Use of a single-atom catalyst in conversion of primary to secondary hydrogen

Abstract

The application discloses application of a single-atom catalyst in ortho-para hydrogen conversion. The application comprises the following steps: contacting raw material containing ortho-hydrogen with a single-atom catalyst, and reacting to obtain a product containing para-hydrogen; the single-atom catalyst comprises an iron oxide carrier and a single-atom active component loaded on the surface of the iron oxide carrier; the single-atom active component is selected from at least one of Pt, Pd and Ru; the catalyst preparation method provided by the application is accurate, controllable, reliable and highly repeatable. The catalyst provided by the application has high metal dispersion and high utilization rate. The catalyst provided by the application is used in ortho-para hydrogen conversion reaction, and the ortho-hydrogen conversion efficiency reaches 90% under the conditions of 78K, 3000cc (H2) / min / cc (catalyst) and 1atm, which is superior to that of a commercial iron oxide hydrate catalyst.

Description

Technical Field

[0001] The present application relates to the application of a single-atom catalyst in the conversion of normal and para-hydrogen, belonging to the field of energy and chemical industry. Background Art

[0002] As an important form of energy, hydrogen, with its cleanliness and high calorific value, is poised to play a pivotal role on the global energy stage. Hydrogen production, storage, transportation, and application technologies have also become a focus of considerable attention. The utilization, storage, and transportation of hydrogen energy are inseparable from liquid hydrogen, which is also a crucial strategic resource for the development of the aerospace and hydrogen energy industries. Therefore, the large-scale application of liquid hydrogen is a key indicator of a country's scientific and technological strength.

[0003] The hydrogen molecule is a simple molecule composed of two hydrogen atoms. However, due to the possible different nuclear spin directions of the two hydrogen atoms, it exists in two states: orthohydrogen and parahydrogen. Orthohydrogen has the same nuclear spin direction, while parahydrogen has the opposite nuclear spin direction. The equilibrium composition of orthohydrogen and parahydrogen is directly related to temperature, with the concentration ratio of orthohydrogen to parahydrogen in equilibrium varying at different temperatures. At room temperature, the equilibrium hydrogen is a mixture of 75% orthohydrogen and 25% parahydrogen, known as normal hydrogen or standard hydrogen. As the temperature decreases, the percentage of parahydrogen in equilibrium increases. For example, at the standard boiling point of liquid nitrogen, the equilibrium concentration of parahydrogen is approximately 51%, while at the standard boiling point of liquid hydrogen, the equilibrium concentration can reach 99.8%. The spontaneous conversion of hydrogen to the orthohydrogen and parahydrogen states is very slow. Therefore, during the low-temperature liquefaction of hydrogen, if a rapid orthohydrogen-parahydrogen catalytic conversion is not performed, the liquid hydrogen produced will be composed of normal hydrogen. In this case, liquid normal hydrogen will spontaneously undergo the orthohydrogen-parahydrogen conversion. Because the normal-para hydrogen conversion is an exothermic process (706 kJ / kg), the heat released exceeds the latent heat of vaporization (447 kJ / kg). For this reason, even if liquid normal hydrogen is stored in an ideally insulated container, it will still vaporize. Therefore, in order to obtain equilibrium hydrogen at the standard boiling point, that is, liquid hydrogen with a para hydrogen concentration of 99.8%, rapid normal-para hydrogen catalytic conversion must be carried out during the hydrogen liquefaction process. Summary of the Invention

[0004] The present application aims to provide a highly dispersed hydrous iron oxide-supported single-atom catalyst for the para-hydrogen conversion reaction. This catalyst exhibits high activity and stability, as well as high controllability and reproducibility. To achieve this objective, the present invention provides a technical solution comprising a catalyst prepared by coprecipitation or impregnation using a high-surface-area hydrous iron oxide as a support and one or more Group VIII or Group IB metals as active components.

[0005] According to one aspect of the present application, there is provided an application of a single-atom catalyst in normal-parahydrogen conversion, comprising the following steps:

[0006] The raw material containing orthohydrogen is contacted with a single-atom catalyst to react and obtain a product containing parahydrogen;

[0007] The single-atom catalyst exhibits excellent activity and stability.

[0008] The single-atom catalyst comprises an iron oxide carrier and a single-atom active component supported on the surface of the iron oxide carrier;

[0009] The single-atom active component is selected from at least one of Pt, Pd, and Ru;

[0010] In the single-atom catalyst, the content of the single-atom active component is 0.01-5 wt %;

[0011] Optionally, in the single-atom catalyst, the content of the single-atom active component is any value of 0.01 wt%, 0.05 wt%, 0.1 wt%, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, or a range value between any two of them.

[0012] The specific surface area of ​​the iron oxide carrier is 50-500 m 2 / g;

[0013] Optionally, the specific surface area of ​​the iron oxide carrier is 50 m 2 / g, 100 m 2 / g, 150 m 2 / g, 200 m 2 / g, 250 m 2 / g, 300 m 2 / g, 350 m 2 / g, 400 m 2 / g, 450 m 2 / g, 500 m 2 Any value in / g or any range between them.

[0014] The pore size of the iron oxide carrier is 1.5 to 25 nm;

[0015] Optionally, the pore size of the iron oxide carrier is any value among 1.5 nm, 2 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, or a range between any two values.

[0016] The pore volume of the iron oxide carrier is 0.15~0.35cm 2 / g.

[0017] Optionally, the pore volume of the iron oxide carrier is 0.15 cm 2 / g, 0.2 cm 2 / g, 0.25 cm 2 / g, 0.3cm 2 / g, 0.35 cm 2 Any value in / g or any range between them.

[0018] In the single-atom catalyst, the content of the single-atom active component is 0.01-2 wt %.

[0019] The particle size of the single-atom catalyst is 20-100 meshes.

[0020] The iron oxide carrier contains bound water.

[0021] The single-atom catalyst is prepared by the following steps:

[0022] An aqueous solution containing an active component precursor and an iron salt is mixed with an aqueous solution containing a precipitant, stirred, allowed to stand, dried, and calcined to obtain the single-atom catalyst.

[0023] The active component precursor is selected from at least one of the nitrates and halides of the Pt element, the nitrates and halides of the Pd element, and the nitrates and halides of the Ru element;

[0024] The iron salt is selected from at least one of ferric nitrate, ferric chloride, and ferric sulfate;

[0025] In the aqueous solution containing the active component precursor and the iron salt,

[0026] The content of the active component precursor is 0.1~50mg / ml;

[0027] The content of the iron salt is 0.1~1 mol / L;

[0028] The precipitant is selected from at least one of sodium carbonate, ammonium carbonate, potassium carbonate, lithium carbonate, sodium hydroxide, potassium hydroxide, and ammonia water;

[0029] In the aqueous solution containing the precipitant, the content of the precipitant is 0.1-2 mol / L;

[0030] The volume ratio of the aqueous solution containing the active component precursor and the iron salt to the aqueous solution containing the precipitant is 0.001-1000.

[0031] The mixing is to dropwise add the aqueous solution containing the active component precursor and the iron salt into the aqueous solution containing the precipitant.

[0032] The stirring temperature is 50-100°C;

[0033] The stirring time is 2 to 20 hours;

[0034] The standing time is 1 to 10 hours.

[0035] After standing, the solid was separated and filtered with water.

[0036] The drying temperature is 25-120°C;

[0037] The drying time is 1 to 24 hours.

[0038] The calcination temperature is 150-600°C;

[0039] The roasting time is 1 to 24 hours.

[0040] The above steps are only one method for preparing the single-atom catalyst described in this application. The single-atom catalyst described in this application can also be obtained by using other preparation methods such as impregnation method or formed carrier precipitation method.

[0041] The reaction is carried out in a low-temperature fixed-bed reactor;

[0042] The pressure of the raw material is 0.1~0.5Mpa;

[0043] The reaction temperature is 21~273K;

[0044] The space velocity of the reaction is 300-3000 cc (H2) / min / cc (catalyst).

[0045] The single-atom catalyst is reduced by hydrogen;

[0046] The temperature of the hydrogen reduction is 50-200°C;

[0047] The hydrogen reduction time is 10 to 120 minutes.

[0048] The beneficial effects of this application include:

[0049] The catalyst preparation method provided in this application is precise and controllable, reliable and highly reproducible.

[0050] The catalyst provided by this application has highly dispersed metals and high utilization rate.

[0051] The catalyst provided in this application is used for the ortho-parahydrogen conversion reaction, and its ortho-hydrogen conversion efficiency reaches 90% under the conditions of 78K, 3000cc(H2) / min / cc(catalyst), and 1atm, which is better than the commercial hydrated iron oxide catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 This is the STEM image of the catalyst of Preparation Example 1, with a scale of 2 nm.

[0053] Figure 2 This is the CO-DRIFTS diagram of the catalyst of Preparation Example 1.

[0054] Figure 3 This is the STEM image of the catalyst of Preparation Example 3, with a scale of 10 nm. DETAILED DESCRIPTION

[0055] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0056] Unless otherwise specified, the raw materials in the examples of this application were purchased through commercial channels.

[0057] Preparation Example 1

[0058] Dissolve 5.0g of anhydrous sodium carbonate in 100mL of deionized water. The resulting solution is designated Solution A. Place 20mL of a 1M ferric nitrate solution in a beaker, add 0.15mL of a 15.0mgPt / mL H2PtCl6 solution, and stir thoroughly. The resulting solution is designated Solution B. Stir Solution A at room temperature, and then add Solution B dropwise to Solution A at a rate of 1mL / min. Continue stirring at the same temperature for 3 hours, then allow to stand for another 3 hours. Filter with 500mL of deionized water, oven dry at 60°C for 5 hours, and then calcine in a muffle furnace at 400°C for 5 hours to obtain a 0.2% Pt / Fe2O3 catalyst.

[0059] Figure 1 This is the STEM image of the catalyst prepared in Example 1, with a scale of 2 nm; Figure 2 This is the CO-DRIFTS diagram of the catalyst prepared in Preparation Example 1. As can be seen from the figure, the metal active components are dispersed on the support surface in the form of single atoms and have a high dispersion.

[0060] Preparation Example 2

[0061] Take 5.0g of anhydrous sodium carbonate and dissolve it in 100mL of deionized water. The resulting solution is recorded as solution A. Take 20ml of 1M ferric nitrate solution in a beaker, add 1.0mL of 15.0mgPt / mL H2PtCl6 solution, stir evenly, and the resulting solution is recorded as solution B. Stir solution A at room temperature, and add solution B dropwise to solution A at a rate of 1mL / min. After the addition is completed, continue stirring at the same temperature for 3 hours, and then let it stand for 3 hours. After filtering with 500mL of deionized water, dry in an oven at 60℃ for 5h, take out and calcine in a muffle furnace at 400℃ for 5h to obtain a 1.0% Pt / Fe2O3 catalyst.

[0062] Preparation Example 3

[0063] Dissolve 5.0g of anhydrous sodium carbonate in 100mL of deionized water. The resulting solution is designated Solution A. Add 20mL of 1M ferric nitrate solution to a beaker, add 1.5mL of a 15.0mgPt / mL H2PtCl6 solution, and stir thoroughly. The resulting solution is designated Solution B. Stir Solution A at room temperature, and then add Solution B dropwise to Solution A at a rate of 1mL / min. Continue stirring at the same temperature for 3 hours, then let it stand for another 3 hours. Filter with 500mL of deionized water, oven dry at 60°C for 5 hours, and then calcine in a muffle furnace at 400°C for 5 hours to obtain a 2.0% Pt / Fe2O3 catalyst.

[0064] Figure 3 This is a STEM image of the catalyst prepared in Example 3, with a scale of 10 nm. It can be seen from the image that the metal active components are dispersed on the support surface in the form of nanoparticles.

[0065] Preparation Example 4

[0066] Dissolve 5.0 g of anhydrous sodium carbonate in 100 mL of deionized water. The resulting solution is designated Solution A. Add 20 mL of 1 M ferric nitrate solution to a beaker, add a 10.0 mg / mL RuCl₃ solution, and stir thoroughly. The resulting solution is designated Solution B. Stir Solution A at room temperature, and then add Solution B dropwise at a rate of 1 mL / min. Continue stirring at the same temperature for 3 hours, then allow to stand for another 3 hours. Filter with 500 mL of deionized water and dry in an oven at 60°C for 5 hours to obtain the Ru / Fe₂O₃ catalyst.

[0067] Preparation Example 5

[0068] Take 5.0g of anhydrous sodium carbonate and dissolve it in 100mL of deionized water. The resulting solution is recorded as solution A. Take 20mL of 1M ferric nitrate solution in a beaker, add a certain amount of 12.0mgPd / mLH2PdCl4 solution, stir evenly, and the resulting solution is recorded as solution B. Stir solution A at room temperature, and add solution B dropwise to solution A at a rate of 1mL / min. After the addition is completed, continue stirring at the same temperature for 3 hours, and then let it stand for 3 hours. After filtering with 500mL of deionized water, dry in an oven at 60℃ for 5h to obtain Pd / Fe2O3 catalyst.

[0069] Example 1

[0070] Weigh 0.1g of the catalyst into a fixed-bed reactor tube and reduce it with 10% H2 / He at 10°C / min to 200°C for 30 minutes, followed by a He purge for 30 minutes. The reactor tube is cooled to reaction conditions, such as normal hydrogen reaction gas at room temperature, at 1 bar, 78K, and a flow rate of 3000cc(H2) / min / cc(catalyst). The product is analyzed by chromatographic detection.

[0071] The specific structures are shown in Table 1, Table 2, and Table 3.

[0072] Table 1 Results of conversion of normal and para hydrogen

[0073]

[0074] Conversion efficiency = (parahydrogen content at the outlet - parahydrogen content at the inlet) / (parahydrogen content at the equilibrium conversion - parahydrogen content at the inlet);

[0075] As shown in Table 1, the prepared catalyst exhibits good conversion efficiency of normal and secondary hydrogen.

[0076] Table 2 Performance of n-parahydrogen conversion of different metal catalysts

[0077]

[0078] Commercial hydrated iron oxide was obtained from Molecular Products Limited, USA.

[0079] As shown in Table 2, when different metals are loaded on hydrated iron oxide, the activity can be maintained at >90%, indicating that the catalyst has good applicability to different metal loadings.

[0080] Table 3 Stability test of n-parahydrogen conversion of Pt / Fe2O3 catalyst (Preparation Example 1)

[0081]

[0082] After the catalyst reacted for 12 h, it was taken out from the reaction tube and re-reduced and tested for the catalytic conversion of normal and para hydrogen.

[0083] Table 3 shows that this type of catalyst has good catalytic stability and can be reduced and reused.

[0084] The above descriptions are merely a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application discloses the preferred embodiments as above, they are not intended to limit the present application. Any technical personnel familiar with the present profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. Application of a single-atom catalyst in the conversion of normal and secondary hydrogen, characterized in that: The following steps are involved: The raw material containing orthohydrogen is contacted with a single-atom catalyst to react and obtain a product containing parahydrogen; The single-atom catalyst comprises an iron oxide carrier and a single-atom active component supported on the surface of the iron oxide carrier; the catalyst is prepared by a co-precipitation method using an aqueous solution containing an active component precursor and an iron salt; The single-atom active component is selected from at least one of Pt, Pd, and Ru; In the single-atom catalyst, the content of the single-atom active component is 0.01-5 wt %; The specific surface area of ​​the iron oxide carrier is 50-500 m 2 / g; The pore size of the iron oxide carrier is 1.5 to 25 nm; The pore volume of the iron oxide carrier is 0.15~0.35cm 2 / g.

2. The use according to claim 1, characterized in that In the single-atom catalyst, the content of the single-atom active component is 0.01-2 wt %.

3. The use according to claim 1, characterized in that The particle size of the single-atom catalyst is 20-100 meshes.

4. The use according to claim 1, characterized in that The single-atom catalyst is prepared by the following steps: An aqueous solution containing an active component precursor and an iron salt is mixed with an aqueous solution containing a precipitant, stirred, allowed to stand, dried, and calcined to obtain the single-atom catalyst.

5. The use according to claim 4, characterized in that The active component precursor is selected from at least one of the nitrates and halides of the Pt element, the nitrates and halides of the Pd element, and the nitrates and halides of the Ru element; The iron salt is selected from at least one of ferric nitrate, ferric chloride, and ferric sulfate; In the aqueous solution containing the active component precursor and the iron salt, The content of the active component precursor is 0.1~50mg / ml; The content of the iron salt is 0.1~1 mol / L; The precipitant is selected from at least one of sodium carbonate, ammonium carbonate, potassium carbonate, lithium carbonate, sodium hydroxide, potassium hydroxide, and ammonia water; In the aqueous solution containing the precipitant, the content of the precipitant is 0.1-2 mol / L; The volume ratio of the aqueous solution containing the active component precursor and the iron salt to the aqueous solution containing the precipitant is 0.001-1000.

6. The use according to claim 4, characterized in that The stirring temperature is 50-100°C; The stirring time is 2 to 20 hours; The standing time is 1 to 10 hours.

7. The use according to claim 4, characterized in that The drying temperature is 25-120°C; The drying time is 1 to 24 hours.

8. The use according to claim 4, characterized in that The calcination temperature is 150-600°C; The roasting time is 1 to 24 hours.

9. The use according to claim 1, characterized in that The reaction is carried out in a low-temperature fixed-bed reactor; The pressure of the raw material is 0.1~0.5Mpa; The reaction temperature is 21~273K; The space velocity of the reaction is 300-3000 cc H2 / min / cc catalyst.

10. The use according to claim 1, characterized in that The single-atom catalyst is reduced by hydrogen; The temperature of the hydrogen reduction is 50-200°C; The time of the hydrogen reduction is 10 to 120 minutes.

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