Modified SCR catalyst and preparation method therefor and use thereof

Abstract

The present invention provides an SCR catalyst and a preparation method therefor and a use thereof. The SCR catalyst comprises a flow-through ceramic honeycomb carrier and a first coating layer. The first coating layer is coated on the pore channel surface of the flow-through ceramic honeycomb carrier. The first coating layer comprises a Mn / Cu-SSZ type first molecular sieve, a cerium oxide, an aluminum oxide, and a manganese oxide. The preparation method for the modified SCR catalyst provided by the present invention has a simple process. After being hydrothermally aged at 800°C, the obtained catalyst still has excellent denitration performance in a low temperature range of 150-200°C without losing denitration performance in a medium-high temperature range of 250-500°C. The catalyst can achieve good NOx conversion over a wider operating temperature window.

Description

A modified SCR catalyst, its preparation method and uses Technical Field

[0001] This invention relates to the field of catalyst technology, and in particular to a modified SCR catalyst, its preparation method, and its uses. Background Technology

[0002] In recent years, with increasing environmental awareness and increasingly stringent regulations, effectively reducing NOx emissions from internal combustion engines, especially diesel engines, has become a crucial research topic. SCR technology, due to its high NOx removal efficiency, is widely used in diesel vehicle exhaust aftertreatment systems. However, existing SCR catalysts exhibit low NOx conversion rates at low temperatures (<250℃), limiting their effectiveness under cold start or low-load conditions. Especially in cold regions, the low exhaust temperature during diesel engine cold starts prevents the catalyst from quickly reaching its operating temperature, thus affecting NOx removal efficiency.

[0003] Manganese-based catalysts exhibit high activity at low temperatures, particularly in the 150-200℃ temperature range, where their NOx conversion rate is significantly higher than that of traditional vanadium-based and copper-based catalysts. This makes Mn-based catalysts perform exceptionally well under cold start and low-load conditions in diesel engines. Traditional manganese-based catalysts use manganese oxides as the active component, accounting for more than 10% by mass. While they exhibit excellent denitrification performance at low temperatures, their performance is poor at high temperatures. Summary of the Invention

[0004] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a modified SCR catalyst, its preparation method and uses, to solve the problems in the prior art.

[0005] To achieve the above and other related objectives, the present invention is obtained through the following technical solution.

[0006] The present invention provides a modified SCR catalyst, comprising a straight-through ceramic honeycomb support and a first coating, wherein the first coating is coated on the pore surface of the straight-through ceramic honeycomb support; the first coating comprises a Mn / Cu-SSZ type first molecular sieve, cerium oxide, aluminum oxide and manganese oxide.

[0007] Preferably, the material of the through-type ceramic honeycomb carrier is cordierite.

[0008] Preferably, the pore density of the through-type ceramic honeycomb carrier is 400–600 pores / square inch, and the wall thickness h is 3–4 mil. mil represents one-thousandth of an inch.

[0009] Preferably, the slurry forming the first coating comprises a Cu-SSZ first molecular sieve, cerium ion-doped alumina material, manganese salt, boehmite, pH adjuster, and water.

[0010] Preferably, based on the mass of solids in the slurry forming the first coating, the content of Cu-SSZ first molecular sieve is 50-81 wt%, the content of cerium ion-doped alumina material is 15-48 wt%, the content of boehmite is 1.0-4.0 wt%, and the content of manganese is 0.5-4.0 wt%.

[0011] For example, the content of Cu-SSZ first molecular sieve is 50-60%, 60-70%, and 70-81%.

[0012] For example, the content of cerium ion-doped alumina materials is 15.8–25%, 25–35%, 35–36.1%, 36.1–38.2%, 38.2–40%, 40–45%, 45–46.1%, and 46.1–48%.

[0013] For example, the Mn element content is 0.5-0.9%, 0.9-1.0%, 1.0-1.2%, 1.2-1.6%, 1.6-2.0%, 2.0-3.0%, 3.0-4.0%, preferably 0.5-2.0%.

[0014] For example, the content of pseudoboehmite is 1.0–2.0%, 2.0–3.0%, and 3.0–4.0%.

[0015] More preferably, the cerium ion-doped alumina material is formed by impregnating alumina with cerium salt.

[0016] More preferably, in the cerium ion-doped alumina material, the molar ratio of cerium to aluminum is (0.01 to 0.05):1.

[0017] More preferably, the cerium salt is selected from acetate and / or nitrate.

[0018] More preferably, the manganese salt is selected from acetate and / or nitrate.

[0019] More preferably, the pH adjuster is one or more selected from tartaric acid, nitric acid, hydrochloric acid, and sulfuric acid, with tartaric acid being preferred. Tartaric acid not only acts as a pH adjuster but also as a chelating agent, enhancing the ability of aluminum oxides in cerium-doped alumina materials to adsorb manganese ions.

[0020] Preferably, the solid content of the slurry forming the first coating is 30-40 wt%.

[0021] Preferably, the pH of the slurry forming the first coating is 4 to 5.

[0022] Preferably, the D50 of the slurry forming the first coating is 2-3 μm.

[0023] Preferably, the cerium oxide is CeO2.

[0024] Preferably, the aluminum oxide is Al2O3.

[0025] Preferably, the Mn / Cu-SSZ type first molecular sieve is Mn 2+ It was obtained by ion exchange with Cu-SSZ type first molecular sieve.

[0026] More preferably, the reaction temperature for the ion exchange is 40–60°C.

[0027] More preferably, the reaction time of the ion exchange method is 2 to 4 hours.

[0028] More preferably, the medium for ion exchange is water.

[0029] More preferably, the Cu content in the Cu-SSZ type first molecular sieve is 1-2 wt%. The low Cu content is to reduce the difficulty of manganese ion exchange, so that more manganese ions can be exchanged into the Cu-SSZ type first molecular sieve.

[0030] More preferably, the silicon-to-aluminum ratio of the Cu-SSZ type first molecular sieve is 20 to 22.

[0031] More preferably, the Cu-SSZ type first molecular sieve is of type Cu-SSZ-13.

[0032] Preferably, the system further includes a second coating, wherein the slurry forming the second coating comprises a Cu-SSZ type second molecular sieve, pseudoboehmite, and water. The second coating and the first coating are applied in sections on the same through-type ceramic honeycomb carrier. If they are applied on different through-type ceramic honeycomb carriers and used in series, this also falls within the scope of protection of this application.

[0033] More preferably, based on the mass of solids in the slurry forming the second coating, the content of the Cu-SSZ type second molecular sieve is 96-99 wt%, and the content of the pseudoboehmite is 1.0-4.0 wt%.

[0034] More preferably, the solid content of the slurry forming the second coating is 25 to 35 wt%.

[0035] More preferably, the D50 of the slurry forming the first coating is 2-3 μm.

[0036] More preferably, the Cu content in the Cu-SSZ type second molecular sieve is 2.5-3.5 wt%.

[0037] More preferably, the silicon-to-aluminum ratio of the Cu-SSZ type second molecular sieve is 20 to 22.

[0038] More preferably, the Cu-SSZ type second molecular sieve is of type Cu-SSZ-13.

[0039] More preferably, the effective catalytic area ratio of the first coating to the second coating is (0.4 to 2.3):1.

[0040] More preferably, the dry loading of the first coating is 80-100 g / L.

[0041] More preferably, the dry loading of the second coating is 80-100 g / L. The dry loading of the second coating is the ratio of the mass of the second coating to the volume of the through-type ceramic honeycomb carrier.

[0042] This invention also discloses a method for preparing the modified SCR catalyst as described above, comprising the following steps:

[0043] The cerium ion-doped alumina material is prepared into a slurry, denoted as Slurry A;

[0044] The Mn / Cu-SSZ type first molecular sieve was prepared into a slurry, denoted as slurry B;

[0045] The slurry A and the slurry B are mixed to obtain a first coating slurry;

[0046] The first coating slurry is applied to the through-type ceramic honeycomb carrier and then dried and calcined.

[0047] Preferably, the pH of the slurry A is 4 to 5.

[0048] More preferably, the pH adjuster of the slurry A is one or more selected from tartaric acid, nitric acid, hydrochloric acid and sulfuric acid, preferably tartaric acid.

[0049] Preferably, the D50 of the slurry A is 2-3 μm.

[0050] Preferably, the D50 of the slurry B is 2-3 μm.

[0051] Preferably, the coating is performed using a bottom-feed vacuum method.

[0052] Preferably, the drying and calcination involves heating to 150℃~250℃ at a heating rate of 5℃ / min~10℃ / min, holding at that temperature for 0.5~1.5h, then continuing to heat to 450~550℃ at a heating rate of 5℃ / min~10℃ / min, holding at that temperature for 1.5h~2.5h, and then cooling.

[0053] Preferably, after drying and calcination, a second coating slurry is applied to the through-type ceramic honeycomb carrier, followed by drying and calcination.

[0054] More preferably, the second coating slurry is obtained by mixing and grinding the Cu-SSZ type second molecular sieve, the pseudo-boehmite, and the water.

[0055] The present invention also discloses the use of the modified SCR catalyst as described above for the conversion of NOx in a low temperature window, wherein the low temperature window is 150 to 250°C.

[0056] Preferably, the modified SCR catalyst comprising the first coating and the second coating converts NOx within a wide temperature window, the wide temperature window being 150–500°C.

[0057] The present invention also discloses a method for NOx conversion using a modified SCR catalyst as described above. In use, the NOx-containing reaction gas flows along the pores of the modified SCR catalyst, first through the first coating region, and then through the second coating region.

[0058] The modified SCR catalyst disclosed in this invention, in its first coating, significantly enhances the catalytic activity of the catalyst in the low-temperature range by incorporating the catalytically active components Mn / Cu-SSZ type first molecular sieve and cerium oxide. In the cerium-doped alumina material, the alumina competes with the Mn / Cu-SSZ type first molecular sieve for the adsorption of unexchanged manganese ions, thus adsorbing manganese ions from the surface of the Mn / Cu-SSZ type first molecular sieve onto the alumina. This prevents the large-scale deposition of manganese ions on the surface of the Mn / Cu-SSZ type first molecular sieve, which would then transform into oxides, block the molecular sieve pores, and drastically reduce catalytic activity. Furthermore, by reducing the Cu content in the Cu-SSZ type first molecular sieve and controlling the amount of manganese added in the first coating, more manganese ions are exchanged into the molecular sieve, reducing the amount adsorbed on the surface of the Mn / Cu-SSZ type first molecular sieve and on the alumina oxide. This prevents the large-scale conversion of adsorbed manganese ions into manganese oxide, which would significantly reduce the denitrification performance in the medium- and high-temperature range. In addition, the use of a zoned coating method further ensures the denitrification performance of the catalyst in the medium- and high-temperature range. The present invention, through the combination of the above-mentioned means, enables the first coating to improve the denitrification performance in the low-temperature range of 150-250℃ while ensuring the denitrification performance in the medium- and high-temperature range of 250-500℃.

[0059] The present invention has the following beneficial effects:

[0060] The modified SCR catalyst preparation method provided by this invention is simple and improves the denitrification activity of the catalyst in the low-temperature range of 150-250℃ after hydrothermal aging at 800℃, without losing the denitrification performance in the medium-high temperature range of 250-500℃, and can achieve good NOx conversion in a wider operating temperature window. Attached Figure Description

[0061] Figure 1 shows a schematic diagram of the structure of a portion of the pore wall in the SCR catalyst of the present invention.

[0062] Figure 2 shows a partial structural schematic diagram of the SCR catalyst of the present invention.

[0063] Figure 3 shows the NOx conversion rate as a function of temperature when the SCR catalyst is used in Examples 1-4 of this invention.

[0064] Figure 4 shows the NOx conversion rate as a function of temperature when the SCR catalyst is used in Examples 1, 5-8 and Comparative Examples 1-2 of this invention.

[0065] Reference numerals: 1 Coating; 11 First coating; 12 Second coating; 3 Straight-through ceramic honeycomb carrier. Detailed Implementation

[0066] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0067] Before further describing specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terminology used in the embodiments of the present invention is for describing specific embodiments and not for limiting the scope of protection of the present invention. Test methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the respective manufacturers.

[0068] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. In addition to the specific methods, apparatus, and materials used in the embodiments, based on the knowledge of the prior art possessed by one of ordinary skill in the art and the description of this invention, any prior art methods, apparatus, and materials similar to or equivalent to those described, apparatus, and materials in the embodiments of this invention may be used to implement the present invention.

[0069] The raw materials used in the following examples:

[0070] The silica-to-alumina ratio of both the Cu-SSZ-13 type first molecular sieve and the Cu-SSZ-13 type second molecular sieve is 21.

[0071] The carriers are all cylindrical cordierite ceramic honeycomb carriers with a mesh size of 400 mesh, an end face diameter of 25 mm, and a length of 60 mm.

[0072] In cerium ion-doped alumina materials, the molar ratio of cerium to aluminum is 0.029:1.

[0073] Cerium ion-doped alumina materials are formed by impregnating alumina materials with an aqueous solution of cerium nitrate hexahydrate.

[0074] The modified SCR catalyst prepared by the present invention, as shown in Figure 1, includes a straight-through ceramic honeycomb carrier 2 and a coating 1 coated on the surface of the straight-through ceramic honeycomb carrier; the coating 1 includes a first coating 11 and a second coating 12.

[0075] The modified SCR catalyst prepared in this invention, as shown in Figure 2, involves reactant gas flowing along the pores of the catalyst and reacting with the first and second coatings applied to the pore surface. The arrows indicate the flow direction of the reactant gas.

[0076] Example 1

[0077] This embodiment provides a specific modified SCR catalyst, and the preparation method is as follows:

[0078] 1. Preparation of the first coating slurry:

[0079] Take 15.14g of cerium nitrate hexahydrate and dissolve it in 17.26g of deionized water to form an impregnation solution. Add the solution dropwise to 54g of alumina and then add it to 113.6g of deionized water. Adjust the pH to 4.5 with tartaric acid and grind the slurry to a D50 of 2.5μm to obtain slurry A.

[0080] Take 84g of Cu-SSZ-13 first molecular sieve (Cu content is 1.5%), add it to 117.79g of deionized water, and grind it until D50 is 2.5μm; add 8.21g of 50% manganese nitrate solution; stir continuously at 50℃ for 3h to obtain slurry B;

[0081] Pour slurry B into 168.47g of slurry A, adjust the pH to 4.5 with tartaric acid, add 4.2g of boehmite, adjust the solid content to 35%, and mix evenly to obtain the first coating slurry.

[0082] 2. Preparation of the second coating slurry:

[0083] Take 67.9g of Cu-SSZ-13 second molecular sieve (Cu content is 2.8%), add it to 90g of deionized water, and grind it until D50 is 2.5μm; add 2.1g of pseudoboehmite, adjust the solid content to 35%, and mix evenly to obtain the second coating slurry.

[0084] 3. Applying grout

[0085] The first coating slurry was coated by bottom feeding and vacuuming, and then dried and calcined. The first coating slurry was then coated again by bottom feeding and vacuuming, and the catalyst sample was obtained after drying and calcination. The coating areas of the first and second coatings were the same, each being half of the total catalyst, and the dry loading was 80 g / L.

[0086] The solid content of the first coating slurry in the catalyst includes 60% Cu-SSZ-13 first molecular sieve, 36.1% cerium ion-doped alumina material, 0.9% Mn element, and 3% pseudoboehmite. The solid content of the second coating slurry includes 97% Cu-SSZ-13 second molecular sieve and 3% pseudoboehmite, as shown in Table 1.

[0087] Example 2

[0088] This embodiment provides a specific modified SCR catalyst, the preparation method of which is basically the same as that in Example 1, except that...

[0089] The preparation methods of the first coating slurry in step 1 are different.

[0090] Specifically: 15.14g of cerium nitrate hexahydrate was dissolved in 17.26g of deionized water to form an impregnation solution, which was then added dropwise to 54g of alumina II and then added to 113.6g of deionized water. After adjusting the pH to 4.5 with tartaric acid, the slurry was ground until the D50 was 2.5μm to obtain slurry A.

[0091] Take 112g of Cu-SSZ-13 first molecular sieve (Cu content is 1.5%), add it to 157.06g of deionized water, and grind it until D50 is 2.5μm; add 10.94g of 50% manganese nitrate solution; stir continuously at 50℃ for 3h to obtain slurry B;

[0092] Pour slurry B into 73.73g of slurry A, adjust the pH to 4.5 with tartaric acid, add 4.2g of boehmite, adjust the solid content to 35%, and mix evenly to obtain the first coating slurry.

[0093] The solid content of the first coating slurry in the catalyst includes 80% Cu-SSZ-13 first molecular sieve, 15.8% cerium ion-doped alumina material, 1.2% Mn element, and 3% pseudoboehmite. The solid content of the second coating slurry includes 97% Cu-SSZ-13 second molecular sieve and 3% pseudoboehmite, as shown in Table 1.

[0094] Example 3

[0095] This embodiment provides a specific modified SCR catalyst, the preparation method of which is basically the same as that in Example 1, except that...

[0096] The preparation methods of the first coating slurry in step 1 are different.

[0097] Specifically, 22.71g of cerium nitrate hexahydrate was dissolved in 25.89g of deionized water to form an impregnation solution, which was then added dropwise to 81g of alumina II and then added to 170.4g of deionized water. After adjusting the pH to 4.5 with tartaric acid, the slurry was ground until the D50 was 2.5μm to obtain slurry A.

[0098] Take 70g of Cu-SSZ-13 first molecular sieve (Cu content is 1%), add it to 100.44g of deionized water, and grind it until D50 is 2.5μm; add 4.56g of 50% manganese nitrate solution; stir continuously at 50℃ for 3h to obtain slurry B;

[0099] Pour slurry B into 217g of slurry A, adjust the pH to 4.5 with tartaric acid, add 4.2g of boehmite, adjust the solid content to 35%, and mix evenly to obtain the first coating slurry.

[0100] The solid content of the first coating slurry in the catalyst includes 50% Cu-SSZ-13 first molecular sieve, 46.5% cerium ion-doped alumina material, 0.5% Mn element, and 3% pseudoboehmite. The solid content of the second coating slurry includes 97% Cu-SSZ-13 second molecular sieve and 3% pseudoboehmite, as shown in Table 1.

[0101] Example 4

[0102] This embodiment provides a specific modified SCR catalyst, the preparation method of which is basically the same as that in Example 1, except that...

[0103] The preparation methods of the first coating slurry in step 1 are different.

[0104] Specifically: 15.14g (0.02g) of cerium nitrate hexahydrate was dissolved in 17.26g of deionized water to form an impregnation solution, which was then added dropwise to 54g (1mol) of alumina II, and then added to 113.6g of deionized water. After adjusting the pH to 4.5 with tartaric acid, the slurry was ground until the D50 was 2.5μm to obtain slurry A.

[0105] Take 84g of Cu-SSZ-13 first molecular sieve (Cu content is 1.5%), add it to 98.64g of deionized water, and grind it until D50 is 2.5μm; add 27.36g of 50% manganese nitrate solution; stir continuously at 50℃ for 3h to obtain slurry B;

[0106] Pour slurry B into 158.67g of slurry A, adjust the pH to 4.5 with tartaric acid, add 4.2g of boehmite, adjust the solid content to 35%, and mix evenly to obtain the first coating slurry.

[0107] The solid content of the first coating slurry in the catalyst includes 60% Cu-SSZ-13 first molecular sieve, 34% cerium ion-doped alumina material, 3% Mn element, and 3% pseudoboehmite. The solid content of the second coating slurry includes 97% Cu-SSZ-13 second molecular sieve and 3% pseudoboehmite, as shown in Table 1.

[0108] Example 5

[0109] This embodiment provides a specific modified SCR catalyst, the preparation method of which is basically the same as that of Example 1, except that in step 3, a first coating slurry is used to coat the entire pore of the through-type ceramic honeycomb carrier, and a second coating slurry is not used, with a dry loading of 160 g / L. The remaining steps are the same as in Example 1.

[0110] Example 6

[0111] This embodiment provides a specific modified SCR catalyst. The preparation method is basically the same as that in Example 1. The difference is that in step 3, the second coating slurry is used to coat the entire channel of the through ceramic honeycomb carrier, instead of the first coating slurry. The dry loading is 160 g / L.

[0112] Preparation method of the second coating slurry: Take 100g of Cu-SSZ-13 second molecular sieve, add it to 120g of deionized water, grind it until the D50 is 2.5μm, add 3g of pseudoboehmite, adjust the solid content to 40%, and mix evenly to obtain the second coating slurry.

[0113] The remaining steps are the same as in Example 1.

[0114] Example 7

[0115] This embodiment provides a specific modified SCR catalyst, which is prepared in a manner that is basically the same as in Example 1. The difference is that 69% nitric acid is used instead of tartaric acid in step 1, while the remaining steps are the same as in Example 1.

[0116] Example 8

[0117] This embodiment provides a specific modified SCR catalyst, prepared using a method essentially the same as in Example 1, except that a Cu-SSZ-13 second molecular sieve is used instead of the Cu-SSZ-13 first molecular sieve. The remaining preparation methods are the same as in Example 1.

[0118] Comparative Example 1

[0119] This comparative example is the same as Example 1, except that in step 1, when preparing the first coating slurry, an equal dry weight of slurry B is used instead of slurry A. The rest of the preparation method is the same as in Example 1.

[0120] Comparative Example 2

[0121] This comparative example is the comparative example of Example 1, the only difference being that the preparation method of the first coating slurry in step 1 is different.

[0122] Specifically: 15.14g of cerium nitrate hexahydrate was dissolved in 17.26g of deionized water to form an impregnation solution, which was then added dropwise to 54g of alumina II and then added to 113.6g of deionized water. After adjusting the pH to 4.5 with tartaric acid, the slurry was ground until the D50 was 2.5μm to obtain slurry A.

[0123] Take 84g of Cu-SSZ-13 first molecular sieve (Cu content is 1.5%), add it to 80.40g of deionized water, and grind it until D50 is 2.5μm; add 45.60g of 50% manganese nitrate solution; stir continuously at 50℃ for 3h to obtain slurry B;

[0124] Pour slurry B into 149.33g of slurry A, adjust the pH to 4.5 with tartaric acid, add 4.2g of boehmite, adjust the solid content to 35%, and mix evenly to obtain the first coating slurry.

[0125] The solid content of the first coating slurry in the catalyst includes 60% Cu-SSZ-13 first molecular sieve, 32% cerium ion-doped alumina material, 5% Mn element, and 3% pseudoboehmite, while the solid content of the second coating slurry includes 97% Cu-SSZ-13 second molecular sieve and 3% pseudoboehmite.

[0126] Table 1

[0127] The modified SCR catalysts prepared in Examples 1-8 and Comparative Examples 1-2 were subjected to hydrothermal aging treatment at 800°C for 16 hours with a water vapor volume concentration of 10%, and then applied to a catalytic performance evaluation device to evaluate the NOx conversion performance of each catalyst within a wide temperature window.

[0128] The test conditions are as follows:

[0129] The gas introduced consisted of: H2O (7% by volume), O2 (10% by volume), NO (400 ppm), NH3 (400 ppm), and the remainder was nitrogen. The space velocity was 60,000 h⁻¹. -1 Test temperature: 150-500℃, heating rate: 10℃ / min, initial stable temperature: 120℃.

[0130] The test method is as follows: Using a blank straight-through ceramic honeycomb carrier, adjust the parameters of each flow meter according to the above flue gas conditions and reach the preset value. After heating to 120℃ and stabilizing, record the concentration of each component at the reactor outlet to ensure stable test conditions. Replace the blank straight-through ceramic honeycomb carrier with the test sample, heat to 120℃ and stabilize, set the heating rate, use a Fourier transform infrared flue gas analyzer to monitor the NO concentration at the outlet online, calculate the NO removal efficiency based on the inlet and outlet NO concentrations, and plot the relationship curve between temperature and NO removal efficiency, as shown in Figures 3 and 4.

[0131] As shown in Figure 3:

[0132] As can be seen from Examples 1 to 3, as the content of Cu-SSZ-13 first molecular sieve increases, the content of cerium ion-doped alumina material and Mn element decreases. After hydrothermal aging at 800℃, the denitrification performance of the modified SCR catalyst improves in the low-temperature range and decreases in the medium- and high-temperature range; conversely, the denitrification performance decreases in the low-temperature range and improves in the medium- and high-temperature range.

[0133] As can be seen from Examples 1 and 4, when the content of cerium ion-doped alumina material increases and the content of Mn element decreases, the denitrification performance of the modified SCR catalyst in the medium and high temperature range decreases after hydrothermal aging at 800℃.

[0134] As shown in Figure 4:

[0135] As can be seen from Examples 1 and 5-6, when modified SCR catalysts are prepared by coating only with the first or second coating slurry, the modified SCR catalysts cannot simultaneously exhibit good denitrification performance in both the medium-high temperature range and the low temperature range after hydrothermal aging at 800℃.

[0136] As can be seen from Examples 1 and 7, without the addition of tartaric acid, the denitrification performance of the modified SCR catalyst is reduced in both the medium-high temperature range and the low temperature range after hydrothermal aging at 800℃.

[0137] As can be seen from Example 1 and Comparative Example 1, if no cerium ion-doped alumina material is added, the denitrification performance of the modified SCR catalyst is reduced in the medium and high temperature range after hydrothermal aging at 800℃, but the denitrification performance in the low temperature range is significantly reduced.

[0138] As can be seen from Examples 1 and 8, increasing the Cu content in the Cu-SSZ-13 first molecular sieve to 2.8% and aging the modified SCR catalyst at 800℃ with hydrothermal aging slightly improves the denitrification performance in the low-temperature range, but significantly reduces the denitrification performance in the medium- and high-temperature range.

[0139] As can be seen from Example 1 and Comparative Example 2, when the Mn element content is increased to 5%, the denitrification performance of the modified SCR catalyst in the medium and high temperature range decreases significantly after hydrothermal aging at 800℃.

[0140] The modified SCR catalyst of this invention uses a Cu-SSZ type first molecular sieve with low copper loading and manganese ion doping, which enables ion exchange under relatively mild conditions. At the same time, the alumina material doped with cerium ions adsorbs most of the unexchanged manganese ions under the promotion of chelating agents, avoiding the conversion of manganese ions into oxides after a large amount of deposition on the molecular sieve surface, which would affect the denitrification performance at high and low temperatures. In addition, the use of a partitioned coating method further ensures the denitrification performance of the catalyst in the medium and high temperature range.

[0141] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A modified SCR catalyst, characterized in that, It includes a through-type ceramic honeycomb carrier and a first coating, wherein the first coating is applied to the surface of the pores of the through-type ceramic honeycomb carrier; The first coating comprises a Mn / Cu-SSZ type first molecular sieve, cerium oxide, aluminum oxide, and manganese oxide.

2. The modified SCR catalyst of claim 1, wherein, The material of the through-type ceramic honeycomb carrier is cordierite; And / or, the pore density of the through-type ceramic honeycomb carrier is 400-600 pores / square inch, and the wall thickness h is 3-4 mil; and / or, the slurry forming the first coating comprises Cu-SSZ first molecular sieve, cerium ion-doped alumina material, manganese salt, boehmite, pH adjuster and water; And / or, based on the mass of solids in the slurry forming the first coating, the content of Cu-SSZ first molecular sieve is 50-81 wt%, the content of cerium ion-doped alumina material is 15-48 wt%, the content of boehmite is 1.0-4.0 wt%, and the content of manganese is 0.5-4.0 wt%. And / or, the solid content of the slurry forming the first coating is 30-40 wt%; And / or, the pH of the slurry forming the first coating is 4 to 5; And / or, the D50 of the slurry forming the first coating is 2-3 μm; And / or, the cerium oxide is CeO2; And / or, the aluminum oxide is Al2O3; and / or the Mn / Cu-SSZ type first molecular sieve is a Mn 2+ obtained by ion exchange with a Cu-SSZ type first molecular sieve.

3. The modified SCR catalyst of claim 2, wherein, The cerium ion-doped alumina material is formed by impregnating alumina with cerium salt; And / or, in the cerium ion-doped alumina material, the molar ratio of cerium to aluminum is (0.01 to 0.05):1; And / or, the manganese salt is selected from acetate and / or nitrate; And / or, the pH adjuster is one or more selected from tartaric acid, nitric acid, hydrochloric acid and sulfuric acid; And / or, the reaction temperature for the ion exchange is 40–60°C; And / or, the medium for ion exchange is water; And / or, the Cu content in the Cu-SSZ type first molecular sieve is 1-2 wt%; And / or, the silica-alumina ratio of the Cu-SSZ type first molecular sieve is 20 to 22; And / or, the Cu-SSZ type first molecular sieve is of type Cu-SSZ-13.

4. The modified SCR catalyst of claim 1, wherein, It also includes a second coating, wherein the slurry forming the second coating comprises a Cu-SSZ type second molecular sieve, pseudoboehmite, and water.

5. The modified SCR catalyst of claim 4, wherein, Based on the mass of solids in the slurry forming the second coating, the content of the Cu-SSZ type second molecular sieve is 96-99 wt%, and the content of the pseudoboehmite is 1.0-4.0 wt%. And / or, the solid content of the slurry forming the second coating is 25-35 wt%; And / or, the D50 of the slurry forming the first coating is 2-3 μm; And / or, the Cu content in the Cu-SSZ type second molecular sieve is 2.5-3.5 wt%; And / or, the silica-alumina ratio of the Cu-SSZ type second molecular sieve is 20 to 22; And / or, the type of Cu-SSZ second molecular sieve is Cu-SSZ-13; And / or, the effective catalytic area ratio of the first coating to the second coating is (0.4–2.3):1; and / or, the dry loading of the first coating layer is 80-100 g / L; and / or, the dry loading of the second coating layer is 80-100 g / L.

6. A process for the preparation of a modified SCR catalyst according to any one of claims 1 to 5, characterized in that, The method comprises the following steps: The cerium ion-doped alumina material is prepared into a slurry, denoted as slurry A; The Mn / Cu-SSZ type first molecular sieve is prepared into a slurry, denoted as slurry B; The slurry A and the slurry B are mixed to obtain a first coating layer slurry; The first coating layer slurry is coated on the straight-through ceramic honeycomb carrier and dried and calcined.

7. The preparation method according to claim 6, characterized in that, One or more of the following technical features are included: After the drying and calcining, a second coating layer slurry is coated on the straight-through ceramic honeycomb carrier and dried and calcined; The pH of the slurry A is 4-5; The coating is performed by a bottom feeding vacuum method; The drying and calcining is performed by heating to 150-250℃ at a heating rate of 5-10℃ / min, holding for 0.5-1.5h, then heating to 450-550℃ at a heating rate of 5-10℃ / min, holding for 1.5-2.5h, and then cooling.

8. The preparation method according to claim 7, characterized in that, The second coating layer slurry is obtained by mixing and grinding the Cu-SSZ type second molecular sieve, the pseudo-boehmite and the water.

9. Use of the modified SCR catalyst according to any one of claims 1-5 for converting NOx into nitrogen at a low temperature window of 150-250℃.

10. A method for the conversion of NOx using the modified SCR catalyst according to any one of claims 1 to 5, characterized in that, In use, a reaction gas containing NOx flows along the channels of the modified SCR catalyst, first through the first coating layer region and then through the second coating layer region. In use, a reaction gas containing NOx flows along the channels of the modified SCR catalyst, first through the first coating layer region and then through the second coating layer region.

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