Materials for carbon dioxide and / or carbon monoxide conversion

Abstract

A methanation catalyst for converting carbon dioxide and / or carbon monoxide into methane is disclosed. The catalyst comprises a phyllosilicate mineral functionalised with a catalyst metal.

Description

MATERIALS FOR CARBON DIOXIDE AND / OR CARBON MONOXIDE CONVERSIONPRIORITY DOCUMENTS

[0001] The present application claims priority from Australian Provisional Patent Application No. 2024903577 titled “MATERIALS FOR CARBON DIOXIDE AND / OR CARBON MONOXIDE CONVERSION” and filed on 1 November 2024, the content of which is hereby incorporated by reference in its entirety.TECHNICAL FIELD

[0002] The present disclosure relates to materials and processes for catalytic conversion of carbon dioxide and / or carbon monoxide into methane.BACKGROUND

[0003] Greenhouse gases (GHGs) emissions have resulted in climate change and global warming. Carbon dioxide (CO2) is the major GHG as it arises from the combustion of fossil fuels. [1]

[0004] There have been increasing efforts to curb CO2 emissions. One way this can be done is to convert CO2 into value added products including fine chemical and fuels such as methanol, formaldehyde, methane, formic acid and so on. However, CO2 is a stable, inert molecule which makes it difficult to react without a catalyst or external energy source. [2]

[0005] Conversion of CO2 to CH4 is a highly sought after operation as the latter is a high energy density fuel that can be used for commercial applications. [3] The methanation of CO2 is called the Sabatier reaction, and is represented by the following equation:CO2+ 4H2= CH4+2H2O Eq. 1

[0006] A highly active catalyst with excellent stability is required for the methanation process to be viable. Over the years, many researchers have developed metal-based catalysts for the hydrogenation of CO2. Due to the availability and low price, transition metals have been investigated extensively over noble metals for this reaction. Despite these efforts, there remains a need for new metal-based catalysts for the hydrogenation of CO2 that are economical, efficient, robust and / or stable.SUMMARY

[0007] The present disclosure arises from the inventors’ surprising discovery that clay mineral materials such as halloysite and attapulgite can be functionalised with metals to produce stable catalysts that can be used to efficiently produce methane from carbon dioxide and / or carbon monoxide.

[0008] According to a first aspect there is provided a methanation catalyst for converting carbon dioxide and / or carbon monoxide into methane, the catalyst comprising a phyllosilicate mineral functionalised with a catalyst metal.

[0009] It will be appreciated by the person of skill in the art that a methanation reaction is a catalytic reaction of hydrogen with carbon dioxide and / or carbon monoxide to produce a methane-rich gas.

[0010] In certain embodiments of the first aspect, the phyllosilicate mineral is an aluminosilicate clay mineral. In certain specific embodiments, the aluminosilicate clay mineral is attapulgite. In other specific embodiments, the aluminosilicate clay mineral is halloysite.

[0011] In certain embodiments of the first aspect, the catalyst metal is selected from the group consisting of nickel (Ni) and iron (Fe).

[0012] In certain embodiments of the first aspect, the methanation catalyst comprises from about 5% to about 20% catalyst metal.

[0013] According to a second aspect there is provided a process for producing a methane-rich gas, the process comprising reacting a gas mixture comprising carbon dioxide and / or carbon monoxide and hydrogen in the presence of the methanation catalyst of the first aspect to produce a methane-rich product gas comprising methane.

[0014] In certain embodiments of the second aspect, the process further comprises a catalyst preparation step that precedes the step of reacting the gas mixture comprising carbon dioxide and / or carbon monoxide and hydrogen in the presence of the methanation catalyst step, the catalyst preparation step comprising heating the methanation catalyst in the presence of hydrogen gas at a temperature and for a time sufficient to reduce the metal catalyst.

[0015] According to a third aspect there is provided an apparatus for producing methane from carbon dioxide and / or carbon monoxide, the apparatus comprising a reactor comprising the methanation catalyst of the first aspect, the reactor configured to allow passage of hydrogen gas and carbon dioxide and / orcarbon monoxide gas through the reactor such that the hydrogen gas and carbon dioxide and / or carbon monoxide gas come into contact with the methanation catalyst contained therein.

[0016] In certain embodiments of the third aspect, the apparatus further comprises a heat source for supplying heat to the reactor.

[0017] According to a fourth aspect there is provided a process for producing a methanation catalyst that is suitable for converting carbon dioxide and / or carbon monoxide into methane, the process comprising:mixing a phyllosilicate mineral with a solution comprising a salt of a catalyst metal and a solvent to provide a mineral / metal salt mixture;removing solvent from the mineral / metal salt mixture to provide a dried mineral / metal salt mixture; andcalcining the dried mineral / metal salt mixture in the presence of air to produce the methanation catalyst comprising a phyllosilicate mineral functionalised with a catalyst metal.

[0018] In certain embodiments of the fourth aspect, the step of mixing a phyllosilicate mineral with a solution comprising a salt of a catalyst metal and a solvent, comprises stirring at room temperature.

[0019] In certain embodiments of the fourth aspect, the step of removing solvent from the mineral / metal salt mixture, comprises evaporating solvent from the mixture by heating.

[0020] In certain embodiments of the fourth aspect, the step of removing solvent from the mineral / metal salt mixture further comprises drying by heating after the solvent is evaporated.

[0021] In certain embodiments of the fourth aspect, the step of calcining the dried mineral / metal salt mixture comprises heating the mixture to greater than 500 °C in the presence of air for a time sufficient to produce the methanation catalyst.BRIEF DESCRIPTION OF THE FIGURES

[0022] Embodiments of the present disclosure will be discussed with reference to the accompanying figures wherein:

[0023] Figure 1 shows (a) XRD pattern of ATP and 5% to 20%Ni-ATP, (b) FTIR spectra of ATP and 5% to 20%Ni-ATP, and (c) N2 adsorption-desorption isotherms of ATP and 5% to 20%Ni-ATP;

[0024] Figure 2 shows SEM images of (a) Attapulgite, (b) 5%Ni-ATP, (c) 10%Ni-ATP, (d) 15%Ni-ATP and (e) 20%Ni-ATP;

[0025] Figure 3 shows (a) CO2 conversion plot of 10% to 20%Ni-H5 at varying temperature from 250 °C to 400 °C, (b) CO2 conversion plot of 10% to 20%Ni-Nz-H (i.e. New Zealand halloysite) at varying temperature from 250 °C to 400 °C, (c) Comparison graph of 20%Ni on different types of clay materials; Pressure: 1.7 Bar, Temperature: 250 °C to 400 °C, Time: 4 hours, Total Flow rate: 100 mL / min, (CO2 / H2 / N2): 5 / 20 / 75 (%), Catalyst Amt: 0.1 g; and

[0026] Figure 4 shows (a) CO2 conversion plot of ATP and 5% to 20%Ni-ATP at varying temperature from 250 °C to 400 °C, (b) Catalytic stability test at 400 °C for 60 hours, (c) Varying the catalyst amount and the reaction was carried out at 400 °C.DESCRIPTION OF EMBODIMENTS

[0027] Embodiments of the present disclosure will be more clearly understood with reference to the following detailed description.

[0028] Details of terms used herein are given below for the purpose of guiding those of ordinary skill in the art in the practice of the present disclosure. The terminology in this disclosure is understood to be useful for the purpose of providing a better description of particular embodiments and should not be considered limiting.

[0029] Unless otherwise explained, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

[0030] In the context of the present disclosure, the terms “about” and “approximately” are used in combination with an amount, number, or value, then that combination describes the recited amount, number, or value alone as well as the amount, number, or value plus or minus 10% of that amount, number, or value. By way of example, the phrases “about 40%” and “approximately 40%” disclose both “40%” and “from 36% to 44%, inclusive”.

[0031] As used herein, % or wt.% means weight % unless otherwise indicated. When used herein % refers to weight % as compared to the total weight percent of the phase or composition that is being discussed.

[0032] The singular terms “a,” “an,” and “the” include plural referents unless context clearly indicates otherwise. The term “comprises” means “includes”. Therefore, comprising “A” or “B” refers to including A, including B, or including both A and B.

[0033] Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present disclosure, suitable methods and materials are described herein. In case of conflict, the present specification, including explanations of terms, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.

[0034] Disclosed herein is a methanation catalyst for converting carbon dioxide and / or carbon monoxide into methane. The catalyst comprises a phyllosilicate mineral functionalised with a catalyst metal.

[0035] A methanation reaction is a catalytic reaction of hydrogen with carbon dioxide and / or carbon monoxide to produce a methane-rich gas. As discussed, the conversion of CO2 to CH4 is a highly sought after operation as the latter is a high energy density fuel that can be used for commercial applications. [3]

[0036] The methanation catalyst disclosed herein comprises a phyllosilicate mineral which acts as a support for the catalyst metal. The phyllosilicate mineral may be an aluminosilicate clay mineral. The aluminosilicate clay mineral may be selected from one or more of the group consisting of halloysite (Al2Si2O5(OH)4), kaolinite (Al2Si2O5(OH)4), pyrophyllite (Al2Si4O10(OH)2), talc (Mg3Si4O10(OH)2), illite ((K, H3O)(Al, Mg, Fe)2(Si, Al)4O10[(OH)2,(H2O)] ), montmorillonite (smectite) ((Na, Ca)0.33(Al, Mg)2Si4O10(OH)2·H2O), chlorite ((Mg, Fe)3(Si, Al)4O10(OH)2·(Mg, Fe)3(OH)6), vermiculite ((Mg, Fe, Al)3(Al, Si)4O10(OH)2·4H2O), sepiolite (Mg4Si6O15(OH)2·6H2O), and attapulgite (or palygorskite) ((Mg, AI)2Si4Oi0(OH) • 4(H2O)).

[0037] In certain specific embodiments, the aluminosilicate clay mineral is attapulgite. Attapulgite (abbreviated herein as “ATP”) is a low-cost and naturally available clay mineral that is also known as palygorskite. It is a magnesium aluminium phyllosilicate with the chemical formula (Mg, Al)2Si4O10(OH)·4(H2O). Attapulgite is a typical aluminium-magnesium silicate material, with parallel rods.

[0038] In other specific embodiments, the aluminosilicate clay mineral is halloysite. Halloysite (abbreviated herein as “HNT” and also referred to as halloysite nanotubes) is a low -cost and naturally occurring alumino silicate with tubular morphology. It has the chemical formula Al2Si2O5(OH)4 -2H2O and has a similar composition to kaolinite (Al2Si2O5(OH)4 -2H2O). Natural halloysite-kaolin nanoclays are readily available in the western region of South Australia.

[0039] Other aluminosilicate clay minerals, such as those listed herein, could also be used either alone or in combination.

[0040] Advantageously, phyllosilicate minerals such as aluminosilicate clay minerals have a porous structure that is particularly suitable for supporting a catalyst, they are relatively low cost and they are environmentally stable materials. The selection of catalyst support is important as it can provide huge differences in metal-support interaction as well as metal dispersion.

[0041] The catalyst metal can be any metal that is able to catalyse the reduction of carbon dioxide or carbon monoxide in the presence of hydrogen to produce methane. For example, the catalyst metal could be nickel (Ni), ruthenium (Ru), rhodium (Rh), platinum (Pt), palladium (Pd), cobalt (Co) or iron (Fe). In particular nickel has been widely researched for the hydrogenation of CO2. The catalyst metal may also comprise a second metal. For example, in the case of a nickel catalyst, a second metal such as palladium or cobalt could be used. A person of skill in the art will appreciate that the catalyst metal may be present in the methanation catalyst as an oxide (for example, NiO, Fe2O3, etc) that can be reduced under methanation reaction conditions (for example in the presence of hydrogen gas) to produce a metallic species that may be the primary catalytic species for the methanation reaction.

[0042] The methanation catalyst may comprise from about 5% to about 20% catalyst metal, such as about 5%, about 6%, about 7%, about 8%, about 9%, about 10%, about 11%, about 12%, about 13%, about 14%, about 15%, about 16%, about 17%, about 18%, about 19% or about 20%.

[0043] The methanation catalyst can be produced by a process comprising mixing the phyllosilicate mineral with a solution comprising a salt of the catalyst metal and a solvent to provide a mineral / metal salt mixture. The solvent is then removed from the mineral / metal salt mixture to provide a dried mineral / metal salt mixture. The dried mineral / metal salt mixture is then calcined in the presence of air to produce the methanation catalyst comprising a phyllosilicate mineral functionalised with a catalyst metal.

[0044] The step of mixing the phyllosilicate mineral with a solution comprising the salt of the catalyst metal and the solvent may comprise stirring at room temperature. Stirring can be carried out for a period of from about 0.5 hours to about 5 hours, such as about 4 hours.

[0045] The solvent can be removed from the mineral / metal salt mixture by evaporation. For example, the mineral / metal salt mixture can be heated to a temperature sufficient to evaporate the solvent from the mixture. By way of example only, a mineral / metal salt mixture comprising ethanol as solvent may be heated to about 80 °C to evaporate the solvent.

[0046] After solvent removal from the mineral / metal salt mixture it may be dried by heating. By way of example only, a solid mineral / metal salt mixture obtained after solvent evaporation may be dried at about 100 °C for a period of from about 1 hour to about 24 hours, such as about 12 hours.

[0047] Following evaporation and drying, the dried mineral / metal salt mixture is calcined by heating the mixture to greater than 500 °C in the presence of air for a time sufficient to produce the methanation catalyst. The calcination reaction may be carried out for a period of from about 1 hour to about 12 hours, such as about 5 hours. The calcination reaction results in oxidation of the metal salt that is dispersed within the phyllosilicate mineral to produce a metal oxide disbursed within the phyllosilicate mineral framework.

[0048] In a specific non-limiting example, the methanation catalyst can be produced by dissolving 5%, 10%, 15% or 20% w / v of a nitrate salt of nickel metal in 25 mL of ethanol with stirring at room temperature. Then 1g of attapulgite can be added and the mixture stirred for 4 hours at room temperature. The temperature can then be raised to 80 °C to evaporate the ethanol. The resultant powder can then be dried in a 100 °C oven for 12 hours before being transferred to muffle furnace for calcination at 550 °C for 5 hours under air flow.

[0049] As discussed, the methanation catalyst is particularly useful as a catalyst in a methanation reaction for converting carbon dioxide and / or carbon monoxide into methane. Thus, also disclosed herein is a process for producing a methane-rich gas. The process comprises reacting a gas mixture comprising carbon dioxide and / or carbon monoxide and hydrogen in the presence of the methanation catalyst disclosed herein to produce a methane-rich product gas.

[0050] The process preferably comprises a catalyst preparation step that precedes the step of reacting the gas mixture comprising carbon dioxide and / or carbon monoxide and hydrogen in the presence of the methanation catalyst step. The catalyst preparation step comprises heating the methanation catalyst in the presence of hydrogen gas at a temperature and for a time sufficient to reduce the metal catalyst. For example, the catalyst preparation step may comprise heating the methanation catalyst at about 400 °C for 2 hours under 10% H2 / N2 flow.

[0051] The process may further comprise treating at least part of the methane-rich product gas to remove carbon dioxide to produce a methane-rich carbon dioxide-lean gas.

[0052] Also disclosed herein is an apparatus for producing methane from carbon dioxide and / or carbon monoxide. The apparatus comprises a reactor comprising the methanation catalyst disclosed herein. The reactor is configured to allow passage of hydrogen gas and carbon dioxide and / or carbon monoxide gas through the reactor such that the hydrogen gas and carbon dioxide and / or carbon monoxide gas come intocontact with the methanation catalyst contained therein. For example, the reactor may comprise a hydrogen flow path to allow passage of hydrogen gas through the reactor and a carbon dioxide and / or carbon monoxide flow path to allow passage of carbon dioxide and / or carbon monoxide through the reactor.

[0053] The reactor may comprise a hydrogen gas inlet configured for connection to a source of hydrogen gas and a carbon dioxide and / or carbon monoxide gas inlet configured for connection to a source of carbon dioxide and / or carbon monoxide. The hydrogen gas may be hydrogen gas mixed with an inert carrier gas such as nitrogen or argon. The flow rates of the respective gases into the reactor can be controlled by any suitable means known in the art. For example, the flow rates of the respective gases into the reactor can be controlled using mass flow controllers.

[0054] Reactors for catalytic methanation of carbon dioxide and / or carbon monoxide are known in the art and any of the known reactors can be modified by introducing the methanation catalyst disclosed herein into the reactor. Reactor configurations often employ catalysts supported on thermally conductive substrates to enhance heat dissipation. The reactor may further comprise a heat management system for controlling feed temperature and / or for thermal management to prevent thermal runaway and ensure consistent CO2 conversion. For example, actively cooled membrane reactors can be used to mitigate catalyst deactivation and improve temperature uniformity.

[0055] The apparatus may further comprise a heat source for supplying heat to the reactor.EXAMPLES

[0056] Catalyst Preparation

[0057] A nitrate salt of the Ni metal was weighed to achieve concentrations of 5%, 10%, 15%, 20% (w / v), and dissolved in 25 mL of ethanol and stirred at room temperature. Then 1g of attapulgite (ATP) was weighed and added to the above solution and stirred for 4 hours at room temperature. The temperature was raised to 80 °C to evaporate the solvent used. After drying the resultant powder was dried in a 100 °C oven for 12 hours before it was transferred to a muffle furnace for calcination at 550 °C for 5 hours under air flow.

[0058] The same procedure was used to produce nickel halloysite (Ni-HNT) catalysts by substituting HNT for ATP.

[0059] Material Characterization

[0060] Powder X-ray diffraction (XRD) patterns were measured on a PANalytical Empyrean platform diffractometer using Bragg-Brentano geometry using Cu Ka radiation operating at 40 kV and 40 mA. A fixed divergence slit of 1 / 8° and a scan rate of 0.01° sec-1were used for high angle measurements (5-80°). Textural properties such as surface area, porosity and pore diameter of the samples were measured at -196 °C using N2 gas on a Micromeritics ASAP 2420 surface area and porosity analyser.Morphologies of Ni-ATP samples were analysed by measuring field emission scanning electron microscope (FESEM, Hitachi SU8230).

[0061] Methanation Reaction

[0062] The CO2 hydrogenation performance of the Ni-ATP and Ni-HNT catalysts (100 mg) was tested in a quartz reactor (inner diameter: 8 mm) under atmospheric pressure. The reactant feed containing CO2 gas (5.0 mL / min) and a mixture gas with 10% H2 and 90% N2 (100 mL / min) was controlled by calibrated mass flow controllers, while the outgoing gases were detected by inline gas chromatography. All catalytic performance tests were carried out at ambient pressure with the temperature ranging from 200 °C to 400 °C after the catalysts were pretreated at 400 °C for 2 hours under 10% H2 / N2 flow. At each plateau of temperature, the catalyst was kept for 5 minutes, corresponding to a steady-state measurement. Gases to be used by catalyst materials, methane and the non-condensable product gases were analyzed qualitatively and quantitatively by Perkin Elmer GCs. The catalytic capacity of the ATP composite for the conversion of CO2 into CH4 was tested similarly to Ni-based catalysts. As expected, CH4 was detected in the outlet product in very low quantity.

[0063] The definitions of catalytic performance are as follows:(1) Xco2=c(CO2)in-c(CO2)out / c(CO2)in(2) SCH4=C(CH4) / C(CH4)+C(CO)where Xco2 and Sa is the CO2 conversion and the selectivity of CH4. c is the product quantities of certain gases of the reactor.

[0064] Results and discussion

[0065] The crystallinity of the developed catalyst materials was investigated by X-ray diffraction. Two types of natural nanoclays, halloysite and atapulgite, were used for the conversion of CO2 into methane.Before performing the catalytic reactions, the samples were characterized to obtain the specific surface area, crystal structure and the nature of the metallic sites. Halloysite and attapulgite are both nanoclays and, in this example, the characterization of the attapulgite catalyst is provided. The powder XRD patterns of ATP and nickel functionalised ATP were recorded and are shown in Figure 1(a). An evident peak at 35.8° is a typical characteristic feature of ATP. The typical NiO peaks observed at 20 = 37.3°, 43.2°, 62.9°, 75.3°, and 79.4° are evident in the product catalyst corresponding to diffracting planes of (111), (200), (220), (311) and (222) respectively. These results confirm the successful functionalisation of ATP with NiO species. [4] The FTIR patterns were recorded and shown in Figure 1(b). The absorption peak around 1032 cm-1corresponds to the Si-O-Si bond in the amorphous SiO2. The absorption peak in the range 3000-3800 cm-1is generated due to mainly the presence of surface hydroxyl groups, which is not that evident as ATP in Ni-ATPs. This shows that the hydroxyl groups were successfully helping the Ni species as its support.

[0066] The textural properties of the developed catalyst materials were analysed using N2-adsorption desorption technique. The measured data is shown in Figure 1(c) and listed in Table 1.

[0067] Table 1: Textural properties of 5% to 20%Ni-ATP

[0068] It is very clear that the mineral hybridization of NiO has improved the specific surface area, while comparing it to the pure NiO species. It demonstrates that attapulgite clay material is acting as a perfect platform for the better dispersion of NiO species. It is also worth noting that while increasing the amount of Ni species over ATP the specific surface area shows a decreasing trend. The isotherms show a narrow pore size distribution with H3 type hysteresis loop. It can be noted that there is a higher N2 adsorption in the modified material, indicating a higher specific surface and a large pore volume, which is achieved by hybridizing the NiO species with rod-shaped clay materials.

[0069] H2-TPR was conducted to assess the metal-support interactions and the reducibility of samples. The peaks at a lower temperature correspond to weak interactions, also known as poor reducibility, whereas peaks at higher temperature are due to the stronger Ni-support interactions with smaller particles of NiO species. The NiO reduction was from 150 °C to 700 °C. For all the hybridized samples, only one major reduction peak was found around 400 °C. With the introduction of ATP matrix in the NiO-NiO catalysts, the peaks of NiO shifted towards higher temperature, suggesting that the surface of ATP may have functional hydroxy groups tightly bounded to the active metal. The poor reducibility of NiO at low reduction temperature may result in the insufficiently activated Ni sites. And the highly dispersed Ni particles are generally reduced at higher temperatures.

[0070] The catalytic performance of CO2 methanation depends on the catalyst size and its crystal structure. The morphologies of the clay mineral ATP and freshly synthesized catalysts are shown in Figure 2. The pristine ATP showed a typical rod-like structure with serious agglomeration. The rod width varied from 100 nm to 200 nm and grew randomly in different directions. The SEM image of NiO-ATP in Figure 2 clearly showed that the surface of ATP becomes rougher when NiO is loaded. Small NiO nanoparticles can be detected on the outer surface of ATP. The random arrangement of ATP and their accompanying serious agglomeration may lead to uneven loading of NiO on this sample. The SEM images of different contents of Ni (as NiO in this sample) loaded on the surface of NiO-ATP in Figure 2. showed that, when a small amount of NiO (about 5%, Figure 2) is loaded on surface of NiO-ATP, the ATP becomes rougher and accompanied by many smaller particles. With further increased Ni content, the NiO nanocrystals were found tightly coordinated with the NiO-ATP composite matrix, rather than forming larger particles (Figure 2). The assembly of very small particles greatly enhanced the exposure of surface sites of Ni and significantly heightened the activity of the catalyst, corresponding to the results obtained in the performance testing experiments.

[0071] Catalytic Performance

[0072] The catalytic performance of natural nanoclays on the conversion of CO2 into methane was investigated. Both attapulgite (ATP) and halloysite nanotubes (HNTs) were used as the catalysts for the thermocatalytic conversion of CO2 into methane and the results are shown in Figures 3 and 4 and Table 2. Figure 3 shows that the CFU selectivity of all the tested samples was very high, and the CO2 conversion increases with the increase in temperature. Figure 3 also shows thermocatalytic conversion of CO2 to CFU with the nickel based catalyst materials by varying the support materials from ATP to HNTs. Among them, the purest form of HNT gave a good conversion of about 57% while another H5 and halloysite from New Zealand gave a conversion of 44% and 47% under the reaction conditions. At 400 °C, the CO2 conversion of 20%Ni-ATP (59.0%) was the highest among all the samples, and those of 15%Ni-ATP and 10%Ni- ATP, 5%Ni- ATP and bare ATP were 57.0%, 52.0%, 42.0% and 23.0% respectively. Eventhough the lower temperature (250 °C, 300 °C and 350 °C) promotes the conversion of CO2 into methane, it is evident that 400 °C is the optimum temperature for obtaining best performance. To find the optimum amount of catalyst that can work around this gaseous concentration, the reactions were carried out by varying the catalyst amount from 50 mg to 200 mg and it was found that 150 mg works best in this gaseous concentration, with more than 71% conversion and 97% selectivity into methane. Furthermore, the durability of the catalyst material was assessed by putting the material under its peak performing conditions. It was found that after 15 hours there was a 5% reduction in conversion and at 60 hours there is a 14% reduction in performance. Even though a reduction in conversion was noticed after 60 hours, the catalyst was still performing well by giving a conversion of 60%. It was also found that the performance of the HNT and ATP based catalysts can be altered with the adjustment of the experimental conditions and surface charge and the functional groups of the catalysts.

[0073] Table 2: Catalytic conversion of 5% to 20%Ni-ATP

[0074] Conclusion

[0075] A cost-effective catalyst material with high catalytic activity for the CO2 methanation process has been developed. The catalytic performance of successfully developed Ni-ATP and Ni-halloysite samples was tested and it was found that a large amount of Ni species can be loaded on ATP to provide high performance towards CO2 methanation. It can be clearly concluded that this approach to load Ni on ATP and halloysite natural minerals benefitted in two main ways; the strong interaction between NiO species and MgAbCF support retards the Ni sintering and the coke formation. From the results shown, itis clear that natural HNTs and attapulgites functionalized with different concentration of Ni can be used as low-cost catalysts for converting CO2 into methane with a high selectivity.

[0076] The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that such prior art forms part of the common general knowledge.

[0077] It will be understood that the terms “comprise” and “include” and any of their derivatives (e.g. comprises, comprising, includes, including) as used in this specification, and the claims that follow, is to be taken to be inclusive of features to which the term refers, and is not meant to exclude the presence of any additional features unless otherwise stated or implied.

[0078] In some cases, a single embodiment may, for succinctness and / or to assist in understanding the scope of the disclosure, combine multiple features. It is to be understood that in such a case, these multiple features may be provided separately (in separate embodiments), or in any other suitable combination. Alternatively, where separate features are described in separate embodiments, these separate features may be combined into a single embodiment unless otherwise stated or implied. This also applies to the claims which can be recombined in any combination. That is a claim may be amended to include a feature defined in any other claim. Further a phrase referring to “at least one of’ a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover: a, b, c, a-b, a-c, b-c, and a-b-c.

[0079] It will be appreciated by those skilled in the art that the disclosure is not restricted in its use to the particular application or applications described. Neither is the present disclosure restricted in its preferred embodiment with regard to the particular elements and / or features described or depicted herein. It will be appreciated that the disclosure is not limited to the embodiment or embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope as set forth and defined by the following claims.REFERENCES

[0080] 1. Singh, G., et al., Emerging trends in porous materials for CC capture and conversion. Chemical Society Reviews, 2020. 49(13): p. 4360-4404.

[0081] 2. Zhao, G., et al., Progress in catalyst exploration for heterogeneous CO 2 reduction and utilization: a critical review. Journal of Materials Chemistry A, 2017. 5(41): p. 21625-21649.

[0082] 3. Fan, W. K. and M. Tahir, Recent trends in developments of active metals and heterogenous materials for catalytic CO2 hydrogenation to renewable methane: A review. Journal of Environmental Chemical Engineering, 2021. 9(4): p. 105460.

[0083] 4. Liang, J., et al., Experimental Identification of the Roles of Fe, Ni and Attapulgite in Nitroreduction and Dechlorination of p-Chloronitrobenzene by Attapulgite-Supported Fe / Ni Nanoparticles. Materials (Basel), 2022. 15(3): p. 1254.

Claims

CLAIMS1. A methanation catalyst for converting carbon dioxide and / or carbon monoxide into methane, the catalyst comprising a phyllosilicate mineral functionalised with a catalyst metal.

2. The methanation catalyst according to claim 1, wherein the phyllosilicate mineral is an aluminosilicate clay mineral.

3. The methanation catalyst according to claim 2, wherein the aluminosilicate clay mineral is attapulgite.

4. The methanation catalyst according to claim 2, wherein the aluminosilicate clay mineral is halloysite.

5. The methanation catalyst according to any one of claims 1 to 4, wherein the catalyst metal is selected from the group consisting of nickel (Ni) and iron (Fe).

6. The methanation catalyst according to any one of claims 1 to 5, wherein the methanation catalyst comprises from about 5% to about 20% catalyst metal.

7. A process for producing a methane-rich gas, the process comprising reacting a gas mixture comprising carbon dioxide and / or carbon monoxide and hydrogen in the presence of the methanation catalyst of any one of claims 1 to 6 to produce a methane-rich product gas comprising methane.

8. The process according to claim 7, further comprising a catalyst preparation step that precedes the step of reacting the gas mixture comprising carbon dioxide and / or carbon monoxide and hydrogen in the presence of the methanation catalyst, the catalyst preparation step comprising heating the methanation catalyst in the presence of hydrogen gas at a temperature and for a time sufficient to reduce the metal catalyst.

9. An apparatus for producing methane from carbon dioxide and / or carbon monoxide, the apparatus comprising a reactor comprising the methanation catalyst of any one of claims 1 to 6, the reactor configured to allow passage of hydrogen gas and carbon dioxide and / or carbon monoxide gas through the reactor such that the hydrogen gas and carbon dioxide and / or carbon monoxide gas come into contact with the methanation catalyst contained therein.

10. The apparatus according to claim 9, further comprising a heat source for supplying heat to the reactor.

11. A process for producing a methanation catalyst that is suitable for converting carbon dioxide and / or carbon monoxide into methane, the process comprising:mixing a phyllosilicate mineral with a solution comprising a salt of a catalyst metal and a solvent to provide a mineral / metal salt mixture;removing solvent from the mineral / metal salt mixture to provide a dried mineral / metal salt mixture; andcalcining the dried mineral / metal salt mixture in air to produce the methanation catalyst comprising a phyllosilicate mineral functionalised with a catalyst metal.

12. The process according to claim 11, wherein the step of mixing a phyllosilicate mineral with a solution comprising a salt of a catalyst metal and a solvent comprises stirring at room temperature.

13. The process according to any one of claims 11 to 12, wherein the step of removing solvent from the mineral / metal salt mixture comprises evaporating solvent from the mixture by heating.

14. The process according to any one of claims 11 to 12, wherein the step of removing solvent from the mineral / metal salt mixture further comprises drying by heating after the solvent is evaporated.

15. The process according to any one of claims 11 to 12, wherein the step of calcining the dried mineral / metal salt mixture comprises heating the mixture to greater than 500 °C in the presence of air for a time sufficient to produce the methanation catalyst.

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