Application of a photo-thermal catalyst in photo-thermal synergistic catalytic reaction of nitrogen and hydrogen to synthesize ammonia

Abstract

The application discloses application of a photo-thermal catalyst in photo-thermal synergic catalysis of nitrogen and hydrogen to synthesize ammonia. The photo-thermal catalyst comprises a carbon-based carrier, metal ruthenium nanoparticles loaded on the carbon-based carrier and an electronic assistant containing potassium. The photo-thermal catalyst is applied to photo-thermal synergic catalysis to synthesize ammonia, has excellent photo-excitation characteristics and photo-thermal conversion efficiency, and can reach high temperature required by the reaction by using pure sunlight. Compared with a pure thermal catalysis process under the same temperature, the introduction of light greatly improves ammonia production rate of the reaction and running stability of the catalyst, and effectively inhibits hydrogen poisoning of the ruthenium nanoparticles.

Description

Technical Field

[0001] This invention relates to the field of ammonia synthesis technology. More specifically, it relates to the application of a photothermal catalyst in the photothermal synergistic catalytic reaction of nitrogen and hydrogen to synthesize ammonia. Background Technology

[0002] NH3, as a chemical raw material, has numerous applications in human production and daily life, including the synthesis of fertilizers, polymers, and pharmaceuticals. Currently, industrial nitrogen fixation is achieved through the classic Haber-Bosch process, which involves stringent reaction conditions (15–25 MPa, 350–550°C) and accounts for nearly 2% of global energy consumption and almost 3% of global CO2 emissions annually. With the increasing depletion of fossil fuels and the increasingly severe environmental situation, developing energy-efficient and environmentally friendly nitrogen fixation processes has become particularly important.

[0003] Solar energy, as a clean energy source, boasts advantages such as abundant supply and sustainability. Utilizing photocatalysis to convert solar energy into chemical energy is considered one of the best ways to solve future energy problems. Therefore, developing solar-driven catalytic nitrogen fixation reaction technology is of great significance. Among these technologies, photothermal synergistic catalytic ammonia synthesis utilizes a photothermal catalyst under sunlight to achieve the reaction temperature required for efficient ammonia synthesis, without requiring any other external energy input. This approach is environmentally friendly and energy-saving. Furthermore, due to the excitation effect of light on the photothermal catalyst, photothermal synergistic catalysis can achieve significantly better activity than pure thermal catalytic ammonia synthesis under the same temperature conditions. Therefore, photothermal synergistic catalytic ammonia synthesis technology shows great application potential, while designing efficient and stable photothermal catalysts is one of the main challenges of this technology. Summary of the Invention

[0004] The purpose of this invention is to provide a photothermal catalyst that can efficiently and stably catalyze the reaction of nitrogen and hydrogen to synthesize ammonia.

[0005] To achieve the objective of this invention, this invention provides an application of a photothermal catalyst in the photothermal synergistic catalytic reaction of nitrogen and hydrogen to synthesize ammonia.

[0006] The photothermal catalyst comprises a carbon-based support, ruthenium nanoparticles supported on the carbon-based support, and a potassium-containing electronic additive.

[0007] It should be noted that in the aforementioned photothermal catalyst, the ruthenium nanoparticles serve as the active center for ammonia synthesis. The hot electron injection of the ruthenium nanoparticles significantly enhances both the nitrogen activation rate and the hydrogenation rate of intermediate species during the ammonia synthesis reaction. The electron promoters grown around the ruthenium nanoparticles further promote the activation of nitrogen molecules by ruthenium, thereby improving the intrinsic activity of the photothermal catalyst. The carbon-based support has a large specific surface area, allowing for uniform loading of ruthenium nanoparticles while synergistically enhancing the photothermal conversion capability of the catalyst.

[0008] Furthermore, in the photothermal catalyst, the content of ruthenium nanoparticles is 1-10 wt.%, and the molar ratio of potassium to ruthenium is 1-6:1.

[0009] Furthermore, the potassium-containing electronic additive is a potassium salt or potassium hydroxide.

[0010] Furthermore, the carbon-based support is activated carbon or carbon black.

[0011] Furthermore, the particle size of the ruthenium nanoparticles is 1–5 nm.

[0012] Furthermore, the preparation method of the supported ruthenium nanoparticle photothermal catalyst includes the following steps:

[0013] Furthermore, the carbon-based support was impregnated with an ethanol solution of ruthenium precursor and then reduced at high temperature to obtain a carbon-based catalyst loaded with ruthenium nanoparticles.

[0014] A carbon-based catalyst loaded with ruthenium nanoparticles was impregnated in a potassium precursor solution and then calcined.

[0015] In the photothermal catalyst prepared by this invention, ruthenium is uniformly loaded on the surface of carbon in the form of nanoparticles with a size that can be controlled to be around 2 nm. This ensures a large proportion of ruthenium atoms are exposed and provides a large number of B5 active sites.

[0016] Furthermore, the potassium precursor is a potassium salt such as potassium hydroxide or potassium carbonate.

[0017] Furthermore, the high-temperature reduction is carried out in an atmosphere containing hydrogen at 400℃~600℃ for 3-5 hours.

[0018] Furthermore, the calcination is carried out in an inert gas atmosphere at 300℃~500℃ for 2~5 hours.

[0019] Furthermore, the application includes the following steps:

[0020] The supported ruthenium nanoparticle photothermal catalyst was placed in a light-transmitting container, and a mixture of nitrogen and hydrogen gas was introduced and irradiated at 25°C to 400°C.

[0021] Furthermore, in the above steps, the light intensity of the illumination is 0–10 W / cm². -2 ;

[0022] The light source is any one or more of xenon lamps, mercury lamps, LED lamps, and natural light.

[0023] The gas flow rate of the mixed gas is 5–100 mL / min; the pressure in the container is 0.1–0.5 MPa.

[0024] The light-transmitting container is preferably the photothermal synergistic gas-solid phase catalytic reaction device disclosed in patent CN108404819B. This device can be equipped with multiple light sources to achieve precise temperature control over a wide range. Reaction conditions such as light intensity, temperature, and pressure can be adjusted independently, and product collection and detection are efficient and fast.

[0025] It should also be noted that, unless otherwise specified, any range described in this invention includes the endpoints, any values ​​between the endpoints, and any subranges formed by the endpoints or any values ​​between the endpoints. Unless otherwise specified, the preparation methods in this invention are conventional methods, and the raw materials used can be obtained from publicly available commercial sources or prepared according to existing technology.

[0026] The beneficial effects of this invention are as follows:

[0027] The photothermal catalyst provided by this invention has the advantages of high spectral utilization and photothermal conversion efficiency, as well as good stability. When this photothermal catalyst is applied to the photothermal synergistic catalytic synthesis of ammonia, it exhibits excellent photoexcitation characteristics and photothermal conversion efficiency, achieving the required high temperature for the reaction using only pure sunlight. Compared to a purely thermal catalytic process at the same temperature, the introduction of light not only significantly improves the ammonia production rate and catalyst stability but also suppresses hydrogen poisoning of ruthenium nanoparticles.

[0028] The photothermal catalyst provided by this invention is simple to synthesize, has good stability, is easy to transport and store, and can also recover the precious metal ruthenium after use. Attached Figure Description

[0029] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0030] Figure 1 The X-ray powder diffraction pattern of K-Ru / C prepared in Example 1 is shown.

[0031] Figure 2The electron microscope scan image of K-Ru / C prepared in Example 1 is shown; wherein, a shows a scanning electron microscope image, b shows a transmission electron microscope image, c shows a high-angle annular dark-field scanning transmission electron microscope image, and d shows an elemental surface distribution map.

[0032] Figure 3 The diffuse reflectance absorption spectra of solid powder Ru / Al2O3 prepared in Comparative Example 1, K-Ru / C and Al2O3 prepared in Example 1 are shown.

[0033] Figure 4 A schematic cross-sectional view of the photothermal catalytic reactor in the reaction apparatus used in Test Example 1 is shown.

[0034] Figure 5 The diagram shows the photothermal catalytic ammonia synthesis rate of K-Ru / C prepared in Example 1 under different light intensities.

[0035] Figure 6 The diagram shows the photothermal and purely thermal catalytic ammonia production activities of the K-Ru / C prepared in Example 1 at different reaction temperatures.

[0036] Figure 7 The diagram shows the calculated activation energies of the K-Ru / C prepared in Example 1 at different reaction temperatures for photothermal catalysis and pure thermal catalysis.

[0037] Figure 8 The diagram shows the ammonia production activity of K-Ru / C prepared in Example 1 under different wavelengths of light.

[0038] Figure 9 The diagram shows a comparison of the reaction orders of K-Ru / C prepared in Example 1 under photothermal catalysis and pure thermal catalysis conditions for nitrogen (left) and hydrogen (right).

[0039] Figure 10 The results of stability tests of K-Ru / C prepared in Example 1 under photothermal catalysis and pure thermocatalysis conditions are shown.

[0040] Figure 11 The experiment of photothermal catalytic reaction of K-Ru / C prepared in Example 1 under pure sunlight is shown; wherein, a shows a photograph of the reaction device, b shows the change of catalyst temperature over time, and c shows the change of ammonia production performance over time. Detailed Implementation

[0041] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments and accompanying drawings, further explains the invention. Similar components in the drawings are indicated by the same reference numerals. Those skilled in the art should understand that the specific description below is illustrative rather than restrictive and should not be construed as limiting the scope of protection of the present invention.

[0042] Example 1

[0043] The photothermal catalyst was prepared by impregnation, comprising the following steps:

[0044] 52 mg RuCl3·3H2O was dissolved in 20 mL of ethanol, and 500 mg of carbon black was added to the solution. The slurry was then ultrasonically dispersed for 1 hour and stirred for 12 hours. Afterward, the resulting mixture was stirred in an oil bath at 70 °C for 4 hours to evaporate the solvent, and then thoroughly dried in an oven at 60 °C to remove the solvent. The prepared sample was reduced in an H2 / Ar (v:v = 1:9) stream at 500 °C for 4 hours to obtain an intermediate product powder. 44.8 mg KOH was dissolved in 20 mL of ethanol, and 500 mg of the above intermediate product powder was dispersed in the solution. The slurry was then ultrasonically dispersed for 1 hour and stirred for 3 hours. Afterward, the obtained mixture was stirred in an oil bath at 70 °C to completely remove the solvent. The prepared sample was calcined in an Ar stream at 400 °C for 2 hours to obtain the desired supported ruthenium nanoparticle photothermal catalyst (denoted as K-Ru / C). The Ru loading was 3.5 wt.%, and the molar ratio of K to Ru was 4:1.

[0045] Figure 1 The X-ray powder diffraction pattern of K-Ru / C is shown, where the peak signals are attributed to the lattice diffraction of metallic ruthenium nanoparticles and graphitized carbon.

[0046] Figure 2 The results show that ruthenium metal particles in K-Ru / C are uniformly loaded on the carbon surface, and the particle size of the ruthenium nanoparticles is 1-3 nm.

[0047] Figure 3 The results show that K-Ru / C exhibits full-spectrum absorption in the ultraviolet-visible-near-infrared region.

[0048] Comparative Example 1

[0049] The Al2O3-supported ruthenium nanoparticle photothermal catalyst was prepared by impregnation, comprising the following steps:

[0050] 52 mg of RuCl3·3H2O was dissolved in 20 mL of ethanol, and 500 mg of nano-Al2O3 powder was added to the solution. The slurry was then ultrasonically dispersed for 1 hour and stirred for 12 hours. Afterward, the resulting mixture was stirred in an oil bath at 70 °C for 4 hours to evaporate the solvent, and then dried in an oven at 60 °C to remove the solvent. The prepared sample was reduced in an H2 / Ar (v:v = 1:9) gas stream at 500 °C for 4 hours to obtain the desired Al2O3-supported ruthenium photothermal catalyst (Ru / Al2O3).

[0051] The absorbance of K-Ru / C, Ru / Al2O3, and pure Al2O3 in the ultraviolet-visible-near-infrared region was compared, and the results are shown in [Figure number missing]. Figure 3 .

[0052] Figure 3 The results show that the difference in absorbance between Ru / Al2O3 and pure Al2O3 in the ultraviolet-visible-near-infrared region can be considered as the light absorption of ruthenium nanoparticles, indicating that ruthenium nanoparticles have significant light absorption properties in the ultraviolet-visible-near-infrared region.

[0053] Comparative Example 2

[0054] The catalyst for preparing Fe-supported particles by impregnation includes the following steps:

[0055] The catalyst preparation steps are the same as in Example 1, except that RuCl3 is replaced with FeCl3 and the reduction temperature is changed from 500℃ to 700℃ to obtain the catalyst K-Fe / C, wherein the Fe loading is 8.5 wt.% and the molar ratio of K to Fe is 4:1.

[0056] Comparative Example 3

[0057] The catalyst for preparing Co-supported particles by impregnation includes the following steps:

[0058] The catalyst preparation steps are the same as in Example 1, except that RuCl3 is replaced with CoCl2 and the reduction temperature is changed from 500℃ to 700℃ to obtain the catalyst K-Co / C, wherein the Co loading is 5.6 wt.% and the molar ratio of K to Co is 4:1.

[0059] Comparative Example 4

[0060] The catalyst for preparing Ru-supported particles by impregnation includes the following steps:

[0061] 52 mg RuCl3·3H2O was dissolved in 20 mL of ethanol, and 500 mg of carbon black was added to the solution. The slurry was then ultrasonically dispersed for 1 hour and stirred for 12 hours. Afterward, the resulting mixture was stirred in an oil bath at 70 °C for 4 hours to evaporate the solvent, and then thoroughly dried in an oven at 60 °C to remove the solvent. The prepared sample was reduced in an H2 / Ar (v:v = 1:9) stream at 500 °C for 4 hours to obtain the desired supported ruthenium nanoparticle catalyst (denoted as Ru / C), with a Ru loading of approximately 4 wt.%.

[0062] Comparative Example 5

[0063] The preparation of TiO2-supported catalysts by impregnation includes the following steps:

[0064] The catalyst preparation steps are the same as in Example 1, except that carbon black is replaced with the same mass of commercial TiO2 to obtain the catalyst K-Ru / TiO2, wherein the Ru loading is 3.5 wt.% and the molar ratio of K to Ru is 4:1.

[0065] Test Example 1

[0066] The catalysts K-Ru / C, K-Fe / C, K-Co / C, Ru / C, and K-Ru / TiO2 were applied to photothermal catalytic ammonia synthesis, and the testing methods included the following steps:

[0067] The photothermal co-catalyzed ammonia synthesis reaction is carried out in a special mobile phase photothermal catalytic reactor, such as... Figure 4 As shown. 50 mg of catalyst powder was spread in the reactor to form an area of ​​6 cm². 2 A thin layer with a thickness of 1 mm was applied. The reactor was sealed. The catalyst temperature was detected by thermocouples and corrected by estimating the temperature using the equilibrium concentration of the reaction. Temperature was controlled by electric heating or condensation. First, an N2 gas stream was introduced for 30 minutes to purge the air from the apparatus, then an N2 / H2 mixture (v:v = 1:3) was introduced. A 300W xenon lamp (PLS-SXE300DUV) was used as the light source, and the apparent temperature was controlled at 350℃ using electric heating or water cooling. The light intensity was adjusted by changing the light source power. The reaction pressure was constant at 0.1 MPa, and the gas flow rate was 30 mL / min. The gas produced after the reaction was passed into a 0.05 mol / L dilute sulfuric acid solution. The solution was sampled every 20 minutes, and the ammonia content was determined using Nessler's reagent method to estimate the ammonia production rate (the test results for catalyst K-Ru / C are shown in [reference needed]). Figure 5 ).

[0068] Test results: at 350℃ and a light intensity of 5.0 W / cm² -2 Under these conditions, the ammonia production efficiency of the K-Fe / C catalyst is less than 10 μmol g. -1 h -1 It exhibits almost no ammonia synthesis performance; the ammonia production efficiency of the K-Co / C catalyst is approximately 350 μmol g. -1 h -1 The photothermal catalytic ammonia synthesis rate of K-Ru / C was 2169 μmol g. -1 h -1 The above results indicate that Ru nanoparticles exhibit higher photothermal catalytic activity for ammonia synthesis compared to Co and Fe nanoparticles; the ammonia production efficiency of the Ru / C catalyst is 100–200 μmol g. -1 h -1This demonstrates the crucial role of potassium as a promoter in enhancing the intrinsic activity of ammonia synthesis catalysts; the ammonia production efficiency of the K-Ru / TiO2 catalyst is 1000-1500 μmol g. -1 h -1 The activity is lower than that of K-Ru / C catalysts, which demonstrates the important role of carbon black support in improving the activity of ammonia synthesis catalysts.

[0069] Figure 5 The display shows that, under a constant apparent temperature of 350℃, as the light intensity reaches 0 W / cm², -2 Up to 5W cm -2 Within a certain range, the photothermal catalytic ammonia synthesis rate of K-Ru / C increased from 319 μmol g / L. -1 h -1 Up to 2169 μmol g -1 h -1 The gradual increase is mainly due to photothermal electron injection, indicating that K-Ru / C has good photothermal synergistic catalytic performance in ammonia synthesis.

[0070] Test Example 2

[0071] The test target was K-Ru / C, and the test procedure was the same as in Test Example 1, except that no external light source was provided during the reaction process. Instead, pure electric heating was used to control the reaction temperature at 350℃ for performance testing (see results). Figure 5 ).

[0072] Figure 5 The results showed that, under purely thermal catalysis, the ammonia synthesis rate of K-Ru / C was 319 μmol g. -1 h -1 .

[0073] Test Example 3

[0074] The test target was K-Ru / C, and the test procedure was the same as in Test Example 1, the only difference being that the light intensity was controlled at 5.0 W / cm². -2 The reaction temperature was kept constant at six points between 200 and 400 °C using electric heating or water cooling. The ammonia production rate of K-Ru / C under photothermal catalysis with and without light was compared (see results). Figure 6 The activation energies of photothermal catalysis and pure thermal catalysis were compared (see results). Figure 7 ).

[0075] Figure 6 Display: at a constant 5.0W cm -2 Under light intensity, the photothermal catalytic ammonia synthesis rate of K-Ru / C conforms to the Arrhenius curve with respect to reaction temperature, and it still exhibits significant ammonia synthesis activity at 230℃.

[0076] Figure 7 Display: at a constant 5.0W cm -2 Under light intensity, the activation energy of the photothermal catalytic synthesis of ammonia by K-Ru / C is 54.9 kJ / mol, while under purely thermal catalytic conditions, the activation energy is 126 kJ / mol.

[0077] Test Example 4

[0078] The test target was K-Ru / C. The test procedure was the same as in Test Example 1, except that the wavelength of the light source was changed. First, the total internal reflection lens of the xenon lamp was replaced with a UV-Vis lens, switching the light source to UV-Vis (UV-Vis 200~800nm), and the photothermal catalytic ammonia synthesis rate of K-Ru / C was tested. Then, a visible light filter was added to the UV-Vis lens, changing the light source to visible light (Vis 400~800nm), and the photothermal catalytic ammonia synthesis rate of K-Ru / C was tested again. Finally, a visible light filter was added to the xenon lamp, changing the light source to infrared light (IR>800nm), and the photothermal catalytic ammonia synthesis rate of K-Ru / C was tested again. The results are shown in [Figure 1]. Figure 8 .

[0079] Figure 8 The results show that, under a constant apparent temperature of 350℃, the photothermal catalytic ammonia synthesis rate of K-Ru / C increases with the increase of ultraviolet or visible light intensity, but there is basically no significant change with the increase of infrared light intensity. This indicates that the photo-enhanced K-Ru / C catalytic ammonia synthesis performance is related to both ultraviolet and visible light, but the phenomenon that the K-Ru / C catalytic ammonia synthesis performance increases with light intensity is not due to infrared light excitation.

[0080] Test Example 5

[0081] The test target was K-Ru / C, and the test procedure was the same as in Test Example 1, except that the temperature was controlled at 350℃ using electric heating or water cooling, and the light intensity was fixed at 5.0 W / cm². -2 First, the hydrogen content was kept constant at 50%, and the nitrogen content in the feed gas was changed. Then, the nitrogen content was kept constant at 30%, and the hydrogen content in the feed gas was changed. The test results are shown below. Figure 9 .

[0082] Test Example 6

[0083] The test target was K-Ru / C, and the test procedure was the same as in Test Example 5, except that no light was applied. The test results are shown below. Figure 9 .

[0084] Figure 9The results show that the introduction of light lowers the nitrogen reaction order, indicating an increase in the nitrogen dissociation rate. The introduction of light also causes the hydrogen reaction order to change directly from negative to positive, meaning that hydrogen poisoning is suppressed.

[0085] Test Example 7

[0086] The target of the test was K-Ru / C, and the test procedure was the same as in Test Example 1. The only difference was that the reaction time and sampling interval were extended under pure thermocatalysis and photothermal catalysis conditions with different light intensities to test the catalyst's operational stability (see results). Figure 10 ).

[0087] Figure 10 The results showed that K-Ru / C did not exhibit performance degradation after 1000 hours of operation at 350℃ under different light intensities. However, significant catalyst activity degradation occurred after 150 hours of operation under pure thermal catalysis at 350℃, indicating that the introduction of light greatly improved the catalyst's operational stability.

[0088] Test Example 8

[0089] The test target was K-Ru / C, and the test procedure was the same as in Test Example 1, except that the light source was replaced with natural sunlight focused by a Fresnel lens (see results). Figure 11 ).

[0090] Figure 11 The results show that the catalyst can achieve highly efficient photothermal catalytic synthesis of ammonia under pure solar energy, with a temperature reaching approximately 380℃ and an ammonia production rate of 3.52 mmol g / L. -1 h -1 .

[0091] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. The application of a photothermal catalyst in the photothermal synergistic catalytic reaction of nitrogen and hydrogen to synthesize ammonia, characterized in that, The photothermal catalyst includes a carbon-based support; ruthenium nanoparticles supported on the carbon-based support; and a potassium-containing electronic additive. In the photothermal catalyst, the content of ruthenium nanoparticles is 1~10 wt.%, and the molar ratio of potassium to ruthenium is 1~6:1; The application includes the following steps: The photothermal catalyst was placed in a light-transmitting container, and a mixture of nitrogen and hydrogen gas was introduced. The mixture was then irradiated at 200°C to 400°C; the light intensity was 0 to 10 W / cm². -2 ; The flow rate of the mixed gas is 5~100 mL / min; the pressure in the container is 0.1~0.5 MPa.

2. The application according to claim 1, characterized in that, The carbon-based carrier is activated carbon or carbon black.

3. The application according to claim 1, characterized in that, The ruthenium nanoparticles have a particle size of 1~5 nm.

4. The application according to claim 1, characterized in that, The preparation method of the photothermal catalyst includes the following steps: A carbon-based catalyst loaded with ruthenium nanoparticles was obtained by impregnating a carbon-based support with an ethanol solution of a ruthenium precursor and reducing it at high temperature. The carbon-based catalyst supported on ruthenium nanoparticles is impregnated in a potassium precursor solution and then calcined to obtain the catalyst.

5. The application according to claim 4, characterized in that, The precursor of potassium is potassium hydroxide or potassium carbonate.

6. The application according to claim 4, characterized in that, The high-temperature reduction is carried out in a hydrogen-containing atmosphere at 400℃~600℃ for 3~5 hours.

7. The application according to claim 4, characterized in that, The calcination is carried out in an inert gas atmosphere at 300 ℃ to 500 ℃ for 2 to 5 hours.

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