CoLa bimetallic catalyst based on two-step xerogel conversion method as well as preparation method and application of CoLa bimetallic catalyst

Abstract

The invention belongs to the technical field of catalyst preparation, and particularly relates to a CoLa bimetallic catalyst based on a two-step xerogel conversion method and a preparation method and application thereof. The preparation method provided by the invention comprises the following steps: firstly, carrying out calcination pretreatment on a ZSM-5 molecular sieve, and then, carrying out etching by utilizing a fluoride solution to construct a hierarchical mesoporous structure, so as to obtain an FZ5 carrier; loading cobalt and lanthanum on FZ5 through an impregnation method, and calcining to obtain a CoLa / FZ5 intermediate; and finally, coating, crystallizing and calcining the CoLa / FZ5 by adopting a xerogel conversion method to finally prepare the packaged CoLa-coated FZ5 catalyst. According to the invention, through the synergistic effect of a hierarchical porous structure and a core-shell encapsulation technology, high dispersion and stable confinement of bimetallic active sites in zeolite crystals are realized. The prepared catalyst shows excellent product selectivity, carbon deposition resistance and cycling stability in a reaction for preparing light aromatic hydrocarbon (BTEXN) through catalytic pyrolysis of lignite or tar, and has a wide industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation technology, specifically relating to a CoLa bimetallic catalyst based on a two-step dry gel conversion method, its preparation method, and its application. Background Technology

[0002] In tar catalytic conversion research, catalyst selection is crucial. Zeolite ZSM-5, due to its uniform pore structure, unique shape selectivity, and excellent hydrothermal stability, has become a key material in industrial catalysis. Introducing metal species into the zeolite framework can effectively regulate the chemical properties of active sites and simultaneously achieve targeted optimization of catalytic performance. Currently, metal encapsulation processes are mainly divided into pretreatment and post-treatment methods. While pretreatment methods have fewer steps and lower costs, they generally suffer from uneven metal dispersion and low encapsulation efficiency. The cobalt-lanthanum bimetallic system, through synergistic effects, can not only improve catalytic activity and product selectivity but also inhibit carbon deposition and extend catalyst lifetime. However, as a microporous zeolite, the pore size limitation of traditional ZSM-5 limits the effectiveness of post-synthetic metal loading through ion exchange or impregnation, making it only suitable for materials with pore sizes greater than 0.7 nm, and difficult to achieve efficient and stable metal dispersion within a microporous framework.

[0003] Dry gel conversion (DGC), as a highly efficient post-synthetic method, offers advantages such as high yield, low water consumption, and simple operation. Unlike hydrothermal synthesis where the precursor directly contacts water, DGC exposes the framework-containing dry gel to steam or a steam-organic structure-directing agent mixture, helping to maintain the compositional and structural integrity of the original gel. In recent years, zeolite materials with mesoporous-microporous hierarchical structures have attracted much attention due to their improved mass transfer capabilities and accessibility, creating favorable conditions for the encapsulation and stable dispersion of metal species. Nevertheless, existing technologies have not effectively solved key technical problems such as the precise positioning of metal nanoparticles within zeolite crystals, long-term stable encapsulation, and insufficient resistance to carbon deposition, thus limiting the industrial application prospects of catalysts. Therefore, it is urgent to combine the advantages of hierarchical pore design and the DGC process to develop a novel synthetic strategy that can stably encapsulate cobalt-lanthanum bimetallic nanoparticles within mesoporous-microporous hierarchical ZSM-5 zeolite, in order to achieve a synergistic improvement in the stability, activity, and selectivity of light aromatics in coal pyrolysis catalysts.

[0004] Lithium-ion batteries are indispensable components in electric vehicles and mobile electronic devices. They have advantages such as excellent electrochemical performance, light weight, long cycle life, and environmental friendliness. With the rapid increase in the consumption of lithium batteries, a large number of retired lithium-ion batteries have been generated. If the valuable metals such as lithium, nickel, cobalt, aluminum, and manganese contained in them are not recycled, they will not only have a negative impact on the environment, but also cause a waste of resources. Summary of the Invention

[0005] Therefore, the purpose of this invention is to provide a CoLa bimetallic catalyst based on a two-step dry gel conversion method, its preparation method and application. The CoLa@FZ5 catalyst prepared by this method has excellent thermal stability, anti-carbon deposition ability and high selectivity for light aromatic hydrocarbons (BTEXN).

[0006] Specifically, this invention provides a two-step method for preparing a CoLa bimetallic catalyst through dry gel conversion, comprising the following steps: S1. Pre-treat the ZSM-5 molecular sieve to remove impurities and moisture from the molecular sieve pores to obtain pre-treated ZSM-5 molecular sieve. S2. The pretreated ZSM-5 molecular sieve is fluorinated and then heat-treated to obtain fluorine-modified ZSM-5 molecular sieve FZ5; S3. Fluorine-modified ZSM-5 molecular sieve FZ5 was added to a mixed solution composed of Co(NO3)2·6H2O, La(NO3)3·6H2O and water, and stirred at a temperature and time sufficient for Co(NO3)2·6H2O and La(NO3)3·6H2O to be fully adsorbed on the support surface; then dried to obtain a dry solid; the dry solid was calcined in an oxygen-containing atmosphere at 500~600℃ to obtain a bimetallic supported CoLa / FZ5 catalyst; S4. The bimetallic supported CoLa / FZ5 catalyst is coated by a dry gel conversion method to obtain a CoLa bimetallic catalyst.

[0007] In some specific embodiments of the present invention, the preprocessing in S1 includes the following steps: ZSM-5 molecular sieve was calcined at 500~600℃ for 3~5 hours.

[0008] In some specific embodiments of the present invention, the preprocessing in S1 includes the following steps: ZSM-5 molecular sieve was calcined at 550℃ for 4 hours.

[0009] In some specific embodiments of the present invention, the fluoride etching in S2 includes the following steps: ZSM-5 molecular sieves were dispersed in an acidic etching solution and stirred until a paste was formed. The mixture was then subjected to solid-liquid separation. The solid was collected, washed with water until neutral, and then dried. The acidic etching solution is composed of an aqueous HF solution and NH4F dissolved therein.

[0010] In some specific embodiments of the present invention, the concentration of the HF aqueous solution is 0.4~0.6 mol / L, and the concentration of NH4F is 130~200 g / L.

[0011] In some specific embodiments of the present invention, the concentration of the HF aqueous solution is 0.5 mol / L, and the concentration of NH4F is 130-200 g / L.

[0012] In some specific embodiments of the present invention, the heat treatment in S2 includes the following steps: The ZSM-5 molecular sieve after fluoride etching is subjected to programmed temperature calcination; wherein, calcination is carried out in an oxygen-containing atmosphere, the final temperature is 500-600℃, the isothermal time in the final temperature section is 1-4 hours, and the heating rate to the final temperature is 5-15℃ / min; after calcination, it is cooled to obtain fluorine-modified ZSM-5 molecular sieve.

[0013] In some specific embodiments of the present invention, the heat treatment in S2 includes the following steps: The ZSM-5 molecular sieve etched with fluoride was subjected to programmed temperature calcination. The calcination was carried out in an oxygen-containing atmosphere, with a final temperature of 550°C, a constant temperature period of 2 hours, and a heating rate of 10°C / min to the final temperature. After calcination, the fluorine-modified ZSM-5 molecular sieve was obtained by cooling.

[0014] In some specific embodiments of the present invention, the mass ratio of Co(NO3)2·6H2O and La(NO3)3·6H2O in the S3 mixed solution is 1:1; the total loading of Co(NO3)2·6H2O and La(NO3)3·6H2O accounts for 1-4 wt% of the mass of the fluorine-modified ZSM-5 molecular sieve FZ5. The temperature and time conditions in S3 are 40°C and 2-4 hours; The drying process is carried out at 105°C for 8-12 hours. The roasting process takes 3-5 hours.

[0015] In some specific embodiments of the present invention, the mass ratio of Co(NO3)2·6H2O and La(NO3)3·6H2O in the S3 mixed solution is 1:1; the total loading of Co(NO3)2·6H2O and La(NO3)3·6H2O accounts for 1-4 wt% of the mass of the fluorine-modified ZSM-5 molecular sieve FZ5. The temperature and time conditions in S3 are 40°C and 3 hours; The drying was carried out at 105°C for 12 hours. The roasting process takes 4 hours.

[0016] In some specific embodiments of the present invention, the coating treatment by the dry gel conversion method in S4 includes the following steps: hydrolyzing the silicon source under the action of an acidic catalyst to form a silica sol; adding a template agent to the silica sol and adjusting the pH of the system to alkaline to obtain an alkaline silica sol; adding a bimetallic supported CoLa / FZ5 catalyst to the alkaline silica sol and mixing it evenly to form a hydrogel; heating the hydrogel to dehydrate and convert it into a dry gel; grinding the dry gel into powder and then crystallizing it in a steam atmosphere in a reactor; calcining the crystallized product to remove the template agent and obtain the CoLa bimetallic catalyst.

[0017] In some specific embodiments of the present invention, the silicon source is tetraethoxysilane, and during the hydrolysis of tetraethoxysilane, the mass ratio of tetraethoxysilane to water is 10:32.5; the acidic condition is a pH value of 1; the hydrolysis time is 20 hours; the template agent is tetrapropylammonium bromide, and the mass ratio of tetrapropylammonium bromide to tetraethoxysilane is 12:100; the pH value of the system is 10; and the mass ratio of the bimetallic supported CoLa / FZ5 catalyst to tetraethoxysilane is 1:5. The specific conditions for crystallization treatment in the steam atmosphere of the reactor are as follows: the mass ratio of the dry gel powder to water in the reactor is 1:20, the crystallization temperature is 180℃, and the crystallization time is 24 hours. The calcination was carried out at 550°C for 5 hours.

[0018] The present invention also provides a CoLa bimetallic catalyst, which is prepared by any of the preparation methods described above.

[0019] The present invention also provides the application of the CoLa bimetallic catalyst prepared by any of the above-described preparation methods, or the CoLa bimetallic catalyst as described, in the catalytic pyrolysis of lignite or tar.

[0020] Compared with the prior art, the present invention has the following beneficial effects: This invention employs a two-step dry gel conversion strategy, utilizing the synergistic effect of fluoride etching and dry gel conversion coating. This process, along with other techniques, enabled the precise encapsulation of bimetallic CoLa nanoparticles within ZSM-5 molecular sieve crystals. Fluoride etching introduced a hierarchical mesoporous structure into ZSM-5, providing abundant conditions for the deposition of metal nanoparticles. Accessible sites; the silica coating formed by dry gel conversion effectively inhibits the sintering of metal particles and Migration maintained the long-term stability of the catalyst.

[0021] The CoLa@FZ5 catalyst prepared in this invention exhibits excellent selectivity for light aromatics in the catalytic pyrolysis of lignite, with a total BTEXN yield reaching 28.6 mg / g, which is more than 38% higher than that of the original ZSM-5 catalyst. The Co sites dominate the dehydrogenation reaction, while the La sites promote hydrogenation and hydrogen transfer. The synergistic effect between Co and La promotes the formation of a hydrogenation-dehydrogenation network, efficiently guiding oxygen-containing compounds and heavy components in the volatile matter of lignite pyrolysis into monocyclic aromatics (BTEXN) and inhibiting the formation of carbon deposit precursors.

[0022] The catalyst of this invention exhibits excellent resistance to carbon deposition. After four regeneration cycles, it retains 91.98% of the initial light aromatic hydrocarbon yield, significantly higher than the stability of the unencapsulated catalyst. Thermogravimetric analysis shows that the catalyst... The carbon deposition on the catalyst was 8.87% lower than that on the unencapsulated sample. This is because the core-shell structure limits the carbon deposition precursor. The diffusion and deposition of the material cause the active metal sites at the core to become "storage rooms" for carbon deposits, effectively protecting the acidic sites near the outer shell.

[0023] The encapsulation structure of this invention enables the metal nanoparticles to maintain a stable size (2 nm) during repeated use, while the unencapsulated metal particles significantly aggregate and grow to approximately 20 nm after three regeneration cycles. The core-shell structure formed by the dry gel conversion effectively inhibits the migration, sintering, and loss of metal nanoparticles during the reaction process, while protecting the acidic sites of the catalyst. This structural stability ensures that the catalyst maintains high catalytic activity after multiple regenerations, providing a practical catalyst design scheme with both high selectivity and long service life for lignite tar upgrading.

[0024] The preparation method of the present invention is simple to operate and the raw materials are readily available. By adjusting the fluoride etching conditions, metal loading and dry gel conversion parameters, the catalyst pore structure, acid properties and metal dispersion can be precisely controlled, which has good prospects for industrial application. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a flowchart illustrating the two-step dry gel conversion process for preparing the CoLa@FZ5 catalyst according to the present invention.

[0027] Figure 2(a) X-ray diffraction (XRD) patterns of different catalysts; (b) pore size distribution (BJH) of ZSM-5, FZ5 and CoLa / FZ5. Figure 3 (a) XRD patterns of CoLa@FZ5 with metal loadings of 1%, 2% and 4%, respectively, with ZSM-5 as a reference; (b) Fourier transform infrared (FTIR) spectra of CoLa / FZ5 and CoLa@FZ5 before and after CO adsorption.

[0028] Figure 4 The images show scanning electron microscope (SEM) images of ZSM-5 (a), FZ5 (b), and CoLa / FZ5 (c).

[0029] Figure 5 Transmission electron microscopy (TEM) images of CoLa@FZ5 with metal loadings of 1% (a), 2% (b), and 4% (c).

[0030] Figure 6 XPS analysis of CoLa / FZ5 and CoLa@FZ5 molecular sieves: (a) XPS spectrum of Co; (b) XPS spectrum of La.

[0031] Figure 7 Temperature-programmed desorption (NH3-TPD) curves for ammonia with different catalysts.

[0032] Figure 8 This is a schematic diagram of a laboratory fixed-bed pyrolysis system.

[0033] Figure 9 For the analysis of coal pyrolysis products using different catalysts: (a) Distribution of pyrolysis products (gases, gases, etc.) (a) Composition of liquids, coke and semi-coke); (b) Composition of gaseous products.

[0034] Figure 10 To analyze the tar composition (a) and specific gravity of coal pyrolysis produced under different catalysts using GC-MS. A magnified view of the larger area (b).

[0035] Figure 11 Benzene, toluene, ethylbenzene, xylene, and naphthalene in coal pyrolysis tar under non-catalytic and catalytic conditions The composition of (BTEXN).

[0036] Figure 12 The regeneration performance of ZSM-5 and CoLa@FZ5 molecular sieves was evaluated in four cycles of catalytic reforming of lignite pyrolysis volatiles.

[0037] Figure 13To evaluate the stability of ZSM-5(a), CoLa / FZ5(b) and CoLa@FZ5(c) molecular sieves in the process of catalytic reforming of lignite pyrolysis volatiles to produce aromatics.

[0038] Figure 14 (a) Weight loss analysis (TG) and weight loss rate analysis (DTG) of coke reactivity on CoLa / FZ5 and CoLa@FZ5 molecular sieves after reaction; (b) Temperature programmed oxidation (TPO) curves comparing the oxidation behavior of coke deposits on CoLa / FZ5 and CoLa@FZ5 after reaction.

[0039] Figure 15 High-resolution transmission electron microscopy (HRTEM) images of the catalyst after three regeneration cycles: (a) CoLa@FZ5; (b) CoLa / FZ5. Detailed Implementation

[0040] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention and should not be used to limit the scope of protection of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Protection range.

[0041] Example 1: Preparation of CoLa bimetallic catalyst based on two-step dry gel conversion method The flowchart for the two-step dry gel conversion preparation of CoLa@FZ5 catalyst is attached. Figure 1 As shown, the specific preparation steps are as follows: Step 1: ZSM-5 molecular sieve (the ZSM-5 molecular sieve used in this example is a commercially available micron-sized zeolite molecular sieve purchased from the catalyst factory of Nankai University, with Si / Al=25 in the ZSM-5 molecular sieve) was pretreated by calcining in air at 550°C for 5 hours, and the resulting sample was denoted as ZSM-5 molecular sieve.

[0042] Step 2: Immerse 5 g of ZSM-5 molecular sieve in 150 mL of acidic etching solution, stir continuously at room temperature for 8 minutes, and then wash with deionized water until neutral. Dry the paste-like product in a 105°C forced-air drying oven, then transfer it to a muffle furnace and calcine at 550°C for 2 hours in air atmosphere. After cooling, the mesoporous-microporous hierarchical molecular sieve is obtained and labeled as FZ5. The acidic etching solution is prepared by dissolving 25 g of NH4F in an appropriate amount of 0.5 mol / L HF aqueous solution, and then continuing to adjust the volume to 150 mL with the same HF solution.

[0043] Step 3: Loading the active component using the equal-volume impregnation method: Add 5 g of FZ5 carrier to 250 mL of a mixed solution of cobalt nitrate and lanthanum nitrate (the solute amount is calculated based on the theoretical loading of 1%, 2% and 4%), stir in a constant temperature water bath at 40°C for 3 hours, then transfer to a forced-air drying oven and evaporate the solvent at 105°C (about 12 hours); the resulting solid is then calcined in a muffle furnace at 600°C in air for 4 hours, and after natural cooling, CoLa / FZ5 is obtained.

[0044] Step 4: Encapsulation of the CoLa / FZ5 intermediate using a dry gel conversion method, specifically including: hydrolyzing tetraethoxysilane in an acidic aqueous solution with pH 1.0 at 20°C for 20 hours, wherein the mass ratio of tetraethoxysilane to water is 1:3.25; adding tetrapropylammonium bromide template agent to the obtained silica sol and stirring, then adjusting the pH to 10 with alkali; adding the CoLa / FZ5 intermediate to the above mixed sol, wherein the mass ratio of CoLa / FZ5 to tetraethoxysilane is 1:1.25, and stirring for 15 minutes to form a uniform hydrogel; heating and stirring the hydrogel at 90°C to convert it into a dry gel, grinding it into a fine powder, and placing it in a sealed reactor for crystallization at 180°C under a steam atmosphere for 24 hours; after crystallization, calcining at 550°C for 4 hours to remove the template agent, obtaining the CoLa@FZ5 catalyst.

[0045] Example 2: Characterization of ZSM-5, FZ5, CoLa / FZ5 and CoLa@FZ5 1. XRD test The crystal structures of ZSM-5, FZ5, CoLa / FZ5 catalysts (calculated based on a theoretical solute loading of 2%, the same below) and CoLa@FZ5 catalysts with different metal loadings (calculated based on theoretical solute loadings of 1%, 2%, and 4%, respectively) were characterized using an X-ray diffractometer (Malvern Panalytical X'Pert3). The instrument was operated under CuKα radiation (λ = 1.5418 nm) at 40 kV and 40 mA. XRD patterns were collected at a scan rate of 10° / min within the 2θ range of 5°–50°. Figure 2 As shown in (a), the original ZSM-5 exhibits characteristic XRD diffraction peaks corresponding to the MFI framework. After fluoride treatment, FZ5 retains the Mobilization Filter (MFI) structure, although its peak intensity is slightly reduced. The crystallinity of FZ5 was determined to be 96.1%, indicating that acidic fluoride treatment slightly disrupted the structural order of the MFI zeolite.

[0046] Nitrogen adsorption-desorption isotherms were determined using an Autosorb-iQ analyzer from Quantachrome Instruments, USA. Specific surface area and pore volume were calculated using Brunauer-Emmett-Teller (BET) theory and the t-plot method. Pore size distributions of ZSM-5, FZ5, and CoLa / FZ5 (calculated based on 2% theoretical solute loading, hereinafter the same) were determined using the Barret-Joyner-Halenda (BJH) method. Figure 2 As shown in (b), FZ5 retained the micropore peak at 0.6 nm and exhibited distinct peaks at 2.2 nm and 3.8 nm, indicating the successful introduction of mesopores, compared to ZSM-5. Table 1 lists the structural characteristics of each catalyst. SBET decreased after acid etching and metal loading, but the total pore volume (Vtotal) of FZ5 was higher than that of its ZSM-5 precursor.

[0047] SBET: Specific surface area (total pore area calculated by the BET method); Smicro: Micropore area; Sext: External surface area; Vtotal: Total pore volume; Vmicro: Micropore volume; Vext: External pore volume. a is calculated using the Multi-point BET method. b is calculated using the total pore volume at P / P0 = 0.99. c is calculated using the t-plot method. The difference subtraction method is used: Sext = SBET - Smicro, Vext = Vtotal - Vmicro. like Figure 3 As shown in (a), CoLa@FZ5 samples with different metal loadings all exhibited characteristic diffraction peaks of the MFI framework, indicating that the coating process did not disrupt the basic crystal structure of ZSM-5. However, increasing the cobalt and lanthanum content in the initial synthetic gel led to a gradual decrease in the crystallinity of the final product. This phenomenon is attributed not only to the inhibitory effect of increased metal loading on secondary crystallization but also to the reduction of silica gel covering the mesoporous CoLa / FZ5 due to higher CoLa content. The change in crystallinity indicates that the MFI zeolite underwent further crystal growth during the secondary crystallization step, with the sample with a metal loading of 2 wt% achieving a relatively high crystallinity (85.2%). Subsequent performance tests, including the catalytic co-pyrolysis of lignite, all used this 2% loading to ensure consistency.

[0048] 2. FT-IR test Given that Fourier transform infrared spectroscopy (FTIR) of CO chemisorption can sensitively reveal the properties of metal particles and their exposure sites, this method has been widely adopted. Therefore, Fourier transform infrared (FTIR) characterization was performed on CoLa / FZ5 (calculated with solute amount based on theoretical loading of 2%) and CoLa@FZ5 (calculated with solute amount based on theoretical loading of 2%) on a Nicolet 560 infrared spectrometer.

[0049] Figure 3 (b) CO chemisorption FTIR spectra of CoLa / FZ5 and CoLa@FZ5 samples, designed to compare the electronic environment of coated and uncoated metal species. The two samples were measured at 2021 cm⁻¹. -1 and 1895cm -1 Absorption bands were observed in the vicinity, corresponding to linearly adsorbed CO and bridging CO species adsorbed on the zeolite surface, respectively. For the CoLa / FZ5 and CoLa@FZ5 samples, at 2021 cm⁻¹... -1 1895cm -1 1320cm -1 and 1210cm -1 The observed differences indicate that the environment of the metal particles in CoLa / FZ5 and CoLa@FZ5 is different.

[0050] 3. SEM testing The morphology of ZSM-5, FZ5, and CoLa / FZ5 was observed using a scanning electron microscope (SEM, Thermo Fisher Scientific ApreoC). Before testing, the samples were pretreated with anhydrous ethanol. The samples were dissolved in anhydrous ethanol and sonicated for 30 min to ensure thorough dispersion. After the ethanol evaporated, the samples were transferred to a Cu metal sheet and finally to a sample cell for testing.

[0051] Figure 4 SEM images in (a) and (b) show that ZSM-5 has a smooth MFI morphology, while FZ5 has a hierarchical porous structure. Acidic fluoride treatment significantly altered the external morphology of ZSM-5, successfully introducing a large number of pores. The pristine ZSM-5 molecular sieve exhibits characteristic microporosity with a pore size of approximately 0.6 nm, compared to... Figure 4 The SEM observations in (a) are consistent. The resulting hierarchical intragranular porosity provides numerous accessible sites for metal deposition. For example... Figure 4 As shown in (c), the loading of Co and La nanoparticles causes changes in the surface morphology of the catalyst, making its surface rougher than that of ZSM-5 and FZ5.

[0052] 4. TEM test CoLa@FZ5 with metal loadings of 1%(a), 2%(b), and 4%(c) were further analyzed using a transmission electron microscope (TEM, FEITecnaiG2F30) equipped with an EDAXEliteT energy-dispersive X-ray spectroscopy (EDS) detector. The EDS detector was used to map the distribution of metal elements in the zeolite matrix.

[0053] Figure 5 TEM images show that all CoLa nanoparticles in the CoLa@FZ5 samples, regardless of loading, have a uniform size and are well distributed. Nanoparticles with sizes between 3-5 nm are uniformly distributed within the zeolite crystallites. However, as... Figure 5 As shown, at a loading of 4 wt%, although the CoLa nanoparticles were generally well distributed, partial aggregation of metal particles was observed. With increasing CoLa content, more FZ5 zeolite was required to accommodate the metal species, which reduced the coverage of the silica sol and consequently affected the crystallization behavior of the FZ5 zeolite.

[0054] 5. XPS Test The oxidation states of metal sites on the catalysts before and after the reaction of CoLa / FZ5 (calculated based on a theoretical solute loading of 2%) and CoLa@FZ5 (calculated based on a theoretical solute loading of 2%) were studied in detail using Thermo Fisher K-Alpha X-ray photoelectron spectroscopy (XPS).

[0055] Figure 6 The XPS results show the changes in the distribution of Co and La elements in CoLa@FZ5 relative to CoLa / FZ5. Figure 6 In (a), the enhanced peak width variation in the Co2p region of CoLa@FZ5 indicates increased surface exposure of cobalt, suggesting a possible change in its chemical environment. Figure 6 In (b), compared to CoLa / FZ5, CoLa@FZ5 exhibits higher peak intensity and sharper peak shape in the La3d spectral region. Although CoLa@FZ5 is designed to confine Co and La within a zeolite framework, vapor-assisted crystallization may induce partial aluminum loss and surface reconstruction. Consequently, some Co and La species migrate and redeposit near the shell. In CoLa / FZ5, uncoated Co and La species are identified as Co3O4 and La2O3, respectively. However, in CoLa@FZ5, shell growth confines more Co and La species within the core. Example 3: Temperature-programmed desorption (analysis) test of ammonia in ZSM-5, FZ5, CoLa / FZ5 and CoLa@FZ5 Ammonia desorption analysis using a programmed temperature-progression chemisorption analyzer (AutoChem II 2920, manufactured by McMurray Tech, USA) equipped with a thermal conductivity detector was performed. Using helium as a protective gas, 100 mg of sample was added to a quartz tube. Under helium atmosphere, the sample was heated from 30 °C to 300 °C at a rate of 10 °C / min, held at that temperature for 30 min, and then cooled. After cooling to 50 °C, a 10% NH3 / He mixture was introduced at a flow rate of 50 mL / min until saturation. Helium purging was then switched to until the signal stabilized. The temperature was then increased to 600 °C at a rate of 10 °C / min for desorption. The desorbed gas was detected using a thermal conductivity detector, and the NH3 desorption curve was obtained.

[0056] Figure 7 NH3-TPD curves are shown for ZSM-5, FZ5, CoLa / FZ5 (calculated based on 2% theoretical solute loading), and CoLa@FZ5 (calculated based on 2% theoretical solute loading). Three desorption peaks were observed in the temperature ranges of approximately 100℃–130℃, 190℃–230℃, and 410℃–440℃, corresponding to weak acid sites, moderate acid sites, and strong acid sites, respectively. For CoLa@FZ5, the desorption feature observed at ≈350℃ appears as an intermediate product in deconvolution and is therefore classified as a moderate / metal-related component rather than treated as a separate high-temperature (strong acid) band. Compared to ZSM-5, the peaks and acid centers in the weak and strong acid regions of acid-etched FZ5 are not prominent. Table 2 shows that fluoride etching leads to a reduction in total acid content. This change is due to the acid treatment disrupting the Si-OH-Al bridged hydroxyl structure in the Z5 zeolite framework. The weak acid sites primarily originate from the decomposition of framework tetrahedral aluminum, framework-interconnected aluminum species, and non-framework aluminum species resulting from complete decomposition. With the introduction of the metal elements Co and La, the total acid content of the metal-supported catalyst decreases compared to FZ5, likely due to partial metal coverage of acid sites. CoLa@FZ5 exhibits significantly higher acid sites than FZ5 and CoLa / FZ5, indicating that dry gel conversion (DGC) partially alters the strength of the acid sites. This change may be attributed to the increased acid site density and the generation of new Brønsted sites, as the vapor-assisted crystallization step can generate new acid centers through the redistribution of framework aluminum and metal-support interactions.

[0057] Example 4: Catalytic pyrolysis experiment and product analysis 1. Fixed bed test The catalysts used in this embodiment are ZSM-5 (the ZSM-5 molecular sieve used in this embodiment is a commercially available micron-sized zeolite molecular sieve purchased from the catalyst factory of Nankai University, with Si / Al ratio of 25 in the ZSM-5 molecular sieve), FZ5, CoLa / FZ5 (calculated based on a theoretical loading of 2% for each solute), and CoLa@FZ5 (calculated based on a theoretical loading of 2% for each solute) prepared in Example 1. The test coal samples used in this embodiment are typical lignite from Shengli Coal Mine in Inner Mongolia Autonomous Region, China. The industrial analysis and elemental analysis are shown in Table 2. The coal samples were air-dried and then stored.

[0058] A non-in-situ catalytic method was employed, with CoLa / FZ5 and SL coal samples (mass ratio 1:1) separately placed in a fixed bed for catalytic pyrolysis experiments. The fixed bed experiment conditions were: heating rate 10℃ / min, final pyrolysis temperature set at 550℃, and N2 flow rate 50 ml / min. The products were collected, and the molecular sieve was recovered. The fixed bed equipment process is as follows: Figure 8 As shown. 20g of lignite sample and 20g of catalyst were weighed and placed in the upper and lower sections of the reactor, respectively, and filled with quartz wool to ensure complete coverage and tightness of the quartz tubes. Before each experiment, high-purity nitrogen gas at a flow rate of 50ml / min was injected into the quartz tubes to maintain the inert atmosphere required for the reaction. The raw lignite in the upper section was pyrolyzed at 550℃ under a continuous N2 flow (50mL / min), producing volatiles. These hot volatiles were directly carried into the catalyst bed in the lower section by the nitrogen flow, where the modified catalyst further catalyzed the reforming and aromatization reactions. After cooling, the coke and deactivated catalyst were collected and weighed.

[0059] The method for separating tar and water in liquid products is as follows: Acetone is used as a solvent to wash the product adhering to the inner walls of the cooler and gas-liquid separator. Then, anhydrous magnesium sulfate is added to separate the tar and dehydrate the product. After completion, the pyrolysis liquid and pyrolytic coke are weighed separately, and the yields of the three-phase products are determined. All experiments are repeated at least three times to ensure the reproducibility of the results.

[0060] In this invention, the product yield, mass, and carbon balance are calculated as follows: Among them, M sample The raw material is dried and has no ash content; M char M gas M coke and are the masses of pyrolysis coke, pyrolysis gas, and carbon deposits on the catalyst after the reaction, respectively; while Mliquid is the mass of the liquid product, which includes the mass of tar and pyrolysis water, and is obtained by subtraction in the calculation.

[0061] Figure 9The distribution and gas composition of pyrolysis products obtained from lignite pyrolysis using different catalysts are shown. For example... Figure 9 As shown in (a), the yields of gaseous, liquid, and solid (coke) products exhibit different trends. Compared to ZSM-5, the FZ5 catalyst increased the yield of gaseous products, decreased the liquid yield, and slightly increased coke formation. The enhanced reactivity of FZ5 compared to ZSM-5 is mainly attributed to the presence of mesopores and micropores, which facilitate deep catalytic cracking of volatile compounds during pyrolysis. The introduction of metal nanoparticles further increased the gaseous and liquid product yields of CoLa / FZ5, while reducing coke formation. This behavior may be because the metal nanoparticles partially blocked the hierarchical structure of FZ5, resulting in a reduction in total specific surface area and mesopore volume. Compared to CoLa / FZ5, coated CoLa@FZ5 zeolite further enhanced gas yield and suppressed coke formation. This improvement is likely due to the optimized pore structure and enhanced mass transfer properties of the coated zeolite, which facilitate the diffusion of pyrolysis volatiles to active catalytic sites, promoting the cracking of macromolecules into lighter gaseous products. Although the catalyst and lignite bed were physically separated in our external pyrolysis experimental setup, slight variations in coke yield were still observed under different catalytic conditions.

[0062] like Figure 9 As shown in (b), the gaseous products from lignite pyrolysis mainly consist of CO2, CO, H2, CH4, and light hydrocarbons (C2-C4). These gases are primarily generated through primary and secondary cracking of oxygen-containing compounds, involving decarboxylation, decarbonylation, dehydrogenation, and CC / CO bond cleavage, leading to alkylation. During the CoLa@FZ5 zeolite-catalyzed pyrolysis of lignite, the H2 yield increased from 0.25 mmol / g to 0.71 mmol / g, indicating that the coated metal species enhanced the dehydrogenation reaction. The Co active center catalyzes CC bond cleavage, promoting molecular hydrogen formation, which is confirmed by the increased hydrogen content in the product gas. The La species enhances hydrogen adsorption and its transfer to aromatic intermediates to promote ring closure. The synergistic effect between Co and La guides the reactants through a hydrocarbon pool mechanism favorable for monocyclic aromatic hydrocarbon formation. Therefore, the bimetallic catalyst exhibits synergistically enhanced deoxygenation performance through decarbonylation and decarboxylation reactions, and improves hydrogenation efficiency, ultimately achieving higher aromatic selectivity and inhibiting coke formation. CoLa@FZ5 also promotes higher yields of CO and CO2 during pyrolysis.

[0063] Figure 10GC-MS analysis of tar composition from coal pyrolysis on different catalysts (a) and magnified view of the comparative region (b). The detected compounds were classified into six classes: monocyclic aromatics (BAHs), bicyclic aromatics (BAHs), polycyclic aromatics (PAHs), alkanes, oxygen-containing compounds (OOSs), and other compounds (including sulfur- and nitrogen-containing compounds). All catalysts exhibited strong deoxygenation and aromatization performance, with aromatics accounting for over 97% of the compounds detected by GC-MS. Compared to ZSM-5 and FZ5, the metal-supported catalysts CoLa / FZ5 and CoLa@FZ5 showed enhanced aromatic selectivity and yield. For CoLa@FZ5, the aromatic products were predominantly monocyclic aromatics, followed by bicyclic aromatics (BAHs), and then polycyclic aromatics (PAHs). Compared to CoLa / FZ5, CoLa@FZ5 produced fewer oxygen-containing compounds and alkanes, indicating that coating enhances the deoxygenation efficiency of the metal-supported catalyst. This improvement is likely due to better dispersion of metal particles achieved through coating, resulting in a more uniform distribution of active sites and enhanced deoxygenation activity. Furthermore, the coating structure may improve thermal stability and resistance to coking, thereby minimizing catalyst deactivation and maintaining catalytic performance during deoxygenation. Compared to ZSM-5, FZ5, and CoLa / FZ5 (all of which possess abundant mesopores and micropores), CoLa@FZ5 further reduces the levels of oxygen-containing compounds and alkanes. This confirms the crucial role of hierarchical pore structure and bimetallic activity in deoxygenation. These results suggest that the hierarchical pore structure and bimetallic active sites of the coated catalyst promote the formation of monocyclic aromatic hydrocarbons through a "hydrocarbon pool" or "phenol pool" mechanism.

[0064] Figure 11The composition of BTEXNs (benzene, toluene, ethylbenzene, xylene, and naphthalene) in coal pyrolysis tar under non-catalytic and catalytic conditions is shown. Compared to the non-catalytic case, all catalysts exhibited enhanced selectivity for light aromatics, with CoLa@FZ5 showing the most significant improvement. This finding highlights the crucial role of catalysts in guiding product distribution towards light aromatics. Compared to ZSM-5 and FZ5, CoLa / FZ5 produced a higher overall yield of light aromatics. This enhancement is attributed to the higher catalytic activity and selectivity of CoLa / FZ5. The introduction of Co and La improved the efficiency of deoxygenation and aromatization, promoting the conversion of oxygen-containing compounds to light aromatics. Introducing Co and La into the hierarchical ZSM-5 synergistically enhanced the yield of BTEXN by coupling Co-mediated CH activation with La-promoted hydrogenation and aromatization. In this bimetallic system, the Co site both weakens the strong Brønsted acidity and catalyzes the dehydrogenation reaction, while the La center adsorbs and provides hydrogen for aromatic intermediates. The electronic interactions between Co and La further increase the electronic defects and activity of each metal, jointly accelerating the hydrogen transfer and deoxygenation cycles. The result is a unified hydrogenation-dehydrogenation network that directs pyrolysis fragments toward monocyclic aromatics, away from the coke precursor, thus significantly improving selectivity. CoLa@FZ5 achieved the highest total yield of light aromatics, reaching 28.6 mg / g. This improvement is attributed to the optimized pore structure of CoLa@FZ5, which enhances reactant diffusion and promotes the formation of light aromatics. Notably, FZ5 exhibits a reduced yield of light aromatics. This reduction is likely due to the partial degradation of the ZSM-5 framework during fluoride treatment, which negatively impacts its catalytic performance.

[0065] 2. Molecular sieve stability evaluation The stability of the catalyst was evaluated through a cyclic regeneration experiment. Specifically, in a fixed-bed reactor, volatiles from lignite pyrolysis were passed through the catalyst bed for catalytic reforming, with each reaction cycle lasting 35 minutes. After the reaction, the deactivated catalyst was removed and calcined in air to remove coke deposits. Subsequently, under the same reaction conditions, the regenerated catalyst was used to repeat the catalytic reforming process multiple times. After each cycle, the reaction products were collected and recorded, and the catalyst stability was quantitatively assessed by calculating changes in product yield and composition. Simultaneously, the recycled catalyst was characterized to analyze changes in its physicochemical properties. Furthermore, the thermal behavior of carbon deposits on the catalyst was analyzed using temperature-programmed oxidation (TPO) testing, and the catalyst microstructure was observed using high-resolution transmission electron microscopy (HRTEM).

[0066] Figure 12The regeneration performance of CoLa@FZ5 molecular sieve after catalytic reaction is shown. Compared with ZSM-5, CoLa@FZ5 maintained a relatively high yield of light aromatics even after three regeneration cycles. However, after three regeneration cycles, the catalyst structure was severely damaged, leading to a significant decrease in aromatic yield. Notably, the decrease in aromatic yield was more significant for ZSM-5 than for CoLa@FZ5. With increasing regeneration cycles, the acidic sites in the molecular sieve underwent gradual changes during roasting. This was mainly due to the damage to the zeolite framework caused by high-temperature roasting and the presence of inherent or pyrolysis-derived moisture. During this process, aluminum atoms may detach or migrate from the framework. Although coke can be partially removed during regeneration to restore activity, acid loss remains the main cause of catalyst deactivation. In the catalytic reforming of lignite pyrolysis volatiles, in addition to converting volatiles into light aromatics, severe coking also occurred. Coke precursors deactivate acidic sites on the surface and within the pores, ultimately leading to pore blockage.

[0067] Figure 13 To assess the stability of ZSM-5(a), CoLa / FZ5(b), and CoLa@FZ5(c) molecular sieves in the catalytic reforming of lignite pyrolysis volatiles to produce aromatics. With increasing reaction time, the aromatic content produced by ZSM-5 and CoLa / FZ5 decreased significantly. This indicates that ZSM-5 and CoLa / FZ5 rapidly lost their inherent active sites during a single pass reaction. The polymerization and coking of coke precursors, forming deposits on the surface or within the pores, significantly reduced the catalyst activity. Correspondingly, the activity of CoLa@FZ5 also decreased over time. The high catalytic activity of CoLa@FZ5 is attributed to the confinement of metal species within its hierarchical pores. The core-shell structure generated by dry gel conversion (DGC) effectively protects acidic sites and maintains the dispersion of metal nanoparticles, thereby maintaining a high aromatization rate and inhibiting the formation of coke precursors. This is because Co and La species promote the hydrogenation of volatiles, while the hierarchical pores enhance molecular diffusion and transport. Coking on catalysts largely depends on the state of the metal active sites, whether they are surface-bound or encapsulated within channels. When the metal sites are fixed, coke accumulation continues and intensifies with increasing reaction time until saturation is reached. At this stage, catalyst deactivation is primarily caused by pore blockage.

[0068] Figure 14 The thermal behavior of carbon deposits on CoLa / FZ5 and CoLa@FZ5 catalysts after the reaction, and the results of temperature-programmed oxidation (TPO) tests. Figure 14As shown in (a), all deactivated catalysts exhibited significant weight loss at approximately 520 °C, likely due to the presence of abundant amorphous carbon in the deposits. At higher temperatures, these unstable carbon species gradually reorganized into more stable graphite structures, releasing volatile small molecules (e.g., H2, CH4, CO). The carbon deposition on CoLa@FZ5 was 8.87% lower than that on CoLa / FZ5, directly indicating that CoLa@FZ5 possesses superior catalytic stability. Compared to CoLa / FZ5, the combustion temperature of coke on CoLa@FZ5 shifted to a higher range. This suggests that in the core-shell structure of CoLa@FZ5, intermediates formed at the metal active sites in the core lead to the aggregation of coke precursors, which are more difficult to diffuse outward, effectively turning the core into a "storage chamber" for coke. Figure 14 (b) shows the temperature-programmed oxidation (TPO) curves of the deactivated CoLa / FZ5 and CoLa@FZ5 catalysts. Both deactivated catalysts exhibited oxidation of amorphous carbon at 152 °C, mainly due to the adsorption of active oligomers or light hydrocarbons generated during pyrolysis onto the catalyst surface. Furthermore, both catalysts showed a stronger and significantly broader peak at 498 °C, indicating the enrichment of complex-compositioned and widely distributed refractory carbon species on the catalyst surface. This behavior may be related to the distribution of metal active sites and the pore structure of the catalyst. In CoLa@FZ5, the coating structure reduces the surface exposure of Co and La, which helps to regulate the distribution of active sites and limit the diffusion of coke precursors, resulting in a significantly lower coke oxidation peak compared to CoLa / FZ5.

[0069] Figure 15 High-resolution transmission electron microscopy (HRTEM) images of CoLa@FZ5 and CoLa / FZ5 after three regeneration cycles were compared. Figure 15 As shown in (a), the CoLa nanoparticles (approximately 2 nm) in CoLa@FZ5 are encapsulated within a well-crystallized MFI framework and maintain their original size, indicating that the encapsulation effectively prevents metal aggregation. In contrast, the CoLa particles in CoLa / FZ5 significantly increase from approximately 2 nm to approximately 20 nm, suggesting that unencapsulated particles tend to aggregate when exposed to the external environment. Some larger particles (approximately 10 nm) were also observed on the surface of CoLa@FZ5, which may be due to local defects or incomplete encapsulation during synthesis. The core-shell structure of CoLa@FZ5 confines the nanoparticles within the MFI framework, effectively suppressing aggregation during repeated cycles. In CoLa / FZ5, the unencapsulated nanoparticles are directly exposed to the environment and have higher surface energy, which promotes aggregation and significant particle growth. The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments described herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a two-step dry gel conversion treatment of a CoLa bimetallic catalyst, characterized in that, Includes the following steps: S1. Pre-treat the ZSM-5 molecular sieve to remove impurities and moisture from the molecular sieve pores to obtain pre-treated ZSM-5 molecular sieve. S2. The pretreated ZSM-5 molecular sieve is fluorinated and then heat-treated to obtain fluorine-modified ZSM-5 molecular sieve FZ5; S3. Fluorine-modified ZSM-5 molecular sieve FZ5 was added to a mixed solution composed of Co(NO3)2·6H2O, La(NO3)3·6H2O and water, and stirred at a temperature and time sufficient for Co(NO3)2·6H2O and La(NO3)3·6H2O to be fully adsorbed on the support surface; then dried to obtain a dry solid; the dry solid was calcined in an oxygen-containing atmosphere at 500~600℃ to obtain a bimetallic supported CoLa / FZ5 catalyst; S4. The bimetallic supported CoLa / FZ5 catalyst is coated by a dry gel conversion method to obtain a CoLa bimetallic catalyst.

2. The method for preparing a two-step dry gel conversion treatment CoLa bimetallic catalyst as described in claim 1, characterized in that, The preprocessing in S1 includes the following steps: ZSM-5 molecular sieve was calcined at 500~600℃ for 3~5 hours.

3. The method for preparing a two-step dry gel conversion treatment CoLa bimetallic catalyst as described in claim 1, characterized in that, The fluoride etching in S2 includes the following steps: ZSM-5 molecular sieves were dispersed in an acidic etching solution and stirred until a paste was formed. The mixture was then subjected to solid-liquid separation. The solid was collected, washed with water until neutral, and then dried. The acidic etching solution is composed of an aqueous HF solution and NH4F dissolved therein.

4. A method for preparing a two-step dry gel conversion treatment CoLa bimetallic catalyst as described in claim 3, characterized in that, The concentration of the HF aqueous solution is 0.4~0.6 mol / L, and the concentration of NH4F is 130~200 g / L.

5. The method for preparing a two-step dry gel conversion treatment CoLa bimetallic catalyst as described in claim 1, characterized in that, The heat treatment in S2 includes the following steps: The ZSM-5 molecular sieve after fluoride etching is subjected to programmed temperature calcination; wherein, calcination is carried out in an oxygen-containing atmosphere, the final temperature is 500-600℃, the isothermal time in the final temperature section is 1-4 hours, and the heating rate to the final temperature is 5-15℃ / min; after calcination, it is cooled to obtain fluorine-modified ZSM-5 molecular sieve.

6. The method for preparing a two-step dry gel conversion treatment CoLa bimetallic catalyst as described in claim 1, characterized in that, The mass ratio of Co(NO3)2·6H2O to La(NO3)3·6H2O in the S3 mixed solution is 1:1; the total loading of Co(NO3)2·6H2O and La(NO3)3·6H2O accounts for 1-4 wt% of the mass of the fluorine-modified ZSM-5 molecular sieve FZ5. The temperature and time conditions in S3 are 40°C and 2-4 hours; The drying process is carried out at 105°C for 8 to 12 hours. The roasting process takes 3 to 5 hours.

7. The method for preparing a two-step dry gel conversion treatment CoLa bimetallic catalyst as described in claim 1, characterized in that, The coating process in S4 using the dry gel conversion method includes the following steps: hydrolyzing the silicon source under the action of an acidic catalyst to form a silica sol; adding a template agent to the silica sol and adjusting the pH of the system to alkaline to obtain an alkaline silica sol; adding a bimetallic supported CoLa / FZ5 catalyst to the alkaline silica sol and mixing them evenly to form a hydrogel; heating the hydrogel to dehydrate it and convert it into a dry gel; grinding the dry gel into powder and then crystallizing it in a steam atmosphere in a reactor; calcining the crystallized product to remove the template agent and obtain the CoLa bimetallic catalyst.

8. The method for preparing a two-step dry gel conversion treatment CoLa bimetallic catalyst according to any one of claims 1-7, characterized in that, The silicon source is tetraethoxysilane, and during the hydrolysis of tetraethoxysilane, the mass ratio of tetraethoxysilane to water is 10:32.5; the acidic condition is a pH of 1; the hydrolysis time is 20 hours; the template agent is tetrapropylammonium bromide, and the mass ratio of tetrapropylammonium bromide to tetraethoxysilane is 12:100; the pH of the system is 10; the mass ratio of the bimetallic supported CoLa / FZ5 catalyst to tetraethoxysilane is 1:

5. The specific conditions for crystallization treatment in the steam atmosphere of the reactor are as follows: the mass ratio of the dry gel powder to water in the reactor is 1:20, the crystallization temperature is 180℃, and the crystallization time is 24 hours. The calcination was carried out at 550°C for 5 hours.

9. A CoLa bimetallic catalyst, characterized in that, The catalyst is prepared by the preparation method according to any one of claims 1-8.

10. The application of the CoLa bimetallic catalyst prepared by any one of claims 1-8 or the CoLa bimetallic catalyst as described in claim 9 in the catalytic pyrolysis of lignite or tar.

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