Multiphase metal-silicon-aluminum molecular sieve composite catalyst and preparation method and application thereof

Abstract

The invention discloses a heterogeneous metal-silicon-aluminum molecular sieve composite catalyst and a preparation method and application thereof, the preparation method comprises the following steps: S1, selecting a silicon-aluminum molecular sieve as a carrier, washing, drying and roasting to obtain a first molecular sieve catalyst; step S2, dropwise adding a metal precursor solution into the first molecular sieve catalyst, and introducing the metal precursor into orifices and the surface of the first molecular sieve catalyst to obtain a second molecular sieve catalyst; and S3, drying the second molecular sieve catalyst at a first temperature, and roasting at a second temperature to obtain the multi-phase metal-silicon-aluminum molecular sieve composite catalyst. According to the heterogeneous metal-silicon-aluminum molecular sieve composite catalyst provided by the invention, the metal components are introduced into the orifices and the surfaces of the silicon-aluminum molecular sieves, so that a synergistic effect is formed between the metal components and Bronsted acid sites on the silicon-aluminum molecular sieves, and the side reaction rate is remarkably reduced while efficient double-bond isomerization of alpha-olefin is ensured.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, specifically to a multiphase metal-silicon-aluminum molecular sieve composite catalyst, its preparation method, and its application. Background Technology

[0002] The double bond isomerization of light olefins has long been a focus of attention as an important conversion process in petrochemical and coal chemical industries. This reaction not only provides a pathway for the high-value utilization of by-product α-olefins, but also plays an important role in lubricant blending, surfactant synthesis, and fine chemicals. Molecular sieves, with their regular pore geometry and acidic characteristics, have become the main catalytic materials driving the migration of α-olefin double bonds.

[0003] However, existing technologies still face challenges in catalyst development. For example, noble metal systems rely on hydrogen and are costly, acidic polymer catalysts lack sufficient thermal stability, and single molecular sieve catalysts are prone to side reactions and carbon deposition due to the lack of hydrogen transfer capabilities. Therefore, constructing catalyst systems that achieve highly selective double bond migration of α-olefins under hydrogen-free or low-hydrogen conditions, while also possessing long lifespan and good regenerability, remains a key issue that urgently needs to be addressed. Summary of the Invention

[0004] This disclosure aims to address the problems existing in the prior art by providing a multiphase metal-silicon-aluminum molecular sieve composite catalyst, its preparation method, and its application.

[0005] According to a first aspect of this disclosure, a method for preparing a multiphase metal-silicon-aluminum molecular sieve composite catalyst is provided, comprising the following steps: Step S1: Select a silica-alumina molecular sieve as a support, then wash, dry, and calcine to obtain the first molecular sieve catalyst; Step S2: Add the metal precursor solution dropwise to the first molecular sieve catalyst in step S1, and introduce the metal precursor into the pores and surface of the first molecular sieve catalyst by means of equal volume impregnation or deposition-precipitation method to obtain the second molecular sieve catalyst. Step S3: Dry the second molecular sieve catalyst from step S2 at a first temperature, and then calcine it at a second temperature to obtain a multiphase metal-silicon-aluminum molecular sieve composite catalyst.

[0006] In one embodiment of this disclosure, step S1 further includes: Step S101: Use 18%-22% by mass of boehmite or silica sol as a binder, mix it with the carrier, and then dry and calcine it. Step S102: The support treated in step S101 is immersed in a dilute nitric acid solution for aluminum removal, washed with deionized water until neutral, dried, and calcined to obtain the first molecular sieve catalyst.

[0007] In one embodiment of this disclosure, when using the equal-volume impregnation method in step S2, the metal precursor solution is added dropwise to the first molecular sieve catalyst in step S1 and then left to stand for a predetermined time to obtain the second molecular sieve catalyst.

[0008] In another embodiment of this disclosure, when the deposition-precipitation method is used in step S2, after adding the metal precursor solution to the first molecular sieve catalyst in step S1, the pH of the solution is adjusted to 8, and after a predetermined reaction time, the second molecular sieve catalyst is obtained.

[0009] In another embodiment of this disclosure, the metal precursor solution includes at least one of Zn(NO3)2, Ga(NO3)3, NiCl2, a soluble salt of Fe, a soluble salt of Co, and a soluble salt of Mo.

[0010] In one embodiment of this disclosure, when the metal precursor solution includes two soluble salts selected from Zn(NO3)2, Ga(NO3)3, NiCl2, a soluble salt of Fe, a soluble salt of Co, and a soluble salt of Mo, the molar ratio between the two soluble salts is 1:1.

[0011] In one embodiment of this disclosure, the metal loading in the multiphase metal-silicon-aluminum molecular sieve composite catalyst is 0.1wt%-10wt%.

[0012] In one embodiment of this disclosure, the carrier in step S1 is a silica-alumina molecular sieve with one-dimensional through-holes or medium-sized pores, and the pore size is 0.4 nm-0.6 nm.

[0013] According to a second aspect of this disclosure, a multiphase metal-silicon-aluminum molecular sieve composite catalyst is provided, wherein the multiphase metal-silicon-aluminum molecular sieve composite catalyst is prepared by the above-described preparation method.

[0014] According to a third aspect of this disclosure, a multiphase metal-silicon-aluminum molecular sieve composite catalyst is provided in C 4- The application of the C6 α-olefin double bond isomerization reaction, wherein the multiphase metal-silicon-aluminum molecular sieve composite catalyst is a multiphase metal-silicon-aluminum molecular sieve composite catalyst prepared according to the above preparation method.

[0015] This disclosure provides a multiphase metal-silica-alumina molecular sieve composite catalyst, its preparation method, and its application. By introducing metal components into the silica-alumina molecular sieve, the metal components are uniformly dispersed in the pores and surface of the molecular sieve catalyst, thereby endowing the molecular sieve catalyst with reversible hydrogen transfer and hydrogenation-dehydrogenation functions. The metal components can convert unsaturated carbocation intermediates into stable saturated hydrocarbons, blocking the coke formation pathway at the source. At the same time, they form a synergistic effect with the Brønsted acidic sites on the silica-alumina molecular sieve, significantly reducing the side reaction rate while ensuring efficient double bond isomerization of α-olefins.

[0016] Other features and advantages of the invention will become clear from the following detailed description of exemplary embodiments of the invention with reference to the accompanying drawings. Attached Figure Description

[0017] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the present disclosure and, together with their description, serve to explain the principles of the present disclosure.

[0018] Figure 1 This is a flowchart of a method for preparing a multiphase metal-silicon-aluminum molecular sieve composite catalyst provided in one embodiment of this disclosure. Detailed Implementation

[0019] To make the inventive objectives, technical solutions, and beneficial technical effects of this application clearer, the following detailed description is provided in conjunction with specific embodiments. It should be understood that the embodiments described in this specification are merely illustrative and not intended to limit the scope of this application.

[0020] For simplicity, this paper only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, although not explicitly stated, every point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can serve as its own lower or upper limit and be combined with any other point or individual value, or with other lower or upper limits, to form an unspecified range.

[0021] In the description of this article, it should be noted that, unless otherwise stated, "above" and "below" include the number itself, and "several" in "one or more" means two or more.

[0022] The foregoing description of this invention is not intended to describe every disclosed embodiment or implementation. Instead, the following description provides more specific examples of exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments that can be used in various combinations. The examples listed are merely representative and should not be construed as exhaustive.

[0023] The double bond isomerization of light olefins has long been a focus of attention as an important conversion process in petrochemical and coal chemical industries. This reaction not only provides a pathway for the high-value utilization of by-product α-olefins, but also plays an important role in lubricant blending, surfactant synthesis, and fine chemicals. Molecular sieves, with their regular pore geometry and acidic characteristics, have become the main catalytic materials driving the migration of α-olefin double bonds.

[0024] However, existing technologies still face challenges in catalyst development. For example, noble metal systems rely on hydrogen and are costly, acidic polymer catalysts lack sufficient thermal stability, and single molecular sieve catalysts are prone to side reactions and carbon deposition due to the lack of hydrogen transfer capabilities. Therefore, constructing catalyst systems that achieve highly selective double bond migration of α-olefins under hydrogen-free or low-hydrogen conditions, while also possessing long lifespan and good regenerability, remains a key issue that urgently needs to be addressed.

[0025] This disclosure aims to address the problems existing in the prior art by providing a multiphase metal-silicon-aluminum molecular sieve composite catalyst, its preparation method, and its application.

[0026] like Figure 1 As shown, according to a first aspect of this disclosure, this disclosure provides a method for preparing a multiphase metal-silicon-aluminum molecular sieve composite catalyst, comprising the following steps: Step S1: Select a silica-alumina molecular sieve as a support, then wash, dry, and calcine to obtain the first molecular sieve catalyst; Step S2: Add the metal precursor solution dropwise to the first molecular sieve catalyst in step S1, and introduce the metal precursor into the pores and surface of the first molecular sieve catalyst by means of equal volume impregnation or deposition-precipitation method to obtain the second molecular sieve catalyst. Step S3: Dry the second molecular sieve catalyst from step S2 at a first temperature, and then calcine it at a second temperature to obtain a multiphase metal-silicon-aluminum molecular sieve composite catalyst.

[0027] Specifically, in step S1, silica-alumina molecular sieve materials with one-dimensional straight or medium-sized pore channels are preferentially selected as carriers. Typical examples include ZSM-5, ZSM-22, ZSM-23, SAPO-11, SAPO-31, Beta, etc. The molecular sieve is washed, dried, and calcined to remove the template agent and residual organic matter, thereby obtaining a first molecular sieve catalyst with a mechanical strength ≥15 N / mm, which meets the requirements of industrial fixed bed packing.

[0028] In step S2, the purpose of adding the metal precursor solution dropwise to the first molecular sieve catalyst in step S1 is to control the deposition position and dispersion state of metal ions on the first molecular sieve catalyst, so that they are preferentially loaded on the pore openings and outer surfaces, rather than penetrating into the pores.

[0029] In step S3, the first temperature is preferably 80℃-120℃, and the second temperature is preferably 450℃-550℃. That is, after drying at 80℃-120℃ for 12h-24h (the optimal condition is drying at 110℃ for 12h), the metal components are calcined at 450℃-550℃ for 4h-6h (the optimal condition is calcining at 500℃ for 4h) to make the metal components highly dispersed and combine with the hydroxyl groups or defect sites on the surface of the carrier to form a stable composite structure.

[0030] In one embodiment of this disclosure, step S1 further includes: Step S101: Use 18%-22% by mass of boehmite or silica sol as a binder, mix it with the carrier, and then dry and calcine it. Step S102: The support treated in step S101 is immersed in dilute nitric acid solution for aluminum removal, washed with deionized water until neutral, dried, and calcined to obtain the first molecular sieve catalyst.

[0031] Specifically, in step S101, a silica-alumina molecular sieve material with one-dimensional straight or medium-sized pore channels is selected, and a 20% by mass ratio of boehmite or silica sol is used as a binder for extrusion molding. After calcination at 550℃ for 5 h, residual template agent and organic matter on the silica-alumina molecular sieve are removed, thereby obtaining a carrier with a mechanical strength ≥15N / mm, which meets the filling requirements of industrial fixed beds.

[0032] In step S102, the support is immersed in a 0.1 mol / L to 0.5 mol / L dilute nitric acid solution for 2 to 4 hours. The optimal condition is to immerse it in a 0.1 mol / L dilute nitric acid solution for 2 hours. This is because the milder the reaction conditions, such as low concentration and short time, the less the aluminum skeleton is affected, thus achieving the purpose of selectively purifying the pores and optimizing the surface properties. If the concentration of dilute nitric acid is high or the time is long during the immersion process, it is easy to damage the molecular sieve skeleton and cause unnecessary losses.

[0033] Furthermore, since silica-alumina molecular sieves, after synthesis or calcination, not only generate framework aluminum to provide Brønsted acid centers, they also generate substances such as Al(OH)2. + AlO + Impurities such as amorphous Al2O3 can easily cause side reactions (e.g., carbon deposition, excessive pyrolysis) by acting as Lewis acid centers. These impurities exist in the channels or on the surface of the molecular sieve. If left untreated, they can clog the channels or trigger non-selective side reactions, reducing the selectivity of the target product. Therefore, soaking the silica-alumina molecular sieve in dilute nitric acid solution aims to utilize the H₂O₂... + Selective dissolution of Al(OH)2 + AlO + Non-framework aluminum impurities such as amorphous Al2O3 are present, thus forming soluble Al. 3+ The acidic content is removed. It can also regulate the acidity distribution, reducing the proportion of strong acid sites from 25% to 18% and generating defect sites, further improving the dispersion of the metal component. This process essentially does not damage the molecular sieve framework structure, cleans the pores, and reduces non-selective Lewis acid sites, thereby providing more uniform and effective anchoring sites for subsequent high-dispersion metal loading and improving catalyst performance.

[0034] In one embodiment of this disclosure, when using the equal-volume impregnation method in step S2, the metal precursor solution is added dropwise to the first molecular sieve catalyst in step S1 and then left to stand for a predetermined time to obtain the second molecular sieve catalyst.

[0035] Specifically, in this embodiment, step S2 employs an equal-volume impregnation method, adding a metal precursor solution exactly equal to the pore volume of the first molecular sieve catalyst to the first molecular sieve catalyst. This ensures that the metal precursor solution is completely absorbed by the support pores without generating excess liquid. The pore volume of the first molecular sieve catalyst can be determined using a low-temperature liquid nitrogen adsorption-desorption method (BJH model). Furthermore, after adding the metal precursor solution dropwise, it needs to be allowed to stand for 2 hours to ensure that the metal precursor solution uniformly penetrates the pore openings and outer surface of the first molecular sieve catalyst.

[0036] In another embodiment of this disclosure, when the deposition-precipitation method is used in step S2, after adding the metal precursor solution to the first molecular sieve catalyst in step S1, the pH of the solution is adjusted to 8, and after a predetermined reaction time, the second molecular sieve catalyst is obtained.

[0037] Specifically, in this embodiment, step S2 adopts a deposition-precipitation method. By adjusting the pH of the solution to 8, the metal precursor is locally hydrolyzed or precipitated at the pores and surface of the first molecular sieve catalyst, thereby depositing the metal component on the first molecular sieve catalyst instead of homogeneously precipitating in the solution to form large particle precipitates.

[0038] In one embodiment of this disclosure, the metal precursor solution includes at least one of Zn(NO3)2, Ga(NO3)3, NiCl2, a soluble salt of Fe, a soluble salt of Co, and a soluble salt of Mo.

[0039] Specifically, the silica-alumina molecular sieve framework can provide moderate Brønsted acid sites (acid density of 0.3 mmol / g-0.5 mmol / g), thereby driving the protonation reaction of α-olefins to generate carbocation intermediates, which then migrate via 1,2-hydrogen (activation energy reduced to below 80 kJ / mol) to form internal olefins. By introducing metal components (such as Zn, Ga, Ni, Fe, Co, Mo) in the form of nanoparticles (particle size 2 nm–3 nm) distributed on the pores or outer surface of the molecular sieve, the catalyst is endowed with hydrogen transfer and hydrogenation-dehydrogenation functions. This is because the metal sites can capture the carbocation intermediates and convert them into saturated hydrocarbons through reversible hydrogenation reactions, preventing the intermediates from polymerizing into oligomers. Subsequently, the saturated hydrocarbons are dehydrogenated at the acid sites to regenerate into internal olefins, thus realizing a cycle of "acid catalysis-metal regulation".

[0040] This bifunctional coupling mechanism of "acid catalysis-metal regulation" effectively inhibits the occurrence of cracking and oligomerization side reactions, reducing the proportion of by-products from 30% of conventional molecular sieves to below 12%, and decreasing the coke formation rate by more than 40%.

[0041] In one embodiment of this disclosure, when the metal precursor solution includes two of the following: Zn(NO3)2, Ga(NO3)3, NiCl2, a soluble salt of Fe, a soluble salt of Co, and a soluble salt of Mo, the molar ratio between the two soluble salts is 1:1.

[0042] Specifically, the two metals can play different functions during the reaction. For example, one metal can activate the olefin substrate, while the other can promote hydrogen transfer or stabilize reaction intermediates, thus forming a synergistic effect and significantly improving catalytic activity and selectivity. Simultaneously, the introduction of the second metal can also modulate the electronic structure of the first metal, altering its adsorption capacity for olefins and the reaction pathway, helping to control the position of double bond migration and avoiding excessive isomerization or side reactions. Furthermore, a specific ratio is beneficial for forming well-defined bimetallic active centers, which can improve catalyst stability and inhibit the aggregation or deactivation of metal particles.

[0043] In one embodiment of this disclosure, the metal loading in the multiphase metal-silicon-aluminum molecular sieve composite catalyst is 0.1wt%-10wt%.

[0044] Specifically, the metal loading in the multiphase metal-silica-alumina molecular sieve composite catalyst is preferably 0.1wt%-10wt%. Within this range, sufficient active sites can be ensured while maintaining high metal dispersion to avoid clogging the molecular sieve channels. If the loading is too low, the catalyst activity will be insufficient; if it is too high, agglomeration will easily occur, thus clogging the channels.

[0045] In one embodiment of this disclosure, the carrier in step S1 is a silica-alumina molecular sieve with one-dimensional through-holes or medium-sized pores, and the pore size is 0.4 nm-0.6 nm.

[0046] Specifically, the molecular sieve in step S1 is preferably a typical material with one-dimensional through-holes or medium pore size, such as ZSM-22, ZSM-23, SAPO-11, ZSM-48, Beta, etc., with a pore size distribution in the range of 0.4nm-0.6nm, which matches the light olefin molecules of C4-C6.

[0047] According to a second aspect of this disclosure, a multiphase metal-silicon-aluminum molecular sieve composite catalyst is provided, which is prepared by the above-described preparation method.

[0048] According to a third aspect of this disclosure, a multiphase metal-silicon-aluminum molecular sieve composite catalyst is provided in C 4- Application in the double bond isomerization reaction of C6 α-olefins: The multiphase metal-silicon-aluminum molecular sieve composite catalyst is prepared according to the above preparation method.

[0049] Specifically, the multiphase metal-silica-alumina molecular sieve composite catalyst prepared in this disclosure is suitable for the double bond isomerization reaction of C4-C6 α-olefins. A fixed-bed reactor is recommended, and the specific operating conditions are as follows: The reaction temperature is 220℃-300℃ (preferably 250℃); the reaction pressure is 0.5MPa-2.0MPa (preferably 1.0MPa); and the mass hourly space velocity (WHSV) is 1 h⁻¹. -1 -3 h -1 (Preferred 2h) -1 ); Reaction atmosphere: no hydrogen or low hydrogen (hydrogen partial pressure ≤0.1MPa, no additional hydrogen replenishment required).

[0050] When C4-C6 α-olefins were placed under the above reaction conditions, this disclosure found that the conversion performance of α-olefins was stable under the above conditions, and the experimental results are as follows: 1-butene conversion rate 78%-82%, 2-butene selectivity 86%-89%; 1-pentene conversion rate 82%-85%, 2-pentene selectivity 88%-92%; 1-hexene conversion rate 80%-83%, total selectivity of internal olefins (2-hexene + 3-hexene) 87%-90%.

[0051] Furthermore, after continuous operation for 100-120 hours, the activity decay rate is ≤5%; regeneration is carried out by calcination in an air atmosphere at 500℃-550℃ (preferably 520℃) for 6 hours, and the coke removal rate is ≥95%; after 5 cycles of regeneration, the catalyst activity and selectivity still maintain more than 90% of the initial level (e.g., after 5 regenerations of Zn / ZSM-22, the 1-pentene conversion rate is 79% and the selectivity is 86%).

[0052] In addition, this disclosure also provides a regeneration process, the specific operation steps of which are as follows: Placing the catalyst to be treated at 520℃ and calcining it in air for 6 hours (heating rate of 5℃ / min to avoid thermal shock to the skeleton) can achieve a coke removal rate of ≥95% and restore the acidity distribution and metal dispersion state of the molecular sieve to their initial levels.

[0053] The embodiments of the present invention will be described in detail below with reference to the examples. The catalysts used in the following examples are all... Figure 1 The preparation method shown is illustrated, but those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified, specific conditions in the examples were performed under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0054] Example 1 10g of silica-alumina molecular sieve material (with a Si / Al mass ratio of 60) was calcined at 550℃ for 5 h to remove the template agent. Zn(NO3)2 solution (concentration of 0.1 mol / L) was added dropwise using an equal-volume impregnation method to control the Zn loading at 1wt%. After standing at room temperature for 2 h, it was dried at 110℃ for 12 h and calcined at 500℃ for 4 h. Catalyst A (compressive strength of 16 N / mm) was obtained by extrusion molding using boehmite (20%).

[0055] In a fixed-bed reactor, 1-pentene was used as the feedstock, and the reaction was carried out at 250 °C, 1.0 MPa, and a mass hourly space velocity (WHSV) of 2 h⁻¹. -1The reaction was carried out under the specified conditions; the product was analyzed by gas chromatography (model: Agilent 7890A) with an HP-5 capillary column (30 m × 0.32 mm × 0.25 μm), an FID detector, and external standard method for quantification.

[0056] Experimental results showed that the initial 1-pentene conversion rate was 82% and the 2-pentene selectivity was 88%; after 100 hours of continuous operation, the conversion rate remained at 78% and the selectivity remained at around 85%, with a coke content of 2.5 wt% on the catalyst surface.

[0057] Formula for calculating 1-pentene conversion:

[0058] Where: n 1-戊烯，初始 The amount of 1-pentene in the reaction feed (calculated by feed flow rate, raw material purity, and sampling time, or directly determined by gas chromatography to measure the peak area of ​​1-pentene in the feed and converted using an external standard curve); n 1-戊烯，未反应 The amount of unconverted 1-pentene in the reaction product (calculated by measuring the peak area of ​​1-pentene in the product using gas chromatography and converting it using the external standard curve).

[0059] Formula for calculating pentene selectivity:

[0060] Where: n 2-戊烯，生成 : The amount of 2-pentene produced in the reaction (calculated by measuring the peak area of ​​2-pentene in the product using gas chromatography and converting it using the external standard curve); ∑n 产物 The total amount of substance of all products generated from the conversion of 1-pentene (i.e., n) 1-戊烯，初始 -n 1-戊烯，未反应 It contains 2-pentene, a small amount of cleavage products and other isoolefins, but does not contain unreacted 1-pentene.

[0061] Example 2 On the same silicon-aluminum support as in Example 1, a mixed solution of Zn(NO3)2 and Ga(NO3)3 was added dropwise using an equal-volume impregnation method, wherein the molar ratio of Zn:Ga was 1:1 and the total metal concentration was 0.2 mol / L, resulting in a total metal loading of 2 wt%. After standing at room temperature for 2 h, the solution was dried at 110 ℃ for 12 h, calcined at 500 ℃ for 4 h, and then extruded into strips (compressive strength of 15.5 N / mm) to obtain catalyst B.

[0062] Tested under the same reaction conditions as in Example 1, the initial conversion rate was 85% and the 2-pentene selectivity was 92%. After running for 120 h, the conversion rate remained at 80% and the selectivity remained at 87%. The coke content on the catalyst surface was 3 wt%, and the metal particle size remained at 2.5 nm (without obvious agglomeration), showing stronger stability and longer lifespan.

[0063] Example 3 By adjusting the concentration of the Zn(NO3)2 solution, this example prepared a series of silica-alumina molecular sieve catalysts with metal (Zn) loadings of 0.1 wt%, 0.5 wt%, 1.0 wt% (control: catalyst A from Example 1), 3.0 wt%, and 10 wt%, respectively, designated as catalyst E (0.1 wt% Zn), catalyst C (0.5 wt% Zn), catalyst A (1.0 wt% Zn), catalyst D (3.0 wt% Zn), and catalyst F (10 wt% Zn). The preparation process for all catalysts was consistent with that of Example 1, and under the same reaction conditions (250°C, 1.0 MPa, mass hourly space velocity 2 h⁻¹). -1 The results of the tests (using 1-pentene as a raw material) are shown in Table 1: Table 1

[0064] As shown in Table 1, when the Zn loading is below 0.8 wt% (e.g., catalysts E and C), the number of metal sites decreases with decreasing loading, and the ability to capture and regulate unsaturated carbocation intermediates gradually weakens, resulting in a downward trend in conversion, selectivity, and lifetime. When the Zn loading is above 1.2 wt% (e.g., catalysts D and F), metal particles tend to agglomerate and cover the Brønsted acidic sites on the molecular sieve surface with increasing loading, while also blocking the target pore size of 0.4 nm-0.6 nm. This not only destroys the "metal-acidic site synergistic effect" but also exacerbates cracking and carbon deposition side reactions, leading to a significant decline in catalyst selectivity and a sharp shortening of lifetime.

[0065] Only when the Zn loading is in the range of 0.8wt%-1.2wt% (represented by catalyst A) can the metal sites be uniformly dispersed in the pores and surface of the molecular sieve (particle size 2nm-3nm), forming an optimal synergistic effect with the Brønsted acidic sites (acid density 0.38-0.42mmol / g), achieving the comprehensive performance goals of high conversion rate (82-83%), high selectivity (88-89%), and long lifetime (100-120h).

[0066] Therefore, the effective range of metal loading is 0.1wt%-10wt%, and the optimal loading range is 0.8wt%-1.2wt%.

[0067] Example 4 The silica-alumina molecular sieve was soaked in 0.1 mol / L HNO3 solution for 2 h, washed with deionized water until neutral, dried at 110 °C for 8 h, calcined at 550 °C for 5 h, and then loaded with 1 wt% Zn using the method in Example 1 to obtain catalyst G.

[0068] At 250℃, 1.0 MPa, and a mass hourly space velocity of 2 h⁻¹ -1 Tests were conducted under the specified conditions, and the experimental results showed that the initial conversion rate was 84%, the 2-pentene selectivity reached 89%, and the lifetime was extended to 110 h. Compared with the untreated supported molecular sieve catalyst (catalyst A), the coke deposition rate was significantly reduced. In this example, the coke content of catalyst G was 2.8 wt% after 110 h, while the coke content of catalyst A in Example 1 was 2.5 wt% after 100 h. This indicates that acid pretreatment helps to increase the metal anchoring sites and optimize the acidity distribution, thereby further improving the catalytic performance.

[0069] Example 5 Catalyst A, which had been running for 100 hours, was placed in a fixed-bed reactor, and air was introduced (flow rate of 50 mL / min). The temperature was increased to 520℃ at a rate of 5℃ / min, and calcined for 6 hours. After cooling, it was calcined again at 250℃, 1.0 MPa, and a mass hourly space velocity of 2 h⁻¹. -1 The reaction was carried out under the specified conditions. The results showed that after 5 cycles of regeneration, catalyst A still achieved a conversion rate of 79% for 1-pentene (initially 82%), a selectivity of 86% (initially 88%), a Zn particle size of 3 nm, and a Brønsted acidic site density of 0.38 mmol / g (initially 0.4 mmol / g), with a performance retention rate of ≥90%. This fully demonstrates the excellent reversibility and industrial application potential of the catalyst of this invention.

[0070] Comparative Example 1 10g of silica-alumina molecular sieve material (Si / Al=60) was calcined at 550℃ for 5 h to remove the template agent. Catalyst H was obtained by extrusion molding of pseudoboehmite (20%).

[0071] Tests were conducted under the same conditions as in Example 1. The results showed that the initial conversion rate was 75%, and the selectivity for 2-pentene was only 70%. After 50 h of operation, the conversion rate dropped to 55%, the coke content on the catalyst surface was 6 wt%, the pore blockage rate was 30% (pore size decreased from 0.45 nm to 0.38 nm), the lifetime was insufficient, and the activity after regeneration only recovered to 60% of the initial level.

[0072] Comparative Example 2 10g of SiO2 was used as a support and calcined at 550℃ for 5h to remove the template agent. Zn(NO3)2 solution (concentration of 0.1 mol / L) was added dropwise by equal volume impregnation method to control the Zn loading at 1wt%. After standing at room temperature for 2h, it was dried at 110℃ for 12h and calcined at 500℃ for 4h. Catalyst I was obtained by extrusion molding using pseudoboehmite (20%).

[0073] At 250℃, 1.0 MPa, and a mass hourly space velocity of 2h... -1 Under the given conditions, the experimental results showed that the initial conversion rate was 60%, the 2-pentene selectivity was less than 65%, and it rapidly declined to 45% within 40 hours. Characterization showed that after operation, the Zn particle size increased from 5 nm to 12 nm, and there were no acidic sites to drive hydrogen migration. The performance was far inferior to that of catalyst A in Example 1.

[0074] This disclosure provides a multiphase metal-silica-alumina molecular sieve composite catalyst, its preparation method, and its application. By introducing metal components into the silica-alumina molecular sieve, the metal components are uniformly dispersed in the pores and surface of the molecular sieve catalyst, thereby endowing the molecular sieve catalyst with reversible hydrogen transfer and hydrogenation-dehydrogenation functions. The metal components can convert unsaturated carbocation intermediates into stable saturated hydrocarbons, blocking the coke formation pathway at the source. At the same time, they form a synergistic effect with the Brønsted acidic sites on the silica-alumina molecular sieve, significantly reducing the side reaction rate while ensuring efficient double bond isomerization of α-olefins.

[0075] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, and are not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein. The scope of the invention is defined by the appended claims.

Claims

1. A method for preparing a multiphase metal-silicon-aluminum molecular sieve composite catalyst, characterized in that, Includes the following steps: Step S1: Select a silica-alumina molecular sieve as a support, then wash, dry, and calcine to obtain the first molecular sieve catalyst; Step S2: Add the metal precursor solution dropwise to the first molecular sieve catalyst in step S1, and introduce the metal precursor into the pores and surface of the first molecular sieve catalyst by means of equal volume impregnation or deposition-precipitation method to obtain the second molecular sieve catalyst. Step S3: Dry the second molecular sieve catalyst from step S2 at a first temperature, and then calcine it at a second temperature to obtain a multiphase metal-silicon-aluminum molecular sieve composite catalyst.

2. The preparation method according to claim 1, characterized in that, Step S1 also includes: Step S101: Use 18%-22% by mass of boehmite or silica sol as a binder, mix it with the carrier, and then dry and calcine it. Step S102: The support treated in step S101 is immersed in dilute nitric acid solution for aluminum removal, washed with deionized water until neutral, dried, and calcined to obtain the first molecular sieve catalyst.

3. The preparation method according to claim 1, characterized in that, When using the equal-volume impregnation method in step S2, the metal precursor solution is added dropwise to the first molecular sieve catalyst in step S1, and then left to stand for a predetermined time to obtain the second molecular sieve catalyst.

4. The preparation method according to claim 1, characterized in that, When using the deposition-precipitation method in step S2, after adding the metal precursor solution to the first molecular sieve catalyst in step S1, the pH of the solution is adjusted to 8, and after a predetermined reaction time, the second molecular sieve catalyst is obtained.

5. The preparation method according to any one of claims 1, characterized in that, The metal precursor solution includes at least one of Zn(NO3)2, Ga(NO3)3, NiCl2, a soluble salt of Fe, a soluble salt of Co, and a soluble salt of Mo.

6. The preparation method according to claim 5, characterized in that, When the metal precursor solution includes two of the following: Zn(NO3)2, Ga(NO3)3, NiCl2, a soluble salt of Fe, a soluble salt of Co, and a soluble salt of Mo, the molar ratio between the two soluble salts is 1:

1.

7. The preparation method according to claim 5, characterized in that, The metal loading in the multiphase metal-silicon-aluminum molecular sieve composite catalyst is 0.1wt%-10wt%.

8. The preparation method according to claim 1, characterized in that, The support in step S1 is a silica-alumina molecular sieve with one-dimensional through-holes or medium-sized pores, with a pore size of 0.4 nm to 0.6 nm.

9. A multiphase metal-silicon-aluminum molecular sieve composite catalyst, characterized in that, The multiphase metal-silicon-aluminum molecular sieve composite catalyst is prepared by any one of the preparation methods in claims 1-8.

10. A multiphase metal-silicon-aluminum molecular sieve composite catalyst in C 4- Its application in the double bond isomerization reaction of C6 α-olefins, characterized by... The multiphase metal-silicon-aluminum molecular sieve composite catalyst is a multiphase metal-silicon-aluminum molecular sieve composite catalyst prepared according to any one of the preparation methods in claims 1-8.

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