Preparation method of bimetallic and multi-metal oxide loaded molecular sieve catalyst

Abstract

The invention relates to a preparation method of a bimetallic and multi-metal oxide loaded molecular sieve catalyst, and belongs to the technical field of molecular sieves. The method comprises the following steps: forming a uniform complex solution from two or more soluble metal salts and a complexing agent, regulating the pH value to 3.0-5.5, and carrying out constant-temperature ion exchange with a molecular sieve (ZSM-5 / Beta / USY) at 30-100 DEG C for 1-10 hours; and after washing and drying, raising the temperature to 400-650 DEG C at the rate of 1-3 DEG C / min and roasting for 2-10 hours to obtain the double / multi-metal oxide loaded molecular sieve catalyst. According to the method, on the premise of not destroying the framework structure of the molecular sieve, the problems of poor double / multi-metal dispersity, uncontrollable target metal proportion and complex process in the traditional technology are solved, atomic-scale uniform dispersion of the metal is realized, and the total metal loading capacity is 1-10wt%.

Description

Technical Field

[0001] This invention relates to a method for preparing bimetallic and polymetallic oxide supported molecular sieve catalysts, belonging to the field of molecular sieve technology. Background Technology

[0002] Molecular sieve-supported bimetallic / multimetallic catalysts play a crucial role in environmental catalysis (such as NH3-SCR denitrification and VOCs oxidation) and energy and chemical engineering (such as methanol-to-olefins and hydrorefining) due to their unique synergistic effects. For example, Fe-Cu bimetallic catalysts aim to combine the high-temperature stability of Fe with the low-temperature activity of Cu to broaden the temperature window of SCR reactions; Ce-Mn bimetallic catalysts utilize the oxygen storage capacity of Ce and the variable valence characteristics of Mn to significantly improve low-temperature oxidation activity, exhibiting better low-temperature activity and hydrocarbon conversion efficiency than single metal catalysts.

[0003] However, existing technologies for preparing bimetallic / multimetallic supported molecular sieve catalysts have inherent and insurmountable defects that severely restrict further improvement in their catalyst performance.

[0004] Co-impregnation method: Although simple, this method suffers from drawbacks during drying. The capillary forces generated by the evaporation of water or solvent cause the metal salt precursor to migrate and accumulate on the particle surface or pores, resulting in large, unevenly sized oxide particles with extremely poor dispersion after calcination. The loaded material is mostly a physical mixture, making it difficult to form an effective synergistic active interface. Furthermore, different metal salts have different solubilities, hydrolysis constants, and affinities for the molecular sieve surface, leading to uneven distribution within the pores. Consequently, the actual metal ratio on the catalyst deviates significantly from the feed ratio. Therefore, catalysts prepared by the co-impregnation method often exhibit weak bi / multi-metal interactions, resulting in limited performance improvement.

[0005] Stepwise impregnation / ion exchange method: This method first loads one metal, then calcines it before loading a second metal. This process is not only cumbersome and time-consuming with low production efficiency, but the first-loaded metal species also occupies the pores or cation exchange sites of the molecular sieve, forming steric hindrance and severely hindering the diffusion of the subsequently loaded metal species into the pores. This results in the latter mainly accumulating on the outer surface with extremely poor dispersion. More importantly, the second heat treatment process easily causes the already dispersed first metal species to sinter and migrate, destroying its original highly dispersed state.

[0006] Co-hydrothermal synthesis method: This method introduces a metal source into the synthetic gel during the molecular sieve crystallization process. Theoretically, it can achieve "in-situ" encapsulation of metal species in the molecular sieve framework or channels with high dispersion. However, multiple metal ions change the chemical equilibrium of the gel, which seriously interferes with the crystallization process and is very easy to cause the formation of impurities or crystallization failure. The conditions are harsh, the success rate is low, and it is difficult to industrialize.

[0007] In addition, the hydrolysis of metal ions will produce a large amount of H₂. + This causes the solution pH environment to be too low, resulting in an excess of free H+ in the solution. + It will fiercely compete with metal cations for negatively charged framework sites on the molecular sieve. And H... + High concentration and small size give them a competitive advantage over cations, resulting in extremely low metal ion exchange efficiency. Most metal ions remain in the filtrate, requiring additional treatment, making it difficult to achieve the target metal ratio in one step. Even worse, for acid-sensitive materials like the USY-type molecular sieve, excessive H+... + Attacking the Al-O-Si bonds can cause aluminum to detach from the molecular sieve framework, resulting in structural damage to the molecular sieve, affecting its crystallinity, and consequently impacting the performance and application of the supported catalyst. Summary of the Invention

[0008] Based on the problems described in the background, the problem that this invention aims to solve is:

[0009] Without damaging the molecular sieve framework structure, dual / multi-metal oxide supported molecular sieves suffer from poor metal dispersion, uncontrollable target metal ratio, and complex processes.

[0010] To achieve the above objectives, the present invention provides the following technical solution:

[0011] A method for preparing bimetallic and polymetallic oxide supported molecular sieve catalysts, characterized by comprising the following steps:

[0012] S1: Dissolve two or more soluble metal salts in water, add a complexing agent, and adjust the pH to 3.0~5.5 with 0.5 mol / L dilute ammonia or 0.5 mol / L dilute nitric acid solution to form a clear and homogeneous complex solution, wherein the molar ratio of the complexing agent to the total metal ions is 1.2~3.0:1.0;

[0013] S2: Add the molecular sieve to the complex solution and carry out ion exchange by stirring at a constant temperature of 30~100℃ for 1~10h;

[0014] S3: The exchanged material is subjected to solid-liquid separation, washed until neutral, and dried. Then, it is calcined in air or an inert atmosphere at a heating rate of 1~3℃ / min to 400~700℃. After cooling, a bi / polymetallic oxide supported molecular sieve catalyst is obtained.

[0015] Preferably, the metal is a solution of two or more metal soluble salts selected from Fe, Cu, Mn, Co, Ni, V, Ce, Zn, La, etc.; wherein the selection principle of the metal salt in this invention is: it has good solubility in water and water-complexing agent solution, and its anion does not form insoluble substances for metal ions with the same load, wherein nitrates are preferred.

[0016] Preferably, the complexing agent is one of citric acid, EDTA, aminotriacetic acid, and tartaric acid; wherein the selection principle of the complexing agent in this invention is: it can form a stable water-soluble complex with the target metal ion, and its molecular size, complexing strength and thermal decomposition behavior are matched with the pore structure and chemical stability of the target molecular sieve.

[0017] Preferably, the molar ratio of the complexing agent to the total metal ions is 1.2~3.0:1.0;

[0018] Preferably, the molecular sieve is one of ZSM-5, Beta, and USY; for different molecular sieves, the pH range is selected according to their sensitivity to acidity, that is: for ZSM-5 molecular sieve, the pH is controlled at 3.5~4.5; for Beta molecular sieve, the pH is controlled at 4.0~5.0; for USY molecular sieve, which has a high skeletal aluminum content and is extremely sensitive to acidic conditions, the pH is controlled at 4.0~5.5.

[0019] Metal ion hydrolysis produces a large amount of H + This results in an excessively low pH environment, where fewer complexing factors are released from the complexing agent, hindering the complexation reaction. Furthermore, when the pH is too low, excess free H₂ in the solution... + It will fiercely compete with metal complex cations for negatively charged framework sites on the molecular sieve. Due to H... + With its high concentration and small size, it has a competitive advantage over metal complexes, resulting in extremely low metal ion exchange efficiency. It cannot be effectively "anchored" to the framework, and most of the metal ions remain in the filtrate and require additional treatment.

[0020] Preferably, the mass ratio of the total metal oxides to the molecular sieve is 1-10%;

[0021] Preferably, the mass ratio of the molecular sieve to the solvent water is 1:3~10;

[0022] Preferably, the calcination is carried out at a heating rate of 1~3℃ / min, the calcination temperature is 400~700℃, and the calcination time is 2~10h. The slow heating rate allows the organic complexing agent to decompose and burn steadily and gently, avoiding violent exothermic reactions and gas impacts. The in-situ gases (CO2, H2O) generated during the decomposition of organic matter act as "templates" and "barriers," effectively inhibiting the migration and sintering of metal oxide nanoparticles at high temperatures. Ultimately, two or more metal oxides are uniformly nucleated and "anchored" on the molecular sieve support in a highly dispersed and closely contacted manner. At the same time, the gases generated during the decomposition process help to form pores, thereby promoting the formation and expansion of the pore structure of the molecular sieve, which is more conducive to improving the catalytic performance.

[0023] The beneficial effects of this invention are:

[0024] 1. This invention achieves atomic-level uniform dispersion of two / multi-metals on molecular sieves through metal ion solution complexation and integrated exchange with molecular sieves, avoiding the problems of easy metal agglomeration and low metal dispersion in co-impregnation methods;

[0025] 2. In this invention, the ratio of dual / multi-metals in the complex is fixed and stable. As long as the initial feed ratio and exchange conditions are precisely controlled, the ratio of dual / multi-metals on the final catalyst can be precisely controlled, avoiding the uncertainty caused by differences in metal migration and adsorption, and ensuring a high degree of consistency in product quality.

[0026] 3. This invention integrates the bi / multi-metal loading process into a "one-step exchange," which, compared to the step-by-step method, results in a shorter process, lower energy consumption, and easier industrial scale-up. It avoids the interference risks of hydrothermal methods on the crystallization process, offering a wider process window and higher success rate. Therefore, this invention achieves top-tier performance (close to hydrothermal methods) while maintaining process simplicity close to impregnation methods, achieving the best balance between performance and cost.

[0027] This invention is carried out under relatively mild pH conditions (pH=3.0-5.5), which promotes the release of complexing factors from the complexing agent and effectively inhibits acid erosion of the molecular sieve framework, protecting its crystallinity and acidic sites. This improves the hydrothermal stability and service life of the final catalyst. At the same time, the gas generated by the complexing agent during calcination helps to form pores, thereby promoting the formation and expansion of the pore structure of the molecular sieve, which is more conducive to improving catalytic performance. Attached Figure Description

[0028] Figure 1 XRD pattern of Example 1 Detailed Implementation

[0029] Example 1

[0030] Preparation of Fe-Cu / ZSM-5 catalyst:

[0031] Add 24.2g of ferric nitrate nonahydrate and 4.8g of copper nitrate trihydrate to 800g of pure water, stir to dissolve, then add 25.2g of citric acid monohydrate. The molar ratio of complexing agent to total metal ions is 1.5:1.0. Continue stirring to form a clear, homogeneous complex solution. Then, add 0.5 mol / L dilute ammonia or 0.5 mol / L dilute ammonia solution dropwise. The pH of the solution was controlled at 3.0 using a mol / L dilute nitric acid solution. 200g of ZSM-5 molecular sieve (SiO2 / Al2O3=28) was slowly added to the complexing solution, and the mixture was heated to 90℃ and kept at that temperature for 2 hours for exchange. After the exchange was complete, the mixture was cooled to below 60℃ and filtered while still hot to separate the solid and liquid. The filter cake was washed multiple times with hot water at 65℃ to neutralize the pH of the filtrate. The washed filter cake was then dried overnight in a 110℃ oven. The dried filter cake was then placed in a muffle furnace and heated to 500℃ at a rate of 1℃ / min under air atmosphere. The mixture was then calcined at 500℃ for 5 hours and cooled to room temperature to obtain the Fe-Cu / ZSM-5 bimetallic molecular sieve catalyst. The loading of Fe2O3 was 4.48%, the loading of CuO was 0.73%, the Fe / Cu molar ratio was 3:1, and the total metal loading was 5.21wt%.

[0032] Example 2

[0033] Preparation of Fe-Cu / ZSM-5 catalyst

[0034] Add 24.2g of ferric nitrate nonahydrate and 4.8g of copper nitrate trihydrate to 800g of pure water, stir to dissolve, then add 25.2g of citric acid monohydrate. The molar ratio of complexing agent to total metal ions is 1.5:1.0. Continue stirring to form a clear, homogeneous complex solution. Then, add 0.5 mol / L dilute ammonia or 0.5 mol / L dilute ammonia solution dropwise. The pH of the solution was controlled at 4.5 using a mol / L dilute nitric acid solution. 200g of ZSM-5 molecular sieve (SiO2 / Al2O3=28) was weighed and slowly added to the complexation solution. The solution was heated to 100℃ and kept at a constant temperature for 1h for exchange. After the exchange was completed, the solution was cooled to below 60℃ and filtered while hot to separate the solid and liquid. The filter cake was washed multiple times with hot water at 65℃ to neutralize the pH of the filtrate. The washed filter cake was dried overnight in an oven at 110℃. The dried filter cake was then placed in a muffle furnace and heated to 400℃ at a rate of 1℃ / min under air atmosphere. The solution was then calcined at 400℃ for 10h and cooled to room temperature to obtain the Fe-Cu / ZSM-5 bimetallic molecular sieve catalyst. The loading of Fe2O3 was 4.48%, the loading of CuO was 0.73%, the Fe / Cu molar ratio was 3:1, and the total metal loading was 5.21wt%.

[0035] Example 3

[0036] Preparation of Ni-Zn / USY catalyst

[0037] 29.1g of nickel nitrate hexahydrate and 3.3g of zinc nitrate hexahydrate were added to 600g of pure water and stirred to dissolve. 64.9g of EDTA was added, and the molar ratio of complexing agent to total metal ions was 2.0:1. The mixture was stirred continuously to form a clear and homogeneous complex solution. The pH of the solution was controlled to 5.5 by adding 0.5 mol / L dilute ammonia or 0.5 mol / L dilute nitric acid solution dropwise. 200g of USY molecular sieve was weighed and slowly added to the complexing solution. The mixture was heated to 30℃ and kept at a constant temperature for 10h for exchange. After the exchange was completed, the mixture was filtered while hot to separate the solid and liquid. The filter cake was washed multiple times with hot water at 60℃ to neutralize the pH of the filtrate. The washed filter cake was dried overnight in an oven at 110℃. The dried filter cake was then placed in a muffle furnace and heated to 400℃ at a rate of 1℃ / min under air atmosphere. It was then calcined at 500℃ for 8h and cooled to room temperature to obtain the Ni-Zn / USY trimetallic molecular sieve catalyst. The NiO loading was found to be 3.52 wt%, and the ZnO loading was 0.44 wt%.

[0038] Example 4

[0039] V-Ce / ZSM-5

[0040] Add 1.2g ammonium vanadate and 4.3g cerium nitrate hexahydrate to 800g pure water, stir to dissolve, then add 3.6g tartaric acid. The molar ratio of the complexing agent to the total metal ions is 1.2:1. Continue stirring to form a clear, homogeneous complex solution. Control the pH of the solution to 4.5 by adding 0.5mol / L dilute ammonia or 0.5mol / L dilute nitric acid solution dropwise. Weigh 200g... ZSM-5 molecular sieve (SiO2 / Al2O3=30) was slowly added to the complexing solution, and the mixture was heated to 80℃ and held at that temperature for 5 hours for exchange. After the exchange was complete, the mixture was cooled to below 60℃ and filtered while still hot to separate the solid and liquid. The filter cake was washed multiple times with hot water at 60-70℃ to neutralize the pH of the filtrate. The washed filter cake was then dried overnight in an oven at 110℃. The dried filter cake was then placed in a muffle furnace and heated to 650℃ at a rate of 2℃ / min under air atmosphere, and calcined at 650℃ for 2 hours. After cooling to room temperature, the Fe-Co / Beta bimetallic molecular sieve catalyst was obtained. The V2O3 loading was 0.89 wt%, and the CeO2 loading was 0.85 wt%.

[0041] Example 5

[0042] Fe-La / Beta

[0043] 20.2 g of ferric nitrate nonahydrate and 5.4 g of lanthanum nitrate hexahydrate were added to 2000 g of pure water and stirred until dissolved. Then, 27.4 g of EDTA was added, with a molar ratio of complexing agent to total metal ions of 1.5:1. The mixture was stirred continuously to form a clear, homogeneous complex solution. The solution was then dissolved by adding 0.5 mol / L dilute ammonia or 0.5 mol / L dilute ammonia solution dropwise. The pH of the solution was controlled at 4.5 using a mol / L dilute nitric acid solution. 200g of Beta molecular sieve (SiO2 / Al2O3=50) was slowly added to the complexing solution, and the mixture was heated to 80℃ and held at that temperature for 3 hours for exchange. After exchange, the mixture was cooled to below 60℃ and filtered while still hot to separate the solid and liquid. The filter cake was washed multiple times with hot water at 60-70℃ to neutralize the pH of the filtrate. The washed filter cake was then dried overnight in a 110℃ oven. The dried filter cake was then placed in a muffle furnace and heated to 500℃ at a rate of 3℃ / min under air atmosphere, and calcined at 500℃ for 10 hours. The mixture was then cooled to room temperature to obtain the Cu-Mn / ZSM-5 bimetallic molecular sieve catalyst. The Fe2O3 loading was determined to be 3.77 wt%, and the La2O3 loading was 1.92 wt%.

[0044] Example 6

[0045] Cu-Ce-Mn / ZSM-5

[0046] Add 14.5g of copper nitrate trihydrate, 4.3g of cerium nitrate hexahydrate, and 2.5g of manganese nitrate tetrahydrate to 800g of pure water, stir to dissolve, then add 50.4g of citric acid monohydrate. The molar ratio of the complexing agent to the total metal ions is 3.0:1. Continue stirring to form a clear, homogeneous complex solution. Control the pH of the solution to 4.0 by adding 0.5 mol / L dilute ammonia or 0.5 mol / L dilute nitric acid solution dropwise. Weigh 200g... ZSM-5 molecular sieve (SiO2 / Al2O3=30) was slowly added to the complexing solution, and the mixture was heated to 90℃ and held at that temperature for 3 hours for exchange. After the exchange was complete, the mixture was cooled to below 60℃ and filtered while still hot to separate the solid and liquid. The filter cake was washed multiple times with hot water at 60-70℃ to neutralize the pH of the filtrate. The washed filter cake was then dried overnight in an oven at 110℃. The dried filter cake was then placed in a muffle furnace and heated to 500℃ at a rate of 1.5℃ / min under air atmosphere, and calcined at 500℃ for 8 hours. After cooling to room temperature, the Fe-Ni-Cr / USY trimetallic molecular sieve catalyst was obtained. The loadings were: CuO 2.3 wt%, CeO2 0.83 wt%, and MnO2 0.42 wt%.

[0047] Comparative Example 1

[0048] Preparation of Fe-Cu / ZSM-5 by co-impregnation method

[0049] Equal amounts of Fe(NO3)3·9H2O and Cu(NO3)2·3H2O from Example 1 were dissolved in 200g of deionized water (this volume is approximately equal to the water absorption rate of ZSM-5). 200g of H-ZSM-5 support was mixed with this solution and impregnated in a sealed container at room temperature for 12 hours, manually turning the container every 2 hours. Subsequent drying and calcination conditions were the same as in Example 1. The loaded Fe2O3 content was 1.53%, and the CuO loading was 0.25%.

[0050] Comparative Example 2:

[0051] Fe-Cu / ZSM-5 prepared by stepwise impregnation method

[0052] The first step involved dissolving half of the Fe(NO3)3·9H2O from Example 1 in water and loading it onto 200g of H-ZSM-5 using an equal-volume impregnation method. After drying at 110°C for 12 hours, the mixture was calcined at 500°C for 4 hours to obtain the Fe / ZSM-5 intermediate. The second step involved dissolving the entire amount of Cu(NO3)2·3H2O in water and again loading it onto the aforementioned Fe / ZSM-5 using the equal-volume impregnation method. After drying at 110°C for 12 hours, the mixture was calcined at 500°C for 4 hours to obtain the final catalyst. This method is cumbersome, and the initially loaded Fe species occupy the pores, hindering the diffusion of the subsequently loaded Cu species. The second calcination easily leads to sintering of the dispersed Fe species. After loading, the Fe2O3 loading was 3.21%, and the CuO loading was 0.22%.

[0053] Comparative Example 3: Consistent with Example 1, but without controlling the pH of the reaction.

[0054] 24.2 g of ferric nitrate nonahydrate and 4.8 g of copper nitrate trihydrate were added to 800 g of pure water and stirred to dissolve. 25.2 g of citric acid monohydrate was added and stirred continuously to form a clear and homogeneous complex solution. 200 g of ZSM-5 molecular sieve (SiO2 / Al2O3=28) was weighed and slowly added to the complex solution. The mixture was heated to 90 °C and kept at a constant temperature for 2 h for exchange. After the exchange was completed, the mixture was cooled to below 60 °C and filtered while hot to separate the solid and liquid. The filter cake was washed multiple times with hot water at 65 °C to neutralize the pH of the filtrate. The washed filter cake was dried overnight in an oven at 110 °C. The dried filter cake was then placed in a muffle furnace and heated to 500 °C at a rate of 1 °C / min under air atmosphere. It was then calcined at 500 °C for 5 h and cooled to room temperature to obtain the Fe-Cu / ZSM-5 bimetallic molecular sieve catalyst. The loading of Fe2O3 was 2.75% and the loading of CuO was 0.62% after loading.

[0055]

[0056] according to Figure 1As shown in Table 1, the XRD patterns all retained the characteristic diffraction peaks of the molecular sieve, and no obvious metal oxide crystal phase peaks were observed, indicating its high dispersion.

[0057] The low loading rate of Comparative Example 3, with the same proportions, indicates a significant loss of metal ions. This not only makes it impossible to accurately control the loading rate, but the lost metal ions also cause environmental pollution and increase environmental protection costs.

Claims

1. A method for preparing bimetallic and polymetallic oxide supported molecular sieve catalysts, characterized in that, Includes the following steps: S1: Dissolve two or more soluble metal salts in water, add a complexing agent, and adjust the pH to 3.0~5.5 with 0.5 mol / L dilute ammonia or 0.5 mol / L dilute nitric acid solution to form a clear and homogeneous complex solution, wherein the molar ratio of the complexing agent to the total metal ions is 1.2~3.0:1.0; S2: Add the molecular sieve to the complex solution obtained in S1 and carry out ion exchange by stirring at a constant temperature of 30~100℃ for 1~10h; S3: After solid-liquid separation, washing to neutrality and drying, the material is calcined at 400-650℃ in air or an inert atmosphere at a heating rate of 1-3℃ / min. After cooling, a bi / polymetallic oxide supported molecular sieve catalyst is obtained.

2. The method for preparing a bimetallic and polymetallic oxide supported molecular sieve catalyst according to claim 1, characterized in that, The metal is a solution of two or more soluble salts of Fe, Cu, Mn, Co, Ni, V, Ce, Zn, and La.

3. The method for preparing a bimetallic and polymetallic oxide supported molecular sieve catalyst according to claim 1, characterized in that, The complexing agent is one of citric acid, EDTA, aminotriacetic acid, and tartaric acid.

4. The method for preparing a bimetallic and polymetallic oxide supported molecular sieve catalyst according to claim 2, characterized in that, The metal-soluble salt solution is a nitrate solution.

5. The method for preparing a bimetallic and polymetallic oxide supported molecular sieve catalyst according to claim 1, characterized in that, The molecular sieve is one of ZSM-5, Beta, and USY. For different molecular sieves, the pH range is selected according to their sensitivity to acidity. Specifically, for ZSM-5 molecular sieve, the pH of the complex solution is controlled at 3.0~4.5; for Beta molecular sieve, the pH is controlled at 4.0~5.0; and for USY molecular sieve, which has a high aluminum content in its framework and is extremely sensitive to acidic conditions, the pH is controlled at 4.0~5.

5.

6. The method for preparing a bimetallic and polymetallic oxide supported molecular sieve catalyst according to claim 1, characterized in that, The mass ratio of the molecular sieve to the solvent water is 1:3~10.

7. The method for preparing a bimetallic and polymetallic oxide supported molecular sieve catalyst according to claim 1, wherein the calcination time is 2-10 h.

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