Plasma-assisted Ce-modified Ni-based catalyst for hydrogen production by ammonia decomposition and preparation method thereof

Abstract

The application relates to the technical field of hydrogen production by ammonia decomposition, in particular to a plasma synergistic Ce-modified Ni-based catalyst for hydrogen production by ammonia decomposition and a preparation method thereof, and the preparation method comprises the following steps: S1, dissolving a nickel salt and a cerium salt in deionized water, then adding gas-phase SiO2, stirring and mixing, then stirring and evaporating at 60-95 DEG C, and then drying to obtain a dry powder; S2, calcining the dry powder at 450-580 DEG C for 3-8 hours to obtain a Ce-modified Ni-based catalyst precursor, and reducing the Ce-modified Ni-based catalyst precursor to obtain a Ce-modified Ni-based catalyst; the Ce-modified Ni-based catalyst has the advantages of reducing the reaction temperature of plasma catalytic ammonia decomposition and improving the efficiency of hydrogen production by ammonia decomposition.

Description

Technical Field

[0001] This application relates to the technical field of ammonia decomposition for hydrogen production, and in particular to a plasma-assisted Ce-modified Ni-based catalyst for ammonia decomposition for hydrogen production and its preparation method. Background Technology

[0002] With the increasing severity of global climate change, carbon emission reduction in the shipping industry has become an urgent priority, necessitating the accelerated application of clean energy sources (such as methanol, ammonia, and hydrogen) on ships. Among zero-carbon energy sources, ammonia (NH3) is considered a highly promising alternative fuel for ships due to its advantages such as high energy density, low storage and transportation costs (the cost of transporting liquid ammonia over 500 kilometers is approximately 1.7% of that of liquid hydrogen), and relatively high safety (narrow explosion limits and a pungent odor). However, ammonia fuel suffers from drawbacks such as high auto-ignition temperature, slow combustion speed, and unstable flame propagation, posing significant challenges to direct combustion.

[0003] To address the combustion challenges of ammonia fuel while leveraging the superior combustion characteristics of hydrogen, in-situ ammonia decomposition for hydrogen production in marine environments has become an effective approach to improving engine thermal efficiency and safety. This involves converting ammonia into a hydrogen-rich mixture as a combustion aid. Currently, ammonia decomposition for hydrogen production primarily utilizes thermocatalysis, photocatalysis, electrocatalysis, and plasma catalysis. While thermocatalysis is relatively mature, its reaction temperatures typically range from 450-700℃, and it often employs large, energy-intensive fixed-bed reactors, resulting in slow cold-start response and difficulty in meeting the rapid start-stop requirements of marine propulsion systems. In contrast, plasma catalysis technology, with its milder reaction conditions, simpler equipment structure, rapid start-stop response, and ability to achieve high-efficiency conversion at lower temperatures, demonstrates broad application prospects in marine propulsion systems.

[0004] In plasma-catalyzed ammonia decomposition systems, nickel (Ni)-based catalysts are abundant, relatively inexpensive, and exhibit high ammonia decomposition activity. Existing research shows that introducing plasma synergy or using supported bimetallic catalysts (such as Fe-Ni, Co-Ni, etc.) can significantly improve ammonia decomposition conversion and reduce reaction temperature. However, current research on plasma-catalyzed ammonia decomposition, both domestically and internationally, generally exceeds 400℃, which is unsuitable for shipboard operating conditions. Furthermore, the interaction between plasma and catalyst during low-temperature plasma-catalyzed ammonia decomposition remains unclear. Therefore, there is an urgent need to develop a plasma-synergistic nickel-based catalyst specifically designed for shipboard applications and possessing excellent low-temperature activity. Summary of the Invention

[0005] To reduce the reaction temperature of plasma-catalyzed ammonia decomposition and improve the efficiency of hydrogen production from ammonia decomposition, this application provides a plasma-assisted Ce-modified Ni-based catalyst for hydrogen production from ammonia decomposition and its preparation method.

[0006] In a first aspect, this application provides a method for preparing a plasma-assisted Ce-modified Ni-based catalyst for hydrogen production from ammonia decomposition, employing the following technical solution: A method for preparing a plasma-assisted Ce-modified Ni-based catalyst for hydrogen production from ammonia decomposition includes the following steps: S1. Dissolve nickel salt and cerium salt in deionized water, then add gaseous SiO2, stir and mix, then stir and evaporate to dryness at 60-95℃, and then dry to obtain dry powder. S2. The dried powder is calcined at 450-580℃ for 3-8 hours to obtain a Ce-modified Ni-based catalyst precursor, which is then reduced to obtain the Ce-modified Ni-based catalyst.

[0007] By adopting the above technical solution, this application prepares Ce-modified nickel-based catalysts by impregnation method using metallic Ce as a dopant. It was found that Ce doping can reduce the particle size of nickel particles, and the abundant oxygen vacancies induced by Ce effectively increase the density of medium-to-strong basic sites in the catalyst, and enhance the Ni-based catalyst through electron-donating effects. 0 The increased electron density at the sites promoted the adsorption and activation of NH3 and the recombination and desorption of N atoms. Emission spectroscopy and plasma discharge parameters indicate that the introduction of the Ce-modified Ni-based catalyst in this application increased the electron energy in the plasma discharge region, which is beneficial for the generation of excited-state species and their subsequent reactions. Ce, as a promoter, effectively improved the plasma-assisted Ni-based catalyst's catalytic effect on ammonia decomposition, significantly reduced the reaction temperature of plasma-catalyzed ammonia decomposition, and simultaneously improved the efficiency of hydrogen production from ammonia decomposition.

[0008] Preferably, in the Ce-modified Ni-based catalyst, the loading of Ni is 6-15 wt.% and the loading of Ce is 2.5-10 wt.%.

[0009] By adopting the above technical solution and further limiting the loading of Ni and Ce, the agglomeration of nickel particles is avoided while ensuring a sufficient number of catalytic active sites, thereby ensuring the catalytic activity and catalytic stability of Ce-modified Ni-based catalysts.

[0010] Preferably, the Ce loading is 2.5-5 wt.%.

[0011] By adopting the above technical solution and further limiting the Ce loading, the best balance between catalytic activity and catalyst structural stability can be achieved. When the discharge power is 20W, the ammonia decomposition rate of the Ce-modified Ni-based catalyst can reach 88-93%.

[0012] As a preferred embodiment, the reduction method for the Ce-modified Ni-based catalyst precursor is as follows: The Ce-modified Ni-based catalyst precursor was placed in a tube furnace and incubated at 480-580°C with a 5-15 vol.% H2 / Ar mixed gas flow at a rate of 50-200 mL·min. -1 The reduction was carried out at a flow rate of 1-5 hours.

[0013] By adopting the above technical solution, reduction can be achieved to convert nickel oxide into metallic Ni. 0 It achieves efficient conversion while avoiding damage to the carrier structure.

[0014] Preferably, in S2, the surface of the Ce-modified Ni-based catalyst precursor is further coated with titanium dioxide.

[0015] By employing the above technical solution, a SiO2@TiO2 core-shell structure is constructed by coating TiO2 onto the surface of the catalyst precursor. The high dielectric constant of TiO2 enhances the plasma discharge intensity, while the shell confinement effect suppresses the sintering and agglomeration of Ni particles. The high dielectric properties of TiO2 increase the reduced field strength to 69.3 Td and the average electron energy to 5.5 eV, promoting the reaction of high-energy electrons with H+. a The generation of active species such as NH3* and Ar* enhances the synergistic effect between plasma and catalyst. TiO2 coating achieves a dual improvement in catalytic activity and energy efficiency by optimizing adsorption performance, increasing oxygen vacancy concentration, and enhancing plasma discharge intensity.

[0016] Preferably, the content of S2 includes the following: The dried powder obtained from S1 was calcined in a muffle furnace at 400-580℃ for 2 hours, then dispersed in ethanol, the pH was adjusted to 9-10.5, tetrabutyl titanate was added dropwise under stirring, and after centrifugation, washing and drying, it was calcined in air at 420-550℃ for 1 hour to obtain a Ce-modified Ni-based catalyst precursor with titanium dioxide coated on the surface, and then the Ce-modified Ni-based catalyst was obtained by reduction.

[0017] By employing the above-mentioned technical solution, a continuous and uniform anatase TiO2 shell is formed on the Ni-Ce / SiO2 surface through pH control and hydrolysis-condensation of tetrabutyl titanate. This process avoids the formation of free TiO2 particles, ensures that reactants can diffuse to the internal Ni active sites, and simultaneously generates a strong local electric field in the plasma field, promoting high-energy electron excitation.

[0018] Preferably, the mass ratio of the tetrabutyl titanate to the fumed silica is (0.001-4):(7-10).

[0019] By adopting the above technical solution, it is ensured that the thickness of the TiO2 shell does not affect the catalytic performance of the catalyst. The appropriate shell thickness not only exerts the confinement effect and dielectric enhancement, but also avoids the increase in mass transfer resistance caused by an excessively thick shell, thus achieving a balance between high ammonia decomposition rate (98%) and high energy yield.

[0020] Preferably, in step S2, before adjusting the pH, polyvinylpyrrolidone is added to the ethanol, and the mass ratio of the amount of polyvinylpyrrolidone added to the tetrabutyl titanate is (0.001-1.5):(0.001-4).

[0021] By adopting the above technical solution, the growth process of the TiO2 shell is regulated by adding PVP, and the steric hindrance effect of PVP is used to suppress the rapid hydrolysis of TBOT, thus avoiding the explosive precipitation of TiO2 particles. As in Example 6, the Ni-Ce / SiO2@TiO2-1 prepared after adding 0.8g of PVP-K30 achieved an ammonia decomposition rate of 99% at 20W power, which was further improved; the PVP-assisted coated catalyst shell is more continuous and uniform, without local thick shells or free particles, which further improves the plasma synergistic catalytic efficiency.

[0022] Preferably, the average molecular weight of the polyvinylpyrrolidone is 3500-50000 Da.

[0023] By adopting the above technical solution, it is ensured that it has good solubility and steric hindrance effect in ethanol. PVP in this molecular weight range can be completely decomposed during calcination at 450℃ and subsequent high-temperature reduction (without carbon residue), avoiding residual carbon covering active sites or affecting plasma discharge characteristics.

[0024] Secondly, this application provides a plasma-assisted Ce-modified Ni-based catalyst for ammonia decomposition to hydrogen production, employing the following technical solution: A plasma-assisted Ce-modified Ni-based catalyst for hydrogen production from ammonia decomposition is prepared by the method described above.

[0025] In summary, this application includes at least one of the following beneficial technical effects: 1. This application describes the preparation of Ce-modified nickel-based catalysts using an impregnation method with metallic Ce as a dopant. It was found that Ce doping reduces the particle size of nickel particles, and the abundant oxygen vacancies induced by Ce effectively increase the density of medium-to-strong basic sites in the catalyst. Furthermore, it enhances the Ni-based catalyst through an electron-donating effect. 0The increased electron density at the sites promoted the adsorption and activation of NH3 and the recombination and desorption of N atoms. Emission spectroscopy and plasma discharge parameters indicate that the introduction of the Ce-modified Ni-based catalyst in this application increased the electron energy in the plasma discharge region, which is beneficial for the generation of excited-state species and their subsequent reactions. Ce, as a promoter, effectively improved the plasma-assisted Ni-based catalyst's catalytic effect on ammonia decomposition, significantly reduced the reaction temperature of plasma-catalyzed ammonia decomposition, and simultaneously improved the efficiency of hydrogen production from ammonia decomposition.

[0026] 2. By coating the catalyst precursor with TiO2 to construct a SiO2@TiO2 core-shell structure, the high dielectric constant of TiO2 enhances the plasma discharge intensity, while the shell confinement effect inhibits the sintering and agglomeration of Ni particles. The high dielectric properties of TiO2 increase the reduced field strength to 69.3 Td and the average electron energy to 5.5 eV, promoting the generation of high-energy electrons and active species such as Hα, NH3*, and Ar*, thus strengthening the synergistic effect between plasma and catalyst. TiO2 coating achieves a dual improvement in catalytic activity and energy efficiency by optimizing adsorption performance, increasing oxygen vacancy concentration, and enhancing plasma discharge intensity.

[0027] 3. By adding PVP to regulate the TiO2 shell growth process, the steric hindrance effect of PVP is used to suppress the rapid hydrolysis of TBOT and avoid the explosive precipitation of TiO2 particles. As in Example 6, the Ni-Ce / SiO2@TiO2-1 prepared after adding 0.8g of PVP-K30 achieved an ammonia decomposition rate of 99% at 20W power, which was further improved; the PVP-assisted coated catalyst shell is more continuous and uniform, without local thick shells or free particles, which further improves the plasma synergistic catalytic efficiency. Attached Figure Description

[0028] Figure 1 (a) is the XRD pattern of the catalysts prepared in Examples 1-4 and Comparative Example 1; Figure 1 (b) is the N2 adsorption-desorption isotherm of the catalysts prepared in Examples 1-4 and Comparative Example 1.

[0029] Figure 2 (ae) are transmission electron microscope images and Ni particle size distribution histograms of Ni / SiO2 (Comparative Example 1), Ni-Ce / SiO2 (Example 1), Ni-La / SiO2 (Comparative Example 4), Ni-Mg / SiO2 (Comparative Example 3) and Ni-Zr / SiO2 (Comparative Example 2), respectively. Figure 2 (f) is a high-resolution transmission electron microscope image of Ni-Ce / SiO2 (Example 1); Figure 2 (g) is the selected area electron diffraction pattern of Ni-Ce / SiO2 (Example 1); Figure 2(h) is a high-angle annular dark-field scanning transmission electron microscope image and energy spectrum of Ni-Ce / SiO2 (Example 1).

[0030] Figure 3 (ac) are graphs showing the ammonia decomposition rate as a function of power, the H2 energy yield as a function of power, and the ammonia decomposition rate as a function of flow rate for Ni / SiO2 (Comparative Example 1), Ni-Ce / SiO2 (Example 1), Ni-La / SiO2 (Comparative Example 4), Ni-Mg / SiO2 (Comparative Example 3), and Ni-Zr / SiO2 (Comparative Example 2), respectively. Figure 3 (d) is a graph showing the change of ammonia decomposition rate of Ni-Ce / SiO2 (Example 1) over time.

[0031] Figure 4 (a) and Figure 4 (b) The graphs show the changes in ammonia decomposition rate and H2 energy yield as a function of power for each catalyst in Examples 1-4 and Comparative Example 1, respectively.

[0032] Figure 5 (a) and Figure 5 (b) shows the XRD pattern and N2 adsorption-desorption isotherm of the catalyst in Example 5.

[0033] Figure 6 (a) and Figure 6 (b) Transmission electron micrographs of SiO2 and SiO2@TiO2, respectively; Figure 6 (cd) are transmission electron microscopy images of Ni-Ce / SiO2@TiO2 (Example 5); Figure 6 (ei) are energy spectra of Ni-Ce / SiO2@TiO2 (Example 5).

[0034] Figure 7 (ab) are graphs showing the changes in ammonia decomposition rate and H2 energy yield of Ni-Ce / SiO2@TiO2 (Example 5) with power.

[0035] Figure 8 This is a SEM image of Ni-Ce / SiO2@TiO2 prepared in Example 5. Figure 8 (a) and Figure 8 (b) are SEM images before and after the catalytic reaction.

[0036] Figure 9 Line graph showing the test data for the catalytic stability of Ni-Ce / SiO2@TiO2 prepared in Example 5. Detailed Implementation

[0037] The following provides a more detailed description of this application in conjunction with specific details.

[0038] raw material All raw materials used in the embodiments of this application are commercially available products with analytical purity. The manufacturer of the fumed silica is Dalian Zhuoran Environmental Protection Technology Co., Ltd. Example

[0039] Example 1 A plasma-assisted Ce-modified Ni-based catalyst for hydrogen production from ammonia decomposition is prepared as follows: S1. First, dissolve 4.26g of nickel acetate and 0.082g of cerium nitrate in 70mL of deionized water. After they are completely dissolved, add 8.75g of gaseous SiO2 and stir for 30min to obtain a mixed solution. Then, heat the mixed solution in a magnetic stirrer at 80℃ until it evaporates to dryness. Then, place it in a drying oven at 100℃ and dry for 12h to obtain a dry powder. S2. The dried powder was calcined in a muffle furnace at 550℃ for 6 hours, then pressed into tablets, ground, and sieved to 50 mesh to obtain the Ce-modified Ni-based catalyst precursor. The Ce-modified Ni-based catalyst precursor was placed in a tube furnace and refluxed at 550℃ with a 10 vol.% H2 / Ar mixed gas flow at 100 mL·min. -1 The flow rate was reduced for 2 hours to obtain a Ce-modified Ni-based catalyst with a nickel loading of 10.0 wt.% and a cerium loading of 2.5 wt.%, denoted as Ni-Ce / SiO2 (Ni-2.5Ce / SiO2).

[0040] Example 2 A plasma-assisted Ce-modified Ni-based catalyst for hydrogen production from ammonia decomposition differs from Example 1 in that the amounts of nickel acetate and cerium nitrate added are adjusted to obtain a Ce-modified Ni-based catalyst with a nickel loading of 10.0 wt.% and a cerium loading of 5.0 wt.%, denoted as Ni-5.0Ce / SiO2. The remaining steps are the same as in Example 1.

[0041] Example 3 A plasma-assisted Ce-modified Ni-based catalyst for hydrogen production from ammonia decomposition differs from Example 1 in that the amounts of nickel acetate and cerium nitrate added are adjusted to obtain a Ce-modified Ni-based catalyst with a nickel loading of 10.0 wt.% and a cerium loading of 7.5 wt.%, denoted as Ni-7.5Ce / SiO2. The remaining steps are the same as in Example 1.

[0042] Example 4 A plasma-assisted Ce-modified Ni-based catalyst for ammonia decomposition to hydrogen production differs from Example 1 in that the amounts of nickel acetate and cerium nitrate added are adjusted to obtain a Ce-modified Ni-based catalyst with a nickel loading of 10.0 wt.% and a cerium loading of 10.0 wt.%, denoted as Ni-10.0Ce / SiO2. The remaining steps are the same as in Example 1.

[0043] Example 5 A plasma-assisted Ce-modified Ni-based catalyst for ammonia decomposition to hydrogen production differs from Example 2 in that the prepared Ni-5Ce / SiO2 is coated with titanium dioxide. The preparation method is the same as in Example 2 except for step S2, which is as follows: The dried powder was calcined in a muffle furnace at 400℃ for 2 hours, then dispersed in 100 mL of anhydrous ethanol. 25% ammonium hydroxide was added to adjust the pH to 9.5. 2.0 g of tetrabutyl titanate was added dropwise under stirring. After centrifugation, washing, and drying, the mixture was calcined in air at 450℃ for 1 hour to obtain the Ni-5Ce / SiO2@TiO2 precursor. This precursor was then placed in a tube furnace and calcined at 550℃ at 100 mL / min using a 10 vol.% H2 / Ar mixed gas stream. -1 The catalyst was obtained by reducing it at a flow rate of 100% for 2 hours, and it was denoted as Ni-Ce / SiO2@TiO2.

[0044] Example 6 A plasma-coordinated Ce-modified Ni-based catalyst for hydrogen production from ammonia decomposition differs from Example 5 in that 0.8 g of PVP K30 is added to anhydrous ethanol before pH adjustment. The remaining steps are the same as in Example 5. The resulting catalyst is denoted as Ni-Ce / SiO2@TiO2-1.

[0045] Comparative Example Comparative Example 1 A plasma-coordinated Ni-based catalyst for hydrogen production from ammonia decomposition differs from Example 1 in that cerium nitrate is not added in S1, i.e., Ce modification is not performed on the catalyst. The remaining steps are the same as in Example 1, and the resulting catalyst is denoted as Ni / SiO2.

[0046] Comparative Example 2 A plasma-coordinated zirconium-modified Ni-based catalyst for ammonia decomposition to produce hydrogen differs from Example 1 in that, in S1, cerium nitrate is replaced with zirconium nitrate pentahydrate, and its dosage is adjusted so that the zirconium loading in the final catalyst is the same as that of Ce. The remaining steps are the same as in Example 1. The resulting catalyst is denoted as Ni-Zr / SiO2.

[0047] Comparative Example 3 A plasma-assisted magnesium-modified Ni-based catalyst for hydrogen production from ammonia decomposition differs from Example 1 in that, in S1, cerium nitrate is replaced with magnesium nitrate hexahydrate, and its dosage is adjusted so that the magnesium loading in the final catalyst is the same as that of Ce. The remaining steps are the same as in Example 1. The resulting catalyst is denoted as Ni-Mg / SiO2.

[0048] Comparative Example 4 A plasma-assisted lanthanum-modified Ni-based catalyst for hydrogen production from ammonia decomposition differs from Example 1 in that, in S1, cerium nitrate is replaced with lanthanum nitrate hexahydrate, and its dosage is adjusted so that the lanthanum loading in the final catalyst is the same as that of Ce. The remaining steps are the same as in Example 1. The resulting catalyst is denoted as Ni-La / SiO2.

[0049] Comparative Example 5 A plasma-assisted Ce-modified Ni-based catalyst for hydrogen production from ammonia decomposition differs from Example 5 in that Ni-5Ce / SiO2 is replaced with fumed silica, while the remaining steps are the same as in Example 5.

[0050] Performance testing Detection methods / test methods Catalysts were prepared according to the preparation methods of Examples 1-6 and Comparative Examples 1-5, and then tested according to the following detection methods. The detection results are shown below.

[0051] I. Detection Methods 1. X-ray diffraction: X-ray diffraction (XRD) was performed using a D / max-2000 instrument manufactured by Rikagu Corporation, Japan, equipped with a Cu-Kα X-ray source. Experimental conditions were set as follows: scanning range 5-90°, scanning step size 0.02°, and scanning rate 10°·min. -1 .

[0052] N2 Physical Adsorption-Desorption: The N2 physical adsorption-desorption (N2-BET) of the catalyst was tested using a TriStar II 3020 instrument manufactured by Micromeritics, USA. Prior to the test, the catalyst was degassed at 250°C for 3 hours to remove surface-adsorbed impurities. Subsequently, the catalyst was subjected to N2 physical adsorption-desorption at -196°C. 2 Adsorption-desorption experiments. The specific surface area, pore volume, and pore size of the catalyst were calculated using the Brunauer-Emmett-Teller (BET) method and the Barrett-Joyner-Halenda (BJH) method, respectively.

[0053] X-ray photoelectron spectroscopy: X-ray electron spectroscopy (XPS) was performed using an ESCALAB 250Xi instrument manufactured by Thermo Fisher Scientific, USA, equipped with an Al-Kα X-ray source.

[0054] Fourier Transform Infrared Spectroscopy: The infrared spectrum of the catalyst was tested using a Bruker Tensor 27 Fourier Transform Infrared Spectrometer. KBr and the sample were mixed and pressed into a pellet at a mass ratio of 100:1. The instrument resolution was 2 cm⁻¹. -1 The scanning range is 400-4000cm. -1 .

[0055] 2. Evaluation of the performance of plasma-assisted catalytic ammonia decomposition The ammonia decomposition performance is calculated using the following formula:

[0056] Formula 1 In Equation 1, C NH3,in and C NH3,out These figures represent the ammonia concentrations measured by gas chromatograph before and after the reaction. These values ​​are the average of three consecutive measurements taken after the reaction reached a stable state.

[0057] The discharge power is calculated using the following formula:

[0058] Formula 2 In the formula, f It is the discharge frequency input to the plasma power supply, C ext A is the fixed capacitance of the plasma power supply, which is 0.47 μF, and A is the area of ​​the Lissajous diagram.

[0059] The H2 energy yield of the DBD plasma reactor is calculated using the following formula:

[0060] Formula 3 In the formula, C NH3 F represents the ammonia concentration. NH3 The ammonia gas flow rate is expressed in mL·min. -1 m c The value represents the mass of the catalyst, expressed in grams (g).

[0061] II. Test Results 1. Detection of the advantages of Ce-modified Ni-based catalysts Table 1. Catalyst structural parameters of Example 1 and Comparative Examples 1-4

[0062] Combination Figure 1 In the XRD patterns of (a), the broad peaks around 21.92° for all catalysts correspond to amorphous SiO2. All samples exhibit sharp diffraction peaks at 44.51°, 51.85°, and 76.37°, corresponding to the (1 1 1), (20 0), and (2 2 0) crystal planes of Ni, indicating that each catalyst exists as a metallic element on the catalyst surface after H2 reduction. The intensity of the metallic diffraction peaks in Ni-Ce / SiO2, Ni-La / SiO2, and Ni-Mg / SiO2 is lower than that in Ni / SiO2, suggesting that the doping of Ce, La, and Mg may lead to smaller Ni particle sizes. Referring to Table 1, the Ni grain size calculated using the Scherrer equation based on the Ni (1 1 1) diffraction peak at a diffraction angle of 44.51° shows that the Ni-Mg / SiO2 catalyst has the smallest Ni grain size, at only 10.4 nm; followed by the Ni-Ce / SiO2 catalyst with a Ni grain size of 11.9 nm; the Ni-La / SiO2 catalyst also has a relatively small Ni grain size; while the Ni-Zr / SiO2 catalyst has the largest Ni grain size, reaching 16.4 nm, even larger than that of Ni / SiO2. This demonstrates that the doping of Ce, La, and Mg metal additives can effectively suppress the migration and aggregation of active metal Ni nanoparticles during the high-temperature reduction process, thereby achieving efficient dispersion of Ni particles.

[0063] Combining Table 1 and Figure 1 (b) The N2 adsorption-desorption isotherms of all catalysts exhibited Type IV characteristics and H3-type hysteresis loops, indicating that all catalysts possess wide-mouth slit-like pores. Obvious hysteresis loops were observed within the relative pressure range of p / p0 = 0.9-1.0, indicating the presence of mesoporous structures in the catalysts. It can be seen that the specific surface area of ​​the catalysts decreased slightly after metal loading. This may be attributed to the active metal Ni and the promoter components entering the pores of the SiO2 support during impregnation, partially occupying the pore space and blocking a small number of micropores, resulting in a slight decrease in the specific surface area of ​​the support. The decrease in specific surface area of ​​Ni-La / SiO2 was more significant, which, combined with the increase in its pore volume and average pore size, may be due to the collapse of some micropores and mesopores during the preparation process. Overall, although different promoter doping has a slight impact on the pore structure parameters of the catalysts, there are no significant differences in the BET specific surface area, pore volume, and average pore size of Ni / SiO2 and each modified catalyst. This indicates that the doping of the additives did not cause drastic damage to the pore structure of the SiO2 support. The support can still maintain a stable mesoporous structure, which can provide a good structural basis for the dispersion of active metals and the adsorption and diffusion of reaction substrates.

[0064] Figure 2The TEM results show that the calculated Ni particle sizes for Ni / SiO2, Ni-Ce / SiO2, Ni-La / SiO2, Ni-Mg / SiO2, and Ni-Zr / SiO2 are 13.0 nm, 11.2 nm, 12.6 nm, 9.5 nm, and 15.6 nm, respectively, which are basically consistent with the XRD results. Figure 2 (f) shows a crystal plane spacing of 0.203 nm, combined with Figure 2 (g) and XRD results show that it corresponds to the (11 1) crystal plane of Ni. Figure 2 As shown in (a), EDS analysis shows that Ce is highly dispersed on the SiO2 surface and highly overlaps with the distribution of Ni.

[0065] Figure 3 : combination Figure 3 (a) and Figure 3 (b) Within a power range of 4-20W, the gas flow rate of 100 mL / min was compared. -1 The ammonia decomposition performance of different catalysts was evaluated. With increasing discharge power, the decomposition rates of unfilled, SiO2-filled, and all-supported metal catalysts all increased rapidly. The ammonia decomposition rate in both unfilled and SiO2-filled catalysts slowed significantly after 8 W with increasing discharge power, ultimately achieving 45% and 55% ammonia decomposition rates, respectively, at 20 W. At 20 W, the ammonia decomposition rate of Ni / SiO2-filled catalysts increased to 72%, further improved by doping with Ce, La, and Zr, while decreasing by 4% with Mg doping. Ni-Ce / SiO2 exhibited the highest ammonia decomposition rate, reaching 88%. Except for the unfilled case, the H2 energy yield of all catalysts decreased with increasing discharge power. Ni-Ce / SiO2 consistently maintained the highest H2 energy yield. Figure 3 As shown in (c), the ammonia decomposition rate was observed to decrease with increasing gas flow rate for all catalysts, which may be due to the shorter residence time of ammonia molecules at the active sites. Traditional thermocatalysis generally suffers from catalyst deactivation after prolonged high-temperature reactions; in contrast, plasma catalysis exhibits superior stability due to its milder reaction conditions. Figure 3 As shown in (d), the ammonia decomposition rate was hardly reduced when using Ni-Ce / SiO2, which is attributed to the mild reaction temperature.

[0066] 2. Detection of different doping ratios of metallic Ce Table 2 Structural parameters of each catalyst in Examples 1-4

[0067] Table 2 shows that the Ni grain size gradually decreases with increasing Ce loading, with the smallest Ni grain size (4.4 nm) observed on Ni-10.0Ce / SiO2. This indicates that Ce loading effectively prevents Ni particle aggregation during the preparation process. The BET specific surface area of ​​the catalyst gradually decreases with increasing Ce loading ratio, from 151.6 m²·g for Ni-2.5Ce / SiO2. -1 Reduced to 142.3 m²·g for Ni-10.0Ce / SiO₂. -1 This may be due to the excessive Ce entering and blocking some of the pores of the SiO2 support during the preparation process. At the same time, the pore volume and average pore size of the catalyst only fluctuated slightly, and all samples showed typical type IV N2 adsorption-desorption isotherms and type H3 hysteresis loops. This feature fully demonstrates that within the Ce loading range of this study, the catalyst as a whole maintained a good and stable mesoporous structure, and the pore configuration of the support was not significantly damaged or collapsed due to changes in Ce loading.

[0068] Combination Figure 4 Within the plasma discharge power range of 4-20W, the ammonia decomposition rates under Ni-Ce / SiO2 catalysts with different Ce doping ratios, pure SiO2 supports, and pure plasma conditions are as follows: Figure 4 As shown in (a), the ammonia decomposition rate of all systems showed a continuous upward trend with increasing plasma discharge power. Among them, the Ni-5Ce / SiO2 catalyst exhibited the best ammonia decomposition activity (93%), followed by Ni-2.5Ce / SiO2, Ni-7.5Ce / SiO2, Ni / SiO2, Ni-10Ce / SiO2, and SiO2. The pure plasma system had the lowest ammonia decomposition rate. Compared with undoped Ni / SiO2, the introduction of appropriate amounts of Ce (2.5 wt.%, 5 wt.%) significantly improved the ammonia decomposition activity of the catalyst, while the introduction of excessive Ce (7.5 wt.%, 10 wt.%) failed to further improve the performance, and the ammonia decomposition rate was even lower than that of Ni / SiO2 when the Ce loading was 10 wt.%.

[0069] like Figure 4 As shown in (b), except under pure plasma conditions, the H2 energy yield under different filling conditions all showed a decreasing trend with increasing discharge power, with the highest H2 energy yield obtained when filling Ni-5Ce / SiO2 catalyst.

[0070] 3. Detection of TiO2-coated Ce-modified Ni-based catalysts Figure 5(a) In the XRD pattern, the pure SiO2 support exhibits broadened diffuse diffraction peaks in the range of 10°-30° at 2θ, indicating that it has an amorphous (non-crystalline) structure and no obvious sharp diffraction peaks. After coating with TiO2, SiO2@TiO2 shows clear characteristic diffraction peaks at approximately 25.3°, 37.8°, 48.1°, 53.9°, 55.1°, 62.7°, and 68.9° at 2θ, which are completely consistent with the characteristic peaks of the standard card anatase TiO (2PDF#44-1159), indicating that the crystalline phase of TiO2 in SiO2@TiO2 transforms from amorphous to anatase after calcination and has strong crystallinity. After loading the Ni-Ce active component, the diffraction peak intensity of Ni-Ce / SiO2@TiO2 was significantly enhanced, and characteristic peaks corresponding to NiO (PDF#21-1272) appeared at approximately 35.3°, 43.3°, and 62.9° of 2θ, indicating that Ni species mainly exist in the form of NiO crystalline phase.

[0071] Table 3 Catalyst structural parameters of Example 5 and Comparative Example 5

[0072] Figure 5 (b) N2 adsorption-desorption isotherms for each catalyst. According to the IUPAC classification, all samples exhibited Type IV isotherms, and a significant hysteresis loop appeared in the medium-to-high relative pressure region (p / p0 = 0.4–1.0), indicating that the catalysts all possessed typical mesoporous structures, consistent with the structural parameter results in Table 3. In Table 3, pure SiO2 had the largest specific surface area, at 60.1 m²·g. -1 In Comparative Example 5, after coating with TiO2, the specific surface area decreased slightly to 52.4 m2·g. -1 This may be because TiO2 partially blocks the micropores and mesopores of SiO2, leading to a decrease in specific surface area. After loading the Ni-Ce active component, the specific surface area of ​​Ni-Ce / SiO2@TiO2 further decreased to 47.3 μm. 2 / g, pore volume also increased from 0.133cm 3 / g decreased to 0.095cm 3 / g. Although the specific surface area and pore volume decreased, the overall decrease was not significant.

[0073] Figure 6 Transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) results visually revealed the microstructure and elemental distribution of the catalyst. For example... Figure 6 As shown in (a), pure SiO2 exhibits a regular spherical morphology with good monodispersity. Figure 6 As shown in (b), after coating with TiO2, the particle surface becomes rough, forming a typical SiO2@TiO2 core-shell structure. Figure 6As shown in (cd), after loading the Ni-Ce active component, the overall morphology of the catalyst remained intact, and no severe particle agglomeration occurred. Figure 6 As shown in (ei), EDS further confirmed that the distribution areas of Ni and Ce elements highly overlap with those of Si, Ti, and O elements, indicating that the Ni-Ce active component was successfully loaded and well dispersed.

[0074] Table 4 Ammonia decomposition rate at 20W with different catalysts

[0075] Combine Table 4 and Figure 7 (a) It can be seen that the ammonia decomposition rate of the catalysts in Examples 2 and 5-6 continuously increases with increasing power. Figure 7 (a) Ni-Ce / SiO2@TiO2 exhibited the best ammonia decomposition activity, achieving an ammonia decomposition rate of 98% at 20W, approaching complete conversion. This was significantly better than SiO2@TiO2 (74%), pure SiO2 (55%), and empty tube (45%), and showed a slight improvement over Ni-5.0Ce / SiO2. This confirms that the synergistic effect of TiO2 coating and Ni-Ce active components can effectively improve ammonia decomposition efficiency. Based on Examples 5-6, it is speculated that under the action of PVP, the titanium dioxide shell structure can be more continuous and uniform, preventing localized thick shells and excessive free titanium dioxide powder.

[0076] Figure 7 (b) The H2 energy yield results show that, except for empty tubes, the energy yield gradually decreases with increasing power in all filled cases. Among them, Ni-Ce / SiO2@TiO2 maintains the highest energy yield in the entire power range, achieving dual optimization of high ammonia decomposition rate and high energy utilization efficiency.

[0077] pass Figure 8 It can be seen that the Ni-Ce / SiO2@TiO2 prepared in Example 5 showed no significant change in morphology before and after the plasma catalytic reaction, indicating that it has good stability.

[0078] pass Figure 9 It can be seen that the ammonia decomposition rate of Ni-Ce / SiO2@TiO2 prepared using Example 5 hardly decreased over time, indicating that it has good stability.

[0079] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A method for preparing a plasma-assisted Ce-modified Ni-based catalyst for hydrogen production from ammonia decomposition, characterized in that: It includes the following steps: S1. Dissolve nickel salt and cerium salt in deionized water, then add gaseous SiO2, stir and mix, then stir and evaporate to dryness at 60-95℃, and then dry to obtain dry powder. S2. The dried powder is calcined at 450-580℃ for 3-8 hours to obtain a Ce-modified Ni-based catalyst precursor, which is then reduced to obtain the Ce-modified Ni-based catalyst.

2. The preparation method of a plasma-assisted Ce-modified Ni-based catalyst for ammonia decomposition to hydrogen production according to claim 1, characterized in that: In the Ce-modified Ni-based catalyst, the Ni loading is 6-15 wt.% and the Ce loading is 2.5-10 wt.%.

3. The method for preparing a plasma-assisted Ce-modified Ni-based catalyst for ammonia decomposition to hydrogen production according to claim 2, characterized in that: The Ce loading is 2.5-5 wt.%.

4. The method for preparing a plasma-assisted Ce-modified Ni-based catalyst for ammonia decomposition to hydrogen production according to claim 1, characterized in that: The reduction method of the Ce-modified Ni-based catalyst precursor is as follows: The Ce-modified Ni-based catalyst precursor was placed in a tube furnace and incubated at 480-580°C with a 5-15 vol.% H2 / Ar mixed gas flow at a rate of 50-200 mL·min. -1 The reduction was carried out at a flow rate of 1-5 hours.

5. The method for preparing a plasma-assisted Ce-modified Ni-based catalyst for ammonia decomposition to hydrogen production according to claim 1, characterized in that: In S2, the surface of the Ce-modified Ni-based catalyst precursor is also coated with titanium dioxide.

6. The method for preparing a plasma-assisted Ce-modified Ni-based catalyst for ammonia decomposition to hydrogen production according to claim 5, characterized in that: The content of S2 includes the following: The dried powder obtained from S1 was calcined in a muffle furnace at 400-580℃ for 2 hours, then dispersed in ethanol, the pH was adjusted to 9-10.5, tetrabutyl titanate was added dropwise under stirring, and after centrifugation, washing and drying, it was calcined in air at 420-550℃ for 1 hour to obtain a Ce-modified Ni-based catalyst precursor with titanium dioxide coated on the surface, and then the Ce-modified Ni-based catalyst was obtained by reduction.

7. The method for preparing a plasma-assisted Ce-modified Ni-based catalyst for ammonia decomposition to hydrogen production according to claim 6, characterized in that: The mass ratio of the tetrabutyl titanate to the fumed silica is (0.001-4):(7-10).

8. The method for preparing a plasma-assisted Ce-modified Ni-based catalyst for ammonia decomposition to hydrogen production according to claim 6, characterized in that: In step S2, before adjusting the pH, polyvinylpyrrolidone is added to the ethanol, and the mass ratio of the amount of polyvinylpyrrolidone added to the tetrabutyl titanate is (0.001-1.5):(0.001-4).

9. The method for preparing a plasma-assisted Ce-modified Ni-based catalyst for ammonia decomposition to hydrogen production according to claim 8, characterized in that: The average molecular weight of the polyvinylpyrrolidone is 3500-50000 Da.

10. A plasma-assisted Ce-modified Ni-based catalyst for hydrogen production from ammonia decomposition, characterized in that: It is prepared by the method for preparing a plasma-assisted Ce-modified Ni-based catalyst for hydrogen production from ammonia decomposition according to any one of claims 1-9.

Images