Ceramic catalyst for synergistically removing no and chlorobenzene, and preparation method and application thereof

Abstract

The application discloses a ceramic-based catalyst for simultaneously removing NO and chlorobenzene, a preparation method and application thereof. The catalyst uses a composite oxide ceramic of titanium dioxide and cerium oxide as a carrier, uses activated carbon powder as a pore-forming agent and a reaction inducer, uses a composite ceramic of tungsten oxide, niobium oxide and nano-iron as an active component, uses nano-magnesium powder as a high-temperature initiator, adopts super-high temperature generated by a magnesium thermal reaction to prepare the ceramic-based catalyst, forms a uniform and ordered ceramic grain boundary and a porous ceramic structure, simultaneously increases the concentration of low-valence metal ions and the concentration of oxygen vacancies of the ceramic-based catalyst, and thus excellent activity of simultaneously removing denitration and chlorobenzene in a wide temperature range is obtained. The catalyst has high conversion efficiency, strong selectivity and strong anti-poisoning performance, the conversion efficiency of NO and chlorobenzene is greater than 85% in the temperature range of 200-400 DEG C, and the catalyst has a wide market application prospect.

Description

TECHNICAL FIELD

[0001] The application provides a ceramic-based catalyst for synergistically removing NO and chlorobenzene and a preparation method thereof, and belongs to the fields of environmental protection catalytic materials and air pollution treatment. BACKGROUND

[0002] VOCs is the abbreviation of volatile organic compounds. In China, VOCs refers to organic compounds with a saturated vapor pressure greater than 70 Pa at room temperature and a boiling point lower than 260 DEG C at normal pressure. VOCs has volatility and can easily volatilize to form VOCs gas under normal temperature conditions, causing air pollution, destroying the ozone layer, and endangering human health and the ecological environment. At the same time, chlorine-containing volatile organic compounds (Cl-VOCs) are a typical representative of VOCs and a kind of difficult-to-degrade organic compounds with great harm. They are widely used in the fields of industry, agriculture, pesticides, medicine, organic synthesis, etc. Nitrogen oxides are mostly derived from coal combustion in industrial applications, and the main components are nitrogen monoxide and nitrous oxide, of which 90% is NO.

[0003] In recent years, research and reports on the synergistic removal of NO x and VOCs have gradually increased, and people have begun to try to use the SCR denitration method to simultaneously remove VOCs, without increasing equipment costs and other auxiliary equipment, to achieve the synergistic removal of two pollutants in existing industrial conditions. However, the development of catalysts with high synergistic performance is still lacking, and there are still problems such as unclear synergistic removal mechanism of two pollutants, numerous types of volatile organic compounds in real environments, and incomplete oxidation of organic compounds leading to coking and carbon deposition phenomena and catalyst deactivation. Therefore, the development of new high-efficiency catalytic materials has attracted much attention from researchers, and the synergistic control of NO x and VOCs using catalytic materials is of great significance to the ecological environment.

[0004] The patent (CN202120713960.8) discloses a VOCs purification processor, which comprises a VOCs collection chamber, a transmission pipeline, a filter screen, a preheating chamber, a recovery pipeline and a VOCs treatment chamber, the VOCs collection chamber, the preheating chamber and the VOCs treatment chamber are sequentially arranged from bottom to top, one end of the transmission pipeline is in communication with the VOCs collection chamber, the other end is in communication with the preheating chamber, the recovery port of the recovery pipeline is in communication with the VOCs treatment chamber, the output port is connected with the preheating chamber, the filter screen is arranged in the preheating chamber, after the VOCs are treated by the catalytic bed, the generated H2O and the released heat flow into the recovery pipeline, the VOCs out of the VOCs collection chamber enter the preheating chamber upward, and then enter the VOCs treatment chamber after the preheating treatment of the filter screen and the recovery pipeline. Such a method increases a plurality of devices and apparatuses, undoubtedly increases the processing cost, and the selectivity of pollutants is not high. SUMMARY

[0005] The purpose of the present application is to propose a catalyst for catalytic removal of NO and chlorobenzene under the condition that NO and chlorobenzene coexist in flue gas, and another purpose of the present application is to provide a preparation method of the catalyst.

[0006] A ceramic-based catalyst for synergistically removing NO and chlorobenzene, the catalyst uses a composite oxide ceramic of titanium dioxide and cerium oxide as a carrier, uses activated carbon powder as a pore-forming agent and a reaction inducer, uses a composite ceramic of tungsten oxide, niobium oxide and nano-iron as an active component, and uses nano-magnesium powder as a high-temperature initiator to produce an ultra-high temperature by a magnesium thermal reaction to prepare the ceramic-based catalyst; the mass ratio of the tungsten oxide, the niobium oxide and the nano-iron is (1-5):(1-10):(1-10) based on the mass of the composite oxide ceramic carrier, and the mass percentage of the active component is 6%-11% based on the mass of the carrier.

[0007] In the technical scheme of the present application: the mass ratio of the titanium dioxide and the cerium oxide in the composite oxide ceramic carrier is (30-45):(3-4);

[0008] Preferably, the mass ratio of the tungsten oxide, the niobium oxide and the nano-iron is (1-3):(2-5):(3-9).

[0009] A preparation method of the catalyst, the preparation method of the catalyst is as follows:

[0010] (1) Preparation of hollow spherical ceramic-based carrier

[0011] The high-molecular polymer solution, the cerium oxide, the TiO2 and the activated carbon powder are uniformly mixed to form a slurry, the hollow spherical embryo is obtained by extrusion printing of a 3D printer, then the hollow spherical embryo is taken out and dried, and high-temperature calcination is performed to obtain the hollow spherical ceramic-based carrier;

[0012] (2) Catalyst preparation precursor

[0013] The hollow spherical ceramic base carrier prepared in step (1) is drilled, and then tungsten oxide, niobium oxide, ferric oxide and carbon nano powder are respectively ground and sieved by using a sander, mixed and stirred uniformly, and then magnesium powder is added and stirred again, and finally the mixed powder is transported to the hollow spherical ceramic base carrier through the reserved hole by using a funnel;

[0014] (3) Catalyst forming

[0015] A layer of carbon powder is laid at the bottom of the crucible, the catalyst preparation precursor prepared in step (2) is moved to the carbon powder layer in the crucible, and then the crucible is moved into a muffle furnace for calcination, and the ceramic-based catalyst is obtained after the reaction is completed.

[0016] In the above preparation method: the high molecular polymer solution in step (1) is a polyvinyl alcohol solution with a mass concentration of 10-20%;

[0017] The mass ratio of the high molecular polymer solution, cerium oxide and carbon nano powder in step (1) is (15-20):(3-4):(10-15);

[0018] The outer diameter of the spherical shell of the hollow spherical ceramic base carrier in step (1) is 30-45mm, and the wall thickness of the spherical shell is 3-5mm.

[0019] In the above preparation method: the drying temperature in step (1) is 100-120℃, and the drying time is 3-5h; the calcination temperature is 400-600℃, and the calcination time is 4-6h.

[0020] In the above preparation method: the hole diameter drilled on the spherical shell in step (2) is 15-25% of the outer diameter of the spherical shell.

[0021] In the above preparation method: the mesh size in step (2) is 300-500 mesh; and the magnesium powder in step (2) is ultra-fine nano magnesium powder with an average particle size of 800-1200nm.

[0022] In the above preparation method: the calcination in step (3) starts from 25℃, the heating rate of calcination is 2-3℃ / min, the calcination temperature is 500-600℃, and the calcination time is 4-6h.

[0023] In the above preparation method, the catalyst is used for catalytic removal of NO and chlorobenzene.

[0024] In the technical scheme of the present application: the mass ratio of the hollow spherical ceramic base carrier and the magnesium powder is 15-30:0.1-3.

[0025] Beneficial effects:

[0026] (1) The magnesium thermal reaction temperature in the present application can be as high as 3 500℃, and such instantaneous ultra-high temperature can make part of the Ce, W, Nb and other metal oxides obtain a higher oxidation-reduction valence. In the case of the coexistence of high valence and low valence of metal oxides, the bond energy will generate a bond energy difference between the high valence and the low valence, and the electron cloud belonging to these metal bonds will also form a shared electron cloud, so that the activity of the metal oxide is stronger, which will be manifested as ceramic crystal phase in the microscopic level, and has very high catalytic activity.

[0027] (2) Carbon powder is used as an igniter inside the spherical shell and in the spherical shell to initiate the magnesium thermal reaction, and the carbon combustion produces carbon dioxide which does not affect other materials, and the generated carbon dioxide can improve the pore structure inside the catalyst. At the same time, the carbon powder in the spherical shell will leave a large number of pore structures in the spherical shell after combustion, greatly increasing the specific surface area of the material, so that there are a large number of hole sites on the carrier for the active components to fall into position when the material is fused at high temperature, and the construction of active sites on the catalyst is strengthened.

[0028] (3) During the magnesium thermal reaction, the carbon powder laid on the bottom of the crucible acts as a sacrificial agent to protect the crucible from being burned through, and when the calcination continues to be heated above 500℃, the carbon powder will all be converted into carbon dioxide and volatilized, protecting the catalyst from introducing new substances or impurities into the catalyst due to ultra-high temperature, and the large amount of gas produced will widen the pore structure of the catalyst, increase the specific surface area of the catalyst, and at the same time, ensure the purity requirement when preparing the catalyst at ultra-high temperature. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The removal rate of NO by the catalyst in Examples 1-3 and Comparative Examples 1-3;

[0030] Figure 2 The removal rate of chlorobenzene by the catalyst in Examples 1-3 and Comparative Examples 1-3;

[0031] DETAILED EMBODIMENT

[0032] The present application will be further described in conjunction with the examples below, but the scope of protection of the present application is not limited thereto:

[0033] Example 1

[0034] (1) Preparation of hollow spherical ceramic base carrier

[0035] A slurry was prepared by mixing 15 g of a 10% by mass polyvinyl alcohol solution, 3 g of cerium oxide, 30 g of TiO2, and 10 g of activated carbon powder, a hollow spherical embryo with an outer diameter of 30 mm and a thickness of 5 mm was printed using a 3D printer with a 0.21 um needle and a pressure of 0.25 Mpa, the hollow spherical embryo was then removed and dried at 100°C for 3 h, and then calcined at 400°C for 4 h to obtain a hollow spherical ceramic-based carrier.

[0036] (2) Catalyst preparation precursor

[0037] A hole with a diameter of 4.5 mm was drilled into the top of the hollow spherical ceramic-based carrier prepared in step (1), the mass of the hollow spherical ceramic-based carrier after drilling was 18.4 g, then 0.19 g of tungsten oxide powder, 0.37 g of niobium oxide powder, 2.21 g of iron sesquioxide powder, and 0.81 g of carbon nano powder were weighed according to the proportion, respectively, and then mixed and stirred uniformly after being ground to 400 mesh using a sander, 0.25 g of magnesium powder (average particle size 1000 nm) was then added and stirred and mixed uniformly, and finally the mixed powder was transported to the hollow spherical ceramic-based carrier through the reserved hole using a plastic funnel.

[0038] (3) Catalyst molding

[0039] 25 g of carbon powder was laid out at the bottom of a crucible, the catalyst preparation precursor prepared in step (2) was then placed on the carbon powder layer in the crucible, the crucible was then moved into a muffle furnace, the temperature was started at room temperature 25°C, and the temperature was raised at a rate of 2°C / min to 500°C and calcined for 4 h, and a ceramic-based catalyst (mass ratio of tungsten oxide, niobium oxide, and nano-iron was 1:2:3) was obtained after the reaction was completed.

[0040] (4) Catalyst activity test

[0041] The prepared 1 ml of catalyst was loaded into a catalyst performance evaluation reaction device, the inner diameter of the quartz tube in the evaluation reaction device was 8 mm, and a simulated gas was introduced for activity evaluation. The composition of the simulated gas was: NO (400 ppm), NH3 (400 ppm), chlorobenzene (40 ppm), O2 (11%), and N2 as the carrier gas, the total gas flow was 1000 mL / min, the catalyst reaction test temperature range was 180-380°C, and the test time was 15 min at each temperature point. The test results showed that the NO removal efficiency was the lowest at 86.5% and the highest at 100% in the temperature range of 180-380°C; the chlorobenzene removal efficiency was the lowest at 85.2% and the highest at 96.8%.

[0042] Example 2

[0043] (1) Preparation of hollow spherical ceramic-based carrier

[0044] A slurry was prepared by uniformly mixing 20g of 15% polyvinyl alcohol solution, 3.5g of cerium oxide, 30g of TiO2 and 15g of activated carbon powder. The slurry was then extruded using a 3D printer with a 0.31µm needle and a pressure of 0.3MPa to obtain a hollow spherical preform with an outer diameter of 38mm and a thickness of 4mm. The hollow spherical preform was then removed and dried at 110℃ for 4h, and then calcined at 500℃ for 5h to obtain a hollow spherical ceramic substrate carrier.

[0045] (2) Catalyst preparation precursor

[0046] A hole with a diameter of 7.6 mm was drilled in the top of the hollow spherical ceramic substrate obtained in step (1). The hollow spherical ceramic substrate after drilling was weighed and found to be 22.6 g. Then, 0.3 g of tungsten oxide powder, 0.5 g of niobium oxide powder, 1.28 g of ferric oxide powder and 3.5 g of carbon nanoparticles were weighed according to the proportion, ground through a 400-mesh sieve using a grinding mill, mixed and stirred evenly. Then, 0.7 g of magnesium powder (average particle size 1000 nm) was added and stirred evenly again. Finally, the mixed powder was conveyed to the hollow spherical ceramic substrate through the reserved hole using a plastic funnel.

[0047] (3) Catalyst Formation

[0048] 25g of carbon powder was spread on the bottom of the crucible. The catalyst preparation precursor obtained in step (2) was transferred to the carbon powder layer in the crucible. Then the crucible was transferred into a muffle furnace and calcined at 550°C for 5 hours with a heating rate of 3°C / min, starting at room temperature of 25°C. After the reaction was completed, a ceramic-based catalyst (the mass ratio of tungsten oxide, niobium oxide and nano iron was 3:5:9) was obtained.

[0049] (4) Catalytic activity test

[0050] One ml of the prepared catalyst was loaded into a catalyst performance evaluation reaction apparatus. The quartz tube in the apparatus had an inner diameter of 8 mm, and simulated gas was introduced for activity evaluation. The simulated gas composition was: NO (400 ppm), NH3 (400 ppm), chlorobenzene (40 ppm), O2 (11%), with N2 as the carrier gas. The total gas flow rate was 1000 mL / min, and the catalytic reaction test temperature range was 180–380 °C. The test time was 15 min at each temperature point before the test. The test results showed that within the temperature range of 180–380 °C, the NO removal efficiency ranged from a minimum of 87.7% to a maximum of 100%; the chlorobenzene removal efficiency ranged from a minimum of 87.3% to a maximum of 99.2%.

[0051] Example 3

[0052] (1) Preparation of hollow spherical ceramic substrate

[0053] A slurry was prepared by uniformly mixing 17g of 20% polyvinyl alcohol solution, 4g of cerium oxide, 45g of TiO2 and 10g of activated carbon powder. The slurry was then extruded using a 3D printer with a 0.41µm needle and a pressure of 0.4MPa to obtain a hollow spherical preform with an outer diameter of 45mm and a thickness of 3mm. The hollow spherical preform was then removed and dried at 120℃ for 5h, and then calcined at 500℃ for 5h to obtain a hollow spherical ceramic substrate carrier.

[0054] (2) Catalyst preparation precursor

[0055] A hole with a diameter of 9 mm was drilled in the top of the hollow spherical ceramic substrate obtained in step (1). The hollow spherical ceramic substrate after drilling was weighed and found to be 25.7 g. Then, 0.5 g of tungsten oxide powder, 0.75 g of niobium oxide powder, 2.22 g of ferric oxide powder and 5.14 g of carbon nanoparticles were weighed according to the proportion, ground through a 400-mesh sieve using a grinding mill, mixed and stirred evenly. Then, 1.21 g of magnesium powder (average particle size 1000 nm) was added and stirred evenly again. Finally, the mixed powder was conveyed to the hollow spherical ceramic substrate through the reserved hole using a plastic funnel.

[0056] (3) Catalyst Formation

[0057] 25g of carbon powder was spread on the bottom of the crucible. The catalyst preparation precursor obtained in step (2) was transferred to the carbon powder layer in the crucible. Then the crucible was transferred into a muffle furnace and calcined at 600℃ for 6h with a temperature starting point of room temperature 25℃ and a heating rate of 3℃ / min. After the reaction was completed, a ceramic-based catalyst (the mass ratio of tungsten oxide, niobium oxide and nano iron was 2:3:6) was obtained.

[0058] (4) Catalytic activity test

[0059] One ml of the prepared catalyst was loaded into a catalyst performance evaluation reaction apparatus. The quartz tube in the apparatus had an inner diameter of 8 mm, and simulated gas was introduced for activity evaluation. The simulated gas composition was: NO (400 ppm), NH3 (400 ppm), chlorobenzene (40 ppm), O2 (11%), with N2 as the carrier gas. The total gas flow rate was 1000 mL / min, and the catalytic reaction test temperature range was 180–380 °C. The test time was 15 min at each temperature point before the test. The test results showed that within the temperature range of 180–380 °C, the NO removal efficiency ranged from a minimum of 90.4% to a maximum of 100%; the chlorobenzene removal efficiency ranged from a minimum of 90.1% to a maximum of 100%.

[0060] Comparative Example 1

[0061] (1) Preparation of hollow spherical ceramic substrate

[0062] In step (1), cerium oxide is not added, and other conditions are the same as in Example 1.

[0063] (2) Catalytic activity test

[0064] The test conditions were the same as in step (4) of Example 1. The test results showed that the NO removal efficiency was as low as 43.1% and as high as 61.7% in the temperature range of 180 to 380°C; the chlorobenzene removal efficiency was as low as 44.1% and as high as 68.5%.

[0065] (3) Comparison effect

[0066] Compared with Example 1, the absence of a portion of the cerium oxide seat support in the preparation of the hollow spherical ceramic matrix support in step (1) may result in low activity of the prepared catalyst support, reduced activity of the generated active centers, and decreased catalytic activity of the catalyst, thus showing a downward trend in degradation efficiency for both pollutants.

[0067] Comparative Example 2

[0068] (2) Catalyst preparation precursor

[0069] In step (2), niobium oxide is not added, and other conditions are the same as in Example 2.

[0070] (3) Catalytic activity test

[0071] The test conditions were the same as in step (4) of Example 2. The test results showed that the NO removal efficiency was as low as 41.6% and as high as 54.8% in the temperature range of 180 to 380°C; the chlorobenzene removal efficiency was as low as 42.6% and as high as 61.6%.

[0072] (4) Comparison effect

[0073] Compared with Example 2, niobium oxide was not added to the catalyst preparation precursor in step (2), which resulted in a decrease in the content of active components in the prepared catalyst and the absence of active components, leading to a decrease in the catalytic activity of the catalyst and thus a downward trend in the degradation efficiency of both pollutants.

[0074] Comparative Example 3

[0075] (2) Catalyst preparation precursor

[0076] No magnesium powder was added in step (2), and the other conditions were the same as in Example 3.

[0077] (3) Catalytic activity test

[0078] The test conditions were the same as in step (4) of Example 3. The test results showed that the NO removal efficiency was as low as 42.5% and as high as 63.2% in the temperature range of 180 to 380°C; the chlorobenzene removal efficiency was as low as 43.5% and as high as 70%.

[0079] (4) Comparison effect

[0080] Compared with Example 3, magnesium powder was not added to the catalyst preparation precursor in step (2), which resulted in the failure of the magnesium thermal reaction to occur during the preparation of the catalyst, and the failure of ferric oxide to be converted into nano iron. At the same time, the catalyst prepared under the ultra-high temperature conditions in the urban area did not generate an electron cloud sharing the metal valence bond, which ultimately led to a decrease in the catalytic activity of the catalyst. The catalyst showed a downward trend in the degradation efficiency of both pollutants.

Claims

1. A ceramic-based catalyst for the synergistic removal of NO and chlorobenzene, characterized in that: This catalyst uses a composite oxide ceramic of titanium dioxide and cerium oxide as a support, activated carbon powder as a pore-forming agent and reaction inducer, a composite ceramic of tungsten oxide, niobium oxide, and nano-iron as the active component, and nano-magnesium powder as a high-temperature initiator. The ceramic-based catalyst is prepared using ultra-high temperature generated by magnesothermic reaction. Based on the mass of the composite oxide ceramic support, the mass percentage of the active component is 6% to 11%. The mass ratio of tungsten oxide, niobium oxide and nano iron in the active components is (1~5):(1~10):(1~10).

2. The catalyst according to claim 1, characterized in that: The mass ratio of titanium dioxide to cerium oxide in the composite oxide ceramic carrier is (30~45):(3~4); The mass ratio of tungsten oxide, niobium oxide and nano iron is (1~3):(2~5):(3~9).

3. A method for preparing the catalyst according to claim 1, characterized in that: The catalyst is prepared as follows: (1) Preparation of hollow spherical ceramic substrate A slurry is prepared by uniformly mixing a polymer solution, cerium oxide, TiO2 and activated carbon powder. The slurry is then extruded using a 3D printer to obtain a hollow spherical preform. The preform is then removed, dried, and calcined at high temperature to obtain a hollow spherical ceramic substrate. (2) Catalyst preparation of precursor Drill holes in the hollow spherical ceramic substrate obtained in step (1), then grind and sieve tungsten oxide, niobium oxide, ferric oxide and carbon nanoparticles respectively using a grinding mill, mix them and stir evenly, then add magnesium powder and stir and mix evenly again, finally use a funnel to transport the mixed powder through the reserved hole to the hollow spherical ceramic substrate. (3) Catalyst Formation A layer of carbon powder is spread on the bottom of the crucible, and the catalyst preparation precursor obtained in step (2) is moved onto the carbon powder layer in the crucible. Then the crucible is moved into a muffle furnace for calcination. After the reaction is completed, a ceramic-based catalyst is obtained.

4. The preparation method according to claim 3, characterized in that: The polymer solution mentioned in step (1) is a polyvinyl alcohol solution with a mass concentration of 10-20%; The mass ratio of the polymer solution, cerium oxide, and activated carbon powder in step (1) is (15~20):(3~4):(10~15). In step (1), the outer diameter of the hollow spherical ceramic substrate is 30~45mm and the wall thickness is 3~5mm.

5. The preparation method according to claim 3, characterized in that: The drying temperature in step (1) is 100~120℃ and the drying time is 3~5h; the calcination temperature is 400℃~600℃ and the calcination time is 4h~6h.

6. The preparation method according to claim 4, characterized in that: In step (2), the borehole diameter is 15% to 25% of the outer diameter of the spherical shell.

7. The preparation method according to claim 3, characterized in that: The sieve mesh size mentioned in step (2) is 300~500 mesh.

8. The preparation method according to claim 3, characterized in that: The roasting in step (3) starts at 25°C, the heating rate is 2~3°C / min, the roasting temperature is 500°C~600°C, and the roasting time is 4h~6h.

9. The application of the catalyst according to claim 1 in the catalytic removal of NO and chlorobenzene.

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