Molecular sieve with metal in gradient distribution as well as preparation method and application of molecular sieve

Abstract

The invention relates to a metal gradient distribution molecular sieve and a preparation method and application thereof. The ratio of the bulk phase silica-alumina ratio (n (SiO2) / n (Al2O3)) to the surface silica-alumina ratio of the molecular sieve is 1.5-5.0. The surface aluminum oxide content of the molecular sieve is x1, the surface metal element content of the molecular sieve is z1, the internal aluminum oxide content of the molecular sieve is x2, the internal metal element content of the molecular sieve is z2, and the following relational expressions are met: x1 is larger than or equal to (10-100) * x2, z1 is smaller than or equal to (0.01-0.1) * z2, the value range of x2 is 0.01-1.0%, and the value range of z2 is 0.1-1.0%. The molecular sieve with metal in gradient distribution is used as an active component to prepare a catalyst, and a high low-carbon olefin yield is maintained in a catalytic cracking reaction of mixed C5 hydrocarbons.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, and relates to a molecular sieve with metal gradient distribution, its preparation method and application. Background Technology

[0002] Propylene and ethylene are important basic organic chemical raw materials. Driven by the rapid growth in demand for polyolefins and their derivatives, the demand for propylene and ethylene has remained strong and grown at a rapid pace in recent years, thus they are considered products with great market potential. The C5 components produced as byproducts of refineries and ethylene plants are complex, with high levels of impurities such as organic sulfur and nitrogen. In addition to C5 olefins, there are also large amounts of C5 alkanes. C5 olefins are highly reactive, and their cracking reactions more easily generate lower-carbon olefins, while C5 alkanes have higher activation energies and are not easily activated for cracking, resulting in low yields of lower-carbon olefins such as ethylene and propylene. Summary of the Invention

[0003] The technical problem to be solved by this invention is to provide a molecular sieve more suitable for the catalytic cracking of C5 hydrocarbons, which contains a gradient distribution of noble metals. Another technical problem to be solved by this invention is to provide a method for preparing the molecular sieve with the gradient distribution of said noble metals and its application in the catalytic cracking of mixed C5 hydrocarbons.

[0004] The first aspect of this invention provides a molecular sieve with a metal gradient distribution, wherein the ratio of the bulk silica-alumina ratio (n(SiO2) / n(Al2O3)) to the surface silica-alumina ratio of the molecular sieve is 1.5-5.0, the surface alumina content of the molecular sieve is x1, the surface metal element content is z1, the internal alumina content of the molecular sieve is x2, and the internal metal element content is z2, satisfying the following relationship: x1≥x2, for example x1≥(10-100)×x2 or x1 is (10-100)×x2, for example (50-95)x2 or (60-92)×x2, z1≤0.1×z2, for example z1≤(0.01-0.1)×z2 or (0-0.1)z2 or (0-0.01)×z2, wherein the value of x2 ranges from 0.01 wt% to 1.0 wt%, and the value of z2 ranges from 0.1 wt% to 1.0 wt%. x1 and z1 represent the concentrations of molecular sieves subjected to Ar ion etching (XPS) at etching times less than 10 s; x2 and z2 represent the concentrations of molecular sieves subjected to Ar ion etching (XPS) at etching times of 300–2000 s, and etching distances (distances to the grain surface) not exceeding half the grain length in the etching direction, for example, 3 / 10–1 / 2. The etching rate can be 0.2–0.45 nm / s, for example, 0.41 nm / s.

[0005] The bulk silicon-aluminum ratio is the silicon-aluminum ratio measured by chemical analysis or XRF analysis, and the surface silicon-aluminum ratio is the silicon-aluminum ratio measured by XPS.

[0006] In one implementation, the XPS experiment can be performed on a Thermo Scientific ESCALab Xi+ X-ray photoelectron spectrometer. The excitation source is monochromatic Al Kα X-rays with an energy of 1486.6 eV and a power of 150 W. The etching rate is 0.41 nm / s per second.

[0007] A second aspect of the present invention provides a method for preparing a molecular sieve with a metal gradient distribution, the method comprising (A) preparing a first molecular sieve solution (or a first molecular sieve dispersion) and / or (B) preparing a second molecular sieve solution (or a second molecular sieve dispersion), and (C) preparing a molecular sieve with a metal gradient distribution; wherein,

[0008] A. Preparation of the first molecular sieve solution, including the following preparation steps:

[0009] (1) Dissolve the silicon source and template agent in water and stir, for example, at 30-60°C for 2-6 hours;

[0010] (2) Add the precious metal salt to the product of step A(1) and stir for example, stir for 0.5-1h;

[0011] (3) Crystallize the product of step A (2), for example, by hydrothermal dynamic crystallization at 140-180°C for 8-24 hours; for example, by hydrothermal dynamic crystallization of the product of step A (2) in a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner.

[0012] (4) The reaction product obtained in step A(3) is denoted as the first molecular sieve solution;

[0013] B. Preparation of the second molecular sieve solution, including the following preparation steps:

[0014] (1) Dissolve the silicon source and template agent in water and stir, for example, at 30-60°C for 2-6 hours;

[0015] (2) Crystallize the product of step B(1), for example, by hydrothermal dynamic crystallization at 140-180°C for 8-24 hours; for example, by performing the hydrothermal dynamic crystallization of the product of B(1) in a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner.

[0016] (3) The reaction product obtained in step B(2) is filtered, dried (e.g., dried by baking), impregnated (e.g., impregnated with an equal volume of noble metal salt solution), dried, and calcined.

[0017] (4) The product obtained in step B (3) is mixed with water to form an aqueous dispersion with a concentration of 5-10% by weight, which is denoted as the second molecular sieve solution;

[0018] C. Preparation of molecular sieves with metal gradient distribution, including the following steps:

[0019] (1) Dissolve the alkali source in water, stir until it is fully dissolved, and then obtain the alkali source solution.

[0020] (2) Dissolve the aluminum source in water, stir until it is fully dissolved, and then obtain an aluminum source solution;

[0021] (3) Dissolve the silicon source in the alkaline source solution described in step C(1) and stir, for example, at room temperature for 10 to 30 minutes;

[0022] (4) The product of step C(3) is optionally mixed with a certain amount of water, and then mixed with the aluminum source solution described in step C(2) under stirring. Stirring is performed, for example, at room temperature for 30 to 60 minutes to obtain a mixture.

[0023] (5) Mix a certain amount of the first molecular sieve solution from step A (4) and / or the second molecular sieve solution from step B (4) with the mixture obtained in step C (4), for example, by adding it to the mixture obtained in step C (4) and stirring, for example, at room temperature for 1 to 6 hours.

[0024] (6) Crystallize the product of step C (5), for example, in a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner, wherein the crystallization is preferably performed by hydrothermal dynamic crystallization at 140-180°C for 6-60 hours.

[0025] (7) The product obtained in step C(6) is filtered, washed, dried, and calcined to obtain a molecular sieve with a noble metal gradient distribution; and optionally...

[0026] (8) Exchange the solid product (metal gradient molecular sieve) obtained in step C (7) and optionally calcine it to obtain H-type (hydrogen type) noble metal gradient molecular sieve.

[0027] According to the present invention, the room temperature is 15–35°C.

[0028] A third aspect of this invention provides the application of the aforementioned metal gradient-distributed molecular sieve in catalytic reactions. For example, its application in the catalytic cracking reaction of light hydrocarbons, such as C5 (C5 refers to hydrocarbons with 5 carbon atoms in a molecule) or mixed C5 (C5) hydrocarbons, can improve the yield of ethylene and propylene.

[0029] The modified molecular sieve provided by this invention contains noble metal elements, which are distributed in a gradient within the sieve. The surface is rich in aluminum, while the interior is rich in silicon and noble metals. This enhances the removal and cracking of hydrogen atoms from alkanes within the sieve, leading to the formation of olefins and improving the yields of ethylene and propylene. The metal gradient-distributed molecular sieve material provided by this invention can promote the efficient catalytic cracking of mixed C5 hydrocarbons, particularly enhancing the catalytic cracking of C5 alkanes.

[0030] The molecular sieves with a noble metal gradient distribution of the present invention can be used for catalyst preparation, such as petrochemical and / or fine chemical catalyst preparation. For example, the prepared catalytic cracking catalysts are used for hydrocarbon conversion, especially in the cracking reaction of C5 hydrocarbons, such as mixed C5 hydrocarbons or C5 alkanes, with higher yields of dienes (ethylene and propylene).

[0031] The method for preparing molecular sieves with metal gradient distribution provided by this invention can obtain molecular sieves with noble metal gradient distribution provided by this invention. The preparation method is simple and can flexibly control the ordered distribution of each element in the molecular sieve. Detailed Implementation

[0032] The following detailed embodiments illustrate specific implementations of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0033] The molecular sieve with metal gradient distribution provided by this invention has a bulk silicon-to-aluminum ratio to a surface silicon-to-aluminum ratio of 1.5-5.0, for example, 1.8-2.5 or 1.8-2.0. The silicon-to-aluminum ratio described in this invention is the n(SiO2) / n(Al2O3) molar ratio.

[0034] In one embodiment of the molecular sieve with metal gradient distribution provided by the present invention, the bulk silicon-to-aluminum ratio (or overall silicon-to-aluminum ratio) is 25-200, for example, 25-60.

[0035] According to the present invention, the alumina content on the surface of the molecular sieve with the metal gradient distribution is x1, the surface metal element content is z1, the alumina content inside the molecular sieve is x2, and the internal metal element content is z2, satisfying the following relationship: x1 / x2≥10, for example x1 / ×x2≥(10-100), for example x1 / x2=10-100 or 60-95 or 62-92 or z1 / z2≤0.1, for example z1 / z2≤(0.01-0.1), for example z1 / z2=(0-0.1) or 0-0.01 or 0.01-0.1, where the value range of x2 is 0.01 wt%-1.0 wt%, and the value range of z2 is 0.1-1.0 wt%. x1 and z1 are the concentrations of molecular sieves subjected to Ar ion etching XPS when the etching time is less than 10 s; x2 and z2 are the concentrations of molecular sieves subjected to Ar ion etching XPS when the etching time is 300–2000 s and the etching distance (distance to the grain surface) does not exceed 1 / 2 of the grain length in the etching direction, for example, 3 / 10–1 / 2. The etching rate can be 0.2–0.45 nm / s, for example, 0.41 nm / s. The concentrations are by weight.

[0036] According to the present invention, the relative crystallinity of the molecular sieve with the metal gradient distribution is 70-100%.

[0037] According to the present invention, the average grain size of the molecular sieve with the metal gradient distribution is 0.5-2.0 μm.

[0038] In one embodiment, the metal gradient-distributed molecular sieve has an MFI structure.

[0039] In one embodiment, the metal gradient-distributed molecular sieve is preferably a hydrogen-type molecular sieve.

[0040] In one embodiment, the molecular sieve with the metal gradient distribution contains phosphorus.

[0041] In this invention, the relative crystallinity of the molecular sieve is based on the ZSM-5 molecular sieve standard sample of the XRD standard of the Petrochemical Research Institute, and the crystallinity of the standard sample is regarded as 100%.

[0042] Grain size refers to the size of the widest part (maximum dimension) of the grain, which can be obtained by measuring the size of the widest part of the grain projection plane in the SEM or TEM image of the sample. The average grain size is obtained by selecting any 10 molecular sieve grains in the SEM or TEM image, measuring their grain size, and calculating the arithmetic mean of their grain sizes.

[0043] According to the present invention, the precious metal is one or more of Pt, Pd, Rh, Ru, and Ir.

[0044] According to the present invention, the total noble metal content in the molecular sieve with the metal gradient distribution is 0.0001 wt% to 0.2 wt%, for example, 0.002 to 0.1 wt% or 0.01 to 0.05 wt%. The total noble metal content can be measured by chemical methods or XRF methods.

[0045] The metal gradient molecular sieve provided by this invention can provide an ordered cracking pathway for hydrocarbons, has the ability to catalyze the conversion of small molecule alkanes into dienes (ethylene and propylene), and can have a higher diene yield.

[0046] According to the method for preparing the molecular sieve with metal gradient distribution provided by the present invention, optionally, in step A(1), the silicon source is one or more of methyl orthosilicate or ethyl orthosilicate, and the template agent is one or more of tetrapropylammonium hydroxide or tetrapropylammonium bromide.

[0047] According to the method for preparing the molecular sieve with metal gradient distribution provided by the present invention, optionally, in step A (1), the template agent R / SiO2 has a molar ratio of 0.05 to 0.50, and the H2O / SiO2 has a molar ratio of 10 to 80.

[0048] According to the method for preparing the molecular sieve with metal gradient distribution provided by the present invention, optionally, in step B(1), the template agent R / SiO2 has a molar ratio of 0.05 to 0.50, and the H2O / SiO2 has a molar ratio of 10 to 80.

[0049] According to the method for preparing the metal gradient distribution molecular sieve provided by the present invention, optionally, the first molecular sieve grain size in step A (4) is 200-800 nm.

[0050] According to the method for preparing the metal gradient distribution molecular sieve provided by the present invention, optionally, the grain size of the second molecular sieve in step B(4) is 200-800 nm.

[0051] According to the method for preparing the metal gradient distribution molecular sieve provided by the present invention, optionally, based on dry weight, the silicon metal element content in the first molecular sieve in step A (4) is 0.1-1.0 wt%. The metal element content in the second molecular sieve in step B (4) is 0.1-1.0 wt%.

[0052] According to the method for preparing the molecular sieve with metal gradient distribution provided by the present invention, optionally, the noble metal salt in step A (2) is one or more of Pt salt, Pd salt, Ru salt, Rh salt, and Ir salt. The Pt salt is, for example, one or more of H2PtCl6, Pt(NH3)4(NO3)2, platinum nitrate, and dichlorotetraammineplatinum. The Pd salt is, for example, one or more of palladium dichloride (PdCl2), sodium tetrachloropalladiumate (Na2PdCl4), and dichlorotetraamminepalladium. The Rh salt is, for example, one or more of RhCl3 and Rh2(AC)4. The Ir salt is, for example, one or more of IrCl3 and IrCl4.

[0053] The noble metal salt mentioned in step B(3) is one or more of Pt salt, Pd salt, Ru salt, Rh salt, and Ir salt. The Pt salt is, for example, one or more of H2PtCl6, Pt(NH3)4(NO3)2, platinum nitrate, and dichlorotetraammineplatinum. The Pd salt is, for example, one or more of palladium dichloride (PdCl2), sodium tetrachloropalladium (Na2PdCl4), and dichlorotetraamminepalladium. The Rh salt is, for example, one or more of RhCl3 and Rh2(AC)4. The Ir salt is, for example, one or more of IrCl3 and IrCl4.

[0054] According to the method for preparing the molecular sieve with metal gradient distribution provided by the present invention, optionally, the concentration of the alkaline source solution in step C(1) is 10-30% by weight, and the alkaline source is one or more of lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide or cesium hydroxide.

[0055] According to the method for preparing the molecular sieve with metal gradient distribution provided by the present invention, optionally, the concentration of the aluminum source solution in step C(2) is 5-20% by weight, and the aluminum source is one or more of aluminum sulfate, aluminum nitrate, aluminum isopropoxide, sodium aluminate or aluminum chloride.

[0056] According to the method for preparing the metal gradient distribution molecular sieve provided by the present invention, optionally, the silicon source in step C(3) is a silica sol, which may be an ammonium silica sol, a sodium silica sol, or a mixture thereof. The content of the silica sol, calculated as SiO2, is 10-45% by weight, for example, it may be any value among 15%, 25%, 30%, and 45%, or any two values ​​within a range.

[0057] According to the method for preparing the molecular sieve with metal gradient distribution provided by the present invention, optionally, the molar ratio of the mixed solution obtained in step C(4) is n(SiO2) / n(Al2O3) = 20~200, n(M2O) / n(SiO2) = 0.10~0.20, n(H2O) / n(SiO2) = 20~60, where M represents an alkali metal, and M is one or more of Li, Na, K, Rb, and Cs;

[0058] According to the method for preparing the metal gradient distribution molecular sieve provided by the present invention, in one embodiment, a first molecular sieve solution is added in step C(5), wherein the silicon in the first molecular sieve solution, calculated as SiO2, is 2 to 50% by weight, for example 5 to 20% by weight, of the silicon in the silicon source in step C(3), calculated as SiO2.

[0059] According to the method for preparing the metal gradient distribution molecular sieve provided by the present invention, in one embodiment, a second molecular sieve solution is added in step C(5), wherein the silicon in the second molecular sieve solution, calculated as SiO2, is 2 to 50% by weight, for example 5 to 20% by weight, of the silicon in the silicon source in step C(3), calculated as SiO2.

[0060] According to the method for preparing the metal gradient distribution molecular sieve provided by the present invention, in one embodiment, a first molecular sieve solution and a second molecular sieve solution are added in step C(5), wherein the total amount of silicon in the first molecular sieve solution and the silicon in the second molecular sieve solution, calculated as SiO2, is 2 to 50% by weight, for example 5 to 20% by weight, of the silicon in the silicon source in step C(3), calculated as SiO2.

[0061] According to the present invention, in step C(6), the product obtained in step C(5) is crystallized, for example, dynamically crystallized at 140 to 180°C for 6 hours or more, for example, 6 to 60 hours or 6 to 48 hours.

[0062] According to the present invention, the dynamic crystallization can be carried out under stirring or rotation. The crystallization can be performed in the presence of water and under autogenous pressure.

[0063] According to the present invention, step C(7) involves filtering, washing, drying, and calcining the product obtained in step C(6). The methods for filtering, washing, drying, and calcining can be existing techniques, and the present invention does not have any special requirements. Step C(7) yields a molecular sieve with a noble metal gradient distribution.

[0064] According to the present invention, the molecular sieve with a noble metal gradient distribution obtained in step C(7) can be further exchanged to obtain a molecular sieve with a hydrogen-type metal gradient distribution. The exchange method can employ existing technology, such as ammonium exchange, which reduces the alkali metal content in the molecular sieve. After calcination, a molecular sieve with a hydrogen-type metal gradient distribution, or a molecular sieve with a noble metal gradient distribution, can be obtained. The ammonium exchange method is well known to those skilled in the art and will not be described further in this invention.

[0065] According to the method for preparing the metal gradient distribution molecular sieve provided by the present invention, a specific embodiment includes:

[0066] A. A method for preparing a first molecular sieve solution. This includes the following preparation steps:

[0067] (1) Dissolve the silicon source and template agent in water and stir and heat at 30-60°C for 2-6 hours;

[0068] (2) Add the precious metal salt to the product of step A(1) and stir for 0.5-1h;

[0069] (3) The product of step A (1) is transferred in the reactor, for example, to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner, and hydrothermally crystallized at 140-180°C for 8-24 hours.

[0070] (4) The reactants obtained in step A (3) are denoted as the first molecular sieve solution.

[0071] B. Preparation of the second molecular sieve solution, including the following preparation steps:

[0072] (1) Dissolve the silicon source and template agent in water and stir and heat at 30-60°C for 2-6 hours;

[0073] (2) The product of step B(1) is transferred in the reactor, for example, to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner, and hydrothermally dynamic crystallized at 140-180°C for 8-24 hours.

[0074] (3) After filtering and drying the reaction product obtained in step B(2), impregnate it with an equal volume of metal salt solution, dry it, and calcine it; the drying process includes, for example, oven drying, airflow drying, or flash drying.

[0075] (4) Prepare an aqueous dispersion with a concentration of 5-10% from the product obtained in step B (3), and denot it as the second molecular sieve solution;

[0076] C. Preparation of molecular sieves with metal gradient distribution, including the following preparation steps:

[0077] (1) Dissolve the alkali source in water, stir until it is fully dissolved, and then obtain the alkali source solution.

[0078] (2) Dissolve the aluminum source in water, stir until it is fully dissolved, and then obtain an aluminum source solution;

[0079] (3) Dissolve the silicon source in the alkaline source solution described in step C(1) and stir at room temperature for 10 to 30 minutes;

[0080] (4) Mix the product obtained in step C(3) with a certain amount of water, and then add the aluminum source solution described in step C(2) under stirring. Stir at room temperature for 30 to 60 minutes to obtain a mixture.

[0081] (5) Slowly add a certain amount of the first molecular sieve solution described in step A (4) or the second molecular sieve solution described in step B (4) to the mixed solution obtained in step C (4), and stir at room temperature for 1 to 6 hours.

[0082] (6) The product of step C(5) is subjected to hydrothermal dynamic crystallization at 140-180℃ for 6-48 hours;

[0083] (7) The product obtained in step C(6) is filtered, washed, dried, and calcined to obtain a molecular sieve with a metal gradient distribution; and

[0084] Optionally (8) the molecular sieve product with metal gradient distribution obtained in step C (7) is subjected to ammonium exchange and optionally calcined to obtain H-type molecular sieve with metal gradient distribution.

[0085] The present invention will be further illustrated by the following examples, but the present invention is not limited thereto.

[0086] In the following examples and comparative examples, the room temperature was 26°C.

[0087] XPS test conditions and Ar + Etching conditions: XPS experiments were conducted at Thermo Scientific's ESCALab Xi. + The experiment was conducted on a type X-ray photoelectron spectrometer. The excitation source was a monochromatic AlK2O3 spectrometer. α X-rays, energy 1486.6 eV, power 150 W. Narrow scan using a penetration energy of 30 eV. The baseline vacuum during analysis is approximately 6.5 × 10⁻⁶. -10mbar. The binding energy can be corrected using the C1s peak (284.8 eV) of alkyl carbon or contaminated carbon. The etching mode is a single Ar. + (Monoatomic) ion energy was 2000 eV, beam current was high, and after etching for a certain time, the sample was allowed to stand for 10 minutes to balance the charge. Then, the sample was scanned according to the above experimental conditions. The above two experimental processes were repeated until the required etching depth was reached, and the experiment ended. The etching time for measuring x1 and z1 was 8 seconds, and the etching time for measuring x2 and z2 was 1200 seconds, with an etching rate of 0.41 nm / s.

[0088] The XRF analysis method used a Rigaku II X-ray fluorescence spectrometer from Japan to analyze the elemental composition of the molecular sieve. The intensity of each element's spectral peak was determined using a scintillation counter and a proportional counter. The bulk silicon-aluminum ratio (n(SiO2) / n(Al2O3)) of the sample was also determined.

[0089] Example 1

[0090] Preparation of the first molecular sieve solution:

[0091] (a) Mix 60.0 g of tetraethyl orthosilicate, 56.2 g of tetrapropylammonium hydroxide solution (concentration 25 wt%) and 73.8 g of deionized water evenly and stir at 40 °C for 4 h;

[0092] (b) Add 0.085 g of dichlorotetraammineplatinum to step (a) and mix thoroughly;

[0093] (c) Stir at room temperature for 30 minutes;

[0094] (d) The solution from step (c) was transferred to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner and dynamically crystallized at 170°C for 12 hours.

[0095] (e) After crystallization, the solution is taken out and recorded as the first molecular sieve solution 1.

[0096] Preparation of molecular sieves with metal gradient distribution:

[0097] (f) Add 2.73 g of potassium hydroxide to 8.19 g of deionized water and stir well to obtain an alkaline source solution;

[0098] (g) Add 2.80 g of aluminum sulfate octadecahydrate to 25.2 g of deionized water and stir until homogeneous to obtain an aluminum source solution;

[0099] (h) Slowly add 30.60 g of silica sol (silica content 30% by weight, sodium silica sol, Qingdao Junqiang New Material Co., Ltd., the same below) to the alkaline source solution obtained in step (f) and stir at room temperature for 30 minutes;

[0100] (i) Add 83.31 g of deionized water to the product of step (h), and then add the aluminum source solution obtained in step (g) while stirring. Stir at room temperature for 30 minutes to obtain the first mixture.

[0101] (j) Add 9.18 g of the first molecular sieve solution 1 to the product of step (i) and stir at room temperature for 4 hours to obtain the second mixture;

[0102] (l) The second mixture obtained in step (j) is transferred to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner and hydrothermally crystallized at 170°C for 48 hours.

[0103] (k) The product obtained in step (l) is filtered, washed, dried and calcined to obtain molecular sieve FZ-1;

[0104] (l) Molecular sieve FZ-1: ammonium chloride: deionized water are mixed evenly in a mass ratio of 1:1:10, stirred and heated in an 80℃ water bath for 30 min, filtered, washed and dried, and then the dried solid: ammonium chloride: deionized water are mixed evenly in a mass ratio of 1:0.5:10, and a second ammonium exchange is performed, filtered, washed and dried, and calcined at 550℃ for 2 h to obtain FZ-1-H.

[0105] Example 2

[0106] Preparation of the second molecular sieve solution:

[0107] (a) Mix 60.0 g of tetraethyl orthosilicate, 56.2 g of tetrapropylammonium hydroxide solution (same as in Example 1) and 73.8 g of deionized water evenly and stir at 40°C for 4 h;

[0108] (b) The product from step (a) was transferred to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner and dynamically crystallized at 170°C for 12 h.

[0109] (c) The product obtained in step (b) is centrifuged and dried to obtain molecular sieve powder;

[0110] (d) Dissolve 0.085 g of dichlorotetraammineplatinum in 10 g of deionized water, then add the molecular sieve powder obtained in step (c), mix evenly, dry, and calcine at 550 °C for 4 hours.

[0111] (e) Prepare an aqueous dispersion with a concentration of 10% by weight of the product obtained in step (d), and denote it as the second molecular sieve solution 1;

[0112] Preparation of molecular sieves with metal gradient distribution:

[0113] (f) Add 2.73 g of potassium hydroxide to 8.19 g of deionized water and stir well to obtain an alkaline source solution;

[0114] (g) Add 2.80 g of aluminum sulfate octadecahydrate to 25.2 g of deionized water and stir until homogeneous to obtain an aluminum source solution;

[0115] (h) Slowly add 30.60 g of silica sol (silica content 30% by weight) to the alkaline source solution described in step (f) and stir at room temperature for 30 minutes;

[0116] (i) Add 83.31 g of deionized water to the product of step (h), and then add the aluminum source solution described in step (g) while stirring. Stir at room temperature for 30 minutes to obtain the first mixture.

[0117] (j) Add 9.18 g of the second molecular sieve solution 1 to the product of step (i) and stir at room temperature for 4 hours to obtain the second mixture;

[0118] (l) The second mixed solution from step (j) is transferred to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner and hydrothermally crystallized at 170°C for 48 hours.

[0119] (k) The product obtained in step (l) is filtered, washed, dried and calcined to obtain molecular sieve FZ-2;

[0120] (l) Molecular sieve FZ-2: ammonium chloride: deionized water are mixed evenly in a mass ratio of 1:1:10, stirred and heated in an 80℃ water bath for 30 min, filtered, washed and dried, and then the dried solid: ammonium chloride: deionized water are mixed evenly in a mass ratio of 1:0.5:10, and a second ammonium exchange is performed, filtered, washed and dried, and calcined at 550℃ for 2 h to obtain FZ-2-H.

[0121] Example 3

[0122] Preparation of the first molecular sieve solution:

[0123] (a) Mix 50.0 g of tetraethyl orthosilicate, 56 g of tetrapropylammonium hydroxide solution (same as in Example 1) and 150 g of deionized water evenly, and stir and heat at 40°C for 4 h;

[0124] (b) Add 0.064 g of palladium chloride to the product of step (a) and mix thoroughly;

[0125] (c) Stir at room temperature for 30 minutes;

[0126] (d) The product from step (c) was transferred to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner and dynamically crystallized at 170°C for 12 hours.

[0127] (e) After crystallization, the solution is taken out and recorded as the first molecular sieve solution 2.

[0128] Preparation of molecular sieves with metal gradient distribution:

[0129] (f) Add 3.43 g of potassium hydroxide to 15.63 g of deionized water and stir until homogeneous to obtain an alkaline source solution;

[0130] (g) Add 1.46 g of aluminum isopropoxide to 16.79 g of deionized water and stir until homogeneous to obtain an aluminum source solution;

[0131] (h) Slowly add 38.70 g of silica sol (silica content 30% by weight) to the alkaline source solution obtained in step (f) and stir at room temperature for 30 minutes;

[0132] (i) Add 132.28 g of deionized water to the product of step (h), and then add the aluminum source solution obtained in step (g) while stirring. Stir at room temperature for 30 minutes to obtain the first mixture.

[0133] (j) Add 11.61 g of the first molecular sieve solution 2 to the product of step (i) and stir at room temperature for 4 hours to obtain the second mixture;

[0134] (l) The second mixture obtained in step (j) is transferred to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner and hydrothermally crystallized at 170°C for 48 hours.

[0135] (k) The product obtained in step (l) is filtered, washed, dried and calcined to obtain molecular sieve FZ-3;

[0136] (l) Molecular sieve FZ-3: ammonium chloride: deionized water are mixed evenly in a mass ratio of 1:1:10, stirred and heated in an 80℃ water bath for 30 min, filtered, washed and dried, and then the dried solid: ammonium chloride: deionized water are mixed evenly in a mass ratio of 1:0.5:10, and a second ammonium exchange is performed, filtered, washed and dried, and calcined at 550℃ for 2 h to obtain FZ-3-H.

[0137] Comparative Example 1

[0138] (a) Mix 60.0 g of tetraethyl orthosilicate, 56.2 g of tetrapropylammonium hydroxide solution (same as in Example 1) and 73.8 g of deionized water evenly and stir at 40°C for 4 h;

[0139] (b) The solution from step (a) was transferred to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner and dynamically crystallized at 170°C for 12 hours.

[0140] (c) Remove after crystallization is complete.

[0141] (d) Add 2.73 g of potassium hydroxide to 8.19 g of deionized water and stir well;

[0142] (e) Add 2.80 g of aluminum sulfate octadecahydrate to 25.2 g of deionized water and stir well;

[0143] (f) Slowly add 30.60 g of silica sol (silica content 30% by weight) to the alkaline source solution in step (d) and stir at room temperature for 30 minutes;

[0144] (g) Add 83.31 g of deionized water to the product of step (f), and then add the aluminum source solution from step (e) while stirring. Stir at room temperature for 30 minutes to obtain the first mixture.

[0145] (h) Add 9.18 g of the product taken out in step (c) to the product of step (g) and stir at room temperature for 4 hours to obtain a second mixture;

[0146] (i) The second mixture from step (h) is transferred to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner and hydrothermally crystallized at 170°C for 48 h.

[0147] (j) The product obtained in step (i) is filtered, washed, dried and calcined to obtain molecular sieve DZ-1;

[0148] (k) Molecular sieve DZ-1: ammonium chloride: deionized water are mixed evenly at a mass ratio of 1:1:10, stirred and heated in an 80℃ water bath for 30 min, filtered, washed and dried, and then the dried solid: ammonium chloride: deionized water are mixed evenly at a mass ratio of 1:0.5:10, and a second ammonium exchange is performed, filtered, washed and dried, and calcined at 550℃ for 2 h to obtain DZ-1-H.

[0149] Comparative Example 2

[0150] Dissolve 0.085 g of dichlorotetraammineplatinum in 20 g of deionized water, then add the molecular sieve powder DZ-1-H from Comparative Example 1, mix well, dry, and calcine at 550 °C for 4 hours to obtain DZ-2-H.

[0151] Comparative Example 3

[0152] Molecular sieves were prepared using the method described in Comparative Example 1, except that 0.085 g of dichlorotetraammineplatinum was added in step g. It is evident that the noble metal distribution z1 / z2 is significantly higher than that of this invention, while the yields of ethylene and propylene are lower.

[0153] The preparation conditions and product properties of Examples 1-3 and Comparative Examples 1-3 are shown in Table 1.

[0154] Table 1

[0155]

[0156] Molecular sieve evaluation

[0157] The molecular sieves in the examples and comparative examples were modified with phosphorus by the equal-volume impregnation method, and then aged and deactivated at 800°C and 100% steam for 17 hours. The resulting tablets were sieved to obtain 40-60 mesh particles, and evaluated on a fixed-bed microreactor. The raw material was C5 hydrocarbons (composition: isopentane 30 wt%, 2-methylbutene 40 wt%, pentene 20 wt%, cyclopentene 10 wt%). The evaluation conditions were: reaction temperature 620°C, weight hourly space velocity 8 h⁻¹. -1 The results are listed in Table 2.

[0158] Table 2

[0159]

[0160] The percentages in Table 2 are by weight.

[0161] As shown in Table 2, compared with the comparative example, the molecular sieve with metal gradient distribution provided by the present invention has higher ethylene and propylene yields for C5 hydrocarbon cracking.

Claims

1. A metal gradient distribution molecular sieve, wherein the ratio of the phase silicon-aluminum ratio (n(Si02) / n(Al203)) to the surface silicon-aluminum ratio is 1.5-5.0; the surface alumina content of the molecular sieve is x1, the surface noble metal element content is z1, the internal alumina content of the molecular sieve is x2, and the internal noble metal element content is z2, satisfying the following relationship: x1≥x2, for example, x1≥(10-100)χ2, and z1≤0.1χz2, for example, z1≤(0.01-0.1)χz2, wherein x2 is in the range of 0.01%-1.0%, z2 is in the range of 0.1%-1.0%, the contents are weight contents; x1 and z1 are the contents when the Ar ion etching XPS of the molecular sieve is performed for less than 10 s; x2 and z2 are the concentrations when the Ar ion etching XPS of the molecular sieve is performed for 300-2000 s and the etching distance is not more than 1 / 2 of the length of the crystal grain in the etching direction; and the etching rate can be 0.2-0.45 nm / s.

2. The metal gradient distribution molecular sieve according to claim 1, wherein the relative crystallinity of the metal gradient distribution molecular sieve is 70-100%, the average crystal grain size of the metal gradient distribution molecular sieve is 0.5-2.0 μm, the noble metal is one or more of Pt, Pd, Rh, Ru, and Ir, and the noble metal content of the metal gradient distribution molecular sieve as a whole is 0.0001%-0.2% by weight.

3. A method for preparing the metal gradient distribution molecular sieve according to any one of claims 1-2, comprising: A. preparing a first molecular sieve solution, comprising the following steps: (1) dissolving a silicon source and a template agent in water, and stirring, for example, at 30-60°C for 2-6 h; (2) adding a noble metal salt to the product of step A(1), and stirring, for example, for 0.5-1 h; (3) crystallizing the product of step A(2), for example, by hydrothermal dynamic crystallization at 140-180°C for 8-24 h; and the product obtained in step A(3) is designated as the first molecular sieve solution; B. preparing a second molecular sieve solution, comprising the following steps: (1) dissolving a silicon source and a template agent in water, and stirring, for example, at 30-60°C for 2-6 h; (2) crystallizing the product of step B(1), for example, by hydrothermal dynamic crystallization at 140-180°C for 8-24 h; (3) filtering and drying the reaction product obtained in step B(2), impregnating with a noble metal salt solution, drying, and calcining; and (4) preparing a product obtained in step B(3) into a water dispersion solution with a concentration of 5-10% by weight to obtain the second molecular sieve solution; and C. preparing a metal gradient distribution molecular sieve, comprising the following steps: (1) dissolving an alkali source in water to obtain an alkali source solution; (2) dissolving an aluminum source in water to obtain an aluminum source solution; (3) dissolving a silicon source in the alkali source solution of step C(1), and stirring, for example, at room temperature for 10-30 min, to obtain a silicon-containing solution; (4) adding the first molecular sieve solution of step A and the second molecular sieve solution of step B to the silicon-containing solution of step C(3), and stirring, for example, at room temperature for 10-30 min; (5) adding the alkali source solution of step C(1) and the aluminum source solution of step C(2) to the product of step C(4), and stirring, for example, at room temperature for 10-30 min; (6) adding the product of step C(5) to a reactor, and crystallizing, for example, by hydrothermal dynamic crystallization at 140-180°C for 8-24 h; and (7) filtering and drying the product obtained in step C(6), impregnating with a noble metal salt solution, drying, and calcining. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (4) mixing the silicon-containing solution obtained in step C(3) with an amount of water, and then mixing the mixture with the aluminum source solution obtained in step C(2) under stirring, for example, stirring at room temperature for 30 to 60 minutes to obtain a mixed solution; (5) mixing the first molecular sieve solution of step A(3) and / or the second molecular sieve solution of step B(4) with the mixed solution obtained in step C(4) under stirring, for example, stirring at room temperature for 1 to 6 hours; (6) crystallizing the product of step C(5); (7) filtering, washing, drying, and calcining the product obtained in step C(6) to obtain a metal gradient distribution molecular sieve; and Optionally, (8) exchanging the metal gradient distribution molecular sieve obtained in step C(7), and optionally calcining to obtain a H-form metal gradient distribution molecular sieve; The room temperature is 15 to 35°C.

4. The method of claim 3, wherein, In steps A(1) and B(1), each of the silicon sources is one or more of tetramethyl orthosilicate or tetraethyl orthosilicate, and each of the template agents is one or more of tetrapropylammonium hydroxide or tetrapropylammonium bromide.

5. The method of claim 3, wherein, In each of steps A(1) and B(1), R / SiO2 is 0.05 to 0.50, and H2O / SiO2 is 10 to 80; R represents the template agent.

6. The method of claim 3, wherein, The average crystal size of the first molecular sieve in step A(4) and the second molecular sieve in step B(4) is each 200 to 800 nm.

7. The method of claim 3, wherein, The noble metal element content of the first molecular sieve in the first molecular sieve solution obtained in step A(3) and the second molecular sieve in the second molecular sieve solution obtained in step B(4) is each 0.1 to 1% by weight.

8. The method of claim 3, wherein, In each of steps A(2) and B(3), the noble metal salt is one or more of H2PtCl6, Pt(NH3)4(NO3)2, platinum nitrate, dichlorotetraamine platinum, palladium dichloride (PdCl2), sodium tetrachloropalladate (Na2PdCl4), dichlorotetraamine palladium, RhCl3, Rh2(AC)4, IrCl3, or IrCl4; and the impregnation in step B(3) is, for example, impregnation by equal volume.

9. The method of claim 3, wherein, In step C(1), the concentration of the alkali source solution is 10 to 30% by weight, and the alkali source is one or more of lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, or cesium hydroxide.

10. The method of claim 3, wherein, In step C(2), the concentration of the aluminum source solution is 5 to 20% by weight, and the aluminum source can be one or more of aluminum sulfate, aluminum nitrate, aluminum isopropoxide, sodium aluminate, or aluminum chloride.

11. The method of claim 3, wherein, In step C(3), the silicon source is a silica sol, and the SiO2 content of the silica sol is 10 to 45% by weight; the silica sol can be an ammonium-type silica sol and / or a sodium-type silica sol.

12. The method of claim 3, wherein, The molar ratio of the mixed solution obtained in step C(4) is: n(SiO2) / n(Al2O3) = 20 to 200, n(M2O) / n(SiO2) = 0.10 to 0.20, and n(H2O) / n(SiO2) = 20 to 60, where M represents an alkali metal, and M is one or more of Li, Na, K, Rb, and Cs.

13. The method of claim 3, wherein, The silicon introduced in the first and / or second molecular sieve solution in step C(5) is 2 to 50 wt% or 5 to 20 wt% of the silicon in the silicon source described in step C(3) based on SiO2; The crystallization in step C(6) can be a hydrothermal dynamic crystallization at 140 to 180°C for 6 to 48 h.

14. The molecular sieve obtained by the process of any one of claims 3 to 13, wherein the noble metal has a gradient distribution.

15. Use of the metal gradient distribution molecular sieve of claim 1, 2 or 14 in catalytic cracking reactions of light hydrocarbons, such as mixed C5 hydrocarbons.

Images