Preparation method of cerium-molybdenum double-doped iron-based denitration catalyst

Abstract

The invention relates to the technical field of denitration catalytic materials. The preparation method is simple in preparation process, high in denitration activity, wide in temperature window and environmentally friendly, and comprises the following steps: (1) dissolving an iron source, a cerium source and a molybdenum source in distilled water to obtain a mixed metal salt aqueous solution; (2) dropwise adding a citric acid solution into the mixed aqueous solution, and stirring to enable citric acid and metal ions to be subjected to complex reaction, so as to obtain a precursor solution; (3) heating the precursor solution in a water bath and continuously stirring to form wet gel; and (4) drying the wet gel, grinding, calcining in a muffle furnace, and cooling to obtain cerium-molybdenum double-doped iron-based denitration catalyst powder. The preparation process is simple, the obtained catalyst is moderate in crystallinity and large in specific surface area through citric acid in-situ pore forming and cerium-molybdenum double-metal synergistic modification, balance of low-temperature redox cycle and high-temperature acid adsorption is effectively promoted, secondary pollution caused by a traditional vanadium-based catalyst is reduced while nitrogen oxide in flue gas is effectively removed, and the catalyst is suitable for industrial production. And a feasible scheme is provided for flue gas denitration in the non-electric industry.

Description

[0001] This invention belongs to the technical field of air pollution control and environmental catalytic materials, specifically relating to a method for low-temperature flue gas degradation of NO in non-power industries. X Preparation method and application of cerium-molybdenum dual-doped iron-based denitration catalyst. Background Technology

[0002] The flue gas temperature in non-power industries such as coking and steel sintering is typically in the low-temperature range of 120-180℃. Existing commercial vanadium-titanium (V2O5-WO3 / TiO2) catalysts have an optimal operating temperature of 300-400℃. Direct application to non-power industries would require secondary heating of massive amounts of flue gas through fossil fuel combustion, resulting in enormous energy consumption. Furthermore, traditional vanadium-containing catalysts are biotoxic, and their disposal after disposal is costly. Therefore, developing non-vanadium-based low-temperature denitrification catalysts that do not require additional heat sources has become an inevitable choice for in-depth industry remediation. Iron-based materials (mainly α-Fe2O3) are considered the most promising alternative materials due to their environmental friendliness, low cost, and good sulfur and water resistance. However, iron-based catalysts still face two major technical bottlenecks in practical applications: First, the intrinsic redox rate of pure iron-based catalysts is low, resulting in severely insufficient denitrification activity at temperatures below 200℃. Secondly, iron oxide precursors prepared by traditional precipitation methods are prone to severe hard agglomeration during the drying and high-temperature calcination stages. This results in dense material packing, extremely small specific surface area, and a lack of effective pore structure, which greatly limits the internal diffusion of reactant gases and the exposure of active sites. To improve the performance of iron-based catalysts, researchers often use metal doping for modification. However, single metal doping often fails to achieve performance across the entire temperature range: for example, while single doping with rare earth metals (such as Ce) can improve low-temperature oxidation capacity, its activity decreases rapidly at high temperatures due to insufficient acidity; while single doping with transition metals (such as Mo) can provide surface acidity to broaden the high-temperature window, its low-temperature ignition ability is weak, and it easily induces severe sintering of iron oxide grains during calcination. In summary, existing iron-based catalysts still have shortcomings in the microstructure control of the preparation process and the synergistic balance of multiple active sites (redox sites and acidic sites). There is an urgent need to develop a novel multi-metal synergistic modified iron-based denitration catalyst that has a simple preparation process, excellent anti-agglomeration performance, and can balance high activity and high selectivity over a wide temperature window. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing a cerium-molybdenum dual-doped iron-based denitration catalyst. The method is simple and easy to operate, and the resulting catalyst has a high specific surface area and abundant mesoporous structure, with many exposed active sites on the surface, and good denitration activity and reaction stability within a wide temperature window.

[0004] The present invention achieves its objective by employing the following technical solution:

[0005] A method for preparing a cerium-molybdenum dual-doped iron-based denitration catalyst includes the following steps:

[0006] (1) Dissolve ferric nitrate nonahydrate, cerium nitrate hexahydrate and ammonium molybdate tetrahydrate in deionized water, wherein the molar ratio of Ce, Mo and Fe is 0.6:0.4:1, and stir for 30 min until completely dissolved.

[0007] (2) Slowly add citric acid solution (the molar ratio of citric acid to total metal ions is 1:1) to the prepared solution and stir continuously for 30 minutes to obtain the precursor solution.

[0008] (3) The precursor solution was placed in a constant temperature water bath at 85°C and stirred vigorously to form a wet gel. Then it was placed in an electric heating drying oven at 105°C and dried for 8 hours to obtain a dry gel.

[0009] (4) The dry gel was heated to 350°C in a muffle furnace at 2°C / min for 4 hours, cooled to room temperature, ground, pressed into tablets, and sieved to 40~60 mesh to obtain cerium-molybdenum dual-doped iron-based photocatalyst powder.

[0010] The aforementioned cerium-molybdenum dual-doped iron-based denitration catalyst is used for photocatalytic degradation / reduction of NOx. The application method involves loading the catalyst into a reactor and introducing flue gas containing NOx and NH3 within a wide temperature window of 180–450 °C to carry out the reaction.

[0011] The beneficial effects of this invention include: Excellent anti-agglomeration performance: By employing the citric acid-assisted sol-gel method and utilizing its in-situ pore-forming effect during calcination, a loose, sponge-like porous network structure with a high specific surface area (67.18 m² / g) is constructed, significantly improving gas mass transfer efficiency. Widened activity temperature window: The introduced Ce mainly enhances low-temperature redox capability by increasing oxygen vacancies, while Mo effectively widens the high-temperature activity window by providing acidic sites. The synergistic effect of both allows the catalyst to maintain high NO activity over a wide temperature range of 180–450 °C. x The conversion rate is consistently above 90%, and the N2 selectivity is better than 95%. It is environmentally friendly: the selected raw materials such as iron, cerium, and molybdenum are non-toxic and harmless, eliminating the secondary pollution problems associated with the waste of traditional vanadium-based catalysts. It is particularly suitable for deep treatment of low-temperature flue gas in non-power industries. Attached Figure Description

[0012] Figure 1 The XRD patterns are of the catalysts prepared in Example 1 and the comparative example.

[0013] Figure 2The images show a comparison of the SEM morphology of the catalysts prepared in Example 1 and the comparative example.

[0014] Figure 3 This is a comparison chart of the NOx conversion rates of Example 1 and the catalysts of each comparative example. Detailed Implementation

[0015] Example 1 (Best Example)

[0016] A method for preparing a cerium-molybdenum dual-doped iron-based denitration catalyst (Ce(0.6)Mo(0.4) / Fe-CA) includes the following steps:

[0017] (1) Accurately weigh ferric nitrate nonahydrate, cerium nitrate hexahydrate and ammonium molybdate tetrahydrate according to the molar ratio Ce / Fe = 0.6 and Mo / Fe = 0.4, dissolve them in deionized water, and stir magnetically for 30 min at room temperature until they are completely dissolved.

[0018] (2) Weigh out citric acid monohydrate and dissolve it in a small amount of deionized water, controlling the molar ratio of citric acid to total metal ions to be 1:1. Add the citric acid solution dropwise to the above metal salt solution and continue stirring for 30 min.

[0019] (3) Place the mixed solution in a constant temperature water bath at 85℃ and stir vigorously to form a wet gel. Place the wet gel in a drying oven at 105℃ for 8 hours to obtain a loose and porous dry gel.

[0020] (4) After preliminary grinding of the dry gel, it was placed in a box-type muffle furnace and heated to 350℃ at a rate of 2℃ / min, and calcined at this temperature for 4 hours. After natural cooling, it was ground, pressed into tablets, and sieved to 40-60 mesh to obtain the target catalyst. Comparative Example 1 (Comparison with traditional coprecipitation method)

[0021] Ce-Mo / Fe catalysts with the same proportions were prepared, but ammonia was used as the precipitant, and citric acid was not added. These were prepared via a traditional co-precipitation method (Fe-CP). Comparative Example 2 (Pure Iron-Based Support Comparison)

[0022] A pure Fe₂O₃ catalyst (Fe-CA) was prepared using only ferric nitrate and citric acid without the addition of cerium and molybdenum sources, following the same steps as in Example 1. Comparative Example 3 (Single-doped Ce comparison)

[0023] No molybdenum source was added during the preparation process; only a cerium source was added in the same proportion. Other steps were the same as in Example 1 to prepare the Ce / Fe-CA catalyst. Comparative Example 4 (Mo-doped comparison)

[0024] No cerium source was added during the preparation process; only a molybdenum source was added in the same proportion. The other steps were the same as in Example 1 to prepare the Mo / Fe-CA catalyst.

[0025] XRD and SEM test results of the catalysts prepared in Example 1 and the comparative example show that: the conventional co-precipitation method used in Comparative Example 1 resulted in severe hard agglomeration of crystals, with dense particles and no obvious pores; while the introduction of citric acid in Example 1 resulted in a significant "fluffy sponge-like" porous network structure, which effectively improved the specific surface area and the mass transfer efficiency of the reactant gas.

[0026] The SCR denitrification activity test results are shown below. Figure 3 Comparative Example 2, with its pure iron support, only achieved peak conversion at around 250℃, exhibiting an extremely narrow effective activity window. Comparative Example 3, with Ce doping, significantly improved low-temperature activity below 150℃, but suffered from poor high-temperature stability. Comparative Example 4, with Mo doping, broadened the high-temperature window (>300℃), but exhibited weak low-temperature ignition performance. Example 1 demonstrated a significantly enhanced denitrification effect compared to all comparative examples, with a stable NOx conversion rate exceeding 90% across a wide temperature range of 180–450℃, confirming that the bimetallic synergistic modification of the iron-based surface by Ce and Mo significantly improved catalytic activity.

Claims

1. A method for preparing a cerium-molybdenum dual-doped iron-based denitration catalyst, characterized in that, Includes the following steps: (1) Dissolve the iron source, cerium source and molybdenum source in deionized water and stir for 30 min until completely dissolved to obtain a mixed metal salt aqueous solution; (2) Add citric acid solution dropwise to the prepared solution and continue stirring for 30 min to allow citric acid to undergo a full complexation reaction with metal ions to obtain the precursor solution; (3) Place the precursor solution in a constant temperature water bath and keep stirring vigorously until the water evaporates slowly to form a uniform wet gel. The wet gel was then placed in a drying oven to dry, forming a dry gel. (4) The prepared dry gel was initially ground into powder, calcined in a muffle furnace, cooled to room temperature, ground and sieved to obtain cerium-molybdenum dual-doped iron-based denitration catalyst.

2. The preparation method of the cerium-molybdenum dual-doped iron-based denitration catalyst as described in claim 1, characterized in that, In step (1), the iron source is ferric nitrate nonahydrate, the cerium source is cerium nitrate hexahydrate, and the molybdenum source is ammonium molybdate tetrahydrate. The molar ratio of Ce to Fe is 0.6:1, and the molar ratio of Mo to Fe is 0.4:

1.

3. The preparation method of the cerium-molybdenum dual-doped iron-based denitration catalyst as described in claim 1, characterized in that, In step (2), the molar ratio of citric acid to the total metal ions in the mixed solution is 1:

1.

4. The preparation method of the cerium-molybdenum dual-doped iron-based denitration catalyst as described in claim 1, characterized in that, In step (3), the water bath heating temperature is 85°C, the drying temperature is 105°C, and the drying time is 8 hours.

5. The preparation method of the cerium-molybdenum dual-doped iron-based denitration catalyst as described in claim 1, characterized in that, In step (4), the heating rate of calcination is 2℃ / min, the calcination temperature is 350℃, and the calcination time is 4h.

6. The cerium-molybdenum dual-doped iron-based denitrification catalyst obtained by the preparation method according to any one of claims 1 to 5 is used for NH3-SCR denitrification of flue gas in non-power industries.

7. The application as described in claim 6, characterized in that, The application method is as follows: the catalyst is applied to industrial flue gas containing NOx, and a catalytic reduction reaction is carried out in a wide temperature window of 180~450 °C.

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