Hollow spherical high-entropy catalyst as well as preparation method and application thereof

Abstract

The invention discloses a preparation method and application of a hollow spherical high-entropy catalyst with a controllable particle size, a spinel high-entropy oxide is used as a design basis to prepare a base metal high-entropy catalyst with an (ABCDE) 3O4 configuration (five metal components A, B, C, D and E comprise Fe, Co, Ni, Cr and Mn, or four of the five metal components A, B, C, D and E is a combination of any four of Fe, Co, Ni, Cr or Mn, and one of the five metal components A, B, C, D and E is any one of Mg or Zn), can be applied to a catalytic reforming technology to prepare hydrogen-rich synthesis gas, and has excellent catalytic performance on pyrolysis / gasification volatile components of complex components and excellent selectivity on hydrogen. In addition, the catalyst has the characteristics of high temperature resistance, multiple functions, high activity, high selectivity, carbon deposition resistance, long service life and the like, the hydrogen yield can be greatly improved, and stable catalysis can be carried out for an extremely long time.

Description

Technical Field

[0001] The present invention relates to the technical field of catalyst preparation, and more particularly to a hollow spherical high-entropy catalyst, a preparation method thereof, and application thereof in catalytic reforming of organic waste pyrolysis gas to produce hydrogen-rich synthesis gas. Background Art

[0002] The main components of waste cooking oil include used animal and vegetable oils and animal and vegetable oil waste generated during various food processing processes. Chemically, it primarily contains organic substances such as triglycerides and free fatty acids. In terms of industrial applications, the most mature energy conversion pathway for waste cooking oil is through biochemical conversion to biodiesel. Due to its widespread availability, low collection costs, and significant energy properties (calorific value of approximately 37-40 MJ / kg), waste cooking oil is considered a highly promising renewable resource. In recent years, researchers have been committed to developing more advanced thermochemical conversion technologies, such as catalytic pyrolysis and plasma gasification. These technologies not only efficiently convert waste cooking oil into high-quality fuel oil and synthesis gas, but also can be synergistically processed with other municipal solid wastes to achieve integrated resource utilization of multi-component wastes. In the context of carbon neutrality, the development of new, green, and low-carbon technologies for the energy utilization of waste cooking oil is of great significance for building a circular economy.

[0003] The energy density of hydrogen is as high as 120-142MJ / kg, far exceeding that of traditional fossil fuels. In the oxidation reaction, hydrogen only produces water, which is an ideal zero-carbon energy carrier. In addition to being a renewable energy storage carrier in the energy field, hydrogen is also an indispensable raw material in industrial fields such as synthetic ammonia and methanol. From the current process of hydrogen production, fossil-based hydrogen production (mainly natural gas reforming) still accounts for the vast majority of global production capacity (about 76%), which is extremely unfavorable for carbon dioxide emission reduction. Under the "dual carbon" goal, the development of a low-carbon hydrogen energy system that mainly uses renewable energy electrolysis to produce hydrogen (green hydrogen) and carbon capture and storage (CCS) fossil-based hydrogen production (blue hydrogen) as a supplement is of strategic significance for building a clean and low-carbon energy system. However, the current production cost of green hydrogen is still significantly higher than that of gray hydrogen, and cost reduction and efficiency improvement remain the key to industrial development.

[0004] Overall, hydrogen production from "carbon-neutral" feedstocks such as municipal solid waste and biomass represents an important development direction for the hydrogen energy industry. These feedstocks offer the advantages of widespread availability and low cost, and the carbon emissions from their thermochemical conversion process can be considered carbon-neutral, highly consistent with the "dual carbon" goals. However, thermochemical hydrogen production processes face stringent process requirements (high temperatures and pressures), which significantly increase equipment investment and operating costs. Currently, new catalytic materials (such as bifunctional catalysts and core-shell catalysts), reaction engineering optimization (such as fluidized and moving beds), and feedstock pretreatment technologies (such as pyrolysis oil upgrading and biomass gasification) are key research areas. The key to future development lies in achieving a balance between scalability, cost-effectiveness, and environmental friendliness through technological innovation, thereby promoting hydrogen to play a more prominent role in the global energy system.

[0005] While the introduction of catalysts can lower the activation energy of reactions and enable efficient conversions under milder conditions, developing materials with excellent catalytic performance still faces numerous challenges. Providing ideal catalysts that combine high-temperature stability, selectivity control, resistance to poisoning, and long life is of great practical significance. Summary of the Invention

[0006] The present invention aims to solve at least one of the technical problems existing in the prior art to a certain extent. To this end, the present invention proposes a hollow spherical high-entropy catalyst with controllable particle size, which can increase the hydrogen content in the product and has excellent selectivity and life.

[0007] According to one aspect of the present invention, a metal oxide catalyst is provided, which has a spinel configuration and comprises five metal components, wherein the five metal components are iron, cobalt, nickel, chromium and manganese, or the five metal components are selected from any four of iron, cobalt, nickel, chromium or manganese, and any one of magnesium or zinc.

[0008] Preferably, in the combination of the five metal components, the molar mass of each metal accounts for 1 / 5 of the total molar mass of the catalyst metal.

[0009] Preferably, the catalyst is in the shape of a hollow sphere.

[0010] According to another aspect of the present invention, a method for preparing a metal oxide catalyst is provided, comprising the following steps: S1. mixing five metal salts in an isopropanol and glycerol environment to obtain a mixed liquid precursor, wherein the five metals are iron, cobalt, nickel, chromium and manganese, or the five metals are selected from any four of iron, cobalt, nickel, chromium or manganese, and any one of magnesium or zinc; S2. subjecting the mixed liquid obtained in step S1 to solvent thermal treatment, centrifuging, washing, and drying to obtain a solid precursor; S3. calcining the solid obtained in step S2 under an air atmosphere, and obtaining the catalyst after cooling.

[0011] Preferably, in step S1, the ratio of the isopropanol and glycerol solvents is 5:1, and the mass fraction of the metal salt in the isopropanol and glycerol solution is 2%-10%.

[0012] Preferably, in step S2, the temperature of the solvent thermal treatment is 160-200° C., and the time of the hydrothermal treatment is 14-18 h.

[0013] Preferably, in step S3, the heating rate of the calcination is 1-5°C / min, the calcination temperature is 950-1050°C, the calcination time is 2-4h, and the air flow rate is 40-100mL / min.

[0014] Preferably, in step S1, the iron, cobalt, nickel, chromium, manganese, magnesium, zinc salt is one of the metal nitrates, chlorides, or sulfates.

[0015] Preferably, in step S1, the mixed salt solution is continuously stirred at 20-40°C until a transparent solution is obtained, with a stirring speed of 600-900 rpm / min and a stirring time of 30-60 min.

[0016] Preferably, in step S2, the temperature of the hydrothermal treatment is 160-200° C., and the time of the hydrothermal treatment is 14-18 hours.

[0017] Preferably, in step S2, the centrifugation operation is performed in a high-speed centrifuge, the number of centrifugation is 4-8 times, the centrifugation rate is 9000-12000 rap / min, and the centrifugation time is 10-15 min.

[0018] Preferably, in step S2, the washing operation is performed by washing with anhydrous ethanol 4-8 times.

[0019] Preferably, in step S2, the drying operation is performed in an oven.

[0020] According to another aspect of the present invention, there is provided an application of the above-mentioned catalyst in the catalytic reforming of organic waste pyrolysis gas to produce hydrogen-rich synthesis gas. Preferably, the reforming is steam reforming. Preferably, the reaction process conditions of the application are: a filler amount of 0.1-5g or a feed flow rate of 10-200μL / min, a catalyst amount of 0.1-2.0g, a reaction temperature of 750-950°C, and a protective gas flow rate of 20-300mL / min. Preferably, the filler or feed is waste cooking oil. Preferably, the protective gas is nitrogen. Preferably, the catalyst uses a two-stage integrated fixed bed of pyrolysis / gasification-reforming.

[0021] The present invention adopts spinel (ABCDE) 3O4 configuration high entropy oxide as the basis, and uses trivalent metal salts and divalent metal salts of base metals as precursors to design high entropy spinel oxides with both tetrahedral and octahedral coordination structures. Different coordination structures provide diversified metal action catalysis. In addition, the preparation of a hollow spherical high entropy catalyst with controllable particle size is achieved through the solvent thermal reaction method of combining isopropyl alcohol and glycerol solutions and changing the mass fraction of the metal salt precursor in the mixed solvent. This morphological characteristic is conducive to the diffusion and adsorption of molecules of different sizes, and can enable complex (oxygen-containing) organic matter to fully and effectively combine with the active sites of the catalyst. In short, the spinel (ABCDE) 3O4 configuration high entropy oxide catalyst of the present invention has the characteristics of high temperature resistance, multifunctionality, high activity, high selectivity, resistance to carbon deposition, and long life. The catalyst of the present invention can be applied to catalytic reforming technology to prepare high-content hydrogen and can stably catalyze for a very long time.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] This invention utilizes a spinel (ABCDE)3O4-structured base metal high-entropy oxide as a basis, using trivalent and divalent metal salts as precursors to design high-entropy spinel oxides with both tetrahedral and octahedral coordination structures. These diverse coordination structures provide diverse metal exposure options, which improves the catalyst's adsorption and conversion efficiency.

[0024] The catalyst of the present invention has the characteristics of high temperature resistance, multifunctionality, high activity, high selectivity, resistance to carbon deposition, and long life. It can be applied to catalytic reforming technology, greatly improving the hydrogen yield and capable of stable catalysis for an extremely long time.

[0025] The catalyst of the present invention can be prepared by preparing hollow spherical high-entropy catalysts with controllable particle size through the formulation of precursors such as solvents and metal salts. This morphological characteristic is conducive to the diffusion and adsorption of molecules of different sizes, and can enable complex (oxygen-containing) organic matter to fully and effectively combine with the active sites of the catalyst, further enhancing the catalytic efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of this application. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0027] Figure 1 1 is an XRD spectrum of catalysts HEO1 and HEO2 provided according to an embodiment of the present invention (HEO2 and HEO3 are materials with the same configuration (the same catalyst), and the difference here is only the difference in granulation size, so the difference in XRD was not characterized again, and only the difference in particles was characterized by SEM);

[0028] Figure 2 2 are Raman spectra of catalysts HEO1 and HEO2 provided according to embodiments of the present invention;

[0029] Figure 3 1 is a SEM photograph of catalysts HEO1, HEO2, and HEO3 provided in an embodiment of the present invention;

[0030] Figure 4 This is a TEM-EDS mapping photo of the catalyst HEO2 provided according to an embodiment of the present invention. DETAILED DESCRIPTION

[0031] The following examples are provided to facilitate a clearer understanding of the present invention for those skilled in the art. It should be noted that the following examples do not limit the scope of the present invention and are provided for illustrative purposes only. Unless otherwise specified, the raw materials, reagents, and devices mentioned in the following examples are commercially available or obtained by known methods.

[0032] Example 1

[0033] A catalyst is a spinel high-entropy oxide with a (ABCDE)3O4 configuration. Five metal components A, B, C, D and E are iron, cobalt, nickel, chromium and manganese. The molar mass of each of the five metals accounts for 1 / 5 of the total molar mass of the catalyst metal.

[0034] The preparation method of the above catalyst comprises the following steps:

[0035] S1. 0.008 mol of Fe(NO3)3·9H2O, 0.008 mol of Co(NO3)2·6H2O, 0.008 mol of Ni(NO3)2·6H2O, 0.008 mol of Mn(NO3)2, and 0.008 mol of Cr(NO3)3·9H2O were added to 200 mL of isopropanol, and the mixture was stirred at 750 rpm / min at room temperature for 30 min. Then, 40 mL of glycerol was added to the solution, and stirring was continued at 750 rpm / min at room temperature for 30 min to obtain a dark brown transparent solution precursor. At this time, the mass fraction of the metal salt in the mixed solution of isopropanol and glycerol was 5.69%;

[0036] S2. The solution precursor was placed in a 500 mL polytetrafluoroethylene solvent thermal reactor lined with a temperature of 180 ° C for 16 h (the temperature was 160-200 ° C, and the hydrothermal treatment time was between 14-18 h). After cooling for 8 h, the precursor after solvent thermal treatment was obtained;

[0037] S3. The precursor after solvent thermal treatment was centrifuged in a high-speed centrifuge at a rate of 10000 rpm / min for 10 minutes, the upper liquid was poured out, the remaining solid was washed with ethanol, and the above steps were repeated 3 times; the solid sample finally obtained was dried in an 80 ° C oven for 4 hours, and then the sample was calcined in a high-temperature tubular furnace with a dry air atmosphere, and the temperature was increased to 1000 ° C at a rate of 1 ° C / min and calcined for 2 hours, with a dry air flow rate of 100 mL / min. After cooling to room temperature, the high entropy spinel (FeCoNiCrMn) 3O4 catalyst sample was obtained, named HEO1 (calcination heating rate 1-5 ° C / min, calcination temperature 950-1050 ° C, calcination time 2-4 hours, air flow rate 40-100 mL / min).

[0038] High-entropy oxides (HEOs), a novel oxide system developed in recent years consisting of five or more oxides in equal or near-equal amounts, have attracted widespread attention from researchers both domestically and internationally due to their simple structures and excellent properties. HEOs primarily have solid solution structures, such as rock salt, fluorite, spinel, or perovskite, and hold great promise for applications in catalysis (including thermocatalysis, electrocatalysis, and photocatalysis).

[0039] In the prior art, the solution combustion synthesis method is to use precursor metal salts (such as nitrates, carbonates, sulfates) as oxidants and glycine (such as citric acid, amino acids) as chelating agents and mix them with fuel to form a uniform solution. After the solution evaporates, it is heated and spontaneously combusted to achieve low-temperature synthesis. Using equal amounts of five metal nitrates (Cu, Co, Ni, Zn, Mg) as raw materials and glycine as fuel, they are dissolved in a certain amount of ethanol or distilled water, stirred evenly to obtain a precursor solution, and the precursor is dried to obtain a blue gel, which is calcined at 850°C in a tubular furnace to obtain a single rock salt-type nanomaterial. The spinel-type (CoCrFeMnNi)3O4 nanocrystalline powder material was prepared using this method. A large amount of gas will be generated during the reaction process of the prior art, including toxic NO x Gas, etc.

[0040] In the prior art, the wet chemical method is to prepare a solution of soluble metal salts according to their composition, then add a suitable precipitant or precipitate the metal ions uniformly through evaporation, hydrolysis, sublimation, etc., and finally obtain a powder through heat treatment. Five metal salts (Cu, Co, Ni, Zn, Mg) of equal amount are mixed as raw materials and then a precipitant (potassium carbonate or sodium hydroxide) is added. After precipitation, filtration, washing, drying and calcination, a single rock salt structure (Co 0.2 Cu 0.2 Mg 0.2 Ni 0.2 Zn 0.2 ) O. In the prior art reaction process, the pH value of the system changes continuously, and the environment in which each metal particle is located also changes continuously, resulting in an uneven composition of the synthesized powder material.

[0041] In this embodiment, a spinel (ABCDE)3O4 high-entropy oxide catalyst is obtained by combining isopropanol and glycerol solutions, dissolving a precursor metal salt in the combined mixed solvent, and performing heat treatment, centrifugation, washing, drying, and calcination. The catalyst has the characteristics of high temperature resistance, multifunctionality, high activity, high selectivity, resistance to carbon deposition, and long life. The catalyst can be applied to catalytic reforming technology to prepare high-content hydrogen and can stably catalyze for an extremely long time.

[0042] Example 2

[0043] A catalyst is a spinel high-entropy oxide with a (ABCDE)3O4 configuration. Five metal components A, B, C, D and E are iron, magnesium, nickel, chromium and manganese. The molar mass of each of the five metals accounts for 1 / 5 of the total molar mass of the catalyst metal.

[0044] The preparation method of the above catalyst is the same as the preparation method of the catalyst in Example 1, except that 0.008 mol Co(NO3)2·6H2O is replaced by 0.008 mol Mg(NO3)2·6H2O (in this case, the mass fraction of the metal salt in the mixed solution of isopropanol and glycerol is 5.57%). The obtained (MgFeNiCrMn)3O4 catalyst sample is named HEO2.

[0045] The present embodiment is to verify the effect of the change of metal salt precursor on the preparation of high entropy catalyst. As an example, the present embodiment records the experimental data of five metal components being iron, magnesium, nickel, chromium and manganese. The high entropy catalyst prepared by selecting five metal components from any four of iron, cobalt, nickel, chromium or manganese, or any one of magnesium or zinc has achieved the same or similar experimental effect as the present embodiment, so the record is omitted here. Those skilled in the art can repeat the operation based on the record of the present embodiment. The principle of the high entropy catalyst prepared by selecting five metal components from any four of iron, cobalt, nickel, chromium or manganese, or any one of magnesium or zinc is to prepare the catalyst by mixing isopropyl alcohol and glycerol solution, and to design a high entropy spinel oxide with both tetrahedral and octahedral coordination structure as a precursor using trivalent metal salts and divalent metal salts of base metals. Different coordination structures provide a variety of metal action catalysis.

[0046] Example 3

[0047] A catalyst is a spinel high-entropy oxide with a (ABCDE)3O4 configuration. Five metal components A, B, C, D and E are iron, magnesium, nickel, chromium and manganese. The molar mass of each of the five metals accounts for 1 / 5 of the total molar mass of the catalyst metal.

[0048] The preparation method of the above catalyst is the same as the preparation method of the catalyst in Example 2, except that all 0.008 mol of nitrate is replaced by 0.006 mol of nitrate (at this time, the mass fraction of the metal salt in the mixed solution of isopropanol and glycerol is 4.24%). The obtained (MgFeNiCrMn)3O4 catalyst sample is named HEO3.

[0049] This example is to verify the effect of the change in the mass fraction of the metal salt precursor in the mixed solution on the particle size of the high entropy catalyst.

[0050] Comparative Example 1

[0051] The catalyst of Comparative Example 1 is a common nickel-iron spinel catalyst NiFe2O4.

[0052] The preparation method of the above catalyst is the same as the preparation method of the catalyst in Example 1, except that all 0.008 mol of nitrate is replaced by 0.0133 mol Ni(NO3)2·6H2O and 0.0267 mol Fe(NO3)3·9H2O. The remaining steps are the same as those of the preparation method of the catalyst in Example 1. The obtained NiFe2O4 catalyst sample is named CS1.

[0053] This embodiment is intended to verify the situation where the five metal components of the catalyst are iron, cobalt, nickel, chromium and manganese, or the five metal components are selected from any four of iron, cobalt, nickel, chromium or manganese, and any one of magnesium or zinc. As an example, this embodiment records the experimental data when the metal components are iron and nickel.

[0054] Product effect testing

[0055] 1. XRD, Raman, SEM and TEM-EDS results

[0056] Figure 1 is the XRD spectrum of catalysts HEO1 and HEO2, Figure 1 It can be seen that the prepared (FeCoNiCrMn)3O4 and (MgFeNiCrMn)3O4 high-entropy catalysts show typical spinel crystal diffraction peaks. The sharp XRD peaks indicate that the prepared HEOs samples have high crystallinity. No prominent impurity diffraction peaks were found, indicating that an impurity-free spinel phase was formed. Single-phase crystal is one of the important bases for determining high-entropy oxides.

[0057] Figure 2 is the Raman spectrum of catalysts HEO1 and HEO2, Figure 2 It can be seen that the prepared high entropy catalyst shows three peaks in the Raman spectrum, located at 506 cm -1 (3F 2g )、620cm -1 (3F 2g ) and 679cm -1 (A 1g ). 680cm -1 The peaks corresponding to the wave numbers nearby represent the tetrahedral lattice, 500-640 cm -1 The wavenumbers between 0 and 1 represent the ferrite octahedral lattice. These peaks are typical Raman peaks of the spinel structure, which again proves the formation of a high-entropy spinel phase.

[0058] Figure 3 SEM photos of catalysts HEO1, HEO2 and HEO3 are shown in Figure 2. Figure 3It can be seen that catalysts HEO1, HEO2, and HEO3 all have spherical structures. The spherical diameters of HEO1 and HEO2 are almost the same, 1330nm and 1327nm respectively, while the spherical diameter of HEO3 is much smaller, 888nm. This shows that the particle size of spherical catalysts can be controlled by adjusting the solvent, metal salt, and other precursors.

[0059] Figure 4 TEM and EDS-HAADF images of the catalyst HEO2 are shown in Figure 1. Figure 4 As can be seen from the TEM image, the spheres are heavily shadowed on the surface and lightly shadowed in the center, indicating that the spherical catalysts prepared using this method have a hollow structure. Energy dispersive spectroscopy (EDS) line scans obtained from the EDS-HAADF images of the hollow spherical high-entropy catalysts clearly demonstrate the presence and uniform distribution of the elements Fe, Mg, Ni, Cr, Mn, and O, a necessary condition for the formation of high-entropy oxides.

[0060] 2. Catalytic effect test

[0061] Reaction material and catalyst filling: Take 1g of the kitchen waste oil mixture and fill it into the middle of the first section of the quartz tube (fixed pyrolysis reaction sample); take 0.5g of the catalyst prepared in each of the above examples and comparative examples and fill it into the middle of the second section of the quartz tube (fixed catalyst sample); place the quartz tube in a fixed bed reactor, connect the gas pipeline, and introduce N2 at a flow rate of 100mL / min.

[0062] Pyrolysis and catalytic reforming: First, heat the second-stage reactor to 850°C at a heating rate of 15°C / min; then, heat the first-stage reactor to 150°C at a heating rate of 15°C / min, introduce ultrapure water at a flow rate of 0.1 mL / min into the second-stage reaction tube, and then begin collecting outlet gases. Gas collection is then terminated after the first-stage reactor is heated to 550°C and the reactants are fully pyrolyzed (the amount of the waste cooking oil mixture can be 0.1-20 g, or the feed flow rate can be 0.1-20 mL / min, the catalyst dosage can be 0.1-20 g, the reaction temperature can be 750-950°C, and the protective gas flow rate can be 20-1000 mL / min).

[0063] Table 1 Yield of reaction products using catalysts from Examples and Comparative Examples (yield unit: mmol / g)

[0064]

[0065]

[0066] In Table 1, the theoretical yield is defined as follows:

[0067] C 55H 100 O6+49H2O→55CO+99H2

[0068] Among them, "C 55 H 100 "O6" is the calculated molecular formula of waste cooking oil (waste cooking oil molecular model); it is assumed that during the reaction process, waste cooking oil can react completely with water and only produce CO and H2.

[0069] 3. Catalytic stability evaluation

[0070] Catalyst filling and catalytic reforming: Take 0.5 g of the catalyst prepared in the above examples and comparative examples and fill it into the middle of the second section of the quartz tube (fixed catalyst sample). Place the quartz tube in a fixed bed reactor, connect the gas pipeline, and introduce N2 at a flow rate of 200 mL / min. First, heat the second section of the reactor to 850°C at a heating rate of 15°C / min.

[0071] Pyrolysis and reaction material feeding: After the first-stage reactor is heated to 150°C at a heating rate of 15°C / min, ultrapure water at a flow rate of 0.1 mL / min is introduced into the second-stage reactor tube, and outlet gas is collected. After the first-stage reactor is heated to 550°C, waste cooking oil is introduced into the middle of the first-stage quartz tube using a syringe pump at a flow rate of 0.10 mL / min for pyrolysis. After the mixture reaches the reactor and begins pyrolysis, timing begins.

[0072] Table 2 Stability evaluation of catalyst HEO1 (yield unit: μmol / g cat .s)

[0073]

[0074]

[0075] In Table 2, the theoretical yield is defined as follows:

[0076] C 55 H 100 O6+49H2O→55CO+99H2

[0077] Among them, "C 55 H 100 "O6" is the calculated molecular formula of waste cooking oil (waste cooking oil molecular model); it is assumed that during the reaction process, waste cooking oil can react completely with water and only produce CO and H2.

[0078] The results in Table 1 demonstrate that, compared to the commonly used spinel catalyst CS1 (NiFe2O4), the high-entropy spinel ferrite catalysts HEO1, HEO2, and HEO3 of the present invention demonstrate superior catalytic steam reforming of volatile components from the pyrolysis of waste cooking oil, increasing H2 production by at least fourfold and CO production by at least sixfold. Furthermore, the difference in gas production between HEO1 and HEO2 indicates that HEO2, or (MgFeNiCrMn)3O4, possesses superior catalytic performance in the reaction system for the catalytic reforming of volatile components from the pyrolysis of waste cooking oil. The difference in gas production between HEO2 and HEO3 indicates that HEO2 with a larger particle size exhibits superior catalytic performance in this reaction system, suggesting that the catalytic performance of HEO3 with a smaller particle size is limited in this reaction system. As shown in Table 2, the H2 yield of the hollow spherical high entropy spinel catalyst HEO2 prepared in Example 2 of the present invention remained stable at 142.42-180.07 μmol·g within 4800 min. cat . -1 ·s -1 (The theoretical yield is 179.23 μmol·g cat . -1 ·s -1 ), and the average percentage yield of hydrogen remained at 89.62% (percent yield: the ratio of actual yield to theoretical yield); the CO yield remained stable at 47.30-87.52 μmol·g within 4800 min. cat . -1 ·s -1 The average carbon monoxide yield was maintained at 67.40%, which indicates that the catalyst has a very long stability time and good catalytic performance.

[0079] Based on the above results, it can be seen that the hollow spherical (ABCDE)3O4 high-entropy spinel configuration catalyst with controllable particle size prepared by the present invention has excellent conversion performance for the pyrolysis / gasification volatiles of complex components and good selectivity for hydrogen. It has the characteristics of high temperature resistance, multifunctionality, high activity, high selectivity, resistance to carbon deposition, and long life, and can stably catalyze for a very long time.

[0080] Spinel-structured catalysts possess these properties and have been widely used in thermochemical catalytic hydrogen production. Spinel-structured catalysts have excellent thermal and chemical stability, tunable pore structure, and flexible element substitution properties. These properties enable them to maintain activity under harsh conditions, improve reactant diffusion and active site exposure, and optimize catalytic performance through transition metal element regulation. However, in complex reaction systems, the activity and selectivity of traditional spinel-structured catalysts may be less than ideal and lack versatility. By introducing the concept of high entropy into spinel-structured catalysts, these limitations can be overcome through rational design and regulation of metal synergistic effects.

[0081] The introduction of high-entropy oxides (HEOs) provides a new research direction for the development of more efficient and multifunctional spinel structure catalysts, which is expected to achieve better catalytic performance in complex reaction systems. HEOs are a new type of multi-component oxide material composed of five or more metal elements. Its configurational entropy is ≥1.5R. When catalyzing reactions at high temperatures or complex atmospheres, it can balance local overheating or electron free dissipation through internal configurational entropy increase to achieve a stable catalytic effect. The key characteristics of HEOs include: (1) high compositional uniformity: multiple elements are evenly distributed to avoid local enrichment; (2) complex crystal structure: providing diverse catalytic properties; (3) high entropy effect: enhancing stability and activity; (4) tunable lattice arrangement: optimizing surface structure and active sites; (5) excellent oxidation resistance: suitable for high-temperature thermochemical reactions. These characteristics enable HEOs to exhibit excellent catalytic activity, selectivity and stability in thermochemical reactions such as oxidation reactions, alcohol dehydrogenation, and methane catalytic reforming / combustion. The multi-component characteristics of HEOs provide a new research direction for the design of efficient and multifunctional catalysts. In addition, the pyrolysis gas of organic waste is usually a complex composition of (oxygen-containing) organic matter. In the catalytic reforming reaction, if the molecular size of the (oxygen-containing) organic matter is large, these organic molecules usually have a large molecular volume and a complex spatial structure. Oxygen-containing groups (such as hydroxyl, carbonyl, etc.) will increase the intermolecular hydrogen bonding effect. Larger catalyst particle sizes provide larger pore structures, which are conducive to the diffusion and adsorption of large molecules, while too small a particle size will cause diffusion restriction and reduce the catalytic efficiency. In addition, the active sites on the catalyst surface need to be in full contact with the reactants. For complex molecules, a suitable spatial configuration is required to effectively combine with the active sites. Too small a particle size will limit the opportunity for large molecules to contact the active sites, and too large a particle size will reduce the surface area per unit mass and reduce the catalytic efficiency. In addition, for the catalyst itself, a uniform particle size distribution also helps to improve the thermal stability of the catalyst, which can reduce the agglomeration phenomenon caused by high-temperature reactions, thereby extending the catalyst life and helping to maintain the continuity of catalytic activity.

[0082] The pyrolysis gas (volatile matter) from municipal organic waste, such as waste cooking oil, has a more complex composition. HEOs with controllable particle size offer unique advantages in addressing the multifunctional catalytic and diffusion-limited requirements of complex pyrolysis gas. While waste cooking oil has a relatively simple chemical composition, the primary pyrolysis products are still complex. HEOs with controllable particle size offer unique advantages in the catalytic reforming of these pyrolysis / gasification volatiles to produce hydrogen.

[0083] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A metal oxide catalyst, characterized in that The catalyst has a spinel structure and contains five metal components, wherein the five metal components are iron, cobalt, nickel, chromium and manganese, or the five metal components are selected from any four of iron, cobalt, nickel, chromium or manganese, and any one of magnesium or zinc.

2. The catalyst according to claim 1, characterized in that In the combination of the five metal components, the molar mass of each metal accounts for 1 / 5 of the total molar mass of the catalyst metals.

3. The catalyst according to claim 1, characterized in that The catalyst is in the shape of a hollow sphere.

4. A method for preparing a metal oxide catalyst, characterized in that: The following steps are involved: S1. Mixing five metal salts in an isopropanol and glycerol environment to obtain a mixed liquid precursor, wherein the five metals are iron, cobalt, nickel, chromium, and manganese, or the five metals are selected from any four of iron, cobalt, nickel, chromium, or manganese, and any one of magnesium or zinc; S2. The mixed solution obtained in step S1 is subjected to solvent thermal treatment, centrifuged, washed, and dried to obtain a solid precursor; S3. calcining the solid obtained in step S2 under air atmosphere and cooling to obtain the catalyst.

5. The method according to claim 4, characterized in that In step S1, the ratio of the isopropanol and glycerol solvents is 5:1, and the mass fraction of the metal salt in the isopropanol and glycerol solution is 2%-10%.

6. The method according to claim 4, characterized in that In step S2, the temperature of the solvent thermal treatment is 160-200° C., and the time of the hydrothermal treatment is 14-18 hours.

7. The method according to claim 4, characterized in that In step S3, the heating rate of the calcination is 1-5°C / min, the calcination temperature is 950-1050°C, the calcination time is 2-4h, and the air flow rate is 40-100mL / min.

8. Use of the catalyst according to any one of claims 1 to 3 or the catalyst prepared according to the method according to any one of claims 4 to 7 in catalytic reforming of organic waste pyrolysis gas to produce hydrogen-rich synthesis gas.

9. The use according to claim 8, characterized in that The reaction temperature of the catalyst is 750-950°C.

10. The use according to claim 8, characterized in that The filler amount of the organic waste is 0.1-20 g or the feed flow rate is 0.1-20 mL / min, the catalyst dosage is 0.1-20 g, the reaction temperature is 750-950° C., and the protective gas flow rate is 20-1000 mL / min.

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