Preparation method of a catalyst supported by double-crystalline-phase titanium dioxide nanosheet tubes

Abstract

The present invention discloses a preparation method of a catalyst supported on a double-crystalline-phase titanium dioxide nanosheet tube. A titanium dioxide nanosheet tube support with anatase phase and rutile phase is prepared by a hydrothermal method, and then the final catalyst is obtained by reduction and loading of ruthenium. The titanium dioxide nanosheet tube support can not only effectively improve the hydrophilicity of the catalyst, making cyclohexene easy to desorb from the catalyst surface and difficult to re-adsorb, but also greatly improve the selectivity of the catalyst. The use of a large number of mutually cross-linked nanosheets grown on the nanosheet tube avoids the agglomeration inactivation of Ru microcrystals caused by the collision of Ru particles loaded on the support, improving the stability of the catalyst. At the same time, the large specific surface area of the nanosheets is beneficial to improving the dispersion of Ru, thereby reducing the dosage of the active metal and greatly reducing the production cost of the catalyst. The present invention is applicable to the preparation of a catalyst supported on a double-crystalline-phase titanium dioxide nanosheet tube.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst preparation for the selective hydrogenation of benzene to cyclohexene, and relates to a preparation method of a supported catalyst of twin-phase titanium dioxide nanosheet tubes. Background Art

[0002] The industrial application history of cyclohexene is long. Cyclohexene is an important organic synthesis intermediate in chemical production. Because cyclohexene has an active carbon-carbon double bond, high-value-added industrial raw materials such as nylon, cyclohexanone, and caprolactam can be easily obtained by addition through traditional olefin reactions. At present, the main synthesis methods of cyclohexene include cyclohexanol dehydration, Birch reduction, dehydrohalogenation of halogenated cyclohexane, and selective hydrogenation of benzene. The first two methods have a long history, but there are problems such as high cost, equipment corrosion, and low atom utilization rate. Now, by selective hydrogenation of benzene to cyclohexene, the by-product is only cyclohexane, the product purity is high, the carbon atom utilization rate is 100%, it has high atom economy, is environmentally friendly, and conforms to the sustainable strategy proposed by the country.

[0003] Benzene hydrogenation is a consecutive reaction, which can directly generate cyclohexane in one step or first generate cyclohexene and then cyclohexene is deeply hydrogenated to cyclohexane. Analyzing from the perspective of thermodynamics, the standard Gibbs free energy change (Δ r G θ m =-98 kJ·mol -1) for the formation of cyclohexane by selective hydrogenation of benzene is lower than the Gibbs free energy change (Δ r G θ m =-23 kJ·mol -1 ) for the formation of cyclohexene, which makes it easier for benzene to be selectively hydrogenated to cyclohexane and more difficult to form cyclohexene. Therefore, in order to improve the yield of selective hydrogenation of benzene to cyclohexene, it is necessary to prepare a highly selective catalyst to regulate the relative rates of the two-step hydrogenation reactions (benzene to cyclohexene and cyclohexene to cyclohexane), and then obtain more cyclohexene products and improve its yield. At present, the non-supported RuZn catalyst is widely used in industry, but the amount of precious metal Ru used in this catalyst is large and the catalyst stability is poor. During use, zirconia must be added as a dispersant to prevent catalyst agglomeration, and the dispersion effect is not easy to control.

[0004] In view of the above problems, many researchers at home and abroad are currently committed to developing new dispersants and supported catalysts. Chinese Patent Publication No. CN 104549207A discloses a novel ZrO2 composite other oxide dispersant. By exploring the dispersant used in the reaction, a relatively high cyclohexene yield can be obtained. Chinese Patent Publication No. CN 108993598A discloses a preparation method of a (Ru / MeOx)@m-MeOx core-shell structured bifunctional catalyst. The use of the unique core-shell structure improves the activity, selectivity and cyclic stability of the catalyst. However, the above catalysts have problems such as low ruthenium dispersion, easy agglomeration or cumbersome synthesis conditions and are not easy to produce on a large scale, which is not conducive to industrial promotion and application. Therefore, it is of great significance to develop a catalyst with high active metal dispersion, strong stability, excellent catalytic performance and easy industrial production and application. Summary of the Invention

[0005] The present invention aims to provide a preparation method of a supported catalyst of twin-phase titanium dioxide nanosheet tubes. A titanium dioxide nanosheet tube support with anatase phase and rutile phase is prepared, and the final catalyst is obtained after loading ruthenium. The titanium dioxide nanosheet tube support can not only effectively improve the hydrophilicity of the catalyst, make cyclohexene easy to desorb from the catalyst surface and difficult to adsorb again, and can greatly improve the selectivity of the catalyst, but also avoid the agglomeration inactivation of Ru microcrystals caused by the collision of Ru particles loaded on the support by using a large number of mutually intersecting nanosheets grown on the nanosheet tubes, thereby improving the stability of the catalyst; at the same time, the large specific surface area nanosheets are beneficial to improving the dispersion of Ru, thereby reducing the dosage of the active metal, and greatly reducing the production cost of the catalyst.

[0006] The technical solution of the present invention is as follows:

[0007] A preparation method of a supported catalyst of twin-phase titanium dioxide nanosheet tubes is sequentially carried out according to the following steps:

[0008] a. Dissolve a Ti compound in an organic solvent, stir for 2 h to obtain solution A, and mix glycerol and ether evenly to obtain solution B;

[0009] b. Rapidly mix solution A and solution B under stirring conditions, stir at room temperature for 10 h, transfer to a reaction kettle, react at 165 °C for 8 h, centrifuge the obtained white precipitate after the reaction is completed, wash it with ethanol 3-4 times, dry it overnight under vacuum, take it out and place it in a muffle furnace, and calcine it in an air atmosphere to obtain titanium dioxide nanosheet tubes;

[0010] c. Disperse the titanium dioxide nanosheet tubes in water, add a ruthenium compound, stir for 1 h, then dropwise add an aqueous solution of sodium borohydride to the solution at a rate of 5 mL / min to load ruthenium onto the titanium dioxide nanosheet tubes. Centrifuge and wash the obtained precipitate 3 - 5 times, and then dry it under vacuum to obtain the catalyst.

[0011] As a limitation of the present invention: in step a, the compound of Ti is titanium oxysulfate hydrate.

[0012] As the second limitation of the present invention, in step b, the calcination process is as follows:

[0013] b1. Heat from room temperature to 200 °C at a heating rate of 5 °C / min and keep the temperature for 1 h;

[0014] b2. Heat from 200 °C to 600 °C at a heating rate of 10 °C / min and keep the temperature for 4 h;

[0015] b3. Cool naturally to room temperature.

[0016] In this application, the titanium dioxide nanosheet tubes finally form titanium dioxide nanosheet tubes with anatase phase and rutile phase through a staged calcination process. This is crucial for the subsequent loading of ruthenium metal to achieve the selective hydrogenation of benzene to cyclohexene. In this process, in stage b1, the nanosheet tubes obtained by solvothermal method are calcined at a low temperature, so that the structure of the nanosheet tubes tends to be stable and there will be no phenomenon of structural collapse and aggregation under high-temperature calcination. At the same time, some organic substances remaining from solvothermal method can also be removed in this stage to ensure the purity of the product; in stage b2, the nanosheet tubes start to react. As the temperature rises, the nanosheet tubes start to transform into anatase-type titanium dioxide nanosheet tubes. When the temperature rises to 600 °C, all the nanosheet tubes are converted into anatase-type titanium dioxide nanosheet tubes. Then, keep the temperature at 600 °C, and a part of the nanosheets on the anatase-type titanium dioxide nanosheet tubes undergo crystal form transformation to generate rutile-type titanium dioxide. After that, the calcination ends, and titanium dioxide nanosheet tubes with anatase phase and rutile phase are obtained.

[0017] As the third limitation of the present invention, in step c, the ruthenium compound is ruthenium trichloride or ruthenium nitrate; the concentration of the sodium borohydride aqueous solution is 1 mol / L, and the molar ratio of the titanium dioxide nanosheet tubes, the ruthenium compound and the sodium borohydride aqueous solution is 12.5:1:4.

[0018] In the present invention, the amount of substance of the sodium borohydride aqueous solution and the dropping rate directly affect the reduction effect of ruthenium ions and the particle state distribution, which in turn affects their distribution and agglomeration on the carrier, and further affects the final catalytic effect; the dropping rate in this application is 5 mL / min. When the dropping rate is too fast, the reaction is violent and a large amount of bubbles will be generated, resulting in a charging phenomenon, making the reduced ruthenium prone to agglomeration and uneven dispersion. When the dropping rate is too slow, the ruthenium particles obtained after reduction and loading will be larger and the efficiency will be lower.

[0019] As the fourth limitation of the present invention, in step c, the temperature of the vacuum drying is 60 °C and the drying time is 10 h.

[0020] As the fifth limitation of the present invention, in step b, the titanium dioxide nanosheet tube is composed of anatase phase and rutile phase, and the mass ratio of the anatase phase is 60-75%; rutile phase titanium dioxide has high stability, and anatase phase titanium dioxide has high activity. A solvent thermal and high-temperature calcination method is used to prepare an anatase / rutile titanium dioxide support material, which can not only effectively improve the stability of the material, but also help to enhance the catalytic activity of the titanium dioxide material. In the present invention, the titanium dioxide nanosheet tube support with this ratio of anatase phase and rutile phase forms a rich anatase / rutile interface, which is easy to realize the electron transfer of Ru to TiO2 and is more likely to generate electron-deficient Ru δ+ species, and electron-deficient Ru δ+ species is beneficial to adsorb benzene on the catalyst, and can effectively improve the hydrophilicity of the catalyst, making cyclohexene easy and fast to desorb from the catalyst surface and difficult to re-adsorb, preventing the progress of the second-step cyclohexene-to-cyclohexane reaction; at the same time, the titanium dioxide nanosheet tube with anatase phase and rutile phase is rich in hydroxyl groups, making the hydrophilicity of the catalyst surface enhanced, preventing the re-adsorption and deep hydrogenation of cyclohexene. The synergistic effect of the two greatly improves the selectivity of cyclohexene.

[0021] There is also a limitation in the present invention that in step c, in the catalyst, the mass ratio of Ru is 3-10% of the titanium dioxide nanosheet tube; in the present invention, too high Ru dosage will lead to too high catalyst cost, and too low content will lead to a decrease in the active component loaded per unit area, affecting the catalytic activity of the catalyst.

[0022] As a whole, the above preparation method, each step is closely related and interrelated, and they jointly determine the selective catalytic performance of the final catalyst.

[0023] Due to the adoption of the above technical solution, the beneficial effects obtained by the present invention are as follows:

[0024] 1. The supported catalyst prepared by the present invention has titanium dioxide nanosheets arranged in a cross pattern in a tubular one-dimensional structure. This structure avoids the disordered distribution and overlap of the nanosheets, and the supported active metal Ru can be evenly distributed on the nanosheets, avoiding the agglomeration inactivation of Ru microcrystals caused by the collision of Ru particles supported on the carrier. On the one hand, the stability of the catalyst is improved, and at the same time, the titanium dioxide nanosheet tube structure with a large specific surface area is conducive to improving the dispersion of Ru, thereby reducing the dosage of the active metal and greatly reducing the production cost of the catalyst, making it have high industrial promotion and application value.

[0025] 2. The supported catalyst prepared by the present invention has a titanium dioxide nanosheet tube support composed of anatase phase and rutile phase. The synergistic effect of the two phases greatly improves the selectivity of cyclohexene, and improves the yield and purity of hydrogenation-catalyzed cyclohexene.

[0026] The present invention is applicable to the preparation of a supported catalyst with a twin-phase titanium dioxide nanosheet tube, and is further used for catalytic selective hydrogenation of benzene to prepare cyclohexene.

[0027] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings of the specification. Description of the Drawings

[0028] Figure 1 Scanning diagram of the titanium dioxide nanosheet tube prepared in Example 1;

[0029] Figure 2 Transmission diagram of the ruthenium-supported titanium dioxide nanosheet tube prepared in Example 1;

[0030] Figure 3 Energy spectrum diagram of the ruthenium-supported titanium dioxide nanosheet tube prepared in Example 1;

[0031] Figure 4 X-ray diffraction diagram of the ruthenium-supported titanium dioxide nanosheet tube prepared in Example 1. Specific Embodiments

[0032] In the following examples, unless otherwise specified, the reagents used are all commercially available reagents. Unless otherwise specified, the following experimental methods and detection methods are all existing experimental methods and detection methods.

[0033] Example 1

[0034] a. Dissolve 1 g of TiOSO4·xH2SO4·yH2O in 20 mL of ethanol to obtain solution A, stir for 2 h, and mix 10 mL of glycerol and 10 mL of ether evenly to obtain solution B;

[0035] b. Rapidly mix Solution A and Solution B under stirring conditions, then stir at room temperature for 10 h, carry out solvothermal reaction at 165 °C for 8 h. After the reaction is completed, centrifuge to obtain a white precipitate. Wash it 3 - 4 times with ethanol and then vacuum dry overnight. Calcinate at high temperature to obtain titanium dioxide nanosheet tubes, and the obtained carrier is denoted as TiO2 NSTs-a;

[0036] The calcination process is as follows:

[0037] b1. Heat from room temperature to 200 °C at a heating rate of 5 °C / min and hold for 1 h;

[0038] b2. Heat from 200 °C to 600 °C at a heating rate of 10 °C / min and hold for 4 h;

[0039] b3. Naturally cool to room temperature;

[0040] c. Disperse 1 g of TiO2 NSTs-a in water, add 0.21 g of RuCl3, stir for 1 h, then add 4 mL of 1 mol / L sodium borohydride aqueous solution at a dropping rate of 5 mL / min to reduce the ruthenium compound, forming ruthenium loaded on the titanium dioxide nanosheet tubes. Centrifuge and wash the obtained precipitate 3 - 5 times, and vacuum dry at 60 °C for 10 h to obtain the catalyst Ru / TiO2 NSTs-a.

[0041] A series of performance tests were carried out on the catalyst prepared in this example, as follows.

[0042] From Figure 1 it can be seen that the nanosheet tubes are cross-assembled by nanosheets, with a complete structure and good morphology.

[0043] From Figure 2 the left figure in it can be seen that the ruthenium active component is evenly distributed on the surface of the nanosheets. From the high-magnification transmission ( Figure 2 right figure) it can be further seen that the ruthenium particles are all dispersed on the TiO2 NSTs carrier, and the distribution is relatively uniform.

[0044] From Figure 3 the energy spectrum diagram it can be seen that the ruthenium active component is evenly distributed on the nanosheet tubes, which is consistent with the transmission electron microscopy characterization results.

[0045] From Figure 4 it can be obtained that the TiO2 NSTs carrier coexists in rutile and anatase phases, and no diffraction peak of the active component Ru is observed. The reason is that the Ru loading amount is relatively low and Ru is highly dispersed, which is also consistent with the above characterization results.

[0046] In addition, from Figure 4It can be seen from the X-ray diffraction pattern that the titanium dioxide nanosheet tubes prepared in this example are composed of anatase and rutile phases, and the mass ratio of the anatase phase is 60-75%; from Figure 3 It can be seen from the energy spectrum that in the finally obtained catalyst, the mass ratio of Ru is 3-10% of the titanium dioxide nanosheet tubes.

[0047] Example 2

[0048] Dissolve 1 g of TiOSO4·xH2SO4·yH2O in 20 mL of ethanol to obtain solution A, stir for 2 h, mix 10 mL of glycerol and 10 mL of ether evenly to obtain solution B. After quickly mixing solution A and solution B under stirring conditions, stir at room temperature for 10 h, carry out a solvothermal reaction at 165 °C for 8 h. The white precipitate obtained by centrifugation is washed 3-4 times with ethanol and then vacuum dried overnight, and then calcined at high temperature to obtain titanium dioxide nanosheet tubes; the obtained support is denoted as TiO2NSTs-a. Disperse 1 g of TiO2 NSTs-a in water, add 0.06 g of RuCl3, stir for 1 h, and then add 1.2 mL of 1 mol / L sodium borohydride aqueous solution at a rate of 5 mL / min to reduce the ruthenium compound, and load ruthenium on the titanium dioxide nanosheet tubes. The obtained precipitate is centrifuged and washed 3-5 times, and vacuum dried at 60 °C for 10 h to obtain the catalyst Ru / TiO2 NSTs-a.

[0049] Example 3

[0050] Dissolve 1 g of TiOSO4·xH2SO4·yH2O in 20 mL of ethanol to obtain solution A, stir for 2 h, mix 10 mL of glycerol and 10 mL of ether evenly to obtain solution B. After quickly mixing solution A and solution B under stirring conditions, stir at room temperature for 10 h, carry out a solvothermal reaction at 165 °C for 8 h. The white precipitate obtained by centrifugation is washed 3-4 times with ethanol and then vacuum dried overnight, and then calcined at high temperature to obtain titanium dioxide nanosheet tubes; the obtained support is denoted as TiO2NSTs-b. Disperse 1 g of TiO2 NSTs-b in water, add 0.11 g of RuCl3, stir for 1 h, and then add 2 mL of 1 mol / L sodium borohydride aqueous solution at a rate of 5 mL / min to reduce the ruthenium compound, and load ruthenium on the titanium dioxide nanosheet tubes. The obtained precipitate is centrifuged and washed 3-5 times, and vacuum dried at 60 °C for 10 h to obtain the catalyst Ru / TiO2 NSTs-b.

[0051] Comparative Example 1

[0052] Replace the support used in Example 1 with a commercial rutile TiO2 support (the support is denoted as TiO2-a), and the rest of the preparation process is the same as that in Example 1.

[0053] Comparative Example 2

[0054] Except that the carrier used in Example 1 was replaced with a commercial anatase TiO2 carrier (the carrier is denoted as TiO2-b), the remaining preparation process was the same as that of Example 1.

[0055] Comparative Example 3

[0056] Except that the carrier used in Example 1 was replaced with a commercial P25 carrier (the carrier is denoted as TiO2-c), the remaining preparation process was the same as that of Example 1.

[0057] The catalytic evaluations of the different catalysts prepared above were carried out as follows:

[0058] The catalyst evaluation method was the method recognized by domestic and foreign literatures, and the data was comparable. The performance test of the liquid-phase benzene selective hydrogenation catalyst was carried out in a 0.25L high-temperature and high-pressure reactor of the YZPR series of Yanzheng Instrument Company. First, 0.5g of the highly dispersed supported Ru / TiO2 catalyst, 60mL of H2O and 12g of ZnSO4·7H2O were added, and hydrogen replacement was carried out 5 times. Then the temperature was raised at a rate of 5°C / min. When the temperature reached 140°C, the hydrogen pressure was maintained at 4.0 Mpa, and the stirring speed was 800 r / min for pre-treatment for 4h. Then 30mL of benzene was added, and timing started. The hydrogen pressure was adjusted to 5.0 Mpa. Samples were taken every 5 minutes, and the contents of benzene, cyclohexene, and cyclohexane in the oil phase were analyzed by a gas chromatograph. The product concentration was calculated by area correction normalization, and then the corresponding conversion rate and cyclohexene selectivity were obtained.

[0059] Table 1 Catalyst Performance Evaluation Table

[0060]

[0061] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. A preparation method of a catalyst supported by double-crystalline-phase titanium dioxide nanosheet tubes, characterized in that, The preparation is carried out in the following step sequence: a. Dissolve the Ti compound in an organic solvent and stir for 2 h to obtain solution A. Mix glycerol and ether evenly to obtain solution B. b. Rapidly mix solution A and solution B under stirring conditions, then stir at room temperature for 10 h. Transfer to a reaction kettle and react at 165 °C for 8 h. After the reaction is completed, centrifuge the obtained white precipitate, wash it with ethanol 3 - 4 times, then dry it under vacuum overnight. Take it out and place it in a muffle furnace, and calcine it in an air atmosphere to obtain titanium dioxide nanosheet tubes. The calcination process is as follows: b1. Heat from room temperature to 200 °C at a heating rate of 5 °C / min and hold for 1 h. b2. Heat from 200 °C to 600 °C at a heating rate of 10 °C / min and hold for 4 h. b3. Naturally cool to room temperature. The titanium dioxide nanosheet tubes are composed of anatase phase and rutile phase, and the mass ratio of the anatase phase is 60 - 75%. c. Disperse the titanium dioxide nanosheet tubes in water, add a ruthenium compound, stir for 1 h, then dropwise add an aqueous solution of sodium borohydride to the solution at a rate of 5 mL / min to load ruthenium onto the titanium dioxide nanosheet tubes. Centrifuge and wash the obtained precipitate 3 - 5 times, and dry it under vacuum to obtain the catalyst. In the catalyst, the mass ratio of Ru is 3 - 10% of the titanium dioxide nanosheet tubes.

2. The preparation method of a supported catalyst of twin-phase titanium dioxide nanosheet tubes according to claim 1, characterized in that, In step a, the Ti compound is titanium oxysulfate hydrate.

3. The preparation method of a catalyst supported on twin-phase titanium dioxide nanosheet tubes according to claim 1, characterized in that, In step c, the ruthenium compound is ruthenium trichloride or ruthenium nitrate; the concentration of the aqueous solution of sodium borohydride is 1 mol / L, and the molar ratio of the titanium dioxide nanosheet tubes, ruthenium compound and aqueous solution of sodium borohydride is 12.5:1:

4.

4. The preparation method of a supported catalyst of twin-phase titanium dioxide nanosheet tubes according to claim 1, characterized in that, In step c, the temperature of the vacuum drying is 60 °C and the drying time is 10 h.

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