A gradient supported catalyst for benzene hydrogenation alkylation reaction and its preparation method

Abstract

This invention discloses a gradient-supported catalyst for the hydrogenation alkylation of benzene and its preparation method. The catalyst uses a hierarchical porous β-molecular sieve with a silicon-to-aluminum molar ratio of 100:1, prepared by controlled desilication, as a support, and is loaded with 1.0 wt% ruthenium. The concentration of ruthenium inside the mesopores of the support is 2.5 to 3.5 times that on the outer surface and in the micropore opening region, and is anchored by ammonium acetate ions. The preparation method includes: support preparation, preparation of two concentrations of ruthenium complex impregnation solution, loading a high-concentration impregnation solution into the mesopores of the support using vacuum impregnation, loading a low-concentration impregnation solution onto the outer surface of the support using spray impregnation, ion anchoring treatment, and reduction. This invention, through gradient loading and ion anchoring technology, retains the mass transfer advantages of the hierarchical pores of the support while precisely controlling the spatial distribution of active sites and enhancing their stability, thereby improving the selectivity of cyclohexylbenzene and the cyclic stability of the catalyst in the hydrogenation alkylation of benzene.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to a gradient supported catalyst for the hydrogenation alkylation reaction of benzene and its preparation method. Background Technology

[0002] Cyclohexylbenzene is a key material for the production of phenol and cyclohexanone, and the direct hydrogenation alkylation of benzene is its most promising synthetic route. This reaction relies on a bifunctional catalyst that combines hydrogenation metal sites and alkylating acid sites, where the support structure is crucial to the catalyst's mass transfer efficiency and the synergistic effect of its bifunctionality.

[0003] In the prior art, β-zeolites with a hierarchical pore structure in which internal micropores and external mesopores are interconnected can effectively promote the diffusion of reactants and products, making them excellent catalyst supports. Controlled desilication techniques using small molecule amines as internal pore directing agents (iPDAs) are known in the art, which can prepare hierarchical β-zeolite supports with a complete microporous framework and mesopores radially distributed from the inside out and interconnected with the micropores. This type of support is well known to those skilled in the art.

[0004] However, even with the aforementioned high-performance supports, the hydrogenation alkylation of benzene still faces significant challenges: conventional metal-supported methods (such as equal-volume impregnation) struggle to precisely control the spatial distribution of the active metal within complex hierarchical channels, leading to two core problems: Limited selectivity: The cyclohexene generated by the hydrogenation reaction stays in the metal-rich region for too long, and is prone to excessive hydrogenation to generate the byproduct cyclohexane, making it difficult to achieve a breakthrough in the selectivity of the target product cyclohexylbenzene; Insufficient stability: The supported metal nanoparticles are prone to migration and aggregation during the reaction, causing rapid deactivation of the catalyst.

[0005] The ruthenium-based β-zeolite catalysts prepared by conventional equal-volume impregnation methods typically exhibit a cyclohexylbenzene selectivity of less than 50% in the hydrogenation alkylation of benzene, and the cyclohexylbenzene yield retention rate is less than 15% after 5 cycles, which cannot meet the requirements for industrial applications.

[0006] Therefore, existing technologies still lack a loading strategy on multi-level porous supports that can simultaneously achieve the following objectives: Precise control of the spatial distribution of metals to solve the selectivity problem; Strengthening the metal-support interaction to solve the stability problem. Summary of the Invention

[0007] This invention provides a gradient-supported catalyst for the hydrogenation alkylation of benzene. This catalyst can achieve a concentration gradient distribution of ruthenium metal and strong ion anchoring on a hierarchical porous β-zeolite support, thereby solving the problems of low selectivity and poor stability of target products in existing catalysts in the hydrogenation alkylation of benzene.

[0008] To achieve the above objectives, this invention provides an ion-anchored gradient loading technology, namely a gradient-loaded catalyst for the hydrogenation alkylation reaction of benzene and its preparation method. This technology constructs a "high internal, low external" gradient distribution of ruthenium through a specific combination of vacuum pressurization and spray impregnation processes, and utilizes ammonium acetate solution for in-situ ion anchoring, thereby forming stable active centers on a hierarchical porous β-zeolite support.

[0009] This invention is achieved through the following technical solution: A gradient-supported catalyst for the hydrogenation alkylation reaction of benzene includes: a hierarchical porous β-zeolite support, and a ruthenium metal active component immobilized on the hierarchical porous β-zeolite support by ion anchoring. The ruthenium active component is spatially distributed in a concentration gradient on the hierarchical β-molecular sieve support, and the concentration of the ruthenium active component inside the mesopores of the support is higher than the concentration of the ruthenium active component on the outer surface of the support and in the micropore opening region. The ruthenium metal active component has a loading mass fraction of 1.0% in the catalyst; The silicon-aluminum molar ratio of the hierarchical porous β molecular sieve support is 100:1; The mass concentration of the active ruthenium metal inside the mesopores of the carrier is 2.5 to 3.5 times that of the active ruthenium metal on the outer surface of the carrier and in the micropore opening region.

[0010] The mesopore size of the β-zeolite support is 2~50 nm, and the micropore size is 0.5~2 nm.

[0011] This invention also provides a method for preparing a gradient supported catalyst for the hydrogenation alkylation reaction of benzene, such as... Figure 2 As shown. This invention uses a vacuum pressurization method to force a high-concentration active component precursor deep into the mesopores, and then introduces a low-concentration precursor onto the outer surface and micropore openings using a spray impregnation method, thereby actively constructing an "inner-high, outer-low" spatial distribution of active components that is completely opposite to the conventional equal-volume impregnation method. The process includes the following steps: S1. Prepare the hierarchical porous β-molecular sieve support; S2. Prepare two ruthenium-containing impregnation solutions of different concentrations: the first impregnation solution has a concentration of 0.045 mol / L, and the second impregnation solution has a concentration of 0.012 mol / L; the ruthenium-containing impregnation solution is a complex solution formed by dissolving ruthenium trichloride and citric acid in deionized water, and the molar ratio of citric acid to ruthenium is 2:1; S3. High-concentration impregnation inside the pores: Using a vacuum pressurization method, at a vacuum degree of -0.08 MPa (absolute pressure of 0.02 MPa) and a temperature of 30°C, the first impregnation solution is impregnated inside the mesopores of the carrier. The ratio of the volume of the impregnation solution (mL) to the mass of the carrier (g) is 2:1. After standing for 8 hours, the first drying is carried out at 100°C for 12 hours to obtain substance M1. S4. Low-concentration impregnation at the pore opening: Using a spray impregnation method, at a temperature of 25°C, the second impregnation solution is impregnated on the outer surface and micropore opening area of ​​M1 after step S3. The volume (mL) of the impregnation solution is 0.8 times the mass (g) of the carrier. After standing for 2 hours, a second drying is carried out at 100°C for 4 hours to obtain substance M2. S5. Ion anchoring treatment: The substance M2 after step S4 is immersed in a 0.01 mol / L ammonium acetate solution and soaked at 30°C for 1 hour. Then, it is filtered and the solid is dried at 100°C for 6 hours to obtain substance M3. During the subsequent reduction process in a hydrogen atmosphere at 450°C, the electrostatic structure transforms into strong chemical bonds. The purpose of ion anchoring treatment is not only to fix the metal, but also to stabilize the special spatial structure constructed by the gradient loading process described above, preventing it from being destroyed during subsequent reduction and use. The two work together to ensure that the design intent is realized and maintained in the final catalyst.

[0012] S6. Reduction treatment: In a hydrogen-argon mixed atmosphere with a hydrogen volume ratio of 10%, the temperature is increased to 450°C at a heating rate of 5°C / min, and the M3 treated in step S5 is reduced at 450°C for 3 hours to obtain the gradient supported catalyst.

[0013] The impregnation time for the vacuum pressurization method is 6-10 hours, and the spray rate for the spray impregnation method is 0.5-1 mL / min.

[0014] This application uses a low-concentration (0.01 mol / L) ammonium acetate solution for treatment, and its core lies in constructing "NH4 + "Electrostatic bridging" anchoring mechanism: Ligand activation: The weakly alkaline environment promotes the deprotonation of the carboxyl groups on the surface of the citric acid-Ru complex, making them negatively charged and in an activated state; Ion bridging: appropriate amount of NH4 + As a "cation bridge," one end connects to the silanol groups on the surface of the support, while the other end adsorbs the activated Ru complex, forming a stable "support-NH4". + -Ru” electrostatic composite structure; Precise locking: The low-concentration design avoids the competition and occupation of pores by high-concentration ammonium salts and the aggregation of Ru species, ensuring that Ru precursors are precisely "locked" deep into the mesopores only through electrostatic interaction. Thermal fixation: During subsequent calcination, the electrostatic structure transforms into strong chemical bonds, effectively inhibiting the migration and loss of Ru nanoparticles during the reaction, thereby significantly improving the long-term stability of the catalyst. Unlike the simple physical / chemical adsorption anchoring in existing technologies, the low-concentration (0.01 mol / L) ammonium acetate design avoids pore competition and achieves precise locking of the ruthenium precursor.

[0015] The hierarchical porous β-molecular sieve support described in S1 is prepared by a controlled desilication method using diethanolamine as the internal pore guiding agent, as detailed below: Z1: Take β molecular sieve and calcine it at 450~650℃ for 5~7h; Z2: After mixing diethanolamine and deionized water evenly, add the calcined β molecular sieve from Z1, mix and stir, and then filter, wash and dry in sequence to obtain material A; the volume ratio of diethanolamine to deionized water is 1:100, and the mass-volume ratio of calcined β molecular sieve to deionized water is 1.0g:40mL. Z3: Take material A obtained in step Z2, sodium hydroxide solid, and deionized water, mix and stir, and then filter, wash, dry, and calcinate to obtain material B; the mass-to-volume ratio of sodium hydroxide solid to deionized water is 1.0 g: 120 mL; the mixing and stirring conditions are: temperature 70℃, rotation speed 500 rpm, time 30 min; the treatment includes filtration, washing, drying, and calcination, wherein the drying temperature is 100℃ for 12 h, and the calcination temperature is 500℃ for 3 h; Z4: Take the ion exchange reagent to perform ion exchange on the material B obtained in step Z3 to obtain a hierarchical porous β molecular sieve support. The ion exchange reagent is NH4Cl solution with a concentration of 1.0 mol / L. The mass-volume ratio of material B to NH4Cl solution is 1.2 g: 25 mL. The ion exchange temperature is 80℃, the time is 2 h, the stirring speed is 500 rpm, and the number of exchanges is 3.

[0016] Correlation analysis between catalyst structure and performance: This invention, based on the construction of a β-zeolite support with a hierarchical porous structure through controlled desilication, utilizes ion anchoring technology to achieve a gradient distribution of the active component, ruthenium. The characterization results and performance of the resulting catalyst are analyzed below: 1) Support Structural Characteristics: After controlled desilication treatment guided by diethanolamine, the β-zeolite, while retaining its original microporous structure, forms a multi-level pore system where internal micropores and external mesopores are interconnected. This structure facilitates the transport and diffusion of reactant molecules within the pores, providing more accessible sites for loading active components. This invention precisely controls the silicon-to-aluminum molar ratio of the support to 100:1. If the silicon-to-aluminum ratio is too low (50:1), the support becomes excessively acidic, triggering a polymerization side reaction of benzene; if the silicon-to-aluminum ratio is too high (150:1), there are insufficient acidic sites, leading to a decrease in the alkylation reaction rate. This invention achieves a synergistic effect of hydrogenation and alkylation at a 100:1 ratio, providing a suitable acidic site environment for the benzene hydrogenation-alkylation reaction.

[0017] 2) Distribution of active components: Scanning results show that the distribution of ruthenium on the support is not uniform, but exhibits a significant concentration gradient. Specifically, the ruthenium signal intensity inside the mesopores is higher than that on the outer surface and at the micropore openings, with a concentration multiple of approximately 3 times. (See schematic diagram below.) Figure 1 As shown, TEM-EDS surface scanning is as follows Figure 8 As shown, this spatial distribution alters the arrangement of active sites within the pores. The signal intensity of ruthenium is significantly higher inside the support (mesoporous region) than on the outer surface, directly demonstrating the successful construction of the gradient distribution. The high concentration of ruthenium inside the mesopores enables the hydrogenation of benzene to cyclohexene, which rapidly diffuses to the acidic sites of the molecular sieve for alkylation. The low concentration of ruthenium on the outer surface prevents excessive hydrogenation of cyclohexene to cyclohexane, thereby improving the selectivity of cyclohexylbenzene.

[0018] 3) Metal-support interaction: XPS (X-ray photoelectron spectroscopy) results show that after ion anchoring treatment, the 3d orbital binding energy of ruthenium in the catalyst underwent a positive shift compared to the untreated sample, such as... Figure 5 As shown, the Ru 3d peak in Example 6 (spectral line 6) underwent a chemical shift relative to Comparative Example 3 (spectral line 5), confirming that ion anchoring treatment enhanced the metal-support interaction. This phenomenon reflects a strong interaction between ruthenium and the hierarchical porous β-zeolite support. This change in interaction state may affect the electronic environment of the active sites.

[0019] 4) Overall Performance: In the evaluation of benzene hydrogenation alkylation reaction, the aforementioned structural features and distribution state jointly influence the catalytic process. Experimental data show that the catalyst with gradient distribution characteristics and ion-anchored treatment exhibits better cyclohexylbenzene selectivity than conventional uniformly supported catalysts and demonstrates better stability in cycling tests. This indicates that the gradient distribution structure and enhanced metal-support interaction have a positive effect on optimizing the reaction pathway and suppressing side reactions.

[0020] Beneficial technical effects This invention provides a gradient loading technology based on ion anchoring. Its core innovation lies in discovering the synergistic effect between the "gradient concentration field" and the "ion anchoring point": the gradient distribution solves the mass transfer limitation and over-hydrogenation problems caused by the enrichment of active ruthenium molecules at the pore openings of traditional catalysts; ion anchoring solves the problem of active metal migration and aggregation in gradient structures during long-term operation; the combination of these two (rather than simple superposition) allows the catalyst to maintain high conversion while improving selectivity. Compared to Comparative Example 2 (selectivity 38.0%, activity retention ≤20% after 5 cycles) which uses an equal-volume impregnation method without gradient distribution, the selectivity (69.1%) of this invention is improved by approximately 82%, and the cycle stability (≥85%) is significantly enhanced.

[0021] Compared to Comparative Example 3 (stability ≤55%, metal dispersion 33.7%), which omits the ion anchoring step, this invention improves stability to ≥85% and metal dispersion to 46.1% through ion anchoring treatment.

[0022] 1) Optimized spatial utilization efficiency of active components: By controlling the concentration of ruthenium metal inside the mesopores of the support to be higher than that on the outer surface and in the micropore opening region (by approximately 3 times), this distribution pattern facilitates mass transfer and diffusion of reactants within the pores, allowing for more complete utilization of active sites. Compared to catalysts with uniformly distributed active components, this gradient distribution structure maintains a high conversion rate while positively regulating product distribution.

[0023] 2) Improved catalyst cycle stability: The binding force between the ruthenium active component fixed by ion anchoring and the support is enhanced, reducing the loss or aggregation of the active component during the reaction process. After multiple cycle reaction tests, the catalyst's activity retention rate and selectivity retention rate remain at a good level (e.g., after 5 cycles, the selectivity retention rate is greater than 80%), demonstrating certain potential for long-term operation.

[0024] 3) Improved selectivity of the target product: Using a β-zeolite treated with diethanolamine-directed desilication as a support, and combining it with ion anchoring technology to construct a concentration gradient distribution of the ruthenium active component, the resulting catalyst can effectively suppress the excessive hydrogenation side reaction of cyclohexene in the benzene hydrogenation alkylation reaction. Experimental data show that, compared with catalysts prepared by conventional impregnation methods, the catalyst provided in this application, under the same reaction conditions, exhibits improved selectivity for cyclohexylbenzene (e.g., from 38%~57.9% in the comparative example to 69.1% in the example), which is beneficial for improving the yield of the target product.

[0025] 4) The process is simple and easy to implement: The preparation method of the present invention mainly involves controlled desilication treatment and stepwise ion anchoring impregnation. The raw materials used are widely available, and the reaction conditions are mild (such as impregnation temperature of 30°C, normal pressure or low pressure operation). It does not require complex high temperature and high pressure equipment or expensive special additives, and is suitable for industrial scale-up production. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the catalyst concentration gradient structure of the present invention; Figure 2 This is a flow chart of the catalyst preparation process of the present invention; Figure 3 This is a TEM image of the catalyst obtained in Example 1 of the present invention; Figure 4 This is a TEM image of the catalyst obtained in Comparative Example 2 of this invention; Figure 5 These are the XPS spectra of the catalysts obtained in Example 1 and Comparative Example 3 of this invention; Figure 6 These are the catalyst cycle stability test graphs obtained from Example 1 and Comparative Example 2 of the present invention; Figure 7 This is a comparison chart of the performance of the catalysts obtained in Example 1, Comparative Example 2, and Comparative Example 3 of this invention in the hydrogenation alkylation reaction of benzene; Figure 8 This is a TEM-EDS surface scan of the ruthenium active component of the catalyst obtained in Example 1 of the present invention.

[0027] Explanation of reference numerals in the attached figures: 1—Mesopores of hierarchical β-molecular sieve supports; 2—Micropores of hierarchical β-molecular sieve supports; 3—Outer surface of the hierarchical porous β-molecular sieve support; 4—Comparative Example 2 yielded catalyst metal ruthenium agglomerates; 5—Comparative Example 3: XPS spectrum of the catalyst was obtained; 6—XPS spectrum of the catalyst obtained in Example 1; 7—A line graph showing the relationship between the number of reaction cycles and the conversion rate of benzene in Example 1; 8—Comparative Example 2: Linear curve showing the number of reaction cycles versus the conversion rate of benzene; 9—Comparative Example 2: Comparison of selectivity of cyclohexylbenzene with conversion of benzene; 10—Comparative Example 3: Comparison of selectivity of cyclohexylbenzene with conversion of benzene; 11—Comparison of selectivity of cyclohexylbenzene and conversion of benzene in Example 1. Detailed Implementation

[0028] The present invention will be further described below with reference to specific embodiments. The following embodiments all embody the gradient loading strategy based on ion anchoring provided by the present invention, wherein the support preparation step (S1) ensures the formation of multi-level channels, while the key catalytic activity construction steps (S2-S4) strictly implement the synergistic process of gradient impregnation and ion anchoring.

[0029] Example 1: S1 support preparation: A multi-level porous β-zeolite support with a silicon-to-aluminum molar ratio of 100:1 and an internal-to-external pore interconnection multi-level pore structure was prepared using commercial β-zeolite and a controlled desilication method with diethanolamine as the internal pore guiding agent.

[0030] S2 Preparation of impregnation solution: Weigh a certain amount of ruthenium trichloride (RuCl3·3H2O) and citric acid (C6H8O7), dissolve them in deionized water at a molar ratio of citric acid:Ru = 2:1, and prepare complex solutions with concentrations of 0.045 mol / L (first impregnation solution) and 0.012 mol / L (second impregnation solution).

[0031] High-concentration impregnation in S3 wells: Take 10g of the above-mentioned carrier and place it in a vacuum impregnation apparatus. Under a vacuum of -0.08 MPa at 30℃, slowly draw 20 mL of the first impregnation solution (the ratio of impregnation solution volume to carrier mass is 2 mL: 1g) into the apparatus, ensuring that the liquid completely covers the carrier. Maintain these conditions and let stand for 8 hours. Then filter and dry at 100℃ for 12 hours to obtain substance M1.

[0032] S4 orifice low-concentration impregnation: Material M1 was placed in a spray impregnation device, and at 25°C, 8 mL of the second impregnation solution (the ratio of impregnation solution volume to carrier mass was 0.8 mL: 1 g) was evenly sprayed onto its surface using a spray method. After standing for 2 hours, it was dried at 100°C for 4 hours to obtain material M2.

[0033] S5 ion anchoring treatment: Substance M2 was immersed in 100 mL of 0.01 mol / L ammonium acetate (CH3COONH4) solution and stirred at 30°C for 1 h. After filtration, it was dried at 100°C for 6 h to obtain substance M3.

[0034] S6 Reduction Treatment: Material M3 was placed in a tube furnace and heated to 450°C at a flow rate of 50 mL / min in an atmosphere of H2 / Ar mixed gas (H2 volume percentage 10%), and reduced at this temperature for 3 hours. After natural cooling to room temperature, the catalyst described in this invention was obtained.

[0035] The following specific method was used in the preparation of the S1 carrier: Z1: Take β molecular sieve and calcine it at 450~650℃ for 5~7h; Z2: After mixing diethanolamine and deionized water evenly, add the calcined β molecular sieve from Z1, mix and stir, and then filter, wash and dry in sequence to obtain material A; the volume ratio of diethanolamine to deionized water is 1:100, and the mass-volume ratio of calcined β molecular sieve to deionized water is 1.0g:40mL. Z3: Take material A obtained in step Z2, sodium hydroxide solid, and deionized water, mix and stir, and then filter, wash, dry, and calcinate to obtain material B; the mass-to-volume ratio of sodium hydroxide solid to deionized water is 1.0 g: 120 mL; the mixing and stirring conditions are: temperature 70℃, rotation speed 500 rpm, time 30 min; the treatment includes filtration, washing, drying, and calcination, wherein the drying temperature is 100℃ for 12 h, and the calcination temperature is 500℃ for 3 h; Z4: Take the ion exchange reagent to perform ion exchange on the material B obtained in step Z3 to obtain a hierarchical porous β molecular sieve support. The ion exchange reagent is NH4Cl solution with a concentration of 1.0 mol / L. The mass-volume ratio of material B to NH4Cl solution is 1.2 g: 25 mL. The ion exchange temperature is 80℃, the time is 2 h, the stirring speed is 500 rpm, and the number of exchanges is 3.

[0036] like Figure 3 As shown, the transmission electron microscopy (TEM) image of the catalyst reveals that the ruthenium particles are uniformly distributed and small in size on the support.

[0037] Comparative Example 1: A common commercial β-zeolite (with all characteristic parameters such as silica-alumina ratio and pore structure consistent with the initial β-zeolite before modification in Example 1) was used as the carrier, and subsequent steps S2 to S6 were exactly the same as in Example 1.

[0038] Comparative Example 2: Based on Example 1, S1, S2, S5, and S6 are exactly the same as in Example 1, but S3 is changed to: "S3 Take 10g of the above carrier and use the conventional equal volume impregnation method. The concentration of the impregnation solution is 0.045 mol / L.", and S4 is deleted.

[0039] Comparative Example 3: Based on Example 1, steps S1, S2, S3, and S4 are exactly the same, but step S5 (ion anchoring treatment) is omitted. The substance M2 treated in step S4 is directly subjected to the reduction treatment in step S6.

[0040] Comparative Example 4: All other conditions were exactly the same as in Example 1, except that the concentration of the impregnation solution was adjusted to 0.8% of the ruthenium loading mass fraction (achieved by proportionally adjusting the concentration and amount of the impregnation solution).

[0041] Comparative Example 5: All other conditions were exactly the same as in Example 1, except that the concentration of the impregnation solution was changed to adjust the mass fraction of ruthenium loading to 1.2%.

[0042] Comparative Example 6: Other conditions were exactly the same as in Example 1, except that the concentration ratio of the first and second impregnation solutions was adjusted so that the ruthenium concentration ratio inside the mesopores to that on the outer surface was approximately 2 times.

[0043] Comparative Example 7: Other conditions were exactly the same as in Example 1, except that the concentration ratio of the first and second impregnation solutions was adjusted so that the ruthenium concentration ratio inside the mesopores to that on the outer surface was approximately 4 times.

[0044] Comparative Example 8: All other conditions are exactly the same as in Example 1, except that the silicon-aluminum molar ratio of the support is changed to 50:1 (a hierarchical porous β-molecular sieve with a corresponding silicon-aluminum ratio needs to be prepared).

[0045] Comparative Example 9: All other conditions were exactly the same as in Example 1, except that the silicon-aluminum molar ratio of the carrier was changed to 150:1.

[0046] All conversion and selectivity data are expressed in mol%. The method for converting peak area data in GCMS to mol% is the external standard method, and the specific process is as follows: Among them, A BZ and A CHB f represents the peak areas of benzene and cyclohexylbenzene in a 1.0 μL reactant mixture in gas chromatography. BZ and f CHB The peak areas of 1.0 μL benzene and cyclohexylbenzene standards in gas chromatography; M BZ and M CHB ρ represents the relative molecular mass of benzene and cyclohexylbenzene; BZ and ρ CHB This represents the density of benzene and cyclohexylbenzene.

[0047] Catalyst stability test: 0.5 g of catalyst and 25 mL of benzene were sequentially placed into a high-pressure reactor, sealed, and subjected to three purging and venting cycles with H2 at room temperature. Subsequently, the reactor was rapidly heated to 200 °C under a 1.0 MPa H2 atmosphere, and then H2 was introduced to stabilize the pressure at 4.0 MPa. The reaction was allowed to proceed for a certain time. After each reaction cycle, the reactor liquid was removed, centrifuged at 8000 rpm, washed with ethanol, and vacuum dried at 60 °C for 12 h to obtain the catalyst for one cycle. If mass loss occurred during the process, the corresponding amount of fresh catalyst was added before the next cycle, and the recovered catalyst was transferred back to the reactor. Fresh benzene was added under the same reaction conditions to start a new round of reaction, and the above steps were repeated until five cycles were completed. The products obtained from each cycle were centrifuged, filtered, and analyzed using gas chromatography to calculate the benzene conversion rate. The catalyst stability was evaluated by comparing the benzene conversion rates of the first and fifth cycles. Figure 6 As shown, the catalyst of Example 1 (broken line 7) retained an activity rate of over 85% after 5 cycles, while the activity of Comparative Example 2 (broken line 8) declined rapidly, indicating that the gradient loading and ion anchoring strategy of the present invention significantly improved the cycling stability.

[0048] Metal dispersion test: CO pulse experiments were used to test the dispersion of metals in the catalyst. 150 mg of sample was weighed and pretreated at 140 °C for 40 min under a He atmosphere, then cooled to room temperature and reduced at 300 °C for 2 h under a H2 atmosphere to ensure complete Ru reduction. Subsequently, the sample was cooled to room temperature and subjected to CO pulse experiments until the adsorption peak intensity remained constant. The dispersion of the metal nanoparticles was calculated based on the CO absorption, with a CO to metal stoichiometry of 1:1.

[0049] Here, V CO The volume of CO adsorbed by the catalyst (under standard conditions) is represented by W, the mass of the catalyst is represented by P, the mass fraction of the metal in the catalyst is represented by M, and the relative atomic mass of the metal is represented by M.

[0050] The 10 types of catalysts obtained were characterized and tested, and the results are shown in Tables 1 and 2.

[0051] Table 1 a: The difference between Comparative Example 3 and Example 1 is that "S5 ion anchoring treatment" was omitted.

[0052] Table 2 From the above, the performance indicators of Embodiment 1 of the present invention and the designed comparative example (such as...) Figure 7As shown in the figure, in Embodiment 1 of the present invention, gradient loading and ion anchoring technology were adopted. Its performance (high selectivity and high stability) was far superior to the scheme that only used a single technology (Comparative Example 2 or 3) or conventional technology (Comparative Example 1). This confirms that there is a significant synergistic effect between "gradient loading" and "ion anchoring".

[0053] Comparison of Example 1 and Comparative Example: 1) Compared with Comparative Example 1 (commercial β-zeolite): Comparative Example 1 uses a common commercial β-zeolite, with a benzene conversion rate of only 36.5%, a cyclohexylbenzene selectivity of 40.7%, a yield of only 14.8%, a stability of ≤20%, and a metal dispersion of only 28.3%. In contrast, the embodiments of this invention use a hierarchical β-zeolite, resulting in significant improvements in all performance aspects. This indicates that the present invention, by constructing a hierarchical pore structure with interconnected internal and external pores, effectively improves mass transfer efficiency and enhances the utilization rate of active sites, overcoming the technical defects of limited mass transfer and low utilization rate of active sites in the prior art.

[0054] 2) Compared with Comparative Example 2 (concentration ratio 1:1): Comparative Example 2, using equal concentration loading, achieved a yield of only 12.4% and stability ≤20%; while the embodiments of this invention, employing a gradient loading strategy of "high concentration inside the pores and low concentration at the pore opening," achieved a yield of 49.8% and stability ≥85%. This indicates that the gradient loading strategy of this invention effectively balances the main reaction and side reactions, avoids excessive hydrogenation on the outer surface, and solves the technical problem of difficulty in balancing selectivity and stability in the prior art. Figure 4 As shown, obvious ruthenium agglomerates can be observed in the TEM image of the catalyst in Comparative Example 2, which is in stark contrast to Example 1 and explains its poor stability.

[0055] 3) Compared with Comparative Example 3 (without ion anchoring): Comparative Example 3 omitted ion anchoring treatment, and its stability was ≤55%, and the metal dispersion decreased to 33.7%; while the embodiment of the present invention, after treatment with ammonium acetate, had a stability ≥85% and a dispersion of 46.1%. This shows that ion anchoring treatment effectively inhibits metal particle agglomeration, improves the cycle stability of the catalyst, and overcomes the technical defects of easy metal sintering and poor stability in the prior art.

[0056] 4) Compared with Comparative Examples 4 and 5 (Ru loading deviation): Comparative Example 4 (0.8 wt%) showed a decrease in conversion rate due to insufficient active sites, while Comparative Example 5 (1.2 wt%) showed a decrease in selectivity and stability due to metal aggregation; however, the embodiment of this invention selected a loading of 1.0 wt%, achieving optimal performance. This indicates that the present invention, by optimizing the loading, balances activity and selectivity, solving the technical problem of difficulty in optimizing the loading in the prior art.

[0057] 5) Compared with Comparative Examples 6 and 7 (concentration ratio deviation): Comparative Example 6 (2:1) showed a decrease in yield due to insufficient active sites within the pores, while Comparative Example 7 (4:1) performed worse than the example. The example of this invention, however, selected a concentration ratio of 3:1, achieving excellent catalytic performance. This indicates that the present invention, by optimizing the concentration ratio, achieves precise control of the main reaction and side reactions, solving the technical problem of difficulty in improving selectivity in the prior art. The reason for this phenomenon is that when the concentration ratio is too high (e.g., 4:1), the active sites deep within the mesopores may be too dense, leading to limited local mass transfer or an increase in side reactions, thereby reducing the selectivity of the target product. Conversely, when the concentration ratio is too low (e.g., 2:1), the concentration difference between the active sites inside the mesopores and the outer surface is insufficient, failing to effectively suppress excessive hydrogenation reactions on the outer surface, resulting in an increase in byproducts. Therefore, controlling the concentration ratio within the range of 2.5 to 3.5 times can balance mass transfer efficiency and reaction selectivity, maximizing the synergistic effect of the dual function.

[0058] 6) Compared with Comparative Examples 8 and 9 (with deviations in silicon-to-aluminum ratio): Comparative Example 8 (50:1) experienced side reactions due to excessive acidity, and Comparative Example 9 (150:1) suffered from decreased activity due to insufficient active sites; while the embodiment of this invention selected a silicon-to-aluminum ratio of 100:1, achieving optimal performance. This indicates that the present invention, by optimizing the silicon-to-aluminum ratio, balances acidity and activity, solving the technical problem of difficulty in controlling the acidity of the carrier in the prior art.

[0059] The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims. All equivalent changes or modifications made in accordance with the spirit and essence of this invention should be included within the protection scope of this invention.

Claims

1. A gradient supported catalyst for the hydrogenation alkylation reaction of benzene, characterized in that, include: A hierarchical porous β-molecular sieve support, and a ruthenium metal active component fixed on the hierarchical porous β-molecular sieve support by ion anchoring; The ruthenium active component is spatially distributed in a concentration gradient on the hierarchical β-molecular sieve support, and the concentration of the ruthenium active component inside the mesopores of the support is higher than the concentration of the ruthenium active component on the outer surface of the support and in the micropore opening region. The ruthenium metal active component has a loading mass fraction of 1.0% in the catalyst; The silicon-aluminum molar ratio of the hierarchical porous β molecular sieve support is 100:1; The mass concentration of the active ruthenium component inside the mesopores of the carrier is 2.5 to 3.5 times that of the active ruthenium component on the outer surface of the carrier and in the micropore opening region.

2. The catalyst according to claim 1, characterized in that, The mesopore size of the β-zeolite support is 2~50 nm, and the micropore size is 0.5~2 nm.

3. A method for preparing the gradient supported catalyst for the hydrogenation alkylation reaction of benzene as described in claim 1, characterized in that, Includes the following steps: S1. Prepare the hierarchical porous β-molecular sieve support; S2. Prepare two ruthenium-containing impregnation solutions of different concentrations: the first impregnation solution has a ruthenium concentration of 0.045 mol / L, and the second impregnation solution has a ruthenium concentration of 0.012 mol / L; the ruthenium-containing impregnation solution is a complex solution formed by dissolving ruthenium trichloride and citric acid in deionized water, and the molar ratio of citric acid to ruthenium is 2:1; S3. High-concentration impregnation inside the pores: Using a vacuum pressure method, at a vacuum degree of -0.08 MPa and a temperature of 30°C, the first impregnation solution is impregnated inside the mesopores of the carrier. The ratio of the volume of the impregnation solution to the mass of the carrier is 2 mL: 1 g. After standing for 8 hours, the first drying is carried out at 100°C for 12 hours to obtain substance M1. S4. Low-concentration impregnation at the pore opening: Using a spray impregnation method, at a temperature of 25°C, the second impregnation solution is impregnated on the outer surface and micropore opening area of ​​M1 after step S3. The ratio of the volume of the impregnation solution to the mass of the carrier is 0.8 mL: 1 g. After standing for 2 h, a second drying is carried out at 100°C for 4 h to obtain substance M2. S5. Ion anchoring treatment: The substance M2 after step S4 is immersed in a 0.01 mol / L ammonium acetate solution and soaked at 30°C for 1 hour. Then, it is filtered and the solid is dried at 100°C for 6 hours to obtain substance M3. S6. Reduction treatment: In a hydrogen-argon mixed atmosphere with a hydrogen volume ratio of 10%, the temperature is increased to 450°C at a heating rate of 5°C / min, and the M3 treated in step S5 is reduced at 450°C for 3 hours to obtain the gradient supported catalyst.

4. The preparation method according to claim 3, characterized in that, The impregnation time for the vacuum pressurization method is 6-10 hours, and the spray rate for the spray impregnation method is 0.5-1 mL / min.

5. The application of the gradient supported catalyst as described in claim 1 for the hydrogenation alkylation of benzene in the hydrogenation alkylation reaction.

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