CN118616041A - Supported noble metal palladium hydrogenation catalyst and preparation method and application thereof - Google Patents

Abstract

The present invention discloses a supported noble metal palladium hydrogenation catalyst, including a carrier and an active component, _wherein the carrier is _Al2O3 , the active component is Pd nanoparticles, _and the loading amount of the Pd nanoparticles is 0.05%-5.0%. The present invention also discloses a preparation method of a supported noble metal palladium hydrogenation catalyst, wherein _Al2O3 and water are mixed, ultrasonically treated, and solution A is obtained; a soluble palladium salt solution is added to solution A, stirred, urea aqueous solution is added to react, sodium borohydride aqueous solution is added to the reaction solution, and centrifuged after stirring to obtain a dark brown solid, which is dried. The supported noble metal palladium hydrogenation catalyst of the present invention can be applied to benzoic acid hydrogenation to produce cyclohexanecarboxylic acid. The catalyst of the present invention has high activity, can make benzoic acid hydrogenation be carried out under mild conditions, and the required reaction time is greatly shortened, greatly improves production efficiency, and has good industrial prospects.

Description

Supported noble metal palladium hydrogenation catalyst and preparation method and application thereof

Technical Field

The invention belongs to the technical field of catalyst preparation, and in particular relates to a supported noble metal palladium hydrogenation catalyst, and also relates to a preparation method and application of the noble metal palladium hydrogenation catalyst.

Background Art

As an important organic synthesis intermediate, cyclohexylcarboxylic acid has extremely high application value in the fields of chemical industry, biomedicine and new materials research and development. In the field of chemical industry, it can be used as a photoinitiator with excellent performance, and can also be used to synthesize the photocuring agent l-hydroxycyclohexyl phenyl ketone. Its derivatives such as trans-p-alkylcyclohexanecarboxylic acid can be used to improve the thermal stability of liquid crystal materials and are widely used in the field of liquid crystal materials; in the field of biomedicine, it can be used to synthesize drugs such as caprolactam and praziquantel, and has extremely high application value.

Catalytic hydrogenation reaction usually generates target product and water, and byproducts are difficult to produce under suitable process conditions, so it meets the requirements of high atomicity and green chemistry. At present, the selective benzene ring hydrogenation reaction of benzoic acid is the most direct and effective method for synthesizing cyclohexanecarboxylic acid, and it has great prospects in industrial application. In the prior art, noble metal catalysts are mainly used for liquid phase catalytic hydrogenation of benzoic acid to generate cyclohexanecarboxylic acid, among which supported catalysts with highly dispersed active centers and high metal utilization rate stand out. The active components of supported catalysts are mainly noble metals Pd, Pt, Ru, Ir and Ni in non-noble metals, and the carrier is mainly based on carbon materials, titanium dioxide, and aluminum oxide. However, the hydrogenation reaction of benzoic acid has the following difficulties: on the one hand, the hydrogenation of benzoic acid needs to overcome the high resonance energy of the benzene ring, and usually needs to be carried out at a higher reaction temperature (>150°C); on the other hand, the benzene ring is connected to the electron-withdrawing group carboxyl, which requires more stringent conditions for hydrogenation than the electron-donating group, which will lead to some side reactions, such as the carboxyl group on the benzene ring being hydrogenated to hydroxyl or the decarboxylation of cyclohexanecarboxylic acid to produce cyclohexane and carbon monoxide.

Due to the structural stability of benzoic acid molecules and their strong adsorption to metals, traditional catalysts often require higher reaction temperatures for this reaction. In addition, the byproducts CO and _CO2 generated by the decarboxylation of carboxylic acids during the reaction are strongly adsorbed on the surface of Pd nanoparticles, resulting in varying degrees of catalyst deactivation. In addition, the selectivity of benzoic acid under mild conditions is not ideal, so it is necessary to develop new hydrogenation catalysts and synthesis methods.

Summary of the invention

The purpose of the present invention is to provide a supported noble metal palladium hydrogenation catalyst, which can enable benzoic acid hydrogenation reaction to be carried out under mild conditions, reduce the reaction time, and improve the activity of the catalyst.

Another object of the present invention is to provide a method for preparing the above-mentioned supported noble metal palladium hydrogenation catalyst, which step is simple to operate, has mild conditions, and the catalyst is evenly dispersed.

The third object of the present invention is to provide the use of the above-mentioned supported noble metal palladium hydrogenation catalyst in the hydrogenation of benzoic acid to cyclohexanecarboxylic acid.

The technical scheme adopted by the present invention is that the supported noble metal palladium hydrogenation catalyst comprises a carrier and an active component supported on the carrier, the carrier is Al ₂ O ₃ , the active component is Pd nanoparticles, and the loading amount of the Pd nanoparticles is 0.05%-5.0%.

Another technical solution adopted by the present invention is a method for preparing a supported noble metal palladium hydrogenation catalyst, which is specifically implemented according to the following steps:

Step 1, mixing Al ₂ O ₃ and water, and performing ultrasonic treatment to obtain solution A;

Step 2, adding a soluble palladium salt solution to solution A, stirring, then adding a urea aqueous solution to react, and after the reaction is completed, cooling to room temperature;

Step 3, adding a sodium borohydride aqueous solution to the reaction solution obtained in step 2, stirring and centrifuging to obtain a dark brown solid, and drying to obtain a supported noble metal palladium hydrogenation catalyst.

The present invention is also characterized in that:

In step 1, the mass ratio of Al ₂ O ₃ to water is 20-50:2-5, and the ultrasonic treatment time is 0.5-2h.

In step 2, the soluble palladium salt solution is any one or more of sodium tetrachloropalladate solution, palladium acetate solution, and palladium nitrate solution.

In step 2, the stirring time is 0.5-3 h; the concentration of the urea aqueous solution is 0.5-1 mmol/mL ^-1 , the reaction temperature is 70-100° C., and the reaction time is 1-3 h.

In step 3, the concentration of the sodium borohydride aqueous solution is 0.01-0.1 mmol/mL ^-1 , and the stirring time is 0.5-3 h.

The third technical scheme adopted by the present invention is the application of a supported noble metal palladium hydrogenation catalyst in the hydrogenation of benzoic acid to cyclohexanecarboxylic acid, specifically: benzoic acid is uniformly dispersed in isopropanol, a supported noble metal palladium hydrogenation catalyst is added and ultrasonically dispersed uniformly, then the mixture is transferred to an autoclave, the air in the reactor is replaced with 1MPa _H2 for three times, and a magnetic stirring reaction is carried out in an _H2 atmosphere to obtain cyclohexanecarboxylic acid; the amount of the supported noble metal palladium hydrogenation catalyst is 5-20% of the weight of the benzoic acid; the stirring reaction temperature is 60-150°C, the stirring reaction pressure is 1-5MPa, and the reaction time is 4-24h.

The beneficial effects of the present invention are:

The supported noble metal palladium hydrogenation catalyst prepared by the method of the present invention has high activity, can enable benzoic acid hydrogenation to be carried out under mild conditions, and the required reaction time is greatly shortened, thereby greatly improving production efficiency. It can realize efficient benzoic acid hydrogenation to produce cyclohexanecarboxylic acid under mild conditions, and has good industrial prospects.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a transmission electron micrograph of the Pd/Al ₂ O ₃ -CP catalyst prepared in Example 1;

FIG2 is a high-resolution transmission image of the Pd/Al ₂ O ₃ -CP catalyst prepared in Example 1;

FIG3 is a diagram showing the hydrogenation effects of the Pd/Al ₂ O ₃ -CP prepared in Example 1 and the Pd/Al ₂ O ₃ -IMP catalyst prepared in the comparative example on benzoic acid;

FIG4 shows the TOF values of the Pd/Al ₂ O ₃ -CP prepared in Example 1 and the Pd/Al ₂ O ₃ -IMP catalyst of the comparative example;

FIG5 is a graph showing the cyclic stability test of the Pd/Al ₂ O ₃ -CP catalyst prepared in Example 1;

FIG6 is a graph showing the cyclic stability test of the Pd/Al ₂ O ₃ -IMP catalyst prepared in the comparative example.

DETAILED DESCRIPTION

The present invention will be further described below through the accompanying drawings and specific embodiments.

The supported noble metal palladium hydrogenation catalyst of the invention comprises a carrier and an active component supported on the carrier, wherein the carrier is Al ₂ O ₃ , the active component is Pd nanoparticles, and the loading amount of the Pd nanoparticles is 0.05%-5.0%.

The loading amount of Pd nanoparticles is preferably 3.0%-5.0%. The specific surface area of _{Al 2} O ₃ is 500-2500 m ² /g, preferably 1000-2000 m ² /g.

The preparation method of the supported noble metal palladium hydrogenation catalyst of the present invention is specifically implemented according to the following steps:

Step 1, mixing Al ₂ O ₃ and water, and performing ultrasonic treatment to obtain solution A;

The mass ratio of Al ₂ O ₃ to water is 20-50:2-5, and the ultrasonic treatment time is 0.5-2h;

Step 2, adding a soluble palladium salt solution to solution A, stirring, then adding a urea aqueous solution to react, and after the reaction is completed, cooling to room temperature;

The soluble palladium salt solution is any one or more of sodium tetrachloropalladate solution, palladium acetate solution, and palladium nitrate solution; the stirring time is 0.5-3h;

The concentration of the urea aqueous solution is 0.5-1mmol/mL ^-1 , the reaction temperature is 70-100°C, and the reaction time is 1-3h;

Step 3, adding a sodium borohydride aqueous solution to the reaction solution obtained in step 2, stirring and centrifuging to obtain a dark brown solid, and drying to obtain a supported noble metal palladium hydrogenation catalyst;

The concentration of the sodium borohydride aqueous solution is 0.01-0.1 mmol/mL ^-1 , and the stirring time is 0.5-3 h.

The supported noble metal palladium hydrogenation catalyst prepared by the method of the present invention is applied to the hydrogenation of benzoic acid to produce cyclohexanecarboxylic acid, specifically:

The reactant benzoic acid is uniformly dispersed in isopropanol, and a supported noble metal palladium hydrogenation catalyst (Pd/Al ₂ O ₃ -CP catalyst) is added for uniform ultrasonic dispersion. The mixture is then transferred to an autoclave, and the air in the autoclave is replaced with 1 MPa H ₂ for three times. The reaction is then carried out under magnetic stirring in a H ₂ atmosphere, and the liquid phase composition is quantitatively analyzed by gas chromatograph, and the benzoic acid conversion rate and cyclohexanecarboxylic acid selectivity are recorded.

The dosage of the supported noble metal palladium hydrogenation catalyst is 5-20% of the weight of the reaction substrate benzoic acid; the stirring reaction temperature is 60-150° C., the stirring reaction pressure is 1-5 MPa, and the reaction time is 4-24 hours.

In terms of catalyst preparation, first, _{the Al2O3 carrier} and the soluble palladium salt are mixed evenly, and then urea is reacted with the soluble palladium salt solution to obtain a palladium salt precursor. This step is simple to operate, the conditions are mild, and the raw materials are cheap and easily available. Finally, the precursor obtained in the previous step is reduced with sodium borohydride to prepare the Pd _{/ Al2O3} catalyst, ensuring that the metal ions are evenly dispersed in the reaction system and completely loaded on _{the Al2O3} carrier.

In the aspect of catalyzing the hydrogenation of benzoic acid, the present invention uses hydrogen as the hydrogen ion source, which is in line with the concept of green chemistry development. Compared with the catalyst prepared by the impregnation method, the catalyst of the present invention has higher activity.

Preparation of Comparative Example Catalyst Pd/Al ₂ O ₃ -IMP

At room temperature, 500 mg Al ₂ O ₃ was weighed and uniformly dispersed in 20 mL ethanol. After stirring for 1 hour, 3 mL of 5 mg/mL sodium tetrachloropalladate aqueous solution was added dropwise to the suspension. After stirring for 2 hours, the mixture was heated to 80°C and maintained at this temperature to completely evaporate the ethanol to obtain a dark brown powder. Then, the mixture was heated to 350°C at a rate of 5°C/min in a 5% H ₂ /Ar mixed gas and calcined for 2 hours to obtain a catalyst prepared by the impregnation method, which was recorded as Pd/Al ₂ O ₃ -IMP. At this time, the noble metal loading was 3 wt%.

Hydrogenation of benzoic acid to cyclohexanecarboxylic acid catalyzed by Pd/Al ₂ O ₃ -IMP

(1) 2 mmol of benzoic acid was uniformly dispersed in 2 mL of isopropanol, and 20 mg of Pd/Al ₂ O ₃ -IMP catalyst was added to the solution and dispersed uniformly by ultrasonication.

(2) The mixture was transferred to an autoclave, and the air in the autoclave was replaced with 1 MPa _H2 for three times. The reaction was carried out in a ₂ MPaH2 atmosphere with magnetic stirring and the temperature was controlled at 100°C.

(3) Use gas chromatograph to quantitatively analyze the liquid phase composition and record the benzoic acid conversion rate and cyclohexanecarboxylic acid selectivity.

Example 1 Preparation of Catalyst Pd/Al ₂ O ₃ -CP

First, weigh 500 mg of Al ₂ O ₃ and dissolve it in 30 mL of water, and disperse it evenly by ultrasonication. Then add 3 mL of 5 mg/mL sodium tetrachloropalladate aqueous solution and start stirring. After stirring for 1 hour, add 4 mL of an aqueous solution containing 200 mg of urea, set the system temperature to 70°C, and keep the temperature to react for 2 hours. After cooling to room temperature, add 5 mL of an aqueous solution containing 10 mg of sodium borohydride and stir for 1 hour, then centrifuge to obtain a dark brown solid, which is dried to obtain a catalyst prepared by coprecipitation method, recorded as Pd/Al ₂ O ₃ -CP. At this time, the precious metal loading is 3 wt%.

Figure 1 is a transmission electron microscope image of the Pd/Al ₂ O ₃ -CP catalyst. Figure 2 shows that the lattice fringe spacing measured by medium and high resolution TEM is 0.22nm, corresponding to the (111) crystal plane of the Pd nanoparticles, indicating that the small bright spot particles in Figure 1 are metal Pd nanoparticles and are successfully loaded on Al ₂ O ₃ .

Preparation of Cyclohexanecarboxylic Acid by Hydrogenation of Benzoic Acid over Pd/Al ₂ O ₃ -CP Catalyst

(1) 2 mmol of benzoic acid was uniformly dispersed in 2 mL of isopropanol, and 20 mg of Pd/Al ₂ O ₃ -CP catalyst was added to the solution and dispersed uniformly by ultrasonication.

(2) The mixture was transferred to an autoclave, and the air in the autoclave was replaced with 1 MPa H ₂ for three times, and then the reaction was carried out in a 2 MPa H ₂ atmosphere with magnetic stirring and the temperature was controlled at 100°C.

(3) Use gas chromatograph to quantitatively analyze the liquid phase composition and record the benzoic acid conversion rate and cyclohexanecarboxylic acid selectivity.

As can be seen from Figure 3, the conversion rate of benzoic acid for the Pd/Al ₂ O ₃ -CP catalyst was 85.1% after 16 hours of reaction. The TOF value of each exposed Pd atom was 108h ^-1 (Figure 4). Under the same experimental conditions, the conversion rate of the Pd/Al ₂ O ₃ -IMP catalyst was 12.6% after 16 hours. The TOF value of Pd/Al ₂ O ₃ -IMP was 13h ^-1 , which was 8.3 times lower than that of Pd/Al ₂ O ₃ -CP. Therefore, the catalyst prepared by the co-precipitation method has a higher catalytic hydrogenation activity than the catalyst obtained by the traditional impregnation method.

Catalyst cycle stability test

The stability of the catalyst is one of the important factors in evaluating the performance of the catalyst. Weigh 20 mg of Pd/Al ₂ O ₃ -CP and Pd/Al ₂ O ₃ -IMP catalysts respectively, add them to 0.5 mmol of benzoic acid, the hydrogen pressure is 2 MPa, the solvent is 2 mL of isopropanol, and the reaction is carried out at 100 ° C. 4 hours is a reaction cycle. The catalyst can be separated by centrifugation and can be recycled without treatment. Four cycles were tested respectively.

The conversion rates of benzoic acid in the 1st, 2nd, 3rd and 4th cycles of the Pd/Al ₂ O ₃ -CP catalyst were 79.40%, 77.87%, 80.38% and 78.58% respectively (Figure 5), indicating that the catalyst has good catalytic stability. In contrast, the catalytic activity of the Pd/Al ₂ O ₃ -IMP catalyst decreased after 4 cycles, and the conversion rate of benzoic acid decreased from 14.40% to 6.66% (Figure 6). Therefore, the Pd/Al ₂ O ₃ -CP catalyst exhibited high catalytic activity and selectivity as well as good stability while catalyzing the hydrogenation reaction of benzoic acid. The above experimental results show that the catalyst Pd/Al ₂ O ₃ -CP has high reuse in the preparation of cyclohexanecarboxylic acid by hydrogenation of benzoic acid.

Example 2

The preparation method of the supported noble metal palladium hydrogenation catalyst of the present invention is specifically implemented according to the following steps:

Step 1, mixing Al ₂ O ₃ and water, and performing ultrasonic treatment to obtain solution A;

The mass ratio of Al ₂ O ₃ to water was 20:5, and the ultrasonic treatment time was 1 h;

Step 2, adding a soluble palladium salt solution to solution A, stirring, then adding a urea aqueous solution to react, and after the reaction is completed, cooling to room temperature;

The soluble palladium salt solution is palladium acetate solution; the stirring time is 2h;

The concentration of urea aqueous solution was 0.5mmol/mL ^-1 , the reaction temperature was 80°C, and the reaction time was 1.5h;

Step 3, adding a sodium borohydride aqueous solution to the reaction solution obtained in step 2, stirring and centrifuging to obtain a dark brown solid, and drying to obtain a supported noble metal palladium hydrogenation catalyst;

The concentration of the sodium borohydride aqueous solution was 0.05 mmol/mL ^-1 , and the stirring time was 2 h.

Example 3

The preparation method of the supported noble metal palladium hydrogenation catalyst of the present invention is specifically implemented according to the following steps:

Step 1, mixing Al ₂ O ₃ and water, and performing ultrasonic treatment to obtain solution A;

The mass ratio of Al ₂ O ₃ to water was 50:2, and the ultrasonic treatment time was 2 h;

Step 2, adding a soluble palladium salt solution to solution A, stirring, then adding a urea aqueous solution to react, and after the reaction is completed, cooling to room temperature;

The soluble palladium salt solution is palladium nitrate solution; the stirring time is 3h;

The concentration of urea aqueous solution was 1mmol/mL ^-1 , the reaction temperature was 100°C, and the reaction time was 3h;

Step 3, adding a sodium borohydride aqueous solution to the reaction solution obtained in step 2, stirring and centrifuging to obtain a dark brown solid, and drying to obtain a supported noble metal palladium hydrogenation catalyst;

The concentration of the sodium borohydride aqueous solution was 0.1 mmol/mL ^-1 , and the stirring time was 3 h.

In the field of heterogeneous catalytic hydrogenation, the precious metal Pd can adsorb a large amount of _H2 at room temperature, and it is easy to desorb _H2 to participate in the reaction when the temperature is greater than 50°C. It also has high selectivity, so it is an excellent catalyst material and is often used in the reaction of hydrogenating benzoic acid to cyclohexanecarboxylic acid. _{Al2O3 is} often selected as a carrier for catalytic hydrogenation reactions due to its high specific area and high dispersion. Compared with the catalyst prepared by the traditional impregnation method, the catalyst prepared by the coprecipitation method of the present invention regulates the electronic structure of the metal Pd, greatly improves the catalytic activity, and greatly improves the stability, providing a new strategy for preparing efficient hydrogenation catalysts.

Claims (9)

1. The supported noble metal palladium hydrogenation catalyst is characterized by comprising a carrier and an active component supported on the carrier, wherein the carrier is Al ₂O₃, the active component is Pd nano particles, and the loading capacity of the Pd nano particles is 0.05% -5.0%.

2. The supported noble metal palladium hydrogenation catalyst of claim 1, wherein the specific surface area of Al ₂O₃ is 500-2500m ²/g.

3. The method for preparing the supported noble metal palladium hydrogenation catalyst according to claim 1, which is characterized by comprising the following steps:

Step 1, mixing Al ₂O₃ with water, and performing ultrasonic treatment to obtain a solution A;

step 2, adding a soluble palladium salt solution into the solution A, stirring, adding a urea aqueous solution for reaction, and cooling to room temperature after the reaction is finished;

And step 3, adding the sodium borohydride aqueous solution into the reaction solution obtained in the step 2, stirring, centrifugally separating to obtain a blackish brown solid, and drying to obtain the supported noble metal palladium hydrogenation catalyst.

4. The method for preparing a supported noble metal palladium hydrogenation catalyst according to claim 3, wherein in the step 1, the mass ratio of Al ₂O₃ to water is 20-50:2-5, and the ultrasonic treatment time is 0.5-2h.

5. The method for preparing a supported noble metal palladium hydrogenation catalyst according to claim 3, wherein in the step 2, the soluble palladium salt solution is any one or more of a sodium tetrachloropalladate solution, a palladium acetate solution and a palladium nitrate solution.

6. The method for preparing a supported noble metal palladium hydrogenation catalyst according to claim 3, wherein in the step 2, the stirring time is 0.5-3h; the concentration of the urea aqueous solution is 0.5-1mmol/mL ^-1, the reaction temperature is 70-100 ℃, and the reaction time is 1-3h.

7. The method for preparing a supported noble metal palladium hydrogenation catalyst according to claim 3, wherein in said step 3, the concentration of the sodium borohydride aqueous solution is 0.01-0.1mmol/mL ^-1, and the stirring time is 0.5-3h.

8. Use of the supported noble metal palladium hydrogenation catalyst according to any one of claims 1-7 in the preparation of cyclohexanecarboxylic acid by hydrogenation of benzoic acid.

9. The use according to claim 8, characterized in that it comprises: uniformly dispersing benzoic acid in isopropanol, adding a supported noble metal palladium hydrogenation catalyst, uniformly dispersing by ultrasonic, transferring the mixture into an autoclave, replacing air in the autoclave with H ₂ under 1MPa for three times, and performing magnetic stirring reaction in H ₂ atmosphere to obtain cyclohexanecarboxylic acid; the dosage of the supported noble metal palladium hydrogenation catalyst is 5-20% of the weight of benzoic acid; the stirring reaction temperature is 60-150 ℃, the stirring reaction pressure is 1-5MPa, and the reaction time is 4-24h.