A multi-layer structure broad-spectrum catalyst for formaldehyde industrial tail gas treatment and a preparation method thereof

Abstract

The application discloses a kind of multilayer structure broad-spectrum catalyst for formaldehyde industry tail gas treatment and preparation method thereof, belong to catalyst technical field.The catalyst uses " carrier-cerium oxide-palladium-zirconium oxide " multilayer structure: with ceramic particles as carrier, load cerium oxide as oxygen storage inner layer, palladium as active middle layer and zirconium oxide protective outer layer;With the total mass of catalyst: palladium 0.01%~0.5%, cerium oxide and zirconium oxide total 1%~10%, the rest is ceramic particle, and the mass ratio of cerium oxide and zirconium oxide is 1:4~4:1;Corresponding source solution or slurry is atomized and sprayed using rolling ball method, and is prepared by drying and calcination.The catalyst has the characteristics of low noble metal consumption, high activity, wide temperature window, good water vapor resistance and stability, can simultaneously and efficiently catalyze removal of carbon monoxide, hydrogen, formaldehyde, methanol, dimethyl ether, methane and other complex components in formaldehyde industry tail gas, suitable for high air speed (10000~50000 h ‑1 ) harsh conditions, simple process, easy industrial production.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to a particulate, multilayered, broad-spectrum catalyst for treating exhaust gases from industrial plants producing formaldehyde, polyoxymethylene, phenolic resins, etc., and its preparation method. Background Technology

[0002] Formaldehyde is a widely used basic organic chemical raw material. Its industrial production is mainly achieved through methanol oxidative dehydrogenation, with mainstream processes including silver catalysis and iron-molybdenum catalysis. Newer projects have a higher proportion of iron-molybdenum processes. The exhaust gas emitted from industrial plants is complex, typically consisting of: carbon monoxide (approximately 1.5%), methanol (approximately 0.1%), formaldehyde (approximately 0.1%), formic acid (approximately 0.1%), dimethyl ether (approximately 0.4%), methane (approximately 0.1%), hydrogen (approximately 0.3%), and water vapor (approximately 2%). Direct emission of this exhaust gas would cause serious environmental pollution. Industrially, catalytic combustion is the primary method for treating formaldehyde industrial waste gas. This method involves preheating the exhaust gas and then, under the action of a catalyst, causing the organic components to undergo a deep oxidation reaction with oxygen, producing harmless carbon dioxide and water. Waste heat is recovered to achieve a self-sustaining reaction. Therefore, developing efficient, stable, and economical catalytic combustion catalysts is crucial for achieving compliant emissions and energy conservation in the formaldehyde industrial sector.

[0003] A series of studies have been conducted on catalysts for treating formaldehyde industrial tail gas. For example, Chinese patent application CN119158608A discloses a highly active monolithic catalyst for purifying formaldehyde production tail gas. It uses cordierite honeycomb ceramic as the matrix, supports a nitrogen-doped carrier, and the active component is Pt or Pd, with In2O3 as the auxiliary agent. This monolithic catalyst reduces bed pressure drop to some extent. However, formaldehyde industrial tail gas treatment devices mainly use small-sphere catalyst packing, resulting in a low proportion of monolithic catalyst reactors and thus limited catalyst adaptability. Chinese patent application CN120169348A discloses a catalyst for treating tail gas from the iron-molybdenum methanol oxidation process to formaldehyde. It uses two different sizes of γ-Al2O3 spherical particles as the carrier, combined with dispersants and auxiliary agents. Precious metals are loaded using a conventional equal-volume impregnation method and packed in a non-uniform manner, achieving efficient and low-cost tail gas treatment. However, this catalyst lacks protection for the active centers of precious metals, its long-term stability cannot be guaranteed, and the amount of precious metals used remains relatively high. Chinese patent application CN121244248A discloses a low-temperature activated hydrothermal stable formaldehyde production tail gas purification catalyst, which uses activated alumina as a support, supports La2O3 and SrO as active agents, and borophosphate as a hydrothermal stabilizing agent. The catalyst has been optimized in terms of activation temperature and hydrothermal stability, but its preparation method is too complicated and not conducive to industrialization.

[0004] In summary, existing formaldehyde industrial tail gas treatment catalysts still have the following technical problems: (1) reactor compatibility issues, with most current devices using granular catalysts; (2) granular catalysts often employ co-impregnation, lacking protection and functional design for active centers; (3) most catalysts struggle to balance low cost with high activity and excellent stability, making it difficult to achieve broad-spectrum and efficient purification of multiple components such as carbon monoxide, hydrogen, formaldehyde, methanol, dimethyl ether, and methane under harsh high-space-velocity conditions. Therefore, developing a novel catalyst that combines low precious metal usage, high activity, high stability, and broad-spectrum purification capability has significant industrial application value. Summary of the Invention

[0005] This invention aims to overcome the technical challenge of balancing low dosage with high activity and high stability in existing precious metal catalysts. It provides a granular catalytic combustion catalyst with low precious metal content, wide operating temperature window, long service life, water vapor resistance, and broad-spectrum purification capabilities, as well as a simple preparation method, to efficiently treat complex formaldehyde industrial exhaust gas.

[0006] To achieve the above objectives, the catalyst used in this invention is granular, with high specific surface area ceramic particles as the support. A unique layered sandwich structure is employed, in which three functional films are sequentially constructed on the support surface: the inner layer is an oxygen storage layer composed of cerium oxide, which utilizes its excellent oxygen storage and release capabilities to adjust the oxygen concentration on the catalyst surface, enhance the oxidation activity of organic components, and improve the catalyst's adaptability under fluctuating operating conditions; the middle layer is an active layer loaded with the noble metal palladium, serving as the main catalytic active center, efficiently activating CH, OH, and other bonds, initiating and promoting deep oxidation reactions of various organic compounds; the outer layer is an anti-poisoning and stabilizing layer composed of zirconium oxide, which has good thermal stability and anti-sintering ability, providing physical protection and isolation for the internal palladium active sites, inhibiting the aggregation and deactivation of active components at high temperatures, and simultaneously enhancing the catalyst's tolerance to potential poisons in complex components.

[0007] The catalysts described above, based on their total mass, consist of: 0.01% to 0.5% palladium, 1% to 10% cerium oxide and zirconium oxide combined, and the remainder being ceramic particles, with a mass ratio of cerium oxide to zirconium oxide of 1:4 to 4:1.

[0008] Furthermore, based on the total mass of the catalyst, the preferred composition of the catalyst is: 0.05% to 0.2% palladium, 2% to 5% cerium oxide and zirconium oxide combined, and the remainder being ceramic particles, with the mass ratio of cerium oxide to zirconium oxide being 1:3 to 3:1.

[0009] Furthermore, the aforementioned ceramic particles are one or more of alumina particles, silica particles, and molecular sieve particles.

[0010] The multilayer broad-spectrum catalyst provided by this invention is prepared by layer-by-layer spraying using the rolling ball method, and includes the following steps:

[0011] Step 1: Atomize and spray the cerium source solution or slurry onto the rolling ceramic particles, wet them evenly, and then dry them.

[0012] Step 2: Atomize and spray the palladium source solution or dispersion onto the particles obtained in Step 1, wet them evenly, and then dry them.

[0013] Step 3: Atomize and spray the zirconium source solution or slurry onto the particles obtained in Step 2, wet them evenly, dry them, and calcine them at 500-600 °C for 2-6 h to obtain the catalyst.

[0014] Furthermore, the cerium source and zirconium source are independently selected from one or more of their corresponding soluble salts, oxide sols, and nano-oxide powders; the palladium source is selected from one or more of palladium nitrate, chloropalladic acid, and palladium sol. When using nano-oxide powders as cerium and zirconium sources, stabilizers need to be added and the powders need to be prepared into solid particles with a particle size D. 90 Spraying is performed after the stabilized slurry with a thickness of ≤ 5 μm is formed; the stabilizer is selected from one or more of cellulose stabilizers, sugar stabilizers, and polymer stabilizers. Specific examples include: hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, polyethylene glycol, polyvinyl alcohol, polyacrylic acid, xanthan gum, guar gum, dextran, etc.

[0015] Furthermore, in step 2 above, the palladium source is pre-reduced by mixing with a reducing agent before spraying. The reduction temperature is 60–200°C, and the reduction time is 1–4 h. The reducing agent is selected from one or more of polyols, organic acids, and hydrazine hydrate, specifically such as methanol, ethanol, propanol, ethylene glycol, glycerol, polyethylene glycol, ascorbic acid, citric acid, oxalic acid, glucose, and hydrazine hydrate.

[0016] This invention provides a multilayered, broad-spectrum catalyst suitable for high-space-velocity catalytic combustion of tail gas from formaldehyde industrial plants. The tail gas contains one or more components selected from carbon monoxide, hydrogen, methane, formaldehyde, methanol, dimethyl ether, and water vapor, with a reaction space velocity of 10,000–50,000 h⁻¹. -1 .

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. This invention constructs a sandwich structure on the surface of a ceramic particle carrier, consisting of an inner cerium oxide layer (oxygen storage layer), an intermediate palladium layer (active layer), and an outer zirconium oxide layer (protective layer). This effectively improves the utilization rate of the catalyst surface and active sites. Furthermore, the surface oxygen regulation capability of the inner cerium oxide layer and the protective isolation of the middle palladium layer by the outer zirconium oxide layer effectively suppress palladium sintering and agglomeration at high temperatures, significantly enhancing the long-term stability of the catalyst under harsh conditions of humidity and high temperature. Through layered functional design, the synergistic effect of each layer is fully utilized, resulting in a low amount of precious metal palladium. Simultaneously, the catalyst exhibits excellent catalytic oxidation performance for various components in formaldehyde industrial exhaust gas, including carbon monoxide, hydrogen, formaldehyde, methanol, dimethyl ether, and methane, with low conversion temperatures for each component, demonstrating good broad-spectrum purification capabilities.

[0019] 2. The catalyst of this invention is in granular form and is prepared by layer-by-layer spraying using a rolling ball method. The process is simple and easy to scale up for production. The catalyst has a shelf life of 10,000–50,000 h. -1 It can maintain high activity and stability even under high air velocity conditions, meeting the actual working conditions of formaldehyde industrial plant exhaust gas treatment.

[0020] 3. This invention employs a rolling ball method for layer-by-layer atomization spraying, requiring no complex equipment and simplifying operation. Common industrial raw materials can be used for cerium, zirconium, and palladium sources, ensuring cost control. When using nano-oxide powders, the uniformity and stability of the multi-layer structure are ensured by adding dispersants and controlling the slurry particle size. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the present invention clearer, the implementation methods of the present invention will be described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited thereto.

[0022] Example 1

[0023] Step 1: Prepare a 50 mL solution by adding 2.52 g of cerium nitrate hexahydrate to water, and spray it onto 95.9 g of γ-alumina balls with a particle size of 3-5 mm in a sugar coating machine. After uniform wetting, dry at 100 ℃ to obtain single-layer coated particles.

[0024] Step 2: Dilute 1.00 g of 10% palladium nitrate solution with water to 50 mL, and spray it onto the single-layer coated particles in the sugar coating machine through atomization. After uniform wetting, dry at 100 °C to obtain double-layer coated particles.

[0025] Step 3: 10.44 g of zirconium nitrate pentahydrate was dissolved in water to prepare a 50 mL solution. This solution was then atomized and sprayed onto the double-layer coated particles in a sugar coating machine. After uniform wetting, the particles were dried at 100 °C to obtain triple-layer coated particles. These particles were then calcined at 500 °C for 2 h to obtain the catalyst. Based on the total mass of the catalyst, the composition of the obtained catalyst was: 95.9% γ-alumina spheres, 1% cerium oxide, 0.1% palladium, and 3% zirconium oxide, denoted as A@Ce@Pd. 0.1 @Zr3.

[0026] Example 2

[0027] Step 1: The amount of cerium nitrate hexahydrate was changed to 5.05 g, and the rest was the same as in Example 1.

[0028] Step 2: Same as Example 1.

[0029] Step 3: The amount of zirconium nitrate pentahydrate was changed to 6.96 g, and the rest was the same as in Example 1. Based on the total mass of the catalyst, the composition of the obtained catalyst was: 95.9% γ-alumina spheres, 2% cerium oxide, 0.1% palladium, and 2% zirconium oxide, denoted as A@Ce2@Pd 0.1 @Zr2.

[0030] Example 3

[0031] Step 1: The amount of cerium nitrate hexahydrate was changed to 7.57 g, and the rest was the same as in Example 1.

[0032] Step 2: Same as Example 1.

[0033] Step 3: The amount of zirconium nitrate pentahydrate was changed to 3.48 g, and the rest was the same as in Example 1. Based on the total mass of the catalyst, the composition of the obtained catalyst was: 95.9% γ-alumina spheres, 3% cerium oxide, 0.1% palladium, and 1% zirconium oxide, denoted as A@Ce3@Pd 0.1 @Zr.

[0034] Example 4

[0035] Step 1: The amount of γ-alumina balls with a particle size of 3-5 mm was changed to 95.95 g, and the rest was the same as in Example 3.

[0036] Step 2: The amount of palladium nitrate solution with a mass concentration of 10% was changed to 0.50 g, and the rest was the same as in Example 1.

[0037] Step 3: Same as Example 3. Based on the total mass of the catalyst, the composition of the obtained catalyst is: 95.95% γ-alumina spheres, 3% cerium oxide, 0.05% palladium, and 1% zirconium oxide, denoted as A@Ce3@Pd 0.05 @Zr.

[0038] Example 5

[0039] Step 1: The amount of γ-alumina balls with a particle size of 3-5 mm was changed to 95.99 g, and the rest was the same as in Example 3.

[0040] Step 2: The amount of palladium nitrate solution with a mass concentration of 10% was changed to 0.10 g, and the rest was the same as in Example 1.

[0041] Step 3: Same as Example 3. Based on the total mass of the catalyst, the composition of the obtained catalyst is: γ-alumina spheres 95.99%, cerium oxide 3%, palladium 0.01%, and zirconium oxide 1%, denoted as A@Ce3@Pd 0.01 @Zr.

[0042] Example 6

[0043] Step 1: The amount of cerium nitrate hexahydrate was changed to 3.79 g, and the amount of alumina balls with a particle size of 3-5 mm was changed to 97.9 g. The rest was the same as in Example 1.

[0044] Step 2: Same as Example 1.

[0045] Step 3: The amount of zirconium nitrate pentahydrate was changed to 1.74 g, and the rest was the same as in Example 1. Based on the total mass of the catalyst, the composition of the obtained catalyst was: 97.9% γ-alumina spheres, 1.5% cerium oxide, 0.1% palladium, and 0.5% zirconium oxide, denoted as A@Ce. 1.5 @Pd 0.1 @Zr 0.5 .

[0046] Example 7

[0047] Step 1: Same as Example 3.

[0048] Step 2: Mix 1.00 g of 10% chloropalladic acid solution, 1.00 g of ethylene glycol, and 5.00 g of ethanol evenly, reduce at 80 ℃ for 2 h, add water to prepare a 50 mL solution and ultrasonically disperse evenly. Spray the solution onto the single-layer coated particles in the sugar coating machine through atomization. After even wetting, dry at 100 ℃ to obtain double-layer coated particles.

[0049] Step 3: Same as Example 3. Based on the total mass of the catalyst, the composition of the obtained catalyst is: 95.9% γ-alumina spheres, 3% cerium oxide, 0.1% palladium, and 1% zirconium oxide, denoted as A@Ce3@r-Pd 0.1 @Zr.

[0050] Example 8

[0051] Step 1: Same as Example 3.

[0052] Step 2: Spray 50 g of commercially available nano-palladium sol (<10 nm, mass concentration 0.2%) onto the single-layer coated particles in the sugar coating machine by atomization. After uniform wetting, dry at 100 ℃ to obtain double-layer coated particles.

[0053] Step 3: Same as Example 3. Based on the total mass of the catalyst, the composition of the obtained catalyst is: 95.9% γ-alumina spheres, 3% cerium oxide, 0.1% palladium, and 1% zirconium oxide, denoted as A@Ce3@g-Pd 0.1 @Zr.

[0054] Example 9

[0055] Step 1: Dilute 15.00 g of nano-cerium sol (20-30 nm, mass concentration 20%) with water to 50 mL, and spray it onto 95.9 g of γ-alumina spheres with a particle size of 3-5 mm in a sugar coating machine. After uniform wetting, dry at 100 °C to obtain single-layer coated particles.

[0056] Step 2: Same as Example 1.

[0057] Step 3: Dilute 5.00 g of nano-zirconium sol (20–30 nm, 20% mass concentration) with water to 50 mL, and atomize it onto the double-layer coated particles in a sugar coating machine. After uniform wetting, dry at 100 °C to obtain triple-layer coated particles, and then calcine at 500 °C for 2 h to obtain the catalyst. Based on the total mass of the catalyst, the composition of the obtained catalyst is: 95.9% γ-alumina spheres, 3% cerium oxide, 0.1% palladium, and 1% zirconium oxide, denoted as A@g-Ce3@Pd 0.1 @g-Zr.

[0058] Example 10

[0059] Step 1: Same as Example 9.

[0060] Step 2: Same as Example 7.

[0061] Step 3: Same as Example 9. Based on the total mass of the catalyst, the composition of the obtained catalyst is: 95.9% γ-alumina spheres, 3% cerium oxide, 0.1% palladium, and 1% zirconium oxide, denoted as A@g-Ce3@r-Pd 0.1 @g-Zr.

[0062] Example 11

[0063] Step 1: Same as Example 9.

[0064] Step 2: Same as Example 8.

[0065] Step 3: Same as in Example 9. Based on the total mass of the catalyst, the composition of the obtained catalyst is: 95.9% γ-alumina spheres, 3% cerium oxide, 0.1% palladium, and 1% zirconium oxide, denoted as A@g-Ce3@g-Pd 0.1 @g-Zr.

[0066] Example 12

[0067] Step 1: Disperse 3.00 g of commercially available nano-cerium dioxide powder and 0.03 g of hydroxyethyl cellulose with water at high speed to form D. 90 A dispersion of ≤ 5 μm in 50 mL was atomized and sprayed onto 95.9 g of γ-alumina spheres with a particle size of 3-5 mm in a sugar coating machine. After uniform wetting, the particles were dried at 100 °C to obtain single-layer coated particles.

[0068] Step 2: Same as Example 1.

[0069] Step 3: Disperse 1.00 g of commercially available nano-zirconia powder and 0.03 g of hydroxyethyl cellulose with water at high speed to form D. 90 A 50 mL dispersion with a particle size ≤ 5 μm was atomized and sprayed onto double-layer coated particles in a sugar coating machine. After uniform wetting, the particles were dried at 100 °C to obtain triple-layer coated particles, which were then calcined at 500 °C for 2 h to obtain the catalyst. Based on the total mass of the catalyst, the composition of the obtained catalyst was: 95.9% γ-alumina spheres, 3% cerium oxide, 0.1% palladium, and 1% zirconium oxide, denoted as A@p-Ce3@Pd. 0.1 @p-Zr.

[0070] Example 13

[0071] Step 1: Same as Example 12.

[0072] Step 2: Same as Example 7.

[0073] Step 3: Same as in Example 12. Based on the total mass of the catalyst, the composition of the obtained catalyst is: 95.9% γ-alumina spheres, 3% cerium oxide, 0.1% palladium, and 1% zirconium oxide, denoted as A@p-Ce3@r-Pd 0.1 @p-Zr.

[0074] Example 14

[0075] Step 1: Same as Example 12.

[0076] Step 2: Same as Example 8.

[0077] Step 3: Same as in Example 12. Based on the total mass of the catalyst, the composition of the obtained catalyst is: 95.9% γ-alumina spheres, 3% cerium oxide, 0.1% palladium, and 1% zirconium oxide, denoted as A@p-Ce3@g-Pd 0.1 @p-Zr.

[0078] Example 15

[0079] Step 1: Replace the γ-alumina spheres with silica spheres, and the rest is the same as in Example 12.

[0080] Step 2: Same as Example 1.

[0081] Step 3: Same as in Example 12. Based on the total mass of the catalyst, the composition of the obtained catalyst is: 95.9% silica spheres, 3% cerium oxide, 0.1% palladium, and 1% zirconium oxide, denoted as S@p-Ce3@Pd 0.1 @p-Zr.

[0082] Example 16

[0083] Step 1: Replace the alumina balls with 5A molecular sieve balls, and the rest is the same as in Example 12.

[0084] Step 2: Same as Example 1.

[0085] Step 3: Same as in Example 12. Based on the total mass of the catalyst, the composition of the obtained catalyst is: 95.9% 5A molecular sieve spheres, 3% cerium oxide, 0.1% palladium, and 1% zirconium oxide, denoted as M@p-Ce3@Pd 0.1 @p-Zr.

[0086] Comparative Example 1

[0087] A 50 mL solution was prepared by adding water to 7.57 g of cerium nitrate hexahydrate, 3.48 g of zirconium nitrate pentahydrate, and 1.00 g of a 10% palladium nitrate solution. 96 g of γ-alumina spheres with a particle size of 3–5 mm were impregnated in this solution for 4 h, dried at 100 °C, and then calcined at 500 °C for 2 h to obtain the catalyst. Based on the total mass of the catalyst, the composition of the obtained catalyst was: 95.9% γ-alumina spheres, 3% cerium oxide, 0.1% palladium, and 1% zirconium oxide, denoted as Ce3-Pd. 0.1 -Zr / A.

[0088] Comparative Example 2

[0089] A 50 mL solution was prepared by adding water to 7.57 g of cerium nitrate hexahydrate, 3.48 g of zirconium nitrate pentahydrate, and 1.00 g of a 10% palladium nitrate solution. This solution was then atomized and sprayed onto 96 g of γ-alumina spheres with a particle size of 3–5 mm in a coating machine. After uniform wetting, the solution was dried at 100 °C and then calcined at 500 °C for 2 h to obtain the catalyst. Based on the total mass of the catalyst, the composition of the obtained catalyst was: 95.9% γ-alumina spheres, 3% cerium oxide, 0.1% palladium, and 1% zirconium oxide, denoted as A@Ce3-Pd. 0.1 -Zr.

[0090] Comparative Example 3

[0091] Step 1: Prepare a 50 mL solution by adding 7.57 g of cerium nitrate hexahydrate to water, and spray it onto 96.9 g of γ-alumina balls with a particle size of 3-5 mm in a sugar coating machine. After uniform wetting, dry at 100 ℃ to obtain single-layer coated particles.

[0092] Step 2: 1.00 g of 10% palladium chloride solution, 1.00 g of ethylene glycol, and 5.00 g of ethanol were mixed evenly and reduced at 80 °C for 2 h. Water was added to prepare a 50 mL solution, which was then ultrasonically dispersed. This solution was atomized and sprayed onto single-layer coated particles in a sugar coating machine. After even wetting, the particles were dried at 100 °C to obtain double-layer coated particles. These particles were then calcined at 500 °C for 2 h to obtain the catalyst. Based on the total mass of the catalyst, the composition of the obtained catalyst was: 96.9% alumina spheres, 3% cerium oxide, and 0.1% palladium, denoted as A@Ce3@r-Pd. 0.1 .

[0093] The catalysts prepared in the above examples and comparative examples were respectively loaded into fixed-bed reactors, and their catalytic performance was evaluated under the same conditions. The simulated reaction gas volume composition was: 0.05% methane, 1.5% carbon monoxide, 0.2% hydrogen, 0.1% formaldehyde, 0.1% methanol, 0.2% dimethyl ether, 4% water vapor, and the remainder being air. The evaluation space velocity was 30,000 h⁻¹. -1 The activity evaluation temperature ranged from 60 to 450 °C, and the process was carried out using a programmed temperature increase method. The conversion temperature of each component was measured separately, with lower temperatures indicating better activity. The stability evaluation temperature was 450 °C, and the evaluation time was 72 h. The smaller the change in methane conversion rate, the more stable the performance. The test results are shown in Table 1.

[0094] Table 1

[0095]

[0096] Comparative tests showed that Comparative Example 1, prepared using traditional co-impregnation, had the worst performance in all indicators, while Comparative Example 2, prepared using spray coating, showed a significant improvement in performance. With consistent precious metal content, Example 3, prepared using multi-layer spray coating, further improved the catalytic performance against various pollutants. Compared to Example 7, Comparative Example 3, lacking an outer layer, showed significantly reduced stability. In summary, Example 11, prepared using sol-gel raw materials through multi-layer spray coating, showed the best performance, but Example 3, prepared using nitrates through multi-layer spray coating, offered the best cost-performance ratio. Furthermore, Examples 15 and 16 demonstrated that the type of ceramic particles has a relatively small impact on the performance of multi-layer catalysts, providing a wider range of alternatives.

[0097] The test results above show that the multilayer catalyst of the present invention exhibits significantly better activity and stability than the catalyst with simple mixed spraying and the catalyst lacking outer protection. The oxygen storage function of the cerium oxide inner layer helps maintain high oxidation activity under dynamic conditions, while the protective effect of the zirconium oxide outer layer effectively inhibits the sintering and poisoning of palladium active sites at high temperatures. Therefore, the catalyst of the present invention achieves a higher complete conversion temperature T for various pollutants. 99 The catalyst exhibits lower temperatures, a smaller decrease in methane conversion rate at 450 °C, and better high-temperature and moisture resistance. This invention's catalyst is expected to meet the urgent needs of formaldehyde and related industries for efficient and deep purification of exhaust gases in terms of activity, stability, and broad applicability.

Claims

1. A multilayered, broad-spectrum catalyst for treating formaldehyde industrial tail gas, characterized in that, The catalyst is granular, with ceramic particles as a carrier. A cerium oxide inner layer, a palladium intermediate layer, and a zirconium oxide outer layer are sequentially loaded on the surface of the carrier. Based on the total mass of the catalyst, its composition is: 0.01% to 0.5% palladium, 1% to 10% cerium oxide and zirconium oxide combined, and the remainder is ceramic particles, with a mass ratio of cerium oxide to zirconium oxide of 1:4 to 4:

1.

2. The multilayered broad-spectrum catalyst for formaldehyde industrial tail gas treatment according to claim 1, characterized in that, Based on the total mass of the catalyst, its composition is: 0.05% to 0.2% palladium, 2% to 5% cerium oxide and zirconium oxide combined, and the remainder is ceramic particles, with the mass ratio of cerium oxide to zirconium oxide being 1:3 to 3:

1.

3. The multilayered, broad-spectrum catalyst for formaldehyde industrial tail gas treatment according to claim 1 or 2, characterized in that, The ceramic particles are one or more of alumina particles, silicon oxide particles, and molecular sieve particles.

4. A method for preparing the multilayer structured broad-spectrum catalyst for formaldehyde industrial tail gas treatment as described in claim 1, characterized in that, The coating is prepared by layer-by-layer spraying using the rolling ball method, and includes the following steps: Step 1: Atomize and spray the cerium source solution or slurry onto the rolling ceramic particles, wet them evenly, and then dry them. Step 2: Atomize and spray the palladium source solution or dispersion onto the particles obtained in Step 1, wet them evenly, and then dry them; Step 3: Atomize and spray the zirconium source solution or slurry onto the particles obtained in Step 2, wet them evenly, dry them, and calcine them at 400-600℃ for 2-6 hours to obtain the catalyst.

5. The method for preparing the multilayer structured broad-spectrum catalyst for formaldehyde industrial tail gas treatment according to claim 4, characterized in that, The cerium source and zirconium source are independently selected from one or more of their corresponding soluble salts, oxide sols, and nano-oxide powders; the palladium source is selected from one or more of palladium nitrate, chloropalladic acid, and palladium sol.

6. The method for preparing the multilayer structured broad-spectrum catalyst for formaldehyde industrial tail gas treatment according to claim 5, characterized in that, When using nano-oxide powder as a cerium source or zirconium source, a stabilizer needs to be added to produce solid particles with a particle size D. 90 Spraying is performed after the slurry with a thickness of ≤ 5 μm is applied; the stabilizer is selected from one or more of cellulose stabilizers, polysaccharide stabilizers, and polymer stabilizers.

7. The method for preparing the multilayer structured broad-spectrum catalyst for formaldehyde industrial tail gas treatment according to claim 6, characterized in that, The stabilizer is selected from one or more of hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, polyethylene glycol, polyvinyl alcohol, polyacrylic acid, xanthan gum, guar gum, and dextran.

8. The method for preparing the multilayer structured broad-spectrum catalyst for formaldehyde industrial tail gas treatment according to claim 4, characterized in that, In step 2, the palladium source is pre-reduced by mixing with a reducing agent before spraying. The reducing agent is selected from one or more of polyols, organic acids, and hydrazine hydrate. The reduction temperature is 60-200 °C and the reduction time is 1-4 hours.

9. The method for preparing the multilayer structured broad-spectrum catalyst for formaldehyde industrial tail gas treatment according to claim 8, characterized in that, The reducing agent is selected from one or more of methanol, ethanol, propanol, ethylene glycol, glycerol, polyethylene glycol, ascorbic acid, citric acid, oxalic acid, glucose, and hydrazine hydrate.

10. The application of the catalyst according to claim 1 in the catalytic combustion treatment of tail gas from a formaldehyde industrial plant, characterized in that, The exhaust gas contains one or more components selected from carbon monoxide, hydrogen, methane, formaldehyde, methanol, dimethyl ether, and water vapor, with a reaction space velocity of 10,000–50,000 h⁻¹. -1 .

Images