CN115845907A - Low-temperature SCR catalyst and preparation method and application thereof - Google Patents

Abstract

The invention discloses a low-temperature SCR catalyst and a preparation method and application thereof, belonging to the technical field of catalysts. The provided low-temperature SCR catalyst comprises a carrier molecular sieve and a layered metal oxide Mn-Cu loaded on the carrier molecular sieve through bridging metal atoms. The low-temperature SCR catalyst provided by the method takes the molecular sieve as a matrix, and carries out the loading of active metal Mn and Cu species in a mode of in-situ growth of a nano flaky metal oxide precursor, so that the low-temperature SCR catalyst which is high in specific surface area, highly dispersed and uniformly distributed in Mn and Cu species is obtained, and the further improvement of the catalytic efficiency is facilitated.

Description

A kind of low temperature SCR catalyst and its preparation method and application

technical field

The invention relates to the technical field of catalysts, in particular to a low-temperature SCR catalyst and its preparation method and application.

Background technique

The current environment is facing serious air pollution problems represented by smog. Nitrogen oxide (NO _x ) is an important one among many precursors that form smog. A large amount of _NOx emissions will not only bring about problems such as acid rain and ozone depletion, but also easily form secondary particulate matter through complex chemical reactions with SO ₂ , NH ₃ and hydrocarbon compounds in the atmosphere, which will bring great harm to human health and the ecological environment. Great harm. Flue gas denitrification in non-electricity industries is the focus of my country's current atmospheric environment control work, and its flue gas temperature is generally 80-300 °C. Selective Catalytic Reduction (SCR) is currently the most effective way to remove NO _x . SCR technology uses NH ₃ as a reducing agent to selectively catalytically reduce NO _x to N ₂ . The core of this technology is a catalyst. However, due to the low flue gas temperature (80-300°C) in the non-electricity industry, it is difficult to match the working temperature range (300-400°C) of the vanadium-tungsten-titanium catalyst in the thermal power industry. The solid waste nature of the species also increases catalyst recovery costs. Therefore, the development of efficient and stable low-temperature SCR catalysts is very important to achieve efficient _NOx treatment of flue gas in non-electric industries.

In view of the above problems, it is necessary to provide a low-temperature SCR catalyst and its preparation method and application.

Contents of the invention

The object of the present invention is to provide a low-temperature SCR catalyst and its preparation method and application in order to overcome the above-mentioned defects in the prior art.

The present invention solves its technical problems by adopting the following technical solutions.

The invention provides a low-temperature SCR catalyst. The low-temperature SCR catalyst includes a carrier and a layered metal oxide supported on the carrier by bridging metal atoms.

The present invention also provides a method for preparing a low-temperature SCR catalyst, which includes: growing a precursor layered metal hydroxide on a carrier in situ, and then calcining to obtain a low-temperature SCR catalyst.

The present invention also provides the use of a low-temperature SCR catalyst for converting NO _x in a low temperature window, and the low temperature window is 80-300°C.

The present invention has the following beneficial effects:

The invention provides a low-temperature SCR catalyst and its preparation method and application. The low-temperature SCR catalyst includes a carrier and a layered metal oxide supported on the carrier by bridging metal atoms. The provided low-temperature SCR catalyst uses the carrier as the matrix, and supports the active metal by bridging metal atoms to grow nano-sheet metal oxides in situ, and it is expected to obtain a high specific surface area, highly dispersed and uniformly distributed active metals. The SCR catalyst is helpful to further improve the catalytic efficiency.

Description of drawings

In order to illustrate the technical solutions of the embodiments of the present invention more clearly, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and thus It should be regarded as a limitation on the scope, and those skilled in the art can also obtain other related drawings based on these drawings without creative work.

Fig. 1 is the scanning electron microscope picture that embodiment 1 and comparative example 1 make catalyst;

Fig. 2 embodiment 1 and comparative example 1 make catalyst N Adsorption _and desorption curve;

Fig. 3 is the denitration efficiency curves of catalysts prepared in Example 1 and Comparative Example 1 at different temperatures.

Detailed ways

In order to make the purpose, 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 who do not indicate the specific conditions in the examples are carried out according to the conventional conditions or the conditions suggested by the manufacturer. The reagents or instruments used were not indicated by the manufacturer, and they were all conventional products that could be purchased from the market.

Active components in low-temperature SCR catalysts are generally transition metal oxides (or metal ions), such as manganese oxides and copper oxides with good redox properties. Molecular sieves (Z) have the advantages of high specific surface area, regular and orderly pores, easy modification of active ions, and good thermal stability, and are widely used as SCR catalyst supports. However, molecular sieve catalysts have the disadvantages of limited loading of active metal species (such as Mn, Cu) and difficulty in uniform distribution, which limits their multifunctional modification and further improvement of activity.

The target metal oxide (layered double oxide, LDO)-based SCR catalyst can be obtained by preparing a layered metal hydroxide (Layered double hydrotalcite, LDH) containing the target active metal (such as Mn, Cu) and then calcining it. The LDO catalyst prepared by this method can maintain the layered structure of LDH and has structural uniformity at the atomic level. Compared with the conventional precipitation method, impregnation method and ion exchange method, it is more conducive to the dispersion of active metal species on the denitration catalyst. However, there are still some shortcomings in the current LDO catalysts: due to the aggregation and stacking of the laminates, the specific surface area is small, which hinders the contact between the reactants and the active components, which is not conducive to the further improvement of the catalytic efficiency. If molecular sieves can be used as substrates to support active metal Mn and Cu species in the form of in-situ growth of nano-sheet metal oxide precursors, it is expected to obtain a high specific surface area, highly dispersed and uniformly distributed Mn and Cu atoms. LDO/Z catalyst contributes to the further improvement of catalytic efficiency.

A low-temperature SCR catalyst provided in an embodiment of the present invention, its preparation method and application are specifically described below.

In a first aspect, an embodiment of the present invention provides a low-temperature SCR catalyst. The low-temperature SCR catalyst includes a carrier and a layered metal oxide supported on the carrier by bridging metal atoms.

In an alternative embodiment, the bridging metal atom is Al, and the layered metal oxide is a layered metal oxide of Mn and/or Cu and Al, wherein the bridging metal atom is connected to each adjacent carrier and layered metal oxide. At least one covalent bond is formed between the oxides.

In an optional embodiment, the molar ratio of Al, Mn and/or Cu in the low temperature SCR catalyst is 0.8-1.2:1.5-2.5.

In an optional embodiment, the layered metal oxide accounts for 40-60% of the low-temperature SCR catalyst.

In an optional embodiment, the carrier is a molecular sieve, and the molecular sieve includes any one of NaY, ZSM-5, 13X, MCM-41, SBA-15, USY, MOR, SSZ-13, SAPO-34, and SSZ-39 kind.

In the second aspect, the embodiment of the present invention also provides a method for preparing a low-temperature SCR catalyst, which includes: growing a precursor layered metal hydroxide on a carrier in situ, and then calcining to obtain a low-temperature SCR catalyst.

In an optional embodiment, the following steps are included: dissolving manganese salts, copper salts, and aluminum salts in water to obtain a first solution, dissolving molecular sieves and carbonates in water to obtain a second solution, and continuing the second solution Stir, then slowly add the first solution to the second solution dropwise, use lye to adjust the pH of the solution during the dropwise addition, continue to stir after the dropwise addition, let it stand for aging, then filter the mixed solution with suction, wash and dry Finally, the carrier-supported precursor layered metal hydroxide powder is obtained, and the obtained powder can be calcined at a high temperature to prepare a low-temperature SCR catalyst.

In an optional embodiment, the manganese salt is manganese chloride, manganese nitrate or manganese sulfate; the aluminum salt is aluminum chloride, aluminum nitrate or aluminum sulfate, and the copper salt is copper chloride, copper nitrate or copper sulfate; It is sodium carbonate or potassium carbonate, and the lye is sodium hydroxide;

Preferably, the rate at which the first solution is added dropwise to the second solution is 0.01-0.5mL/min, and the pH of the solution is adjusted to 9-11 with lye; the aging time is 1-48h.

In an optional embodiment, the mixed solution is suction-filtered and washed, dried at 50-100° C., and calcined at 300-600° C. for 1-6 hours to obtain a low-temperature SCR catalyst.

In a third aspect, the embodiment of the present invention also provides a use of a low-temperature SCR catalyst for converting NO _x in a low temperature window, and the low temperature window is 80-300°C.

The characteristics and performance of the present invention will be described in further detail below in conjunction with the examples.

Example 1

1. Weigh 1.09ml of 50% Mn(NO ₃ ) ₂ solution, 1.79g of Al(NO ₃ ) ₃ ·9H ₂ O and 2.32g of Cu(NO ₃ ) ₂ and dissolve in 200ml of deionized water, marked as solution A. At the same time, another 2g of Na-Y zeolite and 1.06g of NaCO ₃ were weighed and dissolved in 200ml of deionized water, marked as solution B. The solution B was continuously stirred, and at the same time, the solution A was slowly added, and the pH was adjusted while adding dropwise. After the dropwise addition was completed, the stirring was continued for 2h and allowed to stand for 24 hours. After standing still, filter and wash until neutral, dry at 105°C, and then calcinate at 500°C for 4 hours under air atmosphere. The sample number is No. 1.

Sample No. 2-7 prepared in Example 2-7 is prepared in a similar manner to sample No. 1, and the specific dosage is shown in Table 1.

Comparative example 1

Preparation by dipping method: 1.09ml of 50% Mn(NO ₃ ) ₂ solution, 1.79g of Al(NO ₃ ) ₃ ·9H ₂ O and 2.32g of Cu(NO ₃ ) ₂ were dissolved in 200ml of deionized water. After fully stirring, pour 2g of Na-Y zeolite into it, and after standing still, place it in an oven at 80°C for drying, and then pass air at 500°C for 4 hours for calcination. The sample number is No. 8.

Comparative example 2

Similar to the steps of Example 1, the only difference is that the salt solution used is copper nitrate, iron nitrate, aluminum nitrate, and the sample number is No. 9.

Comparative example 3

Similar to the steps of Example 1, the only difference is that the salt solution used is copper nitrate, cerium nitrate, aluminum nitrate, and the sample number is No. 10.

Comparative example 4

Similar to the steps of Example 1, the only difference is: solution B is continuously stirred, directly poured into solution A, and mixed with it. The sample number is No. 11.

Test Results:

Referring to FIG. 1 for the SEM images of the catalysts prepared in Example 1 and Comparative Example 1, it can be seen that the catalyst prepared in Example 1 presents an obvious lamellar structure, which is more conducive to the dispersion of active species (metal oxides). Example 1 and Comparative Example 1 The _N adsorption and desorption curves of the catalysts are shown in Fig. 2, and it can be seen that compared with Comparative Example 1, the catalysts made in Example 1 have a larger specific surface area (374m ² /g) , which is more conducive to the contact between the reactant and the catalyst, thereby promoting the progress of the SCR reaction and obtaining better catalytic efficiency.

Catalyst denitrification activity test method:

In order to compare and illustrate the properties of the catalysts in different examples and comparative examples, the denitrification activities of the catalysts in Examples 1-8 were tested, and the test results are shown in Table 1.

The denitrification activity test method of the denitrification catalyst is as follows: simulate the experimental flue gas through a mixed gas cylinder, the flue gas components include NO, O ₂ , N ₂ (balance gas) and SO ₂ (if required), and the gas is controlled by a mass flow meter Blend in a mixer after flow. The gas is carried out in a tubular reactor with an inner diameter of about 1.5cm. The catalyst is located in the middle of the reactor. The prepared simulated flue gas and the NH ₃ directly entering the tubular reactor undergo redox reactions on the catalyst. The gas after the reaction First pass through the phosphoric acid absorption bottle to remove NH ₃ that did not participate in the reaction, and then pass through an anti-sucking bottle (condensation bottle). The detection system consists of a display and an online infrared flue gas analyzer to detect the concentration of NO, O ₂ and SO ₂ (if used) at the inlet and outlet of the reaction system. The tail gas treatment system absorbs the NO and SO ₂ (if necessary) detected by the online infrared flue gas analyzer through the alkali solution to avoid pollution to the external atmospheric environment.

The simulated flue gas composition for the denitrification activity test is: 536mg/m ³ NO, 304mg/m ³ NH ₃ (that is, the ammonia nitrogen volume ratio is NH ₃ : NO = 1: 1), 5% O ₂ , and N ₂ as the balance gas. The total gas flow rate is 900mL/min, the gas space velocity (GHSV) is 45000h ^-1 , the concentration of NO and _O2 at the inlet and outlet of the reaction system is detected by the GAS-board3000 online infrared flue gas analyzer of Wuhan Sifang Optoelectronics Technology Co., Ltd. The activity test temperature range is 100-300°C. The test results of catalyst denitrification activity take the conversion rate of NO as the evaluation standard, and its calculation formula is shown in formula (1):

In the above formula, NO conversion (%) is the conversion rate of NO _x , and NO _in and NO _out are the inlet and outlet concentrations of NO (mg/m ³ ).

Table 1

In conjunction with Table 1 and Fig. 3, the results of the embodiments of the present invention and comparative examples are analyzed, and the following conclusions can be drawn: the denitrification effect is good, especially with excellent low-temperature denitrification activity, when the temperature is 175 ° C, under high space velocity conditions ( 45000h ^-1 ), the denitrification efficiency is as high as 97.1%, and at 150°C, the denitrification efficiency can also reach 95.8%, which is far from that of Comparative Example 1 (the denitrification efficiency is only 34.0% and 52.8% at 150°C and 175°C) achieved.

To sum up, the embodiments of the present invention provide a low-temperature SCR catalyst and its preparation method and application. The low-temperature SCR catalyst includes a carrier molecular sieve and a layered metal oxide Mn-Cu supported on the carrier molecular sieve by bridging metal atoms. The low-temperature SCR catalyst provided above uses molecular sieves as a substrate to support active metal Mn and Cu species in the form of in-situ growth of nano-sheet metal oxide precursors, thereby obtaining high specific surface area and high dispersion of Mn and Cu species , and evenly distributed low-temperature SCR catalyst, which helps to further improve the catalytic efficiency.

The above are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (10)

1. A low-temperature SCR catalyst, characterized in that the low-temperature SCR catalyst comprises a carrier and a layered metal oxide supported on the carrier through bridging metal atoms.

2. The low temperature SCR catalyst of claim 1, wherein the bridging metal atom is Al and the layered metal oxide is a Mn and/or Cu and Al layered metal oxide, wherein the bridging metal atom forms at least one covalent bond with each adjacent support and layered metal oxide.

3. The low-temperature SCR catalyst of claim 2, wherein the molar ratio of Al, mn and/or Cu in the low-temperature SCR catalyst is 0.8-1.2.

4. The low-temperature SCR catalyst according to claim 1, wherein the proportion of the layered metal oxide in the low-temperature SCR catalyst is 40 to 60%.

5. The low-temperature SCR catalyst of claim 1, wherein the carrier is a molecular sieve comprising any one of NaY, ZSM-5, 13X, MCM-41, SBA-15, USY, MOR, SSZ-13, SAPO-34, SSZ-39.

6. A method for preparing a low temperature SCR catalyst according to any of claims 1 to 5, comprising: and growing a precursor layered metal hydroxide on the carrier in situ, and then calcining to obtain the low-temperature SCR catalyst.

7. The method of claim 6, comprising the steps of: dissolving manganese salt or copper salt and aluminum salt in water to obtain a first solution, dissolving a molecular sieve and carbonate in water to obtain a second solution, continuously stirring the second solution, slowly dropwise adding the first solution into the second solution, adjusting the pH of the solution by using alkali liquor in the dropwise adding process, continuously stirring after dropwise adding is finished, standing and aging, carrying out suction filtration, washing and drying on the mixed solution to obtain precursor layered metal hydroxide powder loaded by a carrier, and calcining the obtained powder at high temperature to obtain the low-temperature SCR catalyst.

8. The method according to claim 6, wherein the manganese salt is manganese chloride, nitrate or sulfate; the aluminum salt is aluminum chloride, aluminum nitrate or aluminum sulfate, and the copper salt is copper chloride, copper nitrate or copper sulfate; the carbonate is sodium carbonate or potassium carbonate, and the alkali liquor is sodium hydroxide;

preferably, the rate of dropwise adding the first solution into the second solution is 0.01-0.5mL/min, the pH of the solution is adjusted to 9-11 by using alkali liquor, and the aging time is 0-48h.

9. The preparation method of claim 6, wherein the mixed solution is subjected to suction filtration and washing, then dried at 50-100 ℃, and then calcined at 300-600 ℃ for 1-6 hours to obtain the low-temperature SCR catalyst.

10. The low-temperature SCR catalyst according to any one of claims 1 to 5 or prepared according to the preparation method of any one of claims 6 to 9 for NO at a low temperature window _x Use for carrying out a transformation, the low temperature window being between 80 and 300 ℃.

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