MgO supported noble metal material, microwave preparation method and application thereof

Abstract

This invention provides a MgO-supported noble metal material, its microwave preparation method, and its application. The method includes the following steps: S1. Mixing a noble metal salt, a magnesium source, and an additive to obtain a first solid-liquid mixture; the additive includes citric acid; S2. Microwave-treating the first slurry to obtain a second solid-liquid mixture; S3. Drying the second solid-liquid mixture to obtain a solid containing noble metal and magnesium; S4. Calcining the solid in an oxygen-containing atmosphere to obtain a calcined product; S5. Reducing the calcined product under a reducing atmosphere. This preparation method uses noble metal as the active component and citric acid or similar chelating agents, and synthesizes it via microwave, resulting in uniform dispersion of the noble metal particles and obtaining a highly efficient and stable catalyst. This avoids the problems of catalyst agglomeration and limited catalytic performance at high temperatures.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, and more specifically, to a MgO-supported noble metal material and its microwave preparation method and application. Background Technology

[0002] With the continued growth of global energy demand, the large-scale use of fossil fuels has led to a significant increase in greenhouse gas emissions, primarily carbon dioxide and methane, resulting in increasingly prominent environmental problems such as the greenhouse effect. Therefore, developing technological pathways that can effectively convert and utilize CO2 and CH4 is of significant practical importance for alleviating environmental pressures and achieving low-carbon sustainable development.

[0003] The methane dual reforming reaction (methane-carbon dioxide-water dual reforming) utilizes methane and carbon dioxide, two major greenhouse gases, as feedstocks, converting them into syngas through a catalytic reforming process. This achieves resource utilization while effectively reducing greenhouse gas emissions, representing a resource-based approach to natural gas and carbon dioxide. Furthermore, the methane dual reforming reaction provides ideal feedstocks for industrial processes such as Fischer-Tropsch synthesis, further enhancing its application potential in the clean energy sector. The methane dual reforming reaction not only provides an alternative route for syngas production but also achieves carbon recycling to a certain extent, demonstrating significant environmental and economic benefits.

[0004] In the research of catalysts for methane reforming, noble metal catalysts have attracted widespread attention due to their excellent catalytic activity. However, the price of noble metal catalysts is higher than that of non-metallic catalysts. Therefore, it is necessary to improve the catalytic efficiency and service life of noble metal catalysts so that they can have greater application advantages in the methane reforming to syngas reaction. Summary of the Invention

[0005] One of the objectives of this invention is to provide a microwave preparation method for MgO-supported noble metal materials.

[0006] A second objective of this invention is to provide a MgO-supported noble metal material prepared by the aforementioned microwave preparation method. The MgO-supported noble metal material prepared by the microwave preparation method exhibits strong metal-support interactions, high catalytic activity, excellent stability and anti-carbon deposition properties, and a long service life.

[0007] The third objective of this invention is to provide the application of the above-mentioned MgO-supported noble metal material in the catalytic double reforming reaction of methane.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: In a first aspect, a microwave preparation method for MgO-supported noble metal materials includes the following steps: S1. A precious metal salt, a magnesium source, and an additive are mixed to obtain a first solid-liquid mixture; the additive includes citric acid. S2. Microwave the first solid-liquid mixture to obtain a second solid-liquid mixture; S3. The second solid-liquid mixture is dried to obtain a solid containing precious metals and magnesium; S4. The solid is calcined in an oxygen-containing atmosphere to obtain the calcined product; S5. The calcined product is subjected to a reduction reaction under a reducing atmosphere.

[0009] To improve catalytic activity and stability, this invention constructs weak Lewis acid sites and surface hydroxyl groups on a catalyst support. By introducing citric acid as a complexing agent during the preparation process, it is beneficial to regulate the acidity distribution on the support surface, induce the formation of weak Lewis acid sites and hydroxyl groups, and thus achieve the regulation of surface acid-base properties.

[0010] Furthermore, by utilizing microwave heating treatment to effectively circumvent the temperature gradient caused by traditional heat conduction, explosive nucleation of metal precursors is induced in a very short time, resulting in fine-sized and densely distributed active metal nanoparticles. This process significantly enhances the interaction between the active metal and the support, thereby inhibiting the sintering of metal particles and the continuous accumulation of carbon species at the interface during high-temperature reforming reactions. Simultaneously, microwave irradiation can induce high concentrations of oxygen vacancies and surface defects in situ within the support. These coordinate unsaturated sites, serving as core centers for CO2 adsorption and activation, can promote the oxidative removal of carbon species, thereby enhancing the catalyst's resistance to carbon deposition. In addition, microwave treatment can effectively modulate the acid-base properties of the catalyst surface, inducing the formation of weak Lewis acid sites and surface hydroxyl groups, further enhancing CO2 adsorption and inhibiting the graphitization transformation of carbon deposition.

[0011] In summary, the microwave preparation method described in this invention can synergistically improve the dispersion of active metals, construct abundant oxygen vacancies, and optimize surface acid-base properties, enabling the prepared catalyst to exhibit higher catalytic activity, lower carbon deposition rate, and excellent long-term stability in methane reforming reactions.

[0012] Optionally, in step S1 of the present invention, the noble metal salt, magnesium source, and additives are dispersed in water to prepare a solid-liquid mixture. Optionally, the obtained solid-liquid mixture is subjected to ultrasound.

[0013] Optionally, the noble metal is one or more of Ru, Ir, Rh, Pd, and Pt. The noble metal salt is one or more of ruthenium chloride, iridium trichloride, rhodium trichloride, tetraammineplatinum nitrate, and tetraaminopalladium nitrate.

[0014] Optionally, the magnesium source is one or more of magnesium chloride, magnesium nitrate, magnesium hydroxide, magnesium carbonate, or magnesium acetate.

[0015] Optionally, in step S1, the molar ratio of the sum of the amounts of the precious metal salt and the magnesium source to the amount of the additive is 1:1 to 1:2.

[0016] Furthermore, in step S2, the microwave power is 80~90 W, the microwave temperature is 100~110 ℃, and the microwave time is 3~4 h.

[0017] Optionally, in step S3 of the present invention, the drying temperature is 80~100 ℃ and the drying time is 10~12 h. As one embodiment, the drying temperature is 100 ℃ and the drying time is 12 h.

[0018] In step S4 of this invention, calcination is carried out at 500-600 °C for 6-8 h in an oxygen-containing atmosphere to obtain the calcined product. In one embodiment, the calcination temperature is 500 °C and the calcination time is 8 h. Optionally, the heating rate during calcination is 5 °C / min.

[0019] Optionally, the oxygen-containing atmosphere is one of static or flowing air or a 5% O2 / N2 mixture.

[0020] In step S5 of this invention, the heating reduction temperature is 550~650 ℃, and the reduction time is 1~2 h. Optionally, the heating reduction heating rate is 5~10 ℃ / min.

[0021] Optionally, the reducing atmosphere is one or more of H2, H2 / N2, or H2 / Ar mixture.

[0022] Secondly, the present invention also provides an MgO-supported noble metal material, which is prepared by the preparation method described in the first aspect. Optionally, the loading amount of noble metal in the MgO-supported noble metal material is 0.1~0.5 wt%.

[0023] In the MgO-supported noble metal material of the present invention, the MgO support prepared by the preparation method has a large specific surface area and abundant alkaline sites, which can promote the dispersion of active noble metals, thereby improving the anti-carbon deposition and anti-sintering ability of the MgO-supported noble metal material. As a result, the MgO-supported noble metal material has good catalytic activity and stability, and can effectively catalyze the methane dual reforming syngas reaction for use in the synthesis of downstream high value-added chemicals.

[0024] Therefore, the application of the MgO-supported noble metal material obtained in this invention as a catalyst in catalytic reactions, especially in the methane double reforming reaction, should also be within the scope of protection of this invention.

[0025] Thirdly, the present invention provides the application of the MgO-supported noble metal material in the catalytic double reforming reaction of methane.

[0026] Compared with the prior art, the beneficial effects of the present invention are: This invention uses noble metal salts and magnesium sources as raw materials, and citric acid as a catalyst. Microwave treatment is used for assisted synthesis to highly disperse the noble metals on the surface of the magnesium precursor. Following calcination and reduction, a MgO-supported noble metal material is obtained. The noble metals are highly dispersed and anchored to the MgO support in the form of isolated single atoms. The resulting MgO-supported noble metal material exhibits strong metal-support interactions. This structure not only provides a large number of highly active single-atom noble metal sites but also significantly improves the catalyst's resistance to carbon deposition, effectively overcoming the problem of easy agglomeration and carbon deposition deactivation of active components in high-temperature methane double reforming reactions. Thus, high catalytic activity and excellent long-term stability are achieved even with low noble metal loading. Attached Figure Description

[0027] Figure 1 The image shows the N2 adsorption-desorption isotherm and pore size distribution curve of the catalyst in Example 1.

[0028] Figure 2 The image shows the HAADF-STEM image of the catalyst in Example 1.

[0029] Figure 3 The image shows the AC-HAADF-STEM image of the catalyst in Example 1.

[0030] Figure 4 The graph shows the test results of the catalyst in Example 1 participating in the catalytic reaction for 150 h. Detailed Implementation

[0031] The present invention will be further illustrated below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions in the art or as recommended by the manufacturer; the raw materials and reagents used, unless otherwise specified, are all commercially available from the conventional market. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention are within the scope of protection claimed by the present invention.

[0032] The sources of the raw materials used in the following examples and comparative examples are as follows: Anhydrous ruthenium trichloride, Maclean, molecular weight: 207.42, CAS No.: 10049-08-8.

[0033] Iridium trichloride hydrate, Maclean, molecular weight: 298.58, CAS No.: 14996-61-3.

[0034] Rhodium trichloride trihydrate, Maclean, molecular weight: 263.31, CAS No.: 20765-98-4.

[0035] Tetraammineplatinum nitrate, Maclean, molecular weight: 387.21, CAS number: 20634-12-2.

[0036] Tetraaminopalladium nitrate, Maclean, molecular weight: 298.55, CAS number: 13601-08-6.

[0037] Commercial MgO, Maclean, purity: 99.9%, molecular weight: 40.30, grade: M761792, CAS number: 1309-48-4.

[0038] Magnesium hydroxide, Maclean, purity: ≥99.0%, molecular weight: 58.32, CAS number: 1309-42-8.

[0039] Anhydrous magnesium chloride, Maclean, purity: 99.9%, molecular weight: 95.21, CAS number: 7786-30-3.

[0040] Magnesium nitrate hexahydrate, Guangzhou Chemical Reagent Factory, molecular weight: 256.41, CAS No.: 13446-18-9.

[0041] Magnesium carbonate hydrate, Maclean, molecular weight: 84.31, CAS No.: 23389-33-5.

[0042] Magnesium acetate, Maclean, purity: 98%, molecular weight: 142.39, CAS number: 142-72-3.

[0043] Ascorbic acid, Maclean, purity: 99.99%, molecular weight: 176.12, CAS number: 50-81-7.

[0044] Citric acid, Maclean, purity: 99.5%, molecular weight: 192.12, CAS number: 77-92-9.

[0045] Glycine, Maclean, purity: 99.5-100.5%, molecular weight: 75.07, CAS number: 56-40-6.

[0046] Examples 1-5

[0047] The purpose of Examples 1-5 is to prepare MgO-supported materials with different noble metals (as shown in Table 1). The specific preparation methods are as follows: Accurately weigh the appropriate amounts of precious metal salt, magnesium nitrate, and citric acid (the molar ratio of the sum of the precious metal salt and magnesium source to the amount of the auxiliary is 1:2), dissolve or disperse them in deionized water, and stir for 30 min to obtain a first solid-liquid mixture. Place the first solid-liquid mixture in a multifunctional microwave synthesizer for microwave treatment at a power of 80 W, a temperature of 100 °C, and a time of 4 h to obtain a uniformly dispersed second solid-liquid mixture. Place the obtained second solid-liquid mixture in an oven at 100 °C for 12 h to obtain a solid containing precious metal and magnesium, such as the precursor Ru. 3+ / Mg(NO3)2-MW. The resulting solid containing precious metals and magnesium was placed in a muffle furnace and calcined at 500 °C for 8 h in air at a heating rate of 5 °C / min. Finally, the calcined product was reduced in situ at 650 °C for 2 h in a 10% H2 / N2 reducing atmosphere.

[0048] The actual loading of noble metals (the percentage of noble metals by mass in the entire catalyst) in the prepared catalyst was tested using ICP-OES technology, and the results are shown in Table 1. The same testing technique was used in subsequent examples and comparative examples. ICP-OES testing showed that the actual loading of noble metals was essentially the same as the theoretical loading.

[0049] Table 1

[0050] Examples 6-9

[0051] The purpose of Examples 6-9 is to investigate the effects of different magnesium sources (see Table 2 for details) on the catalytic performance of MgO-supported noble metal materials. The other raw materials and specific preparation methods used in Examples 6-9 are the same as those in Example 1.

[0052] Table 2

[0053] Example 10

[0054] The preparation method used in Example 10 is basically the same as that in Example 1, except that: The molar ratio of the sum of the amounts of precious metal salt and magnesium source to the amount of additive is 1:1.

[0055] Comparative Example 1

[0056] In this comparative example, commercially available MgO was directly used as a support to load Ru, and Ru / MgO was prepared using the following specific preparation method: Accurately weigh appropriate amounts of ruthenium trichloride, MgO, and citric acid, dissolve or disperse them in deionized water, and stir for 30 min to obtain a solid-liquid mixture. Place the solid-liquid mixture in a multifunctional microwave synthesizer for microwave treatment at a power of 80 W, a temperature of 100 °C, and a time of 4 h to obtain a uniformly dispersed solid-liquid mixture. Dry the obtained solid-liquid mixture in an oven at 100 °C for 12 h to obtain the precursor Ru. 3+ / MgO. The resulting Ru 3+ The MgO was placed in a muffle furnace and calcined at 500 °C for 8 h in air at a heating rate of 5 °C / min to obtain Ru₂O₃ / MgO. Finally, the Ru₂O₃ / MgO was reduced in situ at 650 °C for 2 h in a 10% H₂ / N₂ reducing atmosphere. ICP-OES analysis showed that the actual Ru loading was 0.40 wt%.

[0057] Comparative Example 2

[0058] The purpose of this comparative example is to investigate the effect of not adding additives on the catalytic performance of Ru / MgO materials. The specific preparation method for Ru / MgO is as follows: Accurately weigh appropriate amounts of ruthenium trichloride and magnesium nitrate, dissolve or disperse them in deionized water, and stir for 30 min to obtain a solid-liquid mixture. Place the solid-liquid mixture in a multifunctional microwave synthesizer, set the microwave power to 80 W, the microwave temperature to 100 ℃, and the microwave time to 4 h to obtain a uniformly dispersed solid-liquid mixture. Place the obtained solid-liquid mixture in an oven at 100 ℃ for 12 h to obtain the precursor Ru. 3+ / Mg(NO3)2. The resulting Ru 3+ Mg(NO3)2 was placed in a muffle furnace and calcined at 500 °C for 8 h in air atmosphere to obtain Ru2O3 / MgO. Finally, Ru2O3 / MgO was reduced in situ at 650 °C for 2 h in a 10% H2 / N2 reducing atmosphere. ICP-OES analysis showed that the actual Ru loading was 0.41 wt%.

[0059] Comparative Examples 3-4

[0060] The purpose of Comparative Examples 3 and 4 was to investigate the effects of different additives (see Table 3) on the catalytic performance of Ru / MgO materials. The other raw materials, noble metals, magnesium sources, and additives used in Comparative Examples 3 and 4 were the same as those in Example 1 in terms of molar ratio and specific preparation methods.

[0061] Table 3

[0062] Characterization and performance testing

[0063] 1. Characterization The catalysts prepared in the above examples and comparative examples were characterized using the following methods.

[0064] 1) N2 physical adsorption-desorption test: Specific surface area and pore structure were assessed using a gas adsorption analyzer (Micromeritics ASAP 2460), and the specific surface area was calculated using the Brunauer-Emmett-Teller (BET) method. Specifically, the sample was degassed under vacuum at 300 °C prior to N2 physisorption measurements. N2 physisorption-desorption isotherms were collected at -196 °C. The total specific surface area was determined using the Brunauer-Emmett-Teller (BET) equation based on the linear portion of the adsorption isotherms. The total pore volume and average pore size were calculated using the Barrett-Joyner-Halenda (BJH) model.

[0065] Based on the results of N2 physical adsorption-desorption tests (such as...) Figure 1 The isotherm of the material prepared in Example 1 is classified as Type IV, and it exhibits an H3-type hysteresis loop in the medium-to-high specific pressure range (P / P0 approximately 0.4~0.7), which is a typical characteristic of mesoporous materials. Calculations show that the BET specific surface area of ​​the material prepared in Example 1 is 95.16 m². 2 g −1 The total pore volume is 0.64 cm³. 3 g −1 The average pore size is 13.52 nm.

[0066] 2) HAADFF STEM and AC-HAADF-STEM: The particle size distribution of the catalyst was characterized using a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM, model: Talos F200X G2), while aberration-corrected high-angle annular dark-field scanning transmission electron microscope (AC-HAADF-STEM) images were acquired using a FEI Titan G2 60-300 microscope. Figure 2 No obvious Ru nanoparticles were detected in the HAADF-STEM images shown, indicating that Ru species did not undergo significant aggregation; furthermore, Figure 3 The AC-HAADF-STEM images revealed that Ru species were uniformly anchored on the support surface in the form of highly dispersed isolated single atoms, thus confirming the atomic-level dispersion of the active metal at the atomic scale.

[0067] 2. Performance Testing To evaluate the catalytic performance of the catalyst, a double reforming reaction of methane was carried out in a fixed-bed reactor with an inner diameter of 8 mm under atmospheric pressure. The basic test procedures and conditions were as follows: A quartz tube containing 200 mg of catalyst (20–40 mesh) was placed vertically in a fixed-bed furnace. Pure CH4, CO2, and N2 feed gases were introduced at flow rates of 36 mL / min, 12 mL / min, and 12 mL / min, respectively, using N2 as an internal standard. Liquid water was introduced using a syringe pump (flow rate of 0.0193 mL / min), preheated, vaporized, and mixed with the other feed gases before being injected into the fixed-bed reactor. The stoichiometric ratio was fixed at CH4:CO2:N2:H2O = 3:1:1:2, and the WHSV was approximately 25000 mL g. -1 h -1 Residual water was separated using a gas-liquid separator. Measurements were performed using a gas chromatograph equipped with a thermal conductivity detector (TCD). The gas chromatograph used a molecular sieve 5A column to separate H2, N2, CH4, and CO, and a Porapak Q column to separate CO2.

[0068] Conversion rates of CH4 and CO2 (Con.CH4 and Con.CO2) n (H2) / n (CO) is calculated as follows:

[0069] In the formula, In and out refer to the peak area of ​​the gas chromatograph, and F H2 and F CO This refers to the correction factors for H2 and CO. V CH4 For methane flow rate (2.16 L / h), V m The molar volume of the gas under experimental conditions is 22.4 L / mol.

[0070] catalytic activity Based on the above basic test steps and conditions, the test temperature range was controlled at 600~800 ℃, the heating rate was 10 ℃ / min, and a temperature point was taken at 50 ℃ intervals for testing. Each temperature test point was held for 2 h. The test results of the example and comparative examples at a temperature of 800 ℃ are shown in Tables 4 and 5, respectively: Table 4

[0071] Table 5

[0072] stability To evaluate the long-term catalytic stability of the catalyst in Example 1, the test temperature was controlled at 800 °C, the test time at 150 h, and the heating rate at 10 °C / min, based on the basic test steps and conditions described above.

[0073] Test results are as follows Figure 4 As shown, the catalyst prepared in Example 1 maintained relatively stable CH4 and CO2 conversion rates after continuous catalysis of methane double reforming at 800 °C for 150 h, indicating that the catalyst prepared in Example 1 has high stability.

[0074] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A microwave preparation method for MgO-supported noble metal materials, characterized in that, Includes the following steps: S1. A precious metal salt, a magnesium source, and an additive are mixed to obtain a first solid-liquid mixture; the additive includes citric acid. S2. Microwave the first solid-liquid mixture to obtain a second solid-liquid mixture; S3. The second solid-liquid mixture is dried to obtain a solid containing precious metals and magnesium; S4. The solid is calcined in an oxygen-containing atmosphere to obtain the calcined product; S5. The calcined product is subjected to a reduction reaction under a reducing atmosphere.

2. The microwave fabrication method according to claim 1, characterized in that, The precious metal is one or more of Ru, Ir, Rh, Pd, and Pt.

3. The microwave fabrication method according to claim 1 or 2, characterized in that, The magnesium source is one or more of magnesium chloride, magnesium nitrate, magnesium hydroxide, magnesium carbonate, or magnesium acetate.

4. The microwave fabrication method according to claim 1, characterized in that, In step S1, the molar ratio of the sum of the amounts of the precious metal salt and the magnesium source to the amount of the additive is 1:1 to 1:

2.

5. The microwave fabrication method according to claim 1, characterized in that, The microwave power is 80~90 W, the microwave temperature is 100~110 ℃, and the microwave time is 3~4 h.

6. The microwave fabrication method according to claim 1, characterized in that, In step S4, the oxygen-containing atmosphere is one of static or flowing air or a 5% O2 / N2 mixture; the calcination temperature is 500~600 ℃, and the calcination time is 6~8 h.

7. The microwave fabrication method according to claim 1, characterized in that, In step S5, the heating and reduction temperature is 550~650 ℃, and the reduction time is 1~2 h; the reduction atmosphere is one or more of H2, H2 / N2 or H2 / Ar mixture.

8. A MgO-supported noble metal material, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 7.

9. The MgO-supported noble metal material according to claim 8, characterized in that, The loading of noble metals in the MgO-supported noble metal material is 0.1~0.5 wt%.

10. The application of the MgO-supported noble metal material according to claim 9 in the catalytic double reforming of methane.

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