Method for determining distribution of phosphorus species on inner and outer surfaces of molecular sieve
By combining the solid nuclear magnetic resonance technology with a hydroxymethyl group-containing aromatic hydrocarbon probe molecule with a phosphorus-modified molecular sieve, the problem of difficult to determine the distribution of phosphorus species with a small particle size in the prior art is solved, and the distribution of the inner and outer surfaces of the molecular sieve is clearly depicted, and the research on the catalytic performance of phosphorus-modified molecular sieve is promoted.
Patent Information
- Application Number
- CN202410009608.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-01-02
- Publication Date
- 2025-07-04
AI Technical Summary
The prior art is difficult to effectively determine the distribution of phosphorus species with smaller particle sizes on the inner and outer surfaces of the molecular sieve, which limits the in-depth study of the catalytic performance of phosphorus-modified molecular sieve.
The hydroxymethyl-containing aromatic hydrocarbons are used as probe molecules, and the solvent is removed after mixing them with the phosphorus-modified molecular sieve. The spatial proximity of the probe molecules and the phosphorus species are determined by solid nuclear magnetic resonance technology, and the phosphorus species located on the outer surface of the molecular sieve are screened out.
It can clearly describe the distribution of phosphorus species with smaller particle sizes on molecular sieves, guiding the optimization of phosphorus modification technology and the development of new phosphorus modification technology, providing a simple and easy method.
Smart Images
Figure CN120253929A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of phosphorus-modified molecular sieves, and particularly relates to a method for determining the distribution of phosphorus species on the inner and outer surfaces of molecular sieves. Background Art
[0002] Molecular sieves are an important class of catalytic materials and have extensive applications in the fields of petrochemical industry and so on. However, in the industrial production process, molecular sieves have to face high-temperature and steam environments, which can lead to serious framework dealumination of molecular sieves, and then cause the rapid deactivation of molecular sieves (Ni N, Gao X, Xing E, et al. Phosphorus promotion on hydrothermal stability of ZSM-5 by P precursors with different molecular sizes[J]. Microporous and Mesoporous Materials, 2023:112706.; Van der Bij H E, Weckhuysen B M. Phosphorus promotion and poisoning in zeolite-based materials: synthesis, characterisation and catalysis[J]. Chemical Society Reviews, 2015, 44(20):7406-7428.). Research shows that phosphorus modification of molecular sieves can effectively improve the hydrothermal stability of molecular sieves, and the phosphorus species located on the inner surface (i.e., inside the pores) of molecular sieves will change the diffusion performance of molecular sieves, and the resulting steric effect will affect the product selectivity of catalytic reactions (Van der Bij H E, Weckhuysen B M. Phosphorus promotion and poisoning in zeolite-based materials: synthesis, characterisation and catalysis[J]. Chemical Society Reviews, 2015, 44(20):7406-7428.). In order to deeply understand the influence law of phosphorus on the selectivity of catalytic reactions, it is urgent to characterize in detail the distribution of phosphorus species on the inner and outer surfaces of molecular sieves.At present, the method for determining the distribution of phosphorus species on the inner and outer surfaces of molecular sieves is mainly imaging technology, which has good applicability in the distribution of phosphorus species with larger particle sizes, such as aluminum phosphate (Van Der Bij H E, Cicmil D, Wang J, et al. Aluminum-phosphate binder formation in zeolites as probed with X-ray absorption microscopy[J]. Journal of the American Chemical Society, 2014, 136(51):17774-17787.). However, the resolution of the images obtained by this technology is limited, which restricts the study of the distribution of phosphorus species with smaller particle sizes. Summary of the Invention
[0003] The object of the present invention is to overcome the problem that it is difficult to determine the distribution when the particle size of phosphorus species is small in the existing characterization methods for determining the distribution of phosphorus species on the inner and outer surfaces of molecular sieves, and to provide a method for determining the distribution of phosphorus species on the inner and outer surfaces of molecular sieves. This method can not only be used to determine phosphorus species with larger particle sizes, but also can be used for the study of the distribution of phosphorus species with smaller particle sizes on the inner and outer surfaces of molecular sieves.
[0004] In order to achieve the above object, on the one hand, the present invention provides a method for determining the distribution of phosphorus species on the inner and outer surfaces of molecular sieves, and the method comprises the following steps:
[0005] (1) Mix a probe molecule, a solvent and a phosphorus-modified molecular sieve to obtain a suspension;
[0006] (2) Remove the solvent in the suspension obtained in step (1) to obtain a test sample with a moisture content not higher than 5%, and then test the test sample;
[0007] Wherein, the probe molecule is selected from aromatic hydrocarbons containing hydroxymethyl;
[0008] Wherein, the diameter of the probe molecule is larger than the pore diameter of the phosphorus-modified molecular sieve.
[0009] Through the above technical solution, the beneficial effects of the present invention include:
[0010] The method proposed by the present invention combines experimental means of probe molecules and solid nuclear magnetic resonance technology. It can not only be used to determine the distribution of phosphorus species with larger particle sizes, but also be used for the distribution study of phosphorus species with smaller particle sizes (the particle size of phosphorus is less than 1 micron). The development of this technology is of great significance for exploring the influence of phosphorus distribution on the selectivity of reactants, and has a guiding role in the optimization of existing phosphorus modification technologies and the development of new phosphorus modification technologies. Moreover, the method provided by the present invention is simple and easy to operate and implement. Description of the Drawings
[0011] Figure 1 is the 1 1H solid nuclear magnetic resonance spectrum of Example 1 of the present invention;
[0012] Figure 2 is the 31 31P solid nuclear magnetic resonance spectrum of Example 1 of the present invention;
[0013] Figure 3 is the two-dimensional 1 1H{ 31 31P} heteronuclear correlation solid nuclear magnetic resonance spectrum of Example 1 of the present invention. Detailed Embodiments
[0014] The endpoints and any values within the ranges disclosed herein are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.
[0015] The "moisture content" disclosed in the present invention all refers to the mass moisture content.
[0016] On the one hand, the present invention provides a method for determining the distribution of phosphorus species on the inner and outer surfaces of molecular sieves. The method includes the following steps:
[0017] (1) Mix a probe molecule, a solvent and a phosphorus-modified molecular sieve to obtain a suspension;
[0018] (2) Remove the solvent in the suspension obtained in step (1) to obtain a test sample with a moisture content not higher than 5%, and then test the test sample;
[0019] Among them, the probe molecule is selected from aromatic hydrocarbons containing hydroxymethyl;
[0020] Among them, the diameter of the probe molecule is larger than the pore diameter of the phosphorus-modified molecular sieve.
[0021] In the method provided by the present invention, first, the diameter of the probe molecule used is larger than the pore diameter of the phosphorus-modified molecular sieve and cannot enter the molecular sieve pores. It will be adsorbed on the outer surface of the phosphorus-modified molecular sieve through hydrogen bonds. Then, the spatial proximity between the probe molecule and the phosphorus species on the phosphorus-modified molecular sieve is determined through testing, and thus the phosphorus species located on the outer surface of the molecular sieve are screened out. At the same time, the phosphorus species that do not interact with the probe molecule are located inside the molecular sieve pores. The method of the present invention can not only characterize phosphorus species with larger particle sizes but also clearly depict the distribution of phosphorus species with smaller particle sizes on the molecular sieve.
[0022] The probe molecule of the present invention can form hydrogen bonds with Si-O-Si, Si-O-Al, P-O-Al, or P-OH on the molecular sieve, so that the probe molecule can be fixed near the phosphorus species. These phosphorus species are relatively close to the probe molecule and are located on the outer surface of the molecular sieve; correspondingly, other phosphorus species are located on the inner surface of the molecular sieve.
[0023] In the present invention, the probe molecule is selected from aromatic hydrocarbons containing hydroxymethyl groups, preferably aromatic hydrocarbons containing two or more hydroxymethyl groups. By adopting this preferred embodiment, it is more conducive to fixing the probe molecule on the outer surface of the phosphorus-modified molecular sieve.
[0024] The present invention does not particularly limit the number of benzene rings in the probe molecule. Preferably, the probe molecule contains at least one of phenyl, anthryl, and naphthyl groups.
[0025] According to the present invention, preferably, the molecular formula of the probe molecule is C6H x X 6-x-y (CH2OH) y , where x≥0, y≥2, and X is selected from at least one of -Cl, -Br, -F, -NH4, -(CH2) m CH3, and -(CH2) m OH, where m≥0.
[0026] It can be understood that the H, X, and CH2OH groups in the molecular formula of the probe molecule are all connected to the benzene ring. That is, the X and CH2OH groups both replace the H on the benzene ring.
[0027] The inventors of the present invention have found that by using the above specific types of probe molecules, it is more conducive to determining the distribution of phosphorus species on the molecular sieve and can more clearly depict the distribution of phosphorus species with smaller particle sizes on the molecular sieve.
[0028] The present invention has a wide selection range for the type of substituent X, which can be various common substituents in the art. The main function of adding substituent X is to increase the size of the probe molecule. In fact, whether to add the substituent and the type of substituent can be appropriately selected according to the type of molecular sieve used to ensure that the diameter of the probe molecule is larger than the pore diameter of the phosphorus-modified molecular sieve. Preferably, 5≥m≥0.
[0029] In the present invention, -(CH2) m The hydroxyl group in the OH group can be at the alkyl terminal or at other positions, and the present invention has no requirement for this. Similarly, the above group can carry one hydroxyl group or two or more hydroxyl groups, and all of these are within the protection scope of the present invention.
[0030] According to the present invention, preferably, the diameter of the probe molecule is not less than Preferably, it is Adopting this preferred embodiment, since the pore diameter of the conventional phosphorus-modified molecular sieve is It can ensure that the diameter of the probe molecule is larger than the pore diameter of the phosphorus-modified molecular sieve, so that the probe molecule cannot enter the molecular sieve pore channel.
[0031] The present invention has a wide selection range for the type of molecular sieve in the phosphorus-modified molecular sieve, which can be a conventional selection in the art. Preferably, in the phosphorus-modified molecular sieve, the molecular sieve is ZSM-5 molecular sieve and / or β molecular sieve. The present invention only exemplarily gives two common molecular sieve types in the art, and other types of molecular sieves are also within the protection scope of the present invention.
[0032] The method provided by the present invention is applicable to the test process of phosphorus-modified molecular sieves with different phosphorus contents. Preferably, in the phosphorus-modified molecular sieve, based on the total weight of the phosphorus-modified molecular sieve, the phosphorus content is 0.3-5 wt%.
[0033] In the present invention, the moisture content of the sample to be tested obtained in step (2) is not higher than 5%, preferably not higher than 1%. Specifically, for example, it can be 4.9%, 4.5%, 4%, 3.5%, 3%, 2.5%, 2%, 1.5%, 1%, 0.5%, 0.1%, 0.08%, 0.05% and any value within the range formed by any two of these point values. Adopting this preferred embodiment is beneficial to preventing too high water content from hindering the diffusion of the probe molecule into the molecular sieve pore channel.
[0034] According to the present invention, preferably, the method further includes: before mixing the phosphorus-modified molecular sieve with the probe molecule and the solvent, first performing a vacuum treatment. Adopting this preferred embodiment is beneficial to removing the water molecules adsorbed on the outer surface and inner surface of the molecular sieve.
[0035] The present invention does not particularly limit the conditions of the vacuum treatment, and is based on the water content in the test sample obtained in the subsequent step (2) being not higher than 5%. Preferably, the conditions of the vacuum treatment include: the temperature is 270 - 600 °C, preferably 350 - 500 °C. Specifically, for example, it can be 270 °C, 300 °C, 350 °C, 400 °C, 450 °C, 500 °C, 550 °C, 600 °C, and any value within the range formed by any two of these point values.
[0036] According to the present invention, preferably, relative to 100 mg of the phosphorus-modified molecular sieve, the total volume of the probe molecule and the solvent is 0.2 - 3 mL, preferably 1.2 - 2.5 mL. Specifically, for example, it can be 0.2 mL, 0.5 mL, 0.7 mL, 1 mL, 1.2 mL, 1.5 mL, 1.7 mL, 2 mL, 2.2 mL, 2.5 mL, 2.7 mL, 3 mL, and any value within the range formed by any two of these point values. Adopting this preferred embodiment is beneficial for the probe molecule to be more evenly loaded on the outer surface of the molecular sieve, and at the same time prevents excessive solvent from affecting the efficiency of solvent removal.
[0037] According to the present invention, preferably, based on the total volume of the probe molecule and the solvent, the concentration of the probe molecule is 0.05 - 5 mmol / mL, preferably 0.1 - 1 mmol / mL. Specifically, for example, it can be 0.05 mmol / mL, 0.1 mmol / mL, 0.2 mmol / mL, 0.3 mmol / mL, 0.4 mmol / mL, 0.5 mmol / mL, 0.6 mmol / mL, 0.7 mmol / mL, 0.8 mmol / mL, 0.9 mmol / mL, 1 mmol / mL, 1.5 mmol / mL, 2 mmol / mL, 2.5 mmol / mL, 3 mmol / mL, 3.5 mmol / mL, 4 mmol / mL, 4.5 mmol / mL, 5 mmol / mL, and any value within the range formed by any two of these point values. Adopting this preferred embodiment is more beneficial for the probe molecule to be more evenly loaded on the outer surface of the molecular sieve, further beneficial for determining the spatial proximity between the probe molecule and the phosphorus species on the phosphorus-modified molecular sieve, and thus screening out the phosphorus species located on the outer surface of the molecular sieve.
[0038] The present invention has a wide range of choices for the type of the solvent, which can be a conventional choice in the art, and any organic solvent that does not react with the probe molecule can be used. Preferably, the solvent is selected from at least one of acetone, methanol, and ethanol.
[0039] The present invention does not particularly limit the addition sequence of the solvent, the probe molecule and the phosphorus-modified molecular sieve during the (1) mixing process. They can be added separately or together, and the present invention has no particular requirements in this regard. For thorough and uniform mixing, preferably, step (1) includes: first mixing the probe molecule and the solvent to obtain a mixed solution, and then mixing the mixed solution with the phosphorus-modified molecular sieve to obtain a suspension.
[0040] According to the present invention, preferably, the second mixing is carried out under an inert atmosphere. By adopting this preferred embodiment, the introduction of moisture in the air can be effectively prevented, ensuring that the moisture content in the sample to be measured obtained in subsequent step (2) is not higher than 5%.
[0041] According to the present invention, preferably, the inert atmosphere is selected from at least one of nitrogen, helium, argon and neon.
[0042] Preferably, the second mixing is carried out under ultrasonic conditions.
[0043] The present invention does not particularly limit the specific conditions of the ultrasonic treatment, which can be appropriately selected according to the specific situation, so that the probe molecules can be uniformly dispersed on the outer surface of the molecular sieve.
[0044] According to the present invention, preferably, the method further includes: first degassing the mixed solution, and then performing the second mixing with the phosphorus-modified molecular sieve. By adopting this preferred embodiment, the introduction of moisture in the air can be effectively prevented, ensuring that the moisture content in the sample to be measured obtained in subsequent step (2) is not higher than 5%.
[0045] The present invention does not particularly limit the method of the degassing treatment, which can be carried out with reference to the conventional methods in the art.
[0046] The present invention does not particularly limit the method for removing the solvent in step (2), which can be carried out with reference to the conventional methods in the art.
[0047] According to a preferred embodiment of the present invention, the suspension obtained in step (1) is subjected to vacuum treatment at 45 - 200 °C, preferably at 80 - 200 °C. By adopting this preferred embodiment, the solvent can be removed and the introduction of moisture can be prevented.
[0048] The present invention does not particularly limit the time of the vacuum treatment, which is based on the complete removal of the solvent.
[0049] In the present invention, in 1 the solid-state nuclear magnetic resonance spectrum of H has no signal of the solvent peak, that is, it is considered that the solvent is completely removed.
[0050] According to the present invention, preferably, the test in step (2) is solid nuclear magnetic resonance, preferably heteronuclear correlation solid nuclear magnetic resonance, more preferably including at least one of cross-polarization - heteronuclear correlation solid nuclear magnetic resonance, heteronuclear multiple quantum correlation solid nuclear magnetic resonance, double cross-polarization solid nuclear magnetic resonance, and rotary echo double resonance. Through the heteronuclear correlation solid nuclear magnetic resonance experimental technique, the spatial proximity between the probe molecule and the phosphorus species on the molecular sieve can be determined, and then the phosphorus species located on the outer surface of the molecular sieve can be screened out; correspondingly, the phosphorus species that do not interact with the probe molecule are located inside the pore channels of the molecular sieve.
[0051] According to the present invention, preferably, the test in step (2) includes:
[0052] (1) Through 1 1H solid nuclear magnetic resonance characterization, determine the signal position of the probe molecule in the sample to be tested;
[0053] (2) Through 31 31P solid nuclear magnetic resonance characterization, determine the signal positions of the phosphorus species in the phosphorus-modified molecular sieve and the sample to be tested;
[0054] (3) Through two-dimensional 1 1H{ 31 31P} heteronuclear correlation solid nuclear magnetic resonance to determine the distribution of the phosphorus species on the inner and outer surfaces of the molecular sieve.
[0055] Through the above tests, the phosphorus species located on the outer surface of the molecular sieve can be screened out, and at the same time, the phosphorus species that do not interact with the probe molecule are located inside the pore channels of the molecular sieve.
[0056] According to a specific embodiment of the present invention, transfer the sample to be tested obtained in step (2) to a solid nuclear magnetic resonance device under an inert gas for testing. By adopting the above preferred embodiment, the introduction of moisture in the air can be further prevented.
[0057] In the present invention, the "first" and "second" do not play a limiting role on each substance and operation, but are only used to distinguish the substances introduced in different steps and the operations carried out in different stages.
[0058] The present invention will be described in detail below through examples.
[0059] Example 1
[0060] 1. Vacuum-treat the phosphorus-modified ZSM-5 molecular sieve (P / ZSM-5, phosphorus content 4.5 wt%, pore diameter ) at 420 °C for 4 h.
[0061] 2. Prepare an acetone solution with a concentration of 0.25 mmol / mL of mesityl alcohol (diameter about ), and perform degassing treatment under vacuum conditions to remove air.
[0062] 3. Under a nitrogen atmosphere, transfer 2 mL of the acetone solution of tribenzyl alcohol to 100 mg of P / ZSM-5 that has been vacuum-treated, and then ultrasonicate for 1 hour to obtain a suspension.
[0063] 4. Vacuum-treat the above suspension at 110 °C for 1 hour to remove the acetone solvent, obtaining the sample to be tested. The moisture content of the sample to be tested is approximately 0.8%.
[0064] 5. Transfer the obtained sample to be tested into an NMR rotor under a nitrogen atmosphere and conduct one-dimensional 1 1H solid-state NMR experiment, and the results are as Figure 1 shown. The 31P solid-state NMR spectra before and after the adsorption of tribenzyl alcohol are as 31 shown. Continue to collect two-dimensional Figure 2 1H{ 1 31P} heteronuclear correlation solid-state NMR experiment on the above sample, and the results are as 31 shown. Figure 3 shown.
[0065] It can be seen from Figure 1 that there are a total of four 1 1H NMR signals on the P / ZSM-5 adsorbed with tribenzyl alcohol. Among them, the signals at 4.0 and 6.7 ppm come from the methylene protons and the protons on the benzene ring of tribenzyl alcohol respectively; the signal at 5.4 ppm is the signal of the protons of water molecules; the signal at 2.3 ppm is the signal of the silanol groups on the molecular sieve.
[0066] It can be seen from Figure 2 that there are a total of six different NMR signals on the P / ZSM-5 without adsorbed tribenzyl alcohol, labeled as P A -P F , and the above different 31 31P signals represent different phosphorus species. The chemical shifts of P A -P F are: -22.0 ppm, -25.6 ppm, -29.0 ppm, -34.0 ppm, -40.0 ppm, and -45.0 ppm respectively. After the adsorption of tribenzyl alcohol, 31 the 31P NMR spectrum does not change significantly, indicating that the adsorbed tribenzyl alcohol molecules do not damage the structure of P / ZSM-5.
[0067] It can be seen from Figure 3It can be seen that after the adsorption of tribenzyl alcohol, in addition to the two correlation signals located at (2.3, -34.0) and (3.7, -25.6) ppm (these two correlation signals originate from the spatial proximity between the hydroxyl species and the phosphorus species on the P / ZSM-5 molecular sieve), there are also two other correlation signals located at (4.0, -29.0) and (6.7, -29.0) ppm, and these two correlation signals indicate that the adsorbed tribenzyl alcohol is close to the P C species. Since tribenzyl alcohol is only distributed on the outer surface of the molecular sieve, it can be inferred that the P C species is also located on the outer surface of the molecular sieve. In addition, the correlation signals between other phosphorus species and tribenzyl alcohol did not appear, which indicates that other phosphorus species, that is, P A , P B , P D , P E , P F species are located on the inner surface of the molecular sieve.
[0068] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including the combination of each technical feature in any other suitable manner. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.
Claims
1. A method for determining the distribution of phosphorus species on the inner and outer surfaces of a molecular sieve, characterized in that, The method comprises the following steps: (1) Mix a probe molecule, a solvent and a phosphorus-modified molecular sieve to obtain a suspension; (2) Remove the solvent from the suspension obtained in step (1) to obtain a test sample with a water content not higher than 5%, and then test the test sample; Wherein, the probe molecule is selected from aromatic hydrocarbons containing hydroxymethyl; Wherein, the diameter of the probe molecule is larger than the pore diameter of the phosphorus-modified molecular sieve.
2. The method according to claim 1, wherein, The probe molecule is selected from aromatic hydrocarbons containing two or more hydroxymethyl groups; Preferably, the probe molecule contains at least one of phenyl, anthracenyl and naphthyl.
3. The method according to claim 2, wherein, The molecular formula of the probe molecule is C6H x X 6-x-y (CH2OH) y , where x≥0, y≥2, X is selected from at least one of -Cl, -Br, -F, -NH4, -(CH2) m CH3 and -(CH2) m OH, where m≥0.
4. The method according to claim 3, wherein, The diameter of the probe molecule is not less than preferably 5. The method according to any one of claims 1-4, wherein, In the phosphorus-modified molecular sieve, the molecular sieve is ZSM-5 molecular sieve and / or β molecular sieve.
6. The method according to any one of claims 1-5, wherein, The water content of the test sample obtained in step (2) is not higher than 1%.
7. The method according to any one of claims 1-6, wherein, The method further comprises: before mixing the phosphorus-modified molecular sieve with the probe molecule and the solvent, performing a vacuum treatment first; Preferably, the conditions of the vacuum treatment include: the temperature is 270-600 °C, preferably 350-500 °C.
8. The method according to any one of claims 1-7, wherein, Relative to 100 mg of the phosphorus-modified molecular sieve, the total volume dosage of the probe molecule and the solvent is 0.2-3 mL, preferably 1.2-2.5 mL; Preferably, based on the total volume of the probe molecule and the solvent, the concentration of the probe molecule is 0.05-5 mmol / mL, preferably 0.1-1 mmol / mL; Preferably, the solvent is selected from at least one of acetone, methanol and ethanol.
9. The method according to any one of claims 1-8, wherein, Step (1) includes: first mixing the probe molecule and the solvent to obtain a mixed solution, and then mixing the mixed solution with the phosphorus-modified molecular sieve to obtain a suspension; Preferably, the second mixing is carried out in an inert atmosphere; Preferably, the inert atmosphere is selected from at least one of nitrogen, helium, argon and neon; Preferably, the method further comprises: first degassing the mixed solution, and then performing the second mixing with the phosphorus-modified molecular sieve.
10. The method according to any one of claims 1-9, wherein, The test in step (2) is solid nuclear magnetic resonance, preferably heteronuclear correlation solid nuclear magnetic resonance, more preferably including at least one of cross polarization-heteronuclear correlation solid nuclear magnetic resonance, heteronuclear multiple quantum correlation solid nuclear magnetic resonance, double cross polarization solid nuclear magnetic resonance and rotary echo double resonance; Preferably, the test in step (2) includes: (1) By 1 solid-state nuclear magnetic resonance characterization of H, determine the signal position of the probe molecule in the sample to be measured; (2) By 31 P solid-state nuclear magnetic resonance characterization, determine the signal positions of phosphorus species in the phosphorus-modified molecular sieve and the sample to be measured; (3) By two-dimensional 1 H{ 31 P} heteronuclear correlation solid-state nuclear magnetic resonance to determine the distribution of phosphorus species on the inner and outer surfaces of the molecular sieve.