Cu-SSZ-13 molecular sieve with low surface hydroxyl content as well as preparation method and application of Cu-SSZ-13 molecular sieve

Abstract

The invention provides a preparation method of a Cu-SSZ-13 molecular sieve with low surface hydroxyl content, which comprises the following steps: mixing the Cu-SSZ-13 molecular sieve with a precursor to be coated, filtering, drying and roasting to obtain the Cu-SSZ-13 molecular sieve, the precursor to be coated comprises a solid precursor or a liquid precursor; the solid precursor comprises oxides and hydroxides of Mo and W; the liquid precursor comprises inorganic oxysalts or complexes of Mo and W. The method belongs to post-treatment modification of the Cu-SSZ-13 molecular sieve, and Mo and W oxides coat the surface of the Cu-SSZ-13 molecular sieve through condensation of Mo and W precursors and hydroxyl groups on the surface of the Cu-SSZ-13 molecular sieve in a high-temperature roasting process, so that the content of the hydroxyl groups on the surfaces of crystal grains of the molecular sieve is reduced.

Description

Technical Field

[0001] The present invention relates to the field of catalysis technology, in particular to a Cu-SSZ-13 molecular sieve with low surface hydroxyl content, a preparation method and application thereof. Background Art

[0002] Nitrogen oxides (NO x ) is the main pollutant in automobile exhaust, which is harmful to the ecological environment and human health. x This technology offers advantages such as high conversion efficiency and selectivity. Among numerous molecular sieve catalysts, Cu-SSZ-13 molecular sieve has been used in motor vehicle exhaust treatment systems due to its excellent catalytic activity and hydrothermal stability. However, Cu-SSZ-13 molecular sieve still faces challenges such as poor low-temperature activity in the presence of water and suboptimal high-temperature hydrothermal stability. To further improve the catalytic performance of Cu-SSZ-13 molecular sieve, researchers have proposed a series of strategies from various perspectives.

[0003] CN 116139922 B discloses a method for increasing the surface adhesion of molecular sieve particles. The method uses atomic layer deposition to coat the outer surface of a Cu-SSZ-13 molecular sieve, whose shell comprises one or more oxides (and / or hydroxides) of silicon, aluminum, titanium, zirconium, and rare earth elements. The core of this method is to enhance the adhesion of the Cu-SSZ-13 molecular sieve to a cordierite honeycomb ceramic support by modifying its surface roughness, thereby increasing the service life of the molecular sieve catalyst. Furthermore, the outer surface of the oxide or hydroxide shell inevitably contains hydroxyl groups. Furthermore, the atomic deposition method requires precise control of precursor delivery, vacuum conditions, and reaction parameters, resulting in a long production process, complex operation, and high investment costs.

[0004] Therefore, it is very necessary to provide a method for reducing the surface hydroxyl groups of Cu-SSZ-13 molecular sieves, which can improve the surface properties of Cu-SSZ-13 and enhance its catalytic performance in the NH3-SCR denitrification reaction. Summary of the Invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a Cu-SSZ-13 molecular sieve with low surface hydroxyl content. The Cu-SSZ-13 molecular sieve prepared by the present invention has low surface hydroxyl content and high Cu-SSZ-13 denitrification catalytic performance.

[0006] The present invention provides a method for preparing a Cu-SSZ-13 molecular sieve with a low surface hydroxyl content, comprising the following steps:

[0007] The Cu-SSZ-13 molecular sieve is mixed with the precursor to be coated, filtered, dried and calcined to obtain the product;

[0008] The precursor to be coated includes a solid precursor or a liquid precursor; the solid precursor includes oxides and hydroxides of Mo and W; the liquid precursor includes inorganic oxygen-containing salts or complexes of Mo and W.

[0009] In some specific embodiments, the mixing is mixing the Cu-SSZ-13 molecular sieve with the solid precursor by stirring or ball milling, or mixing the Cu-SSZ-13 molecular sieve with the liquid precursor by stirring;

[0010] The ball milling parameters are mixing at 300-550 rpm for 1 h at room temperature;

[0011] The stirring parameters include stirring at a rate of 400-500 rpm at room temperature for 1-2 hours.

[0012] In some specific embodiments, the solid precursor includes molybdenum hydroxide, molybdenum oxide, tungsten oxide or tungsten hydroxide; the liquid precursor includes one of ammonium molybdate solution, ammonium tungstate solution and molybdenum acetylacetonate solution.

[0013] In some embodiments, the drying parameters include drying at 70-90°C.

[0014] In some specific embodiments, the mass ratio of the Cu-SSZ-13 molecular sieve to the precursor to be coated is 200 to 5000:1.

[0015] In some specific embodiments, the oxide coating layer has a thickness of 0.1 to 2 nm.

[0016] In some specific embodiments, the calcination temperature is 200-600° C. and the calcination time is 2-6 hours.

[0017] The present invention provides a Cu-SSZ-13 molecular sieve with low surface hydroxyl content, which is prepared by the preparation method described in any one of the above technical solutions.

[0018] The present invention provides the use of Cu-SSZ-13 molecular sieve prepared by the preparation method described in any of the above schemes or the Cu-SSZ-13 molecular sieve with low surface hydroxyl content described in the above technical scheme in NH3-SCR denitration reaction.

[0019] The present invention provides an NH3-SCR denitration reaction, using the Cu-SSZ-13 molecular sieve with low surface hydroxyl content described in the above technical solution or the Cu-SSZ-13 molecular sieve prepared by the preparation method described in any one of the above technical solutions as a catalyst.

[0020] Compared with the prior art, the present invention provides a method for preparing a Cu-SSZ-13 molecular sieve with a low surface hydroxyl content, comprising the following steps: mixing the Cu-SSZ-13 molecular sieve with a precursor to be coated, filtering, drying, and calcining to obtain a Cu-SSZ-13 molecular sieve; the precursor to be coated comprises a solid precursor or a liquid precursor; the solid precursor comprises oxides or hydroxides of Mo and W; the liquid precursor comprises inorganic oxygenates or complexes of Mo and W. The present invention relates to post-treatment modification of the Cu-SSZ-13 molecular sieve, and through the condensation of Mo and W precursors with the surface hydroxyl groups of the Cu-SSZ-13 molecular sieve during high-temperature calcination, the surface of the Cu-SSZ-13 molecular sieve is coated with Mo and W oxides, thereby reducing the hydroxyl content on the surface of the molecular sieve grains. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The XRD spectra of Cu-SSZ-13 molecular sieve before and after coating with Mo oxide in Example 1;

[0022] Figure 2 This is the UV-Raman spectrum of the Cu-SSZ-13 molecular sieve before and after coating with Mo oxide in Example 1. DETAILED DESCRIPTION

[0023] The present invention provides a Cu-SSZ-13 molecular sieve with a low surface hydroxyl content and its preparation method and application. Those skilled in the art can refer to the content of this article and appropriately improve the process parameters to achieve it. It is particularly important to point out that all similar replacements and modifications are obvious to those skilled in the art and they all fall within the scope of protection of the present invention. The method and application of the present invention have been described through preferred embodiments. Relevant personnel can obviously modify or appropriately change and combine the method and application of this article without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention.

[0024] Cu-SSZ-13 molecular sieve has excellent NH3-SCR denitrification activity and high-temperature hydrothermal stability, and has been commercially applied in diesel exhaust treatment. However, this catalyst faces challenges such as low activity in low-temperature water-containing conditions and decreased catalytic activity after high-temperature hydrothermal aging.

[0025] The object of the present invention is to provide a method for reducing the surface hydroxyl groups of Cu-SSZ-13 molecular sieve. The method of the present invention can improve the surface properties of Cu-SSZ-13 and enhance its catalytic performance in the NH3-SCR denitrification reaction.

[0026] The present invention provides a method for preparing a Cu-SSZ-13 molecular sieve with a low surface hydroxyl content, comprising the following steps:

[0027] The Cu-SSZ-13 molecular sieve is mixed with the precursor to be coated, filtered, dried and calcined to obtain the product.

[0028] The precursor to be coated in the present invention includes a solid precursor or a liquid precursor.

[0029] The shell layer precursor to be coated in the present invention is preferably an oxide or hydroxide of Mo or W, as well as an inorganic oxygen-containing acid salt, complex, etc. that can be converted into the corresponding Mo or W oxide by high-temperature calcination.

[0030] Specifically, the solid precursor includes oxides and hydroxides of Mo and W;

[0031] In some specific embodiments, the solid precursor includes molybdenum hydroxide, molybdenum oxide, tungsten oxide, or tungsten hydroxide;

[0032] The liquid precursor includes inorganic oxygen-containing salts or complexes of Mo and W.

[0033] In some specific embodiments, the liquid precursor includes: one of ammonium molybdate solution, ammonium tungstate solution, and molybdenum acetylacetonate solution.

[0034] In some specific embodiments, the mixing is performed by stirring or ball milling the Cu-SSZ-13 molecular sieve with the solid precursor, or by stirring the Cu-SSZ-13 molecular sieve with the liquid precursor. The present invention does not limit the mixing method, and any method known to those skilled in the art is sufficient.

[0035] According to the present invention, the ball milling parameters are mixing at a speed of 300-550 rpm at room temperature for 1 hour; specifically, it can be 300 rpm, 310 rpm, 320 rpm, 330 rpm, 340 rpm, 350 rpm, 360 rpm, 370 rpm, 380 rpm, 390 rpm, 400 rpm, 410 rpm, 420 rpm, 430 rpm, 440 rpm, 450 rpm, 460 rpm, 470 rpm, 480 rpm, 490 rpm, 500 rpm, 510 rpm, 520 rpm, 530 rpm, 540 rpm, and 550 rpm.

[0036] The stirring parameters include stirring at a rate of 400-500 rpm for 1-2 hours at room temperature; preferably, it can be 400 rpm, 410 rpm, 420 rpm, 430 rpm, 440 rpm, 450 rpm, 460 rpm, 470 rpm, 480 rpm, 490 rpm, and 500 rpm.

[0037] In some specific embodiments, the drying parameters include drying at 70-90°C;

[0038] Specifically, it can be: 70℃, 71℃, 72℃, 73℃, 74℃, 75℃, 76℃, 77℃, 78℃, 79℃, 80℃, 81℃, 82℃, 83℃, 84℃, 85℃, 86℃, 87℃, 88℃, 89℃, 90℃; or a ratio between any two of the above.

[0039] In some specific embodiments, the mass ratio of the Cu-SSZ-13 molecular sieve to the precursor to be coated is 200 to 5000:1; specifically, it can be 200:1, 300:1, 400:1, 500:1, 600:1, 700:1, 800:1, 900:1, 1000:1, 1100:1, 1200:1, 1300:1, 1400:1, 1500:1, 1600:1, 1700:1, 1800:1, 1900:1, 2000:1, 2100:1, 2200:1, 2300:1, 2400:1, 2500:1, 2600:1, 2700:1, 2800:1, 2900:1, 3000:1, 3100:1, 3200:1, 3300:1, 3400:1, 3500:1, 3600:1, 3700:1, 3800:1, 3900:1, 4000:1, 4100:1, 4200:1, 4300:1, 4400:1, 4500:1, 4600:1, 4700:1, 4800:1, 4900:1, 5000:1, 5100:1, 5200:1, 5300:1, 5400 300:1, 2400:1, 2500:1, 2600:1, 2700:1, 2800:1, 2900:1, 3000:1, 3100:1, 3200:1, 3300:1, 3400:1, 3500:1, 3600:1, 3700:1, 3800:1, 3900:1, 4000:1, 4100:1, 4200:1, 4300:1, 4400:1, 4500:1, 4600:1, 4700:1, 4800:1, 4900:1, 5000:1.

[0040] In some specific embodiments, the thickness of the oxide coating layer is 0.1-2 nm, and can specifically be 0.1 nm, 0.2 nm, 0.3 nm, 0.4 nm, 0.5 nm, 0.6 nm, 0.7 nm, 0.8 nm, 0.9 nm, 1.0 nm, 1.1 nm, 1.2 nm, 1.3 nm, 1.4 nm, 1.5 nm, 1.6 nm, 1.7 nm, 1.8 nm, 1.9 nm, or 2.0 nm.

[0041] In some specific embodiments, the calcination temperature is 200-600°C; specifically, it can be 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, or 600°C.

[0042] The calcination time is 2 to 6 hours, and can be 2 hours, 3 hours, 4 hours, 5 hours, or 6 hours.

[0043] This method uses condensation between a precursor and the surface hydroxyl groups of Cu-SSZ-13 molecular sieve to coat the outer surface of the molecular sieve grains with a hydroxyl-free oxide, thereby reducing the number of hydroxyl groups on the molecular sieve surface. By leveraging the changes in the surface properties of the modified Cu-SSZ-13 molecular sieve, including its adsorption performance, the denitration catalytic performance of the Cu-SSZ-13 is improved.

[0044] The present invention provides a Cu-SSZ-13 molecular sieve with low surface hydroxyl content, which is prepared by the preparation method described in any one of the above technical solutions.

[0045] The present invention has clearly described the above preparation method, which will not be repeated here.

[0046] The present invention provides the use of Cu-SSZ-13 molecular sieve prepared by the preparation method described in any of the above schemes or the Cu-SSZ-13 molecular sieve with low surface hydroxyl content described in the above technical scheme in NH3-SCR denitration reaction.

[0047] The present invention provides an NH3-SCR denitration reaction, using the Cu-SSZ-13 molecular sieve with low surface hydroxyl content described in the above technical solution or the Cu-SSZ-13 molecular sieve prepared by the preparation method described in any one of the above technical solutions as a catalyst.

[0048] This invention involves condensing Mo or W precursors with surface hydroxyl groups on Cu-SSZ-13 molecular sieves to coat the outer surface of the molecular sieve grains with a hydroxyl-free oxide, thereby reducing the number of hydroxyl groups on the molecular sieve surface. Advantageously, this catalyst exhibits excellent low-temperature activity and high-temperature hydrothermal stability in the NH3-SCR denitrification reaction. This makes it suitable for use in automotive exhaust treatment systems.

[0049] The catalyst of the present invention still maintains relatively high activity after being hydrothermally aged for 16 hours in an air flow containing 12.5% ​​water at 750°C.

[0050] It should be understood that the expression "one or more of" includes individually each of the items recited after the expression and various combinations of two or more of the recited items, unless otherwise apparent from the context and usage. The expression "and / or" in conjunction with three or more recited items should be understood to have the same meaning, unless otherwise apparent from the context.

[0051] The terms "comprising", "having" or "containing", including their grammatical synonyms, should generally be understood as open and non-restrictive, e.g., not excluding other unrecited elements or steps, unless otherwise specifically stated or understood from the context.

[0052] In this application, the term "and / or" describes the association relationship between associated objects, indicating that three relationships may exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural.

[0053] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single or plural items.

[0054] It should be understood that the order of steps or the order in which certain actions are performed are not important as long as the present invention remains operable. Additionally, two or more steps or actions may be performed simultaneously.

[0055] The use of any and all examples or exemplary language, such as "such as" or "including," herein is intended merely to better illustrate the invention and does not limit the scope of the invention unless otherwise claimed. No language in this specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

[0056] In addition, the numerical ranges and parameters used to define the present invention are approximate values. The relevant numerical values ​​in the specific examples have been presented as accurately as possible. However, any numerical value inherently inevitably contains standard deviations due to individual testing methods. Therefore, unless otherwise expressly stated, all ranges, amounts, values, and percentages used in this disclosure should be understood to be modified by the word "about." As used herein, "about" generally means that the actual value is within plus or minus 10%, 5%, 1%, or 0.5% of a specified value or range.

[0057] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. Some or all of the steps can be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0058] Some cases are described in the embodiments and comparative examples of the present invention, wherein the embodiments illustrate certain implementations of the present invention. However, this does not mean that the effects of the present invention can only be achieved in these cases.

[0059] The denitrification performance test was evaluated using a fixed-bed reaction system, with a tubular furnace for temperature control and an online mass spectrometer for detecting reactant and product gases. The test was conducted in the temperature range of 150-600°C.

[0060] To further illustrate the present invention, a Cu-SSZ-13 molecular sieve with low surface hydroxyl content provided by the present invention, its preparation method and application are described in detail below with reference to examples.

[0061] Example 1

[0062] 2.0 g of Cu-SSZ-13 molecular sieve was stirred and mixed with ammonium molybdate solution, and the mixture was filtered. The obtained powder was dried at 80° C. and then calcined at 400° C. to obtain molybdenum oxide-coated Cu-SSZ-13 molecular sieve.

[0063] The molybdenum oxide coated Cu-SSZ-13 catalyst was hydrothermally aged at 750° C. in an air flow containing 12.5% ​​water for 16 h.

[0064] Figure 1 The XRD patterns of the Cu-SSZ-13 molecular sieve before and after coating with Mo oxide in Example 1 are shown. The coated sample retains the characteristic diffraction peaks of SSZ-13 molecular sieve, indicating that the coating process does not destroy the molecular sieve framework. Furthermore, no new Mo oxide-related diffraction peaks appear after coating, due to the low and highly dispersed Mo oxide content.

[0065] Figure 2 The UV-Raman spectra of Cu-SSZ-13 molecular sieve before and after coating with Mo oxide in Example 1 are shown. The coated sample has a peak at 520 cm -1 A new shoulder peak appears at the bottom, which corresponds to the disturbance of the molecular sieve framework vibration caused by the neighboring Mo atoms.

[0066] Example 2

[0067] 2.0 g of Cu-SSZ-13 molecular sieve was stirred and mixed with ammonium tungstate solution. The mixture was filtered, and the resulting powder was dried at 80°C and calcined at 600°C to obtain tungsten oxide-coated Cu-SSZ-13 molecular sieve. The tungsten oxide-coated Cu-SSZ-13 catalyst was hydrothermally aged at 750°C for 16 hours in an air stream containing 12.5% ​​water.

[0068] Example 3

[0069] 2.0g of Cu-SSZ-13 molecular sieve was stirred and mixed with ammonium molybdate and ammonium tungstate solutions. The mixture was filtered, and the resulting powder was dried at 80°C and calcined at 600°C to obtain Cu-SSZ-13 molecular sieve coated with molybdenum and tungsten oxides. The molybdenum-tungsten oxide-coated Cu-SSZ-13 catalyst was hydrothermally aged at 750°C for 16 hours in an air stream containing 12.5% ​​water.

[0070] Example 4

[0071] 2.0g of Cu-SSZ-13 molecular sieve was ball-milled with molybdenum hydroxide and then calcined at 550°C to obtain molybdenum oxide-coated Cu-SSZ-13 molecular sieve. The molybdenum oxide-coated Cu-SSZ-13 catalyst was hydrothermally aged at 750°C for 16 hours in an air stream containing 12.5% ​​water.

[0072] Example 5

[0073] 10.0 g of Cu-SSZ-13 molecular sieve was mixed with a molybdenum acetylacetonate solution, the mixture was filtered, and the solid powder was dried at 80°C and then calcined at 550°C to obtain molybdenum oxide-coated Cu-SSZ-13 molecular sieve. The molybdenum oxide-coated Cu-SSZ-13 catalyst was hydrothermally aged at 750°C in an air stream containing 12.5% ​​water for 16 hours.

[0074] Example 6

[0075] The activity of the Cu-SSZ-13 catalyst in the NH3-SCR denitration reaction before and after coating in Example 1 was tested. The NO conversion within the reaction temperature range is shown in Table 1. Reaction conditions: catalyst dosage 50 mg, 500 ppm NO, 500 ppm NH3, 5 vol% O2, 5 vol% H2O, Ar as the balance gas, and a total gas flow rate of 200 mL / min.

[0076] Comparative Example 1

[0077] 2.0 g of Cu-SSZ-13 molecular sieve was mixed with 100 mL of a 0.4 g / L ethyl orthosilicate ethanol solution and stirred for 6 hours. The mixture was filtered, the solid powder dried at 80°C, and then calcined at 550°C to obtain silica-coated Cu-SSZ-13 molecular sieve. The silica-coated Cu-SSZ-13 catalyst was hydrothermally aged at 750°C for 16 hours in an air stream containing 12.5% ​​water.

[0078] Comparative Example 2

[0079] 2.0 g of Cu-SSZ-13 molecular sieve was mixed with 5 mL of an acetone solution containing 0.22 g of molybdenum acetylacetonate. The mixture was filtered, and the solid powder was dried at 80°C and then calcined at 550°C to obtain molybdenum oxide-coated Cu-SSZ-13 molecular sieve. The molybdenum oxide-coated Cu-SSZ-13 catalyst was hydrothermally aged at 750°C in an air stream containing 12.5% ​​water for 16 hours.

[0080] Table 1 NH3-SCR denitrification performance of different catalysts before and after hydrothermal aging

[0081]

[0082]

[0083] As shown in Table 1, the NH3-SCR catalytic activity of the coated Cu-SSZ-13 molecular sieve catalyst of Example 1 is relatively high, and the activity is still relatively high after aging at 750°C with 12.5% ​​water vapor.

[0084] The catalyst of Comparative Example 1 has low activity in the high-temperature region after hydrothermal aging; the catalyst of Comparative Example 2 has low activity in the low-temperature region both before and after hydrothermal aging.

[0085] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing Cu-SSZ-13 molecular sieve with low surface hydroxyl content, characterized in that: The steps include: The Cu-SSZ-13 molecular sieve is mixed with the precursor to be coated, filtered, dried and calcined to obtain the product; The precursor to be coated includes a solid precursor or a liquid precursor; the solid precursor includes oxides and hydroxides of Mo and W; the liquid precursor includes inorganic oxygen-containing salts or complexes of Mo and W.

2. The preparation method according to claim 1, characterized in that The mixing is to mix the Cu-SSZ-13 molecular sieve with the solid precursor by stirring or ball milling, or to mix the Cu-SSZ-13 molecular sieve with the liquid precursor by stirring; The ball milling parameters include mixing at a rotation speed of 300-550 rpm at room temperature for 1 hour; the stirring parameters include stirring at a speed of 400-500 rpm at room temperature for 1-2 hours.

3. The preparation method according to claim 1, characterized in that The solid precursor includes molybdenum hydroxide, molybdenum oxide, tungsten oxide or tungsten hydroxide; the liquid precursor includes one of ammonium molybdate solution, ammonium tungstate solution and molybdenum acetylacetonate solution.

4. The preparation method according to claim 1, characterized in that The drying parameters include drying at 70-90°C.

5. The preparation method according to claim 1, characterized in that The mass ratio of the Cu-SSZ-13 molecular sieve to the precursor to be coated is 200 to 5000:

1.

6. The preparation method according to claim 1, characterized in that The thickness of the oxide coating layer is 0.1-2 nm.

7. The preparation method according to claim 1, characterized in that The calcination temperature is 200-600° C., and the calcination time is 2-6 hours.

8. A Cu-SSZ-13 molecular sieve with low surface hydroxyl content, characterized in that: The compound is prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the Cu-SSZ-13 molecular sieve prepared by the preparation method according to any one of claims 1 to 7 or the Cu-SSZ-13 molecular sieve with low surface hydroxyl content according to claim 8 in NH3-SCR denitration reaction.

10. NH3-SCR denitration reaction, characterized in that: The Cu-SSZ-13 molecular sieve with low surface hydroxyl content as claimed in claim 8 or the Cu-SSZ-13 molecular sieve prepared by the preparation method according to any one of claims 1 to 7 is used as the catalyst.

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