Double-noble-metal-modified carbon-coated cerium dioxide catalyst as well as preparation method and application thereof

Abstract

The invention relates to a double-noble-metal-modified carbon-coated cerium dioxide catalyst and a preparation method and application thereof.The preparation method of the double-noble-metal-modified carbon-coated cerium dioxide catalyst comprises the following steps that a cerium source and a carbon source are subjected to ball milling and mixing and then calcined, and carbon-coated cerium dioxide is obtained; the carbon-coated cerium dioxide obtained in the step S1, a precious metal R source and a precious metal M source are subjected to ball-milling mixing and then calcined, and the double-precious-metal-modified carbon-coated cerium dioxide catalyst is obtained. According to the prepared double-noble-metal modified carbon-coated cerium dioxide catalyst, on one hand, the active component cerium dioxide is protected by utilizing a carbon coating technology, the stability of the cerium dioxide is improved, carbon coating is also beneficial to adsorbing heat and increasing and maintaining the temperature of the surface of the catalyst, and generated active H species can be transferred in time in the reaction process; inactivation of cerium dioxide caused by hydrogen poisoning is prevented; on the other hand, the activity and selectivity of the cerium dioxide catalyst can be further improved through modification of precious metal.

Description

Technical Field

[0001] The present invention relates to the field of thermal catalysis technology, and in particular to a dual noble metal modified carbon coated cerium dioxide catalyst and a preparation method and application thereof. Background Art

[0002] Ammonia is a key chemical for fertilizers, chemical raw materials and energy storage. It is traditionally produced under high temperature and high pressure through the Haber-Bosch process, which is suitable for continuous, centralized and large-scale synthetic ammonia production. In recent years, the global annual synthetic ammonia production is about 250 million tons. However, it cannot be ignored that this method uses fossil energy such as coal and natural gas as raw materials, and its energy consumption accounts for about 2% of global energy consumption. In the process of synthetic ammonia production, more than 500 million tons of CO2 are emitted each year, accounting for about 1%-2% of the total global carbon emissions and 15%-20% of the CO2 emissions in the chemical industry.

[0003] In the field of catalyst research, ceria, as an important rare earth oxide, has been widely studied due to its unique electronic and catalytic properties and excellent performance in redox reactions. However, ceria alone exhibits relatively poor thermal catalytic ammonia synthesis performance due to problems such as hydrogen poisoning and poor electronic response. Summary of the invention

[0004] Based on this, the purpose of the present invention is to provide a double precious metal modified carbon coated cerium dioxide catalyst and its preparation method and application. The prepared double precious metal modified carbon coated cerium dioxide catalyst has good catalytic activity and selectivity. When used as a thermal catalytic ammonia synthesis catalyst, it can achieve good catalytic effect under low temperature and low pressure conditions.

[0005] To achieve the above object, the present invention adopts the following technical solutions: The present invention first provides a method for preparing a dual noble metal modified carbon coated ceria catalyst, which comprises the following steps: S1. After ball-milling and mixing the cerium source and the carbon source, calcining to obtain carbon-coated cerium dioxide; S2. The carbon-coated cerium dioxide, the noble metal R source and the noble metal M source obtained in step S1 are ball-milled and mixed, and then calcined to obtain a dual-noble metal-modified carbon-coated cerium dioxide catalyst.

[0006] As a further improvement of the above scheme of the present invention, in step S1, the cerium source is one of cerium nitrate, cerium acetate, cerium carbonate, cerium sulfate, and cerium oxalate; And / or, in step S1, the carbon source is one of flake graphite, glucose, sucrose, stearic acid, starch, and cellulose; And / or, in step S1, in the carbon-coated cerium dioxide, the mass ratio of cerium dioxide to carbon is 1:(0.01-1).

[0007] As a further improvement of the above scheme of the present invention, in step S1, the ball-to-material ratio of the ball milling is 1-50:1, the ball milling speed is 200-800 rpm, and the ball milling time is 1-24 hours; And / or, in step S1, the calcination is carried out in a muffle furnace at 200-500° C. for 2-10 h, and the heating rate of the calcination is 2-10° C. / min.

[0008] As a further improvement of the above solution of the present invention, in step S2, the noble metal R is ruthenium; and / or, in step S2, the noble metal M is one of Rh, Pd, Ag, Ir, Pt, and Au; And / or, in step S2, in the dual precious metal modified carbon-coated cerium dioxide catalyst, the mass ratio of carbon-coated cerium dioxide, precious metal R, and precious metal M is 1:(0.01~0.1):(0.01~0.1).

[0009] As a further improvement of the above scheme of the present invention, in step S2, the noble metal R source is one of ruthenium acetate, triruthenium dodecacarbonyl, ruthenium trichloride hydrate, and trinitronitrosyl ruthenium; And / or, in step S2, the source of the noble metal M is a nitrate, acetate or carbonyl complex of the noble metal M.

[0010] As a further improvement of the above scheme of the present invention, in step S2, the ball-to-material ratio of the ball milling is 1-50:1, the ball milling speed is 200-800 rpm, and the ball milling time is 1-24 hours; And / or, in step S2, the calcination is carried out in a tubular furnace in a 10% H2 / Ar mixed atmosphere at 200-500°C for 2-10 hours, and the heating rate of the calcination is 1-5°C / min.

[0011] The present invention also provides a dual noble metal modified carbon coated cerium dioxide catalyst, which is prepared by the above-mentioned preparation method.

[0012] The present invention also provides an application of a dual noble metal modified carbon coated cerium dioxide catalyst prepared by the above-mentioned preparation method in thermal catalytic synthesis of ammonia.

[0013] As a further improvement of the above scheme of the present invention, it includes the following steps: loading the dual noble metal modified carbon coated cerium dioxide catalyst into the reaction tube of the synthetic ammonia fixed reaction bed, introducing a mixed gas of N2 and H2, and heating for catalytic reaction.

[0014] As a further improvement of the above scheme of the present invention, the molar ratio of N2 to H2 is 1:0.5-5, and the flow rate of the mixed gas is 20-300 mL / min; And / or, the temperature of the heating catalytic reaction is 100-400° C. and the pressure is 0.1-5 MPa.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The invention simply and efficiently prepares a large amount of dual-noble metal-modified carbon-coated cerium dioxide by a two-step ball milling and calcining method: firstly, a cerium source and a carbon source are directly dry-milled to make the carbon source evenly distributed on the surface of the cerium source, and then the carbon-coated cerium dioxide is obtained after calcination; then the noble metal source and the carbon-coated cerium dioxide are further ball-milled to make the noble metal source evenly distributed on the surface of the carbon-coated cerium dioxide, and after calcination with reducing gas, the dual-noble metal-modified carbon-coated cerium dioxide is obtained. The preparation method is simple, a large amount of catalysts can be simply and quickly synthesized, and the atomic utilization rate is high, the obtained catalyst has good activity, the requirements for equipment and raw materials are low, the economic effect is high, the noble metals are evenly dispersed on the surface of the carbon-coated cerium dioxide, the atomic utilization rate is high, and no raw material waste is caused.

[0016] The dual noble metal modified carbon coated cerium dioxide catalyst prepared by the present invention, on the one hand, utilizes the carbon coating technology to protect the active component cerium dioxide and prevent sintering of cerium dioxide, thereby improving the stability of cerium dioxide. The carbon coating is also conducive to adsorbing heat, increasing and maintaining the temperature of the catalyst surface, and can also timely transfer the generated active H species during the reaction to prevent the catalyst from being deactivated by hydrogen poisoning. On the other hand, the activity and selectivity of the catalyst can be further improved through the modification of the noble metals, and the synergistic effect of the dual noble metals can effectively reduce the limiting relationship between the reaction energy barrier of a single metal and the adsorption energy of the reaction species, thereby achieving strong N2 adsorption during the reaction and having strong NH3 desorption ability, which can further improve the activity and selectivity of the cerium dioxide catalyst, and achieve a good catalytic synthesis of ammonia under low temperature and low pressure conditions.

[0017] The dual noble metal modified carbon coated cerium dioxide catalyst prepared by the present invention is used as a thermal catalytic ammonia synthesis catalyst, can achieve good catalytic effect under low temperature and low pressure conditions, and has good cycle stability. Compared with the traditional industrial ammonia synthesis process, it can effectively reduce energy consumption and carbon dioxide emissions, greatly broaden the research and development in the field of green ammonia, and solve the problems of high energy consumption and low efficiency in the prior art, providing new ideas and methods for the development of ammonia synthesis technology, which has important scientific significance and application value for promoting the green transformation of ammonia synthesis technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The scanning electron microscope image and element distribution map of Ru-Rh / CeO2@C prepared in Example 1 of the present invention; Figure 2 The activity diagram of the thermal catalytic synthesis of ammonia in Application Example 1 of the present invention; Figure 3 The activity diagram of the thermal catalytic synthesis of ammonia in Application Example 2 of the present invention; Figure 4 The activity diagram of the thermal catalytic synthesis of ammonia in Application Example 3 of the present invention; Figure 5 This is the activity diagram of the thermal catalytic synthesis of ammonia according to Application Example 4 of the present invention. DETAILED DESCRIPTION

[0019] For ease of understanding of the present invention, the present invention will be described more fully below in conjunction with specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thoroughly understood.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0021] Example 1 This embodiment provides a dual noble metal modified carbon coated ceria catalyst, the preparation method of which comprises the following steps: S1. 21.7 g of Ce(NO3)3·6H2O and 4.3 g of flake graphite were placed in a zirconia grinding jar of a planetary ball mill for ball milling, with a ball-to-material ratio of 30:1, a ball milling speed of 400 rpm, and a ball milling time of 10 h. After the ball milling was completed, the material was taken out and placed in a muffle furnace, and the temperature was raised to 300 ° C at a heating rate of 5 ° C / min, and kept at 300 ° C for 4 h to obtain carbon-coated cerium dioxide CeO2@C.

[0022] S2. Take 1g of CeO2@C obtained in step S1, 92.4mg of RuCl3·xH2O, and 73.4mg of (CH3COO)3Rh and place them in the zirconia grinding jar of a planetary ball mill for ball milling, with a ball-to-material ratio of 20:1, a ball milling speed of 500rpm, and a ball milling time of 8h. After the ball milling is completed, take out the material, wash it with deionized water to remove Cl ions, dry it, place it in a tube furnace, pass 10% H2 / Ar gas at a rate of 30mL / min, heat it to 400℃ at a heating rate of 2℃ / min, and keep it at 400℃ for 4h to obtain a dual noble metal modified carbon-coated cerium dioxide catalyst RuRh-CeO2@C.

[0023] Figure 1 The scanning electron microscope image and surface scanning mapping of RuRh-CeO2@C prepared in this embodiment are shown in FIG. Figure 1It can be seen that the overall morphology of RuRh-CeO2@C is a rod-like structure, C covers CeO2, and Ru and Rh are evenly distributed on the surface of CeO2@C.

[0024] Example 2 This embodiment provides a dual noble metal modified carbon coated ceria catalyst, the preparation method of which comprises the following steps: S1. 21.7 g of Ce(NO3)3·6H2O and 32.3 g of glucose were placed in a zirconia grinding jar of a planetary ball mill for ball milling, with a ball-to-material ratio of 30:1, a ball milling speed of 500 rpm, and a ball milling time of 12 h. After the ball milling was completed, the material was taken out and placed in a muffle furnace, heated to 300 °C at a heating rate of 3 °C / min, and kept at 300 °C for 6 h to obtain carbon-coated cerium dioxide CeO2@C.

[0025] S2. Take 1g of CeO2@C obtained in step S1 and 0.5g of Ru3(CO) 12 42.2 mg of Pd(O2CCH3)2 was placed in a zirconia grinding jar of a planetary ball mill for ball milling, with a ball-to-material ratio of 30:1, a ball milling speed of 400 rpm, and a ball milling time of 12 h. After the ball milling was completed, the material was taken out and placed in a tube furnace, 10% H2 / Ar gas was introduced at a rate of 50 mL / min, and the temperature was raised to 400 °C at a heating rate of 3 °C / min, and kept at 400 °C for 4 h to obtain a dual noble metal modified carbon-coated cerium dioxide catalyst RuPd-CeO2@C.

[0026] Example 3 This embodiment provides a dual noble metal modified carbon coated ceria catalyst, the preparation method of which comprises the following steps: S1. 21.7 g of Ce(NO3)3·6H2O and 30 g of cellulose were placed in a zirconia grinding jar of a planetary ball mill for ball milling, with a ball-to-material ratio of 30:1, a ball milling speed of 400 rpm, and a ball milling time of 15 h. After the ball milling was completed, the material was taken out and placed in a muffle furnace, and the temperature was raised to 400 ° C at a heating rate of 3 ° C / min, and kept at 400 ° C for 6 h to obtain carbon-coated cerium dioxide CeO2@C.

[0027] S2. Take 1g of CeO2@C obtained in step S1, 220.2mg of C6H9O6Ru, and 130.86mg of N2O6Pt and place them in the zirconia grinding jar of a planetary ball mill for ball milling, with a ball-to-material ratio of 30:1, a ball milling speed of 500rpm, and a ball milling time of 8h. After the ball milling is completed, take out the material, place it in a tubular furnace, introduce 10% H2 / Ar gas at a rate of 20mL / min, increase the temperature to 400℃ at a heating rate of 3℃ / min, and keep it at 400℃ for 4h to obtain a dual noble metal modified carbon-coated cerium dioxide catalyst RuPt-CeO2@C.

[0028] Example 4 This embodiment provides a dual noble metal modified carbon coated ceria catalyst, the preparation method of which comprises the following steps: S1. 21.7 g of Ce(NO3)3·6H2O and 28.4 g of stearic acid were placed in a zirconia grinding jar of a planetary ball mill for ball milling, with a ball-to-material ratio of 30:1, a ball milling speed of 500 rpm, and a ball milling time of 16 h. After the ball milling was completed, the material was taken out and placed in a muffle furnace, and the temperature was raised to 300 ° C at a heating rate of 5 ° C / min, and kept at 300 ° C for 10 h to obtain carbon-coated cerium dioxide CeO2@C.

[0029] S2. Take 1g of CeO2@C obtained in step S1 and 188.2mg of N4O 10 Ru and 113.96 mg of (CH3COO)3Au were placed in a zirconia grinding jar of a planetary ball mill for ball milling, with a ball-to-material ratio of 30:1, a ball milling speed of 500 rpm, and a ball milling time of 8 hours. After the ball milling was completed, the material was taken out and placed in a tube furnace, 10% H2 / Ar gas was introduced at a rate of 20 mL / min, and the temperature was raised to 400°C at a heating rate of 5°C / min, and kept at 400°C for 6 hours to obtain a dual noble metal modified carbon-coated cerium dioxide catalyst RuAu-CeO2@C.

[0030] Comparative Example 1 This comparative example proposes a cerium dioxide catalyst, and its preparation method comprises the following steps: 21.7g of Ce(NO3)3·6H2O is placed in a zirconia grinding tank of a planetary ball mill for ball milling, the ball-to-material ratio is 30:1, the ball milling speed is 400rpm, and the ball milling time is 10h. After the ball milling is completed, the material is taken out, placed in a muffle furnace, and the temperature is raised to 300℃ at a heating rate of 5℃ / min, and kept at 300℃ for 4h to obtain cerium dioxide CeO2.

[0031] Comparative Example 2 This comparative example adopts the same implementation method as Example 1, and the difference from Example 1 is that no flake graphite is added in step S1 of this comparative example to prepare a dual precious metal modified cerium dioxide catalyst RuRh-CeO2.

[0032] Comparative Example 3 This comparative example adopts the same implementation method as Example 1, and the difference from Example 1 is that no (CH3COO)3Rh is added in step S2 of this comparative example to prepare a single precious metal Ru modified carbon-coated cerium dioxide catalyst Ru-CeO2@C.

[0033] Comparative Example 4 This comparative example adopts the same implementation method as Example 1, and the difference from Example 1 is that in step S2 of this comparative example, no RuCl3·xH2O is added to prepare a single precious metal Rh modified carbon-coated cerium dioxide catalyst Rh-CeO2@C.

[0034] Comparative Example 5 This comparative example proposes a cerium dioxide catalyst, and its preparation method comprises the following steps: 21.7g of Ce(NO3)3·6H2O is placed in a zirconia grinding tank of a planetary ball mill for ball milling, the ball-to-material ratio is 30:1, the ball milling speed is 500rpm, and the ball milling time is 12h. After the ball milling is completed, the material is taken out, placed in a muffle furnace, and the temperature is raised to 300°C at a heating rate of 3°C / min, and kept at 300°C for 6h to obtain cerium dioxide CeO2.

[0035] Comparative Example 6 This comparative example adopts the same implementation method as Example 2, and the difference from Example 2 is that glucose is not added in step S1 of this comparative example to prepare a dual noble metal modified cerium dioxide catalyst RuPd-CeO2.

[0036] Comparative Example 7 This comparative example adopts the same implementation method as Example 2, and the difference from Example 2 is that Pd(O2CCH3)2 is not added in step S2 of this comparative example to prepare a single precious metal Ru modified carbon-coated cerium dioxide catalyst Ru-CeO2@C.

[0037] Comparative Example 8 This comparative example adopts the same implementation method as Example 2, and the difference from Example 2 is that Ru3(CO) is not added in step S2 of this comparative example. 12 , and prepared the single precious metal Pd modified carbon-coated cerium dioxide catalyst Pd-CeO2@C.

[0038] Comparative Example 9 This comparative example proposes a cerium dioxide catalyst, and its preparation method comprises the following steps: 21.7g of Ce(NO3)3·6H2O is placed in a zirconia grinding tank of a planetary ball mill for ball milling, the ball-to-material ratio is 30:1, the ball milling speed is 400rpm, and the ball milling time is 15h. After the ball milling is completed, the material is taken out, placed in a muffle furnace, and heated to 400℃ at a heating rate of 3℃ / min, and kept at 400℃ for 6h to obtain cerium dioxide CeO2.

[0039] Comparative Example 10 This comparative example adopts the same implementation as Example 3, and the difference from Example 3 is that in step S1 of this comparative example, no cellulose is added to prepare a dual noble metal modified cerium dioxide catalyst RuPt-CeO2.

[0040] Comparative Example 11 This comparative example adopts the same implementation method as Example 3, and the difference from Example 3 is that: in step S2 of this comparative example, no N2O6Pt is added, and a single precious metal Ru-modified carbon-coated cerium dioxide catalyst Ru-CeO2@C is prepared.

[0041] Comparative Example 12 This comparative example adopts the same implementation method as Example 3, and the difference from Example 3 is that: C6H9O6Ru is not added in step S2 of this comparative example, and a single precious metal Pt-modified carbon-coated cerium dioxide catalyst Pt-CeO2@C is prepared.

[0042] Comparative Example 13 This comparative example proposes a cerium dioxide catalyst, and its preparation method comprises the following steps: 21.7g of Ce(NO3)3·6H2O is placed in a zirconia grinding tank of a planetary ball mill for ball milling, the ball-to-material ratio is 30:1, the ball milling speed is 500rpm, and the ball milling time is 16h. After the ball milling is completed, the material is taken out, placed in a muffle furnace, and the temperature is raised to 300°C at a heating rate of 5°C / min, and kept at 300°C for 10h to obtain cerium dioxide CeO2.

[0043] Comparative Example 14 This comparative example adopts the same implementation as Example 4, and the difference from Example 4 is that stearic acid is not added in step S1 of this comparative example to prepare a dual noble metal modified cerium dioxide catalyst RuAu-CeO2.

[0044] Comparative Example 15 This comparative example adopts the same implementation method as Example 4, and the difference from Example 4 is that no (CH3COO)3Au is added in step S2 of this comparative example to prepare a single precious metal Ru modified carbon-coated cerium dioxide catalyst Ru-CeO2@C.

[0045] Comparative Example 16 This comparative example adopts the same implementation method as Example 4, and the difference from Example 4 is that in step S2 of this comparative example, no N4O is added. 10 Ru, and prepared the single precious metal Au modified carbon coated cerium dioxide catalyst Au-CeO2@C.

[0046] Application Example 1 In this application example, RuRh-CeO2@C prepared in Example 1, CeO2@C prepared in step S1 of Example 1, CeO2 prepared in Comparative Example 1, RuRh-CeO2 prepared in Comparative Example 2, Ru-CeO2@C prepared in Comparative Example 3, and Rh-CeO2@C prepared in Comparative Example 4 are used as thermal catalytic ammonia synthesis catalysts for thermal catalytic ammonia synthesis. The thermal catalytic ammonia synthesis method is as follows: 500 mg of the catalyst is loaded in a quartz reaction tube of a fixed bed reactor for ammonia synthesis, the reaction temperature is fixed at 400°C, the reaction pressure is 5 MPa, the molar ratio of N2:H2 is 1:3, the flow rate is 60 mL / min, and the generated ammonia is detected.

[0047] Figure 2 The thermal catalytic ammonia synthesis activity diagram of the above catalysts is shown in Figure 2. Figure 2 It can be seen that the thermal catalytic ammonia synthesis activity of RuRh-CeO2@C is significantly higher than that of CeO2@C, CeO2, RuRh-CeO2, Ru-CeO2@C, and Rh-CeO2@C, indicating that there is a corresponding promotion effect between the Ru and Rh noble metals, which is conducive to the improvement of the thermal catalytic ammonia synthesis efficiency. Figure 2 It can be found that CeO2@C and RuRh-CeO2@C have significantly improved activities compared to CeO2 and RuRh-CeO2 without C coating, which is attributed to the dual role of C: C is conducive to the adsorption of heat to increase and maintain the temperature of the catalyst surface and to timely transfer the active H species generated during the reaction, preventing the catalyst from being deactivated by hydrogen poisoning.

[0048] Application Example 2 In this application example, RuPd-CeO2@C prepared in Example 2, CeO2@C prepared in step S1 of Example 2, CeO2 prepared in Comparative Example 5, RuPd-CeO2 prepared in Comparative Example 6, Ru-CeO2@C prepared in Comparative Example 7, and Pd-CeO2@C prepared in Comparative Example 8 are used as thermal catalytic ammonia synthesis catalysts for thermal catalytic ammonia synthesis. The thermal catalytic ammonia synthesis method is as follows: 500 mg of the catalyst is loaded into a quartz reaction tube of a fixed bed reactor for ammonia synthesis, the reaction temperature is fixed at 400°C, the reaction pressure is 3 MPa, the molar ratio of N2:H2 is 2:3, the flow rate is 180 mL / min, and the generated ammonia is detected.

[0049] Figure 3 The thermal catalytic ammonia synthesis activity diagram of the above catalysts is shown in Figure 2. Figure 3 It can be seen that the thermal catalytic ammonia synthesis activity of RuPd-CeO2@C is significantly higher than that of CeO2@C, CeO2, RuPd-CeO2, Ru-CeO2@C, and Pd-CeO2@C, indicating that there is a corresponding promotion effect between the Ru and Pd noble metals, which is conducive to the improvement of the thermal catalytic ammonia synthesis efficiency. Figure 3It can be found that CeO2@C and RuPd-CeO2@C have significantly improved activity compared to CeO2 and RuPd-CeO2 without C coating, which is attributed to the dual role of C: C is conducive to adsorbing heat to increase and maintain the temperature of the catalyst surface, and timely transfer of active H species generated during the reaction to prevent the catalyst from being deactivated by hydrogen poisoning.

[0050] Application Example 3 In this application example, RuPt-CeO2@C prepared in Example 3, CeO2@C prepared in step S1 of Example 3, CeO2 prepared in Comparative Example 9, RuPt-CeO2 prepared in Comparative Example 10, Ru-CeO2@C prepared in Comparative Example 11, and Pt-CeO2@C prepared in Comparative Example 12 are used as thermal catalytic ammonia synthesis catalysts for thermal catalytic ammonia synthesis. The thermal catalytic ammonia synthesis method is as follows: 500 mg of the catalyst is loaded in a quartz reaction tube of a fixed bed reactor for ammonia synthesis, the reaction temperature is fixed at 400°C, the reaction pressure is 4 MPa, the molar ratio of N2:H2 is 1:3, the flow rate is 90 mL / min, and the generated ammonia is detected.

[0051] Figure 4 The thermal catalytic ammonia synthesis activity diagram of the above catalysts is shown in Figure 2. Figure 4 It can be seen that the thermal catalytic ammonia synthesis activity of RuPt-CeO2@C is significantly higher than that of CeO2@C, CeO2, RuPt-CeO2, Ru-CeO2@C, and Pt-CeO2@C, indicating that there is a corresponding promotion effect between the Ru and Pt noble metals, which is conducive to the improvement of the thermal catalytic ammonia synthesis efficiency. Figure 4 It can be found that CeO2@C and RuPt-CeO2@C have significantly improved activity compared to CeO2 and RuPt-CeO2 without C coating, which is attributed to the dual role of C: C is conducive to the adsorption of heat to increase and maintain the temperature of the catalyst surface, and to the timely transfer of the active H species generated during the reaction to prevent the catalyst from being deactivated by hydrogen poisoning.

[0052] Application Example 4 In this application example, RuAu-CeO2@C prepared in Example 4, CeO2@C prepared in step S1 of Example 4, CeO2 prepared in Comparative Example 13, RuAu-CeO2 prepared in Comparative Example 14, Ru-CeO2@C prepared in Comparative Example 15, and Au-CeO2@C prepared in Comparative Example 16 are used as thermal catalytic ammonia synthesis catalysts for thermal catalytic ammonia synthesis. The thermal catalytic ammonia synthesis method is as follows: 500 mg of the catalyst is loaded into a quartz reaction tube of a fixed bed reactor for ammonia synthesis, the reaction temperature is fixed at 400°C, the reaction pressure is 5 MPa, the molar ratio of N2:H2 is 2:3, the flow rate is 90 mL / min, and the generated ammonia is detected.

[0053] Figure 5 The thermal catalytic ammonia synthesis activity diagram of the above catalysts is shown in Figure 2. Figure 5 It can be seen that the thermal catalytic ammonia synthesis activity of RuAu-CeO2@C is significantly higher than that of CeO2@C, CeO2, RuAu-CeO2, Ru-CeO2@C, and Au-CeO2@C, indicating that there is a corresponding promotion effect between Ru and Au noble metals, which is conducive to the improvement of the thermal catalytic ammonia synthesis efficiency. Figure 5 It can be found that CeO2@C and RuAu-CeO2@C have significantly improved activity compared to CeO2 and RuAu-CeO2 without C coating, which is attributed to the dual role of C: C is conducive to the adsorption of heat to increase and maintain the temperature of the catalyst surface and to timely transfer the active H species generated during the reaction, preventing the catalyst from being deactivated by hydrogen poisoning.

[0054] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0055] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing a dual noble metal modified carbon-coated ceria catalyst, characterized in that: It includes the following steps: S1. After ball-milling and mixing the cerium source and the carbon source, calcining to obtain carbon-coated cerium dioxide; S2. The carbon-coated cerium dioxide, the noble metal R source and the noble metal M source obtained in step S1 are ball-milled and mixed, and then calcined to obtain a dual-noble metal-modified carbon-coated cerium dioxide catalyst.

2. The method for preparing a dual noble metal modified carbon-coated ceria catalyst according to claim 1, characterized in that: In step S1, the cerium source is one of cerium nitrate, cerium acetate, cerium carbonate, cerium sulfate, and cerium oxalate; And / or, in step S1, the carbon source is one of flake graphite, glucose, sucrose, stearic acid, starch, and cellulose; And / or, in step S1, in the carbon-coated cerium dioxide, the mass ratio of cerium dioxide to carbon is 1:(0.01-1).

3. The method for preparing a dual noble metal modified carbon-coated ceria catalyst according to claim 1, characterized in that: In step S1, the ball-to-material ratio of the ball milling is 1-50:1, the ball milling speed is 200-800 rpm, and the ball milling time is 1-24 h; And / or, in step S1, the calcination is carried out in a muffle furnace at 200-500° C. for 2-10 h, and the heating rate of the calcination is 2-10° C. / min.

4. The method for preparing a dual noble metal modified carbon-coated ceria catalyst according to claim 1, characterized in that: In step S2, the noble metal R is ruthenium; and / or, in step S2, the noble metal M is one of Rh, Pd, Ag, Ir, Pt, and Au; And / or, in step S2, in the dual precious metal modified carbon-coated cerium dioxide catalyst, the mass ratio of carbon-coated cerium dioxide, precious metal R, and precious metal M is 1:(0.01~0.1):(0.01~0.1).

5. The method for preparing a dual noble metal modified carbon coated ceria catalyst according to claim 4, characterized in that: In step S2, the noble metal R source is one of ruthenium acetate, triruthenium dodecacarbonyl, ruthenium trichloride hydrate, and trinitronitrosyl ruthenium; And / or, in step S2, the source of the noble metal M is a nitrate, acetate or carbonyl complex of the noble metal M.

6. The method for preparing a dual noble metal modified carbon coated ceria catalyst according to claim 1, characterized in that: In step S2, the ball-to-material ratio of the ball milling is 1-50:1, the ball milling speed is 200-800 rpm, and the ball milling time is 1-24 h; And / or, in step S2, the calcination is carried out in a tubular furnace in a 10% H2 / Ar mixed atmosphere at 200-500°C for 2-10 hours, and the heating rate of the calcination is 1-5°C / min.

7. A dual noble metal modified carbon coated ceria catalyst, characterized in that: The invention is prepared by the preparation method described in any one of claims 1 to 6.

8. Use of a dual noble metal modified carbon coated cerium dioxide catalyst prepared by the preparation method according to any one of claims 1 to 6 in thermal catalytic synthesis of ammonia.

9. The use according to claim 8, characterized in that: It includes the following steps: The dual noble metal modified carbon coated cerium dioxide catalyst is loaded into the reaction tube of the synthetic ammonia fixed reaction bed, and a mixed gas of N2 and H2 is introduced to heat and react catalytically.

10. The use according to claim 9, characterized in that: In the mixed gas, the molar ratio of N2 to H2 is 1:0.5-5, and the flow rate of the mixed gas is 20-300 mL / min; And / or, the temperature of the heating catalytic reaction is 100-400° C. and the pressure is 0.1-5 MPa.

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