Catalyst for direct synthesis of ammonia from nitrogen and water using non-thermal plasma

Abstract

The application relates to the technical field of ammonia synthesis, and discloses a catalyst applied to the direct synthesis of ammonia from nitrogen and water by non-thermal plasma. TiO2 with oxygen-enriched vacancies is prepared, and the TiO2 with oxygen vacancies is applied to the direct synthesis of ammonia by catalyzing N2 and H2O in dielectric barrier discharge non-thermal plasma for the first time, N2 and water vapor are simultaneously fed, high yield and excellent selectivity of ammonia synthesis are realized at low temperature and normal pressure, and no CO2 is generated in the process. In addition, the catalyst can always maintain high activity and NH3 selectivity in the process of multiple cycle experiments.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of ammonia synthesis, and particularly relates to a catalyst for synthesizing ammonia directly from nitrogen and water in a non-thermal plasma. BACKGROUND

[0002] Ammonia is widely used in the fields of chemical fertilizer, medicine, polymer and fine chemical industry as an important active nitrogen source. In addition, ammonia is considered as a potential liquid fuel and hydrogen storage molecule in the future due to its high energy density and convenience in storage and transportation. At present, the traditional industrial synthesis of ammonia is under harsh conditions, consumes huge energy and produces a large amount of CO2; the synthesis of ammonia under common mild conditions (such as electrocatalysis and photocatalysis) is inefficient; and the selectivity and yield of ammonia synthesized by non-catalytic non-thermal plasma with H2O as the hydrogen source are low. Therefore, it is necessary to introduce a catalyst into the non-thermal plasma system for synthesizing ammonia from N2 and H2O to improve the selectivity and yield of ammonia.

[0003] In industry, ammonia is synthesized by the H-B method The synthesis of ammonia requires high temperature and high pressure (350-550 DEG C, 150-250 atm), which consumes about 2% of the global energy and emits more than 300 million tons of CO2 per year, which is not conducive to the development of economy and environment.

[0004] In the synthesis of ammonia under mild conditions with H2O as the hydrogen source, N2 is difficult to be activated in the electrocatalysis and photocatalysis synthesis of ammonia due to the extremely low solubility of N2 in H2O and the high bond energy of N≡N, so the efficiency of synthesizing ammonia is very low; and the selectivity and yield of ammonia synthesized by non-catalytic plasma are very low due to the high energy density in the plasma system. SUMMARY

[0005] In view of the above problems in the prior art, the purpose of the present application is to provide a catalyst for synthesizing ammonia directly from nitrogen and water in a non-thermal plasma.

[0006] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0007] A catalyst for synthesizing ammonia directly from nitrogen and water in a non-thermal plasma, the preparation method of the catalyst comprising the following steps:

[0008] 1) drop HF solution into tetrabutyl titanate, and stir until the mixture becomes a gel;

[0009] 2) transfer the gel obtained in step 1) to a hydrothermal autoclave, and perform crystallization;

[0010] 3) after cooling, obtain a powder by centrifugation, and then wash the powder;

[0011] 4) stirring the product obtained after washing in step 3) in NaOH solution to remove residual fluoride ions;

[0012] 5) centrifuging the mixture after removing fluoride ions in step 4), washing and drying to obtain TiO2 raw powder, denoted as TiO2-p.

[0013] 6) after purifying the quartz pipeline with a reducing atmosphere, putting the obtained TiO2 raw powder into the quartz pipeline,

[0014] 7) heat treating at 200-400℃ to obtain TiO2 rich in oxygen vacancies.

[0015] Preferably, in step 1), the volume ratio of the HF solution to tetrabutyl titanate is 3:25.

[0016] Preferably, the concentration of the HF solution is 40wt%.

[0017] Preferably, in step 2), the crystallization temperature is 180℃ and the crystallization time is 36 hours.

[0018] Preferably, in step 3), the powder is washed several times with deionized water and C2H5OH respectively.

[0019] Preferably, in step 4), the concentration of the NaOH solution is 0.1M, stirring is carried out at room temperature, and the stirring time is 8 hours.

[0020] Preferably, in step 5), after washing several times with deionized water and C2H5OH, drying at 80℃ overnight to obtain TiO2 raw powder.

[0021] Preferably, in step 6), the reducing atmosphere refers to a mixed gas of Ar and hydrogen, wherein the content of hydrogen is 5vol.%.

[0022] Further, the obtained TiO2 rich in oxygen vacancies is formed into tablets to obtain particles with a diameter of 0.425-0.850mm.

[0023] Further, the formed particle catalyst is filled into the plasma discharge area of a non-thermal plasma reactor, the reaction pressure is normal pressure, the reaction temperature is about 50℃, the discharge input power is 20W, the flow rate of N2 passing through a flask containing H2O is 100mL / min, the mixed gas of N2 and H2O enters the reaction system, and the synthesis of ammonia is carried out.

[0024] Compared with the prior art, the present application has the following beneficial effects:

[0025] The application prepares TiO2 with oxygen vacancy, and for the first time, TiO2 with oxygen vacancy is applied to the direct synthesis of ammonia from N2 and H2O by dielectric barrier discharge non-thermal plasma catalysis. N2 and water vapor are fed simultaneously, and high yield and excellent selectivity of ammonia synthesis are realized at low temperature and normal pressure, and no CO2 is produced in the process. In addition, the catalyst can always maintain high activity and NH3 selectivity during multiple cycle experiments. BRIEF DESCRIPTION OF DRAWINGS

[0026] Other features, objects, and advantages of the application will become more apparent from the following detailed description of non-limiting embodiments, when read in conjunction with the accompanying drawings:

[0027] Figure 1 XRD results of TiO2-p, TiO2-200, TiO2-300 and TiO2-400;

[0028] Figure 2 EPR spectra of TiO2 and TiO2 after reduction at different temperatures;

[0029] Figure 3 NH3 synthesis rate and selectivity of different catalysts;

[0030] Figure 4 Cycle test of NH3 synthesis rate and selectivity of TiO2-300;

[0031] Figure 5 Schematic diagram of the application scheme. DETAILED DESCRIPTION

[0032] The application will be described in detail below with specific examples. The following examples will help those skilled in the art to further understand the application, but do not limit the application in any form. It should be noted that for those skilled in the art, without departing from the concept of the application, a number of modifications and improvements can be made. These are within the scope of the application.

[0033] Example 1

[0034] 3 mL of HF solution (40 wt%) was added dropwise to 25 mL of tetrabutyl titanate, and the mixture was stirred for 2 h until it became a gel. The gel was then transferred to a hydrothermal autoclave and crystallized at 180 °C for 36 h. After cooling, the product was centrifuged at high speed to obtain powder, which was then washed several times with deionized water and C2H5OH. The product was then stirred in 0.1 M NaOH solution at room temperature for 8 h to remove residual fluoride ions. After centrifugation, the mixture was washed several times with deionized water and C2H5OH and dried overnight at 80 °C to obtain TiO2 raw powder, denoted as TiO2-p. The TiO2 raw powder was placed in a quartz tube and purified with a reducing atmosphere (a mixture of Ar and hydrogen, with a hydrogen content of 5 vol.%) for 2 h. The tube was then heat-treated at 200 °C, 300 °C, and 400 °C for 2 h respectively to obtain oxygen-vacancy-rich TiO2, named TiO2-200, TiO2-300, and TiO2-400. The powder X-ray diffraction (XRD) results of each catalyst were obtained by testing on a Rigaku Smart Lab diffractometer (Japan). Figure 1 The electron paramagnetic resonance (EPR) spectrum of the catalyst was obtained on a Bruker E500-9.5 / 12 spectrometer at room temperature using X-band microwaves and a scanning magnetic field. Figure 2 .

[0035] like Figure 1 As shown, the main diffraction peaks of the prepared TiO2 are located at 25.36°, 37.85°, 48.14°, 53.97°, and 55.18°, which correspond to the (101), (004), (200), (105), and (211) crystal planes of the anatase phase, respectively (JCPDS No. 89-4921). The diffraction peaks of TiO2 reduced at different temperatures are consistent with those of the unreduced TiO2, and no other impurity peaks appear, indicating that the reduction process has no significant effect on the crystal structure of the catalyst.

[0036] Oxygen vacancies will produce a distinct simple harmonic vibration peak at g = 2.003 in the EPR spectrum. For example... Figure 2 As shown, the unreduced TiO2-p catalyst did not exhibit a significant peak at g = 2.003, indicating the absence of oxygen vacancies in TiO2-p. However, the reduced catalysts all showed characteristic peaks of oxygen vacancies, with TiO2-300 exhibiting the largest peak, indicating that TiO2-300 possesses the highest number of oxygen vacancies compared to other catalysts.

[0037] Example 2

[0038] The catalyst obtained in Example 1 was pressed into tablets to obtain particles with a size of 0.425–0.850 mm, and 0.5 g of the shaped catalyst was filled into the plasma discharge region of the non-thermal plasma reactor, such as…Figure 5 As shown in the figure, the non-thermal plasma reactor is a quartz coaxial reactor, the reaction pressure is normal pressure, the reaction temperature is about 50 DEG C, the discharge input power P in = 20 W, and the flow rate of N2 is 100 mL / min. After the N2 passes through the flask containing H2O, the mixed gas of N2 and H2O enters the reaction system.

[0039] The oscilloscope is used to detect the electrical signal during the operation of the plasma, and the actual discharge output power P out = 14 W is calculated by the Lissajous method. V(t) is the voltage measured by the oscilloscope, q(t) is the charge measured by the oscilloscope in C, f is the frequency in kHz, and S is the area under a period curve.

[0040] H2O is used to absorb the products (NH3, NO3 - and NO2 - ) after the reaction, and the concentrations of NH4 + , NO3 - and NO2 - in the products are measured by colorimetry on an ultraviolet spectrophotometer, and the selective calculation formula of NH3 is .

[0041] The evaluation results are as follows:

[0042] As Figure 3 shown, compared with only plasma, the synthesis rate and selectivity of NH3 are obviously improved regardless of the catalyst used. Among them, the selectivity and yield of NH3 on TiO2-300 are the highest, which are 92.8% and 47.2 μmol g cat -1 h -1 .

[0043] As Figure 4 can be seen, after 10 cycles of experiments, the synthesis rate and selectivity of NH3 only appear slight fluctuations, which indicates that the TiO2-300 catalyst has high stability in the reaction process and does not appear to be deactivated.

[0044] The specific embodiments of the present application are described above. It should be understood that the present application is not limited to the above specific embodiments, and those skilled in the art can make various modifications or modifications within the scope of the claims, which does not affect the essential content of the present application.

Claims

1. Use of a catalyst for the direct synthesis of ammonia from nitrogen and water in a non-thermal plasma catalysis, characterized in that, The preparation method of the catalyst comprises the following steps: 1) drop HF solution into butyl titanate, stir until the mixture becomes gel; 2) transfer the gel obtained in step 1) into a hydrothermal autoclave for crystallization; 3) after cooling, obtain powder by centrifugation, then wash; 4) stir the product obtained after washing in step 3) in NaOH solution to remove residual fluoride ions; 5) centrifuge the mixture after removing fluoride ions in step 4), then wash and dry to obtain TiO2 raw powder, denoted as TiO2-p; 6) after purifying the quartz pipeline with a reducing atmosphere, put the obtained TiO2 raw powder into the quartz pipeline; 7) heat treatment at 200-400 ℃ to obtain TiO2 rich in oxygen vacancies; obtain particles with a diameter of 0.425-0.850 mm by tabletting the obtained TiO2 rich in oxygen vacancies, fill the shaped particle catalyst into the plasma discharge area of a non-thermal plasma reactor, the reaction pressure is normal pressure, the reaction temperature is 50 ℃, the discharge input power is 20 W, the flow rate of N2 passing through the flask containing H2O is 100 mL / min, then the mixed gas of N2 and H2O enters the reaction system, and the synthesis of ammonia is carried out.

2. Use of the catalyst according to claim 1 for the direct synthesis of ammonia from nitrogen and water in a non-thermal plasma catalysis, characterized in that, In step 1), the volume ratio of the HF solution to butyl titanate is 3:

25.

3. Use of the catalyst according to claim 1 for the direct synthesis of ammonia from nitrogen and water in a non-thermal plasma catalysis, characterized in that, The concentration of the HF solution is 40 wt%.

4. Use of the catalyst according to claim 1 for the direct synthesis of ammonia from nitrogen and water in a non-thermal plasma catalysis, characterized in that, In step 2), the crystallization temperature is 180 ℃, and the crystallization time is 36 hours.

5. Use of the catalyst according to claim 1 for the direct synthesis of ammonia from nitrogen and water in a non-thermal plasma catalysis, characterized in that, In step 3), the powder is washed with deionized water and C2H5OH several times, respectively.

6. Use of the catalyst according to claim 1 for the direct synthesis of ammonia from nitrogen and water in a non-thermal plasma catalysis, characterized in that, In step 4), the concentration of NaOH solution is 0.1 M, stirring is carried out at room temperature, and the stirring time is 8 hours.

7. Use of the catalyst according to claim 1 for the direct synthesis of ammonia from nitrogen and water in a non-thermal plasma catalysis, characterized in that, In step 5), after washing with deionized water and C2H5OH several times, dry overnight at 80 ℃ to obtain TiO2 raw powder.

8. Use of the catalyst according to claim 1 for the direct synthesis of ammonia from nitrogen and water in a non-thermal plasma catalysis, characterized in that, In step 6), the reducing atmosphere refers to a mixed gas of Ar gas and hydrogen, wherein the content of hydrogen is 5 vol.%.

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