Aerobic stable type layered double-oxide catalyst for CO-SCR denitration as well as preparation method and application of aerobic stable type layered double-oxide catalyst

Abstract

The invention discloses an aerobic stable layered double-oxide catalyst for CO-SCR denitration as well as a preparation method and application of the aerobic stable layered double-oxide catalyst, and belongs to the technical field of CO selective catalytic reduction of nitrogen oxides (CO-SCR). The preparation method comprises the following steps: carrying out hydrothermal reaction on Fe (NO3) 3.9 H2O, C4H6MgO4. 4H2O and urea to obtain a FeMg-LDH precursor, then adding Cu (NO3) 2.3 H2O and Cr (NO3) 3.9 H2O, stirring, and roasting to obtain the Cu7.5-Cr7.2 / LDO catalyst. The catalyst disclosed by the invention has excellent wide temperature range stability and sintering resistance under an aerobic condition, and stable and efficient NOx purification can be realized in a wide temperature range of 200-800 DEG C. The catalyst has the advantages of being simple in preparation process, low in cost, environmentally friendly and the like, is suitable for efficient wide-temperature-zone removal of NOx in oxygen-containing industrial flue gas, and has wide industrial application prospects.

Description

Technical Field

[0001] This invention belongs to the field of CO selective catalytic reduction of nitrogen oxides (CO-SCR) technology, specifically relating to an aerobic stable layered double oxide catalyst for CO-SCR denitrification, its preparation method, and its application. Background Technology

[0002] Nitrogen oxides (NOx) are among the major air pollutants, posing a serious threat to human health, ecosystems, and the environment. Selective catalytic reduction (SCR) technology is one of the most effective methods for eliminating NOx. Although NH3-SCR technology, using NH3 as a reducing agent, has been industrialized, it suffers from problems such as ammonia leakage, equipment corrosion, catalyst poisoning, and high storage and transportation costs. CO-SCR technology, using CO as a reducing agent (CO + NO → N2 + CO2), offers an alternative that can simultaneously eliminate two harmful gases (NO and CO), achieving "waste treatment with waste." It boasts significant advantages such as low cost and process safety, and has received widespread attention in recent years. The core of this technology lies in developing efficient, stable, and widely applicable catalysts. Currently, catalysts used for CO-SCR mainly include noble metal catalysts and transition metal oxide catalysts. While noble metal catalysts (such as Pt, Rh, and Pd) possess high low-temperature activity, their high price, scarcity, and susceptibility to poisoning limit large-scale industrial applications. Therefore, research has focused on non-noble metal catalysts, among which copper-based catalysts have been extensively studied due to their excellent low-temperature catalytic activity.

[0003] Layered double hydroxides (LDHs), derived from LDOs after calcination, possess characteristics such as large specific surface area, high metal dispersion, abundant basic sites, and good thermal stability, making them ideal catalyst supports. In existing technologies, CO-SCR catalysts prepared by supporting a single copper active component on supports such as CoFe-LDH and CuAl-LDH exhibit certain catalytic activity at low temperatures (≤150℃), but their active temperature range is generally narrow. Especially in oxygen-containing atmospheres, at high temperatures (>350℃), catalytic performance is easily significantly degraded due to oxidation and sintering of the active component, collapse of the support structure, or increased surface acidity, making it difficult to simultaneously achieve high activity and high stability over a wide temperature range of 200–800℃. Furthermore, the presence of oxygen competes for adsorption and consumes reducing agents, exacerbating the deactivation of conventional catalysts and severely limiting their application in real industrial flue gas (typically oxygen-containing) conditions. To address the critical issue of insufficient stability of existing catalysts in a wide temperature range and oxygen-containing environments, this invention provides a layered double oxide catalyst with excellent oxygen stability. This catalyst uses FeMg-LDO as a support and introduces Cu-Cr dual active components. It aims to significantly improve the catalyst's high-temperature resistance to sintering, activity stability, and temperature window width in oxygen-containing atmospheres through support alkalinity regulation, active site structure optimization, and intermetallic synergistic effects, thereby meeting the needs of NOx purification in actual industrial flue gas. Summary of the Invention

[0004] To address the problems of existing technologies, this invention provides an aerobic-stable layered double oxide catalyst for CO-SCR denitrification, its preparation method, and its application.

[0005] The technical solution adopted in this invention is: an aerobic-stabilized layered double oxide catalyst for CO-SCR denitrification, the preparation method of which includes the following steps:

[0006] 1) Fe(NO3)3·9H2O and C4H6MgO4·4H2O were dissolved in deionized water in a certain proportion. After ultrasonic treatment, urea was added, and the rust-colored solution was ultrasonically treated. Then, it was transferred to an autoclave for hydrothermal reaction. The product was collected by filtration, washing, and drying to obtain FeMg-LDH precursor.

[0007] 2) Dissolve Cu(NO3)2·3H2O and Cr(NO3)3·9H2O in deionized water, then add the FeMg-LDH precursor and stir vigorously at room temperature. Stir the mixture until dry, then calcine it in a muffle furnace to obtain Cu. 7.5 -Cr 7.2 / LDO CO-SCR catalyst.

[0008] In the above-mentioned aerobic stable layered double oxide catalyst for CO-SCR denitrification, in step 1), the molar ratio is Fe(NO3)3·9H2O:C4H6MgO4·4H2O:urea = 0.8:12.4:7.2.

[0009] In the above-mentioned aerobic stable layered double oxide catalyst for CO-SCR denitration, in step 2), Cu(NO3)2·3H2O:Cr(NO3)3·9H2O:FeMg-LDH precursor = 0.19mmol:0.19mmol:0.2g.

[0010] In the aforementioned aerobic-stabilized layered double oxide catalyst for CO-SCR denitration, step 1) involves ultrasonic treatment of the aqueous solution for 10 min and ultrasonic treatment of the rust-colored solution for 30 min. The filtration and washing process consists of two washes with deionized water and three washes with anhydrous ethanol.

[0011] In the above-mentioned aerobic stable layered double oxide catalyst for CO-SCR denitrification, the hydrothermal reaction temperature in step 1) is 150℃ and the reaction time is 6h.

[0012] In the above-mentioned aerobic stable layered double oxide catalyst for CO-SCR denitration, the vigorous stirring time in step 2) is 1 hour.

[0013] In the above-mentioned aerobic stable layered double oxide catalyst for CO-SCR denitration, in step 2), the muffle furnace calcination temperature is 600℃ and the calcination time is 4h.

[0014] In the above-mentioned aerobic stable layered double oxide catalyst for CO-SCR denitration, the drying temperature in steps 1) and 2) is 60°C.

[0015] The above-mentioned aerobic-stabilized layered double oxide catalyst for CO-SCR denitration is applied in denitration.

[0016] The above application is carried out as follows: In an atmospheric pressure fixed-bed reactor, the above-mentioned aerobic stable layered double oxide catalyst for CO-SCR denitrification is placed in a quartz glass boat, and the reaction gas is introduced. The reaction device is heated from room temperature to 800°C, kept at the temperature for 10 min, and then heated at 5°C / min. NO is introduced to carry out denitrification.

[0017] Further, the above application is carried out using the following method: The activity evaluation of the catalyst's NO conversion rate is conducted in an atmospheric pressure fixed-bed reactor apparatus, which mainly consists of a gas supply section, a mixing section, a fixed-bed reactor, and an analyzer. The quartz tube used for the reaction is 120 cm long and 11 mm in inner diameter, and a horizontal tube furnace is used for programmed temperature rise. 0.2 g of catalyst is placed in a quartz glass boat (50 mm long, 10 mm wide, and 5 mm high), which is placed in the central heating zone of the fixed-bed reactor. The tube furnace provides the required temperature for the denitrification reaction through programmed temperature control, with a heating rate set at 5 °C / min. The sample is treated at 110 °C for 60 min under a nitrogen atmosphere (200 mL / min) to remove impurities. Next, the sample is cooled to room temperature, and the valve is switched to the reaction gas for 60 minutes. The inlet and outlet concentrations of NO are quantitatively analyzed online using a Thermo Model 42i NOx analyzer. The reaction apparatus was heated from room temperature to 800℃ using a programmed temperature ramp-up method, held at that temperature for 10 minutes, and then increased at a rate of 5℃ / min. The performance of the denitrification catalyst was measured by the NO conversion rate (QNO) flowing through the bed, calculated using the following formula:

[0018]

[0019] In the formula: [NO] in [NO] represents the inlet concentration of NO. out This represents the outlet concentration of NO. Both are recorded after the NO concentration reaches a stable value.

[0020] The simulated flue gas composition consisted of NO (7.5 mL / min, 4008 ppm nitrogen mixture), CO (60 mL / min, 5% argon mixture), (75 mL / min, 5% argon mixture), and (100 mL / min, 5% argon mixture), with N2 (150 mL / min) as the balance gas and air (15 mL / min). All conditions remained unchanged except for the CO concentration.

[0021] The beneficial effects of this invention are as follows:

[0022] 1. The oxygen-stable layered double oxide CO-SCR catalyst prepared by this invention uses FeMg-LDH as a support, which has a stable structure and strong interaction between the Cu-Cr active component and the support. This effectively inhibits the agglomeration, sintering and phase transformation of the active component at high temperatures, resulting in catalytic activity over a wide temperature range of 200℃ to 800℃. In particular, it can maintain a NO conversion rate of nearly 100% for 3 hours at 800℃, overcoming the defect of easy deactivation of traditional copper-based catalysts at high temperatures and greatly expanding the applicable operating conditions of the catalyst.

[0023] 2. The catalyst prepared in this invention, combined with Cr doping, significantly optimizes the valence state distribution of supported copper species, promoting more active Cu... + The formation and stabilization of species, along with the increased concentration of chemisorbed oxygen and oxygen vacancies on the catalyst surface, provide abundant active sites for the CO-SCR reaction.

[0024] 3. The catalyst prepared by this invention employs mature hydrothermal and impregnation methods, resulting in a simple, reproducible, and easily scalable production process. The iron, magnesium, copper, and chromium used are all abundant and inexpensive metallic elements, containing no precious metals, thus possessing significant cost advantages and industrial application potential. Attached Figure Description

[0025] Figure 1 The LDO catalyst prepared in Example 1 and the Cu catalyst prepared in Example 2 of this invention. 7.5 -Cr 7.2 XRD pattern of LDO catalyst.

[0026] Figure 2 Cu 7.5 -Cr 7.2 / LDO catalyst NO conversion rate as a function of temperature and adjustment of CO gas ratio.

[0027] Figure 3 This is a stability graph of the catalyst at 800℃ for 3 hours. Detailed Implementation

[0028] Example 1

[0029] The preparation method of LDO catalyst is as follows:

[0030] First, Fe(NO3)3·9H2O (0.8 mmol) and C4H6MgO4·4H2O (2.4 mmol) were dissolved in 60 mL of deionized water. The aqueous solution was sonicated for 10 min, and then urea (7.2 mmol) was added. Next, the rust-colored solution was sonicated for 30 min, then transferred to a Teflon stainless steel autoclave, sealed, and heated at 150 °C for 6 h. The product was then collected by filtration and washed twice with deionized water and three times with anhydrous ethanol. Finally, the FeMg-LDH precursor was dried in an oven at 60 °C to obtain the FeMg-LDH precursor. The precursor was calcined in a muffle furnace at 600 °C for 4 h to obtain the LDO catalyst.

[0031] Example 2

[0032] Cu 7.5 -Cr 7.2 The preparation method of / LDO catalyst is as follows:

[0033] 0.19 mmol Cu(NO3)2·3H2O and 0.19 mmol Cr(NO3)3·9H2O were dissolved in 25 mL of deionized water, and then 0.2 g of the above FeMg-LDH precursor was added. The mixture was stirred vigorously with a stirrer for 1 h at room temperature. The mixture was then dried at 60 °C and calcined in a muffle furnace at 600 °C for 4 h. Cu was finally obtained. 7.5 -Cr 7.2 / LDO catalyst.

[0034] Example 3

[0035] Figure 1 The LDO catalyst prepared in Example 1 and the Cu catalyst prepared in Example 2 7.5 -Cr 7.2 X-ray diffraction pattern of the LDO catalyst. The LDO catalyst contains MgO, α-Fe2O3, and γ-Fe2O3 phases simultaneously. The generated γ-Fe2O3 nanoparticles are highly dispersed in the MgO matrix. MgO acts as a physical separator, preventing contact and growth between γ-phase particles, thereby inhibiting the transformation of the γ-phase to the α-phase. The characteristic diffraction peaks 2θ = 42.8° and 62.2° correspond to the (200) and (220) crystal planes of MgO, respectively. 2θ = 33.0° corresponds to the (104) crystal plane of α-Fe2O3. 2θ = 35.5° corresponds to the (311) crystal plane of γ-Fe2O3. This is consistent with the PDF standard card for MgO (PDF#45-0946), the standard card for α-Fe2O3 (PDF#33-0664), and the standard card for γ-Fe2O3 (PDF#39-1346). The crystal phases of the catalyst supported on 7.5% copper and 7.2% chromium remained unchanged, still consisting of MgO, α-Fe₂O₃, and γ-Fe₂O₃ phases. However, the diffraction peaks of the α-Fe₂O₃, γ-Fe₂O₃, and MgO catalysts were broader and weaker than those of the catalyst without copper and chromium support, indicating a decrease in both crystallinity and grain size. Reduced crystallinity leads to more crystal defects, increasing the number of adsorbed oxygen species on the surface, thereby enhancing the reaction activity. Figure 1 As can be seen from this, Cu 7.5- Cr 7.2 / LDO was successfully prepared.

[0036] Example 4

[0037] The catalytic efficiency of a catalyst is evaluated or calculated using the following methods:

[0038] 1) Cu 7.5 -Cr 7.2 Catalytic performance evaluation of LDO catalysts

[0039] The activity evaluation of the catalyst's NO conversion rate was conducted in an atmospheric pressure fixed-bed reactor apparatus, which mainly consisted of a gas supply section, a gas mixing section, a fixed-bed reactor, and an analyzer. The quartz tube used in the reaction was 120 cm long and 11 mm in inner diameter, and a horizontal tube furnace was used for programmed temperature rise. 0.2 g of catalyst was placed in a quartz glass boat (50 mm long, 10 mm wide, and 5 mm high) and placed in the central heating zone of the fixed-bed reactor. The tube furnace provided the required temperature for the denitrification reaction through programmed temperature control, with a heating rate set at 5 °C / min. The sample was treated at 110 °C for 60 min under a nitrogen atmosphere (200 mL / min) to remove impurities. Next, the sample was cooled to room temperature, and the valve was switched to the NO reaction gas for 60 minutes. The inlet and outlet concentrations of NO were quantitatively analyzed online using a Thermo Model 42i NOx analyzer. The reaction apparatus was heated from room temperature to 800℃ using a programmed temperature ramp-up method, held at that temperature for 10 minutes, and then increased at a rate of 5℃ / min. The performance of the denitrification catalyst was measured by the NO conversion rate (QNO) flowing through the bed, calculated using the following formula:

[0040]

[0041] In the formula: [NO] in [NO] represents the inlet concentration of NO. out This represents the outlet concentration of NO. Both are recorded after the NO concentration reaches a stable value.

[0042] 2) Following step 1), simulate the flue gas composition as follows: NO (7.5 mL / min, 4008 ppm nitrogen mixture), CO (60 mL / min, 5% argon mixture), (75 mL / min, 5% argon mixture), and (100 mL / min, 5% argon mixture), with N2 (150 mL / min) as the balance gas and air (15 mL / min). Except for changing the CO, all other conditions remain unchanged.

[0043] Figure 2 The graphs show the NO conversion rate of the catalyst as a function of temperature and different CO gas ratios. It can be seen that the performance of all three gas ratios begins to improve around 200℃. When the CO gas flow rate is 60 mL / min, the NO conversion rate reaches 99.9% at 543℃; when the CO gas flow rate is 75 mL / min, the NO conversion rate reaches 99.9% at 640℃; and when the CO gas flow rate is 100 mL / min, the conversion rate reaches 99.9% at 685℃.

[0044] Example 5

[0045] Figure 3The figure shows the CO-SCR denitrification stability curve of the sample after being kept at 800℃ for 3 hours. As can be seen from the figure, under the simulated industrial extreme high temperature long-term operation conditions, the NO conversion rate of the catalyst remained stable in the range of 99.90% to 99.99%, without a significant downward trend throughout the process, with only a slight fluctuation of ±0.1%, demonstrating high temperature stability.

Claims

1. An aerobic-stabilized layered double oxide catalyst for CO-SCR denitrification, characterized in that, The preparation method includes the following steps: 1) Fe(NO3)3·9H2O and C4H6MgO4·4H2O were dissolved in deionized water in a certain proportion. After ultrasonic treatment, urea was added, and the rust-colored solution was ultrasonically treated. The solution was then transferred to an autoclave for hydrothermal reaction. The product was collected by filtration, washing, and drying to obtain the FeMg-LDH precursor. 2) Dissolve Cu(NO3)2·3H2O and Cr(NO3)3·9H2O in deionized water, then add FeMg-LDH precursor, stir vigorously at room temperature, and stir the mixture until dry. Then calcine in a muffle furnace to obtain Cu 7.5 -Cr 7.2 / LDO CO-SCR catalyst.

2. The aerobic-stabilized layered double oxide catalyst for CO-SCR denitration according to claim 1, characterized in that, In step 1), the molar ratio is Fe(NO3)3·9H2O:C4H6MgO4·4H2O:urea = 0.8:12.4:7.

2.

3. The aerobic-stabilized layered double oxide catalyst for CO-SCR denitrification according to claim 1, characterized in that, In step 2), Cu(NO3)2·3H2O:Cr(NO3)3·9H2O:FeMg-LDH precursor = 0.19mmol:0.19mmol:0.2g.

4. The aerobic-stabilized layered double oxide catalyst for CO-SCR denitration according to claim 1, characterized in that, In step 1), the aqueous solution is ultrasonically treated for 10 minutes, the rust-colored solution is ultrasonically treated for 30 minutes, and the filtration and washing are performed by washing twice with deionized water and three times with anhydrous ethanol.

5. The aerobic-stabilized layered double oxide catalyst for CO-SCR denitration according to claim 1, characterized in that, In step 1), the hydrothermal reaction temperature is 150℃ and the reaction time is 6h.

6. The aerobic-stabilized layered double oxide catalyst for CO-SCR denitration according to claim 1, characterized in that, In step 2), the vigorous stirring time is 1 hour.

7. The aerobic-stabilized layered double oxide catalyst for CO-SCR denitration according to claim 1, characterized in that, In step 2), the temperature of the muffle furnace is 600℃ and the roasting time is 4h.

8. The preparation method according to claim 1, characterized in that, In steps 1) and 2), the drying temperature is 60°C.

9. The application of an aerobic stable layered double oxide catalyst for CO-SCR denitrification according to any one of claims 1-8 in denitrification.

10. The application according to claim 9, characterized in that: The method is as follows: In an atmospheric pressure fixed-bed reactor, the aerobic stable layered double oxide catalyst for CO-SCR denitrification as described in any one of claims 1-8 is placed in a quartz glass boat, and a reaction gas is introduced. The reaction device is heated from room temperature to 800°C, kept at that temperature for 10 min, and then heated at 5°C / min. NO is introduced to carry out denitrification.

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