A cerium framework-substituted S-1 molecular sieve supported nickel metal catalyst, preparation method and application

Abstract

The present invention relates to the technical field of catalysts, and specifically relates to a cerium framework-substituted S-1 molecular sieve supported nickel metal catalyst, a preparation method and an application. The catalyst is prepared by this method. The method includes forming a transparent sol; mixing a blue transparent complex solution with the transparent sol to obtain a synthetic gel; subjecting the synthetic gel to hydrothermal crystallization treatment to obtain a crystallized product; performing post-treatment to obtain a white powder precursor; and performing calcination treatment to obtain the catalyst. The application is the application of the catalyst in the catalytic CO2 methanation reaction. The catalyst prepared by the present invention has the advantages of high low-temperature activity, sufficient oxygen vacancies, good stability and uniform dispersion of active components.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and particularly relates to a cerium framework-substituted S-1 molecular sieve supported nickel metal catalyst, a preparation method and an application thereof. Background Art

[0002] With the increasing global carbon emissions, the hydrogenation of CO2 to high-value chemicals (such as methane and light olefins) has become a research hotspot in the field of carbon neutrality. Nickel-based catalysts are widely used in the CO2 methanation reaction due to their high activity.

[0003] For example, in the Chinese invention application with the publication number CN119386919A, a nickel-based methanation catalyst supported on mesoporous molecular sieve SBA-16 and its application in the hydrogenation of carbon dioxide are disclosed. It uses SBA-16 as a carrier and loads nickel metal by the impregnation method (nickel loading is 10%-30%), and the applicable temperature is 200-400°C. The disadvantages of this application include: poor metal dispersion, aggregation of nickel particles; insufficient oxygen vacancies, weak CO2 adsorption activity; high nickel loading leading to high cost and easy sintering; low CO2 conversion rate at low temperature and dependence on high temperature operation.

[0004] For example, in the Chinese invention application with the publication number CN115970743A, a ZSM-5 molecular sieve composite material, its preparation method and application, and a method for preparing methane are disclosed. Its stability and activity of the nickel-based catalyst are improved by confining pure silica ZSM-5 molecular sieve and designing manganese promoters, but only relying on manganese promoters makes the interaction between nickel and the molecular sieve weak, and the oxygen vacancy generation ability of manganese oxides is weak, which may lead to insufficient CO2 adsorption and activation ability and limited low-temperature activity.

[0005] For example, in the Chinese invention application with the publication number CN118162189A, a methanation reaction catalyst, a preparation method and its application are disclosed. It loads nickel on the all-silica zeolite S-1 carrier and adds promoter Mo, and the composite carrier is prepared by physical mixing; NiO is loaded on the surface of the composite carrier, but the particle size is large and it is easy to agglomerate and deactivate at high temperature. This method uses multiple-step impregnation and high-temperature calcination, and the nickel content is as high as 10%-30%, resulting in a complex process and high cost.

[0006] It can be seen that when nickel-based catalysts are used in the CO2 methanation reaction, there are still the following bottlenecks:

[0007] 1) Insufficient low-temperature activity, such as the low conversion rate of existing nickel-based catalysts to CO2 at low temperature;

[0008] 2) Insufficient oxygen vacancies, such as weak oxygen vacancy generation ability, which may lead to insufficient CO2 adsorption and activation ability and limited low-temperature activity;

[0009] 3) Insufficient stability. Existing nickel-based catalysts are prone to deactivation due to metal sintering and carbon deposition during high-temperature reactions, resulting in a decline in stability.

[0010] 4) Insufficient dispersion of active components. For example, when zeolite is used as a carrier, the weak bonding between the silicon-based framework and nickel leads to easy migration of the active components, thereby reducing the dispersion of the active components, causing agglomeration of the active components, and resulting in a decline in catalytic performance and even deactivation.

[0011] In summary, it is necessary to develop a cerium framework-substituted S-1 zeolite-supported nickel metal catalyst, a preparation method, and an application to solve the problems existing in the prior art. Summary of the Invention

[0012] The object of the present invention is to provide a cerium framework-substituted S-1 zeolite-supported nickel metal catalyst, a preparation method, and an application. The specific technical solutions are as follows:

[0013] In the first aspect, the present invention provides a preparation method of a cerium framework-substituted S-1 zeolite-supported nickel metal catalyst, which includes:

[0014] Step S1: Mix deionized water and tetraethyl orthosilicate under the first stirring; then add cerium nitrate and mix under the second stirring, wherein the molar ratio of cerium atoms in cerium nitrate to silicon atoms in tetraethyl orthosilicate is controlled to be 1:30 - 150; finally, add tetrapropylammonium hydroxide and form a transparent sol under the third stirring;

[0015] Step S2: Dissolve nickel nitrate in deionized water, and then add ethylenediamine and form a blue transparent complex solution under the fourth stirring; mix the blue transparent complex solution and the transparent sol under the fifth stirring to obtain a synthesis gel;

[0016] Step S3: Transfer the synthesis gel to a hydrothermal reaction kettle for hydrothermal crystallization treatment to obtain a crystallized product;

[0017] Step S4: After cooling the crystallized product to room temperature, perform post-treatment to obtain a white powder precursor;

[0018] Step S5: Calcinate the white powder precursor to obtain a cerium framework-substituted S-1 zeolite-supported nickel metal catalyst.

[0019] Optionally, in step S1 and step S2, the content of SiO2 in tetraethyl orthosilicate, the molar ratio of tetrapropylammonium hydroxide to the total amount of deionized water used is 1:0.4:35; the mass percentage of SiO2 in tetraethyl orthosilicate is 28%.

[0020] Optionally, in the step S1, the first stirring is performed by magnetic stirring, the stirring temperature is 25 ± 5 °C, the stirring speed is 300 - 600 rpm, and the stirring time is 10 - 30 min; the second stirring is performed by magnetic stirring, the stirring temperature is 25 ± 5 °C, the stirring speed is 300 - 600 rpm, and the stirring time is 1 - 2 h; the third stirring is performed by magnetic stirring, the stirring temperature is 25 ± 5 °C, the stirring speed is 300 - 600 rpm, and the stirring time is 6 - 8 h.

[0021] Optionally, in the step S2, the mass of nickel in the nickel nitrate accounts for 4% - 5% of the mass of the SiO2.

[0022] Optionally, in the step S2, the fourth stirring is performed by magnetic stirring, the stirring temperature is 25 ± 5 °C, the stirring speed is 300 - 600 rpm, and the stirring time is 10 - 30 min; the fifth stirring is performed by magnetic stirring, the stirring temperature is 25 ± 5 °C, the stirring speed is 300 - 600 rpm, and the stirring time is 30 - 60 min.

[0023] Optionally, in the step S3, the hydrothermal crystallization treatment is carried out at a treatment temperature of 175 - 190 °C and a treatment time of 4 ± 1 days.

[0024] Optionally, in the step S4, the post-treatment includes washing treatment, centrifugation treatment, and drying treatment carried out in sequence; the washing treatment includes washing the crystallized product with deionized water until it is neutral; the centrifugation treatment is used to centrifuge and separate the precipitate from the crystallized product after the washing treatment; the centrifugation rate used in the centrifugation treatment is 8000 - 10000 rpm, and the centrifugation time is 8 - 10 min; the drying temperature used in the drying treatment is 70 - 80 °C, and the drying time is 12 - 24 h.

[0025] Optionally, in the step S5, the calcination treatment includes a heating calcination stage, a constant-temperature calcination stage, and a natural cooling stage carried out in sequence; the starting temperature used in the heating calcination stage is 25 ± 5 °C, the ending temperature is 550 ± 10 °C, and the heating rate is 2 - 3 °C / min; the calcination temperature used in the constant-temperature calcination stage is 550 ± 10 °C, and the calcination time is 500 ± 20 min; the starting temperature of the natural cooling stage is 550 ± 10 °C, and the ending temperature is 25 ± 5 °C.

[0026] In a second aspect, the present invention provides a cerium framework-substituted S-1 molecular sieve-supported nickel metal catalyst, which is prepared by using the preparation method of the cerium framework-substituted S-1 molecular sieve-supported nickel metal catalyst.

[0027] In a third aspect, the present invention provides the use of the cerium framework-substituted S-1 molecular sieve supported nickel metal catalyst in the catalytic CO2 methanation reaction.

[0028] Applying the technical solution of the present invention has at least the following beneficial effects:

[0029] (1) The preparation method of the cerium framework-substituted S-1 molecular sieve supported nickel metal catalyst provided by the present invention can prepare a catalyst with high efficiency in catalyzing the CO2 methanation reaction. This catalyst has the advantages of high low-temperature activity, sufficient oxygen vacancies, good stability, and uniform dispersion of active components. Specifically, in step S1 of the present invention, the molar ratio of cerium atoms in cerium nitrate to silicon atoms in tetraethyl orthosilicate is controlled to be 1:30 to 150. On the one hand, under the action of tetrapropylammonium hydroxide, cerium nitrate and tetraethyl orthosilicate are promoted to hydrolyze together, and the hydrolysis products form the S-1 molecular sieve framework under the hydrothermal crystallization treatment in step S3. Among them, cerium atoms directly replace silicon atoms in the S-1 molecular sieve framework, rather than simple adsorption on the surface of the S-1 molecular sieve, forming a stable Ce-O-Si bonding structure; on the other hand, it is used to increase the oxygen vacancy density to ensure sufficient oxygen vacancies; among them, the principle of oxygen vacancy formation is as follows: cerium atoms will appear Ce 3+ and Ce 4+ redox pairs. During the catalytic CO2 methanation reaction, under the action of the reaction gas H2, Ce 4+ is reduced to Ce 3+ , resulting in the detachment of adjacent lattice oxygen of the catalyst to form sufficient oxygen vacancies; these oxygen vacancies, as highly active sites, capture CO2 molecules through chemical adsorption, significantly enhancing the polarization and dissociation ability of CO2, activating CO2 to form intermediates (such as CO·, CH3O·), Ce 3+ is oxidized to Ce 4+ , and the oxygen vacancies are filled. Therefore, the Ce 3+ and Ce 4+ redox pair dynamically circulates to continuously provide active sites for the CO2 methanation reaction; in addition, these oxygen vacancies, as weak acid sites, capture H2 molecules through chemical adsorption and promote their dissociation to provide active hydrogen. Further, the active hydrogen reacts with the intermediate to form methane. In step S2, ethylenediamine complexes Ni 2+ in nickel nitrate to form a [Ni(en)3] 2+ complex (with a diameter of about 0.5 nm, see the literature: Lu Haifen, Chen Yingying, Zhou Hu, etc. Synthesis and crystal structure of one-dimensional chain-like cyanide-bridged coordination polymer {[Ni(en)2][Ni(CN)4]} n Journal of Soochow University (Natural Science Edition), 2006, (04): 69-73) that matches the size of the micropores of the molecular sieve (with a diameter of about 0.55 nm), realizing the control of Ni2+ Confined and loaded in the micropores of the molecular sieve; compared with the conventional method of impregnating and loading nickel, the method of complexing and confining and loading nickel in step S2 of the present invention can reduce the nickel loading amount and save raw material costs. After the hydrothermal crystallization treatment in step S3, Ni 2+ is uniformly confined and loaded in the micropores of the molecular sieve, and then reduced by the reaction gas H2 to form ultra-small Ni nanoparticles. The formed Ni nanoparticles are not only physically confined in the microporous structure of the molecular sieve, but also can be confined in the microporous structure of the molecular sieve through chemical actions (such as ligand protection, hydrothermal crystallization, strong interaction between metal Ni and the carrier Ce-O-Si framework, etc.), inhibiting its high-temperature migration and sintering, improving the catalyst stability, and ensuring the uniform dispersion of Ni particles; at the same time, the micropores of the molecular sieve limit the diffusion and polymerization of carbon deposition precursors through steric hindrance, inhibiting carbon deposition formation and improving the catalyst stability; in addition, H2 dissociates into active hydrogen under the action of weak acid sites on the surface of Ni particles, further promoting the CO2 methanation reaction; if the hydrothermal crystallization treatment is incomplete, it will lead to the residue of amorphous substances, blocking the pores of the molecular sieve, and may also cause local pore collapse. The post-treatment in step S4 is convenient for purifying the catalyst. The calcination treatment in step S5 facilitates the removal of tetrapropylammonium hydroxide on the one hand, and on the other hand, facilitates the formation of a strong bond Ni-O-Ce bond between Ni particles and Ce-O groups, enhancing the interaction between the active component Ni and the carrier Ce-O-Si framework, further improving the anti-sintering performance of the catalyst, and enabling the uniform dispersion of the active component Ce, improving the low-temperature activity of the catalyst, so that the catalyst has a CO2 conversion rate of 45% under the low-temperature condition of 100 °C reaction temperature and a CO2 conversion rate of 100% under the low-temperature condition of 200 °C reaction temperature.

[0030] (2) The calcination treatment adopted by the present invention in step S5 includes a heating calcination stage, a constant-temperature calcination stage, and a natural cooling stage carried out in sequence. Among them, the heating calcination stage is used to gradually remove tetrapropylammonium hydroxide to avoid blocking the micropores of the molecular sieve by residual organic matter; if tetrapropylammonium hydroxide remains, it may carbonize in the high-temperature reaction to form a carbon deposition core; the constant-temperature calcination stage can, on the one hand, promote the complete formation of Ce-O-Si bonds, enhance the rigidity and stability of the molecular sieve framework, and then maintain the integrity of the microporous structure of the molecular sieve, restricting the free migration of reaction intermediates (such as CO·, CH3O·) and preventing their polymerization to form carbon deposition; on the other hand, it is convenient for Ni particles to form a strong bond Ni-O-Ce bond with Ce-O groups; on the third hand, the constant-temperature calcination stage helps to completely remove tetrapropylammonium hydroxide, keep the micropores of the molecular sieve open, and inhibit the formation of macromolecular intermediates such as polycyclic aromatic hydrocarbons; the natural cooling stage is convenient for taking out the catalyst after cooling.

[0031] In addition to the purposes, features, and advantages described above, the present invention has other purposes, features, and advantages. The following will refer to the drawings and make a further detailed description of the present invention. Brief Description of the Drawings

[0032] The drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0033] Figure 1 are the graphs of the results of XRD tests on the respective transparent sols synthesized by the steps S1 in Examples 1 to 3 of the present invention and the S-1 molecular sieve framework without the incorporation of Ce, respectively sampled;

[0034] Figure 2 is Figure 1 an enlarged view of the region of 2θ = 5° to 11° in;

[0035] Figure 3 are the graphs of the results of XRD tests on the respective catalysts prepared by Examples 1 to 3 of the present invention and the S-1 molecular sieve framework without treatment, respectively sampled;

[0036] Figure 4 is Figure 3 a graph of the result after magnifying the peak intensity in the region of 2θ = 40° to 50° in by 10 times;

[0037] Figure 5 are the graphs of the results of XRD tests on the respective catalysts prepared by Comparative Examples 1 to 3 of the present invention and the S-1 molecular sieve framework without treatment, respectively sampled;

[0038] Figure 6 is Figure 5 a graph of the result after magnifying the peak intensity in the region of 2θ = 40° to 50° in by 10 times;

[0039] Figure 7 is the stability test result of the catalyst prepared in Example 1 in the CO2 methanation reaction at a test temperature of 200°C; wherein, S CH4 represents methane selectivity; S CO represents carbon monoxide selectivity; S CH4 / S CO (%) respectively represent the percentages of methane selectivity and carbon monoxide selectivity; X CO2 represents carbon dioxide conversion; X CO2 (%) represents the percentage of carbon dioxide conversion. Detailed Description of the Invention

[0040] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention belong to the scope of protection of the present invention.

[0041] Example 1:

[0042] A preparation method of a cerium framework-substituted S-1 molecular sieve supported nickel metal catalyst, comprising:

[0043] Step S1: Mix deionized water and tetraethyl orthosilicate under the first stirring; then add cerium nitrate Ce(NO3)2·6H2O and mix under the second stirring, wherein the molar ratio of cerium atoms in cerium nitrate to silicon atoms in tetraethyl orthosilicate is controlled to be 1:100; finally, add tetrapropylammonium hydroxide and form a transparent sol under the third stirring;

[0044] Step S2: Dissolve nickel nitrate Ni(NO3)2·6H2O in deionized water, then add an excessive amount of ethylenediamine (specifically 1 mL) and form a blue transparent complex solution under the fourth stirring; mix the blue transparent complex solution and the transparent sol under the fifth stirring to obtain a synthetic gel;

[0045] Step S3: Transfer the synthetic gel to a hydrothermal reaction kettle with a polytetrafluoroethylene lining (volume: 40 mL) for hydrothermal crystallization treatment to obtain a crystallized product;

[0046] Step S4: After cooling the crystallized product to room temperature, perform post-treatment to obtain a white powder precursor;

[0047] Step S5: Calcinate the white powder precursor in a muffle furnace to obtain a cerium framework-substituted S-1 molecular sieve supported nickel metal catalyst.

[0048] In the step S1 and the step S2, the SiO2 content in the tetraethyl orthosilicate, the molar ratio of the total amount of tetrapropylammonium hydroxide to deionized water is 1:0.4:35; the mass percentage of SiO2 in the tetraethyl orthosilicate is 28%. Specifically, the mass of deionized water in the step S1 is 15.00 g, the mass of deionized water in the step S1 is 4.00 g; the mass of tetraethyl orthosilicate is 7.67 g; the mass of tetrapropylammonium hydroxide is 11.81 g.

[0049] In the step S1, the first stirring is carried out by magnetic stirring, the stirring temperature is 25±5°C (specifically 26°C), the stirring speed is 500 rpm, and the stirring time is 10 min; the second stirring is carried out by magnetic stirring, the stirring temperature is 25±5°C (specifically 26°C), the stirring speed is 500 rpm, and the stirring time is 1 - 2 h (specifically 1 h); the third stirring is carried out by magnetic stirring, the stirring temperature is 25±5°C (specifically 26°C), the stirring speed is 500 rpm, and the stirring time is 6 h.

[0050] In the step S2, the mass of nickel in nickel nitrate accounts for 4% of the mass of SiO2. Specifically, the mass of nickel nitrate is 0.48 g.

[0051] In the step S2, the fourth stirring is carried out by magnetic stirring, the stirring temperature is 25±5°C (specifically 26°C), the stirring speed is 500 rpm, and the stirring time is 10 - 30 min (specifically 20 min); the fifth stirring is carried out by magnetic stirring, the stirring temperature is 25±5°C (specifically 26°C), the stirring speed is 500 rpm, and the stirring time is 30 - 60 min (specifically 40 min).

[0052] In the step S3, the hydrothermal crystallization treatment is carried out at a treatment temperature of 180°C and a treatment time of 4±1 days (specifically 4 days).

[0053] In the step S4, the post-treatment includes washing treatment, centrifugation treatment and drying treatment carried out in sequence; the washing treatment includes washing the crystallized product with deionized water until it is neutral; the centrifugation treatment is used to centrifuge and separate the precipitate from the crystallized product after the washing treatment; the centrifugation rate used in the centrifugation treatment is 8000 - 10000 rpm (specifically 8000 rpm), and the centrifugation time is 10 min; the drying temperature used in the drying treatment is 70°C, and the drying time is 12 - 24 h (specifically 24 h).

[0054] In the step S5, the calcination treatment includes a heating calcination stage, a constant temperature calcination stage and a natural cooling stage carried out in sequence; the starting temperature of the heating calcination stage is 20°C, the ending temperature is 550°C, the heating time is 265 min, and the heating rate is 2°C / min; the calcination temperature of the constant temperature calcination stage is 550°C, and the calcination time is 480 min; the starting temperature of the natural cooling stage is 550°C, the ending temperature is 30°C, and the cooling method is to open the furnace door of the muffle furnace for natural cooling.

[0055] Example 2:

[0056] Different from Example 1, the molar ratio of cerium atoms in cerium nitrate to silicon atoms in tetraethyl orthosilicate was controlled to be 1:30.

[0057] Example 3:

[0058] Different from Example 1, the molar ratio of cerium atoms in cerium nitrate to silicon atoms in tetraethyl orthosilicate was controlled to be 1:150.

[0059] Comparative Example 1:

[0060] Different from Example 1, cerium nitrate was not used.

[0061] Comparative Example 2:

[0062] The Ni-loaded Ce-S-1 catalyst was synthesized by the impregnation method. Specifically, 0.48 g of Ni(NO3)2·6H2O was dissolved in 3 mL of absolute ethanol. After stirring until Ni(NO3)2·6H2O was completely dissolved, the transparent sol synthesized in Step S1 of Example 1 was added; subsequently, absolute ethanol was added until the liquid level submerged the transparent sol; then, it was covered and left to stand at room temperature for 1 day and then transferred to an oven at 70 °C to be dried to obtain a solid powder; finally, the calcination treatment in Step S5 of Example 1 was adopted to obtain the Ni-loaded Ce-S-1 catalyst synthesized by the impregnation method.

[0063] Comparative Example 3:

[0064] Different from Comparative Example 2, cerium nitrate was not used.

[0065] The catalysts prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were respectively subjected to methanation performance tests. The test results are shown in Table 1. The methanation performance test method is as follows:

[0066] The CO2 methanation reaction evaluation was carried out in a fixed-bed reactor. The required catalyst dosage was 100 mg, and the reaction space velocity (GHSV) was 36000 mL·g -1 ·h -1 ; the molar ratio of the components in the mixed gas was N2:CO2:H2 = 1:1:4; the outlet gas was detected and analyzed by a gas chromatograph (model GC-8890A); the whole reaction process was carried out under atmospheric pressure. Before the reaction started, the catalyst needed to be reduced with H2 at 700 °C for 2 h (for activating the catalyst); subsequently, the temperature of the fixed-bed reactor was reduced to room temperature and then raised to the set reaction temperature (100 °C and 200 °C).

[0067] Table 1 Methanation performance test results

[0068]

[0069] As can be seen from the data in Table 1, compared with Comparative Examples 1 to 3, the catalysts prepared by Examples 1 to 3 of the present invention have higher low-temperature catalytic activity. Among them, the catalyst prepared with a molar ratio of cerium atoms in cerium nitrate to silicon atoms in tetraethyl orthosilicate of 1:100 in Example 1 has the best low-temperature catalytic activity. Specifically, the conversion rate of CO2 of this catalyst reaches 45% and the methane selectivity reaches 83% under the low-temperature condition of a reaction temperature of 100°C. Under the low-temperature condition of a reaction temperature of 200°C, the conversion rate of CO2 reaches 100% and the methane selectivity reaches 100%.

[0070] Compared with Example 1, for the catalyst prepared with a higher amount of cerium nitrate in Example 2, the conversion rate of CO2 decreased to 28% and the methane selectivity decreased to 65% at a reaction temperature of 100°C. At a reaction temperature of 200°C, the conversion rate of CO2 decreased to 98%. This is because a higher amount of cerium nitrate results in a higher Ce content, which may cause excessive distortion of the molecular sieve framework, block the micropores, limit the confinement effect of Ni nanoparticles, and further lead to poor dispersion of the active component Ce, ultimately resulting in a decrease in the low-temperature activity of the catalyst.

[0071] Compared with Example 1, for the catalyst prepared with a lower amount of cerium nitrate in Example 3, the conversion rate of CO2 decreased to 37% and the methane selectivity decreased to 76% at a reaction temperature of 100°C. This is because a lower amount of cerium nitrate results in a lower Ce content, leading to insufficient oxygen vacancy density in the catalyst and a decrease in low-temperature activity.

[0072] Compared with Example 1, in Comparative Example 1, cerium nitrate was not used, resulting in a significant decrease in the low-temperature activity of the catalyst. This is because the absence of cerium nitrate cannot form oxygen vacancies in the catalyst, and thus cannot provide active sites to promote the adsorption and activation of CO2 at low temperatures, leading to a significant decrease in the low-temperature activity of the catalyst.

[0073] Compared with Example 1, in Comparative Example 2, nickel was loaded by the impregnation method, resulting in a significant decrease in the low-temperature activity of the catalyst. This is because the nickel loaded by the impregnation method is mostly loaded on the surface of the molecular sieve, which is prone to agglomeration and sintering, thus leading to a significant decrease in the low-temperature activity of the catalyst.

[0074] Compared with Comparative Example 2, in Comparative Example 3, cerium nitrate was not used, resulting in a further significant decrease in the low-temperature activity of the catalyst.

[0075] To study the actual amount of Ni loaded on the molecular sieve in the catalyst and the molar ratio of cerium atoms to silicon atoms, the elements in the catalyst prepared in Example 2 were tested by ICP in the present invention. The test results are shown in Table 2. The ICP test method is as follows: The content of the elements was determined by measuring with an OPTIMA 4300DV type inductively coupled plasma spectrometer (ICP) produced by PerkinElmer. Specifically, 0.01 g of the catalyst sample was taken in a 50 mL centrifuge tube, 4 mL of deionized water and 0.4 mL of a hydrofluoric acid solution with a mass concentration of 40% were added, and it was oscillated at 25 ± 5 °C for 5 min. Then, 3 drops of a concentrated nitric acid solution with a mass concentration of 32% were added thereto. After the catalyst sample in the centrifuge tube was completely dissolved, 0.25 g of boric acid was added to the centrifuge tube and it was continuously oscillated until the solution in the centrifuge tube was completely clear. Then, the liquid was transferred to a 50 mL plastic volumetric flask for volume fixation; finally, it was sent for testing.

[0076] Table 2 ICP test results

[0077]

[0078] As can be seen from Table 2, the actual amount of Ni loaded on the molecular sieve in the catalyst prepared in Example 2 and the molar ratio of cerium atoms to silicon atoms are close to the actual added amounts. It shows that the doping amount of Ce and the loading amount of Ni can be effectively controlled, and at the same time, it also proves that Ni and Ce have been successfully doped in the catalyst.

[0079] To verify that Ce is incorporated into the S-1 molecular sieve framework to replace the silicon atom position, the present invention respectively sampled the transparent sols synthesized in step S1 in Examples 1 to 3 and the S-1 molecular sieve framework without Ce incorporated for XRD testing. The test results are shown in Figure 1 and Figure 2 .

[0080] From Figure 1 and Figure 2 it can be seen that as the Ce loading amount increases, the peaks at the (101) crystal plane and the (200) crystal plane gradually shift significantly towards a small angle. The 2θ change trend diagram of the corresponding (101) crystal plane more intuitively reflects the trend of the (101) crystal plane moving towards a low angle. This is because the radius of Ce ions is larger than that of Si ions. Therefore, when Ce ions are incorporated into the S-1 molecular sieve framework, the unit lattice parameter will increase, which intuitively reflects the trend of the (101) crystal plane moving towards a low angle; similarly, the increase in the unit lattice parameter also verifies that Ce is incorporated into the S-1 molecular sieve framework to replace the silicon atom position.

[0081] To verify the purity and crystallization performance of the catalysts prepared in Examples 1 to 3, the present invention respectively sampled the catalysts prepared in Examples 1 to 3 and the untreated S-1 molecular sieve framework for XRD testing. The test results are shown inFigure 3 and Figure 4 。

[0082] It is known from Figure 3 and Figure 4 that for each catalyst prepared in Examples 1 - 3 of the present invention, at the characteristic peak positions of S-1 zeolite: 2θ = 7.9° (101), 8.9° (200), 23.1° (501), 23.3° (051), 23.9° (303), characteristic peaks of MFI zeolite appear, and there is no obvious impurity phase, indicating that all catalyst samples are pure phases and have good crystallization. Moreover, the yields of the catalysts using cerium nitrate as the cerium source are all about 95%. No characteristic peak of CeO2 is found in all catalyst samples, which is consistent with the untreated S-1 zeolite framework, indicating that no CeO2 crystal phase is observed, avoiding the formation of free cerium oxide phase, and also indirectly indicating that Ce is incorporated into the S-1 zeolite framework. In the angular range of 2θ from 40° to 50°, no characteristic peak of NiO is observed, indicating that Ni exists in the state of highly dispersed Ni particles and no NiO particles are formed.

[0083] To verify the purity and crystallization performance of the catalysts prepared in Comparative Examples 1 - 3, XRD tests were respectively carried out on each catalyst prepared in Comparative Examples 1 - 3 and the untreated S-1 zeolite framework. The test results are shown in Figure 5 and Figure 6 。

[0084] It is known from Figure 5 and Figure 6 that for each catalyst prepared in Comparative Examples 1 - 3 of the present invention, at the characteristic peak positions of S-1 zeolite: 2θ = 7.9° (101), 8.9° (200), 23.1° (501), 23.3° (051), 23.9° (303), characteristic peaks of MFI zeolite appear, indicating that all catalyst samples have good crystallization. No characteristic peak of NiO is observed in the catalyst prepared in Comparative Example 1 in the range of 2θ = 40° - 50°, indicating that Ni exists as elemental particles. However, for the catalyst prepared by the impregnation method in Comparative Example 3, an obvious NiO characteristic peak appears at 2θ = 43°, indicating the existence of NiO nanoparticles. According to the Scherrer formula, the particle size is about 14.9 nm. In the catalytic CO2 methanation reaction, larger metal NiO particles usually mean lower surface activity, a relatively reduced number of active sites, and easier particle agglomeration. The catalyst prepared by the impregnation method in Comparative Example 2 has a relatively weak NiO characteristic peak and a relatively small grain size, about 7.3 nm, indicating that the addition of Ce significantly inhibits the oxidation tendency of Ni at high temperatures by enhancing the metal-support interaction (SMSI) between Ni and the support (Ce-O-Si framework), regulating the interfacial electron transfer path, and thus reducing the formation of NiO.

[0085] To verify the stability level of the catalyst prepared in Example 1 in the CO2 methanation reaction, the present invention conducts a CO2 methanation reaction stability test on the catalyst prepared in Example 1. The test results are shown in Figure 7 . The method for the CO2 methanation reaction stability test is as follows: The test temperature is 200 °C, and the CO2 methanation reaction evaluation is carried out in a fixed-bed reactor. The required catalyst dosage is 100 mg, and the reaction space velocity (GHSV) is 36000 mL·g -1 ·h -1 ; the molar ratio of the components in the mixed gas is N2:CO2:H2 = 1:1:4; the outlet gas is detected and analyzed by a gas chromatograph (model GC-8890A); the whole reaction process is carried out under atmospheric pressure. Before the reaction starts, the catalyst needs to be reduced with H2 at 700 °C for 2 h (for activating the catalyst); subsequently, the temperature of the fixed-bed reactor is reduced to room temperature and then raised to the set test temperature of 200 °C.

[0086] It can be seen from Figure 7 this that the catalyst prepared in Example 1 of the present invention has good stability in the CO2 methanation reaction at the test temperature of 200 °C.

[0087] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a cerium framework-substituted S-1 molecular sieve-supported nickel metal catalyst, characterized in that, Including: Step S1: Mix deionized water and tetraethyl orthosilicate under the first stirring; then add cerium nitrate and mix under the second stirring, wherein the molar ratio of cerium atoms in cerium nitrate to silicon atoms in tetraethyl orthosilicate is controlled to be 1:30 - 150; finally, add tetrapropylammonium hydroxide and form a transparent sol under the third stirring; Step S2: Dissolve nickel nitrate in deionized water, and then add ethylenediamine and form a blue transparent complex solution under the fourth stirring; mix the blue transparent complex solution and the transparent sol under the fifth stirring to obtain a synthetic gel; Step S3: Transfer the synthetic gel to a hydrothermal reaction kettle for hydrothermal crystallization treatment to obtain a crystallized product; Step S4: After cooling the crystallized product to room temperature, perform post-treatment to obtain a white powder precursor; Step S5: Calcinate the white powder precursor to obtain a cerium framework-substituted S-1 molecular sieve supported nickel metal catalyst.

2. The preparation method of the cerium framework-substituted S-1 molecular sieve-supported nickel metal catalyst according to claim 1, characterized in that, In the step S1 and the step S2, the molar ratio of the SiO2 content in tetraethyl orthosilicate, tetrapropylammonium hydroxide to the total amount of deionized water used is 1:0.4:35; the mass percentage of SiO2 in tetraethyl orthosilicate is 28%.

3. The preparation method of the cerium framework-substituted S-1 molecular sieve-supported nickel metal catalyst according to claim 1, characterized in that, In the step S1, the first stirring is carried out by magnetic stirring, the stirring temperature is 25 ± 5 °C, the stirring speed is 300 - 600 rpm, and the stirring time is 10 - 30 min; the second stirring is carried out by magnetic stirring, the stirring temperature is 25 ± 5 °C, the stirring speed is 300 - 600 rpm, and the stirring time is 1 - 2 h; the third stirring is carried out by magnetic stirring, the stirring temperature is 25 ± 5 °C, the stirring speed is 300 - 600 rpm, and the stirring time is 6 - 8 h.

4. The preparation method of the cerium framework-substituted S-1 molecular sieve supported nickel metal catalyst according to claim 2, characterized in that, In the step S2, the mass of nickel in nickel nitrate accounts for 4% - 5% of the mass of SiO2.

5. The preparation method of the cerium framework-substituted S-1 molecular sieve supported nickel metal catalyst according to claim 1, characterized in that, In the step S2, the fourth stirring is carried out by magnetic stirring, the stirring temperature is 25 ± 5 °C, the stirring speed is 300 - 600 rpm, and the stirring time is 10 - 30 min; the fifth stirring is carried out by magnetic stirring, the stirring temperature is 25 ± 5 °C, the stirring speed is 300 - 600 rpm, and the stirring time is 30 - 60 min.

6. The preparation method of the cerium framework-substituted S-1 molecular sieve supported nickel metal catalyst according to claim 1, characterized in that, In the step S3, the treatment temperature for the hydrothermal crystallization treatment is 175 - 190 °C, and the treatment time is 4 ± 1 day.

7. The preparation method of the cerium framework-substituted S-1 molecular sieve supported nickel metal catalyst according to claim 1, characterized in that, In the step S4, the post-treatment includes washing treatment, centrifugation treatment and drying treatment carried out in sequence; the washing treatment includes washing the crystallized product with deionized water until it is neutral; the centrifugation treatment is used to centrifuge and separate the precipitate from the crystallized product after the washing treatment; the centrifugation rate for the centrifugation treatment is 8000 - 10000 rpm, and the centrifugation time is 8 - 10 min; the drying temperature for the drying treatment is 70 - 80 °C, and the drying time is 12 - 24 h.

8. The preparation method of the cerium framework-substituted S-1 molecular sieve-supported nickel metal catalyst according to any one of claims 1 to 7, characterized in that, In the step S5, the calcination treatment includes a heating-up calcination stage, an isothermal calcination stage, and a natural cooling stage carried out in sequence; the starting temperature adopted in the heating-up calcination stage is 25 ± 5 °C, the ending temperature is 550 ± 10 °C, and the heating rate is 2 - 3 °C / min; the calcination temperature adopted in the isothermal calcination stage is 550 ± 10 °C, and the calcination time is 500 ± 20 min; the starting temperature of the natural cooling stage is 550 ± 10 °C, and the ending temperature is 25 ± 5 °C.

9. A cerium framework-substituted S-1 molecular sieve-supported nickel metal catalyst, characterized in that, It is prepared by using the preparation method of the cerium framework-substituted S-1 molecular sieve supported nickel metal catalyst as described in claim 8.

10. Application of the cerium framework-substituted S-1 molecular sieve supported nickel metal catalyst as described in claim 9 in the catalytic CO2 methanation reaction.

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