A bimetallic catalyst for highly selective preparation of hexafluoropropylene oxide and its application

Abstract

The present invention discloses a bimetallic catalyst for preparing hexafluoropropylene oxide with high selectivity and its application, belonging to the field of catalysts. The active component of the bimetallic catalyst of the present invention is gold-palladium (Au-Pd) alloy nanoparticles supported on anatase-type TiO2 carrier. The molar ratio of Au to Pd is 1:1 to 3:1. Within this ratio range, the Au-Pd alloy can give full play to its unique electronic effect, that is, the d-band center of Pd moves downward, and Au presents an electron-enriched state. The two act synergistically to significantly optimize the adsorption and activation capacity for oxygen. The application of the catalyst of the present invention to the gas-phase catalytic oxidation of HFP to prepare HFPO can overcome the bottlenecks of low conversion rate and selectivity, harsh reaction conditions and short catalyst life in the existing technology, and provide technical support for the green and efficient industrial production of HFPO.

Description

Technical Field

[0001] The present invention belongs to the field of fluorine chemical industry, and particularly relates to a bimetallic catalyst for preparing hexafluoropropylene oxide with high selectivity and application thereof. Background Art

[0002] Hexafluoropropylene oxide (HFPO), a key fluorinated organic intermediate, serves as a building block for the synthesis of perfluoropolyethers, hexafluoroacetone, fluorinated surfactants, and key raw materials for pharmaceuticals and pesticides. The epoxy groups in its molecular structure impart unique reactivity, leading to its widespread application in high-end fluorinated materials (such as perfluorosulfonic acid ion membranes), electronic chemicals (such as etchants), and high-end anesthetics (such as sevoflurane). Currently, the mainstream industrial preparation methods include liquid-phase oxidation and gas-phase catalytic oxidation. The former uses sodium hypochlorite or hydrogen peroxide as an oxidant, and while exhibiting high selectivity (approximately 75-85%), it presents challenges in treating large amounts of fluorinated wastewater and can lead to severe equipment corrosion. The latter, using molecular oxygen as an oxidant, offers advantages of process simplicity and environmental friendliness, but catalyst performance remains a key bottleneck restricting its industrialization.

[0003] Existing Ag-based catalysts suffer from poor selectivity and inadequate stability during use. For example, Chinese patent CN1954911A reports an Ag-based catalyst that, while active in the 130–180°C range, exhibits byproduct selectivity as high as 15%, and the Ag component is susceptible to sintering and deactivation. Bimetallic catalysts, often using impregnation or coprecipitation methods, suffer from low metal dispersion, which can easily lead to active site deactivation. Furthermore, the single support selection prevents effective synergy between the metal active centers. Chinese patent CN118304925A discloses a catalyst using a Cu-Ce / Co / Cr bimetallic oxide and an HZSM-5 molecular sieve support. The reaction temperature must be maintained between 140 and 220°C, resulting in high energy consumption and limited efficiency. Therefore, developing highly active and selective catalysts and lowering the reaction temperature have become key technical challenges that urgently need to be overcome in this field. Summary of the Invention

[0004] To address the challenges of the prior art, the present invention proposes a highly selective bimetallic catalyst for the preparation of hexafluoropropylene oxide and its application. By designing a synergistic catalytic system of Au-Pd alloy nanoparticles and high-surface-area anatase TiO2, combined with a unique sol-gel preparation process, the present invention overcomes the bottlenecks of the prior art, which include low conversion and selectivity, harsh reaction conditions, and short catalyst life. This provides technical support for the green and efficient industrial production of HFPO.

[0005] The technical solutions of the present invention are as follows:

[0006] The present invention first provides a bimetallic catalyst for preparing hexafluoropropylene oxide with high selectivity. The bimetallic catalyst uses anatase-type titanium dioxide (TiO2) as a carrier, and supports gold-palladium (Au-Pd) alloy nanoparticles on the carrier as an active component. The molar ratio of Au to Pd in ​​the alloy nanoparticles is 1:1 to 3:1, and the specific surface area of ​​the carrier is 200 to 300 m 2 / g, the alloy nanoparticle size is 10~20 nm, and the total metal loading is 5~10 wt%.

[0007] The present invention also provides a method for preparing the bimetallic catalyst, which comprises the following steps:

[0008] 1) Preparation of anatase TiO2 support by sol-gel method: Tetrabutyl titanate was added dropwise to an ethanol-water mixture and hydrolyzed at 25-35°C for 2-4 hours. The anatase TiO2 support was obtained after aging, filtration, and calcination.

[0009] 2) Metal salt solution impregnation reduction: Mix the mixed solution of HAuCl4 and Pd(NO3)2 with the support obtained in step 1), adjust the pH to 7-8, and then add a reducing agent for liquid phase reduction;

[0010] 3) Hydrogen reduction treatment: reducing the reduced precursor in a hydrogen atmosphere at 250-350° C. for 1-3 hours to form Au-Pd alloy nanoparticles; thereby obtaining the highly selective bimetallic catalyst for preparing hexafluoropropylene oxide.

[0011] According to a preferred embodiment of the present invention, in step 1), the volume ratio of ethanol to water is 4:1, the roasting temperature is 450-550° C., and the roasting time is 3-5 hours.

[0012] According to a preferred embodiment of the present invention, in step 2), the reducing agent is a sodium borohydride solution with a concentration of 0.5 to 1.5 mol / L, and the molar amount added is 1.1 to 1.5 times the molar amount that can completely reduce Au and Pd, i.e., 1.1 to 1.5× (3n Au +2n Pd ) / 8, n Au 、n Pd are the molar amounts of Au and Pd in ​​the system, respectively.

[0013] According to a preferred embodiment of the present invention, in step 2), the molar ratio of HAuCl4 to Pd(NO3)2 is 1:1 to 3:1.

[0014] According to a preferred embodiment of the present invention, in step 3), the hydrogen flow rate is 50-100 mL / min.

[0015] The present invention further provides an application of the bimetallic catalyst in the gas-phase oxidation of hexafluoropropylene to prepare hexafluoropropylene oxide.

[0016] According to a preferred embodiment of the present invention, the application is as follows: adding a catalyst to a fixed bed reactor, introducing hexafluoropropylene and oxygen to carry out gas-phase oxidation of hexafluoropropylene to prepare hexafluoropropylene oxide, the reaction temperature of the gas-phase oxidation is 120-150°C, the reaction pressure is 0.5-1.0 MPa, the molar ratio of hexafluoropropylene to oxygen is 2:1-3:1, and the space velocity is 20-200 h -1 .

[0017] Compared with the prior art, the present invention has at least the following beneficial effects:

[0018] 1. Synergistic catalytic advantages: Existing Ag- and Cu-based catalysts generally have hexafluoropropylene (HFP) conversion rates below 80%, HFPO selectivity below 85%, and overall selectivity for byproducts (such as carbonyl fluoride and trifluoroacetyl fluoride) ≥15%, resulting in low target product yields and high separation costs. The synergistic catalytic effect formed by the Au-Pd alloy nanoparticles and the anatase TiO2 support in the bimetallic catalyst provided by the present invention significantly improves catalytic performance, achieving hexafluoropropylene conversion rates ≥90% and HFPO selectivity ≥85%, a significant improvement over existing Cu- and Ag-based catalysts. It also improves product purity and simplifies subsequent separation processes.

[0019] 2. Mild and efficient reaction conditions: Traditional gas-phase catalytic oxidation processes require reactions at high temperatures of 140-250°C and pressures above 1.5 MPa, resulting in high energy consumption, stringent requirements on equipment materials, and low process safety. The use of the bimetallic catalyst of the present invention for gas-phase catalytic oxidation of hexafluoropropylene requires only lower reaction temperatures and milder pressure conditions, enabling high-throughput continuous production at low pressures of 0.5-1.0 MPa. This not only reduces energy consumption but also lowers the requirements on equipment materials, improves process safety, and creates favorable conditions for industrial scale-up production.

[0020] 3. Excellent catalyst stability: Existing bimetallic catalysts have low metal dispersion and weak carrier synergy, resulting in an activity loss of over 15% after 10 reuses, requiring frequent replacement and affecting process economics. The bimetallic catalyst provided by the present invention has a metal loading of only 5-10wt%. Through the strong interaction between highly dispersed Au-Pd alloy nanoparticles and Ti-OM bonds, the activity retention rate is >95% after 5 cycles, preventing precious metal loss. The overall cost is more than 30% lower than that of barium-based catalysts, making it economical for industrial application.

[0021] 4. Green and environmentally friendly process: The low-temperature and low-pressure process reduces energy consumption and CO2 emissions, while precisely inhibiting the over-oxidation of hexafluoropropylene. The amount of by-products generated is extremely low, reducing the pressure of fluorine-containing waste gas treatment from the source, in line with the needs of green chemistry and sustainable development. DETAILED DESCRIPTION

[0022] The present invention will be further described and illustrated below in conjunction with specific embodiments. The embodiments are merely illustrative of the present disclosure and do not limit its scope. The technical features of the various embodiments of the present invention may be combined accordingly, provided that there is no conflict between them.

[0023] Example 1:

[0024] 1. Catalyst preparation: Au-Pd molar ratio is 1:1, loading amount is 5 wt%.

[0025] (1) Preparation of TiO2 carrier: 100 mL of tetrabutyl titanate was added dropwise to 500 mL of ethanol-water (volume ratio 4:1) mixed solution, stirred and hydrolyzed at 28 °C for 3 h, aged at room temperature for 24 h, filtered and calcined at 500 °C for 4 h.

[0026] (2) Metal salt solution immersion reduction: Prepare a mixed solution of 0.05M HAuCl4 and 0.05M Pd (NO3)2, add 5g TiO2 carrier, ultrasonically disperse for 30min, add NaOH solution dropwise to adjust pH=7.5, add 2ml of 1mol / L sodium borohydride solution under stirring and reduce for 1h.

[0027] (3) Hydrogen reduction treatment: After filtration, washing, and drying, the product was reduced at 300 °C for 2 h in a hydrogen atmosphere (flow rate 80 mL / min) to obtain the Au-Pd / TiO2 catalyst.

[0028] 2. Reaction evaluation: 10 g of catalyst was added to a fixed bed reactor, HFP and oxygen (molar ratio 2:1) were introduced, the reaction temperature was 130 ° C, the pressure was 0.8 MPa, and the space velocity was 100 h -1 .

[0029] The product composition was analyzed and calculated by gas chromatography. The hexafluoropropylene conversion was 90.2%, the HFPO selectivity was 87.6%, and the activity retention rate after 10 regenerations was about 90%.

[0030] Example 2:

[0031] 1. Catalyst preparation: Au-Pd molar ratio is 2:1, loading amount is 5 wt%.

[0032] (1) Preparation of TiO2 carrier: 100 mL of tetrabutyl titanate was added dropwise to 500 mL of ethanol-water (volume ratio 4:1) mixed solution, stirred and hydrolyzed at 28 °C for 3 h, aged at room temperature for 24 h, filtered and calcined at 500 °C for 4 h.

[0033] (2) Metal salt solution immersion reduction: Prepare a mixed solution of 0.075M HAuCl4 and 0.0375M Pd(NO3)2, add 5g TiO2 carrier, ultrasonically disperse for 30min, add NaOH solution dropwise to adjust pH to 7.5, and add 3.2ml 1M sodium borohydride solution under stirring for 1h.

[0034] (3) Hydrogen reduction treatment: After filtration, washing, and drying, the product was reduced at 300 °C for 2 h in a hydrogen atmosphere (flow rate 80 mL / min) to obtain the Au-Pd / TiO2 catalyst.

[0035] 2. Reaction evaluation: 10 g of catalyst was added to a fixed bed reactor, HFP and oxygen (molar ratio 2:1) were introduced, the reaction temperature was 130 ° C, the pressure was 0.8 MPa, and the space velocity was 100 h -1 .

[0036] The product composition was analyzed and calculated by gas chromatography. The hexafluoropropylene conversion was 92.3%, the HFPO selectivity was 87.0%, and the activity retention rate after 10 regenerations was about 90%.

[0037] Example 3:

[0038] 1. Catalyst preparation: Au-Pd molar ratio is 3:1, loading amount is 10 wt%.

[0039] (1) Preparation of TiO2 carrier: 100 mL of tetrabutyl titanate was added dropwise to 500 mL of ethanol-water (volume ratio 4:1) mixed solution, stirred and hydrolyzed at 28 °C for 3 h, aged at room temperature for 24 h, filtered and calcined at 500 °C for 4 h.

[0040] (2) Metal salt solution immersion reduction: Prepare a mixed solution of 0.1M HAuCl4 and 0.033M Pd (NO3)2, add 5g TiO2 carrier, ultrasonically disperse for 30min, add NaOH solution dropwise to adjust pH=7.5, add 4.1ml 1M sodium borohydride solution under stirring and reduce for 1h.

[0041] (3) Hydrogen reduction treatment: After filtration, washing, and drying, the product was reduced at 300 °C for 2 h in a hydrogen atmosphere (flow rate 80 mL / min) to obtain the Au-Pd / TiO2 catalyst.

[0042] 2. Reaction evaluation: 10 g of catalyst was added to a fixed bed reactor, HFP and oxygen (molar ratio 2:1) were introduced, the reaction temperature was 150 ° C, the pressure was 1.0 MPa, and the space velocity was 120 h -1 .

[0043] The product composition was analyzed and calculated by gas chromatography. The hexafluoropropylene conversion was 92.8%, the HFPO selectivity was 87.0%, and the activity retention rate after 10 regenerations was about 91%.

[0044] Comparative Example 1:

[0045] 1. Catalyst preparation: According to the method of CN118304925A, Cu (NO3)2 and Ce (NO3)3 were impregnated into HZSM-5 molecular sieve and calcined at 500℃ to prepare Cu-Ce / HZSM-5 catalyst (Cu:Ce=1:1, metal loading 15wt%).

[0046] 2. Reaction evaluation: 10 g of catalyst was added to a fixed bed reactor, HFP and oxygen (molar ratio 2:1) were introduced, the reaction temperature was 140 ° C, the pressure was 1.5 MPa, and the space velocity was 10 h -1 . (Recommended conditions for this patent)

[0047] The product composition was analyzed and calculated by gas chromatography. The hexafluoropropylene conversion was 75.4%, the HFPO selectivity was 82.3%, and the activity retention rate after 10 regenerations was about 81%.

[0048] Comparative Example 2:

[0049] 1. Catalyst preparation: According to the method of CN112142912A, AgNO3 solution was impregnated into γ-Al2O3 support and calcined at 400℃ to obtain 10wt% Ag / Al2O3 catalyst.

[0050] 2. Reaction evaluation: 10 g of catalyst was added to a fixed bed reactor, HFP and oxygen (molar ratio 2:1) were introduced, the reaction temperature was 150 ° C, the pressure was 1.2 MPa, and the space velocity was 8 h -1 . (Recommended conditions for this patent)

[0051] The product composition was analyzed and calculated by gas chromatography. The hexafluoropropylene conversion was 78.0%, the HFPO selectivity was 83.7%, and the activity retention rate after 10 regenerations was about 72%.

[0052] Comparative Example 3:

[0053] Catalyst preparation: The Au-Pd alloy molar ratio was 2:1, consistent with Example 2, and the loading amount was 5 wt%.

[0054] (1) Preparation of γ-Al2O3 carrier: γ-Al2O3 was ball-milled and sieved (100-200 mesh), and calcined at 500℃ for 4h.

[0055] (2) Metal salt solution impregnation reduction: A mixed solution of 0.075M HAuCl4 and 0.0375M Pd(NO3)2 was impregnated into 5g of γ-Al2O3 carrier, the pH was adjusted to 7.5, and 3.2mL of 1M NaBH4 solution was added (the reducing agent was the same as in Example 2).

[0056] (3) Hydrogen reduction treatment: After filtration, washing, and drying, the product was reduced at 300 °C for 2 h in a hydrogen atmosphere (flow rate 80 mL / min) to obtain the Au-Pd / γ-Al2O3 catalyst.

[0057] 2. Reaction evaluation: As in Example 2, 10 g of catalyst was added to the fixed bed reactor, HFP and oxygen (molar ratio 2:1) were introduced, the reaction temperature was 130 ° C, the pressure was 0.8 MPa, and the space velocity was 100 h -1 .

[0058] Gas chromatography analysis and calculation of the product composition revealed a hexafluoropropylene conversion of 82.1%, a HFPO selectivity of 78.5%, and an activity retention of approximately 82% after 10 regenerations. This is due to excessive oxidation of HFP due to the acidic sites on the γ-Al2O3 surface, and a lack of strong Ti-OM interaction, resulting in severe sintering of the alloy particles (size >30 nm after regeneration), significantly reducing their activity and stability.

[0059] Comparative Example 4:

[0060] Catalyst preparation: Au-Pd alloy molar ratio 1:4, loading amount 5 wt%.

[0061] (1) Preparation of TiO2 carrier: 100 mL of tetrabutyl titanate was added dropwise to 500 mL of ethanol-water (volume ratio 4:1) mixed solution, stirred and hydrolyzed at 28 °C for 3 h, aged at room temperature for 24 h, filtered and calcined at 500 °C for 4 h.

[0062] (2) Metal salt solution immersion reduction: Prepare a mixed solution of 0.025M HAuCl4 and 0.1M Pd(NO3)2, add 5g TiO2 carrier, ultrasonically disperse for 30min, add NaOH solution dropwise to adjust pH=7.5, add 2.5ml 1M sodium borohydride solution under stirring and reduce for 1h.

[0063] (3) Hydrogen reduction treatment: As in Example 1, after filtration, washing, and drying, the product was reduced at 300°C for 2 h in a hydrogen atmosphere (flow rate 80 mL / min) to obtain an Au-Pd / TiO2 catalyst.

[0064] 2. Reaction evaluation: As in Example 1, 10 g of catalyst was added to the fixed bed reactor, HFP and oxygen (molar ratio 2:1) were introduced, the reaction temperature was 130 ° C, the pressure was 0.8 MPa, and the space velocity was 100 h -1 .

[0065] Gas chromatography analysis and calculation of the product composition revealed an 88.7% hexafluoropropylene conversion, 72.4% HFPO selectivity, and approximately 81% activity retention after 10 regenerations. This is due to the high Pd content (Pd-enriched surface) overactivating the C-H bonds, promoting the cleavage of hexafluoropropylene to form trifluoroacetyl fluoride (CF3COF), which leads to a sudden drop in selectivity. Furthermore, Pd is easily oxidized and deactivated, resulting in poor cyclic stability.

[0066] The above-described embodiments merely illustrate several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. Persons skilled in the art will readily appreciate that variations and modifications may be made without departing from the scope of the present invention, all of which fall within the scope of protection of the present invention.

Claims

1. A bimetallic catalyst for preparing hexafluoropropylene oxide with high selectivity, characterized in that: The bimetallic catalyst uses anatase-type titanium dioxide as a carrier, and gold-palladium alloy nanoparticles are loaded on the carrier as an active component. The molar ratio of Au to Pd in ​​the alloy nanoparticles is 1:1-3:1, and the specific surface area of ​​the carrier is 200-300 m 2 / g, the alloy nanoparticle size is 10~20 nm, and the total metal loading is 5~10 wt%.

2. A method for preparing the bimetallic catalyst according to claim 1, characterized in that: The following steps are involved: 1) Preparation of anatase TiO2 support by sol-gel method: Tetrabutyl titanate was added dropwise to an ethanol-water mixture and hydrolyzed at 25-35°C for 2-4 hours. The anatase TiO2 support was obtained after aging, filtration, and calcination. 2) Metal salt solution impregnation reduction: Mix the mixed solution of HAuCl4 and Pd(NO3)2 with the support obtained in step 1), adjust the pH to 7-8, and then add a reducing agent for liquid phase reduction; 3) Hydrogen reduction treatment: reducing the reduced precursor in a hydrogen atmosphere at 250-350° C. for 1-3 hours to form Au-Pd alloy nanoparticles; thereby obtaining the highly selective bimetallic catalyst for preparing hexafluoropropylene oxide.

3. The preparation method according to claim 2, characterized in that In step 1), the volume ratio of ethanol to water is 4:1, the roasting temperature is 450-550° C., and the roasting time is 3-5 hours.

4. The preparation method according to claim 2, wherein In step 2), the reducing agent is a sodium borohydride solution with a concentration of 0.5 to 1.5 mol / L, and the molar amount added is 1.1 to 1.5 times the molar amount capable of completely reducing Au and Pd.

5. The preparation method according to claim 2, characterized in that In step 2), the molar ratio of HAuCl4 and Pd(NO3)2 is 1:1~3:

1.

6. The preparation method according to claim 2, wherein In step 3), the hydrogen flow rate is 50-100 mL / min.

7. Use of the bimetallic catalyst according to claim 1 in the gas-phase oxidation of hexafluoropropylene to produce hexafluoropropylene oxide.

8. The use according to claim 7, characterized in that A bimetallic catalyst is added to a fixed bed reactor, and hexafluoropropylene and oxygen are introduced to carry out gas-phase oxidation of hexafluoropropylene to prepare hexafluoropropylene oxide. The reaction temperature of the gas-phase oxidation is 120-150°C, the reaction pressure is 0.5-1.0 MPa, the molar ratio of hexafluoropropylene to oxygen is 2:1-3:1, and the space velocity is 20-200 h -1 .