Modified SCR (Selective Catalytic Reduction) catalyst for cooperatively removing NO and VOCs (Volatile Organic Compounds) at low temperature, preparation and application

Abstract

The invention relates to a modified SCR (Selective Catalytic Reduction) catalyst for cooperatively removing NO and VOCs (Volatile Organic Compounds) at low temperature as well as preparation and application and belongs to the technical field of flue gas denitration. The SCR catalyst disclosed by the invention is obtained by doping a V2O5-WO3 / TiO2 catalyst with a copper oxide or a cerium oxide. According to the catalyst, V2O5-WO3 / TiO2 is taken as a carrier, Cu or Ce is taken as a main active component, and metal elements of copper or cerium are loaded through an impregnation method. The Cu / SCR or Ce / SCR catalyst prepared by the preparation method disclosed by the invention has relatively high NO and VOCs (Volatile Organic Compounds) removal efficiency. Meanwhile, the catalyst shows good activity and catalytic performance at low temperature, and an operation temperature window is widened.

Description

Technical Field

[0001] The present invention relates to the technical field of flue gas denitration, and more specifically, to a modified SCR catalyst for synergistically removing NO and VOCs at low temperature, and its preparation and application. Background Art

[0002] In addition to traditional controlled inorganic pollutants such as SOx, NO, mercury and dust, there are also a series of volatile organic compounds (VOCs) in coal-fired flue gas. These SOx, NO and VOCs are highly irritating and toxic, causing serious harm to human health and the ecological environment. At present, the removal technology of SOx and NO in flue gas has been widely used, but the removal of VOCs in flue gas has just begun to attract attention.

[0003] At present, selective catalytic reduction (SCR) is the most commonly used and effective technology for removing NO in coal-fired power plants. The key to this technology lies in the SCR catalyst. Although SCR catalysts have made remarkable achievements in reducing NOx emissions, they also have some shortcomings. SCR catalysts usually achieve optimal catalytic activity at relatively high temperatures (above 320°C). This makes it more difficult to efficiently remove NOx (above 85%) under low temperature conditions (below 300°C). In addition, traditional SCR catalysts have obvious effects on NOx removal, but the removal efficiency of VOCs is low. In order to meet the needs of efficient treatment of various types of flue gas pollutants in coal-fired power plants, the coordinated control technology of NO and VOCs has received more and more attention. Therefore, there is an urgent need for an SCR catalyst that can be used in medium and low temperature zones to synergistically remove NO and VOCs. Summary of the invention

[0004] In order to overcome the defects of the above-mentioned prior art, the present invention proposes a method for preparing a Cu and / or Ce modified SCR catalyst for synergistic removal of NO and VOCs at low temperature (200-300°C). The modified SCR catalyst prepared by the method provided by the present invention has little effect on the removal effect of NO under low temperature conditions, and also shows a high removal efficiency for typical VOCs such as benzene, toluene, chlorobenzene, dichloromethane, and xylene. This solves the technical problems of low removal efficiency of nitrogen oxides under low temperature (200-300°C) conditions of the selective catalytic reduction (SCR) catalyst in the prior art and the inability to synergistically remove nitrogen oxides and volatile organic compounds.

[0005] According to a first aspect of the present invention, a modified SCR catalyst for synergistic removal of NO and VOCs at low temperature is provided. The modified SCR catalyst is TiO 2 As a carrier, and in TiO 2 The carrier is loaded with V 2 O 5 and WO3 , the V 2 O 5 The mass of TiO 2 0.4% to 1% of mass, WO 3 The mass of TiO 2 6% to 10% by mass; the modified SCR catalyst also includes a catalyst supported on TiO 2 The active component on the carrier is copper oxide and / or cerium oxide, and the mass of the active component is TiO 2 The modified SCR catalyst can synergistically remove NO and VOCs at 200-300°C.

[0006] Preferably, the copper oxide is cupric oxide or cuprous oxide; and the cerium oxide is cerium trioxide or cerium oxide.

[0007] Preferably, when the active components are copper oxide and cerium oxide, the molar ratio of the copper oxide to the cerium oxide is (0.2-5):1.

[0008] Preferably, the modified SCR catalyst is a spherical structure with a specific surface area of ​​60 to 70 m 2 / g, particle size is 0.20~0.30nm, pore volume is 0.90~1.10cm 3 ·g -1 .

[0009] According to another aspect of the present invention, a method for preparing a modified SCR catalyst is provided, comprising the following steps:

[0010] (1) Dissolve the active component precursor to obtain a transparent solution; then 2 As carrier, and composite V 2 O 5 and WO 3 The catalyst is added to the transparent solution and mixed thoroughly; the active component precursor is at least one of copper nitrate, copper chloride, copper sulfate, cerium nitrate, cerium chloride, and cerium sulfate;

[0011] (2) evaporating the solvent in the slurry obtained in step (1) to obtain a dry sample;

[0012] (3) Grinding and crushing the dried sample obtained in step (2), and then calcining it to obtain a modified SCR catalyst.

[0013] Preferably, the calcination temperature is 460-530° C., the calcination time is 4-6 hours, and the heating rate is 3-8° C. / min.

[0014] Preferably, in step (2), water bath heating is first performed to partially volatilize the solvent, and then the mixture is placed in a drying oven for drying; a magnetic stirrer is used for stirring while the water bath heating is performed to fully impregnate the active component.

[0015] Preferably, the temperature of the water bath is 70-90° C., the heating time is 3-5 h, and the speed of the magnetic stirrer is 500-800 r / min.

[0016] Preferably, the drying temperature is 160-220° C., and the drying time is 8-12 hours.

[0017] According to another aspect of the present invention, there is provided an application of a modified SCR catalyst for synergistically removing NO and VOCs from flue gas at low temperature, wherein the low temperature is 200 to 300°C;

[0018] Preferably, the low temperature is 220-300°C.

[0019] In general, the above technical solution conceived by the present invention has the following technical advantages compared with the prior art:

[0020] (1) Aiming at the synergistic removal of multiple pollutants in flue gas from coal-fired power plants, the present invention has developed a Cu and / or Ce doped modified SCR catalyst. By introducing copper (Cu) and / or cerium (Ce), the active sites on the catalyst surface are optimized and increased, which significantly improves the synergistic removal effect of the catalyst on NO and VOCs, achieving a good synergistic catalytic effect.

[0021] (2) The Cu / Ce modified SCR catalyst of the present invention exhibits excellent catalytic activity under low temperature (200-300°C) conditions, and can efficiently and synergistically remove NO and VOCs, thereby achieving synergistic removal of multiple pollutants.

[0022] (3) The preparation method of the present invention is simple and feasible, suitable for industrial-scale production, and helps promote the promotion and application of the catalyst in practical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 XRD diffraction patterns of SCR and Cu / SCR catalysts with different doping ratios.

[0024] Figure 2 XRD diffraction patterns of SCR and Ce / SCR catalysts with different doping ratios.

[0025] Figure 3SEM images of SCR modified by different amounts of Cu doping are shown, wherein a: SCR; b: 5% Cu / SCR; c: 10% Cu / SCR; d: SCR; e: a local magnification of 5% Cu / SCR; f: a local magnification SEM image of 10% Cu / SCR.

[0026] Figure 4 SEM images of SCR modified by different amounts of Ce doping are shown, wherein a: SCR; b: 5% Ce / SCR; c: 10% Ce / SCR; d: SCR; e: a partially enlarged SEM image of 5% Ce / SCR; f: a partially enlarged SEM image of 10% Ce / SCR.

[0027] Figure 5 (a) NO and (b) toluene removal efficiencies of SCR and Cu / SCR at different temperatures.

[0028] Figure 6 (a) NO and (b) toluene removal efficiency of SCR and Ce / SCR at different temperatures.

[0029] Figure 7 These are the test results of the denitrification activity and VOCs removal performance of the catalyst prepared in Example 3.

[0030] Figure 8 These are the test results of the denitration activity and VOCs removal performance of the catalyst prepared in Example 4. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0032] Example 1

[0033] The steps for preparing Cu / SCR catalyst are as follows:

[0034] 3.775g and 7.55g Cu(NO 3 ) 2 ·3H 2O nitrate was added to 30ml of deionized water and stirred until completely dissolved to obtain a transparent solution. 20g of SCR catalyst was added to the above transparent solution to obtain a mixed slurry. The mixed solution was stirred at 30°C with a magnetic stirrer for 30min, and then heated in a water bath at 80°C for 4h to make it evenly impregnated. The mixture after preliminary evaporation was further dried in a drying oven at 200°C for 10h. After the catalyst was cooled and dried, it was ground and crushed, and sent to a muffle furnace for calcination at 500°C for 5h. The heating rate of the muffle furnace was 5°C / min. After the catalyst was baked, it was sieved with a 60-mesh screen and finally stored in a dryer. The prepared catalysts were named 5% Cu / SCR and 10% Cu / SCR.

[0035] Example 2

[0036] The steps for preparing Ce / SCR catalyst are as follows:

[0037] 3.913 g and 7.826 g Ce(NO 3 ) 3 6H 2 O nitrate was added to 30ml of deionized water and stirred until completely dissolved to obtain a transparent solution. 20g of SCR catalyst was added to the above transparent solution to obtain a mixed slurry. The mixed solution was stirred at 30°C with a magnetic stirrer for 30min, and then heated in a water bath at 80°C for 4h to make it evenly impregnated. The mixture after preliminary evaporation was further dried in a drying oven at 200°C for 10h. After the catalyst was cooled and dried, it was ground and crushed, and sent to a muffle furnace for calcination at 500°C for 5h. The heating rate of the muffle furnace was 5°C / min. After the catalyst was baked, it was sieved with a 60-mesh screen and finally stored in a dryer. The prepared catalysts were named 5% Ce / SCR and 10% Ce / SCR.

[0038] Example 3

[0039] The steps for preparing Cu / Ce / SCR catalyst are as follows:

[0040] 3.775 g Cu(NO 3 ) 2 ·3H 2 O and 7.826g Ce(NO 3 ) 3 6H 2O nitrate was added to 30ml of deionized water and stirred until completely dissolved to obtain a transparent solution. 20g of SCR catalyst was added to the above transparent solution to obtain a mixed slurry. The mixed solution was stirred at 30°C with a magnetic stirrer for 30min, and then heated in a water bath at 80°C for 4h to make it evenly impregnated. The mixture after preliminary evaporation was further dried in a drying oven at 200°C for 10h. After the catalyst was cooled and dried, it was ground and crushed, and sent to a muffle furnace for calcination at 500°C for 5h. The heating rate of the muffle furnace was 5°C / min. After the catalyst was baked, it was sieved with a 60-mesh screen and finally stored in a dryer. The prepared catalyst was named Cu1 / Ce2 / SCR.

[0041] Example 4

[0042] The steps for preparing Cu / Ce / SCR catalyst are as follows:

[0043] 7.55g Cu(NO 3 ) 2 ·3H 2 O and 3.913g Ce(NO 3 ) 3 6H 2 O nitrate was added to 30ml of deionized water and stirred until completely dissolved to obtain a transparent solution. 20g of SCR catalyst was added to the above transparent solution to obtain a mixed slurry. The mixed solution was stirred at 30°C with a magnetic stirrer for 30min, and then heated in a water bath at 80°C for 4h to make it evenly impregnated. The mixture after preliminary evaporation was further dried in a drying oven at 200°C for 10h. After the catalyst was cooled and dried, it was ground and crushed, and sent to a muffle furnace for calcination at 500°C for 5h. The heating rate of the muffle furnace was 5°C / min. After the catalyst was baked, it was sieved with a 60-mesh screen and finally stored in a dryer. The prepared catalyst was named Cu1 / Ce0.5 / SCR.

[0044] Result analysis:

[0045] XRD characterization of SCR catalysts with different Cu and Ce doping amounts was performed. Figure 1 , Figure 2 shown.

[0046] The results show that the addition of Cu or Ce did not change the crystal structure of the original SCR catalyst during the synthesis of the catalyst. TiO 2 (PDF21-1272) characteristic peak, TiO 2There is no significant difference in the intensity of the diffraction peaks. XRD analysis shows that the characteristic peak of CuO (JCPDS 80-0076) is located at 2θ = 32°. In addition, the peak height and peak area of ​​CuO in the XRD spectrum increase with the increase of Cu element loading.

[0047] The catalysts with different Cu and Ce doping contents were characterized by SEM. Figure 3 , Figure 4 As shown. After adding Cu, the microscopic morphology of the SCR catalyst under a micron-level magnifying glass has no obvious change. With the increase of metal loading, the particle size of the 10% Cu / SCR catalyst is uniform, and there is a tendency to form grain agglomeration, which is because the 10% Cu / SCR catalyst has a larger specific surface area. After adding Ce, the microscopic morphology of the SCR catalyst under a micron-level magnifying glass has no obvious change. With the increase of metal loading, the particle size of the 10% Ce / SCR catalyst is uniform, and there is a tendency to form grain agglomeration.

[0048] Catalyst denitrification activity test method:

[0049] In order to compare the properties of the catalysts in different embodiments, the denitration activity and VOCs removal performance of the catalysts prepared in Example 1 and Example 2 were tested. The test results are as follows: Figure 5 and Figure 6 .

[0050] The test method is as follows:

[0051] The flue gas is simulated by a mixed gas cylinder, and the flue gas components include NO, O 2 、N 2 (balance gas) and SO 2 (If necessary), the gas is mixed in the gas mixing bottle after the flow rate is controlled by a mass flow meter. The reaction section is mainly composed of a fixed bed reactor, which is equipped with a vertical quartz tube with an inner diameter of 8mm and a length of 500mm. The catalyst is placed in the middle of the quartz tube. The flue gas analysis section uses a flue gas analyzer and a gas chromatograph to detect the concentration of nitric oxide and VOCs (toluene) respectively.

[0052] The simulated flue gas composition is: 500ppm of NO, 500ppm of NH 3 , 5.5% O 2 , 50ppm toluene, 100ppm SO 2 , ammonia nitrogen ratio is 1:1, total gas flow rate is 1000ml / min, and the space velocity (GHSV) is 20000h -1 , the calculation formulas for toluene removal efficiency and denitrification efficiency are as follows:

[0053]

[0054] where [X]in and [X]out represent the inlet and outlet concentrations (ppm), respectively.

[0055] The curves showing the change of the conversion of NO and toluene with the reaction temperature of the catalyst in Example 1 are as follows: Figure 5 shown.

[0056] according to Figure 5 It can be seen that the performance of SCR catalyst in removing NO and VOCs toluene is not as good as Cu / SCR catalyst. Among them, 5% Cu / SCR catalyst has the highest removal efficiency for NO and toluene. At 300℃, the removal conversion efficiency of NO and toluene reached 100% and 95.6% respectively. This is because the loading of copper ions enhances the redox ability of the catalyst and increases the number of acidic sites.

[0057] The curves showing the change of the conversion of NO and toluene with the reaction temperature of the catalyst in Example 2 are as follows: Figure 6 shown.

[0058] according to Figure 6 It can be seen that the performance of SCR catalyst in removing NO and VOCs toluene is not as good as Ce / SCR catalyst. Figure 5 , Figure 6 By comparison, it was found that the optimal temperature for the removal of NO and toluene by Ce / SCR catalyst was lower. For example, at 200°C, the removal conversion efficiency of NO and toluene by 10% Ce / SCR catalyst reached 97% and 89% respectively, while the removal conversion efficiency of NO and toluene by 5% Cu / SCR catalyst at the same temperature was 92% and 69% respectively.

[0059] The denitration activity and VOCs removal performance of the catalysts prepared in Example 3 and Example 4 were tested. The test results are as follows: Figure 7 and Figure 8 As shown in the figure, the denitration activity window of the catalyst has been significantly widened, and the denitration efficiency can be stabilized at around 90% at 200℃ to 300℃. At the corresponding temperature, the removal efficiency of VOCs can also be stabilized at around 90%.

[0060] The modified SCR catalyst in the present invention has a denitration active temperature of 200-300°C, and a VOCs removal active temperature of 220-300°C. The present invention proposes a method for preparing a Cu and / or Ce modified SCR catalyst for low-temperature synergistic removal of NO and VOCs, which can efficiently reduce NOx and VOCs emissions through redox reactions. The catalyst exhibits good catalytic activity at medium and low temperatures and is suitable for a variety of industrial conditions. After commercial research and development and optimization, the SCR catalyst has a long service life, reduces the frequency of replacement and maintenance, and improves the stability and reliability of the system. With the increasing attention to environmental protection and the continuous improvement of emission standards, the catalyst will play a key role in the power industry and industrial fields.

[0061] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A modified SCR catalyst for synergistic removal of NO and VOCs at low temperature, characterized in that: The modified SCR catalyst uses TiO2 as a carrier, and V2O5 and WO3 are loaded on the TiO2 carrier, the mass of the V2O5 is 0.4% to 1% of the mass of TiO2, and the mass of the WO3 is 6% to 10% of the mass of TiO2; the modified SCR catalyst also includes an active component loaded on the TiO2 carrier, the active component is copper oxide and / or cerium oxide, and the mass of the active component is 3% to 12% of the mass of TiO2; the modified SCR catalyst can synergistically remove NO and VOCs at 200 to 300°C.

2. The modified SCR catalyst for low-temperature synergistic removal of NO and VOCs according to claim 1, characterized in that: The copper oxide is cupric oxide or cuprous oxide; the cerium oxide is cerium trioxide or cerium oxide.

3. The modified SCR catalyst for low-temperature synergistic removal of NO and VOCs according to claim 1, characterized in that: When the active components are copper oxide and cerium oxide, the molar ratio of the copper oxide to the cerium oxide is (0.2-5):

1.

4. The modified SCR catalyst for low-temperature synergistic removal of NO and VOCs according to claim 1, characterized in that: The modified SCR catalyst is a spherical structure with a specific surface area of ​​60 to 70 m 2 / g, particle size is 0.20~0.30nm, pore volume is 0.90~1.10cm 3 ·g -1 .

5. The method for preparing a modified SCR catalyst according to any one of claims 1 to 4, characterized in that: The following steps are involved: (1) dissolving an active component precursor to obtain a transparent solution; then adding a catalyst having TiO2 as a carrier and a composite of V2O5 and WO3 to the transparent solution and mixing the catalyst thoroughly; the active component precursor is at least one of copper nitrate, copper chloride, copper sulfate, cerium nitrate, cerium chloride, and cerium sulfate; (2) evaporating the solvent in the slurry obtained in step (1) to obtain a dry sample; (3) Grinding and crushing the dried sample obtained in step (2), and then calcining it to obtain a modified SCR catalyst.

6. The method for preparing the modified SCR catalyst according to claim 5, characterized in that: The calcination temperature is 460-530°C, the calcination time is 4-6h, and the heating rate is 3-8°C / min.

7. The method for preparing the modified SCR catalyst according to claim 5, characterized in that: In the step (2), the mixture is first heated in a water bath to partially volatilize the solvent, and then placed in a drying oven for drying; while heating in the water bath, a magnetic stirrer is used for stirring to fully impregnate the active component.

8. The method for preparing the modified SCR catalyst according to claim 7, characterized in that: The temperature of the water bath is 70-90° C., the heating time is 3-5 hours, and the speed of the magnetic stirrer is 500-800 r / min.

9. The method for preparing the modified SCR catalyst according to claim 5, characterized in that: The drying temperature is 160-220° C., and the drying time is 8-12 hours.

10. Use of the modified SCR catalyst according to any one of claims 1 to 4 for synergistically removing NO and VOCs from flue gas at low temperature, characterized in that: The low temperature is 200-300°C; Preferably, the low temperature is 220-300°C.

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