Catalyst for low-temperature oxidation treatment of sintering flue gas CO and preparation method thereof

Abstract

The invention relates to a catalyst for sintering flue gas CO low-temperature oxidation treatment and a preparation method thereof. Belongs to the technical field of air pollution control. According to the catalyst disclosed by the invention, CeO2-La2O3 composite oxide is taken as a carrier, Mn3O4-Fe2O3-CuO active components are loaded, and low-temperature efficient catalysis, strong sulfur resistance and low cost are realized through the synergistic effect of a Pr6O11 nano coating layer and an alkali metal additive (K2O / Na2O). The preparation method comprises the processes of coprecipitation, impregnation, vapor deposition and secondary roasting. And at 200 DEG C, the CO conversion rate is greater than or equal to 90%, the activity loss is less than 5% after the catalyst operates in sulfur-containing flue gas for 100 hours, and the raw material cost is reduced by 80-90%. The catalyst is suitable for iron-making sintering machine tail gas treatment, solves the problems of insufficient low-temperature activity, easy sulfur poisoning and high cost of the existing catalyst, and assists green transformation of the iron and steel industry.

Description

Technical Field

[0001] The present invention belongs to the technical field of air pollution control, and particularly relates to a catalyst for low-temperature oxidation treatment of CO in sintering flue gas and a preparation method thereof. In particular, it aims at the application of a catalyst based on rare earth-transition metal composite oxides in treating CO in the tail gas of an iron-smelting sintering machine under sulfur-containing and high-humidity conditions. Background Art

[0002] As a pillar industry of the national economy, the iron-smelting sintering process in the steel industry will generate a large amount of sintering flue gas during the production process, becoming one of the important sources of air pollution. During the high-temperature process of sintering iron ore, fuel and flux to form sintered ore, the discharged tail gas contains pollutants such as carbon monoxide (CO), sulfur dioxide (SO2), nitrogen oxides (NOx) and dust. Among them, CO, as an incomplete combustion product, usually has a relatively high concentration of 2000-5000 ppm. It not only causes energy waste, but also poses a serious threat to the ecological environment and human health due to its high toxicity. With the promotion of the global "dual carbon" goal and the increasingly strict relevant regulations such as the "Air Pollution Prevention and Control Law", efficiently purifying CO in sintering flue gas has become a technical problem that steel enterprises must overcome to achieve sustainable development.

[0003] Currently, the treatment technologies for CO in sintering flue gas mainly include catalytic oxidation method, adsorption method, combustion method, etc. The catalytic oxidation method has received extensive attention in practical applications due to its advantages such as no need for additional fuel and a wide operating temperature range. However, existing catalysts still face many challenges in actual use:

[0004] Limitations of noble metal catalysts: Noble metal catalysts represented by platinum (Pt) and palladium (Pd) have excellent activity at low temperatures (150-200 °C) (CO conversion rate > 90%). For example, the Pt / Al2O3 catalyst disclosed in patent CN110XXXXXXB can achieve a CO conversion rate of 95% at 180 °C. However, due to the scarcity of noble metal resources, the catalyst cost is high, and its cost accounts for more than 60% of the total cost of the entire system. At the same time, SO2 (50-200 ppm) and H2O (5-15%) commonly present in sintering flue gas will strongly adsorb on the noble metal active sites, forming a sulfate or hydroxide coating layer, which will further lead to irreversible poisoning of the catalyst. The latest research shows that in sulfur-containing flue gas, after the noble metal catalyst operates for 100 hours, the activity loss is as high as 40%-60%. In addition, the high-humidity environment will accelerate the hydrothermal sintering of the carrier Al2O3, further reducing the stability of the catalyst.

[0005] Performance Defects of Transition Metal Catalysts: To address the high cost of noble metal catalysts, transition metal oxide catalysts such as iron (Fe), copper (Cu), and manganese (Mn) have attracted attention due to their low cost. For example, the CeO2-MnOx composite catalyst proposed in Patent CN112XXXXXXA can achieve a CO conversion rate of 80% at 250°C. However, transition metal catalysts generally suffer from insufficient low-temperature activity. The conversion rate of Fe-based catalysts is less than 50% below 200°C, and the temperature needs to be raised above 300°C to reach a conversion rate of 80%, which significantly increases energy consumption; although Cu-based catalysts have high activity in the low-temperature range (150 - 200°C), their sulfur resistance is extremely poor, and SO2 will react with CuO to form copper sulfate (CuSO4), clogging the catalyst pores and causing structural collapse; Mn-based catalysts are easily inhibited by water vapor, and their activity drops by more than 30% under high-humidity conditions.

[0006] Research Bottlenecks in Sulfur Resistance Technology: The presence of SO2 in sintering flue gas seriously threatens the service life of catalysts. Existing technologies for improving the sulfur resistance of catalysts mainly involve carrier modification or adding sulfur-resistant additives. For example, Patent CN113XXXXXXC uses TiO2 as a carrier and utilizes its surface acidic sites to adsorb SO2, but TiO2 is prone to crystal phase transformation at high temperatures, resulting in carrier failure; Patent CN114XXXXXXD proposes doping ZrO2 in the Co3O4 catalyst to delay sulfur poisoning by forming Zr(SO4)2. However, this doping process is complex and the cost increases by more than 50%. Another type of solution is to isolate SO2 through a surface coating layer. For example, CN115XXXXXXE uses SiO2 to coat Fe2O3, but when the coating layer is too thick (>10 nm), it will hinder the diffusion of reactants and reduce the catalytic efficiency.

[0007] Comprehensive Performance Comparison of Existing Technologies: Table 1 summarizes the performance data of representative catalysts in recent years:

[0008] Catalyst Performance Comparison Table

[0009]

[0010] As can be seen from the table, although noble metal catalysts have excellent low-temperature activity, their cost and sulfur resistance are difficult to meet industrial requirements; transition metal catalysts have a lower cost, but they need to operate at high temperatures and their sulfur resistance performance varies. In addition, existing patent technologies mostly focus on optimizing single performance and lack the coordinated improvement of low-temperature activity, sulfur resistance, and cost control.

[0011] 5. Market demand and technology gap: According to the "Development Report on Energy Conservation and Emission Reduction in the Chinese Iron and Steel Industry", in 2022, the number of sintering machines in key iron and steel enterprises nationwide exceeded 900, and the total annual CO emissions were approximately 1.2 million tons. If traditional noble metal catalysts were used, the procurement cost of the catalysts alone would exceed 10 billion yuan, and frequent replacement would further increase the operation and maintenance burden. Therefore, developing a CO oxidation catalyst with low-temperature high efficiency, strong sulfur resistance, and low cost is of great significance for the green transformation of the iron and steel industry.

[0012] In summary, the existing technologies have not yet broken through the triple contradiction of "low-temperature activity - sulfur resistance - cost", and there is an urgent need to construct a new catalyst system through material design and preparation process innovation. Based on the synergistic effect of rare earth - transition metals and combined with nanocoating technology, the present invention aims to provide an efficient and reliable technical solution for the treatment of CO in sintering flue gas. Summary of the Invention

[0013] Object of the Invention: Aiming at the problems of high cost and easy poisoning of noble metal catalysts and low low-temperature activity and poor sulfur resistance of transition metal catalysts in the existing technologies, the present invention aims to provide a catalyst based on the synergistic effect of rare earth - transition metals. The specific objectives are as follows:

[0014] Low-temperature high efficiency: By means of the synergistic effect of rare earth - transition metal composite oxides, the CO oxidation activity of the catalyst at low temperatures (150 - 200 °C) is enhanced. The goal is to achieve a CO conversion rate of over 90% at 200 °C to realize the efficient purification of CO in the tail gas of iron-making sintering machines under low-temperature conditions and reduce energy consumption.

[0015] Strong sulfur resistance: By using nanocoating technology and introducing rare earth elements, the stability of the catalyst in an environment containing sulfur (SO2) and high humidity (H2O) is enhanced. The goal is that the activity loss is less than 5% after 100 hours of sulfur-containing flue gas testing, effectively extending the service life of the catalyst, reducing frequent replacement due to sulfur poisoning, and reducing the operation and maintenance cost.

[0016] Low cost: Abandoning expensive noble metals and using inexpensive rare earth and transition metal oxides, the raw material cost is reduced by 80 - 90%, improving the competitiveness of the product in the market and promoting the green transformation of the iron and steel industry.

[0017] The present invention belongs to a catalyst and a preparation method for the low-temperature oxidation treatment of CO in sintering flue gas. More precisely, it is a low-temperature oxidation catalyst for CO in sintering flue gas based on rare earth - transition metal composite oxides and its preparation method, wherein the catalyst consists of the following four parts:

[0018] Support: CeO2-La2O3 composite oxide, where the Ce / La molar ratio is 1:1 to 3:1, accounting for 50 - 70 wt%. CeO2 has excellent oxygen storage capacity and redox performance, and the introduction of La2O3 can further improve the thermal stability and sulfur resistance of the support.

[0019] Active component: Mn3O4-Fe2O3-CuO ternary transition metal oxide (Mn:Fe:Cu = 4:3:1), accounting for 20 - 40 wt%. Mn3O4 has high low-temperature oxidation activity, and the introduction of Fe2O3 and CuO can further enhance the redox ability and sulfur resistance of the catalyst.

[0020] Sulfur-resistant layer: Pr6O 11 nano-coating layer (thickness 2 - 5 nm), accounting for 5 - 15 wt%. Pr6O 11 has excellent sulfur resistance and can effectively isolate the poisoning effect of SO2 on the active component.

[0021] Promoter: K2O or Na2O (loading amount 1 - 3 wt%). The introduction of alkali metal promoters can adjust the surface acidity and basicity of the catalyst and further improve its sulfur resistance and low-temperature activity.

[0022] A preparation method of the catalyst for low-temperature oxidation treatment of sintering flue gas CO as described above, the specific steps are as follows:

[0023] 1. Prepare the CeO2-La2O3 composite oxide support by the co-precipitation method: Accurately weigh Ce(NO3) 3· 6H2O and La(NO3) 3· 6H2O, dissolve them in an appropriate amount of deionized water according to the set molar ratio of 1:1 to 3:1, slowly add ammonia water under stirring conditions, adjust the pH of the solution to 9. After the precipitation reaction is completed, filter the precipitate, and wash it repeatedly with deionized water to remove impurity ions. Then place the washed precipitate in an oven, dry it at 120 °C for 12 h, and finally put it into a muffle furnace and calcine it at 550 °C for 4 h to prepare the CeO2-La2O3 composite oxide support.

[0024] 2. Loading active components by impregnation method: The prepared CeO2-La2O3 composite oxide support is impregnated in a mixed solution of Mn(NO3)2, Fe(NO3)3, and Cu(NO3)2 prepared according to the molar ratio of Mn:Fe:Cu of 4:3:1, ensuring that the CeO2-La2O3 composite oxide support is fully wetted. The impregnation time is 12 h, so that metal ions are fully adsorbed on the surface of the CeO2-La2O3 composite oxide support. After impregnation, it is taken out, dried at 80 °C for 12 h, and then placed in a muffle furnace and calcined at 500 °C for 3 h to form a catalyst matrix loaded with Mn3O4-Fe2O3-CuO active components;

[0025] 3. Generating Pr6O 11 coating layer by chemical vapor deposition: The catalyst matrix loaded with Mn3O4-Fe2O3-CuO active components is placed in a tubular furnace, and Pr(NO3)3 vapor is introduced. It is deposited at 350 °C for 2 - 3 h, so that Pr(NO3)3 vapor decomposes and deposits on the surface of the catalyst matrix loaded with Mn3O4-Fe2O3-CuO active phase to form Pr6O 11 nano-coating layer. The thickness of the coating layer is measured by XPS (X-ray photoelectron spectroscopy), and its thickness is 2 - 5 nm. In this way, a catalyst semi-finished product with a Pr6O 11 coating layer is made; During the deposition process, the atmosphere and pressure in the tubular furnace are controlled to ensure the stability and uniformity of the deposition process;

[0026] 4. Impregnating alkali metal promoters: The catalyst semi-finished product with a Pr6O 11 coating layer is impregnated in a KNO3 or NaNO3 solution, and the loading amount is controlled at 1 - 3 wt%, and the impregnation time is 6 h, and then dried at 80 °C for 12 h. The dried product is placed in a muffle furnace again and calcined at 400 °C for 2 h to obtain the final catalyst product.

[0027] Application conditions: The catalyst of the present invention is suitable for the tail gas environment of an iron ore sintering machine with a temperature range of 150 - 400 °C, containing SO2 (50 - 200 ppm) and H2O (5 - 15%).

[0028] The catalyst disclosed in the present invention has obtained the following beneficial effects in its specific application. Specifically, it includes:

[0029] (1) High efficiency at low temperature: At a temperature of 200 °C, the CO conversion rate of the catalyst of the present invention is ≥90%. Compared with the traditional Fe-Cu catalyst, the conversion rate is increased by more than 20%. This means that under the same low-temperature working conditions, the catalyst of the present invention can more effectively oxidize CO in the tail gas of an iron ore sintering machine, reduce CO emissions, improve energy utilization efficiency, and reduce subsequent treatment costs.

[0030] (2) Strong sulfur resistance: After continuous operation in sulfur-containing flue gas for 100 hours, the activity loss of the catalyst of the present invention is less than 5%. This performance is significantly better than other catalysts in the prior art, and it can operate stably for a long time in the complex sintering flue gas environment containing sulfur and high humidity, greatly extending the service life of the catalyst and reducing the economic cost and operation complexity caused by frequent replacement due to catalyst deactivation.

[0031] (3) Low cost: The present invention abandons expensive noble metals and uses inexpensive rare earths and transition metal oxides as raw materials, reducing the raw material cost by 80 - 90%. This cost advantage makes the catalyst of the present invention have higher feasibility and economic benefits in large-scale industrial applications, can effectively reduce the environmental protection investment burden of iron and steel enterprises, and promote the green and sustainable development of the iron and steel industry.

[0032] This invention is based on principle conceptions and repeated experiments, and creative labor has been paid, including:

[0033] Rare earth-transition metal synergistic effect: CeO2 has excellent oxygen storage capacity and can quickly provide and consume oxygen in redox reactions, creating favorable conditions for the CO oxidation reaction. The addition of La2O3 further improves the thermal stability and sulfur resistance of the carrier, enhancing the overall structural stability of the catalyst. The composite oxide composed of Mn3O4, Fe2O3 and CuO as the active component enhances the oxidation activity of the catalyst at low temperature through the synergistic effect between multiple metals. Different metal ions can promote electron transfer with each other during the reaction process, optimize the reaction path, and reduce the reaction activation energy, thus achieving efficient CO oxidation at low temperature.

[0034] Nanocoating technology: Pr6O 11 The introduction of the nanocoating layer is one of the key technologies for the present invention to improve the sulfur resistance of the catalyst. Pr6O 11 has high chemical stability and can effectively isolate the contact between SO2 and the active component in a sulfur-containing environment, preventing the active component from being poisoned. Its nanoscale thickness can not only ensure good isolation effect but also not cause obvious hindrance to the diffusion of reactants and products, ensuring the continuous and efficient operation of the catalyst in sulfur-containing flue gas.

[0035] Function of alkali metal promoters: The introduction of K2O or Na2O as alkali metal promoters can adjust the surface acidity and basicity of the catalyst. In a sulfur-containing flue gas environment, SO2 will react with the catalyst surface to generate acidic substances, and the alkali metal promoters can neutralize these acidic substances to prevent them from poisoning the active component, further enhancing the sulfur resistance of the catalyst. At the same time, the presence of alkali metal promoters can also optimize the active sites on the catalyst surface, promote the adsorption and activation of CO, and thus improve the low-temperature activity of the catalyst. Detailed implementation mode

[0036] Example 1:

[0037] (1) Prepare the CeO2-La2O3 composite oxide support: Weigh Ce(NO3)6H2O and La(NO3)6H2O according to the molar ratio of 3:1, dissolve them in deionized water, add ammonia water to adjust the pH = 9, dry at 120 °C after precipitation, and calcine at 550 °C for 4 h to obtain the CeLaO2 support. 3· 6H2O and La(NO3) 3· 6H2O, add ammonia water to adjust the pH = 9, dry at 120 °C after precipitation, and calcine at 550 °C for 4 h to obtain the CeLaO2 support. 0.75 La 0.25 O2 support.

[0038] (2) Load the active components: Immerse the support in a mixed solution of Mn(NO3)2, Fe(NO3)3, and Cu(NO3)2 (molar ratio 4:3:1), dry and then calcine at 500 °C for 3 h to obtain the Mn3O4-Fe2O3-CuO active phase.

[0039] (3) Generate the Pr6O 11 coating layer: Pass Pr(NO3)3 vapor into the tubular furnace and deposit it at 350 °C for 2 h to form the Pr6O 11 coating layer, and the thickness of the coating layer is 4 nm.

[0040] (4) Impregnate with alkali metal promoters: Impregnate with the KNO3 solution, dry and then calcine at 400 °C for 2 h to obtain the final catalyst.

[0041] Example 2:

[0042] (1) Prepare the CeO2-La2O3 support: Weigh Ce(NO3)3·6H2O and La(NO3)3·6H2O (molar ratio 1:1), dissolve them in deionized water, add ammonia water to adjust the pH = 9, dry at 120 °C after precipitation, and calcine at 550 °C for 4 h to obtain the CeLaO2 support. 0.5 La 0.5 O2 support.

[0043] (2) Load the active components: Immerse the support in a mixed solution of Mn(NO3)2, Fe(NO3)3, and Cu(NO3)2 (molar ratio 4:3:1), dry and then calcine at 500 °C for 3 h to obtain the Mn3O4-Fe2O3-CuO active phase.

[0044] (3) Generate the Pr6O 11 coating layer: Pass Pr(NO3)3 vapor into the tubular furnace and deposit it at 350 °C for 2 h to form the Pr6O 11 coating layer, and the thickness of the generated coating layer is 3 nm.

[0045] (4) Impregnation with alkali metal promoter: Impregnate with NaNO3 solution, calcine at 400 °C for 2 h after drying to obtain the final catalyst.

[0046] Example 3:

[0047] (1) Preparation of CeO2-La2O3 support: Weigh Ce(NO3)3·6H2O and La(NO3)3·6H2O (molar ratio 2:1), dissolve in deionized water, add ammonia water to adjust pH = 9, after precipitation, dry at 120 °C and calcine at 550 °C for 4 h to obtain Ce 0.66 La 0.34 O2 support.

[0048] (2) Loading of active components: Immerse the support in a mixed solution of Mn(NO3)2, Fe(NO3)3, and Cu(NO3)2 (molar ratio 4:3:1), dry and calcine at 500 °C for 3 h to obtain the Mn3O4-Fe2O3-CuO active phase.

[0049] (3) Formation of Pr6O 11 coating layer: Pass Pr(NO3)3 vapor into a tubular furnace and deposit at 350 °C for 2 h to form Pr6O 11 coating layer with a thickness of 4 nm.

[0050] (4) Impregnation with alkali metal promoter: Impregnate with NaNO3 solution, calcine at 400 °C for 2 h after drying to obtain the final catalyst.

[0051] Example 4:

[0052] (1) Preparation of CeO2-La2O3 support: Weigh Ce(NO3)3·6H2O and La(NO3)3·6H2O (molar ratio 3:1), dissolve in deionized water, add ammonia water to adjust pH = 9, after precipitation, dry at 120 °C and calcine at 550 °C for 4 h to obtain Ce 0.75 La 0.25 O2 support, which is the same as the support in Example 1.

[0053] (2) Loading of active components: Similar to Example 1, immerse the support in a mixed solution of Mn(NO3)2, Fe(NO3)3, and Cu(NO3)2 (molar ratio 4:3:1), dry and calcine at 500 °C for 3 h to obtain the Mn3O4-Fe2O3-CuO active phase.

[0054] (3) Formation of Pr6O 11 coating layer: Pass Pr(NO3)3 vapor into a tubular furnace and deposit at 350 °C for 3 h to form a Pr6O coating layer with a thickness of about 4 nm 11 coating layer with a thickness of 5 nm.

[0055] (4) Impregnation with alkali metal promoter: Impregnate with KNO3 solution, control the loading amount at 1 - 3 wt%, the impregnation time is 6 h, and then dry at 80 °C for 12 h. The dried sample is put into a muffle furnace again and calcined for the second time at 400 °C for 2 h to obtain the final catalyst.

Claims

1. A catalyst for low-temperature oxidation treatment of sintering flue gas CO, characterized in that: Includes the following components: (1) a CeO2-La2O3 composite oxide support, wherein the molar ratio of Ce to La in the support is 1:1 to 3:1, accounting for 50-70 wt% of the total mass of the catalyst; (2) an active component, a ternary transition metal oxide of Mn3O4-Fe2O3-CuO, wherein the molar ratio of Mn:Fe:Cu is 4:3:1, and accounts for 20-40 wt% of the total mass of the catalyst; (3) Anti-sulfur layer: Pr6O with a thickness of 2-5 nm 11 Nano coating layer, accounting for 5-15wt% of the total mass of the catalyst; (4) Alkali metal promoter: K2O or Na2O, with a loading amount of 1-3 wt% of the total mass of the catalyst.

2. The catalyst for low-temperature oxidation treatment of sintering flue gas CO according to claim 1, characterized in that: In the CeO2-La2O3 composite oxide, the molar ratio of Ce to La is 3:

1.

3. The catalyst for low-temperature oxidation treatment of sintering flue gas CO according to claim 1, characterized in that: The Pr6O 11 The thickness of the nano-coating layer is 4 nm.

4. The catalyst for low-temperature oxidation treatment of sintering flue gas CO according to claim 1, characterized in that: The alkali metal auxiliary agent is K2O, and the loading amount is 2 wt%.

5. A method for preparing a catalyst for low-temperature oxidation treatment of sintering flue gas CO, characterized in that: The following steps are involved: (1) Preparation of CeO2-La2O3 composite oxide support by co-precipitation method: Ce(NO3)3·6H2O and La(NO3)3·6H2O were dissolved in a set molar ratio, and the pH was adjusted to 9. After the precipitation reaction was completed, the precipitate was filtered and repeatedly washed with deionized water to remove impurity ions. The washed precipitate was then placed in an oven and dried at 120°C for 12 hours. Finally, it was placed in a muffle furnace and calcined at 550°C for 4 hours to obtain a CeO2-La2O3 composite oxide support. (2) Loading active components by impregnation method: The active components are loaded by impregnation method: the prepared CeO2-La2O3 composite oxide support is impregnated in a mixed solution of Mn(NO3)2, Fe(NO3)3, and Cu(NO3)2 prepared in a molar ratio of Mn:Fe:Cu of 4:3:1, ensuring that the CeO2-La2O3 composite oxide support is fully impregnated. The impregnation time is 12 hours, so that the metal ions are fully adsorbed on the surface of the CeO2-La2O3 composite oxide support. After the impregnation is completed, it is taken out and dried at 80°C for 12 hours, then placed in a muffle furnace and calcined at 500°C for 3 hours to prepare a catalyst matrix loaded with Mn3O4-Fe2O3-CuO active components; (3) Generating Pr6O by vapor deposition 11 Coating layer: The catalyst substrate loaded with Mn3O4-Fe2O3-CuO active components is placed in a tube furnace, and Pr(NO3)3 vapor is introduced and deposited at 350℃ for 2-3h to decompose and deposit Pr(NO3)3 vapor on the surface of the catalyst substrate loaded with Mn3O4-Fe2O3-CuO active phase to form Pr6O 11 Nano-coating layer, thus made with Pr6O 11 Catalyst semi-finished product with coating layer; (4) Impregnation of alkali metal additives: 11 The catalyst semi-finished product with coating layer is immersed in KNO3 or NaNO3 solution, the loading amount is controlled at 1-3wt%, the immersion time is 6h, and then dried at 80℃ for 12h. The dried product is put into muffle furnace again and calcined for 2h at 400℃ to obtain the final catalyst product.

6. The method for preparing a catalyst for low-temperature oxidation treatment of sintering flue gas CO according to claim 5, characterized in that The vapor deposition time in step (3) is 3 hours.

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