Metal oxides perovskite for the production of hydrogen

Abstract

A combination of a first metal oxide and a second metal oxide, wherein the second metal oxide is a mixed ionic-electronic conductor.

Description

[0001]Materials Technical Field The invention relates to combinations, vessels, uses and processes. The combinations, vessels, uses and processes are particularly useful for the production of hydrogen and / or carbon dioxide. Background of Invention Conventional hydrogen production systems usually fall into one of the following categories: electrolysis of water, high temperature water splitting, photobiological water splitting, photoelectrochemical water splitting, fermentation of carbohydrate feedstocks and natural gas reforming. Each of these systems is energy intensive and as such to ensure a return on investment, the resulting hydrogen must be priced accordingly (making it an expensive component in some industries). Furthermore, systems that produce hydrogen are usually large (to ensure scale and thus reduce costs as much as possible) and are therefore situated in geographical locations that are not necessarily near to the end consumers. This results in the produced hydrogen needing to be transported (often over vast distances) to industrial consumers or into a local gas network. A separate industry has evolved to manage this distribution and has its own associated drawbacks (for example, hydrogen is often transported in compressed liquid form using haulage vehicles which produce harmful emissions). Conventional carbon dioxide productions systems usually work either by steam reforming methane or by adsorbing carbon dioxide from gas streams. When using a steam reforming of methane process, the process produces hydrogen as well as carbon monoxide (which can be converted to carbon dioxide via a water-gas shift reaction). However, because the availability and pricing of methane is heavily dependent on economic factors, it is often not cost effective to produce carbon dioxide using these methods (which results in carbon dioxide shortages or drastically increased costs). Furthermore, conventional carbon dioxide production systems often need to be situated in geographical locations that are not necessarily near to the end consumers which results in the need for the carbon dioxide to be liquified and transported over vast distances. In some industries hydrogen or carbon dioxide is produced as a by-product of an industrial process or is present in an output stream (such as an output from a vacuum furnace). Usually, this fluid is treated as a waste product and the most economical solution is to dispose of it. For example, in industries that rely on vacuum furnaces, hydrogen and carbon dioxide are often present in the output gas stream. When hydrogen and / or carbon dioxide is in an output gas stream or is considered to be a waste product, it is usually combined with other low value gas streams and sent to a facility that deals specifically with disposing of this gas. Such facilities are usually located far away from the source of the waste gases and are primarily aimed at disposing of the gas at low cost. Alternatively, when a given industrial plant has its own on-site waste product-processing facility, it is an integral part of the plant (usually designed and built when the plant is built). Such wate product-processing facilities are difficult and expensive to retro fit to existing industrial facilities. Summary of Invention The invention relates to combinations, vessels, uses and processes. The combinations, vessels, uses and processes are particularly useful for the production of hydrogen and / or carbon dioxide. The inventors have developed combinations, vessels, uses and processes that are specifically designed to be particularly useful in industries that produce carbon containing fluid streams and / or hydrogen containing fluid streams. For example, some industries produce these fluids as by-products or they are part of their output streams (usually in low amounts). However, the inventors have identified that these conventional systems result in the disposal of the carbon or hydrogen containing components. As such, the systems described herein have been developed so that they are particularly useful to such industries. The present invention is based on the discovery that it is not feasible for many industries to convert low value carbon containing and / or hydrogen containing fluids into high value fluids. Whilst it is known that some carbon containing and / or hydrogen containing fluids can be converted into other fluids (for example by using conventional metal oxide chemical looping reactions), these systems have not been used in industry as their output is low value and therefore it is not feasible for industries to do so. It is also difficult to implement such systems / processes in many industries because they require high temperatures and pressures to produce any high value fluids. As such, the low value carbon containing and / or hydrogen containing fluids produced in industry are discarded (for example, they may be flared off). In contrast, the inventors have identified that it is possible to convert low value carbon containing and / or hydrogen containing fluids into high value fluids using the combinations, vessels, uses and processes described herein. Specifically, the combinations, vessels, uses and processes described herein are able to covert low value carbon containing and / or hydrogen containing fluids into high value fluids (such as food grade carbon dioxide or high purity hydrogen). More importantly, the combinations, vessels, uses and processes described herein are able to produce high value fluids under conditions that allow them to be used in many industries. This is because they can be used at much lower temperatures and pressures than conventional systems and as such are easier to implement “on-site”. That is, they may be deployed in a specific facility and convert the low value carbon containing and / or hydrogen containing fluids to high value fluids (without the need for large and expensive scrubbing apparatus or disposing apparatus). Other features and advantages of the invention are described throughout the specification. In particular, the present combinations, vessels, uses and processes are able to process very low concentration fluid streams. This again means that they can be implemented “on-site”, i.e. where the low concentration fluid streams are being produced. Implementing “on-site” has many advantages. For example, it is possible to retrofit a facility such that it can make use of fluids that conventionally would be discarded. Furthermore, it is no longer necessary to “concentrate up” low concentration “waste” fluid streams for disposal as they can be directly processed by the present invention. As such, the present combinations, vessels, uses and processes represent a significant improvement on conventional counterparts used in these industries. In a first aspect, the invention relates to a combination of a first metal oxide and a second metal oxide, wherein the second metal oxide is a mixed ionic-electronic conductor, the first metal oxide comprises a metal (M) and oxygen, and the first metal oxide’s change in standard Gibbs energy (in J / mol O2) for the reaction: ^^^^+ ^^= ^^^^^^wherein x is from 0.1 to 5, and y is from 0 to 5; is bounded by: 25.7T − 488470 < ΔG^^^^ < 178.9^ − 488470 for T being from 300 K to 1000 K. The inventors have found that the combination of the above described first metal oxide and second metal oxide are able to produce high value fluids at surprisingly lower temperatures and pressures than conventional systems. Additionally, these combinations are able to produce such high value fluids from very low concentration fluid streams which may include additional impurities. As shown in the examples section, the combinations described herein are able to produce carbon dioxide and / or water from low value “waste” fluid streams by contacting a first fluid with said combinations (thereby producing a second fluid). Additionally, by converting a first fluid into a second fluid, the state of the combination is changed so that it is capable of splitting water. For example, a metal oxide may be reduced by the first fluid to form a reduced metal oxide. By contacting the reduced material with a fluid comprising water, high value hydrogen may be produced. Figure 2 shows the general Ellingham diagram for the metal oxide oxidation and reduction reaction: Lines of constant log%^^"-$".$ / ^ bound a desired property of a metal oxide is the ratio of hydrogen to steam at chemical equilibrium with a metal oxide for the reaction: 20^+ ^^^= 20^^ + ^ (2) The feasible region for a metal oxide phase transition is shown in the shaded area. As an example, the oxidization and reduction between Fe and FeO (wustite) falls within the feasible region. The corresponding equilibrium oxygen fugacities are indicated, defined by the Δ^ = ^^^ !"#$%&'(). Metal phase transitions above the bound region could produce a large amount of hydrogen from water (steam) in the reverse of (2). However, in the forward reaction of (2) the oxide cannot be easily reduced by waste fluid streams and a large amount of unconverted hydrogen (and carbon monoxide) may be forced to pass through the reactor. Metal phase transitions above the bound region would produce only a small amount of hydrogen from steam in the reverse of (2). In some embodiments, the first metal oxide’s change in standard Gibbs energy (in J / mol O2) for the reaction: ^^^^+ ^^= ^^^^^^is bounded by: 64.0^ − 488470 < ΔG^^^^ < 140.6T − 488470 for T being from 300 K to 1000 K. In some embodiments, the metal of the first metal oxide is selected from the group consisting of transition metals, lanthanides, p-block metals, s-block metals and mixtures thereof. In some embodiments, the transition metal is selected from the group consisting of iron, manganese, cobalt, molybdenum, tungsten, and mixtures thereof. In some embodiments, the first metal oxide comprises iron. In some embodiments, the first metal oxide is selected from the group consisting of Fe2O3, Fe3O4, FeO, and mixtures thereof. In some embodiments, the second metal oxide is a perovskite type metal oxide at standard temperature and pressure. In some embodiments, the second metal oxide has the formula ABX3-δ, wherein A is one or more metals; B is one or more metals; X is oxygen; and δ is from 0 to 0.5. In some embodiments, A is selected from the group consisting of transition metals, lanthanides, actinides, p-block metals, s-block metals and mixtures thereof; and / or B is selected from the group consisting of transition metals, lanthanides, actinides, p-block metals, s-block metals and mixtures thereof. In some embodiments, A is A1xA2(1-x), and wherein A1and A2are each independently the same as described for A. In some embodiments, A is independently selected from the group consisting of La, Sr, Gd, Ca, Ce, K, Y, and mixtures thereof. In some embodiments, B is , wherein B1and B2are each independently the same as described for B. In some embodiments, B is independently selected from the group consisting of Fe, Mn, Cu, Ce, Co, Ti, Ni, and mixtures thereof. In some embodiments, the second metal oxide has the formula SrFeO3-δ, LaFeO3-δ, δ, may be any value from 0.01 to 0.99, such as 0.05 to 0.95. For example, x is 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, or 0.95. Preferably, x is 0.25, 0.4, 0.5, 0.6, 0.75, or 0.95. In some embodiments, the combination comprises from about 5 wt.% to about 95 wt.% of the first metal oxide; and / or from about 5 wt.% to about 95 wt.% of the second metal oxide. In some embodiments, the combination comprises a third component which comprises at least one promoter. In some embodiments, the third component is a metal oxide, a metal, or a compound. In some embodiments, the at least one promoter is selected from the group of alkali metals, alkali earth metals, and mixtures thereof. In some embodiments, the at least one promoter is selected from the group of K, Na, Cs, Rb, Li and mixtures thereof. In some embodiments, the combination comprises a catalytic amount of the third component. Preferably, the first metal oxide is Fe2O3, Fe3O4, or FeO, the second metal oxide has the formula SrxLa(1-x)FeO3-δ, SrFeO3-δor LaFeO3-δ, and the third component is a metal oxide or combination of metal oxides wherein each metal of each (third component) metal oxide is independently selected from the group consisting of K, Na, Ag, Cs, Rb, Li and mixtures thereof. Preferably, each metal of each (third component) metal oxide is independently selected from the group consisting of K, Na, Rb, Ag, and Cs. X may be any value from 0.01 to 0.99, such as 0.05 to 0.95. For example, x is 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, or 0.95. Preferably, x is 0.25, 0.4, 0.5, 0.6, 0.75, or 0.95. More preferably, the first metal oxide is Fe2O3, Fe3O4, or FeO, the second metal oxide has the formula SrxLa(1-x)FeO3-δ, SrFeO3-δ or LaFeO3-δ, and the third component is a metal oxide or combination of metal oxides wherein each (third component) metal oxide is independently selected from the group consisting of K2O, Na2O, Cs2O, Rb2O, and Ag2O. X may be any value from 0.01 to 0.99, such as 0.05 to 0.95. For example, x is 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, or 0.95. Preferably, x is 0.25, 0.4, 0.5, 0.6, 0.75, or 0.95. For example, the first metal oxide is Fe2O3, Fe3O4, or FeO, the second metal oxide has the formula SrxLa(1-x)FeO3-δ, SrFeO3-δ or LaFeO3-δ, and the third component is a metal oxide or combination of metal oxides wherein each (third component) metal oxide is independently selected from the group consisting of K2O, Na2O, Cs2O, Rb2O, and Ag2O; and wherein the combination comprises from about 0.1 wt.% to about 20 wt.% of the third component. Preferably, the combination comprises from about 1 wt.% to about 20 wt.% of the third component, such as from about 1 wt.% to about 15 wt.% of the third component or from about 5 wt.% to about 15 wt.% of the third component. X may be any value from 0.01 to 0.99, such as 0.05 to 0.95. For example, x is 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, or 0.95. Preferably, x is 0.25, 0.4, 0.5, 0.6, 0.75, or 0.95. For example, the first metal oxide is Fe2O3, Fe3O4, or FeO, the second metal oxide has the formula SrxLa(1-x)FeO3-δ, SrFeO3-δ or LaFeO3-δ, and the third component is a metal oxide or combination of metal oxides wherein each (third component) metal oxide is independently selected from the group consisting of K2O, Na2O, Cs2O, Rb2O, and Ag2O; wherein the combination comprises a ratio of second metal oxide to first metal oxide of from about 1:0.9 to about 1:90; and wherein the combination comprises from about 0.1 wt.% to about 20 wt.% of the third component. Preferably, the combination comprises from about 1 wt.% to about 20 wt.% of the third component, such as from about 1 wt.% to about 15 wt.% of the third component or from about 5 wt.% to about 15 wt.% of the third component. For example, the ratio of second metal oxide to first metal oxide is from about 1:4.5 to about 1:45. Preferably, the ratio of second metal oxide to first metal oxide is about 1:5, about 1:6, about 1:7, about 1:8, about 1:9, about 1:10, about 1:11, about 1:12, about 1:13, about 1;14 or about 1:15. Preferably, the ratio of second metal oxide to first metal oxide is about 1:7, about 1:8, about 1:9, about 1:10, about 1:11, or about 1:12. X may be any value from 0.01 to 0.99, such as 0.05 to 0.95. For example, x is 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, or 0.95. Preferably, x is 0.25, 0.4, 0.5, 0.6, 0.75, or 0.95. For example, the first metal oxide is Fe2O3, Fe3O4, or FeO, the second metal oxide has the formula SrxLa(1-x)FeO3-δ, SrFeO3-δor LaFeO3-δ, and the third component is a metal oxide or combination of metal oxides wherein each (third component) metal oxide is independently selected from the group consisting of K2O, Na2O, Cs2O, Rb2O, and Ag2O; wherein the combination comprises from about 5 wt.% to about 95 wt.% of the first metal oxide; and / or from about 5 wt.% to about 95 wt.% of the second metal oxide; and wherein the combination comprises from about 0.1 wt.% to about 20 wt.% of the third component. The total composition of the combination does not exceed 100 wt.%. Preferably, the combination comprises from about 1 wt.% to about 20 wt.% of the third component, such as from about 1 wt.% to about 15 wt.% of the third component or from about 5 wt.% to about 15 wt.% of the third component. X may be any value from 0.01 to 0.99, such as 0.05 to 0.95. For example, x is 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, or 0.95. Preferably, x is 0.25, 0.4, 0.5, 0.6, 0.75, or 0.95. In a second aspect, the invention relates to a composition comprising a combination as described herein. The composition and / or combination described herein may be in solid form. For example, the composition and / or combination may be a powder or any other solid form (such as a tablet or pellet). Preferably, the composition and / or combination is in the form of a pellet. In a third aspect, the invention relates to a material comprising a composition or combination as described herein. In a fourth aspect, the invention relates to a combination of a first metal oxide and a second metal oxide, wherein the second metal oxide is a perovskite type metal oxide, and the first metal oxide may have any of the individual features as described herein, in isolation or in combination with any other individual features as described herein. In a fifth aspect, the invention relates to a vessel comprising a combination, composition or material as described herein. In a sixth aspect, the invention relates to a process, the process comprising the steps of: contacting a first fluid with a combination, composition or material as described herein to produce a second fluid; wherein: the first fluid comprises: a carbon containing compound, a hydrogen containing molecule that is not a hydrocarbon, or a combination of a carbon containing compound and a hydrogen containing molecule that is not a hydrocarbon. In some embodiments, the process further comprises the step of providing the first fluid at a temperature of from about 300 °C to about 1000 °C. In a seventh aspect, the invention relates to a process, the process comprising the steps of: contacting a third fluid with a combination, composition or material as described herein to produce a fourth fluid; wherein: the third fluid comprises water, and the fourth fluid comprises hydrogen. In some embodiments, the process further comprises the step of providing the third fluid at a temperature of from about 300 °C to about 1000 °C. In an eighth aspect, the invention relates to a use of a combination, composition or material as described herein for producing hydrogen and / or carbon dioxide. In a ninth aspect, the invention relates to a process of preparing a combination, composition or material as described herein. In a tenth aspect, the invention relates to a combination, composition or material prepared by a process as described herein. Brief Description of Drawings The present invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a schematic of a vessel according to an embodiment described herein, wherein (1) is an input, (2) is an output, (3) is a vessel. Figure 2 shows the general Ellingham diagram for the metal oxide oxidation escribed herein. Figure 3 is a schematic of a thermogravimetric analyser setup described herein. Figures 3 to 32 are graphs showing the thermogravimetric results of experiments described herein. Figure 33 is a schematic of a packed bed reactor setup described herein. Figures 34 to 38 are graphs showing the packed bed reactor results of experiments described herein. Detailed Description In a first aspect, the invention relates to a combination of a first metal oxide and a second metal oxide, wherein the second metal oxide is a mixed ionic-electronic conductor, the first metal oxide comprises a metal (M) and oxygen, and the first metal oxide’s change in standard Gibbs energy (in J / mol O2) for the reaction: ^^^^+ ^^= ^^^^^^wherein x is from 0.1 to 5, and y is from 0 to 5; is bounded by: 25.7T − 488470 < ΔG^^^^ < 178.9^ − 488470 for T being from 300 K to 1000 K. In some embodiments, the first metal oxide’s change in standard Gibbs energy (in J / mol O2) for the reaction: ^^^^+ ^^= ^^^^^^is bounded by: 64.0^ − 488470 < ΔG^^^^ < 140.6T − 488470 for T being from 300 K to 1000 K. In some embodiments, the first metal oxide’s change in standard Gibbs energy (in J / mol O2) for the reaction: ^^^^+ ^^= ^^^^^^is between the lower limit and upper limit for a given temperature as defined in any of tables 1 to 4. Table 1 ΔG^^^^ (J / mol O2)T (K) Lower Limit Upper Limit 300 -479968 -434023 400 -478426 -417166 500 -476381 -399806 600 -473950 -382060 700 -471215 -364011 800 -468239 -345719 900 -465067 -327233 1000 -461738 -308589 Table 2 ΔG^^^^ (J / mol O2)T (K) Lower Limit Upper Limit 300 -434800 -480760 400 -416910 -478190 500 -399020 -475620 600 -381130 -473050 700 -363240 -470480 800 -345350 -467910 900 -327460 -465340 1000 -309570 -462770 Table 3 ΔG^^^^(J / mol O2) T (K) Lower Limit Upper Limit 300 -468482 -445510 400 -463111 -432481 500 -457237 -418950 600 -450977 -405032 700 -444414 -390812 800 -437609 -376349 900 -430608 -361691 1000 -423451 -346876 Table 4 ΔG^^^^ (J / mol O2)T (K) Lower Limit Upper Limit 300 -446290 -469270 400 -432230 -462870 500 -418170 -456470 600 -404110 -450070 700 -390050 -443670 800 -375990 -437270 900 -361930 -430870 1000 -347870 -424470 Figure 2 and tables 1 to 4 are derived from data publicly available, for example at: https: / / cearun.grc.nasa.gov / ThermoBuild / . The change in standard Gibbs energy can be calculated for a given metal oxide as described in equation 1 described herein. The standard Gibbs energy for known metal oxides described herein are publicly available, for example at: https: / / cearun.grc.nasa.gov / ThermoBuild / . If this is not available, the skilled person can simply retrieve or determine experimentally the pO2 values for a given metal oxide reaction, and thus deduce the standard Gibbs energy. First metal oxide: In some embodiments, the metal of the first metal oxide is selected from the group consisting of transition metals, lanthanides, p-block metals, s-block metals and mixtures thereof. In some embodiments, the transition metal is selected from the group consisting of iron, manganese, cobalt, molybdenum, tungsten, and mixtures thereof. In some embodiments, the first metal oxide comprises iron. Preferably, the first metal oxide consists of iron and oxygen. For example, the first metal oxide is selected from the group consisting of Fe2O3, Fe3O4, FeO, and mixtures thereof. Preferably, the first metal oxide comprises or consists of FeO. Preferably, the first metal oxide comprises or consists of Fe3O4. In some embodiments, the first metal oxide may be a reduced first metal oxide. For example, after the first metal oxide has been contacted with a first fluid as described herein. Second metal oxide: In some embodiments, the second metal oxide is a mixed ionic-electronic conductor. In some embodiments, the second metal oxide is perovskite type metal oxide. That is, the second metal oxide is a perovskite type metal oxide at standard temperature and pressure (0 °C and 1 atmosphere of pressure). The second metal oxide may also be a perovskite type metal oxide at room temperature and pressure (about 25 °C and about 1 atmosphere of pressure). The second metal oxide may also be a perovskite type metal oxide at a temperature and pressure used in the processes described herein. In some embodiments, the second metal oxide has the formula ABX3-δ, wherein A is one or more metals; B is one or more metals; X is oxygen; and δ is from 0 to 0.5. δ represents the non-stoichiometry of the second metal oxide (perovskite type metal oxide). In some embodiments, A is selected from the group consisting of transition metals, lanthanides, actinides, p-block metals, s-block metals and mixtures thereof; and / or B is selected from the group consisting of transition metals, lanthanides, actinides, p-block metals, s-block metals and mixtures thereof. In some embodiments, A is selected from the group consisting of transition metals, lanthanides, actinides, p-block metals, s-block metals and mixtures thereof. In some embodiments, A is independently selected from the group consisting of La, Sr, Gd, Ca, Ce, K, Y, and mixtures thereof. Preferably, A is independently selected from the group consisting of La, Sr, Gd, Ca, Ce, and mixtures thereof. For example, A is independently selected from the group consisting of La, Sr, Gd, and mixtures thereof. In some embodiments, A comprises Sr or La. In some embodiments, B consists of Sr or La. In some embodiments, A is Sr or La. In some embodiments, A is A1xA2(1-x), and wherein A1and A2are each independently the same as described for A. In such embodiments, A1and A2are independently the same or different, for example different. X may be any value from 0.01 to 0.99, such as 0.05 to 0.95. For example, x is 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, or 0.95. Preferably, x is 0.5, 0.6, 0.75, or 0.95. For example, each A1and A2is independently selected from the group consisting of transition metals, lanthanides, actinides, p-block metals, s-block metals and mixtures thereof. In some embodiments, each A1and A2is independently selected from the group consisting of La, Sr, Gd, Ca, Ce, K, Y, and mixtures thereof. Preferably, each A1and A2is independently selected from the group consisting of La, Sr, Gd, Ca, Ce, and mixtures thereof. For example, each A1and A2is independently selected from the group consisting of La, Sr, Gd, and mixtures thereof. In some embodiments, A1is Sr or La, and A2is Ce, Sr, La or Ca. For example, A1xA2(1-x), is SrxCe(1-x), SrxLa(1-x), or example, A1xA2(1-x), is LaxCe(1-x), LaxSr(1-x), or LaxCa(1-x). For example, Sr0.75La0.25, Sr0.5La0.5, or Sr0.6Ca0.4. For example, A1xA2(1-x), is La0.95Ce0.05, La0.75Sr0.25, or La0.6Ca0.4. For example, B is selected from the group consisting of transition metals, lanthanides, actinides, p-block metals, s-block metals and mixtures thereof. In some embodiments, B is independently selected from the group consisting of Fe, Mn, Cu, Ce, Co, Ti, Ni, and mixtures thereof. Preferably, B is independently selected from the group consisting of Fe, Mn, Cu, Ce, Co, Ti, Ni, and mixtures thereof. For example, A is independently selected from the group consisting of Fe, Mn, Cu, Ce, Ti, Ni, and mixtures thereof. In some embodiments, B comprises Fe. In some embodiments, B consists of Fe. In some embodiments, B is Fe. In some embodiments, B is B1xB2(1-x), and wherein B1and B2are each independently the same as described for B. In such embodiments, B1and B2are independently the same or different, for example different. x may be any value from 0.01 to 0.99, such as 0.05 to 0.95. For example, x is 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, or 0.95. Preferably, x is 0.4, 0.5, or 0.25. In some embodiments, B2may be B2Ay1B2By2, wherein y1 + y2 = (1-x). For example, when x = 0.4, y1 + y2 = 0.6. For example, when x = 0.5, y1 + y2 = 0.5. For example, y1 and y2 may each individually be 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, provided that y1 + y2 = (1-x). In some embodiments, each B2Amay as described for B2herein. In some embodiments, each B2Bmay as described for B2herein. For example, each B1and B2is selected from the group consisting of transition metals, lanthanides, actinides, p-block metals, s-block metals and mixtures thereof. In some embodiments, each B1and B2is independently selected from the group consisting of Fe, Mn, Cu, Ce, Co, Ti, Ni, and mixtures thereof. Preferably, each B1and B2is independently selected from the group consisting of Fe, Mn, Cu, Ce, Co, Ti, Ni, and mixtures thereof. For example, each B1and B2is independently selected from the group consisting of Fe, Mn, Cu, Ce, Ti, Ni, and mixtures thereof. In some embodiments, B1is Fe and B2is Mn, Cu, Ce, Co, Ti, Ni, or mixtures thereof. For example, B1is Fe and B2is Mn, Cu, Ti, or Ni. For example, B1xB2(1-x), is FexCu(1-x), FexMn(1-x), or Fex(NiTi)(1-x). For example, B1xB2(1-x), is Fe0.95Cu0.05, Fe0.4Mn0.6, or Fe0.5Ni0.25Ti0.25. In some embodiments, the second metal oxide has the formula A1xA2(1-x)BX3-δ. In some embodiments, the second metal oxide has the formula AB1xB2(1-x)X3-δ. In some embodiments, A is Sr, B1is Fe and B2is Mn, Cu, Ce, Co, Ti, Ni, or mixtures thereof. For example, A is Sr, B1is Fe and B2is Mn, Cu, Ti, Ni, or mixtures thereof. For example, A is Sr, and B1xB2(1-x), is FexCu(1-x), FexMn(1-x), or Fex(NiTi)(1-x). For example, B1xB2(1-x), is Fe0.95Cu0.05, Fe0.4Mn0.6, or Fe0.5Ni0.25Ti0.25. In some embodiments, A is La, B1is Fe and B2is Mn, Cu, Ce, Co, Ti, Ni, or mixtures thereof. For example, A is La, B1is Fe and B2is Mn, Cu, Ti, Ni, or mixtures thereof. For example, A is La, and B1xB2(1-x), is FexCu(1-x), FexMn(1-x), or Fex(NiTi)(1-x). For example, B1xB2(1-x), is Fe0.95Cu0.05, Fe0.4Mn0.6, or Fe0.5Ni0.25Ti0.25. In some embodiments, A1is Sr or La, and A2is Ce, Sr, La or Ca; and B is Fe. For example, A1xA2(1-x), is SrxCe(1-x), SrxLa(1-x), or SrxCa(1-x); and B is Fe. For example, A1xA2(1-x), is LaxCe(1-x), LaxSr(1-x), or LaxCa(1-x); and B is Fe. For example, A1xA2(1-x), is Sr0.95Ce0.05, Sr0.75La0.25, Sr0.5La0.5, or Sr0.6Ca0.4; and B is Fe. For example, A1xA2(1-x), is La0.95Ce0.05, La0.75Sr0.25, or La0.6Ca0.4; and B is Fe. In some embodiments, A is A1xA2(1-x) and B is B1xB2(1-x). In some embodiments, A1is Sr or La, and A2is Ce, Sr, La or Ca; and B1is Fe and B2is Mn, Cu, Ce, Co, Ti, Ni, or mixtures thereof. For example, (1-x), SrxLa(1-x), or SrxCa(1-x); and B1xB2(1-x), is FexCu(1-x), FexMn(1-x), or For example, A1xA2(1-x), is LaxCe(1-x), LaxSr(1-x), or LaxCa(1-x); and B1xB2(1-x), (1-x), or Fex(NiTi)(1-x). For example, A1xA2(1-x), is Sr0.95Ce0.05, Sr0.75La0.25, Sr0.5La0.5, or Sr0.6Ca0.4; and B1xB2(1-x), is Fe0.95Cu0.05, Fe0.4Mn0.6, or Fe0.5Ni0.25Ti0.25. For example, A1xA2(1-x), is La0.95Ce0.05, La0.75Sr0.25, or La0.6Ca0.4; and B1xB2(1-x), is Fe0.95Cu0.05, Fe0.4Mn0.6, or Fe0.5Ni0.25Ti0.25. In some embodiments, the second metal oxide has the formula SrFeO3-δ, LaFeO3-δ, δ, X may be any value from 0.01 to 0.99, such as 0.05 to 0.95. For example, x is 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, or 0.95. Preferably, x is 0.25, 0.4, 0.5, 0.6, 0.75, or 0.95. In some embodiments, the second metal oxide is a mixed ionic-electronic conductor such as Gd0.3Ce0.7O2-δ or Cu0.25Co0.25Fe2.5O3-δ. Preferably, the first metal oxide is selected from the group consisting of Fe2O3, Fe3O4, FeO, and mixtures thereof. More preferably, the first metal oxide comprises or consists of FeO. More preferably, the first metal oxide comprises or consists of Fe3O4. In such embodiments, the second metal oxide has the formula SrFeO3-δ, LaFeO3-δ, SrxLa(1-x)FeO3-δ, La0.75Sr0.25FeO3-δ, SrFe0.95Cu0.05O3-δ, Sr0.95Ce0.05FeO3-δ, La0.6Ca0.4Fe0.4Mn0.6O3-δ, or Sr0.5La0.5Fe0.5Ni0.25Ti0.25O3-δ. X may be any value from 0.01 to 0.99, such as 0.05 to 0.95. For example, x is 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, or 0.95. Preferably, x is 0.25, 0.4, 0.5, 0.6, 0.75, or 0.95. In some embodiments, the combination comprises from about 5 wt.% to about 95 wt.% of the first metal oxide; and / or from about 5 wt.% to about 95 wt.% of the second metal oxide. The total composition of the combination does not exceed 100 wt.%. Preferably, the combination comprises a (wt.% or molar, preferably molar) ratio of second metal oxide to first metal oxide of from about 1:0.9 to about 1:90. For example, the ratio of second metal oxide to first metal oxide is from about 1:4.5 to about 1:45. Preferably, the ratio of second metal oxide to first metal oxide is about 1:5, about 1:6, about 1:7, about 1:8, about 1:9, about 1:10, about 1:11, about 1:12, about 1:13, about 1;14 or about 1:15. Preferably, the ratio of second metal oxide to first metal oxide is about 1:7, about 1:8, about 1:9, about 1:10, about 1:11, or about 1:12. In some embodiments, the combination comprises a (wt.% or molar, preferably molar) ratio of first metal oxide to second metal oxide of from about 1:0.9 to about 1:90. For example, the ratio of first metal oxide to second metal oxide is from about 1:4.5 to about 1:45. Preferably, the ratio of first metal oxide to second metal oxide is about 1:5, about 1:6, about 1:7, about 1:8, about 1:9, about 1:10, about 1:11, about 1:12, about 1:13, about 1;14 or about 1:15. Preferably, the ratio of first metal oxide to second metal oxide is about 1:7, about 1:8, about 1:9, about 1:10, about 1:11, or about 1:12. In some embodiments, the combination comprises a third component which comprises at least one promoter. In some embodiments, the third component is a compound. For example, the third component is a metal oxide or mixture of metal oxides. For example, the third component is a metal. The term “third” means that the third component is in addition to the “first” metal oxide and “second” metal oxide. The third component may be on the surface of the first metal oxide and / or the second metal oxide. The third component may be impregnated within the first metal oxide and / or the second metal oxide. In some embodiments, the at least one promoter is selected from the group consisting of alkali metals, alkali earth metals, and mixtures thereof. In some embodiments, the promoter is an ion. In some embodiments, the at least one promoter is selected from the group consisting of alkali metals, alkali earth metals, and mixtures thereof. In some embodiments, the third component is a metal oxide or mixture of metal oxides, wherein each metal of each metal oxide is independently selected from the group consisting of alkali metals, alkali earth metals, and mixtures thereof. In some embodiments, the at least one promoter is selected from the group consisting of K, Na, Ag, Cs, Rb, Li, and mixtures thereof. Preferably, the at least one promoter is selected from the group of K, Na, Ag, and Cs. In some embodiments, the third component is a metal oxide or mixture of metal oxides, wherein each metal of each metal oxide is independently selected from the group consisting of K, Na, Ag, Cs, Rb, Li and mixtures thereof. Preferably, each metal of each metal oxide is independently selected from the group consisting of K, Na, Ag, and Cs. In some embodiments, the third component is a metal oxide or mixture of metal oxides, wherein each metal oxide is independently selected from the group consisting of K2O, Na2O, Cs2O, Rb2O, Ag2O, and Li2O. Preferably, the third component is a metal oxide or mixture of metal oxides, wherein each metal oxide is independently selected from the group consisting of K2O, Na2O, Cs2O, and Ag2O. In some embodiments, the combination comprises a catalytic amount of the third component. In some embodiments, the combination comprises a non-stoichiometric amount of the third component. For example, the combination comprises from about 0.1 wt.% to about 20 wt.% of the third component. Preferably, the combination comprises from about 1 wt.% to about 20 wt.% of the third component, such as from about 1 wt.% to about 15 wt.% of the third component or from about 5 wt.% to about 15 wt.% of the third component. In some embodiments, the combination comprises about 1 wt%, about 5 wt.% about 10 wt% or about 15 wt.% of the third component. Preferably, the first metal oxide is selected from the group consisting of Fe2O3, Fe3O4, FeO, and mixtures thereof. More preferably, the first metal oxide comprises or consists of FeO. In such embodiments, the second metal oxide has the formula SrFeO3-δ, δ, Sr0.95Ce0.05FeO3-δ, may be any value from 0.01 to 0.99, such as 0.05 to 0.95. For example, x is 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, or 0.95. Preferably, x is 0.25, 0.4, 0.5, 0.6, 0.75, or 0.95. In such embodiments, the third component is a metal oxide or mixture of metal oxides, wherein each metal oxide is independently selected from the group consisting of K2O, Na2O, Cs2O, Rb2O, and Ag2O. In some embodiments, the first metal oxide is Fe2O3, Fe3O4, or FeO, the second metal oxide has the formula SrxLa(1-x)FeO3-δ, SrFeO3-δor LaFeO3-δ, and the third component is a metal oxide wherein each metal oxide is independently selected from the group consisting of K2O, Na2O, Cs2O, Rb2O, and Ag2O. X may be any value from 0.01 to 0.99, such as 0.05 to 0.95. For example, x is 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, or 0.95. Preferably, x is 0.25, 0.4, 0.5, 0.6, 0.75, or 0.95. Preferably, the first metal oxide is Fe2O3, Fe3O4, or FeO, the second metal oxide has the formula SrxLa(1-x)FeO3-δ, SrFeO3-δor LaFeO3-δ, and the third component is a metal oxide or combination of metal oxides wherein each metal of each (third component) metal oxide is independently selected from the group consisting of K, Na, Ag, Cs, Rb, Li and mixtures thereof. Preferably, each metal of each (third component) metal oxide is independently selected from the group consisting of K, Na, Rb, Ag, and Cs. X may be any value from 0.01 to 0.99, such as 0.05 to 0.95. For example, x is 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, or 0.95. Preferably, x is 0.25, 0.4, 0.5, 0.6, 0.75, or 0.95. More preferably, the first metal oxide is Fe2O3, Fe3O4, or FeO, the second metal oxide has the formula SrxLa(1-x)FeO3-δ, SrFeO3-δ or LaFeO3-δ, and the third component is a metal oxide or combination of metal oxides wherein each (third component) metal oxide is independently selected from the group consisting of K2O, Na2O, Cs2O, Rb2O, and Ag2O. X may be any value from 0.01 to 0.99, such as 0.05 to 0.95. For example, x is 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, or 0.95. Preferably, x is 0.25, 0.4, 0.5, 0.6, 0.75, or 0.95. For example, the first metal oxide is Fe2O3, Fe3O4, or FeO, the second metal oxide has the formula SrxLa(1-x)FeO3-δ, SrFeO3-δ or LaFeO3-δ, and the third component is a metal oxide or combination of metal oxides wherein each (third component) metal oxide is independently selected from the group consisting of K2O, Na2O, Cs2O, Rb2O, and Ag2O; and wherein the combination comprises from about 0.1 wt.% to about 20 wt.% of the third component. Preferably, the combination comprises from about 1 wt.% to about 20 wt.% of the third component, such as from about 1 wt.% to about 15 wt.% of the third component or from about 5 wt.% to about 15 wt.% of the third component. X may be any value from 0.01 to 0.99, such as 0.05 to 0.95. For example, x is 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, or 0.95. Preferably, x is 0.25, 0.4, 0.5, 0.6, 0.75, or 0.95. For example, the first metal oxide is Fe2O3, Fe3O4, or FeO, the second metal oxide has the formula SrxLa(1-x)FeO3-δ, SrFeO3-δ or LaFeO3-δ, and the third component is a metal oxide or combination of metal oxides wherein each (third component) metal oxide is independently selected from the group consisting of K2O, Na2O, Cs2O, Rb2O, and Ag2O; wherein the combination comprises a ratio of second metal oxide to first metal oxide of from about 1:0.9 to about 1:90; and wherein the combination comprises from about 0.1 wt.% to about 20 wt.% of the third component. Preferably, the combination comprises from about 1 wt.% to about 20 wt.% of the third component, such as from about 1 wt.% to about 15 wt.% of the third component or from about 5 wt.% to about 15 wt.% of the third component. For example, the ratio of second metal oxide to first metal oxide is from about 1:4.5 to about 1:45. Preferably, the ratio of second metal oxide to first metal oxide is about 1:5, about 1:6, about 1:7, about 1:8, about 1:9, about 1:10, about 1:11, about 1:12, about 1:13, about 1;14 or about 1:15. Preferably, the ratio of second metal oxide to first metal oxide is about 1:7, about 1:8, about 1:9, about 1:10, about 1:11, or about 1:12. X may be any value from 0.01 to 0.99, such as 0.05 to 0.95. For example, x is 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, or 0.95. Preferably, x is 0.25, 0.4, 0.5, 0.6, 0.75, or 0.95. For example, the first metal oxide is Fe2O3, Fe3O4, or FeO, the second metal oxide has the formula SrxLa(1-x)FeO3-δ, SrFeO3-δor LaFeO3-δ, and the third component is a metal oxide or combination of metal oxides wherein each (third component) metal oxide is independently selected from the group consisting of K2O, Na2O, Cs2O, Rb2O, and Ag2O; wherein the combination comprises from about 5 wt.% to about 95 wt.% of the first metal oxide; and / or from about 5 wt.% to about 95 wt.% of the second metal oxide; and wherein the combination comprises from about 0.1 wt.% to about 20 wt.% of the third component. The total composition of the combination does not exceed 100 wt.%. Preferably, the combination comprises from about 1 wt.% to about 20 wt.% of the third component, such as from about 1 wt.% to about 15 wt.% of the third component or from about 5 wt.% to about 15 wt.% of the third component. X may be any value from 0.01 to 0.99, such as 0.05 to 0.95. For example, x is 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, or 0.95. Preferably, x is 0.25, 0.4, 0.5, 0.6, 0.75, or 0.95. In a second aspect, the invention relates to a composition comprising a combination as described herein. In a third aspect, the invention relates to a material comprising a composition or combination as described herein. In the compositions and materials described herein, the first metal oxide and second metal oxides may be distributed in any way. For example, the first metal oxide and second metal oxides may be distributed non-uniformly throughout the composition or material. Preferably, the first metal oxide and second metal oxides are distributed uniformly throughout the composition or material. In a fourth aspect, the invention relates to a combination of a first metal oxide and a second metal oxide, wherein the second metal oxide is a mixed ionic-electronic conductor (such as a perovskite type metal oxide), and the first metal oxide may have any of the individual features as described herein, in isolation or in combination with any other individual features as described herein. In a fifth aspect, the invention relates to a vessel comprising a combination, composition or material as described herein. The vessel may comprise an input and an output. The input may be configured to accept a first fluid. The output may be configured to output a second fluid. The combination, composition or material described herein may be positioned between the input and the output of the vessel. As such, the first vessel is configured such that the first fluid can enter the vessel and pass across and / or through the combination, composition or material. The first fluid is thereby converted into the second fluid. The second fluid may exit the vessel via the output. In some embodiments, the vessel has an internal volume of from about 1 L to about 100 L. In some embodiments, the vessel has an internal volume of from about 1 L to about 75 L, from about 1 L to about 50 L, from about 1 L to about 25 L, from about 1 L to about 10 L, or from about 1 L to about 5 L. Preferably, the vessel has an internal volume of from about 1 L to about 22 L. The vessel may be configured to operate at a temperature of from about 300 °C to about 1000 °C and at a pressure of between 1 and 10 bar. For example, the vessel may be configured to operate at a temperature of from about 300 °C to about 800 °C and at a pressure of between 1 and 10 bar. For example, the vessel may be configured to operate at a temperature of from about 350 °C to about 750 °C and at a pressure of between 1 and 10 bar. In particular, the vessel may be a reaction vessel (such as a combustion vessel). The vessel may be a fixed bed reactor (such as a packed bed reactor) or a fluidised bed reactor. In a sixth aspect, the invention relates to a process, the process comprising the steps of: contacting a first fluid with a combination, composition or material as described herein to produce a second fluid; wherein: the first fluid comprises: a carbon containing compound, a hydrogen containing molecule that is not a hydrocarbon, or a combination of a carbon containing compound and a hydrogen containing molecule that is not a hydrocarbon. In some embodiments, when the first fluid comprises a carbon containing compound, the second fluid comprises carbon dioxide and optionally at least one impurity. In some embodiments, the process comprises the step of converting at least a proportion of the carbon containing compound into carbon dioxide and optionally at least one impurity. In some embodiments, when the first fluid comprises a hydrogen containing molecule that is not a carbon containing compound, the second fluid comprises water and optionally at least one impurity. In some embodiments, the process comprises the step of converting at least a proportion of the hydrogen containing molecule that is not a carbon containing compound into water and optionally at least one impurity. In some embodiments, when the first fluid comprises a combination of a carbon containing compound and a hydrogen containing molecule that is not a carbon containing compound, the second fluid comprises carbon dioxide, water, and optionally at least one impurity. In some embodiments, the process comprises the step of converting at least a proportion of the combination of the carbon containing compound and the hydrogen containing molecule that is not a carbon containing compound, into carbon dioxide, water, and optionally at least one impurity. In some embodiments, the combination, composition or material is comprised in a vessel as described herein. The process may comprise the step of providing a combination, composition or material as described herein. For example, the process may comprise the step of providing a vessel as described herein (which may comprise the combination, composition or material as described herein). The process may comprise the step of heating the combination, composition or material to a temperature (for example an internal temperature) of from about 300 °C to about 1000 °C. For example, the process may comprise the step of heating the combination, composition or material to a temperature (for example an internal temperature) of from about 300 °C to about 800 °C. For example, the process may comprise the step of heating the combination, composition or material to a temperature (for example an internal temperature) of from about 350 °C to about 750 °C. For example, the process may comprise the step of heating the combination, composition or material to a temperature (for example an internal temperature) of from about 350 °C to about 650 °C. The process may comprise the step of heating the vessel to a temperature (for example an internal temperature) of from about 300 °C to about 1000 °C. For example, the process may comprise the step of heating the vessel to a temperature (for example an internal temperature) of from about 300 °C to about 800 °C. For example, the process may comprise the step of heating the vessel to a temperature (for example an internal temperature) of from about 300 °C to about 800 °C. For example, the process may comprise the step of heating the vessel to a temperature (for example an internal temperature) of from about 300 °C to about 750 °C. For example, the process may comprise the step of heating the vessel to a temperature (for example an internal temperature) of from about 300 °C to about 650 °C. The process may comprise the step of heating the vessel to a temperature (for example an internal temperature) of from about 300 °C to about 1000 °C, whilst maintaining the pressure inside the vessel at from about 1 bar to about 10 bar. For example, the process may comprise the step of heating the vessel to a temperature (for example an internal temperature) of from about 300 °C to about 800 °C, whilst maintaining the pressure inside the vessel at from about 1 bar to about 10 bar. For example, the process may comprise the step of heating the vessel to a temperature (for example an internal temperature) of from about 350 °C to about 750 °C, whilst maintaining the pressure inside the vessel at from about 1 bar to about 10 bar. For example, the process may comprise the step of heating the vessel to a temperature (for example an internal temperature) of from about 350 °C to about 650 °C, whilst maintaining the pressure inside the vessel at from about 1 bar to about 10 bar. The process may comprise the step of providing the first fluid. In some embodiments, the process comprises the step of providing the first fluid at a temperature of from about 300 °C to about 1000 °C. In some embodiments, the process comprises the step of providing the first fluid at a temperature of from about 300 °C to about 800 °C. In some embodiments, the process comprises the step of providing the first fluid at a temperature of from about 300 °C to about 750 °C. Preferably, the process comprises the step of providing the first fluid at a temperature of from about 300 °C to about 650 °C, or from about 300 °C to about 550 °C. In some embodiments, the process comprises the step of providing the first fluid at a temperature of from about 400 °C to about 1000 °C. In some embodiments, the process comprises the step of providing the first fluid at a temperature of from about 400 °C to about 800 °C. In some embodiments, the process comprises the step of providing the first fluid at a temperature of from about 400 °C to about 750 °C. Preferably, the process comprises the step of providing the first fluid at a temperature of from about 400 °C to about 650 °C, or from about 400 °C to about 550 °C. In some embodiments, the process comprises the step of providing the first fluid at a temperature of from about 400 °C to about 1000 °C. In some embodiments, the process comprises the step of providing the first fluid at a temperature of from about 500 °C to about 800 °C. In some embodiments, the process comprises the step of providing the first fluid at a temperature of from about 500 °C to about 750 °C. Preferably, the process comprises the step of providing the first fluid at a temperature of from about 500 °C to about 650 °C, or from about 500 °C to about 550 °C. In some embodiments, the process comprises the step of maintaining the pressure inside the vessel at from about 1 bar to about 10 bar. Preferably, the process comprises the step of maintaining the pressure inside the vessel at from about 1 bar to about 5 bar, or at from about 1 bar to about 2 bar. In some embodiments, the process comprises the step of contacting the first fluid with the combination, composition or material for a period of between 0.01 seconds and 60 seconds. For example, the process comprises the step of contacting the first fluid with the combination, composition or material for a period of between 0.01 seconds and 10 seconds. In some embodiments, the flow rate of fluid though the vessel is from about 10 mL / min to about 10000 mL / min. For example, the flow rate of fluid though the vessel is from about 100 mL / min to about 10000 mL / min, from about 100 mL / min to about 1000 mL / min, or from about 100 mL / min to about 500 mL / min. In some embodiments, contacting the first fluid with the combination, composition or material results in the combination, composition or material being (at least partially) reduced to a form a reduced a combination, composition or material. In some embodiments, contacting the first fluid with the combination, composition or material results in the first metal oxide being (at least partially) reduced to form a reduced first metal oxide. That is, the first metal oxide loses a proportion or all of its oxygen. Preferably, the first metal oxide loses a proportion of its oxygen. In some embodiments, contacting the first fluid with the combination, composition or material results in the second metal oxide being (at least partially) reduced to form a reduced second metal oxide. That is, the second metal oxide loses a proportion or all of its oxygen. Preferably, the second metal oxide loses a proportion of its oxygen. In some embodiments, the process comprises the step of reducing (at least a proportion of) the combination, composition or material. In some embodiments, the process comprises the step of reducing (at least a proportion of) the first metal oxide and / or second metal oxide. Preferably, the process comprises the step of reducing (at least a proportion of) the first metal oxide. In a seventh aspect, the invention relates to a process, the process comprising the steps of: contacting a third fluid with a combination, composition or material as described herein to produce a fourth fluid; wherein: the third fluid comprises water, and the fourth fluid comprises hydrogen. In some embodiments, the process comprises the step of converting at least a proportion of the water into hydrogen. In some embodiments, the combination, composition or material is comprised in a vessel as described herein. In preferred embodiments, the combination, composition or material is a reduced combination, composition or material as described herein. The process may comprise the step of providing a combination, composition or material as described herein. For example, the process may comprise the step of providing a vessel as described herein (which may comprise the combination, composition or material as described herein). The process may comprise the step of heating the combination, composition or material to a temperature (for example an internal temperature) of from about 300 °C to about 1000 °C. For example, the process may comprise the step of heating the combination, composition or material to a temperature (for example an internal temperature) of from about 300 °C to about 800 °C. For example, the process may comprise the step of heating the combination, composition or material to a temperature (for example an internal temperature) of from about 350 °C to about 750 °C. For example, the process may comprise the step of heating the combination, composition or material to a temperature (for example an internal temperature) of from about 350 °C to about 650 °C. The process may comprise the step of heating the vessel to a temperature (for example an internal temperature) of from about 300 °C to about 1000 °C. For example, the process may comprise the step of heating the vessel to a temperature (for example an internal temperature) of from about 300 °C to about 800 °C. For example, the process may comprise the step of heating the vessel to a temperature (for example an internal temperature) of from about 300 °C to about 800 °C. For example, the process may comprise the step of heating the vessel to a temperature (for example an internal temperature) of from about 300 °C to about 750 °C. For example, the process may comprise the step of heating the vessel to a temperature (for example an internal temperature) of from about 300 °C to about 650 °C. The process may comprise the step of heating the vessel to a temperature (for example an internal temperature) of from about 300 °C to about 1000 °C, whilst maintaining the pressure inside the vessel at from about 1 bar to about 10 bar. For example, the process may comprise the step of heating the vessel to a temperature (for example an internal temperature) of from about 300 °C to about 800 °C, whilst maintaining the pressure inside the vessel at from about 1 bar to about 10 bar. For example, the process may comprise the step of heating the vessel to a temperature (for example an internal temperature) of from about 350 °C to about 750 °C, whilst maintaining the pressure inside the vessel at from about 1 bar to about 10 bar. For example, the process may comprise the step of heating the vessel to a temperature (for example an internal temperature) of from about 350 °C to about 650 °C, whilst maintaining the pressure inside the vessel at from about 1 bar to about 10 bar. The process may comprise the step of providing the third fluid. In some embodiments, the process comprises the step of providing the third fluid at a temperature of from about 300 °C to about 1000 °C. In some embodiments, the process comprises the step of providing the third fluid at a temperature of from about 300 °C to about 800 °C. In some embodiments, the process comprises the step of providing the third fluid at a temperature of from about 300 °C to about 750 °C. Preferably, the process comprises the step of providing the third fluid at a temperature of from about 300 °C to about 650 °C, or from about 300 °C to about 550 °C. In some embodiments, the process comprises the step of providing the third fluid at a temperature of from about 400 °C to about 1000 °C. In some embodiments, the process comprises the step of providing the third fluid at a temperature of from about 400 °C to about 800 °C. In some embodiments, the process comprises the step of providing the third fluid at a temperature of from about 400 °C to about 750 °C. Preferably, the process comprises the step of providing the third fluid at a temperature of from about 400 °C to about 650 °C, or from about 400 °C to about 550 °C. In some embodiments, the process comprises the step of providing the third fluid at a temperature of from about 400 °C to about 1000 °C. In some embodiments, the process comprises the step of providing the third fluid at a temperature of from about 500 °C to about 800 °C. In some embodiments, the process comprises the step of providing the third fluid at a temperature of from about 500 °C to about 750 °C. Preferably, the process comprises the step of providing the third fluid at a temperature of from about 500 °C to about 650 °C, or from about 500 °C to about 550 °C. In some embodiments, the process comprises the step of maintaining the pressure inside the vessel at from about 1 bar to about 10 bar. Preferably, the process comprises the step of maintaining the pressure inside the vessel at from about 1 bar to about 5 bar, or at from about 1 bar to about 2 bar. In some embodiments, the process comprises the step of contacting the third fluid with the combination, composition or material for a period of between 0.01 seconds and 60 seconds. For example, the process comprises the step of contacting the third fluid with the combination, composition or material for a period of between 0.01 seconds and 10 seconds. In some embodiments, the flow rate of fluid though the vessel is from about 10 mL / min to about 10000 mL / min. For example, the flow rate of fluid though the vessel is from about 100 mL / min to about 10000 mL / min, from about 100 mL / min to about 1000 mL / min, or from about 100 mL / min to about 500 mL / min. In some embodiments, contacting the third fluid with the combination, composition or material results in the combination, composition or material being (at least partially) oxidised to a form an oxidised a combination, composition or material. In some embodiments, contacting the third fluid with the combination, composition or material results in the first metal oxide being (at least partially) oxidised to form an oxidised first metal oxide. In some embodiments, contacting the third fluid with the combination, composition or material results in the second metal oxide being (at least partially) reduced to form a reduced second metal oxide. That is, the second metal oxide loses a proportion or all of its oxygen. Preferably, the second metal oxide loses a proportion of its oxygen. In some embodiments, the process comprises the step of reducing (at least a proportion of) the combination, composition or material. In some embodiments, the process comprises the step of reducing (at least a proportion of) the first metal oxide and / or second metal oxide. Preferably, the process comprises the step of reducing (at least a proportion of) the first metal oxide. In some embodiments, the invention relates to a process which comprises the process of the sixth aspect (and embodiments thereof) and the process of the seventh aspect (and embodiments thereof). For example, the invention relates to a process, the process comprising the steps of: contacting a first fluid with a combination, composition or material as described herein to produce a second fluid; wherein: (a) the first fluid comprises: a carbon containing compound, a hydrogen containing molecule that is not a hydrocarbon, or a combination of a carbon containing compound and a hydrogen containing molecule that is not a hydrocarbon; and (b) contacting a third fluid with a combination, composition or material as described herein to produce a fourth fluid; wherein: the third fluid comprises water, and the fourth fluid comprises hydrogen. Other features and embodiments of the this process are described in relation to the process of the sixth and seventh aspects (and embodiments thereof) and are each independently combinable with this process. In some embodiments, contacting the first fluid with the combination, composition or material results in the combination, composition or material being (at least partially) reduced to a form a reduced a combination, composition or material. In some embodiments, contacting the third fluid with the combination, composition or material results in the combination, composition or material being (at least partially) oxidised to a form an oxidised a combination, composition or material. The process may comprise the step of providing a combination, composition or material as described herein. For example, the process may comprise the step of providing a vessel as described herein (which may comprise the combination, composition or material as described herein). First Fluid In some embodiments, the first fluid is a fluid from an industrial process. In some embodiments, the first fluid is a waste fluid or by-product from an industrial process. For example, the industrial process may be a steel manufacturing process, metal processing process, organic compound production process, cosmetic industry process, semiconductor manufacturing process, semiconductor processing process, biogas production process and / or a biogas processing process. In some embodiments, the first fluid is an organic solvent or reducing gas (such as one from an industrial process). For example, the first fluid is a waste / by-product organic solvent or reducing gas (such as one from an industrial process). The first fluid comprises a carbon containing compound, a hydrogen containing molecule that is not a hydrocarbon, or a combination of a carbon containing compound and a hydrogen containing molecule that is not a hydrocarbon. In some embodiments, the first fluid consists of a carbon containing compound, a hydrogen containing molecule that is not a hydrocarbon, or a combination of a carbon containing compound and a hydrogen containing molecule that is not a hydrocarbon. In some embodiments, the first fluid comprises an auxiliary fluid. In some embodiments, the first fluid comprises a carbon containing compound and an auxiliary fluid; a hydrogen containing molecule that is not a hydrocarbon and an auxiliary fluid; or a combination of a carbon containing compound, a hydrogen containing molecule that is not a hydrocarbon and an auxiliary fluid. In some embodiments, the first fluid consists of carbon containing compound and an auxiliary fluid; a hydrogen containing molecule that is not a hydrocarbon and an auxiliary fluid; or a combination of a carbon containing compound, a hydrogen containing molecule that is not a hydrocarbon and an auxiliary fluid. In all embodiments, the sum of the components in the first fluid does not exceed 100 vol%. In some embodiments, the first fluid comprises from about 0.1 vol% to about 100 vol% of the carbon containing compound. In some embodiments, the first fluid comprises from about 0.1 vol% to about 100 vol%, about 99 vol%, about 95 vol%, about 90 vol%, about 80 vol%, about 70 vol%, about 60 vol%, about 50 vol%, about 40 vol%, about 30 vol%, about 20 vol%, about 10 vol%, or about 5 vol% of the carbon containing compound. In some embodiments, the first fluid comprises from about 0.1 vol%, about 1 vol%, about 2 vol%, about 5 vol%, about 10 vol%, about 20 vol%, about 30 vol%, about 40 vol%, about 50 vol%, about 60 vol%, about 70 vol%, about 80 vol%, or about 90 vol%, to about 100 vol% of the carbon containing compound. In some embodiments, the first fluid comprises from about 0.1 vol% to about 100 vol% of the hydrogen containing molecule that is not a hydrocarbon. In some embodiments, the first fluid comprises from about 0.1 vol% to about 100 vol%, about 99 vol%, about 95 vol%, about 90 vol%, about 80 vol%, about 70 vol%, about 60 vol%, about 50 vol%, about 40 vol%, about 30 vol%, about 20 vol%, about 10 vol%, or about 5 vol% of the hydrogen containing molecule that is not a hydrocarbon. In some embodiments, the first fluid comprises from about 0.1 vol%, about 1 vol%, about 2 vol%, about 5 vol%, about 10 vol%, about 20 vol%, about 30 vol%, about 40 vol%, about 50 vol%, about 60 vol%, about 70 vol%, about 80 vol%, or about 90 vol%, to about 100 vol% of the hydrogen containing molecule that is not a hydrocarbon. In some embodiments, the first fluid comprises from about 0.1 vol% to about 100 vol% of a combination of the carbon containing compound and the hydrogen containing molecule that is not a hydrocarbon. In some embodiments, the first fluid comprises from about 0.1 vol% to about 100 vol%, about 99 vol%, about 95 vol%, about 90 vol%, about 80 vol%, about 70 vol%, about 60 vol%, about 50 vol%, about 40 vol%, about 30 vol%, about 20 vol%, about 10 vol%, or about 5 vol% of a combination of the carbon containing compound and the hydrogen containing molecule that is not a hydrocarbon. In some embodiments, the first fluid comprises from about 0.1 vol%, about 1 vol%, about 2 vol%, about 5 vol%, about 10 vol%, about 20 vol%, about 30 vol%, about 40 vol%, about 50 vol%, about 60 vol%, about 70 vol%, about 80 vol%, or about 90 vol%, to about 100 vol% of a combination of the carbon containing compound and the hydrogen containing molecule that is not a hydrocarbon. When the first fluid comprises a combination of a carbon containing compound and a hydrogen containing molecule that is not a hydrocarbon, each of the carbon containing compound and a hydrogen containing molecule that is not a hydrocarbon may independently be present in a vol% as described herein. In some embodiments, the first fluid comprises from about 0.1 vol% to about 99.9 vol% of an auxiliary fluid. In some embodiments, the first fluid comprises from about 0.1 vol% to about 99.9 vol%, about 99 vol%, about 95 vol%, about 90 vol%, about 80 vol%, about 70 vol%, about 60 vol%, about 50 vol%, about 40 vol%, about 30 vol%, about 20 vol%, about 10 vol%, or about 5 vol% of the auxiliary fluid. In some embodiments, the first fluid comprises from about 1 vol%, about 2 vol%, about 5 vol%, about 10 vol%, about 20 vol%, about 30 vol%, about 40 vol%, about 50 vol%, about 60 vol%, about 70 vol%, about 80 vol%, or about 90 vol%, to about 99.9 vol% of the auxiliary fluid. In some embodiments, the first fluid comprises from about 0.1 vol% to about 99 vol%, about 95 vol%, about 90 vol%, about 80 vol%, about 70 vol%, about 60 vol%, about 50 vol%, about 40 vol%, about 30 vol%, about 20 vol%, about 10 vol%, or about 5 vol% of water. Carbon Containing Compound In some embodiments, the carbon containing compound is an organic compound with a boiling point (at standard temperature and pressure) of below about 300 °C, optionally below about 250 °C, below about 200 °C, or below about 180 °C. The carbon containing compound may be an organic compound with a boiling point (at standard temperature and pressure) of above -200 °C, optionally above about -190 °C, above about -180 °C, or above about -170 °C. In some embodiments, the carbon containing compound is selected from the group consisting of substituted or unsubstituted alkanes, substituted or unsubstituted alkenes, substituted or unsubstituted alkynes, substituted or unsubstituted alcohols, substituted or unsubstituted ketones, substituted or unsubstituted aldehydes, substituted or unsubstituted amides, substituted or unsubstituted carboxylic acids, substituted or unsubstituted esters, substituted or unsubstituted carbocyclic compounds, substituted or unsubstituted aromatic compounds, substituted or unsubstituted heteroaromatic compounds, carbon monoxide, carbon dioxide and mixtures thereof. In some embodiments, the carbon containing compound is selected from the group consisting of substituted or unsubstituted C1-C10 alkanes, substituted or unsubstituted C2-C10alkenes, substituted or unsubstituted C2-C10alkynes, substituted or unsubstituted C2-C10alcohols, substituted or unsubstituted C2-C10ketones, substituted or unsubstituted C2-C10 aldehydes, substituted or unsubstituted C2-C10 amides, substituted or unsubstituted C2-C10 carboxylic acids, substituted or unsubstituted C2-C10 esters, substituted or unsubstituted C5-C10carbocyclic compounds, substituted or unsubstituted C5-C10aromatic compounds, substituted or unsubstituted C5-C10heteroaromatic compounds, carbon monoxide, carbon dioxide and mixtures thereof. For example, the carbon containing compound may be selected from the group consisting of substituted or unsubstituted C1-C8alkanes, substituted or unsubstituted C2-C8alkenes, substituted or unsubstituted C2-C8alkynes, substituted or unsubstituted C2-C8alcohols, substituted or unsubstituted C2-C8 ketones, substituted or unsubstituted C2-C8 aldehydes, substituted or unsubstituted C2-C8 amides, substituted or unsubstituted C2-C8 carboxylic acids, substituted or unsubstituted C2-C8esters, substituted or unsubstituted C5-C8carbocyclic compounds, substituted or unsubstituted C5-C8aromatic compounds, substituted or unsubstituted C5-C8 heteroaromatic compounds, carbon monoxide, carbon dioxide and mixtures thereof. For example, the carbon containing compound may be selected from the group consisting of substituted or unsubstituted C1-C5alkanes, substituted or unsubstituted C2-C5alkenes, substituted or unsubstituted C2-C5alkynes, substituted or unsubstituted C1-C5 alcohols, substituted or unsubstituted C2-C5 ketones, substituted or unsubstituted C2-C5 aldehydes, substituted or unsubstituted C2-C5 amides, substituted or unsubstituted C2-C5carboxylic acids, substituted or unsubstituted C2-C5esters, substituted or unsubstituted C5-C8carbocyclic compounds, substituted or unsubstituted C5-C8 aromatic compounds, substituted or unsubstituted C5-C8 heteroaromatic compounds, carbon monoxide, carbon dioxide and mixtures thereof. In some embodiments, the carbon containing compound is selected from the group consisting of substituted or unsubstituted C2-C10 alkanes, substituted or unsubstituted C2-C10 alkenes, substituted or unsubstituted C2-C10 alkynes, substituted or unsubstituted C2-C10alcohols, substituted or unsubstituted C2-C10ketones, substituted or unsubstituted C2-C10aldehydes, substituted or unsubstituted C2-C10amides, substituted or unsubstituted C2-C10 carboxylic acids, substituted or unsubstituted C2-C10 esters, substituted or unsubstituted C5-C10 carbocyclic compounds, substituted or unsubstituted C5-C10aromatic compounds, substituted or unsubstituted C5-C10heteroaromatic compounds, carbon monoxide, carbon dioxide and mixtures thereof. For example, the carbon containing compound may be selected from the group consisting of substituted or unsubstituted C2-C8 alkanes, substituted or unsubstituted C2-C8 alkenes, substituted or unsubstituted C2-C8alkynes, substituted or unsubstituted C2-C8alcohols, substituted or unsubstituted C2-C8ketones, substituted or unsubstituted C2-C8aldehydes, substituted or unsubstituted C2-C8 amides, substituted or unsubstituted C2-C8 carboxylic acids, substituted or unsubstituted C2-C8 esters, substituted or unsubstituted C5-C8 carbocyclic compounds, substituted or unsubstituted C5-C8aromatic compounds, substituted or unsubstituted C5-C8heteroaromatic compounds, carbon monoxide, carbon dioxide and mixtures thereof. For example, the carbon containing compound may be selected from the group consisting of substituted or unsubstituted C2-C5 alkanes, substituted or unsubstituted C2-C5alkenes, substituted or unsubstituted C2-C5alkynes, substituted or unsubstituted C1-C5alcohols, substituted or unsubstituted C2-C5ketones, substituted or unsubstituted C2-C5 aldehydes, substituted or unsubstituted C2-C5 amides, substituted or unsubstituted C2-C5 carboxylic acids, substituted or unsubstituted C2-C5 esters, substituted or unsubstituted C5-C8carbocyclic compounds, substituted or unsubstituted C5-C8aromatic compounds, substituted or unsubstituted C5-C8heteroaromatic compounds, carbon monoxide, carbon dioxide and mixtures thereof. In some embodiments, the substituted C1-C10alkanes, substituted C2-C10alkenes, substituted C2-C10alkynes, substituted C1-C10alcohols, substituted C2-C10ketones, substituted C2-C10 aldehydes, substituted C2-C10 amides, substituted C2-C10 carboxylic acids, substituted C2-C10 esters, substituted C5-C10 carbocyclic compounds, substituted C5-C10aromatic compounds, and / or substituted C5-C10heteroaromatic compounds, are independently substituted with a group selected from the group consisting of amino, nitro, cyano, and halo. In some embodiments, the carbon containing compound is selected from the group consisting of carbon dioxide, carbon monoxide, methane, ethane, heptane, glycerol, ethanol, acetone, butanol, toluene and mixtures thereof. In some embodiments, the carbon containing compound is selected from the group consisting of carbon monoxide, methane, ethane, heptane, glycerol, ethanol, acetone, butanol, toluene and mixtures thereof. The carbon containing compound may be a mixture of one or more carbon containing compounds. In some embodiments, the carbon containing compound is a mixture of from 1 to 10 carbon containing compounds. For example, the carbon containing compound may be a mixture of from 1 to 8, 1 to 5, or 1 to 3 carbon containing compounds. For example, the carbon containing compound may be a mixture of 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 carbon containing compounds. When the carbon containing compound is a mixture of carbon containing compounds, each carbon containing compound of the mixture of carbon containing compounds may independently be as described herein. In some embodiments, the carbon containing compound is not carbon dioxide. In some embodiments, when the first fluid comprises a carbon containing compound which is carbon dioxide, the first fluid further comprises a carbon containing compound as described herein. In some embodiments, when the first fluid comprises a carbon containing compound which is carbon dioxide and does not comprise a hydrogen containing molecule that is not a hydrocarbon, the first fluid further comprises a carbon containing compound as described herein. Hydrogen Containing Molecule In some embodiments, the hydrogen containing molecule that is not a hydrocarbon is selected from the group consisting of hydrogen, amines, and hydrides. In some embodiments, the hydrogen containing molecule that is not a hydrocarbon is selected from the group consisting of hydrogen, ammonia, metal hydrides (optionally wherein the metal of the metal hydride is selected from the group consisting of As, Sb, and mixtures thereof. The hydrogen containing molecule that is not a hydrocarbon may be a mixture of one or more hydrogen containing molecules that are not a hydrocarbon. In some embodiments, the hydrogen containing molecule that is not a hydrocarbon is a mixture of from 1 to 10 hydrogen containing molecules that are not a hydrocarbon. For example, the hydrogen containing molecule that is not a hydrocarbon may be a mixture of from 1 to 10, 1 to 5, or 1 to 3 hydrogen containing molecules that are not a hydrocarbon. For example, the hydrogen containing molecule that is not a hydrocarbon may be a mixture of 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 hydrogen containing molecules that are not a hydrocarbon. When the hydrogen containing molecule that is not a hydrocarbon is a mixture of hydrogen containing molecules that are not a hydrocarbon, each hydrogen containing molecule that is not a hydrocarbon of the mixture of hydrogen containing molecules that are not a hydrocarbon may independently be as described herein. Auxiliary Fluid In some embodiments, the first fluid comprises an auxiliary fluid. The auxiliary fluid may be a mixture. The auxiliary fluid may comprise one or more carrier fluids and / or one or more auxiliary impurity. The auxiliary fluid may consist of one or more carrier fluid and / or one or more auxiliary impurities. In some embodiments, the auxiliary fluid does not comprise oxygen gas (O2) or nitrogen dioxide. The carrier fluid may be selected from fluids that do not contain hydrogen and / or carbon. For example, the carrier fluid may be selected from the group consisting of noble gases (such as helium, neon, argon, krypton, xenon, and / or radon), nitrogen, or mixtures thereof. The auxiliary impurity may be selected from impurities found in a fluid from an industrial process. In some embodiments, the auxiliary impurity is silane. Second Fluid In all embodiments, the sum of the components in the second fluid does not exceed 100 vol%. (i) When the first fluid comprises a carbon containing compound, the second fluid comprises carbon dioxide and at least one impurity. In some embodiments, the second fluid comprises from about 0.1 vol% to about 99 vol% of carbon dioxide. In some embodiments, the second fluid comprises from about 0.1 vol% to about 99 vol%, about 95 vol%, about 90 vol%, about 80 vol%, about 70 vol%, about 60 vol%, about 50 vol%, about 40 vol%, about 30 vol%, about 20 vol%, about 10 vol%, or about 5 vol% of carbon dioxide. In some embodiments, the second fluid comprises from about 0.1 vol%, about 1 vol%, about 2 vol%, about 5 vol%, about 10 vol%, about 20 vol%, about 30 vol%, about 40 vol%, about 50 vol%, about 60 vol%, about 70 vol%, about 80 vol%, or about 90 vol%, to about 99 vol% of carbon dioxide. In some embodiments, the second fluid comprises water. In some embodiments, the second fluid comprises from about 0.1 vol% to about 99 vol% of water. In some embodiments, the second fluid comprises from about 0.1 vol% to about 99 vol%, about 95 vol%, about 90 vol%, about 80 vol%, about 70 vol%, about 60 vol%, about 50 vol%, about 40 vol%, about 30 vol%, about 20 vol%, about 10 vol%, about 5 vol%, or about 1 vol% of water. In some embodiments, the second fluid comprises from about 0.1 vol%, about 1 vol%, about 2 vol%, about 5 vol%, about 10 vol%, about 20 vol%, about 30 vol%, about 40 vol%, about 50 vol%, about 60 vol%, about 70 vol%, about 80 vol%, or about 90 vol%, to about 99 vol% of water. In some embodiments, when the first fluid comprises a carbon containing compound that does not comprise hydrogen (for example, carbon monoxide and / or carbon dioxide), the second fluid comprises substantially no water. For example, the second fluid comprises from about 0.001 vol% to about 0.1 vol% of water, from about 0.01 vol% to about 0.1 vol% of water, or from about 0.05 vol% to about 0.1 vol% of water. In some embodiments, the second fluid comprises from about 0.1 vol% to about 99 vol% of the at least one impurity. In some embodiments, the second fluid comprises from about 0.1 vol% to about 99 vol%, about 95 vol%, about 90 vol%, about 80 vol%, about 70 vol%, about 60 vol%, about 50 vol%, about 40 vol%, about 30 vol%, about 20 vol%, about 10 vol%, or about 5 vol% of the at least one impurity. In some embodiments, the second fluid comprises from about 0.1 vol%, about 1 vol%, about 2 vol%, about 5 vol%, about 10 vol%, about 20 vol%, about 30 vol%, about 40 vol%, about 50 vol%, about 60 vol%, about 70 vol%, about 80 vol%, or about 90 vol%, to about 99 vol% of the at least one impurity. (ii) When the first fluid comprises a hydrogen containing molecule that is not a carbon containing compound, the second fluid comprises water, and at least one impurity. In some embodiments, the second fluid comprises from about 0.1 vol% to about 99 vol% of water. In some embodiments, the second fluid comprises from about 0.1 vol% to about 99 vol%, about 95 vol%, about 90 vol%, about 80 vol%, about 70 vol%, about 60 vol%, about 50 vol%, about 40 vol%, about 30 vol%, about 20 vol%, about 10 vol%, or about 5 vol% of water. In some embodiments, the second fluid comprises from about 0.1 vol%, about 1 vol%, about 2 vol%, about 5 vol%, about 10 vol%, about 20 vol%, about 30 vol%, about 40 vol%, about 50 vol%, about 60 vol%, about 70 vol%, about 80 vol%, or about 90 vol%, to about 99 vol% of water. In some embodiments, the second fluid comprises from about 0.1 vol% to about 99 vol% of the at least one impurity. In some embodiments, the second fluid comprises from about 0.1 vol% to about 99 vol%, about 95 vol%, about 90 vol%, about 80 vol%, about 70 vol%, about 60 vol%, about 50 vol%, about 40 vol%, about 30 vol%, about 20 vol%, about 10 vol%, or about 5 vol% of the at least one impurity. In some embodiments, the second fluid comprises from about 0.1 vol%, about 1 vol%, about 2 vol%, about 5 vol%, about 10 vol%, about 20 vol%, about 30 vol%, about 40 vol%, about 50 vol%, about 60 vol%, about 70 vol%, about 80 vol%, or about 90 vol%, to about 99 vol% of the at least one impurity. (iii) When the first fluid comprises a combination of a carbon containing compound and a hydrogen containing molecule that is not a carbon containing compound, the second fluid comprises carbon dioxide, water, and at least one impurity. In some embodiments, the second fluid comprises from about 0.1 vol% to about 99 vol% of carbon dioxide. In some embodiments, the second fluid comprises from about 0.1 vol% to about 99 vol%, about 95 vol%, about 90 vol%, about 80 vol%, about 70 vol%, about 60 vol%, about 50 vol%, about 40 vol%, about 30 vol%, about 20 vol%, about 10 vol%, or about 5 vol% of carbon dioxide. In some embodiments, the second fluid comprises from about 0.1 vol%, about 1 vol%, about 2 vol%, about 5 vol%, about 10 vol%, about 20 vol%, about 30 vol%, about 40 vol%, about 50 vol%, about 60 vol%, about 70 vol%, about 80 vol%, or about 90 vol%, to about 99 vol% of carbon dioxide. In some embodiments, the second fluid comprises from about 0.1 vol% to about 99 vol% of water. In some embodiments, the second fluid comprises from about 0.1 vol% to about 99 vol%, about 95 vol%, about 90 vol%, about 80 vol%, about 70 vol%, about 60 vol%, about 50 vol%, about 40 vol%, about 30 vol%, about 20 vol%, about 10 vol%, or about 5 vol% of water. In some embodiments, the second fluid comprises from about 0.1 vol%, about 1 vol%, about 2 vol%, about 5 vol%, about 10 vol%, about 20 vol%, about 30 vol%, about 40 vol%, about 50 vol%, about 60 vol%, about 70 vol%, about 80 vol%, or about 90 vol%, to about 99 vol% of water. In some embodiments, the second fluid comprises from about 0.1 vol% to about 99 vol% of the at least one impurity. In some embodiments, the second fluid comprises from about 0.1 vol% to about 99 vol%, about 95 vol%, about 90 vol%, about 80 vol%, about 70 vol%, about 60 vol%, about 50 vol%, about 40 vol%, about 30 vol%, about 20 vol%, about 10 vol%, or about 5 vol% of the at least one impurity. In some embodiments, the second fluid comprises from about 0.1 vol%, about 1 vol%, about 2 vol%, about 5 vol%, about 10 vol%, about 20 vol%, about 30 vol%, about 40 vol%, about 50 vol%, about 60 vol%, about 70 vol%, about 80 vol%, or about 90 vol%, to about 99 vol% of the at least one impurity. Impurity In some embodiments, the at least one impurity is selected from the group consisting of a carbon containing compound, a hydrogen containing molecule that is not a hydrocarbon, an auxiliary fluid and mixtures thereof. Each of the carbon containing compound, the hydrogen containing molecule that is not a hydrocarbon, and the auxiliary fluid may independently be as described herein. For example, the at least one impurity may be a partially oxygenated counterpart of the carbon containing compound, the hydrogen containing compound that is not a hydrocarbon, the auxiliary fluid, or mixtures thereof. In some embodiments, the at least one impurity is selected from the group consisting of hydrogen, carbon monoxide, methane, ethane, glycerol, ethanol, acetone, butanol, heptane, toluene and mixtures thereof. In some embodiments, when the first fluid comprises a carbon containing compound, the at least one impurity is selected from the group consisting of carbon monoxide, hydrogen and the carbon containing compound. In some embodiments, when the first fluid comprises a carbon containing compound, the at least one impurity is selected from the group consisting of carbon monoxide, methane, ethane, glycerol, ethanol, acetone, butanol, heptane, toluene and mixtures thereof. In some embodiments, when the first fluid comprises a hydrogen containing molecule that is not a hydrocarbon, the at least one impurity may be the hydrogen containing molecule that is not a hydrocarbon. In some embodiments, when the first fluid comprises a hydrogen containing molecule that is not a hydrocarbon, the at least one impurity may be hydrogen. The at least one impurity of the third fluid may independently be as described herein in relation to the second fluid. In some embodiments, the concentration of the at least one impurity in the third fluid is less than the concentration of the at least one impurity in the second fluid. Without wishing to be bound by theory, this is because at least a proportion of the at least one impurity in the second fluid has been converted to carbon dioxide and / or water. For example, the second vessel is configured to convert the at least one impurity into carbon dioxide and / or water. In some embodiments, the concentration of the at least one impurity in the third fluid is from about 1% to about 500% less than the concentration of carbon dioxide in the second fluid. For example, the concentration of the at least one impurity in the third fluid is from about 1% to about 200% less than the concentration of carbon dioxide in the second fluid. For example, the concentration of the at least one impurity in the third fluid is about 1%, 2%, 5%, 10%, 20%, 25%, 50%, 75%, 100%, 150%, 200% or 500% less than the concentration of the at least one impurity in the second fluid. In some embodiments, the third fluid comprises from about 0.01 vol% to about 10 vol% of the at least one impurity. For example, the third fluid comprises from about 0.01 vol% to about 5 vol% of the at least one impurity. For example, the third fluid comprises from about 0.01 vol% to about 1 vol% of the at least one impurity. Third fluid The third fluid comprises water. In some embodiments, the water is deionised water. In some embodiments, the water is distilled water. In some embodiments, the third fluid comprises an auxiliary fluid as described herein. In some embodiments, the third fluid does not comprise a carbon containing molecule or hydrogen containing molecule that is not a hydrocarbon as described herein. In all embodiments, the sum of the components in the third fluid does not exceed 100 vol%. In some embodiments, the third fluid comprises from about 1 vol% to about 100 vol% of water. For example, the third fluid comprises from about 2 vol% to about 100 vol% of water. In some embodiments, the third fluid comprises from about 1 vol% to about 100 vol%, about 99 vol%, about 95 vol%, about 90 vol%, about 80 vol%, about 70 vol%, about 60 vol%, about 50 vol%, about 40 vol%, about 30 vol%, about 20 vol%, about 10 vol%, or about 5 vol% of water. In some embodiments, the third fluid comprises from about 1 vol%, about 2 vol%, about 5 vol%, about 10 vol%, about 20 vol%, about 30 vol%, about 40 vol%, about 50 vol%, about 60 vol%, about 70 vol%, about 80 vol%, or about 90 vol%, to about 100 vol% of water. Fourth fluid The fourth fluid comprises hydrogen. In some embodiments, the fourth fluid comprises hydrogen and water. In some embodiments, the fourth fluid comprises an auxiliary fluid as described herein. In all embodiments, the sum of the components in the fourth fluid does not exceed 100 vol%. In some embodiments, the fourth fluid comprises from about 1 vol% to about 100 vol% of hydrogen. In some embodiments, the fourth fluid comprises from about 1 vol% to about 100 vol%, about 99 vol%, about 95 vol%, about 90 vol%, about 80 vol%, about 70 vol%, about 60 vol%, about 50 vol%, about 40 vol%, about 30 vol%, about 20 vol%, about 10 vol%, or about 5 vol% of hydrogen. In some embodiments, the fourth fluid comprises from about 1 vol%, about 2 vol%, about 5 vol%, about 10 vol%, about 20 vol%, about 30 vol%, about 40 vol%, about 50 vol%, about 60 vol%, about 70 vol%, about 80 vol%, or about 90 vol%, to about 100 vol% of hydrogen. In some embodiments, the fourth fluid comprises from about 1 vol% to about 60 vol% of hydrogen and from about 1 vol% to about 40 vol% of water. In an eighth aspect, the invention relates to a use of a combination, composition or material as described herein for producing hydrogen and / or carbon dioxide. In a ninth aspect, the invention relates to a process of preparing a combination, composition or material as described herein. In some embodiments, the process comprises the steps of: mixing a first metal oxide as described herein with a second metal oxide as described herein in the presence of a solvent to produce a mixture; grinding the mixture; and calcining ground mixture at a temperature of between 500 °C and 1500 °C (preferably between 800 °C and 1100 °C. In some embodiments, the solvent is an organic solvent (such as ethanol). In some embodiments, the ratio of first metal oxide to second metal oxide of from about 1:0.9 to about 1:90. For example, the ratio of first metal oxide to second metal oxide is from about 1:4.5 to about 1:45. Preferably, the ratio of first metal oxide to second metal oxide is about 1:5, about 1:6, about 1:7, about 1:8, about 1:9, about 1:10, about 1:11, about 1:12, about 1:13, about 1;14 or about 1:15. Preferably, the ratio of first metal oxide to second metal oxide is about 1:7, about 1:8, about 1:9, about 1:10, about 1:11, or about 1:12. In some embodiments, the invention relates to a process of preparing a combination, composition or material as described herein. In some embodiments, the process comprises the steps of: combining a first metal nitrate with a second metal nitrate to form a mixture; adding an acid (such as citric acid) to the mixture to form an acidified mixture; mixing the acidified mixture with a first metal oxide as described herein; and calcining ground mixture at a temperature of between 300 °C and 1200 °C (preferably between 800 °C and 1000 °C. In some embodiments, the process comprises the step of adding a gelling agent (such as ethylene glycol) to the acidified mixture. In some embodiments, the metal of the first metal nitrate is the same as described herein in relation to A. In some embodiments, the metal of the second metal nitrate is the same as described herein in relation to B. In a tenth aspect, the invention relates to a combination, composition or material prepared by a process as described herein. Definitions The term mixed ionic-electronic conductor (MIEC) is known to the skilled person who clearly understands its bounds. An MIEC is any material that has significant electronic and ionic conductions (for example at standard temperature and pressure). A MIEC may be a non-stoichiometric compounds such as a non-stoichiometric oxide. For example, a MIEC may be a perovskite type metal oxide or a fluorite type metal oxide In some embodiments, the term perovskite type metal oxide may be replaced with the term perovskite metal oxide or perovskite. The second metal oxide may also be a perovskite type metal oxide at the temperature used in the processes described herein. A first metal oxide may satisfy the change in standard Gibbs energy defined herein at its operating temperature (e.g. at the temperature of a process as described herein). also be a perovskite type metal oxide at the temperature used in the processes described herein. As used herein, δ represents the non-stoichiometry of a material / metal oxide and is from 0 to 0.5. Any fluid described herein may be a gas or a liquid. As such, the term fluid refers to a gas, a liquid, or a combination of a gas and a liquid. Whether a specific fluid component is a gas or a liquid will depend on its temperature and / or pressure. In some embodiments, the fluid described herein is a liquid. Preferably, in some embodiments, the fluid described herein is a gas. The term “water” refers to fluid water. That is, the water described herein may be liquid water or gaseous water (sometimes referred to as steam or water vapour). In some embodiments, the water described herein is liquid water. Preferably, the water described herein is gaseous water. The term vol% means volume %. Unless otherwise stated, the term vol% refers to the volume % of a specific component relative to the total volume of the composition that the specific component is comprised in. The materials described herein are described as being between inputs and outputs of vessels. In such embodiments, the materials may be positioned in any way such that the relevant fluid passes across and / or through the material when moving from the input towards the output. The materials may be positioned spatially in any way to achieve this purpose. The vessels described herein may be combustion vessels. That is, the vessels described herein may be configured to allow a combustion reaction to proceed within them. The features of such vessels depend on the kind of combustion reaction that occurs within and will be known to the skilled person. Examples, of combustion vessels include fixed bed reactors (such as a packed bed reactors) or fluidised bed reactors. In some embodiments, the combustion vessel(s) is a chemical looping combustion vessel (for example, a fluidised bed reactor comprising a material configured to allow a chemical looping combustion reaction). Examples Materials used herein are commercially available and can be obtained from Sigma Aldrich or Fisher Scientific. The planetary ball mill used is the Planetary Mono Mill PULVERISETTE 6 classic line, Manufactured by Fritsch. The thermogravimetric analyser setup used is the Owlstone V-OVG combined with a TGA / DSC 1 Mettler Toledo thermogravimetric analyser (see figure 3). The packed bed reactor setup used was designed and constructed in house. A diagrammatic description is presented in figure 33. A vertical-oriented 3 / 4-inch stainless steel tube was used as the packed bed reactor by first packing the tube with quartz wool. The tube was then filled with 10 g of the sample material followed by 4 g inert Al2O3to form the packed bed and the assembly was placed within a tubular furnace. A Type-K thermocouple was used to probe the centre of the active bed materials for temperature control and temperature logging. An in-line gas analyser (ABB URAS 26) was used to determine the outlet gas composition. Example 1 – Material Synthesis Perovskite Type Metal Oxides Perovskite type metal oxides were synthesised using method 1 or method 2 below. Method 1 (ball milling): Strontium Ferrite Perovskite: SrCO3and Fe2O3were weighed and manually mixed in a 2:1 molar ratio, then placed in a stainless steel crucible with 13 stainless steel balls (20 mm diameter). Then, 60 ml of anhydrous ethanol was added per each 0.25 mol of Fe2O3 added. The crucible was placed in the planetary ball mill (Pulversitte 6) and ball-milled 15 times, each time for 2^min at 600 rpm, followed by 20^min rest. The sample was then dried in an oven at 50 ºC for 24 h, then calcined 3 times at 1000 ºC for 4 h, allowing cooling to room temperature between cycles and using a ramp rate of 5 ºC / min. Other Perovskites: Other perovskites were synthesised using method 1 wherein SrCO3was replaced with the appropriate amount of the corresponding metal carbonate. The appropriate amounts of the corresponding metal carbonate and Fe2O3 were calculated so that the molar ratio of the metal to Fe used was 1:1. For example, a lanthanum ferrite perovskite (LaFeO3) was synthesised using the appropriate amount of La2(CO3)2. Additionally, further perovskites were synthesised using method 1 but using a second metal precursor compound. For example, Sr0.95Ce0.05FeO3-δ was synthesised by using an appropriate amount of CeO2 mixed with the SrCO3 and Fe2O3. The appropriate amount of the CeO2, SrCO3and Fe2O3was calculated so that the molar ratio of the Sr to Fe used was 0.95:1, and the molar ratio of the Ce to Fe used was 0.05:1. For example, SrFe0.95Cu0.05O3-δ was synthesised by using an appropriate amount of CuO mixed with the SrCO3and Fe2O3. The appropriate amount of the CuO, SrCO3and Fe2O3was calculated so that the molar ratio of the Fe to Sr used was 0.95:1, and the molar ratio of the Cu to Sr used was 0.05:1. Method 2 (wet mixing): Strontium Ferrite Perovskite: Sr(NO3)2 and Fe(NO3)3 (in a 1:1 molar ratio) were dissolved in deionised water, heated to 50 ºC and stirred for 30 min. Then, citric acid (CA) was added and stirred for another 30 min. The amount of CA used was calculated so that the molar ratio of CA:metal cations in the resulting solution was 3:1. Ethylene glycol (EG) was added to the resulting mixture and stirred until the formation of a sticky gel at 80 ºC. The amount of EG used was calculated so that the molar ratio of EG to CA used was 2:1. The gel was dried overnight at 130 ºC, followed by calcination at 450 ºC for 4 h with a ramping ratio of 5 ºC / min, then at 900 ºC for 6 h with the same ramp rate. Other Perovskites: Other perovskites were synthesised using method 2 wherein Sr(NO3)2was replaced with the appropriate amount of the corresponding metal nitrate. The appropriate amounts of the corresponding metal nitrate and Fe(NO3)3 were calculated so that the molar ratio of the metal to Fe used was 1:1. For example, a lanthanum ferrite perovskite was synthesised using the appropriate amount of La(NO3)3. Additionally, further perovskites were synthesised using method 2 but using further metal precursor compounds. For example, La0.75Sr0.25FeO3-δwas synthesised by using an appropriate amount of Sr(NO3)2and La(NO3)3with the Fe(NO3)3.The appropriate amounts of the Sr(NO3)2, La(NO3)3 and Fe(NO3)3 were calculated so that the molar ratio of the La to Fe used was 0.75:1, and the molar ratio of the Sr to Fe used was 0.25:1. For example, La0.6Ca0.4Fe0.4Mn0.6O3-δwas synthesised by using an appropriate amount of MnCO3, CaCO3 and La(NO3)3 with the Fe(NO3)3. The appropriate amounts of the MnCO3, CaCO3, La(NO3)3 and Fe(NO3)3 were calculated so that the molar ratio of the La:Ca:fe:Mn used was 0.6:0.4:0.4:0.6. For example, Sr0.5La0.5Fe0.5Ni0.25Ti0.25O3-δ was synthesised by using an appropriate amount of Ni(NO3)3, TiO2 and La(NO3)3 with the Sr(NO3)2 and Fe(NO3)3. The appropriate amounts of the Ni(NO3)3, TiO2, La(NO3)3, Sr(NO3)2and Fe(NO3)3were calculated so that the molar ratio of the Sr:La:Fe:Ni:Ti used was 0.5:0.5:0.5:025:0.25. Perovskite Type Metal Oxide Composites Perovskite type metal oxide composites were synthesised using method 3 or method 4 below. Method 3 (ball milling): Perovskite type metal oxides (synthesised according to method 1 or method 2 above) and Fe2O3 were placed in a crucible in a 1:9 molar ratio. Then, 60 ml of anhydrous ethanol was added per each 0.25 mol of Fe2O3 added. The crucible was placed in the planetary ball mill (Pulversitte 6) and ball-milled 30 times, each for 2 min active milling and 20 min pause. The sample was then dried in an oven at 50 ºC for 24 h, then calcined at 900 ºC for 6 h. For example, the perovskite type metal oxides used were: strontium ferrite perovskite and lanthanum ferrite perovskite. Method 4 (wet mixing): Strontium Ferrite Perovskite Composite: Composite materials were prepared using a modified Pechini method. Fe2O3 powder was dispersed in an excess of 60 vol% ethanol solution and stirred for 5 min, then settled for 3 h and the excess ethanol was decanted, to form an Fe2O3paste. Sr(NO3)2 and Fe(NO3)3 (in a 1:1 molar ratio) were dissolved in deionised water, heated to 50 ºC and stirred for 30 min. Then, citric acid (CA) was added and stirred for another 30 min to form a CA containing solution. The amount of CA used was calculated so that the molar ratio of CA:metal cations in the resulting solution was 3:1. An amount of the Fe2O3paste was mixed with an amount of the CA containing solution and stirred for 30 min at 50 ºC, to form a mixture. The amount of Fe2O3paste and CA containing solution used was calculated so that the molar ratio of the Fe2O3 to resulting perovskite (SrFeO3) was 9:1. Ethylene glycol (EG) was added to the resulting mixture and stirred until the formation of a sticky gel at 80 ºC. The amount of EG used was calculated so that the molar ratio of EG to CA used was 2:1. The gel was dried overnight at 130 ºC, followed by calcination at 450 ºC for 4 h with a ramping ratio of 5 ºC / min, then at 900 ºC for 6 h with the same ramp rate. Other Perovskite Composites: Other perovskite composites were synthesised using method 4 wherein Sr(NO3)2 was replaced with the appropriate amount of the corresponding metal nitrate. The appropriate amounts of the corresponding metal nitrate and Fe(NO3)3were calculated so that the molar ratio of the metal to Fe used was 1:1. For example, a lanthanum ferrite perovskite composite was synthesised using the appropriate amount of La(NO3)3. Gd0.3Ce0.7O2was synthesised using method 4 wherein Sr(NO3)2and Fe(NO3)3were replaced with an appropriate amount of Gd(NO3)3and Ce(NO3)3. The appropriate amounts of the Gd(NO3)3 and Ce(NO3)3 were calculated so that the molar ratio of the Gd:Ce used was 0.3:0.7. Promoted Perovskite Type Metal Oxide Composites Promoted perovskite type metal oxide composites were synthesised using method 5 below. Method 5: Potassium promoted Strontium Ferrite Perovskite Composite: Potassium promoted strontium ferrite perovskite composites were synthesised by depositing KNO3onto a strontium ferrite perovskite composite (synthesised according to method 4 or method 5 above) using an incipient wetness method. KNO3was dissolved in deionised water, and the resulting solution was added dropwise to particles of the strontium ferrite perovskite composite under constant manual stirring. The resulting material was then dried at 120˚C for 12^h in an oven, followed by calcination at 600 ºC for 4 h with a ramp rate of 5 ºC / min. The obtained loading was 10 wt.% based on the oxide of the promoting metal. That is, the amount of KNO3used was determined by calculating an amount of K2O that was 10 wt.% of the resulting promoted composite and then calculating the amount of KNO3 needed to provide this amount of K2O (noting that the nitrate decomposes to the corresponding oxide during the thermal process). Other Promoted Strontium Perovskite Composites: Other promoted strontium perovskite composites were synthesised using method 5 wherein KNO3was replaced with the appropriate amount of the corresponding promoter nitrate. For example, a sodium promoted strontium ferrite perovskite composite was synthesised using the appropriate amount of NaNO3. For example, a caesium promoted strontium ferrite perovskite composite was synthesised using the appropriate amount of CsNO3. For example, a silver promoted strontium ferrite perovskite composite was synthesised using the appropriate amount of AgNO3. Other Promoted Perovskite Composites: Other promoted perovskite composites were synthesised using method 5 wherein the strontium ferrite perovskite composite was replaced with the appropriate amount of the corresponding metal oxide type perovskite composite. For example, a potassium promoted lanthanum perovskite composite was synthesised according to method 5, wherein the strontium perovskite composite was replaced with a lanthanum perovskite composite. For example, a sodium promoted lanthanum perovskite composite was synthesised according to method 5, wherein the strontium perovskite composite was replaced with a lanthanum perovskite composite, and the KNO3was replaced with the appropriate amount of NaNO3. For example, a caesium promoted lanthanum perovskite composite was synthesised according to method 5, wherein the strontium perovskite composite was replaced with a lanthanum perovskite composite, and the KNO3was replaced with the appropriate amount of CsNO3. Example 2 Experimental investigations were carried out in a Mettler Toledo’s TGA 1 unit with a horizontal reaction chamber (figure 3). A balance arm was located in the middle of the chamber, upon where an alumina crucible containing a test material was placed. The total gas flowrate through the chamber was 150 mL / min, created using the reducing or oxidising components and diluting gases. The mixture was created using Owlstone V- OVG, where the composition of the gas was manipulated by changing the setpoint temperature of the Owlstone unit. Experiments were carried out by heating the sample from 50 to 900 ºC, then cooling it back to 50 ºC; both steps with a rate of 10 ºC / min. The steps also differed in the composition of the gas introduced to the TGA analyser. The materials tested all showed exceptional cyclability, oxidation capability and water splitting (hydrogen production) capability. Of particular note are the materials shown in Table 5 and figures 1 to 32. Table 5 Fig. Material Step I Step II Step III Step IV 4 SrFe0.95Cu0.05O3-δ 50 °C to 700 °C 700 °C to 50 - - at 10 °C / min °C at -10 (under 0.7%vol °C / min (under Acetone in N2) N2 for the first 60 sec followed by Air) 5 SrFe0.95Cu0.05O3-δ50 °C to 700 °C 700 °C to 50 - - at 10 °C / min °C at -10 (under °C / min 0.24%vol (under N2 for Ethanol in N2) the first 60 sec followed by Air) Ag (15wt.%) on 50 °C to 900 °C 900 °C to 50 - - SrCeFeO3-δat 10 °C / min °C at -10 (under 3.8%vol °C / min Acetone in N2) (under N2 for the first 60 sec followed by Air) Ag (15wt.%) on 50 °C to 900 °C 900 °C to 50 - - SrCeFeO3-δat 10 °C / min °C at -10 (under 3.8%vol °C / min Acetone in N2) (under N2 for the first 60 sec followed by Humid N2) La0.75Sr0.25FeO3-δ 50 °C to 900 °C 900 °C to 50 - - at 10 °C / min °C at -10 (under 5%vol H2°C / min in N2) (under humid N2) La0.75Sr0.25FeO3-δ50 °C to 900 °C 900 °C to 50 - - at 10°C / min °C at -10 (under 3.8%vol °C / min Acetone in N2) (under humid N2) La0.75Sr0.25FeO3-δ50 °C to 900 °C 900 °C to 50 - - at 10°C / min °C at -10 (under 3.7%vol °C / min Ethanol in N2) (under humid N2) NiFe2O4 50 °C to 800 °C 800 °C to 50 - - at 10°C / min °C at -10 (under 3.8%vol °C / min Acetone in N2) (under 60 sec N2 followed by Air) NiFe2O450 °C to 800 °C 800 °C to 50 - - at 10 °C / min °C at -10 (under 3.8%vol °C / min Acetone in N2) (under humid N2) La0.6Ca0.4Fe0.4Mn0.6 50 °C to 900 °C 900 °C to 50 - - O3-δat 10 °C / min °C at -10 (under 5%vol H2°C / min in N2) (under 60 sec N2 followed by Air) La0.6Ca0.4Fe0.4Mn0.6 50 °C to 900 °C 900 °C to 50 - - O3-δat 10 °C / min °C at -10 (under 5%vol H2°C / min in N2) (under Humid N2) La0.6Ca0.4Fe0.4Mn0.6 50 °C to 900 °C 900 °C to 50 - - O3-δ at 10 °C / min °C at -10 (under 3.7%vol °C / min Ethanol) (under Humid N2) Sr0.5La0.5Fe0.5Ni0.25Ti 50 °C to 900 °C 900 °C to 50 50 °C to 900 °C to0.25O3-δat 10 °C / min °C at -10 900 °C at 50 °C at - (under 5%vol H2°C / min 10 10 in N2) (under °C / min °C / min Humid N2) (under (under 5%vol H260 sec in N2) N2 followed by Air) Sr0.5La0.5Fe0.5Ni0.25Ti 50 °C to 900 °C 900 °C to 50 - - 0.25O3-δ at 10 °C / min °C at -10 (under 3.7%vol °C / min H2in N2) (under Humid N2) Cu0.25Co0.25Fe2.5O3-δ 50 °C to 900 °C 900 °C to 50 50 °C to 900 °C to at 10 °C / min °C at -10 900 °C at 50 °C at - (under 5%vol H2°C / min 10 10 in N2) (under °C / min °C / min Humid N2) (under (under 5%vol H2 60 sec in N2) N2 followed by Air) Cu0.25Co0.25Fe2.5O3-δ50 °C to 900 °C 900 °C to 50 - - at 10 °C / min °C at -10 (under 3.7%vol °C / min Ethanol in N2) (under Humid N2) Fe2O3on 50 °C to 750 °C 750 °C to 50 - - Gd0.3Ce0.7O2-δat 10 °C / min °C at -10 (under 5%vol H2 °C / min in N2) (under Humid N2) 1 Fe2O3 on 50 °C to 750 °C 750 °C to 50 - - Gd0.3Ce0.7O2-δat 10 °C / min °C at -10 (under 5%vol °C / min in air H2, 3.7%vol Ethanol, 3.8%vol Acetone, or 0.75%vol Butanol in N2) In Table 5 and figures 1 to 32, δ represents the non-stoichiometry of the material and is from 0 to 0.5. Example 3 – Packed Bed Reactor A system was designed and constructed (see figure 33). A first packed bed reactor was created by inserting 10 g of sample material and 4 g of Al2O3 (inert material), all with a particle size of 180-355 micrometres, into the stainless- steel vertical tube (15 mm internal diameter). The tube was placed in the electrically- heated furnace. From the top of the tube, a gas mixture was provided. The gas mixture was created using mass-flow controllers and rotameters, mixing N2, CO, CO2, H2 and air (all BOC), as needed. Water vapour was also used, first vaporising water in a dedicated heated tube. Flowrate of the gas mixture introduced to the reactor was always 350 mL / min. The gas leaving the reactor was directed to ABB analysers (EL3020 and URAS 26) to measure CO, CO2, O2, and H2, or to a second packed bed reactor. The reactor was heated in a flow of air. The experimental temperature was set using a proportional integral derivative (PID) controller against a temperature reading from a thermocouple positioned in the middle of the material bed. When the setpoint temperature was reached, the gas was changed to N2 for 2 min, then to a gas mixture of the required composition. The internal pressure of the reactor was maintained 1 bar. The second reactor was the same as the first reactor except that it included a packed bed comprising a second metal oxide material. The resulting gas stream from the second vessel was directed to an analyser. The materials used in the first reactor were the same as those tested in Example 2 and all showed exceptional cyclability, oxidation capability and water splitting (hydrogen production) capability. Of particular note are the materials shown in Table 6 and figures 34 to 38. Table 6 Fig. Material Step I Step II 34 K2O impregnated Fe2O3 Operating Temperature: 7%vol H2O in N2 on LaFeO3-δ 500 °C; until ~0%vol H2 9%vol CO in N2for 5 min 35 Fe2O3on LaFeO3-δOperating Temperature: 7%vol H2O in N2500 °C; until ~0%vol H2 9%vol CO in N2 for 5 minutes 36 K2O impregnated Fe2O3 Operating Temperature: Oxidation Step: on LaFeO3-δ600 °C; 7%vol H2O in N29%vol CO in N2for 5 until ~0%vol H2minutes 37 Fe2O3on LaFeO3-δOperating Temperature: 7%vol H2O in N2600 °C; until ~0%vol H2 9%vol CO in N2 for 5 minutes In Table 6 and figures 34 to 38, δ represents the non-stoichiometry of the material and is from 0 to 0.5. Figure 34: Average H2 yield: 75 ml → 3.141 mmolH2 Specific H2yield: 0.3141 mmolH2 / gmaterialNormalised to reduction step duration: 0.06282 mmolH2 / gmaterial / minred. Figure 35: Average H2yield: 60 ml → 2.513 mmolH2Specific H2yield: 0.2513 mmolH2 / gmaterialNormalised to reduction step duration: 0.05025 mmolH2 / gmaterial / minred Figure 36: Average H2yield: 96 ml → 4.020 mmolH2Specific H2yield: 0.4020 mmolH2 / gmaterialNormalised to reduction step duration: 0.08040 mmolH2 / gmaterial / minre Figure 37: Average H2yield: 93 ml → 3.894 mmolH2Specific H2yield: 0.3894 mmolH2 / gmaterialNormalised to reduction step duration: 0.07789 mmolH2 / gmaterial / minred Modifications It will be appreciated that many modifications may be made to the embodiments hereinbefore described. Such modifications may involve equivalent and other features which are already known to the skilled person and which may be used instead of or in addition to features already described herein. Features of one embodiment may be replaced or supplemented by features of another embodiment. Although claims have been formulated in this application to particular combinations of features, it should be understood that the scope of the disclosure of the present invention also includes any novel features or any novel combination of features disclosed herein either explicitly or implicitly or any generalization thereof, whether or not it relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as does the present invention. The applicant hereby gives notice that new claims may be formulated to such features and / or combinations of such features during the prosecution of the present application or of any further applications.

Claims

Claims 1. A combination of a first metal oxide and a second metal oxide, wherein the second metal oxide is a mixed ionic-electronic conductor, the first metal oxide comprises a metal (M) and oxygen, and the first metal oxide’s change in standard Gibbs energy (in J / mol O2) for the reaction: ^^^^+ ^^= ^^^^^^wherein x is from 0.1 to 5, and y is from 0 to 5; is bounded by: 25.7T − 488470 < ΔG^^^^ < 178.9^ − 488470 for T being from 300 K to 1000 K.

2. The combination according to claim 1, wherein the metal of the first metal oxide is selected from the group consisting of transition metals, lanthanides, p-block metals, s-block metals and mixtures thereof.

3. The combination according to claim 1 or claim 2, wherein the transition metal is selected from the group consisting of iron, manganese, cobalt, molybdenum, tungsten, and mixtures thereof.

4. The combination according to any of claims 1 to 3, wherein the first metal oxide comprises iron.

5. The combination according to any of claims 1 to 4, wherein the first metal oxide is selected from the group consisting of Fe2O3, Fe3O4, FeO, and mixtures thereof.

6. The combination according to any of claims 1 to 5, wherein the first metal oxide’s change in standard Gibbs energy (in J / mol O2) for the reaction: ^^^^+ ^^= ^^^^^^is bounded by: 64.0^ − 488470 < ΔG^^^^< 140.6T − 488470 for T being from 300 K to 1000 K.

7. The combination according to any of claims 1 to 6, wherein the second metal oxide is a perovskite type metal oxide (for example at standard temperature and pressure).

8. The combination according to any of claims 1 to 7, wherein the second metal oxide has the formula ABX3-δ, wherein A is one or more metals; B is one or more metals; X is oxygen; and δ is from 0 to 0.

5.

9. The combination according to claim 8, wherein A is selected from the group consisting of transition metals, lanthanides, actinides, p-block metals, s-block metals and mixtures thereof; and / or B is selected from the group consisting of transition metals, lanthanides, actinides, p-block metals, s-block metals and mixtures thereof.

10. The combination according to claim 8 or 9, wherein A is A1xA2(1-x), and wherein A1and A2are each independently the same as described for A.

11. The combination according to any one of claims 8 to 10, wherein A is independently selected from the group consisting of La, Sr, Gd, Ca, Ce, K, Y, and mixtures thereof.

12. The combination according to any one of claims 8 to 11, wherein B is B1xB2(1-x), wherein B1and B2are each independently the same as described for B.

13. The combination according to any one of claims 8 to 12, wherein B is independently selected from the group consisting of Fe, Mn, Cu, Ce, Co, Ti, Ni, and mixtures thereof.

14. The combination according to any one of claims 1 to 13, wherein the second metal oxide has the formula SrxLa(1-x)FeO3-δ, SrFeO3-δ, LaFeO3-δ, La0.75Sr0.25FeO3-δ,15. The combination according to any one of claims 1 to 14, wherein the combination comprises from about 5 wt.% to about 95 wt.% of the first metal oxide; and / or from about 5 wt.% to about 95 wt.% of the second metal oxide.

16. The combination according to any one of claims 1 to 15, wherein the combination comprises a third component which comprises at least one promoter.

17. The combination according to claim 16, wherein the third component is a metal oxide, a metal, or a compound.

18. The combination according to claim 16 or 17, wherein the at least one promoter is selected from the group of alkali metals, alkali earth metals, and mixtures thereof.

19. The combination according to any one of claims 16 to 18, wherein the at least one promoter is selected from the group of K, Na, Cs, Rb, Li and mixtures thereof.

20. The combination according to any one of claims 16 to 19, wherein the combination comprises a catalytic amount of the third component.

21. The combination according to any one of claims 16 to 20, wherein the first metal oxide is Fe2O3, Fe3O4, or FeO, the second metal oxide has the formula SrxLa(1-x)FeO3-δ, SrFeO3-δ or LaFeO3-δ, and the third component is a metal oxide or combination of metal oxides wherein each metal of each (third component) metal oxide is independently selected from the group consisting of K, Na, Ag, Cs, Rb, Li and mixtures thereof, wherein x is any value from 0.01 to 0.99, such as 0.05 to 0.

95.

22. The combination according to any one of claims 16 to 20, wherein the first metal oxide is Fe2O3, Fe3O4, or FeO, the second metal oxide has the formula SrxLa(1-x)FeO3-δ, SrFeO3-δor LaFeO3-δ, and the third component is a metal oxide or combination of metal oxides wherein each (third component) metal oxide is independently selected from the group consisting of K2O, Na2O, Cs2O, Rb2O, and Ag2O, wherein x is any value from 0.01 to 0.99, such as 0.05 to 0.

95.

23. A vessel comprising the combination as described in any one of claims 1 to 22.

24. A process, the process comprising the steps of: contacting a first fluid with a combination as described in any one of claims 1 to 22 to produce a second fluid; wherein: the first fluid comprises:a carbon containing compound, a hydrogen containing molecule that is not a hydrocarbon, or a combination of a carbon containing compound and a hydrogen containing molecule that is not a hydrocarbon.

25. A process according to claim 24, further comprising the step of providing the first fluid at a temperature of from about 300 °C to about 1000 °C.

26. A process, the process comprising the steps of: contacting a third fluid with a combination as described in any one of claims 1 to 22 to produce a fourth fluid; wherein: the third fluid comprises water, and the fourth fluid comprises hydrogen.

27. Use of a combination as described in any one of claims 1 to 22 or a vessel as described in claim 23 for producing hydrogen and / or carbon dioxide.

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