Cu-SSZ-13 molecular sieve catalyst, organic-template-free one-pot synthesis method of Cu-SSZ-13 molecular sieve catalyst and application of Cu-SSZ-13 molecular sieve catalyst in NH3-SCR denitration

Abstract

The invention discloses a Cu-SSZ-13 molecular sieve catalyst, an organic-template-free one-pot synthesis method thereof and application of the Cu-SSZ-13 molecular sieve catalyst in NH3-SCR denitration. The synthesis method comprises the following steps: preparing a potassium tetrahydroxy aluminate aqueous solution, adding the potassium tetrahydroxy aluminate aqueous solution into silica sol, uniformly mixing, then adding metal inorganic copper salt, and continuously stirring for 5-15 minutes to obtain a mixture; putting the mixture into a homogeneous reactor, and aging at room temperature for 20-28 hours at the rotating speed of 15-25 rpm; after aging is finished, the temperature is raised to 150-170 DEG C, and hydrothermal crystallization is carried out for 90-110 h; and then cleaning and drying to obtain the Cu-SSZ-13 molecular sieve catalyst. By adopting the technical scheme of the invention, the Cu-SSZ-13 molecular sieve catalyst can be synthesized in one step by a hydrothermal method under the condition that an organic template agent is not used, and the synthesized catalyst has efficient NH3-SCR denitration performance; and the method is low in cost, small in pollution and simple in process.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, in particular to a Cu-SSZ-13 molecular sieve catalyst and an organic template-free one-pot synthesis method thereof, and application thereof in NH3-SCR denitration. Background Art

[0002] Nitrogen oxides (NO x ) emissions seriously threaten the atmospheric environment and human health. Ammonia selective catalytic reduction (NH3-SCR) is a method to reduce NO x The mainstream solution for emissions. Among them, the copper-based catalyst (Cu-SSZ-13) with SSZ-13 molecular sieve as the carrier has become the core material of NH3-SCR denitrification technology due to its unique CHA topological structure. However, the traditional synthesis of SSZ-13 molecular sieve relies on expensive organic structure directing agent (OSDA), and the fluorine medium synthesis method without OSDA will produce difficult-to-treat high-fluorine wastewater. The synthesis mechanism is unclear, and the method is complex and energy-intensive, which seriously restricts its practical application. In addition, the existing multi-step synthesis of Cu-SSZ-13 has the problems of high cost and hydrothermal stability that needs to be improved.

[0003] Traditional molecular sieves loaded with metals are mainly formed into catalysts through ion exchange methods: there are problems with complicated operation procedures, high energy consumption, and long cycles; at the same time, they must undergo multiple hydrothermal treatments and multiple water washings as well as repeated high-temperature (550°C) roasting to produce polluting gases. Therefore, the traditional ion exchange process of forming molecular sieve catalysts through multiple steps will produce three wastes pollution, which is extremely unfriendly to the environment and limits its industrial application. At present, a large number of researchers are actively developing a one-step (one-pot) in-situ synthesis of metal-loaded molecular sieve catalysts. Combined with literature reviews, the one-pot synthesis still requires the use of expensive templates or seed crystals to assist in the technical bottleneck problem, which cannot be broken through. Summary of the Invention

[0004] In response to the above technical problems, the present invention discloses a Cu-SSZ-13 molecular sieve catalyst and its one-pot synthesis method without an organic template and its application in NH3-SCR denitrification. No organic template is required, the one-pot synthesis method is simple, low cost, and low pollution. The obtained catalyst has efficient NH3-SCR denitrification catalytic performance.

[0005] To this end, the technical solution adopted in the present invention is:

[0006] The one-pot synthesis method of Cu-SSZ-13 without organic template comprises the following steps:

[0007] Step S1, preparing an aqueous solution of potassium tetrahydroxyaluminate;

[0008] Step S2, the potassium tetratungstate aqueous solution is added into the silica sol and mixed uniformly, then the metal inorganic copper salt is added, and stirring is continuously performed for 5-15 min to obtain a mixture; the pKa value of the metal inorganic copper salt is 7.5-8.5;

[0009] Step S3, the mixture is placed in a homogeneous reactor, and is aged at room temperature for 20-28 h at a rotation speed of 15-25 rpm;

[0010] Step S4, after aging, the temperature is increased to 150-170 DEG C, and hydrothermal crystallization is performed for 90-110 h; then the product after hydrothermal crystallization is washed and dried;

[0011] Step S5, the product obtained in Step S4 is calcined at 500-600 DEG C in an air atmosphere for 4-8 h.

[0012] By adopting the technical scheme, the metal inorganic copper salt serves as both a copper source and an etchant; Cu 2+ The pure-phase Cu-SSZ-13 molecular sieve catalyst is successfully synthesized, and the obtained catalyst has high NH3-SCR denitration catalytic performance. The method breaks through the dependence on traditional template agents, avoids the high cost of traditional template agents and the environmental protection risk of fluorine medium, and lays a foundation for green and scalable synthesis.

[0013] As a further improvement of the application, the one-pot synthesis method of the Cu-SSZ-13 without an organic template further comprises Step S5, wherein the product obtained in Step S4 is calcined at 500-600 DEG C in an air atmosphere for 4-8 h. The calcination in this step can make the molecular sieve framework more stable, which is beneficial to the subsequent NH3-SCR catalytic effect. Further, the calcination temperature is 550 DEG C, and the calcination time is 6 h.

[0014] As a further improvement of the application, Step S1 comprises: adding aluminum hydroxide into the potassium hydroxide solution, and stirring at 90-110 DEG C for 2-4 h to obtain a clear solution; the molar ratio of potassium hydroxide to aluminum hydroxide is 7:3.5-4.5.

[0015] As a further improvement of the application, in Step S1 and Step S2, the molar ratio of potassium hydroxide, aluminum hydroxide, silica sol and metal inorganic copper salt is 7:4:10:1.0-1.4.

[0016] As a further improvement of the application, in Step S1 and Step S2, the molar ratio of potassium hydroxide, aluminum hydroxide, silica sol and metal inorganic copper salt is 7:4:10:1.3-1.4.

[0017] As a further improvement of the application, the metal inorganic copper salt is copper sulfate or Cu(NO3)2·3H2O.

[0018] As a further improvement of the present invention, in step S3, aging is performed for 24 hours, and in step S4, hydrothermal crystallization is performed for 96 hours. Using this technical solution, when the aging time is 24 hours and the crystallization time is 96 hours, pure high-crystallinity Cu-SSZ-13 molecular sieve can be obtained.

[0019] As a further improvement of the present invention, the cleaning in step S4 includes: dispersing the hydrothermal crystallization product in a (NH4)2SO4 solution, performing a hydrothermal treatment at 75-85°C with stirring for 6-10 hours, then washing the solid product by centrifugation with deionized water, and drying the resulting solid product. Furthermore, the hydrothermal treatment temperature is 80°C for 8 hours. Furthermore, the drying temperature is 80°C for 12 hours.

[0020] The invention discloses Cu-SSZ-13, which is prepared by adopting the above-mentioned Cu-SSZ-13 one-pot synthesis method without organic template.

[0021] The present invention discloses the application of the Cu-SSZ-13 catalyst in NH3-SCR denitration. The Cu-SSZ-13 catalyst has high-efficiency NH3-SCR denitration catalytic performance.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The technical solution of the present invention allows the hydrothermal synthesis of Cu-SSZ-13 molecular sieve in a single step without the use of an organic template. The synthesized SSZ-13 molecular sieve catalyst exhibits highly efficient NH3-SCR denitrification performance. Furthermore, the method is low-cost, low-pollution, and simple to manufacture. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The present invention is a schematic diagram of the one-pot process for preparing Cu-SSZ-13 molecular sieve catalyst and the prior art, wherein (a) is a schematic diagram of the prior art process and (b) is a schematic diagram of the one-pot process for preparing Cu-SSZ-13 molecular sieve catalyst.

[0025] Figure 2 2 is the XRD pattern of K-nCu(NO3)2 samples synthesized in the examples and comparative examples of the present invention.

[0026] Figure 3 These are SEM images of K-nCu(NO3)2 samples synthesized in the embodiments of the present invention and the comparative examples; wherein, (a), (b), (c), and (d) are K-1.0Cu(NO3)2; (b) K-1.3Cu(NO3)2; (c) K-1.4Cu(NO3)2; and (d) K-1.5Cu(NO3)2, respectively.

[0027] Figure 4EDS figure of K-1.4Cu(NO3)2 sample synthesized by one-pot method of embodiment 1 of the present application.

[0028] Figure 5 Comparison of NH3-SCR denitration performance of K-1.4Cu(NO3)2 sample synthesized by one-pot method of embodiment 1 of the present application and H-1.4Cu(NO3)2 catalyst of embodiment 4; wherein (a) is NO x conversion rate, (b) is NO x concentration. DETAILED DESCRIPTION

[0029] The preferred embodiments of the present application are further described in detail below.

[0030] The one-pot synthesis method of Cu-SSZ-13 molecular sieve catalyst without organic template agent, as shown in (b), comprises the following steps: Figure 1

[0031] Step S1, potassium hydroxide is added to deionized water, aluminum hydroxide is added, and stirring is carried out in an oil bath at 100℃ for 3h, and it is observed that the milky white mixed liquid becomes clear, obtaining a potassium tetrahydroxy aluminate aqueous solution;

[0032] Step S2, the potassium tetrahydroxy aluminate aqueous solution is added to silica sol and mixed uniformly, then metal inorganic copper salt is added, and stirring is continuously carried out for 5-15min, obtaining a mixture; the pKa value of the metal inorganic copper salt aqueous solution is 7.3-7.7;

[0033] Step S3, the mixture is placed in a homogeneous reactor, and aging is carried out at room temperature for 20-28h at a rotation speed of 15-25rpm;

[0034] Step S4, after aging, the temperature is increased to 150-170℃, and hydrothermal crystallization is carried out for 90-110h; then washing and drying are carried out.

[0035] Step S5, the product obtained in step S4 is calcined in an air atmosphere at 500-600℃ for 4-8h.

[0036] The synthesis flowchart of prior art Cu-SSZ-13 molecular sieve catalyst is shown in (a), the method of the present application can synthesize Cu-SSZ-13 molecular sieve by one step by hydrothermal method without using OSDA, and compared with the prior art method, the method is simple, the cost is low, and the pollution is small. Figure 1

[0037] The specific embodiments are described below.

[0038] Embodiment 1

[0039] The one-pot synthesis method of Cu-SSZ-13 molecular sieve catalyst comprises the following steps:​​

[0040] (1) 1.4547 g of potassium hydroxide (0.0233 mol of KOH) was added to 4.3271 mL of deionized water. 1.0400 g of aluminum hydroxide (0.0133 mol of Al(OH)3) was then added to the potassium hydroxide aqueous solution. The mixture was placed in an oil bath at 100°C and stirred for 3 h. The milky white mixed liquid was observed to become clear.

[0041] (2) After the clear liquid was cooled to room temperature, 6.6755 g of JN-30 silica sol (0.0333 mol of SiO2 containing 70% by mass of H2O) was added and stirred for 10 min. Then, a certain amount of Cu(NO3)2·3H2O was added and stirred for 10 min to obtain a mixture. The Cu(NO3)2·3H2O can be replaced by CuSO4.

[0042] In the above steps, the molar ratio of KOH:Al(OH)3:SiO2:Cu(NO3)2:H2O is 7:4:10:n:150, and n is 1.4 in this embodiment.

[0043] (3) The polytetrafluoroethylene (PTFE) lining of the above mixture was fixed in a stainless steel autoclave and moved into a homogeneous reactor.

[0044] (4) Aging in a homogeneous reactor at room temperature (25°C) and a rotation speed of 20 rpm for 24 h.

[0045] (5) After aging, the sample was hydrothermally crystallized from room temperature to 160 °C at a heating rate of 10 °C / min for 96 h.

[0046] (6) After crystallization, the product was washed three times by centrifugation with deionized water and dried at 80°C for 12 h to obtain a Cu-SSZ-13 molecular sieve catalyst. The synthesized product was named K-nCu(NO3)2. In this embodiment, n is 1.4, and the product is K-1.4Cu(NO3)2.

[0047] Example 2

[0048] Based on Example 1, the difference of this example is that n is 1.3, and the product is named K-1.3Cu(NO3)2.

[0049] Example 3

[0050] Based on Example 1, the difference of this example is that n is 1.0, and the product is named K-1.0Cu(NO3)2.

[0051] Comparative Examples 1 to 7

[0052] Based on Example 1, the difference between Comparative Examples 1 to 7 is that n is 0.2, 0.5, 1.45, 1.47, 1.5, 1.8, and 2.0, and the products are named K-0.2Cu(NO3)2, K-0.5Cu(NO3)2, K-1.45Cu(NO3)2, K-1.47Cu(NO3)2, K-1.5Cu(NO3)2, K-1.8Cu(NO3)2, and K-2.0Cu(NO3)2.

[0053] Example 4

[0054] Based on Example 1, the cleaning in step S4 is a simple cleaning treatment using an aqueous solution of ammonium sulfate ((NH4)2SO4). The steps include:

[0055] First, 1g of K-1.4Cu(NO3)2 was dispersed in 30mL of 2.5M (NH4)2SO4 solution and hydrothermally treated at 80°C under magnetic stirring for 8h. The product was then washed three times with deionized water by centrifugation, and the resulting solid product was dried at 80°C for 12h.

[0056] Finally, the product was calcined at 550 °C for 6 h in an air atmosphere using a muffle furnace and naturally cooled to room temperature to obtain a Cu-SSZ-13 molecular sieve catalyst, which was named H-1.4Cu(NO3)2 molecular sieve catalyst.

[0057] The XRD patterns of the products K-nCu(NO3)2 synthesized in Examples 1 to 3 and Comparative Examples 1 to 7 are as follows: Figure 2 As shown, through XRD analysis, it can be seen that the copper salt content plays a decisive role in the selection of molecular sieve crystal phase: low copper salt leads to the competitive growth of W molecular sieve (MER structure) impurities, and an appropriate amount of copper salt (n=1.4) realizes the synthesis of pure SSZ-13 molecular sieve, while excessive copper salt induces structural etching. This may be because copper salt preferentially removes unstable phases (such as W molecular sieve) through dynamic dissolution-recrystallization equilibrium, driving the formation of high crystallinity, multi-level pore (micropore + mesopore) molecular sieves. Specifically, when the copper salt content is 1.0Cu(NO3)2 or less (such as 0.2Cu(NO3)2 and 0.5Cu(NO3)2), W molecular sieve impurities will still be produced. Increasing the copper salt to an appropriate amount (1.3Cu(NO3)2 and 1.4Cu(NO3)2), it can be seen from the XRD standard card that at 9.5 o , 20.5 o , 30.5 o These three typical SSZ-13 molecular sieve XRD peaks were observed, and pure SSZ-13 molecular sieve was successfully synthesized at 1.4Cu(NO3)2. When excessive amount was used, extensive etching resulted in crystallization failure.

[0058] The SEM images of the K-nCu(NO3)2 samples synthesized in Examples 1 to 3 and Comparative Examples 1 to 7 are as follows: Figure 3 As shown in the figure, the K-1.0Cu(NO3)2 sample shows a relatively regular block structure with a relatively smooth surface and some obvious crystal faces and corners, indicating a certain degree of crystallinity, which is a typical W molecular sieve structure. With the increase of copper salt, the SSZ-13 molecular sieve crystallizes into walnut-shaped particles, and the embedded nanocrystalline particles become clearer (such as Figure 3 (b) and 3(c)). The K-1.4Cu(NO3)2 sample exhibits a very regular block structure with a very smooth surface and distinct crystal faces and corners, indicating high crystallinity. The uniform and large particle size indicates the formation of high-quality SSZ-13 molecular sieve crystals. The morphology of the excess copper salt K-1.5Cu(NO3)2 becomes irregular, with some amorphous structures appearing on the surface.

[0059] The K-1.4Cu(NO3)2 molecular sieve catalyst forming SSZ-13 structure was subjected to EDS energy spectrum elemental analysis. The results are as follows Figure 4 and as shown in Table 1. EDS spectra reveal a relatively uniform distribution of elements such as Cu, O, Al, and Si in both samples, contributing to the formation of a stable molecular sieve framework. The elemental composition of K-1.4Cu(NO3)2 shows a Cu content of 1.6 atomic percent, indicating that this catalyst has a relatively high Cu content, which contributes to its enhanced catalytic activity.

[0060] Table 1 Composition analysis of catalyst

[0061]

[0062] From the above comparison, it can be seen that the K-1.4Cu(NO3)2 catalyst prepared in Example 1 exhibits optimal crystallinity, regular morphology and uniform element distribution in XRD, SEM and EDS characterizations.

[0063] Next, we further evaluate its NH3-SCR performance under sulfur-containing and water-containing conditions. By performing a simple ion exchange on the K-1.4Cu(NO3)2 catalyst, we prepared the H-1.4Cu(NO3)2 catalyst and evaluated its NH3-SCR denitrification performance. Under fixed conditions (500ppm NO x 、500ppm NH3、5vol.%O2、100ppm SO2、5vol.%H2O,space velocity 23600h -1 ), and the performance test was carried out using a heating program of 3°C / min to 550°C.

[0064] The results are as follows Figure 5 As shown, from Figure 5 It can be seen that the K-1.4Cu(NO3)2 catalyst synthesized by one-pot method has almost no catalytic activity for NH3-SCR when it is not treated. Instead, an oxidation reaction occurs in the high temperature section, which may be caused by K + Occupies the molecular sieve pores, seriously hindering the diffusion of NO / NH3. Example 4: After a simple cleaning, the H-1.4Cu(NO3)2 molecular sieve catalyst obtained showed a typical NH3-SCR catalytic denitrification reaction. In a water-sulfur atmosphere, when the temperature was raised to 270°C, NO x The conversion rate is close to 100%, and it can maintain NO in the temperature range of 270℃-520℃ x The complete conversion of H + With K + After the exchange, the pore structure of the molecular sieve is opened up, exposing more Acid sites (Si-OH-Al) promote NH3 adsorption and activation, and trace amounts of Cu 2+ would provide redox and catalytically active sites.

[0065] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art of the present invention, without departing from the concept of the present invention, several simple deductions or substitutions can be made, which should be considered to fall within the scope of protection of the present invention.

Claims

1. A one-pot synthesis method of Cu-SSZ-13 molecular sieve catalyst without organic template, characterized in that: The steps include: Step S1, preparing an aqueous solution of potassium tetrahydroxyaluminate; Step S2, adding the potassium tetrahydroxyaluminate aqueous solution to the silica sol and mixing them evenly, then adding a metal inorganic copper salt and stirring continuously for 5 to 15 minutes to obtain a mixture; the metal inorganic copper salt aqueous solution has a pKa value of 7.3 to 7.7; Step S3, placing the mixture in a homogeneous reactor and aging it at room temperature for 20 to 28 hours at a rotation speed of 15 to 25 rpm; Step S4: After aging, the temperature is raised to 150-170°C and hydrothermally crystallized for 90-110 hours; the hydrothermally crystallized product is then washed and dried; Step S5, calcining the product obtained in step S4 at 500-600° C. for 4-8 hours under air atmosphere.

2. The one-pot synthesis method of the Cu-SSZ-13 molecular sieve catalyst without an organic template according to claim 1, characterized in that: The cleaning in step S4 includes: dispersing the product after hydrothermal crystallization in a (NH4)2SO4 solution, performing hydrothermal treatment at 75-85°C with stirring for 6-10 hours, then centrifugally washing with deionized water, and drying the obtained solid product.

3. The one-pot synthesis method of the Cu-SSZ-13 molecular sieve catalyst without organic template according to claim 1, characterized in that: Step S1 comprises: adding aluminum hydroxide to a potassium hydroxide solution, and stirring at 90-110° C. for 2-4 hours to obtain a clear solution; the molar ratio of potassium hydroxide to aluminum hydroxide is 7:3.5-4.

5.

4. The one-pot synthesis method of the Cu-SSZ-13 molecular sieve catalyst without organic template according to claim 1, characterized in that: In step S1 and step S2, the molar ratio of potassium hydroxide, aluminum hydroxide, silica sol, and metal inorganic copper salt is 7:3.5-4.5:10:1.0-1.

4.

5. The one-pot synthesis method of the Cu-SSZ-13 molecular sieve catalyst without organic template according to claim 4, characterized in that: In step S1 and step S2, the molar ratio of potassium hydroxide, aluminum hydroxide, silica sol, and metal inorganic copper salt is 7:4:10:1.3-1.

4.

6. The one-pot synthesis method of the Cu-SSZ-13 molecular sieve catalyst without organic template according to claim 1, characterized in that: The metallic inorganic copper salt is copper sulfate or copper nitrate.

7. The one-pot synthesis method of the Cu-SSZ-13 molecular sieve catalyst without organic template according to claim 1, characterized in that: In step S3, aging is performed for 24 hours. In step S4, hydrothermal crystallization is performed for 96 hours. In step S5, the calcination temperature is 550° C. and the calcination time is 6 hours.

8. Cu-SSZ-13, characterized by: The Cu-SSZ-13 molecular sieve catalyst is prepared by a one-pot synthesis method without an organic template according to any one of claims 1 to 7.

9. Use of the Cu-SSZ-13 according to claim 8 in NH3-SCR denitrification.

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