A nickel-cerium dioxide hollow catalyst, a preparation method and application thereof

Abstract

The present application relates to the field of catalyst, especially to a kind of nickel-cerium dioxide hollow catalyst and its preparation and application.The metal active component of the catalyst is Ni, carrier is CeO2, with double-layer hollow structure, namely the outermost layer is CeO2, inner layer is Ni, the most inside is hollow structure, based on the total weight of catalyst, the content of metal Ni is 1-30wt.%, and can be adjusted by changing calcination temperature its catalytic performance.The catalyst uses cheap SiO2 as template, uses non-noble metal component, by constructing special morphology to adjust metal carrier interaction, greatly improves its carbon dioxide conversion rate on carbon dioxide methanation reaction in low temperature interval (<300 DEG C) And can maintain very high methane selectivity.Overcome the low carbon dioxide conversion rate of traditional non-noble metal catalyst in low temperature interval (<300 DEG C).The nickel-cerium dioxide hollow catalyst in the present application is low in cost, has high catalyst activity at low temperature and stable performance, and is easy to realize industrial application.

Description

Technical Field

[0001] This invention relates to the field of catalysts, and more particularly to a nickel-cerium dioxide hollow catalyst for the methanation of carbon dioxide, its preparation and application. Background Technology

[0002] The excessive use of fossil fuels has led to a rapid increase in atmospheric CO2 levels, causing numerous serious environmental problems. Simultaneously, rapid advancements in CO2 capture and enrichment technologies, objective industrial demands, and legal and ethical constraints are all driving the rapid development of research into carbon dioxide methanation, providing a new pathway to carbon neutrality. CH4, a major component of natural gas, is an important chemical raw material and fuel. Furthermore, the established systems of natural gas pipelines and intermittent power generation facilities (such as hydropower, wind power, and solar power) in industry have made carbon dioxide methanation an economical and efficient way to utilize CO2. The carbon dioxide methanation reaction mainly involves two reactions: the main reaction, carbon dioxide methanation, is exothermic, while the other reaction, a side reaction (reverse water-gas reaction), is endothermic. In industrial production, it is costly to separate byproducts and unreacted CO2. Therefore, improving the selectivity and activity of the catalyst can reduce the costs of separation and recycling. From a thermodynamic equilibrium perspective, low temperatures are favorable for the carbon dioxide methanation reaction and help suppress CO formation. Therefore, it is valuable to prepare catalysts with high activity and selectivity under low temperature conditions (<300℃).

[0003] However, the C=O bond in CO2 is difficult to activate at low temperatures. Although noble metal catalysts (such as Rh, Pd, Ir, and Ru) generally exhibit excellent catalytic performance, their high cost hinders industrial application. Therefore, supporting non-noble metals (such as Ni, Co, and Fe) on oxides (such as Al2O3, SiO2, ZrO2, TiO2, and CeO2) to achieve high conversion and selectivity is of great industrial value. Catalysts composed of Ni as the active metal component supported on CeO2 have attracted significant attention due to their high conversion, high selectivity, and relatively low price. However, Ni / CeO2 catalytic carbon dioxide methanation typically requires high temperatures (>350℃), and prolonged exposure to high temperatures can lead to a decrease in activity and stability. Therefore, to improve the catalytic performance of this type of catalyst at low temperatures, many researchers have explored various approaches, such as optimizing the Ni loading, adjusting the particle size of Ni or CeO2 particles, increasing the oxygen vacancy concentration, regulating the interaction between the metal support, constructing special microstructures, and doping with other components.

[0004] Among these research directions, catalysts with special microstructures have unique advantages in terms of specific surface area, number of active sites, Ni dispersion, oxygen vacancy concentration, metal-support interaction, and anti-sintering properties. Ye et al. synthesized Ni / CeO2-SGM via the sol-gel method. It exhibits strong metal-support interaction, allowing Ni to embed into CeO2, thereby increasing the Ni-CeO2 contact area and synergistic effect, achieving a carbon dioxide conversion rate of 80.5% at 250℃. However, its corresponding mass hourly space velocity (WHSV) is too low (10 L·g⁻¹). -1 ·h -1 This is not conducive to industrial application (Appl. Catal. B 2020, 268, 118474). Hu et al. prepared NiNPs@CeO2NF by electrospinning, which enhanced the metal-support interaction, allowing Ni nanoparticles to be encapsulated by CeO2 nanofibers, creating more oxygen vacancies, and achieving a carbon dioxide conversion rate of 50.6% at 250℃ (mass hourly space velocity = 36 L·g). -1 ·h -1 Furthermore, it exhibited stable performance during a 60-hour stability test (400℃), but its preparation method was too demanding, hindering industrialization (Appl. Catal. B 2022, 317, 121715). Varvoutis et al. prepared Ni / CeO2-NR via a hydrothermal method; its unique nanorod structure enabled it to achieve a carbon dioxide conversion rate of 92.1% at 300℃ (mass hourly space velocity = 30 L·g⁻¹). -1 ·h -1 However, its reaction temperature is still too high (Catal.Commun.2020,142,106036).

[0005] Chinese patent CN 117225417A discloses a nickel-based catalyst for the carbon dioxide methanation reaction, with a tetragonal t-ZrO2 support, Ni as the active metal, and one or more of Zn(NO3)2·6H2O, Al(NO3)3·9H2O, Mg(NO3)2·6H2O, and Ce(NO3)3·6H2O as the promoter. This invention has a simple preparation method, low cost, and convenient operation, but its catalytic activity is not prominent in the low-temperature range, which is not conducive to reducing industrial production costs. Chinese patent CN 117123205A discloses a non-precious metal single-atom catalyst or nano-metal catalyst supported on nano-carbon materials for the carbon dioxide methanation reaction. This catalyst can convert carbon dioxide to methane with high selectivity. The oxygen, nitrogen, and other heteroatoms on the carbon support surface can anchor metal single atoms or nanoparticles, giving it good thermal stability. However, its preparation conditions are relatively harsh, and the tested mass hourly space velocity (MSV) is too low (5 L·g⁻¹). -1 ·h -1Therefore, there is an urgent need to develop nickel-cerium dioxide catalysts for carbon dioxide methanation reactions with high performance in the low-temperature range.

[0006] To address the above problems, this invention is proposed. Summary of the Invention

[0007] The present invention aims to provide a nickel-cerium dioxide hollow catalyst for carbon dioxide methanation reaction, which has the characteristics of high carbon dioxide conversion, high methane selectivity and high stability in the low temperature range (<300℃).

[0008] Another objective of this invention is to provide a preparation method for a nickel-cerium dioxide hollow catalyst for the carbon dioxide methanation reaction, which has the advantages of high reliability and low cost.

[0009] Based on the above objectives, this invention provides a nickel-cerium dioxide hollow catalyst for the carbon dioxide methanation reaction, its preparation, and its application. The catalyst's active metallic component is Ni, and its support is CeO2. It has a double-layered hollow structure, with the outermost layer being CeO2 and the innermost layer being Ni. Based on the total weight of the catalyst, the Ni content is 1-30 wt.%, and its catalytic performance can be modulated by changing the calcination temperature. The catalyst preparation process involves first preparing a SiO2 template, then loading Ni and CeO2 onto it separately, removing the SiO2 core by etching, and finally obtaining the Ni@CeO2 catalyst through high-temperature reduction. The Ni@CeO2 catalyst possesses a unique hollow structure, resulting in a large specific surface area and high metal dispersion. This modulates the interaction between the metal and support, significantly improving the carbon dioxide methanation performance in the low-temperature range (<300℃), overcoming the low carbon dioxide conversion rate of traditional non-precious metal catalysts in the low-temperature range. The nickel-cerium dioxide hollow catalyst of this invention is low in cost, has high carbon dioxide conversion rate and high methane selectivity in the low temperature range (<300℃), and has stable performance, making it easy to implement in industrial applications.

[0010] To achieve the objectives of this invention, the specific technical solution is as follows:

[0011] The first aspect of this invention provides a nickel-cerium dioxide hollow catalyst, wherein the active metallic component of the catalyst is Ni, the support is CeO2, and it has a double-layer hollow structure, namely, the outermost layer is CeO2 and the inner layer is Ni. Based on the total weight of the catalyst, the content of metallic Ni is 1-30 wt.%.

[0012] A second aspect of the present invention provides a method for preparing the nickel-cerium dioxide hollow catalyst described in the first aspect of the present invention, comprising the following steps:

[0013] 1) Preparation of SiO2 template: TEOS was added to anhydrous ethanol, and then a mixture of ammonia and deionized water was added to it. The mixture was stirred and reacted under water bath conditions to obtain a liquid containing SiO2 template.

[0014] 2) Ni loading: Prepare a nickel ammonia solution, and then add the nickel ammonia solution to the liquid containing the SiO2 template obtained in step 1). Stir the reaction under water bath conditions until the pH of the solution reaches 7.

[0015] 3) Separation: The liquid mixture in step 2) is separated by suction filtration and washed with water to obtain a filter cake containing the catalyst;

[0016] 4) Drying: The filter cake obtained in step 3) is dried to obtain the catalyst precursor;

[0017] 5) Calcination: The catalyst precursor obtained in step 4) is calcined in a muffle furnace to obtain SiO2@NiO;

[0018] 6) Loading CeO2: Dissolve the SiO2@NiO and cerium salt obtained in step 5) in anhydrous ethanol, then prepare an aqueous solution of hexamethylenetetramine and add it to the ethanol mixture mentioned above, and stir the reaction under water conditions.

[0019] 7) Separation: The liquid mixture in step 6) is separated by suction filtration and washed with water to obtain a filter cake containing the catalyst;

[0020] 8) Drying: The filter cake obtained in step 7) is dried to obtain the catalyst precursor;

[0021] 9) Calcination: The catalyst precursor obtained in step 8) is calcined in a muffle furnace to obtain SiO2@NiO@CeO2;

[0022] 10) Etching: The SiO2@NiO@CeO2 obtained in step 9) is introduced into an aqueous sodium hydroxide solution and stirred to etch away the SiO2 template;

[0023] 11) Separation: The liquid mixture in step 10) is separated by vacuum filtration and washed with water to obtain a filter cake containing the catalyst;

[0024] 12) Drying: The filter cake obtained in step 11) is dried to obtain the catalyst precursor;

[0025] 13) Activation: The catalyst precursor obtained in step 12) is directly reduced in a reducing atmosphere to obtain the nickel-cerium dioxide hollow catalyst Ni@CeO2.

[0026] Preferably, in step 1), the temperature of the stirring reaction under water bath conditions is 30-60℃, and the reaction time is 6.0-24.0h.

[0027] Preferably, in step 2), the nickel ammonia solution is obtained by adding an appropriate amount of 25wt.% ammonia water to Ni(NO3)2·6H2O, and the molar ratio of NH3·H2O to Ni is 6-20; the stirring reaction temperature is 50-90℃, and the reaction time is 2.0-6.0h.

[0028] Preferably, the drying described in steps 4), 8), and 12) is carried out in air at a temperature of 80-110°C for a time of 12.0-24.0 hours.

[0029] Preferably, the calcination conditions in steps 5) and 9) are: heating the sample from room temperature to 350-800℃ at a heating rate of 1-10℃ / min, and calcining for 2.0-8.0 hours.

[0030] Preferably, the cerium salt in step 6) is Ce(NO3)3·6H2O; the molar ratio of hexamethylenetetramine to Ce(NO3)3·6H2O is 1:10-1:40.

[0031] Preferably, in step 10), the concentration of the sodium hydroxide aqueous solution is 1-5 mol / L, and the etching time is 24.0-72.0 h.

[0032] Preferably, in step 13), the reducing gas is pure hydrogen with a purity greater than 99.9%, or the reducing gas is a hydrogen-containing mixture with a hydrogen content of 10%-100%, and the other gases besides hydrogen are nitrogen or helium; the flow rate of the reducing gas is 10-50 mL / min, the reduction temperature is 300-400℃, the temperature is increased from room temperature to the target reduction temperature using a programmed temperature rise method with a heating rate of 1-10℃ / min, the pressure is atmospheric pressure, and the reduction time is 1.0-4.0 h.

[0033] A third aspect of the present invention provides an application of the nickel-cerium dioxide hollow catalyst described in the first aspect of the present invention, wherein the nickel-cerium dioxide hollow catalyst is applied to the carbon dioxide methanation reaction.

[0034] Preferably, the nickel-cerium dioxide hollow catalyst is used for a gas-solid fixed-bed carbon dioxide methanation reaction, under the following conditions: the reactants are a mixture of CO2:H2:N2 in a molar ratio of 2:8:5; the reaction temperature is 200-350℃; the pressure is atmospheric or near-atmospheric; and the mass hourly space velocity is 36-360 L·g. -1 ·h -1 .

[0035] The fourth aspect of the present invention provides a method for improving the carbon dioxide conversion rate and methane selectivity in a carbon dioxide methanation reaction, using the nickel-cerium dioxide hollow catalyst described in the first aspect of the present invention as the catalyst in the reaction, and preparing the nickel-cerium dioxide hollow catalyst by the preparation method described in the second aspect of the present invention.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] 1. The nickel-cerium dioxide hollow catalyst provided by this invention exhibits high catalytic activity for the carbon dioxide methanation reaction in the low-temperature range (<300℃), especially significantly improving the carbon dioxide conversion rate in the low-temperature range. The unique hollow structure of this catalyst gives it a large specific surface area and high dispersion of active components, and modulates the metal-support interaction, enabling it to operate at 225℃ and atmospheric pressure (mass hourly space velocity 36 L·g⁻¹). -1 ·h -1 The carbon dioxide conversion rate is higher than 60%.

[0038] 2. The nickel-cerium dioxide hollow catalyst of this invention has only nickel and cerium as its metal components and no precious metal components, which has high economic value and market prospects and is suitable for industrial application.

[0039] 3. The nickel-cerium dioxide hollow catalyst provided by this invention has extremely high methane selectivity (>99%) for the carbon dioxide methanation reaction, which greatly inhibits the generation of the byproduct carbon monoxide, reduces the cost of separating byproducts, and helps to reduce production costs.

[0040] 4. The nickel-cerium dioxide hollow catalyst provided by this invention exhibits high stability for the carbon dioxide methanation reaction. Figure 7 ), which within 72 hours (225℃, normal pressure, mass hourly space velocity 36 L·g), -1 ·h -1 The carbon dioxide conversion rate remained at around 60%, and the methane selectivity remained above 99%.

[0041] 5. More importantly, this invention determines the preparation conditions of the nickel-cerium dioxide hollow catalyst that are most conducive to improving carbon dioxide conversion. This mainly involves determining the optimal loading of the active component, nickel, and the optimal calcination temperature.

[0042] As the Ni loading increased from 0.5 wt.% to 30 wt.%, the CO2 conversion initially increased and then decreased, reaching its peak at a Ni loading of 15 wt.%. Figure 3 The CH4 selectivity remained almost unchanged, consistently >99%. This indicates that the number of Ni active sites initially increases and then decreases with increasing Ni loading. The preferred Ni loading should be 15 wt.%.

[0043] As the calcination temperature increases from 350℃ to 800℃, the CO2 conversion rate initially increases and then decreases, reaching its peak at 650℃. Figure 4 The CH4 selectivity remained almost unchanged, consistently >99%. This indicates that calcination temperature can modulate the interaction between the metal support, thereby regulating the number of active sites and adsorption intensity of H2 and CO2. The preferred calcination temperature is 650℃. Attached Figure Description

[0044] Figure 1 XRD patterns of Ni@CeO2-650 catalysts with different Ni contents (calcination temperature of all catalysts was 650℃, reaction conditions: CO2:H2:N2 molar ratio of 2:8:5, mass hourly space velocity of 36 L·g⁻¹). -1 ·h -1 The reaction temperature is 200-350℃, and the pressure is atmospheric pressure.

[0045] Figure 2 XRD patterns of 15% Ni@CeO2 catalysts at different calcination temperatures (Ni loading was 15 wt.% for all catalysts; reaction conditions: CO2:H2:N2 molar ratio 2:8:5; mass hourly space velocity 36 L·g⁻¹). -1 ·h -1 The reaction temperature is 200-350℃, and the pressure is atmospheric pressure.

[0046] Figure 3 XRD patterns of 15% Ni@CeO2-650 catalyst before and after stability testing (reaction conditions: CO2:H2:N2 molar ratio of 2:8:5, mass hourly space velocity of 36 L·g). -1 ·h -1 The reaction temperature was 225℃ and the pressure was atmospheric pressure.

[0047] Figure 4 Comparison of catalytic performance of Ni@CeO2-650 catalysts with different Ni contents (calcination temperature of all catalysts was 650℃, reaction conditions: CO2:H2:N2 molar ratio of 2:8:5, mass hourly space velocity of 36 L·g⁻¹). -1 ·h -1 The reaction temperature is 200-350℃, and the pressure is atmospheric pressure.

[0048] Figure 5 Comparison of catalytic performance of 15% Ni@CeO2 catalysts at different calcination temperatures (Ni loading of all catalysts was 15 wt.%, reaction conditions: CO2:H2:N2 molar ratio of 2:8:5, mass hourly space velocity of 36 L·g). -1 ·h -1The reaction temperature is 200-350℃, and the pressure is atmospheric pressure.

[0049] Figure 6 Comparison of catalytic performance of catalysts containing 15% Ni and CeO2 prepared by different methods (Ni loading of all catalysts is 15 wt.%, reaction conditions: CO2:H2:N2 molar ratio of 2:8:5, mass hourly space velocity of 36 L·g⁻¹). -1 ·h -1 The reaction temperature is 200-350℃, and the pressure is atmospheric pressure.

[0050] Figure 7 The stability test results of the 15% Ni@CeO2-650 catalyst are shown in the figure (reaction conditions: CO2:H2:N2 molar ratio of 2:8:5, mass hourly space velocity of 36 L·g). -1 ·h -1 The reaction temperature was 225℃ and the pressure was atmospheric pressure.

[0051] Figure 8 TEM morphology and EDS-MAPPING elemental distribution diagram of the 15% Ni@CeO2-650 catalyst. Detailed Implementation

[0052] The present invention will be described below with reference to specific embodiments, but the implementation of the present invention is not limited thereto. Experimental methods not specifically described in the embodiments are generally performed under conventional conditions and conditions described in the manual, or according to the manufacturer's recommendations. The general equipment, materials, reagents, etc. used are commercially available unless otherwise specified. The raw materials required in the following embodiments and comparative examples are all commercially available.

[0053] Examples 1-6 illustrate the preparation of Ni@CeO2 catalysts with different Ni contents:

[0054] Example 1

[0055] 8 mL of TEOS was added to 280 mL of anhydrous ethanol, followed by a mixture of 8 mL of ammonia (25 wt.%) and 50 mL of deionized water. The mixture was stirred in a 30°C water bath for 24 h. 0.1982 g of Ni(NO3)2·6H2O was dissolved in 30 mL of deionized water, and 1 mL of ammonia was added to obtain a nickel-ammonia solution. This nickel-ammonia solution was then added to a liquid containing SiO2, and the mixture was stirred in a 70°C water bath until the pH reached 7. The solution was separated by filtration and washed with water. It was dried at 80°C for 12 h and then calcined at 650°C for 4 h to obtain SiO2@NiO. All the prepared SiO2@NiO and 5.0015 g of Ce(NO3)2·6H2O were dissolved in 320 mL of anhydrous ethanol. 16.1476 g of hexamethylenetetramine was dissolved in 50 mL of deionized water. The two liquids were mixed and stirred in a 70°C water bath for 8 h. Separation was achieved by vacuum filtration and washing with water. The mixture was dried at 80℃ for 12 h and then calcined at 650℃ for 4 h to obtain SiO2@NiO@CeO2. All the prepared SiO2@NiO@CeO2 was added to 60 mL of a 5 mol / L NaOH aqueous solution and etched by stirring at room temperature for 72 h. Separation was achieved by vacuum filtration, washing with water until the pH of the filtrate reached 7, and drying at 80℃ for 12 h to obtain NiO@CeO2. The obtained sample was sieved to 20-40 mesh, and the NiO@CeO2 was reduced and activated at 380℃ in a hydrogen atmosphere at 10 mL / min for 2 h to obtain 1% Ni@CeO2-650.

[0056] Example 2

[0057] Except for the amounts of Ni(NO3)3·6H2O (0.4955 g), ammonia (25 wt.%) (2 mL), Ce(NO3)2·6H2O (4.7994 g), and hexamethylenetetramine (15.4951 g), the preparation method was exactly the same as in Example 1, yielding 5% Ni@CeO2-650.

[0058] Example 3

[0059] Except for the amounts of Ni(NO3)3·6H2O (0.9909 g), ammonia (25 wt.%) (3 mL), Ce(NO3)2·6H2O (4.5468 g), and hexamethylenetetramine (14.6796 g), the preparation method was exactly the same as in Example 1, yielding 10% Ni@CeO2-650.

[0060] Example 4

[0061] Except for the amounts of Ni(NO3)3·6H2O (1.4864 g), ammonia (25 wt.%) (5 mL), Ce(NO3)2·6H2O (4.2942 g), and hexamethylenetetramine (13.8640 g), the preparation method was exactly the same as in Example 1, yielding 15% Ni@CeO2-650. The microstructure and elemental distribution of the 15% Ni@CeO2-650 catalyst are shown in the figure. Figure 8 As shown, it has a distinct hollow structure (with an average external diameter of 189.4 nm) and a double-layer structure, with CeO2 on the outside, Ni on the inside, and a cavity at the very center.

[0062] Example 5

[0063] Except for the amounts of Ni(NO3)3·6H2O (1.9819 g), ammonia (25 wt.%) (6 mL), Ce(NO3)2·6H2O (4.0416 g), and hexamethylenetetramine (13.0485 g), the preparation method was exactly the same as in Example 1, yielding 20% ​​Ni@CeO2-650.

[0064] Example 6

[0065] Except for the amounts of Ni(NO3)3·6H2O (2.9728 g), ammonia (25 wt.%) (9 mL), Ce(NO3)2·6H2O (3.5364 g), and hexamethylenetetramine (11.4175 g), the preparation method was exactly the same as in Example 1, yielding 30% Ni@CeO2-650.

[0066] Examples 7-11 illustrate the preparation of Ni@CeO2 catalysts at different calcination temperatures:

[0067] Example 7

[0068] 8 mL of TEOS was added to 280 mL of anhydrous ethanol, followed by a mixture of 8 mL of ammonia (25 wt.%) and 50 mL of deionized water. The mixture was stirred in a 30°C water bath for 24 h. 1.4864 g of Ni(NO3)2·6H2O was dissolved in 30 mL of deionized water, and 5 mL of ammonia was added to obtain a nickel-ammonia solution. This nickel-ammonia solution was then added to a liquid containing SiO2, and the mixture was stirred in a 70°C water bath until the pH reached 7. The solution was separated by filtration and washed with water. It was dried at 80°C for 12 h and then calcined at 350°C for 4 h to obtain SiO2@NiO. All the prepared SiO2@NiO and 4.2942 g of Ce(NO3)2·6H2O were dissolved in 320 mL of anhydrous ethanol. 13.8640 g of hexamethylenetetramine was dissolved in 50 mL of deionized water. The two liquids were mixed and stirred in a 70°C water bath for 8 h. Separation was achieved by vacuum filtration and washing with water. The mixture was dried at 80℃ for 12 h and then calcined at 350℃ for 4 h to obtain SiO2@NiO@CeO2. All the prepared SiO2@NiO@CeO2 was added to 60 mL of a 5 mol / L NaOH aqueous solution and etched by stirring at room temperature for 72 h. Separation was achieved by vacuum filtration, washing with water until the pH of the filtrate reached 7, and drying at 80℃ for 12 h to obtain NiO@CeO2. The obtained sample was sieved to 20-40 mesh, and the NiO@CeO2 was reduced and activated at 380℃ in a hydrogen atmosphere at 10 mL / min for 2 h to obtain 15% Ni@CeO2-350.

[0069] Example 8

[0070] Except for the calcination temperature of 450℃, the preparation method is exactly the same as in Example 7, and 15% Ni@CeO2-450 calcined at 450℃ is obtained.

[0071] Example 9

[0072] Except for the calcination temperature of 550℃, the other preparation methods are exactly the same as in Example 7, and 15% Ni@CeO2-550 calcined at 550℃ is obtained.

[0073] Example 10

[0074] Except for the calcination temperature of 650℃, the preparation method is exactly the same as in Example 7, and 15% Ni@CeO2-650 calcined at 650℃ is obtained.

[0075] Example 11

[0076] Except for the calcination temperature of 800℃, the preparation method is exactly the same as in Example 7, and 15% Ni@CeO2-800 calcined at 800℃ is obtained.

[0077] Comparative Example 1

[0078] The difference from Example 1 is that carbon spheres were used as a template agent, resulting in a catalyst with a hollow structure, named @15%Ni+CeO2-650. The specific preparation method is as follows:

[0079] 15g of glucose was dissolved in 150mL of deionized water and hydrothermally treated at 180℃ for 24h. Separation was achieved by filtration, followed by washing with water and drying at 80℃ for 12h to obtain a carbon sphere template. 0.25g of the carbon sphere template was weighed, and 4.2942g of Ce(NO3)3·6H2O, 1.4864g of Ni(NO3)2·6H2O, and the carbon sphere template were dissolved together in 50mL of deionized water and hydrothermally treated at 160℃ for 6h. Separation was achieved by filtration, followed by washing with water. The mixture was dried at 80℃ for 12h and then calcined at 650℃ for 4h to obtain @15%NiO+CeO2-650. The obtained sample was sieved to 20-40 mesh and reduced and activated in a hydrogen atmosphere at 380℃ and 10mL / min for 2h to obtain @15%Ni+CeO2-650.

[0080] Comparative Example 2

[0081] The difference from Example 1 is that the etching step is omitted, resulting in SiO2@15%Ni@CeO2-650, which is a solid structure (with SiO2 as the core).

[0082] Comparative Example 3

[0083] The impregnation method for preparing 15% Ni / CeO2-650 is as follows:

[0084] CeO2 support was obtained by calcining 4.2942 g of Ce(NO3)3·6H2O at 650 °C for 4 h. All the CeO2 support and 1.4864 g of Ni(NO3)2·6H2O were added to 50 mL of deionized water and stirred for 8 h. A solid precursor was obtained by rotary evaporation. The precursor was dried at 80 °C for 12 h and then calcined at 650 °C for 4 h to obtain 15% NiO / CeO2-650. The obtained sample was sieved to 20-40 mesh and then reduced and activated in a hydrogen atmosphere at 380 °C and 10 mL / min for 2 h to obtain 15% Ni / CeO2-650.

[0085] The XRD patterns of the catalysts obtained in Comparative Examples 3-6 are shown in the attached figures. Figure 1 As shown, the characteristic peaks of CeO2 are very obvious in the XRD spectrum, but the characteristic peaks of Ni are almost invisible. Only when the Ni loading reaches 30 wt.% is there an extremely weak Ni characteristic peak signal, indicating that the Ni particles are very small and highly dispersed, so they are difficult to detect because they are below or close to the detection limit.

[0086] The XRD patterns of the catalysts obtained in Comparative Examples 7-11 are shown in the attached figures. Figure 2 As shown, Ni@CeO2 at all calcination temperatures exhibits only characteristic peaks of CeO2 without obvious characteristic peaks of Ni, indicating that Ni particles are very small and highly dispersed. The crystal size of CeO2 in Ni@CeO2 can be calculated from the XRD data. It was found that this value increases with increasing calcination temperature, but remains relatively small (<10 nm), indicating that the hollow structure effectively prevents sintering caused by increased calcination temperature, thus maintaining smaller CeO2 and Ni nanoparticle sizes.

[0087] The XRD patterns of the catalyst obtained in Example 4 (same as Example 7) before and after the stability test are shown in the attached figure. Figure 3 As shown, the XRD peak shapes of both showed no significant change. The CeO2 crystal particle sizes calculated from the XRD data were 6.4 nm and 6.5 nm before and after the stability test, respectively, and neither showed a significant Ni peak. This indicates that the catalyst did not undergo significant agglomeration before and after the stability test, confirming that the hollow structure prevented the sintering and agglomeration of Ni and CeO2 nanoparticles under long-term reaction conditions, allowing its activity to remain stable at a high level for a long time.

[0088] The catalysts obtained in Examples 3-11 were used in the carbon dioxide methanation reaction, and their catalytic activities were compared. The catalytic reaction method was as follows:

[0089] Step 1: Catalyst loading. Sieve the catalyst, take 50 mg of 20-40 mesh catalyst, and load it into a fixed-bed quartz tube reactor.

[0090] Step 2: Reduction and activation of the catalyst. The reducing gas is pure hydrogen with a purity greater than 99.9%, at a flow rate of 10 mL / min. The temperature is increased from 25℃ to 380℃ at a rate of 10℃ / min, and the reduction time is 120 min.

[0091] Step 3: Catalyst performance testing. The reactants were a mixture of CO2:H2:N2 in a molar ratio of 2:8:5, with a mass hourly space velocity (WHSV) of 36 L·g⁻¹. -1 ·h -1 The reaction temperature was 200-350℃, and the pressure was atmospheric or near-atmospheric. The reaction conditions for catalyst stability testing were: temperature 225℃, pressure atmospheric or near-atmospheric, and mass hourly space velocity (WHSV) 36 L·g⁻¹. -1 ·h -1 The duration is 72 hours.

[0092] The gas composition at the reaction outlet was detected and analyzed in real time by a gas chromatograph (Shimadzu 2014C). The chromatograph is equipped with three column channels: a Porapak-N packed column (1.0m × 3.2mm), a molecular sieve 13X packed column (3.0m × 3.2mm), and a Wondercap WAX capillary column (25m × 0.32mm). Two detectors were configured: a gas chromatographic flame ionization detector (FID) and a thermal conductivity detector (TCD) to achieve the separation and analysis of CO2, CO, CH4, H2, and N2. Data processing was performed using GCsolution Lite software, and the reactant and product contents were obtained based on the internal standard curve.

[0093] The test results are attached. Figure 4 Appendix Figure 5 Appendix Figure 6 and attached Figure 7 .

[0094] For Ni@CeO2 catalysts with different Ni loadings, catalysts with Ni loadings of 10 wt.%, 15 wt.%, 20 wt.%, and 30 wt.% were selected for performance comparison, and the results are as follows: Figure 4 As shown, the catalyst activities (based on carbon dioxide conversion rate) are as follows: 20% Ni@CeO2 = 15% Ni@CeO2 > 30% Ni@CeO2 > 10% Ni@CeO2. That is, as the Ni loading increases, the catalytic performance first increases and then decreases. The performance of 20% Ni@CeO2 and 15% Ni@CeO2 is very similar. To maintain a smaller particle size and better dispersion of the active Ni component, a Ni loading of 15 wt.% is selected as the preferred option.

[0095] For Ni@CeO2 catalysts calcined at different temperatures, catalysts calcined at 350℃, 450℃, 550℃, 650℃, and 800℃ were selected for performance comparison. The results are as follows: Figure 5 As shown, the catalyst activities (based on carbon dioxide conversion rate) are as follows: 15% Ni@CeO2-650 > 15% Ni@CeO2-800 > 15% Ni@CeO2-550 > 15% Ni@CeO2-450 > 15% Ni@CeO2-350. That is, the catalytic performance first increases and then decreases with increasing calcination temperature, reaching its highest point at 650℃. This is because calcination temperature can regulate the interaction between the metal support and also lead to sintering. Furthermore, the influence of the metal support interaction strength on catalytic performance exhibits a volcanic-shaped trend. Therefore, under the influence of multiple factors, 650℃ becomes the preferred calcination temperature.

[0096] To compare the catalytic performance advantages of the catalyst in the carbon dioxide methanation reaction of this invention, catalysts containing 15% Ni and CeO2 prepared by different methods were prepared and compared. The results are as follows: Figure 6 As shown. The characteristics of @15%Ni+CeO2-650 are: it uses carbon spheres as a template agent and also has a hollow structure, but the template agent is different from that of 15%Ni@CeO2-650. The characteristics of SiO2@15%Ni@CeO2-650 are: a solid structure (SiO2 core), prepared using the same method as 15%Ni@CeO2-650, except for the lack of an etching step. The characteristics of 15%Ni / CeO2-650 are: no special morphology, prepared by impregnation method, i.e., the most common method. Comparing the performance of the four catalysts, it can be seen that the catalytic performance of 15%Ni@CeO2-650 is consistently higher than the other three catalysts, especially in the 200-250℃ range, where its catalytic performance advantage is very obvious, further demonstrating the excellent performance of 15%Ni@CeO2-650 in this reaction system.

[0097] The stability test results of the 15% Ni@CeO2-650 catalyst are as follows: Figure 7 As shown, it performed well in the 72-hour stability test, with the carbon dioxide conversion rate consistently remaining around 60% and the methane selectivity consistently >99%. This indicates that the hollow structure not only enhances catalytic performance but also endows it with strong stability, allowing its performance to remain at a high level over a long period.

[0098] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the field; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0099] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A nickel-cerium dioxide hollow catalyst, characterized in that, The active metallic component is Ni, and the support is CeO2. It has a double-layer hollow structure, that is, the outermost layer is CeO2, the innermost layer is Ni, and the innermost layer is hollow. Based on the total weight of the catalyst, the metallic Ni content is 1-30 wt.%.

2. A method for preparing the nickel-cerium dioxide hollow catalyst according to claim 1, characterized in that, Includes the following steps: 1) Preparation of SiO2 template: TEOS was added to anhydrous ethanol, and then a mixture of ammonia and deionized water was added to it. The mixture was stirred and reacted under water bath conditions to obtain a liquid containing SiO2 template. 2) Ni loading: Prepare a nickel ammonia solution, and then add the nickel ammonia solution to the liquid containing the SiO2 template obtained in step 1). Stir the reaction under water bath conditions until the pH of the solution reaches 7. 3) Separation: The liquid mixture in step 2) is separated by suction filtration and washed with water to obtain a filter cake containing the catalyst; 4) Drying: The filter cake obtained in step 3) is dried to obtain the catalyst precursor; 5) Calcination: The catalyst precursor obtained in step 4) is calcined in a muffle furnace to obtain SiO2@NiO; 6) Loading CeO2: Dissolve the SiO2@NiO and cerium salt obtained in step 5) in anhydrous ethanol, then prepare an aqueous solution of hexamethylenetetramine and add it to the ethanol mixture, and stir the reaction under water bath conditions. 7) Separation: The liquid mixture in step 6) is separated by suction filtration and washed with water to obtain a filter cake containing the catalyst; 8) Drying: The filter cake obtained in step 7) is dried to obtain the catalyst precursor; 9) Calcination: The catalyst precursor obtained in step 8) is calcined in a muffle furnace to obtain SiO2@NiO@CeO2; 10) Etching: The SiO2@NiO@CeO2 obtained in step 9) is introduced into an aqueous sodium hydroxide solution and stirred to etch away the SiO2 template; 11) Separation: The liquid mixture in step 10) is separated by vacuum filtration and washed with water to obtain a filter cake containing the catalyst; 12) Drying: The filter cake obtained in step 11) is dried to obtain the catalyst precursor; 13) Activation: The catalyst precursor obtained in step 12) is directly reduced in a reducing atmosphere to obtain the nickel-cerium dioxide hollow catalyst Ni@CeO2.

3. The method for preparing the catalyst according to claim 2, characterized in that: In step 1), the temperature of the stirring reaction under water bath conditions is 30-60 ℃, and the reaction time is 6.0-24.0 h.

4. The method for preparing the catalyst according to claim 2, characterized in that: In step 2), the nickel ammonia solution is obtained by adding an appropriate amount of 25 wt.% ammonia water to Ni(NO3)2·6H2O, and the molar ratio of NH3·H2O to Ni is 6-20; the stirring reaction temperature is 50-90 ℃, and the reaction time is 2.0-6.0 h.

5. The method for preparing the catalyst according to claim 2, characterized in that: The drying described in steps 4), 8), and 12) is carried out in air at a temperature of 80-110 ℃ for a time of 12.0-24.0 h.

6. The method for preparing the catalyst according to claim 2, characterized in that: The calcination conditions described in steps 5) and 9) are as follows: the sample is heated from room temperature to 350-800 ℃ at a heating rate of 1-10 ℃ / min, and calcined for 2.0-8.0 hours.

7. The method for preparing the catalyst according to claim 2, characterized in that: The cerium salt mentioned in step 6) is Ce(NO3)3·6H2O; the molar ratio of hexamethylenetetramine to Ce(NO3)3·6H2O is 1:10-1:

40.

8. The method for preparing the catalyst according to claim 2, characterized in that: In step 10), the concentration of the sodium hydroxide aqueous solution is 1-5 mol / L, and the etching time is 24.0-72.0 h.

9. The method for preparing the catalyst according to claim 2, characterized in that: In step 13), the reducing gas is pure hydrogen with a purity greater than 99.9%, or the reducing gas is a hydrogen-containing mixture with a hydrogen content of 10%-100%, and the other gases besides hydrogen are nitrogen or helium; the flow rate of the reducing gas is 10-50 mL / min, the reduction temperature is 300-400 ℃, the temperature is programmed to rise from room temperature to the target reduction temperature at a rate of 1-10 ℃ / min, the pressure is atmospheric pressure, and the reduction time is 1.0-4.0 h.

10. The application of the nickel-cerium dioxide hollow catalyst according to claim 1 or the nickel-cerium dioxide hollow catalyst obtained by the preparation method of the catalyst according to any one of claims 2-9 in the carbon dioxide methanation reaction, characterized in that: The nickel-cerium dioxide hollow catalyst is used for gas-solid fixed-bed carbon dioxide methanation reaction. The reaction conditions are as follows: the reactant is a mixture of CO2:H2:N2 in a molar ratio of 2:8:5; the reaction temperature is 200-350 °C; the pressure is atmospheric or near-atmospheric; and the mass hourly space velocity is 36-360 L·g. -1 ·h -1 .

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