Plate-like NiMAl2O4 spinel catalyst, its preparation method, and its application in photothermal synergistic ammonia decomposition for hydrogen production.

Abstract

This invention relates to the fields of hydrogen catalysis technology and functional materials, particularly to a plate-like NiMAl2O4 spinel catalyst, its preparation method, and its application in photothermal synergistic ammonia decomposition for hydrogen production. In the plate-like NiMAl2O4 spinel catalyst, M is selected from Ce, Zr, or La. This invention achieves low-temperature, high-efficiency hydrogen production and long-term stability by controlling the structure of the NiAl2O4 spinel support and rare-earth doping. It is a low-cost, high-activity, structurally stable catalyst system with good photothermal response, enabling efficient hydrogen production and overcoming the technical defects of Ni-based catalysts.

Description

Technical Field

[0001] This invention relates to the fields of hydrogen energy catalysis technology and functional materials technology, and in particular to a plate-like NiMAl2O4 spinel catalyst, its preparation method, and its application in photothermal synergistic ammonia decomposition for hydrogen production. Background Technology

[0002] Hydrogen energy is considered a next-generation clean energy source, boasting advantages such as high calorific value and zero pollution, making it widely applicable in fuel cells, transportation, and distributed energy. In hydrogen production, ammonia (NH3) serves as a hydrogen storage carrier, offering advantages such as high hydrogen storage density (17.7 wt%), no COx byproducts, and ease of transportation and storage. However, ammonia decomposition exhibits high thermodynamic stability and a high NH bond breaking energy, making efficient decomposition difficult even at high temperatures without a catalyst, resulting in low hydrogen yield.

[0003] Existing catalytic systems mainly include noble metal catalysts (such as Ru, Rh, and Pt), which have high ammonia decomposition activity and good thermal stability, but are expensive and scarce, which seriously limits their industrial application. Ni-based catalysts have attracted much attention as an economical and feasible alternative due to their low cost, abundant reserves, and good CN bond activation ability, but they still have problems such as easy sintering of active components, insufficient catalytic activity at low temperatures, and poor long-term stability.

[0004] In addition, the catalyst support structure and pore design have a direct impact on the photothermal synergistic effect. Low photothermal absorption efficiency and unsatisfactory hydrogen production rate, and existing Ni-based catalysts are difficult to achieve both high conversion rate and long-term stability under low-temperature photothermal conditions. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a sheet-like NiMAl2O4 spinel catalyst, its preparation method, and its application in photothermal synergistic ammonia decomposition for hydrogen production. In the sheet-like NiMAl2O4 spinel catalyst, M is selected from Ce, Zr, or La. This invention achieves low-temperature, high-efficiency hydrogen production and long-term stability by controlling the structure of the NiAl2O4 spinel support and rare-earth doping. It is a low-cost, high-activity, structurally stable catalyst system with good photothermal response, enabling efficient hydrogen production and overcoming the technical defects of Ni-based catalysts.

[0006] Based on the above technical objectives, the present invention adopts the following technical solution: This invention protects a sheet-like NiMAl2O4 spinel catalyst, which is a NiMAl2O4 composite oxide. The sheet-like NiMAl2O4 spinel catalyst is obtained by surface / interface modification of a NiAl2O4 spinel support using an M oxide promoter, specifically a NiMAl2O4 composite spinel catalyst system formed after surface / interface modification of the NiAl2O4 spinel support using Ce, Zr, or La oxide promoters. The sheet-like NiMAl2O4 spinel catalyst possesses advantages such as good thermal stability, structural stability, abundant pore structure, and inhibition of high-temperature sintering, providing stable anchoring sites for active components in the ammonia decomposition reaction.

[0007] M is Ce, Zr, or La, and in the preferred plate-like NiMAl2O4 spinel catalyst, the molar percentage of M is 8 mol% to 12 mol%. When the M doping amount is too low, its regulatory effect on NiAl2O4 lattice defects, oxygen vacancies, specific surface area, and light absorption capacity is insufficient; when the M doping amount is too high, it is easy to form independent oxide agglomerates, covering active sites, reducing the mass transfer efficiency of reactants, which is detrimental to improving the performance of photothermal catalytic ammonia decomposition.

[0008] In plate-like NiMAl2O4 spinel catalysts, M doping reduces the crystallinity and grain size of NiAl2O4 spinel, making the plate-like morphology more pronounced. Simultaneously, the ratio of surface defect oxygen to adsorbed oxygen increases, promoting oxygen vacancy formation. Taking Ce modification as an example, the introduction of CeO2 enhances light absorption and promotes the separation of photogenerated carriers, thereby improving the photothermal synergistic ammonia decomposition activity.

[0009] Preferably, the specific surface area of ​​the plate-like NiMAl2O4 spinel catalyst is 35 m². 2 / g~55m 2 / g, pore volume 0.1cm 3 / g~0.16cm 3 The average pore size is 6 nm to 8.5 nm, with a uniform pore structure. The high specific surface area exposes more Ni active sites and ammonia adsorption sites; the larger pore volume facilitates the diffusion and mass transfer of NH3, H2, and N2 within the pores, reducing diffusion resistance; the moderate mesopore size balances the dispersion of active components with unobstructed reactant channels, avoiding mass transfer limitations caused by excessively small pores. Characterization results show that NiCeAl2O4 possesses a high specific surface area and pore volume, thus being more favorable for the photothermal ammonia decomposition reaction.

[0010] This invention also protects a method for preparing a sheet-like NiMAl2O4 spinel catalyst, comprising the following steps: Soluble nickel and aluminum salts were mixed together in ethanol, then citric acid was added, and the mixture was stirred until a transparent green gel was formed. After drying, grinding, and calcination, a NiAl₂O₄ spinel support was obtained. Sodium hydroxide solution was added dropwise to the M precursor solution and mixed thoroughly. Then, the NiAl₂O₄ spinel support was added and mixed thoroughly to obtain an intermediate. The intermediate underwent a hydrothermal / solvothermal reaction to obtain a plate-like precursor. The plate-like precursor was dried and then calcined to obtain a plate-like NiMAl₂O₄ spinel catalyst. The calcination step promotes the dehydration and decomposition of the precursor, forming a stable NiMAl₂O₄ spinel crystal phase, while improving the structural and mechanical stability of the plate-like NiMAl₂O₄ spinel catalyst. Appropriate calcination can also remove residual organic matter and impurities such as nitrate, stabilizing the plate-like framework structure.

[0011] Preferably, the molar ratio of soluble nickel salt, soluble aluminum salt, and citric acid is 1:1.5~2.5:3.5~4.5. The nickel salt is selected from nickel nitrate, nickel acetate, nickel chloride, and nickel sulfate, with nickel nitrate being preferred; the aluminum salt is selected from aluminum nitrate, aluminum chloride, and aluminum isopropoxide, with aluminum nitrate being preferred; in the M precursor, the Ce precursor is selected from cerium nitrate and cerium ammonium nitrate, the Zr precursor is selected from zirconium nitrate and zirconium oxychloride, and the La precursor is selected from lanthanum nitrate and lanthanum chloride, with the corresponding nitrate being preferred, to reduce the introduction of impurity ions and improve component homogeneity.

[0012] Preferably, the calcination conditions are: first calcination at 690℃~710℃ for 5 hours, and then calcination at 840℃~860℃ for 5 hours. These conditions were obtained through screening to ensure that the obtained NiAl2O4 spinel support does not contain excess NiO species.

[0013] Preferably, the molar ratio of sodium hydroxide to the M precursor is 33~133:1. If there is too little sodium hydroxide, the obtained NiMAl2O4 will have a nanosphere morphology, while if there is too much sodium hydroxide, the spinel structure will collapse.

[0014] Preferably, the hydrothermal / solvothermal reaction conditions are: hydrothermal / solvothermal reaction at 100℃~120℃ for 12h~24h. The lamellar morphology is mainly controlled by the solution chemical precipitation / hydrothermal process, metal salt concentration, reaction temperature, reaction time, and subsequent calcination temperature. If the hydrothermal temperature is too low or the time is too short, the precursor nucleation and lamellar growth will be insufficient, and irregular particles will easily form; if the temperature is too high or the time is too long, the lamellars will easily agglomerate, thicken, or collapse locally, resulting in a decrease in specific surface area. If the calcination temperature is too low, the crystal phase will be incomplete; if the calcination temperature is too high, grain growth and lamellar sintering will easily occur.

[0015] Preferably, the calcination conditions are: calcination at 400℃~500℃ for 2h~4h. More preferably, calcination at 400℃~500℃ for 2h.

[0016] This invention also protects the application of sheet-like NiMAl2O4 spinel catalysts in the preparation of photothermal synergistic ammonia decomposition hydrogen production catalysts.

[0017] Preferably, the application method is as follows: A plate-like NiMAl2O4 spinel catalyst is packed into a fixed-bed quartz tube reactor, and an ammonia decomposition reaction is carried out under a pure NH3 atmosphere, with a GHSV of 15000 mL·g. cat -1 ·h -1 ~35000 mL·g cat -1 ·h -1 The reaction temperature is 400℃~650℃, preferably 600℃; the light source is a xenon lamp to create photothermal synergistic reaction conditions. Before the reaction, the plate-like NiMAl2O4 spinel catalyst can be pre-reduced in an H2 or H2 / Ar atmosphere to obtain active Ni metallic centers.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention provides a sheet-like NiMAl2O4 spinel catalyst. The structure of the NiAl2O4 spinel support is controlled by rare earth doping, and Ce, Zr, and La are used to adjust lattice defects to improve catalytic activity. The improved catalytic performance mainly comes from the following synergistic effects: the sheet-like structure exposes more active sites; the higher specific surface area and pore volume promote NH3 diffusion and adsorption; Ce and other promoters increase oxygen vacancies and medium-to-strong acid / basic sites; light irradiation promotes carrier separation and interfacial electron transfer, weakens Ni-N bonding and accelerates N2 desorption.

[0019] The reason why Ce, Zr, and La regulate lattice defects is that the defects related to oxygen species on the NiAl2O4 spinel support and its surface are adjusted by introducing Ce, Zr, or La additives, thereby increasing oxygen vacancies and surface adsorbed oxygen species, which promotes NH3 adsorption activation and photogenerated carrier separation.

[0020] In addition, this invention overcomes the problem of insufficient utilization of existing rare earth additives. This invention introduces M additive after the formation of NiAl2O4 and combines it with calcination treatment to make Ce, Zr or La species uniformly dispersed on the surface or interface region of the lamellar spinel, avoiding the failure of additives by agglomeration. This process is mainly achieved through precipitation deposition / hydrothermal reaction and subsequent calcination steps, so that the additives participate in the regulation of lattice defects, oxygen vacancies and interface electronic structure.

[0021] This invention achieves a synergistic mechanism for the photothermal effect through Ce, Zr, and La doping. M doping broadens the light absorption range of the plate-like NiMAl2O4 spinel catalyst, reduces the probability of photogenerated electron-hole recombination, and promotes the transfer of photogenerated electrons to Ni active sites. At the same time, the oxygen vacancies and interface defects generated by M doping can serve as carrier capture and transfer centers, thereby improving the photothermal synergistic efficiency.

[0022] This invention achieves low-temperature, high-efficiency ammonia decomposition and ensures the long-term stability of the plate-like NiMAl2O4 spinel catalyst through spinel support regulation, rare-earth doping, and photothermal synergistic design. Specifically, it regulates the grain size, plate morphology, specific surface area, pore volume, oxygen vacancy concentration, surface acid / basic sites, and photogenerated carrier separation capability of NiAl2O4.

[0023] 2. The structure and pore optimization of the sheet-like NiMAl2O4 spinel catalyst of the present invention: uniform pore size and large specific surface area, which improves photothermal absorption efficiency and reactant contact opportunities.

[0024] 3. The sheet-like NiMAl2O4 spinel catalyst of this invention has a significant photothermal synergistic effect: the ammonia conversion rate reaches 82%~85% under low temperature light irradiation conditions of 450℃~600℃, which is higher than that of conventional Ni / Al2O3 catalysts.

[0025] 4. The plate-like NiMAl2O4 spinel catalyst of this invention exhibits excellent long-term stability: after 50 hours of photothermal testing, it still maintains ≥80% of its initial activity, and Ni sintering and agglomeration are significantly reduced. The reason for this reduction is that the M-modified plate-like NiMAl2O4 spinel catalyst has a higher Ni content. 0 The increased proportion of active sites, more abundant NH3 adsorption sites and oxygen vacancies, and light-induced electron transfer promote NH bond breaking and N2 desorption, thereby lowering the reaction energy barrier. Attached Figure Description

[0026] Figure 1 The XRD patterns of NiMAl2O4 and NiAl2O4 are shown.

[0027] Figure 2 The images are scanning electron microscope (SEM) images, where (a) is NiAl2O4, (b) is NiCeAl2O4, (c) is NiLaAl2O4, and (d) is NiZrAl2O4.

[0028] Figure 3 The image shows the EDS spectrum of NiCeAl2O4.

[0029] Figure 4 In the figure, (a) is the N2 adsorption-desorption isotherm of NiMAl2O4 and NiAl2O4, and (b) is the pore size distribution curve of NiMAl2O4 and NiAl2O4.

[0030] Figure 5 The images show the XPS spectra of NiMAl2O4 and NiAl2O4, where (a) represents Ni 2p, (b) represents Al 2p and Ni 3p, and (c) represents O 1s.

[0031] Figure 6 The H2-TPR curves of NiMAl2O4 and NiAl2O4 are shown.

[0032] Figure 7 The CO2-TPD curves for NiMAl2O4 and NiAl2O4 are shown.

[0033] Figure 8 The NH3-TPD curves for NiCeAl2O4 and NiAl2O4 are shown.

[0034] Figure 9 In the figure, (a) shows the ultraviolet-visible spectra of NiCeAl2O4 and NiAl2O4, and (b) shows the calculated band gap energy of NiCeAl2O4 and NiAl2O4.

[0035] Figure 10 The figures show the electrochemical impedance spectroscopy curves for NiMAl2O4 and NiAl2O4.

[0036] Figure 11 The PL curves for NiCeAl2O4 and NiAl2O4 are shown.

[0037] Figure 12 The XRD patterns of NiMAl2O4 and NiAl2O4 after the reaction are shown.

[0038] Figure 13 The images show SEM images of NiMAl2O4 and NiAl2O4 after the reaction. (a) shows NiAl2O4, (b) shows NiCeAl2O4, (c) shows NiLaAl2O4, and (d) shows NiZrAl2O4. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0040] Example 1 The preparation method of plate-like NiCeAl2O4 spinel catalyst includes the following steps: S1. Preparation of NiAl2O4 by sol-gel method: 3.24 g of Ni(NO3)2·6H2O and 8.48 g of Al(NO3)3·9H2O were dissolved in 80 mL of ethanol and stirred for 1 h. Then 8.52 g of citric acid was added and stirred in an oil bath at 80 °C for 4 h until a transparent green gel was formed. After drying in an oven at 120 °C, the powder was ground and finally calcined in a muffle furnace at 700 °C for 5 h and then at 850 °C for 5 h. After cooling, NiAl2O4 spinel support was obtained.

[0041] S2. Dissolve 3.6g of NaOH in 20mL of deionized water to obtain a NaOH solution; dissolve 0.325g of Ce(NO3)3·6H2O in deionized water to obtain a precursor solution; add the NaOH solution dropwise to the precursor solution, stir for 30min, then add the NiAl2O4 spinel support and continue stirring for 30min to obtain an intermediate.

[0042] S3. The intermediate is subjected to hydrothermal treatment at 100℃ for 24 hours to obtain a sheet-like precursor. After drying the sheet-like precursor, it is calcined at 450℃ for 2 hours to form a sheet-like NiCeAl2O4 spinel catalyst.

[0043] The BET specific surface area of ​​the plate-like NiCeAl2O4 spinel catalyst is 54.24 m². 2 / g, grain size is 6.18nm, average pore size is 8.06nm, pore volume is 0.151cm³. 3 / g. Ce-modified plate-like NiCeAl2O4 spinel catalysts have smaller grain size, higher specific surface area, and suitable pore structure, which is beneficial to improving the mass transfer process of NH3 and the product H2 / N2, thus providing a structural basis for improving the performance of subsequent photothermal ammonia decomposition.

[0044] Test conditions: photothermal reaction temperature 450℃~600℃, space velocity 15,000 mL·g cat -1 ·h -1 ~35,000 mL·g cat -1 ·h -1 The ammonia conversion rate can reach 82%~85%, and the hydrogen production rate is 12mmol / g / min~14mmol / g / min; under photothermal conditions at 600℃ (light irradiation using a xenon lamp), the ammonia conversion rate of the plate-like NiCeAl2O4 spinel catalyst is 82.6%, and the hydrogen production rate is 13.8mmol·g. -1 ·min -1 Under thermocatalytic conditions at 600℃, the ammonia conversion rate of the plate-like NiCeAl2O4 spinel catalyst was 70.6%, and the hydrogen production rate was 11.7 mmol·g.-1 ·min -1 The apparent activation energy is 86.79 kJ / mol. The hydrogen production rate under photothermal synergy is 15%–25% higher than that under thermocatalytic conditions, demonstrating the effectiveness of the photothermal synergy.

[0045] Example 2 The preparation method of the plate-like NiLaAl2O4 spinel catalyst is the same as that in Example 1, except that Ce(NO3)3·6H2O is replaced with an equimolar amount of La(NO3)3·6H2O.

[0046] Example 3 The preparation method of the plate-like NiZrAl2O4 spinel catalyst is the same as that in Example 1, except that Ce(NO3)3·6H2O is replaced with an equimolar amount of ZrOCl2·8H2O.

[0047] Example 4 The preparation method of plate-like NiCeAl2O4 spinel catalyst includes the following steps: S1. Preparation of NiAl2O4 by sol-gel method: 3.24 g of Ni(NO3)2·6H2O and 8.48 g of Al(NO3)3·9H2O were dissolved in 80 mL of ethanol and stirred for 1 h. Then 7.45 g of citric acid was added and stirred in an oil bath at 80 °C for 4.5 h until a transparent green gel was formed. After drying in an oven at 120 °C, the powder was ground and finally calcined in a muffle furnace at 690 °C for 5 h and then at 860 °C for 5 h. After cooling, NiAl2O4 spinel support was obtained.

[0048] S2. Dissolve 1g of NaOH in 20mL of deionized water to obtain a NaOH solution; dissolve 0.26g of Ce(NO3)3·6H2O in deionized water to obtain a precursor solution; add the NaOH solution dropwise to the precursor solution, stir for 30min, then add the NiAl2O4 spinel support and continue stirring for 30min to obtain an intermediate.

[0049] S3. The intermediate is subjected to hydrothermal treatment at 110°C for 18 hours to obtain a sheet-like precursor. After drying the sheet-like precursor, it is calcined at 500°C for 3 hours to form a sheet-like NiCeAl2O4 spinel catalyst.

[0050] Example 5 The preparation method of plate-like NiCeAl2O4 spinel catalyst includes the following steps: S1. Preparation of NiAl2O4 by sol-gel method: 3.24 g of Ni(NO3)2·6H2O and 8.48 g of Al(NO3)3·9H2O were dissolved in 80 mL of ethanol and stirred for 1 h. Then 9.58 g of citric acid was added and stirred in an oil bath at 80 °C for 5 h until a transparent green gel was formed. After drying in an oven at 120 °C, the powder was ground and finally calcined in a muffle furnace at 710 °C for 5 h and then at 840 °C for 5 h. After cooling, NiAl2O4 spinel support was obtained.

[0051] S2. Dissolve 4g of NaOH in 20mL of deionized water to obtain a NaOH solution; dissolve 0.39g of Ce(NO3)3·6H2O in deionized water to obtain a precursor solution; add the NaOH solution dropwise to the precursor solution, stir for 30min, then add the NiAl2O4 spinel support and continue stirring for 30min to obtain an intermediate.

[0052] S3. The intermediate is subjected to hydrothermal treatment at 120°C for 12 hours to obtain a plate-like precursor. After drying the plate-like precursor, it is calcined at 400°C for 4 hours to form a crystalline plate-like NiCeAl2O4 spinel support.

[0053] The following study uses the sheet-like NiMAl2O4 spinel catalysts prepared in Examples 1-3 as examples. The specific research methods and results are shown below: Figure 1 The XRD pattern of the plate-like NiCeAl2O4 spinel catalyst is shown. The main diffraction peaks of the NiCeAl2O4 sample are highly consistent with the face-centered cubic structure (space group Fd-3m) of NiAl2O4. The diffraction peaks at 19.1°, 31.5°, 37°, 45°, 59.8°, 65.5°, and 78.7° correspond to the (111), (220), (311), (400), (511), (440), and (622) diffraction planes of the NiAl2O4 phase (JCPDS#10-0339), respectively. After the introduction of the additive, the intensity of the diffraction peaks of the NiAl2O4 phase is significantly weakened and the full width at half maximum (FWHM) is significantly increased, indicating that its crystallinity decreases and the grain size decreases.

[0054] The grain sizes of NiCeAl2O4, NiLaAl2O4, NiZrAl2O4, and NiAl2O4 were calculated using the Scherer equation, and the results are shown in Table 1. As shown in Table 1, NiCeAl2O4 exhibits a smaller grain size. In the reduction pretreatment involved in the ammonia decomposition reaction, the finer NiCeAl2O4 spinel grains are more easily reduced, exposing a large number of low-coordination active centers, thereby significantly improving the reaction rate of ammonia dissociation and nitrogen desorption. Notably, no characteristic diffraction peaks belonging to the NiO phase were detected in the XRD patterns of any of the samples. For the CeO2-modified catalyst, Ce... 3+ / Ce 4+ Redox pairs generate vacancies on the surface and in the bulk, significantly enhancing the oxygen migration ability of the support and moderately modulating the metal-support interaction. This promotes the reduction of NiAl2O4 and the interaction of metallic Ni. 0 On the one hand, the nucleation and dispersion of ammonia molecules can be achieved. On the other hand, oxygen vacancies themselves can directly participate in the activation of ammonia molecules as active centers, and optimize the adsorption of reaction intermediates by changing the local electronic structure of the interface, thereby synergistically improving the overall ammonia decomposition catalytic performance.

[0055] Table 1 Physicochemical Properties of Catalysts The structure and morphology of undoped and doped NiAl2O4 nanosheets were characterized using scanning electron microscopy (SEM). Figure 2 As shown in the SEM observations, the undoped NiAl₂O₄ spinel catalyst exhibits an irregular, blocky structure with uneven distribution and significant agglomeration. The doped catalyst, however, displays a plate-like appearance. The NiCeAl₂O₄ sample shows the most uniform plate formation. These nanoplatelets effectively increase the specific surface area of ​​the catalyst, exposing more active sites and thus enhancing its catalytic activity for ammonia decomposition. Therefore, the introduction of oxides effectively optimizes the morphology and structure of the catalyst and significantly reduces agglomeration.

[0056] Depend on Figure 3 EDS analysis showed that all elements were uniformly distributed in the plate-like NiCeAl2O4 spinel catalyst, confirming the presence of Ni, Al and Ce elements, as well as the uniform dispersion of Ce species.

[0057] like Figure 4As shown, all catalysts exhibited type IV isotherms and, according to IUPAC classification, possessed distinct H2-type hysteresis loops. The presence of H2-type hysteresis loops indicates the existence of narrow bottleneck-like pores or cage-like pore structures within the catalysts. After introducing oxide promoters, the pore size distribution of NiMAl2O4 significantly shifted towards larger pores, and the specific surface area and pore volume were also significantly improved. Specifically, the specific surface areas of NiCeAl2O4, NiLaAl2O4, and NiZrAl2O4 reached 54.24 m². 2 / g, 50.94m 2 / g and 52.71m 2 / g. Compared to other catalysts, NiCeAl2O4 has a higher specific surface area and pore volume, which is beneficial for the exposure of active sites and enhances the contact efficiency between ammonia molecules and metal active centers. Simultaneously, the presence of the mesoporous structure facilitates the rapid diffusion of reactant NH3 and the timely desorption of product gases, thereby promoting the overall ammonia decomposition reaction. This is consistent with SEM observations.

[0058] X-ray photoelectron spectroscopy (XPS) analysis was used to reveal the chemical composition of the reduced sample. Figure 5 Figure (a) shows the XPS spectra of Ni 2p in NiMAl2O4 and NiAl2O4 samples. The Ni 2p spectrum shows two characteristic peaks at approximately 855.4 eV and 873.3 eV, corresponding to Ni 2p3 / 2 and Ni 2p1 / 2, respectively. This is generally attributed to Ni 2+ Two distinct satellite peaks are observed at approximately 861.8 eV and 879.9 eV, with Ni... 2+ The presence of this species is likely attributed to surface oxidation of the NiMAl2O4 sample under environmental conditions, a result consistent with H2-TPR analysis. Notably, the characteristic peak at 851.3 eV is attributed to the presence of Ni. 0 species, Ni on the surface of NiMAl2O4 sample 0 The proportion of the substance was significantly higher than in other samples, with abundant Ce. 3+ Species can stabilize Ni 0 This allows it to be in an electron-rich state, thereby effectively promoting the rate-determining step and inhibiting nickel oxidation. Figure 5 Figure (b) shows the Al 2p and Ni 3p spectra of NiMAl2O4 and NiAl2O4 samples, both exhibiting a single peak at approximately 74.1 eV, corresponding to Al in Al2p. 3+ An additional peak of 67.9 eV next to the Al 2p spectrum is assigned to Ni in the Ni 3p spectrum. 2+ .like Figure 5As shown in Figure (c), the O 1s spectrum of the NiCeAl2O4 sample decomposes into three peaks. The 529 eV peak is attributed to lattice oxygen (O latt), the peak at 531.4 eV is attributed to O species in NiAl2O4, and the peak at 532.6 eV is attributed to surface-adsorbed oxygen or defect oxygen species. The presence of vacancies on the catalyst surface enhances the enrichment of surface-adsorbed oxygen. The proportions of these three oxygen species were calculated, with NiCeAl2O4 having a surface oxygen species proportion of 22.98%, higher than NiAl2O4 (12.51%), NiLaAl2O4 (13.33%), and NiZrAl2O4 (15.65%). The high level of oxygen-containing species adsorbed on the surface of the NiCeAl2O4 sample indicates its high oxygen migration capacity and catalytic activity. Abundant oxygen vacancies induce strong metal-support interactions, generating electron-rich Ni active sites. On the one hand, the oxygen vacancies themselves can serve as Lewis base sites to enhance the adsorption of NH3 molecules; on the other hand, electron-rich Ni sites facilitate the activation and breaking of NH bonds and promote the recombination and desorption between adsorbed N atoms, thereby increasing the reaction rate.

[0059] The effect of different additives on the reducing properties of NiAl2O4, such as Figure 6 As shown in the figure. The study found that adding CeO2 to the catalyst weakens the interaction between Ni and Al2O3, promotes the activation of more easily reducible Ni species, and improves the dispersibility of Ni species, thereby increasing the reactivity.

[0060] The alkalinity of the catalyst is one of the key factors affecting the performance of ammonia decomposition. Figure 7The CO2-TPD results for NiAl2O4, NiCeAl2O4, NiLaAl2O4, and NiZrAl2O4 catalysts are presented. CO2-TPD is an effective method for characterizing the basicity of catalysts, where desorption temperature characterizes the basicity strength, and peak area quantifies the number of weak (<300℃), medium (300℃~600℃), and strong (>600℃) basic sites. NiAl2O4 exhibits a broad CO2 desorption peak at approximately 280℃, due to the presence of weakly to moderately basic sites; no significant strongly basic sites are observed at higher temperatures. After the introduction of the promoter, all NiMAl2O4 samples showed similar desorption peaks in the 100℃~300℃ range, corresponding to weakly basic adsorption centers. The low-temperature desorption peak can be attributed to physisorption, while the high-temperature desorption peak can be attributed to chemisorption. Therefore, the desorption peak appearing at a peak temperature of approximately 100℃ to 300℃ can be attributed to the removal of CO2 molecules through physical adsorption and weak chemisorption; the desorption peak appearing at a peak temperature of approximately 300℃ to 750℃ can be attributed to the removal of CO2 molecules through strong chemisorption. Adding La2O3, CeO2, and ZrO2 promoters can increase the desorption temperature of the NiAl2O4 catalyst. According to previous reports, moderately strong basic sites play a key role in ammonia decomposition and enhance N2 desorption by promoting electron transfer to the antibonding orbitals of the Ni-N bond, thereby reducing the strength of the Ni-N bond and promoting the associated desorption of N*. Among all catalysts, the NiCeAl2O4 catalyst has more basic sites and a higher desorption temperature, indicating that it possesses strong Lewis basicity and strong CO2 adsorption capacity. This will promote the breaking of the Ni-N bond and the associated desorption of N*, which is beneficial to the synergistic effect of ammonia adsorption and N2 desorption, thus enhancing the ammonia decomposition process.

[0061] To investigate the adsorption behavior of ammonia on the catalyst, the NH3-TPD technique was used to characterize the samples. Figure 8 As shown, all samples exhibit two distinct desorption peaks, indicating that they possess similar acid centers. Compared to the NiAl2O4 sample, the NiCeAl2O4 sample shows a larger desorption peak area, suggesting that cerium oxide modification significantly increases ammonia adsorption sites and results in higher ammonia adsorption capacity. Sufficient NH3 adsorption is a prerequisite for its subsequent dissociation. This may be attributed to the abundant available oxygen defect sites on the catalyst surface. These vacancies enrich electrons in surface Ni through electron transfer, exciting Ni-N* species and thus promoting N2 desorption. This combination is a core element contributing to the superior performance of cerium-promoted catalysts.

[0062] Ultraviolet-visible (UV-visDRS) spectroscopy shows light absorption at different wavelengths, such as... Figure 9As shown, NiMAl2O4 exhibits three main absorption bands in the ultraviolet and visible light regions, located in the ranges of 200 nm–300 nm, 300 nm–500 nm, and 550 nm–800 nm, respectively. With the introduction of oxides, the absorption of NiMAl2O4 in the 200 nm–400 nm range is enhanced, indicating that the additives effectively improve the light absorption capacity of NiAl2O4. The ultraviolet absorption band (200 nm–300 nm) mainly originates from ligand-to-metal charge transfer (LMCT), involving electronic transitions from O 2p orbitals to Ni 3d orbitals. According to literature reports, the highest absorption peak at 310 nm in the NiCeAl2O4 sample is attributed to the transition from O 2p orbitals to Ce orbitals. 4+ Electron transitions in the conduction band, Ce 4+ It can act as an electron trapping agent, effectively extending the lifetime of photogenerated electron-hole pairs. The absorption band in the 300nm~500nm range corresponds to Ni in octahedral coordination. 2+ The characteristic dd transition. The shoulder peak between 550 nm and 800 nm indicates the presence of Ni. 2+ This is related to nickel aluminates. The band gap energy was further calculated using the Tauc equation, and the Tauc plot in the figure shows the decrease in band gap energy in oxide-doped NiAl₂O₄. The narrowing of the band gap may be due to the introduction of impurities into the NiAl₂O₄ band gap, or to electron charge transfer between dopants in the conduction or valence bands. A smaller band gap leads to the absorption of a wider range of photons, indicating that NiCeAl₂O₄ has excellent light absorption properties. This is consistent with its potential for superior performance in photothermal catalytic reactions.

[0063] Electrochemical impedance spectroscopy (EIS) is an effective method for evaluating the separation efficiency of photogenerated carriers in catalysts. The size of the semicircle in the spectrum is directly related to the charge transfer resistance. Generally, a smaller semicircle radius indicates a lower charge transfer resistance and a higher separation efficiency of photogenerated electrons and holes, which helps to suppress carrier recombination and thus improve photocatalytic performance. Figure 10 As shown, the resistance semicircle decreases significantly with the introduction of oxides. Experimental data show that the NiCeAlO4 catalyst has the smallest semicircle, indicating that its low carrier diffusion resistance significantly improves the charge transport efficiency of the active sites, thereby achieving efficient transfer to the active sites.

[0064] To further investigate the separation and recombination dynamics of photogenerated carriers, photoluminescence spectroscopy (PL) was used to analyze the charge transfer and recombination behavior of photogenerated electron-hole pairs in the samples. Figure 11As shown, under 420 nm laser excitation, all samples exhibited broad emission peaks in the range of 400 nm to 600 nm. The NiCeAl2O4 catalyst showed lower photoluminescence intensity, indicating lower charge migration resistance and thus improved separation ability of photogenerated electron-hole pairs. A decrease in photoluminescence intensity typically signifies a decrease in recombination efficiency, i.e., superior photocatalytic performance. This phenomenon may be attributed to the tendency of photogenerated electrons accumulated in the conduction band of NiAl2O4 to recombine with photogenerated holes in the valence band of CeO2 at the heterojunction interface, thereby suppressing ineffective recombination of high-energy carriers, retaining strongly oxidizing holes participating in oxidation reactions and strongly reducing electrons participating in reduction reactions, ultimately improving the bulk photocatalytic performance.

[0065] Figure 12 and Figure 13 Stability tests showed that the NiCeAl2O4 catalyst retained 82% of its initial activity after continuous reaction at 600℃ under photothermal conditions for 50 h. Furthermore, XRD analysis after the reaction showed that the spinel structure was still maintained, and SEM analysis showed that the lamellar structure did not undergo significant collapse or severe sintering, demonstrating its good long-term stability.

[0066] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A sheet-like NiMAl2O4 spinel catalyst, characterized in that, The plate-like NiMAl2O4 spinel catalyst is a NiMAl2O4 composite oxide with oxygen vacancies on its surface; The plate-like NiMAl2O4 spinel catalyst is obtained by surface / interface modification of NiAl2O4 spinel support with M oxide promoter, where M is Ce, Zr or La. The molar percentage of M in the plate-like NiMAl2O4 spinel catalyst is 8 mol% to 12 mol.

2. The plate-like NiMAl2O4 spinel catalyst according to claim 1, characterized in that, The specific surface area of ​​the plate-like NiMAl2O4 spinel catalyst is 35 m². 2 / g~55m 2 / g, pore volume 0.1cm 3 / g~0.16cm 3 / g, with an average pore size of 6nm~8.5nm and a uniform pore structure.

3. A method for preparing the sheet-like NiMAl2O4 spinel catalyst according to claim 1, characterized in that, Includes the following steps: Soluble nickel salt and soluble aluminum salt were mixed together in ethanol, then citric acid was added and stirred until a transparent green gel was formed. After drying, grinding and calcination, NiAl2O4 spinel support was obtained. Sodium hydroxide solution was added dropwise to the precursor solution M and mixed thoroughly. Then, NiAl2O4 spinel support was added and mixed thoroughly to obtain the intermediate. The intermediate was subjected to a hydrothermal / solvothermal reaction to obtain a sheet-like precursor. The sheet-like precursor was dried and then calcined to obtain a sheet-like NiMAl2O4 spinel catalyst.

4. The method for preparing the sheet-like NiMAl2O4 spinel catalyst according to claim 3, characterized in that, The molar ratio of soluble nickel salt, soluble aluminum salt and citric acid is 1:1.5~2.5:3.5~4.

5.

5. The method for preparing the sheet-like NiMAl2O4 spinel catalyst according to claim 3, characterized in that, The calcination conditions are as follows: first calcinate at 690℃~710℃ for 5 hours, and then calcinate at 840℃~860℃ for 5 hours.

6. The method for preparing the sheet-like NiMAl2O4 spinel catalyst according to claim 3, characterized in that, The molar ratio of sodium hydroxide to the M precursor is 33~133:

1.

7. The method for preparing the sheet-like NiMAl2O4 spinel catalyst according to claim 3, characterized in that, The hydrothermal / solvothermal reaction conditions are: hydrothermal / solvothermal at 100℃~120℃ for 12h~24h.

8. The method for preparing the sheet-like NiMAl2O4 spinel catalyst according to claim 3, characterized in that, The calcination conditions are: calcination at 400℃~500℃ for 2h~4h.

9. The application of the sheet-like NiMAl2O4 spinel catalyst according to claim 1 in the preparation of a photothermal synergistic ammonia decomposition hydrogen production catalyst.

10. The application according to claim 9, characterized in that, The application method is as follows: A sheet-like NiMAl2O4 spinel catalyst is packed into a fixed-bed quartz tube reactor, and under xenon lamp irradiation and a pure NH3 atmosphere, the catalyst is reacted at 15000 mL·g⁻¹. cat -1 ·h -1 ~35000 mL·g cat -1 ·h -1 The ammonia decomposition reaction is carried out at a temperature of 400℃~650℃.

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