Denitrification catalyst, its preparation method and application

Abstract

The present invention relates to the technical field of flue gas purification, and discloses a denitration catalyst, a preparation method thereof and an application thereof. The denitration catalyst contains a carrier oxide and an active component, wherein the carrier oxide is Co3O4 derived from ZIF-67, and the active component is a composite oxide of cerium oxide and tin oxide. The denitration catalyst not only has high low-temperature activity but also has good anti-poisoning ability.

Description

Technical Field

[0001] The present invention relates to the technical field of flue gas purification, and particularly relates to a denitration catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] With the development of economy and the improvement of industrialization, environmental pollution problems are constantly emerging. As an important substance for forming acid rain, photochemical smog, and consuming O3, nitrogen oxides (NO x ) are one of the main air pollutants; at the same time, nitrogen oxides mainly composed of nitric oxide and nitrogen dioxide can stimulate the lungs, cause respiratory diseases, and are also easily combined with hemoglobin in the human body to cause methemoglobinemia, seriously damaging human health.

[0003] The selective catalytic reduction (SCR) technology using NH3 as a reducing agent is currently the most widely used and effective method for controlling the emission of nitrogen oxides (NO x ). However, there is still a problem to be solved in the NH3-SCR technology. For example, in industrial applications of the NH3-SCR technology, the working temperature window of vanadium-titanium catalysts is generally in the medium-high temperature range (300~400°C), and the denitration activity is poor in the low temperature range. At the same time, vanadium by-products have biological toxicity and pose great harm to the human body and the environment; in addition, the SCR reactor is located between the economizer and the air preheater, and the flue gas entering the SCR reactor contains a large amount of dust, alkali (earth) metals, heavy metals and other substances, which will block the pores of the catalyst, resulting in catalyst poisoning and inactivation. Especially, as one of the typical heavy metal elements in flue gas, a small amount of Pb will cause catalyst inactivation, reduce its service life, and affect economic benefits.

[0004] Therefore, there is an urgent need to develop a denitration catalyst that not only has high low-temperature activity but also has good anti-poisoning ability. Summary of the Invention

[0005] The purpose of the present invention is to overcome the problems existing in the prior art that in the NH3-SCR field, the vanadium-titanium catalyst has poor denitration activity in the low temperature range, is easily poisoned and inactivated, and the vanadium by-products have biological toxicity and pose great harm to the human body and the environment. The present invention provides a denitration catalyst, a preparation method thereof, and an application thereof. The technical solution uses a cobalt-based metal-organic framework (MOF) material as a carrier precursor, which has the advantages of high specific surface area, high porosity, and controllable structure. By rapidly decomposing nitrates through argon dielectric barrier discharge plasma, the catalyst particle size is reduced, the dispersion degree of active substances is increased, and the interaction with the carrier is enhanced. The prepared denitration catalyst for the NH3-SCR field not only has high low-temperature denitration activity but also exhibits good anti-poisoning ability.

[0006] To achieve the above object, a first aspect of the present invention provides a denitration catalyst, which contains a support oxide and an active component. Among them, the support oxide is Co3O4 derived from ZIF-67, and the active component is a composite oxide of cerium oxide and tin oxide.

[0007] Preferably, the molar ratio of the content of the support oxide in terms of Co element to the content of the active component in terms of Ce and Sn elements is 1:(2 - 4).

[0008] Preferably, in the active component, in terms of Ce and Sn elements, the molar ratio of the cerium oxide to the tin oxide is 1:(1 - 2).

[0009] A second aspect of the present invention provides a preparation method of a denitration catalyst, which includes the following steps:

[0010] (1) Mix the metal-organic framework material ZIF-67, tin salt, cerium salt and water, separate the solid phase from the obtained mixture, and then wash and dry it in sequence;

[0011] (2) Perform plasma treatment on the mixture powder obtained in step (1) through dielectric barrier discharge.

[0012] Preferably, the molar ratio of the dosage of the metal-organic framework material ZIF-67 in terms of Co element to the dosages of the cerium salt and the tin salt in terms of Ce and Sn elements respectively is 1:(2 - 4).

[0013] Preferably, in the active component, in terms of Ce and Sn elements, the molar ratio of the dosages of the cerium salt and the tin salt in terms of Ce and Sn elements respectively is 1:(1 - 2).

[0014] Preferably, the conditions of the plasma treatment include: the time is 1 - 30 min, the voltage is 40 - 60 V, and the current is 1.5 - 2 A.

[0015] Preferably, the preparation process of the metal-organic framework material ZIF-67 includes: mixing cobalt nitrate, 2-methylimidazole and a solvent and performing a hydrothermal reaction.

[0016] Preferably, the molar ratio of the cobalt nitrate to the 2-methylimidazole is 1:(35 - 50).

[0017] Preferably, the conditions of the hydrothermal reaction include: the temperature is 100 - 120 °C, and the time is 12 - 24 h.

[0018] Preferably, the method further includes: before implementing step (1), pretreating the metal-organic framework material ZIF-67, and the process of the pretreatment includes: mixing the metal-organic framework material ZIF-67, polyvinylpyrrolidone, and alcohol, separating the solid phase from the obtained mixture, and then successively performing washing and drying.

[0019] Preferably, the mass ratio of the metal-organic framework material ZIF-67, the polyvinylpyrrolidone, and the alcohol is 1:(4 - 6):(30 - 50).

[0020] The third aspect of the present invention provides a denitration catalyst prepared by the above method.

[0021] The fourth aspect of the present invention provides an application of the above denitration catalyst in removing NO in lead-containing flue gas.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] (1) The present invention uses a cobalt-based metal-organic framework (MOF) material as a carrier precursor. The MOF material has advantages such as a high specific surface area, a high porosity, and a controllable structure. Using Co3O4 derived from the metal-organic framework material ZIF-67 as the carrier and a composite oxide of tin oxide and cerium oxide as the active component, effective removal of NO at a relatively low temperature is achieved. At the same time, the catalyst also exhibits excellent lead poisoning resistance.

[0024] (2) The present invention rapidly decomposes nitrates through argon dielectric barrier discharge plasma to obtain the corresponding metal oxides. The dielectric barrier discharge plasma is to add an insulating medium into the discharge space, and ionization is generated through electromagnetic waves and a high-intensity electric field via gas discharge; compared with traditional methods such as pyrolysis in a muffle furnace, using dielectric barrier discharge plasma to prepare the catalyst can reduce energy consumption, shorten the catalyst preparation time, obtain highly dispersed active substances, and at the same time improve the performance and stability of the catalyst. Description of the Drawings

[0025] Figure 1 It is a denitration performance comparison diagram of an embodiment of the denitration catalyst of the present invention;

[0026] Figure 2 It is a denitration performance comparison diagram of an embodiment and a comparative example of the denitration catalyst of the present invention. Detailed Description of the Invention

[0027] The following provides a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0028] The endpoints and any values disclosed in this text for a range are not limited to the exact range or value. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered specifically disclosed in this text.

[0029] The denitration catalyst described in the present invention contains a support oxide and an active component. Among them, the support oxide is Co3O4 derived from ZIF-67, and the active component is a composite oxide of cerium oxide and tin oxide. According to the denitration catalyst of the present invention, using a metal-organic framework material as a support precursor, nitrate is rapidly decomposed by argon dielectric barrier discharge plasma technology, the catalyst particle size is reduced, the dispersion degree of the active component is increased, and at the same time, the interaction between the active component and the support oxide is enhanced. Therefore, the denitration catalyst described in the present invention not only has high low-temperature denitration activity, but also exhibits better anti-poisoning ability, and has strong industrial application value.

[0030] In the denitration catalyst described in the present invention, the molar ratio of the content of the support oxide in terms of Co element to the content of the active component in terms of Ce and Sn elements can be 1:(2 - 4), preferably 1:(2.5 - 3.5). Specifically, for example, it can be 1:2.5, 1:2.6, 1:2.7, 1:2.8, 1:2.9, 1:3, 1:3.1, 1:3.2, 1:3.3, 1:3.4 or 1:3.5.

[0031] In the denitration catalyst described in the present invention, in the active component, in terms of Ce and Sn elements, the molar ratio of the cerium oxide to the tin oxide can be 1:(1 - 2), preferably 1:(1.5 - 2). Specifically, for example, it can be 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9 or 1:2.

[0032] In some embodiments, the denitration catalyst described in the present invention contains a support oxide and an active component. Among them, the support oxide is Co3O4 derived from ZIF-67, the active component is a composite oxide of cerium oxide and tin oxide, the ratio of the content of the support oxide in terms of Co element to the content of the active component in terms of Ce and Sn elements is 1:(2 - 4), and in the active component, in terms of Ce and Sn elements, the molar ratio of the cerium oxide to the tin oxide is 1:(1 - 2).

[0033] The second aspect of the present invention provides a preparation method of a denitration catalyst, and this method includes the following steps:

[0034] (1) Mix the metal-organic framework material ZIF-67, tin salt, cerium salt and water, separate the solid phase from the resulting mixture, and then wash and dry it successively.

[0035] (2) Subject the mixture powder obtained in step (1) to plasma treatment by dielectric barrier discharge.

[0036] According to the method of the present invention, by using Co3O4 derived from ZIF-67 as the support oxide and the composite oxide of tin oxide and cerium oxide as the active component, effective removal of NO at a relatively low temperature is achieved. At the same time, this catalyst also exhibits excellent resistance to lead poisoning. Moreover, preparing the catalyst by dielectric barrier discharge plasma can reduce energy consumption, shorten the catalyst preparation time, obtain highly dispersed active substances, and improve the performance and stability of the catalyst.

[0037] In the method of the present invention, the molar ratio of the amount of the metal-organic framework material ZIF-67 in terms of Co element to the amounts of the cerium salt and the tin salt in terms of Ce and Sn elements respectively is 1:(2 - 4), preferably 1:(2.5 - 3.5), and specifically, for example, it can be 1:2.5, 1:2.6, 1:2.7, 1:2.8, 1:2.9, 1:3, 1:3.1, 1:3.2, 1:3.3, 1:3.4 or 1:3.5.

[0038] In the method of the present invention, in the active component, in terms of Ce and Sn elements, the molar ratio of the amounts of the cerium salt and the tin salt in terms of Ce and Sn elements respectively is 1:(1 - 2), preferably 1:(1.5 - 2), and specifically, for example, it can be 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9 or 1:2.

[0039] In the method of the present invention, the tin salt can be a water-soluble tin salt, preferably tin nitrate. The cerium salt can be a water-soluble cerium salt, preferably cerium nitrate.

[0040] In the method of the present invention, in step (1), the specific process of mixing the metal-organic framework material ZIF-67, the tin salt, the cerium salt and water includes: mixing the metal-organic framework material ZIF-67 and water by ultrasonic treatment, and then mixing with the mixed solution of the tin salt and the cerium salt by stirring. The mass ratio of the amount of the metal-organic framework material ZIF-67 to the amount of water can be 1:(30 - 50), preferably 1:(35 - 45). The mass ratio of the total mass of the tin salt and the cerium salt to the amount of water can be 1:(10 - 30), preferably 1:(15 - 25). The molar ratio of the amounts of the cerium salt and the tin salt in terms of Ce and Sn elements is 1:(1 - 2), preferably 1:(1.5 - 2). The conditions for the stirring and mixing include: the rotation speed can be 400 - 600 rpm, preferably 450 - 550 rpm; the temperature can be 20 - 30 °C, preferably 20 - 25 °C; the time can be 2.5 - 5 h, preferably 3 - 4 h.

[0041] In the method of the present invention, in step (1), a solid phase is separated from the obtained mixture by first centrifugation and washed. The conditions for the first centrifugation include: the rotation speed can be 5000 - 7000 rpm, preferably 5500 - 6500 rpm; the time can be 6 - 10 min, preferably 7 - 9 min. During the washing process, the solid phase is washed with water 2 - 4 times and with methanol 1 - 2 times.

[0042] In the method of the present invention, in step (1), the conditions for drying include: the temperature can be 70 - 90 °C, preferably 75 - 85 °C; the time can be 10 - 14 h, preferably 11 - 13 h.

[0043] In the method of the present invention, the conditions for the plasma treatment include: the time can be 1 - 30 min, preferably 1 - 5 min; the voltage can be 40 - 60 V, preferably 45 - 55 V; the current can be 1.5 - 2 A, preferably 1.5 - 1.8 A.

[0044] In the method of the present invention, the specific process of step (2) can include: spreading the mixture powder obtained in step (1) flat on a dielectric plate, and continuously introducing argon into the dielectric plate at a speed of 70 - 90 mL / min for 2 - 4 min to discharge the remaining air in the dielectric plate, and then treating the sample by dielectric barrier discharge (DBD) plasma technology.

[0045] In the method of the present invention, the preparation process of the metal-organic framework material ZIF-67 can include: mixing cobalt nitrate, 2-methylimidazole and a solvent and performing a hydrothermal reaction.

[0046] In the method of the present invention, cobalt nitrate, 2-methylimidazole and a solvent are mixed by first stirring and ultrasound. The conditions of the first stirring include: the rotation speed can be 400 - 600 rpm, preferably 450 - 550 rpm; the temperature can be 20 - 30 °C, preferably 20 - 25 °C; the time can be 25 - 40 min, preferably 30 - 40 min.

[0047] In the method of the present invention, the molar ratio of cobalt nitrate to 2-methylimidazole can be 1:(35 - 50), preferably 1:(40 - 45), and specifically can be 1:40, 1:41, 1:42, 1:43, 1:44 or 1:45. In the specific implementation manner, the cobalt nitrate is Co(NO3)2∙6H2O, and the mass ratio of Co(NO3)2∙6H2O to 2-methylimidazole is 1:(10 - 14), and specifically can be 1:10, 1:11, 1:12, 0.9:11, 1:13 or 1:14.

[0048] In the method of the present invention, the solvent can be at least one of water, methanol and ethanol, preferably water. The mass ratio of the amount of 2-methylimidazole to the solvent can be 1:(1 - 3), preferably 1:(1.5 - 2.5).

[0049] In the method of the present invention, the conditions of the hydrothermal reaction include: the temperature can be 100 - 120 °C, preferably 110 - 120 °C; the time can be 12 - 24 h, preferably 18 - 24 h. The hydrothermal reaction can be carried out in a polytetrafluoroethylene-lined reaction kettle.

[0050] In the method of the present invention, the method further includes separating the solid phase and washing the mixture obtained from the hydrothermal reaction by second centrifugation, and then performing first drying. The conditions of the second centrifugation include: the rotation speed can be 5000 - 7000 rpm, preferably 5500 - 6500 rpm; the time can be 6 - 10 min, preferably 7 - 9 min. During the washing process, the solid phase is washed with methanol 2 - 4 times. The conditions of the first drying include: the temperature can be 70 - 90 °C, preferably 75 - 85 °C; the time can be 10 - 14 h, preferably 11 - 13 h.

[0051] In the method of the present invention, the method further includes: before implementing step (1), pretreating the metal-organic framework material ZIF-67, and the pretreatment process includes: mixing the metal-organic framework material ZIF-67, polyvinylpyrrolidone and an alcohol, separating the solid phase from the obtained mixture, and then sequentially performing washing and second drying.

[0052] In the method of the present invention, the metal-organic framework material ZIF-67, polyvinylpyrrolidone and alcohol are mixed by second stirring. The conditions of the second stirring include: the rotation speed can be 400-600 rpm, preferably 450-550 rpm; the temperature can be 20-30 °C, preferably 20-25 °C; the time can be 2.5-5 h, preferably 3-4 h.

[0053] In the specific embodiment, during the pretreatment process, the solid phase and washing are separated from the obtained mixture by third centrifugation. The conditions of the third centrifugation include: the rotation speed can be 5000-7000 rpm, preferably 5500-6500 rpm; the time can be 6-8 min, preferably 7-9 min. During the washing process, the solid phase is washed with methanol 2-4 times. The conditions of the second drying include: the temperature can be 70-90 °C, preferably 75-85 °C; the time can be 3-6 h, preferably 4-5 h.

[0054] In the method of the present invention, the mass ratio of the metal-organic framework material ZIF-67, the polyvinylpyrrolidone and the alcohol can be 1:(4-6):(30-50), preferably 1:(4.5-5.5):(35-45). The alcohol can be at least one of methanol, ethanol and ethylene glycol, preferably methanol.

[0055] In some embodiments, the method for preparing the denitration catalyst of the present invention comprises the following steps:

[0056] (1) Cobalt nitrate, 2-methylimidazole and a solvent are dissolved by ultrasonic, then stirred and mixed at a rotation speed of 400-600 rpm and a temperature of 20-30 °C for 25-40 min and transferred to a polytetrafluoroethylene-lined reaction kettle for hydrothermal reaction at a temperature of 100-120 °C for 12-24 h. The mixture obtained from the hydrothermal reaction is separated into a solid phase by centrifugation at a rotation speed of 5000-7000 rpm for 6-10 min and washed with methanol 2-4 times, and then dried at a temperature of 70-90 °C for 10-14 h;

[0057] (2) The metal-organic framework material ZIF-67 prepared in step (1) and water are mixed by ultrasonic, then stirred and mixed with a mixed solution of tin nitrate and cerium nitrate at a rotation speed of 400-600 rpm and a temperature of 20-30 °C for 2.5-5 h. The solid phase is separated from the obtained mixture by centrifugation at a rotation speed of 5000-7000 rpm for 6-10 min, and the solid phase is washed with water 2-4 times and with methanol 1-2 times respectively, and then dried at a temperature of 70-90 °C for 10-14 h;

[0058] (3) Spread the mixture powder obtained in step (2) flat on a dielectric plate, and continuously introduce argon into the dielectric plate at a speed of 70 - 90 mL / min. Ventilate for 2 - 4 min to discharge the remaining air in the dielectric plate, and then perform plasma treatment for 1 - 30 min under the conditions of a voltage of 40 - 60 V and a current of 1.5 - 2 A through dielectric barrier discharge.

[0059] In some other embodiments, the preparation method of the denitration catalyst of the present invention includes the following steps:

[0060] (1) Ultrasonically dissolve cobalt nitrate, 2 - methylimidazole and a solvent, then stir and mix at a rotation speed of 400 - 600 rpm and a temperature of 20 - 30 °C for 25 - 40 min and transfer to a polytetrafluoroethylene - lined reaction kettle for hydrothermal reaction at a temperature of 100 - 120 °C for 12 - 24 h. Separate the solid phase of the mixture obtained from the hydrothermal reaction by centrifugation at a rotation speed of 5000 - 7000 rpm for 6 - 10 min and wash with methanol 2 - 4 times, then dry at a temperature of 70 - 90 °C for 10 - 14 h;

[0061] (2) Stir and mix the metal - organic framework material ZIF - 67, polyvinylpyrrolidone and alcohol prepared in step (1) at a rotation speed of 400 - 600 rpm and a temperature of 20 - 30 °C for 2.5 - 5 h. Separate the solid phase from the obtained mixture by centrifugation at a rotation speed of 5000 - 7000 rpm for 6 - 10 min and wash the solid phase with methanol 2 - 4 times, then dry at a temperature of 70 - 90 °C for 3 - 6 h;

[0062] (3) Ultrasonically mix the pretreated metal - organic framework material ZIF - 67 and water in step (2), then mix with a mixed solution of tin nitrate and cerium nitrate and stir and mix at a rotation speed of 400 - 600 rpm and a temperature of 20 - 30 °C for 2.5 - 5 h. Separate the solid phase from the obtained mixture by centrifugation at a rotation speed of 5000 - 7000 rpm for 6 - 10 min and wash the solid phase with water 2 - 4 times and with methanol 1 - 2 times respectively, then dry at a temperature of 70 - 90 °C for 10 - 14 h;

[0063] (4) Spread the mixture powder obtained in step (3) flat on a dielectric plate, and continuously introduce argon into the dielectric plate at a speed of 70 - 90 mL / min. Ventilate for 2 - 4 min to discharge the remaining air in the dielectric plate, and then perform plasma treatment for 1 - 30 min under the conditions of a voltage of 40 - 60 V and a current of 1.5 - 2 A through dielectric barrier discharge.

[0064] The third aspect of the present invention provides a denitration catalyst prepared by the above method. According to the denitration catalyst of the present invention, the metal-organic framework material ZIF-67 is treated by argon dielectric barrier discharge plasma technology to obtain its derived metal oxide Co3O4 as a carrier, and cerium nitrate and tin nitrate are rapidly decomposed by argon dielectric barrier discharge plasma to obtain the corresponding metal oxides. While the catalyst retains the advantages of high specific surface area, high porosity and controllable structure of the MOF material, it can reduce energy consumption, shorten the catalyst preparation time, obtain highly dispersed active substances, and improve the performance and stability of the catalyst.

[0065] The fourth aspect of the present invention provides the application of the above denitration catalyst in removing NO in lead-containing flue gas. According to the application of the present invention, the denitration catalyst of the present invention realizes the effective removal of NO at a lower temperature, and at the same time, the catalyst also exhibits excellent lead poisoning resistance.

[0066] The denitration catalyst of the present invention, its preparation method and application will be further described below by examples. The examples are implemented on the premise of the technical solution of the present invention, and detailed implementation manners and specific operation processes are given, but the protection scope of the present invention is not limited to the following examples.

[0067] Unless otherwise specified, the experimental methods in the following examples are all conventional methods in the art. Unless otherwise specified, the experimental materials used in the following examples are all commercially available.

[0068] Example 1

[0069] Preparation of denitration catalyst:

[0070] (1) 0.9 g of Co(NO3)2∙6H2O, 11 g of 2-methylimidazole and 20 g of water are dissolved by ultrasonic wave, stirred and mixed at a rotation speed of 500 rpm and a temperature of 25 °C for 30 min, and then transferred to an 80 mL polytetrafluoroethylene-lined reaction kettle for hydrothermal reaction at a temperature of 120 °C for 24 h. The mixture obtained by the hydrothermal reaction is separated into a solid phase by centrifugation at a rotation speed of 6000 rpm for 8 min, washed 3 times with methanol, and then dried at a temperature of 80 °C for 12 h to obtain a purple powder, which is the metal-organic framework material ZIF-67;

[0071] (2) The metal-organic framework material ZIF-67 prepared in step (1) and water are mixed by ultrasonic treatment (the mass ratio of the dosage of the metal-organic framework material ZIF-67 to the water is 1:40). Then, it is mixed with a mixed solution of tin nitrate and cerium nitrate under the conditions of a rotation speed of 500 rpm and a temperature of 25 °C with stirring for 3 h. The ratio of the content of the metal-organic framework material ZIF-67 in terms of Co element to the content of the active components in terms of Ce and Sn elements is 1:3; in terms of Ce and Sn elements, the molar ratio of cerium nitrate to tin nitrate is 1:2; the solid phase is separated from the obtained mixture by centrifugation at a rotation speed of 6000 rpm for 8 min, and the solid phase is washed with water 3 times and with methanol 1 time respectively, and then dried at a temperature of 80 °C for 12 h;

[0072] (3) The mixture powder obtained in step (2) is spread flat on a dielectric plate, and argon is continuously introduced into the dielectric plate at a speed of 80 mL / min for 3 min to discharge the remaining air in the dielectric plate. Then, plasma treatment is carried out for 1 min under the conditions of a voltage of 50 V and a current of 2 A by dielectric barrier discharge.

[0073] Example 2

[0074] Preparation of denitration catalyst:

[0075] (1) 0.9 g of Co(NO3)2∙6H2O, 11 g of 2-methylimidazole and 20 g of water are dissolved by ultrasonic treatment and stirred and mixed at a rotation speed of 500 rpm and a temperature of 25 °C for 30 min, and then transferred to an 80 mL polytetrafluoroethylene-lined reaction kettle for hydrothermal reaction at a temperature of 120 °C for 24 h. The mixture obtained from the hydrothermal reaction is separated into a solid phase by centrifugation at a rotation speed of 6000 rpm for 8 min and washed with methanol 3 times, and then dried at a temperature of 80 °C for 12 h to obtain a purple powder, which is the metal-organic framework material ZIF-67;

[0076] (2) 0.2 g of the metal-organic framework material ZIF-67 prepared in step (1), 1 g of polyvinylpyrrolidone and 8 g of methanol are stirred and mixed at a rotation speed of 500 rpm and a temperature of 25 °C for 3 h. The solid phase is separated from the obtained mixture by centrifugation at a rotation speed of 6000 rpm for 8 min and the solid phase is washed with methanol 3 times, and then dried at a temperature of 80 °C for 4 h;

[0077] (3) Ultrasonically mix the pretreated metal-organic framework material ZIF-67 and water in step (2) (the mass ratio of the dosage of the metal-organic framework material ZIF-67 to the water is 1:40), then stir and mix it with an aqueous solution of tin nitrate and an aqueous solution of cerium nitrate at a rotation speed of 500 rpm and a temperature of 25 °C for 3 h. The ratio of the content of the metal-organic framework material ZIF-67 in terms of Co element to the content of the active components in terms of Ce and Sn elements is 1:3; in terms of Ce and Sn elements, the molar ratio of cerium nitrate to tin nitrate is 1:2; Centrifuge the obtained mixture at a rotation speed of 6000 rpm for 8 min to separate the solid phase, wash the solid phase with water 3 times and wash the solid phase with methanol once, and then dry it at a temperature of 80 °C for 12 h;

[0078] (4) Spread the mixture powder obtained in step (3) flat on a dielectric plate, and continuously pass through the dielectric plate at a speed of 80 mL / min. Ventilate for 3 min to discharge the remaining air in the dielectric plate, and then carry out plasma treatment for 1 min under the conditions of a voltage of 50 V and a current of 2 A through dielectric barrier discharge.

[0079] Example 3

[0080] Preparation of denitration catalyst:

[0081] (1) Ultrasonically dissolve 1 g of Co(NO3)2∙6H2O, 10 g of 2-methylimidazole and 20 g of water, stir and mix at a rotation speed of 400 rpm and a temperature of 20 °C for 40 min, and transfer it to an 80 mL polytetrafluoroethylene-lined reaction kettle. Carry out hydrothermal reaction at a temperature of 110 °C for 18 h. Centrifuge the mixture obtained from the hydrothermal reaction at a rotation speed of 5000 rpm for 10 min to separate the solid phase and wash it with methanol 3 times, and then dry it at a temperature of 75 °C for 14 h to obtain a purple powder, which is the metal-organic framework material ZIF-67;

[0082] (2) Stir and mix 0.2 g of the metal-organic framework material ZIF-67 prepared in step (1), 0.8 g of polyvinylpyrrolidone and 6 g of methanol at a rotation speed of 500 rpm and a temperature of 20 °C for 4 h. Centrifuge the obtained mixture at a rotation speed of 5000 rpm for 8 min to separate the solid phase and wash the solid phase with methanol 3 times, and then dry it at a temperature of 75 °C for 5 h;

[0083] (3) Ultrasonically mix the pretreated metal-organic framework material ZIF-67 and water in step (2) (the mass ratio of the amount of the metal-organic framework material ZIF-67 to the amount of the water is 1:40), then mix it with a mixed solution of tin nitrate and cerium nitrate and stir and mix for 4 h under the conditions of a rotation speed of 400 rpm and a temperature of 20 °C. The ratio of the content of the metal-organic framework material ZIF-67 in terms of Co element to the content of the active components in terms of Ce and Sn elements is 1:2.5; in terms of Ce and Sn elements, the molar ratio of cerium nitrate to tin nitrate is 1:2; separate the solid phase from the obtained mixture by centrifugation at a rotation speed of 5000 rpm for 10 min, wash the solid phase with water 3 times and with methanol 1 time respectively, and then dry it at a temperature of 75 °C for 14 h;

[0084] (4) Spread the mixture powder obtained in step (3) flat on a dielectric plate, and continuously pass in at a speed of 70 mL / min into the dielectric plate, ventilate for 4 min to discharge the remaining air in the dielectric plate, and then perform plasma treatment for 1 min under the conditions of a voltage of 40 V and a current of 1.5 A through dielectric barrier discharge.

[0085] Example 4

[0086] Preparation of denitration catalyst:

[0087] (1) Ultrasonically dissolve 1 g of Co(NO3)2∙6H2O, 14 g of 2-methylimidazole and 20 g of water, stir and mix for 30 min under the conditions of a rotation speed of 600 rpm and a temperature of 25 °C, and transfer it to an 80 mL polytetrafluoroethylene-lined reaction kettle for hydrothermal reaction at a temperature of 100 °C for 12 h. Separate the solid phase of the mixture obtained from the hydrothermal reaction by centrifugation at a rotation speed of 7000 rpm for 6 min and wash it with methanol 3 times, and then dry it at a temperature of 85 °C for 11 h to obtain a purple powder, which is the metal-organic framework material ZIF-67;

[0088] (2) Stir and mix 0.2 g of the metal-organic framework material ZIF-67 prepared in step (1), 1.2 g of polyvinylpyrrolidone and 10 g of methanol under the conditions of a rotation speed of 600 rpm and a temperature of 25 °C for 3 h. Separate the solid phase from the obtained mixture by centrifugation at a rotation speed of 6000 rpm for 8 min and wash the solid phase with methanol 3 times, and then dry it at a temperature of 85 °C for 2.5 h;

[0089] (3) The pretreated metal-organic framework material ZIF-67 and water in step (2) are mixed by ultrasonic waves (the mass ratio of the dosage of the metal-organic framework material ZIF-67 to the water is 1:40), and then mixed with a mixed solution of tin nitrate and cerium nitrate under the conditions of a rotation speed of 600 rpm and a temperature of 25 °C for 3 h. The ratio of the content of the metal-organic framework material ZIF-67 in terms of Co element to the content of the active component in terms of Ce and Sn elements is 1:3.5; in terms of Ce and Sn elements, the molar ratio of cerium nitrate to tin nitrate is 1:2; the solid phase is separated from the obtained mixture by centrifugation at a rotation speed of 6000 rpm for 8 min, and the solid phase is washed with water 3 times and with methanol 1 time respectively, and then dried at a temperature of 75 °C for 14 h;

[0090] (4) The mixture powder obtained in step (3) is spread out on a dielectric plate, and a gas is continuously introduced into the dielectric plate at a speed of 90 mL / min. The gas is introduced for 2 min to discharge the remaining air in the dielectric plate, and then plasma treatment is carried out for 1 min under the conditions of a voltage of 60 V and a current of 2 A by dielectric barrier discharge.

[0091] Example 5

[0092] The denitration catalyst is prepared according to the method of Example 2, except that the plasma treatment for 1 min is replaced by plasma treatment for 5 min.

[0093] Example 6

[0094] The denitration catalyst is prepared according to the method of Example 2, except that the plasma treatment for 1 min is replaced by plasma treatment for 30 min.

[0095] Example 7

[0096] The denitration catalyst is prepared according to the method of Example 2, except that the molar ratio of cerium nitrate to tin nitrate of 1:2 is replaced by a molar ratio of cerium nitrate to tin nitrate of 1:1.5.

[0097] Example 8

[0098] The denitration catalyst is prepared according to the method of Example 2, except that the molar ratio of cerium nitrate to tin nitrate of 1:2 is replaced by a molar ratio of cerium nitrate to tin nitrate of 1:1.

[0099] Example 9

[0100] The denitration catalyst was prepared according to the method of Example 2, except that the ratio of the content of the metal-organic framework material ZIF-67 in terms of Co element to the content of the active components in terms of Ce and Sn elements was changed from 1:3 to 1:2.

[0101] Example 10

[0102] The denitration catalyst was prepared according to the method of Example 2, except that the ratio of the content of the metal-organic framework material ZIF-67 in terms of Co element to the content of the active components in terms of Ce and Sn elements was changed from 1:3 to 1:4.

[0103] Comparative Example 1

[0104] The denitration catalyst was prepared according to the method of Example 2, except that the plasma treatment by dielectric barrier discharge was replaced by heating in a muffle furnace. Specifically, in step (4), after the mixture powder obtained in step (3) was ground evenly, it was placed in a muffle furnace and heated to 500 °C at a rate of 4 °C / min and calcined for 2 h.

[0105] Comparative Example 2

[0106] The denitration catalyst was prepared according to the method of Example 2, except that tin nitrate was replaced by manganese nitrate.

[0107] Test Example: Before the activity evaluation of NO in lead-containing flue gas removal, the denitration catalysts prepared in Examples 1-10 and Comparative Examples 1-2 were controllably poisoned by the impregnation method, that is, the target catalyst was immersed in a lead-containing solution. The model poison used was lead acetate, the poison concentration was 1000 ppm (mass concentration of Pb element in the solution), and the impregnation time was 10 min.

[0108] The activity evaluation of NO in lead-containing flue gas removal was carried out on the above Pb-poisoned catalyst in a fixed-bed reactor. The reactor was a quartz reaction tube with a flat structure, and the detection device was Fourier transform infrared spectroscopy (FTIR). Before loading the quartz tube into the furnace, an appropriate amount of quartz wool was filled in the tube to ensure the contact between the powder catalyst and the thermocouple, and then an appropriate amount of catalyst was filled. The simulated flue gas consisted of 500 ppm of NH3, 500 ppm of NO, 5% O2 by volume concentration, and N2 as the balance gas, the total gas flow rate was 100 mL / min, and the space velocity was 30000 h -1 . Taking 50 °C as a temperature node, through programmed temperature rise, the catalytic activity of the powder catalyst was evaluated in the temperature range of 50 °C to 400 °C.

[0109] The denitration conversion rate is calculated using the following formula:

[0110]

[0111] In the formula: —— NO content in the flue gas at the inlet (ppm); x Content (ppm);

[0112] —— NO content in the flue gas at the outlet (ppm). x Content (ppm).

[0113] In the experiment, the contents of NH3 and NO used were both 1250 ppm, and the purities of CO and NO were both 99.99 wt%.

[0114] The NO conversion rate results of the denitration catalysts prepared in Examples 1-10 and Comparative Examples 1-2 in the application of removing NO in lead-containing flue gas are shown in Table 1.

[0115] Table 1

[0116]

[0117] It can be seen from the data in Table 1 that the examples of the denitration catalyst of the present invention still have better denitration activity after being impregnated and poisoned with 1000 ppm lead.

[0118] Figure 1 Figure shows the denitration performance of catalysts with different molar ratios of carrier oxides (calculated based on Co element in the carrier oxide) and active components (calculated based on Ce and Sn elements). As shown, Example 2 has the best denitration activity, followed by Example 4, Example 3, and Example 9 in sequence, and the denitration activity of Example 10 is relatively poor. Initially, as the content of the active component increases, the denitration activity of the catalyst continuously increases. When the molar ratio of the carrier oxide to the active component content is 1:3, the prepared catalyst (Example 2) has the best denitration activity. Subsequently, as the content of the active component increases, the activity no longer increases and shows a downward trend.

[0119] From Figure 2 It can be seen that the denitration activity of the catalyst in Example 2 is significantly superior to that of the catalyst prepared in Comparative Example 2, indicating that the denitration activity of the active component Sn selected in the present invention in lead-containing flue gas is better than that of Mn. As the content of Sn element in the active component increases, the denitration activity of the catalyst continuously increases. Calculated based on Ce and Sn elements, when the molar ratio of cerium nitrate to tin nitrate is 1:2, the denitration catalyst has the best denitration activity, and the highest NO conversion rate can reach 93.2% (200 °C), that is, Example 2.

[0120] Different from the traditional muffle furnace pyrolysis method in Comparative Example 1, the denitrification activity of the catalyst in the example prepared by using dielectric barrier discharge (DBD) plasma technology is significantly excellent. The denitrification activity of the catalyst prepared when the plasma treatment time is 5 min (Example 5) is the best. After being poisoned by 1000 ppm lead, the activity can still reach 100% (200 °C), and the temperature window is relatively wider than that of other catalysts. It is a denitrification catalyst with great application prospects.

[0121] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the technical concept scope of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A denitration catalyst, characterized in that, The denitration catalyst contains a support oxide and an active component. Among them, the support oxide is Co3O4 derived from ZIF-67, and the active component is a composite oxide of cerium oxide and tin oxide.

2. The denitration catalyst according to claim 1, characterized in that The molar ratio of the content of the support oxide in terms of Co element to the content of the active component in terms of Ce and Sn elements is 1:(2 - 4).

3. The denitration catalyst according to claim 1 or 2, characterized in that, In the active component, in terms of Ce and Sn elements, the molar ratio of the cerium oxide to the tin oxide is 1:(1 - 2).

4. A preparation method of a denitration catalyst, characterized in that, This method includes the following steps: (1) Mix the metal-organic framework material ZIF-67, tin salt, cerium salt, and water, separate the solid phase from the resulting mixture, and then wash and dry it in sequence. (2) Subject the mixture powder obtained in step (1) to plasma treatment by dielectric barrier discharge.

5. The method according to claim 4, wherein The molar ratio of the dosage of the metal-organic framework material ZIF-67 in terms of Co element to the dosages of the cerium salt and the tin salt in terms of Ce and Sn elements respectively is 1:(2 - 4).

6. The method according to claim 4 or 5, characterized in that, The molar ratio of the dosages of the cerium salt and the tin salt in terms of Ce and Sn elements respectively is 1:(1 - 2).

7. The method according to claim 4 or 5, characterized in that The conditions of the plasma treatment include: the time is 1 - 30 min, the voltage is 40 - 60 V, and the current is 1.5 - 2 A.

8. The method according to claim 4 or 5, characterized in that, The preparation process of the metal-organic framework material ZIF-67 includes: mixing cobalt nitrate, 2-methylimidazole, and a solvent and performing a hydrothermal reaction.

9. The method according to claim 8, characterized in that, The molar ratio of the cobalt nitrate to the 2-methylimidazole is 1:(35 - 50).

10. The method according to claim 8, wherein The conditions of the hydrothermal reaction include: the temperature is 100 - 120 °C, and the time is 12 - 24 h.

11. The method according to claim 4 or 5, characterized in that This method further includes: before implementing step (1), pre-treating the metal-organic framework material ZIF-67. The pre-treatment process includes: mixing the metal-organic framework material ZIF-67, polyvinylpyrrolidone, and alcohol, separating the solid phase from the resulting mixture, and then washing and drying it in sequence.

12. The method according to claim 11, characterized in that, The mass ratio of the dosages of the metal-organic framework material ZIF-67, the polyvinylpyrrolidone, and the alcohol is 1:(4 - 6):(30 - 50).

13. A denitration catalyst prepared by the method according to any one of claims 4 - 12.

14. Application of the denitration catalyst according to any one of claims 1 - 3 and 13 in removing NO in lead-containing flue gas.

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