Preparation method and application of carbon-based ammonia cracking hydrogen production catalyst

Abstract

The invention discloses a preparation method and application of a carbon-based ammonia cracking hydrogen production catalyst, and the preparation method comprises the following steps: carrying out two-stage pretreatment of acid pickling and potassium salt solution dipping activation on a nano onion carbon carrier to obtain an activated carrier K-CNO '; and carrying out a reaction on a cobalt salt, a magnesium salt, urea and the activated carrier under a hydrothermal condition by adopting a uniform deposition precipitation method, and carrying out precipitation, filtration, washing, drying and calcination to prepare the final catalyst CoxMg / K-CNO '. Oxygen-containing functional groups are introduced to the surfaces of the CNOs through acid pickling, the alkalinity and specific surface area of the carrier are improved through potassium activation, and the carrier, the active component Co and the auxiliary agent MgO generate a strong synergistic effect, so that high dispersion, strong stability and abundant surface alkaline sites of a Co-based active center are realized. The catalyst shows excellent low-temperature catalytic activity and stability in ammonia decomposition hydrogen production reaction, the ammonia conversion rate reaches up to 99.6% under specific conditions, and the catalyst can stably run at 500 DEG C for a long time.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of catalysts, and particularly relates to a preparation method of a carbon-based ammonia cracking hydrogen production catalyst and application thereof. BACKGROUND

[0002] Hydrogen is an important part of the future energy system as a clean energy carrier. Ammonia (NH3) is considered as an ideal hydrogen storage medium due to its high hydrogen storage density, easy liquefaction, and mature infrastructure. High-purity hydrogen can be efficiently and conveniently obtained through ammonia decomposition reaction (2NH3→N2+3H2), and the key of this technology lies in developing a catalyst with low temperature, high activity, high stability, and low cost.

[0003] At present, Ru-based catalysts have the best performance, but their high cost limits their wide application. Non-noble metals such as Co, Fe, and Ni have become a research hotspot, but their catalytic activity, especially in the medium and low temperature range, still needs to be improved. The performance of the catalyst depends largely on the dispersion of the active metal, the particle size, the interaction with the carrier, and the surface acidity and basicity of the catalyst.

[0004] Nano-onion carbon (CNOs) is a new type of carbon material with a multi-layer concentric shell structure, has a large specific surface area, and is rich in surface defects, which is conducive to the dispersion and anchoring of metal nanoparticles and can effectively inhibit sintering. However, the original CNOs have few surface functional groups, weak interaction with metal ions, and insufficient basic sites on the surface to efficiently activate ammonia molecules. Therefore, how to modify CNOs and synergistically optimize the active components is a core problem to improve the ammonia decomposition catalytic performance. SUMMARY

[0005] The main purpose of the present application is to overcome the shortcomings and deficiencies of the prior art, and to provide a preparation method of a carbon-based ammonia cracking hydrogen production catalyst with low temperature, high activity, good stability, and low cost and application thereof. The method significantly improves the comprehensive performance of the catalyst by precisely acid washing and potassium activation pretreatment of the CNOs carrier and synergistic effect with cobalt and magnesium oxide additives.

[0006] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0007] In a first aspect, the present application provides a preparation method of a carbon-based ammonia cracking hydrogen production catalyst, characterized in that the preparation method comprises the following steps:

[0008] S1, carrier pretreatment: the nano onion carbon is sequentially subjected to acid pickling treatment and potassium salt solution immersion activation treatment, and the following nano onion carbon is referred to as CNOs, to obtain an activated carrier K-CNO'; this step aims to remove metal impurities on the surface of the CNOs and introduce oxygen-containing functional groups (such as -COOH, -OH) as active sites for anchoring metal ions in the subsequent process. Then, the specific surface area of the carrier is further increased through the etching action of alkali, and the K element with strong positive electricity is introduced to significantly enhance the basicity of the surface of the carrier.

[0009] S2, catalyst preparation: a uniform deposition precipitation method is adopted to mix a cobalt salt, a magnesium salt, urea and the activated carrier K-CNO' in an aqueous solution, and the hydroxides or carbonates of cobalt and magnesium are uniformly deposited on the activated carrier K-CNO' under the condition of heating and stirring; after the reaction is completed, the final catalyst Co x Mg y / K-CNO' is obtained through filtration, washing, drying and calcination.

[0010] Further, in step S1, the acid pickling treatment process is as follows: the CNOs are dispersed in a 1M hydrochloric acid solution, stirred for 12-36 hours, filtered and washed to neutral, and dried at 100-150 ℃ to obtain CNO'.

[0011] The operation purpose of this step is to remove the exposed catalyst and amorphous carbon on the surface of the CNOs, thereby obtaining CNO'.

[0012] Further, in step S1, the potassium salt solution immersion activation treatment process is as follows: the CNO' obtained after acid pickling and drying is added to a 1M potassium carbonate K2CO3 solution, stirred at 90-100 ℃ for 12-36 hours, then filtered, dried, and calcined at 300-400 ℃ for 1-3 hours to obtain K-CNO'.

[0013] In this step, a large number of carboxyl and hydroxyl functional groups are introduced on the surface of the CNO', and the K element is increased.

[0014] Further, in step S2, the cobalt salt is cobalt nitrate Co(NO3)2·6H2O, the magnesium salt is magnesium nitrate Mg(NO3)2·6H2O, and the molar ratio of urea to the total of the cobalt salt and the magnesium salt is (3-5):1.

[0015] In this step, the appropriate ratio of urea to active metal is given to allow the active metal to slowly and uniformly settle on the surface of the K-CNO'

[0016] Further, in step S2, the molar ratio of cobalt to magnesium is 1-4:1, and the total loading amount of cobalt and magnesium, in terms of metal mass, accounts for 25%-35% of the total mass of the catalyst.

[0017] In this step, the appropriate active metal loading is given, forming a strong interaction between the metal and the carrier, making the catalyst more active.

[0018] Further, in step S2, the temperature of the heated stirring reaction is 90-100℃, and the time is 20-28 hours.

[0019] In this step, the temperature is 90-100℃, which mainly enhances the hydrolysis of urea.

[0020] Further, in step S2, the calcination conditions are: in air or inert atmosphere, the temperature is raised to 450-550℃ at a rate of 1-5℃ / min, and the temperature is kept for 3-5 hours.

[0021] In this step, the combustion scheme is given, which converts the hydroxide of the active metal into the oxide of the active metal, better exerting the performance of the catalyst.

[0022] In a second aspect, the application provides the application of the carbon-based ammonia cracking hydrogen production catalyst prepared by the above-mentioned preparation method, wherein the catalyst is first reduced and pretreated in a hydrogen atmosphere at 450-550℃ for 1-3 hours before being used for ammonia decomposition reaction; the ammonia decomposition reaction conditions are: reaction temperature 450-600℃, space velocity 6000-15000 mL·g cat -1 ·h -1 .

[0023] The application of the carbon-based ammonia cracking hydrogen production catalyst uses homogeneous deposition precipitation method (HDP) to synthesize Co2MgO4 and Co2Mg / CNO catalysts for ammonia decomposition reaction to produce CO x free hydrogen. The specific improvements are as follows:

[0024] 1. The active metal Co forms a cobalt-magnesium spinel structure with the additive MgO, and the activity test results show that the interaction between the carrier CNOs and the additive MgO improves the catalyst activity.

[0025] 2. CNOs improves the electronic conductivity, makes Co2MgO4 nanoparticles uniformly distributed, and increases the number of basic active sites and ammonia adsorption capacity.

[0026] 3. The introduction of CNOs can increase the number of medium basic sites, and the addition of K additive can further improve the surface concentration of basic sites and enhance the catalytic performance.

[0027] 4, CNOs, MgO, K and Co synergistically regulate the structure, particle size and performance of the catalyst. Stability tests show that Co2Mg / K-CNO' can be continuously and stably operated for 90 hours at 500 DEG C without obvious deactivation, and has potential for industrial application.

[0028] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0029] (1) Carrier synergistic modification: through the continuous pretreatment of "pickling + potassium activation", on the one hand, abundant oxygen-containing functional groups are introduced on the surface of CNOs, enhancing the metal-support interaction; on the other hand, strong alkaline K additives are introduced and the pore is expanded and increased, which together provide an ideal platform for the construction of highly dispersed and small-sized active centers.

[0030] (2) Active component synergistic effect: the active component Co and the additive MgO form a spinel structure of CoMgO4, which can produce highly dispersed metal Co nanoparticles and MgO after reduction, and the two have strong interaction (SMSI) with the K-CNO' carrier, stabilizing the active center.

[0031] (3) Surface alkaline optimization: the introduction of K and the coexistence of MgO greatly optimize the distribution of alkaline sites on the surface of the catalyst, increase the number and strength of medium-strong alkaline sites, and effectively promote the adsorption and activation of NH3 and the desorption of N2, which is the key to obtaining high activity.

[0032] (4) Excellent performance: the Co2Mg / K-CNO' catalyst prepared by the present application has an ammonia conversion rate of 99.6% under harsh conditions of 550 DEG C, space velocity 12000 mL·g cat -1 ·h -1 ; under the condition of 500 DEG C, space velocity 600 mL·g cat -1 ·h -1 , it can be stably operated for 90 hours without obvious deactivation, and the performance is significantly better than most reported non-noble metal catalysts, and has broad industrial application prospects. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0034] Figure 1 is a flow chart of a preparation method of a carbon-based ammonia cracking hydrogen catalyst disclosed by the present application;

[0035] Figure 2 SEM image of carbon-based ammonia cracking hydrogen production catalyst Co2Mg / K-CNO' in Example 2;

[0036] Figure 3 TEM image of carbon-based ammonia cracking hydrogen production catalyst Co2Mg / K-CNO' in Example 2;

[0037] Figure 4 SEM image of carbon-based ammonia cracking hydrogen production catalyst Co4Mg / K-CNO' in Comparative Example 1;

[0038] Figure 5 SEM image of carbon-based ammonia cracking hydrogen production catalyst Co3Mg2 / K-CNO' in Comparative Example 2;

[0039] Figure 6 SEM image of carbon-based ammonia cracking hydrogen production catalyst Co3Mg / K-CNO' in Comparative Example 3;

[0040] Figure 7 SEM image of carbon-based ammonia cracking hydrogen production catalyst CoMg / K-CNO' in Comparative Example 4;

[0041] Figure 8 Ammonia decomposition activity comparison chart of different catalysts in Example 3;

[0042] Figure 9 Ammonia cracking conversion rate-operation time chart of carbon-based ammonia cracking hydrogen production catalyst Co2Mg / K-CNO' in Example 4. DETAILED DESCRIPTION

[0043] In order to make the personnel in the technical field better understand the scheme of the present application, the technical scheme in the embodiments of the present application will be clearly and completely described below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by the person skilled in the art without making creative efforts fall within the scope of protection of the present application.

[0044] In the present application, the phrase "embodiment" means that the specific features, structures or characteristics described in combination with the embodiment can be contained in at least one embodiment of the present application. The appearance of this phrase at various places in the specification does not necessarily mean the same embodiment, nor is it an independent or alternative embodiment to other embodiments. The person skilled in the art explicitly and implicitly understands that the embodiments described in the present application can be combined with other embodiments.

[0045] Example 1

[0046] As Figure 1As shown, the embodiment discloses a preparation method of a carbon-based ammonia cracking hydrogen production catalyst, comprising the following steps:

[0047] S1, carrier pretreatment:

[0048] a. Acid washing: disperse nano-onion carbon (CNOs) in a 1M hydrochloric acid (HCl) solution, uniformly ultrasonic disperse, then stir at room temperature for 24 hours. Then vacuum filter, repeatedly wash with deionized water until the filtrate is neutral, and finally dry in an oven at 120°C overnight to obtain the acid-washed CNOs, denoted as CNO'. This step aims to remove metal impurities on the surface of CNOs and introduce oxygen-containing functional groups (such as -COOH, -OH) as active sites for subsequent anchoring of metal ions.

[0049] b. Potassium activation: add the obtained CNO' to a 1M potassium carbonate (K2CO3) solution, and stir vigorously at 95°C for 24 hours. Then vacuum filter, dry at 120°C for 4 hours, and then calcine in a muffle furnace at 350°C (heating rate 5°C / min) for 2 hours to obtain a potassium-activated carrier, denoted as K-CNO'. This step further increases the specific surface area of the carrier through the etching effect of the base and introduces K elements with strong positive charge, significantly enhancing the basicity of the carrier surface.

[0050] S2, catalyst preparation:

[0051] A homogeneous deposition precipitation method is adopted. Cobalt nitrate (Co(NO3)2·6H2O) and magnesium nitrate (Mg(NO3)2·6H2O) are weighed according to a cobalt-magnesium molar ratio of 1-4:1, and dissolved in distilled water together with excess urea. Then add the K-CNO' carrier prepared in step S1, and stir vigorously at 95°C for 24 hours. In this process, the slow hydrolysis of urea uniformly raises the pH value of the solution, promoting the uniform deposition of cobalt and magnesium hydroxides or basic carbonates on the surface of the K-CNO' carrier. After the reaction is completed, the mixture is filtered and washed with deionized water until neutral, and the obtained solid is dried at 120°C for 4 hours. Finally, the dried precursor is calcined in a muffle furnace at 500°C (heating rate 2°C / min) for 4 hours to obtain the final catalyst, denoted as Co x Mg y / K-CNO'.

[0052] Example 2

[0053] The embodiment continues to disclose a preparation method of a carbon-based ammonia cracking hydrogen production catalyst, comprising the following steps:

[0054] S1, carrier pretreatment:

[0055] Acid washing: 20 g CNOs were weighed and dispersed in 500 ml 1 M HC1 with ultrasonic dispersion. After stirring at room temperature for 24 h, the sample was filtered, washed with water until neutral, and dried at 120 °C overnight to obtain CNO'.

[0056] Potassium activation: 10 g CNO' were added to 200 ml 1 M K2CO3 solution and stirred at 95 °C for 24 h. After filtration, the sample was dried at 120 °C for 4 h and calcined at 350 °C (5 °C / min) for 2 h to obtain K-CNO'.

[0057] S2, catalyst preparation:

[0058] 11.64 g Co(N03)2-6H20, 5.12 g Mg(N03)2-6H20, and 36 g urea were dissolved in distilled water. 2.84 g K-CNO' were added and stirred at 95 °C for 24 h. After the reaction was completed, the sample was filtered, washed with water until neutral, dried at 120 °C for 4 h, and finally calcined at 500 °C (2 °C / min) for 4 h to obtain the catalyst Co2Mg / K-CNO'. As shown in FIG. 2, Figure 2 , Figure 2 is a SEM image of the carbon-based ammonia cracking hydrogen production catalyst Co2Mg / K-CNO' prepared by adjusting the Co-Mg atomic molar ratio to 2:1, which makes Co and Mg uniformly deposited on the K-CNO' carrier at an atomic molar ratio of 2:1, so that the catalyst has excellent ammonia cracking performance. As shown in FIG. 3, Figure 3 , Figure 3 is a TEM image of the carbon-based ammonia cracking hydrogen production catalyst Co2Mg / K-CNO' prepared by adjusting the Co-Mg atomic molar ratio to 2:1, which makes Co and Mg uniformly deposited on the K-CNO' carrier at an atomic molar ratio of 2:1, so that the catalyst has excellent ammonia cracking performance. As shown in FIG. 3,

[0059] Comparative Example 1

[0060] The Co4Mg / K-CNO' catalyst was prepared according to the same procedure as in Example 2, but 23.28 g Co(N03)2-6H20 was used in the catalyst preparation step. As shown in FIG. 4, Figure 4 , Figure 4 is a SEM image of the carbon-based ammonia cracking hydrogen production catalyst Co4Mg / K-CNO' prepared by adjusting the Co-Mg atomic molar ratio to 4:1, which makes Co and Mg uniformly deposited on the K-CNO' carrier at an atomic molar ratio of 4:1, so that the catalyst has excellent ammonia cracking performance.

[0061] Comparative Example 2

[0062] The Co3Mg2 / K-CNO' catalyst was prepared according to the same procedure as in Example 2, but 8.73 g Co(N03)2-6H20 was used in the catalyst preparation step. Figure 5is the SEM image of carbon-based ammonia cracking hydrogen production catalyst Co3Mg2 / K-CNO' prepared by adjusting the Co-Mg atomic molar ratio to 3:2, which makes Co and Mg uniformly deposit on the K-CNO' carrier in an atomic molar ratio of 3:2, so that the catalyst has excellent ammonia cracking performance.

[0063] Comparative Example 3

[0064] The Co3Mg / K-CNO' catalyst was prepared according to the steps of Example 2, but 17.46 g of Co(NO3)2·6H2O was used in the catalyst preparation step. As shown in Figure 6 , Figure 6 is the SEM image of carbon-based ammonia cracking hydrogen production catalyst Co3Mg / K-CNO' prepared by adjusting the Co-Mg atomic molar ratio to 3:1, which makes Co and Mg uniformly deposit on the K-CNO' carrier in an atomic molar ratio of 3:1, so that the catalyst has excellent ammonia cracking performance.

[0065] Comparative Example 4

[0066] The CoMg / K-CNO' catalyst was prepared according to the steps of Example 2, but 5.82 g of Co(NO3)2·6H2O was used in the catalyst preparation step. As shown in Figure 7 , Figure 7 is the SEM image of carbon-based ammonia cracking hydrogen production catalyst CoMg / K-CNO' prepared by adjusting the Co-Mg atomic molar ratio to 1:1, which makes Co and Mg uniformly deposit on the K-CNO' carrier in an atomic molar ratio of 1:1, so that the catalyst has excellent ammonia cracking performance.

[0067] Example 3: Catalyst performance test

[0068] The catalysts prepared in Example 2 and Comparative Examples were evaluated for performance. 0.1 g of catalyst was loaded into a fixed bed reactor, and was reduced at 500°C for 2 h under a 50% H2 / Ar atmosphere at a flow rate of 30 mL / min. Then, the temperature was lowered to the reaction temperature, and NH3 was introduced, with a gas hourly space velocity (GHSV) of 12000 mL·g cat -1 ·h -1 , and the tail gas composition was analyzed by gas chromatography to calculate the ammonia conversion rate.

[0069] The results are shown in Table 1:

[0070] Table 1. Ammonia conversion rate results table for different catalysts

[0071] Catalyst 550°C Ammonia conversion (%) Co2Mg / K-CNO 99.6% Co4Mg / K-CNO 92.5% Co3Mg2 / K-CNO 93.8% Co3Mg / K-CNO 98.9% CoMg / K-CNO' 96.7%

[0072] As Figure 8The comparison of ammonia decomposition activities of different catalysts shows that the Co2Mg / K-CNO' catalyst prepared in this invention exhibits extremely excellent low-temperature ammonia decomposition activity. Performance testing of carbon-based catalysts prepared with different Co-Mg ratios demonstrates that the prepared Co2Mg / K-CNO' catalyst... x Mg y All / K-CNO' carbon-based ammonia cracking catalysts exhibit excellent ammonia cracking conversion rates, indicating that they all possess superior catalytic performance, with Co2Mg / K-CNO' showing the best performance.

[0073] Example 4: Catalyst stability test

[0074] At 500℃, GHSV = 600 mL·g cat -1 ·h -1 Under these conditions, the Co2Mg / K-CNO' catalyst underwent a continuous operation test for up to 90 hours. Figure 9 The results of the ammonia cracking conversion-runtime graph of the medium-carbon-based ammonia cracking hydrogen production catalyst Co2Mg / K-CNO' show that the ammonia conversion rate remained at around 99.7%, indicating that the catalyst exhibited excellent stability. Figure 9 As shown, Figure 9 To investigate the excellent catalytic performance of the carbon-based ammonia cracking hydrogen production catalyst Co2Mg / K-CNO', a long-term stability test was conducted, and the results showed that Co2Mg / K-CNO' maintained excellent catalytic performance at 500℃ and GHSV = 600 mL·g. cat -1 ·h -1 Under the specified conditions, the catalyst prepared by this method can operate stably for up to 90 hours, indicating that it has the ability to operate stably for a long period of time.

[0075] In summary, this invention successfully prepared a high-performance, low-cost ammonia decomposition hydrogen production catalyst through innovative carrier pretreatment and component design, solving the problems of insufficient low-temperature activity and poor stability of existing non-precious metal catalysts, and has good prospects for industrial application.

[0076] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0077] 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 a carbon-based ammonia cracking catalyst for hydrogen production, characterized in that, The preparation method includes the following steps: S1. Carrier pretreatment: The nano-onion carbon is sequentially subjected to acid washing and potassium salt solution immersion activation treatment. The nano-onion carbon is referred to as CNOs below to obtain the activated carrier K-CNO'. S2. Catalyst Preparation: Using a uniform deposition precipitation method, cobalt salt, magnesium salt, urea, and the activated support K-CNO' are mixed in an aqueous solution and reacted under heating and stirring conditions, causing cobalt and magnesium hydroxides or carbonates to be uniformly deposited on the activated support K-CNO'. After the reaction is complete, the mixture is filtered, washed, dried, and calcined to obtain the final catalyst Co. x Mg y / K-CNO'.

2. The preparation method according to claim 1, characterized in that, In step S1, the acid washing process is as follows: CNOs are dispersed in a 1M hydrochloric acid solution, stirred for 12-36 hours, filtered, washed until neutral, and dried at 100-150 °C to obtain CNO'.

3. The preparation method according to claim 2, characterized in that, In step S1, the potassium salt solution impregnation and activation process is as follows: CNO' obtained after acid washing and drying is added to a 1M potassium carbonate K2CO3 solution, stirred at 90-100 ℃ for 12-36 hours, then filtered, dried, and calcined at 300-400 ℃ for 1-3 hours to obtain K-CNO'.

4. The preparation method according to claim 1, characterized in that, In step S2, the cobalt salt is cobalt nitrate Co(NO3)2·6H2O, and the magnesium salt is magnesium nitrate Mg(NO3)2·6H2O.

5. The preparation method according to claim 4, characterized in that, In step S2, the molar ratio of urea to the total of cobalt salt and magnesium salt is (3-5):

1.

6. The preparation method according to claim 1, characterized in that, In step S2, the molar ratio of cobalt to magnesium is 1-4:

1.

7. The preparation method according to claim 6, characterized in that, In step S2, the total loading of cobalt and magnesium accounts for 25%-35% of the total mass of the catalyst by metal mass.

8. The preparation method according to claim 1, characterized in that, In step S2, the temperature for heating and stirring the reaction is 90-100℃, and the time is 20-28 hours.

9. The preparation method according to claim 1, characterized in that, In step S2, the calcination conditions are as follows: in air or an inert atmosphere, the temperature is raised to 450-550℃ at a rate of 1-5℃ / min and held for 3-5 hours.

10. The application of a carbon-based ammonia cracking hydrogen production catalyst prepared by the preparation method according to any one of claims 1 to 9, characterized in that, Before being used in the ammonia decomposition reaction, the catalyst is first subjected to a reduction pretreatment in a hydrogen atmosphere at 450-550℃ for 1-3 hours; the conditions for the ammonia decomposition reaction are: reaction temperature 450-600℃, space velocity 6000-15000 mL·g cat -1 ·h -1 .

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