Catalyst composition, methods for its production and use thereof

Abstract

Provided is a pre-catalyst and catalyst composition obtainable therefrom and its use in a method for providing a composition comprising carbon monoxide. Also provided is a method is provided for the preparation of a pre-catalyst composition and catalyst composition.

Description

CATALYST COMPOSITION, METHODS FOR ITS PRODUCTION AND USE THEREOF INTRODUCTION

[0001] The present invention relates to a pre-catalyst and / or catalyst composition and their use in the conversion of carbon dioxide to carbon monoxide. Also provided is a method for the preparation of a pre-catalyst composition and catalyst composition. These compositions have uniform dispersion and stable nano-structure and demonstrate high carbon dioxide conversion without considerable methanation in a reverse water gas shift reaction. BACKGROUND OF THE INVENTION

[0002] Continuously increasing greenhouse gas emissions is causing a climate crisis. A key challenge in reducing greenhouse gas is the reduction in carbon dioxide emissions. The International Energy Agency reported in 2018 that global energy-related carbon dioxide emissions grew to reach a historic high of 33.1 gigatonnes of carbon dioxide, and only a small amount of this (approximately 230 megatonnes per year globally) is currently recycled or mitigated.

[0003] Using low carbon technologies, intense efforts are being made to develop carbon capture for storage (CCS) or utilisation (CCU) technologies. While CCS mainly deals with carbon dioxide capture to avoid carbon dioxide emissions into the atmosphere, CCU technologies are designed to transform carbon dioxide into a number of value-added products, e.g. olefins, formic acid, dimethylether (DME), urea, dimethylcarbonate (DMC), acetic acid, methanol or synthetic natural gas (syngas).

[0004] An important reaction in the conversion of carbon dioxide to value-added products is the reverse water gas shift reaction (RWGS). In the RWGS, catalysts are often used to convert carbon dioxide to carbon monoxide by hydrogenation. Carbon monoxide is an important starting material in a number of commercially important processes for the preparation of useful materials, such as the manufacture of hydrocarbons via the Fischer-Tropsch process.

[0005] The RWGS has been studied with a variety of different catalysts, which include precious / noble metals such as Pt, Pd, Ru and Au. As reported in González-Castaño et al. (React. Chem. Eng., 2021, 6, 954), the catalytic activity and selectivity toward carbon monoxide has recently been analysed for Pd, Cu, Ni, Fe and Pt catalysts. Pt catalysts exhibited the highest carbon dioxide conversions, but lower selectivity toward CO than Fe and Cu. Ni presented the highest methanation rates.

[0006] Bimetallic catalyst compositions have also been employed in order to enhancecatalytic performance in the RWGS. In particular, Cu-ZnO systems have been employed where the ZnO promotion has been related to higher Cu dispersions, and Pt-Co catalysts have demonstrated improved carbon monoxide selectivity relative to monometallic systems.

[0007] Alkali metal doping has been reported to lead to improvements in carbon monoxide selectivity and higher carbon dioxide conversion. For Pt and Au catalysts, the catalytic promotion obtained through the addition of alkali metal is attributed to a metal-O(OH)-alkali interface which stabilizes the metal particles and promotes carbon dioxide dissociation and favours carbon monoxide desorption.

[0008] Deactivation of catalysts can occur for a number of reasons, primarily metal sintering, carbon deposits and sulphur poisoning. Susceptibility to sintering depends on the nature of the metal and its interaction with any support material. The high stability displayed by Pt supported on zeolite catalysts has been attributed to the encapsulation of the metal particles.

[0009] Despite the higher reaction rates exhibited by noble metal catalysts, their high prices and limited availability hinder their implementation at larger scales. The present invention aims to provide a pre-catalyst and / or catalyst composition which can be manufactured cheaply enough to be employed at scale and has good stability whilst demonstrating good catalytic performance in the RWGS. Furthermore, the pre-catalyst composition and / or catalyst composition is suitably free of chromium species due to the potential for formation of hexavalent chromium Cr[VI], a known human carcinogen.

[0010] Suitably, the pre-catalyst and catalyst composition advantageously provide one or more of high carbon dioxide conversion, high carbon monoxide selectivity and low methanation rate. SUMMARY OF THE INVENTION

[0011] The presently disclosed subject matter provided herein is a pre-catalyst composition, catalyst composition and a method for their production which is in general inexpensive, safe and uses abundant materials. The pre-catalyst and / or catalyst composition can be used in a reverse water gas shift reaction, providing high selectivity for carbon monoxide with little methane by-product and high carbon dioxide conversion rates.

[0012] In a first aspect, the present invention relates to a method for preparing a pre-catalyst composition comprising:(i) combining an iron salt or hydrate thereof; at least one further metal species selected from one or more of the group consisting of a cerium salt or hydrate thereof, a cerium oxide or hydrate thereof, an aluminium salt or hydrate thereof, an aluminium oxide or hydrate thereof, a titanium salt or hydrate thereof and a titanium oxide or a hydrate thereof; and an organic compound comprising one or more functional groups selected from the group consisting of a carboxyl, hydroxyl, amido and amino group; and (ii) subjecting the product of (i) to calcination to provide a pre-catalyst composition.

[0013] In a second aspect, the present invention provides a pre-catalyst composition obtained or obtainable according to the method of the first aspect.

[0014] In a third aspect, the present invention provides a method for preparing a catalyst composition comprising: (a) providing a pre-catalyst composition according to the second aspect; (b) optionally subjecting said pre-catalyst composition to calcination; and (c) activating said pre-catalyst composition to obtain a catalyst composition.

[0015] In a fourth aspect, the present invention provides a catalyst composition obtained or obtainable by the method of the third aspect.

[0016] In a fifth aspect, the present invention provides a shaped composition comprising a pre-catalyst composition according to the second aspect, or a catalyst composition according to the fourth aspect.

[0017] In a sixth aspect, the present invention provides a method for producing a composition comprising carbon monoxide, wherein said method comprises contacting a feed gas composition comprising carbon dioxide and hydrogen with a pre-catalyst composition according to the second aspect, or a catalyst composition according to the fourth aspect, at a temperature of at least 400°C.

[0018] In a seventh aspect, the present invention provides a reactor comprising a pre-catalyst composition according to the second aspect, or a catalyst composition according to the fourth aspect.

[0019] In an eight aspect, the present invention provides a method for producing a composition comprising carbon monoxide, wherein said method comprises contacting a feed gas composition comprising carbon dioxide and hydrogen with a pre-catalyst composition orcatalyst obtainable therefrom at a temperature of at least 400°C, wherein the pre-catalyst composition comprises iron or one or more oxide thereof and cerium or one or more oxide thereof.

[0020] Preferred, suitable, and optional features of any one particular aspect of the present invention are also preferred, suitable, and optional features of any other aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The subject matter of the application will be more readily understood from the following detailed description when read in conjunction with the accompanying drawings, in which:

[0022] Figure 1 shows the results of stability testing of Fe-Ce-K-Al pre-catalyst (100:100:5:80) (example 36) on reverse water gas shift reaction under atmospheric pressure and a temperature of 600oC.

[0023] Figure 2 shows XRD spectra of pre-catalyst compositions of example 11, example 20, example 36, example 37, example 34, example 33 and example 41. DETAILED DESCRIPTION OF THE INVENTION

[0024] The methods of the present disclosure can be used to prepare a pre-catalyst and / or catalyst composition for the conversion of carbon dioxide to carbon monoxide. Also provided is a method for the preparation of a pre-catalyst composition and catalyst composition. These and other aspects of the disclosed subject matter are discussed in more detail below. Definitions

[0025] The terms used in this specification generally have their ordinary meanings in the art, within the context of this subject matter and in the specific context where each term is used. Certain terms are defined below to provide additional guidance in describing the compositions and methods of the disclosed subject matter and how to make and use them.

[0026] As used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a compound” includes mixtures of compounds.

[0027] The term “about” means within an acceptable error range for the particular value as determined by one of ordinary skill in the art, which will depend in part on how the value ismeasured or determined, i.e., the limitations of the measurement system. For example, “about” can mean within three or more than three standard deviations, per the practice in the art. Alternatively, “about” can mean a range of up to 20%, preferably up to 10%, more preferably up to 5%, and more preferably still up to 1% of a given value. Also, particularly with respect to systems or processes, the term can mean within an order of magnitude, preferably within five-fold, and more preferably within two-fold, of a value.

[0028] As used herein, the terms “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0029] In the detailed description herein, references to “embodiment,” “an embodiment,” “one embodiment,” “in various embodiments,” etc., indicate that the embodiment(s) described can include a particular feature, structure, or characteristic, but every embodiment might not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. After reading the description, it will be apparent to one skilled in the relevant art(s) how to implement the disclosure in alternative embodiments.

[0030] As used herein, the term “pre-catalyst” refers to a precursor of the catalytically active species. Typically, the pre-catalyst will require conversion to the catalytically active species, for instance by oxidation, reduction and / or heat treatment, or a combination thereof. Suitably, activation is via reduction. The pre-catalyst may be converted to the catalytically active species (i.e. “activated”) in-situ (i.e. under the reaction conditions) or the pre-catalyst may also be converted to the catalytically active species prior to use in the reaction, for instance as a preliminary step.

[0031] As used herein, the term “solid” unless otherwise specified refers to a solid physical form at standard ambient temperature and pressure (SATP), i.e. at a temperature of 298.15 K (25 °C) and at 100,000 Pa (1 bar, 14.5 psi, 0.9869 atm).

[0032] As used herein, the term “gaseous” or “gas” refers unless otherwise specified refers to gaseous physical form at standard ambient temperature and pressure (SATP), i.e. at a temperature of 298.15 K (25 °C) and at 100,000 Pa (1 bar, 14.5 psi, 0.9869 atm).

[0033] As used herein, the term “metal species” is any compound comprising a metal. As such, a metal species, unless otherwise provided, includes the elemental metal, metal oxides and other compounds comprising a metal, i.e. metal salts, alloys, hydroxides, carbides and hydrides. When a specific example of a metal species is stated, said term includes all compounds comprising that metal, e.g. iron species, unless provided otherwise, includes elemental iron, iron oxides, iron salts, iron alloys, iron hydroxides, iron carbides and iron hydrides for instance. Similarly, chromium species includes all compounds comprising chromium, such as chromium salts or hydrates thereof etc.

[0034] As used herein, the term “elemental metal” or specific examples thereof, refers to the metal only when in an oxidation state of zero.

[0035] Unless stated to the contrary, reference to elements by use of standard notation refers to said element in any available oxidation state. Similarly, wherein the term “metal” is used without further restriction no limitation to oxidation state is intended other than to those available.

[0036] As used herein, the term “transition metal” refers to an element of one of the three series of elements arising from the filling of the 3d, 4d and 5d shells. Unless stated to the contrary, reference to transition metals in general or by use of standard notation of specific transition metals refers to said element in any available oxidation state.

[0037] As used herein, the term “alkali metal” refers to an element of Group 1 of the periodic table.

[0038] As used herein, the term “alkaline earth metal” refers to an element of Group 2 of the periodic table.

[0039] As used herein, the term “rare earth metal” refers to an element selected from scandium, yttrium, lanthanum and the lanthanide series of the periodic table.

[0040] As used herein, the term “syngas” (also known as synthesis gas), is a fuel gas mixture essentially consisting of hydrogen and carbon monoxide. However, minor quantities of carbon dioxide and hydrocarbons may be present.

[0041] As used herein, the term “molar ratio” refers to a ratio between the amounts in moles of any two or more components comprised in a composition, reaction, or product distribution. A molar ratio may be represented as a single number, e.g.3, which may also be represented as 3:1 and is a 3 to 1 ratio of a first component and a second component. In instances where more than two components are present, molar ratio may be represented as a series of ratios, e.g.100:2:10:10, which is a 100 to 2 to 10 to 10 ratio between a first component, a second component, a third component, and a fourth component. Method for preparing pre-catalyst composition

[0042] In a first aspect, the present invention relates to a method for preparing a pre-catalyst composition comprising: (i) combining an iron salt or hydrate thereof; at least one further metal species selected from one or more of the group consisting of a cerium salt or hydrate thereof, a cerium oxide or hydrate thereof, an aluminium salt or hydrate thereof, an aluminium oxide or hydrate thereof, a titanium salt or hydrate thereof and a titanium oxide or a hydrate thereof; and an organic compound comprising one or more functional groups selected from the group consisting of a carboxyl, hydroxyl, amido and amino group; and (ii) subjecting the product of (i) to calcination to provide a pre-catalyst composition.

[0043] In one embodiment, the iron salt or hydrate thereof, the at least one further metal species and the organic compound are combined with water to yield an aqueous solution or mixture, suitably an aqueous solution. Suitably, the aqueous solution or mixture is stirred until essentially homogenous.

[0044] In one embodiment, the aqueous solution or mixture is then dried to remove water and the resulting dried material (e.g. powder, paste or slurry) is subjected to calcination. Typically, the drying step is conducted at a temperature of about 70°C to about 120°C, suitably about 70°C to about 90°C, suitably about 80°C.

[0045] Accordingly, in one embodiment, the present invention relates to a method for preparing a pre-catalyst composition comprising: (i)(a) combining an iron salt or hydrate thereof; at least one further metal species selected from one or more of the group consisting of a cerium salt or hydrate thereof, a cerium oxide or hydrate thereof, an aluminium salt or hydrate thereof, an aluminium oxide or hydrate thereof, a titanium salt or hydrate thereof and a titanium oxide or a hydrate thereof; and anorganic compound comprising one or more functional groups selected from the group consisting of a carboxyl, hydroxyl, amido and amino group; and water to provide an aqueous solution or mixture; (i)(b) drying the aqueous solution or mixture of (i)(a) to provide a dried material or slurry; (ii) subjecting the dried material or slurry of (i)(b) to calcination to provide a pre- catalyst composition.

[0046] In one embodiment, the present invention relates to a method for preparing a pre- catalyst composition comprising: (i)(a) combining an iron salt or hydrate thereof; at least one further metal species selected from one or more of the group consisting of a cerium salt or hydrate thereof, an aluminium salt or hydrate thereof and a titanium salt or hydrate thereof; an organic compound comprising one or more functional groups selected from the group consisting of a carboxyl, hydroxyl, amido and amino group; and water to provide an aqueous solution; (i)(b) drying the aqueous solution of (i)(a) to provide a dried material or slurry; (ii) subjecting the dried material or slurry of (i)(b) to calcination to provide a pre- catalyst composition.

[0047] Suitably, in step (i)(b) of any of the above embodiments the aqueous solution or mixture is dried at a temperature of about 70°C to about 100°C, more suitably about 80°C to about 100°C, in order to at least partially remove water, suitably the majority of water. Suitably, the dried material is obtained as a slurry, powder or a paste.

[0048] In one embodiment, it is a proviso of the method that no chromium species is present in step (i) or used in any step in the method.

[0049] Accordingly, the present invention relates to a method for preparing a pre-catalyst composition comprising: (i) combining an iron salt or hydrate thereof; at least one further metal species selected from one or more of the group consisting of a cerium salt or hydrate thereof, a cerium oxide or hydrate thereof, an aluminium salt or hydrate thereof, an aluminium oxide or hydrate thereof, a titanium salt or hydrate thereof and a titanium oxide or a hydrate thereof; and anorganic compound comprising one or more functional groups selected from the group consisting of a carboxyl, hydroxyl, amido and amino group; and (ii) subjecting the product of (i) to calcination to provide a pre-catalyst composition; with the proviso that a chromium species is not used in the method.

[0050] In one embodiment the present invention relates to a method for preparing a pre- catalyst composition comprising: (i) combining an iron salt or hydrate thereof; at least one further salt or hydrate thereof selected from one or more of the group consisting of a cerium salt or hydrate thereof, an aluminium salt or hydrate thereof and a titanium salt or hydrate thereof; and an organic compound comprising one or more functional groups selected from the group consisting of a carboxyl, hydroxyl, amido and amino group; and (ii) subjecting the product of (i) to calcination to provide a pre-catalyst composition; with the proviso that a chromium species is not used in the method. Step (i)

[0051] In one embodiment, in step (i) the at least one further metal species of step (i) is a cerium salt or hydrate thereof, or a cerium oxide or hydrate thereof. Suitably, the proportion of iron salt or hydrate thereof to cerium salt or hydrate thereof, cerium oxide or hydrate thereof, is such that the molar ratio of iron precursor to cerium precursor is about 10:1 to 2:5; suitably about 2:1 to about 1:2, suitably about 3:2 to about 2:3; suitably about 5:4 to about 4:5; suitably about 1:1.

[0052] In one embodiment, in step (i) the at least one further metal species of step (i) is a titanium salt or hydrate thereof or a titanium oxide or hydrate thereof. Suitably, the proportion of iron salt or hydrate thereof to titanium salt or hydrate thereof, or titanium oxide or hydrate thereof, is such that the molar ratio of iron precursor to titanium precursor is about 2:1 to about 1:2, suitably about 3:2 to about 2:3; suitably about 5:4 to about 4:5; suitably about 1:1.

[0053] In one embodiment, in step (i) the at least one further metal species of step (i) is an aluminium salt or hydrate thereof or aluminium oxide or hydrate thereof. Suitably, the proportion of iron salt or hydrate thereof to aluminium salt or hydrate thereof, or aluminium oxide or hydrate thereof, is such that the molar ratio of iron precursor to aluminium precursoris about 2:1 to about 1:2, suitably about 3:2 to about 2:3; suitably about 5:4 to about 4:5; suitably about 5:4 or about 1:1.

[0054] In one embodiment, in step (i) at least two further metal species are combined with the iron salt or hydrate thereof selected from the group consisting of a cerium salt or hydrate thereof, a cerium oxide or hydrate thereof, an aluminium salt or hydrate thereof, an aluminium oxide or hydrate thereof, a titanium salt or hydrate thereof and a titanium oxide or a hydrate thereof. Suitably the at least two further metal species include: (a) a cerium salt or hydrate thereof and an aluminium salt or hydrate thereof; or (b) a cerium salt or hydrate thereof and a titanium salt or hydrate thereof; or (c) an aluminium or hydrate thereof and a titanium salt or hydrate thereof; or (d) a cerium salt or hydrate thereof and a titanium oxide or hydrate thereof; or (e) an aluminium or hydrate thereof and a titanium oxide or hydrate thereof.

[0055] In one embodiment, in step (i) at least three further metal species are combined with the iron salt or hydrate thereof selected from the group consisting of a cerium salt or hydrate thereof, a cerium oxide or hydrate thereof, an aluminium salt or hydrate thereof, an aluminium oxide or hydrate thereof, a titanium salt or hydrate thereof and a titanium oxide or a hydrate thereof. Suitably, the at least three further metal species include a cerium salt or hydrate thereof, a titanium salt or hydrate thereof and an aluminium salt or hydrate thereof. Alternatively, the at least three further metal species include a cerium salt or hydrate thereof, a titanium oxide or hydrate thereof and an aluminium salt or hydrate thereof.

[0056] In one embodiment, step (i) comprises combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof; and an organic compound comprising one or more functional groups selected from the group consisting of a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0057] In another embodiment, step (i) comprises combining an iron salt or hydrate thereof; a titanium salt or hydrate thereof; and an organic compound comprising one or more functional groups selected from the group consisting of a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0058] In another embodiment, step (i) comprises combining an iron salt or hydrate thereof; a titanium oxide or hydrate thereof; and an organic compound comprising one or more functionalgroups selected from the group consisting of a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0059] In another embodiment, step (i) comprises combining an iron salt or hydrate thereof; an aluminium salt or hydrate thereof; and an organic compound comprising one or more functional groups selected from the group consisting of a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0060] In another embodiment, step (i) comprises combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, a titanium salt or hydrate thereof; and an organic compound comprising one or more functional groups selected from the group consisting of a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0061] In another embodiment, step (i) comprises combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, a titanium oxide or hydrate thereof; and an organic compound comprising one or more functional groups selected from the group consisting of a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0062] In another embodiment, step (i) comprises combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, an aluminium salt or hydrate thereof; and an organic compound comprising one or more functional groups selected from the group consisting of a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0063] In another embodiment, step (i) comprises combining an iron salt or hydrate thereof; a titanium salt or hydrate thereof, an aluminium salt or hydrate thereof; and an organic compound comprising one or more functional groups selected from the group consisting of a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0064] In another embodiment, step (i) comprises combining an iron salt or hydrate thereof; a titanium oxide or hydrate thereof, an aluminium salt or hydrate thereof; and an organic compound comprising one or more functional groups selected from the group consisting of a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0065] In another embodiment, step (i) comprises combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, a titanium salt or hydrate thereof, an aluminium salt or hydrate thereof; and an organic compound comprising one or more functional groups selected from the group consisting of a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0066] In another embodiment, step (i) comprises combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, a titanium oxide or hydrate thereof, an aluminium salt or hydratethereof; and an organic compound comprising one or more functional groups selected from the group consisting of a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0067] In one embodiment, in step (i) the iron salt or hydrate thereof is an iron (II) or iron (III) salt, or hydrate thereof. For example, suitable non-limiting examples of iron (II) salts or a hydrate thereof are FeCl2, Fe(OAc)2, FeSO4, and Fe(NO3)2 or a hydrate thereof. Suitable, non-limiting examples of iron (III) salts or a hydrate thereof are Fe(NO3)3, FeCl3and Fe2(SO4)3or a hydrate thereof.

[0068] In one embodiment, the iron salt or hydrate thereof of step (i) is selected from one or more of the group consisting of FeCl2, Fe(OAc)2, FeSO4, Fe(NO3)2, Fe(NO3)3, FeCl3 and Fe2(SO4)3, or a hydrate thereof.

[0069] In another embodiment, the iron salt or hydrate thereof of step (i) is selected from one or more of the group consisting of FeCl2, Fe(NO3)2, Fe(NO3)3, FeCl3 and Fe2(SO4)3, or a hydrate thereof. In another embodiment, the iron salt or hydrate thereof of step (i) is selected from one or more of the group consisting of Fe(NO3)2, Fe(NO3)3, FeCl3 and Fe2(SO4)3, or a hydrate thereof. In another embodiment, the iron salt or hydrate thereof of step (i) is selected from one or more of Fe(NO3)2 and Fe(NO3)3, or a hydrate thereof.

[0070] In one embodiment, the cerium salt or hydrate thereof of step (i) is a cerium (III) or (IV) salt, or hydrate thereof. For example, suitable non-limiting examples of cerium (III) salts or a hydrate thereof are Ce(NO3)3, Ce2(SO4)3, CePO4, Ce(CO3)3 and CeCl3 or a hydrate thereof. In another embodiment, the cerium (III) salt is selected from cerium(III) tartrate or cerium cinnamate, or a hydrate thereof. Suitably, the cerium salt or hydrate thereof is Ce(NO3)3. Suitable non-limiting examples of cerium (IV) salts are Ce(SO4)2, ammonium cerium(IV) nitrate, or a hydrate thereof.

[0071] In one embodiment, the cerium oxide or hydrate thereof of step (i) is a cerium (III) or (IV) oxide, or hydrate thereof.

[0072] In one embodiment, the titanium salt or hydrate thereof of step (i) is a titanium (III) or (IV) salt, or hydrate thereof. For example, suitable non-limiting examples of titanium (III) salts or a hydrate thereof are TiCl3 or a hydrate thereof. Suitably the titanium salt is a titanium (IV) salt or hydrate thereof. Suitable non-limiting examples of titanium (IV) salts or a hydrate thereof are Ti(NO3)4, Ti(SO4)2, ammonium titanyl oxalate, titanium bis(acetylacetonate)dichloride or a hydrate thereof.

[0073] In one embodiment, the titanium oxide or hydrate thereof of step (i) is a titanium (IV) oxide, or hydrate thereof.

[0074] In one embodiment, the aluminum salt or hydrate thereof of step (i) is an aluminum (III) salt, or hydrate thereof. For example, suitable non-limiting examples of aluminum (III) salts or a hydrate thereof are Al(NO3)3, Al2(SO4)3, AlCl3, aluminium monoacetate ((HO)2AlCH3CO2),aluminium diacetate (HOAl(CH3CO2)2) or a hydrate thereof. Suitably, the aluminum salt or hydrate thereof is Al(NO3)3.

[0075] In one embodiment, the aluminum oxide or hydrate thereof of step (i) is an aluminum (III) oxide, or hydrate thereof.

[0076] In another embodiment, step (i) comprises combining an iron (II) or (III) salt or hydrate thereof; a cerium (III) salt or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0077] In another embodiment, step (i) comprises combining an iron (II) or (III) salt or hydrate thereof; an aluminium (III) salt or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0078] In another embodiment, step (i) comprises combining an iron (II) or (III) salt or hydrate thereof; a titanium (III) or (IV) salt or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0079] In another embodiment, step (i) comprises combining an iron (II) or (III) salt or hydrate thereof; a titanium (IV) oxide or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0080] In another embodiment, step (i) comprises combining an iron (II) or (III) salt or hydrate thereof; a cerium (III) salt or hydrate thereof, an aluminium (III) salt or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0081] In another embodiment, step (i) comprises combining an iron (II) or (III) salt or hydrate thereof; a cerium (III) salt or hydrate thereof, a titanium (III) or (IV) salt or hydrate thereof; anorganic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0082] In another embodiment, step (i) comprises combining an iron (II) or (III) salt or hydrate thereof; a cerium (III) salt or hydrate thereof, a titanium (IV) oxide or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0083] In another embodiment, step (i) comprises combining an iron nitrate or hydrate thereof; a cerium nitrate or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0084] In another embodiment, step (i) comprises combining an iron nitrate or hydrate thereof; a cerium nitrate or hydrate thereof; an aluminium nitrate or hydrate thereof; and an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0085] In another embodiment, step (i) comprises combining an iron nitrate or hydrate thereof; a cerium nitrate or hydrate thereof; an aluminium nitrate or hydrate thereof, a titanium oxide or hydrate thereof; and an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0086] In another embodiment, step (i) comprises combining an iron nitrate or hydrate thereof; a cerium nitrate or hydrate thereof, a titanium oxide or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0087] In one embodiment, step (i) further comprises combining one or more of an alkali metal species, an alkaline earth metal species and a rare earth metal species. Suitably, step (i) further comprises combining one or more of an alkali metal species and / or an alkaline earth metal species. Suitably, step (i) further comprises combining one or more of an alkali metal species and / or a rare earth metal species. Suitably, step (i) further comprises combining an alkali metal species. The alkali metal species, alkaline earth metal species or rare earth metal species are suitably added in step (i) in the form of a salt, hydroxide, oxide or a hydrate thereof, suitably in the form of a salt or hydrate thereof.

[0088] In one embodiment, the alkali metal species is an alkali metal salt or hydrate thereof. In another embodiment, the alkali metal salt is an alkali metal nitrate, an alkali metal carbonate, an alkali metal bicarbonate, an alkali metal acetate, or a hydrate thereof. In anotherembodiment, the alkali metal salt is an alkali metal nitrate or an alkali metal carbonate, or a hydrate thereof.

[0089] In one embodiment, the alkali metal is selected from the group consisting of lithium, sodium, potassium and cesium. In another embodiment, the alkali metal is selected from cesium, sodium and potassium. In another embodiment, the alkali metal is potassium.

[0090] Suitably the alkali metal species is selected from potassium nitrate, potassium carbonate, sodium nitrate, sodium carbonate, lithium carbonate, cesium carbonate, or a hydrate thereof. Suitably the alkali metal species is selected from potassium nitrate or potassium carbonate.

[0091] Suitably, the proportion of iron salt or hydrate thereof to alkali metal species, is such that the iron precursor to alkali metal precursor molar ratio in step (i) is about 100:1 to about 5:1. Suitably, the iron precursor to alkali metal precursor molar ratio is about 50:1 to about 5:1. Suitably, the iron precursor to alkali metal precursor molar ratio is about 40:1 to about 5:1, or about 25:1 to about 5:1.

[0092] In another embodiment, the iron precursor to alkali metal precursor molar ratio in step (i) is about 50:1 to about 5:1. Suitably, the iron precursor to alkali metal precursor molar ratio is about 50:1 to about 10:1. Suitably, the iron precursor to alkali metal precursor molar ratio is about 50:1 to about 15:1, or about 50:1 to about 20:1.

[0093] In another embodiment, the iron precursor to alkali metal precursor molar ratio in step (i) is about 40:1 to about 5:1. Suitably, the iron precursor to alkali metal precursor molar ratio is about 40:1 to about 10:1. Suitably, the iron precursor to alkali metal precursor molar ratio is about 40:1 to about 15:1, or about 40:1 to about 20:1. Suitably, the iron precursor to alkali metal precursor molar ratio is about 20:1.

[0094] In one embodiment, the alkaline earth metal species is an alkaline earth metal salt, hydroxide, oxide or hydrate thereof. In another embodiment, the alkaline earth metal species is an alkaline earth metal salt or hydrate thereof.

[0095] In one embodiment, the alkaline earth metal salt is an alkaline earth metal nitrate, an alkaline earth metal carbonate, an alkaline earth metal bicarbonate, an alkaline earth metal acetate, or a hydrate thereof. In another embodiment, the alkaline earth metal salt is an alkaline earth metal nitrate or an alkaline earth metal carbonate, or a hydrate thereof.

[0096] In one embodiment, the alkaline earth metal is selected from the group consisting of magnesium, calcium and barium, suitably magnesium and calcium, more suitably calcium.

[0097] Suitably, the alkaline earth metal species is selected from a calcium salt or hydrate thereof or a magnesium salt or hydrate thereof. In one embodiment, the alkaline earth metal species is selected from calcium nitrate, calcium carbonate, magnesium nitrate and magnesium carbonate, or a hydrate thereof. In another embodiment, the alkaline earth metal species is selected from calcium nitrate and calcium carbonate.

[0098] Suitably, the proportion of iron salt or hydrate thereof to alkaline earth metal species, is such that, the iron precursor to alkaline earth metal precursor molar ratio in step (i) is about 100:1 to about 5:1. Suitably, the iron precursor to alkaline earth metal precursor molar ratio is about 50:1 to about 5:1. Suitably, the iron precursor to alkaline earth metal precursor molar ratio is about 40:1 to about 5:1 or about 25:1 to about 5:1.

[0099] In another embodiment, the iron precursor to alkaline earth metal precursor molar ratio in step (i) is about 50:1 to about 5:1. Suitably, the iron precursor to alkaline earth metal precursor molar ratio is about 50:1 to about 10:1. Suitably, the iron precursor to alkaline earth metal precursor molar ratio is about 50:1 to about 15:1 or about 50:1 to about 20:1.

[0100] In another embodiment, the iron precursor to alkaline earth metal precursor molar ratio in step (i) is about 40:1 to about 5:1. Suitably, the iron precursor to alkaline earth metal precursor molar ratio is about 40:1 to about 10:1. Suitably, the iron precursor to alkaline earth metal precursor molar ratio is about 40:1 to about 15:1 or about 40:1 to about 20:1.

[0101] In one embodiment, the rare earth metal species is a rare earth metal salt, hydroxide, oxide, or a hydrate thereof. In another embodiment, the rare earth metal species is a rare earth metal salt or a hydrate thereof.

[0102] In one embodiment, the rare earth metal salt is a rare earth metal nitrate, a rare earth metal carbonate, a rare earth metal bicarbonate, a rare earth metal acetate, or a hydrate thereof. In one embodiment, the rare earth metal salt is a rare earth metal nitrate or a rare earth metal carbonate, or a hydrate thereof.

[0103] In one embodiment, the rare earth metal is selected from the group consisting of yttrium, lanthanum, cerium, praseodymium and erbium.

[0104] Suitably the rare earth metal species is selected from yttrium nitrate, cerium nitrate, lanthanum nitrate, praseodymium nitrate, erbium nitrate, or a hydrate thereof.

[0105] Suitably, the proportion of iron salt or hydrate thereof to rare earth metal species, is such that the iron precursor to rare earth metal precursor molar ratio in step (i) is about 200:1 to about 50:1. Suitably, the iron precursor to rare earth metal precursor molar ratio is about 150:1 to about 50:1. Suitably, the iron precursor to rare earth metal precursor molar ratio is about 100:1 to about 50:1 or about 100:1 to about 75:1.

[0106] In another embodiment, the iron precursor to rare earth metal precursor molar ratio in step (i) is about 300:1 to about 50:1. Suitably, the iron precursor to rare earth metal precursor molar ratio is about 300:1 to about 75:1. Suitably, the iron precursor to rare earth metal precursor molar ratio is about 200:1 to about 75:1 or about 150:1 to about 75:1.

[0107] In one embodiment, step (i) comprises / essentially consists of / consists combining an iron salt or hydrate thereof; at least one further metal species selected from one or more of the group consisting of a cerium salt or hydrate thereof, a cerium oxide or hydrate thereof, an aluminium salt or hydrate thereof, an aluminium oxide or hydrate thereof, a titanium salt or hydrate thereof and a titanium oxide or a hydrate thereof; an alkali metal salt or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0108] In one embodiment, step (i) comprises / essentially consists of / consists combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, an alkali metal salt or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0109] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a titanium salt or hydrate thereof, an alkali metal salt or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0110] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a titanium oxide or hydrate thereof, an alkali metal salt or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0111] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; an aluminium salt or hydrate thereof, an alkali metal salt or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0112] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, a titanium salt or hydrate thereof, an alkali metal salt or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0113] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, a titanium oxide or hydrate thereof, an alkali metal salt or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0114] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, an aluminium salt or hydrate thereof, an alkali metal salt or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0115] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; an aluminium salt or hydrate thereof, a titanium salt or hydrate thereof, an alkali metal salt or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0116] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; an aluminium salt or hydrate thereof, a titanium oxide or hydrate thereof, an alkali metal salt or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0117] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, an aluminium salt or hydrate thereof, a titanium salt or hydrate thereof, an alkali metal salt or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0118] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, an aluminium salt or hydrate thereof, a titanium oxide or hydrate thereof, an alkali metal salt or hydrate thereof;an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0119] In step (i) an organic compound comprising one or more function groups selected from a carboxyl, hydroxyl, amido and amino group is combined with the iron salt or hydrate thereof and further salts or hydrates thereof. Suitably, the organic compound comprises two or more functional groups selected from a carboxyl, hydroxyl, amido and amino groups. In another embodiment, the organic compound comprises three or more functional groups selected from a carboxyl, hydroxyl, amido and amino groups.

[0120] Suitably, the organic compound is suitable for complexing metal cations, in particular iron cations. Accordingly, suitable organic compounds comprise one or more functional groups selected from carboxylic acids, hydroxyl groups, amide groups or amino groups.

[0121] In one embodiment, the organic compound is selected from a hydroxycarboxylic acid, an aminocarboxylic acid, multicarboxylic acids or salts thereof. Suitably, the organic compound is selected from a hydroxycarboxylic acid and a multicarboxylic acid, or a salt thereof. Alternatively, the organic compound is selected from a hydroxycarboxylic acid and an aminocarboxylic acid, or a salt thereof.

[0122] In one embodiment, the organic compound is a bi- or multi-dentate hydroxycarboxylic acid or a salt thereof.

[0123] In one embodiment, the organic compound is a C4 to C12 carboxylic acid or urea.

[0124] In one embodiment, the organic compound is selected from glycolic acid, lactic acid, hydracylic acid, hydroxybutyric acid, hydroxyvaleric acid, ascorbic acid, malic acid, mandelic acid, citric acid, sugar acids, tartronic acid, tartaric acid, oxalic acid, malonic acid, maleic acid, tannic acid, succinic acid, salicylic acid, glutaric acid, adipic acid, glycine, hippuric acid, urea, EDTA (ethylenediaminetetraacetic acid), NTA (nitroilotiracetic acid), DTPA (diethylenetriaminepentaacetic acid), HEDTA (N-(2-hydroxyethyl)ethylenediamine-N,N′,N′- triacetic acid), alanine, valine, leucine and isoleucine, and salts thereof.

[0125] In one embodiment, the organic compound is selected from glycolic acid, lactic acid, hydracylic acid, hydroxybutyric acid, hydroxyvaleric acid, ascorbic acid, malic acid, mandelic acid, citric acid, sugar acids, tartronic acid, tartaric acid, oxalic acid, malonic acid, maleic acid, tannic acid, succinic acid, salicylic acid, glutaric acid, adipic acid, hippuric acid,urea, EDTA (ethylenediaminetetraacetic acid), NTA (nitroilotiracetic acid), DTPA (diethylenetriaminepentaacetic acid), and HEDTA (N-(2-hydroxyethyl)ethylenediamine- N,N′,N′-triacetic acid), or a salt thereof.

[0126] In one embodiment, the organic compound is selected from hydroxybutyric acid, hydroxyvaleric acid, ascorbic acid, malic acid, mandelic acid, citric acid, sugar acids, tartronic acid, tartaric acid, oxalic acid, malonic acid, maleic acid, tannic acid, succinic acid, salicylic acid, glutaric acid, adipic acid, hippuric acid, urea, EDTA (ethylenediaminetetraacetic acid), NTA (nitroilotiracetic acid), DTPA (diethylenetriaminepentaacetic acid), and HEDTA (N- (2-hydroxyethyl)ethylenediamine-N,N′,N′-triacetic acid), or a salt thereof.

[0127] In one embodiment, the organic compound is selected from hydroxybutyric acid, hydroxyvaleric acid, ascorbic acid, malic acid, mandelic acid, citric acid, sugar acids, tartronic acid, tartaric acid, oxalic acid, malonic acid, maleic acid, tannic acid, succinic acid, salicylic acid, urea, EDTA (ethylenediaminetetraacetic acid), NTA (nitroilotiracetic acid), DTPA (diethylenetriaminepentaacetic acid), and HEDTA (N-(2-hydroxyethyl)ethylenediamine- N,N′,N′-triacetic acid), or a salt thereof.

[0128] In one embodiment, the organic compound is selected from citric acid, sugar acids, ascorbic acid, tartaric acid, oxalic acid, salicylic acid, urea, EDTA (ethylenediaminetetraacetic acid), NTA (nitroilotiracetic acid), DTPA (diethylenetriaminepentaacetic acid), and HEDTA (N-(2-hydroxyethyl)ethylenediamine- N,N′,N′-triacetic acid), or a salt thereof.

[0129] In one embodiment, the organic compound is selected from citric acid, sugar acids, tartaric acid, ascorbic acid, oxalic acid, salicylic acid, urea, EDTA (ethylenediaminetetraacetic acid), NTA (nitroilotiracetic acid), DTPA (diethylenetriaminepentaacetic acid), and HEDTA (N-(2-hydroxyethyl)ethylenediamine- N,N′,N′-triacetic acid), or a salt thereof.

[0130] In one embodiment, the organic compound is selected from citric acid, tartaric acid, oxalic acid, urea, ascorbic acid, EDTA (ethylenediaminetetraacetic acid), NTA (nitroilotiracetic acid), DTPA (diethylenetriaminepentaacetic acid), and HEDTA (N-(2- hydroxyethyl)ethylenediamine-N,N′,N′-triacetic acid), or a salt thereof. Suitably, the organic compound is citric acid or urea.

[0131] In another embodiment, the organic compound is selected from malic acid, salicylic acid, tartaric acid, urea, ascorbic acid, oxalic acid, citric acid, NTA (nitroilotiraceticacid), and HEDTA (N-(2-hydroxyethyl)ethylenediamine-N,N′,N′-triacetic acid), or a salt thereof.

[0132] In another embodiment, the organic compound is selected from malic acid, EDTA, ascorbic acid, citric acid, NTA (nitroilotiracetic acid), urea and HEDTA (N-(2- hydroxyethyl)ethylenediamine-N,N′,N′-triacetic acid), or a salt thereof.

[0133] In another embodiment, the organic compound is selected from malic acid, EDTA, ascorbic acid, citric acid and NTA (nitroilotiracetic acid), or a salt thereof.

[0134] In one embodiment, the organic compound to metal precursor molar ratio in step (i) is about 0.4:1 to about 10:1. Suitably, the organic compound to metal precursor molar ratio is about 0.4:1 to about 5:1. Suitably, the organic compound to metal precursor molar ratio is about 0.4:1 to about 2:1 or about 0.4:1 to about 1:1.

[0135] In one embodiment, the organic compound to metal precursor molar ratio in step (i) is about 1:1 to about 10:1. Suitably, the organic compound to metal precursor molar ratio is about 1:1 to about 5:1. Suitably, the organic compound to metal precursor molar ratio is about 1:1 to about 3:1 or about 1:1 to about 1:1.

[0136] In one embodiment, the organic compound to metal precursor molar ratio in step (i) is about 0.8:1 to about 10:1. Suitably, the organic compound to metal precursor molar ratio is about 0.8:1 to about 5:1. Suitably, the organic compound to metal precursor molar ratio is about 0.8:1 to about 2:1 or about 0.8: to about 1:1.

[0137] In one embodiment, the organic compound to metal precursor molar ratio in step (i) is about 1:1 to about 10:1. Suitably, the organic compound to metal precursor molar ratio is about 1:1 to about 5:1. Suitably, the organic compound to metal precursor molar ratio is about 1:1 to about 2:1.

[0138] In one embodiment, step (i) comprises / essentially consists of / consists combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, an alkali metal salt or hydrate thereof; an organic compound selected from a C4to C12carboxylic acid (suitably citric acid) or urea; and optionally water.

[0139] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a titanium salt or hydrate thereof, an alkali metal salt or hydrate thereof; an organic compound selected from a C4to C12carboxylic acid (suitably citric acid) or urea; and optionally water.

[0140] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a titanium oxide or hydrate thereof, an alkali metal salt or hydrate thereof; an organic compound selected from a C4to C12carboxylic acid (suitably citric acid) or urea; and optionally water.

[0141] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; an aluminium salt or hydrate thereof, an alkali metal salt or hydrate thereof; an organic compound selected from a C4to C12carboxylic acid (suitably citric acid) or urea; and optionally water.

[0142] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, a titanium salt or hydrate thereof, an alkali metal salt or hydrate thereof; an organic compound selected from a C4 to C12 carboxylic acid (suitably citric acid) or urea; and optionally water.

[0143] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, a titanium oxide or hydrate thereof, an alkali metal salt or hydrate thereof; an organic compound selected from a C4 to C12 carboxylic acid (suitably citric acid) or urea; and optionally water.

[0144] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, an aluminium salt or hydrate thereof, an alkali metal salt or hydrate thereof; an organic compound selected from a C4 to C12 carboxylic acid (suitably citric acid) or urea; and optionally water.

[0145] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; an aluminium salt or hydrate thereof, a titanium salt or hydrate thereof, an alkali metal salt or hydrate thereof; an organic compound selected from a C4 to C12 carboxylic acid (suitably citric acid) or urea; and optionally water.

[0146] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; an aluminium salt or hydrate thereof, a titanium oxide or hydrate thereof, an alkali metal salt or hydrate thereof; an organic compound selected from a C4 to C12 carboxylic acid (suitably citric acid) or urea; and optionally water.

[0147] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, an aluminium salt or hydrate thereof, a titanium salt or hydrate thereof, an alkali metal salt or hydrate thereof; anorganic compound selected from a C4to C12carboxylic acid (suitably citric acid) or urea; and optionally water.

[0148] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, an aluminium salt or hydrate thereof, a titanium oxide or hydrate thereof, an alkali metal salt or hydrate thereof; an organic compound selected from a C4to C12carboxylic acid (suitably citric acid) or urea; and optionally water.

[0149] In each of the above mentioned aspects and embodiments, in one embodiment, step (i) further comprises combining a transition metal species selected from one or more of a zinc salt or hydrate thereof, a zinc oxide or hydrate thereof, a manganese salt or hydrate thereof, a manganese oxide or hydrate thereof, a zirconium salt or hydrate thereof, a zirconium oxide or hydrate thereof, a cobalt salt or hydrate thereof, a cobalt oxide or hydrate thereof, a copper salt or hydrate thereof and a copper oxide or hydrate thereof.

[0150] In one embodiment, step (i) further comprises combining a transition metal species selected from one or more of a zinc salt or hydrate thereof, a manganese salt or hydrate thereof, a zirconium salt or hydrate thereof, a cobalt salt or hydrate thereof and a copper salt or hydrate thereof.

[0151] In one embodiment, step (i) further comprises combining a transition metal species selected from one or more of a zinc salt or hydrate thereof, a zinc oxide or hydrate thereof, a manganese salt or hydrate thereof, a manganese oxide or hydrate thereof, a zirconium salt or hydrate thereof and a zirconium oxide or hydrate thereof.

[0152] In one embodiment, step (i) further comprises combining a transition species selected from one or more of a zinc salt or hydrate thereof, a manganese salt or hydrate thereof, and a zirconium salt or hydrate thereof.

[0153] In one embodiment, one or two further transition metal species are combined in step (i). In one embodiment, the transition metal species is selected from two of the group consisting of a zinc salt or hydrate thereof, a zinc oxide or hydrate thereof, a manganese salt or hydrate thereof, a manganese oxide or hydrate thereof, a zirconium salt or hydrate thereof, a zirconium oxide or hydrate thereof, a cobalt salt or hydrate thereof, a cobalt oxide or hydrate thereof, a copper salt or hydrate thereof and a copper oxide or hydrate thereof.

[0154] In one embodiment, the transition metal species is selected from two of the group consisting of a zinc salt or hydrate thereof, a manganese salt or hydrate thereof, azirconium salt or hydrate thereof, a cobalt salt or hydrate thereof, a copper salt or hydrate thereof.

[0155] In another embodiment, the transition metal species is selected from one of a zinc salt or hydrate thereof, a manganese salt or hydrate thereof, a zirconium salt or hydrate thereof, a cobalt salt or hydrate thereof, and a copper salt or hydrate thereof. Suitably, the transition metal species is selected from one of a zinc salt or hydrate thereof, a manganese salt or hydrate thereof and a zirconium salt or hydrate thereof.

[0156] In one embodiment, step (i) comprises / essentially consists of / consists combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a zinc oxide or hydrate thereof, a manganese salt or hydrate thereof, a manganese oxide or hydrate thereof, a zirconium salt or hydrate thereof and a zirconium oxide or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0157] In one embodiment, step (i) comprises / essentially consists of / consists combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a manganese salt or hydrate thereof and a zirconium salt or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0158] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a titanium salt or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a zinc oxide or hydrate thereof, a manganese salt or hydrate thereof, a manganese oxide or hydrate thereof, a zirconium salt or hydrate thereof and a zirconium oxide or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0159] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a titanium oxide or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a zinc oxide or hydrate thereof, a manganese salt or hydrate thereof, a manganese oxide or hydrate thereof, a zirconium salt or hydrate thereof and a zirconium oxide or hydrate thereof;an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0160] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a titanium salt or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a zinc oxide or hydrate thereof, a manganese salt or hydrate thereof, a manganese oxide or hydrate thereof, a zirconium salt or hydrate thereof and a zirconium hydrate or oxide thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0161] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a titanium oxide or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a zinc oxide or hydrate thereof, a manganese salt or hydrate thereof, a manganese oxide or hydrate thereof, a zirconium salt or hydrate thereof and a zirconium hydrate or oxide thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0162] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a titanium salt or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a zinc oxide or hydrate thereof, a manganese salt or hydrate thereof, a manganese oxide or hydrate thereof, a zirconium salt or hydrate thereof and zirconium oxide or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0163] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a titanium oxide or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a zinc oxide or hydrate thereof, a manganese salt or hydrate thereof, a manganese oxide or hydrate thereof, a zirconium salt or hydrate thereof and zirconium oxide or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0164] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a titanium salt or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, azinc oxide or hydrate thereof, a manganese salt or hydrate thereof, a manganese oxide or hydrate thereof, a zirconium salt or hydrate thereof and a zirconium oxide or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0165] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a titanium oxide or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a zinc oxide or hydrate thereof, a manganese salt or hydrate thereof, a manganese oxide or hydrate thereof, a zirconium salt or hydrate thereof and a zirconium oxide or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0166] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a titanium salt or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a manganese salt or hydrate thereof and a zirconium salt or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0167] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a titanium oxide or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a manganese salt or hydrate thereof and a zirconium salt or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0168] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; an aluminium salt or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a zinc oxide or hydrate thereof, a manganese salt or hydrate thereof, a manganese oxide or hydrate thereof, a zirconium salt or hydrate thereof and a zirconium oxide or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0169] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; an aluminium salt or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof,a manganese salt or hydrate thereof and a zirconium salt or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0170] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, a titanium salt or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a zinc oxide or hydrate thereof, a manganese salt or hydrate thereof, a manganese oxide or hydrate thereof, a zirconium salt or hydrate thereof and a zirconium oxide or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0171] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, a titanium oxide or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a zinc oxide or hydrate thereof, a manganese salt or hydrate thereof, a manganese oxide or hydrate thereof, a zirconium salt or hydrate thereof and a zirconium oxide or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0172] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, a titanium salt or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a manganese salt or hydrate thereof and a zirconium salt or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0173] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, a titanium oxide or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a manganese salt or hydrate thereof and a zirconium salt or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0174] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, an aluminium salt or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a zinc oxide or hydrate thereof, a manganese salt or hydratethereof, a manganese oxide or hydrate thereof, a zirconium salt or hydrate thereof and a zirconium oxide or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0175] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, an aluminium salt or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a manganese salt or hydrate thereof and a zirconium salt or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0176] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; an aluminium salt or hydrate thereof, a titanium salt or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a zinc oxide or hydrate thereof, a manganese salt or hydrate thereof, a manganese oxide or hydrate thereof, a zirconium salt or hydrate thereof and a zirconium oxide or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0177] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; an aluminium salt or hydrate thereof, a titanium oxide or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a zinc oxide or hydrate thereof, a manganese salt or hydrate thereof, a manganese oxide or hydrate thereof, a zirconium salt or hydrate thereof and a zirconium oxide or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0178] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; an aluminium salt or hydrate thereof, a titanium salt or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a manganese salt or hydrate thereof and a zirconium salt or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0179] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; an aluminium salt or hydrate thereof, a titanium oxide or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal speciesselected from a zinc salt or hydrate thereof, a manganese salt or hydrate thereof and a zirconium salt or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0180] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, an aluminium salt or hydrate thereof, a titanium salt or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a zinc oxide or hydrate thereof, a manganese salt or hydrate thereof, a manganese oxide or hydrate thereof, a zirconium salt or hydrate thereof and a zirconium oxide or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0181] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, an aluminium salt or hydrate thereof, a titanium oxide or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a zinc oxide or hydrate thereof, a manganese salt or hydrate thereof, a manganese oxide or hydrate thereof, a zirconium salt or hydrate thereof and a zirconium oxide or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0182] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, an aluminium salt or hydrate thereof, a titanium salt or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a zinc oxide or hydrate thereof, a manganese salt or hydrate thereof, a manganese oxide or hydrate thereof, a zirconium salt or hydrate thereof and a zirconium oxide or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0183] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, an aluminium salt or hydrate thereof, a titanium oxide or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a zinc oxide or hydrate thereof, a manganese salt or hydrate thereof, a manganese oxide or hydrate thereof, a zirconium salt or hydrate thereof and a zirconium oxide or hydrate thereof; an organiccompound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0184] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, an aluminium salt or hydrate thereof, a titanium salt or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a manganese salt or hydrate thereof and a zirconium salt or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0185] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, an aluminium salt or hydrate thereof, a titanium oxide or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a manganese salt or hydrate thereof and a zirconium salt or hydrate thereof; an organic compound comprising one or more functional groups selected from a carboxyl, hydroxyl, amido and amino group; and optionally water.

[0186] In one embodiment, step (i) comprises / essentially consists of / consists combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a manganese salt or hydrate thereof and a zirconium salt or hydrate thereof; an organic compound selected from a C4 to C12 carboxylic acid (suitably citric acid) or urea; and optionally water.

[0187] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a titanium salt or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a manganese salt or hydrate thereof and a zirconium salt or hydrate thereof; an organic compound selected from a C4 to C12 carboxylic acid (suitably citric acid) or urea; and optionally water.

[0188] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a titanium oxide or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a manganese salt or hydrate thereof and a zirconium salt or hydrate thereof; an organiccompound selected from a C4to C12carboxylic acid (suitably citric acid) or urea; and optionally water.

[0189] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; an aluminium salt or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a manganese salt or hydrate thereof and a zirconium salt or hydrate thereof; an organic compound selected from a C4to C12carboxylic acid (suitably citric acid) or urea; and optionally water.

[0190] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, a titanium salt or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a manganese salt or hydrate thereof and a zirconium salt or hydrate thereof; an organic compound selected from a C4 to C12 carboxylic acid (suitably citric acid) or urea; and optionally water.

[0191] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, a titanium oxide or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a manganese salt or hydrate thereof and a zirconium salt or hydrate thereof; an organic compound selected from a C4 to C12 carboxylic acid (suitably citric acid) or urea; and optionally water.

[0192] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, an aluminium salt or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a manganese salt or hydrate thereof and a zirconium salt or hydrate thereof; an organic compound selected from a C4 to C12 carboxylic acid (suitably citric acid) or urea; and optionally water.

[0193] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; an aluminium salt or hydrate thereof, a titanium salt or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a manganese salt or hydrate thereof and a zirconium salt or hydrate thereof; an organic compound selected from a C4to C12carboxylic acid (suitably citric acid) or urea; and optionally water.

[0194] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; an aluminium salt or hydrate thereof, a titanium oxide or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a manganese salt or hydrate thereof and a zirconium salt or hydrate thereof; an organic compound selected from a C4to C12carboxylic acid (suitably citric acid) or urea; and optionally water.

[0195] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, an aluminium salt or hydrate thereof, a titanium salt or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a manganese salt or hydrate thereof and a zirconium salt or hydrate thereof; an organic compound selected from a C4 to C12 carboxylic acid (suitably citric acid) or urea; and optionally water.

[0196] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron salt or hydrate thereof; a cerium salt or hydrate thereof, an aluminium salt or hydrate thereof, a titanium oxide or hydrate thereof, an alkali metal salt or hydrate thereof; a transition metal species selected from a zinc salt or hydrate thereof, a manganese salt or hydrate thereof and a zirconium salt or hydrate thereof; an organic compound selected from a C4 to C12 carboxylic acid (suitably citric acid) or urea; and optionally water.

[0197] In one embodiment, step (i) comprises combining a manganese salt or a hydrate thereof with the iron salt or hydrate thereof and the further metal species. In one embodiment, in step (i) the manganese salt or hydrate thereof is a manganese (II) or (III) salt or a hydrate thereof, suitably a manganese (II) salt or a hydrate thereof. For example, suitable non-limiting examples of manganese salts or a hydrate thereof are Mn(NO3)2, MnSO4, MnCl2, Mn(OAc)2, and manganese citrate or a hydrate thereof. Suitably, the manganese salt or hydrate thereof is Mn(NO3)2 or a hydrate thereof.

[0198] In one embodiment, step (i) comprises combining a manganese oxide or a hydrate thereof with the iron salt or hydrate thereof and the further metal species. In one embodiment, in step (i) the manganese oxide or hydrate thereof is a manganese (II), (III) or (IV) oxide or a hydrate thereof.

[0199] In one embodiment, the proportion of iron salt and manganese salt or oxide or hydrate thereof is such that the molar ratio of iron precursor to manganese precursor is about 10:1 to about 2:5. Suitably, the molar ratio of iron precursor to manganese precursor is about 5:1 to about 4:5. Suitably, the molar ratio of iron precursor to manganese precursor is about2:1 to about 1:1. Suitably, the molar ratio of iron precursor to manganese precursor is about 3:2 to about 1:1, suitably about 5:4 to about 1:1.

[0200] In one embodiment, step (i) comprises combining a zirconium salt or a hydrate thereof with the iron salt or hydrate thereof and the further salt or hydrate thereof. In one embodiment, in step (i) the zirconium salt or hydrate thereof is a zirconium (III) or (IV) salt or a hydrate thereof, suitably a zirconium (IV) salt or a hydrate thereof. For example, suitable non-limiting examples of zirconium salts or hydrate thereof are Zr(NO3)4, ZrO(NO3)2, ZrOCl2, zirconium acetate or a hydrate thereof. Suitably, the zirconium salt or hydrate thereof is ZrO(NO3)2 or a hydrate thereof.

[0201] In one embodiment, step (i) comprises combining a zirconium oxide or a hydrate thereof with the iron salt or hydrate thereof and the further metal species. In one embodiment, in step (i) the zirconium oxide or hydrate thereof is a zirconium (IV) oxide or a hydrate thereof.

[0202] In one embodiment, the proportion of iron salt or hydrate thereof and zirconium salt, oxide or hydrate thereof is such that the molar ratio of iron precursor to zirconium precursor is about 50:1 to about 2:5. In another embodiment, the proportion of iron salt or hydrate thereof and zirconium salt or hydrate thereof is such that the molar ratio of iron precursor to zirconium precursor is about 20:1 to about 4:5, suitably, the molar ratio of iron precursor to zirconium precursor is about 10:1 to about 1:1, suitably about 5:1 to about 1:1, suitably about 3:2 to about 1:1, suitably about 5:4 to about 1:1.

[0203] In one embodiment, step (i) comprises combining a copper salt or a hydrate thereof with the iron salt or hydrate thereof and the further salt or hydrate thereof. In one embodiment, in step (i) the copper salt is a copper (I) or (II) salt or a hydrate thereof, suitably a copper (II) salt or a hydrate thereof. For example, suitable non-limiting examples of copper salts or hydrate thereof are Cu(NO3)2, Cu(OAc)2, CuCl2, CuSO4, Cu2CO3(OH)2, CuCl, Cu2SO4, and CuNO3 or a hydrate thereof.

[0204] Suitably, the copper salt or hydrate thereof is selected from one or more of the group consisting of Cu(NO3)2, Cu(OAc)2, CuCl2, CuSO4, and Cu2CO3(OH)2, or a hydrate thereof. Suitably, the copper salt or hydrate thereof is selected from one or more of Cu(NO3)2and Cu2CO3(OH)2or a hydrate thereof.

[0205] In one embodiment, step (i) comprises combining a copper oxide or a hydrate thereof with the iron salt or hydrate thereof and the further metal species. In one embodiment, in step (i) the copper oxide or hydrate thereof is a copper (I) or (II) oxide or a hydrate thereof.

[0206] In one embodiment, the proportion of iron salt or hydrate thereof and copper salt, oxide or hydrate thereof is such that the molar ratio of iron precursor to copper precursor is about 50:1 to about 2:5. In another embodiment, the proportion of iron salt or hydrate thereof and copper salt or hydrate thereof is such that the molar ratio of iron precursor to copper precursor is about 20:1 to about 4:5, suitably, the molar ratio of iron precursor to copper precursor is about 10:1 to about 1:1, suitably about 5:1 to about 1:1, suitably about 3:2 to about 1:1, suitably about 5:4 to about 1:1.

[0207] In one embodiment, step (i) comprises combining a zinc salt or a hydrate thereof with the iron salt or hydrate thereof and further salts or hydrate thereof. In one embodiment, in step (i) the zinc salt is a zinc (II) salt or a hydrate thereof. For example, suitable non-limiting examples of zinc salts or hydrates thereof are Zn(NO3)2, Zn(OAc)2, ZnCl2 and ZnSO4 or a hydrate thereof. Suitably, the zinc salt or hydrate thereof is Zn(NO3)2 or a hydrate thereof.

[0208] In one embodiment, step (i) comprises combining a zinc oxide or a hydrate thereof with the iron salt or hydrate thereof and the further metal species. In one embodiment, in step (i) the zinc oxide or hydrate thereof is a zinc (II) oxide or a hydrate thereof.

[0209] In one embodiment, the proportion of iron salt or hydrate thereof and zinc salt, oxide or hydrate thereof is such that the molar ratio of iron precursor to zinc precursor is about 50:1 to about 2:5. In another embodiment, the proportion of iron salt or hydrate thereof and zinc salt or hydrate thereof is such that the molar ratio of iron precursor to zinc precursor is about 20:1 to about 4:5, suitably, the molar ratio of iron precursor to zinc precursor is about 10:1 to about 1:1, suitably about 5:1 to about 1:1, suitably about 3:2 to about 1:1, suitably about 5:4 to about 1:1.

[0210] In one embodiment, step (i) comprises combining a cobalt salt or a hydrate thereof with the iron salt or hydrate thereof and further salts or hydrate thereof. In one embodiment, in step (i) the cobalt salt is a cobalt (II) salt or a hydrate thereof. For example, suitable non-limiting examples of cobalt salts or hydrates thereof are Co(NO3)2, Co(OAc)2, Co(CO3)2, CoCl2and CoSO4or a hydrate thereof. Suitably, the cobalt salt or hydrate thereof is Co(NO3)2or a hydrate thereof.

[0211] In one embodiment, step (i) comprises combining a cobalt oxide or a hydrate thereof with the iron salt or hydrate thereof and the further metal species. In one embodiment, in step (i) the cobalt oxide or hydrate thereof is a cobalt (II) or (III) oxide or a hydrate thereof.

[0212] In one embodiment, the proportion of iron salt or hydrate thereof and cobalt salt, oxide or hydrate is such that the molar ratio of iron precursor to cobalt precursor is about 50:1 to about 2:5. In another embodiment, the proportion of iron salt or hydrate thereof and cobalt salt or hydrate thereof is such that the molar ratio of iron precursor to cobalt precursor is about 20:1 to about 4:5, suitably, the molar ratio of iron precursor to cobalt precursor is about 10:1 to about 1:1, suitably about 5:1 to about 1:1 , suitably about 3:2 to about 1:1, suitably about 5:4 to about 1:1.

[0213] In one embodiment, in step (i), the iron salt or hydrate thereof, the further metal species selected from one or more of the group consisting of a cerium salt or hydrate thereof, a cerium oxide or hydrate thereof, an aluminium salt or hydrate thereof, an aluminium oxide or hydrate thereof, a titanium salt or hydrate thereof and a titanium oxide or a hydrate thereof, the organic compound, the optional alkali metal salt or hydrate thereof; and the optional one or more transition metal species, are each combined in solid form under ambient conditions and mixed or milled to form a paste or powder. Suitable techniques for mixing and milling are known in the art and at least include grinding in a pestle and mortar, or bead or ball milling.

[0214] In another embodiment, in step (i), one or more components may be mixed with water, and the components combined to form an aqueous solution or mixture. Suitably, the aqueous solution or mixture is stirred, suitably until homogeneous. In one embodiment, the weight ratio of metal species and organic compound to water is about 1:1 to about 5:1, suitably about 1:1 to about 3:1, suitably about 2:1.

[0215] The aqueous solution or mixture is suitably at least partially dried before proceeding to the calcination step. In one embodiment, the aqueous solution or mixture is dried at a temperature of about 70°C to about 100°C, more suitably about 80°C to about 100°C, in order to remove water. Suitably, the resulting dried material is obtained as a slurry, powder or a paste.

[0216] In one embodiment, step (i) comprises / essentially consists of / consists of combining an iron (II) or (III) salt or hydrate thereof, a cerium (III) salt or hydrate thereof, an organic compound selected from a C4to C12carboxylic acid (suitably citric acid) or urea, a potassium salt or hydrate thereof, a zinc (II) salt or hydrate thereof; and optionally water. Suitably, the molar ratio of Fe precursor to Ce precursor is about 3:2 to about 2:3 and / or the molar ratio of Fe precursor to Zn precursor is about 3:2 to about 1:1, and / or the molar ratio of Fe precursor to K precursor is about 100:1 to about 20:1.

[0217] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron (II) or (III) salt or hydrate thereof, a cerium (III) salt or hydrate thereof, an organic compound selected from a C4to C12carboxylic acid (suitably citric acid) or urea, a potassium salt or hydrate thereof, a manganese (II) salt or hydrate thereof; and optionally water. Suitably, the molar ratio of Fe precursor to Ce precursor is about 3:2 to about 2:3 and / or the molar ratio of Fe precursor to Mn precursor is about 3:2 to about 1:1, and / or the molar ratio of Fe precursor to K precursor is about 100:1 to about 20:1.

[0218] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron (II) or (III) salt or hydrate thereof, a cerium (III) salt or hydrate thereof, an organic compound selected from a C4 to C12 carboxylic acid (suitably citric acid) or urea, a potassium salt or hydrate thereof, a cobalt (II) salt or hydrate thereof; and optionally water. Suitably, the molar ratio of Fe precursor to Ce precursor is about 3:2 to about 2:3 and / or the molar ratio of Fe precursor to Co precursor is about 5:1 to about 1:1, and / or the molar ratio of Fe precursor to K precursor is about 100:1 to about 20:1.

[0219] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron (II) or (III) salt or hydrate thereof, a cerium (III) salt or hydrate thereof, an organic compound selected from a C4 to C12 carboxylic acid (suitably citric acid) or urea, a potassium salt or hydrate thereof, a zirconium (IV) salt or hydrate thereof; and optionally water. Suitably, the molar ratio of Fe precursor to Ce precursor is about 3:2 to about 2:3 and / or the molar ratio of Fe precursor to Zr precursor is about 20:1 to about 4:5, and / or the molar ratio of Fe precursor to K precursor is about 100:1 to about 20:1.

[0220] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron (II) or (III) salt or hydrate thereof, an aluminium salt or hydrate thereof; an organic compound selected from a C4 to C12 carboxylic acid (suitably citric acid) or urea, a potassium salt or hydrate thereof; and optionally water. Suitably, the molar ratio of Fe precursor to Al precursor is about 3:2 to about 2:3, and / or the molar ratio of Fe precursor to K precursor is about 100:1 to about 20:1.

[0221] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron (II) or (III) salt or hydrate thereof, a cerium (III) salt or hydrate thereof, an aluminium salt or hydrate thereof; an organic compound selected from a C4to C12carboxylic acid (suitably citric acid) or urea, a potassium salt or hydrate thereof; and optionally water. Suitably, the molar ratio of Fe precursor to Ce precursor is about 3:2 to about 2:3 and / or the molar ratio of Fe precursor to Al precursor is about 3:2 to about 2:3, and / or the molar ratio of Fe precursor to K precursor is about 100:1 to about 20:1.

[0222] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron (II) or (III) salt or hydrate thereof, a titanium (IV) salt or hydrate thereof; an organic compound selected from a C4to C12carboxylic acid (suitably citric acid) or urea, a potassium salt or hydrate thereof; and optionally water. Suitably, the molar ratio of Fe precursor to Ti precursor is about 3:2 to about 2:3, and / or the molar ratio of Fe precursor to K precursor is about 100:1 to about 20:1.

[0223] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron (II) or (III) salt or hydrate thereof, a titanium (IV) oxide or hydrate thereof; an organic compound selected from a C4 to C12 carboxylic acid (suitably citric acid) or urea, a potassium salt or hydrate thereof; and optionally water. Suitably, the molar ratio of Fe precursor to Ti precursor is about 3:2 to about 2:3, and / or the molar ratio of Fe precursor to K precursor is about 100:1 to about 20:1.

[0224] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron (II) or (III) salt or hydrate thereof, a cerium (III) salt or hydrate thereof, a titanium (IV) salt or hydrate thereof; an organic compound selected from a C4 to C12 carboxylic acid (suitably citric acid) or urea, a potassium salt or hydrate thereof; and optionally water. Suitably, the molar ratio of Fe precursor to Ce precursor is about 3:2 to about 2:3; and / or the molar ratio of Fe precursor to Ti precursor is about 3:2 to about 2:3, and / or the molar ratio of Fe precursor to K precursor is about 100:1 to about 20:1.

[0225] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron (II) or (III) salt or hydrate thereof, a cerium (III) salt or hydrate thereof, a titanium (IV) oxide or hydrate thereof; an organic compound selected from a C4 to C12 carboxylic acid (suitably citric acid) or urea, a potassium salt or hydrate thereof; and optionally water. Suitably, the molar ratio of Fe precursor to Ce precursor is about 3:2 to about 2:3; and / or the molar ratio of Fe precursor to Ti precursor is about 3:2 to about 2:3, and / or the molar ratio of Fe precursor to K precursor is about 100:1 to about 20:1.

[0226] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron (II) or (III) salt or hydrate thereof, a cerium (III) salt or hydrate thereof, an aluminium salt or hydrate thereof; an organic compound selected from a C4to C12carboxylic acid (suitably citric acid) or urea, a potassium salt or hydrate thereof; and optionally water. Suitably, the molar ratio of Fe precursor to Ce precursor is about 3:2 to about 2:3; and / or the molar ratio of Fe precursor to Al precursor is about 3:2 to about 2:3, and / or the molar ratio of Fe precursor to K precursor is about 100:1 to about 20:1.

[0227] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron (II) or (III) salt or hydrate thereof, a cerium (III) salt or hydrate thereof, an aluminium salt or hydrate thereof; a titanium (IV) salt or hydrate thereof; an organic compound selected from a C4to C12carboxylic acid (suitably citric acid) or urea, a potassium salt or hydrate thereof; and optionally water. Suitably, the molar ratio of Fe precursor to Ce precursor is about 3:2 to about 2:3; and / or the molar ratio of Fe precursor to Al precursor is about 3:2 to about 2:3, and / or the molar ratio of Fe precursor to Ti precursor is about 3:2 to about 2:3, and / or the molar ratio of Fe precursor to K precursor is about 100:1 to about 20:1.

[0228] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron (II) or (III) salt or hydrate thereof, a cerium (III) salt or hydrate thereof, an aluminium salt or hydrate thereof; a titanium (IV) oxide or hydrate thereof; an organic compound selected from a C4 to C12 carboxylic acid (suitably citric acid) or urea, a potassium salt or hydrate thereof; and optionally water. Suitably, the molar ratio of Fe precursor to Ce precursor is about 3:2 to about 2:3; and / or the molar ratio of Fe precursor to Al precursor is about 3:2 to about 2:3, and / or the molar ratio of Fe precursor to Ti precursor is about 3:2 to about 2:3, and / or the molar ratio of Fe precursor to K precursor is about 100:1 to about 20:1.

[0229] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron (II) or (III) salt or hydrate thereof, a titanium (IV) salt or hydrate thereof; an organic compound selected from a C4 to C12 carboxylic acid (suitably citric acid) or urea, a potassium salt or hydrate thereof; a manganese salt or hydrate thereof; and optionally water. Suitably, the molar ratio of Fe precursor to Ti precursor is about 3:2 to about 2:3, and / or the molar ratio of Fe precursor to Mn precursor is about 3:2 to about 1:1, and / or the molar ratio of Fe precursor to K precursor is about 100:1 to about 20:1.

[0230] In another embodiment, step (i) comprises / essentially consists of / consists of combining an iron (II) or (III) salt or hydrate thereof, a titanium (IV) oxide or hydrate thereof; an organic compound selected from a C4to C12carboxylic acid (suitably citric acid) or urea, a potassium salt or hydrate thereof; a manganese salt or hydrate thereof; and optionally water. Suitably, the molar ratio of Fe precursor to Ti precursor is about 3:2 to about 2:3, and / or the molar ratio of Fe precursor to Mn precursor is about 3:2 to about 1:1, and / or the molar ratio of Fe precursor to K precursor is about 100:1 to about 20:1. Step (ii) - Calcination

[0231] In one embodiment, the product of step (i) is subjected to calcination to provide a pre-catalyst composition, suitably as a powder. Calcination suitably serves to providecombustion or decomposition of the organic compound and any organic salts remaining in the combination, and the formation of metal oxides.

[0232] Suitably the combustion of the organics imparts one or more advantageous properties on the resulting pre-catalyst composition such as nanostructure and advantageous dispersity of metal species and promotors.

[0233] In one embodiment, the calcination is performed at a temperature of between about 400°C to about 1000°C, or about 400°C to about 700°C, or about 400°C to about 600°C, or about 500°C to about 700°C, or about 500°C to about 600°C.

[0234] In another embodiment, the calcination is performed at a temperature of between about 500°C to about 1000°C, or about 500°C to about 800°C, or about 500°C to about 700°C, or about 600°C to about 800°C, or about 600°C to about 700°C.

[0235] In another embodiment, the calcination is performed at a temperature of between about 600°C to about 1000°C, or about 600°C to about 800°C, or about 600°C to about 700°C.

[0236] In another embodiment, the calcination is performed at a temperature of between about 700°C to about 1000°C, or about 700°C to about 800°C, or about 700°C to about 750°C.

[0237] Suitably, the calcination is performed by heating the sample at a heating rate of about 3 to about 10°C per minute, suitably about 5°C per minute. Suitably, the sample is heated up to a temperature of about 500°C, suitably up to about 600°C, suitably up to about 700°C, suitably up to about 750°C, suitably up to about 800°C.

[0238] Suitably the calcination is performed in air, suitably static air. Typically, the calcination will result in decomposition or partial combustion of organic components of step (i). In one embodiment, the product of step (ii) is a carbon-free product.

[0239] In one embodiment, the combination is calcined for a period of about 1 to about 24 hours, suitably about 1 to about 10 hours, suitably about 2 to about 10 hours.

[0240] In one embodiment, in step (ii), the product of step (i) is subjected to calcination at about 400°C to about 1000°C for about 1 to 24 hours to provide a pre-catalyst composition.

[0241] In one embodiment, in step (ii), the product of step (i) is subjected to calcination at about 400°C to about 800°C for about 1 to 24 hours to provide a pre-catalyst composition.

[0242] In one embodiment, in step (ii), the product of step is subjected to calcination at about 400°C to about 700°C for about 1 to 24 hours to provide a pre-catalyst composition.

[0243] In one embodiment, in step (ii), the product of step (i) is subjected to calcination at about 400°C to about 600°C for about 1 to 24 hours to provide a pre-catalyst composition.

[0244] In one embodiment, in step (ii), the product of step (i) is subjected to calcination at about 500°C to about 800°C for about 2 to 10 hours to provide a pre-catalyst composition.

[0245] In one embodiment, in step (ii), the product of step (i) is subjected to calcination at about 500°C to about 700°C for about 2 to 10 hours to provide a pre-catalyst composition.

[0246] In one embodiment, in step (ii), the product of step (i) is subjected to calcination at about 500°C to about 600°C for about 2 to 10 hours to provide a pre-catalyst composition.

[0247] In one embodiment, in step (ii), the product of step (i) is subjected to calcination by heating at a rate of about 5°C / minute up to about 700°C. Suitably, the product subject to calcination is held at about 700°C for about 4 to 8 hours, suitably about 6 hours.

[0248] In one embodiment, the pre-catalyst composition is shaped into pre-catalyst units. In another embodiment, the product of step (ii) is shaped into a pre-catalyst unit, such as pellets or tablets.

[0249] In one embodiment, the product of step (ii) is mixed with a lubricant or binder prior to shaping into pre-catalyst units. Suitable lubricants and binders are known in the art. In one embodiment, the lubricant or binder is selected from one or more of the group consisting of alumina, graphite, sesbania gum powder, calcium aluminate cement or a clay (e.g. bentonite). In one embodiment, the lubricant or binder is selected from alumina or graphite. In one embodiment, the lubricant or binder is selected from one or more of the group consisting of sesbania gum powder, calcium aluminate cement or a clay. Suitably, the binder is sesbania gum powder.

[0250] In one embodiment, the lubricant or binder is added to the product of step (ii) in an amount of about 0.1 % to about 50 % (w / w), suitably about 0.1 % to about 40 % (w / w), or about 0.1 % to about 30 % (w / w), or about 0.1 % to about 20 % (w / w).

[0251] In another embodiment, the lubricant or binder is added to the product of step (ii) in an amount of about 5 % to about 50 % (w / w), suitably about 5 % to about 40 % (w / w), or about 5 % to about 30 % (w / w), or about 5 % to about 20 % (w / w).

[0252] In one embodiment, the lubricant or binder is added to the product of step (ii) in an amount of about 0.1 % to about 5 % (w / w).

[0253] The shaped pre-catalyst units may be prepared by suitable means known in the art. For instance, the product of step (ii) may be combined with lubricant and / or binder and subjected to granulation and tableting in a tablet press, or extruded to in an extruder to give, for example, pellets of suitable dimensions.

[0254] Preferably the shaped pre-catalyst units have maximum and minimum dimensions in the range about 0.5 mm to about 25 mm, suitably about 0.5 mm to about 20 mm. Shaped Composition

[0255] In one aspect, the present invention relates to a shaped composition comprising a pre-catalyst composition obtained or obtainable according to the method of the first aspect as described in any of the above-mentioned embodiments.

[0256] In one embodiment, the shaped composition is in the form of a pellet or a tablet. Suitably, the shaped composition has maximum and minimum dimensions in the range about 0.5 to about 25 mm, suitably about 0.5 to about 20 mm.

[0257] Suitably, the shaped article is a cylindrical pellet or an extruded strip.

[0258] In one embodiment, in addition to the pre-catalyst composition, the shaped composition comprises a lubricant or a binder. In one embodiment, the lubricant or binder is selected from one or more of the group consisting of alumina, graphite, sesbania gum powder, guar gum, calcium aluminate cement or a clay (e.g. bentonite). In one embodiment, the lubricant or binder is selected from alumina or graphite. In one embodiment, the lubricant or binder is selected from one or more of the group consisting of sesbania gum powder, calcium aluminate cement or a clay. Suitably, the binder is sesbania gum powder.

[0259] In one embodiment, the lubricant or binder is present in the shaped composition in an amount of about 0.1 % to about 50 % (w / w), suitably about 0.1 % to about 40 % (w / w), or about 0.1 % to about 30 % (w / w), or about 0.1 % to about 20 % (w / w).

[0260] In another embodiment, the lubricant or binder is present in the shaped composition in an amount of about 5 % to about 50 % (w / w), suitably about 5 % to about 40 % (w / w), or about 5 % to about 30 % (w / w), or about 5 % to about 20 % (w / w).

[0261] In one embodiment, the lubricant or binder is present in the shaped composition in an amount of about 0.1 % to about 5 % (w / w). Pre-catalyst and Catalyst Composition

[0262] In another aspect, the present invention relates to a pre-catalyst composition obtained or obtainable according to the method of the first aspect as described in any of the above-mentioned embodiments.

[0263] The pre-catalyst composition obtained or obtainable according to the method of the first aspect is suitable for producing a composition comprising carbon monoxide from a feed gas composition comprising carbon dioxide and hydrogen. In particular, the pre-catalyst composition obtained or obtainable according to the method of the first aspect is suitable for use in a reverse water gas shift reaction.

[0264] The pre-catalyst composition obtained or obtainable according to the method of the first aspect has advantageous nano-structure and dispersity of components resulting in high activity and selectivity in a reverse water gas shift reaction.

[0265] In one embodiment, the pre-catalyst composition obtained or obtainable according to the method of the first aspect is chromium-free. In another embodiment, the pre- catalyst composition obtained or obtainable according to the method of the first aspect is carbon-free. In another embodiment, the pre-catalyst composition obtained or obtainable according to the method of the first aspect is chromium-free and carbon-free.

[0266] In another aspect, the present invention provides a method for preparing a catalyst composition comprising: (a) providing a pre-catalyst composition obtained or obtainable according to the method of the first aspect, as described any of the above-mentioned embodiments; (b) optionally subjecting said pre-catalyst composition to calcination; and (c) activating said pre-catalyst composition to obtain a catalyst composition.

[0267] In another aspect, the present invention relates to a catalyst composition obtained or obtainable according to the method of the immediately above aspect.

[0268] The catalyst composition of the above aspects is suitable for producing a composition comprising carbon monoxide from a feed gas composition comprising carbon dioxide and hydrogen. In particular, the catalyst composition according to the above aspects is suitable for use in a reverse water gas shift reaction.

[0269] Suitably, the calcination is performed at a temperature of between about 100°C to about 1000°C, or about 200°C to about 700°C, or about 200°C to about 600°C, suitably about 200°C to about 500°C, more suitably about 300°C to about 450°C. Suitably the calcination is performed in air, suitably static air.

[0270] The calcined pre-catalyst material of step (b) or the pre-catalyst composition of step (a) may be activated, for instance by reduction. Suitably, the material to be activated is exposed to a gaseous composition comprising hydrogen at a temperature of about 250°C to about 500°C, more suitably about 300 to about 350°C.

[0271] In one embodiment, the gaseous composition comprising hydrogen is a mixture of hydrogen and nitrogen. In another embodiment, the gaseous composition is mixture of carbon dioxide and hydrogen gas. In one embodiment, the pre-catalyst activation of (c) occurs in situ in the reaction, i.e. by means of the process gas.

[0272] In another aspect, the present invention provides a pre-catalyst composition comprising iron or one or more oxide thereof and cerium or one or more oxide thereof.

[0273] In one embodiment, the one or more iron oxide is selected from Fe3O4, Fe2O3 or FeO. In one embodiment, the one or more cerium oxide comprises or consists of CeO2.

[0274] In one embodiment, the molar ratio of iron to cerium in the pre-catalyst composition is about 10:1 to 2:5; suitably about 2:1 to about 1:2, suitably about 3:2 to about 2:3; suitably about 5:4 to about 4:5; suitably about 1:1.

[0275] In one embodiment, the pre-catalyst composition further comprises one or more further metal or an oxide thereof. In one embodiment, the further metal or oxide thereof is selected from one or more of the group consisting of aluminium, titanium, copper, zinc, manganese, cobalt, zirconium, or an oxide thereof. In another embodiment, the further metal species is selected from one or more of the groups consisting of aluminium, titanium, zinc, manganese, zirconium, or an oxide thereof.

[0276] In one embodiment, the molar ratio of iron to the further metal in the pre-catalyst composition is about 10:1 to 2:5; suitably about 2:1 to about 1:2, suitably about 3:2 to about 2:3; suitably about 5:4 to about 4:5; suitably about 1:1.

[0277] In one embodiment, the pre-catalyst composition comprises: ^ iron or one or more oxide thereof, cerium or one or more oxide thereof and aluminum or one or more oxide thereof;^ iron or one or more oxide thereof, cerium or one or more oxide thereof and zirconium or one or more oxide thereof; ^ iron or one or more oxide thereof, cerium or one or more oxide thereof and titanium or one or more oxide thereof; ^ iron or one or more oxide thereof, cerium or one or more oxide thereof, aluminum or one or more oxide thereof, and titanium or one or more oxide thereof; ^ iron or one or more oxide thereof, cerium or one or more oxide thereof and zinc or one or more oxide thereof; or ^ iron or one or more oxide thereof, cerium or one or more oxide thereof and manganese or one or more oxide thereof.

[0278] In one embodiment, the pre-catalyst composition further comprises an alkali metal or one or more oxides thereof, an alkaline earth metal or one or more oxides thereof, or a rare earth metal or one or more oxides thereof.

[0279] In one embodiment, the pre-catalyst composition comprises an alkali metal or one or more oxides thereof. In one embodiment, the alkali metal is selected from the group consisting of lithium, sodium, potassium and cesium. In another embodiment, the alkali metal is selected from cesium, sodium and potassium. In another embodiment, the alkali metal is potassium or sodium.

[0280] In one embodiment, the iron to alkali metal molar ratio in the pre-catalyst composition is about 40:1 to about 5:1. Suitably, the iron to alkali metal molar ratio is about 40:1 to about 10:1. Suitably, about 40:1 to about 15:1, or about 40:1 to about 20:1. Suitably, the iron to alkali metal molar ratio is about 20:1.

[0281] In one embodiment, the pre-catalyst composition comprises an alkaline earth metal or one or more oxides thereof. In one embodiment, the alkaline earth metal is selected from the group consisting of magnesium, calcium and barium, suitably magnesium and calcium, more suitably calcium.

[0282] In one embodiment, the iron to alkaline earth metal molar ratio in the pre- catalyst composition is about 40:1 to about 5:1. Suitably, the iron to alkaline earth metal molar ratio is about 40:1 to about 10:1. Suitably, about 40:1 to about 15:1, or about 40:1 to about 20:1. Suitably, the iron to alkaline earth metal molar ratio is about 20:1.

[0283] In one embodiment, the pre-catalyst composition comprises a rare earth metal or one or more oxides thereof. In one embodiment, the rare earth metal is selected from the group consisting of yttrium, lanthanum, cerium, praseodymium and erbium.

[0284] In one embodiment, the iron to rare earth metal molar ratio in the pre-catalyst composition is about 300:1 to about 50:1. Suitably, the iron to rare earth metal molar ratio is about 300:1 to about 75:1. Suitably, the iron to rare earth metal molar ratio is about 200:1 to about 75:1 or about 150:1 to about 75:1.

[0285] In one embodiment, the pre-catalyst composition comprises / essentially consists of / consists of: ^ iron or one or more oxide thereof, cerium or one or more oxide thereof, aluminum or one or more oxide thereof and potassium or one or more oxide thereof; suitably wherein the molar ratio of iron:cerium:potassium:aluminium is about 100:100:5:100. ^ iron or one or more oxide thereof, cerium or one or more oxide thereof and potassium or one or more oxide thereof; suitably wherein the molar ratio of iron:cerium:potassium is about 100:100:5; ^ iron or one or more oxide thereof, cerium or one or more oxide thereof, zirconium or one or more oxide thereof, and potassium or one or more oxide thereof; suitably, wherein the molar ratio of iron:cerium:potassium:zirconium is about 100:100:5:100. ^ iron or one or more oxide thereof, cerium or one or more oxide thereof, titanium or one or more oxide thereof and potassium or one or more oxide thereof; suitably wherein the molar ratio of iron:cerium:potassium:titanium is about 100:100:5:100. ^ iron or one or more oxide thereof, cerium or one or more oxide thereof, aluminum or one or more oxide thereof, titanium or one or more oxide thereof, and potassium or one or more oxide thereof; suitably wherein the molar ratio of iron:cerium:potassium:titanium, aluminium is about 100:100:5:100:100. ^ iron or one or more oxide thereof, cerium or one or more oxide thereof, zinc or one or more oxide thereof, and potassium or one or more oxide thereof; suitably wherein the molar ratio of iron:cerium:potassium:zinc is about 100:100:5:80 or about 100:100:5:100; and ^ iron or one or more oxide thereof, cerium or one or more oxide thereof, manganese or one or more oxide thereof, and potassium or one or oxide thereof; suitably wherein the molar ratio of iron:cerium:potassium:manganese is about 100:100:5:100.

[0286] In another aspect, the present invention provides a pre-catalyst composition comprising / essentially consisting of / consisting of one or more iron oxide, one or more cerium oxide, one or more titanium oxide, and one or more potassium oxide.

[0287] In another aspect, the present invention provides a pre-catalyst composition comprising / essentially consisting of / consisting of one or more iron oxide, one or more cerium oxide, one or more aluminium oxide, and one or more potassium oxide.

[0288] In another aspect, the present invention provides a pre-catalyst composition comprising / essentially consisting of / consisting of one or more iron oxide, one or more cerium oxide, one or more aluminium oxide, one or more titanium oxide, and one or more potassium oxide.

[0289] In another aspect, the present invention provides a pre-catalyst composition comprising / essentially consisting of / consisting of one or more iron oxide, one or more titanium oxide, and one or more potassium oxide. In another aspect, the present invention provides a pre-catalyst composition comprising / essentially consisting of / consisting of one or more iron oxide, one or more aluminium oxide, one or more titanium oxide, and one or more potassium oxide.

[0290] In one embodiment, the pre-catalyst composition may comprise one or more further transition metal oxides selected from one or more of a zinc oxide, a manganese oxide, a zirconium salt oxide, a cobalt oxide, and a copper oxide.

[0291] In another embodiment, the pre-catalyst composition may comprise one or more further transition metal oxides selected from one or more of a zinc oxide, a manganese oxide, and a zirconium salt oxide.

[0292] Suitably, the proportion of iron oxide and any other metal oxide is such that the molar ratio of iron oxide to other metal oxide is about 2:1 to about 1:2, suitably about 6:4 to about 4:6; suitably about 5:4 to about 4:5; suitably about 1:1. For example, in relation to a pre- catalyst composition comprising one or more titanium oxide, the molar ratio of iron oxide to titanium oxide is about 2:1 to about 1:2, suitably about 6:4 to about 4:6; suitably about 5:4 to about 4:5; suitably about 1:1.

[0293] In one embodiment, the pre-catalyst composition further comprises a binder or lubricant. Suitable lubricants and binders are known in the art. In one embodiment, the lubricant or binder is selected from one or more of the group consisting of alumina, graphite, guar gum, sesbania gum powder, calcium aluminate cement or a clay (e.g. bentonite). In oneembodiment, the lubricant or binder is selected from alumina or graphite. In one embodiment, the lubricant or binder is selected from one or more of sesbania gum powder, calcium aluminate cement, calcium magnesium oxide (CaMgO2) or a clay. Suitably, the binder is sesbania gum powder.

[0294] In one embodiment, the lubricant or binder is present in the pre-catalyst composition in an amount of about 0.1 % to about 50 % (w / w), suitably about 0.1 % to about 40 % (w / w), or about 0.1 % to about 30 % (w / w), or about 0.1 % to about 20 % (w / w).

[0295] In another embodiment, the lubricant or binder is present in the pre-catalyst composition in an amount of about 5 % to about 50 % (w / w), suitably about 5 % to about 40 % (w / w), or about 5 % to about 30 % (w / w), or about 5 % to about 20 % (w / w).

[0296] In one embodiment, the lubricant or binder is present in the pre-catalyst composition in an amount of about 0.1 wt.% to about 5 wt.%.

[0297] In one embodiment, the pre-catalyst composition is formed into a shaped composition or article as described in any of the above-mentioned embodiments.

[0298] In one embodiment, the pre-catalyst composition comprises from about 20 to about 60 wt.% of one or more iron oxide. Suitably, the pre-catalyst composition comprises about 20 to about 50 wt. % of one or more iron oxide. Suitably, from about 30 to about 50 wt. % of one or more iron oxide.

[0299] In one embodiment, the pre-catalyst composition comprises from about 20 to about 60 wt.% of one or more cerium oxide. Suitably, the pre-catalyst composition comprises about 20 to about 50 wt. % of one or more cerium oxide. Suitably, from about 30 to about 50 wt. % of one or more cerium oxide.

[0300] In one embodiment, the pre-catalyst composition comprises from about 20 to about 60 wt.% of one or more titanium oxide. Suitably, the pre-catalyst composition comprises about 20 to about 50 wt. % of one or more titanium oxide. Suitably, from about 30 to about 50 wt. % of one or more titanium oxide.

[0301] In one embodiment, the pre-catalyst composition comprises from about 20 to about 60 wt.% of one or more aluminium oxide. Suitably, the pre-catalyst composition comprises about 20 to about 50 wt. % of one or more aluminium oxide. Suitably, from about 30 to about 50 wt. % of one or more aluminium oxide.

[0302] In one embodiment, the pre-catalyst composition comprises about 40 to about 50 wt.% of one or more iron oxides, about 40 to about 50 wt.% of one or more titanium oxide, about 1 to about 10 wt.% of one or more zirconium oxide, and about 1 to about 5 wt.% of one or more potassium oxide.

[0303] In one embodiment, the pre-catalyst composition comprises about 30 to about 40 wt.% of one or more iron oxides, about 30 to about 40 wt.% of one or more titanium oxide, about 30 to about 40 wt.% of one or more aluminium oxide, and about 1 to about 5 wt.% of one or more potassium oxide.

[0304] In one embodiment, the pre-catalyst is activated to provide a catalyst obtainable therefrom. In one embodiment, the catalyst is obtainable by reduction of the pre- catalyst. For instance, the pre-catalyst is exposed to a gaseous composition comprising hydrogen at a temperature of about 250°C to about 500°C, more suitably about 300 to about 350°C. In one embodiment, catalyst is obtainable from the pre-catalyst by activation in situ in the reaction, i.e. by means of the feed gas composition.

[0305] Suitably, the pre-catalyst composition or catalyst obtainable therefrom is used for producing a composition comprising carbon monoxide from a feed gas composition comprising carbon dioxide and hydrogen. Suitably, the pre-catalyst composition or catalyst obtainable therefrom is used in a reverse water gas shift reaction. Further suitable methods in which in the pre-catalyst composition can be used are described below. Method for producing a composition comprising carbon monoxide

[0306] In another aspect, the present invention relates to a method for producing a composition comprising carbon monoxide, wherein said method comprises contacting a feed gas composition comprising carbon dioxide and hydrogen with a pre-catalyst composition, or a catalyst composition, as described in any of the embodiments above, at a temperature of at least 400°C.

[0307] In one embodiment, the method for producing a composition comprising carbon monoxide comprises providing a pre-catalyst composition by carrying out the methods described above. In another embodiment, the method for producing a composition comprising carbon monoxide comprises providing a catalyst composition by carrying out the methods described above.

[0308] In one embodiment of the claimed methods, the catalyst composition or pre- catalyst composition is charged into a reaction zone. The catalyst having been activated exsitu (for instance by heating, and / or if required by optional oxidation and subsequent reduction e.g. with hydrogen). Alternatively, the pre-catalyst composition may be used directly in the reaction if it is activated in situ, for instance, under the conditions of the reaction.

[0309] The catalyst may be used in a fixed bed, a moving bed or fluidized bed. Suitably, the catalyst is used in a fixed bed reactor. In one embodiment, the pre-catalyst composition or catalyst composition is packed in a fixed bed reactor and the feed gas composition is fed through the bed. In some embodiments, the feed gas composition is continuously fed over the pre-catalyst composition or catalyst composition.

[0310] In one embodiment, the feed gas composition comprising carbon dioxide and hydrogen at a suitable H2:CO2 molar ratio is contacted with the bed of catalyst or pre-catalyst composition, and reacted at reaction conditions. Generally, the molar ratio of H2:CO2 ranges from about 1:1 to about 10:1, suitably from about 1:1 to about 5:1, more suitably about 1:1 to about 4:1, more suitably about 1:1 to about 3:1, suitably about 1:1 to about 2:1.

[0311] In one embodiment, the feed gas composition is substantially free of oxygen, and / or water. In another embodiment, the feed gas composition is free of oxygen and / or water.

[0312] In another embodiment, the molar ratio of H2:CO2 in the feed gas composition is about 1:1, or about 2:1, or about 3:1, or about 4:1.

[0313] The reaction temperatures are elevated. As used herein elevated temperature is a temperature which is elevated with respect to standard ambient temperature, i.e. a temperature of 298.15 K (25 °C). In one embodiment, the feed gas composition is contacted with the pre-catalyst composition or catalyst composition at a temperature of at least 400°C, suitably at least about 450°C, suitably at least about 500°C, suitably at least about 550°C, suitably at least about 600°C, suitably at least about 650°C.

[0314] In another embodiment the feed gas composition is contacted with the pre- catalyst composition or catalyst composition at a temperature of about 400°C to about 1000°C, or about 400°C to about 900°C, or about 400°C to about 800°C, or about 400°C to about 700°C, or about 400°C to about 650°C, or about 400°C to about 600°C, or about 400°C to about 550°C.

[0315] In another embodiment the feed gas composition is contacted with the pre- catalyst composition or catalyst composition at a temperature of about 450°C to about 1000°C,or about 450°C to about 900°C, or about 450°C to about 800°C, or about 450°C to about 700°C, or about 450°C to about 650°C, or about 450°C to about 600°C.

[0316] In another embodiment the feed gas composition is contacted with the pre- catalyst composition or catalyst composition at a temperature of about 500°C to about 1000°C, or about 500°C to about 900°C, or about 500°C to about 800°C, or about 500°C to about 650°C, or about 500°C to about 600°C.

[0317] In another embodiment the feed gas composition is contacted with the pre- catalyst composition or catalyst composition at a temperature of about 600°C to about 1000°C, or about 600°C to about 900°C, or about 600°C to about 800°C, or about 600°C to about 700°C, or about 600°C to about 650°C.

[0318] In another embodiment the feed gas composition is contacted with the pre- catalyst composition or catalyst composition at a temperature of about 700°C to about 1000°C, or about 700°C to about 900°C, or about 700°C to about 800°C, or about 700°C to about 750°C.

[0319] The reaction pressure may be below atmospheric pressure, atmospheric pressure, or elevated pressure. In one embodiment., the reaction pressure may be atmospheric or may be elevated pressure. As used herein elevated pressure is a pressure which is elevated with respect to standard ambient pressure, i.e. a pressure of 100,000 Pa (1 bar, 14.5 psi, 0.9869 atm). In one embodiment, the feed gas composition is contacted with the pre-catalyst composition or catalyst composition at a pressure of about 100 KPa to about 2000 KPa, or about 100 KPa to about 500 KPa, suitably about 100 KPa to about 400 KPa, suitably about 100 KPa to about 300 KPa, suitably about 100 KPa to about 200 KPa, suitably about 100 KPa to about 150 KPa.

[0320] In another embodiment, the feed gas composition is contacted with the pre- catalyst composition or catalyst composition at a pressure of about 0 KPa to about 2000 KPa, or about 0 KPa to about 500 KPa, suitably about 0 KPa to about 400 KPa, suitably about 0 KPa to about 300 KPa, suitably about 0 KPa to about 200 KPa, suitably about 0 KPa to about 150 KPa.

[0321] In another embodiment, the feed gas composition is contacted with the pre- catalyst composition or catalyst composition at a pressure of about 0 KPa to about 100 KPa, or about 0 KPa to about 50 KPa.

[0322] In one embodiment, the feed gas composition is contacted with the pre-catalyst composition or catalyst composition at a GHSV (gas hourly space velocity) of about 1 to about 20,000 h-1, suitably about 1000 to about 10000 h-1, suitably about 1000 to about 8000 h-1, suitably about 1000 to about 7000 h-1, suitably about 1000 to about 5000 h-1.

[0323] In one embodiment, the method provides a methane selectivity of about 2% or less, more suitably about 1.8 % or less, more suitably about 1.5 % or less, more suitably about 1.0 % or less, more suitably about 0.6 % or less, more suitably about 0.5 % or less, more suitably about 0.4 % or less, more suitably about 0.3 % or less, more suitably about 0.2 % or less, more suitably about 0.1 % or less, more suitably about 0.05 % or less, more suitably about 0.01 vol. % or less.

[0324] Methane selectivity refers to the amount of production of methane as a proportion of the converted CO2. The methane selectivity (SCH4%) can be calculated according to the following equation: SCH4% = YCH4 out / (YCO2in-YCO2out) in which Yco2 in refers to the CO2 amount (ml / min) in the feed gas composition and YCO2 out and YCH4 out refers to amount of CO2 and CH4 respectively in the product stream.

[0325] In one embodiment, the method provides a carbon dioxide conversion of at least about 40%, at least about 50%, suitably at least about 55%, suitably at least about 60%, suitably at least about 65%.

[0326] In another embodiment, the method provides a carbon dioxide conversion of about 50% to about 65%, suitably about 55% to about 65%, suitably about 60% to about 65%.

[0327] The carbon dioxide conversion (Xco2 %) can be calculated according to the following equation: Xco2%= 1-((YCO2 out) / ( YCO2 in)) In which Yco2 in refers to the CO2 amount (ml / min) in the feed gas composition and YCO2 out refers to amount of CO2 (ml / min) in the product stream.

[0328] In one embodiment, the method provides a carbon monoxide selectivity of at least about 80%, suitably at least about 90%, suitably at least about 95%, suitably at leastabout 96%, suitably at least about 98%, suitably at least about 99%, suitably at least about 99.5%, suitably at least about 99.9%.

[0329] In one embodiment, the method provides a carbon monoxide selectivity of from about 90% to 100%, suitably from about 95% to 100%, suitably from about 96% to 100%, suitably from about 98% to 100%.

[0330] Carbon monoxide selectivity refers to the amount of production of carbon monoxide as a proportion of the converted CO2. The carbon monoxide selectivity (Sco%) can be calculated according to the following equation: SCO%=YCO out / (YCO2 in-YCO2 out) in which Yco2 in refers to the CO2 amount (ml / min) in the feed gas composition and YCO2 out and YCO out refers to amount of CO2 and CO respectively in the product stream.

[0331] In one embodiment, the method provides a carbon dioxide conversion of about 50% to about 65%, a carbon monoxide selectivity of from about 90% to 100%, and a methane selectivity of about 1.8% or less.

[0332] In one embodiment, the method provides a carbon dioxide conversion of about 55% to about 65%, a carbon monoxide selectivity of from about 95% to 100%, and a methane selectivity of about 1.8% or less.

[0333] In another embodiment, the method provides a carbon dioxide conversion of about 55% to about 65%, a carbon monoxide selectivity of from about 95% to 100%, and a methane selectivity of about 0.6% or less.

[0334] In another embodiment, the method provides a carbon dioxide conversion of about 55% to about 65%, a carbon monoxide selectivity of from about 98% to 100%, and a methane selectivity of about 0.01% or less.

[0335] In another embodiment, the method provides a carbon dioxide conversion of about 60% to about 65%, a carbon monoxide selectivity of from about 98% to 100%, and a methane selectivity of about 0.01% or less.

[0336] In another embodiment, the method provides a carbon dioxide conversion of about 60% to about 65%, and a carbon monoxide selectivity of from about 98% or more.

[0337] In another embodiment, the method provides a carbon dioxide conversion of about 60% to about 65%, and a carbon monoxide selectivity of from about 99% or more.

[0338] In another embodiment, the method provides a carbon dioxide conversion of about 60% to about 65%, and a carbon monoxide selectivity of from about 99% or more, and a methane selectivity of about 0.6% or less.

[0339] In another embodiment, the method provides a carbon dioxide conversion of about 60% to about 66%, and a carbon monoxide selectivity of 100%.

[0340] The method for producing a composition comprising carbon monoxide may comprise preparation of the pre-catalyst composition or catalyst composition described above as a preliminary step.

[0341] The invention will now be further described by the following numbered clauses which are not claims: 1. A method for preparing a pre-catalyst composition comprising: (i) combining an iron salt or hydrate thereof; at least one further metal species selected from one or more of the group consisting of a cerium salt or hydrate thereof, a cerium oxide or hydrate thereof, an aluminium salt or hydrate thereof, an aluminium oxide or hydrate thereof, a titanium salt or hydrate thereof and a titanium oxide or a hydrate thereof; and an organic compound comprising one or more functional groups selected from the group consisting of a carboxyl, hydroxyl, amido and amino group; and (ii) subjecting the product of (i) to calcination to provide a pre-catalyst composition. 2. A method for preparing a pre-catalyst composition according to clause 1, comprising: (i)(a) combining an iron salt or hydrate thereof; at least one further metal species selected from one or more of the group consisting of a cerium salt or hydrate thereof, a cerium oxide or hydrate thereof, an aluminium salt or hydrate thereof, an aluminium oxide or hydrate thereof, a titanium salt or hydrate thereof and a titanium oxide or a hydrate thereof; and an organic compound comprising one or more functional groups selected from the group consisting of a carboxyl, hydroxyl, amido and amino group; and water to provide an aqueous solution or mixture;(i)(b) drying the aqueous solution or mixture of (i)(a) to provide a dried material or slurry; (ii) subjecting the dried material or slurry of (i)(b) to calcination to provide a pre- catalyst composition. 3. A method according to clause 2, wherein the drying of step (i)(b) is performed at a temperature of about 70°C to about 100°C. 4. A method according to any one of clauses 1 to 3, wherein the at least one further metal species of step (i) is: (a) a cerium salt or hydrate thereof; or (b) a titanium salt or hydrate; or (c) a titanium oxide or hydrate; or (d) an aluminium salt or hydrate thereof. 5. A method according to any one of the preceding clauses, wherein the at least one further metal species of step (i) is: (a) a cerium salt or hydrate thereof; or (b) a titanium oxide or hydrate; or (c) an aluminium salt or hydrate thereof. 6. A method according to any one of clauses 1 to 5, wherein at least two further metal species are combined with the iron salt or hydrate thereof in step (i) selected from the group consisting of a cerium salt or hydrate thereof, an aluminium salt or hydrate thereof, a titanium salt or hydrate thereof and a titanium oxide or hydrate thereof. 7. A method according to clause 6, wherein the at least two further metal species of step (i) is: (a) a cerium salt or hydrate thereof and an aluminium salt or hydrate thereof; or (b) a cerium salt or hydrate thereof and a titanium oxide or hydrate thereof; or (c) an aluminium salt or hydrate thereof and a titanium oxide or hydrate thereof; or (d) a cerium salt or hydrate thereof and a titanium salt or hydrate thereof; or(e) an aluminium salt or hydrate thereof and a titanium salt or hydrate thereof. 8. A method according to any one of the preceding clauses, wherein at least three further metal species are combined with the iron salt or hydrate thereof in step (i) which are a cerium salt or hydrate thereof, a titanium oxide or hydrate thereof and an aluminium salt or hydrate thereof. 9. A method according to any one of clauses 1 to 7, wherein at least three further metal species are combined with the iron salt or hydrate thereof in step (i) which are a cerium salt or hydrate thereof, a titanium salt or hydrate thereof and an aluminium salt or hydrate thereof. 10. A method according to any one of the preceding clauses, wherein step (i) further comprises combining one or more of an alkali metal species, an alkaline earth metal species and a rare earth metal species. 11. A method according to any one of the preceding clauses, wherein step (i) further comprises combining one or more of an alkali metal species selected from an alkali metal salt or hydrate thereof. 12. A method according to clause 10 or 11, wherein the iron salt or hydrate thereof to alkali metal species molar ratio in step (i) is about 100:1 to about 5:1, suitably about 25:1 to about 5:1. 13. A method according to any one of clauses 10 to 12, wherein the alkali metal salt or hydrate thereof is selected from potassium nitrate, potassium carbonate, sodium nitrate, sodium carbonate, lithium carbonate and cesium carbonate, or a hydrate thereof. 14. A method according to any one of the preceding clauses, wherein the iron salt or hydrate of step (i) is an iron nitrate, suitably selected from one or more of Fe(NO3)2 and Fe(NO3)3 or a hydrate thereof. 15. A method according to any one of the preceding clauses, wherein the cerium salt or hydrate thereof of step (i) is a cerium (III) or (IV) salt, or hydrate thereof. 16. A method according to any one of the preceding clauses, wherein, the titanium salt or hydrate thereof of step (i) is a titanium (III) or (IV) salt, or hydrate thereof. 17. A method according to any one of the preceding clauses, wherein, the aluminum salt or hydrate thereof of step (i) is an aluminum (III) salt, or hydrate thereof.18. A method according to any one of the preceding clauses, wherein the proportion of iron salt or hydrate thereof to each further metal species, selected from one or more of the group consisting of cerium salt or hydrate thereof, a cerium oxide or hydrate thereof, an aluminium salt or hydrate thereof, an aluminium oxide or hydrate thereof, a titanium salt or hydrate thereof and a titanium oxide or a hydrate thereof, is such that the molar ratio of iron salt or hydrate thereof to cerium, aluminium or titanium salt, oxide or hydrate thereof is about 2:1 to about 1:2, suitably about 1:1. 19. A method according to any one of the preceding clauses, wherein the organic compound comprises two or more functional groups selected from a carboxyl, hydroxyl, amido and amino groups. 20. A method according to any one of the preceding clauses, wherein the organic compound is a C4 to C12 carboxylic acid or urea. 21. A method according to any one of the preceding clauses, wherein the organic compound is citric acid. 22. A method according to any one of clauses 1 to 3, wherein step (i) comprises combining an iron (II) or (III) salt or hydrate thereof, a cerium (III) salt or hydrate thereof, an alkali metal salt or hydrate thereof; an organic compound selected from a C4 to C12 carboxylic acid (suitably citric acid) or urea; and water. 23. A method according to any one of clauses 1 to 3, wherein step (i) comprises combining an iron (II) or (III) salt or hydrate thereof, a titanium (IV) salt or hydrate thereof, an alkali metal salt or hydrate thereof; an organic compound selected from a C4 to C12 carboxylic acid (suitably citric acid) or urea; and water. 24. A method according to any one of clauses 1 to 3, wherein step (i) comprises combining an iron (II) or (III) salt or hydrate thereof, a titanium (IV) oxide or hydrate thereof, an alkali metal salt or hydrate thereof; an organic compound selected from a C4 to C12 carboxylic acid (suitably citric acid) or urea; and water. 25. A method according to any one of clause 22 or 24, wherein step (i) further comprises combining an aluminium (III) salt, oxide or hydrate thereof. 26. A method according to any one of the preceding clauses, wherein step (i) further comprises combining a transition metal species selected from one or more of a zinc salt or hydrate thereof, a zinc oxide or hydrate thereof, a manganese salt or hydrate thereof, amanganese oxide or hydrate thereof, a zirconium salt or hydrate thereof, a zirconium oxide or hydrate thereof, a cobalt salt or hydrate thereof, a cobalt oxide or hydrate thereof, a copper salt or hydrate thereof and a copper oxide or hydrate thereof. 27. A method according to clause 26, wherein step (i) further comprises combining a transition metal species selected from one or more of a zinc salt, oxide or hydrate thereof, a manganese salt, oxide or hydrate thereof and a zirconium salt, oxide or hydrate thereof. 28. A method according to clause 26, wherein step (i) further comprises combining a transition metal species selected from one or more of a zinc salt or hydrate thereof, a manganese salt or hydrate thereof and a zirconium salt or hydrate thereof. 29. A method according to any one of clauses 26 to 28, wherein the proportion of iron salt or hydrate thereof to each transition metal species is such that the molar ratio of iron salt or hydrate thereof to each transition metal species is about 10:1 to about 1:1, suitably about 5:4 to about 1:1. 30. A method according to any one of the preceding clauses, with the proviso that the method does not comprise the use of a chromium species in any step. 31. A method according to any one of the preceding clauses, wherein the calcination step is performed at a temperature of between about 400°C to about 1000°C. 32. A pre-catalyst composition obtained or obtainable according to the method of any one of clauses 1 to 31. 33. A method for preparing a catalyst composition comprising: (a) providing a pre-catalyst composition according to clause 32; (b) optionally subjecting said pre-catalyst composition to calcination; and (c) activating said pre-catalyst composition to obtain a catalyst composition. 34. A catalyst composition obtained or obtainable according to the method of clause 33. 35. A method for producing a composition comprising carbon monoxide, wherein said method comprises contacting a feed gas composition comprising carbon dioxide and hydrogen with a pre-catalyst composition according to clause 32, or a catalyst composition according to clause 34, at a temperature of at least 400°C.36. A method according to clause 35, wherein the feed gas composition is contacted with the pre-catalyst composition or catalyst composition at a temperature of about 450°C to about 650°C. 37. A method according to clause 35 or 36, wherein the feed gas composition is contacted with the pre-catalyst composition or catalyst composition at a pressure of about 100 KPa to about 300 KPa. 38. A method according to clause 35 to 37, wherein the feed gas composition comprises a hydrogen to carbon dioxide ratio of about 1:1 to about 5:1. 39. A pre-catalyst composition comprising iron or one or more oxide thereof and cerium or one or more oxide thereof. 40. A pre-catalyst composition according to clause 39, wherein the pre-catalyst composition has a molar ratio of iron to cerium of about 10:1 to 2:5, suitably about 2:1 to about 1:2, suitably about 3:2 to about 2:3; suitably about 5:4 to about 4:5; suitably about 1:1. 41. A pre-catalyst composition according to clause 39 or 40, wherein the pre-catalyst composition comprises one or more further metal or an oxide thereof. 42. A pre-catalyst composition according to any one of clauses 39 to 41, wherein the further metal or an oxide thereof is selected from one or more of the group consisting of aluminium, titanium, copper, zinc, manganese, cobalt, zirconium, or an oxide thereof. 43. A pre-catalyst composition according to any one of clauses 39 to 42, wherein the further metal or an oxide thereof is selected from one or more of the group consisting of aluminium, titanium, zinc, manganese, zirconium, or an oxide thereof. 44. A pre-catalyst composition according to any one of clauses 39 to 43, wherein the further metal or an oxide thereof is selected from one or more of aluminium and titanium. 45. A pre-catalyst composition according to any one of clauses 41 to 44, wherein the molar ratio of iron to the further metal in the pre-catalyst composition is about 10:1 to 2:5; suitably about 2:1 to about 1:2, suitably about 3:2 to about 2:3; suitably about 5:4 to about 4:5; suitably about 1:1. 46. A pre-catalyst composition according to any one of clauses 39 to 45, wherein the pre- catalyst composition comprises:^ iron or one or more oxide thereof, cerium or one or more oxide thereof and aluminum or one or more oxide thereof; ^ iron or one or more oxide thereof, cerium or one or more oxide thereof and zirconium or one or more oxide thereof; ^ iron or one or more oxide thereof, cerium or one or more oxide thereof and titanium or one or more oxide thereof; ^ iron or one or more oxide thereof, cerium or one or more oxide thereof, aluminum or one or more oxide thereof, and titanium or one or more oxide thereof; ^ iron or one or more oxide thereof, cerium or one or more oxide thereof and zinc or one or more oxide thereof; or ^ iron or one or more oxide thereof, cerium or one or more oxide thereof and manganese or one or more oxide thereof. 47. A pre-catalyst composition according to any one of clauses 39 to 46, further comprising an alkali metal or one or more oxides thereof, an alkaline earth metal or one or more oxides thereof, or a rare earth metal or one or more oxides thereof. 48. A pre-catalyst composition according to any one of clauses 39 to 47, further comprising an alkali metal or one or more oxides thereof. 49. A pre-catalyst composition according to any one of clauses 39 to 48, wherein the alkali metal is selected from the group consisting of lithium, sodium, potassium and cesium, suitably wherein the alkali metal is sodium or potassium. 50. A pre-catalyst composition according to any one of clauses 47 to 49, wherein the pre- catalyst composition has an iron to alkali metal molar ratio of about 40:1 to about 5:1, suitably, about 40:1 to about 10:1, or about 40:1 to about 20:1, or about 20:1. 51. A pre-catalyst composition according to any one of clauses 39 to 47, further comprising an alkaline earth metal or one or more oxides thereof. 52. A pre-catalyst composition according to clause 51, wherein the alkaline earth metal is selected from the group consisting of magnesium, calcium and barium, suitably magnesium and calcium, more suitably calcium. 53. A pre-catalyst composition according to clause 51 or 52, wherein the pre-catalyst composition has an iron to alkaline earth metal molar ratio of about 40:1 to about 5:1, suitably, about 40:1 to about 10:1, or about 40:1 to about 20:1, or about 20:1.54. A pre-catalyst composition according to any one of clauses 39 to 47, further comprising a rare earth metal or one or more oxides thereof. 55. A pre-catalyst composition according to clause 54, wherein the rare earth metal is selected from the group consisting of yttrium, lanthanum, cerium, praseodymium and erbium. 56. A pre-catalyst composition according to clause 54 or 55, wherein the pre-catalyst composition has an iron to rare earth metal molar ratio of about 300:1 to about 50:1, suitably, about 300:1 to about 75:1, or about 200:1 to about 75:1, or about 150:1 to about 75:1. 57. A pre-catalyst composition according to any one of clauses 39 to 50, wherein the pre- catalyst composition comprises / essentially consists of / consists of: ^ iron or one or more oxide thereof, cerium or one or more oxide thereof, aluminum or one or more oxide thereof and potassium or one or more oxide thereof; suitably wherein the molar ratio of iron:cerium:potassium:aluminium is about 100:100:5:100. ^ iron or one or more oxide thereof, cerium or one or more oxide thereof and potassium or one or more oxide thereof; suitably wherein the molar ratio of iron:cerium:potassium is about 100:100:5; ^ iron or one or more oxide thereof, cerium or one or more oxide thereof, zirconium or one or more oxide thereof, and potassium or one or more oxide thereof; suitably, wherein the molar ratio of iron:cerium:potassium:zirconium is about 100:100:5:100. ^ iron or one or more oxide thereof, cerium or one or more oxide thereof, titanium or one or more oxide thereof and potassium or one or more oxide thereof; suitably wherein the molar ratio of iron:cerium:potassium:titanium is about 100:100:5:100. ^ iron or one or more oxide thereof, cerium or one or more oxide thereof, aluminum or one or more oxide thereof, titanium or one or more oxide thereof, and potassium or one or more oxide thereof; suitably wherein the molar ratio of iron:cerium:potassium:titanium, aluminium is about 100:100:5:100:100. ^ iron or one or more oxide thereof, cerium or one or more oxide thereof, zinc or one or more oxide thereof, and potassium or one or more oxide thereof; suitably wherein the molar ratio of iron:cerium:potassium:zinc is about 100:100:5:80 or about 100:100:5:100; and ^ iron or one or more oxide thereof, cerium or one or more oxide thereof, manganese or one or more oxide thereof, and potassium or one or oxide thereof; suitably wherein the molar ratio of iron:cerium:potassium:manganese is about 100:100:5:100. 58. A pre-catalyst composition according to any one of clauses 39 to 57, wherein the pre- catalyst composition further comprises a binder or lubricant.59. A pre-catalyst composition according to clause 58, wherein the lubricant or binder is selected from one or more of the group consisting of alumina, graphite, guar gum, sesbania gum powder, calcium aluminate cement or a clay (e.g. bentonite). 60. A pre-catalyst composition according to clause 58 or 59, wherein the lubricant or binder is present in the pre-catalyst composition in an amount of about 0.1 % to about 50 % (w / w), suitably about 0.1 % to about 40 % (w / w), or about 0.1 % to about 30 % (w / w), or about 0.1 % to about 20 % (w / w). 61. A pre-catalyst composition according to any one of clauses 39 to 60, which does not comprise chromium. 62. A shaped composition comprising a pre-catalyst composition according to any one of clauses 39 to 61. 63. A shaped composition according to clause 62, wherein the shaped composition is in the form of a pellet, a tablet or extruded strip. 64. A shaped composition according to clause 62 or 63, wherein, the shaped composition has maximum and minimum dimensions in the range about 0.5 to about 25 mm, suitably about 0.5 to about 20 mm. 65. A method for producing a composition comprising carbon monoxide, wherein said method comprises contacting a feed gas composition comprising carbon dioxide and hydrogen with a pre-catalyst composition according to any one of clauses 39 to 61, or a shaped composition according to any one of clauses 62 to 64, at a temperature of at least 400°C. 66. A method according to clause 65, wherein the feed gas composition is contacted with the pre-catalyst composition or catalyst composition at a temperature of about 450°C to about 650°C. 67. A method according to clause 65 or 66, wherein the feed gas composition is contacted with the pre-catalyst composition or catalyst composition at a pressure of about 100 KPa to about 300 KPa. 68. A method according to clause 65 to 67, wherein the feed gas composition comprises a hydrogen to carbon dioxide ratio of about 1:1 to about 5:1. The invention will further be described by the following numbered paragraphs:1. A method for preparing a pre-catalyst composition comprising: (i) combining an iron salt or hydrate thereof; at least one further metal species selected from one or more of the group consisting of a cerium salt or hydrate thereof, a cerium oxide or hydrate thereof, an aluminium salt or hydrate thereof, an aluminium oxide or hydrate thereof, a titanium salt or hydrate thereof and a titanium oxide or a hydrate thereof; and an organic compound comprising one or more functional groups selected from the group consisting of a carboxyl, hydroxyl, amido and amino group; and (ii) subjecting the product of (i) to calcination to provide a pre-catalyst composition. 2. A method for preparing a pre-catalyst composition according to paragraph 1, comprising: (i)(a) (i) combining an iron salt or hydrate thereof; at least one further metal species selected from one or more of the group consisting of a cerium salt or hydrate thereof, a cerium oxide or hydrate thereof, an aluminium salt or hydrate thereof, an aluminium oxide or hydrate thereof, a titanium salt or hydrate thereof and a titanium oxide or a hydrate thereof; and an organic compound comprising one or more functional groups selected from the group consisting of a carboxyl, hydroxyl, amido and amino group; and water to provide an aqueous solution or mixture; (i)(b) drying the aqueous solution or mixture of (i)(a) to provide a dried material or slurry; (ii) subjecting the dried material or slurry of (i)(b) to calcination to provide a pre- catalyst composition. 3. A method according to paragraph 1 or 2, wherein the at least one further metal species of step (i) is: (a) a cerium salt or hydrate thereof; or (b) a titanium oxide or hydrate; or (c) an aluminium salt or hydrate thereof. 4. A method according to any one of paragraphs 1 to 3, wherein at least two further metal species are combined with the iron salt or hydrate thereof in step (i) selected from the group consisting of a cerium salt or hydrate thereof, an aluminium salt or hydrate thereof and a titanium oxide or hydrate thereof.5. A method according to paragraph 4, wherein the at least two further metal species of step (i) is: (a) a cerium salt or hydrate thereof and an aluminium salt or hydrate thereof; or (b) a cerium salt or hydrate thereof and a titanium oxide or hydrate thereof; or (c) an aluminium or hydrate thereof and a titanium oxide or hydrate thereof. 6. A method according to any one of paragraphs 1 to 3, wherein at least three further metal species are combined with the iron salt or hydrate thereof in step (i) which are a cerium salt or hydrate thereof, a titanium oxide or hydrate thereof and an aluminium salt or hydrate thereof. 7. A method according to any one of the preceding paragraphs, wherein step (i) further comprises combining one or more of an alkali metal species, an alkaline earth metal species and a rare earth metal species. 8. A method according to any one of the preceding paragraphs, wherein step (i) further comprises combining one or more of an alkali metal species selected from an alkali metal salt or hydrate thereof. 9. A method according to paragraph 8, wherein the alkali metal salt or hydrate thereof is selected from potassium nitrate, potassium carbonate, sodium nitrate, sodium carbonate, lithium carbonate and cesium carbonate, or a hydrate thereof. 10. A method according to any one of the preceding paragraphs, wherein the iron salt or hydrate of step (i) is an iron nitrate, suitably selected from one or more of Fe(NO3)2 and Fe(NO3)3 or a hydrate thereof. 11. A method according to any one of the preceding paragraphs, wherein the proportion of iron salt or hydrate thereof and each further metal species, selected from one or more of the group consisting of cerium salt or hydrate thereof, a cerium oxide or hydrate thereof, an aluminium salt or hydrate thereof, an aluminium oxide or hydrate thereof, a titanium salt or hydrate thereof and a titanium oxide or a hydrate thereof, is such that the molar ratio of iron salt or hydrate to cerium, aluminium or titanium salt, oxide or hydrate thereof is about 2:1 to about 1:2, suitably about 1:1.12. A method according to any one of the preceding paragraphs, wherein the organic compound comprises two or more functional groups selected from a carboxyl, hydroxyl, amido and amino groups. 13. A method according to any one of the preceding paragraphs, wherein the organic compound is a C4to C12carboxylic acid or urea. 14. A method according to any one of the preceding paragraphs, wherein the organic compound is citric acid. 15. A method according to any one of paragraphs 1 to 3, wherein step (i) comprises combining an iron (II) or (III) salt or hydrate thereof, a cerium (III) salt or hydrate thereof, an alkali metal salt or hydrate thereof; an organic compound selected from a C4 to C12 carboxylic acid (suitably citric acid) or urea; and water. 16. A method according to any one of paragraphs 1 to 3, wherein step (i) comprises combining an iron (II) or (III) salt or hydrate thereof, a titanium (IV) oxide or hydrate thereof, an alkali metal salt or hydrate thereof; an organic compound selected from a C4 to C12 carboxylic acid (suitably citric acid) or urea; and water. 17. A method according to paragraph 15 or 16, wherein step (i) further comprises combining an aluminium (III) salt or hydrate thereof. 18. A method according to any one of the preceding paragraphs, wherein step (i) further comprises combining a transition metal species selected from one or more of a zinc salt or hydrate thereof, a zinc oxide or hydrate thereof, a manganese salt or hydrate thereof, a manganese oxide or hydrate thereof, a zirconium salt or hydrate thereof, a zirconium oxide or hydrate thereof, a cobalt salt or hydrate thereof, a cobalt oxide or hydrate thereof, a copper salt or hydrate thereof and a copper oxide or hydrate thereof. 19. A method according to paragraph 18, wherein step (i) further comprises combining a transition metal species selected from one or more of a zinc salt or hydrate thereof, a manganese salt or hydrate thereof and a zirconium salt or hydrate thereof. 20. A method according to any one of the preceding paragraphs, with the proviso that the method does not comprise the use of a chromium species in any step. 21. A method according to any one of the preceding paragraphs, wherein the calcination step is performed at a temperature of between about 400°C to about 1000°C.22. A pre-catalyst composition obtained or obtainable according to the method of any one of paragraphs 1 to 21. 23. A method for preparing a catalyst composition comprising: (a) providing a pre-catalyst composition according to paragraph 22; (b) optionally subjecting said pre-catalyst composition to calcination; and (c) activating said pre-catalyst composition to obtain a catalyst composition. 24. A catalyst composition obtained or obtainable according to the method of paragraph 23. 25. A method for producing a composition comprising carbon monoxide, wherein said method comprises contacting a feed gas composition comprising carbon dioxide and hydrogen with a pre-catalyst composition according to paragraph 22, or a catalyst composition according to paragraph 24, at a temperature of at least 400°C. 26. A method according to paragraph 25, wherein the feed gas composition is contacted with the pre-catalyst composition or catalyst composition at a temperature of about 450°C to about 650°C. 27. A method according to paragraph 25 or 26, wherein the feed gas composition is contacted with the pre-catalyst composition or catalyst composition at a pressure of about 100 KPa to about 300 KPa. EXAMPLES

[0342] The following examples are merely illustrative of the presently disclosed subject matter and they should not be considered as limiting the scope of the subject matter in any way. I. Preparation of the pre-catalyst compositions

[0343] The pre-catalyst compositions were prepared using an organic combustion method. Citric acid was used as the organic combustion fuel, the iron (III) nitrate, cerium(III) nitrate, zinc nitrate, manganese (II) nitrate, cobalt nitrate, aluminium nitrate, zirconium (IV) oxynitrate, copper (II) nitrate, titanium (IV) oxide, sodium carbonate, cesium carbonate and potassium carbonate were used as metal sources for the various pre-catalysts.

[0344] For example, a Fe-Ce-Al-K pre-catalyst with a molar ratio of 100:100:80:5 was prepared from citric acid (6.9g, 99%, Acros Organics), iron (III) nitrate nonahydrate (5.0g, 98%, Sigma-Aldrich Alfa Aesar), cerium (III) nitrate hexahydrate (5.4g, 99.5%, Thermo Scientific), aluminium nitrate nonahydrate (3.7g, 98%, Thermo Scientific), potassium carbonate (0.09g, Fisher Chemical). The molar ratio of citric acid:metal precursors is 1:1 and the weight ratio of (metal precursors + citric acid):water is 2:1. The metal precursors, citric acid and water were mixed in a beaker. This initial mixture was stirred overnight to form a homogeneous aqueous solution and heated at 80°C until a citric acid-based slurry or viscous paste was obtained. The obtained dried material was heated at 5°C / minute to 700°C and maintained for 6 hours to produce a carbon-free powder.

[0345] Pre-catalysts with varying transition metal (e.g. Zn, Co, Zr, Cu and Mn etc.) and alkali metal (e.g. K, Na, Cs) promoters were also prepared using the same method.

[0346] The above described method yielded pre-catalyst compositions 1 to 52 (see Table 1a, below). Table 1a Sample Composition Example No. Precursor Components Molar ratio 1 Fe-Ce 100:10 2 Fe-Ce 100:20 3 Fe-Ce 100:40 4 Fe-Ce 100:60 5 Fe-Ce 100:80 6 Fe-Ce 100:100 7 Fe-Ce 100:110 8 Fe-Ce 100:125 9 Fe-Ce 100:150 10 Fe-Ce 100:250 11 Fe-Ce-K 100:100:5 12 Fe-Cu-Ce 100:5:100 13 Fe-Cu-Ce 100:40:100 14 Fe-Cu-Ce 100:60:100 15 Fe-Cu-Ce 100:80:100 16 Fe-Cu-Ce 100:100:100Sample Composition Example No. Precursor Components Molar ratio 17 Fe-Ce-K-Zn 100:5:80:5 18 Fe-Ce-K-Zn 100:10:80:5 19 Fe-Ce-K-Zn 100:100:5:40 20 Fe-Ce-K-Zn 100:100:5:80 21 Fe-Ce-K-Zn 100:100:5:100 22 Fe-Ce-K-Mn 100:100:5:100 23 Fe-Ce-K-Mn 100:100:5:50 24 Fe-Ce-K-Co 100:100:5:5 25 Fe-Ce-K-Co 100:100:5:10 26 Fe-Ce-K-Co 100:100:5:20 27 Fe-Ce-K-Zr 100:100:5:5 28 Fe-Ce-K-Zr 100:100:5:10 29 Fe-Ce-K-Zr 100:100:5:20 30 Fe-Ce-K-Zr-Cu 100:100:5:40:100 31 Fe-Ce-K-Zr 100:100:5:60 32 Fe-Ce-K-Zr 100:100:5:80 33 Fe-Ce-K-Zr 100:100:5:100 34 Fe-K-Al 100:5:100 35 Fe-Ce-K-Al 100:100:5:100 36 Fe-Ce-K-Al 100:100:5:80 37 Fe-Ti-K 100:100:5 38 Fe-Ce-Ti-K 100:100:100:5 39 Fe-Ti-Mn-K 100:100:100:5 40 Fe-Ti-Al-K 100:100:100:5 41 Fe-Ti-Ce-Al-K 100:100:100:100:5 42 Fe-Ti-K 100:50:5 43 Fe-Ti-Zr-K 100:100:80:5 44 Fe-Ti-Zr-K 100:100:100:5 45 Fe-Ti-Zn-K 100:100:60:5 46 Fe-Ti-Zn-K 100:100:80:5 47 Fe-Ti-Zn-K 100:100:100:5 48 Fe-Ce-Al 100:100:80 49 Fe-Ce-Al-K 100:100:80:2.5 50 Fe-Ce-Al-K 100:100:80:1 51 Fe-Ce-Al-Na 100:100:80:5Sample Composition Example No. Precursor Components Molar ratio 52 Fe-Ce-Al-Cs 100:100:80:5

[0347] The above described method was also used to prepare pre-catalyst compositions 53 to 56 (see Table 1b, below), however, in place of citric acid the organic compound indicated against each example was used such that the molar ratio of organic :metal precursors is 1:1 and the weight ratio of (metal precursors + organic compound):water is 2:1. Table 1b Sample Composition Example No. Precursor Organic Compound Components Molar ratio 53 Fe-Ce-Al-K 100:100:80:5 EDTA 54 Fe-Ce-Al-K 100:100:80:5 Ascorbic acid 55 Fe-Ce-Al-K 100:100:80:5 NTA 56 Fe-Ce-Al-K 100:100:80:5 Malic acid II. Reverse water gas shift reaction with catalysts obtained from pre-catalysts 1 to 56

[0348] RWGS experiments were carried out in a stainless-steel fixed bed reactor with an inner diameter of 1.0 cm with a typical 1.2 g pre-catalyst and 4.8 g SiC load. A feed gas mixture with a H2 to CO2 ratio of 3.5:1 and N2 (as an internal standard gas) is used at a GHSV (gas hourly space velocity) of 2500 mL / (g∙h).

[0349] Pre-catalyst activation was performed in situ using the feed gas. The reactor was heated at 5°C / min up to 600 °C under atmospheric pressure. The catalyst was reacted with the CO2 / H2 gas mixture at a temperature of about 600°C and GHSV of 2500 mL / (g∙h) at atmospheric pressure unless otherwise stated. The exit gas was analysed using an online Gas Chromatograph (Agilent 8890 GC) with flame ionization (FID) and thermal conductivity detectors (TCD).

[0350] The effects of various catalysts were evaluated and the performance results are provided below.

[0351] In Table 2, the data was collected at a temperature of 600 ⁰C, H2:CO2=3:1, GHSV 2500mL / (g•h), atmospheric pressure and different ratios of iron and cerium precursors were assessed. At an Fe:Ce ratio of 1:1, the average CO2conversion and CO selectivity reach 57.92% and 100%, respectively. Table 2 Example No. Sample CO2 CO CH49 Fe-Ce 100:150 54.80 100.00 0.00 10 Fe-Ce 100:250 51.02 100.00 0.00

[0352] The effect of alkali metal promotors on the catalyst performance is shown in Table 3. The data was collected at a temperature of 600 ⁰C, H2:CO2=3:1, GHSV 2500mL / (g•h), atmospheric pressure. It can be seen from Table 3, when potassium is added as promoter an enhancement in CO2 conversion (58.46%) and CO selectivity (100 %) is observed. Table 3 Example Sample Composition CO2 CO CH411 Fe-Ce-K 100:100:5 58.46 100.00 0.00

[0353] The effect of including further transition metals (Cu, Zn, Co, Mn) in the pre- catalyst of Example 11 was investigated. Table 4 displays the assessment results for the containing iron, copper, and cerium. The data was collected at a temperature of 600 ⁰C, H2:CO2=3:1, GHSV 2500mL / (g•h), atmospheric pressure Table 4 Example CO2 CO CH4 No. conversion selectivity selectivity 12 54.72 99.73 0.27 1354.44 99.08 0.92Example Sample Composition CO2CO CH4

[0354] Table 5 displays the assessment of catalysts containing iron, cerium, and zinc or manganese. The data was collected at a temperature of 600 ⁰C, H2:CO2=3:1, GHSV 2500mL / (g•h), atmospheric pressure. Table 5 Example Sample Composition CO2CO CH4conversion selectivity selectivity 17 Fe-Ce-K-Zn 100:5:80:5 54.34 100.00 0.00 18 Fe-Ce-K-Zn 100:10:80:5 54.24 100.00 0.00 19 Fe-Ce-K-Zn 100:100:5:40 59.49 100.00 0.00 20 Fe-Ce-K-Zn 100:100:5:80 60.18 100.00 0.00 21 Fe-Ce-K-Zn 100:100:5:100 59.87 100.00 0.00 22 Fe-Ce-K-Mn 100:100:5:100 58.64 100.00 0.00 23 Fe-Ce-K-Mn 100:100:5:50 57.55 100.00 0.00

[0355] Table 6 presents the evaluation results of doping cobalt in the Fe:Ce:K (100:100:5) pre-catalyst of Example 11. The data was collected at a temperature of 600 ⁰C, H2:CO2=3:1, GHSV 2500mL / (g•h), atmospheric pressure. Table 6 Example Sample Composition CO2 CO CH4conversion selectivity selectivity 24 Fe-Ce-K-Co 100:100:5:5 56.12 99.92 0.08 25 Fe-Ce-K-Co 100:100:5:10 56.95 99.80 0.20 26 Fe-Ce-K-Co 100:100:5:20 58.16 99.83 0.17

[0356] Table 7 presents the evaluation results of doping zirconium in the Fe:Ce:K (100:100:5) pre-catalyst of Example 11. The data was collected at a temperature of 600 ⁰C, H2:CO2=3:1, GHSV 2500mL / (g•h), atmospheric pressure.

[0357] As the molar ratio of zirconium increases, CO2conversion improves, achieving a rate of 60%. Table 7Example Sample Composition CO2CO CH4No. conversion selectivity selectivity 27 Fe-Ce-K-Zr 100:100:5:5 55.45 100.00 0.00 28 Fe-Ce-K-Zr 100:100:5:10 56.61 100.00 0.00 29 Fe-Ce-K-Zr 100:100:5:20 57.97 100.00 0.00 30 Fe-Ce-K-Zr-Cu 100:100:5:40:100 59.06 99.89 0.11 31 Fe-Ce-K-Zr 100:100:5:60 57.16 100.00 0.00 32 Fe-Ce-K-Zr 100:100:5:80 59.71 100.00 0.00 33 Fe-Ce-K-Zr 100:100:5:100 60.03 100.00 0.00

[0358] The findings for catalysts utilizing iron and aluminium are presented in Table 8. The data was collected at a temperature of 600 ⁰C, H2:CO2=3:1, GHSV 2500mL / (g•h) and atmospheric pressure.

[0359] All catalysts exhibited excellent characteristics. In particular, Fe-Ce-K-Al catalysts exhibited CO2conversion rates exceeding 60% and a 100% CO selectivity. Table 8

[0360] Table 9 presents the evaluation results of the catalysts based on Iron and Titanium. The data was collected at a temperature of 600 ⁰C, H2:CO2=3:1, GHSV 2500mL / (g•h), atmospheric pressure.

[0361] It is evident that the Fe-Ti-K (100:100:5) catalyst achieves a CO2conversion rate of over 61% and a 100% CO selectivity. Table 9 Example Sample Composition CO2CO CH441 Fe-Ti-Ce-Al-K 100:100:100:100:5 57.30 100.00 0.00

[0362] Table 10 evaluates catalysts based on Iron and Titanium. The data was collected at a temperature of 600 ⁰C, H2:CO2=3:1, GHSV 2500mL / (g•h), atmospheric pressure. Example Sample Composition CO2CO CH4No. conversion selectivity selectivity 42 Fe-Ti-K 100:50:5 60.84 100.00 0.00 43 Fe-Ti-Zr-K 100:100:80:5 58.49 100.00 0.00 44 Fe-Ti-Zr-K 100:100:100:5 58.12 100.00 0.00 45 Fe-Ti-Zn-K 100:100:60:5 57.96 100.00 0.00 46 Fe-Ti-Zn-K 100:100:80:5 58.19 100.00 0.00 47 Fe-Ti-Zn-K 100:100:100:5 58.35 100.00 0.00

[0363] Table 11 evaluates the performance of catalysts with different contents of potassium or with sodium and caesium instead of potassium. The data was collected at a temperature of 600 ⁰C, H2:CO2=3:1, GHSV 2500mL / (g•h), atmospheric pressure. Example Sample Composition CO2CO CH4conversion selectivity selectivity 48 Fe-Ce-Al 100:100:80 58.35 100.00 0.00 49 Fe-Ce-Al-K 100:100:80:2.5 58.10 100.00 0.00 50 Fe-Ce-Al-K 100:100:80:1 57.94 100.00 0.00 51 Fe-Ce-Al-Na 100:100:80:5 59.20 100.00 0.00 52 Fe-Ce-Al-Cs 100:100:80:5 59.64 100.00 0.00

[0364] Table 12 evaluates the performance of catalysts prepared with different organic compounds. The data was collected at a temperature of 600 ⁰C, H2:CO2=3:1, GHSV 2500mL / (g•h), atmospheric pressure. Example Sample Composition CO2CO CH4No. conversion selectivity selectivity 53 Fe-Ce-Al-K 59.60 100.00 0.00 (prep’d with EDTA)54 Fe-Ce-Al-K 58.57 100.00 0.00 (prep’d with ascorbic 100:100:80:5III. Catalyst stability test

[0365] Catalyst stability test was carried out in a stainless-steel fixed bed reactor with an inner diameter of 1.0 cm with a 1.2 g prepared Fe-Ce-Al-K pre-catalyst (100:100:80:5) and 9.8 g SiC load. A feed gas mixture with a H2to CO2ratio of 3:1 and N2(as an internal standard gas).

[0366] Pre-catalyst activation was performed in situ using the feed gas. The reactor was heated at 2°C / min up to 600 °C under atmospheric pressure. The catalyst was reacted with the CO2 / H2 gas mixture at a temperature of 600°C, atmospheric pressure, and the GHSV (gas hourly space velocity) range from 2500 mL / (g∙h) to 25000 mL / (g∙h). The exit gas was analysed using an online Gas Chromatograph (Agilent 8890 GC) with flame ionization (FID) and thermal conductivity detectors (TCD).

[0367] The CO2 conversion and products selectivity were showed in Figure 1. Both CO2 conversion and products selectivity showed high stability over the reaction conditions, even with fluctuation of the GHSV; the CO2 conversion was maintained at about 60%, with practically no methane formation. IV. Catalyst Characterisation

[0368] The powder X-ray diffraction (XRD) analyses of catalysts used a Cu Kα (0.154056 nm) X-ray source (25 kV, 40 mA) on a Bruker D8 Advance diffractometer. Diffraction patterns were recorded over a 10-80° 2θ angular range using a step size of 0.02 °. Crystallite sizes were determined using the Scherrer equation.

[0369] The powder X-ray diffraction (XRD) spectrum of various pre-catalysts compositions is presented in Figure 2.

[0370] All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference in their entirety and to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein (to the maximum extent permitted by law).

[0371] All headings and sub-headings are used herein for convenience only and should not be construed as limiting the invention in any way.

[0372] The use of any and all examples, or exemplary language (e.g., "such as") provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise paragraphed. No language in thespecification should be construed as indicating any non-paragraphed element as essential to the practice of the invention.

[0373] The citation and incorporation of patent documents herein is done for convenience only and does not reflect any view of the validity, patentability, and / or enforceability of such patent documents.

[0374] This invention includes all modifications and equivalents of the subject matter recited in the paragraphs appended hereto as permitted by applicable law.

Claims

CLAIMS 1. A method for producing a composition comprising carbon monoxide, wherein said method comprises contacting a feed gas composition comprising carbon dioxide and hydrogen with a pre-catalyst composition or catalyst obtainable therefrom at a temperature of at least 400°C, wherein the pre-catalyst composition comprises iron or one or more oxide thereof and cerium or one or more oxide thereof.

2. A method according to claim 1, wherein the pre-catalyst composition comprises one or more further metal or an oxide thereof.

3. A method according to claim 1 or 2, wherein the further metal or an oxide thereof is selected from one or more of the group consisting of aluminium, titanium, copper, zinc, manganese, cobalt, zirconium, or an oxide thereof.

4. A method according to any one of claims 1 to 3, wherein the further metal or an oxide thereof is selected from one or more of aluminium and titanium.

5. A method according to any one of claims 1 to 4, wherein the pre-catalyst composition comprises: ^ iron or one or more oxide thereof, cerium or one or more oxide thereof and aluminum or one or more oxide thereof; ^ iron or one or more oxide thereof, cerium or one or more oxide thereof and zirconium or one or more oxide thereof; ^ iron or one or more oxide thereof, cerium or one or more oxide thereof and titanium or one or more oxide thereof; ^ iron or one or more oxide thereof, cerium or one or more oxide thereof, aluminum or one or more oxide thereof, and titanium or one or more oxide thereof; ^ iron or one or more oxide thereof, cerium or one or more oxide thereof and zinc or one or more oxide thereof; or ^ iron or one or more oxide thereof, cerium or one or more oxide thereof and manganese or one or more oxide thereof.

6. A method according to any one of claims 1 to 4, wherein the pre-catalyst composition comprises iron or one or more oxide thereof, cerium or one or more oxide thereof and aluminum or one or more oxide thereof.

7. A method according to any one of claims 1 to 6, wherein the pre-catalyst composition further comprises an alkali metal or one or more oxides thereof, an alkaline earth metal or one or more oxides thereof, or a rare earth metal or one or more oxides thereof.

8. A method according to any one of claims 1 to 7, wherein the pre-catalyst composition further comprises an alkali metal or one or more oxides thereof.

9. A method according to claim 8, wherein the alkali metal is sodium or potassium.

10. A method according to any one of claims 1 to 7, wherein the pre-catalyst composition further comprises an alkaline earth metal or one or more oxides thereof.

11. A method according to claim 10, wherein the alkaline earth metal is selected from magnesium and calcium.

12. A method according to any one of claims 1 to 7, wherein the pre-catalyst composition further comprises a rare earth metal or one or more oxides thereof.

13. A method according to claim 12, wherein the rare earth metal is selected from the group consisting of yttrium, lanthanum, cerium, praseodymium and erbium.

14. A method according to any one of claims 1 to 9, wherein the pre-catalyst composition comprises: ^ iron or one or more oxide thereof, cerium or one or more oxide thereof, aluminum or one or more oxide thereof and potassium or one or more oxide thereof; ^ iron or one or more oxide thereof, cerium or one or more oxide thereof and potassium or one or more oxide thereof; ^ iron or one or more oxide thereof, cerium or one or more oxide thereof, zirconium or one or more oxide thereof, and potassium or one or more oxide thereof; ^ iron or one or more oxide thereof, cerium or one or more oxide thereof, titanium or one or more oxide thereof and potassium or one or more oxide thereof; or ^ iron or one or more oxide thereof, cerium or one or more oxide thereof, aluminum or one or more oxide thereof, titanium or one or more oxide thereof, and potassium or one or more oxide thereof.

15. A method according to any one of claims 1 to 9, wherein the pre-catalyst composition comprises wherein the pre-catalyst composition comprises iron or one or more oxide thereof,cerium or one or more oxide thereof, aluminum or one or more oxide thereof and potassium or one or more oxide thereof.

16. A method according to claim 15, wherein the molar ratio of iron:cerium:potassium: aluminium is about 100:100:5:

100.

17. A method according to any to one of claims 1 to 16, wherein the pre-catalyst composition further comprises a binder or lubricant.

18. A method according to any to one of claims 1 to 17, wherein the pre-catalyst composition does not comprise chromium.

19. A method according to any one of claims 1 to 18, wherein the feed gas composition is contacted with the pre-catalyst composition or catalyst composition at a temperature of about 450°C to about 650°C.

20. A method according to any one of claims 1 to 19, wherein the feed gas composition is contacted with the pre-catalyst composition or catalyst composition at a pressure of about 100 KPa to about 300 KPa.

21. A method according to any one of claims 1 to 20, wherein the feed gas composition comprises carbon dioxide and hydrogen in a molar ratio of molar ratio of H2:CO2 in the feed gas composition is about 1:1 to about 3:

1.

22. A method according to any one of claims 1 to 21, wherein the method has a methane selectivity of about about 0.05 vol. % or less.

23. A method according to any one of claims 1 to 22, wherein the method has a carbon dioxide conversion of at least about 50%.

24. A method according to any one of claims 1 to 23, wherein the method has a carbon monoxide selectivity of at least about 99%.

25. A method according to any one of claims 1 to 24, wherein the catalyst is obtainable or obtained by reduction of the pre-catalyst in situ by the feed gas composition.

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