Preparation method of Fe-doped cobalt-manganese spinel catalyst

Abstract

The invention provides a preparation method of a Fe-doped cobalt-manganese spinel catalyst, the cobalt-manganese spinel catalyst is prepared by a sol-gel method, and Fe is introduced for doping by an impregnation method. Firstly, a cobalt-manganese spinel catalyst is synthesized from raw materials such as cobalt nitrate hexahydrate, manganese acetate tetrahydrate and oxalic acid; and then, dipping the Fe-doped cobalt-manganese spinel in a mixed solution of iron nitrate nonahydrate and deionized water, drying, grinding and calcining to obtain the Fe-doped cobalt-manganese spinel catalyst. Fe doping can effectively improve the surface property and catalytic performance of the cobalt-manganese spinel catalyst. As a common 3d transition metal, the introduction of Fe enhances the activity of the catalyst to the reduction reaction of nitrogen oxides (NOx), and especially shows a significant catalytic effect at low temperature. At the temperature of 250 DEG C, the NOx conversion rate of the Fe-doped cobalt-manganese spinel catalyst reaches 84%. The preparation method of the catalyst is simple and convenient, low in cost, high in yield and suitable for treating NOx in industrial waste gas and automobile exhaust.

Description

Technical Field

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

[0002] Nitrogen oxides are one of the main air pollutants, and their large-scale emissions have led to serious air pollution problems, including acid rain, photochemical smog, and ozone pollution. The selective catalytic reaction (SCR) of nitrogen oxides with NH3 using V2O5-WO3 / TiO2 catalysts has become the most effective remediation technology for coal-fired power plants due to its high denitrification efficiency. The flue gas temperature of coking flue gas emitted by steel mills is usually in the range of 180-300℃. However, the optimal operating temperature range of the widely used V2O5WO3 / TiO2 catalyst is 350-450℃. Therefore, coking flue gas cannot be effectively treated by VW-Ti catalysts. In addition, the flue gas heating energy consumption is high, vanadium oxide is biotoxic to humans, and the price of tungsten oxide is also high. Therefore, the development of new SCR catalysts is of great significance for the effective elimination of nitrogen oxides in such low-temperature flue gases.

[0003] Doping spinels with foreign elements to form new ternary solid solutions has not received much attention. Many studies have reported that the selective catalytic reduction activity of common transition metal oxides is greatly improved by doping, because the structural deformation caused by different metal cation radii usually leads to favorable changes in the physicochemical properties of the catalyst. Cobalt manganese spinel has been shown to have good catalytic properties as a catalyst for the selective catalytic reduction of nitrogen oxides, but few studies have been conducted on the doping modification of cobalt manganese spinel.

[0004] In order to further improve the catalytic activity of cobalt manganese spinel catalysts, 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 object of the present invention is to provide a method for preparing an Fe-doped cobalt-manganese spinel catalyst, which 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) Cobalt nitrate hexahydrate and manganese acetate tetrahydrate are dissolved in anhydrous ethanol, and heated and stirred 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) Add ferric nitrate nonahydrate to deionized water to form a ferric nitrate solution, then add a certain amount of cobalt manganese spinel catalyst to the ferric nitrate solution, and after sufficient stirring and ultrasonication, stir at 80°C until dry to obtain a black powder. Then, 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. It is only necessary that the molar ratio of cobalt nitrate hexahydrate to manganese acetate tetrahydrate is 1:2, and anhydrous ethanol is added according to a certain proportion. The inventor adjusts the amounts of cobalt nitrate hexahydrate, manganese acetate tetrahydrate and anhydrous ethanol according to the actual situation to meet the above conditions to control the output 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 h.

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

[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 h.

[0017] Beneficial effects of the present invention:

[0018] (1) Fe-doped cobalt-manganese spinel catalysts can be obtained by a simple sol-gel method and impregnation method. 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 13 and 4. These are the XRD patterns of the cobalt-manganese spinel catalysts calcined at 400°C, 500°C, 600°C and 700°C in Example 1.

[0022] Figure 2 3 is the XRD diagram of the cobalt manganese spinel catalyst before and after Fe doping in Example 1.

[0023] Figure 3 This is the EDS image 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 This 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 is further described in detail below in conjunction with specific embodiments, but the protection scope of the present invention is not limited to the described contents.

[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, add the two substances to 15 mL of anhydrous ethanol to dissolve, and stir with a magnetic stirrer in an oil bath at 60°C for 5 min 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. Add the substance obtained in step (1) to the oxalic acid solution and stir vigorously in an oil bath at 60° C. for 30 minutes using a magnetic stirrer. 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) is placed in a drying oven and dried at 60° C. for 8 h, the product is 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 is shown that cobalt manganese spinel catalysts can be generated at four temperatures, but the cobalt manganese spinel catalysts obtained at calcination temperatures of 400°C and 500°C have poor crystallinity, the material obtained at a calcination temperature of 700°C is not a cobalt manganese spinel catalyst, and the cobalt manganese spinel catalyst obtained at a calcination temperature of 600°C has the best XRD performance.

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

[0035] (5) Weigh 0.1165 g of the cobalt manganese spinel catalyst obtained in step (3), place it in the Fe salt solution obtained in step (4), fully magnetically stir it at room temperature, and then ultrasonically immerse it 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, the XRD after Fe doping shifts to a high angle, indicating that Fe is successfully doped into the Mn site and still maintains the spinel structure; Figure 3 It is the EDS image of the cobalt manganese spinel catalyst before and after Fe doping. After impregnation, Fe was found to appear, and the 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 nitrogen oxide conversion rate 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 a sol-gel method and an impregnation method, and comprises the following steps: (1) dissolving cobalt nitrate hexahydrate and manganese acetate tetrahydrate in anhydrous ethanol, heating and stirring 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) Add ferric nitrate nonahydrate to deionized water to form a ferric nitrate solution, then add a certain amount of cobalt manganese spinel catalyst to the ferric nitrate solution, and after sufficient stirring and ultrasonication, stir at 80°C until dry to obtain a black powder. Then, 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, characterized in that: 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, characterized in that: 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, characterized in that: 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, characterized in that: 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 3h.

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.

Images