Nanoscale metal-supported SSZ-39 molecular sieve, its preparation and application as a denitrification catalyst

Abstract

This invention relates to the field of environmental catalysis technology, specifically to a nanoscale metal-supported SSZ-39 molecular sieve, its preparation, and its application as a denitrification catalyst. The preparation method involves: adding a metal salt to an aqueous complexing agent to form a metal complex; then mixing the metal complex with aluminosilicate gel mixture, adding SSZ-39 molecular sieve as a seed crystal, and performing a hydrothermal reaction to obtain a metal-supported SSZ-39 molecular sieve; using the obtained metal-supported SSZ-39 molecular sieve as a seed crystal, and repeating the above process to obtain a nanoscale metal-supported SSZ-39 molecular sieve. Compared to micron-sized metal-supported SSZ-39 molecular sieves, the nanoscale metal-supported SSZ-39 molecular sieve catalyst synthesized by this method exhibits higher NH3-SCR activity, N2 selectivity, and high-temperature hydrothermal stability. This makes this catalyst promising for broad applications in mobile and stationary source exhaust gas denitrification.

Description

Technical Field

[0001] This invention relates to the field of environmental catalysis technology, and more specifically, to a nanoscale metal-supported SSZ-39 molecular sieve, its preparation, and its application as a denitrification catalyst. Background Technology

[0002] With the acceleration of industrialization and the growth of transportation, nitrogen oxides (NOx) have increased. x Emissions of NO are constantly increasing, seriously threatening environmental quality and human health. x NO is a significant component of air pollutants; its emissions not only lead to environmental problems such as acid rain and photochemical smog, but also contribute to the destruction of the atmospheric ozone layer. To reduce NO... x To address emissions, various control technologies have been researched and applied. Among them, NH3-SCR technology has attracted much attention due to its high efficiency and selectivity. This technology is not only suitable for industrial waste gas treatment but can also be widely used in the purification of automobile exhaust. In NH3-SCR technology, the catalyst is considered a key factor. Currently, Cu-SSZ-13 molecular sieves (with a CHA structure) are highly regarded for their extremely high SCR activity and excellent resistance to CH4 emissions. x Due to its good poisoning resistance and hydrothermal stability, Cu-SSZ-13 catalyst is considered one of the most promising NH3-SCR catalysts. However, Cu-SSZ-13 catalysts have some problems, such as susceptibility to sulfide poisoning and the formation of N2O as a byproduct in the NH3-SCR reaction. Compared with Cu-SSZ-13, Fe-SSZ-13 exhibits superior sulfur resistance and N2 selectivity in the NH3-SCR reaction. Therefore, the combined use of Cu-SSZ-13 and Fe-SSZ-13 catalysts can fully utilize the high catalytic activity and CH4 resistance of Cu-SSZ-13. x The poisoning resistance and hydrothermal stability, as well as the sulfur resistance and N2 selectivity of Fe-SSZ-13, were studied. Besides Cu-SSZ-13 and Fe-SSZ-13, other types of molecular sieves have also been investigated. To fully utilize the respective advantages of Cu-based and Fe-based SSZ-39 molecular sieves and improve the overall performance of the catalyst, a systematic study of these two types of molecular sieves is necessary.

[0003] It is worth noting that conventional SSZ-39 molecular sieves are generally in the micrometer range, while those with sizes in the 1–100 nm range are referred to as nanoscale molecular sieves. Nanoscale SSZ-39 molecular sieves possess a larger specific surface area and more active sites, which increase the adsorption capacity of reactants, thereby enhancing the NH3-SCR reaction performance of the catalyst. Furthermore, the smaller particle size of nanoscale catalysts means they can adsorb and release reactant molecules more quickly, while reducing mass transfer resistance and promoting faster diffusion of reactants to the vicinity of active sites, further improving the catalyst's reaction performance. In summary, the preparation of nanoscale Cu and Fe supported SSZ-39 molecular sieve catalysts has many advantages in the NH3-SCR reaction, including high catalytic activity, good selectivity, and thermal stability. These advantages make nanoscale Cu and Fe supported SSZ-39 molecular sieves a promising catalyst with broad application prospects in industrial waste gas and automotive exhaust purification. Summary of the Invention

[0004] This invention addresses the shortcomings of existing technologies by providing a method for preparing nanoscale metal-supported SSZ-39 molecular sieves. The obtained nanoscale Cu and Fe-supported SSZ-39 molecular sieve catalysts exhibit numerous advantages in the NH3-SCR reaction, including high catalytic activity, good N2 selectivity, and thermal stability. These advantages make nanoscale Cu and Fe-supported SSZ-39 molecular sieves a promising denitrification catalyst with broad application prospects in industrial waste gas and automotive exhaust purification.

[0005] According to a first aspect of the present invention, a method for preparing nanoscale metal-supported SSZ-39 molecular sieves is provided, comprising the following steps:

[0006] (1) Add the complexing agent to water to form an aqueous solution of the complexing agent. Add the metal salt to the aqueous solution of the complexing agent and mix thoroughly to form a metal complex. Add the inorganic base, aluminum source, organic template agent and silicon source to water to obtain a mixture of aluminosilicate gel.

[0007] (2) The aluminosilicate gel mixture obtained in step (1) is mixed with the metal complex, and SSZ-39 molecular sieve is added as seed crystal. Then, a hydrothermal reaction is carried out. After the hydrothermal reaction is completed, the resulting solid powder is filtered, washed, dried and subjected to ammonium exchange treatment. Then, calcination is carried out to remove the organic template agent to obtain metal-loaded SSZ-39 molecular sieve.

[0008] (3) Use the obtained metal-loaded SSZ-39 molecular sieve as seed crystal for the next round of hydrothermal reaction, and repeat the process of step (2) at least once until nanoscale metal-loaded SSZ-39 molecular sieve is obtained.

[0009] Preferably, in step (3), the repetition is performed 2-4 times.

[0010] Preferably, the metal salt is an iron salt and / or a copper salt;

[0011] Preferably, the iron salt is FeCl2, FeSO4, Fe2(SO4)3, or Fe(NO3)3; and the copper salt is CuCl2, CuSO4, or Cu(NO3)2.

[0012] Preferably, in step (1), the complexing agent is any one of ethylenediaminetetraacetic acid tetrasodium salt, diethylamine, triethylamine, triethylenetetraamine, or tetraethylenepentamine;

[0013] The inorganic base is any one or a mixture of several of LiOH, NaOH, KOH, and CsOH;

[0014] The template agent is any one or a mixture of several of N,N-dimethyl-3,5-dimethylpiperidine onium salt, N,N-diethyl-3,5-dimethylpiperidine onium salt, N,N-dimethyl-2,6-dimethylpiperidine onium salt, and N,N-diethyl-2,6-dimethylpiperidine onium salt;

[0015] Preferably, in step (1), the molar ratio of the aluminum source, silicon source, inorganic alkali, organic template agent, water, metal salt, and complexing agent is aluminum source: silicon source: inorganic alkali: organic template agent: water: metal salt: complexing agent = (0.017~0.15):(0.1~2.5):(0.03~0.2):(0.01~1.0):(0.5~1.4):(0.0006~0.003):(0.0006~0.003);

[0016] The amount of seed crystal added in step (2) is 3 to 10 wt.% of the amount of silicon source added in step (1).

[0017] Preferably, the hydrothermal reaction temperature is 160–200°C, and the reaction time is 2–7 days;

[0018] The ammonium salt used in the ammonium exchange is any one or a mixture of several of (NH4)2SO4, NH4Cl or NH4NO3;

[0019] The calcination temperature is 400–700℃, and the calcination time is 2–6 hours.

[0020] According to another aspect of the present invention, a nanoscale metal-supported SSZ-39 molecular sieve prepared by the method of the present invention is provided, characterized in that the grain size of the nanoscale metal-supported SSZ-39 molecular sieve is 1 to 100 nm.

[0021] Preferably, the grain size of the nanoscale metal-supported SSZ-39 molecular sieve is 50–100 nm.

[0022] According to another aspect of the present invention, the application of the aforementioned nanoscale metal-supported SSZ-39 molecular sieve in a denitrification catalyst is provided.

[0023] According to another aspect of the present invention, a selective catalytic reduction device is provided, comprising a nanoscale metal-supported SSZ-39 molecular sieve.

[0024] According to another aspect of the present invention, a mobile source and / or stationary source exhaust gas treatment system is provided, including the aforementioned selective catalytic reduction device.

[0025] Compared with the prior art, the technical solutions conceived in this invention have the following main technical advantages:

[0026] The Fe-SSZ-39 molecular sieve prepared in Example 1 has a nanoscale size (approximately 50 nm), while the Fe-SSZ-39 molecular sieve prepared in Comparative Example 1 has a micrometer-scale size (approximately 2.5 μm). The nanoscale Fe-SSZ-39 of Example 1 exhibits superior activity in the NH3-SCR reaction compared to the micrometer-scale Fe-SSZ-39 molecular sieve of Comparative Example 1. This is because the smaller size of the nanoscale Fe-SSZ-39 provides more active sites and a larger specific surface area, thereby increasing the contact area with the reactants and promoting the reaction. Furthermore, at low temperatures, the N2 selectivity of the nanoscale Fe-SSZ-39 molecular sieve of Example 1 is slightly better than that of the micrometer-scale Fe-SSZ-39 molecular sieve of Comparative Example 1. After aging at 750 °C, the NH3-SCR activity of both the Fe-SSZ-39 molecular sieves of Example 1 and Comparative Example 1 decreased. However, the Fe-SSZ-39 molecular sieve of Example 1 still exhibited high activity, even higher than that of the Fe-SSZ-39 molecular sieve in Comparative Example 1 after aging. This indicates that the nano-sized Fe-SSZ-39 molecular sieve has better high-temperature hydrothermal stability, better maintaining the performance and activity of the catalyst and extending its service life. In Example 2, the Cu-SSZ-39 molecular sieve prepared by this invention exhibited higher activity in the NH3-SCR reaction compared to the Cu-SSZ-39 molecular sieve in Comparative Example 2. Their N2 selectivity was relatively similar. After aging at 750°C, the NH3-SCR activity and N2 selectivity of the Cu-SSZ-39 molecular sieves of Example 2 and Comparative Example 2 decreased. However, compared to the Cu-SSZ-39 molecular sieve in Comparative Example 2, their activity after aging was still higher. This indicates that the nano-sized Cu-SSZ-39 molecular sieve has better high-temperature hydrothermal stability, maintaining the activity and selectivity of the catalyst for longer periods.

[0027] In summary, the nanoscale metal-supported SSZ-39 molecular sieve conceived in this invention exhibits superior NH3-SCR activity, N2 selectivity, and high-temperature hydrothermal stability. The small size and good dispersibility of the nanoscale metal-supported SSZ-39 molecular sieve provide more active sites and a larger specific surface area, increasing the contact area between reactants and catalyst, and improving reaction efficiency. Simultaneously, the nanoscale metal-supported SSZ-39 molecular sieve demonstrates better high-temperature hydrothermal stability, maintaining the activity and selectivity of the catalyst for a longer period and extending its lifespan. These technical advantages give the nanoscale metal-supported SSZ-39 molecular sieve broad application potential, enabling it to improve catalyst efficiency and environmental protection in fields such as mobile and stationary source exhaust gas purification. Attached Figure Description

[0028] Figure 1 Scanning electron microscope (SEM) images of the Fe-SSZ-39 molecular sieves prepared in Example 1(a) and Comparative Example 1(b).

[0029] Figure 2 The X-ray diffraction (XRD) patterns of the metal-supported SSZ-39 molecular sieves prepared in Examples 1-6 and Comparative Examples 1 and 2 are shown.

[0030] Figure 3 NO content of metal-loaded SSZ-39 molecules prepared in Examples 1 and 2 and Comparative Examples 1 and 2 before and after hydrothermal aging at 750°C for 12 hours. x Conversion rate and N2 selectivity plot. Detailed Implementation

[0031] 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.

[0032] In a first aspect, the present invention provides a method for preparing nanoscale metal-supported SSZ-39 molecular sieves, the method comprising the following steps:

[0033] (1) Using any one of the inorganic bases LiOH, NaOH, KOH, or CsOH, any one of the silica-alumina sources of USY molecular sieve or Beta molecular sieve, any one or more of the supplementary silica sources of silicon chloride, sodium silicate, silica acetate, or silica sol, and any one or more of the organic template agents of N,N-dimethyl-3,5-dimethylpiperidinium salt, N,N-diethyl-3,5-dimethylpiperidinium salt, N,N-dimethyl-2,6-dimethylpiperidinium salt, and N,N-diethyl-2,6-dimethylpiperidinium salt, add them to distilled water and react under stirring conditions for 0.5–3 h to obtain a silicate-aluminate gel mixture. Then, transfer the silicate-aluminate gel mixture to a stainless steel reactor with a polytetrafluoroethylene liner and carry out a crystallization reaction at a temperature of 160–200 °C for 2–7 days. After the reaction is completed, filter and wash the product, and dry it at 80–150 °C to obtain a solid powder. Next, the solid powder was placed in a 0.05–1 M solution of (NH4)2SO4, NH4Cl, or NH4NO3 at 50–90℃ for ammonium exchange. Finally, it was calcined at a high temperature of 400–700℃ for 2–6 hours to remove the template agent, and the SSZ-39 molecular sieve was finally obtained.

[0034] (2) Add any one of the Fe or Cu salts selected from FeCl2 / CuCl2, FeSO4 / CuSO4, Fe2(SO4)3, or Fe(NO3)3 / Cu(NO3)2 and any one of the complexing agents selected from EDTA4Na, DEA, TEA, TETA, or TEPA to an aqueous solution and react for 0.5–3 h to obtain a metal complex. Then, prepare an aluminosilicate gel mixture using the same method as in step (1). Mix the obtained aluminosilicate gel mixture with the metal complex and add the SSZ-39 molecular sieve synthesized in step (1) as a seed crystal to form an initial gel. Transfer the initial gel mixture to a stainless steel reactor with a polytetrafluoroethylene liner and carry out a crystallization reaction at 160–200 °C for 2–7 days. After the reaction is complete, filter and wash the product, and dry it at 80–150 °C to obtain a solid powder. Next, the solid powder was placed in a 0.05–1 M solution of (NH4)2SO4, NH4Cl, or NH4NO3 at 50–90 °C for ammonium exchange. Finally, it was calcined at a high temperature of 400–700 °C for 2–6 h to remove the template agent, ultimately obtaining the metal-supported SSZ-39 molecular sieve.

[0035] (3) Using the metal-loaded SSZ-39 molecular sieve synthesized in step (2) as a seed crystal, repeat the hydrothermal synthesis process in step (2) to obtain metal-loaded SSZ-39 molecular sieve.

[0036] (4) Using the metal-supported SSZ-39 molecular sieve synthesized in step (3) as seed crystals, repeat the hydrothermal synthesis process in step (2) to obtain metal-supported SSZ-39 molecular sieves. Finally, nanoscale metal-supported SSZ-39 molecular sieves with a grain size of 1 to 100 nm are obtained.

[0037] In a second aspect, the present invention provides a denitrification catalyst, namely a nanoscale metal-supported SSZ-39 molecular sieve, wherein the active component is an Fe species or a Cu species.

[0038] In some embodiments, the loading of the active component Fe or Cu in the support is 0.3 to 5 wt.%, with a more preferred Cu loading of 2.5 wt.% and an Fe loading of 1.5 wt.%.

[0039] In a third aspect, the present invention provides a selective catalytic reduction apparatus comprising the above-mentioned nanoscale metal-supported SSZ-39 molecular sieve catalyst.

[0040] In a fourth aspect, the present invention provides a mobile source and a stationary source exhaust gas treatment system comprising the above-described selective catalytic reduction device.

[0041] The following are specific embodiments.

[0042] Example 1

[0043] A method for preparing nanoscale Fe-SSZ-39 molecular sieves includes the following steps:

[0044] (1) 2g sodium hydroxide, 10g USY molecular sieve, 25g silica sol, and 25g N,N-diethyl-3,5-dimethylpiperidinium salt were added to 10g distilled water and stirred for 0.5h to obtain an aluminosilicate gel mixture. The aluminosilicate gel mixture was transferred to a stainless steel reactor with a polytetrafluoroethylene liner and crystallized at 160℃ for 7 days. After crystallization, the solid powder was obtained by filtration, washing, and drying. The obtained solid powder was subjected to ammonium exchange with 0.3M (NH4)2SO4 at 80℃. After the exchange was completed, it was filtered, washed, and dried again. Finally, the dried powder was calcined at 550℃ for 5h to obtain SSZ-39 molecular sieve.

[0045] (2) Dissolve 1.1g of tetrasodium ethylenediaminetetraacetate in 10g of distilled water, stir until homogeneous, then add 0.8g of ferrous sulfate and continue stirring for 0.5h to obtain the Fe complex. Add 2g of sodium hydroxide, 10g of USY molecular sieve, 25g of silica sol and 25g of N,N-diethyl-3,5-dimethylpiperidinium salt to 10g of distilled water and stir for 0.5h to obtain aluminosilicate gel mixture. Add the above aluminosilicate gel mixture to the Fe complex, then add the SSZ-39 molecular sieve synthesized in step (1) as a seed crystal and continue stirring for 1.5h to obtain the initial gel of the reactants. Transfer the initial gel of the reactants to a stainless steel reactor with a polytetrafluoroethylene liner and crystallize at 160℃ for 7 days. After crystallization, obtain solid powder by filtration, washing and drying. Perform ammonium exchange on the obtained solid powder with 0.3M (NH4)2SO4 at 80℃. After the exchange is completed, filter, wash and dry again. Finally, the dried powder was calcined at 550℃ for 5 hours to obtain a Fe-SSZ-39 molecular sieve catalyst with an Fe loading of 1.8 wt.%.

[0046] (3) Using the Fe-SSZ-39 molecular sieve synthesized in step (2) as seed crystals, the hydrothermal synthesis process in step (2) was repeated to finally obtain a Fe-SSZ-39 molecular sieve catalyst with an Fe loading of 1.8 wt.%.

[0047] (4) Using the Fe-SSZ-39 molecular sieve synthesized in step (3) as seed crystals, the hydrothermal synthesis process in step (2) was repeated to finally obtain a nano-scale Fe-SSZ-39 molecular sieve catalyst with an Fe loading of 1.8 wt.%.

[0048] Comparative Example 1

[0049] A method for preparing micron-sized Fe-SSZ-39 molecular sieves includes the following steps:

[0050] 1.1 g of tetrasodium ethylenediaminetetraacetate was dissolved in 10 g of distilled water and stirred until homogeneous. Then, 0.8 g of ferrous sulfate was added, and stirring continued for 0.5 h to obtain an Fe complex. 2 g of sodium hydroxide, 10 g of USY molecular sieve, 25 g of silica sol, and 25 g of N,N-diethyl-3,5-dimethylpiperidinium salt were added to 10 g of distilled water and stirred for 0.5 h to obtain an aluminosilicate gel mixture. This aluminosilicate gel mixture was added to the Fe complex, and stirring continued for 1.5 h to obtain the initial gel of the reactants. The initial gel was transferred to a stainless steel reactor with a polytetrafluoroethylene liner and crystallized at 160 °C for 7 days. After crystallization, a solid powder was obtained by filtration, washing, and drying. The obtained solid powder was subjected to ammonium exchange with 0.3 M (NH₄)₂SO₄ at 80 °C. After the exchange was completed, it was filtered, washed, and dried again. Finally, the dried powder was calcined at 550℃ for 5 hours to obtain a Fe-SSZ-39 molecular sieve catalyst with an Fe loading of 1.8 wt.%.

[0051] SEM analysis was performed on the Fe-SSZ-39 molecular sieve catalysts prepared in Example 1 and Comparative Example 1. The results are as follows: Figure 1 As shown, the Fe-SSZ-39 molecular sieve obtained in Example 1 has a nanoscale size (around 50 nm), while the Fe-SSZ-39 molecular sieve obtained in Comparative Example 1 has a micrometer-scale size (around 2.5 μm).

[0052] Example 2

[0053] A method for preparing nanoscale Cu-SSZ-39 molecular sieves includes the following steps:

[0054] (1) 2g sodium hydroxide, 10g USY molecular sieve, 28g silica sol, and 25g N,N-diethyl-3,5-dimethylpiperidinium salt were added to 10g distilled water and stirred for 0.5h to obtain an aluminosilicate gel mixture. The aluminosilicate gel mixture was transferred to a stainless steel reactor with a polytetrafluoroethylene liner and crystallized at 170℃ for 6 days. After crystallization, the solid powder was obtained by filtration, washing, and drying. The obtained solid powder was subjected to ammonium exchange with 0.3M (NH4)2SO4 at 80℃. After the exchange was completed, it was filtered, washed, and dried again. Finally, the dried powder was calcined at 550℃ for 5h to obtain SSZ-39 molecular sieve.

[0055] (2) Dissolve 0.55g of triethylenetetramine in 10g of distilled water, stir until homogeneous, then add 0.95g of copper sulfate and continue stirring for 0.5h to obtain a Cu complex. Add 2g of sodium hydroxide, 10g of USY molecular sieve, 28g of silica sol and 25g of N,N-diethyl-3,5-dimethylpiperidinium salt to 10g of distilled water and stir for 0.5h to obtain an aluminosilicate gel mixture. Add the above aluminosilicate gel mixture to the Cu complex, then add the SSZ-39 molecular sieve synthesized in step (1) as a seed crystal and continue stirring for 1.5h to obtain the initial gel of the reactants. Transfer the initial gel of the reactants to a stainless steel reactor with a polytetrafluoroethylene liner and crystallize at 170℃ for 6 days. After crystallization, obtain a solid powder by filtration, washing and drying. Perform ammonium exchange on the obtained solid powder with 0.3M (NH4)2SO4 at 80℃. After the exchange is completed, filter, wash and dry again. Finally, the dried powder was calcined at 550℃ for 5 hours to obtain a Cu-SSZ-39 molecular sieve catalyst with a Cu loading of 2.7 wt.%.

[0056] (3) Using the Cu-SSZ-39 molecular sieve synthesized in step (2) as a seed crystal, the hydrothermal synthesis process in step (2) was repeated to finally obtain a Cu-SSZ-39 molecular sieve catalyst with a Cu loading of 2.7 wt.%.

[0057] (4) Using the Cu-SSZ-39 molecular sieve synthesized in step (3) as seed crystals, the hydrothermal synthesis process in step (2) was repeated to finally obtain a nanoscale Fe-SSZ-39 molecular sieve catalyst with a Cu loading of 2.7 wt.%.

[0058] Comparative Example 2

[0059] A method for preparing micron-sized Cu-SSZ-39 molecular sieves includes the following steps:

[0060] 0.55 g of triethylenetetramine was dissolved in 10 g of distilled water and stirred until homogeneous. Then, 0.95 g of copper sulfate was added, and stirring continued for 0.5 h to obtain a Cu complex. 2 g of sodium hydroxide, 10 g of USY molecular sieve, 28 g of silica sol, and 25 g of N,N-diethyl-3,5-dimethylpiperidinium salt were added to 10 g of distilled water and stirred for 0.5 h to obtain an aluminosilicate gel mixture. This aluminosilicate gel mixture was added to the Cu complex, and stirring continued for 1.5 h to obtain the initial gel of the reactants. The initial gel was transferred to a stainless steel reactor with a polytetrafluoroethylene liner and crystallized at 170 °C for 6 days. After crystallization, a solid powder was obtained by filtration, washing, and drying. The obtained solid powder was subjected to ammonium exchange with 0.3 M (NH₄)₂SO₄ at 80 °C. After the exchange was completed, it was filtered, washed, and dried again. Finally, the dried powder was calcined at 550℃ for 5 hours to obtain a Cu-SSZ-39 molecular sieve catalyst with a Cu loading of 2.7 wt.%.

[0061] Examples 3-6

[0062] A method for preparing nanoscale metal-supported SSZ-39 molecular sieves using different complexing agents includes the following steps:

[0063] (1) 2.3 g sodium hydroxide, 13 g USY molecular sieve, 30 g silica sol, and 35 g N,N-diethyl-2,6-dimethylpiperidinium salt were added to 12 g distilled water and stirred for 0.5 h to obtain an aluminosilicate gel mixture. The aluminosilicate gel mixture was transferred to a stainless steel reactor with a polytetrafluoroethylene liner and crystallized at 190 °C for 5 days. After crystallization, the solid powder was obtained by filtration, washing, and drying. The obtained solid powder was subjected to ammonium exchange with 0.8 M NH4Cl at 70 °C. After the exchange was completed, it was filtered, washed, and dried again. Finally, the dried powder was calcined at 600 °C for 4 h to obtain SSZ-39 molecular sieve.

[0064] (2) Dissolve 0.83g tetraethylenepentamine (0.2g diethylamine, 0.4g triethylamine, or 0.39g triethylenetetramine) in 12g distilled water, stir until homogeneous, then add 0.98g copper sulfate (0.75g ferrous sulfate, 0.54g copper chloride, or 0.55g ferrous chloride), and continue stirring for 0.5h to obtain a metal complex. Add 2.3g sodium hydroxide, 13g USY molecular sieve, 30g silica sol, and 35g N,N-diethyl-2,6-dimethylpiperidinium salt to 12g distilled water, and stir for 0.5h to obtain an aluminosilicate gel mixture. Add the above aluminosilicate gel mixture to the metal complex, then add the SSZ-39 molecular sieve synthesized in step (1) as a seed crystal, and continue stirring for 1.5h to obtain the initial gel of the reactants. Transfer the initial gel of the reactants to a stainless steel reactor with a polytetrafluoroethylene liner, and crystallize at 190℃ for 5 days. After crystallization, a solid powder was obtained by filtration, washing, and drying. The obtained solid powder was subjected to ammonium exchange with 0.8M NH4Cl at 70℃. After the exchange, it was filtered, washed, and dried again. Finally, the dried powder was calcined at 600℃ for 4 hours to obtain a Cu-SSZ-39 molecular sieve catalyst with a Cu loading of 2.5 wt.% (or Fe-SSZ-39 with a Fe loading of 1.5 wt.%, Cu-SSZ-39 with a Cu loading of 2.5 wt.%, or Fe-SSZ-39 with a Fe loading of 1.5 wt.%).

[0065] (3) Using the metal-supported SSZ-39 molecular sieve synthesized in step (2) as seed crystals, repeat the hydrothermal synthesis process in step (2) to finally obtain Cu-SSZ-39 (Fe-SSZ-39 with 1.5 wt.% Fe, Cu-SSZ-39 with 2.5 wt.% Cu or Fe-SSZ-39 with 1.5 wt.% Fe) molecular sieve catalyst with a Cu loading of 2.5 wt.%

[0066] (4) Using the metal-supported SSZ-39 molecular sieve synthesized in step (3) as a seed crystal, repeat the hydrothermal synthesis process in step (2) to finally obtain a nanoscale Cu-SSZ-39 molecular sieve catalyst with a Cu loading of 2.5 wt.% (Fe-SSZ-39 with a Fe loading of 1.5 wt.%, Cu-SSZ-39 with a Cu loading of 2.5 wt.%, or Fe-SSZ-39 with a Fe loading of 1.5 wt.%).

[0067] XRD tests were performed on the metal-supported SSZ-39 molecular sieve catalysts prepared in Examples 1-6 and Comparative Examples 1 and 2, and the results are as follows: Figure 2 As shown, all the prepared catalysts exhibited typical AEI structures.

[0068] Figure 3 NO content of metal-loaded SSZ-39 molecules prepared in Examples 1 and 2 and Comparative Examples 1 and 2 before and after hydrothermal aging at 750°C for 12 hours. x Conversion rate and N2 selectivity plot.

[0069] Depend on Figure 3 It can be seen that at low temperatures, the N2 selectivity of the nano-sized Fe-SSZ-39 molecular sieve in Example 1 is slightly better than that of the micron-sized Fe-SSZ-39 molecular sieve in Comparative Example 1. After aging at 750℃, the NH3-SCR activity of the Fe-SSZ-39 molecular sieves in both Example 1 and Comparative Example 1 decreased. However, the Fe-SSZ-39 molecular sieve in Example 1 still exhibited high activity, and its activity after aging was still higher than that of the Fe-SSZ-39 molecular sieve in Comparative Example 1. This indicates that the nano-sized Fe-SSZ-39 molecular sieve has better high-temperature hydrothermal stability, can better maintain the performance and activity of the catalyst, and extend the service life of the catalyst. In Example 2, the Cu-SSZ-39 molecular sieve prepared by this invention exhibited higher activity in the NH3-SCR reaction compared to the Cu-SSZ-39 molecular sieve in Comparative Example 2. Their N2 selectivity was relatively similar. After aging at 750℃, the NH3-SCR activity and N2 selectivity of the Cu-SSZ-39 molecular sieves in Example 2 and Comparative Example 2 decreased. However, compared to the Cu-SSZ-39 molecular sieve in Comparative Example 2, their activity after aging was still higher. This indicates that the nanoscale Cu-SSZ-39 molecular sieve has better high-temperature hydrothermal stability and can maintain the activity and selectivity of the catalyst for a longer period.

[0070] Examples 7-10

[0071] A method for preparing nanoscale metal-supported SSZ-39 molecular sieves using different inorganic bases includes the following steps:

[0072] (1) 3.0 g sodium hydroxide (1.7 g lithium hydroxide, 4 g potassium hydroxide or 7.5 g cesium hydroxide), 12 g USY molecular sieve, 25 g sodium silicate and 30 g N,N-dimethyl-2,6-dimethylpiperidinium salt were added to 12 g distilled water and stirred for 0.5 h to obtain an aluminosilicate gel mixture. The aluminosilicate gel mixture was transferred to a stainless steel reactor with a polytetrafluoroethylene liner and crystallized at 175 °C for 5 days. After crystallization, the solid powder was obtained by filtration, washing and drying. The obtained solid powder was subjected to ammonium exchange with 1 M NH4Cl at 70 °C. After the exchange was completed, it was filtered, washed and dried again. Finally, the dried powder was calcined at 600 °C for 5 h to obtain SSZ-39 molecular sieve.

[0073] (2) Dissolve 0.38g tetraethylenepentamine (0.66g tetraethylenepentamine, 0.26g triethylenetetramine, or 0.46g triethylenetetramine) in 12g distilled water, stir until homogeneous, then add 0.50g ferrous sulfate (0.79g copper sulfate, 0.50g ferrous sulfate, or 0.79g copper sulfate), and continue stirring for 0.5h to obtain a metal complex. Add 3.0g sodium hydroxide (1.7g lithium hydroxide, 4g potassium hydroxide, or 7.5g cesium hydroxide), 12g USY molecular sieve, 25g sodium silicate, and 30g N,N-dimethyl-2,6-dimethylpiperidinium salt to 12g distilled water, and stir for 0.5h to obtain an aluminosilicate gel mixture. Add the above aluminosilicate gel mixture to the metal complex, then add the SSZ-39 molecular sieve synthesized in step (1) as a seed crystal, and continue stirring for 1.5h to obtain the initial gel of the reactants. The initial gel of the reactants was transferred to a stainless steel reactor lined with polytetrafluoroethylene (PTFE) and crystallized at 175°C for 5 days. After crystallization, a solid powder was obtained by filtration, washing, and drying. The obtained solid powder was subjected to ammonium exchange with 1M NH₄Cl at 70°C. After the exchange, it was filtered, washed, and dried again. Finally, the dried powder was calcined at 600°C for 5 hours to obtain a Fe-SSZ-39 molecular sieve catalyst with a Fe loading of 1.0 wt.% (or Cu-SSZ-39 with a Cu loading of 2.0 wt.%, Fe-SSZ-39 with a Fe loading of 1.0 wt.%, or Cu-SSZ-39 with a Cu loading of 2.0 wt.%).

[0074] (3) Using the metal-supported SSZ-39 molecular sieve synthesized in step (2) as seed crystals, repeat the hydrothermal synthesis process in step (2) to finally obtain Fe-SSZ-39 molecular sieve catalyst with Fe loading of 1.0 wt.% (Cu-SSZ-39 with Cu loading of 2.0 wt.%, Fe-SSZ-39 with Fe loading of 1.0 wt.%, or Cu-SSZ-39 with Cu loading of 2.0 wt.%).

[0075] (4) Using the metal-supported SSZ-39 molecular sieve synthesized in step (3) as seed crystals, repeat the hydrothermal synthesis process in step (2) to finally obtain a nanoscale Fe-SSZ-39 molecular sieve catalyst with a Fe loading of 1.0 wt.% (Cu-SSZ-39 with a Cu loading of 2.0 wt.%, Fe-SSZ-39 with a Fe loading of 1.0 wt.%, or Cu-SSZ-39 with a Cu loading of 2.0 wt.%).

[0076] Examples 11-14

[0077] A method for preparing metal-supported SSZ-39 molecular sieves using different organic template agents or silica-alumina sources includes the following steps:

[0078] (1) Add 3g sodium hydroxide, 20g Beta molecular sieve (15g USY molecular sieve, 23g Beta molecular sieve, or 17g USY molecular sieve), 32g sodium silicate, and 30g N,N-dimethyl-3,5-dimethylpiperidinium salt (33g N,N-dimethyl-2,6-dimethylpiperidinium salt, 45g N,N-diethyl-3,5-dimethylpiperidinium salt, or 40g N,N-diethyl-2,6-dimethylpiperidinium salt) to 18g distilled water and stir for 1h to obtain an aluminosilicate gel mixture. Transfer the aluminosilicate gel mixture to a stainless steel reactor with a polytetrafluoroethylene liner and crystallize at 185℃ for 5 days. After crystallization, obtain a solid powder by filtration, washing, and drying. Perform ammonium exchange on the obtained solid powder with 1M NH4NO3 at 80℃. After the exchange is completed, filter, wash, and dry again. Finally, the dried powder was calcined at 600℃ for 4 hours to obtain SSZ-39 molecular sieve.

[0079] (2) Dissolve 0.56g of tetrasodium ethylenediaminetetraacetate (0.33g of triethylamine, 2.56g of tetrasodium ethylenediaminetetraacetate or 0.70g of triethylamine) in 12g of distilled water, stir well, and then add 0.37g of ferrous sulfate (0.82g of copper sulfate, 1.71g of ferrous sulfate or 1.73g of copper sulfate), and continue stirring for 1h to obtain a metal complex. 3g sodium hydroxide, 20g Beta molecular sieve (15g USY molecular sieve, 23g Beta molecular sieve, or 17g USY molecular sieve), 32g sodium silicate, and 30g N,N-dimethyl-3,5-dimethylpiperidine onium salt (33g N,N-dimethyl-2,6-dimethylpiperidine onium salt, 45g N,N-diethyl-3,5-dimethylpiperidine onium salt, or 40g N,N-diethyl-2,6-dimethylpiperidine onium salt) were added to 18g distilled water and stirred for 1 hour to obtain an aluminosilicate gel mixture. This aluminosilicate gel mixture was added to a metal complex, followed by the SSZ-39 molecular sieve synthesized in step (1) as a seed crystal. Stirring continued for 2 hours to obtain the initial gel of the reactants. The initial gel of the reactants was transferred to a stainless steel reactor with a polytetrafluoroethylene liner and crystallized at 185°C for 5 days. After crystallization, a solid powder was obtained by filtration, washing, and drying. The obtained solid powder was subjected to ammonium exchange with 1M NH4NO3 at 80℃. After the exchange, it was filtered, washed, and dried again. Finally, the dried powder was calcined at 600℃ for 4 hours to obtain a Fe-SSZ-39 molecular sieve catalyst with a Fe loading of 0.5 wt.% (or Cu-SSZ-39 with a Cu loading of 1.6 wt.%, 2.0 wt.%, or 3.0 wt.%).

[0080] (3) Using the metal-supported SSZ-39 molecular sieve synthesized in step (2) as seed crystals, repeat the hydrothermal synthesis process in step (2) to finally obtain Fe-SSZ-39 molecular sieve catalyst with Fe loading of 0.5 wt.% (Cu-SSZ-39 with Cu loading of 1.6 wt.%, Fe-SSZ-39 with Fe loading of 2.0 wt.%, or Cu-SSZ-39 with Cu loading of 3.0 wt.%).

[0081] (4) Using the metal-supported SSZ-39 molecular sieve synthesized in step (3) as seed crystals, repeat the hydrothermal synthesis process in step (2) to finally obtain nanoscale Fe-SSZ-39 (Cu-SSZ-39 with 1.6 wt.% Cu, 2.0 wt.% Fe or 3.0 wt.% Cu) molecular sieve catalyst with a Fe loading of 0.5 wt.% (Cu-SSZ-39 with 1.6 wt.% Cu, 2.0 wt.% Fe or 3.0 wt.% Cu) molecular sieve catalyst.

[0082] 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 nanoscale metal-supported SSZ-39 molecular sieves, characterized in that, Includes the following steps: (1) Add the complexing agent to water to form an aqueous solution of the complexing agent, add the metal salt to the aqueous solution of the complexing agent, mix thoroughly to form a metal complex; add the inorganic base, aluminum source, organic template agent and silicon source to water to obtain a mixture of aluminosilicate gel; the complexing agent is any one of ethylenediaminetetraacetic acid tetrasodium salt, diethylamine, triethylamine, triethylenetetraamine or tetraethylenepentamine; (2) The aluminosilicate gel mixture obtained in step (1) is mixed with the metal complex, and SSZ-39 molecular sieve is added as a seed crystal. Then, a hydrothermal reaction is carried out. After the hydrothermal reaction is completed, the resulting solid powder is filtered, washed, dried and subjected to ammonium exchange treatment. Then, calcination treatment is carried out to remove the organic template agent to obtain metal-loaded SSZ-39 molecular sieve. The ammonium salt used for ammonium exchange is any one or a mixture of several of (NH4)2SO4, NH4Cl or NH4NO3. (3) Use the obtained metal-supported SSZ-39 molecular sieve as the seed crystal for the next round of hydrothermal reaction, and repeat the process of step (2) 2-4 times until nanoscale metal-supported SSZ-39 molecular sieve is obtained.

2. The preparation method of nanoscale metal-supported SSZ-39 molecular sieve as described in claim 1, characterized in that, The metal salt is an iron salt and / or a copper salt.

3. The preparation method of nanoscale metal-supported SSZ-39 molecular sieve as described in claim 2, characterized in that, The iron salt is FeCl2, FeSO4, Fe2(SO4)3, or Fe(NO3)3; the copper salt is CuCl2, CuSO4, or Cu(NO3)2.

4. The method for preparing nanoscale metal-supported SSZ-39 molecular sieve as described in claim 1, characterized in that, In step (1), The inorganic base is any one or a mixture of several of LiOH, NaOH, KOH, and CsOH; The template agent is any one or a mixture of several of N,N-dimethyl-3,5-dimethylpiperidine onium salt, N,N-diethyl-3,5-dimethylpiperidine onium salt, N,N-dimethyl-2,6-dimethylpiperidine onium salt, and N,N-diethyl-2,6-dimethylpiperidine onium salt.

5. The method for preparing nanoscale metal-supported SSZ-39 molecular sieve as described in claim 1, characterized in that, The amount of seed crystals added in step (2) is 3 to 10 wt.% of the amount of silicon source added in step (1).

6. The method for preparing nanoscale metal-supported SSZ-39 molecular sieve as described in claim 1, characterized in that, The hydrothermal reaction is carried out at a temperature of 160-200 ℃ for 2-7 days. The calcination temperature is 400~700 ℃, and the calcination time is 2~6 h.

7. The nanoscale metal-supported SSZ-39 molecular sieve prepared by the method according to any one of claims 1-6, characterized in that, The grain size of the nanoscale metal-supported SSZ-39 molecular sieve is 1~100 nm.

8. The nanoscale metal-supported SSZ-39 molecular sieve as described in claim 7, characterized in that, The grain size of the nanoscale metal-supported SSZ-39 molecular sieve is 50~100 nm.

9. The application of the nanoscale metal-supported SSZ-39 molecular sieve as described in claim 7 or 8 as a denitrification catalyst.

10. A selective catalytic reduction apparatus, characterized in that, Includes the nanoscale metal-supported SSZ-39 molecular sieve as described in claim 7 or 8.

11. A mobile source and / or stationary source exhaust gas treatment system, characterized in that, Includes the selective catalytic reduction apparatus as described in claim 10.

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