Quantum dot modified Pt / sic catalyst, preparation method and application thereof

Abstract

The application belongs to the technical field of catalyst preparation, and particularly relates to a preparation method of a quantum dot modified Pt / SiC catalyst and application of the quantum dot modified Pt / SiC catalyst in preparation of cinnamyl alcohol from cinnamyl aldehyde. Through quantum dot modification, the adsorption mode of cinnamyl aldehyde on the SiC surface is changed, and the hydrogen overflow of the SiC surface is enhanced, so that the active hydrogen concentration on the surface of the carrier is improved, and efficient selective hydrogenation of cinnamyl aldehyde to generate cinnamyl alcohol can be realized under the premise of low Pt loading.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of catalyst preparation, and particularly relates to a quantum dot (QDs) modified Pt / SiC catalyst, a preparation method and application thereof, and more particularly to the application thereof in selective hydrogenation of cinnamyl aldehyde to prepare cinnamyl alcohol. BACKGROUND

[0002] Cinnamyl alcohol is a white crystal with a scent similar to that of hyacinth and a sweet taste, and is also an important organic synthesis intermediate, which is often used in the synthesis of medicines, fragrances and the like, and has a broad development prospect. At present, cinnamyl alcohol is mostly obtained by direct reduction of cinnamyl aldehyde with strong reducing agents such as sodium borohydride and isopropyl aluminum in industry, or by saponification of two kinds of methods of heating balsam of Peru and benzoin with sodium hydroxide solution. However, these methods not only have high production cost and harsh reaction conditions, but also pollute the environment and do not meet the requirements of modern chemical industry and green chemistry. Therefore, it is of great significance to develop a new synthesis method for preparing cinnamyl alcohol.

[0003] The selective hydrogenation method of catalytic cinnamyl aldehyde to prepare cinnamyl alcohol under mild reaction conditions is a green and energy-saving production method. However, the difficulty of catalytic hydrogenation lies in that there are both C=C bond and C=O bond in cinnamyl aldehyde, and the bond energy of C=C bond is lower than that of C=O bond, so it is difficult to hydrogenate on the C=O bond without destroying the C=C bond.

[0004] Supported catalysts are often used for selective hydrogenation of cinnamyl aldehyde. Noble metals such as Pt and Pd can dissociate H2 to generate H atoms, so they are often used as active components of supported catalysts. However, these noble metals are difficult to have high activity while having high selectivity. According to literature reports, some people introduce a second noble metal to prepare a bimetallic catalyst for selective hydrogenation of cinnamyl aldehyde on this basis. Zheng Q et al. prepared Pt-Co / SBA-15 catalyst by impregnation method, and investigated its performance in selective hydrogenation of cinnamyl aldehyde. The conversion rate of cinnamyl aldehyde was 71%, and the selectivity of cinnamyl alcohol generated was 91%(Catalysis letters,2016,146(8):1535-1543). In addition, Li Lei et al. prepared SiC-O(x) by heating the surface of SiC to obtain SiC-O(x) and used it for selective hydrogenation of cinnamyl aldehyde. Under the conditions of 40℃, 1MPa and 3h, the conversion rate of cinnamyl aldehyde can reach 90%, and the selectivity of cinnamyl alcohol is 85%(Journal of Catalysis,2023,425,314-321).

[0005] In view of the problems in the prior art, such as low selectivity of cinnamyl alcohol and relatively harsh reaction conditions, the application utilizes the hydrogen overflow existing on the surface of SiC, improves the hydrogen overflow concentration on the surface of SiC by modifying quantum dots on the surface of SiC, and the rich oxygen-containing groups such as hydroxyl and carboxyl on the surface of the quantum dots can preferentially adsorb C=O bonds and activate them, so that cinnamyl alcohol can be obtained with high selectivity under low Pt loading and mild conditions. SUMMARY

[0006] The purpose of the present application is to outline some aspects of embodiments of the present application and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of the specification to avoid obscuring the purpose of this section, the abstract and the title, and such simplifications or omissions cannot be used to limit the scope of the present application.

[0007] In view of the above and / or problems in the prior art, the present application is proposed.

[0008] Therefore, the purpose of the present application is to overcome the deficiencies in the prior art, provide a preparation method of quantum dot (QDs) modified Pt / SiC catalyst and apply the catalyst to the preparation of cinnamyl alcohol from cinnamyl aldehyde hydrogenation.

[0009] To achieve the above-mentioned purpose of the application, the present application provides the following technical solutions:

[0010] A quantum dot modified Pt / SiC catalyst, in which quantum dots modified SiC is used as the carrier of the catalyst, Pt is loaded on the surface of the carrier by liquid phase reduction method to obtain the quantum dot modified Pt / SiC catalyst; wherein: the modification amount of quantum dots in the quantum dot modified SiC carrier is 3-20wt.%; the content of platinum in the quantum dot modified Pt / SiC catalyst is 0.1-3wt.%.

[0011] The preparation method of the above-mentioned quantum dot modified Pt / SiC catalyst comprises the following steps:

[0012] (1) Mix SiC with quantum dot aqueous solution, ultrasonically shake for 0.5-3h, then transfer to a hydrothermal kettle for heating, and then wash by centrifugation to obtain quantum dot modified SiC;

[0013] (2) Stir H2PtCl4·6H2O solution and quantum dot modified SiC for 30min, then drop lysine and stir for 30min, finally drop sodium borohydride solution and dilute hydrochloric acid and stir for 12h, filter, wash and dry to obtain the quantum dot modified Pt / SiC catalyst.

[0014] As a preferred scheme of the preparation method of the quantum dot modified Pt / SiC catalyst, the quantum dot comprises one of SiC QDs, carbon quantum dots (CD) and g-C3N4.

[0015] As a preferred scheme of the preparation method of the quantum dot modified Pt / SiC catalyst, the mass fraction of the quantum dot in step (1) is 0.1-20wt.% of SiC.

[0016] As a preferred scheme of the preparation method of the quantum dot modified Pt / SiC catalyst, the heating temperature in step (1) is 150-300℃, and the heating time is 6-24h.

[0017] As a preferred scheme of the preparation method of the quantum dot modified Pt / SiC catalyst, the centrifugal speed in step (1) is 5000-10000rpm, the centrifugal time is 5-15min, and the washing is two times with water and one time with ethanol.

[0018] As a preferred scheme of the preparation method of the quantum dot modified Pt / SiC catalyst, the concentration of the H2PtCl4·6H2O solution in step (2) is 4mg·ml -1 The molar concentration of the lysine aqueous solution is 0.53mol / L; the molar concentration of the sodium borohydride solution is 0.35mol / L; and the molar concentration of the dilute hydrochloric acid is 0.3mol / L.

[0019] As a preferred scheme of the preparation method of the quantum dot modified Pt / SiC catalyst, the volume ratio of the lysine aqueous solution, the sodium borohydride solution and the dilute hydrochloric acid is 2:1:1.

[0020] Another object of the present application is to provide an application of the quantum dot modified Pt / SiC catalyst.

[0021] To solve the above technical problems, the present application provides the following technical scheme: the application is to catalyze the selective hydrogenation of cinnamyl aldehyde to prepare cinnamyl alcohol, which comprises,

[0022] The cinnamyl aldehyde, the organic solvent and the quantum dot modified Pt / SiC catalyst are uniformly mixed to form a suspension; the suspension is transferred to a high-temperature and high-pressure reaction kettle for sealing, and after purging with hydrogen, the reaction is carried out at 20-80℃ under stirring for 1-5h.

[0023] As a preferred scheme of the application of the quantum dot modified Pt / SiC catalyst, wherein: the organic solvent is one of ethanol, methanol, isopropanol and 1,4-dioxane, the molar concentration of the cinnamyl aldehyde in the suspension is 0.1 mol / L, and the mass ratio of the cinnamyl aldehyde to the catalyst is 1:0.1-0.5.

[0024] As a preferred scheme of the application of the quantum dot modified Pt / SiC catalyst, wherein: the pressurization after the hydrogen blowing includes that after the reaction kettle is blown by hydrogen for 3-4 times, the hydrogen pressure in the reaction kettle is maintained at 0.5-2 MPa.

[0025] The application has the following beneficial effects:

[0026] The application uses quantum dots to modify the SiC surface, the quantum dot surface contains rich oxygen-containing groups such as hydroxyl and carboxyl, can preferentially adsorb C=O double bonds to activate them. Meanwhile, the modification of the quantum dots increases the specific surface area of the SiC and enhances the concentration of the active hydrogen on the SiC surface, can reduce the loading amount of the noble metal while maintaining good catalytic activity, and has good selectivity to cinnamyl alcohol. The conversion rate and selectivity of cinnamyl alcohol by the method of the application are close to 100%. The method has mild reaction conditions, simple operation, is green and pollution-free, and has high product yield. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The SiC prepared in Example 1 of the application 10 HRTEM images of QDs-SiC at different magnifications

[0028] Figure 2 Pt1 / SiC prepared in Example 1 of the application 10 HRTEM images of QDs-SiC at different magnifications

[0029] Figure 3 Pt1 / SiC prepared in Example 1 of the application 10 XRD images of QDs-SiC

[0030] Figure 4 Infrared spectra of the quantum dot modified SiC prepared in Example 1 and Example 2 of the application

[0031] Figure 5 Pt1 / SiC prepared in Example 1 of the application 10 XPS images of QDs-SiC. DETAILED DESCRIPTION

[0032] In order to make the above objectives, features and advantages of the present application more obvious and comprehensible, the specific embodiments of the present application will be described in detail below with reference to the description and examples.

[0033] In the following description, a large number of specific details are set forth in order to provide a thorough understanding of the present application, but the present application can also be implemented in other manners different from those described herein, and those skilled in the art can make similar generalizations without departing from the concept of the present application, therefore the present application is not limited to the specific embodiments disclosed below.

[0034] Secondly, "one embodiment" or "an embodiment" referred to herein means that a specific feature, structure or characteristic can be included in at least one implementation of the present application. "In one embodiment" appearing in different places in the specification does not mean the same embodiment, nor is it an embodiment that is independent of or mutually exclusive with other embodiments.

[0035] Example 1

[0036] Take 167.7 mg of SiC and disperse it in 40 ml of 0.5 mg / ml SiC quantum dot (SiC QDs) aqueous solution, ultrasonic for 2 h, transfer to a hydrothermal kettle and seal, heat at 200 ℃ for 12 h, take out and cool to room temperature. After centrifugation, discard the supernatant, wash with water twice and ethanol once, and dry in a 60 ℃ oven for 12 h to obtain 10% SiC QDs-SiC.

[0037] Mix 1.11 ml of 4 mg·ml -1 Mix 1.11 ml of 4 mg·ml

[0038] Take 30 mg of 1wt.% Pt / 10% SiC QDs-SiC catalyst prepared by the above method and place it in a high-pressure reaction kettle, measure 10 ml of ethanol and 1 mmol of cinnamyl aldehyde into the reaction kettle, seal it, hydrogen flush 4 times, maintain the oxygen pressure at 1 MPa, heat the reaction system to 40 ℃ under stirring, and the reaction time is 3 h. The results are shown in Table 1.

[0039] Example 2

[0040] The difference between this embodiment and embodiment 1 is that the modification amount of SiC QDs is adjusted (the amount of quantum dot solution is changed to 10 ml), and 1wt.%Pt / 3%SiC QDs-SiC catalyst is prepared. The influence on the catalytic activity is explored, and the results are shown in Table 1.

[0041] Example 3

[0042] The difference between this embodiment and embodiment 1 is that the modification amount of SiC QDs is adjusted (the amount of quantum dot solution is changed to 20 ml), and 1wt.%Pt / 5%SiC QDs-SiC catalyst is prepared. The influence on the catalytic activity is explored, and the results are shown in Table 1.

[0043] Example 4

[0044] The difference between this embodiment and embodiment 1 is that the modification amount of SiC QDs is adjusted (the amount of quantum dot solution is changed to 60 ml), and 1wt.%Pt / 15%SiC QDs-SiC catalyst is prepared. The influence on the catalytic activity is explored, and the results are shown in Table 1.

[0045] Example 5

[0046] The difference between this embodiment and embodiment 1 is that the modification amount of SiC QDs is adjusted (the amount of quantum dot solution is changed to 80 ml), and 1wt.%Pt / 20%SiC QDs-SiC catalyst is prepared. The influence on the catalytic activity is explored, and the results are shown in Table 1.

[0047] Example 6

[0048] The difference between this embodiment and embodiment 1 is that the carrier is Al2O3, and 1wt.%Pt / 10%SiC QDs-Al2O3 catalyst is prepared. The influence on the catalytic activity is explored, and the method is the same as that of embodiment 1, and the results are shown in Table 1.

[0049] Example 7

[0050] The difference between this embodiment and embodiment 1 is that the carrier is SiO2, and 1wt.%Pt / 10%SiC QDs-SiO2 catalyst is prepared. The influence on the catalytic activity is explored, and the rest of the preparation process is the same as that of embodiment 1, and the results are shown in Table 1.

[0051] Example 8

[0052] The difference between this embodiment and embodiment 1 is that the quantum dot is CDs, and 1wt.%Pt / 10%CDs-SiC catalyst is prepared. The influence on the catalytic activity is explored, and the results are shown in Table 1.

[0053] Example 9

[0054] The difference between this embodiment and embodiment 1 is that the quantum dots are g-C3N4, and 1wt.% Pt / 10% g-C3N4-SiC catalyst is obtained to explore its effect on catalytic activity, and the results are shown in Table 1.

[0055] Comparative example 1

[0056] Preparation method of 1wt.% Pt-SiC catalyst:

[0057] 1.11ml of H2PtCl4·6H2O solution and 162mg of SiC were mixed in a 100ml beaker and stirred for 30min, 20ml of lysine solution was added dropwise and stirred for another 30min, then 10ml of sodium borohydride solution and 10ml of dilute hydrochloric acid were added dropwise and stirred for 24h. After filtration, washing and drying, 1wt.% Pt / SiC catalyst was obtained.

[0058] Table 1 Effect of catalysts of examples 1-9 on catalytic activity

[0059] SiC QDs modification amount Conversion rate (%) Selectivity (%) 1 wt.% Pt / SiC 32.26 70.99 1 wt.% Pt / 3% SiC QDs-SiC 63.70 82.77 1 wt.% Pt / 5% SiC QDs-SiC 88.65 69.71 1 wt.% Pt / 10% SiC QDs-SiC 90.92 98.76 1 wt.% Pt / 15% SiC QDs-SiC 39.41 90.70 1 wt.% Pt / 20% SiC QDs-SiC 28.15 91.88 1 wt. % Pt / 10 % SiC QDs - Al2O3 47.53 86.27 1 wt. % Pt / 10% SiC QDs-SiO2 35.84 89.38 1 wt.% Pt / 10% CDs-SiC 84.96 91.20 1 wt. % Pt / 10 % g-C3N4-SiC 75.46 86.98

[0060] As can be seen from Table 1, the modification of SiC surface by quantum dots in examples 1-5 can improve the catalytic activity, and the catalytic activity increases with the increase of SiC QDs content, but when the mass fraction of SiC QDs is more than 15%, the selectivity of cinnamic alcohol decreases slightly, but the conversion rate of cinnamaldehyde decreases rapidly.

[0061] Examples 6-7 adjust the carrier of the catalyst, and as can be seen from Table 1, the catalytic activity of 1wt.% Pt / 10% SiC QDs-SiC with SiC as the carrier is the best.

[0062] Examples 8-9 adjust the type of quantum dots of the catalyst, and as can be seen from Table 1, the modification of different quantum dots can improve the catalytic activity and has good selectivity to cinnamaldehyde. The modification of quantum dots can change the interaction between metal and carrier and improve the catalytic activity. The rich oxygen-containing groups such as hydroxyl and carboxyl on the surface of quantum dots can preferentially adsorb C=O double bond and activate it. Among them, the hydrogen overflow effect on the surface of SiC as the best carrier is further enhanced after the modification of quantum dots. This hydrogen overflow only exists near the Pt site, and in the presence of quantum dots, the range of this effect can be enhanced, so that the reactant molecules near the Pt site can also be activated.

[0063] Example 10

[0064] 1wt.% Pt / 10% SiC QDs-SiC prepared according to the method of example 1 was used to catalyze the selective hydrogenation reaction of cinnamaldehyde. The effect of different organic solvents on catalytic activity was investigated. The results are shown in Table 2.

[0065] Table 2 Influence of different organic solvents on catalytic activity

[0066] Organic solvent type Conversion rate (%) Selectivity (%) Ethanol 90.92 98.76 Isopropanol 77.89 85.54 Methanol 92.12 98.55 DMF 55.40 72.18 1,4-dioxane 30.29 79.86

[0067] As can be seen from Table 2, the protonic solvent is more conducive to the selective hydrogenation of cinnamaldehyde molecules. The -OH in the protonic solvent can interact with the C=O bond, promoting the conversion of cinnamaldehyde.

[0068] Example 11

[0069] This example is different from Example 1 in that the reaction time in the selective hydrogenation reaction of cinnamaldehyde is adjusted to explore its influence on catalytic activity, and the results are shown in Table 3.

[0070] Table 3 Influence of different reaction times on catalytic activity

[0071] Time Conversion rate (%) Selectivity (%) 1 38.44 95.20 2 65.74 97.82 3 90.92 98.76 4 99.99 96.71 5 99.99 86.82

[0072] As can be seen from Table 3, under the same catalyst, the reaction time has a certain influence on the selective hydrogenation of cinnamaldehyde. With the extension of the reaction time, the conversion rate is continuously improved, and the selectivity of cinnamyl alcohol shows a trend of first increasing and then decreasing. This is because at the beginning of the reaction, cinnamaldehyde molecules have two different adsorption modes on the surface of the catalyst, which are C=O bond flat adsorption and vertical adsorption. With the progress of the reaction, more molecules are adsorbed on the surface of the catalyst, and due to the steric hindrance effect, the flat adsorption of the C=O bond is prevented, thereby improving the selectivity. However, when the reaction time exceeds 3h, the selectivity of cinnamyl alcohol decreases, so the optimal reaction time is selected as 3h.

[0073] High-resolution electron microscopy (HRTEM) was used to observe the microstructure of the catalyst. XPS was used to characterize the electronic state and content of the elements on the surface of the catalyst. FTIR was used to measure the molecular composition on the surface of the catalyst.

[0074] As shown in Figure 1 and 2 , quantum dots and Pt particles are both supported on SiC. As shown in Figure 3 , the diffraction peaks at 35.6°, 41.4°, 60.0°, 71.8° and 75.5° in XRD correspond to the (111), (200), (220), (311) and (222) crystal planes of β-SiC, respectively. Since the Pt particles are small, no diffraction peak of Pt is found at 39.8°, which is because the Pt particles on the surface of the catalyst are small. As shown in Figure 4 , in the infrared spectrum, only a sharp peak at 850 cm -1 appears, which is the stretching vibration of Si-C bond in silicon carbide, because the content of quantum dots in the modified SiC is low.

[0075] The application utilizes quantum dots to modify the surface of SiC. Since the surface of the quantum dots has rich oxygen-containing groups such as hydroxyl and carboxyl, the C=O double bond can be preferentially adsorbed and activated. At the same time, the modification of the quantum dots enhances the concentration of active hydrogen on the surface of SiC. Generally speaking, when the loading amount is low, the conversion rate of the reactant is low. With the increase of the loading amount, the conversion rate will continue to rise. However, when the loading amount is too high, excessive hydrogenation will occur to generate saturated alcohol. However, after the modification of the quantum dots, the application enhances the concentration of active hydrogen on the surface of SiC, so that high conversion rate can be achieved under the premise of low loading amount, and the application also has high selectivity to cinnamic alcohol.

[0076] It should be noted that the above examples are only used to illustrate the technical solutions of the application and are not limiting. Although the application has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the application, and they should be covered in the scope of the claims of the application.

Claims

1. The application of a quantum dot-modified Pt / SiC catalyst in the selective hydrogenation of cinnamaldehyde to cinnamyl alcohol, characterized in that, The quantum dot-modified Pt / SiC catalyst is obtained by loading platinum onto the surface of quantum dot-modified SiC as a catalyst support via liquid-phase reduction. The quantum dots are SiC QDs. The amount of quantum dots in the quantum dot-modified SiC support is 3~20 wt.%. The platinum content in the quantum dot-modified Pt / SiC catalyst is 0.1-3 wt.%.

2. The application according to claim 1, characterized in that, The preparation method of the quantum dot-modified Pt / SiC catalyst includes the following steps: (1) SiC is mixed with quantum dot aqueous solution, ultrasonically vibrated for 0.5-3h, and then transferred to a hydrothermal reactor for heating and reaction. After centrifugation and washing, quantum dot modified SiC is obtained. (2) After mixing H2PtCl4·6H2O solution with quantum dot modified SiC, add lysine aqueous solution and stir until homogeneous. Then add sodium borohydride solution and hydrochloric acid and stir for 6-24 hours. After filtration, washing and drying, the quantum dot modified Pt / SiC catalyst can be obtained.

3. The application according to claim 2, characterized in that, The mass fraction of the quantum dot aqueous solution in step (1) is 0.1-20 wt.% of SiC.

4. The application according to claim 2, characterized in that, Step (1) The temperature for heating the reaction is 150-300℃ and the heating time is 6-24h.

5. The application according to claim 2, characterized in that, The concentration of the H2PtCl4·6H2O solution in step (2) is 4 mg·mL. -1 The molar concentration of lysine aqueous solution is 0.53 mol / L; the molar concentration of sodium borohydride solution is 0.35 mol / L; and the molar concentration of dilute hydrochloric acid is 0.3 mol / L.

6. The application according to claim 5, characterized in that, The volume ratio of the lysine aqueous solution, sodium borohydride solution, and dilute hydrochloric acid is 2:1:

1.

7. The application according to claim 1, characterized in that, Cinnamaldehyde, organic solvent, and the quantum dot-modified Pt / SiC catalyst are mixed evenly to form a suspension. The suspension is transferred to a high-temperature and high-pressure reactor and sealed. After being purged with hydrogen, the hydrogen pressure in the reactor is maintained at 0.5-2 MPa. The reactor is reacted at 20-80°C under stirring for 1-5 hours to selectively hydrogenate cinnamaldehyde to prepare cinnamyl alcohol.

8. The application according to claim 7, characterized in that, The molar concentration of cinnamaldehyde in the suspension is 0.1 mol / L; the mass ratio of cinnamaldehyde to the quantum dot-modified Pt / SiC catalyst is 1:0.1-0.

5.

9. The application of the quantum dot-modified Pt / SiC catalyst according to claim 7, characterized in that, The organic solvent is one of ethanol, methanol, isopropanol or 1,4-dioxane.

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