A low-temperature high-activity high-selectivity ammonia oxidation catalyst, a preparation method and application thereof

Abstract

The application relates to a low-temperature high-activity high-selectivity ammonia oxidation catalyst in the field of catalytic environmental protection technology as well as a preparation method and application thereof. The catalyst comprises two parts of an active component and a carrier. The active component is composed of three metals of silver, cobalt and copper. Metal particles are uniformly loaded on the surface of nano gamma-Al2O3. The loading amount of silver is 10 wt%, and the loading amount of cobalt and copper is 2.5 wt% respectively. The catalyst is prepared by a step-by-step impregnation method. Silver, cobalt and copper precursor solutions are mixed with the carrier in sequence, and after stirring, rotary evaporation, drying and air calcination, a multi-metal composite oxide catalyst is obtained. The catalyst prepared by the application has the advantages of uniform dispersion of the active component, stable structure, high catalytic activity, good selectivity and the like, and can be widely applied to the selective catalytic oxidation reaction process of ammonia in tail gas.

Description

Technical Field

[0001] This invention relates to the field of catalysis and environmental protection technology, specifically to a low-temperature, highly active, and highly selective ammonia oxidation catalyst, its preparation method, and its application. Background Technology

[0002] Ammonia (NH3), as a highly efficient hydrogen storage carrier and zero-carbon fuel, is widely used in marine propulsion, fuel cells, and other fields. However, unburned ammonia leaks can cause environmental problems such as smog and eutrophication of water bodies, while also harming human health. NH3-SCO is a core technology for cryogenic ammonia leak removal, which can directionally convert NH3 into harmless N2 and H2O.

[0003] Ag / γ-Al₂O₃ catalysts possess excellent low-temperature NH₃ oxidation activity, but suffer from poor N₂ selectivity and easy formation of N₂O byproducts at low temperatures. Introducing transition metals such as Cu and Co to construct bifunctional catalysts can improve N₂ selectivity, but traditional co-impregnation methods easily lead to agglomeration of active components and a significant decrease in low-temperature activity, making it difficult to balance low-temperature activity with high N₂ selectivity. Currently, there is a lack of highly efficient catalysts that can achieve complete NH₃ conversion at 175℃ and N₂ selectivity ≥85% across the entire temperature range. Furthermore, their preparation processes are complex, and the dispersion and stability of precious metals are poor, limiting their application in marine low-temperature exhaust gas conditions.

[0004] Therefore, developing an Ag-based bifunctional NH3-SCO catalyst with high low-temperature activity, excellent N2 selectivity, and simple preparation process is of great significance for the purification of exhaust gas from ammonia-fueled engines. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies by proposing a method for preparing and applying a low-temperature, highly active, and highly selective ammonia oxidation catalyst. On the one hand, it meets the requirements of low-temperature efficiency, high N2 selectivity, and structural stability. On the other hand, the method has a simple preparation process, good noble metal dispersion, and is easy to scale up for production, showing great promise for industrial applications.

[0006] This invention is achieved through the following technical solution: This invention provides a low-temperature, highly active, and highly selective ammonia oxidation catalyst, comprising an active component, a bimetallic promoter, and a support. The active component is Ag, the support is γ-Al2O3, and the bimetallic promoter is Co and Cu.

[0007] Furthermore, in this invention, the loading amount of Ag is 10 wt%, the loading amount of Co is 2.5 wt%, and the loading amount of Cu is 2.5 wt%.

[0008] Furthermore, in this invention, the particle size of the catalyst is 40-60 mesh.

[0009] This invention also provides a method for preparing a low-temperature, highly active NH3-SCO catalyst, comprising the following steps: S1: Disperse nano-γ-Al2O3 powder in deionized water and stir to obtain a carrier suspension; dissolve silver nitrate solid in deionized water and stir to obtain a silver nitrate solution; S2: Silver nitrate solution was added dropwise to the γ-Al2O3 support suspension while stirring continuously. After rotary evaporation, drying, and calcination in air atmosphere, Ag / γ-Al2O3 intermediate was obtained. S3: Disperse the Ag / γ-Al2O3 intermediate in deionized water and stir to obtain an intermediate suspension; dissolve the cobalt nitrate hexahydrate solid in deionized water and stir to obtain a cobalt nitrate solution; S4: Cobalt nitrate solution was added dropwise to the intermediate suspension while stirring continuously. After rotary evaporation, drying, and calcination in air atmosphere, Ag-Co / γ-Al2O3 intermediate was obtained. S5: Disperse the Ag-Co / γ-Al2O3 intermediate in deionized water and stir to obtain an intermediate suspension; dissolve copper nitrate solid in deionized water and stir to obtain a copper nitrate solution; S6: Add copper nitrate solution dropwise to the intermediate suspension while stirring continuously. After rotary evaporation, drying, and calcination in air, Ag-Co1Cu1 / γ-Al2O3-600 catalyst is obtained.

[0010] Furthermore, in steps S1, S3, and S5 above, the stirring time is 15 min and the stirring speed is 400~600 r / min.

[0011] Furthermore, in steps S2, S4, and S6 above, the active component solution is added dropwise and stirring is continued for 2 h; the rotary evaporation temperature is 80 ℃, the pressure is -0.05 MPa, and the rotation speed is 2 r / s; the drying temperature is 80 ℃ and the time is 12 h.

[0012] Furthermore, in steps S2, S4, and S6 above, the calcination atmosphere is air, the calcination temperature is 600 ℃, and the calcination time is 3 h.

[0013] The present invention also provides an application of the above-mentioned catalyst, which is used in the NH3-SCO reaction.

[0014] Furthermore, in the application of the above catalyst, the catalyst is packed in the quartz tube of the NH3-SCO reaction apparatus, activated at 200 °C for 2 h under N2 atmosphere, and then the NH3-SCO reaction is carried out.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention employs a stepwise impregnation method to construct an Ag-CoCu bifunctional system, using γ-Al₂O₃ as a support. Ag provides strong low-temperature oxidation activity, while Co and Cu synergistically regulate the reaction pathway, significantly improving N₂ selectivity while simultaneously inhibiting N₂O and NO. x This method avoids the formation of harmful byproducts. Compared to traditional methods such as co-impregnation and deposition / precipitation, this invention can precisely control the dispersion of active sites, effectively avoid metal agglomeration, and maintain high catalyst activity in the low-temperature range.

[0016] Test results show that the Ag-Co1Cu1 / γ-Al2O3 catalyst prepared in this invention can achieve complete NH3 conversion at 175 ℃, and the N2 selectivity remains stable above 85% across the entire temperature range of 100~300 ℃, while also exhibiting good water resistance and thermal stability. The catalyst prepared by this method has uniformly dispersed active components, small particle size, and a reasonable match between acidic and oxidizing sites, demonstrating excellent performance in the low-temperature exhaust gas purification of marine ammonia-fueled engines. It is a low-temperature, high-activity, and high-selectivity NH3-SCO catalyst. Attached Figure Description

[0017] Figure 1 The NH3 conversion rates of different embodiments; Figure 2 N2 selectivity curves for different embodiments; Figure 3 The conversion rates of NH3 were calculated for different control ratios. Figure 4 The N2 selectivity curves are for different comparative proportions. Detailed Implementation

[0018] To make the content of this invention easier to understand, the technical solution of this invention is further explained below with reference to specific embodiments, such as... Figures 1 to 4 As shown. The examples are for illustrative purposes only, and the invention is not limited thereto. Operations not specifically described in the following examples are generally performed under conventional conditions or according to the product instructions. Chemical reagents not specifying manufacturers are all conventional pharmaceuticals that comply with national standards and are available on the market.

[0019] Example 1 2.00 g of nano-γ-Al₂O₃ powder was weighed into 80 mL of deionized water and stirred at room temperature for 15 min to obtain a uniformly dispersed γ-Al₂O₃ support solution. Then, 0.315 g of silver nitrate solid was weighed and dissolved in 20 mL of deionized water, and stirred at 500 rpm. -1The mixture was stirred under magnetic stirring for 15 min. Silver nitrate solution was added dropwise to the γ-Al2O3 support solution, and stirring was continued for 2 h. The mixture was transferred to a rotary evaporator and evaporated to dryness at 80 ℃ and -0.05 MPa. It was then dried at 80 ℃ for 12 h and calcined in air at 600 ℃ for 3 h to obtain the Ag / γ-Al2O3 intermediate.

[0020] Weigh 2.00 g of the above Ag / γ-Al₂O₃ intermediate and dissolve it in 80 mL of deionized water, stirring until uniformly dispersed. Weigh 0.148 g of cobalt nitrate hexahydrate and 0.148 g of copper nitrate and dissolve them separately in 20 mL of deionized water, mix thoroughly, and then add the intermediate solution dropwise at 500 r·min⁻¹. -1 Continue stirring for 2 hours. The mixture was then subjected to rotary evaporation, drying, and calcination in air at 600 °C for 3 hours. After tableting, grinding, and sieving through a 40-60 mesh sieve, the Ag-Co1Cu1 / γ-Al2O3-600 catalyst sample was obtained.

[0021] Example 2 2.00 g of nano-γ-Al₂O₃ powder was weighed into 80 mL of deionized water and stirred at room temperature for 15 min to obtain a uniformly dispersed γ-Al₂O₃ support solution. Then, 0.315 g of silver nitrate solid was weighed and dissolved in 20 mL of deionized water, and stirred at 500 rpm. -1 The mixture was stirred under magnetic stirring for 15 min. Silver nitrate solution was added dropwise to the γ-Al2O3 support solution, and stirring was continued for 2 h. The mixture was transferred to a rotary evaporator and evaporated to dryness at 80 ℃ and -0.05 MPa. It was then dried at 80 ℃ for 12 h and calcined in air at 600 ℃ for 3 h to obtain the Ag / γ-Al2O3 intermediate.

[0022] Weigh 2.00 g of the above Ag / γ-Al₂O₃ intermediate and dissolve it in 80 mL of deionized water, stirring until uniformly dispersed. Weigh 0.098 g of cobalt nitrate hexahydrate and 0.197 g of copper nitrate and dissolve them separately in 20 mL of deionized water, mix thoroughly, and then add the intermediate solution dropwise at 500 r·min⁻¹. -1 Continue stirring for 2 hours. The mixture was then subjected to rotary evaporation, drying, and calcination in air at 600 °C for 3 hours. After tableting, grinding, and sieving through a 40-60 mesh sieve, the Ag-Co1Cu2 / γ-Al2O3 catalyst sample was obtained.

[0023] Example 3 Weigh 2.00 g of nano-γ-Al₂O₃ powder into 80 mL of deionized water and stir for 15 min at room temperature to obtain a uniformly dispersed γ-Al₂O₃ support solution. Then weigh 0.315 g of silver nitrate solid and dissolve it in 20 mL of deionized water, stirring at 500 rpm. -1 The mixture was stirred under magnetic stirring for 15 min. Silver nitrate solution was added dropwise to the γ-Al2O3 support solution, and stirring was continued for 2 h. The mixture was transferred to a rotary evaporator and evaporated to dryness at 80 ℃ and -0.05 MPa. It was then dried at 80 ℃ for 12 h and calcined in air at 600 ℃ for 3 h to obtain the Ag / γ-Al2O3 intermediate.

[0024] Weigh 2.00 g of the above Ag / γ-Al₂O₃ intermediate and dissolve it in 80 mL of deionized water, stirring until uniformly dispersed. Weigh 0.197 g of cobalt nitrate hexahydrate and 0.098 g of copper nitrate and dissolve them separately in 20 mL of deionized water, mix thoroughly, and then add the intermediate solution dropwise at 500 r·min⁻¹. -1 Continue stirring for 2 hours. The mixture was then subjected to rotary evaporation, drying, and calcination in air at 600 °C for 3 hours. After tableting, grinding, and sieving through a 40-60 mesh sieve, the Ag-Co2Cu1 / γ-Al2O3 catalyst sample was obtained.

[0025] Example 4 The preparation steps are exactly the same as in Example 1, except that the final calcination temperature is changed to 400 °C.

[0026] Example 5 The preparation steps are exactly the same as in Example 1, except that the final calcination temperature is changed to 500 °C.

[0027] Example 6 The preparation steps are exactly the same as in Example 1, except that the final calcination temperature is changed to 700 °C.

[0028] Comparative Example 1 2.00 g of nano-γ-Al₂O₃ powder was weighed into 80 mL of deionized water and stirred at room temperature for 15 min to obtain a uniformly dispersed γ-Al₂O₃ support solution. Then, 0.315 g of silver nitrate solid was weighed and dissolved in 20 mL of deionized water, and stirred at 500 rpm. -1 The mixture was stirred under magnetic stirring for 15 min. Silver nitrate solution was added dropwise to the γ-Al2O3 support solution, and stirring was continued for 2 h. The mixture was transferred to a rotary evaporator and evaporated to dryness at 80 ℃ and -0.05 MPa. It was then dried at 80 ℃ for 12 h and calcined in air at 600 ℃ for 3 h to obtain the Ag / γ-Al2O3 intermediate.

[0029] Weigh 2.00 g of the above Ag / γ-Al₂O₃ intermediate and dissolve it in 80 mL of deionized water, stirring until uniformly dispersed. Weigh 0.295 g of copper nitrate and dissolve it in 20 mL of deionized water, then add the intermediate solution dropwise at 500 r·min⁻¹. -1 Continue stirring for 2 hours. The mixture was then subjected to rotary evaporation, drying, and calcination in air at 600 °C for 3 hours. After tableting, grinding, and sieving through a 40-60 mesh sieve, the Ag-Cu / γ-Al2O3 catalyst sample was obtained.

[0030] Comparative Example 2 Weigh 2.00 g of nano-γ-Al₂O₃ powder into 80 mL of deionized water and stir for 15 min at room temperature to obtain a uniformly dispersed γ-Al₂O₃ support solution. Then weigh 0.315 g of silver nitrate solid and dissolve it in 20 mL of deionized water, stirring at 500 rpm. -1 The mixture was stirred under magnetic stirring for 15 min. Silver nitrate solution was added dropwise to the γ-Al2O3 support solution, and stirring was continued for 2 h. The mixture was transferred to a rotary evaporator and evaporated to dryness at 80 ℃ and -0.05 MPa. It was then dried at 80 ℃ for 12 h and calcined in air at 600 ℃ for 3 h to obtain the Ag / γ-Al2O3 intermediate.

[0031] Weigh 2.00 g of the above Ag / γ-Al₂O₃ intermediate and dissolve it in 80 mL of deionized water, stirring until uniformly dispersed. Weigh 0.295 g of cobalt nitrate hexahydrate and dissolve it in 20 mL of deionized water, then add the intermediate solution dropwise at 500 r·min⁻¹. -1 Continue stirring for 2 hours. The mixture was then subjected to rotary evaporation, drying, and calcination in air at 600 °C for 3 hours. After tableting, grinding, and sieving through a 40-60 mesh sieve, the Ag-Co / γ-Al2O3 catalyst sample was obtained.

[0032] Comparative Example 3 The preparation steps are exactly the same as in Example 1, except that the final calcination temperature is changed to 300 °C.

[0033] Comparative Example 4 The preparation steps are exactly the same as in Example 1, except that the final calcination temperature is changed to 800 °C.

[0034] Application Example 1 To better illustrate the catalytic effect of the present invention, the catalytic activity of the ammonia selective catalytic oxidation catalysts prepared in Examples 1–6 and Comparative Examples 1–4 was tested in an NH3-SCO reaction system. The test process is as follows: 0.1 g of the catalyst (40-60 mesh) was placed in a quartz reaction tube, and an N2 atmosphere was introduced. The catalyst was pretreated and activated at 200 °C for 2 h. The reaction gas composition was adjusted to: 500 ppm NH3, 10 vol.% O2, with N2 as the equilibrium gas, and a total flow rate of 100 mL / min, ensuring an experimental space velocity of 60000 mL·g. -1 ·h -1 .

[0035] The NH3 conversion and N2 selectivity of the catalyst were recorded at temperatures of 100 ℃, 125 ℃, 150 ℃, 175 ℃, 200 ℃, 225 ℃, 250 ℃, 275 ℃, and 300 ℃. The results are as follows: Figure 1 , Figure 2 As shown.

[0036] The above description is only a preferred embodiment of the present invention. Any equivalent changes and modifications made by those skilled in the art within the scope of the patent application of the present invention shall also fall within the scope covered by the appended claims.

Claims

1. A low-temperature, highly active, and highly selective ammonia oxidation catalyst, characterized in that, It includes an active component, a bimetallic additive, and a carrier; the active component is Ag, the bimetallic additive is Co and Cu, and the carrier is γ-Al2O3; the loading of Ag is 10 wt.%, the loading of Co is 2.5 wt.%, and the loading of Cu is 2.5 wt.%.

2. The low-temperature, high-activity, and highly selective ammonia oxidation catalyst according to claim 1, characterized in that, The catalyst has a particle size of 40-60 mesh.

3. A method for preparing a low-temperature, highly active, and highly selective ammonia oxidation catalyst as described in any one of claims 1-2, characterized in that, The step-by-step impregnation method includes the following steps: S1: Disperse nano-γ-Al2O3 powder in deionized water and stir to obtain a carrier suspension; dissolve silver nitrate solid in deionized water and stir to obtain a silver nitrate solution; S2: Silver nitrate solution was added dropwise to the γ-Al2O3 support suspension while stirring continuously. After rotary evaporation, drying, and calcination in air atmosphere, Ag / γ-Al2O3 intermediate was obtained. S3: Disperse the Ag / γ-Al2O3 intermediate in deionized water and stir to obtain an intermediate suspension; dissolve the cobalt nitrate hexahydrate solid in deionized water and stir to obtain a cobalt nitrate solution; S4: Cobalt nitrate solution was added dropwise to the intermediate suspension while stirring continuously. After rotary evaporation, drying, and calcination in air atmosphere, Ag-Co / γ-Al2O3 intermediate was obtained. S5: Disperse the Ag-Co / γ-Al2O3 intermediate in deionized water and stir to obtain an intermediate suspension; dissolve copper nitrate solid in deionized water and stir to obtain a copper nitrate solution; S6: Add copper nitrate solution dropwise to the intermediate suspension while stirring continuously. After rotary evaporation, drying, and calcination in air, Ag-Co1Cu1 / γ-Al2O3-600 catalyst is obtained.

4. The preparation method according to claim 3, characterized in that, In step S1, the stirring time is 15 min and the stirring speed is 400-600 r / min.

5. The preparation method according to claim 3, characterized in that, In steps S2, S4, and S6, the stirring time after dropwise addition is 2 h; the rotary evaporation temperature is 80℃, the pressure is -0.05 MPa, and the rotation speed is 2 r / s; the drying temperature is 80℃ and the time is 12 h.

6. The preparation method according to claim 3, characterized in that, In steps S2, S4, and S6, the calcination temperature is 600℃, the calcination time is 3 h, and the calcination atmosphere is air.

7. The application of a catalyst according to any one of claims 1-2 or a catalyst prepared by the method according to any one of claims 3-6, characterized in that, The catalyst is used in the NH3-SCO reaction.

8. The application according to claim 7, characterized in that, The catalyst was packed in a fixed-bed reactor and activated at 200°C for 2 h under a nitrogen atmosphere, followed by activation at 100-300°C and a space velocity of 60,000 mL·g. -1 ·h -1 The NH3-SCO reaction was carried out under the specified conditions.

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