A magnesium-aluminum hydrotalcite-based solid base supported ruthenium catalyst, a preparation method and applications thereof

Abstract

This invention discloses a magnesium-aluminum layered double hydroxide (MLD)-based solid alkali-supported ruthenium catalyst, its preparation method, and its application, belonging to the field of chemical catalytic materials technology. This invention uses magnesium-aluminum MLD as a support, metallic ruthenium as the hydrogenation active component, and magnesium oxide as the alkaline component. The preparation method involves mixing an aqueous dispersion of magnesium-aluminum MLD with frozen magnesium salt and an alkaline solution. The core step is to utilize a freeze-thaw process to perform high-dispersion exfoliation and hydrolysis reactions between the magnesium-aluminum MLD layers, generating magnesium hydroxide attached to the support. This magnesium hydroxide is then pyrolyzed to form a MgO / LDHs solid alkali catalyst precursor. This precursor is dispersed in water, mixed with an aqueous ruthenium salt solution, and reduced with a reducing agent solution to obtain the final catalyst. The freeze-thaw process of this invention significantly improves the dispersibility of the active component, achieving a catalyst specific surface area of ​​185 m² / g and a pore volume of 0.28 m³ / g. Applied to the selective hydrogenation reaction of nitrobenzene using methanol as a hydrogen source, no external alkali is required, achieving a nitrobenzene conversion rate of 61.50% and an aniline selectivity of 100%.

Description

Technical Field

[0001] This invention belongs to the field of chemical catalytic materials technology, specifically relating to a magnesium-aluminum hydrotalcite-based solid alkali supported ruthenium catalyst, its preparation method, and its application in the selective hydrogenation reaction of nitrobenzene using methanol as the hydrogen source. Background Technology

[0002] Aniline is an important organic chemical raw material, mainly produced industrially via the catalytic hydrogenation of nitrobenzene. Traditional hydrogenation routes suffer from high equipment safety requirements and high storage and transportation costs. To overcome these shortcomings, the selective hydrogenation route of nitrobenzene using alcohols as hydrogen sources has attracted attention due to its advantages such as wide availability of raw materials, safe storage and transportation, and mild reaction conditions. However, existing alcohol-based hydrogen supply systems require the addition of large amounts of liquid alkali (such as NaOH or KOH), which significantly increases production costs and wastewater treatment pressure, and is also prone to equipment corrosion, limiting its industrial application. Therefore, there is an urgent need to develop a solid alkali catalyst that can provide a stable, locally alkaline microenvironment.

[0003] While magnesium aluminum layered double hydroxides (LDHs) inherently possess certain basicity sites, their inherent basicity is weak and the supply of basicity is insufficient when applied to the hydrogenation reaction of nitrobenzene using methanol as the hydrogen source. This fails to provide the necessary basic catalytic environment for the reaction, hindering their ability to fully exert their catalytic synergistic effect. To overcome the deficiency of insufficient basicity in LDHs, existing technologies have explored various modification strategies.

[0004] Currently, there are few patents related to combining LDHs with other active metals to expand their applications. Relevant patents include: Patent CN106622220A discloses a hydrogenation catalyst using hydrotalcite as a support to support ruthenium, used for the hydrogenation reaction of diaminodiphenylmethane. However, it only utilizes the weak basicity of hydrotalcite itself and does not solve the core problem of insufficient basicity. If used for the hydrogenation of nitrobenzene using methanol as a hydrogen source, it still faces the challenge of low conversion rate. Patent CN120662349A describes a composite hydrotalcite catalyst containing multiple metals such as ruthenium, magnesium, and aluminum prepared by co-precipitation, used for the dehydrogenation of cyclohexanol coupled with the hydrogenation of phenol. However, this method co-precipitates all metal ions into the hydrotalcite layer in one step, which can generate some basic sites. However, the functions of each component in this structure (such as the structural role of the support, the basic role of the additives, and the catalytic role of the active center) are interdependent and difficult to optimize independently. In particular, the balance between basicity and the dispersion of active metals is difficult to control. Furthermore, to optimize the pore structure of hydrotalcite materials, patent CN113275004A employs a template agent (such as P123) modified co-precipitation method to prepare palladium-supported mesoporous magnesium-aluminum hydrotalcite catalysts. While this method can achieve a larger average pore size (approximately 15.26 nm) by removing the template agent through calcination, its preparation process involves the introduction of the template agent and subsequent high-temperature removal steps, making the process relatively complex. More importantly, this method focuses on adjusting the pore structure and fails to design for the strongly alkaline microenvironment required for the catalytic reaction. Moreover, its application is in the hydrogenation of cumene hydroperoxide, which differs significantly from the hydrogenation reaction system of nitrobenzene using methanol as the hydrogen source.

[0005] In summary, while some researchers have attempted to use solid metal oxides to replace liquid alkalis to compensate for the alkalinity deficiency in the system, conventional loading or composite methods (such as co-precipitation, impregnation, and template methods) often struggle to simultaneously control the microstructure and effectively construct alkaline sites. Specifically, the prepared composite supports generally exhibit defects such as significantly reduced specific surface area, collapsed pore structure, easy aggregation of active components, or insufficient exposure of surface alkaline sites. In particular, how to controllably and highly disperse strong alkaline sites (such as MgO) into the interlayer or surface of LDHs without disrupting their original layered structure, while simultaneously maintaining or even increasing the specific surface area and pore volume of the support and ensuring high dispersion of the subsequently loaded noble metal active components, remains a comprehensive technological challenge. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, the present invention aims to provide a magnesium-aluminum hydrotalcite-based solid alkali supported ruthenium catalyst and its preparation method, with the aim of providing a simple preparation process, low raw material cost, and suitability for industrial production. The prepared catalyst can achieve high dispersion of active components, stable pore structure, and tunable alkalinity.

[0007] Another objective of this invention is to provide the application of the above-mentioned catalyst in the selective hydrogenation reaction of nitrobenzene using methanol as a hydrogen source, so as to achieve high hydrogenation activity of nitrobenzene and high selectivity of aniline without the need for additional alkali.

[0008] The above-mentioned objective of this invention is achieved through the following technical solutions.

[0009] This invention provides a method for preparing a magnesium aluminum layered double hydroxide (LDHs)-based solid base supported ruthenium catalyst. Using LDHs as the base support, MgO is loaded onto the LDHs via a freeze-thaw precipitation method to obtain the LDH-based solid base support. Then, a ruthenium catalyst supported by the Ru active component is introduced. The steps are as follows:

[0010] (1) Solid magnesium aluminum hydrotalcite (LDHs) powder is mixed with water at a mass ratio of 1:100 to 1:1000, stirred at room temperature and then ultrasonically dispersed to obtain an LDHs dispersion;

[0011] (2) Freeze a magnesium salt solution with a concentration of 0.002~0.008 mol / L into ice blocks, wherein the mass ratio of the magnesium salt (based on pure solute) to the LDHs in step (1) is 1:5~8; the magnesium salt in step (2) is either magnesium chloride hexahydrate or magnesium nitrate hexahydrate.

[0012] (3) Freeze an alkaline solution with a concentration of 0.01~0.03mol / L into ice cubes. The mass ratio of the alkaline solution (based on the total mass of the solution) to the LDHs in step (2) is 1:3~12. The alkaline solution is either sodium hydroxide or potassium hydroxide.

[0013] (4) The ice obtained in steps (2) and (3) is added to the LDHs dispersion obtained in step (1) at room temperature by melting and releasing. The mixture is stirred while melting until the ice is completely melted. The ice is then separated, washed, and dried at 80-100℃ for 10-12 hours to obtain the Mg(OH)2 / LDHs catalyst precursor.

[0014] (5) The Mg(OH)2 / LDHs catalyst precursor obtained in step (4) is calcined in a reducing atmosphere and cooled to obtain MgO / LDHs solid base catalyst precursor;

[0015] (6) The MgO / LDHs solid base catalyst precursor obtained in step (5) is uniformly dispersed in water, and a ruthenium precursor solution is added and stirred. Then a reducing agent is added to carry out a reduction reaction to obtain the magnesium aluminum hydrotalcite-based solid base supported ruthenium catalyst.

[0016] The ruthenium precursor is any one of ruthenium trichloride, ruthenium trichloride hydrate, and ruthenium acetylacetonate; the reducing agent is any one of sodium borohydride, hydrazine hydrate, and hydrogen.

[0017] Furthermore, the magnesium salt in step (2) is magnesium nitrate hexahydrate.

[0018] Furthermore, the alkaline solution in step (3) is sodium hydroxide.

[0019] Furthermore, the calcination in a reducing atmosphere in step (5) refers to calcination in a hydrogen atmosphere at 400~600℃ for 1~4 hours.

[0020] Furthermore, the calcination in a reducing atmosphere in step (5) refers to calcination in a hydrogen atmosphere at 500°C for 2 hours.

[0021] Furthermore, in step (6), the ruthenium precursor is ruthenium trichloride (RuCl3), and the reducing agent is sodium borohydride (NaBH4).

[0022] The present invention also provides a magnesium-aluminum hydrotalcite-based solid alkali supported ruthenium catalyst prepared by the above method. The catalyst uses LDHs as a support and magnesium oxide as an alkaline component. The optimal catalyst has a specific surface area of ​​185 m² / g, a pore volume of 0.28 cm³ / g, and the ruthenium particles have a stable structure without obvious agglomeration.

[0023] The present invention also provides the application of the above catalyst in the selective hydrogenation reaction of nitrobenzene with methanol as the hydrogen source, wherein the product of the reaction is aniline.

[0024] The selective hydrogenation performance of nitrobenzene using a magnesium-aluminum layered double hydroxide (TLD)-based solid base supported on ruthenium catalyst was tested according to the following steps and conditions: The selective hydrogenation reaction of nitrobenzene was carried out in a 60 mL batch high-pressure reactor. 0.2 mL of nitrobenzene, 9.8 mL of methanol, and 10 mL of Ru-MgO / LDHs aqueous dispersible catalyst were added to the reactor. After thorough stirring, 2 MPa of nitrogen gas was introduced into the reactor as a protective atmosphere. The temperature was raised to 150 °C under continuous stirring, and the reaction was carried out for 2 hours. After the reaction, the peak area method was used to analyze the results using an Agilent 8806 gas chromatograph.

[0025] Compared with the prior art, the present invention has the following technical effects:

[0026] (1) Mg(OH)2 is generated in situ between magnesium aluminum hydrotalcite nanosheets by freeze-thaw precipitation method. After pyrolysis, MgO / LDHs solid alkali carrier is obtained. The preparation process is simple and low cost, and is suitable for industrial production.

[0027] (2) It melts naturally at room temperature, avoiding the violent agglomeration in the traditional precipitation method and significantly improving the dispersibility of the active components; in addition, the introduction of MgO further improves the specific surface area and pore volume of the catalyst, with the optimal catalyst having a specific surface area of ​​up to 185 m² / g and a pore volume of 0.28 m³ / g.

[0028] (3) The catalyst of the present invention has a stable structure and good Ru nanoparticle dispersion. By flexibly adjusting the MgO loading, the alkali strength and alkali amount can be controlled and the hydrogenation performance of the catalyst can be optimized.

[0029] (4) The catalyst is used for selective hydrogenation of nitrobenzene with methanol as hydrogen source. No external alkali is required. The hydrogenation activity of nitrobenzene is high and the conversion rate of nitrobenzene can reach 61.50%. The selectivity of aniline can reach as high as 100%. At the same time, it can also avoid equipment corrosion and wastewater generation. Attached Figure Description

[0030] Figure 1 The image shows the XRD pattern of the Ru-MgO / LDHs-n (n=0, 2, 4, 6) catalyst of this invention.

[0031] Figure 2 This is a nitrogen physisorption isotherm diagram of the Ru-MgO / LDHs-n (n=0, 2, 4, 6) catalyst of the present invention.

[0032] Figure 3 This is a CO2-TPD diagram of the Ru-MgO / LDHs-n (n=0, 2, 4, 6) catalyst of the present invention.

[0033] Figure 4 These are SEM and TEM images of the Ru-MgO / LDHs-4 catalyst of this invention. Detailed Implementation

[0034] To further illustrate the present invention, the following embodiments are provided, but they do not limit the scope of the invention as defined by the claims.

[0035] I. Preparation of Magnesium Aluminum Layered Double Hydrotalcite-Based Solid Base Supported Ruthenium Catalyst

[0036] Example 1

[0037] Weigh 0.1 g of LDHs solution, dilute with 50 mL of water, and stir thoroughly on a magnetic stirrer for 2 hours. Then, ultrasonically disperse for 20 min to obtain a uniform and stable LDHs aqueous dispersion. Freeze 20 mL of 0.00248 mol / L magnesium nitrate hexahydrate solution and 20 mL of 0.0099 mol / L sodium hydroxide solution into ice cubes, and then slowly melt them naturally at room temperature and dropwise add them to a continuously stirred hydrotalcite solution. After the ice cubes have completely melted, the mixture is centrifuged and washed three times. The resulting solid product is dried at 80 °C for 10 hours and then ground into powder. The obtained powder is calcined at 500 °C for 2 hours in a hydrogen atmosphere and cooled to room temperature to obtain a 2 wt% magnesium oxide-supported magnesium aluminum hydrotalcite solid base catalyst precursor, denoted as MgO / LDHs-2. Next, 0.025 g of MgO / LDHs-2 support was weighed and dissolved in 25 ml of deionized water. Then, 2.2 ml of a 0.0152 mol / L ruthenium trichloride (RuCl3) aqueous solution was added. The mixture was magnetically stirred at 2000 r / min for 30 minutes at room temperature. Subsequently, while continuing stirring, 5 ml of a 0.21 mol / L sodium borohydride (NaBH4) solution was slowly added dropwise at a rate of approximately 10 s / drop for reduction. After the addition was complete, the reaction was stirred for another 2 h to ensure complete reduction. After the reaction was complete, an appropriate amount of deionized water was added for dilution, and after thorough stirring, a water-dispersible Ru-MgO / LDHs-2 catalyst with a ruthenium element concentration of 0.0013376 mol / L was obtained.

[0038] Example 2

[0039] Weigh 0.1 g of LDHs solution, dilute with 50 mL of water, and stir thoroughly on a magnetic stirrer for 2 hours. Then, ultrasonically disperse for 20 min to obtain a uniform and stable LDHs aqueous dispersion. Freeze 20 mL of 0.00496 mol / L magnesium nitrate hexahydrate solution and 20 mL of 0.0198 mol / L sodium hydroxide solution into ice cubes, and then slowly melt them naturally at room temperature and dropwise add them to a continuously stirred hydrotalcite solution. After the ice cubes have completely melted, the mixture is centrifuged and washed three times. The resulting solid product is dried at 80 °C for 10 hours and then ground into powder. The obtained powder is calcined at 500 °C for 2 hours in a hydrogen atmosphere and cooled to room temperature to obtain a 4 wt% magnesium oxide-supported magnesium aluminum hydrotalcite solid base catalyst precursor, denoted as MgO / LDHs-4. Next, 0.025 g of MgO / LDHs-4 support was weighed and dissolved in 25 ml of deionized water. Then, 2.2 ml of a 0.0152 mol / L ruthenium trichloride (RuCl3) aqueous solution was added. The mixture was magnetically stirred at 2000 r / min for 30 minutes at room temperature. Subsequently, while continuing stirring, 5 ml of a 0.21 mol / L sodium borohydride (NaBH4) solution was slowly added dropwise at a rate of approximately 10 s / drop for reduction. After the addition was complete, the reaction was stirred for another 2 h to ensure complete reduction. After the reaction was complete, an appropriate amount of deionized water was added for dilution, and after thorough stirring, a water-dispersible Ru-MgO / LDHs-4 catalyst with a ruthenium element concentration of 0.0013376 mol / L was obtained.

[0040] Example 3

[0041] Weigh 0.1 g of LDHs solution, dilute with 50 mL of water, and stir thoroughly on a magnetic stirrer for 2 hours. Then, ultrasonically disperse for 20 min to obtain a uniform and stable LDHs aqueous dispersion. Freeze 20 mL of 0.00744 mol / L magnesium nitrate hexahydrate solution and 20 mL of 0.0297 mol / L sodium hydroxide solution into ice cubes, and then slowly melt them naturally at room temperature and dropwise add them to a continuously stirred hydrotalcite solution. After the ice cubes have completely melted, the mixture is centrifuged and washed three times. The resulting solid product is dried at 80 °C for 10 hours and then ground into powder. The obtained powder is calcined at 500 °C for 2 hours in a hydrogen atmosphere and cooled to room temperature to obtain a 6 wt% magnesium oxide-supported magnesium aluminum hydrotalcite solid base catalyst precursor, denoted as MgO / LDHs-6. Next, 0.025 g of MgO / LDHs-6 support was weighed and dissolved in 25 ml of deionized water. Then, 2.2 ml of a 0.0152 mol / L ruthenium trichloride (RuCl3) aqueous solution was added. The mixture was magnetically stirred at 2000 r / min for 30 minutes at room temperature. Subsequently, while continuing stirring, 5 ml of a 0.21 mol / L sodium borohydride (NaBH4) solution was slowly added dropwise at a rate of approximately 10 s / drop for reduction. After the addition was complete, the reaction was stirred for another 2 h to ensure complete reduction. After the reaction was complete, an appropriate amount of deionized water was added for dilution, and after thorough stirring, a water-dispersible Ru-MgO / LDHs-6 catalyst with a ruthenium element concentration of 0.0013376 mol / L was obtained.

[0042] The magnesium-aluminum layered double hydroxide-based solid alkali supported ruthenium catalyst of this invention was characterized by XRD. X-ray diffraction (XRD) of the catalyst was performed on a Rigaku X-ray diffractometer (Ultima IV type) in Japan. The X-ray diffraction (XRD) analysis results are as follows: Figure 1 As shown, all catalysts exhibit characteristic peaks of the layered structure of LDHs. With increasing MgO loading, characteristic diffraction peaks attributable to MgO appear in the spectra, indicating that MgO was successfully loaded and influenced the crystal structure of LDHs.

[0043] In this invention, the Ru-MgO / LDHs-4 catalyst was tested for nitrogen physical adsorption using a Micromeritics ASAP 2420 physical adsorption analyzer. The results are as follows: Figure 2 As shown in the figure. Nitrogen physical adsorption tests indicate that Ru-MgO / LDHs-4 has a specific surface area of ​​185 m² / g and a pore volume of 0.28 cm³ / g, and its structure is stable with no obvious agglomeration.

[0044] This invention uses the CO2-TPD method on a CHEMBET-300 chemisorption analyzer manufactured by Quanta Computer in the United States to test the relationship between the basicity and basicity of Ru-MgO / LDHs-4 and magnesium oxide. The results are as follows: Figure 3 As shown. From Figure 3 The data shows that magnesium aluminum hydrotalcite contains desorption peaks, indicating that it possesses a certain degree of alkalinity. Ru-MgO / LDHs-4 exhibits significant desorption peaks between 100℃ and 500℃, indicating the presence of weakly alkaline (below 200℃) and moderately alkaline (200~400℃) sites. The above analysis suggests that the introduction of magnesium oxide significantly enhances the alkalinity of the catalyst.

[0045] The Ru-MgO / LDHs-4 catalyst was characterized by scanning electron microscopy and transmission electron microscopy (SEM, TEM). The morphology of the catalyst was observed using a Zeiss Gemini SEM 360 from FEI. SEM and TEM showed that the catalyst has a layered porous nanosheet structure, with Ru nanoparticles having an average particle size of approximately 1.61 nm, and MgO and Ru being co-dispersed.

[0046] Comparison Example 1

[0047] Weigh 0.1 g of LDHs powder, add 50 mL of water, stir for 2 hours, and ultrasonically disperse for 20 min to obtain an aqueous LDHs dispersion. Without performing the freeze-thaw precipitation and loading of MgO with magnesium salt and alkaline solution, directly calcine the LDHs powder at 500℃ in a hydrogen atmosphere for 2 hours, and cool to obtain the LDHs support. Dissolve 0.025 g of the LDHs support in 25 mL of deionized water, add 2.2 mL of 0.0152 mol / L ruthenium trichloride solution, stir at 2000 r / min for 30 minutes at room temperature, and reduce by adding 5 mL of 0.21 mol / L sodium borohydride solution dropwise at a rate of 10 s / drop. After the addition is complete, continue stirring for 2 hours, and dilute to obtain an aqueous Ru / LDHs comparative catalyst.

[0048] Comparison Example 2

[0049] Weigh 0.1 g of LDHs powder, add 50 mL of water, stir for 2 hours, and ultrasonically disperse for 20 min to obtain an LDHs aqueous dispersion. A comparative catalyst with the same MgO loading (e.g., 4 wt%) was prepared by directly mixing LDHs with a magnesium salt solution and then adding alkali for precipitation (without freezing into ice and thawing to release the precipitate). This catalyst is denoted as Ru-MgO / LDHs-4(un)

[0050] II. Activity Evaluation of the Hydrotalcite-Based Solid Alkali-Supported Ruthenium Catalyst of the Present Invention

[0051] Example 4

[0052] Evaluation of the selective hydrogenation activity of ruthenium catalyst supported on a magnesium-aluminum layered double hydroxide (LDH) solid base in the selective hydrogenation of nitrobenzene using methanol as a hydrogen source: The hydrogenation reaction of nitrobenzene using the Ru-MgO / LDHs catalyst was carried out in a 60 mL batch high-pressure reactor. The specific steps and conditions were as follows: 0.2 mL of nitrobenzene, 9.8 mL of methanol, and 10 mL of ruthenium catalyst supported on a layered double hydroxide (LDH) solid base were added to the high-pressure reactor. After stirring thoroughly, nitrogen gas at 2 MPa was introduced into the reactor as a protective atmosphere. The temperature was raised to 150 °C under continuous stirring, and the reaction was carried out for 2 hours. After the reaction, the peak area method was used to analyze the reaction results using an Agilent 8806 gas chromatograph.

[0053] The activity evaluation of Ru / LDHs, Ru-MgO / LDHs-2, Ru-MgO / LDHs-4, Ru-MgO / LDHs-4 (untreated), and Ru-MgO / LDHs-6 catalysts in the selective hydrogenation of nitrobenzene with methanol as the hydrogen source is shown in Table 1.

[0054] Table 1. Selective hydrogenation performance of ruthenium nitrobenzene catalysts with different magnesium oxide loadings and solid bases supported on magnesium aluminum hydrotalcite.

[0055] catalyst Reaction temperature (°C) Nitrobenzene conversion rate (%) Aniline selectivity (%) <![CDATA[Space-time yield of aniline (h -1 )]]> Ru / LDHs 150 2.06 100 2.51 Ru-MgO / LDHs-2 150 6.60 100 8.04 Ru-MgO / LDHs-4 150 15.70 100 19.13 Ru-MgO / LDHs-4 (not yet available) 150 3.36 100 4.10 Ru-MgO / LDHs-6 150 8.68 100 10.58 Ru-MgO / LDHs-4 180 61.50 100 74.95

[0056] Reaction conditions: 10 ml catalyst, 2.0 mmol nitrobenzene, 9.8 ml methanol, 2 MPa N2, 2 h, 1800 r / min.

[0057] STY represents the formula for calculating the molar amount of aniline generated per mole of active component per unit time:

[0058] STY = The unit is h -1

[0059] Table 1 shows that the introduction of MgO significantly improved the catalytic activity. The conversion rate of the unmodified Ru / LDHs catalyst was only 2.06%, while the activity was greatly improved after loading with MgO. There is an optimal value for the MgO loading. When the loading is 4 wt% (Ru-MgO / LDHs-4), the conversion rate reaches 15.70% at 150℃, and the space-time yield is 19.13 h⁻¹; too low a loading (2 wt%) or too high a loading (6 wt%) both lead to a decrease in activity. Compared with Example 2 (Ru-MgO / LDHs-4), the catalytic activity of Comparative Example 1 (Ru / LDHs) (conversion rate 2.06%) is significantly lower than that of the sample with introduced MgO (conversion rate 15.70%). Compared with Example 2 (Ru-MgO / LDHs-4 (untreated)), its catalytic activity (conversion rate 3.36%) was significantly lower than that of the sample with introduced MgO (conversion rate 15.70%). When the reaction temperature was raised to 180℃, the conversion rate further increased to 61.50%, and the space-time yield reached 74.95 h⁻¹, which is the best performance. This comparative result proves that the specific technical solution of this invention has outstanding effects in the freeze-thaw precipitation method of this invention. The above results show that this invention successfully prepared a magnesium-aluminum layered double hydroxide-based solid base supported ruthenium catalyst with high specific surface area, suitable pore structure and tunable alkalinity through the freeze-thaw precipitation method. This catalyst exhibits excellent catalytic performance in the hydrogenation of nitrobenzene to aniline using methanol as a hydrogen source, and the preparation method is simple and has potential for industrial application.

Claims

1. A method for preparing a magnesium-aluminum hydrotalcite-based solid alkali supported ruthenium catalyst, characterized in that... Includes the following steps: (1) Mix LDHs powder with water at a mass ratio of 1:100 to 1:1000, stir at room temperature and then ultrasonically disperse to obtain LDHs dispersion; (2) Freeze a magnesium salt solution with a concentration of 0.002~0.008 mol / L into ice blocks. The mass ratio of the magnesium salt to the LDHs in step (1) is 1:5~8. The magnesium salt is measured as a solute. The magnesium salt is magnesium nitrate hexahydrate or magnesium chloride hexahydrate. (3) Freeze an alkaline solution with a concentration of 0.01~0.03mol / L into ice cubes. The mass ratio of the alkaline solution to the LDHs in step (1) is 1:3~12. The alkaline solution is measured by the total mass of the solution. The alkaline solution is sodium hydroxide or potassium hydroxide. (4) The ice obtained in steps (2) and (3) is added to the LDHs dispersion obtained in step (1) at room temperature by melting and releasing. The mixture is stirred while melting until the ice is completely melted. The ice is then separated, washed, and dried at 80-100℃ for 10-12 hours to obtain the Mg(OH)2 / LDHs catalyst precursor. (5) The Mg(OH)2 / LDHs solid base catalyst precursor obtained in step (4) is calcined in a reducing atmosphere and cooled to obtain MgO / LDHs solid base catalyst precursor; (6) The MgO / LDHs solid base catalyst precursor obtained in step (5) is uniformly dispersed in water, a ruthenium precursor solution is added and stirred, and then a reducing agent is added to carry out a reduction reaction to obtain the catalyst. The ruthenium precursor is any one of ruthenium trichloride, ruthenium trichloride hydrate, and ruthenium acetylacetonate; the reducing agent is any one of sodium borohydride, hydrazine hydrate, and hydrogen.

2. The preparation method of the magnesium-aluminum hydrotalcite-based solid alkali supported ruthenium catalyst as described in claim 1, characterized in that, The magnesium salt in step (2) is magnesium nitrate hexahydrate.

3. The preparation method of the magnesium-aluminum hydrotalcite-based solid alkali supported ruthenium catalyst as described in claim 1, characterized in that, The alkaline solution in step (3) is sodium hydroxide.

4. The preparation method of the magnesium-aluminum hydrotalcite-based solid alkali supported ruthenium catalyst as described in claim 1, characterized in that, The calcination in a reducing atmosphere in step (5) refers to calcination in a hydrogen atmosphere at 400~600℃ for 1~4 hours.

5. The method for preparing the magnesium-aluminum hydrotalcite-based solid alkali-supported ruthenium catalyst as described in claim 4, characterized in that, The calcination in a reducing atmosphere in step (5) refers to calcination in a hydrogen atmosphere at 500°C for 2 hours.

6. The method for preparing the magnesium-aluminum layered double hydroxide-based solid alkali-supported ruthenium catalyst as described in claim 1, characterized in that, In step (6), the ruthenium precursor is ruthenium trichloride and the reducing agent is sodium borohydride.

7. The magnesium-aluminum hydrotalcite-based solid base supported ruthenium catalyst obtained by the preparation method of claim 1.

8. The application of the magnesium-aluminum hydrotalcite-based solid base supported ruthenium catalyst as described in claim 7 in the selective hydrogenation reaction of nitrobenzene using methanol as the hydrogen source.

9. The application as described in claim 8, characterized in that: The product of the selective hydrogenation reaction of nitrobenzene is aniline.

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