Non-noble metal doped LaCoO3-based system as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of photo-thermal catalytic hydrogen production, and discloses a non-noble metal doped LaCoO3-based system as well as a preparation method and application thereof. Firstly, uniform mixing and complexing of metal precursor ions at a molecular level are realized by adopting a sol-gel method, and then under a specific stepped program temperature control air calcination condition, Co < 3 + > is replaced by an isovalent substitution effect (Cu < 2 + >, Cr < 3 + > or Ni < 2 + >) of non-noble metal copper ions, the Cu / Cr / Ni doped LaCoO3-based solid solution photo-thermal catalyst has the advantages that a large number of uniformly distributed oxygen vacancy defects are forcibly and in-situ induced in perovskite (LaCoO3) crystal lattices, and the pure-phase Cu / Cr / Ni doped LaCoO3-based solid solution photo-thermal catalyst is finally obtained and is used for efficient photo-thermal methanol cracking hydrogen production reaction.

Description

Technical Field

[0001] This invention belongs to the field of photothermal catalytic hydrogen production technology, specifically referring to a non-precious metal-doped LaCoO3-based system, its preparation method, and its applications. Background Technology

[0002] In recent years, against the backdrop of increasingly pressing energy depletion and severe environmental problems, the production of hydrogen using photocatalysis or photothermal catalysis technologies as a zero-carbon emission green fuel has been considered fundamental to the future application of renewable energy technologies (DM Zhao, et al.). Nat. Energy 2021, 6, 388-397. However, the safe storage and long-distance transportation of hydrogen have always been bottlenecks limiting the large-scale application of hydrogen energy. Methanol, as a stable liquid hydrogen storage medium at room temperature and pressure, has an extremely high hydrogen-to-carbon ratio and is convenient to store and transport, and is considered an ideal liquid hydrogen carrier. Therefore, in-situ hydrogen production via methanol steam reforming has become a fundamental and key direction of current energy conversion technologies (M. Zhang, D. Liu, et al., 2021, 6, 388-397). Catalysts (2025, 15, 36). In practical applications, traditional methanol steam reforming is a strongly endothermic reaction, usually requiring high temperatures, which not only consumes a large amount of heat energy but also easily leads to rapid catalyst deactivation. Photothermal catalysis driven by sunlight provides a green and efficient way to reduce the reforming reaction temperature. However, from the perspective of solar spectrum composition, the near-infrared region accounts for more than 50% (ZC Lian, et al., J. Am. Chem. Soc. 2019, 141, 2446-2450). How to maximize the utilization of full-spectrum solar energy and obtain high hydrogen production efficiency at lower temperatures remains a huge challenge. In recent years, scholars at home and abroad have carried out a series of studies on high-entropy photothermal catalytic materials and near-infrared light response systems in order to break through the bottleneck of full-spectrum absorption.

[0003] Currently, the design concepts and active components of MSR catalysts mainly focus on two major categories: noble metals (Pt, Ru, etc.) and non-noble metal copper-based catalysts (X. Liu, L. Wang, et al., Acta Phys. -Chim. Sin. 2025, 41, 100049). Noble metal single-atom catalysts (such as single-center Pt1 / CeO2) exhibit excellent low-temperature catalytic activity and CH / OH bond activation ability (Z. Qi, L. Chen, et al., J. Am. Chem. Soc.(2021, 143, 60-64) The photothermal methanol-to-hydrogen mechanism based on the Pt / TiO2 system has been extensively explored. Meanwhile, supported noble metal single-atom (NM-SA) co-catalysts (such as Pt or Pd single atoms) can effectively promote the photocharge separation efficiency of the photocatalyst, thereby significantly improving hydrogen production performance (JMWang, et al.). Adv. Energy Mater. 2021, 11, 2003575). However, the high price of precious metals severely restricts their large-scale commercial application. In contrast, non-precious metal Cu-based systems, which are inexpensive and naturally exhibit high selectivity for MSR reactions, have become the mainstream. In 2021, Professor Zhang Tierui's research group used plasmonic Cu nanoparticles derived from layered bimetallic hydroxides (L-Cu) to achieve photo-driven methanol reforming for hydrogen production, demonstrating good potential in photothermal conversion (Z. Li, J. Liu, et al., Adv. Funct. Mater. (2021). Professor Wei Jinjia's research group at Xi'an Jiaotong University proposed a full-spectrum synergistic photothermal catalysis technology to construct Pt-CuO. x / Cu2O / CuO heterojunction photothermal catalyst significantly reduces the energy barrier of the water-gas shift process (D. Li, J. Sun, et al., Journal of Energy Chemistry 2022, 71, 467-474), and developed a highly efficient sunlight-driven dual-bed photothermal catalytic reactor (DBPTR) (D. Li, J. Sun, et al., Fuel 2023, 349, 129895). Although the aforementioned work has greatly advanced the field, under high-temperature photothermal cycling conditions, traditional Cu-based catalysts (such as the Cu-Al spinel system) are prone to sintering and agglomeration of surface copper particles, leading to rapid catalyst deactivation and poor stability (X. Hou, Y. Liu, et al., 2023, 349, 129895). Angew. Chem. Int. Ed. (2014, 53, 11886-11889). Therefore, developing an MSR catalyst system that combines high photothermal conversion efficiency, high stability, and complete independence from precious metals remains a significant challenge.

[0004] For non-precious metal systems, achieving efficient and stable photothermal methanol cracking for hydrogen production requires not only materials with full-spectrum light absorption capabilities but also surface defect sites capable of efficiently adsorbing and activating water molecules. In recent years, perovskite oxide (ABO3) nanomaterials have shown considerable potential in hydrogen reforming due to their extremely high thermochemical stability, flexible and tunable electronic structure, and excellent intrinsic photothermal properties (M. Usman, T. Yamada, et al.). ACS Eng. Au2025, 5, 314-346. Theoretically, by introducing metal complexes into inorganic lattices or performing defect engineering, the photophysical and chemical properties of materials can be effectively improved (YJ Yuan, ZT Yu, et al.). Chem. Soc. Rev. (2017, 46, 603-631). Considering the inherent advantages of Cu in methanol reforming, a "heterovalent substitution" strategy in crystal engineering can be used to in-situ replace the high-valence perovskite B-site metal with low-valence non-noble metal Cu ions (e.g., constructing a LaCoO3-based solid solution system). Based on a rigorous charge compensation mechanism, this will inevitably induce a large number of uniformly distributed oxygen vacancies within the crystal lattice. These built-in oxygen vacancies not only effectively extend the lifetime of photogenerated charges by acting as electron traps, but also serve as excellent catalytic active sites for the efficient adsorption and activation of water and methanol molecules. Based on this theory, the design of non-noble metal-doped perovskite catalysts is expected to completely overcome the sintering defects of traditional copper-based catalysts, achieving efficient and sustained photothermal methanol cracking for hydrogen production. Summary of the Invention

[0005] The purpose of this invention is to provide a new direction and approach for synthesizing efficient and stable non-noble metal-doped LaCoO3-based photothermal methanol cracking catalysts for hydrogen production. First, a sol-gel method is used to achieve uniform mixing and complexation of metal precursor ions (La, Co, M) at the molecular level. Then, under specific step-controlled temperature-programmed air calcination conditions, the heterovalent substitution effect of non-noble metal copper ions (M...) is utilized... 2+ Or M 3+ Replace Co 3+ By forcibly and in situ inducing a large number of uniformly distributed oxygen vacancy defects within the perovskite (LaCoO3) lattice, a pure-phase M-doped LaCoO3-based solid solution photothermal catalyst was finally obtained. This system has excellent broad-spectrum photothermal conversion capability and defect activation synergistic effect, and was used for efficient photothermal methanol cracking to produce hydrogen.

[0006] The specific technical solution of this invention includes the following steps: (1) Weigh lanthanum salt, cobalt salt and non-precious metal salt according to the proportion and dissolve them in deionized water to obtain a clear mixed metal salt solution. Then, add complexing agent and crosslinking agent to the solution in sequence, and add pH adjuster dropwise. Continue stirring to obtain a uniform precursor solution. (2) The precursor solution obtained in step (1) is placed in a constant temperature heating device and heated continuously while being slowly stirred until a viscous wet gel is formed. (3) The wet gel obtained in step (2) along with the reaction vessel is transferred to a drying device for continuous drying to dehydrate and expand it to form a low-density, fluffy sponge-like dry gel precursor. Then it is scraped off and ground into fine powder. (4) The dry gel powder obtained in step (3) is placed in a covered crucible and calcined in a muffle furnace using a stepped temperature program. After the reaction is complete, the mixture is allowed to cool naturally to room temperature, thus obtaining a non-noble metal-doped LaCoO3-based photothermal catalyst with abundant oxygen vacancies, i.e., LaCoO3. 0.9 M 0.1 O3.

[0007] In step (1), the ratio of the amount of lanthanum salt, cobalt salt, non-precious metal salt, complexing agent, and crosslinking agent is 10 mmol: 9 mmol: 1 mmol: 6.304 g: 1.8~2.2 mL; wherein, the lanthanum salt is La(NO3)3·6H2O, the cobalt salt is Co(NO3)2·6H2O, and the non-precious metal salt is anhydrous Cu(NO3)2, Cr(NO3)3·9H2O, or Ni(NO3)2·6H2O; the complexing agent is citric acid monohydrate, the crosslinking agent is ethylene glycol; and the pH adjuster is ammonia water, which precisely adjusts the pH value of the solution to between 6.0 and 7.0.

[0008] In step (2), the constant temperature heating device is a water bath or a heat-collecting constant temperature magnetic stirrer, and the heating temperature is set to 80~90 ℃.

[0009] In step (3), the drying equipment is a blower drying oven with a drying temperature of 120°C and a continuous drying time of 12 hours.

[0010] In step (4), the stepped temperature-programmed calcination includes two continuous stages: the first stage is to raise the temperature from room temperature to 300 ℃ at a rate of 2~3 ℃ / min and hold it for 2 h; the second stage is to raise the temperature from 300 ℃ to 700 ℃ at a rate of 2 ℃ / min and hold it for 4~6 h; the crucible lid is kept half-closed (leaving a small gap) throughout the calcination process.

[0011] The non-precious metal-doped LaCoO3 matrix prepared in this invention is used to efficiently drive the photothermal methanol cracking hydrogen production reaction.

[0012] The beneficial effects of this invention are as follows: First, it completely eliminates the dependence of traditional photocatalytic systems on expensive precious metal co-catalysts such as platinum (Pt). It does not require additional complex deposition or reduction equipment, and can form phase in one step by using extremely simple air atmosphere calcination, which greatly reduces the cost of catalyst preparation and is easy to scale up. Second, the obtained catalytic active sites are extremely precise and stable, through Cu2+ Cr 3+ or Ni 2+ Heterovalent substitution Co 3+ The oxygen vacancies induced in situ within the crystal lattice not only broaden the photothermal absorption band, but also serve as highly active trap sites to precisely adsorb and activate the chemical bonds in methanol and water molecules. Third, this solid solution strategy, which locks the active metals (Cu / Cr / Ni) inside the stable perovskite lattice, completely solves the industry pain point that traditional supported copper-based catalysts are prone to metal sintering, agglomeration and deactivation during high-temperature photothermal cycling. For the first time, it has achieved efficient, stable and long-lasting photothermal methanol cracking to produce hydrogen in a completely non-precious metal system. Attached Figure Description

[0013] Figure 1 This is the X-ray diffraction pattern of the sample in Example 1 of the present invention.

[0014] Figure 2 This is a performance test diagram of the sample prepared in Example 1 of the present invention.

[0015] Figure 3 This is a performance test diagram of the sample prepared in Example 2 of the present invention.

[0016] Figure 4 This is a performance test diagram of the sample prepared in Example 3 of the present invention. Detailed Implementation

[0017] The present invention will be described in detail below with reference to embodiments, so that those skilled in the art can better understand the present invention, but the present invention is not limited to the following embodiments.

[0018] Example 1

[0019] Step 1: Accurately weigh 4.330 g of La(NO3)3·6H2O, 2.619 g of Co(NO3)2·6H2O, and 0.188 g of anhydrous Cu(NO3)2 into a beaker, add 40.0 mL of deionized water, and stir magnetically until completely dissolved. Then add 6.304 g of citric acid monohydrate and 2.0 mL of ethylene glycol, followed by slowly adding ammonia to adjust the pH of the solution to between 6.0 and 7.0, obtaining a homogeneous and clear precursor mixture solution A.

[0020] Step 2: Place the precursor mixture solution A in a constant temperature water bath (or a heat-collecting constant temperature magnetic stirrer) at 85℃ and stir slowly. As a large amount of water evaporates, the citric acid and ethylene glycol in the system undergo esterification and polycondensation reactions, the viscosity of the solution gradually increases, and finally a viscous, semi-transparent wet gel B is formed.

[0021] Step 3: Transfer the beaker containing wet gel B directly to a forced-air drying oven and dry continuously at 120 °C for 12 h. During this process, the gel dehydrates and swells, forming a low-density, fluffy, sponge-like dry gel precursor. Scrape it off and grind it thoroughly in an agate mortar for 10 min into a fine powder to obtain sample C.

[0022] Step 4: Sample C is uniformly packed into a covered corundum crucible, with the lid partially closed, leaving a small gap. The crucible is then placed in a muffle furnace for step-by-step calcination: first, the temperature is increased from room temperature to 300℃ at a rate of 2℃ / min and held for 2 hours to remove the organic framework; then, the temperature is increased to 700℃ at a rate of 2℃ / min and calcined for 5 hours. After the reaction is complete and the furnace is allowed to cool naturally to room temperature, the ground sample is removed. This is the pure-phase non-noble metal-doped photothermal catalyst, denoted as LaCo. 0.9 Cu 0.1 O3.

[0023] Figure 1 The X-ray diffraction pattern of the sample in this embodiment of the invention shows that the main diffraction peaks (such as 2θ≈23.2° and subsequent high-angle peaks) completely correspond to the standard rhombohedral perovskite structure, with no visible impurity bulges.

[0024] Figure 2 This is a performance test graph of the sample prepared in the embodiments of the present invention. From the graph, we can see that LaCo... 0.9 Cu 0.1 O3 consistently exhibited higher hydrogen production across all cycles, peaking at 1580 mmol g in the second cycle. -1 h -1 .

[0025] Through non-precious metal copper ions (Cu) 2+ Cobalt ions (Co) on the B sites of the perovskite lattice are substituted with different valences. 3+ In the LaCoO3-based solid solution system, a large number of uniformly distributed oxygen vacancy defects were generated in situ. These oxygen vacancies not only broaden the material's wide-spectrum photothermal absorption capacity, but also serve as highly active electron traps and chemical bond activation sites, thereby achieving efficient methanol cracking and hydrogen production performance driven by full-spectrum sunlight (including near-infrared thermal effects). Moreover, by anchoring active Cu species inside the crystal lattice, the problem of easy sintering and deactivation of traditional supported copper-based catalysts under high-temperature conditions is completely solved. After continuous cycling tests, the catalytic activity did not decay, demonstrating excellent structural stability.

[0026] Example 2

[0027] Step 1: Accurately weigh 4.330 g of La(NO3)3·6H2O, 2.619 g of Co(NO3)2·6H2O, and 0.400 g of Cr(NO3)3·9H2O into a beaker, add 40.0 mL of deionized water, and stir magnetically until completely dissolved. Then add 6.304 g of citric acid monohydrate and 2.0 mL of ethylene glycol, followed by slowly adding ammonia to adjust the pH of the solution to between 6.0 and 7.0, obtaining a homogeneous and clear precursor mixture solution A.

[0028] Step 2: Place the precursor mixture solution A in a constant temperature water bath (or a heat-collecting constant temperature magnetic stirrer) at 85℃ and stir slowly. As a large amount of water evaporates, the citric acid and ethylene glycol in the system undergo esterification and polycondensation reactions, the viscosity of the solution gradually increases, and finally a viscous, semi-transparent wet gel B is formed.

[0029] Step 3: Transfer the beaker containing wet gel B directly to a forced-air drying oven and dry continuously at 120 °C for 12 h. During this process, the gel dehydrates and swells, forming a low-density, fluffy, sponge-like dry gel precursor. Scrape it off and grind it thoroughly in an agate mortar for 10 min into a fine powder to obtain sample C.

[0030] Step 4: Sample C is uniformly packed into a covered corundum crucible, with the lid partially closed, leaving a small gap. The crucible is then placed in a muffle furnace for step-by-step calcination: first, the temperature is increased from room temperature to 300℃ at a rate of 2℃ / min and held for 2 hours to remove the organic framework; then, the temperature is increased to 700℃ at a rate of 2℃ / min and calcined for 5 hours. After the reaction is complete and the furnace is allowed to cool naturally to room temperature, the ground sample is removed. This is the pure-phase non-noble metal-doped photothermal catalyst, denoted as LaCo. 0.9 Cr 0.1 O3.

[0031] Figure 3 This is a performance test graph of the sample prepared in the embodiments of the present invention. From the graph, we can see that LaCo... 0.9 Cr 0.1 O3 consistently exhibited higher hydrogen production across all cycles, peaking at 1821 mmol g in the second cycle. -1 h -1 .

[0032] Example 3

[0033] Step 1: Accurately weigh 4.330 g of La(NO3)3·6H2O, 2.619 g of Co(NO3)2·6H2O, and 0.291 g of Ni(NO3)2·6H2O into a beaker, add 40.0 mL of deionized water, and stir magnetically until completely dissolved. Then add 6.304 g of citric acid monohydrate and 2.0 mL of ethylene glycol, followed by slowly adding ammonia to adjust the pH of the solution to between 6.0 and 7.0, obtaining a homogeneous and clear precursor mixture solution A.

[0034] Step 2: Place the precursor mixture solution A in a constant temperature water bath (or a heat-collecting constant temperature magnetic stirrer) at 85℃ and stir slowly. As a large amount of water evaporates, the citric acid and ethylene glycol in the system undergo esterification and polycondensation reactions, the viscosity of the solution gradually increases, and finally a viscous, semi-transparent wet gel B is formed.

[0035] Step 3: Transfer the beaker containing wet gel B directly to a forced-air drying oven and dry continuously at 120℃ for 12 h. During this process, the gel dehydrates and swells, forming a low-density, fluffy, sponge-like dry gel precursor. Scrape it off and grind it thoroughly in an agate mortar for 10 min into a fine powder to obtain sample C.

[0036] Step 4: Sample C is uniformly packed into a covered corundum crucible, with the lid partially closed, leaving a small gap. The crucible is then placed in a muffle furnace for step-by-step calcination: first, the temperature is increased from room temperature to 300℃ at a rate of 2℃ / min and held for 2 hours to remove the organic framework; then, the temperature is increased to 700℃ at a rate of 2℃ / min and calcined for 5 hours. After the reaction is complete and the furnace is allowed to cool naturally to room temperature, the ground sample is removed. This is the pure-phase non-noble metal-doped photothermal catalyst, denoted as LaCo. 0.9 Ni 0.1 O3.

[0037] Figure 4 This is a performance test graph of the sample prepared in the embodiments of the present invention. From the graph, we can see that LaCo... 0.9 Ni 0.1 O3 consistently exhibited higher hydrogen production across all cycles, peaking at 1299 mmol g in the third cycle. -1 h -1 .

Claims

1. A method for preparing a non-noble metal-doped LaCoO3-based system, characterized in that, Includes the following steps: (1) Weigh lanthanum salt, cobalt salt and non-precious metal salt according to the proportion and dissolve them in deionized water to obtain a clear mixed metal salt solution. Then, add complexing agent and crosslinking agent to the solution in sequence, and add pH adjuster dropwise. Continue stirring to obtain a uniform precursor solution. (2) The precursor solution obtained in step (1) is placed in a constant temperature heating device and heated continuously while being slowly stirred until a viscous wet gel is formed. (3) The wet gel obtained in step (2) along with the reaction vessel is transferred to a drying device for continuous drying to dehydrate and expand it to form a low-density, fluffy sponge-like dry gel precursor. Then it is scraped off and ground into fine powder. (4) The dry gel powder obtained in step (3) is placed in a covered crucible and calcined in a muffle furnace using a stepped temperature program. After the reaction is complete, the mixture is allowed to cool naturally to room temperature, thus obtaining a non-noble metal-doped LaCoO3-based photothermal catalyst with abundant oxygen vacancies, i.e., LaCoO3. 0.9 M 0.1 O3, where M is Cu, Cr or Ni.

2. The preparation method according to claim 1, characterized in that, In step (1), the ratio of the amount of lanthanum salt, cobalt salt, non-precious metal salt, complexing agent and crosslinking agent is 10 mmol: 9 mmol: 1 mmol: 6.304 g: 1.8~2.2 mL.

3. The preparation method according to claim 1, characterized in that, In step (1), the lanthanum salt is La(NO3)3·6H2O, the cobalt salt is Co(NO3)2·6H2O, and the non-precious metal salt is anhydrous Cu(NO3)2, Cr(NO3)3·9H2O or Ni(NO3)2·6H2O.

4. The preparation method according to claim 1, characterized in that, In step (1), the complexing agent is citric acid monohydrate and the crosslinking agent is ethylene glycol.

5. The preparation method according to claim 1, characterized in that, In step (1), the pH adjuster is ammonia water, which precisely adjusts the pH value of the solution to between 6.0 and 7.

0.

6. The preparation method according to claim 1, characterized in that, In step (2), the constant temperature heating device is a water bath or a heat-collecting constant temperature magnetic stirrer, and the heating temperature is set to 80~90 ℃.

7. The preparation method according to claim 1, characterized in that, In step (3), the drying equipment is a blower drying oven with a drying temperature of 120°C and a continuous drying time of 12 hours.

8. The preparation method according to claim 1, characterized in that, In step (4), the stepped temperature-programmed calcination includes two continuous stages: the first stage is to raise the temperature from room temperature to 300 ℃ at a rate of 2~3 ℃ / min and hold it for 2 h; the second stage is to raise the temperature from 300 ℃ to 700 ℃ at a rate of 2 ℃ / min and hold it for 4~6 h; the crucible lid is kept half-covered throughout the calcination process.

9. The use of the non-precious metal-doped LaCoO3 matrix prepared by the preparation method according to any one of claims 1 to 8 for efficiently driving the photothermal methanol cracking hydrogen production reaction.

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