Catalysts for carbon-supported Pd nanoparticles or PdNi alloy nanoparticles, their preparation methods and applications

Abstract

This invention discloses a catalyst supported on carbon-loaded Pd nanoparticles or PdNi alloy nanoparticles, its preparation method, and its application, belonging to the field of chemical engineering technology. The preparation method includes: preparing an aqueous solution of a metal salt by adding water to a metal salt and a surface modifier; mixing the aqueous solution of the metal salt and an aqueous solution of a reducing agent under enhanced mass transfer conditions, reacting to obtain a Pd / PdNi alloy nanoparticle dispersion; immersing a support in the dispersion to obtain a precursor; then removing the solvent, washing, and calcining to obtain the catalyst supported on carbon-loaded Pd / PdNi alloy nanoparticles. This invention also discloses the catalyst supported on carbon-loaded Pd nanoparticles or the catalyst supported on carbon-loaded PdNi alloy nanoparticles prepared by the above method, and its application as a hydrogenation catalyst. The Pd and PdNi alloy nanoparticles in the catalyst of this invention have high crystallinity / alloying degree, small particle size, and uniform distribution; good catalytic effect, improved catalyst lifetime and loading stability, and reduced catalyst cost.

Description

Technical Field

[0001] This invention belongs to the field of chemical technology, specifically the field of catalyst technology, and specifically relates to catalysts for carbon-supported Pd nanoparticles or PdNi alloy nanoparticles, their preparation methods and applications. Background Technology

[0002] Palladium (Pd), a member of the platinum group elements, has extremely scarce proven reserves. Therefore, palladium is typically supported on porous supports for heterogeneous catalytic reactions to minimize catalyst loss. Palladium-on-carbon catalysts are among the most commonly used catalysts in catalytic hydrogenation, widely applied in the hydrogenation of double bonds, nitro groups, nitroso groups, and carbonyl groups. Industrially, activated carbon is often used as the carbon support for Pd catalysts due to its large specific surface area, excellent pore structure, abundant surface groups, and good loading and reducing properties. When palladium is supported on activated carbon, highly dispersed palladium can be prepared, and the activated carbon can act as a reducing agent, providing a reducing environment that lowers reaction temperature and pressure, thereby improving catalyst activity.

[0003] The porous carbon support selected for Pd catalysts has a complex and multifaceted impact on their performance. Factors such as the support's structure, specific surface area, pore structure, strength, particle size distribution, impurity content, and ash content affect the loading and distribution of active components in the Pd catalyst. The interaction between the metal and the support not only affects the catalyst's heat resistance and stability but also relates to the valence state distribution of the active metal components on the catalyst surface. Therefore, the performance of carbon-supported Pd catalysts is not only related to the surface, pore structure, and surface physicochemical properties of the carbon support but is also influenced by the raw materials and production processes used to produce the carbon support.

[0004] In the industrial application of Pd catalysts, besides the choice of support, the selectivity, catalytic activity, and lifetime of the catalyst are also important considerations. Because Pd catalysts are expensive and prone to loss of activity due to carbon deposition, metal promoters are often added to Pd catalysts in industry to reduce costs and extend their lifespan. Adding a second metal promoter changes the geometry and electronic structure of the nanoparticles on the catalyst surface, thereby altering the adsorption and desorption capabilities of Pd nanoparticles for hydrogenation feedstocks. Compared to single Pd catalysts, the activity and selectivity of Pd-based bimetallic catalysts can be significantly improved.

[0005] Existing processes for preparing carbon-supported Pd catalysts still face the following challenges:

[0006] 1. Quality issues of activated carbon carriers: For commonly used coconut shell activated carbon carriers, the production process of imported coconut shell activated carbon is more stringent and complex than that of domestically produced ones. Imported coconut shell activated carbon has a more uniform particle size and pore size distribution, higher porosity, and a larger specific surface area. The performance of palladium-on-carbon catalysts largely depends on the quality of the activated carbon raw materials, and domestically produced coconut shell activated carbon struggles to meet the standards of imported products, making it difficult to substitute.

[0007] 2. Palladium loading: Palladium is a scarce precious metal resource in my country, and its loading directly affects the performance of palladium-carbon catalysts. To ensure high catalyst efficiency, a high Pd loading is usually required, which leads to very high catalyst costs.

[0008] 3. Stability issues of Pd nanoparticles: The loading stability of Pd nanoparticles still needs further improvement. During catalyst use, the leaching of Pd nanoparticles is difficult to avoid and cannot be completely recovered, resulting in significant economic losses.

[0009] In summary, the aforementioned issues render conventionally prepared palladium-on-carbon catalysts, while feasible for industrial applications, unsatisfactory in terms of catalytic performance and economics. Existing bimetallic catalysts, while possessing certain advantages, suffer from problems such as low alloying degree and poor dispersibility, limiting their market application. Therefore, the core challenge in this field is how to prepare high-performance, highly dispersed, and low-leaching carbon-supported Pd and its bimetallic alloy catalysts, while reducing Pd loading and cost. Summary of the Invention

[0010] One objective of this invention is to provide a method for preparing a catalyst supported on carbon-supported Pd nanoparticles or PdNi alloy nanoparticles. The catalyst prepared by this method has high crystallinity / alloying degree of Pd and PdNi alloy nanoparticles, with an average particle size of 1-8 nm and uniform particle size distribution. The catalyst of this invention can achieve the same catalytic effect under reduced Pd loading conditions, and the catalyst life and loading stability are improved, while reducing the catalyst cost.

[0011] A second objective of this invention is to provide a catalyst for carbon-supported Pd nanoparticles or PdNi alloy nanoparticles prepared by the above-described method.

[0012] A third objective of this invention is to provide applications of the catalyst.

[0013] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0014] In a first aspect, the present invention discloses a method for preparing a catalyst supported on carbon-supported Pd nanoparticles or PdNi alloy nanoparticles, the method comprising the following steps:

[0015] Step 1. Dissolve the metal salt and surface modifier in water to prepare an aqueous solution of the metal salt; the metal salt is a Pd salt, or a Pd salt and a Ni salt;

[0016] Step 2. Dissolve the reducing agent in water to obtain a reducing agent aqueous solution;

[0017] Step 3. Under enhanced mass transfer conditions, the aqueous solution of metal salt and the aqueous solution of reducing agent are mixed and reacted to obtain Pd nanoparticle dispersion or PdNi alloy nanoparticle dispersion;

[0018] Step 4. Immerse the support in Pd nanoparticle dispersion or PdNi alloy nanoparticle dispersion so that the pores of the support are completely filled with liquid to obtain carbon-supported Pd nanoparticle precursor or carbon-supported PdNi alloy nanoparticle precursor.

[0019] Step 5. Remove the solvent from the carbon-supported Pd nanoparticle precursor or the carbon-supported PdNi alloy nanoparticle precursor, wash, and calcine to obtain the catalyst of carbon-supported Pd or PdNi alloy nanoparticles.

[0020] In some embodiments of the present invention, the Pd salt is selected from at least one of palladium nitrate, sodium chloropalladium, palladium chloride, palladium acetate, palladium sulfate, and palladium acetylacetonate;

[0021] Or / and the Ni salt is selected from at least one of nickel nitrate and its hydrate, nickel chloride and its hydrate, nickel acetate and its hydrate, and nickel sulfate and its hydrate;

[0022] Or / and the surface modifier is selected from at least one of hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, decyldimethylammonium chloride, hexadecyldimethylbenzylammonium chloride, and polyvinylpyrrolidone;

[0023] Preferably, the concentration of the metal salt in the aqueous solution is 1-100 mmol / L;

[0024] More preferably, when the metal salt is a Pd salt and a Ni salt, the molar ratio of the Pd salt to the Ni salt is greater than or equal to 1:2;

[0025] More preferably, the mass of the surface modifier is 0.1-1.0% of the total mass of the metal salt aqueous solution and the reducing agent aqueous solution.

[0026] In some embodiments of the present invention, the reducing agent is selected from at least one of formaldehyde, sodium borohydride, hydrazine hydrate, hydroxylamine, sodium formate, ascorbic acid, glucose, and citric acid;

[0027] Preferably, the concentration of the reducing agent aqueous solution is 5-1500 mmol / L;

[0028] Preferably, the molar ratio of the metal salt to the reducing agent is 1:4 to 1:10;

[0029] More preferably, the volume ratio of the metal salt aqueous solution to the reducing agent aqueous solution is 2:1 to 6:1.

[0030] In some embodiments of the present invention, the reaction temperature in step 3 is 40-80°C and the reaction time is 1-4 hours.

[0031] In some embodiments of the present invention, the carrier is selected from at least one of carbon nanotubes, pretreated MOF / COF, pretreated mesoporous carbon, and pretreated activated carbon;

[0032] Preferably, the pretreated MOF / COF refers to MOF / COF obtained by high-temperature vacuum degassing;

[0033] Preferably, the pretreated mesoporous carbon refers to mesoporous carbon obtained by high-temperature vacuum degassing;

[0034] More preferably, the temperature for high-temperature vacuum degassing of MOF / COF and mesoporous carbon is 120–180°C, more preferably 150°C; the degassing time is preferably 6–24 h, more preferably 12 h.

[0035] Preferably, the pretreatment method for the pretreated activated carbon is as follows: placing the activated carbon in a container, adding a 10-20 wt% nitric acid aqueous solution, and refluxing at 60-80°C; more preferably, the concentration of the nitric acid aqueous solution is 15 wt%, the reflux temperature is 70°C, and the treatment time is 2-12 hours, and even more preferably 6 hours.

[0036] In some embodiments of the present invention, in step 4, the carrier is immersed in a Pd nanoparticle dispersion or a PdNi alloy nanoparticle dispersion and stirred to completely fill the pores of the carrier with liquid. The stirring time is 1 to 3 hours.

[0037] In some embodiments of the present invention, in step 5, the carbon-supported Pd nanoparticle precursor or the carbon-supported PdNi alloy nanoparticle precursor is subjected to depressurized distillation to remove the solvent, and the resulting solid product is washed with deionized water and then calcined in a protective gas environment.

[0038] Preferably, the protective gas includes nitrogen or an inert gas.

[0039] In some embodiments of the present invention, the calcination temperature is 400-600℃ and the calcination time is 1-6h.

[0040] Secondly, the present invention discloses a catalyst for carbon-supported Pd nanoparticles, which is prepared by the above-described method, wherein the metal salt is a Pd salt.

[0041] Thirdly, the present invention discloses a catalyst for carbon-supported PdNi alloy nanoparticles, which is prepared by the above-mentioned method, wherein the metal salts are Pd salt and Ni salt.

[0042] Fourthly, the present invention discloses the application of the above-mentioned carbon-supported Pd nanoparticle catalyst or carbon-supported PdNi alloy nanoparticle catalyst as a hydrogenation catalyst.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] This invention features a scientifically designed and ingeniously conceived method. It utilizes one or more of MOF / COF (metal-organic framework / covalent organic framework), carbon nanotubes, mesoporous carbon, and activated carbon as a support, providing greater porosity and specific surface area for the catalyst's active components. The MOF material can be further optimized by selecting materials with Ni as the metal site, thereby enhancing catalyst activity. The method involves adding a surface modifier to prepare a stable dispersion of small-sized Pd nanoparticles or highly alloyed PdNi nanoparticles. The pretreated support is then added to the dispersion for uniform adsorption. The solvent is removed by vacuum distillation, resulting in the uniform concentration and loading of Pd and PdNi alloy nanoparticles onto the support. Finally, calcination under a nitrogen atmosphere transforms the support material into a support-derived porous carbon material, removing the added surface modifier and exposing the dispersed Pd and PdNi alloy active sites, further increasing their loading stability.

[0045] The Pd and PdNi alloy nanoparticles prepared by the method of this invention have high crystallinity / alloying degree, with average particle sizes of 1-8 nm and uniform particle size distribution. The PdNi alloy nanoparticles do not simply exhibit an additive effect between the two metals, but rather a synergistic enhancement effect. Under reduced Pd loading conditions, the same catalytic effect can be achieved, significantly reducing costs. Furthermore, calcination helps improve lifetime and loading stability, further reducing catalyst costs. Attached Figure Description

[0046] Appendix Figure 1 This is a transmission electron microscope image of the Pd nanoparticle dispersion prepared in Example 1.

[0047] Appendix Figure 2 The transmission electron microscope (TEM) image of the Pd nanoparticle dispersion prepared in Example 1 corresponds to the particle size distribution.

[0048] Appendix Figure 3 This is a transmission electron microscope (TEM) image of the activated carbon-supported Pd nanoparticle catalyst prepared in Example 1.

[0049] Appendix Figure 4This is a transmission electron microscope image of the PdNi alloy nanoparticle dispersion prepared in Example 2.

[0050] Appendix Figure 5 The transmission electron microscope image of the PdNi alloy nanoparticle dispersion prepared in Example 2 corresponds to the particle size distribution.

[0051] Appendix Figure 6 This is a transmission electron microscope (TEM) image of the activated carbon-supported PdNi alloy nanoparticle catalyst prepared in Example 2.

[0052] Appendix Figure 7 This is a transmission electron microscope (TEM) image of the PdNi alloy nanoparticle dispersion prepared in Comparative Example 1. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0054] Example 1

[0055] This embodiment discloses a method for preparing a carbon-supported Pd nanoparticle catalyst, as detailed below:

[0056] S1. Pretreatment of activated carbon: Add 400g of activated carbon to 4L of 15% nitric acid aqueous solution, slowly heat to 70℃, and continuously treat for 6h under reflux and stirring conditions; then filter and wash until the pH value is 6-7, and dry at 80℃ for later use.

[0057] S2. Preparation of aqueous solution of metal salt: Dissolve 5.884 g of sodium chloropalladium and 10 g of polyvinylpyrrolidone in 0.3 L of deionized water to prepare aqueous solution of metal salt;

[0058] S3. Preparation of reducing agent aqueous solution: Dissolve 3.782g of sodium borohydride in 0.1L of deionized water to prepare reducing agent aqueous solution;

[0059] S4. Preparation of Pd nanoparticle dispersion: The aqueous solution of metal salt and the aqueous solution of reducing agent were preheated to 50°C. Under the condition of mechanical stirring speed of 1000 rpm, the aqueous solution of reducing agent was added dropwise to the aqueous solution of metal salt. After the addition was completed, the reaction was stirred for 2 hours to obtain the Pd nanoparticle dispersion.

[0060] S5. Loading and calcination: 400g of pretreated activated carbon obtained in S1 was soaked in the Pd nanoparticle dispersion obtained in S4 and stirred for 2h to obtain carbon-supported Pd nanoparticle precursor; then the solvent was completely removed by vacuum distillation and washed 3 times with deionized water, 0.4L each time; finally, the obtained solid was placed in a nitrogen environment and calcined at 450℃ for 2h to obtain the product activated carbon-supported Pd nanoparticle catalyst.

[0061] Experimental Example 1

[0062] This experimental example analyzed and tested the Pd nanoparticle dispersion and activated carbon-supported Pd nanoparticle catalyst prepared in Example 1.

[0063] 1. Take 1 mL of the Pd nanoparticle dispersion prepared in step S4 of Example 1 and add it to 3 mL of acetone. After rotary evaporation and concentration, take a small amount and drop it onto a carbon support film for transmission electron microscopy. Observe the morphology, size and structure of the particles using transmission electron microscopy.

[0064] A transmission electron microscope image of the Pd nanoparticle dispersion is attached. Figure 1 As shown: the obtained product particles have a spherical morphology.

[0065] right Figure 1 Perform particle size analysis to obtain the corresponding particle size distribution map, such as Figure 2 As shown, the Pd nanoparticles have a particle size of 2-6 nm, an average particle size of 3.55 nm, a narrow particle size distribution, and relatively uniform particle size and morphology.

[0066] 2. Take a small amount of the activated carbon-supported Pd nanoparticle catalyst from Example 1, place it in an aqueous solution and stir thoroughly. Then, drop the suspension onto the carbon support film. After it is completely dry, blow the surface of the carbon support film with a syringe and observe the uniformity and agglomeration of the catalyst loading using a transmission electron microscope.

[0067] Transmission electron microscopy (TEM) images of Pd nanoparticle catalysts supported on activated carbon are attached. Figure 3 As shown, Pd nanoparticles are distributed in the porous structure of activated carbon, with small particle size and no serious agglomeration.

[0068] Example 2

[0069] This embodiment discloses a method for preparing a carbon-supported PdNi alloy nanoparticle catalyst. Compared with Example 1, when preparing the metal salt aqueous solution, the step of "dissolving 5.884g of sodium chloropalladium and 10g of polyvinylpyrrolidone in 0.3L of deionized water" in Example 1 is replaced with "dissolving 2.942g of sodium chloropalladium, 2.377g of nickel chloride hexahydrate, and 10g of polyvinylpyrrolidone in 0.3L of deionized water". All other steps are the same. Finally, the activated carbon-supported PdNi alloy nanoparticle catalyst is obtained through a PdNi alloy nanoparticle dispersion system.

[0070] Experimental Example 2

[0071] This experimental example analyzed and tested the PdNi alloy nanoparticle dispersion and activated carbon-supported PdNi alloy nanoparticle catalyst prepared in Example 2. The testing methods were the same as in Example 1.

[0072] 1. The transmission electron microscope (TEM) image of the PdNi alloy nanoparticle dispersion prepared in Example 2 is attached. Figure 4 As shown: The PdNi alloy nanoparticles have a regular morphology and are spherical. There is slight agglomeration between the particles (which may be caused by excessively high sample concentration due to rotary evaporation concentration). However, the dispersion solution is well dispersed and there is no obvious precipitation after standing for 1 day. Its dispersion has no significant impact on subsequent loading.

[0073] right Figure 4 Particle size analysis was performed to obtain the corresponding particle size distribution map, as shown in the attached figure. Figure 5 As shown, the PdNi alloy nanoparticles have a particle size of 3-8 nm and an average particle size of 5.54 nm. Although the particle size is slightly larger than that of the Pd nanoparticles in Example 1, the particle size distribution is still relatively narrow, and the particle size and morphology are relatively uniform.

[0074] 2. The transmission electron microscope (TEM) results of the activated carbon-supported PdNi alloy nanoparticle catalyst prepared in Example 2 are shown in the attached figure. Figure 6 As shown, the PdNi alloy nanoparticles are still relatively small and uniform in size. After several nanoparticles agglomerate into a structure similar to nanoflowers, they are uniformly dispersed on the activated carbon carrier.

[0075] Example 3

[0076] This embodiment discloses a method for preparing a carbon-supported Pd nanoparticle catalyst. Compared with Example 1, when preparing the metal salt aqueous solution, the amount of sodium chloropalladium added is increased from 5.884g to 11.768g, the amount of polyvinylpyrrolidone added is increased from 10g to 20g, and the amount of sodium borohydride added is increased from 3.782g to 7.564g; the remaining steps are the same.

[0077] The particle size and distribution of the activated carbon-supported Pd nanoparticle catalyst obtained in Example 3 are basically the same as those in Example 1. It was observed that the loading of Pd nanoparticles on the activated carbon increased significantly, and there was no obvious agglomeration phenomenon.

[0078] Example 4

[0079] This example investigates the preparation of carbon-supported Pd nanoparticle catalysts using different Pd salts. The preparation was carried out according to the method of Example 1, except that sodium chloropalladium in Example 1 was replaced with one or more of palladium nitrate, sodium chloropalladium, palladium chloride, palladium acetate, palladium sulfate, and palladium acetylacetonate. The molar amount of Pd salt was 0.02 mol in all examples, as detailed below:

[0080] Table 1 Results of the preparation of carbon-supported Pd nanoparticle catalysts with different Pd salts

[0081]

[0082]

[0083] The results showed that the particle size and distribution of the carbon-supported Pd nanoparticle catalyst prepared by the above-mentioned Pd metal salt were basically the same as those in Example 1. Pd nanoparticles were uniformly loaded on the activated carbon without obvious agglomeration.

[0084] Example 5

[0085] This embodiment examines and discloses the preparation of carbon-supported PdNi alloy nanoparticle catalysts using different Ni salts. The preparation was carried out according to the method of Example 2, except that the nickel chloride hexahydrate in Example 2 was replaced with one or more of nickel nitrate, nickel chloride, nickel acetate, nickel sulfate, and their hydrates. Details are as follows:

[0086] Table 2 Results of the preparation of carbon-supported PdNi alloy nanoparticle catalysts with different Ni salts

[0087]

[0088]

[0089] The results showed that the particle size and distribution of the carbon-supported PdNi alloy nanoparticle catalyst prepared by the above Ni salt were basically the same as those in Example 2. It was observed that the loading of PdNi alloy nanoparticles on activated carbon increased significantly, and there was no obvious agglomeration phenomenon.

[0090] Example 6

[0091] This example investigated the preparation of carbon-supported Pd nanoparticle catalysts using different surface modifiers. The preparation was carried out according to the method of Example 1, except that the surface modifier was replaced with one or more of hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, disdecyldimethylammonium chloride, hexadecyldimethylbenzylammonium chloride, and polyvinylpyrrolidone, while all other conditions remained the same.

[0092] The details are as follows:

[0093] Table 3 Results of the preparation of carbon-supported Pd nanoparticle catalysts with different surface modifiers

[0094]

[0095] The results showed that the particle size and distribution of the carbon-supported Pd nanoparticle catalyst prepared by the above surface modifier were basically the same as those in Example 1. It was observed that the Pd alloy nanoparticles on the activated carbon had high dispersion and no obvious agglomeration.

[0096] Example 7

[0097] This embodiment investigates the preparation of carbon-supported Pd nanoparticle catalysts using different reducing agents. The preparation was carried out according to the method of Example 1, except that the reducing agent was replaced with one or more of formaldehyde, sodium borohydride, hydrazine hydrate, hydroxylamine, sodium formate, ascorbic acid, glucose, and citric acid; all other conditions remained the same.

[0098] The details are as follows:

[0099] Table 4 Results of the preparation of carbon-supported Pd nanoparticle catalysts with different reducing agents

[0100]

[0101] The results showed that the carbon-supported Pd nanoparticle catalyst prepared in this embodiment had similar effects to that in Example 1.

[0102] Example 8

[0103] This example investigated the preparation of carbon-supported Pd nanoparticle catalysts and carbon-supported PdNi alloy nanoparticle catalysts at different reaction temperatures. The carbon-supported Pd nanoparticle catalyst was prepared according to the method of Example 1, and the carbon-supported PdNi alloy nanoparticle catalyst was prepared according to the method of Example 2. The difference lay in the reaction temperature. Details are as follows:

[0104] Table 5 Results of the preparation of carbon-supported Pd nanoparticles / PdNi alloy nanoparticle catalysts at different reaction temperatures

[0105]

[0106]

[0107] The results showed that when the reaction temperature was 40–80 °C, the carbon-supported Pd nanoparticle catalyst and the carbon-supported PdNi alloy nanoparticle catalyst prepared both had relatively regular morphology, small size and high dispersion.

[0108] Example 9

[0109] This embodiment investigated the preparation of carbon-supported Pd nanoparticle catalysts and carbon-supported PdNi alloy nanoparticle catalysts with different reaction times. The carbon-supported Pd nanoparticle catalyst was prepared according to the method of Example 1, and the carbon-supported PdNi alloy nanoparticle catalyst was prepared according to the method of Example 2. The difference lay in the reaction time; in this embodiment, reaction times of 1 h, 3 h, and 4 h were used to prepare the carbon-supported Pd nanoparticle catalyst and the carbon-supported PdNi alloy nanoparticle catalyst, respectively. Details are as follows:

[0110] Table 6 Results of the preparation of carbon-supported Pd nanoparticle / PdNi alloy nanoparticle catalysts at different reaction times

[0111]

[0112] The results showed that when the reaction temperature was 1–4 h, the carbon-supported Pd nanoparticle catalyst and the carbon-supported PdNi alloy nanoparticle catalyst prepared both had relatively regular morphology, small size and high dispersion.

[0113] Example 10

[0114] This embodiment investigated the preparation of carbon-supported Pd nanoparticle catalysts and carbon-supported PdNi alloy nanoparticle catalysts under different calcination conditions. The carbon-supported Pd nanoparticle catalyst was prepared according to the method of Example 1, and the carbon-supported PdNi alloy nanoparticle catalyst was prepared according to the method of Example 2. The difference lay in the calcination temperature and calcination time.

[0115] Table 7 Results of the preparation of carbon-supported Pd nanoparticle / PdNi alloy nanoparticle catalysts under different calcination conditions

[0116]

[0117] The results showed that when the calcination temperature was 400–600℃ and the calcination time was 1–6h, the carbon-supported Pd nanoparticle catalyst and the carbon-supported PdNi alloy nanoparticle catalyst prepared both had relatively regular morphology, small size and high dispersion.

[0118] Example 11

[0119] This embodiment investigated the preparation of carbon-supported Pd nanoparticle catalysts and carbon-supported PdNi alloy nanoparticle catalysts using different supports. The carbon-supported Pd nanoparticle catalyst was prepared according to the method in Example 1, and the carbon-supported PdNi alloy nanoparticle catalyst was prepared according to the method in Example 2. The difference lay in the support used.

[0120] Table 8 Results of the preparation of carbon-supported Pd nanoparticle / PdNi alloy nanoparticle catalysts with different supports

[0121]

[0122]

[0123] The mesoporous carbon in the table above is degassed under vacuum at 150°C for 12 hours before being used as a carrier.

[0124] The results show that the carbon-supported Pd nanoparticle catalysts and carbon-supported PdNi alloy nanoparticle catalysts prepared using the supports in the table above both have relatively regular morphologies, small sizes, and high dispersion.

[0125] Example 12

[0126] This embodiment discloses a method for preparing a carbon-supported PdNi alloy nanoparticle catalyst, as detailed below:

[0127] S1. Pretreatment of the carrier: Place 1g of Ni-dhbq (a Ni-based MOF material) in a vacuum oven at 150℃ overnight, and set aside for use after activation and degassing;

[0128] S2. Preparation of aqueous solution of metal salt: Dissolve 29.42 mg sodium chloropalladium, 23.77 mg nickel chloride hexahydrate and 100 mg polyvinylpyrrolidone in 30 mL of deionized water to prepare aqueous solution of metal salt;

[0129] S3. Preparation of reducing agent aqueous solution: Dissolve 37.82 mg sodium borohydride in 10 mL of deionized water by stirring to obtain reducing agent aqueous solution;

[0130] S4. Preparation of PdNi alloy nanoparticle dispersion: The aqueous solution of metal salt and the aqueous solution of reducing agent were preheated to 50°C. Under the condition of mechanical stirring speed of 1000 rpm, the aqueous solution of reducing agent was added dropwise to the aqueous solution of metal salt. After the addition was completed, the reaction was stirred for 2 hours to obtain the PdNi alloy nanoparticle dispersion.

[0131] S5. Loading and calcination: The pretreated Ni-based MOF material Ni-dhbq obtained in S1 was soaked in a dispersion and stirred for 2 hours to obtain a carbon-supported PdNi alloy nanoparticle precursor. After completely removing the solvent by vacuum distillation, it was washed three times with 40 mL of deionized water each time. Finally, the obtained solid was placed in a nitrogen environment and calcined at 600 °C for 6 hours. Ni-dhbq was converted into MOF-derived porous carbon material at high temperature, and its Ni metal sites were retained. Thus, the product Ni-dhbq-derived porous carbon-supported PdNi alloy nanoparticle catalyst was obtained.

[0132] Example 13

[0133] The catalysts obtained in Examples 1 and 2 were prepared in batches to obtain 50 kg of each catalyst. ICP characterization revealed that the Pd loading was approximately 0.5% and 0.25%, respectively. In addition, a commercially available 0.5% Pd / C sheet catalyst was purchased as a performance control group.

[0134] Commercially available Pd / C and the catalysts prepared in Examples 1 and 2 were loaded into a reaction chamber with a volume of 0.15 m³. 3 The performance of the catalyst was evaluated in a pilot hydrogenation unit. The results of the catalyst evaluation are shown in Table 9.

[0135] Evaluation method: The catalyst loading is 40 kg; the hydrogenation feedstock is unsaturated acid.

[0136] Unsaturated acid solid powder is added to a circulating aqueous solution system through a hopper to dissolve, and after hydrogenation, the saturated acid product is removed through a cooling crystallization step.

[0137] Reaction process conditions: Unsaturated acid feed rate is 2.5 kg / h, aqueous solution circulation rate is 0.55 m³ / h. 3 / h; reaction pressure 1.5MPa, reaction temperature 50℃; hydrogen feed is pressure controlled, maintaining the reaction pressure at 1.5MPa; the concentration of unsaturated acid at sampling points before and after the hydrogenation reactor after 2 weeks of reaction is characterized by liquid chromatography, and the single-pass conversion rate of the hydrogenation reaction is calculated.

[0138] Table 9 Catalyst Evaluation Results

[0139]

[0140] As can be seen from the comparison of catalyst evaluation results in Table 9:

[0141] All three catalysts exhibited good stability under the same process conditions and a two-week observation period, using unsaturated acids as raw materials. However, the catalyst of Example 1 showed significantly superior hydrogenation activity compared to commercially available Pd / C, achieving complete conversion (~100%) of the unsaturated acid under the same reaction conditions. The activated carbon-supported PdNi alloy nanoparticle catalyst prepared in Example 2, with only half the Pd content, not only showed better catalytic performance than commercially available Pd / C, but its catalytic performance was even close to that of the activated carbon-supported Pd alloy nanoparticle catalyst prepared in Example 1, further illustrating the synergistic enhancement effect of PdNi alloy nanoparticles. These results indicate that the catalysts prepared by this invention all possess excellent catalytic activity and stability.

[0142] Comparative Example 1

[0143] Compared with Example 2, Comparative Example 1 did not contain the surface modifier polyvinylpyrrolidone.

[0144] The transmission electron microscope (TEM) image of the PdNi alloy nanoparticle dispersion prepared in this proportion is attached. Figure 7 As shown. (From the appendix) Figure 7 It can be seen that the PdNi alloy nanoparticle dispersion contains two sizes of PdNi alloy nanoparticles: small nanoparticles with spherical morphology and large PdNi alloy nanoparticles with irregular spherical morphology. This is presumably because, without a surface modifier to provide intermolecular repulsion during the reaction, the small PdNi alloy nanoparticles tend to aggregate. Due to the Ostwald ripening process, the particles gradually grow, eventually forming large, irregular morphological structures. Ultimately, this results in the final activated carbon-supported PdNi alloy nanoparticle catalyst, where the boundaries of the supported nanoparticles are difficult to distinguish and the particle size range determined under a transmission electron microscope. Under these conditions, it is impossible to obtain a carbon-supported PdNi alloy nanoparticle catalyst with high crystallinity and uniform particle size.

[0145] Comparative Example 2

[0146] Compared with Example 12, Comparative Example 2 differs in its calcination temperature, while all other conditions remain the same. The calcination temperature of this comparative example is 300°C.

[0147] The results showed that the organic framework on Ni-dhbq could not be carbonized at the low temperature, and the residual surface modifier could not be decomposed at the low temperature, which ultimately resulted in the failure to obtain Ni-dhbq-derived porous carbon-supported PdNi alloy nanoparticle catalyst materials.

[0148] The above description is merely a preferred embodiment of the present invention and is illustrative in nature, not intended to limit the scope of the invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the invention should fall within the protection scope defined by the claims.

Claims

1. A method for preparing a catalyst supported on carbon-supported Pd nanoparticles or PdNi alloy nanoparticles, characterized in that, Includes the following steps: Step 1. Dissolve the metal salt and surface modifier in water to prepare an aqueous solution of the metal salt; the metal salt is a Pd salt, or a Pd salt and a Ni salt; Step 2. Dissolve the reducing agent in water to obtain a reducing agent aqueous solution; Step 3. Under enhanced mass transfer conditions, the aqueous solution of metal salt and the aqueous solution of reducing agent are mixed and reacted to obtain Pd nanoparticle dispersion or PdNi alloy nanoparticle dispersion; Step 4. Immerse the support in Pd nanoparticle dispersion or PdNi alloy nanoparticle dispersion so that the pores of the support are completely filled with liquid to obtain carbon-supported Pd nanoparticle precursor or carbon-supported PdNi alloy nanoparticle precursor. Step 5. Remove the solvent from the carbon-supported Pd nanoparticle precursor or the carbon-supported PdNi alloy nanoparticle precursor, wash, and calcine to obtain the catalyst of carbon-supported Pd or PdNi alloy nanoparticles.

2. The method for preparing a catalyst based on carbon-supported Pd nanoparticles or PdNi alloy nanoparticles according to claim 1, characterized in that, The Pd salt is selected from at least one of palladium nitrate, sodium chloropalladium, palladium chloride, palladium acetate, palladium sulfate, and palladium acetylacetonate. Or / and the Ni salt is selected from at least one of nickel nitrate and its hydrate, nickel chloride and its hydrate, nickel acetate and its hydrate, and nickel sulfate and its hydrate; Or / and the surface modifier is selected from at least one of hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, decyldimethylammonium chloride, hexadecyldimethylbenzylammonium chloride, and polyvinylpyrrolidone; Preferably, the concentration of the metal salt in the aqueous solution is 1-100 mmol / L; More preferably, when the metal salt is a Pd salt and a Ni salt, the molar ratio of the Pd salt to the Ni salt is greater than or equal to 1:2; More preferably, the mass of the surface modifier is 0.1-1.0% of the total mass of the metal salt aqueous solution and the reducing agent aqueous solution.

3. The method for preparing a catalyst based on carbon-supported Pd nanoparticles or PdNi alloy nanoparticles according to claim 1, characterized in that, The reducing agent is selected from at least one of formaldehyde, sodium borohydride, hydrazine hydrate, hydroxylamine, sodium formate, ascorbic acid, glucose, and citric acid; Preferably, the concentration of the reducing agent aqueous solution is 5-1500 mmol / L; Preferably, the molar ratio of the metal salt to the reducing agent is 1:4 to 1:10; More preferably, the volume ratio of the metal salt aqueous solution to the reducing agent aqueous solution is 2:1 to 6:

1.

4. The method for preparing a catalyst based on carbon-supported Pd nanoparticles or PdNi alloy nanoparticles according to claim 1, characterized in that, The reaction temperature in step 3 is 40–80°C, and the reaction time is 1–4 hours.

5. The method for preparing a catalyst based on carbon-supported Pd nanoparticles or PdNi alloy nanoparticles according to claim 1, characterized in that, The carrier is selected from at least one of carbon nanotubes, pretreated MOF / COF, pretreated mesoporous carbon, and pretreated activated carbon; Preferably, the pretreated MOF / COF refers to MOF / COF obtained by high-temperature vacuum degassing; Preferably, the pretreated mesoporous carbon refers to mesoporous carbon obtained by high-temperature vacuum degassing; More preferably, the temperature for high-temperature vacuum degassing of MOF / COF and mesoporous carbon is 120–180°C, more preferably 150°C; the degassing time is preferably 6–24 h, more preferably 12 h. Preferably, the pretreatment method for the pretreated activated carbon is as follows: placing the activated carbon in a container, adding a 10-20 wt% nitric acid aqueous solution, and refluxing at 60-80°C; more preferably, the concentration of the nitric acid aqueous solution is 15 wt%, the reflux temperature is 70°C, and the treatment time is 2-12 hours, and even more preferably 6 hours.

6. The method for preparing a catalyst based on carbon-supported Pd nanoparticles or PdNi alloy nanoparticles according to claim 1, characterized in that, In step 4, the carrier is immersed in a Pd nanoparticle dispersion or a PdNi alloy nanoparticle dispersion and stirred to completely fill the pores of the carrier with liquid. The stirring time is 1 to 3 hours.

7. The method for preparing a catalyst based on carbon-supported Pd nanoparticles or PdNi alloy nanoparticles according to claim 1, characterized in that, In step 5, the carbon-supported Pd nanoparticle precursor or the carbon-supported PdNi alloy nanoparticle precursor is subjected to vacuum distillation to remove the solvent. The resulting solid product is washed with deionized water and then calcined in a protective gas environment. Preferably, the protective gas includes nitrogen or an inert gas; Preferably, the calcination temperature is 400–600℃ and the calcination time is 1–6 hours.

8. A catalyst for carbon-supported Pd nanoparticles, characterized in that, The metal salt is prepared by any one of the methods described in claims 1 to 7, wherein the metal salt is a Pd salt.

9. A catalyst for carbon-supported PdNi alloy nanoparticles, characterized in that, The metal salt is prepared by any one of the methods described in claims 1 to 7, wherein the metal salt is a Pd salt or a Ni salt.

10. The application of the catalyst with carbon-supported Pd nanoparticles according to claim 8 or the catalyst with carbon-supported PdNi alloy nanoparticles according to claim 9, characterized in that, Its application as a hydrogenation catalyst.

Images