A rod-shaped Cr-doped Silicalite-1 catalyst, its preparation method and application

Abstract

This invention provides a rod-shaped Cr-doped Silicalite-1 catalyst, its preparation method, and its application. The catalyst crystallite dimensions range from (0.6–2.0) μm (0.2–0.3) μm (0.05–0.15) μm (length–width–height). The Cr loading is 3–12% of the SiO2 mass. The catalyst is prepared by first preparing a chromium-based S-1 molecular sieve crystallization slurry using hydrothermal crystallization, drying it to the required water content to prepare a dry gel material, performing a dry gel crystallization reaction, and then oxidatively calcining it in air to obtain the catalyst. This rod-shaped Cr-doped Silicalite-1 catalyst preparation method is simple. Using propane dehydrogenation as a model reaction to evaluate its performance in dehydrogenating low-carbon alkanes, it can be seen that it has high propane conversion and propylene selectivity, enabling commercial application.

Description

Technical Field

[0001] This invention relates to a rod-shaped Cr-doped Silicalite-1 catalyst, its preparation method, and its application. Specifically, it relates to a hydrothermal crystallization method for preparing a Cr-containing crystallization slurry, drying the crystallization slurry to prepare a dry gel material, and then performing a re-crystallization reaction on the dry gel material to obtain a rod-shaped Cr-doped Silicalite-1 catalyst. Background Technology

[0002] Existing methods for preparing low-carbon olefins (ethylene, propylene, butene, etc.) through the dehydrogenation of low-carbon alkanes are relatively common. This method is characterized by high olefin selectivity, hydrogen production as a byproduct, and good atom economy. However, at high temperatures, the high conversion rate and high selectivity are contradictory. This is because higher conversion rates require higher reaction temperatures, but high temperatures significantly exacerbate side reactions such as CC cracking, leading to reduced catalyst selectivity, carbon deposition, or coking and deactivation. Therefore, currently, to improve the lifespan of low-carbon alkane dehydrogenation catalysts, the solution often requires frequent carbon burning regeneration of the deactivated catalyst.

[0003] As a type of metal support, molecular sieves are widely used as catalyst supports due to their regular pore structure, tunable acidity, excellent hydrothermal stability, and chemical stability. Among the many methods of loading metals onto molecular sieves, molecular sieve-encapsulated metal catalysts prepared from metal chelates can effectively inhibit metal particle aggregation and reduce particle size by fully utilizing the internal microporous structure of the molecular sieve. Simultaneously, it can significantly improve the hydrothermal stability of the metal particles, thereby enhancing their catalytic performance, making it one of the preferred preparation methods. However, the stability of metal chelates under the strongly alkaline conditions of molecular sieve synthesis and the hydrothermal autogenous pressure reaction at 100–200℃ remains a problem that needs to be addressed.

[0004] Molecular sieve-encapsulated metal catalysts typically use pure silica molecular sieves. Alloying designs for preparing molecular sieve-encapsulated metal catalysts (such as by combining platinum with auxiliary metal elements like tin, gallium, copper, and zinc) are considered an effective synthetic strategy for improving the stability and olefin selectivity of platinum-based catalysts. Silicalite-1 molecular sieves (S-1 molecular sieves) with an MFI topology are all-silica molecular sieves. Due to their good adsorption and separation characteristics, thermal stability, and simple synthesis process, they are considered an ideal molecular sieve for encapsulating metals. Patents CN106669768A, CN110026230A, and CN110479353A disclose a series of methods for preparing Pt-based composite metal@silicalite-1 molecular sieve catalysts. Patents CN113509955A, CN110614117A, and CN113289671A disclose a series of methods for preparing Co and Zn oxide molecular sieve composite dehydrogenation catalysts.

[0005] Non-precious metal oxide-based dehydrogenation catalysts are considered promising for the dehydrogenation of low-carbon alkanes due to their rich properties, easily tunable structure, simple synthesis, and low cost. Besides the industrially available chromium oxide catalysts, Co₂O₃, ZnO, and SnO₂ catalytic systems have been reported in recent years, all exhibiting excellent dehydrogenation performance in low-carbon alkanes. However, existing catalysts have not yet achieved commercial application due to complex preparation methods and unstable products. Summary of the Invention

[0006] To address the shortcomings of existing technologies for dehydrogenation catalysts for low-carbon alkanes, the present invention aims to provide a rod-shaped Cr@S-1 catalyst, its preparation method, and its application in the dehydrogenation of low-carbon alkanes. Taking propane dehydrogenation as an example, this method can significantly improve the catalyst's activity, selectivity, and stability.

[0007] The present invention provides a rod-shaped Cr-doped Silicalite-1 catalyst, which is prepared by loading metallic Cr onto Silicalite-1 molecular sieves, and its grain morphology is rod-shaped.

[0008] The dimensions of the rod-shaped Cr-doped Silicalite-1 catalyst are (0.6–2.0) μm (0.2–0.3) μm (0.05–0.15) μm (length–width–height), and the loading of metallic Cr is 3–12% of the mass of SiO2.

[0009] The method for preparing the rod-shaped Cr@Silicalite-1 catalyst of the present invention includes the following steps:

[0010] (1) After stirring and mixing deionized water, chromium source, ethylenediamine, template agent and silicon source evenly, a mixed slurry is obtained;

[0011] (2) Transfer the mixed slurry obtained in step (1) to a crystallization kettle and carry out crystallization reaction under the conditions of reaction temperature of 150℃-180℃, stirring speed of 50~200 rpm, and reaction time of 24-96 hours.

[0012] (3) The slurry obtained after crystallization reaction in step (2) is dried to obtain dry adhesive material, and the water content of the dry adhesive material is controlled to be in the range of 17-25%.

[0013] (4) Transfer the dry adhesive material obtained in step (3) to the dry adhesive crystallization kettle again, and carry out the dry adhesive crystallization reaction at a reaction temperature of 150℃-180℃ and a reaction time of 24-96 hours.

[0014] (5) The crystallized product obtained in (4) was dried, shaped and oxidized and calcined in air to obtain a rod-shaped Cr@Silicalite-1 catalyst.

[0015] In the above technical solution, the silicon source in the mixed slurry in step (1) is SiO2, and the molar ratio of SiO2:Cr:EDA:ROH:H2O is 100.0:(3.5~13.9):(10.0~40.0):(7.0~21.0):(1400.0~1800.0), where Cr is the chromium content in the chromium source, EDA is ethylenediamine, and ROH is a template agent.

[0016] In the above technical solution, as a preferred embodiment, the chromium source in step (1) is either chromium nitrate or chromium hydroxide; the template agent is a 25-35% aqueous solution of tripropylethylammonium hydroxide; and the silicon source is fumed silica.

[0017] In the above technical solution, the drying temperature in step (3) is 70-90℃, and the water content of the dried adhesive material after drying is 17-25% by mass. As is well known to those skilled in the art, the water content of the dried adhesive material is tested using a halogen moisture analyzer under the following conditions: test temperature 120℃ and test time 10 minutes.

[0018] In the above technical solution, the drying temperature in step (5) is 90-120℃ and the drying time is 12-24 hours; the oxidation roasting temperature in the air atmosphere is 550-600℃ and the holding time is 3-9 hours. The roasting is carried out in a flowing air atmosphere with an air flow rate of 3-10 L / min.

[0019] In the above technical solution, the molding method in step (5) can be processed in a manner known to those skilled in the art. The rod-shaped Cr@Silicalite-1 catalyst powder is mixed with a commonly used carrier (such as diatomaceous earth), a commonly used binder (such as silica sol), and water according to conventional methods in the art. After molding by conventional methods, it can be used directly in an industrial device to complete the oxidation and calcination process under an air atmosphere to obtain the dehydrogenation catalyst.

[0020] The application of a rod-shaped Cr-doped Silicalite-1 catalyst of the present invention is as follows: when used as a catalyst for the dehydrogenation of low-carbon alkanes, the selectivity is 89% to 91% and the conversion rate is 37% to 42% after 1 hour of dehydrogenation reaction; after 17 hours of dehydrogenation reaction, the selectivity is 92% to 94% and the conversion rate is 31% to 36%.

[0021] As is well known to those skilled in the art, the method for evaluating the activity of dehydrogenation catalysts in a tubular reactor is as follows: Rod-shaped Cr-doped Silicalite-1 catalyst powder is pressed into tablets using a tablet press, then pulverized and sieved to a mesh size of 10–20 for activity evaluation. The oxidation calcination process under air atmosphere can be completed in the tubular reactor to obtain rod-shaped Cr-doped Silicalite-1 catalyst with dehydrogenation activity. The low-carbon alkane is selected from ethane, propane, and butane. The evaluation conditions in the tubular reactor are: reaction pressure of 0.05–0.3 MPa, reaction temperature of 500–650 °C, and weight hourly space velocity (WHSV) of the low-carbon alkane feed of 2–100 h⁻¹. -1 The performance of the catalyst in the dehydrogenation reaction was evaluated under the specified conditions.

[0022] Furthermore, as a specific implementation method for catalyst evaluation, the performance of the dehydrogenation catalyst was evaluated using the propane dehydrogenation reaction as a model reaction. The tubular reactor had an inner diameter of 10 mm and a catalyst loading height of approximately 30 mm. The evaluation conditions were: reaction pressure of 0.05 MPa, reaction temperature of 580 °C, and WHSV of propane gas feed of 8 h⁻¹. -1 The performance of the catalyst in the dehydrogenation reaction was evaluated under the specified conditions.

[0023] Furthermore, the specific steps for evaluating the performance of the dehydrogenation catalyst using propane dehydrogenation reaction as a model reaction are as follows: 1. The rod-shaped Cr-doped Silicalite-1 catalyst powder is pressed into tablets using a tablet press, then pulverized and sieved to obtain a 10-20 mesh sample to be evaluated; 2. 1.0 g of the above sample to be evaluated is mixed with 3.0 g of quartz sand and packed into a tubular reactor. The mixture is heated to 580 °C in an air atmosphere of 200 ml / min and oxidized for 6 hours. Then, the mixture is switched to a high-purity nitrogen atmosphere of 200 ml / min and purged at 580 °C for 30 minutes; 3. After purging with high-purity nitrogen atmosphere, the reaction temperature is maintained at 580 °C, and the atmosphere is switched to propane gas at 72.9 ml / min for dehydrogenation reaction. The products are analyzed using gas chromatography.

[0024] Furthermore, the catalyst regeneration evaluation method is as follows: 1. After catalyst deactivation, the reaction atmosphere is switched to a high-purity nitrogen atmosphere of 200 ml / min, and the reaction temperature is lowered to 500℃. Then, the atmosphere is switched to an air atmosphere of 200 ml / min for 3 hours of oxidation. Then, the temperature is raised to 550℃ for 3 hours of oxidation, and finally, the temperature is raised to 580℃ for 3 hours of oxidation. 2. After the air atmosphere oxidation is completed, the reaction temperature is maintained at 580℃, and the atmosphere is switched to propane gas of 72.9 ml / min for continued evaluation of the dehydrogenation reaction. The products are analyzed by gas chromatography.

[0025] The present invention provides a rod-shaped Cr@Silicalite-1 catalyst, its preparation method, and its application in the dehydrogenation of low-carbon alkanes. Compared with the prior art, the advantages of the present invention are:

[0026] 1. The crystallization slurry is dried directly using a drying method, which avoids the loss of active components and reduces the discharge of wastewater containing metals and template agents;

[0027] 2. The dried crystallized slurry is subjected to a secondary crystallization transformation of Silicalite-1 molecular sieve loaded or doped with active metals using a dry gel conversion method. This is very beneficial for the redispersion and coating of active metals, improves the utilization rate of metals, and avoids the loss of metals with the crystallization mother liquor during the hydrothermal crystallization process.

[0028] 3. The catalyst preparation method is simple. The dehydrogenation catalyst can be obtained by drying, shaping and oxidizing and calcining the secondary crystallization product in an air atmosphere. The obtained catalyst does not require a hydrogen reduction step. The preparation process technology is relatively mature and is very conducive to the industrial scale-up production of the catalyst.

[0029] 4. The performance of this catalyst in the dehydrogenation of low-carbon alkanes was evaluated by using the propane dehydrogenation reaction as a model reaction. The reaction process does not require the addition of hydrogen and can achieve high propane conversion and propylene selectivity. Moreover, the catalyst has good stability and has good prospects for industrial application.

[0030] 5. Preparing the catalyst support molecular sieve into a rod shape has the advantage of having a shorter transport path on the one-dimensional cross-section of the molecular sieve, which is more conducive to the transport of reactants and products on the surface of the molecular sieve. Attached Figure Description

[0031] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0032] Figure 1 Scanning electron microscope image of the rod-shaped Cr-doped Silicalite-1 catalyst prepared in Example 1;

[0033] Figure 2 This is the powder X-ray diffraction pattern of the rod-shaped Cr-doped Silicalite-1 catalyst prepared in Example 3;

[0034] Figure 3 The image shows a scanning electron microscope (SEM) image of the rod-shaped Cr-doped Silicalite-1 catalyst prepared in Example 3. Detailed Implementation

[0035] In the description of this invention, it should be noted that unless specific conditions are specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0036] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0037] The following examples provide a detailed description of specific implementations of the technical solution of the present invention, but the present invention is not limited to the following description. The performance evaluation of propane dehydrogenation reaction further illustrates the technology of the present invention.

[0038] Example 1

[0039] A rod-shaped Cr-doped Silicalite-1 catalyst and its preparation method are described below:

[0040] (1) Weigh 1256.59g of deionized water, 21.63g of chromium hydroxide and 36.05g of ethylenediamine (EDA), stir and dissolve to obtain a uniform mixture, add 317.98g of 25% tripropylethylammonium hydroxide (ROH) aqueous solution to the above mixture, then add 367.77g of fumed silica (Jiangxi Black Cat Co., Ltd., model HM150, dry basis measured at 850℃ for 2h, the same below), stir and mix for 2h to prepare a mixed slurry;

[0041] The mass of SiO2 is calculated based on the dry basis measured by calcining fumed silica at 850℃ for 2 hours. If the dry basis of commercially available fumed silica used in this invention patent is 98%, then the mass of SiO2 contained in the raw material = the mass of the raw material * the dry basis, and the same applies below.

[0042] In this embodiment, the molar ratio of SiO2:Cr:EDA:ROH:H2O in the mixed slurry is 100.0:3.5:10.0:7.0:1400.0.

[0043] (2) The mixed slurry obtained in step (1) is transferred to a hydrothermal crystallization kettle and crystallized for 24 hours at a reaction temperature of 180°C and a stirring speed of 50 rpm to obtain the crystallized slurry.

[0044] (3) The crystallized slurry obtained in step (2) is dried at a drying temperature of 70°C for a certain period of time until the water content of the dry adhesive material is between 17% and 25%, and the dry adhesive material is obtained.

[0045] (4) Transfer the dry adhesive material obtained in step (3) to a dry adhesive crystallization kettle, and crystallize it for 96 hours at a reaction temperature of 150°C to obtain the crystallized product.

[0046] (5) The crystallized product obtained in (4) was dried at a drying temperature of 90°C for 24 hours, and then heated to 550°C and calcined for 9 hours at an air flow rate of 3L / min and a heating rate of 5°C / min to obtain a rod-shaped Cr-doped Silicalite-1 catalyst.

[0047] Figure 1 Scanning electron microscopy (SEM) images showed that the crystallite dimensions (length x width x height) of the obtained catalyst sample ranged from (0.6–2.0) μm to (0.2–0.3) μm to (0.05–0.15) μm. X-ray fluorescence spectroscopy (XRF) analysis revealed that the Cr content was 3.03% of the silica mass. The propane dehydrogenation performance of the catalyst prepared in this example is shown in Table 1.

[0048] Example 2

[0049] A rod-shaped Cr-doped Silicalite-1 catalyst and its preparation method are described below:

[0050] (1) Weigh 882.15g of deionized water, 244.22g of chromium nitrate nonahydrate and 105.56g of ethylenediamine (EDA), stir and dissolve to obtain a uniform mixture, add 498.83g of 35% tripropylethylammonium hydroxide aqueous solution to the above mixture, then add 269.24g of fumed silica, stir and mix for 2h to prepare a mixed slurry;

[0051] In this embodiment, the molar ratio of SiO2:Cr:EDA:ROH:H2O in the mixed slurry is 100.0:13.9:40.0:21.0:1800.0.

[0052] (2) The mixed slurry obtained in step (1) is transferred to a hydrothermal crystallization kettle and crystallized for 96 hours at a reaction temperature of 150°C and a stirring speed of 200 rpm to obtain the crystallized slurry.

[0053] (3) The crystallized slurry obtained in step (2) is dried at a drying temperature of 90°C for a certain period of time until the water content of the dry adhesive material is between 17% and 25%, and the dry adhesive material is obtained.

[0054] (4) Transfer the dry adhesive material obtained in step (3) to a dry adhesive crystallization kettle, and crystallize it for 24 hours at a reaction temperature of 180°C to obtain the crystallized product.

[0055] (5) The crystallized product obtained in (4) was dried at a drying temperature of 120°C for 12 hours, and then heated to 600°C and calcined for 3 hours at an air flow rate of 10 L / min and a heating rate of 5°C / min to obtain a rod-shaped Cr-doped Silicalite-1 catalyst.

[0056] X-ray fluorescence spectroscopy (XRF) analysis showed that the Cr content was 12.07% of the silica mass. The propane dehydrogenation performance of the catalyst prepared in this example is shown in Table 1.

[0057] Example 3

[0058] A rod-shaped Cr-doped Silicalite-1 catalyst and its preparation method are described below:

[0059] (1) Weigh 1022.30g of deionized water, 142.55g of chromium nitrate nonahydrate and 73.41g of ethylenediamine (EDA), stir and dissolve to obtain a uniform mixture, add 449.68g of 30% tripropylethylammonium hydroxide aqueous solution to the above mixture, then add 312.06g of fumed silica, stir and mix for 2h to prepare a mixed slurry;

[0060] In this embodiment, the molar ratio of SiO2:Cr:EDA:ROH:H2O in the mixed slurry is 100.0:7.0:24.0:14.0:1600.0.

[0061] (2) The mixed slurry obtained in step (1) is transferred to a hydrothermal crystallization kettle and crystallized for 72 hours at a reaction temperature of 170°C and a stirring speed of 120 rpm to obtain the crystallized slurry.

[0062] (3) The crystallized slurry obtained in step (2) is dried at a drying temperature of 80°C for a certain period of time until the water content of the dry adhesive material is between 17% and 25%, and the dry adhesive material is obtained.

[0063] (4) Transfer the dry adhesive material obtained in step (3) to a dry adhesive crystallization kettle, and crystallize it for 48 hours at a reaction temperature of 170°C to obtain the crystallized product.

[0064] (5) The crystallized product obtained in (4) was dried at a drying temperature of 100°C for 16 hours, and then heated to 580°C and calcined for 6 hours under the conditions of air flow rate of 7L / min and heating rate of 5°C / min to obtain rod-shaped Cr-doped Silicalite-1 catalyst.

[0065] Figure 2 The powder X-ray diffraction pattern of the rod-shaped Cr-doped Silicalite-1 catalyst obtained in step (5) shows that the product still has an MFI structure and no metal peaks, indicating that the metal has good dispersion. Figure 3 Scanning electron microscopy (SEM) images show that the crystallite dimensions (length x width x height) of the catalyst sample obtained in this embodiment range from (0.6–2.0) μm to (0.2–0.3) μm to (0.05–0.15) μm. X-ray fluorescence spectroscopy (XRF) analysis revealed that the Cr content was 6.11% of the silica mass. The propane dehydrogenation performance of the catalyst prepared in this embodiment is shown in Tables 1 and 2.

[0066] Comparative Example 1

[0067] Rod-shaped Cr-doped Silicalite-1 catalysts were directly prepared using a one-step hydrothermal crystallization method. The amounts of metal Cr source, ethylenediamine, tripropylethylammonium hydroxide, and silicon source were the same as in Example 3. The specific steps are as follows:

[0068] (1) Weigh 1022.30g of deionized water, 142.55g of chromium nitrate nonahydrate and 73.41g of ethylenediamine (EDA), stir and dissolve to obtain a uniform mixture, add 449.68g of 30% tripropylethylammonium hydroxide aqueous solution to the above mixture, then add 312.06g of fumed silica, stir and mix for 2h to prepare a mixed slurry;

[0069] In this embodiment, the molar ratio of SiO2:Cr:EDA:ROH:H2O in the mixed slurry is 100.0:7.0:24.0:14.0:1600.0.

[0070] (2) The mixed slurry obtained in step (1) is transferred to a hydrothermal crystallization kettle and crystallized for 72 hours at a reaction temperature of 170°C and a stirring speed of 120 rpm to obtain the crystallized slurry. After filtration and washing with water until the pH is 7-8, it is dried at a drying temperature of 100°C for 16 hours. Then, under the conditions of an air flow rate of 7 L / min and a heating rate of 5°C / min, it is heated to 580°C and calcined for 6 hours to obtain a rod-shaped Cr-doped Silicalite-1 catalyst.

[0071] X-ray fluorescence spectroscopy (XRF) analysis showed that the Cr content was 4.89% of the silica mass. Compared with Example 3, it can be seen that the product prepared by the one-step hydrothermal crystallization method had a greater loss of metallic Cr with the crystallization mother liquor and washing water. The propane dehydrogenation performance of the catalysts prepared in the comparative examples is shown in Tables 1 and 2.

[0072] Comparative Example 2

[0073] Similar to Example 1, the difference is that without the secondary crystallization process in step (4), the metal utilization rate is low, the catalytic activity is low, and the initial conversion rate of propane is only 19.7% (reaction for 1 hour).

[0074] Comparative Example 3

[0075] The doping metal was changed to other metals such as Fe and Ni. It was verified that only Cr doping was effective during the doping process. For example, when Fe was doped, the initial conversion rate of propane was only 10.3%, and when Ni was doped, the initial conversion rate of propane was only 9.3% (after 1 hour of reaction).

[0076] Comparative Example 4

[0077] Similar to Example 1, the difference is that in step (1), the mass fraction of tetrapropylammonium hydroxide is 25%, so the morphology of the prepared catalyst is spherical. The initial conversion rate of propane is 28.8%, and the selectivity is 71.7% (reaction for 1 hour), indicating that the effect of its use in propane dehydrogenation catalysis is reduced after the morphology is changed.

[0078] Comparative Example 5

[0079] Similar to Example 1, the difference is that in step (3), the water content of the dry adhesive material is 10%, so a molecular sieve with good crystallinity cannot be obtained.

[0080] Comparative Example 6

[0081] Similar to Example 1, the difference is that in step (3), the water content of the dry adhesive material is 30%, so a molecular sieve with good crystallinity cannot be obtained, and the product is viscous.

[0082] Table 1. Activity evaluation data of the catalysts prepared in Examples 1-3 and the comparative examples for use as propane dehydrogenation catalysts.

[0083]

[0084] Note: The reaction pressure was 0.05 MPa, the reaction temperature was 580℃, and the WHSV of the propane gas feed was 8 h. -1 The performance of the catalyst in the dehydrogenation reaction was evaluated under the specified conditions.

[0085] Table 2. Stability data of the catalysts prepared in Example 3 and the comparative examples for use as propane dehydrogenation catalysts.

[0086]

[0087] Note: Propane conversion and selectivity data are taken at the 16th hour after propane is introduced and the reaction time is 17 hours after each regeneration.

[0088] The embodiments described are merely illustrative of the technical concept and features of the present invention, intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. The application of a rod-shaped Cr@Silicalite-1 catalyst in the catalytic dehydrogenation of low-carbon alkanes, wherein the grain size of the rod-shaped Cr@Silicalite-1 catalyst is in the range of (0.6~2.0) μm (0.2~0.3) μm (0.05~0.15) μm (length~width~height), and the loading of metallic Cr element is 3~12% of the mass of SiO2; the preparation method of the rod-shaped Cr@Silicalite-1 catalyst includes the following steps: (1) After stirring and mixing deionized water, chromium source, ethylenediamine, template agent and silicon source evenly, a mixed slurry is obtained; (2) Transfer the mixed slurry obtained in step (1) to a crystallization kettle and carry out crystallization reaction under the conditions of reaction temperature of 150℃-180℃, stirring speed of 50~200 rpm, and reaction time of 24-96 hours; (3) The slurry obtained after crystallization reaction in step (2) is dried to obtain dry adhesive material, and the water content of the dry adhesive material is controlled to be in the range of 17~25% by mass. (4) Transfer the dry adhesive material obtained in step (3) to the dry adhesive crystallization kettle again, and carry out the dry adhesive crystallization reaction at a reaction temperature of 150℃-180℃ and a reaction time of 24-96 hours. (5) The crystallized product obtained in (4) was dried, shaped, and oxidized and calcined in air to obtain a rod-shaped Cr@Silicalite-1 catalyst. In step (1), the silicon source in the mixed slurry is SiO2, and the molar ratio of SiO2:Cr:EDA:ROH:H2O is 100.0:(3.5~13.9):(10.0~40.0):(7.0~21.0):(1400.0~1800.0), where Cr is the chromium content in the chromium source, EDA is ethylenediamine, and a 25~35% tripropylethylammonium hydroxide aqueous solution is used as a template agent.

2. The application according to claim 1, characterized in that, In step (1), the chromium source is either chromium nitrate or chromium hydroxide; the silicon source is fumed silica.

3. The application according to claim 1, characterized in that, The drying temperature in step (3) is 70-90℃.

4. The application according to claim 1, characterized in that, In step (5), the drying temperature is 90-120℃ and the drying time is 12-24 hours.

5. The application according to claim 1, characterized in that, In step (5), the oxidation calcination temperature under air atmosphere is 550~600℃, the holding time is 3~9h, and the calcination is carried out under flowing air atmosphere with an air flow rate of 3~10L / min.

6. According to claim 1, after 1 h of dehydrogenation reaction of the rod-shaped Cr@Silicalite-1 catalyst, the selectivity of low-carbon olefins is 89%~91% and the conversion rate of low-carbon alkanes is 37%~42%. After 17 h of dehydrogenation reaction, the selectivity of low-carbon olefins is 92%~94% and the conversion rate of low-carbon alkanes is 31%~36%.

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