Hydrotalcite derivative catalyst for synthesis of ammonia and method for preparing the same

Abstract

The application belongs to the field of catalyst preparation, and discloses a hydrotalcite derivative catalyst for synthesizing ammonia and a preparation method thereof.The hydrotalcite derivative takes Fe and Ni as active components, and the molar ratio of the Fe and the Ni is 1-2:1-2.The molar ratio of the Fe and the Ni is preferably 2:1.The iron-nickel hydrotalcite derivative is prepared by using a double titration method, so that the metal components in the catalyst are uniformly distributed, the specific surface area is high, and the surface oxygen vacancies are more abundant, so that the catalyst has high denitration efficiency and high ammonia gas selectivity at a lower use temperature.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of catalyst preparation, and more particularly relates to a hydrotalcite derivative catalyst for synthesizing ammonia and a preparation method thereof. BACKGROUND

[0002] Ammonia is an important basic chemical raw material in the field of chemical fertilizer production and fiber manufacturing, and its production ranks first among various chemical products. At present, the Haber-Bosch process is widely used in the industrial synthesis of ammonia, that is, nitrogen and hydrogen are combined to generate ammonia under the action of a catalyst (iron) at high temperature (500 DEG C) and high pressure (20-50 MPa). Since the nitrogen molecule is a stable substance with a triple bond energy of 941 KJ·mol -1 , it is inert and difficult to activate, so the cost is high and a large amount of energy is consumed. The energy consumption per year accounts for 1-2% of the total energy consumption in the world, so a new method for synthesizing ammonia with low energy consumption needs to be developed to save energy and reduce costs.

[0003] With the advancement of industrialization, environmental pollution has become an inevitable development problem that needs to be faced. Nitrogen oxides contained in industrial waste gas and automobile exhaust are one of the main sources of air pollution. The emission of nitrogen oxides into the air can cause acid rain, photochemical smog pollution, and damage to the ozone layer, among other adverse consequences. Among the current widely used nitrogen oxide control technologies is the reduction method denitration technology, which is considered the most beneficial technology for removing nitrogen oxides in industry today, mainly involving selective catalytic reduction technology (SCR) and non-selective catalytic reduction (NSCR) technology. The selective catalytic reduction technology (SCR) has higher denitration efficiency and less pollution, so it is the mainstream denitration method at present. Using NH3 or CO for SCR denitration is a relatively economical and effective method, but using NH3 or CO can cause NH3 and CO to escape, causing environmental pollution. Moreover, the existing catalysts have poor activity, low NO conversion rate, and low NH3 selectivity. Therefore, developing a catalyst that can convert NOx in the air into NH3 is still a challenge in the field of catalysis.

[0004] Therefore, how to provide a hydrotalcite derivative catalyst for synthesizing ammonia and a preparation method thereof is a problem that needs to be solved by those skilled in the art. SUMMARY

[0005] In order to overcome the shortcomings and deficiencies in the prior art, the present application provides a hydrotalcite derivative catalyst for synthesizing ammonia and a preparation method thereof, which generates a hydrotalcite derivative with Fe and Ni as active components, plays a catalytic role of the active components, increases the surface oxygen vacancies of the carrier, and has a simple preparation process and strong operability, thereby having high denitration efficiency and NH3 selectivity.

[0006] To achieve the above object, the present application adopts the following technical solutions:

[0007] A hydrotalcite derivative catalyst for synthesizing ammonia, the hydrotalcite derivative taking Fe and Ni as active components; the molar ratio of the Fe and Ni being 1-2:1-2.

[0008] Preferably, the molar ratio of the Fe and Ni is 2:1.

[0009] The preparation method of the above hydrotalcite derivative catalyst for synthesizing ammonia comprises the following steps:

[0010] (1) preparing a mixed solution of iron salt and nickel salt to obtain solution A;

[0011] (2) respectively preparing NaOH solution and Na2CO3 solution, titrating solution A to pH 8-10 by using double titration method, stirring the obtained solution for 10-12 h after titration, and standing for aging overnight to obtain a precipitate;

[0012] (3) filtering the precipitate with water to pH 8-10, and obtaining the catalyst through drying, primary grinding, calcination, and secondary grinding.

[0013] Preferably, the iron salt in step (1) is ferric nitrate nonahydrate, and the nickel salt is nickel nitrate hexahydrate.

[0014] Preferably, the concentration of the NaOH solution in step (2) is 0.5 mol / L, and the concentration of the Na2CO3 solution is 0.25 mol / L.

[0015] Preferably, the volume of the NaOH solution and the Na2CO3 solution used in double titration is the same.

[0016] The above technical solution has the beneficial effects that: the iron-nickel hydrotalcite derivative is prepared by using double titration method, so that the metal components in the catalyst are uniformly distributed, have a higher specific surface area, and have more abundant surface oxygen vacancies, thereby having higher denitration efficiency and higher ammonia gas selectivity at a lower use temperature.

[0017] Preferably, the standing time for aging in step (2) is 12-24 h.

[0018] Preferably, the stirring rate in step (2) is 400-600 r / min.

[0019] Preferably, the drying temperature in step (3) is 80-100℃.

[0020] Preferably, the temperature of the calcination in step (3) is 250-350℃, and the time is 2-4h.

[0021] Compared with the prior art, the water slatite derivative catalyst for synthesizing ammonia and the preparation method thereof provided by the application have the following beneficial effects:

[0022] (1) The catalyst has high denitration efficiency, and the use of double transition metals as active components reduces the preparation cost of the catalyst, and overcomes the defects of uneven dispersion of the active components of traditional supported catalysts, easy surface agglomeration, poor activity, and the like.

[0023] (2) The preparation method can make the active metal components in the catalyst be uniformly distributed, have a high specific surface area, make the catalyst surface have more active sites, and have more abundant surface oxygen vacancies, so that the catalyst has high NO conversion rate and NH3 selectivity. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only a part of the embodiments of the present application, and for those skilled in the art, other drawings can be obtained without creative labor on the basis of the provided drawings.

[0025] Figure 1 NO conversion rate of the catalyst obtained in each embodiment.

[0026] Figure 2 NH3 selectivity of the catalyst obtained in each embodiment. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0028] Embodiment 1

[0029] A preparation method of a water slatite derivative catalyst for synthesizing ammonia comprises the following steps:

[0030] (1) At normal temperature and pressure, 2.545 g of iron nitrate nonahydrate and 0.915 g of nickel nitrate hexahydrate were added into a beaker, dissolved in 100 ml of deionized water, and continuously stirred in a magnetic stirrer at a stirring rate of 500 r / min to make the solution uniform, and the stirring was continued for 1 h to obtain solution A;

[0031] (2) 2 g of sodium hydroxide and 2.65 g of sodium carbonate were weighed, and 100 ml of a 0.5 mol / L NaOH solution and 100 ml of a 0.25 mol / L Na2CO3 solution were prepared; solution A was titrated to a pH value of 8-10 by a double titration method, stirred for 12 h, and aged overnight for 24 h to obtain a precipitate;

[0032] (3) The obtained precipitate was filtered with distilled water to a pH value of 8-10, dried in a 80°C air-drying oven, to obtain a catalyst precursor, the precursor was ground once, and then calcined at 250°C in a muffle furnace for 3 h, and then ground twice to obtain a FeNi-LDO catalyst, wherein the molar ratio of Fe to Ni was 2:1.

[0033] Example 2

[0034] A preparation method of a hydrotalcite derivative catalyst for synthesizing ammonia, comprising the following steps:

[0035] (1) At normal temperature and pressure, 1.63 g of iron nitrate nonahydrate and 2.345 g of nickel nitrate hexahydrate were added into a beaker, dissolved in 100 ml of deionized water, and continuously stirred in a magnetic stirrer at a stirring rate of 500 r / min to make the solution uniform, and the stirring was continued for 1 h to obtain solution A;

[0036] (2) 2 g of sodium hydroxide and 2.65 g of sodium carbonate were weighed, and 100 ml of a 0.5 mol / L NaOH solution and 100 ml of a 0.25 mol / L Na2CO3 solution were prepared; solution A was titrated to a pH value of 8-10 by a double titration method, stirred for 12 h, and aged overnight for 24 h to obtain a precipitate;

[0037] (3) The obtained precipitate was filtered with distilled water to a pH value of 8-10, dried in a 80°C air-drying oven, to obtain a catalyst precursor, the precursor was ground once, and then calcined at 250°C in a muffle furnace for 3 h, and then ground twice to obtain a FeNi-LDO catalyst, wherein the molar ratio of Fe to Ni was 2:1.

[0038] Performance evaluation of catalyst for denitration and ammonia synthesis

[0039] The catalysts prepared in Examples 1 and 2 were used for denitration synthesis of ammonia reaction, and the denitration synthesis of ammonia performance test was carried out in a fixed bed reactor. The reactor was a stainless steel pipe with an inner diameter of 10.0 mm. Before the experiment, quartz sand and quartz wool were put into the reaction tube to ensure the contact between the powder catalyst and the thermocouple. The simulated flue gas was composed of 350 ppm of NO, 2000 ppm of H2, and N2 as the balance gas, and the space velocity was 30000 mL·g -1 ·h -1 The reaction device was programmed to rise from room temperature to 500℃, with each temperature point being 50℃. The detection device was a Fourier infrared, and the denitration synthesis of ammonia performance at different temperatures was detected at each temperature point. The results are shown in Figure 1 and Figure 2 The NO conversion rate and NH3 selectivity were calculated by the following formula:

[0040] NO conversion(%) = ([NO]in - [NO]out) / [NO]in x 100%

[0041] NH3 selectivity(%) = ([NH3]out) / [NO]in x 100%

[0042] From Figure 1 and Figure 2 it can be seen that the catalyst with a molar ratio of iron to nickel of 2:1 showed a higher NH3 selectivity (87%) at 350℃. The catalyst with a molar ratio of iron to nickel of 1:2 had the highest NH3 selectivity of 60% at 350℃, which was relatively low.

[0043] In the specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the scheme disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple, and the related parts can be referred to the method part.

[0044] The above description of the disclosed embodiments enables a person skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. Use of a hydrotalcite derivative catalyst in a dehydrogenation synthesis of ammonia reaction, characterized in that, The hydrotalcite derivative takes Fe and Ni as active components; the molar ratio of Fe and Ni is 2:1; The preparation method of the hydrotalcite derivative catalyst comprises the following steps: (1) preparing a mixed solution of iron salt and nickel salt to obtain solution A; (2) respectively preparing NaOH solution and Na2CO3 solution, titrating solution A to pH 8-10 by using double titration method, stirring the obtained solution for 10-12 h after titration, and standing for aging overnight to obtain a precipitate; (3) filtering the precipitate with water to pH 8-10, and obtaining the catalyst through drying, primary grinding, calcination and secondary grinding.

2. Use according to claim 1, characterized in that, The iron salt in step (1) is ferric nitrate nonahydrate, and the nickel salt is nickel nitrate hexahydrate.

3. Use according to claim 1, characterized in that, The concentration of the NaOH solution in step (2) is 0.5 mol / L, and the concentration of the Na2CO3 solution is 0.25 mol / L.

4. Use according to claim 3, characterized in that, The volume of the NaOH solution and the Na2CO3 solution used in double titration is the same.

5. The use according to claim 1, characterized in that, The standing time for aging in step (2) is 12-24 h.

6. Use according to claim 1, characterized in that, The stirring rate in step (2) is 400-600 r / min.

7. Use according to claim 1, characterized in that, The drying temperature in step (3) is 80-100℃.

8. The use according to claim 1, characterized in that, The calcination temperature in step (3) is 250-350℃, and the time is 2-4 h.

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