Metal confined catalyst, its preparation method and application

Abstract

The application provides a metal confined catalyst and a preparation method and application thereof, metal is wrapped in a zeolite in the form of metal atoms or metal nanoclusters, the metal confined catalyst is obtained through hydrothermal pretreatment and hydrothermal crystallization, and is applied in automobile exhaust purification. The technical scheme of the application is simple to prepare, the metal confined catalyst has high stability and unique catalytic activity, and exhibits unique advantages in the purification of automobile exhaust.

Description

Technical Field

[0001] This invention relates to the field of environmental catalysis technology, and more specifically, to a zeolite-based metal confined catalyst, its preparation method, and its application. Background Technology

[0002] Diesel engines have garnered widespread attention due to their high fuel efficiency, but they also emit significant amounts of exhaust gases, such as CO, hydrocarbons (HCs), and particulate matter, causing a range of environmental problems. Therefore, designing highly efficient catalysts to eliminate these pollutants is urgently needed.

[0003] Metal-based catalysts, especially those made of precious metals, have seen rapid development in automotive exhaust treatment due to their unique physical and chemical properties, but their high cost has also greatly limited their application.

[0004] Typically, noble metal nanoparticles are highly dispersed on metal oxides or porous supports to reduce costs and improve atom utilization, such as Pt-supported Al2O3.

[0005] However, these metal catalysts are prone to deactivation at high temperatures due to the sintering and agglomeration of the metals. Summary of the Invention

[0006] To address the problems in the prior art, the present invention aims to provide a metal confined catalyst that can improve catalyst stability, its preparation method, and its application.

[0007] According to one aspect of the present invention, a metal confined catalyst is provided, comprising a zeolite and a metal, wherein the zeolite has mesoporous channels and the metal is encapsulated within the zeolite in the form of metal atoms or metal nanoclusters.

[0008] Preferably, the metal is one or more of Pt, Cu, Bi, and Fe.

[0009] Preferably, the mass of the metal is 0.1 to 2 wt% of the total mass of the metal-confined catalyst.

[0010] Preferably, the metal-confined catalyst has oxygen vacancy defects.

[0011] According to another aspect of the present invention, a method for preparing the above-described metal confinement catalyst is provided, comprising the following steps:

[0012] Step 1: Dissolve inorganic silicon source, titanium / aluminum source, carbonate, and alkali metal salt in an aqueous solution containing a structure guiding agent for hydrothermal pretreatment, and obtain zeolite precursor solution after filtration and washing.

[0013] Step 2: Add metal solution to zeolite precursor solution, then perform hydrothermal crystallization treatment, filter, wash, dry and calcinate to obtain metal confined catalyst.

[0014] Preferably, the silicon source in step 1 is inorganic silicon, orthosilicic acid, or sodium silicate.

[0015] Preferably, the titanium source in step 1 is titanium sulfate or titanium chloride.

[0016] Preferably, the carbonate in step 1 is sodium carbonate or potassium carbonate.

[0017] Preferably, the alkali metal salt in step 1 is sodium chloride or potassium chloride.

[0018] According to another aspect of the present invention, the application of the above-described metal confined catalyst in automobile exhaust purification is provided.

[0019] Compared with existing technologies, the present invention not only has a simple synthesis method, but also encapsulates the metal into the catalyst. By utilizing the unique pore confinement growth strategy of mesoporous zeolite to enhance the interaction between the metal and the support, the stability of the catalyst can be significantly improved, providing a foundation for the practical application of metal-zeolite catalysts. Attached Figure Description

[0020] Other features, objects, and advantages of the invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings.

[0021] Figure 1 These are HAADF and HAADF-STEM images of the metal Pt confined catalyst based on titanium silicate zeolite obtained in Example 1 of this invention.

[0022] Figure 2 The images show the Pt@TS-1 metal Pt confined catalyst based on titanium silicate zeolite prepared in Example 1 of this invention, the Pt-supported titanium silicate zeolite Pt / TS-1 prepared in Comparative Example 2, and the Pt L3 edge XANES and FT-EXAFS spectra of PtO2 and Pt foil (Pt foil). In the images, a is the XANES spectrum with the ordinate being the normalized absorption coefficient, and b is the FT-EXAFS spectrum with the ordinate being the intensity.

[0023] Figure 3The graphs show the CO oxidation activity of the metal Pt confined catalyst prepared in Example 1, TS-1 prepared in Comparative Example 1, and Pt / TS-1 prepared in Comparative Example 2 for different samples. The horizontal axis represents temperature, and the vertical axis represents CO conversion rate. Among them, a is the CO conversion rate graph of TS-1, Pt@TS-1, and Pt / TS-1; b and c are the CO conversion rate graphs of Pt@TS-1 and Pt / TS-1; and d is the circulating CO conversion rate graph of Pt@TS-1. Detailed Implementation

[0024] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art. The same reference numerals in the drawings denote the same or similar structures, and therefore repeated descriptions of them will be omitted.

[0025] In an embodiment of the present invention, a metal confined catalyst comprises a zeolite and a metal, wherein the zeolite has mesoporous channels and the metal is encapsulated within the zeolite in the form of metal atoms or metal nanoclusters.

[0026] Mesoporous pores refer to channels with a pore size between 2 and 50 nanometers, falling between micropores and macropores. Zeolites are a general term for zeolite group minerals, which are hydrous alkali or alkaline earth metal aluminosilicate minerals. Zeolites possess mesoporous channels. The metal refers to metal atoms or metal nanoclusters that grow in a confined environment within the zeolite.

[0027] The confined metal is preferably present in the form of metal atoms or metal nanoclusters. The mass of the confined metal is preferably 0.1–2 wt% of the total mass. Too low a metal content results in low catalytic activity, while too high a metal content not only makes it difficult to form a zeolite framework with a specific topological structure, but also makes it easy for the metal to migrate to the zeolite surface.

[0028] The confinement effect of mesoporous zeolite channels can effectively improve the activity and stability of catalysts, thereby enhancing the overall performance of the catalysts.

[0029] The preferred metal is one or more of Pt, Cu, Bi, and Fe.

[0030] Furthermore, the metal-confined catalyst prepared in the embodiments of the present invention has abundant oxygen vacancy defects.

[0031] In addition, in the embodiments of the present invention, a zeolite precursor liquid rich in zeolite sub-nano crystals is first obtained by hydrothermal pretreatment, and then a metal solution precursor liquid is added to obtain a metal confined catalyst based on mesoporous zeolite by hydrothermal crystallization.

[0032] Hydrothermal crystallization is a method that uses an aqueous solution as the reaction medium in a specially designed closed reactor (such as an autoclave or hydrothermal reactor). By heating the reactor, a high-temperature and high-pressure reaction environment is created, which allows substances that are usually difficult to dissolve or insoluble to dissolve and recrystallize to form dispersed nanocrystal nuclei.

[0033] Hydrothermal pretreatment involves preheating the material in a high-temperature, high-pressure reaction environment for a period of time before hydrothermal crystallization.

[0034] Specifically, the following steps are included:

[0035] Step 1: Dissolve inorganic silicon source, titanium / aluminum source, carbonate, and alkali metal salt in an aqueous solution containing a structure-directing agent for hydrothermal pretreatment, and obtain zeolite precursor solution after filtration and washing.

[0036] The preferred structure-directing agent is tetrapropylammonium hydroxide (TPAOH) or tetraethylammonium hydroxide (TEAOH).

[0037] The preferred silicon source is one of inorganic silicon, orthosilicic acid, sodium silicate, etc.; the preferred titanium source is one of titanium sulfate, titanium chloride, etc.; the preferred carbonate is one of sodium carbonate, potassium carbonate, etc.; and the preferred alkali metal salt is one of sodium chloride, potassium chloride, etc.

[0038] The preferred concentrations of alkali metal salts and carbonates in the zeolite precursor solution are 1–3 mg / mL and 3–9 mg / mL, respectively. The Si / M atomic ratio (where M represents Ti or Al atoms) is 15–50.

[0039] In an embodiment of the present invention, zeolite sub-nano crystals are obtained by hydrothermal pretreatment at a certain temperature. Preferably, the hydrothermal pretreatment temperature is 120–200°C, and the hydrothermal pretreatment time is 6–12 hours.

[0040] Step 2: Add metal solution to zeolite precursor solution, react for a period of time, and then perform hydrothermal crystallization treatment. After filtration, washing, drying and calcination, metal confined catalyst is obtained.

[0041] The preferred metal solution is a metal precursor solution formed by dissolving a metal source in a mixed solution of deionized water and ethylene glycol. The preferred volume ratio of ethylene glycol to water is 3–1.

[0042] Specifically, a certain amount of metal source was weighed and dissolved in a mixed solution of deionized water and ethylene glycol. The resulting homogeneous mixed solution was added to a filtered and washed zeolite precursor solution, and the reaction was allowed to proceed for a period of time. The solution was then transferred to a hydrothermal reactor and subjected to hydrothermal reaction at 120–200°C for 12–24 hours. After filtration, washing, drying, and calcination, the zeolite-based metal confined catalyst of this invention was finally obtained.

[0043] The preferred metal source is at least one of chloroplatinic acid, palladium nitrate, ferrous chloride, cuprous chloride, etc.

[0044] Furthermore, the preferred concentration of the metal precursor solution is 10–100 mg / mL. The preferred hydrothermal crystallization temperature is 120–200 °C, and the preferred time is 12–24 h. The preferred subsequent drying temperature is 80–120 °C; the preferred calcination temperature is 500–600 °C, and the preferred time is 4–8 h.

[0045] In addition, the synthesis method of the present invention is simple, the metal in the metal confined catalyst exists in the form of atoms or nanoclusters, and the obtained catalyst has excellent catalytic oxidation activity and stability, and can be applied to thermocatalysis and environmental catalysis, such as in the field of automobile exhaust purification.

[0046] Example 1

[0047] Dissolve 0.11 g sodium carbonate, 50 mmol orthosilicic acid and 0.05 g potassium chloride in 6 mL of H2O and 10 g tetrapropyl ammonium hydroxide (TPAOH, 50 wt%) aqueous solution, and stir continuously at 60 °C for 30 min to obtain solution 1.

[0048] Then, 2 mmol of titanium sulfate was dissolved in 4 mL of H2O to obtain solution 2.

[0049] Then, solution 2 was added dropwise to solution 1, and the mixture was stirred vigorously at 40°C for 4 hours. The mixture was then transferred to a hydrothermal reactor and pretreated hydrothermally at 150°C for 12 hours. Finally, the mixture was washed twice with a mixture of ethanol and water to obtain the zeolite precursor solution.

[0050] Dissolve 8 mg of chloroplatinic acid in a mixed solution of 20 mL of ethylene glycol and 10 mL of H2O. Then, add this solution to the zeolite precursor solution.

[0051] The mixed solution was subjected to hydrothermal crystallization at 150°C for 24 hours.

[0052] Next, the mixture was cooled to room temperature, washed with ethanol and water, the upper aqueous layer was removed by centrifugation, dried overnight in a drying oven at 80°C, and then calcined at 550°C for 4 h to obtain the metal Pt confined catalyst Pt@TS-1 based on titanium silicate zeolite.

[0053] like Figure 1As shown in the figure, the HAADF and HAADF-STEM images of the metal Pt confined catalyst based on titanium silicate zeolite prepared in Example 1 of the present invention show that the sample prepared in Example 1 of the present invention consists of 300-500 nm nanoparticles, the zeolite exhibits a loose and porous morphology, and there are no obvious metal Pt nanoparticles on the zeolite surface; at the same time, by using aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), it was found that Pt is encapsulated in the zeolite in the form of nanoparticles or nanoclusters, suggesting the successful preparation of the metal Pt confined catalyst.

[0054] Comparative Example 1

[0055] Dissolve 0.11 g sodium carbonate, 50 mmol orthosilicic acid and 0.05 g potassium chloride in 6 mL of H2O and 10 g tetrapropyl ammonium hydroxide (TPAOH, 50 wt%) aqueous solution, and stir continuously at 60 °C for 30 min to obtain solution 1.

[0056] Then, 2 mmol of titanium sulfate was dissolved in 4 mL of H2O to obtain solution 2.

[0057] Then, solution 2 was added dropwise to solution 1, and the mixture was stirred vigorously at 40°C for 4 hours. The mixture was then transferred to a hydrothermal reactor and hydrothermally crystallized at 150°C for 24 hours.

[0058] The mixture was cooled to room temperature, washed with ethanol and water, the upper aqueous layer was removed by centrifugation, dried overnight in a drying oven at 80°C, and then calcined at 550°C for 4 hours to obtain mesoporous titanium silicate zeolite TS-1 with abundant oxygen vacancy defects.

[0059] Comparative Example 2

[0060] Dissolve 0.11 g sodium carbonate, 50 mmol orthosilicic acid and 0.05 g potassium chloride in 6 mL of H2O and 10 g tetrapropyl ammonium hydroxide (TPAOH, 50 wt%) aqueous solution, and stir continuously at 60 °C for 30 min to obtain solution 1.

[0061] Then, 2 mmol of titanium sulfate was dissolved in 4 mL of H2O to obtain solution 2.

[0062] Then, solution 2 was added dropwise to solution 1, and the mixture was stirred vigorously at 40°C for 4 hours. The mixture was then transferred to a hydrothermal reactor and hydrothermally crystallized at 150°C for 24 hours.

[0063] The mixture was cooled to room temperature, washed with ethanol and water, the upper aqueous layer was removed by centrifugation, and dried overnight in a drying oven at 80°C to obtain uncalcined TS-1.

[0064] Dissolve 8 mg of chloroplatinic acid in a mixed solution of 20 mL ethylene glycol and 10 mL H₂O, then add 4 mL of 1 mg / L 5NaBH₄ solution and stir vigorously at 80 °C for 6 h. Dissolve the above-mentioned uncalcined TS-1 in the solution and react for 30 min, then wash three times with ethanol and water.

[0065] The final product Pt / TS-1 was dried at 80℃ and calcined at 550℃ for 4 hours to obtain Pt-supported titanium silicate zeolite Pt / TS-1.

[0066] like Figure 2 The images show the Pt L3 edge XANES and FT-EXAFS spectra of the Pt@TS-1 metal Pt confined catalyst based on titanium silicate zeolite prepared in Example 1 of this invention, and the Pt-supported titanium silicate zeolite Pt / TS-1, PtO2, and Pt foil prepared in Comparative Example 2. It can be observed that the Pt atoms in Pt@TS-1 of the examples have a higher oxidation state than those in Pt / TS-1. In Pt@TS-1, Pt mainly exists in the form of Pt-O, unlike in Pt / TS-1 where Pt mainly exists in the form of Pt-Pt. This result indicates that the pore confinement of mesoporous zeolite channels can regulate the electronic state of the metal, and the presence of low oxidation state Pt helps improve catalytic activity.

[0067] Performance testing

[0068] Test 1:

[0069] 100 mg of catalysts Pt@TS-1, TS-1, and Pt / TS-1 from Example 1, Comparative Examples 1 and 2, respectively, were loaded into fixed-bed quartz reactors and dried at 150 °C for 1 h. The reaction feed gas, containing 1 vol.% CO, 10 vol.% O2, and N2, served as the equilibrium gas, and the total flow rate was 200 mL / min. -1 The heating rate is 2℃ / min.

[0070] Under steady-state conditions, the product was detected using an online gas chromatograph (GC) equipped with an FID detector, and its oxidation activity against CO was determined in the range of 30–300 °C. The results are as follows: Figure 3 As shown in a.

[0071] Test 2:

[0072] 100 mg of the catalyst Pt@TS-1 from Example 1 and Pt / TS-1 from Comparative Example 2 were respectively loaded into fixed-bed quartz reactors and dried at 150 °C for 1 h. The reaction feed gas, containing 1 vol.% CO, 10 vol.% O2, 8 vol.% H2O, and N2, served as the equilibrium gas, and the total flow rate was 200 mL / min. -1 The heating rate was 2℃ / min, and the water resistance of the catalyst was determined.

[0073] Under steady-state conditions, the product was detected using an online gas chromatograph (GC) equipped with an FID detector, and its oxidation activity against CO was determined in the range of 30–300 °C. The results are as follows: Figure 3 As shown in b.

[0074] Test 3:

[0075] 100 mg of the catalysts Pt@TS-1 (Example 1) and Pt / TS-1 (Comparative Example 2) were respectively loaded into fixed-bed quartz reactors and dried at 150 °C for 1 h. The reaction feed gas, containing 1 vol.% CO, 10 vol.% O2, 8 vol.% H2O, 200 ppm SO2, and N2, served as the equilibrium gas, with a total flow rate of 200 mL / min. -1 The heating rate was 2℃ / min, and the sulfur resistance of the catalyst was measured.

[0076] Under steady-state conditions, the product was detected using an online gas chromatograph (GC) equipped with an FID detector, and its oxidation activity against CO was determined in the range of 30–300 °C. The results are as follows: Figure 3 As shown in c.

[0077] Test 4:

[0078] 100 mg of catalyst Pt@TS-1 was loaded into a fixed-bed quartz reactor and dried at 150 °C for 1 h. The equilibrium gas consisted of 1 vol.% CO, 10 vol.% O2, 8 vol.% H2O, 200 ppm SO2, and N2. The total flow rate was 200 mL / min. -1 The heating rate was 2℃ / min, and the durability and stability of the catalyst were determined.

[0079] Under steady-state conditions, the products were detected using an online gas chromatograph (GC) equipped with an FID detector, and their oxidation activity against CO was determined within the range of 30–300 °C. Once one cycle was completed and the reactor cooled to room temperature, a new cycle began, with results as follows: Figure 3 As shown in d.

[0080] like Figure 3 The graph shows the CO oxidation activity of the catalyst for different samples. It can be seen that the confined growth metal catalyst Pt@TS-1 of Example 1 of this invention, under conditions of low noble metal content (~0.2 wt%), not only achieves complete conversion of 90% (T90) CO at 175 °C, but also exhibits excellent resistance to water and sulfur. More importantly, the catalytic performance of the catalyst of Example 1 remained essentially unchanged in three cycles, demonstrating excellent stability.

[0081] In summary, the synthesis method of this invention is simple. By encapsulating the metal in the catalyst and utilizing the unique pore confinement growth strategy of mesoporous zeolite to enhance the interaction between the metal and the support, the stability of the catalyst can be significantly improved, providing a foundation for the practical application of metal-zeolite catalysts.

[0082] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A metal-confined catalyst, characterized in that, The catalyst comprises zeolite and metal, wherein the zeolite has mesoporous channels, and the metal is encapsulated within the zeolite in the form of metal atoms or metal nanoclusters; the metal is one or more of Pt, Cu, Bi, and Fe; the metal-confined catalyst has oxygen vacancy defects; the preparation method of the metal-confined catalyst includes the following steps: Step 1: Dissolve inorganic silicon source, titanium source, carbonate, and alkali metal salt in an aqueous solution containing a structure-directing agent for hydrothermal pretreatment, and obtain zeolite precursor solution after filtration and washing; the carbonate in Step 1 is sodium carbonate or potassium carbonate; the alkali metal salt in Step 1 is sodium chloride or potassium chloride. Step 2: Add metal solution to zeolite precursor solution, then perform hydrothermal crystallization treatment, filter, wash, dry and calcinate to obtain metal confined catalyst.

2. The metal confinement catalyst according to claim 1, characterized in that: The mass of the metal is 0.1 to 2 wt% of the total mass of the metal-confined catalyst.

3. The metal confinement catalyst according to claim 1, characterized in that: In step 1, the silicon source is inorganic silicon, orthosilicic acid, or sodium silicate.

4. The metal confinement catalyst according to claim 1, characterized in that: In step 1, the titanium source is titanium sulfate or titanium chloride.

5. The application of the metal confined catalyst according to claim 1 in automobile exhaust purification.

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