A copper-zinc-aluminum catalyst containing a zirconium promoter, its preparation method and use

Abstract

The application discloses a preparation method of a copper-zinc-aluminum catalyst containing a zirconium promoter, and comprises the following steps: (1) dissolving a water-soluble copper salt, a zinc salt, an aluminum salt and a zirconium salt in deionized water to obtain a metal salt solution; (2) adding an aqueous precipitant solution into the metal salt solution to perform co-precipitation, and then transferring the obtained mixture into a 70 DEG C thermostat to perform aging, suction filtration, water washing, drying and calcination, so as to obtain a metal oxide precursor; and (3) placing the metal oxide precursor into a reaction tube to perform a reduction reaction in a hydrogen atmosphere, so as to obtain the copper-zinc-aluminum catalyst containing the zirconium promoter. By introducing the zirconium promoter with a specific structure into the copper-based catalyst, the organizational structure of the catalyst is optimized, a novel catalyst with high catalytic activity and high selectivity of a target product in aniline and methanol N-methylation reaction is obtained, and therefore, a more reliable and efficient catalytic scheme is provided for the industrial reaction.

Description

Technical Field

[0001] This invention relates to the field of catalysts for the synthesis of N-methylaniline, specifically to a copper-zinc-aluminum catalyst containing a zirconium promoter and its preparation method, and more specifically to the application of this catalyst in the N-methylation reaction of aniline and methanol to prepare N-methylaniline. Background Technology

[0002] N-methylation of amines is an important reaction in organic synthesis, and its products have wide applications in pharmaceuticals, dyes, and pesticides. In recent years, N-methylation using methanol as a green methylating agent has attracted considerable attention. However, the N-methylation of aniline with methanol faces challenges such as C-alkylation side reactions and overmethylation. Heterogeneous catalysis, due to its ease of separation and reusability, has become an important direction for achieving selective N-methylation of aniline.

[0003] Cu / ZnO / Al2O3 catalysts, as classic copper-based heterogeneous catalysts, are widely used in reactions such as methanol reforming and water-gas shift reaction. In recent years, they have also been attempted for the N-methylation reaction of aniline and methanol. However, directly applying traditional Cu / ZnO / Al2O3 catalysts to the N-methylation reaction of aniline and methanol has the following technical drawbacks: (1) Insufficient active sites: The dispersion of copper in traditional catalysts is limited and there are few effective active sites exposed, resulting in low catalytic activity and difficulty in meeting the requirements of high-efficiency conversion.

[0004] (2) Active components are prone to deactivation: During the reaction process (usually involving high temperature and methanol / water reaction medium), the active component Cu nanoparticles are prone to migration and aggregation, resulting in a decrease in active specific surface area, poor catalyst stability, and shortened service life, which restricts its industrial application prospects.

[0005] Therefore, how to provide a catalyst that combines high activity, high selectivity and excellent stability to overcome the above-mentioned defects of traditional Cu / ZnO / Al2O3 catalysts in the catalytic N-methylation reaction of aniline and methanol is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] Therefore, the purpose of this invention is to provide a copper-zinc-aluminum catalyst containing a zirconium promoter, its preparation method, and its application. By introducing a zirconium promoter with a specific structure, the catalyst's microstructure is optimized, resulting in a novel catalyst with both high catalytic activity and high selectivity for the target product in the N-methylation reaction of aniline and methanol, thereby providing a more reliable and efficient catalytic solution for this industrial reaction.

[0007] The first aspect of this invention provides a method for preparing a copper-zinc-aluminum catalyst containing a zirconium promoter, comprising the following steps: (1) Dissolve water-soluble metal copper salts, zinc salts, aluminum salts and zirconium salts simultaneously in deionized water to obtain metal salt solutions; (2) The aqueous solution of the precipitant is added dropwise to the metal salt solution for co-precipitation. The resulting mixture is then aged, filtered, washed with water, dried, and calcined to obtain the metal oxide precursor. (3) The metal oxide precursor is placed in a reaction tube and a reduction reaction is carried out under a hydrogen atmosphere to obtain a copper-zinc-aluminum catalyst containing zirconium promoter.

[0008] In an optional embodiment, in step (1), the mass ratio of copper salt, zinc salt, aluminum salt and zirconium salt is (5-10):(2-5):(1-3):(1-4).

[0009] In one alternative embodiment, in step (2), the precipitant is sodium carbonate, the concentration of the sodium carbonate aqueous solution is 0.09 g / mL, and the co-precipitation temperature is 60°C.

[0010] In one alternative embodiment, in step (2), the drying temperature is 100-120°C and the time is 8-12 hours.

[0011] In one alternative embodiment, in step (2), the calcination temperature is 400°C, the time is 4 h, and the heating rate is 5°C / min.

[0012] In an optional embodiment, in step (3), the metal oxide precursor is first treated at 200°C for 1 h before the reduction reaction, and then heated to 300-400°C for 3 h. The heating rate is 3-5°C / min, and the hydrogen flow rate is 20-100 ml / min.

[0013] A second aspect of the present invention is to provide a copper-zinc-aluminum catalyst containing a zirconium accelerator.

[0014] A third aspect of the present invention is to provide the application of a copper-zinc-aluminum catalyst containing a zirconium promoter in the catalytic reaction of aniline with methanol to produce N-methylaniline.

[0015] In one alternative embodiment, the reaction temperature of aniline and methanol is 220–260°C, the pressure is 0.1–4 MPa, and the molar ratio of aniline to methanol is 1:(1–2).

[0016] Compared with the prior art, the technical solution of the present invention has the following advantages: (1) Based on the inexpensive copper-based non-precious metal system, this invention successfully solves the problem of insufficient activity of traditional Cu / ZnO / Al2O3 catalysts in the N-methylation reaction of aniline by precisely introducing ZrO2 promoters with structural confinement (forming "nano-gates" in the Cu / ZnO / Al2O3 matrix to physically block the migration and sintering of Cu active components) and surface modulation (utilizing the oxygen vacancy characteristics of ZrO2 and its synergistic effect with ZnO to optimize the electronic environment of the catalyst and make it more suitable for the reaction system of aniline and methanol). This invention achieves catalytic performance close to that of precious metal systems, while forming significant advantages in terms of cost, preparation process complexity and scale-up feasibility, providing a practical and feasible technical path for the industrial application of non-precious metal catalysts in fine chemical amination reactions.

[0017] (2) This invention finely controls the precursor crystallization process and calcination kinetics by introducing ZrO2 precursor during the co-precipitation stage, utilizing Zr 4+ Hydrolysis characteristics and Cu 2+ Zn 2+ The formation of highly miscible (hydroxy)carbonate composite precursors ensures high dispersion of active components and uniform distribution of ZrO2 promoter in the catalyst matrix from the source.

[0018] (3) When Cu / ZnO / Al2O3 catalyst is applied to the N-methylation reaction of aniline and methanol, the strong adsorption of the reactant aniline and the product organic amine may poison some active sites, while the water generated in the reaction may accelerate the hydrothermal aging of the catalyst. ZrO2 has good hydrophobicity and chemical inertness. Its introduction can enhance the hydrothermal stability of the catalyst in water-containing and amine-containing reaction environments, making it more adaptable to the harsh atmosphere of the N-methylation reaction than the traditional Cu / ZnO / Al2O3 catalyst. At the same time, it can reduce other side reactions besides N-methylation.

[0019] (4) The Cu / ZnO / Al2O3 catalyst of the present invention can adjust the pore structure of the catalyst by introducing ZrO2. After adding Zr, the specific surface area of ​​the catalyst increases by more than double, while the average pore size decreases (from 26 nm to 19 nm), forming a new pore structure with finer particles, tighter packing and richer pores. This texture feature of "high specific surface area-fine pore size" induced by ZrO2 is the direct physical basis for the improvement of catalyst performance. It effectively increases the number and accessibility of reactive sites, which is more conducive to the formation and desorption of N-methylaniline or N,N-dimethylaniline and reduces the occurrence of deep methylation or other side reactions.

[0020] (5) The Cu / ZnO / Al2O3 / ZrO2 catalyst of the present invention has higher low-temperature activity, with an aniline conversion rate of up to 96.6% at 220℃, which is much higher than the 78.3% of Cu / ZnO / Al2O3 without Zr. It also has a higher ability to suppress side reactions, with a total conversion rate of up to 99.8% for N-methylaniline and N,N-dimethylaniline at 220℃. Attached Figure Description

[0021] Figure 1 The XRD patterns of the Cu / ZnO / Al2O3 / ZrO2 catalyst of Example 1 and the Cu / ZnO / Al2O3 catalyst of Comparative Example 1 are shown below. Figure 2 XPS spectra of the Cu / ZnO / Al2O3 / ZrO2 catalyst of Example 1 and the Cu / ZnO / Al2O3 catalyst of Comparative Example 1 of this invention; Figure 3 SEM images of the Cu / ZnO / Al2O3 / ZrO2 catalyst of Example 1 and the Cu / ZnO / Al2O3 catalyst of Comparative Example 1 of the present invention; Figure 4 These are TEM images of the Cu / ZnO / Al2O3 / ZrO2 catalyst of Example 1 and the Cu / ZnO / Al2O3 catalyst of Comparative Example 1 of the present invention. Detailed Implementation

[0022] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0023] Example 1 A copper-zinc-aluminum catalyst containing a zirconium accelerator is prepared by the following method: Weigh out 7.85 g Cu(NO3)2·3H2O, 3.72 g Zn(NO3)2·6H2O, 1.88 g Al(NO3)3·9H2O, and 2.17 g Zr(NO3)4·5H2O respectively, and add them to a 250 mL Erlenmeyer flask. Then add 110 mL of deionized water and place the flask in a constant temperature water bath at 60℃. Stir and dissolve for 30 min to prepare a nitrate mixed solution with a total metal ion concentration of 0.5 mol / L. Separately, weigh out 7.95 g of anhydrous sodium carbonate and place it in a beaker. Add 90 L of deionized water and sonicate to dissolve it. After complete dissolution, transfer the solution to a 250 mL dropping funnel and add it dropwise to the nitrate mixed solution at a rate of 1 drop / s. After the addition is complete, seal the Erlenmeyer flask and continue stirring at 60℃ for 4 h. After stirring, transfer the mixture to a constant temperature incubator at 70℃ for 12 hours of aging. After aging, the precipitate was filtered and washed with deionized water until the filtrate was neutral. The filter cake was collected and dried in a 100℃ oven for 12 hours. The dried filter cake was ground into a uniform powder, placed in a crucible, and calcined in a muffle furnace at 400℃ for 4 hours at a heating rate of 5℃ / min to obtain the metal oxide precursor. Finally, the precursor was reduced in a reaction tube under H2 atmosphere by programmed temperature rise. The specific operation of the temperature rise reduction was as follows: first, it was treated at 200℃ for 1 hour, and then the temperature was raised to 310℃ for 3 hours. The heating rate was 3℃ / min, and the gas flow rate was 20 ml / min. After the reduction was completed, the modified catalyst Cu / ZnO / Al2O3 / ZrO2 was obtained.

[0024] Example 2 A copper-zinc-aluminum catalyst containing a zirconium accelerator is prepared by the following method: Weigh out 6.64 g Cu(NO3)2·3H2O, 2.35 g Zn(NO3)2·6H2O, 2.15 g Al(NO3)3·9H2O, and 1.86 g Zr(NO3)4·5H2O respectively, and add them to a 250 mL Erlenmeyer flask. Then add 110 mL of deionized water and place the flask in a constant temperature water bath at 60℃ and stir to dissolve for 30 min. Separately, weigh out 5.95 g of anhydrous sodium carbonate and place it in a beaker. Add 90 mL of deionized water and sonicate to dissolve it. After complete dissolution, transfer the solution to a 250 mL dropping funnel and add it dropwise to the nitrate mixture at a rate of 1 drop / s. After the addition is complete, seal the Erlenmeyer flask and continue stirring at 60℃ for 4 h. After stirring, transfer the mixture to a 70℃ constant temperature incubator for 12 hours of aging. After aging, the precipitate was filtered and washed with deionized water until the filtrate was neutral. The filter cake was collected and dried in an oven at 110°C for 10 hours. The dried filter cake was ground into a uniform powder, placed in a crucible, and calcined in a muffle furnace at 400°C for 4 hours at a heating rate of 5°C / min to obtain a metal oxide precursor. Finally, the precursor was reduced in a reaction tube under H2 atmosphere by a programmed temperature rise. The specific operation of the temperature rise reduction was as follows: first, it was treated at 200°C for 1 hour, and then reduced at 350°C for 3 hours. The heating rate was 4°C / min, and the gas flow rate was 40 ml / min. After the reduction was completed, the modified catalyst was obtained.

[0025] Example 3 A copper-zinc-aluminum catalyst containing a zirconium accelerator is prepared by the following method: 9.52 g of Cu(NO3)2·3H2O, 4.28 g of Zn(NO3)2·6H2O, 2.46 g of Al(NO3)3·9H2O, and 3.56 g of Zr(NO3)4·5H2O were weighed out and added to a 250 mL Erlenmeyer flask. Then, 110 mL of deionized water was added, and the mixture was placed in a 60°C water bath and stirred for 30 min to dissolve. Separately, 8.87 g of anhydrous sodium carbonate was weighed out and placed in a beaker. 90 mL of deionized water was added and sonicated to dissolve the sodium carbonate. After complete dissolution, the solution was transferred to a 250 mL dropping funnel and added dropwise to the nitrate mixture at a rate of 1 drop / s. After the addition was complete, the Erlenmeyer flask was sealed and stirred at 60°C for 4 h. After stirring, the mixture was transferred to a 70°C incubator for 12 hours of aging. After aging, the precipitate was filtered and washed with deionized water until the filtrate was neutral. The filter cake was collected and dried in a 120°C oven for 10 hours. The dried filter cake was ground into a uniform powder, placed in a crucible, and calcined in a muffle furnace at 400°C with a heating rate of 5°C / min for 4 hours to obtain a metal oxide precursor. Finally, the precursor was reduced in a reaction tube under H2 atmosphere by a programmed temperature rise. The specific operation of the temperature rise reduction was as follows: first, it was treated at 200°C for 1 hour, and then reduced at 350°C for 3 hours. The heating rate was 4°C / min, and the gas flow rate was 20 ml / min. After the reduction was completed, the modified catalyst was obtained.

[0026] Comparative Example 1 The difference from Example 1 is that Zr(NO3)4·5H2O is not added, but otherwise the same as in Example 1, and a Cu / ZnO / Al2O3 catalyst is prepared.

[0027] Comparative Example 2 The difference from Example 1 is that Zr(NO3)4·5H2O is replaced with Mg(NO3)2·6H2O, while the rest is the same as in Example 1, and a Cu / ZnO / Al2O3 / MgO catalyst is prepared.

[0028] Test Example 1: Characterization of the Catalyst I. XRD Characterization of Catalysts The Cu / ZnO / Al2O3 / ZrO catalyst and Cu / ZnO / Al2O3 catalyst samples prepared in Example 1 and Comparative Example 1 were subjected to X-ray diffraction tests, respectively. The scanning range was 2θ = 5 ~ 80°, and the scanning speed was 5° / min. -1 The result is as follows Figure 1 As shown.

[0029] Figure 1The presence of multiple diffraction peaks in Cu / ZnO / Al2O3 and Cu / ZnO / Al2O3 / ZrO2 indicates good crystallinity in both catalysts. The spectra primarily show two distinct clusters of diffraction peaks. The first cluster appears at approximately 43.4°, 50.5°, and 74.1° at 2θ angles, which highly coincide with the diffraction peak positions of the face-centered cubic (FCC) structure (111), (200), and (220) crystal planes of metallic copper (Cu) in standard PDF card PDF#04-0836. This indicates that during catalyst preparation and activation, the copper species in the precursor were successfully reduced to metallic Cu, which is the main active component in the reaction. The second significant cluster of diffraction peaks appears at approximately 36.2° at 2θ angles, corresponding to the (002) characteristic peak of the hexagonal wurtzite structure of zinc oxide (ZnO) in standard PDF card PDF#36-1451. In this catalyst system, ZnO plays a dual role as both a structural aid and an electronic aid. It can interact strongly with Cu particles, regulate the electron cloud density on the Cu surface, and thus affect its catalytic activity and selectivity.

[0030] In the XRD patterns of Cu / ZnO / Al2O3 and Cu / ZnO / Al2O3 / ZrO2 catalysts, no sharp diffraction peaks attributable to crystalline Al2O3 were observed. This is because the Al2O3 component usually exists in an amorphous state, and during the co-precipitation process, Al... 3+ The ions are highly dispersed in the support, forming amorphous alumina after calcination. Amorphous Al₂O₃ has a large specific surface area and abundant surface hydroxyl groups, which not only improves the mechanical strength of the catalyst but also provides a favorable support environment for the dispersion of active components and contributes a certain degree of surface acidity. Furthermore, no characteristic peaks of the corresponding oxide were observed after the introduction of Zr as a promoter, indicating that Zr is highly dispersed in the catalyst.

[0031] II. XPS Characterization of Catalysts The Cu / ZnO / Al2O3 / ZrO2 catalyst prepared in Example 1 and the Cu / ZnO / Al2O3 catalyst prepared in Comparative Example 1 were subjected to full-spectrum and fine-spectrum analysis using X-ray photoelectron spectroscopy (Thermo Scientific K-Alpha, USA). The results are as follows: Figure 2 As shown. Figure 2 Figure (a) shows the Cu2p XPS spectra of Cu / ZnO / Al2O3 and Cu / ZnO / Al2O3 / ZrO2; Figure 2 Figure (b) shows the Zr3dXPS spectrum of Cu / ZnO / Al2O3 / ZrO2.

[0032] from Figure 2As can be observed in Figure (a), the catalyst Cu / ZnO / Al2O3 exhibits two distinct main peaks at binding energies of approximately 932.2 eV and 952.1 eV, corresponding to the spin-orbit splitting peaks of Cu 2p3 / 2 and Cu 2p1 / 2, respectively. The binding energy near 932.2 eV is the Cu... 0 The weak satellite peak characteristics strongly rule out a large amount of Cu. 2+ (>334 eV). Therefore, it can be concluded that the main copper species on the catalyst surface is zero-valent copper (Cu0). Compared with the reference sample, the Cu 2p spectrum of Zr-doped Cu / ZnO / Al2O3 / ZrO2 changed. The position of the Cu 2p3 / 2 main peak shifted slightly from about 932.2 eV to about 932.3 eV, indicating that the chemical environment of copper was slightly altered.

[0033] Combination Figure 2 The XPS spectrum of Zr(3d) in Figure (b) suggests that this change may originate from the electronegativity of Zr ions (Zr). 4+ Zr has a high affinity for oxygen ions, slightly altering the electron cloud density of neighboring Cu atoms, resulting in a slight increase in the effective positive charge of Cu atoms and a higher binding energy. However, overall, the introduction of Zr has little effect on the Cu 2p spectrum. The morphology of the spectrum is basically consistent with the reference sample Cu / ZnO / Al2O3, with its main characteristic peak (Cu 2p3 / 2) still located near 932.2 eV, and the satellite peak signal remaining weak. This indicates that Zr doping did not significantly change the main chemical valence state of surface copper, and its dominant valence state remains Cu. 0 .

[0034] In summary, the changes and improvements in the performance of the benchmark catalyst after Zr doping are primarily due to the optimization of the overall catalyst structure and metal-support interactions by the corresponding oxide itself, rather than changes in the valence state of the copper active component. The stability of the Cu valence state shown in the XPS spectra also indicates that Zr is a "mild" promoter, acting without altering the Cu valence state. 0 Under the premise of active centers, the structural performance of catalysts is optimized in a "gentle" way.

[0035] III. Morphological Characterization of Catalysts The Cu / ZnO / Al2O3 / ZrO2 catalyst prepared in Example 1 and the Cu / ZnO / Al2O3 catalyst prepared in Comparative Example 1 were used as samples and analyzed by scanning electron microscopy (SEM). The results are as follows: Figure 3 As shown. Among them, Figure 3 Figure a shows the morphology of the Cu / ZnO / Al2O3 catalyst; Figure 3 Figure b shows the morphology of the Cu / ZnO / Al2O3 / ZrO2 catalyst.

[0036] from Figure 3 As shown in Figure a, Cu / ZnO / Al2O3 exhibits large agglomerates composed of numerous tightly packed fine particles. These agglomerates are unevenly sized and varied in shape, displaying a "fragmented" or "clustered" morphology, exhibiting significant high agglomeration characteristics. This indicates that strong interactions exist between primary nanoparticles during material preparation or calcination, spontaneously forming micron-sized secondary particles. This structure reduces the specific surface area of ​​the catalyst and hinders mass transfer processes between and within the particles, thus affecting the overall catalytic efficiency.

[0037] from Figure 3 As observed in Figure b, the introduction of Zr significantly optimized the catalyst morphology, inhibiting particle growth and agglomeration. Compared to the Cu / ZnO / Al2O3 catalyst, the Zr-doped catalyst particles exhibited a distinct "filamentous" or "flocculent" morphology. This morphology allows the Cu / ZnO / Al2O3 / ZrO2 catalyst to achieve a larger specific surface area, providing more active sites. Furthermore, the EDS spectra indicate that the metals are well dispersed, with no agglomeration occurring.

[0038] The two samples were further scanned using a transmission electron microscope (TEM), and the results are as follows: Figure 4 As shown. Among them, in Figure 4 Figure a shows the Cu / ZnO / Al2O3 catalyst. Figure 4 Figure b shows the Cu / ZnO / Al2O3 / ZrO2 catalyst.

[0039] from Figure 4 The TEM images show that the lattice fringes of the two catalysts are clearly visible, indicating that the Cu / ZnO / Al2O3 and Cu / ZnO / Al2O3 / ZrO2 catalysts have good crystallization properties. At the same time, Cu can be observed to be uniformly distributed on the catalyst.

[0040] IV. Determination of specific surface area and pore size The specific surface area and pore volume of the samples were determined using a BET specific surface area and pore size analyzer (ASAP2460, Micromeriti SA, USA) at 77 K using the N2 adsorption-desorption isotherm method. The specific surface areas of Cu / ZnO / Al2O3 and Cu / ZnO / Al2O3 / ZrO2 catalysts are shown in Table 1.

[0041] Table 1. Specific surface area (BET), pore volume, and average pore size of Cu / ZnO / Al2O3 and Cu / ZnO / Al2O3 / ZrO2

[0042] The above results indicate that the specific surface area of ​​the catalyst increased dramatically from 22.35 m² / g to 45.39 m² / g after the addition of Zr, more than doubling. This demonstrates that the Cu-Zn-Al system without Zr underwent severe grain agglomeration or sintering during co-precipitation and calcination, resulting in coarse particles and surface densification. The doubling of the specific surface area after Zr addition suggests that Zr acts as an "anti-sintering agent" or "isolating agent." The significant reduction in pore size is evidence of ZrO2 remodeling the pores. Combined with the doubling of the specific surface area, it can be inferred that the Cu / ZnO / Al2O3 sample originally contained a small number of macropores (26.38 nm) due to particle packing; however, after the addition of ZrO2, the particles became finer and more densely packed, resulting in a large number of micropores (19.32 nm). The data reveals a typical case of "structure promotion". The addition of ZrO2 transforms the Cu-Zn-Al system, which was originally easy to sinter, into an ideal catalytic system with high specific surface area and fine pore size, laying a solid physical structural foundation for the high activity and high stability of the N-methylation reaction of aniline and methanol.

[0043] Test Example 2: Catalytic Performance Evaluation I. Catalytic activity and selectivity of the catalyst for the target product A continuous synthesis of N-methylaniline was carried out in a fixed-bed reactor. Aniline and methanol were used as raw materials, with two parallel-flow pumps for sample injection. The aniline injection flow rate was 0.01 mL / min, and the methanol injection flow rate was 0.006 mL / min; the reaction pressure was atmospheric pressure; the reaction temperature was 220℃; the gas flow rate (N2) was 50 mL / min; and the weight hourly space velocity (WHSV) was 0.45 h⁻¹. -1 The activity and selectivity of the catalysts were compared and analyzed based on the experimental results.

[0044] The fixed-bed reactor is installed as follows: First, 0.3 g of quartz wool is placed at the catalyst support plate in the reaction tube as a base and properly compressed to prevent excessive gas flow from blowing the catalyst off. Then, 2 g of catalyst is added. Another 0.3 g of quartz wool is added to stabilize the catalyst layer. Finally, 2 g of quartz sand is placed on top of the bed as a top packing to prevent the initial gas or liquid flow from dispersing the catalyst. Simultaneously, the interparticle gaps in the sand rectify and distribute the carrier gas and feed liquid, eliminating channeling and ensuring uniform fluid flow through the catalyst bed. Furthermore, because quartz sand has excellent thermal conductivity, it can preheat the incoming cold feed, reducing and buffering bed temperature fluctuations caused by liquid introduction, thereby maintaining a stable reaction temperature and space velocity, ensuring the accuracy and repeatability of catalyst performance evaluation.

[0045] After the reaction tube was installed, an airtightness check was performed to confirm that the system was well sealed. Then, under a hydrogen flow rate of 20–100 mL / min, the temperature was increased to 310 °C at a rate of 5 °C / min for in-situ reduction of the catalyst for 3 hours. After reduction, nitrogen was switched at a flow rate of 50 mL / min to cool the reaction tube to 220 °C. Simultaneously, two horizontal flow pumps were started, delivering the reaction solution to the pipeline at set flow rates and set space velocity, respectively, to formally begin the continuous reaction. Considering that the system had not yet reached a stable state in the initial stage of the reaction, the product from the first 6 hours was not used; the reaction solution from 6 to 12 hours was collected for analysis to ensure the accuracy and representativeness of the evaluation results. Qualitative analysis was performed using gas chromatography-mass spectrometry (GC-MS), and quantitative analysis was performed using gas chromatography (GC), determining product selectivity and reactant conversion to systematically evaluate the catalyst performance. Samples were taken and analyzed every 6 hours, and the average conversion and selectivity were calculated. The catalytic performance of the catalyst samples prepared in Examples 1-3 and Comparative Examples 1-2 is shown in Table 2 below.

[0046] Table 2 Catalytic performance of catalysts in Examples 1-3 and Comparative Examples 1-2

[0047] As shown in the table above, compared with Comparative Example 1, the aniline conversion rate of Examples 1-3 is above 90%, while the selectivity of N-methylaniline is slightly improved. This indicates that the modified catalyst significantly improves the aniline conversion rate while maintaining the high selectivity of N-methylaniline. In Example 1, the aniline conversion rate is as high as 94.8%, the selectivity of N-methylaniline is as high as 98.2%, and the selectivity of N,N-dimethylaniline is 1.6%. From the total selectivity of N-methylaniline and N,N-dimethylaniline in Examples 1-3, it is above 99%, and can even approach 100%, showing excellent ability to suppress other side reactions.

[0048] Compared with Comparative Example 1, Comparative Example 2 showed a decrease in aniline conversion rate, indicating that Mg metal element not only failed to play a synergistic role with the copper-based catalyst, but also exhibited a certain antagonistic effect, greatly reducing the catalytic activity of the catalyst. This shows that not any metal element can modify the copper-based catalyst.

[0049] II. Catalytic stability test of the catalyst The stability of the Cu / ZnO / Al2O3 / ZrO2 catalyst prepared in Example 1 was further tested. The catalyst of Example 1 was reacted continuously under the above conditions for 500 h, and the test results of its aniline conversion and N-methylaniline selectivity are shown in Table 3 below.

[0050] Table 3. Stability test results of the Cu / ZnO / Al2O3 / ZrO2 catalyst in Example 1

[0051] The above results show that the catalyst Cu / ZnO / Al2O3 / ZrO2 obtained in Example 1 still has good catalytic activity for aniline during a continuous reaction of 500 h, with the conversion rate of aniline remaining at almost above 93%. At the same time, the N-methylaniline selectivity is also above 98%, indicating that the modified catalyst has good hydrothermal stability, long service life, and is not easily deactivated. It can still maintain good catalytic activity and high N-methylaniline selectivity for a long time under high temperature conditions.

[0052] Although the present invention has been described using the above preferred embodiments, it is not intended to limit the scope of protection of the present invention. Any changes and modifications made by those skilled in the art to the above embodiments without departing from the spirit and scope of the present invention shall still fall within the scope of protection of the present invention.

Claims

1. A method for preparing a copper-zinc-aluminum catalyst containing a zirconium accelerator, characterized in that, Includes the following steps: (1) Dissolve water-soluble metal copper salts, zinc salts, aluminum salts and zirconium salts simultaneously in deionized water to obtain metal salt solutions; (2) The aqueous solution of the precipitant is added dropwise to the metal salt solution for co-precipitation. The resulting mixture is then aged, filtered, washed with water, dried, and calcined to obtain the metal oxide precursor. (3) The metal oxide precursor is placed in a reaction tube and a reduction reaction is carried out under a hydrogen atmosphere to obtain a copper-zinc-aluminum catalyst containing zirconium promoter.

2. The method for preparing the copper-zinc-aluminum catalyst containing a zirconium accelerator according to claim 1, characterized in that, In step (1), the mass ratio of copper salt, zinc salt, aluminum salt and zirconium salt is (5-10):(2-5):(1-3):(1-4).

3. The method for preparing the copper-zinc-aluminum catalyst containing a zirconium accelerator according to claim 1, characterized in that, In step (2), the precipitant is sodium carbonate, the concentration of the sodium carbonate aqueous solution is 0.09 g / mL, and the co-precipitation temperature is 60℃.

4. The method for preparing the copper-zinc-aluminum catalyst containing a zirconium accelerator according to claim 1, characterized in that, In step (2), the drying temperature is 100-120℃ and the time is 8-12h.

5. The method for preparing the copper-zinc-aluminum catalyst containing a zirconium accelerator according to claim 1, characterized in that, In step (2), the calcination temperature is 400℃, the time is 4 h, and the heating rate is 5℃ / min.

6. The method for preparing the copper-zinc-aluminum catalyst containing a zirconium accelerator according to claim 1, characterized in that, In step (3), the metal oxide precursor is first treated at 200°C for 1 h before the reduction reaction, and then heated to 300-400°C for 3 h. The heating rate is 3-5°C / min, and the hydrogen flow rate is 20-100 ml / min.

7. The copper-zinc-aluminum catalyst containing zirconium accelerator prepared by the method for preparing the copper-zinc-aluminum catalyst containing zirconium accelerator according to any one of claims 1-6.

8. The application of the copper-zinc-aluminum catalyst containing zirconium accelerator as described in claim 7 in the catalytic reaction of aniline with methanol to produce N-methylaniline.

9. The application according to claim 8, characterized in that, In the reaction of aniline and methanol, the reaction temperature is 220-260℃, the pressure is 0.1-4MPa, and the molar ratio of aniline to methanol is 1:(1-2).

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