Preparation method and application of high-dispersion and high-stability pd-based catalyst

Abstract

The application discloses a preparation method of a high-dispersion and high-stability Pd-based catalyst and application thereof, and adopts a traditional impregnation method to attach metal salt on the surface of titanium dioxide nanosheet, then metal atoms are introduced into the titanium dioxide crystal lattice through a reducing agent auxiliary strategy to induce the generation of oxygen vacancies and Ti 4+ defects, and Ti 3+ defects are used as active components, and the generated oxygen vacancies and Ti 3+ defects are used as anchor sites of the active components, so that the efficient dispersion and stable loading of the active component Pd are realized. The catalyst obtained by the application has a typical layered structure, can effectively eliminate the diffusion limitation of the polymer in the catalyst channel, and the surface defect sites can be used as the electron donor and anchor site of the active metal to accurately control the geometry and electronic structure of the noble metal particles, thereby significantly improving the hydrogenation activity of NBR, and thus has a good application prospect in the preparation of high-value-added HNBR.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of catalyst preparation, and particularly relates to a method for preparing a Pd-based catalyst with high dispersion and stability by using a reducing agent as an auxiliary and application of the Pd-based catalyst in the heterogeneous catalytic hydrogenation of butyl nitrile rubber. BACKGROUND

[0002] Hydrogenated butyl nitrile rubber (HNBR) is a high value-added special rubber obtained by selectively hydrogenating the double bonds on the molecular chain segments of butyl nitrile rubber (NBR) and retaining the cyano group. Therefore, it has better heat resistance, cold resistance, ozone resistance, chemical resistance and mechanical strength while maintaining the original oil resistance of NBR, and is a special rubber with good comprehensive performance and development potential and a strategic material. Due to good comprehensive performance, HNBR is widely used in the fields of aerospace, new energy batteries, automobile manufacturing, rail transportation and oil field exploration.

[0003] There are three main production technologies for HNBR at present: ethylene-acrylonitrile copolymerization, NBR emulsion hydrogenation and NBR solution hydrogenation. Among them, the solution hydrogenation method is the main production method currently adopted in industry. The catalysts used in the NBR solution hydrogenation method mainly include homogeneous catalysts of noble metals such as palladium, rhodium and ruthenium and non-homogeneous supported catalysts. Among them, the homogeneous solution hydrogenation catalyst has been widely studied and applied due to its high activity and good selectivity, but the noble metal catalyst is expensive, has poor stability and is difficult to separate after the reaction, which increases the production cost and seriously damages the physical and chemical properties of the rubber due to the residual metal. The non-homogeneous solution hydrogenation can separate the product from the catalyst by simple centrifugation, which not only effectively avoids the catalyst residue in the product, but also makes it possible to reuse the noble metal catalyst, greatly reduces the cost of HNBR production and has good industrial application prospect.

[0004] The first Pd-based supported catalysts were prepared by Nippon Shokubai Co. Ltd. using carbon black and SiO2 as supports for the hydrogenation of NBR (Patents: US Patent 04384081, US Patent 4452951). Although the catalysts showed more than 90% hydrogenation activity in the hydrogenation of NBR, the weak interaction between the active component and the support led to the agglomeration and loss of noble metal during the reaction, which affected the performance of the hydrogenation product and the secondary use of the noble metal catalyst. In recent years, a large number of studies have been carried out by functionalizing the surface of the support to realize the effective loading of the active component by using the coordination between the active metal and the nitrogen-containing group. The supported Pd-based catalysts prepared by this method not only achieved 97% hydrogenation degree in the hydrogenation of NBR, but also effectively avoided the agglomeration and loss of Pd nanoparticles. However, the use of expensive support modifiers and the use of large amounts of organic solvents and complex operation processes in this method make the production and use cost high. In addition to the easy agglomeration and even loss of the active component, the significant mass transfer limitation of high-viscosity polymer molecules in the catalyst pores is also a key factor affecting the hydrogenation performance (Patents: CN 109317178A, CN 104119478A). In order to eliminate the pore diffusion limitation, SiO2 supported Pd catalysts with large pore structure were developed for NBR hydrogenation (CN 114505072B, Journal of Materials Science 2018, 53, 15064-15080). Although the large-pore catalysts greatly eliminated the influence of pore diffusion, the large pore size led to a low specific surface area, which was not conducive to the dispersion of active substances, thus to a certain extent, reducing the number of active centers. In addition, Han et al. developed a monolithic Pd / CNTs@NF catalyst to try to eliminate the diffusion limitation of polymer in the catalyst pores, but the hydrogenation activity in the NBR hydrogenation reaction could only reach 85% (Industrial & Engineering Chemistry Research 2019, 28, 1812-1822). In summary, it is of great scientific significance and practical value to develop a low-cost, simple operation method for preparing high-activity, high-utilization rate supported noble metal catalysts for the preparation of high-value-added HNBR. SUMMARY

[0005] To solve the above problems, the present application provides a method for preparing a Pd-based catalyst with high dispersion and high stability assisted by a reducing agent, which is low in cost, simple in preparation process and has excellent catalytic hydrogenation activity and good recycling performance in the hydrogenation of NBR.

[0006] To achieve the above object, the present application adopts the following technical scheme:

[0007] A highly dispersed and stable Pd-based catalyst is developed by using NaBH4 as a reducing agent, mixing it with titanium dioxide nanosheets with metal salts attached to their surface, and then calcining the mixture under an inert atmosphere. This process allows metal heteroatoms to be doped into the TiO2 lattice, partially replacing Ti. 4+ And while further inducing the formation of oxygen vacancies, it also causes the original Ti in TiO2 to become... 4+ Ion reduction to form Ti 3+ The defect sites are then loaded with active metal Pd using an equal-volume impregnation method, followed by reduction to obtain the final product. The specific preparation method includes the following steps:

[0008] 1) Preparation of titanium dioxide nanosheets: 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 dropwise and 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 titanium dioxide nanosheets.

[0009] 2) Rich in oxygen vacancies and Ti 3+ Preparation of titanium dioxide nanosheets with defect sites: Titanium dioxide nanosheets were first dispersed in a metal salt solution and stirred at 60-90 °C for 6-12 h. After centrifugation and drying, a certain amount of NaBH4 was added and the mixture was ground and mixed. The mixture was then calcined under an inert atmosphere to obtain titanium dioxide nanosheets rich in oxygen vacancies and Ti. 3+ Titanium dioxide nanosheets with defect sites;

[0010] 3) Preparation of supported Pd-based catalysts: The palladium precursor was dissolved in a solvent by ultrasonication, and the resulting solution was uniformly added dropwise to the oxygen-vacancy-rich and Ti-rich catalyst under stirring. 3+ The titanium dioxide nanosheets with defect sites were placed at room temperature for 12 h and then fed into a tube furnace for high-temperature reduction under H2 atmosphere to obtain the Pd-based catalyst.

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

[0012] Furthermore, the mass ratio of titanium dioxide nanosheets to NaBH4 used in step 2) is 1:0.01-1.

[0013] Furthermore, the calcination temperature in step 2) is 400-600 ℃, and the time is 2-6 h.

[0014] Further, the palladium precursor in step 3) is one or more of palladium acetate, palladium chloride, and palladium nitrate.

[0015] Further, the solvent in step 3) is one or more of dichloromethane, hydrochloric acid, deionized water, and ethylene glycol.

[0016] Further, the temperature of the high-temperature reduction in step 3) is 140-250 ℃, and the time is 2-6 h.

[0017] Further, the loading of Pd in the obtained Pd-based catalyst is 0.1-2 wt%, and the metal atom doping amount is 1.5-15 wt%.

[0018] The obtained Pd-based catalyst with high dispersion and stability can be used for heterogeneous catalytic hydrogenation of butyl nitrile rubber. Specifically, butyl nitrile rubber is dissolved in an organic solvent, and then the Pd-based catalyst is added, and the reaction is carried out at 30-90 ℃ under a hydrogen pressure of 0.5-4 MPa for 0.5-6 h, and then the product is flocculated by deionized water to obtain HNBR.

[0019] Further, the mass ratio of the used organic solvent, catalyst, and butyl nitrile rubber is (80-10):(0.1-1):1. The organic solvent is one or more of acetone, cyclohexane, n-heptane, cyclohexanone, dichloromethane, trichloromethane, chlorobenzene, butanone, decaline, and tetrahydrofuran.

[0020] The beneficial effects of the present application are:

[0021] (1) The Pd-based catalyst prepared by the present application has a typical layered structure, which not only provides a high external specific surface area to facilitate efficient dispersion of the active component, but also effectively eliminates the diffusion limitation of macromolecular polymers in the catalyst pores, thereby improving the utilization rate of active sites.

[0022] (2) The abundant oxygen vacancy defects and Ti 3+ defects introduced on the surface of the titanium dioxide nanosheet can act as electron donors and anchoring sites for active metals, achieving efficient and stable loading of the active component Pd, thereby improving the hydrogenation activity and reusability of the catalyst.

[0023] (3) Even at a NBR glue concentration of 5 wt%, the Pd-based catalyst prepared by the present application can still achieve a hydrogenation activity of more than 90%, which is of great significance for reducing production costs in the industrialization of NBR heterogeneous hydrogenation. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1EPR diagrams of the supported Pd-based catalysts prepared in Examples 1(a), 1(b), 2(c), and 3(d).

[0025] Figure 2 XRD patterns of the supported Pd-based catalysts prepared in Examples 1(a), 1(b), and 2(c).

[0026] Figure 3 Nitrogen adsorption-desorption isotherms and pore size distribution diagrams of the supported Pd-based catalysts prepared in Examples 1(a), 1(b), and 2(c).

[0027] Figure 4 TEM images and particle size distribution statistics of the supported Pd-based catalysts prepared in Examples 1(a), 1(b), and 2(c) are shown.

[0028] Figure 5 The infrared spectra of the hydrogenated product HNBR obtained by catalytic hydrogenation using the supported catalysts prepared in Example 1(a), Comparative Example 1(b), and Comparative Example 2(c) are shown in comparison. Detailed Implementation

[0029] A highly dispersed and highly stable Pd-based catalyst, the preparation method of which includes the following steps:

[0030] 1) Preparation of titanium dioxide nanosheets: 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 (content 40-70 wt%) dropwise. React at 160-250 ℃ for 8-16 h. After that, wash with 0.1-5 mol / L sodium hydroxide solution and deionized water until neutral. Dry at 80 ℃ and place in a muffle furnace. Calcine at 400-600 ℃ for 2-6 h to obtain titanium dioxide nanosheets.

[0031] 2) Rich in oxygen vacancies and Ti 3+ Preparation of titanium dioxide nanosheets with defect sites: Titanium dioxide nanosheets were first dispersed in a 0.001-0.06 mol / L metal salt solution at a mass-to-volume ratio of 1:20-50 g / mL, and stirred at 60-90 °C for 6-12 h. After centrifugation and drying, NaBH4 was added at a mass ratio of 0.01-1:1 to the titanium dioxide nanosheets and ground to mix. The mixture was then calcined at 400-600 °C for 2-6 h under an inert atmosphere to obtain titanium dioxide nanosheets rich in oxygen vacancies and Ti. 3+ Titanium dioxide nanosheets with defect sites;

[0032] 3) Preparation of supported Pd-based catalysts: The palladium precursor was dissolved in a solvent by ultrasonication, and the resulting solution was uniformly added dropwise to the oxygen-vacancy-rich and Ti-rich catalyst under stirring. 3+ Titanium dioxide nanosheets with defect sites were placed at room temperature for 12 h and then fed into a tube furnace for high-temperature reduction at 140-250 °C for 2-6 h in H2 atmosphere to obtain the Pd-based catalyst, which has a Pd loading of 0.1-2 wt% and a metal atom doping amount of 1.5-15 wt%.

[0033] In step 2), the metal salt used is an oxide or nitrate of one or more of Mn, Cu, Fe, V, and Mo.

[0034] 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, deionized water, and ethylene glycol.

[0035] 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.

[0036] Example 1

[0037] (1) 10 g tetrabutyl titanate was dispersed in 15 mL of anhydrous ethanol, and then 4.5 g mL 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. The precipitate 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.

[0038] (2) 1 g of titanium dioxide nanosheets were dispersed in a 0.02 mol / L V2O5 solution and stirred at 60 °C for 6 h. After centrifugation and drying, the nanosheets were mixed evenly with 0.041 g of NaBH4 by grinding. The mixture was then placed in a tube furnace and heated to 400 °C at a rate of 2 °C / min under an Ar atmosphere and held for 2 h to obtain a mixture rich in oxygen vacancies and Ti. 3+ Titanium dioxide nanosheets with defect sites.

[0039] (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 oxygen-vacancy-rich Ti. 3+ A supported catalyst with a Pd loading of 1.0 wt% and a V doping of 5.1 wt% was prepared by standing at room temperature for 12 h in titanium dioxide nanosheets with defect sites and then reducing them at 140 °C for 2 h in H2 atmosphere.

[0040] Take 2 g NBR dissolved in 80 g acetone, make NBR glue liquid with concentration of 2.5 wt%, then add 1.5 g catalyst into high pressure reactor at 60 ℃, hydrogen pressure of 1 MPa, stirring rate of 1200 rpm for 3 h, after reaction, hydrogenated product is obtained by deionized water flocculation, and the catalyst after reaction is recovered for use.

[0041] Example 2

[0042] The 0.02 mol / L V2O5 solution in Example 1 is replaced with 0.038 mol / L KMnO4 solution, and the remaining steps are the same as Example 1, to obtain a supported catalyst with Mn doping amount of 5.2 wt%. The same reaction conditions as Example 1 are used to investigate the catalytic hydrogenation performance of NBR.

[0043] Example 3

[0044] The 0.02 mol / L V2O5 solution in Example 1 is replaced with 0.021 mol / L (NH4)2MoO4 solution, and the remaining steps are the same as Example 1, to obtain a supported catalyst with Mo doping amount of 4.3 wt%. The same reaction conditions as Example 1 are used to investigate the catalytic hydrogenation performance of NBR.

[0045] Example 4

[0046] The 0.02 mol / L V2O5 solution in Example 1 is replaced with 0.032 mol / L Cu(NO3)2 solution, and the remaining steps are the same as Example 1, to obtain a supported catalyst with Cu doping amount of 5.1 wt%. The same reaction conditions as Example 1 are used to investigate the catalytic hydrogenation performance of NBR.

[0047] Example 5

[0048] The 0.02 mol / L V2O5 solution in Example 1 is replaced with 0.038 mol / L Fe(NO3)2 solution, and the remaining steps are the same as Example 1, to obtain a supported catalyst with Fe doping amount of 5.3 wt%. The same reaction conditions as Example 1 are used to investigate the catalytic hydrogenation performance of NBR.

[0049] The NBR hydrogenation activity of catalysts doped with different metals is shown in Table 1.

[0050] Table 1 Effect of doping of different metals on NBR hydrogenation activity

[0051]

[0052] From Table 1, it can be seen that the doping of different metals is beneficial to improving the hydrogenation performance of the catalyst, and the effect of V doping is the best.

[0053] Example 6

[0054] The concentration of the V2O5 solution in Example 1 was adjusted to 0.01 mol / L, and the remaining steps were the same as in Example 1, to obtain a supported Pd-based catalyst with a V doping amount of 2.5 wt.%. The catalytic hydrogenation performance of NBR was investigated under the same reaction conditions as in Example 1.

[0055] Example 7

[0056] The concentration of the V2O5 solution in Example 1 was adjusted to 0.03 mol / L, and the remaining steps were the same as in Example 1, to obtain a supported Pd-based catalyst with a V doping amount of 7.7 wt.%. The catalytic hydrogenation performance of NBR was investigated under the same reaction conditions as in Example 1.

[0057] Example 8

[0058] The concentration of the V2O5 solution in Example 1 was adjusted to 0.06 mol / L, and the remaining steps were the same as in Example 1, to obtain a supported Pd-based catalyst with a V doping amount of 15.3 wt.%. The catalytic hydrogenation performance of NBR was investigated under the same reaction conditions as in Example 1.

[0059] The effect of different concentrations of V2O5 solution on the NBR hydrogenation activity of the obtained catalyst is shown in Table 2.

[0060] Table 2 Effect of different concentrations of potassium permanganate solution on NBR hydrogenation activity

[0061]

[0062] As can be seen from Table 2, with the increase of the doping amount of metal V, the hydrogenation performance of the catalyst first increases and then decreases, and the effect is the best when the doping amount is 5.1 wt.%.

[0063] Example 9

[0064] The loading amount of Pd in Example 1 was adjusted to 0.5 wt.%, and the remaining steps were the same as in Example 1. The catalytic hydrogenation performance of NBR was investigated under the same reaction conditions as in Example 1.

[0065] Example 10

[0066] The loading amount of Pd in Example 1 was adjusted to 0.75 wt.%, and the remaining steps were the same as in Example 1. The catalytic hydrogenation performance of NBR was investigated under the same reaction conditions as in Example 1.

[0067] Example 11

[0068] The loading of Pd in Example 1 was adjusted to 1.5 wt.%, and the remaining steps were the same as in Example 1, and the catalytic hydrogenation performance of NBR was investigated under the same reaction conditions as in Example 1.

[0069] Example 12

[0070] The loading of Pd in Example 1 was adjusted to 2 wt.%, and the remaining steps were the same as in Example 1, and the catalytic hydrogenation performance of NBR was investigated under the same reaction conditions as in Example 1.

[0071] The effects of different Pd loadings on the NBR hydrogenation activity of the obtained catalysts are shown in Table 3.

[0072] Table 3 Effects of different Pd loadings on NBR hydrogenation activity

[0073]

[0074] As can be seen from Table 3, with the increase of the loading of metal Pd, the hydrogenation performance of the catalyst first increases and then decreases, and the effect is best when the loading is 1 wt.%.

[0075] Example 13

[0076] The recovered catalyst after reaction in Example 1 was washed with a mixed solution of acetone and azoniomethylpyrrolidine (1:1, v / v), and then the catalytic hydrogenation of NBR was repeated once under the same reaction conditions as in Example 1, and the catalytic hydrogenation performance of NBR was investigated.

[0077] Example 14

[0078] The recovered catalyst after reaction in Example 13 was washed with a mixed solution of acetone and azoniomethylpyrrolidine (1:1, v / v), and then the catalytic hydrogenation of NBR was repeated once under the same reaction conditions as in Example 1, and the catalytic hydrogenation performance of NBR was investigated.

[0079] Example 15

[0080] The recovered catalyst after reaction in Example 14 was washed with a mixed solution of acetone and azoniomethylpyrrolidine (1:1, v / v), and then the catalytic hydrogenation of NBR was repeated once under the same reaction conditions as in Example 1, and the catalytic hydrogenation performance of NBR was investigated.

[0081] The NBR hydrogenation activity of the catalysts with different recovery times is shown in Table 4.

[0082] Table 4 Effects of catalysts with different recovery times on NBR hydrogenation activity

[0083]

[0084] From Table 4, it can be seen that the hydrogenation activity is basically stable after multiple cycles, proving that the prepared supported catalyst has excellent cycle performance.

[0085] Comparative Example 1

[0086] Titanium dioxide nanosheets doped with only V were used as the carrier, and the active component Pd was loaded by the same method as in Example 1 for comparison with Example 1. The same reaction conditions as in Example 1 were used to investigate the catalytic hydrogenation performance on NBR.

[0087] Comparative Example 2

[0088] Titanium dioxide nanosheets reduced only with NaBH4 were used as the carrier, and the active component Pd was loaded by the same method as in Example 1 for comparison with Example 1. The same reaction conditions as in Example 1 were used to investigate the catalytic hydrogenation performance on NBR.

[0089] Comparative Example 3

[0090] Titanium dioxide nanosheets were directly used as the carrier, and the active component Pd was loaded by the same method as in Example 1 for comparison with Example 1. The same reaction conditions as in Example 1 were used.

[0091] The NBR hydrogenation activity of the catalysts prepared with different carriers is shown in Table 5.

[0092] Table 5 Influence of different carriers on NBR hydrogenation activity

[0093]

[0094] As can be seen from Table 5, reduction with NaBH4 can significantly improve the hydrogenation activity of the V-doped catalyst.

[0095] Figure 1 EPR diagrams of the supported Pd-based catalysts prepared in Example 1 (a), Comparative Example 1 (b), Comparative Example 2 (c) and Comparative Example 3 (d), wherein the signal peak at g = 1.983 belongs to Ti 3+ defect sites, and the signal peak at g = 2.006 belongs to the signal peak of oxygen vacancies. From Figure 1 It can be seen that the Pd catalyst supported on TiO2 without any treatment has no signal of oxygen vacancies or Ti 3+ When the metal V is doped, oxygen vacancies are generated due to the substitution of part of Ti 4+ by the metal V, so the signal peak at g = 2.002 belonging to the oxygen vacancies is detected; when further treated with NaBH4 as the reducing agent, not only can the metal atoms be introduced into the titanium dioxide lattice to induce the generation of oxygen vacancies, but also the Ti4+ Reduce to generate Ti 3+ Defect site.

[0096] Figure 2 The XRD patterns of the supported Pd-based catalysts prepared in Examples 1(a), 1(b), and 2(c) are shown. The strong diffraction peaks at 2θ = 25.3°, 37.8°, 48.0°, and 55.1° are characteristic peaks of the anatase phase TiO2 (JCPDS: 21-1272), and no characteristic diffraction peaks belonging to species such as vanadium oxide and palladium oxide were detected. This indicates that metal doping and sodium borohydride reduction do not change the original crystal phase of TiO2 or form a new phase.

[0097] Figure 3 The figures show the nitrogen adsorption-desorption isotherms and pore size distributions of the supported Pd-based catalysts prepared in Examples 1(a), 1(b), and 2(c). As can be seen from the figures, their specific surface areas are 75, 72, and 82 m² / g, respectively, indicating that metal doping or sodium borohydride reduction slightly reduces the specific surface area of ​​the samples.

[0098] Figure 4 TEM images and particle size distribution statistics of the supported Pd-based catalysts prepared in Examples 1(a), 1(b), and 2(c) are shown. As can be seen from the figures, the average particle sizes of the Pd nanoparticles are 1.59, 2.38, and 2.90 nm, respectively. This can well explain the absence of Pd diffraction peaks in the XRD images and also demonstrates that, compared to metal doping alone and sodium borohydride reduction strategies, the reducing agent-assisted metal doping strategy can significantly improve the dispersibility of Pd.

[0099] Figure 5 The figures show a comparison of the infrared spectra of the hydrogenation products obtained by catalytic hydrogenation using the supported catalysts prepared in Examples 1(a), 1(b), and 2(c). As can be seen from the figures, compared to the NBR feedstock, the hydrogenation products HNBR obtained in Examples 1 and 1(c) have infrared spectral density values ​​at 970 and 920 cm⁻¹, respectively. -1 The characteristic absorption peaks of the 1,4-trans-CH=CH- and 1,2-CH=CH2 structures were significantly reduced, while a new peak appeared at 723 cm⁻¹. -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, indicating its excellent hydrogenation activity.

[0100] The above merely describes preferred embodiments of the present application, and any equivalent changes and modifications made within the scope of the present application should be included in the scope of the present application.

Claims

1. A method for preparing a highly dispersed and highly stable Pd-based catalyst, characterized in that: Using NaBH4 as a reducing agent, it is mixed with titanium dioxide nanosheets with metal salts attached to their surface and then calcined under an inert atmosphere. This process not only incorporates metal atoms into the TiO2 lattice and further induces the formation of oxygen vacancies, but also rejuvenates the original TiO2 crystal structure. 4+ Ion reduction to form Ti 3+ The defect sites are then loaded with active metal Pd using an equal-volume impregnation method, and after reduction, the highly dispersed and highly stable Pd-based catalyst is obtained. It includes the following steps: 1) First, titanium dioxide nanosheets were dispersed in a metal salt solution and stirred at 60-90 °C for 6-12 h. Then, the mixture was centrifuged, dried, and a certain amount of NaBH4 was added and ground together. The mixture was then calcined under an inert atmosphere to obtain a product rich in oxygen vacancies and Ti. 3+ Titanium dioxide nanosheets with defect sites; 2) After ultrasonically dissolving the palladium precursor in a solvent, the resulting solution is uniformly added dropwise to the oxygen-vacancy-rich Ti substrate under stirring. 3+ The Pd-based catalyst was obtained by high-temperature reduction of titanium dioxide nanosheets with defect sites after standing at room temperature for 12 h in H2 atmosphere. The metal salts used are nitrates of one or more of Mn, Cu, V, and Mo.

2. The preparation method according to claim 1, characterized in that: In step 1), the mass-to-volume ratio of titanium dioxide nanosheets to metal salt solution is 1:20-50 g / mL; the concentration of the metal salt solution is 0.001-0.06 mol / L; the mass ratio of titanium dioxide nanosheets to NaBH4 is 1:0.01-1; and the calcination temperature is 400-600 ℃ for 2-6 h.

3. The preparation method according to claim 1, characterized in that: The palladium precursor in step 2) is one or more of palladium acetate, palladium chloride, and palladium nitrate; the solvent is one or more of dichloromethane, hydrochloric acid, deionized water, and ethylene glycol; the high-temperature reduction temperature is 140-250 °C, and the time is 2-6 h.

4. The preparation method according to claim 1, characterized in that: The Pd-based catalysts obtained contained 0.1-2 wt% Pd and 1.5-15 wt% metal atom doping.

5. A highly dispersed and highly stable Pd-based catalyst prepared by any of the methods described in claims 1-4.

6. The application of the Pd-based catalyst as described in claim 5 in the heterogeneous catalytic hydrogenation of nitrile rubber, characterized in that: Nitrile rubber was dissolved in an organic solvent, and then the Pd-based catalyst was added. The reaction was carried out at 30-90 °C and a hydrogen pressure of 0.5-4 MPa for 0.5-6 h. The product was then flocculated with deionized water to obtain hydrogenated nitrile rubber.

7. The application according to claim 6, characterized in that: The mass ratio of the organic solvent, catalyst, and nitrile rubber used is (80-10):(0.1-1):

1.

8. The application according to claim 6 or 7, characterized in that: The organic solvent is one or more of acetone, cyclohexane, n-heptane, cyclohexanone, dichloromethane, chloroform, chlorobenzene, butanone, decahydronaphthalene, and tetrahydrofuran.

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