A method for modifying a Pd catalyst support medium and its application

Abstract

This invention discloses a method for modifying the support medium of a Pd catalyst and its application. The preparation method of the Pd catalyst includes reacting zirconium salt, organic ligands, and acid to obtain a support UiO-66-X; then loading Pd onto the support UiO-66-X and reducing it to obtain the catalyst Pd@UiO-66-X; the organic ligands include 2-nitroterephthalic acid, 2-methoxyterephthalic acid, 2-aminoterephthalic acid, and terephthalic acid, and X is selected from NO2, OMe, NH2, and H. This invention changes the surface electron cloud density of the supported Pd nanoparticles by changing the ligands (-NO2, -H, -OMe, -NH2) of the support UiO-66, resulting in different abilities to activate hydrogen, thereby regulating the dehydrogenation and hydrogenation reactions in the racemicization process of Pd catalysis. The synergistic effect of different ligands with Pd changes the racemicization catalytic activity.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, specifically to changing the surface electron cloud density of Pd nanoparticles by confining them in the channels of different ligands UiO-66, thereby improving the catalytic activity for the racemicization of (R)-1-phenylethylamine. Background Technology

[0002] Chiral amines are present in many bioactive substances and are important chiral auxiliaries. They are also key intermediates in the synthesis of natural products and chiral drugs. Enantiomerically pure chiral amines are important chemical intermediates and have wide applications in many fields such as pharmaceuticals, natural products, agricultural chemistry, and liquid crystal materials. Currently, the main method for preparing single chiral compounds is dynamic kinetic resolution (DKR), which involves a one-pot reaction using a metal catalyst as a racemic catalyst and an enzyme as a resolution catalyst. In the DKR reaction, the metal catalyst requires excessively high reaction temperatures (70-110℃) and long reaction times, making it the rate-determining step. However, excessively high reaction temperatures lead to enzyme inactivation and an increase in byproducts. Therefore, improving the catalytic efficiency of the racemic catalyst under mild conditions is crucial.

[0003] Pd nanoparticles are considered excellent racemic catalysts, with the accessibility, high dispersion, and modulation of the surrounding electronic state of the metal active sites playing crucial roles in the catalytic reaction. In racemization, dehydrogenation first occurs to an imine intermediate, followed by hydrogenation to 1-phenylethylamine with an R or S configuration. Currently, the main approach to improving racemization catalytic performance is to control the pore size of the metal nanoparticles. Studies have shown that altering the microenvironment surrounding the metal can further enhance its activity. Racemization includes both hydrogenation and dehydrogenation reactions. Research indicates that increasing the electron cloud density around Pd metal can improve the catalyst's adsorption and activation capacity for hydrogen. Therefore, controlling the electron cloud density on the Pd surface holds promise for achieving dynamic kinetic resolution of α-phenylethylamine under mild conditions. Summary of the Invention

[0004] Purpose of the invention: The technical problem to be solved by the present invention is to provide a Pd catalyst that addresses the shortcomings of the prior art.

[0005] Another technical problem to be solved by the present invention is to provide a method for modifying the above-mentioned Pd catalyst support medium.

[0006] Another technical problem to be solved by the present invention is to provide the application of the above-mentioned Pd catalyst.

[0007] Invention Concept: Addressing the technical problem of enzyme inactivation and increased byproducts caused by excessively high reaction temperatures in the DKR reaction, this invention provides a method for modifying the Pd catalyst loading medium. The method includes altering the UiO-66 ligand to use Zr...4+ Using 2-nitroterephthalic acid, terephthalic acid, 2-methoxyterephthalic acid, and 2-aminoterephthalic acid as the metal center, respectively, UiO-66-X was obtained. Pd precursors were then introduced into the pores of UiO-66-X via a two-solvent method to obtain Pd. 2+ @UiO-66-X; Pd@UiO-66-X catalyst was obtained by high-temperature reduction with hydrogen.

[0008] To solve the first technical problem mentioned above, the present invention discloses a Pd catalyst, which is prepared by the following method: (1) Zirconium salt and organic ligand are mixed evenly, acid is added, and reaction is carried out to obtain support UiO-66-X; (2) Pd is then loaded onto support UiO-66-X and reduced to obtain catalyst Pd@UiO-66-X.

[0009] The organic ligand includes 2-nitroterephthalic acid, 2-methoxyterephthalic acid, 2-aminoterephthalic acid, and terephthalic acid, preferably 2-methoxyterephthalic acid; X is selected from NO2, OMe, NH2, and H, preferably OMe.

[0010] In order to solve the second technical problem mentioned above, the present invention discloses a method for modifying the support medium of Pd catalyst, comprising (1) mixing zirconium salt and organic ligand evenly, adding acid, reacting to obtain support UiO-66-X; (2) loading Pd onto support UiO-66-X, reducing to obtain catalyst Pd@UiO-66-X.

[0011] The organic ligand includes 2-nitroterephthalic acid, 2-methoxyterephthalic acid, 2-aminoterephthalic acid, and terephthalic acid, preferably 2-methoxyterephthalic acid; X is selected from NO2, OMe, NH2, and H, preferably OMe.

[0012] In the first and second technical issues mentioned above

[0013] In step (1),

[0014] The zirconium salt includes ZrCl4; the molar ratio of the zirconium salt to the organic ligand is 1.1-1.6:1.

[0015] The acid includes glacial acetic acid; the ratio of the organic ligand to the acid is 20-60 mg: 0.5 mL.

[0016] The process of uniformly mixing the zirconium salt and the organic ligand specifically involves uniformly mixing the zirconium salt, the organic ligand, and the solvent; the solvent includes N,N-dimethylformamide.

[0017] Further, the zirconium salt is dissolved in a solvent to obtain a zirconium salt solution, and the organic ligand is dissolved in a solvent to obtain an organic ligand solution. The zirconium salt solution and the organic ligand solution are mixed, and glacial acetic acid is added to the mixed solution. The mixture is then transferred to a stainless steel reactor with a polytetrafluoroethylene liner to react and obtain a precipitate. The precipitate is centrifuged, washed, and dried to obtain UiO-66-X.

[0018] The zirconium salt concentration in the zirconium salt solution is 5-10 mg / ml, and the organic ligand concentration in the organic ligand solution is 8-12 mg / ml.

[0019] The reaction temperature is 110-140℃, and the reaction time is 12-36h.

[0020] In step (2),

[0021] The dual-solvent method for introducing the Pd precursor into the pores of UiO-66-X involves dispersing UiO-66-X in n-hexane, and then adding an aqueous solution of the Pd precursor dropwise to the dispersion under vigorous stirring to obtain Pd. 2+ @UiO-66-X; will Pd 2+ @UiO-66-X was placed in a ceramic boat and then placed in a tube furnace. A mixed gas was introduced, and the mixture was reduced at a high temperature at a heating rate of 5℃ / min to obtain the Pd@UiO-66-X catalyst. Alternatively, the support UiO-66-X was dispersed in an organic solvent to obtain a mixture. An aqueous solution of the Pd precursor was added to the mixture, stirred, dried, and then reduced by a mixture of hydrogen and inert gas to obtain the catalyst Pd@UiO-66-X.

[0022] The organic solvent includes n-hexane; the Pd precursor includes K2PdCl4.

[0023] The vigorous stirring time is 2-4 hours.

[0024] The mass ratio of the carrier UiO-66-X to the Pd precursor is 50:3-6; the volume ratio of the carrier UiO-66-X to the organic solvent is 50mg:8-10mL.

[0025] The inert gas is Ar; the volume fraction of hydrogen in the mixed gas is 2%-8%.

[0026] The reduction temperature is 100-300℃, preferably 180-250℃, and more preferably 200℃; the reduction time is 3-5h, preferably 3.5-4.5h.

[0027] In this invention, the Pd element loading in the Pd catalyst is 1%-3%.

[0028] Thirdly, the present invention discloses the application of the Pd catalyst described in the first aspect above or the Pd catalyst prepared by the method described in the second aspect above in the catalytic racemization of (R)-1-phenylethylamine.

[0029] The solvent for the reaction is toluene.

[0030] The ratio of Pd catalyst to (R)-1-phenylethylamine is 20-40 mg: 10-40 μL; further, the ratio of Pd content to (R)-1-phenylethylamine in the Pd@UiO-66-X catalyst is 0.8 mg: 10-40 μL.

[0031] The catalytic temperature is 50-70℃.

[0032] The reaction time is 2-4 hours.

[0033] Beneficial effects:

[0034] (1) This invention changes the surface electron cloud density of Pd nanoparticles at the active center by changing the ligand of UiO-66, which makes the ability to activate hydrogen different and affects the dehydrogenation and hydrogenation reaction in the racemic process. Previous technologies mainly controlled the pore size of metal nanoparticles to improve the catalytic performance of racemicization. This invention changes the catalytic activity of racemicization through the synergistic effect of different ligands and Pd.

[0035] (2) The Pd@UiO-66-X catalyst preparation process provided by the present invention is simple and easy to control, with a metal loading of only about 2%. Previous technologies required a reaction temperature of over 70°C. The present invention achieves high catalytic activity at a lower loading. Attached Figure Description

[0036] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0037] Figure 1 Figure 1 shows the N2 adsorption-desorption isotherms for UiO-66-X and Pd@UiO-66-X, where Figure (a) is for UiO-66-X and Figure (b) is for Pd@UiO-66-X.

[0038] Figure 2 Figure 1 shows the pore size distribution of UiO-66-X and Pd@UiO-66-X, where Figure (a) shows UiO-66-X and Figure (b) shows Pd@UiO-66-X.

[0039] Figure 3Transmission electron microscopy (TEM) images of the prepared Pd@UiO-66-NO2, Pd@UiO-66, Pd@UiO-66-OMe, and Pd@UiO-66-NH2 catalysts are shown in Figures (a) and (e), Pd@UiO-66-NO2, Pd@UiO-66, Pd@UiO-66, Pd@UiO-66-OMe, and Pd@UiO-66-NH2.

[0040] Figure 4 The images show the transmission electron microscopy (TEM) energy dispersive spectroscopy (EDS) spectra of the prepared Pd@UiO-66-NO2, Pd@UiO-66, Pd@UiO-66-OMe, and Pd@UiO-66-NH2 catalysts. Figure (a) shows Pd@UiO-66-NO2, Figure (b) shows Pd@UiO-66, Figure (c) shows Pd@UiO-66-OMe, and Figure (d) shows Pd@UiO-66-NH2.

[0041] Figure 5 A comparison of the catalytic performance of Pd@UiO-66-X and commercial Pd / C within a temperature range of 50-70℃. Detailed Implementation

[0042] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; the reagents and materials described are commercially available unless otherwise specified.

[0043] Example 1: Synthesis of Pd@UiO-66-X

[0044] (1) Preparation of UiO-66-X:

[0045] Preparation of UiO-66: 40.8 mg of zirconium chloride was dissolved by sonication in 5 mL of N,N-dimethylformamide solution, and 26.6 mg of terephthalic acid was dissolved by sonication in 5 mL of N,N-dimethylformamide solution. The two solutions were then mixed and sonicated for 20 min. 0.5 mL of glacial acetic acid was added without stirring, and the mixture was sealed in a polytetrafluoroethylene-lined hydrothermal reactor and reacted in an oven at 120 °C for 24 h to obtain a white suspension. The product was collected by centrifugation, and then washed three times each with DMF and methanol. Finally, UiO-66 was vacuum dried overnight at 60 °C.

[0046] Preparation of UiO-66-Ome: 40.0 mg of zirconium chloride was dissolved by sonication in 5 mL of N,N-dimethylformamide solution. 33.5 mg of 2-methoxyterephthalic acid was dissolved by sonication in 5 mL of N,N-dimethylformamide solution. The two solutions were then mixed and sonicated for 20 min. 0.5 mL of glacial acetic acid was added without stirring, and the mixture was sealed in a polytetrafluoroethylene-lined hydrothermal reactor and reacted in an oven at 120 °C for 24 h to obtain a white suspension. The product was collected by centrifugation and then washed three times each with DMF and methanol. Finally, it was vacuum dried overnight at 60 °C.

[0047] Preparation of UiO-6-NH2: 40.8 mg of zirconium chloride was dissolved by sonication in 5 mL of N,N-dimethylformamide solution, and 29.0 mg of 2-aminoterephthalic acid was dissolved by sonication in 5 mL of N,N-dimethylformamide solution. The two solutions were then mixed and sonicated for 20 min. 0.5 mL of glacial acetic acid was added without stirring, and the mixture was sealed in a polytetrafluoroethylene-lined hydrothermal reactor and reacted in an oven at 120 °C for 24 h to obtain a white suspension. The product was collected by centrifugation, and then washed three times each with DMF and methanol. Finally, it was vacuum dried overnight at 60 °C.

[0048] Preparation of UiO-66-NO2: 61.0 mg of zirconium chloride was dissolved by sonication in 10 mL of N,N-dimethylformamide solution. 55.0 mg of 2-nitroterephthalic acid was dissolved by sonication in 5 mL of N,N-dimethylformamide solution. The two solutions were then mixed and sonicated for 20 min. 0.5 mL of glacial acetic acid was added without stirring, and the mixture was sealed in a polytetrafluoroethylene-lined hydrothermal reactor and reacted in an oven at 120 °C for 24 h to obtain a white suspension. The product was collected by centrifugation, and then washed three times each with DMF and methanol. Finally, it was vacuum dried overnight at 60 °C.

[0049] (2) Preparation of Pd@UiO-66-X:

[0050] 50.0 mg UiO-66-X was ultrasonically dispersed in 10 mL of n-hexane. After ultrasonic treatment of the mixture for 1 h, 25 μL of K2PdCl4 (3.1 mg) aqueous solution was added dropwise to the mixture under vigorous stirring. The mixture was then vigorously stirred for 3 h, centrifuged, and the obtained sample was further dried. Then it was treated at 200 °C in 5% H2 / Ar for 4 h to obtain the Pd@UiO-66-X catalyst.

[0051] The Pd content of the Pd@UiO-66-X catalyst was detected by inductively coupled plasma atomic emission spectrometry, and the results are shown in Table 1.

[0052] Table 1. Pd element content in the Pd@UiO-66-X catalyst in Example 1

[0053] Entry catalyst Pd content / % 1 <![CDATA[Pd@UiO-66-NO2]]> 2.37 2 Pd@UiO-66 2.04 3 Pd@UiO-66-OMe 2.15 4 <![CDATA[Pd@UiO-66-NH2]]> 2.41

[0054] The N2 adsorption-desorption tests, transmission electron microscopy (TEM) characterization, and TEM energy dispersive spectroscopy (EDS) analysis of UiO-66-X and Pd@UiO-66-X were performed. The results are as follows:

[0055] Figure 1 These are the N2 adsorption-desorption isotherms of UiO-66-X and Pd@UiO-66-X in Example 1. Both UiO-66-X and Pd@UiO-66-X have microporous structures.

[0056] Figure 2 This is a pore size distribution diagram of UiO-66-X and Pd@UiO-66-X in Example 1. The pore size of UiO-66-X is distributed in the range of 0.6-1.4 nm, and the particle size of the loaded Pd nanoparticles is controlled to be in the range of 0.6-1.4 nm.

[0057] Figure 3 This is a transmission electron microscope image of Pd@UiO-66-X in Example 1, where the presence of Pd nanoparticles is almost invisible.

[0058] Figure 4 The image shown is a transmission electron microscope-EDS image of Pd@UiO-66-X in Example 1, which shows that the Pd element is uniformly dispersed, indicating that the Pd nanoparticles are dispersed in the pores with a particle size smaller than or equal to the pore size of UiO-66-X.

[0059] Example 2: Application of Pd@UiO-66-X catalyst, Pd@UiO-66-X catalyst for racemic reaction of (R)-1-phenylethylamine.

[0060]

[0061] The Pd@UiO-66-X catalyst with a Pa content of 0.8 mg prepared in Example 1 and commercial Pd / C with a Pa content of 0.8 mg, along with 50 mg of anhydrous sodium carbonate, were weighed and placed in a Schlenk flask. 2 mL of toluene and 38 μL of (R)-1-phenylethylamine were added. After evacuation, a 5% H2-Ar mixture was introduced, maintaining a pressure of 0.01 MPa. Catalysis was carried out at a specific temperature for 2 h. The reaction product was derivatized using 40 μL of acetic anhydride, and the reaction was detected by gas chromatography.

[0062] Figure 5This is a comparison graph of Pd@UiO-66-X and Pd / C catalyzing the racemic reaction of (R)-1-phenylethylamine for 2 hours at 50-70℃ in Example 2. The conversion rate comparison shows that Pd@UiO-66-OMe has the best catalytic effect, and it is 14.2 times that of Pd / C at 60℃, indicating that Pd can catalyze under relatively mild conditions.

[0063] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. Use of a Pd catalyst in the catalysis of the racemization of ( R )-1-phenylethylamine, characterized in that, The preparation method of the Pd catalyst comprises the following steps: reacting a zirconium salt, an organic ligand and an acid to obtain a carrier UiO-66-X; loading Pd in the carrier UiO-66-X and reducing to obtain the catalyst Pd@UiO-66-X. The organic ligand comprises 2-methoxy terephthalic acid; and the X is selected from OMe.

2. Use according to claim 1, characterized in that, The zirconium salt comprises ZrCl4.

3. Use according to claim 1, characterized in that, The acid comprises glacial acetic acid; and the ratio of the amount of the organic ligand to the amount of the acid is 20-60 mg:0.5 mL.

4. Use according to claim 1, characterized in that, The zirconium salt is dissolved in a solvent to obtain a zirconium salt solution, the organic ligand is dissolved in a solvent to obtain an organic ligand solution, and the zirconium salt solution and the organic ligand solution are mixed, wherein the solvent comprises N,N-dimethylformamide.

5. The use according to claim 1, characterized in that, The carrier UiO-66-X is dispersed in an organic solvent to obtain a mixture, an aqueous solution of a Pd precursor is added to the mixture, and the mixture is stirred and dried, and then a mixed gas of hydrogen and an inert gas is introduced to reduce to obtain the catalyst Pd@UiO-66-X.

6. Use according to claim 5, characterized in that, The organic solvent comprises n-hexane; the Pd precursor comprises K2PdCl4; and the mass ratio of the carrier UiO-66-X to the Pd precursor is 50:3-6.

7. Use according to claim 5, characterized in that, The inert gas is Ar; and the volume fraction of hydrogen in the mixed gas is 2%-8%.

8. Use according to claim 5, characterized in that, The temperature of the reduction is 180-200 DEG C; and the time of the reduction is 3-5 h.

9. The use according to claim 1, characterized in that, The Pd catalyst is used in a ratio of 20-40 mg: 10-40 μL to the -1-phenylethylamine. R The Pd catalyst is used in a ratio of 20-40 mg: 10-40 μL to the -1-phenylethylamine.

10. The use according to claim 1, characterized in that, The temperature of the catalysis is 50-70 DEG C.

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