A method for preparing a zeolite molecular sieve-supported platinum-tin catalyst and its application in propane dehydrogenation.

Abstract

This invention discloses a method for preparing a platinum-tin catalyst supported on a zeolite molecular sieve and its application in propane dehydrogenation. Unlike traditional methods that use strong acids to remove aluminum from the zeolite molecular sieve framework to create silanol nests for supporting platinum-tin components, this invention prepares a supported platinum-tin catalyst through a combination of high-temperature calcination and boiling water washing with equal-volume impregnation of the borosilicate molecular sieve. This catalyst exhibits superior conversion rate, product selectivity, and stability in the propane dehydrogenation reaction. The preparation method disclosed in this invention is simple to operate, highly applicable, and the process of high-temperature calcination, boiling water washing, and equal-volume impregnation is low-cost, pollution-free, and emission-free, overcoming the shortcomings of traditional technical routes in terms of environment, safety, and economy.

Description

Technical Field

[0001] This invention belongs to the field of chemical catalysis technology, specifically relating to a method for preparing a zeolite molecular sieve-supported platinum-tin catalyst and its application in propane dehydrogenation. Background Technology

[0002] Propylene is a basic petrochemical feedstock, traditionally produced by naphtha thermal cracking or catalytic cracking processes. Propane catalytic dehydrogenation is another important industrial route for increasing propylene production. Currently, the catalysts used in propane dehydrogenation mainly include platinum-based and chromium oxide-based catalysts. Chromium oxide-based catalysts are severely limited due to their environmental hazards and pollution. While alumina-supported platinum-tin catalysts are widely used due to their superior performance and environmental friendliness, they still suffer from the drawback of being prone to sintering and deactivation under harsh operating conditions. Therefore, improving the stability and extending the service life of platinum-tin catalysts remains a pressing technical challenge in this field.

[0003] Zeolite molecular sieves are a class of crystalline aluminosilicate minerals with nanoscale ordered pore structures, exhibiting high thermal and chemical stability. Their use for dispersing and immobilizing noble metal particles, and for enhancing reactivity and stability, has long been a focus of scientific research. For propane dehydrogenation, Corma et al. in-situ encapsulated platinum-tin nanoclusters within the pores of molecular sieves such as MCM-22 and ZSM-5, improving the stability and regeneration performance of the propane dehydrogenation reaction (Nat. Mater., 2019, 18, 866). Recent studies indicate that, in addition to the physical confinement characteristics of the molecular sieve pores, the chemical immobilization force of silanol nest defects in the molecular sieve framework plays a more crucial role in dispersing and stabilizing active components. Ryoo et al. created silanol nests by removing heteroatoms from the molecular sieve framework, promoting the formation of alloys between platinum and rare earth elements, which exhibited high stability, activity, and selectivity in the propane dehydrogenation reaction (Nature, 2020, 585, 221). Bell et al. prepared a platinum-zinc catalyst by removing framework aluminum from Beta molecular sieves to create silanol nests, which showed high reactivity and good stability (JACS, 2021, 143, 21364).

[0004] As mentioned above, existing techniques for preparing silanol nest defects in zeolites mainly focus on high-temperature washing with strong acids or bases, with strong acid removal of aluminum from the zeolite molecular sieve framework being the most common method. However, the use of large amounts of strong acid solutions and multiple high-temperature washing processes, along with the emission of large amounts of waste liquid and gas, makes large-scale industrial use unsuitable from both environmental and economic perspectives. Furthermore, heteroatomic aluminum atoms in zeolites are firmly bonded to the framework and difficult to remove; even high-temperature washing with strong acids cannot completely remove the framework aluminum. Therefore, protonated acid sites remain on the zeolite molecular sieve support after treatment, which can exacerbate carbon deposition side reactions in propane dehydrogenation. Therefore, there is an urgent need to develop new, low-cost, easy-to-operate, pollution-free methods for preparing silanol nest defects in zeolites. Summary of the Invention

[0005] To address the above technical challenges, this invention proposes a method for preparing a supported platinum-tin catalyst using high-temperature calcination combined with boiling water washing of borosilicate molecular sieves, followed by equal-volume impregnation. This method is applied to propane dehydrogenation. Compared to platinum-tin catalysts prepared by traditional acid washing of molecular sieves, the catalyst prepared by the method disclosed in this invention not only improves the conversion rate, product selectivity, and reaction stability of the propane dehydrogenation reaction, but also offers advantages in terms of low cost, ease of operation, safety, and pollution-free operation, demonstrating economic and practical advantages.

[0006] To achieve the above-mentioned objectives, the present invention is implemented through the following technical solution:

[0007] A method for preparing a zeolite molecular sieve-supported platinum-tin catalyst includes the following steps:

[0008] S1 Weigh borosilicate molecular sieve powder, pre-treat it by high-temperature calcination, wash it with boiling water multiple times, filter it, and then dry it for later use.

[0009] S2 weigh out platinum precursor salt and tin precursor salt, dissolve them in ethanol to form a solution, and impregnate the powder sample obtained in step S1 with an equal volume. After standing at room temperature, drying and reduction, the zeolite molecular sieve supported platinum-tin catalyst is obtained.

[0010] The borosilicate molecular sieve described in S1 has a crystal form of *BEA, CON, MWW or MFI, and the silicon-to-boron atomic ratio is in the range of 10-100.

[0011] The roasting temperature described in S1 is 450-650℃, and the processing time is 6-12h.

[0012] The boiling water washing temperature described in S1 is 90-100℃, and the washing time is 3-6 hours.

[0013] The platinum precursor salt mentioned in S2 is one of chloroplatinic acid and tetraammine nitrate platinum, and the tin precursor salt is one of tin chloride and tin dichloride. The mass fraction of platinum in the solution is 0.1-1.0%, and the mass fraction of tin is 0.3%-3%.

[0014] The reducing atmosphere described in S2 is 20-80 vol% H2 / N2, the reduction temperature is 450-650℃, and the reduction time is 2-6h.

[0015] The present invention also provides a zeolite molecular sieve supported platinum-tin catalyst obtained by the above method.

[0016] The catalyst comprises a platinum active component, a tin additive, and a borosilicate molecular sieve support. Based on the total mass of the catalyst, the platinum active component has a mass fraction of 0.1%-1.0%, and the tin additive has a mass fraction of 0.3%-3%.

[0017] The present invention also provides an application of a zeolite molecular sieve-supported platinum-tin catalyst obtained by the above method in the dehydrogenation of propane to propylene.

[0018] The dehydrogenation reaction is carried out in a differential fixed-bed reactor at a reaction temperature of 520-620℃, a reaction pressure of 0-0.2MPa, and a total gas flow rate controlled at 10-300mL / min.

[0019] Before the reaction, the catalyst is pretreated by passing a hydrogen-nitrogen mixture through it for 1-20 hours. -1 The propane mass hourly space velocity (MHSV) is used to cut into the reaction gas, which consists of propane and nitrogen, with a propane to nitrogen flow ratio of 1:1-5. Nitrogen is the equilibrium gas.

[0020] The beneficial effects of this invention are:

[0021] Unlike traditional methods for removing platinum-tin components immobilized on the aluminum framework of zeolite molecular sieves using strong acids, this invention prepares a supported platinum-tin catalyst through a combination of high-temperature calcination and boiling water washing with equal-volume impregnation of borosilicate molecular sieves. This catalyst exhibits superior conversion, product selectivity, and reaction stability in propane dehydrogenation. This invention utilizes the physical confinement of the unique pores of zeolite molecular sieves and the chemical anchoring effect of silanol nest defects in the framework to prepare a platinum-tin catalyst with high activity and good stability. The method disclosed in this invention can replace the traditional route of creating silanol nest defects by removing aluminum framework from zeolite molecular sieves using strong acids, overcoming the shortcomings of traditional techniques in terms of environment, safety, and economy. The preparation method disclosed in this invention is simple to operate, highly applicable, and the process of high-temperature calcination, boiling water washing, and equal-volume impregnation is virtually pollution-free and emission-free. The treatment process requires almost no chemical reagents, resulting in low cost and significant economic advantages. Attached Figure Description

[0022] Figure 1This is a comparison graph showing the change in the activity of propane dehydrogenation reaction on the platinum-tin catalyst prepared in Comparative Example 1 and Example 1 of the present invention as a function of reaction time.

[0023] Figure 2 This is a comparison graph showing the change in the selectivity of propane dehydrogenation products over reaction time on the platinum-tin catalyst prepared in Comparative Example 1 and Example 1 of the present invention.

[0024] Figure 3 The X-ray diffraction (XRD) patterns of the B-MCM-22 support used in Comparative Example 2 and the MCM-22-De-B support used in Example 1 of the present invention, as well as the prepared PtSn / MCM-22-De-B catalyst, are shown. Detailed Implementation

[0025] The present invention is described below through specific embodiments, but the present invention is not limited to the following embodiments.

[0026] In the propane dehydrogenation catalytic performance test of the example, the product was analyzed online using a gas chromatograph, and the reaction conversion rate and selectivity were calculated using the normalization method based on the alkane and olefin content in the dehydrogenation product.

[0027] Comparative Example 1 (not the present invention)

[0028] (1) Weigh 200mg of zeolite molecular sieve (Al-MCM-22, silicon-aluminum atomic ratio of 12.5) powder and put it into a three-necked flask. Add 5mL of 13M nitric acid solution, heat to 80℃ under magnetic stirring, reflux with cooling water for 12h, centrifuge and wash until neutral, and dry overnight for later use.

[0029] (2) Measure 24 μL of chloroplatinic acid ethanol solution (0.04 mg / μL), mix it with 44 μL of tin dichloride ethanol solution (0.0477 mg / μL), and make up the total volume of the solution to 210 μL. Then, immerse 120 mg of acid-washed and dried aluminosilicate molecular sieve sample in an equal volume. After immersion, let the sample stand for 2 hours and then put it in a vacuum oven at 50°C to dry overnight.

[0030] (3) The dried powder sample was reduced at 550℃ and 20% hydrogen atmosphere for 2h to obtain a platinum-tin catalyst. The theoretical loading (mass fraction) of platinum in the catalyst was 0.3wt% and the theoretical loading (mass fraction) of tin was 0.9wt%. It was named PtSn / MCM-22-De-Al catalyst.

[0031] (4) 100 mg of the prepared PtSn / MCM-22-De-Al catalyst was weighed and loaded into a fixed-bed reactor. Before the reaction, a 20% hydrogen-nitrogen mixture was introduced, and the reactor was pretreated at 550 °C for 0.5 h. The reaction was carried out for 6 hours at a reaction temperature of 550 °C and 0.11 MPa under the following conditions: propane and nitrogen flow rates of 4 mL / min and 12 mL / min, respectively. The propane dehydrogenation evaluation results are shown in Table 1 and... Figure 1-2 .

[0032] Comparative Example 2 (not the present invention)

[0033] (1) Weigh 120 mg of borosilicate zeolite molecular sieve (B-MCM-22, silicon-boron atomic ratio of 12.5), measure 24 μL of chloroplatinic acid ethanol solution (0.04 mg / μL), mix with 44 μL of tin dichloride ethanol solution (0.0477 mg / μL), and bring the total volume of the solution to 210 μL. Then, impregnate the borosilicate zeolite molecular sieve with an equal volume. After impregnation, let the sample stand for 2 h and dry it overnight in an oven at 50 °C.

[0034] (2) After drying, the powder sample was reduced at 550℃ and 20% hydrogen atmosphere for 2h to obtain a platinum-tin catalyst. The theoretical loading of platinum in the obtained catalyst was 0.3wt% and the theoretical loading of tin was 0.9wt%. It was named PtSn / B-MCM-22 catalyst.

[0035] (3) Weigh 100 mg of the prepared PtSn / B-MCM-22 catalyst and load it into a fixed bed reactor. Before the reaction, introduce a 20% hydrogen-nitrogen mixture and pretreat at 550℃ for 0.5 h. React for 6 hours under the conditions of propane and nitrogen flow rates of 4 mL / min and 12 mL / min, reaction temperature of 550℃ and 0.11 MPa. The propane dehydrogenation evaluation results are shown in Table 1.

[0036] Comparative Example 3 (not the present invention)

[0037] The preparation and reaction were carried out using the method of Comparative Example 1, the only difference being that in step (1), Al-MCM-22 molecular sieve was replaced with B-MCM-22 molecular sieve (B-MCM-22, silicon-boron atomic ratio of 12.5). The resulting catalyst was named PtSn / Beta-De-B-HNO3, and the performance evaluation results are shown in Table 1.

[0038] Example 1

[0039] (1) Weigh 200 mg of borosilicate zeolite molecular sieve (B-MCM-22, silicon-boron atomic ratio of 12.5), place it in a muffle furnace, and calcine it at 550 °C for 6 h in a static air atmosphere. The heating rate is set to 5 °C / min.

[0040] (2) After calcination, the B-MCM-22 powder sample was transferred to a round-bottom flask, placed in a 90℃ constant temperature water bath, and 10mL of boiling water was added. The sample was washed for 0.5h under magnetic stirring and then filtered. This washing process was repeated 3 times. The powder was collected, dried overnight, and labeled as MCM-22-De-B for later use. The XRD pattern (…) Figure 3 The results showed that the sample maintained the typical MWW crystal phase, the pretreatment process did not damage the crystal structure of the sample, and no diffraction peaks attributable to boron oxide species were observed.

[0041] (3) Measure 24 μL of chloroplatinic acid ethanol solution (0.04 mg / μL), mix it with 44 μL of tin dichloride ethanol solution (0.0477 mg / μL), and make up the total volume of the solution to 210 μL. Then, impregnate the sample with 120 mg of MCM-22-De-B in equal volume. After impregnation, let the sample stand for 2 hours and then put it in a vacuum oven at 50°C to dry overnight.

[0042] (4) The dried powder sample was reduced at 550℃ in a 20% hydrogen atmosphere for 2 h to obtain a platinum-tin catalyst. The theoretical loading (mass fraction) of platinum in the obtained catalyst was 0.3 wt%, and the theoretical loading (mass fraction) of tin was 0.9 wt%. It was named PtSn / MCM-22-De-B catalyst. XRD spectrum ( Figure 3 The results showed that the catalyst still maintained the typical MWW crystal phase, and no characteristic peaks of platinum and tin species were observed.

[0043] (5) Weigh 100 mg of the prepared PtSn / MCM-22-De-B catalyst and load it into a fixed-bed reactor. Before the reaction, introduce a 20% hydrogen-nitrogen mixture and pretreat at 550℃ for 0.5 h. React for 6 hours at a reaction temperature of 550℃ and 0.11 MPa under the following conditions: propane and nitrogen flow rates of 4 mL / min and 12 mL / min, respectively. The propane dehydrogenation evaluation results are shown in Table 1 and... Figure 1-2 .

[0044] Compared with the catalyst prepared in Comparative Example 1, the catalyst prepared in this example exhibits superior propane conversion, propylene selectivity, and reaction stability in the propane dehydrogenation reaction, indicating that the method of preparing platinum-tin catalyst by high-temperature calcination combined with boiling water washing has significant advantages. Further comparison of the reaction data in Table 1 between this example and Comparative Example 3 shows that complete removal of the boron component from the zeolite molecular sieve is detrimental to improving reaction performance, while the framework boron component has a significant promoting effect on the propane dehydrogenation performance of the platinum-tin catalyst.

[0045] Example 2

[0046] The preparation and reaction were carried out using the method of Example 1, the only difference being that in step (1), the borosilicate zeolite molecular sieve was selected as B-Beta, the crystal form was *BEA, the silicon-boron atomic ratio was 20, and the resulting catalyst was named PtSn / Beta-De-B. The performance evaluation results are shown in Table 1.

[0047] Example 3

[0048] The preparation and reaction were carried out using the method of Example 1, the only difference being that in step (1), the borosilicate zeolite molecular sieve was selected as B-SSZ-33, the crystal form was CON, the silicon-boron atomic ratio was 30, and the resulting catalyst was named PtSn / SSZ-33-De-B. The performance evaluation results are shown in Table 1.

[0049] Example 4

[0050] The preparation and reaction were carried out using the method of Example 1, the only difference being that in step (1), the borosilicate molecular sieve was selected as B-Silicalite-1, the crystal form was MFI, the silicon-boron atomic ratio was 100, and the resulting catalyst was named PtSn / Silicalite-1-De-B. The performance evaluation results are shown in Table 1.

[0051] Example 5

[0052] The preparation and reaction were carried out using the method of Example 1, the only difference being that in step (1), the borosilicate zeolite molecular sieve was selected as B-ZSM-5, the crystal form was MFI, the silicon-boron atomic ratio was 50, and the resulting catalyst was named PtSn / ZSM-5-De-B. The performance evaluation results are shown in Table 1.

[0053] Table 1. Summary of the performance of propane catalytic dehydrogenation to propylene reaction

[0054]

Claims

1. The application of a zeolite molecular sieve-supported platinum-tin catalyst in propane dehydrogenation to propylene, characterized in that, The preparation method of platinum-tin catalyst supported on zeolite molecular sieves includes the following steps: S1 Weigh borosilicate molecular sieve powder, pre-treat it by high-temperature calcination, wash it with boiling water multiple times, filter it, and then dry it for later use. S2 Weigh platinum precursor salt and tin precursor salt, dissolve them in ethanol to form a solution, and impregnate the powder sample obtained in step S1 with an equal volume. After standing at room temperature, drying and reduction, zeolite molecular sieve supported platinum-tin catalyst is obtained. The calcination pretreatment temperature described in S1 is 450-650°C, and the treatment time is 6-12 hours. The boiling water washing temperature described in S1 is 90-100°C, and the washing time is 3-6 hours.

2. The application of the zeolite molecular sieve-supported platinum-tin catalyst according to claim 1 in the propane dehydrogenation to propylene, characterized in that: The borosilicate molecular sieve described in S1 has a crystal form of *BEA, CON, MWW or MFI, and a silicon-to-boron atomic ratio of 10-100.

3. The application of the zeolite molecular sieve-supported platinum-tin catalyst according to claim 1 in the propane dehydrogenation to propylene, characterized in that: The platinum precursor salt mentioned in S2 is chloroplatinic acid or tetraammine nitrate platinum, and the tin precursor salt is tin chloride or tin dichloride. The mass fraction of platinum in the solution is 0.1-1.0%, and the mass fraction of tin is 0.3%-3%.

4. The application of the zeolite molecular sieve-supported platinum-tin catalyst according to claim 1 in the propane dehydrogenation to propylene, characterized in that: The reducing atmosphere described in S2 is 20-80 vol% H2 / N2, the reduction temperature is 450-650°C, and the reduction time is 2-6 h.

5. The application of the zeolite molecular sieve-supported platinum-tin catalyst according to claim 1 in the propane dehydrogenation to propylene, characterized in that: The dehydrogenation reaction is carried out in a differential fixed-bed reactor at a reaction temperature of 520-620°C, a reaction pressure of 0-0.2 MPa, and a total gas flow rate controlled at 10-300 mL / min.

6. The application of the zeolite molecular sieve-supported platinum-tin catalyst according to claim 1 in the propane dehydrogenation to propylene, characterized in that: Before the reaction, the catalyst is pretreated by passing a hydrogen-nitrogen mixture through it for 1-20 hours. -1 The propane mass hourly space velocity (MHSV) is used to cut into the reaction gas, which consists of propane and nitrogen, with a propane to nitrogen flow ratio of 1:1-5. Nitrogen is the equilibrium gas.

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