Preparation method of manganese-cerium oxide catalyst for low-temperature NH3-SCR (Selective Catalytic Reduction) reaction

Abstract

The invention discloses a synthesis method of a novel manganese-cerium oxide catalyst, and MnCeOx catalysts with different Mn-Ce ratios are prepared and are used in a low-temperature NH3-SCR (Selective Catalytic Reduction) denitration reaction. The method comprises the following implementation steps: dissolving a certain amount of KMnO4 and Ce (NO3) 3.6 H2O in deionized water, dropwise adding a H2O2 solution with a certain concentration into a Ce-Mn solution at room temperature, and filtering, washing, drying and roasting the generated precipitate at high temperature to obtain the required MnCeOx bimetallic catalyst. Preferably, in the NH3-SCR reaction, when the air speed is 120000 h <-1 >, the NOx conversion rate within the temperature range of 100-230 DEG C reaches 90% or above by using the catalyst with the ratio of Mn to Ce being 2: 1; and compared with single metal oxide CeO2, the catalytic activity is obviously improved. The preparation method is simple, and the problems of incomplete precipitation, uneven bimetallic mixing and the like of a traditional coprecipitation method can be solved.

Description

Technical Field

[0001] The present invention relates to a new method for synthesizing a Mn-Ce bimetallic oxide suitable for NH3-SCR low-temperature catalysis, belonging to the technical field of chemical catalysts and their preparation. Background Art

[0002] Nitrogen oxides (NO x ) is one of the main air pollutants produced by the combustion of fuels from stationary and mobile sources, which can cause a series of environmental problems, such as acid rain, ozone layer depletion, photochemical smog, nitrate aerosols and greenhouse effect. So far, a variety of technologies have been developed to reduce nitrogen oxides, among which the most common technologies include selective catalytic reduction (SCR), selective non-catalytic reduction (SNCR), three-way catalysis (TWC) and nitrogen oxide storage reduction (NSR). Among them, NH3-SCR (4NO+4NH3+O2→4N2+6H2O) uses liquid ammonia or urea as the ammonia source and converts NO into CO under the action of a catalyst. x Due to its high catalytic efficiency, good selectivity and low cost, this method has been proven to be the most effective way to remove nitrogen oxides from stationary pollution sources such as power plants, industrial boilers, and steel mills.

[0003] Catalysts play a key role in the development of NH3-SCR technology. It uses NH3 to react with nitrogen oxides on the surface or inside the catalyst for selective catalytic reduction, thereby achieving the purpose of emission reduction. At present, the most widely used NH3-SCR commercial catalyst is V2O5-WO3 (MoO3) / TiO2 (anatase). However, there are also certain defects, including biological toxicity, high energy consumption, unsatisfactory stability, and a narrow active temperature window (350 ~ 450 ℃). It cannot meet the requirements of medium and low temperature (below 300 ℃) industrial flue gas such as waste incineration, coking, cement and steel, which limits its further application. Therefore, it is still of great significance to develop low-temperature NH3-SCR catalysts that can meet the needs of different scenarios, have cost-effectiveness and high denitrification performance. Metal oxides (V, Mn, Ce, Co, Fe, Cu, Ni, Ti) are widely used in denitrification and are easy to prepare. Previous studies have shown that V2O5-WO3(MoO3) / TiO2 composites have excellent catalytic performance in NH3-SCR reactions, however, many inherent defects limit their application. It is generally believed that vanadium-free transition metal oxides (Ce, Mn, Fe, Cu, etc.) have unique inherent characteristics in the NH3-SCR catalytic process, and their comprehensive performance is superior to other types of catalysts.

[0004] Cerium-based NH3-SCR catalysts have attracted extensive attention due to their high oxygen storage capacity and excellent redox characteristics. However, they have good catalytic activity at medium and high temperatures, but poor catalytic activity at low temperatures. Manganese-based catalysts show great potential in low-temperature NH3-SCR. The variable valence state of manganese in manganese oxide will lead to internal defects and vacancies in the crystal, which is conducive to the movement and storage of oxygen, promotes the redox cycle, and improves the NO conversion in the SCR reaction. x or the adsorption and activation of NH3 on its surface. However, the narrow operating temperature window and poor hydrothermal stability are the main obstacles for Mn-based catalysts in NH3-SCR applications. Since cerium can store and release oxygen through the conversion of its own valence state, forming more unstable oxygen vacancies and free radicals, and manganese due to its special valence electron configuration (3d 5 4s 2 ), with a variety of valence states, including +2, +3, +4, +5 and some non-integer valence states. The mutual conversion between different valence states is conducive to the formation of surface active oxygen species, which is beneficial to improving the SCR activity. In addition, when Mn and Ce coexist in the same system, Mn may enter the CeO2 lattice to replace some Ce atoms, thereby distorting the CeO2 lattice and forming a solid solution or a new crystalline phase, thereby improving the catalytic performance by inducing interaction. In addition, it is generally believed that multi-metal doping can inhibit the sintering of active metals to a certain extent, thereby producing a synergistic effect, improving the dispersion of active ingredients, and then promoting the SCR reaction cycle. In this context, the construction of CeMnO x Bimetallic oxide catalysts should be an effective way to realize the complementary advantages of Ce-based and Mn-based catalysts, with good low-temperature catalytic activity, a wide temperature window and suitable thermal stability.

[0005] Currently, CeMnO x The synthesis methods of bimetallic oxides mainly include coprecipitation and impregnation, which face the problems of insufficient bimetallic mixing, long reaction cycle, and large amount of wastewater and waste residue. Therefore, the present invention aims to use hydrolysis-driven redox reaction to quickly prepare CeMnO with high atomic-level dispersion. x and applied it in low-temperature NH3-SCR. Summary of the invention

[0006] The present invention provides a simple and fast CeMnO x Preparation method: hydrolysis driven redox method, CeMnO with different metal ratios was prepared x -a catalyst suitable for low temperature NH3-SCR.

[0007] Dissolve KMnO4 and Ce(NO3)3·6H2O in a certain volume of deionized water to form a dark purple aqueous solution 1; dilute 2 times the theoretical equivalent of analytically pure H2O2 (content 30%) to form solution 2; add solution 2 dropwise into solution 1 with rapid stirring at room temperature to form a large amount of precipitate; stir for 6 hours, filter and wash with deionized water for 3-5 times; dry at 100°C for 10 hours, calcine in air to 200°C and keep warm for 4 hours; sieve out catalyst particles of 40-60 days.

[0008] In the preparation method of the manganese-cerium metal oxide catalyst of the present invention, the Ce / Mn molar ratio a is in the range of 1-5.

[0009] In the preparation method of the manganese-cerium metal oxide catalyst of the present invention, the H2O2 concentration used is 30% and is diluted 10-20 times.

[0010] In the preparation method of the manganese-cerium metal oxide catalyst of the present invention, the oxidation process is to place the dried sample in a muffle furnace, raise the temperature to 200° C. at a rate of 10° C. / min and keep the temperature for 4 hours.

[0011] In the preparation method of the manganese-cerium metal oxide catalyst of the present invention, the synthesized CeMnO x Atomic-level mixing can be achieved.

[0012] The manganese-cerium metal oxide catalyst prepared according to the method of the present invention has the following characteristics: The disappearance of the peak in the XRD spectrum indicates that it is an amorphous structure, so it can be inferred that the introduction of Ce ions into the MnO2 lattice will cause crystal disorder. The introduction of Ce ions into the MnO2 lattice matrix leads to amorphization, thereby promoting the appearance of lattice defects and the exposure of internal atoms.

[0013] The manganese-cerium metal oxide catalyst provided by the present invention can be used for low-temperature NH 3- SCR reaction and showed excellent catalytic activity.

[0014] The manganese-cerium metal oxide catalyst provided by the present invention has the following advantages: the hydrolysis-driven redox method is simple, and the synthesized CeMnO x It can achieve mutual mixing at the atomic level and precisely control the metal ratio in metal oxides from an atomic perspective. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 XRD spectra of manganese-cerium metal oxide catalysts obtained in Examples 1, 2, 3, 4, and 5 Figure 2 The catalytic activity diagram of the manganese-cerium metal oxide catalyst in the present invention in the NH3-SCR reaction DETAILED DESCRIPTION

[0015] The specific implementation of the invention will be described in detail below with reference to the accompanying drawings.

[0016] Example 1: Weigh 5.5 g Ce(NO3)3·6H2O and dissolve it in 150 mLH2O, then add 2.012 g KMnO4 and stir thoroughly to form a dark purple mixed solution 1, in which the molar ratio of Mn to Ce is 1. Take 12.86 g of 30 wt% H2O2 solution and dissolve it in 150 mLH2O to form solution 2. At room temperature, add solution 2 dropwise into solution 1 with rapid stirring to form a large amount of precipitation; stir for 6 h, filter and wash with deionized water 3-5 times; dry at 100℃ for 10 h, grind and sieve after cooling, and then place the sample in a muffle furnace, heat to 200℃ at a rate of 2℃ / min and keep warm for 4 hours. 1Mn1Ce bimetallic oxide catalyst can be obtained.

[0017] Example 2: Weigh 5.5 g Ce(NO3)3·6H2O and dissolve it in 150 mLH2O, then add 4.023 g KMnO4 and stir thoroughly to form a dark purple mixed solution 1, in which the molar ratio of Mn to Ce is 12. Take 12.86 g of 30 wt% H2O2 solution and dissolve it in 150 mLH2O to form solution 2. At room temperature, add solution 2 dropwise into solution 1 with rapid stirring to form a large amount of precipitation; stir for 6 h, filter and wash with deionized water 3-5 times; dry at 100℃ for 10 h, grind and sieve after cooling, and then place the sample in a muffle furnace, heat to 200℃ at a rate of 2℃ / min and keep warm for 4 hours. The 2Mn1Ce bimetallic oxide catalyst can be obtained.

[0018] Example 3: Weigh 5.5 g Ce(NO3)3·6H2O and dissolve it in 150 mLH2O, then add 6.034 g KMnO4 and stir thoroughly to form a dark purple mixed solution 1, in which the molar ratio of Mn to Ce is 3. Take 12.86 g of 30 wt% H2O2 solution and dissolve it in 150 mLH2O to form solution 2. At room temperature, add solution 2 dropwise into solution 1 with rapid stirring to form a large amount of precipitation; stir for 6 h, filter and wash with deionized water 3-5 times; dry at 100℃ for 10 h, grind and sieve after cooling, and then place the sample in a muffle furnace, heat to 200℃ at a rate of 2℃ / min and keep warm for 4 hours. The 3Mn1Ce bimetallic oxide catalyst can be obtained.

[0019] Example 4: Weigh 5.5 g Ce(NO3)3·6H2O and dissolve it in 150 mLH2O, then add 8.045 g KMnO4 and stir thoroughly to form a dark purple mixed solution 1, in which the molar ratio of Mn to Ce is 4. Take 12.86 g of 30 wt% H2O2 solution and dissolve it in 150 mLH2O to form solution 2. At room temperature, add solution 2 dropwise into solution 1 with rapid stirring to form a large amount of precipitation; stir for 6 h, filter and wash with deionized water 3-5 times; dry at 100℃ for 10 h, grind and sieve after cooling, and then place the sample in a muffle furnace, heat to 200℃ at a rate of 2℃ / min and keep warm for 4 hours. The 4Mn1Ce bimetallic oxide catalyst can be obtained.

[0020] Example 5: Weigh 5.5 g Ce(NO3)3·6H2O and dissolve it in 150 mLH2O, then add 10.057 g KMnO4, stir thoroughly, and form a dark purple mixed solution 1, in which the molar ratio of Mn to Ce is 1. Take 12.86 g of 30 wt% H2O2 solution and dissolve it in 150 mL H2O to form solution 2. At room temperature, add solution 2 dropwise into solution 1 with rapid stirring to form a large amount of precipitation; stir for 6 h, filter and wash with deionized water 3-5 times; dry at 100℃ for 10 h, grind and sieve after cooling, and then place the sample in a muffle furnace, heat to 200℃ at a rate of 2℃ / min and keep warm for 4 hours. 5Mn1Ce bimetallic oxide catalyst can be obtained.

[0021] Application examples: 0.1 g of 40-60 mesh catalyst was placed in a fixed bed reactor. The simulated flue gas consisted of NO, NH3, O2 and N2, with NO: 500ppm, NH3: 600ppm, O2: 5%, and the balance gas was N2. The reaction temperature was 50-290℃, and the space velocity was 120000h -1 ,The smoke components before and after the reaction were detected and analyzed by a smoke analyzer.

[0022] Depend on Figure 2 It can be seen that at an airspeed of 120000 h -1 When the catalysts with different Mn / Ce ratios have different denitrification activities, the catalytic activity of 2Mn1Ce catalyst is the best, and the NO x The conversion rate is over 90%.

Claims

1. A manganese-cerium metal oxide catalyst for low-temperature NH3-SCR, characterized in that: The metal oxide catalyst is represented by MnCeO x -a; where a is the synthetic MnCeO x The catalyst is synthesized by a hydrolysis-driven redox method, and the synthesized Mn-Ce bimetallic oxide can achieve atomic-level mutual mixing; the catalyst has more than 90% NO in the range of 100-230°C when a=2 x Transformation activity.

2. The method for preparing the manganese-cerium metal oxide catalyst comprises the following steps: Dissolve KMnO4 and Ce(NO3)3·6H2O in a certain volume of deionized water to form a dark purple aqueous solution 1; dilute 2 times the theoretical equivalent of analytically pure H2O2 (content 30%) to form solution 2; add solution 2 dropwise into solution 1 with rapid stirring at room temperature to form a large amount of precipitation; stir for 6 hours, filter and wash with deionized water for 3-5 times; dry at 100°C for 10 hours, calcine in air to 200°C and keep warm for 4 hours; sieve out catalyst particles of 40-60 mesh.

3. In the preparation method of the manganese-cerium metal oxide catalyst, the H2O concentration used is 30% and is diluted 10-20 times.

4. The oxidation process is to place the dried sample in a muffle furnace, raise the temperature to 200°C at a rate of 10°C / min and keep it at that temperature for 4 hours.

5. During synthesis, the Mn / Ce molar ratio a ranges from 1 to 5, preferably MnCeO x -2.

6. The use of the manganese-cerium metal oxide catalyst as claimed in claim 1, characterized in that: The catalyst is used for selective catalytic reduction of NO by NH3 x reaction.

Images