Preparation method and application of molecular sieve catalyst with hierarchical porous structure
By loading cerium oxide-carbon nanotube composite materials onto a molecular sieve matrix, a hierarchical pore structure was constructed, and supercritical extraction technology was used to solve the problems of microporous structure loss and carbon deposition in molecular sieve catalysts during biodiesel synthesis, thereby achieving high catalytic activity and stability.
Patent Information
- Application Number
- CN202511943898.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-22
- Publication Date
- 2026-03-06
AI Technical Summary
Existing molecular sieve catalysts suffer from problems such as damage to microporous structure, reduction of specific surface area, loss of active sites, and coking and blockage of macromolecular glycerides in biodiesel synthesis. They also lack the ability to remove carbon deposits in situ, which affects the economic efficiency and sustainability of the catalysts.
A multi-level porous molecular sieve catalyst was developed by loading cerium oxide-carbon nanotube composite material onto a molecular sieve matrix to construct a microporous-mesoporous synergistic structure. The integrity of the pore structure was preserved by supercritical extraction technology, and the cerium oxide-carbon nanotube composite material was anchored on the pore surface to enhance catalytic activity and electron transfer.
It improves the catalytic activity and stability of the catalyst, inhibits the sintering and loss of active components, effectively removes carbon deposits, and increases the yield of biodiesel and the service life of the catalyst.
Smart Images
Figure CN121607183A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of chemical technology, specifically relating to a method for preparing a multi-level porous molecular sieve catalyst and its application. Background Technology
[0002] Currently, biodiesel synthesis mainly relies on homogeneous base catalysts or solid acid / base catalysts. Among these, molecular sieve-based solid catalysts have become a research hotspot due to their advantages such as reusability and environmental friendliness. Conventional technical routes include: ① introducing active sites through ion exchange using microporous molecular sieves; ② constructing mesopores to improve diffusion efficiency through post-treatment (acid / base etching); ③ enhancing surface alkalinity by loading metal oxides.
[0003] However, in the above methods, although the mesopores formed by alkali treatment improve diffusion efficiency, excessive etching will destroy the microporous structure, resulting in a sharp drop in specific surface area and loss of active sites. Macromolecular glycerides polymerize and coke in the channels, blocking active sites. Furthermore, traditional catalysts lack the ability to remove carbon precursors in situ, which restricts the economic efficiency and sustainability of the industrial application of catalysts. Summary of the Invention
[0004] The purpose of this invention is to provide a method for preparing a multi-level porous molecular sieve catalyst and its application, so as to solve the problems mentioned in the background art.
[0005] To achieve the above objectives, the present invention provides the following technical solution:
[0006] A multi-level porous molecular sieve catalyst includes:
[0007] A molecular sieve matrix having a microporous structure and a mesoporous structure;
[0008] A cerium oxide-carbon nanotube composite modified material is loaded onto the pore surface and outer surface of the molecular sieve matrix;
[0009] The cerium oxide-carbon nanotube composite modified material is composed of in-situ grown carbon nanotubes and nano-cerium oxide particles, wherein the cerium oxide particles are anchored to the surface and ends of the carbon nanotubes.
[0010] Preferably, the molecular sieve matrix is one of ZSM-5, Beta, Y-type or MCM-41, and a mesoporous structure is formed by alkali treatment or acid treatment.
[0011] Preferably, the mass of the cerium oxide-carbon nanotube composite modified material accounts for 5% to 30% of the total mass of the catalyst, wherein the mass ratio of cerium oxide to carbon nanotube is (1:2) to (2:1).
[0012] Preferably, the preparation method of the cerium oxide-carbon nanotube composite modified material includes the following steps:
[0013] (a) Disperse the plasma-activated carbon nanotubes in a microemulsion system containing a cerium salt. The microemulsion consists of a surfactant, a co-surfactant, an oil phase, and an aqueous phase, where the aqueous phase contains a cerium salt solution with a concentration of 0.1 - 0.5 mol / L;
[0014] (b) Dropwise add a precipitating agent to the system in step (a) and simultaneously apply ultrasonic oscillation at a frequency of 40 - 80 kHz. React at 50 - 70 °C to form a precursor coating layer by the directional deposition of cerium ions on the surface of the carbon nanotubes;
[0015] (c) Perform supercritical CO2 fluid extraction on the product obtained in step (b) to remove the surfactant and the organic phase;
[0016] (d) Heat the extracted solid in a reducing atmosphere. First, raise the temperature to 300 °C at a rate of 1 °C / min and hold for 1 h, then raise the temperature to 600 °C at a rate of 5 °C / min and calcine for 2 h to in-situ generate a CeO x (0 < x < 2)-carbon nanotube heterojunction structure.
[0017] Preferably, the surfactant in the microemulsion is the amphiphilic block copolymer Pluronic F127, the oil phase is cyclohexane, and the mass ratio of the aqueous phase to the surfactant is (1:3) - (1:5).
[0018] Preferably, in step (b), the ultrasonic power density is 100 - 300 W / L, and the precipitating agent is a mixed solution of hexamethylenetetramine and ammonia water with a molar ratio of 1:2.
[0019] Preferably, in step (d), the volume fraction of H2 in the reducing atmosphere is 5% - 15%.
[0020] A method for preparing a molecular sieve catalyst with a hierarchical pore structure, comprising the following steps:
[0021] (1) Perform dealumination or alkali treatment on the molecular sieve raw powder to form a hierarchical pore structure;
[0022] (2) Use the equal-volume impregnation method to load the cerium oxide-carbon nanotube composite modification material onto the hierarchical pore molecular sieve obtained in step (1);
[0023] (3) Calcinate the loaded molecular sieve at 400 - 550 °C for 3 - 6 hours to obtain the final catalyst.
[0024] Application of the molecular sieve catalyst with a hierarchical pore structure described in any one of the above in the catalytic transesterification reaction for synthesizing biodiesel.
[0025] Compared with the prior art, the beneficial effects of the present invention are:
[0026] (1) By constructing a multi-level pore system with micropore-mesopore synergy, the mesoporous network formed by the molecular sieve matrix through directional etching effectively solves the diffusion limitation of macromolecular oils in traditional micropores, while the microporous structure maintains a high specific surface area and active site density. The loaded cerium oxide-carbon nanotube composite modified material is anchored on the pore surface in an in-situ growth manner. The three-dimensional conductive network formed by carbon nanotubes accelerates the electron transfer process. At the same time, the oxygen defect sites on the surface of nano-cerium oxide particles provide highly active adsorption and activation centers for reactants. The two work together to significantly enhance the catalytic activity.
[0027] (2) Supercritical extraction technology was used to replace the traditional high-temperature calcination to remove the template agent, which fully preserved the continuity and mechanical strength of the multi-level pore structure; the anchoring effect of cerium oxide particles on the surface and ends of carbon nanotubes effectively inhibited the sintering and loss of active components. The reversible adsorption of oxygen at oxygen defect sites continuously removed carbon precursors during the reaction, while the hydrophobic surface and electronic conduction of carbon nanotubes further blocked the coke deposition path. Attached Figure Description
[0028] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation
[0029] 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 only some embodiments of the present invention, and not all embodiments. 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.
[0030] Example 1:
[0031] Please see Figure 1 As shown, a multi-level porous molecular sieve catalyst comprises:
[0032] Molecular sieve matrix, which has microporous and mesoporous structures;
[0033] Cerium oxide-carbon nanotube composite modified material, loaded on the pore surface and outer surface of molecular sieve matrix;
[0034] The cerium oxide-carbon nanotube composite modified material is composed of in-situ grown carbon nanotubes and nano-cerium oxide particles, wherein the cerium oxide particles are anchored to the surface and ends of the carbon nanotubes.
[0035] In one embodiment of the present invention, the molecular sieve matrix is ZSM-5, and a mesoporous structure is formed by alkali treatment or acid treatment.
[0036] In one embodiment of the present invention, the preparation method of the cerium oxide-carbon nanotube composite modified material includes the following steps:
[0037] (a) 0.5 g of plasma-activated carbon nanotubes (CNTs) were dispersed in a microemulsion system (containing 15 g of Pluronic F127, 50 mL of cyclohexane, and 5 mL of 0.3 mol / L Ce(NO3)3 aqueous solution).
[0038] (b) Add the precipitant (hexamethylenetetramine: ammonia = 1:2 molar ratio) dropwise, and simultaneously apply 60 kHz ultrasound (power density 200 W / L), and react at 65℃ for 3 h;
[0039] (c) Removal of organic matter by supercritical CO2 extraction (40°C, 15 MPa);
[0040] (d) In a 10% H2 / Ar atmosphere, the temperature was programmed to rise from 1℃ / min to 300℃ and hold for 1 h, then calcined at 5℃ / min to 600℃ for 2 h to obtain CeO. x -CNTs complex (cerium oxide:CNTs mass ratio = 1:1).
[0041] A method for preparing a multi-level porous molecular sieve catalyst includes the following steps:
[0042] (1) Take 10 g of ZSM-5 molecular sieve raw powder, add 100 mL of 0.2 mol / L NaOH solution, stir at 80℃ for 2 h, filter and wash until neutral, dry at 110℃ for 12 h to obtain ZSM-5 support with microporous-mesoporous multi-level structure;
[0043] (2) 0.75 g CeO x -CNTs complex was loaded onto the ZSM-5 support in step 1 by equal volume impregnation (complex accounted for 15% of the total mass of the catalyst).
[0044] (3) Calcination at 500℃ for 4 h yielded the final catalyst Cat-1.
[0045] Example 2:
[0046] Please see Figure 1 As shown, a multi-level porous molecular sieve catalyst comprises:
[0047] Molecular sieve matrix, which has microporous and mesoporous structures;
[0048] Cerium oxide-carbon nanotube composite modified material, loaded on the pore surface and outer surface of molecular sieve matrix;
[0049] The cerium oxide-carbon nanotube composite modified material is composed of in-situ grown carbon nanotubes and nano-cerium oxide particles, wherein the cerium oxide particles are anchored to the surface and ends of the carbon nanotubes.
[0050] In one embodiment of the present invention, the molecular sieve matrix is Beta, and a mesoporous structure is formed by alkali treatment or acid treatment;
[0051] In one embodiment of the present invention, the preparation method of the cerium oxide-carbon nanotube composite modified material includes the following steps:
[0052] (a) 0.5 g of plasma-activated carbon nanotubes (CNTs) were dispersed in a microemulsion system (containing 15 g of Pluronic F127, 50 mL of cyclohexane, and 3 mL of 0.1 mol / L Ce(NO3)3 aqueous solution).
[0053] (b) Add the precipitant (hexamethylenetetramine: ammonia = 1:2 molar ratio) dropwise, and simultaneously apply 80 kHz ultrasound (power density 300 W / L), and react at 65°C for 3 h;
[0054] (c) Removal of organic matter by supercritical CO2 extraction (40°C, 15 MPa);
[0055] (d) In a 5% H2 / Ar atmosphere, the temperature was programmed to rise from 1℃ / min to 300℃ and hold for 1 h, then calcined at 5℃ / min to 600℃ for 2 h to obtain CeO. x -CNTs complex (cerium oxide:CNTs mass ratio = 2:1).
[0056] A method for preparing a multi-level porous molecular sieve catalyst includes the following steps:
[0057] (1) Take 10 g of Beta molecular sieve raw powder, add 100 mL of 0.5 mol / L NaOH solution, stir at 70℃ for 4 h, filter and wash until neutral, dry at 110℃ for 12 h to obtain ZSM-5 support with microporous-mesoporous multi-level structure;
[0058] (2) 0.75 g CeO x -CNTs complex was loaded onto the ZSM-5 support in step 1 by an equal-volume impregnation method (complex accounted for 25% of the total mass of the catalyst).
[0059] (3) Calcination at 450℃ for 6 h yielded the final catalyst Cat-2.
[0060] Application example:
[0061] First, 100g of soybean oil was added to a 500ml three-necked flask (equipped with a reflux condenser, mechanical stirrer, and thermometer), heated to 65°C in a constant-temperature oil bath, and maintained at this temperature. The mixture was stirred at 300 rpm for 30 minutes to dehydrate the raw material for pretreatment. Simultaneously, 32.4g of anhydrous methanol (calculated at an oil-to-methanol molar ratio of 1:15) was weighed and placed in a constant-pressure dropping funnel for later use. 0.5g of the Cat-1 catalyst prepared in Example 1 was taken and pretreated and activated at 300°C for 1 hour under a nitrogen atmosphere. After activation, the catalyst was cooled to 65°C for later use. After pretreatment and catalyst activation, the Cat-1 catalyst cooled to 65°C was added to the soybean oil in the reactor, and mechanical stirring was started and the speed was increased to 600 rpm.
[0062] Subsequently, anhydrous methanol was slowly added dropwise through a constant-pressure dropping funnel at a rate of 2 mL / min, while strictly maintaining the reaction temperature at 65 ± 1 °C. Timing was started after the methanol addition was complete, and the reaction was continued for 4 hours at 65 ± 1 °C with stirring at 600 rpm. After the reaction, the reactor was immediately cooled to room temperature in an ice-water bath. The solid catalyst was then recovered by centrifugation (8000 rpm, 10 minutes), washed three times with anhydrous methanol, and then vacuum dried at 60 °C for later use. The upper layer of crude biodiesel from the centrifuged reaction mixture was transferred to a separatory funnel, and 50 mL of 70 °C hot water was added for stirring and washing. The mixture was allowed to stand and separate into layers; this washing process was repeated until the aqueous phase was neutral (usually requiring 3 times). Finally, the washed organic phase was dried with anhydrous magnesium sulfate for 12 hours, and after filtration, the refined biodiesel product was obtained.
[0063] Comparative example:
[0064] Preparation of unmodified hierarchical porous ZSM-5 support: 10 g of ZSM-5 molecular sieve powder was added to 100 mL of 0.2 mol / L NaOH solution and stirred at 80 °C for 2 hours. The mixture was then filtered and washed until neutral, and dried at 110 °C for 12 hours (without CeO₂ treatment). x -CNTs loaded), and finally the obtained solid was directly calcined at 500℃ for 4 hours to obtain the unmodified catalyst Cat-0.
[0065] Experimental example:
[0066] The tests for Examples 1 and 2, and the comparative examples, are shown in the table below:
[0067] Detection target Detection methods Test conditions acidic sites <![CDATA[NH3 Temperature Programmed Desorption (NH3-TPD)]]> 50→600℃, heating rate 10℃ / min Reactivity Gas chromatography-FID (GC-FID) analysis of biodiesel yield HP-INNOWax column, internal standard method for quantification Carbon deposition behavior Thermogravimetric-mass spectrometry (TG-MS) Atmospheric temperature, rising to 800°C at a rate of 10°C / min. Electrochemical performance Electrochemical impedance spectroscopy (EIS) Frequency 0.1 Hz~100 kHz, amplitude 10 mV
[0068] The test results are compared below:
[0069] Testing items Cat-0 (Comparative Example) Cat-1 (Example 1) Cat-2 (Example 2) Difference mechanism 3. Reaction performance Biodiesel yield (%) 41.7 92.3 90.1 Synergistic catalytic effect improves conversion efficiency Activation energy (kJ / mol) 78.6 46.2 48.7 Conductive CNTs lower the energy barrier 4. Stability Yield (%) after 5 cycles 22.5 85.3 86.0 Oxygen Deficiency Regeneration Inhibits Inactivation Carbon deposits (wt%) 18.7 5.2 5.8 Nanoconfinement effect prevents coke deposition 5. Mass transfer characteristics <![CDATA[Effective diffusion coefficient (×10⁻ 9 m² / s)]]> 1.3 3.5 3.2 Multi-level channels + CNTs accelerate molecular migration Charge transfer resistance (Ω) 214 68 75 CNTs networks improve electron conduction efficiency
[0070] As can be seen from the above, CeOx -CNT complex structure improves yield and lowers activation energy, oxygen vacancy sites (Ce 3+ It can be reversibly regenerated in an H2 atmosphere, and supercritical CO2 extraction increases the mesopore volume.
[0071] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.
Claims
1. A molecular sieve catalyst of hierarchical pore structure characterized by, The application relates to a catalyst for synthesizing biodiesel, which comprises the following components: a molecular sieve base body with microporous structure and mesoporous structure; a cerium oxide-carbon nanotube composite modifier loaded on the channel surface and outer surface of the molecular sieve base body; the cerium oxide-carbon nanotube composite modifier is composed of in-situ grown carbon nanotubes and nano cerium oxide particles, wherein the cerium oxide particles are anchored on the surface and port of the carbon nanotubes.
2. The catalyst of claim 1, wherein the catalyst has a hierarchical pore structure. the molecular sieve base body is one of ZSM-5, Beta, Y type or MCM-41, and the mesoporous structure is formed by alkali treatment or acid treatment.
3. The catalyst of claim 1 wherein: the mass of the cerium oxide-carbon nanotube composite modifier accounts for 5-30% of the total mass of the catalyst, and the mass ratio of cerium oxide to carbon nanotube is (1:2)-(2:1).
4. The catalyst of claim 1 wherein the catalyst has a hierarchical pore structure. the preparation method of the cerium oxide-carbon nanotube composite modifier comprises the following steps: (a) dispersing plasma-activated carbon nanotubes in a microemulsion system containing cerium salt, wherein the microemulsion is composed of a surfactant, a co-surfactant, an oil phase and an aqueous phase, and the aqueous phase contains a cerium salt solution with a concentration of 0.1-0.5 mol / L; (b) adding a precipitant drop by drop into the system of step (a) and synchronously applying ultrasonic oscillation with a frequency of 40-80 kHz, and reacting at 50-70 DEG C to make cerium ions deposit on the surface of the carbon nanotubes to form a precursor wrapping layer; (c) performing supercritical CO2 fluid extraction on the product obtained in step (b) to remove the surfactant and organic phase; (d) The extracted solid is calcined in a reducing atmosphere, first at 1 °C / min up to 300 °C for 1 h, then at 5 °C / min up to 600 °C for 2 h, in situ generating CeO with oxygen defects x (0 < x < 2) - carbon nanotube heterojunction structure.
5. The catalyst of claim 4 wherein: the surfactant in the microemulsion is an amphiphilic block copolymer Pluronic F127, the oil phase is cyclohexane, and the mass ratio of the aqueous phase to the surfactant is (1:3)-(1:5).
6. The catalyst of claim 4 wherein: in step (b), the ultrasonic power density is 100-300 W / L, the precipitant is a mixed solution of hexamethylene tetramine and ammonia water with a molar ratio of 1:
2.
7. The catalyst of claim 1 wherein: in step (d), the volume ratio of H2 in the reducing atmosphere is 5%-15%.
8. A method for preparing a molecular sieve catalyst of hierarchical pore structure, characterized in that, the application further discloses a preparation method of the catalyst, which comprises the following steps: (1) performing dealumination or alkali treatment on a molecular sieve raw powder to form a multi-stage channel structure; (2) loading the cerium oxide-carbon nanotube composite modifier on the multi-stage channel molecular sieve obtained in step (1) by using an equal-volume impregnation method; (3) calcining the loaded molecular sieve at 400-550 DEG C for 3-6 hours to obtain the final catalyst.
9. Application of the multi-stage channel structure molecular sieve catalyst in the catalytic ester exchange reaction for synthesizing biodiesel.