A supported CuCe(O x ) / ZSM-5 molecular sieve catalyst, its preparation method and application

Abstract

The present invention belongs to the fields of environmental protection and environmental catalysis, and particularly relates to a supported CuCe(O x ) / ZSM-5 molecular sieve catalyst, a preparation method thereof, and an application thereof. The supported CuCe(O x ) / ZSM-5 molecular sieve catalyst is prepared by an ethanol dispersion method. A copper source and a cerium source are dispersed in absolute ethanol, and then supported on a ZSM-5 molecular sieve as a carrier. After removing the solvent, drying, and calcining, a CuCe composite metal oxide is loaded onto the ZSM-5 molecular sieve carrier to obtain a CuCe(O x ) / ZSM-5 molecular sieve catalyst; wherein, the loading amount of the CuCe composite metal oxide on the ZSM-5 molecular sieve is 15-25 wt%, and the molar ratio of Cu to Ce is (0.4-1):1. This catalyst has high catalytic activity and stable performance for multi-component VOCs containing chlorine.

Description

Technical Field

[0001] The present invention belongs to the fields of environmental protection and environmental catalysis, and particularly relates to a supported CuCe(O x ) / ZSM-5 molecular sieve catalyst, its preparation method and application. Background Art

[0002] Volatile organic compounds (VOCs) refer to any carbon compounds that participate in atmospheric photochemical reactions. Most VOCs are highly toxic and carcinogenic substances. In addition, VOCs are key precursors of fine particulate matter (PM2.5) and ozone (O3) pollution.

[0003] Catalytic combustion technology is a process in which VOCs undergo flameless combustion on the catalyst surface to decompose into CO2 and H2O, while releasing heat. The temperature is usually in the range of 200 - 500 °C, which is much lower than the temperature of direct combustion, greatly reducing the reaction energy consumption and producing fewer toxic by-products. Li Z et al. studied and mentioned that molecular sieves are a class of carriers mainly characterized by acidity, which have a large specific surface area, rich and adjustable pore structures, and good thermal stability, and have received extensive attention in the field of environmental catalysis (Applied Catalysis B: Environmental, 2023, 339: 123131). Under the condition of multi-component VOCs, there is competition for active sites, and differences in molecular diameter, shape and size, as well as the strength of intermolecular forces, will significantly affect the adsorption behavior and process of single VOCs on the adsorbent. At the same time, catalytic combustion of multi-component chlorinated VOCs poses higher requirements for the catalytic activity and stability of the catalyst.

[0004] The present invention aims to provide a catalyst with high catalytic activity and stability for multi-component chlorinated VOCs and its preparation method. Summary of the Invention

[0005] In order to overcome the deficiencies of the prior art, the purpose of the present invention is to provide a supported CuCe(O x ) / ZSM-5 molecular sieve catalyst, its preparation method and application, which have high catalytic activity and stable performance for multi-component chlorinated VOCs.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] The purpose of the present invention is to provide a supported CuCe(O x) Preparation method of CuCe(O / ZSM-5 molecular sieve catalyst, using ethanol dispersion method, dispersing copper source and cerium source in absolute ethanol, and then loading on ZSM-5 molecular sieve as carrier, and removing solvent, drying and calcining to load CuCe composite metal oxide on ZSM-5 molecular sieve carrier to obtain CuCe(O x ) / ZSM-5 molecular sieve catalyst;

[0008] Among them, the loading amount of the CuCe composite metal oxide is 15-25 wt%, and the molar ratio of Cu to Ce is (0.4-1):1.

[0009] In the present invention, by modulating the molar ratio of the composite metal Cu-Ce and the carrier, the redox ability, acid strength and quantity of the catalyst are enhanced, the synergistic effect between the acidity of the molecular sieve carrier and the defective oxygen vacancies of the Cu-Ce composite metal oxide is realized, and the activity and stability of the catalyst are significantly improved. At the same time, the catalyst has a regular pore structure, high catalytic activity, stability and CO2 selectivity.

[0010] The supported CuCe(O x ) / ZSM-5 molecular sieve catalyst prepared in the present invention has strong acidity and defective oxygen vacancies, has strong deep oxidation (mineralization) ability, can realize the oxidation of VOCs at lower temperature, and the mesoporous and microporous channel structure provides a suitable VOCs adsorption and desorption environment.

[0011] Furthermore, its preparation method includes the following steps:

[0012] S1. Dispersing copper source and cerium source in absolute ethanol to obtain a Cu-Ce composite metal salt solution;

[0013] S2. Adding ZSM-5 molecular sieve to the Cu-Ce composite metal salt solution obtained in S1, and dispersing by stirring-ultrasonic stirring-stirring in sequence to obtain a dispersion;

[0014] S3. Heating the dispersion obtained in S2 and continuously stirring to volatilize the solvent, and drying and calcining the solid to obtain CuCe(O x ) / ZSM-5 molecular sieve catalyst.

[0015] Furthermore, in S1, the copper source is copper acetate monohydrate, and the cerium source is cerium nitrate hexahydrate.

[0016] Furthermore, the method of stirring-ultrasonic stirring-stirring in S2 is to ultrasonically disperse for 0.5-3 h after stirring evenly, and then magnetically stir for 1-5 h;

[0017] Preferably, the method of stirring-ultrasonic stirring-stirring in S2 is to ultrasonically disperse for 1 h after stirring evenly, and then magnetically stir for 2 h.

[0018] Further, the method of continuously stirring to volatilize the solvent in S3 is to continuously stir and volatilize ethanol in a water bath at 50-95 °C.

[0019] Further, the drying in S3 is carried out at 70-120 °C for 8-24 h.

[0020] Further, the calcination in S3 is carried out in an air atmosphere at 300-500 °C for 1-6 h.

[0021] The present invention also provides a supported CuCe(O x ) / ZSM-5 molecular sieve catalyst prepared by the above preparation method.

[0022] The present invention also provides the application of the supported CuCe(O x ) / ZSM-5 molecular sieve catalyst in the catalytic combustion of multi-component chlorinated VOCs;

[0023] Preferably, the multi-component chlorinated VOCs is a mixture including toluene and chlorobenzene.

[0024] Further, the reaction conditions adopted for catalytic combustion are: the concentration of toluene is 500-1500 ppm, the concentration of chlorobenzene is 100-400 ppm, and the reaction space velocity is 10000-20000 mL·g -1 ·h -1 .

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] 1. By adjusting the molar ratio of the composite metal Cu-Ce and the optimization of the support, the present invention enhances the redox ability, acid strength and quantity of the catalyst, realizes the synergistic effect between the acidity of the molecular sieve support and the defective oxygen vacancies of the Cu-Ce composite metal oxide, and significantly improves the activity and stability of the catalyst. Toluene and chlorobenzene are catalytically combusted simultaneously at a lower reaction temperature. In the mixed atmosphere of toluene and chlorobenzene, the reaction temperatures at which the conversion rates of toluene and chlorobenzene reach more than 90% are 240 °C and 260 °C respectively.

[0027] 2. The preparation method provided by the present application not only has a short synthesis time, but also has simple equipment requirements, saving time and energy. At the same time, the raw materials are inexpensive, the samples have excellent stability and high catalytic activity, and have high reference and research value for the catalytic oxidation of industrial multi-component chlorinated VOCs. Description of the Drawings

[0028] Figure 1 is the activity evaluation diagram of Example 1, Comparative Example 1 and Comparative Example 2 in the present invention;

[0029] Figure 2 These are the activity evaluation diagrams of Example 1, Example 2, and Example 3 in the present invention;

[0030] Figure 3 These are the activity evaluation diagrams of Example 1, Comparative Example 3, and Comparative Example 4 in the present invention;

[0031] Figure 4 These are the stability test diagrams of Example 1, Example 2, and Example 3 in the present invention;

[0032] Figure 5 These are the N2 adsorption - desorption isotherm diagrams of Example 1, Comparative Example 1, and Comparative Example 2 in the present invention. Detailed implementation manners

[0033] Next, in combination with the embodiments of the present invention, the technical solutions of the present invention will be clearly and completely described. The described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0034] In the following examples, copper(II) acetate monohydrate was purchased from Macklin, and cerium(III) nitrate hexahydrate was purchased from Shanghai Aladdin. The methods are all conventional methods unless otherwise specified, and the raw materials can be obtained from public commercial channels unless otherwise specified.

[0035] Example 1

[0036] The Cu4Ce6(O x ) / ZSM - 5 catalyst provided in this example (abbreviated as Cu4Ce6 / ZSM - 5, with a molar ratio of Cu to Ce of 4:6) was prepared as follows:

[0037] Weigh 0.289 g of copper(II) acetate monohydrate and 0.947 g of cerium(III) nitrate hexahydrate, mix them in 30 mL of absolute ethanol, then add 1.6 g of ZSM - 5 molecular sieve support. The loading amount of the Cu - Ce composite metal oxide is 20 wt%. Stir at room temperature for 1 h, then ultrasonically disperse for 1 h at an ultrasonic frequency of 40 kHz. After taking it out, magnetically stir at room temperature for 2 h to obtain a mixed solution. After stirring, continuously stir in a water bath at 80°C to volatilize ethanol. Dry the obtained solid at 105°C, and finally place it in a tubular furnace and heat it at a heating rate of 10°C / min to 400°C, and continuously calcine for 4 h to obtain the Cu4Ce6(O x ) / ZSM - 5 molecular sieve catalyst.

[0038] Example 2

[0039] The Cu3Ce7(Ox ) / ZSM-5 catalyst (abbreviated as Cu3Ce7 / ZSM-5, with a molar ratio of Cu to Ce of 3:7), and its preparation method is as follows:

[0040] Weigh 0.204 g of copper acetate monohydrate and 1.033 g of cerium nitrate hexahydrate, mix them in 30 mL of absolute ethanol, then add 1.6 g of ZSM-5 molecular sieve support, stir at room temperature for 1 h, then ultrasonically disperse for 1 h at an ultrasonic frequency of 40 kHz, take it out and magnetically stir at room temperature for 2 h. After stirring, continuously stir in an 80°C water bath to volatilize ethanol, dry the obtained solid at 105°C, and finally place it in a tube furnace and heat it to 400°C at a heating rate of 10°C / min and continuously calcine for 4 h to obtain Cu3Ce7(O x ) / ZSM-5 molecular sieve catalyst, and the loading of Cu-Ce composite metal oxide is 20 wt%.

[0041] Example 3

[0042] The Cu5Ce5(O x ) / ZSM-5 catalyst provided in this example (abbreviated as Cu5Ce5 / ZSM-5, with a molar ratio of Cu to Ce of 5:5), and its preparation method is as follows:

[0043] Weigh 0.390 g of copper acetate monohydrate and 0.846 g of cerium nitrate hexahydrate, mix them in 30 mL of absolute ethanol, then add 1.6 g of ZSM-5 molecular sieve support, stir at room temperature for 1 h, then ultrasonically disperse for 1 h at an ultrasonic frequency of 40 kHz, take it out and magnetically stir at room temperature for 2 h. After stirring, continuously stir in an 80°C water bath to volatilize ethanol, dry the obtained solid at 105°C, and finally place it in a tube furnace and heat it to 400°C at a heating rate of 10°C / min and continuously calcine for 4 h to obtain Cu5Ce5(O x ) / ZSM-5 molecular sieve catalyst, and the loading of Cu-Ce composite metal oxide is 20 wt%.

[0044] Comparative Example 1

[0045] The Cu4Ce6(O x ) / SAPO-34 catalyst provided in this comparative example (abbreviated as Cu4Ce6 / SAPO-34, with a molar ratio of Cu to Ce of 4:6), and its preparation method is as follows:

[0046] Weigh 0.289 g of copper acetate monohydrate and 0.947 g of cerium nitrate hexahydrate, mix them in 30 mL of absolute ethanol, then add 1.6 g of SAPO-34 molecular sieve support. Stir at room temperature for 1 h, then ultrasonically disperse for 1 h at an ultrasonic frequency of 40 kHz. After taking it out, magnetically stir at room temperature for 2 h. After stirring, continuously stir in an 80°C water bath to evaporate ethanol. Dry the obtained solid at 105°C, and finally place it in a tube furnace and heat it to 400°C at a heating rate of 10°C / min and continuously calcine for 4 h to obtain Cu4Ce6(O x ) / SAPO-34 molecular sieve catalyst, and the loading of Cu-Ce composite metal oxide is 20 wt%.

[0047] Comparative Example 2

[0048] The Cu4Ce6(O x ) / MCM-41 catalyst (abbreviated as Cu4Ce6 / MCM-41, molar ratio of Cu to Ce is 4:6) provided in this comparative example is prepared as follows:

[0049] Weigh 0.289 g of copper acetate monohydrate and 0.947 g of cerium nitrate hexahydrate, mix them in 30 mL of absolute ethanol, then add 1.6 g of AlMCM-41 molecular sieve support. Stir at room temperature for 1 h, then ultrasonically disperse for 1 h at an ultrasonic frequency of 40 kHz. After taking it out, magnetically stir at room temperature for 2 h. After stirring, continuously stir in an 80°C water bath to evaporate ethanol. Dry the obtained solid at 105°C, and finally place it in a tube furnace and heat it to 400°C at a heating rate of 10°C / min and continuously calcine for 4 h to obtain Cu4Ce6(O x ) / MCM-41 molecular sieve catalyst, and the loading of Cu-Ce composite metal oxide is 20 wt%.

[0050] Comparative Example 3

[0051] The CuO x / ZSM-5 catalyst (abbreviated as Cu / ZSM-5) provided in this example is prepared as follows:

[0052] Weigh 1.255 g of copper acetate monohydrate, mix it in 30 mL of absolute ethanol, then add 1.6 g of ZSM-5 molecular sieve support. Stir at room temperature for 1 h, then ultrasonically disperse for 1 h at an ultrasonic frequency of 40 kHz. After taking it out, magnetically stir at room temperature for 2 h. After stirring, continuously stir in an 80°C water bath to evaporate ethanol. Dry the obtained solid at 105°C, and finally place it in a tube furnace and heat it to 400°C at a heating rate of 10°C / min and continuously calcine for 4 h to obtain CuO x / ZSM-5 catalyst molecular sieve catalyst, with a Cu metal oxide loading of 20 wt%.

[0053] Comparative Example 4

[0054] The CeO provided in this example x / ZSM-5 catalyst (abbreviated as Ce / ZSM-5), and its preparation method is as follows:

[0055] Weigh 1.247 g of cerium nitrate hexahydrate and mix it in 30 mL of absolute ethanol. Then add 1.6 g of ZSM-5 molecular sieve support, stir at room temperature for 1 h, then ultrasonically disperse it at an ultrasonic frequency of 40 kHz for 1 h, take it out and stir magnetically at room temperature for 2 h. After stirring, continuously stir in an 80°C water bath to volatilize ethanol. Dry the obtained solid at 105°C, and finally place it in a tubular furnace and heat it at a heating rate of 10°C / min to 400°C and calcine it continuously for 4 h to obtain CeO x / ZSM-5 molecular sieve catalyst, with a Ce metal oxide loading of 20 wt%.

[0056] Test Example 1: Catalytic performance test

[0057] The test method is as follows: Load 400 mg of catalyst into a quartz fixed-bed micro-reactor, and the evaluated parameters are as follows: the flow rate is 100 ml·min -1 , toluene gas with an initial concentration of 1000 ppm, chlorobenzene gas with an initial concentration of 250 ppm, the balance gas is 80% N2 + 20% O2, measure the concentration of its tail gas with a GC (GC-9790, Fuli) gas chromatograph, and the space velocity is 15000 mL·g -1 ·h -1 , and the reaction pressure is 0.1 MPa; when water vapor is introduced, the concentration is 5 vol%, and the total gas flow rate is 100 mL / min.

[0058] In this example, the conversion rate = ((toluene / chlorobenzene) initial concentration - (toluene / chlorobenzene) concentration in the tail gas) / (toluene / chlorobenzene) initial concentration × 100%. The test results are shown in Table 1, Table 2, and Figure 1 , Figure 2 as follows:

[0059] Table 1 Evaluation results of toluene removal activity of examples and comparative examples

[0060]

[0061] Table 2 Evaluation results of chlorobenzene removal activity of examples and comparative examples

[0062]

[0063] As can be seen from Table 1 and Table 2, the CuCe / ZSM-5 prepared in Example 1 with a molar ratio of 0.66 (4:6) reached a toluene conversion rate of 90% first. At 240 °C, the conversion rates of Examples 2 and 3 and Comparative Examples 1 and 2 did not reach 50%. For the conversion rate of chlorobenzene, Example 1 reached 50% and 90% first. Generally speaking, the low-temperature catalytic activity of Example 1 is better than that of other examples. The catalytic activities from high to low are: Example 1 > Example 3 > Example 2 > Comparative Example 3 > Comparative Example 1 > Comparative Example 2 > Comparative Example 4.

[0064] As Figure 1 shown, with the molar ratio of the active components CuCe being 0.66 (4:6), Example 1 had the highest low-temperature catalytic activity throughout the catalytic process. For toluene and chlorobenzene T 90 reached 240 °C and 260 °C respectively, and under the mixed conditions at 240 °C, the toluene conversion rate was about 75% higher than that of Comparative Examples 1 and 2, and the chlorobenzene conversion rate was about 40% higher than that of Comparative Examples 1 and 2.

[0065] As Figure 2 shown, for the CuCe(O x ) / ZSM-5 catalysts with the active components CuCe and ZSM-5 as the molecular sieve carrier, all had excellent catalytic activities. The CuCe(O x ) / ZSM-5 catalyst with a CuCe molar ratio of 0.66 (4:6) had the highest low-temperature catalytic activity throughout the catalytic process. Under the mixed conditions at 240 °C, the toluene conversion rate was about 50% higher than that of Examples 2 and 3, and the chlorobenzene conversion rate was about 55% higher than that of Examples 2 and 3.

[0066] As Figure 3 shown, for the CuCe(O x ) / ZSM-5 catalysts with the active components CuCe and ZSM-5 as the molecular sieve carrier, all had excellent catalytic activities. The CuCe(O x ) / ZSM-5 catalyst with a CuCe molar ratio of 0.66 (4:6) had the highest low-temperature catalytic activity throughout the catalytic process. Under the mixed conditions at 240 °C, the toluene conversion rate was about 50% higher than that of Comparative Examples 3 and 4, and the chlorobenzene conversion rate was about 40% higher than that of Comparative Examples 3 and 4.

[0067] Test Example 2: Stability Test

[0068] Method of the stability test:: Load 400 mg of the catalyst into a quartz fixed-bed microreactor, and the evaluation parameters are as follows: the flow rate is 100 ml·min -1, Toluene gas with an initial concentration of 1000 ppm, chlorobenzene gas with an initial concentration of 250 ppm, and the balance gas is 80% N2 + 20% O2. The concentration of its tail gas is measured by a GC (GC-9790, Fuli) gas chromatograph, and the space velocity is 15000 mL·g -1 ·h -1 , and the reaction pressure is 0.1 MPa; the test temperature is 240 °C from 0 to 90 min, and then the temperature is raised. From 90 to 180 min, the test temperature is 260 °C, and then the temperature is raised. From 180 to 280 min, the test temperature is 280 °C.

[0069] As Figure 4 shown, the active component CuCe, the CuCe(O x ) / ZSM-5 catalyst with ZSM-5 as the molecular sieve carrier has excellent stability at 280 °C, and no deactivation phenomenon occurs during long-term testing.

[0070] Test Example 3: N2 adsorption-desorption test

[0071] Method of N2 adsorption-desorption test: Physical adsorption and desorption of N2 are measured at -196 by an American Micromeritics ASAP 2020 analyzer. Before the test starts, the catalyst is pretreated at 250 °C for 1 h to remove surface moisture and impurities.

[0072] As Figure 5 shown, Comparative Example 1 shows a typical Type I adsorption / desorption isotherm, indicating that the microporous structure of the original SAPO-34 is retained; Comparative Example 2 shows a Type IV adsorption / desorption isotherm, indicating the presence of a microporous structure. At the same time, when P / P0 > 0.4, the isotherm rises and a hysteresis loop appears, indicating the coexistence of mesopores. Cu4Ce6(O x ) / ZSM-5 shows a combination of Type I and Type IV isotherms, that is, it has both micropores and a small amount of mesoporous structure.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and are not intended to limit them; although the present application has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that: modifications can still be made to the specific implementation manners of the present application or equivalent replacements can be made to some technical features, and they should all be covered within the scope of the technical solutions claimed in the present application.

Claims

1. Application of a supported CuCe(O x ) / ZSM-5 molecular sieve catalyst in catalytic combustion of multi-component chlorine-containing VOCs, characterized in that, The multi-component chlorine-containing VOCs is a mixture including toluene and chlorobenzene, and the preparation method of the supported CuCe(O x ) / ZSM-5 molecular sieve catalyst comprises the following steps: S1. Disperse a copper source and a cerium source in absolute ethanol to obtain a Cu-Ce composite metal salt solution; S2. Add ZSM-5 molecular sieve into the Cu-Ce composite metal salt solution obtained in S1, and disperse it by stirring-ultrasonic-stirring in sequence to obtain a dispersion; S3. For the dispersion obtained in S2, continuously stir while heating to volatilize the solvent, and dry and calcine the solid to obtain the CuCe(O x ) / ZSM-5 molecular sieve catalyst; The loading amount of the CuCe composite metal oxide is 15-25 wt%, and the molar ratio of Cu to Ce is (0.4-1):

1.

2. The application according to claim 1, characterized in that, The copper source in S1 is copper acetate monohydrate, and the cerium source is cerium nitrate hexahydrate.

3. The application according to claim 1, characterized in that, The method of stirring-ultrasonic-stirring in S2 is to stir evenly and then ultrasonically disperse for 0.5-3 h, and then magnetically stir for 1-5 h.

4. The application according to claim 3, characterized in that, The method of stirring-ultrasonic-stirring in S2 is to stir evenly and then ultrasonically disperse for 1 h, and then magnetically stir for 2 h.

5. The application according to claim 1, characterized in that, The method of volatilizing the solvent by heating and continuously stirring in S3 is to continuously stir in a water bath at 50-95 °C to volatilize ethanol.

6. The application according to claim 1, characterized in that, Drying in S3 is carried out at 70-120 °C for 8-24 h.

7. The application according to claim 1, wherein Calcination in S3 is carried out in an air atmosphere at 300-500 °C for 1-6 h.

8. The application according to claim 1, characterized in that, The reaction conditions for catalytic combustion are as follows: the concentration of toluene is 500 - 1500 ppm, the concentration of chlorobenzene is 100 - 400 ppm, and the reaction space velocity is 10000 - 20000 mL·g -1 ·h -1 .

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