Palladium-based catalyst for semi-hydrogenation of alkynols to alkenols, method of preparation and use

Abstract

This invention discloses a palladium-based catalyst for the semi-hydrogenation of alkynols to enols and its preparation method. Specifically, a metal salt is added to deionized water and ultrasonically dispersed to obtain a uniformly dispersed metal salt solution. A support powder is uniformly spread on a polytetrafluoroethylene plate. The metal salt solution is loaded into a syringe pump and slowly added dropwise onto the support. The solution is allowed to stand and age to obtain a wet support. The wet support is transferred to an oven for calcination. The calcined sample is transferred to a tube furnace for reduction to obtain the palladium-based catalyst. The palladium-based catalyst of this invention can be applied to the selective hydrogenation reaction of alkynols. By controlling the impregnation rate, the active precursor solution is ensured to be absorbed instantaneously and completely, and the enrichment of the active component at the edges is effectively suppressed. High-temperature reduction achieves partial encapsulation of palladium nanoparticles with indium oxide, thereby altering their electronic structure and improving the selectivity for the semi-hydrogenation of alkynols to enols.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation technology, specifically relating to a method for preparing palladium-based catalysts for the semi-hydrogenation of alkynols to enols, and also relating to palladium-based catalysts for the semi-hydrogenation of alkynols to enols and their applications. Background Technology

[0002] The traditional impregnation method is one of the most commonly used methods for preparing supported catalysts in industry. Its core principle is to immerse a porous support in a solution containing a precursor of the active component. Capillary force allows the solution to penetrate into the pores of the support. Subsequent drying, calcination, and activation steps fix the active component onto the support surface. However, the active particles (such as metal nanoparticles) formed after impregnation often have a wide size distribution, easily resulting in uneven particle size and even severe agglomeration. The active component may randomly block some of the pores of the support, affecting the mass transfer and diffusion of reactants. Furthermore, small fluctuations in process parameters (such as drying rate and humidity) can lead to batch-to-batch performance differences, affecting catalytic activity.

[0003] The semi-hydrogenation of alkynyl alcohols to enols is a core process in the production of fine chemicals such as vitamins, pharmaceuticals, fragrances, and synthetic materials (e.g., corrosion inhibitors, synthetic fibers). To improve hydrogenation selectivity, the content of over-hydrogenation products must be strictly controlled. The core principle is to moderately regulate and reduce the activity of the catalyst, thereby effectively inhibiting the occurrence of over-hydrogenation side reactions and ensuring the selective formation of the target product, enol. Chinese patent (application number: 202410881250.4; publication number: CN118847177B; publication date: 2025.11.04) discloses a catalyst for the preparation of enols from alkynyl alcohols, its preparation method, and the method for preparing enols. By precisely controlling the particle size, specific surface area, and poisoning agent dosage of the Lindela catalyst, a synergistic improvement in catalytic efficiency and selectivity is achieved. It also proposes a general principle for modifying Lindela catalysts with nitrogen-, phosphorus-, and sulfur-containing compounds, providing a technical approach for the semi-hydrogenation of alkynyl alcohols to enols. However, this general modification principle and corresponding catalytic method still have limitations in applicability under certain specific reaction systems and conditions, making it difficult to meet the precise catalytic needs of various scenarios. Chinese Patent (Application No.: 201910449643.7, Publication No.: CN110124742B, Publication Date: 2023.05.26) discloses a catalyst and preparation method for the partial hydrogenation of alkynols to enols, and a method for preparing enols using the catalyst. It selects metal salts or metal carbonyl compounds as poisoning agents, which can modify the partially hydrogenation catalyst. However, metals such as manganese and chromium are highly toxic, and the modified catalyst may be deactivated. Sodium and magnesium are less toxic, and their poisoning effect is not significant. Chinese Patent (Application No.: 202011211691.1, Publication No.: CN112225640B, Publication Date: 2025.07.15) discloses a method for the selective hydrogenation of alkynols to enols. Under acidic conditions, crown ethers are added to work together with the hydrogenation catalyst to prepare enols. However, this method requires strict control of the pH value of the reaction system, resulting in a narrow applicability. Summary of the Invention

[0004] The primary objective of this invention is to provide a method for preparing a palladium-based catalyst for the semi-hydrogenation of alkynols to enols, thereby solving the problem of poor selectivity of existing noble metal catalysts in hydrogenation reactions.

[0005] A second objective of this invention is to provide a palladium-based catalyst for the semi-hydrogenation of alkynols to enols.

[0006] A third objective of this invention is to provide the application of palladium-based catalysts for the semi-hydrogenation of alkynols to enols in the selective hydrogenation reaction of alkynols.

[0007] The technical solution adopted in this invention is a method for preparing a palladium-based catalyst for the semi-hydrogenation of alkynols to enols, specifically implemented according to the following steps:

[0008] Step 1: Add the metal salt to deionized water and disperse it by ultrasonication to obtain a uniformly dispersed metal salt solution; Step 2: Spread the carrier powder evenly on the polytetrafluoroethylene plate, load the metal salt solution prepared in Step 1 into the injection pump, and slowly drop the solution onto the carrier to ensure that the solution is completely and evenly absorbed by the carrier. After impregnation, let it stand and age to obtain a wet carrier. Step 3: Transfer the wet carrier obtained in Step 2 to an oven for calcination; Step 4: Transfer the calcined sample to a tube furnace for reduction to obtain a palladium-based catalyst for the semi-hydrogenation of alkynols to enols.

[0009] The invention is further characterized in that, In step 1, the ultrasonic temperature is 20-50℃, the ultrasonic time is 2-10h, and the ultrasonic frequency is 30-60kHz.

[0010] In step 1, the mass concentration of the metal salt solution is 0.002-0.010 g / mL, and the metal salt is any one or more of palladium nitrate, palladium chloride, sodium tetrachloropalladiumate, and palladium acetate.

[0011] In step 2, the carrier powder is indium oxide or cerium oxide, and the particle size of the powder is 50nm-100μm; the drop rate is controlled at 20-60mL / h, and the aging time is 2-8h.

[0012] In step 3, the roasting process is as follows: the temperature is increased to 100-150℃ at 2-5℃ / min and held for 1-2 hours; then the temperature is increased to 180-200℃ at 2-5℃ / min and held for 3-5 hours, and then naturally cooled to room temperature.

[0013] In step 4, the reduction temperature is 200-500℃, the reduction time is 1-5h, and the palladium content in the palladium-based catalyst for the semi-hydrogenation of alkynols to enols is 0.5%-5%.

[0014] Another technical solution adopted in this invention is a palladium-based catalyst prepared by a method for preparing palladium-based catalysts for the semi-hydrogenation of alkynols to enols.

[0015] The beneficial effects of this invention are: The present invention discloses a method for preparing a palladium-based catalyst for the semi-hydrogenation of alkynols to enols. By controlling the impregnation rate, the active precursor solution is ensured to be absorbed instantaneously and completely, and the enrichment of the active component at the edges is effectively suppressed. High-temperature reduction achieves partial encapsulation of palladium nanoparticles with indium oxide, thereby altering their electronic structure and improving the selectivity for the semi-hydrogenation of alkynols to enols. Furthermore, this method is simple, low-cost, and requires no addition of any toxic substances during the reaction, thus possessing broad application prospects. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the selective hydrogenation palladium-based catalyst prepared in Example 1.

[0017] Figure 2 Transmission electron microscope image of the selective hydrogenation palladium-based catalyst prepared in Example 1.

[0018] Figure 3 A schematic diagram of the palladium atom crystal planes of the selective hydrogenation palladium-based catalyst prepared by the traditional impregnation method.

[0019] Figure 4 This is a schematic diagram of the palladium atom crystal planes of the selective hydrogenation palladium-based catalyst prepared in Example 1. Detailed Implementation

[0020] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0021] The method for preparing a palladium-based catalyst for the semi-hydrogenation of alkynols to enols according to the present invention is specifically implemented according to the following steps: Step 1: Add the metal salt to deionized water and disperse it by ultrasonication to obtain a uniformly dispersed metal salt solution; The mass concentration of the metal salt solution is 0.002-0.010 g / mL, the ultrasonic temperature is 20-50℃, the ultrasonic time is 2-10 h, and the ultrasonic frequency is 30-60 kHz. The metal salt is any one or more of palladium nitrate, palladium chloride, sodium tetrachloropalladiumate, and palladium acetate; Step 2: Spread the carrier powder evenly on the polytetrafluoroethylene plate. Put the metal salt solution prepared in Step 1 into a micro-injection pump and slowly add the solution to the carrier. Control the dropping rate to 20-60 mL / h to ensure that the solution is completely and evenly absorbed by the carrier. After impregnation, let it stand at room temperature for 2-8 hours to obtain a wet carrier. The carrier powder is indium oxide or cerium oxide; the particle size is 50nm-100μm. The ratio of carrier powder to metal salt solution is 1.5 g / mL to 2 g / mL; The metal salt solution is slowly added dropwise to the support, and the low surface energy of the polytetrafluoroethylene plate ensures good penetration uniformity of the support layer. Subsequently, the prepared active precursor solution is slowly introduced into the support layer through micro-precision dripping at a programmed rate, driving the solution to selectively fill the mesoporous and microporous confined spaces. By using the catalyst confined space controllable impregnation method, the synergy between droplet dynamics and carrier capillary action is actively controlled to ensure that the active precursor solution is instantaneously and completely absorbed, and to effectively suppress the enrichment of active components at the edges, thereby achieving high-precision control of the loading position, dispersion and structure of active components.

[0022] Step 3: Transfer the wet carrier obtained in Step 2 to an oven, heat it to 100-150℃ in flowing air at a rate of 2-5℃ / min, and keep it at that temperature for 1-2 hours; then continue to heat it to 180-200℃ in flowing air at a rate of 2-5℃ / min and keep it at that temperature for 3-5 hours, and then let it cool naturally to room temperature. Step 4: Transfer the calcined sample to a tube reduction furnace and reduce it at 200-500℃ for 1-5 hours to finally obtain the supported palladium-based catalyst. The mass content of palladium in the supported palladium-based catalyst is 0.5%-5%.

[0023] The core mechanism of the high-temperature reduction method of this invention for partially encapsulating palladium nanoparticles with indium oxide or cerium oxide is that, under a high-temperature reducing atmosphere, partial reduction occurs on the surface of the support, generating low-valence oxide species rich in oxygen vacancies and with high migration ability. Driven by interfacial energy, these species migrate to the surface of the supported palladium nanoparticles and spread out to form a non-stoichiometric, partially encapsulated oxide film. This process is a manifestation of the classic SMSI effect, which aims to reduce the total energy of the system, enhance the metal-support electronic interaction to improve stability, and ultimately create a composite catalytic material with a unique geometric and electronic structure.

[0024] The palladium-based catalyst of this invention can be used in the selective hydrogenation reaction of alkynyl alcohols, wherein the alkynyl alcohol feedstock is butynediol, 2 Pentyne 1 Any one of the following: alcohol, 1-ethynylcyclohexanol, dehydrolinalool, and dehydroisophytol; the hydrogenation reaction process is as follows: Palladium-based catalyst, organic solvent, and alkynol material are added to a high-pressure hydrogenation reactor, and hydrogen gas at 0.2-0.8 MPa is introduced. The reaction temperature is 30-80℃, and samples are taken for analysis every half hour. The reaction is stopped when the material is completely converted. The amount of selective hydrogenation catalyst used is 0.5-2 wt% of the alkynol material mass. The organic solvent is one or more of methanol and ethanol. The general formula for the reaction of semi-hydrogenation of alkynyl alcohols to enols is:

[0025] Among them, R1 and R2 are hydrogen or hydrocarbon groups; Example 1 The method for preparing a palladium-based catalyst for the semi-hydrogenation of alkynols to enols according to the present invention is specifically implemented according to the following steps: Step 1: Add sodium tetrachloropalladium to deionized water and ultrasonically disperse to obtain a uniformly dispersed metal salt solution; wherein the mass concentration of the metal salt solution is 0.002 g / mL, the ultrasonic temperature is 50℃, the ultrasonic time is 2 h, and the ultrasonic frequency is 50 kHz.

[0026] Step 2: Spread indium oxide evenly on a polytetrafluoroethylene plate, load the active metal salt solution prepared in Step 1 into a micro-injection pump, and slowly add the solution dropwise onto the carrier, controlling the drop rate to 20 mL / h to ensure that the solution is completely and uniformly absorbed by the carrier; after impregnation, let it stand at room temperature for 12 hours to age. Step 3: Transfer the wet carrier obtained in Step 2 to an oven, heat it to 110°C in flowing air at 3°C / min, and keep it at that temperature for 1 hour; continue to heat it to 180°C in flowing air at 3°C / min and keep it at that temperature for 3 hours, then let it cool naturally to room temperature.

[0027] Step 4: Transfer the calcined sample to a tube furnace and reduce it at 200°C for 3 hours to finally obtain a Pd / In2O3 catalyst with a palladium content of 1%.

[0028] Example 2 The method for preparing a palladium-based catalyst for the semi-hydrogenation of alkynols to enols according to the present invention is specifically implemented according to the following steps: Step 1: Add sodium tetrachloropalladium to deionized water and ultrasonically disperse to obtain a uniformly dispersed metal salt solution; wherein, the mass concentration of the metal salt solution is 0.004 g / mL, the ultrasonic temperature is 50℃, the ultrasonic time is 2 h, and the ultrasonic frequency is 50 kHz.

[0029] Step 2: Spread indium oxide evenly on a polytetrafluoroethylene plate. Load the active metal salt solution prepared in Step 1 into a micro-injection pump and slowly add the solution dropwise onto the carrier, controlling the drop rate at 20 mL / h to ensure complete and uniform absorption of the solution by the carrier. After impregnation, allow to stand at room temperature for 12 hours to age.

[0030] Step 3: Transfer the wet carrier obtained in Step 2 to an oven, heat it to 110°C in flowing air at 3°C / min, and keep it at that temperature for 1 hour; continue to heat it to 180°C in flowing air at 3°C / min and keep it at that temperature for 3 hours, then let it cool naturally to room temperature.

[0031] Step 4: Transfer the calcined sample to a tube furnace and reduce it at 200-500℃ for 1-5 hours to finally obtain a Pd / In2O3 catalyst with a palladium content of 2%.

[0032] Example 3 The method for preparing a palladium-based catalyst for the semi-hydrogenation of alkynols to enols according to the present invention is specifically implemented according to the following steps: Step 1: Add sodium tetrachloropalladium to deionized water and ultrasonically disperse to obtain a uniformly dispersed metal salt solution. The mass concentration of the metal salt solution is 0.006 g / mL, the ultrasonic temperature is 50℃, the ultrasonic time is 2 h, and the ultrasonic frequency is 50 kHz.

[0033] Step 2: Spread indium oxide evenly on a polytetrafluoroethylene plate. Load the active metal salt solution prepared in Step 1 into a micro-injection pump and slowly add the solution dropwise onto the carrier, controlling the drop rate at 20 mL / h to ensure complete and uniform absorption of the solution by the carrier. After impregnation, allow to stand at room temperature for 12 hours to age.

[0034] Step 3: Transfer the wet carrier obtained in Step 2 to an oven, heat it to 110°C in flowing air at 3°C / min, and keep it at that temperature for 1 hour; continue to heat it to 180°C in flowing air at 3°C / min and keep it at that temperature for 3 hours, then let it cool naturally to room temperature.

[0035] Step 4: Transfer the calcined sample to a tube furnace and reduce it at 200-500℃ for 1-5 hours to finally obtain a Pd / In2O3 catalyst with a palladium content of 3%.

[0036] Example 4 The method for preparing a palladium-based catalyst for the semi-hydrogenation of alkynols to enols according to the present invention is specifically implemented according to the following steps: Step 1: Add sodium tetrachloropalladium to deionized water and ultrasonically disperse to obtain a uniformly dispersed metal salt solution. The mass concentration of the metal salt solution is 0.008 g / mL, the ultrasonic temperature is 50℃, the ultrasonic time is 2 h, and the ultrasonic frequency is 50 kHz.

[0037] Step 2: Spread indium oxide evenly on a polytetrafluoroethylene plate. Load the metal salt solution prepared in Step 1 into a micro-injection pump and slowly add the solution dropwise onto the carrier, controlling the drop rate at 20 mL / h to ensure complete and uniform absorption of the solution by the carrier. After impregnation, allow to stand at room temperature for 12 hours to age.

[0038] Step 3: Transfer the wet carrier obtained in Step 2 to an oven, heat it to 110°C in flowing air at 3°C / min, and keep it at that temperature for 1 hour; continue to heat it to 180°C in flowing air at 3°C / min and keep it at that temperature for 3 hours, then let it cool naturally to room temperature.

[0039] Step 4: Transfer the calcined sample to a tube furnace and reduce it at 200-500℃ for 1-5 hours to finally obtain a Pd / In2O3 catalyst with a palladium content of 5%.

[0040] Example 5 The method for preparing a palladium-based catalyst for the semi-hydrogenation of alkynols to enols according to the present invention is specifically implemented according to the following steps: Step 1: Add sodium tetrachloropalladium to deionized water and ultrasonically disperse to obtain a uniformly dispersed metal salt solution; wherein the mass concentration of the metal salt solution is 0.002 g / mL, the ultrasonic temperature is 50℃, the ultrasonic time is 2 h, and the ultrasonic frequency is 50 kHz.

[0041] Step 2: Spread indium oxide evenly on a polytetrafluoroethylene plate. Load the active metal salt solution prepared in Step 1 into a micro-injection pump and slowly add the solution dropwise onto the carrier, controlling the drop rate at 20 mL / h to ensure complete and uniform absorption of the solution by the carrier. After impregnation, allow to stand at room temperature for 12 hours to age.

[0042] Step 3: Transfer the wet carrier obtained in Step 2 to an oven, heat it to 110°C in flowing air at 3°C / min, and keep it at that temperature for 1 hour; continue to heat it to 180°C in flowing air at 3°C / min and keep it at that temperature for 3 hours, then let it cool naturally to room temperature.

[0043] Step 4: Transfer the calcined sample to a tube furnace and reduce it at 300℃ for 1-5 hours to finally obtain a Pd / In2O3 catalyst with a palladium content of 5%.

[0044] Figure 1 This is a schematic diagram of the selective hydrogenation catalyst prepared in Example 1. The hydrogenation catalyst forms oxygen vacancies on its surface through high-temperature reduction. Figure 2 This is a transmission electron microscope image of the selective hydrogenation catalyst prepared in Example 1. Palladium metal is uniformly dispersed on the surface of the hydrogenation catalyst on the surface of the indium oxide support.

[0045] Figure 3 This is a schematic diagram of the palladium atomic crystal plane of the selective hydrogenation catalyst prepared by the conventional impregnation method in Example 1. The palladium atomic crystal plane is a flat Pd(111). Figure 4 This is a schematic diagram of the palladium atomic crystal plane of the selective hydrogenation catalyst prepared in Example 1. The palladium atomic crystal plane exhibits Pd (10,8,7) with step defects.

[0046] The experimental results of selective hydrogenation catalysts with different loadings were tested by gas chromatography, as shown in Table 1. It can be seen that the catalysts prepared in Examples 1-5 of this invention all have high conversion rates and selectivity.

[0047] Table 1 Experimental results of selective hydrogenation catalysts with different loadings

[0048] Example 6 The present invention discloses a method for preparing a palladium-based catalyst for the semi-hydrogenation of alkynols to enols. This method actively controls the synergy between droplet dynamics and carrier capillary action through a "confined space controllable impregnation" approach, ensuring instantaneous and complete absorption of the active precursor solution and effectively suppressing the enrichment of active components at the edges. Secondly, a high-temperature reduction-induced strategy induces the directional migration of partially reduced carrier species to the surface of palladium nanoparticles, forming a discontinuous, sub-monolayer selective coating, thereby precisely constructing "partially encapsulated" palladium active sites. This unique structure not only effectively suppresses the migration and sintering of palladium particles during the reaction process through strong metal-support interactions, improving catalytic stability, but more importantly, it modulates the electron density of palladium through interfacial charge transfer and stable oxygen vacancies, selectively shielding its highly active, low-selectivity edge and corner sites. This design enables the catalyst to simultaneously overcome the traditional trade-off between activity and selectivity in the selective hydrogenation of enol-sensitive compounds, achieving highly efficient and selective conversion. Furthermore, this method is simple and the conditions are controllable, providing a new approach for the industrial-scale production of high-performance selective hydrogenation catalysts.

Claims

1. A method for preparing a palladium-based catalyst for the semi-hydrogenation of alkynols to enols, characterized in that, The specific steps are as follows: Step 1: Add the metal salt to deionized water and disperse it by ultrasonication to obtain a uniformly dispersed metal salt solution; Step 2: Spread the carrier powder evenly on the polytetrafluoroethylene plate, load the metal salt solution prepared in Step 1 into the injection pump, and slowly drop the solution onto the carrier to ensure that the solution is completely and evenly absorbed by the carrier. After impregnation, let it stand and age to obtain a wet carrier. Step 3: Transfer the wet carrier obtained in Step 2 to an oven for calcination; Step 4: Transfer the calcined sample to a tube furnace for reduction to obtain a palladium-based catalyst for the semi-hydrogenation of alkynols to enols.

2. The method for preparing a palladium-based catalyst for the semi-hydrogenation of alkynols to enols as described in claim 1, characterized in that, In step 1, the ultrasonic temperature is 20-50℃, the ultrasonic time is 2-10h, and the ultrasonic frequency is 30-60kHz.

3. The method for preparing a palladium-based catalyst for the semi-hydrogenation of alkynols to enols as described in claim 1, characterized in that, In step 1, the mass concentration of the metal salt solution is 0.002-0.010 g / mL, and the metal salt is any one or more of palladium nitrate, palladium chloride, sodium tetrachloropalladiumate, and palladium acetate.

4. The method for preparing a palladium-based catalyst for the semi-hydrogenation of alkynols to enols as described in claim 1, characterized in that, In step 2, the carrier powder is indium oxide or cerium oxide, and the particle size of the powder is 50nm-100μm; the drop rate is controlled at 20-60mL / h, and the aging time is 2-8h.

5. The method for preparing the palladium-based catalyst for the semi-hydrogenation of alkynols to enols as described in claim 1, characterized in that, In step 3, the roasting process is as follows: the temperature is increased to 100-150℃ at 2-5℃ / min and held for 1-2 hours; then the temperature is increased to 180-200℃ at 2-5℃ / min and held for 3-5 hours, and then naturally cooled to room temperature.

6. The method for preparing a palladium-based catalyst for the semi-hydrogenation of alkynols to enols as described in claim 1, characterized in that, In step 4, the reduction temperature is 200-500℃, the reduction time is 1-5h, and the palladium content in the palladium-based catalyst for the semi-hydrogenation of alkynols to enols is 0.5%-5%.

7. The palladium-based catalyst prepared by the method for preparing palladium-based catalysts for the semi-hydrogenation of alkynols to enols as described in any one of claims 1-6.

8. The application of the palladium-based catalyst for the partial hydrogenation of alkynols to enols as described in any one of claims 1-6 in the selective hydrogenation reaction of alkynols.

9. The application as described in claim 8, characterized in that, Specifically, palladium-based catalyst, organic solvent and alkynol material are added to a high-pressure hydrogenation reactor, hydrogen gas at 0.2-0.8 MPa is introduced, the reaction temperature is 30-80℃, samples are taken for analysis every half hour, and the reaction is stopped when the material is completely converted; wherein, the amount of palladium-based catalyst is 0.5-2 wt% of the mass of alkynol material.

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