A palladium-polyoxometalate self-assembled sub-nanowire, its preparation method and application in the selective hydrogenation of olefins

Abstract

The present invention relates to a palladium-polyoxometalate self-assembled sub-nanowire, a preparation method thereof, and an application in the selective hydrogenation of olefins, belonging to the technical field of catalysts. It solves the technical problems in the prior art such as harsh use conditions of supported catalysts, lack of effective hydrogenation sites, easy agglomeration / sintering of active metals, easy leaching of active phases, complex synthesis, and environmental pollution. The preparation method of the present invention is: reacting a palladium precursor in a mixed system of polyoxometalate, fatty acid, fatty amine, and organic solvent to obtain a palladium-polyoxometalate self-assembled sub-nanowire material. This preparation method is simple and easy to operate. The prepared palladium-polyoxometalate self-assembled sub-nanowire has unique geometric and electronic properties, including a high density of active sites, a low coordination environment, and suitable surface electronic characteristics; it can be used as a selective hydrogenation catalyst for olefins and has excellent catalytic performance and cycle stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and particularly relates to a palladium-polyoxometalate self-assembled sub-nanowire, a preparation method and an application thereof, and more particularly to the application of the palladium-polyoxometalate self-assembled sub-nanowire as a selective hydrogenation catalyst in the preferential selective hydrogenation of C═C double bonds. Background Art

[0002] There is a wide demand for chemoselective hydrogenation of unsaturated compounds in dyes, pharmaceuticals and fine chemicals. Selective hydrogenation can catalyze target unsaturated bonds to synthesize specific chemicals. (Chem. Soc. Rev. 28 (1999) 199-207) When the substrate contains one or more reducible groups (such as -C═C, -C═O, -NO2 or -C≡N), efficient selective hydrogenation of the C═C bond is necessary, especially for multi-step organic synthesis processes. Although the hydrogenation of the C═C double bond is thermodynamically more favorable than the hydrogenation of the C═O double bond or other functional groups, in most cases, the hydrogenation of other reducible groups such as the C═O double bond competes with the C═C double bond, producing by-products. Traditional supported catalysts often show undifferentiated hydrogenation results under reaction conditions. Therefore, how to specifically selectively hydrogenate a certain target chemical bond is challenging. Among them, the catalyst plays a key role in improving catalytic activity and selectivity. Therefore, rationally designing and developing a selective hydrogenation catalyst for specific functional groups (such as C═C double bonds) is an important method to realize this chemical process. However, traditional supported catalysts (including noble metal-based and non-noble metal-based) all have the following defects:

[0003] (1) Often very harsh reaction conditions are required to obtain good yields, such as high pressure, high temperature, using high-purity hydrogen, etc., which pose great safety risks in actual industrial production.

[0004] (2) Due to the weak interaction between the metal and the support in traditional supported catalysts, the contact between the support and the active metal is limited, resulting in a lack of effective hydrogenation sites. Similarly, problems such as agglomeration / sintering of the active metal during hydrogenation and easy leaching of the active phase often occur, and their stability is often poor.

[0005] (3) The synthesis process of supported catalysts often requires multi-step synthesis routes, including impregnation, calcination and reduction processes. Most of the reduction processes use chemical reducing reagents (such as sodium borohydride) and gaseous hydrogen, which pose great environmental pollution problems, technical operation difficulties and potential safety problems. Summary of the Invention

[0006] In view of this, the present invention provides a palladium-polyoxometalate self-assembled sub-nanowire, a preparation method thereof, and an application in the selective hydrogenation of olefins to solve the technical problems in the prior art such as harsh use conditions of supported catalysts, lack of effective hydrogenation sites, easy aggregation / sintering of active metals, easy leaching of active phases, complex synthesis, and environmental pollution.

[0007] The technical solutions adopted by the present invention to achieve the above purposes are as follows.

[0008] The preparation method of the palladium-polyoxometalate self-assembled sub-nanowire of the present invention comprises the following steps:

[0009] React a palladium precursor in a mixed system of polyoxometalate, fatty acid, fatty amine and organic solvent to obtain a palladium-polyoxometalate self-assembled sub-nanowire.

[0010] Preferably, the steps are as follows:

[0011] Step 1: Dissolve the palladium precursor in an organic solvent and mix evenly to obtain a palladium precursor solution;

[0012] Step 2: Dissolve the polyoxometalate in an organic solvent and mix evenly to obtain a polyoxometalate solution;

[0013] Step 3: Mix the palladium precursor solution and the polyoxometalate solution evenly, and then add fatty acid and fatty amine and mix evenly to obtain a mixed solution;

[0014] Step 4: Heat the mixed solution under sealing at 120 °C - 180 °C for reaction, wash with ethanol under ultrasonic treatment, centrifuge, repeat multiple times, and vacuum-dry the obtained black solid to obtain a palladium-polyoxometalate self-assembled sub-nanowire.

[0015] Preferably, in Step 1, the organic solvent is toluene.

[0016] Preferably, in Step 1, the palladium precursor is palladium acetylacetonate or palladium acetate.

[0017] Preferably, in Step 2, the organic solvent is absolute ethanol.

[0018] Preferably, in Step 2, the polyoxometalate is phosphotungstic acid, silicotungstic acid or phosphomolybdic acid.

[0019] Preferably, in Step 3, the fatty acid is oleic acid.

[0020] Preferably, in Step 3, the fatty amine is oleylamine.

[0021] Preferably, in step 3, in the mixed solution, the ratio of palladium precursor: polyoxometalate: fatty acid: fatty amine is (0.01 - 0.05 mmol): (0.01 - 0.05 mmol): (1 - 3 mL): 1 mL.

[0022] Preferably, in steps 1, 2 and 3, the way of mixing evenly is stirring; more preferably, the stirring rate is 500 rpm - 1200 rpm, and the stirring time is 5 min - 20 min.

[0023] Preferably, in step 4, the heating reaction time is 2 h - 6 h.

[0024] Preferably, in step 4, the centrifugation speed is 7000 rpm - 10000 rpm, and the centrifugation time is 3 min - 10 min.

[0025] Preferably, in step 4, the temperature of vacuum drying is 40 °C - 80 °C.

[0026] The present invention also provides palladium - polyoxometalate self - assembled sub - nanowires prepared by the above - mentioned preparation method.

[0027] The present invention also provides the application of the above - mentioned palladium - polyoxometalate self - assembled sub - nanowires as an olefin selective hydrogenation catalyst.

[0028] Preferably, the application of the palladium - polyoxometalate self - assembled sub - nanowires as an olefin selective hydrogenation catalyst is in the selective hydrogenation of C = C double bonds in unsaturated compounds containing C = C double bonds.

[0029] More preferably, the palladium - polyoxometalate self - assembled sub - nanowires, unsaturated olefin compound and organic solvent are mixed evenly, first flushed with a mixed gas of 5% - 100% H2 and N2 at 0.1 - 2 MPa for multiple times, then filled with a mixed gas of 5% - 100% H2 and N2 at 0.5 - 3 MPa, and stirred at 20 - 40 °C for 10 min - 60 min to obtain the product of selective hydrogenation of C = C double bonds.

[0030] Preferably, the organic solvent is cyclohexane.

[0031] Preferably, the way of mixing evenly is stirring, more preferably, the stirring rate is 500 rpm - 1200 rpm, and more preferably 800 rpm.

[0032] Preferably, the ratio of the palladium - polyoxometalate self - assembled sub - nanowires to the unsaturated compound is (5 - 10 mg): (0.1 - 2 mmol).

[0033] The principle of the present invention is as follows: Polyoxometalates are a class of inorganic oxide molecular clusters with a definite molecular structure and composition. They can gain or lose several electrons without changing the original structure, acting as an "electronic sponge" and can be used as a promoter to regulate the catalytic performance of active metals. Based on the reversible electron-proton storage ability of polyoxometalates and the excellent hydrogen activation ability of noble metals (palladium), polyoxometalates and noble metals (palladium) can form a superlattice structure through self-assembly under solvothermal conditions. This process realizes the full formation of the interfacial sites between polyoxometalates and palladium, facilitating the transfer of active hydrogen species between the two. At the same time, the noble metal sites serve as the adsorption sites for C=C double bonds. During the hydrogenation process, polyoxometalates can effectively transfer active hydrogen to the metal sites, thus achieving the improvement of the selective hydrogenation performance.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0035] 1. The palladium-polyoxometalate self-assembled sub-nanowires of the present invention are synthesized by a one-pot solvothermal method, which is simple and easy to operate. The prepared palladium-polyoxometalate self-assembled sub-nanowires successfully confine the noble metal size at the sub-nanometer level. Compared with single atoms and nanoparticles, sub-nanoclusters are usually composed of a very small number of atoms and often have unique geometric and electronic properties, including a high density of active sites, a low-coordination environment, and appropriate surface electronic characteristics, which provide effective active sites for hydrogenation.

[0036] 2. The palladium-polyoxometalate self-assembled sub-nanowires of the present invention are used as an olefin selective catalyst and show a preferential hydrogenation ability for the C=C double bonds of various unsaturated organic compounds, and have excellent cyclic stability performance (at least five cycles).

[0037] 3. The palladium-polyoxometalate self-assembled sub-nanowires of the present invention can achieve the selective hydrogenation of the C=C double bonds of unsaturated compounds under low-temperature and low-pressure conditions, and have excellent catalytic performance (generally, the yield of C=C hydrogenation products is at least above 95%). Description of the Drawings

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0039] Figure 1 It is the Fourier transform infrared (FTIR) spectrum of the palladium-polyoxometalate self-assembled sub-nanowires prepared in Example 1 of the present invention.

[0040] Figure 2TEM image (left) and high-resolution image (right) of the palladium-polyoxometalate self-assembled sub-nanowires prepared in Example 1 of the present invention.

[0041] Figure 3 Gas chromatogram of the products of the selective hydrogenation of the C═C double bond of unsaturated compounds using the palladium-polyoxometalate self-assembled sub-nanowires prepared in Example 1 of the present invention as a selective catalyst, before the selective hydrogenation reaction of 4-vinylbenzaldehyde.

[0042] Figure 4 Gas chromatogram of the products of the selective hydrogenation of the C═C double bond of unsaturated compounds using the palladium-polyoxometalate self-assembled sub-nanowires prepared in Example 1 of the present invention as a selective catalyst, after the selective hydrogenation reaction of 4-vinylbenzaldehyde.

[0043] Figure 5 Fourier transform infrared (FTIR) spectrum of the selective catalyst after the selective hydrogenation cycle of 4-vinylbenzaldehyde using the palladium-polyoxometalate self-assembled sub-nanowires prepared in Example 1 of the present invention. Detailed implementation mode

[0044] To further understand the present invention, the preferred implementation modes of the present invention are described below. However, it should be understood that these descriptions are only for further explaining the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0045] The preparation method of the palladium-polyoxometalate self-assembled sub-nanowires of the present invention comprises the following steps:

[0046] React a palladium precursor in a mixed system of a polyoxometalate, a fatty acid, a fatty amine and an organic solvent to obtain the palladium-polyoxometalate self-assembled sub-nanowires.

[0047] In the above preparation method, the reaction preferably refers to a sealed heating reaction, the heating temperature is 120 °C - 180 °C, and the heating reaction time is 2 h - 6 h.

[0048] The steps of the above preparation method are preferably as follows:

[0049] Step 1: Dissolve the palladium precursor in an organic solvent and mix evenly to obtain a precursor solution;

[0050] Step 2: Dissolve the polyoxometalate in an organic solvent and mix evenly to obtain a polyoxometalate solution;

[0051] Step 3: Mix the palladium precursor solution and the polyoxometalate solution evenly, and then add the fatty acid and the fatty amine and mix evenly to obtain a mixed solution;

[0052] Step 4: Heat the mixed solution in a sealed manner at 120°C - 180°C for reaction, wash it with ethanol under ultrasound, centrifuge, and repeat multiple times. Vacuum dry the obtained black solid to obtain palladium-polyoxometalate self-assembled sub-nanowires.

[0053] In the above technical solution, in Step 1, the organic solvent is preferably toluene. It should be noted that there is no special limitation on the organic solvent, as long as it can play a dissolving role. Those skilled in the art can select other organic solvents according to common knowledge.

[0054] In the above technical solution, in Step 1, the palladium precursor is preferably palladium acetylacetonate or palladium acetate.

[0055] In the above technical solution, in Step 2, the organic solvent is preferably ethanol. It should be noted that there is no special limitation on the organic solvent, as long as it can play a dissolving role. Those skilled in the art can select other organic solvents according to common knowledge.

[0056] In the above technical solution, in Step 2, the polyoxometalate is preferably phosphotungstic acid, phosphomolybdic acid, or silicotungstic acid.

[0057] In the above technical solution, the volume ratio of the organic solvent in Step 1 to the organic solvent in Step 2 is preferably (1 - 8) : (8 - 1); more preferably 2:7.

[0058] In the above technical solution, in Step 3, the fatty acid is preferably oleic acid, and the fatty amine is preferably oleylamine. It should be noted that there is no special limitation on the selection of the fatty acid or fatty amine, as long as it can play a reducing and stabilizing role. Those skilled in the art can select other fatty acids or fatty amines according to common knowledge.

[0059] In the above technical solution, in the mixed solution in Step 3, the ratio of palladium precursor : polyoxometalate : fatty acid : fatty amine is (0.01 - 0.05 mmol) : (0.01 - 0.05 mmol) : (1 - 3 mL) : 1 mL.

[0060] In the above technical solution, in Steps 1, 2, and 3, the method of mixing evenly is all stirring, the stirring rate is 500 rpm - 1200 rpm, and the stirring time is 5 min - 20 min. It should be noted that other methods of mixing evenly well-known to those skilled in the art are also applicable to the present invention.

[0061] In the above technical solution, in Step 4, it is preferably to repeat the washing and centrifugation processes three times.

[0062] In the above technical solution, in Step 4, the heating reaction time is 2 h - 6 h.

[0063] In the above technical solution, in step four, the centrifugation speed is preferably 7000 rpm - 10000 rpm, and the centrifugation time is 3 min - 10 min. More preferably, the centrifugation speed is 9000 rpm and the centrifugation time is 5 min.

[0064] In the above technical solution, in step four, the vacuum drying temperature is preferably 40°C - 80°C, more preferably 60°C, and the equipment is usually a vacuum drying oven.

[0065] The palladium-polyoxometalate self-assembled sub-nanowires of the present invention can be used as an olefin selective hydrogenation catalyst, especially in the selective hydrogenation of C=C double bonds in compounds containing multiple functional groups.

[0066] In the above technical solution, the preferred process is as follows: Mix the palladium-polyoxometalate self-assembled sub-nanowires, unsaturated olefin compounds, and organic solvent evenly. First, rinse with a mixed gas of 5% - 100% H2 and N2 at 0.1 - 2 MPa for multiple times, and then fill with a mixed gas of 5% - 100% H2 and N2 at 0.5 - 3 MPa and stir at 20°C - 40°C for 10 min - 60 min to obtain the product of selective hydrogenation of C=C double bonds.

[0067] The general reaction equation for the above olefin selective catalytic hydrogenation is as follows:

[0068]

[0069] In the above technical solution, in the mixed gas of H2 and N2, preferably H2 accounts for 20%.

[0070] In the above technical solution, the preferred ratio of the palladium-polyoxometalate self-assembled sub-nanowires to the unsaturated compound is (5 - 10 mg):(0.1 - 2 mmol), and the ratio of the palladium-polyoxometalate self-assembled sub-nanowires to the organic solvent is (5 - 10 mg):(5 - 20 mL).

[0071] In the above technical solution, the method of mixing evenly is all stirring.

[0072] In the above technical solution, the organic solvent is preferably cyclohexane.

[0073] In the above technical solution, the stirring speed is preferably 500 rpm - 1200 rpm, more preferably 800 rpm.

[0074] In the above technical solution, the reaction equipment can be an intermittent reactor; the pressure gauge range is 0 - 6 MPa.

[0075] The terms used in the present invention generally have the meanings commonly understood by those of ordinary skill in the art, unless otherwise specified. To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below in conjunction with embodiments.

[0076] In the following embodiments, various processes and methods not described in detail are conventional methods well known in the art. The materials, reagents, devices, instruments, equipment, etc. used in the following embodiments can be obtained from commercial sources without special instructions.

[0077] The present invention will be further described below in conjunction with embodiments.

[0078] Example 1

[0079] Add 28 mg of phosphotungstic acid (purchased from Aladdin, 95%) to a 20 mL PTFE reaction kettle liner containing 7 mL of absolute ethanol, and then add palladium acetylacetonate (3.5 mg, purchased from Macklin, 98%) dissolved in 2 mL of toluene to the above solution and stir for 10 min. Then, add 2 mL of oleylamine and 1 mL of oleic acid, and continue to stir for 10 min. Transfer the PTFE reaction kettle liner into the reaction kettle, seal it and heat it at 160 °C for 4 h. After the reaction is completed, wash the product with ethanol under ultrasonic action, centrifuge at 9000 rpm for 5 min, and repeat the above process 3 times. Finally, dry the black solid overnight in a vacuum oven at 60 °C (40 °C - 80 °C) to obtain palladium-polyoxometalate self-assembled sub-nanowires. Recorded as Pd / PW 12 NBs.

[0080] Add palladium-polyoxometalate self-assembled sub-nanowires (5 mg), cyclohexane (10 mL), and 4-vinylbenzaldehyde (0.5 mmol) to a 100 mL stainless steel reaction kettle respectively. Flush the reaction kettle five times with 0.5 MPa 20% H2 / N2 mixed gas, and then inject 1 MPa 20% H2 / N2 mixed gas. The reaction kettle is maintained in a water bath (25 °C), the stirring speed is 800 rpm, react for 15 min, and centrifuge to obtain the reaction product.

[0081] Perform Fourier transform infrared (FTIR) spectroscopy detection on the palladium-polyoxometalate self-assembled sub-nanowires prepared in Example 1, and the test results are as Figure 1 shown. From Figure 1 it can be seen that the peaks of ν(P-O) (1075 cm -1 ), ν(W-O) (975 cm -1 ), and ν(W-O-W) (890 and 782 cm -1 ) appear in the sub-nanowire structure, indicating that the phosphotungstic acid structure exists intact on the catalyst. At the same time, 2920 cm -1and 2851 cm -1 The vibration peaks at correspond to the stretching vibration modes of -CH2- and -CH3, and the signal at 1458 cm -1 corresponds to the vibration of the N-H bond, indicating the presence of fatty acids and fatty amines on the surface of the catalyst.

[0082] The palladium-polyoxometalate self-assembled sub-nanowires prepared in Example 1 were subjected to transmission electron microscopy and high-resolution detection. The results are as Figure 2 shown. Figure 2 (Left) shows that the purity of the sub-nanowires is relatively high. Figure 2 (Right) shows that the diameter of the sub-nanowires is about 1 nm.

[0083] The reaction products were analyzed by GC Agilent 7820 equipped with an HP-5 30 m×0.32 mm×0.25 μm capillary column, and the catalytic results are as Figure 3 and Figure 4 shown. Figure 3 Before the selective hydrogenation of 4-vinylbenzaldehyde, Figure 4 After the selective hydrogenation of 4-vinylbenzaldehyde. From Figure 3 and Figure 4 it can be seen that within the reaction time used, all of 4-vinylbenzaldehyde was converted to 4-ethylbenzaldehyde (selectivity greater than 99%).

[0084] Figure 5 This is the Fourier transform infrared (FTIR) spectrum of the selective catalyst after the selective hydrogenation cycle of the palladium-polyoxometalate self-assembled sub-nanowires prepared in Example 1 of the present invention. From Figure 5 it can be seen that the palladium-polyoxometalate self-assembled sub-nanowires have good catalytic cycle stability, and the conversion rate and selectivity basically do not change after five cycles.

[0085] Example 2

[0086] The palladium-polyoxometalate self-assembled sub-nanowires prepared in Example 1 were used as a catalyst for the selective hydrogenation of olefin compounds with different substituents. Only 4-vinylbenzaldehyde in Example 1 was replaced with the olefin compounds in Table 1 and the reaction time in Table 1, and other steps were the same as in Example 1. The results are shown in Table 1. The amount of substance of the olefin compounds used was 0.5 mmol each.

[0087] Table 1 Selective hydrogenation results of the palladium-polyoxometalate self-assembled sub-nanowires prepared in Example 1 for olefin compounds with different substituents

[0088]

[0089]

[0090] Obviously, the above-described embodiments are merely examples for clear illustration and are not limitations on the embodiments. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all embodiments here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. Preparation method of palladium-polyoxometalate self-assembled sub-nanowires as olefin selective hydrogenation catalyst, characterized in that, The steps are as follows: Step 1: Dissolve the palladium precursor in an organic solvent and mix evenly to obtain a palladium precursor solution; Step 2: Dissolve the polyoxometalate in an organic solvent and mix evenly to obtain a polyoxometalate solution; the polyoxometalate is phosphotungstic acid or phosphomolybdic acid; Step 3: Mix the palladium precursor solution and the polyoxometalate solution evenly, and then add fatty acid and fatty amine and mix evenly to obtain a mixed solution; the fatty acid is oleic acid and the fatty amine is oleylamine; Step 4: Heat the mixed solution in a sealed manner at 120 °C - 180 °C for reaction, wash with ethanol under ultrasonic treatment, centrifuge, repeat multiple times, and vacuum-dry the obtained black solid to obtain palladium-polyoxometalate self-assembled sub-nanowires as an olefin selective hydrogenation catalyst.

2. The preparation method of palladium-polyoxometalate self-assembled sub-nanowires as an olefin selective hydrogenation catalyst according to claim 1, wherein in Step 1, the organic solvent is toluene, and the palladium precursor is palladium acetylacetonate or palladium acetate; in Step 2, the organic solvent is absolute ethanol.

3. The preparation method of the palladium-polyoxometalate self-assembled sub-nanowire as an olefin selective hydrogenation catalyst according to claim 1, characterized in that, in Step 3, in the mixed solution, the ratio of palladium precursor: polyoxometalate: fatty acid: fatty amine is (0.01 - 0.05 mmol): (0.01 - 0.05 mmol): (1 - 3 mL): 1 mL.

4. The preparation method of the palladium-polyoxometalate self-assembled sub-nanowires as an olefin selective hydrogenation catalyst according to claim 1, characterized in that, In Step 1, Step 2 and Step 3, the way of mixing evenly is all stirring, the stirring rate is 500 rpm - 1200 rpm, and the stirring time is 5 min - 20 min; In Step 4, the time for the heating reaction is 2 h - 6 h; the centrifugation speed is 7000 rpm - 10000 rpm, and the centrifugation time is 3 min - 10 min; the temperature for vacuum drying is 40 °C - 80 °C.

5. Palladium-polyoxometalate self-assembled sub-nanowires prepared by the preparation method according to any one of claims 1 - 4 as an olefin selective hydrogenation catalyst.

6. Application of the palladium-polyoxometalate self-assembled sub-nanowires according to claim 5 as an olefin selective hydrogenation catalyst.

7. The application according to claim 6, characterized in that, Application in the selective hydrogenation of C=C double bonds in unsaturated compounds containing C=C double bonds.

8. The application according to claim 7, characterized in that, Mix the palladium-polyoxometalate self-assembled sub-nanowires, unsaturated olefin compound and organic solvent evenly, first rinse with a mixed gas of 5% - 100% H2 and N2 at 0.1 - 2 MPa for multiple times, and then fill with a mixed gas of 5% - 100% H2 and N2 at 0.5 - 3 MPa, and stir at 20 - 40 °C for 10 min - 60 min to obtain the product of selective hydrogenation of C=C double bonds.

9. The application according to claim 8, wherein the organic solvent is cyclohexane; the way of mixing evenly is all stirring, and the stirring speed is 500 rpm - 1200 rpm; the ratio of the palladium-polyoxometalate self-assembled sub-nanowires to the unsaturated compound is (5 - 10 mg): (0.1 - 2 mmol).

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