Catalyst for removing nitrogen oxides and preparation method thereof

Abstract

The invention discloses a catalyst for removing nitrogen oxides and a preparation method thereof, the catalyst for removing nitrogen oxides comprises coal gangue and cerium salt, the cerium salt is loaded on the coal gangue through an impregnation method and calcination decomposition in sequence, and the cerium element introduced by the cerium salt accounts for more than or equal to 5% of the weight of the coal gangue. The Ce / coal gangue catalyst is prepared by directly taking the aluminum-rich coal gangue as a carrier, and solid wastes are directly utilized, so that the activity and high-temperature selectivity of the catalyst are improved, and the cost of the catalyst is greatly reduced.

Description

Technical Field

[0001] This invention relates to a catalyst for removing nitrogen oxides, and also to a method for preparing the catalyst. Background Technology

[0002] Coal gangue is an industrial solid waste generated during coal mining and washing. Typically, 0.15 to 0.25 tons of coal gangue are produced per ton of coal produced. Large-scale accumulation of coal gangue not only occupies significant land resources, but the heavy metals it contains also pollute surface and groundwater resources, posing a serious threat to the ecological environment and human health. The main components of coal gangue are SiO2 and Al2O3, along with small amounts of CaO, MgO, Fe2O3, and heavy metals. Direct resource utilization of coal gangue is difficult to achieve at a high added value; acid leaching and the addition of additives are necessary to realize its high-value-added resource utilization.

[0003] Nitrogen oxides (NO) x NO is a collective term for five common nitrogen oxides. Flue gas from coal-fired power plants contains large amounts of NO. x In existing technologies, NO in the flue gas of coal-fired power plants x The removal of [the substance] mainly employs selective catalytic reduction (SCR), with the commercially available catalyst being V₂O₅-WO₃(MoO₃) / TiO₂. However, this catalyst is relatively expensive (20,000-30,000 RMB / m³). 3 Vanadium exhibits low high-temperature selectivity, poor thermal stability, and is biotoxic, easily leading to secondary pollution. Furthermore, its active temperature window is unsuitable for flue gas denitrification below 300℃, such as in industries like cement kilns and glass furnaces.

[0004] CN 102814192A discloses a cerium / molecular sieve catalyst for selective catalytic reduction of nitrogen oxides and its preparation. The catalyst, formed by supporting cerium oxide nanoparticles on a molecular sieve, exhibits the widest temperature window and the best denitrification performance. Similarly, coal gangue possesses excellent adsorption properties and a well-developed pore structure. In particular, its high Al2O3 content gives it good anti-sintering ability and strong thermal stability, making it suitable as a catalyst support. Using aluminum-rich coal gangue as a support, NO2O3 can be prepared... x Removing catalysts holds promise for solid waste recycling. The scheme in CN 102814192A indicates that reducing the silica-alumina ratio in molecular sieves is detrimental to broadening the catalyst's temperature window. Therefore, how to prepare a catalyst for NO removal using coal gangue as a carrier is a key research area. x Removing the catalyst is a problem that needs to be solved. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide a catalyst for removing nitrogen oxides, using coal gangue as a carrier, thereby reducing the cost of catalyst raw materials; another purpose of this invention is to provide a method for preparing the catalyst for removing nitrogen oxides.

[0006] Technical solution: The catalyst for removing nitrogen oxides according to the present invention includes coal gangue and cerium salt. The cerium salt is loaded onto the coal gangue by impregnation and calcination decomposition in sequence. The proportion of cerium element introduced by the cerium salt to the weight of the coal gangue is ≥5%.

[0007] Preferably, to improve high-temperature selectivity, the cerium element introduced by the cerium salt accounts for 15% to 30% of the weight of the coal gangue. More preferably, the cerium element introduced by the cerium salt accounts for 18% to 25% of the weight of the coal gangue.

[0008] Preferably, the Al2O3 content in the coal gangue is 15% to 50%. More preferably, the Al2O3 content in the coal gangue is 30% to 48%. Most preferably, the aluminum content in the coal gangue is 40% to 48%.

[0009] Preferably, to avoid introducing heteroatoms that are difficult to remove, the cerium salt is a water-soluble cerium salt, and the cerium salt is one or a mixture of cerium chloride, cerium acetate, cerium sulfate, and cerium oxalate.

[0010] The aforementioned method for preparing the catalyst for removing nitrogen oxides includes the following steps:

[0011] (1) Take coal gangue, grind it, and calcine it to obtain coal gangue carrier;

[0012] (2) Weigh out the coal gangue carrier and cerium salt according to the proportion, mix with water, dissolve the cerium salt, and dry;

[0013] (3) The sample after calcination and drying at a temperature above the decomposition temperature of cerium salt is used to obtain a catalyst for removing nitrogen oxides.

[0014] In step (1), the purpose of calcination is to remove organic impurities from the coal gangue solid waste and expand its internal pore size. There are no strict limitations on the temperature and duration. Calcination can be carried out at a lower temperature, such as 600°C, or at a higher temperature, such as 950°C. Preferably, the calcination temperature is 700–900°C, and the calcination duration is 1.5–3 hours.

[0015] In step (2), the purpose of mixing with water is to dissolve the cerium salt and improve its dispersibility, and the purpose of drying is to remove water. Preferably, the drying temperature is 60–120°C.

[0016] In step (2), the main purpose of calcination is to partially decompose the cerium salt to form cerium oxide (CeO2). This calcination step must be carried out above the decomposition temperature of the cerium salt. Preferably, the calcination temperature is 400–600°C, and the calcination duration is 2.5–4 hours.

[0017] Beneficial Effects: Compared with existing technologies, this invention has the following significant advantages: 1. Reduced Costs: Ce / coal gangue catalyst is prepared directly using aluminum-rich coal gangue as a carrier, utilizing solid waste and significantly reducing costs; 2. Simple Preparation Method: Water-soluble cerium salts are used directly, employing a simple impregnation method and calcination decomposition to prepare the catalyst, eliminating the need for other precipitants, dispersants, organic solvents, and pre-forming cerium salts into nanoparticles, simplifying the catalyst preparation process; 3. High Catalyst Activity and Wide Temperature Range: Denitrification efficiency exceeds 80% in the temperature range of 270–420℃ and exceeds 90% in the temperature range of 300–420℃; 4. Low Metal Dosage and High Selectivity: Introducing 20% ​​cerium element by mass of coal gangue results in 100% selectivity for the Ce / coal gangue catalyst across the entire temperature range. Attached Figure Description

[0018] Figure 1 The graphs show the performance test curves of different catalyst samples prepared in the embodiments of the present invention. Detailed Implementation

[0019] The technical solution of the present invention will be further described below with reference to the accompanying drawings. In the following embodiments, the chemical composition of the coal gangue used is shown in Table 1 below:

[0020] Table 1: Chemical composition of coal gangue samples

[0021]

[0022] Example 1: Preparation of catalyst sample, the steps are as follows:

[0023] (1) Take coal gangue solid waste for pretreatment: grind it into powder with a particle size of about 200-300 mesh, then place it in a muffle furnace and calcine it at 800℃ for 2 hours to prepare coal gangue carrier.

[0024] (2) Weigh 8g of coal gangue carrier and 1.240g of cerium nitrate hexahydrate into a beaker and add 100mL of deionized water. Stir for 1 hour at 25℃ and 800 rpm to dissolve the cerium nitrate hexahydrate. After standing, put it into an oven and dry at 105℃.

[0025] (3) Collect the dried sample and calcine it in a muffle furnace at 500°C for 3 hours to obtain the catalyst product. The amount of cerium element (relative atomic mass 140.11) introduced by cerium nitrate hexahydrate in the catalyst product is about 0.4g, accounting for 5% of the mass of coal gangue. The catalyst sample is labeled as 5Ce / coal gangue.

[0026] The preparation methods of Examples 2 to 4 are similar to those of Example 1, except that in step (2), the amount of cerium nitrate hexahydrate added is 2.481 g, 3.721 g, and 4.963 g, respectively, and the catalyst samples obtained are recorded as 10Ce / coal gangue, 15Ce / coal gangue, and 20Ce / coal gangue, respectively.

[0027] The catalytic performance of the catalyst samples prepared in Examples 1-4 was tested. The specific test method was as follows: each catalyst was placed in a fixed-bed reactor, and the composition of the reaction gas was 600 ppm NO (volume ratio). x 600ppm NH3, 3% O2, N2 as balance gas, total gas flow rate 1500ml / min, GHSV 18000h -1 The reaction temperature range was from 120℃ to 420℃, and the NO concentration at the inlet and outlet was monitored to investigate the denitrification efficiency.

[0028] Figure 1 This refers to the denitrification efficiency and selectivity of different catalysts. From Figure 1 (a) It can be seen that the denitrification efficiency of the coal gangue carrier is very low throughout the entire temperature test range, with the highest efficiency being only about 10%. When the Ce loading is increased to 5%, the denitrification efficiency increases sharply; when the Ce loading is further increased to 10% and 15%, the denitrification efficiency continues to increase; when the Ce loading is increased to 20%, the denitrification efficiency reaches its maximum, exceeding 80% in the temperature range of 270-420℃ and exceeding 90% in the temperature range of 300-420℃, demonstrating excellent denitrification performance.

[0029] Figure 1 (b) shows the N2O generation during the denitrification process using different catalysts. As can be seen from the figure, below 300℃, the selectivity differences among them are not significant, and all are relatively low. However, as the reaction temperature continues to increase, significant differences in selectivity emerge. Among them, the coal gangue support alone produces the most N2O, but has the worst selectivity. With the gradual increase in Ce loading and loading amount, the selectivity gradually increases, especially with 20Ce / coal gangue exhibiting the strongest selectivity, where the N2O generation is 0 and the selectivity is 100% throughout the entire reaction temperature range. The results indicate that the Ce-coal gangue catalyst prepared using simply treated coal gangue as a support possesses high catalytic activity and selectivity, and can be efficiently applied to NO… xThe removal of waste achieves the goal of treating waste with waste.

Claims

1. A catalyst for removing nitrogen oxides, characterized in that, It includes coal gangue and cerium salts, wherein the cerium salts are loaded onto the coal gangue through impregnation and calcination decomposition in sequence, and the cerium element introduced by the cerium salts accounts for ≥5% of the weight of the coal gangue.

2. The catalyst for removing nitrogen oxides according to claim 1, characterized in that, The cerium element introduced by cerium salts accounts for 15-30% of the weight of coal gangue.

3. The catalyst for removing nitrogen oxides according to claim 1, characterized in that, The Al2O3 content in the coal gangue is 15-50%.

4. The catalyst for removing nitrogen oxides according to claim 3, characterized in that, The Al2O3 content in the coal gangue is 30-48%.

5. The catalyst for removing nitrogen oxides according to claim 1, characterized in that, The cerium salt is one or a mixture of cerium chloride, cerium acetate, cerium sulfate, and cerium oxalate.

6. A method for preparing the catalyst for removing nitrogen oxides according to any one of claims 1 to 5, characterized in that, Includes the following steps: (1) Take coal gangue, grind it, and calcine it to obtain coal gangue carrier; (2) Weigh out the coal gangue carrier and cerium salt according to the proportion, mix with water, dissolve the cerium salt, and dry; (3) The sample after calcination and drying at a temperature above the decomposition temperature of cerium salt is used to obtain a catalyst for removing nitrogen oxides.

7. The method for preparing the catalyst for removing nitrogen oxides according to claim 6, characterized in that, In step (1), the calcination temperature is 700-900℃ and the calcination duration is 1.5-3 hours.

8. The method for preparing the catalyst for removing nitrogen oxides according to claim 6, characterized in that, In step (2), the drying temperature is 60 to 120°C.

9. The method for preparing the catalyst for removing nitrogen oxides according to claim 6, characterized in that, In step (3), the calcination temperature is 400-600℃ and the calcination duration is 2.5-4 hours.

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