A growth directing agent modified rhk@mfi catalyst, preparation method and application thereof

Abstract

This invention discloses a growth-directing agent-modified RhK@MFI catalyst, its preparation method, and its application. The RhK@MFI catalyst comprises active centers Rh and K, and the support is an MFI molecular sieve. Rh is encapsulated in the framework or channels of the MFI molecular sieve in atomic-level or nano-cluster form, and K is distributed on the framework or surface of the MFI molecular sieve. The loading of Rh is 0.1–2.0 wt% and the loading of K is 0.05–1.0 wt% by total catalyst mass. This catalyst exhibits excellent catalytic activity, high n-butyraldehyde selectivity, and good structural stability in the propylene hydroformylation reaction, while also possessing the advantages of being a heterogeneous catalyst that is easy to separate and recover.

Description

Technical Field

[0001] This invention belongs to the field of molecular sieve catalyst technology; in particular, it relates to a growth-directing agent modified RhK@MFI catalyst, its preparation method and its application, and more specifically to an RhK@MFI molecular sieve catalyst with a thinned MFI structure molecular sieve as a support and rhodium as the active component, its preparation method and the industrial application of the catalyst in the hydroformylation reaction of propylene to prepare n-butyraldehyde. Background Technology

[0002] Propylene hydroformylation is a key process in the industrial production of butyraldehyde (n-butyraldehyde and isobutyraldehyde), with n-butyraldehyde being an important precursor for the synthesis of bulk chemicals such as 2-ethylhexanol, and its demand continues to grow. Currently, this process industrially mainly relies on a homogeneous catalytic system with rhodium (Rh) as the central metal and organophosphorus compounds (such as triphenylphosphine) as ligands. Although this system has the advantages of high catalytic activity and relatively mild reaction conditions, its inherent defects limit further greening of the technology and improvement of economic efficiency. First, due to thermodynamic control, this system has a strong tendency to generate branched isobutyraldehyde, making it difficult to meet the growing market demand for high-value-added n-butyraldehyde by the selectivity of the n-butyraldehyde product (usually characterized by the n / i ratio of 3 to 5). Second, the homogeneous catalyst and product are in the same liquid phase, making the separation and recovery steps after the reaction cumbersome, involving energy-intensive distillation or extraction processes, and easily causing the loss of expensive rhodium metal. Third, organophosphorus ligands are expensive and are prone to decomposition, oxidation, or loss under reaction conditions, which not only increases production costs, but their degradation products may also pollute the product, corrode equipment, and bring additional environmental pressure. In addition, the entire process involves high-pressure syngas operation and a possible acidic environment, which places higher demands on equipment materials and safety protection.

[0003] To overcome the aforementioned bottlenecks in homogeneous catalysis, researchers have focused on developing heterogeneous hydroformylation catalysts, aiming to achieve convenient separation and recycling of the catalyst. A common strategy is to immobilize rhodium active centers on supports such as activated carbon, silica, alumina, and molecular sieves. Among these, MFI-type molecular sieves (such as ZSM-5), due to their regular pore structure and tunable acidity, are considered to potentially enhance reaction selectivity through spatial confinement effects. However, heterogeneity processes often bring new challenges: active metals tend to aggregate or sinter after immobilization, resulting in significantly lower catalytic activity compared to homogeneous systems; in liquid-phase reaction environments, active metal components may leach from the support, causing catalyst deactivation and loss of precious metals; more importantly, precisely controlling the microenvironment of the active centers in heterogeneous systems to achieve electronic and steric effects similar to phosphine ligands, thereby significantly improving the selectivity of n-butyraldehyde, remains a significant challenge. Many reported heterogeneous rhodium-based catalysts either face the dilemma of not being able to simultaneously achieve activity and selectivity, or suffer from insufficient stability. Therefore, developing a novel heterogeneous catalyst that combines high activity, high selectivity for orthoform products, excellent stability, and easy separation and recovery is of great significance for promoting the upgrading and development of propylene hydroformylation technology, and is also an important research direction in this field. Summary of the Invention

[0004] The first technical problem this application aims to solve is to provide a growth-directed agent-modified RhK@MFI catalyst. This catalyst employs a novel process of growth-directed agent-assisted modification and in-situ simultaneous encapsulation, introducing and highly dispersing rhodium (Rh) and potassium (K) active centers in situ during the synthesis of MFI molecular sieves. Post-modification using a growth-directed agent optimizes the catalyst's surface properties and pore environment. The resulting catalyst exhibits excellent catalytic activity, high n-butyraldehyde selectivity, and good structural stability in the propylene hydroformylation reaction, while also possessing the advantages of being a heterogeneous catalyst that is easy to separate and recover.

[0005] The second technical problem to be solved by this application is to provide a method for preparing a growth-directing agent modified RhK@MFI catalyst, which is simple and has mild conditions.

[0006] The third technical problem to be solved by this application is to provide an application of a growth-directing agent modified RhK@MFI catalyst in the preparation of n-butyraldehyde by the hydroformylation of propylene.

[0007] To solve the first technical problem mentioned above, the present invention adopts the following technical solution: a growth-directing agent modified RhK@MFI catalyst, comprising active centers Rh and K, with MFI molecular sieve as the support; wherein Rh is encapsulated in the framework or channels of the MFI molecular sieve in the form of atomic-level or nano-clusters, and K is distributed in the framework or surface of the MFI molecular sieve; the loading of Rh is 0.1-2.0 wt% and the loading of K is 0.05-1.0 wt% based on the total mass of the catalyst.

[0008] To solve the second technical problem mentioned above, the present invention adopts the following technical solution: a method for preparing a growth-directing agent modified RhK@MFI catalyst, comprising the following steps: S1. Mix the template agent, silicon source and deionized water in a certain proportion, stir and pre-hydrolyze to obtain a silicate gel mixture; S2. Dissolve the rhodium source and potassium source in a mixed solvent prepared from deionized water and ethylenediamine, and stir to form a metal precursor solution; S3. Add the metal precursor solution to the silicate gel mixture, stir evenly, and then perform an aging treatment to obtain an aged gel. S4. Add growth-directing agent to the aged gel, mix well and modify to obtain the final gel; S5. The final gel is subjected to a hydrothermal crystallization reaction. After the reaction is completed, it is separated by centrifugation, washed and dried to obtain the catalyst precursor. S6. The catalyst precursor is calcined and then reduced in a reducing atmosphere to obtain the RhK@MFI molecular sieve catalyst.

[0009] Preferably, in step S1, the template agent is tetrapropylammonium hydroxide; the silicon source is tetraethyl orthosilicate or silica sol; and the molar ratio of the template agent, silicon source (calculated as SiO2) and deionized water is 2-4:1:30-40.

[0010] Preferably, in step S2, the rhodium source is rhodium trichloride or rhodium nitrate; the potassium source is potassium nitrate or potassium hydroxide; and the molar ratio of the rhodium source to the potassium source is 1:100-700.

[0011] Preferably, in step S2, the volume ratio of ethylenediamine to deionized water is 1:5-10; the rhodium source is rhodium trichloride or rhodium nitrate.

[0012] Preferably, in step S3, the aging treatment temperature is 30-50℃ and the time is 6-12 hours.

[0013] Preferably, in step S4, the growth guiding agent is an aqueous solution of one or more of ammonium fluoride, pyrrolidine, amino acids, tetrahydrofuran, urea, ethanol, isopropanol, n-butanol, and methanol; the amount of growth guiding agent added is: the molar ratio of the growth guiding agent to the silicon source (calculated as SiO2) in step S1 is 0.05-1:1.

[0014] Preferably, in step S5, the temperature of the hydrothermal crystallization reaction is 150-180℃ and the time is 48-72 hours; the drying temperature is 80-120℃ and the time is 8-12 hours.

[0015] Preferably, in step S6, the calcination is carried out in an air atmosphere at a temperature of 500-600°C for 4-6 hours; the reducing atmosphere is a hydrogen atmosphere or a hydrogen-containing atmosphere at a temperature of 300-450°C for 2-5 hours.

[0016] To solve the third technical problem mentioned above, the present invention adopts the following technical solution: the application of a growth-directing agent modified RhK@MFI catalyst in the preparation of n-butyraldehyde by propylene hydroformylation reaction.

[0017] Preferably, the propylene hydroformylation reaction is carried out in a fixed-bed or batch reactor; the process conditions are: reaction temperature 60-120℃; reaction pressure 3-7MPa; the volume ratio of hydrogen to carbon monoxide (H2 / CO) in the syngas is 0.8:1-2:1; and the volume ratio of propylene to syngas feed is 1:1-1:5.

[0018] More preferably, the process conditions are: reaction temperature 70-100℃; reaction pressure 3.0-6.0MPa; and the volume ratio of hydrogen to carbon monoxide (H2 / CO) in the synthesis gas is 1:1.

[0019] Any range described in this invention includes the endpoint, any value between the endpoints, and any subrange consisting of the endpoint or any value between the endpoints.

[0020] Unless otherwise specified, all raw materials used in this invention can be obtained commercially, and the equipment used in this invention can be conventional equipment in the relevant field or refer to existing technology in the relevant field.

[0021] Compared with the prior art, the present invention has the following beneficial effects.

[0022] 1) This invention introduces a growth-directing agent after gel aging, which has a key impact on the catalyst precursor: First, the alkaline environment and intermediate products generated by decomposition promote the uniform distribution and stable anchoring of metal precursors (Rh, K) in the silicate network, effectively preventing the aggregation of active components during high-temperature treatment and ensuring the high dispersion of Rh species; Second, it moderately adjusts the acidity and alkalinity of the catalyst surface, providing a more suitable catalytic microenvironment for the reaction.

[0023] (2) The synergistic effect between the Rh and K active centers is significant. Electronic interactions occur between the Rh and K species introduced in situ via a one-step encapsulation method. K modulates the electron density of the Rh center, making it more favorable for a linear reaction pathway. This electronic effect, combined with the inherent pore shape-selective effect of MFI molecular sieves, jointly guides the reaction to generate n-butyraldehyde with high selectivity, thus achieving a high n:i ratio (n:i>60) without the addition of expensive organophosphorus ligands. Attached Figure Description

[0024] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. Figure 1 The XRD pattern of the catalyst prepared in Example 1 of this invention; Figure 2 This is a SEM image of the catalyst prepared in Example 1 of the present invention; Figure 3 This is a TEM image of the catalyst prepared in Example 1 of the present invention. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0026] It should be noted that the technical terms used in this invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of this invention. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the following embodiments of this invention can be purchased from the market or prepared by existing methods.

[0027] As one aspect of the present invention, a growth-directing agent modified RhK@MFI catalyst is provided, comprising active centers Rh and K, and the support is an MFI molecular sieve; the Rh is encapsulated in the framework or channels of the MFI molecular sieve in the form of atomic-level or nano-clusters, and the K is distributed in the framework or surface of the MFI molecular sieve; the loading of Rh is 0.1-2.0 wt% and the loading of K is 0.05-1.0 wt% based on the total mass of the catalyst.

[0028] As another aspect of the present invention, a method for preparing a growth-directing agent modified RhK@MFI catalyst includes the following steps: S1. Mix the template agent, silicon source and deionized water in a certain proportion, stir and pre-hydrolyze to obtain a silicate gel mixture; S2. Dissolve the rhodium source and potassium source in a mixed solvent prepared from deionized water and ethylenediamine, and stir to form a metal precursor solution; S3. Add the metal precursor solution to the silicate gel mixture, stir evenly, and then perform an aging treatment to obtain an aged gel. S4. Add growth-directing agent to the aged gel, mix well and modify to obtain the final gel; S5. The final gel is subjected to a hydrothermal crystallization reaction. After the reaction is completed, it is separated by centrifugation, washed and dried to obtain the catalyst precursor. S6. The catalyst precursor is calcined and then reduced in a reducing atmosphere to obtain the RhK@MFI molecular sieve catalyst.

[0029] According to certain embodiments of the present invention, in step S1, the template agent is tetrapropylammonium hydroxide; the silicon source is tetraethyl orthosilicate or silica sol; and the molar ratio of the template agent, silicon source (calculated as SiO2) and deionized water is 2-4:1:30-40.

[0030] According to certain embodiments of the present invention, in step S2, the rhodium source is rhodium trichloride or rhodium nitrate; the potassium source is potassium nitrate or potassium hydroxide; and the molar ratio of the rhodium source to the potassium source is 1:100-700.

[0031] According to certain embodiments of the present invention, in step S2, the volume ratio of ethylenediamine to deionized water is 1:5-10; the rhodium source is rhodium trichloride or rhodium nitrate.

[0032] According to certain embodiments of the present invention, in step S3, the aging treatment temperature is 30-50°C and the time is 6-12 hours.

[0033] According to certain embodiments of the present invention, in step S4, the growth guiding agent is an aqueous solution of one or more of ammonium fluoride, pyrrolidine, amino acid, tetrahydrofuran, urea, ethanol, isopropanol, n-butanol, and methanol; the amount of growth guiding agent added is such that the molar ratio of the growth guiding agent to the silicon source (calculated as SiO2) in step S1 is 0.05-1:1.

[0034] According to certain embodiments of the present invention, in step S5, the temperature of the hydrothermal crystallization reaction is 150-180°C and the time is 48-72 hours; the drying temperature is 80-120°C and the time is 8-12 hours.

[0035] According to certain embodiments of the present invention, in step S6, the calcination is carried out in an air atmosphere at a temperature of 500-600°C for 4-6 hours; the reducing atmosphere is a hydrogen atmosphere or a hydrogen-containing atmosphere at a temperature of 300-450°C for 2-5 hours.

[0036] As another aspect of the present invention, the present invention provides the application of a growth-directing agent modified RhK@MFI catalyst in the preparation of n-butyraldehyde by propylene hydroformylation.

[0037] According to certain embodiments of the present invention, the propylene hydroformylation reaction is carried out in a fixed-bed or batch reactor; the process conditions are: reaction temperature 60-120℃; reaction pressure 3-7MPa; the volume ratio of hydrogen to carbon monoxide (H2 / CO) in the syngas is 0.8:1-2:1; and the volume ratio of propylene to syngas feed is 1:1-1:5.

[0038] According to certain embodiments of the present invention, the process conditions are as follows: reaction temperature 70-100℃; reaction pressure 3.0-6.0MPa; and the volume ratio of hydrogen to carbon monoxide (H2 / CO) in the synthesis gas is 1:1.

[0039] Example 1 A method for preparing an RhK@MFI molecular sieve catalyst includes the following steps: S1. Mix 16.24 g of tetrapropylammonium hydroxide (TPAOH, 25% aqueous solution) with 25.0 g of deionized water, and slowly add 8.24 g of tetraethyl orthosilicate (TEOS) while stirring. Continue stirring for 2 hours to perform pre-hydrolysis. Then add 0.3 g of potassium nitrate (KNO3) and stir until completely dissolved to obtain a homogeneous silicate gel mixture.

[0040] S2. Dissolve 0.0045 g of rhodium trichloride trihydrate (RhCl3·3H2O) in 200 μL of a mixed solvent prepared from 100 μL of ethylenediamine and 100 μL of deionized water, and sonicate for 30 minutes to obtain a yellow metal precursor solution.

[0041] S3. Slowly add the solution from step S2 dropwise to the gel mixture from step S1, and stir continuously at room temperature for 4 hours. Then transfer the mixture to a constant temperature water bath and age it at 40°C for 12 hours to obtain an aged gel.

[0042] S4. Add 1.188 g of growth-directing agent to the aged gel and stir continuously for 2 hours to ensure uniform dispersion of the growth-directing agent, thus obtaining the final gel.

[0043] S5. The final gel was transferred to a high-pressure reactor lined with polytetrafluoroethylene and crystallized in an oven at 180°C for 48 hours. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, centrifuged, washed three times each with deionized water and ethanol, and dried at 80°C for 10 hours to obtain the catalyst precursor.

[0044] S6. The dried precursor was placed in a muffle furnace and calcined at 550°C for 5 hours under air atmosphere at a rate of 5°C / min. The calcined powder was then placed in a tube furnace and reduced at 600°C for 3 hours under a 5% H₂ / Ar atmosphere at a rate of 5°C / min. After natural cooling, the RhK@MFI catalyst was obtained. ICP-OES analysis showed that the Rh loading was 0.149 wt% and the K loading was 0.512 wt%.

[0045] Catalytic reaction conditions: reaction pressure 3.0 MPa, reaction temperature 90℃, reaction time 2 h, catalyst amount 50 mg.

[0046] Figure 1 The XRD pattern of the catalyst prepared in Example 1 of this invention; Figure 2 This is a SEM image of the catalyst prepared in Example 1 of the present invention; Figure 3 This is a TEM image of the catalyst prepared in Example 1 of the present invention. Example 2

[0047] Example 1 was repeated, except that the reaction pressure was 4.0 MPa. Example 3

[0048] Example 1 was repeated, except that the reaction pressure was 5.0 MPa. Example 4

[0049] Example 1 was repeated, except that the reaction pressure was 6.0 MPa. Example 5

[0050] Example 1 was repeated, except that the reaction pressure was 7.0 MPa. Example 6

[0051] Example 4 was repeated, except that the reaction time was 3 h. Example 7

[0052] Example 4 was repeated, except that the reaction time was 6 h. Example 8

[0053] Example 4 was repeated, except that the reaction time was 9 h. Comparative Example 1

[0054] Repeat Example 1, except that step S4 (without adding the growth guide agent) is completely omitted. Comparative Example 2

[0055] Example 1 was repeated, except that 0.713 g of growth-directing agent was added in step S4. Comparative Example 3

[0056] Example 1 was repeated, except that 1.663 g of growth-directing agent was added in step S4.

[0057] Figure 1 The X-ray diffraction (XRD) pattern of the catalyst prepared in Example 1 is shown. As shown, the sample exhibits typical MFI topological characteristic diffraction peaks at 2θ of 7.9°, 8.8°, 23.1°, 23.9°, and 24.4°, indicating that a well-crystallized MFI molecular sieve framework was successfully synthesized via hydrothermal crystallization. No obvious characteristic diffraction peaks belonging to rhodium or rhodium oxides were observed in the pattern, indicating that the Rh species exist in a highly dispersed form. Figure 2 Scanning electron microscopy (SEM) images visually reveal the overall morphology of the catalyst. As seen in the images, the catalyst sample exhibits relatively uniform, micrometer-sized crystal particles with smooth surfaces, displaying the typical coffin-like morphology of MFI molecular sieves. However, compared to unmodified conventional MFI molecular sieves, some crystals show reduced thickness in specific directions (especially perpendicular to the b-axis), with clearer edges. This provides direct morphological evidence for the regulatory effect of the "growth-directing agent thinning strategy" on the growth of molecular sieve crystals. Figure 3Transmission electron microscopy (TEM) images and high-resolution images further revealed the microstructure of the catalyst. Under low-magnification TEM, the uniform internal contrast of the molecular sieve crystals can be clearly seen.

[0058] The catalysts prepared in Examples 1-8 and Comparative Examples 1-3 were used in the hydroformylation of propylene to n-butyraldehyde. The catalytic reaction was carried out in a 100 mL stainless steel autoclave in a batch operation mode. Before the reaction, the catalyst was activated at 320°C for 3 hours in a reducing atmosphere (H2). The catalyst dosage was 0.05 g and 0.5 g, respectively. The catalytic reaction pressure was 4-6 MPa, the reaction temperature was 90°C, and the reaction time was 2-12 hours. The conversion rate of propylene (Xp) and the selectivity for aldehyde formation (S) were tested. A The results of the positive-to-negative ratio (n:i) and the positive-to-negative ratio (n:i) are shown in Table 1.

[0059] The specific process is as follows: The propylene hydroformylation reaction was evaluated in a 100 mL stainless steel high-pressure reactor in a batch manner. 0.05 g of catalyst and 15 mL of toluene solvent were placed in the reactor, sealed, and purged three times sequentially with nitrogen and hydrogen. Then, propylene and syngas (H2 / CO = 1:1) were quantitatively introduced, the temperature was raised to the target temperature, and the pressure was adjusted to initiate the reaction. After the reaction, the product was rapidly cooled, collected, and qualitatively and quantitatively analyzed using gas chromatography equipped with an FID detector. The core evaluation indicators included propylene conversion (Xp) and total aldehyde selectivity (S). A The positive-to-negative ratio (n:i) and the evaluation results of the catalysts in the examples and comparative examples at 90°C are summarized in Table 1 below.

[0060] Table 1 Catalytic performance of the catalyst

[0061] Analysis of the data in Table 1 shows that the composition of the catalyst and the reaction conditions have a significant impact on the performance.

[0062] First, the role of growth-directing agents as modifiers is crucial: 1) After reacting for 2 hours at 6.0 MPa pressure, the comparative example 1 without growth-directing agent showed extremely low catalytic activity (Xp=5.32%) and a positive-to-inverse ratio of 7.21; 2) In Example 4, prepared using the preferred amount of growth-directing agent of the present invention (1.188 g), the propylene conversion rate was significantly increased to 30.75%, and the positive-to-iso ratio reached an extremely high 62.42; 3) The catalysts with low (Comparative Example 2) or high (Comparative Example 3) growth-directing agent dosages were not as good as those in Example 4. This indicates that there is an optimal growth-directing agent addition window to achieve the most effective modification of molecular sieve channels and the most ideal dispersion of metal species, thereby synergistically optimizing catalytic activity and selectivity.

[0063] Secondly, reaction pressure is a key operating parameter: 1) Within the range of 3.0 to 6.0 MPa (Examples 1 to 4), as the pressure increased, the propylene conversion rate and the positive-to-iso ratio both showed a significant trend of synchronous increase, and the total aldehyde selectivity remained at an excellent level of over 98%. 2) The positive-to-negative ratio reaches its peak at 6.0 MPa; this is mainly attributed to the fact that higher pressure not only promotes the adsorption and activation of syngas at active sites, but also is thermodynamically more favorable for the reaction pathway that generates linear positive products. 3) However, when the pressure was further increased to 7.0 MPa (Example 5), although the conversion rate still increased slightly, the positive-to-negative ratio dropped significantly, suggesting that excessive pressure may have triggered adverse side reactions or altered the diffusion behavior of reactants and products.

[0064] Finally, the effect of reaction time on performance exhibits a trade-off between conversion rate and selectivity: 1) Under a pressure of 6.0 MPa, the reaction time was extended from 2 hours to 9 hours (Examples 4, 6, 7, 8), and the propylene conversion rate continued to increase, confirming that the catalyst has good sustained reaction capability; 2) However, the ratio of positive to negative decreased monotonically over time, dropping sharply from 62.42 at 2 hours to 5.28 at 9 hours. This trend is likely because as the reaction proceeds, aldehyde products accumulate in the system, increasing the probability of secondary reactions (such as condensation or isomerization of aldehydes), leading to an increase in the proportion of branched products.

[0065] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is impossible to exhaustively list all embodiments here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A growth-directing agent-modified RhK@MFI catalyst, characterized in that: It includes active centers Rh and K, and the support is MFI molecular sieve; Rh is encapsulated in the framework or channels of MFI molecular sieve in the form of atomic or nano-clusters, and K is distributed in the framework or surface of MFI molecular sieve; the loading of Rh is 0.1-2.0 wt% and the loading of K is 0.05-1.0 wt% based on the total mass of the catalyst.

2. The method for preparing the growth-directing agent-modified RhK@MFI catalyst as described in claim 1, characterized in that, Includes the following steps: S1. Mix the template agent, silicon source and deionized water in a certain proportion, stir and pre-hydrolyze to obtain a silicate gel mixture; S2. Dissolve the rhodium source and potassium source in a mixed solvent prepared from deionized water and ethylenediamine, and stir to form a metal precursor solution; S3. Add the metal precursor solution to the silicate gel mixture, stir evenly, and then perform an aging treatment to obtain an aged gel. S4. Add growth-directing agent to the aged gel, mix well and modify to obtain the final gel; S5. The final gel is subjected to a hydrothermal crystallization reaction. After the reaction is completed, it is separated by centrifugation, washed and dried to obtain the catalyst precursor. S6. The catalyst precursor is calcined and then reduced in a reducing atmosphere to obtain the RhK@MFI molecular sieve catalyst.

3. The method for preparing the growth-directing agent-modified RhK@MFI catalyst according to claim 2, characterized in that: In step S1, the template agent is tetrapropylammonium hydroxide; the silicon source is tetraethyl orthosilicate or silica sol; and the molar ratio of the template agent, silicon source (calculated as SiO2) and deionized water is 2-4:1:30-40.

4. The method for preparing the RhK@MFI catalyst modified with the growth-directing agent according to claim 2, characterized in that: In step S2, the rhodium source is rhodium trichloride or rhodium nitrate; the potassium source is potassium nitrate or potassium hydroxide; and the molar ratio of the rhodium source to the potassium source is 1:100-700.

5. The method for preparing the RhK@MFI catalyst modified with the growth-directing agent according to claim 2, characterized in that: In step S2, the volume ratio of ethylenediamine to deionized water is 1:5-10; the rhodium source is rhodium trichloride or rhodium nitrate.

6. The method for preparing the growth-directing agent-modified RhK@MFI catalyst according to claim 2, characterized in that: In step S3, the aging treatment is carried out at a temperature of 30-50°C for 6-12 hours.

7. The method for preparing the RhK@MFI catalyst modified with the growth-directing agent according to claim 2, characterized in that: In step S4, the growth guiding agent is an aqueous solution of one or more of the following: ammonium fluoride, pyrrolidine, amino acids, tetrahydrofuran, urea, ethanol, isopropanol, n-butanol, and methanol; the amount of growth guiding agent added is: the molar ratio of the growth guiding agent to the silicon source (calculated as SiO2) in step S1 is 0.05-1:

1.

8. The method for preparing the growth-directing agent-modified RhK@MFI catalyst according to claim 2, characterized in that: In step S5, the hydrothermal crystallization reaction is carried out at a temperature of 150-180°C for 48-72 hours; the drying temperature is 80-120°C for 8-12 hours.

9. The method for preparing the growth-directing agent-modified RhK@MFI catalyst according to claim 2, characterized in that: In step S6, the calcination is carried out in an air atmosphere at a temperature of 500-600°C for 4-6 hours; the reduction atmosphere is a hydrogen atmosphere or a hydrogen-containing atmosphere at a temperature of 300-450°C for 2-5 hours.

10. The application of the growth-directing agent-modified RhK@MFI catalyst as described in claim 1 in the preparation of n-butyraldehyde by propylene hydroformylation, characterized in that: The propylene hydroformylation reaction is carried out in a fixed-bed or batch reactor; the process conditions are: reaction temperature 60-120℃; reaction pressure 3-7MPa; hydrogen to carbon monoxide volume ratio (H2 / CO) in syngas is 0.8:1-2:1; propylene to syngas feed volume ratio is 1:1-1:5; Preferably, the process conditions are: reaction temperature 70-100℃; reaction pressure 3.0-6.0MPa; and the volume ratio of hydrogen to carbon monoxide (H2 / CO) in the synthesis gas is 1:1.

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