A method for preparing a hydrotalcite-supported catalyst in an ultrasound-assisted microreactor

Abstract

This invention discloses a rapid and continuous preparation method for ultrasonically assisted hydrotalcite-supported catalysts, belonging to the field of inorganic material preparation technology. The method involves preparing solutions A, B, and C using metal salts, sodium carbonate, and an active metal salt. Solutions A and B are injected into one end of a microchannel reactor to undergo a precipitation reaction, yielding a precursor slurry containing LDH particles. This slurry is then mixed uniformly with solution C in another microchannel reactor. Ultrasonic-assisted isomorphic substitution of active metal ions onto the LDH and propagates to the other end of the microchannel reactor before being discharged. The discharged material is then crystallized, washed, dried, and subsequently calcined and reduced to obtain the hydrotalcite-supported catalyst. This method utilizes a reactor combined with ultrasonic assistance to effectively enhance mass transfer and diffusion, eliminating localized concentration inconsistencies during the preparation process. The isomorphic substitution loading method improves the dispersion of the active catalyst components, enabling continuous production.

Description

Technical Field

[0001] This invention belongs to the field of inorganic material preparation technology, specifically relating to a rapid and continuous preparation method for ultrasonic-assisted hydrotalcite-supported catalysts. Background Technology

[0002] With the upgrading of the global energy structure and increasingly stringent environmental protection requirements, efficient catalytic conversion technology has become crucial for solving energy shortages and environmental pollution. Among various catalytic systems, Ni-based catalysts, due to their abundant reserves, low cost, and high catalytic activity, have become an ideal alternative to precious metal catalysts and are widely used in various catalytic reactions, especially suitable for reactions such as CO2 reduction, NH3 decomposition, and furfural hydrogenation. They can meet the needs of greenhouse gas resource utilization and fine chemical product synthesis, and have significant industrial application prospects in the fields of energy conversion and environmental governance.

[0003] Under high-temperature reaction conditions, Ni active components are prone to agglomeration and sintering, leading to a reduction in catalyst active sites. Simultaneously, carbon deposits easily form during the reaction, encapsulating active metal sites and causing rapid catalyst deactivation, severely limiting its industrial application and lifespan. Ni-based derivative catalysts prepared using hydrotalcite and hydrotalcite-like materials (LDH) as precursors possess high specific surface area and tunable acid-base properties. Furthermore, their unique lamellar structure allows active metal ions to embed into vacancies in the hydrotalcite lamellar metals, forming a stable lattice substitution structure. This not only significantly improves the dispersion of the active metal in the support but also greatly enhances the metal-support interaction, effectively suppressing the agglomeration and sintering of the active metal, achieving precise loading of the active components, and ensuring the catalyst's catalytic activity and structural stability.

[0004] The structure of the precursor largely determines the structure and performance of the derived catalyst. Currently, Ni-based layered double hydroxide (LDH) precursors are commonly prepared through co-precipitation, which can achieve high Ni loading. However, the mixing process of the alkaline solution and metal salt solution in traditional co-precipitation methods is difficult to control, resulting in uneven local reaction conditions and poor catalyst performance repeatability, making it difficult to meet the requirements for catalyst performance stability in industrial production. Microchannel reactors, as a novel continuous reaction device, possess high mass and heat transfer efficiency and precise material mixing control capabilities, enabling rapid and uniform mixing of reactants, eliminating local backmixing and concentration gradient problems, and providing a stable reaction environment for the continuous preparation of LDH. Simultaneously, microchannel reactors allow for precise control of reaction parameters, providing controllable reaction conditions for isomorphous substitution of active metal ions. Combined with ultrasonic assistance, this can further accelerate the diffusion of active metal ions, improve their contact efficiency with vacancies in the LDH layers, and significantly enhance the reaction efficiency and uniformity of isomorphous substitution. Summary of the Invention

[0005] This invention aims to overcome the shortcomings of existing technologies and provide a rapid and continuous preparation method for hydrotalcite-supported catalysts. The method uses sodium carbonate alkaline solution as a precipitant, which is uniformly mixed with a metal salt solution in a microchannel reactor. The reaction rapidly forms an LDH particle slurry within the reactor, and then, under ultrasonic assistance, active metal ions are loaded onto the LDH support via isomorphic substitution. In this method, the microchannel reactor, with its high mass and heat transfer efficiency, enables rapid and thorough mixing of the reactants, creating favorable reaction conditions for the rapid formation of LDH particles and subsequent isomorphic substitution reactions. Ultrasonic action effectively accelerates the diffusion rate of active metal ions in the solution, allowing them to more efficiently contact the vacancies formed on the LDH layers, thereby achieving efficient loading of active metal ions onto the LDH support. Compared with traditional preparation processes, this invention integrates the preparation of the hydrotalcite support with the active metal loading and modification process, achieving continuous operation of both processes, significantly improving catalyst production efficiency, and providing continuous and automated operation throughout the entire preparation process. Meanwhile, relying on the isomorphous substitution loading method, the dispersion of the loaded metal on the hydrotalcite support can be significantly improved, ensuring the catalytic performance of the catalyst.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A rapid preparation method for an ultrasound-assisted hydrotalcite-supported catalyst includes the following steps: (1) Dissolve the metal salt in deionized water and stir at room temperature until completely dissolved to obtain a uniform and clear solution A; dissolve anhydrous sodium carbonate in deionized water and stir at room temperature until no solid particles remain to obtain a uniform solution B; dissolve the active metal salt in deionized water and stir to obtain a uniform solution C. (2) Liquid A and liquid B are continuously fed into a micro mixer by a horizontal flow pump for rapid and thorough mixing, and then fed into a microchannel reactor for continuous precipitation reaction to obtain a carrier slurry containing LDH particles. The carrier slurry is then thoroughly mixed with liquid C and ultrasonically treated to obtain the product slurry.

[0007] (3) Liquidize the product slurry obtained in step (2), separate it, wash it with deionized water until neutral, and dry it to obtain LDH solid.

[0008] (4) The LDH solid obtained in step (3) is calcined and reduced to obtain the corresponding catalyst.

[0009] Furthermore, the metal salt mentioned in step (1) is two of the following: nitrates or chlorides of nickel, magnesium, aluminum, zinc, zirconium, and calcium.

[0010] Furthermore, the active metal salt mentioned in step (1) is one of the nitrates or chlorides of nickel, ruthenium, platinum, palladium and copper.

[0011] Furthermore, the total concentration of the metal salt ions in step (1) is 0.3–0.54 mol·L⁻¹. -1 .

[0012] Furthermore, the molar ratio of divalent to trivalent metal salt ions in step (1) is 2:1.

[0013] Furthermore, the concentration of sodium carbonate in step (1) is 0.35–0.63 mol·L⁻¹. -1 .

[0014] Furthermore, the molar concentration of the active metal salt ions in step (1) is 2–45 mmol·L⁻¹. -1 .

[0015] Furthermore, the flow rate of the advection pump mentioned in step (2) is 1–40 mL·min. -1 .

[0016] Furthermore, the inner diameter of the microchannel reactor described in step (2) is 0~6 mm and the effective length is 0~20 m.

[0017] Furthermore, the reaction temperature in step (2) is 30–300 °C.

[0018] Furthermore, the power of the ultrasonic treatment in step (2) is 50 to 2000 W.

[0019] Furthermore, the calcination and reduction temperatures in step (4) are 300~1000 ℃ and 200~550 ℃, respectively.

[0020] Application of the hydrotalcite-supported catalyst prepared by the method described above in the hydrogenation catalytic reaction of benzyltoluene.

[0021] The beneficial effects of this invention are as follows: (1) The preparation of hydrotalcite support and the process of isomorphous substitution of active metal are integrated into the design. The continuous conveying, mixing and precipitation reaction of materials are realized by relying on the horizontal flow pump and microchannel reactor. Compared with the traditional stepwise preparation process, the efficient mass and heat transfer characteristics of microchannel reactor allow the reactants to be mixed quickly and fully, which greatly shortens the preparation cycle of LDH supported catalyst. Moreover, the parameters of the entire preparation process are controllable and can be automated, which significantly improves the production efficiency and has good prospects for industrial scale-up application.

[0022] (2) Ultrasonic assistance effectively accelerates the diffusion rate of active metal ions in the solution, enabling them to contact the vacancies formed by the LDH layer more efficiently to complete isomorphic substitution, significantly improving the dispersion of the loaded metal on the hydrotalcite support, avoiding the problem of active metal agglomeration, and the isomorphic substitution loading method makes the active component more firmly bonded to the support, further improving the structural stability of the catalyst. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the continuous preparation process of the hydrotalcite-supported catalyst of the present invention.

[0024] Figure 2 This is a TEM image of the Ni / MgAl-LDH catalyst prepared in Example 1 of the present invention.

[0025] Figure 3 The image shows the XRD pattern of the Ru / NiAl-LDH catalyst prepared in Example 4 of this invention. Detailed Implementation

[0026] To make the content of this invention easier to understand, the technical solution of this invention will be further described below with reference to specific embodiments, but this invention is not limited thereto.

[0027] Figure 1 This is a schematic diagram of the continuous preparation process of the hydrotalcite-supported catalyst of the present invention. The apparatus mainly includes: a liquid pump, a gas mass flow meter, a micromixer, a microchannel reactor, a water bath, and an ultrasonic generator.

[0028] The hydrogenation activity evaluation of the hydrotalcite-supported catalyst was conducted on a small-scale fixed-bed hydrogenation experimental setup: the catalyst was loaded into a fixed-bed reactor, and hydrogen and benzyltoluene were pumped into the reactor at a molar ratio of 6.6:1 for the reaction. The reaction temperature was 140℃, the reaction pressure was 2 MPa, and the space velocity was 0.5 h⁻¹. -1 Raw materials and products were analyzed using gas chromatography.

[0029] Example 1: Prepare solution A with a magnesium ion concentration of 0.2 mol·L⁻¹. -1 The aluminum ion concentration is 0.1 mol·L⁻¹ -1 Prepare solution B with a sodium carbonate concentration of 0.35 mol·L⁻¹. -1 Prepare solution C with a nickel ion concentration of 45 mmol·L⁻¹. -1 The flow rates of solutions A, B, and C are 2 mL / min. -1 2.5 mL·min -1 and 2 mL·min -1The ultrasonic-assisted power was 200 W and the ultrasonic frequency was 20 kHz. The LDH slurry was continuously collected and post-treated to obtain the Ni / MgAl-LDH catalyst.

[0030] The specific surface area of ​​the obtained catalyst is 109.3 m². 2 ·g -1 The pore volume is 0.322 cm³. 3 ·g -1 The obtained catalyst was tested using the above-mentioned activity testing method. After analysis, the conversion rate of benzyltoluene was 97.91%, and the selectivity for fully hydrogenated benzyltoluene was 30.26%.

[0031] Example 2: Prepare solution A with a zirconium ion concentration of 0.2 mol·L⁻¹. -1 The aluminum ion concentration is 0.1 mol·L⁻¹ -1 Prepare solution B with a sodium carbonate concentration of 0.35 mol·L⁻¹. -1 Prepare solution C with a nickel ion concentration of 45 mmol·L⁻¹. -1 The flow rates of solutions A, B, and C are 2 mL / min. -1 2.5 mL·min -1 and 2 mL·min -1 The ultrasonic-assisted power was 200 W and the ultrasonic frequency was 20 kHz. The LDH slurry was continuously collected and post-treated to obtain the Ni / ZrAl-LDH catalyst.

[0032] The specific surface area of ​​the obtained catalyst is 111.2 m². 2 ·g -1 The pore volume is 0.331 cm. 3 ·g -1 The obtained catalyst was tested using the above-described activity testing method. Analysis showed a benzyltoluene conversion rate of 98.32% and a selectivity of 31.17% for fully hydrogenated benzyltoluene.

[0033] Example 3: Preparation of solution A with a nickel ion concentration of 0.2 mol·L⁻¹ -1 The aluminum ion concentration is 0.1 mol·L⁻¹ -1 Prepare solution B. The sodium carbonate concentration is 0.35 mol·L⁻¹. -1 Prepare solution C with a ruthenium ion concentration of 2.6 mmol·L⁻¹. -1 The flow rates of solutions A, B, and C are 2 mL / min. -1 2.5 mL·min -1 and 2 mL·min -1 The ultrasonic-assisted power was 200 W and the ultrasonic frequency was 20 kHz. The LDH slurry was continuously collected and post-treated to obtain the Ru / NiAl-LDH catalyst.

[0034] The specific surface area of ​​the obtained catalyst is 124.5 m². 2 ·g -1 The pore volume is 0.341 cm. 3 ·g -1 The obtained catalyst was tested using the above-described activity testing method. Analysis showed that the benzyltoluene conversion rate was 100.0%, and the selectivity for fully hydrogenated benzyltoluene was 91.98%.

[0035] Example 4: Prepare solution A with a nickel ion concentration of 0.2 mol·L⁻¹. -1 The aluminum ion concentration is 0.1 mol·L⁻¹ -1 Prepare solution B. The sodium carbonate concentration is 0.35 mol·L⁻¹. -1 Prepare solution C with a ruthenium ion concentration of 10.4 mmol·L⁻¹. -1 The flow rates of solutions A, B, and C are 2 mL / min. -1 2.5 mL·min -1 and 2 mL·min -1 The ultrasonic-assisted power was 200 W and the ultrasonic frequency was 20 kHz. The LDH slurry was continuously collected and post-treated to obtain the Ru / NiAl-LDH catalyst.

[0036] The specific surface area of ​​the obtained catalyst is 123.7 m². 2 ·g -1 The pore volume is 0.342 cm³. 3 ·g -1 The obtained catalyst was tested using the above-described activity testing method. Analysis showed that the benzyltoluene conversion rate was 100.0%, and the selectivity for fully hydrogenated benzyltoluene was 99.41%.

[0037] Example 5: Prepare solution A with a magnesium ion concentration of 0.2 mol·L⁻¹. -1 The aluminum ion concentration is 0.1 mol·L⁻¹ -1 Prepare solution B. The sodium carbonate concentration is 0.35 mol·L⁻¹. -1 Prepare solution C with a palladium ion concentration of 3 mmol·L⁻¹. -1 The flow rates of solutions A, B, and C are 2 mL / min. -1 2.5 mL·min -1 and 2 mL·min -1 The ultrasonic-assisted power was 200 W and the ultrasonic frequency was 20 kHz. The LDH slurry was continuously collected and post-treated to obtain the Ru / MgAl-LDH catalyst.

[0038] The specific surface area of ​​the obtained catalyst is 124.3 m². 2 ·g-1 The pore volume is 0.344 cm. 3 ·g -1 The obtained catalyst was tested using the above-described activity testing method. Analysis showed that the benzyltoluene conversion rate was 100.0%, and the selectivity for fully hydrogenated benzyltoluene was 46.31%.

[0039] Comparative Example 1: Prepare solution A with a magnesium ion concentration of 0.2 mol·L⁻¹. -1 The aluminum ion concentration is 0.1 mol·L⁻¹ -1 The nickel ion concentration was 45 mmol·L⁻¹. -1 Prepare solution B with a sodium carbonate concentration of 0.35 mol·L⁻¹. -1 Prepare solution C using pure deionized water; the flow rates of solutions A, B, and C are 2 mL / min. -1 2.5 mL·min -1 and 2 mL·min -1 The ultrasonic-assisted power was 200 W and the ultrasonic frequency was 20 kHz. The LDH slurry was continuously collected and post-treated to obtain the Ni / MgAl-LDH catalyst.

[0040] The specific surface area of ​​the obtained catalyst is 112.3 m². 2 ·g -1 The pore volume is 0.317 cm. 3 ·g -1 The obtained catalyst was tested using the above-described activity testing method. Analysis showed that the benzyltoluene conversion rate was 79.10%, and the selectivity for fully hydrogenated benzyltoluene was 12.17%.

[0041] Comparative Example 2: Prepare solution A with a nickel ion concentration of 0.2 mol·L⁻¹. -1 The aluminum ion concentration is 0.1 mol·L⁻¹ -1 Prepare solution B. The sodium carbonate concentration is 0.35 mol·L⁻¹. -1 ; 2 mL / min of solution A and solution B -1 2.5 mL·min -1 The LDH slurry was continuously collected and post-processed to obtain a NiAl-LDO support, which was then loaded with 1 wt of ruthenium by an equal-volume impregnation method and reduced to obtain a Ru / NiAl-LDH catalyst.

[0042] The specific surface area of ​​the obtained catalyst is 120.8 m². 2 ·g -1 The pore volume is 0.336 cm³. 3 ·g -1 The obtained catalyst was tested using the above-mentioned activity testing method. After analysis, the conversion rate of benzyltoluene was 100.0%, and the selectivity of fully hydrogenated benzyltoluene was 69.34%.

[0043] The characteristic parameters and catalytic activities of the catalysts in the examples and comparative examples are shown in Table 1.

[0044]

[0045] As shown in Table 1, the hydrotalcite-supported catalyst prepared by the present invention using an ultrasound-assisted microchannel continuous integrated process exhibits significant advantages in its benzyltoluene hydrogenation catalytic performance. This invention integrates the preparation of the hydrotalcite support with the isomorphic substitution loading of the active metal. Utilizing the synergistic effect of efficient mass and heat transfer in the microchannel reactor and ultrasound-assisted accelerated ion diffusion, the dispersion of the active metal in the prepared catalyst is significantly improved. The absence of ruthenium characteristic peaks in the XRD results of the highly loaded ruthenium catalyst in Example 4 demonstrates good metal dispersion. Compared with the catalyst prepared by the conventional one-step co-precipitation method in Comparative Example 1, both the conversion rate and the selectivity of fully hydrogenated benzyltoluene are significantly improved. Compared with the catalyst prepared by the conventional equal-volume impregnation method in Comparative Example 2, the catalyst obtained by the present invention through isomorphic substitution loading of the active component significantly improves the selectivity of the fully hydrogenated product. Furthermore, the catalytic performance can be further optimized by controlling the concentration of the active metal salt, achieving 100% conversion of benzyltoluene while obtaining extremely high selectivity for fully hydrogenated benzyltoluene. Furthermore, the preparation method of this invention is highly continuous and automated, with a short preparation cycle and strong controllability of process parameters. The resulting catalyst has both excellent structural characteristics and hydrogenation catalytic performance, and has good potential for industrial scale-up applications.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a hydrotalcite-supported catalyst in an ultrasonic-assisted microchannel reactor, characterized in that: Includes the following steps: (1) Dissolve the metal salt into solution A, dissolve the anhydrous sodium carbonate into solution B, and dissolve the active metal salt into solution C; (2) Liquid A and liquid B are continuously fed into the micro mixer by a horizontal flow pump for rapid and thorough mixing, and then fed into a microchannel reactor for continuous precipitation reaction to obtain a carrier slurry containing LDH particles. The slurry is then thoroughly mixed with liquid C and ultrasonically treated to obtain the product slurry. (3) Liquid crystallize the product slurry obtained in step (2), wash it with deionized water until neutral, dry it, calcine it, and reduce it to obtain the hydrotalcite supported catalyst.

2. The method according to claim 1, characterized in that: In step (1), the metal salt is two of the following: nitrates or chlorides of nickel, magnesium, aluminum, zinc, zirconium, and calcium; the concentration of solution A is 0.3–0.54 mol·L⁻¹. -1 The molar ratio of divalent to trivalent metals is 2:

1.

3. The method according to claim 1, characterized in that: In step (1), the concentration of solution B is 0.35–0.63 mol·L⁻¹. -1 .

4. The method according to claim 1, characterized in that: In step (1), the active metal salt is one of the nitrates or chlorides of nickel, ruthenium, platinum, palladium, or copper; the concentration of solution C is 2–45 mmol·L⁻¹. -1 .

5. The method according to claim 1, characterized in that: In step (2), the flow rate of the advection pump is 1–40 mL·min. -1 .

6. The method according to claim 1, characterized in that: In step (2), the precipitation reaction temperature is 30~300 ℃.

7. The method according to claim 1, characterized in that: In step (2), the ultrasonic processing power is 50 to 2000 W.

8. The method according to claim 1, characterized in that: In step (3), the calcination temperature is 300~1000 ℃ and the reduction temperature is 200~550 ℃.

9. A hydrotalcite-supported catalyst prepared by the method according to any one of claims 1-8, characterized in that: The resulting catalyst has a layered structure and the active components are highly dispersed.

10. The application of a hydrotalcite-supported catalyst prepared by the method according to any one of claims 1-8 in the catalytic hydrogenation reaction of benzyltoluene.

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