Composite catalyst and its preparation method and application

Abstract

The present invention provides a composite catalyst, a preparation method, and applications thereof. The composite catalyst comprises a ceramic aerogel carrier and active components, wherein the active components include cerium oxide and a transition metal oxide. The composite catalyst has a high active component loading, high catalytic activity, and high stability. Furthermore, the composite catalyst contains no precious metals, is low in cost, and can effectively degrade VOCs at relatively low temperatures.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and in particular to a composite catalyst and a preparation method and application thereof. Background Art

[0002] Volatile Organic Compounds (VOCs), as an important source of air pollution, have attracted widespread attention. VOCs are a class of highly volatile hydrocarbons with diverse chemical structures and a wide variety. They are produced in many products and processes in industries and daily life, such as petrochemicals, fertilizer manufacturing, paint production, furniture manufacturing, etc. After VOCs enter the atmosphere, they can undergo complex photochemical reactions to generate secondary pollutants such as PM2.5, photochemical smog, ozone, etc. In addition, VOCs can also directly affect the human respiratory system, nervous system, etc., and even cause diseases such as cancer. In order to address the air pollution problem caused by VOCs, scholars have carried out a lot of research.

[0003] Catalytic degradation is a method that uses catalysts to induce the chemical degradation of VOCs, thereby reducing their environmental pollution. In addition to the commonly used platinum-, aluminum-, and cobalt-based catalysts, other catalyst types, such as metal oxides and alkali metals, have been used in research. This method offers advantages such as high efficiency, cost-effectiveness, and the absence of harmful gases, and is widely used in industrial applications. Low-temperature catalytic oxidation of VOCs is a technique that achieves high-efficiency degradation of VOCs at relatively low temperatures. The core of this technology is the selection of high-performance catalysts. Currently, the most widely studied and applied catalysts include precious metal catalysts (such as Pt, Pd, and Rh), transition metal oxide catalysts (such as Mn, Co, and Cu), and porous material-supported catalysts (such as zeolites and activated carbon). These catalysts can achieve efficient oxidation of VOCs at relatively low temperatures. In recent years, high-temperature catalytic oxidation of VOCs has garnered widespread attention. This process uses precious metals such as Pt and Pd as catalysts, supported by alumina, and employs high-temperature oxidation (500°C) to decompose VOCs into CO2 and H2O. However, the high cost of the precious metal catalysts used in this process and the high energy consumption of the reaction process limit their large-scale application. Furthermore, the currently used alumina support, due to its small specific surface area and high density, significantly reduces the exposure of the active sites of the precious metal catalyst, resulting in a large precious metal loading and low catalytic efficiency. To prevent the precious metal-based catalyst from agglomerating and thus reducing catalytic efficiency, and to maintain a secure loading, complex preparation processes are typically required. Therefore, it is necessary to seek a VOCs catalyst that can be used at lower temperatures, has a simple preparation method, high catalytic efficiency, and is low-cost. Summary of the Invention

[0004] To address one of the aforementioned technical problems in the prior art, the present invention provides a composite catalyst using a ceramic aerogel as a carrier. The active components of the catalyst include cerium oxide and a transition metal oxide. Through the synergistic catalytic effect between the cerium oxide and the transition metal oxide, and the use of the ceramic aerogel with a large specific surface area and high porosity as a carrier, the catalyst's catalytic performance and stability are significantly improved. The catalyst exhibits particularly excellent performance in the degradation of VOCs, achieving complete VOC degradation at relatively low temperatures. The present invention also features a simple method for preparing the composite catalyst, utilizing readily available and inexpensive raw materials, resulting in low cost.

[0005] In a first aspect, the present invention provides a composite catalyst comprising a ceramic aerogel carrier and an active component, wherein the active component comprises cerium oxide and a transition metal oxide.

[0006] In some embodiments, the molar ratio of cerium oxide to transition metal oxide is (0.1-10):1, such as 0.1:1, 0.5:1, 0.8:1, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1 or any value therebetween. In some preferred embodiments, the molar ratio of cerium oxide to transition metal oxide is (0.5-5):1. In some preferred embodiments, the molar ratio of cerium oxide to transition metal oxide is (0.5-2):1.

[0007] In some preferred embodiments, the cerium oxide and the transition metal oxide form a CeMO3 perovskite-type composite oxide, where M is a transition metal. In some embodiments, the X-ray diffraction pattern of the catalyst has diffraction peaks at 2θ=33.2°, 2θ=47.6°, 2θ=56.4°, 2θ=69.5°, and 2θ=76.8°.

[0008] The transition metal oxide of the present invention includes but is not limited to at least one of oxides of transition metals such as titanium, vanadium, manganese, copper, iron, zinc, cobalt, nickel, etc. In some preferred embodiments, the transition metal is manganese.

[0009] In some embodiments, the cerium oxide is nano-cerium oxide. In some embodiments, the transition metal oxide is nano-transition metal oxide. In some preferred embodiments, the transition metal oxide is nano-manganese oxide.

[0010] In some embodiments, the average particle size of the CeMO3 type perovskite composite oxide is 1 nm-100 nm.

[0011] In some embodiments, the carrier is a SiO2 / Al2O3 ceramic fiber aerogel. In some specific embodiments, the diameter of the ceramic fiber is 0.1 μm-1 μm. In some specific embodiments, the porosity of the SiO2 / Al2O3 ceramic fiber aerogel is 93%-98%. In some embodiments, the SiO2 / Al2O3 ceramic fiber aerogel is prepared by the following method:

[0012] PVA is mixed with water and heated under reflux to obtain a mixed solution; aluminum salt, inorganic acid, silane reagent and alcohol are added to the mixed solution, and fiber filaments are obtained through spinning technology; and the fiber filaments are calcined to obtain SiO2 / Al2O3 ceramic fiber aerogel.

[0013] In some embodiments, the heating reflux temperature is 100° C.-300° C., and the heating reflux time is 1-3 hours.

[0014] In some embodiments, the aluminum salt is selected from one or more of aluminum chloride, aluminum nitrate, and aluminum sulfate.

[0015] In some embodiments, the inorganic acid is phosphoric acid.

[0016] In some embodiments, the silane reagent is tetraethoxysilane.

[0017] In some embodiments, the alcohol is a C1-C6 low-carbon alcohol, including but not limited to ethanol, propanol, n-butanol, isopentanol, and the like.

[0018] In some embodiments, the mass volume ratio of the aluminum salt to the silane reagent is (0.2-3.0): 1 g / mL.

[0019] In some embodiments, the calcination temperature is 500° C.-1800° C., and the calcination time is 2-5 hours.

[0020] In a second aspect, the present invention provides a method for preparing the composite catalyst according to the first aspect, comprising the following steps:

[0021] (1) impregnating the ceramic aerogel support in a first solution containing a cerium salt and a transition metal salt;

[0022] (2) The ceramic aerogel carrier after impregnation treatment is sintered to obtain a composite catalyst.

[0023] In some embodiments, the solvent in the first solution is water.

[0024] In some embodiments, the first solution further comprises a ligand. The ligand of the present invention includes, but is not limited to, one or more of an organic acid, an alcohol, an amine, and a nitrile. In some specific embodiments, the ligand comprises at least one of phthalic acid, acetic acid, ethylene glycol, triethylamine, ethylenediaminetetraacetic acid, citric acid, methanol, and acetonitrile. In some specific embodiments, the ligand comprises ethylene glycol, ethylenediaminetetraacetic acid, and citric acid. In some specific embodiments, the ligand comprises ethylene glycol.

[0025] In some embodiments, the mass concentration of the ligand in the first solution is 10-80wt%, such as 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt%, 80wt% or any value therebetween. In some preferred embodiments, the mass concentration of the ligand in the first solution is 10-50wt%.

[0026] In some embodiments, the molar ratio of Ce to transition metal in the first solution is (0.1-10):1, such as 0.1:1, 0.5:1, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, or any value therebetween. In some preferred embodiments, the molar ratio of Ce to transition metal in the first solution is (1-10):1.

[0027] The transition metal salts of the present invention include but are not limited to nitrates, hydrochlorides, sulfates and carbonates of transition metals, such as manganese nitrate, manganese chloride, manganese sulfate and the like.

[0028] In some embodiments, the method for preparing the ceramic aerogel carrier comprises the following steps:

[0029] PVA solution, aluminum salt, inorganic acid, silane reagent and alcohol are mixed, and fiber filaments are obtained through spinning technology. The fiber filaments are calcined to obtain SiO2 / Al2O3 ceramic fiber aerogel.

[0030] In some embodiments, the inorganic acid is phosphoric acid.

[0031] In some embodiments, the aluminum salt is selected from one or more of aluminum chloride, aluminum nitrate, and aluminum sulfate.

[0032] In some embodiments, the silane reagent is tetraethoxysilane.

[0033] In some embodiments, the alcohol is a C1-C6 low-carbon alcohol, including but not limited to ethanol, propanol, n-butanol, isopentanol, and the like.

[0034] In some embodiments, the mass volume ratio of the aluminum salt to the silane reagent is (0.2-3):1 g / mL.

[0035] In some embodiments, the calcination temperature is 500° C.-1800° C., and the calcination time is 2-5 hours.

[0036] In some embodiments, in step (1), the immersion time is 5-50 minutes. In some preferred embodiments, the immersion time is 25-35 minutes.

[0037] In some embodiments, in step (2), the sintering temperature is 300°C-550°C.

[0038] In some embodiments, in step (2), the sintering time is 1-8 hours, preferably 2-5 hours.

[0039] In a third aspect, the present invention provides use of the composite catalyst described in the first aspect or the composite catalyst obtained by the preparation method described in the second aspect in catalytic degradation of VOCs.

[0040] The VOCs (volatile organic compounds) described in the present invention include, but are not limited to, alkanes (straight-chain alkanes and cycloalkanes), alkenes, alkynes, benzene series, alcohols, aldehydes, ethers, ketones, acids, esters, halogenated hydrocarbons, and the like. In some embodiments, the VOCs include at least one of benzene, toluene, xylene, formaldehyde, styrene, trichloroethylene, chloroform, trichloroethane, ethyl acetate, n-hexane, diisocyanates, and diisocyanatomethylbenzene. In some embodiments, the VOCs include toluene. In some embodiments, the VOCs include n-hexane. In some embodiments, the VOCs include ethyl acetate.

[0041] In some embodiments, the applying includes reacting VOCs with the composite catalyst and air under heating conditions.

[0042] In some embodiments, the initial concentration of volatile organic compounds is 1.0-1000 ppm.

[0043] In some embodiments, the amount of the composite catalyst is 0.5-10 g, preferably 1-5 g.

[0044] In some embodiments, the flow rate of the volatile organic compounds is 10-100 L / min, preferably 50-70 L / min.

[0045] In some embodiments, the ratio of the volatile organic compound flow rate to the air flow rate is 1:(0.2-10).

[0046] In some embodiments, the reaction is carried out at a temperature of 0-500°C.

[0047] In some embodiments, the reaction time is 0.1 seconds to 10 seconds, preferably 0.2 seconds to 5 seconds, and more preferably 0.2 to 0.5 seconds.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] 1. By choosing ceramic aerogel as a carrier, not only can the dispersion of cerium oxide and transition metal oxides on the carrier be improved, but also the synergistic catalytic effect between transition metals and cerium oxide can achieve high-throughput, rapid, and efficient catalytic degradation of volatile organic pollutants in the atmosphere under low-temperature conditions, and the catalyst has high stability.

[0050] 2. The preparation process of the composite catalyst of the present invention is simple. By selecting specific organic ligands, the loading of cerium oxide and transition metal oxide on the carrier can be effectively increased, thereby realizing the preparation of a composite catalyst with a high loading of active components. Excellent catalytic effect can be achieved without the use of precious metal catalysts.

[0051] 3. The composite catalyst of the present invention has a wide range of applications and can be used to catalyze the degradation of various hydrocarbons. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 The SEM images of the catalyst prepared in Example 1 are shown, wherein A: silica-aluminum mullite fiber aerogel, and B: silica-aluminum mullite fiber aerogel loaded with cerium oxide and manganese oxide.

[0053] Figure 2 The XRD pattern of the catalyst prepared in Example 1 is shown.

[0054] Figure 3 The results of catalytic degradation of toluene by the catalysts of Examples 1-3 and Comparative Example 3 are shown.

[0055] Figure 4 The results of catalytic degradation of toluene by the catalysts of Examples 4-8 are shown.

[0056] Figure 5 The results of catalytic degradation of toluene by the catalysts of Comparative Examples 1-2 are shown. DETAILED DESCRIPTION

[0057] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments and drawings. The specific embodiments described herein are only used to illustrate the present invention and are not intended to constitute any limitation to the present invention.

[0058] Unless otherwise specified, the reagents, instruments and equipment used in the following examples and comparative examples of the present invention can be obtained through commercial channels.

[0059] Example 1

[0060] (1) Preparation of ceramic fiber aerogel

[0061] Add 2.25 g of PVA-1788 to 12.5 ml of deionized water and heat on a hot plate at 120°C with stirring for 2 hours until the PVA-1788 is completely dissolved. After cooling, add 20 μl of phosphoric acid and stir for 30 minutes. Then add 2.25 g of AlCl₃·6H₂O and stir until completely dissolved. Add 5 ml of TEOS (tetraethoxysilane), 6 ml of n-butanol, and 1 ml of ethanol. Stir for 2 hours until a transparent, homogeneous solution is formed.

[0062] The solution prepared in the previous step was placed in a 10 ml screw-capped syringe, which was placed in an air spinning machine and sprayed at a rate of 3 ml per hour to prepare a ceramic fiber aerogel precursor.

[0063] The aerogel precursor prepared in the above steps was placed in a resistance furnace and heated to 1200 degrees Celsius at a heating rate of 5 degrees Celsius / minute. After keeping the temperature for 3 hours, the aerogel precursor was naturally cooled and taken out to obtain silica-aluminum mullite fiber aerogel.

[0064] SEM images of silica-aluminum mullite fiber aerogel Figure 1 As shown in Figure A, a smooth, non-porous fibrous structure with uniform length and a diameter of about 0.2-0.3 microns can be seen. These fibers have no obvious breaks and are relatively long.

[0065] (2) Preparation of CeMnO3 composite ceramic fiber aerogel catalyst

[0066] Weigh 0.5 g of the ceramic fiber aerogel prepared in step (1) and place it in a crucible. Prepare a 20% aqueous solution of ethylene glycol with 0.0025 mol Mn(NO₃)₂ and 0.005 mol Ce(NO₃)₂·6H₂O and add it to the crucible. Soak the ceramic fiber aerogel in the crucible for 30 minutes, then heat it to 350°C at a rate of 50°C per minute. After holding for 2 hours, allow it to cool naturally to room temperature to obtain the composite catalyst product.

[0067] The SEM of the product is as follows Figure 1 As shown, by comparing the SEM photos before and after loading ( Figure 1 A and Figure 1B), it can be seen that before loading cerium oxide and transition metal oxides, the surface of mullite ceramic fiber aerogel is relatively flat. After loading cerium oxide and transition metal oxides, the surface of mullite ceramic fiber aerogel becomes rougher and visible tiny protrusions appear, which indicates that the catalyst is successfully loaded on the fiber surface. This rough surface morphology can increase the active surface area of the catalyst, enable the catalytic reaction to proceed more effectively, and improve the activity and selectivity of the catalyst.

[0068] To further investigate the catalyst loading, elemental distribution analysis was performed on the sample using an EDX detector in STEM mode. This analysis revealed that cerium and manganese were uniformly loaded onto the fibers, forming a thin film on the surface. This demonstrates that the method of the present invention not only effectively increases the specific surface area of the catalyst but also prevents catalyst agglomeration. Furthermore, after ultrasonic cleaning for 30 minutes, the catalyst content on the aerogel support did not significantly decrease, demonstrating that cerium-manganese oxide is securely loaded onto the aerogel fibers, ensuring the catalyst's longevity and stability.

[0069] The XRD results of the product are as follows Figure 2 By comparing the XRD patterns before and after loading, it was found that the diffraction peaks of the perovskite crystal plane were at 2θ=33.2°, 2θ=47.6°, 2θ=56.4°, 2θ=69.5° and 2θ=76.8°, showing the good perovskite structure of CeMnO3.

[0070] Examples 2-8

[0071] The only difference from Example 1 is that the "ligand type" in step (2) is different, or the "molar ratio of added Ce(NO3)2·6H2O to Mn(NO3)2" is different, see Table 1 for details.

[0072] Table 1

[0073] Example ligand Molar ratio Ce:Mn Example 1 Ethylene glycol 2:1 Example 2 EDTA 2:1 Example 3 citric acid 2:1 Example 4 Ethylene glycol 1:1 Example 5 Ethylene glycol 1:4 Example 6 Ethylene glycol 1:6 Example 7 Ethylene glycol 1:8 Example 8 Ethylene glycol 1:10

[0074] Experiment 1: VOCs catalytic performance test

[0075] (1) Basic test conditions: space velocity 33 SCCM, toluene content 1000 ppm, oxygen flow rate 20 SCCM. 0.5 g of catalyst was used in each experiment, effective catalyst content 0.05 g (determined by ICP-AES), WHSV = 40,000 ml / g / h.

[0076] VOCs degradation test was carried out with toluene as the VOCs target pollutant.

[0077] The catalysts used were the composite catalysts in Examples 1-8 and the catalysts in Comparative Examples 1-3, respectively. The catalyst in Comparative Example 1 was cerium oxide (CeOx), the catalyst in Comparative Example 2 was manganese oxide (MnOx), and the catalyst in Comparative Example 3 was a mixture of cerium oxide and manganese oxide without a carrier (the atomic ratio of cerium to manganese was 1:1).

[0078] (2) Experimental results:

[0079] The catalyst test results of Examples 1-3 are as follows Figure 3 shown. Figure 3 A shows that the catalyst prepared using ethylene glycol as a ligand carries more effective catalytic components (cerium oxide and manganese oxide), and has a better catalytic effect. It can completely degrade VOCs at 240 degrees Celsius, while the catalyst synthesized using EDTA and citric acid as ligands requires 290 degrees Celsius to completely degrade VOCs. The catalyst of Comparative Example 3 can only degrade 80% of VOCs pollutants at 310 degrees Celsius. This may be due to the use of different ligand solutions, resulting in different contents of effective catalytic components loaded on the ceramic fiber aerogel carrier (see Figure 3 B).

[0080] The catalytic test results in Examples 4-8 are shown in Figure 4 As the molar ratio of Ce decreases, the overall catalytic performance of the catalyst shows a significant decline. Compared with the condition of Ce:Mn molar ratio of 2:1 in Example 1, the complete degradation of toluene in Example 8 under the condition of Ce:Mn molar ratio of 1:10 requires a temperature of 300 degrees Celsius, and the T of catalytic oxidation of toluene is 50 、T 90 and T 100 All increased significantly.

[0081] The test results of Comparative Example 1-2 are as follows Figure 5 As shown. Figure 5 It can be seen that, under the condition of the total amount of catalyst remaining unchanged, when Ce and Mn elements form the CeMnO3 perovskite catalyst, its catalytic performance is significantly improved compared to using cerium oxide or manganese oxide alone as catalysts. In addition, experiments show that at 240 degrees Celsius, neither cerium oxide nor manganese oxide alone can catalyze the oxidation of volatile organic compounds (VOCs), while the CeMnO3 perovskite catalyst can achieve 100% catalytic oxidation of VOCs under this temperature condition.

[0082] The present invention also tested the catalytic performance of the catalysts in Examples 1-8 against other VOCs, including organic compounds such as ethyl acetate and n-hexane. These tests revealed that the catalysts of the present invention also exhibited good catalytic performance against these organic compounds, achieving complete degradation. This demonstrates that the catalysts prepared by the present invention can effectively catalyze the oxidation of various hydrocarbons and are suitable for the degradation of most VOCs.

[0083] To verify the broad applicability of the catalyst of the present invention, high-throughput testing was performed. While maintaining the toluene concentration constant, the total space velocity was increased, starting from an initial space velocity of 33 SCCM and continuing until the space velocity reached 133 SCCM. These tests revealed that the catalyst of the present invention exhibited excellent catalytic performance over a wider concentration range and exhibited an extremely high upper limit for catalytic concentration.

[0084] Experiment 2: Stability Test

[0085] The stability test of the composite catalysts in Examples 1-8 of the present invention was carried out under the conditions of a space velocity of 33 SCCM, a toluene content of 1000 ppm, and an oxygen flow rate of 20 SCCM.

[0086] The results show that after 300 hours of continuous use, the catalytic performance of the catalyst has not decreased at all, which proves that the catalyst of the present invention has high stability.

[0087] Although the embodiments disclosed herein are as described above, the contents described herein are merely embodiments for facilitating understanding of the present invention and are not intended to limit the present invention. Any person skilled in the art may make any modifications and variations in the form and details of the embodiments without departing from the spirit and scope of the present invention. However, the scope of protection of the present invention shall remain subject to the scope defined by the appended claims.

Claims

1. A composite catalyst comprising a ceramic aerogel carrier and an active component, wherein the active component comprises cerium oxide and a transition metal oxide; the cerium oxide and the transition metal oxide form a CeMO3 perovskite-type composite oxide, where M is a transition metal, and the transition metal is manganese; and the carrier is a SiO2 / Al2O3 ceramic fiber aerogel. in, The preparation method of the composite catalyst comprises the following steps: (1) impregnating the ceramic aerogel support in a first solution containing a cerium salt and a transition metal salt; (2) Sintering the impregnated ceramic aerogel carrier to obtain a composite catalyst; The first solution further comprises a ligand, and the ligand is ethylene glycol.

2. The catalyst according to claim 1, characterized in that The diameter of the ceramic fiber is 0.1 μm-1 μm; and / or, The average particle size of the cerium oxide and the transition metal oxide is 1 nm to 100 nm, and / or The X-ray diffraction spectrum of the catalyst has diffraction peaks at 2θ=33.2°, 2θ=47.6°, 2θ=56.4°, 2θ=69.5° and 2θ=76.8°.

3. The catalyst according to claim 1, characterized in that In the first solution, the mass concentration of the ligand is 10-80 wt%.

4. The catalyst according to claim 3, characterized in that The mass concentration of the ligand is 10-50 wt%.

5. The catalyst according to any one of claims 1 to 3, characterized in that The preparation method of the ceramic aerogel carrier comprises the following steps: PVA solution, aluminum salt, inorganic acid, silane reagent and alcohol are mixed, and fiber filaments are obtained through spinning technology. The fiber filaments are calcined to obtain SiO2 / Al2O3 ceramic fiber aerogel.

6. The catalyst according to claim 5, characterized in that The aluminum salt is selected from one or more of aluminum chloride, aluminum nitrate, and aluminum sulfate; The inorganic acid is phosphoric acid; The silane reagent is tetraethoxysilane; The alcohol is a C1-C6 low-carbon alcohol; The mass volume ratio of the aluminum salt to the silane reagent is (0.2-3): 1 g / mL; The calcination temperature is 500° C.-1800° C., and the calcination time is 2-5 hours.

7. The catalyst according to claim 6, characterized in that The alcohol is ethanol, propanol, n-butanol or isoamyl alcohol.

8. The catalyst according to any one of claims 1 to 3, characterized in that The immersion time in step (1) is 5-50 minutes, and / or, In step (2), the sintering temperature is 300°C-550°C, and the sintering time is 1-8 hours.

9. Use of the composite catalyst according to any one of claims 1 to 8 in catalytic degradation of VOCs.

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