A metal-doped, defect-rich pd-based catalyst and methods of making same

Abstract

This invention discloses a metal-doped defect-rich Pd-based catalyst, its preparation, and its application in the heterogeneous catalytic hydrogenation of nitrile butadiene rubber (NBR). The catalyst involves doping hydrothermally synthesized TiO2 nanosheets with metal atoms in the TiO2 lattice using a pre-impregnation followed by calcination strategy, inducing numerous defect sites on the surface. Then, active metal Pd is loaded using an equal-volume impregnation method, followed by reduction to obtain the catalyst. The catalyst obtained by this invention exhibits high stability and high dispersibility of the metal active component. Its application in the NBR hydrogenation reaction demonstrates high catalytic efficiency and good recyclability, which is of significant importance for the preparation of high-value-added hydrogenated NBR.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation, specifically relating to a metal-doped defect-rich Pd-based catalyst, its preparation method, and its application in heterogeneous catalytic hydrogenation of nitrile rubber. Background Technology

[0002] Hydrogenated nitrile butadiene rubber (HNBR) is a high-value-added specialty rubber prepared by selectively hydrogenating the C=C segments of the butadiene chain in nitrile butadiene rubber (NBR) while retaining the nitrile units. Because HNBR retains the nitrile groups in the NBR molecular chain, it not only inherits the oil and abrasion resistance of NBR but also possesses excellent heat resistance, weather resistance, oxygen resistance, chemical corrosion resistance, and high tensile strength, especially with significantly improved heat aging resistance. Thanks to its excellent comprehensive properties, HNBR has wide applications in the automotive industry, petrochemical industry, aerospace industry, and lithium battery industry.

[0003] Due to the high technological barriers to industrial production of hydrogenated nitrile butadiene rubber (HNBR), there are relatively few companies with large-scale production capabilities. Global suppliers of HNBR mainly include Zeon of Japan, Lanxess of Germany, and Zannan Technology and Dawn of China. Zeon and Lanxess together account for over 90% of global production capacity. The core challenge of HNBR production is selectively hydrogenating unsaturated C=C groups on the molecular chain while maintaining the integrity of the cyano groups. Currently, industrial production of HNBR mainly employs homogeneous solution hydrogenation and heterogeneous solution hydrogenation. Compared to homogeneous hydrogenation, heterogeneous hydrogenation systems not only solve the problem of catalyst separation, recovery, and reuse in homogeneous hydrogenation, but also avoid the residue of precious metals in the HNBR product, significantly reducing the cost of NBR hydrogenation and attracting widespread attention from researchers.

[0004] Due to the large molecular size and high viscosity of NBR, the key factors affecting the hydrogenation performance of NBR are the diffusion limitations of unsaturated polymers in the catalyst pores and the efficient and stable loading of active components. However, based on the currently reported literature and patents, existing research mainly focuses on developing Pd / SiO2 catalysts with macroporous structures and Pd / CNT catalysts with high external specific surface areas to eliminate the diffusion limitations of polymer pores (Patent CN 109317178 A; Ind. Eng. Chem. Res., 2013, 52, 17750-17759). However, the interaction between the above supports and metals is weak, resulting in serious loss of active components. To avoid the loss of active components, patents CN 103537304B and CN 106268735A disclose a method for functionalizing the surface of the support to achieve efficient and stable loading of active components. However, the modifiers used are expensive, and the modification process consumes a large amount of organic solvents, resulting in high operating costs and environmental pollution. Therefore, developing a highly active, highly stable, and highly utilized supported Pd-based catalyst is of great significance and practical value for the industrial production of high-value-added HNBR. Summary of the Invention

[0005] The purpose of this invention is to provide a metal-doped defect-rich Pd-based catalyst and its preparation method. This method is low in cost, simple in preparation process, and the resulting catalyst has excellent catalytic hydrogenation activity and good recyclability in NBR hydrogenation reaction.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A metal-doped defect-rich Pd-based catalyst is prepared by doping TiO2 nanosheets with metal atoms into the TiO2 lattice using a strategy of first impregnation followed by calcination, while simultaneously inducing a large number of defect sites on the surface using charge compensation effect. Then, active metal Pd is loaded using an equal-volume impregnation method, followed by reduction to obtain the metal-doped defect-rich Pd-based catalyst. The preparation method includes the following steps:

[0008] 1) Preparation of TiO2 nanosheets by hydrothermal method: Weigh 10 g of tetrabutyl titanate and add it to 20-60 mL of anhydrous ethanol. Then, add 3-10 g of hydrofluoric acid dropwise while stirring. React at 160-250 °C for 8-16 h. After that, wash with sodium hydroxide solution and deionized water until neutral. Dry at 80 °C and calcine at 400-600 °C for 2-6 h to obtain TiO2 nanosheets.

[0009] 2) Preparation of metal-doped defective TiO2 nanosheets: The prepared TiO2 nanosheets were dispersed in a metal salt solution and stirred at 60-90 °C for 6-12 h. After the reaction was completed, the nanosheets were separated, dried, and then calcined at 400-600 °C for 2-6 h to obtain metal-doped defective TiO2 nanosheets.

[0010] 3) Loading of active metal Pd: After the palladium precursor is dissolved in a solvent by ultrasonication, it is uniformly dropped onto the metal-doped defect state TiO2 nanosheets obtained in step 2) under stirring. After standing at room temperature for 12 h, it is dried in an oven and reduced under H2 atmosphere to obtain the catalyst.

[0011] Further, in step 2), the mass-to-volume ratio of TiO2 nanosheets to metal salt solution is 1:20-50 g / mL; the concentration of the metal salt solution is 0.001-0.1 mol / L, preferably 0.01-0.06 mol / L, and the metal salt used is one or more oxides or nitrates of Mn, Cu, Fe, V, and Mo.

[0012] Further, the palladium precursor mentioned in step 3) is one or more of palladium acetate, palladium chloride, and palladium nitrate.

[0013] Further, the solvent mentioned in step 3) is one or more of dichloromethane, hydrochloric acid, acetic acid, deionized water, and ethylene glycol.

[0014] Furthermore, the reduction temperature in step 3) is 160-250 °C, and the time is 2-6 h.

[0015] Furthermore, the doping amount of metal atoms in the metal-doped defect-rich Pd-based catalyst is 1.5-15 wt%, and the loading amount of active metal Pd is 0.1-2 wt%.

[0016] The obtained metal-doped defect-rich Pd-based catalyst can be applied to the heterogeneous catalytic hydrogenation of nitrile rubber. Specifically, nitrile rubber is dissolved in an organic solvent, and the reaction is carried out in the presence of the catalyst at 30-90°C and a hydrogen pressure of 0.5-4 MPa for 0.5-6 h. The resulting product is then flocculated with deionized water to obtain hydrogenated nitrile rubber.

[0017] Furthermore, the mass ratio of the organic solvent, catalyst, and nitrile rubber used is (80-10):(0.1-1):1. The organic solvent is one or more of acetone, cyclohexane, n-heptane, cyclohexanone, dichloromethane, trichloromethane, chlorobenzene, butanone, decahydronaphthalene, and tetrahydrofuran.

[0018] The beneficial effects of this invention are as follows:

[0019] (1) The metal-doped defect-rich Pd-based catalyst prepared in this invention has a typical two-dimensional layered structure, which is beneficial to eliminating the diffusion restriction of macromolecules in the catalyst channels in the NBR hydrogenation reaction and improving the utilization rate of active sites.

[0020] (2) The defect sites induced by metal atom doping in the Pd-based catalyst prepared in this invention can serve as anchoring points for the active metal components, making the active components in the catalyst less prone to agglomeration, with small particle size, good dispersion, and less prone to loss, thus improving the hydrogenation activity and reusability in the NBR reaction.

[0021] (3) The above-mentioned heterogeneous hydrogenation method for NBR provided by the present invention achieves a hydrogenation degree of over 97% for NBR, a selectivity of up to 100%, and a low metal residue in the hydrogenation product (only 3.4 ppm). Attached Figure Description

[0022] Figure 1 EPR diagrams of the catalyst supports prepared in Example 1(a) and Comparative Example 1(b).

[0023] Figure 2 XRD patterns of the supported catalysts prepared in Example 1(a) and Comparative Example 1(b).

[0024] Figure 3 TEM images of the supported catalysts prepared for Example 1(a) and Comparative Example 1(b) and their corresponding particle size distribution statistics of Pd nanoparticles (a1, b1).

[0025] Figure 4 The infrared spectra of HNBR obtained by catalytic hydrogenation using the supported catalysts prepared in Example 1 and Comparative Example 1 are compared. Detailed Implementation

[0026] A metal-doped defect-rich Pd-based catalyst, the preparation method of which includes the following steps:

[0027] 1) Preparation of TiO2 nanosheets by hydrothermal method: Weigh 10 g of tetrabutyl titanate and add it to 20-60 mL of anhydrous ethanol. Then, while stirring, add 3-10 g of hydrofluoric acid (40-60 wt%) dropwise. React at 160-250 °C for 8-16 h. After that, wash with 0.1-5 mol / L sodium hydroxide solution and deionized water until neutral. Dry at 80 °C and place in a muffle furnace. Calcine at 400-600 °C for 2-6 h to obtain TiO2 nanosheets.

[0028] 2) Preparation of metal-doped defective TiO2 nanosheets: The prepared TiO2 nanosheets were dispersed in a 0.001-0.1 mol / L metal salt solution at a mass-volume ratio of 1:20-50 g / mL. The mixture was stirred at 60-90 °C for 6-12 h. After the reaction was completed, the nanosheets were separated, dried, and then placed in a muffle furnace. The temperature was increased to 400-600 °C at a rate of 2 °C / min and calcined for 2-6 h to obtain metal-doped defective TiO2 nanosheets.

[0029] 3) Loading of active metal Pd: After the palladium precursor is dissolved in a solvent by ultrasonication, it is uniformly dropped onto the metal-doped defect state TiO2 nanosheets obtained in step 2) under stirring. After standing at room temperature for 12 h, it is dried in an oven and then reduced at 160-250 ℃ for 2-6 h in H2 atmosphere to obtain a catalyst with a Pd loading of 0.1-2 wt%, wherein the doping amount of metal atoms is 1.5-15 wt%.

[0030] In step 2), the metal salt used is an oxide or nitrate of one or more of Mn, Cu, Fe, V, and Mo.

[0031] The palladium precursor mentioned in step 3) is one or more of palladium acetate, palladium chloride, and palladium nitrate. The solvent is one or more of dichloromethane, hydrochloric acid, acetic acid, deionized water, and ethylene glycol.

[0032] To make the content of this invention easier to understand, the technical solution of this invention will be further described below with reference to specific embodiments, but this invention is not limited thereto.

[0033] Example 1

[0034] (1) First, 10 g of tetrabutyl titanate was dispersed in 15 mL of anhydrous ethanol, and then 4.5 g of hydrofluoric acid (concentration of 40 wt%) was added dropwise. After stirring for 15 min, it was transferred to a hydrothermal reactor and hydrothermally reacted at 180 ℃ for 8 h. After the reaction was completed, a white precipitate was obtained by centrifugation. It was washed with 0.1 mol / L sodium hydroxide solution and deionized water until neutral. After drying at 80 ℃, it was calcined in a muffle furnace at 400 ℃ for 2 h to obtain titanium dioxide nanosheets.

[0035] (2) Subsequently, 1g of the prepared titanium dioxide nanosheets were dispersed in 30 mL of 0.038 mol / L KMnO4 solution and reacted at 60℃ for 6 h. After the reaction was completed, the nanosheets were centrifuged, dried at 80℃, and placed in a muffle furnace. The temperature was increased to 400℃ at a rate of 2℃ / min and held for 2 h to obtain defect-rich titanium dioxide nanosheets.

[0036] (3) Accurately weigh 0.0213 g of palladium acetate and dissolve it in 3.5 ml of acetic acid. Add it dropwise to 1.0 g of defect-rich titanium dioxide nanosheets. After standing at room temperature for 12 h, reduce it at 140 °C for 2 h in H2 atmosphere to obtain a supported catalyst with a Pd loading of 1.0 wt% and a Mn doping of 5.2 wt%.

[0037] The obtained catalyst was used for the catalytic hydrogenation of NBR. Specifically, 1.0 g of NBR was dissolved in 80 g of acetone, and 1.0 g of catalyst was added together and then added to a high-pressure reactor. The reaction was carried out at 60 °C, hydrogen pressure of 1 MPa, and stirring speed of 800 rpm for 3 h. After the reaction was completed, the hydrogenation product was obtained by flocculation with deionized water. The catalyst was recovered and kept for later use.

[0038] Example 2

[0039] The 0.038 mol / L KMnO4 solution in Example 1 was replaced with an equal volume of 0.019 mol / L V2O5 solution, and the remaining steps were the same as in Example 1, resulting in a supported Pd-based catalyst with a V doping content of 5.2 wt%. Its catalytic hydrogenation performance for NBR was investigated using the same reaction conditions as in Example 1.

[0040] Example 3

[0041] The 0.038 mol / L KMnO4 solution in Example 1 was replaced with an equal volume of 0.022 mol / L (NH4)2MoO4 solution, and the remaining steps were the same as in Example 1, resulting in a supported Pd-based catalyst with a Mo doping content of 5.2 wt%. Its catalytic hydrogenation performance for NBR was investigated using the same reaction conditions as in Example 1.

[0042] Example 4

[0043] The 0.038 mol / L KMnO4 solution in Example 1 was replaced with an equal volume of 0.032 mol / L Cu(NO3)2 solution, and the remaining steps were the same as in Example 1, resulting in a supported Pd-based catalyst with a Cu doping content of 5.2 wt%. Its catalytic hydrogenation performance for NBR was investigated using the same reaction conditions as in Example 1.

[0044] Example 5

[0045] The 0.038 mol / L KMnO4 solution in Example 1 was replaced with an equal volume of 0.037 mol / L Fe(NO3)2 solution, and the remaining steps were the same as in Example 1, resulting in a supported Pd-based catalyst with an Fe doping content of 5.2 wt%. Its catalytic hydrogenation performance for NBR was investigated using the same reaction conditions as in Example 1.

[0046] The NBR hydrogenation activities of catalysts with different metal doping are shown in Table 1.

[0047] Table 1. Effect of doping with different metals on the hydrogenation activity of NBR

[0048]

[0049] As shown in Table 1, doping with different metals is beneficial to improving the hydrogenation performance of the catalyst, with Mn doping showing the best effect.

[0050] Example 6

[0051] The concentration of the KMnO4 solution in Example 1 was replaced with 0.01 mol / L, and the remaining steps were the same as in Example 1, to obtain a supported Pd-based catalyst with a Mn doping content of 1.4 wt%. Its catalytic hydrogenation performance for NBR was investigated using the same reaction conditions as in Example 1.

[0052] Example 7

[0053] The concentration of the KMnO4 solution in Example 1 was replaced with 0.06 mol / L, and the remaining steps were the same as in Example 1, resulting in a supported Pd-based catalyst with a Mn content of 8.3 wt%. Its catalytic hydrogenation performance for NBR was investigated using the same reaction conditions as in Example 1.

[0054] Example 8

[0055] The concentration of the KMnO4 solution in Example 1 was replaced with 0.1 mol / L, and the remaining steps were the same as in Example 1, resulting in a supported Pd-based catalyst with a Mn doping content of 13.8 wt%. Its catalytic hydrogenation performance for NBR was investigated using the same reaction conditions as in Example 1.

[0056] The effects of different potassium permanganate solution concentrations on the NBR hydrogenation activity of the prepared catalyst are shown in Table 2.

[0057] Table 2. Effect of different potassium permanganate solution concentrations on the hydrogenation activity of NBR

[0058]

[0059] As shown in Table 2, the hydrogenation performance of the catalyst first increases and then decreases with the increase of the amount of metal Mn doping, and the effect is best when the doping amount is 5.5 wt%.

[0060] Example 9

[0061] The catalyst recovered after the reaction in Example 1 was washed with a mixed solution of acetone and N-methylpyrrolidine (1:1, v / v), and the catalytic hydrogenation of NBR was repeated once under the same reaction conditions as in Example 1 to examine its catalytic hydrogenation performance for NBR.

[0062] Example 10

[0063] The catalyst recovered after the reaction in Example 9 was washed with a mixed solution of acetone and N-methylpyrrolidine (1:1, v / v), and then the catalytic hydrogenation of NBR was repeated once under the same reaction conditions as in Example 1 to examine its catalytic hydrogenation performance for NBR.

[0064] Example 11

[0065] The catalyst recovered after the reaction in Example 10 was washed with a mixed solution of acetone and N-methylpyrrolidine (1:1, v / v), and then the catalytic hydrogenation of NBR was repeated once under the same reaction conditions as in Example 1 to examine its catalytic hydrogenation performance for NBR.

[0066] The NBR hydrogenation activity of catalysts with different recycling cycles is shown in Table 3.

[0067] Table 3. Effect of different recycling cycles on NBR hydrogenation activity

[0068]

[0069] As shown in Table 3, the supported catalyst prepared in this invention has excellent cycling performance. This is because the defect sites introduced after metal doping can serve as anchoring points for the active components, resulting in a strong interaction between the metal and the support. This is beneficial for improving the hydrogenation activity and reusability of the catalyst.

[0070] Comparative Example 1

[0071] Undoped TiO2 nanosheets were used directly as a support, and the active component Pd was loaded using the same method as in Example 1 to obtain a TiO2 catalyst with a Pd loading of 1.0 wt%, for comparison with Example 1. Its catalytic hydrogenation performance for NBR was investigated using the same reaction conditions as in Example 1.

[0072] Comparative Example 2

[0073] Commercial TiO2 nanoparticles were used as a support, and the active component Pd was loaded using the same method as in Example 1 to obtain a TiO2 catalyst with a Pd loading of 1.0 wt%, for comparison with Example 1. Its catalytic hydrogenation performance for NBR was investigated using the same reaction conditions as in Example 1.

[0074] Comparative Example 3

[0075] Commercial TiO2 nanoparticles were used as a support, and metal doping and Pd loading of the active component were carried out using the same method as in Example 1 to obtain a TiO2 catalyst with Mn doping of 5.2 wt% and Pd loading of 1.0 wt%, for comparison with Example 1. Its catalytic hydrogenation performance for NBR was investigated using the hydrogenation method and reaction conditions in Example 1.

[0076] The NBR hydrogenation activity of catalysts prepared on different supports is shown in Table 4.

[0077] Table 4 Effect of different supports on NBR hydrogenation activity

[0078]

[0079] As shown in Table 4, 1) the strategy of using metal doping can significantly improve the hydrogenation activity of the catalyst and this strategy is universal for different supports; 2) the two-dimensional layered TiO2 nanosheets as a support can eliminate the diffusion restriction of macromolecules in the catalyst channels, thus exhibiting superior hydrogenation activity.

[0080] Figure 1 The figures show the EPR spectra of the catalyst supports prepared in Example 1(a) and Comparative Example 1(b). As can be seen from the figures, oxygen vacancies and Ti atoms were detected at g=2.006 and g=1.976 in the metal-doped Mn-TiO2 support, respectively. 3+ The EPR signal peaks at the sites indicate that the doped metal introduces a large number of defect sites on the TiO2 surface.

[0081] Figure 2 XRD patterns of the supported catalysts prepared in Example 1(a) and Comparative Example 1(b). Figure 1 It can be seen that the strong diffraction peaks of the sample at 2θ=25.3°, 37.8°, 48.0°, and 55.1° belong to the characteristic peaks of the anatase phase TiO2 (JCPDS: 21-1272), which means that doping with Mn will not change the original crystal phase of TiO2 or form a new phase.

[0082] Figure 3 TEM images of the supported catalysts prepared in Example 1(a) and Comparative Example 1(b), and their corresponding particle size distribution statistics of Pd nanoparticles. As can be seen from the figures, the average particle sizes of the Pd nanoparticles in the obtained catalysts are 1.59 and 2.90 nm, respectively. The TEM images show that the metal doping strategy significantly improved the dispersion of the metal Pd particles and reduced their particle size.

[0083] Figure 4The image shows a comparison of the infrared spectra of the hydrogenation products obtained by catalytic hydrogenation using the supported catalysts prepared in Example 1 and Comparative Example 1. As can be seen from the image, compared to the NBR feedstock, the hydrogenation product HNBR generated using the catalysts obtained in Example 1 and Comparative Example 1 has a wavelength at 970 cm⁻¹. -1 and 920 cm -1 The characteristic absorption peaks belonging to the 1,4-trans-CH=CH- and 1,2-CH=CH2 structures were significantly reduced, while the newly appearing peaks at 723 cm⁻¹ were significantly reduced. -1 (-CH2-) n (n>4) The structural peak intensities gradually increase, with the HNBR product generated using the catalyst obtained in Example 1 showing peak intensities at 970 and 920 cm⁻¹. -1 The absorption peak almost disappeared, which also indicates that its degree of hydrogenation is higher.

[0084] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. Use of a metal-doped, defect-rich Pd-based catalyst in the heterogeneous catalytic hydrogenation of butadiene-acrylonitrile rubber, characterized in that: The butyronitrile rubber is dissolved in an organic solvent, and is reacted in the presence of a metal-doped defect-rich Pd-based catalyst at 30-90 DEG C under a hydrogen pressure of 0.5-4 MPa for 0.5-6 h, and then the obtained product is flocculated by deionized water to obtain hydrogenated butyronitrile rubber; The metal-doped defect-rich Pd-based catalyst is prepared by doping metal atoms into a TiO2 lattice by a strategy of post-impregnation calcination on TiO2 nanosheets, inducing a large number of defect sites on the surface, and then loading active metal Pd by an equal-volume impregnation method, and reduction The metal atoms are one or more of Mn, Cu, Fe, V and Mo.

2. Use according to claim 1, characterized in that: The mass ratio of the used organic solvent, metal-doped defect-rich Pd-based catalyst and butyronitrile rubber is (80-10):(0.1-1):

1.

3. Use according to claim 1 or 2, characterized in that: The organic solvent is one or more of acetone, cyclohexane, n-heptane, cyclohexanone, dichloromethane, trichloromethane, chlorobenzene, butanone, decaline and tetrahydrofuran.

4. Use according to claim 1, characterized in that: The doping amount of metal atoms in the metal-doped defect-rich Pd-based catalyst is 1.5-15 wt%, and the loading amount of active metal Pd is 0.1-2 wt%.

5. The use according to claim 1, characterized in that: The preparation of the metal-doped defect-rich Pd-based catalyst specifically comprises the following steps: 1) preparing TiO2 nanosheets by a hydrothermal method; 2) preparing metal-doped defect-state TiO2 nanosheets: dispersing the prepared TiO2 nanosheets in a metal salt solution, stirring and reacting at 60-90 DEG C for 6-12 h, separating and drying after the reaction is completed, and calcining at 400-600 DEG C for 2-6 h to obtain metal-doped defect-state TiO2 nanosheets; 3) loading active metal Pd: ultrasonically dissolving a palladium precursor with a solvent, and then uniformly dropping it on the metal-doped defect-state TiO2 nanosheets obtained in step 2) under stirring, standing at room temperature for 12 h, and then reducing under a H2 atmosphere to obtain the metal-doped defect-rich Pd-based catalyst.

6. Use according to claim 5, characterized in that: In step 2), the mass-volume ratio of the TiO2 nanosheets to the metal salt solution is 1:20-50 g / mL; the concentration of the metal salt solution is 0.001-0.1 mol / L, and the metal salt is one or more of nitrate salts of Mn, Cu, Fe, V and Mo.

7. Use according to claim 5, characterized in that: In step 3), the palladium precursor is one or more of palladium acetate, palladium chloride and palladium nitrate; the solvent in step 3) is one or more of dichloromethane, hydrochloric acid, acetic acid, deionized water and ethylene glycol; and the reduction temperature is 160-250 DEG C, and the time is 2-6 h.

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