Catalyst for carboxybenzaldehyde hydrogenation process and preparation method thereof

Abstract

The invention belongs to the technical field of selective catalytic hydrogenation and catalyst preparation, and particularly discloses a catalyst for a carboxybenzaldehyde hydrogenation process and a preparation method of the catalyst. Wherein the catalyst is composed of a carrier SiC, M (Pd, Pt, Fe, Ni and the like) metal active components loaded on the surface of the SiC and a carbon layer, and the mass fraction of the metal active components in the catalyst is 0.1-1%. When the catalyst is applied to a carboxybenzaldehyde hydrogenation process, the conversion rate of carboxybenzaldehyde is greater than or equal to 95%, and the selectivity of p-toluic acid is greater than or equal to 46%. In addition, after five cycle experiments, the catalyst still keeps high catalytic performance and shows good cycle stability. The catalyst can resist high temperature, can be recycled, has high reaction activity, and is an efficient, stable and environment-friendly catalyst.

Description

Technical Field

[0001] The present invention belongs to the technical fields of selective catalytic hydrogenation and catalyst preparation, and particularly relates to a catalyst for the hydrogenation process of carboxybenzaldehyde and a preparation method thereof. Background Art

[0002] Polyethylene terephthalate (PET) is one of the fastest growing and most important plastic materials in recent years. Terephthalic acid (TA) is an important intermediate for manufacturing polyethylene terephthalate (PET), mainly used in the production of fibers. The purified terephthalic acid (PTA) process developed by Amoco has quickly become the preferred process. Briefly, crude terephthalic acid (CTA) is obtained by the homogeneous oxidation of p-xylene, and its main impurity is p-carboxybenzaldehyde (4-CBA), and several colored polyaromatic compounds are also contained.

[0003] Industrially, crude terephthalic acid (CTA) is produced by the oxidation of p-xylene (PX) on a homogeneous catalyst, containing a small amount of by-product p-carboxybenzaldehyde (4-CBA). The removal of 4-CBA is generally carried out in a trickle-bed reactor under a hydrogen atmosphere using Pd as a catalyst. Among the catalyst carriers (TiO2, SiC, SiO2, AC, etc.) used, the Pd catalyst supported on activated carbon (AC) is still considered to be one of the most effective catalysts for 4-CBA hydrogenation. However, traditional Pd / AC has some disadvantages. Under the reaction conditions (260 - 280 °C), due to the weak interaction between Pd and AC, Pd nanoparticles are prone to aggregation, resulting in problems such as limited stability and lifespan of Pd / AC.

[0004] SiC is a typical non-oxide semiconductor material, with good thermal and electrical conductivity, high temperature resistance, and resistance to acid and alkali corrosion, etc., and is a very promising catalyst support material. This patent prepares a catalyst by loading transition metal nanoparticles on SiC to hydrogenate p-carboxybenzaldehyde to prepare p-methylbenzoic acid. Summary of the Invention

[0005] In order to solve the problem that Pd is easily deactivated industrially and improve the catalyst activity, the present invention provides a catalyst using modified silicon carbide loaded with transition metal to catalyze the hydrogenation of p-carboxybenzaldehyde to prepare p-methylbenzoic acid, which has high conversion rate of p-carboxybenzaldehyde and selectivity of p-methylbenzoic acid at a lower temperature.

[0006] To achieve the purpose of the present invention, the technical solution adopted by the present invention is: a catalyst, the catalyst includes a carrier, an active component, and a carbon layer; the carrier is modified silicon carbide; the active component is a metal.

[0007] Furthermore, the modified silicon carbide is amino-modified silicon carbide or hydroxyl-modified silicon carbide.

[0008] Furthermore, the amino-modified silicon carbide is prepared from 3-aminopropyltrimethoxysilane and silicon carbide, and includes the following steps: First, disperse the silicon carbide in a n-hexane solution by ultrasonic treatment, then add 3-aminopropyltrimethoxysilane to the solution, continue ultrasonic treatment, and finally obtain the amino-modified silicon carbide through washing, filtration, and drying steps;

[0009] Preferably, the mass ratio of the silicon carbide to 3-aminopropyltrimethoxysilane is 0.005 - 0.01.

[0010] Furthermore, the hydroxyl-modified silicon carbide is prepared from hydrogen peroxide and silicon carbide, and includes the following steps: First, disperse the silicon carbide in deionized water by ultrasonic treatment, then add a hydrogen peroxide solution for reflux reaction, and finally obtain the hydroxyl-modified silicon carbide through washing, filtration, and drying steps;

[0011] Preferably, the mass ratio of the silicon carbide to hydrogen peroxide is 0.005 - 0.01.

[0012] Preferably, the mass concentration of the hydrogen peroxide solution is 20 - 30%.

[0013] Furthermore, the metal includes Pd, Pt, Ni, Fe, etc.

[0014] Furthermore, the specific surface area of the silicon carbide is 20 - 90 m 2 / g.

[0015] Furthermore, the mass percentage of the metal in the catalyst is 0.1 - 1% (preferably 0.5 - 1).

[0016] Furthermore, the carbon layer is prepared by carbonizing sucrose.

[0017] The preparation method of the above catalyst uses modified silicon carbide as a catalyst support, and loads transition metal M nanoparticles on the surface of the support by photoreduction method, thus obtaining the catalyst. The specific steps are as follows: Disperse the modified silicon carbide and the metal precursor in water, first disperse them by ultrasonic treatment, then stir evenly, and then reduce them by ultraviolet light irradiation for 5 - 12 h. After reduction, filter them using a microporous filter membrane and wash them with deionized water until neutral, and then dry them in a vacuum drying oven to obtain the M / SiC-X precursor. Immerse the prepared M / SiC-X precursor in the carbon precursor solution and stir. After stirring, make the surface of the catalyst cover the carbon precursor by rotary evaporation. Then, through high-temperature carbonization, sucrose is transformed into a C layer and covers the surface of the catalyst to obtain the catalyst.

[0018] Furthermore, the metal precursor is a soluble metal salt, including chloropalladic acid, chloroplatinic acid, ferric chloride, nickel chloride, etc.

[0019] Further, the drying temperature is 40 - 100 °C, and the time is 6 - 12 h.

[0020] Further, the dosage ratio of the carbon precursor solution to the M / SiC-X precursor is 20 mL:80 mg; the concentration of the carbon precursor solution is 10 - 15 wt%.

[0021] Further, the carbon precursor includes sucrose.

[0022] Further, the carbonization temperature is 300 - 400 °C, and the time is 30 - 60 min.

[0023] The above catalyst is applied to the catalytic hydrogenation reaction of p-carboxybenzaldehyde. The application includes the following steps:

[0024] Fully dissolve p-carboxybenzaldehyde in a solvent and mix evenly, add the catalyst and mix well to form a suspension, then maintain the hydrogen pressure at 0.5 - 2 MPa, and keep the temperature of the reaction system at ≥30 °C under stirring conditions for the hydrogenation reaction.

[0025] Further, the solvent is one or a mixture of methanol, absolute ethanol, isopropanol, and water.

[0026] Further, the mass ratio of p-carboxybenzaldehyde to the solvent is 0.005 - 0.01.

[0027] Preferably, the temperature of the reaction system is 50 - 90 °C.

[0028] Further, the time of the hydrogenation reaction is 0.5 - 2 h.

[0029] Advantages of the present invention:

[0030] The present invention uses silicon carbide (SiC) as a carrier, modifies the properties of the silicon carbide carrier, and successfully prepares a catalyst (M / SiC-X) by loading transition metal nanoparticles, and applies it to the hydrogenation reaction of p-carboxybenzaldehyde, achieving a conversion rate of p-carboxybenzaldehyde ≥95% and a selectivity of p-methylbenzoic acid ≥46%.

[0031] In addition, after five cyclic experiments, the catalyst still maintains high catalytic performance, showing good cyclic stability. The catalyst carrier SiC-NH2 can withstand high temperatures and can be recycled during the catalyst recovery stage. The operation is simple and the reaction cycle is short. It is an efficient, stable, and environmentally friendly catalyst. Description of the Drawings

[0032] Figure 1 The cyclic experiment results of the catalyst prepared in Example VII;

[0033] Figure 2 Cyclic experiment results of the catalyst prepared in Example 20;

[0034] Figure 3 TEM images of the catalyst prepared in Example 20 before and after the reaction, where a is before the reaction and b is after the reaction. Specific embodiments

[0035] The present invention is not limited to the following specific embodiments. Those of ordinary skill in the art can implement the present invention in other various specific embodiments according to the content disclosed in the present invention, or any simple changes or modifications made using the design structure and concept of the present invention fall within the protection scope of the present invention. It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0036] The present invention is further described in detail below in conjunction with embodiments:

[0037] The preparation steps of the SiC-NH2 support in the following embodiments are as follows:

[0038] Put 0.5 g of silicon carbide into 250 mL of n-hexane and ultrasonically disperse for 30 min. Then add 2 mL of 3-aminopropyltrimethoxysilane to the solution and continue ultrasonic treatment for 60 min. Finally, the modified silicon carbide with amino groups is obtained through washing, filtration, and drying steps; the silicon carbide is purchased from Changzhou Ruizhen Materials Technology Co., Ltd., and the specific surface area is 20 - 90 m 2 / g.

[0039] Example 1

[0040] (1) Weigh 0.72 mL of H2PdCl4 (4 mg / mL) and dissolve it in 180 mL of deionized water. After fully dissolving, add 238.8 mg of the SiC-NH2 support. After stirring for 1 h, irradiate with ultraviolet light for reduction for 9 h. After reduction, filter with a microporous filter membrane and wash with deionized water until neutral, and then dry in a vacuum drying oven to obtain a Pd / SiC-NH2 catalyst loaded with 0.5 wt.%. Take 80 mg of the Pd / SiC-NH2 catalyst and soak it in 20 mL of a 15% sucrose solution by mass and stir. After stirring, the surface of the catalyst is covered with sucrose by rotary evaporation, and then the sucrose is converted into a C layer and covered on the surface of the catalyst by high-temperature carbonization (300 °C, 30 min, air atmosphere) to prevent the agglomeration of Pd metal particles during subsequent recycling. The average particle size of the Pd metal is about 2.5 nm.

[0041] (2) Weigh 30 mg of the above Pd / SiC-NH2 catalyst, 20 mL of anhydrous ethanol solution, and 150.1 mg of p-carboxybenzaldehyde (1 mmol) and add them to a high-pressure reaction kettle. Seal the reaction kettle, and after ensuring airtightness, fill it with 1 MPa of high-purity H2. Place the high-pressure reaction kettle in a heating device, set the stirring rate at 600 rpm, the temperature at 50 °C, and the time at 1 h. After the reaction is completed, turn off the heating and stirring. After cooling to room temperature, collect the reaction solution, remove the catalyst particles through a filter, and then conduct gas chromatography-mass spectrometry analysis. Among them, the conversion rate of p-carboxybenzaldehyde is 97.7%, and the selectivity for p-methylbenzoic acid is 52.5%.

[0042] Example 2

[0043] (1) The same as Example 1.

[0044] (2) Weigh 30 mg of the above Pd / SiC-NH2 catalyst, 20 mL of anhydrous ethanol solution, and 150.1 mg of p-carboxybenzaldehyde (1 mmol) and add them to a high-pressure reaction kettle. Seal the reaction kettle, and after ensuring airtightness, fill it with 1 MPa of high-purity H2. Place the high-pressure reaction kettle in a heating device, set the stirring rate at 600 rpm, the temperature at 60 °C, and the time at 1 h. After the reaction is completed, turn off the heating and stirring. After cooling to room temperature, collect the reaction solution, remove the catalyst particles through a filter, and then conduct gas chromatography-mass spectrometry analysis. Among them, the conversion rate of p-carboxybenzaldehyde is 98.7%, and the selectivity for p-methylbenzoic acid is 75.7%.

[0045] Example 3

[0046] (1) The same as Example 1.

[0047] (2) Weigh 30 mg of the above Pd / SiC-NH2 catalyst, 20 mL of anhydrous ethanol solution, and 150.1 mg of p-carboxybenzaldehyde (1 mmol) and add them to a high-pressure reaction kettle. Seal the reaction kettle, and after ensuring airtightness, fill it with 1 MPa of high-purity H2. Place the high-pressure reaction kettle in a heating device, set the stirring rate at 600 rpm, the temperature at 70 °C, and the time at 1 h. After the reaction is completed, turn off the heating and stirring. After cooling to room temperature, collect the reaction solution, remove the catalyst particles through a filter, and then conduct gas chromatography-mass spectrometry analysis. Among them, the conversion rate of p-carboxybenzaldehyde is 96.7%, and the selectivity for p-methylbenzoic acid is 94.2%.

[0048] Example 4

[0049] (1) Weigh 0.72 mL of H2PdCl4 (4 mg / mL) and dissolve it in 180 mL of deionized water. After complete dissolution, add 238.8 mg of the SiC-NH2 support. Stir well for 1 h and then irradiate with ultraviolet light for reduction for 9 h. After reduction, filter through a microporous membrane and wash with deionized water until neutral, and then dry in a vacuum drying oven to obtain a Pd / SiC-NH2 catalyst loaded with 0.5 wt.%. Take 80 mg of the Pd / SiC-NH2 catalyst and soak it in 20 mL of a 10% sucrose solution by mass and stir. After stirring, use rotary evaporation to cover the catalyst surface with sucrose, and then convert the sucrose into a C layer by high-temperature carbonization (300 °C, 30 min, air atmosphere) and cover it on the catalyst surface to prevent the agglomeration of Pd metal particles during subsequent recycling. The average particle size of the Pd metal is about 2.5 nm.

[0050] (2) Weigh 30 mg of the above Pd / SiC-NH2 catalyst, 20 mL of anhydrous ethanol solution, and 150.1 mg of p-carboxybenzaldehyde (1 mmol) and add them to a high-pressure reaction kettle. Seal the reaction kettle, ensure airtightness, and then fill it with 1 MPa of high-purity H2. Place the high-pressure reaction kettle in a heating device, set the stirring rate at 600 rpm, the temperature at 30 °C, and the time at 1 h. After the reaction is completed, turn off heating and stirring. After cooling to room temperature, collect the reaction solution, remove the catalyst particles through a filter, and then perform gas chromatography-mass spectrometry analysis. The conversion rate of p-carboxybenzaldehyde is 96.8%, and the selectivity for p-methylbenzoic acid is 38.9%.

[0051] Example 5

[0052] (1) The same as Example 4.

[0053] (2) Weigh 30 mg of the above Pd / SiC-NH2 catalyst, 20 mL of anhydrous ethanol solution, and 150.1 mg of p-carboxybenzaldehyde (1 mmol) and add them to a high-pressure reaction kettle. Seal the reaction kettle, ensure airtightness, and then fill it with 1 MPa of high-purity H2. Place the high-pressure reaction kettle in a heating device, set the stirring rate at 600 rpm, the temperature at 40 °C, and the time at 1 h. After the reaction is completed, turn off heating and stirring. After cooling to room temperature, collect the reaction solution, remove the catalyst particles through a filter, and then perform gas chromatography-mass spectrometry analysis. The conversion rate of p-carboxybenzaldehyde is 97.2%, and the selectivity for p-methylbenzoic acid is 57.2%.

[0054] Example 6

[0055] (1) The same as Example 4.

[0056] (2) Weigh 30 mg of the above Pd / SiC-NH2 catalyst, 20 mL of anhydrous ethanol solution, and 150.1 mg of p-carboxybenzaldehyde (1 mmol) and add them to a high-pressure reactor. Seal the reactor, ensure airtightness, and then fill it with 1 MPa of high-purity H2. Place the high-pressure reactor in a heating device, set the stirring rate at 600 rpm, the temperature at 50 °C, and the time at 1 h. After the reaction is completed, turn off the heating and stirring. After cooling to room temperature, collect the reaction solution, remove the catalyst particles through a filter, and then perform gas chromatography-mass spectrometry analysis. The conversion rate of p-carboxybenzaldehyde is 97.5%, and the selectivity for p-methylbenzoic acid is 69.1%.

[0057] Example VII

[0058] (1) The same as Example IV.

[0059] (2) Weigh 30 mg of the above Pd / SiC-NH2 catalyst, 20 mL of anhydrous ethanol solution, and 150.1 mg of p-carboxybenzaldehyde (1 mmol) and add them to a high-pressure reactor. Seal the reactor, ensure airtightness, and then fill it with 1 MPa of high-purity H2. Place the high-pressure reactor in a heating device, set the stirring rate at 600 rpm, the temperature at 60 °C, and the time at 1 h. After the reaction is completed, turn off the heating and stirring. After cooling to room temperature, collect the reaction solution, remove the catalyst particles through a filter, and then perform gas chromatography-mass spectrometry analysis. The conversion rate of p-carboxybenzaldehyde is 97%, and the selectivity for p-methylbenzoic acid is 91.1%.

[0060] Example VIII

[0061] (1) The same as Example IV.

[0062] (2) Weigh 30 mg of the above Pd / SiC-NH2 catalyst, 20 mL of anhydrous ethanol solution, and 150.1 mg of p-carboxybenzaldehyde (1 mmol) and add them to a high-pressure reactor. Seal the reactor, ensure airtightness, and then fill it with 1 MPa of high-purity H2. Place the high-pressure reactor in a heating device, set the stirring rate at 600 rpm, the temperature at 70 °C, and the time at 1 h. After the reaction is completed, turn off the heating and stirring. After cooling to room temperature, collect the reaction solution, remove the catalyst particles through a filter, and then perform gas chromatography-mass spectrometry analysis. The conversion rate of p-carboxybenzaldehyde is 98.2%, and the selectivity for p-methylbenzoic acid is 97.8%.

[0063] Example IX

[0064] (1) The same as Example IV.

[0065] (2) Weigh 30 mg of the above Pd / SiC-NH2 catalyst, 20 mL of anhydrous ethanol solution and 150.1 mg of p-carboxybenzaldehyde (1 mmol), and add them to a high-pressure reactor. Seal the reactor, ensure airtightness, and then fill it with 1 MPa of high-purity H2. Place the high-pressure reactor in a heating device, set the stirring rate to 600 rpm, the temperature to 80 °C, and the time to 1 h. After the reaction is completed, turn off the heating and stirring. After cooling to room temperature, collect the reaction solution, remove the catalyst particles through a filter, and then perform gas chromatography-mass spectrometry analysis. The conversion rate of p-carboxybenzaldehyde is 98.3%, and the selectivity for p-methylbenzoic acid is 98.0%.

[0066] Example X

[0067] (1) First, put silicon carbide into deionized water and disperse it by ultrasonic wave, then add a hydrogen peroxide solution with a mass concentration of 20% and reflux at 50 °C for 300 min. Finally, obtain silicon carbide modified with hydroxyl groups through washing, filtering, and drying steps; the mass ratio of silicon carbide to hydrogen peroxide is 0.005 - 0.01.

[0068] (2) Weigh 0.72 mL of H2PdCl4 (4 mg / mL) and dissolve it in 180 mL of deionized water. After complete dissolution, add 238.8 mg of the SiC-OH support. Stir well for 1 h, then irradiate with ultraviolet light for reduction for 9 h. After reduction, filter with a microporous filter membrane and wash with deionized water until neutral, and then dry in a vacuum drying oven to obtain a Pd / SiC-OH catalyst loaded with 0.5 wt.%. Take 80 mg of the Pd / SiC-OH catalyst and soak it in 20 mL of a 10% sucrose solution by mass and stir. After stirring, make the catalyst surface covered with sucrose by rotary evaporation, and then convert the sucrose into a C layer and cover it on the catalyst surface through high-temperature carbonization (300 °C, 30 min, air atmosphere). The average particle size of Pd metal is about 2.5 nm.

[0069] (3) Weigh 30 mg of the above Pd / SiC-OH catalyst, 20 mL of anhydrous ethanol solution and 150.1 mg of p-carboxybenzaldehyde (1 mmol), and add them to a high-pressure reactor. Seal the reactor, ensure airtightness, and then fill it with 1 MPa of high-purity H2. Place the high-pressure reactor in a heating device, set the stirring rate to 600 rpm, the temperature to 60 °C, and the time to 1 h. After the reaction is completed, turn off the heating and stirring. After cooling to room temperature, collect the reaction solution, remove the catalyst particles through a filter, and then perform gas chromatography-mass spectrometry analysis. The conversion rate of p-carboxybenzaldehyde is 96%, and the selectivity for p-methylbenzoic acid is 78.2%.

[0070] Example XI

[0071] (1) Weigh 0.144 mL of H2PdCl4 (4 mg / mL) and dissolve it in 180 mL of deionized water. After complete dissolution, add 239.76 mg of the SiC-NH2 support. Stir well for 1 h and then irradiate with ultraviolet light for reduction for 9 h. After reduction, filter using a microporous filter membrane and wash with deionized water until neutral, and then dry in a vacuum drying oven to obtain a Pd / SiC-NH2 catalyst loaded with 0.1 wt.%. Take 80 mg of the Pd / SiC-NH2 catalyst and soak it in 20 mL of a 10% sucrose solution by mass and stir. After stirring, evaporate the solvent by rotary evaporation to cover the catalyst surface with sucrose, and then convert the sucrose into a C layer by high-temperature carbonization (300 °C, 30 min, air atmosphere) to cover the catalyst surface and prevent the agglomeration of Pd metal particles during subsequent recycling. The average particle size of the Pd metal is about 1.8 nm.

[0072] (2) Weigh 30 mg of the above Pd / SiC-NH2 catalyst, 20 mL of anhydrous ethanol solution, and 150.1 mg of p-carboxybenzaldehyde (1 mmol) and add them to a high-pressure reaction kettle. Seal the reaction kettle, ensure airtightness, and then fill it with 1 MPa of high-purity H2. Place the high-pressure reaction kettle in a heating device, set the stirring rate to 600 rpm, the temperature to 60 °C, and the time to 1 h. After the reaction is completed, turn off heating and stirring. After cooling to room temperature, collect the reaction solution, remove the catalyst particles through a filter, and then perform gas chromatography-mass spectrometry analysis. The conversion rate of p-carboxybenzaldehyde is 95.5%, and the selectivity for p-methylbenzoic acid is 17.2%.

[0073] Example Twelve

[0074] (1) Weigh 1.44 mL of H2PdCl4 (4 mg / mL) and dissolve it in 180 mL of deionized water. After complete dissolution, add 239.76 mg of the SiC-NH2 support. Stir well for 1 h and then irradiate with ultraviolet light for reduction for 9 h. After reduction, filter using a microporous filter membrane and wash with deionized water until neutral, and then dry in a vacuum drying oven to obtain a Pd / SiC-NH2 catalyst loaded with 1 wt.%. Take 80 mg of the Pd / SiC-NH2 catalyst and soak it in 20 mL of a 10% sucrose solution by mass and stir. After stirring, evaporate the solvent by rotary evaporation to cover the catalyst surface with sucrose, and then convert the sucrose into a C layer by high-temperature carbonization (300 °C, 30 min, air atmosphere) to cover the catalyst surface and prevent the agglomeration of Pd metal particles during subsequent recycling. The average particle size of the Pd metal is about 3.7 nm.

[0075] (2) Weigh 30 mg of the above Pd / SiC-NH2 catalyst, 20 mL of anhydrous ethanol solution and 150.1 mg of p-carboxybenzaldehyde (1 mmol), and add them to a high-pressure reactor. Seal the reactor, and after ensuring airtightness, fill it with 1 MPa of high-purity H2. Place the high-pressure reactor in a heating device, set the stirring rate at 600 rpm, the temperature at 50 °C, and the time at 1 h. After the reaction is completed, turn off the heating and stirring. After cooling to room temperature, collect the reaction solution, remove the catalyst particles through a filter, and then conduct gas chromatography-mass spectrometry analysis. Among them, the conversion rate of p-carboxybenzaldehyde is 98.3%, and the selectivity of p-methylbenzoic acid is 97.8%.

[0076] Example Thirteen

[0077] (1) Weigh 0.81 mL of H2PtCl6·6H2O (4 mg / mL) and dissolve it in 180 mL of deionized water. After complete dissolution, add 239.29 mg of SiC-NH2 support. Stir well for 1 h and then use ultraviolet light irradiation for reduction for 9 h. After reduction, filter with a microporous filter membrane and wash with deionized water until neutral, and then dry in a vacuum drying oven to obtain a Pt / SiC-NH2 catalyst loaded with 0.5 wt.%. Take 80 mg of the Pt / SiC-NH2 catalyst and soak it in 20 mL of a 10% sucrose solution and stir. After stirring, evaporate the solvent by rotary evaporation to cover the catalyst surface with sucrose, and then convert the sucrose into a C layer by high-temperature carbonization (300 °C, 30 min, air atmosphere) to cover the catalyst surface and prevent the agglomeration of Pt metal particles during subsequent recycling. The average particle size of the Pt metal is about 2.8 nm.

[0078] (2) Weigh 30 mg of the above Pt / SiC-NH2 catalyst, 20 mL of anhydrous ethanol solution and 150.1 mg of p-carboxybenzaldehyde (1 mmol), and add them to a high-pressure reactor. Seal the reactor, and after ensuring airtightness, fill it with 1 MPa of high-purity H2. Place the high-pressure reactor in a heating device, set the stirring rate at 600 rpm, the temperature at 60 °C, and the time at 1 h. After the reaction is completed, turn off the heating and stirring. After cooling to room temperature, collect the reaction solution, remove the catalyst particles through a filter, and then conduct gas chromatography-mass spectrometry analysis. Among them, the conversion rate of p-carboxybenzaldehyde is 97.7%, and the selectivity of p-methylbenzoic acid is 84.2%.

[0079] Example Fourteen

[0080] (1) Weigh 0.81 mL of H2PtCl6·6H2O (4 mg / mL) and dissolve it in 180 mL of deionized water. After complete dissolution, add 239.29 mg of the SiC-NH2 support. Stir well for 1 h and then irradiate with ultraviolet light for reduction for 9 h. After reduction, filter through a microporous membrane and wash with deionized water until neutral, and then dry in a vacuum drying oven to obtain a Pt / SiC-NH2 catalyst loaded with 0.5 wt.%.

[0081] Take 80 mg of the Pt / SiC-NH2 catalyst and soak it in 20 mL of a 10% sucrose solution by mass and stir. After stirring, use rotary evaporation to cover the catalyst surface with sucrose, and then convert the sucrose into a C layer by high-temperature carbonization (300 °C, 30 min) to cover the catalyst surface and prevent the agglomeration of Pt metal particles during subsequent recycling. The average particle size of the Pt metal is about 2.8 nm.

[0082] (2) Weigh 30 mg of the above Pt / SiC-NH2 catalyst, 20 mL of a methanol solution, and 150.1 mg of p-carboxybenzaldehyde (1 mmol) and add them to a high-pressure reactor. Seal the reactor, ensure airtightness, and then fill it with 1 MPa of high-purity H2. Place the high-pressure reactor in a heating device, set the stirring rate to 600 rpm, the temperature to 70 °C, and the time to 1 h. After the reaction is completed, turn off heating and stirring. After cooling to room temperature, collect the reaction solution, remove the catalyst particles through a filter, and then perform gas chromatography-mass spectrometry analysis. The conversion rate of p-carboxybenzaldehyde is 97.9%, and the selectivity for p-methylbenzoic acid is 98.2%.

[0083] Example 15

[0084] (1) Weigh 0.288 mL of H2PdCl4 (4 mg / mL) and 0.741 mL of NiCl4·6H2O (4 mg / mL) and dissolve them in 180 mL of deionized water. After complete dissolution, add 238.971 mg of the SiC-NH2 support. Stir well for 1 h and then irradiate with ultraviolet light for reduction for 9 h. After reduction, filter through a microporous membrane and wash with deionized water until neutral, and then dry in a vacuum drying oven to obtain a Pd-Ni / SiC-NH2 catalyst, where the mass fractions of Pd and Ni are 0.2% and 0.3% respectively. Take 80 mg of the Pd-Ni / SiC-NH2 catalyst and soak it in 20 mL of a 10% sucrose solution by mass and stir. After stirring, use rotary evaporation to cover the catalyst surface with sucrose, and then convert the sucrose into a C layer by high-temperature carbonization (300 °C, 30 min, in an air atmosphere) to cover the catalyst surface and prevent the agglomeration of Pd-Ni metal particles during subsequent recycling. The average particle size of the Pd-Ni mixed metal is about 2.5 nm.

[0085] (2) Weigh 30 mg of the above Pd-Ni / SiC-NH2 catalyst, 20 mL of anhydrous ethanol solution, and 150.1 mg of p-carboxybenzaldehyde (1 mmol) and add them to a high-pressure reactor. Seal the reactor, ensure airtightness, and then fill it with 1 MPa of high-purity H2. Place the high-pressure reactor in a heating device, set the stirring rate to 600 rpm, the temperature to 60 °C, and the time to 1 h. After the reaction is completed, turn off the heating and stirring. After cooling to room temperature, collect the reaction solution, remove the catalyst particles through a filter, and then perform gas chromatography-mass spectrometry analysis. The conversion rate of p-carboxybenzaldehyde is 98.8%, and the selectivity for p-methylbenzoic acid is 46.4%.

[0086] Example XVI

[0087] (1) The same as Example XV.

[0088] (2) Weigh 30 mg of the above Pd-Ni / SiC-NH2 catalyst, 20 mL of anhydrous ethanol solution, and 150.1 mg of p-carboxybenzaldehyde (1 mmol) and add them to a high-pressure reactor. Seal the reactor, ensure airtightness, and then fill it with 1 MPa of high-purity H2. Place the high-pressure reactor in a heating device, set the stirring rate to 600 rpm, the temperature to 70 °C, and the time to 1 h. After the reaction is completed, turn off the heating and stirring. After cooling to room temperature, collect the reaction solution, remove the catalyst particles through a filter, and then perform gas chromatography-mass spectrometry analysis. The conversion rate of p-carboxybenzaldehyde is 97.0%, and the selectivity for p-methylbenzoic acid is 63.6%.

[0089] Example XVII

[0090] (1) The same as Example XV.

[0091] Weigh 30 mg of the above Pd-Ni / SiC-NH2 catalyst, 20 mL of anhydrous ethanol solution, and 150.1 mg of p-carboxybenzaldehyde (1 mmol) and add them to a high-pressure reactor. Seal the reactor, ensure airtightness, and then fill it with 1 MPa of high-purity H2. Place the high-pressure reactor in a heating device, set the stirring rate to 600 rpm, the temperature to 80 °C, and the time to 1 h. After the reaction is completed, turn off the heating and stirring. After cooling to room temperature, collect the reaction solution, remove the catalyst particles through a filter, and then perform gas chromatography-mass spectrometry analysis. The conversion rate of p-carboxybenzaldehyde is 96.9%, and the selectivity for p-methylbenzoic acid is 80.8%.

[0092] Example XVIII

[0093] (1) The same as Example XV.

[0094] (2) Weigh 30 mg of the above Pd-Ni / SiC-NH2 catalyst, 20 mL of methanol solution and 150.1 mg of p-carboxybenzaldehyde (1 mmol), and add them to a high-pressure reactor. Seal the reactor, ensure airtightness, and then fill it with 1 MPa of high-purity H2. Place the high-pressure reactor in a heating device, set the stirring rate to 600 rpm, the temperature to 90 °C, and the time to 1 h. After the reaction is completed, turn off heating and stirring. After cooling to room temperature, collect the reaction solution, remove the catalyst particles through a filter, and then perform gas chromatography-mass spectrometry analysis. The conversion rate of p-carboxybenzaldehyde is 95.2%, and the selectivity for p-toluic acid is 94.6%.

[0095] Example XIX

[0096] (1) Weigh 0.72 mL of H2PdCl4 (4 mg / mL) and dissolve it in 180 mL of deionized water. After complete dissolution, add 238.8 mg of SiC support. Stir well for 1 h, then use ultraviolet light irradiation to reduce for 9 h. After reduction, filter through a microporous membrane and wash with deionized water until neutral, and then dry in a vacuum drying oven to obtain a Pd / SiC catalyst loaded with 0.5 wt.%. Take 80 mg of the Pd / SiC catalyst and soak it in 20 mL of a 10% by mass sucrose solution and stir. After stirring, use rotary evaporation to cover the catalyst surface with sucrose, and then through high-temperature carbonization (300 °C, 30 min, air atmosphere), the sucrose is transformed into a C layer and covers the catalyst surface. The average particle size of Pd metal is about 3.8 nm.

[0097] (2) Weigh 30 mg of the above Pd / SiC catalyst, 20 mL of absolute ethanol solution and 150.1 mg of p-carboxybenzaldehyde (1 mmol), and add them to a high-pressure reactor. Seal the reactor, ensure airtightness, and then fill it with 1 MPa of high-purity H2. Place the high-pressure reactor in a heating device, set the stirring rate to 600 rpm, the temperature to 60 °C, and the time to 1 h. After the reaction is completed, turn off heating and stirring. After cooling to room temperature, collect the reaction solution, remove the catalyst particles through a filter, and then perform gas chromatography-mass spectrometry analysis. The conversion rate of p-carboxybenzaldehyde is 96%, and the selectivity for p-toluic acid is 16.7%.

[0098] It is found that after the transition metal is loaded on SiC modified by amino group (-NH2), the activity of catalyzing the hydrogenation of p-carboxybenzaldehyde is significantly increased, and the incorporation of amino group (-NH2) makes the nano-metal particles smaller and more uniformly dispersed, and the active M sites on the catalyst surface increase, so the selectivity for p-toluic acid is significantly improved.

[0099] Example XX

[0100] (1) Weigh 0.72 mL of H2PdCl4 (4 mg / mL) and dissolve it in 180 mL of deionized water. After complete dissolution, add 238.8 mg of SiC-NH2 support. Stir well for 1 h and then irradiate with ultraviolet light for reduction for 9 h. After reduction, filter through a microporous filter membrane and wash with deionized water until neutral, and then dry in a vacuum drying oven to obtain a Pd / SiC-NH2 catalyst loaded with 0.5 wt.%. The average particle size of Pd metal is about 2.1 nm.

[0101] (2) Weigh 30 mg of the above Pd / SiC-NH2 catalyst, 20 mL of anhydrous ethanol solution and 150.1 mg of p-carboxybenzaldehyde (1 mmol) and add them to a high-pressure reaction kettle. Seal the reaction kettle, ensure airtightness, and then fill it with 1 MPa of high-purity H2. Place the high-pressure reaction kettle in a heating device, set the stirring rate at 600 rpm, the temperature at 60 °C, and the time at 1 h. After the reaction is completed, turn off heating and stirring. After cooling to room temperature, collect the reaction solution, remove catalyst particles through a filter, and then perform gas chromatography-mass spectrometry analysis.

[0102] The conversion rate of p-carboxybenzaldehyde is 95.8%, and the selectivity for p-methylbenzoic acid is 95.4%. From Figure 2 and Figure 3 the results of the cycle experiment and the change in the size of Pd metal particles before and after the experiment, it can be seen that for the catalyst lacking the C layer, the Pd metal particles agglomerate during the subsequent cycle experiment, resulting in a decrease in activity. Therefore, it is selected to cover the C layer on the catalyst surface.

[0103] Inspired by the ideal embodiments of the present invention described above, through the above description, relevant staff can completely make various changes and modifications without departing from the technical idea of this invention. The technical scope of this invention is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A catalyst for the hydrogenation process of carboxybenzaldehyde, characterized in that, The catalyst includes a support, an active component, and a carbon layer; the support is modified silicon carbide, and the active component is a metal.

2. The catalyst for the hydrogenation process of carboxybenzaldehyde according to claim 1, characterized in that, The metal is one or more of Pt, Pd, Ni, and Fe; the mass percentage of the metal in the catalyst is 0.1-1%.

3. The catalyst for the hydrogenation process of carboxybenzaldehyde according to claim 1, characterized in that, The modified silicon carbide is amino-modified silicon carbide or hydroxy-modified silicon carbide.

4. A method for preparing a catalyst according to any one of claims 1-3, characterized in that, It includes the following steps: dispersing the modified silicon carbide and the metal precursor in water, first dispersing them in ultrasonic waves, then stirring evenly, and then reducing them by ultraviolet light irradiation for 5-12 h, filtering, washing, and drying to obtain the M / SiC-X precursor; mixing the M / SiC-X precursor and the carbon precursor solution, and making the carbon precursor coat on the surface of the M / SiC-X precursor by rotary evaporation to obtain the catalyst.

5. The preparation method according to claim 4, wherein The metal precursor is a soluble metal salt.

6. The preparation method according to claim 4, wherein The carbon precursor includes sucrose; the dosage ratio of the M / SiC-X precursor to the carbon precursor is 20 mL:80 mg; the concentration of the carbon precursor solution is 10-15 wt%.

7. Use of the catalyst according to any one of claims 1-3, characterized in that, The application is to catalyze the hydrogenation reaction of p-carboxybenzaldehyde.

8. The application according to claim 7, wherein The application includes the following steps: fully dissolving p-carboxybenzaldehyde in a solvent and mixing evenly, adding the catalyst and fully mixing to form a suspension, then maintaining the hydrogen pressure at 0.5-2 MPa, and keeping the temperature of the reaction system at ≥30°C under stirring conditions to carry out the hydrogenation reaction.

9. The application according to claim 8, characterized in that, The temperature of the reaction system is 30-90°C.

10. The application according to claim 8, characterized in that, The solvent is one or more of methanol, absolute ethanol, isopropanol, and water.

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