Fe-zsm-5 molecular sieve catalyst with high fe species dispersion and method for preparing the same

Abstract

The application discloses an Fe-ZSM-5 molecular sieve catalyst with high Fe species dispersity, wherein Fe species is in a form of bonding with Si species and Al species to form a basic framework of the molecular sieve ZSM-5, and the Fe species is uniformly dispersed on the surface of the ZSM-5 and embedded in the internal crystal lattice of the ZSM-5; the Fe species in the prepared Fe-ZSM-5 molecular sieve catalyst is in a form of bonding with Si species and Al species to form a basic framework of the molecular sieve ZSM-5, so that the Fe species is not only dispersed on the surface of the ZSM-5 but also embedded in the internal crystal lattice of the ZSM-5, the dispersity of the Fe species in the ZSM-5 is greatly improved, the cubic packing spherical Fe-ZSM-5 molecular sieve has a large specific surface area, has good high-temperature stability and catalytic activity in an NH3-SCR selective catalytic reduction reaction, the NO conversion rate is more than 80% in a temperature range of 380 DEG C to 480 DEG C, the catalytic activity is the highest at 460 DEG C, the corresponding NO conversion rate is as high as about 90%, and the requirement of denitration under a high-temperature environment of an automobile internal combustion engine is met.

Description

Technical Field

[0001] This invention relates to the field of inorganic nanocatalytic materials, specifically to a Fe-ZSM-5 molecular sieve catalyst with high Fe species dispersion suitable for high-temperature denitrification of automobile exhaust and its preparation method. Background Technology

[0002] Nitrogen oxides (NO) x NO has become one of the main components of air pollutants, causing serious harm to the ecological environment and human health. x The main sources are industrial waste gas from coal-fired power plants and vehicle exhaust. Domestically and internationally, there are regulations regarding the concentration of NO in waste gas or exhaust. x The most reliable method for removing NO is the use of ammonia selective catalytic reduction (NH3-SCR) technology. Regarding vehicle exhaust, NO in diesel vehicle exhaust... x The concentration of NO is highest at these temperatures, and the exhaust temperature of diesel internal combustion engines often reaches between 300°C and 500°C. Traditional vanadium-based and manganese-based metal oxide catalysts exhibit low catalytic activity at high temperatures, leading to high NO concentrations. x The removal rate of NOx is often low. Currently, metal-modified molecular sieve catalysts used for the selective catalytic reduction of ammonia include Cu-ZSM-5, CuSSZ-13, Fe-ZSM-5, and Fe-BETA. Cu-ZSM-5 is greatly affected by H2O; if the reactants contain 2% water vapor, its catalytic activity will be severely affected. Motor vehicle exhaust contains as much as 10%–16% water vapor, which greatly affects the NOx conversion rate. Molecular sieves such as SSZ-13 and BETA require the introduction of template agents during synthesis and have long crystallization cycles, resulting in high preparation costs and limiting their application. Studies have shown that the Fe-ZSM-5 catalyst maintains a high NOx conversion rate even in the presence of SO2 and H2O, exhibiting good hydrothermal stability and sulfur resistance. Although Fe-ZSM-5 prepared by the traditional impregnation method has good activity at high temperatures, the Fe species are only loaded onto the surface of ZSM-5 in the form of ion exchange, resulting in poor dispersion of Fe species and the catalyst performance needs to be improved. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a Fe-ZSM-5 molecular sieve catalyst with high Fe species dispersion and its preparation method, so as to solve the technical problem of poor Fe species dispersion in ZSM-5.

[0004] The present invention relates to a Fe-ZSM-5 molecular sieve catalyst with high Fe species dispersion, wherein the Fe species of the catalyst form the basic framework of the molecular sieve ZSM-5 in the form of bonding with Si and Al species, and the Fe species are uniformly dispersed on the surface of ZSM-5 and embedded in the ZSM-5 lattice.

[0005] Furthermore, the catalyst has a cubic stacked spherical structure.

[0006] This invention also discloses a method for preparing Fe-ZSM-5 molecular sieve catalyst with high Fe species dispersion. Using Si-Al-Fe as the basic framework of molecular sieve ZSM-5, the raw materials are first formed into a gel, then white crystals are synthesized by hydrothermal method, and finally powdered Fe-ZSM-5 molecular sieve catalyst is obtained by calcination.

[0007] Furthermore, the raw materials for preparing the catalyst include NaOH, TPABr, NH4F, Na2SiO3·9H2O, NaAlO2, FeCl3·6H2O, and EDTA-Na;

[0008] Furthermore, in the molar ratio, NaOH:TPABr:NH4F:Na2SiO3·9H2O:NaAlO2=5~30:5~25:10~40:50~150:2~10; FeCl3·6H2O:EDTA-Na=1;

[0009] Furthermore, the following steps are included:

[0010] S1, solution A is prepared by dissolving NaOH, NaAlO2 and TPABr in deionized water and then sonicating; solution B is prepared by dissolving Na2SiO3·9H2O and NH4F in deionized water and then sonicating; solution C is prepared by dissolving FeCl3·6H2O and EDTA-Na in deionized water and then sonicating.

[0011] S2, add solutions A and C dropwise to solution B in sequence and stir until homogeneous. Adjust the pH to neutral. Continue stirring for 1 to 3 hours after gelation occurs.

[0012] S3, the gel is subjected to a hydrothermal reaction to synthesize white crystals;

[0013] S4, Fe-ZSM-5 molecular sieve catalyst was prepared by calcining the dried white crystals;

[0014] Further, in step S3, the gel is placed in a high-pressure hydrothermal reactor and hydrothermally reacted at a temperature of 170℃~190℃ until white crystals appear at the bottom of the reactor. The white crystals are obtained by centrifugation and then dried at a temperature of 70℃~90℃.

[0015] Further, in step S4, the dried white crystals are transferred to a muffle furnace, the heating rate is set to 5℃ / min, and calcined at 450~650℃ for 7~8h.

[0016] The beneficial effects of this invention are as follows: The Fe-ZSM-5 molecular sieve catalyst with high Fe species dispersion disclosed in this invention and its preparation method are as follows: In the prepared Fe-ZSM-5 molecular sieve catalyst, Fe species form the basic framework of molecular sieve ZSM-5 in the form of bonds with Si species and Al species, so that Fe species are not only dispersed on the surface of ZSM-5, but also embedded in the internal lattice of ZSM-5, which greatly improves the dispersion of Fe species in ZSM-5. Moreover, the cubic packed spherical Fe-ZSM-5 molecular sieve has a large specific surface area and has good high-temperature stability and catalytic activity in the NH3-SCR selective catalytic reduction reaction. The NO conversion rate is more than 80% in the temperature range of 380℃ to 480℃, and the catalytic activity is the highest at 460℃, with a corresponding NO conversion rate of up to about 90%, which meets the requirements of denitrification in the high-temperature environment of automotive internal combustion engines. Attached Figure Description

[0017] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0018] Figure 1 The X-ray diffraction (XRD) spectra of the cubically packed spherical Fe-ZSM-5 molecular sieve samples are shown, where curves H-ZSM-5, 1Fe-ZSM-5, 2Fe-ZSM-5, 3Fe-ZSM-5, and 4Fe-ZSM-5 correspond to the XRD spectra of samples from Examples 1, 2, 3, 4, and 5, respectively.

[0019] Figure 2 The activity curves of the prepared cubic packed spherical Fe-ZSM-5 molecular sieve samples in simulated flue gas denitrification are shown. H-ZSM-5, 1Fe-ZSM-5, 2Fe-ZSM-5, 3Fe-ZSM-5, and 4Fe-ZSM-5 correspond to the NO conversion rate curves of the samples in Examples 1, 2, 3, 4, and 5, respectively.

[0020] Figure 3 and Figure 4 All images are SEM images of the cubic packed spherical Fe-ZSM-5 molecular sieve samples from Example 4. Detailed Implementation

[0021] Example 1 (Comparative Experiment)

[0022] First, weigh 2 mmol NaOH, 0.8 mmol NaAlO2, and 2 mmol TPABr, add them to 20 ml of deionized water, and sonicate for 10 min to prepare a solution, labeled as solution A. Then, weigh 20 mmol Na2SiO3·9H2O and 4 mmol NH4F, add them to 20 ml of deionized water, and sonicate for 10 min to prepare a solution, labeled as solution B. Next, measure 25 ml of deionized water and label it solution C. Then, magnetically stir solution B and add solution A dropwise to it. After stirring for 20 min, add solution C dropwise to solution B and continue stirring for 15 min. Adjust the pH to 7.5 with concentrated hydrochloric acid; a pale white gel will appear. Continue stirring for 2 h, then transfer the gel to a 100 ml high-pressure hydrothermal reactor and hydrothermally treat at 180 °C for 3 days. Finally, the white crystals were obtained by centrifugation, dried at 80°C for 12 hours, and then transferred to a muffle furnace and calcined at 550°C for 6 hours to obtain H-ZSM-5.

[0023] Example 2

[0024] First, weigh 2 mmol NaOH, 0.8 mmol NaAlO2, and 2 mmol TPABr (TPABr is tetrapropylammonium bromide), add them to 20 ml of deionized water, and sonicate for 10 min to prepare a solution, labeled as solution A. Then, weigh 20 mmol Na2SiO3·9H2O and 4 mmol NH4F, add them to 20 ml of deionized water, and sonicate for 10 min to prepare a solution, labeled as solution B. Next, weigh 0.2 mmol FeCl3·6H2O and 0.2 mmol EDTA-Na (sodium ethylenediaminetetraacetate), add them to 25 ml of deionized water, and sonicate for 10 min to prepare a solution, labeled as solution C. Next, solution B was magnetically stirred, and solution A was added dropwise to solution B. After stirring for 20 minutes, solution C was added dropwise to solution B, and stirring continued for 15 minutes. The pH was adjusted to 7.5 with concentrated hydrochloric acid, resulting in a pale yellow gel. After stirring for another 2 hours, the gel was transferred to a 100 ml high-pressure hydrothermal reactor and hydrothermally heated at 180°C for 3 days. Finally, the gel was centrifuged to obtain white crystals, which were then dried at 80°C for 12 hours and then transferred to a muffle furnace and calcined at 550°C for 7 hours to obtain 1Fe-ZSM-5.

[0025] Example 3

[0026] First, weigh 2 mmol NaOH, 0.8 mmol NaAlO2, and 2 mmol TPABr, add them to 20 ml of deionized water, and sonicate for 10 min to prepare a solution, labeled as solution A. Then, weigh 20 mmol Na2SiO3·9H2O and 4 mmol NH4F, add them to 20 ml of deionized water, and sonicate for 10 min to prepare a solution, labeled as solution B. Next, weigh 0.4 mmol FeCl3·6H2O and 0.4 mmol EDTA-Na, add them to 25 ml of deionized water, and sonicate for 10 min to prepare a solution, labeled as solution C. Afterward, magnetically stir solution B and add solution A dropwise to it. After stirring for 20 min, add solution C dropwise to solution B and continue stirring for 15 min. Adjust the pH to 7.5 with concentrated hydrochloric acid. A pale yellow gel will appear. Continue stirring for 2 h, then transfer the gel to a 100 ml high-pressure hydrothermal reactor and hydrothermally treat at 180 °C for 3 days. Finally, the white crystals were obtained by centrifugation, dried at 80°C for 12 hours, and then transferred to a muffle furnace and calcined at 550°C for 7.5 hours to obtain 2Fe-ZSM-5.

[0027] Example 4

[0028] First, weigh 2 mmol NaOH, 0.8 mmol NaAlO2, and 2 mmol TPABr, add them to 20 ml of deionized water, and sonicate for 10 min to prepare a solution, labeled as solution A. Then, weigh 20 mmol Na2SiO3·9H2O and 4 mmol NH4F, add them to 20 ml of deionized water, and sonicate for 10 min to prepare a solution, labeled as solution B. Next, weigh 0.6 mmol FeCl3·6H2O and 0.6 mmol EDTA-Na, add them to 25 ml of deionized water, and sonicate for 10 min to prepare a solution, labeled as solution C. Then, magnetically stir solution B and add solution A dropwise to it. After stirring for 20 min, add solution C dropwise to solution B and continue stirring for 15 min. Adjust the pH to 7.5 with concentrated hydrochloric acid. A pale yellow gel will appear. Continue stirring for 2 h, then transfer the gel to a 100 ml high-pressure hydrothermal reactor and hydrothermally treat at 180 °C for 3 days. Finally, the white crystals were obtained by centrifugation, dried at 80°C for 12 hours, and then transferred to a muffle furnace and calcined at 550°C for 7 hours to obtain 3Fe-ZSM-5.

[0029] Example 5

[0030] First, weigh 2 mmol NaOH, 0.8 mmol NaAlO2, and 2 mmol TPABr, add them to 20 ml of deionized water, and sonicate for 10 min to prepare a solution, labeled as solution A. Then, weigh 20 mmol Na2SiO3·9H2O and 4 mmol NH4F, add them to 20 ml of deionized water, and sonicate for 10 min to prepare a solution, labeled as solution B. Next, weigh 0.8 mmol FeCl3·6H2O and 0.8 mmol EDTA-Na, add them to 25 ml of deionized water, and sonicate for 10 min to prepare a solution, labeled as solution C. Afterward, magnetically stir solution B and add solution A dropwise to it. After stirring for 20 min, add solution C dropwise to solution B and continue stirring for 15 min. Adjust the pH to 7.5 with concentrated hydrochloric acid. A pale yellow gel will appear. Continue stirring for 2 h, then transfer the gel to a 100 ml high-pressure hydrothermal reactor and hydrothermally treat at 180 °C for 3 days. Finally, the white crystals were obtained by centrifugation, dried at 80°C for 12 hours, and then transferred to a muffle furnace and calcined at 550°C for 8 hours to obtain 4Fe-ZSM-5.

[0031] Test Example 1

[0032] XRD tests were performed on the H-ZSM-5, 1Fe-ZSM-5, 2Fe-ZSM-5, 3Fe-ZSM-5, and 4Fe-ZSM-5 samples prepared in each embodiment. The test results are as follows: Figure 1 As shown. By Figure 1 It can be seen that the phase structures of H-ZSM-5, 1Fe-ZSM-5, 2Fe-ZSM-5, 3Fe-ZSM-5, and 4Fe-ZSM-5 samples are all ZSM-5 molecular sieve frameworks, indicating that the introduction of Fe does not lead to the destruction of the ZSM-5 framework. The reason why no obvious characteristic peaks such as α-Fe2O3 were observed at 2θ of 35.6, 40.9, and 49.5 is twofold: firstly, Fe species did not form oxides, but instead formed the basic framework of molecular sieve ZSM-5 through bonding with Si and Al species; secondly, it also indicates that the amount of Fe introduced was too small. Furthermore, it is not difficult to observe that after the introduction of Fe, the characteristic peaks of 1Fe-ZSM-5, 2Fe-ZSM-5, 3Fe-ZSM-5, and 4Fe-ZSM-5 are lower than those of H-ZSM-5, indicating that the introduction of Fe reduces the crystallinity of ZSM-5, thus requiring reasonable control of the Fe content.

[0033] Test Example 2

[0034] The H-ZSM-5, 1Fe-ZSM-5, 2Fe-ZSM-5, 3Fe-ZSM-5, and 4Fe-ZSM-5 samples from each embodiment were placed in a fixed-bed reactor system for simulated flue gas denitrification activity evaluation experiments. 0.9g of quartz sand mixed with 100mg of catalyst was placed in a quartz tube reactor, with quartz sand and quartz wool on both sides. The feed gas composition consisted of 500ppm NO, 500ppm NH3, 8% O2, 5% CO2, 8% H2O, and a balance gas N2. The total gas volumetric flow rate was 5670ml / min, and the space velocity (GHSV) was 5000h⁻¹. -1 The reaction temperature is controlled by thermocouples, and the temperature measuring device can detect the temperature of the fixed bed in real time. The heating rate is 10℃·min. -1 The concentration of NO in the mixed gas after passing through the catalyst was detected online using an infrared gas analyzer. The test results are as follows: Figure 2 As shown. By Figure 2 It can be seen that the 1Fe-ZSM-5, 2Fe-ZSM-5, 3Fe-ZSM-5 and 4Fe-ZSM-5 samples have better activity above 380℃, and the NO conversion rate is more than 80% in the temperature range of 380℃ to 480℃. The 3Fe-ZSM-5 has the highest activity, with the highest NO conversion rate of about 90% at 460℃.

[0035] Test Example 3

[0036] Scanning electron microscopy (SEM) was performed on the 3Fe-ZSM-5 sample from Example 4, and the results are as follows: Figure 3 and Figure 4 As shown, these are SEM images magnified 1000x and 9000x, respectively. (Source: [Insert Source Here]) Figure 3 and Figure 4 It can be seen that the obtained catalyst is a cubic packed spherical molecular sieve.

[0037] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a Fe-ZSM-5 molecular sieve catalyst with high Fe species dispersion, characterized in that: Includes the following steps: S1, solution A is prepared by dissolving NaOH, NaAlO2 and TPABr in deionized water and then sonicating; solution B is prepared by dissolving Na2SiO3·9H2O and NH4F in deionized water and then sonicating; solution C is prepared by dissolving FeCl3·6H2O and EDTA-Na in deionized water and then sonicating. S2, add solutions A and C dropwise to solution B in sequence and stir until homogeneous, adjust the pH to neutral, and continue stirring for 1-3 hours after gelation occurs; S3, the gel is subjected to a hydrothermal reaction to synthesize white crystals; S4, the dried white crystals were calcined to obtain the Fe-ZSM-5 molecular sieve catalyst.

2. The method for preparing the Fe-ZSM-5 molecular sieve catalyst with high Fe species dispersion according to claim 1, characterized in that: In step S3, the gel is placed in a high-pressure hydrothermal reactor and hydrothermally reacted at a temperature of 170℃~190℃ until white crystals appear at the bottom of the reactor. The white crystals are obtained by centrifugation and then dried at a temperature of 70℃~90℃.

3. The method for preparing the Fe-ZSM-5 molecular sieve catalyst with high Fe species dispersion according to claim 1, characterized in that: In step S4, the dried white crystals are transferred to a muffle furnace, the heating rate is set to 5℃ / min, and calcined at 450~650℃ for 7~8 h.

4. The method for preparing the Fe-ZSM-5 molecular sieve catalyst with high Fe species dispersion according to claim 1, characterized in that: In step S1, the molar ratios are: NaOH : TPABr : NH4F : Na2SiO3·9H2O : NaAlO2 = 5~30 : 5~25 : 10~40 : 50~150 : 2~10; FeCl3·6H2O : EDTA-Na = 1.

5. An Fe-ZSM-5 molecular sieve catalyst prepared by the method for preparing the Fe-ZSM-5 molecular sieve catalyst with high Fe species dispersion as described in claim 1, characterized in that: The Fe species in the catalyst form the basic framework of molecular sieve ZSM-5 in the form of bonds with Si and Al species. The Fe species are uniformly dispersed on the surface of ZSM-5 and embedded in the ZSM-5 lattice.

6. The Fe-ZSM-5 molecular sieve catalyst with high Fe species dispersion according to claim 5, characterized in that: The catalyst has a cubic stacked spherical structure.

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