A metal oxide modified Pt / SiC catalyst and its preparation method and application

Abstract

The present invention discloses a metal oxide-modified Pt / SiC catalyst, its preparation method, and application. The effects of different metal oxides and their contents on the catalyst activity are explored. By modifying the catalyst with metal oxides, the basic sites on the catalyst are increased, allowing Pt nanoparticles to be stabilized and highly dispersed on the SiC surface. Furthermore, the oxide modification enhances surface hydrogen overflow, increasing the active hydrogen concentration on the carrier surface and enabling selective hydrogenation of cinnamaldehyde at low Pt loading. Using oxide-modified SiC as a carrier allows for highly selective hydrogenation of cinnamaldehyde under mild conditions.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst preparation, and in particular relates to a metal oxide modified Pt / SiC catalyst and a preparation method and application thereof. Background Art

[0002] Cinnamyl alcohol is an important organic intermediate, commonly used in the synthesis of drugs, flavors, etc. Currently, cinnamyl alcohol is mostly obtained in industry by directly reducing cinnamaldehyde with a reducing agent. The reducing agent is generally aluminum isopropoxide, sodium borohydride or lithium aluminum tetrahydride. These reducing agents are not only expensive but also have harsh reaction conditions. The reducing agent is difficult to separate, and it produces a lot of three wastes, which pollutes the environment and is not in line with the concept of green chemistry. Catalytic hydrogenation to prepare cinnamyl alcohol is a green production method. However, because the cinnamaldehyde molecule contains both a C=C double bond and a C=O double bond, where the bond energy of the C=C double bond is relatively low, it is very difficult to achieve highly selective hydrogenation of the C=O double bond from the perspective of thermodynamics and kinetics.

[0003] Supported catalysts are commonly used for the selective hydrogenation of cinnamaldehyde, with precious metals such as Pt, Ru, and Au often serving as active components. Generally, these supported catalysts struggle to achieve high selectivity while maintaining high activity. Literature reports indicate that 5 wt% Pt was supported on SiC–C for the selective hydrogenation of cinnamaldehyde, achieving a selectivity of approximately 80% for cinnamyl alcohol at 2 MPa H₂ pressure. Typically, Pt catalysts supported on pure SiC exhibit low selectivity for cinnamyl alcohol. Furthermore, Pt catalysts supported on microporous ceria have been reported, achieving a 97% conversion of cinnamaldehyde and approximately 88% selectivity for cinnamyl alcohol at 70°C and 2 MPa H₂ pressure for 6 h.

[0004] To address the problems of low selectivity for cinnamyl alcohol and relatively harsh reaction conditions in existing systems, the present invention utilizes the presence of hydrogen overflow on the SiC surface and increases the hydrogen overflow concentration on the SiC surface by modifying its surface with rare earth metal oxides. At the same time, the abundant oxygen sites on the surface of the rare earth oxides can preferentially adsorb and activate C=O bonds, thereby obtaining cinnamyl alcohol with high selectivity under low Pt loading and mild conditions. Summary of the Invention

[0005] The purpose of this section is to summarize some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of this application to avoid obscuring the purpose of this section, the abstract and the title of the invention, and such simplifications or omissions should not be used to limit the scope of the present invention.

[0006] In view of the above problems and / or the problems existing in the prior art, the present invention is proposed.

[0007] Therefore, the purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for preparing a metal oxide-modified Pt / SiC catalyst.

[0008] To solve the above technical problems, the present invention provides the following technical solution: a method for preparing a metal oxide-modified Pt / SiC catalyst.

[0009] As a preferred embodiment of the method for preparing the metal oxide-modified Pt / SiC catalyst of the present invention, the metal oxide comprises one of Al2O3, CeO2, and ZrO2.

[0010] As a preferred embodiment of the preparation method of the metal oxide modified Pt / SiC catalyst of the present invention, the modification method comprises:

[0011] Disperse SiC and metal oxide precursors in water and stir for 5 to 12 hours;

[0012] After drying, the SiC is placed in a Joule heating device and heated at 600-1000° C. for 1-6 minutes to obtain metal oxide-modified SiC.

[0013] As a preferred solution of the method for preparing the metal oxide-modified Pt / SiC catalyst of the present invention, the mass fraction of the metal oxide precursor is 0.1 to 20 wt.% of SiC.

[0014] As a preferred embodiment of the method for preparing the metal oxide modified Pt / SiC catalyst of the present invention, wherein: the method for loading Pt on the surface of the carrier by liquid phase reduction method comprises:

[0015] The H2PtCl4·6H2O solution and KOH solution were added to a beaker containing 25 ml of ethylene glycol and sonicated for 5 min. Then, the metal oxide-modified SiC was added and sonicated for 30 min.

[0016] After ultrasonication, the beaker was placed in a microwave oven and heated for 1 to 3 minutes, filtered, washed, and then dried.

[0017] As a preferred embodiment of the method for preparing the metal oxide-modified Pt / SiC catalyst of the present invention, the content of platinum in the Pt / SiC catalyst is 0.1 to 3 wt.% of the mass fraction of silicon carbide.

[0018] As a preferred embodiment of the method for preparing the metal oxide-modified Pt / SiC catalyst of the present invention, the drying temperature is 40 to 100° C. and the drying time is 6 to 12 hours.

[0019] Another object of the present invention is to overcome the deficiencies in the prior art and provide an application of a metal oxide modified Pt / SiC catalyst.

[0020] In order to solve the above technical problems, the present invention provides the following technical solution: the application is to catalyze the selective hydrogenation of cinnamaldehyde to prepare cinnamyl alcohol, comprising:

[0021] mixing cinnamaldehyde, an organic solvent and a Pt / SiC catalyst uniformly to form a suspension;

[0022] The suspension was transferred to a high-pressure reactor, sealed, purged with hydrogen, pressurized, and stirred at 20-100°C for 2-8 hours.

[0023] As a preferred embodiment of the application of the metal oxide-modified Pt / SiC catalyst of the present invention, the organic solvent is one of ethanol, methanol, isopropanol, DMF and 1,4-dioxane, wherein the mass ratio of the cinnamaldehyde to the solvent is 0.01-0.1:5-50, and the mass ratio of the cinnamaldehyde to the catalyst is 1:0.1-0.5.

[0024] As a preferred application of the metal oxide-modified Pt / SiC catalyst of the present invention, the pressurization after purging with hydrogen comprises purging the reactor with hydrogen three times and maintaining the hydrogen pressure of the reactor at 0.5-2 MPa.

[0025] Beneficial effects of the present invention:

[0026] The present invention utilizes metal oxides to modify the SiC surface. The metal oxide surface has oxygen vacancies that preferentially adsorb C=O double bonds for activation. Furthermore, metal oxide modification enhances the concentration of active hydrogen on the SiC surface, reducing the precious metal loading while maintaining excellent catalytic activity and high selectivity for cinnamyl alcohol. The method achieves 100% conversion and selectivity for cinnamyl alcohol. This method is environmentally friendly, low-cost, mild in reaction, simple to operate, and produces a high product yield. DETAILED DESCRIPTION

[0027] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification.

[0028] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0029] Secondly, the term "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive of other embodiments.

[0030] Example 1

[0031] Weigh 980 mg of SiC and 74.0 mg of Ce(NO3)3·6H2O, add 10 ml of deionized water, stir for 12 hours, dry at 60℃ for 12 hours, place in a Joule heating device, introduce 10% O2 / Ar mixed gas, maintain at 900℃ for 3 minutes, and obtain 3% CeO2-SiC after cooling.

[0032] Neutralize 6.65 ml of H₂PtCl₄·6H₂O solution and 0.3 M KOH solution in a beaker containing 20 ml of ethylene glycol. Ultrasonicate for 5 minutes. Add 990 mg of 3% CeO₂-SiC and sonicate for 30 minutes. Heat the beaker in a microwave for 1.5 minutes. Filter, wash, and dry to obtain a 1 wt.% Pt / 3% CeO₂-SiC catalyst.

[0033] 30 mg of the 1 wt.% Pt / 3% CeO2-SiC catalyst prepared by the above method was placed in an autoclave. 10 ml of ethanol and 1 mmol of cinnamaldehyde were also added. The autoclave was sealed and purged with hydrogen three times. The hydrogen pressure was maintained at 0.5 MPa. The reaction system was heated to 30°C with stirring for 3 hours. The conversion of cinnamaldehyde was 100%, and the selectivity for cinnamyl alcohol was 100%.

[0034] Example 2

[0035] The difference between this embodiment and embodiment 1 is that the modification amount of CeO2 is adjusted to explore its effect on the catalytic activity. The rest of the preparation process is the same as that of comparative document 1. The results are shown in Table 1.

[0036] Preparation method of 1wt.%Pt / 0%CeO2-SiC catalyst:

[0037] 6.65 ml of H2PtCl4·6H2O solution and 0.3 M KOH solution were neutralized and added to a beaker containing 20 ml of ethylene glycol. The mixture was ultrasonically treated for 5 minutes. 990 mg of SiC was then added and ultrasonicated for 30 minutes. The beaker was placed in a microwave and heated for 1.5 minutes. The mixture was filtered, washed, and dried to obtain a 1 wt.% Pt / 0% CeO2-SiC catalyst.

[0038] Table 1 Effect of different CeO2 modification amounts on catalytic activity

[0039] <![CDATA[CeO2 modification amount]]> Conversion rate (%) Selectivity (%) <![CDATA[1wt.%Pt / 0%CeO2-SiC]]> 51 78 <![CDATA[1wt.%Pt / 1%CeO2-SiC]]> 71 85 <![CDATA[1wt.%Pt / 2%CeO2-SiC]]> 78 90 <![CDATA[1wt.%Pt / 3%CeO2-SiC]]> 100 100 <![CDATA[1wt.%Pt / 5%CeO2-SiC]]> 100 87

[0040] It can be seen from Table 1 that the catalytic activity can be improved by modifying the SiC surface with metal oxides, and the catalytic activity increases continuously with the increase of cerium oxide content. However, when the mass fraction of cerium oxide exceeds 3%, the conversion rate of cinnamaldehyde does not change, but the selectivity for cinnamyl alcohol decreases. Therefore, 3% CeO2-SiC is selected as the catalyst support.

[0041] Example 3

[0042] The difference between this embodiment and embodiment 1 is that the type of metal oxide is adjusted to explore its effect on the catalytic activity. The rest of the preparation process is the same as that of comparative document 1. The results are shown in Table 2.

[0043] Table 2 Effects of different types of metal oxide modifications on catalytic activity

[0044] Types of metal oxides Conversion rate (%) Selectivity (%) <![CDATA[1wt.%Pt / 3%CeO2-SiC]]> 100 100 <![CDATA[1wt.%Pt / 3%Al2O3-SiC]]> 70 80 <![CDATA[1wt.%Pt / 3%ZrO2-SiC]]> 78 82

[0045] As can be seen from Table 2, the modification of metal oxides can improve the catalytic activity and has good selectivity for cinnamyl alcohol. The modification of metal oxides can change the interaction between the metal and the support, thereby improving the catalytic activity. The surface of metal oxides has abundant oxygen vacancies, which can preferentially adsorb and activate C=O double bonds. Among them, CeO2 modification has the best effect. This is because the Ce on the surface of CeO2 4+ Will be converted into Ce 3+ , more oxygen vacancies are formed, which is conducive to the adsorption and activation of C=O bonds. At the same time, there is a hydrogen overflow effect on the SiC surface, but this hydrogen overflow can only be around the Pt site. The presence of CeO2 enhances this effect, allowing reactant molecules far away from the Pt site to activate the reaction.

[0046] Example 4

[0047] This example differs from Example 1 in that the type of organic solvent in the selective hydrogenation reaction of cinnamaldehyde is adjusted to explore its effect on the catalytic activity. The rest of the preparation process is the same as that in Comparative Document 1. The results are shown in Table 3.

[0048] Table 3 Effects of different types of organic solvents on catalytic activity

[0049] Types of organic solvents Conversion rate (%) Selectivity (%) ethanol 100 100 Isopropyl alcohol 83 86 Methanol 85 80 DMF 60 78 1,4-Dioxane 50 82

[0050] It can be seen from Table 3 that protic solvents are more conducive to the selective hydrogenation of cinnamaldehyde molecules. The -OH group in the protic solvent can interact with the C=O bond and promote the conversion of cinnamaldehyde.

[0051] Example 5

[0052] The difference between this example and Example 1 is that the time of the selective hydrogenation reaction of cinnamaldehyde is adjusted to explore its effect on the catalytic activity. The rest of the preparation process is the same as that of the comparative document 1. The results are shown in Table 3.

[0053] Table 4 Effect of different reaction times on catalytic activity

[0054] time Conversion rate (%) Selectivity (%) 1 30 78 2 55 89 3 100 100 4 100 93 5 100 87

[0055] Table 4 shows that, under the same catalyst conditions, reaction time has a certain influence on the selective hydrogenation of cinnamaldehyde. With increasing reaction time, the conversion rate continues to increase, while the selectivity for cinnamyl alcohol shows a trend of first increasing and then decreasing. This is because at the beginning of the reaction, cinnamyl alcohol molecules have two different adsorption modes on the catalyst surface: flat adsorption of the C=O bond and vertical adsorption. As the reaction proceeds, more molecules are adsorbed on the catalyst surface. Due to the steric effect, the flat adsorption of the C=O bond is prevented, thereby improving the selectivity. When the reaction time exceeds 3 hours, the selectivity for cinnamyl alcohol decreases, so the optimal reaction time is 3 hours.

[0056] The present invention utilizes metal oxides to modify the SiC surface. Because the metal oxide surface has oxygen vacancies, it can preferentially adsorb C=O double bonds for activation. Furthermore, metal oxide modification enhances the concentration of active hydrogen on the SiC surface. Generally, low loadings result in low reactant conversion rates, which increase with increasing loadings. However, excessive loadings can lead to excessive hydrogenation to produce saturated alcohols. However, the present invention utilizes metal oxide modification to enhance the concentration of active hydrogen on the SiC surface, enabling high conversion rates even at low loadings, while also exhibiting high selectivity for cinnamyl alcohol.

[0057] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. Application of a metal oxide modified Pt / SiC catalyst, characterized in that: The application is to catalyze the selective hydrogenation of cinnamaldehyde to prepare cinnamyl alcohol, including: Cinnamaldehyde, organic solvent ethanol and metal oxide modified Pt / SiC catalyst are mixed uniformly to form a suspension; The suspension was transferred to a sealed autoclave, purged with hydrogen, and pressurized, and stirred at 20-100°C for 3-4 h. The preparation method of the metal oxide modified Pt / SiC catalyst is as follows: SiC modified with metal oxide CeO2 is used as a catalyst carrier, and Pt is loaded on the surface of the carrier by a liquid phase reduction method, thereby obtaining a metal oxide modified Pt / SiC catalyst; The mass fraction of the metal oxide precursor CeO2 is 3-5% of SiC, and the platinum content in the Pt / SiC catalyst is 1wt% of the mass fraction of silicon carbide.

2. The use of the metal oxide-modified Pt / SiC catalyst according to claim 1, characterized in that: The mass ratio of the cinnamaldehyde to the solvent is 0.01-0.1:5-50, and the mass ratio of the cinnamaldehyde to the catalyst is 1:0.1-0.

5.

3. The use of the metal oxide modified Pt / SiC catalyst according to claim 1, characterized in that: The pressurization after purging with hydrogen includes purging the reactor with hydrogen three times and maintaining the hydrogen pressure of the reactor at 0.5-2 MPa.

4. The use of the metal oxide-modified Pt / SiC catalyst according to claim 1, characterized in that: Modification methods include, Disperse SiC and metal oxide precursors in water and stir for 5-12 h; After drying, the product is placed in a Joule heating device and heated at 600-1000°C for 1-6 minutes to obtain metal oxide-modified SiC.

5. Use of the metal oxide-modified Pt / SiC catalyst according to claim 1, characterized in that: The method of loading Pt on the surface of the carrier by liquid phase reduction includes: The H2PtCl4•6H2O solution and KOH solution were added to a beaker containing 25 ml of ethylene glycol and ultrasonicated for 5 min. Then, the metal oxide-modified SiC was added and ultrasonicated for 30 min. After ultrasonication, the beaker was placed in a microwave oven and heated for 1-3 min, filtered, washed, and then dried.

6. Use of the metal oxide-modified Pt / SiC catalyst according to claim 5, characterized in that: The drying temperature is 40-100°C and the drying time is 6-12 hours.