Monolithic catalyst for methanation of carbon dioxide as well as preparation method and application of monolithic catalyst

Abstract

The invention provides a monolithic catalyst for methanation of carbon dioxide as well as a preparation method and application of the monolithic catalyst. The preparation method comprises the following steps: (1) mixing hydrated salt of transition metal, acrylic acid, hydroxyethyl acrylate and a photoinitiator according to a certain proportion to obtain uniform and stable slurry; (2) constructing a monolithic catalyst three-dimensional model and a support thereof; (3) printing the slurry into a monolithic catalyst blank through a digital photocuring 3D printer; (4) cleaning the residual resin, removing the support and carrying out secondary curing to obtain a catalyst precursor; and (5) carrying out gradient degreasing-reduction treatment on the catalyst precursor to obtain the monolithic catalyst. The 3D printing technology is adopted, accurate construction of a complex geometric structure is achieved, a micropore-mesopore-macropore multi-stage pore system is successfully constructed, and the problems that a traditionally prepared monolithic catalyst material is poor in compatibility and post-treatment process defect, poor in catalytic effect and the like are effectively solved.

Description

Technical Field

[0001] This invention belongs to the field of 3D printing and catalyst preparation technology, specifically relating to an integral catalyst for carbon dioxide methanation, its preparation method and application. Background Technology

[0002] Ecological crises such as climate change and ocean acidification caused by CO2 released from the use of fossil fuels urgently need to be addressed. Carbon capture, utilization and storage (CCUS) technology, especially the CO2 hydrogenation conversion pathway, combines captured CO2 with green hydrogen produced from renewable energy sources to produce bulk chemicals such as methane, achieving both emission reduction and economic benefits.

[0003] Thermodynamic analysis shows that CO2 methanation is a strongly exothermic reaction. Under suitable H / C ratio conditions, low-temperature thermocatalytic conversion can theoretically achieve nearly 100% CO2 conversion and CH4 selectivity, and effectively suppress side reactions and deactivation problems such as reverse water-gas shift reaction (RWGS), catalyst sintering, and carbon deposition. However, kinetically, the chemical inertness and thermodynamic stability of CO2 molecules, coupled with the octetral transfer involved in methanation, result in a significant kinetic energy barrier for its low-temperature activation. Therefore, the development of low-temperature, highly active CO2 methanation catalysts is of great significance for developing low-energy-consumption, low-cost CO2 resource utilization technologies.

[0004] Traditional particulate catalysts have limited their kinetic research and application optimization due to problems such as high bed pressure drop, unvisualized flow field distribution, and large diffusion resistance. Monolithic catalysts, with their high geometrical specific surface area, low pressure drop, excellent radial mass / heat transfer performance, low diffusion resistance, and good mechanical strength and thermal stability, have provided new directions for catalyst design and process intensification, and have become a research hotspot.

[0005] In the design of monolithic catalyst structures, 3D printing technologies (such as fused deposition modeling, direct ink writing, digital light processing, and selective laser sintering) have demonstrated unique advantages. Among them, digital light processing (DLP) technology is highly competitive in realizing complex and customized catalyst structures due to its high structural precision manufacturing capabilities, simple post-processing, fast printing speed, and outstanding potential for large-scale production, opening up a new dimension for the rational design and preparation of high-performance monolithic catalysts.

[0006] The main methods for printing catalysts using DLP technology include impregnation and one-pot methods. Impregnation requires printing the carrier skeleton first, then loading the active component. While this avoids encapsulation problems to some extent, it easily clogs micropores and increases the number of process steps. The one-pot method involves directly mixing the active component, photosensitive resin, and other functional additives, followed by photocuring and printing, resulting in a simpler process. Currently, DLP technology still faces several technical bottlenecks when preparing monolithic catalysts using the one-pot method. Among these, insufficient material system compatibility, particularly the compatibility of commercial photosensitive resins with nitrate hydrates such as Co(NO3)2·6H2O and Ni(NO3)2·6H2O, urgently needs to be addressed, hindering its preparation. Based on this, this application is proposed. Summary of the Invention

[0007] The purpose of this invention is to overcome the defects of the prior art and provide a monolithic catalyst for carbon dioxide methanation, its preparation method and application, which effectively solves the problems of material compatibility, post-processing defects and poor catalytic effect of traditionally prepared monolithic catalysts.

[0008] This invention provides the following technical solution:

[0009] This invention provides a method for preparing a monolithic catalyst for carbon dioxide methanation, comprising the following steps:

[0010] (1) A homogeneous and stable slurry is obtained by mixing a hydrated salt of a transition metal, acrylic acid, hydroxyethyl acrylate and a photoinitiator in a certain proportion.

[0011] (2) Constructing a three-dimensional model of the overall catalyst and its supporting elements;

[0012] (3) The slurry is printed into an integral catalyst preform using a digital photopolymerization 3D printer;

[0013] (4) Clean the residual resin, remove the support and perform secondary curing to obtain the catalyst precursor;

[0014] (5) The catalyst precursor is subjected to gradient degreasing-reduction treatment to obtain the monolithic catalyst.

[0015] Further, in step (1), the hydrated salt of the transition metal is any one or a combination of Co(NO3)2·6H2O, Ni(NO3)2·6H2O, Fe(NO3)2·6H2O, and RuCl3·xH2O.

[0016] Further, in step (1), the photoinitiator is any one of diphenyl (2,4,6-trimethylbenzoyl)phosphine oxide, benzophenone, 1-hydroxycyclohexylbenzophenone, and 2-hydroxy-2-methyl-1-phenylpropanone.

[0017] Further, in step (1), the ratio of the hydrated salt of the transition metal, acrylic acid, hydroxyethyl acrylate and diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide is (0.08-0.10) mmol:2.5 g:2.5 g:(0.045-0.075) g.

[0018] Furthermore, in step (2), the model is a hollowed-out cylinder with turbulence-inducing effect.

[0019] Furthermore, in step (2), the model support is designed using PiocreatBox software, and the contact shape of the model has a diameter of (0.2-0.4) mm, a contact depth of (0.3-0.5) mm, an upper diameter of (0.2-0.4) mm, a lower diameter of 0.8 mm, and a connection length of 2.5 mm.

[0020] Furthermore, in step (3), the optical power of the digital photopolymerization 3D printer is (3-6) mW / cm². 2 Initial exposure time: (10-15) s; Number of bottom layers: 3-6; Printing exposure time: (1-5) s.

[0021] Furthermore, in step (5), the degreasing atmosphere is nitrogen or argon, and the gradient of the thermal degreasing rate (from room temperature to 250°C at 5°C / min, then to 550°C at 1°C / min, and held for 3 hours) is precisely controlled by thermogravimetric analysis.

[0022] The present invention also provides a monolithic catalyst for carbon dioxide methanation prepared by the above preparation method.

[0023] The present invention also provides the application of the above-described monolithic catalyst for carbon dioxide methanation in the catalytic hydrogenation of carbon dioxide to methane reaction.

[0024] The present invention has the following beneficial effects:

[0025] 1. The preparation strategy proposed in this invention is based on the "structure-function integration" design paradigm, which can realize the synergistic optimization of the integral catalyst from the microscopic active site to the macroscopic multi-level pore structure. It effectively solves the problems of low-temperature CO2 activation, reaction intermediate generation rate and hydrogenation rate matching in the methanation reaction, and meets the dual requirements of industrial methanation for long-term stability and anti-carbon deposition compatibility.

[0026] 2. The carbon support with higher thermal stability in this invention helps maintain excellent anti-carbon deposition ability. In the 200h stability test, the CO2 conversion rate decreased by only 5%.

[0027] 3. The monolithic catalyst prepared by this invention has stable chemical properties, uniform distribution of active components, simple process, and low cost, making it suitable for industrial production. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the three-dimensional model and supporting structure constructed in the embodiments of the present invention;

[0030] Figure 2 This is a schematic diagram of the structure of the model constructed in Comparative Example 4 of this invention. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] This invention provides a method for preparing a monolithic catalyst for carbon dioxide methanation, comprising the following steps:

[0033] (1) A homogeneous and stable slurry is obtained by mixing a hydrated salt of a transition metal, acrylic acid, hydroxyethyl acrylate and a photoinitiator in a certain proportion.

[0034] (2) Constructing a three-dimensional model of the overall catalyst and its supporting elements;

[0035] (3) Print the slurry into a monolithic catalyst using a digital photopolymerization 3D printer;

[0036] (4) Clean the residual resin, remove the support and perform secondary curing to obtain the catalyst precursor;

[0037] (5) The catalyst precursor is subjected to gradient degreasing-reduction treatment to obtain the monolithic catalyst.

[0038] Traditional monolithic catalysts, limited by extrusion molding processes, often suffer from simple pore structures and low mass transfer efficiency. This invention utilizes 3D printing technology to precisely construct complex geometries and successfully build a hierarchical pore system with micropores, mesopores, and macropores. This structure not only significantly increases the contact area between reactants and active sites but also effectively reduces internal diffusion resistance, making it particularly suitable for catalytic reactions under high space velocity conditions. Taking the CO2 methanation reaction as an example, the hierarchical pore structure promotes the association and adsorption of CO2 and H2, while accelerating the formation of intermediates during hydrogenation, enabling a dynamic match between reactant conversion rates and hydrogenation rates, thereby effectively suppressing the occurrence of carbon deposition side reactions.

[0039] The uniform dispersion of transition metal salts in the slurry, combined with subsequent degreasing and reduction processes, allows the active metal components to be firmly anchored in a highly dispersed state on the surface of the porous carbon framework. Compared with the traditional impregnation method, this method effectively avoids the drawback of the active components being embedded in the carrier, significantly improving the exposure degree and utilization efficiency of the active sites.

[0040] In terms of manufacturing process innovation, DLP technology, with its integrated molding advantage, eliminates multiple processes such as impregnation and coating in traditional catalyst preparation, significantly shortening the production cycle. Meanwhile, 3D printing technology supports highly customized designs, enabling precise optimization of the internal flow channel structure of the catalyst based on the characteristics of the reaction flow field—for example, introducing fractal biomimetic designs that simulate blade veins, thereby effectively enhancing mass and heat transfer efficiency.

[0041] Traditional photosensitive resins (such as epoxy acrylates and polyurethane acrylates) contain polar groups such as epoxy groups, ester groups, and urethane bonds in their molecular chains. These groups readily undergo ion-dipole interactions or complexation reactions with metal ions (such as Co2+ and Fe3+) in transition metal nitrates. Furthermore, their high viscosity hinders the uniform dispersion of metal salts, leading to thermodynamic instability and subsequent layering or precipitation. During curing, side reactions can exacerbate phase separation problems. However, acrylic acid and hydroxyethyl acrylate exhibit excellent chemical compatibility due to their molecular structure advantages. The carboxyl groups of acrylic acid can bind to metal ions through ion exchange or coordination bonds, while the additional hydroxyl groups in hydroxyethyl acrylate provide more coordination sites. The complexes formed by these two materials are both hydrophilic and amphiphilic. Combined with their low viscosity, this facilitates the rapid diffusion and dispersion of metal salts. Weakly acidic conditions (pH 4-6) further optimize the coordination ability between the carboxyl groups and metal ions. Moreover, their free radical curing reactions are highly compatible with metal salts, and metal ions can even assist in initiating curing. This provides a feasible solution for preparing monolithic catalysts for printing paste formulations.

[0042] Traditional photosensitive resins can exhibit stratification when incompatible with transition metal nitrates. In this solution, acrylic acid and hydroxyethyl acrylate are used, which have excellent chemical compatibility.

[0043] The present invention will be further illustrated below through specific embodiments.

[0044] The model and support constructed in step (2) of the following embodiments are as follows: Figure 1 As shown: (a), (b), (c), and (d) are respectively the 3D view, cross-sectional view, top view, and support view;

[0045] The model support was designed using PiocreatBox software. The model's contact shape has a diameter of 0.3mm, a contact depth of 0.4mm, an upper diameter of 0.3mm, a lower diameter of 0.8mm, and a connection length of 2.5mm.

[0046] The constructed model is a hollow cylindrical structure with turbulence-inducing effect, with a height of 35 mm, a diameter of 12 mm, a porosity of 65%, an average equivalent pore diameter of 0.5 mm, and a solid skeleton of 0.3 mm.

[0047] Example 1

[0048] (1) Preparation of printing paste: Take 2.22 mmol Co(NO3)2·6H2O, 2.22 mmol Ni(NO3)2·6H2O, 2.5 g acrylic acid, 2.5 g hydroxyethyl acrylate and 0.075 g diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide respectively and mix them. Stir magnetically for 10 min to obtain a homogeneous paste;

[0049] (2) Constructing an integrated catalyst model and its supporting elements;

[0050] (3) The slurry was printed into a monolithic catalyst using digital photopolymerization 3D printing technology. The optical power of the digital photopolymerization 3D printer is 6mW / cm². 2 Initial exposure time: 15s; Number of bottom layers: 6; Printing exposure time: 5s.

[0051] (4) Clean the residual resin, remove the support and perform secondary curing to obtain the catalyst precursor;

[0052] (5) The monolithic catalyst was degreased and reduced by passing nitrogen gas at a rate of 50 ml / min through a tube furnace from room temperature to 550℃ at a heating rate of 1℃ / min to obtain a high-precision monolithic catalyst CoNi@C-0.08 (where 0.08 represents the amount of active metal / photosensitive monomer).

[0053] Example 2

[0054] The only difference from Example 1 is step (1): 2.5 mmol Co(NO3)2·6H2O, 2.5 mmol Ni(NO3)2·6H2O, 2.5 g acrylic acid, 2.5 g hydroxyethyl acrylate and 0.075 g diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide were mixed and magnetically stirred for 10 min to obtain a homogeneous slurry; the final monolithic catalyst was denoted as CoNi@C-0.09.

[0055] Example 3

[0056] The only difference from Example 1 is that 2.78 mmol Co(NO3)2·6H2O, 2.78 mmol Ni(NO3)2·6H2O, 5.0 g acrylic acid, 2.5 g hydroxyethyl acrylate and 0.075 g diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide were mixed and magnetically stirred for 10 min to obtain a homogeneous slurry; the final monolithic catalyst was denoted as CoNi@C-0.10.

[0057] Example 4

[0058] The preparation method of the 3D printed monolithic catalyst in this embodiment is basically the same as that in Example 1. The only difference from Example 1 is step (1): 2.5 mmol Co(NO3)2·6H2O, 2.5 mmol Fe(NO3)2·6H2O, 2.5 g acrylic acid, 2.5 g hydroxyethyl acrylate and 0.075 g diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide are mixed and magnetically stirred for 10 min to obtain a homogeneous slurry; the monolithic catalyst obtained is denoted as CoFe@C-0.09.

[0059] Example 5

[0060] The preparation method of the 3D printed monolithic catalyst in this embodiment is basically the same as that in Example 1. The only difference from Example 1 is step (1): 2.5 mmol Co(NO3)2·6H2O, 2.5 mmol RuCl3·xH2O, 2.5 g acrylic acid, 2.5 g hydroxyethyl acrylate and 0.075 g diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide are mixed and magnetically stirred for 10 min to obtain a homogeneous slurry; the monolithic catalyst obtained is denoted as CoRu@C-0.09.

[0061] Comparative Example 1

[0062] The powder catalyst preparation method in this example specifically includes the following steps:

[0063] (1) Preparation of printing paste: Take 2.5 mmol Co(NO3)2·6H2O, 2.5 mmol Ni(NO3)2·6H2O, 2.5 g acrylic acid, 2.5 g hydroxyethyl acrylate and 0.075 g diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide and mix them. Stir magnetically for 10 min to obtain a homogeneous paste;

[0064] (2) Take a small amount of slurry and place it on a glass plate. Use a coater to spread it to 0.2 mm and then use a UV flashlight (405 nm) to cure it.

[0065] The catalyst obtained in step (2) was treated under the same tube furnace degreasing and reduction conditions as in Example 1, and then uniformly ground to obtain the monolithic catalyst CoNi@C-0.09-powder.

[0066] Comparative Example 2

[0067] In this example, the preparation method of the 3D printed monolithic catalyst is basically the same as that in Example 1. The only difference from Example 1 is step (1): 1.67 mmol Co(NO3)2·6H2O, 1.67 mmol Ni(NO3)2·6H2O, 2.5 g acrylic acid, 2.5 g hydroxyethyl acrylate and 0.075 g diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide are mixed and magnetically stirred for 10 min to obtain a homogeneous slurry; the monolithic catalyst obtained is denoted as CoNi@C-0.06.

[0068] Comparative Example 3

[0069] In this example, the preparation method of the 3D printed monolithic catalyst is basically the same as that in Example 1. The only difference from Example 1 is step (1): 3.58 mmol Co(NO3)2·6H2O, 3.58 mmol Ni(NO3)2·6H2O, 5.0 g acrylic acid, 2.5 g hydroxyethyl acrylate and 0.075 g diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide are mixed and magnetically stirred for 10 min to obtain a homogeneous slurry; the monolithic catalyst obtained is denoted as CoNi@C-0.12.

[0070] Comparative Example 4

[0071] In this example, the preparation method of the 3D printed monolithic catalyst is basically the same as that in Example 2, except for step (2). The monolithic catalyst model in this example adopts a traditional honeycomb structure (such as...). Figure 2 As shown), it is labeled CoNi@C-0.09-honey.

[0072] The catalysts prepared in Examples 1-5 and Comparative Examples 1-4 were evaluated in a micro-stationary reactor. The specific operating steps are as follows: 1.0 g of the monolithic catalyst was weighed and loaded into the isothermal zone in the middle of the reaction tube. The feed gas H2 / CO2 ratio was 4, the temperature was 250℃, the pressure was 2 MPa, and the space velocity (GHSV) was 10000 ml / (g·h). After reaching a stable state, samples were taken for analysis, with sampling every 3 hours. Quantitative and qualitative analyses of the feed gas and products were performed using gas chromatography. The CO2 conversion rate and the selectivity of each component were calculated using the methane correlation method in "Determination of H2, N2, CO, CO2 and C1-C8 Hydrocarbons in Coal-Based Fischer-Tropsch Synthesis Tail Gas by Gas Chromatography". Specific results are shown in Table 1.

[0073] Table 1. Comparison of CO2 methanation performance test results of the monolithic catalysts prepared in Examples 1-5 and Comparative Examples 1-4

[0074] catalyst <![CDATA[CO2 conversion rate %]]> <![CDATA[CH4 selectivity %]]> CoNi@C-0.08 66 98.6 CoNi@C-0.09 81 98.7 CoNi@C-0.10 72 98.4 CoFe@C-0.09 74 98.9 CoRu@C-0.09 78 98.8 CoNi@C-0.06 56 98.2 CoNi@C-0.12 62 98.7 CoNi@C-0.09-powder 64 98.3 CoNi@C-0.09-honey 70 98.6

[0075] Under evaluation conditions of H2 / CO2 molar ratio of 4, reaction temperature of 250℃, reaction pressure of 2MPa, and space velocity (GHSV) of 10000ml / (g·h), the CO2 methanation reaction performance of the catalysts prepared in Examples 1-5 and Comparative Examples 1-4 was tested. The results showed that different combinations of active metals, metal loading, catalyst morphology, and microstructure have a significant impact on catalytic performance. Moreover, the monolithic catalyst preparation scheme based on digital photopolymerization 3D printing technology proposed in this invention shows outstanding advantages in improving CO2 conversion rate. At the same time, all tested samples maintained excellent CH4 selectivity, providing an efficient and feasible catalytic system for low-temperature CO2 resource utilization.

[0076] From the perspective of the influence of active metal combination and loading, the CoNi binary metal system exhibits the best catalytic activity. In Examples 1-3, using CoNi as the active component, only the molar ratio of active metal to photosensitive monomer was changed (0.08, 0.09, and 0.10, respectively), and the corresponding CO2 conversion rates were 66%, 81%, and 72%, respectively, while the CH4 selectivity remained stable between 98.4% and 98.7%. This result indicates that there is an optimal value for metal loading in the CoNi system: when the molar ratio is 0.09, the active component can be uniformly dispersed on the carbon support surface, fully exposing active sites, thereby maximizing CO2 activation efficiency; when the loading is below 0.08, the number of active sites is insufficient, resulting in a lower conversion rate (see Comparative Example 2); when the loading is above 0.10, metal particles are prone to agglomeration, which reduces the effective active sites and decreases the conversion rate (see Comparative Example 3). Comparing the performance of different binary metal combinations, it can be seen that, at the same molar ratio (0.09), the CO2 conversion rate of CoNi@C-0.09 (81%) is significantly higher than that of CoFe@C-0.09 (74%) and CoRu@C-0.09 (78%). This further proves that the synergistic effect of Co and Ni is more conducive to breaking the chemical inertness of CO2 molecules and promoting its low-temperature activation and hydrogenation reaction. Moreover, the CH4 selectivity of the three metal combinations is close to 99% (98.8%-98.9%), indicating that the combination of transition metals and carbon support can effectively suppress side reactions such as reverse water-gas shift reaction and ensure that the product is mainly methane.

[0077] The influence of catalyst morphology on reaction performance is mainly reflected in CO2 conversion. The CO2 conversion of CoNi@C-0.09-powder is only 64%, which is 20.9% lower than the 81% of the monolithic catalyst in Example 2, while the CH4 selectivity only slightly decreases from 98.7% to 98.3%. This difference stems from the structural advantages of the monolithic catalyst: the monolithic structure constructed by 3D printing has a lower bed pressure drop and a better flow field distribution, avoiding the problem of excessive diffusion resistance that is prone to occur in powder catalyst beds, allowing reactants to reach the active sites more efficiently, while accelerating the desorption of methane and water, thereby improving the reaction kinetic rate; while the stacked structure of powder catalysts is prone to mass transfer limitation, and even with the same active components, it is difficult to fully exert the catalytic efficiency.

[0078] Optimization of the catalyst microstructure further improved the performance of the monolithic catalyst. Comparative Example 2, using a traditional honeycomb structure (CoNi@C-0.09-honey), achieved a CO2 conversion rate of 70%, lower than the hollow cylindrical structure of Example 2 (81%). This is because the model of Example 2 was designed with a hollow structure that induces turbulence. This structure can break the laminar boundary layer, enhance the mixing and mass transfer efficiency of reactants inside the catalyst, and significantly increase the contact probability between active sites and reactants. In contrast, the flow channels of the traditional honeycomb structure are relatively regular, easily forming stable laminar flow, leading to insufficient reactant supply in some areas, reduced utilization of active sites, and thus affecting the CO2 conversion rate.

[0079] In summary, this invention utilizes digital photopolymerization 3D printing technology to prepare a monolithic catalyst. Through an integrated structure-function design, it achieves synergistic optimization of microscopic active sites (uniformly dispersed transition metals) and macroscopic hierarchical pore structures (micropores-mesopores-macropores). The combination of the CoNi binary metal pair (molar ratio 0.09) and the hollow cylindrical structure exhibits optimal performance, achieving a CO2 conversion rate of 81% and a CH4 selectivity of nearly 99%. Compared to powder catalysts and traditional honeycomb catalysts, it demonstrates significant improvements in mass transfer efficiency and active site utilization. Furthermore, the high methane selectivity of all catalysts indicates that this preparation method effectively suppresses side reactions, meeting the industrial requirements for low-energy consumption and high-selectivity CO2 hydrogenation to methane production, and possesses promising prospects for industrial application.

[0080] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for the preparation of a monolithic catalyst for the methanation of carbon dioxide, characterized in that, It comprises the following steps: (1) mixing the hydrated salt of transition metal, acrylic acid, hydroxyethyl acrylate and photoinitiator in a certain proportion to obtain a uniform stable slurry; (2) constructing a three-dimensional model of the monolithic catalyst and its support; (3) printing the slurry into a monolithic catalyst embryo by a digital light curing 3D printer; (4) cleaning the residual resin, removing the support and secondary curing to obtain the catalyst precursor; (5) performing gradient debinding-reduction treatment on the catalyst precursor to obtain the monolithic catalyst.

2. The method for preparing a monolithic catalyst for carbon dioxide methanation according to claim 1, characterized by: In step (1), the hydrated salt of transition metal is any one or combination of Co(NO3)2·6H2O, Ni(NO3)2·6H2O, Fe(NO3)2·6H2O and RuCl3·xH2O.

3. The method for preparing a monolithic catalyst for carbon dioxide methanation according to claim 1, characterized by: In step (1), the photoinitiator is any one of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, benzophenone, 1-hydroxycyclohexyl phenyl ketone and 2-hydroxy-2-methyl-1-phenylpropanone.

4. The method for preparing a monolithic catalyst for carbon dioxide methanation according to claim 1, characterized by: In step (1), the amount ratio of the hydrated salt of transition metal, acrylic acid, hydroxyethyl acrylate and diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide is (0.08-0.10) mmol:2.5 g:2.5 g:(0.045-0.075) g.

5. The method for preparing a monolithic catalyst for carbon dioxide methanation according to claim 1, characterized by: The model is a hollow structure cylinder with turbulence induction effect.

6. The method for preparing a monolithic catalyst for carbon dioxide methanation according to claim 1, characterized by, The model support is designed by PiocreatBox software, and the contact shape diameter of the model is (0.2-0.4) mm, the contact depth is (0.3-0.5) mm, the upper end diameter is (0.2-0.4) mm, the lower end diameter is 0.8 mm, and the connection length is 2.5 mm.

7. The method for preparing a monolithic catalyst for carbon dioxide methanation according to claim 1, characterized by: The digital light-cured 3D printer has a light power of (3-6) mW / cm 2 , an initial exposure time of (10-15) s, 3-6 layers of bottom exposure, and a printing exposure time of (1-5) s.

8. The method for making a monolithic catalyst for carbon dioxide methanation according to claim 1, characterized in that: The debinding atmosphere is nitrogen or argon, and the gradient precision control of thermal debinding rate is realized by thermogravimetric curve analysis.

9. A monolithic catalyst for carbon dioxide methanation prepared by the preparation method of any one of claims 1-8.

10. The use of the monolithic catalyst for carbon dioxide methanation of claim 9 in the reaction of catalytic hydrogenation of carbon dioxide to produce methane.

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