Method for synthesizing Cu-SAPO-42 molecular sieve by ionothermal method

Abstract

The invention belongs to the technical field of molecular sieve preparation, and particularly discloses a method for synthesizing a Cu-SAPO-42 molecular sieve by an ionothermal method, which comprises the following steps: by adopting the ionothermal method, taking 1-ethyl-3-methylimidazolium bromide and tetrapropylammonium hydroxide as template agents, taking a complex of copper ions and triethylene diamine as a copper source, adding an aluminum source, a phosphorus source, a silicon source and a mineralizing agent, and reacting to obtain the Cu-SAPO-42 molecular sieve. And crystallizing after uniformly mixing, so as to synthesize the Cu-SAPO-42 molecular sieve in situ in one step. The Cu-SAPO-42 molecular sieve prepared by the method only needs to be roasted once, so that the damage of multiple ion exchange and high-temperature roasting to the structure of a molecular sieve framework is avoided, the energy consumption and waste liquid are also reduced, and the method is simple and convenient to operate and is green and environment-friendly. The Cu-SAPO-42 molecular sieve prepared by the method disclosed by the invention is adjustable in copper loading capacity, has excellent NH3-SCR activity, and has wide application in a nitrogen oxide removal process.

Description

Technical Field

[0001] The present invention belongs to the technical field of molecular sieve preparation, relates to the synthesis of Cu-SAPO-42 molecular sieve, and particularly relates to a method for synthesizing Cu-SAPO-42 molecular sieve by an ionothermal method. Background Art

[0002] Nitrogen oxides (NO x ) are one of the key components of air pollutants, which not only have important impacts on public health and the ecological environment, but also are important precursors for the formation of secondary air pollutants such as PM2.5 and ozone. Currently, mobile source NO x is the main source of NO x pollution in China. Selective catalytic reduction of ammonia (NH3-SCR) has become one of the most promising mobile source NO x control technologies due to its high NO x removal efficiency, good N2 selectivity, and strong stability.

[0003] Catalysts are the core of the NH3-SCR process. In recent years, copper-based small-pore SCR catalysts represented by Cu-SSZ-13 (silicoaluminophosphate molecular sieve) and Cu-SAPO-34 (phosphosilicoaluminophosphate molecular sieve) have received extensive attention due to their high catalytic activity and good hydrothermal stability. Recently, Yan Nana et al. disclosed an ion-exchange preparation method of a Cu-SAPO-42 molecular sieve with an LTA structure, and used the catalyst for NH3-SCR reaction to remove NO x(Yan Nana, et al., Rational design of a novel catalyst Cu-SAPO-42 for NH3-SCR reaction, Small, 2020, 16, 2000902.) The catalyst described in this scheme exhibits better hydrothermal stability than the Cu-SAPO-34 catalyst, indicating that the molecular sieve with the LTA configuration has good application prospects in the field of NH3-SCR. However, the copper ions in this method are introduced by the ion exchange method. To control the amount of copper ions introduced, multiple ion exchange processes are usually required, and multiple calcination processes are also accompanied during this process. The ion exchange in the aqueous solution and the high-temperature calcination process will cause partial hydrolysis and deformation of the framework of the phosphosilicoaluminate molecular sieve, which will in turn cause the collapse of the framework and the decrease of the specific surface area, affecting the activity and hydrothermal stability of the catalyst (Gao Feng, et al., Synthesis and evaluation of Cu / SAPO-34 catalysts for NH3-SCR2: Solid-state ion exchange and one-pot synthesis, 2015, 162, 501-514.). At the same time, a large amount of wastewater will be generated during multiple ion exchanges, and multiple high-temperature calcinations are time-consuming and energy-consuming, which is not conducive to industrial applications. Therefore, developing a simple and fast preparation method for Cu-SAPO-42 molecular sieve with adjustable copper loading is of great significance for promoting the practical application of molecular sieve-based NH3-SCR catalysts. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a method for synthesizing Cu-SAPO-42 molecular sieve by the ionothermal method. By selecting a template agent composed of copper amine complex, 1-ethyl-3-methylimidazolium bromide and tetrapropylammonium hydroxide, a process for preparing Cu-SAPO-42 molecular sieve by one-step ionothermal synthesis is developed. The operation of the present invention is simple, the preparation process of the molecular sieve is significantly shortened, multiple ion exchanges and multiple calcinations can be avoided, the energy consumption can be effectively reduced and the waste liquid output can be reduced, and the obtained Cu-SAPO-42 molecular sieve has a stable structure and excellent nitrogen oxide removal performance.

[0005] The present invention is realized by the following technical solutions:

[0006] A method for synthesizing Cu-SAPO-42 molecular sieve by the ionothermal method, comprising the following steps:

[0007] S1: Thoroughly stir and mix deionized water and a copper source to form a uniform solution; slowly drop an organic amine template agent into the uniform solution while stirring and continue to stir for a certain time to prepare a copper amine complex solution;

[0008] S2: Mix 1-ethyl-3-methylimidazolium bromide, an aluminum source, phosphoric acid, hydrofluoric acid, tetrapropylammonium hydroxide, and a silicon source, and heat and stir in an oil bath for a certain period of time to form a homogeneous mixed solution;

[0009] S3: Add the copper amine complex solution prepared in step S1 to the mixed solution prepared in step S2 and continue to heat and stir for a certain period of time to form a homogeneous mixed solution;

[0010] S4: Place the mixed solution prepared in step S3 into a hydrothermal autoclave, perform ionothermal crystallization for a certain period of time, and then obtain the Cu-SAPO-42 molecular sieve after washing with water, drying, and calcination.

[0011] A further improvement scheme of the present invention is as follows:

[0012] In step S1, the copper source is copper nitrate trihydrate or copper sulfate pentahydrate or a mixture of both.

[0013] Furthermore, the organic amine template agent is triethylenediamine or tetraethylenepentamine or a mixture of both.

[0014] Furthermore, the molar ratio of the copper source to the organic amine template agent is 1:0.8 - 1.2.

[0015] Preferably, the molar ratio of the copper source to the organic amine template agent is 1:1.

[0016] Furthermore, the time for continuous stirring after adding the organic amine template agent is 0.5 - 2 h.

[0017] Preferably, the time for continuous stirring after adding the organic amine template agent is 1 h.

[0018] Furthermore, in step S2, the molar ratio of the aluminum source, phosphoric acid, silicon source, 1-ethyl-3-methylimidazolium bromide, tetrapropylammonium hydroxide, and hydrofluoric acid is 1:0.8 - 1.2:0.2 - 0.8:35 - 45:1.9 - 2.5:0.8 - 1.2.

[0019] Preferably, in step S2, the molar ratio of the aluminum source, phosphoric acid, silicon source, 1-ethyl-3-methylimidazolium bromide, tetrapropylammonium hydroxide, and hydrofluoric acid is 1:1:0.6:40:2.1:1.

[0020] Furthermore, the aluminum source is aluminum isopropoxide or pseudo-boehmite or a mixture of both.

[0021] Furthermore, the silicon source is tetraethyl orthosilicate or silica sol or a mixture of both.

[0022] Furthermore, in step S2, the mass concentration of the phosphoric acid is 80 - 90 wt%.

[0023] Preferably, the mass concentration of the phosphoric acid is 85 wt%.

[0024] Furthermore, the mass concentration of the hydrofluoric acid is 30 - 50 wt%.

[0025] Preferably, the mass concentration of the hydrofluoric acid is 40 wt%.

[0026] Furthermore, the mass concentration of the tetrapropylammonium hydroxide is 20 - 30 wt%.

[0027] Preferably, the mass concentration of the tetrapropylammonium hydroxide is 25 wt%.

[0028] Furthermore, in step S2, the time for heating and stirring is 0.5 - 2 h.

[0029] Preferably, in step S2, the time for heating and stirring is 1 h.

[0030] Furthermore, in step S3, the molar ratio of the copper source of the copper - amine complex to the silicon source in the mixed solution obtained in step S2 is 0.2 - 0.7.

[0031] Furthermore, in step S3, the time for stirring is 0.5 - 2 h.

[0032] Preferably, in step S3, the time for stirring is 1 h.

[0033] Furthermore, in step S4, the crystallization temperature is 160 - 200 °C, and the crystallization time is 24 - 48 h.

[0034] Preferably, in step S4, the crystallization temperature is 180 °C, and the crystallization time is 24 h.

[0035] Furthermore, in step S4, the calcination temperature is 450 - 550 °C, and the calcination time is 4 - 8 h.

[0036] Preferably, in step S4, the calcination temperature is 550 °C, and the calcination time is 6 h.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. The present invention proposes a one - step ionothermal synthesis of Cu - SAPO - 42 zeolite molecular sieve. By introducing copper in the form of a complex in - situ into the Cu - SAPO - 42 zeolite molecular sieve through a one - step method, the prepared molecular sieve can be applied only after one calcination, which simplifies the preparation process, reduces energy consumption and reduces waste liquid production, and solves the problem of the collapse of the molecular sieve framework structure caused by multiple ion exchanges and multiple calcinations in the existing preparation methods.

[0039] 2. The Cu-SAPO-42 molecular sieve of the present invention has high crystallinity, and copper exists in the form of ions at the cation sites; when the synthesized Cu-SAPO-42 molecular sieve of the present invention is used for the selective catalytic reduction of nitrogen oxides by ammonia, it exhibits good catalytic performance and excellent NH3-SCR catalytic activity, providing a new path for the simple and green synthesis of novel denitration catalysts. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 XRD patterns of the Cu-SAPO-42 molecular sieves synthesized in Examples 1 to 4;

[0041] Figure 2 Scanning electron microscope (SEM) image of the Cu-SAPO-42 molecular sieve synthesized in Example 1;

[0042] Figure 3 Solid ultraviolet spectra of the Cu-SAPO-42 molecular sieves synthesized in Examples 1 to 4;

[0043] Figure 4 NH3-SCR catalytic performance diagrams of the Cu-SAPO-42 molecular sieves synthesized in Examples 1 to 4;

[0044] Figure 5 XRD patterns of the Cu-SAPO-34 molecular sieves synthesized in Comparative Examples 1 to 2. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0045] The present invention will be described in detail below with reference to specific embodiments.

[0046] Example 1

[0047] This example provides a preparation method for synthesizing Cu-SAPO-42 molecular sieve by the ionothermal method, including the following steps:

[0048] Prepare a copper-triethylenediamine (Cu-TETA) solution: Add 0.148 g of copper nitrate trihydrate to 3.0 g of deionized water, stir well to dissolve, and then slowly add 0.117 g of triethylenediamine (TETA) to the above solution, and continue to stir for 1 h.

[0049] Weigh 26.4 g of 1-ethyl-3-methylimidazolium bromide and place it in a beaker. Subsequently, add 0.7 g of aluminum isopropoxide, 0.4 g of phosphoric acid (85 wt%), 0.043 g of hydrofluoric acid (40 wt%), 5.86 g of tetrapropylammonium hydroxide (25 wt%), and 0.429 g of tetraethyl orthosilicate (TEOS). Heat and stir the above mixture in an oil bath at 110 °C for 1 h, then add the previously prepared Cu-TETA solution, continue to heat and stir for 1 h, and then place the solution in a hydrothermal reaction kettle, heat it to 180 °C, and crystallize for 24 h. After the crystallization is completed, wash the obtained solid with water, dry it, and calcine it at 550 °C for 6 h to obtain Cu-SAPO-42 with a Cu / Si of 0.3, denoted as Cu-SAPO-42-0.3.

[0050] Example 2

[0051] In this example, the feeding amount of copper nitrate trihydrate is 0.197 g, and the feeding amount of TETA is 0.156 g. Other operations are the same as those in Example 1 and will not be elaborated here. Cu-SAPO-42 with a Cu / Si of 0.4 is prepared and denoted as Cu-SAPO-42-0.4.

[0052] Example 3

[0053] In this example, the feeding amount of copper nitrate trihydrate is 0.246 g, and the feeding amount of TETA is 0.195 g. Other operations are the same as those in Example 1 and will not be elaborated here. Cu-SAPO-42 with a Cu / Si of 0.5 is prepared and denoted as Cu-SAPO-42-0.5.

[0054] Example 4

[0055] In this example, the feeding amount of copper nitrate trihydrate is 0.295 g, and the feeding amount of TETA is 0.234 g. Other operations are the same as those in Example 1 and will not be elaborated here. Cu-SAPO-42 with a Cu / Si of 0.6 is prepared and denoted as Cu-SAPO-42-0.6.

[0056] Comparative Example 1

[0057] In this comparative example, di-n-propylamine, which can direct the synthesis of SAPO-42 in the hydrothermal crystallization method, is used to replace 1-ethyl-3-methylimidazolium bromide as the template agent, and Cu-TETA is used as the copper source. The conventional hydrothermal crystallization method is used to attempt one-step in-situ synthesis of Cu-SAPO-42. The specific operation steps are as follows:

[0058] Prepare a copper-triethylenediamine (Cu-TETA) solution: Add 0.148 g of copper nitrate trihydrate to 3.0 g of deionized water, stir well to dissolve, and then slowly add 0.117 g of triethylenediamine (TETA) to the above solution, and continue to stir for 1 h.

[0059] Weigh 4.094 g of phosphoric acid (85 wt%) and 9.08 g of aluminum isopropoxide and place them in a beaker. Add 47.0 g of deionized water, then add 2.31 g of tetraethyl orthosilicate, 9 g of di-n-propylamine, and 2.43 g of cetyltrimethylammonium bromide. Age for 12 h under stirring. Place the solution in a hydrothermal reactor and heat it to 200 °C for crystallization for 48 h. After the crystallization is completed, wash the obtained solid with water, dry it, and calcine it at 550 °C for 6 h to obtain the molecular sieve.

[0060] Comparative Example 2

[0061] In this comparative example, the organic amine used is tetraethylenepentamine (TEPA), and its addition amount is 0.197 g. Other operations are the same as those in Comparative Example 1 and will not be elaborated here. The molecular sieve is prepared.

[0062] Test Example 1

[0063] The crystal structures and crystallinities of Examples 1 to 4 were evaluated by X-ray powder diffraction. The XRD results are as Figure 1 shown. It can be seen from the figure that Examples 1 to 4 are all Cu-SAPO-42 molecular sieves with good crystallinity. SEM detection was carried out on Example 1. As Figure 2 shown, the size of the synthesized Cu-SAPO-42 molecular sieve is about 5 - 20 μm. The states and coordination of copper species in Examples 1 to 4 were studied by ultraviolet-visible diffuse reflectance spectroscopy. The UV-Vis DRS results are as Figure 3 shown. In Examples 1 to 4, a narrow absorption band centered at 230 nm attributed to the isolated Cu 2- ions due to the charge transfer from O 2+ to the catalyst cation sites can be observed, indicating that the copper species in Examples 1 to 4 exist in the form of ions at the cation sites.

[0064] Test Example 2

[0065] The Cu-SAPO-42 molecular sieve catalysts prepared in Examples 1 to 4 were tableted and sieved. Take 0.1 g of the catalyst passed through a 60 - 80 mesh sieve and place it in a fixed-bed reactor for NH3-SCR reaction testing. The composition of the reaction gas is: 500 ppm NO, 500 ppm NH3, 3% H2O, and 5% O2, with N2 as the carrier gas. The total flow rate of the reaction gas is 250 ml / min, and the corresponding gas hourly space velocity (GHSV) is 200000 h -1 . The results of the NH3-SCR reaction testing are as Figure 4 shown. It can be seen from Figure 4 that Examples 1 to 4 have good performance for nitrogen oxides (NO x)The removal rate is maintained above 80%, indicating that the Cu-SAPO-42 molecular sieves prepared in Examples 1 to 4 all have excellent NH3-SCR activity.

[0066] Test Example 3

[0067] The crystal structures of Comparative Examples 1 to 2 were evaluated by X-ray powder diffraction, and the XRD results are as Figure 5 shown. It can be seen from the figure that the characteristic peaks of the LTA configuration to which SAPO-42 belongs did not appear in Comparative Examples 1 to 2, and all diffraction peaks highly match the characteristic peaks of the CHA configuration, indicating that Comparative Examples 1 to 2 exhibit the crystal structure of the CHA configuration and are SAPO-34 molecular sieves of the aluminophosphate type. The reason for this situation may be that both Cu-TETA and Cu-TEPA are more compatible with the molecular sieves of the CHA configuration (Martínez-Franco Raquel, et al., Rational direct synthesis methodology of very active and hydrothermally stable Cu-SAPO-34 molecular sieves for the SCR of NO x , 2012, 127, 73 - 280.). At the same time, the small molecule DPA template is easily interfered by the copper amine complex. Therefore, it is relatively difficult to in-situ synthesize Cu-SAPO-42 in one step with DPA as the template and the copper amine complex as the copper source in the hydrothermal crystallization system.

[0068] The above embodiments are only to illustrate the technical concept and features of the present invention, and the purpose is to enable those who are familiar with this technology to understand the content of the present invention and implement it accordingly, and it cannot be used to limit the protection scope of the present invention. All equivalent transformations or modifications made according to the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for synthesizing Cu-SAPO-42 molecular sieve by ionic thermal method, characterized in that, It includes the following steps: S1: Thoroughly stir and mix deionized water and a copper source to form a homogeneous solution; while stirring, slowly drop an organic amine template agent into the homogeneous solution and continue stirring for a certain period of time to prepare a copper-amine complex solution; S2: Mix 1-ethyl-3-methylimidazolium bromide, an aluminum source, phosphoric acid, hydrofluoric acid, tetrapropylammonium hydroxide, and a silicon source, and heat and stir in an oil bath for a certain period of time to form a homogeneous mixed solution; S3: Add the copper-amine complex solution prepared in step S1 to the mixed solution prepared in step S2 and continue heating and stirring for a certain period of time to form a homogeneous mixed solution; S4: Place the mixed solution prepared in step S3 into a hydrothermal autoclave, after ionothermal crystallization for a certain period of time, wash, dry, and calcine to obtain the Cu-SAPO-42 molecular sieve.

2. The method for synthesizing Cu-SAPO-42 molecular sieve by ionic thermal method according to claim 1, characterized in that: In step S1, the copper source is copper nitrate trihydrate or copper sulfate pentahydrate or a mixture of both; and / or, the organic amine template agent is triethylenediamine or tetraethylenepentamine or a mixture of both.

3. A method for synthesizing Cu-SAPO-42 molecular sieve by ionothermal method according to claim 1, characterized in that: In step S1, the molar ratio of the copper source to the organic amine template agent is 1:0.8 - 1.2; and / or, the time for continuing stirring after adding the organic amine template agent is 0.5 - 2 h.

4. A method for synthesizing Cu-SAPO-42 molecular sieve by an ionothermal method according to claim 1, characterized in that: In step S2, the molar ratio of the aluminum source, phosphoric acid, silicon source, 1-ethyl-3-methylimidazolium bromide, tetrapropylammonium hydroxide, and hydrofluoric acid is 1:0.8 - 1.2:0.2 - 0.8:35 - 45:1.9 - 2.5:0.8 - 1.

2.

5. A method for synthesizing Cu-SAPO-42 molecular sieve by ionothermal method according to claim 1, characterized in that: The aluminum source is aluminum isopropoxide or pseudo-boehmite or a mixture of both; and / or, the silicon source is tetraethyl orthosilicate or silica sol or a mixture of both.

6. A method for synthesizing Cu-SAPO-42 molecular sieve by ionic thermal method according to claim 1, characterized in that: In step S2, the mass concentration of phosphoric acid is 80 - 90 wt%; and / or, the mass concentration of hydrofluoric acid is 30 - 50 wt%; and / or, the mass concentration of tetrapropylammonium hydroxide is 20 - 30 wt%.

7. A method for synthesizing Cu-SAPO-42 molecular sieve by an ionic thermal method according to claim 1, characterized in that: In step S2, the time for heating and stirring is 0.5 - 2 h.

8. A method for synthesizing Cu-SAPO-42 molecular sieve by an ionic thermal method according to claim 1, characterized in that: In step S3, the molar ratio of the copper source of the copper-amine complex to the silicon source in the mixed solution obtained in step S2 is 0.2 - 0.7; and / or, the time for stirring is 0.5 - 2 h.

9. A method for synthesizing Cu-SAPO-42 molecular sieve by ionic thermal method according to claim 1, characterized in that: In step S4, the crystallization temperature is 160 - 200 °C, and the crystallization time is 24 - 48 h.

10. A method for synthesizing Cu-SAPO-42 molecular sieve by ionothermal method according to claim 1, characterized in that: The calcination temperature is 450 - 550 °C, and the calcination time is 4 - 8 h.

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