A ruthenium-based ammonia synthesis catalyst with alumina as a carrier and a method for preparing the same

Abstract

The application discloses a ruthenium-based ammonia synthesis catalyst with alumina as a carrier and a preparation method thereof. The catalyst is prepared by the following steps: first, impregnating alumina with a water solution containing carbon-containing organic matters, and then high-temperature heat treatment in an oxygen-containing atmosphere to obtain an alumina carrier; then, introducing cerium additives by a precipitation method, and calcining in an inert atmosphere; then, introducing active components ruthenium and performing heat treatment in a carbon-containing gas; and finally, reduction to obtain the catalyst. Compared with the alumina-supported ruthenium catalyst prepared by the prior art, the catalyst prepared by the application has higher ammonia synthesis activity, and has a good application prospect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of ammonia synthesis catalysts, and particularly relates to a ruthenium-based ammonia synthesis catalyst with alumina as a carrier and a preparation method thereof. BACKGROUND

[0002] Ammonia is a key chemical for food security and social development, so the ammonia synthesis industry occupies a very important position in the national economy. The development of ammonia synthesis catalysts is the key to energy saving and emission reduction of the ammonia synthesis industry. Ruthenium catalysts are known as the second generation of ammonia synthesis catalysts due to their excellent performance. Currently, only ruthenium catalysts with activated carbon as a carrier have been industrialized. However, under the harsh conditions of high temperature and high pressure for ammonia synthesis, the activated carbon carrier is prone to methanation, which seriously affects the stability of the ruthenium catalyst. Therefore, finding a ruthenium catalyst carrier with high stability has always been the focus of researchers.

[0003] Magnesium oxide, rare earth oxides, and alumina are considered as potential carrier materials for preparing ruthenium catalysts with high stability. However, although alumina has good heat resistance, the ammonia synthesis performance of alumina-supported ruthenium catalysts is not good, which is mainly due to the strong acidity of the alumina carrier itself and the strong interaction between alumina and ruthenium metal, which is not conducive to the adsorption, dissociation, and desorption of reaction gases such as nitrogen, hydrogen, and ammonia. Zhang Xinbo et al. (Preparation conditions and carrier modification of alumina-supported ruthenium-based ammonia synthesis catalysts, Catalysis, 2002 Vol. 23 (3): 207-213) reported that calcination of γ-Al2O3 can improve the ammonia synthesis activity of alumina-supported ruthenium catalysts. They found that the ideal calcination temperature of alumina is 800℃, and further increasing the calcination temperature will significantly reduce the specific surface area of alumina and the ammonia synthesis activity of the catalyst. Although the treatment of the above-mentioned carrier can improve the ammonia synthesis activity of alumina-supported ruthenium catalysts to some extent, it still cannot solve the problems of strong acidity of the alumina carrier and strong interaction between alumina and ruthenium metal, so the ammonia synthesis activity needs to be further improved to meet the needs of industrial applications. SUMMARY

[0004] To solve the problems in the prior art, the present application provides a ruthenium-based ammonia synthesis catalyst with alumina as a carrier and a preparation method thereof. Compared with the alumina-supported ruthenium catalyst prepared by the traditional method, the catalyst prepared by the present application has higher ammonia synthesis activity and better application prospects.

[0005] To achieve the above-mentioned purposes, the present application adopts the following technical solutions:

[0006] The application discloses a ruthenium-based ammonia synthesis catalyst with alumina as a carrier, which is composed of alumina as a carrier, ruthenium as an active component and cerium as an additive, wherein the mass ratio of ruthenium to alumina is 0.02:1-0.15:1, and the mass ratio of cerium to alumina is 0.01:1-0.1:1.

[0007] The application further discloses a preparation method of the ruthenium-based ammonia synthesis catalyst with alumina as a carrier.

[0008] 1) after alumina is immersed in a water solution containing carbon-containing organic matter, high-temperature heat treatment is carried out in an oxygen-containing atmosphere to obtain an alumina carrier;

[0009] 2) the alumina carrier obtained in step 1) is placed in a cerium salt solution, and a precipitant is slowly added during stirring until the pH value of the mixed solution is 8-11; after filtration and drying, calcination is carried out in an inert atmosphere to obtain cerium-loaded alumina;

[0010] 3) the cerium-loaded alumina obtained in step 2) is impregnated with a ruthenium salt solution, and after drying, heat treatment is carried out in a carbon-containing gas;

[0011] 4) the sample after step 3) is reduced to obtain the ruthenium-based ammonia synthesis catalyst with alumina as a carrier.

[0012] Further, the mass ratio of the amount of the carbon-containing organic matter to alumina in step 1) is 0.03:1-0.15:1.

[0013] Further, the carbon-containing organic matter in step 1) is any one of glucose, sucrose and fructose.

[0014] Further, the oxygen-containing atmosphere in step 1) is air or a mixed gas composed of oxygen and any one of nitrogen, a 0th group gas; wherein the volume content of oxygen is 10%-95%.

[0015] Further, the high-temperature heat treatment in step 1) is carried out at a temperature of 850-1300 ℃ for 2-60 hours.

[0016] Further, the cerium salt used in step 2) is cerium nitrate or cerium chloride.

[0017] Further, the precipitant in step 2) is any one of ammonia water and urea.

[0018] Further, the inert atmosphere in step 2) is nitrogen or a 0th group gas.

[0019] Further, the calcination in step 2) is carried out at a temperature of 450-800 ℃ for 2-20 hours.

[0020] Further, the ruthenium salt solution in step 3) is a solution of ruthenium chloride or ruthenium nitrite in water and / or methanol or ethanol.

[0021] Further, the carbon-containing gas in step 3) is any one of methane, ethane, acetylene, propane, carbon monoxide, and carbon dioxide, and its gas flow rate is 5-1000 mL / min.

[0022] Furthermore, the heat treatment in step 3) is carried out at a temperature of 450-700 ℃ for 2-20 hours.

[0023] Further, the reduction in step 4) is performed by treating the sample in a hydrogen-containing gas at 200-600 °C for 0.2-48 hours.

[0024] Furthermore, the hydrogen-containing gas is a mixture of hydrogen and nitrogen or group 0 gases, wherein the volume content of hydrogen is 1%-100%.

[0025] This invention provides a ruthenium-based ammonia synthesis catalyst supported on alumina, wherein alumina is used as the support, ruthenium is the active component, and cerium is used as a promoter. Compared with alumina-supported ruthenium catalysts prepared by existing methods, the catalyst obtained by this invention has the advantages of large specific surface area, uniform distribution of Ce and Ru elements, and high ruthenium reduction degree, thus exhibiting higher ammonia synthesis activity and promising application prospects. Attached Figure Description

[0026] Figure 1 The catalyst 10Ru / 5Ce-Al2O3-suc1000 obtained in Example 1 and the catalyst 10Ru obtained in Comparative Example 3 are... H CO infrared spectrum of / 5Ce-Al2O3-suc1000.

[0027] Figure 2 The catalyst 10Ru / 5Ce-Al2O3-suc1000(a) obtained in Example 1 and the catalyst 10Ru / 5Ce obtained in Comparative Example 4 are examples of catalysts. imp Elemental distribution diagram of -Al2O3-suc1000(b). Detailed Implementation

[0028] A ruthenium-based ammonia synthesis catalyst supported on alumina is prepared by the following steps:

[0029] 1) After impregnating alumina with an aqueous solution containing carbonaceous organic matter, the alumina carrier is obtained by high-temperature heat treatment in an oxygen-containing atmosphere;

[0030] 2) Place the alumina support obtained in step 1) in a cerium salt solution, and slowly add a precipitant while stirring until the pH of the mixture is 8-11. After filtration and drying, calcine in an inert atmosphere to obtain cerium-loaded alumina.

[0031] 3) impregnating the cerium-loaded alumina obtained in step 2) with a ruthenium salt solution, drying and then heat-treating in a carbon-containing gas;

[0032] 4) reducing the sample treated in step 3) to obtain a ruthenium-based ammonia synthesis catalyst with the alumina as the carrier.

[0033] In step 1), the mass ratio of the carbon-containing organic matter to the alumina is 0.03:1-0.15:1; the carbon-containing organic matter is any one of glucose, sucrose or fructose. The oxygen-containing atmosphere is air or a mixture of oxygen and any one of nitrogen, a 0-group gas, wherein the volume content of oxygen is 10%-95%. The temperature of the high-temperature heat treatment is 850-1300 ℃, and the time is 2-60 hours.

[0034] In step 2), the cerium salt is cerium nitrate or cerium chloride, and the precipitant is any one of ammonia water or urea. The inert atmosphere is nitrogen or a 0-group gas. The temperature of the calcination is 450-800 ℃, and the time is 2-20 hours.

[0035] In step 3), the ruthenium salt solution is a water and / or methanol, ethanol solution of ruthenium chloride or ruthenium nitrosyl nitrate. The carbon-containing gas is any one of methane, ethane, acetylene, propane, carbon monoxide or carbon dioxide, and the gas flow rate is 5-1000 mL / min. The temperature of the heat treatment is 450-700 ℃, and the time is 2-20 hours.

[0036] In step 4), the reduction is a treatment in a hydrogen-containing gas at 200-600 ℃ for 0.2-48 hours. The hydrogen-containing gas is a mixture of hydrogen and nitrogen or a 0-group gas, wherein the volume content of hydrogen is 1%-100%.

[0037] In the obtained catalyst, the mass ratio of ruthenium to alumina is 0.02:1-0.15:1, and the mass ratio of cerium to alumina is 0.01:1-0.1:1.

[0038] In order to make the content of the present application more convenient to understand, the technical solutions of the present application are further described below in combination with specific embodiments, but the present application is not limited thereto.

[0039] Example 1:

[0040] 1) impregnating alumina with a sucrose solution (the mass ratio of sucrose to alumina is 0.1:1), and then calcining in air with an oxygen content of about 20.9% at 1000 ℃ for 6 hours to obtain an alumina carrier.

[0041] 2) The alumina support obtained in step 1) was put into a 7.2 mmol / L aqueous solution of cerium nitrate, and a 28 vol% ammonia water solution was slowly added during stirring until the pH value of the mixture was 10. After standing for 3 hours, the mixture was filtered, dried, and calcined in argon at 600°C for 3 hours to obtain cerium-loaded alumina;

[0042] 3) The cerium-loaded alumina obtained in step 2) was impregnated with a 1.5% w / v aqueous solution of ruthenium nitrosyl nitrate, and dried before being heat-treated in carbon monoxide gas (500 mL / min) at 500°C for 4 hours;

[0043] 4) The sample obtained in step 3) was reduced in pure hydrogen at 450°C for 6 hours to obtain catalyst 10Ru / 5Ce-Al2O3-suc1000 (where suc is the abbreviation for sucrose, and 1000 is the calcination temperature of alumina, and the following expressions have the same meaning), in which the mass ratio of ruthenium to alumina was 0.1:1, and the mass ratio of cerium to alumina was 0.05:1.

[0044] Example 2:

[0045] 1) Alumina was impregnated with a glucose solution (the mass ratio of glucose to alumina used was 0.13:1), and then calcined in oxygen-argon mixed gas with an oxygen content of about 2% at 1000°C for 48 hours to obtain an alumina support.

[0046] 2) The alumina support obtained in step 1) was put into an 11.5 mmol / L aqueous solution of cerium nitrate, and a 20% w / v urea solution was slowly added during stirring until the pH value of the mixture was 8. After standing for 3 hours, the mixture was filtered, dried, and calcined in argon at 700°C for 2 hours to obtain cerium-loaded alumina;

[0047] 3) The cerium-loaded alumina obtained in step 2) was impregnated with a 3 mol / L ruthenium chloride ethanol solution, and dried before being heat-treated in acetylene gas (200 mL / min) at 600°C for 2 hours;

[0048] 4) The sample obtained in step 3) was reduced in a 10% H2+90% Ar mixed gas at 550°C for 2 hours to obtain catalyst 13Ru / 8Ce-Al2O3-glu1200, in which the mass ratio of ruthenium to alumina was 0.13:1, and the mass ratio of cerium to alumina was 0.08:1.

[0049] Example 3:

[0050] 1) Alumina was impregnated with a fructose solution (the mass ratio of fructose to alumina used was 0.05:1), and then calcined in oxygen-nitrogen mixed gas with an oxygen content of about 70% at 900°C for 16 hours to obtain an alumina support.

[0051] 2) The alumina support obtained in step 1) was put into a 4.3 mmol / L aqueous solution of cerium nitrate, and 20 vol% ammonia water was slowly added during stirring until the pH value of the mixture was 11. After standing for 3 hours, the mixture was filtered and dried, and then calcined in helium at 700°C for 2 hours to obtain cerium-loaded alumina;

[0052] 3) The cerium-loaded alumina obtained in step 2) was impregnated with a 1.5% w / v aqueous solution of ruthenium nitrosyl nitrate, and then dried and heat-treated in methane gas (900 mL / min) at 600°C for 15 hours;

[0053] 4) The sample obtained in step 3) was reduced in a mixed gas of 10% H2+90% Ar at 400°C for 16 hours to obtain catalyst 8Ru / 3Ce-Al2O3-fru900, wherein the mass ratio of ruthenium to alumina was 0.08:1, and the mass ratio of cerium to alumina was 0.03:1.

[0054] Comparative Example 1:

[0055] 1) Alumina was calcined in air with an oxygen content of about 20.9% at 1000°C for 6 hours to obtain an alumina support.

[0056] 2) The alumina support obtained in step 1) was put into a 7.2 mmol / L aqueous solution of cerium nitrate, and 28 vol% concentrated ammonia water was slowly added during stirring until the pH value of the mixture was 10. After standing for 3 hours, the mixture was filtered and dried, and then calcined in argon at 600°C for 3 hours to obtain cerium-loaded alumina;

[0057] 3) The cerium-loaded alumina obtained in step 2) was impregnated with a 1.5% w / v aqueous solution of ruthenium nitrosyl nitrate, and then dried and heat-treated in carbon monoxide gas (500 mL / min) at 500°C for 4 hours;

[0058] 4) The sample obtained in step 3) was reduced in pure hydrogen at 450°C for 6 hours to obtain catalyst 10Ru / 5Ce-Al2O3-1000, wherein the mass ratio of ruthenium to alumina was 0.1:1, and the mass ratio of cerium to alumina was 0.05:1.

[0059] Comparative Example 2:

[0060] 1) Alumina was impregnated with a sucrose solution (the mass ratio of sucrose to alumina used was 0.1:1), and then calcined in air with an oxygen content of about 20.9% at 1000°C for 6 hours to obtain an alumina support.

[0061] 2) The alumina support obtained in step 1) was impregnated with 1.5% w / v aqueous solution of ruthenium nitrosyl nitrate, dried and then heat treated in carbon monoxide gas (500 mL / min) at 500 °C for 4 hours;

[0062] 3) The sample obtained in step 2) was reduced in pure hydrogen at 450 °C for 6 hours to obtain catalyst 10Ru / Al2O3-suc1000, wherein the mass ratio of ruthenium to alumina is 0.1:1.

[0063] Comparative Example 3:

[0064] 1) The alumina was impregnated with a sucrose solution (the mass ratio of sucrose to alumina used was 0.1:1), and then calcined in air with an oxygen content of about 20.9% at 1000 °C for 6 hours to obtain an alumina support.

[0065] 2) The alumina support obtained in step 1) was placed in an aqueous solution of cerium nitrate of 7.2 mmol / L, and an aqueous solution of 28 vol% ammonia was slowly added during stirring until the pH value of the mixture was 10. After standing for 3 hours, the mixture was filtered, dried, and then calcined in argon at 600 °C for 3 hours to obtain cerium-loaded alumina;

[0066] 3) The cerium-loaded alumina obtained in step 2) was impregnated with a 1.5% w / v aqueous solution of ruthenium nitrosyl nitrate, and dried;

[0067] 4) The dried sample obtained in step 3) was reduced in pure hydrogen at 450 °C for 6 hours to obtain catalyst 10Ru H / 5Ce-Al2O3-suc1000, wherein the mass ratio of ruthenium to alumina is 0.1:1, and the mass ratio of cerium to alumina is 0.05:1.

[0068] Figure 1 The CO infrared spectra of the catalyst 10Ru / 5Ce-Al2O3-suc1000 obtained in Example 1 and the catalyst 10Ru H / 5Ce-Al2O3-suc1000 obtained in Comparative Example 3 were determined. As can be seen from the figure, almost no CO absorption peak belonging to ruthenium material in the oxidation state was observed in the catalyst 10Ru / 5Ce-Al2O3-suc1000 prepared in Example 1, indicating that the reduction degree of the ruthenium material in the catalyst prepared in the present application is higher, and the utilization rate of the ruthenium component is also higher, thus improving the ammonia synthesis activity of the catalyst.

[0069] Comparative Example 4:

[0070] 1) The alumina was impregnated with a sucrose solution (the mass ratio of sucrose to alumina used was 0.1:1), and then calcined in air with an oxygen content of about 20.9% at 1000 °C for 6 hours to obtain an alumina support.

[0071] 2) The alumina support obtained in step 1) was impregnated with a 7.2 mmol / L aqueous solution of cerium nitrate, dried and calcined in argon at 600 °C for 3 hours to obtain cerium-loaded alumina;

[0072] 3) The cerium-loaded alumina obtained in step 2) was impregnated with a 1.5% w / v aqueous solution of ruthenium nitrosyl nitrate, dried and heat-treated in carbon monoxide gas (500 mL / min) at 500 °C for 4 hours;

[0073] 4) The sample obtained in step 3) was reduced in pure hydrogen at 450 °C for 6 hours to obtain catalyst 10Ru / 5Ce imp -Al2O3-suc1000, wherein the mass ratio of ruthenium to alumina is 0.1:1 and the mass ratio of cerium to alumina is 0.05:1.

[0074] Figure 2 Elemental distribution diagrams of the catalyst 10Ru / 5Ce-Al2O3-suc1000 (a) obtained in Example 1 and the catalyst 10Ru / 5Ce imp -Al2O3-suc1000 (b) obtained in Comparative Example 4. As can be seen from the diagrams, the Ce and Ru elements are more uniformly distributed in the 10Ru / 5Ce-Al2O3-suc1000 catalyst prepared in Example 1 than in the catalyst 10Ru / 5Ce imp -Al2O3-suc1000 prepared in Comparative Example 4, which is conducive to the catalytic action of the ruthenium and cerium components, and which is free of carbon residues.

[0075] Comparative Example 5:

[0076] 1) Alumina was impregnated with a sucrose solution (the mass ratio of sucrose to alumina used was 0.1:1) and then calcined in air with an oxygen content of about 20.9% at 1000 °C for 6 hours to obtain an alumina support.

[0077] 2) The alumina support obtained in step 1) was impregnated with a 1.5% w / v aqueous solution of ruthenium nitrosyl nitrate, dried and heat-treated in carbon monoxide gas (500 mL / min) at 500 °C for 4 hours;

[0078] 3) The sample obtained in step 2) was placed in a 7.2 mmol / L aqueous solution of cerium nitrate, and a 28 vol% aqueous ammonia solution was slowly added during stirring until the pH value of the mixture was 10. After standing for 3 hours, the sample was filtered, dried and calcined in argon at 600 °C for 3 hours;

[0079] 4) The sample obtained in step 3) is reduced in pure hydrogen at 450 ℃ for 6 hours to obtain catalyst 5Ce-10Ru / Al2O3-suc1000, wherein the mass ratio of ruthenium to alumina is 0.1:1, and the mass ratio of cerium to alumina is 0.05:1.

[0080] Comparative Example 6:

[0081] The alumina is heated to 900 ℃ in nitrogen, then replaced with methane gas with a purity of 20% and maintained for 0.4 h to make the carbon content 0.22 g C / g Al2O3 , then the obtained carbon-alumina composite material is used as a carrier to impregnate a 1.5% w / v ruthenium nitrosyl nitrate solution to a mass ratio of ruthenium metal to carbon-alumina composite carrier of 0.1:1, the obtained sample is reduced in a mixed gas of 10% H2+90% Ar at 550 ℃ for 4 hours, and then a 7.2 mmol / L cerium nitrate aqueous solution is further impregnated into the reduced sample to a mass ratio of cerium to carbon-alumina composite carrier of 0.05:1, and after drying, the 5Ce-10Ru / C-Al2O3 ammonia synthesis catalyst is obtained.

[0082] The ammonia synthesis catalysts prepared in the examples and comparative examples are subjected to catalytic activity evaluation in a high-pressure activity test device. In the test process, 0.3 g of catalyst is mixed with quartz sand and packed in the isothermal zone of the reactor. The reaction gas is a nitrogen and hydrogen mixed gas obtained by high-temperature catalytic cracking of ammonia, and the hydrogen to nitrogen ratio is 3:1; the reaction conditions are: pressure 1 MPa, reaction temperature 400 ℃, reaction space velocity 3.6x10 4 cm 3 g -1 h -1 , and the catalytic activity determination results are shown in Table 1.

[0083] Table 1

[0084]

[0085] As can be seen from Table 1, the specific surface area and ammonia synthesis rate of the catalysts prepared in the absence of organic matter in the alumina calcination, without adding cerium promoters, without heat treatment in the carbon-containing gas during the addition of ruthenium, by impregnation method for adding cerium promoters, or using carbon-containing-alumina as the carrier are low, and under the same conditions, the ammonia synthesis rate of the catalysts obtained in the examples is significantly higher than that of the catalysts obtained in the comparative examples, proving that they have good ammonia synthesis catalytic activity and good application prospects.

[0086] The above only describes the preferred embodiments of the present application, and any equivalent changes and modifications made within the scope of the patent application of the present application shall be included in the scope of the present application.

Claims

1. A process for the preparation of a ruthenium-based ammonia synthesis catalyst with alumina as a support, characterized in that: The catalyst is composed of alumina as carrier, ruthenium as active component and cerium as additive, wherein the mass ratio of ruthenium to alumina is 0.02:1-0.15:1, and the mass ratio of cerium to alumina is 0.01:1-0.1:1; the preparation method comprises the following steps: 1) impregnating alumina with an aqueous solution containing carbon-containing organic matter, and then performing high-temperature heat treatment in an oxygen-containing atmosphere to obtain an alumina carrier; 2) placing the alumina carrier obtained in step 1) in a cerium salt solution, slowly adding a precipitant during stirring until the pH value of the mixture is 8-11, filtering and drying, and then calcining in an inert atmosphere to obtain cerium-loaded alumina; 3) impregnating the cerium-loaded alumina obtained in step 2) with a ruthenium salt solution, drying, and then performing heat treatment in a carbon-containing gas; 4) reducing the sample treated in step 3) to obtain the ruthenium-based ammonia synthesis catalyst with alumina as carrier; The carbon-containing organic matter in step 1) is any one of glucose, sucrose or fructose.

2. The process for the preparation of a ruthenium-based ammonia synthesis catalyst on an alumina support according to claim 1, characterized in that: The mass ratio of the amount of carbon-containing organic matter to alumina in step 1) is 0.03:1-0.15:

1.

3. The process for the preparation of a ruthenium-based ammonia synthesis catalyst on an alumina support according to claim 1, characterized in that: The oxygen-containing atmosphere in step 1) is air or a mixture of oxygen and any one of nitrogen, a 0-group gas; wherein the volume content of oxygen is 10%-95%; the temperature of the high-temperature heat treatment is 850-1300 ℃, and the time is 2-60 hours.

4. The process for the preparation of a ruthenium-based ammonia synthesis catalyst on an alumina support according to claim 1, characterized in that: The cerium salt used in step 2) is cerium nitrate or cerium chloride; and the precipitant is any one of ammonia water or urea.

5. The process for the preparation of a ruthenium-based ammonia synthesis catalyst on an alumina support according to claim 1, characterized in that: The inert atmosphere in step 2) is nitrogen or a 0-group gas; the temperature of the calcination is 450-800 ℃, and the time is 2-20 hours.

6. The process for the preparation of a ruthenium-based ammonia synthesis catalyst on an alumina support according to claim 1, characterized in that: The ruthenium salt solution in step 3) is any one of an aqueous solution, a methanol solution, an ethanol solution, a water-containing methanol solution or a water-containing ethanol solution of ruthenium chloride or ruthenium nitrosyl nitrate.

7. The process for the preparation of a ruthenium-based ammonia synthesis catalyst on an alumina support according to claim 1, characterized in that: The carbon-containing gas in step 3) is any one of methane, ethane, acetylene, propane, carbon monoxide or carbon dioxide, and the gas flow rate of the carbon-containing gas is 5-1000 mL / min; the temperature of the heat treatment is 450-700 ℃, and the time is 2-20 hours.

8. The process for the preparation of a ruthenium-based ammonia synthesis catalyst on an alumina support according to claim 1, characterized in that: The reduction in step 4) is performed in a hydrogen-containing gas at 200-600 ℃ for 0.2-48 hours; the hydrogen-containing gas is a mixture of hydrogen and nitrogen or a 0-group gas, wherein the volume content of hydrogen is 1%-100%.

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