Efficient supported Ru catalyst for methanation reaction of carbon dioxide as well as preparation method and application of efficient supported Ru catalyst

Abstract

The invention relates to a preparation method of a supported Ru nano-particle material, in particular to Ru / Al2O3 for a CO2 methanation reaction and a heterogeneous catalyst containing Ru metal particles and Al2O3.

Description

Field of the Invention

[0001] The present invention generally relates to the field of supported Ru catalysts for CO2 methanation reactions. More specifically, the present invention relates to γ-Al2O3 supported Ru nanoparticle catalysts, preparation methods, and uses thereof. Background of the Invention

[0003] To overcome the shortage of fossil fuels for future generations, the development of renewable energy is crucial. Hydrocarbons synthesized from CO2 captured from the air and hydrogen obtained through water electrolysis are considered not only renewable chemical energy carriers but also a process that can close the carbon cycle (Moioli et al., 2019, Renewable and Sustainable Energy Reviews 107, 497–506; et al., 2016, Renewable Power-to-Gas: A technological and economic review. Renewable Energy 85, 1371–1390).

[0004] Current technology allows for the highly selective conversion of CO₂ and hydrogen to methane via the Sabatier reaction. First described by French chemist Paul Sabatier in 1910, the Sabatier reaction has important applications, such as as a power-to-gas process. In this process, methane produced from renewable H₂ and CO₂ can be injected into existing natural gas networks or stored for transport or heating (Lewandowska-Bernat et al., 2018, Applied Energy, 228, 57–67; Falbo et al., 2018, Applied Catalysis B: Environmental, 225, 354–363; Schiebahn et al., 2015, International Journal of Hydrogen Energy, 40, 4285–4294). Over the past few decades, due to widespread concern about CO₂ emissions, significant effort has been invested in developing catalysts and reactors suitable for the Sabatier reaction.

[0005] According to previous studies, CO2 hydrogenation to CH4 can be achieved by using metal catalysts such as ruthenium (Ru), nickel (Ni), cobalt (Co), platinum (Pt), and rhodium (Rh) (Frontera et al., 2017, Catalysts vol. 7; Ashok et al., 2020, Catalysis Today 356, 471–489; Mutschler et al., 2019, Journal of Catalysis 375, 193–201).

[0006] Among them, Ru-based catalysts have shown superior high selectivity and long-term stability. Since the hydrogenation of CO2 to produce methane is an exothermic process, in order to ensure high CO2 conversion and 100% methane selectivity, the low-temperature activity of the catalyst is crucial. Although a large amount of literature shows that under certain conditions, nickel or cobalt catalysts can achieve reaction activity comparable to that of ruthenium catalysts, the sintering phenomenon of metal particles and high activation temperature have always been challenges for the industrialization of the "power-to-gas" process using nickel-based catalysts (Frontera et al., 2017, ibid.; Ashok et al., 2020, ibid.). In addition, a commercial Ru 0.5wt.％ A ruthenium / Al2O3 catalyst (Sigma-Aldrich #206199) achieves 99% CO2 conversion and 99% methane selectivity in the temperature range of 250°C to 300°C without reactant recycling (Gallandat et al., 2018, Sustainable Energy and Fuels 2, 1101–1110). To reduce catalyst costs due to the high price of ruthenium, it is necessary to synthesize ruthenium catalysts with higher mass-specific activity and reduce production costs by simplifying the manufacturing process.

[0007] Ruthenium-supported catalysts are typically synthesized by impregnation and precipitation methods (Peng et al., 2016, ChemCatChem, 8, 139–141; US ​​4,049,584; Zeng et al., 1997, Applied Catalysis B: Environmental, vol. 13; Lin et al., 2019, ACS Catalysis, 9, 1635–1644; Kowalczyk et al., 2008, Applied Catalysis A: General 342, 35–39; Liang et al., 2012, International Journal of Hydrogen Energy 37, 17921–17927). In the traditional impregnation process, the industrial support material (such as Al2O3 or TiO2) is impregnated in an aqueous solution containing a ruthenium component, such as RuCl3·xH2O, RuN4O 10 xH2O and ruthenium(III) acetate, etc. Due to its simple process and high yield of metal components, this method has been widely used in industry (Munnik et al., 2015, Chemical Reviews, vol. 115, 6687–6718; Adrian et al., 2020, CATALYSISTODAY, 356, 419–432; Baddour F, The Engineering of Catalyst Scale Up, BETO peer review 2021, pp. 20-21). In most patents and articles using the impregnation method to synthesize Ru / Al2O3 catalysts, the size and distribution of Ru metal particles on the support vary significantly with the Ru loading (Bobadilla et al., 2019, Chemical Engineering Journal, 357, 248–257). Despite its simplicity, this method has several drawbacks, the most important of which is the uneven distribution of metal particle size and shape (Okal et al., 2007, Applied Catalysis A: General, 319, 202–209). For example, in EP 1 048 347, the Ru / Al 2 O 3 catalyst has a Ru weight percentage between 0.5% and 5% and contains Ru particles with a wide size distribution, ranging from 0.5 nm to 100 nm.

[0008] Yan et al., 2018, Journal of Catalysis, 367, 194-205, used a water-insoluble ruthenium precursor, ruthenium acetylacetone, with ethanol as the solvent for the precursor solution. This method is more preferred than ruthenium chloride because ruthenium (III) acetylacetone has a template effect when synthesizing Ru / Al2O3 catalysts, which helps to disperse Ru, thereby improving the reactivity of the CO2 methanation reaction (Renda et al, 2020, Applied Energy, 279, 115767). However, the use of this alternative precursor and the required solvent leads to higher costs due to the high price of raw materials. In addition, the STEM image of the 3% Ru / Al2O3 sample shows that the size of the Ru particles detected based on the average value of the scale bar (shown as bright spots) is greater than 4nm, while the Ru / Al2O3 catalyst prepared with 1% Ru loading only achieved a CO2 conversion rate of about 5% at 300°C.

[0009] Furthermore, if RuCl3·xH2O is used as a precursor, Cl- contamination on the metal surface is unavoidable (Gates et al., 1995, Chem. Rev, vol. 95, 511-522). In this system, another source of metal contamination may be the alumina support dissolved in the highly acidic solution used during the impregnation process (Munnik et al., 2015, supra; Gates et al., 1995, supra; et al., 2013, Applied Catalysis A: General, 451, 251–281). Furthermore, it has been reported that the size of Ru particles increases with increasing Ru weight percentage and significantly affects the CH selectivity in CO2 methanation (Kwak et al., 2013, ACS Catalysis, 3, 2449–2455). Another method for obtaining supported Ru / Al2O3 is through the reduction of RuCl3 in ethylene glycol (Chen et al., 2008, Materials Letters 62, 1018–1021; US ​​9,499,402 B2). Typically, supported Ru / Al2O3 catalysts are prepared by impregnating an Al2O3 support with a ruthenium solution followed by H2 reduction at high temperature, or by synthesizing Ru colloids using an ethylene glycol reduction method and then depositing them onto the Al2O3 support. In this method, the distribution and dispersion of Ru particles strongly depend on the surface properties of the various Al2O3 products, while the size of the Ru particles is influenced by a variety of factors, including the ruthenium loading, drying temperature, calcination temperature, and atmosphere. In this process, nearly all ruthenium ions can be reduced to the metallic state by polyol reagents, and chloride ions can be easily removed by solution. However, the KNO3 / NaNO3 used in this process often results in K or Na impurities in the final Ru / Al2O3 product. The presence of K and Na has been reported to negatively affect the activity of CO2 methanation reactions, affecting not only CO2 conversion but also methane selectivity (Cimino et al., 2020, Journal of CO2 Utilization, 37, 195–203). However, it is well known that the properties of Ru nanoparticles, including size, dispersion, and interaction with the support, significantly influence their catalytic performance (activity and stability) (Xu et al., 2016, Journal of Catalysis 333, 227–237).

[0010] Although there are several patents or articles reporting the synthesis of Ru / Al2O3 supported catalysts by impregnation method, none of them claims a process capable of obtaining highly dispersed Ru metal particles with a narrow Ru size distribution range.

[0011] Therefore, it is necessary to develop an economical and efficient industrial-scale preparation method of Ru / Al2O3 catalysts to obtain products with high activity, selectivity and long-term stability under the harsh conditions of CO2 methanation reaction. Summary of the Invention

[0012] The general object of the present invention is to provide a supported Ru particle as a highly active, selective and durable catalyst in CO2 methanation reaction, and a cost-effective method for preparing the catalyst.

[0013] A specific object of the present invention is to provide a process for preparing supported Ru particles, in particular Ru / Al2O3 materials, which can be used as catalysts for CO2 methanation reactions.

[0014] It would be advantageous to provide a simple and scalable method for preparing supported Ru particles.

[0015] It is advantageous to provide a method for preparing supported Ru particles that can control the Ru particle size.

[0016] It is advantageous to provide a method for preparing supported Ru particles that is applicable to different porous Al2O3 materials.

[0017] It would be advantageous to provide a process for preparing a catalyst having highly dispersed, small-sized, and stable ruthenium metal particles.

[0018] It would be advantageous to provide a method for preparing supported Ru particles using incipient wetness impregnation that is simple and scalable.

[0019] The object of the present invention is to provide a heterogeneous catalyst for CO2 methanation reaction, comprising Ru metal particles supported by Al2O3.

[0020] A Ru / Al2O3 material is provided having Ru particles with a narrow size distribution in Al2O3, which has the advantage of being able to be dispersed in a uniform manner.

[0021] A Ru / Al2O3 material is provided, which has Ru particles of smaller size and improved mass specific reactivity in CO2 methanation reaction, thereby improving the economic efficiency of ruthenium-supported catalysts, which has the advantage of improving the economic efficiency of ruthenium-supported catalysts.

[0022] A Ru / Al2O3 material is provided which has a CO2 conversion efficiency greater than 40% at a temperature below 300°C and uses an economical and effective Ru loading (typically a Ru loading below 1%), which has the advantage.

[0023] Provided are Ru / Al2O3 particles that exhibit strong resistance to sintering or agglomeration under high temperature conditions, which has the advantage of being able to withstand high temperatures.

[0024] The object of the present invention is achieved by providing a preparation method according to claim 1 and a use according to claim 15.

[0025] The present invention discloses a method for preparing Al2O3-loaded Ru particles, comprising the following steps:

[0026] a) providing a porous Al2O3 carrier material pretreated with an ammonia solution;

[0027] b) providing a low-acidity ruthenium precursor solution, in particular a ruthenium precursor solution comprising an aqueous solution of a soluble ruthenium salt, wherein the mass content of Ru in the Ru precursor solution is about 0.1 g / L to about 5 g / L;

[0028] c) impregnating the surface of the pretreated Al2O3 support material with a ruthenium precursor solution by incipient wetness impregnation;

[0029] d) drying the obtained impregnated Ru / Al2O3 material;

[0030] e) subjecting the dried impregnated Ru / Al2O3 material to temperature treatment under a H2 atmosphere to reduce the ruthenium precursor to a Ru metal phase;

[0031] f) contacting the obtained Ru / Al2O3 material with an ammonia solution;

[0032] g) Drying the obtained ammonia-treated Ru / Al2O3 material.

[0033] The present invention also discloses Ru metal particles supported by Al2O3 obtained by the method of the present invention.

[0034] The present invention also discloses a heterogeneous catalyst comprising Ru metal particles and Al2O3, wherein the Ru mass loading of the catalyst is 0.1%wt to 2.5%wt, and the size of the Ru particles is less than 2nm.

[0035] The present invention also discloses the use of Ru metal particles supported by Al2O3 as a catalyst for CO2 methanation reaction.

[0036] Other features and advantages of the invention will appear from the claims, the detailed description and the accompanying drawings.

[0037] BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a schematic diagram of the steps of the method for preparing Ru metal particles supported by Al2O3 in the present invention.

[0039] Figure 2 STEM images of inventive examples and commercial Ru / Al2O3 samples are shown, as described in Example 7.

[0040] Figure 3Shown is a comparison of the methane production rate in the CO2 hydrogenation reaction using the Ru / Al2O3 catalyst of the present invention, a comparative commercial catalyst (CS) and the one described in Comparative Example 1 (C), measured under the same conditions of 285°C, 1 bar, GHSV = 6 L / g / h.

[0041] Figure 4 The relationship between CO2 conversion and reaction time (T) under accelerated reaction conditions (10 bar, T = 310 ° C, GHSV = 6 L / g / h) is shown, as described in Example 8.

[0042] Figure 5 The behavior of the Ru particle size of the catalyst samples of the present invention (Ru 0.5wt% / Al2O3) after calcination at different temperatures and 5% H2 in N2 balance is shown, characterized by STEM images (A) and calculated size distribution (B), with the sample calcined at 400°C on the left and the sample calcined at 800°C on the right, and the evolution of the average particle size with temperature (C), as described in Examples 1 and 6.

[0043] Figure 6 Characterization of a catalyst sample produced by the process of the present invention on a 5 kg scale, including Ru particle size distribution (A) and CO2 conversion activity (1), is shown and compared (B) with the same catalyst synthesized under laboratory conditions (2), as described in Example 9. E represents thermodynamic equilibrium.

[0044] Figure 7 Shown are the Ru particle sizes of samples prepared by different steps of impregnation of RuCl3·xH2O solution (all with Ru concentration of 3 mg / ml), as described in Example 7.

[0045] Figure 8 The CO2 conversion of Ru 0.5 wt% / Al2O3 samples synthesized using RuCl3·xH2O but pretreated with water and ammonia, respectively, as described in Example 7 are shown.

[0046] Figure 9 The CO2 conversion (%) of Ru / Al2O3 catalyst at a loading of 0.5 wt% ruthenium is shown, synthesized using unpretreated Al2O3 (not of the present invention) and Al2O3 pretreated with ammonia solution (3 M, 3 hours), as described in Example 7. DETAILED DESCRIPTION

[0047] With reference to the accompanying drawings, and in particular first with reference to Figure 1 , provides a schematic diagram of the preparation method of supported Ru particles.

[0048] More specifically, Figure 1The steps of the embodiment shown in include:

[0049] a) providing a porous Al2O3 carrier material pretreated with an ammonia solution;

[0050] b) providing a ruthenium precursor solution containing an aqueous solution of a soluble ruthenium salt (such as RuCl3 or ruthenium nitrosylnitrate), wherein the mass content of Ru in the Ru precursor solution is between 0.1 g / L and 5 g / L;

[0051] c) impregnating the surface of the pretreated Al2O3 support material with a ruthenium precursor solution by incipient wetness impregnation;

[0052] d) drying the obtained impregnated Ru / Al2O3 material;

[0053] e) subjecting the dried impregnated Ru / Al2O3 material to temperature treatment under a H2 atmosphere to reduce the ruthenium precursor to a Ru metal phase;

[0054] f) contacting the obtained Ru / Al2O3 material with an ammonia solution;

[0055] g) Drying the obtained ammonia-treated Ru / Al2O3 material.

[0056] According to one embodiment, the porous Al2O3 support material is provided in the form of cylindrical or spherical Al2O3 particles.

[0057] According to another embodiment, the porous Al2O3 support material is calcined before being impregnated with the ammonia solution to remove moisture and any adsorbed substances. Typically, the calcination temperature ranges from about 400°C to about 800°C (e.g., 500°C).

[0058] According to one embodiment, the porous Al2O3 support material is pretreated in an ammonia solution having a concentration ranging from 1M to 3M, and the pretreatment time is about 3 hours to about 15 hours.

[0059] According to one embodiment, the surface area of ​​the porous Al2O3 support material is 100 m 2 / g or higher (e.g., from about 100m 2 / g to approximately 1,000m 2 / g, usually from 200m 2 / g to about 500m 2 / g), with a total pore volume of 0.4 cm 3 / g or higher (e.g., from about 0.4 cm 3 / g to approximately 2cm 3 / g, usually from about 0.5cm3 / g to about 1cm 3 / g).

[0060] According to a specific aspect, the advantage of this pretreatment is that it removes impurities (such as chloride and sulfur) that may exist in the Al2O3 material, and at the same time changes the zero charge point of the Al2O3 surface, thereby promoting the Ru 3+ Stable anchoring of ions on the Al2O3 surface.

[0061] According to one embodiment, the pretreated Al2O3 support material is dried before the impregnation step, for example, at about 70-120°C (such as 70-90°C, for example 80°C) for about 2 to 15 hours.

[0062] According to a further embodiment, the pretreated Al2O3 support material is washed with deionized water before the drying step.

[0063] According to another further embodiment, if the Al2O3 support material is not immediately subjected to the impregnation step after the ammonia solution pretreatment and washing / drying step, it can be stored in a dry and sealed environment at a temperature below 80°C, preferably below 20°C, for a few hours, but not more than about 2 days, to avoid conversion or decomposition of aluminum (OH)x species.

[0064] According to one specific aspect, the concentration of Ru in the precursor solution is defined by the following equation (1):

[0065]

[0066] Where Rucatalyst% is the target mass percentage of Ru metal content in the final catalyst; Mcatalyst is the mass of the final synthesized catalyst (g); N is the number of impregnations, which should be an integer to ensure that C Ru,溶液 Less than 5g / L.

[0067] According to a specific aspect, the Ru in the precursor solution is a ruthenium chloride hydrate (RuCl 3 ·xH 2 O) solution.

[0068] According to another specific aspect, the Ru in the precursor solution is a ruthenium nitrosyl nitrate solution.

[0069] According to one specific aspect, the Ru in the precursor solution is either freshly prepared before impregnation or prepared earlier (but not more than 48 hours) and stored in an environment with a temperature between 3°C and below 20°C, typically about 3°C ​​to about 10°C, and in an atmosphere that avoids contact with air.

[0070] According to one specific aspect, the pretreated Al2O3 support material is then impregnated with a ruthenium precursor solution (eg, RuCl3·xH2O solution) via incipient wetness impregnation.

[0071] According to a further embodiment, the incipient wetness impregnation comprises at least one impregnation sequence, preferably at least two (typically 3 to 5) events, comprising the following steps: i) wetting the surface of the pretreated Al2O3 support material dropwise with a solution containing a ruthenium precursor, with the volume of the solution corresponding to the pore volume thereof, until the entire pore volume of the support material is filled and a slurry is finally formed; ii) drying the impregnated Al2O3 support material, typically by heating to about 50°C to 100°C under air or vacuum conditions for about 30 minutes to several hours, for example, 2 hours.

[0072] According to one specific aspect, the number of impregnation events is determined by the pore volume of the support material, the concentration of Ru in the aqueous precursor solution, and the Ru loading, as described in equation (1).

[0073] Generally, the concentration of Ru in the precursor solution used in the impregnation step varies with the Ru loading on the support material and the total pore volume of Al2O3. The present invention has found that maintaining the Ru mass content in the Ru precursor aqueous solution between 0.1 g / L and about 5 g / L, preferably between about 2 g / L and 5 g / L (e.g., 3 g / L), ensures that the Ru nanoparticles are small in size and well dispersed.

[0074] According to a further embodiment, in each impregnation event, the volume of the Ru precursor solution is 1.15 times the total volume of the pretreated Al2O3 support material and is added dropwise onto the pretreated Al2O3 support material.

[0075] According to another further embodiment, in each impregnation event, after the Ru precursor aqueous solution is filled into the pores of the Al2O3 by capillary action, the impregnated product is dried at a temperature of 20°C to below 120°C, typically for a drying time of about 30 minutes to about 2 hours. The drying temperature should be strictly controlled below 120°C to prevent agglomeration of Ru species during rapid water evaporation.

[0076] According to another further embodiment, the evaporation rate of water is kept below 10 mg / m 2 The evaporation rate can be determined from thermogravimetric measurements normalized to the surface area of ​​the catalyst support material.

[0077] According to another further embodiment, in each drying step of the impregnation event, the evaporation rate of water is 0.2 mg / m 2 / min to 1.2 mg / m 2 / min (e.g. 0.5 mg / m 2 / min).

[0078] According to another further embodiment, at the end of the impregnation step, the obtained dry impregnated Al2O3 support material is subjected to a temperature treatment under a reducing atmosphere to reduce the ruthenium precursor to the Ru metal phase.

[0079] According to a further embodiment, the temperature treatment of the obtained dry impregnated Al2O3 support material is carried out in a diluted hydrogen H2 atmosphere, typically in a volume ratio of 1% to 20% with an inert gas such as N2, argon or helium.

[0080] According to a further embodiment, the temperature treatment of the obtained dry impregnated Al2O3 support material is carried out in an N2-diluted H2 atmosphere with an H2 concentration of 1% to 20% mol / mol.

[0081] According to another further embodiment, the temperature treatment of the obtained dry impregnated Al2O3 support material is performed at an annealing temperature of about 300°C to about 800°C (eg, 400°C to 700°C).

[0082] According to another further embodiment, the temperature treatment is performed at a heating rate not exceeding 10°C / min (typically between about 1°C / min and about 10°C / min) and the holding time is at least 2 hours (e.g., about 2 hours to 3 hours).

[0083] According to a further embodiment, the annealed Ru / Al2O3 material is contacted with an ammonia solution (eg, 3M to 5M), for example, by being immersed in a 3M ammonia solution.

[0084] According to another further embodiment, the annealed Ru / Al2O3 material is contacted with a 3M or higher concentration ammonia solution, typically 3M to 5M (e.g., 5.6 wt%), which increases the presence of OH groups, enhances the dispersion of Ru metal, and modifies the surface of the Al2O3 material, thereby helping to form more active sites to promote CO2 conversion.

[0085] According to a further embodiment, the annealed Ru / Al2O3 material is immersed in an ammonia solution for about 1 to 6 hours (eg, 1 to 5 hours).

[0086] According to a further embodiment, the ammonia treated annealed Ru / Al2O3 material is dried before storage.

[0087] According to another embodiment, the ammonia treated annealed Ru / Al2O3 material can be stored in a dry and sealed environment with the temperature maintained below 80°C before use.

[0088] According to another specific aspect, the Ru / Al2O3 material obtained is characterized by highly dispersed Ru particles with a narrow particle size distribution (typically about 0.8 nm to about 1.5 nm), a long service life (typically more than 400 hours), and a high efficiency of converting CO2 to methane when used as a catalyst in a CO2 methanation process (especially through the Sabatier reaction).

[0089] According to another specific aspect, the obtained Ru / Al2O3 material has a strong resistance to sintering or agglomeration, especially under high temperature conditions. In particular, the size of the Ru particles remains unchanged even when heated to 800°C in a H2 atmosphere.

[0090] According to another specific aspect, a heterogeneous catalyst comprising Ru metal particles supported by Al2O3 is provided, wherein the catalyst is obtainable by the method of the present invention.

[0091] According to another specific aspect, a heterogeneous catalyst comprising Ru metal particles and Al2O3 is provided, wherein the mass content of Ru is between 0.1%wt and 2.5%wt, and the size of the Ru particles is less than 2 nm.

[0092] According to another specific aspect, a heterogeneous catalyst comprising Ru metal particles and Al2O3 is provided, wherein the mass content of Ru is between 0.1%wt and 2.5%wt, and the size of the Ru particles is less than 2nm, wherein the CO2 conversion efficiency exceeds 40% at a temperature of about 250°C to about 300°C.

[0093] According to a specific aspect, the size of the Ru metal particles in the catalyst of the present invention ranges from about 0.5 to 1.5 nm, such as from about 0.8 nm to about 1.5 nm.

[0094] According to one specific aspect, the size analysis of the Ru particles is performed using a transmission electron microscope (TEM), particularly a scanning transmission electron microscope (STEM) mode. To facilitate analysis, the Ru / Al2O3 catalyst can be dispersed in ethanol and deposited onto a carbon-coated copper TEM grid. The average diameter or size of the Ru particles is then derived using a correlation based on this method (Karim et al, 2009, J. Am. Chem. Soc., 131, 34, 12230–12239).

[0095]

[0096] di is the diameter of the Ru particles measured by scanning in the horizontal direction from the STEM image, and ni is the number of particles. This is the most powerful and direct method for determining the size distribution of metal particles, especially in the case of catalysts loaded with noble metals (Mishra et al., 2013, Journal of Molecular Catalysis A Chemical 376: 63–70; Berger et al., Particle Size and Dispersion Measurements. Handbook of Heretogeneous Catalysis, 2, Wiley-VCH, pp. 738-765, 2008).

[0097] According to one specific aspect, the dispersion of Ru particles in the Al2O3 support material is about 0.17 atoms / nm 2 to 0.3 atoms / nm 2 (usually about 0.175 atoms / nm 2 ). Quantification of dispersion can be assessed by standard methods, such as described in Comas-Vives et al., 2016, Phys. Chem. Chem. Phys., 18, 1969-1979.

[0098] According to one specific aspect, in the presence of the catalyst of the present invention, the conversion rate of CO2 to methane in a fixed bed microreactor at 1 bar and about 250°C is about 80 μm0 / g. Ru / s to about 90μmo / g Ru / s. Quantification of reactivity is based on equations (2) to (4), as shown in the Examples.

[0099] According to another specific aspect, a method for methanation of CO and / or CO2 with hydrogen using the Ru / Al2O3 material of the present invention is provided.

[0100] According to another specific aspect, there is provided a method for producing methane, which comprises contacting the catalyst of the present invention with a mixed gas containing CO and / or CO2 and hydrogen at a temperature of at least 200°C.

[0101] Therefore, the present invention provides a process based on impregnation method, which can produce Ru / Al2O3 catalyst with Ru particles smaller than 2nm in size and comparable to commercial Ru 0.5％wt / Al2O3 catalyst (Sigma-Aldrich #206199) and catalysts prepared by traditional methods have better Ru mass ratio reactivity in terms of methane yield.

[0102] The present invention has been described above, and the following examples are intended to be illustrative only and not limiting.

[0103] Example

[0104] The method of the present invention is illustrated by the following examples and comparative examples.

[0105] Ruthenium chloride hydrate (RuCl3·xH2O, CAS#14898-67-0) was purchased from ABCR Chemical Company, product number AB112073. The Ru content in this ruthenium precursor was 38-43% (by weight). Commercial γ-Al2O3 particles were used as the support material. The purity of Al2O3 was confirmed by X-ray photoelectron spectroscopy (XPS), which showed only characteristic peaks of Al, O and C, which were attributed to the presence of surface carbonate adsorbates. The ammonia solution was prepared from a commercial ammonia solution (28-30 wt%) Sigma-Aldrich (product number #3587154) and deionized (DI) water.

[0106] Step a) Pretreatment of the carrier material

[0107] Commercial Al2O3 (cylindrical particles) material (from AliExpress, cylindrical, 3 mm in diameter, 4 mm in length, with a surface area of ​​approximately 240 m2) 2 / g) as the support / carrier material for the catalyst, in the form of commercial Al2O3 pellets, which were first calcined at 500°C to remove moisture and adsorbates. For each batch of synthesis, the support material was first pretreated in a 1-3 M aqueous ammonia solution. The pellets were soaked in the solution for at least 3 to 15 hours and then washed with deionized (DI) water. The entire process can be carried out in an ambient temperature and atmospheric pressure environment. After washing with DI water, the pellets were dried at 80-120°C for approximately 2 to 15 hours. It was confirmed that this pretreatment did not change the porosity of the original Al2O3 support material.

[0108] This step not only enhances CO2 conversion performance but also improves selectivity to methane (CH4). Longer pretreatment times, typically 3 to 15 hours, result in higher low-temperature Ru mass-to-reactivity for higher CH4 yields.

[0109] Step b) Preparation of ruthenium precursor solution

[0110] Ruthenium chloride hydrate (RuCl3·xH2O) or ruthenium nitrosyl nitrate is used as the precursor of the Ru metal phase. An aqueous solution ([RuCl2(H2O)4] ++Cl- in water), and keep it at a low temperature (e.g., 3-20°C) to avoid long-term exposure to air. The concentration of Ru in the precursor solution is adjusted according to equation (1).

[0111] Steps c) & d) impregnation and drying

[0112] Ruthenium is loaded onto the Al2O3 support material using a multi-step incipient wetness impregnation method. During each impregnation step, Ru in the precursor solution (in an amount 1.2 times the volume of the support material) is added dropwise to the pretreated support material, and the solution fills the pores of Al2O3 by capillary action, and then is dried for 30 minutes to 2 hours at a temperature range of 20°C to 120°C (e.g., 50°C, 80°C, 100°C, and 120°C). The relationship between Ru particle size and water evaporation rate has been clearly revealed. A higher evaporation rate results in larger Ru particle size and a wider Ru size distribution because the balance between evaporation rate and interaction is disturbed. Therefore, a lower evaporation rate (typically about 0.2 mg / m 2 / min to 1.2 mg / m 2 / min) for drying, which is more conducive to obtaining small and uniform Ru particle size.

[0113] Step e) Temperature treatment and reduction

[0114] After impregnation and drying, the product was annealed in a nitrogen-diluted H2 atmosphere with an H2 concentration of 1%-20% mol / mol (RuCl3+H2→Ru+HCl). The annealing temperature was between 300°C and 800°C, particularly between 400°C and 800°C (e.g., 400°C, 500°C, 600°C, 700°C, and 800°C), with a heating rate not exceeding 10°C / min and a hold time of at least 2 hours. The Ru particle size remained constant in the Ru / Al2O3 catalysts annealed at different temperatures, which can be attributed to the strong adsorption between the Ru precursor complex and Al2O3, as well as the high dispersion of Ru species in the previous step.

[0115] Step f) Catalyst activation

[0116] After the annealing step, the resulting material is further soaked in a 3M ammonia solution for at least 3 hours and then washed with DI water. This removes residual chloride from the Ru / Al2O3 catalyst: NH4OH+HCl→NH4Cl+H2O. The sample washed with ammonia solution is twice as active in the CH4 formation reaction as the corresponding untreated catalyst (as tested in Example 7). Compared with washing with ammonia solution, the improvement effect of conventional water-washed catalysts is limited, indicating that chlorine is strongly attached to the catalyst. Therefore, it is necessary to use a strong alkaline solution to effectively remove chlorine. In addition, pretreatment with ammonia solution before use not only maintains the alkalinity of the catalyst, but also avoids the introduction of other metal impurities (such as Na, K), which can affect the performance of CO2 conversion and CH4 selectivity. Therefore, step f) is preferably performed before the catalyst is stored.

[0117] The activation step f) and the drying step g) are performed before storage to optimize the reactivity and stability of the catalyst product.

[0118] Although it has been reported that residual chlorine on supported Ru / Al2O3 catalysts inhibits H2 adsorption in ammonia synthesis (Miyazaki et al., 2001, Journal of Catalysis, 204, 364–37), other studies have shown that the presence of chlorine helps activate H2 adsorption sites (Lin et al., 2011, Catalysis Letters 141, 1557–1568; González-Carballo et al., 2015, Journal of Catalysis 332, 177–186). This conflicting discussion indicates that the effect of chlorine on the reactivity of Ru catalysts remains unclear, especially its effect on CO2 methanation, which has not been studied or reported.

[0119] Comparative samples: Comparative samples were prepared by traditional methods (Mi et al., 2012, Physics Procedia, 25, 1285–1291; US20110014114; JP2008194615).

[0120] Commercial γ-Al2O3 particles with a surface area of ​​294m 2 / g, with a total pore volume of 0.72 cm 3 / g and calcined at 500°C to remove adsorbates. Al2O3 particles (not pretreated according to step a)) were impregnated using a pore volume technique with an aqueous solution of 0.0272g of RuCl3·xH2O and 1.56ml of DI water. This material was dried in air at 90°C for 12 hours and then annealed at 400°C for 2 hours in a 5% H2, 95% N2 atmosphere. The reduced Ru / Al2O3 catalyst was then washed multiple times with DI water until no Cl- was detected using an AgNO3 solution.

[0121] The %wt of Ru was determined by ICP-OES and the average ruthenium particle size was analyzed by STEM, as shown in the table below.

[0122] Catalyst characterization

[0123] The specific surface area, pore volume, and average pore diameter of the Al2O3 and Ru / Al2O3 samples were analyzed using N2 adsorption-desorption isotherms using a BELSORP MAX II (from MICROTRACT MRB). The specific surface area and cumulative pore volume were calculated using the Brunauer-Emmett-Teller (BET) theory. The average pore diameter was calculated using the Barrett-Joyner-Halenda (BJH) model. Prior to measurement, the samples were vacuum degassed at 120°C for 3 hours using a BELP REP V AC II (from MICROTRACT). Wide-scan X-ray photoelectron spectroscopy (XPS) of the samples (from 1200 eV to 0 eV) was performed using a monochromated Kα line from an aluminum X-ray source (1486.6 eV), with the analyzer pass energy set to 90 eV. The Ru content in the final catalysts was determined using an Agilent 5110 inductively coupled plasma optical emission spectrometer (ICP-OES). The Ru particle size on the AlO support material was analyzed based on scanning transmission electron microscopy (STEM) images and ImageJ software, while elemental mapping was obtained using STEM energy-dispersive X-ray (EDX) spectroscopy. For each sample, the size distribution was based on measurements of over hundreds of particles using multiple microscopic images taken from different areas.

[0124] Thermogravimetric analysis (TGA) was used to determine the evaporation rate of water from the particles. Al2O3 particles were impregnated with a certain amount of water. After impregnation, the particles were left to stand for 10 minutes and then subjected to TGA measurement using a NETZSCH TG 209F1 Libra. TGA was performed by increasing the temperature to the target temperature at a rate of 10°C / min. The experiment continued at a constant temperature until all the water was evaporated. The target temperatures were set at 50°C, 80°C, 100°C, 120°C, and 150°C. The evaporation rate below 120°C was calculated from the TGA curve. For temperatures above 120°C, the evaporation rate of water was determined by model simulation.

[0125] Example 1: Preparation method of supported Ru particles of the present invention

[0126] The method of the present invention is applied to a BET surface area of ​​294m 2 / g, pore volume of 0.72cm 3 / g porous Al2O3 support material.

[0127] Step a) Pretreatment of the carrier material

[0128] 2 g of commercial γ-Al2O3 particles (AliExpress, cylindrical, 3 mm in diameter, 4 mm in length) were immersed in 5 ml of 3 M ammonia solution for 12 h and then dried at 90°C for 12 h.

[0129] Step b) Preparation of ruthenium precursor solution

[0130] 0.0272 g of RuCl 3 ·xH 2 O was dissolved in 3.256 ml of deionized water to make the Ru concentration 5 g / L.

[0131] Steps c) & d) impregnation and drying

[0132] The solution was then deposited onto the Al2O3 material through two impregnation steps. After each Ru solution impregnation, the Ru / Al2O3 sample was dried at 80°C for 30 minutes.

[0133] Step e) Temperature Treatment & Reduction

[0134] Subsequently, the impregnated Ru / Al2O3 sample was annealed in a tube furnace in a gas mixture of 5% H2 and N2 at 400°C for 2 hours.

[0135] Step f) & g) Catalyst Activation

[0136] After annealing, the samples were immersed in 5 ml of 3 M ammonia solution for 3 h and dried at 90 °C for 2 h.

[0137] Example 2: Preparation method of supported Ru particles of the present invention

[0138] The method of the present invention is applied to a BET surface area of ​​242 m 2 / g, pore volume of 0.80cm 3 / g porous Al2O3 support material.

[0139] Step a) Pretreatment of the carrier material

[0140] 2 g of commercial γ-Al2O3 particles (Alfa Aesar) were immersed in 5 ml of 3 M ammonia solution for 3 h and then dried at 90°C for 12 h.

[0141] Step b) Preparation of ruthenium precursor solution

[0142] 0.0272 g of RuCl3·xH2O was dissolved in 5.256 ml of deionized water to make the Ru concentration 2 g / L.

[0143] Steps c) & d) impregnation and drying

[0144] The above solution was then deposited onto the Al2O3 material through four impregnation steps. After each Ru solution impregnation, the Ru / Al2O3 sample was dried in air at 80°C for 30 minutes.

[0145] Step e) Temperature Treatment & Reduction

[0146] Subsequently, the impregnated Ru / Al2O3 sample was annealed in a tube furnace at 400°C for 2 hours in an atmosphere of 5% H2 and N2.

[0147] Step f) & g) Catalyst Activation

[0148] After reduction, the samples were immersed in 5 ml of 3 M ammonia solution again for 3 hours and dried at 90°C for 2 hours for storage.

[0149] Example 3-6: Preparation method of supported Ru particles of the present invention

[0150] The preparation method and Al2O3 materials used for the Ru / Al2O3 catalyst were the same as those in Example 1, except that the Ru loading was different, corresponding to the different impregnation times and as detailed in Table 1 below. In Example 6, the Ru / Al2O3 catalyst was prepared using the same materials and process as in Example 1, except that the reduction / annealing temperature was 800°C.

[0151] Example 7: Characterization of Catalyst

[0152] The % wt of Ru and the average size of Ru particles of various catalysts prepared by the process of the present invention are compared in Table 1 with those of a comparative commercial catalyst (CS) and a comparative example (C).

[0153] Table 1

[0154]

[0155] As observed, by maintaining the Ru content of the diluted precursor solution at no more than 5 mg / ml, the average Ru size remained below 1.5 nm in Examples 1 to 6 of the present invention, while the Ru loading was increased to 2.5%. In a catalytic evaluation comparing the treated Ru / Al2O3 catalyst with a conventional untreated catalyst (lacking step a), significant differences in CO2 methanation activity were observed, with the ammonia-treated catalyst achieving superior CO2 conversion under the same conditions.

[0156] This can be explained by the fact that the dispersed deposition of Ru species in highly diluted precursor solutions effectively suppresses the growth of Ru clusters on the support surface. After each impregnation, the Ru species in the solution tend to attach individually to the support surface until all accessible adsorption sites are occupied by small clusters. As all active sites are saturated with small clusters of Ru species, further increasing the Ru loading will lead to the growth of Ru clusters on localized sites.

[0157] Ru-based eggshell catalysts were formed using Al2O3 particles (cylindrical or spherical) as supports via a dry impregnation method. The thickness of the outer layer of the Ru component obtained through multi-step impregnation was approximately 400 ± 37 μm, as measured using EDX-SEM. Penetration of the Ru precursor solution into the particle center appears to be inhibited by stronger interactions between the Ru complex and the Al2O3 surface. This strong interaction between Ru activity and adsorption sites on the Al2O3 surface makes the Ru clusters more resistant to agglomeration.

[0158] The STEM-EDX element distribution results confirmed that the bright spots were Ru particles, which were evenly distributed on the Al2O3 carrier of the material of the present invention, while large agglomerates were observed to be randomly distributed in the comparative material, showing obvious differences.

[0159] Studies on the number of impregnation events show that if we keep the Ru precursor solution in a dilute state (e.g., 3 mg / ml Ru concentration), a small Ru size of 1 nm can be maintained even if the Ru loading is increased from 0.5% to 1.5%. Figure 7 As shown, using a dilute RuCl3·xH2O solution (e.g., 3 mg / ml of Ru), the size of the Ru particles can be maintained below 1.5 nm at higher loadings (up to 1.5 wt%) even after 18 impregnation events.

[0160] The effectiveness of ammonia pretreatment was tested as follows: A batch of Ru / Al2O3 catalysts was prepared with the same loading (0.5 wt%) and synthesis parameters (except for pretreatment step a) as described above. These catalysts were divided into three batches: one batch was pretreated with hot water, another batch was pretreated with 3M ammonia solution according to the present invention, and the third batch remained unpretreated. The three batches were then tested in the CO2 methanation reaction under the same conditions as described in Example 8. Figure 8 The different CO2 conversion rates of the three catalysts were demonstrated, and the results showed that the sample washed with ammonia solution showed the highest reactivity for CH4 formation, which was twice that of the untreated catalyst. Compared with ammonia solution washing, the traditional water washing method had limited improvement, indicating that chlorine was firmly attached to the catalyst. Therefore, it is necessary to use a strong alkaline solution to efficiently remove chlorine. In addition, ammonia solution pretreatment not only maintains the alkalinity of the catalyst, but also avoids the introduction of other metal impurities (such as Na, K), which can have a negative impact on CO2 conversion and CH4 selectivity.

[0161] Another comparative experiment was conducted between two Ru / Al2O3 samples, using untreated Al2O3 (SigmaAldrich) and Al2O3 pretreated with ammonia solution (3M ammonia solution for 3 hours). Throughout the synthesis, except for the pretreatment of the support material, all other procedural steps remained consistent, following the standards specified in the method of the present invention and using the same parameters. Ruthenium nitrosyl nitrate was used as the ruthenium precursor with a Ru loading of 0.5 wt%. CO2 reactivity tests were performed under the conditions detailed in this application. The final results are shown in Figure 2. Figure 9 As shown, the significant influence of the support material pretreatment (step a) on the CO2 methanation reactivity is clearly demonstrated.

[0162] Example 8: CO2 methanation using the supported Ru particles of the present invention

[0163] The performance evaluation of the materials of the present invention as catalysts in the CO2 methanation reaction is as follows.

[0164] 200 mg of the materials of the comparative example, Example 1 and Example 2 were respectively loaded into the stainless steel tube of the fixed bed flow reactor, and the CO2 methanation reactivity test was carried out as follows:

[0165] The reactor consisted of two sections of stainless steel tubing with an outer diameter of 10 mm, serving as the gas inlet and outlet, forming a stainless steel tubular reactor with an inner diameter of 8 mm and a length of 1 cm. The catalyst sample was placed within the reactor through quartz wool. The reaction temperature was measured using a K-type thermocouple that passed through the reactor and contacted the catalyst bed.

[0166] The material was heated in a dilute H2 flow (12 ml / min) from room temperature to 400°C at a rate of 10°C / min and maintained for 2 hours, then cooled to 150°C. At 150°C, the reactant mixed gas flow (22 ml / min, containing 18% CO2, 72% H2 and 10% N2) was replaced by a dilute H2 flow. Based on the test and gas chromatography (GC) quantitative analysis, the CO2 conversion rate and CH4 selectivity can be obtained by the following formula:

[0167] CO2 conversion rate:

[0168] CH4 selectivity:

[0169] Among them, CO 2,出 / 进 and CH 4,出 is the molar concentration at the reactor inlet and outlet under each condition. The concentrations of CO2 and CH4 are quantified by multiplying the GC peak area by the response factor of each gas (determined by external calibration). In principle, X CO2 and S CH4 It is direct data quantitatively obtained by GC and used to evaluate catalyst performance. In addition, the injection and analysis of gas samples are carried out under steady-state conditions, that is, the temperature, gas flow and pressure are all stable. N2 is used as an internal standard gas to calibrate the concentration of reactants at the reactor outlet, which is due to the decrease in total volume (pressure). The mass ratio of ruthenium to CH4 generation rate is determined by formula (4):

[0170]

[0171] Among them, r CH4 is the methane production rate in mol.g -1 Ru .S -1 ;X CO2 and S CH4 are the CO2 conversion rate and CH4 selectivity under specific conditions (pressure, temperature); F CO2 is the CO2 flow rate entering the reactor, measured by a mass flow controller, in L / s; m Ru is the mass of ruthenium used in each measurement, which is determined by weighing the catalyst loaded into the reactor and multiplying it by the Ru weight content monitored by the MS-ICP technique, in g; V m is the molar volume of an ideal gas under standard conditions, which is 22.4 L / mol.

[0172] The CO2 conversion rate used to calculate the CH4 generation rate was obtained under constant measurement conditions (285℃, 1 bar, 6 L·g -1The kinetic region under h-1) reflects the intrinsic conversion of the catalyst for all samples for comparison. The deviation of the CO2 conversion was determined to be ±2% by repeating the same measurement 3-5 times. Figure 3 The reactivity of the materials of Examples 1 and 2 is shown, with the mass ratio of Ru being higher than the CH4 generation rate due to the better dispersion of the ruthenium particle size. For the same amount of Ru mass, the catalyst synthesized by the present method induces at least 20% more CH4 generation compared to the comparative commercial catalyst (Sigma-Aldrich).

[0173] Example 9: Stability of the catalyst of the present invention

[0174] The stability and durability of the catalyst synthesized in the present invention were evaluated under the harsh conditions of high pressure and high temperature, as described below.

[0175] 300 mg of the catalyst from Example 3 was loaded into the tubular fixed-bed flow microreactor described above. After reduction at 400°C for 2 hours, 20% CO₂ and 80% H₂ were introduced into the reactor and heated to 310°C in the reactor bed at a total pressure of 10 bar. Under these conditions, the CO₂ conversion was continuously monitored by GC. Figure 4 As shown, the time-varying performance of the catalyst measured by CO2 conversion % showed that the CO2 conversion remained stable (up to 97.8%) for up to 200 hours, confirming the high stability of the Ru nanoparticles in the catalyst of the present invention.

[0176] The STEM image of the catalyst after 50 hours of use showed that the Ru particles were uniformly distributed with an average size of 0.97 nm, and the same size and distribution of Ru particles were also observed in the fresh catalyst.

[0177] Figure 5 The stability of the catalyst of the present invention is further confirmed by the results showing that the catalyst of Example 3 is still resistant to agglomeration at temperatures up to 800°C, which provides a huge advantage in avoiding catalyst deactivation caused by hot spots in the methanation reactor, thereby affecting the production cost and productivity of the methanation unit.

[0178] Example 9: Scaled application of the method of the present invention

[0179] The method of the present invention was used to prepare 5 kg of the catalyst of the present invention. Approximately 5 kg of commercial Al2O3 pellets were pretreated in 15 L of 3 M ammonia solution for 5 hours, followed by drying at 100°C for 2 hours. For each impregnation event, approximately 4 L of a 3 g / L RuCl3·xH2O aqueous solution was prepared and impregnated into the pretreated support material. The Ru-impregnated Al2O3 was then dried in air at 100°C for 2 hours. After three impregnation and drying events, the sample was annealed in 10 vol.% H2 at 400°C for 3 hours, with a heating rate of 1°C / min and a gas flow rate of 1000 L / h. After annealing and cooling, the sample was soaked in 3 M ammonia solution for 5 hours and washed with cold water. The sample was then dried in air at 100°C overnight for storage.

[0180] like Figure 6 As shown in A, the obtained catalyst has highly dispersed and uniform Ru particles with an average size of 1.3 nm. In addition, the catalytic activity evaluated according to the above method shows that at P = 1 bar, CO2 / H2 = 4 mol / mol, N2% = 20%, GHSV = 6 (L / g cat / h), the catalyst synthesized under industrial conditions has the same CO2 conversion rate ( Figure 6 B).

[0181] Overall, these data demonstrate that the method of the present invention enables the preparation of Ru / Al2O3 catalysts with Ru mass loadings ranging from 0.1% wt to 2.5% wt, which exhibit good methane yields in the CO2 hydrogenation reaction (Sabatier reaction). Furthermore, compared to commercial Ru / Al2O3 catalysts and catalysts synthesized by conventional methods, the catalyst of the present invention exhibits an active phase in which the Ru metal is highly dispersed, resulting in a higher mass-specific reactivity of ruthenium than in the corresponding commercial catalysts, and its production process can be easily scaled up.

[0182] In addition, the catalyst of the present invention is characterized by a strong interaction between the Ru nanoparticles and the Al2O3 support material, which can maintain a high dispersion of Ru metal under the harsh conditions of the CO2 methanation reaction and avoid particle agglomeration.

Claims

1. A method for preparing Al2O3-supported Ru particles, comprising the following steps: a) providing a porous Al2O3 carrier material pretreated with an ammonia solution; b) providing a ruthenium precursor solution containing an aqueous solution of a soluble ruthenium salt, wherein the Ru content of the Ru precursor solution is about 0.1 g / L to 5 g / L; c) impregnating the surface of the pretreated Al2O3 support material with a ruthenium precursor solution by incipient wetness impregnation; d) drying the obtained impregnated Ru / Al2O3 material; e) subjecting the dried impregnated Ru / Al2O3 material to a temperature treatment in a H2 atmosphere to reduce the ruthenium precursor to a Ru metal phase; f) contacting the obtained Ru / Al2O3 material with an ammonia solution; g) drying the obtained ammonia-treated Ru / Al2O3 material.

2. The method according to claim 1, characterized in that The porous Al2O3 support material is provided in the form of cylindrical or spherical Al2O3 particles.

3. The method according to claim 1 or 2, characterized in that The porous Al2O3 support material is pretreated in an ammonia solution having a concentration of 1M to 3M for about 3 hours to about 15 hours.

4. A method according to any preceding claim, characterised in that The specific surface area of ​​the porous Al2O3 carrier material is greater than 100m 2 / g, with a total pore volume greater than 0.4 cm 3 / g.

5. A method according to any preceding claim, characterised in that The ruthenium precursor solution contains a soluble ruthenium salt aqueous solution, wherein the Ru mass content in the Ru precursor solution is about 3 g / L; 6. A method according to any preceding claim, characterised in that The ruthenium precursor solution is a ruthenium chloride hydrate (RuCl3·xH2O) solution.

7. The method according to any one of claims 1 to 5, characterized in that The ruthenium precursor solution is a ruthenium nitrosyl nitrate solution.

8. A method according to any preceding claim, characterised in that The pretreated Al2O3 support material is subjected to a drying step prior to the impregnation step, for example, at about 70-90°C, such as 80°C, for about 3-15 hours.

9. A method according to any preceding claim, characterised in that The incipient wetness impregnation comprises at least one impregnation event, preferably at least two steps: i) wetting the surface of the pretreated Al2O3 support material dropwise with a solution containing a ruthenium precursor, wherein the volume of the ruthenium precursor solution corresponds to the pore volume of the support material, until the entire pore volume of the support material is filled and a slurry is finally formed; ii) drying the impregnated Al2O3 support material, typically by heating to about 50°C to 100°C under air or vacuum conditions for about 30 minutes to several hours.

10. A method according to any preceding claim, characterised in that In each impregnation event, after the Ru precursor aqueous solution fills the pores of the Al2O3 by capillary action, the impregnated product is dried at a temperature between 20°C and below 120°C, typically for about 30 minutes to about 2 hours.

11. A method according to any preceding claim, characterised in that During each drying step of the immersion event, the evaporation rate of water is kept below 10 mg / m 2 / min.

12. The method according to claim 11, characterized in that During each drying step of the immersion event, the evaporation rate of water was 0.2 mg / m 2 / min and 1.2mg / m 2 / min (e.g. 0.5 mg / m 2 / min).

13. A method according to any preceding claim, characterised in that The temperature treatment of the dried impregnated Al2O3 support material is carried out in a diluted H2 atmosphere, usually in an inert gas N2, argon or helium, with a volume ratio of H2 of 1% to 20%.

14. A method according to any preceding claim, characterised in that The obtained dried impregnated Al2O3 support material is subjected to temperature treatment at an annealing temperature of about 400°C to about 800°C (e.g., 400-700°C, typically at a heating rate of less than 10°C / min (typically 1°C / min to 10°C / min) and a holding time of at least 2 hours).

15. A method according to any preceding claim, characterised in that The annealed Ru / Al2O3 material is contacted with an ammonia solution, preferably by immersing in a 3M ammonia solution.

16. A method according to any preceding claim, characterised in that The ammonia treated annealed Ru / Al2O3 material is dried before storage.

17. A Ru / Al2O3 material prepared by the method according to any one of claims 1 to 16.

18. A heterogeneous catalyst containing Ru metal particles and Al2O3, characterized in that: The Ru mass loading amount of the catalyst is 0.1%wt to 2.5%wt, and the size of the Ru particles is less than 2nm.

19. The heterogeneous catalyst of claim 18 having a CO2 conversion efficiency greater than 40% at a temperature of about 250°C to about 300°C.

20. Use of the Ru metal particles supported by Al2O3 according to any one of claims 17 to 19 as a catalyst for CO2 methanation reaction.

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