A core-shell catalyst of NH3-SCO and its synthesis and application

Abstract

The application relates to the field of selective catalytic oxidation, and relates to an NH3-SCO core-shell catalyst and synthesis and application thereof, and comprises the following steps: S1: catalyst core material preparation: preparing a metal precursor solution as a catalyst core material, adding a pore-forming agent, heating, and then placing in an oven for drying, grinding, and calcining to obtain a powder-shaped precursor as the catalyst core material; S2: dispersing the precursor obtained in S1 in an organic solvent, sequentially adding a template agent, tetrabutyl titanate as a shell material, and a precipitating agent, stirring, filtering, washing, drying, grinding, and calcining to obtain the core-shell catalyst. Compared with the prior art, the application adjusts the dosage ratio of the core-shell material, adjusts the thickness of the shell, and then improves the catalytic efficiency and selectivity of the catalyst, and realizes efficient removal of ammonia-containing waste gas by the catalyst.

Description

Technical Field

[0001] This invention relates to the field of selective catalytic oxidation, and in particular to an NH3-SCO core-shell catalyst and its synthesis and application. Background Technology

[0002] Ammonia-containing waste gas mainly originates from agriculture and animal husbandry, fossil fuel combustion, nitrate production, and vehicle exhaust. Currently, the primary technology for treating ammonia-containing waste gas in my country is selective catalytic oxidation (SCO). SCO is simple, efficient, and stable, making it suitable for industrial ammonia emission reduction. Compared to other flue gas ammonia removal methods, the NH3-SCO method offers greater adaptability and feasibility in ammonia removal applications.

[0003] Selective catalytic oxidation (NH3-SCO) refers to the selective catalytic oxidation of NH3 to N2 and H2O within a certain temperature range under the action of a catalyst. The core of NH3-SCO technology is the catalytic effect; therefore, developing highly efficient catalysts is crucial, aiming to improve the ammonia removal rate and reduce the catalyst's operating temperature range.

[0004] Ideally, NH3-SCO selectively catalytically oxidizes NH3 to harmless N2 and H2O. However, in practical applications, NH3 may undergo some degree of over-oxidation, producing byproducts such as NO, NO2, and N2O. Therefore, in catalyst development research, improving both ammonia removal rate and catalyst selectivity is crucial.

[0005] Chinese patent CN114405541B discloses a method for preparing a catalyst for the selective oxidation of ammonia, comprising: firstly, adding copper nitrate trihydrate, zirconium nitrate pentahydrate, and cerium nitrate hexahydrate separately to an organic compound and water to form a gel, mixing them evenly to obtain a mixture; then drying and calcining the mixture to obtain an intermediate; finally, ball milling the intermediate, adding a metal alkoxide (including zirconium isopropoxide, titanium isopropoxide, and aluminum isopropoxide), continuing ball milling, and then calcining to obtain the final catalyst. This catalyst can be used for the selective oxidation of ammonia, but it suffers from poor catalytic efficiency and selectivity for ammonia. Summary of the Invention

[0006] The purpose of this invention is to overcome the defects of the prior art and provide an NH3-SCO core-shell catalyst with high catalytic performance, improved catalytic efficiency and selectivity, as well as its synthesis and application. By adjusting the dosage ratio of the core and shell materials and the thickness of the shell, the catalytic efficiency and selectivity of the catalyst are improved, thereby achieving the efficient removal of ammonia-containing waste gas by the catalyst.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] A method for synthesizing an NH3-SCO core-shell catalyst includes the following steps:

[0009] S1: Catalyst core material preparation: Prepare a metal precursor solution, add a pore-forming agent, heat and stir to form a gel, dry, grind and calcine to obtain a powdered precursor as the catalyst core material;

[0010] S2: The precursor obtained in S1 is dispersed in an organic solvent, and a template agent, tetrabutyl titanate as the shell material, and a precipitant are added in sequence. The mixture is stirred, filtered to obtain the precipitate, washed, dried, ground, and calcined to obtain the shell catalyst.

[0011] Furthermore, in step S1, the precursor solution is a mixed solution of copper nitrate and chromium nitrate, wherein the molar ratio of copper nitrate to chromium nitrate is 1:1-1.5.

[0012] Furthermore, in step S1, the pore-forming agent is citric acid.

[0013] Furthermore, in step S1, the molar amount of the added pore-forming agent is 2-2.5 times the molar amount of metal ions in the metal precursor solution.

[0014] Furthermore, in step S2, the template agent is hexadecyltrimethylammonium bromide, and the molar ratio of the template agent to the total molar amount of metal ions in the precursor is 1-1.5:2.

[0015] Furthermore, in step S2, the molar ratio of the added tetrabutyl titanate to the total molar amount of metal ions in the precursor is (1-10):1. The tetrabutyl titanate exhibits greater stability than metal alkoxides such as titanium isopropoxide, which is beneficial for the formation and stabilization of the catalyst's core-shell structure.

[0016] Furthermore, in step S2, the precipitant is ammonia water, and the precipitant is added to make the pH of the system 8-10.

[0017] Furthermore, in step S2, the organic solvent includes ethanol, acetone, and methanol, and the amount of the organic solvent added is 60-80 ml.

[0018] An NH3-SCO core-shell catalyst was prepared using the above-described synthesis method.

[0019] Application of an NH3-SCO core-shell catalyst, which is used as a deammoniation catalyst.

[0020] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0021] This invention utilizes an active metal oxide precursor as the catalyst core, adding a template agent and tetrabutyl titanate under water bath heating and stirring conditions, followed by calcination to form a titanium dioxide shell, thus obtaining a core-shell structured catalyst. The synthesized core-shell catalyst can be used for NH3-SCO with good deammoniation efficiency and selectivity. Furthermore, by rationally adjusting the molar ratio of metal ions to tetrabutyl titanate, the shell thickness of the core-shell catalyst can be controlled, thereby effectively controlling the deammoniation efficiency and selectivity, demonstrating promising industrial application prospects.

[0022] Compared with metal oxide catalysts, the core-shell catalyst synthesized in this invention can reduce the amount of catalyst used while ensuring catalytic efficiency, and compared with metal supported catalysts, it can effectively improve the catalytic performance of the catalyst. Detailed Implementation

[0023] The present invention will now be described in detail with reference to specific embodiments.

[0024] A method for synthesizing an NH3-SCO core-shell catalyst includes the following steps:

[0025] S1: Prepare a metal precursor solution, add a pore-forming agent, heat in a water bath until it becomes gel-like, then dry in an oven, grind, and calcine to obtain a powdered precursor;

[0026] S2: The precursor obtained from S1 is dispersed in an organic solvent, and a template agent, tetrabutyl titanate, and a precipitant are added in sequence. The mixture is heated and stirred, filtered, washed, dried, ground, and calcined to obtain the core-shell catalyst.

[0027] In some specific embodiments, in step S1, the precursor solution is a mixed solution of copper nitrate and chromium nitrate, wherein the molar ratio of copper nitrate to chromium nitrate is 1:1-1.5, preferably 1:1.

[0028] In some specific embodiments, in step S1, the pore-forming agent is citric acid, and the molar amount of citric acid added is 2-2.5 times the molar amount of metal ions in the metal precursor solution, preferably 2 times.

[0029] In some specific embodiments, the water bath heating temperature in step S1 is preferably 80°C.

[0030] In some specific embodiments, the drying temperature in step S1 is preferably 105°C.

[0031] In some specific embodiments, in step S1, the calcination temperature is preferably 500°C and the calcination time is preferably 4 hours.

[0032] In some specific embodiments, in step S2, the template agent is hexadecyltrimethylammonium bromide, and the ratio of the molar amount of the template agent to the total molar amount of metal ions in the precursor is 1-1.5:2, preferably 1:2.

[0033] In some specific embodiments, in step S2, the organic solvent includes one of ethanol, acetone or methanol, preferably ethanol, and the amount of ethanol added is 60-80 ml.

[0034] In some specific embodiments, in step S2, the molar ratio of tetrabutyl titanate to the metal ions in the precursor is 1:1-10:1, preferably 3:1-6:1.

[0035] In some specific embodiments, in step S2, the precipitant is ammonia water, and the precipitant is added to make the pH of the system 8-10.

[0036] In some specific embodiments, in step S2, the heating and stirring temperature is 50℃-60℃, and the stirring time is preferably 12h.

[0037] In some specific embodiments, in step S2, the calcination temperature is preferably 600°C and the calcination time is preferably 2 hours.

[0038] This invention provides a method for synthesizing a core-shell catalyst for NH3-SCO. A metal salt and citric acid are dissolved in a beaker at a molar ratio of 1:2. The mixture is stirred in a water bath until a gel forms. After drying and grinding, the gel is calcined in a muffle furnace at 500°C for 4 hours. The resulting powder is a metal oxide. The metal oxide is then fully dispersed in an ethanol solution. Hexadecyltrimethylammonium bromide is added as a template agent. Tetrabutyl titanate is added at a molar ratio of metal ions to tetrabutyl titanate of 1:3-1:6. Ammonia is added until the pH reaches 8-10. The mixture is stirred in a water bath at 50°C-60°C for 12 hours. After filtration, washing, and drying, the catalyst is calcined in a muffle furnace at 600°C for 2 hours. The resulting powder is the core-shell catalyst.

[0039] An NH3-SCO core-shell catalyst was prepared using the above-described synthesis method.

[0040] Application of an NH3-SCO core-shell catalyst, which is used as a deammoniation catalyst.

[0041] The following embodiments are implemented based on the above-described technical solution of the present invention, and provide detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments.

[0042] The following are more detailed implementation examples, which further illustrate the technical solution of the present invention and the technical effects that can be obtained.

[0043] Example 1

[0044] This embodiment provides an NH3-SCO core-shell catalyst and its synthesis, including the following steps:

[0045] 1) Dissolve copper nitrate and chromium nitrate in deionized water at a molar ratio of 1:1, add citric acid (twice the molar amount of the sum of metal ions), stir in an 80°C water bath until a gel forms, dry at 105°C, grind, and calcine in a muffle furnace at 500°C for 4 hours. Grind after calcination to obtain CuCr metal oxide powder.

[0046] 2) Add the powder obtained in step 1) to 75 mL of ethanol, sonicate for 20 min to fully disperse the powder, add 1.323 g of hexadecyltrimethylammonium bromide as a template agent, stir in a 50 °C water bath, add tetrabutyl titanate at a molar ratio of 1:1 with the metal ions, add ammonia water until the pH of the system reaches 10, and maintain stirring in a 50 °C water bath for 12 h. After filtration, wash three times with ethanol and deionized water, dry at 105 °C, grind, and calcine in a muffle furnace at 600 °C for 2 h. After calcination and grinding, a CuCr@TiO2 core-shell catalyst with a core-shell ratio of 1:1 is obtained.

[0047] Example 2-10

[0048] This embodiment provides an NH3-SCO core-shell catalyst and its synthesis. The only difference from Example 1 is that in step 2), the molar ratio of the amount of tetrabutyl titanate added to the total amount of metal ions in the precursor is 2, 3, 4, 5, 6, 7, 8, 9, 10:1.

[0049] The NH3-SCO core-shell catalysts prepared in Examples 1-10 were used as deammoniation catalysts. Deammoniation and selectivity tests were conducted using temperature-programmed methods. The catalysts prepared in the examples were used with a loading of 1 g and a gas flow rate and space velocity of 12000 h⁻¹. -1 The O2 intake concentration is controlled at 5%.

[0050] The gas flow rate is controlled as follows: 10 mL / min -1 NH3 / N2 content of 10 vol%; 50 mL·min -1 High-purity O2 gas; 940 mL·min -1 High-purity N2 gas; heated to a reaction temperature of 200℃ in a tube furnace, with a reaction pressure of atmospheric pressure.

[0051] The contents of NH3, NOx and N2 at the outlet were detected using a flue gas analyzer and an NH3 detector to calculate the ammonia removal efficiency and selectivity of the catalyst. The results are shown in the table below.

[0052]

[0053]

[0054] As can be seen from Examples 3-6, the ammonia removal catalyst synthesized by this invention can efficiently remove ammonia and exhibits high selectivity. A comparison between Examples 1-2 and Examples 3-6 shows that the shell thickness of the core-shell catalyst can be controlled by changing the core-shell ratio. A thinner shell has less impact on the ammonia removal efficiency, while a thicker shell gradually enhances the selectivity, reduces the likelihood of byproduct formation, and results in superior catalytic performance. A comparison between Examples 7-10 and Examples 3-6 shows that as the shell thickness of the core-shell catalyst increases beyond a certain range, both the ammonia removal efficiency and selectivity decrease significantly. Therefore, properly controlling the shell thickness is crucial for improving the ammonia removal efficiency and selectivity of the catalyst.

[0055] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. The application of an NH3-SCO core-shell catalyst, characterized in that, This catalyst is used for the selective catalytic oxidation of NH3, and the synthesis method of the catalyst includes the following steps: S1: Catalyst core material preparation: Prepare a metal precursor solution, add a pore-forming agent, heat and stir to form a gel, dry, grind and calcine to obtain a powdered precursor as the catalyst core material; S2: The precursor obtained in S1 is dispersed in an organic solvent, and a template agent, tetrabutyl titanate as the shell material, and a precipitant are added in sequence. The mixture is stirred, filtered, and the precipitate is collected, washed, dried, ground, and calcined to obtain the shell catalyst. In step S1, the metal precursor solution is a mixed solution of copper nitrate and chromium nitrate, wherein the molar ratio of copper nitrate to chromium nitrate is 1:1-1.5; the pore-forming agent is citric acid; and the amount of the pore-forming agent added is 2-2.5 times the total molar amount of metal ions in the metal precursor solution. In step S2, the template agent is hexadecyltrimethylammonium bromide, and the molar ratio of the template agent to the total molar amount of metal ions in the precursor is 1-1.5:2; the molar ratio of the tetrabutyl titanate to the total molar amount of metal ions in the precursor is (1-10):

1.

2. The application of the NH3-SCO core-shell catalyst according to claim 1, characterized in that, In step S2, the precipitant is ammonia water, and the precipitant is added to make the pH of the system 8-10.

3. The application of the NH3-SCO core-shell catalyst according to claim 1, characterized in that, In step S2, the organic solvent is selected from ethanol, acetone or methanol, and the amount of organic solvent added is 10-15 ml / g of precursor.

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