A highly water-resistant Ce-Mn bimetallic oxide and its preparation method and application

Abstract

The present invention discloses a Ce-Mn bimetallic oxide modified by high anti-water acetic acid etching, and its preparation method and application. First, manganese nitrate tetrahydrate and cerium nitrate hexahydrate are used as raw materials to prepare a CeMnOx bimetallic composite oxide through a hydrothermal method and high-temperature calcination, and then a CeMnOx-CH3COOH high anti-water low-temperature denitration catalyst is obtained through acetic acid etching modification (a composite modification method of "metal Ce doping" and "weak acid CH3COOH etching"). After the surface of the Ce-Mn bimetallic catalyst provided by the present invention is etched and preferentially dissolved by acetic acid, it has a rich internal pore structure and a high specific surface area, which is more conducive to the adsorption of NH3; it reaches a high denitration rate at low temperature, and the NOx removal rate can reach nearly 100% at only 80 °C; it reaches a stable high anti-water performance of nearly 100% at 200 °C, and has application prospects in the fields of environmental catalytic materials and air pollution control.

Description

Technical Field

[0001] The present invention relates to a low-temperature denitration catalyst and a preparation method thereof, and specifically relates to a preparation method and acid etching modification method of a highly water-resistant Ce-Mn bimetallic oxide and an application thereof; the catalyst can be used for denitration by catalytic reduction (NH3-SCR) with ammonia as a reducing agent at a low temperature (<240°C) of flue gas, and the nitrogen oxide (NOx) removal rate is close to 100% at 80-240°C, and the catalyst has ultra-high water resistance, and belongs to the field of environmental catalytic materials and air pollution control. Background Art

[0002] The harmful properties of nitrogen oxides (NOx) have become a serious environmental issue of great public concern. They are mainly emitted by fixed sources (such as coal-fired power plants) and mobile sources (such as motor vehicles). These emissions can cause acid rain, photochemical smog and other problems, which can harm human health. Among the currently available technologies, NH3 selective catalytic reduction of NOx (NH3-SCR) has been proven to be an effective, reliable and economical method to control NOx emissions. However, the traditional V2O5-WO3(MoO3) / TiO2 catalyst is usually placed upstream of the electrostatic precipitator and desulfurization device, and has the disadvantages of a high and narrow operating temperature window (300-420℃); if it is placed downstream of the electrostatic precipitator and desulfurization device, the flue gas temperature is generally lower than 250℃, and some water adheres to the catalyst surface in liquid form at low temperature, causing catalyst deactivation. Therefore, how to improve the low-temperature high denitrification rate and high water resistance of the catalyst is a hot topic of current research.

[0003] MnOx-based catalysts have excellent catalytic activity for NH3-SCR reaction at low temperature, which has the advantages of being eco-friendly, abundant in earth resources and inexpensive. However, pure MnOx catalysts also have some challenges to overcome, including low specific surface area, narrow operating temperature window, poor thermal stability and poor resistance to H2O. CeO2 has good redox properties and can react with oxygen vacancies and Ce in the material. 4+ / Ce 3+ Redox pairs are widely used for NOx removal due to their high oxygen storage / release capacity, which can promote NOx adsorption, provide stronger acid sites, enhance NO to NO2 oxidation, and improve the water resistance of the catalyst, which is particularly beneficial for NH3-SCR reaction. Therefore, the combination of manganese oxide (MnOx) and CeO2 to form Ce-Mn bimetallic catalysts may improve the denitrification activity and water resistance of materials for NH3-SCR of NOx.

[0004] In addition, acetic acid etching modification of the catalyst can significantly improve its denitrification activity and water resistance. According to relevant studies, in the SCR reaction, the activity of the catalyst is affected by the amount of NH3 adsorbed. The MnOx-based catalyst mainly has Lewis and Bronsted acid sites, and the Bronsted acid site has little effect on the SCR reaction because the strength of the Bronsted acid site is greatly reduced or even disappears after loading MnOx, while NH3 adsorbed on the Lewis weak acid site of Mn ions or MnOx can effectively participate in the low-temperature SCR reaction. Since acetic acid is a weak acid, in the process of etching the Ce-Mn bimetallic acid, the Lewis weak acid sites on the surface of the catalyst carrier are effectively increased, and the elements on the catalyst surface are dissolved, the internal pore structure and specific surface area are increased, thereby promoting the improvement of its catalytic reduction ability, which is more conducive to the adsorption of NH3, and then the denitrification activity and water resistance of the catalyst are significantly improved.

[0005] Due to the tail end arrangement, the MnOx-based catalyst is easily covered by part of the water vapor and deactivated when exposed to the low temperature environment. Therefore, the removal efficiency of NOx using only a single technology is low and the water resistance is poor. Therefore, the present invention aims to study and develop a highly water-resistant and low-temperature denitrification catalyst prepared by the "dual-site (oxidation-reduction and acid-base site) regulation" coupling technology. Summary of the invention

[0006] The purpose of the present invention is to provide a MnOx-based high water-resistant low-temperature denitration catalyst prepared by a composite modification method of "metal Ce doping" and "weak acid CH3COOH etching" to address the defects existing in the aforementioned prior art. Among them, "metal Ce doping" can effectively increase defects such as oxygen vacancies, improve redox capacity, increase low-temperature denitration rate and resistance to H2O poisoning by introducing Ce to form a Mn-Ce solid solution structure; while "weak acid CH3COOH etching" effectively increases the specific surface area while increasing Lewis weak acid sites, significantly improving water resistance and catalytic activity.

[0007] The specific steps of the present invention are as follows:

[0008] In a first aspect, the present invention provides a Ce-Mn bimetallic oxide with high resistance to aqueous acetic acid etching, which is obtained by adding a solution containing manganese ions and cerium ions into an alkaline solution and heating the solution to obtain a solid phase product, and then sequentially subjecting the solid phase product to a first calcination, acid etching and a second calcination.

[0009] Preferably, in the mixed solution obtained by adding the solution containing manganese ions and cerium ions to the alkaline solution, the manganese ion concentration is 0.2-0.8 mol / L, the cerium ion concentration is 0.2-0.8 mol / L, and the hydroxide ion concentration is 1.0-2.0 mol / L. The heating reaction temperature is 120-150° C. and the duration is 24-48 hours.

[0010] As a preferred embodiment, the acid etching process is as follows: adding a hydrogen ion molar concentration of 0.6 to 2.4 mol·L -1 Etch in CH3COOH solution for 0.2 to 0.6h.

[0011] Preferably, the calcination temperature of the first calcination is 300-500°C, and the calcination time is 3-5 hours. The calcination temperature of the second calcination is 300-500°C, and the calcination time is 3-5 hours.

[0012] In a second aspect, the present invention provides a method for preparing the aforementioned Ce-Mn bimetallic oxide with high resistance to aqueous acetic acid etching, which comprises the following steps:

[0013] 1. Use hydrothermal method to obtain Ce-Mn bimetallic oxide:

[0014] Step (1) Prepare a NaOH solution as reaction solution A.

[0015] Step (2) dissolving the manganese salt and the cerium salt in deionized water and stirring the mixture sufficiently to obtain a solution B.

[0016] Step (3) Add the reaction solution A dropwise into the solution B and stir thoroughly to obtain a suspension C.

[0017] Step (4) The suspension C is transferred to a high-pressure reactor and heated for 24 to 48 hours, and then filtered to obtain a precipitate D.

[0018] Step (5) The precipitate D is washed alternately with deionized water and anhydrous ethanol for several times to remove the Na+ ions therein until the pH of the solution remains unchanged, thereby obtaining a precipitate E.

[0019] Step (6) Dry the precipitate E and then calcine it in air to obtain a modified Ce-Mn bimetallic oxide F.

[0020] 2. Use acetic acid to etch and modify Ce-Mn bimetallic oxide F:

[0021] Step (7) Prepare a CH3COOH solution as etching solution G.

[0022] Step (8) Immerse the modified Ce-Mn bimetallic oxide F in an etching solution G for etching to obtain a precipitate H.

[0023] Step (9) Filter and dry the precipitate H, and then calcine it in air to obtain a highly water-resistant Ce-Mn bimetallic oxide.

[0024] Preferably, the manganese salt is prepared by Mn(NO3)2·4H2O powder, and the cerium salt is prepared by Ce(NO3)3·6H2O powder.

[0025] Preferably, in step (2), the stirring time of solution B is controlled within 1 to 2 hours. In step (3), the stirring time of suspension C is controlled within 3 to 6 hours.

[0026] Preferably, in step (6), the drying temperature is 60-80°C, and the drying time is controlled within 6-12 hours. In step (9), the drying temperature is 60-80°C, and the drying time is controlled within 3-6 hours. The calcination temperature is 300-500°C, and the calcination time is controlled within 3-5 hours.

[0027] In a third aspect, the present invention provides a Ce-Mn bimetallic oxide modified with high resistance to aqueous acetic acid etching and used as a catalyst in SCR denitrification.

[0028] Preferably, the SCR denitration is carried out at a temperature of 80-240°C.

[0029] With respect to the prior art, the beneficial effects achieved by the present invention are:

[0030] 1. After being etched and dissolved with acetic acid, the surface of the Ce-Mn bimetallic catalyst provided by the present invention has a rich internal pore structure and a high specific surface area, which is more conducive to the adsorption of NH3 and exhibits better low-temperature denitrification activity and water resistance;

[0031] 2. Compared with the prior art [for example: the invention patent (application number: 202011333961.6) has a NOx conversion rate of 100% within 150-200°C; the invention patent (application number: 202010583208.6) maintains a denitrification efficiency of more than 80% at 160-300°C, and maintains more than 80% water resistance at 180°C in the presence of water content (14 vol%)], the present invention achieves a high denitrification rate at low temperatures, and can achieve a NOx removal rate of nearly 100% at only 80°C (the temperature is nearly 70°C earlier); a stable high water resistance of nearly 100% is achieved at 200°C (and there is no downward trend), which has potential application prospects in the fields of environmental catalytic materials and air pollution control. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a graph of the NOx conversion rate of the acetic acid etched modified Ce-Mn bimetallic oxide low-temperature denitration catalyst at 50-240°C prepared in Example 1 of the present invention.

[0033] Figure 2This is a water resistance curve of the acetic acid etched modified Ce-Mn bimetallic oxide low-temperature denitration catalyst prepared in Example 1 of the present invention at 200°C and 10 vol% H2O.

[0034] Figure 3 This is a high-resolution transmission electron microscope (TEM) image of the acetic acid-etched modified Ce-Mn bimetallic oxide low-temperature denitration catalyst prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0035] The present invention will be further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0036] Example 1

[0037] The preparation method of the highly resistant to water acetic acid etching modified Ce-Mn bimetallic low-temperature SCR denitration catalyst is as follows: 2.51g Mn(NO3)2·4H2O and 4.34g Ce(NO3)3·6H2O are dissolved in 20ml deionized water and stirred for 1 hour, and then 60ml 4mol·L -1 of NaOH solution, the solution was stirred for another 3 hours to obtain a suspension, and transferred to a reactor, the mixture was heated to 120°C, and kept at this temperature for 24 hours. The resulting precipitate was then washed several times with deionized water and once with anhydrous ethanol until the pH of the solution remained unchanged. After drying in an oven at 60°C for 12 hours, the sample was finally calcined in air at 500°C for 5 hours. 1 g of the prepared Ce-Mn bimetallic oxide was weighed and immersed in 0.6 mol·L -1 The obtained precipitate was filtered and fully dried in a drying oven at 60°C for 3 h, and finally calcined in air at 500°C for 5 h.

[0038] The catalyst prepared in this example has a NOx conversion rate close to 100% within 80-240°C (e.g. Figure 1 The water resistance at 200°C and 10 vol% H2O is close to 100% (as shown in Figure 2 The TEM image of the catalyst prepared in this example is shown in FIG. Figure 3 As shown, Figure 3 CeO2 exposing a high proportion of {111} facets, Mn2O3 with {222} and {400} facets, and Mn3O4 with {112} facets were characterized.

[0039] Example 2

[0040] The preparation method of the highly resistant acetic acid etching modified Ce-Mn bimetallic low-temperature SCR denitration catalyst is as follows: 8.03g Mn(NO3)2·4H2O and 3.47g Ce(NO3)3·6H2O are dissolved in 20ml deionized water and stirred for 1.5 hours, and then 45ml 4mol·L -1 of NaOH solution, the solution was stirred for another 3 hours to obtain a suspension, and transferred to a reactor, the mixture was heated to 120°C, and kept at this temperature for 24 hours. The resulting precipitate was then washed several times with deionized water and once with anhydrous ethanol until the pH of the solution remained unchanged. After drying in an oven at 60°C for 12 hours, the sample was finally calcined in air at 500°C for 4 hours. 1 g of the prepared Ce-Mn bimetallic oxide was weighed and immersed in 0.8 mol·L -1 The obtained precipitate was filtered and fully dried in a drying oven at 60°C for 3h, and finally calcined in air at 500°C for 4h.

[0041] The catalyst has a NOx conversion rate of more than 97% within the range of 80-240° C., and a water resistance of more than 98% at 200° C. and 10 vol% H2O.

[0042] Example 3

[0043] The preparation method of the highly resistant acetic acid etching modified Ce-Mn bimetallic low-temperature SCR denitration catalyst is as follows: 7.03g Mn(NO3)2·4H2O and 5.21g Ce(NO 3)3 ·6H2O was dissolved in 20ml of deionized water and stirred for 2 hours, then 50ml of 4mol·L -1 of NaOH solution, the solution was stirred for another 3 hours to obtain a suspension, and transferred to a reactor, the mixture was heated to 130°C, and kept at this temperature for 24 hours. The resulting precipitate was then washed several times with deionized water and once with anhydrous ethanol until the pH of the solution remained unchanged. After drying in an oven at 60°C for 8 hours, the sample was finally calcined in air at 500°C for 3 hours. 1 g of the prepared Ce-Mn bimetallic oxide was weighed and immersed in 1.0 mol·L -1 The obtained precipitate was filtered and fully dried in a drying oven at 60°C for 4h, and finally calcined in air at 500°C for 3h.

[0044] The catalyst has a NOx conversion rate of more than 96% within the range of 80-240° C., and a water resistance of more than 97% at 200° C. and 10 vol% H2O.

[0045] Example 4

[0046] The preparation method of the highly resistant to acetic acid etching modified Ce-Mn bimetallic low-temperature SCR denitration catalyst is as follows: 3.01g Mn(NO3)2·4H2O and 12.15g Ce(NO3)3·6H2O are dissolved in 20ml deionized water and stirred for 2 hours, and then 50ml 4mol·L -1 of NaOH solution, the solution was stirred for another 3 hours to obtain a suspension, and transferred to a reactor, the mixture was heated to 150°C, and kept at this temperature for 24 hours. The resulting precipitate was then washed several times with deionized water and once with anhydrous ethanol until the pH of the solution remained unchanged. After drying in an oven at 60°C for 10 hours, the sample was finally calcined in air at 500°C for 3 hours. 1 g of the prepared Ce-Mn bimetallic oxide was weighed and immersed in 0.5 mol·L -1 The obtained precipitate was filtered and fully dried in a drying oven at 60°C for 4h, and finally calcined in air at 500°C for 3h.

[0047] The catalyst has a NOx conversion rate of more than 98% within the range of 80-240° C., and a water resistance of more than 99% at 200° C. and 10 vol% H2O.

[0048] Example 5

[0049] The preparation method of the highly resistant to water acetic acid etching modified Ce-Mn bimetallic low-temperature SCR denitration catalyst is as follows: 9.04g Mn(NO3)2·4H2O and 1.74g Ce(NO3)3·6H2O are dissolved in 20ml deionized water and stirred for 2 hours, and then 55ml 4mol·L -1 of NaOH solution, the solution was stirred for another 3 hours to obtain a suspension, and transferred to a reactor, the mixture was heated to 120°C, and kept at this temperature for 24 hours. The resulting precipitate was then washed several times with deionized water and once with anhydrous ethanol until the pH of the solution remained unchanged. After drying in an oven at 60°C for 12 hours, the sample was finally calcined in air at 500°C for 5 hours. 1 g of the prepared Ce-Mn bimetallic oxide was weighed and immersed in 2.0 mol·L -1 The obtained precipitate was filtered and fully dried in a drying oven at 60°C for 5h, and finally calcined in air at 500°C for 5h.

[0050] The catalyst has a NOx conversion rate of more than 96% within the range of 80-240° C., and a water resistance of more than 96% at 200° C. and 10 vol% H2O.

Claims

1. Application of a highly water-resistant Ce-Mn bimetallic oxide as a catalyst in SCR denitration at 80°C, characterized in that: The highly water-resistant Ce-Mn bimetallic oxide is obtained by adding a solution containing manganese ions and cerium ions to an alkaline solution for heating to obtain a solid phase product, and then sequentially performing a first calcination, acid etching and a second calcination on the solid phase product; in the mixed solution obtained by adding the solution containing manganese ions and cerium ions to the alkaline solution, the manganese ion concentration is 0.2-0.8 mol / L, the cerium ion concentration is 0.2-0.8 mol / L, and the hydroxide ion concentration is 1.0-2.0 mol / L; the heating reaction temperature is 120-150° C., and the duration is 24-48 hours; The acid etching process is as follows: the solid phase product is added with a hydrogen ion molar concentration of 0.6~2.4 mol∙L -1 Etch in CH3COOH solution for 0.2~0.6h; The calcination temperature of the first calcination is 300~500℃, and the calcination time is 3~5h; the calcination temperature of the second calcination is 300~500℃, and the calcination time is 3~5h.

2. The use according to claim 1, characterized in that: The preparation process of the highly water-resistant Ce-Mn bimetallic oxide comprises the following steps:

1. Use hydrothermal method to obtain Ce-Mn bimetallic oxide: Step (1) preparing a NaOH solution as a reaction solution A; Step (2) dissolving the manganese salt and the cerium salt in deionized water and stirring thoroughly to obtain a solution B; Step (3) adding the reaction solution A dropwise into the solution B and stirring thoroughly to obtain a suspension C; Step (4) transferring the suspension C to a high pressure reactor and heating it for 24 to 48 hours, and then filtering to obtain a precipitate D; Step (5) Wash the precipitate D with deionized water and anhydrous ethanol alternately several times to remove the Na + ions until the pH of the solution remains unchanged and precipitate E is obtained; Step (6) drying the precipitate E and then calcining it in air to obtain a modified Ce-Mn bimetallic oxide F; 2. Use acetic acid to etch and modify Ce-Mn bimetallic oxide F: Step (7) preparing a CH3COOH solution as an etching solution G; Step (8) immersing the modified Ce-Mn bimetallic oxide F in an etching solution G for etching to obtain a precipitate H; Step (9) Filter and dry the precipitate H, and then calcine it in air to obtain a highly water-resistant Ce-Mn bimetallic oxide.

3. The use according to claim 2, characterized in that: The manganese salt is prepared by Mn(NO3)2•4H2O powder, and the cerium salt is prepared by Ce(NO3)3•6H2O powder.

4. The use according to claim 2, characterized in that: In step (2), the stirring time of solution B is controlled within 1 to 2 hours; in step (3), the stirring time of suspension C is controlled within 3 to 6 hours.

5. The use according to claim 2, characterized in that: In step (6), the drying temperature is 60-80°C, and the drying time is controlled within 6-12 hours; in step (9), the drying temperature is 60-80°C, and the drying time is controlled within 3-6 hours; the calcination temperature is 300-500°C, and the calcination time is controlled within 3-5 hours.

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