A magnetic field enhanced NO removal x Monolithic catalyst for VOCs and its preparation method and application

Abstract

The present invention discloses an integral catalyst for magnetic field-enhanced removal of NOx and VOCs, as well as a preparation method and application. The catalyst carrier is TiO2, with oxides of cerium, manganese and praseodymium as active components, and ferric oxide as a forming aid component. The carrier is combined with the active component and the forming aid component using a hydrothermal method, and then the catalyst is evenly loaded onto the modified magnetic rod using a hard template method. Based on the mass of the carrier, the active component accounts for 7% to 10% of the carrier mass. The catalyst has high conversion efficiency, strong selectivity, and strong resistance to water poisoning. It can remove NOx and VOCs within 200 to 400°C. x The conversion efficiency of VOCs is greater than 90%, and it has broad market application prospects.

Description

Technical Field

[0001] The present invention provides a method for removing NO by magnetic field enhancement. x The invention discloses a preparation method of an integral catalyst for VOCs, belonging to the field of environmentally friendly catalytic materials and air pollution control. Background Art

[0002] With the advancement of clean energy, biomass energy has become the fourth largest energy source in the world after oil, coal and natural gas, and has become an important force in the international energy transformation. With the large-scale construction of biomass boilers, biomass / sludge mixed combustion boilers, etc., its NO x The proportion of emissions is increasing year by year, so biomass boiler flue gas purification is a major national strategic need. Compared with the flue gas emitted by coal-fired power plants, the flue gas composition of biomass boilers is more complex, containing not only NOx but also unconventional pollutants such as VOCs. In order to reduce the operating costs of enterprises, the catalyst must complete the NOx removal under the conditions of complex flue gas composition. x The coordinated purification of NO and VOCs is particularly important. x and VOCs are the main pollutants and are also important precursors to the formation of fine particulate matter and ozone (O3), which can easily cause air pollution such as acid rain, atmosphere, haze and photochemical smog. Among them, VOCs have the characteristics of irritation, persistence, high toxicity and photochemical reactivity. The use of catalysts to catalyze the degradation of these two pollutants will produce water, which in turn affects the catalytic performance of the catalyst. Therefore, the effect of water production on NO x The coordinated removal of VOCs is very necessary.

[0003] Existing synergistic removal of NO x Among the VOCs patents, patent CN201711347207.6 discloses an absorbent for simultaneous desulfurization, denitrification and de-VOCs of flue gas, as well as its preparation and application. The absorbent is composed of the following components by mass percentage: 5-10% ammonium salt, 0.01-0.50% surfactant, 1‰-2% complexing agent and water balance. The absorbent of this invention can achieve efficient purification of multiple pollutants such as dust, SO2, NOX and VOCs in flue gas in one set of equipment at the same time. However, compared with the SCR method, this invention has the disadvantages of complex equipment, large floor space, high investment and operating costs. Such a method will significantly increase the cost of pollutant treatment and is complicated to operate.

[0004] In recent years, the x There are more and more research reports on the synergistic removal of NO and VOCs. Some scholars have studied the synergistic removal of NO xThe catalysts for NO and VOCs have been studied, but there are still problems such as unclear synergistic removal mechanism of the two pollutants and the catalyst is prone to water poisoning. Therefore, the development of efficient and water-resistant new catalytic materials has attracted much attention from scientific researchers. x The coordinated control of VOCs is of great significance to the ecological environment. Summary of the Invention

[0005] The present invention aims to x Under the conditions of synergistic removal of VOCs, a series of catalyst poisoning and deactivation problems caused by the H2O produced during the reaction are proposed. x A method for preparing an integral catalyst for removing VOCs.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A magnetic field enhanced NO removal x The preparation method of the integral catalyst for removing VOCs is as follows:

[0008] (1) Hydrothermal synthesis of catalyst powder

[0009] The catalyst carrier TiO2, ferric oxide, Ce salt, Mn salt and Pr salt are added to deionized water and stirred evenly, and then transferred to a hydrothermal reactor for hydrothermal activation. After hydrothermal activation, the catalyst is taken out and calcined. After calcination, the catalyst powder loaded with active components is finally obtained by grinding and sieving.

[0010] The catalyst contains TiO2 as the carrier, cerium, manganese and praseodymium oxides as the active components, and ferric oxide as the auxiliary component for forming.

[0011] (2) Magnetic rod modification

[0012] The surface of the magnetic rod is threaded using a thread tap, and then the magnetic rod is placed in a dilute hydrochloric acid solution for preliminary acid leaching, and then the magnetic rod is placed in a hydrothermal reactor and the dilute hydrochloric acid solution is added for hydrothermal reaction activation to obtain a modified magnetic rod;

[0013] (3) Preparation of monolithic catalyst

[0014] The modified magnetic rod is fixed at the center of the cylindrical hard template, and the catalyst powder prepared in step (1) is added to the bonding solution and stirred evenly, and then added to the hard mold to evenly fill the gap between the mold and the modified magnetic rod. After filling tightly, it is placed in a muffle furnace for drying and the mold is removed. Finally, after roasting, a monolithic catalyst is obtained.

[0015] In the technical solution of the present invention, based on the mass of the carrier, the active component accounts for 7% to 10% of the carrier mass, and ferric oxide accounts for 10% to 15% of the carrier mass; and the mass ratio of cerium oxide, manganese oxide and praseodymium oxide in the active components is 3 to 4:2 to 3:2 to 3.

[0016] In the technical solution of the present invention: the TiO2 described in step (1) is nano-anatase titanium dioxide, the ferric oxide is nano-ferric oxide; the Ce salt, Mn salt and Pr salt are Ce(NO3)3, Mn(NO3)2·6H2O and PrCl3 respectively.

[0017] In the technical solution of the present invention: the hydrothermal activation temperature in step (1) is 180-220° C., and the hydrothermal activation time is 6-8 h;

[0018] In the technical solution of the present invention: the mesh size of the grinding and sieving in step (1) is 60 to 80 meshes; the roasting temperature is 500 to 600° C., and the roasting time is 4 to 6 hours.

[0019] In the technical solution of the present invention: the magnetic rod described in step (2) is a samarium cobalt magnet with a diameter of 3 to 8 mm; the thread tap has a thread-cutting torque of 15 to 20 Nm.

[0020] In the technical solution of the present invention: the concentration of dilute hydrochloric acid in the preliminary acid leaching described in step (2) is 0.1-1 mol / L, and the acid leaching time is 2-3 hours; the concentration of dilute hydrochloric acid in the hydrothermal reaction described in step (2) is 0.1-1 mol / L, the hydrothermal temperature is 160-180° C., and the hydrothermal reaction time is 2-3 hours.

[0021] In the technical solution of the present invention: the bonding solution in step (3) is a 15-25 g / L polyvinyl alcohol solution; the mass ratio of the bonding solution to the catalyst powder is (3-8): (8-12).

[0022] The drying temperature in step (3) is 80-100° C., and the roasting time is 2-3 hours.

[0023] The calcination temperature in step (3) is 300-400° C., and the calcination time is 4-6 hours.

[0024] A magnetic field enhanced NO removal x The invention relates to an integral catalyst for removing VOCs, wherein the catalyst is prepared by the above method.

[0025] In the technical solution of the present invention, the catalyst prepared above is used to remove NO x Applications related to VOCs.

[0026] Beneficial effects:

[0027] A magnetic field enhanced NO removal method prepared by the present invention x The preparation method of the integral catalyst for VOCs, Ce oxide can provide more acid sites, enhance the reduction performance of the catalyst, and the modification of Pr and Mn oxides can provide more oxygen vacancy sites, enhance the oxidation performance of the catalyst. At the same time, the magnetic rod in the middle of the catalyst can provide a directional stable magnetic field, and in the presence of a magnetic field, it can reduce the viscosity of water, thereby reducing the resistance of water in the reaction system so that the generated water can pass through the catalyst faster, thereby reducing the catalyst poisoning caused by water occupying active sites. In addition, when conventional oxide active components are loaded on magnetic rods, the oxide active components and the magnetic rod have a low bonding strength, resulting in the active components being easily detached. In the present invention, ferric oxide is added to the catalyst. Under the condition that a magnetic rod exists in the center of the catalyst, a magnetic attraction is generated on the catalyst powder, making the catalyst powder adhere more tightly to the magnetic rod. After the magnetic rod is initially acid-leached with dilute hydrochloric acid and hydrothermally activated with an acidic solution, the number of hydroxyl groups on the surface of the magnetic rod is greatly increased, thereby enhancing the bonding strength between the magnetic rod and the active components, thereby ensuring the stable bonding between the active components and the magnetic rod. The magnetic field is provided by a samarium-cobalt permanent magnet rod at the catalyst's center. This samarium-cobalt permanent magnet boasts strong magnetic properties, improved magnetic field continuity and stability, and can generate a stable and continuous magnetic field. The permanent magnets also require no energy, further reducing costs. The catalysts of this invention boast high conversion efficiency, strong resistance to water poisoning, and a simple preparation process, promising broad market applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is the removal rate of NO by the catalyst in Examples 1 to 3 and Comparative Examples 1 to 3.

[0029] Figure 2 It is the removal rate of toluene by the catalyst in Examples 1 to 3 and Comparative Examples 1 to 3.

[0030] Figure 3 is the adsorption ratio of the catalyst to water in Examples 1 to 3 and Comparative Examples 1 to 3. DETAILED DESCRIPTION

[0031] The present invention will be further described below with reference to the embodiments, but the protection scope of the present invention is not limited thereto:

[0032]

[0033] Example 1

[0034] (1) Hydrothermal synthesis of catalyst powder

[0035] 100g TiO2, 10g ferric oxide, 5.7g Ce salt, 7g Mn salt and 3g Pr salt were added to 100g deionized water and stirred evenly, and then transferred to a hydrothermal reactor for hydrothermal activation at 200°C for 6h. After hydrothermal activation, the mixture was taken out and calcined at 500°C for 4h. After calcination, the mixture was ground and sieved to retain 60-80 mesh, and finally a catalyst powder loaded with active components was obtained;

[0036] (2) Magnetic rod modification

[0037] The surface of a 5 mm diameter samarium cobalt magnetic rod was tapped using a thread tap with a tapping torque of 15 Nm. Then, 12 g of the magnetic rod was placed in 30 g of a 0.5 mol / L dilute hydrochloric acid solution for preliminary acid leaching for 2 h. After the preliminary acid leaching, the magnetic rod was placed in a hydrothermal reactor and hydrothermally activated at 160°C for 2 h in 45 g of a 0.3 mol / L dilute hydrochloric acid solution to obtain the modified magnetic rod.

[0038] (3) Preparation of monolithic catalyst

[0039] The modified magnetic rod in step (2) is fixed at the center of the cylindrical hard template. 10 g of the catalyst powder prepared in step (1) is added to 4 g of a polyvinyl alcohol solution with a mass concentration of 20 g / L and stirred evenly. The mixture is then added to the hard mold to evenly fill the gap between the mold and the magnetic rod. After filling tightly, the mixture is placed in a muffle furnace and dried at 80°C for 2 h. The mold is then removed and calcined at 300°C for 4 h to finally obtain a monolithic catalyst.

[0040] (4) Catalytic activity test

[0041] The resulting 1 cm long catalyst was weighed and loaded into a catalyst performance evaluation reactor, yielding a mass of 2.736 g. The reactor contained a 30 mm inner diameter quartz tube and was fed with simulated gas for activity evaluation. The simulated gas composition consisted of 400 ppm NO, 400 ppm NH, 40 ppm toluene, 11% O, and N as a carrier gas, with a total gas flow rate of 1000 mL / min. The catalytic reaction was tested at a temperature range of 200-400°C. Test results showed that after 15 minutes at 200°C, the NO removal efficiency was 91.7%, and the toluene removal efficiency was 90.6%. After two hours of reaction, the catalyst gained 0.232 g, representing an 8.4% weight gain.

[0042] Example 2

[0043] (1) Hydrothermal synthesis of catalyst powder

[0044] 100g TiO2, 12.5g ferric oxide, 6.4g Ce salt, 8g Mn salt and 3.5g Pr salt were added to 100g deionized water and stirred evenly, and then transferred to a hydrothermal reactor for hydrothermal activation at 200°C for 6h. After hydrothermal activation, the mixture was taken out and calcined at 600°C for 6h. After calcination, the mixture was ground and sieved to retain the 60-80 mesh range to finally obtain a catalyst powder loaded with active components;

[0045] (2) Magnetic rod modification

[0046] The surface of a 5 mm diameter samarium cobalt magnetic rod was tapped using a thread tap with a tapping torque of 15 Nm. Then, 12 g of the magnetic rod was placed in 30 g of a 0.5 mol / L dilute hydrochloric acid solution for preliminary acid leaching for 2 h. After the preliminary acid leaching, the magnetic rod was placed in a hydrothermal reactor and hydrothermally activated at 180°C for 3 h in 45 g of a 0.3 mol / L dilute hydrochloric acid solution to obtain the modified magnetic rod.

[0047] (3) Preparation of monolithic catalyst

[0048] The modified magnetic rod in step (2) is fixed at the center of the cylindrical hard template. 10 g of the catalyst powder prepared in step (1) is added to 5 g of a polyvinyl alcohol solution with a mass concentration of 20 g / L and stirred evenly. The mixture is then added to the hard mold to evenly fill the gap between the mold and the magnetic rod. After filling tightly, the mixture is placed in a muffle furnace and dried at 80°C for 2 h. The mold is then removed and calcined at 400°C for 4 h to finally obtain a monolithic catalyst.

[0049] (4) Catalytic activity test

[0050] The resulting 1 cm long catalyst was weighed and loaded into a catalyst performance evaluation reactor, yielding a mass of 2.932 g. The reactor contained a 30 mm inner diameter quartz tube and was fed with simulated gas for activity evaluation. The simulated gas composition consisted of 400 ppm NO, 400 ppm NH, 40 ppm toluene, 11% O, and N as a carrier gas, with a total gas flow rate of 1000 mL / min. The catalytic reaction was tested at a temperature range of 200-400°C. Test results showed that at 200°C, after 15 minutes, the NO removal efficiency was 94.5%, and the toluene removal efficiency was 89.7%. After two hours of reaction, the catalyst gained 0.334 g, representing an 11.3% weight gain.

[0051] Example 3

[0052] (1) Hydrothermal synthesis of catalyst powder

[0053] 100g TiO2, 15g ferric oxide, 7.5g Ce salt, 9.5g Mn salt and 4.3g Pr salt were added to 100g deionized water and stirred evenly, and then transferred to a hydrothermal reactor for hydrothermal activation at 200°C for 6h. After hydrothermal activation, the mixture was taken out and calcined at 500°C for 6h. After calcination, the mixture was ground and sieved to retain 60-80 mesh, and finally a catalyst powder loaded with active components was obtained;

[0054] (2) Magnetic rod modification

[0055] The surface of a 5 mm diameter samarium cobalt magnetic rod was tapped using a thread tap with a tapping torque of 15 Nm. Then, 12 g of the magnetic rod was placed in 35 g of a 0.5 mol / L dilute hydrochloric acid solution for preliminary acid leaching for 2 h. After the preliminary acid leaching, the magnetic rod was placed in a hydrothermal reactor and hydrothermally activated at 160°C for 3 h in 50 g of a 0.3 mol / L dilute hydrochloric acid solution to obtain the modified magnetic rod.

[0056] (3) Preparation of monolithic catalyst

[0057] The modified magnetic rod in step (2) is fixed at the center of the cylindrical hard template. 10 g of the catalyst powder prepared in step (1) is added to 6 g of a polyvinyl alcohol solution with a mass concentration of 20 g / L and stirred evenly. The mixture is then added to the hard mold to evenly fill the gap between the mold and the magnetic rod. After filling tightly, the mixture is placed in a muffle furnace and dried at 100°C for 2 h. The mold is then removed and calcined at 300°C for 6 h to finally obtain a monolithic catalyst.

[0058] (4) Catalytic activity test

[0059] The 1 cm long catalyst was weighed and loaded into a catalyst performance evaluation reactor, resulting in a mass of 2.852 g. The reactor contained a 30 mm inner diameter quartz tube and was fed with simulated gas for activity evaluation. The simulated gas composition consisted of 400 ppm NO, 400 ppm NH, 40 ppm toluene, 11% O, and N as a carrier gas, with a total gas flow rate of 1000 mL / min. The catalytic reaction was tested at a temperature range of 200-400°C. Test results showed that after 15 minutes at 200°C, the NO removal efficiency was 96.7%, and the toluene removal efficiency was 91.2%. After two hours of reaction, the catalyst gained 0.285 g, representing a 9.9% weight gain.

[0060] Comparative Example 1

[0061] (1) Hydrothermal synthesis of catalyst powder

[0062] The conditions are the same as step (1) in Example 1;

[0063] (2) Magnetic rod modification

[0064] Replace the magnetic rod with a non-magnetic iron rod of the same size, and other conditions are the same as step (2) in Example 1;

[0065] (3) Preparation of monolithic catalyst

[0066] The conditions are the same as step (3) in Example 1;

[0067] (4) Catalytic activity test

[0068] The test conditions were the same as those in step (4) of Example 1, and the catalyst weighed 2.865 g. The test results showed that within the temperature range of 200°C to 400°C, the NO removal efficiency ranged from a minimum of 83.5% to a maximum of 95.3%. The toluene removal efficiency ranged from a minimum of 64.6% to a maximum of 75.2%. After two hours of reaction, the catalyst gained 0.584 g, a weight gain of 20.3%.

[0069] (4) Contrast effect

[0070] Compared to Example 1, replacing the magnetic rod with an iron rod of the same size did not significantly reduce the NO and toluene removal efficiency of the resulting catalyst. However, after two hours of reaction, catalyst weight analysis revealed a 0.584g increase in weight, representing a 20.3% weight gain. This significant weight gain may be due to the lack of magnetic rods, which hinder the magnetic field effect on the catalyst. Consequently, the viscosity of water remained unchanged, resulting in a constant resistance of water adsorbed on the catalyst and a dramatic increase in the amount of water adsorbed on the catalyst.

[0071] Comparative Example 2

[0072] (1) Hydrothermal synthesis of catalyst powder

[0073] In step (1), ferric oxide is not added, and other conditions are the same as those in step (1) in Example 2;

[0074] (2) Magnetic rod modification

[0075] The conditions are the same as step (2) in Example 2;

[0076] (3) Preparation of monolithic catalyst

[0077] The conditions are the same as step (3) in Example 2;

[0078] (4) Catalytic activity test

[0079] The test conditions were the same as those in step (4) of Example 2, and the catalyst weighed 2.935 g. The test results showed that within the temperature range of 200°C to 400°C, the NO removal efficiency ranged from a minimum of 68.3% to a maximum of 79.5%. The toluene removal efficiency ranged from a minimum of 83.8% to a maximum of 87.4%. After two hours of reaction, the catalyst gained 0.447 g, a weight gain of 15.2%.

[0080] (4) Contrast effect

[0081] Compared with Example 2, ferric oxide is not added in step (1), and the catalyst powder in the catalyst prepared in step (2) does not contain substances such as iron, resulting in no magnetic attraction between the catalyst powder and the magnetic rod, and the catalyst powder cannot be well attached to the magnetic rod, resulting in a decrease in the removal efficiency of NO and toluene and an increase in the amount of water adsorbed by the catalyst.

[0082] Comparative Example 3

[0083] (1) Hydrothermal synthesis of catalyst powder

[0084] Ce(NO3)3 was not added, and other conditions were the same as step (1) in Example 3;

[0085] (2) Magnetic rod modification

[0086] The conditions are the same as step (2) in Example 3;

[0087] (3) Preparation of monolithic catalyst

[0088] The conditions are the same as step (3) in Example 3;

[0089] (4) Catalytic activity test

[0090] The test conditions were the same as those in step (4) of Example 3, and the catalyst weighed 2.751 g. The test results showed that within the temperature range of 200°C to 400°C, the NO removal efficiency ranged from a minimum of 62.1% to a maximum of 71.3%. The toluene removal efficiency ranged from a minimum of 65.5% to a maximum of 71.5%. After two hours of reaction, the catalyst gained 0.296 g, a weight gain of 10.7%.

[0091] (4) Contrast effect

[0092] Compared with Example 3, Ce(NO3)3 was not added in step (2), and the removal effect of NO and toluene by the obtained catalyst was significantly reduced. Analysis showed that the reason may be that the lack of Ce oxide resulted in insufficient active sites of the catalyst, resulting in reduced catalytic activity of the catalyst.

Claims

1. A magnetic field enhanced NO removal method x The preparation method of the integral catalyst for VOCs is characterized by: The preparation method of the catalyst is as follows: (1) Hydrothermal synthesis of catalyst powder The catalyst carrier TiO2, ferric oxide, Ce salt, Mn salt and Pr salt are added to deionized water and stirred evenly, and then transferred to a hydrothermal reactor for hydrothermal activation. After hydrothermal activation, the catalyst is taken out and calcined. After calcination, the catalyst powder loaded with active components is finally obtained by grinding and sieving. The catalyst contains TiO2 as the carrier, cerium, manganese and praseodymium oxides as the active components, and ferric oxide as the auxiliary component for forming. (2) Magnetic rod modification The surface of the magnetic rod is threaded using a thread tap, and then the magnetic rod is placed in a dilute hydrochloric acid solution for preliminary acid leaching, and then the magnetic rod is placed in a hydrothermal reactor and the dilute hydrochloric acid solution is added for hydrothermal reaction activation to obtain a modified magnetic rod; (3) Preparation of monolithic catalyst The modified magnetic rod is fixed at the center of the cylindrical hard template, and the catalyst powder prepared in step (1) is added to the bonding solution and stirred evenly, and then added to the hard mold to evenly fill the gap between the mold and the modified magnetic rod. After filling tightly, it is placed in a muffle furnace for drying and the mold is removed. Finally, after roasting, a monolithic catalyst is obtained.

2. The preparation method according to claim 1, wherein: Based on the mass of the carrier, the active component accounts for 7%~10% of the carrier mass, and ferric oxide accounts for 10%~15% of the carrier mass; and the mass ratio of cerium oxide, manganese oxide and praseodymium oxide in the active components is 3~4:2~3:2~3.

3. The preparation method according to claim 1, wherein: The TiO2 described in step (1) is nano-anatase titanium dioxide, the ferric oxide is nano-ferric oxide; the Ce salt, Mn salt and Pr salt are Ce(NO3)3, Mn(NO3)2·6H2O and PrCl3 respectively.

4. The preparation method according to claim 1, wherein: The hydrothermal activation temperature in step (1) is 180-220° C., and the hydrothermal activation time is 6-8 h.

5. The preparation method according to claim 1, wherein: The mesh size of the grinding and sieving in step (1) is 60-80 mesh; the roasting temperature is 500-600°C, and the roasting time is 4-6 hours.

6. The preparation method according to claim 1, wherein: The magnetic rod described in step (2) is a samarium cobalt magnet with a diameter of 3 to 8 mm; the thread tap has a thread-cutting torque of 15 to 20 Nm.

7. The preparation method according to claim 1, wherein: The concentration of dilute hydrochloric acid in the preliminary acid leaching described in step (2) is 0.1~1 mol / L, and the acid leaching time is 2~3 hours; the concentration of dilute hydrochloric acid in the hydrothermal reaction described in step (2) is 0.1~1 mol / L, the hydrothermal temperature is 160~180℃, and the hydrothermal reaction time is 2~3 hours.

8. The preparation method according to claim 1, wherein: The bonding solution in step (3) is a 15-25 g / L polyvinyl alcohol solution; the mass ratio of the bonding solution to the catalyst powder is (3-8): (8-12); The drying temperature in step (3) is 80-100°C and the drying time is 2-3 hours; The calcination temperature in step (3) is 300-400°C, and the calcination time is 4-6 hours.

9. A magnetic field enhanced NO removal method x An integral catalyst for VOCs, characterized by: The catalyst is prepared by the method according to any one of claims 1 to 8.

10. The catalyst according to claim 9 is used to remove NO from the atmosphere. x Applications related to VOCs.

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