A multi-transition metal phosphide catalyst for methane dry reforming and a preparation method and application thereof

Abstract

The application belongs to the technical field of preparation of plasma methane dry reforming catalysts, and relates to a multi-transition metal phosphide catalyst for methane dry reforming, a preparation method of the catalyst, and application of the catalyst in catalyzing methane dry reforming reaction in cooperation with plasma. The multi-transition metal phosphide catalyst provided by the application has high catalytic activity, excellent carbon deposition resistance and long-term stability, and comprises a foamed nickel substrate and a multi-transition metal phosphide active layer arranged on the surface of the foamed nickel substrate. The active layer at least contains nickel, iron, vanadium and phosphorus elements, and the nickel, iron and vanadium exist in the form of phosphide. The application improves the problems of insufficient activity, poor carbon deposition resistance and poor long-term stability of the catalyst for methane dry reforming in the prior art, can significantly improve the conversion rate of CO2 and CH4 and the syngas yield, and improves the energy utilization efficiency. Moreover, the preparation method is simple and convenient for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of preparation technology of plasma methane dry reforming catalysts. Specifically, it relates to a multi-component transition metal phosphide catalyst for methane dry reforming, its preparation method, and the application of the catalyst in synergistic plasma-catalyzed methane dry reforming reaction. Background Technology

[0002] In recent years, the continuous and massive emissions of greenhouse gases such as carbon dioxide (CO2) and methane (CH4) have exacerbated global warming and triggered an imbalance in the carbon cycle. Therefore, developing green, efficient, and sustainable greenhouse gas resource utilization technologies has become an important research direction in the energy and environment fields. Currently, greenhouse gas conversion technologies mainly include various pathways such as carbon capture and storage (CCS), photocatalytic / electrocatalytic reduction, microbial conversion, thermocatalytic conversion, and plasma catalytic conversion. Among these technologies, dry reforming of methane (DRM) can simultaneously convert CO2 and CH4 into syngas (CO + H2) with industrial application value, showing broad application prospects in energy and chemical fields such as synthetic fuels, methanol, and Fischer-Tropsch synthesis. However, the dry reforming of methane is a strongly endothermic reaction. As shown in Eq. (1), the C=O and C–H bonds in the CO2 and CH4 molecules in this reaction have high bond energies. Traditional thermocatalytic DRM processes usually need to be operated at temperatures above 700°C to obtain high reaction conversion rates and syngas yields. High-temperature operation not only significantly increases energy consumption and reduces energy utilization efficiency, but also triggers a series of side reactions. For example, the methane cracking reaction shown in Eq. (2) and the Boudouard reaction shown in Eq. (3) will form carbon deposits on the catalyst surface, leading to the covering of active sites, structural sintering, and deactivation, which seriously restricts the stability and industrial application of DRM technology. Carbon dioxide can react with activated carbon to regenerate carbon monoxide, as shown in Eq. (4). This reaction is crucial for effectively solving the carbon deposition problem in the DRM conversion process.

[0003] (1) (2) (3) (4) To overcome the dependence of traditional thermocatalytic DRM processes on high-temperature conditions, non-thermal plasma (NTP) catalysis technology has gradually attracted attention in recent years. With its characteristics of room temperature discharge, high excitation particle energy and strong reaction selectivity, it provides a new way to break through the temperature barrier of traditional thermocatalysis and improve the efficiency of DRM reaction.

[0004] Meanwhile, transition metal phosphides, due to their unique metal-phosphorus synergistic electronic structure and high conductivity, have shown good application potential in various catalytic reactions. Currently, in the research on plasma-co-catalyzed methane dry reforming, the status of conventionally used nickel-based catalysts is as follows: Kristy et al. used a hydrothermal method to load dendritic Ni nanoparticles with highly exposed (111) crystal planes as the core catalyst onto a self-supporting porous γ-Al2O3 matrix, enhancing CO2 adsorption and plasma discharge, thus achieving an excellent CO2 conversion rate of 43%, exceeding the 16% and 23% of empty tubes and pure γ-Al2O3, respectively; Furthermore, Shao's group designed a layered nickel silicate based on Zr-MCM-41. Using Ni-PS salt catalysts as DBD filling media, CO2 / CH4 conversion efficiencies reached 75.5% and 69.9%, respectively, significantly exceeding those of unsupported catalysts and the previously reported Ni-MCM-41. Zheng's group also proposed a self-supporting DRM catalyst, which improved CO2 / CH4 conversion to 52.31% / 71.50% by distributing bimetallic Co / Ni-MOFs on 3D bacterial cellulose foam. This improvement was mainly attributed to the abundant mesoporous and macroporous structures on the catalyst surface and the enhanced basic active sites.

[0005] However, existing research reports on the application of multi-element transition metal phosphide catalysts in non-thermal plasma-assisted dry reforming of methane are relatively limited, especially regarding the structural regulation of multi-metal synergistic phosphating, the plasma-catalyst interface coupling mechanism, and the achievement of efficient and stable DRM reactions under lower temperature and energy consumption conditions. Specifically, existing catalytic systems for methane dry reforming mainly suffer from the following technical problems: First, there is the problem of limited catalyst structure. Traditional packed catalysts are mostly in the form of particles or powders. Particle catalysts tend to reduce the discharge gap in plasma reactors, which hinders the diffusion and transport of reactant gases and reduces the effective exposed area of ​​the catalyst, thus limiting the efficiency of methane dry reforming reaction. Powdered catalysts are prone to agglomeration and diffuse to both ends of the reactor under the action of plasma, resulting in the loss of active sites and the degradation of catalytic performance.

[0006] Secondly, there is a lack of application of multi-component phosphide catalysts. Although transition metal phosphides exhibit good catalytic activity and stability in thermocatalysis and electrocatalysis, their application in non-thermal plasma synergistic catalysis of methane dry reforming is still relatively scarce. In particular, there is a lack of systematic research on the synergistic mechanism of binary or multi-component transition metal phosphides, and a mature and stable catalyst system has not yet been formed.

[0007] Third, there is the problem of insufficient catalytic activity and long-term stability. Existing methane dry reforming catalysts generally face problems such as limited catalytic activity, insufficient resistance to coking, and poor stability under long-term operating conditions, making it difficult to meet the comprehensive requirements of high conversion rate, low energy consumption, and long-term stable operation in practical applications.

[0008] Therefore, there is an urgent need to develop a multi-component transition metal phosphide catalyst with a reasonable structure, excellent activity, strong anti-coking ability, and suitability for non-thermal plasma conditions, and to construct a matching preparation method and application system to overcome the problems of high energy consumption, severe coking, and insufficient stability in the existing technology, thereby promoting the development of methane dry reforming reaction in the direction of high efficiency and low energy consumption. Summary of the Invention

[0009] The purpose of this invention is to provide a multi-component transition metal phosphide catalyst for methane dry reforming, its preparation method, and its application, to solve the problems of insufficient activity, poor resistance to coking, and poor long-term stability of existing catalysts. The multi-component transition metal phosphide catalyst V-NiFeP@NF provided by this invention has high catalytic activity, excellent resistance to coking, and long-term stability. It is suitable for methane dry reforming under non-thermal plasma conditions, significantly improving the conversion rates of CO2 and CH4 and the syngas yield, and improving energy utilization efficiency. Furthermore, the preparation method is simple and convenient for industrial production.

[0010] The technical solution of the present invention is as follows: A multi-component transition metal phosphide catalyst for dry reforming of methane, the catalyst comprising a nickel foam substrate and a multi-component transition metal phosphide active layer disposed on the surface of the nickel foam substrate (abbreviated as NF), the multi-component transition metal phosphide active layer comprising at least nickel, iron, vanadium and phosphorus, wherein nickel, iron and vanadium exist in phosphated form.

[0011] Furthermore, the multi-element transition metal phosphide active layer is formed in situ on the surface of the foamed nickel substrate, and the multi-element transition metal phosphide active layer includes a Ni-Fe-P phosphide phase, and vanadium is introduced to form a multi-metal synergistic phosphating structure.

[0012] Furthermore, in the multi-element transition metal phosphide active layer, the molar ratio of nickel, iron, vanadium, and phosphorus is: Ni: Fe: V: P = (0.5~2.5): (0.05~0.50): (0.05~0.50): (1~4).

[0013] Furthermore, the multi-component transition metal phosphide active layer has a nanoflower-like structure.

[0014] Furthermore, the present invention also provides the use of the multi-component transition metal phosphide catalyst for methane dry reforming as described above in the methane dry reforming reaction.

[0015] Furthermore, the methane dry reforming reaction is carried out under non-thermal plasma conditions (room temperature, atmospheric pressure).

[0016] Preferably, the non-thermal plasma is a dielectric barrier discharge plasma.

[0017] Because in nonthermal plasma NTP systems, the electron temperature can reach as high as 10°C. 4 ~10 5 K, high-energy electrons can excite reactant gas molecules to generate highly reactive substances such as free radicals, ions, and various excited-state particles, while the overall reaction system temperature can be maintained at a relatively low level. This allows for the activation and transformation of reactants at lower temperatures, thus helping to alleviate carbon buildup and energy consumption problems. Dielectric barrier discharge (DBD), a typical form of non-thermal plasma, is characterized by two parallel electrodes, at least one of which is coated with a dielectric material. This configuration is designed to restrict charge movement and achieve uniform distribution within the discharge region. It reduces the operating voltage and enhances the electric field discharge of gas molecule interactions. It offers advantages such as easy installation, uniform discharge, a wide range of active substances, and convenient synergy with catalysts, making it a preferred choice for methane dry reforming processes.

[0018] Furthermore, the present invention also provides a method for preparing the multi-component transition metal phosphide catalyst for dry reforming of methane as described above, comprising the following steps: (1) Dissolve the nickel source, iron source, vanadium source and precipitant in a solvent to obtain a metal precursor solution; (2) After the nickel foam substrate is acid-washed to remove its surface oxide layer, the nickel foam substrate and the metal precursor solution are placed together in a closed reaction vessel and reacted under heating and pressure conditions to allow the nickel, iron and vanadium-containing precursors to grow in situ on the surface of the nickel foam substrate to obtain the precursor material. (3) The precursor material and the phosphorus source are placed in a reactor and phosphating is performed under an inert atmosphere. The phosphorus source is decomposed and released under heating conditions to convert the precursor material into a multi-component transition metal phosphide active layer, thereby obtaining the multi-component transition metal phosphide catalyst V-NiFeP@NF for methane dry reforming.

[0019] Furthermore, the nickel source is selected from nickel nitrate or its hydrate; The iron source is selected from ferric nitrate or its hydrate; The vanadium source is selected from vanadium chloride or its hydrate; The precipitant is urea; The phosphorus source is a hypophosphite compound.

[0020] Preferably, the hypophosphite compound is NaH2PO2.

[0021] Furthermore, the reaction temperature of the heating conditions in step (2) is 100~150℃, and the reaction time is 6~24 hours; The phosphating treatment is carried out under an inert atmosphere, at a temperature of 300~400℃, and for a holding time of 1~4 hours.

[0022] Furthermore, the phosphating process involves heating at a rate of 1~5℃ / min.

[0023] Currently, catalysts used in methane dry reforming face problems such as insufficient activity, poor resistance to coking, and poor long-term stability. To address these issues, this invention successfully prepared a multi-component transition metal phosphide catalyst, V-NiFeP@NF, supported on nickel foam for methane dry reforming via a hydrothermal-phosphating method. This catalyst effectively improves the conversion rates of CO2 and CH4, and enhances its resistance to coking and long-term stability. Specifically, this invention uses nickel foam as the supporting material, leveraging its excellent supporting effect to provide a stable framework for the catalyst. Simultaneously, the synergistic effect between the multi-component transition metal phosphides (V-NiFeP) enhances the catalytic performance. The V-NiFeP active layer of the methane dry reforming multi-component transition metal phosphide catalyst V-NiFeP@NF of this invention exhibits a nanoflower-like structure. This structure significantly increases the exposed area of ​​the catalyst, enabling it to demonstrate excellent activity during plasma catalysis, achieving CO2 and CH4 conversion rates of 40.9% and 56.6%, respectively. Furthermore, in this invention, the doping of vanadium V effectively increases the alkaline adsorption sites on the catalyst surface, promoting CO2 adsorption and carbon deposition gasification, thereby improving the catalyst's resistance to carbon deposition. The V-NiFeP@NF catalyst of this invention exhibits excellent catalytic performance, good long-term stability, and strong resistance to carbon deposition in the DRM reaction. It can provide a theoretical basis and practical guidance for the design of high-performance catalysts in plasma catalysis systems, and has significant application value for the development of green and low-carbon energy technologies.

[0024] like Figure 13 The mechanism diagram of the synergistic catalytic reaction of methane dry reforming by low-temperature plasma and V-NiFeP@NF catalyst of this invention is shown. Methane molecules and carbon dioxide molecules are synergistically converted into H2, CO and C by the V-NiFeP@NF catalyst and plasma of this invention. x H y One benefit is the layered nanostructure of the V-NiFeP@NF catalyst material, which facilitates mass transfer and diffusion of gas molecules, promoting the catalytic reaction. Another benefit is the abundant moderately alkaline sites and appropriate CO2 adsorption and desorption capacity, which directs the catalytic reaction towards CO production while reducing carbon deposition, potentially improving the long-term stability of the catalyst.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The multi-component transition metal phosphide catalyst for dry reforming of methane provided by the present invention uses nickel foam as a support substrate and constructs a multi-component transition metal phosphide active layer on its surface, so that the catalyst forms a self-supporting three-dimensional structure, which effectively avoids the problems of limited discharge gap, obstructed gas diffusion and easy agglomeration of active components in traditional particulate or powder catalysts. At the same time, by introducing vanadium into the Ni-Fe-P phosphide system, a multi-metal synergistic phosphating structure is formed, which significantly regulates the electronic structure and surface alkaline site distribution of the catalyst, thereby enhancing the activation ability of CO2 and CH4, improving the catalytic reaction activity, effectively inhibiting the formation of coke, and improving the anti-coking performance and long-term stability of the catalyst.

[0026] (2) This invention employs a preparation method combining hydrothermal reaction and gas-phase phosphating, enabling nickel, iron, and vanadium-containing precursors to grow in situ on the surface of a nickel foam substrate and uniformly transform into a multi-component transition metal phosphide active layer during subsequent phosphating treatment. This preparation method has a simple process flow and good repeatability, providing a good and stable loading space for the active components. This is beneficial for obtaining a catalyst with stable structure, uniform composition, and strong bonding with the substrate, thus providing a reliable guarantee for the efficient operation and long-term stable use of the catalyst in the dry reforming reaction of methane.

[0027] (3) When the multi-component transition metal phosphide catalyst described in this invention is used for methane dry reforming under non-thermal plasma conditions, it can enhance the activation efficiency of reactant molecules in the plasma discharge region and improve the interfacial coupling effect between the catalyst and the plasma by relying on the synergistic effect of the nickel foam support structure and the nano-flower-like multi-component phosphide active layer, thereby achieving efficient conversion of CO2 and CH4 under low energy consumption conditions. At the same time, the introduction of vanadium increases the alkaline adsorption sites on the catalyst surface, promotes CO2 adsorption and carbon deposition gasification reaction, and makes the catalyst exhibit excellent reactivity, good anti-carbon deposition ability and stable long-term operating performance in plasma-assisted methane dry reforming reaction. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the synthesis of the catalyst V-NiFeP@NF in Example 1 of the present invention; Figure 2 This is a diagram of the reaction apparatus of the present invention; Figure 3The graphs show the performance of the catalyst V-NiFeP@NF in Example 1 of this invention, the material NiFeP@NF in Comparative Example 1, an empty tube, and NF under the conditions of a power of 22.5 W, a feed flow rate of 30 ml / min, and a CH4 / CO2 / Ar molar ratio of 1:1:8. (a) shows the electrical signal; (b) compares the CH4 / CO2 conversion rates; (c) show the yields of H2, CO, C2H6, and C3H8; (d) show the selectivity of H2, CO, C2H6, and C3H8; and (e) show the H2 / CO molar ratio. Figure 4 The figures show the performance test results of the catalyst V-NiFeP@NF in Example 1 of this invention, the material NiFeP@NF in Comparative Example 1, an empty tube, and NF. (a) shows the CO2 and CH4 conversion rates of NiFeP@NF and V-NiFeP@NF materials in plasma-assisted DRM over 3.5 hours; (b) shows the conversion rates at 22.5 W discharge power and 30 mL / min. -1 Energy efficiency of empty tube, NF, NiFeP@NF and V-NiFeP@NF under conditions of gas feed rate and CH4 / CO2 / Ar molar ratio of 1:1:8; Figure 5 The graphs show the performance of NiFeP powder (Comparative Example 2), V-NiFeP powder (Comparative Example 3), empty tube, and NF under the conditions of 22.5 W power, 30 ml / min feed flow rate, and CH4 / CO2 / Ar molar ratio of 1:1:8. (a) CH4 / CO2 conversion rate comparison; (b) yields of H2, CO, C2H6, and C3H8; (c) selectivity of H2, CO, C2H6, and C3H8; and (d) CO2 and CH4 conversion rates of NiFeP powder and V-NiFeP powder materials within 2 hours. Figure 6 The images are SEM images of the catalyst V-NiFeP@NF in Example 1 of the present invention, where (a) is the SEM image before the reaction and (b) is the SEM image after the reaction. Figure 7The figures show the CO2-TPD test results of the catalyst V-NiFeP@NF in Example 1 and the material NiFeP@NF in Comparative Example 1. (a) is a schematic diagram of weakly basic sites (≤150℃), moderately basic sites (150~450℃), and strongly basic sites (≥450℃). (b) is a CO2-TPD diagram. The CO2 adsorption capacity of V-NiFeP@NF at 50~150℃, 150~450℃, and 450~800℃ is 0.058, 0.404, and 0.046 mmol / g, respectively, while the CO2 adsorption capacity of NiFeP@NF at 50~150℃, 150~450℃, and 450~800℃ is 0.035, 0.353, and 0.079 mmol / g, respectively. Figure 8 The images show the XRD patterns of the catalyst V-NiFeP@NF in Example 1 of this invention before and after plasma treatment, where the right image (b) is a magnified view of the left image (a) in the 10~45 degree region; Figure 9 Transmission electron microscope (TEM) image (a) of the catalyst V-NiFeP@NF in Example 1 of this invention; high-resolution TEM image (bc); elemental mapping of Ni, Fe, V and P in V-NiFeP@NF, scale bar: 200 nm (d). Figure 10 This is a comparison of the XRD patterns of the catalyst V-NiFeP@NF in Example 1 of the present invention and the V-NiFeP powder in Comparative Example 3. Figure 11 The high-resolution XPS spectrum of the catalyst V-NiFeP@NF in Example 1 of this invention is shown, where (a) Ni 2p; (b) Fe 2p; (c) V 2p; and (d) P 2p. Figure 12 The high-resolution XPS spectrum of the catalyst NiFeP@NF in Comparative Example 1 of this invention is shown, where (a) Ni 2p; (b) Fe 2p; (c) P 2p. Figure 13 This is a schematic diagram of the mechanism of methane dry reforming reaction catalyzed by low-temperature plasma and V-NiFeP@NF catalyst. Detailed Implementation

[0029] The technical solutions of the present invention will be described in detail below with reference to specific embodiments and accompanying drawings. The embodiments described herein are specific implementations of the present invention, used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary, and should not be construed as limiting the implementation methods or the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can employ other obvious technical solutions based on the content disclosed in the claims and specification of this application. These technical solutions include those that make any obvious substitutions and modifications to the embodiments described herein.

[0030] Unless otherwise specified, all reagents and equipment used in the following examples were purchased from commercial sources.

[0031] Example 1 Put Ni(NO3)2⋅ 6H2O (0.96 mmol), Fe(NO3)3 9H₂O (0.16 mmol), VCl₃ (0.16 mmol), and urea (2 mmol) were dissolved in 15 mL of deionized water and stirred for 10 minutes at room temperature to obtain a metal precursor solution. Nickel foam (approximately 2 cm × 2.5 cm) was sonicated in 3 M HCl aqueous solution for 30 minutes to remove the surface NiO layer, and then ultrasonically cleaned three times each with deionized water and anhydrous ethanol. The metal precursor solution and nickel foam were then transferred to a 20 mL PTFE-lined stainless steel autoclave, sealed, and maintained at 120 °C for 12 hours, followed by natural cooling to room temperature. The material was washed three times with deionized water and ethanol and dried at 60 °C for 4 hours to obtain the precursor material. The prepared precursor material and 2.8 mmol NaH2PO2 were placed in two separate ceramic boats. The ceramic boat containing NaH2PO2 was closer to the gas inlet end of the tube furnace, while the ceramic boat containing the precursor was farther away from the gas inlet end. The two boats were about 5 cm apart. Then, under an argon atmosphere, the tube furnace was heated from room temperature to 350 °C at a rate of 3 °C / min. After holding at the temperature for 2 hours, it was naturally cooled to obtain a black multi-component transition metal phosphide catalyst V-NiFeP@NF for methane dry reforming.

[0032] The synthesis diagram of Example 1 is shown below. Figure 1 As shown; the experimental setup used is illustrated in the diagram. Figure 2As shown. The coaxial DBD reactor is a quartz tube with an inner diameter of 18 mm, a thickness of 1 mm, and a length of 40 cm; the high-voltage positive electrode is a 304 stainless steel tube with a diameter of 8 mm, which is connected to the high-voltage output terminal; a 304 stainless steel mesh is wrapped around the quartz tube and grounded as the high-voltage negative electrode; the discharge length and discharge gap are 8 cm and 5 mm, respectively; a high-frequency AC high-voltage generator (CTP-2000 K, Suman Nanjing Co., Ltd.) is used to generate plasma. This device has an adjustable output frequency function. During the experiment, the frequency was set to 120 Hz, and the input voltage of the power supply was recorded using this instrument; the electrical signal was recorded using a digital oscilloscope (TBS 2000B series, Tektronix Co., Ltd.); a gas mixture of CH4, CO2, and Ar (10%, 10%, and 80%) was controlled by a mass flow controller (MFC, Beijing Qixing Flow Co., Ltd.), and then discharged at a rate of 30 mL / min. -1 The gaseous products were purged into the DBD reactor at a flow rate of [missing information]; after the reaction, the gaseous products were analyzed online using a gas chromatograph (GC 7900, Shanghai Tianmei Co., Ltd.) equipped with a thermal conductivity detector and a flame ionization detector.

[0033] Example 2 The difference from Example 1 is that Ni(NO3)2 6H2O is 0.5 mmol, Fe(NO3)3 The amounts of 9H2O were 0.05 mmol, VCl3 were 0.05 mmol, urea was 1 mmol, and NaH2PO2 was 1 mmol. Other preparation steps were similar to those in Example 1.

[0034] Example 3 The difference from Example 1 is that Ni(NO3)2 6H2O is 2.5 mmol, Fe(NO3)3 The amounts of 9H2O were 0.5 mmol, VCl3 was 0.5 mmol, urea was 3 mmol, and NaH2PO2 was 4 mmol. Other preparation steps were similar to those in Example 1.

[0035] Comparative Example 1 The difference from Example 1 is that VCl3 was not added, but the other preparation steps were similar to those in Example 1, resulting in a vanadium-free (V-doped) NiFeP@NF material.

[0036] Comparative Example 2 The difference from Comparative Example 1 is that no nickel foam substrate was introduced during the preparation process, and the resulting product was separated, washed and dried to obtain NiFeP powder material.

[0037] Comparative Example 3 The difference from Example 1 is that no nickel foam substrate was introduced during the preparation process, and the resulting product was separated, washed and dried to obtain V-NiFeP powder material.

[0038] Test case Catalytic activity tests were conducted in a horizontally configured DBD nonthermal plasma reactor with a quartz tube packed bed, measuring 40 cm in length, 18 mm in inner diameter, and 20 mm in outer diameter. An 8 mm diameter 304 stainless steel tube served as the high-voltage (HV) positive electrode, positioned at the center of the quartz tube reactor. An 8 cm long section of iron mesh served as the grounding electrode, wrapped around the outside of the reactor. The resulting catalyst was cut into 2 cm × 2.5 cm pieces, sandwiched in the center of the plasma reactor and separated by quartz wool, with a 5 mm discharge gap and an 8 cm discharge length. A CTP-2000 K AC power supply (Nanjing Suman Electronics Co., Ltd., China) was used to provide the high voltage and connected to a voltage regulator. This device featured an adjustable output frequency; the frequency was set to 120 Hz during the experiment, and the input voltage was recorded using this instrument. The applied voltage and current were recorded using a dual-channel digital oscilloscope (Tektronix TBS 2000B, Tektronix, Inc., USA). A gas mixture of CH4, CO2, and Ar (molar ratio 1:1:8) was controlled by a mass flow controller (MFC, Beijing Qixing Flow Co., Ltd.), and then flowed at 30 mL / min. -1 The product gas was purged into the DBD reactor at a flow rate of [missing information]. The product gas was analyzed by an online gas chromatograph (GC 7900, Shanghai Tianmei Co., Ltd.), equipped with a flame ionization detector (FID) and a thermal conductivity detector (TCD).

[0039] The inventors used the foamed nickel catalyst V-NiFeP@NF obtained in Example 1 as a substrate to catalyze the dry reforming reaction (DRM) of methane. The catalytic performance of the multi-metal phosphide V-NiFeP@NF obtained in Example 1 was studied by comparing it with that of an empty tube, metallic foamed nickel NF, NiFeP@NF of Comparative Example 1, NiFeP powder of Comparative Example 2, and V-NiFeP powder of Comparative Example 3. The test results are shown in Tables 1 and 2. Figure 3 , Figure 4 and Figure 5 As shown.

[0040] Table 1 Conversion Rate Test Results

[0041] Table 2 Yield Test Results

[0042] First, such as Figure 3As shown in Figure a, in the catalytic activity experiment, the electrical signal of V-NiFeP@NF in Example 1 showed a higher peak value. Except for a few current spikes, the peak electrical signal of the conductive nickel foam decreased to 0.053 A, while the peak electrical signal of the empty tube was approximately 0.064 A. When the reaction zone was filled with NiFeP@NF from Comparative Example 1 and V-NiFeP@NF catalyst from Example 1, the electrical signal intensity increased. The peak electrical signal of NiFeP@NF from Comparative Example 1 was approximately 0.058 A, while V-NiFeP@NF from Example 1 showed a higher peak value, reaching approximately 0.066 A. The experimental results show that the V-NiFeP@NF catalyst of Example 1 performed excellently in terms of CO2 and CH4 conversion, with a CO2 conversion rate of 40.9% and a CH4 conversion rate of 56.6%, representing increases of 16.6% and 17.0% respectively compared to the empty tube (e.g., ...). Figure 3 (As shown in b). Furthermore, the H2 and CO yields of the V-NiFeP@NF catalyst in Example 1 were 34.4% and 31.0%, respectively, representing increases of 10.4% and 9.4% compared to the empty tube (e.g., ...). Figure 3 (As shown in c). Compared to NiFeP@NF in Comparative Example 1, V-NiFeP@NF in Example 1 showed improvements in both conversion and yield, with CO2 and CH4 conversions increasing by 15.2% and 10.0%, respectively; and exhibited a better H2 / CO ratio (1.109), lower than the 1.257 of NiFeP@NF in Comparative Example 1 (as shown in c). Figure 3 (As shown in e), this indicates that the V-NiFeP@NF of Example 1 is closer to the ideal methane dry reforming reaction, further demonstrating the synergistic effect of multi-metal phosphides on improving catalytic performance. The selectivity of the V-NiFeP@NF of Example 1 for different products is as follows: hydrogen (60.8%), carbon monoxide (63.4%), ethane (10.6%), and propane (5.0%) (as shown in e). Figure 3 (As shown in d). Furthermore, the energy efficiencies (E) of the V-NiFeP@NF of Example 1, the NiFeP@NF of Comparative Example 1, the empty tube, and the NF, arranged in descending order, were 0.104, 0.0801, 0.0689, and 0.0567, respectively (as shown in d). Figure 4 (As shown in b) This trend indicates that the V-NiFeP@NF of Example 1 has the highest energy yield.

[0043] Secondly, such as Figure 4 As shown, the V-NiFeP@NF catalyst of Example 1 exhibits significant stability. Long-term reaction tests show (e.g.) Figure 4As shown in a), the CO2 and CH4 conversions of V-NiFeP@NF in Example 1 remained at high levels, at 40.2% and 55.2%, respectively, after 210 minutes of reaction. In contrast, the conversion of NiFeP@NF in Comparative Example 1 began to decline slowly after 30 minutes.

[0044] Furthermore, the V-NiFeP powder in Comparative Example 3 agglomerates and tends to accumulate at both ends of the reactor, far from the discharge region, thus reducing the catalytic effect and resulting in a worse catalytic performance than the empty tube. Figure 5 As shown, the experimental results indicate that the CO2 / CH4 conversion rates of the NiFeP powder catalyst in Comparative Example 2 and the V-NiFeP powder catalyst in Comparative Example 3 were 17.4% / 32.1% and 19.2% / 37.7%, respectively. The CO2 / CH4 conversion rate of the NiFeP powder catalyst in Comparative Example 2 was 7.0% / 7.5% lower than that of the empty catalyst, and the CO2 / CH4 conversion rate of the V-NiFeP powder catalyst in Comparative Example 3 was 5.2% / 1.9% lower than that of the empty catalyst. However, it can also be seen that the V-NiFeP powder in Comparative Example 3 has improved catalytic performance compared to the NiFeP powder in Comparative Example 2, proving that the synergistic effect between multi-metal phosphides is more beneficial to improving DRM performance than that of binary metal phosphides. The V-NiFeP@NF catalyst of Example 1 supported on nickel foam provides a new loading strategy and improves the catalytic performance of the catalyst.

[0045] Furthermore, the SEM image of the V-NiFeP@NF catalyst in Example 1 of this invention (e.g.) Figure 6 (as shown) and XRD (as shown) Figure 8 As shown in the figure, the test results showed that the morphology and crystallinity of the catalyst remained stable after the reaction without significant changes, further proving its good stability.

[0046] Moreover, such as Figure 7 As shown, after carbon dioxide temperature-programmed desorption (CO2-TPD) testing, the inventors found that the catalyst V-NiFeP@NF in Example 1 of this invention has more moderately alkaline adsorption sites than NiFeP@NF in Comparative Example 1 (weakly alkaline sites are difficult to adsorb; while strong alkaline sites are too strong to adsorb and thus difficult to desorb). The moderately alkaline sites have moderate adsorption and desorption capabilities, which is beneficial to the activation and conversion of CO2.

[0047] Specifically, such as Figure 7As shown in Figure a, moderately strong basic sites provide optimal CO2 adsorption strength without excessively retaining CO2 molecules, thus helping to prevent carbon deposition. While excessively strong basic sites promote CO2 adsorption, they can also easily lead to over-adsorption of CO2 molecules. When the CO2 decomposition rate exceeds the hydrogenation rate, the catalyst is prone to carbon deposition and subsequent deactivation because the accumulated carbon occupies active sites and reduces catalytic activity. In contrast, weakly basic sites cannot effectively adsorb CO2, resulting in poor activation efficiency. Therefore, maintaining an appropriate amount of moderately strong basic sites is crucial for CO2 activation, as these sites promote CO bond formation while preventing excessive carbon deposition. This balance enhances CO2 activation efficiency and the catalyst's resistance to carbon deposition, thereby significantly improving catalytic performance and lifespan. Moreover, from Figure 7 As shown in b, the CO2 adsorption capacity per unit mass of V-NiFeP@NF at 50–150 °C and 150–450 °C is 0.058 mmol / g and 0.404 mmol / g, respectively, which are 0.013 and 0.051 mmol / g higher than that of NiFeP@NF. This indicates that the trimetallic phosphide V-NiFeP@NF of the present invention provides better moderate CO2 adsorption capacity than bimetallic NiFeP@NF in the 150–450 °C range. Furthermore, the CO2 adsorption capacity per unit mass of V-NiFeP@NF of the present invention at 450–800 °C is 0.046 mmol / g, lower than that of NiFeP@NF (0.079 mmol / g). The comparative bimetallic NiFeP@NF exhibits a significantly stronger alkalinity above 450 °C, which may be detrimental to the desorption of CO2 activation products, potentially leading to carbon deposition.

[0048] Therefore, the abundant basic adsorption sites of V doping play a crucial role in activating CO2, as they effectively promote CO bond formation while preventing excessive decomposition. This enhances both the activation efficiency of CO2 and the catalyst's resistance to coking (CO2 + C = 2CO), significantly improving the catalyst's catalytic performance and lifespan. Coking is a side reaction that hinders the reaction process; increased coking leads to catalyst deactivation, reducing catalytic activity and lifespan. Improving resistance to coking is achieved by inhibiting the coking reaction and by converting the coking back into usable substances. For example, in this invention, the catalyst's catalytic effect is enhanced to react the coking with activated CO2 and convert it back into the desired product, CO. Resistance to coking may be due to the catalyst's high catalytic activity; improved resistance inhibits coking formation, thus preventing catalyst deactivation and extending its lifespan, resulting in better long-term reaction stability.

[0049] Figure 9 Transmission electron microscope (TEM) image (a) of the catalyst V-NiFeP@NF in Example 1 of the present invention; high-resolution transmission electron microscope (TEM) images (b) and (c); elemental mapping of Ni, Fe, V and P in V-NiFeP@NF, scale bar: 200 nm (d).

[0050] Based on high-resolution transmission electron microscopy (HRTEM) images (such as...) Figure 9 As shown in b and 9c), metal phosphides are present on the nickel foam substrate. Clear and continuous lattice fringes are visible, exhibiting a relatively concentrated distribution over a large area. Clear lattice fringes with spacings of 0.45, 0.22, and 0.34 nm correspond to the (101) crystal plane of V2P, the (111) crystal plane of Ni2P, and the (001) crystal plane of Fe2P, respectively. A fringe with a spacing of 0.32 nm corresponds to the (200) crystal plane of V2P. This result is in high agreement with subsequent XRD analysis, revealing the high crystallinity of the V-NiFeP nanosheets. Furthermore, energy dispersive spectroscopy elemental mapping images (such as...) Figure 9 As shown in d), the uniform distribution of Ni, Fe, V and P elements in the prepared V-NiFeP@NF catalyst was further confirmed.

[0051] Figure 10 The XRD patterns of the catalyst V-NiFeP@NF in Example 1 and the V-NiFeP powder in Comparative Example 3 are compared.

[0052] To investigate the crystal structure of the prepared V-NiFeP@NF catalyst, the inventors performed XRD diffraction analysis on the V-NiFeP@NF catalyst sample of Example 1 and the V-NiFeP powder sample of Comparative Example 3. Figure 10As shown, V-NiFeP@NF (red line) exhibits three distinct peaks at 44.5°, 51.8°, and 76.4°, corresponding to the (111), (200), and (220) crystal planes of Ni foam crystal (JCPDS No. 04-0850), respectively. Due to the high intensity of the diffraction peaks in Ni foam, the diffraction peaks of the metal phosphide are not obvious. Comparing the XRD patterns of V-NiFeP@NF with magnified views reveals that its peak shape highly matches that of V-NiFeP powder, indicating that different morphologies of V-NiFeP possess consistent crystallinity. For the trimetallic V-NiFeP@NF, the typical peaks at 40.8°, 44.6°, 47.3°, and 74.7° are assigned to the (111), (201), (210), and (400) planes of Ni2P, respectively (JCPDS No. 03-0953), while the peaks at 25.7°, 35.3°, 54.1°, and 66.3° correspond to the (001), (200), (300), and (310) planes of Fe2P, respectively (JCPDS No. 27-1171). Furthermore, the signals at 18.5°, 28.7°, 29.5°, and 38.6° correspond to the (101), (200), (011), and (103) planes of V2P (JCPDS No. 32-1414). The XRD data and HRTEM measurements of crystal planes and lattice fringes are in high agreement, successfully demonstrating the formation of Ni2P, Fe2P and V2P ternary metal phosphides.

[0053] Figure 11 High-resolution XPS spectra of the catalyst V-NiFeP@NF in Example 1 of this invention: (a) Ni 2p; (b) Fe 2p; (c) V 2p; (d) P 2p.

[0054] Figure 12 High-resolution XPS spectra of the catalyst NiFeP@NF in Comparative Example 1 of this invention: (a) Ni 2p; (b) Fe 2p; (c) P 2p.

[0055] The inventors further investigated the surface chemical states of the free-standing V-NiFeP@NF catalyst using X-ray photoelectron spectroscopy (XPS). Due to the complex valence states of transition metal elements in metal phosphides, Ni, Fe, and V may exhibit multiple metal valence states. For the Ni 2p spectrum, as shown... Figure 11 As shown in figure a, the fitted peak values ​​of 874.7 and 856.9 eV are attributed to Ni. 2+ The oxidation states of Ni are 2p1 / 2 and Ni 2p3 / 2, while the other two accompanying peaks (852.7 and 869.9 eV) may represent metallic Ni. 0The existence of this is due to the presence of partially charged Ni species (Ni δ+ This is due to the fact that δ is close to 0. Furthermore, the peaks at 880.4 and 861.8 eV are attributed to Ni 2p¹ / ² satellite peaks and 2p³ / ² satellite peaks, respectively. Regarding the Fe 2p spectrum, see... Figure 11 As shown in b, the peak positions of Fe 2p1 / 2 and 2p3 / 2 are located at 725.1 and 711.9 eV, respectively, indicating that Fe is in the Fe... 3+ Oxidation state. Accordingly, the peaks at 714.6 and 706.3 eV are attributed to Fe-P, while the peak at 706.3 eV corresponds to Fe. 2+ 2p³ / 2. Both Ni and Fe exhibit a metallic valence state of 0, thus making the formation of Ni₂P and Fe₂P with an average valence state of +1.5 reliable, consistent with XRD phase-matching analysis. Notably, the V 2p spectrum shows significant peaks at approximately 516.9 / 524.5 eV and 515.0 / 523.0 eV, respectively, attributable to V. 4+ and V 2+ ,like Figure 11 As shown in c. Although metallic V 0 The intensity of the 512.3 eV peak is not significant, but it still exists. This is presumably due to surface oxidation leading to a high chemical valence state of V. Furthermore, due to surface oxidation and passivation, the high-resolution spectrum of P 2p shows a typical peak position for phosphate species at approximately 134.8 eV, indicating the formation of PO bonds, such as... Figure 11 As shown in d. The peaks at 129.7 and 130.7 eV are attributed to the 2p3 / 2 and 2p1 / 2 orbitals of the metal phosphide (MP) species, respectively. Interestingly, by comparing with the high-resolution XPS spectra of Ni, Fe, and P of bimetallic NiFeP@NF, as shown in d. Figure 12 As shown in ac, the peak value in V-NiFeP@NF shifts slightly, further demonstrating the change in the electrochemical environment due to V2P incorporation.

[0056] In summary, the V-NiFeP@NF catalyst obtained in the embodiments of the present invention exhibits excellent catalytic performance and stability through the synergistic effect of multiple transition metal phosphides and the structural advantages of nickel foam, providing a new approach for the efficient catalytic reaction of methane dry reforming and showing great application potential.

[0057] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A multi-transition metal phosphide catalyst for dry reforming of methane, characterized by, The catalyst comprises a nickel foam substrate and a multi-element transition metal phosphide active layer disposed on the surface of the nickel foam substrate. The multi-element transition metal phosphide active layer contains at least nickel, iron, vanadium and phosphorus elements, and the nickel, iron and vanadium exist in the form of phosphide.

2. The multi-component transition metal phosphide catalyst for dry reforming of methane as described in claim 1, characterized in that, The multi-element transition metal phosphide active layer is formed in situ on the surface of the nickel foam substrate, and the multi-element transition metal phosphide active layer includes a Ni-Fe-P phosphide phase and introduces vanadium to form a multi-metal synergistic phosphating structure.

3. The multi-component transition metal phosphide catalyst for dry reforming of methane as described in claim 1, characterized in that, In the multi-element transition metal phosphide active layer, the molar ratio of nickel, iron, vanadium, and phosphorus is: Ni: Fe: V: P = (0.5~2.5): (0.05~0.5): (0.05~0.5): (1~4).

4. The multi-component transition metal phosphide catalyst for dry reforming of methane as described in claim 1, characterized in that, The multi-component transition metal phosphide active layer has a nanoflower-like structure.

5. The use of a multi-component transition metal phosphide catalyst for dry reforming of methane as described in any one of claims 1 to 4 in the dry reforming reaction of methane.

6. The use as described in claim 5, characterized in that, The methane dry reforming reaction is carried out under non-thermal plasma conditions.

7. The method for preparing the multi-component transition metal phosphide catalyst for dry reforming of methane as described in any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Dissolve the nickel source, iron source, vanadium source and precipitant in a solvent to obtain a metal precursor solution; (2) The nickel foam substrate is acid-washed to remove its surface oxide layer. The nickel foam substrate and the metal precursor solution are placed together in a closed reaction vessel and reacted under heating and pressure conditions to allow the nickel, iron and vanadium-containing precursors in the metal precursor solution to grow in situ on the surface of the nickel foam substrate to obtain the precursor material. (3) The precursor material and the phosphorus source are placed in a reactor and phosphating is performed under an inert atmosphere. The phosphorus source is decomposed and released under heating conditions to convert the precursor material into a multi-component transition metal phosphide active layer, thereby obtaining the multi-component transition metal phosphide catalyst V-NiFeP@NF for methane dry reforming.

8. The method for preparing the multi-component transition metal phosphide catalyst for dry reforming of methane as described in claim 7, characterized in that, The nickel source is selected from nickel nitrate or its hydrate; The iron source is selected from ferric nitrate or its hydrate; The vanadium source is selected from vanadium chloride or its hydrate; The precipitant is urea; The phosphorus source is a hypophosphite compound.

9. The method for preparing the multi-component transition metal phosphide catalyst for dry reforming of methane as described in claim 7, characterized in that, The reaction temperature in step (2) is 100~150℃ and the reaction time is 6~24 hours. The phosphating treatment in step (3) is carried out under an inert atmosphere, with a phosphating temperature of 300~400℃ and a holding time of 1~4 hours.

10. The method for preparing the multi-component transition metal phosphide catalyst for dry reforming of methane as described in claim 7, characterized in that, The phosphating process involves heating at a rate of 1~5℃ / min.

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