CN114700100B - Preparation method of catalyst for nitrogen reduction reaction - Google Patents

Abstract

The invention provides a catalyst for nitrogen reduction reaction and a preparation method thereof, belonging to the technical field of catalyst preparation. The catalyst of the present invention is prepared by a liquid-phase one-pot method, wherein the nitrogen-doped carbon structure carrier formed by co-pyrolysis of the carbon source and the nitrogen source has a huge specific surface area and is rich in defect sites, realizing the Adsorption and activation of nitrogen molecules. The metal atoms of the active phase supported in the catalyst of the present invention realize the activation of hydrogen molecules, and at the same time, the doping of the non-metallic element boron will form a relatively stable CN-B carrier at high temperature, which can promote the synthesis of ammonia under mild conditions. The catalyst prepared by the invention can efficiently synthesize ammonia under mild reaction conditions at one atmospheric pressure.

Description

A kind of preparation method of catalyst for nitrogen reduction reaction

technical field

The invention relates to the technical field of catalyst preparation, in particular to a method for preparing a catalyst for nitrogen reduction reaction.

Background technique

As an important chemical product, ammonia has good application prospects in agricultural production, energy storage and transportation, and green energy development. At present, more than 90% of the ammonia in my country comes from the Haber-Bosch process, but the process has extremely harsh reaction conditions, high energy consumption, large carbon emissions, and poor safety. This high-energy, high-carbon production model has seriously changed the environment we live in, leading to increasingly frequent extreme weather. It can be seen that research on new methods that can replace the Haber-Bosch process for ammonia synthesis is of great importance to industrial production and sustainable human development. Significance.

Nowadays, photocatalytic ammonia synthesis, electrocatalytic ammonia synthesis, low temperature plasma ammonia synthesis and thermocatalytic ammonia synthesis are the main research directions of ammonia synthesis under mild conditions. Considering that the demand for ammonia is huge, large-scale production is required, and the requirements for ammonia yield, energy utilization efficiency and technology maturity are high, under the existing chemical system, the thermocatalytic ammonia synthesis process is the most suitable, only need to prepare efficient reaction The thermal catalyst can improve the traditional heterogeneous thermal catalytic process and realize ammonia synthesis at normal temperature and pressure. In the development of thermocatalytic ammonia synthesis, supported Ru-based catalysts, intermetallic electronic compounds, metal nitrides and metal hydride catalysts have been introduced, but both advantages and disadvantages coexist, and there are still problems such as low NRR reaction yield and production scale far from meeting industrial requirements. . Therefore, it is still imminent to prepare a high-efficiency NRR reaction heat catalyst with low energy consumption, mild reaction conditions and simple preparation conditions for practical production.

Contents of the invention

In view of this, the present invention provides a method for preparing a catalyst for nitrogen reduction reaction, and constructs a carbon-nitrogen-supported metal atomic-level active site catalyst (M/CN-B catalyst, wherein M is the metal element supported in the catalyst) , the use of heteroatom doping modification improves the activity of the catalyst. Under one atmospheric pressure, under the condition of relatively mild reaction temperature, nitrogen catalytic hydrogenation reduction synthesis ammonia is realized, and at the same time, the energy consumption and pollution of synthetic ammonia are greatly reduced, and green production is further realized.

The method for preparing a catalyst for nitrogen reduction reaction provided by the present invention, the catalyst is prepared by a liquid-phase one-pot method, comprising the following steps:

S1. Weigh nitrogen source, carbon source, boron source, and metal source to mix, add ethanol and deionized water, and ultrasonically mix to obtain a mixed solution;

S2. Put the mixed solution in a vacuum drying oven, first react at 80-100°C for 30-40min, then raise the temperature to 150-200°C and continue drying for 60-90min to form a fluffy and porous structure; cool to Grind after room temperature, and pass through a 20-40 mesh sieve to obtain a uniform powder;

S3. Put the powder obtained in step S2 into a covered crucible, calcinate at 350-650°C for 60-90min, raise the temperature at a rate of 4-10°C·min ^-1 , and keep it at 350-650°C for 90-90min. 150min, then naturally cooled to room temperature to form a block sample;

S4. Take out the block sample and grind it, pass it through a 40-70 mesh sieve, then transfer it to a tube furnace, and under the protection of nitrogen, heat up to 600-1000°C for calcination for 100-180min, and then naturally cool to room temperature to obtain the obtained said catalyst.

Preferably, the nitrogen source in step S1 is any one of dicyandiamide, melamine, ethylenediaminetetraacetic acid, and urea.

Preferably, the carbon source in step S1 is any one of glucose, ethylenediaminetetraacetic acid, carbonized straw, and soluble starch.

Preferably, the boron source in step S1 is any one of boric acid and borate.

Preferably, the metal source in step S1 is any one of palladium chloride and nickel nitrate hexahydrate.

Preferably, the mass ratio of the carbon source to the nitrogen source in step S1 is 1-12:5; the added amount of the boron source is 2.5-15% of the total mass of the carbon source and the nitrogen source; the added amount of the metal source is carbon 1% to 4.5% of the total mass of nitrogen source and nitrogen source.

Preferably, the volume-mass ratio of the ethanol to the nitrogen source in step S1 is 2-12 mL/g; the volume-mass ratio of the deionized water to the nitrogen source is 1-9 mL/g.

Preferably, the heating rate in step S4 is 6-12°C·min ^-1 , and the nitrogen flow rate is 80-120 mL·min ^-1 .

Another object of the present invention is to provide a catalyst for nitrogen reduction reaction prepared by the above method, the catalyst has atomic-level active sites, denoted as M/CN-B.

The catalyst for nitrogen reduction reaction prepared by the invention can be used for nitrogen reduction reaction to synthesize ammonia under mild conditions, the reaction pressure is one atmosphere, and the reaction temperature is 80°C.

Compared with the prior art, the present invention has the following beneficial effects:

The invention discloses a method for preparing a catalyst for nitrogen reduction reaction. By constructing a catalyst with M/CN-B atomic-level active sites, efficient activation of nitrogen and hydrogen molecules is realized. The nitrogen-doped carbon structure carrier formed by co-pyrolysis of carbon source and nitrogen source has a huge specific surface area and is rich in defect sites, which realizes the adsorption and activation of nitrogen molecules; the supported active phase metal atoms realize the adsorption of hydrogen Activation of molecules; the incorporation of non-metal element boron will form a relatively stable CN-B carrier at high temperature, which can promote the synthesis of ammonia under mild conditions. Thus, an atomic-scale active-site catalyst capable of synthesizing ammonia under mild conditions was prepared.

Detailed ways

The present invention provides a method for preparing an atomic-level active site catalyst for synthesizing ammonia under mild conditions. In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with examples describe. Obviously, the described embodiments are only some embodiments of the present invention. The test methods or test methods described in the following examples are conventional methods unless otherwise specified; the raw materials and auxiliary agents are obtained from conventional commercial channels or prepared by conventional methods unless otherwise specified.

Example 1

A preparation method of a catalyst for nitrogen reduction reaction, the steps are as follows:

S1. Accurately weigh 1.26g of melamine, 2.70g of glucose, 0.49g of boric acid, and 0.1634g of nickel nitrate hexahydrate into a beaker, add 10mL of ethanol and 10mL of deionized water, stir evenly, and perform ultrasonication for 30min to obtain a mixed solution;

S2. Put the mixed solution obtained in step S1 in a vacuum drying oven at 100°C for 30 minutes, then raise the oven temperature to 180°C and continue drying for 70 minutes to form a fluffy and porous structure; take out the dried sample and cool it to room temperature, and place Grind in a mortar and pass through a 40-mesh sieve to obtain a uniform powder;

S3. Put the powder obtained in step S2 into a covered crucible, put it into a muffle furnace, and calcinate at 500°C for 80min, raise the temperature at a rate of 6°C·min ^-1 , keep it at 500°C for 120min, and then Naturally cool to room temperature to form block samples;

S4. Take out the block sample in step S3, grind it evenly, pass it through a 70-mesh sieve, and then transfer it to a tube furnace. In the presence of nitrogen, heat up to 700°C for calcination for 120 minutes. The nitrogen flow rate is 100ml·min ^-1 , and the heating rate is 6 ℃·min ^-1 , after it is naturally cooled to room temperature, the catalyst Ni/CN-B is obtained, denoted as A.

Example 2

A preparation method of a catalyst for nitrogen reduction reaction, the steps are as follows:

S1. Accurately weigh 8.76g ethylenediaminetetraacetic acid (as carbon source and nitrogen source), place 0.25g sodium borate and 0.2451g nickel nitrate hexahydrate in a beaker, add 20mL ethanol and 15mL deionized water, stir evenly, and Ultrasound was carried out for 40min to obtain a mixed solution;

S2. Put the mixed solution obtained in step S1 in a vacuum drying oven at 90°C for 40 minutes to react, increase the temperature of the oven to 150°C and continue drying for 100 minutes to form a fluffy and porous structure; take out the dried sample and cool it to room temperature, place Grind in a mortar and pass through a 30-mesh sieve to obtain a uniform powder;

S3. Put the powder obtained in step S2 into a covered crucible, put it into a muffle furnace, and calcinate at 400°C for 90min, raise the temperature at a rate of 4°C·min ^-1 , keep it at 400°C for 150min, and then Naturally cool to room temperature to form block samples;

S4. Take out the block sample in step S3, grind it evenly, pass through a 50-mesh sieve, and then transfer it to a tube furnace. In the presence of nitrogen, heat up to 600°C for calcination for 180min. The nitrogen flow rate is 80ml·min ^-1 and the heating rate is 8 ℃·min ^-1 , after it is naturally cooled to room temperature, the catalyst Ni/CN-B is obtained, denoted as B.

Example 3

A preparation method of a catalyst for nitrogen reduction reaction, the steps are as follows:

S1. Accurately weigh 1.80g of urea, 4.05g of water-soluble starch, 0.47g of boric acid, and 0.06g of palladium chloride in a beaker, add 10mL of ethanol and 15mL of deionized water, stir evenly, and perform ultrasonication for 50min to obtain a mixed solution;

S2. Put the mixed solution obtained in step S1 in a vacuum drying oven at 100°C for 30 minutes, then increase the oven temperature to 190°C and continue drying for 60 minutes to form a fluffy and porous structure; take out the dried sample and cool it to room temperature, and place Grind in a mortar and pass through a 40-mesh sieve to obtain a uniform powder;

S3. Put the powder obtained in step S2 into a covered crucible, put it into a muffle furnace, and calcinate at 650°C for 60min, raise the temperature at a rate of 10°C·min ^-1 , keep it at 650°C for 90min, and then Naturally cool to room temperature to form block samples;

S4. Take out the block sample in step S3, grind it evenly, pass it through a 70-mesh sieve, and then transfer it to a tube furnace. In the presence of nitrogen, heat up to 1000°C for calcination for ¹⁰⁰ min. ℃·min ^-1 , after it is naturally cooled to room temperature, the catalyst Pd/CN-B is obtained, denoted as C.

Example 4

A preparation method of a catalyst for nitrogen reduction reaction, the steps are as follows:

S1. Accurately weigh 1.26g of dicyandiamide, 0.36g of carbonized straw, 0.24g of sodium borate, and 0.04g of palladium chloride in a beaker, add 15mL of ethanol and 10mL of deionized water, stir evenly, and perform ultrasonication for 60min to obtain a mixture solution;

S2. Put the mixed solution obtained in step S1 in a vacuum drying oven at 90°C for 40 minutes, then increase the oven temperature to 160°C and continue drying for 90 minutes to form a fluffy and porous structure; take out the dried sample and cool it to room temperature, and place Grind in a mortar and pass through a 20-mesh sieve to obtain a uniform powder;

S3. Put the powder obtained in step S2 into a covered crucible, put it into a muffle furnace, calcinate at 600°C for 80min, raise the temperature at a rate of 8°C·min ^-1 , keep it at 600°C for 110min, and then Naturally cool to room temperature to form block samples;

S4. Take out the block sample in step S3 and grind it evenly, pass it through a 40-mesh sieve, and then transfer it to a tube furnace. In the presence of nitrogen, heat up to 800°C for calcination for ^160min . ℃·min ^-1 , after it is naturally cooled to room temperature, the catalyst Pd/CN-B is obtained, denoted as D.

Comparative example 1

A preparation method of a catalyst for nitrogen reduction reaction, the steps are as follows:

S1. Accurately weigh 0.1634g of nickel nitrate hexahydrate and 0.31g of boric acid into a beaker, dissolve in 10mL of ethanol and 10mL of deionized aqueous solution, and stir evenly.

S2. Accurately weigh 1.26g of melamine and 2.70g of glucose, place them in a covered crucible, put them into a muffle furnace, and calcinate at 500°C for 80min, raise the temperature at a rate of 6°C·min ^-1 , keep it at 500°C for 2h, Afterwards, after it was naturally cooled to room temperature, the bulk sample was taken out and ground into a uniform powder.

S3. Add the ground powder obtained in step S2 into the solution obtained in S1, and stir magnetically at 70° C. for 5 hours. The reacted sample was taken out, transferred to a tube furnace for calcination, the nitrogen flow rate was 100mL·min ^-1 , the calcination temperature was 600°C for 2h, the heating rate was about 6°C·min ^-1 , kept for 2h, and allowed to cool naturally to At room temperature, the catalyst Ni/CN-B was obtained, denoted as E.

Comparative example 2

A preparation method of a catalyst for nitrogen reduction reaction, the steps are as follows:

S1. Accurately weigh 2.04g of γ-Al2O3, 2.70 of glucose, 0.31g of boric acid, and 0.1634g of nickel nitrate hexahydrate into a beaker, add 10mL of ethanol and 10mL of deionized water, stir evenly, and perform ultrasonication for 30min;

S2. Put the mixed solution obtained in step S1 in a vacuum drying oven at 100°C for 30 minutes, then raise the oven temperature to 180°C and continue drying for 70 minutes to form a fluffy and porous structure; take out the dried catalyst sample and cool it to room temperature, and place Grind into a uniform powder in a mortar and pass through a 40-mesh sieve;

S3. Put the catalyst powder obtained in step S2 into a covered crucible, put it into a muffle furnace, calcinate at 500°C for 80min, raise the temperature at a rate of 6°C·min ⁻¹ , keep it at 500°C for 120min, and then Natural cooling to room temperature;

S4. Take out the block sample and grind it evenly, pass it through a 70-mesh sieve, and then transfer it to a tube furnace to continue calcination at 700°C for 120min, with a nitrogen flow rate of 100ml·min ^-1 and a heating rate of 6°C·min ^-1 , and wait for it to cool naturally To room temperature, the catalyst Ni/γ-Al ₂ O ₃ dB was obtained, denoted as F.

Comparative example 3

A preparation method of a catalyst for nitrogen reduction reaction, the steps are as follows:

S1. Accurately weigh 1.26g of melamine, 2.70g of glucose, 0.29g of sodium chloride, and 0.1631g of cobalt nitrate hexahydrate into a beaker, add 10mL of ethanol and 10mL of deionized water, stir evenly, and perform ultrasonication for 30min.

S2. Put the mixed solution obtained in step S1 in a vacuum drying oven at 100°C for 30 minutes, then raise the oven temperature to 180°C and continue drying for 70 minutes to form a fluffy and porous structure; take out the dried catalyst sample and cool it to room temperature, and place Grind into a uniform powder in a mortar and pass through a 40-mesh sieve;

S3. Put the catalyst powder obtained in step S2 into a covered crucible, put it into a muffle furnace, calcinate at 500°C for 80min, raise the temperature at a rate of 6°C·min ⁻¹ , keep it at 500°C for 120min, and then Wait for it to cool down to room temperature naturally;

S4. Take out the block sample and grind it evenly, pass it through a 70-mesh sieve, and then transfer it to a tube furnace to continue calcination at 700°C for 120min, with a nitrogen flow rate of 100ml·min ^-1 and a heating rate of 6°C·min ^-1 , and wait for it to cool naturally To room temperature, the catalyst Co/CN-Cl is obtained, denoted as G.

Comparative example 4

A preparation method of a catalyst for nitrogen reduction reaction, the steps are as follows:

S1. Accurately weigh 1.26g of melamine, 2.70g of glucose, 0.87g of dipotassium hydrogen phosphate, and 0.2386g of ferric nitrate nonahydrate into a beaker, add 10mL of ethanol and 10mL of deionized water, stir evenly, and perform ultrasonication for 30min;

S2. Put the mixed solution obtained in step S1 in a vacuum drying oven at 100°C for 30 minutes, then raise the oven temperature to 180°C and continue drying for 70 minutes to form a fluffy and porous structure; take out the dried catalyst sample and cool it to room temperature, and place Grind into a uniform powder in a mortar and pass through a 40-mesh sieve;

S3. Put the catalyst powder obtained in step S2 into a covered crucible, put it into a muffle furnace, and calcinate at 500°C for 80min, raise the temperature at a rate of 6°C·min ^-1 , and keep it for 120min after reaching 500°C , then wait for it to cool naturally to room temperature;

S4. Take out the block sample and grind it evenly, pass it through a 70-mesh sieve, and then transfer it to a tube furnace to continue calcination at 700°C for 120min, with a nitrogen flow rate of 100ml·min ^-1 and a heating rate of 6°C·min ^-1 , and wait for it to cool naturally To room temperature, the catalyst Fe/CN-P was obtained, denoted as H.

Put the catalysts prepared in Examples 1 to 4 and Comparative Examples 1 to 4 into the reaction device for catalytic reduction to synthesize ammonia. The reaction conditions are nitrogen flow rate 10ml·min ^-1 , hydrogen flow rate 30ml·min ^-1 , reaction pressure Atmospheric pressure, the reaction temperature is 80°C, the reaction time is 10h, and the ammonia concentration is detected by Nessler's reagent spectrophotometry. The catalytic activity is shown in Table 1:

Table 1

It can be seen from Table 1 that the M/CN-B catalyst prepared by the present invention can prepare ammonia under a relatively mild condition of 80° C., and has a higher yield. The yield of the Ni/CN-B catalyst prepared in Example 1 is more impressive than that of the catalyst doped with other elements, and the yield of ammonia gas can reach 0.93.

The above is only a preferred embodiment of the present invention, it should be pointed out that for those skilled in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications are also It should be regarded as the protection scope of the present invention.

Claims (5)

1. A preparation method of a catalyst for nitrogen reduction reaction is characterized in that the catalyst is prepared by adopting a liquid phase one-pot method, and comprises the following steps:

s1, weighing a nitrogen source, a carbon source, a boron source and a metal source, mixing, adding ethanol and deionized water, and performing ultrasonic mixing to obtain a mixed solution;

the nitrogen source is any one of dicyandiamide, melamine, ethylene diamine tetraacetic acid and urea;

the carbon source is any one of glucose, ethylene diamine tetraacetic acid, carbonized straws and soluble starch;

the boron source is any one of boric acid and borate;

the metal source is any one of palladium chloride and nickel nitrate hexahydrate;

the mass ratio of the carbon source to the nitrogen source is 1 to 12:5; the addition amount of the boron source is 2.5 to 15 percent of the total mass of the carbon source and the nitrogen source; the addition amount of the metal source is 1 to 4.5 percent of the total mass of the carbon source and the nitrogen source;

s2, placing the mixed solution in a vacuum drying oven, firstly reacting at the temperature of 80-100 ℃ for 30-40min, then heating to the temperature of 150-200 ℃, and continuously drying for 60-90min to form a fluffy porous structure; cooling to room temperature, grinding, and sieving with a 20-40-mesh sieve to obtain uniform powder;

s3, filling the powder obtained in the step S2 into a covered crucible, calcining at 350-650 ℃ for 60-90 min, and raising the temperature at a rate of 4-10 ℃ min ^-1 Heating to 350-650 ℃, keeping for 90-150 min, and then naturally cooling to room temperature to form a block sample;

and S4, taking out the block sample, grinding, sieving with a 40-70 mesh sieve, transferring to a tubular furnace, heating to 600-1000 ℃ under the protection of nitrogen, calcining for 100-180 min, and naturally cooling to room temperature to obtain the catalyst.

2. The method for preparing a catalyst for nitrogen reduction according to claim 1, wherein the volume-to-mass ratio of the ethanol to the nitrogen source in step S1 is 2 to 12ml/g; the volume-mass ratio of the deionized water to the nitrogen source is 1 to 9mL/g.

3. The method for producing a catalyst for nitrogen reduction according to claim 1, wherein the rate of temperature rise in step S4 is 6 to 12 ℃ min ^-1 The nitrogen flow rate is 80 to 120 mL/min ^-1 。

4. A catalyst for nitrogen reduction reaction, characterized in that it is prepared by the method of any one of claims 1~3, said catalyst having active sites on atomic scale.

5. The use of the catalyst for nitrogen reduction according to claim 4, wherein the catalyst is used for ammonia synthesis by nitrogen reduction under mild conditions, the reaction pressure is one atmosphere, and the reaction temperature is 80 ℃.