INTRODUCTION

[0001] The present invention relates to catalyst compositions. More specifically, the present invention relates to catalyst compositions comprising rhodium and indium, and to the use of these catalyst compositions in the hydrogenation of carbon dioxide to methanol and in the steam reforming of methanol.

BACKGROUND OF THE INVENTION

[0002] In recent years, methanol has become one of the largest chemical feedstocks. This is in part because methanol can be used as a raw material for a wide array of chemical products, including, for example, acetic acid, formaldehyde, methyl methacrylate and methyl tertiary- butyl ether (MTBE). However, it is also because methanol can be used directly as a fuel or fuel supplement, particularly in the automotive industry.

[0003] Methanol is conventionally manufactured from syngas in a high-pressure reaction that is typically catalysed by a Cu/ZnO/A C catalyst(3). However, to fulfil the global commitments for more environmentally friendly and sustainable synthetic procedures for both methanol and the products it is used to make, there is currently a demand for alternative, greener and renewable feedstocks for methanol production, such as, for example, biomass.

[0004] Biomass is known to take up carbon dioxide during its growth and, in many cases, releases an equal amount of carbon dioxide during its combustion, thereby creating a so- called "carbon neutral" process. However, the gaseous feedstocks generated from biomass sources typically comprise a large excess of carbon dioxide (CO2) compared to the amounts of hydrogen generated. This excess of CO2 can have adverse effects for many of the commercially available catalysts used in the hydrogenation of CO2, with most commercially available catalysts performing suboptimally when gaseous feedstocks comprise an excess of

[0005] Thus, what is presently required for biomass feedstocks to be used in the hydrogenation of carbon dioxide is a stoichiometric adjustment of the gaseous feedstock prior to use. This is achieved either by adding additional hydrogen to the feedstock, or by removing CC from the feedstock. However, stoichiometric adjustments of this type are both expensive and require specialist equipment (8, 9). [0006] Accordingly, there remains a need for new and improved catalyst compositions that are capable of producing methanol both efficiently and selectivity from feedstocks in which CO2 is in excess (i.e. H2 deficient feedstocks).

[0007] The present invention was devised with the foregoing in mind.

[0008] In addition to the demands for new and improved methods for methanol production, there is also a growing demand for new methodologies for producing hydrogen. Hydrogen is growing in popularity as a fuel source, predominately in the automotive industry, due to the fact that emissions from hydrogen are non-polluting and also because hydrogen offers a high efficiency when used as in, for example, proton exchange membrane (PEM) fuel cells.

[0009] There are currently a number of known methods for obtaining hydrogen, both from renewable and non-renewable sources. However, problems in utilising hydrogen as an efficient fuel source usually reside with the storage and subsequent transfer of hydrogen, which stem from hydrogen's poor volumetric and weight energy densities.

[0010] Thus, as an alternative to hydrogen storage, the use of the steam reformation of methanol, which converts methanol and water (steam) to carbon dioxide and hydrogen in the presence of a catalyst (e.g. Cu/ZnO/A C ), has been suggested as a means for producing hydrogen "on demand" in fuel cells. Given that the storage and transfer of methanol is far easier than it is for hydrogen, this could provide a solution to the above noted problems. However, current commercially available catalyst compositions, when subjected to conditions commonly used in the steam reformation of methanol, tend to produce significant amounts of carbon monoxide by-products, which lowers the overall purity, and thus efficiency, of the hydrogen fuel source.

[0011] Therefore, there also remains a need for new and improved catalyst compositions that are capable of producing carbon dioxide and hydrogen efficiently and selectively from methanol and steam, with much lower concentrations of carbon monoxide impurities being produced.

[0012] The present invention was also devised with the foregoing in mind.

SUMMARY OF THE INVENTION

[0013] According to a first aspect of the present invention there is provided a use of a catalyst composition comprising rhodium and indium in the hydrogenation of carbon dioxide to methanol. Suitably, the catalyst composition comprises greater than or equal to 5 wt% of indium. [0014] According to a second aspect of the present invention there is provided a use of a catalyst composition comprising rhodium and indium in the steam reforming of methanol. Suitably, the catalyst composition comprises greater than or equal to 5 wt% of indium.

[0015] According to a third aspect of the present invention, there is provided a process for the preparation of a catalyst composition, said process comprising the steps of:

a) providing a support, wherein the support comprises greater than or equal to 5 wt% of an indium salt;

b) applying a rhodium salt to said support; and

c) calcining the product of step b) at a temperature of between 100°C and 700°C.

[0016] According to a fourth aspect of the present invention there is provided a process for the preparation of a catalyst composition, said process comprising the steps of:

1) adding:

i) a solution of an indium salt;

ii) a solution of a rhodium salt;

iii) optionally, a solution of one or more other metallic salts; and

iv) a solution of base;

to a reaction vessel and mixing said components together;

2) collecting the precipitate formed during step 1) above; and

3) calcining the precipitate of step 2) at a temperature of between 100°C and 700°C.

[0017] According to a fifth aspect of the present invention there is provided a catalyst composition comprising rhodium and indium, wherein the catalyst composition comprises greater than 5 wt% of indium.

[0018] Features, including optional, suitable, and preferred features in relation to one aspect of the invention may also be features, including optional, suitable and preferred features in relation to any other aspects of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Definitions

[0019] Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of them mean "including but not limited to", and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0020] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0021] The terms "indium salt" and "rhodium salt" used herein we be readily understood as referring to any suitable indium or rhodium complex respectively. Suitably, an indium salt is an indium (III) complex (e.g. ln(NC>3)3) and, suitably, a rhodium salt is a rhodium (III) complex (e.g. Rh(N0 ₃ ) ₃ ).

[0022] Where the quantity or concentration of a particular component is specified as a weight (or mass) percentage (wt% or %w/w), said weight (or mass) percentage refers to the percentage of said component by weight (or mass) relative to the total weight (or mass) of the composition as a whole. It will be understood by those skilled in the art that the sum of weight (or mass) percentages of all components of a composition will total 100 wt%. However, where not all components are listed (e.g. where compositions are said to "comprise" one or more particular components), the weight (or mass) percentage balance may optionally be made up to 100 wt% by unspecified ingredients (e.g. a diluent, such as water, or other non-essentially but suitable additives).

Use of the catalyst compositions

i) Hydrogenation of carbon dioxide to methanol

[0023] As described hereinbefore, the present invention provides a provided a use of a catalyst composition comprising rhodium and indium in the hydrogenation of carbon dioxide to methanol.

[0024] It will be understood that the hydrogenation of carbon dioxide to methanol refers to the following reaction:

[0025] It will be appreciated that the above reaction is in equilibrium with other competing reactions such as, for example, the steam reforming of methanol, the water gas shift reaction and the complete hydrogenation of carbon dioxide to methane.

[0026] The inventors have surprisingly found that in using catalyst compositions comprising both rhodium and indium superior selectivity for methanol in the hydrogenation of carbon dioxide could be achieved compared to industry standard catalyst compositions. Furthermore, the catalyst compositions of the present invention also displayed superior conversion rates and weight time yields compared with commercially available catalyst compositions. Moreover, the catalyst compositions of the present invention were also shown to be functional and display excellent selectivities for methanol in atmospheres comprising an excess of carbon dioxide, something that is currently challenging to achieve using commercially available catalyst systems.

[0027] Thus, in an embodiment of the above use, the carbon dioxide in the gas feedstock is in excess to hydrogen. Suitably, the ratio of carbon dioxide to hydrogen in the gas feedstock is greater than or equal to 2:1. More suitably, the ratio of carbon dioxide to hydrogen in the gas feedstock is greater than or equal to 3: 1. Most suitably, the ratio of carbon dioxide to hydrogen in the gas feedstock is greater than or equal to 5:1.

[0028] In another embodiment of the above use, the hydrogenation of carbon dioxide to methanol is carried out at a pressure of greater than or equal to 0.1 MPa. Suitably, the hydrogenation of carbon dioxide to methanol is carried out at a pressure of greater than or equal to 0.5 MPa. More suitably, the hydrogenation of carbon dioxide to methanol is carried out at a pressure of greater than or equal to 1 MPa. Yet more suitably, the hydrogenation of carbon dioxide to methanol is carried out at a pressure of greater than or equal to 2 MPa. Even more suitably, the hydrogenation of carbon dioxide to methanol is carried out at a pressure of greater than or equal to 3 MPa. Most suitably, the hydrogenation of carbon dioxide to methanol is carried out at a pressure of greater than or equal to 4 MPa.

[0029] In another embodiment of the above use, the hydrogenation of carbon dioxide to methanol is carried out at a pressure of between 0.5 MPa and 10 MPa. Suitably, the hydrogenation of carbon dioxide to methanol is carried out at a pressure of between 1 MPa and 8 MPa. More suitably, the hydrogenation of carbon dioxide to methanol is carried out at a pressure of between 1 MPa and 5 MPa. Yet more suitably, the hydrogenation of carbon dioxide to methanol is carried out at a pressure of between 3 MPa and 5 MPa.

[0030] It will be appreciated that the hydrogenation of carbon dioxide to methanol may be carried out at any suitable temperature. In an embodiment of the above use, the hydrogenation of carbon dioxide to methanol is carried out at a temperature of greater than or equal to 100°C. Suitably, the hydrogenation of carbon dioxide to methanol is carried out at a temperature of greater than or equal to 150°C. Most suitably, the hydrogenation of carbon dioxide to methanol is carried out at a temperature of greater than or equal to 200°C.

[0031] In another embodiment of the above use, the hydrogenation of carbon dioxide to methanol is carried out at a temperature of between 100°C and 800°C. Suitably, the hydrogenation of carbon dioxide to methanol is carried out at a temperature of between 100°C and 500°C. More suitably, the hydrogenation of carbon dioxide to methanol is carried out at a temperature of between 100°C and 400°C. Yet more suitably, the hydrogenation of carbon dioxide to methanol is carried out at a temperature of between 150°C and 400°C. Even more suitably, the hydrogenation of carbon dioxide to methanol is carried out at a temperature of between 200°C and 350°C. Most suitably, the hydrogenation of carbon dioxide to methanol is carried out at a temperature of between 200°C and 300°C.

[0032] In yet another embodiment of the above use, the catalyst composition is exposed to a reducing atmosphere prior to use in the hydrogenation of carbon dioxide to methanol. Suitably, the reducing atmosphere is a hydrogen atmosphere.

[0033] In another embodiment of the above use, the catalyst composition is exposed to a reducing atmosphere (e.g. hydrogen) at temperature of between 100°C and 400°C prior to use in the hydrogenation of carbon dioxide to methanol. Suitably, the catalyst composition exposed to a reducing atmosphere (e.g. hydrogen) at temperature of between 150°C and 350°C prior to use in the hydrogenation of carbon dioxide to methanol. Most suitably, the catalyst composition exposed to a reducing atmosphere (e.g. hydrogen) at temperature of between 200°C and 350°C prior to use in the hydrogenation of carbon dioxide to methanol.

[0034] In another embodiment of the above use, the catalyst composition is exposed to a reducing atmosphere (e.g. hydrogen) at temperature of between 100°C and 400°C and for a duration of between 30 minutes and 12 hours, prior to use in the hydrogenation of carbon dioxide to methanol. Suitably, the catalyst composition is exposed to a reducing atmosphere (e.g. hydrogen) at temperature of between 100°C and 400°C and for a duration of between 30 minutes and 6 hour, prior to use in the hydrogenation of carbon dioxide to methanol. More suitably, the catalyst composition exposed to a reducing atmosphere (e.g. hydrogen) at temperature of between 150°C and 350°C and for a duration of between 1 hour and 4 hours prior to use in the hydrogenation of carbon dioxide to methanol.

[0035] In another embodiment of the above use, carbon dioxide and hydrogen are passed over the catalyst composition at a rate of greater than or equal to 5 ml. min ^"1 . Suitably, carbon dioxide and hydrogen are passed over the catalyst composition at a rate of greater than or equal to 10 mL mirr ¹ . More suitably, carbon dioxide and hydrogen are passed over the catalyst composition at a rate of greater than or equal to 20 mL mirr ¹ . Most suitably, carbon dioxide and hydrogen are passed over the catalyst composition at a rate of greater than or equal to 30 mL min ¹ .

/V) Steam reforming of methanol

[0036] Furthermore, the present invention also provides a use of a catalyst composition comprising rhodium and indium in the steam reforming of methanol.

[0037] It will be understood the steam reforming of methanol refers to the following reaction:

CH ₃ OH + H ₂ 0 -> C0 ₂ + 3H ₂

[0038] It will again be appreciated that the above reaction is in equilibrium with other competing reactions.

[0039] In an embodiment of the above use, the steam reforming of methanol is carried out at a pressure of less than or equal to 5 MPa. Suitably, the steam reforming of methanol is carried out at a pressure of less than or equal to 1 MPa. More suitably, the steam reforming of methanol is carried out at a pressure of less than or equal to 0.5 MPa. Yet more suitably, the steam reforming of methanol is carried out at a pressure of less than or equal to 0.3 MPa. Even more suitably, the steam reforming of methanol is carried out at a pressure of less than or equal to 0.2 MPa. Most suitably, the steam reforming of methanol is carried out at a pressure of less than or equal to 0.1 MPa.

[0040] In another embodiment of the above use, the steam reforming of methanol is carried out at a pressure of between 0.01 MPa and 1 MPa. Suitably, the hydrogenation of carbon dioxide to methanol is carried out at a pressure of between 0.01 MPa and 0.5 MPa. More suitably, the hydrogenation of carbon dioxide to methanol is carried out at a pressure of between 0.01 MPa and 0.25 MPa. Yet more suitably, the hydrogenation of carbon dioxide to methanol is carried out at a pressure of between 0.01 MPa and 0.1 MPa.

[0041] In a particular embodiment of the above use, the steam reforming of methanol is carried out at atmospheric pressure (i.e. 0.1 MPa).

[0042] It will be appreciated that the steam reforming of methanol may be conducted at any suitable temperature. In an embodiment of the above use, the steam reforming of methanol is carried out at a temperature of greater than or equal to 50°C. Suitably, the steam reforming of methanol is carried out at a temperature of greater than or equal to 75°C. More suitably, the steam reforming of methanol is carried out at a temperature of greater than or equal to 100°C. Most suitably, the steam reforming of methanol is carried out at a temperature of greater than or equal to 150°C.

[0043] In another embodiment of the above use, the steam reforming of methanol is carried out at a temperature of between 50°C and 700°C. Suitably, the steam reforming of methanol is carried out at a temperature of between 50°C and 500°C. More suitably, the steam reforming of methanol is carried out at a temperature of between 100°C and 400°C. Yet more suitably, the steam reforming of methanol is carried out at a temperature of between 100°C and 300°C. Even more suitably, the steam reforming of methanol is carried out at a temperature of between 100°C and 250°C. Most suitably, the steam reforming of methanol is carried out at a temperature of between 150°C and 250°C.

[0044] In another embodiment, steam is in excess to hydrogen in the gas feedstock. Suitably, the ratio of steam to methanol in the gas feedstock is greater than or equal to 1.5:1. More suitably, the ratio of steam to methanol in the gas feedstock is greater than or equal to 2:1. Yet more suitably, the ratio of steam to methanol in the gas feedstock is greater than or equal to 3: 1. Most suitably, the ratio of steam to methanol in the gas feedstock is greater than or equal to 5: 1.

[0045] In another embodiment of the above use, methanol and steam (H ₂ 0) are passed over the catalyst composition at a rate of greater than or equal to 0.001 ml. min ^-1 . Suitably, methanol and steam (H ₂ 0) are passed over the catalyst composition at a rate of greater than or equal to 0.01 ml. min ^"1 . More suitably, methanol and steam (H ₂ 0) are passed over the catalyst composition at a rate of greater than or equal to 0.05 ml. min ¹ . Most suitably, methanol and steam (H ₂ 0) are passed over the catalyst composition at a rate of greater than or equal to 0.1 ml. min ¹ .

[0046] It will be appreciated that in utilising a catalyst composition comprising rhodium and indium in the steam reformation of methanol, good purity of the resulting products (e.g. H2 and C02) can be achieved. It will be understood that one of the major impurities of the steam reformation of methanol is carbon monoxide (CO).

[0047] Thus, in an embodiment of the above use, the amount (e.g. concentration) carbon monoxide produced is less than or equal to 100 ppm. Suitably, the amount (e.g. concentration) carbon monoxide produced is less than or equal to 50 ppm. More suitably, the amount (e.g. concentration) carbon monoxide produced is less than or equal to 20 ppm. Yet more suitably, the amount (e.g. concentration) carbon monoxide produced is less than or equal to 10 ppm Even more suitably, the amount (e.g. concentration) carbon monoxide produced is less than or equal to 5 ppm. Most suitably, the amount (e.g. concentration) carbon monoxide produced is less than or equal to 1 ppm. Embodiments of uses i) and it) above

[0048] It will be appreciated that the catalyst composition may comprise any suitable amount of rhodium. However, due to the high cost of rhodium, it will be understood that in order to make the catalyst composition cost effective in the hydrogenation of carbon dioxide to methanol and/or the steam reforming of methanol, lower quantities of rhodium are preferred.

[0049] In an embodiment, the catalyst composition comprises less than or equal to 10 wt% of rhodium. Suitably, the catalyst composition comprises less than or equal to 5 wt% of rhodium. More suitably, the catalyst composition comprises less than or equal to 3 wt% of rhodium. Most suitably, the catalyst composition comprises less than or equal to 2 wt% of rhodium.

[0050] In another embodiment, the catalyst composition comprises between 0.01 wt% and 10 wt% of rhodium. Suitably, the catalyst composition comprises between 0.1 wt% and 5 wt% of rhodium. More suitably, the catalyst composition comprises between 0.1 wt% and 3 wt% of rhodium. Most suitably, the catalyst composition comprises between 0.5 wt% and 3 wt% of rhodium.

[0051] It will also be appreciated that the catalyst composition may comprise any suitable amount of indium. In an embodiment, the catalyst composition comprises greater than or equal to 0.1 wt% of indium. Suitably, the catalyst composition comprises greater than or equal to 0.5 wt% of indium. More suitably, the catalyst composition comprises greater than or equal to 1 wt% of indium. Yet more suitably, the catalyst composition comprises greater than or equal to 3 wt% of indium. Even more suitably, the catalyst composition comprises greater than or equal to 5 wt% of indium. Still more suitably, the catalyst composition comprises greater than or equal to 7 wt% of indium. Most suitably, the catalyst composition comprises greater than or equal to 10 wt% of indium.

[0052] In another embodiment, the catalyst composition comprises a support.

[0053] It will be understood that the support may be any suitable material that has a surface area and/or porosity that lends itself for application in a catalytic process. Suitable supports will be well known to the person skilled in the art and, as such, the skilled person will be suitable how and when these may be used in the catalyst compositions of the present invention.

[0054] In an embodiment, the support comprises carbon, silicon carbide, silicon nitride, boron nitride, magnesium silicate, bentonite, zeolites, zirconia, alumina, silica, silica-alumina, ceria-alumina, aluminates, magnesium oxide, magnesium oxide-silicon oxide mixtures, layered double hydroxide, zinc oxide, gallium oxide, indium oxide or mixtures thereof. [0055] Suitably, the support comprises carbon, silicon carbide, silicon nitride, boron nitride, magnesium silicate, zeolites, zirconia, alumina, silica, silica-alumina, ceria-alumina, aluminates, zinc oxide, gallium oxide, indium oxide or mixtures thereof. More suitably, the support comprises carbon, zeolites, zirconia, alumina, silica, silica-alumina, ceria-alumina, aluminates, zinc oxide, gallium oxide, indium oxide or mixtures thereof. Yet more suitably, the support comprises zirconia, alumina, silica, silica-alumina, ceria-alumina, aluminates, zinc oxide, gallium oxide, indium oxide or mixtures thereof. Most suitably, the support comprises zirconia, alumina, silica, zinc oxide, gallium oxide, indium oxide or mixtures thereof.

[0056] In another embodiment, the support comprises indium and/or an indium salt.

[0057] In yet another embodiment, the support comprises an indium salt and optionally one or more of the following:

- an aluminium salt (e.g. alumina);

- a zirconium salt (e.g. zirconia);

- silica;

- a zinc salt (e.g. zinc oxide); and/or

- a gallium salt (e.g. gallium oxide).

[0058] Suitably, the support comprises an indium salt and optionally one or more of the following:

- an aluminium salt (e.g. alumina);

- a zirconium salt (e.g. zirconia);

- a zinc salt (e.g. zinc oxide); and/or

- a gallium salt (e.g. gallium oxide).

[0059] More suitably, the support comprises an indium salt and optionally one or more of the following:

an aluminium salt (e.g. alumina); and/or

a zirconium salt (e.g. zirconia).

[0060] Most suitably, the support comprises an indium salt and optionally an aluminium salt (e.g. alumina).

[0061] In a further embodiment, the support comprises between 10 and 100 wt% of an indium salt and between 0 and 90 wt% of one or more of the following:

- an aluminium salt (e.g. alumina);

- a zirconium salt (e.g. zirconia);

- silica; - a zinc salt (e.g. zinc oxide); and/or

- a gallium salt (e.g. gallium oxide).

[0062] Suitably, the support comprises between 30 and 100 wt% of an indium salt and between 0 and 70 wt% of one or more of the following:

- an aluminium salt (e.g. alumina);

- a zirconium salt (e.g. zirconia);

- silica;

- a zinc salt (e.g. zinc oxide); and/or

- a gallium salt (e.g. gallium oxide).

[0063] More suitably, the support comprises between 40 and 100 wt% of an indium salt and between 0 and 60 wt% of one or more of the following:

- an aluminium salt (e.g. alumina);

- a zirconium salt (e.g. zirconia);

- silica;

- a zinc salt (e.g. zinc oxide); and/or

- a gallium salt (e.g. gallium oxide).

[0064] Yet more suitably, the support comprises between 50 and 100 wt% of an indium salt and between 0 and 50 wt% of one or more of the following:

- an aluminium salt (e.g. alumina);

- a zirconium salt (e.g. zirconia);

- silica;

- a zinc salt (e.g. zinc oxide); and/or

- a gallium salt (e.g. gallium oxide).

[0065] Still more suitably, the support comprises between 50 and 100 wt% of an indium salt and between 0 and 50 wt% of one or more of the following:

- an aluminium salt (e.g. alumina); and/or

- a zirconium salt (e.g. zirconia).

[0066] Most suitably, the support comprises between 50 and 100 wt% of an indium salt and between 0 and 50 wt% of an aluminium salt (e.g. alumina).

[0067] In another embodiment, the support consists essentially of/consists of indium and/or an indium salt. Suitably, the indium salt is indium oxide. [0068] It will be understood that the catalyst compositions of the present invention may have any suitable surface area. Surface area may be determined using any suitable technique known in the art. In an embodiment, the catalyst compositions of the present invention have a Brunauer-Emmett-Teller (BET) surface area of greater than or equal to 5 m ² g ^_1 . Suitably, the catalyst compositions of the present invention have a Brunauer-Emmett-Teller (BET) surface area of greater than or equal to 10 m ² g ¹ . More suitably, the catalyst compositions of the present invention have a Brunauer-Emmett-Teller (BET) surface area of greater than or equal to 15 m ² g ^"1 . Yet more suitably, the catalyst compositions of the present invention have a Brunauer-Emmett-Teller (BET) surface area of greater than or equal to 25 m ² g ^_1 . Even more suitably, the catalyst compositions of the present invention have a Brunauer-Emmett-Teller (BET) surface area of greater than or equal to 50 m ² g ¹ . Still more suitably, the catalyst compositions of the present invention have a Brunauer-Emmett-Teller (BET) surface area of greater than or equal to 100 m ² g ^_1 . Most suitably, the catalyst compositions of the present invention have a Brunauer-Emmett-Teller (BET) surface area of greater than or equal to 125 m ² g- ¹ .

[0069] It will be appreciated that the catalyst compositions of the present invention may be in any suitable form. In an embodiment, the catalyst compositions are in particulate or granular form.

[0070] In another embodiment, the catalyst composition is in particulate form and the particles have a particle size of less than or equal to 10 nm. Suitably, the catalyst composition is in particulate form and the particles have a particle size of less than or equal to 5 nm. More suitably, the catalyst composition is in particulate form and the particles have a particle size of less than or equal to 3 nm.

[0071] In yet another embodiment, the catalyst composition is in particulate form and the particles have a particle size between 0.1 nm and 10 nm. Suitably, the catalyst composition is in particulate form and the particles have a particle size between 0.1 nm and 5 nm. More suitably, the catalyst composition is in particulate form and the particles have a particle size between 0.1 nm and 3 nm. Yet more suitably, the catalyst composition is in particulate form and the particles have a particle size between 0.5 nm and 3 nm. Even more suitably, the catalyst composition is in particulate form and the particles have a particle size between 1 nm and 3 nm. Most suitably, the catalyst composition is in particulate form and the particles have a particle size between 2 nm and 3 nm.

Particular embodiments of uses i) and ii) above

Particular embodiments of use i) In a particular embodiment, there is provided a use of a catalyst composition comprising: i) less than or equal to 5 wt% of rhodium; and

II greater than or equal to 0.1 wt% of indium

in the hydrogenation of carbon dioxide to methanol,

wherein the hydrogenation of carbon dioxide to methanol is carried out at a pressure of greater than or equal to 0.5 MPa.

In another particular embodiment, there is provided a use of a catalyst composition comprising:

i) less than or equal to 5 wt% of rhodium; and

ii) greater than or equal to 0.5 wt% of indium

in the hydrogenation of carbon dioxide to methanol,

wherein the hydrogenation of carbon dioxide to methanol is carried out at a pressure of greater than or equal to 0.5 MPa and at a temperature of greater than or equal to 100°C.

In another particular embodiment, there is provided a use of a catalyst composition comprising:

i) less than or equal to 5 wt% of rhodium;

ii) greater than or equal to 0.5 wt% of indium; and

iii) a support, wherein the support comprises carbon, silicon carbide, silicon nitride, boron nitride, magnesium silicate, bentonite, zeolites, zirconia, alumina, silica, silica-alumina, ceria-alumina, aluminates, magnesium oxide, magnesium oxide-silicon oxide mixtures, layered double hydroxide, zinc oxide, gallium oxide, indium oxide or mixtures thereof;

in the hydrogenation of carbon dioxide to methanol,

wherein the hydrogenation of carbon dioxide to methanol is carried out at a pressure of greater than or equal to 0.5 MPa and at a temperature of greater than or equal to 100°C.

In another particular embodiment, there is provided a use of a catalyst composition comprising:

i) less than or equal to 5 wt% of rhodium; ii) greater than or equal to 0.5 wt% of indium; and

iii) a support, wherein the support comprises an indium salt and optionally one or more of the following:

- an aluminium salt (e.g. alumina);

- a zirconium salt (e.g. zirconia);

- silica;

- a zinc salt (e.g. zinc oxide); and/or

a gallium salt (e.g. gallium oxide);

in the hydrogenation of carbon dioxide to methanol,

wherein the hydrogenation of carbon dioxide to methanol is carried out at a pressure of greater than or equal to 0.5 MPa and at a temperature of greater than or equal to 100°C.

In another particular embodiment, there is provided a use of a catalyst composition comprising:

i) less than or equal to 5 wt% of rhodium;

ii) greater than or equal to 0.5 wt% of indium; and

iii) a support, wherein the support comprises between 30 and 100 wt% of an indium salt and between 0 and 70 wt% of one or more of the following:

- an aluminium salt (e.g. alumina);

- a zirconium salt (e.g. zirconia);

- silica;

- a zinc salt (e.g. zinc oxide); and/or

a gallium salt (e.g. gallium oxide);

in the hydrogenation of carbon dioxide to methanol,

wherein the hydrogenation of carbon dioxide to methanol is carried out at a pressure of greater than or equal to 0.5 MPa and at a temperature of greater than or equal to 100°C.

In another particular embodiment, there is provided a use of a catalyst composition comprising:

i) less than or equal to 5 wt% of rhodium;

ii) greater than or equal to 0.5 wt% of indium; and iii) a support, wherein the support comprises between 50 and 100 wt% of an indium salt (e.g. ln ₂ C>3) and between 0 and 50 wt% of an aluminium salt (e.g. alumina);

in the hydrogenation of carbon dioxide to methanol,

wherein the catalyst composition has a Brunauer-Emmett-Teller (BET) surface area of greater than or equal to 5 m ² g ^_1 .

and wherein the hydrogenation of carbon dioxide to methanol is carried out:

at a pressure of greater than or equal to 0.5 MPa;

at a temperature of greater than or equal to 100°C; and

- with a ratio of carbon dioxide to hydrogen in the gas feedstock is greater than or equal to 2: 1.

Particular embodiments of use ii)

2.1 In a particular embodiment, there is provided a use of a catalyst composition comprising:

i) less than or equal to 5 wt% of rhodium; and

ii) greater than or equal to 0.1 wt% of indium

in the steam reforming of methanol,

wherein the steam reforming of methanol is carried out at a pressure of less than or equal to 0.5 MPa.

2.2 In another particular embodiment, there is provided a use of a catalyst composition comprising:

i) less than or equal to 5 wt% of rhodium; and

ii) greater than or equal to 0.5 wt% of indium

in the steam reforming of methanol,

wherein the steam reforming of methanol is carried out at a pressure of less than or equal to 0.5 MPa and at a temperature of greater than or equal to 75°C.

2.3 In another particular embodiment, there is provided a use of a catalyst composition comprising:

i) less than or equal to 5 wt% of rhodium; ii) greater than or equal to 0.5 wt% of indium; and

iii) a support, wherein the support comprises carbon, silicon carbide, silicon nitride, boron nitride, magnesium silicate, bentonite, zeolites, zirconia, alumina, silica, silica-alumina, ceria-alumina, aluminates, magnesium oxide, magnesium oxide-silicon oxide mixtures, layered double hydroxide, zinc oxide, gallium oxide, indium oxide or mixtures thereof;

in the steam reforming of methanol,

wherein the steam reforming of methanol is carried out at a pressure of less than or equal to 0.5 MPa and at a temperature of greater than or equal to 75°C.

In another particular embodiment, there is provided a use of a catalyst composition comprising:

i) less than or equal to 5 wt% of rhodium;

ii) greater than or equal to 0.5 wt% of indium; and

iii) a support, wherein the support comprises an indium salt and optionally one or more of the following:

- an aluminium salt (e.g. alumina);

- a zirconium salt (e.g. zirconia);

- silica;

- a zinc salt (e.g. zinc oxide); and/or

a gallium salt (e.g. gallium oxide);

in the steam reforming of methanol,

wherein the steam reforming of methanol is carried out at a pressure of less than or equal to 0.5 MPa and at a temperature of greater than or equal to 75°C.

In another particular embodiment, there is provided a use of a catalyst composition comprising:

i) less than or equal to 5 wt% of rhodium;

ii) greater than or equal to 0.5 wt% of indium; and

iii) a support, wherein the support comprises between 30 and 100 wt% of an indium salt and between 0 and 70 wt% of one or more of the following:

an aluminium salt (e.g. alumina);

a zirconium salt (e.g. zirconia);

silica; - a zinc salt (e.g. zinc oxide); and/or

a gallium salt (e.g. gallium oxide);

in the steam reforming of methanol,

wherein the steam reforming of methanol is carried out at a pressure of greater than or equal to 0.3 MPa and at a temperature of greater than or equal to 75°C.

2.6 In another particular embodiment, there is provided a use of a catalyst composition comprising:

i) less than or equal to 5 wt% of rhodium;

ii) greater than or equal to 0.5 wt% of indium; and

iii) a support, wherein the support comprises between 50 and 100 wt% of an indium salt (e.g. ln ₂ C>3) and between 0 and 50 wt% of an aluminium salt (e.g. alumina);

in the steam reforming of methanol,

wherein the catalyst compositions has a Brunauer-Emmett-Teller (BET) surface area of greater than or equal to 5 m ² g ^_1 .

and wherein steam reforming of methanol is carried out:

at a pressure of less than or equal to 0.3 MPa;

at a temperature of greater than or equal to 100°C; and

- with a ratio of steam to methanol in the gas feedstock of greater than or equal to 2: 1.

Process of the present invention

Applying rhodium to the support

[0072] According another aspect of the present invention, there is provide a process for the preparation of a catalyst composition, said process comprising the steps of:

a) providing a support, wherein the support comprises greater than or equal to 5 wt% of an indium salt;

b) applying a rhodium salt to said support; and

c) calcining the product of step b) at a temperature of between 100°C and 700°C.

Step a [0073] It will appreciated that any suitable support may be used. The support may consist essentially of/consist of an indium salt (e.g. indium oxide) or it may comprise a mixture of an indium salt (e.g. indium oxide) and one or more other suitable support materials.

[0074] Non-limiting examples of suitable support materials are described in paragraphs [0054] to [0067] hereinabove.

[0075] In an embodiment of the above process, the support comprises greater than or equal to 10 wt% of an indium salt. Suitably, the support comprises greater than or equal to 20 wt% of an indium salt. More suitably, the support comprises greater than or equal to 30 wt% of an indium salt. Yet more suitably, the support comprises greater than or equal to 40 wt% of an indium salt. Most suitably, the support comprises greater than or equal to 50 wt% of an indium salt.

[0076] In another embodiment, the catalyst composition comprises greater than or equal to 1 wt% of indium. Suitably, the catalyst composition comprises greater than or equal to 3 wt% of indium. More suitably, the catalyst composition comprises greater than or equal to 5 wt% of indium. Yet more suitably, the catalyst composition comprises greater than or equal to 7 wt% of indium. Most suitably, the catalyst composition comprises greater than or equal to 10 wt% of indium.

[0077] It will be understood that the support of step a) may be prepared using any conventional technique known in the art. The skilled person will be able to select suitable support materials and methods of synthesis. Non-limiting examples of suitable methods for preparing the support of step a) include a precipitation process, chemical vapour deposition or decomposition of metal salts onto a suitable template.

[0078] In an embodiment, the support of step a) is prepared by a precipitation process.

[0079] In another embodiment, the support of step a) is prepared by the following process:

1) adding:

i) a solution of an indium salt;

ii) optionally, a solution of one or more other metallic salts; and

iii) a solution of base;

to a reaction vessel and mixing said components together;

2) collecting the precipitate formed during step 1) above; and

3) calcining the precipitate of step 2) at a temperature of between 100°C and 700°C.

[0080] In an embodiment, the solution of an indium salt is an aqueous solution of indium salt. Suitably, the solution of an indium salt is an aqueous solution of indium nitrate. [0081] In an embodiment, step ii) involves adding a solution of one or two other metallic salts. Suitably, step ii) involves adding a solution of one other metallic salt.

[0082] In another embodiment, the solution of one or more other metallic salts is an aqueous solution of one or more other metallic salts.

[0083] Suitably, the one or more other metallic salts are selected from aluminium salts, zinc salts, gallium salts or mixtures thereof. More suitably, the one or more other metallic salts are selected from aluminium nitrate, zinc nitrate, gallium nitrate or mixtures thereof. Yet more suitably, the one or more other metallic salts are selected from aluminium salts (e.g. aluminium nitrate).

[0084] In another embodiment, the solution of base is a solution of inorganic base. Suitably, the solution of base is an aqueous solution of inorganic base. Non-limiting examples of suitable inorganic bases include lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, caesium hydroxide, magnesium hydroxide, calcium hydroxide, strontium hydroxide, sodium carbonate, potassium carbonate, rubidium carbonate, caesium carbonate, magnesium carbonate, calcium carbonate, strontium carbonate or barium carbonate.

[0085] In yet another embodiment, the solution of base is an aqueous solution of sodium carbonate.

[0086] In a further embodiment, the solution of base has a concentration of between 0.01 M and 2 M. Suitably, the solution of base has a concentration of between 0.01 M and 1 M. More suitably, the solution of base has a concentration of between 0.05 M and 0.5 M. Most suitably, the solution of base has a concentration of between 0.1 M and 0.5 M.

[0087] In a particular embodiment, the solution of base is an aqueous solution of between 0.1 M and 0.5 M sodium carbonate.

[0088] In a further embodiment, the pH of step 1) is maintained at a pH of between 7.5 and 10. Suitably, the pH of step 1) is maintained at a pH of between 8 and 9.5. Most suitably, step 1) is maintained at a pH of between 8.5 and 9.5.

[0089] In yet a further embodiment, the ratio of indium salt to the one or more other metallic salts is between 5:95 and 100:0. Suitably, the ratio of indium salt to the one or more other metallic salts is between 10:90 and 100:0. More suitably, the ratio of indium salt to the one or more other metallic salts is between 20:80 and 100:0. Yet more suitably, the ratio of indium salt to the one or more other metallic salts is between 30:70 and 100:0. Still more suitably, the ratio of indium salt to the one or more other metallic salts is between 40:60 and 100:0. Most suitably, the ratio of indium salt to the one or more other metallic salts is between 50:50 and 100:0. [0090] In another embodiment, no solution of one or more other metallic salts is added.

[0091] It will be understood that the precipitate of step 2) may be collected by any conventional technique known in the art. Non-limiting examples of suitable techniques include, for example, filtration, centrifugation, sedimentation and/or decantation.

[0092] In another embodiment, the precipitate of step 2) is calcined at a temperature of between 200°C and 600°C. Suitably, the precipitate of step 2) is calcined at a temperature of between 300°C and 600°C. More suitably, the precipitate of step 2) is calcined at a temperature of between 300°C and 500°C. Most suitably, the precipitate of step 2) is calcined at a temperature of between 400°C and 500°C.

[0093] It will be understood that the precipitate of step 2) may be calcined for any suitable duration. In an embodiment, the precipitate of step 2) is calcined for at least 1 minute. Suitably, the precipitate of step 2) is calcined for at least 15 minutes. More suitably, the precipitate of step 2) is calcined for at least 30 minutes. Yet more suitably, the precipitate of step 2) is calcined for at least 1 hour. Even more suitably, the precipitate of step 2) is calcined for at least 2 hours. Still more suitably, precipitate of step 2) is calcined for at least 3 hours. Most suitably, precipitate of step 2) is calcined for at least 4 hours.

[0094] In yet another embodiment, the precipitate of step 2) is calcined at a temperature of between 100°C and 600°C for at least 30 minutes. Suitably, the precipitate of step 2) is calcined at a temperature of between 300°C and 600°C for at least 1 hour. Most suitably, the precipitate of step 2) is calcined at a temperature of between 300°C and 500°C for at least 4 hours.

[0095] In a particular embodiment, the support of step a) is prepared by the following process:

1) adding:

i) an aqueous solution of an indium salt (e.g. indium oxide);

ii) optionally, an aqueous solution of one or more other metallic salts,

wherein the one or more other metallic salts are selected from aluminium salts (e.g. aluminium nitrate), zinc salts (zinc nitrate), gallium salts (e.g. zinc nitrate) or mixtures thereof; and

iii) an aqueous solution of inorganic base (e.g. sodium carbonate); to a reaction vessel and mixing said components together;

2) collecting the precipitate formed during step 1) above; and

3) calcining the precipitate of step 2) at a temperature of between 100°C and 600°C for at least 1 hour (e.g. at least 4 hours); wherein the ratio of indium salt to the one or more other metallic salts is between 30:70 and 100:0; and

wherein the pH of step 1) is maintained at a pH of between 7.5 and 10.

[0096] In another particular embodiment, the support of step a) is prepared by the following process:

1) adding:

i) an aqueous solution of an indium salt (e.g. indium oxide);

ii) optionally, an aqueous solution of one or more other metallic salts,

wherein the one or more other metallic salts are selected from aluminium salts (e.g. aluminium nitrate), zinc salts (zinc nitrate), gallium salts (e.g. zinc nitrate) or mixtures thereof; and

iii) an aqueous solution of inorganic base (e.g. sodium carbonate); to a reaction vessel and mixing said components together;

2) collecting the precipitate formed during step 1) above; and

3) calcining the precipitate of step 2) at a temperature of between 300°C and 600°C for at least 1 hour (e.g. at least 4 hours);

wherein the ratio of indium salt to the one or more other metallic salts is between 50:50 and 100:0; and

wherein the pH of step 1) is maintained at a pH of between 8.5 and 9.5.

[0097] In another particular embodiment, the support of step a) is prepared by the following process:

1) adding:

i) an aqueous solution of an indium salt (e.g. indium oxide);

ii) optionally, an aqueous solution of an aluminium salt (e.g. aluminium

nitrate); and

iii) an aqueous solution of inorganic base (e.g. sodium carbonate); to a reaction vessel and mixing said components together;

2) collecting the precipitate formed during step 1) above; and

3) calcining the precipitate of step 2) at a temperature of between 300°C and 600°C for at least 1 hour (e.g. at least 4 hours);

wherein the ratio of indium salt to aluminium salt is between 50:50 and 100:0; and wherein the pH of step 1) is maintained at a pH of between 8.5 and 9.5.

Step b [0098] In an embodiment, the rhodium salt is applied to the support in step b) of the process by precipitating the rhodium salt from a solution of the rhodium salt.

[0099] In an embodiment, the solution of rhodium salt is an aqueous solution of a rhodium salt.

[00100] In another embodiment, the rhodium salt is rhodium nitrate. Step c

[00101] In an embodiment, the product of step b) is calcined at a temperature of between 200°C and 600°C. Suitably, the precipitate of step b) is calcined at a temperature of between 300°C and 600°C. More suitably, the precipitate of step b) is calcined at a temperature of between 300°C and 500°C. Most suitably, the precipitate of step b) is calcined at a temperature of between 400°C and 500°C.

[00102] It will be understood that the precipitate of step b) may be calcined for any suitable duration. In an embodiment, the precipitate of step b) is calcined for at least 30 minutes. Suitably, the precipitate of step b) is calcined for at least 1 hour. More suitably, the precipitate of step b) is calcined for at least 2 hours. Yet more suitably, precipitate of step b) is calcined for at least 3 hours. Most suitably, precipitate of step b) is calcined for at least 4 hours.

[00103] In yet another embodiment, the precipitate of step b) is calcined at a temperature of between 100°C and 600°C for at least 30 minutes. Suitably, the precipitate of step b) is calcined at a temperature of between 300°C and 600°C for at least 1 hour. Most suitably, the precipitate of step b) is calcined at a temperature of between 300°C and 500°C for at least 4 hours.

Co-precipitation process

[00104] In another aspect, the present invention provides a process for the preparation of a catalyst composition, said process comprising the steps of:

1) adding:

i) a solution of an indium salt;

ii) a solution of a rhodium salt;

iii) optionally, a solution of one or more other metallic salts; and

iv) a solution of base;

to a reaction vessel and mixing said components together;

2) collecting the precipitate formed during step 1) above; and

3) calcining the precipitate of step 2) at a temperature of between 100°C and 700°C. [00105] It will be understood that features, including optional, suitable, and preferred features in relation to the process of the present invention detailed in paragraphs [0073] to [0094] above are also features, including optional, suitable and preferred features in relation to the co- precipitation process of the invention.

Catalyst compositions of the present invention

[00106] According to another aspect of the present invention, there is provided a catalyst composition comprising rhodium and indium, wherein the catalyst composition comprises greater than 5 wt% of indium.

[00107] In an embodiment, the catalyst composition comprises greater than or equal to 6 wt% of indium. Suitably, the catalyst composition comprises greater than or equal to 7 wt% of indium. More suitably, the catalyst composition comprises greater than or equal to 8 wt% of indium. Yet more suitably, the catalyst composition comprises greater than or equal to 9 wt% of indium. Even more suitably, the catalyst composition comprises greater than or equal to 10 wt% of indium. Still more suitably, the catalyst composition comprises greater than or equal to 12 wt% of indium. Most suitably, the catalyst composition comprises greater than or equal to 15 wt% of indium.

[00108] In another embodiment, the catalyst composition comprises less than or equal to 10 wt% of rhodium. Suitably, the catalyst composition comprises less than or equal to 5 wt% of rhodium. More suitably, the catalyst composition comprises less than or equal to 3 wt% of rhodium. Most suitably, the catalyst composition comprises less than or equal to 2 wt% of rhodium.

[00109] In another embodiment, the catalyst composition comprises between 0.01 wt% and 10 wt% of rhodium. Suitably, the catalyst composition comprises between 0.1 wt% and 5 wt% of rhodium. More suitably, the catalyst composition comprises between 0.1 wt% and 3 wt% of rhodium. Most suitably, the catalyst composition comprises between 0.5 wt% and 3 wt% of rhodium.

[00110] In another embodiment, the catalyst composition comprises a support.

[00111] Suitable supports are described in paragraphs [0054] to [0067] above.

[00112] In a particular embodiment, the support comprises between 30 and 100 wt% of an indium salt and between 0 and 70 wt% of one or more of the following:

- an aluminium salt (e.g. alumina); - a zirconium salt (e.g. zirconia);

- silica;

a zinc salt (e.g. zinc oxide); and/or

a gallium salt (e.g. gallium oxide).

[00113] More suitably, the support comprises between 50 and 100 wt% of an indium salt and between 0 and 50 wt% of one or more of the following:

- an aluminium salt (e.g. alumina);

- a zirconium salt (e.g. zirconia);

- silica;

- a zinc salt (e.g. zinc oxide); and/or

- a gallium salt (e.g. gallium oxide).

[00114] Still more suitably, the support comprises between 50 and 100 wt% of an indium salt and between 0 and 50 wt% of one or more of the following:

- an aluminium salt (e.g. alumina); and/or

- a zirconium salt (e.g. zirconia).

[00115] Most suitably, the support comprises between 50 and 100 wt% of an indium salt and between 0 and 50 wt% of an aluminium salt (e.g. alumina).

[00116] In another embodiment, the support consists essentially of/consists of indium and/or an indium salt. Suitably, the indium salt is indium oxide.

[00117] It will be understood that the catalyst compositions of the present invention may have any suitable surface area. Suitable surface areas are described in paragraph [0068] above.

[00118] In another embodiment, the catalyst compositions are in particulate or granular form.

[00119] In another embodiment, the catalyst composition is in particulate form and the particles have a particle size of less than or equal to 10 nm. Suitably, the catalyst composition is in particulate form and the particles have a particle size of less than or equal to 5 nm. More suitably, the catalyst composition is in particulate form and the particles have a particle size of less than or equal to 3 nm.

[00120] In yet another embodiment, the catalyst composition is in particulate form and the particles have a particle size between 0.1 nm and 10 nm. Suitably, the catalyst composition is in particulate form and the particles have a particle size between 0.1 nm and 5 nm. More suitably, the catalyst composition is in particulate form and the particles have a particle size between 0.1 nm and 3 nm. Yet more suitably, the catalyst composition is in particulate form and the particles have a particle size between 0.5 nm and 3 nm. Even more suitably, the catalyst composition is in particulate form and the particles have a particle size between 1 nm and 3 nm. Ivlost suitably, the catalyst composition is in particulate form and the particles have a particle size between 2 nm and 3 nm.

EXAMPLES

Description of drawings

[00121] Embodiments of the invention will be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows a schematic representation of a renewable-based methanol production process via catalytic hydrogenation of CO∑ using biomass-derived CO ₂ /H ₂ mixture over Rh-ln catalyst.

Figure 2 shows the measured catalytic performance of CO ₂ hydrogenation towards methanol synthesis at 4.5 MPa for the studied catalysts. GHSV = 18,000 h ¹ . (A) Methanol selectivities at 270 °C of the Rh and Ru catalysts with different In/AI ratios and different synthesis methods. (B) Methanol selectivities at 250 °C and 270 °C of the Copre-Rh/(5ln5AI)0 sample compared with the commercial Cu/ZnO/A C catalyst under different CC^Kb ratios. The dotted lines indicate the methanol selectivities from thermodynamic prediction. (C) Weight time yield of methanol at 250°C and 270°C of the Copre-Rh/(5ln5AI)0 sample compared with the commercial Cu/ZnO/AI ₂ C>3 catalyst under different CC^ b ratios.

Figure 3 shows the XPS Rh 3d and In 3d spectra of the reduced Rh-containing sample.

Figure 4 shows the normalized Rh K-edge XANES spectra of the reduced Rh-containing catalysts and the rhodium reference material.

Figure 5 shows the k ³ -weighted Rh K-edge Fourier transforms of the reduced Rh-containing samples.

Figure 6 shows the temperature programmed reduction profiles of the Rh-containing samples.

Figure 7 shows the HR-TEM images and the corresponding fast-Fourier Transform (FFT) analyses of the selected area of the reduced Copre-Rh/(5ln5AI)0 sample.

Figure 8 shows the XRD patterns of the calcined (in N ₂ ) and spent Copre-Rh/(5ln5AI)0 samples.

Figure 9 shows the in-situ FTIR spectra of the adsorbed species on the reduced surface. (A) Copre-Rh/(10AI)O sample; (B) Copre-Rh/(5ln5AI)0 sample; and (C) commercial Cu/ZnO/AI ₂ C>3 catalyst. The gas flow of 25% CO2 and 75% H ₂ was passed through the catalyst pellets made by 20 mg of samples at various temperatures. Figure 10 shows the XRD patterns of the binary metal oxides supported Rh samples after 450 °C thermal treatment in N ₂ .

Figure 1 1 shows the methanol selectivities of the binary metal oxides supported Rh samples at 4.5 MPa with different reaction temperatures. Gas composition: 75% H ₂ and 25% CO2. GHSV: 18,000 IT ¹ .

Figure 12 shows the methanol selectivities of Rh samples on the indium-aluminium oxides support with different N ₂ heat treatment temperature. Gas composition: 4.5 MPa of 75% H ₂ and 25% C0 ₂ . GHSV: 18,000 IT ¹ .

Figure 13 shows the methanol selectivities of indium-aluminium oxides supported Rh samples with different Rh loading. Gas composition: 4.5 MPa of 75% H ₂ and 25% C0 ₂ . GHSV: 18,000 h- ¹ .

Figure 14 shows: (A) the C0 ₂ conversion, CH3OH selectivity and yield of the Copre- Rh/(5ln5AI)0 catalyst under various reaction temperatures. Reaction conditions: 4.5 MPa of 75% H ₂ and 25% C0 ₂ , GHSV = 18,000 IT ¹ ); and (B) the CH ₃ OH selectivity and weight time yield of the Copre-Rh/(5ln5AI)0 catalyst under various GHSV. Reaction conditions: 4.5 MPa of 75% H ₂ and 25% C0 ₂ at 270 °C.

Figure 15 shows the XANES spectra for the Copre-Rh/(5ln5AI)0 catalyst before and after H ₂ reduction: (A) Rh L ₃ -edge XANES; and (B) In L ₃ -edge XANES.

Figure 16 shows: (A) the Fourier transforms of Rh K-edge EXAFS for the reduced Rh- containing catalysts; and (B) the k ³ -weighted Rh K-edge EXAFS spectra for the reduced Rh- containing catalysts.

Figure 17 shows the Fourier transforms of Rh K-edge EXAFS for the reduced Copre- Rh/(5ln5AI)0 sample: (A) the fit without Rhln ₃ structure; and (B) the fit with Rhln ₃ structure.

Materials and Methods

Synthesis of the catalyst

Synthesis of the binary metal oxide supports

[00122] The binary metal oxide supports were synthesized using a co-precipitation method. The metal precursors were hydrated metal nitrate salts: AI(NOs) ₂ -3H ₂ 0 (Aldrich), Zn(N0 ₃ ) ₂ -6H ₂ 0 (Aldrich), Ιη(Ν0 ₃ )3-χΗ ₂ 0 (Aldrich) and Ga(N0 ₃ ) ₃ -9H ₂ 0 (Aldrich). Two of the selected metal nitrates were dissolved completely in 150 mL deionized water to make a solution with concentration of 0.05M. A Na ₂ CC>3 aqueous solution was prepared by dissolving 7.5 g of Na ₂ CC>3 in 300 ml. of deionized water. The solutions were added simultaneously into a plastic reactor containing 50 mL of preheated deionized water at 80 °C. A delivery pump was used to inject the metal nitrate solution at a constant rate of 0.4 mL min ¹ in an automatic and reproducible manner. An HPLC pump was used to deliver the Na ₂ CC>3 solution at a rate of 0.4-0.8 mL min ¹ . The mixture was stirred at 1 ,000 rpm, with pH of the precipitating solution carefully maintained at 9 ± 0.1. Once the addition of the precursor metal nitrate solution was completed, the resulting precipitate was aged in solution for 18 h. After the aging process, the precipitate was extracted by centrifugation at 5,000 rpm. The centrifuged precipitate was washed with deionized water several times at 5,000 rpm to remove residual Na ⁺ ions and then washed with acetone before drying in vacuum. The dried powder was then calcined in N2 at a ramp of 5 °C min ¹ up to desired temperature (450 °C, if not indicated) for 4 h to get the final binary metal oxide supports.

Synthesis of the binary metal oxides supported Rh samples

[00123] The loading of Rh onto above synthesized binary metal oxide support was achieved by the wet-impregnation method: the selected binary metal oxide support was immersed into a Rh(NC>3)3 (Aldrich) aqueous solution and the mixture was kept stirring until the solid and liquid were mixed evenly. The slurry was set aside in air for one night before drying in an oven at 80 °C. The dried powder was then calcined in N ₂ at a ramp of 5 °C min ^-1 up to 450 °C for 4 h to get the final binary metal oxides supported Rh samples. The detailed information of the samples is listed in Table 1 below.

Synthesis of the Rh-containing and Ru-containing samples and the indium-aluminium oxides support with different In/AI ratios.

[00124] The detailed information of the samples is listed in Table 2. In this part, the samples are classified in two categories: i) those loaded Rh or Ru by wet-impregnation method; and ii) those by co-precipitation method.

[00125] For the wet-impregnation samples, the synthesis followed the same process as the binary metal oxides supported Rh samples described above: The rhodium-indium supports with different recipe Rh:ln ratios were synthesised using co-precipitation method. Then the derived supports were loaded with Rh or Ru using wet-impregnation method and dried, calcined in N ₂ to get the final catalyst.

[00126] The co-precipitation samples were prepared by the following process: metal nitrates (Rh(NC>3)3 aqueous solution, AI(N03) ₂ -3H ₂ 0 and/or ln(NC>3)3 xH ₂ 0) were dissolved completely in 150 ml_ deionized water to make a solution with concentration of 0.05M. A Na ₂ CC>3 aqueous solution was prepared by dissolving 7.5 g of Na ₂ CC>3 in 300 ml. of deionized water. The solutions were added simultaneously into a plastic reactor containing 50 ml_ of preheated deionized water at 80 °C. A delivery pump was used to inject the metal nitrate solution at a constant rate of 0.4 mL min ^-1 in an automatic and reproducible manner. An HPLC pump was used to deliver the Na ₂ CC>3 solution at a rate of 0.4-0.8 mL min ^-1 . The mixture was stirred at 1 ,000 rpm, with pH of the precipitating solution carefully maintained at 9 ± 0.1. Once the addition of the precursor metal nitrate solution was completed, the resulting precipitate was aged in solution for 18 h. After the aging process, the precipitate was extracted by centrifugation at 5,000 rpm. The centrifuged precipitate was washed with deionized water several times at 5,000 rpm to remove residual Na ⁺ ions and then washed with acetone before drying in vacuum. The dried powder was then calcined in N ₂ at a ramp of 5 °C min ^~1 up to desired temperature (450 °C, if not indicated) for 4 h to get the final catalysts.

Catalytic testing of C0 ₂ hydrogenation reaction

[00127] Catalyst tests in hydrogenation of C0 ₂ to produce methanol were carried out in a tubular fixed bed reactor (12.7 mm outside diameter) by using a catalystweight of 0.1 g. Before each test, the catalyst was pre-reduced at 290 °C for 2 h under the H ₂ flow of 20 stp mL min ¹ (stp = standard temperature and pressure; P = 101.3 kPa, T = 298 K). The catalyst bed was then cooled to room temperature. C0 ₂ /H ₂ reaction mixture with molar ratios ranging from C0 ₂ :H ₂ = 1 :3 to 3:1 were fed at a rate of 30 stp mL min ¹ through the catalyst bed, and the system pressure was held at 4.5MPa controlled by a back-pressure regulator. The reaction temperature was set from 210 °C to 310 °C. The products were analysed by a gas chromatograph equipped with the calibrated thermal conductivity detector (TCD) and flame ionization detector (FID).

X-ray powder diffraction (XRD)

[00128] The X-ray diffraction (XRD) profile was collected by a Philips PW-1729 diffractometer with Bragg-Brentano focusing geometry using Cu Ka radiation (lambda= 1.5418 A) from a generator operating at 40 kV and 40 mA.

X-ray photoelectron spectroscopy (XPS)

[00129] After reduction at 290 °C, samples were carefully transferred in a glove bag filled with nitrogen to prevent the air exposure and analyzed by XPS. XPS was performed using a Quantum 2000 Scanning ESCA Microprob instrument (Physical Electronics) equipped with an Al Ka X-ray radiation source (hv = 1486.6 eV). A flood gun with variable electron voltage (from 6 eV to 8 eV) was used for charge compensation. The raw data were corrected for substrate charging with the BE of the C peak (285 eV), as shown in the XPS handbook. The measured spectra were fitted using a least-squares procedure to a product of Gaussian-Lorentzian functions after removing the background noise. The concentration of each element was calculated from the area of the corresponding peak and calibrated with the sensitivity factor of Wagner.

X-ray absorption spectroscopy (XAS) Rh K-edge & Rh, In L-edge

[00130] After reduction at 290 °C, samples were carefully transferred into capillary tubes (quartz NMR tubes) in a nitrogen glove box. The reduced samples were sandwiched between silica wool to fix the samples in the middle of the capillary tubes, and then the capillary tubes were sealed properly and stored in a glove box until the XAS experiments. Local structures surrounding Rh atoms were probed by using XAS technique at beamline BL01 C of Taiwan Light Source at National Synchrotron Radiation Research Center (NSRRC) in Taiwan. A Si(111) Double Crystal Monochromator (DCM) was used to scan the photon energy. The energy resolution (ΔΕ/Ε) for the incident X-ray photons was estimated to be 2* 10 ^"4 . Fluorescence mode was adopted for Rh K-edge XAS measurements. To ascertain the reproducibility of the experimental data, at least two scan sets were collected and compared for each sample. The EXAFS data analysis was performed using IFEFFIT with Horae packages (Athena and Artemes). The spectra were calibrated with Rh foils as a reference to avoid energy shifts of the samples, and the amplitude reducing factor was obtained from EXAFS data analysis of the foil, which was used as a fixed input parameter in the data fitting to allow the refinement in the coordination number of the absorption element. In this work, the first shell data analyses under the assumption of single scattering were performed with the errors estimated by R-factor.

Temperature-programmed reduction (TPR)

[00131] Temperature- prog rammed reduction (TPR) measurements were obtained using a ThermoQuest TPRO 1100 instrument. Inside the TPR quartz tube, 0.02 g of the calcined catalyst sample was sandwiched between two layers of glass wool with a thermocouple placed in contact with the sample. The TPR tube was then inserted into the instrument for a helium pretreatment. The helium gas pretreatment (He running through the TPR tube at 10 mL min ^"1 at a temperature ramp of 10 °C min ¹ from 40 to 150 °C, then held for 5 min before cooling) cleaned the catalyst surface by removing any absorbed ambient gas molecules. After the pretreatment, a reduction treatment (5% H ₂ in Argon flowing through the TPR tube at 20 mL min ¹ at a temperature ramp of 10 °C min ^-1 from 40 to 600 °C then cooling to room temperature) was carried out to reduce the Rh species and the surface In species within the sample. The consumption of hydrogen gas changed the conductivity of the gas stream; hence, the change in conductivity was measured and calibrated as a function of both temperature and time to produce the TPR profile.

Transmission electron microscopy (TEM)

[00132] TEM images were taken using a JEOL 2100 Transmission Electron Microscope at 200 kV. The sample particles were deposited on an Agar Scientific Holey carbon supported copper 400 mesh grid. TEM samples were prepared by sonicating a suitable amount of material in 1 mL ethanol for 15 minutes before drop wise adding the solution onto the copper grid.

In situ Fourier transform infrared spectroscopy (FTIR)

[00133] In situ Fourier transform infrared (in situ FTIR) spectra were recorded using a Thermo Scientific Nicolet 6700 FTIR spectrometer equipped with a Specac's high temperature high pressure cell. Spectra were obtained by collecting 32 scans with a resolution of 4 cm ^"1 and are presented in absorbance units. The powders of Copre-Rh/(10AI)O sample, Copre-Rh/(5ln5AI)0 sample and the commercial Cu/ZnO/AbC catalyst were pressed into pellets and loaded onto the sample holder. The sample was then flushed with 5% H2/Ar (20 mL min ^-1 ) for 20 min and then reduced for 2 h at 290 °C. After the pre-reduction, the backgrounds were recorded at 50 °C, 100 °C, 150 °C, 200 °C, 250 °C and 290 °C in the atmosphere of 5% H ₂ /Ar. After collecting the backgrounds, a mixture of CO2/H2 (CO2 : H ₂ = 1 : 3) was passed through the reduced sample pellet and then the in situ FTIR spectra were collected at 50 °C, 100 °C, 150 °C, 200 °C, 250 °C and 290 °C with each temperatures maintaining for at least 30 min.

BET surface area analysis

[00134] The surface area and the pore size were determined by N2 adsorption at -196 °C using the Micromeritics ASAP 2020M analyser. Prior to N2 adsorption measurement, the samples were degassed at 200 °C for 3 h.

Hydrogen/Oxygen titration method for measurement ofRh dispersion

[00135] The metal dispersion test was conducted on the PCA-1200 Chemisorption Analyzer (Bejing Biaode Electronic Technology Co., Ltd, China). Prior to the reduction process, the samples were degassed at 300 °C for 1 hour under helium flow (30 mL/min). Once the degas completed the samples were heated up to 400 °C and then reduced in hydrogen (30 mL min) at 400 °C for 1 hour. After that, the samples were cooled to 100 °C in helium and oxidized with oxygen (20 mL/min) at 100 °C for 1 h. The oxidized samples were then reduced at 200 °C with pulsed hydrogen until the peak area of hydrogen recorded by a thermal conductivity detector stayed unchanged. The metal dispersions were calculated by the consumption of hydrogen.

Results and discussion

Catalyst compositions for the hydrogenation of carbon dioxide to methanol

Binary oxide supports

[00136] Firstly, a series of binary metal oxides were prepared as the supports by co- precipitation method and Rh was loaded on them using a wet-impregnation method. The prepared catalysts were then screened for methanol production; details on those binary oxides supported Rh samples can be found in Table 1. Table 1 - The details of the binary metal oxides supported Rh samples.

[00137] After thermal treatment in N ₂ at 450 °C, the XRD was recorded and the patterns of the prepared binary metal oxides supported Rh samples showed broad diffraction peaks from the supports but no peaks from the Rh compounds were detected, indicating that Rh species were well-dispersed in the small crystalline metal oxide particles (Figure 10).

[00138] Figure 11 shows that all of the binary oxides supported Rh samples synthesised in this study could catalyse CO ₂ hydrogenation to form methanol, and the highest methanol selectivity was observed using the Rh/lnAIO sample.

[00139] The synthesis parameters of the indium-aluminium oxide supported Rh catalyst was then further studied with various temperatures of thermal treatment in N2 as well as different Rh loadings. It was found that thermal treatment at 450 °C and around 3% loading were preferred for methanol production (Figure 12 and 13).

Indium-aluminium supported Rh catalyst compositions

[00140] After optimising the synthetic conditions for the indium-aluminium oxide supported Rh samples, a series of Rh-containing samples with different In/AI compositions were next prepared (see Table 2) and tested as catalysts in the CO ₂ hydrogenation reaction.

Table 2 - The details of the Rh-containing, Ru-containing samples and the indium-aluminium oxides support with different In/AI ratio.

Sample Rh or Ru loading & method I Recipe composition of the j

support

In : Al

Rh/(10AI)O 5%, wet-impregnation 0 : 10

Rh/(1 ln9AI)0 5%, wet-impregnation 1 : 9

Rh/(3ln7AI)0 5%, wet-impregnation 3 : 7

Rh/(5ln5AI)0 5%, wet-impregnation 5 : 5

Rh/(10ln)O 5%, wet-impregnation 10 : 0

(5ln5AI)0 support 5 : 5

Copre-Rh/(5ln5AI)0 2.5% , co-precipitation 5 : 5

Copre-Rh/(10AI)0 2.5% , co-precipitation 0: 10

Ru/(5ln5AI)0 5%, wet-impregnation 5 : 5

[00141] As can be seen from Figure 2, the samples with In/AI ratios from 0 to 1 give diverse product compositions. The sample containing no indium (i.e. the Rh/(10AI)O sample) showed total conversion of CO ₂ to methane, while CO predominated the product phases when the Rh/(1 ln9AI)0 was used. However, some methanol was produced using the Rh/(1 ln9AI)0 sample.

[00142] The amount of methanol produced began surpassing the other products of the reaction when the Rh/(3ln7AI)0 catalyst was used, before the reaction became substantially selective for methanol (-85% selectivity) when the Rh/(5ln5AI)0 and Rh/(10ln)O samples were used.

[00143] Increases in CO2 conversion (>10%) were also found to be possible when using the Copre-Rh/(5ln5AI)0 sample, which was made by co-precipitation of all three Rh, In and Al species. The specific surface areas (3.2 m ² g ^_1 for the Rh/(5ln5AI)0 and 279.5 m ² g ^"1 for the Copre-Rh/(5ln5AI)0) determined by BET as well as the rhodium surface areas (17.3 m ² g ^"1 for the Rh/(5ln5AI)0 sample and 132.6 m ² g ^"1 for the Copre-Rh/(5ln5AI)0) sample, determined by hydrogen/oxygen titration, reveal that adding rhodium together with indium and aluminium species in the co-precipitation process greatly increases the specific surface area of the catalyst, as well as the surface exposure of rhodium compared to the catalyst made by loading rhodium on the supports via wet-impregnation method. [00144] It is well-accepted that the active sites become abundant when the surface area of a catalyst increases, thus this beneficial increase in surface area of the Copre-Rh/(5ln5AI)0 sample is believed to contribute to the enhanced conversion rate of the reactants.

[00145] The indium-aluminium oxides support alone was also tested in the CO ₂ hydrogenation reaction, which was labelled as "(5ln5AI)0 support" (Figure 3). It was found that in using the (5ln5AI)0 support as a catalyst a selectivity for methanol of just 30% was achieved, together with a really low CO ₂ conversion. This result suggests that the indium oxide alone does not contribute for the high methanol selectivity (~85%) in our indium-modified rhodium samples.

Methanol selectivity

[00146] In preparing methanol from the CO2 hydrogenation reaction, the reversed water gas shift (RWGS) reaction is commonly known to be a major competing reaction to the methanol production. Therefore, the high methanol selectivity displayed by the indium-modified rhodium samples of the present invention must possess the ability to inhibit the RWGS reaction, thereby minimising the formation of CO.

[00147] To get the reaction states according to equilibrium thermodynamics of the CO2 hydrogenation to methanol under our reaction conditions, theoretical calculations were performed to derive the equilibrium thermodynamics values (using standard HSC Chemistry 5.11) where only the intrinsic properties of the gas species were considered. Here the reactant mixtures of 1 mole of CO∑(g) and 3 moles of ¾(g) were considered, and product species of H ₂ 0(g), CO(g) and CH ₃ OH(g) were taken into account (experimentally identified). It has been found that in CO ₂ hydrogenation reaction to methanol, higher C0 ₂ : H ₂ ratio is not thermodynamically favourable.

[00148] Figure 2B shows the catalytic result of CO2 hydrogenation with different C0 ₂ : H2 ratios (from 1 : 3 to 3 : 1) over the Copre-Rh/(5ln5AI)0 catalyst sample. A commercial Cu/ZnO/A Os catalyst (HiFUEL R120, Johnson Matthey) was also tested as the comparison.

[00149] It was found that in increasing the CO ₂ : H ₂ ratio from 1 : 3 to 3 : 1 , the methanol selectivity over the Copre-Rh/(5ln5AI)0 catalyst sample, especially when excess CC was present in the reactant mixture, were surprisingly well beyond the thermodynamic prediction (indicated by the dotted line in Figure 2B). This result suggests that the reaction rate of RWGS was significantly suppressed for the Copre-Rh/(5ln5AI)0 catalyst sample. In contrast, the methanol selectivity for the commercial Cu/ZnO/A C catalyst decreased sharply to below 10% at the conditions of CO ₂ : H ₂ = 3 : 1 , indicating that the decreasing trend of methanol selectivity in the commercial Cu/ZnO/AI ₂ C>3 catalyst was governed by thermodynamics.

[00150] Figure 2C shows the methanol weight time yield (gMeoH gactive meta*h) of the Copre- Rh/(5ln5AI)0 and the commercial Cu/ZnO/AI ₂ C>3 catalyst. It can be seen that the methanol yields displayed by the commercial Cu/ZnO/AI ₂ 03 catalyst compared to those of the Copre- Rh/(5ln5AI)0 catalyst sample were significantly reduced. This is a clear indicator of the significant improvement in methanol production achieved using the indium-modified rhodium catalyst compositions of the present invention.

[00151] It is worth noting that the Copre-Rh/(5ln5AI)0 catalyst maintained both high methanol selectivity and yield when used as a catalyst in reactions comprising C0 ₂ in excess, conditions which were previously known to be unfavourable for methanol production.

[00152] Moreover, the methanol selectivity, as well as the weight time yield of the Copre- Rh/(5ln5AI)0 catalyst at C0 ₂ : H ₂ = 1 : 3, can also be turned by adjusting the gas hourly space velocity (GHSV) to higher values, as is seen in Figure 14. The Copre-Rh/(5ln5AI)0 catalyst achieved nearly 100% CH ₃ OH selectivity with a weight time yield of over 40 gMeoH gactive meta*h, which is so far the highest value we are aware of being reported in the literatures for C0 ₂ hydrogenation reactions. (70)

Investigations into the electronic properties of the catalyst compositions

[00153] The electronic properties of the rhodium catalysts were next studied by XPS. The characteristic photoemission from the Rh 3d, In 3d, Al 2p and 0 1s core levels were recorded for each sample. For consistency, all of the binding energies that are reported have been calibrated to the C 1s transition at 285 eV. The XPS of Rh 3d and In 3d of the reduced Rh- containing catalysts are shown in Figure 3.

[00154] The Rh 3d XPS doublet peaks have appreciably shifted towards a low binding energy, which indicates a lowering of the oxidation state of rhodium as the amount of indium in the catalyst composition is increased from no indium (i.e. the Rh(10AI)O) to 100% indium components in the support (i.e. the Rh(10ln)O sample).

[00155] It is known that rhodium particles supported on alumina are easily oxidized after exposure to air(77), therefore the Rh-containing samples of the present invention may have encounter a certain degree of air-exposure during the sample transportation while performing the ex-situ XPS analysis, as the oxidic rhodium species detected. Further investigations of the samples before and after H ₂ reduction were thus conducted by rhodium and indium l_3-edge XANES (Figure 15). The results show that when a greater indium content in the Rh-containing sample, results in less oxidic rhodium being observed through ex-situ XPS analysis. This suggests the presence of indium can prevent the re-oxidation of the rhodium species, suggesting the indium modification can change the properties of rhodium and make rhodium species less reactive to oxygen.

[00156] However, from In 3d XPS spectra, no distinguishable shifts were observed, indicating that most of the indium species stayed as oxidic following reduction.

[00157] Next, an Rh K-edge XAFS experiment was carried out, which gave information on the oxidation state and local atomic structure of the catalyst compositions. Figure 4 shows the normalized Rh K-edge XANES spectra of the reduced Rh-containing catalysts and the rhodium reference material. In agreement with the XPS result (Figure 3), the rhodium species of the samples containing less indium were more oxidised. The rhodium species in the Rh/(5ln5AI)0, Rh/(10ln)O and Copre-Rh/(5ln5AI)0 samples, all of which have higher indium content, showed metallic characteristics as the absorption edge positions of these samples were close to that of the rhodium foil.

[00158] Figure 5 shows the Fourier-transform Rh K-edge EXAFS of the reduced Rh- containing samples. The k ³ -weighted EXAFS and the corresponding fitting of the Rh- containing samples are shown in Figure 16 and the structural fitting parameters are detailed in Table 3 below. It can be seen from Figure 5 that in general each Rh-containing sample contains two main shells, that is, a Rh-0 shell at around 2k and the Rh-metal shell at longer distance. For the Rh/(ln9AI)0 sample, the observed distance of Rh-0 at 2.04 A along with the Rh-Rh at 2.66 A and 3.05 A indicate the first three Rh-(neighbour atoms) distances in a hexagonal (corundum) Rh ₂ 03 structure(77). The Rh/(3ln7AI)0 sample gives similar peak positions but the bond lengths and the coordination numbers that fit the experimental data are slightly different from the Rh/(1 ln9AI)0 sample, as can be seen in Table 3.

[00159] It is considered that the Rh/(3ln7AI)0 sample may contain a mixed structure including Rh ₂ C>3 and other potential rhodium compounds, i.e., metallic rhodium and Rh-ln alloy, since those compounds have Rh-(neighbour atoms) bonds in the similar distance range. As the indium content further increased, the coordination number of Rh-0 decreased as well as the distance of the Rh-Rh bond at around 2.66-2.70 A increased, suggesting less oxidic rhodium existed in the system when the indium concentration was higher. Besides in the Rh/(5ln5AI)0 and Copre-Rh/(5ln5AI)0 samples, there are three distinctive bonds observed at the distances of 2.64, 2.82 and 3.07 A, that are attributed to the Rh-ln, Rh-ln and Rh-Rh bonds, respectively, from the tetragonal Rhln3 structure. The Rh/(10ln)O sample gives even higher Rh-ln alloy content due to its higher coordination number of the Rh-ln bond. In addition, the Rh/(10ln)O sample contains no oxidic rhodium species (no Rh-0 bond detected). To show that the incorporation of the Rhln ₃ alloy structure is necessary to achieve a satisfactory fitting, a comparison of the fit, both with and without Rhln ₃ alloy structure is presented in Figure 17.

Table 3 - The structural fitting parameters of the Rh K-edge EXAFS of the reduced Rh- containing samples.

Further characterisation of the catalytic compositions

[00160] TPR profiles of some of the Rh-containing catalysts as well as the (5ln5AI)0 support are presented in Figure 6. The profile for the Rh/(10AI)O catalyst showed peaks at 135 and 248 °C, which are attributed to the reduction of well-dispersed Rh ₂ C>3 and of larger Rh ₂ C>3 particles(78). After indium incorporation, we can see that only the reduction peak of well- dispersed Rh ₂ C>3 can be observed in the Rh/(1 ln9AI)0 sample, suggesting that indium addition can enhance the dispersion of rhodium species. As the indium content further increased, the reduction temperature of the well-dispersed Rh ₂ 03 increased in the Rh/(3ln7AI)0 sample, and the reduction peak then became insignificant in the Rh/(5ln5AI)0 and Rh/(10ln)O samples.

[00161] The (5ln5AI)0 support sample started the reduction at around 200 °C, which is attributed to the reduction of the surface or the dispersed indium oxide phase with smaller particles sizes( 79). Therefore, under at a reduction temperature of 290 °C, the temperate that was applied prior to the catalytic testing, the reduction of rhodium species may occur simultaneously with the reduction of the surface indium species, possibly forming the Rh-ln alloy that was observed from EXAFS analysis.

[00162] The HR-TEM images of the reduced Copre-Rh/(5ln5AI)0 sample and the corresponding fast-Fourier Transform (FFT) analyses of the selected area presented in Figure 7, reveal the existence of nano-clusters of tetragonal Rhln ₃ structure with the particle sizes of less than 5 nm (the majority is 1~2 nm).

[00163] Hexagonal ln ₂ C>3 species were also observed as light-colour particles in the vicinity of the Rh-containing clusters. This is in agreement with the XRD patterns in Figure 8, which show that the hexagonal ln ₂ C>3 phase is the predominant structure in the Copre-Rh/(5ln5AI)0 sample either before or after catalytic testing.

[00164] No rhodium species were detected from the XRD, probably due to the low loading (-2.5 wt.%) of rhodium used, and, furthermore, the absence of aluminium oxide phases from XRD patterns would tend to indicates that aluminium species were in the form of amorphous structure.

Surface absorption properties

[00165] To investigate the surface adsorption properties of the Rh-containing catalysts of the present invention, we performed the in-situ FTIR measurement with CO ₂ /H ₂ flow at 50 °C to 290 °C. It can be seen from Figure 9A that for the Copre-Rh/(10AI)O sample without indium addition, the Rh(CO) ₂ gem-dicarbonyls species adsorbed on rhodium surfaces gave the peaks at 1960-1990 cm ^-1 and 2030-2050 cm ^-1 , which are believed to be the key intermediate for the methane formation(27). Other adsorbed species, namely linear CO, bridging CO, adsorbed H ₂ O and mono-dentate formate(22, 23), could also be observed in the temperature range from 50°C to 290°C, but the intensities of the adsorbed H2O and mono-dentate formate decreased as temperature increased.

[00166] In contrast, different adsorbed species were detected for the Copre-Rh/(5ln5AI)0 sample during the in-situ FTIR measurement. It can be seen from Figure 9B that at 50°C, the intermediates including bi-dentate and poly-dentate carbonates as well as mono-dentate and bi-dentate formats, which are regarded as the key intermediates for the methanol production(24, 25), could all be observed. It can also be noted that a weak band attributed to linear CO at around 2000-2010 cm ^-1 (26). As the temperature increased, those infrared bands increased, moreover, at the elevated temperature some peaks appeared at the water vapour absorption region (1300-2000 cm ^-1 ) which might be resulted from the water as the side-product in the methanol production. [00167] In-situ FTIR measurements were also performed for the commercial Cu/ZnO/A C sample using the identical conditions as that for those Rh-containing samples. It is shown in Figure 9C that at low temperature the water species could be observed, and the small sharp peaks at around 2060-2080 cm ^-1 are the bands corresponding to the chemisorbed CO on a low Miller-index plane of Cu(25). When the temperature increased, the vibrations of water vapour enhanced. In addition, two strong and broad bands at 2110 and 2180 cm ^-1 attributed to the gas-phase carbon monoxide demonstrated that the RWGS reaction had occurred(27). Compared to the Copre-Rh/(5ln5AI)0 sample, the commercial Cu/ZnO/A 03 catalyst gave relatively weak adsorption to the intermediates (formats and carbonates) of the methanol production, and the Cu surface showed predominantly the products of the RWGS reaction (CO and H2O) when temperature increased. This result has confirmed that the intermediates of methanol production can be stabilised (have stronger adsorption) on the Rh-ln sites provided by the Rh-ln alloys.

[00168] Moreover, CO vapour phases were not detected in the Copre-Rh/(5ln5AI)0 sample, suggesting the RWGS reaction was suppressed on the indium-modified rhodium surfaces.

Methanol steam reforming reaction

[00169] The Copre-Rh/(5ln5AI)0 catalyst composition was also tested in a fixed-bed reactor for the possible direct production of hydrogen and carbon dioxide from steam reformation of methanol at ambient pressure, with the reaction conditions of: 0.1g catalyst, liquid feed of CH30H:H ₂ 0 = 1 : 2 at 0.025ml/min; N ₂ carrier at 2.5 ml/min; and a reaction temperature at 195 °C being used. The test results are shown in Table 4 below.

[00170] It can be seen that the H ₂ / CO ₂ molar ratio obtained from the catalyst under these conditions was around 3: 1 with low amounts of CO present. This result indicates that the steam reforming of methanol can indeed take place under the applied reaction conditions using Copre-Rh/(5ln5AI)0 as a catalyst.

Table 4 - The results of methanol steam reforming reaction using the Copre-Rh/(5ln5AI)0 catalyst composition in a fixed-bed reactor. Reaction conditions: 0. 1g catalyst, liquid feed of CH ₃ OH:H ₂ 0 = 1: 2 at 0.025ml/min; N ₂ carrier at 2.5 ml/min; reaction temperature at 195 °C; reaction pressure at ambient pressure.

[00171] While specific embodiments of the invention have been described herein for the purpose of reference and illustration, various modifications will be apparent to a person skilled in the art without departing from the scope of the invention as defined by the appended claims.

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