Medium and low temperature denitration catalyst and preparation method and application thereof

Abstract

The invention provides a medium and low temperature denitration catalyst and a preparation method and application thereof.The medium and low temperature denitration catalyst comprises a carrier, V2O5 and auxiliary active metal oxide, the carrier is a carbon nitride-like / titanium dioxide composite carrier, and in the composite carrier, titanium dioxide is loaded on carbon nitride-like of a two-dimensional lamellar structure in a bonding mode; the V2O5 and the auxiliary active metal oxide are loaded on the composite carrier to form a sandwich structure of the auxiliary active metal oxide-V2O5-composite carrier, and a composite oxide of vanadium and the auxiliary active metal is formed on an interface where the auxiliary active metal oxide is in contact with the V2O5. The medium and low temperature denitration catalyst has excellent resistance, is suitable for medium and low temperature denitration, can give consideration to denitration effects of a low temperature zone and a medium temperature zone, has NOx conversion rates of more than 90% in a temperature range of 170-370 DEG C, and solves the problems of poor denitration efficiency, poor water resistance and the like in a lower temperature section of an existing vanadium-based medium and low temperature denitration catalyst.

Description

Technical Field

[0001] The invention relates to a medium-low temperature denitration catalyst and a preparation method and application thereof, belonging to the technical field of environmental protection catalyst development and atmospheric pollutant control. Background Art

[0002] Most industrial chemical processes require thermal energy to drive them, with fossil fuels as the main energy source. During combustion or reaction, they react with oxygen in the air to form 2 and N 2 The reaction produces NOx (NO and NO 2 ) pollution. SCR (Selective Catalytic Reduction) denitrification technology has the advantages of high efficiency (up to 80%-90%), no secondary pollution, good economy, etc., and is suitable for various types of flue gas denitrification systems. 2 O 5 -WO 3 / TiO 2 The catalyst is the most widely used industrial denitrification catalyst at present. It shows excellent NH 3 -SCR catalytic activity and durability. However, with the changes in production demand and the improvement of industrial equipment, there are a large number of heating furnaces and superheating furnaces in refining and chemical enterprises with flue gas exhaust temperatures between 100-250℃. 2 O 5 -WO 3 / TiO 2 The denitration performance of the catalyst is seriously reduced in this temperature range; on the other hand, the denitration equipment of the current refining and chemical enterprises is generally set at the front end of the desulfurization equipment. The sulfide in the flue gas is easy to cause catalyst poisoning and salt formation in the back-end equipment, affecting the long-term operation of the device. The subsequent design of tail-end denitration can fundamentally avoid the problems of catalyst poisoning and device salt formation, and reduce the replacement and maintenance costs of the denitration catalyst. However, the flue gas temperature drops after desulfurization, and the water content in the flue gas increases significantly, which also puts higher requirements on the low-temperature activity and water resistance of the SCR catalyst.

[0003] The development of low-temperature SCR denitrification catalysts is the fundamental solution to the above market needs. The low-temperature SCR catalysts currently used mainly include precious metal catalysts, metal oxide catalysts, molecular sieve catalysts and carbon-based material catalysts. Among them, molecular sieve catalysts and metal oxide catalysts are the two most widely used in practice. Traditional molecular sieve catalysts have poor resistance, and the preparation conditions or methods required for modification are too complicated, which increases the difficulty of industrial application. Among metal oxide catalysts, manganese-based catalysts have excellent low-temperature activity, but their resistance to SO 2 and H 2Poor O deactivation ability has become a bottleneck problem that limits its application. At the same time, catalysts with high Mn and Ce content also have problems such as difficult molding and low yield. The production process of vanadium-based catalysts is relatively mature, and its preparation basically involves a combination of multiple metal oxides. However, most vanadium-based catalysts have high activation temperatures and low low-temperature denitrification rates, indicating that simply changing the type and mixing method of metal oxides cannot effectively improve the low-temperature activity of the catalyst. Developing vanadium-based low-temperature catalysts is an effective means to meet the market demand for low-temperature denitrification and reduce the R&D process.

[0004] Therefore, providing a new medium- and low-temperature denitrification catalyst and its preparation method and application has become a technical problem that urgently needs to be solved in this field. Summary of the invention

[0005] In order to solve the above-mentioned shortcomings and deficiencies, an object of the present invention is to provide a medium-low temperature denitration catalyst.

[0006] Another object of the present invention is to provide a method for preparing the above-mentioned medium- and low-temperature denitration catalyst.

[0007] Another object of the present invention is to provide application of the above-mentioned medium-low temperature denitration catalyst in medium-low temperature denitration.

[0008] In order to achieve the above objectives, on the one hand, the present invention provides a medium-low temperature denitration catalyst, wherein the medium-low temperature denitration catalyst comprises a carrier, V 2 O 5 and an auxiliary active metal oxide, wherein the carrier is a carbon nitride-like / titanium dioxide composite carrier, in which titanium dioxide (TiO 2 ) is supported on a carbon nitride-like structure having a two-dimensional layer structure in a bonding form;

[0009] V 2 O 5 and the auxiliary active metal oxide are loaded on the carbon nitride-like / titanium dioxide composite support to form an auxiliary active metal oxide-V 2 O 5 -Sandwich structure of carbon nitride / titanium dioxide composite carrier, and active metal oxide and V 2 O 5 The contact interface forms a composite oxide of vanadium and the auxiliary active metal.

[0010] As a specific embodiment of the medium and low temperature denitrification catalyst described above in the present invention, the auxiliary active metal oxide includes one or a combination of oxides of Ce, Fe, Mo, Nb, Sb, Sm and W.

[0011] As a specific embodiment of the medium and low temperature denitration catalyst of the present invention, V 2 O5 、TiO 2 The mass ratio of nitride-like carbon and active metal oxide is 2-10:100:5-50:2-10.

[0012] As a specific embodiment of the medium and low temperature denitration catalyst of the present invention, the specific surface area of ​​the medium and low temperature denitration catalyst is greater than 70m 2 / g, with mesoporous and microporous structures.

[0013] On the other hand, the present invention also provides a method for preparing the above-mentioned medium-low temperature denitration catalyst, wherein the preparation method comprises:

[0014] Step (1): mixing a vanadium salt solution, titanium dioxide and a nitrogen-containing small molecule structure modifier to obtain a suspension;

[0015] Step (2): subjecting the suspension to a low-temperature heat treatment and a first high-temperature heat treatment in sequence in an inert atmosphere to obtain a powder;

[0016] Step (3): uniformly mixing the active metal salt solution, the molding additive and the powder to obtain a slurry;

[0017] Step (4): aging the mud material and then extruding it to obtain a catalyst embryo, drying the catalyst embryo and then performing a second high-temperature heat treatment to obtain the medium- and low-temperature denitration catalyst.

[0018] As a specific embodiment of the preparation method described above, the mass ratio of vanadium salt, titanium dioxide, nitrogen-containing small molecule structure modifier and auxiliary active metal salt is 3-15:100:10-80:3-14.

[0019] As a specific embodiment of the preparation method described above, the mass ratio of titanium dioxide to nitrogen-containing small molecule structure modifier is preferably 100:20-50.

[0020] As a specific embodiment of the preparation method described above, in step (1), the vanadium salt includes one or a combination of ammonium orthovanadate, ammonium metavanadate, potassium metavanadate and ammonium polyvanadate.

[0021] As a specific embodiment of the preparation method described above of the present invention, in step (1), the nitrogen-containing small molecule structure modifier is an amino organic compound that can undergo a condensation reaction at a certain temperature, including one or a combination of urea, melem, carbonamide, cyanamide, semicarbazide and carbonyl hydrazide compounds.

[0022] As a specific embodiment of the preparation method described above in the present invention, in step (1), titanium dioxide and nitrogen-containing small molecule structure modifier are first mixed and ground to ensure that the nitrogen-containing small molecule structure modifier is evenly coated on the surface of titanium dioxide, and then the obtained mixture is mixed with a vanadium salt solution to obtain a suspension.

[0023] As a specific embodiment of the preparation method described above, in step (1), the vanadium salt solution, titanium dioxide and nitrogen-containing small molecule structure modifier are mixed and then ultrasonically stirred to obtain a suspension.

[0024] As a specific embodiment of the preparation method described above, in step (2), the temperature of the low-temperature heat treatment is 60-120°C, preferably 80-100°C, the heating rate is 1-4°C / min, and the time is 6-12h. Under the low-temperature heat treatment conditions, the solvent can be evaporated slowly, thereby ensuring that the vanadium salt can be deposited on the surface of the carrier as evenly as possible.

[0025] As a specific embodiment of the preparation method described above of the present invention, in step (2), the temperature of the first high temperature heat treatment is 350-600°C, the heating rate is 2-5°C / min, and the time is 1-6h;

[0026] Preferably, the temperature of the first high temperature heat treatment is 400-550° C., and the time is 2-4 hours.

[0027] In the present invention, the duration of the first high-temperature heat treatment determines the size of the formed carbon nitride-like structure, and a too fast heating rate will affect the formation of the carbon nitride-like structure.

[0028] As a specific embodiment of the preparation method described above, in step (2), the inert atmosphere comprises N 2 , Ar atmosphere, etc.

[0029] In step (2) of the preparation method described above, the purpose of low-temperature heat treatment is concentrated deposition. During the low-temperature heat treatment, the water in the solution evaporates slowly, and the vanadium salt is uniformly deposited on the surface of the carrier. The purpose of the first high-temperature heat treatment is structural modulation and the generation of the main active component. On the one hand, during the first high-temperature heat treatment, the nitrogen-containing small molecule structure modifier undergoes self-polymerization reaction to form carbon nitrides of different sizes, wherein the larger carbon nitrides (particle size ≥ 10nm) are two-dimensional sheet structures, which form a composite carrier through bonding with titanium dioxide, thereby improving the electronic conductivity of the carrier; while the smaller carbon nitrides (particle size <10nm) have poor thermal stability, which decompose in situ to form small mesopores (diameter of less than 10nm) and micropores during the second high-temperature heat treatment in step (4), thereby increasing the specific surface area of ​​the overall catalyst and forming a multi-level pore structure in the catalyst. Therefore, the specific surface area and pore structure of the catalyst can be controlled by adjusting the mass ratio of titanium dioxide and the nitrogen-containing small molecule structure modifier. On the other hand, during the first high-temperature heat treatment, the vanadium salt uniformly deposited on the surface of the carrier is oxidized to form nano-V 2 O 5 Since the specific surface area of ​​the two-dimensional layer structure is larger than that of TiO 2 There is a significant improvement, which can ensure the formation of nano V 2 O 5 loaded on the carrier surface, thereby reducing V 2 O 5 Aggregation. In the first high temperature heat treatment process, the heating rate, temperature and holding time jointly determine the catalyst structure and the formed nano V 2 O 5 size.

[0030] As a specific embodiment of the above preparation method of the present invention, in step (3), the mass ratio of the auxiliary active metal salt to the powder is 3-14:100.

[0031] As a specific embodiment of the preparation method described above of the present invention, in step (3), the auxiliary active metal salt includes one or a combination of soluble ammonium salts or organic acid salts of Ce, Fe, Mo, Nb, Sb, Sm and W.

[0032] Since the main active metal has been converted into V in step (2), 2 O 5 It is anchored on the carrier in the form of a catalyst and introduced into the catalyst system after the active metal salt, so it is easy to react with V 2 O 5 The contact reaction forms a composite oxide M of vanadium and active metal with higher reducibility. x VO y, where M is the auxiliary active metal, x and y are different due to the different auxiliary active metals, and the x and y corresponding to different auxiliary active metals are quite different, thereby improving the denitration efficiency of the obtained catalyst; at the same time, the auxiliary active metal oxide is after V 2 O 5 The catalyst system is introduced to form a catalyst with "auxiliary agent-V 2 O 5 -Sandwich structure of the catalyst, which can reduce the active center and H 2 O, SO 2 It can also improve the resistance of the catalyst by preventing it from coming into contact with components that can deactivate it, such as ammonium bisulfate.

[0033] As a specific embodiment of the preparation method described above, in step (3), the molding additives include a binder, a plasticizer, a pH regulator, a pore-forming agent, etc., and may include oxalic acid, polyvinyl alcohol, carboxymethyl cellulose, hydroxymethyl cellulose, hydroxypropyl cellulose, polyethylene oxide, glycerol, nano-SiO 2 , glass fiber and water, etc. or a combination thereof. The present invention does not make specific requirements on the amount of molding additives used, and the amount can be reasonably adjusted according to the actual operation needs, as long as the purpose of molding can be achieved. In addition, in step (3), it can also be determined whether to add water according to the required hardness of the clay, and the amount of water added can be reasonably adjusted if water is added.

[0034] As a specific embodiment of the preparation method described above, the uniform mixing in step (3) can be achieved by stirring, and the stirring time can be reasonably adjusted according to the actual needs of the on-site operation. For example, in some embodiments of the present invention, the stirring time is 2-3 hours.

[0035] As a specific embodiment of the preparation method described above of the present invention, in step (4), the aging time is 8-20 hours.

[0036] As a specific embodiment of the preparation method described above of the present invention, wherein, in step (4), the drying temperature is 60-100° C. and the drying time is 12-72 hours.

[0037] As a specific embodiment of the preparation method described above in the present invention, in step (4), the temperature of the second high-temperature heat treatment is 400-600°C, preferably 400-550°C, the heating rate is 2-5°C / min, and the time is 6-10h.

[0038] As a specific embodiment of the preparation method described above of the present invention, in step (4), the atmosphere of the second high-temperature heat treatment includes one of nitrogen, argon or a nitrogen / air mixture, wherein the volume ratio of nitrogen to air in the nitrogen / air mixture is not less than 1: 1. By changing the atmosphere of the second high-temperature heat treatment, the composition ratio of the atmosphere and the heating rate, the decomposition degree of the carbon nitride-like in the obtained catalyst can be controlled.

[0039] In step (4) of the preparation method described above, a second high-temperature heat treatment is carried out at a temperature of 400-600°C in an atmosphere of nitrogen, argon or a nitrogen / air mixture. On the one hand, the above-mentioned auxiliary active metal salt can be completely converted into oxides; on the other hand, the titanium dioxide in the composite carrier still maintains an anatase structure at this temperature, avoiding its activity reduction caused by its conversion to a rutile structure; on the third hand, the smaller-sized carbon nitride-like in the composite carrier decomposes. If the temperature is too high and the decomposition ratio is too large, the physical properties and catalytic performance of the catalyst will be reduced. The micropores and small mesopores generated by partial decomposition are the key to increasing the specific surface area of ​​the catalyst and accelerating gas transmission during the reaction.

[0040] In addition, since the amount of active metal salt, i.e. vanadium salt, is relatively high, a large amount of gas will overflow during the second high-temperature heat treatment, which will cause the catalyst to break. In step (2) of the present invention, the vanadium salt has been subjected to a high-temperature heat treatment and formed into nano-V 2 O 5 , which can avoid the damage to the obtained catalyst caused by the gas generated during the high-temperature heat treatment in step (4), thereby improving the catalyst yield.

[0041] In another aspect, the present invention further provides the use of the above-mentioned medium-low temperature denitration catalyst in medium-low temperature denitration, wherein the temperature of the medium-low temperature denitration is 170-370°C.

[0042] Compared with the prior art, the beneficial technical effects that can be achieved by the present invention include:

[0043] 1) When preparing the medium and low temperature denitration catalyst, a nitrogen-containing small molecule structure modifier is used. During the first high temperature heat treatment, the nitrogen-containing small molecule structure modifier undergoes a self-polymerization reaction to form carbon nitrides of different sizes, wherein the larger carbon nitrides are two-dimensional sheet structures, which form a composite carrier through bonding with titanium dioxide, thereby improving the electronic conductivity of the carrier, thereby improving the NOx conversion rate in the denitration reaction, and the composite carrier is also beneficial to improve the nano V 2 O 5 The dispersion of V 2 O 5The catalytic activity is reduced due to agglomeration; while the smaller carbon nitride-like materials are in situ decomposed during the second high-temperature heat treatment to form small mesopores (with a diameter of less than 10 nm) and micropores, which increase the specific surface area of ​​the catalyst. The formation of small mesopores and micropores can also enhance the adsorption and transmission capacity of gas reactants during medium and low temperature denitrification.

[0044] 2) In the process of preparing the medium and low temperature denitrification catalyst, the main active metal and the auxiliary active metal are introduced step by step, and the auxiliary agent is deposited on the catalyst surface after the main active component: on the one hand, the V 2 O 5 It is easy to contact with the auxiliary active metal component and react with the two to form M with higher catalytic activity during the second high temperature heat treatment. x VO y , improves the unstable V 4+ 、V 3+ The number of species increases, thereby improving the reduction performance of the catalyst, which is not only beneficial to improving the medium and low temperature denitrification activity of the catalyst, but also can promote the decomposition of the by-product ammonium bisulfate generated on the catalyst surface; on the other hand, it is easy to form "auxiliary agent-V 2 O 5 -Sandwich structure of the carrier", which can reduce the active components and H 2 O, SO 2 The probability of side reactions occurring due to contact with ammonium bisulfate, etc., can be reduced, thereby improving the resistance of the catalyst.

[0045] 3) In the process of preparing the medium- and low-temperature denitration catalyst, high-temperature heat treatment is performed in the process of forming the catalyst active precursor and the process of catalyst molding, respectively corresponding to the above steps (2) and (4), so as to avoid the catalyst fragmentation caused by the rapid overflow of excess gas generated by the reaction of the metal salt during a single calcination, thereby improving the catalyst yield.

[0046] 4) In summary, the medium and low temperature denitrification catalyst provided by the present invention has excellent resistance, is suitable for medium and low temperature denitrification, can take into account the denitrification effects in the low temperature zone and the medium temperature zone, and the NOx conversion rate in the temperature range of 170-370°C is above 90%, which solves the problems of low specific surface area and low effective binding rate of active centers and additives in existing vanadium-based medium and low temperature denitrification catalysts, resulting in poor denitrification efficiency and poor water resistance in lower temperature sections. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0048] Figure 1 This is a pore distribution curve diagram of the medium and low temperature denitration catalysts provided in Examples 1 to 3 of the present invention and the denitration catalyst provided in Comparative Example 1.

[0049] Figure 2 This is a denitration rate curve of the medium and low temperature denitration catalyst provided in Example 1 of the present invention at different temperatures.

[0050] Figure 3 XRD patterns of the medium and low temperature denitration catalyst provided in Example 1 of the present invention and the denitration catalyst provided in Comparative Example 3.

[0051] Figure 4a This is the XPS spectrum of V 2p in the medium and low temperature denitration catalyst provided in Example 1 of the present invention.

[0052] Figure 4b This is the XPS spectrum of V 2p in the denitration catalyst provided in Comparative Example 3.

[0053] Figure 5 This is a graph showing the water resistance performance of the medium- and low-temperature denitration catalyst provided in Example 1 of the present invention and the denitration catalyst provided in Comparative Examples 2 and 3 in denitration catalysis. DETAILED DESCRIPTION

[0054] It should be noted that the term "comprises" and any variations thereof in the specification and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0055] "Scope" disclosed in the present invention is given in the form of lower limit and upper limit. It can be one or more lower limits, and one or more upper limits respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower limit and upper limit define the boundaries of a particular range. All ranges defined in this way are combinable, i.e. any lower limit can be combined with any upper limit to form a range. For example, for a specific parameter, a range of 60-120 and 80-110 is listed, and it is understood that a range of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​listed are 1 and 2, and the maximum range values ​​listed are 3, 4 and 5, then the following ranges can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5.

[0056] In the present invention, unless otherwise specified, the numerical range "ab" represents an abbreviation of any real number combination between a and b, where a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed in the present invention, and "0-5" is just an abbreviation of these numerical combinations.

[0057] In the present invention, unless otherwise specified, all embodiments and preferred embodiments mentioned in the present invention can be combined with each other to form a new technical solution.

[0058] In the present invention, unless otherwise specified, all technical features and preferred features mentioned in the present invention can be combined with each other to form a new technical solution.

[0059] In the present invention, unless otherwise specified, "first", "second" and "third" do not indicate a sequence or limit the materials or steps, but are only used to distinguish that they are not the same steps or materials. For example, "first" and "second" in "first high-temperature heat treatment" and "second high-temperature heat treatment" are only used to indicate that they are not the same high-temperature heat treatment.

[0060] In the present invention, unless otherwise specified, all steps mentioned herein may be performed sequentially or randomly, but are preferably performed sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0061] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with the attached table, drawings and examples. The following described embodiments are some embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention. If the specific conditions are not specified in the embodiments, they are carried out according to the normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified in the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0062] Example 1

[0063] This embodiment provides a medium-low temperature denitration catalyst, which is prepared by a preparation method comprising the following specific steps:

[0064] Step (1): add 8 parts by weight of ammonium metavanadate to 150 parts by weight of 5 wt% acetic acid solution, heat the solution to 60°C until the ammonium metavanadate is dissolved, add 100 parts by weight of mixed and ground titanium dioxide and 30 parts by weight of urea, and stir ultrasonically for 1 hour to form a suspension.

[0065] Step (2): Place the suspension in step (1) in a ceramic crucible and 2 The low-temperature heat treatment and the first high-temperature heat treatment were carried out in sequence by programmed temperature rise in the atmosphere, wherein the temperature was first increased to 100°C at a heating rate of 2°C / min and maintained for 9 hours, and then increased to 550°C at a heating rate of 2°C / min and maintained for 3 hours to obtain powder A.

[0066] Step (3): 8 parts by weight of ammonium molybdate, 1 part by weight of antimony acetate, 1 part by weight of cerium acetate, and 0.5 parts by weight of niobium oxalate are dissolved in 180 parts by weight of 5 wt% acetic acid solution, heated to 80° C., stirred until the metal salt components are completely dissolved, and then all the powder A obtained in step (2), 1.5 parts by weight of hydroxymethyl cellulose, 1.5 parts by weight of polyvinyl alcohol, and 1.5 parts by weight of nano-SiO 2 , 3 parts by weight of glass fiber and 2 parts by weight of glycerol, and continue stirring for 2 hours to form mud B.

[0067] Step (4): Place the slurry B for 10 hours, then extrude it into a honeycomb catalyst embryo through a mold, dry the catalyst embryo at 80°C for 24 hours, place it in a muffle furnace with a nitrogen / air mixed atmosphere with a volume ratio of nitrogen to air of 2:1, heat it to 500°C at a heating rate of 2°C / min, and calcine (second high-temperature heat treatment) for 8 hours to obtain the medium- and low-temperature denitrification catalyst.

[0068] Example 2

[0069] This embodiment provides a medium-low temperature denitration catalyst, which differs from Embodiment 1 only in that:

[0070] In step (1), the amount of urea used is 10 parts by weight.

[0071] Example 3

[0072] This embodiment provides a medium-low temperature denitration catalyst, which differs from Embodiment 1 only in that:

[0073] The nitrogen-containing small molecule structure modifier used in step (1) is diphenylcarbazide.

[0074] Example 4

[0075] This embodiment provides a medium-low temperature denitration catalyst, which differs from Embodiment 1 only in that:

[0076] In step (1), the amount of ammonium metavanadate is 3 parts by weight;

[0077] In step (3), the amount of ammonium molybdate used is 3 parts by weight, the amount of antimony acetate used is 0.3 parts by weight, the amount of cerium acetate used is 0.3 parts by weight, and the amount of niobium oxalate used is 0.1 parts by weight.

[0078] Example 5

[0079] This embodiment provides a medium-low temperature denitration catalyst, which differs from Embodiment 1 only in that:

[0080] In step (2), the low temperature heat treatment is to increase the temperature to 80°C at a heating rate of 1°C / min and keep it for 12 hours, and the first high temperature heat treatment is to increase the temperature to 400°C at a heating rate of 5°C / min and keep it for 3 hours.

[0081] Example 6

[0082] This embodiment provides a medium-low temperature denitration catalyst, which is prepared by a preparation method comprising the following specific steps:

[0083] Step (1): add 14 parts by weight of ammonium metavanadate to 250 parts by weight of 5 wt% acetic acid solution, heat the solution to 60°C until the ammonium metavanadate is dissolved, add 100 parts by weight of mixed and ground titanium dioxide and 80 parts by weight of urea, and stir ultrasonically for 1 hour to form a suspension.

[0084] Step (2): Place the suspension in step (1) in a ceramic crucible and 2 The low-temperature heat treatment and the first high-temperature heat treatment were carried out in sequence by programmed temperature rise in the atmosphere, wherein the temperature was first increased to 120°C at a heating rate of 4°C / min and maintained for 6 hours, and then increased to 600°C at a heating rate of 4°C / min and maintained for 2 hours to obtain powder A.

[0085] Step (3): 11 parts by weight of ammonium molybdate, 0.5 parts by weight of antimony acetate, 1 part by weight of cerium acetate, and 1 part by weight of niobium oxalate are dissolved in 220 parts by weight of 5 wt% acetic acid solution, heated to 80°C, stirred until the metal salt components are completely dissolved, and then all the powder A obtained in step (2), 3 parts by weight of hydroxymethyl cellulose, 2 parts by weight of polyvinyl alcohol, 3 parts by weight of nano-SiO 2 , 3 parts by weight of glass fiber and 2 parts by weight of glycerol, and continue stirring for 2 hours to form mud B.

[0086] Step (4): Place the slurry B for 20 hours, then extrude it into a honeycomb catalyst embryo through a mold, dry the catalyst embryo at 65°C for 72 hours, place it in a muffle furnace with a nitrogen / air mixed atmosphere with a volume ratio of nitrogen to air of 2:1, heat it to 600°C at a heating rate of 5°C / min, and calcine (second high-temperature heat treatment) for 6 hours to obtain the low-medium temperature denitrification catalyst.

[0087] Example 7

[0088] This embodiment provides a medium-low temperature denitration catalyst, which is prepared by a preparation method comprising the following specific steps:

[0089] Step (1): add 10 parts by weight of ammonium metavanadate to 200 parts by weight of 5 wt% acetic acid solution, heat the solution to 60°C until the ammonium metavanadate is dissolved, add 100 parts by weight of mixed and ground titanium dioxide and 50 parts by weight of urea, and stir ultrasonically for 1 hour to form a suspension.

[0090] Step (2): Place the suspension in step (1) in a ceramic crucible and 2 The low-temperature heat treatment and the first high-temperature heat treatment were carried out in sequence by programmed temperature rise in the atmosphere, wherein the temperature was first increased to 70°C at a heating rate of 4°C / min and maintained for 12 hours, and then increased to 350°C at a heating rate of 3°C / min and maintained for 6 hours to obtain powder A.

[0091] Step (3): 5 parts by weight of ammonium molybdate, 0.5 parts by weight of antimony acetate, 0.5 parts by weight of cerium acetate, and 0.5 parts by weight of niobium oxalate are dissolved in 140 parts by weight of 5 wt% acetic acid solution, heated to 80° C., stirred until the metal salt components are completely dissolved, and then all the powder A obtained in step (2), 1.5 parts by weight of hydroxymethyl cellulose, 1.5 parts by weight of polyvinyl alcohol, and 1.5 parts by weight of nano-SiO 2 , 3 parts by weight of glass fiber and 2 parts by weight of glycerol, and continue stirring for 2 hours to form mud B.

[0092] Step (4): Place the slurry B for 8 hours, then extrude it into a honeycomb catalyst embryo through a mold, dry the catalyst embryo at 100°C for 12 hours, place it in a muffle furnace with a nitrogen / air mixed atmosphere with a volume ratio of nitrogen to air of 2:1, heat it to 400°C at a heating rate of 3°C / min, and calcine it (second high-temperature heat treatment) for 10 hours to obtain the medium- and low-temperature denitrification catalyst.

[0093] Comparative Example 1

[0094] This comparative example provides a denitration catalyst, which differs from Example 1 only in that:

[0095] In step (1), no nitrogen-containing small molecule structure modifier is used. The specific steps are: 8 parts by weight of ammonium metavanadate is added to 150 parts by weight of 5wt% acetic acid solution, the solution is heated to 60°C until the ammonium metavanadate is dissolved, 100 parts by weight of titanium dioxide is added thereto, and ultrasonic stirring is performed for 1 hour to form a suspension.

[0096] Comparative Example 2

[0097] This comparative example provides a denitration catalyst, which differs from Example 1 only in that the order of adding the main active metal and the auxiliary active metal is changed, that is, in step (1), the auxiliary active metal salt is first added, and in step (3), the powder A formed in step (2) is mixed with vanadium salt, molding additives, etc. for subsequent preparation. The preparation method of the denitration catalyst comprises the following specific steps:

[0098] Step (1): 8 parts by weight of ammonium molybdate, 1 part by weight of antimony acetate, 1 part by weight of cerium acetate, and 0.5 parts by weight of niobium oxalate are added to 180 parts by weight of a 5wt% acetic acid solution, the solution is heated to 60°C until the ammonium molybdate is dissolved, 100 parts by weight of mixed and ground titanium dioxide and 30 parts by weight of urea are added thereto, and ultrasonic stirring is performed for 1 hour to form a suspension.

[0099] Step (2): Place the suspension obtained in step (1) in a ceramic crucible and 2 The low-temperature heat treatment and the first high-temperature heat treatment were carried out in sequence by programmed temperature rise in the atmosphere, wherein the temperature was first increased to 100°C at a heating rate of 2°C / min and maintained for 9 hours, and then increased to 550°C at a heating rate of 2°C / min and maintained for 3 hours to obtain powder A.

[0100] Step (3): 8 parts by weight of ammonium metavanadate was dissolved in 150 parts by weight of 5 wt% acetic acid solution, heated to 80°C, stirred until the ammonium metavanadate was completely dissolved, and then all the powder A obtained in step (2), 1.5 parts by weight of hydroxymethyl cellulose, 1.5 parts by weight of polyvinyl alcohol, 1.5 parts by weight of nano-SiO 2 , 3 parts by weight of glass fiber and 2 parts by weight of glycerol, and continue stirring for 2 hours to form mud B.

[0101] Step (4): Place the slurry B for 10 hours, then extrude it into a honeycomb catalyst embryo through a mold, dry the catalyst embryo at 80°C for 24 hours, place it in a muffle furnace with a nitrogen / air mixed atmosphere with a volume ratio of nitrogen to air of 2:1, heat it to 500°C at a heating rate of 2°C / min, and calcine (second high-temperature heat treatment) for 8 hours to obtain the denitration catalyst.

[0102] Comparative Example 3

[0103] This comparative example provides a denitration catalyst, which differs from Example 1 in that: no nitrogen-containing small molecule structure modifier is added, vanadium salt solution, auxiliary active metal salt solution, titanium dioxide and molding additives are mixed together and only calcined once, and the preparation method of the denitration catalyst includes the following specific steps:

[0104] Step (1): adding 8 parts by weight of ammonium metavanadate to an acid solution, heating the solution to 60° C. until the ammonium metavanadate is dissolved to form a solution A;

[0105] Step (2): dissolving 8 parts by weight of ammonium molybdate, 1 part by weight of antimony acetate, 1 part by weight of cerium acetate, and 0.5 parts by weight of niobium oxalate in an acetic acid solution, heating to 80° C., and stirring until the metal salt components are completely dissolved to form a solution B;

[0106] Step (3): Add solution A and solution B to 100 parts by weight of titanium dioxide at the same time, and add 1.5 parts by weight of hydroxymethyl cellulose, 1.5 parts by weight of polyvinyl alcohol, and 1.5 parts by weight of nano-SiO 2 , 3 parts by weight of glass fiber, 2 parts by weight of glycerin and appropriate amount of water, and continue stirring for 2 hours to form mud B.

[0107] Step (4): the slurry B is placed for 10 hours, and then extruded through a mold to obtain a honeycomb catalyst embryo. The catalyst embryo is then dried at 80° C. for 12 hours, placed in a muffle furnace and calcined at 500° C. for 8 hours to obtain the denitration catalyst.

[0108] Since the comparative example only performs a single calcination during the catalyst forming process, the formed catalyst has a high internal crack ratio, which seriously reduces the catalyst yield.

[0109] Comparative Example 4

[0110] This comparative example provides a denitration catalyst, which differs from Example 1 in that:

[0111] In step (4), the atmosphere used for the second high temperature heat treatment is an air atmosphere, and the calcination is carried out at 400° C. for 6 hours.

[0112] Test Example 1

[0113] In this test example, the specific surface area, mesopore area and pore volume of the medium and low temperature denitration catalysts provided in Examples 1 to 7 and the denitration catalysts provided in Comparative Examples 1 to 4 were tested respectively. The experimental results are shown in Tables 1 and Figure 1 shown.

[0114] Table 1 Pore structure parameters of the medium and low temperature denitration catalysts provided by Examples 1 to 7 and the denitration catalysts provided by Comparative Examples 1 to 4

[0115] <![CDATA[Specific surface area (m 2 / g)]]> <![CDATA[Total pore volume (cm 3 / g)]]> <![CDATA[Mesoporous area (m 2 / g)]]> Example 1 91.55 0.26 82.88 Example 2 72.14 0.22 58.89 Example 3 86.27 0.25 64.34 Example 4 89.41 0.26 79.33 Example 5 92.67 0.27 79.71 Example 6 95.23 0.28 86.11 Example 7 92.87 0.27 84.86 Comparative Example 1 61.24 0.20 50.36 Comparative Example 2 88.56 0.25 80.29 Comparative Example 3 59.71 0.19 46.83 Comparative Example 4 98.81 0.28 84.66

[0116] It can be seen from Table 1 above that compared with the medium and low temperature denitration catalysts provided in Examples 1 to 7, the specific surface area and pore volume of the denitration catalyst prepared in Comparative Example 1 without using a nitrogen-containing small molecule structure modifier are significantly reduced, which indicates that TiO 2 The specific surface area of ​​the carrier is low, and the pore distribution is located in the mesoporous section above 20nm. In the process of catalyst preparation, the present invention introduces a nitrogen-containing small molecule structure modifier to construct a composite carrier, which can increase the specific surface area of ​​the catalyst and construct a multi-level pore structure where micropores and mesopores coexist, which is beneficial to increase the NOx and reducing agent NH in the denitration reaction. 3 The transport and adsorption of H in the reaction process is also facilitated by the high specific surface area of ​​the carrier. 2 O, SO 2 and ammonium bisulfate salts, thereby reducing their attack on the active centers of the catalyst.

[0117] By comparing the pore structure parameters of the medium and low temperature denitration catalysts provided in Example 1 and Example 2, it can be seen that when the amount of the nitrogen-containing small molecule structure modifier is reduced, the specific surface area and pore volume of the obtained medium and low temperature denitration catalyst are reduced. Figure 1 It can be seen that due to the pore-forming effect of the nitrogen-containing small molecule structure modifier, the pore size distribution of the catalysts provided by Examples 1 to 3 of the present invention migrates to a small scale compared to the denitration catalyst provided by Comparative Example 1. Compared to Example 1, Example 3 uses different types of nitrogen-containing small molecule structure modifiers, and the micropore distribution in the medium and low temperature denitration catalyst prepared therefrom is significantly increased, which indicates that the pore size distribution in the prepared medium and low temperature denitration catalyst can be adjusted by selecting different nitrogen-containing small molecule structure modifiers.

[0118] Compared with Example 1, the first high-temperature heat treatment temperature in step (2) of Example 5 is reduced to 400°C. The specific surface area and pore volume of the medium- and low-temperature denitration catalyst prepared in Example 5 are increased compared with the medium- and low-temperature denitration catalyst provided in Example 1. This is because the carbon nitride-like structure formed by the polymerization of the nitrogen-containing small molecule structure modifier at this temperature is relatively small in size and has a low thermal stability. It is easily decomposed into pores during the second high-temperature heat treatment process in step (4), and a high proportion of micropores is formed, resulting in a decrease in the mesopore area.

[0119] Compared with Example 1, the specific surface area and pore volume of the denitration catalyst provided in Comparative Example 4 are improved. This is because the second high-temperature heat treatment in an air atmosphere will cause the carbon nitride-like transition decomposition.

[0120] Test Example 2

[0121] This test example evaluates the denitration performance of the medium and low temperature denitration catalysts provided in Examples 1 to 7 and the denitration catalysts provided in Comparative Examples 1 to 4, i.e., the NOx conversion rate under different temperature conditions. x The reaction conditions for conversion evaluation include: inlet NO concentration of 420 mg / Nm 3 , ammonia nitrogen volume ratio is 1, 6.5v%O 2 , 15v%H 2 O,N 2 As a balance gas, GHSV = 3400h -1 , the reaction temperature is 140-230℃.

[0122] The denitrification evaluation data obtained in this test example are shown in Table 2 below.

[0123] Table 2 Denitration evaluation data of the medium and low temperature denitration catalysts provided in Examples 1 to 7 and the denitration catalysts provided in Comparative Examples 1 to 4

[0124]

[0125]

[0126] It can be seen from Table 2 above that the medium and low temperature denitration catalysts provided in Examples 1 to 7 of the present invention and the denitration catalysts provided in Comparative Examples 1 to 4 all exhibit good denitration effects under temperature conditions above 200°C. The difference in denitration effects is mainly reflected in the low temperature section below 170°C. Specifically:

[0127] For Example 1, Example 2 and Comparative Example 1, the amount of nitrogen-containing small molecule structure modifier used in the three is gradually reduced. It can be seen from Table 2 that as the amount of nitrogen-containing small molecule structure modifier in the raw material decreases, the denitration effect of the denitration catalyst decreases successively. On the one hand, this is because the proportion of the composite structure formed in the catalyst carrier decreases, thereby failing to form an effective heterojunction electronic conduction mode. On the other hand, it is because the formed (CN 2 ) The reduction of x structure leads to a decrease in porosity (sacrificial pore formation), which reduces the adsorption and mass transfer level of the catalyst;

[0128] The denitration rate of the medium and low temperature denitration catalysts provided in Examples 1 and 3 at a temperature of 160° C. is more than 85%, indicating that a relatively high denitration level can be achieved by changing the type of nitrogen-containing small molecule structure modifier;

[0129] By comparing the medium and low temperature denitration catalysts provided in Example 1, Example 4 and Example 6, it can be seen that when the input amount of vanadium salt or auxiliary active metal salt is reduced, the denitration effect of the medium and low temperature denitration catalyst is significantly reduced, which indicates that the metal content is the basis for ensuring the low temperature catalytic performance;

[0130] For Example 1 and Example 5, as shown in Table 1 above, the physical properties of the medium-low temperature denitration catalyst provided by Example 5 are better, but due to the large amount of decomposition of the smaller-sized carbon nitride-like particles, the proportion of carbon nitride-like particles in the composite support structure is too low, resulting in a decrease in the conduction effect and a decrease in the denitration rate;

[0131] Compared with Example 1, the reaction conditions in Examples 6 and 7 are changed to still ensure the denitration rate of the medium-low temperature denitration catalyst prepared therefrom at medium-low temperature.

[0132] Comparative Example 3 uses a conventional preparation method to prepare a denitration catalyst. Compared with the medium- and low-temperature denitration catalyst provided in the embodiment of the present invention, the low-temperature performance of the denitration catalyst prepared in Comparative Example 3 is poor. It can be seen that in the preparation method of the medium- and low-temperature denitration catalyst provided in the embodiment of the present invention, on the one hand, by adding a nitrogen-containing small molecule structure modifier to construct a composite carrier, the conductivity and mass transfer level can be improved, and the effect on the reaction kinetics under low temperature conditions is more significant; on the other hand, by step-by-step loading of the main active metal and the auxiliary active metal to form a "sandwich structure", it is conducive to the formation of a more active M x VO y , and this structure is the key to lowering the catalyst activation temperature, improving the catalyst reduction level, and achieving the "fast SCR" reaction.

[0133] In Comparative Example 4, the second high-temperature heat treatment uses an air atmosphere, which will increase the proportion of oxidative decomposition of the carbon nitride-like structure in the carrier compared to Example 1. Although the porosity of the prepared denitration catalyst is increased, the structure of the composite carrier is destroyed. Therefore, in order to balance the retention and decomposition of the carbon nitride-like structure in the medium and low temperature denitration catalyst, the atmosphere used, the temperature and time of the second high-temperature heat treatment, etc. should be adjusted.

[0134] Furthermore, this test example also evaluates the wide temperature range denitration effect of the medium and low temperature denitration catalyst provided in Example 1, and the results are as follows: Figure 2 As shown. Figure 2 It can be seen that the denitration efficiency of the medium and low temperature denitration catalyst provided in Example 1 of the present invention can reach more than 90% in the temperature range of 170-370°C. It can be reasonably inferred that the denitration efficiency of the medium and low temperature denitration catalyst provided in the embodiment of the present invention can reach more than 90% in the temperature range of 170-370°C.

[0135] Test Example 3

[0136] In this test example, XRD analysis was performed on the medium and low temperature denitration catalyst provided in Example 1 and the denitration catalyst provided in Comparative Example 3. The obtained XRD patterns are as follows: Figure 3 As shown. Figure 3It can be seen that the diffraction peaks at 25.3°, 38.0°, 48.0°, 54.0° and 55.1° correspond to the (101), (004), (200), (105) and (211) crystal planes of anatase titanium dioxide (JCPDS No. 21-1272), respectively, indicating that the preparation method provided in this embodiment can retain the anatase titanium dioxide structure with a high degree of crystallization in the obtained medium and low temperature denitration catalyst. In addition, in addition to the diffraction peak representing titanium dioxide, no obvious diffraction peaks formed by other metals are observed in the medium and low temperature denitration catalyst provided in Example 1 of the present invention, which indicates that the metal oxides formed by the main active metal and the auxiliary active metal are small in size and have good dispersibility; while the denitration catalyst provided in Comparative Example 3 shows small diffraction peaks near 21° and 26.5°, which may be due to V 2 O 5 It can be seen that in the embodiment of the present invention, the main active metal and the auxiliary active metal are loaded step by step, that is, firstly V 2 O 5 Anchored on the composite support When the active metal oxide is loaded on V 2 O 5 This is beneficial to prevent the V 2 O 5 aggregation, thus ensuring its catalytic activity.

[0137] Test Example 4

[0138] In this test example, XPS analysis was performed on the medium and low temperature denitration catalyst provided in Example 1 and the denitration catalyst provided in Comparative Example 3. The XPS spectra of V 2p in the catalysts were as follows: Figure 4a and Figure 4b shown. Figure 4a Three V species can be distinguished on the surface of the medium and low temperature denitrification catalyst, namely, V represented by the binding energies of 515.8eV, 516.6eV and 517.5eV respectively. 3+ 2p 2 / 3 、V 4+ 2p 2 / 3 and V 5+ 2p 2 / 3 Three V species. M is formed in the low temperature denitrification catalyst x VO y After that, the unstable V 3+ 、V 4+ The number of species increases, thereby improving the reducibility of the catalyst. Figure 4a and Figure 4b It can be seen from the data in that in the medium and low temperature denitration catalyst provided in Example 1 of the present invention, (V 3+ +V 4+ ) / V 5+The peak area ratio of is 0.75, while in the denitration catalyst provided in Comparative Example 3, (V 3+ +V 4+ ) / V 5+ The peak area ratio is only 0.36, which shows that the present invention can effectively increase the content of non-stable active components in the medium and low temperature denitration catalyst.

[0139] Test Example 5

[0140] This test case examines H 2 O on the denitration performance of the medium and low temperature denitration catalyst provided in Example 1 and the denitration catalyst provided in Comparative Examples 2 and 3, the reaction conditions include: the inlet NO concentration is 420 mg / Nm 3 , ammonia nitrogen volume ratio is 1, 6.5v%O 2 , 15v%H 2 O,N 2 As a balance gas, GHSV = 3400h -1 The reaction temperatures are 150°C, 160°C, 170°C and 180°C.

[0141] The H obtained in this test case 2 The results of the influence of the medium and low temperature denitration catalyst provided in Example 1 and the denitration catalyst provided in Comparative Examples 2-3 on the denitration effect are as follows: Figure 5 As shown in the figure. For medium and low temperature denitrification catalyst, when the flue gas temperature is low, H 2 O will adsorb on the active center V 2 O 5 This causes the catalyst denitrification efficiency to drop significantly. Figure 5 It can be seen that the medium and low temperature denitration catalyst provided in Example 1 of the present invention can achieve a denitration rate of 97% or more under the reaction conditions of 150-180°C without water flow, but after water flow, the denitration rate decreases with the decrease of reaction temperature, which indicates that H 2 O is an important factor affecting the denitration performance of medium and low temperature denitration catalysts. When the reaction temperature is ≥170°C, the water resistance of the medium and low temperature denitration catalyst provided in Example 1 is significantly improved, and when the water flow is stopped, the denitration performance of the medium and low temperature denitration catalyst is restored to the previous level. For the denitration catalysts provided in Comparative Examples 2 and 3, their denitration rates are low under water flow conditions, and the denitration performance of the denitration catalysts recovers slowly after the water is stopped, which indicates that the active sites of the denitration catalysts provided in Comparative Examples 2 and 3 are irreversibly deactivated during the water flow process.

[0142] This indicates that in the medium- and low-temperature denitration catalyst provided by the embodiment of the present invention, the auxiliary active metal oxide is coated on the outer layer of the main active metal oxide, which can effectively improve the water resistance of the catalyst.

[0143] The above is only a specific embodiment of the present invention, and cannot be used to limit the scope of the invention. Therefore, the replacement of equivalent components, or equivalent changes and modifications made according to the protection scope of the patent of the present invention, should still fall within the scope of this patent. In addition, the technical features of the present invention can be freely combined with each other, with each other and with each other, and with each other.

Claims

1. A medium and low temperature denitration catalyst, wherein: The medium-low temperature denitration catalyst comprises a carrier, V2O5 and an active metal oxide, wherein the carrier is a carbon nitride-like / titanium dioxide composite carrier, in which titanium dioxide is loaded on a carbon nitride-like having a two-dimensional sheet structure in a bonding form; V2O5 and the auxiliary active metal oxide are loaded on the carbon nitride / titanium dioxide composite carrier to form a sandwich structure of the auxiliary active metal oxide-V2O5-carbon nitride / titanium dioxide composite carrier, and the interface where the auxiliary active metal oxide contacts with V2O5 forms a composite oxide of vanadium and the auxiliary active metal.

2. The medium and low temperature denitration catalyst according to claim 1, wherein: The auxiliary active metal oxide includes one or a combination of Ce, Fe, Mo, Nb, Sb, Sm and W oxides.

3. The medium and low temperature denitration catalyst according to claim 1, wherein: The mass ratio of V2O5, TiO2, carbon nitride-like and active metal oxide is 2-10:100:5-50:2-10.

4. The medium and low temperature denitration catalyst according to any one of claims 1 to 3, wherein: The specific surface area of ​​the medium and low temperature denitration catalyst is greater than 70m 2 / g, with mesoporous and microporous structures.

5. The method for preparing the medium-low temperature denitration catalyst according to any one of claims 1 to 4, wherein: The preparation method comprises: Step (1): mixing a vanadium salt solution, titanium dioxide and a nitrogen-containing small molecule structure modifier to obtain a suspension; Step (2): subjecting the suspension to a low-temperature heat treatment and a first high-temperature heat treatment in sequence in an inert atmosphere to obtain a powder; Step (3): uniformly mixing the active metal salt solution, the molding additive and the powder to obtain a slurry; Step (4): aging the mud material and then extruding it to obtain a catalyst embryo, drying the catalyst embryo and then performing a second high-temperature heat treatment to obtain the medium- and low-temperature denitration catalyst.

6. The preparation method according to claim 5, wherein: The mass ratio of vanadium salt, titanium dioxide, nitrogen-containing small molecule structure modifier and auxiliary active metal salt is 3-15:100:10-80:3-14; Preferably, the mass ratio of titanium dioxide to nitrogen-containing small molecule structure modifier is 100:20-50.

7. The preparation method according to claim 5 or 6, wherein: In step (1), the vanadium salt includes one or a combination of ammonium orthovanadate, ammonium metavanadate, potassium metavanadate and ammonium polyvanadate.

8. The preparation method according to claim 5 or 6, wherein: In step (1), the nitrogen-containing small molecule structure modifier includes one or a combination of urea, melem, carbonamide, cyanamide, semicarbazide and carbonyl hydrazide compounds.

9. The preparation method according to claim 5, wherein: In step (2), the temperature of the low-temperature heat treatment is 60-120°C, preferably 80-100°C, the heating rate is 1-4°C / min, and the time is 6-12h.

10. The preparation method according to claim 5 or 9, wherein: In step (2), the temperature of the first high temperature heat treatment is 350-600°C, the heating rate is 2-5°C / min, and the time is 1-6h; Preferably, the temperature of the first high temperature heat treatment is 400-550° C., and the time is 2-4 hours.

11. The preparation method according to claim 5 or 6, wherein: In step (3), the auxiliary active metal salt includes one or a combination of soluble ammonium salts or organic acid salts of Ce, Fe, Mo, Nb, Sb, Sm and W.

12. The preparation method according to claim 5 or 6, wherein: In step (3), the molding additive includes one or a combination of oxalic acid, polyvinyl alcohol, carboxymethyl cellulose, hydroxymethyl cellulose, hydroxypropyl cellulose, polyethylene oxide, glycerol, nano-SiO2, glass fiber and water.

13. The preparation method according to claim 5, wherein: In step (4), the temperature of the second high temperature heat treatment is 400-600°C, preferably 400-550°C, the heating rate is 2-5°C / min, and the time is 6-10h.

14. The preparation method according to claim 5 or 13, wherein: In step (4), the atmosphere of the second high-temperature heat treatment includes one of nitrogen, argon or a nitrogen / air mixture, wherein the volume ratio of nitrogen to air in the nitrogen / air mixture is not less than 1:

1.

15. Use of the medium-low temperature denitration catalyst according to any one of claims 1 to 4 in medium-low temperature denitration, wherein: The temperature of medium and low temperature denitrification is 170-370℃.

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