A manganese-zinc bimetal denitration catalyst, a preparation method and application thereof

Abstract

The application provides a manganese-zinc bimetallic denitration catalyst and a preparation method and application thereof. The preparation method of the manganese-zinc bimetallic denitration catalyst comprises the following steps: mixing a manganese source, a zinc source, 2,5-dihydroxyterephthalic acid and an organic solvent to obtain a suspension; performing a hydrothermal reaction on the suspension to obtain a manganese-zinc bimetallic framework; sequentially performing nitrogen atmosphere calcination and air atmosphere calcination on the manganese-zinc bimetallic framework to obtain the manganese-zinc bimetallic denitration catalyst; the temperature of the nitrogen atmosphere calcination is 230-240 DEG C, and the temperature of the air atmosphere calcination is 230-240 DEG C. The manganese-zinc bimetallic denitration catalyst achieves charge mild redistribution, acid site regulation and oxygen vacancy introduction through manganese-zinc bimetallic synergistic effect; there is one-way electron transfer between manganese and zinc, zinc is an electron donor, manganese is an electron acceptor, and the two form a synergistic active site, so that NH3 is effectively activated and does not participate in the side reaction to generate N2O, and the denitration efficiency and N2 selectivity of the catalyst are significantly improved.

Description

Technical Field

[0001] This application belongs to the field of industrial flue gas purification and treatment technology, specifically relating to a manganese-zinc bimetallic denitrification catalyst, its preparation method, and its application. Background Technology

[0002] Nitrogen oxides (NO) x Nitrogen oxides (NOx) are a core air pollutant that causes environmental problems such as acid rain, photochemical smog, and ozone layer depletion. Strictly controlling their emissions is a key task in air pollution control. Selective catalytic reduction (NH3-SCR) technology has become the mainstream technology for industrial flue gas denitrification due to its high denitrification efficiency, low secondary pollution, and wide applicability.

[0003] Traditional NH3-SCR catalysts are mainly suitable for medium- and high-temperature operating conditions of 300-400℃, while industrial production has a large demand for ultra-low temperature (≤150℃) flue gas denitrification, such as natural gas combustion tail gas, gas turbine tail gas, and coal-fired tail gas that has been reheated to around 140℃ after wet desulfurization. Existing commercial medium- and high-temperature catalysts (such as VW / TiO2) have extremely low denitrification activity at ultra-low temperatures; conventional single-metal low-temperature denitrification catalysts suffer from problems such as simple electronic structure and imbalance of redox capabilities, leading to NO... x Insufficient conversion rate and excessive oxidation of NH3 lead to poor N2 selectivity. Simultaneously, low NH3 conversion efficiency results in wasted reducing agent and secondary pollution. While developed bimetallic denitrification catalysts have made breakthroughs in water resistance, high activity, and sulfur resistance, they struggle to simultaneously achieve NO reduction. x The synergistic optimization of conversion rate, N2 selectivity and NH3 conversion rate severely limits its application in scenarios with stringent environmental protection requirements. Summary of the Invention

[0004] This application provides a manganese-zinc bimetallic denitration catalyst, its preparation method, and its application, aiming to solve the problem that existing denitration catalysts are unable to simultaneously achieve NO removal. x The problem of synergistic optimization of conversion rate, N2 selectivity and NH3 conversion rate.

[0005] The first aspect of this application provides a method for preparing a manganese-zinc bimetallic denitration catalyst, comprising the following steps:

[0006] (1) A manganese source, a zinc source, 2,5-dihydroxyterephthalic acid and an organic solvent are mixed to obtain a suspension; the suspension is subjected to a hydrothermal reaction to obtain the manganese-zinc bimetallic framework; (2) The manganese-zinc bimetallic framework is calcined in a nitrogen atmosphere and then in an air atmosphere to obtain the manganese-zinc bimetallic denitration catalyst. The calcination temperature in the nitrogen atmosphere is 230-240℃, and the calcination temperature in the air atmosphere is 230-240℃.

[0007] According to some embodiments of the preparation method of the manganese-zinc bimetallic denitration catalyst described in this application, in step (1), the molar ratio of manganese in the manganese source to zinc in the zinc source is (5.5-6.5):1.

[0008] According to some embodiments of the preparation method of the manganese-zinc bimetallic denitration catalyst described in this application, the molar ratio of manganese element in the manganese source to 2,5-dihydroxyterephthalic acid is (1.7-2):1.

[0009] According to some embodiments of the preparation method of the manganese-zinc bimetallic denitration catalyst described in this application, the manganese source includes one or more of manganese acetate, manganese nitrate, and manganese chloride.

[0010] According to some embodiments of the preparation method of the manganese-zinc bimetallic denitration catalyst described in this application, the zinc source includes one or more of zinc acetate, zinc nitrate, and zinc chloride.

[0011] According to some embodiments of the preparation method of the manganese-zinc bimetallic denitration catalyst described in this application, in step (1), the organic solvent includes a mixture of N,N-dimethylacetamide, water and ethanol in a volume ratio of (7-8):1:1.

[0012] According to some embodiments of the preparation method of the manganese-zinc bimetallic denitration catalyst described in this application, in step (1), the mixing temperature is 20-30℃ and the time is 2-3h.

[0013] According to some embodiments of the preparation method of the manganese-zinc bimetallic denitration catalyst described in this application, the hydrothermal reaction temperature is 110-120℃ and the time is 20-28h.

[0014] According to some embodiments of the preparation method of the manganese-zinc bimetallic denitration catalyst described in this application, in step (2), the calcination temperature under nitrogen atmosphere is 234-236℃ and the time is 2-4h.

[0015] According to some embodiments of the preparation method of the manganese-zinc bimetallic denitration catalyst described in this application, in step (2), the temperature of the air atmosphere calcination is 234-236℃ and the time is 4-6h.

[0016] The second aspect of this application provides a manganese-zinc bimetallic denitration catalyst, which is prepared by the preparation method described in the first aspect of this application.

[0017] According to some embodiments of the manganese-zinc bimetallic denitration catalyst described in this application, the manganese-zinc bimetallic denitration catalyst has a rod-shaped mesoporous structure, with a pore size of 7-27 nm and a pore volume of 0.2-0.4 cm³. 3 / g, specific surface area is 80-90m² 2 / g.

[0018] According to some embodiments of the manganese-zinc bimetallic denitration catalyst described in this application, the manganese element in the manganese-zinc bimetallic denitration catalyst is Mn 2+ Mn 3+ and Mn 4+ Mixed valence states exist.

[0019] According to some embodiments of the manganese-zinc bimetallic denitration catalyst described in this application, the manganese-zinc bimetallic denitration catalyst contains Mn 2+ Mn 3+ and Mn 4+ The molar percentages are (45-50%) : (40-45%) : (8-13%).

[0020] According to some embodiments of the manganese-zinc bimetallic denitration catalyst described in this application, the zinc element in the manganese-zinc bimetallic denitration catalyst is Zn. 2+ The valence state exists.

[0021] The third aspect of this application provides the application of the manganese-zinc bimetallic denitrification catalyst described in the second aspect of this application in the catalytic reduction of low-temperature flue gas denitrification.

[0022] According to some embodiments of the application described in this application, the low-temperature flue gas includes low-temperature industrial flue gas at 100-220°C.

[0023] The beneficial effects of this application include: the manganese-zinc bimetallic denitration catalyst described herein achieves mild charge redistribution, acid site regulation, and oxygen vacancy introduction through the synergistic effect of manganese and zinc bimetals; there is unidirectional electron transfer between manganese and zinc, with zinc acting as an electron donor and manganese as an electron acceptor, forming synergistic active sites, resulting in a ratio of weak acid, medium acid, and strong acid sites in the catalyst of 1:(4-4.5):(1-1.5), and the Raman spectrum of the catalyst is in the range of 600-650 cm⁻¹. -1 Characteristic peaks representing oxygen vacancies appeared between the peaks. Oxygen vacancies can significantly improve catalytic performance by promoting reactant activation, enhancing redox capacity, increasing oxygen migration rate, and regulating acidic structure. A greater number of intermediate-acidic sites can stably adsorb NH3 without binding it too strongly, ensuring effective activation of NH3 rather than its participation in side reactions to generate N2O, thus significantly improving the catalyst's denitrification efficiency and N2 selectivity. Attached Figure Description

[0024] Figure 1 a represents the NO content of the manganese-zinc bimetallic denitrification catalyst (q-MnZn-MOF) described in Example 1 of this application. x Conversion rate test results; Figure 1 b represents the N2 selectivity test result of the manganese-zinc bimetallic denitration catalyst (q-MnZn-MOF) described in Example 1 of this application; Figure 1 c represents the NH3 conversion rate test result of the manganese-zinc bimetallic denitration catalyst (q-MnZn-MOF) described in Example 1 of this application; Figure 2 a is a scanning electron microscope image of the manganese-zinc bimetallic organic framework (MnZn-MOF-74) described in Example 1 of this application; Figure 2 b is a scanning electron microscope image of the manganese-zinc bimetallic denitration catalyst (q-MnZn-MOF) described in Example 1 of this application; Figure 2 c is a transmission electron microscope image of the manganese-zinc bimetallic organic framework (MnZn-MOF-74) described in Example 1 of this application; Figure 2 d is a transmission electron microscope image of the manganese-zinc bimetallic denitration catalyst (q-MnZn-MOF) described in Example 1 of this application; Figure 3 a is the nitrogen adsorption-desorption isotherm diagram of the manganese-zinc bimetallic denitration catalyst (q-MnZn-MOF) described in Example 1 of this application; Figure 3 b is a pore structure diagram of the manganese-zinc bimetallic denitration catalyst (q-MnZn-MOF) described in Example 1 of this application; Figure 4 This is an X-ray photoelectron spectroscopy (XPS) result of the manganese-zinc bimetallic denitration catalyst (q-MnZn-MOF) described in Example 1 of this application. Figure 5 This is a Raman spectrum of the manganese-zinc bimetallic denitration catalyst (q-MnZn-MOF) described in Example 1 of this application. Figure 6 The results of NH3 temperature-programmed desorption of the manganese-zinc bimetallic denitration catalyst (q-MnZn-MOF) described in Example 1 of this application are as follows: Figure 6 a) and the area integral results of its corresponding acid sites ( Figure 6 b) Figure 7 The differential charge density diagram is obtained by functional density theory calculation of the manganese-zinc bimetallic denitration catalyst (q-MnZn-MOF) described in Example 1 of this application. Detailed Implementation

[0025] The embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0026] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0027] This application provides a method for preparing a manganese-zinc bimetallic denitration catalyst, comprising the following steps: (1) A manganese source, a zinc source, 2,5-dihydroxyterephthalic acid and an organic solvent are mixed to obtain a suspension; the suspension is subjected to a hydrothermal reaction to obtain the manganese-zinc bimetallic framework; (2) The manganese-zinc bimetallic framework is calcined in a nitrogen atmosphere and then in an air atmosphere to obtain the manganese-zinc bimetallic denitration catalyst. The calcination temperature in the nitrogen atmosphere is 230-240℃, and the calcination temperature in the air atmosphere is 230-240℃.

[0028] The manganese-zinc bimetallic denitration catalyst described in this application uses manganese and zinc as bimetallic active centers and 2,5-dihydroxyterephthalic acid as an organic ligand, and is prepared by a solvothermal reaction combined with a two-step calcination under nitrogen and air. Through the synergistic effect of the manganese-zinc bimetallic catalyst, charge redistribution, acid site regulation, and oxygen vacancy introduction are achieved. Density functional theory calculations prove that there is a unidirectional electron transfer between manganese and zinc, with zinc acting as the electron donor and manganese as the electron acceptor. These two form synergistic active sites, resulting in a ratio of weak acid, medium acid, and strong acid sites in the catalyst of 1:(4-4.5):(1-1.5). The Raman spectrum of the catalyst is in the range of 600-650 cm⁻¹. -1 Characteristic peaks representing oxygen vacancies appeared between the peaks. Oxygen vacancies can significantly improve catalytic performance by promoting reactant activation, enhancing redox capacity, increasing oxygen migration rate, and regulating acidic structure. A greater number of intermediate-acidic sites can stably adsorb NH3 without binding it too strongly, ensuring effective activation of NH3 rather than its participation in side reactions to generate N2O, thus significantly improving the catalyst's denitrification efficiency and N2 selectivity.

[0029] In some embodiments of this application, in step (1), the molar ratio of manganese in the manganese source to zinc in the zinc source is (5.5-6.5):1; for example, 5.5:1, 5.8:1, 6:1, 6.2:1, 6.3:1, 6.5:1, etc. A suitable ratio of manganese and zinc can achieve sufficient unidirectional electron transfer from zinc to manganese, ensuring a mild redistribution of charge, regulation of acid sites and introduction of oxygen vacancies, which is more conducive to the denitrification reaction.

[0030] In some embodiments of this application, the molar ratio of manganese in the manganese source to 2,5-dihydroxyterephthalic acid is (1.7-2):1.

[0031] In some embodiments of this application, the manganese source includes one or more of manganese acetate, manganese nitrate, and manganese chloride.

[0032] In some embodiments of this application, the zinc source includes one or more of zinc acetate, zinc nitrate, and zinc chloride.

[0033] In some embodiments of this application, in step (1), the organic solvent comprises a mixture of N,N-dimethylacetamide, water and ethanol in a volume ratio of (7-8):1:1.

[0034] In some embodiments of this application, in step (1), the mixing temperature is 20-30°C, such as 20°C, 25°C, 28°C, 30°C, etc., and the time is 2-3h; such as 2h, 2.2h, 2.5h, 3h, etc.

[0035] In some embodiments of this application, the temperature of the hydrothermal reaction is 110-120°C, such as 110°C, 115°C, 118°C, 120°C, etc., and the time is 20-28h, such as 20h, 22h, 25h, 26h, 28h, etc.

[0036] In some embodiments of this application, in step (2), the nitrogen atmosphere calcination temperature is 234-236°C and the time is 2-4 hours; In some embodiments of this application, in step (2), the temperature of the air atmosphere calcination is 234-236°C and the time is 4-6 hours.

[0037] This application also provides a manganese-zinc bimetallic denitration catalyst, which is prepared by the preparation method described in the first aspect of this application.

[0038] The moderate electronegativity difference between manganese and zinc in the manganese-zinc bimetallic denitration catalyst described in this application drives a mild charge redistribution between the bimetallic centers, optimizing the valence state distribution of manganese and the strength of acid sites; Zn 2+ With Mn 2+The high matching degree of ionic radii stabilizes the catalyst framework structure, inducing the formation of a broadly distributed mesoporous structure of 7-27 nm, promoting the adsorption capacity of active sites for NH3, and inhibiting excessive oxidation of NH3. The synergistic effect of the bimetallic catalyst promotes the formation of abundant oxygen vacancies on the catalyst surface, enabling the manganese-zinc bimetallic denitration catalyst to exhibit excellent NO removal performance at ultra-low temperatures. x High conversion rate, high N2 selectivity and high NH3 conversion efficiency.

[0039] In some embodiments of this application, the manganese-zinc bimetallic denitration catalyst has a rod-shaped mesoporous structure, with a pore size of 7-27 nm and a pore volume of 0.2-0.4 cm³. 3 / g, specific surface area is 80-90m² 2 / g. The manganese-zinc bimetallic denitration catalyst possesses highly efficient active sites, abundant oxygen vacancies, and a high specific surface area. At 30000h... -1 At high air speeds, NO x The temperature window for achieving a 90% conversion rate is 100-220℃, and NO conversion is achieved at an ultra-low temperature of 140℃. x With a conversion rate of over 97.1%, the active temperature window is widened by more than 40°C compared to single-metal manganese benchmark MOF catalysts.

[0040] In some embodiments of this application, the manganese element in the manganese-zinc bimetallic denitration catalyst is Mn 2+ Mn 3+ and Mn 4+ Mixed valence states exist; Mn in manganese-zinc bimetallic denitration catalyst 2+ Mn 3+ and Mn 4+ The molar percentages are (45-50%) : (40-45%) : (8-13%).

[0041] In some embodiments of this application, the zinc element in the manganese-zinc bimetallic denitration catalyst is Zn. 2+ The valence state exists.

[0042] The manganese-zinc bimetallic denitration catalyst described in this application utilizes the synergistic regulation of redox balance and acid site strength by manganese and zinc bimetals to prevent excessive oxidation of NH3 to generate secondary pollutants such as N2O. The catalyst contains a low proportion of Mn. 4+ It possesses relatively mild oxidizing properties, and its N2 selectivity remains above 94.1% throughout the entire temperature range of 40-240℃, effectively reducing the risk of secondary pollution and meeting stringent environmental protection requirements.

[0043] This application also provides an application of the manganese-zinc bimetallic denitrification catalyst described in the second aspect of this application in catalytic reduction of low-temperature flue gas denitrification.

[0044] In some embodiments of this application, the low-temperature flue gas includes low-temperature industrial flue gas at 100-220°C. The catalyst described in this application maintains an NH3 conversion rate of over 81.2% within a temperature window of 100-220°C, achieving a highly efficient unification of the denitrification reaction and the utilization of the reducing agent.

[0045] The technical solution of this application will be further described below with reference to specific embodiments.

[0046] Example 1 A method for preparing a manganese-zinc bimetallic denitration catalyst includes the following steps: (1) Dissolve 1.2g Mn(CH3COOH)2•4H2O and 0.17g Zn(CH3COOH)2•2H2O in a mixed solvent of 70mL N,N-dimethylacetamide, ultrapure water and ethanol (volume ratio of the three is 7.5:1:1). Stir until completely dissolved, then add 0.45g 2,5-dihydroxyterephthalic acid. Stir magnetically at room temperature (25℃) for 2.5h to obtain a mixed reaction solution. Transfer it to a stainless steel reactor with a Teflon liner and react at 115℃ for 24h. After the reaction is completed, collect, wash and dry the brown product at the bottom of the reactor to obtain a manganese-zinc bimetallic organic framework, denoted as MnZn-MOF-74 (molar ratio of manganese and zinc in this example is 6.3:1). (2) MnZn-MOF-74 was placed in a tube furnace and heated to 236°C at a heating rate of 1°C / min under a nitrogen atmosphere, and calcined at a constant temperature for 3 hours. Then, the atmosphere was switched to air and calcined at a constant temperature of 236°C for 5 hours. The mixture was then naturally cooled to room temperature to obtain the manganese-zinc bimetallic denitration catalyst, denoted as q-MnZn-MOF.

[0047] Example 2 The only difference between the preparation method of the manganese-zinc bimetallic denitration catalyst in Example 2 and that in Example 1 is that the amount of Mn(CH3COOH)2•4H2O and Zn(CH3COOH)2•2H2O added during the preparation of the manganese-zinc bimetallic denitration catalyst in Example 2 is different from that in Example 1.

[0048] The specific operating steps include: (1) Dissolve 1.04g Mn(CH3COOH)2•4H2O and 0.17g Zn(CH3COOH)2•2H2O in a mixed solvent of 70mL N,N-dimethylacetamide, ultrapure water and ethanol (volume ratio of the three is 7.5:1:1). Stir until completely dissolved, then add 0.45g 2,5-dihydroxyterephthalic acid. Stir magnetically at room temperature (25℃) for 2.5h to obtain a mixed reaction solution. Transfer it to a stainless steel reactor with a Teflon liner and react at 115℃ for 24h. After the reaction is completed, collect, wash and dry the brown product at the bottom of the reactor to obtain a manganese-zinc bimetallic organic framework. The remaining operation steps are the same as in Example 1 (the molar ratio of manganese and zinc in this example is 5.5:1).

[0049] Example 3 The only difference between the preparation method of the manganese-zinc bimetallic denitration catalyst in Example 3 and that in Example 1 is that the amount of Mn(CH3COOH)2•4H2O and Zn(CH3COOH)2•2H2O added during the preparation of the manganese-zinc bimetallic denitration catalyst in Example 3 is different from that in Example 1.

[0050] The specific operating steps include: (1) Dissolve 1.23g Mn(CH3COOH)2•4H2O and 0.17g Zn(CH3COOH)2•2H2O in a mixed solvent of 70mL N,N-dimethylacetamide, ultrapure water and ethanol (volume ratio of the three is 7.5:1:1). Stir until completely dissolved, then add 0.45g 2,5-dihydroxyterephthalic acid. Stir magnetically at room temperature (25℃) for 2.5h to obtain a mixed reaction solution. Transfer it to a stainless steel reactor with a Teflon liner and react at 115℃ for 24h. After the reaction is completed, collect, wash and dry the brown product at the bottom of the reactor to obtain a manganese-zinc bimetallic organic framework. The remaining operation steps are the same as in Example 1 (the molar ratio of manganese and zinc in this example is 6.5:1).

[0051] Example 4 The only difference between the preparation method of the manganese-zinc bimetallic denitration catalyst in Example 4 and that in Example 1 is that the amount of Mn(CH3COOH)2•4H2O and Zn(CH3COOH)2•2H2O added during the preparation of the manganese-zinc bimetallic denitration catalyst in Example 4 is different from that in Example 1.

[0052] The specific operating steps include: (1) Dissolve 1.2g Mn(CH3COOH)2•4H2O and 0.168g Zn(CH3COOH)2•2H2O in a mixed solvent of 70mL N,N-dimethylacetamide, ultrapure water and ethanol (volume ratio of the three is 7.5:1:1). Stir until completely dissolved, then add 0.45g 2,5-dihydroxyterephthalic acid. Stir magnetically at room temperature (25℃) for 2.5h to obtain a mixed reaction solution. Transfer it to a stainless steel reactor with a Teflon liner and react at 115℃ for 24h. After the reaction is completed, collect, wash and dry the brown product at the bottom of the reactor to obtain a manganese-zinc bimetallic organic framework. The remaining operation steps are the same as in Example 1 (the molar ratio of manganese and zinc in this example is 6.4:1).

[0053] Example 5 The only difference between the preparation method of the manganese-zinc bimetallic denitration catalyst in Example 5 and that in Example 1 is that the amount of Mn(CH3COOH)2•4H2O and Zn(CH3COOH)2•2H2O added during the preparation of the manganese-zinc bimetallic denitration catalyst in Example 5 is different from that in Example 1.

[0054] The specific operating steps include: (1) Dissolve 1.2g Mn(CH3COOH)2•4H2O and 0.19g Zn(CH3COOH)2•2H2O in a mixed solvent of 70mL N,N-dimethylacetamide, ultrapure water and ethanol (volume ratio of the three is 7.5:1:1). Stir until completely dissolved, then add 0.45g 2,5-dihydroxyterephthalic acid. Stir magnetically at room temperature (25℃) for 2.5h to obtain a mixed reaction solution. Transfer it to a stainless steel reactor with a Teflon liner and react at 115℃ for 24h. After the reaction is completed, collect, wash and dry the brown product at the bottom of the reactor to obtain a manganese-zinc bimetallic organic framework. The remaining operation steps are the same as in Example 1 (the molar ratio of manganese and zinc in this example is 5.8:1).

[0055] Example 6 The only difference between the preparation method of the manganese-zinc bimetallic denitration catalyst in Example 6 and that in Example 1 is that the calcination temperature in air atmosphere during the preparation of the manganese-zinc bimetallic denitration catalyst in Example 6 is 232°C.

[0056] Example 7 The only difference between the preparation method of the manganese-zinc bimetallic denitration catalyst in Example 7 and that in Example 1 is that the calcination temperature in air atmosphere during the preparation of the manganese-zinc bimetallic denitration catalyst in Example 7 is 234°C.

[0057] Example 8 The only difference between the preparation method of the manganese-zinc bimetallic denitration catalyst in Example 8 and that in Example 1 is that the calcination temperature in air atmosphere during the preparation of the manganese-zinc bimetallic denitration catalyst in Example 8 is 238°C.

[0058] Comparative Example 1 The only difference between the preparation method of the manganese-zinc bimetallic denitration catalyst in Comparative Example 1 and Example 1 is that no raw material Zn(CH3COOH)2•2H2O was added during the preparation of the manganese-zinc bimetallic denitration catalyst in Comparative Example 1, and the amount of Mn(CH3COOH)2•4H2O added was 1.37g.

[0059] Comparative Example 2 The only difference between the preparation method of the manganese-zinc bimetallic denitration catalyst in Comparative Example 2 and Example 1 is that no raw material Mn(CH3COOH)2•4H2O was added during the preparation of the manganese-zinc bimetallic denitration catalyst in Comparative Example 2, and the amount of Zn(CH3COOH)2•2H2O added was 1.37g.

[0060] 1. Performance study of the denitrification catalysts described in Examples 1-8 and Comparative Examples 1-2 of this application Denitrification performance test: The denitrification activity of the catalyst fixed in a quartz tube with an inner diameter of 8 mm was tested using a simulated airflow method. The total flow rate of the simulated flue gas was 100 mL / min, and the gas hourly space velocity (GHSV) was 30,000 h⁻¹. -1 The flue gas composition includes 500 ppm NO, 500 ppm NH3, and 5% O2, with N2 used as a balance gas. The reaction temperature is 40-240℃. The reaction tail gas is monitored in real time using a Testo350 NO / NO2 flue gas analyzer. x The conversion rate is calculated using formula (1):

[0061] The N2O concentration was tested using an N2O detector (SKY2000), and the NH3 concentration in the reaction tail gas was monitored in real time using an NH3 detector (HD-P900). The N2 selectivity was calculated using formula (2):

[0062] The NH3 concentration in the reaction tail gas was monitored in real time using an NH3 detector (HD-P900). The NH3 conversion rate was calculated using formula (3):

[0063] The calculation results are shown in Table 1 and Figure 1 As shown.

[0064] Table 1

[0065] Table 1 shows that in simulated flue gas containing 500ppm NO + 500ppm NH3 + 5% O2 and a space velocity of 30000 h⁻¹ -1 Under the conditions described in Examples 1-8 of this application, the catalysts all exhibit excellent low-temperature denitrification activity, high N2 selectivity, and NH3 conversion rate, with NO concentration between 100-220℃. x The conversion rate exceeds 90% at a low temperature of 140℃, NO x The conversion rates all reached over 97.1%, and within the temperature range of 100-220℃, the N2 selectivity remained above 91.5%, and the NH3 conversion rate remained above 80%. Among them, the catalyst described in Example 1 exhibited the best low-temperature denitrification activity, N2 selectivity, and NH3 conversion rate.

[0066] When the dosage of Zn(CH3COOH)2·2H2O remains constant, but the dosage of Mn(CH3COOH)2·4H2O is changed, the N2 selectivity and NH3 conversion of the catalysts described in Examples 1-3 first increase and then decrease with the increase of the Mn(CH3COOH)2·4H2O dosage. Similarly, when the dosage of Mn(CH3COOH)2·4H2O remains constant, but the dosage of Zn(CH3COOH)2·2H2O is changed, the N2 selectivity and NH3 conversion of the catalysts described in Examples 1 and 4-5 also first increase and then decrease with the increase of the Zn(CH3COOH)2·2H2O dosage. This indicates that the molar ratio of Mn to Zn has a significant impact on the N2 selectivity and NH3 conversion of the catalysts. When the Mn ratio is low, the limited number of Mn sites reduces the catalyst's adsorption capacity and activation ability for NH3, thus decreasing the NH3 conversion rate. Simultaneously, unreacted NH3 readily undergoes non-selective oxidation on the catalyst surface, generating N2O, thereby reducing N2 selectivity. When the ratio is moderate, electrons are gently redistributed between the bimetallic centers, avoiding excessively high Mn valence states that would lead to overly strong redox properties, while ensuring sufficient Mn content. 3+ / Mn 4+ The site is used for NH3 activation, at which point NH3 is mainly used to reduce NO. x N2 is generated, thus significantly improving N2 selectivity and NH3 conversion; when the Mn dosage exceeds the optimal value, the Mn content in the catalyst decreases. 3+ / Mn 4+ With an increased proportion of NH3 and excessively strong redox capabilities, NH3 is more easily oxidized by strong oxidizing sites into byproducts such as N2O, leading to a decrease in N2 selectivity. In addition, excessive Mn is prone to aggregation, resulting in uneven distribution of active sites, which further exacerbates the decline in N2 selectivity and NH3 conversion rate.

[0067] With increasing calcination temperature in air atmosphere, the low-temperature denitrification activity, N2 selectivity, and NH3 conversion of the catalysts described in Examples 1 and 6-8 initially increased and then decreased. The catalyst prepared in Example 1 exhibited the highest NO content. x The highest conversion rate (100%), the highest N2 selectivity (≥95.9%), and the highest NH3 conversion rate (82.6%) demonstrate that the calcination temperature under air atmosphere has a significant impact on the catalyst's denitrification activity, N2 selectivity, and NH3 conversion rate. The denitrification performance can be further regulated by influencing the catalyst's porosity and specific surface area, the degree of removal of organic ligands, the oxygen vacancy content, and the valence state distribution of Mn.

[0068] The denitrification performance, N2 selectivity, and NH3 conversion of the catalyst described in Comparative Example 1 of this application were tested. The catalyst with only Mn(CH3COOH)2·4H2O added exhibited NO conversion performance between 80 and 160 °C. x The conversion rate reached over 90%, and at 140 ℃, it exhibited only 94.8% NO removal. x The conversion rate was high, and within the temperature range of 100–220 °C, the N2 selectivity remained above 79.6%, and the NH3 conversion rate remained above 80.2%. This indicates that the single Mn site catalyst has excellent ultra-low temperature denitrification activity, thus exhibiting a lower operating temperature. However, due to the excessive redox ability, NH3 is oxidized, resulting in lower N2 selectivity.

[0069] The denitrification performance, N2 selectivity, and NH3 conversion rate of the catalyst described in Comparative Example 2 of this application were tested. The catalyst with only Zn(CH3COOH)2·2H2O added was used for NO... x The conversion rate remained below 90%, and at 140 °C, it only exhibited 65.2% NO. x The conversion rate was good, and within the temperature range of 100–220 °C, the N2 selectivity remained above 70.3% and the NH3 conversion rate remained above 63.8%. The Zn sites have low redox properties and limited adsorption and activation capacity for NH3; therefore, catalysts with single Zn sites exhibited poor low-temperature denitrification activity, N2 selectivity, and NH3 conversion rate.

[0070] The manganese-zinc bimetallic denitrification catalyst described in Example 1 of this application contains NO. x The conversion rate test, N2 selectivity, and NH3 conversion rate calculation results are as follows: Figure 1 a, Figure 1 b and Figure 1 As shown in c.

[0071] from Figure 1 As can be seen, within the ultra-low temperature range of 40~240℃, the catalyst described in Example 1 exhibits ≥90% NO content within the range of 100~220℃.x The catalyst exhibits excellent conversion rate and denitrification activity at ultra-low temperatures. Furthermore, within this temperature range, the N2 selectivity of the catalyst consistently exceeds 97%, and the NH3 conversion rate consistently exceeds 82.6%, indicating that the reaction process has high NH3 utilization and low secondary pollution, demonstrating excellent environmental friendliness.

[0072] 2. Scanning electron microscope (SEM) images of the manganese-zinc bimetallic organic framework (MnZn-MOF-74) and the manganese-zinc bimetallic denitration catalyst (q-MnZn-MOF) described in Example 1 of this application are shown below. Figure 2 a and Figure 2 As shown in b, the transmission electron microscope images are as follows: Figure 2 c and Figure 2 As shown in d.

[0073] from Figure 2 As can be seen from the above, the manganese-zinc bimetallic organic framework (MnZn-MOF-74) and the manganese-zinc bimetallic denitration catalyst (q-MnZn-MOF) described in Example 1 of this application exhibit rod-shaped mesoporous structures with a length of 10-20 μm, and a large number of uniform and transversely distributed pores on the surface. After two-step calcination, q-MnZn-MOF can maintain the morphology and structural characteristics of the original MnZn-MOF-74.

[0074] 3. Whole-pore adsorption test of the manganese-zinc bimetallic denitration catalyst described in Example 1 of this application. Test Method: Nitrogen adsorption-desorption isotherms were determined using a Quantachrome analyzer. The sample was degassed at 200°C for 5 hours under a degassing program with a heating rate of 10°C / min. After degassing, the samples were tested directly. Specific surface area data were calculated using the Brunauer-Emmett-Teller (BET) formula, and pore structure parameters were determined using the Barrett-Joyner-Halenda (BJH) method. The nitrogen adsorption-desorption isotherm of the manganese-zinc bimetallic denitration catalyst (q-MnZn-MOF) described in Example 1 of this application is shown below. Figure 3 As shown in Figure a, the pore structure diagram is as follows: Figure 3 As shown in b.

[0075] from Figure 3 As can be seen from the data, the BET specific surface area of ​​the manganese-zinc bimetallic denitration catalyst (q-MnZn-MOF) described in Example 1 of this application is 81 m². 2 / g, pore volume 0.3cm 3 The adsorption-desorption curves of N2 both exhibited type IV adsorption isotherms and type H3 hysteresis loops, indicating the presence of mesoporous capillary condensation. The pore size is mainly distributed in a wide range of 7-27 nm, which enhances gas transfer during the reaction and significantly improves catalytic efficiency.

[0076] 4. The X-ray photoelectron spectroscopy test results of the manganese-zinc bimetallic denitration catalyst (q-MnZn-MOF) described in Example 1 of this application are as follows: Figure 4 As shown.

[0077] from Figure 4 As can be seen from the graph, fitting the Mn 2p spectrum of the manganese-zinc bimetallic denitration catalyst (q-MnZn-MOF) described in Example 1 of this application yields six peaks, each corresponding to a different Mn peak. 4+ Mn 3+ and Mn 2+ Mn in high valence state 3+ and Mn 4+ Mn originates from the calcination process 2+ The oxidation of Mn and the presence of these elements are more conducive to the activation of reactants and promote the reaction. The main oxidation states of Mn are +2 and +3. A higher proportion of trivalent manganese is conducive to the formation of oxygen vacancies. A low proportion of Mn 4+ This imparts relatively mild oxidizing properties to the catalyst, thereby improving denitrification activity, N2 selectivity, and NH3 conversion.

[0078] Fitting the Zn 2p spectrum revealed that zinc exists in the +2 valence state in q-MnZn-MOF, acting as a co-active site for manganese to regulate the electronic environment. Fitting the C 1s spectrum yielded characteristic peaks for CH bonds (284.8 eV), CC bonds (285 eV), and C=O bonds (288 eV), indicating that the organic ligands of the catalyst mainly exist in the form of CH bonds. Fitting the O 1s spectrum revealed characteristic peaks for lattice oxygen, surface active oxygen, and CO bonds at approximately 529 eV, 532 eV, and 533 eV, respectively. Surface active oxygen exhibits high mobility due to its low coordination at low temperatures, which is beneficial for electron transport during the reaction. Further comparison of the elemental contents of the catalyst showed that the molar percentage of Mn in different valence states in q-MnZn-MOF was [missing information - likely a percentage]. 2+ Mn 3 + Mn 4+ = 47.8% : 41.8% : 10.3%, and the ratio of Mn, Zn, C and O elements is 41.62% : 6.8% : 24.1% : 27.48%.

[0079] 5. The Raman spectroscopy results of the manganese-zinc bimetallic denitration catalyst (q-MnZn-MOF) described in Example 1 of this application are as follows: Figure 5 As shown.

[0080] from Figure 5As can be seen from the data, the Raman spectrum of the denitrification catalyst q-MnZn-MOF described in Example 1 of this application is in the range of 600-650 cm⁻¹. -1 Characteristic peaks representing oxygen vacancies appear between the peaks. Oxygen vacancies can significantly enhance catalytic performance by promoting reactant activation, enhancing redox capabilities, increasing oxygen migration rates, and regulating acidic structures.

[0081] 6. The NH3 temperature-programmed desorption results of the manganese-zinc bimetallic denitration catalyst (q-MnZn-MOF) described in Example 1 of this application and the area integral of the corresponding acid sites. Test method: NH3 was first introduced into an adsorption tube containing 0.1 g of catalyst for pre-adsorption for 30 minutes. The system was then purged with helium at 30 ml / min for 2 hours to remove weakly adsorbed species, with the temperature increased during this process. The desorption curves were recorded. After baseline calibration and peak fitting of the desorption curves, the peak areas were integrated to obtain the area integral of the acid sites.

[0082] from Figure 6 As can be seen from the above, the NH3 temperature-programmed desorption results of the denitrification catalyst (q-MnZn-MOF) described in this application (e.g.) Figure 6 (As shown in a) Seven desorption peaks appeared at 176℃, 270℃, 323℃, 352℃, 465℃, 546℃, and 618℃. The peak at 176℃ corresponds to a weak acid site, the peaks at 270℃, 323℃, and 352℃ correspond to intermediate acid sites, and the peaks at 465℃, 546℃, and 618℃ correspond to strong acid sites. Peak area integration was performed on the peaks corresponding to the weak, intermediate, and strong acid sites (e.g.,...). Figure 6 As shown in b), the ratio of weak acid sites, medium acid sites, and strong acid sites was 1:4.2:1.3, indicating that the acid sites of the denitrification catalyst (q-MnZn-MOF) described in this application are mainly medium acid sites. The medium-strength acid sites can stably adsorb NH3 without binding too strongly, which can effectively activate NH3 and participate in the redox reaction, significantly improving the denitrification efficiency, N2 selectivity, and NH3 conversion rate.

[0083] 7. The differential charge density diagram of the manganese-zinc bimetallic denitration catalyst (q-MnZn-MOF) described in Example 1 of this application, calculated by functional density theory.

[0084] Computational Method: Based on DFT calculations, the differential charge density of the catalyst was calculated at the atomic scale using the VASP program. Exchange-related interactions were controlled using the GGA function proposed by Perdew, Burke, and Ernzerhof (PBE) during the calculations. In the structural optimization calculations, the force convergence threshold was 10. -3 eV•Å, energy convergence threshold is 10 -5eV. The van der Waals effect was corrected using Grimme D3, and the test results are as follows. Figure 7 As shown.

[0085] from Figure 7 As can be seen, in the manganese-zinc bimetallic denitration catalyst (q-MnZn-MOF) described in this application, electrons are mainly enriched around O atoms, which is conducive to the formation of Brønsted acid sites. Both Mn and O atoms exhibit electron gain (yellow) and loss (blue), while Zn atoms only exhibit electron loss (blue). This indicates that Zn plays a unidirectional role in the q-MnZn-MOF cluster, with electrons from Zn unidirectionally transferring to the vicinity of Mn or O atoms in the structure. This increases the electron cloud density, regulates the d-band center of the cluster, and lowers the reaction energy barrier. Therefore, Zn is only a cooperating active site for Mn.

[0086] Although the above embodiments have been shown and described, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions and variations made to the above embodiments by those skilled in the art are within the protection scope of the present invention.

Claims

1. A method for preparing a manganese-zinc bimetallic denitration catalyst, characterized in that, Includes the following steps: (1) A manganese source, a zinc source, 2,5-dihydroxyterephthalic acid and an organic solvent are mixed to obtain a suspension; the suspension is subjected to a hydrothermal reaction to obtain the manganese-zinc bimetallic framework; (2) The manganese-zinc bimetallic framework is calcined in a nitrogen atmosphere and then in an air atmosphere to obtain the manganese-zinc bimetallic denitration catalyst. The calcination temperature in the nitrogen atmosphere is 230-240℃, and the calcination temperature in the air atmosphere is 230-240℃.

2. The preparation method of the manganese-zinc bimetallic denitration catalyst according to claim 1, characterized in that, In step (1), the molar ratio of manganese in the manganese source to zinc in the zinc source is (5.5-6.5):1; And / or, the molar ratio of manganese in the manganese source to 2,5-dihydroxyterephthalic acid is (1.7-2):

1.

3. The preparation method of the manganese-zinc bimetallic denitration catalyst according to claim 1, characterized in that, The manganese source includes one or more of manganese acetate, manganese nitrate, and manganese chloride; And / or, the zinc source includes one or more of zinc acetate, zinc nitrate, and zinc chloride.

4. The preparation method of the manganese-zinc bimetallic denitration catalyst according to claim 1, characterized in that, In step (1), the organic solvent includes a mixture of N,N-dimethylacetamide, water and ethanol in a volume ratio of (7-8):1:

1.

5. The preparation method of the manganese-zinc bimetallic denitration catalyst according to claim 1, characterized in that, In step (1), the mixing temperature is 20-30℃ and the time is 2-3h; And / or, the hydrothermal reaction is carried out at a temperature of 110-120°C for a time of 20-28 hours.

6. The preparation method of the manganese-zinc bimetallic denitration catalyst according to claim 1, characterized in that, In step (2), the nitrogen atmosphere calcination temperature is 234-236℃ and the time is 2-4h; And / or, in step (2), the temperature of the air atmosphere calcination is 234-236℃ and the time is 4-6h.

7. A manganese-zinc bimetallic denitration catalyst, characterized in that, It is prepared by the preparation method described in any one of claims 1-6.

8. The manganese-zinc bimetallic denitration catalyst according to claim 7, characterized in that, The manganese-zinc bimetallic denitration catalyst has a rod-shaped mesoporous structure with a pore size of 7-27 nm and a pore volume of 0.2-0.4 cm³. 3 / g, specific surface area is 80-90m² 2 / g.

9. The manganese-zinc bimetallic denitration catalyst according to claim 7, characterized in that, The manganese element in the manganese-zinc bimetallic denitration catalyst is Mn 2+ Mn 3+ and Mn 4+ Mixed valence states exist; Preferably, the manganese-zinc bimetallic denitration catalyst contains Mn 2+ Mn 3+ and Mn 4+ The molar percentage is (45-50%) : (40-45%) : (8-13%); And / or, the zinc element in the manganese-zinc bimetallic denitration catalyst is in the form of Zn. 2+ The valence state exists.

10. The application of the manganese-zinc bimetallic denitrification catalyst according to any one of claims 7-9 in catalytic reduction of low-temperature flue gas denitrification; Preferably, the low-temperature flue gas includes low-temperature industrial flue gas at 100-220°C.

Images