Preparation method of ferrocerium / molecular sieve catalyst and application of ferrocerium / molecular sieve catalyst in preparation of acetic acid through methane oxidation

Abstract

The invention discloses a preparation method of a ferrocerium / molecular sieve catalyst and an application of the ferrocerium / molecular sieve catalyst in preparation of acetic acid by mild oxidation of methane, and the specific preparation method comprises the following steps: taking metal cerium, ferric salt and a microporous molecular sieve as raw materials, dipping, drying and calcining to prepare the ferrocerium / molecular sieve catalyst. The preparation method is simple in process, easy to implement, simple, convenient and safe to operate, process parameters are easy to control, and active metal cerium and iron in the obtained cerium-iron / molecular sieve catalyst are anchored in micropore channels of a molecular sieve in a monodisperse cation state, so that the cerium-iron / molecular sieve catalyst can selectively oxidize small molecules such as methane and carbon monoxide under mild conditions; and the preparation of high-yield acetic acid chemicals is realized, few byproducts are produced, and large-scale production can be realized.

Description

Technical Field

[0001] The invention belongs to the field of methane energy science and technology, and particularly relates to a preparation method of a ferrocerium / molecular sieve catalyst and its application in methane oxidation to acetic acid. Background Art

[0002] In recent years, with the gradual depletion of fossil fuels, methane has garnered widespread attention as a high-quality, clean energy source. Methane is primarily burned for heating, power generation, and vehicle power. In oil extraction and refining, methane is often produced as a byproduct. This type of methane, due to its dispersed production and small scale, is difficult to transport or convert into hydrocarbons via syngas for utilization. Therefore, it is typically disposed of by direct combustion or venting, which not only wastes resources but also pollutes the environment. Currently, direct conversion of methane into high-value-added chemicals and liquid fuels has become a research hotspot. However, most current processes not only consume large amounts of energy and result in high economic costs, but also induce undesirable reactions (such as over-oxidation to CO2), resulting in low catalytic activity and selectivity. Therefore, there is an urgent need to develop efficient and cost-effective catalysts for methane conversion.

[0003] Molecular sieves have a rich topological pore structure that effectively influences the adsorption and desorption of reactants and products, exerting a significant selectivity effect on specific reactions. The highly dispersed aluminum sites within their framework serve as important acidic sites, selectively activating molecules such as methane and hydrogen peroxide. Patent CN118791385A discloses a supported iron molecular sieve catalyst for the catalytic oxidation of methane to acetic acid. It uses a mesoporous molecular sieve ZSM-5 as a support, supported by metallic Fe as the active component. However, the high metal loading and high reaction temperature, coupled with the dispersion of Fe nanoparticles on the surface and / or pores of the support, result in numerous and difficult-to-control byproducts during the oxidation reaction. Therefore, reducing the metal loading and synthesizing ferrocerium / molecular sieve catalysts that efficiently and selectively oxidize small molecules such as methane and carbon monoxide to produce chemicals under mild conditions are crucial for the efficient utilization of energy molecules. Summary of the Invention

[0004] To address the above technical problems, the present invention provides a method for preparing a ferrocerium / molecular sieve catalyst and its application in the mild oxidation of methane to acetic acid. This catalyst exhibits a simple preparation process, high atomic utilization, and high yields in the selective oxidation of energy molecules such as methane and carbon monoxide to produce chemicals. This provides a new approach for the efficient conversion of methane into high-value-added chemicals.

[0005] To achieve the above object, the present invention adopts the following technical solutions: A ferrocerium / molecular sieve catalyst, wherein Ce and Fe in the catalyst are anchored in the micropores of a ZSM-5 molecular sieve in a monodisperse cation state, the loading amount of Ce in the catalyst is 0.05-2wt%, and the loading amount of Fe in the catalyst is 0.05-2wt%.

[0006] A method for preparing the above-mentioned ferrocerium / molecular sieve catalyst comprises the following steps: (1) Tetraethyl orthosilicate, aluminum nitrate, and tetrapropylammonium hydroxide were mixed with water, and then treated with ammonia water. The mixture was stirred at room temperature for 2 h and then hydrothermally crystallized. (2) washing the crystallized solid product obtained in step (1) with deionized water until neutral, then centrifuging, filtering, and drying; (3) calcining the powder sample obtained in step (2) in a muffle furnace under air to obtain ZSM-5 molecular sieve; (4) dissolving cerium nitrate and ferric nitrate in water and adding them dropwise to the ZSM-5 molecular sieve obtained in step (3), and aging them by ultrasonication at room temperature; (5) The sample obtained in step (4) is dried and then calcined in an air environment to obtain a ferrocerium / molecular sieve catalyst.

[0007] Furthermore, in step (1), the molar ratio of tetraethyl orthosilicate: aluminum nitrate: tetrapropylammonium hydroxide: ammonia water: water is 1.0:0.03:0.25:2.3:34.

[0008] Furthermore, the hydrothermal crystallization temperature in step (1) is 100-250 °C, and the crystallization time is 4-48 h.

[0009] Furthermore, the drying temperature in step (2) is 30-100 °C, and the drying time is 1-24 h.

[0010] Furthermore, the calcination temperature in step (3) is 200-600 °C, and the calcination time is 4-24 h.

[0011] Furthermore, in step (4), the molar ratio of cerium nitrate to ferric nitrate is 0.1-5, the amount of ZSM-5 molecular sieve is 0.5-5 g, and the aging time is 1-12 h.

[0012] Furthermore, the calcination temperature in step (5) is 200-600 °C, and the calcination time is 4-24 h.

[0013] The ferrocerium / ZSM-5 catalyst can be used in the mild oxidation of methane to acetic acid. Under the conditions of 70 °C, 2 MPa methane, 0.5 MPa CO, and aqueous hydrogen peroxide, the yield and selectivity of acetic acid in the product were 5.4 mmol·g, respectively. cat-1 and 50%.

[0014] The beneficial effects of the present invention are: The present invention uses cerium, iron salts, and microporous molecular sieves as raw materials, and prepares a Ce-Fe / molecular sieve catalyst by equal volume impregnation, drying, and calcination, wherein Ce and Fe are anchored in the molecular sieve in a monodisperse cationic state. The preparation process of the present invention is simple and easy to implement, easy and safe to operate, and the process parameters are easy to control. In the obtained ferrocerium / molecular sieve catalyst, the active metal is in a monodisperse cationic state, which can effectively reduce the amount of metal used. It is applied to the selective oxidation of energy molecules such as methane and carbon monoxide to produce high-value-added chemicals, and can show high yield and good catalytic effect, with few by-products. The reaction does not require the addition of other auxiliary agents or the use of organic solvents. It is environmentally friendly and suitable for large-scale production, and has good application prospects in the field of small molecule catalytic conversion. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 These are the XRD patterns of catalysts Ce-Fe / ZMS-5, Fe / ZMS-5, Ce / ZMS-5 and molecular sieve ZMS-5.

[0016] Figure 2 (a) Scanning electron microscopy image, (b) transmission electron microscopy image, and (c) element distribution map of the Ce-Fe / ZMS-5 catalyst prepared in Example 1.

[0017] Figure 3 (a) Fe K-edge X-ray absorption spectrum and (b) EXAFS spectrum, (c) Ce L3-edge X-ray absorption spectrum and (d) EXAFS spectrum of the Ce-Fe / ZMS-5 catalyst prepared in Example 1.

[0018] Figure 4 The effect of different reaction temperatures on the performance of Ce-Fe / ZMS-5 catalyst in Example 2.

[0019] Figure 5 This is the cycle test diagram of Ce-Fe / ZMS-5 catalyst in Example 3. DETAILED DESCRIPTION

[0020] In order to make the contents of the present invention easier to understand, the technical solutions of the present invention are further described below in conjunction with specific implementation methods, but the present invention is not limited thereto.

[0021] Example 1 Synthesis of ZSM-5 molecular sieve: Tetraethyl orthosilicate, aluminum nitrate, and tetrapropylammonium hydroxide were mixed with water and then treated with 25% aqueous ammonia. The molar ratio of tetraethyl orthosilicate: aluminum nitrate: tetrapropylammonium hydroxide: aqueous ammonia: water was 1.0:0.03:0.25:2.3:34. After stirring at room temperature for 2 hours, the mixture was hydrothermally crystallized at 170°C for 48 hours. The resulting solid product was washed with deionized water until neutral and then dried at 80°C for 12 hours. The resulting powder sample was calcined in a muffle furnace at 550°C in air for 6 hours to obtain ZSM-5 molecular sieve.

[0022] 1.5 mg of cerium nitrate and 1.5 mg of ferric nitrate were dissolved in 0.8 mL of water, and then 1 g of a 0.22 cm pore volume was added dropwise while stirring. 3 / g ZSM-5 molecular sieve, and continued stirring for 60 min after the addition was completed, followed by ultrasonic aging for 2 h. The obtained solid product was then dried in an 80 °C oven and finally calcined at 550 °C for 12 h to obtain a Ce-Fe / ZSM-5 catalyst with a specific surface area of ​​362 m 2 / g, pore volume 0.24 cm 3 / g, the metal loading is shown in Table 1.

[0023] The specific surface area of ​​the ferrocerium / min sieve catalyst prepared above is 362 m 2 / g, pore volume 0.24 cm 3 / g.

[0024] Comparative Example 1 Dissolve 1.5 mg of cerium nitrate in 0.8 mL of water, and then add 1 g of a pore volume of 0.22 cm 3 / g ZSM-5 molecular sieve, and continued stirring for 60 min after the dropwise addition was completed, followed by ultrasonic aging for 2 h. The obtained solid product was then dried in an 80 °C oven and finally calcined at 550 °C for 12 h to obtain the Ce / ZSM-5 catalyst. The metal loading is shown in Table 1.

[0025] Comparative Example 2 Dissolve 1.5 mg of ferric nitrate in 0.8 mL of water, and then add 1 g of a pore volume of 0.22 cm 3 / g ZSM-5 molecular sieve, and continued stirring for 60 min after the dropwise addition was completed, followed by ultrasonic aging for 2 h. The obtained solid product was then dried in an 80 °C oven and finally calcined at 550 °C for 12 h to obtain the Fe / ZSM-5 catalyst. The metal loading is shown in Table 1.

[0026] The molecular sieve catalysts prepared in Example 1 and Comparative Examples 1-2 and the ZSM-5 molecular sieve were characterized by XRD. Figure 1 The figure only shows the diffraction peaks of the molecular sieve, while the diffraction peaks of Ce, Fe, CeO2 and Fe2O3 particles are not observed, indicating that the prepared Ce-Fe / ZSM-5 catalyst does not form metal particles and the metal species are highly dispersed.

[0027] The catalyst prepared in Example 1 was characterized by transmission electron microscopy and element distribution analysis. The results are shown in Figure 2 and Table 1. Transmission electron microscopy images of the Ce-Fe / ZSM-5 catalyst revealed only hexagonal molecular sieves, without any metal or metal oxide particles on the surface, which is consistent with the XRD results. High-resolution transmission electron microscopy images of the Ce-Fe / ZSM-5 catalyst revealed the pores of the ZSM-5 support, but no obvious metal particles were present. High-angle dark field images of the Ce-Fe / ZSM-5 catalyst and the elemental distribution maps of Ce and Fe clearly indicate the presence of dispersed Ce and Fe active sites.

[0028] The catalyst prepared in Example 1 was characterized by X-ray absorption spectroscopy. Figure 3 . From the K-edge absorption spectrum of Fe in the figure, it can be concluded that the active metal Fe of Ce-Fe / ZSM-5 is in a cationic state; from the EXAFS in the figure, it can be concluded that Ce-Fe / ZSM-5 does not form Fe-Fe bonds of metal Fe and Fe-O-Fe bonds of Fe2O3, indicating that Fe is in a monodisperse state, further proving that Fe is anchored in the molecular sieve micropores in a monodisperse cationic state. From the L3-edge absorption spectrum of Ce in the figure, it can be concluded that the active metal Ce of Ce-Fe / ZSM-5 is in a cationic state; from the EXAFS in the figure, it can be concluded that Ce-Fe / ZSM-5 does not form Ce-Ce bonds of metal Ce and Ce-O-Ce bonds of CeO2, indicating that Ce is in a monodisperse state, further proving that Ce and Fe are anchored in the molecular sieve micropores in a monodisperse cationic state.

[0029] The element contents of the catalysts prepared in Example 1 and Comparative Examples 1-2 were measured, and the results are shown in Table 1. The contents of Ce and Fe were both less than 0.5 wt %, and theoretically, they were highly dispersed on the surface of the molecular sieve.

[0030] Table 1 Metal content of molecular sieve catalysts prepared in Example 1 and Comparative Examples 1-2 Application Examples The metal / molecular sieve catalyst of Example 1 and Comparative Example 1-2 is applied to the selective hydrogenation reaction of methane, specifically 20 mg of metal / molecular sieve catalyst is placed in a reactor, and 15 mL of 30% aqueous hydrogen peroxide solution is added as a solvent. After sealing the reactor, 2 MPa of CH4, 0.5 MPa of CO are charged, the setting temperature is 70 DEG C, and the reaction time is 0.5 h. After completion of the reaction, the reactor is cooled to room temperature, and the reacted gas is collected with an air bag for gas chromatography detection. The gas product shows that there is CO2 and a trace amount of H2 produced, which is close to the gas chromatograph detection limit; The reacted catalyst is washed with water, and the supernatant is taken after centrifugation for liquid nuclear magnetic resonance test (0.01 wt% of D2O-DSS is used as internal standard). Product selectivity and yield are measured and calculated, and the results are shown in Table 2.

[0031] Table 2 Catalyst performance Example 2 The effect of different reaction temperatures on the performance was investigated. The specific steps were as follows: 0.02 g of Ce-Fe / ZSM-5 catalyst was weighed and placed in a reactor, and a specific pressure of CH4 and CO (see Figure 4 ), respectively, and then heated to 50 ° C, 70 ° C and 90 ° C for 0.5 h, and then cooled to room temperature and collected. The product was processed as described in the application example. Figure 4 As shown in the figure, the acetic acid yield increased significantly with increasing temperature, and the selectivity reached the highest at 70 °C.

[0032] Example 3 Catalytic cycle stability test: The Ce-Fe / ZSM-5 catalyst was collected after the reaction and washed to remove the reaction products. The catalyst was washed with water until no product adhered, centrifuged, and then dried in an oven at 80°C for 4 h.

[0033] The dried catalyst was placed in a muffle furnace and calcined in static air at 550 °C for 4 h, then cooled to room temperature for later use.

[0034] 0.02 g of regenerated Ce-Fe / ZSM-5 catalyst was weighed and placed in a reactor. 2 MPa CH4 and 0.5 MPa CO were charged into the reactor. The temperature was raised to 70 °C and the reaction was carried out for 0.5 h. After cooling to room temperature, the product was collected and processed as described in the application example.

[0035] The product was quantitatively analyzed and the cyclic stability test results of the catalyst after the reaction were as follows: Figure 5 As shown in the figure, the regenerated catalyst still has good reaction activity.

[0036] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A ferrocerium / molecular sieve catalyst, characterized in that: The Ce and Fe in the catalyst are anchored in the micropores of the ZSM-5 molecular sieve in a monodisperse cation state. The loading amount of Ce in the catalyst is 0.05-2 wt %, and the loading amount of Fe is 0.05-2 wt %.

2. A method for preparing the ferrocerium / molecular sieve catalyst according to claim 1, characterized in that: The following steps are involved: (1) Tetraethyl orthosilicate, aluminum nitrate, and tetrapropylammonium hydroxide were mixed with water, then treated with ammonia water, stirred at room temperature for 2 h, and then hydrothermally crystallized; (2) washing the crystallized solid product obtained in step (1) with deionized water until neutral, then centrifuging, filtering, and drying; (3) calcining the powder sample obtained in step (2) in a muffle furnace under air to obtain ZSM-5 molecular sieve; (4) dissolving cerium nitrate and ferric nitrate in water and adding them dropwise to the ZSM-5 molecular sieve obtained in step (3), and aging them by ultrasonication at room temperature; (5) The sample obtained in step (4) is dried and then calcined in an air environment to obtain a ferrocerium / molecular sieve catalyst.

3. The preparation method according to claim 2, wherein: In step (1), the molar ratio of tetraethyl orthosilicate: aluminum nitrate: tetrapropylammonium hydroxide: ammonia water: water is 1.0:0.03:0.25:2.3:

34.

4. The preparation method according to claim 2, wherein: The temperature of the hydrothermal crystallization in step (1) is 100-250 °C, and the crystallization time is 4-48 h.

5. The preparation method according to claim 2, wherein: The drying temperature in step (2) is 30-100°C, and the drying time is 1-24 h.

6. The preparation method according to claim 2, wherein: The calcination temperature in step (3) is 200-600°C, and the calcination time is 4-24 h.

7. The preparation method according to claim 2, characterized in that: In step (4), the molar ratio of cerium nitrate to ferric nitrate is 0.1-5, the amount of ZSM-5 molecular sieve is 0.5-5 g, and the aging time is 1-12 h.

8. The preparation method according to claim 2, wherein: The calcination temperature in step (5) is 200-600 °C, and the calcination time is 4-24 h.

9. Use of the ferrocerium / ZSM-5 catalyst as claimed in claim 1 in the mild oxidation of methane to produce acetic acid.

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