A method for hydrogen production by ammonia decomposition based on ceria reverse phase catalyst

Abstract

The application relates to the technical field of hydrogen production by ammonia decomposition, and discloses a method for hydrogen production by ammonia decomposition based on a ceria reverse-phase catalyst, which comprises the following steps: (1) mixing a nickel precursor, a cobalt precursor and an iron precursor as metal precursors, mixing the metal precursors and ceria powder to obtain an A solution; preparing an alkali solution as a B solution; (2) adding the B solution into the A solution while stirring, and after the adding is completed, performing centrifugation, drying and aerobic calcination to obtain a reverse-phase catalyst; and (3) contacting ammonia gas with the reverse-phase catalyst to react, wherein the temperature is 400-500 DEG C, and the pressure is 0.01-1 MPa, so that hydrogen gas is obtained. Through multi-metal component design, interface synergistic construction and preparation process optimization, the reverse-phase catalyst with ceria small particles anchored and highly dispersed on a Ni-Co-Fe multi-metal oxide carrier is formed, so that high-efficiency catalytic activity is realized.

Description

Technical Field

[0001] This invention relates to the technical field of ammonia decomposition for hydrogen production, and in particular to a method for ammonia decomposition for hydrogen production based on a cerium dioxide reverse-phase catalyst. Background Technology

[0002] Ammonia decomposition is an important hydrogen production technology with broad application prospects in hydrogen storage and transportation, fuel cell hydrogen supply, and dehydrogenation. Traditional ammonia decomposition catalysts mostly use precious metals (such as Ru, Rh, and Pt) as active centers. Although they possess excellent reaction performance and stability, their high cost and scarcity severely limit their industrial application. Therefore, researchers have gradually turned their attention to transition metal catalysts, especially Ni, Co, and Fe systems, which are abundant, inexpensive, and possess certain activity, making them viable alternatives to precious metals. However, single-metal catalysts generally suffer from poor metal dispersion, a limited number of active sites, and a tendency to sinter and agglomerate at high temperatures, resulting in limited catalytic efficiency and lifespan.

[0003] Therefore, research has gradually shifted towards constructing multi-metal synergistic systems. Multi-metal synergistic catalysts can not only enhance catalytic performance through alloying effects (such as electronic structure optimization and hydrogen adsorption regulation), but also improve stability through interfacial structure regulation. Intermetallic electron transfer can also regulate the surface active state, significantly affecting the dissociation of NH3 and the desorption pathway of intermediates. Among these, the support plays a crucial role in catalyst performance by providing a high specific surface area to disperse active components and regulating metal-support interactions. Patent CN114471601A discloses a metal-supported catalyst and its application in ammonia decomposition. The metal-supported catalyst has the following weight percentage composition: nickel oxide 12.1-15.4%, iron oxide 7.0-9.6%, tungsten trioxide 6.8-9.1%, with the balance being the support. However, this catalyst requires a high temperature of 550℃ for ammonia decomposition. This is because in conventional supported catalysts, metals are not only difficult to disperse uniformly, but the interfacial effect between the support and the supported metal is also poor, resulting in low catalytic activity and poor low-temperature reaction performance. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a method for hydrogen production from ammonia via a cerium dioxide reverse-phase catalyst. By controlling the ratio of cerium dioxide powder to the metal precursor and the preparation steps, small cerium dioxide particles are anchored and highly dispersed on a Ni-Co-Fe multi-metal oxide support, resulting in a reverse-phase catalyst with abundant interfacial sites. This achieves highly efficient ammonia decomposition catalytic activity and low-temperature reaction performance.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] This invention provides a method for hydrogen production from ammonia via a cerium dioxide reverse-phase catalyst, comprising the following steps:

[0007] (1) Mix nickel precursor, cobalt precursor and iron precursor in a molar ratio of 40~60%: 20~30%: 10~30% as metal precursor. Mix the metal precursor with cerium dioxide powder accounting for 20~50% of the mass of the metal precursor and add it to water to make solution A; prepare an alkaline solution as solution B.

[0008] (2) While adding solution B dropwise to solution A, stir. After the addition is complete, centrifuge, dry, and calcine with oxygen to obtain the reversed catalyst;

[0009] (3) Ammonia gas is reacted with a reverse catalyst at a temperature of 400~500℃ and a pressure of 0.01~1 MPa to obtain hydrogen gas.

[0010] Reverse catalysts refer to catalysts that load small oxide nanoparticles onto a large metal matrix to generate abundant interfacial sites. This invention achieves the anchoring and high dispersion of small cerium dioxide particles on a Ni-Co-Fe multi-metal oxide support by adding cerium dioxide powder to a multi-component mixed metal precursor solution and controlling the ratio of cerium dioxide powder to the metal precursor and the preparation conditions. CeO2, due to its unique Ce... 4+ / Ce 3+ CeO2's reversible redox properties and abundant oxygen vacancies not only provide electron buffering and allow surface oxygen to participate in the reaction, but also effectively modulate the activation energy barrier of the reaction pathway by forming a tight interface with active metals. Through the construction of an inverted interface structure, CeO2 is embedded in the surface of a multi-element mixed metal as highly dispersed nano-islands / particles, generating more abundant interface sites. CeO2 and the multi-element metal phases can form a more excellent interfacial synergy, thereby achieving highly efficient ammonia decomposition catalytic activity and low-temperature reaction performance.

[0011] Ni, as the main active metal site, participates in the breaking of the NH bond in the ammonia molecule; Co, by forming an alloy structure with Ni, regulates its electronic state distribution, improving hydrogen dissociation efficiency and enhancing anti-sintering performance; Fe, as an electron modulator, guides interfacial electronic reconstruction and assists in the desorption of N2 intermediates. All three metal elements are indispensable, working synergistically to construct a stable and efficient Ni-Co-Fe / CeO2 interfacial structure, significantly reducing the reaction activation energy. The absence of any one metal component leads to poor construction of the reversed-phase interfacial structure; the regular structure results in a large number of unexposed active sites, leading to poor catalytic activity in ammonia decomposition. Furthermore, the ratio of the multiple metal components and the proportion of CeO2 are also crucial. This ratio can form a Ni-rich and electronically matched multi-metal oxide support and a stable reversed-phase interfacial structure, enhancing electron transfer and reaction intermediate dissociation capabilities, resulting in higher catalytic activity.

[0012] Preferably, the total ion concentration of nickel, cobalt and iron in solution A is 0.1~1.0 mol / L; solution B is added dropwise to solution A while stirring, and the temperature of the mixed solution is maintained at 40~70℃ during the process.

[0013] Preferably, the cerium dioxide powder has the microstructure of nanorods, nanospheres, or polyhedra.

[0014] Preferably, the iron precursor is ferric nitrate, ferric chloride, or ferric oxalate.

[0015] Preferably, the nickel precursor is nickel nitrate, nickel chloride, or nickel acetate.

[0016] Preferably, the cobalt precursor is cobalt nitrate, cobalt chloride, or cobalt acetate.

[0017] Preferably, the B solution is one or more of sodium hydroxide solution, sodium carbonate solution, and ammonia solution; the solute concentration of the B solution is 0.1~2M.

[0018] Preferably, the temperature of the aerobic roasting is 400~600℃ and the roasting time is 3~6h.

[0019] Preferably, the aerobic roasting uses a mixture of oxygen and an inert gas, wherein the volume content of oxygen in the mixture is 20-80%.

[0020] Preferably, the space velocity of the reaction is 100~50000 h⁻¹. -1 .

[0021] Compared with existing technologies, the nanocatalyst of this invention has the following beneficial effects:

[0022] (1) By designing multi-metal components, constructing interfaces and optimizing the preparation process, a uniformly dispersed multiphase metal catalytic system is formed. Small cerium dioxide particles are anchored and highly dispersed on the Ni-Co-Fe multi-metal oxide support, while forming more layered and sheet-like micro-folded structures. The resulting reverse catalyst has abundant interface sites and high specific surface area, which is conducive to the exposure of active sites and the diffusion of reactants, thereby achieving high-efficiency catalytic activity.

[0023] (2) The catalyst exhibits excellent low-temperature performance in the ammonia decomposition reaction, achieving an NH3 conversion rate of over 90% at 480℃, which is far superior to conventional Ni-based catalysts (the initial reaction temperature is usually ≥550℃).

[0024] (3) This method has the advantages of simple operation, uniform distribution of additives and controllable structure, and has significant technological progress and broad industrial application prospects. Attached Figure Description

[0025] Figure 1 Scanning electron microscope (SEM) images of catalysts prepared with different Ce doping ratios. Detailed Implementation

[0026] The technical solution of the present invention will be illustrated below with specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0027] The method for producing hydrogen from ammonia by decomposition based on a cerium dioxide reverse-phase catalyst in this invention includes the following steps:

[0028] (1) Mix nickel precursor, cobalt precursor and iron precursor in a molar ratio of 40~60%: 20~30%: 10~30% as metal precursor (i.e., mix according to the molar ratio of Ni:Co:Fe of 40~60%: 20~30%: 10~30%). Mix the metal precursor and cerium dioxide powder accounting for 20~50% of the mass of the metal precursor evenly. Add the mixed material to water to prepare a suspension with a total ion concentration of nickel, cobalt and iron of 0.1~1.0 mol / L as solution A; prepare an alkaline solution with a solute concentration of 0.1~2M as solution B.

[0029] (2) Slowly add solution B to solution A at a temperature of 40~70℃ while stirring, and keep the temperature of the mixed solution at 40~70℃. After the addition is complete, centrifuge, wash and dry the solution, and finally calcine it in a mixed atmosphere of oxygen and inert gas. The volume content of oxygen in the mixed gas is 20~80%, the calcine temperature is 400~600℃, and the calcine time is 4h to obtain the catalyst.

[0030] (3) The prepared catalyst was loaded into a stainless steel fixed-bed reactor, and pure ammonia gas was introduced into the reactor, with the space velocity controlled at 100~50000 h⁻¹. -1 The reaction temperature was set at 400~500℃ and the pressure at 0.01~1 MPa, and the reaction produced hydrogen and nitrogen.

[0031] In a specific embodiment of the present invention, the microstructure of the cerium dioxide powder is nanorods, nanospheres, or polyhedra.

[0032] In a specific embodiment of the present invention, the iron precursor is ferric nitrate, ferric chloride, or ferric oxalate.

[0033] In a specific embodiment of the present invention, the nickel precursor is nickel nitrate, nickel chloride, or nickel acetate.

[0034] In a specific embodiment of the present invention, the cobalt precursor is cobalt nitrate, cobalt chloride, or cobalt acetate.

[0035] In a specific embodiment of the present invention, the alkaline solution is one or more of sodium hydroxide solution, sodium carbonate solution, and ammonia solution.

[0036] Example 1

[0037] (1) Nickel nitrate, cobalt nitrate, and iron nitrate were mixed in a molar ratio of Ni:Co:Fe of 50%:25%:25% as a metal precursor. The metal precursor and cerium dioxide powder (polyhedron) accounting for 40% of the mass of the metal precursor were mixed evenly. The mixed material was added to water and stirred evenly. The mixture was then dispersed in water, and the total ion concentration of nickel, cobalt, and iron was controlled to be 0.5 mol / L to obtain solution A. A 0.5 mol / L sodium hydroxide solution was prepared as solution B.

[0038] (2) Solution B was slowly added dropwise to solution A at 60°C while stirring, and the temperature of the mixed solution was maintained at 60°C. After the addition was complete, the solution was centrifuged, washed, and dried. Finally, it was calcined in a mixed atmosphere of oxygen and inert gas, with an oxygen volume content of 50%, a calcination temperature of 500°C, and a calcination time of 4 hours to obtain Ni. 0.5 Co 0.25 Fe 0.25 / CeO2 catalyst;

[0039] (3) The prepared catalyst was loaded into a stainless steel fixed-bed reactor with a loading volume of 5 mL; pure ammonia gas was introduced into the reactor and the space velocity was controlled at 5000 h⁻¹. -1 (Ammonia gas flow rate 416 mL / min), reaction temperature set at 480℃, pressure at 0.1 MPa, the reaction produces hydrogen and nitrogen; the single-pass conversion rate of ammonia is calculated by analyzing the reaction gases by gas chromatography.

[0040] Example 2

[0041] The difference from Example 1 is that the molar ratio of Ni:Co:Fe is controlled to be 60%:20%:20%.

[0042] (1) Nickel nitrate, cobalt nitrate, and iron nitrate were mixed in a molar ratio of Ni:Co:Fe of 60%:20%:20% as a metal precursor. The metal precursor and cerium dioxide powder (polyhedron) accounting for 40% of the mass of the metal precursor were mixed evenly. The mixed material was added to water and stirred evenly. The total ion concentration of nickel, cobalt, and iron was controlled to be 0.5 mol / L to obtain solution A. A 0.5 mol / L sodium hydroxide solution was prepared as solution B.

[0043] (2) Solution B was slowly added dropwise to solution A at 60°C while stirring, and the temperature of the mixed solution was maintained at 60°C. After the addition was complete, the solution was centrifuged, washed, and dried. Finally, it was calcined in a mixed atmosphere of oxygen and inert gas, with an oxygen volume content of 50%, a calcination temperature of 500°C, and a calcination time of 4 hours to obtain Ni. 0.6 Co 0.2 Fe 0.2 / CeO2 catalyst;

[0044] (3) The prepared catalyst was loaded into a stainless steel fixed-bed reactor with a loading volume of 5 mL; pure ammonia gas was introduced into the reactor and the space velocity was controlled at 5000 h⁻¹. -1 (Ammonia gas flow rate 416 mL / min), reaction temperature set at 480℃, pressure at 0.1 MPa, the reaction produces hydrogen and nitrogen; the single-pass conversion rate of ammonia is calculated by analyzing the reaction gases by gas chromatography.

[0045] Example 3

[0046] The difference from Example 1 is that the molar ratio of Ni:Co:Fe is controlled to be 40%:20%:40%.

[0047] (1) Nickel nitrate, cobalt nitrate, and iron nitrate were mixed in a molar ratio of Ni:Co:Fe of 40%:20%:40% as a metal precursor. The metal precursor and cerium dioxide powder (polyhedron) accounting for 40% of the mass of the metal precursor were mixed evenly. The mixed material was added to water and stirred evenly. The total ion concentration of nickel, cobalt, and iron was controlled to be 0.5 mol / L to obtain solution A. A 0.5 mol / L sodium hydroxide solution was prepared as solution B.

[0048] (2) Solution B was slowly added dropwise to solution A at 60°C while stirring, and the temperature of the mixed solution was maintained at 60°C. After the addition was complete, the solution was centrifuged, washed, and dried. Finally, it was calcined in a mixed atmosphere of oxygen and inert gas, with an oxygen volume content of 50%, a calcination temperature of 500°C, and a calcination time of 4 hours to obtain Ni. 0.4 Co 0.2 Fe 0.4 / CeO2 catalyst;

[0049] (3) The prepared catalyst was loaded into a stainless steel fixed-bed reactor with a loading volume of 5 mL; pure ammonia gas was introduced into the reactor and the space velocity was controlled at 5000 h⁻¹. -1 (Ammonia gas flow rate 416 mL / min), reaction temperature set at 480℃, pressure at 0.1 MPa, the reaction produces hydrogen and nitrogen; the single-pass conversion rate of ammonia is calculated by analyzing the reaction gases by gas chromatography.

[0050] Example 4

[0051] The difference from Example 1 is that the amount of cerium dioxide powder added is controlled to be 30% of the mass of the metal precursor.

[0052] (1) Nickel nitrate, cobalt nitrate, and iron nitrate were mixed in a molar ratio of Ni:Co:Fe of 50%:25%:25% as a metal precursor. The metal precursor and cerium dioxide powder (polyhedron) accounting for 30% of the mass of the metal precursor were mixed evenly. The mixed material was added to water and stirred evenly. The total ion concentration of nickel, cobalt, and iron was controlled to be 0.5 mol / L to obtain solution A. A 0.5 mol / L sodium hydroxide solution was prepared as solution B.

[0053] (2) Solution B was slowly added dropwise to solution A at 60°C while stirring, and the temperature of the mixed solution was maintained at 60°C. After the addition was complete, the solution was centrifuged, washed, and dried. Finally, it was calcined in a mixed atmosphere of oxygen and inert gas, with an oxygen volume content of 50%, a calcination temperature of 500°C, and a calcination time of 4 hours to obtain Ni. 0.5 Co 0.25 Fe 0.25 / CeO2 catalyst;

[0054] (3) The prepared catalyst was loaded into a stainless steel fixed-bed reactor with a loading volume of 5 mL; pure ammonia gas was introduced into the reactor and the space velocity was controlled at 5000 h⁻¹. -1 (Ammonia gas flow rate 416 mL / min), reaction temperature set at 480℃, pressure at 0.1 MPa, the reaction produces hydrogen and nitrogen; the single-pass conversion rate of ammonia is calculated by analyzing the reaction gases by gas chromatography.

[0055] Example 5

[0056] The difference from Example 1 is that the alkaline solution used is different, as are the molar ratio of Ni:Co:Fe, the amount of cerium dioxide powder added, and the temperature of solution A.

[0057] (1) Nickel nitrate, cobalt nitrate, and iron nitrate were mixed in a molar ratio of Ni:Co:Fe of 50%:30%:20% as a metal precursor. The metal precursor and cerium dioxide powder (polyhedron) accounting for 50% of the mass of the metal precursor were mixed uniformly. The mixed material was added to water and stirred evenly. The total ion concentration of nickel, cobalt, and iron was controlled to be 0.5 mol / L to obtain solution A. A 0.5 mol / L ammonia solution was prepared as solution B.

[0058] (2) Solution B was slowly added dropwise to solution A at 40°C while stirring, and the temperature of the mixed solution was maintained at 40°C. After the addition was complete, the solution was centrifuged, washed, and dried. Finally, it was calcined in a mixed atmosphere of oxygen and inert gas, with an oxygen volume content of 50%, a calcination temperature of 500°C, and a calcination time of 4 hours to obtain Ni. 0.5 Co 0.3 Fe 0.2 / CeO2 catalyst;

[0059] (3) The prepared catalyst was loaded into a stainless steel fixed-bed reactor with a loading volume of 5 mL; pure ammonia gas was introduced into the reactor and the space velocity was controlled at 5000 h⁻¹. -1 (Ammonia gas flow rate 416 mL / min), reaction temperature set at 480℃, pressure at 0.1 MPa, the reaction produces hydrogen and nitrogen; the single-pass conversion rate of ammonia is calculated by analyzing the reaction gases by gas chromatography.

[0060] Example 6

[0061] The difference from Example 1 is that the types of nickel precursor, cobalt precursor, and iron precursor used are different.

[0062] (1) Nickel chloride, cobalt acetate, and ferric chloride are mixed in a molar ratio of Ni:Co:Fe of 50%:25%:25% as a metal precursor. The metal precursor and cerium dioxide powder (polyhedron) accounting for 40% of the mass of the metal precursor are mixed evenly. The mixed material is added to water and stirred evenly. The total ion concentration of nickel, cobalt, and iron is controlled to be 0.5 mol / L to obtain solution A. A 0.5 mol / L sodium hydroxide solution is prepared as solution B.

[0063] (2) Solution B was slowly added dropwise to solution A at 60°C while stirring, and the temperature of the mixed solution was maintained at 60°C. After the addition was complete, the solution was centrifuged, washed, and dried. Finally, it was calcined in a mixed atmosphere of oxygen and inert gas, with an oxygen volume content of 50%, a calcination temperature of 500°C, and a calcination time of 4 hours to obtain Ni. 0.5 Co 0.25 Fe 0.25 / CeO2 catalyst;

[0064] (3) The prepared catalyst was loaded into a stainless steel fixed-bed reactor with a loading volume of 5 mL; pure ammonia gas was introduced into the reactor and the space velocity was controlled at 5000 h⁻¹. -1 (Ammonia gas flow rate 416 mL / min), reaction temperature set at 480℃, pressure at 0.1 MPa, the reaction produces hydrogen and nitrogen; the single-pass conversion rate of ammonia is calculated by analyzing the reaction gases by gas chromatography.

[0065] Comparative Example 1

[0066] The difference from Example 1 is that the molar ratio of Ni:Co:Fe is 25%:25%:50%.

[0067] (1) Nickel nitrate, cobalt nitrate, and iron nitrate were mixed in a molar ratio of Ni:Co:Fe of 25%:25%:50% as a metal precursor. The metal precursor and cerium dioxide powder (polyhedron) accounting for 40% of the mass of the metal precursor were mixed evenly. The mixed material was added to water and stirred evenly. The total ion concentration of nickel, cobalt, and iron was controlled to be 0.5 mol / L to obtain solution A. A 0.5 mol / L sodium hydroxide solution was prepared as solution B.

[0068] (2) Solution B was slowly added dropwise to solution A at 60°C while stirring, and the temperature of the mixed solution was maintained at 60°C. After the addition was complete, the solution was centrifuged, washed, and dried. Finally, it was calcined in a mixed atmosphere of oxygen and inert gas, with an oxygen volume content of 50%, a calcination temperature of 500°C, and a calcination time of 4 hours to obtain Ni. 0.25 Co 0.25 Fe 0.5 / CeO2 catalyst;

[0069] (3) The prepared catalyst was loaded into a stainless steel fixed-bed reactor with a loading volume of 5 mL; pure ammonia gas was introduced into the reactor and the space velocity was controlled at 5000 h⁻¹. -1 (Ammonia gas flow rate 416 mL / min), reaction temperature set at 480℃, pressure at 0.1 MPa, the reaction produces hydrogen and nitrogen; the single-pass conversion rate of ammonia is calculated by analyzing the reaction gases by gas chromatography.

[0070] Comparative Example 2

[0071] The difference from Example 1 is that the molar ratio of Ni:Co:Fe is 50%:10%:40%.

[0072] (1) Nickel nitrate, cobalt nitrate, and iron nitrate were mixed in a molar ratio of Ni:Co:Fe of 50%:10%:40% as a metal precursor. The metal precursor and cerium dioxide powder (polyhedron) accounting for 40% of the mass of the metal precursor were mixed evenly. The mixed material was added to water and stirred evenly. The total ion concentration of nickel, cobalt, and iron was controlled to be 0.5 mol / L to obtain solution A. A 0.5 mol / L sodium hydroxide solution was prepared as solution B.

[0073] (2) Solution B was slowly added dropwise to solution A at 60°C while stirring, and the temperature of the mixed solution was maintained at 60°C. After the addition was complete, the solution was centrifuged, washed, and dried. Finally, it was calcined in a mixed atmosphere of oxygen and inert gas, with an oxygen volume content of 50%, a calcination temperature of 500°C, and a calcination time of 4 hours to obtain Ni. 0.5 Co 0.1 Fe 0.4 / CeO2 catalyst;

[0074] (3) The prepared catalyst was loaded into a stainless steel fixed-bed reactor with a loading volume of 5 mL; pure ammonia gas was introduced into the reactor and the space velocity was controlled at 5000 h⁻¹. -1 (Ammonia gas flow rate 416 mL / min), reaction temperature set at 480℃, pressure at 0.1 MPa, the reaction produces hydrogen and nitrogen; the single-pass conversion rate of ammonia is calculated by analyzing the reaction gases by gas chromatography.

[0075] Comparative Example 3

[0076] The difference from Example 1 is that the molar ratio of Ni:Fe is 50%:50%.

[0077] (1) Nickel nitrate and iron nitrate were mixed in a molar ratio of Ni:Fe of 50%:50% as a metal precursor. The metal precursor and cerium dioxide powder (polyhedron) accounting for 40% of the mass of the metal precursor were mixed evenly. The mixed material was added to water and stirred evenly. The total ion concentration of nickel and iron was controlled to be 0.5 mol / L to obtain solution A. A 0.5 mol / L sodium hydroxide solution was prepared as solution B.

[0078] (2) Solution B was slowly added dropwise to solution A at 60°C while stirring, and the temperature of the mixed solution was maintained at 60°C. After the addition was complete, the solution was centrifuged, washed, and dried. Finally, it was calcined in a mixed atmosphere of oxygen and inert gas, with an oxygen volume content of 50%, a calcination temperature of 500°C, and a calcination time of 4 hours to obtain Ni. 0.5 Fe 0.5 / CeO2 catalyst;

[0079] (3) The prepared catalyst was loaded into a stainless steel fixed-bed reactor with a loading volume of 5 mL; pure ammonia gas was introduced into the reactor and the space velocity was controlled at 5000 h⁻¹. -1 (Ammonia gas flow rate 416 mL / min), reaction temperature set at 480℃, pressure at 0.1 MPa, the reaction produces hydrogen and nitrogen; the single-pass conversion rate of ammonia is calculated by analyzing the reaction gases by gas chromatography.

[0080] Comparative Example 4

[0081] The difference from Example 1 is that instead of using cerium dioxide powder directly, a cerium precursor is used in conjunction with nickel, cobalt, and iron precursors to participate in a co-precipitation reaction.

[0082] (1) Nickel nitrate, cobalt nitrate, iron nitrate, and cerium nitrate were mixed in a molar ratio of Ni:Co:Fe:Ce of 5:2.5:2.5:4.4. The above mixed precursor was dissolved in deionized water, and the total ion concentration of nickel, cobalt, and iron was controlled to be 0.5 mol / L to obtain solution A. A 0.5 mol / L sodium hydroxide solution was prepared as solution B.

[0083] (2) Solution B was slowly added dropwise to solution A at 60°C while stirring, and the temperature of the mixed solution was maintained at 60°C to allow the metal components to co-precipitate. After the addition was complete, the solution was centrifuged, washed, and dried. Finally, it was calcined in a mixed atmosphere of oxygen and inert gas, with an oxygen volume content of 50%, a calcination temperature of 500°C, and a calcination time of 4 hours to obtain Ni. 0.5 Co 0.25 Fe 0.25 Ce 0.44 O x Composite oxide catalysts;

[0084] (3) The prepared catalyst was loaded into a stainless steel fixed-bed reactor with a loading volume of 5 mL; pure ammonia gas was introduced into the reactor and the space velocity was controlled at 5000 h⁻¹. -1 (Ammonia gas flow rate 416 mL / min), reaction temperature set at 480℃, pressure at 0.1 MPa, the reaction produces hydrogen and nitrogen; the single-pass conversion rate of ammonia is calculated by analyzing the reaction gases by gas chromatography.

[0085] Comparative Example 5

[0086] The difference from Example 1 is that the proportion of cerium dioxide powder added is too high.

[0087] (1) Nickel nitrate, cobalt nitrate, and iron nitrate were mixed in a molar ratio of Ni:Co:Fe of 50%:25%:25% as a metal precursor. The metal precursor and cerium dioxide powder (polyhedron) accounting for 60% of the mass of the metal precursor were mixed evenly. The mixed material was added to water and stirred evenly. The total ion concentration of nickel, cobalt, and iron was controlled to be 0.5 mol / L to obtain solution A. A 0.5 mol / L sodium hydroxide solution was prepared as solution B.

[0088] (2) Solution B was slowly added dropwise to solution A at 60°C while stirring, and the temperature of the mixed solution was maintained at 60°C. After the addition was complete, the solution was centrifuged, washed, and dried. Finally, it was calcined in a mixed atmosphere of oxygen and inert gas, with an oxygen volume content of 50%, a calcination temperature of 500°C, and a calcination time of 4 hours to obtain Ni. 0.5 Co 0.25 Fe 0.25 / CeO2 catalyst;

[0089] (3) The prepared catalyst was loaded into a stainless steel fixed-bed reactor with a loading volume of 5 mL; pure ammonia gas was introduced into the reactor and the space velocity was controlled at 5000 h⁻¹. -1 (Ammonia gas flow rate 416 mL / min), reaction temperature set at 480℃, pressure at 0.1 MPa, the reaction produces hydrogen and nitrogen; the single-pass conversion rate of ammonia is calculated by analyzing the reaction gases by gas chromatography.

[0090] Table 1 Catalytic reaction data of Examples 1-6 and Comparative Examples 1-5

[0091]

[0092] like Figure 1 As shown, Figure 1 Image (a) shows the catalyst morphology using the cerium precursor in Comparative Example 4. Figure 1 Image (b) shows the morphology of the catalyst (cerium dioxide mass ratio of 30%) in Example 4. Figure 1 Image (c) shows the morphology of the catalyst (40% cerium dioxide by mass) in Example 1. Figure 1 Image (d) shows the morphology of the catalyst (cerium dioxide mass ratio of 50%) in Example 5. Figure 1Figure (e) shows the morphology of the catalyst (cerium dioxide mass ratio of 60%) in Comparative Example 5. As can be seen from the figure, the catalyst doped with a certain proportion of cerium dioxide forms more layered and lamellar micro-wrinkled structures on its surface, which is significantly different from the structure of catalyst samples using cerium precursors or high-content cerium dioxide doping. This is because when using cerium precursors to prepare catalysts, the resulting flat CeO2 surface is uniform, and Ni is uniformly spread into a dense film. However, when using cerium dioxide powder to prepare catalysts, CeO2 is embedded in the surface of the multi-component mixed metal as highly dispersed nano-islands / particles, forming an antiphase interface. Furthermore, CeO2, due to its unique Ce... 4+ / Ce 3+ Due to its reversible redox properties and abundant oxygen vacancies, Ni preferentially deposits along these vacancies, forming a wrinkled structure that effectively increases the catalyst's specific surface area and porosity. This facilitates the exposure of active sites and reactant diffusion, thereby improving the catalytic activity and low-temperature reaction performance of ammonia decomposition. However, excessive cerium dioxide doping leads to homogenization of Ni deposition sites, resulting in a return to a dense structure and passivation of surface activity. As shown in Table 1, the conversion rates of Examples 1 and 4-5 are significantly higher than those of Comparative Examples 4-5.

[0093] Furthermore, the conversion rates of Comparative Examples 1-3 were significantly lower than those of Example 1. This indicates that the absence of any metal component in the Ni-Co-Fe multi-metal complex leads to poor construction of the reversed-phase interface structure. The regular structure results in a large number of unexposed active sites, leading to poor catalytic activity in ammonia decomposition. Moreover, the ratio of the multi-metal components is also crucial. This ratio can form a Ni-rich and electronically matched multi-metal oxide support and a stable reversed-phase interface structure, enhancing electron transfer and the dissociation of reaction intermediates, resulting in higher catalytic activity.

[0094] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for hydrogen production by ammonia decomposition based on ceria reverse phase catalyst, characterized by, The method comprises the following steps: (1) mixing nickel precursor, cobalt precursor and iron precursor as metal precursors in a molar ratio of 40-60:20-30:10-30, mixing the metal precursors and cerium dioxide powder accounting for 20-50% of the mass of the metal precursors, and adding water to obtain an A solution; preparing an alkali solution as a B solution; (2) adding the B solution to the A solution while stirring, and after the addition is completed, obtaining a reverse phase catalyst through centrifugation, drying and aerobic roasting; (3) contacting ammonia gas with the reverse phase catalyst to obtain hydrogen gas at a temperature of 400-500 DEG C and a pressure of 0.01-1 MPa.

2. The method of claim 1, wherein the ceria-based reverse phase catalyst is used for ammonia decomposition for hydrogen production. The total ion concentration of nickel, cobalt and iron in the A solution is 0.1-1.0 mol / L; the B solution is added to the A solution while stirring, and the temperature of the mixed solution is maintained at 40-70 DEG C during the process.

3. The method of claim 1 or 2, wherein the ceria-based reverse phase catalyst is used for ammonia decomposition for hydrogen production. The micro-morphology of the cerium dioxide powder is nanorod, nanosphere or polyhedron.

4. The method of claim 1, wherein the ceria-based reverse phase catalyst is prepared by a method comprising: The iron precursor is ferric nitrate, ferric chloride or ferric oxalate. ​ 5. The method for hydrogen production from ammonia decomposition based on a cerium dioxide reverse-phase catalyst according to claim 1, characterized in that, The nickel precursor is nickel nitrate, nickel chloride or nickel acetate.

6. The method for hydrogen production from ammonia decomposition based on a cerium dioxide reverse-phase catalyst according to claim 1, characterized in that, The cobalt precursor is cobalt nitrate, cobalt chloride or cobalt acetate.

7. The method for hydrogen production by ammonia decomposition using a ceria-based reverse phase catalyst according to claim 1 or 4 or 5 or 6, characterized in that, The B solution is one or more of sodium hydroxide solution, sodium carbonate solution and ammonia solution; the solute concentration of the B solution is 0.1-2 M.

8. The method of claim 1, wherein the ceria-based reverse phase catalyst is prepared by a method comprising: The temperature of the aerobic roasting is 400-600 DEG C, and the roasting time is 3-6 h. ​ 9. The method of claim 1 or 8, wherein the ceria-based reverse phase catalyst is used for ammonia decomposition for hydrogen production. The aerobic roasting is carried out using a mixed gas of oxygen and inert gas, and the volume content of oxygen in the mixed gas is 20-80%.

10. The method of claim 1, wherein the ceria-based reverse phase catalyst is prepared by a method comprising: The space velocity of the reaction is 100-50000 h -1 . ​

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