Pt / beta molecular sieve catalyst, preparation method thereof and application of Pt / beta molecular sieve catalyst in isobutane normalization

Abstract

This invention discloses a Pt / Beta molecular sieve catalyst, its preparation method, and its application in the normalization of isobutane, belonging to the field of molecular sieve catalyst technology. The Pt / Beta molecular sieve catalyst comprises a Beta molecular sieve and an active metal component Pt supported thereon, with a total acid content of 0.85~1 mmol / g, and strong acids accounting for 20~50% of the total acid content. This invention regulates the Al distribution on the surface of the H-Beta molecular sieve through programmed temperature-controlled calcination, allowing precise adjustment of the ratio of tetracoordinate framework aluminum (AlO4) to penta / hexacoordinate non-framework aluminum (AlO5 / AlO6), thereby optimizing the ratio of Brønsted acid sites to Lewis acid sites and achieving synergistic catalysis between metal Pt sites and acidic sites. This catalyst avoids the use of chlorine and is suitable for use at 300~400℃, 2.0 MPa, and an isobutane mass hourly space velocity of 2 h⁻¹. ‑1 Under the condition of a hydrogen-to-hydrocarbon ratio of 5.5, the selectivity of n-butane in the low-temperature region can reach about 80%, and the yield of n-butane in the high-temperature region can reach more than 34%, which has good prospects for industrial application.

Description

Technical Field

[0001] This invention belongs to the field of molecular sieve catalyst technology, specifically relating to a Pt / Beta molecular sieve catalyst, its preparation method, and its application in the isobutane normalization. Background Technology

[0002] Isobutane n-assembly is a crucial process for converting low-octane branched alkanes into straight-chain n-butane. n-Butane is an important feedstock for the production of maleic anhydride and ethylene cracking, possessing significant economic value. Currently, the widely used catalyst in industry is the Pt-Cl / Al₂O₃ system. This system, with its high dehydrogenation activity and acidic centers, can achieve high isobutane conversion and n-butane yield at relatively low temperatures. However, this system relies on halogens (chlorine) to maintain sufficient strong acid sites. The presence of chlorine easily causes equipment corrosion and rapid catalyst deactivation, and the regeneration process is complex, failing to meet the requirements of green chemistry and sustainable development. Therefore, developing chlorine-free, stable, and highly selective alternative catalysts has become a research hotspot.

[0003] Supported Pt catalysts based on molecular sieves show promising application prospects due to the avoidance of halogen use. Beta molecular sieves possess a three-dimensional twelve-membered ring cross-channel structure, and their proton-type H-Beta molecular sieves simultaneously possess Brønsted and Lewis acid sites on their surface. These two types of acidic sites play protonation and deprotonation, and dehydrogenation and hydrogenation functions, respectively, in alkane skeleton isomerization reactions. Studies have shown that the type, intensity, and density of acidic sites directly affect the reaction pathway and the extent of side reactions in isobutane normalization. However, current technologies mainly focus on the silica-alumina ratio and total acid content of molecular sieves, lacking systematic research on the intrinsic relationship between the placement of surface Al (i.e., the relative distribution of tetracoordinated framework Al and pentacoordinate / hexacoordinated non-framework Al) and the ratio of acidic sites. Currently, there is no clear technical solution for actively controlling the surface Al distribution of H-Beta molecular sieves during the preparation process to optimize the Brønsted / Lewis acid site ratio and achieve synergistic catalysis between metal Pt sites and acidic sites.

[0004] In existing preparation methods, the calcination step is mainly used to remove template agents and stabilize the framework structure. The calcination temperature is mostly selected based on conventional experience, without recognizing its significant impact on surface Al migration, dealumination, and redistribution, and even less so as a means to regulate the acid site ratio to improve the isobutane n-assembly reaction performance. This application addresses these shortcomings by providing a method for preparing a Pt / Beta catalyst that regulates surface Al distribution through programmed temperature-controlled calcination, thereby optimizing the acid site ratio. The resulting catalyst exhibits high n-butane selectivity and yield in the isobutane n-assembly reaction and avoids the use of chlorine, demonstrating potential for industrial application. Summary of the Invention

[0005] The technical problem to be solved by this invention is to provide a Pt / Beta molecular sieve catalyst that does not require the use of chlorine and optimizes the acid site ratio by controlling the surface Al distribution through programmed temperature-controlled calcination, thus addressing the shortcomings of existing technologies that rely on the difficulty of actively controlling the ratio of chlorine and acid sites.

[0006] Another technical problem to be solved by the present invention is to provide a method for preparing the above-mentioned Pt / Beta molecular sieve catalyst.

[0007] The final technical problem to be solved by this invention is to provide the application of the above-mentioned Pt / Beta molecular sieve catalyst in the isobutane normalization.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0009] The first aspect of the present invention provides a Pt / Beta molecular sieve catalyst, the Pt / Beta molecular sieve catalyst comprising a Beta molecular sieve and an active metal component Pt supported on the Beta molecular sieve;

[0010] The catalyst contains 0.85 to 1 mmol / g of total acid, with strong acids accounting for 20 to 50% of the total acid content.

[0011] In some embodiments, the total acid content in the catalyst is 0.879 to 0.994 mmol / g, and strong acids account for 23.5 to 43.8% of the total acid content.

[0012] In some embodiments, the catalyst has a total acid content of 0.898 mmol / g, with strong acids accounting for 32% of the total acid content.

[0013] In the Pt / Beta molecular sieve catalyst, the Pt loading is 0.03 ~ 0.06 wt%, and the molar ratio of SiO2 to Al2O3 is 10 ~ 20 : 1.

[0014] In some embodiments, the Pt / Beta molecular sieve catalyst has a Pt loading of 0.03 to 0.05 wt% and a SiO2 to Al2O3 molar ratio of 14 to 16:1.

[0015] In some embodiments, the Pt / Beta molecular sieve catalyst has a Pt loading of 0.4 wt% and a SiO2 to Al2O3 molar ratio of 15:1.

[0016] The specific surface area of ​​the Pt / Beta molecular sieve catalyst is 350~500 m². 2 / g, with an average pore size of 2.5~3.5 nm and a pore volume of 0.12~0.15 cm³.3 / g.

[0017] In some embodiments, the specific surface area of ​​the Pt / Beta molecular sieve catalyst is 450~460 m². 2 / g, with an average pore size of 2.8 ~ 3.0 nm and a pore volume of 0.14 ~ 0.15 cm³. 3 / g.

[0018] In some embodiments, the specific surface area of ​​the Pt / Beta molecular sieve catalyst is 456 m². 2 / g, with an average pore size of 2.89 nm and a pore volume of 0.14 cm³. 3 / g.

[0019] A second aspect of this invention provides a method for preparing a Pt / Beta molecular sieve catalyst, comprising the following steps:

[0020] Step 1: Dissolve sodium hydroxide in tetraethylammonium hydroxide solution, add sodium aluminate, mix well to obtain the first mixture, add silica gel, chloroplatinic acid solution and ethylenediamine, carry out the first reaction to obtain the first reaction solution, and perform hydrothermal treatment to obtain Pt / Na-Beta molecular sieve.

[0021] Step 2: The Pt / Na-Beta molecular sieve prepared in Step 1 is subjected to a first calcination to obtain a Pt / Na-Beta molecular sieve with regulated surface Al distribution. The Pt / Na-Beta molecular sieve with regulated surface Al distribution is then subjected to ammonium exchange to obtain a Pt / NH4-Beta molecular sieve.

[0022] Step 3: The Pt / NH4-Beta molecular sieve prepared in step 2 is subjected to a second calcination to obtain the final product.

[0023] In step 1, the tetraethylammonium hydroxide solution is in water as the solvent, with a concentration of 20-30 wt%; the mass ratio of sodium hydroxide to tetraethylammonium hydroxide in the tetraethylammonium hydroxide solution is 1:(10-15); the silica gel has a mesh size of 100-200 mesh; the mass ratio of silica gel to tetraethylammonium hydroxide in the tetraethylammonium hydroxide solution is 1:(1-1.5); the chloroplatinic acid solution is in water as the solvent, with a concentration of 7-9 wt%; the amount of chloroplatinic acid solution used is controlled such that the mass ratio of chloroplatinic acid to tetraethylammonium hydroxide in the tetraethylammonium hydroxide solution is 1:(1560-1565), and the molar ratio of chloroplatinic acid to ethylenediamine is 1:(50-55); the first reaction is carried out under the following conditions: stirring at a temperature of 70-90°C for 2-4 hours; the hydrothermal treatment is carried out under the following conditions: temperature of 130-160°C, time of 24-30 hours. 72 h.

[0024] In some embodiments, in step 1, the concentration of the tetraethylammonium hydroxide solution is 25 wt%; the mass ratio of sodium hydroxide to tetraethylammonium hydroxide in the tetraethylammonium hydroxide solution is 1:12.5; the mesh size of the silica gel is 100-200 mesh; the mass ratio of silica gel to tetraethylammonium hydroxide in the tetraethylammonium hydroxide solution is 1:1.25; the chloroplatinic acid solution is water in solvent and has a concentration of 8 wt%; the amount of chloroplatinic acid solution used is controlled such that the mass ratio of chloroplatinic acid to tetraethylammonium hydroxide in the tetraethylammonium hydroxide solution is 1:1562.5, and the molar ratio of chloroplatinic acid to ethylenediamine is 1:51; the first reaction is carried out under the following conditions: stirring at 80°C for 3 h; the hydrothermal treatment is carried out under the following conditions: temperature of 130-150°C and time of 36-48 h.

[0025] In some embodiments, the hydrothermal treatment is performed under the following conditions: a temperature of 150°C and a time of 48 h.

[0026] In some embodiments, before adding silica gel, chloroplatinic acid and ethylenediamine to the first mixture in step 1, the first mixture is filtered to remove undissolved aluminum hydroxide, carbonates and metal impurities, to obtain a uniform and clear alkaline mother liquor.

[0027] In some embodiments, in step 1, after the first reaction solution undergoes hydrothermal treatment, the resulting solid product is washed and dried to obtain the Pt / Na-Beta molecular sieve. In some embodiments, the washing is performed with water; the drying is carried out at a temperature of 80°C for 12 hours.

[0028] In step 2, the first calcination is carried out under the following conditions: a heating rate of 2 to 10 °C / min, an air atmosphere, and calcination at 500 to 700 °C for 3 to 5 h; the ammonium exchange is carried out by adding the Pt / Na-Beta molecular sieve with regulated surface Al distribution to an ammonium salt solution to carry out an ion exchange reaction, and washing and drying the resulting solid product to obtain the Pt / NH4-Beta molecular sieve.

[0029] In some embodiments, in step 2, the first calcination is carried out under the following conditions: a heating rate of 5°C / min, an air atmosphere, and calcination at 600°C for 4 hours.

[0030] In some embodiments, in step 2, the ammonium salt solution is an ammonium chloride solution, and the ammonium salt solution contains NH4+. +The concentration is 1 mol / L; the mass ratio of the Pt / Beta molecular sieve with regulated surface Al distribution to the volume of the ammonium salt solution is 1 g : 10 mL.

[0031] In some embodiments, step 2 involves repeating the ammonium exchange reaction 2 to 4 times. Specifically, the Na-Beta molecular sieve with regulated surface Al distribution is added to an ammonium salt solution for the first ion exchange reaction. The resulting solid product is then washed, dried, and added back to the ammonium salt solution for the next ion exchange reaction. This process is repeated 2 to 4 times. The washing is performed with water, and the drying is carried out at 80°C for 12 hours.

[0032] In some embodiments, the ion exchange reaction is carried out under the following conditions: a temperature of 70-90°C and a stirring period of 7-9 h.

[0033] In step 3, the second calcination is carried out under the following conditions: calcination at 500-700°C for 1-3 hours in a mixed atmosphere of hydrogen and nitrogen.

[0034] In some embodiments, in step 3, the heating rate of the second calcination is 2 ~ 10 °C / min.

[0035] In some embodiments, in step 3, the heating rate of the second calcination is 5°C / min.

[0036] In some embodiments, in step 3, the second calcination is carried out under the following conditions: calcination at 600°C for 2 hours in a mixed atmosphere of hydrogen and nitrogen.

[0037] In some embodiments, the hydrogen gas component in the hydrogen and nitrogen mixed atmosphere is 5%.

[0038] The third aspect of this invention provides the application of the aforementioned Pt / Beta molecular sieve catalyst in the isobutane normalization.

[0039] The method for the normalization of isobutane using the Pt / Beta molecular sieve catalyst includes the following steps: under hydrogen-exposed conditions, isobutane is contacted with the Pt / Beta molecular sieve catalyst to carry out the normalization reaction.

[0040] The ortho-configuration reaction is carried out under the following conditions: reaction temperature 300-400℃, reaction pressure (1.0-3.0) MPa, and isobutane mass hourly space velocity (WHSV) 1-3 h⁻¹. -1 The hydrogen-hydrogen molar ratio is (4.5 ~ 6.5): 1.

[0041] In some embodiments, the normalization reaction is carried out under the following conditions: reaction temperature 400°C, reaction pressure 2 MPa, and isobutane mass hourly space velocity 2 h⁻¹. -1 The hydrogen-to-hydrogen molar ratio is 5.5:1.

[0042] Beneficial effects:

[0043] (1) This invention actively regulates the surface Al distribution of H-Beta molecular sieves through programmed temperature-controlled calcination, thereby adjusting the ratio of tetracoordinated framework aluminum (AlO4) to pentacoordinated / hexacoordinated non-framework aluminum (AlO5 / AlO6), thus optimizing the acidity of the catalyst, especially the ratio of Brønsted acid sites to Lewis acid sites. An appropriate amount of Lewis acid sites and metal Pt sites synergistically promote the initial dehydrogenation of isobutane, while sufficient Brønsted acid sites facilitate the effective protonation and framework rearrangement of isobutene intermediates, thereby improving the selectivity of n-butane and inhibiting side reactions such as cracking, oligomerization, and carbon deposition.

[0044] (2) The catalyst of this invention is a chlorine-free system, avoiding the equipment corrosion and environmental pollution problems caused by the use of chlorine in traditional Pt-Cl / Al2O3 catalysts. The Pt / Beta catalyst prepared by the method of this invention can withstand temperatures of 300~400℃, 2.0 MPa, and isobutane mass hourly space velocity of 2 h⁻¹. -1 Under the condition of a hydrogen-to-hydrocarbon ratio of 5.5, the selectivity of n-butane in the low-temperature region can reach about 80%, and the yield of n-butane in the high-temperature region can reach more than 34%, which has good prospects for industrial application. Attached Figure Description

[0045] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0046] Figure 1 The XRD patterns are of the Pt / Beta molecular sieve catalysts prepared in Examples 1 to 3 and the unsupported Pt H-Beta molecular sieve prepared in Comparative Example 1.

[0047] Figure 2 TEM image and STEM-EDS elemental distribution map of the Pt / Beta-2 molecular sieve catalyst prepared in Example 1.

[0048] Figure 3 Pt / Beta molecular sieve catalysts with different surface Al distributions prepared in Examples 1 to 3 27 Al MAS NMR spectrum.

[0049] Figure 4 The NH3-TPD spectra of Pt / Beta molecular sieve catalysts with different surface Al distributions prepared in Examples 1 to 3 are shown.

[0050] Figure 5 The isobutane conversion rate varies with temperature in the isobutane ortho-configuration reaction of different catalysts in Example 5.

[0051] Figure 6 The n-butane selectivity of different catalysts in the isobutane n-assembly reaction as a function of temperature is shown in Example 5.

[0052] Figure 7 The n-butane yield varies with temperature in the isobutane n-assembly reaction of different catalysts in Example 5. Detailed Implementation

[0053] The present invention will be further described below with reference to the following embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the present invention.

[0054] Example 1

[0055] This embodiment provides a method for preparing a Pt / Beta molecular sieve catalyst, including the following steps:

[0056] (1) Add 0.5 g of sodium hydroxide to 25 g of 25% tetraethylammonium hydroxide aqueous solution and stir until dissolved. Add 0.8 g of sodium aluminate and stir until dissolved. After filtration, slowly add 5.0 g of silica gel (100~200 mesh), 0.05 g of chloroplatinic acid aqueous solution (chloroplatinic acid concentration of 8 wt%) and 0.03 g of ethylenediamine under stirring. Stir continuously in a constant temperature oil bath at 80℃ for 2 h. Transfer the resulting mixture to a 100 mL polytetrafluoroethylene-lined reactor and hydrothermally treat it at 150℃ for 48 h. Wash the solid product with deionized water until the washing waste liquid is neutral. Dry it at 80℃ for 12 h to obtain Pt / Na-Beta molecular sieve.

[0057] (2) The Pt / Na-Beta molecular sieve obtained in step (1) was placed in a muffle furnace and heated to 600°C at a heating rate of 5°C / min, and calcined in air atmosphere for 4 h.

[0058] (3) Take 2 g of the Pt / Na-Beta molecular sieve after calcination in step (2) and place it in 100 mL of ammonium chloride solution with a concentration of 1 mol / L. Perform ion exchange for 8 h under constant temperature oil bath stirring at 80℃. After washing the solid product with deionized water 3 times, dry it at 80℃ for 12 h. Repeat the above ion exchange operation 3 times to obtain Pt / NH4-Beta molecular sieve.

[0059] (4) The Pt / NH4-Beta molecular sieve obtained in step (3) is ground and placed in a muffle furnace. The temperature is raised to 600°C at a rate of 5°C / min and calcined for 4 h in a mixed atmosphere of hydrogen and nitrogen to obtain Pt / Beta molecular sieve, which is denoted as Pt / Beta-2.

[0060] The Pt / Beta molecular sieve prepared in this embodiment has an actual Pt loading of 0.04 wt% and a specific surface area of ​​449 m². 2 / g, pore volume 0.14 cm 3 / g, with an average pore size of 3.0 nm and a silicon-to-aluminum ratio (molar ratio of silicon dioxide to aluminum oxide) of 15:1.

[0061] Example 2

[0062] This embodiment provides a method for preparing a Pt / Beta molecular sieve catalyst. The only difference between this method and Example 1 is that the calcination temperature in steps (2) and (4) of this embodiment is 500°C. The resulting catalyst is designated as Pt / Beta-1.

[0063] The Pt / Beta molecular sieve prepared in this embodiment has an actual Pt loading of 0.03 wt% and a specific surface area of ​​456 m². 2 / g, pore volume 0.14 cm 3 / g, with an average pore size of 2.89 nm and a silicon-to-aluminum ratio (molar ratio of silicon dioxide to aluminum oxide) of 15:1.

[0064] Example 3

[0065] This embodiment provides a method for preparing a Pt / Beta molecular sieve catalyst. The only difference between this method and Example 1 is that the calcination temperature in steps (2) and (4) is 700°C. The resulting catalyst is designated as Pt / Beta-3.

[0066] The Pt / Beta molecular sieve prepared in this embodiment has an actual Pt loading of 0.043 wt% and a specific surface area of ​​400 m². 2 / g, pore volume is 0.13 cm³ 3 / g, with an average pore size of 3.2 nm and a silicon-to-aluminum ratio (molar ratio of silicon dioxide to aluminum oxide) of 15:1.

[0067] Comparative Example 1

[0068] This comparative example provides a method for preparing Pt-unloaded H-Beta molecular sieves, including the following steps:

[0069] (1) Add 0.5 g of sodium hydroxide to 25 g of 25% tetraethylammonium hydroxide aqueous solution and stir until dissolved. Add 0.8 g of sodium aluminate and stir until dissolved. After filtration, slowly add 5.0 g of silica gel (100~200 mesh) under stirring. Stir continuously in an oil bath at 80℃ for 3 h. Transfer the resulting mixture to a 100 mL polytetrafluoroethylene-lined reactor and hydrothermally treat it at 150℃ for 48 h. Wash the product with deionized water until the washing waste liquid is neutral. Dry it at 80℃ for 12 h to obtain Na-Beta molecular sieve.

[0070] (2) The obtained Na-Beta molecular sieve was placed in a muffle furnace and heated to 600°C at a heating rate of 5°C / min, and calcined in air atmosphere for 4 h.

[0071] (3) Ammonium exchange was performed in the same manner as in step (3) of Example 1 to obtain NH4-Beta molecular sieve;

[0072] (4) After grinding the NH4-Beta molecular sieve, place it in a muffle furnace and heat it to 600°C at a heating rate of 5°C / min. Then, calcine it for 4 h in a mixed atmosphere of hydrogen and nitrogen to obtain H-Beta molecular sieve.

[0073] Example 4

[0074] The catalysts obtained in Examples 1 to 3 and the H-Beta molecular sieve obtained in Comparative Example 1 were characterized by the following tests:

[0075] (1) X-ray diffraction (XRD): Figure 1 The XRD patterns are shown for the Pt / Beta molecular sieve catalysts prepared in Examples 1 to 3 and the unsupported Pt H-Beta molecular sieve prepared in Comparative Example 1. Figure 1 As shown, all samples exhibited characteristic H-Beta diffraction peaks at 2θ of 7.76° and 22.30°, indicating that each sample possesses a complete Beta molecular sieve framework structure, and calcination at different temperatures did not disrupt the crystalline structure of the molecular sieve. No characteristic Pt diffraction peaks were observed in any sample, indicating that the Pt particles were highly dispersed on the support, and their particle size was smaller than the detection limit of XRD.

[0076] (2) Transmission electron microscopy (TEM): Figure 2 TEM images and STEM-EDS elemental distribution maps of the Pt / Beta-2 molecular sieve catalyst prepared in Example 1. Figure 2 As shown, Pt particles are uniformly dispersed on the surface of the Beta molecular sieve support, with uniform particle size and no obvious particle aggregation. The STEM-EDS elemental distribution map shows that Pt elements are uniformly distributed throughout the catalyst particle surface, which is consistent with the XRD characterization results.

[0077] (3) 27 Al solid-state nuclear magnetic resonance ( 27 Al MAS NMR): Figure 3 The Pt / Beta molecular sieve catalysts prepared in Examples 1 to 3 27 Al MAS NMR spectrum. (See image) Figure 3 As shown, the main peak at approximately 55 ppm corresponds to tetracoordinate framework aluminum (AlO4, i.e., framework aluminum), while the weak peaks at approximately 35 ppm and 0 ppm correspond to pentacoordinate non-framework aluminum (AlO5) and hexacoordinate non-framework aluminum (AlO6), respectively. As the calcination temperature increases from 500℃ to 700℃, the ratio of the AlO4 peak area to the AlO5 or AlO6 peak area gradually decreases, indicating that increasing the calcination temperature promotes the removal of framework aluminum and the formation of non-framework aluminum, meaning that the Al distribution on the catalyst surface is effectively regulated. Tetracoordinate framework aluminum is the main source of Brønsted acid active sites, while pentacoordinate / hexacoordinate non-framework aluminum is associated with Lewis acid sites.

[0078] (4) Ammonia temperature-programmed desorption (NH3-TPD): Figure 4 The NH3-TPD spectra of the Pt / Beta molecular sieve catalysts prepared in Examples 1 to 3 are shown. The acid content distribution of the molecular sieve catalysts prepared in each example is shown in Table 1. Figure 4 As shown in Table 1, with increasing calcination temperature (from Pt / Beta-1 to Pt / Beta-2 to Pt / Beta-3), the desorption peak area of ​​weak acids below 430℃ gradually decreases, while the desorption peak area of ​​strong acids above 430℃ but below 800℃ gradually increases, resulting in a decreasing total acid content. The weak acid sites are mainly attributed to Lewis acid sites (originating from non-framework aluminum), and the strong acid sites are mainly attributed to Brønsted acid sites (originating from framework aluminum). Figure 3 As shown 27 Al MAS NMR results showed that increasing the calcination temperature caused some skeletal aluminum to be removed and transformed into non-skeletal aluminum, accompanied by dehydroxylation and structural rearrangement, which transformed some weak Lewis acid sites into stronger acid sites, resulting in a significant change in the acid site ratio.

[0079] Table 1. Acidity distribution of catalysts prepared in Examples 1-3

[0080]

[0081] Example 5

[0082] A fixed-bed reactor was used, with 3.0 g (20-40 mesh) each of the Pt / Beta molecular sieve catalysts obtained in Examples 1 to 3 and the H-Beta molecular sieve catalyst obtained in Comparative Example 1. Isobutane was used as the reactant, and the n-assembly reaction was carried out under hydrogen-induced conditions. The reaction conditions were: reaction temperature 300-400℃ (programmed temperature increase at equal intervals), reaction pressure 2.0 MPa, and isobutane mass hourly space velocity 2 h⁻¹. -1 The hydrogen-to-hydrocarbon molar ratio was 5.5. The product was analyzed online using a GC8690A gas chromatograph.

[0083] The relationships between isobutane conversion, n-butane selectivity, and n-butane yield of each catalyst at different reaction temperatures are as follows: Figures 5 to 7 As shown, the isobutane conversion of all catalysts increased with increasing reaction temperature; at the same reaction temperature, the sample with a lower calcination temperature (Pt / Beta-1) exhibited a higher isobutane conversion. The n-butane selectivity initially increased and then decreased with increasing reaction temperature; at reaction temperatures of 340–360 °C, the n-butane selectivity of the Pt / Beta-2 catalyst was higher than that of Pt / Beta-1, Pt / Beta-3, and H-Beta. Regarding n-butane yield, the Pt / Beta-2 catalyst was higher than Pt / Beta-3 throughout the entire reaction temperature range, and also higher than Pt / Beta-1 in the high-temperature region (approximately 400 °C). Compared to the unsupported Pt H-Beta, the conversion rate of H-Beta was higher than that of Pt / Beta-2 in the low-temperature region, while the conversion rate and n-butane yield of Pt / Beta-2 were superior to those of H-Beta in the high-temperature region (approximately 400 °C). Taking into account both n-butane selectivity and yield, the Pt / Beta-2 catalyst (obtained by calcination at 600℃) exhibits the best isobutane n-assembly performance.

[0084] This invention provides a Pt / Beta molecular sieve catalyst, its preparation method, and its application in the isobutane normalization process. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. A Pt / Beta molecular sieve catalyst, characterized in that, The Pt / Beta molecular sieve catalyst comprises a Beta molecular sieve and an active metal component Pt supported on the Beta molecular sieve. The catalyst contains 0.85 to 1 mmol / g of total acid, with strong acids accounting for 20 to 50% of the total acid content.

2. The Pt / Beta molecular sieve catalyst according to claim 1, characterized in that, The catalyst contains 0.879 to 0.994 mmol / g of total acid, with strong acids accounting for 23.5 to 43.8% of the total acid content.

3. The Pt / Beta molecular sieve catalyst according to claim 2, characterized in that, The catalyst contains 0.898 mmol / g of total acid, with strong acids accounting for 32% of the total acid content.

4. The Pt / Beta molecular sieve catalyst according to claim 1, characterized in that, In the Pt / Beta molecular sieve catalyst, the Pt loading is 0.03 ~ 0.06 wt%, and the molar ratio of SiO2 to Al2O3 is 10 ~ 20 :

1.

5. The Pt / Beta molecular sieve catalyst according to claim 1, characterized in that, The specific surface area of ​​the Pt / Beta molecular sieve catalyst is 350~500 m². 2 / g, with an average pore size of 2.5 ~ 3.5 nm and a pore volume of 0.12 ~ 0.15 cm³. 3 / g.

6. The method for preparing the Pt / Beta molecular sieve catalyst according to any one of claims 1 to 5, characterized in that, Includes the following steps: Step 1: Dissolve sodium hydroxide in tetraethylammonium hydroxide solution, add sodium aluminate, mix well to obtain the first mixture, add silica gel, chloroplatinic acid solution and ethylenediamine, carry out the first reaction to obtain the first reaction solution, and perform hydrothermal treatment to obtain Pt / Na-Beta molecular sieve. Step 2: The Pt / Na-Beta molecular sieve prepared in Step 1 is subjected to a first calcination to obtain a Pt / Na-Beta molecular sieve with regulated surface Al distribution. The Pt / Na-Beta molecular sieve with regulated surface Al distribution is then subjected to ammonium exchange to obtain a Pt / NH4-Beta molecular sieve. Step 3: The Pt / NH4-Beta molecular sieve prepared in step 2 is subjected to a second calcination to obtain the final product.

7. The preparation method according to claim 6, characterized in that, In step 1, the tetraethylammonium hydroxide solution is in water as the solvent, with a concentration of 20-30 wt%; the mass ratio of sodium hydroxide to tetraethylammonium hydroxide in the tetraethylammonium hydroxide solution is 1:(10-15); the silica gel has a mesh size of 100-200 mesh; the mass ratio of silica gel to tetraethylammonium hydroxide in the tetraethylammonium hydroxide solution is 1:(1-1.5); the chloroplatinic acid solution is in water as the solvent, with a concentration of 7-9 wt%; the amount of chloroplatinic acid solution used is controlled such that the mass ratio of chloroplatinic acid to tetraethylammonium hydroxide in the tetraethylammonium hydroxide solution is 1:(1560-1565), and the molar ratio of chloroplatinic acid to ethylenediamine is 1:(50-55); the first reaction is carried out under the following conditions: stirring at a temperature of 70-90°C for 2-4 hours; the hydrothermal treatment is carried out under the following conditions: temperature of 130-160°C, time of 24-30 hours. 72 h.

8. The preparation method according to claim 6, characterized in that, In step 2, the first calcination is carried out under the following conditions: a heating rate of 2 to 10 °C / min, an air atmosphere, and calcination at 500 to 700 °C for 3 to 5 hours; the ammonium exchange is carried out by adding the Pt / Na-Beta molecular sieve with regulated surface Al distribution to an ammonium salt solution to carry out an ion exchange reaction, and washing and drying the resulting solid product to obtain the Pt / NH4-Beta molecular sieve.

9. The preparation method according to claim 6, characterized in that, In step 3, the second calcination is carried out under the following conditions: a heating rate of 2 to 10 °C / min, a mixed atmosphere of hydrogen and nitrogen, and calcination at 500 to 700 °C for 1 to 3 hours.

10. The use of the Pt / Beta molecular sieve catalyst according to any one of claims 1 to 5 in the normalization of isobutane.

11. The application according to claim 10, characterized in that, The method for the normalization of isobutane using the Pt / Beta molecular sieve catalyst includes: contacting isobutane with the Pt / Beta molecular sieve catalyst under hydrogen conditions to carry out the normalization reaction.

12. The application according to claim 11, characterized in that, The normalization reaction is carried out under the following conditions: reaction temperature 300-400℃, reaction pressure 1.0-3.0 MPa, and isobutane mass hourly space velocity (WHSV) 1-3 h⁻¹. -1 The hydrogen-hydrogen molar ratio is (4.5 ~ 6.5): 1.

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