CN108786843A - A kind of supported precious metal catalyst, preparation method and applications - Google Patents

Abstract

The invention provides a loaded noble metal catalyst, a preparation method and its application. The steps are: a) fixing the carrier below the liquid level of a reaction vessel filled with deionized water, and after the temperature stabilizes, vigorously stir at the bottom of the vessel; Adding an aqueous solution containing noble metal adjusted to be neutral at a uniform speed; taking out the carrier after the reaction; b) washing and drying the taken out carrier to obtain the loaded noble metal catalyst. Compared with the prior art, the noble metal prepared by the invention has high dispersion, stable catalytic performance and little loss of noble metal. And according to the needs of different reaction equipment and reaction types, catalysts with different components and different noble metal loadings can be prepared, with flexible operation and easy control, and are suitable for gas/liquid phase and aqueous/non-aqueous phase reaction systems. After the reaction, it is easy to separate from the product.

Description

A kind of loaded precious metal catalyst, preparation method and application thereof

technical field

The invention relates to the field of catalyst preparation, in particular to a loaded noble metal catalyst, a preparation method and an application thereof.

Background technique

As an effective catalyst, noble metals have the advantages of good stability, strong catalytic activity, high efficiency, and mild reaction conditions. As active components of catalysts, noble metals have been widely used in industrial catalysis. At present, precious metals are rarely used alone as catalyst materials, and are mostly supported on other materials, such as carbon materials, oxides, polymer materials, etc. Due to the suitable pore size, special structure and electronic properties of these support materials, it is beneficial to increase the specific surface area of the catalyst, form a suitable empty island structure, change the electronic properties of the noble metal surface, and provide a certain macroscopic three-dimensional structure and mechanical strength for the catalyst. , easy to use and recycle. At the same time, part of the carrier also has a certain catalytic function to enhance the catalytic activity and selectivity of noble metals, so the same noble metal loaded on different carriers will have great differences in the same catalytic performance. Therefore, the introduction of catalyst supports can better exert the catalytic performance of noble metals.

At present, there are many ways to prepare supported noble metal catalysts, such as sol-gel method, deposition precipitation method, impregnation method, organic chemical vapor deposition method and ion exchange method. These methods can prepare supported noble metal catalysts with good performance, but there are still many problems. For example, the process price of deposition and precipitation is complicated, the raw material cost of sol-gel method is high, and the dispersibility of impregnation method is often poor. They also have some defects that the precious metal and the supporting material are often only physically adsorbed together, which makes the force between them small. During use, the precious metal particles will easily aggregate and lose, making its catalytic activity This will not only reduce the recyclability of the catalyst, increase the cost of use, but also have a certain impact on the quality of the catalytic product. At the same time, part of the noble metal will be covered by the carrier during the preparation of the catalyst, which reduces the effective activity of the catalyst and the utilization rate of the noble metal.

Contents of the invention

In order to solve the above-mentioned technical problems, the present invention provides a supported noble metal catalyst and a preparation method thereof. The reticulated/foamed metal-supported noble metal catalyst is prepared by in-situ replacement. The prepared catalyst has high dispersion of noble metal, stable catalytic performance, and noble metal The loss is small.

Another object of the present invention is to provide an application of a supported noble metal catalyst as a catalyst, especially in the application of catalyzing the conversion of cinnamaldehyde.

Concrete technical scheme of the present invention is as follows:

A method for preparing a loaded noble metal catalyst, comprising the following steps:

a) The carrier is fixed below the liquid level of the reaction vessel with deionized water, and after the temperature is stable, stir, and at the same time, under stirring conditions, add the aqueous solution containing precious metal ions adjusted to be neutral at a constant speed; keep stirring while keeping warm until the reaction End, take out the carrier;

b) The removed carrier is washed and dried to obtain a supported noble metal catalyst.

The carrier described in step a) is selected from metal mesh or metal foam;

Further, the carrier in step a) is selected from any one of nickel mesh, nickel foam, cobalt mesh, cobalt foam, copper mesh, copper foam, iron mesh or iron foam.

Stable temperature in step a) means that the temperature of the system in the reaction vessel is controlled at 10-60°C.

Stirring in step a) refers to stirring at 800 rpm.

The uniform addition rate in step a) is 1 mL/min.

Adjusting the aqueous solution containing noble metal ions to be neutral in step a) refers to adjusting the aqueous solution containing noble metal ions to neutral pH=7.0 with 0.0001moL/L hydrochloric acid or 0.0001moL/L sodium hydroxide solution.

The aqueous solution containing noble metal ions described in step a) is selected from any aqueous solution of chloroauric acid, aqueous solution of chloroplatinic acid, aqueous solution of chloropalladic acid, aqueous solution of potassium chloroplatinate, aqueous solution of potassium chloropalladate, aqueous solution of rhodium chloride or aqueous solution of ruthenium chloride one or several.

The heat preservation and stirring time described in step a) is 3-4h.

The noble metal ion concentration in the neutral noble metal ion-containing aqueous solution adjusted in step a) is 0.0001-0.1 moL/L.

A supported noble metal catalyst provided by the present invention is used as a catalyst, which is prepared by the above-mentioned method.

The application of the loaded noble metal catalyst provided by the invention as a catalyst, especially in the application of catalyzing the conversion of cinnamaldehyde. The catalytic conversion rate of cinnamaldehyde is as high as 99%.

The present invention prepares a method for reticular/foamy metal-loaded noble metal catalysts by means of in-situ replacement. In this method, vigorous stirring is helpful for the uniform dispersion of noble metals on the surface of the carrier, and the stable control and stability of the temperature is conducive to the improvement of the reaction speed. Controlling and adjusting the pH value can reduce the influence of the pH value of the solution on the carrier. Therefore, the catalyst prepared by the method is a supported catalyst with high dispersion of precious metals, stable catalytic performance and small loss of precious metals. This method is especially suitable for the preparation of noble metal catalysts with high utilization rate and low content of noble metals. And according to the requirements of different reaction equipment and reaction types, catalysts with different components and different precious metal loadings can be prepared. The operation is flexible and easy to control, and it is suitable for gas/liquid phase and water phase/non-aqueous phase reaction systems; The product separates. Since the precious metal is mainly loaded on the surface of the carrier, the exposed surface of the precious metal is relatively large, there are many opportunities to participate in the reaction, and the utilization rate of the precious metal is high. At the same time, since the noble metal replaces the metal atoms on the surface of the carrier, a metal bond will be formed between the noble metal atom and the carrier, and the force is stronger than ordinary physical adsorption, so it can ensure the stable existence of the noble metal on the carrier surface, and it is not easy to agglomerate and lose. The special three-dimensional network structure of the carrier enables the reactants to diffuse and flow smoothly in the carrier body, and this structure can be well used in tubular reactors.

Detailed ways

Example 1

A method for preparing a loaded noble metal catalyst, comprising the following steps:

a) Utilize 0.0001moL/L sodium hydroxide solution to adjust the pH value of 10mL of 0.005moL/L chloropalladium acid aqueous solution to neutrality, dilute to 50mL with deionized water, and set aside; in a 50mL deionized water reaction vessel 2.6g nickel foam was fixed below the liquid surface of deionized water, the temperature of the deionized water in the reaction vessel was controlled at a stable 40°C, the reaction vessel was placed on a magnetic stirrer, and vigorous stirring was started at 800 rpm At the same time, the aqueous solution of chloropalladium acid was added to the vigorously stirred reaction system with an electric syringe pump at a speed of 1 mL/min. After the dropwise addition was completed, the mixture was kept warm and stirred for 4 hours. After the reaction is completed, take out the prepared foam nickel supported palladium catalyst;

b) Wash the prepared palladium foam catalyst supported on nickel with 10% ethanol solution for 2-3 times, and finally wash once with deionized water, and dry it in a vacuum environment at 60° C. for 4 hours to obtain the obtained product.

The performance test method of the catalyst is as follows:

0.2g of the above-mentioned prepared foamed nickel supported palladium catalyst is cut into particles and placed in a catalytic hydrogenation reactor, and 15ml of deionized water and 1mmol of cinnamaldehyde are added to the reactor, the air in the reactor is discharged, and the reactor is fed to the reactor. Hydrogen at a pressure of 1 MPa was introduced into the kettle. The temperature of the reaction kettle was raised under the condition of stirring, and the reaction was stirred and reacted at 60° C. for 5 h. After the reaction was completed, the temperature was lowered and the gas in the reactor was discharged, and the reaction solution was taken out and extracted three times with 3 mL of butyl acetate, and the solvents extracted three times were mixed, and the reactants and products were analyzed by gas chromatography. The analysis results are shown in Table 1 below:

Table 2:

project Conversion rate of cinnamaldehyde Cinnamyl Alcohol Yield Phenylpropanol yield percentage/% >99% 89% 10%

Example 2

A method for preparing a loaded noble metal catalyst, comprising the following steps:

a) Use 0.0001moL/L hydrochloric acid solution to adjust the pH value of 10mL of the mixed solution containing 0.0025moL/L potassium chloropalladate and 0.0025moL/L potassium chloroplatinate to neutral, and use the neutral mixed solution Dilute to 50mL with deionized water and set aside; in a 50mL deionized water reaction vessel, fix 2.5g of nickel foam below the deionized water level, and control the temperature of the deionized water in the reaction vessel at a stable 50°C. And placed on a magnetic stirrer, started vigorous stirring at 800 rpm. At the same time, the above-prepared neutral mixed solution of potassium chloropalladate and potassium chloroplatinate was added to the vigorously stirred reaction system at a rate of 1 mL/min. After the dropwise addition was completed, the mixture was incubated and stirred for 3 hours. After the reaction is completed, take out the palladium and platinum catalyst supported on foamed nickel. b) The catalyst was washed 2-3 times with 10% ethanol solution, and finally washed once with deionized water, and dried in a vacuum environment at 50° C. for 4 hours.

The performance test method of the catalyst is as follows:

Cut 0.2g of nickel foam supported palladium and platinum catalyst into a suitable shape and fix it in a catalytic hydrogenation reactor. And add 15ml of deionized water and 1mmol of cinnamaldehyde to the reaction kettle to ensure that the catalyst is below the liquid level of the reaction solution. The air in the reactor was exhausted, and hydrogen gas at a pressure of 1 MPa was introduced into the reactor. Under the condition of stirring, the temperature of the reaction kettle was raised, and the reaction was stirred and reacted at 50° C. for 4 h. After the reaction was completed and the temperature was lowered, the gas in the reaction kettle was discharged, and the reaction solution was taken out and extracted three times with 3 mL of butyl acetate, and the solvents extracted three times were mixed, and the reactants and products were analyzed by gas chromatography. The analysis results are shown in Table 2 below:

Table 2:

project Conversion rate of cinnamaldehyde Cinnamyl Alcohol Yield Phenylpropanol yield percentage/% >99% 93% 6%

Example 3

A method for preparing a loaded noble metal catalyst, comprising the following steps:

a) Use 0.0001moL/L sodium hydroxide solution to adjust 10mL of 0.005moL/L chloropalladium acid aqueous solution to neutrality, and dilute the neutral solution to 50mL with deionized water for subsequent use; In the deionized water reactor, fix 2.5 foamed cobalt below the deionized water level, control the temperature of the deionized water in the reactor at a stable 45°C, and place it on a magnetic stirrer, starting at 800 rpm Stir vigorously. At the same time, the neutral aqueous solution of chloropalladium acid was added into the vigorously stirred reactor at a rate of 1 mL/min, and after the dropwise addition was completed, the reaction was continued with stirring for 4 h while being kept warm. After the reaction was completed, the foam cobalt-supported palladium catalyst was taken out.

b) The catalyst that has completed the reaction is washed 2-3 times with 10% ethanol solution, and finally washed once with deionized water, and dried in a vacuum environment at 40° C. for 4 hours.

The performance test method of the catalyst is as follows:

2.6 g of palladium-loaded cobalt foam catalyst was placed in a tubular reactor made of quartz. The length of the catalyst in the reaction tube was 10 cm. Put 50ml of deionized water and 4mmol of cinnamaldehyde reaction solution in a tubular reactor, and keep the whole reaction system under 0.1MPa pressure of hydrogen. Cycle the reaction at 60°C for 6h. After cooling down, the reaction solution was taken out and extracted three times with 5 mL of butyl acetate, the solvents extracted three times were mixed, and the reactants and products were analyzed by gas chromatography. The analysis results are shown in Table 3 below:

table 3:

project Conversion rate of cinnamaldehyde Cinnamyl Alcohol Yield Phenylpropanol yield percentage/% >99% 91% 8%

The loaded noble metal catalyst prepared by the invention has stable performance, simple preparation method and high catalytic efficiency.

Claims (10)

1. a preparation method of loaded noble metal catalyst, is characterized in that, described preparation method comprises the following steps: a) The carrier is fixed below the liquid level of the reaction vessel with deionized water, and after the temperature is stable, stir, and at the same time, under stirring conditions, add the aqueous solution containing precious metal ions adjusted to be neutral at a constant speed; keep stirring while keeping warm until the reaction End, take out the carrier; b) The removed carrier is washed and dried to obtain a supported noble metal catalyst. 2. The preparation method according to claim 1, characterized in that the carrier in step a) is selected from metal mesh or metal foam. 3. The preparation method according to claim 1 or 2, characterized in that, the carrier described in step a) is selected from nickel mesh, nickel foam, cobalt mesh, cobalt foam, copper mesh, copper foam, iron mesh or iron foam any kind. 4. The preparation method according to claim 1, characterized in that, the stable temperature in step a) means that the temperature of the system in the reaction vessel is controlled at 10-60°C. 5. The preparation method according to claim 1, characterized in that, the neutral aqueous solution containing noble metal ions adjusted in step a) refers to: the aqueous solution containing noble metal ions is mixed with 0.0001moL/L hydrochloric acid or 0.0001moL /L sodium hydroxide solution to adjust to neutral pH=7.0. 6. according to the described preparation method of claim 1 or 5, it is characterized in that, the aqueous solution containing noble metal ion described in step a) is selected from chloroauric acid aqueous solution, chloroplatinic acid aqueous solution, chloropalladic acid aqueous solution, potassium chloroplatinate Any one or more of aqueous solution, potassium chloropalladate aqueous solution, rhodium chloride aqueous solution or ruthenium chloride aqueous solution. 7. The preparation method according to any one of claims 1, 5 or 6, characterized in that the concentration of noble metal ions in the neutral noble metal-containing aqueous solution adjusted in step a) is 0.0001-0.1moL/L. 8. The preparation method according to claim 1, characterized in that, the heat preservation and stirring time described in step a) is 3-4h. 9. A loaded noble metal catalyst prepared by the preparation method according to any one of claims 1-8. 10. the application of a supported noble metal catalyst as claimed in claim 9 as a catalyst.