Preparation and application of size-controllable nickel particle loaded lanthanum trioxide catalyst

Abstract

The invention discloses preparation and application of a size-controllable nickel particle loaded lanthanum trioxide catalyst, and belongs to the field of nano materials and chemical catalysis. The preparation method of the catalyst comprises the following steps: preparing nano nickel particles by a complex cracking method, preparing a catalyst carrier by an electrostatic spinning method, calcining at high temperature, dipping, drying and the like to obtain the target catalyst. The temperature of the complexing cracking method is 180-400 DEG C, the voltage of electrostatic spinning is 15-20 kV, the high-temperature calcination temperature is 500-800 DEG C, the dipping time is 12-36 hours, the drying temperature is 60-80 DEG C, the nickel content accounts for 5-30% of the weight of the catalyst, and the weight ratio of the catalyst carrier is 70-95%. The size range of nickel particles of the prepared catalyst is 2-20 nm, and the growth speed and size of the nickel particles can be controlled by adjusting conditions. The prepared catalyst shows excellent carbon dioxide hydrogenation performance and has an obvious size effect.

Description

Technical Field

[0001] The present invention belongs to the fields of nanomaterials and chemical catalysis, and particularly relates to the preparation and application of a catalyst with nickel particles of controllable size supported on lanthanum sesquioxide. Background Art

[0002] At present, environmental problems and energy crises are two major crises in today's society. The concentration of carbon dioxide has been increasing year by year, which requires us to put forward higher requirements for the efficiency of carbon dioxide capture, storage and utilization. For the conversion and utilization of carbon dioxide, its hydrogenation to high-value chemicals is considered to be one of the potential technologies. Usually, such reactions require catalysts to improve efficiency. Among them, nickel metal plays a crucial role in many chemical reactions, especially as the active metal component of the catalyst. It is inexpensive, highly active, and has extremely strong activity towards hydrogen, so it shows unique activity in some hydrogenation reactions. However, nickel is prone to sintering at high temperatures, and in some catalytic reactions, the catalytic activity of different sizes varies greatly, showing an obvious size effect. Some studies have pointed out that in patent No. CN111517379 A, nickel particles with a relatively concentrated size distribution were prepared, but their particle size was 1 - 2 µm, far from the nanoscale. Patent CN 106920755 A prepared uniform nickel particles with a size of 3 - 4 nm. This method needs to be prepared by means of pulses and other methods under high temperature and NH 3 atmosphere, but its process is cumbersome and expensive, which is not conducive to large-scale preparation. Therefore, it is of great significance to explore a method for preparing nickel particles with simple steps, environmental friendliness and low cost. Summary of the Invention

[0003] The purpose of the present invention is to provide the preparation and application of a catalyst with nickel particles of controllable size supported on lanthanum sesquioxide. This method is simple to operate, the particle size is uniformly controllable, and it can be repeatedly prepared in large quantities. This catalyst has high activity and strong stability when applied to carbon dioxide methanation catalysts.

[0004] In response to the problems mentioned in the background art, the technical solution adopted by the present invention is as follows:

[0005] A catalyst with nickel particles of controllable size supported on lanthanum sesquioxide, wherein the active components of the catalyst are nickel and lanthanum sesquioxide;

[0006] Among them, the nickel particles with controllable size have a size distribution of 2 nm, 10 nm and 20 nm, and their content in the catalyst is 1% - 20%. The lanthanum sesquioxide is in the shape of mesoporous nanofibers, and its content in the catalyst is 80% - 99%. It has a highly dispersed mesoporous structure, the pore diameter is concentrated in 5 - 20 nm, and the fiber size is basically the same. The fiber length is 20 nm - 2 µm, and the diameter is 50 - 500 nm.

[0007] Further, the preparation method of the nickel particles is the complexation pyrolysis method. The precursor is a mixture of nickel salt and organic acid, and the reaction occurs through syringe injection at high temperature to grow nickel particles. Among them, the precursors of nickel salts include but are not limited to nickel acetate, nickel acetate, nickel acetylacetonate, etc.; the composition of organic acids includes but is not limited to oxalic acid, citric acid, oleic acid, benzoic acid, etc.

[0008] The preparation method of nickel nanoparticles by complexation pyrolysis includes the following steps:

[0009] 1) The whole preparation process is completed in a closed space to ensure an anaerobic state.

[0010] 2) Take a certain amount of nickel salt as the precursor, dissolve it in a certain amount of ethanol or water, reflux at 80 °C for 2 hours. After the nickel salt is fully dissolved, raise the temperature to 180 °C.

[0011] 3) At the same time, quantitatively preheat the selected organic acid to 180 °C, keep it for 30 minutes, and then inject it into the solution in step 2).

[0012] 4) After mixing, keep it at 180 °C for 1 hour, continue to raise the temperature to 300 °C in the second step, keep it for 1 hour. During the process, add polyvinylpyrrolidone (PVP) with 2 - 10 times the molar mass of nickel, continue to keep warm and stir for 1 h, and then cool to room temperature. The whole experiment needs to maintain an anaerobic and anhydrous state.

[0013] 5) After complete cooling, add propanol for centrifugal washing at a speed of 5000 r / min for 5 - 10 minutes until the upper solution is clear. The precipitate obtained by centrifugation is redispersed in n - hexane solution and stored in a low - temperature and shady place.

[0014] Further, the lanthanum sesquioxide in the shape of mesoporous nanofibers is prepared by an electrospinning method using a lanthanum salt precursor. The preparation method includes the following steps:

[0015] 1) Dissolve the lanthanum salt precursor in DMF solution, add PAN with 2 - 3 times the mass of the lanthanum salt, and place it in a 60 ºC water bath and stir overnight for use.

[0016] 2) Load the solution obtained in step 1) into a syringe, set the voltage to 16 kV, and collect it using the roller aluminum foil of an electrospinning machine. The collected product is vacuum - dried at 60 °C for 12 h and then calcined in a muffle furnace at 500 °C for 2 hours to obtain lanthanum sesquioxide in the shape of mesoporous nanofibers.

[0017] A catalyst with size - controllable nickel particles supported on lanthanum sesquioxide includes:

[0018] The obtained Ni particles and lanthanum sesquioxide in the shape of mesoporous nanofibers are used to obtain the target catalyst by the impregnation method.

[0019] Furthermore, the nickel particle-loaded lanthanum sesquioxide catalyst with controllable nickel particle size is applied to the carbon dioxide hydrogenation reaction. The application conditions are as follows: normal pressure, the reaction temperature is 200 - 400 °C, the reaction space velocity is 12000 - 36000 h -1 , and the molar ratio of H 2 :CO 2 = 4:1.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: the size of Ni particles is precisely controlled, and it is effectively combined with lanthanum sesquioxide, showing excellent catalytic effects. Brief Description of the Drawings

[0021] Figure 1 It is the TEM image of the nickel nanoparticles prepared in Example 1 of the present invention.

[0022] Figure 2 It is the SEM image of the lanthanum sesquioxide in the shape of mesoporous nanofibers prepared in Example 1 of the present invention. Detailed Embodiments

[0023] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments. The methods are conventional methods unless otherwise specified, and the raw materials can be obtained from public commercial channels unless otherwise specified.

[0024] Example 1

[0025] (1) Take a clean beaker, completely dissolve 0.258 g of nickel acetate in an ethanol solution, then transfer it to a three-necked flask, introduce argon, and reflux at 80 °C for 2 hours;

[0026] (2) Then raise the temperature to 180 °C, keep the argon atmosphere, and at the same time heat 7.8 ml of citric acid to 180 °C. After maintaining for 30 minutes, transfer the citric acid solution to the three-necked flask and continue to maintain for 1 hour;

[0027] (3) Continue to raise the temperature in the second step to 300 °C and maintain for 1 hour. During the process, add 1.29 g of polyvinylpyrrolidone (PVP), continue to keep warm and stir for 1 h, and then cool to room temperature. The whole experiment needs to maintain an oxygen-free and water-free state;

[0028] (4) After complete cooling, add propanol for centrifugal washing at a rotation speed of 5000 r / min for 10 minutes until the upper solution is clear. Disperse the centrifuged precipitate in 20 ml of n-hexane solution and store it in a low-temperature and shady place. ( Figure 1TEM image of the nickel particles prepared in this example. As shown in the figure, the nickel nanoparticles are 15 nm in size, arranged orderly, and have uniform size.

[0029] (5) Weigh 2.3 g of lanthanum chloride and dissolve it in 20 ml of DMF solution. Add 4.6 g of PAN and place it in a 60 ºC water bath, stirring overnight for later use.

[0030] (6) Load the solution obtained in step (5) into a syringe, set the voltage at 16 kV, and collect it using the roller aluminum foil of an electrospinning machine. The collected product is dried in vacuum at 60 ºC for 12 h and then calcined in a muffle furnace at 500 ºC for 2 h to obtain lanthanum oxide in the shape of mesoporous nanofibers. Figure 2 SEM image of the lanthanum oxide in the shape of mesoporous nanofibers prepared in this example. As shown in the figure, the fibrous structure is obvious and the diameters are uniform.

[0031] (7) Prepare a catalyst with nickel particles supported on lanthanum oxide by the impregnation method using the Ni particles obtained in (5) and the lanthanum oxide in the shape of mesoporous nanofibers obtained in (6).

[0032] (8) Test the performance of the obtained catalyst in a fixed-bed evaluation device. The molar ratio of the reaction gas H 2 :CO 2 =4:1, the space velocity is 36000 h -1 , and the products are analyzed online using gas chromatography.

[0033] Examples 2 - 6

[0034] Prepare the catalyst according to the parameters designed in Table 1. Except for the different designed parameters, other parameters and steps are the same as those in Example 1.

[0035] Table 1: Design parameters for Examples 4 - 9

[0036]

[0037] Detect and analyze the activities of the catalysts prepared in Examples 2 - 6, and obtain Table 2 by combining the detection and analysis results of Example 1.

[0038] Table 2: Detection and analysis results of catalyst activities

[0039]

[0040] As shown in Table 2, the mesoporous fibrous catalyst prepared in the present invention enhances the adsorption of the carrier for CO 2 , reduces the optimal activity temperature, and improves the conversion rate of CO 2 , and is very suitable for CO 2Hydroconversion reaction.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and not to limit them; although the present application has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that: it is still possible to modify the specific implementation manners of the present application or perform equivalent replacements on some technical features, and they should all be covered within the scope of the technical solutions claimed in the present application.

Claims

1. A size-controlled nickel particle supported on a lanthanum trioxide catalyst, characterized in that: The active components of the catalyst are nickel particles and a catalyst carrier, lanthanum trioxide; wherein the size of the nickel particles is 2-20 nanometers, the content is 5-30%, the proportion of lanthanum trioxide is 70-95%, and the nickel particles are evenly distributed on the lanthanum trioxide carrier.

2. The size-controlled nickel particles supported on a lanthanum trioxide catalyst according to claim 1, characterized in that: The preparation method of the nickel particles is a high-temperature injection method, and its precursor is a mixture of nickel salt and organic acid, and the nickel particles are grown by a complex cleavage method; wherein the precursor of the nickel salt includes but is not limited to nickel acetate, nickel acetate, nickel acetylacetonate, etc.; the composition of the organic acid includes but is not limited to oxalic acid, citric acid, oleic acid, benzoic acid, etc.

3. The size-controlled nickel particles supported on a lanthanum trioxide catalyst according to claim 2, characterized in that: The high temperature range of the high temperature injection method is between 180-400 degrees Celsius, and the reaction time at high temperature is 1-3 hours.

4. The size-controlled nickel particles supported on a lanthanum trioxide catalyst according to claim 3, characterized in that: After the injection using the syringe in the high temperature injection method, the container is kept closed to prevent air from entering.

5. The size-controlled nickel particles supported on lanthanum trioxide catalyst according to claim 1, characterized in that: The method for preparing the nickel particles by complex pyrolysis method comprises the following steps: 1) Take a well-sealed round-bottom flask, add an appropriate amount of organic acid (so that the bottom of the flask is submerged), set the target temperature, and maintain it at the target temperature for 30 minutes; 2) Take an appropriate amount of nickel salt precursor in a certain proportion of organic acid, stir at 80 degrees Celsius until completely dissolved, and then heat to a high temperature; 3) Use a syringe to draw the solution prepared in step 2) and inject it into the round-bottom flask in step 1), and continue to maintain the same temperature for 1 hour, then continue to heat to a higher temperature and maintain for 1 hour, add PVP and continue to maintain for 1 hour. The capacity of the syringe should be larger than the amount of the solution to ensure that one injection is sufficient; 4) After the above solution has completed the reaction, it is cooled and allowed to stand, then washed with a large amount of propanol, centrifuged, and dispersed in 50 ml of n-hexane.

6. The lanthanum trioxide carrier according to claim 1, characterized in that The lanthanum trioxide carrier is prepared by an electrostatic spinning method, and the preparation method comprises the following steps: 1) Add appropriate amount of N-N-dimethylformamide and polyacrylonitrile to the salt precursor of lanthanum trioxide, ultrasonicate for 10 min, and stir overnight at 60 degrees Celsius until completely dissolved to obtain a uniform light yellow transparent solution; 2) The darkened solution obtained in step 1) is loaded into an electrospinning machine and set to a voltage of 16 kV. The product is collected using an aluminum foil on the electrospinning machine drum. The collected product is vacuum dried at 60 degrees Celsius for 12 hours and then calcined at 500 degrees Celsius for 2 hours to obtain a lanthanum trioxide carrier.

7. A catalyst prepared by impregnating the nickel particles with controllable size supported on a lanthanum trioxide catalyst according to claims 1-6.

8. The size-controlled nickel particles supported on a lanthanum trioxide catalyst according to claim 7, characterized in that: The catalyst is used for carbon dioxide methanation, and the application conditions are: normal pressure, reaction temperature of 225-425 ° C, reaction space velocity of 3000-72000 h -1 , molar ratio H2:CO2=4:1.

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