Preparation method and application of two-dimensional oriented nanosheet Cu-SSZ-39 molecular sieve

Abstract

The invention belongs to the technical field of environmental catalysis, and discloses a preparation method and application of a two-dimensional oriented nanosheet Cu-SSZ-39 molecular sieve, the preparation method comprises the following steps: (1) mixing an inorganic base, a silicon source, an organic template agent, water, a USY molecular sieve and an SSZ-39 seed crystal to form initial gel; (2) carrying out hydrothermal reaction and carrying out double-temperature crystallization to obtain an M-SSZ-39 molecular sieve; (3) carrying out ammonium ion exchange to obtain an NH4-SSZ-39 molecular sieve; and (4) adding the NH4-SSZ-39 molecular sieve into the copper precursor solution, carrying out heat-enhanced stirring and dipping, and then drying and calcining to obtain the two-dimensional nano flaky Cu-SSZ-39 catalyst. The preparation method is improved, and dual-temperature crystallization is matched with heat strengthening impregnation, so that a synergistic strategy of carrier morphology regulation and accurate active site construction is realized, and the technical problems of narrow working temperature window, serious internal diffusion limitation and low active site utilization rate of a traditional Cu-SSZ-39 catalyst are solved.

Description

Technical Field

[0001] This invention belongs to the field of environmental catalysis technology, and more specifically, relates to a method for preparing and applying a two-dimensional oriented nanosheet Cu-SSZ-39 molecular sieve, which can be applied to NH3-SCR reaction, especially in diesel vehicle exhaust denitrification. Background Technology

[0002] Nitrogen oxides (NOx) emitted from diesel engine exhaust x NOx is one of the major air pollutants, seriously endangering the environment and public health. It is a major cause of acid rain and photochemical smog, and induces respiratory and cardiovascular diseases. To address this challenge, countries have successively introduced and tightened regulations on motor vehicle emissions. The national standard GB 17691—2018 specifies NOx for diesel vehicles... x The emission limit has been drastically reduced to 35 mg / km, placing stringent demands on catalyst technology. This necessitates that exhaust purification catalysts maintain extremely high conversion efficiency across the entire operating temperature range of a vehicle under real-world driving conditions. Any performance shortcomings under low-temperature (e.g., 200℃, or even 150℃~200℃) or high-temperature (e.g., 450℃, or even 450℃~500℃) conditions could lead to the vehicle exceeding emission standards.

[0003] NH3-SCR technology, with its superior denitrification efficiency and technological maturity, has become the preferred choice for NOx emissions testing in diesel vehicles. x The mainstream technology for SCR control. Among them, copper-based small-pore molecular sieves, especially Cu-SSZ-39 with AEI topology, are recognized as the most promising next-generation commercial SCR catalysts due to their excellent comprehensive performance.

[0004] However, Cu-SSZ-39 catalysts prepared using existing conventional techniques still face a series of interconnected technical bottlenecks that limit their final performance. First, the effective operating temperature window is narrow: in the low-temperature region (below 200°C), the catalyst exhibits insufficient activity due to slow redox cycle kinetics; while in the high-temperature region (above 450°C), side reactions such as the competitive oxidation of ammonia lead to a decrease in selectivity, making it difficult to meet the requirements for efficient purification under all operating conditions. Second, the support exhibits internal diffusion limitations: SSZ-39 molecular sieves synthesized by conventional methods are typically micron-sized crystals (1~5 μm). Their narrow, elongated microporous channels significantly hinder the transport of reactant molecules, resulting in a large number of active sites in the crystal core region remaining unutilized, leading to low catalytic efficiency. Third, the active site construction methods are crude: conventional copper-supported techniques such as impregnation lack precise control capabilities, easily leading to the enrichment of active copper species on the outer surface of the molecular sieve, which then agglomerate into poor-performing copper oxide (CuO) clusters during subsequent heat treatment. These clusters not only have low catalytic activity themselves but also exacerbate side reactions at high temperatures, further deteriorating the overall performance of the catalyst.

[0005] In summary, there is an urgent need in this field for a novel, integrated catalyst preparation strategy that can eliminate diffusion limitations by synergistically controlling the nanomorphology of molecular sieve supports and achieve precise and uniform loading of active copper species. This would fundamentally overcome the limitations of existing technologies in terms of operating temperature window, active site utilization, and selectivity, and enable the development of high-performance diesel vehicle exhaust purification catalysts that can meet the future GB 17691—2018 standard. Summary of the Invention

[0006] To address the aforementioned deficiencies or improvement needs of existing technologies, the present invention aims to provide a method for preparing and applying two-dimensional oriented nanosheet Cu-SSZ-39 molecular sieves. By improving the preparation method, employing dual-temperature crystallization combined with thermally enhanced impregnation, a synergistic strategy of controlling support morphology and precisely constructing active sites is achieved. This solves the technical problems of narrow operating temperature window, severe internal diffusion restriction, and low active site utilization in traditional Cu-SSZ-39 catalysts. Compared to traditionally prepared Cu-SSZ-39 catalysts, the method of the present invention enables two-dimensional oriented growth of Cu-SSZ-39 catalysts. The synthesized two-dimensional nanosheet Cu-SSZ-39 catalyst exhibits a significant increase in external surface area, maximizing the retention of active Cu. 2+ This catalyst effectively inhibits CuO aggregation and exhibits excellent NH3-SCR denitrification activity and N2 selectivity over a wide temperature range of 150–500 °C, providing a highly efficient technical solution for diesel vehicle exhaust treatment and possessing significant industrial application value.

[0007] To achieve the above objectives, according to one aspect of the present invention, a method for preparing two-dimensional oriented nanosheet Cu-SSZ-39 molecular sieve is provided, characterized by comprising the following steps: (1) First, an initial gel is formed by mixing an inorganic base, a silicon source, an organic template agent, water, USY molecular sieve, and SSZ-39 seed crystals; wherein, the amount of SSZ-39 seed crystals is 1.0~2.0 wt% of the total mass of the gel. (2) The initial gel obtained in step (1) is used as a hydrothermal reaction precursor to carry out a hydrothermal reaction to achieve crystallization; the hydrothermal reaction is a dual-temperature crystallization, first crystallizing at a low temperature of 75~95°C for 20~30 hours, and then continuing to crystallize at a high temperature of 165~185°C for 60~80 hours; after the hydrothermal reaction is completed, the obtained solid product is collected and washed and dried, and then calcined to remove the organic template agent to obtain M-SSZ-39 molecular sieve; wherein, M represents a metal element, which is the same as the metal element in the inorganic base; (3) The M-SSZ-39 molecular sieve obtained in step (2) is subjected to ammonium ion exchange to obtain NH4-SSZ-39 molecular sieve; (4) The NH4-SSZ-39 molecular sieve obtained in step (3) is added to the copper precursor solution and subjected to thermally enhanced stirring and impregnation under water bath conditions of 50~90℃. The solution is evaporated to 1~5% of its original volume, and then dried and calcined to obtain the two-dimensional nanosheet Cu-SSZ-39 catalyst.

[0008] As a further preferred embodiment of the present invention, in step (2), the dual-temperature crystallization is first crystallization at 85~95°C for 22~26 hours, and then crystallization at 175~185°C for 68~76 hours; Preferably, the dual-temperature crystallization involves first crystallizing at 90°C for 24 hours, and then crystallizing at 180°C for 72 hours.

[0009] As a further preferred embodiment of the present invention, in step (4), the heat-enhanced stirring impregnation is carried out under a water bath at 65~75°C and stirring at 200~300 rpm for 8~12 hours; Preferably, the heat-enhanced stirring impregnation is carried out under a water bath at 68-72°C and stirring at 230-270 rpm for 9-11 hours, so that the solution evaporates to 1.5-3% of its original volume; More preferably, the heat-enhanced stirring impregnation is carried out by stirring at 250 rpm for 10 hours under a 70°C water bath condition, so that the solution evaporates to 2% of its original volume.

[0010] As a further preferred embodiment of the present invention, in step (4), the drying temperature is 100~120°C and the time is 10~14 hours; the calcination temperature is 500~600°C and the time is 4~6 hours.

[0011] As a further preferred embodiment of the present invention, in step (4), the copper precursor contained in the copper precursor solution is one or more of copper nitrate, copper sulfate or copper acetate. The copper element contained in the copper precursor solution is 2 to 5 wt% of the total mass of the NH4-SSZ-39 molecular sieve.

[0012] As a further preferred embodiment of the present invention, in step (3), the ammonium ion exchange is performed in multiple steps, preferably in three steps; The ammonium salt used in the ammonium ion exchange is one or more of (NH4)2SO4, NH4Cl, or NH4NO3. Each ammonium ion exchange involves adding M-SSZ-39 molecular sieve to the ammonium salt solution for the exchange. The solid-liquid ratio of M-SSZ-39 molecular sieve to the ammonium salt solution is 1 g : 20~40 mL, and the mass ratio of M-SSZ-39 molecular sieve to the amount of ammonium salt in the ammonium salt solution is 1 g : 20~40 mmol. Preferably, for each ammonium ion exchange, the solid-liquid ratio of M-SSZ-39 molecular sieve to the ammonium salt solution is 1 g : 25~35 mL, and the mass ratio of M-SSZ-39 molecular sieve to the amount of ammonium salt in the ammonium salt solution is 1 g : 25~35 mmol. The temperature for ammonium ion exchange is 70~90°C, and the time for each ammonium ion exchange is 6~10 h; preferably, the temperature for ammonium ion exchange is 75~85°C, and the time for each ammonium ion exchange is 7~9 hours. The NH4-SSZ-39 molecular sieve is obtained by collection through vacuum filtration or centrifugation, followed by washing and drying.

[0013] As a further preferred embodiment of the present invention, in step (1), the mixing is carried out by stirring at room temperature for 1 to 3 hours to achieve uniform mixing; The collection is performed by vacuum filtration or centrifugation. The washing is performed until the solution is neutral; The calcination is carried out at 500-600°C for 4-6 hours; The amounts of inorganic alkali, silicon source, organic template agent (OSDA), water, and USY molecular sieve are sufficient to ensure that the initial gel contains components in a molar ratio of SiO2: Al2O3: Na2O: OSDA: H2O = 1: 0.05~0.2: 0.4~0.8: 0.2~0.8: 10~40. The silicon source is selected from one of silica sol, tetraethyl orthosilicate, and sodium silicate. The Si / Al molar ratio of the USY molecular sieve is 10~25; The alkaline source is one of sodium hydroxide, potassium hydroxide, and lithium hydroxide; The organic template agent is one of 1,1,3,5-tetramethylpiperidine, N,N-dimethyl-3,5-dimethylpiperidine, and N,N-diethyl-2,6-dimethylpiperidine.

[0014] According to another aspect of the present invention, the present invention provides a two-dimensional nanosheet Cu-SSZ-39 catalyst prepared by the above method.

[0015] As a further preferred embodiment of the present invention, the two-dimensional nanosheet Cu-SSZ-39 catalyst has a two-dimensional planar dimension of 100~200 nm, a thickness dimension of 30~40 nm, and an aspect ratio of 3.3~5.0. Preferably, the specific surface area is 750~800 m². 2 / g, total pore volume is 0.26~0.30 cm³ 3 / g; copper species include isolated Cu 2+ Ions and CuO nanoclusters, wherein the average particle size of the CuO nanoclusters is less than 5 nm, Cu 2+ The CuO mass ratio is 0.65 ~ 0.85.

[0016] According to another aspect of the present invention, the present invention provides the application of the above-mentioned two-dimensional nanosheet Cu-SSZ-39 catalyst in NH3-SCR denitrification; preferably, the application is specifically in the application of NH3-SCR denitrification of diesel vehicle exhaust.

[0017] Compared with the prior art, the present invention employs a seed-assisted dual-temperature crystallization technique. This involves uniformly mixing a silicon source, aluminum source, alkali source, organic template agent, water, and an appropriate amount of seed crystals to obtain an initial gel. Nucleation is first controlled at a low temperature, followed by a transfer to a high temperature to promote the two-dimensional directional growth of the crystals (i.e., nucleation is controlled at 75-95°C for 20-30 hours, then transferred to 165-185°C for another 60-80 hours to promote directional growth). This process prepares a molecular sieve support with a two-dimensional nanosheet morphology. Combined with a thermally enhanced impregnation technique, mechanical stirring is performed under heating conditions to achieve uniform loading and precise control of active copper species. The final sample is obtained after drying and calcination.

[0018] The catalyst prepared by this invention exhibits a two-dimensional nanosheet morphology with a planar dimension of 100-200 nm, a thickness dimension of 30-40 nm, and an aspect ratio of 3.3-5.0; its specific surface area is 750-800 m². 2 / g, total pore volume is 0.26~0.30 cm³ 3 / g; copper species include isolated Cu 2+ Ions and highly dispersed CuO nanoclusters, wherein the average particle size of the CuO nanoclusters is less than 5 nm, Cu 2+ The CuO mass ratio is 0.65 ~ 0.85.

[0019] Specifically, the present invention can achieve the following beneficial effects: (1) By using a seed-assisted dual-temperature crystallization strategy, the morphology of SSZ-39 molecular sieve was precisely controlled, and a carrier with a two-dimensional nanosheet structure was prepared. Its planar size was controlled at 100 ~ 200 nm and its thickness was only 30-40 nm. Compared with traditional micron-sized bulk crystals (1~5 μm), the diffusion path was shortened by 85~95%, effectively eliminating the internal diffusion limitation.

[0020] (2) By using thermally enhanced impregnation technology to replace traditional static impregnation, the uniform dispersion and precise control of copper species are achieved through the synergistic effect of temperature field and mechanical stirring. 2+ The CuO mass ratio was increased to 0.65~0.85 (compared to only 0.40~0.50 in traditional methods), and the CuO nanocluster particle size was controlled to below 5 nm (compared to >10 nm in traditional methods), which significantly improved the utilization efficiency of active sites.

[0021] (3) The working temperature window of the catalyst is significantly widened, exhibiting excellent denitrification performance across the entire temperature range of 150~500°C: NO at a low temperature of 200°C x The conversion rate reached 88-93%, which is 20-28 percentage points higher than that of traditional catalysts; NO under high temperature conditions of 500°C x The conversion rate remains at 78-85%, which is 15-25 percentage points higher than that of traditional catalysts.

[0022] (4) The N2 selectivity is significantly improved, and the amount of N2O byproducts generated is controlled below 10 ppm in the entire temperature range, which is 60-80% lower than that of traditional catalysts, meeting the stringent environmental emission standards.

[0023] (5) The catalyst exhibits excellent stability, maintaining NO levels for 100 hours of continuous operation at 200°C and 450°C. x Conversion rate decay is less than 5%.

[0024] (6) The preparation process has good reproducibility, with crystal size deviation between batches less than 5%, and copper loading control accuracy reaching ±2%, making it suitable for industrial-scale production. Under the same performance conditions, the amount of catalyst can be reduced by 15-20%, the service life can be extended by 30-40%, and the overall cost can be reduced by more than 25%.

[0025] (7) This invention overcomes the technical challenge of simultaneously controlling the morphology and crystallinity of molecular sieves, demonstrating the originality of the method. In the traditional understanding of molecular sieve synthesis, obtaining small-sized, high-specific-surface-area nanocrystals often comes at the cost of sacrificing crystallinity or poor process stability. Those skilled in the art usually choose a single crystallization temperature for experimentation, but this makes it difficult to decouple the two mutually restrictive processes of crystal "nucleation" and "growth," resulting in the inability to simultaneously achieve the goals of "nanoscale size" and "high crystallinity." This invention breaks through this technical bias and creatively adopts a "seed-assisted dual-temperature crystallization" strategy: by pre-adding SSZ-39 seed crystals and performing the first-step crystallization at a relatively low temperature (75~95°C), the first-step crystallization is not for directly obtaining the product, but for inducing and controlling the rate and quantity of secondary nucleation in terms of kinetics, forming a large number of uniform and stable growth units. This step is the key to overcoming the uncontrollability of size. Subsequently, the reaction system was raised to a high temperature (165~185°C) to provide sufficient thermodynamic driving force for the previously formed excellent crystal nuclei, enabling them to grow rapidly and preferentially along the two-dimensional direction. This resulted in the successful acquisition of the ideal nanosheet morphology while maintaining high crystallinity. This "divide and conquer" design of the nucleation and growth processes is one of the core creative manifestations of this invention.

[0026] (8) This invention discovers the synergistic conditions for achieving precise loading of active copper species, solving the industry pain point of active site aggregation. For nanosheet-like carriers with high external surface area, how to uniformly load active components rather than simply enrich them on the surface is a recognized technical challenge. Conventional static impregnation methods, due to the capillary force during the drying process, easily cause copper species to migrate to the outer surface and aggregate into large, low-activity CuO species. The experimental results of Comparative Example 2 (with CuO particle size reaching 8.2 nm on the same nanosheet carrier as Example 1) also confirm this problem. This invention has made great efforts in solving this problem and finally determined the key synergistic parameters in the "thermally enhanced impregnation" technology: by applying continuous mechanical stirring (200-300 rpm) at a specific temperature (65~75°C), not only is the mass transfer efficiency increased, but more importantly, sufficient energy is provided to promote Cu 2+ The migration of ions into the exchange sites inside the molecular sieve enables simultaneous "ion exchange" and "impregnation," reducing surface physical adsorption at the source. Under the aforementioned heat-enhanced impregnation conditions, the solution system is evaporated to 1-5% of its original volume, avoiding the sudden precipitation and aggregation of solutes during traditional rapid drying processes. This allows copper species to settle more evenly on the carrier surface and within the pores.

[0027] In summary, this invention innovatively combines seed-assisted dual-temperature crystallization technology and thermally enhanced impregnation technology, synergistically optimizing from two dimensions: support morphology design and active site construction. This breakthrough overcomes the performance bottleneck of traditional Cu-SSZ-39 catalysts and provides a practical technical route for the development of a new generation of wide-temperature-window NH3-SCR catalysts. Attached Figure Description

[0028] Figure 1 The XRD patterns of the catalysts prepared in Examples 1-5 and Comparative Examples 1-2 are shown in comparison.

[0029] Figure 2 These are TEM images of the Cu-SSZ-39 catalyst prepared in Example 1 at different magnifications; where, Figure 2 In (a), the dimension scale represents 200 nm. Figure 2 In (b), the dimension scale represents 5 nm.

[0030] Figure 3 The images show a UV comparison of the catalysts prepared in Example 1 and Comparative Example 1.

[0031] Figure 4 SEM and TEM images of the Cu-SSZ-39 catalyst prepared in Comparative Example 1; where, Figure 4 (a) in the image is a SEM image, with the size bar representing 5 μm; Figure 4 (b) in the image is a TEM image, with a size bar representing 10 nm.

[0032] Figure 5 The graph shows a comparison of the kinetic tests of the catalysts prepared in Example 1 and Comparative Example 1. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0034] Example 1 Includes the following steps: (1) Synthesis of two-dimensional nanosheet Na-SSZ-39 molecular sieve Sodium hydroxide, USY molecular sieve, silica sol, 1,1,3,5-tetramethylpiperidine (OSDA) solution, and deionized water were added to a beaker and stirred at room temperature for 2 hours to form a homogeneous synthetic gel. This gel system can be considered to consist of SiO2, Al2O3, Na2O, OSDA, and H2O, with the following molar ratios: 1.0 SiO2: 0.08 Al2O3: 0.50 Na2O: 0.35 OSDA: 25H2O.

[0035] Add 0.05 g of SSZ-39 seed crystals (1.5 wt% of the total gel mass) to 3.33 g of gel, and continue stirring for 60 minutes to ensure uniform seed crystal dispersion. Transfer the mixture to a 500 mL PTFE-lined stainless steel reactor and then seal it.

[0036] A dual-temperature crystallization procedure was adopted: first, the reactor was placed in a 90°C oven for static crystallization for 24 hours to control nucleation, and then the temperature was raised to 180°C for another 72 hours to promote crystal growth. After crystallization, it was naturally cooled to room temperature.

[0037] The solid product was repeatedly filtered and washed until neutral. It was then dried at 110°C for 12 hours, and then calcined in a muffle furnace at a heating rate of 2°C / min to 550°C for 6 hours to obtain a white powdery Na-SSZ-39 molecular sieve.

[0038] (2) Preparation of NH4-SSZ-39 by ion exchange 10.0 g of the above-mentioned Na-SSZ-39 molecular sieve was added to 200 mL of a 1.0 mol / L ammonium nitrate solution (the solid-liquid ratio of Na-SSZ-39 molecular sieve to ammonium nitrate solution was 1:20 g / mL). Ion exchange was carried out at 80°C with magnetic stirring for 8 hours. After filtration, washing, and separation, the above ion exchange operation was repeated three times. Then, it was dried at 110°C for 12 hours to obtain NH4-SSZ-39 molecular sieve.

[0039] (3) Cu species loaded by heat-strengthened impregnation method Accurately weigh 5.00 g of the above-mentioned Na-SSZ-39 molecular sieve and add it to 100 mL of deionized water containing 0.76 g of Cu(NO3)2·3H2O (containing 0.20 g of Cu element, with a theoretical Cu loading of 4 wt%). Place the impregnation system in a 70°C constant temperature water bath and perform heat-intensified impregnation at 250 rpm for 10 hours. During the impregnation process, the solution is slowly evaporated to 2% of its original volume by controlling the water bath temperature and ventilation conditions.

[0040] The impregnated solid was dried at 110°C for 12 hours to completely remove residual moisture. Then, the temperature was increased to 550°C at a rate of 2°C / min and calcined in air for 5 hours to obtain a light blue Cu-SSZ-39 catalyst.

[0041] The test was conducted using transmission electron microscopy, and the results are as follows: Figure 2 As shown in (a), the obtained catalyst's two-dimensional nanosheets exhibit a small-sized, sheet-like morphology, with a planar dimension of 150 ± 20 nm, a thickness of 35 ± 3 nm, and an aspect ratio of 4.3. Figure 2 As shown in (b), the CuO particles in the product are small and highly dispersed, with an average particle size of 3.5 ± 0.5 nm for the CuO nanoclusters. The BET specific surface area is 785 m². 2 / g, total pore volume is 0.28 cm³ 3 / g, micropore volume is 0.24 cm³ 3 / g. ICP-OES determined the actual Cu loading to be 3.98 wt%, and the Si / Al molar ratio to be 11.8. XPS testing of Cu... 2+ The CuO mass ratio is 0.75.

[0042] Example 2 The preparation method of this embodiment is basically the same as that of embodiment 1, except that: in step (3), the amount of Cu(NO3)2·3H2O is 0.38 g (containing 0.10 g of Cu element, and the theoretical Cu loading is 2.0 wt%); the heat-enhanced impregnation conditions are adjusted to: temperature 65°C, stirring speed 200 rpm, impregnation time 12 hours, and the solution evaporates to 5% of the original volume.

[0043] Example 3 The preparation method of this embodiment is basically the same as that of embodiment 1, except that: in step (3), the amount of Cu(NO3)2·3H2O is 0.57 g (containing 0.15 g of Cu element, and the theoretical Cu loading is 3.0 wt%); the heat-enhanced impregnation conditions are adjusted to: temperature 68°C, stirring speed 230 rpm, impregnation time 11 hours, and the solution evaporates to 3% of the original volume.

[0044] Example 4 The preparation method of this embodiment is basically the same as that of Example 1, except that: in step (3), the amount of Cu(NO3)2·3H2O is 0.95 g (containing 0.25 g of Cu element, and the theoretical Cu loading is 5.0 wt%); the heat-enhanced impregnation conditions are adjusted to: temperature 72±0.5°C, stirring speed 270 rpm, impregnation time 9 hours, and the solution evaporates to 1% of the original volume.

[0045] Example 5 This embodiment investigates the effect of seed crystal dosage on catalyst structure and performance, using seed crystal dosages of 0.5 wt%, 1.0 wt%, 2.0 wt%, and 3.0 wt%, respectively, with other conditions the same as in Example 1.

[0046] The results are as follows: When the seed crystal dosage is 0.5 wt%, the resulting molecular sieve crystals have an uneven size distribution, with an average size of 280±60 nm, and some crystals agglomerate; after Cu loading, Cu... 2+ The CuO mass ratio is 0.68.

[0047] When the seed crystal dosage is 1.0 wt%: the crystal size is uniform, with an average size of 180±25 nm and a thickness of 38±4 nm; Cu 2+ The CuO mass ratio is 0.73.

[0048] When the seed crystal dosage is 2.0 wt%, the crystal size further decreases, with an average size of 130 ± 20 nm and a thickness of 32 ± 3 nm; Cu 2+ The CuO mass ratio is 0.76.

[0049] When the seed crystal dosage is 3.0 wt%: the crystals are too small, with an average size of 95 ± 15 nm, and the crystallinity decreases (relative crystallinity 85%); Cu 2+ The CuO mass ratio is 0.71.

[0050] The results show that ideal two-dimensional nanosheet morphology and Cu species distribution can be obtained when the seed content is in the range of 1.0~2.0 wt%.

[0051] The optimal seed crystal amount was 1.0 wt%. The sample prepared under these conditions was further characterized, and the structural parameters are shown in Table 1. Meanwhile, the NH3-SCR performance of the sample prepared under these conditions was tested, and the results are shown in Table 2.

[0052] Example 6 This embodiment examines the effect of dual-temperature crystallization conditions on the catalyst structure and designs three crystallization schemes: Option A: 85°C / 30 h + 175°C / 75 h Option B: 90°C / 24 h + 180°C / 72 h (Conditions of Example 1) Option C: 95°C / 20 h + 185°C / 65 h Other conditions are the same as in Example 1.

[0053] The results are as follows: The catalyst obtained by scheme A has a crystal size of 165±22 nm, a thickness of 40±4 nm, a relative crystallinity of 92%, and a total crystallization time of 105 h.

[0054] The catalyst obtained by scheme B has a crystal size of 150±20 nm, a thickness of 35±3 nm, a relative crystallinity of 100%, and a total crystallization time of 96 h.

[0055] The catalyst obtained by scheme C has a crystal size distribution of 120-200 nm, a relative crystallinity of 88%, and a total crystallization time of 85 h.

[0056] Schemes A, B, and C can all yield two-dimensional oriented nanosheets of Cu-SSZ-39 molecular sieve. Of course, Scheme B (90°C / 24 h + 180°C / 72 h) is the optimal crystallization condition, which can obtain two-dimensional nanosheets with high crystallinity and uniform morphology.

[0057] Comparative Example 1 Includes the following steps: (1) Synthesis of conventional SSZ-39 molecular sieve: The same gel composition as in Example 1 was used, but without the addition of seed crystals. The hydrothermal reaction corresponding to the single-temperature crystallization conditions was used, and the crystals were directly statically crystallized at 180°C for 96 hours.

[0058] (2) Preparation of NH4-SSZ-39 by ion exchange: Similar to Example 1, the Na-SSZ-39 crystal obtained in step (1) above was subjected to ion exchange to obtain the corresponding NH4-SSZ-39.

[0059] (3) Static impregnation method for loading Cu: 5.00 g of ion-exchanged NH4-SSZ-39 was mixed with 100 mL of solution containing 0.76 g Cu(NO3)2·3H2O, allowed to stand at room temperature for 24 hours, then dried at 110°C for 12 hours and calcined at 550°C for 5 hours.

[0060] The average sample size of the obtained catalyst was 3 ± 0.5 μm, and the actual Cu loading of the sample was 3.92 wt%. The BET specific surface area was 556 m². 2 / g. Cu 2+ The CuO mass ratio was only 0.42, and TEM observation showed that the average particle size of the CuO agglomerates reached 12.5 ± 2.0 nm. Figure 4 As shown.

[0061] Comparative Example 2 Two-dimensional nanosheets Na-SSZ-39 synthesized by the method in Example 1 were used as the support, but Cu species were loaded using a static impregnation method, and the impregnation conditions were the same as step (3) of Comparative Example 1.

[0062] Although the obtained sample was supported by nanosheets, the Cu content was low due to improper impregnation method. 2+ The CuO mass ratio is only 0.53, which is significantly lower than that of the thermally enhanced impregnation method. The average particle size of CuO nanoclusters is 8.2±1.5 nm, which is significantly larger than that of the thermally enhanced impregnation method.

[0063] Comparative Example 3 The micron-sized Na-SSZ-39 molecular sieve synthesized in Comparative Example 1 using conventional methods was used as a carrier, and copper species were loaded using the same heat-enhanced impregnation technique as step (3) in Example 1.

[0064] The resulting sample support was a micron-sized bulk crystal, but thanks to improvements in the impregnation method, its Cu... 2+ The CuO mass ratio was increased to 0.58, which is better than the static impregnation method (Comparative Example 1 and Comparative Example 2); the average particle size of CuO nanoclusters was reduced to 7.5±1.0 nm, which is also better than the static impregnation method.

[0065] After the reaction, the target catalyst was successfully prepared. Analysis showed that, compared to Comparative Example 1 which used static impregnation, the thermally enhanced impregnation technique employed in this example did indeed improve the dispersion of copper species on the micron-sized support to some extent, resulting in a relatively higher proportion of isolated Cu. 2+ Active site.

[0066] The XRD patterns of the catalysts prepared in Examples 1-5 and Comparative Examples 1-3 are as follows: Figure 1 As shown, they are not very different from each other, indicating that Cu-SSZ-39 molecular sieve crystals were successfully synthesized.

[0067] The structural parameters of the catalysts obtained in Examples 1-5 and Comparative Examples 1-3 are shown in Table 1, and the NH3-SCR performance is shown in Table 2. It is easy to see that the NH3-SCR performance of the catalysts obtained in Examples 1-5 is generally good, regardless of the NO content at 200℃. x Conversion rate, NO at 500℃ x Conversion rates, whether for T50 or T90, are superior to those of Comparative Examples 1, 2, and 3.

[0068] Figure 3 The image shows a comparison of the UV-Vis diffuse reflectance spectra of the catalysts obtained in Example 1 and Comparative Example 1. As can be seen from the image, the sample from Example 1 belongs to isolated Cu. 2+The characteristic absorption peak of the ions (located at approximately 220 nm) is significantly stronger than that of Comparative Example 1, while the broad absorption peak attributed to CuO nanoclusters (located at approximately 750 nm) is significantly weaker than that of Comparative Example 1. This strongly demonstrates that the preparation strategy employed in this invention can effectively promote the formation of highly active isolated Cu. 2+ Ions enter the molecular sieve exchange sites and simultaneously inhibit the aggregation of low-activity CuO species on the surface, thereby obtaining a greater number and more efficient active centers.

[0069] To further reveal the root cause of the improved catalyst performance, the reaction kinetics of Example 1 and Comparative Example 1 were studied, and their Arrhenius curves are shown below. Figure 5 As shown in the figure. Based on the curve slope, the apparent activation energy (Ea) of Example 1 (two-dimensional nanosheet catalyst) is 26.44 kJ / mol, significantly lower than the 61.70 kJ / mol of Comparative Example 1 (traditional micron-scale catalyst). This substantial reduction in apparent activation energy is direct evidence of reduced diffusion limitation, clearly demonstrating that the two-dimensional nanosheet structure prepared in this invention successfully eliminates the internal diffusion bottleneck by shortening the diffusion path by more than 85%, allowing reactant molecules to reach the active site more rapidly, thereby greatly improving the intrinsic catalytic efficiency of the catalyst.

[0070] Table 1 Summary of structural parameters of different catalysts

[0071] Table 2 Comparison of NH3-SCR performance of different catalysts

[0072] Example 7 The preparation method of this embodiment is basically the same as that of Example 1, except that: in step (1), the molar ratios of SiO2, Al2O3, Na2O, OSDA and H2O in the gel system are as follows: 1.0 SiO2: 0.05 Al2O3: 0.4 Na2O: 0.2 OSDA: 10 H2O.

[0073] After crystallization, the target catalyst was successfully prepared by washing, drying, impregnation, and calcination. Analysis confirmed that, similar to the sample obtained in Example 1, the sample obtained in this example possesses a two-dimensional nanosheet morphology and a highly crystalline Cu-SSZ-39 structure, exhibiting excellent catalytic activity in the NH3-SCR reaction.

[0074] Example 8 The preparation method of this embodiment is basically the same as that of Example 1, except that: in step (1), the molar ratios of SiO2, Al2O3, Na2O, OSDA and H2O in the gel system are as follows: 1.0 SiO2: 0.2 Al2O3: 0.8 Na2O: 0.8 OSDA: 40 H2O.

[0075] After crystallization, the target catalyst was successfully prepared by washing, drying, impregnation, and calcination. Analysis confirmed that, similar to the sample obtained in Example 1, the sample obtained in this example possesses a two-dimensional nanosheet morphology and a highly crystalline Cu-SSZ-39 structure, exhibiting excellent catalytic activity in the NH3-SCR reaction.

[0076] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a two-dimensionally oriented nanosheet Cu-SSZ-39 molecular sieve, characterized in that, The method comprises the following steps: (1) mixing inorganic base, silicon source, organic template agent, water, USY molecular sieve and SSZ-39 crystal seeds to form an initial gel; wherein the amount of the SSZ-39 crystal seeds is 1.0-2.0 wt% of the total mass of the gel; (2) subjecting the initial gel obtained in step (1) to hydrothermal reaction as a precursor of hydrothermal reaction to realize crystallization; the hydrothermal reaction is double-temperature crystallization, first crystallization at a low temperature of 75-95°C for 20-30 hours, and then continued crystallization at a high temperature of 165-185°C for 60-80 hours; after the hydrothermal reaction, the obtained solid product is collected and subjected to washing, drying treatment, and then calcination treatment to remove the organic template agent, thereby obtaining M-SSZ-39 molecular sieve; wherein M represents a metal element, which is the same as the metal element in the inorganic base; (3) subjecting the M-SSZ-39 molecular sieve obtained in step (2) to ammonium ion exchange to obtain NH4-SSZ-39 molecular sieve; (4) adding the NH4-SSZ-39 molecular sieve obtained in step (3) into a copper precursor solution, and performing heat strengthening stirring impregnation under a water bath condition at 50-90°C, evaporating the solution to 1-5% of the original volume, and then drying and calcining to obtain a two-dimensional nanosheet Cu-SSZ-39 catalyst.

2. The preparation method according to claim 1, characterized in that, In step (2), the double-temperature crystallization is first crystallization at 85-95°C for 22-26 hours, and then crystallization at 175-185°C for 68-76 hours; Preferably, the double-temperature crystallization is first crystallization at 90°C for 24 hours, and then crystallization at 180°C for 72 hours.

3. The preparation method according to claim 1, characterized in that, In step (4), the heat strengthening stirring impregnation is stirring impregnation at 65-75°C under a water bath condition at 200-300 rpm for 8-12 hours; Preferably, the heat strengthening stirring impregnation is stirring impregnation at 68-72°C under a water bath condition at 230-270 rpm for 9-11 hours, so that the solution is evaporated to 1.5-3% of the original volume; More preferably, the heat strengthening stirring impregnation is stirring impregnation at 70°C under a water bath condition at 250 rpm for 10 hours, so that the solution is evaporated to 2% of the original volume.

4. The preparation method according to claim 1, characterized in that, In step (4), the drying temperature is 100-120°C, and the time is 10-14 hours; the calcination temperature is 500-600°C, and the time is 4-6 hours.

5. The preparation method according to claim 1, characterized in that, In step (4), the copper precursor solution contains one or more of copper nitrate, copper sulfate or copper acetate; The copper element contained in the copper precursor solution is 2-5 wt% of the total mass of the NH4-SSZ-39 molecular sieve.

6. The method of claim 1, wherein the step of forming the first and second layers is performed by a method selected from the group consisting of: sputtering, evaporation, and chemical vapor deposition. In step (3), the ammonium ion exchange is performed in multiple times, preferably three times. The ammonium salt used in the ammonium ion exchange is one or more of (NH4)2SO4, NH4Cl or NH4NO3, and each time of ammonium ion exchange is carried out by adding M-SSZ-39 molecular sieve into the ammonium salt solution for ammonium ion exchange, the solid-liquid ratio of M-SSZ-39 molecular sieve to the ammonium salt solution is 1 g: 20-40 mL, and the mass ratio of M-SSZ-39 molecular sieve to the amount of substance of ammonium salt contained in the ammonium salt solution is 1 g: 20-40 mmol; preferably, the solid-liquid ratio of M-SSZ-39 molecular sieve to the ammonium salt solution is 1 g: 25-35 mL, and the mass ratio of M-SSZ-39 molecular sieve to the amount of substance of ammonium salt contained in the ammonium salt solution is 1 g: 25-35 mmol each time of ammonium ion exchange; The temperature of the ammonium ion exchange is 70-90°C, and the time of each ammonium ion exchange is 6-10 h; preferably, the temperature of the ammonium ion exchange is 75-85°C, and the time of each ammonium ion exchange is 7-9 h; The NH4-SSZ-39 molecular sieve is collected by suction filtration or centrifugal separation, and then washed and dried.

7. The preparation method according to claim 1, characterized in that, In step (1), the mixing is carried out by stirring at room temperature for 1-3 h to mix uniformly; The collection is carried out by suction filtration or centrifugal separation; The washing is carried out until neutral; The calcination is carried out at 500-600°C for 4-6 h; The amounts of inorganic base, silicon source, organic template (OSDA), water and USY molecular sieve can satisfy that the components contained in the initial gel correspond to the molar ratio SiO2:Al2O3:Na2O:OSDA:H2O = 1:0.05-0.2:0.4-0.8:0.2-0.8:10-40; The silicon source is selected from one of silica sol, tetraethyl orthosilicate and sodium silicate; The Si / Al molar ratio of the USY molecular sieve is 10-25; The alkali source is one of sodium hydroxide, potassium hydroxide and lithium hydroxide; The organic template is one of 1,1,3,5-tetramethylpiperidine, N,N-dimethyl-3,5-dimethylpiperidine and N,N-diethyl-2,6-dimethylpiperidine.

8. The two-dimensional nanosheet Cu-SSZ-39 catalyst prepared by the method of any one of claims 1-7.

9. The two-dimensional nanosheet Cu-SSZ-39 catalyst of claim 8, wherein, The two-dimensional nanosheet Cu-SSZ-39 catalyst has a two-dimensional planar dimension of 100-200 nm and a thickness dimension of 30-40 nm, and a length-thickness ratio of 3.3-5.0; Preferably, the specific surface area is 750-800 m 2 / g, and the total pore volume is 0.26-0.30 cm 3 / g; the copper species include isolated Cu 2+ ions and CuO nanoclusters, wherein the average particle size of the CuO nanoclusters is less than 5 nm, and the Cu 2+ / CuO mass ratio is 0.65-0.

85.

10. The application of the two-dimensional nanosheet Cu-SSZ-39 catalyst of claim 8 or 9 in NH3-SCR denitrification; preferably, the application is specifically in NH3-SCR denitrification of diesel vehicle exhaust.

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