Catalyst, method for preparing the catalyst, and use thereof

Abstract

The application discloses a catalyst, a preparation method of the catalyst and application of the catalyst. The catalyst comprises a base body and an outer layer covering at least part of the base body. The base body comprises titanium elements, vanadium elements and tungsten elements. The outer layer comprises silicon elements, molybdenum elements and auxiliary elements. The auxiliary elements are selected from one or more of zirconium elements, magnesium elements, scandium elements, titanium elements, niobium elements, iron elements and germanium elements. The catalyst has a wide working temperature range (160 DEG C to 400 DEG C) and high strength, and can be applied to flue gas denitration.

Description

Technical Field

[0001] This application relates to the field of denitrification catalyst technology, specifically to a catalyst, a method for preparing the catalyst, and its application. Background Technology

[0002] Currently, industries such as coal power, steel, cement, petrochemicals, glass, and incineration produce nitrogen oxides (NOx). x ) gas, NO x NO is a major precursor to the greenhouse effect, acid rain, ozone layer depletion, photochemical smog, and haze. Direct emission of these gases causes severe air pollution. Selective catalytic reduction (SCR) of ammonia is commonly used to remove NO from these gases. x Or reduce NO x The content of SCR catalyst is one of the key factors affecting the denitrification effect.

[0003] In related technologies, common SCR catalysts are V2O5-WO3 / TiO2 system catalysts, which have the disadvantages of a narrow operating temperature range (generally 300℃~350℃) and weak titanium-based strength, thus limiting their application range. Therefore, how to provide an SCR catalyst that has both a wide operating temperature range and high strength is the technical problem to be solved in this application. Summary of the Invention

[0004] This application provides a catalyst, a method for preparing the catalyst, and its application, to provide an SCR catalyst that has both a wide operating temperature range and high strength.

[0005] The technical solution of this application is as follows:

[0006] In a first aspect, this application provides a catalyst comprising a matrix and an outer layer, wherein the outer layer at least covers a portion of the matrix, the matrix comprising titanium, vanadium and tungsten, and the outer layer comprising silicon, molybdenum and auxiliary elements, wherein the auxiliary elements are selected from one or more of zirconium, magnesium, scandium, titanium, niobium, iron and germanium.

[0007] In the matrix, one of the forms in which titanium exists is TiO2, one of the forms in which vanadium exists is V2O5, and one of the forms in which tungsten exists is WO3.

[0008] In the outer layer, one of the forms in which silicon exists is SiO2, one of the forms in which molybdenum exists is MoO3, and one of the forms in which the auxiliary elements exist is an oxide of the auxiliary elements.

[0009] Secondly, this application provides a method for preparing a catalyst, comprising the following steps:

[0010] A first solution containing a titanium source and a tungsten source and a second solution containing a vanadium source and oxalic acid are provided. The first solution and the second solution are mixed to obtain a mixture. The solvent in the mixture is removed to obtain a solid first substance, the first substance containing titanium, vanadium and tungsten.

[0011] A third solution containing a silicon source, a molybdenum source, and an auxiliary element source is provided. The solvent in the third solution is removed to obtain a solid second substance. Then, the second substance is subjected to a first calcination treatment under an inert gas atmosphere to obtain a third substance containing silicon, molybdenum, and an auxiliary element.

[0012] The first substance and the third substance are mixed to obtain a fourth substance, and the fourth substance is subjected to a second calcination treatment to obtain the catalyst;

[0013] The auxiliary element in the auxiliary element source is selected from one or more of zirconium, magnesium, scandium, titanium, niobium, iron, and germanium.

[0014] Thirdly, this application provides the application of a catalyst as described in any of the first aspects, or a catalyst prepared by any of the preparation methods described in any of the second aspects, in flue gas denitrification. The catalyst, or the catalyst prepared by the aforementioned method, is at least used to remove NO from the flue gas. x Or reduce NO in flue gas x The content of.

[0015] This application provides a catalyst, a method for preparing the catalyst, and its application, which has the following technical advantages:

[0016] In the catalyst of this application embodiment, the catalyst includes a matrix and an outer layer. The outer layer covers at least a portion of the matrix. The matrix includes titanium, vanadium, and tungsten. Silicon, molybdenum, and auxiliary elements are distributed on the surface of the matrix. Strong Mo-Si covalent bonds are formed between silicon and molybdenum to form MoSi unit cells, thereby improving the strength of the catalyst. Since the atomic radius of the auxiliary elements is relatively close to that of Si atoms (e.g., the atomic radius difference is less than ±20%), the auxiliary elements can modify the MoSi unit cells. That is, the auxiliary elements can replace some of the Si atoms in the MoSi unit cells, resulting in the loss of some lattice oxygen, thereby increasing the proportion of metallic bonds in the unit cells, improving the asymmetry of the unit cell structure, and thus increasing the fracture energy of the unit cells, further improving the strength of the catalyst. The mechanical strength of the catalyst can reach 228.7 N / m. In addition, by introducing auxiliary elements to control the grain size of the catalyst, the dispersion of active sites in the catalyst is improved, and more active sites can be exposed, thereby improving the activity of the catalyst and giving the catalyst a wide operating temperature range (160℃~400℃). Attached Figure Description

[0017] The technical solution and other beneficial effects of this application will become apparent from the following detailed description of specific embodiments in conjunction with the accompanying drawings.

[0018] Figure 1 A schematic flowchart illustrating a method for preparing a catalyst provided in this application embodiment;

[0019] Figure 2 The image shown is a transmission electron microscope image of the catalyst prepared in Example 1.

[0020] Figure 3 The X-ray diffraction patterns of the catalysts prepared in Example 1 and Comparative Example 2 are shown below.

[0021] Figure 4 The graph shows the pore volume-pore size characteristics of the catalysts in Example 1, Comparative Examples 2 to 5 in Experimental Example 1.

[0022] Figure 5 NO was detected during the low-temperature average activity testing of the catalysts in Example 1, Comparative Examples 2 to 5 in Experimental Example 2. x Conversion rate versus temperature characteristic curve. Detailed Implementation

[0023] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those familiar to those skilled in the art, and the materials or reagents used in the embodiments and comparative examples of this application are commercially available. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to this invention. The preferred embodiments and materials described herein are for illustrative purposes only and do not limit the scope of this application.

[0025] It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of embodiments. Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is indicated herein, it means including any referenced number (fraction or integer) within the indicated range.

[0026] In the description of this application, the term "comprising" means "including but not limited to".

[0027] The term "at least one" means one or more, and "multiple" means two or more. The terms "at least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c" or "at least one of a, b, and c" can be expressed as: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0028] The term "and / or" encompasses any one of two or more of the listed items, as well as any and all combinations of the listed items. These combinations include any two listed items, any number of listed items, or a combination of all listed items. For example, "A and / or B" includes three parallel solutions: A, B, and A+B. Similarly, the technical solution "A, and / or, B, and / or, C, and / or, D" includes any one of A, B, C, and D (i.e., all connected by "logical OR"), any and all combinations of A, B, C, and D, including combinations of any two or three of A, B, C, and D, and combinations of all four of A, B, C, and D (i.e., all connected by "logical AND").

[0029] This application provides a catalyst comprising a matrix and an outer layer. The outer layer covers at least a portion of the matrix. The matrix comprises titanium, vanadium, and tungsten. The outer layer comprises silicon, molybdenum, and auxiliary elements. The auxiliary elements are selected from one or more of zirconium, magnesium, scandium, titanium, niobium, iron, and germanium. In the matrix, one of the forms in which titanium exists is TiO2, one of the forms in which vanadium exists is V2O5, and one of the forms in which tungsten exists is WO3. In the outer layer, one of the forms in which silicon exists is SiO2, one of the forms in which molybdenum exists is MoO3, and one of the forms in which the auxiliary elements exist is an oxide of the auxiliary elements.

[0030] In the catalyst of this application embodiment, silicon, molybdenum, and auxiliary elements are distributed on the surface of the matrix. Silicon and molybdenum form strong Mo-Si covalent bonds to form MoSi unit cells, thereby improving the strength of the catalyst. Since the atomic radius of the auxiliary elements is small compared with that of Si atoms (e.g., the atomic radius difference is less than ±20%), the auxiliary elements can modify the MoSi unit cells. That is, the auxiliary elements can replace some of the Si atoms in the MoSi unit cells, resulting in the loss of some lattice oxygen, thereby increasing the proportion of metal bonds in the unit cells, improving the asymmetry of the unit cell structure, and thus increasing the fracture energy of the unit cells, further improving the strength of the catalyst. Furthermore, by introducing auxiliary elements to control the grain size of the catalyst, the dispersion of active sites in the catalyst is improved, and more active sites can be exposed, thereby improving the activity of the catalyst and giving the catalyst a wide operating temperature range (160℃~400℃).

[0031] In some embodiments of this application, the catalyst, calculated by mass percentage, comprises: 65% to 95% TiO2, where the mass percentage of TiO2 can be, for example, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or any value between any two of the aforementioned values; 0.5% to 3.3% V2O5, where the mass percentage of V2O5 can be, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.3%, or any value between any two of the aforementioned values; and 0.5% to 5.4% WO3, where the mass percentage of WO3 can be, for example, 0.5%, 1%, 2%, 3%, 4%, 5%. 4% or any value between any two of the aforementioned values; 2.25% to 19% SiO2, the mass percentage of SiO2 may be, for example, 2.25%, 5%, 8%, 10%, 13%, 15%, 19% or any value between any two of the aforementioned values; 0.05% to 0.3% oxide of auxiliary element, the oxide of auxiliary element may be, for example, 0.05%, 0.1%, 0.2%, 0.3% or any value between any two of the aforementioned values; 1.7% to 17% MoO3, MoO3 may be, for example, 1.7%, 5%, 8%, 10%, 13%, 15%, 17% or any value between any two of the aforementioned values.

[0032] To further enhance the asymmetry of the MoSi unit cell, thereby increasing the grain fracture energy and thus the catalyst strength, in some embodiments of this application, for auxiliary elements including zirconium, the oxide of the auxiliary element includes ZrO2; and / or, for auxiliary elements including magnesium, the oxide of the auxiliary element includes MgO; and / or, for auxiliary elements including scandium, the oxide of the auxiliary element includes Sc2O3; for auxiliary elements including titanium, the oxide of the auxiliary element includes Ti2O3; for auxiliary elements including niobium, the oxide of the auxiliary element includes NbO; for auxiliary elements including iron, the oxide of the auxiliary element includes Fe2O3; and for auxiliary elements including germanium, the oxide of the auxiliary element includes GeO.

[0033] In some embodiments of this application, the catalyst is spherical, and the average specific surface area of ​​the catalyst is 55 m². 2 / g~83m 2 / g, for example, could be 55m 2 / g、58m 2 / g、60m 2 / g、65m 2 / g、70m 2 / g、75m 2 / g、80m 2 / g、83m 2 / g or a value between any two of the aforementioned values; the average particle size of the catalyst is 3.2nm to 9.7nm, for example, it can be 3.2nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 9.7nm or a value between any two of the aforementioned values; the average pore volume of the catalyst is 0.18cm. 3 / g~0.94cm 3 / g, for example, could be 0.18cm 3 / g, 0.20cm 3 / g, 0.30cm 3 / g, 0.40cm 3 / g, 0.50cm 3 / g, 0.60cm 3 / g, 0.70cm 3 / g, 0.80cm 3 / g, 0.90cm 3 / g, 0.97cm 3 / g or any value between the two values ​​mentioned above.

[0034] This application also provides a method for preparing a catalyst, such as... Figure 1 As shown, it includes the following steps:

[0035] S1. Provide a first solution containing a titanium source and a tungsten source and a second solution containing a vanadium source and oxalic acid; mix the first solution and the second solution to obtain a mixture; remove the solvent from the mixture to obtain a solid first substance, the first substance containing titanium, vanadium and tungsten.

[0036] S2. Provide a third solution containing a silicon source, a molybdenum source, and an auxiliary element source; remove the solvent from the third solution to obtain a solid second substance; and then, under an inert gas atmosphere, perform a first calcination treatment on the second substance to obtain a third substance containing silicon, molybdenum, and auxiliary elements.

[0037] S3. Mix the first substance and the third substance to obtain the fourth substance, and subject the fourth substance to a second calcination treatment to obtain the catalyst.

[0038] In the catalyst preparation method of this application embodiment, a first substance containing titanium, vanadium and tungsten and a third substance containing silicon, molybdenum and auxiliary elements are first prepared. Strong covalent bonds are formed between silicon and molybdenum and between silicon and auxiliary elements in the third substance. Then, the first substance and the third substance are mixed and calcined to couple the molybdenum in the third substance with the vanadium occupying the active sites on the surface of the first substance, thereby giving the catalyst both good strength and catalytic activity.

[0039] It should be noted that if a third substance is not prepared, and instead a solution containing a silicon source, a solution containing a molybdenum source, and a solution containing auxiliary elements are added to the first substance in a specific order, and a catalyst is prepared through impregnation, calcination, or other processes, it is impossible to guarantee that strong covalent bonds are formed between silicon and molybdenum and / or between silicon and auxiliary elements, thus limiting the improvement in catalyst strength.

[0040] Specifically, in step S1, the preparation method of the first solution includes, for example, the step of dispersing a titanium source and a tungsten source in a solvent to obtain the first solution. The titanium source and the tungsten source can be dispersed in the solvent sequentially, for example, titanium source first, then tungsten source, or tungsten source first, then titanium source, or both titanium and tungsten sources can be dispersed simultaneously in the solvent. In some embodiments of this application, the solvent of the first solution includes water, for example, water is the solvent of the first solution. It is understood that the first solution may also include one or more additives that can promote the dissolution of the titanium source and / or tungsten source. In some embodiments of this application, the titanium source and the tungsten source are dispersed in the solvent by stirring.

[0041] The titanium source and tungsten source can be substances commonly used in the art. In some embodiments of this application, the titanium source is selected from one or more of titanium dioxide and titanium oxides, and / or the tungsten source is selected from one or more of tungsten oxides and tungsten-containing salts. The titanium oxides include, but are not limited to, TiO2; the tungsten oxides include, but are not limited to, WO3; and the tungsten-containing salts include, but are not limited to, one or more of ammonium tungstate, ammonium metatungstate, and ammonium paratungstate.

[0042] In some embodiments of this application, the molar ratio of titanium in the titanium source to tungsten in the tungsten source in the first solution is 1:(0.01 to 0.06), for example, 1:0.01, 1:0.02, 1:0.03, 1:0.04, 1:0.05, 1:0.06, or any value between any two of the aforementioned ratios. Under the premise that the molar amount of titanium in the first solution is constant, if the molar amount of tungsten in the first solution is small, the resulting catalyst will have a small molar amount of tungsten, resulting in limited high-temperature (e.g., 300℃ to 400℃) activity. If the molar amount of tungsten in the first solution is large, the tungsten will preempt the active sites of vanadium (the main active element), resulting in limited mid-to-low-temperature activity (e.g., 160℃ to 300℃) of the resulting catalyst, and also increasing the manufacturing cost of the catalyst.

[0043] Continuing with step S1, the preparation method of the second solution includes, for example, the step of dispersing a vanadium source and oxalic acid in a solvent to obtain the second solution. The vanadium source and oxalic acid can be dispersed in the solvent sequentially, for example, vanadium source first, then oxalic acid, or oxalic acid first, then vanadium source, or both can be dispersed simultaneously in the solvent. Oxalic acid can form a complex with the vanadium element in the vanadium source, promoting the dissolution of the vanadium source and significantly enhancing the activity of the catalyst's active intermediate. In some embodiments of this application, the vanadium source and oxalic acid are dispersed in the solvent by stirring.

[0044] In some embodiments of this application, the solvent of the second solution includes water, for example, water is the solvent of the second solution. It is understood that the second solution may also include one or more aids that promote the dissolution of the vanadium source.

[0045] The vanadium source can be a substance commonly used in the art. In some embodiments of this application, the vanadium source is selected from one or more of vanadium oxides and vanadium-containing salts. Among them, vanadium oxides include, but are not limited to, V2O5, and vanadium-containing salts include, but are not limited to, one or more of ammonium metavanadate, vanadium tetrachloride, vanadium oxyacetylacetonate, vanadium oxysulfate, and vanadium oxyoxalate.

[0046] In some embodiments of this application, the molar ratio of vanadium to oxalic acid in the vanadium source in the second solution is 1:(0.3–1.8), for example, 1:0.3, 1:0.5, 1:0.8, 1:1, 1:1.2, 1:1.5, 1:8, or any two of the aforementioned ratios. Assuming a constant molar amount of vanadium in the second solution, if the oxalic acid content in the second solution is too low, the promotion of the activity of the catalyst intermediate will be limited; if the oxalic acid content in the second solution is too high, the pH value of the second solution will be too low, resulting in a limited improvement in the strength of the prepared catalyst.

[0047] In some embodiments of this application, the pH of the second solution is 0.73 to 4.74, for example, it can be 0.73, 1, 2, 3, 4, 4.74 or any value between the two aforementioned values.

[0048] In step S1, the mixing of the first solution and the second solution can be achieved by: adding the second solution to the first solution, adding the first solution to the second solution, or mixing the first solution and the second solution together. Specifically, adding the second solution to the first solution can be achieved by adding the second solution dropwise to the first solution at a uniform rate; similarly, adding the first solution to the second solution can be achieved by adding the first solution dropwise to the second solution at a uniform rate.

[0049] In step S1, the method for removing the solvent from the mixture includes, but is not limited to, one or more of heating evaporation and vacuum drying. In at least one embodiment of this application, the removal of the solvent from the mixture includes the step of: placing the mixture at 65°C to 85°C and stirring until the solvent is completely evaporated.

[0050] To further balance the strength and catalytic activity of the catalyst, in some embodiments of this application, the molar ratio of titanium to vanadium in the first substance is 1:(0.01~0.92), for example, it can be 1:0.01, 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:0.92, or any value between the aforementioned two ratios. If the content of titanium in the first substance is too low, the improvement in catalyst strength will be limited; if the content of vanadium in the first substance is too low, the improvement in low-temperature activity of the catalyst will be limited.

[0051] In step S2, the auxiliary element in the auxiliary element source is selected from one or more of zirconium, magnesium, scandium, titanium, niobium, iron, and germanium. The preparation method of the third solution includes, for example, the steps of dispersing a silicon source, a molybdenum source, and an auxiliary element source in a solvent to obtain the third solution. The silicon source, molybdenum source, and auxiliary element source can be dispersed in the solvent sequentially in a specific order, or at least two of the silicon source, molybdenum source, and auxiliary element source can be dispersed simultaneously in the solvent. In some embodiments of this application, the solvent of the third solution includes water, for example, water is the solvent of the third solution. It is understood that the third solution may also include one or more aids that can promote the dissolution of at least one of the silicon source, molybdenum source, and auxiliary element source. In some embodiments of this application, the silicon source, molybdenum source, and auxiliary element source are dispersed in the solvent by stirring.

[0052] The silicon source, molybdenum source, and auxiliary element source can all be substances commonly used in the art. In some embodiments of this application, the silicon source is selected from one or more of SiO2 and silica sol; and / or, the molybdenum source is selected from one or more of molybdenum oxides and molybdenum-containing salts, wherein the molybdenum oxides include, but are not limited to, molybdenum trioxide, and the molybdenum-containing salts include, but are not limited to, one or more of ammonium dimolybdate, ammonium tetramolybdate, ammonium heptamolybdate, and ammonium octamolybdate; and / or, the auxiliary element source is selected from one or more of the oxides of auxiliary elements and salts containing auxiliary elements.

[0053] To reduce the difficulty of substituting some Si atoms with auxiliary elements and thus improve the modification effect of the auxiliary elements, in some embodiments of this application, the auxiliary element source includes one or more of zirconium oxides, zirconium-containing salts, magnesium-containing salts, scandium-containing salts, titanium-containing salts, niobium-containing salts, iron-containing salts, and germanium-containing salts; wherein, the zirconium oxide can be, for example, zirconium dioxide, and the zirconium-containing salt cation includes Zr.4+ Magnesium-containing cations include Mg 2+ Scandium-containing cations include Sc 3+ The cations containing titanium salts include Ti 3+ Niobium-containing cations include Nb 2+ The cations of iron salts include Fe. 3+ The cations containing germanium salts include Ge 2+ Due to Mg 2+ ,Sc 3+ Ti 3+ 、Nb 2+ Fe 3+ and Ge 2+ respectively with Zr 4+ The radius difference is small (e.g., the ionic radius difference is less than ±20%), so it can be expected that the auxiliary element source will be Zr cation. 4+ The salts were replaced with Mg cations respectively. 2+ The salt and cation are Sc 3+ The salt and cation are Ti 3+ The salt and cation are Nb 2+ The salt and cation are Fe 3+ The salt or cation is Ge 2+ Salts can achieve similar modification effects.

[0054] Furthermore, the anions in the zirconium-containing, magnesium-containing, scandium-containing, titanium-containing, niobium-containing, iron-containing, and germanium-containing salts are independently selected from one or more of the following: sulfate ions, hydrogen sulfate ions, hydrogen phosphate ions, dihydrogen phosphate ions, carbonate ions, bicarbonate ions, nitrate ions, organic acid anions, and halide ions. Among these, organic acid anions include, but are not limited to, oxalate ions or acetate ions, and halide ions include, but are not limited to, Cl- ions. - ,Br - Or I - Zirconium salts include, but are not limited to, one or more of zirconium nitrate, zirconium sulfate, and zirconium chloride; magnesium salts include, but are not limited to, one or more of magnesium nitrate, magnesium sulfate, and magnesium chloride; scandium salts include, but are not limited to, one or more of scandium sulfate and scandium nitrate; titanium salts include, but are not limited to, one or more of Ti(NO3)3, Ti2(CO3)3, and TiBr3; niobium salts include, but are not limited to, one or more of niobium powder, niobium pentachloride, ammonium oxalate hydrate of niobate, and niobium oxalate hydrate; iron salts include, but are not limited to, one or more of ferric chloride, ferric sulfate, and ferric nitrate; germanium salts include, but are not limited to, germanium powder.

[0055] In some embodiments of this application, the solvent of the third solution includes water, for example, water is the solvent of the third solution. It is understood that the third solution may also include one or more aids that promote the dissolution of at least one of the silicon source, molybdenum source, and auxiliary element source.

[0056] In step S2, the method for removing the solvent from the third solution includes, but is not limited to, one or more of heating evaporation and vacuum drying. In at least one embodiment of this application, the removal of the solvent from the third solution includes the step of: placing the third solution at 65°C to 85°C and stirring until the solvent is completely evaporated.

[0057] To further improve both the strength and catalytic activity of the catalyst, in some embodiments of this application, the molar ratio of molybdenum, silicon, and auxiliary elements in the third solution is molybdenum:silicon:auxiliary element = 1:(0.4-25):(0.01-0.4). The molar ratio of molybdenum to silicon is, for example, 1:0.4, 1:0.5, 1:1, 1:2, 1:5, 1:10, 1:15, 1:20, 1:25, or any two of the aforementioned ratios; the molar ratio of molybdenum to auxiliary elements is, for example, 1:0.01, 1:0.05, 1:0.08, 1:0.1, 1:0.2, 1:0.3, 1:0.4, or any two of the aforementioned ratios.

[0058] In step S2, the purpose of the first calcination treatment is to induce a solid-state reaction between the silicon source and the molybdenum source to generate MoSi unit cells containing strong Mo-Si covalent bonds. Furthermore, auxiliary elements will replace some of the Si atoms in the MoSi unit cells, preventing the auxiliary elements from preferentially combining with vanadium and tungsten elements in subsequent processes. This facilitates the substitution of some Si atoms by the auxiliary elements, resulting in a high-strength third substance. It should be noted that the first calcination treatment is carried out in an oxygen-isolated environment, such as in an inert gas atmosphere. Inert gases include, but are not limited to, one or more of nitrogen, helium, neon, argon, krypton, and xenon. This is because the first calcination process generates oxygen vacancies in the material, facilitating the substitution of silicon elements to form MoSi unit cells containing strong Mo-Si covalent bonds.

[0059] In some embodiments of this application, the temperature of the first calcination treatment is 250°C to 650°C, for example, it can be 250°C, 280°C, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C or any value between any two of the aforementioned values; the time of the first calcination treatment is 1h to 7h, for example, 1h, 2h, 3h, 4h, 5h, 6h, 7h or any value between any two of the aforementioned values.

[0060] In some embodiments of this application, the heating rate from room temperature to the first calcination treatment temperature is 1.0℃ to 5.0℃, for example, it can be 1.0℃, 1.5℃, 2.0℃, 2.5℃, 3.0℃, 3.3℃, ​​3.5℃, 4.0℃, 4.5℃, 5.0℃ or any value between any two of the aforementioned temperature values.

[0061] To improve the uniformity of the first calcination treatment and facilitate control of crystal growth particle size during the first calcination treatment, thereby facilitating catalyst size control, in some embodiments of this application, after the step of obtaining the solid second substance and before the step of performing the first calcination treatment on the second substance, the catalyst preparation method further includes the step of: grinding the obtained solid second substance to refine the raw material; the first calcination treatment on the second substance refers to performing the first calcination treatment on the second substance after the grinding treatment. The particle size distribution range of the second substance after the grinding treatment is, for example, 2 nm to 30 nm, with a maximum abundance of 5 nm to 10 nm.

[0062] In step S3, the purpose of the second calcination is to induce a solid-state reaction between the first and third substances to obtain a catalyst with both a wide operating temperature range and high strength. It is understood that, to improve the uniformity of the second calcination process and facilitate control of crystal growth particle size during the second calcination, thereby enabling further control of the catalyst size, the first and third substances can be mixed and ground, and then the resulting mixture can be subjected to the second calcination process. It should be noted that the second calcination process can be carried out in an oxygen-containing gas atmosphere, which can be an oxygen atmosphere or an air atmosphere, or it can be carried out in an inert gas atmosphere.

[0063] In some embodiments of this application, the temperature of the second calcination treatment is 250°C to 650°C, for example, it can be 250°C, 280°C, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C or any value between any two of the aforementioned values; the time of the second calcination treatment is 1h to 7h, for example, 1h, 2h, 3h, 4h, 5h, 6h, 7h or any value between any two of the aforementioned values.

[0064] In some embodiments of this application, the heating rate from room temperature to the second calcination treatment temperature is 1.0℃ to 5.0℃, for example, it can be 1.0℃, 1.5℃, 2.0℃, 2.5℃, 3.0℃, 3.3℃, ​​3.5℃, 4.0℃, 4.5℃, 5.0℃ or any value between any two of the aforementioned temperature values.

[0065] To further improve the strength and processability of the catalyst, in some embodiments of this application, the fourth substance further includes a binder, the mass of which accounts for 1% to 10% of the total mass of the fourth substance, for example, 1%, 3%, 5%, 8%, 10%, or any value between the two aforementioned percentages; the mixing of the first and third substances to obtain the fourth substance includes the steps of: mixing and grinding the first and third substances to obtain a first mixture, then mixing the first mixture with the binder to obtain a second mixture, and then molding the second mixture to obtain the fourth substance. The binder includes, but is not limited to, one or more of hydroxypropyl methylcellulose, starch, carboxymethyl cellulose, polyvinyl alcohol, monoethanolamine, polyoxyethylene, glycerol, tung oil, stearic acid, polyacrylamide, polyethylene glycol, and diatomaceous earth. It should be noted that the binder may degrade during the calcination process.

[0066] To further improve the mechanical strength of the catalyst, in some embodiments of this application, the manufacturing process includes the steps of: mixing a second mixture with water to obtain a third mixture, then extruding the third mixture, and finally drying it to obtain a fourth substance; in the step of mixing the second mixture with water to obtain the third mixture, the mass of water is 15% to 60% of the mass of the second mixture, for example, 15%, 20%, 30%, 40%, 50%, 60%, or any two of the aforementioned values. By controlling the ratio of the second mixture to water, the extrusion pressure during the molding process is adjusted. When the mass of water is 15% to 60% of the mass of the second mixture, the extrusion pressure is increased while ensuring continuous strip extrusion, thereby improving the mechanical strength of the catalyst.

[0067] It should be noted that for any of the catalysts described above, or the catalysts prepared by any of the methods described above, titanium mainly exists in the form of TiO2, vanadium mainly exists in the form of V2O5, tungsten mainly exists in the form of WO3, silicon mainly exists in the form of SiO2, molybdenum mainly exists in the form of MoO3, and auxiliary elements mainly exist in the form of oxides. Furthermore, each element may also exist in the catalyst in the form of oxides with other valence states, but the content of these oxides with other valence states is relatively small. For example, in the catalyst, vanadium may also exist in the catalyst in one or more forms of VO, VO2, and V2O3.

[0068] This application also provides the application of any of the catalysts described above, or the catalysts prepared by any of the preparation methods described above, in flue gas denitrification. The catalysts described above, or the catalysts prepared by the preparation methods described above, are at least used to remove NO from the flue gas. x Or reduce NO in flue gas xThe content of the flue gas. The sources of the flue gas include, but are not limited to, boilers, steel sintering machines, waste incinerators, solid waste co-firing furnaces, cement rotary kilns, or iron and zinc extraction rotary kilns.

[0069] In some embodiments of this application, the water content in the flue gas is 5.0 VOL% to 15.0 VOL%, meaning that the volume of water vapor accounts for 5.0% to 15.0% of the total flue gas volume; and / or, the concentration of NH3 is 500 ppm to 1200 ppm; and / or, the concentration of SO2 is 200 ppm to 800 ppm; and / or, the concentration of O2 is 30000 ppm to 100000 ppm; and / or, the concentration of NO... x The concentration is 500ppm to 1200ppm.

[0070] In some embodiments of this application, the catalyst or the catalyst prepared by the preparation method has an activity temperature of 160°C to 400°C, for example, it can be 160°C, 180°C, 200°C, 250°C, 300°C, 320°C, 350°C, 400°C or any value between the two aforementioned values.

[0071] In some embodiments of this application, the application of any of the catalysts described above, or the catalysts prepared by any of the methods described above, in flue gas denitrification includes the steps of: fixing the catalyst in a gas-solid fixed-bed reactor; and introducing flue gas to perform denitrification treatment on the flue gas. The gas-solid fixed-bed reactor includes, but is not limited to, laboratory-grade or industrial-grade gas-solid fixed-bed reactors, such as SCR reactors.

[0072] The technical solutions and effects of this application will be described in detail below through specific embodiments, comparative examples and experimental examples. The following embodiments are only some embodiments of this application and are not intended to limit this application.

[0073] Example 1

[0074] This embodiment provides a catalyst and its preparation method. The catalyst includes a matrix and an outer layer, with the outer layer covering at least a portion of the matrix. The matrix is ​​composed of TiO2, V2O5, and WO3, and the outer layer is composed of SiO2, MoO3, and ZrO2. Calculated by mass percentage, the catalyst comprises 79.71% TiO2, 2.23% V2O5, 3.13% WO3, 7.23% SiO2, 4.07% MoO3, and 0.1% ZrO2.

[0075] The catalyst preparation method in this embodiment includes the following steps:

[0076] S1.1 Providing the first solution: Take 8.3g of titanium dioxide and 0.36g of ammonium metatungstate in a beaker, add 32mL of water to the beaker, and stir at 80℃ to fully dissolve the titanium dioxide and ammonium metatungstate in the water to obtain the first solution; Providing the second solution: Take 0.30g of ammonium metavanadate and 0.36g of oxalic acid in another beaker, add 24mL of water to the beaker, and stir at 80℃ for 30min to fully dissolve the ammonium metavanadate and oxalic acid in the water. The color of the solution in the beaker changes from yellow, orange, green and dark green with stirring time. When the color is green, start collecting the liquid and stop collecting the liquid when the color turns dark green. The collected liquid is the second solution; Then, titrate the second solution into the first solution at a uniform rate, mix well to obtain a mixed solution, and stir the mixed solution at 80℃ until the solvent evaporates to obtain a solid first substance, which contains titanium, vanadium and tungsten elements;

[0077] S1.2, Providing a third solution: Take 0.048g of Zr(NO3)4·5H2O, 0.50g of ammonium heptamolybdate tetrahydrate (CAS No. 12054-85-2, molecular weight 1235.85) and 0.71g of nano-silica and place them in a beaker. Add 10mL of water to the beaker and stir at 80℃ to fully dissolve Zr(NO3)4·5H2O, ammonium heptamolybdate and nano-silica in the water. Continue stirring at 80℃ until the solvent evaporates to obtain a solid second substance. Grind the second substance and then place it in a tube furnace. In an Ar atmosphere, raise the furnace temperature from room temperature to 420℃ at a heating rate of 3.5℃ / min, and then maintain it at 420℃ for 4h to obtain a third substance containing silicon, molybdenum and auxiliary elements.

[0078] S1.3. The first substance and the third substance are mixed and ground at a mass ratio of 9:1 to obtain a first mixture. Then, the first mixture and carboxymethyl cellulose are mixed at a mass ratio of 1:0.03 to obtain a dry powder second mixture. The second mixture is mixed with water to obtain a third mixture (the mass of water is 33% of the mass of the second mixture). The third mixture is then extruded into strips twice and dried at 65°C for 10 hours to obtain a fourth substance. Subsequently, the fourth substance is placed in a calcining furnace, and the furnace temperature is raised from room temperature to 520°C at a heating rate of 2°C / min in an air atmosphere. The temperature is then maintained at 520°C for 6 hours to obtain a catalyst.

[0079] The morphology of the catalysts prepared by the above method was observed using transmission electron microscopy (TEM). Figure 2 The morphology of the catalyst prepared by the above method is shown. The catalyst has good lattice fringes, is uniformly dispersed, and has a particle size of approximately 3 nm to 5 nm. Inductively coupled plasma mass spectrometry (ICP-MS) and analysis of the elemental composition and content of the catalyst prepared in step S1.3 were performed. The content of each element was not significantly different from the content set in the preparation process, indicating that there was essentially no element loss during the preparation process. X-ray diffraction (XRD) was used to analyze the catalyst prepared by the above method, and the XRD pattern is shown below. Figure 3 As shown.

[0080] Example 2

[0081] This embodiment provides a catalyst and its preparation method. Compared with the catalyst preparation method in Example 1, the difference in the catalyst preparation method in this embodiment is that the mass of Zr(NO3)4·5H2O in step S1.2 is replaced with "0.012g".

[0082] Example 3

[0083] This embodiment provides a catalyst and its preparation method. Compared with the catalyst preparation method in Example 1, the difference in the catalyst preparation method in this embodiment is that the mass of Zr(NO3)4·5H2O in step S1.2 is replaced with "0.48g".

[0084] Example 4

[0085] This embodiment provides a catalyst and its preparation method. Compared with the catalyst preparation method in Example 1, the difference in the catalyst preparation method in this embodiment is that the mass of Zr(NO3)4·5H2O in step S1.2 is replaced with "0.24g".

[0086] Example 5

[0087] This embodiment provides a catalyst and its preparation method. Compared with the catalyst preparation method in Example 1, the difference in the catalyst preparation method in this embodiment is that the mass of SiO2 in step S1.2 is replaced with "0.08g".

[0088] Example 6

[0089] This embodiment provides a catalyst and its preparation method. Compared with the catalyst preparation method in Example 1, the difference in the catalyst preparation method in this embodiment is that the mass of ammonium heptamolybdate in step S1.2 is replaced with "0.22g", and the mass of SiO2 in step S1.2 is replaced with "1.9g".

[0090] Example 7

[0091] This embodiment provides a catalyst and its preparation method. Compared with the catalyst preparation method in Example 1, the difference in the catalyst preparation method in this embodiment is that the mass of SiO2 in step S1.2 is replaced with "1.37g".

[0092] Example 8

[0093] This embodiment provides a catalyst and its preparation method. Compared with the catalyst preparation method in Example 1, the difference in the catalyst preparation method in this embodiment is that the mass of ammonium heptamolybdate in step S1.2 is replaced with "0.294g", and the mass of SiO2 in step S1.2 is replaced with "1.60g".

[0094] Example 9

[0095] This embodiment provides a catalyst and its preparation method. Compared with the catalyst preparation method in Example 1, the difference in the catalyst preparation method in this embodiment is that the mass of Zr(NO3)4·5H2O in step S1.2 is replaced with "0.012g", and the mass of SiO2 in step S1.2 is replaced with "1.90g".

[0096] Example 10

[0097] This embodiment provides a catalyst and its preparation method. Compared with the catalyst preparation method in Example 1, the difference in the catalyst preparation method in this embodiment is that the mass of Zr(NO3)4·5H2O in step S1.2 is replaced with "0.48g", and the mass of SiO2 in step S1.2 is replaced with "0.08g".

[0098] Example 11

[0099] This embodiment provides a catalyst and its preparation method. Compared with the catalyst preparation method in Example 1, the difference in the catalyst preparation method in this embodiment is that the mass of Zr(NO3)4·5H2O in step S1.2 is replaced with "0.24g", and the mass of SiO2 in step S1.2 is replaced with "1.00g".

[0100] Example 12

[0101] This embodiment provides a catalyst and its preparation method. Compared with the catalyst preparation method in Example 1, the difference in the catalyst preparation method in this embodiment is that the mass of ammonium heptamolybdate in step S1.2 is replaced with "0.25g".

[0102] Example 13

[0103] This embodiment provides a catalyst and its preparation method. Compared with the catalyst preparation method in Example 1, the difference in the catalyst preparation method in this embodiment is that the mass of ammonium heptamolybdate in step S1.2 is replaced with "0.75g".

[0104] Example 14

[0105] This embodiment provides a catalyst and its preparation method. Compared with the catalyst preparation method in Example 1, the difference in the catalyst preparation method in this embodiment is that the mass of ammonium heptamolybdate in step S1.2 is replaced with "1.0g".

[0106] Example 15

[0107] This embodiment provides a catalyst and its preparation method. Compared with the catalyst preparation method in Example 1, the difference in the catalyst preparation method in this embodiment is that the mass of ammonium heptamolybdate in step S1.2 is replaced with "1.0g", the mass of Zr(NO3)4·5H2O in step S1.2 is replaced with "0.012g", and the mass of SiO2 in step S1.2 is replaced with "1.90g".

[0108] Example 16

[0109] This embodiment provides a catalyst and its preparation method. Compared with the catalyst preparation method in Example 1, the difference in the catalyst preparation method in this embodiment is that the mass of ammonium heptamolybdate in step S1.2 is replaced with "0.25g", the mass of Zr(NO3)4·5H2O in step S1.2 is replaced with "0.48g", and the mass of SiO2 in step S1.2 is replaced with "0.08g".

[0110] Example 17

[0111] This embodiment provides a catalyst and its preparation method. Compared with the catalyst preparation method in Example 1, the difference in the catalyst preparation method in this embodiment is that the mass of ammonium heptamolybdate in step S1.2 is replaced with "0.75g", the mass of Zr(NO3)4·5H2O in step S1.2 is replaced with "0.072g", and the mass of SiO2 in step S1.2 is replaced with "0.8g".

[0112] Example 18

[0113] This embodiment provides a catalyst and its preparation method. Compared with the catalyst preparation method in Example 1, the difference in the catalyst preparation method in this embodiment is that the phrase "heating the furnace temperature from room temperature to 420°C at a heating rate of 3.5°C / min" in step S1.2 is replaced with "heating the furnace temperature from room temperature to 280°C at a heating rate of 3.5°C / min".

[0114] Example 19

[0115] This embodiment provides a catalyst and its preparation method. Compared with the catalyst preparation method in Example 1, the difference in the catalyst preparation method in this embodiment is that the phrase "heating the furnace temperature from room temperature to 420°C at a heating rate of 3.5°C / min" in step S1.2 is replaced with "heating the furnace temperature from room temperature to 250°C at a heating rate of 3.5°C / min".

[0116] Example 20

[0117] This embodiment provides a catalyst and its preparation method. Compared with the catalyst preparation method in Example 1, the difference in the catalyst preparation method in this embodiment is that the phrase "heating the furnace temperature from room temperature to 420°C at a heating rate of 3.5°C / min" in step S1.2 is replaced with "heating the furnace temperature from room temperature to 600°C at a heating rate of 3.5°C / min".

[0118] Example 21

[0119] This embodiment provides a catalyst and its preparation method. Compared with the catalyst preparation method in Example 1, the difference in the catalyst preparation method in this embodiment is that the phrase "heating the furnace temperature from room temperature to 420°C at a heating rate of 3.5°C / min" in step S1.2 is replaced with "heating the furnace temperature from room temperature to 650°C at a heating rate of 3.5°C / min".

[0120] Example 22

[0121] This embodiment provides a catalyst and its preparation method. Compared with the catalyst preparation method in Example 1, the difference in the catalyst preparation method in this embodiment is that the phrase "heating the furnace temperature from room temperature to 420°C at a heating rate of 3.5°C / min" in step S1.2 is replaced with "heating the furnace temperature from room temperature to 420°C at a heating rate of 1.5°C / min".

[0122] Example 23

[0123] This embodiment provides a catalyst and its preparation method. Compared with the catalyst preparation method in Example 1, the difference in the catalyst preparation method in this embodiment is that the phrase "heating the furnace temperature from room temperature to 420°C at a heating rate of 3.5°C / min" in step S1.2 is replaced with "heating the furnace temperature from room temperature to 420°C at a heating rate of 4.5°C / min".

[0124] Example 24

[0125] This embodiment provides a catalyst and its preparation method. Compared with the catalyst preparation method in Example 1, the difference in the catalyst preparation method in this embodiment is that "holding at 420℃ for 4h" in step S1.2 is replaced with "holding at 420℃ for 2h".

[0126] Example 25

[0127] This embodiment provides a catalyst and its preparation method. Compared with the catalyst preparation method in Example 1, the difference in the catalyst preparation method in this embodiment is that "holding at 420℃ for 4h" in step S1.2 is replaced with "holding at 420℃ for 6h".

[0128] Example 26

[0129] This embodiment provides a catalyst and its preparation method. Compared with the catalyst preparation method in Example 1, the difference in the catalyst preparation method in this embodiment is that Zr(NO3)4·5H2O in step S1.2 is replaced with "magnesium chloride".

[0130] Comparative Example 1

[0131] This comparative example provides a catalyst and its preparation method. The catalyst is a V2O5-WO3 / TiO2 system catalyst. The preparation method of the catalyst can be found in the literature (link: https: / / dx.doi.org / 10.1021 / acs.iecr.0c00327). The preparation method of the catalyst includes the following steps:

[0132] S10. Providing a support precursor: In a beaker, 0.064 mol of tetrabutyl titanate and 0.128 mol of acetylacetone are mixed, and then 50 mL of ethanol is added to react and obtain the support.

[0133] S20, 0.30g of ammonium metavanadate and 0.104g of (NH4)6W7O 24 • Dissolve 6H2O in 50 mL of deionized water and stir in an 80 °C water bath for 2 h to obtain a mixed solution;

[0134] S30. The support obtained in step S10 is immersed in the mixture obtained in step S20 for 3 hours, then dried at 80°C, and then placed in a calcining furnace. In an air atmosphere, the furnace temperature is raised from room temperature to 500°C at a heating rate of 2°C / min, and held at 500°C for 2 hours to obtain the catalyst.

[0135] Comparative Example 2

[0136] This comparative example provides a catalyst and its preparation method. Compared with the catalyst in Example 1, the catalyst in this comparative example differs in that it does not have an outer layer.

[0137] Compared to the catalyst preparation method in Example 1, the difference in the catalyst preparation method in this comparative example is that step S1.2 is omitted, and step S1.3 is replaced by "mixing the first substance and carboxymethyl cellulose at a mass ratio of 1:0.03 to obtain a dry powder mixture, mixing the dry powder mixture with water to obtain a first material (the mass of water is 33% of the mass of the second mixture), then extruding the first material into strips twice, and then drying it at 65°C for 10 hours to obtain a second material; subsequently, placing the second material in a calcining furnace, and in an air atmosphere, raising the furnace temperature from room temperature to 520°C at a heating rate of 2°C / min, and then maintaining it at 520°C for 6 hours to obtain the catalyst." The catalyst prepared by the above method was analyzed using X-ray diffraction (XRD) technology, and the XRD pattern is shown below. Figure 3 As shown.

[0138] Comparative Example 3

[0139] This comparative example provides a catalyst and its preparation method. Compared with the catalyst in Example 1, the catalyst in this comparative example differs in that it does not contain silicon or zirconium.

[0140] Compared with the catalyst preparation method in Example 1, the difference in the catalyst preparation method in this comparative example is that the step S1.2, "take 0.048g of Zr(NO3)4·5H2O, 0.50g of ammonium heptamolybdate and 0.71g of nano silica and put them in a beaker", is replaced with "take 0.50g of ammonium heptamolybdate".

[0141] Comparative Example 4

[0142] This comparative example provides a catalyst and its preparation method. Compared with the catalyst in Example 1, the catalyst in this comparative example differs in that it does not contain molybdenum and zirconium.

[0143] Compared with the catalyst preparation method in Example 1, the difference in the catalyst preparation method in this comparative example is that the step S1.2, "take 0.048g of Zr(NO3)4·5H2O, 0.50g of ammonium heptamolybdate and 0.71g of nano silica and place them in a beaker", is replaced with "take 0.71g of nano silica and place it in a beaker".

[0144] Comparative Example 5

[0145] This comparative example provides a catalyst and its preparation method. Compared with the catalyst in Example 1, the catalyst in this comparative example differs in that it does not contain molybdenum or silicon.

[0146] Compared with the catalyst preparation method in Example 1, the difference in the catalyst preparation method in this comparative example is that the step S1.2, "take 0.048g of Zr(NO3)4·5H2O, 0.50g of ammonium heptamolybdate and 0.71g of nano silica and put them into a beaker", is replaced with "take 0.048g of Zr(NO3)4·5H2O and put them into a beaker".

[0147] Experimental Example 1

[0148] The specific surface area, average pore size, and average pore volume of the catalysts in Example 1, Comparative Examples 2 to 5 were characterized using a Micro ASAP 2020 instrument. The results are shown in Table 1 below.

[0149] Table 1

[0150]

[0151] From Table 1 and Figure 4It can be seen that, compared with the catalysts in Comparative Examples 2 to 5, the catalyst in Example 1 has better overall performance, specifically: the catalyst in Example 1 has a higher specific surface area, a smaller average particle size, and good pore abundance. Compared with the catalyst in Comparative Example 2, the specific surface area and pore abundance of Comparative Example 3 are significantly increased, indicating that modifying the matrix with Mo alone can improve the specific surface area and pore abundance of the catalyst, thereby improving the catalyst activity, but may lead to a decrease in catalyst strength. Compared with the catalyst in Comparative Example 2, the catalyst in Comparative Example 4 shows smaller changes in specific surface area, pore abundance, and average particle size, indicating that modifying the matrix with Si alone has a smaller impact on catalyst activity, but modifying the matrix with Si alone can improve the catalyst strength to a certain extent. Compared to the catalyst in Comparative Example 2, the catalyst in Comparative Example 4 showed little change in specific surface area and pore abundance, but its average particle size was significantly reduced. This indicates that modifying the matrix with Zr alone can effectively reduce the average particle size of the catalyst. The catalyst modified with Si, Zr, and Mo can drastically reduce pore volume and particle size, while increasing specific surface area. The reduction in particle size can effectively increase specific surface area, and the reduction in pore volume can enhance the compressive strength of the catalyst to a certain extent.

[0152] Experiment Example 2

[0153] The catalysts in Example 1, Comparative Example 3, and Comparative Example 5 were subjected to low-temperature average activity and mechanical strength tests, respectively. The method for detecting low-temperature average activity included the following steps: setting a test temperature window of 180℃ to 280℃ for each catalyst sample, taking a point every 20℃, stabilizing each temperature point for 30 minutes, and obtaining NO. x The concentration value of NO was obtained at each temperature point. x The conversion rate, and the NO at each temperature point x The conversion rates were summed and then divided by the total number of tested temperature points to calculate the effect of each catalyst on NO at temperatures ranging from 180℃ to 280℃. x The average conversion rate (E,%) was as follows: NO concentration was 1000 ppm, NH3 concentration was 1000 ppm, SO2 concentration was 500 ppm, O2 volume accounted for 3% of the total flue gas volume, and H2O was 10 vol%.

[0154] The mechanical strength test method includes the following steps: the prepared catalyst is cut into short strips (0.5cm to 1cm in length), and then placed in a strength tester for pressure testing. Each catalyst sample is tested ten times, the highest and lowest values ​​are removed, and then the average pressure value is calculated. Mechanical strength (N / cm) = average pressure value (N) / length of catalyst sample (cm).

[0155] The test results are shown in Table 2 below:

[0156] Table 2

[0157]

[0158]

[0159] From Table 2 and Figure 5 It can be seen that the catalysts in Examples 1 to 25 have better overall performance than the catalysts in Comparative Examples 1 to 5. Taking Example 1 and Comparative Example 2 as examples, the E of the catalyst in Example 1 is 20% higher than the E1 of the catalyst in Comparative Example 2, and the mechanical strength of the catalyst in Example 1 is 50% higher than that of the catalyst in Comparative Example 2.

[0160] This demonstrates that Mo, Zr, and Si all have beneficial effects on the catalyst activity, with the degree of activity being: Mo > Zr > Si. However, the intensity shows the opposite trend; that is, the higher the pore abundance of the catalyst, the larger the usable internal space, but the lower the intensity. To balance the catalyst activity and intensity, in the catalyst of this application embodiment, silicon, molybdenum, and auxiliary elements are distributed on the surface of the matrix. Strong Mo-Si covalent bonds are formed between silicon and molybdenum, thereby improving the catalyst intensity. The atomic radius of the auxiliary elements is relatively close to that of Si atoms (e.g., less than ±20%). The auxiliary elements can replace some Si atoms in the MoSi unit cell, resulting in the absence of lattice oxygen in the MoSi unit cell. This increases the proportion of metallic bonds in the unit cell, enhances the asymmetry of the unit cell structure, and thus increases the cell fracture energy, further improving the catalyst intensity. Furthermore, by introducing auxiliary elements to control the crystallite size of the catalyst, the dispersion of active sites in the catalyst is improved, exposing more active sites and thus enhancing the catalyst activity. This results in a catalyst with a wide operating temperature range (160℃~400℃).

[0161] In addition, by Figure 3 It can be seen that both Example 1 and Comparative Example 2 show TiO2 peaks. Among them, the strongest peak (~25) shifts to a higher angle, indicating that large-sized grains are doped into the TiO2 crystal phase in Example 1. This is the result of the combined effect of MoSiZr unit cells, which causes the change in TiO2 peaks and is beneficial to improving the problem of weak TiO2 substrate strength.

[0162] The catalyst, its preparation method, and its application, as provided in the embodiments of this application, have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are merely for the purpose of helping to understand the technical solutions and core ideas of this application. 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 of the technical features; and these modifications or substitutions do not cause the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A catalyst, characterized in that, The catalyst includes a matrix and an outer layer, the outer layer at least covering a portion of the matrix, the matrix including titanium, vanadium and tungsten, the outer layer including silicon, molybdenum and auxiliary elements, the auxiliary elements being selected from zirconium or magnesium; In the matrix, one of the forms in which titanium exists is TiO2, one of the forms in which vanadium exists is V2O5, and one of the forms in which tungsten exists is WO3. In the outer layer, one of the forms in which silicon exists is SiO2, one of the forms in which molybdenum exists is MoO3, and one of the forms in which the auxiliary elements exist is an oxide of the auxiliary elements; The preparation method of the catalyst includes the following steps: A first solution containing a titanium source and a tungsten source and a second solution containing a vanadium source and oxalic acid are provided. The first solution and the second solution are mixed to obtain a mixture. The solvent in the mixture is removed to obtain a solid first substance. The first substance contains titanium, vanadium and tungsten. A third solution containing a silicon source, a molybdenum source, and an auxiliary element source is provided. The solvent in the third solution is removed to obtain a solid second substance. Then, the second substance is subjected to a first calcination treatment under an inert gas atmosphere to generate a substance containing Mo. A third substance containing silicon, molybdenum, and auxiliary elements is obtained from a MoSi unit cell with strong covalent bonds of Si, wherein the auxiliary elements replace some of the Si atoms in the MoSi unit cell. as well as The first substance and the third substance are mixed to obtain a fourth substance, and the fourth substance is subjected to a second calcination treatment to obtain the catalyst.

2. The catalyst according to claim 1, characterized in that, The catalyst, calculated by mass percentage, comprises: 65%–95% TiO2, 0.5%–3.3% V2O5, 0.5%–5.4% WO3, 2.25%–19% SiO2, 0.05%–0.3% oxides of auxiliary elements, and 1.7%–17% MoO3; and / or For the auxiliary element including the zirconium element, the oxide of the auxiliary element includes ZrO2; and / or For the auxiliary element that includes the magnesium element, the oxide of the auxiliary element includes MgO.

3. The catalyst according to claim 1, characterized in that, The catalyst is spherical, and its average specific surface area is 55 m². 2 / g~83 m 2 / g, the catalyst has an average particle size of 3.2nm to 9.7nm, and an average pore volume of 0.18 cm³. 3 / g~0.94 cm 3 / g.

4. The catalyst according to claim 1, characterized in that, In the first solution, the molar ratio of titanium in the titanium source to tungsten in the tungsten source is 1:(0.01~0.06); and / or In the second solution, the molar ratio of vanadium in the vanadium source to oxalic acid is 1:(0.3–1.8), and / or the pH of the second solution is 0.73–4.74; and / or In the first substance, the molar ratio of titanium to vanadium is 1:(0.01~0.92); and / or The solvent of the first solution includes water, and / or the titanium source is selected from one or more titanium oxides and titanium-containing salts, and / or the tungsten source is selected from one or more tungsten oxides and tungsten-containing salts, and / or the vanadium source is selected from one or more vanadium oxides and vanadium-containing salts.

5. The catalyst according to claim 1, characterized in that, In the third solution, the molar ratio of molybdenum, silicon, and the auxiliary element is 1:(0.4–25):(0.01–0.4); and / or The solvent of the third solution includes water; and / or The silicon source is selected from one or more of SiO2 and silica sol, and / or the molybdenum source is selected from one or more of molybdenum oxide and molybdenum-containing salt; and / or The auxiliary element source includes one or more of zirconium oxides, zirconium-containing salts, and magnesium-containing salts; wherein the zirconium-containing salt cation includes Zr. 4+ The magnesium-containing salt cation includes Mg 2+ ; and / or After the step of obtaining the solid second substance and before the step of performing the first calcination treatment on the second substance, the preparation method further includes the steps of: grinding the obtained solid second substance; the first calcination treatment on the second substance is a first calcination treatment performed on the second substance after the grinding treatment; and / or The temperature of the first calcination treatment is 250 ℃~650 ℃, and the time of the first calcination treatment is 1 h~7 h.

6. The catalyst according to claim 1, characterized in that, In the step of mixing the first substance and the third substance to obtain the fourth substance, the molar ratio of titanium in the first substance to molybdenum in the third substance is 1:(0.01~0.16); and / or The fourth substance further includes a binder, wherein the mass of the binder accounts for 1% to 10% of the total mass of the fourth substance, and the step of mixing the first substance and the third substance to obtain the fourth substance includes the steps of: mixing and grinding the first substance and the third substance to obtain a first mixture, then mixing the first mixture and the binder to obtain a second mixture, and then manufacturing the second mixture to obtain the fourth substance; and / or The temperature of the second calcination treatment is 250 ℃~650 ℃, and the time of the second calcination treatment is 1 h~7 h.

7. The catalyst according to claim 6, characterized in that, The manufacturing process includes the steps of: mixing the second mixture with water to obtain a third mixture, then extruding the third mixture into a mold, and then drying it to obtain the fourth substance; The mass of the water is 15% to 60% of the mass of the second mixture.

8. The application of the catalyst according to any one of claims 1 to 7 in flue gas denitrification, characterized in that, The catalyst is used at least to remove NO from flue gas. x Or reduce NO in flue gas x The content of.

9. The application according to claim 8, characterized in that, The water content in the flue gas is 5.0 VOL% to 15.0 VOL%; and / or The concentration of NH3 in the flue gas is 500 ppm to 1200 ppm; and / or The concentration of SO2 in the flue gas is 200 ppm to 800 ppm; and / or The concentration of O2 in the flue gas is 30,000 ppm to 100,000 ppm; and / or NO in flue gas x The concentration is 500 ppm to 1200 ppm; and / or The catalyst described herein, or the catalyst prepared by the method described herein, has an activity temperature of 160 ℃ to 400 ℃.

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