CN116966914A - A kind of gamma iron oxide catalyst, preparation method and application - Google Patents

Abstract

The application discloses a gamma ferric oxide catalyst, a preparation method and application, wherein the gamma ferric oxide catalyst comprises the following components: iron oxide and a metal monoatom, the iron oxide exposing a [440] crystal plane; the metal monoatoms are loaded on the [440] crystal face; wherein the metal monoatoms comprise monoatomic Pt, monoatomic Pd, monoatomic Ir and monoatomic Ru. In the application, the catalyst is treated at 200 ℃, so that the interaction degree between single atoms and the carrier gamma ferric oxide [440] can be effectively regulated, and the reaction performance of the catalyst can be regulated. The prepared normal-para-hydrogen conversion catalyst shows excellent activity and stability. The preparation method of the catalyst is simple and easy to implement, the cost is low, the catalytic conversion efficiency of the normal para-hydrogen is high, the catalytic conversion efficiency can reach 87%, and the equilibrium concentration of the para-hydrogen reaches 45.4-50.4.

Description

A kind of gamma iron oxide catalyst, preparation method and application

Technical field

The present application relates to a gamma iron oxide catalyst, preparation method and application, and belongs to the technical field of n-parahydrogen conversion.

Background technique

Liquid hydrogen is an important strategic resource for the development of aerospace and hydrogen energy industries. With the development of my country's aerospace industry and the continuous advancement of the lunar and fire exploration program, the demand for heavy-load rockets is increasing. The demand for liquid hydrogen, which is the best energy source for heavy-load rocket liquid hydrogen-liquid oxygen engines, is increasing.

The hydrogen molecule is composed of two hydrogen atoms. Due to the different spin directions of the two hydrogen nuclei, there are two states of hydrogen, normal and secondary. The nuclei of orthohydrogen have the same spin direction, while the nuclei of parahydrogen have the opposite spin direction. The composition of equilibrium hydrogen in the normal and secondary states is related to temperature. The concentration ratios of equilibrium hydrogen in the normal and secondary states are different at different temperatures. At normal temperature, equilibrium hydrogen is a mixture containing normal hydrogen and 25% parahydrogen, which is called normal hydrogen or standard hydrogen: as the temperature decreases, the percentage of parahydrogen increases. For example, at the standard boiling point of liquid nitrogen, the parahydrogen content is about 51%, and at the standard boiling point of liquid hydrogen, the parahydrogen content can reach 99.8%. The spontaneous transformation of the normal-para state of hydrogen is very slow. Therefore, during the cooling and liquefaction process of hydrogen, if the normal-para catalytic conversion of hydrogen is not performed, the liquid hydrogen produced will be normal hydrogen, and the liquid normal hydrogen will spontaneously undergo secondary transformation. The normal-to-secondary transformation of hydrogen is an exothermic reaction, and the heat released during the transformation of liquid normal hydrogen exceeds the latent heat of vaporization (447kJ/kg). For this reason, even if liquid normal hydrogen is stored in an ideally insulated container, liquid hydrogen will still vaporize. Therefore, in order to obtain equilibrium hydrogen at the standard boiling point, that is, liquid hydrogen with a parahydrogen concentration of 99.8%, in hydrogen During the liquefaction process, several levels of normal-secondary catalytic conversion must be carried out.

There is a balance ratio between orthohydrogen and parahydrogen in orthoparahydrogen. The equilibrium proportion of orthohydrogen and parahydrogen is different at different temperatures. For example, at room temperature, orthohydrogen is 75% and parahydrogen is 25%. As the temperature decreases to 80K, orthohydrogen and parahydrogen are 25%. Hydrogen is 51% and parahydrogen is 49%. As the temperature continues to decrease, the proportion of parahydrogen becomes higher and higher. When the liquefaction point of hydrogen is around 20K, parahydrogen is 99.8%. Under normal circumstances, without the action of a catalyst, normal hydrogen is converted is very slow. Currently, the commonly used n-parahydrogen conversion catalysts are all hydrated iron oxide catalysts of the same format. Therefore, there is an urgent need for a novel n-parahydrogen conversion catalyst that can always maintain high activity and high conversion efficiency.

Contents of the invention

The purpose of this application is to provide a catalyst for n-parahydrogen catalytic conversion, which catalyst has the characteristics of high activity and high stability for n-parahydrogen catalytic conversion reaction.

The object of the present invention is to provide a method for preparing a catalyst for catalytic conversion of n-parahydrogen, which method has the characteristics of simple operation, strong repeatability, and high universality.

According to one aspect of the present application, a gamma iron oxide catalyst is provided, the gamma iron oxide catalyst includes: iron oxide and metal single atoms, the iron oxide exposes the [440] crystal plane;

The metal single atom is supported on the [440] crystal plane;

Wherein, the metal single atom includes at least one of single atom Pt, single atom Pd, single atom Ir, and single atom Ru.

Optionally, the mass content of the metal single atoms in the gamma iron oxide catalyst is 0.1 to 5 wt%.

Optionally, the mass content of the metal single atoms in the gamma iron oxide catalyst is selected from 0.1wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, Any value among 4wt%, 4.5wt%, 5wt% or a range value between any two of the above.

Optionally, the mass content of the iron oxide in the gamma iron oxide catalyst is 95 to 99.9 wt%.

According to another aspect of the present application, a method for preparing the above-mentioned gamma iron oxide catalyst is provided, and the preparation method includes:

React, dry and roast a mixture containing a metal single atom precursor and iron oxide to obtain a gamma iron oxide catalyst;

The iron oxide is iron oxide with exposed [440] crystal plane;

The metal single atom precursor is selected from at least one of Pt precursor, Pd precursor, Ir precursor, and Ru precursor.

Optionally, the preparation method of iron oxide with exposed [440] crystal plane includes:

In a sealed container, add water, ammonia, and ethanol to the iron precursor compound in sequence, react I, and dry I to obtain exposed [440] crystal plane iron oxide.

Alternatively, the gamma iron oxide carrier with the [440] crystal face exposed is prepared by a hydrothermal method, and the process is as follows:

1) Accurately weigh 1.08g FeCl ₃ ·6H ₂ O and place it in a clean beaker. Add 4mL H ₂ O, 4mL ammonia water, and 60mL ethanol in order. Ultrasonic for 30 minutes and then stir thoroughly for 30 minutes. After thorough stirring, transfer the mixed solution to the lining of a polytetrafluoroethylene hydrothermal reactor with a volume capacity of 100 mL, and seal the lining;

2) Then transfer the reaction kettle to an electric blast drying oven at 180°C for reaction for 24 hours.

3) After the reaction is completed, cool to room temperature naturally, centrifuge the hydrothermal sample solution, and wash it thoroughly three times with deionized water and ethanol. The washed sample was then dried in a drying oven at 80°C to obtain a gamma iron oxide carrier with exposed [440] crystal plane.

Optionally, the iron precursor compound is selected from at least one of FeCl ₃ ·6H ₂ O, Fe(NO ₃ ) ₃ ·9H ₂ O, and Fe ₂ (SO ₄ ) ₃ ·2H ₂ O.

Optionally, the mass-to-volume ratio of the iron precursor compound: water: ammonia water: ethanol is: 1 to 2 g: 2 to 10 mL: 2 to 10 mL: 30 to 100 mL.

Optionally, the mass ratio of the metal single atom precursor to the iron oxide is 0.001-5g:0.999-9.5g.

Optionally, the Pt precursor is selected from at least one of H ₂ PtCl ₆ , Na ₂ PtCl ₆ , and K ₂ PtCl ₆ .

Optionally, the Pd precursor is at least one of H ₂ PdCl ₆ , Na ₂ PdCl ₆ , and K ₂ PdCl ₆ .

Optionally, the Ir precursor is at least one of H ₂ IrCl ₆ , Na ₂ IrCl ₆ , and K ₂ IrCl ₆ .

Optionally, the Ru precursor is at least one of RuCl ₃ ·3H ₂ O, Ru(NO)(NO ₃ ) ₃ , Ru ₂ Cl ₄ (CO) ₆ and Ru(Ac) ₃ .

Optionally, the reaction temperature is 40-85°C, and the reaction time is 4-24 hours.

Optionally, the temperature of the reaction is selected from any value among 40°C, 45°C, 50°C, 60°C, 70°C, 80°C, 85°C or a range value between any two of the above.

Optionally, the reaction time is selected from any value among 4h, 8h, 12h, 16h, 20h, 24h or a range value between any two of the above.

Optionally, the drying temperature is 60-150°C, and the drying time is 4-24 hours.

Optionally, the drying temperature is selected from any value among 60°C, 70°C, 80°C, 90°C, 100°C, 120°C, 150°C or a range value between any two of the above.

Optionally, the drying time is selected from any value among 4h, 8h, 12h, 16h, 20h, 24h or a range value between any two of the above.

Optionally, the roasting temperature is 200-400°C, and the roasting time is 1-10 hours.

Optionally, the roasting temperature is 200-300°C, and the roasting time is 2-3 hours.

Optionally, the calcining temperature is selected from any value among 200°C, 250°C, 300°C, 350°C, 400°C or a range value between any two of the above.

Optionally, the roasting time is selected from any value among 1h, 2h, 4h, 8h, 10h or a range value between any two of the above.

Optionally, the temperature of reaction I is 150-250°C, and the time of reaction I is 16-48 hours.

Optionally, the temperature of reaction I is selected from any value among 150°C, 160°C, 180°C, 200°C, 220°C, 250°C or a range value between any two of the above.

Optionally, the time of reaction I is selected from any value among 16h, 18h, 24h, 28h, 30h, 38h, 48h or a range value between any two of the above.

Optionally, the temperature of drying I is 50-120°C, and the time of drying I is 2-8 hours.

Optionally, the temperature of the drying I is selected from any value among 50°C, 70°C, 80°C, 90°C, 100°C, 120°C or a range value between any two of the above.

Optionally, the drying time I is selected from any value among 2h, 3h, 4h, 5h, 6h, 7h, 8h or a range value between any two of the above.

According to another aspect of the present application, there is provided an application of the above-mentioned gamma iron oxide catalyst in n-parahydrogen conversion.

Optionally, the temperature of the gamma iron oxide catalyst in n-parahydrogen conversion is 0K to 298K.

Optionally, the temperature of the gamma iron oxide catalyst in n-parahydrogen conversion is selected from any value among 0K, 15K, 20K, 50K, 100K, 150K, 200K, 250K, 298K or a range between any two of the above. value.

The catalyst provided in this application is used to evaluate the catalytic conversion performance of n-parahydrogen. The reaction temperature range is 0-100K, and the preferred temperature is 15-80K. The prepared Pd/γ-Fe ₂ O ₃ [440] catalyst is used for n-parahydrogen catalytic conversion reaction. The single-atom active components (Pt, Pd, Ir, Ru) are highly dispersed and the metal utilization rate is significantly improved. This catalyst The activity and stability of the n-parahydrogen catalytic conversion reaction are significantly improved.

The catalyst provided in this application is composed of metal single atoms, including single atom Pt, single atom Pd, single atom Ir, single atom Ru, and the single atom metal active component is loaded onto the carrier through an impregnation method. Treating the catalyst at 200 degrees Celsius can effectively adjust the degree of interaction between single atoms and the carrier γ iron oxide [440], thereby regulating the reaction performance of the catalyst. The prepared n-parahydrogen conversion catalyst shows excellent activity and stability. The catalyst preparation method in this application is simple and easy, has low cost, has high catalytic conversion efficiency of n-parahydrogen, the catalytic conversion efficiency can reach 87%, and the equilibrium concentration of parahydrogen can reach 45.4-50.4.

The beneficial effects this application can produce include:

The catalyst preparation method provided by this application is simple to operate, reliable, and is conducive to large-scale production and use. The catalyst provided by this application has single-atom active components (Pt, Pd, Ir, Ru) that are highly dispersed and have a high metal utilization rate. Through roasting treatment, the degree of interaction between the metal and the carrier can be effectively adjusted, thereby significantly improving the activity and stability of the catalyst. The catalyst provided by this application is used for the catalytic conversion reaction of n-parahydrogen. The catalytic conversion efficiency of n-parahydrogen is high, the catalytic conversion efficiency can reach 87%, and the equilibrium concentration of parahydrogen reaches 45.4-50.4.

Description of the drawings

Figure 1 is a 20 nm HRTEM image of the γ-Fe ₂ O ₃ [440] catalyst prepared in Example 1 of the present application.

Figure 2 shows γ-Fe ₂ O ₃ [440], Pt/γ-Fe ₂ O ₃ [440], Pd/γ-Fe ₂ O ₃ [440], Ir/γ- prepared in Examples 1 to 5 of the present application. XRD patterns of Fe ₂ O ₃ [440], Ru/γ-Fe ₂ O ₃ [440] catalysts.

Detailed ways

The present application will be described in detail below with reference to examples, but the present application is not limited to these examples.

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

In this application, room temperature refers to "25°C".

In this application, ortho-parahydrogen conversion rate = product parahydrogen concentration/raw material 75% orthohydrogen + 25% parahydrogen concentration.

1. Pt/γ-Fe ₂ O ₃ [440] catalyst is prepared by impregnation method. The specific process is as follows:

1) Take a Pt precursor solution containing 0.001 to 0.5g of metal Pt in deionized water to form a 20 to 150ml uniform solution, and add 0.999 to 9.5g of γ-Fe ₂ O ₃ [440] carrier to the solution to form a uniform mixture. Based on the catalyst, the content of Pt based on single atoms is 0.1~5wt%, and the content based on γ-Fe ₂ O ₃ [440] carrier is 95~99.9wt%; the resulting mixture is heated at 40~85°C Heat and stir until the solvent evaporates to dryness, and dry the obtained solid in an oven at 60-150°C for 4-24 hours;

2) Calculate in a tube furnace under an argon atmosphere at 200-400°C for 1-10 hours to obtain a γ-iron oxide-supported Pt single-atom catalyst with exposed [440] crystal plane, Pt/γ-Fe ₂ O ₃ [440].

In step 1), one or more of H ₂ PtCl ₆ , Na ₂ PtCl ₆ , and K ₂ PtCl ₆ are used as the Pt precursor; the exposed crystal plane of the carrier γ-Fe ₂ O ₃ is [440].

In step 2), the calcination temperature is preferably 200 to 300°C and the time is 2 to 3 hours.

The reducing atmosphere in step 2) can be high-purity Ar, a mixture of H ₂ and Ar in different proportions.

2. Pd/γ-Fe ₂ O ₃ [440] catalyst is prepared by impregnation method. The specific process is as follows:

1) Take a Pd precursor solution containing 0.001 to 0.5g of metal Pd in deionized water to form a 20 to 150ml uniform solution, and add 0.999 to 9.5g of γ-Fe ₂ O ₃ [440] carrier to the solution to form a uniform mixture. Based on the catalyst, the content of Pd in terms of single atoms is 0.1~5wt%, and the content in terms of γ-Fe ₂ O ₃ [440] carrier is 95~99.9wt%; the resulting mixture is heated at 40~85°C Heat and stir until the solvent evaporates to dryness, and dry the obtained solid in an oven at 60-150°C for 4-24 hours;

2) Calculate in a tube furnace under an argon atmosphere at 200-400°C for 1-10 hours to obtain a γ-iron oxide-supported Pd single-atom catalyst with exposed [440] crystal plane, Pd/γ-Fe ₂ O ₃ [440].

Step 1) The Pd precursor uses one or more of H ₂ PdCl ₆ , Na ₂ PdCl ₆ , and K ₂ PdCl ₆ ; the exposed crystal plane of the carrier γ-Fe ₂ O ₃ is [440].

In step 2), the calcination temperature is preferably 200 to 300°C and the time is 2 to 3 hours.

The reducing atmosphere in step 2) can be high-purity Ar, a mixture of H ₂ and Ar in different proportions.

3. Ir/γ-Fe ₂ O ₃ [440] catalyst is prepared by impregnation method. The specific process is as follows:

1) Take an Ir precursor solution with 0.001~0.5g metal Pd in deionized water to form a 20~150ml uniform solution, and add 0.999~9.5g γ-Fe ₂ O ₃ [440] carrier to the solution to form a uniform mixture. Based on the catalyst, the content of Ir in terms of single atoms is 0.1~5wt%, and the content in terms of γ-Fe ₂ O ₃ [440] carrier is 95~99.9wt%; the resulting mixture is heated at 40~85°C Heat and stir until the solvent evaporates to dryness, and dry the obtained solid in an oven at 60-150°C for 4-24 hours;

2) Calculate in a tube furnace under an argon atmosphere at 200-400°C for 1-10 hours to obtain a γ-iron oxide-supported Ir single-atom catalyst with exposed [440] crystal plane, Ir/γ-Fe ₂ O ₃ [440].

Step 1) The Ir precursor uses one or more of H ₂ IrCl ₆ , Na ₂ IrCl ₆ , and K ₂ IrCl ₆ ; the exposed crystal plane of the carrier γ-Fe ₂ O ₃ is [440].

In step 2), the roasting temperature is preferably 200 to 300°C and the time is 2 to 3 hours.

The reducing atmosphere in step 2) can be high-purity Ar, a mixture of H ₂ and Ar in different proportions.

4. Ru/γ-Fe ₂ O ₃ [440] catalyst is prepared by impregnation method. The specific process is as follows:

1) Take a Pd precursor solution containing 0.001~0.5g of metal Ru in deionized water to form a 20~150ml uniform solution, and add 0.999~9.5g of γ-Fe ₂ O ₃ [440] carrier to the solution to form a uniform mixture. Based on the catalyst, the Ru content based on single atoms is 0.1~5wt%, and the content based on γ-Fe ₂ O ₃ [440] carrier is 95~99.9wt%; the formed mixture is at 40~85°C. Heat and stir until the solvent evaporates to dryness, and dry the obtained solid in an oven at 60-150°C for 4-24 hours;

2) Calculate in a tube furnace under an argon atmosphere at 200-400°C for 1-10 hours to obtain a γ-iron oxide-supported Ru single-atom catalyst with exposed [440] crystal plane, Ru/γ-Fe ₂ O ₃ [440].

Step 1) The Ru precursor adopts one or more of RuCl ₃ ·3H ₂ O, Ru(NO)(NO ₃ ) ₃ , Ru ₂ Cl ₄ (CO) ₆ , and Ru(Ac) ₃ ; the carrier γ-Fe The exposed crystal face of ₂ O ₃ is [440].

In step 2), the calcination temperature is preferably 200 to 300°C and the time is 2 to 3 hours.

The reducing atmosphere in step 2) can be high-purity Ar, a mixture of H ₂ and Ar in different proportions.

Example 1

1) Accurately weigh 1.08g FeCl ₃ ·6H ₂ O and place it in a clean beaker. Add 4mL H ₂ O, 4mL ammonia water, and 60mL ethanol in order. Ultrasonic for 30 minutes and then stir thoroughly for 30 minutes. After thorough stirring, transfer the mixed solution to the lining of a polytetrafluoroethylene hydrothermal reactor with a volume capacity of 100 mL, and seal the lining.

2) Then transfer the reaction kettle to an electric blast drying oven at 180°C for reaction for 24 hours.

3) After the reaction is completed, cool to room temperature naturally, centrifuge the hydrothermal sample solution, and wash it thoroughly three times with deionized water and ethanol. The washed sample was then dried in a drying oven at 80°C to obtain a gamma iron oxide carrier with exposed [440] crystal plane (named γ-Fe ₂ O ₃ [440]). It can be seen from Figure 1 that the prepared γ-Fe ₂ O ₃ with special exposed crystal face [440] exists in the form of uniform nanoparticles of about 10 nm, and the γ-Fe ₂ O ₃ [440] is uniform in size.

Example 2

Take a H ₂ PtCl ₆ ·6H ₂ O solution with a Pt content of 0.06g, add deionized water to dilute it into a 50ml uniform solution, stir evenly, and add 1.94g γ-Fe ₂ O ₃ [440] carrier to the solution to form a uniform mixture; The mixture was heated and stirred at 60°C until the solvent evaporated to dryness. The obtained solid was dried in an oven at 100°C for 12 hours, and then calcined in a tube furnace under an argon atmosphere at 200°C for 2 hours. That is, Pt/γ-Fe ₂ O ₃ [440] catalyst is obtained.

Example 3

Take a H ₂ PdCl ₆ ·6H ₂ O solution with a Pd content of 0.06g, add deionized water to dilute it into a 50ml uniform solution, stir evenly, and add 1.94g γ-Fe ₂ O ₃ [440] carrier to the solution to form a uniform mixture; The mixture was heated and stirred at 60°C until the solvent evaporated to dryness. The obtained solid was dried in an oven at 100°C for 12 hours, and then calcined in a tube furnace under an argon atmosphere at 200°C for 2 hours. That is, Pd/γ-Fe ₂ O ₃ [440] catalyst is obtained.

Example 4

Take a H ₂ IrCl ₆ ·6H ₂ O solution with an Ir content of 0.06g, add deionized water to dilute it into a 50ml uniform solution, stir evenly, and add 1.94g γ-Fe ₂ O ₃ [440] carrier to the solution to form a uniform mixture; The mixture was heated and stirred at 60°C until the solvent evaporated to dryness. The obtained solid was dried in an oven at 100°C for 12 hours, and then calcined in a tube furnace under an argon atmosphere at 200°C for 2 hours. That is, Ir/γ-Fe ₂ O ₃ [440] catalyst is obtained.

Example 5

Take a RuCl ₃ ·3H ₂ O solution with a Ru content of 0.06g, add deionized water to dilute it into a 50ml uniform solution, stir evenly, add 1.94g γ-Fe ₂ O ₃ [440] carrier to the solution to form a uniform mixture; this mixture Heat and stir at 60°C until the solvent evaporates to dryness. The obtained solid is dried in an oven at 100°C for 12 hours, and then calcined in a tube furnace under an argon atmosphere at 200°C for 2 hours. That is, Ru/γ-Fe ₂ O ₃ [440] catalyst is obtained.

Figure 2 shows that compared with the carrier γ-Fe ₂ O ₃ [440], the catalysts loaded with single atoms include Pt/γ-Fe ₂ O ₃ [440], Pd/γ-Fe ₂ O ₃ [440] , Ir/γ-Fe ₂ O ₃ [440], Ru/γ-Fe ₂ O ₃ [440] show exactly the same crystal phase structure as the carrier, proving the absence of nanoparticles, Pt, Pd, Ir, Ru, etc. The components all exist in the form of single atoms on the γ-Fe ₂ O ₃ [440] carrier.

Example 6 n-parahydrogen conversion reaction

When reacting in a low-temperature Dewar tank and operating at a temperature of 77K, liquid nitrogen is used as the refrigerant medium, and the pressure in the liquid nitrogen tank is controlled through the back pressure valve on the liquid nitrogen storage tank to ensure that the refrigerant medium is maintained at a temperature of 77K stability. Using the gamma iron oxide carrier with exposed [440] crystal plane prepared in Example 1 and 0.5-3g of the catalyst prepared in Examples 2-5, the reaction space velocity is 100 mL·H ₂ /min/mL·catalyst, and the reaction pressure is 0MPa (normal pressure). The specific reaction conditions are shown in Table 1.

Table 1: Experimental Example 1 γ-Fe ₂ O ₃ [440] and the catalyst prepared in Examples 2 to 5 for n-parahydrogen conversion reaction

As can be seen from Table 1, Table 1 shows γ-Fe ₂ O ₃ [440], Pt/γ-Fe ₂ O ₃ [440], Pd/γ-Fe ₂ O ₃ [440], Ir/γ-Fe ₂ O ₃ [440], Ru/γ-Fe ₂ O ₃ [440] catalyst n-parahydrogen conversion rate of n-parahydrogen conversion catalyst, compared with pure γ-Fe ₂ O ₃ [440] support, Pt/γ- Parahydrogen conversion rate of Fe ₂ O ₃ [440], Pd/γ-Fe ₂ O ₃ [440], Ir/γ-Fe ₂ O ₃ [440], Ru/γ-Fe ₂ O ₃ [440] catalysts All showed varying degrees of improvement.

The above are only a few embodiments of the present application, and are not intended to limit the present application in any way. Although the present application is disclosed as above with preferred embodiments, they are not intended to limit the present application. Any skilled person familiar with this field, Without departing from the scope of the technical solution of this application, slight changes or modifications made using the technical content disclosed above are equivalent to equivalent implementation examples and fall within the scope of the technical solution.

Claims (10)

1. A gamma iron oxide catalyst, characterized in that the gamma iron oxide catalyst comprises: iron oxide and a metal monoatom, the iron oxide exposing a [440] crystal plane;

the metal monoatoms are loaded on the [440] crystal face;

wherein the metal monoatoms comprise at least one of monoatomic Pt, monoatomic Pd, monoatomic Ir and monoatomic Ru.

2. The gamma iron oxide catalyst according to claim 1, wherein the metal monoatoms account for 0.1 to 5wt% of the gamma iron oxide catalyst;

the iron oxide accounts for 95 to 99.9 weight percent of the gamma iron oxide catalyst.

3. A method for producing a gamma iron oxide catalyst according to any one of claims 1 to 2, characterized in that the production method comprises:

reacting, drying and roasting a mixture containing a metal monoatomic precursor and ferric oxide to obtain a gamma ferric oxide catalyst;

the ferric oxide is ferric oxide with an exposed [440] crystal face;

the metal monoatomic precursor is selected from at least one of Pt precursor, pd precursor, ir precursor and Ru precursor.

4. A method of preparing an exposed [440] crystal face iron oxide according to claim 3, comprising:

adding water, ammonia water and ethanol into an iron precursor compound in turn in a closed container, reacting I, and drying I to obtain exposed [440] crystal face ferric oxide;

preferably, the iron precursor compound is selected from FeCl ₃ ·6H ₂ O、Fe(NO ₃ ) ₃ ·9H ₂ O、Fe ₂ (SO ₄ ) ₃ ·2H ₂ At least one of O.

5. The method of preparing as claimed in claim 4, wherein the iron precursor compound: water: ammonia water: the mass volume ratio of the ethanol is as follows: 1-2 g: 2-10 mL: 2-10 mL: 30-100 mL.

6. The method according to claim 3, wherein the mass ratio of the metal monoatomic precursor to the iron oxide is 0.001 to 5g: 0.999-9.5 g;

preferably, the Pt precursor is selected from H ₂ PtCl ₆ 、Na ₂ PtCl ₆ 、K ₂ PtCl ₆ At least one of (a) and (b);

preferably, the Pd precursor H ₂ PdCl ₆ 、Na ₂ PdCl ₆ 、K ₂ PdCl ₆ At least one of (a) and (b);

preferably, the Ir precursor H ₂ IrCl ₆ 、Na ₂ IrCl ₆ 、K ₂ IrCl ₆ At least one of (a) and (b);

preferably, the Ru precursor RuCl ₃ ·3H ₂ O、Ru(NO)(NO ₃ ) ₃ 、Ru ₂ Cl ₄ (CO) ₆ 、Ru(Ac) ₃ At least one of them.

7. The method according to claim 3, wherein the reaction temperature is 40-85 ℃ and the reaction time is 4-24 hours;

preferably, the drying temperature is 60-150 ℃ and the drying time is 4-24 hours;

preferably, the roasting temperature is 200-400 ℃, and the roasting time is 1-10 h.

8. The preparation method according to claim 4, wherein the temperature of the reaction I is 150-250 ℃, and the time of the reaction I is 16-48 h;

preferably, the temperature of the drying I is 50-120 ℃, and the time of the drying I is 2-8 h.

9. Use of the gamma iron oxide catalyst of any one of claims 1 to 2 in the conversion of normal para-hydrogen.

10. The use according to claim 9, characterized in that the temperature of the gamma iron oxide catalyst in the conversion of normal para-hydrogen is between 0K and 298K.