CN115646483A - Low-temperature denitration catalyst of Sm-Mn-Ce composite oxide loaded on cordierite and preparation method thereof - Google Patents

Abstract

The invention relates to a cordierite-loaded Sm-Mn-Ce composite oxide low-temperature denitration catalyst and a preparation method thereof. The method comprises the following specific steps: pretreating cordierite to be used as a catalyst carrier, and performing one-step impregnation on MnO _x Loaded on the surface of the alloy and doped with rare earth elements Sm and Ce to MnO _x And modifying to obtain the cordierite loaded Sm-Mn-Ce composite oxide low-temperature denitration catalyst. The catalyst of the present invention is characterized in that: the mass ratio of the active component to the cordierite is 0.4-0.6, and the molar ratio of Sm, ce and Mn in the active component is Sm: ce: mn = (0.05-0.3) to (0.15-0.4) to 1. The catalyst has good low-temperature denitration performance within 20,000 hours ^‑1 At a test airspeed of 60 to 270 ℃, NO _x Removal efficiency and nitrogen selectionThe performance can reach 80%, and in addition, the sulfur-resistant performance is relatively excellent. The interaction among Sm, mn and Ce effectively improves the physical and chemical properties of the surface of the catalyst, and is beneficial to improving NO at low temperature _x The removal efficiency of (2). Therefore, the catalyst has stronger practical significance and development prospect.

Description

Low-temperature denitration catalyst of Sm-Mn-Ce composite oxide loaded on cordierite and preparation method thereof

Technical Field

The invention belongs to the technical field of a novel low-temperature denitration catalyst and a preparation method thereof, and particularly relates to a Sm-Mn-Ce composite oxide loaded catalyst taking cordierite as a carrier, which can be used for selective catalytic reduction denitration of flue gas at low temperature (less than 300 ℃).

Background

Currently, due to the unique energy structure of China, primary energy sources such as coal, petroleum, natural gas and the like occupy a main position, and after being combusted, the primary energy sources can discharge gas which is not friendly to the environment to the atmosphere. For example, nitrogen oxides in coal-fired flue gas are atmospheric pollutants which are harmful to the environment and human bodies, and can react with water and oxygen in the atmosphere to generate acidic substances such as nitric acid and the like, so that acid rain is formed, and then, the natural world, buildings and the like are corroded. And can also have chemical reaction with body fluid substances in human body, which causes serious harm to nervous system, respiratory system, etc. Therefore, the method is very important for treating nitrogen oxides in the atmosphere.

At present, the means for treating nitrogen oxides discharged by coal-fired power plants is mainly a selective catalytic reduction technology in a flue gas post-treatment technology. The technology is that after flue gas passes through a denitration catalyst, ammonia or urea is used as a reducing agent to react with nitrogen oxides in the flue gas, and the nitrogen oxides are selectively converted into nitrogen and water. The technology has the advantages of good actual denitration effect, low cost and the like, and is beneficial to the transformation of old power plants, so that the technology is widely applied to coal-fired power plants. At present, when the technology is applied to a coal-fired power plant, a denitration device is generally arranged in a high-dust mode, and a vanadium-titanium catalyst (such as V) is applied as the catalyst ₂ O ₅ /TiO ₂ 、V ₂ O ₅ -WO ₃ /TiO ₂ ) Its active temperature is high (300-400 deg.C), and it is easy to cause blockage and poisoning. And a low-temperature catalyst (the temperature window is below 300 ℃) can be used in the low-dust low-temperature arrangement, so that the blockage can be reduced, the catalyst can be prevented from being reheated, and the cost is saved. Therefore, the development of a novel low-temperature denitration catalyst has important significance.

Manganese oxide (MnO) _x ) Due to its excellent low-temperature denitration performance, rich reserves and comparison with V ₂ O ₅ Has the advantages of environmental friendliness and the like, and has been widely paid attention in the field of flue gas denitration in recent years. However, there are some disadvantages in itself, such as: poor resistance to sulfur poisoning and operating temperatureThe window is narrow and the nitrogen selectivity is poor at high temperatures. In order to solve the above problems, the researchers have conducted extensive and intensive studies and found that, on the one hand, it is possible to obtain a compound having a structure represented by the following formula (I): noble metals gold (Au), silver (Ag), platinum (Pt); transition metals iron (Fe), cobalt (Co), copper (Cu); modifying rare earth elements such as cerium (Ce), samarium (Sm), europium (Eu) and the like; alternatively, by selecting a suitable support, such as titanium dioxide (TiO) ₂ ) Aluminum oxide (Al) ₂ O ₃ ) Etc., loading the active component on the surface of the carrier; the denitration performance of the catalyst can be improved by designing and regulating the structure of the catalyst to protect the active sites of the catalyst, such as designing and constructing a core-shell structure and the like. Therefore, how to modify the manganese oxide to improve the comprehensive performance of the catalyst is the current research focus and focus, and modification by introducing other elements is a relatively simple implementation manner.

In a practical commercial environment, the structure of the catalyst and the reactor is very important, and the heat transfer of the catalyst in practical application can be reduced, so that the denitration performance and the nitrogen selectivity of the catalyst are improved. NH (NH) ₃ SCR is a complex gas-solid catalytic reaction involving NH ₃ NO and O ₂ So that good diffusive transport of reactant gases is critical to the ability of the reactants to fully contact the active sites on the catalyst surface. Furthermore, NH ₃ SCR is also a highly exothermic reaction and must effectively remove heat from the catalyst bed, otherwise excessive ambient temperatures may lead to NH ₃ Over oxidation to N ₂ O、SO ₂ Over oxidation to SO ₃ The problems of reaction efficiency reduction, catalyst deactivation and the like are caused. Therefore, in practical applications, the catalyst powder is usually extruded or coated onto a honeycomb or plate-shaped monolithic support. Cordierite, as a bulk solid having a honeycomb shape, is often used in the field of denitration as a catalyst carrier. In conclusion, the cordierite is used as a carrier, rare earth elements Sm and Ce are doped, and a loading method of one-step impregnation is utilized to prepare the cordierite loaded Sm-Mn-Ce composite oxide low-temperature denitration catalyst.

At present, the invention patent about cordierite mainly focuses on the preparation of ceramics and the like by taking cordierite as a raw material, and the cordierite is applied to various scenes. For example, chinese patent CN112110719B "a ceramic tile with natural granular sensation and a preparation method thereof"; for example, chinese patent CN112194376B, "red light emitting glass ceramic and its preparation method and LED/LD light emitting device", etc. In the field of flue gas denitration, the carrier is mainly used as a carrier, and other active components are loaded. For example, chinese patent CN110882691B 'a cordierite loaded medium-temperature denitration catalyst and a preparation method thereof'; for example, chinese patent CN111530463B, "denitration catalyst of honeycomb ceramic supported double oxide rice husk ash carrier, preparation method and application"; for example, chinese patent CN105688892B, "a method for preparing a honeycomb SCR denitration catalyst", etc. Therefore, the invention uses cordierite as carrier, and uses simple impregnation method to load MnO on the surface _x And rare earth elements Sm and Ce are doped for modification to prepare the cordierite loaded Sm-Mn-Ce composite oxide low-temperature denitration catalyst.

Disclosure of Invention

The invention aims to provide a catalyst which has the advantages of wide temperature window, good nitrogen selectivity, good sulfur resistance and simple preparation method. The catalyst is a Sm-Mn-Ce composite oxide loaded by cordierite, and is mainly applied to removal of nitrogen oxides in coal-fired flue gas and other fixed sources needing to remove the nitrogen oxides.

The second purpose of the invention is to provide a preparation method of the low-temperature denitration catalyst which takes cordierite as a carrier and Sm-Mn-Ce composite oxide as an active component.

In order to achieve the purpose, the invention adopts the following technical scheme:

the technical scheme mainly comprises the following two preparation steps: pretreatment of cordierite and loading of active components.

Specifically, the cordierite is pretreated as follows:

(1) Cordierite was cut into rectangular parallelepiped small pieces of 4X 8 cm for subsequent loading with active components and testing of denitration performance. And then adding cut cordierite into a beaker filled with a certain amount of deionized water, wherein the mass ratio of the cordierite to the deionized water is 0.01-0.02, putting the beaker into an ultrasonic cleaning machine, washing for 5-10 min, and washing off dust and debris generated on the surface of the beaker in the production process and cutting. (2) And putting the washed cordierite into a new beaker, adding deionized water according to the proportion, putting the beaker on a magnetic stirring table, stirring and soaking at normal temperature for 2-4h, taking out the cordierite, and putting the cordierite into an oven to dry for 8-12 h. (3) And putting the dried cordierite into a muffle furnace for calcining at the temperature of 500-800 ℃ for 2-4h at the heating rate of 3-5 ℃/min. And finishing the cordierite pretreatment link, and packaging the obtained cordierite for later use.

Specifically, the loading steps of the active components are as follows:

(1) The mass ratio of the active component to the cordierite is 0.4-0.6 when the active component is loaded, and the molar ratio of Sm, ce and Mn in the active component is Sm: ce: mn = (0.05-0.3) to (0.15-0.4) 1. (2) Firstly, weighing metal salt precursors (samarium nitrate hexahydrate, cerium nitrate hexahydrate and manganese nitrate tetrahydrate) with corresponding mass according to different Sm/Ce/Mn molar ratios, putting the metal salt precursors into a beaker, adding a certain amount of deionized water, wherein the mass ratio of the metal salt to the deionized water is 0.03-0.05, and carrying out ultrasonic treatment for 5-15 min to completely dissolve the metal salt. (3) And then placing the pretreated cordierite into a salt solution, violently stirring for 8-12 h on a magnetic stirring table at the temperature of 85-100 ℃ until the water is completely evaporated, taking out the sample, and placing the sample in an oven to dry for 8-12 h. (4) And calcining the dried sample for 2-4h at 380-460 ℃ by using a muffle furnace at the heating rate of 1-3 ℃/min. This is the end of the loading of the active ingredient. Obtaining the cordierite loaded Sm-Mn-Ce composite oxide low-temperature denitration catalyst.

The catalyst of the present invention is characterized in that: the catalyst is a Sm-Mn-Ce composite oxide loaded on cordierite, an active component Sm-Mn-Ce composite oxide is in an amorphous state, the molar ratio of the Sm-Mn-Ce composite oxide to the active component Sm-Ce-Mn = (0.05-0.3) to (0.15-0.4) to 1, the mass ratio of the active component to the cordierite is 0.4-0.6, and the Mn oxide is formed by Mn ²⁺ 、Mn ^{3 +} 、Mn ⁴⁺ Three valence state compositions, the mol percentage content is Mn ²⁺ : Mn ³⁺ : Mn ⁴⁺ 45 to 47 percent of (wt%), 31 to 35 percent of (wt%) and 19 to 23 percent of (wt%). The catalyst contains a large amount of mesoporous structures of 4 to 6 nm, and the specific surface area of the catalyst is 40 to 60 m ² /g。

The catalyst preparation method of the invention is characterized in that: the pretreated cordierite is used as a carrier, the Sm-Mn-Ce composite oxide is used as an active component, and the loading is realized by adopting an impregnation method.

Compared with the prior art, the invention has the following advantages: (1) The prepared catalyst has good low-temperature denitration performance, and NO is in the temperature range of 60-270 ℃ at the test airspeed of 20,000 h < -1 > _x The removal efficiency can reach more than 80 percent, and the nitrogen selectivity can also be maintained at more than 80 percent. (2) The prepared catalyst has excellent sulfur resistance within 20,000 h ^-1 At test space velocity of (2), SO of 100 ppm ₂ Under the existing condition, the denitration performance of the catalyst at 180 ℃ is still kept above 80% within 15 h. (3) The preparation method is simple, the active component is loaded by using a one-step impregnation method after the cordierite as the carrier is simply pretreated, the loading method is simple, and the preparation cost of the catalyst is reduced. (4) After rare earth elements Sm and Ce are doped for modification, the interaction among the active components Sm, mn and Ce improves the quantity and distribution of acid sites on the surface of the catalyst and the redox capability of the catalyst, and provides a favorable reaction environment for the surface of the catalyst. (5) The introduction of Sm element makes Mn on the surface of the catalyst ⁴⁺ And surface chemical adsorption of oxygen (O) _S ) The concentration of the catalyst is in a higher level, the adsorption capacity of the catalyst to nitrogen oxide species is improved, and the improvement of NO at low temperature is facilitated _x The removal efficiency of (2).

Drawings

[1] FIG. 1 shows the morphology (scanning electron microscope photographs) of a carrier cordierite and a Sm-Mn-Ce composite oxide catalyst loaded on cordierite obtained in examples 1 and 2.

[2] FIG. 2 is a graph showing the denitration performance and nitrogen selectivity test results of a control sample (MnCe/cordierite catalyst prepared without introduction of Sm) and cordierite supported Sm-Mn-Ce composite oxide catalysts obtained according to examples 1-3.

[3] FIG. 3 is a graph showing the results of a water and sulfur resistance test of a control sample (MnCe/cordierite catalyst prepared without introduction of Sm) and a cordierite supported Sm-Mn-Ce composite oxide catalyst obtained in example 2.

Detailed Description

Example 1:

first, cordierite is cut into 4X 8 cm rectangular blocks, then 0.4 g of cut cordierite carrier is put into a beaker filled with 40 mL of deionized water, and the beaker is put into an ultrasonic cleaning machine to be washed for 5 min. And putting the washed cordierite into a new beaker, adding 40 mL of deionized water, putting the beaker on a magnetic stirring table, stirring and soaking at normal temperature for 2 hours, taking out the cordierite, and putting the cordierite into an oven to dry for 8 hours. And putting the dried cordierite into a muffle furnace for calcining, wherein the calcining temperature is 500 ℃, the calcining time is 4h, and the heating rate is 3 ℃/min. The following is the loading of the active ingredients: firstly, 0.63 g of manganese nitrate tetrahydrate, 0.43 g of cerium nitrate hexahydrate and 0.06 g of samarium nitrate hexahydrate are taken, the metal salts are mixed and added into a beaker filled with 30 mL of deionized water, and the mixture is subjected to ultrasonic treatment for 5 min. And then putting the pretreated cordierite into a salt solution, violently stirring for 8 hours at the temperature of 100 ℃ on a magnetic stirring table until the water is completely evaporated, taking out the sample, and drying the sample in an oven for 8 hours. And calcining the dried sample for 4 hours at 380 ℃ by using a muffle furnace at the heating rate of 1 ℃/min. Obtaining the cordierite loaded Sm-Mn-Ce composite oxide low-temperature denitration catalyst.

The catalyst is a cordierite-loaded Sm-Mn-Ce composite oxide low-temperature denitration catalyst, wherein the molar ratio of Sm to Ce to Mn is 0.05. The catalyst has excellent low-temperature denitration performance, the denitration performance is over 80% in the temperature range of 60-240 ℃, and the denitration efficiency of 90-210 ℃ is close to 100%. In addition, the active components of the catalyst are distributed on the surface of the carrier in an amorphous state, all elements are uniformly distributed, the surface of the catalyst has rich acid sites and good redox performance, mnO _x Consisting of three valence states, in which Mn ⁴⁺ The ratio is 19 percent, and the interaction among Sm, mn and Ce is beneficial to the catalyst to oxidize nitrogenThe adsorption of the seeds can improve the low-temperature denitration performance of the catalyst.

Example 2:

first, cordierite is cut into 4X 8 cm rectangular blocks, then 0.4 g of cut cordierite carrier is put into a beaker filled with 30 mL of deionized water, and the beaker filled with cordierite is put into an ultrasonic cleaning machine to be washed for 8 min. And putting the washed cordierite into a new beaker, adding 30 mL of deionized water, putting the beaker on a magnetic stirring table, stirring and soaking at normal temperature for 3 hours, taking out the cordierite, and putting the cordierite into an oven to dry for 10 hours. And putting the dried cordierite into a muffle furnace for calcining at 600 ℃ for 3 h at the heating rate of 4 ℃/min. The following is the loading of the active ingredient: firstly, 0.63 g of manganese nitrate tetrahydrate, 0.19 g of cerium nitrate hexahydrate and 0.11 g of samarium nitrate hexahydrate are taken, the metal salts are mixed and added into a beaker filled with 25 mL of deionized water, and the mixture is subjected to ultrasonic treatment for 10 min. And then placing the pretreated cordierite into a salt solution, violently stirring for 10 hours on a magnetic stirring table in an environment of 90 ℃ until the water is completely evaporated, taking out a sample, and placing the sample in an oven to dry for 10 hours. And calcining the dried sample for 3 hours at 420 ℃ by using a muffle furnace, wherein the heating rate is 2 ℃/min. Obtaining the cordierite loaded Sm-Mn-Ce composite oxide low-temperature denitration catalyst.

The catalyst is a cordierite-loaded Sm-Mn-Ce composite oxide low-temperature denitration catalyst, wherein the molar ratio of Sm to Ce to Mn is 0.1. The catalyst has excellent low-temperature denitration performance, the denitration performance is over 80% in the temperature range of 60-270 ℃, and the denitration efficiency of 90-240 ℃ is close to 100%. The catalyst has excellent sulfur resistance, and 100 ppm of SO at a test space velocity of 20,000 h < -1 > ₂ Under the existing condition, the denitration performance of the catalyst at 180 ℃ is still maintained to be more than 80% within 15 h. In addition, the active components of the catalyst are distributed on the surface of the carrier in an amorphous state, all elements are uniformly distributed, the surface of the catalyst has rich acid sites and good redox performance, mnO _x Consisting of three valence states, in which Mn ⁴⁺ The ratio is 23 percent, and the interaction among Sm, mn and Ce is beneficial to the nitrogen oxide of the catalystThe adsorption of the seeds can improve the low-temperature denitration performance of the catalyst.

Example 3:

first, cordierite is cut into 4X 8 cm rectangular blocks, and then 0.4 g of the cut cordierite carrier is put into a beaker containing 20 mL of deionized water, and the beaker is put into an ultrasonic cleaning machine to be washed for 10 min. And (3) putting the washed cordierite into a new beaker, adding 20 mL of deionized water, putting the beaker on a magnetic stirring table, stirring and soaking at normal temperature for 4 hours, taking out the cordierite, and putting the cordierite into an oven to dry for 12 hours. And putting the dried cordierite into a muffle furnace for calcining, wherein the calcining temperature is 800 ℃, the calcining time is 2 h, and the heating rate is 5 ℃/min. The following is the loading of the active ingredients: firstly, 0.63 g of manganese nitrate tetrahydrate, 0.16 g of cerium nitrate hexahydrate and 0.33 g of samarium nitrate hexahydrate are taken, the metal salts are mixed and added into a beaker filled with 20 mL of deionized water, and the mixture is subjected to ultrasonic treatment for 15 min. And then putting the pretreated cordierite into a salt solution, violently stirring for 12 hours at the temperature of 85 ℃ on a magnetic stirring table until the water is completely evaporated, taking out the sample, and drying the sample in an oven for 12 hours. And calcining the dried sample for 2 h at 460 ℃ by using a muffle furnace, wherein the heating rate is 3 ℃/min. Obtaining the cordierite loaded Sm-Mn-Ce composite oxide low-temperature denitration catalyst.

The catalyst is a cordierite-loaded Sm-Mn-Ce composite oxide low-temperature denitration catalyst, wherein the molar ratio of Sm to Ce to Mn is 0.3. The catalyst has excellent low-temperature denitration performance, the denitration performance is over 80 percent in the temperature range of 60-240 ℃, and the denitration efficiency at 90-210 ℃ is close to 100 percent. In addition, the active components of the catalyst are distributed on the surface of the carrier in an amorphous state, all elements are uniformly distributed, the surface of the catalyst has rich acid sites and good redox performance, mnO is added _x Consisting of three valence states, in which Mn ⁴⁺ The ratio is 21%, and the interaction among Sm, mn and Ce is favorable for the adsorption of the catalyst on nitrogen oxide species, so that the low-temperature denitration performance of the catalyst is improved.

Claims (5)

1. Low temperature of cordierite loaded Sm-Mn-Ce composite oxideDenitration catalyst, its characterized in that: the catalyst is Sm-Mn-Ce composite oxide loaded on cordierite, an active component Sm-Mn-Ce composite oxide is in an amorphous state, and three metal elements of Sm, ce and Mn are uniformly distributed on the surface of the cordierite, wherein MnO is added _x From Mn ²⁺ 、Mn ³⁺ 、Mn ⁴⁺ Three valence states, and the mol percentage content ranges of each valence state are as follows: mn ²⁺ : Mn ³⁺ : Mn ⁴⁺ The catalyst comprises a large amount of mesoporous structures with the sizes of 4 to 6 nm and the specific surface area of the catalyst is 40 to 60 m (45 to 47%) ² /g。

2. The low-temperature denitration catalyst of a cordierite-supported Sm-Mn-Ce composite oxide as claimed in claim 1, wherein the mass ratio of active component to cordierite is in the range of 0.4-0.6, and the composition ratio of active component is Sm: ce: mn = (0.05-0.3) to (0.15-0.4) 1 in molar ratio.

3. The low-temperature denitration catalyst of the cordierite-loaded Sm-Mn-Ce composite oxide, which is disclosed by claim 1, is characterized in that: the preparation process comprises two steps of cordierite pretreatment and active component loading; the pretreated cordierite is used as a carrier, the Sm-Mn-Ce composite oxide is used as an active component, and the catalyst is prepared by adopting an impregnation method.

4. The method for preparing the cordierite-loaded Sm-Mn-Ce composite oxide low-temperature denitration catalyst according to claim 3, wherein the cordierite pretreatment steps are as follows:

(1) Cutting cordierite into 4 multiplied by 8 cm cuboid small blocks, adding the cut cordierite into a beaker filled with a certain amount of deionized water, wherein the mass ratio of the cordierite to the deionized water is 0.01-0.02, putting the beaker into an ultrasonic cleaning machine for washing for 5-10 min, and washing off dust and debris generated in the production process and the cutting process on the surface of the beaker;

(2) Putting the washed cordierite into a new beaker, adding deionized water according to the proportion, putting the beaker on a magnetic stirring table, stirring and soaking at normal temperature for 2-4h, taking out the cordierite, and putting the cordierite into an oven to dry for 8-12 h;

(3) And putting the dried cordierite into a muffle furnace for calcining at the temperature of 500-800 ℃ for 2-4h at the heating rate of 3-5 ℃/min.

5. The preparation method of the cordierite-loaded Sm-Mn-Ce composite oxide low-temperature denitration catalyst according to claim 3, wherein the loading steps of the active components are as follows:

(1) When the active component is loaded each time, the mass ratio of the active component to cordierite is 0.4-0.6, and the molar ratio of Sm, ce and Mn in the active component is Sm: ce: mn = (0.05-0.3) to (0.15-0.4) to 1;

(2) Firstly, weighing metal salt precursors (samarium nitrate hexahydrate, cerium nitrate hexahydrate and manganese nitrate tetrahydrate) with corresponding mass according to different Sm/Ce/Mn molar ratios, putting the metal salt precursors into a beaker, adding a certain amount of deionized water, wherein the mass ratio of the metal salt to the deionized water is 0.03-0.05, and carrying out ultrasonic treatment for 5-15 min to completely dissolve the metal salt;

(3) Then placing the pretreated cordierite into a salt solution, violently stirring for 8-12 h on a magnetic stirring table at 85-100 ℃ until the water is completely evaporated, taking out a sample, and placing the sample in an oven to dry for 8-12 h;

(4) And calcining the dried sample for 2-4h at 380-460 ℃ by using a muffle furnace at the heating rate of 1-3 ℃/min.

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