A dual-noble-metal modified carbon-coated cerium dioxide catalyst, its preparation method and application

Abstract

This invention relates to a dual-noble-metal modified carbon-coated cerium dioxide catalyst, its preparation method, and its application. The dual-noble-metal modified carbon-coated cerium dioxide catalyst comprises the following steps: ball milling and mixing a cerium source and a carbon source, followed by calcination to obtain carbon-coated cerium dioxide; ball milling and mixing the carbon-coated cerium dioxide obtained in step S1, a noble metal R source, and a noble metal M source, followed by calcination, to obtain the dual-noble-metal modified carbon-coated cerium dioxide catalyst. The dual-noble-metal modified carbon-coated cerium dioxide catalyst prepared by this invention, on the one hand, utilizes carbon coating technology to protect the active component cerium dioxide, improving the stability of cerium dioxide. Carbon coating also facilitates heat adsorption, increasing and maintaining the temperature of the catalyst surface, and can promptly transfer the generated active H species during the reaction, preventing cerium dioxide from undergoing hydrogen poisoning and deactivation. On the other hand, through the modification with noble metals, the activity and selectivity of the cerium dioxide catalyst can be further improved.

Description

Technical Field

[0001] This invention relates to the field of thermocatalysis technology, and in particular to a dual-noble-metal modified carbon-coated cerium dioxide catalyst, its preparation method, and its application. Background Technology

[0002] Ammonia is a key chemical in fertilizers, chemical raw materials, and energy storage. Traditionally, it is produced using the Haber-Bosch process under high temperature and pressure conditions, suitable for continuous, centralized, and large-scale synthetic ammonia production. In recent years, the global annual synthetic ammonia production has been around 250 million tons. However, it is undeniable that this method uses fossil fuels such as coal and natural gas as raw materials, consuming approximately 2% of global energy consumption. The synthetic ammonia production process emits more than 500 million tons of CO2 annually, accounting for about 1%-2% of global carbon emissions and 15%-20% of CO2 emissions from the chemical industry.

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

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

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] This invention first provides a method for preparing a cerium dioxide catalyst modified with two noble metals and coated with carbon, which includes the following steps:

[0007] S1. After ball milling and mixing the cerium source and carbon source, calcination is performed to obtain carbon-coated cerium dioxide;

[0008] S2. After ball milling and mixing the carbon-coated cerium dioxide, noble metal R source, and noble metal M source obtained in step S1, the mixture is calcined to obtain the dual-noble metal modified carbon-coated cerium dioxide catalyst.

[0009] As a further improvement to the above-mentioned solution of the present invention, in step S1, the cerium source is one of cerium nitrate, cerium acetate, cerium carbonate, cerium sulfate, and cerium oxalate.

[0010] And / or, in step S1, the carbon source is one of flake graphite, glucose, sucrose, hard acid, starch, and cellulose;

[0011] And / or, in step S1, the mass ratio of cerium dioxide to carbon in the carbon-coated cerium dioxide is 1:(0.01~1).

[0012] As a further improvement to the above-mentioned solution of the present invention, in step S1, the ball-to-material ratio of the ball mill is 1-50:1, the ball milling speed is 200-800 rpm, and the ball milling time is 1-24 h.

[0013] And / or, in step S1, the calcination is carried out in a muffle furnace at 200~500℃ for 2~10h, and the heating rate of the calcination is 2~10℃ / min.

[0014] As a further improvement to the above-described solution of the present invention, in step S2, the noble metal R is ruthenium;

[0015] And / or, in step S2, the precious metal M is one of Rh, Pd, Ag, Ir, Pt, and Au;

[0016] And / or, in step S2, the mass ratio of carbon-coated cerium dioxide, noble metal R, and noble metal M in the dual noble metal modified carbon-coated cerium dioxide catalyst is 1:(0.01~0.1):(0.01~0.1).

[0017] As a further improvement to the above-mentioned scheme of the present invention, in step S2, the noble metal R source is one of ruthenium acetate, dodecyltriruthenium, ruthenium trichloride hydrate, and trinitronitrosylruthenium;

[0018] And / or, in step S2, the source of noble metal M is a nitrate, acetate, or carbonyl complex of noble metal M.

[0019] As a further improvement to the above-mentioned solution of the present invention, in step S2, the ball-to-material ratio of the ball mill is 1-50:1, the ball milling speed is 200-800 rpm, and the ball milling time is 1-24 h.

[0020] And / or, in step S2, the calcination is carried out in a tube furnace at 200~500℃ for 2~10h in a 10% H2 / Ar mixed atmosphere, with a heating rate of 1~5℃ / min.

[0021] The present invention also provides a cerium dioxide catalyst with carbon-coated by dual noble metal modification, which is prepared by the preparation method described above.

[0022] The present invention also provides the application of a cerium dioxide catalyst with dual noble metal modified carbon prepared by the preparation method described above in the thermocatalytic synthesis of ammonia.

[0023] As a further improvement to the above-mentioned scheme of the present invention, it includes the following steps: filling the reaction tube of the fixed reaction bed for ammonia synthesis with the dual noble metal modified carbon-coated cerium dioxide catalyst, introducing a mixture of N2 and H2 gas, and heating to catalyze the reaction.

[0024] As a further improvement to the above-mentioned scheme of the present invention, the molar ratio of N2 and H2 is 1:0.5-5, and the flow rate of the mixed gas is 20-300 mL / min;

[0025] And / or, the temperature of the heating catalytic reaction is 100-400℃ and the pressure is 0.1-5MPa.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] This invention provides a simple and efficient method for the large-scale preparation of carbon-coated cerium dioxide modified with dual noble metals through a two-step ball milling and calcination process: First, a cerium source and a carbon source are directly dry-milled to ensure uniform distribution of the carbon source on the cerium source surface, followed by calcination to obtain carbon-coated cerium dioxide; then, the noble metal source and carbon-coated cerium dioxide are further ball-milled to ensure uniform distribution of the noble metal source on the carbon-coated cerium dioxide surface, followed by calcination with reducing gas to obtain carbon-coated cerium dioxide modified with dual noble metals. The preparation method is simple, allowing for the rapid and easy synthesis of large quantities of catalysts with high atom utilization, good catalyst activity, low requirements for equipment and raw materials, and high economic efficiency. The noble metals are uniformly dispersed on the surface of the carbon-coated cerium dioxide, resulting in high atom utilization and avoiding raw material waste.

[0028] The cerium dioxide catalyst modified with dual noble metals and coated with carbon obtained by this invention has two advantages. First, the carbon coating technology protects the active component cerium dioxide, preventing cerium dioxide sintering and thus improving the stability of cerium dioxide. The carbon coating also helps to adsorb heat, increase and maintain the temperature of the catalyst surface, and can promptly transfer the generated active H species during the reaction, preventing the catalyst from being deactivated by hydrogen poisoning. Second, the modification with noble metals can further improve the activity and selectivity of the catalyst. The synergistic effect of the two noble metals can effectively reduce the limiting relationship between the reaction energy barrier of a single metal and the adsorption energy of the reactants, achieving strong N2 adsorption and strong NH3 desorption capacity during the reaction. This can further improve the activity and selectivity of the cerium dioxide catalyst, and achieve good catalytic ammonia synthesis under low temperature and low pressure conditions.

[0029] The cerium dioxide catalyst with dual noble metal modified carbon prepared by this invention can be used as a thermocatalytic ammonia synthesis catalyst. It 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 of the green ammonia field, and solve the problems of high energy consumption and low efficiency in the existing technology. It provides new ideas and methods for the development of ammonia synthesis technology and has important scientific significance and application value for promoting the green transformation of ammonia synthesis technology. Attached Figure Description

[0030] Figure 1 The scanning electron microscope image and elemental distribution map of Ru-Rh / CeO2@C prepared in Example 1 of this invention are shown.

[0031] Figure 2 This is an activity diagram of the thermocatalytic synthesis of ammonia in Application Example 1 of the present invention;

[0032] Figure 3 This is an activity diagram of the thermocatalytic synthesis of ammonia in Application Example 2 of the present invention;

[0033] Figure 4 This is an activity diagram of the thermocatalytic synthesis of ammonia in Example 3 of the present invention;

[0034] Figure 5 This is an activity diagram of the thermocatalytic synthesis of ammonia in Application Example 4 of the present invention. Detailed Implementation

[0035] To facilitate understanding of the present invention, a more comprehensive description will be given below with reference to specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0037] Example 1

[0038] This embodiment proposes a dual-noble-metal modified carbon-coated cerium dioxide catalyst, the preparation method of which includes the following steps:

[0039] S1. 21.7 g of Ce(NO3)3·6H2O and 4.3 g of flake graphite were placed in the zirconium grinding jar of a planetary ball mill and ball-to-material ratio was 30:1. The ball milling speed was 400 rpm and the ball milling time was 10 h. After ball milling, the material was removed and placed in a muffle furnace. The temperature was increased to 300 °C at a heating rate of 5 °C / min and held at 300 °C for 4 h to obtain carbon-coated cerium dioxide CeO2@C.

[0040] 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 zirconium oxide grinding jar of a planetary ball mill for ball milling. The ball-to-material ratio is 20:1, the ball milling speed is 500rpm, and the ball milling time is 8h. After ball milling, remove the material, wash it with deionized water to remove Cl ions, dry it, and place it in a tube furnace. 10% H2 / Ar gas is introduced at a rate of 30mL / min, and the temperature is raised to 400℃ at a rate of 2℃ / min. The temperature is then maintained at 400℃ for 4h to obtain the dual noble metal modified carbon-coated cerium dioxide catalyst RuRh-CeO2@C.

[0041] Figure 1 The images and area scan mappings of RuRh-CeO2@C obtained in this embodiment are obtained from scanning electron microscopy. Figure 1 It can be seen that the overall morphology of RuRh-CeO2@C is a rod-shaped structure, with C coating CeO2 and Ru and Rh uniformly distributed on the surface of CeO2@C.

[0042] Example 2

[0043] This embodiment proposes a dual-noble-metal modified carbon-coated cerium dioxide catalyst, the preparation method of which includes the following steps:

[0044] S1. 21.7 g of Ce(NO3)3·6H2O and 32.3 g of glucose were placed in the zirconium grinding jar of a planetary ball mill and ball-to-material ratio was 30:1. The ball milling speed was 500 rpm and the ball milling time was 12 h. After ball milling, the material was removed and placed in a muffle furnace. The temperature was increased to 300 °C at a heating rate of 3 °C / min and held at 300 °C for 6 h to obtain carbon-coated cerium dioxide CeO2@C.

[0045] S2. Take 1g of CeO2@C obtained in step S1 and 0.5g of Ru3(CO). 1242.2 mg of Pd(O2CCH3)2 was placed in the zirconium oxide grinding jar of a planetary ball mill and ball-to-material ratio was 30:1. The ball milling speed was 400 rpm, and the ball milling time was 12 h. After ball milling, the material was removed 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 rate of 3 °C / min. The temperature was then maintained at 400 °C for 4 h to obtain the dual noble metal modified carbon-coated cerium dioxide catalyst RuPd-CeO2@C.

[0046] Example 3

[0047] This embodiment proposes a dual-noble-metal modified carbon-coated cerium dioxide catalyst, the preparation method of which includes the following steps:

[0048] S1. 21.7g of Ce(NO3)3·6H2O and 30g of cellulose were placed in the zirconium grinding jar of a planetary ball mill and ball-to-material ratio was 30:1. The ball milling speed was 400 rpm and the ball milling time was 15h. After ball milling, the material was removed and placed in a muffle furnace. The temperature was increased to 400℃ at a heating rate of 3℃ / min and held at 400℃ for 6h to obtain carbon-coated cerium dioxide CeO2@C.

[0049] S2. Take 1g of CeO2@C obtained in step S1, 220.2mg of C6H9O6Ru, and 130.86mg of N2O6Pt and place them in the zirconium grinding jar 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 8h. After ball milling, remove the material and place it in a tube furnace. 10% H2 / Ar gas is introduced at a rate of 20mL / min, and the temperature is raised to 400℃ at a rate of 3℃ / min. The temperature is then maintained at 400℃ for 4h to obtain the dual noble metal modified carbon-coated cerium dioxide catalyst RuPt-CeO2@C.

[0050] Example 4

[0051] This embodiment proposes a dual-noble-metal modified carbon-coated cerium dioxide catalyst, the preparation method of which includes the following steps:

[0052] S1. 21.7 g of Ce(NO3)3·6H2O and 28.4 g of stearic acid were placed in the zirconium grinding jar of a planetary ball mill and ball-to-material ratio was 30:1. The ball milling speed was 500 rpm and the ball milling time was 16 h. After ball milling, the material was removed and placed in a muffle furnace. The temperature was increased to 300 °C at a heating rate of 5 °C / min and held at 300 °C for 10 h to obtain carbon-coated cerium dioxide CeO2@C.

[0053] S2. Take 1g of CeO2@C obtained in step S1 and 188.2mg of N4O 10Ru and 113.96 mg of (CH3COO)3Au were ball-milled in a zirconium oxide grinding jar of a planetary ball mill at a ball-to-material ratio of 30:1, a milling speed of 500 rpm, and a milling time of 8 h. After ball milling, the material was removed 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 rate of 5 °C / min and held at 400 °C for 6 h to obtain the dual noble metal modified carbon-coated cerium dioxide catalyst RuAu-CeO2@C.

[0054] Comparative Example 1

[0055] This comparative example presents a cerium dioxide catalyst, the preparation method of which includes the following steps: 21.7 g of Ce(NO3)3·6H2O is placed in the zirconium oxide 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 ball milling, the material is removed and placed in a muffle furnace, heated to 300 °C at a heating rate of 5 °C / min, and held at 300 °C for 4 h to obtain cerium dioxide (CeO2).

[0056] Comparative Example 2

[0057] This comparative example uses the same implementation method as Example 1. The difference from Example 1 is that flake graphite was not added in step S1 of this comparative example to obtain the dual noble metal modified cerium dioxide catalyst RuRh-CeO2.

[0058] Comparative Example 3

[0059] This comparative example uses the same implementation method as Example 1. The difference from Example 1 is that (CH3COO)3Rh was not added in step S2 of this comparative example to obtain a single noble metal Ru modified carbon-coated cerium dioxide catalyst Ru-CeO2@C.

[0060] Comparative Example 4

[0061] This comparative example uses the same implementation method as Example 1. The difference from Example 1 is that RuCl3·xH2O was not added in step S2 of this comparative example to obtain the single noble metal Rh modified carbon-coated cerium dioxide catalyst Rh-CeO2@C.

[0062] Comparative Example 5

[0063] This comparative example presents a cerium dioxide catalyst, the preparation method of which includes the following steps: 21.7 g of Ce(NO3)3·6H2O is placed in the zirconium oxide 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 ball milling, the material is removed and placed in a muffle furnace, heated to 300 °C at a heating rate of 3 °C / min, and held at 300 °C for 6 h to obtain cerium dioxide (CeO2).

[0064] Comparative Example 6

[0065] This comparative example uses the same implementation method as Example 2, except that glucose was not added in step S1 of this comparative example to prepare the dual noble metal modified cerium dioxide catalyst RuPd-CeO2.

[0066] Comparative Example 7

[0067] This comparative example uses the same implementation method as Example 2. The difference from Example 2 is that Pd(O2CCH3)2 was not added in step S2 of this comparative example, and a single noble metal Ru modified carbon-coated cerium dioxide catalyst Ru-CeO2@C was obtained.

[0068] Comparative Example 8

[0069] This comparative example uses the same implementation method as Example 2, except that Ru3(CO) is not added in step S2 of this comparative example. 12 A single noble metal Pd-modified carbon-coated cerium dioxide catalyst, Pd-CeO2@C, was prepared.

[0070] Comparative Example 9

[0071] This comparative example presents a cerium dioxide catalyst, the preparation method of which includes the following steps: 21.7 g of Ce(NO3)3·6H2O is placed in the zirconium oxide 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 ball milling, the material is removed and placed in a muffle furnace, heated to 400 °C at a heating rate of 3 °C / min, and held at 400 °C for 6 h to obtain cerium dioxide (CeO2).

[0072] Comparative Example 10

[0073] This comparative example uses the same implementation method as Example 3. The difference from Example 3 is that cellulose was not added in step S1 of this comparative example to obtain the dual noble metal modified cerium dioxide catalyst RuPt-CeO2.

[0074] Comparative Example 11

[0075] This comparative example uses the same implementation method as Example 3. The difference from Example 3 is that N2O6Pt was not added in step S2 of this comparative example, and a single noble metal Ru modified carbon-coated cerium dioxide catalyst Ru-CeO2@C was obtained.

[0076] Comparative Example 12

[0077] This comparative example uses the same implementation method as Example 3. The difference from Example 3 is that C6H9O6Ru was not added in step S2 of this comparative example to obtain a single noble metal Pt modified carbon-coated cerium dioxide catalyst Pt-CeO2@C.

[0078] Comparative Example 13

[0079] This comparative example presents a cerium dioxide catalyst, the preparation method of which includes the following steps: 21.7 g of Ce(NO3)3·6H2O is placed in the zirconium oxide 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 ball milling, the material is removed and placed in a muffle furnace, heated to 300 °C at a heating rate of 5 °C / min, and held at 300 °C for 10 h to obtain cerium dioxide (CeO2).

[0080] Comparative Example 14

[0081] This comparative example uses the same implementation method as Example 4, except that stearic acid was not added in step S1 of this comparative example to obtain the dual noble metal modified cerium dioxide catalyst RuAu-CeO2.

[0082] Comparative Example 15

[0083] This comparative example uses the same implementation method as Example 4, except that (CH3COO)3Au is not added in step S2 of this comparative example to obtain a single noble metal Ru modified carbon-coated cerium dioxide catalyst Ru-CeO2@C.

[0084] Comparative Example 16

[0085] This comparative example uses the same implementation method as Example 4, except that N4O is not added in step S2 of this comparative example. 10 Ru, a single noble metal Au-modified carbon-coated cerium dioxide catalyst Au-CeO2@C was prepared.

[0086] Application Example 1

[0087] 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 were used as catalysts for thermocatalytic ammonia synthesis. The thermocatalytic ammonia synthesis method was as follows: 500 mg of catalyst was loaded into the quartz reaction tube of the fixed-bed reactor for ammonia synthesis. The reaction temperature was fixed at 400 °C, the reaction pressure at 5 MPa, the molar ratio of N2:H2 was 1:3, the flow rate was 60 mL / min, and the generated ammonia was detected.

[0088] Figure 2 The above catalysts have the following thermocatalytic activity diagrams for ammonia synthesis: Figure 2 It can be seen that the thermocatalytic 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 promoting effect between the Ru and Rh noble metals, which is beneficial to improving the efficiency of thermocatalytic ammonia synthesis. Furthermore, from... Figure 2 It can be observed that CeO2@C and RuRh-CeO2@C have significantly improved activity compared to CeO2 and RuRh-CeO2 without C coating. This is attributed to the dual role of C: C is beneficial for increasing the adsorption heat and maintaining the temperature of the catalyst surface, as well as for timely transfer of the generated active H species during the reaction, preventing the catalyst from being deactivated by hydrogen poisoning.

[0089] Application Example 2

[0090] 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 were used as catalysts for thermocatalytic ammonia synthesis. The thermocatalytic ammonia synthesis method was as follows: 500 mg of catalyst was loaded into the quartz reaction tube of the fixed-bed reactor for ammonia synthesis. The reaction temperature was fixed at 400 °C, the reaction pressure at 3 MPa, the molar ratio of N2:H2 was 2:3, the flow rate was 180 mL / min, and the generated ammonia was detected.

[0091] Figure 3 The above catalysts have the following thermocatalytic activity diagrams for ammonia synthesis: Figure 3 It can be seen that the thermocatalytic 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 promoting effect between the Ru and Pd noble metals, which is beneficial to improving the efficiency of thermocatalytic ammonia synthesis. Furthermore, from... Figure 3 It can be observed that CeO2@C and RuPd-CeO2@C have significantly improved activity compared to CeO2 and RuPd-CeO2 without C coating. This is attributed to the dual role of C: C is beneficial for adsorbing heat to increase and maintain the temperature of the catalyst surface, and it can also facilitate the timely transfer of active H species generated during the reaction, preventing the catalyst from being deactivated by hydrogen poisoning.

[0092] Application Example 3

[0093] 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 were used as catalysts for thermocatalytic ammonia synthesis. The thermocatalytic ammonia synthesis method was as follows: 500 mg of catalyst was loaded into the quartz reaction tube of the fixed-bed reactor for ammonia synthesis. The reaction temperature was fixed at 400 °C, the reaction pressure at 4 MPa, the molar ratio of N2:H2 was 1:3, the flow rate was 90 mL / min, and the generated ammonia was detected.

[0094] Figure 4 The above catalysts have the following thermocatalytic activity diagrams for ammonia synthesis: Figure 4 It can be seen that the thermocatalytic 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 promoting effect between the Ru and Pt noble metals, which is beneficial to improving the efficiency of thermocatalytic ammonia synthesis. Furthermore, from... Figure 4 It can be observed that CeO2@C and RuPt-CeO2@C have significantly improved activity compared to CeO2 and RuPt-CeO2 without C coating. This is attributed to the dual role of C: C is beneficial for adsorbing heat to increase and maintain the temperature of the catalyst surface, and it can also facilitate the timely transfer of active H species generated during the reaction, preventing the catalyst from being deactivated by hydrogen poisoning.

[0095] Application Example 4

[0096] 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 were used as catalysts for thermocatalytic ammonia synthesis. The thermocatalytic ammonia synthesis method was as follows: 500 mg of catalyst was loaded into the quartz reaction tube of the fixed-bed reactor for ammonia synthesis. The reaction temperature was fixed at 400 °C, the reaction pressure at 5 MPa, the molar ratio of N2:H2 was 2:3, the flow rate was 90 mL / min, and the generated ammonia was detected.

[0097] Figure 5 The above catalysts have thermocatalytic ammonia synthesis activity diagrams. Figure 5 It can be seen that the thermocatalytic 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 promoting effect between the Ru and Au noble metals, which is beneficial to improving the efficiency of thermocatalytic ammonia synthesis. Furthermore, from... Figure 5 It can be observed that CeO2@C and RuAu-CeO2@C have significantly improved activity compared to CeO2 and RuAu-CeO2 without C coating. This is attributed to the dual role of C: C facilitates the adsorption of heat to increase and maintain the temperature of the catalyst surface, and timely transfers the generated active H species during the reaction process, preventing the catalyst from being deactivated by hydrogen poisoning.

[0098] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above 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.

[0099] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a carbon-coated cerium dioxide catalyst modified with two noble metals, characterized in that, It includes the following steps: S1. After ball milling and mixing the cerium source and carbon source, calcination is performed to obtain carbon-coated cerium dioxide; S2. After ball milling and mixing the carbon-coated cerium dioxide, noble metal R source, and noble metal M source obtained in step S1, calcine them under a 10% H2 / Ar mixed atmosphere to obtain a dual-noble metal modified carbon-coated cerium dioxide catalyst. The noble metal R is ruthenium; the noble metal M is one of Rh, Pd, Ag, Ir, Pt, and Au; in the dual noble metal modified carbon-coated cerium dioxide catalyst, the mass ratio of carbon-coated cerium dioxide, noble metal R, and noble metal M is 1:(0.01~0.1):(0.01~0.1).

2. The preparation method of the dual noble metal modified carbon-coated cerium dioxide 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, the mass ratio of cerium dioxide to carbon in the carbon-coated cerium dioxide is 1:(0.01~1).

3. The preparation method of the dual noble metal modified carbon-coated cerium dioxide catalyst according to claim 1, characterized in that, In step S1, the ball-to-material ratio of the ball mill 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℃ for 2~10h, and the heating rate of the calcination is 2~10℃ / min.

4. The preparation method of the dual noble metal modified carbon-coated cerium dioxide catalyst according to claim 1, characterized in that, In step S2, the noble metal R source is one of ruthenium acetate, dodecyltriruthenium, ruthenium trichloride hydrate, and trinitronitrosylruthenium; And / or, in step S2, the source of noble metal M is a nitrate, acetate, or carbonyl complex of noble metal M.

5. The preparation method of the dual noble metal modified carbon-coated cerium dioxide catalyst according to claim 1, characterized in that, In step S2, the ball-to-material ratio of the ball mill 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 tube furnace at 200~500℃ for 2~10h in a 10% H2 / Ar mixed atmosphere, with a heating rate of 1~5℃ / min.

6. A cerium dioxide catalyst with carbon-coated and modified by two noble metals, characterized in that, It is prepared by the preparation method described in any one of claims 1-5.

7. The application of a cerium dioxide catalyst with dual noble metal modified carbon prepared by any one of claims 1-5 in the thermocatalytic synthesis of ammonia.

8. The application according to claim 7, characterized in that, It includes the following steps: The dual-noble-metal modified carbon-coated cerium dioxide catalyst is packed into a reaction tube of a fixed-bed ammonia synthesis reactor, and a mixture of N2 and H2 is introduced to heat and catalyze the reaction.

9. The application according to claim 8, 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℃ and the pressure is 0.1-5MPa.

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