La2O3-ZnO-NiO / ZrO2 oxygen carrier, its preparation method and application

Abstract

The application discloses a La2O3-ZnO-NiO / ZrO2 oxygen carrier and a preparation method and application thereof, and belongs to the technical field of ammonia decomposition. The technical scheme comprises the following steps: 1) synthesis of a ZrO2 carrier: adding NH3H2O into a zirconyl nitrate solution to induce precipitation; 2) preparation of La2O3 / ZrO2: adding lanthanum nitrate hexahydrate and urea to obtain a precipitate, drying and finally calcining; 3) preparation of La2O3-ZnO / ZrO2: adding zinc nitrate hexahydrate and urea, standing to obtain a precipitate, drying and calcining; and 4) preparation of La2O3-ZnO-NiO / ZrO2: adding NH3H2O, then adding nickel acetate and thiourea, reacting, drying and twice calcining to obtain a target product. The application adopts lattice oxygen in the oxygen carrier to catalyze and oxidize ammonia gas decomposition, the oxygen carrier can be used repeatedly, and is suitable for future industrial application.

Description

Technical Field

[0001] This invention belongs to the field of ammonia decomposition technology, specifically relating to a La2O3-ZnO-NiO / ZrO2 oxygen carrier, its preparation method, and its application. Background Technology

[0002] Traditional ammonia decomposition for hydrogen production typically employs thermocatalytic oxidation, a process that uses oxygen or air as an oxidant to decompose ammonia at high temperatures. However, the introduction of oxygen results in a mixture with ammonia, and the high reaction temperature increases the risk of explosion. Furthermore, the introduction of oxygen can cause some ammonia to be oxidized to NO. x (e.g., 4NH3+5O2→4NO+6H2O), additional denitrification equipment (e.g., SCR) is required, increasing costs and operational risks.

[0003] The risk of explosion in the high-temperature mixture caused by the introduction of oxygen in traditional ammonia decomposition for hydrogen production has become a core bottleneck restricting its large-scale application. To address the safety hazards of traditional processes, existing technologies employ pure thermal catalytic decomposition, using nickel-based / ruthenium-based catalysts to decompose NH3 into nitrogen and hydrogen at 500-700℃. This process eliminates the risk of explosion by eliminating oxygen, but still requires high temperatures and has high catalyst costs. Another approach uses plasma-assisted decomposition, generating high-energy electrons through dielectric barrier discharge to break the NH3 molecular bonds: e - +NH3→NH2+H - →N2 + H2. This process can be achieved at room temperature, requires no catalyst, and poses no risk of explosion, but the equipment is energy-intensive, requiring a large amount of electricity. Therefore, there is a need to develop a new ammonia decomposition method that can not only completely eliminate safety hazards but also reduce energy consumption and costs. Summary of the Invention

[0004] This invention provides a La2O3-ZnO-NiO / ZrO2 oxygen carrier, its preparation method, and its applications. It utilizes lattice oxygen within the oxygen carrier to catalyze the decomposition of ammonia gas, which is relatively safer compared to traditional processes. Furthermore, the oxygen carrier can be recycled multiple times, making it suitable for future industrial applications.

[0005] The technical solution of this invention is as follows:

[0006] In the first aspect, a method for preparing La2O3-ZnO-NiO / ZrO2 oxygen carrier is disclosed, including the following steps:

[0007] 1) Synthesis of ZrO2 support: NH3·H2O was added to zirconium oxynitrate solution to induce precipitation, stirred at room temperature for 12-24 h, filtered, washed with water and ethanol, and then dried at 80-100℃ for 24-36 h; the precipitate was calcined at 700-750℃ for 2-4 h to obtain ZrO2 support;

[0008] 2) Preparation of La2O3 / ZrO2: ZrO2 was dispersed in water, lanthanum nitrate hexahydrate was added, and the mixture was stirred at room temperature for 2-4 hours. Urea was then added as a precipitant, and the mixture was reacted at 80-100℃ for 7-9 hours. After standing at room temperature for 10-15 hours, the precipitate was obtained. The precipitate was filtered, washed, dried at 80-100℃ for 6-8 hours, and finally calcined in a muffle furnace at 600-650℃ for 2-3 hours to obtain La2O3 / ZrO2.

[0009] 3) Preparation of La2O3-ZnO / ZrO2: La2O3 / ZrO2 was dispersed in water, and then zinc nitrate hexahydrate was added under stirring to prepare an oxygen carrier. After stirring at room temperature for 2-4 hours, urea was added as a precipitant, and the reaction was carried out at 80-100℃ for 7-9 hours. After standing at room temperature for 10-15 hours, the precipitate was obtained. After filtration, the precipitate was washed with water, dried at 80-100℃ for 6-8 hours, and finally calcined in a tube furnace at 600-700℃ under a He or Ar gas flow for 5-6 hours to obtain La2O3-ZnO / ZrO2.

[0010] 4) Preparation of La2O3-ZnO-NiO / ZrO2: La2O3-ZnO / ZrO2 and NH3·H2O were added to water to make an aqueous solution. Then, nickel acetate and thiourea were added to the aqueous solution. The mixture was stirred in a water bath at 60-100℃ for 6-12 hours and precipitated at room temperature for 12-24 hours. The mixture was filtered, washed, and dried at 60-100℃ for 8-16 hours. The resulting solid was ground to 400-500 μm and calcined in a tube furnace at 400-500℃ for 3-6 hours under argon or nitrogen conditions. The resulting precipitate was ground to 100-200 μm and then calcined again in a muffle furnace at 500-600℃ for 1-2 hours to obtain the target product, La2O3-ZnO-NiO / ZrO2 oxygen carrier.

[0011] Preferably, the mass ratio of zirconium oxynitrate, lanthanum nitrate hexahydrate, zinc nitrate hexahydrate, and nickel acetate is (50-60):(3-4):(1-2):(5-6).

[0012] Preferably, in step 1), the mass ratio of zirconium oxynitrate to NH3·H2O is (50-60):(2-3).

[0013] Preferably, in step 2), the mass ratio of lanthanum nitrate hexahydrate to urea is (3-4):(0.15-0.2).

[0014] Preferably, in step 3), the mass ratio of zinc nitrate hexahydrate to urea is (1-2):(0.06-0.1).

[0015] Preferably, in step 4), the mass ratio of NH3·H2O, nickel acetate and thiourea added is (0.1-0.2):(5-6):(0.25-0.3).

[0016] Secondly, the La2O3-ZnO-NiO / ZrO2 oxygen carrier prepared by the aforementioned preparation method is disclosed.

[0017] Thirdly, the application of the oxygen carrier in ammonia decomposition for hydrogen production is disclosed. Before the experiment, a leak test was conducted using nitrogen to ensure no leaks occurred throughout the experiment. To control the flow rate, a mass flow meter was used to adjust the gas velocities of nitrogen and ammonia. The resulting gas mixture was discharged from the bottom of the fixed-bed reactor and guided through a condenser for effective cooling. Subsequently, a gas-liquid separator was used to separate the condensed gas from the liquid phase, and water was discharged from the bottom of the separator. The content of the products in the post-reaction gas was analyzed online using gas chromatography-mass spectrometry.

[0018] The application of oxygen carriers in the ammonia decomposition to produce hydrogen includes the following steps:

[0019] a. Add 1g of oxygen carrier to the fixed bed reactor, pretreat with nitrogen at a flow rate of 100-200mL / min for 20-30min, set the preheater temperature to 200-400℃, set the fixed bed reactor reaction temperature to 450-550℃, raise the temperature, and set the reaction pressure to 0.3-1MPa.

[0020] b. Introduce ammonia gas, setting the ammonia gas inlet flow rate to 30-40 mL / min, to obtain the gaseous product hydrogen gas.

[0021] c. After the reaction is complete, nitrogen gas is introduced to purge the remaining gas in the reactor. Oxygen gas is then introduced into the fixed bed reactor at a temperature of 450-550℃ to obtain a La2O3-ZnO-NiO / ZrO2 composite oxygen carrier with restored lattice oxygen, which will be used in the next experiment.

[0022] The lattice oxygen provided by the oxygen carriers La2O3, ZnO, and NiO acts as an oxidant, directly reacting with NH4+. x reaction:

[0023] NH x Oxidized to N2 and H2: NH x * +O 2- lattice →N2+H2+Oxygen vacancy.

[0024] La2O3 provides basic sites to promote NH3 adsorption and stabilizes the ZrO2 structure, enhancing oxygen vacancy formation; NiO acts as a reducing component (Ni 2+ / Ni 0(Cyclic), ZnO regulates the electronic structure and promotes the breaking of NH bonds; ZrO2 has a high specific surface area and oxygen vacancy stability, which can support the dispersion of active components.

[0025] The mechanism of ammonia adsorption and activation is as follows: NH3 molecules are first adsorbed on the surface of an oxygen carrier (such as the active sites of La2O3, NiO, or ZnO), and then activated through the following means:

[0026] Chemisorption of NH3: NH3 reacts with surface Lewis acid sites (such as Zn) 2+ Ni 2+ It binds to either a base site (such as an oxygen vacancy in La2O3) to form adsorbed NH4+. x (x = 1, 2). The reaction formula is: NH3+*→NH3* (* represents the surface active site);

[0027] NH bond breaking: Adsorbed NH3 gradually dehydrogenates to generate NH2, NH, and H*, etc. This process is driven by the reducing property of NiO (Ni 2 + / Ni 0 (or oxygen vacancy promotion in ZnO)

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] 1. This invention uses lattice oxygen instead of gaseous oxygen, which is safer and avoids the risk of explosion.

[0030] 2. The La2O3-ZnO-NiO / ZrO2 oxygen carrier of the present invention exhibits excellent activity in the ammonia decomposition for hydrogen production, with an NH3 conversion rate of 99.3% and an H2 selectivity of 93.1%, while also demonstrating good recycling performance.

[0031] 3. The La2O3-ZnO-NiO / ZrO2 oxygen carrier of the present invention has a large specific surface area and excellent mechanical properties. The oxygen carrier regeneration only requires the introduction of O2 and does not require complex activation. The raw material is an inexpensive metal salt, which reduces production costs. Attached Figure Description

[0032] Figure 1 This is a scanning electron microscope (SEM) image of the catalyst prepared in Example 3 of this invention.

[0033] Figure 2 This is a morphology image of the catalyst prepared in Example 3 of the present invention under a high magnification microscope.

[0034] Figure 3 This is the XRD pattern of the catalyst prepared in Example 3 of this invention. Detailed Implementation

[0035] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions will be clearly and completely described below in conjunction with the embodiments of this invention.

[0036] Example 1

[0037] The La2O3-ZnO-NiO / ZrO2 oxygen carrier includes a ZrO2 support and La2O3, ZnO and NiO loaded on the support, with the loading amounts of La2O3, ZnO and NiO being 18%, 4% and 24% of the support mass, respectively.

[0038] The method for preparing the La2O3-ZnO-NiO / ZrO2 oxygen carrier includes the following steps:

[0039] 1) Synthesis of ZrO2 support: ZrO2 support was synthesized by coprecipitation method. 50g of zirconium nitrate dihydrate was added to 200mL of water to form a solution. 2g of NH3·H2O was added to the solution to induce precipitation. The mixture was stirred at room temperature for 12h, filtered, washed with water and ethanol, and then dried at 80℃ for 36h. The precipitate was calcined at 700℃ for 4h to obtain ZrO2 support.

[0040] 2) Preparation of La2O3 / ZrO2: ZrO2 was dispersed in 100 mL of water, 3 g of lanthanum nitrate hexahydrate was added, and the mixture was stirred at room temperature for 2 h. Then, 0.15 g of urea was added as a precipitant, and the mixture was reacted at 80 °C for 9 h. After standing at room temperature for 10 h, the precipitate was obtained. After filtration, the precipitate was washed with deionized water, dried at 80 °C for 8 h, and finally calcined in a muffle furnace at 600 °C for 3 h to obtain La2O3 / ZrO2.

[0041] 3) Preparation of La2O3-ZnO / ZrO2: La2O3 / ZrO2 was dispersed in 100mL of water, and then 1g of zinc nitrate hexahydrate was added under stirring to prepare an oxygen carrier; after stirring at room temperature for 2h, 0.06g of urea was added as a precipitant, and the reaction was carried out at 80℃ for 9h. After standing at room temperature for 10h, the precipitate was obtained, filtered, washed with water, dried at 80℃ for 8h, and finally calcined in a tube furnace at 600℃ under Ar gas flow for 6h to obtain La2O3-ZnO / ZrO2;

[0042] 4) Preparation of La2O3-ZnO-NiO / ZrO2: La2O3-ZnO / ZrO2 and 0.1g of NH3·H2O were added to 100mL of water to make an aqueous solution. Then, 5g of nickel acetate and 0.25g of thiourea precipitant were added to the aqueous solution. The mixture was stirred in a 60℃ water bath for 12h and precipitated at room temperature for 12h. After filtration and washing, the solid was dried at 60℃ for 16h. The obtained solid was ground to 500μm and calcined in a tube furnace at 400℃ for 6h under nitrogen conditions. The precipitate was ground to 200μm and then calcined again in a muffle furnace at 500℃ for 2h to obtain the target product La2O3-ZnO-NiO / ZrO2 oxygen carrier.

[0043] The application of the oxygen carrier in ammonia decomposition for hydrogen production includes the following steps:

[0044] a. Add 1g of oxygen carrier to the fixed bed reactor, pretreat with nitrogen at a flow rate of 100mL / min for 30min, set the preheater temperature to 200℃, set the fixed bed reactor reaction temperature to 450℃, raise the temperature, and set the reaction pressure to 0.3MPa.

[0045] b. Introduce ammonia gas, setting the ammonia gas inlet flow rate to 30 mL / min, to obtain the gaseous product hydrogen gas.

[0046] c. After the reaction is complete, nitrogen gas is introduced to purge the remaining gas in the reactor. Oxygen gas is then introduced into the fixed bed reactor at a set temperature of 450℃ to obtain a La2O3-ZnO-NiO / ZrO2 composite oxygen carrier with restored lattice oxygen, which will be used in the next experiment.

[0047] Example 2

[0048] The La2O3-ZnO-NiO / ZrO2 oxygen carrier includes a ZrO2 support and La2O3, ZnO and NiO loaded on the support, with the loading amounts of La2O3, ZnO and NiO being 20%, 7% and 24% of the support mass, respectively.

[0049] The method for preparing the La2O3-ZnO-NiO / ZrO2 oxygen carrier includes the following steps:

[0050] 1) Synthesis of ZrO2 support: ZrO2 support was synthesized by coprecipitation method. 60g of zirconium nitrate dihydrate was added to 200mL of water to form a solution. 3g of NH3·H2O was added to the solution to induce precipitation. The mixture was stirred at room temperature for 24h, filtered, washed with water and ethanol, and then dried at 100℃ for 24h. The precipitate was calcined at 750℃ for 2h to obtain ZrO2 support.

[0051] 2) Preparation of La2O3 / ZrO2: ZrO2 was dispersed in 100 mL of water, 4 g of lanthanum nitrate hexahydrate was added, and the mixture was stirred at room temperature for 4 h. Then, 0.2 g of urea was added as a precipitant, and the mixture was reacted at 100 °C for 7 h. After standing at room temperature for 15 h, the precipitate was obtained. After filtration, the precipitate was washed with deionized water, dried at 100 °C for 6 h, and finally calcined in a muffle furnace at 650 °C for 2 h to obtain La2O3 / ZrO2.

[0052] 3) Preparation of La2O3-ZnO / ZrO2: La2O3 / ZrO2 was dispersed in 100mL of water, and then 2g of zinc nitrate hexahydrate was added under stirring to prepare an oxygen carrier; after stirring at room temperature for 4h, 0.1g of urea was added as a precipitant, and the reaction was carried out at 100℃ for 7h. After standing at room temperature for 15h, the precipitate was obtained, filtered, washed with water, dried at 100℃ for 6h, and finally calcined in a tube furnace at 700℃ under a He gas flow for 5h to obtain La2O3-ZnO / ZrO2;

[0053] 4) Preparation of La2O3-ZnO-NiO / ZrO2: La2O3-ZnO / ZrO2 and 0.2g of NH3·H2O were added to 100mL of water to make an aqueous solution. Then, 6g of nickel acetate and 0.3g of thiourea precipitant were added to the aqueous solution. The mixture was stirred in a water bath at 100℃ for 6h and precipitated at room temperature for 24h. The mixture was filtered, washed, and dried at 100℃ for 8h. The resulting solid was ground to 450μm and calcined at 500℃ for 3h in a tube furnace under argon conditions. The resulting precipitate was ground to 150μm and then calcined again in a muffle furnace at 600℃ for 1h to obtain the target product La2O3-ZnO-NiO / ZrO2 oxygen carrier.

[0054] The application of the oxygen carrier in ammonia decomposition for hydrogen production includes the following steps:

[0055] a. Add 1g of oxygen carrier to the fixed bed reactor, pretreat with nitrogen at a flow rate of 200mL / min for 20min, set the temperature of the preheater to 400℃, set the reaction temperature of the fixed bed reactor to 550℃, heat up, and set the reaction pressure to 1MPa.

[0056] b. Introduce ammonia gas, setting the ammonia gas inlet flow rate to 40 mL / min, to obtain the gaseous product hydrogen gas.

[0057] c. After the reaction is complete, nitrogen gas is introduced to purge the remaining gas in the reactor. Oxygen gas is then introduced into the fixed bed reactor at a set temperature of 550℃ to obtain a La2O3-ZnO-NiO / ZrO2 composite oxygen carrier with restored lattice oxygen, which will be used in the next experiment.

[0058] Example 3

[0059] The La2O3-ZnO-NiO / ZrO2 oxygen carrier includes a ZrO2 support and La2O3, ZnO and NiO loaded on the support, with the loading amounts of La2O3, ZnO and NiO being 23%, 6% and 24% of the support mass, respectively.

[0060] The method for preparing the La2O3-ZnO-NiO / ZrO2 oxygen carrier includes the following steps:

[0061] 1) Synthesis of ZrO2 support: ZrO2 support was synthesized by coprecipitation method. 55g of zirconium nitrate dihydrate was added to 200mL of water to form a solution. 2.5g of NH3·H2O was added to the solution to induce precipitation. The mixture was stirred at room temperature for 16h, filtered, washed with water and ethanol, and then dried at 90℃ for 30h. The precipitate was calcined at 720℃ for 3h to obtain ZrO2 support.

[0062] 2) Preparation of La2O3 / ZrO2: ZrO2 was dispersed in 100 mL of water, and 3.5 g of lanthanum nitrate hexahydrate was added. After stirring at room temperature for 3 h, 0.18 g of urea was added as a precipitant. The mixture was reacted at 90 °C for 8 h, and then allowed to stand at room temperature for 12 h to obtain the precipitate. After filtration, the precipitate was washed with deionized water, dried at 90 °C for 7 h, and finally calcined in a muffle furnace at 630 °C for 2.5 h to obtain La2O3 / ZrO2.

[0063] 3) Preparation of La2O3-ZnO / ZrO2: La2O3 / ZrO2 was dispersed in 100mL of water, and then 1.5g of zinc nitrate hexahydrate was added under stirring to prepare an oxygen carrier; after stirring at room temperature for 3h, 0.08g of urea was added as a precipitant, and the reaction was carried out at 90℃ for 8h. After standing at room temperature for 12h, the precipitate was obtained, filtered, washed with water, dried at 90℃ for 7h, and finally calcined in a tube furnace at 650℃ under a He gas flow for 5.5h to obtain La2O3-ZnO / ZrO2;

[0064] 4) Preparation of La2O3-ZnO-NiO / ZrO2: La2O3-ZnO / ZrO2 and 0.15 g of NH3·H2O were added to 100 mL of water to prepare an aqueous solution. Then, 5.5 g of nickel acetate and 0.28 g of thiourea precipitant were added to the aqueous solution. The mixture was stirred in an 80℃ water bath for 10 h, precipitated at room temperature for 16 h, filtered, washed with water, and dried at 80℃ for 12 h. The resulting solid was ground to 400 μm and calcined in a tube furnace at 450℃ for 5 h under argon conditions. The resulting precipitate was ground to 100 μm and then calcined again in a muffle furnace at 550℃ for 1.5 h to obtain the target product, La2O3-ZnO-NiO / ZrO2 oxygen carrier. The morphology of the oxygen carrier under a scanning electron microscope is shown in the figure below. Figure 1 As shown, the morphology of the oxygen carrier under high magnification is as follows: Figure 2As shown, the XRD test pattern is as follows: Figure 3 As shown.

[0065] The application of the oxygen carrier in ammonia decomposition for hydrogen production includes the following steps:

[0066] a. Add 1g of oxygen carrier to the fixed bed reactor, pretreat with nitrogen at a flow rate of 150mL / min for 25min, set the preheater temperature to 300℃, set the fixed bed reactor reaction temperature to 500℃, raise the temperature, and set the reaction pressure to 0.6MPa.

[0067] b. Introduce ammonia gas, setting the ammonia gas inlet flow rate to 35 mL / min, to obtain the gaseous product hydrogen gas.

[0068] c. After the reaction is complete, nitrogen gas is introduced to purge the remaining gas in the reactor. Oxygen gas is then introduced into the fixed bed reactor at a set temperature of 500℃ to obtain a La2O3-ZnO-NiO / ZrO2 composite oxygen carrier with restored lattice oxygen, which will be used in the next experiment.

[0069] Comparative Example 1

[0070] Unlike Example 3, the oxygen carrier in this comparative example lacks La2O3. Specifically, the preparation method of the ZnO-NiO / ZrO2 oxygen carrier includes the following steps:

[0071] 1) Synthesis of ZrO2 support: ZrO2 support was synthesized by coprecipitation method. 55g of zirconium nitrate dihydrate was added to 200mL of water to form a solution. 2.5g of NH3·H2O was added to the solution to induce precipitation. The mixture was stirred at room temperature for 16h, filtered, washed with water and ethanol, and then dried at 90℃ for 30h. The precipitate was calcined at 720℃ for 3h to obtain ZrO2 support.

[0072] 2) Preparation of ZnO / ZrO2: ZrO2 support was dispersed in 100 mL of water, and then 1.5 g of zinc nitrate hexahydrate was added under stirring to prepare oxygen carrier; after stirring at room temperature for 3 h, 0.08 g of urea was added as precipitant, and the reaction was carried out at 90 °C for 8 h. After standing at room temperature for 12 h, the precipitate was obtained, filtered, washed with water, dried at 90 °C for 7 h, and finally calcined in a tube furnace at 650 °C under He gas flow for 5.5 h to obtain ZnO / ZrO2;

[0073] 3) Preparation of ZnO-NiO / ZrO2: ZnO / ZrO2 and 0.15g of NH3·H2O were added to 100mL of water to make an aqueous solution. Then, 5.5g of nickel acetate and 0.28g of thiourea precipitant were added to the aqueous solution. The mixture was stirred in an 80℃ water bath for 10h and precipitated at room temperature for 16h. The mixture was filtered, washed with water, and dried at 80℃ for 12h. The resulting solid was ground to 400μm and calcined in a tube furnace at 450℃ for 5h under argon conditions. The resulting precipitate was ground to 100μm and then calcined again in a muffle furnace at 550℃ for 1.5h to obtain the target product ZnO-NiO / ZrO2 oxygen carrier.

[0074] The application of the oxygen carrier in ammonia decomposition for hydrogen production includes the following steps:

[0075] a. Add 1g of oxygen carrier to the fixed bed reactor, pretreat with nitrogen at a flow rate of 150mL / min for 25min, set the preheater temperature to 300℃, set the fixed bed reactor reaction temperature to 500℃, raise the temperature, and set the reaction pressure to 0.6MPa.

[0076] b. Introduce ammonia gas, setting the ammonia gas inlet flow rate to 35 mL / min, to obtain the gaseous product hydrogen gas.

[0077] c. After the reaction is complete, nitrogen gas is introduced to purge the remaining gas in the reactor. Oxygen gas is then introduced into the fixed bed reactor at a set temperature of 500℃ to obtain a ZnO-NiO / ZrO2 composite oxygen carrier with restored lattice oxygen.

[0078] Comparative Example 2

[0079] Unlike Example 3, the oxygen carrier in this comparative example lacks ZnO, specifically:

[0080] The method for preparing the La2O3-NiO / ZrO2 oxygen carrier includes the following steps:

[0081] 1) Synthesis of ZrO2 support: ZrO2 support was synthesized by coprecipitation method. 55g of zirconium nitrate dihydrate was added to 200mL of water to form a solution. 2.5g of NH3·H2O was added to the solution to induce precipitation. The mixture was stirred at room temperature for 16h, filtered, washed with water and ethanol, and then dried at 90℃ for 30h. The precipitate was calcined at 720℃ for 3h to obtain ZrO2 support.

[0082] 2) Preparation of La2O3 / ZrO2: ZrO2 was dispersed in 100 mL of water, and 3.5 g of lanthanum nitrate hexahydrate was added. After stirring at room temperature for 3 h, 0.18 g of urea was added as a precipitant. The mixture was reacted at 90 °C for 8 h, and then allowed to stand at room temperature for 12 h to obtain the precipitate. After filtration, the precipitate was washed with deionized water, dried at 90 °C for 7 h, and finally calcined in a muffle furnace at 630 °C for 2.5 h to obtain La2O3 / ZrO2.

[0083] 3) Preparation of La2O3-NiO / ZrO2: La2O3 / ZrO2 and 0.15g of NH3·H2O were added to 100mL of water to make an aqueous solution. Then, 5.5g of nickel acetate and 0.28g of thiourea precipitant were added to the aqueous solution. The mixture was stirred in an 80℃ water bath for 10h and precipitated at room temperature for 16h. The mixture was filtered, washed with water, and dried at 80℃ for 12h. The resulting solid was ground to 400μm and calcined in a tube furnace at 450℃ for 5h under argon conditions. The resulting precipitate was ground to 100μm and then calcined again in a muffle furnace at 550℃ for 1.5h to obtain the target product, La2O3-NiO / ZrO2 oxygen carrier.

[0084] The application of the oxygen carrier in ammonia decomposition for hydrogen production includes the following steps:

[0085] a. Add 1g of oxygen carrier to the fixed bed reactor, pretreat with nitrogen at a flow rate of 150mL / min for 25min, set the preheater temperature to 300℃, set the fixed bed reactor reaction temperature to 500℃, raise the temperature, and set the reaction pressure to 0.6MPa.

[0086] b. Introduce ammonia gas, setting the ammonia gas inlet flow rate to 35 mL / min, to obtain the gaseous product hydrogen gas.

[0087] c. After the reaction is complete, nitrogen gas is introduced to purge the remaining gas in the reactor. Oxygen gas is then introduced into the fixed bed reactor at a set temperature of 500℃ to obtain the La2O3-NiO / ZrO2 composite oxygen carrier with restored lattice oxygen.

[0088] Comparative Example 3

[0089] Unlike Example 3, step 4) in this comparative example does not include secondary calcination. Specifically, the preparation method of the La2O3-ZnO-NiO / ZrO2 oxygen carrier includes the following steps:

[0090] 1) Synthesis of ZrO2 support: ZrO2 support was synthesized by coprecipitation method. 55g of zirconium nitrate dihydrate was added to 200mL of water to form a solution. 2.5g of NH3·H2O was added to the solution to induce precipitation. The mixture was stirred at room temperature for 16h, filtered, washed with water and ethanol, and then dried at 90℃ for 30h. The precipitate was calcined at 720℃ for 3h to obtain ZrO2 support.

[0091] 2) Preparation of La2O3 / ZrO2: ZrO2 was dispersed in 100 mL of water, and 3.5 g of lanthanum nitrate hexahydrate was added. After stirring at room temperature for 3 h, 0.18 g of urea was added as a precipitant. The mixture was reacted at 90 °C for 8 h, and then allowed to stand at room temperature for 12 h to obtain the precipitate. After filtration, the precipitate was washed with deionized water, dried at 90 °C for 7 h, and finally calcined in a muffle furnace at 630 °C for 2.5 h to obtain La2O3 / ZrO2.

[0092] 3) Preparation of La2O3-ZnO / ZrO2: La2O3 / ZrO2 was dispersed in 100mL of water, and then 1.5g of zinc nitrate hexahydrate was added under stirring to prepare an oxygen carrier; after stirring at room temperature for 3h, 0.08g of urea was added as a precipitant, and the reaction was carried out at 90℃ for 8h. After standing at room temperature for 12h, the precipitate was obtained, filtered, washed with water, dried at 90℃ for 7h, and finally calcined in a tube furnace at 650℃ under a He gas flow for 5.5h to obtain La2O3-ZnO / ZrO2;

[0093] 4) Preparation of La2O3-ZnO-NiO / ZrO2: La2O3-ZnO / ZrO2 and 0.15g of NH3·H2O were added to 100mL of water to make an aqueous solution. Then, 5.5g of nickel acetate and 0.28g of thiourea precipitant were added to the aqueous solution. The mixture was stirred in an 80℃ water bath for 10h and precipitated at room temperature for 16h. The mixture was filtered, washed with water, and dried at 80℃ for 12h. The resulting solid was ground to 400μm and calcined in a tube furnace at 450℃ for 5h under argon conditions. The resulting precipitate was ground to 100μm to obtain the target product La2O3-ZnO-NiO / ZrO2 oxygen carrier.

[0094] The application of the oxygen carrier in ammonia decomposition for hydrogen production includes the following steps:

[0095] a. Add 1g of oxygen carrier to the fixed bed reactor, pretreat with nitrogen at a flow rate of 150mL / min for 25min, set the preheater temperature to 300℃, set the fixed bed reactor reaction temperature to 500℃, raise the temperature, and set the reaction pressure to 0.6MPa.

[0096] b. Introduce ammonia gas, setting the ammonia gas inlet flow rate to 35 mL / min, to obtain the gaseous product hydrogen gas.

[0097] c. After the reaction is complete, nitrogen gas is introduced to purge the remaining gas in the reactor. Oxygen gas is then introduced into the fixed bed reactor at a set temperature of 500℃ to obtain a La2O3-ZnO-NiO / ZrO2 composite oxygen carrier with restored lattice oxygen.

[0098] Comparative Example 4

[0099] Unlike Example 3, in step 4) of this comparative example, sodium hydroxide was used instead of thiourea as the precipitant. Step 4) is as follows: Preparation of La2O3-ZnO-NiO / ZrO2: La2O3-ZnO / ZrO2 and 0.15g of NH3·H2O were added to 100mL of water to make an aqueous solution. Then, 5.5g of nickel acetate and 0.28g of sodium hydroxide as the precipitant were added to the aqueous solution. The mixture was stirred in an 80℃ water bath for 10h, precipitated at room temperature for 16h, filtered, washed with water, and dried at 80℃ for 12h. The obtained solid was ground to 400μm and calcined in a tube furnace at 450℃ for 5h under argon conditions. The obtained precipitate was ground to 100μm and then calcined again in a muffle furnace at 550℃ for 1.5h to obtain the target product La2O3-ZnO-NiO / ZrO2 oxygen carrier. The remaining preparation methods and steps are the same as in Example 3.

[0100] The oxygen carriers prepared in the above examples and comparative examples were subjected to performance testing, and the test results are shown in Table 1.

[0101] Table 1 Test Results

[0102] project Average specific surface area Average aperture Crushing strength Example 1 <![CDATA[1g0m 2 / g]]> 20nm <![CDATA[33N·cm -1 ]]> Example 2 <![CDATA[230m 2 / g]]> 24nm <![CDATA[37N·cm -1 ]]> Example 3 <![CDATA[260m 2 / g]]> 31nm <![CDATA[43N·cm -1 ]]> Comparative Example 1 <![CDATA[78m 2 / g]]> 6nm <![CDATA[8N·cm -1 ]]> Comparative Example 2 <![CDATA[79m 2 / g]]> 7nm <![CDATA[9N·cm -1 ]]> Comparative Example 3 <![CDATA[69m 2 / g]]> 5nm <![CDATA[9N·cm -1 ]]> Comparative Example 4 <![CDATA[60m 2 / g]]> 8nm <![CDATA[10N·cm -1 ]]>

[0103] The performance of the oxygen carriers prepared in the above examples and comparative examples in the ammonia decomposition hydrogen production is evaluated as shown in Table 2. The NH3 conversion rate and H2 selectivity were calculated according to the following formulas:

[0104]

[0105] Table 2 Performance Evaluation of Ammonia Decomposition for Hydrogen Production

[0106] project <![CDATA[NH3 conversion rate]]> <![CDATA[H2 selectivity]]> Example 1 95.6％ 90.3％ Example 2 97.8％ 91.9％ Example 3 99.3％ 93.1％ Comparative Example 1 31.6％ 26.1％ Comparative Example 2 35.2％ 14.8％ Comparative Example 3 36.8％ 22.3％ Comparative Example 4 41.3％ 14.3％

[0107] The absence of La2O3 in Comparative Example 1 leads to insufficient basic sites, weak NH3 adsorption, and a significant reduction in both NH3 conversion and H2 selectivity.

[0108] The absence of ZnO in Comparative Example 2 hindered the breaking of NH bonds, increased side reactions, and resulted in a significant decrease in both NH3 conversion and H2 selectivity.

[0109] Comparative Example 3 does not include secondary calcination, which results in a loose oxygen carrier structure and a significant reduction in crushing strength.

[0110] In Comparative Example 4, sodium hydroxide was used instead of thiourea as the precipitant, resulting in severe aggregation of the oxygen carrier and a decrease in specific surface area.

[0111] For the catalyst prepared in Example 1, after the reaction was completed, nitrogen was introduced to purge the gas in the reactor, and then oxygen was introduced into the fixed bed. The fixed bed reactor was set to a temperature of 500°C for 3 hours, and then cooled to room temperature for use in the next experiment. The catalyst prepared in Example 1 was circulated 10 times, and the cycling performance of the ammonia decomposition to hydrogen production was evaluated as shown in Table 3.

[0112] Table 3 Cyclic performance results

[0113] project <![CDATA[NH3 conversion rate]]> <![CDATA[H2 selectivity]]> Example 1-1 95.6％ 90.3％ Examples 1-2 95.8％ 89.7％ Examples 1-3 96.3％ 90.6％ Examples 1-4 95.9％ 90.8％ Examples 1-5 96.2％ 90.5％ Examples 1-6 96.5％ 91.1％ Examples 1-7 96.1％ 89.5％ Examples 1-8 95.7％ 89.8％ Examples 1-9 96.1％ 89.3％ Examples 1-10 96.3％ 90.5％

Claims

1. A method for preparing La2O3-ZnO-NiO / ZrO2 oxygen carrier, characterized in that, Includes the following steps: 1) Synthesis of ZrO2 support: NH3·H2O was added to zirconium oxynitrate solution to induce precipitation, stirred at room temperature for 12-24 h, filtered, washed with water and ethanol, and then dried at 80-100℃ for 24-36 h; the precipitate was calcined at 700-750℃ for 2-4 h to obtain ZrO2 support; 2) Preparation of La2O3 / ZrO2: ZrO2 was dispersed in water, lanthanum nitrate hexahydrate was added, and the mixture was stirred at room temperature for 2-4 hours. Urea was then added as a precipitant, and the mixture was reacted at 80-100℃ for 7-9 hours. After standing at room temperature for 10-15 hours, the precipitate was obtained. The precipitate was filtered, washed, dried at 80-100℃ for 6-8 hours, and finally calcined in a muffle furnace at 600-650℃ for 2-3 hours to obtain La2O3 / ZrO2. 3) Preparation of La2O3-ZnO / ZrO2: La2O3 / ZrO2 was dispersed in water, and then zinc nitrate hexahydrate was added under stirring to prepare an oxygen carrier. After stirring at room temperature for 2-4 hours, urea was added as a precipitant, and the reaction was carried out at 80-100℃ for 7-9 hours. After standing at room temperature for 10-15 hours, the precipitate was obtained. After filtration, the precipitate was washed with water, dried at 80-100℃ for 6-8 hours, and finally calcined in a tube furnace at 600-700℃ under a He or Ar gas flow for 5-6 hours to obtain La2O3-ZnO / ZrO2. 4) Preparation of La2O3-ZnO-NiO / ZrO2: La2O3-ZnO / ZrO2 and NH3·H2O were added to water to make an aqueous solution. Then, nickel acetate and thiourea were added to the aqueous solution. The mixture was stirred in a water bath at 60-100℃ for 6-12 hours and precipitated at room temperature for 12-24 hours. The mixture was filtered, washed, and dried at 60-100℃ for 8-16 hours. The resulting solid was ground to 400-500 μm and calcined in a tube furnace at 400-500℃ for 3-6 hours under argon or nitrogen conditions. The resulting precipitate was ground to 100-200 μm and then calcined again in a muffle furnace at 500-600℃ for 1-2 hours to obtain the target product, La2O3-ZnO-NiO / ZrO2 oxygen carrier.

2. The method for preparing the La2O3-ZnO-NiO / ZrO2 oxygen carrier as described in claim 1, characterized in that, The mass ratio of zirconium oxynitrate, lanthanum nitrate hexahydrate, zinc nitrate hexahydrate, and nickel acetate is (50-60):(3-4):(1-2):(5-6).

3. The method for preparing the La2O3-ZnO-NiO / ZrO2 oxygen carrier as described in claim 1, characterized in that, In step 1), the mass ratio of zirconium oxynitrate to NH3·H2O is (50-60):(2-3).

4. The method for preparing the La2O3-ZnO-NiO / ZrO2 oxygen carrier as described in claim 1, characterized in that, In step 2), the mass ratio of lanthanum nitrate hexahydrate to urea is (3-4):(0.15-0.2).

5. The method for preparing the La2O3-ZnO-NiO / ZrO2 oxygen carrier as described in claim 1, characterized in that, In step 3), the mass ratio of zinc nitrate hexahydrate to urea is (1-2):(0.06-0.1).

6. The method for preparing the La2O3-ZnO-NiO / ZrO2 oxygen carrier as described in claim 1, characterized in that, In step 4), the mass ratio of NH3·H2O, nickel acetate, and thiourea added is (0.1-0.2):(5-6):(0.25-0.3).

7. The La2O3-ZnO-NiO / ZrO2 oxygen carrier prepared by the preparation method according to any one of claims 1-6.

8. The application of the oxygen carrier as described in claim 7 in ammonia decomposition for hydrogen production, characterized in that, Includes the following steps: a. Add 1g of oxygen carrier to the fixed bed reactor, pretreat with nitrogen at a flow rate of 100-200mL / min for 20-30min, set the preheater temperature to 200-400℃, set the fixed bed reactor reaction temperature to 450-550℃, raise the temperature, and set the reaction pressure to 0.3-1MPa. b. Introduce ammonia gas, setting the ammonia gas inlet flow rate to 30-40 mL / min, to obtain the gaseous product hydrogen gas. c. After the reaction is complete, nitrogen gas is introduced to purge the remaining gas in the reactor. Oxygen gas is then introduced into the fixed bed reactor at a temperature of 450-550℃ to obtain a La2O3-ZnO-NiO / ZrO2 composite oxygen carrier with restored lattice oxygen, which will be used in the next experiment.

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