A porous chromium-based composite denitration catalyst, a preparation method and application thereof

Abstract

The application discloses a porous chromium-based composite denitration catalyst and a preparation method and application thereof, and belongs to the technical field of denitration catalyst preparation. The preparation method of the porous chromium-based composite denitration catalyst is as follows: a chromium salt, an organic ligand and an Anderson-type polyoxometalate are dissolved in water to perform a hydrothermal reaction to obtain a precursor; wherein the Anderson-type polyoxometalate is selected from one or more of (NH4)4[NiMo6O 24 H6]·5H2O, (NH4)3[CoMo6O 24 H6]·7H2O or (NH4)3[FeMo6O 24 H6]·6H2O; and the precursor is calcined, and the porous chromium-based composite denitration catalyst is obtained. Compared with a single MOF porous chromium-based catalyst, the denitration efficiency of the porous chromium-based composite denitration catalyst can be increased by more than 90%. Meanwhile, the preparation method is simple, easy to control, low in requirement on a synthesis device, can save the amount of active components, reduces the production cost of the catalyst in an all-round way, and is suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention relates to the field of denitrification catalyst preparation technology, and in particular to a porous chromium-based composite denitrification catalyst, its preparation method, and its application. 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 (NO) x NO is one of the major gaseous pollutants and a major contributor to smog, photochemical smog, the greenhouse effect, and environmental acidification. x Emission reduction has been extensively studied and various methods (selective catalytic reduction, selective non-catalytic reduction, and non-selective catalytic reduction) have been implemented. Among these, ammonia selective catalytic reduction (NH3-SCR) is currently the most advanced industrial technology. This technology effectively reduces NO emissions within the ideal temperature range of the catalyst. x It is converted into harmless N2 and H2O.

[0004] The performance of a catalyst determines its denitrification efficiency; therefore, the preparation of highly efficient catalysts is a current research hotspot. Transition metal oxides are catalysts that are simple to prepare, abundant in resources, and far cheaper than precious metals. Metal-organic frameworks (MOFs) are porous crystalline materials with a periodic, multidimensional network structure formed by the coordination of metal ions and organic ligands. Their advantages, such as large specific surface area, rich hierarchical porosity, and diverse building blocks, make them excellent self-template precursors for the pyrolysis synthesis of metal oxides.

[0005] However, the low content of active metals in single MOFs limits the activity of oxides and prevents them from realizing their practical application potential. Some current studies use traditional loading methods to introduce active metals into MOFs, but the loaded metals obtained by this method often have poor dispersibility and stability.

[0006] Therefore, how to obtain a multi-metal composite denitration catalyst with good dispersibility, stability and catalytic activity is an urgent problem to be solved. Summary of the Invention

[0007] In view of this, the present invention provides a porous chromium-based composite denitration catalyst, its preparation method and application, which solves the problems of low active metal content and poor denitration activity in single MOFs, as well as poor dispersibility and poor stability of active metal-MOF composite catalysts.

[0008] In a first aspect, the present invention provides a method for preparing a porous chromium-based composite denitration catalyst, comprising the following steps:

[0009] The precursor was obtained by hydrothermal reaction of chromium salt, organic ligand, and Anderson-type polyoxometalate dissolved in water; wherein the Anderson-type polyoxometalate was selected from (NH4)4[NiMo6O 24 H6]·5H2O、(NH4)3[CoMo6O 24 H6]·7H2O or (NH4)3[FeMo6O 24 One or more of [H6]·6H2O;

[0010] The precursor is calcined to obtain the final product.

[0011] Preferably, the chromium salt is selected from one or more of chromium nitrate, chromium perchlorate, chromium sulfate, and chromium chloride.

[0012] Preferably, the organic ligand is selected from one or more of terephthalic acid, 2-nitroterephthalic acid, or benzoic acid.

[0013] Preferably, the molar ratio of the chromium salt to the organic ligand is 1:1 to 3, and the mass ratio of the chromium salt to the Anderson-type polyoxometalate is 32:1 to 5.

[0014] Preferably, the hydrothermal reaction temperature is 100–220°C, and the hydrothermal reaction time is 12–36 h.

[0015] Preferably, the hydrothermal reaction further includes centrifuging the solution after the hydrothermal reaction, and then washing and drying the precipitate obtained by centrifugation to obtain the precursor.

[0016] Preferably, the heating rate of the calcination is 1-5℃ / min, the calcination temperature is 400-600℃, and the calcination time is 1-3h.

[0017] Preferably, the preparation method of the Anderson-type polyoxometalate is as follows: a transition metal sulfate and (NH4)6Mo7O are reacted... 24 • 4H2O is dissolved in water, mixed evenly, evaporated in a steam bath until anhydrous, and dried to obtain the product; the transition metal sulfate is selected from one or more sulfates of Ni, Co or Fe.

[0018] Furthermore, the transition metal sulfate and (NH4)6Mo7O 24 The molar ratio of ·4H2O is 1:1.4 to 1.7; the drying temperature is 60 to 100°C, and the drying time is 10 to 20 hours.

[0019] Secondly, the present invention provides a porous chromium-based composite denitration catalyst obtained by the above preparation method.

[0020] Thirdly, the present invention provides the application of the above-mentioned porous chromium-based composite denitrification catalyst in the NH3-SCR denitrification reaction.

[0021] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0022] The porous chromium-based composite denitration catalyst of this invention uses MOF-confined polyoxometalates as precursors, embedding polyoxometalate clusters containing heterogeneous metals into the cavities of MOFs. The synergistic effect among multiple active metals enhances the performance of the denitration catalyst, resulting in high denitration catalytic efficiency. Compared to single MOF porous chromium-based catalysts, the denitration efficiency can be increased by up to 90% or more. Furthermore, the preparation method of this invention is simple and easy to control, requires minimal synthesis equipment, and saves on the amount of active components used, thus comprehensively reducing the production cost of the catalyst and making it suitable for large-scale industrial production. Attached Figure Description

[0023] 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.

[0024] Figure 1 These are XRD patterns of the precursors prepared in Example 1 and Comparative Example 1 of this invention;

[0025] Figure 2 These are the XRD patterns of the porous chromium-based denitration catalysts of Example 1 and Comparative Example 1 of the present invention;

[0026] Figure 3 These are evaluation diagrams of the denitration reaction catalytic activity of the porous chromium-based denitration catalysts in Examples 1-3 and Comparative Example 1 of the present invention. Detailed Implementation

[0027] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0028] This invention provides a method for preparing a porous chromium-based composite denitration catalyst, comprising the following steps:

[0029] A precursor is obtained by dissolving chromium salt, organic ligand and Anderson-type polyoxometalate in water and carrying out a hydrothermal reaction; the precursor is then calcined to obtain the final product.

[0030] In this invention, chromium salts, organic ligands, and Anderson-type polyoxometalates are subjected to a hydrothermal reaction. Polyoxometalate (POM) clusters with sizes as small as ~1 nm can smoothly enter the cavity of a MOF through strong interactions with the cavity wall, enabling the preparation of MOF-confined Anderson-type polyoxometalate precursors. POMs possess strong... Its acidity, excellent redox reversibility, size tunability, and multifunctionality enable it to synergistically enhance the overall denitration catalytic performance with active chromium. This confinement strategy allows the prepared catalyst to be uniformly dispersed without aggregation, exposing abundant active sites. A two-step method, i.e., impregnating pre-synthesized MOFs in a polyoxometalate solution to prepare the precursor, easily leads to the loss of POMs groups and blockage of MOF pores. Furthermore, this confinement strategy saves on the amount of active component used, comprehensively reducing the production cost of the catalyst; the immobility of the POMs core during pyrolysis allows for controlled growth of the POMs@MOF derivative nanostructure.

[0031] The type of Anderson-type polyoxometalate affects the denitration performance of the catalyst. In order to exert a synergistic effect with the active metal chromium to jointly improve the denitration performance, the preferred catalyst in this invention is (NH4)4[NiMo6O 24 H6]·5H2O、(NH4)3[CoMo6O 24 H6]·7H2O or (NH4)3[FeMo6O 24 One or more of [H6]·6H2O, more preferably (NH4)4[NiMo6O] 24 H6]·5H2O or (NH4)3[CoMo6O 24 H6]·7H2O.

[0032] This invention does not impose any special restrictions on the type of chromium salt, which can be selected from one or more of chromium nitrate, chromium perchlorate, chromium sulfate, and chromium chloride.

[0033] In this invention, the organic ligand is selected from one or more of terephthalic acid, 2-nitroterephthalic acid, or benzoic acid.

[0034] The preferred molar ratio of chromium salt to organic ligand in this invention is 1:1 to 3, and the preferred mass ratio of chromium salt to Anderson-type polyoxometalate is 32:1 to 5.

[0035] In this invention, the temperature of the hydrothermal reaction is 100–220°C, more preferably 150–200°C; the time of the hydrothermal reaction is 12–36 h.

[0036] Following the hydrothermal reaction, this invention further includes centrifugation, washing, and drying of the resulting solution to obtain a MOF-confined Anderson-type polyoxometalate precursor. The washing process involves sequentially washing with N,N-dimethylformamide (DMF) and water 1-3 times to remove unreacted raw materials and impurities. Finally, the precursor is dried at 60-80°C for 10-20 hours.

[0037] The calcination heating rate of this invention is 1–5 °C / min, the calcination temperature is 400–600 °C, and the calcination time is 1–3 h. After calcination, the target MMo / Cr2O3 porous chromium-based composite denitration catalyst is obtained, where M = Ni, Co, and Fe.

[0038] In this invention, the preparation method of the Anderson-type polyoxometalate is as follows: a transition metal sulfate and (NH4)6Mo7O are reacted... 24 • 4H2O is dissolved in water, mixed evenly, evaporated in a steam bath until anhydrous, and dried to obtain the product; the transition metal sulfate is selected from one or more sulfates of Ni, Co or Fe.

[0039] In the preparation of Anderson-type polyoxometalates, transition metal sulfates and (NH4)6Mo7O 24 The molar ratio of ·4H2O is 1:1.4 to 1.7; the drying temperature is 60 to 100°C, and the drying time is 10 to 20 hours.

[0040] Furthermore, in the preparation of Anderson-type polyoxometalates, H₂O₂ can be added, with a molar ratio of 1 to 3:1 to the transition metal sulfate. The purpose of adding H₂O₂ is to oxidize the low-valence metal ions to the high-valence state.

[0041] The present invention also provides a porous chromium-based composite denitration catalyst obtained by the above preparation method.

[0042] This invention also provides the application of the above-mentioned porous chromium-based composite denitration catalyst in the NH3-SCR denitration reaction. Under the action of the above-mentioned porous chromium-based composite denitration catalyst, the reducing agent NH3 effectively removes NO. x It is reduced to harmless N2 and H2O (4NH3+4NO+O2→4N2+6H2O).

[0043] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0044] Example 1

[0045] This embodiment provides a method for preparing a porous chromium-based composite denitration catalyst.

[0046] Weigh 0.78 g of NiSO4·6H2O (3 mmol) and add it to 20 mL of distilled water, stirring until dissolved. Then add the above solution to 80 mL of a solution containing 5.2 g of (NH4)6Mo7O. 24 The mixture was further evaporated in boiling water containing 4.2 mmol of 4H₂O. The resulting mixture was then further evaporated in a steam bath until anhydrous. Finally, it was dried overnight at 60 °C to give a light blue Anderson-type polyoxometalate (NH₄)₄[NiMo₆O₅]. 24 H6]·5H2O (denoted as NiMo6).

[0047] Weigh 1.60g Cr(NO3)3·9H2O(4mmol), 0.67g H2BDC(4mmol), 0.1g(NH4)4[NiMo6O 24 [H6]·5H2O(NiMo6) was dissolved in 60 mL of distilled water by stirring. The resulting homogeneous solution was then placed in a 100 mL high-pressure reactor lined with polytetrafluoroethylene (PTFE) and reacted at 180 °C for 20 h. After the reactor cooled naturally, the reacted solution was centrifuged to obtain a precipitate, which was washed with N,N-dimethylformamide and distilled water, and finally dried at 70 °C for 12 h to obtain the MIL-101 confined polyoxometalate precursor (denoted as NiMo6@MIL-101(Cr)). The precursor was placed in a crucible at the center of a muffle furnace and heated to 500 °C at a heating rate of 1 °C / min and held for 2 h to finally obtain a porous chromium-based composite denitration catalyst (denoted as NiMo6 / Cr2O3).

[0048] Example 2

[0049] This embodiment provides a method for preparing a porous chromium-based composite denitration catalyst.

[0050] Weigh 2.1 g of CoSO4·7H2O (7.5 mmol) and 1 g of H2O2 (30%), add 15 mL of distilled water and stir until dissolved. Then add the above solution to 130 mL of solution containing 15.5 g of (NH4)6Mo7O 24 The mixture was further evaporated in boiling water containing 12.5 mmol of 4H₂O. The resulting mixture was then further evaporated in a steam bath until anhydrous. Finally, it was dried overnight at 60 °C to give a green Anderson-type polyoxometalate (NH₄)₃[CoMo₆O₅]. 24 H6]·7H2O (denoted as CoMo6).

[0051] Weigh 1.60g Cr(NO3)3·9H2O(4mmol), 0.67g H2BDC(4mmol), 0.1g(NH4)3[CoMo6O 24[H6]·7H2O(CoMo6) was dissolved in 60 mL of distilled water by stirring. The resulting homogeneous solution was then placed in a 100 mL high-pressure reactor lined with polytetrafluoroethylene (PTFE) and reacted at 180 °C for 20 h. After the reactor cooled naturally, the resulting solution was centrifuged to obtain a precipitate, which was washed with N,N-dimethylformamide and distilled water, and finally dried at 70 °C for 12 h to obtain the MIL-101 confined polyoxometalate precursor (denoted as CoMo6@MIL-101(Cr)). The precursor was placed in a crucible at the center of a muffle furnace and heated to 500 °C at a heating rate of 1 °C / min and held for 2 h to finally obtain a porous chromium-based composite denitration catalyst (denoted as CoMo6 / Cr2O3).

[0052] Example 3

[0053] This embodiment provides a method for preparing a porous chromium-based composite denitration catalyst.

[0054] Weigh 1.2 g of Fe₂(SO₄)₃·6H₂O (3.1 mmol), add 20 mL of distilled water and stir until dissolved. Then add the above solution to 80 mL of solution containing 5.2 g of (NH₄)₆Mo₇O. 24 The mixture was further evaporated in boiling water containing 4.2 mmol of 4H₂O. The resulting mixture was then further evaporated in a steam bath until anhydrous. Finally, it was dried overnight at 60 °C to give a yellow Anderson-type polyoxometalate (NH₄)₃[FeMo₆O₅]. 24 H6]·6H2O (denoted as FeMo6).

[0055] Weigh 1.60g Cr(NO3)3·9H2O(4mmol), 0.67g H2BDC(4mmol), 0.1g(NH4)3[FeMo6O 24 [H6]·6H2O(FeMo6) was dissolved in 60 mL of distilled water by stirring. The resulting homogeneous solution was then placed in a 100 mL high-pressure reactor lined with polytetrafluoroethylene (PTFE) and reacted at 180 °C for 20 h. After the reactor cooled naturally, the reacted solution was centrifuged to obtain a precipitate, which was washed with N,N-dimethylformamide and distilled water, and finally dried at 70 °C for 12 h to obtain the MIL-101 confined polyoxometalate precursor (denoted as FeMo6@MIL-101(Cr)). The precursor was placed in a crucible at the center of a muffle furnace and heated to 500 °C at a heating rate of 1 °C / min and held for 2 h to finally obtain a porous chromium-based composite denitration catalyst (denoted as FeMo6 / Cr2O3).

[0056] Comparative Example 1

[0057] Weigh 1.60 g Cr(NO3)3·9H2O (4 mmol) and 0.67 g H2BDC (4 mmol), add 60 mL of distilled water and stir until dissolved. Then place the above homogeneous solution in a 100 mL high-pressure reactor with a polytetrafluoroethylene liner and react at 180 °C for 20 h. After the reactor cools naturally, centrifuge the reacted solution to obtain a precipitate, wash with N,N-dimethylformamide and distilled water, and finally dry at 70 °C for 12 h to obtain the MIL-101 precursor (denoted as MIL-101(Cr)). Place the precursor in a crucible in the center of a muffle furnace and heat to 500 °C at a heating rate of 1 °C / min and hold for 2 h to finally obtain a porous chromium-based denitration catalyst (denoted as Cr2O3).

[0058] XRD (X-ray diffraction) analysis was performed on the precursors prepared in Example 1 and Comparative Example 1, as follows: Figure 1 As shown, the diffraction peaks at 2.8°, 3.2°, 5.1°, 8.9°, and 16.4° of the MIL-101(Cr) precursor are consistent with literature reports, indicating the successful synthesis of the MIL-101(Cr) template. For NiMo6@MIL-101(Cr), its XRD pattern is similar to that of MIL-101(Cr), and no diffraction peaks belonging to the NiMo6 crystal were observed, indicating that NiMo6 was uniformly embedded in the MIL-101(Cr) nanocage without altering the crystal structure of MIL-101(Cr).

[0059] XRD analysis was performed on the precursor pyrolysis products of Example 1 and Comparative Example 1, such as... Figure 2 As shown, the diffraction peaks of the MIL-101(Cr) precursor pyrolysis product (Cr2O3) appear at 2θ = 24.5°, 33.6°, 36.2°, 41.5°, 50.2°, 54.9°, 63.4°, and 65.2°, which are in excellent agreement with the standard Cr2O3 pattern (JCPDS 82-1484). Obvious Cr2O3 characteristic peaks were also observed in the NiMo6@MIL-101(Cr) precursor pyrolysis product (NiMo6 / Cr2O3), and no peaks belonging to Ni and Mo species were detected. This may be due to their low content or high dispersion in the catalyst.

[0060] Application examples

[0061] The porous chromium-based denitration catalysts of Examples 1-3 and Comparative Example 1 were applied to the NH3-SCR denitration reaction under the following conditions: gas concentrations of [NO] = [NH3] = 500 ppm, [O2] = 5 vol%, N2 as the balance gas, total flow rate of 200 mL / min, and space velocity of 60,000 h⁻¹. -1The activity testing temperature range is 100–450℃, with a window width of 350℃; activity data are collected after the reaction reaches equilibrium; NO x Conversion rate is calculated using the following formula:

[0062]

[0063] Among them, [NO x ] in NO at the inlet of the catalyst performance testing system x Concentration, [NO x ] out NO at the outlet of the catalyst performance testing system x concentration.

[0064] Specific test results are as follows Figure 3 As shown in the figure, the NiMo / Cr2O3 porous chromium-based composite denitration catalyst of Example 1 exhibits the most outstanding performance, with its NO... x The highest conversion rate was achieved at 74.1% under medium-low temperature conditions of 200℃. Example 2 showed the highest NO conversion rate for CoMo / Cr2O3. x The conversion rate was 65.8%, and the NO content of FeMo / Cr2O3 in Example 3 was... x The conversion rate was 62.4%, far exceeding the 45% of commercially available V2O5-WO3 / TiO2 catalysts. In Comparative Example 1, the pure Cr2O3 exhibited significantly weaker catalytic activity under the same reaction conditions, and could not achieve a conversion rate of 50% within the temperature range of 100–450 °C.

[0065] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a porous chromium-based composite denitration catalyst, characterized in that, Includes the following steps: The precursor was obtained by hydrothermal reaction of chromium salt, organic ligand, and Anderson-type polyoxometalate dissolved in water; wherein the Anderson-type polyoxometalate was selected from (NH4)4[NiMo6O 24 H6]·5H2O、(NH4)3[CoMo6O 24 H6]·7H2O or (NH4)3[FeMo6O 24 One or more of H6]·6H2O; the precursor is a precursor of MOFs-confined Anderson-type polyoxometalate; The chromium salt is selected from one or more of chromium nitrate, chromium perchlorate, chromium sulfate, and chromium chloride; the organic ligand is selected from one or more of terephthalic acid, 2-nitroterephthalic acid, or benzoic acid. The precursor is calcined to obtain the target MMo / Cr2O3 porous chromium-based composite denitration catalyst, where M = Ni, Co, and Fe.

2. The preparation method according to claim 1, characterized in that, The molar ratio of the chromium salt to the organic ligand is 1:1 to 3, and the mass ratio of the chromium salt to the Anderson-type polyoxometalate is 32:1 to 5.

3. The preparation method according to claim 1, characterized in that, The hydrothermal reaction temperature is 100~220℃, and the hydrothermal reaction time is 12~36h.

4. The preparation method according to claim 1, characterized in that, The hydrothermal reaction process further includes centrifuging the solution after the hydrothermal reaction, and then washing and drying the precipitate obtained by centrifugation to obtain the precursor.

5. The preparation method according to claim 1, characterized in that, The calcination heating rate is 1~5℃ / min, the calcination temperature is 400~600℃, and the calcination time is 1~3h.

6. The preparation method according to claim 1, characterized in that, The preparation method of the Anderson-type polyoxometalate is as follows: a transition metal sulfate and (NH4)6Mo7O are reacted... 24 • 4H2O is dissolved in water, mixed evenly, evaporated in a steam bath until anhydrous, and dried to obtain the product; the transition metal sulfate is selected from one or more sulfates of Ni, Co or Fe.

7. The preparation method according to claim 6, characterized in that, The transition metal sulfate and (NH4)6Mo7O 24 The molar ratio of ·4H2O is 1:1.4~1.7; the drying temperature is 60~100℃, and the drying time is 10~20h.

8. The porous chromium-based composite denitration catalyst prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the porous chromium-based composite denitration catalyst as described in claim 8 in the NH3-SCR denitration reaction.

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