Sr-doped Co / CeO2 catalyst prepared based on sol-gel method and preparation method of Sr-doped Co / CeO2 catalyst

Abstract

The invention provides a Sr-doped Co / CeO2 catalyst prepared on the basis of a sol-gel method and a preparation method of the Sr-doped Co / CeO2 catalyst. The preparation method comprises the following steps: mixing cobalt salt, cerium salt and strontium salt to prepare a mixed solution, adding a metal complexing agent, dehydrating and drying to prepare xerogel, and roasting to prepare the Sr-doped Co / CeO2 catalyst. The catalyst can reach 95% of ammonia decomposition conversion rate under the conditions that the pure NH3 mass space velocity (GHSV) is 30000 ml / (gcat) and the temperature is 550 DEG C, the catalyst can keep long-term stability for at least 100 hours or more, and it is verified that under the sol-gel method preparation process condition, the ammonia decomposition conversion rate can be obviously increased by selecting alkaline earth metal Sr doping in a specific proportion, and the catalyst can be used for preparing the ammonia decomposition catalyst. Meanwhile, the relatively simple synthesis method is suitable for industrial large-scale production.

Description

Sr-doped Co / CeO2 catalyst prepared by sol-gel method and its preparation method Technical Field

[0001] This invention belongs to the field of ammonia decomposition hydrogen production catalyst technology, and relates to a Sr-doped Co / CeO2 catalyst prepared by the sol-gel method and its preparation method. Background Technology

[0002] Hydrogen energy, as a clean and efficient secondary energy carrier, is key to promoting energy structure transformation and achieving carbon neutrality. However, the safe and efficient storage and transportation of hydrogen remain bottlenecks for its large-scale application. Ammonia (NH3), due to its high hydrogen density (17.6 wt%), ease of liquefaction, mature storage and transportation infrastructure, and carbon-free properties, is considered a highly promising liquid hydrogen storage medium. On-site, on-demand hydrogen production via ammonia decomposition (2NH3 → N2 + 3H2) is one of the effective technological routes to solve the hydrogen storage and transportation challenges. The core of this technology lies in developing low-cost catalysts that combine high activity, high selectivity, and excellent stability.

[0003] Currently, while Ru-based noble metal catalysts exhibit excellent ammonia decomposition activity, their high cost and scarcity limit large-scale industrial applications. Therefore, research has focused on developing non-noble metal catalysts, among which cobalt (Co)-based catalysts have attracted considerable attention due to their moderate nitrogen binding energy and relatively low cost.

[0004] Cerium dioxide (CeO2) is often used as a catalyst support due to its excellent redox properties and oxygen storage / release capabilities, allowing for the modulation of the electronic state of active centers through metal-support interactions. However, single Co / CeO2 catalysts still suffer from insufficient activity and the tendency of cobalt nanoparticles to sinter and deactivate at high temperatures. Studies have shown that modulating the electronic structure of CeO2 supports through heterovalent element doping is an effective strategy for improving catalyst performance. Among these strategies, alkaline earth metal doping (such as Sr) is particularly effective. 2+ It has been shown that it can induce a large number of oxygen vacancies in CeO2 lattice, regulate its surface acidity and basicity and change its electronic structure, thereby enhancing metal-support interaction, stabilizing active centers and optimizing the adsorption behavior of reaction intermediates.

[0005] In its prior patent application "A Catalyst and a Method for Preparing the Same" (CN108686669A), the applicant of this invention disclosed a metal composite oxide catalyst for catalytic combustion treatment of xylene waste gas. This catalyst contains cobalt and cerium as active elements and strontium as a co-catalytic element; wherein cobalt, cerium, and strontium are all present in oxide form and are composited together. This catalyst is prepared based on a co-precipitation method.

[0006] In the aforementioned disclosed patented technology, the inventors' research group improved the catalytic combustion thermal stability of the Co / CeO2 catalyst by doping it with the alkaline earth metal strontium. Their results showed that when doped with 7 wt% strontium, compared to other doping ratios, the catalyst exhibited the ability to achieve 100% conversion of xylene at a lower temperature (325 °C). However, whether strontium doping is beneficial for improving the ammonia decomposition conversion rate of the catalyst under relatively low temperature conditions remains unknown.

[0007] In another prior patent application by the applicant of this invention, entitled "A Low-Temperature High-Efficiency Co-Based Catalyst for Ammonia Decomposition to Hydrogen and Its Preparation Method," a Co-based catalyst prepared by calcination using a hexagonal nanosheet metal-organic framework with Prussian blue analogue Ce and Co equally coordinated as a precursor is disclosed. This catalyst can be prepared at a pure NH3 mass hourly space velocity (GHSV) of 30000 ml / (g⁻¹). cat •h) and achieves a 90% ammonia decomposition conversion rate under relatively low temperature conditions, and the catalyst can maintain long-term stability for at least 100 hours.

[0008] Although the above-mentioned patented technology has produced a catalyst with a high ammonia decomposition conversion rate under relatively low temperature conditions, the preparation process of the hexagonal nanosheet metal-organic framework with Prussian blue analogues Ce and Co in equal coordination is still relatively complex and requires control of the reaction rate, resulting in high costs for its industrial production.

[0009] Therefore, if a low-cost catalyst that matches current conventional industrial conditions and can further improve the ammonia decomposition conversion rate under relatively low temperature conditions is available, it would be highly beneficial for the further promotion and application of hydrogen energy. Summary of the Invention

[0010] To address the problems in the prior art, this invention provides a Sr-doped Co / CeO2 catalyst prepared by the sol-gel method and its preparation method. This catalyst can be used when the mass hourly space velocity (GHSV) of pure NH3 is 30,000 ml / (g· ... cat •h) and achieves an ammonia decomposition conversion rate of 95% at 550 °C, and the catalyst can maintain long-term stability for at least 100 hours. It also verifies that under the preparation process based on sol-gel method, the ammonia decomposition conversion rate can be significantly improved by selecting a specific proportion of alkaline earth metal Sr doping. At the same time, its relatively simple synthesis method is suitable for large-scale industrial production.

[0011] To achieve the above objectives, the present invention employs a technical solution consisting of the following technical measures.

[0012] In one aspect, the present invention provides a method for preparing a Sr-doped Co / CeO2 catalyst, which mainly includes the following steps:

[0013] (1) Cobalt salt, cerium salt and strontium salt are mixed and dissolved in deionized water to obtain a mixed solution. Anhydrous citric acid and ethylene glycol as metal complexing agents are added based on the sol-gel method and mixed evenly. The mixture is then dehydrated and dried at a temperature of 90~100 °C for at least 16 h to prepare a dry gel.

[0014] The molar ratio of cerium, strontium, and cobalt in the mixed solution is (8~9):(1~2):40;

[0015] (2) The Sr-doped Co / CeO2 catalyst was prepared by calcining the dry gel obtained in step (1).

[0016] In this paper, the cerium salt mentioned in step (1) is a conventionally used metal salt raw material for preparing cerium ion solutions. Those skilled in the art can make specific selections based on conventional metal salts known in the prior art that can be added as metal ion solutions and in combination with actual needs, including but not limited to cerium nitrate, cerium chloride, etc. To simplify experimental operations and facilitate the design of control experiments, the cerium salt selected in the following specific embodiments is uniformly cerium nitrate. Those skilled in the art should clearly understand that the cerium salt mentioned in step (1) mainly provides cerium ions, and the selection of specific anions in the cerium salt usually does not affect the technical effect obtained by the present invention. However, it should still be noted that the selected cerium salt should be soluble in deionized water to form a cerium ion solution. Similarly, for cobalt and strontium salts, to simplify experimental operations and facilitate the design of control experiments, the cobalt and strontium salts selected in the following specific embodiments are uniformly cobalt nitrate and strontium nitrate.

[0017] Typically, in step (1), the cobalt salt, cerium salt, and strontium salt are mixed and dissolved in deionized water to obtain a mixed solution. The solute concentration can be referenced from the appropriate concentration recorded in the conventional sol-gel method, provided that complete dissolution is ensured. For example, the molar concentration of cobalt salt is 0.5~1.2 mmol / mL.

[0018] In this paper, step (1) involves adding anhydrous citric acid and ethylene glycol as metal complexing agents using a sol-gel method, mixing them evenly. Theoretically, the amount of anhydrous citric acid and ethylene glycol added is determined by balancing their complexation reactions with cerium, strontium, and cobalt ions in the mixed solution. Anhydrous citric acid and ethylene glycol are conventional metal complexing agents in the sol-gel method, and those skilled in the art can directly refer to relevant textbooks and existing technical literature to determine their addition amounts. In one technical solution, to ensure the full occurrence of the complexation reaction, it is preferable to add an excess of anhydrous citric acid and ethylene glycol. For example, when the molar amount of cobalt is 40 mmol, 17.29~21.13 g of anhydrous citric acid and 5.03~6.15 mL of ethylene glycol are added.

[0019] In this article, the dehydration and drying at a temperature of 90~100 ℃ for at least 16 h described in step (1) to form a dry gel is a routine procedure in the sol-gel method. Those skilled in the art can choose a suitable dehydration and drying method based on common knowledge or conventional processes, such as water bath heating or oven drying.

[0020] In this paper, step (2) describes the preparation of Sr-doped Co / CeO2 catalyst by calcining the dry gel obtained in step (1). Calcination is the process of converting the metal components in the dry gel into oxides. Specifically, it follows the conventional calcination method / calcination parameters in chemical engineering. Those skilled in the art can directly refer to the conventional method of calcination to prepare cerium dioxide.

[0021] To better illustrate the present invention and provide a technical solution for reference, step (2) describes preparing a Sr-doped Co / CeO2 catalyst by calcining the dry gel obtained in step (1). The specific calcination process parameters are as follows: heating to 250-350 ℃ at a heating rate of 4.5-5.5 ℃ / min, holding for 2.5-3.5 h, then heating to 550-650 ℃ at a heating rate of 4.5-5.5 ℃ / min, holding for 4.5-5.5 h, and finally cooling naturally to room temperature.

[0022] Typically, in step (2), the dry gel obtained in step (1) is calcined to prepare the Sr-doped Co / CeO2 catalyst. Before and after calcination, grinding can also be selected. Grinding is a conventional process for processing the dry gel and calcination product into powder, following the conventional principles in chemical processes. Those skilled in the art can perform specific operations based on common knowledge.

[0023] It should be noted that although the inventor's research group has disclosed in its prior research (CN108686669A) that doping strontium in the catalyst is beneficial to the combustion thermal stability of xylene waste gas, based on common knowledge in the field, whether the doping of alkaline earth metal elements can bring effective gains depends mainly on the selection and combination of specific active substances, supports, and other factors in the catalyst. Different selections of alkaline earth metal elements, active substances, and supports will produce unpredictable technical effects. At present, there is no unified guiding theory for those skilled in the art to refer to and select.

[0024] In the early exploratory experiments related to this invention, the inventors first discovered through comparative experiments that not all alkaline earth metal elements have obvious enhancement effects on the Co / CeO2 catalyst system prepared based on the sol-gel method. In the experiment, Sr, La, Ba, Y, Sm and Ca were tried respectively, but the final results showed that only Sr had a significant effect on enhancing the ammonia decomposition conversion rate of the catalyst.

[0025] Secondly, a comparative experiment was conducted on the Sr doping amount. The results showed that when the ratio of Sr to Ce was greater than (1~2):(8~9), the catalyst showed a decrease in ammonia decomposition conversion rate, proving that the effective gain of Sr doping requires a specific element ratio to be met in the Co / CeO2 catalyst system.

[0026] Finally, for the Sr-doped Co / CeO2 catalyst system prepared by the sol-gel method, a variable comparison experiment was conducted on the active component Co element. It was found that only when the cobalt element met a specific ratio did the catalyst show a significant enhancement in ammonia decomposition conversion rate, while catalysts with other element ratios showed ammonia decomposition conversion rate that was the same as or significantly worse than that of the undoped Sr catalyst.

[0027] The comparative experiments described above confirm that Sr doping can only achieve effective gains in the Co / CeO2 catalyst system under specific element ratio conditions.

[0028] Furthermore, it was unexpectedly discovered that the Sr-doped Co / CeO2 catalyst prepared by the sol-gel method used in this invention exhibits a significantly higher ammonia decomposition conversion rate than catalysts with the same elemental ratio prepared by the conventional co-precipitation method. The conventional impregnation method, due to its excessively high Co content, cannot produce catalysts with a consistent elemental ratio. Since the aforementioned conventional preparation methods all involve converting the metal components into oxides at high temperatures, theoretically, the performance differences should conform to general understanding under conditions of consistent elemental ratios. However, experimental results confirm that the Sr-doped Co / CeO2 catalyst prepared based on the sol-gel method has a significantly better ammonia decomposition conversion rate, which exceeded our expectations.

[0029] In this document, the dissolution, mixing, dehydration and drying processes all follow conventional principles in chemical processes, and those skilled in the art can perform the specific operations based on common knowledge.

[0030] The present invention has the following beneficial effects:

[0031] 1. This invention provides a Sr-doped Co / CeO2 catalyst prepared by the sol-gel method and its preparation method. In one preferred embodiment, the prepared Sr-doped Co / CeO2 catalyst has a pure NH3 mass hourly space velocity (GHSV) of 30000 ml / (g· ... cat Under the conditions of (•h), the ammonia decomposition conversion rate can reach 95% at a temperature of 550℃; tests showed that its long-term stability is as high as 100 hours, indicating that the catalyst has a very beneficial long-term effect.

[0032] 2. This invention confirms that for a Co / CeO2 catalyst system at a specific ratio, quantitative doping with a specific alkaline earth metal element strontium can significantly improve the ammonia decomposition conversion rate of the prepared catalyst. In addition, it was unexpectedly discovered that the catalyst system prepared by the sol-gel method has significantly better catalytic performance than other conventional preparation methods.

[0033] 3. The preparation method of this invention is simple, and the resulting catalyst has excellent ammonia decomposition conversion rate under relatively low temperature conditions, which can effectively reduce costs. Attached Figure Description

[0034] Figure 1 is a comparison of the ammonia decomposition conversion rates of the catalyst samples prepared in Example 1 and Comparative Examples 1-6 of the present invention under various temperature conditions.

[0035] Figure 2 is a comparison of the ammonia decomposition conversion rate (a) and hydrogen production rate (b) of the catalyst samples prepared in Examples 1-2, Comparative Examples 1, and Comparative Examples 7-9 of the present invention.

[0036] Figure 3 is a comparison of the ammonia decomposition conversion rate (a) and hydrogen production rate (b) of the catalyst samples prepared in Example 1, Comparative Example 1, and Comparative Examples 9-12 of this invention.

[0037] Figure 4 is a comparison of the ammonia decomposition conversion rate (a) and hydrogen production rate (b) of the catalyst samples prepared in Example 1 and Comparative Example 1 of the present invention under various temperature conditions.

[0038] Figure 5 shows the changes in the long-term activity and stability of the catalyst sample prepared in Example 1 of the invention under a temperature of 550 °C.

[0039] Figure 6 shows the changes in ammonia decomposition conversion rate of the catalyst sample prepared in Example 1 of the present invention under pure ammonia and different GHSV conditions.

[0040] Figure 7 is a comparison of XRD (a) and ammonia decomposition conversion rate (b) of the catalyst samples prepared in Example 1 and Comparative Example 13 of the present invention. Detailed Implementation

[0041] To further understand the present invention, preferred embodiments are described below with reference to examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims. Those skilled in the art can refer to the content of this document to appropriately improve the process parameters. In particular, it should be noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included within the scope of the present invention. The methods and applications of the present invention have been described through preferred embodiments, and those skilled in the art can obviously make modifications or appropriate changes and combinations to the methods and applications described herein without departing from the content, spirit and scope of the present invention to realize and apply the technology of the present invention. Although it is believed that those skilled in the art will fully understand the following terms, the following definitions are set forth to help illustrate the subject matter disclosed in the present invention.

[0042] In one aspect, the present invention provides a method for preparing a Sr-doped Co / CeO2 catalyst, which mainly includes the following steps:

[0043] (1) Cobalt salt, cerium salt and strontium salt are mixed and dissolved in deionized water to obtain a mixed solution. Anhydrous citric acid and ethylene glycol as metal complexing agents are added based on the sol-gel method and mixed evenly. The mixture is then dehydrated and dried at a temperature of 90~100 °C for at least 16 h to prepare a dry gel.

[0044] The molar ratio of cerium, strontium, and cobalt in the mixed solution is (8~9):(1~2):40;

[0045] (2) The Sr-doped Co / CeO2 catalyst was prepared by calcining the dry gel obtained in step (1).

[0046] In this paper, the cerium salt mentioned in step (1) is a conventionally used metal salt raw material for preparing cerium ion solutions. Those skilled in the art can make specific selections based on conventional metal salts known in the prior art that can be added as metal ion solutions and in combination with actual needs. In one embodiment, the cerium salt includes, but is not limited to, cerium nitrate, cerium chloride, etc. To simplify experimental operations and facilitate the design of control experiments, the cerium salt selected in the following specific embodiments is uniformly cerium nitrate. Those skilled in the art should clearly understand that the cerium salt mentioned in step (1) mainly provides cerium ions, and the selection of specific anions in the cerium salt usually does not affect the technical effect obtained by the present invention. However, it should still be noted that the selected cerium salt should be soluble in deionized water to form a cerium ion solution. Similarly, for cobalt and strontium salts, to simplify experimental operations and facilitate the design of control experiments, the cobalt and strontium salts selected in the following specific embodiments are uniformly cobalt nitrate and strontium nitrate.

[0047] Typically, in step (1), the cobalt salt, cerium salt, and strontium salt are mixed and dissolved in deionized water to obtain a mixed solution. The solute concentration, provided that complete dissolution is ensured, can refer to the appropriate concentration recorded in conventional sol-gel methods. In one embodiment, the molar concentration of the cobalt salt is 0.5 to 1.2 mmol / mL, for example, 0.5 mmol / mL, 0.6 mmol / mL, 0.7 mmol / mL, 0.8 mmol / mL, 0.9 mmol / mL, 1 mmol / mL, 1.1 mmol / mL, 1.2 mmol / mL, or any range or point value between them.

[0048] In this paper, the anhydrous citric acid and ethylene glycol, which are added as metal complexing agents in step (1), are mixed evenly based on the sol-gel method. Theoretically, the amount of anhydrous citric acid and ethylene glycol added is based on their complexation reaction with cerium ions, strontium ions, and cobalt ions in the mixed solution to balance the ratio. Anhydrous citric acid and ethylene glycol are conventional metal complexing agents in the sol-gel method, and those skilled in the art can directly refer to relevant textbooks and existing technical literature to know their addition amount. In one embodiment, to ensure the full occurrence of the complexation reaction, an excess of anhydrous citric acid and ethylene glycol is preferably added. When the molar amount of cobalt is 40 mmol, 17.29~21.13 g of anhydrous citric acid is added, for example, 17.29 g, 18 g, 19 g, 20 g, 21 g, 21.13 g or any range or point value between them; and 5.03~6.15 mL of ethylene glycol is added, for example, 5.03 mL, 5.1 mL, 5.2 mL, 5.3 mL, 5.4 mL, 5.5 mL, 5.6 mL, 5.7 mL, 5.8 mL, 5.9 mL, 6 mL, 6.1 mL, 6.15 mL or any range or point value between them.

[0049] In this paper, the dehydration and drying at a temperature of 90~100 °C for at least 16 h described in step (1) to form a dry gel is a routine procedure in the sol-gel method. Those skilled in the art can choose a suitable dehydration and drying method based on common knowledge or conventional processes, such as water bath heating or oven drying. It should be noted that extending the dehydration and drying time to ensure sufficient dehydration and formation of a dry gel usually does not have a significant impact on the catalyst prepared by calcination.

[0050] In this paper, step (2) describes the preparation of Sr-doped Co / CeO2 catalyst by calcining the dry gel obtained in step (1). Calcination is the process of converting the metal components in the dry gel into oxides. Specifically, it follows the conventional calcination method / calcination parameters in chemical engineering. Those skilled in the art can directly refer to the conventional method of calcination to prepare cerium dioxide.

[0051] To better illustrate the present invention and provide a reference embodiment, step (2) describes preparing a Sr-doped Co / CeO2 catalyst by calcining the dry gel obtained in step (1). The specific calcination process parameters are as follows: heating to 250-350 ℃ at a heating rate of 4.5-5.5 ℃ / min, holding at that temperature for 2.5-3.5 h, then heating to 550-650 ℃ at a heating rate of 4.5-5.5 ℃ / min, holding at that temperature for 4.5-5.5 h, and finally cooling naturally to room temperature.

[0052] Typically, in step (2), the dry gel obtained in step (1) is calcined to prepare the Sr-doped Co / CeO2 catalyst. Before and after calcination, grinding can also be selected. Grinding is a conventional process for processing the dry gel and calcination product into powder, following the conventional principles in chemical processes. Those skilled in the art can perform specific operations based on common knowledge.

[0053] It should be noted that although the inventor's research group has disclosed in its prior research (CN108686669A) that doping strontium in the catalyst is beneficial to the combustion thermal stability of xylene waste gas, based on common knowledge in the field, whether the doping of alkaline earth metal elements can bring effective gains depends mainly on the selection and combination of specific active substances, supports, and other factors in the catalyst. Different selections of alkaline earth metal elements, active substances, and supports will produce unpredictable technical effects. At present, there is no unified guiding theory for those skilled in the art to refer to and select.

[0054] In the early exploratory experiments related to this invention, the inventors first discovered through comparative experiments that not all alkaline earth metal elements have obvious enhancement effects on the Co / CeO2 catalyst system prepared based on the sol-gel method. In the experiment, Sr, La, Ba, Y, Sm and Ca were tried respectively, but the final results showed that only Sr had a significant effect on enhancing the ammonia decomposition conversion rate of the catalyst.

[0055] Secondly, a comparative experiment was conducted on the Sr doping amount. The results showed that when the ratio of Sr to Ce was greater than (1~2):(8~9), the catalyst showed a decrease in ammonia decomposition conversion rate, proving that the effective gain of Sr doping requires a specific element ratio to be met in the Co / CeO2 catalyst system.

[0056] Finally, for the Sr-doped Co / CeO2 catalyst system prepared by the sol-gel method, a variable comparison experiment was conducted on the active component Co element. It was found that only when the cobalt element met a specific ratio did the catalyst show a significant enhancement in ammonia decomposition conversion rate, while catalysts with other element ratios showed ammonia decomposition conversion rate that was the same as or significantly worse than that of the undoped Sr catalyst.

[0057] The comparative experiments described above confirm that Sr doping can only achieve effective gains in the Co / CeO2 catalyst system under specific element ratio conditions.

[0058] Furthermore, it was unexpectedly discovered that the Sr-doped Co / CeO2 catalyst prepared by the sol-gel method used in this invention exhibits a significantly higher ammonia decomposition conversion rate than catalysts with the same elemental ratio prepared by the conventional co-precipitation method. The conventional impregnation method, due to its excessively high Co content, cannot produce catalysts with a consistent elemental ratio. Since the aforementioned conventional preparation methods all involve converting the metal components into oxides at high temperatures, theoretically, the performance differences should conform to general understanding under conditions of consistent elemental ratios. However, experimental results confirm that the Sr-doped Co / CeO2 catalyst prepared based on the sol-gel method has a significantly better ammonia decomposition conversion rate, which exceeded our expectations.

[0059] In this document, the dissolution, mixing, dehydration and drying processes all follow conventional principles in chemical processes, and those skilled in the art can perform the specific operations based on common knowledge.

[0060] The present application will be further explained in detail below with reference to embodiments. However, those skilled in the art should understand that these embodiments are provided for illustrative purposes only and are not intended to limit the present application.

[0061] Example

[0062] The embodiments of this application will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be construed as limiting the scope of this application. Where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Where the manufacturers of reagents or instruments are not specified, they are all commercially available conventional products. This application should not be construed as being limited to the specific embodiments described.

[0063] 1. Raw materials

[0064]

[0065] 2. Testing Methods

[0066] The test method was as follows: 0.1 g of catalyst sample (20-40 mesh) was placed in a stainless steel reactor with an inner diameter of 8 mm. The temperature was increased to 400 °C at a rate of 8 °C / min under an Ar atmosphere, and the gas was replaced with 20% H2 / Ar (30 ml / min) for 1 h of reduction. Subsequently, the gas was replaced with Ar, and the temperature was lowered to 350 °C for purging for 30 min. Then, pure NH3 (50 ml / min) was introduced into the reactor, and the reactor was heated to the required temperature. The product was analyzed using a gas chromatograph (GC9790Ⅱ), with a detection temperature range of 350-600 °C, and an activity test point was taken every 50 °C.

[0067] ammonia decomposition conversion rate calculate:

[0068] ,

[0069] This represents the peak area of ​​ammonia gas before the reaction.

[0070] This indicates the peak area of ​​ammonia gas after the reaction.

[0071] H2 production rate calculate:

[0072]

[0073] This indicates the NH3 flow rate, measured in ml / min.

[0074] This indicates the mass of the catalyst.

[0075] Example 1

[0076] This embodiment describes a method for preparing a Sr-doped Co / CeO2 catalyst, which mainly includes the following steps:

[0077] (1) Co(NO3)3•6H2O (40 mmol), Sr(NO3)2•6H2O (2 mmol) and Ce(NO3)3•6H2O (8 mmol) were dissolved in 50 mL of deionized water, and then 19.21 g of anhydrous citric acid and 5.59 mL of ethylene glycol were added. After the mixture was homogeneous, it was dehydrated and dried at 100 °C for 18 h to prepare a dry gel.

[0078] (2) The dry gel obtained in step (1) was first calcined at 300 °C for 3 hours and then calcined at 600 °C for 5 hours to prepare Sr-doped Co / CeO2 catalyst as a sample, which was named Co@Sr-CeO2, Co / Sr2-CeO2, and 40Co / Sr-CeO2.

[0079] Example 2

[0080] This embodiment describes a method for preparing a Sr-doped Co / CeO2 catalyst, which mainly includes the following steps:

[0081] (1) Co(NO3)3•6H2O (40 mmol), Sr(NO3)2•6H2O (1 mmol) and Ce(NO3)3•6H2O (9 mmol) were dissolved in 50 mL of deionized water, and then 19.21 g of anhydrous citric acid and 5.59 mL of ethylene glycol were added. After the mixture was homogeneous, it was dehydrated and dried at 100 °C for 18 h to prepare a dry gel.

[0082] (2) The dry gel obtained in step (1) was first calcined at 300 °C for 3 hours and then calcined at 600 °C for 5 hours to prepare the Sr-doped Co / CeO2 catalyst as a sample, denoted as Co / Sr1-CeO2.

[0083] Comparative Example 1

[0084] Comparative Example 1 is a method for preparing a Co / CeO2 catalyst without Sr doping, which mainly includes the following steps:

[0085] (1) Co(NO3)3•6H2O (40 mmol) and Ce(NO3)3•6H2O (10 mmol) were dissolved in 50 mL of deionized water, and then 19.21 g of anhydrous citric acid and 5.59 mL of ethylene glycol were added. After the mixture was homogeneous, it was dehydrated and dried at 100 °C for 18 h to prepare a dry gel.

[0086] (2) The dry gel obtained in step (1) was first calcined at 300 °C for 3 hours and then calcined at 600 °C for 5 hours to prepare Co / CeO2 catalyst as a sample, denoted as Co@CeO2 and Co / CeO2.

[0087] Comparative Example 2

[0088] Comparative Example 2 is a La-doped Co / CeO2 catalyst preparation method, which mainly includes the following steps:

[0089] (1) Co(NO3)3•6H2O (40 mmol), La(NO3)3•6H2O (2 mmol) and Ce(NO3)3•6H2O (8 mmol) were dissolved in 50 mL of deionized water, and then 19.21 g of anhydrous citric acid and 5.59 mL of ethylene glycol were added. After the mixture was homogeneous, it was dehydrated and dried at 100 °C for 18 h to prepare a dry gel.

[0090] (2) The dry gel obtained in step (1) was first calcined at 300 °C for 3 hours and then calcined at 600 °C for 5 hours to prepare a La-doped Co / CeO2 catalyst as a sample, denoted as Co@La-CeO2.

[0091] Comparative Example 3 is a Ba-doped catalyst prepared in the same way as Comparative Example 2, except that La(NO3)3•6H2O (2 mmol) was replaced with Ba(NO3)2•6H2O (2 mmol). The resulting Ba-doped Co / CeO2 catalyst was denoted as Co@Ba-CeO2.

[0092] Comparative Example 4 is a Y-doped catalyst prepared in the same way as Comparative Example 2, except that La(NO3)3•6H2O (2 mmol) is replaced with Y(NO3)3•6H2O (2 mmol). The resulting Y-doped Co / CeO2 catalyst is denoted as Co@Y-CeO2.

[0093] Comparative Example 5 is a Sm-doped catalyst, prepared in the same way as Comparative Example 2, except that La(NO3)3•6H2O (2 mmol) is replaced with Sm(NO3)3•6H2O (2 mmol). The Sm-doped Co / CeO2 catalyst was prepared as a sample and denoted as Co@Sm-CeO2.

[0094] Comparative Example 6 is a Ca-doped catalyst, prepared in the same way as Comparative Example 2, except that La(NO3)3•6H2O (2 mmol) was replaced with Ca(NO3)2•6H2O (2 mmol). The Ca-doped Co / CeO2 catalyst was prepared as a sample and denoted as Co@Ca-CeO2.

[0095] Comparative Example 7

[0096] Comparative Example 7, with a different formulation than the examples, describes a method for preparing a Sr-doped Co / CeO2 catalyst, which mainly includes the following steps:

[0097] (1) Co(NO3)3•6H2O (40 mmol), Sr(NO3)2•6H2O (3 mmol) and Ce(NO3)3•6H2O (7 mmol) were dissolved in 50 mL of deionized water, and then 19.21 g of anhydrous citric acid and 5.59 mL of ethylene glycol were added. After the mixture was homogeneous, it was dehydrated and dried at 100 °C for 18 h to prepare a dry gel.

[0098] (2) The dry gel obtained in step (1) was first calcined at 300 °C for 3 hours and then calcined at 600 °C for 5 hours to prepare the Sr-doped Co / CeO2 catalyst as a sample, denoted as Co / Sr3-CeO2.

[0099] Comparative Example 8

[0100] Comparative Example 8 uses a different formulation than in the examples. A method for preparing a Sr-doped Co / CeO2 catalyst mainly includes the following steps:

[0101] (1) Co(NO3)3•6H2O (40 mmol), Sr(NO3)2•6H2O (5 mmol) and Ce(NO3)3•6H2O (5 mmol) were dissolved in 50 mL of deionized water, and then 19.21 g of anhydrous citric acid and 5.59 mL of ethylene glycol were added. After the mixture was homogeneous, it was dehydrated and dried at 100 °C for 18 h to prepare a dry gel.

[0102] (2) The dry gel obtained in step (1) was first calcined at 300 °C for 3 hours and then calcined at 600 °C for 5 hours to prepare the Sr-doped Co / CeO2 catalyst as a sample, which was denoted as Co / Sr5-CeO2.

[0103] Comparative Example 9

[0104] Comparative Example 9 describes a method for preparing a Sr-doped Co-based catalyst without the addition of Ce, which mainly includes the following steps:

[0105] (1) Co(NO3)3•6H2O (40 mmol) and Sr(NO3)2•6H2O (10 mmol) were dissolved in 50 mL of deionized water, and then 19.21 g of anhydrous citric acid and 5.59 mL of ethylene glycol were added. After the mixture was homogeneous, it was dehydrated and dried at 100 °C for 18 h to prepare a dry gel.

[0106] (2) The dry gel obtained in step (1) was first calcined at 300 °C for 3 hours and then calcined at 600 °C for 5 hours to prepare a Sr-doped Co-based catalyst as a sample, denoted as Co / SrO.

[0107] Comparative Example 10

[0108] Comparative Example 10 uses a different formulation than in the examples. A method for preparing a Sr-doped Co / CeO2 catalyst mainly includes the following steps:

[0109] (1) Dissolve Co(NO3)3•6H2O (20 mmol), Sr(NO3)2•6H2O (2 mmol) and Ce(NO3)3•6H2O (8 mmol) in 50 mL of deionized water, then add 19.21 g of anhydrous citric acid and 5.59 mL of ethylene glycol. After mixing evenly, dehydrate and dry at 100 °C for 18 h to prepare a dry gel.

[0110] (2) The dry gel obtained in step (1) was first calcined at 300 °C for 3 hours and then calcined at 600 °C for 5 hours to prepare the Sr-doped Co / CeO2 catalyst as a sample, which was denoted as 20Co / Sr-CeO2.

[0111] Comparative Example 11

[0112] Comparative Example 11 uses a different ratio than in the examples. A method for preparing a Sr-doped Co / CeO2 catalyst mainly includes the following steps:

[0113] (1) Co(NO3)3•6H2O (30 mmol), Sr(NO3)2•6H2O (2 mmol) and Ce(NO3)3•6H2O (8 mmol) were dissolved in 50 mL of deionized water, and then 19.21 g of anhydrous citric acid and 5.59 mL of ethylene glycol were added. After the mixture was homogeneous, it was dehydrated and dried at 100 °C for 18 h to prepare a dry gel.

[0114] (2) The dry gel obtained in step (1) was first calcined at 300 °C for 3 hours and then calcined at 600 °C for 5 hours to prepare the Sr-doped Co / CeO2 catalyst as a sample, which was denoted as 30Co / Sr-CeO2.

[0115] Comparative Example 12

[0116] Comparative Example 12 uses a different ratio than in the examples. A method for preparing a Sr-doped Co / CeO2 catalyst mainly includes the following steps:

[0117] (1) Co(NO3)3•6H2O (50 mmol), Sr(NO3)2•6H2O (2 mmol) and Ce(NO3)3•6H2O (8 mmol) were dissolved in 50 mL of deionized water, and then 19.21 g of anhydrous citric acid and 5.59 mL of ethylene glycol were added. After the mixture was homogeneous, it was dehydrated and dried at 100 °C for 18 h to prepare a dry gel.

[0118] (2) The dry gel obtained in step (1) was first calcined at 300 °C for 3 hours and then calcined at 600 °C for 5 hours to prepare the Sr-doped Co / CeO2 catalyst as a sample, which was denoted as 50Co / Sr-CeO2.

[0119] Comparative Example 13

[0120] Comparative Example 13 describes a method for preparing an Sr-doped Co / CeO2 catalyst using a co-precipitation method under the same raw material ratio. The method mainly includes the following steps:

[0121] (1) Dissolve Co(NO3)3•6H2O (40 mmol), Sr(NO3)2•6H2O (2 mmol) and Ce(NO3)3•6H2O (8 mmol) in 50 mL of deionized water, adjust the pH to 9 with ammonia, then age at room temperature for 5 h, and then filter and wash according to routine to obtain the precursor;

[0122] (2) The precursor obtained in step (1) was first calcined at 300 °C for 3 hours and then calcined at 600 °C for 5 hours to prepare Sr-doped Co / CeO2 catalyst as a sample, denoted as Co / Sr-CeO2-DP.

[0123] As shown in Figure 1, the Co / CeO2 catalyst can be used at 500 °C with a pure NH3 mass hourly space velocity (GHSV) of 30000 ml / (g). cat •h) can achieve a NH3 decomposition conversion rate of 60%. To further improve the NH3 decomposition conversion rate, different alkaline earth metal elements (Sr, La, Ba, Y, Sm, Ca) were incorporated into the CeO2 support. Among them, alkali metal Sr showed the most significant promoting effect, and the Co@Sr-CeO2 catalyst had the best NH3 decomposition conversion rate.

[0124] Subsequently, the Sr doping concentration was optimized. As the Sr content increased, the NH3 decomposition conversion rate exhibited a volcano plot trend, reaching its peak when Sr:Ce = 1:4, as shown in Figure 2.

[0125] As shown in Figure 3, the Co loading in the catalyst was adjusted, and the results showed that the highest activity for NH3 decomposition to hydrogen production was achieved when Co:(Sr+Ce) = 4:1. This optimal ratio likely ensures a high density of Co active sites in the catalyst while maintaining effective dispersion and strong metal-support interactions. The optimized Co@Sr-CeO2 catalyst (Example 1) was tested at 30000 ml / (g) cat Under GHSV conditions of 500 °C and 550 °C, NH3 conversion rates of 76% and 95% can be achieved, respectively. As shown in Figure 4, the maximum hydrogen production rate of the Co@Sr-CeO2 catalyst at 550 °C can reach 33 mmol / g•min. This performance is superior to most Co-based catalysts reported in the literature.

[0126] The long-term stability of the Co / Sr-CeO2 catalyst for NH3 decomposition is crucial for evaluating its industrial application value. As shown in Figure 5, the catalyst exhibits stability at 550 °C and 30000 ml / (g) NH3 decomposition. cat We conducted a stability test on the catalyst at a space velocity of 100 h for up to 100 hours. The results showed that the NH3 conversion remained stable throughout the test period without significant decrease. This indicates that the Co / Sr-CeO2 catalyst possesses excellent catalytic stability.

[0127] To investigate the effect of GHSV on NH3 conversion, we evaluated the ammonia decomposition performance of the Co / Sr-CeO2 catalyst at different temperatures and under GHSV conditions. As shown in Figure 6, even at 54000 ml / (g) cat At high gas flow rates (GHSV), the NH3 conversion remains above 99% at 600 °C, attributed to the rapid reaction kinetics at this temperature. However, below 600 °C, the NH3 conversion decreases with increasing GHSV. This is because the higher gas flow rate shortens the contact time between NH3 and the catalyst, resulting in insufficient time for some reactants to complete the reaction.

[0128] A Co / Sr-CeO2-DP catalyst synthesized by precipitation method was compared with the Co / Sr-CeO2 catalyst synthesized by sol-gel method in Example 1. As shown in Figure 7, the XRD patterns of the Co / Sr-CeO2-DP catalyst exhibit stronger intensities in both CeO2 and Co3O4 related diffraction peaks, indicating better crystallinity. This is likely because the interaction between CeO2 and Co3O4 is weaker in the precipitation-synthesized sample, allowing both to form independent phases. Furthermore, the ammonia decomposition hydrogen production performance of the Co / Sr-CeO2-DP catalyst is significantly lower than that of the Co / Sr-CeO2 catalyst, possibly also due to the weaker interaction between CeO2 and Co3O4.

[0129] To better illustrate the excellent catalytic performance of the Co-based non-noble metal catalyst provided by this invention, a comparison is made with Co-based catalysts in currently published literature, as shown in Table 2 below:

[0130] Table 2. Horizontal comparison between the catalyst obtained in Example 1 and Co-based catalysts in published literature.

[0131]

[0132] The references mentioned in Table 2 are as follows:

[0133]

[0134] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing an Sr-doped Co / CeO2 catalyst, characterized in that... The main steps include: (1) Cobalt salt, cerium salt and strontium salt are mixed and dissolved in deionized water to obtain a mixed solution. Anhydrous citric acid and ethylene glycol as metal complexing agents are added based on the sol-gel method and mixed evenly. The mixture is dehydrated and dried at a temperature of 90~100 ℃ for at least 16 h to prepare a dry gel. The molar ratio of cerium, strontium and cobalt in the mixed solution is (8~9):(1~2):

40. (2) The dry gel obtained in step (1) is calcined to prepare an Sr-doped Co / CeO2 catalyst.

2. The preparation method according to claim 1, characterized in that: The cobalt salts, cerium salts, and strontium salts include their nitrates and chlorides.

3. The preparation method according to claim 1, characterized in that: The molar concentration of cobalt salt in the mixed solution is 0.5~1.2 mmol / mL.

4. The preparation method according to claim 1, characterized in that: Excessive addition of anhydrous citric acid and ethylene glycol.

5. The preparation method according to claim 1, characterized in that: In step (2), the dry gel obtained in step (1) is calcined to prepare the Sr-doped Co / CeO2 catalyst. The specific calcination process parameters are as follows: the temperature is increased to 250-350 ℃ at a heating rate of 4.5-5.5 ℃ / min, and held for 2.5-3.5 h. Then the temperature is increased to 550-650 ℃ at a heating rate of 4.5-5.5 ℃ / min, and held for 4.5-5.5 h. Finally, the temperature is allowed to cool naturally to room temperature.

6. The Sr-doped Co / CeO2 catalyst prepared by the method described in claim 1.

7. The application of the Sr-doped Co / CeO2 catalyst as described in claim 6 in the field of ammonia decomposition for hydrogen production.

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