CeMn catalyst, preparation method thereof and application of CeMn catalyst in catalytic oxidation of toluene

Abstract

The invention discloses a CeMn catalyst and a preparation method and application thereof in catalytic oxidation of toluene, the CeMn catalyst is prepared through two-step alcohol synergistic modification, a certain number of oxygen vacancy defects are introduced into a bulk phase of the catalyst through primary alcohol treatment, and under the action of alcohol, the CeMn catalyst forms a specific microstructure assembled by small particles, so that the specific microstructure is formed. After ultrasonic treatment, particles are further dispersed, the specific surface area of the catalyst is increased, and toluene can be adsorbed on the surface of the catalyst. In the secondary alcohol treatment process, the surface of the catalyst is subjected to a reduction reaction, and part of oxygen atoms are taken away to form an oxygen vacancy defect, so that the activation performance of the CeMn catalyst on gas-phase oxygen and the fluidity of oxygen species of the CeMn catalyst are improved, and the catalytic oxidation performance of the CeMn catalyst on VOCs is enhanced. The method has the advantages of high economic benefit, simple treatment process, effective improvement of the performance of the modified catalyst, and good stability and water resistance.

Description

Technical Field

[0001] The invention belongs to the technical field of catalyst preparation and environmental catalysis, and particularly relates to a CeMn catalyst and a preparation method thereof, and application in catalytic oxidation of toluene. Background Art

[0002] Volatile organic compounds (VOCs) are currently one of the major atmospheric pollutants, originating from a wide range of sectors, including the chemical industry, petroleum refining, coatings, transportation, and interior decoration. As the primary precursors of secondary pollutants such as ozone, fine particulate matter, and secondary aerosols, VOCs directly contribute to environmental problems such as photochemical smog and urban haze, severely impacting the ecological environment and human health. Furthermore, VOCs pose multiple health risks, including irritation, teratogenicity, carcinogenicity, and reproductive toxicity. Long-term exposure can lead to serious health problems, including respiratory diseases and immune system disorders. Among these VOCs, toluene is widely studied as a typical pollutant due to its high volatility, toxicity, and potential harm to human health.

[0003] VOCs end-of-pipe treatment technologies primarily include adsorption, condensation recovery, biological purification, direct combustion, and catalytic oxidation. Catalytic oxidation technology has a wide range of applications, features a low ignition temperature, eliminates secondary pollution, and enables rapid and efficient VOC emission reduction. Its easy-to-control operating conditions, simple process flow, and high safety factor make it widely used in industrial production.

[0004] The core of VOCs catalytic oxidation technology lies in the development and design of efficient catalysts. CeMn composite oxide catalysts have attracted widespread attention due to their excellent oxygen storage / release capacity and redox performance. However, CeMn catalysts prepared by traditional methods (such as impregnation, coprecipitation, and sol-gel methods) have disadvantages such as easy agglomeration, difficulty in uniformly dispersing metal particles, few active sites, and low oxygen vacancy content. These disadvantages result in demanding reaction conditions, and complete VOC conversion can only be achieved at higher temperatures, which increases process complexity and actual reaction energy consumption. Summary of the Invention

[0005] The purpose of this section is to summarize some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of this application to avoid obscuring the purpose of this section, the abstract and the title of the invention, and such simplifications or omissions should not be used to limit the scope of the present invention.

[0006] In view of the above problems and / or the problems existing in the prior art, the present invention is proposed.

[0007] Therefore, the purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for preparing a CeMn catalyst.

[0008] To solve the above technical problems, the present application provides the following technical solutions: comprising,

[0009] Ce(NO3)3·6H2O and Mn(NO3)2·4H2O are dissolved in a mixed solution of monohydric alcohol and polyhydric alcohol to obtain a precursor solution, the precursor solution is treated at constant temperature, the obtained precipitate is washed, dried and calcined to obtain a CeMn catalyst treated by alcohol for the first time;

[0010] The CeMn catalyst treated by alcohol for the first time is ground to a particle size of less than 200 mesh, dispersed in a reducing dispersant, and then treated by high-frequency ultrasonic and low-frequency ultrasonic, and the obtained dispersion system is treated at constant temperature again, and the obtained precipitate is washed and dried to obtain a CeMn catalyst.

[0011] As a preferred scheme of the preparation method of the CeMn catalyst, in the precursor solution, the sum of the amounts of substance of Ce(NO3)3·6H2O and Mn(NO3)2·4H2O is 0.008 mol to 0.012 mol, and the ratio of the amounts of substance is 1 to 3:1.

[0012] The monohydric alcohol in the precursor solution includes one of ethanol or isopropanol, and the polyhydric alcohol is glycerol, and the usage ratio is 45 to 55:8 to 12.

[0013] As a preferred scheme of the preparation method of the CeMn catalyst, in the dispersion system, the content of the CeMn catalyst is 2% to 3%.

[0014] As a preferred scheme of the preparation method of the CeMn catalyst, in the preparation method of the CeMn catalyst, the treatment time of the precursor solution treated at constant temperature is 6 to 8 hours, and the treatment temperature is 140 to 180°C.

[0015] As a preferred scheme of the preparation method of the CeMn catalyst, after the precursor solution is treated at constant temperature, the obtained precipitate is washed, dried and calcined, wherein the washing is alternately washed by deionized water and anhydrous ethanol; the drying temperature is 60 to 80°C, and the drying time is 10 to 12 hours; the calcination temperature is 400 to 500°C, and the calcination time is 2 to 4 hours.

[0016] As a preferred scheme of the preparation method of the CeMn catalyst, the reducing dispersant is a mixed solution of alcohol and N,N-dimethylformamide, and the volume ratio is 0.5 to 2:1, wherein the alcohol includes one of methanol, ethanol and isopropanol.

[0017] As a preferred solution of the preparation method of the CeMn catalyst of the present invention, the high-frequency ultrasonic treatment is 80-100 Hz for 3-4 hours, and the low-frequency ultrasonic treatment is 40-80 Hz for 2-3 hours.

[0018] As a preferred embodiment of the preparation method of the CeMn catalyst of the present invention, the dispersion is subjected to constant temperature treatment again, and the obtained precipitate is washed and dried, wherein the constant temperature treatment time is 6 to 8 hours and the temperature is 60 to 100°C; the washing is performed by alternating washing with deionized water and anhydrous ethanol; the drying temperature is 40 to 60°C and the drying time is 2 to 4 hours.

[0019] Another object of the present invention is to provide a CeMn catalyst.

[0020] Another object of the present invention is to provide an application of a CeMn catalyst in the catalytic oxidation of VOCs.

[0021] Beneficial effects of the present invention:

[0022] (1) The present invention prepares the CeMn catalyst through a two-step alcohol synergistic modification. The first alcohol treatment introduces a certain number of oxygen vacancy defects into the bulk phase of the catalyst. Under the action of alcohol, the CeMn catalyst forms a specific microstructure composed of small particles. After ultrasonic treatment, the particles are further dispersed, increasing the specific surface area of ​​the catalyst, which is conducive to the adsorption of toluene on the catalyst surface.

[0023] During the second alcohol treatment, a reduction reaction occurs on the catalyst surface, and some oxygen atoms are taken away to form oxygen vacancy defects, which improves the activation performance of the CeMn catalyst for gas-phase oxygen and the mobility of its own oxygen species, thereby enhancing the catalytic oxidation performance of VOCs.

[0024] (2) The present invention modifies the CeMn catalyst. The raw materials are readily available and inexpensive, which has high economic benefits. The treatment process is simple. The performance of the modified catalyst is effectively improved, and it has good stability and water resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort. Among them:

[0026] Figure 1 The stability test results of the catalyst prepared in Example 1 of the present invention are shown.

[0027] Figure 2The figure shows the water resistance test results of the catalyst prepared in Example 1 of the present invention.

[0028] Figure 3 1 is a comparison chart of toluene conversion and CO2 yield of CeMn catalysts prepared in Examples 1 to 3.

[0029] Figure 4 The figure is a comparison chart of toluene conversion and CO2 yield of the catalysts prepared in Comparative Example 1 and Example 1.

[0030] Figure 5 The figure is a comparison chart of toluene conversion and CO2 yield of the catalysts prepared in Comparative Example 2 and Example 1.

[0031] Figure 6 The figure is a comparison chart of toluene conversion and CO2 yield of the catalysts prepared in Comparative Example 3 and Example 1.

[0032] Figure 7 The figure is a comparison chart of toluene conversion and CO2 yield of the catalysts prepared in Comparative Example 4 and Example 1.

[0033] Figure 8 The figure is a comparison chart of toluene conversion and CO2 yield of the catalysts prepared in Comparative Example 5 and Example 1. DETAILED DESCRIPTION

[0034] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification.

[0035] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0036] Secondly, the term "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive of other embodiments.

[0037] Unless otherwise specified, the raw materials used in the present invention are commonly available in the market.

[0038] The non-noble metal catalysts prepared in the examples of the present invention and the comparative examples were placed in a fixed bed reactor to evaluate their catalytic activity. Specifically:

[0039] Catalyst is tableted, crushed and screened, and the control catalyst particle size is 40~60 mesh. Weigh 0.1g catalyst and install in quartz tube (inner diameter=8mm), and fill quartz wool at both ends of quartz tube to fix catalyst and ensure that reaction gas passes through. Reaction gas is 1000ppm toluene+21vol% oxygen+nitrogen (balance gas), wherein toluene is blown in by nitrogen bubbling method, and the total flow control of reaction gas is 100mL / min, and corresponding space velocity (WHSV) is 60000mL / (gh). Reaction process adopts programmed temperature rising, and reaction temperature interval is controlled at 160~300 ℃, adopts gas chromatograph on-line test reactant and product concentration equipped with flame ionization detector (FID) and thermal conductivity detector (TCD), and the temperature (T 50 and T 90 ) to evaluate the catalytic activity, toluene conversion (X toluene ) and CO2 production rate The calculation formula is as follows:

[0040] Toluene conversion rate:

[0041]

[0042] CO2 production rate:

[0043]

[0044] Among them, [C7H8] in is the inlet toluene concentration, ppm; [C7H8] out is the outlet toluene concentration, ppm; [CO2] out is the outlet CO2 concentration, ppm.

[0045] Example 1

[0046] This embodiment provides a method for preparing a CeMn catalyst based on two-step alcohol synergistic modification, specifically:

[0047] 1) 0.006 mol of Ce(NO3)3·6H2O and 0.004 mol of Mn(NO3)2·4H2O were added to a mixture of 50 mL of ethanol and 10 mL of glycerol, mixed evenly, and transferred to a 100 mL polytetrafluoroethylene-lined reactor. The mixture was reacted at 160°C for 8 h. The resulting precipitate was washed four times with deionized water and anhydrous ethanol by centrifugation, dried at 60°C for 12 h, and then heated to 450°C at a rate of 5°C / min and calcined for 2 h to obtain the first alcohol-treated CeMn catalyst.

[0048] 2) 1 g of the first alcohol-treated CeMn catalyst was thoroughly ground to a particle size of less than 200 mesh. The mixture was then dispersed in a mixture of 20 mL of methanol and 20 mL of DMF. Ultrasonic treatment was first performed at 100 Hz for 3 hours, followed by ultrasonic treatment at 60 Hz for 3 hours. The ultrasonically treated dispersions were mixed and then treated at 60°C for 6 hours. The resulting precipitate was washed three times with deionized water and anhydrous ethanol, alternating between the two steps, and dried at 40°C for 2 hours. This yielded the CeMn catalyst of this example based on two-step alcohol synergistic modification.

[0049] Figure 1 The stability test results of the catalyst prepared in this example (reaction conditions: 1000 ppm toluene + 21 vol% oxygen + nitrogen (balance gas), total gas flow rate of 100 mL / min, space velocity of 60,000 mL / (gh), reaction temperature of 240°C) show that the toluene conversion rate is stable at 95% during the 12-h continuous reaction, which proves that the catalyst has excellent stability.

[0050] Figure 2 The water resistance test results of the catalyst prepared in this embodiment (1000ppm toluene + 21vol% oxygen + nitrogen (balance gas), total gas flow rate of 100mL / min, space velocity of 60000mL / (gh), reaction temperature of 240℃, water vapor concentration of 5vol%, 10vol%, 20vol%), can be seen that during the 12-hour continuous reaction process, when no water vapor was introduced in the first 2 hours, the toluene conversion rate was stable at 95%. After introducing about 5vol% water vapor, the toluene conversion rate remained basically unchanged; when the water vapor concentration increased to about 10vol%, the toluene conversion rate decreased slightly. When further introducing about 20vol% water vapor, the toluene conversion rate dropped to 75%, indicating that the introduction of water vapor did occupy some active sites, thereby affecting the catalytic activity. However, after removing the water vapor, the toluene conversion rate returned to the initial level, indicating that the catalyst of Example 1 has good water resistance.

[0051] Example 2

[0052] The difference between this embodiment and embodiment 1 is that the alcohol solution selected for the second alcohol treatment in step 2) is ethanol, and the remaining steps and processes are the same as those in embodiment 1, thereby obtaining the CeMn catalyst based on two-step alcohol synergistic modification in this embodiment.

[0053] Example 3

[0054] The difference between this embodiment and embodiment 1 is that the alcohol solution selected for the second alcohol treatment in step 2) is isopropanol, and the remaining steps and processes are the same as those in embodiment 1, thereby obtaining the CeMn catalyst based on two-step alcohol synergistic modification in this embodiment.

[0055] Figure 31 is a comparison chart of toluene conversion and CO2 yield of CeMn catalysts prepared in Examples 1 to 3.

[0056] Comparative Example 1

[0057] The difference between this comparative example and Example 1 is that step 2) is omitted, and the remaining steps and processes are the same as those in Example 1, to obtain the CeMn catalyst of this comparative example that has been treated with one alcohol.

[0058] Figure 4 The figure is a comparison of the toluene conversion rate and CO2 yield of the catalyst prepared in this comparative example and the catalyst in Example 1.

[0059] Table 1 shows the comparative results of the catalytic performance of the catalysts prepared in Examples 1 to 3 and Comparative Example 1.

[0060] Table 1

[0061]

[0062] From Table 1 and Figures 3-4 It can be seen that the catalyst prepared by the present invention has a higher catalytic activity. The samples of Example 1 in which the CeMn catalyst was prepared by solvent thermal treatment with ethanol and the CeMn catalyst was subjected to secondary treatment with methanol have the strongest catalytic activity for toluene (T90 = 238°C).

[0063] In the scheme of the present invention, the first alcohol treatment introduces a certain number of oxygen vacancy defects into the bulk phase of the catalyst. Under the action of alcohol, the CeMn catalyst forms a specific microstructure assembled from small particles. After ultrasonic treatment, the particles are further dispersed, increasing the specific surface area of ​​the catalyst, which is conducive to the adsorption of toluene on the catalyst surface. During the second alcohol treatment, a reduction reaction occurs on the catalyst surface, and some oxygen atoms are carried away to form oxygen vacancy defects. This improves the activation performance of the CeMn catalyst for gas-phase oxygen and the mobility of its own oxygen species, thereby enhancing the catalytic oxidation performance of VOCs.

[0064] Comparative Example 2

[0065] The difference between this comparative example and Example 1 is that the methanol in the alcohol solution in step 2) is replaced by deionized water, and the remaining steps and processes are the same as those in Example 1 to obtain the CeMn catalyst of this example.

[0066] Figure 5 The figure is a comparison of the toluene conversion rate and CO2 yield of the catalyst prepared in this comparative example and the catalyst in Example 1.

[0067] Comparative Example 3

[0068] The difference between the present comparative example and Example 1 is that the alcohol solution in step 1) is replaced by isopropanol, and the remaining steps are the same as those in Example 1 to obtain the CeMn catalyst of the present example.

[0069] Figure 6 The toluene conversion and CO2 yield of the catalyst prepared in the present comparative example are compared with those of the catalyst of Example 1.

[0070] Table 2 shows the comparison of the catalytic performance of the catalysts prepared in Example 1 and Comparative Examples 2-3.

[0071] Table 2

[0072]

[0073] As shown in Table 2, the two-step alcohol treatment process of the present application has a synergistic optimization effect, i.e., the first alcohol treatment uses a combination of ethanol / glycerol, and the second alcohol treatment uses a combination of methanol / DMF (Example 1), which can make the CeMn catalyst obtain the best low-temperature catalytic performance, and the T90 (238℃) is reduced by 17℃ and 12℃ compared with Comparative Example 2 (255℃) and Comparative Example 3 (250℃), respectively. This is because in the second alcohol treatment, the introduction of methanol is beneficial to the regulation of the surface oxygen vacancy concentration of the catalyst; in the first alcohol treatment, the molecular structure and polarity of ethanol promote the uniform dispersion of the metal precursor and the formation of active sites.

[0074] Comparative Example 4

[0075] The difference between the present comparative example and Example 1 is that step 2) is omitted, and the CeMn catalyst is prepared by a sol-gel method, the alcohol solution in step 1) is replaced by water, and 2 times the molar amount of citric acid is added, and the gel is obtained by stirring and evaporating to dryness, and the drying and calcination steps are the same as those in Example 1 to obtain the CeMn catalyst of the present example.

[0076] Figure 7 The toluene conversion and CO2 yield of the catalyst prepared in the present comparative example are compared with those of the catalyst of Example 1.

[0077] Comparative Example 5

[0078] The difference between the present comparative example and Example 1 is that step 2) is omitted, and the CeMn catalyst is prepared by a co-precipitation method, the alcohol solution in step 1) is replaced by water, and 1 mol / L of ammonia solution is added until no precipitate is formed, and the remaining steps are the same as those in Example 1 to obtain the CeMn catalyst of the present example.

[0079] Figure 8 The toluene conversion and CO2 yield of the catalyst prepared in the present comparative example are compared with those of the catalyst of Example 1.

[0080] Table 3 shows the comparative results of the catalytic performance of the catalysts prepared in Example 1 and Comparative Examples 4-5.

[0081] Table 3

[0082]

[0083] As shown in Table 3, the CeMn catalyst prepared using the two-step alcohol treatment process in Example 1 of the present invention achieved a T90 of 238°C, significantly superior to that of Comparative Example 4 (sol-gel method, T90 = 276°C) and Comparative Example 5 (coprecipitation method, T90 = 288°C). This difference fully demonstrates the technical advantages of the two-step alcohol treatment process, indicating that it significantly improves the catalyst's low-temperature oxidation performance. Compared with traditional sol-gel and coprecipitation methods, the present invention effectively promotes the formation of oxygen vacancies on the catalyst surface through the step-by-step treatment with a specific alcohol solvent combination, optimizing the distribution of active sites and significantly enhancing its low-temperature catalytic oxidation activity.

[0084] In summary, the present invention discloses a CeMn catalyst, a preparation method thereof, and its application in the catalytic oxidation of toluene. The CeMn catalyst is prepared by two-step alcohol synergistic modification. The first alcohol treatment introduces a certain number of oxygen vacancy defects in the bulk phase of the catalyst. Under the action of alcohol, the CeMn catalyst forms a specific microstructure assembled from small particles. After ultrasonic treatment, the particles are further dispersed, increasing the specific surface area of ​​the catalyst, which is conducive to the adsorption of toluene on the catalyst surface. During the second alcohol treatment, a reduction reaction occurs on the catalyst surface, and some oxygen atoms are taken away to form oxygen vacancy defects, which improves the activation performance of the CeMn catalyst for gas-phase oxygen and the mobility of its own oxygen species, thereby enhancing the catalytic oxidation performance of VOCs. The present invention modifies the CeMn catalyst, the raw materials are easily available and low-priced, and it has high economic benefits. The treatment process is simple, and the performance of the modified catalyst is effectively improved, with good stability and water resistance.

[0085] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a CeMn catalyst, characterized in that: include, Ce(NO3)3·6H2O and Mn(NO3)2·4H2O are dissolved in a mixed solution of a monohydric alcohol and a polyhydric alcohol to obtain a precursor solution, the precursor solution is subjected to constant temperature treatment, and the resulting precipitate is washed, dried, and calcined to obtain a CeMn catalyst subjected to the first alcohol treatment; The CeMn catalyst treated with alcohol for the first time is ground to a particle size of less than 200 mesh, dispersed in a reducing dispersant, first treated with high-frequency ultrasound and then with low-frequency ultrasound, the obtained dispersion is treated at a constant temperature again, and the obtained precipitate is washed and dried to obtain the CeMn catalyst.

2. The method for preparing a CeMn catalyst according to claim 1, wherein: The sum of the amounts of Ce(NO3)3·6H2O and Mn(NO3)2·4H2O in the precursor solution is 0.008 mol to 0.012 mol, and the molar ratio is 1 to 3:1; The monohydric alcohol in the precursor solution includes one of ethanol and isopropanol, and the polyhydric alcohol is glycerol, and the usage ratio is 45-55:8-12.

3. The method for preparing the CeMn catalyst according to claim 2, wherein: The content of CeMn catalyst in the dispersion system is 2-3%.

4. The method for preparing the CeMn catalyst according to claim 3, wherein: The precursor solution is subjected to constant temperature treatment for 6 to 8 hours at a temperature of 140 to 180°C.

5. The method for preparing the CeMn catalyst according to claim 4, wherein: The precipitate obtained after the precursor solution is treated at a constant temperature is washed, dried and calcined, wherein the washing is performed by alternating washing with deionized water and anhydrous ethanol; the drying temperature is 60-80° C., and the drying time is 10-12 hours; the calcination temperature is 400-500° C., and the calcination time is 2-4 hours.

6. The method for preparing the CeMn catalyst according to claim 1, wherein: The reducing dispersant is a mixture of alcohol and N,N-dimethylformamide, with a volume ratio of 0.5 to 2:1, wherein the alcohol includes one of methanol, ethanol, and isopropanol.

7. The method for preparing a CeMn catalyst according to claim 1, wherein: The high-frequency ultrasonic treatment is 80-100 Hz for 3-4 hours, and the low-frequency ultrasonic treatment is 40-80 Hz for 2-3 hours.

8. The method for preparing a CeMn catalyst according to claim 1, wherein: The dispersion is subjected to constant temperature treatment again, and the obtained precipitate is washed and dried, wherein the constant temperature treatment time is 6 to 8 hours and the temperature is 60 to 100° C.; the washing is performed by alternating washing with deionized water and anhydrous ethanol; the drying temperature is 40 to 60° C. and the drying time is 2 to 4 hours.

9. The CeMn catalyst prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the CeMn catalyst according to claim 9 in catalytic oxidation of VOCs.

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