Denitration catalyst as well as preparation method and application thereof

Abstract

The invention discloses a denitration catalyst as well as a preparation method and application thereof, and relates to the technical field of denitration catalysts. The denitration catalyst comprises a matrix and an active outer layer coating at least part of the surface of the matrix, the preparation method of the matrix comprises the following steps: S1, mixing titanium dioxide and a molecular sieve to obtain a first mixture; preparing a first mixed solution containing a phosphorus source and a first alkali source; preparing a second alkali source solution comprising a second alkali source; s2, adding a second alkali source solution into the first mixed solution to obtain a second mixed solution; s3, adding the second mixed solution into the first mixture to obtain an off-white substance, and performing drying and first calcination on the off-white substance to obtain a matrix; the first alkali source comprises at least one of hydroxide and ammonia water; the second alkali source is at least one of alkali containing carbonate and alkali containing bicarbonate. The denitration catalyst has good water resistance and sulfur poisoning resistance, and has good denitration activity and stability within the range of 160-400 DEG C.

Description

Technical Field

[0001] The present invention relates to the technical field of denitration catalysts, and in particular, to a denitration catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] Nitrogen oxides (NO x ) emitted from the combustion of fossil fuels are considered to be one of the main sources of air pollution, causing many health-related environmental problems such as the greenhouse effect, acid rain, particulate matter (PM2.5), and ozone depletion. Selective catalytic reduction (SCR) denitration is a temperature-dependent reaction and is considered to be the best method for removing NO x from various combustion products. Currently, as the load of power plants decreases, the flue gas temperature also decreases, and the flue gas temperature varies according to the power plant load. Therefore, it is very necessary to design a catalyst applicable to scenarios with variable temperatures.

[0003] The problems that need to be solved by wide-temperature catalysts are usually the activity problems of denitration catalysts below 280°C, because the activity drive in the high-temperature region (280 - 400°C) is much easier than that in the low temperature (160 - 280°C). However, in the current related technology industry, in addition to NO x gas, it also contains uneven amounts of SO2 and H2O, which will inevitably lead to a large amount of NH4HSO4 deposition on the SCR catalyst. The state of NH4HSO4 is closely related to the reaction temperature. In the range above 280°C, NH4HSO4 begins to decompose, having little impact on the stability of the catalyst itself. While in the range of 160 - 280°C, NH4HSO4 is in a hydrated state, highly adhered to the catalyst surface, having an adverse effect on the SCR reaction. The modification work of researchers in this temperature range mainly focuses on introducing elements to change the oxidizing property of the catalyst itself so as to weaken the oxidation process of SO2, thereby reducing the probability of catalyst sulfur poisoning. However, the current effect is very limited because the active lattice oxygen of the catalyst itself is very active, and the existence of oxidizing property is also the cause for driving the reaction to start. Therefore, it is impossible to develop a stable catalyst applicable to low temperature (160 - 280°C) with high water and sulfur resistance through simple doping modification. The active range of the vanadium-tungsten-titanium catalyst sold on the market currently is 300 - 400°C, which is a stable water and sulfur resistance temperature range. On this basis, modifying and developing a full-temperature catalyst is much more practical than preparing a completely new catalyst. Therefore, providing a flue gas denitration for widening the temperature window of the vanadium-tungsten-titanium catalyst to be applicable to full temperature (160 - 400°C) with water and sulfur resistance is the technical problem to be solved in this application. Summary of the Invention

[0004] The main object of the present invention is to provide a denitration catalyst, a preparation method thereof and an application thereof, so as to solve the problem of low denitration activity of the denitration catalyst at temperatures below 280 °C in the prior art.

[0005] To achieve the above object, according to the first aspect of the present invention, there is provided a denitration catalyst, which comprises a matrix and an active outer layer coated on at least a part of the surface of the matrix. The preparation method of the matrix includes:

[0006] S1, mixing titanium dioxide and molecular sieve to obtain a first mixture; preparing a first mixed solution containing a phosphorus source and a first base source; preparing a second base source solution containing a second base source;

[0007] S2, adding the second base source solution to the first mixed solution to obtain a second mixed solution;

[0008] S3, adding the second mixed solution to the first mixture to obtain an off-white substance, and drying and first calcining the off-white substance to obtain the matrix;

[0009] Wherein, the first base source is at least one of hydroxides and ammonia water; the second base source is at least one of a base containing carbonate and a base containing bicarbonate.

[0010] Further, the molecular sieve includes at least one of X-type molecular sieve, Z-type molecular sieve and Y-type molecular sieve.

[0011] Further, the phosphorus source includes at least one of phosphorus-containing oxides and phosphorus-containing salts.

[0012] Further, the mass ratio of the first base source to the second base source is (0.5 - 4):1.

[0013] Further, the mass ratio of the first base source to the phosphorus source is (0.8 - 5.5):1.

[0014] Further, using the phosphorus source, the first base source and the second base source as modifiers, the mass ratio of titanium dioxide, molecular sieve and modifier is 30:(8 - 27):(0.8 - 12).

[0015] Further, the pH value of the second mixed solution is 4 - 8.3.

[0016] Further, the first calcination includes a first heating program and a second heating program. The first heating program is: heating at a heating rate of 3 - 5 °C / min to 200 °C - 350 °C and holding for 1 - 3 h; the second heating program is: heating at a heating rate 0.2 - 0.8 times that of the first heating program to 350 °C - 500 °C and holding for 1 - 5 h.

[0017] Further, the components of the active outer layer include vanadium element, tungsten element and auxiliary elements; among them, the auxiliary elements are selected from at least one of silicon element, iron element, zirconium element, molybdenum element and lanthanum element; in the active outer layer, the existing form of vanadium element includes V2O5, and the existing form of tungsten element includes WO3; the existing form of the auxiliary element includes the oxide of the auxiliary element.

[0018] Further, the molar ratio of vanadium element to tungsten element is (0.8 - 6.5):1.

[0019] Further, the molar ratio of titanium element to auxiliary element is (15 - 75):1.

[0020] Further, in the denitration catalyst, the molar ratio of vanadium element to titanium element is 1:(45 - 115).

[0021] Further, the specific surface area of the denitration catalyst is 180 - 250 m 2 / g, the average pore diameter is 1.5 - 6.8 nm, and the average pore volume is 0.18 - 0.8 cm 3 / g.

[0022] According to the second aspect of the present invention, a preparation method of a denitration catalyst is provided, including the following steps:

[0023] S1, crushing and grinding the substrate to obtain a first solid substance;

[0024] S2, adding a vanadium source and a cosolvent into water to obtain a vanadium source solution; dissolving a tungsten source in water to obtain a tungsten source solution; adding the tungsten source solution into the vanadium source solution to obtain a third mixture;

[0025] S3, mixing an auxiliary element source, a binder, a reinforcing agent and the first solid substance to obtain a second mixture;

[0026] S4, adding the third mixture into the second mixture, stirring, extruding into a shape, drying, and performing a second calcination to obtain a denitration catalyst.

[0027] Further, the mass ratio of the binder, the auxiliary element source, the reinforcing agent and the first solid substance is (0.5 - 8):(0.5 - 2):(0.5 - 6):(25 - 40).

[0028] Further, the method of the second calcination is: heating up to 350 - 750 °C at a rate of 0.5 - 5 °C / min and holding for 2 - 7 h.

[0029] According to the third aspect of the present invention, an application of the catalyst of the first aspect of the present invention or the catalyst prepared by the preparation method of the second aspect of the present invention is provided, and the denitration catalyst is used to remove NO in flue gas x or reduce NO in flue gasx The flue gas contains NH3, NO, O2, SO2 and H2O; the concentration of NH3 in the flue gas is 40 to 1600 ppm.

[0030] Furthermore, the concentration of SO2 in the flue gas is 500-1500 ppm.

[0031] Furthermore, the concentration of O2 in the flue gas is 30000-100000 ppm.

[0032] Furthermore, NO in flue gas x The concentration is 50~2000ppm.

[0033] By applying the technical solution of the present invention, a molecular sieve is introduced into the matrix of the denitration catalyst. The molecular sieve has a stronger adsorption capacity for hydrated ammonium bisulfate. The cations and protons in the molecular sieve can specifically bind to the hydrogen sulfate in the adsorbed ammonium bisulfate, causing the automatic decomposition of the ammonium bisulfate, so that the catalyst exhibits super stability. In addition, by introducing a phosphorus source, it will be introduced into the molecular sieve in the form of phosphate or its derivatives, and the phosphate and The acid sites (B acid) react to reduce The strength of the acid sites; The reduction of acid sites, part of which was originally used as Acidic site AlO4 - The structure may change to a more Lewis acidic structure (L acid), such as [AlO6] 9- Or other highly coordinated aluminum species, this conversion process makes the aluminum species that originally do not show Lewis acidity become active Lewis acid sites. Therefore, after phosphorus modification The acid is greatly weakened, and the L acid is slightly increased; the weakened Acid can reduce the adsorption of NO. The increase of L acid can drive the catalyst to adsorb more NH3 species and activate the reaction of the catalyst in the low temperature (160-280°C) area. In addition, the introduction of phosphorus will affect the pores of the matrix. The introduction of the first alkali source and the second alkali source can protect the structure of the matrix pores and ensure that the denitrification catalyst has good denitrification activity and denitrification stability in a wide temperature range (160-400°C). BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a flow chart for preparing a substrate of a denitration catalyst in one embodiment of the present application;

[0035] Figure 2 The transmission electron microscope image, mapping image and scanning electron microscope image of the denitration catalyst substrate in Example 1;

[0036] Figure 3 Pyridine IR test comparison diagrams of the denitration catalysts in Example 1 and Comparative Examples 1-2;

[0037] Figure 4 NH₃-TPD comparison diagrams of the denitration catalysts in Example 1 and Comparative Examples 1-2;

[0038] Figure 5 NOₓ-TPD comparison diagrams of the denitration catalysts in Example 1 and Comparative Examples 1-2;

[0039] Figure 6 NO conversion rate - temperature characteristic curve diagrams of the denitration catalysts in Example 1 and Comparative Examples 1-4 in flue gas containing H₂O and SO₂ at 200 °C. x Detailed implementation manners

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Those not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. Reagents or instruments not specified in the manufacturer are all conventional products that can be obtained through commercial purchase.

[0041] As described in the background art of the present invention, there is a problem in the prior art that the low-temperature denitration performance of denitration catalysts is poor. To solve the above technical problem, in a typical implementation manner of the present invention, a denitration catalyst is provided, which includes a matrix and an active outer layer coated on at least part of the surface of the matrix. The preparation method flow chart of the matrix is as Figure 1 shown, including:

[0042] S1, mixing titanium dioxide and molecular sieve to obtain a first mixture; preparing a first mixed solution containing a phosphorus source and a first base source; preparing a second base source solution containing a second base source;

[0043] S2, adding the second base source solution to the first mixed solution to obtain a second mixed solution;

[0044] S3, adding the second mixed solution to the first mixture to obtain an off-white substance, drying and first calcining the off-white substance to obtain the matrix;

[0045] Among them, the first base source is at least one of hydroxides and ammonia water, and the hydroxide is at least one of sodium hydroxide, calcium hydroxide, and potassium hydroxide; the second base source is at least one of bases containing carbonate and bicarbonate, such as at least one of calcium carbonate, sodium carbonate, and sodium bicarbonate.

[0046] ​Molecular sieves have a stronger ability to adsorb hydrated ammonium bisulfate than titanium dioxide. Compared with the traditional catalyst with titanium dioxide as the matrix, the molecular sieve introduced in the present invention can reduce the adsorption rate of hydrated ammonium bisulfate on titanium dioxide, and there is H + 、Na + NH4 + The cations can combine with the bisulfate in the adsorbed ammonium bisulfate, thereby causing the ammonium bisulfate to automatically decompose, making the catalyst exhibit super stability. In addition, the introduction of a phosphorus source can adjust the acid distribution in the catalyst. In the phosphorus modification process, phosphorus is usually present in the form of phosphate (PO4 3- ) or its derivatives are introduced into the molecular sieve phosphorus, phosphate and Acidic sites (AlO4 - Related H + ) reacts, thereby reducing The strength of the acid sites; The reduction of acid sites, part of which was originally used as The structure of the acidic site may be transformed into a more Lewis acidic structure. This transformation process makes the aluminum species that originally did not show Lewis acidity become active Lewis acid sites. Therefore, after phosphorus modification, the B acid is greatly weakened and the L acid is slightly increased; the weakened Acid can reduce the adsorption of NO, prevent it from blocking the active sites and affecting the reaction efficiency; the increase of L acid can drive the catalyst to adsorb more NH3 species, and can activate the reaction of the catalyst in the low temperature (160-280℃) area; by introducing the first alkali source and the second alkali source, the influence of the phosphorus source on the matrix pores can be reduced, ensuring the stability of the pore structure of the denitrification catalyst, and the introduction of two different bases is to introduce different anions, such as CO3 2- This is conducive to the release of gas from the matrix during the calcination process, thereby increasing the effective area of ​​the matrix and making it fluffy and soft, thereby making the denitrification catalyst have better denitrification activity in a wide temperature range.

[0047] In some embodiments, the molecular sieve includes at least one of an X-type molecular sieve, a Z-type molecular sieve, and a Y-type molecular sieve; the X-type molecular sieve is specifically 13X, 5A, etc.; the Y-type molecular sieve is specifically NAY, HY, USY, etc.; the Z-type is specifically ZSM-5, ZSM-11, etc.; in this system, the Y-type molecular sieve is preferred, and the Y-type molecular sieve has a three-dimensional pore structure and can effectively adsorb the ammonium bisulfate generated by the reaction; further preferably, the pore size of the Y-type molecular sieve is 0.5 to 1 nm. By limiting the pore size, on the one hand, sufficient space can be provided to accommodate ammonium bisulfate, and on the other hand, ammonium bisulfate can be bonded to protons in the pores to improve the removal efficiency of ammonium bisulfate.

[0048] In some embodiments, the phosphorus source includes at least one of phosphorus-containing oxides and phosphorus-containing salts, such as phosphoric acid, sodium phosphate, diammonium hydrogen phosphate, etc. The above phosphorus source can be dissolved in water, can form a uniform first mixed solution with the first base source, is easy to modify the substrate, and at the same time ensures that the substrate has a good pore structure.

[0049] In some embodiments, the mass ratio of the first base source to the phosphorus source is (0.8 to 5.5):1, and the mass ratio of the first base source to the second base source is (0.5 to 4):1.

[0050] On the premise that the content of the phosphorus source in the first mixed solution is constant, the dosage of the first base source has a great effect on adjusting the proportion of Bronsted acid in the substrate. Within the above range, the proportion of Bronsted acid is moderate, which is easy to adsorb NO, can promote the reaction, and also helps to maintain the structural stability of the denitration catalyst. Controlling the mass ratio of the first base source and the second base source within the above range can not only regulate the pH, that is, regulate the proportion of Bronsted acid, but also improve the pore structure of the denitration catalyst and improve the denitration efficiency.

[0051] In some embodiments, using the phosphorus source, the first base source, and the second base source as modifiers, the mass ratio of titanium dioxide, molecular sieve, and modifier is 30:(8 to 27):(0.8 to 12).

[0052] Controlling the mass ratio of titanium dioxide, molecular sieve, and modifier within the above range can, on the one hand, decompose ammonium bisulfate in the environment and improve the low-temperature activity of the denitration catalyst, and on the other hand, ensure good structural stability of the catalyst, so that the denitration catalyst has good catalytic activity in the range of 160 to 400 °C.

[0053] In some embodiments, in S1, the first solvent and the second solvent are water. An auxiliary agent that promotes the dissolution of the phosphorus source, the first base source, and the second base source can also be added to the first mixed solution and the second base source solution, and the first mixed solution is transparent; during the preparation of the first mixed solution and the second base source solution, they are mixed evenly by stirring. Among them, the method for preparing the first mixed solution includes: adding the phosphorus source and the first base source to the first solvent successively, such as adding the phosphorus source to the first solvent first and then adding the first base source, or adding the first base source to the first solvent first and then adding the phosphorus source; or, dissolving the phosphorus source and the base source in the first solvent respectively and then mixing them to obtain the first mixed solution. The reason for separately preparing the first mixed solution and the second base source solution is that the second base source may cause a large amount of heat release in the solution system, resulting in caking of the components in the mixed solution and affecting the modification of the molecular sieve by phosphate.

[0054] In some embodiments, the pH value of the second mixed solution is 4 to 8.3, preferably 5 to 6.5.

[0055] By adjusting the pH value of the second mixed solution, the content of carbonate ions therein can be maintained within a suitable range, which can not only ensure that the denitration catalyst has appropriate strength, but also improve the adsorption efficiency of the denitration catalyst for reaction gases, and effectively improve the catalytic activity of the denitration catalyst.

[0056] In some embodiments, in S3, the drying temperature is 60-90 °C and the time is 4-6 h; the first calcination includes a first heating program and a second heating program. The first heating program is: heating at a heating rate of 3-5 °C / min to 200-350 °C and holding for 1-3 h; the second heating program is: heating at a heating rate 0.2-0.8 times that of the first heating program to 350-500 °C, holding for 1-5 h, and finally cooling naturally.

[0057] The heating rate of the first heating program is faster and the holding time is shorter. In this temperature range, phosphate can modify and decorate the matrix, with high action efficiency. There is no need to reduce the heating rate or extend the holding time, which is beneficial to improving the preparation efficiency. And a slower heating rate is adopted in the second heating program to fully decompose carbonate and volatilize CO2, so that the matrix density becomes smaller and it becomes more fluffy.

[0058] In some embodiments, the components of the active outer layer include vanadium element, tungsten element and auxiliary element; wherein, the auxiliary element is selected from at least one of silicon element, iron element, zirconium element, molybdenum element, lanthanum element; in the active outer layer, the existing form of vanadium element includes V2O5, and the existing form of tungsten element includes WO3; the existing form of the auxiliary element includes the oxide of the auxiliary element, specifically, at least one of SiO2, Fe2O3, Mn2O3, Mn3O4, MnO2, MnO, CeO2, ZrO2, MoO2, MoO3, La2O3.

[0059] Vanadium element, as the main active component of the denitration catalyst, can drive the reaction of the denitration catalyst. The compounding of tungsten element and vanadium element can improve the reaction activity of the denitration catalyst in the high-temperature section; in addition, the above-mentioned auxiliary elements can reduce the oxidation rate of sulfur dioxide, that is, can improve the low-temperature reaction activity of the denitration catalyst. By selecting the components of the active outer layer, the denitration catalyst can have excellent catalytic activity in both the low-temperature section and the high-temperature section, and broaden the application range of the denitration catalyst.

[0060] In some embodiments, the molar ratio of vanadium element to tungsten element is (0.8-6.5):1, and the molar ratio of titanium element to auxiliary element is (15-75):1.

[0061] Controlling the molar ratio of vanadium element to tungsten element and the molar ratio of titanium element to auxiliary element can further improve the catalytic activity of the denitration catalyst in a wide temperature range.

[0062] In some embodiments, in the denitration catalyst, the molar ratio of vanadium element to titanium element is 1:(45 - 115). When the molar ratio of the two elements in the denitration catalyst meets the above limitations, the denitration catalyst has good denitration catalytic activity and stability in the range of 160 - 400 °C.

[0063] In some embodiments, the specific surface area of the denitration catalyst is 180 - 250 m 2 / g, the average pore diameter is 1.5 - 6.8 nm, and the average pore volume is 0.18 - 0.80 cm 3 / g.

[0064] Controlling the specific surface area, average pore diameter, and average pore volume of the denitration catalyst within the above ranges can increase the number of active sites, enhance the adsorption capacity of the catalyst for nitrogen oxides, improve the denitration reaction rate and efficiency, and also help to improve the overall stability of the denitration catalyst.

[0065] In another typical embodiment of the present invention, a preparation method of a denitration catalyst is provided, including the following steps:

[0066] S1, crushing and grinding the substrate to obtain a first solid material;

[0067] S2, adding a vanadium source and a cosolvent to water to obtain a vanadium source solution; dissolving a tungsten source in water to obtain a tungsten source solution; adding the tungsten source solution to the vanadium source solution to obtain a third mixture, which is a light green liquid;

[0068] S3, mixing an auxiliary element source, a binder, a reinforcing agent, and the first solid material to obtain a second mixture;

[0069] S4, adding the third mixture to the second mixture, stirring, extruding into a shape, drying, and performing a second calcination to obtain the denitration catalyst.

[0070] In S1, after crushing and grinding the substrate, it is easier to uniformly coat the vanadium source and the auxiliary element source on the surface of the substrate, which is beneficial to improving the catalytic performance of the denitration catalyst. In S2, preparing the vanadium source solution and the tungsten source solution step by step can improve the uniformity of the third mixture. In S3, adding a binder and a reinforcing agent can improve the structural stability of the denitration catalyst and extend its service life.

[0071] In some embodiments, in S2, the mass ratio of the vanadium source to the cosolvent is 1:(1-2), and the cosolvent is preferably oxalic acid. The vanadium source and oxalic acid are added to water, and after stirring from blue to dark green, a vanadium source solution is obtained; oxalic acid can form a complex with the vanadium element in the vanadium source, which can promote the dissolution of the vanadium source and can greatly promote the activity of the active intermediate of the denitration catalyst. Controlling its dosage can also improve the strength of the denitration catalyst. In S2, the vanadium source and oxalic acid are dispersed in water by stirring. Specifically, it can be: first add the vanadium source to water, then add oxalic acid, or first add oxalic acid to water, then add the vanadium source, or add both at the same time, or dissolve both in water and then mix; the preparation method of the third mixed solution is: uniformly drop the tungsten source solution into the vanadium source solution, or uniformly drop the vanadium source solution into the tungsten source solution. In S4, the third mixed solution is uniformly dropped into the second mixture to obtain a fluffy sandy substance, while dropping and stirring.

[0072] In some embodiments, the vanadium source is selected from one or more of vanadium oxides and vanadium-containing salts; among them, the vanadium oxides include but are not limited to V2O5, and the vanadium-containing salts include but are not limited to ammonium metavanadate, vanadium tetrachloride, vanadyl acetylacetonate, vanadyl sulfate, vanadyl oxalate; the tungsten source is selected from one or more of WO3, ammonium metatungstate, sodium tungstate, ammonium tungstate; the auxiliary element source is selected from one or more of auxiliary element oxides and auxiliary element-containing salts. For example, for the auxiliary element including silicon element, the auxiliary element source includes but is not limited to silicon dioxide, sodium silicate, tetraethyl orthosilicate, silicon chloride. For the auxiliary element including manganese element, the auxiliary element source includes but is not limited to manganese sulfate, manganese chloride, manganese oxide, potassium permanganate, manganese carbonate. For the auxiliary element including cerium element, the auxiliary element source includes but is not limited to cerium sulfate, cerium nitrate, cerium oxide and cerium carbonate; for the auxiliary element including zirconium element, the auxiliary element source includes but is not limited to zirconium dioxide, zirconium chloride, zirconium nitrate, zirconium oxychloride and zircon sand. For the auxiliary element including molybdenum element, the auxiliary element source includes but is not limited to ammonium tetramolybdate, ammonium heptamolybdate, molybdenum oxide and sodium molybdate. For the auxiliary element including lanthanum element, the auxiliary element source includes but is not limited to lanthanum nitrate, lanthanum oxide, lanthanum carbonate, lanthanum chloride.

[0073] The above components are suitable for preparing the active outer layer of the denitration catalyst of the present invention, and the component distribution of the prepared active outer layer is uniform and has good catalytic activity.

[0074] In some embodiments, the binder is selected from at least one of hydroxypropyl cellulose, sodium carboxymethyl cellulose, aluminum phosphate, aluminum dihydrogen phosphate, silica sol; the reinforcing agent is selected from glass fiber, etc. The above binder has good binding effect and has no influence on the catalytic activity of the denitration catalyst; the above reinforcing agent is beneficial to improving the strength of the denitration catalyst and prolonging the service life of the denitration catalyst.

[0075] In some embodiments, the mass ratio of the binder, the auxiliary element source, the enhancer, and the first solid substance is (0.5 - 8):(0.5 - 2):(0.5 - 6):(25 - 40).

[0076] By limiting the dosages of the above components, on the one hand, the stability of the denitration catalyst can be improved, and on the other hand, the low-temperature catalytic activity of the denitration catalyst can be improved.

[0077] In some embodiments, the method of the second calcination is: heating up to 350 - 750 °C at a rate of 0.5 - 5 °C / min and holding for 2 - 7 h.

[0078] Under the above conditions, each component in the denitration catalyst can be well dispersed and interact with the matrix to form a sufficient number of highly active catalytic sites.

[0079] In another typical embodiment of the present invention, there is provided an application of the denitration catalyst in the above embodiments of the present invention or the denitration catalyst prepared by the preparation method in the above embodiments. The above denitration catalyst is used to remove NO in the flue gas x or reduce the content of NO in the flue gas x The flue gas contains NH3, NO, O2, SO2, and H2O; the concentration of NH3 in the flue gas is 40 - 1600 ppm; in some embodiments, the concentration of SO2 in the flue gas is 500 - 1500 ppm; in some embodiments, the concentration of O2 in the flue gas is 30000 - 100000 ppm; in some embodiments, the concentration of NO in the flue gas x is 50 - 2000 ppm. The denitration catalyst can remove nitrogen oxides in the above flue gas in the temperature range of 160 - 400 °C, and has a wide application range.

[0080] Typical but non-limiting, the application method of the denitration catalyst includes the following steps: cutting the catalyst into samples with a length of ~4 mm, measuring 30 mL of the catalyst, fixing the catalyst in a gas-solid fixed bed reaction device; introducing the flue gas and performing denitration treatment on the flue gas. Among them, the gas-solid fixed bed reaction device includes but is not limited to a laboratory-level gas-solid fixed bed reaction device or an industrial-level gas-solid fixed bed reaction device. The gas-solid fixed bed reaction device can be, for example, an SCR reactor, etc.

[0081] The following further describes the present application in detail with specific examples, and these examples should not be construed as limiting the scope claimed by the present application.

[0082] Performance test method

[0083] 1) Ammonia slip rate: Set the test temperature at 200 °C for each denitration catalyst sample to be tested. Turn on the reaction gases (including NO, NH3, H2O, SO2, and O2). Preset that all gases do not pass through the catalyst (introduce them into the bypass). After stabilizing for 60 min, obtain the concentration value of NH x , which is recorded as the injection concentration N1 (ppm) of the catalyst. Subsequently, pass the gases through the catalyst. After stabilizing for 10 min, obtain the concentration value of NH3, which is recorded as the initial concentration N2 (ppm) of the catalyst. After reacting for 100 h, obtain the final concentration value of NH3 for each denitration catalyst, which is recorded as N3 (ppm). Calculate the difference between N2 and N3. The ratio of the difference to the injection concentration N1 (ppm) is the ammonia slip rate.

[0084] 2) SO2 oxidation rate: Set the test temperature at 200 °C for each denitration catalyst sample to be tested. Turn on the reaction gases (including NO, NH3, H2O, SO2, and O2). Preset that all gases do not pass through the catalyst (introduce them into the bypass). After stabilizing for 60 min, obtain the concentration value of SO2, which is recorded as the injection concentration S1 (ppm) of the catalyst. Subsequently, pass the gases through the catalyst. After stabilizing for 10 min, obtain the concentration value of SO2, which is recorded as the initial concentration S2 (ppm) of the catalyst. After reacting for 100 h, obtain the final concentration value of SO2 of the catalyst, which is recorded as S3 (ppm). Calculate the difference between S2 and S3. The ratio of the difference to the injection concentration S1 (ppm) is the SO2 oxidation rate.

[0085] 3) Decline in sulfur and water resistance activity: Set the test temperature at 200 °C for each catalyst sample to be tested. Turn on the reaction gases (including NO, NH3, and O2). Stabilize for 60 min at this temperature point to obtain the concentration value of NO x , and calculate the conversion rate of NO x , which is recorded as the initial activity C I (%) of the catalyst. Subsequently, turn on the reaction gases of H2O and SO2. After reacting for 100 h, obtain the concentration value of NO x , and calculate the conversion rate of NO x , which is recorded as C II (%). Calculate the difference between C II and C I . This is the stability data during the sulfur and water resistance test. The lower the value, the better the stability.

[0086] In the reaction gases, the concentration of NO is 1000 ppm, the concentration of NH3 is 1000 ppm, the concentration of SO2 is 500 ppm, the volume of O2 accounts for 3% of the total volume of the flue gas, and H2O is 10 vol%.

[0087] 4) Specific surface area, average pore diameter, and average pore volume: Measured using Micromeritics ASAP 2020. First, weigh the sample tube for testing, denoted as M0. Pour the dried sample (100 - 300 mg) into the sample tube and record it as M1. Place the sample tube with the sample into the degassing station of Micromeritics ASAP 2020, heat it to 200 °C under vacuum conditions, and set the degassing time to 8 h to further remove the adsorbed gas on the surface and in the pores. After degassing, weigh the mass of the sample + tube, denoted as M2. The difference between M2 and M1 is the mass loss (M3) of the sample during degassing. Further transfer the sample to the test station, input the value of M3 in the test program, and immerse the sample tube in liquid nitrogen (temperature maintained at 77 K) to ensure that the nitrogen adsorption process occurs at a constant low temperature. After the test is completed, output the relevant test report.

[0088] Example 1

[0089] An embodiment of the denitration catalyst of the present invention. The preparation method of the denitration catalyst in this embodiment includes the following steps:

[0090] S1, Take 300 g of titanium dioxide and 120 g of Y-type molecular sieve with a pore diameter of 0.74 nm and mix them in a molding machine, stir and mix for 15 min to obtain a first mixture; Weigh 7.5 g of ammonium dihydrogen phosphate and mix it in 15 g of ammonia water (mass fraction of NH3 is 18%), stir for 30 min to obtain a transparent first mixed solution; Weigh 7.5 g of ammonium bicarbonate and dissolve it in 20 mL of water to obtain a sodium carbonate solution;

[0091] S2, Slowly add the sodium carbonate solution dropwise into the first mixed solution to obtain a second mixed solution with a pH value of 5.5;

[0092] S3, Slowly add the second mixed solution dropwise into the first mixture until the first mixture becomes a grayish-white loose material. Dry it at 80 °C for 5 h, heat it in a muffle furnace from room temperature to 250 °C at a rate of 4 °C / min, hold for 2 h, then heat it from 250 °C to 450 °C at a rate of 2 °C / min, hold for 3 h, and cool it naturally to obtain a brown and fluffy matrix material;

[0093] S4, Crush and grind the matrix material to obtain a first solid substance;

[0094] S5, Mix 7.78 g of ammonium metavanadate and 10 g of oxalic acid in 40 mL of distilled water, stir from blue to dark green to obtain a vanadium source solution; Dissolve 6.38 g of ammonium metatungstate in 40 mL of distilled water to obtain a tungsten source solution, and slowly add the tungsten source solution dropwise to the vanadium source solution to obtain a light green third mixed solution;

[0095] S6. Mix an auxiliary element source (containing 18 g of iron oxide and 7.36 g of ammonium tetramolybdate dihydrate), hydroxypropyl cellulose, glass fiber, and a first solid substance in a mass ratio of 2.7:1:1:30 in a molding machine to obtain a second mixture;

[0096] S7. Slowly and evenly drip the third mixed solution into the second mixture. Stop stirring until the first solid substance presents a fluffy sandy material. After extrusion molding by the molding machine, dry it at 60 °C for 5 h, then heat it from room temperature to 550 °C at a heating rate of 4 °C / min in a muffle furnace, keep it at this temperature for 5 h, and then naturally cool it to obtain a red-brown denitration catalyst.

[0097] Examples 2 to 24

[0098] Examples 2 to 24 are examples of the denitration catalyst of the present invention. Their preparation methods are the same as those of Example 1, except for the dosages of each component and the preparation conditions, as specifically shown in Tables 1 to 3.

[0099] Table 1

[0100]

[0101]

[0102] Table 2

[0103]

[0104]

[0105] Table 3

[0106]

[0107] As can be seen from Tables 1 to 3, the denitration catalyst of the present application has good denitration activity, good selectivity, can effectively inhibit the oxidation of SO2. In addition, it has high anti-sulfur and anti-water activity and good stability, and is suitable for application at low temperatures. In addition, by comparing the performance test results of Example 1 and Example 15, it can be found that when the molar ratio of vanadium element and tungsten element is not within the range of (0.8 to 6.5):1, its denitration stability is relatively poor. By comparing the performance test results of Example 1 and Example 14, it can be found that when the molar ratio of titanium element and auxiliary element is not within the range of (15 to 75):1, its denitration stability is also relatively poor.

[0108] Comparative Example 1

[0109] A denitration catalyst, and its preparation method includes the following steps:

[0110] S1. Mix 0.064 mol of tetrabutyl titanate and 0.128 mol of acetylacetone, then add 50 mL of ethanol and react to obtain the support;

[0111] S2. Mix 0.30 g of ammonium metavanadate and 0.104 g of (NH4)6W7O 24 ·6H2O, dissolve them in 50 mL of deionized water, and stir for 2 h in a water bath at 80 °C to obtain the mixed solution;

[0112] S3. Immerse the support in the mixed solution for 3 h, then dry it at 80 °C, then place it in a calcination furnace, and in an air atmosphere, raise the temperature of the furnace from room temperature to 500 °C at a heating rate of 2 °C / min and hold it at 500 °C for 2 h to obtain the denitration catalyst.

[0113] Comparative Example 2

[0114] A denitration catalyst, the difference in its preparation method from that of Example 1 is only that in S1, Y-type molecular sieve is not added, and the other steps are the same.

[0115] Comparative Example 3

[0116] A denitration catalyst, the difference in its preparation method from that of Example 1 is only that in S1, ammonium dihydrogen phosphate is not added, and 15 g of ammonia water (mass fraction of NH3 is 18%) is used to replace the first mixed solution, and the other steps are the same.

[0117] Comparative Example 4

[0118] A denitration catalyst, the difference in its preparation method from that of Example 1 is only that the substrate is not alkali-modified. In S1, 7.5 g of ammonium dihydrogen phosphate is dissolved in 15 mL of water to obtain a phosphorus source solution, which is used to replace the first mixed solution; S2 is omitted. In S3, the phosphorus source solution is dropped into the first mixture, and the other steps are the same.

[0119] Comparative Example 5

[0120] A denitration catalyst, the difference in its preparation method from that of Example 1 is only that there is no active outer layer, that is, S4 to S7 are not carried out during preparation.

[0121] Comparative Example 6

[0122] A denitration catalyst, the difference in its preparation method from that of Example 1 is only that it is not modified with the second alkali source ammonium bicarbonate, S2 is absent, and in S3, the first mixed solution is uniformly dropped into the first mixture, and the other steps are the same.

[0123] Table 4 shows the performance test results of Example 1 and Comparative Examples 1 to 6.

[0124] Table 4

[0125]

[0126]

[0127] As can be seen from Table 4, the decline in the sulfur and water resistance activity of the denitration catalysts in Comparative Examples 1-6 is significantly lower than that of the present invention, and there are significant differences in the low-temperature denitration stability between the denitration catalysts of the present application. In addition, the ammonia slip rates of Comparative Examples 1-6 are high, indicating that less ammonia participates in the reduction reaction, that is, the denitration activity is poor and the denitration efficiency is low.

[0128] Table 5 shows the specific surface area, average pore diameter, and average pore volume data of the denitration catalysts in Example 1 and Comparative Examples 1-6.

[0129] Table 5

[0130] Catalyst <![CDATA[Specific surface area (m 2 / g)]]> <![CDATA[Average pore volume (cm 3 / g)]]> Average pore diameter (nm) Example 1 237.8 0.38 2.0 Comparative Example 1 55.6 0.18 4.7 Comparative Example 2 66.8 0.35 3.9 Comparative Example 3 230.8 0.36 2.8 Comparative Example 4 204.5 0.21 2.6 Comparative Example 5 225.7 0.34 2.7 Comparative Example 6 219.7 0.29 2.3

[0131] Table 5 shows the specific surface area, pore volume, and pore diameter data of Example 1 and Comparative Examples 1-6. Among them, according to the data of Example 1 and Comparative Example 2, it can be seen that Y-type molecular sieve contributes the most to the specific surface area of the catalyst. Combining Example 1 and Comparative Example 3, it can be known that the phosphorus source plays a certain inhibitory role in the particle size growth of the catalyst. This is because phosphorus modification may preferentially adsorb at active sites or lattice defects during the crystal nucleation process, interfering with the combination and growth of particles. In addition, combining Example 1 with Comparative Examples 4 and 6, it can be seen that the second alkali source contributes more to the specific surface area of the catalyst than ammonia water, and the presence of the second alkali source can promote the increase of the pore volume of the catalyst and the decrease of the particle size. Combining the data of Example 1 and Comparative Example 5, it can be known that the active outer layer of the catalyst can inhibit the growth of the specific surface area, mainly because it promotes the particle size growth. Comparative Example 1 prepared by other processes has a small specific surface area, a small pore volume, and a large average pore diameter, so its activity is poor.

[0132] Figure 2 (a-b) are the transmission electron microscope images, Mapping images, and scanning electron microscope images of the denitration catalyst matrix in Example 1. As can be seen from the figure, the matrix exhibits a uniform block stacking structure, and the side length of each block is 500-800 nm. Figure 3 It shows that the Lewis acid sites of the denitration catalyst in Example 1 increase, the acid sites decrease; in order to further verify the adsorption of NO and NH3 on the surface of the denitration catalyst, characterization tests of ammonia-temperature programmed desorption test (NH3-TPD) and nitrogen oxide-temperature programmed desorption test (NO-TPD) were carried out, and the test results are as Figures 4 - 5 shown. As can be seen from Figure 4It can be seen that the NH3 adsorption area of the denitration catalyst in Example 1 is much higher than that in Comparative Example 1, especially in the low-temperature region (150-300 °C), indicating that this modification method can maximize the acid sites on the catalyst surface, especially the weakly adsorbed acid sites. Figure 5 It is shown that the NO adsorption in Comparative Example 1 has two adsorption peaks (the low-temperature segment is a weak adsorption peak, and the high-temperature segment is a strong adsorption peak), while the strong adsorption peak of the denitration catalyst in Example 1 is weakened and the weak adsorption peak is enhanced, indicating that under the modification of the method described in the present invention, the strong and weak adsorption of NO by the catalyst can be greatly improved. As a reactant, NO first needs to be adsorbed on the catalyst surface before it can react with a reducing agent (such as NH3). If NO can be moderately adsorbed on the catalyst surface, it will be more likely to contact the active sites and participate in the reaction, thereby increasing the reaction rate. From Figure 6 it can be seen that the catalytic activity of the denitration catalyst in Example 1 at low temperatures is significantly better than that in the comparative example.

[0133] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, various modifications and changes can be made to the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A denitration catalyst, characterized in that, It includes a substrate and an active outer layer coated on at least part of the surface of the substrate; The preparation method of the substrate includes: S1, mixing titanium dioxide and molecular sieve to obtain a first mixture; preparing a first mixed solution containing a phosphorus source and a first base source; preparing a second base source solution containing a second base source; S2, adding the second base source solution to the first mixed solution to obtain a second mixed solution; S3, adding the second mixed solution to the first mixture to obtain a grayish-white substance, drying and first calcining the grayish-white substance to obtain the substrate; Wherein, the first base source includes at least one of hydroxides and ammonia water; the second base source is at least one of bases containing carbonate and bicarbonate.

2. The denitration catalyst according to claim 1, characterized in that, The molecular sieve includes at least one of X-type molecular sieve, Z-type molecular sieve, and Y-type molecular sieve; and / or, the phosphorus source includes at least one of phosphorus-containing oxides and phosphorus-containing salts; and / or, the mass ratio of the first base source to the second base source is (0.5-4):1; and / or, the mass ratio of the first base source to the phosphorus source is (0.8-5.5):1; and / or, using the phosphorus source, the first base source, and the second base source as modifiers, the mass ratio of the titanium dioxide, the molecular sieve, and the modifier is 30:(8-27): (0.8～12)。 3. The denitration catalyst according to claim 1, characterized in that, The pH value of the second mixed solution is 4-8.3; and / or, the first calcination includes a first heating program and a second heating program. The first heating program is: heating at a heating rate of 3-5 °C / min to 200-350 °C and holding for 1-3 h. The second heating program is: heating at a heating rate 0.2-0.8 times that of the first heating program to 350-500 °C and holding for 1-5 h.

4. The denitration catalyst according to any one of claims 1 to 3, characterized in that, The composition of the active outer layer contains vanadium element, tungsten element, and auxiliary elements. The auxiliary elements are selected from at least one of silicon element, iron element, zirconium element, molybdenum element, and lanthanum element; in the active outer layer, the existence form of the vanadium element includes V2O5, the existence form of the tungsten element includes WO3; the existence form of the auxiliary elements includes oxides of the auxiliary elements.

5. The denitration catalyst according to claim 4, characterized in that, The molar ratio of the vanadium element to the tungsten element is (0.8-6.5):1; and / or, in the denitration catalyst, the molar ratio of the titanium element to the auxiliary element is (15-75):

1.

6. The denitration catalyst according to any one of claims 1 to 3, characterized in that, In the denitration catalyst, the molar ratio of the vanadium element to the titanium element is 1:(45-115).

7. The denitrification catalyst according to any one of claims 1 to 3, characterized in that, The specific surface area of the denitration catalyst is 180-250 m 2 / g, the average pore diameter is 1.5-6.8 nm, and the average pore volume is 0.18-0.8 m 3 / g.

8. A method for preparing a denitration catalyst according to any one of claims 1 to 7, characterized in that, It includes the following steps: S1, crushing and grinding the substrate to obtain a first solid substance; S2, adding a vanadium source and a cosolvent to water to obtain a vanadium source solution; dissolving a tungsten source in water to obtain a tungsten source solution; adding the tungsten source solution to the vanadium source solution to obtain a third mixed solution; S3, mixing an auxiliary element source, a binder, a reinforcing agent, and the first solid substance to obtain a second mixture; S4, adding the third mixed solution to the second mixture, stirring, extruding into shape, drying, and second calcining to obtain the denitration catalyst.

9. The preparation method according to claim 8, characterized in that, The mass ratio of the binder, the auxiliary element source, the reinforcing agent, and the first solid substance is (0.5 to 8):(0.5 to 2):(0.5 to 6):(25 to 40); and / or, the method for the second calcination is: heating to 350 to 750 °C at a rate of 0.5 to 5 °C / min and holding for 2 to 7 h.

10. Application of a denitrification catalyst, characterized in that, The denitration catalyst is the denitration catalyst described in any one of claims 1 to 7 or the denitration catalyst prepared by the preparation method described in any one of claims 8 to 9; the denitration catalyst is used to remove NO in the flue gas x or reduce the content of NO in the flue gas x wherein the flue gas contains NH3, NO, O2, SO2 and H2O; The concentration of NH3 in the flue gas is 40 to 1600 ppm; and / or The concentration of SO2 in the flue gas is 500 to 1500 ppm; and / or The concentration of O2 in the flue gas is 30000 to 100000 ppm; and / or The NO in the flue gas x has a concentration of 50 - 2000 ppm.

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