A method for preparing Y molecular sieve loaded with noble metal single atoms

Abstract

A method for preparing a Y molecular sieve loaded with a single noble metal atom is characterized by adding choline chloride to a Y molecular sieve synthesis system comprising a silicon source, an aluminum source, and an alkali source and stirring the mixture uniformly, then adding a noble metal precursor coordinated by ethylenediamine, aging the mixture, and subjecting the mixture to in-situ static hydrothermal crystallization, and finally calcining and reducing the crystallized product with hydrogen.

Description

Technical Field

[0001] The present invention relates to a method for preparing a heterogeneous catalyst, and more particularly to a method for preparing a Y molecular sieve loaded with noble metals. Background Art

[0002] Noble metal single-atom catalysts can increase the utilization rate of noble metal active centers to 100%, greatly improving the efficiency of noble metal use. In addition, the unique interaction between noble metal single atoms and supports can regulate the surface valence electron structure of noble metal single atoms, thereby promoting the selectivity of noble metal catalysts.

[0003] Molecular sieve is a crystalline silicate or aluminosilicate with a regular structure and good thermal and hydrothermal stability. At the same time, the unique shape selectivity of the molecular sieve pores can improve the catalytic performance of the loaded single atoms.

[0004] Professor Bruce C. Gates of the United States used KLTL molecular sieve as a carrier and based on the traditional ion exchange method, he converted Pt(NH3)4(NO3)2 into 2+ Ions and alkali metal ions K of molecular sieves + Ion exchange was performed to form isolated Pt single atom active centers, and then Pt was obtained after being treated in a 10% (volume fraction) O2 / He oxidation atmosphere at 360°C for 4 hours. 1 / KLTL single-atom catalysts (Angew. Chem. Int. Ed., 2014, 53, 8904–8907) require very strict water and oxygen removal during the preparation of Pt single atoms, which brings great difficulties to practical industrial applications.

[0005] Professor Avelino Corma and his colleagues in Spain mixed a thiol-stabilized H2PtCl6 precursor with a precursor for synthesizing CHA-structured zeolites. Through in-situ crystallization and subsequent calcination and reduction, they were able to prepare CHA-structured zeolite-encapsulated Pt clusters of ~1 nm. This was then followed by high-temperature calcination in an oxygen atmosphere at 450-650°C to obtain a CHA-structured zeolite-encapsulated Pt single-atom catalyst (J. Am. Chem. Soc., 2016, 138, 15743–15750). This method, which involved cumbersome steps for preparing single Pt atoms and required multiple reduction and calcination treatments, hindered its industrial application.

[0006] Professor Li Yadong’s research group reported a new method for preparing metal single atom sites (M-ISAS) catalysts in Y-type molecular sieves (M-ISAS@Y, M = Pt, Pd, Ru, Rh, Co, Ni, Cu). The method first uses an in-situ encapsulation technique to simultaneously encapsulate, for example, an ethylenediamine-coordinated Pt precursor into the supercage and SOD cage of the Y molecular sieve. The supercage pores are large and the SOD cage pores are very small. Ethanol and water are used as extractants. The Pt precursor located in the supercage is separated by multiple washings, leaving only the Pt precursor in the SOD cage. The single-atom Pt catalyst confined in the SOD cage of the Y molecular sieve is prepared by calcination and reduction treatment (J.Am.Chem.Soc., 2019, 141, 9305-9311). This method requires a large number of multiple washings to separate the Pt precursor located in the supercage. The process is more complicated and, more importantly, it causes a waste of precious metal Pt. Summary of the Invention

[0007] The purpose of the present invention is to address the deficiencies in the prior art and provide a simple and generally suitable industrial production method for preparing Y molecular sieves loaded with noble metal single atoms confined into SOD cages.

[0008] Therefore, the preparation method of Y molecular sieve loaded with noble metal single atoms provided by the present invention is characterized by comprising: adding choline chloride to a Y molecular sieve synthesis system including a silicon source, an aluminum source and an alkali source and stirring uniformly, then adding a noble metal precursor coordinated by ethylenediamine, aging and then subjecting the product to in-situ static hydrothermal crystallization, and calcining and hydrogen reduction of the crystallized product.

[0009] In the present invention, the molar ratio of the silicon source, aluminum source and alkali source in the Y molecular sieve synthesis system is (9.0-11.0):1:(4.0-6.0), preferably (9.5-10.6):1:(4.0-5.4), wherein the silicon source is calculated as SiO2 and the aluminum source is calculated as Al2O3.

[0010] A specific embodiment of the present invention is characterized in that sodium aluminate, sodium hydroxide, choline chloride and water are mixed uniformly, and then silica sol is added and stirred continuously. After the sol is formed, a noble metal precursor solution coordinated by ethylenediamine is added and stirred continuously. The resulting mixture is aged and then subjected to in-situ static hydrothermal crystallization, and the crystallized product is recovered, roasted and reduced with hydrogen.

[0011] The molar ratio of the choline chloride to the silica sol is (0.19-0.21):1, and the silica sol is calculated as SiO2; the ratio of the mass of the noble metal to the sum of the masses of sodium aluminate and the silica sol is 0.01-0.25:100, and the noble metal precursor is calculated as the noble metal element, the sodium aluminate is calculated as Al2O3, and the silica sol is calculated as SiO2.

[0012] The ethylenediamine-coordinated noble metal precursor is obtained by mixing an aqueous solution of a noble metal salt with ethylenediamine. The molar ratio of the noble metal to ethylenediamine in the noble metal salt is preferably 1:15-20. The noble metal salt is preferably chloroplatinic acid. The ethylenediamine-coordinated noble metal precursor is preferably added slowly dropwise at room temperature.

[0013] In the preparation method of the present invention, the aging conditions are preferably stirring at (25-30)°C for (8-12) hours; the in-situ static hydrothermal crystallization has a crystallization temperature of 100-150°C and a crystallization time of 8-15 days.

[0014] The process of recovering the crystallized product is well known to those skilled in the art, and generally includes filtering, washing and drying the crystallized product.

[0015] The calcination temperature is 300-350°C, and the hydrogen reduction temperature is 200-250°C. To avoid Pt atom agglomeration caused by excessively high temperatures, the heating rates during the calcination and hydrogen reduction treatments are preferably controlled. Preferably, the calcination heating rate is 0.2-0.6°C / min, and the hydrogen reduction heating rate is 0.1-0.5°C / min.

[0016] The Y molecular sieve prepared by the preparation method provided by the present invention has a silicon-aluminum molar ratio of 5-7.

[0017] The Y molecular sieve loaded with noble metal single atoms obtained by the preparation method of the present invention is a Y molecular sieve loaded with noble metal single atoms confined by a SOD cage, and the mass content of the noble metal is 0.01-0.2%.

[0018] The preparation method of the Y molecular sieve loaded with noble metal single atoms provided by the present invention, on the one hand, utilizes the characteristic that choline chloride occupies a supercage during the synthesis process of the Y molecular sieve to ensure that the noble metal precursor coordinated by ethylenediamine does not appear in the supercage, but can only occupy the SOD cage, thereby avoiding the aggregation of the noble metal precursor in the supercage (one supercage of the Y molecular sieve can accommodate multiple noble metal precursors); on the other hand, utilizes the characteristic that one SOD cage can only accommodate one noble metal precursor to ensure that only noble metal single atoms can be formed after calcination and reduction treatment, thereby obtaining the Y molecular sieve with noble metal single atoms confined by the SOD cage.

[0019] Through observation and analysis under spherical aberration electron microscope, the Y molecular sieve loaded with precious metals obtained by the preparation method provided by the present invention has a platinum atom size at the single-atom level, such as Figure 2 As shown, single-atom platinum is uniformly dispersed in the Y molecular sieve crystal and the size of platinum just matches the size of single-atom platinum. Figure 3The typical structure example of the single-atom platinum Y molecular sieve loaded with SOD cage confinement obtained by DFT theoretical calculation is shown. It can be seen that the relative energy of 0 kcal / mol indicates that the system is the most stable, which further illustrates that the SOD cage-confined platinum single atom is obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the XRD pattern of the sample in Example 1.

[0021] Figure 2 This is the spherical aberration electron microscope image of the sample in Example 1.

[0022] Figure 3 This is an example diagram of DFT theoretical calculation of a single platinum atom in the SOD cage of Y molecular sieve.

[0023] Figure 4 This is the TEM image of the sample in Comparative Example 1. DETAILED DESCRIPTION

[0024] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that, unless there is a conflict, the embodiments and features in the embodiments of the present application can be combined with each other.

[0025] The following detailed description is an exemplary description, which is intended to provide further detailed description of the present invention. Unless otherwise indicated, all technical terms used in the present invention have the same meaning as those generally understood by those skilled in the art. The terms used in the present invention are only for describing specific embodiments, and are not intended to limit the exemplary embodiments according to the present invention.

[0026] The instruments used for characterization and the basic operating parameters of the characterization in the examples are as follows:

[0027] XRD: Philips Magix-601 X-ray fluorescence (XRF) spectrometer.

[0028] Spherical aberration electron microscope: TEM (Themis Z, Thermo Fisher Scientific) at 300kV with aspherical aberration (Cs) corrector (CEOS GmbH).

[0029] Transmission electron microscope: a JEM-3200FS from JEOL.

[0030] Example 1

[0031] 2.0g of sodium metaaluminate (NaAlO2) was dissolved in 24.2g of H2O, followed by 2.68g of NaOH and mixing. 3.45g of choline chloride was then added and ultrasonically mixed. Under vigorous stirring, 24.6g of 30% silica sol was added dropwise to the mixture to form the system for synthesizing Y molecular sieve. 0.042g of chloroplatinic acid hexahydrate and 0.11ml of ethylenediamine were dissolved in 16ml of deionized water. Under vigorous stirring, the ethylenediamine-coordinated platinum precursor solution was slowly added dropwise to the above system for synthesizing Y molecular sieve and mixed thoroughly.

[0032] In the system for synthesizing Y molecular sieve:

[0033] The molar ratio of SiO2, Al2O3 and NaOH is 10:1:5.4;

[0034] The molar ratio of choline chloride to silica sol is 0.2:1, and the silica sol is calculated as SiO2;

[0035] The ratio of the mass of platinum to the sum of the masses of sodium metaaluminate and silica sol is 0.2:100;

[0036] The molar ratio of chloroplatinic acid to ethylenediamine is 1:20.

[0037] The mixed liquid was then placed in a polytetrafluoroethylene-lined crystallization reactor for static crystallization at 110°C for 10 days. After crystallization, the sample was filtered, washed, and dried. The resulting sample was calcined at 350°C in an air atmosphere in a tube furnace for 2 hours (heating rate 0.3°C / min), followed by reduction at 200°C in a hydrogen atmosphere for 1 hour (heating rate 0.3°C / min) to obtain a molecular sieve sample.

[0038] Figure 1 From the XRD spectrum, it can be seen that the prepared molecular sieve is Y molecular sieve. Figure 1 It can also be seen that no obvious Pt element characteristic peak is observed in the XRD spectrum data of the Pt-loaded molecular sieve, which indirectly indicates that the Pt loaded on the molecular sieve has no obvious agglomeration and the structure of the Y molecular sieve itself is not significantly affected.

[0039] Figure 2 This is a spherical aberration electron microscope photo. The bright spot in the picture is a single Pt atom. Figure 2 It can be seen that single-atom Pt is uniformly dispersed in the Y molecular sieve crystal, and the size of Pt just matches the size of single-atom Pt, indicating that the platinum loaded on the molecular sieve is at the atomic level.

[0040] Figure 3 The structure obtained by DFT calculation, the relative energy of 0kcal / mol indicates that the system is most stable when the platinum atom is confined by the SOD cage, which further shows that the Pt single atom confined by the SOD cage is obtained.

[0041] The molar ratio of silicon oxide to aluminum oxide in the Y molecular sieve is about 6:1, and the platinum content in the molecular sieve is 0.1%.

[0042] Comparative Example 1

[0043] The same as Example 1, except that 3.45 g of choline chloride was not added in this comparative example, to obtain a comparative sample.

[0044] Figure 4 TEM photos of the comparison samples are shown in Figure 2. Figure 4 It can be seen that the size of the Pt nanoparticles is much larger than the single-atom size (TEM images show a size of about 1.5 nm), indicating that the SOD-confined single-atom Y molecular sieve was not obtained in this comparative example.

[0045] Choline chloride was not added in this comparative example. This comparative example illustrates the role of choline chloride in the preparation method provided by the present invention. In the present invention, choline chloride participates in the preparation of the Y molecular sieve loaded with precious metals and occupies the supercage, playing a key role in confining the single-atom platinum SOD.

[0046] The platinum content of this sample was approximately 0.1%.

[0047] Example 2

[0048] Dissolve 2.0g of sodium metaaluminate (NaAlO2) in 24.2g of H2O, then add 2.68g of NaOH and mix thoroughly. Add 3.45g of choline chloride and mix thoroughly with ultrasound. Under vigorous stirring, add 24.6g of 30% silica sol dropwise to the mixture. This constitutes the system for synthesizing Y molecular sieve. Mix 0.042g of chloroplatinic acid hexahydrate with 0.083ml of ethylenediamine. Under vigorous stirring, slowly add the ethylenediamine-coordinated platinum precursor solution dropwise to the above system for synthesizing Y molecular sieve and mix thoroughly.

[0049] In the system for synthesizing Y molecular sieve:

[0050] The molar ratio of SiO2, Al2O3 and NaOH is 10:1:5.4;

[0051] The molar ratio of choline chloride to silica sol is 0.2:1, and the silica sol is calculated as SiO2;

[0052] The ratio of the mass of platinum to the sum of the masses of sodium metaaluminate and silica sol is 0.2:100;

[0053] The molar ratio of chloroplatinic acid to ethylenediamine is 1:15.

[0054] The mixed liquid was then placed in a polytetrafluoroethylene-lined crystallization reactor for static crystallization at 110°C for 10 days. After crystallization, the sample was washed and dried. The resulting sample was then calcined at 350°C in an air atmosphere in a tube furnace for 2 hours (heating rate 0.3°C / min), followed by reduction at 200°C in a hydrogen atmosphere for 1 hour (heating rate 0.3°C / min) to obtain a molecular sieve sample.

[0055] The structures obtained from XRD spectra, electron microscopy photos and DFT calculations are Figure 1 、 Figure 2 and Figure 3 characteristics.

[0056] The molar ratio of silicon oxide to aluminum oxide in the Y molecular sieve is about 6:1, and the platinum content in the molecular sieve is about 0.1%.

[0057] Example 3

[0058] Dissolve 2.0g of sodium metaaluminate (NaAlO2) in 24.2g of H2O, then add 2.68g of NaOH and mix thoroughly. Add 3.45g of choline chloride and mix thoroughly by ultrasonication. Under vigorous stirring, add 24.6g of 30% silica sol dropwise to the mixture. This constitutes the system for synthesizing Y molecular sieve. Mix 0.042g of chloroplatinic acid hexahydrate with 0.096ml of ethylenediamine. Under vigorous stirring, slowly add the ethylenediamine-coordinated platinum precursor solution dropwise to the above system for synthesizing Y molecular sieve and mix thoroughly.

[0059] In the system for synthesizing Y molecular sieve:

[0060] The molar ratio of SiO2, Al2O3 and NaOH is 10:1:5.4;

[0061] The molar ratio of choline chloride to silica sol is 0.2:1, and the silica sol is calculated as SiO2;

[0062] The ratio of the mass of platinum to the sum of the masses of sodium metaaluminate and silica sol is 0.2:100;

[0063] The molar ratio of chloroplatinic acid to ethylenediamine is 1:17.5.

[0064] The mixed liquid was then placed in a polytetrafluoroethylene-lined crystallization reactor for static crystallization at 110°C for 10 days. After crystallization, the sample was washed and dried. The resulting sample was then calcined at 350°C in an air atmosphere in a tube furnace for 2 hours (heating rate 0.3°C / min), followed by reduction at 200°C in a hydrogen atmosphere for 1 hour (heating rate 0.3°C / min) to obtain a molecular sieve sample.

[0065] The structures obtained from XRD spectra, electron microscopy photos and DFT calculations are Figure 1 、 Figure 2 and Figure 3 characteristics.

[0066] The molar ratio of silicon oxide to aluminum oxide in the Y molecular sieve is 6:1, and the platinum content in the molecular sieve is about 0.1%.

[0067] Example 4

[0068] Take 2.0g sodium aluminate (NaAlO2) and dissolve it in 24.2g H2O, then add 2.68g NaOH and mix well. Continue to add 3.45g choline chloride and mix it evenly by ultrasonic. Under vigorous stirring, add 24.6g of 30% silica sol dropwise to the above mixed system to form a system for synthesizing Y molecular sieve. Then take 0.042g hexahydrate chloroplatinic acid and 0.11ml ethylenediamine and dissolve them in 16ml deionized water. Under vigorous stirring, slowly add the ethylenediamine-coordinated platinum precursor solution to the above-mentioned system for synthesizing Y molecular sieve and mix evenly. In the system for synthesizing Y molecular sieve:

[0069] The molar ratio of SiO2, Al2O3 and NaOH is 10:1:5.4;

[0070] The molar ratio of choline chloride to silica sol is 0.2:1, and the silica sol is calculated as SiO2;

[0071] The ratio of the mass of platinum to the sum of the masses of sodium metaaluminate and silica sol is 0.2:100;

[0072] The molar ratio of chloroplatinic acid to ethylenediamine is 1:20.

[0073] The mixed liquid was then placed in a polytetrafluoroethylene-lined crystallization reactor for static crystallization at 110°C for 10 days. After crystallization, the sample was filtered, washed, and dried. The resulting sample was calcined in a tube furnace at 325°C for 2 hours (heating rate 0.3°C / min) in air atmosphere, and then reduced at 200°C for 1 hour (heating rate 0.3°C / min) in a hydrogen atmosphere to obtain a molecular sieve sample.

[0074] The structures obtained from XRD spectra, electron microscopy photos and DFT calculations are Figure 1 、 Figure 2 and Figure 3 characteristics.

[0075] The molar ratio of silicon oxide to aluminum oxide in the Y molecular sieve is 6:1, and the platinum content in the molecular sieve is about 0.1%.

[0076] Example 5

[0077] Dissolve 2.0g of sodium metaaluminate (NaAlO2) in 24.2g of H2O, then add 2.68g of NaOH and mix thoroughly. Add 3.45g of choline chloride and mix thoroughly with ultrasound. Under vigorous stirring, add 24.6g of 30% silica sol dropwise to the mixture. This constitutes the system for synthesizing Y molecular sieve. Mix 0.042g of chloroplatinic acid hexahydrate with 0.083ml of ethylenediamine. Under vigorous stirring, slowly add the ethylenediamine-coordinated platinum precursor solution dropwise to the above system for synthesizing Y molecular sieve and mix thoroughly.

[0078] In the system for synthesizing Y molecular sieve:

[0079] The molar ratio of SiO2, Al2O3 and NaOH is 10:1:5.4;

[0080] The molar ratio of choline chloride to silica sol is 0.2:1, and the silica sol is calculated as SiO2;

[0081] The ratio of the mass of platinum to the sum of the masses of sodium metaaluminate and silica sol is 0.2:100;

[0082] The molar ratio of chloroplatinic acid to ethylenediamine is 1:15.

[0083] The mixed liquid was then placed in a polytetrafluoroethylene-lined crystallization reactor for static crystallization at 110°C for 10 days. After crystallization, the sample was washed and dried. The resulting sample was then calcined in a tube furnace at 325°C for 2 hours (heating rate 0.3°C / min) in air atmosphere, followed by reduction at 200°C for 1 hour (heating rate 0.3°C / min) in a hydrogen atmosphere to obtain a molecular sieve sample.

[0084] The structures obtained from XRD spectra, electron microscopy photos and DFT calculations are Figure 1 、 Figure 2 and Figure 3 characteristics.

[0085] The molar ratio of silicon oxide to aluminum oxide in the Y molecular sieve is 6:1, and the platinum content in the molecular sieve is about 0.1%.

[0086] Example 6

[0087] Dissolve 2.0g of sodium metaaluminate (NaAlO2) in 24.2g of H2O, then add 2.68g of NaOH and mix thoroughly. Add 3.45g of choline chloride and mix thoroughly with ultrasound. Under vigorous stirring, add 24.6g of 30% silica sol dropwise to the mixture. This constitutes the system for synthesizing Y molecular sieve. Mix 0.042g of chloroplatinic acid hexahydrate with 0.096ml of ethylenediamine. Under vigorous stirring, slowly add the ethylenediamine-coordinated platinum precursor solution dropwise to the above system for synthesizing Y molecular sieve and mix thoroughly.

[0088] In the system for synthesizing Y molecular sieve:

[0089] The molar ratio of SiO2, Al2O3 and NaOH is 10:1:5.4;

[0090] The molar ratio of choline chloride to silica sol is 0.2:1, and the silica sol is calculated as SiO2;

[0091] The ratio of the mass of platinum to the sum of the mass of sodium aluminate and silica sol is 0.2:100

[0092] The molar ratio of chloroplatinic acid to ethylenediamine is 1:17.5

[0093] The mixed liquid was then placed in a polytetrafluoroethylene-lined crystallization reactor for static crystallization at 110°C for 10 days. After crystallization, the sample was washed and dried. The resulting sample was then calcined in a tube furnace at 325°C for 2 hours (heating rate 0.3°C / min) in air atmosphere, followed by reduction at 200°C for 1 hour (heating rate 0.3°C / min) in a hydrogen atmosphere to obtain a molecular sieve sample.

[0094] The structures obtained from XRD spectra, electron microscopy photos and DFT calculations are Figure 1 、 Figure 2 and Figure 3 characteristics.

[0095] The molar ratio of silicon oxide to aluminum oxide in the Y molecular sieve is 6:1, and the platinum content in the molecular sieve is about 0.1%.

[0096] Example 7

[0097] 2.0g of sodium metaaluminate (NaAlO2) was dissolved in 24.2g of H2O, followed by 2.68g of NaOH and mixing. 3.45g of choline chloride was then added and ultrasonically mixed. Under vigorous stirring, 24.6g of 30% silica sol was added dropwise to the mixture to form the system for synthesizing Y molecular sieve. 0.042g of chloroplatinic acid hexahydrate and 0.11ml of ethylenediamine were dissolved in 16ml of deionized water. Under vigorous stirring, the ethylenediamine-coordinated platinum precursor solution was slowly added dropwise to the above system for synthesizing Y molecular sieve and mixed thoroughly.

[0098] In the system for synthesizing Y molecular sieve:

[0099] The molar ratio of SiO2, Al2O3 and NaOH is 10:1:5.4;

[0100] The molar ratio of choline chloride to silica sol is 0.2:1, and the silica sol is calculated as SiO2;

[0101] The ratio of the mass of platinum to the sum of the masses of sodium metaaluminate and silica sol is 0.2:100;

[0102] The molar ratio of chloroplatinic acid to ethylenediamine is 1:20.

[0103] The mixed liquid was then placed in a polytetrafluoroethylene-lined crystallization reactor for static crystallization at 110°C for 10 days. After crystallization, the sample was filtered, washed, and dried. The resulting sample was calcined in a tube furnace at 300°C for 2 hours (heating rate 0.3°C / min) in air atmosphere, and then reduced at 200°C for 1 hour (heating rate 0.3°C / min) in a hydrogen atmosphere to obtain a molecular sieve sample.

[0104] The structures obtained from XRD spectra, electron microscopy photos and DFT calculations are Figure 1 、 Figure 2 and Figure 3 characteristics.

[0105] The molar ratio of silicon oxide to aluminum oxide in the Y molecular sieve is 6:1, and the platinum content in the molecular sieve is about 0.1%.

[0106] Example 8

[0107] Dissolve 2.0g of sodium metaaluminate (NaAlO2) in 24.2g of H2O, add 1.95g of NaOH, mix thoroughly, then add 3.45g of choline chloride and mix thoroughly under ultrasound. Under vigorous stirring, add 23.42g of 30% silica sol dropwise to the mixture. This constitutes the system for synthesizing Y molecular sieve. Mix 0.042g of chloroplatinic acid hexahydrate with 0.066ml of ethylenediamine. Under vigorous stirring, slowly add the ethylenediamine-coordinated platinum precursor solution dropwise to the above system for synthesizing Y molecular sieve and mix thoroughly.

[0108] In the system for synthesizing Y molecular sieve:

[0109] The molar ratio of SiO2, Al2O3 and NaOH is 9.52:1:4;

[0110] The molar ratio of choline chloride to silica sol is 0.21:1, and the silica sol is calculated as SiO2;

[0111] The ratio of the mass of platinum to the sum of the masses of sodium metaaluminate and silica sol is 0.21:100;

[0112] The molar ratio of chloroplatinic acid to ethylenediamine is 1:15.

[0113] The mixed liquid was then placed in a polytetrafluoroethylene-lined crystallization reactor for static crystallization at 110°C for 10 days. After crystallization, the sample was washed and dried. The resulting sample was then calcined in a tube furnace at 300°C for 2 hours (heating rate 0.3°C / min) in air, followed by reduction at 200°C for 1 hour (heating rate 0.3°C / min) in a hydrogen atmosphere to obtain a molecular sieve sample.

[0114] The structures obtained from XRD spectra, electron microscopy photos and DFT calculations are Figure 1 、 Figure 2 and Figure 3 characteristics.

[0115] The molar ratio of silicon oxide to aluminum oxide in the Y molecular sieve is 6.2:1, and the platinum content in the molecular sieve is about 0.11%.

[0116] Comparative Example 2

[0117] The same as Example 8, except that choline chloride was not added in this comparative example, to obtain a comparative sample.

[0118] Its TEM image has Figure 4 feature.

[0119] The platinum content in the sample was approximately 0.1%.

[0120] Example 9

[0121] Dissolve 2.0g of sodium metaaluminate (NaAlO2) in 26.65g of H2O, add 1.95g of NaOH, mix thoroughly, then add 3.45g of choline chloride and mix thoroughly under ultrasound. Under vigorous stirring, add 24.6g of 30% silica sol dropwise to the mixture. This constitutes the system for synthesizing Y molecular sieve. Mix 0.042g of chloroplatinic acid hexahydrate with 0.11ml of ethylenediamine. Under vigorous stirring, slowly add the ethylenediamine-coordinated platinum precursor solution dropwise to the above system for synthesizing Y molecular sieve and mix thoroughly.

[0122] In the system for synthesizing Y molecular sieve:

[0123] The molar ratio of SiO2, Al2O3 and NaOH is 10:1:4;

[0124] The molar ratio of choline chloride to silica sol is 0.2:1, and the silica sol is calculated as SiO2;

[0125] The ratio of the mass of platinum to the sum of the masses of ammonium metaaluminate and silica sol is 0.2:100;

[0126] The molar ratio of chloroplatinic acid to ethylenediamine is 1:20.

[0127] The mixed liquid was then placed in a polytetrafluoroethylene-lined crystallization reactor for static crystallization at 110°C for 10 days. After crystallization, the sample was washed and dried. The resulting sample was then calcined in a tube furnace at 300°C for 2 hours (heating rate 0.3°C / min) in air, followed by reduction at 200°C for 1 hour (heating rate 0.3°C / min) in a hydrogen atmosphere to obtain a molecular sieve sample.

[0128] The structures obtained from XRD spectra, electron microscopy photos and DFT calculations are Figure 1 、 Figure 2 and Figure 3 characteristics.

[0129] The molar ratio of silicon oxide to aluminum oxide in the Y molecular sieve is 6.4:1, and the content of platinum in the molecular sieve is 0.1%.

[0130] Comparative Example 3

[0131] The same as Example 9, except that choline chloride was not added in this comparative example, to obtain a comparative sample.

[0132] Its TEM image has Figure 4 feature.

[0133] The platinum content of the sample was approximately 0.1%.

Claims

1. A method for preparing a Y molecular sieve loaded with noble metal single atoms, characterized in that: Choline chloride is added to a Y molecular sieve synthesis system including a silicon source, an aluminum source and an alkali source and stirred evenly, and then a noble metal precursor coordinated by ethylenediamine is added. After aging, the system is subjected to in-situ static hydrothermal crystallization, and the crystallized product is calcined and reduced with hydrogen.

2. The preparation method according to claim 1, wherein In the Y molecular sieve synthesis system, the molar ratio of silicon source, aluminum source and alkali source is (9.0-11.0):1:(4.0-6.0), the silicon source is calculated as SiO2, and the aluminum source is calculated as Al2O3.

3. The preparation method according to claim 2, wherein In the Y molecular sieve synthesis system, the molar ratio of silicon source, aluminum source and alkali source is (9.5-10.6):1:(4.0-5.4).

4. The preparation method according to claim 1, characterized in that Sodium aluminate, sodium hydroxide, choline chloride and water are mixed evenly, and then silica sol is added and stirred continuously. After the sol is formed, a noble metal precursor solution coordinated by ethylenediamine is added and stirred continuously. The resulting mixture is aged and then subjected to in-situ static hydrothermal crystallization. The crystallized product is recovered, calcined and reduced with hydrogen.

5. The preparation method according to claim 4, wherein The molar ratio of the choline chloride to the silica sol is (0.19-0.21):1, and the silica sol is calculated as SiO2; the ratio of the mass of the noble metal to the sum of the masses of sodium aluminate and the silica sol is 0.01-0.25:100, and the noble metal precursor is calculated as the noble metal element, the sodium aluminate is calculated as Al2O3, and the silica sol is calculated as SiO2.

6. The preparation method according to claim 5, wherein The ethylenediamine coordinated noble metal precursor is obtained by mixing an aqueous solution of a noble metal salt with ethylenediamine.

7. The preparation method according to claim 6, wherein In the noble metal salt, the molar ratio of the noble metal salt to ethylenediamine is 1:(15-20).

8. The preparation method according to claim 6 or 7, wherein The noble metal salt is chloroplatinic acid.

9. The preparation method according to claim 1, wherein The ethylenediamine coordinated noble metal precursor is added by slow dropwise addition at room temperature.

10. The preparation method according to claim 1, wherein The aging condition is to stir at (25-30)°C for (8-12) hours.

11. The preparation method according to claim 1, wherein The in-situ static hydrothermal crystallization has a crystallization temperature of 100 to 150° C. and a crystallization time of 8 to 15 days.

12. The preparation method according to claim 1, wherein The calcination temperature is 300-350°C, and the hydrogen reduction temperature is 200-250°C.

13. The preparation method according to claim 12, wherein The heating rate of the calcination is 0.2-0.6°C / min, and the heating rate of the hydrogen reduction is 0.1-0.5°C / min.

14. The preparation method according to claim 1, characterized in that The Y molecular sieve loaded with noble metal single atoms has a silicon-aluminum molar ratio of 5 to 7.

15. The Y molecular sieve loaded with noble metal single atoms obtained by the preparation method according to any one of claims 1 to 14.

16. The Y molecular sieve according to claim 15, characterized in that The Y molecular sieve is a single-atom noble metal Y molecular sieve confined by a SOD cage.

17. The Y molecular sieve according to claim 16, wherein Based on the Y molecular sieve, the mass content of the single-atom noble metal is 0.05-0.2%.

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