Preparation method of ceria catalyst suitable for ultra-high temperature water-gas shift reaction

Abstract

This invention discloses a method for preparing a cerium dioxide catalyst for ultra-high temperature catalytic water-gas conversion reaction. The method involves first synthesizing cerium dioxide nanoparticles via a hydrothermal method, and then subjecting the nanoparticles to multi-step heat treatment in a gaseous environment to achieve surface modification, resulting in a cerium dioxide catalyst with a large number of exposed coordination unsaturated sites. The catalyst prepared by this method exhibits excellent catalytic performance for water-gas conversion reaction in the ultra-high temperature range above 600℃. Traditional industrial Fe-based catalysts deactivate above 600℃, while the cerium dioxide catalyst prepared by this invention maintains high performance at temperatures above 600℃ and is not easily deactivated. Furthermore, cerium dioxide catalysts are environmentally friendly materials with advantages such as low cost and minimal environmental pollution, showing broad application prospects in industrial water-gas conversion reaction for hydrogen production.

Description

Technical Field

[0001] This invention belongs to the field of industrial catalysis, specifically relating to a method for preparing a cerium dioxide catalyst suitable for ultra-high temperature water-gas conversion reaction. Background Technology

[0002] The water-gas conversion reaction is a major source of industrial hydrogen production and a primary pathway for hydrogen production in industrial ammonia synthesis. This reaction converts coal resources into hydrogen, which can then be used in hydrogen-oxygen fuel cells and ammonia synthesis. The former is crucial for the automotive and energy industries, while ammonia synthesis is vital for agricultural sectors such as fertilizer production, industrial sectors such as nitric acid preparation, and environmental protection. Therefore, developing high-performance catalysts for the water-gas conversion reaction is essential to improving hydrogen production efficiency and reducing costs, which is of great significance for both industrial hydrogen production and ammonia synthesis.

[0003] Currently, the catalysts used in industrial water-gas conversion reactions mainly include Fe-based catalysts, Cu-based catalysts, and Au catalysts. Au catalysts are primarily suitable for low-temperature water-gas conversion reactions, but they are expensive. While Fe-based and Cu-based catalysts are less expensive, their applicable temperature is below 600℃; they suffer from deactivation at temperatures above 600℃. However, the outlet syngas temperature of modern coal chemical or biomass gasification furnaces is typically above 900℃, even exceeding 1300℃. Using Fe-based and Cu-based catalysts requires cooling the high-temperature syngas to ~400℃ using a large waste heat boiler before it can enter the traditional conversion stage, necessitating expensive high-temperature alloy boilers and extensive heat exchange equipment.

[0004] Therefore, developing a catalyst that maintains excellent catalytic performance in the water-gas conversion reaction at temperatures above 600℃ would have significant application value. This would allow the shift reactor to be placed directly downstream of the gasifier, enabling the reaction to occur before the syngas cools. On one hand, this eliminates the need for an expensive waste heat boiler, significantly reducing equipment investment costs. On the other hand, the heat of reaction can exist directly in the syngas as high-temperature heat, which can then be used to generate higher-grade steam or power. Summary of the Invention

[0005] The purpose of this invention is to provide a highly efficient catalyst and its preparation process suitable for ultra-high temperature water-gas conversion reactions above 600℃. Existing Fe-based catalysts are mainly used in temperature ranges below 600℃, and catalyst deactivation occurs at temperatures above 600℃. However, the inventors of this application have discovered that surface modification of cerium dioxide catalysts alters their morphology and exposes a large number of unsaturated coordination sites, which can become active sites for catalyzing water-gas conversion reactions at ultra-high temperatures above 600℃. This invention innovatively utilizes a multi-stage heat treatment process to modify the surface of cerium dioxide catalysts, obtaining cerium dioxide catalysts that still exhibit excellent catalytic performance in the ultra-high temperature range above 600℃.

[0006] The present invention adopts the following technical solution: A method for preparing a cerium dioxide catalyst suitable for ultra-high temperature water-gas conversion reaction includes the following steps: (1) First, prepare a sodium hydroxide solution with a concentration of 6-9 mol / L and stir it on a magnetic stirrer; (2) Dissolve 0.002-0.004 mol of cerium salt in 5-10 mL of deionized water, then mix with 35-70 mL of sodium hydroxide solution and stir with a magnetic stirrer; (3) Transfer the mixed solution to a 50-100 mL high-pressure reactor and place it in an oven to carry out a hydrothermal reaction for 24 hours; (4) After the reaction is complete, the powder obtained is washed with deionized water until neutral, then rinsed with anhydrous ethanol several times, and then dried in an oven at 60°C for 24 hours. (5) The dried solid powder is calcined in air, and the calcination temperature, heating rate and holding time are set to obtain cerium dioxide nanoparticles with fewer defects and better crystallinity. (6) The above-mentioned cerium dioxide nanoparticles are heat-treated with reducing gas in a tube furnace to obtain a cerium dioxide catalyst with excellent catalytic performance in water gas conversion reaction at ultra-high temperature above 600℃.

[0007] The cerium dioxide catalyst and its preparation method for ultra-high temperature water-gas conversion reaction of the present invention also include the following preferred embodiments.

[0008] In a preferred embodiment of the present invention, in step (1), the temperature of the magnetic stirrer is set at 25-30°C and the stirring time is set at 30-60 min.

[0009] In a preferred embodiment of the present invention, the cerium salt in step (2) is at least one of cerium nitrate, cerium chloride and cerium sulfate.

[0010] In a preferred embodiment of the present invention, the hydrothermal reaction temperature in step (3) is 100-250°C.

[0011] In a preferred embodiment of the present invention, the oven drying temperature in step (4) is 60-100°C and the drying time is 12-24 hours.

[0012] In a preferred embodiment of the present invention, the calcination temperature in step (5) is 400-600℃, the heating rate is 5-10℃ / min, and the calcination time is 12-24 hours.

[0013] In a preferred embodiment of the present invention, in step (6), the reducing gas is one of CO, H2, and methane, or a mixture of these.

[0014] In a preferred embodiment of the present invention, in step (6), the heat treatment temperature is 800-1100℃, the heating rate is 5-10℃ / min, and the heat treatment time is 1-3 hours. The heat treatment temperature in this step is crucial in determining whether ordered unsaturated sites can be formed on the final catalyst surface, thus affecting its catalytic performance at ultra-high temperatures. When the heat treatment temperature is below 800℃, it is impossible to effectively induce surface reconstruction to form an ordered monolayer step structure; when the temperature is above 1100℃, the catalyst particles will undergo severe sintering, resulting in a significant decrease in specific surface area, which in turn leads to a reduction in catalytic activity. The temperature range of 800-1100℃ is the optimal range for balancing surface reconstruction and particle sintering.

[0015] A cerium dioxide catalyst suitable for ultra-high temperature water-gas conversion reaction is prepared by the above method and can be used as a catalyst for hydrogen production from water-gas conversion reaction at ultra-high temperature above 600℃.

[0016] Compared with existing technologies, the beneficial effects of the present invention are as follows: This invention utilizes a multi-stage heat treatment process to modify the surface of cerium dioxide nanoparticles, exposing a large number of coordination unsaturated sites. These sites have been proven to be active sites for ultra-high temperature catalytic water-gas conversion reactions above 600℃, exhibiting excellent catalytic performance in water-gas conversion reactions and improving hydrogen production efficiency. This is mainly achieved through the following aspects: (1) Cerium dioxide nanoparticles have excellent oxygen storage and release capabilities, which can provide a redox pathway for water-gas conversion reactions. Nano-sized cerium dioxide nanoparticles are prepared by a hydrothermal method, giving them a large specific surface area, thereby increasing the contact area between the catalyst and the reactant gas. Then, calcination in air enhances crystallinity and reduces bulk defects, making the catalyst more structurally stable at high temperatures, thus improving the stability of its catalytic performance and reducing deactivation.

[0017] (2) The surface of cerium dioxide nanoparticles is modified using reducing gas to expose a large number of unsaturated sites in an orderly manner. These sites are ordered structures composed of single-layer steps and still exhibit excellent catalytic performance in the water-gas conversion reaction at high temperatures above 600℃. Setting the treatment temperature for modifying the surface of cerium dioxide nanoparticles with reducing gas in the temperature range of 800-1100℃ can effectively induce the reconstruction of the cerium dioxide surface to form an ordered single-layer step structure, while also preventing the cerium dioxide particles from sintering. Attached Figure Description

[0018] Figure 1 Electron micrographs of cerium dioxide nanoparticles prepared in Examples 1-2.

[0019] Figure 2 Electron micrographs of the surface-modified cerium dioxide catalysts prepared in Examples 3-5.

[0020] Figure 3 The graph shows the performance of the cerium dioxide catalysts prepared in Examples 1 and 3 in the water-gas conversion reaction.

[0021] Figure 4 Electron micrograph of the cerium dioxide catalyst prepared for comparison. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0023] Example 1 A method for preparing a cerium dioxide catalyst suitable for ultra-high temperature water-gas conversion reaction includes the following steps: (1) preparing a sodium hydroxide solution with a concentration of 6 mol / L; (2) dissolving 0.864 g of Ce(NO3)3·6H2O in 5 mL of deionized water, then mixing it with 35 mL of sodium hydroxide solution and stirring with a magnetic stirrer for 30 min; (3) transferring the mixed solution to a 50 mL high-pressure reactor, placing it in an oven and heating it at 180 °C for 24 hours; (4) after the reaction is complete, washing the powder obtained with deionized water until neutral, then rinsing it multiple times with anhydrous ethanol, and then drying it in an oven at 60 °C for 24 hours to obtain cerium dioxide nanoparticles before surface modification. The morphology of the cerium dioxide nanoparticles is as follows. Figure 1 As shown in a, its particle size is between 25-40 nm.

[0024] Example 2 The difference between Example 2 and Example 1 is that the hydrothermal reaction temperature used was 100 degrees Celsius, the reaction time was 24 hours, and the resulting cerium dioxide nanoparticles were shaped as follows: Figure 1 As shown in b, the morphology of the cerium dioxide nanoparticles at this time is that of nanorods, with a length of approximately 100 nm and a width of 10 nm.

[0025] The only difference between Examples 1 and 2 is the morphology of the cerium dioxide nanoparticles obtained, but both are nanoparticles with very small particle size and large specific surface area, which are suitable for further surface modification.

[0026] Example 3 A method for preparing a cerium dioxide catalyst suitable for ultra-high temperature water-gas conversion reaction includes the following steps: (1) preparing a sodium hydroxide solution with a concentration of 6 mol / L; (2) dissolving 0.864 g of Ce(NO3)3·6H2O in 5 mL of deionized water, then mixing it with 35 mL of sodium hydroxide solution and stirring it in a magnetic stirrer for 30 min; (3) transferring the mixed solution to a 50 mL high-pressure reactor, placing it in an oven and heating it at 180 °C for 24 hours; (4) washing the powder obtained after the reaction with deionized water until neutral, then rinsing it multiple times with anhydrous ethanol, and then drying it in an oven at 60 °C for 24 hours to obtain cerium dioxide nanoparticles before surface modification; (5) calcining the cerium dioxide powder in air at 600 °C for 24 hours at a heating rate of 10 °C / min; (6) heat-treating the above powder in a tube furnace with CO gas at 900 °C for 1 hour to obtain a cerium dioxide catalyst suitable for ultra-high temperature water-gas conversion reaction. The surface structure of cerium dioxide catalysts is as follows: Figure 2 As shown in a, after the treatment in step (6), the cerium dioxide nanoparticles are transformed from cubic to spherical particles, indicating that the surface of cerium dioxide is exposed with coordination unsaturated sites mainly composed of single-layer steps. These sites are ordered sites and are highly active sites for high-temperature catalytic water-gas conversion reactions above 600℃.

[0027] Example 4 The difference between Example 4 and Example 3 is that the reducing gas in step (6) is hydrogen, and the resulting cerium dioxide surface structure is as follows. Figure 2 As shown in b, the cerium dioxide nanoparticles are spherical, indicating that a large number of monolayer steps are exposed. These steps are ordered coordination unsaturated sites, which are highly active sites for high-temperature catalytic water-gas conversion reactions above 600℃.

[0028] Example 5 The difference between Example 5 and Example 3 is that the reducing gas in step (6) is a mixture of CO and hydrogen, and the resulting cerium dioxide surface structure is as follows. Figure 2As shown in c, the cerium dioxide nanoparticles are spherical, indicating that a large number of monolayer steps are exposed. These steps are ordered coordination unsaturated sites, which are highly active sites for high-temperature catalytic water-gas conversion reactions above 600℃.

[0029] The catalysts prepared in Examples 1 and 3 were subjected to high-temperature catalytic water-gas conversion reaction performance tests, specifically including the following steps: (1) 36 mg of the prepared catalyst was weighed and placed in a fixed-bed quartz reaction tube; (2) the reactor inlet contained 5 vol% CO, 20 vol% H2O, and the remainder was Ar, the total gas flow rate was 100 mL / min, and the test reaction temperature was 400℃-800℃. The performance of the catalysts prepared in Examples 1 and 3 in catalytic water-gas conversion reaction was as follows: Figure 3 As shown in the figure, the surface-modified cerium dioxide catalyst achieves an H2 yield of nearly 90% in the water-gas conversion reaction at 800℃. Therefore, the surface-modified cerium dioxide catalyst prepared in this invention possesses excellent performance in catalyzing water-gas conversion reactions at temperatures above 600℃, and can be used industrially for hydrogen production in the ultra-high temperature range.

[0030] Comparative Example The difference between this comparative example and Example 3 is that the temperature of the reducing gas heat treatment in step (6) is different.

[0031] Step (6) specifically involves passing CO gas through the powder in a tube furnace and heat-treating it at 600°C (lower than the 800-1100°C required by this invention) for 1 hour. The resulting electron micrograph of the comparative catalyst is shown below. Figure 4 As shown, the surface of cerium dioxide is still very smooth at this time, indicating that a single-layer step structure has not been formed.

[0032] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a cerium dioxide catalyst suitable for ultra-high temperature water-gas conversion reaction, characterized in that, Includes the following steps: (1) The cerium dioxide nanoparticles were washed with deionized water until the pH value became neutral, then rinsed with anhydrous ethanol several times, and then dried. (2) The dried cerium dioxide solid powder was calcined in air to obtain cerium dioxide nanoparticles with fewer volume defects and better crystallinity. (3) By heat-treating cerium dioxide nanocube powder with reducing gas, a cerium dioxide catalyst with excellent catalytic performance in water-gas conversion reaction at ultra-high temperatures above 600℃ can be obtained.

2. The method for preparing a cerium dioxide catalyst suitable for ultra-high temperature water-gas conversion reaction according to claim 1, characterized in that, The calcination temperature in step (2) is 400-600℃, the heating rate is 5-10℃ / min, and the calcination time is 12-24 hours.

3. The method for preparing a cerium dioxide catalyst suitable for ultra-high temperature water-gas conversion reaction according to claim 1, characterized in that, In step (3), the reducing gas is one of CO, H2, methane, or a mixture thereof.

4. The method for preparing a cerium dioxide catalyst suitable for ultra-high temperature water-gas conversion reaction according to claim 1, characterized in that, In step (3), the heat treatment temperature is 800-1100℃, the heating rate is 5-10℃ / min, and the heat treatment time is 1-3 hours.

5. The method for preparing a cerium dioxide catalyst suitable for ultra-high temperature water-gas conversion reaction according to claim 1, characterized in that, The preparation method of the cerium dioxide nanoparticles specifically includes the following steps: First, prepare a sodium hydroxide solution with a concentration of 6-9 mol / L for later use; Then, dissolve 0.002-0.004 mol of cerium salt in 5-10 mL of deionized water, then mix with 35-70 mL of sodium hydroxide solution and stir continuously for 30-60 minutes; Finally, the resulting mixed solution was transferred to a high-pressure reactor and placed in an oven to heat for 24 hours for hydrothermal reaction.

6. The method for preparing a cerium dioxide catalyst suitable for ultra-high temperature water-gas conversion reaction according to claim 5, characterized in that, The cerium salt is at least one of cerium nitrate, cerium chloride, and cerium sulfate.

7. The method for preparing a cerium dioxide catalyst suitable for ultra-high temperature water-gas conversion reaction according to claim 5, characterized in that, The hydrothermal reaction temperature is between 100-250℃.

8. A cerium dioxide catalyst suitable for ultra-high temperature water-gas conversion reaction, characterized in that, It is prepared by the method described in any one of claims 1-6.

9. A cerium dioxide catalyst suitable for ultra-high temperature water-gas conversion reaction, characterized in that, It serves as a catalyst for hydrogen production via ultra-high temperature catalytic water-gas conversion reaction at temperatures above 600℃.

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