CN116116412A - Preparation method of catalyst for synthesizing ammonia at low temperature and low pressure - Google Patents

Abstract

The invention provides a preparation method of a catalyst for synthesizing ammonia at low temperature and low pressure, which comprises the following steps: adding lanthanum nitrate and ferric nitrate into deionized water, ultrasonically dissolving, then adding citric acid, completely dissolving, and then adding ammonia water solution to keep the pH value at about 7-8; stirring and heating with water bath at 70-80deg.C until gel is formed; drying the gel product in an oven, and then annealing the gel product in a muffle furnace to obtain a LaFeO3 carrier; finally, a certain amount of RuCl3 solution is used for dipping, and then the dipped RuCl3 solution is placed in a tube furnace for reduction in H2/Ar atmosphere to obtain a catalyst finished product, wherein the catalyst is Ru/LaFeO3 catalyst, and compared with the prior art, the preparation method has the following beneficial effects: compared with the traditional Fe-based catalyst, the required reaction condition is mild, the reaction rate of the synthetic ammonia is excellent, and the thermal stability is good.

Description

Preparation method of catalyst for synthesizing ammonia at low temperature and low pressure

Technical Field

The invention belongs to the technical field of preparation of synthetic ammonia catalyst materials, relates to a catalyst synthesis method for loading ruthenium on a perovskite type rare earth oxide carrier and application of low-temperature and low-pressure synthetic ammonia, and in particular relates to a preparation method for a low-temperature and low-pressure synthetic ammonia catalyst.

Background

Ammonia (NH) ₃ ) Is an important raw material for producing chemical fertilizers, dyes, medical products and the like in agriculture and industry, and is also an important potential hydrogen energy carrier.

The Haber-Bosch (Haber-Bosch) process, which is currently used by the traditional ammonia synthesis industry, still has some unavoidable problems: (1) Limited by thermodynamic and nitrogen hydrogenationThe conversion efficiency is lower, about 10% -15%; (2) The energy consumption is high, and 1% -3% of the total energy consumption in the world is consumed for synthesizing ammonia every year; (3) The H2 required for synthesis of ammonia is mainly derived from natural gas and steam cracking reforming, and consumes 3% -5% of the total amount of natural gas worldwide each year with emission of a large amount of CO2 (1 ton of ammonia is produced to about 1.87 tons of CO) ₂ ). Therefore, the artificial ammonia synthesis technology for developing low temperature and low pressure without using fossil resources and without greenhouse gas emission has great research significance.

If using NH ₃ The hydrogen storage carrier is prepared by electrolyzing water by using renewable energy power as a hydrogen source, and separating nitrogen from air as a nitrogen source, so that the synthesis of green ammonia and the safe storage and transportation of hydrogen can be synchronously realized by using renewable energy clean and high-efficiency.

In addition, the current pressure type water electrolysis hydrogen production system requires output pressure less than or equal to 5.0MPa, the general output pressure is 1.6-3.2MPa, and the temperature of the electrolyzed H2 after deep dehydration and deoxidation is about 300-400 ℃. Therefore, to realize complementary fusion of renewable energy power and synthetic ammonia technology, development of synthetic ammonia technology (reaction conditions: 300-400 ℃ C., 1.6-3.2 MPa) under relatively mild conditions matched with renewable energy power electrolysis hydrogen production system is needed, and the existing industrial synthetic ammonia catalyst facing fossil energy is difficult to meet the requirements under the relatively mild conditions, so that the development of a novel efficient synthetic ammonia catalyst is designed and becomes a key point of penetrating a renewable energy-ammonia-hydrogen circulation route.

Disclosure of Invention

Aiming at the defects existing in the prior art, the invention aims to provide a preparation method of a catalyst applied to low-temperature and low-pressure synthesis of ammonia, which solves the problems in the prior art.

The invention is realized by the following technical scheme: the preparation method of the catalyst for synthesizing ammonia at low temperature and low pressure comprises the following steps:

adding lanthanum nitrate and ferric nitrate into deionized water, ultrasonically dissolving, then adding citric acid, completely dissolving, and then adding ammonia water solution to keep the pH value at about 7-8;

stirring and heating with water bath at 70-80deg.C until gel is formed;

drying the gel product in an oven, and then annealing the gel product in a muffle furnace to obtain a LaFeO3 carrier;

finally, a certain amount of RuCl3 solution is used for dipping, and then the dipped material is placed in a tubular furnace for reduction in H2/Ar atmosphere to obtain a catalyst finished product, wherein the catalyst is Ru/LaFeO3 catalyst.

After the technical scheme is adopted, the invention has the beneficial effects that: compared with a carrier without Ru or La, the preparation method of the invention prepares Ru doped LaFeO ₃ Has excellent ammonia synthesizing performance under mild condition and high heat stability. The invention can obtain Ru doped LaFeO with different compositions through simple impregnating solutions with different Ru concentrations and different annealing temperatures ₃ The catalyst has higher thermal stability and certain industrial application value.

Drawings

In order to more clearly illustrate the embodiments of the invention or the technical solutions of the prior art, the drawings which are used in the description of the embodiments or the prior art will be briefly described, it being obvious that the drawings in the description below are only some embodiments of the invention, and that other drawings can be obtained according to these drawings without inventive faculty for a person skilled in the art.

FIG. 1 is a 5% Ru/LaFeO of example 2 prepared ₃ -scanning electron microscope image (SEM) of 800.

FIG. 2 is a 5% Ru/LaFeO of prepared example 2 ₃ -transmission electron microscope image (TEM) of 800.

FIG. 3 is 5% Ru/LaFeO in example 2 ₃ -800 XRD spectrum.

FIG. 4 is a graph of ammonia synthesis rates at various temperatures for example 2

FIG. 5 is a graph of catalytic activity versus time.

Figure 6 is a graph of overall catalyst activity versus control for the example.

Detailed Description

The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

The invention provides a technical scheme that: the preparation method of the catalyst for synthesizing ammonia at low temperature and low pressure comprises the following steps:

adding lanthanum nitrate and ferric nitrate into deionized water, ultrasonically dissolving, then adding citric acid, completely dissolving, and then adding ammonia water solution to keep the pH value at about 7-8;

stirring and heating with water bath at 70-80deg.C until gel is formed;

drying the gel product in an oven, and annealing in a muffle furnace to obtain LaFeO ₃ A carrier;

finally, a certain amount of RuCl is used ₃ Dipping the solution, and then placing the dipped solution in a tube furnace in H ₂ Reducing in Ar atmosphere to obtain the final catalyst, wherein the catalyst is Ru/LaFeO ₃ A catalyst.

Example 1

Dissolving 0.01mol of lanthanum nitrate, 0.01mol of ferric nitrate and 0.03mol of citric acid in 30mL of deionized water, stirring to form a uniform solution, and adding ammonia water to adjust the pH to 8;

heating and stirring the solution at 80 ℃ until gel is generated, and then drying the solution at 120 ℃ for 12 hours to obtain a yellowish green powdery sample;

annealing the obtained sample in a muffle furnace at 900 ℃ for 6 hours to obtain LaFeO ₃ A carrier;

1g of the above carrier was taken, the obtained carrier was completely dissolved with deionized water, and 500. Mu.L of 10 mg/. Mu.L of RuCl was added ₃ Soaking in the solution, evaporating in water bath, and drying;

then the impregnated carrier is placed in a tube furnace for H ₂ Reducing at 450 ℃ in Ar atmosphere to obtain 5 percent Ru/LaFeO ₃ -900 catalyst.

Example 2

Dissolving 0.01mol of lanthanum nitrate, 0.01mol of ferric nitrate and 0.03mol of citric acid in 30mL of deionized water, stirring to form a uniform solution, and adding ammonia water to adjust the pH to 8;

heating and stirring the solution at 80 ℃ until gel is generated, and then drying the solution at 120 ℃ for 12 hours to obtain a yellowish green powdery sample;

annealing the obtained sample in a muffle furnace at 800 ℃ for 6 hours to obtain LaFeO ₃ A carrier;

1g of the above carrier was taken, the obtained carrier was completely dissolved with deionized water, and 500. Mu.L of 10 mg/. Mu.L of RuCl was added ₃ Soaking in the solution, evaporating in water bath, and drying;

then the impregnated carrier is placed in a tube furnace for H ₂ Reducing at 450 ℃ in Ar atmosphere to obtain 5 percent Ru/LaFeO ₃ -800 catalyst.

Example 3

Dissolving 0.01mol of lanthanum nitrate, 0.01mol of ferric nitrate and 0.03mol of citric acid in 30mL of deionized water, stirring to form a uniform solution, and adding ammonia water to adjust the pH to 8;

heating and stirring the solution at 80 ℃ until gel is generated, and then drying the solution at 120 ℃ for 12 hours to obtain a yellowish green powdery sample;

annealing the obtained sample in a muffle furnace at 700 ℃ for 6 hours to obtain LaFeO ₃ A carrier;

1g of the above carrier was taken, the obtained carrier was completely dissolved with deionized water, and 500. Mu.L of 10 mg/. Mu.L of RuCl was added ₃ Soaking in the solution, evaporating in water bath, and drying;

then the impregnated carrier is placed in a tube furnace for H ₂ Reducing at 450 ℃ in Ar atmosphere to obtain 5 percent Ru/LaFeO ₃ -700 catalyst.

Example 4

Dissolving 0.01mol of lanthanum nitrate, 0.01mol of ferric nitrate and 0.03mol of citric acid in 30mL of deionized water, stirring to form a uniform solution, and adding ammonia water to adjust the pH to 8;

heating and stirring the solution at 80 ℃ until gel is generated, and then drying the solution at 120 ℃ for 12 hours to obtain a yellowish green powdery sample;

annealing the obtained sample in a muffle furnace at 800 ℃ for 6 hours to obtain LaFeO ₃ A carrier;

1g of the above carrier was taken, the obtained carrier was completely dissolved with deionized water, and 100. Mu.L of 10 mg/. Mu.L of RuCl was added ₃ Soaking in the solution, evaporating in water bath, and drying;

then the impregnated carrier is placed in a tube furnace for H ₂ Reducing at 450 ℃ in Ar atmosphere to obtain 5 percent Ru/LaFeO ₃ -800 catalyst.

Control group 1

0.01mol of lanthanum nitrate, 0.01mol of ferric nitrate and 0.03mol of citric acid are dissolved in 30mL of deionized water, and after stirring to form a uniform solution, a certain amount of ammonia water is added to adjust the pH to 8.

Further, the solution was heated and stirred at 80 ℃ until a gel was formed. Followed by drying at 120℃for 12 hours, to give a yellowish green powdery sample.

Further, annealing the obtained sample in a muffle furnace at 800 ℃ for 6 hours to obtain LaFeO ₃ A carrier.

Control group 2

0.02mol of ferric nitrate and 0.03mol of citric acid are dissolved in 30mL of deionized water, and after stirring to form a uniform solution, a certain amount of ammonia water is added to adjust the pH to 8.

Further, the solution was heated and stirred at 80 ℃ until a gel was formed. Subsequently dried at 120℃for 12 hours, a brownish red powdery sample was obtained.

Further, the obtained sample was annealed at 800℃for 6 hours in a muffle furnace to obtain a FeO carrier.

Further, 1g of the above carrier was taken, the obtained carrier was completely dissolved with deionized water, and 500. Mu.L of 10 mg/. Mu.L of RuCl was added thereto ₃ The solution was immersed, then evaporated to dryness in a water bath and dried.

And then placing the impregnated carrier in a tube furnace for reduction at 450 ℃ in an H2/Ar atmosphere to obtain the 5% Ru/FeO catalyst.

The invention is further described below with reference to the drawings and the specific embodiments, but the scope of the invention is not limited to these.

Evaluation of catalyst Performance

The catalysts prepared in examples 1-4 and comparative examples 1-2 were used in an amount of 0.5g each, respectively, with a mass space velocity of 20000ml ^-1 g ^-1 h ^-1 The ammonia synthesis conversion was measured on a fixed bed reactor, and the reaction gas composition was: 75% H ₂ -25％N ₂ And (3) mixing gas. The conversion rate of the catalyst to ammonia synthesis was determined at a pressure of 3MPa and 400 ℃

FIG. 1 is a photograph taken on a Hitachi S4800-type Scanning Electron Microscope (SEM) operated at a high pressure of 5kV to obtain 5% Ru/LaFeO in the preparation example 2 ₃ -800 scanning electron microscope image. The porous sheet structure can be seen in fig. 1.

FIG. 2 shows the result of obtaining 5% Ru/LaFeO in example 2 prepared using a JEMRM 200F Transmission Electron Microscope (TEM) operating at a high pressure of 200kV ₃ -800 transmission electron microscope image. As can be seen from fig. 2, the ruthenium element supported was uniformly dispersed throughout the lamellar structure.

FIG. 3 is a graph of the radiation at 40kV and 40mA using Nifiltered monochromatic Cu Ka

Scanning of 5% Ru/LaFeO in example 2 by X-ray diffractometer analysis (XRD, philips X' pert PRO) ₃ -800 XRD spectrum. The spectrogram shows that each characteristic peak of the catalyst is equal to LaFeO ₃ The characteristic peaks in the standard card are in one-to-one correspondence. Indicating successful synthesis of the base material. The content of Ru element is low, so no distinct characteristic peak is detected.

The prepared samples were tested for ammonia synthesis catalytic activity for accurate evaluation. The ammonia synthesis activity of all prepared catalysts was tested in a ZK2021-JN101 thermocatalytic synthesis ammonia catalyst evaluation device. Catalyst loading was 0.5g; volume ratio H2/n2=3: 1, a step of; mass space velocity (WHSV) of 20000mLg ^-1 h ^-1 . After the programming temperature was raised to the set temperature, activation was performed for two hours. Reuse of thinH ₂ SO ₄ Solution (0.02 mol L) ^-1 ) And taking a sample every one hour after absorbing the produced ammonia gas, and measuring the absorbance of the solution after absorbing for different time by using an indoxyl blue method to calculate the ammonia production rate.

Example 2 the ammonia synthesis rate at 3MPa at different temperatures is shown in fig. 4, and it can be seen from fig. 4 that as the temperature increases, the ammonia production rate increases. It can be seen from fig. 5 that the catalytic activity was more stable with time.

As can be seen from a comparison of FIG. 6, the activity of the catalyst is 5% Ru/LaFeO ₃ -800>5％Ru/LaFeO ₃ -900>5％Ru/LaFeO ₃ -700>1％Ru/LaFeO ₃ -800>5％Ru/FeO>LaFeO ₃ The Ru dipping is favorable for improving the activity of the synthetic ammonia, and the addition of the rare earth element La is obvious in activity improvement. In addition, different annealing temperatures have an effect on the activity of the catalyst.

The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, alternatives, and improvements that fall within the spirit and scope of the invention.

Claims (5)

1. The preparation method of the catalyst for synthesizing ammonia at low temperature and low pressure is characterized by comprising the following steps:

adding lanthanum nitrate and ferric nitrate into deionized water, ultrasonically dissolving, then adding citric acid, completely dissolving, and then adding ammonia water solution to keep the pH value at about 7-8;

stirring and heating with water bath at 70-80deg.C until gel is formed;

drying the gel product in an oven, and annealing in a muffle furnace to obtain LaFeO ₃ A carrier;

finally, a certain amount of RuCl is used ₃ Dipping the solution, and then placing the dipped solution in a tube furnace in H ₂ Reducing in Ar atmosphere to obtain the final catalyst, wherein the catalyst is Ru/LaFeO ₃ A catalyst.

2. The method for preparing the catalyst for synthesizing ammonia at low temperature and low pressure according to claim 1, which is characterized in that: dissolving 0.01mol of lanthanum nitrate, 0.01mol of ferric nitrate and 0.03mol of citric acid in 30mL of deionized water, stirring to form a uniform solution, and adding ammonia water to adjust the pH to 8;

heating and stirring the solution at 80 ℃ until gel is generated, and then drying the solution at 120 ℃ for 12 hours to obtain a yellowish green powdery sample;

annealing the obtained sample in a muffle furnace at 900 ℃ for 6 hours to obtain LaFeO ₃ A carrier;

1g of the above carrier was taken, the obtained carrier was completely dissolved with deionized water, and 500. Mu.L of 10 mg/. Mu.L of RuCl was added ₃ Soaking in the solution, evaporating in water bath, and drying;

then the impregnated carrier is placed in a tube furnace for H ₂ Reducing at 450 ℃ in Ar atmosphere to obtain 5 percent Ru/LaFeO ₃ -900 catalyst.

3. The method for preparing the catalyst for synthesizing ammonia at low temperature and low pressure according to claim 1, which is characterized in that: dissolving 0.01mol of lanthanum nitrate, 0.01mol of ferric nitrate and 0.03mol of citric acid in 30mL of deionized water, stirring to form a uniform solution, and adding ammonia water to adjust the pH to 8;

heating and stirring the solution at 80 ℃ until gel is generated, and then drying the solution at 120 ℃ for 12 hours to obtain a yellowish green powdery sample;

annealing the obtained sample in a muffle furnace at 800 ℃ for 6 hours to obtain LaFeO ₃ A carrier;

1g of the above carrier was taken, the obtained carrier was completely dissolved with deionized water, and 500. Mu.L of 10 mg/. Mu.L of RuCl was added ₃ Soaking in the solution, evaporating in water bath, and drying;

then the impregnated carrier is placed in a tube furnace for H ₂ Reducing at 450 ℃ in Ar atmosphere to obtain 5 percent Ru/LaFeO ₃ -800 catalyst.

4. The method for preparing the catalyst for synthesizing ammonia at low temperature and low pressure according to claim 1, which is characterized in that: dissolving 0.01mol of lanthanum nitrate, 0.01mol of ferric nitrate and 0.03mol of citric acid in 30mL of deionized water, stirring to form a uniform solution, and adding ammonia water to adjust the pH to 8;

heating and stirring the solution at 80 ℃ until gel is generated, and then drying the solution at 120 ℃ for 12 hours to obtain a yellowish green powdery sample;

annealing the obtained sample in a muffle furnace at 700 ℃ for 6 hours to obtain LaFeO ₃ A carrier;

1g of the above carrier was taken, the obtained carrier was completely dissolved with deionized water, and 500. Mu.L of 10 mg/. Mu.L of RuCl was added ₃ Soaking in the solution, evaporating in water bath, and drying;

then the impregnated carrier is placed in a tube furnace for H ₂ Reducing at 450 ℃ in Ar atmosphere to obtain 5 percent Ru/LaFeO ₃ -700 catalyst.

5. The method for preparing the catalyst for synthesizing ammonia at low temperature and low pressure according to claim 1, which is characterized in that: dissolving 0.01mol of lanthanum nitrate, 0.01mol of ferric nitrate and 0.03mol of citric acid in 30mL of deionized water, stirring to form a uniform solution, and adding ammonia water to adjust the pH to 8;

heating and stirring the solution at 80 ℃ until gel is generated, and then drying the solution at 120 ℃ for 12 hours to obtain a yellowish green powdery sample;

annealing the obtained sample in a muffle furnace at 800 ℃ for 6 hours to obtain LaFeO ₃ A carrier;

1g of the above carrier was taken, the obtained carrier was completely dissolved with deionized water, and 100. Mu.L of 10 mg/. Mu.L of RuCl was added ₃ Soaking in the solution, evaporating in water bath, and drying;

then the impregnated carrier is placed in a tube furnace for H ₂ Reducing at 450 ℃ in Ar atmosphere to obtain 5 percent Ru/LaFeO ₃ -800 catalyst.

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