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

Abstract

The invention discloses a preparation method and application of a halogen-modified spherical flower-shaped nickel-cobalt-molybdenum composite oxide denitration catalyst, and belongs to the technical field of catalyst material preparation and air pollution control. The preparation method of the denitration catalyst provided by the invention comprises the following steps: mixing a metal salt solution with urea and a halogen source solution, and carrying out a hydrothermal reaction; and roasting the obtained precipitate to obtain the halogen-modified spherical flower-shaped nickel-cobalt-molybdenum composite oxide denitration catalyst. The halogen modified catalyst shows abundant oxygen vacancies, relatively strong oxidation-reduction performance and excellent denitration activity (the NOx conversion rate is 93.6% at 250 DEG C). The raw materials involved in the method are low in cost, and the preparation method is simple, high in operability, environmentally friendly and wide in application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of catalyst material preparation and air pollution control, and specifically relates to a preparation method and application of a halogen-modified spherical flower-shaped nickel-cobalt-molybdenum composite oxide denitration catalyst. Background Art

[0002] The information disclosed in the background of the invention is only intended to enhance the understanding of the overall background of the invention and should not be necessarily regarded as an acknowledgment or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] Nitrogen oxides (NO x ) is a major source of acid rain, greenhouse effect, photochemical smog and fine particulate matter, which has a significant impact on global ecosystems and human well-being. Ammonia selective catalytic reduction (NH3-SCR) is a NO x The mainstream technology for treatment, the choice of catalyst is crucial. Vanadium-tungsten-titanium (V2O5-WO3 / TiO2) catalysts have been used as commercial SCR catalysts for more than half a century. However, the inherent disadvantages of vanadium-based catalysts, such as high toxicity to biological systems and a limited operating temperature range of 300-400°C, have hindered their further application. Vanadium-based catalysts have poor application in non-power industries such as steel, cement, glass, coking and ceramics, where the flue gas temperature is usually below 300°C. Therefore, there is an urgent need to develop environmentally friendly vanadium-free catalysts that can continuously achieve denitrification at lower temperatures (<300°C). As a catalyst that is simple to prepare, abundant in resources, and cheaper than precious metals, transition metal oxides have become star materials in the field of NH3-SCR research in recent years. In addition, halogens with strong electronegativity and active chemical properties can act as electron donors and affect the valence state of cations through their strong electron-withdrawing properties, effectively regulating the catalyst, thereby improving the efficiency and selectivity of transition metal oxides in the denitrification process. Summary of the invention

[0004] The invention provides a method for preparing a halogen-modified spherical flower-shaped nickel-cobalt-molybdenum composite oxide denitration catalyst. The method has high product yield, simple preparation process, environmental friendliness and low raw material price.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present 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 were dissolved in deionized water, which was recorded as solution A.

[0008] Urea and a halogen source are dissolved in deionized water, which is referred to 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 are mixed and stirred continuously at room temperature, and a precipitate is obtained by crystallization, washing, centrifugation and drying.

[0010] The precipitate is placed in a muffle furnace for calcination to obtain a spherical flower-shaped denitration catalyst.

[0011] Preferably, the molar ratio of the nickel nitrate hexahydrate, the cobalt nitrate hexahydrate and the sodium molybdate dihydrate is 1:1:1, and the volume of the 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 0.5-2h.

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

[0015] Preferably, the calcination temperature is 200-600°C, the calcination time is 2-5h, and the heating rate is 1-10°C / min. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings constituting 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 description are used to explain the present invention and do not constitute an improper limitation of the present invention. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0017] Figure 1 The NO of the catalyst prepared in Examples 1-5 x Conversion rate versus temperature curve;

[0018] Figure 2 is a scanning electron microscope image of the catalyst prepared in Example 4; DETAILED DESCRIPTION

[0019] The present invention will be further described below in conjunction with the embodiments.

[0020] Example 1

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

[0022] Example 2

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

[0024] Example 3

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

[0026] Example 4

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

[0028] Example 5

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

[0030] Application Example 1

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

[0032] Example 1-5 Preparation of Catalyst NO x Conversion rate Figure 1 As shown in the figure, NiCoMoO x The catalyst has a narrow active temperature window, NO x The conversion rate can reach up to 83%. As the temperature increases further, the activity decreases sharply. At 400℃, NOx The conversion rate is only 17.7%. In contrast, halogen doping has a significant effect on NiCoMoO x The SCR catalytic activity of the catalyst was positively affected and the active temperature window was expanded. The highest NO x The order of conversion 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 ~94% and ~57% NO at 250°C and 400°C, respectively. x Conversion rate.

[0033] The catalyst prepared in Example 4 was observed by scanning electron microscope, and its morphology is shown in the following figure: Figure 2 As shown. The figure shows Br-NiCoMoO x It is a three-dimensional spherical flower-like structure composed of countless two-dimensional nanosheets. This structural feature provides a large accessible surface area and 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: The steps include: (1) dissolving nickel nitrate hexahydrate, cobalt nitrate hexahydrate and sodium molybdate dihydrate in deionized water, which is referred to as solution A; (2) dissolving urea and a halogen source in deionized water, referred to as solution B. The halogen source is one or more of ammonium fluoride, ammonium chloride, ammonium bromide, and ammonium iodide; (3) mixing solution A and solution B and continuously stirring at room temperature, and obtaining a precipitate through crystallization, washing, centrifugation, and drying; (4) The precipitate is placed in a muffle furnace for calcination to obtain a spherical flower-shaped denitration catalyst.

2. The method for preparing the halogen-modified spherical flower-shaped nickel-cobalt-molybdenum composite oxide denitration catalyst according to claim 1, characterized in that: In step (1), 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.

3. The method for preparing the halogen-modified spherical flower-shaped nickel-cobalt-molybdenum composite oxide denitration catalyst according to claim 1, characterized in that: The molar ratio of the halogen source to urea in step (2) is 1-3:10, and the volume of deionized water is 10-50 mL.

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

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

6. A halogen-modified spherical flower-shaped nickel-cobalt-molybdenum composite oxide denitration catalyst prepared by the preparation method according to any one of claims 1 to 5.

7. Use of the halogen-modified spherical flower-shaped nickel-cobalt-molybdenum composite oxide denitration catalyst according to claim 6 in the selective reduction of nitrogen oxides.

Images