Preparation method of CeO2-loaded carrier catalyst taking ZrB2 aerogel as carrier

Abstract

The invention belongs to the field of air pollution prevention and control, and provides a preparation method of a CeO2-loaded carrier catalyst taking ZrB2 aerogel as a carrier. The technical problems that pure CeO2 is poor in physical and chemical properties and the VOCs degradation temperature is too high are solved. The preparation method disclosed by the invention is simple, and the Ce-MOF-ZrB2 composite material is prepared by adding the ZrB2 aerogel into the Ce-MOFs precursor. And then the CeO2-ZrB2 composite thermal catalytic material is prepared by carrying out pyrolysis on the Ce-MOF-ZrB2 composite material. Due to the high specific surface area, a large number of active sites and a special porous structure of the ZrB2 aerogel, toluene molecules can be in better contact with the CeO2 catalyst, so that the concentration of toluene around the CeO2 catalyst is increased, the catalytic reaction efficiency is improved, and due to the excellent thermal stability of the ZrB2 aerogel, in the high-temperature reaction process of the ZrB2 aerogel, the catalytic activity of the CeO2 catalyst is improved. The efficient catalytic activity can be kept for a long time. Under the conditions that the air speed is 40000ml / (g.h) and the toluene concentration is 1000ppm, the toluene complete degradation temperature is 225 DEG C which is reduced by 36 DEG C compared with the degradation temperature of a pure CeO2 catalyst, so that the catalyst has a very good application prospect.

Description

Technical Field

[0001] The present invention belongs to the field of thermal catalytic material preparation, and specifically relates to CeO 2 -ZrB 2 Preparation of thermal catalytic materials and testing of their thermal catalytic degradation of a VOCs gas (toluene). Background Art

[0002] Air purification has become one of the issues of public concern and has been widely studied. Among them, volatile organic compounds (VOC S ) refers to the main atmospheric pollutants with a boiling point below 260°C at room temperature, that is, any organic compound that can participate in atmospheric photochemical reactions. Common volatile organic compounds include ethyl acetate (EtOAc), toluene, benzene, ethanol and acetone. The various volatile organic compounds contained in VOCs can react with nitrogen oxides in the environment, thereby increasing the oxidizability of the atmosphere, promoting the formation of secondary particulate matter, and then forming photochemical smog. These harmful substances will pose a huge threat to the atmospheric ozone layer. It has a profound impact on our daily life and healthy growth, and has an impact on the sustainable development of the ecosystem that cannot be ignored.

[0003] Currently targeting VOC s There are two main types of VOC control: source control and end-of-pipe control. However, in actual application, source control can only be used as a preventive measure due to various constraints. VOC must be controlled through end-of-pipe control. s Effective control. The technologies used in end-of-pipe treatment can be mainly summarized into three categories: physical, biological and chemical. Among these methods, catalytic oxidation technology is considered to be an effective method because of its high economic feasibility, low cost and low level of secondary pollutant generation, and it can operate at a lower temperature while controlling the selectivity of by-products. Therefore, it can be considered as an environmentally friendly and cost-effective technology. In the catalytic oxidation method, the reaction rate of volatile organic compounds in the degradation process is highly dependent on catalytic nanomaterials. Therefore, in order to eliminate volatile organic compounds, the rational design and manufacture of highly active and cost-effective catalytic nanomaterials are crucial in practical applications.

[0004] The most notable feature of cerium-based oxides is their strong redox ability. 4+ (oxidation state) and Ce 3 +(reduced state) and each other, which makes it very flexible in catalyzing redox reactions. Specifically, the redox cycle of cerium enables it to effectively store and release oxygen during the catalytic process, which is critical for a variety of reactions, especially those that require redox exchange. Nowadays, nanoscale cerium-based oxides are usually prepared by adjusting their nanostructures or through synthetic techniques (such as hydrothermal methods). They usually have a higher specific surface area, and a higher surface area can provide more active sites for catalytic reactions, thereby improving catalytic efficiency. However, its catalytic activity will decrease when working at high temperatures, and the ideal catalytic efficiency will not be achieved.

[0005] Aerogel has unique advantages in catalyst carrier due to its high specific surface area, porous structure and thermal stability. Its extremely high specific surface area provides a large number of active sites for the catalyst, improving the catalytic activity and reaction rate of the catalyst; the rich nanoporous structure promotes the effective diffusion of reactants and products, reduces diffusion restrictions, and thus improves the reaction efficiency. In addition, SiO 2 and ZrB 2 The excellent thermal stability of aerogel materials enables them to maintain structural integrity under high temperature conditions, making them suitable for catalytic reactions under extreme conditions. Summary of the invention

[0006] The present invention mainly solves the problem of too high reaction temperature of thermal catalytic degradation of VOCs under the existing technical conditions, thereby providing a new CeO 2 -ZrB 2 The invention relates to a method for preparing a composite thermal catalytic material.

[0007] A ZrB 2 Aerogel-based CeO 2 A method for preparing a supported catalyst, the method specifically comprising the following steps: 1. Ce-MOF-ZrB 2 Composite Materials At room temperature, add 0.708g of terephthalic acid powder to 24mL of N,N-dimethylformamide solution, stir magnetically to dissolve, mix evenly, the solution is colorless and transparent and there is no terephthalic acid powder in the solution, which means that the terephthalic acid is completely dissolved; at room temperature, add 1.361g of tannic acid to 30ml of deionized water, stir magnetically to dissolve, mix evenly, there is no tannic acid powder in the solution, which means that the tannic acid is completely dissolved, and add 0.2g of ZrB to the solution. 2 aerogel, completely immersed, taken out after 30 minutes of complete immersion, and dried at room temperature for 2 hours; 2.32g of ammonium cerium nitrate was added to 8ml of deionized water, magnetically stirred to dissolve, mixed evenly, the solution turned orange-red, and there was no ammonium cerium nitrate powder, which means that the ammonium cerium nitrate was completely dissolved, and the dried ZrB was added to this solution.2 Aerogel, completely immersed for 30min; ammonium cerium nitrate solution and ZrB 2 The aerogel was added to the terephthalic acid solution and stirred slowly to mix the two solutions evenly without breaking the ZrB 2 aerogel; the mixed solution was added into a 100 ml polytetrafluoroethylene reactor and placed in an oven for hydrothermal treatment at 100 °C for 1 h; the ZrB 2 The aerogel was vacuum dried at 60-80 °C for 4 h to obtain Ce-MOF-ZrB 2 Composite materials. 2. CeO 2 -ZrB 2 Composite Catalytic Materials The prepared Ce-MOF-ZrB 2 The composite material is placed in a muffle furnace with a heating rate of 5°C / min, a holding time of 2 to 4 hours, a calcination temperature of 300 to 350°C, and cooled with the furnace. After calcination, CeO 2 -ZrB 2 Composite thermal catalytic material. In step 1, the molar mass ratio of terephthalic acid to ammonium cerium nitrate is 1:1. Step 1 ZrB 2 The complete impregnation time of the aerogel is 30 min. In step 1, the hydrothermal temperature of the reactor is 100° C. and the hydrothermal time is 1 h. In step 1, the drying temperature is 60-80°C and the drying time is 4 hours. In step 2, the calcination temperature is 300-350°C and the holding time is 2-4 hours.

[0008] In this study, Ce-MOF was prepared by hydrothermal method, and then Ce-MOF-ZrB was prepared by wet impregnation method. 2 Composite materials, and finally CeO was prepared by sacrificial template method 2 -ZrB 2 Composite catalytic materials. Polyhedral CeO 2 Nanoparticles and ZrB 2 The composite of aerogel materials retains the three-dimensional porous structure and large specific surface area of ​​Ce-MOF, increases the adsorption and catalytic capacity of toluene and improves the catalytic efficiency. 2 Aerogel materials have a large surface area, many acidic active sites, and an excellent porous structure that allows toluene molecules to contact the catalyst more fully, allowing toluene to form a stable structure in CeO 2 The increase in the surrounding concentration is more conducive to the oxidation reaction and improves the efficiency of the catalytic reaction.

[0009] The beneficial effects of the present invention are:

[0010] This invention is the first to use ZrB 2 Aerogel as carrier to load CeO 2 catalyst, and prepared CeO 2 -ZrB 2 Composite thermal catalyst. ZrB 2 The high specific surface area, large number of active sites and special porous structure of aerogel enable toluene molecules to be more fully adsorbed on ZrB 2 The aerogel surface and pores allow toluene molecules to better interact with CeO 2 The catalyst contacts toluene in CeO 2 The concentration around the catalyst increases, thereby improving the catalytic reaction efficiency. 2 The excellent thermal stability of aerogel makes the overall catalyst have better catalyst stability, making it possible to 2 The catalyst will not easily agglomerate or deactivate and can maintain efficient catalytic activity for a long time.

[0011] The CeO prepared by the present invention 2 -ZrB 2 The composite thermal catalyst has high thermal catalytic performance. Taking toluene as the target pollutant, 0.15g of the composite material was used to degrade toluene gas with a space velocity of 40000ml / (g·h) and a concentration of 1000ppm. 2 The temperature T90 (the temperature corresponding to 90% conversion rate of toluene) for complete degradation of pollutants is 255°C, while the temperature T90 for complete degradation of pollutants by the composite material is 219°C. 2 -ZrB 2 The catalytic performance of the composite thermal catalyst for toluene has been greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 The thermal catalytic material CeO synthesized in Example 1 2 , ZrB 2 Aerogel, CeO 2 -ZrB 2 XRD pattern of

[0013] Figure 2 The thermal catalytic material CeO synthesized in Example 1 2 , ZrB 2 Aerogel, CeO 2 -ZrB 2 Adsorption-desorption isotherms;

[0014] Figure 3The thermal catalytic materials Ce-MOF (a) and CeO synthesized in Example 1 are 2 (b) ZrB 2 Aerogel (c) and CeO 2 -ZrB 2 (d) SEM image;

[0015] Figure 4 is CeO of the thermal catalytic material synthesized in Example 1 2 and CeO 2 -ZrB 2 Efficiency diagram of catalytic degradation of toluene; DETAILED DESCRIPTION

[0016] The present invention is further described in detail below in conjunction with specific embodiments.

[0017] Example 1:

[0018] In this example, a CeO 2 -ZrB 2 The preparation method of the aerogel composite thermal catalyst is specifically carried out according to the following steps:

[0019] 1. At room temperature, add 0.708g of terephthalic acid powder to 24mL of N,N-dimethylformamide solution, stir magnetically to dissolve, mix evenly, the solution is colorless and transparent and there is no terephthalic acid powder in the solution, which means that the terephthalic acid is completely dissolved; at room temperature, add 1.361g of tannic acid to 30ml of deionized water, stir magnetically to dissolve, mix evenly, there is no tannic acid powder in the solution, which means that the tannic acid is completely dissolved, add 0.2g of ZrB to the solution 2 aerogel, completely immersed, taken out after 30 minutes of complete immersion, and dried at room temperature for 2 hours; 2.32g of ammonium cerium nitrate was added to 8ml of deionized water, magnetically stirred to dissolve, mixed evenly, the solution turned orange-red, and there was no ammonium cerium nitrate powder, which means that the ammonium cerium nitrate was completely dissolved, and the dried ZrB was added to this solution. 2 Aerogel, completely immersed for 30min; ammonium cerium nitrate solution and ZrB 2 The aerogel was added to the terephthalic acid solution and stirred slowly to mix the two solutions evenly without breaking the ZrB 2 aerogel; the mixed solution was added into a 100 ml polytetrafluoroethylene reactor and placed in an oven for hydrothermal treatment at 100 °C for 1 h; the ZrB 2 The aerogel was dried under vacuum at 60 °C for 4 h to obtain Ce-MOF-ZrB 2 Composite material. The prepared Ce-MOF-ZrB 2The composite material was placed in a muffle furnace with a heating rate of 5°C / min, a holding time of 2h, a calcination temperature of 300°C, and then cooled in the furnace. 2 -ZrB 2 Composite thermal catalytic material.

[0020] The prepared catalyst is subjected to X-ray diffraction analysis to obtain the XRD pattern of the catalyst, such as Figure 1 As shown, the catalyst also exhibits CeO 2 and ZrB 2 Mutually.

[0021] The specific surface area of ​​the prepared catalyst was tested, such as Figure 2 Pure CeO 2 , ZrB 2 and CeO 2 -ZrB 2 N 2 Adsorption-desorption curve. According to the test, CeO 2 , ZrB 2 Aerogel and CeO 2 -ZrB 2 The specific surface areas of the composite materials are 87.9971m 2 / g, 134.5512m 2 / g and 114.4555m 2 / g. It can be seen that after loading, the specific surface area of ​​the catalyst increased by about 28m 2 / g, but ZrB 2 The specific surface area of ​​aerogel decreased by 20m 2 / g. This indicates that ZrB 2 Aerogel is CeO 2 The catalyst provides a relatively higher specific surface area, but CeO 2 The catalyst must have blocked the ZrB 2 The pores of the aerogel.

[0022] The SEM image of the catalyst obtained by SEM electron microscopy scanning of the prepared catalyst is as follows: Figure 3 As shown, Ce-MOF is a smooth polyhedral structure. The CeO 2 The polyhedral structure of MOF was maintained, but shrinkage occurred due to high temperature calcination. 2 The surface of aerogel is composed of smooth spherical pores. 2 -ZrB 2 We can see on the surface of the composite thermal catalytic material that many CeO have grown on its original spherical surface. 2 Catalyst small particles.

[0023] Example 2: CeO prepared based on Ce-MOF precursor in Example 1 2 -ZrB 2 Composite thermal catalytic material, take 0.15g CeO 2 -ZrB 2 The composite thermal catalytic material was loaded into a fixed bed reactor (a glass reaction tube with an inner diameter of about 6 mm), and nitrogen (flow rate of 9 ml / min) was passed through the bubbling device to carry out the toluene, and the toluene content was 1000 ppm. The total gas flow rate entering the quartz reaction bed was 100 mL / min, and the mass space velocity 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 for continuous toluene catalytic oxidation reaction. Figure 4 As shown, pure CeO 2 and CeO 2 -ZrB 2 The composite thermal catalytic material can achieve a toluene removal rate of 90% at 255°C and 219°C respectively.

Claims

1. A method for preparing a CeO2-loaded catalyst using ZrB2 aerogel as a carrier, characterized in that The specific steps of this method are as follows:

1. 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 stirred magnetically to dissolve and mixed evenly. The solution was colorless and transparent, and there was no terephthalic acid powder 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 stirred magnetically to dissolve and mixed evenly. There was no tannic acid powder in the solution, indicating that the tannic acid was completely dissolved. 0.2 g of ZrB2 aerogel was added to the solution to fully immerse it. After being fully immersed for 30 minutes, it was taken out and dried at room temperature for 2 hours. Add 2.32g of ammonium cerium nitrate to 8ml of deionized water, stir magnetically to dissolve, mix evenly, the solution turns orange-red and there is no ammonium cerium nitrate powder, which means that the ammonium cerium nitrate is completely dissolved, add the dried ZrB2 aerogel to this solution, and immerse it completely for 30min; add the cerium nitrate solution and ZrB2 aerogel to the terephthalic acid solution together, stir slowly to mix the two solutions evenly, and control not to break the ZrB2 aerogel; add the above mixed solution to a 100ml polytetrafluoroethylene reactor, and put it into an oven for hydroheating at 100℃ for 1h; take out the hydroheated ZrB2 aerogel, and vacuum dry it at 60-80℃ for 4h to obtain a Ce-MOF-ZrB2 composite material.

2. CeO2-ZrB2 composite catalytic material The prepared Ce-MOF-ZrB2 composite material was placed in a muffle furnace with a heating rate of 5°C / min, a heat preservation time of 2 to 4 hours, a calcination temperature of 300 to 350°C, and cooled with the furnace. After the calcination, a CeO2-ZrB2 composite thermal catalytic material was obtained.

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

1.

3. The method for preparing a CeO2-loaded catalyst using ZrB2 aerogel as a carrier according to claim 1, characterized in that In step 1, the complete impregnation time of ZrB2 aerogel is 30 minutes.

4. The method for preparing a CeO2-loaded catalyst using ZrB2 aerogel as a carrier according to claim 1, characterized in that In step 1, the hydrothermal temperature of the reactor is 100° C. and the hydrothermal time is 1 h.

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

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

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

Images