Manganese-based composite zirconium-tungsten oxide denitration catalyst, preparation method and application thereof

Abstract

The application discloses a manganese-based composite zirconium-tungsten oxide denitration catalyst and a preparation method and application thereof. a W b The Zr a W b The MnO2 precursor is prepared by mixing soluble manganese salt, ammonium persulfate and a solvent, stirring until transparent, adding soluble zirconium salt and soluble tungsten salt, stirring and dissolving, transferring into a reaction kettle, hydrothermal reaction at 80-120 DEG C for 5-50 hours, cooling to room temperature after taking out, and filtering, washing and drying the obtained solid-liquid mixture. Compared with a single-component manganese-based metal oxide low-temperature catalyst, the application utilizes the modification of the active substrate MnO2 by Zr and W, effectively improves the low-temperature catalytic activity, and widens the overall working temperature window.

Description

TECHNICAL FIELD

[0001] The present application relates to the SCR (selective catalytic reduction) flue gas denitration technology, in particular to a low-temperature SCR denitration catalyst using NH3 as a reducing agent, a preparation method and application thereof, and belongs to the field of air purification technology and environmental protection catalytic materials. BACKGROUND

[0002] Currently commonly used NO x Treatment technologies include catalytic and non-catalytic reduction, wet scrubbing, photocatalysis, plasma catalysis, etc. Catalytic and non-catalytic reduction is the most widely used method in current industrial plants. It includes selective catalytic reduction (SCR) technology and selective non-catalytic reduction (SNCR) technology. Compared with SNCR technology, SCR technology has higher denitration efficiency and lower required reaction temperature. The core factor is the participation of catalysts in the reaction process. Catalytic activity, N2 selectivity, high conversion rate working temperature window, resistance to toxic molecules such as SO2 / H2O, etc. are important standards for judging the quality of catalysts, and are also key indicators for measuring whether they can be used for industrialization. However, the traditional V2O5-WO3 / TiO2 catalyst has a narrow temperature window (300-400℃) and the active component V has biological toxicity, etc. In the application scenarios such as steel plants and cement plants with low processing temperature, the catalytic efficiency of the V2O5-based catalyst is affected by temperature, and cannot meet the industrial demand. On the other hand, due to the presence of a large amount of SO2, heavy metal ions and other elements that poison the catalyst in industrial waste gas, the catalytic device needs to be placed after the desulfurization and dust removal device, at which time the waste gas temperature is low. Therefore, it is necessary to develop an SCR catalyst that can catalytically convert at low temperature with high efficiency.

[0003] Chinese patent application 202410636962.X discloses a preparation method of a modified denitration catalyst with manganese and cerium loaded on modified biochar and its application. The technology modifies the surface of biochar with strong acid, and then loads manganese acetate, cerium nitrate and iron nitrate on the modified biochar. The technology can catalyze the conversion of NO x at 80-240℃, and significantly improves the sulfur resistance of the catalyst. However, the catalyst involved in the present application has a narrow temperature window for maintaining high conversion rate at low temperature, especially the working temperature window for NO x conversion rate higher than 90% is only 80℃.

[0004] Chinese invention patent application 202210504112.5 discloses a low-temperature manganese-based catalyst, its preparation method, and its application. A co-precipitation method is used to introduce manganese salt, cerium salt, and tetraethyl silicate, followed by calcination to obtain a composite metal oxide. The catalyst is then acidified with an inorganic acid. In this invention, some active components of the SCR catalyst exist on the surface in the form of metal sulfates. Utilizing the synergistic acid-base-oxidation effect of sulfates and surface metal salts, the storage of active oxygen is increased, effectively promoting the adsorption of NH3 and NO. Furthermore, the sulfation of the metal salts increases the acidity sites on the catalyst, enhancing the adsorption of NH3 at medium to high temperatures, thereby improving the medium- and high-temperature performance. This allows the catalyst to effectively adsorb NO within the temperature range of 110–260℃. x The conversion rate remained above 90%. However, the air velocity during the technology testing was only 50,000 h⁻¹. -1 The NO concentration used in the flue gas is only 500 ppm, and the catalyst can achieve more than 90% NO reduction at a relatively low space velocity. x The temperature window for conversion is only 150℃, and when the catalyst's NO... x Once the conversion rate reaches its maximum efficiency, it drops sharply as the temperature increases, indicating that the catalyst designed in this patent has very low applicability outside of its effective temperature range.

[0005] Chinese invention patent CN114308053B discloses a denitrification catalyst with high-entropy oxides as the active component, its preparation, and its application. By loading high-entropy oxides, including ferric nitrate, cobalt nitrate, manganese nitrate, cerium nitrate, and neodymium nitrate, onto TiO2, these oxides participate in the gas adsorption, activation, and desorption processes of the denitrification reaction based on their high-entropy effect, lattice distortion effect, and retarded diffusion effect. However, the optimal activity temperature window of this technology remains narrow even after modification, only within the NO range of 175-275℃. x The conversion rate remained above 90%, indicating that it is difficult to apply to low-temperature ranges below 150°C. Furthermore, the catalyst activity varied significantly across the entire temperature range, and the catalytic efficiency was highly susceptible to temperature fluctuations, making it unsuitable for treating waste gas from mobile sources. Summary of the Invention

[0006] To address the issues of high operating temperatures and limited applicability of existing commercial catalysts, this invention aims to provide a manganese-based composite zirconium tungsten oxide denitration catalyst and its preparation method, which possesses high stability, excellent low-temperature catalytic activity, and a wide operating temperature window.

[0007] Another objective of this invention is to provide the application of the aforementioned manganese-based composite zirconium tungsten oxide denitrification catalyst in flue gas denitrification. The catalyst obtained by this invention ensures a catalyst efficiency of over 90% within a temperature range of 120-320℃, achieves 100% conversion at 160℃, and exhibits good reaction stability.

[0008] The purpose of the present application is achieved by the following technical solutions:

[0009] The manganese-based composite zirconium-tungsten oxide denitration catalyst is prepared by mixing Zr a W b The MnO2 precursor is obtained by heat treatment of the MnO2 precursor at 300-500 DEG C under an air atmosphere; the Zr a W b The MnO2 precursor is prepared by mixing soluble manganese salt, ammonium persulfate, dissolving in a solvent, stirring until transparent, adding soluble zirconium salt and soluble tungsten salt, stirring and dissolving, transferring into a reaction kettle, hydrothermal reaction at 80-120 DEG C for 5-50 h, taking out and cooling to room temperature, filtering, washing and drying the obtained solid-liquid mixture; wherein a and b represent the mole fraction of Zr and W respectively, and the mole ratio of Mn, Zr and W is 1:a:b, a and b are 1-10%.

[0010] The preparation method of the manganese-based composite zirconium-tungsten oxide denitration catalyst comprises the following steps:

[0011] 1) mixing soluble manganese salt and ammonium persulfate, dissolving in a solvent, stirring until transparent, adding soluble zirconium salt and soluble tungsten salt, stirring and dissolving, transferring into a reaction kettle, hydrothermal reaction at 80-120 DEG C for 5-50 h, taking out and cooling to room temperature, filtering, washing and drying the obtained solid-liquid mixture to obtain a solid precursor;

[0012] 2) calcining the solid precursor obtained in step 1) at 300-500 DEG C to obtain a manganese-based composite zirconium-tungsten oxide denitration catalyst.

[0013] To further achieve the purpose of the present application, preferably, the soluble manganese salt is one or more of manganese sulfate monohydrate, manganese acetate tetrahydrate, manganese nitrate tetrahydrate, manganese chloride tetrahydrate and potassium permanganate;

[0014] The soluble zirconium salt is one or more of zirconyl chloride, zirconyl nitrate and zirconium nitrate pentahydrate;

[0015] The soluble tungsten salt is ammonium metatungstate and / or ammonium tungstate.

[0016] Preferably, the mole ratio of the soluble manganese salt to the soluble zirconium salt is 1:0.01-0.1; the mole ratio of the soluble manganese salt to ammonium persulfate is 1:1-10; the mole ratio of the soluble manganese salt to the soluble tungsten salt is 1:0.0008-0.008;

[0017] The solvent is deionized water or a citric acid solution; the mass ratio of the solvent to the soluble manganese salt is 1:0.03-0.06.

[0018] Preferably, the drying is carried out in a 60-120℃ blast drying oven or vacuum drying oven for 4-30h.

[0019] Preferably, the calcination is carried out for 1-10h.

[0020] Application of the manganese-based composite zirconium-tungsten oxide De-NOx catalyst in flue gas De-NOx.

[0021] Preferably, the method comprises the following steps:

[0022] 1) tablet granulation of the manganese-based composite zirconium-tungsten oxide De-NOx catalyst;

[0023] 2) the granulated catalyst obtained in step 1) is fixed in a fixed bed reactor by quartz wool, the fixed bed reactor mainly comprises a quartz tube reactor, a reaction furnace and a gas circuit; the catalyst is fixed in the quartz tube by quartz wool, and the quartz tube is placed in the reaction furnace, the reaction temperature is controlled by controlling the temperature of the reaction furnace, and the flue gas is combined according to the set flow rate and discharged through the quartz tube, the flue gas flow rate for each 0.5g of catalyst is 600-1400mL / min;

[0024] 3) the reaction temperature is controlled by a programmed temperature reaction furnace at 60-320℃.

[0025] Preferably, the catalyst granulation mesh number in step 1) is 40-80 mesh;

[0026] In step 2), the composition of the flue gas is: the concentration ratio of NO to NH3 is 1:1-1.5, the O2 concentration is 2.8-4.5%, and N2 is the balance gas.

[0027] Preferably, in step 3), the reaction temperature is programmed to increase from 60℃ to 320℃ at a rate of 1-10℃ / min; the holding time for each data collection temperature section is 15-20min.

[0028] Compared with the prior art, the technical scheme of the present application has the following advantages:

[0029] 1) Compared with the single-component Mn-based metal oxide catalyst, the present application effectively improves the low-temperature catalytic conversion capacity of the catalyst and widens the working temperature window by utilizing the synergistic effect between Zr, W and Mn, and the test results show that the catalyst has excellent NO x conversion capacity at low temperature. Under the condition of excessive oxygen content, high space velocity of 120000mL of flue gas per hour per unit mass (g) of catalyst, and in the temperature range of 120-320℃, the NO x conversion rate of the catalyst can be maintained above 90%, and the activity curve tends to be flat in the entire temperature range without sudden drop.

[0030] 2) The catalyst of the present invention has strong stability. After being used for more than 12 hours and after being recycled three times, its activity does not decrease significantly, which is significantly better than some existing catalysts.

[0031] 3) The catalyst used in this invention employs an in-situ doping method during preparation to regulate the formation state of Zr and W elements on the MnO2 surface. The better doping ratio synergistically regulates the balance between the catalyst's oxidation capacity and acidity, and the catalyst possesses excellent NH3-SCR performance.

[0032] 4) Compared to the operating temperature of commercial catalysts, which is at least above 400°C, the NO content of the catalyst in this invention is lower in the temperature range of 120-320°C. x The conversion rate can be maintained above 90%, with a lower operating temperature range and a wider temperature window, resulting in better low-temperature denitrification efficiency. It is suitable for applications with low processing temperatures, such as steel plants and cement plants, eliminating the need for secondary heating of waste gas and reducing energy consumption. Attached Figure Description

[0033] Figure 1 The catalysts Zr1W1-MnO2 and Zr in Comparative Example 1 and Examples 1-4 of this invention are Zr1W1-MnO2 and Zr 2.5 W 2.5 -MnO2, Zr5W5-MnO2, Zr 10 W 10 NO of MnO2 x Conversion rate;

[0034] Figure 2 The catalysts Zr1W1-MnO2 and Zr in Comparative Example 1 and Examples 1-4 of this invention are Zr1W1-MnO2 and Zr 2.5 W 2.5 -MnO2, Zr5W5-MnO2, Zr 10 W 10 XRD pattern of MnO2;

[0035] Figure 3 The catalysts Zr1W1-MnO2 and Zr in Comparative Example 1 and Examples 1-4 of this invention are Zr1W1-MnO2 and Zr 2.5 W 2.5 -MnO2, Zr5W5-MnO2, Zr 10 W 10 -N2 physical adsorption-desorption isotherm of MnO2.

[0036] Figure 4 The catalysts Zr1W1-MnO2 and Zr in Comparative Example 1 and Examples 1-4 of this invention are Zr1W1-MnO2 and Zr 2.5 W 2.5 -MnO2, Zr5W5-MnO2, Zr 10W 10 Pore ​​size distribution diagram of MnO2. Detailed Implementation

[0037] To better understand the present invention, the invention will be further described below with reference to the accompanying drawings and embodiments, but the implementation of the present invention is not limited thereto.

[0038] Mn-based catalysts are representative low-temperature SCR catalysts, with Mn as their active center being inexpensive and widely available. However, single Mn-based catalysts have many limitations, making it difficult to achieve efficient low-temperature catalytic conversion of NO. x Therefore, this invention uses MnO2 as a carrier and addresses the problems of narrow operating temperature window and poor stability of current low-temperature catalysts by in-situ doping with transition metal elements with significantly different oxidizing properties and by changing the preparation conditions to directionally regulate the crystal form and phase of the active phase of the catalyst.

[0039] Comparative Example 1: The preparation of MnO2 metal oxide denitration catalyst is shown in the following steps:

[0040] Preparation of MnO2: Weigh 6.32 g of manganese sulfate monohydrate (MnSO4·H2O) and 8.578 g of ammonium persulfate ((NH4)2S2O8), add 200 mL of water, stir and dissolve, and transfer to a 200 mL hydrothermal reactor. React at 90 °C for 24 h to obtain a solid-liquid mixture. After cooling to room temperature, filter and wash, dry in a 60 °C forced-air drying oven, grind the obtained precursor into powder, transfer to a crucible, place it in a muffle furnace, raise the temperature to 320 °C at a heating rate of 2 °C / min, and hold at the temperature for 4 h to obtain a MnO2 metal oxide solid denitration catalyst.

[0041] The obtained catalyst was granulated and pressed into tablets. After granulation to a mesh size of 40-60, the catalyst was loaded into a fixed-bed reactor. The catalyst activity was evaluated using a fixed-bed reactor. The fixed-bed reactor mainly consisted of a quartz tube reactor, a reactor, and gas paths. The reactor temperature was controlled by a programmed temperature rise, with a K-type thermocouple detecting and providing temperature feedback. An 8mm quartz tube served as the reaction channel, and quartz wool was used as the fixed bed. The catalyst was fixed within the quartz tube using quartz wool, and the quartz tube was then placed in the reactor. The reaction temperature was controlled by adjusting the reactor temperature. Each gas path was regulated by a pressure reducing valve and a flow meter to form a mixed gas at a set flow rate. This mixed gas was then introduced into the quartz tube, where it underwent catalytic denitrification by the catalyst before being discharged. The inlet and outlet gas concentrations were measured using a German ecom EN2-F flue gas analyzer. The catalyst dosage was 0.5g, and the total gas flow rate was set to 800mL / min. The reaction temperature was controlled at 60-320℃ using a programmed heating reactor, with a heating rate of 2℃ / min. The flow rates of each gas in the outlet flue gas at each temperature point were collected, and the nitrogen oxide conversion rate at the corresponding temperature point was calculated.

[0042] Example 1: The preparation steps of the Zr1W1-MnO2 composite metal oxide denitration catalyst are as follows:

[0043] Preparation of Zr1W1-MnO2: Weigh 7.4 g of manganese chloride tetrahydrate (MnCl2·4H2O) and 12.867 g of ammonium persulfate ((NH4)2S2O8), add 200 mL of water, stir and dissolve, then add 0.1634 g of zirconium nitrate pentahydrate (Zr(NO3)2·5H2O) and 0.094 g of ammonium metatungstate ((NH4)6H2W1-MnO2). 12 O 40 (xH₂O, where x is the amount of water of crystallization) was stirred and dissolved. The solution was transferred to a 200mL hydrothermal reactor and reacted at 90℃ for 24h to obtain a solid-liquid mixture. After cooling to room temperature, the mixture was filtered, washed, and dried in a 60℃ forced-air drying oven. The obtained precursor was then ground into a fine powder, transferred to a crucible, and placed in a muffle furnace. The temperature was increased to 320℃ at a rate of 2℃ / min and held at that temperature for 4h to obtain a Zr1W1-MnO₂ composite metal oxide denitration catalyst. The subscripts 1 and 1 represent the molar ratios of Zr, W, and Mn used, respectively.

[0044] The obtained catalyst was granulated and pressed into tablets. After granulation to a mesh size of 40-60, the catalyst was loaded into a fixed-bed reactor. The catalyst activity was evaluated using a fixed-bed reactor. The fixed-bed reactor mainly consisted of a quartz tube reactor, a reactor, and gas paths. The reactor temperature was controlled by a programmed temperature rise, with a K-type thermocouple detecting and providing temperature feedback. An 8mm quartz tube served as the reaction channel, and quartz wool was used as the fixed bed. The catalyst was fixed within the quartz tube using quartz wool, and the quartz tube was then placed in the reactor. The reaction temperature was controlled by adjusting the reactor temperature. Each gas path was regulated by a pressure reducing valve and a flow meter to form a mixed gas at a set flow rate. This mixed gas was then introduced into the quartz tube, where it underwent catalytic denitrification by the catalyst before being discharged. The inlet and outlet gas concentrations were measured using a German ecom EN2-F flue gas analyzer. The catalyst dosage was 0.5g, and the total gas flow rate was set to 1400mL / min. The reaction temperature was controlled at 60-320℃ using a programmed heating reactor, with a heating rate of 2℃ / min. The flow rates of each gas in the outlet flue gas at each temperature point were collected, and the nitrogen oxide conversion rate at the corresponding temperature point was calculated.

[0045] Example 2: Zr 2.5 W 2.5 The preparation steps of the MnO2 composite metal oxide denitration catalyst are as follows:

[0046] Zr 2.5 W 2.5Preparation of MnO2: 9.38 g of manganese nitrate tetrahydrate (Mn(NO3)2-4H2O) and 17.156 g of ammonium persulfate ((NH4)2S2O8) were weighed and added to 180 mL of a citric acid solution with stirring and dissolution, and then 0.227 g of zirconyl nitrate (ZrO(NO3)2-xH2O) and 0.2424 g of ammonium metatungstate ((NH4)6H2W 12 O 40 The solution was transferred to a 180 mL hydrothermal kettle and reacted at 110°C for 28 h to obtain a solid-liquid mixture, which was cooled to room temperature, filtered, washed, and dried in a blast drying oven at 80°C. The obtained precursor was ground into a fine powder, transferred to a crucible, and placed in a muffle furnace to be heated to 360°C at a heating rate of 2°C / min and kept at this temperature for 6 h to obtain Zr 2.5 W 2.5 MnO2 composite metal oxide type denitration catalyst. The subscripts 2.5 and 2.5 represent the mole fractions of Zr and W used, respectively.

[0047] The obtained catalyst was tabletted and granulated, and 40-60 mesh granulated catalyst was loaded into a fixed bed reactor. The activity of the catalyst was evaluated by a fixed bed reaction device. The fixed bed reactor mainly consisted of a quartz tube reactor, a reaction furnace, and a gas circuit. The temperature of the reaction furnace was controlled by a programmed temperature rise, and a K-type thermocouple was used to detect and feedback the temperature signal. An 8 mm quartz tube was used as the reaction channel, and quartz wool was used as the fixed bed layer. The catalyst was placed in the quartz tube through the quartz wool and then placed in the reaction furnace. The reaction temperature was controlled by controlling the temperature of the reaction furnace. The gases were adjusted to a set flow rate by a pressure reducing valve and a flow meter after being mixed, and then introduced into the quartz tube. The mixed gas was catalytically denitrified by the catalyst and then discharged. The concentrations of the inlet and outlet gases were detected by a German ecom EN2-F type flue gas analyzer. The amount of catalyst used was 0.5 g, and the total gas flow rate was set to 1000 mL / min. The reaction temperature was controlled by a programmed temperature rise reaction furnace at 60-320°C, and the heating rate was controlled at 4°C / min. The flow rates of each gas in the outlet flue gas at each temperature point were collected, and the nitrogen oxide conversion rate at the corresponding temperature point was calculated.

[0048] Example 3: The preparation steps of the Zr5W5-MnO2 composite metal oxide type denitration catalyst are as follows:

[0049] Preparation of Zr5W5-MnO2: 9.16 g of manganese acetate tetrahydrate (MnC4H6O4-4H2O) and 21.445 g of ammonium persulfate ((NH4)2S2O8) were weighed and added to 160 mL of water with stirring and dissolution, and then 0.37 g of zirconyl chloride (ZrOCl2-nH2O) and 0.5117 g of ammonium metatungstate ((NH4)6H2W 12 O40 • xH2O) stirring, dissolving, transferring the solution to a 160 mL hydrothermal kettle to react at 130 °C for 32 h to obtain a solid-liquid mixture, after cooling to room temperature, filtering, washing, drying in a blast drying oven at 100 °C, then grinding the obtained precursor into fine powder, transferring to a crucible, placing it in a muffle furnace to rise to 400 °C at a heating rate of 2 °C / min, and keeping constant temperature for 8 h to obtain Zr5W5-MnO2 composite metal oxide type denitration catalyst. Wherein the subscripts 5, 5 respectively represent the mole fraction of Zr and W used.

[0050] The obtained catalyst was pressed into granules, and the 40-60 mesh granulated catalyst was loaded into a fixed bed reactor to evaluate the catalyst activity by a fixed bed reaction device. The fixed bed reactor mainly consisted of a quartz tube reactor, a reaction furnace and a gas circuit. The temperature of the reaction furnace was controlled by programmed temperature, and the temperature signal was detected and fed back by a K-type thermocouple. The reaction channel was an 8 mm quartz tube, and the fixed bed layer was quartz wool. The catalyst was placed in the quartz tube through the quartz wool, and then the quartz tube was placed in the reaction furnace. The reaction temperature was controlled by controlling the temperature of the reaction furnace. After adjusting the flow rate of each gas by pressure reducing valve and flow meter, the mixed gas was introduced into the quartz tube. After the mixed gas was catalytically denitrated by the catalyst, it was discharged. The concentration of the inlet and outlet gas was detected by a German ecom EN2-F type flue gas analyzer. The amount of catalyst used was 0.5 g, and the total gas flow rate was set to 600 mL / min. The reaction temperature was controlled by a programmed temperature reaction furnace at 60-320 °C, and the heating rate was controlled at 6 °C / min. The flow rate of each gas in the outlet flue gas at each temperature point was collected, and the nitrogen oxide conversion rate at the corresponding temperature point was calculated.

[0051] Example 4: Zr 10 W 10 The preparation steps of Zr5W5-MnO2 composite metal oxide type denitration catalyst are as follows:

[0052] Zr 10 W 10 Preparation of Zr5W5-MnO2: 5.91 g of potassium permanganate (KMnO4) and 8.578 g of ammonium persulfate ((NH4)2S2O8) were weighed, stirred and dissolved in 140 mL of citric acid solution, and then 2.01 g of zirconium nitrate pentahydrate (Zr(NO3)2·5H2O) and 1.15 g of ammonium tungstate ((NH4)2W2O7) were added. The solution was stirred and dissolved, and then transferred to a 140 mL hydrothermal kettle to react at 150 °C for 36 h to obtain a solid-liquid mixture. After cooling to room temperature, the mixture was filtered, washed, and dried in a blast drying oven at 120 °C. The obtained precursor was ground into fine powder, transferred to a crucible, and placed in a muffle furnace to rise to 440 °C at a heating rate of 2 °C / min, and kept constant temperature for 10 h to obtain Zr5W5-MnO2 composite metal oxide type denitration catalyst. 10 H2(W2O7)6) stirring, dissolving, transferring the solution to a 160 mL hydrothermal kettle to react at 130 °C for 32 h to obtain a solid-liquid mixture, after cooling to room temperature, filtering, washing, drying in a blast drying oven at 100 °C, then grinding the obtained precursor into fine powder, transferring to a crucible, placing it in a muffle furnace to rise to 400 °C at a heating rate of 2 °C / min, and keeping constant temperature for 8 h to obtain Zr5W5-MnO2 composite metal oxide type denitration catalyst. Wherein the subscripts 5, 5 respectively represent the mole fraction of Zr and W used. 10W 10 -MnO2 composite metal oxide type denitration catalyst. The subscripts 10 and 10 represent the mole fractions of Zr and W used, respectively.

[0053] The obtained catalyst was granulated and pressed into tablets. After granulation to a mesh size of 40-60, the catalyst was loaded into a fixed-bed reactor. The catalyst activity was evaluated using a fixed-bed reactor. The fixed-bed reactor mainly consisted of a quartz tube reactor, a reactor, and gas paths. The reactor temperature was controlled by a programmed temperature rise, with a K-type thermocouple detecting and providing temperature feedback. An 8mm quartz tube served as the reaction channel, and quartz wool was used as the fixed bed. The catalyst was fixed within the quartz tube using quartz wool, and the quartz tube was then placed in the reactor. The reaction temperature was controlled by adjusting the reactor temperature. Each gas path was regulated by a pressure reducing valve and a flow meter to form a mixed gas at a set flow rate. This mixed gas was then introduced into the quartz tube, where it underwent catalytic denitrification by the catalyst before being discharged. The inlet and outlet gas concentrations were measured using a German ecom EN2-F flue gas analyzer. The catalyst dosage was 0.5g, and the total gas flow rate was set to 1200mL / min. The reaction temperature was controlled at 60-320℃ using a programmed heating reactor, with a heating rate of 8℃ / min. The flow rates of each gas in the outlet flue gas at each temperature point were collected, and the nitrogen oxide conversion rate at the corresponding temperature point was calculated.

[0054] The activity of the catalyst is determined using NO x The conversion rate is used for evaluation. By calculating the changes in the concentration components of each gas in the inlet and outlet flue gas at each test temperature point, the change in nitrogen oxide gas concentration after passing through the catalyst is calculated, and a temperature-concentration curve is plotted. The specific calculation formula is: NO x Conversion rate = ([NO x ] in -[NO x ] out ) / [NO x ] in , of which [NO x ] in NO x ] out These represent the NO values ​​at the inlet of the fixed-bed reactor. x Concentration and outlet NO x The concentration of NO at the reactor outlet was recorded after the denitrification reaction had stabilized. x The concentration is read directly from the flue gas analyzer. Figure 1 NO for the catalysts with different Zr and W contents prepared in Examples 1-5 x Conversion rate graph. It can be seen that MnO2 exhibits better low-temperature catalytic performance, achieving a conversion rate of 90% at 150℃; however, NO... xThe working temperature window with conversion rate higher than 90% is only 50℃. However, the effective working temperature window of the catalyst is obviously widened after introducing Zr and W elements. Especially Zr 2.5 W 2.5 The NO x conversion rate of MnO2 catalyst in the temperature range of 120℃-320℃ is kept above 90%. The NO x conversion rate of MnO2 catalyst in the temperature range of 120℃-320℃ is kept above 90%. The NO 2.5 conversion rate of MnO2 catalyst in the temperature range of 120℃-320℃ is kept above 90%. The NO 2.5 The overall catalytic activity of MnO2 and Zr5W5-MnO2 is better, and the temperature window with conversion rate higher than 90% of W-90(NO x conversion rate) reaches 200℃. The Zr1W1-MnO2 and Zr 10 W 10 The catalytic activity of the highest temperature test point of MnO2 is slightly inferior, but its test space velocity is higher, reaching 210,000h -1 and 180,000h -1 , and the overall nitrogen oxide conversion rate in the target temperature range (120-320℃) can still be kept at about 90%. In summary, the synergistic effect between Zr and W promotes the catalytic reduction performance of low-temperature NO x , significantly widens the working temperature window of the catalyst, and the overall catalytic effect remains good after changing the space velocity of the introduced atmosphere.

[0055] Figure 2 The XRD patterns of the catalysts with different Zr and W contents prepared in Examples 1-5 can be found that the MnO xThe characteristic peaks at 22.4°(1 2 0), 34.5°(0 3 1), 37.1°(1 3 1), 38.8°(2 3 0), 42.6°(3 0 0), 56.1°(1 6 0), 57.4°, 65.6°(4 2 1), 68.9°(0 0 3) are consistent with the characteristic diffraction peaks of the standard card of γ-MnO2(JCPDS NO.14-0644). When the total amount of Zr and W is 2 mol%, the two diffraction peaks at 2θ of 22.4°(1 2 0) and 34.5°(0 3 1) cannot be observed on the spectrum; when the total amount of Zr and W continues to increase, the characteristic peak at 2θ of 65.6°(4 2 1) also disappears, and the diffraction peak intensity at 2θ of 37.1°(1 3 1), 38.8°(2 3 0) and 42.6°(3 0 0) decreases compared with MnO2, indicating that the mixed oxide particles with weaker crystallinity are obtained by doping Zr and W. In addition, when the total amount of Zr and W reaches 5 mol%, new characteristic peaks at 2θ of 24.1°(1 1 0) and 30.4°(1 1 1) can be observed. The former corresponds to MnWO4(JCPDS NO.72-0478), and the latter corresponds to Mn 0.2 Zr 0.8 O 1.8 (JCPDS NO.77-2157). It indicates that a new composite metal oxide crystal phase appears in the catalyst. The evolution of XRD spectrum diffraction peaks and grain size before and after Zr and W doping is listed in Table 1, wherein the average grain size (D) is calculated based on the (1 6 0) and (1 3 1) diffraction crystal faces according to the Scherrer formula. The results show that the FWHM of the catalyst diffraction peak gradually increases with the increase of the amount of Zr and W doping, and the average grain size corresponding thereto gradually decreases.

[0056] Table 1 XRD results and grain size

[0057]

[0058] Figure 3 The N2 physical adsorption-desorption isotherms of the catalysts with different Zr and W contents prepared in Examples 1-5 can be seen that the isotherms of all catalyst samples show type IV isotherms, but after the introduction of Zr and W elements, capillary condensation phenomenon occurs in a certain pressure range (0.4<P / P0<1.0), and the required pressure is smaller than that of the carrier (0.8<P / P0<1.0), which is due to the blockage of the pore by the introduction of Zr and W, thereby leading to the decrease of the catalyst pore size.

[0059] Figure 4The diagram shows the pore size distribution of catalysts with different Zr and W contents prepared in Examples 1-5. It can be seen that the pores of the support MnO2 mainly consist of mesopores with a small number of macropores, while the main pores of the modified catalysts are mesopores with a small number of micropores. This indicates that the entry of Zr and W particles into the pores has changed the pore size structure.

[0060] Table 2 shows the Brunauer-Emmett-Teller (BET) specific surface area, pore volume, and pore size test results for the catalysts in Examples 1-5. It can be seen that the specific surface area of ​​the catalyst first decreases and then increases with the introduction of Zr and W. This is because the specific surface area decreases when the introduced Zr and W particles fill the pore structure. As the element doping concentration increases, combined with XRD results, it is speculated that Zr, W, and MnO2 form a solid solution, and the specific surface area gradually increases. Similarly, the total pore volume initially decreases due to pore blockage, until the newly formed pores compensate for this deficiency (i.e., when the total element doping ratio reaches 5 mol%), at which point the total pore volume begins to increase, while the pore size continues to decrease.

[0061] Compared to the modified denitrification catalyst with manganese and cerium supported on modified biochar in Chinese invention patent application 202410636962.X, which only maintains a conversion rate of over 90% within an operating temperature window of 140-220℃, the ZrW-MnO2 composite metal oxide complex denitrification catalyst used in this invention selects Zr and W elements as active components. By enhancing the reducing power of manganese metal oxide at low temperatures and its acidity at high temperatures, its operating temperature range is increased in both directions, giving it a wider low-temperature catalytic operating temperature window covering 120-320℃. It can be applied to various application scenarios with different operating temperature ranges without the need to replace the catalyst.

[0062] Compared to Chinese invention patent application 202210504112.5, which utilizes an inorganic acid-acidified manganese-cerium-silicon composite metal oxide catalyst at 500 ppm NO, 500 ppm NH3, and 50,000 h⁻¹, this invention... -1 Efficient conversion of NO under air velocity conditions x The catalyst of this invention, at a W90 temperature range of 150°C (the temperature range in which 90% conversion is achieved), increases the number of acidic sites for NH3 adsorption and alters the properties of NO adsorption sites at high temperatures, enabling the catalyst to operate at higher space velocities (150,000 h⁻¹). -1 (and larger NO) x This invention achieves higher catalytic conversion capacity at a NO concentration of 1000 ppm, and maintains high conversion efficiency even at higher temperatures after reaching optimal catalytic efficiency. As a result, the catalyst of this invention can be applied to treatment environments with higher concentrations of flue gas and to a wider range of applications, reducing the cost of flue gas treatment.

[0063] Table 2 Physical structural properties of catalysts

[0064]

[0065] Compared with the denitration catalyst with high-entropy oxides as the active component in Chinese invention patent CN114308053B, the selection of the active component of the catalyst of the present application is mainly based on oxidation. On the one hand, the formation of Zr and Mn clusters enhances the reducibility of the catalyst itself and improves its low-temperature catalytic performance. Therefore, the catalyst of the present application can be applied to a lower temperature treatment environment. On the other hand, in view of the strong oxidizing property of the active substrate MnO2, in order to increase the high-temperature catalytic conversion efficiency, two metal elements Zr and W with weaker oxidizing property are selected to weaken the excessive oxidation of NH3 by the catalyst and change the adsorption state of NH3 and NO by the catalyst at high temperature. Within the range of 150°C after reaching the highest conversion rate (100%), the activity only decreases by less than 10%. Finally, the decline trend of the activity of the catalyst at higher temperature is suppressed, and the overall activity curve tends to be flat, which is less affected by temperature. When encountering exhaust gas with higher temperature, the catalyst still has good treatment effect and will not be affected by the temperature fluctuation of the exhaust gas to affect the treatment efficiency of the catalyst.

[0066] It should be noted that the embodiments of the present application are not limited by the above examples, and any changes, modifications, substitutions, combinations and simplifications made without departing from the spirit and principles of the present application shall be equivalent replacement methods and shall be within the scope of protection of the present application.

Claims

1. A manganese-based composite zirconium-tungsten oxide denitration catalyst, characterized in that, By Zr a W b - The MnO2 precursor is obtained by heat treatment at 300-500℃ in air atmosphere; the Zr a W b The MnO2 precursor is prepared by dissolving soluble manganese salt and ammonium persulfate in a solvent, mixing them, stirring until transparent, then adding soluble zirconium salt and soluble tungsten salt, stirring until dissolved, transferring to a reaction vessel, and hydrothermally reacting at 80-120℃ for 5-50 hours. After removal and cooling to room temperature, the resulting solid-liquid mixture is filtered, washed, and dried. Here, a and b represent the molar fractions of Zr and W used, respectively, and the molar ratio of Mn, Zr, and W is 1:a:b, where a and b are 1%-10%.

2. The preparation method of the manganese-based composite zirconium tungsten oxide denitration catalyst according to claim 1, characterized in that... Includes the following steps: 1) Mix soluble manganese salt and ammonium persulfate, add solvent to dissolve, stir until transparent, then add soluble zirconium salt and soluble tungsten salt, stir to dissolve, transfer to a reaction vessel, and hydrothermally react at 80-120℃ for 5-50 hours. After removal, cool to room temperature, filter, wash and dry the obtained solid-liquid mixture to obtain a solid precursor. 2) The solid precursor obtained in step 1) is calcined at 300-500℃ to obtain a manganese-based composite zirconium tungsten oxide denitration catalyst.

3. The preparation method of the manganese-based composite zirconium-tungsten oxide denitration catalyst according to claim 2, characterized in that, The soluble manganese salt is one or more of manganese sulfate monohydrate, manganese acetate tetrahydrate, manganese nitrate tetrahydrate, manganese chloride tetrahydrate, and potassium permanganate. The soluble zirconium salt is one or more of zirconium oxychloride, zirconium oxynitrate, and zirconium nitrate pentahydrate; The soluble tungsten salts are ammonium metatungstate and / or ammonium tungstate.

4. The preparation method of the manganese-based composite zirconium-tungsten oxide denitration catalyst according to claim 3, characterized in that, The molar ratio of the soluble manganese salt to the soluble zirconium salt is 1:0.01-0.1; the molar ratio of the soluble manganese salt to ammonium persulfate is 1:1-10; and the molar ratio of the soluble manganese salt to the soluble tungsten salt is 1:0.0008-0.

008. The solvent is deionized water or citric acid solution; the mass ratio of the solvent to the soluble manganese salt is 1:0.03-0.

06.

5. The preparation method of the manganese-based composite zirconium-tungsten oxide denitration catalyst according to claim 2, characterized in that, The drying process involves drying in a forced-air drying oven or vacuum drying oven at 60-120℃ for 4-30 hours.

6. The preparation method of the manganese-based composite zirconium-tungsten oxide denitration catalyst according to claim 2, characterized in that, The roasting time is 1-10 hours.

7. The application of the manganese-based composite zirconium tungsten oxide denitrification catalyst according to claim 1 in flue gas denitrification.

8. The application of the manganese-based composite zirconium tungsten oxide denitrification catalyst according to claim 7 in flue gas denitrification, characterized in that... Includes the following steps: 1) The manganese-based composite zirconium tungsten oxide denitration catalyst is compressed into tablets and granulated; 2) The granulated catalyst obtained in step 1) is fixed in a fixed-bed reactor using quartz wool. The fixed-bed reactor mainly consists of a quartz tube reactor, a reactor, and a gas path. The catalyst is fixed in a quartz tube using quartz wool, and then the quartz tube is placed in the reactor. The reaction temperature is controlled by controlling the reactor temperature. The flue gas is collected at a set flow rate and discharged through the quartz tube. The flow rate of the flue gas for every 0.5g of catalyst is 600-1400mL / min. 3) The reaction temperature is controlled at 60-320℃ by a programmed heating reactor.

9. The application of the manganese-based composite zirconium-tungsten oxide denitrification catalyst according to claim 8 in flue gas denitrification, characterized in that, The catalyst granulation mesh size in step 1) is 40-80 mesh; the composition of the flue gas in step 2) is: the concentration ratio of NO to NH3 is 1:1-1.5, the O2 concentration is 2.8-4.5%, and N2 is the balance gas.

10. The application of the manganese-based composite zirconium-tungsten oxide denitrification catalyst according to claim 8 in flue gas denitrification, characterized in that, Step 3) The reaction temperature is increased from 60℃ to 320℃ at a rate of 1-10℃ / min.

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