Preparation method of Fe-doped cobalt-manganese spinel catalyst

Abstract

This paper proposes a preparation method of Fe-doped cobalt manganese spinel catalyst. The cobalt manganese spinel catalyst is prepared by the sol-gel method, and Fe doping is introduced by the impregnation method. First, the cobalt manganese spinel catalyst is synthesized using raw materials such as cobalt nitrate hexahydrate, manganese acetate tetrahydrate and oxalic acid. Subsequently, it is immersed in a mixed solution of ferric nitrate nonahydrate and deionized water, and the Fe-doped cobalt manganese spinel catalyst is obtained after drying, grinding and calcination. Fe doping can effectively improve the surface properties and catalytic performance of the cobalt manganese spinel catalyst. As a common 3d transition metal, the introduction of Fe enhances the catalyst's reaction to nitrogen oxides (NO x ) reduction reaction, especially at low temperatures. At 250 ° C, the Fe-doped cobalt-manganese spinel catalyst has a significant catalytic effect on NO x The conversion rate reaches 84%. The preparation method of this catalyst is simple, low-cost, and has a high yield. It is suitable for NO in industrial waste gas and automobile exhaust. x deal with.

Description

Technical Field

[0001] The invention relates to a preparation method of an Fe-doped cobalt-manganese spinel catalyst, belonging to the technical field of material preparation. Background Art

[0002] Nitrogen oxides (NOx) are a major atmospheric pollutant, and their high emissions contribute to severe air pollution problems, including acid rain, photochemical smog, and ozone pollution. The selective catalytic reaction (SCR) of NOx with NH3 using a V2O5-WO3 / TiO2 catalyst has become the most effective remediation technology for coal-fired power plants due to its high denitrification efficiency. Coking flue gas emitted by steel mills typically has a flue gas temperature in the range of 180-300°C. However, the optimal operating temperature range of the widely used V2O5-WO3 / TiO2 catalyst is 350-450°C. Therefore, coking flue gas cannot be effectively treated by VW-Ti catalysts. Furthermore, flue gas heating consumes high energy consumption, vanadium oxide is biotoxic to humans, and tungsten oxide is expensive. Therefore, the development of novel SCR catalysts is crucial for effectively removing NOx from this low-temperature flue gas.

[0003] Doping spinels with foreign elements to form new ternary solid solutions has received relatively little attention. Numerous studies have reported that the selective catalytic reduction activity of common transition metal oxides can be significantly enhanced by doping, as structural deformations induced by varying metal cation radii often lead to favorable changes in the catalyst's physicochemical properties. Cobalt-manganese spinels have been shown to exhibit promising catalytic properties for the selective catalytic reduction of nitrogen oxides, but their doping and modification have been limited.

[0004] In order to further improve the catalytic activity of cobalt manganese spinel catalyst, Fe is doped into the cobalt manganese spinel, which can provide more reaction sites, promote electron transfer, and have a better improvement on the catalytic effect. Summary of the Invention

[0005] The present invention aims to provide a method for preparing an Fe-doped cobalt-manganese spinel catalyst. The method uses cheap raw materials, has a simple preparation method, has a large output, improves the catalytic activity of the cobalt-manganese spinel catalyst, and is applied to the treatment of nitrogen oxides in industrial waste gas and automobile exhaust. The method specifically comprises the following steps:

[0006] A method for preparing an Fe-doped cobalt-manganese spinel catalyst comprises the following steps:

[0007] (1) Dissolve cobalt nitrate hexahydrate and manganese acetate tetrahydrate in anhydrous ethanol, heat and stir to form a purple-red gel precursor.

[0008] (2) adding solid oxalic acid into deionized water to form an oxalic acid solution, then adding the purple-red gel precursor into the oxalic acid solution and stirring to dissolve, filtering, washing, drying, grinding, and calcining to obtain a cobalt-manganese spinel catalyst.

[0009] (3) Ferric nitrate nonahydrate is added to deionized water to form a ferric nitrate solution, and then a certain amount of cobalt manganese spinel catalyst is added to the ferric nitrate solution. After sufficient stirring and ultrasonication, the mixture is stirred at 80°C until dry to obtain a black powder. Subsequently, the black powder is dried, ground, and calcined to obtain an Fe-doped cobalt manganese spinel catalyst.

[0010] Preferably, in step (1) of the present invention, the ratio of cobalt nitrate hexahydrate to anhydrous ethanol is 0.01:15 mol / mL, and the ratio of manganese acetate tetrahydrate to anhydrous ethanol is 0.02:15 mol / mL.

[0011] The amounts of cobalt nitrate hexahydrate, manganese acetate tetrahydrate, and anhydrous ethanol are not fixed; instead, the molar ratio of cobalt nitrate hexahydrate to manganese acetate tetrahydrate is 1:2, and anhydrous ethanol is added in a certain proportion. The inventors adjusted the amounts of cobalt nitrate hexahydrate, manganese acetate tetrahydrate, and anhydrous ethanol to meet the above conditions based on actual conditions to control the yield of the cobalt manganate spinel catalyst.

[0012] Preferably, in step (2) of the present invention, the concentration of the oxalic acid solution is 0.24 mol / L.

[0013] Preferably, in step (2) of the present invention, the drying temperature is 60° C. and the drying time is 8 hours.

[0014] Preferably, in step (2) of the present invention, the calcination temperature is 600° C. and the calcination time is 3 hours.

[0015] Preferably, in step (2) of the present invention, the ultrasonic time is 3 hours.

[0016] Preferably, in step (2) of the present invention, the calcination temperature is 600° C. and the calcination time is 3 hours.

[0017] Beneficial effects of the present invention:

[0018] (1) Fe-doped cobalt-manganese spinel catalysts can be obtained by simple sol-gel and impregnation methods. The raw materials used are cheap and the preparation method is simple.

[0019] (2) Fe-doped cobalt-manganese spinel catalyst has smaller and more uniform grains.

[0020] (3) The catalytic performance of Fe-doped cobalt-manganese spinel catalyst is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 11 is the XRD pattern of the cobalt-manganese spinel catalyst calcined at 400°C, 500°C, 600°C and 700°C in Example 1.

[0022] Figure 2 1 is the XRD pattern of the cobalt-manganese spinel catalyst before and after Fe doping in Example 1.

[0023] Figure 3 3 is the EDS graph of the cobalt-manganese spinel catalyst before and after Fe doping in Example 1.

[0024] Figure 4 3 is the SEM image of the cobalt-manganese spinel catalyst before and after Fe doping in Example 1.

[0025] Figure 5 3 is the Raman spectrum of the cobalt-manganese spinel catalyst before and after Fe doping in Example 1.

[0026] Figure 6 This is a diagram of the selective catalytic reduction of nitrogen oxides by the cobalt-manganese spinel catalyst before and after Fe doping in Example 1. DETAILED DESCRIPTION

[0027] The present invention will be further described in detail below with reference to specific embodiments, but the protection scope of the present invention is not limited to the contents described above.

[0028] Example 1

[0029] A method for preparing an Fe-doped cobalt-manganese spinel catalyst comprises the following steps:

[0030] (1) Weigh 2.9103 g of Co(NO3)2·6H2O and 4.9018 g of Mn(CH3COO)2·4H2O, dissolve them in 15 mL of anhydrous ethanol, and stir them in an oil bath at 60°C for 5 min using a magnetic stirrer to obtain a purple-red gel precursor.

[0031] (2) Weigh 3.24144 g of solid oxalic acid and add it to 150 mL of deionized water to form an oxalic acid solution. Then, add the substance obtained in step (1) to the oxalic acid solution and vigorously stir it in an oil bath at 60° C. with a magnetic stirrer for 30 minutes. Then, filter the suspension and wash it three times with deionized water and three times with anhydrous ethanol.

[0032] (3) The product obtained in step (2) was placed in a drying oven and dried at 60° C. for 8 h, the product was ground into powder, and then placed in a tubular furnace and calcined at 400° C., 500° C., 600° C., and 700° C. for 3 h, respectively, to obtain a cobalt-manganese spinel catalyst.

[0033] The XRD pattern of the cobalt-manganese spinel prepared in this example is as follows: Figure 1As shown, after comparison with the standard card, it was shown that cobalt manganese spinel catalysts could be generated at four temperatures, but the cobalt manganese spinel catalysts obtained at calcination temperatures of 400°C and 500°C had poor crystallinity, the material obtained at a calcination temperature of 700°C was not a cobalt manganese spinel catalyst, and the cobalt manganese spinel catalyst obtained at a calcination temperature of 600°C had the best XRD performance.

[0034] (4) Weigh 0.00404 g of Fe(NO3)3·9H2O, place it in a beaker and dissolve it in deionized water to prepare an Fe salt solution.

[0035] (5) Weigh 0.1165 g of the cobalt manganese spinel catalyst obtained in step (3) and place it in the Fe salt solution obtained in step (4). After sufficient magnetic stirring at room temperature, ultrasonic immersion is performed for 3 hours. Then, the solution is magnetically stirred at 80°C until the solution evaporates. The product obtained after evaporation is placed in a drying oven at 60°C and dried for 8 hours. The product is taken out, ground into powder, and calcined at 600°C in a tubular furnace for 3 hours to obtain an Fe-doped cobalt manganese spinel catalyst.

[0036] The XRD patterns of the cobalt-manganese spinel catalyst before and after Fe doping prepared in this example are shown in FIG. Figure 2 As shown in Figure 2, the XRD pattern after Fe doping shifts to a higher angle, indicating that Fe is successfully doped into the Mn site and still maintains the spinel structure. Figure 3 This is the EDS image of the cobalt-manganese spinel catalyst before and after Fe doping. After impregnation, Fe was found to appear, and an Fe-doped cobalt-manganese spinel catalyst was generated. Figure 4 The SEM images of the cobalt-manganese spinel catalyst before and after Fe doping show that more small-sized grains are produced after Fe doping. Figure 5 The Raman spectra of the cobalt-manganese spinel catalyst before and after Fe doping show that after Fe doping, the 640 cm -1 The peak moves to a lower wave number and red shifts. This is because the radius of Fe ions is smaller than that of Mn ions, which results in a decrease in the force constant and the vibration frequency. Figure 6 Figure 2 is the selective catalytic reduction of nitrogen oxides by cobalt-manganese spinel catalyst before and after Fe doping. It is found that after Fe doping, the conversion rate of nitrogen oxides is significantly improved. x The conversion rate reached 84% at 250°C.

Claims

1. A method for preparing an Fe-doped cobalt-manganese spinel catalyst, characterized in that: The preparation method adopts the sol-gel method and the impregnation method, and comprises the following steps: (1) Dissolve cobalt nitrate hexahydrate and manganese acetate tetrahydrate in anhydrous ethanol, heat and stir to form a purple-red gel precursor; (2) adding solid oxalic acid to deionized water to form an oxalic acid solution, then adding the purple-red gel precursor to the oxalic acid solution and stirring to dissolve, filtering, washing, drying, grinding, and calcining to obtain a cobalt-manganese spinel catalyst; (3) Ferric nitrate nonahydrate is added to deionized water to form a ferric nitrate solution, and then a certain amount of cobalt manganese spinel catalyst is added to the ferric nitrate solution. After sufficient stirring and ultrasonication, the mixture is stirred at 80°C until dry to obtain a black powder. Subsequently, the black powder is dried, ground, and calcined to obtain an Fe-doped cobalt manganese spinel catalyst.

2. The method for preparing the Fe-doped cobalt-manganese spinel catalyst according to claim 1, wherein: In step (1), the molar ratio of cobalt nitrate hexahydrate to manganese acetate tetrahydrate is 1:

2.

3. The method for preparing the Fe-doped cobalt-manganese spinel catalyst according to claim 1, wherein: In step (1), the ratio of cobalt nitrate hexahydrate to anhydrous ethanol is 0.01:15 mol / mL, and the ratio of manganese acetate tetrahydrate to anhydrous ethanol is 0.02:15 mol / mL.

4. The method for preparing the Fe-doped cobalt-manganese spinel catalyst according to claim 1, wherein: The concentration of the oxalic acid solution in step (2) is 0.24 mol / L.

5. The method for preparing the Fe-doped cobalt-manganese spinel catalyst according to claim 1, wherein: In step (2), the drying temperature is 60° C. and the drying time is 8 h.

6. The method for preparing the Fe-doped cobalt-manganese spinel catalyst according to claim 1, characterized in that: In step (2), the calcination temperature is 600° C. and the calcination time is 3 h.

7. The method for preparing the Fe-doped cobalt-manganese spinel catalyst according to claim 1, characterized in that: The ultrasonic time in step (3) is 3 h.

8. The method for preparing the Fe-doped cobalt-manganese spinel catalyst according to claim 1, characterized in that: In step (3), the calcination temperature is 600° C. and the calcination time is 3 h.

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