Preparation method and application of a rare earth fluoride-modified single-atom Ru-based catalyst

Abstract

This invention belongs to the field of catalysts and provides a method for preparing and applying a rare-earth fluoride-modified single-atom Ru-based catalyst, specifically a rare-earth fluoride-modified single-atom Ru-based nanocomposite material. A series of Ru / XF3 / Al2O3 (X = La, Ce, Pr, and Nd) catalysts were prepared using a simple and easy-to-implement solvothermal and calcination method. Experimental results show that the noble metal Ru is distributed in single-atom form on the surface of XF3 / Al2O3. The addition of rare-earth fluorides improves the basicity of the catalyst, increases the CO2 adsorption sites, and also improves the dispersion of Ru active sites, resulting in a high loading of 5-6%. This achieves high catalytic performance at low temperatures and has good practical application value.

Description

Technical Field

[0001] This invention belongs to the field of catalysts, and specifically relates to the preparation of a rare earth fluoride-modified single-atom Ru-based nanocomposite material, which is mainly used in photothermal synergistic catalytic CO2 methanation reaction. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] CO2 emissions from fossil fuel utilization have severely impacted the ecological environment and sustainable social development, making large-scale CO2 capture and conversion a global consensus. Photothermal synergistic catalysis to convert CO2 into hydrocarbons or chemical substances offers a feasible approach to addressing these issues and has become an important research direction. Among these methods, CO2 methanation is widely considered an efficient, reliable, and promising CO2 conversion technology because CH4 is a major component of natural gas, which can be injected into existing natural gas networks. While CO2 methanation is thermodynamically favorable, overcoming a high kinetic energy barrier is necessary to reduce CO2 to CH4. Therefore, developing efficient catalysts to promote CO2 methanation is crucial.

[0004] Currently, single-atom catalysts have exhibited unprecedented performance in many catalytic reactions. The uniform and singular loading of metals in single-atom form onto supports with high specific surface areas improves the utilization efficiency of metal atoms, significantly enhancing the catalytic effect of each metal atom on the catalyst and strengthening the overall reactivity. Simultaneously, single-atom catalysts possess a single catalytic active site, resulting in excellent selectivity in catalytic reactions. However, their metal atom loading, especially for noble metals, is typically limited to less than 1% by weight, significantly lower than that of commercial catalysts, thus limiting catalytic activity. Therefore, finding universal synthetic methods to increase the metal atom loading in single-atom catalysts will play a crucial role in this field. Summary of the Invention

[0005] To address the problems of low CO2 conversion efficiency and product selectivity, and low metal atom loading in single-atom catalysts in existing photothermal CO2 methanation technologies, this invention provides a method for preparing a single-atom Ru-based nanocomposite material modified with rare-earth fluorides. The addition of rare-earth fluorides to this catalyst improves its basicity, increases CO2 adsorption sites, and also improves the dispersion of Ru active sites, resulting in a high Ru loading of 5-6%, achieving highly efficient catalytic performance at low temperatures.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A first aspect of the present invention provides a rare-earth fluoride-modified single-atom Ru-based catalyst, comprising:

[0008] Porous XF3 / Al2O3;

[0009] The porous XF3 / Al2O3 surface is loaded with Ru single atoms;

[0010] Where X is La, Ce, Pr or Nd.

[0011] Specifically, the Ru / XF3 / Al2O3 (X = La, Ce, Pr or Nd) catalyst includes Ru single-atom active sites, XF3 promoters and Al2O3 supports, with Ru single atoms dispersed on the porous XF3 / Al2O3 surface.

[0012] The catalyst of this invention has a Ru single-atom loading of up to 5-6%, providing abundant catalytic active sites for the CO2 methanation reaction. Furthermore, the addition of rare earth fluorides can improve the basicity of the catalyst, increase the CO2 adsorption sites, and promote the catalytic reaction. Thanks to the synergistic effect of Ru single atoms and rare earth fluorides, this catalyst exhibits excellent photothermal synergistic catalytic activity for CO2 methanation.

[0013] In some embodiments, the loading of Ru single atoms is 5-6% of the total mass of the catalyst. Higher metal loading has more catalytic active sites and can greatly improve catalytic activity.

[0014] In some embodiments, the molar ratio of ruthenium salt, X salt, and aluminum salt is 0.05-0.2:0.25-4:2.5-10.

[0015] In some embodiments, the Ru / XF3 / Al2O3 catalyst has a pore size of approximately 5-10 nm and a specific surface area of ​​approximately 150-180 m². 2 / g.

[0016] In some more effective embodiments, the Ru / XF3 / Al2O3 catalyst has an average pore size of approximately 5.3 nm and a specific surface area of ​​approximately 173 m². 2 / g.

[0017] A second aspect of the present invention provides a method for preparing a rare-earth fluoride-modified single-atom Ru-based catalyst, comprising:

[0018] The RuXAl hydrotalcite precursor was synthesized using a solvothermal method.

[0019] The RuXAl hydrotalcite precursor was calcined under a hydrogen atmosphere to obtain a Ru / XF3 / Al2O3 composite material. Traditional preparation methods typically involve metal atom loading of less than 1% and require cumbersome preparation conditions. This catalyst is prepared using a one-step solvothermal and calcination method, which is simple, easy to perform, and the reaction is safe and reliable.

[0020] In some embodiments, the specific steps of the solvothermal synthesis include: mixing ruthenium salt, X salt, aluminum salt, and organic compound uniformly in an organic solvent, and carrying out a solvothermal reaction to obtain the product;

[0021] The ratio of the amounts of ruthenium salt, X salt, aluminum salt, organic compound (urea, ammonium fluoride) and organic solvent is 0.05-0.2 mmol: 0.25-4 mmol: 2.5-10 mmol: 5-20 mmol: 1.5-5 mmol: 15-80 mL.

[0022] In some embodiments, the ruthenium salt is one or more of ruthenium acetate, ruthenium acetylacetone, and ruthenium chloride;

[0023] In some embodiments, the X salt (X = La, Ce, Pr or Nd) is nitrate X;

[0024] In some embodiments, the aluminum salt is aluminum nitrate;

[0025] In some embodiments, the organic compounds are urea (for pH control) and ammonium fluoride (for providing a source of sulfur).

[0026] In some embodiments, the organic solvent is methanol.

[0027] In some embodiments, the conditions for preparing RuXAl LDH by solvothermal method are: temperature of 120-170℃ and reaction time of 10-20h.

[0028] In some embodiments, the calcination temperature is 300-450℃ and the calcination time is 1-3h.

[0029] In some implementations, the RuXAl LDH precursor is calcined in a tube furnace.

[0030] A third aspect of the present invention provides the application of the above-described catalyst and / or the catalyst prepared by the above-described method in the photothermal synergistic catalytic CO2 methanation reaction.

[0031] In some embodiments, the catalytic conditions are: a 300W xenon lamp as the light source, a wavelength of 200-1100nm, and a light intensity of 1.8-3.0W·cm. -2The CO2 flow rate was 4 mL / min, the H2 flow rate was 16 mL / min, the reaction temperature was 100-250℃, and the reaction apparatus was a gas-phase flow reactor.

[0032] In some more effective implementations, the catalytic conditions are: a 300W xenon lamp as the light source, a wavelength of 200-1100nm, and a light intensity of 1.8W·cm². -2 The CO2 flow rate was 4 mL / min, the H2 flow rate was 16 mL / min, the reaction temperature was 100-250℃, and the reaction apparatus was a gas-phase flow reactor.

[0033] Beneficial effects of the present invention

[0034] (1) The photothermal synergistic catalytic CO2 methanation technology used in this invention can efficiently and selectively convert CO2 into CH4 at lower reaction temperatures and atmospheric pressures, which largely avoids the excessive energy consumption and safety issues caused by the high temperature and high pressure of traditional thermocatalytic reactions.

[0035] (2) The Ru / XF3 / Al2O3 (X = La, Ce, Pr and Nd) catalyst exhibited better catalytic activity than the Ru / Al2O3 catalyst, indicating that the addition of rare earth fluorides can effectively improve catalytic performance.

[0036] (3) The Ru / LaF3 / Al2O3, Ru / CeF3 / Al2O3, Ru / PrF3 / Al2O3 and Ru / NdF3 / Al2O3 catalysts exhibited excellent CO2 conversion rates of 97.04%, 90.19%, 93.35% and 93.47% at 250℃ and under light irradiation, respectively.

[0037] (4) A series of Ru / XF3 / Al2O3 catalysts were obtained by preparing RuXAl LDH precursor by one-step solvothermal method and then calcining. The method is simple and easy to operate.

[0038] (5) The addition of rare earth fluorides can improve the basicity of the catalyst and increase the adsorption sites for CO2. At the same time, it can also improve the dispersibility of Ru species, prevent Ru single atoms from sintering during the catalytic process, and enhance the stability of the catalyst.

[0039] (6) The catalytic system has mild reaction conditions, is easy to operate, saves energy, and does not produce excess harmful substances during the production process. It is green and environmentally friendly and helps to realize industrial production. Attached Figure Description

[0040] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. Exemplary embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0041] Figure 1 These are TEM and HRTEM images of Ru / LaF3 / Al2O3 prepared in Example 1.

[0042] Figure 2 These are XRD patterns of the Ru / LaF3 / Al2O3, Ru / CeF3 / Al2O3, Ru / PrF3 / Al2O3, and Ru / NdF3 / Al2O3 catalysts prepared in Examples 1, 2, 3, and 4.

[0043] Figure 3 These are the CO2 conversion rate curves as a function of reaction temperature for the photothermal synergistic catalytic CO2 methanation reaction prepared by Ru / LaF3 / Al2O3, Ru / CeF3 / Al2O3, Ru / PrF3 / Al2O3, Ru / NdF3 / Al2O3, Ru / Al2O3, and LaF3 / Al2O3 catalysts prepared in Examples 1, 2, 3, 4, Comparative Examples 1 and 2.

[0044] Figure 4 These are the curves showing the change in CH4 yield as a function of reaction temperature during the photothermal synergistic catalysis of CO2 methanation reaction by Ru / LaF3 / Al2O3, Ru / CeF3 / Al2O3, Ru / PrF3 / Al2O3, Ru / NdF3 / Al2O3 and Ru / Al2O3 catalysts prepared in Examples 1, 2, 3, 4 and Comparative Example 1.

[0045] Figure 5 The product selectivity of the photothermal synergistic catalytic CO2 methanation reaction of the Ru / LaF3 / Al2O3, Ru / CeF3 / Al2O3, Ru / PrF3 / Al2O3, Ru / NdF3 / Al2O3 and Ru / Al2O3 catalysts prepared in Examples 1, 2, 3, 4 and Comparative Example 1 is shown.

[0046] Figure 6 This is a comparison of the thermocatalytic and photothermal synergistic catalytic performance of the Ru / LaF3 / Al2O3 catalyst prepared in Example 1 for CO2 methanation. Detailed Implementation

[0047] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0048] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are explanations of the present invention and not limitations thereof.

[0049] Example 1

[0050] (1) Add 0.1 mmol of ruthenium acetate, 1 mmol of lanthanum nitrate, 5 mmol of aluminum nitrate, 10 mmol of urea and 2.5 mmol of ammonium fluoride to 30 mL of methanol solution and stir until dissolved;

[0051] (2) Transfer the mixed solution from step (1) to a reaction vessel, keep it at 150°C for 12 hours, then centrifuge and wash the product, and dry it at 70°C to obtain RuLaAl LDH.

[0052] (3) The prepared RuLaAl LDH was placed in a muffle furnace and calcined at 450°C for 2 hours under a hydrogen atmosphere to obtain the Ru / LaF3 / Al2O3 catalyst.

[0053] Figure 1 These are TEM and HRTEM images of Ru / LaF3 / Al2O3 prepared in Example 1. The TEM and HRTEM images show that Ru single atoms are uniformly dispersed on the surface of LaF / Al2O3; the lattice stripes with interplanar spacings of 0.20 nm and 0.33 nm correspond to the (113) and (111) crystal planes of LaF3, respectively.

[0054] Figure 6 This is a comparison of the CO2 methanation performance of the Ru / LaF3 / Al2O3 catalyst prepared in Example 1 under thermocatalytic and photothermal synergistic catalytic conditions. Figure 6 As can be seen, the CH4 generation rate under photothermal coupling conditions is higher than that under thermocatalytic conditions, indicating that the introduction of light can significantly improve catalytic activity.

[0055] Example 2

[0056] (1) Add 0.1 mmol ruthenium acetate, 1 mmol cerium nitrate, 5 mmol aluminum nitrate, 10 mmol urea and 2.5 mmol ammonium fluoride to 30 mL methanol solution and stir until dissolved;

[0057] (2) Transfer the mixed solution from step (1) to a reaction vessel, keep it at 150°C for 12 hours, then centrifuge and wash the product, and dry it at 70°C to obtain RuCeAl LDH.

[0058] (3) The prepared RuCeAl LDH was placed in a muffle furnace and calcined at 450°C for 2 hours under a hydrogen atmosphere to obtain the Ru / CeF3 / Al2O3 catalyst.

[0059] Example 3

[0060] (1) Add 0.1 mmol ruthenium acetate, 1 mmol praseodymium nitrate, 5 mmol aluminum nitrate, 10 mmol urea and 2.5 mmol ammonium fluoride to 30 mL methanol solution and stir until dissolved;

[0061] (2) Transfer the mixed solution from step (1) to a reaction vessel, keep it at 150°C for 12 hours, then centrifuge and wash the product, and dry it at 70°C to obtain RuPrAl LDH.

[0062] (3) The prepared RuPrAl LDH was placed in a muffle furnace and calcined at 450°C for 2 hours under a hydrogen atmosphere to obtain the Ru / PrF3 / Al2O3 catalyst.

[0063] Example 4

[0064] (1) Add 0.1 mmol ruthenium acetate, 1 mmol neodymium nitrate, 5 mmol aluminum nitrate, 10 mmol urea and 2.5 mmol ammonium fluoride to 30 mL methanol solution and stir until dissolved;

[0065] (2) Transfer the mixed solution from step (1) to a reaction vessel, keep it at 150°C for 12 hours, then centrifuge and wash the product, and dry it at 70°C to obtain RuNdAl LDH.

[0066] (3) The prepared RuNdAl LDH was placed in a muffle furnace and calcined at 450°C for 2 hours under a hydrogen atmosphere to obtain the Ru / NdF3 / Al2O3 catalyst.

[0067] Comparative Example 1

[0068] (1) Add 0.1 mmol ruthenium acetate, 5 mmol aluminum nitrate, 10 mmol urea and 2.5 mmol ammonium fluoride to 30 mL methanol solution and stir until dissolved;

[0069] (2) Transfer the mixed solution from step (1) to a reaction vessel, keep it at 150°C for 12 hours, then centrifuge and wash the product, and dry it at 70°C to obtain RuAl LDH.

[0070] (3) The prepared RuAl LDH was placed in a muffle furnace and calcined at 300°C for 2 hours under a hydrogen atmosphere to obtain the Ru / Al2O3 catalyst.

[0071] Comparative Example 2

[0072] (1) Add 1 mmol lanthanum nitrate, 5 mmol aluminum nitrate, 10 mmol urea and 2.5 mmol ammonium fluoride to 30 mL methanol solution and stir until dissolved;

[0073] (2) Transfer the mixed solution from step (1) to a reaction vessel, keep it at 150°C for 12 hours, then centrifuge and wash the product, and dry it at 70°C to obtain LaAl LDH.

[0074] (3) The prepared LaAl LDH was placed in a muffle furnace and calcined at 450°C for 2 hours under a hydrogen atmosphere to obtain the LaF3 / Al2O3 catalyst.

[0075] Figure 2 These are the XRD patterns of the Ru / LaF3 / Al2O3, Ru / CeF3 / Al2O3, Ru / PrF3 / Al2O3, and Ru / NdF3 / Al2O3 catalysts prepared in Examples 1, 2, 3, and 4. From... Figure 2 The XRD patterns of the four catalysts show diffraction peaks for LaF3, CeF3, PrF3, and NdF3, respectively. The absence of diffraction peaks for Al2O3 indicates that Al2O3 in this catalyst is in an amorphous state. Furthermore, no characteristic peaks for Ru species were found in the XRD patterns of these four catalysts, further confirming the successful preparation of single-atom Ru.

[0076] Figure 3 These are the photothermal synergistic catalytic CO2 conversion rate versus reaction temperature curves for the Ru / LaF3 / Al2O3, Ru / CeF3 / Al2O3, Ru / PrF3 / Al2O3, Ru / NdF3 / Al2O3, Ru / Al2O3, and LaF3 / Al2O3 catalysts prepared in Examples 1, 2, 3, 4, Comparative Examples 1 and 2. Figure 3 As can be seen, the LaF3 / Al2O3 catalyst exhibits almost no catalytic activity, indicating that the presence of active sites is necessary. Compared to Ru / Al2O3, Ru / LaF3 / Al2O3, Ru / CeF3 / Al2O3, Ru / PrF3 / Al2O3, and Ru / NdF3 / Al2O3 show higher catalytic activity, indicating that the addition of rare earth fluorides can effectively improve catalytic activity. Among them, the Ru / LaF3 / Al2O3 catalyst shows the highest CO2 conversion rate of 97.04% under 250℃ and full-spectrum illumination.

[0077] Figure 4 These are the curves showing the change in CH4 yield as a function of reaction temperature in the photothermal synergistic catalytic CO2 methanation reaction of the Ru / LaF3 / Al2O3, Ru / CeF3 / Al2O3, Ru / PrF3 / Al2O3, Ru / NdF3 / Al2O3, and Ru / Al2O3 catalysts prepared in Examples 1, 2, 3, 4, and Comparative Example 1. Figure 4 As can be seen, the change in CH4 yield is consistent with the CO2 conversion rate. Under 250℃ and full-spectrum illumination, the Ru / LaF3 / Al2O3 catalyst exhibits the highest CH4 yield of 194.3 mmol g. cat -1 h -193.8

[0078] Figure 5 The product selectivity of the Ru / LaF3 / Al2O3, Ru / CeF3 / Al2O3, Ru / PrF3 / Al2O3, Ru / NdF3 / Al2O3, and Ru / Al2O3 catalysts prepared in Examples 1, 2, 3, 4, and Comparative Example 1 under 250°C and full-spectrum illumination is shown. Figure 5 As can be seen, the CH4 selectivity of these five catalysts is all above 93%, indicating that the catalyst has excellent CH4 selectivity.

[0079] Photothermal Co-catalytic CO2 Methanation Test:

[0080] The photothermal synergistic catalytic reaction of CO2 methanation with different catalysts was evaluated in a continuous flow fixed-bed reactor. A 300W xenon lamp was used as the light source, with a wavelength of 200-1100 nm and a light intensity of 1.8 W·cm⁻¹. -2 The volume ratio of CO2 to H2 was 1:4, with flow rates of 4 and 16 mL / min, respectively; the reaction temperature was 100-250℃. 50 mg of catalyst was weighed and thoroughly mixed with 1.2 g of quartz sand, then placed in a transparent quartz tube. The quartz tube was placed in a heating furnace, and CO2 and H2 were introduced. The light source was turned on, and the concentrations of CO2 and products were obtained using an online gas chromatograph to compare the catalytic activity of different catalysts. The Ru / LaF3 / Al2O3 catalyst exhibited the best catalytic activity, achieving a CH4 production rate of 194.3 mmol / g under 250℃ and light irradiation conditions. cat -1 h -1 The catalytic activities of different catalysts, from highest to lowest, are: Ru / LaF3 / Al2O3 > Ru / PrF3 / Al2O3 > Ru / NdF3 / Al2O3 > Ru / CeF3 / Al2O3 > Ru / Al2O3.

[0081] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A rare-earth fluoride-modified single-atom Ru-based catalyst, characterized in that, include: Porous XF3 / Al2O3; The porous XF3 / Al2O3 surface is loaded with Ru single atoms; Where X is La, Ce, Pr or Nd.

2. The rare-earth fluoride-modified single-atom Ru-based catalyst as described in claim 1, characterized in that, The loading of Ru single atoms is 5-6% of the total mass of the catalyst.

3. The rare-earth fluoride-modified single-atom Ru-based catalyst as described in claim 1, characterized in that, The Ru / XF3 / Al2O3 catalyst has a pore size of 5-10 nm and a specific surface area of ​​150-180 m². 2 / g.

4. A method for preparing a rare-earth fluoride-modified single-atom Ru-based catalyst, characterized in that, include: The RuXAl hydrotalcite precursor was synthesized using a solvothermal method. The RuXAl hydrotalcite precursor was calcined in a hydrogen atmosphere to obtain a Ru / XF3 / Al2O3 composite material. The specific steps of the solvothermal synthesis method include: mixing ruthenium salt, X salt, aluminum salt, and organic compound evenly in an organic solvent, and carrying out a solvothermal reaction to obtain the product; The organic compounds are urea and ammonium fluoride; The ratio of the amounts of ruthenium salt, X salt, aluminum salt, urea, ammonium fluoride, and organic solvent is 0.05-0.2 mmol: 0.25-4 mmol: 2.5-10 mmol: 5-20 mmol: 1.5-5 mmol: 15-80 mL; Wherein, salt X is nitrate X, and X is La, Ce, Pr or Nd; The calcination temperature is 300-450 ℃, and the calcination time is 1-3 h.

5. The method for preparing the rare earth fluoride-modified single-atom Ru-based catalyst as described in claim 4, characterized in that, The ruthenium salt is one or more of ruthenium acetate, ruthenium acetylacetone, and ruthenium chloride.

6. The method for preparing the rare earth fluoride-modified single-atom Ru-based catalyst as described in claim 4, characterized in that, The aluminum salt is aluminum nitrate.

7. The method for preparing the rare earth fluoride-modified single-atom Ru-based catalyst as described in claim 4, characterized in that, The organic solvent is methanol.

8. The method for preparing the rare earth fluoride-modified single-atom Ru-based catalyst as described in claim 4, characterized in that, The conditions for preparing RuXAl LDH by solvothermal method are: temperature 120-170 ℃, reaction time 10-20 h.

9. The application of the catalyst according to any one of claims 1-3 and / or the catalyst prepared by the method according to any one of claims 4-8 in the photothermal synergistic catalytic CO2 methanation reaction.

10. The application according to claim 9, characterized in that, The catalytic conditions are as follows: the light source is a 300 W xenon lamp, the wavelength is 200-1100 nm, and the light intensity is 1.8-3.0 W·cm. -2 The CO2 flow rate was 4 mL / min, the H2 flow rate was 16 mL / min, the reaction temperature was 100-250 ℃, and the reaction apparatus was a gas-phase flow reactor.

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