Preparation method and application of a three-way catalyst applicable to an ammonia-coal co-fired boiler

Abstract

The present invention belongs to the field of removal of gaseous pollutants from flue gas of ammonia-coal co-fired boilers and catalyst materials, and relates to a preparation method of a three-way catalyst suitable for ammonia-coal co-fired boilers, including: using the sol-gel method to prepare a copper-manganese-based oxide support CuMnO x , to achieve a high degree of dispersion of Cu and Mn sites; using an alkali solution to etch CuMnO x , so that uniform and dispersed oxygen defects and Cu defects appear on the surface of the support. These defect sites are good noble metal binding sites. After impregnating the noble metal, uniform noble metal nanoparticles appear on the surface; using a liquid reducing agent to selectively reduce the noble metal, zero-valent and high-valent noble metal dipole active sites appear, which directionally activate the polar molecules of the reactants (N2O, NH3, CO), and directly affect their adsorption and desorption characteristics, as well as the formation and transformation behavior of intermediate products. Compared with the catalysts with noble metals impregnated on common supports, the present invention can weaken the competitive adsorption phenomenon of N2O, NH3, and CO, and exhibit good reaction activity and selectivity for harmless products.

Description

Technical Field

[0001] The present invention belongs to the technical field of flue gas pollutant removal and catalyst materials for ammonia-coal co-fired boilers, and specifically relates to a preparation method and application of a three-way catalyst suitable for ammonia-coal co-fired boilers. Background Art

[0002] Disclosing the information of this background art section is only intended to enhance the overall understanding of the present invention, and it is not necessarily regarded as an admission or an implication in any form that this information constitutes the prior art already known to those of ordinary skill in the art.

[0003] In 2021, the global CO2 emissions reached 36.3 billion tons, hitting a record high. Among them, the CO2 emissions from coal-fired power plants accounted for more than 30% of the total. It is imperative to find efficient and green zero-carbon energy carriers. Ammonia has a high energy density, is easy to store and transport, and has a low cost. It is a new type of green energy with great potential value and has received high attention globally. Co-firing it with pulverized coal can effectively avoid its defects such as low calorific value and slow combustion speed, and it is a feasible technical route with great potential to solve the problem of high-concentration CO2 emissions from coal-fired units.

[0004] However, ammonia-coal co-firing will inevitably lead to ammonia escape. In addition, due to the low flame temperature, in addition to the complete combustion product N2, there will also be the generation of higher-concentration N2O and the high-concentration emission of incomplete combustion product CO. In short, the ammonia-coal co-firing mode can accelerate the green and low-carbon transformation of energy, but it also brings new problems to the deep purification of flue gas. The industry urgently needs a three-way catalyst that is suitable for ammonia-coal co-fired boilers and can simultaneously remove N2O, NH3, and CO.

[0005] Noble metal catalysts are widely used in the decomposition of N2O and the oxidation of NH3 and CO due to their excellent catalytic activity. However, noble metal resources are limited and expensive, so improving the utilization efficiency of noble metal atoms is of great significance for the practical application of noble metal catalysts. Summary of the Invention

[0006] To solve the above problems, the present invention provides a three-way catalyst suitable for the synergistic removal of N2O, NH3, and CO in the flue gas of ammonia-coal co-fired boilers, specifically involving a noble metal-loaded copper-manganese oxide catalyst for the synergistic removal of N2O-NH3-CO in the flue gas of ammonia-coal co-fired boilers.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] In the first aspect of the present invention, a preparation method of a three-way catalyst suitable for ammonia-coal co-fired boilers is provided, including:

[0009] After mixing the copper source precursor solution and the manganese source precursor solution, an adhesive is added and mixed evenly to obtain a wet gel, which is dried to obtain a dry gel, and then calcined to obtain CuMnO x ;

[0010] The CuMnO x is etched in an alkaline solution for 0.5 - 4 h, filtered, washed and dried to obtain CuMnO x -AT with rich surface defects;

[0011] An aqueous solution of a noble metal precursor is added to the CuMnO x -AT suspension, and a reduction reaction is carried out in the presence of a liquid reducing agent, followed by drying to obtain the product;

[0012] The stoichiometric ratio of the copper source precursor to the manganese source precursor is 0.5 - 2:1.

[0013] By finely regulating the interaction between the noble metal and the support and the direction of electron transfer, the present invention realizes the electronic state differentiation of the noble metal, completes the directional construction of multi - oxidation - state noble metals (dipolar active sites) to activate polar molecules, enhances the adsorption and desorption characteristics of reactant molecules, as well as the formation and transformation behavior of intermediate products, and thus improves the utilization rate of noble metal sites and the selectivity of harmless products on the premise of meeting actual requirements.

[0014] In the second aspect of the present invention, a three - way catalyst suitable for an ammonia - coal co - firing boiler prepared by the above - mentioned method is provided.

[0015] In the third aspect of the present invention, an application of the above - mentioned three - way catalyst in the removal of flue gas pollutants from an ammonia - coal co - firing boiler is provided.

[0016] Advantages of the present invention

[0017] (1) Compared with the existing single catalyst, the N2O - NH3 - CO synergistic purification three - way catalyst of the present invention can achieve deep synergistic treatment of multiple pollutants in the same process, with great value potential, and significantly reduce the operating cost of a coal - fired power plant with ammonia retrofit.

[0018] (2) The present invention uses the sol - gel method to prepare a copper - manganese - based oxide support CuMnO x , realizing a high degree of dispersion of Cu and Mn sites; etching CuMnO x, uniform and dispersed oxygen defects and Cu defects appear on the surface of the support. These defect sites are good noble metal binding sites. After impregnating with noble metals, uniform noble metal nanoparticles appear on the surface; using a liquid reducing agent to selectively reduce the noble metals, zero-valent and high-valent noble metal dipole active sites appear, which directionally activate the polar molecules of the reactants (N2O, NH3, CO), and directly affect their adsorption and desorption characteristics, as well as the formation and transformation behavior of intermediate products. Compared with the catalysts prepared by impregnating noble metals on common supports, the defect sites generated by alkali etching of copper-manganese oxides proposed in the present invention result in a stronger noble metal-support interaction and a stronger anti-sintering ability. At the same time, the multi-valent noble metals and the rich active centers such as Cu and Mn sites on the support can weaken the competitive adsorption effect of N2O, NH3, and CO, showing good reaction activity and selectivity for harmless products.

[0019] (3) The preparation method of the present invention is simple, highly practical, and easy to promote. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings forming a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention.

[0021] Figure 1 It is a fixed-bed denitrification reaction test bench, and the reaction conditions are as follows: the simulated flue gas flow rate is 2000 mL / min, and the percentage contents of N2O, NH3, CO, and O2 are 0.05%, 0.1%, 0.1%, and 3.0% respectively. N2 is used as the balance gas, and the space velocity ratio (GHSV) is set to 30,000 h -1 . The temperature range for the catalytic reaction test is 200 - 500 °C.

[0022] Among them: 1. Mass flowmeter; 2. Gas pre-mixer; 3. Flue gas preheating section; 4. Temperature controller; 5. Fixed-bed quartz reactor; 6. Concentrated phosphoric acid; 7. Drying bottle; 8. Flue gas analyzer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0024] A preparation method and application of a three-way catalyst applicable to an ammonia-coal co-fired boiler, comprising the following steps:

[0025] (1) Copper-manganese-based oxide support (CuMnO x) Preparation: After mixing the copper- and manganese-containing precursors in a certain ratio, an adhesive is added and continuous stirring is carried out to obtain a wet gel. Subsequently, it is dried to obtain a dry gel, and finally calcined to obtain CuMnO x .

[0026] (2) Etching CuMnO with an alkali solution of a certain concentration x , after stirring and filtering, washing and drying to obtain CuMnO x -AT with rich surface defects.

[0027] (3) Dropwise adding an aqueous solution of a noble metal precursor into the CuMnO x -AT suspension under stirring conditions, and obtaining the target catalyst after treatment under certain reduction conditions and drying.

[0028] In the catalyst of the present invention, the copper source precursor and the manganese source precursor can be selected from the precursors commonly used in the art.

[0029] In some embodiments, the copper source precursor and the manganese source precursor are copper nitrate and manganese nitrate respectively.

[0030] In some embodiments, the stoichiometric ratio of the copper source precursor to the manganese source precursor is 0.5 - 2:1.

[0031] In the catalyst of the present invention, the adhesive can be selected from the materials commonly used in the art, such as citric acid.

[0032] In some embodiments, using citric acid as the adhesive, its total stoichiometric ratio with the precursor is 1 - 2.5:1.

[0033] In some embodiments, the drying temperature is 80 - 120 °C and the drying time is 8 - 24 h.

[0034] In some embodiments, the calcination temperature is 250 - 500 °C and the calcination time is 8 - 24 h.

[0035] In some embodiments, the alkali solution for etching is an aqueous solution of NaOH or KOH with a concentration of 2 - 4 M.

[0036] In some embodiments, the noble metal precursor is a noble metal nitrate, chloride, or organic complex such as chloroplatinic acid, tetraammineplatinum nitrate, tetraammineplatinum hydroxide, platinum acetylacetonate, rhodium(III) chloride solution, chloropalladic acid, chloroiridic acid, ruthenium(III) chloride, or chloroauric acid solution.

[0037] In some embodiments, the concentration of the noble metal solution is 0.001 - 0.5 M, and the proportion of the noble metal is 0.01 - 0.5 wt%.

[0038] In some embodiments, the reduction condition is not the common treatment with reducing gas, but the treatment with reducing liquid. Compared with reducing gas, reducing liquid can control the reduction degree more precisely and is simpler and more convenient.

[0039] In some embodiments, the liquid reducing agent is one or more of methanol, formic acid, ethanol, ethylene glycol, ascorbic acid, hydrazine hydrate, and sodium borohydride. These reducing agents can enter the carrier pores to reduce the noble metal ions free and attached to the carrier pores or surface, and solidify them in the carrier pores or on the surface. Moreover, the contact in the liquid phase is good and the reaction is complete.

[0040] In some embodiments, the stoichiometric ratio of the reducing agent to the noble metal is 1 - 5:1, and it is stirred at 0 - 90 °C for 0.5 - 4 h.

[0041] The following combines specific embodiments to further elaborate on the present invention. It should be noted that the specific embodiments are interpretations rather than limitations of the present invention.

[0042] Example 1

[0043] Take a certain amount of copper nitrate and manganese nitrate solutions and mix them in a ratio of 1:2. After adding a certain amount of citric acid (the amount of added citric acid is calculated according to the stoichiometric ratio of citric acid to the metal precursor of 1.5:1), continuously stir to obtain a wet gel. Then dry it at 100 °C for 12 h to obtain a dry gel, and finally calcine it at 400 °C for 4 h to obtain Cu1Mn2O x 。

[0044] Use a certain amount of 3M NaOH solution to etch the Cu1Mn2O x carrier, with a solid-liquid ratio of 20:1. After magnetic stirring for 2 h, filter, wash, and dry at 100 °C for 12 h to obtain Cu1Mn2O x -AT with abundant surface oxygen defects and Cu defects.

[0045] Use a certain amount of 0.05M aqueous solution of tetraammineplatinum nitrate and add it dropwise to the CuMn2O x -AT suspension under stirring conditions, ensuring that the noble metal content is 0.05 wt%. Stir magnetically for 10 min and dry at 100 °C for 12 h until constant weight. Dropwise add sodium borohydride reducing agent for treatment (the stoichiometric ratio of the reducing agent to the noble metal is 1:1), and vacuum dry to obtain the target catalyst.

[0046] Example 2

[0047] Take a certain amount of copper nitrate and manganese nitrate solutions and mix them in a ratio of 1:1.5. After adding a certain amount of citric acid (the amount of added citric acid is calculated according to the stoichiometric ratio of citric acid to the metal precursor of 1.5:1), continuously stir to obtain a wet gel. Then dry it at 100 °C for 12 h to obtain a dry gel, and finally calcine it at 400 °C for 4 h to obtain Cu1Mn1.5 O x 。

[0048] Etch Cu1MnO with a certain amount of 3M NaOH solution 1.5 O x support, with a solid-liquid ratio of 20:1. After magnetic stirring for 2 h, filter, wash, and dry at 100 °C for 12 h to obtain Cu1MnO-AT with abundant surface oxygen defects and Cu defects 1.5 O x -AT.

[0049] Dropwise add a certain amount of 0.05M platinum tetraamine nitrate aqueous solution into the Cu1MnO-AT suspension under stirring conditions, ensuring that the noble metal content is 0.05 wt%. Magnetic stir for 10 min and dry at 100 °C for 12 h until constant weight. Dropwise add sodium borohydride reducing agent for treatment (the stoichiometric ratio of the reducing agent to the noble metal is 1:1), and vacuum dry to obtain the target catalyst 1.5 O x -AT suspension, ensuring that the noble metal content is 0.05 wt%. Magnetic stir for 10 min and dry at 100 °C for 12 h until constant weight. Dropwise add sodium borohydride reducing agent for treatment (the stoichiometric ratio of the reducing agent to the noble metal is 1:1), and vacuum dry to obtain the target catalyst

[0050] Example 3

[0051] Mix a certain amount of copper nitrate and manganese nitrate solutions in a ratio of 1:1.5, add a certain amount of citric acid (the amount of citric acid added is calculated according to the stoichiometric ratio of citric acid to the metal precursor of 2:1), and continuously stir to obtain a wet gel. Then dry at 100 °C for 12 h to obtain a dry gel, and finally calcine at 400 °C for 4 h to obtain Cu1MnO 1.5 O x 。

[0052] Etch Cu1MnO 15 O x support, with a solid-liquid ratio of 15:1. After magnetic stirring for 1.5 h, filter, wash, and dry at 100 °C for 12 h to obtain CuMn2O-AT with abundant surface oxygen defects and Cu defects x -AT.

[0053] Dropwise add a certain amount of 0.05M platinum tetraamine nitrate aqueous solution into the CuMn2O-AT suspension under stirring conditions, ensuring that the noble metal content is 0.01 wt%. Magnetic stir for 10 min and dry at 100 °C for 12 h until constant weight. Dropwise add hydrazine hydrate reducing agent for treatment (the stoichiometric ratio of the reducing agent to the noble metal is 2:1), and vacuum dry to obtain the target catalyst x -AT suspension, ensuring that the noble metal content is 0.01 wt%. Magnetic stir for 10 min and dry at 100 °C for 12 h until constant weight. Dropwise add hydrazine hydrate reducing agent for treatment (the stoichiometric ratio of the reducing agent to the noble metal is 2:1), and vacuum dry to obtain the target catalyst

[0054] Example 4

[0055] A certain amount of copper nitrate and manganese nitrate solutions were mixed in a 1:1 ratio, and a certain amount of citric acid was added (the amount of citric acid added was calculated according to the stoichiometric ratio of citric acid to metal precursor of 2:1), and then continuous stirring was carried out to obtain a wet gel. Subsequently, it was dried at 100 °C for 12 h to obtain a dry gel, and finally calcined at 400 °C for 4 h to obtain Cu1Mn1O x 。

[0056] A certain amount of 3M NaOH solution was used to etch the Cu1Mn1O x support. The solid-liquid ratio was 15:1. After magnetic stirring for 1.5 h, it was filtered, washed and dried at 100 °C for 12 h to obtain CuMn2O with rich surface oxygen defects and Cu defects x -AT.

[0057] A certain amount of 0.05M aqueous solution of palladium chloride was added dropwise to the Cu1Mn1O x -AT suspension under stirring conditions, ensuring that the noble metal content was 0.05 wt%, magnetic stirring for 10 min, and drying at 100 °C for 12 h until constant weight. Hydrazine hydrate reducing agent was added for treatment (the stoichiometric ratio of reducing agent to noble metal was 2:1), and the target catalyst was obtained by vacuum drying.

[0058] Comparative Example 1

[0059] The difference from Example 1 was that alkali solution etching was not carried out.

[0060] Comparative Example 2

[0061] The difference from Example 1 was that SiO2 was used to replace Cu1Mn 1.5 O x as the support, and the same mass fraction of noble metal was loaded.

[0062] On a fixed-bed denitrification reaction test bench ( Figure 1 ), the performance of the catalysts prepared in the above examples and comparative examples was tested. The conversion rates of each example and comparative example at 300 °C are shown in Table 1.

[0063] Table 1

[0064]

[0065] * The flue gas flow rate was 2000 mL / min, and the percentage contents of N2O, NH3, CO, and O2 were: 0.05%, 0.1%, 0.1%, and 3.0% respectively. N2 was used as the balance gas, and the space velocity ratio (GHSV) was 30000 h -1 。The reaction temperature was 300 °C.

[0066] From the comparison between Example 1 and Comparative Example 1, it can be seen that the defect sites generated by alkaline etching of copper manganese oxide result in a stronger noble metal-support interaction and better anti-sintering ability. At the same time, the competitive adsorption effects of N2O, NH3, and CO are weakened, showing good reaction activity and selectivity for harmless products.

[0067] From the comparison between Example 1 and Comparative Example 2, it can be seen that the gel-sol method is used to prepare the copper manganese-based oxide support CuMnO x , achieving a high degree of dispersion of Cu and Mn sites. An alkaline solution with a certain concentration is used to etch CuMnO x , causing uniform and dispersed oxygen defects and Cu defects to appear on the surface of the support. These defect sites are good noble metal binding sites. After impregnating with noble metals, uniform noble metal nanoparticles appear on the surface. The multivalent noble metals and the abundant active centers such as Cu and Mn sites on the support can weaken the competitive adsorption effects of N2O, NH3, and CO, showing good reaction activity and selectivity for harmless products.

[0068] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a three-way catalyst applicable to an ammonia-coal co-fired boiler, characterized in that, Comprising: After mixing the copper source precursor solution and the manganese source precursor solution, an adhesive is added and mixed evenly to obtain a wet gel, which is dried to obtain a dry gel, and then calcined to obtain CuMnO x ; The CuMnO x is etched in an alkaline solution for 0.5 - 4 h, filtered, washed, and dried to obtain CuMnO x -AT with abundant surface defects; Add an aqueous solution of a noble metal precursor to the CuMnO x -AT suspension, carry out a reduction reaction in the presence of a liquid reducing agent, and dry to obtain the product; The stoichiometric ratio of the copper source precursor to the manganese source precursor is 0.5 - 2:

1.

2. The preparation method of a three-way catalyst applicable to an ammonia-coal co-fired boiler according to claim 1, characterized in that, The copper source precursor is copper nitrate; Or, the manganese source precursor is manganese nitrate.

3. The preparation method of a three-way catalyst applicable to an ammonia-coal co-fired boiler according to claim 1, characterized in that, The binder is citric acid, and its total stoichiometric ratio with the copper source precursor and the manganese source precursor is 1 - 2.5:

1.

4. The preparation method of a three-way catalyst applicable to an ammonia-coal co-fired boiler according to claim 1, characterized in that, During the dry gel preparation process, the drying temperature is 80 - 120 °C and the drying time is 8 - 24 h.

5. The preparation method of a three-way catalyst applicable to an ammonia-coal co-fired boiler according to claim 1, characterized in that, The calcination temperature is 250 - 500 °C and the calcination time is 8 - 24 h.

6. The preparation method of a three-way catalyst applicable to an ammonia-coal co-fired boiler according to claim 1, characterized in that, The alkali solution is an aqueous solution of NaOH or KOH with a concentration of 2 - 4 M.

7. The preparation method of a three-way catalyst applicable to an ammonia-coal co-fired boiler according to claim 1, characterized in that, The noble metal precursor is at least one of noble metal nitrates, chlorides, and organic complexes; Or, the concentration of the noble metal solution is 0.001 - 0.5 M, and the proportion of the noble metal is 0.01 - 0.5 wt%.

8. The preparation method of a three-way catalyst applicable to an ammonia-coal co-fired boiler according to claim 7, characterized in that, The noble metal precursor is selected from at least one of chloroplatinic acid, tetraammineplatinum nitrate, tetraammineplatinum hydroxide, platinum acetylacetonate, rhodium(III) chloride solution, chloropalladic acid, chloroiridic acid, ruthenium(III) chloride, and chloroauric acid.

9. The preparation method of a three-way catalyst applicable to an ammonia-coal co-fired boiler according to claim 1, characterized in that, The liquid reducing agent is one or several of methanol, formic acid, ethanol, ethylene glycol, ascorbic acid, hydrazine hydrate, and sodium borohydride; Or, the stoichiometric ratio of the reducing agent to the noble metal is 1 - 5:1, and stirring is carried out at 0 - 90 °C for 0.5 - 4 h.

10. A three-way catalyst prepared by the method according to any one of claims 1-9.

11. Application of the three-way catalyst according to claim 10 in the removal of flue gas pollutants in an ammonia-coal co-fired boiler.

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