Preparation method and application of halogen-modified spherical flower-shaped nickel-cobalt-molybdenum composite oxide denitration catalyst

Abstract

The application discloses a preparation method and application of a halogen-modified spherical flower-like nickel-cobalt-molybdenum composite oxide denitration catalyst, and belongs to the technical field of catalyst material preparation and atmospheric pollution control. The preparation method of the denitration catalyst comprises the following steps: mixing a metal salt solution, urea and a halogen source solution, and performing a hydrothermal reaction; and roasting the obtained precipitate to obtain the halogen-modified spherical flower-like nickel-cobalt-molybdenum composite oxide denitration catalyst. The halogen-modified catalyst has rich oxygen vacancies, strong oxidation-reduction performance and excellent denitration activity (NO x conversion rate of 93.6% at 250 DEG C). The method has low raw material cost, simple preparation method, strong operability, environmental friendliness and wide application prospect.

Description

Technical Field

[0001] This invention belongs to the field of catalyst material preparation and air pollution control technology, specifically relating to a method for preparing and applying a halogen-modified spherical flower-shaped nickel-cobalt-molybdenum composite oxide denitration catalyst. Background Technology

[0002] The information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Nitrogen oxides (NOx) emitted from stationary sources and mobile vehicles x Ammonia is a major source of acid rain, the greenhouse effect, photochemical smog, and fine particulate matter, significantly impacting global ecosystems and human well-being. Selective catalytic reduction of ammonia (NH3-SCR) is a method for controlling NO emissions. x In mainstream denitrification technologies, catalyst selection is crucial. Vanadium-tungsten-titanium (V₂O₅-WO₃ / TiO₂) catalysts have been commercial SCR catalysts for over half a century. However, inherent drawbacks of vanadium-based catalysts, such as high toxicity to biological systems and a limited operating temperature range of 300-400℃, hinder their further application. Vanadium-based catalysts also perform poorly in non-power industries such as steel, cement, glass, coking, and ceramics, where flue gas temperatures are typically below 300℃. Therefore, there is an urgent need to develop environmentally friendly vanadium-free catalysts capable of continuous denitrification at lower temperatures (<300℃). Transition metal oxides, as catalysts that are simple to prepare, abundant in resources, and cheaper than precious metals, have become star materials in NH₃-SCR research in recent years. Furthermore, halogens, with their strong electronegativity and active chemical properties, can act as electron donors and influence the valence state of cations through their strong electron-withdrawing properties, effectively regulating the catalyst and thus improving the efficiency and selectivity of transition metal oxides in the denitrification process. Summary of the Invention

[0004] This invention provides a method for preparing a halogen-modified spherical flower-shaped nickel-cobalt-molybdenum composite oxide denitration catalyst. This method has high product yield, simple preparation process, is environmentally friendly, and uses inexpensive raw materials.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing a halogen-modified spherical flower-shaped nickel-cobalt-molybdenum composite oxide denitration catalyst, comprising the following steps:

[0007] Nickel nitrate hexahydrate, cobalt nitrate hexahydrate, and sodium molybdate dihydrate are dissolved in deionized water and denoted as solution A.

[0008] Urea and a halogen source are dissolved in deionized water, denoted as solution B. The halogen source is one or more of ammonium fluoride, ammonium chloride, ammonium bromide, and ammonium iodide.

[0009] Solution A and solution B were mixed and stirred continuously at room temperature. The mixture was then crystallized, washed, centrifuged, and dried to obtain the precipitate.

[0010] The precipitate was calcined in a muffle furnace to obtain a spherical flower-shaped denitrification catalyst.

[0011] Preferably, the molar ratio of nickel nitrate hexahydrate, cobalt nitrate hexahydrate, and sodium molybdate dihydrate is 1:1:1, and the volume of deionized water is 10-50 mL.

[0012] Preferably, the molar ratio of the halogen source to urea is 1-3:10.

[0013] Preferably, the stirring time is 0.5-2 hours.

[0014] Preferably, the crystallization temperature is 100-180℃ and the crystallization time is 10-24h.

[0015] Preferably, the calcination temperature is 200-600℃, and the calcination time is 2-5 hours. The heating rate is 1-10℃ / min. Attached Figure Description

[0016] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation thereof. Obviously, those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0017] Figure 1 NO for the catalysts prepared in Examples 1-5 x Conversion rate versus temperature curve;

[0018] Figure 2 A scanning electron microscope image of the catalyst prepared in Example 4; Detailed Implementation

[0019] The present invention will be further described below with reference to embodiments.

[0020] Example 1

[0021] 0.582 g Ni(NO3)2·6H2O, 0.582 g Co(NO3)2·6H2O, and 0.484 g Na2MoO4·2H2O were dissolved in 20 mL of deionized water, denoted as solution A. 0.96 g urea was dissolved in 10 mL of deionized water, denoted as solution B. Solutions A and B were mixed and stirred vigorously at room temperature for 30 minutes. The mixture was then transferred to a PTFE-lined stainless steel reactor and hydrothermally reacted at 120 °C for 12 h. After the solution cooled to room temperature, the precipitate was collected by centrifugation, washed repeatedly with ethanol and deionized water, and dried overnight at 60 °C. Finally, the solid was calcined at 400 °C for 4 h (heating rate 1 °C / min) to obtain the final target product, named NiCoMoO. x .

[0022] Example 2

[0023] 0.582 g Ni(NO3)2·6H2O, 0.582 g Co(NO3)2·6H2O, and 0.484 g Na2MoO4·2H2O were dissolved in 20 mL of deionized water, denoted as solution A. 0.96 g urea and 0.22 g NH4F were dissolved in 10 mL of deionized water, denoted as solution B. Solutions A and B were mixed and stirred vigorously at room temperature for 30 minutes. The mixture was then transferred to a PTFE-lined stainless steel reactor and hydrothermally reacted at 120 °C for 12 h. After the solution cooled to room temperature, the precipitate was collected by centrifugation, washed repeatedly with ethanol and deionized water, and dried overnight at 60 °C. Finally, the solid was calcined at 400 °C for 4 h (heating rate 1 °C / min) to obtain the final target product, named F-NiCoMoO. x .

[0024] Example 3

[0025] 0.582 g Ni(NO3)2·6H2O, 0.582 g Co(NO3)2·6H2O, and 0.484 g Na2MoO4·2H2O were dissolved in 20 mL of deionized water, denoted as solution A. 0.96 g urea and 0.32 g NH4Cl were dissolved in 10 mL of deionized water, denoted as solution B. Solutions A and B were mixed and stirred vigorously at room temperature for 30 minutes. The mixture was then transferred to a PTFE-lined stainless steel reactor and hydrothermally reacted at 120 °C for 12 h. After the solution cooled to room temperature, the precipitate was collected by centrifugation, washed repeatedly with ethanol and deionized water, and dried overnight at 60 °C. Finally, the solid was calcined at 400 °C for 4 h (heating rate 1 °C / min) to obtain the final target product, named Cl-NiCoMoO. x .

[0026] Example 4

[0027] 0.582 g Ni(NO3)2·6H2O, 0.582 g Co(NO3)2·6H2O, and 0.484 g Na2MoO4·2H2O were dissolved in 20 mL of deionized water, denoted as solution A. 0.96 g urea and 0.59 g NH4Br were dissolved in 10 mL of deionized water, denoted as solution B. Solutions A and B were mixed and stirred vigorously at room temperature for 30 minutes. The mixture was then transferred to a PTFE-lined stainless steel reactor and hydrothermally reacted at 120 °C for 12 h. After the solution cooled to room temperature, the precipitate was collected by centrifugation, washed repeatedly with ethanol and deionized water, and dried overnight at 60 °C. Finally, the solid was calcined at 400 °C for 4 h (heating rate 1 °C / min) to obtain the final target product, named Br-NiCoMoO. x .

[0028] Example 5

[0029] 0.582 g Ni(NO3)2·6H2O, 0.582 g Co(NO3)2·6H2O, and 0.484 g Na2MoO4·2H2O were dissolved in 20 mL of deionized water, denoted as solution A. 0.96 g urea and 0.87 g NH4I were dissolved in 10 mL of deionized water, denoted as solution B. Solutions A and B were mixed and stirred vigorously at room temperature for 30 minutes. The mixture was then transferred to a PTFE-lined stainless steel reactor and hydrothermally reacted at 120 °C for 12 h. After cooling to room temperature, the precipitate was collected by centrifugation, washed repeatedly with ethanol and deionized water, and dried overnight at 60 °C. Finally, the solid was calcined at 400 °C for 4 h (heating rate 1 °C / min) to obtain the final target product, named I-NiCoMoO. x .

[0030] Application Example 1

[0031] The catalysts prepared in Examples 1-5 were placed in a fixed-bed quartz tube microreactor with a diameter of 8 mm and a length of 400 mm for selective reduction. The catalyst loading was 0.2 g. The reaction temperature was 50–400 °C, and the reaction volume hourly space velocity was 20,000 h⁻¹. -1 NO concentration in flue gas: 500 ppm; NH3 concentration: 500 ppm; O2 concentration: 5 vol%; the remaining component is N2.

[0032] Examples 1-5 Preparation of NO catalysts x Conversion rate, etc. Figure 1 As shown in the figure. It can be seen from the figure that NiCoMoO x The catalyst has a narrow active temperature window, with NO at 250℃. x The conversion rate can reach up to 83%. However, as the temperature increases further, the activity decreases sharply; at 400℃, NO...x The conversion rate was only 17.7%. In contrast, halogen doping significantly improved the conversion rate of NiCoMoO. x The catalyst's SCR catalytic activity is positively affected, and the active temperature window is expanded. The highest NO content in samples with different halogen doping... x The conversion rate order is Br-NiCoMoO x >F-NiCoMoO x >I-NiCoMoO x Cl-NiCoMoO x Br-NiCoMoO x The catalyst has the widest active temperature window, achieving NO removal rates of ~94% and ~57% at 250℃ and 400℃, respectively. x Conversion rate.

[0033] The catalyst prepared in Example 4 was observed using a scanning electron microscope, and its morphology is shown in the figure below. Figure 2 As shown in the figure. The figure shows Br-NiCoMoO x It exhibits a three-dimensional spherical flower-like structure composed of countless stacked two-dimensional nanosheets. This structural feature provides a large accessible surface area, offering abundant active sites for catalytic reactions.

Claims

1. A method for preparing a halogen-modified spherical flower-shaped nickel-cobalt-molybdenum composite oxide denitration catalyst, characterized in that, Comprising the following steps: (1) Dissolve nickel nitrate hexahydrate, cobalt nitrate hexahydrate and sodium molybdate dihydrate in deionized water to obtain a metal precursor solution A, wherein the molar ratio of Ni, Co and Mo is 1:1:1, and the volume of deionized water is 10-50 mL; (2) Dissolve urea and halogen source in deionized water, denoted as solution B; the halogen source is one or more of ammonium fluoride, ammonium chloride, ammonium bromide and ammonium iodide, and the molar ratio of halogen source to urea is 1-3:10; (3) After mixing solution A and solution B, continuously stir at room temperature, and obtain a precipitate after crystallization, washing, centrifugation and drying; (4) The precipitate was calcined in a muffle furnace to obtain a halogen-modified spherical flower-shaped nickel-cobalt-molybdenum composite oxide denitration catalyst. When the halogen source was ammonium bromide, the obtained catalyst could achieve NOx conversion rates of 94% and 57% at 250℃ and 400℃, respectively. The highest NOx conversion rate of different halogen-doped samples was... x The conversion rate order is Br-NiCoMoO x >F-NiCoMoO x >I-NiCoMoO x Cl-NiCoMoO x .

2. The preparation method of the halogen-modified spherical flower-like nickel cobalt molybdenum composite oxide denitration catalyst according to claim 1, characterized in that: In step (2), the halogen source is ammonium bromide, and Br-NiCoMoOx has a three-dimensional spherical flower-like structure stacked by countless two-dimensional nanosheets.

3. The preparation method of the halogen-modified spherical flower-like nickel cobalt molybdenum composite oxide denitration catalyst according to claim 1, characterized in that: In step (3), the stirring time is 0.5-2h, and the crystallization refers to crystallization at 100-180℃ for 10-24h.

4. The preparation method of the halogen-modified spherical flower-like nickel cobalt molybdenum composite oxide denitration catalyst according to claim 2, characterized in that: In step (4), the calcination is carried out in an air atmosphere, the calcination temperature is 200-600℃, the calcination time is 2-5h, and the heating rate to the calcination pyrolysis temperature is 1-10℃ / min.

5. The halogen-modified spherical flower-like nickel cobalt molybdenum composite oxide denitration catalyst prepared by the preparation method of any one of claims 1-4, characterized in that: Dissolve 0.582g Ni(NO3)2·6H2O, 0.582g Co(NO3)2·6H2O and 0.484g Na2MoO4·2H2O in 20mL deionized water, denoted as solution A; dissolve 0.96g urea and 0.59g NH4Br in 10mL deionized water, denoted as solution B; mix solution A and solution B and stir vigorously at room temperature for 30 minutes; then transfer to a polytetrafluoroethylene-lined stainless steel reaction kettle, hydrothermal reaction at 120℃ for 12h; after the solution cools to room temperature, centrifuge to collect the precipitate, wash repeatedly with ethanol and deionized water, and dry at 60℃ overnight; finally, calcine the solid at 400℃ for 4h with a heating rate of 1℃ / min to obtain the final target product; By adjusting the halogen doping ratio to adjust the oxygen vacancy density and electronic structure of the catalyst, the selective reduction activity of NOx is improved, and the NOx conversion rate can reach 94% and 57% at 250℃ and 400℃, respectively.

6. The application of the halogen-modified spherical flower-like nickel-cobalt-molybdenum composite oxide denitration catalyst in the selective reduction of nitrogen oxides.

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