³/min with continuous stirring. Concurrently, base solution was added at a sufficient rate to ensure that the reaction mixture maintained a constant pH of 8. Once all of the mixed metal solution was added, the pH was monitored and controlled for a further 10 mins to ensure complete precipitation of the material.

This precipitate was filtered under suction and washed with an amount of water equal to twice the volume of the mixed metal solution used in the precipitation (i.e. 400 cm³ for a reaction involving 200 cm³ of mixed metal solution) to remove excess sodium salts. This material was then washed with an amount of ethanol or acetone equal to twice the amount of water used in the previous step. This wet cake was added to an amount of acetone or ethanol equal to the volume of the mixed metal solution used in the precipitation and stirred for 1 hour. This re-dispersed material was then filtered under suction and dried at 1 10 °C for 16 hours to give the catalyst precursor, a layered double hydroxide.

The catalyst precursor was calcined at 300 °C (thermal ramp rate of 5 °C/min) in static air for 2 hours.

It was surprisingly found that a stable hydrotalcite material comprising copper and zinc was formed by the co-precipitation and solvent treatment.

The specific surface area of the material prior to and after calcining were measured as described herein. This was compared to the specific surface area of a malachite catalyst precursor prior to and after calcining, and also to a hydrotalcite material comprising copper, zinc and aluminium that was made by the same method as described above except that the washing with ethanol or acetone was not performed. Instead, the precipitate was allowed to age in solution at 65 °C for 3 hours.

This precipitate was filtered under suction and washed with water to remove excess sodium salts. This material was then dried at 1 10 °C for 16 hours before being calcined at 330 °C (thermal ramp rate 5 °C/min) in static air for 3 hours. This precipitate was filtered under suction and washed with water to remove excess sodium salts. This material was then dried at 1 10 °C for 16 hours before being calcined at 330 °C (thermal ramp rate 5 °C/min) in static air for 3 hours. The malachite catalyst precursor was obtained by coprecipitation of metal salts using a Toledo Metrohm autotitrator. Copper nitrate hemipentahydrate (Cu(N0₃)₂-2.5H₂0), zinc nitrate hexahydrate (Zn(N0₃)₂-6H₂0) and aluminium nitrate nonahydrate (AI(N0₃)₂-9H₂0) were dissolved in deionised water to create a mixed metal solution with a total molar concentration of 0.25 M. Additionally, a base solution was created by dissolving sodium carbonate (Na₂C0₃) in deionised water to give a concentration of 1 .5 M Na₂C0₃.

A small aliquot (20 cm³) of the mixed metal solution was added to the reaction vessel, which was maintained at a temperature of 65°C, and stirred continuously. The amount of liquid was chosen such that it was sufficient to cover the pH probe. This initial aliquot was brought to pH 6.5 by the addition of the base solution until the target pH was reached.

Subsequently, the mixed metal solution was added to the vessel at a rate of 5 cm³/min with continuous stirring. Concurrently, base solution was added at a sufficient rate to ensure that the reaction mixture maintained a constant pH of 8. Once all of the mixed metal solution was added, the pH was monitored and controlled for a further 10 mins to ensure complete precipitation of the material. Thereafter, the precipitate was allowed to age in solution at 65 °C for 3 hours.

This precipitate was filtered under suction and washed with water to remove excess sodium salts. This material was then dried at 1 10 °C for 16 hours before being calcined at 330 °C (thermal ramp rate 5 °C/min) in static air for 3 hours.

The malachite material, hydrotalcite material (without solvent treatment) and material including separate layers of hydrotalcite (with solvent treatment) were reduced in a mixture of hydrogen and helium (5% H₂ / He). The temperature was raised to 140°C at 10°C/min, and further raised to 225°C at 1 °C/min before being held at this temperature for 2 h.

The results are shown in Table 1 .

Table 1. Specific Surface Area Copper Surface Area

Material

(m²/a) (m²/a)

Material prior to calcining

Malachite precursor 85-100 -

Hydrotalcite (no solvent

2

treatment)

Separate layers of

hydrotalcite (solvent 339

treatment with acetone)

Separate layers of

hydrotalcite (solvent 321

treatment with ethanol)

After calcining

Malachite precursor 75-90 -

Hydrotalcite (no solvent

21

treatment)

Separate layers of

hydrotalcite (solvent 210-220

treatment with acetone)

Separate layers of

hydrotalcite (solvent 180-200

treatment with ethanol)

After reduction

Malachite precursor - 30-35

Hydrotalcite (no solvent 2-3

- treatment)

Separate layers of 50

hydrotalcite (solvent - treatment with acetone)

Transmission electron microscopy was used to observe the morphology of the materials made by the methods described above. The results are shown in Figure 2. It can be seen that the materials formed by the co-precipitation and solvent (ethanol or acetone) treatment as described above include separate sheets. The delaminated morphology is maintained after calcination. Small particles believed to be copper nanoparticles can be seen on the surface of the (reduced) catalyst.

X-ray diffraction was used to characterise the materials made by the methods described above. The results are shown in Figures 3, 4 and 5. It can be seen that the materials that were made by co-precipitation and solvent treatment as described above have a different structure to that of the malachite materials (both before and after calcination). It can also be seen that the material made by co-precipitation and solvent treatment as described above has a smaller particle size after calcination. After reduction of the material made by the co-precipitation and solvent treatment, a broad peak corresponding to metallic copper is seen.

The size of the copper nanoparticles of the catalyst comprising separate layers of hydrotalcite was measured by using X-ray diffraction and the Scherrer equation. It was found that the copper particles of the catalyst comprising separate layers of hydrotalcite had an average particle diameter of about 4 nm. The average particle diameter of the copper particles in the industrial catalyst is reported in the literature as being approximately 10 nm. Example 3

Hydrotalcite layered double hydroxide structures of general formula (M)6AI₂C03(OH) i6, wherein M is either Mg, Zn or Cu were made by coprecipitation of metal salts using a Toledo Metrohm autotitrator in the presence of a solvent. The delamination step occurs simultaneously to the coprecipitation to produce separate double hydroxide layers of a hydrotalcite structure.

Copper nitrate hemipentahydrate (Cu(N0₃)₂ 2.5 H₂0), zinc nitrate hexahydrate (Zn(N0₃)₂ 6 H₂0) and magnesium nitrate hexahydrate (Mg(N0₃)₂ 6 H₂0) plus aluminium nitrate nonahydrate (AI(N0₃)₂-9 H₂0) were dissolved in absolute ethanol to create a mixed metal solution with a total molar concentration of 0.25 M, with individual concentrations of 0.1875 M for the (M) salt and 0.0625 M of aluminium nitrate. Additionally, a base solution was created by dissolving sodium hydroxide (NaOH) in absolute ethanol to give a concentration of 0.55 M NaOH. A small aliquot (20 cm³) of the mixed metal solution was added to the reaction vessel, which was maintained at a temperature of 25 °C, and stirred continuously.

Subsequently, the mixed metal solution was added to the vessel at a rate of 5 cm³/min with continuous stirring. Concurrently, base solution was added at 2.5 cm³/min. A total amount of 200 ml mixed metal solution and 100 ml base solution were added in this manner. This ratio is equivalent to the amount of base required to keep the solution at pH 8 in the method described in Example 2. Due to the use of pure ethanol, a standard pH measurement cannot be used to monitor the reaction.

This precipitate was filtered under suction and washed with an amount of ethanol equal to twice the volume of the mixed metal solution used in the precipitation (i.e. 400 cm³ for a reaction involving 200 cm³ of mixed metal solution) to remove excess sodium salts. This washed material was then dried at 1 10 °C for 16 hours to give the catalyst precursor, a layered double hydroxide.

The catalyst precursor was calcined at 300 °C (thermal ramp rate of 5 °C/min) in static air for 2 hours. The specific surface area of the material prior to and after calcining were measured as described herein. It was found that the material formed had a surface area of about 204 m²/g prior to calcination and a surface area of about 1 10 m²/g after calcination.

Example 4

The reduced catalyst made by the co-precipitation and solvent treatment method described in Example 2 above was used in a method of making methanol from carbon dioxide and hydrogen. This was compared to the industrial catalyst formed from a malachite precursor.

The method was performed at 250°C (external temperature) and 2000 kPa. The temperature of the catalyst bed was about 20 to 30°C lower than the external temperature. The gas flow rate was 30 ml/min. The gas was C02:H₂:N₂ at a ratio of 20:60:20. Samples were taken every 7 minutes over the course of 5 hours and analysed by online gas chromatography. The average of the CO2 conversions and CO and methanol selectivities are shown in Table 2 below.

Table 2.

The catalyst made by the method described in Example 1 provided an improved carbon dioxide conversion compared to the industrial catalyst and provided 100% selectivity to carbon monoxide and methanol. The catalyst made by the method described in Example 1 favoured the production of methanol to a greater degree than the standard.

Example 5

The hydrotalcite materials including separate layers of hydrotalcite formed by the methods described in Examples 2 and 3 and hyrdotalcite materials not including separate layers formed by the method described in Example 2 (i.e. without solvent treatment) were reduced in a mixture of hydrogen and helium (5% H₂ / He). The temperature was raised to 140°C at 10°C/min, and further raised to 225°C at 1 °C/min before being held at this temperature for 1 hour.

The reduced catalysts were used in a method of making methanol from carbon dioxide and hydrogen. This was compared to the industrial catalyst formed from the hydrotalcite material not including separate layers (i.e. formed without solvent treatment). The reactor set-up was different to the reactor set-up used for Example 4. The measuring thermocouple was situated centrally in the catalyst bed, whereas the thermocouple was located in the oven heating cavity in Example 4. The method was performed at 250°C (measured in the catalyst bed) and 2000 kPa. The gas flow rate was 30 ml/min. The gas was C02:H₂:N₂ at a ratio of 20:60:20. Samples were taken every 25 minutes over the course of 24 hours and analysed by online gas chromatography.

The average of the CO2 conversions and CO and methanol selectivities are shown in Table 3 below.

Table 3.

CO2 conversion Methanol

Catalyst CO selectivity (%)

(%) selectivity (%)

Untreated

hydrotalcite (i.e.

17.28 94.63 5.33 without solvent

treatment)

Delaminated

hydrotalcite (formed

by two-step method

17.86 80.67 19.33 described in

Example 2 using

ethanol solvent)

Delaminated

hydrotalcite (formed

by one-step method

18.09 88.69 1 1 .31 described in

Example 3 using

ethanol solvent) For the avoidance of doubt, the following numbered paragraphs define particular embodiments of the present invention.

1 .A method for making a catalyst precursor, the method comprising making

separate double hydroxide layers of a hydrotalcite structure comprising copper, zinc, and aluminium.

2. The method of paragraph 1 , wherein the method comprises separating double hydroxide layers of a hydrotalcite structure comprising copper, zinc and aluminium.

3. The method of paragraph 1 or 2, wherein the method comprises making a

hydrotalcite structure comprising copper, zinc and aluminium and separating the double hydroxide layers of the hydrotalcite structure.

4. The method of paragraph 3, wherein making the double hydroxide layers of the hydrotalcite structure comprising copper, zinc and aluminium and separating the double hydroxide layers of the hydrotalcite structure occur simultaneously. 5. The method of any one of paragraphs 1 to 4, wherein the double hydroxide

layers of the hydrotalcite structure comprising copper, zinc and aluminium are made by a precipitation process.

6. The method of paragraph 5, wherein a hydroxide salt is added to a solution of copper, zinc and aluminium precursors to induce precipitation of the double hydroxide layers of the hydrotalcite structure.

7. The method of paragraph 6, wherein an additional salt, for example a metal salt, is added to the solution of copper, zinc and aluminium precursors.

8. The method of paragraph 7, wherein the salt is a carbonate, for example a metal carbonate.

9. The method of paragraph 6, wherein the hydroxide salt is sodium hydroxide, potassium hydroxide, ammonium hydroxide or a combination thereof.

10. The method of paragraph 8, wherein the carbonate is a sodium carbonate, potassium carbonate, ammonium carbonate or a combination thereof. The method of paragraph 7, wherein the ratio of hydroxide salt to additional salt is equal to or greater than about 5:1 . The method of any one of paragraphs 6 to 1 1 , wherein the copper precursor is copper nitrate, copper acetate, copper chloride or combination thereof, and/or the zinc precursor is zinc nitrate, zinc acetate, zinc chloride or a combination thereof, and/or the aluminium precursor is aluminium nitrate, aluminium acetate, aluminium chloride or a combination thereof. The method of any one of paragraphs 5 to 12, wherein the precipitation occurs at a pH ranging from about 7 to about 9. The method of any one of paragraphs 5 to 13, wherein the precipitation occurs at a temperature ranging from about 20°C to about 50°C. The method of any one of paragraphs 1 to 14, wherein the ratio of copper to zinc in the double hydroxide layers of the hydrotalcite structure is equal to or greater than about 1 :5. The method of any one of paragraphs 1 to 15, wherein the ratio of zinc to aluminium in the double hydroxide layers of the hydrotalcite structure is equal to or greater than about 1 :2. The method of any one of paragraphs 1 to 16, wherein the ratio of copper to aluminium in the double hydroxide layers of the hydrotalcite structure is equal to or greater than about 1 :2. The method of any one of paragraphs 2 to 17, wherein the double hydroxide layers of the hydrotalcite structure are separated by treating with a water- miscible organic solvent. The method of paragraph 18, wherein the water-miscible organic solvent is a polar organic solvent. The method of paragraph 18 or 19, wherein the water-miscible organic solvent is acetone and/or ethanol.

A method for making a catalyst, the method comprising making a catalyst precursor by a method of any one of paragraphs 1 to 20; calcining the catalyst precursor; and

optionally reducing the catalyst precursor after calcining or concurrently with the calcining. . A catalyst precursor obtained or obtainable by the method of any one of paragraphs 1 to 20. . A catalyst obtained or obtainable by the method of paragraph 21 . . A catalyst precursor comprising separate double hydroxide layers of a hydrotalcite structure comprising copper, zinc and aluminium. . The catalyst precursor of paragraph 22 or 24, wherein the catalyst precursor has a specific surface area equal to or greater than about 100 m²/g, for example equal to or greater than about 200 m²/g. . A catalyst precursor of any one of paragraphs 22, 24 or 25, comprising copper oxide. . A catalyst precursor of any one of paragraphs 22 or 24 to 26, wherein the catalyst precursor has an X-Ray diffraction pattern consistent with a substituted hydrotalcite structure. . The catalyst precursor of paragraph 27, wherein the catalyst precursor has an X-Ray diffraction pattern with diffraction peaks at about 10.0° - 12.CP, about 22.0° - 2Α.ϋ, about 33.0° - 35.CP, and about 58.0° - 61 .(?. . The catalyst precursor of any one of paragraphs 22 or 24 to 28, wherein transmission electron microscopy of the catalyst precursor shows discrete sheets of material. . The catalyst precursor of paragraph 29, wherein the discrete sheets of material have a diameter ranging from about 50 nm to about 150 nm. . The catalyst precursor of paragraph 29 or 30, wherein the discrete sheets of material have a thickness ranging from about 5 nm to about 15 nm. 32. A catalyst comprising separate double hydroxide layers comprising copper, zinc and aluminium.

33. The catalyst of paragraph 23 or 32, wherein the catalyst has a specific surface area equal to or greater than about 100 m²/g, for example equal to or greater than about 200 m²/g.

34. The catalyst of paragraph 23, 32 or 33, wherein the catalyst has a copper

surface area equal to or greater than about 30 m²/g.

35. The catalyst of paragraph 23 or 32 to 34, wherein the catalyst comprises copper nanoparticles.

36. The catalyst of paragraph 23 or 32 to 35, wherein the catalyst has an X-Ray diffraction pattern consistent with copper (II) oxide.

37. The catalyst of paragraph 36, wherein the catalyst has a diffraction peak at about 35° to about 38°. 38. The catalyst of paragraph 23 or 32 to 35, wherein the catalyst has an X-Ray diffraction pattern consistent with elemental copper combined with zinc oxide.

39. The catalyst of paragraph 38, wherein the catalyst has diffraction peaks at

about 42.0 ° - 44.CP and about 49.0° - 52.0°.

40. The catalyst of any one of paragraphs 23 or 32 to 37, wherein transmission electron microscopy of the catalyst shows discrete sheets of material.

41 . The catalyst of paragraph 23 or 32 to 37 or 40, wherein the discrete sheets of material have a diameter ranging from about 50 nm to about 150 nm.

42. The catalyst of paragraph 23 or 32 to 37 or 40 or 41 , wherein the discrete

sheets of material have a thickness ranging from about 5 nm to about 15 nm. 43. The catalyst of any one of paragraphs 23 or 32 to 36, or 38 to 40, wherein the discrete sheets of material have a diameter ranging from about 50 nm to about 150 nm. 44. The catalyst of any one of paragraphs 23 or 32 to 36 or 38 to 40 or 43, wherein the discrete sheets of material have a thickness ranging from about 5 nm to about 15 nm. 45. Use of a catalyst or catalyst precursor according to any one of paragraphs 22 to 44 in a method of making methanol.

Claims

A method for making a catalyst precursor, the method comprising making separate double hydroxide layers of a hydrotalcite structure comprising copper, zinc, and aluminium.

The method of claim 1 , wherein the method comprises separating double hydroxide layers of a hydrotalcite structure comprising copper, zinc and aluminium, for example wherein the method comprises making a hydrotalcite structure comprising copper, zinc and aluminium and separating the double hydroxide layers of the hydrotalcite structure.

The method of claim 1 or 2, wherein the double hydroxide layers of the

hydrotalcite structure comprising copper, zinc and aluminium are made by a precipitation process.

The method of claim 3, wherein a hydroxide salt is added to a solution of copper, zinc and aluminium precursors to induce precipitation of the double hydroxide layers of the hydrotalcite structure.

The method of claim 4, wherein an additional salt, for example a metal salt, is added to the solution of copper, zinc and aluminium precursors.

The method of any one of claims 3 to 5, wherein the precipitation occurs at a pH ranging from about 7 to about 9 and/or at a temperature ranging from about 20°C to about 50°C.

The method of any one of claims 2 to 6, wherein the double hydroxide layers of the hydrotalcite structure are separated by treating with a water-miscible organic solvent, for example acetone and/or ethanol.

A method for making a catalyst, the method comprising making a catalyst precursor by a method of any one of claims 1 to 7;

calcining the catalyst precursor; and

optionally reducing the catalyst precursor after calcining or concurrently with the calcining.

9. A catalyst precursor comprising separate double hydroxide layers of a hydrotalcite structure comprising copper, zinc and aluminium.

10. The catalyst precursor of claim 9, wherein the catalyst precursor has a specific surface area equal to or greater than about 100 m²/g, for example equal to or greater than about 200 m²/g.

1 1 . The catalyst precursor of claim 9 or 10, comprising copper oxide.

12. The catalyst precursor of any one of claims 9 to 1 1 , wherein the catalyst

precursor has an X-Ray diffraction pattern consistent with a substituted hydrotalcite structure, for example wherein the catalyst precursor has an X-Ray diffraction pattern with diffraction peaks at about 10.0° - 12. CP, about 22.0° - 24.0°, about 33.0° - 35.&, and about 58.0 ° - 61 .CP.

13. A catalyst comprising separate double hydroxide layers comprising copper, zinc and aluminium.

14. The catalyst of claim 13, wherein the catalyst has a specific surface area equal to or greater than about 100 m²/g, for example equal to or greater than about 200 m²/g and/or wherein the catalyst has a copper surface area equal to or greater than about 30 m²/g.

15. The catalyst of claim 13 or 14, wherein the catalyst comprises copper

nanoparticles.

16. The catalyst of any of claims 13 to 15, wherein the catalyst has an X-Ray

diffraction pattern:

a) consistent with copper (II) oxide;

b) having a diffraction peak at about 35° to about 38°;

c) consistent with elemental copper combined with zinc oxide;

d) having diffraction peaks at about 42.0° - 44. CP and about 49.0° - 52.0°.

17. Use of a catalyst or catalyst precursor according to any one of claims 9 to 16 in a method of making methanol.