CN108452796A - A kind of preparation method of the modified montmorillonite used base SCR denitration of Supported Manganese and cerium - Google Patents

Abstract

The invention relates to a preparation method of a modified montmorillonite-based catalyst loaded with manganese and cerium, and belongs to the field of preparation of catalytic materials. The invention provides a preparation method of a modified montmorillonite-based catalyst loaded with manganese and cerium, aiming at the disadvantages of the prior art, such as high carrier price, low reactivity, and narrow temperature window. The titanium tetrachloride solution is used to modify the montmorillonite, and the ion exchange method is used to load the active metal on the carrier, so that the active metal is evenly distributed on the carrier, and then the SCR denitrification catalyst is prepared by calcining. The catalyst has high denitration efficiency and a wide reaction temperature window, and has application prospects as an industrial denitration catalyst.

Description

Preparation method of a modified montmorillonite-based SCR denitration catalyst loaded with manganese and cerium

technical field

The invention relates to a preparation method of a modified montmorillonite-based catalyst loaded with manganese and cerium, and belongs to the field of preparation of catalytic materials.

Background technique

Flue gas denitrification refers to the process of removing nitrogen oxides in combustion flue gas, which is an important measure to prevent environmental pollution. Nitrogen oxides are one of the main sources of air pollution and are toxic to humans and animals. It is also the main culprit of acid rain. It produces nitric acid and nitrous acid when it meets water, thus forming acid rain and acid fog. In addition, it can also cause photochemical smog and ozone holes, seriously pollute the environment, and cause difficulty to the environment we depend on for survival. Repair damage. At present, the main methods of flue gas denitrification are selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR). Among them, SCR flue gas denitrification technology has become the most researched and applied technology due to its high denitrification efficiency and small impact on the boiler system. Wide range of denitrification technologies. Catalyst is the core product of SCR flue gas denitrification, its quality directly determines the conversion rate of nitrogen oxides, and plays a vital role in the entire SCR denitrification technology.

Manganese dioxide is a widely studied catalyst at this stage, and it has a relatively prominent catalytic effect in many reactions, and has been widely used in the fields of hydrogen peroxide decomposition and carbon monoxide oxidation. The research results of some SCR denitration catalysts show that manganese dioxide has high catalytic activity, and can convert most nitrogen oxides into nitrogen in the presence of ammonia. The denitration efficiency is high and the reaction temperature is low, which is in line with the current denitrification Catalyst requirements.

As a rare earth material with low price, good thermal stability, high activity and long service life, cerium dioxide is widely used in the field of catalysis, whether it is used as a single catalyst or as a carrier additive. The main reason is that ceria has the property of storing and releasing a large amount of oxygen, and this property is mainly determined by the lattice oxygen defect of ceria. The experimental results show that the introduction of ceria significantly improves the catalytic conversion activity of nitrogen oxides and widens the reaction temperature window.

Montmorillonite is an aluminosilicate and is the main component of bentonite. Montmorillonite is a clay mineral with a three-layer sheet structure, with alumina octahedron in the middle and silica tetrahedron up and down. Montmorillonite particles are small, about 0.2 to 1 micron, with colloidal dispersion characteristics, containing crystal water and some exchange cations between the crystal structure layers, with high ion exchange capacity and strong cation exchange capacity, in a certain physical Under chemical conditions, cations such as K ⁺ , Ti ⁴⁺ , Mg ²⁺ , Fe ³⁺ , and Cu ²⁺ can be used for ion exchange. Montmorillonite is a good catalyst carrier because of its high reserves and low price in my country.

Contents of the invention

The purpose of the present invention is to overcome the disadvantages of the prior art, such as high carrier price, low reactivity, and narrow temperature window, and provide a preparation method of a modified montmorillonite-based catalyst loaded with manganese and cerium.

The technical scheme that the present invention adopts is to comprise the steps:

1) Weigh a certain amount of montmorillonite, add it into deionized water and stir at room temperature for 12-36h. According to the amount corresponding to 5-10mmol Ti ⁴⁺ per gram of montmorillonite, prepare a TiCl4 solution as a pillar solution (a certain amount of concentrated hydrochloric acid is added to the solution to prevent its hydrolysis), stir at room temperature for 6-12h, and age for 12-24h. adding the aged pillared solution dropwise to the montmorillonite suspension, stirring at room temperature for 12-36 hours, centrifuging, removing the supernatant, washing, drying, and roasting to obtain Ti-modified pillared montmorillonite;

2) Prepare a mixed solution of manganese nitrate and cerium nitrate according to the mass fraction of the total metal loading of 12%, wherein the ratio of manganese and cerium is between 1:10 and 10:1. Add Ti-modified pillared montmorillonite into the mixed solution, stir at 60°C for 6-36h, and centrifuge;

3) Step 2) is repeated several times until the amount of metal loaded does not change. After washing and drying, the obtained sample is placed in a muffle furnace, calcined at 400-550° C. for 4-8 hours, stopped heating and cooled to room temperature to prepare Ti-modified montmorillonite-based supported manganese dioxide and ceria catalysts.

The advantages of the present invention are:

(1) The ion exchange method is used to load the active metal on the carrier, which overcomes the shortcomings of the traditional impregnation method such as uneven distribution and excessive loading, so that the active metal is evenly distributed on the carrier and can just reach the maximum loading capacity.

(2) Use titanium tetrachloride solution to modify montmorillonite, insert titanium element between montmorillonite layers, form co-pillars with titanium dioxide formed after calcination, supported manganese dioxide and ceria, and make the catalyst The whole structure presents a three-dimensional three-dimensional channel structure.

(3) Using montmorillonite as a carrier, montmorillonite is rich in reserves and low in price in my country, which can greatly reduce the cost of catalyst production, and the structural characteristics of montmorillonite itself determine its unique physical and chemical properties, such as a large specific surface area etc., which is beneficial to the catalytic reaction.

(4) Two metals, manganese and cerium, are used as catalytically active metals, and their co-catalysis effect greatly improves the conversion rate, and the temperature window is larger.

Detailed ways

Further provide 3 embodiments of the present invention below:

Example 1

Weigh 2.000g of montmorillonite, add it into a 200ml beaker, add 98ml of deionized water to it to make a 2wt% montmorillonite suspension, and stir at room temperature for 24h to make it absorb water and swell. Use a pipette to pipette 1.7ml of concentrated hydrochloric acid with a concentration of 6M into a 100ml beaker, add 2.2ml of TiCl ₄ to it under vigorous stirring, slowly add deionized water dropwise to dilute the solution to 50ml, and then let the solution age at room temperature 24h prepared pillar solution. The pillaring solution was added dropwise to the montmorillonite suspension, stirred at room temperature for 24 h, and then the resulting solution was centrifuged and washed with deionized water until the supernatant contained no Cl ⁻ . The resulting solid product was dried at 80°C overnight, and then calcined in a muffle furnace at 500°C for 6h. Take by weighing 0.500g mass fraction and be 50% manganese nitrate solution and 0.607g hexahydrate cerium nitrate solid in 200ml beaker (the ratio of the amount of substance of Mn and Ce is 1:1), adds 100ml deionized water wherein, will The obtained Ti pillared montmorillonite was added thereto, stirred at 60° C. for 12 hours, and centrifuged. Repeat this ion exchange step 3 times to maximize the exchange capacity, then dry at 80°C overnight, and calcinate at 500°C in a muffle furnace for 6h to obtain Ti pillared montmorillonite-based loaded manganese dioxide, Cerium denitrification catalyst.

Using the SCR denitration catalyst evaluation device, weigh 0.65g of Ti pillared montmorillonite-based manganese dioxide and ceria denitration catalyst, press mold it, crush it, and then pass it through a 30-50 mesh sample sieve, and place it in the reaction tube middle. The total flow rate of reaction gas is 1080ml/min, of which NO is 810ppm, NH ₃ is 810ppm, O ₂ is 5.84%, the rest of filling gas is N ₂ , and the space velocity is 80000h ^-1 . At 350°C, 400°C, and 450°C, the NO conversion rates were 56.8%, 71.1%, and 78.0%.

Example 2

Weigh 2.000g of montmorillonite, put it into a 200ml beaker, add 98ml of deionized water to it to make a 2wt% montmorillonite suspension, and stir at room temperature for 30h to make it absorb water and swell. Use a pipette to pipette 1.7ml of concentrated hydrochloric acid with a concentration of 6M into a 100ml beaker, add 2.2ml of TiCl ₄ to it under vigorous stirring, slowly add deionized water to dilute the solution to 50ml, stir at room temperature for 9h, and age 18h prepared pillar solution. The pillaring solution was added dropwise to the montmorillonite suspension, stirred at room temperature for 30 h, and then the resulting solution was centrifuged and washed with deionized water until the supernatant contained no Cl ⁻ . The resulting solid product was dried at 65°C overnight, and then calcined in a muffle furnace at 500°C for 6h. Take by weighing 1.177g mass fraction and be 50% manganese nitrate solution and 0.286g hexahydrate cerium nitrate solid in 200ml beaker (the ratio of the amount of substance of Mn and Ce is 5:1), adds 100ml deionized water wherein, will The obtained Ti pillared montmorillonite was added thereto, stirred at 60° C. for 24 hours, and centrifuged. Repeat this ion exchange step 3 times to maximize the exchange capacity, then dry at 80°C overnight, and calcinate at 500°C in a muffle furnace for 8h to obtain Ti pillared montmorillonite-based loaded manganese dioxide, Cerium denitrification catalyst.

Using the SCR denitration catalyst evaluation device, weigh 0.65g of Ti pillared montmorillonite-based manganese dioxide and ceria denitration catalyst, press mold it, crush it, and then pass it through a 30-50 mesh sample sieve, and place it in the reaction tube middle. The total flow rate of reaction gas is 1080ml/min, of which NO is 810ppm, NH ₃ is 810ppm, O ₂ is 5.84%, the rest of filling gas is N ₂ , and the space velocity is 80000h ^-1 . At 250°C, 300°C, and 350°C, the NO conversion rates were 40.1%, 69.8%, and 80.5%.

Example 3

Weigh 2.000g of montmorillonite, add it into a 200ml beaker, add 98ml of deionized water to it to make a 2wt% montmorillonite suspension, and stir at room temperature for 36h to make it absorb water and swell. Use a pipette to pipette 1.7ml of concentrated hydrochloric acid with a concentration of 6M into a 100ml beaker, add 2.2ml of TiCl ₄ to it under vigorous stirring, slowly add deionized water to dilute the solution to 50ml, stir at room temperature for 12h, and age 24h prepared pillar solution. The pillaring solution was added dropwise to the montmorillonite suspension, stirred at room temperature for 36 h, and then the resulting solution was centrifuged and washed with deionized water until the supernatant contained no Cl ⁻ . The resulting solid product was dried overnight at 65°C, and then calcined in a muffle furnace at 500°C for 8h. Take by weighing 1.245g mass fraction and be 50% manganese nitrate solution and 0.151g hexahydrate cerium nitrate solid in 200ml beaker (the ratio of the amount of substance of Mn and Ce is 10:1), adds 100ml deionized water wherein, will The obtained Ti pillared montmorillonite was added thereto, stirred at 60° C. for 36 hours, and centrifuged. Repeat this ion exchange step 3 times to maximize the exchange capacity, then dry at 80°C overnight, and calcinate at 500°C in a muffle furnace for 8h to obtain Ti pillared montmorillonite-based loaded manganese dioxide, Cerium denitrification catalyst.

Using the SCR denitration catalyst evaluation device, weigh 0.65g of Ti pillared montmorillonite-based manganese dioxide and ceria denitration catalyst, press mold it, crush it, and then pass it through a 30-50 mesh sample sieve, and place it in the reaction tube middle. The total flow rate of reaction gas is 1080ml/min, of which NO is 810ppm, NH ₃ is 810ppm, O ₂ is 5.84%, the rest of filling gas is N ₂ , and the space velocity is 80000h ^-1 . At 250°C, 300°C, and 350°C, the NO conversion rates were 44.8%, 70.9%, and 83.6%.

Claims (6)

1. a preparation method of a modified montmorillonite-based SCR denitration catalyst loaded with manganese and cerium, is characterized in that it comprises the steps: 1) Weigh a certain amount of montmorillonite, add it to deionized water and stir at room temperature for 12-36h; make a _TiCl4 solution as a pillar solution, add a certain amount of concentrated hydrochloric acid to the solution to prevent its hydrolysis, and stir at room temperature Stirring for 6-12 hours, aging for 12-24 hours; adding the aged pillar solution dropwise to the montmorillonite suspension, stirring at room temperature for 12-36 hours, centrifuging, removing the supernatant, washing and drying, and roasting to obtain Ti-modified pillared montmorillonite; 2) According to the total metal loading mass fraction of 12%, a mixed solution of manganese nitrate and cerium nitrate is made, wherein the ratio of the amount of manganese and cerium is between 1:10 and 10:1; the Ti-modified Pillared montmorillonite is added to the mixed solution, stirred at 60°C for 6-36h, and centrifuged; 3) Repeat step 2) several times until the amount of metal loaded no longer changes; wash and dry, place the obtained sample in a muffle furnace, bake at 400-550°C for 4-8h, stop heating and cool to room temperature, and obtain Ti Modified montmorillonite-based supported manganese dioxide and ceria catalysts. 2. The preparation method of a modified montmorillonite-based SCR denitration catalyst loaded with manganese and cerium according to claim 1, characterized in that: the prepared catalyst substrate is Ti pillared montmorillonite. 3. The preparation method of a modified montmorillonite-based catalyst loaded with manganese and cerium according to claim 1, characterized in that: the active metal supported by the prepared catalyst is manganese and cerium. 4. the preparation method of the modified montmorillonite-based catalyst of a kind of loaded manganese and cerium according to claim 1, is characterized in that: the method for synthesizing pillared montmorillonite is impregnation method, and the pillared liquid that uses is aging HCl solution of TiCl ₄ . 5. The preparation method of a modified montmorillonite-based catalyst loaded with manganese and cerium according to claim 1, characterized in that: when the active metal is loaded onto the substrate, the loading method used is an ion exchange method. 6. the preparation method of the modified montmorillonite-based catalyst of a kind of loaded manganese and cerium according to claim 1, is characterized in that: the total mass fraction of loaded active metal is 12%, and the consumption of pillar metal Ti is every Ke montmorillonite 5-10mmolTi ⁴⁺ .