A platinum-based catalyst for propane dehydrogenation to propylene and its preparation method

Abstract

The present invention relates to the field of catalysts, and discloses a platinum-based catalyst for propane dehydrogenation to propylene and a preparation method thereof. The catalyst comprises a zinc isomorphously substituted all-silicon molecular sieve carrier and a platinum nanoparticle component encapsulated in the above-mentioned carrier. The present invention uses prefabricated platinum nanoparticles as raw materials, utilizes dopamine oxidative self-polymerization to modify the surface of the platinum nanoparticles, and utilizes the active groups on the surface of polydopamine to bond zinc ions, adds the above-mentioned modified platinum nanoparticles to the all-silicon molecular sieve synthesis gel, and directly encapsulates the platinum nanoparticles and the zinc attached to the surface thereof in the molecular sieve crystal while synthesizing the molecular sieve carrier under dynamic hydrothermal conditions, thereby obtaining a platinum-based catalyst. The present invention solves the problem of poor stability of platinum-based catalysts, and the catalyst exhibits excellent performance in catalyzing the propane dehydrogenation to propylene reaction, and has the characteristics of high conversion rate, high propylene selectivity and good stability.

Description

Technical Field

[0001] The invention belongs to the technical field of catalysts, and particularly relates to a platinum-based catalyst for producing propylene by dehydrogenating propane and a preparation method thereof. Background Art

[0002] Propylene is one of the important petrochemical products and the basic raw material of the three major synthetic materials. It is the main raw material for bulk chemical products such as polypropylene, acrylonitrile, propylene oxide, and acrylic acid. At present, most of the world's propylene comes from by-products of ethylene steam cracking and catalytic cracking in refineries. In recent years, due to the growth of propylene demand and the development of shale gas, propane dehydrogenation to propylene technology (PDH) has attracted widespread attention in the industry. Compared with other olefin production technologies, PDH has the advantages of high product yield and simple route, and can produce high-value-added hydrogen as a by-product. It is considered to be a better choice to solve the growing global demand for propylene. At present, platinum-based catalysts are widely used in commercial PDH processes due to their excellent activation ability for alkane CH bonds, low CC bond cracking activity, and environmentally friendly characteristics. However, propane dehydrogenation is a strongly endothermic reversible reaction in thermodynamics. Platinum nanoparticles with high surface free energy are prone to severe sintering during high-temperature reactions, resulting in rapid deactivation of the catalyst. In addition, the high cost of platinum also hinders the application and development of platinum-based catalysts in industrial production. The process of propane dehydrogenation to propylene has been industrialized for more than 20 years, and there have been many studies on platinum-based dehydrogenation catalysts. However, the current catalysts still have defects such as low reaction activity and easy deactivation, which need to be further improved and perfected. Therefore, it is of practical significance to develop platinum-based propane dehydrogenation catalysts with excellent performance. Summary of the invention

[0003] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a platinum-based catalyst having high activity, high propylene selectivity and long life and which can be used for propane dehydrogenation reaction, as well as a preparation method and application thereof.

[0004] The present invention also provides a method for preparing a platinum-based catalyst, wherein the method comprises:

[0005] (1) Using ethanol as a reducing agent and solvent and polyvinylpyrrolidone (PVP) as a stabilizer, potassium chloroplatinite was reduced under solvothermal conditions to obtain PVP-stabilized platinum nanoparticles.

[0006] (2) The PVP-coated platinum nanoparticles obtained in (1) are dispersed in a buffer solution, a certain amount of dopamine hydrochloride is added and stirred, dopamine is oxidized and self-polymerized to form polydopamine which is coated on the surface of the platinum nanoparticles, and platinum nanoparticles coated with polydopamine are obtained. Subsequently, a certain concentration of zinc acetate aqueous solution is added, and after ultrasonic treatment for a certain period of time, the platinum nanoparticles are centrifuged and re-dispersed in a certain amount of deionized water to obtain a suspension of surface-modified platinum nanoparticles.

[0007] (3) The suspension obtained in (2) is added to the molecular sieve synthesis gel and mixed thoroughly to obtain an initial gel, and the initial gel is crystallized under dynamic hydrothermal conditions. The obtained solid product is sequentially washed, dried, and calcined to finally obtain a platinum-based catalyst.

[0008] In step (1), the solvent thermal reaction temperature is 90-130°C, the concentration of potassium chloroplatinite is 0.02-0.1 mol / L, and the concentration of PVP (MW=10000) ethanol solution is 1-5 mg / mL.

[0009] In step (2), the reaction conditions are: the pH range of the buffer solution is 8-9; the molar ratio of platinum to dopamine hydrochloride is 1:50-100; the stirring time is 1-5 h; the concentration of the zinc acetate solution is 0.05-0.2 mol / L; the ultrasonic treatment is 1-3 h; the centrifugal speed is 10000 rpm, and the centrifugal treatment time is 5-10 min.

[0010] In step (3), the concentration of the platinum nanoparticle suspension is 0.3-1 g / L, and the chemical composition of the molecular sieve synthesis gel is silicon dioxide: structure directing agent: water in a molar ratio of 1:0.2-0.6:35-45.

[0011] In step (3), the dynamic hydrothermal crystallization conditions are: temperature of 150-200 °C and rotation speed of 20-60 rpm.

[0012] The present invention also provides a platinum-based catalyst prepared by the method described in the present invention.

[0013] In addition, the present invention also provides the use of the platinum-based catalyst of the present invention in the dehydrogenation of propane to produce propylene.

[0014] The dehydrogenation catalyst provided by the present invention and its preparation method and application have the following advantages:

[0015] (1) By modifying the surface of platinum nanoparticles with dopamine, the platinum nanoparticles can be directly encapsulated in the molecular sieve crystals during the molecular sieve crystallization process. The platinum nanoparticles cannot move freely in the molecular sieve crystals because their size is larger than the molecular sieve micropores. This spatial confinement effect effectively prevents the metal nanoparticles from deactivating due to migration and aggregation during the reaction, thereby effectively extending the catalyst life.

[0016] (2) Zinc ions are immobilized on the surface of platinum nanoparticles by reacting with the surface groups of polydopamine. In this way, zinc is introduced into the molecular sieve carrier together with platinum nanoparticles as an additive, and the distance between the two in the catalyst is precisely controlled, which effectively enhances the interaction between zinc and platinum, regulates the adsorption performance of platinum on the product propylene, promotes the rapid desorption of propylene, and inhibits carbon deposition caused by deep dehydrogenation of propylene, thereby improving the catalyst performance.

[0017] (3) Zinc enters the framework of the zeolite by isomorphous substitution. Zinc not only regulates the propylene adsorption capacity of the adjacent platinum sites through electron transfer, but also adsorbs propylene itself. In this way, the zinc atoms in the zeolite framework compete with the platinum sites for the adsorption of propylene, which effectively promotes the diffusion of propylene, further prevents the deep dehydrogenation of propylene to form carbon deposits, and helps to improve the stability of the catalyst.

[0018] (4) The present invention directly uses pre-synthesized platinum nanoparticles as raw materials and adopts a simple hydrothermal one-pot synthesis method, which has a short preparation cycle and easy-to-control conditions.

[0019] (5) The platinum-based catalyst provided by the present invention has high reaction activity, high propane conversion rate, high propylene selectivity and long catalyst life.

[0020] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the XRD diagram of the catalyst 0.13wt%PtNP@Zn-S-1 obtained in Example 2 of the present invention;

[0022] Figure 2 This is a TEM image of the catalyst 0.13wt%PtNP@Zn-S-1 obtained in Example 2 of the present invention;

[0023] Figure 3 This is the XRD diagram of the catalyst 0.21wt%PtNP@Zn-S-1 obtained in Example 3 of the present invention;

[0024] Figure 4 This is a TEM image of the catalyst 0.21wt%PtNP@Zn-S-1 obtained in Example 3 of the present invention;

[0025] Figure 5 This is the XRD diagram of the catalyst 0.36wt%PtNP@Zn-S-1 obtained in Example 4 of the present invention;

[0026] Figure 6 This is a TEM image of the catalyst 0.36wt%PtNP@Zn-S-1 obtained in Example 4 of the present invention;

[0027] Figure 7This is the XRD diagram of the catalyst 0.54wt%PtNP@Zn-S-1 obtained in Example 5 of the present invention;

[0028] Figure 8 This is a TEM image of the catalyst 0.54wt%PtNP@Zn-S-1 obtained in Example 5 of the present invention;

[0029] Fig. 9 is the XRD diagram of the catalyst PtNP@S-1 obtained in Comparative Example 1 of the present invention;

[0030] Fig.10 is a TEM image of the catalyst PtNP@S-1 obtained in Comparative Example 1 of the present invention;

[0031] Fig.11 It is the XRD diagram of the catalyst PtNP / Zn / S-1 and S-1 obtained in Comparative Example 2 of the present invention;

[0032] Fig.12 is a TEM image of the catalyst PtNP / Zn / S-1 obtained in Comparative Example 2 of the present invention; DETAILED DESCRIPTION

[0033] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0034] The endpoints of the ranges and any values ​​disclosed herein are not limited to the exact range or value, and these ranges or values ​​should be understood to include values ​​approximating these ranges or values.

[0035] Example 1

[0036] 420 μL potassium chloroplatinite solution (0.02407 mol / L) was added to 18 mL of 1 mg / mL PVP ethanol solution, and after ultrasonication for 20 min, it was transferred to a hydrothermal reactor and hydrothermally reacted at 110 °C for 3 h. After natural cooling, centrifugation was performed to obtain platinum nanoparticles (Pt@PVP). Subsequently, 0.006 g of the prepared platinum nanoparticles and 0.5 g of dopamine hydrochloride were added to 40 mL of buffer solution (pH=8-9), stirred at room temperature for 3 h, and centrifuged to obtain polydopamine-coated platinum nanoparticles (Pt@PVP@PDA). Finally, Pt@PVP@PDA was added to 20 mL of zinc acetate solution (0.1 mol / L), ultrasonicated for 1 h, and then centrifuged to obtain surface-grafted Zn 2+ of platinum nanoparticles (Pt@PVP@PDA-Zn).

[0037] Example 2

[0038] At room temperature, 5.383 g of 40 wt% tetrapropylammonium hydroxide solution, 5.5 g of tetraethyl orthosilicate (TEOS) and 5.5 g of deionized water were mixed evenly and stirred at 500 rpm until TEOS was completely hydrolyzed. 0.003 g of Pt@PVP@PDA-Zn prepared in Example 1 was prepared into 10 mL of platinum nanoparticle suspension, added to the synthetic gel, and continued to stir for 2 h. Finally, the synthetic gel was poured into a hydrothermal kettle and dynamically crystallized at 180 °C for 4 d. Subsequently, after cooling to room temperature, the product was filtered and washed with distilled water several times, and dried at 80 °C overnight. Finally, the product was calcined at 550 °C for 8 h in an air atmosphere to obtain PtNP@Zn-S-1 with a platinum loading of 0.13 wt%. The X-ray diffraction spectrum and transmission electron microscopy of the sample are shown as follows: Figure 1 and Figure 2 shown.

[0039] Example 3

[0040] 0.006 g of Pt@PVP@PDA-Zn prepared in Example 1 was prepared into 10 mL of platinum nanoparticle suspension, and the other operations were the same as in Example 2. The obtained sample was 0.21 wt% PtNP@Zn-S-1. The X-ray diffraction spectrum and transmission electron microscopy images of the sample are shown in Figure 3 and Figure 4 shown.

[0041] Example 4

[0042] 0.009 g of Pt@PVP@PDA-Zn prepared in Example 1 was prepared into 10 mL of platinum nanoparticle suspension, and the other operations were the same as in Example 2. The obtained sample was 0.36 wt% PtNP@Zn-S-1. The X-ray diffraction spectrum and transmission electron microscopy images of the sample are shown in Figure 5 and Figure 6 shown.

[0043] Example 5

[0044] 0.012 g of Pt@PVP@PDA-Zn prepared in Example 1 was prepared into 10 mL of platinum nanoparticle suspension, and the other operations were the same as in Example 2. The obtained sample was 0.54 wt% PtNP@Zn-S-1. The X-ray diffraction pattern and transmission electron microscopy image of the sample were as follows: Figure 7 and Figure 8 shown.

[0045] Comparative Example 1

[0046] 0.006 g of Pt@PVP prepared in Example 1 was prepared into 10 mL of platinum nanoparticle suspension, and the other operations were the same as in Example 2. The obtained sample was PtNP@S-1. The X-ray diffraction spectrum and transmission electron microscopy image of the sample were as follows: Fig. 9 and Fig.10 shown.

[0047] Comparative Example 2

[0048] At room temperature, 5.383 g of 40 wt% tetrapropylammonium hydroxide solution, 5.5 g of TEOS and 15.5 g of deionized water were mixed evenly and stirred at 500 rpm until TEOS was completely hydrolyzed to form a synthetic gel. The gel was dynamically crystallized at 180 °C for 4 d, and the product was washed, dried and calcined to obtain the S-1 molecular sieve. Subsequently, 0.006 g of Pt@PVP@PDA-Zn and 1 g of the prepared S-1 molecular sieve were dispersed in 10 mL of water, stirred at 80 °C for 4 h and evaporated to dryness. Finally, the obtained product was calcined at 550 °C for 8 h in an air atmosphere to obtain PtNP / Zn / S-1. The X-ray diffraction spectrum and transmission electron microscopy of the sample are shown as follows, respectively. Fig.11 and Fig.12 shown.

[0049] Performance Testing

[0050] The catalytic performance of the catalysts obtained in Examples 2-5 and Comparative Examples 1 and 2 above for the dehydrogenation of propane to propylene was evaluated. The specific reaction conditions are as follows: 0.1 g of the catalyst was weighed and placed in a quartz reaction tube. Before the reaction, the catalyst was reduced in a pure hydrogen atmosphere at 550°C for 1 h. The raw gas was a mixture of propylene and nitrogen (C 3 H 8 :N 2 =1:10), the flow rate was 30 mL / min, the reaction pressure was normal pressure, the reaction temperature was 550°C, and the contents of each component at the reactor outlet were detected by online gas chromatography every 30 min after the start of the reaction. The propane conversion rate and propylene selectivity of each sample are listed in Table 1.

[0051] Table 1: Propane dehydrogenation reaction test results of the catalysts obtained in Examples 2-5 and Comparative Examples 1 and 2.

[0052] catalyst Reaction time (h) Propane conversion rate (%) Propylene selectivity (%) Example 2 0.13 %wt PtNP@Zn-S-1 20 50-0 98.0-99.1 Example 3 0.21 %wt PtNP@Zn-S-1 120 58-51 96.2-99.3 Example 4 0.36 %wt PtNP@Zn-S-1 48 55-41 96.2-99.2 Example 5 0.54 %wt PtNP@Zn-S-1 48 54-36 95.6-99.5 Comparative Example 1 PtNP@S-1 12 ＜5 - Comparative Example 2 PtNP / Zn / S-1 12 ＜5 -

[0053] As can be seen from Table 1, when the dehydrogenation catalyst PtNP@Zn-S-1 prepared by the method of the present invention is used for the propane dehydrogenation to propylene reaction, its catalytic performance is significantly better than that of PtNP / Zn / S-1 prepared by the impregnation method and PtNP@S-1 without a Zn carrier. This shows that the spatial restriction effect of the molecular sieve on the platinum nanoparticles and the synergistic effect of Zn on the S-1 molecular sieve framework play an important role in achieving efficient propane dehydrogenation, so that the average conversion rate of propane and the average selectivity of propylene are significantly improved. This shows that the preparation method of the platinum-based catalyst provided by the present invention can achieve the effect of improving the catalytic performance of the catalyst for propane dehydrogenation to propylene.

[0054] Furthermore, it can be seen from Table 1 as a whole that the dehydrogenation catalyst prepared by the method provided by the present invention exhibits good catalytic performance in the propane dehydrogenation reaction to produce propylene, and has high propane conversion rate, propylene selectivity and catalytic life.

[0055] The above embodiments describe the basic principles and main features of the present invention and the advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention, and are not intended to limit the scope of the present invention in any way. Without departing from the scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements fall within the scope of the protection required.

[0056] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A platinum-based catalyst for dehydrogenating propane to propylene, characterized in that The catalyst uses an all-silicon molecular sieve isomorphously substituted with zinc as a carrier, and the platinum component is in the form of platinum nanoparticles, some of which are embedded in the molecular sieve crystals and some of which are located on the outer surface of the molecular sieve crystals, and zinc occupies the position of silicon atoms in the molecular sieve framework. The preparation method of the catalyst comprises the following steps: (1) Using polyvinyl pyrrolidone (PVP) as a stabilizer and ethanol as a reducing agent, potassium chloroplatinite was reduced under solvothermal conditions to obtain PVP-stabilized platinum nanoparticles; (2) dispersing the PVP-coated platinum nanoparticles obtained in (1) in a buffer solution, adding a certain amount of dopamine hydrochloride and stirring to obtain platinum nanoparticles coated with polydopamine, then adding a certain concentration of zinc acetate aqueous solution, ultrasonically treating for a certain period of time, then centrifuging to separate the platinum nanoparticles and re-dispersing them in a certain amount of deionized water to obtain a suspension of surface-modified platinum nanoparticles; (3) Adding the surface-modified platinum nanoparticle suspension obtained in (2) to the molecular sieve synthesis gel and mixing them thoroughly to obtain an initial gel, transferring the initial gel to a hydrothermal reactor and crystallizing it under dynamic hydrothermal conditions, and sequentially washing, drying, and calcining the obtained product to finally obtain a platinum-based catalyst.

2. A platinum-based catalyst for dehydrogenation of propane to propylene according to claim 1, characterized in that: The topological structure type of the molecular sieve is MFI and *BEA type, the zinc substitution amount is 0.1-5.0 wt %, the particle size of the platinum nanoparticles is 1.0-10.0 nm, the loading amount of the platinum nanoparticles is 0.05-3.0 wt %, and the molecular sieve carrier content is 92.0-99.85 wt %.

3. A method for preparing a platinum-based catalyst for dehydrogenating propane to propylene according to any one of claims 1 to 2, characterized in that: The following steps are involved: (1) Using polyvinyl pyrrolidone (PVP) as a stabilizer and ethanol as a reducing agent, potassium chloroplatinite was reduced under solvothermal conditions to obtain PVP-stabilized platinum nanoparticles; (2) dispersing the PVP-coated platinum nanoparticles obtained in (1) in a buffer solution, adding a certain amount of dopamine hydrochloride and stirring to obtain platinum nanoparticles coated with polydopamine, then adding a certain concentration of zinc acetate aqueous solution, ultrasonically treating for a certain period of time, then centrifuging to separate the platinum nanoparticles and re-dispersing them in a certain amount of deionized water to obtain a suspension of surface-modified platinum nanoparticles; (3) Adding the surface-modified platinum nanoparticle suspension obtained in (2) to the molecular sieve synthesis gel and mixing them thoroughly to obtain an initial gel, transferring the initial gel to a hydrothermal reactor and crystallizing it under dynamic hydrothermal conditions, and sequentially washing, drying, and calcining the obtained product to finally obtain a platinum-based catalyst.

4. The method for preparing a platinum-based catalyst for dehydrogenating propane to propylene according to claim 3, wherein: The solvent thermal reaction temperature of step (1) is 90-130°C, the concentration of potassium chloroplatinite is 0.02-0.1 mol / L, and the concentration of PVP, MW=10000 ethanol solution is 1-5 mg / mL.

5. The method for preparing a platinum-based catalyst for dehydrogenating propane to propylene according to claim 3, wherein: The reaction conditions of step (2) are as follows: the pH range of the buffer solution is 8-9; The molar ratio of platinum to dopamine hydrochloride is 1:50-100; the stirring time is 1-5 h; the concentration of the zinc acetate solution is 0.05-0.2 mol / L; the ultrasonic treatment is 1-3 h; and the centrifugation is performed at 10,000 rpm for 5-10 minutes.

6. The method for preparing a platinum-based catalyst for dehydrogenating propane to propylene according to claim 3, wherein: The concentration of the platinum nanoparticle suspension in step (3) is 0.3-1.0 g / L, and the gel composition is silica: structure directing agent: water in a molar ratio of 1:0.2-0.6:35-45.

7. The method for preparing a platinum-based catalyst for dehydrogenating propane to propylene according to claim 3, wherein: The dynamic hydrothermal crystallization conditions in step (3) are: temperature of 150-200 °C and rotation speed of 20-60 rpm.

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