SCR (Selective Catalytic Reduction) denitration catalyst as well as preparation method and application thereof
By mixing inorganic fiber materials with catalytic active components in the upstream part of the support and freeze-drying them, combined with reducing the amount of downstream active components coated, the problem of reduced specific surface area caused by catalyst coating is solved, achieving high catalytic performance and cost control.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- QINGDAO NAPOTEC ENVIRONMENT PROTECTION TECH CO LTD
- Filing Date
- 2024-10-30
- Publication Date
- 2026-05-01
AI Technical Summary
In existing technologies, the coating process of catalysts leads to a reduction in the specific surface area of the support, and the coating amount and active sites cannot adapt to the actual conditions at different stages, affecting the efficiency and cost of the catalyst.
A catalyst with a porous structure was prepared by mixing inorganic fiber materials with catalytic active components in the upstream part of the support and then freeze-drying the mixture, combined with reducing the content of active components and the amount of coating in the downstream part.
This increased the specific surface area of the catalyst, extended its service life, reduced production costs, and improved its activity and high-temperature resistance.
Smart Images
Figure CN121945031A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of catalyst technology, and particularly relates to an SCR denitrification catalyst, its preparation method, and its application. Background Technology
[0002] Vanadium-titanium SCR catalysts have been widely used. The most commonly used corrugated SCR catalysts are usually prepared by first preparing a multi-component active slurry, and then processing the catalyst, which involves pre-forming the catalyst active powder, coating the fiber support with the active slurry, and drying it with hot air or microwave.
[0003] Catalysts mostly undergo surface or shallow layer reactions during catalytic reactions. However, the slurry coating process of the catalytic active components can partially reduce the specific surface area of the support, especially for fibrous supports. This results in a problem where the coating amount is high but the number of catalytic active sites is insufficient.
[0004] Meanwhile, in corrugated or honeycomb carriers, due to the distance between the inlet and outlet, the coating amount and active sites at each stage need to be deployed according to the actual situation of different gases to be treated and the concentration at different stages or locations, so as to achieve a balance between efficiency and cost.
[0005] In view of this, the present invention is proposed. Summary of the Invention
[0006] The purpose of this invention is to provide an SCR denitrification catalyst, its preparation method, and its application, aiming to solve the problem that the coating amount and active sites of the support at different stages cannot adapt to actual conditions.
[0007] To achieve the above objectives, the present invention adopts the following specific technical solution:
[0008] In a first aspect, the present invention provides a method for preparing an SCR denitrification catalyst, comprising:
[0009] The first catalytic active component, inorganic fiber material, binder, pH adjuster, dispersant, defoamer and water are mixed evenly to prepare the first catalytic active slurry;
[0010] The second catalytic active component, binder, pH adjuster, dispersant, defoamer and water are mixed evenly to prepare the second catalytic active slurry;
[0011] The upstream portion h of the carrier is immersed in the first catalyst active slurry from the inlet end to the outlet end, and then the downstream portion of the carrier is immersed in the second catalyst active slurry from the inlet end to the outlet end. After drying and calcination, the product is obtained.
[0012] Furthermore, the drying can be carried out by methods such as air drying, oven drying, forced air drying, and microwave drying; the calcination temperature is 300-500℃, and the calcination time is 2h-24h.
[0013] Further, the first catalytically active component is obtained by uniformly mixing titanium dioxide, tungsten source, molybdenum source, vanadium source and water, drying and calcining; the calcination temperature is 300-500℃, and the calcination time is 2h-24h. Based on oxides, the mass ratio of titanium dioxide, tungsten source, molybdenum source and vanadium source in the first catalytically active component is 100:(0-10):(0-10):(0.5-7).
[0014] Furthermore, the second catalytic active component is a uniform mixture of titanium dioxide, tungsten source, molybdenum source, vanadium source and water; the mass ratio of titanium dioxide, tungsten source, molybdenum source and vanadium source in the second catalytic active component is 100:(0-5):(0-5):(0.2-3).
[0015] Optionally, the tungsten source includes one or more of tungsten trioxide, ammonium metatungstate, or ammonium paratungstate.
[0016] Optionally, the molybdenum source includes molybdenum trioxide and / or ammonium molybdate.
[0017] Optionally, the vanadium source is one or more of vanadium pentoxide, ammonium metavanadate, or vanadium oxalate.
[0018] Furthermore, the mass ratio of the first catalytic active component, inorganic fiber material, binder, pH adjuster, dispersant, defoamer and water is 100:(2-20):(20-70):(5-10):(0.3-3):(1-7):(50-250).
[0019] Furthermore, the mass ratio of the second catalytic active component, binder, pH adjuster, dispersant, defoamer and water is 100:(20-70):(5-10):(0.3-3):(1-7):(50-250).
[0020] Optionally, the inorganic fiber material includes one or more of glass fiber, ceramic fiber, alumina fiber, basalt fiber, high silica fiber, or quartz fiber.
[0021] Preferably, the inorganic fiber has a diameter of 2-20 μm and a length of 3-30 mm.
[0022] Optionally, the carrier is a corrugated carrier or a honeycomb carrier. Further optionally, the carrier material includes one or more of the following: glass fiber, ceramic fiber, alumina fiber, basalt fiber, high-silica fiber, or quartz fiber.
[0023] Preferably, the upstream portion of the carrier accounts for 20-80% of the length from the air inlet end to the air outlet end of the carrier.
[0024] More preferably, the upstream portion of the carrier accounts for 60-75% of the length from the inlet end to the outlet end of the carrier.
[0025] Furthermore, in the step of impregnating the upstream portion of the carrier with the first catalyst active slurry, after impregnation, excess slurry in the pores is removed by vacuuming, followed by freeze drying, which can generally be carried out below 0°C; the coating amount of the impregnation is 80-140 g / L. To achieve the required coating amount, impregnation can typically be performed for 10-300 seconds and / or multiple times.
[0026] Further, in the step of impregnating the downstream portion of the carrier with the second catalyst active slurry, the impregnation is followed by drying; the coating amount of the impregnation is 20-60 g / L. To achieve the required coating amount, impregnation can typically be performed for 10-300 seconds and / or multiple times.
[0027] Optionally, the binder includes one or more of silica sol, alumina sol, or aluminosilicate sol.
[0028] Optionally, the pH adjuster includes ammonia and / or ethanolamine.
[0029] Optionally, the dispersant includes one or more of resins, emulsions, polyethylene glycols, alcohols, polycarboxylates, or polyacrylic acids.
[0030] Optionally, the defoamer includes polyacetylene, polyether, organosilicon, mineral oil, and polyether defoamers.
[0031] Secondly, the present invention also provides an SCR denitrification catalyst, which is prepared by the aforementioned preparation method.
[0032] Thirdly, the present invention also provides an application of the aforementioned SCR denitrification catalyst: the catalyst is loaded into a reactor, the reaction temperature is 150-500℃; ammonia is used as a reducing agent, the NOx concentration is 100-1000ppm, the NH3 / NOx ratio is 1.0-1.1, and the gas space velocity is 10000h⁻¹. -1 Selective catalytic reduction of nitrogen oxides is carried out.
[0033] Compared with existing technologies, this invention firstly coats the upstream portion of the support with a mixture of active component powder and an inorganic fiber material similar in texture to the support. This effectively solves the problem of reduced catalyst specific surface area caused by direct coating of active components in traditional processes. It further increases the surface structure of the catalyst, improves its performance, delays the risk of activity reduction due to decreased specific surface area during use, and extends the catalyst's lifespan. Simultaneously, it integrates well with the support, whereas other porous materials such as activated carbon cannot integrate well with the support and similarly do not contribute to restoring the specific surface area.
[0034] Secondly, because inorganic fiber materials are used for coating, high temperatures can cause partial deformation of the material, which can easily reduce the specific surface area. More importantly, it can easily mask or cause the active sites to be lost. This invention avoids the problem of fiber deformation caused by high-temperature drying by impregnating the upstream part of the carrier and then freeze-drying it. It also avoids the problem of surface hardening, and forms a porous sponge-like structure inside, which can effectively maintain the specific surface area and solidify the active sites.
[0035] Because the high activity of the catalyst in the upstream part of the support can significantly reduce the NOx concentration, the slurry coating prepared in one step in the downstream part of the support reduces the content of active components and the overall coating amount, ultimately achieving the goal of reducing catalyst production costs and increasing catalyst lifespan. Attached Figure Description
[0036] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation on the scope of this application.
[0037] Figure 1 This is a schematic diagram of the overall structure of the SCR denitrification catalyst of the present invention;
[0038] Figure 2 The diagram shows the denitrification activity of the catalysts prepared in Examples 1-5 and Comparative Examples 1-2 of this invention. Detailed Implementation
[0039] As used in this article:
[0040] "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.
[0041] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1–5” is disclosed, the described range should be interpreted as including ranges “1–4”, “1–3”, “1–2”, “1–2 and 4–5”, “1–3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.
[0042] In these embodiments, unless otherwise specified, all parts and percentages are by weight, and all unstated proportions can be made in any proportion.
[0043] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).
[0044] Example 1
[0045] A method for preparing an SCR denitration catalyst:
[0046] S1. Catalyst front coating
[0047] S11. Mix 20 kg of titanium dioxide, 1.5 kg of vanadium oxalate and 40 kg of deionized water evenly, add 2 kg of ammonium molybdate and stir ultrasonically for 30 min, then dry by forced air and calcine at 350℃ for 4 h to obtain catalyst active powder.
[0048] S12. Stir the active powder prepared in S11 with 40 kg of deionized water until uniform. Then, add 1 kg of glass fiber (diameter 2-20 μm, length 3-30 mm), 12 kg of silica sol, 1.2 kg of ammonia, 60 g of fatty alcohol sulfate and 120 g of methyl phenyl ether at 10-minute intervals and stir for 30 minutes to obtain the first active slurry.
[0049] S13. Immerse a corrugated glass fiber carrier with a height of 500 mm (from the inlet end to the outlet end) into the first active slurry prepared in S12. The immersion height is 350 mm. After immersion for 100 seconds, the carrier is lifted and the slurry in the pores is removed by vacuum suction. After freeze drying at below 0°C, a catalyst semi-finished product with a coating amount of 140 g / L is prepared.
[0050] S2. Catalyst back-end coating
[0051] S21. Mix 20kg titanium dioxide, 0.5kg vanadium oxalate, and 50kg deionized water evenly, add 1kg ammonium molybdate and ultrasonically stir for 30min; then add 12kg silica sol, 1.1kg ammonia, 50g fatty alcohol sulfate, and 100g methyl phenyl ether sequentially at 10min intervals and stir for 30min to obtain the second active slurry.
[0052] S22. The catalyst semi-finished product prepared in S13 with a remaining height of 150 mm is immersed in the second active slurry in S21. The carrier is immersed for 60 seconds. After removal, it is purged with air and dried with hot air. The weight gain of the catalyst section is 30 g / L.
[0053] S3. Catalyst finished product
[0054] The catalyst obtained from S2 was calcined at 480℃ for 4.0 h, followed by horizontal calcination at 5℃ / min (holding at 100, 200, and 300℃ for 1.0 h each). This allows the catalyst components to fully react and decompose, which is beneficial for a firm coating and uniform activity.
[0055] The catalyst module prepared through the above steps has a total catalyst active coating coverage of 170 g / L. The catalyst as a whole is as follows: Figure 1 As shown, h is the length of the carrier impregnated with the first active slurry.
[0056] The obtained catalyst was loaded into a fixed-bed reactor for selective catalytic reduction of nitrogen oxides at a reaction temperature of 300 °C. Ammonia was used as the reducing agent, the NOx concentration was 1000 ppm, the NH3 / NOx ratio was 1.0, the O2 vol% was 6%, and the gas space velocity was 10000 h⁻¹. -1 .
[0057] The catalyst inlet and outlet concentrations before and after the reaction were measured using a flue gas analyzer, and the catalytic activity was calculated.
[0058] Example 2
[0059] A method for preparing an SCR denitration catalyst:
[0060] S1. Catalyst front coating
[0061] S11. Mix 20 kg of titanium dioxide, 0.5 kg of vanadium oxalate, and 40 kg of deionized water evenly, add 1 kg of ammonium molybdate and stir ultrasonically for 30 min, then dry by forced air and calcine at 350℃ for 4 h to obtain catalyst active powder.
[0062] S12. Stir the active powder prepared in S11 with 40 kg of deionized water until homogeneous. Then, add 2 kg of glass fiber (diameter 2-20 μm, length 3-30 mm), 11 kg of silica sol, 1.4 kg of ammonia, 60 g of fatty alcohol sulfate and 120 g of methyl phenyl ether at 10-minute intervals and stir for 30 minutes to obtain the first active slurry.
[0063] S13. Immerse a corrugated glass fiber carrier with a height of 500 mm (from the inlet end to the outlet end) into the first active slurry prepared in S12, with an immersion height of 320 mm. After immersion for 100 seconds, pull it up and remove the slurry in the pores by vacuum suction. After freeze drying at below 0°C, a catalyst semi-finished product with a coating amount of 100 g / L is prepared.
[0064] S2. Catalyst back-end coating
[0065] S21. Mix 20kg titanium dioxide, 0.75kg vanadium oxalate, and 50kg deionized water evenly, add 1.5kg ammonium molybdate and ultrasonically stir for 30min; then add 11kg silica sol, 1.4kg ammonia, 50g fatty alcohol sulfate, and 100g methyl phenyl ether sequentially at 10min intervals and stir for 30min to obtain the second active slurry.
[0066] S22. The catalyst semi-finished product prepared in S13 with a remaining height of 180 mm is immersed in the second active slurry in S21. The carrier is immersed for 60 seconds. After being removed, it is purged with air and dried with hot air. The weight gain of the catalyst section is 60 g / L.
[0067] S3. Catalyst finished product
[0068] The catalyst obtained from S2 was calcined at 450℃ for 6.0h and then subjected to horizontal calcination at 5℃ / min (holding at 100, 200, and 300℃ for 1.0h each).
[0069] The catalyst module prepared by the above steps has a total coating amount of 160 g / L for the catalyst active coating.
[0070] The test conditions are the same as in Example 1.
[0071] Example 3
[0072] A method for preparing an SCR denitration catalyst:
[0073] S1. Catalyst front coating
[0074] S11. Mix 20 kg of titanium dioxide, 1 kg of vanadium oxalate, and 40 kg of deionized water evenly, add 1.5 kg of ammonium molybdate and stir ultrasonically for 30 min. After drying by forced air and calcining at 350℃ for 4 h, the catalyst active powder is obtained.
[0075] S12. Stir the active powder prepared in S11 with 40 kg of deionized water until homogeneous. Then, add 1.5 kg of glass fiber (diameter 2-20 μm, length 3-30 mm), 10 kg of silica sol, 1.1 kg of ammonia, 60 g of fatty alcohol sulfate, and 120 g of methyl phenyl ether at 10-minute intervals and stir for 30 minutes to obtain the first active slurry.
[0076] S13. Immerse a corrugated glass fiber carrier with a height of 500 mm (from the inlet end to the outlet end) into the first active slurry prepared in S12. The immersion height is 360 mm. After immersion for 100 s, the carrier is lifted and the slurry in the pores is removed by vacuum suction. After freeze drying at below 0°C, a catalyst semi-finished product with a coating amount of 120 g / L is prepared.
[0077] S2. Catalyst back-end coating
[0078] S21. Mix 20kg titanium dioxide, 0.5kg vanadium oxalate, and 50kg deionized water evenly, add 1kg ammonium molybdate and ultrasonically stir for 30min; then add 10kg silica sol, 1.1kg ammonia, 50g fatty alcohol sulfate, and 100g methyl phenyl ether sequentially at 10min intervals and stir for 30min to obtain the second active slurry.
[0079] S22. The remaining height of the catalyst semi-finished product prepared in S13 (140 mm) is immersed in the second active slurry in S21. The carrier is immersed for 60 seconds. After removal, it is purged with air and dried with hot air. The weight gain of the catalyst in the latter section is 50 g / L.
[0080] S3. Catalyst finished product
[0081] The catalyst obtained from S2 was calcined at 350℃ for 6.0h and then subjected to horizontal calcination at 5℃ / min (holding at 100, 200, and 300℃ for 1.0h each).
[0082] The catalyst module prepared by the above steps has a total coating amount of 170 g / L for the catalyst active coating.
[0083] The test conditions are the same as in Example 1.
[0084] Example 4
[0085] The difference from Example 1 is that the first active slurry is immersed to a depth of 100 mm, and the second active slurry is immersed to a depth of 400 mm. The coating amounts of the first and second active slurries for the two immersions remain 80 g / L and 110 g / L, respectively.
[0086] Example 5
[0087] The difference from Example 1 is that the first active slurry is immersed to a depth of 400 mm, and the second active slurry is immersed to a depth of 100 mm. The coating amounts of the first and second active slurries for the two immersions remain 150 g / L and 20 g / L, respectively.
[0088] Example 6
[0089] The difference from Example 1 is that ammonium molybdate in the active slurry is replaced with ammonium metatungstate.
[0090] Comparative Example 1
[0091] The difference from Example 1 is that no glass fiber was added when preparing the first active slurry.
[0092] Comparative Example 2
[0093] The difference from Example 1 is that the first active slurry was not freeze-dried after immersion, but was dried with hot air at 90°C.
[0094] Table 1. Performance comparison of catalysts prepared in Examples 1-6 and Comparative Examples 1-2
[0095]
[0096] Table 2 Comparison of denitrification activity data in Examples 1-6
[0097]
[0098]
[0099] Table 3 Comparison of denitrification activity data for Comparative Examples 1-2
[0100]
[0101] Combining the catalyst performance in Table 1 and Figure 2 Denitrification activity (Tables 2 and 3 are respectively) Figure 2(Based on the corresponding data), it can be seen that, compared with Examples 1-3, the higher the vanadium-molybdenum content of the active components, the higher the catalytic activity of the catalyst. Compared with Example 4, Example 1 requires a certain length of the front-end coating to broaden the catalyst's active window. Example 5 shows that its catalytic performance is similar to that of Example 1, but the cost is relatively high. That is, increasing the front-end catalyst coating length has an upper limit to improving the catalyst's performance window. This further illustrates that we can reduce the overall coating cost of the catalyst by reducing the amount of active components and coating in the later stages. Example 6 shows that the tungsten active component can shift the active window to the later stage, improving the high-temperature activity of the catalyst. The active window of the catalyst in Comparative Example 1 is narrowed because the catalyst lacks the macroscopic surface area provided by glass fibers, resulting in a decrease in the catalyst's active reaction rate. The active window of Comparative Example 2 is narrowed because hot air drying causes the catalyst surface to clump together. Compared with freeze drying, the catalyst's reaction surface area decreases, leading to a smaller catalyst window.
[0102] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.
[0103] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are meant to be within the scope of the invention and form different embodiments. For example, in the foregoing claims, any of the claimed embodiments can be used in any combination. The information disclosed in this background section is intended only to enhance the understanding of the general background of the invention and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.
Claims
1. A method for preparing an SCR denitration catalyst, characterized in that, include: The first catalytic active component, inorganic fiber material, binder, pH adjuster, dispersant, defoamer and water are mixed evenly to prepare the first catalytic active slurry; The second catalytic active component, binder, pH adjuster, dispersant, defoamer and water are mixed evenly to prepare the second catalytic active slurry; The upstream portion of the carrier is impregnated with the first catalyst active slurry from the inlet end to the outlet end, and then the downstream portion of the carrier is impregnated with the second catalyst active slurry from the inlet end to the outlet end. After drying and calcination, the product is obtained.
2. The preparation method according to claim 1, characterized in that, The first catalytically active component is obtained by uniformly mixing titanium dioxide, tungsten source, molybdenum source, vanadium source and water, and then drying and calcining it. Based on oxides, the mass ratio of titanium dioxide, tungsten source, molybdenum source, and vanadium source in the first catalytically active component is 100:(0-10):(0-10):(0.5-7); And / or, the second catalytically active component is a uniform mixture of titanium dioxide, tungsten source, molybdenum source, vanadium source and water; the mass ratio of titanium dioxide, tungsten source, molybdenum source and vanadium source in the second catalytically active component is 100:(0-5):(0-5):(0.2-3); Preferably, the tungsten source includes one or more of tungsten trioxide, ammonium metatungstate, or ammonium paratungstate; Preferably, the molybdenum source comprises molybdenum trioxide and / or ammonium molybdate; Preferably, the vanadium source is one or more of vanadium pentoxide, ammonium metavanadate, or vanadium oxalate.
3. The preparation method according to claim 1 or 2, characterized in that, The mass ratio of the first catalytically active component, inorganic fiber material, binder, pH adjuster, dispersant, defoamer and water is 100:(2-20):(8-20):(5-10):(0.3-3):(1-7):(50-250); And / or, the mass ratio of the second catalytically active component, binder, pH adjuster, dispersant, defoamer and water is 100:(8-20):(5-10):(0.3-3):(1-7):(50-250).
4. The preparation method according to claim 1, characterized in that, The inorganic fiber material includes one or more of glass fiber, ceramic fiber, alumina fiber, basalt fiber, high silica fiber, or quartz fiber. Preferably, the inorganic fiber has a diameter of 2-20 μm and a length of 3-30 mm.
5. The preparation method according to claim 1, characterized in that, The carrier is either a corrugated carrier or a honeycomb carrier; Preferably, the carrier is made of one or more of the following materials: glass fiber, ceramic fiber, alumina fiber, basalt fiber, high silica fiber, or quartz fiber.
6. The preparation method according to claim 1, characterized in that, The upstream portion of the carrier accounts for 20-80% of the length from the inlet end to the outlet end of the carrier; Preferably, the upstream portion of the carrier accounts for 60-75% of the length from the inlet end to the outlet end of the carrier.
7. The preparation method according to claim 1, characterized in that, In the step of impregnating the upstream portion of the carrier with the first catalyst active slurry, after impregnation, excess slurry in the pores is removed by vacuuming, and then dried at below 0°C; the coating amount of the impregnation is 80-140 g / L. And / or, in the step of impregnating the downstream portion of the carrier with the second catalyst active slurry, the impregnation is followed by drying; the coating amount of the impregnation is 20-60 g / L.
8. The preparation method according to claim 1, characterized in that, The binder includes one or more of silica sol, alumina sol, or silica-alumina sol. And / or, the pH adjuster includes ammonia and / or ethanolamine; And / or, the dispersant includes one or more of resins, emulsions, polyethylene glycols, alcohols, polycarboxylates, or polyacrylic acids; And / or, the defoamer includes polyacetylene, polyether, organosilicon, mineral oil, and polyether defoamers.
9. An SCR denitration catalyst, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.
10. The application of the SCR denitrification catalyst according to claim 9, characterized in that, The catalyst was loaded into a reactor, and the reaction temperature was 150-500℃; ammonia was used as the reducing agent, the NOx concentration was 100-1000 ppm, the NH3 / NOx ratio was 1.0-1.1, and the gas space velocity was 10000 h⁻¹. -1 Selective catalytic reduction of nitrogen oxides is carried out.