A method for preparing a CeO2 supported catalyst using ZrB2 aerogel as a support.

Abstract

This invention belongs to the field of air pollution control and provides a method for preparing a CeO2-supported catalyst using ZrB2 aerogel as a carrier. This invention solves the technical problems of poor physicochemical properties of pure CeO2 and excessively high VOC degradation temperatures. The preparation method is simple: a Ce-MOF-ZrB2 composite material is prepared by adding ZrB2 aerogel to a Ce-MOF precursor. Then, a CeO2-ZrB2 composite thermocatalyst is prepared by pyrolysis of the Ce-MOF-ZrB2 composite material. The high specific surface area, numerous active sites, and unique porous structure of ZrB2 aerogel allow toluene molecules to better contact the CeO2 catalyst, thereby increasing the concentration of toluene around the CeO2 catalyst and improving the catalytic reaction efficiency. Furthermore, its excellent thermal stability allows it to maintain high catalytic activity for extended periods during high-temperature reactions. At a space velocity of 40,000 ml / (g·h) and a toluene concentration of 1,000 ppm, the complete degradation temperature of toluene is 225℃, which is 36℃ lower than that of pure CeO2 catalyst, indicating a promising application prospect.

Description

Technical Field

[0001] This invention belongs to the field of thermocatalytic material preparation, specifically involving the preparation of CeO2-ZrB2 thermocatalytic material and its test for thermocatalytic degradation of a VOCs gas (toluene). Background Technology

[0002] Air purification has become a major public concern and has been extensively studied. Among these studies, volatile organic compounds (VOCs) are particularly important. S Volatile organic compounds (VOCs) refer to major air pollutants with a boiling point below 260°C at room temperature. They are any organic compounds that can participate in atmospheric photochemical reactions, with common examples including ethyl acetate (EtOAc), toluene, benzene, ethanol, and acetone. Many VOCs can react with nitrogen oxides in the environment, increasing atmospheric oxidation, promoting the formation of secondary particulate matter, and ultimately leading to photochemical smog. These harmful substances pose a significant threat to the ozone layer, profoundly impacting our daily lives and healthy growth, and having a substantial influence on the sustainable development of ecosystems.

[0003] Currently targeting VOCs s VOCs control can be broadly categorized into two types: source control and end-of-pipe treatment. However, in practice, source control is often limited by various constraints and can only serve as a preventative measure. End-of-pipe treatment is essential for effectively controlling VOCs. s Effective control of volatile organic compounds (VOCs) is crucial. End-of-pipe treatment technologies can be broadly categorized into three types: physical, biological, and chemical. Among these methods, catalytic oxidation is considered an effective approach due to its high economic feasibility, low cost, low level of secondary pollutant generation, and ability to operate at relatively low temperatures while controlling the selectivity of byproducts. Therefore, it can be considered an environmentally friendly and cost-effective technology. In catalytic oxidation, the reaction rate of VOCs during degradation is highly dependent on the catalytic nanomaterials. Therefore, the rational design and fabrication of highly active and cost-effective catalytic nanomaterials are essential for the practical application of VOC elimination.

[0004] The most notable characteristic of cerium-based oxides is their strong redox ability. Cerium can react with Ce... 4+ (Oxidized state) and Ce 3 +The interconversion between its reduced and normal states makes it highly flexible in catalyzing redox reactions. Specifically, cerium's redox cycle allows it to effectively store and release oxygen during catalysis, which is crucial for many reactions, especially those requiring redox exchange. Currently, nanoscale cerium-based oxides are typically prepared by adjusting their nanostructure or through synthetic techniques (such as hydrothermal methods). These oxides usually possess a high specific surface area, which provides more active sites for catalytic reactions, thereby improving catalytic efficiency. However, their catalytic activity decreases at high temperatures, failing to achieve the desired catalytic efficiency.

[0005] Aerogels possess unique advantages as catalyst supports due to their high specific surface area, porous structure, and thermal stability. Their extremely high specific surface area provides numerous active sites for catalysts, enhancing catalytic activity and reaction rates. The abundant nanoporous structure promotes efficient diffusion of reactants and products, reducing diffusion limitations and thus improving reaction efficiency. Furthermore, the excellent thermal stability of aerogel materials such as SiO2 and ZrB2 allows them to maintain structural integrity even at high temperatures, making them suitable for catalytic reactions under extreme conditions. Summary of the Invention

[0006] This invention addresses the problem of excessively high reaction temperatures in the thermocatalytic degradation of VOCs under existing technological conditions, thereby providing a novel method for preparing CeO2-ZrB2 composite thermocatalytic materials.

[0007] A method for preparing a CeO2-supported catalyst using ZrB2 aerogel as a support, the method specifically comprising the following steps:

[0008] I. Ce-MOF-ZrB2 composite materials

[0009] At room temperature, add 0.708 g of terephthalic acid powder to 24 mL of N,N-dimethylformamide solution, stir magnetically to dissolve, and mix thoroughly. A colorless and transparent solution with no terephthalic acid powder present indicates complete dissolution of terephthalic acid. At room temperature, add 1.361 g of tannic acid to 30 mL of deionized water, stir magnetically to dissolve, and mix thoroughly. No tannic acid powder present indicates complete dissolution of tannic acid. Add 0.2 g of ZrB2 aerogel to this solution, allowing it to completely impregnate. After 30 minutes of complete impregnation, remove and dry at room temperature for 2 hours. Add 2.32 g of cerium ammonium nitrate to 8 mL of deionized water, stir magnetically... Stir to dissolve and mix evenly. The solution turns orange-red and no cerium ammonium nitrate powder is visible, indicating that the cerium ammonium nitrate is completely dissolved. Add the dried ZrB2 aerogel to this solution and completely impregnate for 30 minutes. Add the cerium ammonium nitrate solution and ZrB2 aerogel together to the terephthalic acid solution and stir slowly to mix the two solutions evenly, taking care not to break the ZrB2 aerogel. Add the above mixed solution to a 100ml polytetrafluoroethylene reactor and place it in an oven for hydrothermal treatment at 100℃ for 1 hour. Remove the hydrothermally treated ZrB2 aerogel and vacuum dry it at 60-80℃ for 4 hours to obtain the Ce-MOF-ZrB2 composite material.

[0010] II. CeO2-ZrB2 Composite Catalytic Materials

[0011] The prepared Ce-MOF-ZrB2 composite material was placed in a muffle furnace with a heating rate of 5℃ / min, a holding time of 2–4 h, and a calcination temperature of 300–350℃, followed by furnace cooling. After calcination, the CeO2-ZrB2 composite thermocatalytic material was obtained.

[0012] In step one, the molar mass ratio of terephthalic acid to cerium ammonium nitrate is 1:1.

[0013] In step one, the ZrB2 aerogel is completely impregnated for 30 minutes.

[0014] In step one, the hydrothermal temperature of the reactor is 100℃ and the hydrothermal time is 1 hour.

[0015] In step one, the drying temperature is 60-80℃ and the drying time is 4 hours.

[0016] In step two, the calcination temperature is 300–350℃, and the holding time is 2–4 hours.

[0017] This experiment prepared Ce-MOF via a hydrothermal method, then Ce-MOF-ZrB2 composite material via a wet impregnation method, and finally CeO2-ZrB2 composite catalytic material via a sacrificial template method. The combination of polyhedral CeO2 nanoparticles and ZrB2 aerogel material retains the three-dimensional porous structure and large specific surface area of ​​Ce-MOF, increasing its adsorption and catalytic capacity for toluene and improving catalytic efficiency. Furthermore, the large surface area and numerous acidic active sites of ZrB2 aerogel material, along with its excellent porous structure, allow for more thorough contact between toluene molecules and the catalyst, increasing the concentration of toluene around CeO2 and further promoting the oxidation reaction, thus improving catalytic efficiency.

[0018] The beneficial effects of this invention are:

[0019] This invention marks the first time that a CeO2 catalyst has been supported on ZrB2 aerogel, and a CeO2-ZrB2 composite thermal catalyst has been prepared. The high specific surface area, numerous active sites, and unique porous structure of ZrB2 aerogel allow for more complete adsorption of toluene molecules on the surface and within the pores of the ZrB2 aerogel. This enables better contact between toluene molecules and the CeO2 catalyst, increasing the concentration of toluene around the CeO2 catalyst and thus improving the catalytic reaction efficiency. Simultaneously, the excellent thermal stability of ZrB2 aerogel contributes to the overall catalyst's improved stability, preventing the CeO2 catalyst from easily agglomerating and deactivating during high-temperature reactions, and allowing it to maintain high catalytic activity for extended periods.

[0020] The CeO2-ZrB2 composite thermocatalyst prepared in this invention exhibits high thermocatalytic performance. Using toluene as the target pollutant, 0.15 g of the composite material degraded toluene gas at a space velocity of 40000 ml / (g·h) and a concentration of 1000 ppm. The complete degradation temperature T90 (the temperature corresponding to 90% toluene conversion) of the pollutant by CeO2 alone was 255 °C, while the complete degradation temperature T90 of the pollutant by the composite material was 219 °C. Therefore, the catalytic performance of the CeO2-ZrB2 composite thermocatalyst prepared in this invention for toluene is significantly improved. Attached Figure Description

[0021] Figure 1 The images show the XRD patterns of the thermocatalytic materials CeO2, ZrB2 aerogel, and CeO2-ZrB2 synthesized in Example 1.

[0022] Figure 2 These are the adsorption-desorption isotherms of CeO2, ZrB2 aerogel, and CeO2-ZrB2 synthesized in Example 1;

[0023] Figure 3These are SEM images of the thermocatalytic materials Ce-MOF (a), CeO2 (b), ZrB2 aerogel (c), and CeO2-ZrB2 (d) synthesized in Example 1;

[0024] Figure 4 This is a graph showing the catalytic degradation efficiency of toluene by CeO2 and CeO2-ZrB2, the thermocatalytic materials synthesized in Example 1. Detailed Implementation

[0025] The present invention will now be described in further detail with reference to specific embodiments.

[0026] Example 1:

[0027] This example describes a method for preparing a CeO2-ZrB2 aerogel composite thermal catalyst, which is carried out according to the following steps:

[0028] 1. At room temperature, add 0.708g of terephthalic acid powder to 24mL of N,N-dimethylformamide solution, stir magnetically to dissolve, and mix thoroughly. The solution should be colorless and transparent with no terephthalic acid powder present, indicating complete dissolution of the terephthalic acid. 2. At room temperature, add 1.361g of tannic acid to 30mL of deionized water, stir magnetically to dissolve, and mix thoroughly. The solution should be free of tannic acid powder, indicating complete dissolution of the tannic acid. Add 0.2g of ZrB2 aerogel to this solution, allowing it to completely impregnate for 30 minutes. After impregnation, remove and dry at room temperature for 2 hours. 3. Add 2.32g of cerium ammonium nitrate to 8mL of deionized water. The solution was magnetically stirred until dissolved and homogeneous. The solution turned orange-red and no cerium ammonium nitrate powder was observed, indicating complete dissolution. Dried ZrB2 aerogel was then added to this solution and completely impregnated for 30 minutes. The cerium ammonium nitrate solution and ZrB2 aerogel were then added together to a terephthalic acid solution, and the mixture was slowly stirred to ensure homogeneity, taking care not to break the ZrB2 aerogel. The resulting solution was then added to a 100 ml polytetrafluoroethylene (PTFE) reactor and placed in an oven for hydrothermal treatment at 100°C for 1 hour. The hydrothermally treated ZrB2 aerogel was then removed and vacuum-dried at 60°C for 4 hours to obtain the Ce-MOF-ZrB2 composite material. The prepared Ce-MOF-ZrB2 composite material was then placed in a muffle furnace with a heating rate of 5°C / min, a holding time of 2 hours, and a calcination temperature of 300°C, followed by furnace cooling. After calcination, the CeO2-ZrB2 composite thermocatalyst material was obtained.

[0029] The prepared catalyst was subjected to X-ray diffraction analysis to obtain the XRD pattern of the catalyst, such as... Figure 1 As shown, the catalyst exhibits both CeO2 and ZrB2 phases.

[0030] The specific surface area of ​​the prepared catalyst was tested, such as... Figure 2The N2 adsorption-desorption curves of pure CeO2, ZrB2, and CeO2-ZrB2 are shown. The specific surface areas of CeO2, ZrB2 aerogel, and CeO2-ZrB2 composite material were found to be 87.9971 m² / s, respectively. 2 / g, 134.5512m 2 / g and 114.4555m 2 / g. Therefore, after loading, the specific surface area of ​​the catalyst increased by approximately 28m². 2 / g, but the specific surface area of ​​ZrB2 aerogel decreased by 20m². 2 / g. This indicates that ZrB2 aerogel provides a relatively higher specific surface area for CeO2 catalyst, but CeO2 catalyst also blocks the pores of ZrB2 aerogel to some extent.

[0031] The SEM image of the prepared catalyst obtained by SEM scanning is shown below. Figure 3 As shown, Ce-MOF has a smooth polyhedral structure. CeO2 obtained after calcination maintains the polyhedral structure of MOF, but shrinkage occurs due to high-temperature calcination, resulting in a porous structure composed of smooth spherical surfaces on the surface of ZrB2 aerogel. On the surface of the CeO2-ZrB2 composite thermocatalytic material, we can see that many small CeO2 catalyst particles have grown on the original spherical surfaces.

[0032] Example 2: 0.15 g of the CeO2-ZrB2 composite thermocatalyst material prepared based on the Ce-MOF precursor in Example 1 was loaded into a fixed-bed reactor (a glass reaction tube with an inner diameter of approximately 6 mm). Nitrogen gas was purged (flow rate of 9 ml / min) to carry away toluene from the bubbling device; the toluene content was 1000 ppm. The total gas flow rate entering the quartz reaction bed was 100 mL / min, and the mass hourly space velocity (MSV) was 40000 mL·g. -1 ·h -1 First, the toluene concentration at room temperature was measured, and then the temperature was raised to 120–280 °C to carry out a continuous toluene catalytic oxidation reaction. The catalyst activity was as follows: Figure 4 As shown, pure CeO2 and CeO2-ZrB2 composite thermocatalytic materials can achieve a toluene removal rate of 90% at 255℃ and 219℃, respectively.

Claims

1. A method for preparing a CeO2-supported catalyst using ZrB2 aerogel as a support, characterized in that... The specific steps of this method are as follows: I. Ce-MOF-ZrB2 composite materials At room temperature, 0.708 g of terephthalic acid powder was added to 24 mL of N,N-dimethylformamide solution, and the solution was magnetically stirred until dissolved and mixed evenly. The solution was colorless and transparent, and no terephthalic acid powder was found in the solution, indicating that the terephthalic acid was completely dissolved. At room temperature, 1.361 g of tannic acid was added to 30 mL of deionized water, and the solution was magnetically stirred until dissolved and mixed evenly. No tannic acid powder was found in the solution, indicating that the tannic acid was completely dissolved. 0.2 g of ZrB2 aerogel was added to this solution and the solution was completely impregnated. After 30 min of complete impregnation, the solution was removed and dried at room temperature for 2 h. Add 2.32g of cerium ammonium nitrate to 8ml of deionized water, stir magnetically to dissolve, mix thoroughly, and the solution turns orange-red with no cerium ammonium nitrate powder remaining, indicating complete dissolution. Add dried ZrB2 aerogel to this solution and impregnate completely for 30min. Add the cerium ammonium nitrate solution and ZrB2 aerogel together to a terephthalic acid solution, stirring slowly to mix the two solutions thoroughly, taking care not to break the ZrB2 aerogel. Add the mixed solution to a 100ml polytetrafluoroethylene reactor and place it in an oven for hydrothermal treatment at 100℃ for 1h. Remove the hydrothermally treated ZrB2 aerogel and vacuum dry it at 60-80℃ for 4h to obtain the Ce-MOF-ZrB2 composite material. II. CeO2-ZrB2 Composite Catalytic Materials The prepared Ce-MOF-ZrB2 composite material was placed in a muffle furnace with a heating rate of 5℃ / min, a holding time of 2-4h, and a calcination temperature of 300-350℃. After furnace cooling, CeO2-ZrB2 composite thermocatalytic material was obtained.

2. The method for preparing a CeO2-supported catalyst using ZrB2 aerogel as a support according to claim 1, characterized in that... In step one, the molar ratio of terephthalic acid to cerium ammonium nitrate is 1:

1.

3. The method for preparing a CeO2-supported catalyst using ZrB2 aerogel as a support according to claim 1, characterized in that... In step one, the ZrB2 aerogel is completely impregnated for 30 minutes.

4. The method for preparing a CeO2-supported catalyst using ZrB2 aerogel as a support according to claim 1, characterized in that... In step one, the hydrothermal temperature of the reactor is 100℃ and the hydrothermal time is 1 hour.

5. The method for preparing a CeO2-supported catalyst using ZrB2 aerogel as a support according to claim 1, characterized in that... In step one, the drying temperature is 60-80℃ and the drying time is 4 hours.

6. The method for preparing a CeO2-supported catalyst using ZrB2 aerogel as a support according to claim 1, characterized in that... In step two, the calcination temperature is 300–350℃, and the holding time is 2–4 hours.

7. The application of the CeO2-supported composite thermocatalytic material with ZrB2 aerogel as a carrier according to claim 1 in the oxidation of toluene, characterized in that... The specific method is as follows: (1) Preliminary preparation for catalytic experiment: 0.15g of composite catalyst with CeO2 supported by ZrB2 aerogel was loaded into a fixed bed reactor. (2) Catalytic oxidation of toluene: The reaction mixture contains 1000 ppm toluene, with air and N2 as equilibrium gases. The total gas flow rate entering the quartz reaction bed is 100 mL / min, and the mass hourly space velocity is 40000 mL·g. -1 ·h -1 First, the concentration of toluene at room temperature was measured, and then the temperature was raised to 120–280 °C to carry out a continuous toluene catalytic oxidation reaction.

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