Preparation method of Ni-based high entropy oxide catalyst and its application in preparing synthesis gas by reforming carbon dioxide and methane

Abstract

The invention discloses a preparation method of a Ni-based high entropy oxide catalyst and its application in preparing synthesis gas by reforming carbon dioxide and methane, and relates to the technical field of preparation of environmental catalytic materials. The catalyst is prepared by a high-energy ball milling method, and high-content reversible Ni particles are used as active sites of methane gas. Other metals introduced by the high entropy strategy greatly reduce the carbon deposits produced by methane cracking while activating carbon dioxide; the catalyst prepared by the invention not only effectively overcomes the problem of poor stability of Ni-based catalysts in dry reforming reactions, but also promotes the activation of carbon dioxide and improves the efficiency of methane dry reforming. The preparation method of the high entropy oxide catalyst of the invention is simple, stable, economical and reliable, and has good development prospects in the industrial application field of carbon dioxide and methane dry reforming technology.

Description

Technical Field

[0001] The present invention belongs to the technical field of environmental catalytic material preparation, and specifically relates to a method for preparing a Ni-based high entropy oxide catalyst and its application in preparing synthesis gas by reforming carbon dioxide and methane. Background Art

[0002] In today's society, the large-scale use of fossil energy by humans has led to a large amount of carbon dioxide (CO2) emissions. Excessive CO2 in the atmosphere has caused a series of environmental problems, such as the intensification of the greenhouse effect, the increase in global average temperature, the melting of glaciers, and the rise in sea levels. Converting CO2 into carbon-containing chemicals can effectively reduce the CO2 content in the atmosphere. The dry reforming reaction (DRM) can simultaneously eliminate two greenhouse gases, CO2 and CH4, and convert them into synthesis gas, which can be further synthesized into other high-value chemicals.

[0003] CO2 methane dry reforming technology has attracted widespread attention from scholars at home and abroad. The core of this technology is to develop catalysts that can efficiently convert CO2 and CH4. In the current research results, precious metal catalysts have good performance in DRM reactions and can maintain activity for a long time, but their expensive raw material costs limit their application in industry. In addition, nickel-based catalysts also have very excellent catalytic performance for CO2 methane dry reforming reactions. Compared with precious metals, their relatively low prices make them more advantageous in industrial applications. However, during the reaction process, nickel-based catalysts are often deactivated because the deposited carbon covers the surface of the active sites.

[0004] In order to solve the problem of short catalyst life, researchers found that doping rare earth elements in nickel-based catalysts, limiting the size of nickel nanoparticles, and adjusting the interaction between the carrier and the active metal are all effective means, so some nickel-based DRM reaction catalysts have been developed. The catalysts developed in the past usually use solution synthesis methods, which require a series of tedious operations such as mixing, dissolving, stirring, washing, drying, and calcining. Not only is the preparation process complicated, but the operation is uncontrollable and the product yield is low.

[0005] This shows that the prior art needs to be further improved. Summary of the invention

[0006] One of the purposes of the present invention is to provide a method for preparing a Ni-based high entropy oxide catalyst for methane dry reforming, which adopts a solid high-energy ball milling method, then the obtained precursor is calcined at high temperature, and finally calcined in a reducing gas to obtain the catalyst. The prepared catalyst is applied to the methane dry reforming reaction and has high efficiency and stable catalytic performance.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for preparing a Ni-based high entropy oxide catalyst comprises the following steps:

[0009] (1) mixing any four metal source powders of magnesium, aluminum, zinc, manganese, cobalt, copper, molybdenum, and iron with the complex and metallic nickel, and then ball milling them at a ball milling frequency of 20-50 Hz and a ball milling time of 30-60 min to obtain a precursor;

[0010] (2) calcining the precursor obtained in step (1) at high temperature to obtain a Ni-based high entropy oxide catalyst powder;

[0011] (3) calcining the Ni-based high entropy oxide catalyst powder obtained in step (2) in a reducing gas to form reversible Ni particles.

[0012] In the above-mentioned method for preparing a Ni-based high entropy oxide catalyst, in step (1), the metal source is one or more of oxides, chlorides, acetates, nitrates, carbonates, sulfates, sulfates, ammonium oxalates, citrates and gluconates.

[0013] In the above-mentioned method for preparing a Ni-based high entropy oxide catalyst, in step (1), the molar ratio of metallic nickel to other metals is 2.6:1-18:1.

[0014] In the above-mentioned method for preparing a Ni-based high entropy oxide catalyst, in step (1), the complex is one or more of sodium citrate, citric acid, diethanolamine, ethylenediaminetetraacetic acid, acetylacetone, dithizone, and sodium triphosphate.

[0015] In the above-mentioned method for preparing a Ni-based high entropy oxide catalyst, in step (2), the high-temperature calcination temperature is 850-1200°C, the calcination time is 1-6h, and the heating rate during calcination is 1-10°C / min.

[0016] In the above-mentioned method for preparing a Ni-based high entropy oxide catalyst, in step (3), the reducing gas is hydrogen, methane or carbon monoxide, the calcination temperature is 200-850°C, and the calcination time is 20-200min.

[0017] Another object of the present invention is to provide a catalyst prepared by the above-mentioned method for preparing a Ni-based high entropy oxide catalyst.

[0018] Another object of the present invention is to provide an application of the above catalyst in the preparation of synthesis gas by reforming carbon dioxide and methane, wherein the volume ratio of carbon dioxide to methane is 0.8 to 1.2, the reaction temperature is 650 to 850°C, the reaction pressure is 0 to 2 MPa, and the reaction raw gas space velocity is 3000 to 60000 mL·g-1 ·h -1 .

[0019] Compared with the prior art, the present invention brings the following beneficial technical effects:

[0020] (1) The raw materials for preparing the catalyst of the present invention are widely available, the preparation process is simple, the time consumption is short, the preparation conditions are easy to accurately control, and the obtained catalyst has good reproducibility.

[0021] (2) In the present invention, under the reaction conditions, the high-content reversible Ni particles are the active sites of methane, and the other metals in the high-entropy oxide act as alkaline sites to adsorb and activate carbon dioxide molecules, quickly releasing a large amount of active oxygen and the carbon produced by methane cracking to form carbon monoxide, which not only promotes the forward progress of the reforming reaction, but also greatly reduces carbon deposition, thereby improving the stability of the catalyst; in addition, the five metals form a single-phase high-entropy oxide, and the high-entropy effect caused by the disordered chemical composition and lattice distortion significantly slows down the diffusion rate of the metal elements, further improving the high-temperature stability of the catalyst.

[0022] (3) The present invention can change the type and composition of the precursor metal salt in the preparation of the high entropy oxide catalyst to prepare a high entropy oxide catalyst with different active centers, which can be widely used in other reaction catalytic systems and has good universality.

[0023] (4) The catalyst prepared by the present invention exhibits efficient and stable catalytic performance, has a relatively economical preparation cost, is environmentally friendly, and has good application prospects in catalyzing gases such as CO2 and CH4. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the XRD pattern of the high entropy oxide catalyst.

[0025] Figure 2 This is the EDX image of the high entropy oxide catalyst.

[0026] Figure 3 This is a stability test diagram of high entropy oxide catalysts used for methane dry reforming. DETAILED DESCRIPTION

[0027] The present invention provides a method for preparing a Ni-based high entropy oxide catalyst and its application in preparing synthesis gas by reforming carbon dioxide and methane. In order to make the advantages and technical solutions of the present invention clearer and more specific, the present invention is further described below in conjunction with specific embodiments.

[0028] The raw materials described in the present invention can be purchased through commercial channels.

[0029] The methods described in the present invention are all conventional processing methods unless otherwise specified.

[0030] Embodiment 1:

[0031] A method for preparing a Ni-based high entropy oxide catalyst specifically comprises the following steps:

[0032] (1) mixing metal source powders of magnesium, cobalt, copper and zinc with metal nickel and a complex and then ball milling to obtain a precursor;

[0033] (2) calcining the precursor obtained in step (1) at high temperature to obtain a Ni-based high entropy oxide catalyst powder;

[0034] (3) The Ni-based high entropy oxide catalyst obtained in step (2) is calcined in a reducing gas to form reversible Ni particles.

[0035] The metal source in step (1) is an oxide.

[0036] The molar ratio of metallic nickel to other metals in step (1) is 6:1.

[0037] The complex in step (1) is citric acid.

[0038] The ball milling frequency in step (1) is 20 Hz and the ball milling time is 60 min.

[0039] The heating rate of calcination in step (2) is 2°C / min, the calcination temperature is 900°C, and the calcination time is 2h.

[0040] The reducing gas in step (3) is hydrogen, the calcination temperature is 700° C., and the calcination time is 120 min.

[0041] The prepared catalyst is recorded as HEO-Ni, wherein the molar ratio of Ni is 60%, and the molar ratio of the other four metals is 40%.

[0042] The XRD pattern of the Ni-based high entropy oxide catalyst prepared in this example is shown in Figure 1 The EDX images of Ni-based high entropy oxide catalysts are shown in Figure 2 shown.

[0043] Embodiment 2:

[0044] A method for preparing a Ni-based high entropy oxide catalyst, which differs from Example 1 in that the metal source in step (1) is acetate.

[0045] The molar ratio of metallic nickel to other metals in step (1) is 2.6:1.

[0046] The complex in step (1) is sodium citrate.

[0047] The ball milling frequency in step (1) is 20 Hz and the ball milling time is 30 min.

[0048] The heating rate of calcination in step (2) is 1°C / min, the calcination temperature is 850°C, and the calcination time is 1h.

[0049] The reducing gas in step (3) is carbon monoxide, the calcination temperature is 850° C., and the calcination time is 200 min.

[0050] The prepared catalyst is recorded as HEO-Ni-1, wherein the molar ratio of Ni is 20%, and the molar ratio of the other four metals is 80%.

[0051] Embodiment 3:

[0052] A method for preparing a Ni-based high entropy oxide catalyst, which differs from Example 1 in that the metal source in step (1) is nitrate.

[0053] The molar ratio of metallic nickel to other metals in step (1) is 18:1.

[0054] The complex in step (1) is sodium citrate.

[0055] The ball milling frequency in step (1) is 50 Hz and the ball milling time is 60 min.

[0056] The heating rate of calcination in step (2) is 10°C / min, the calcination temperature is 1200°C, and the calcination time is 6h.

[0057] The reducing gas in step (3) is methane, the calcination temperature is 200° C., and the calcination time is 20 min.

[0058] The prepared catalyst is recorded as HEO-Ni-2, in which the molar ratio of Ni is 82%, and the molar ratio of the other four metals is 18%.

[0059] Comparative Example 1:

[0060] A method for preparing a Ni-based high entropy oxide catalyst, which differs from Example 1 in that: in step (1), four metals, nickel, magnesium, copper and zinc, are used, and the prepared catalyst is recorded as Ni x MgCuZnO.

[0061] Comparative Example 2:

[0062] A method for preparing a Ni-based high entropy oxide catalyst, which differs from Example 1 in that: in step (1), four metals, nickel, cobalt, copper and zinc, are used, and the prepared catalyst is recorded as Ni x CoCuZnO.

[0063] Comparative Example 3:

[0064] A method for preparing a Ni-based high entropy oxide catalyst, which differs from Example 1 in that the molar ratio of metallic nickel to other metals in step (1) is 1:1, and the prepared catalyst is recorded as HEO-Ni-3.

[0065] Comparative Example 4:

[0066] A method for preparing a Ni-based high entropy oxide catalyst, which differs from Example 1 in that: the ball milling frequency in step (1) is 10 Hz, and the ball milling time is 20 min; the prepared catalyst is recorded as HEO-Ni-4.

[0067] Comparative Example 5:

[0068] A method for preparing a Ni-based high entropy oxide catalyst, which differs from Example 1 in that: the heating rate of calcination in step (2) is 10°C / min, the calcination temperature is 800°C, the calcination time is 1h, and the prepared catalyst is recorded as HEO-Ni-5.

[0069] The catalysts prepared in the above examples and comparative examples were applied to prepare synthesis gas by reforming carbon dioxide and methane. The specific steps and effects are shown in Experimental Example 1 and Table 1.

[0070] The catalytic performance of the catalyst samples prepared in all the examples and comparative examples was evaluated. The reaction was carried out in a fixed bed reactor with continuous gas flow. 0.05 g of catalyst was loaded in a small diameter ratio quartz tube. The reaction conditions were 750°C, CO2:CH4:N2=1:1:8 (V:V:V), normal pressure, and a space velocity of 14400 mL·g -1 ·h -1 After the reaction, the gas was analyzed by gas chromatography, and the reaction results are shown in Table 1.

[0071] Table 1

[0072]

[0073] It can be seen from Table 1 that the Ni-based catalyst for methane dry reforming prepared by the preparation method provided in Examples 1-3 of the present invention has a higher reaction activity in the reaction of methane dry reforming to produce synthesis gas, which is much higher than that of Comparative Examples 1-5. Figure 3 It can be seen that the catalyst still maintains good activity and stability after running for 100 h.

[0074] In summary, the present invention provides a method for preparing a Ni-based high entropy oxide catalyst, which uses a configuration entropy strategy to construct a nickel-based oxide catalyst. The synthesized Ni-based catalyst can generate reversible Ni particles in a reducing atmosphere, and its reversibility is manifested in that the formed Ni particles can be restored to high entropy oxides after oxidation, preventing the catalyst from sintering and completing the regeneration of the catalyst. Through a simple solid ball milling method, a large number of catalysts are prepared at one time, successfully solving the problem of catalyst deactivation in the CO2 methane dry reforming reaction, and greatly improving the service life of the catalyst and the reaction catalytic efficiency.

[0075] Those skilled in the art should recognize that the above embodiments are only used to illustrate the present application and are not intended to be limiting of the present application. As long as they are within the spirit and scope of the present application, appropriate changes and modifications to the above embodiments are within the scope of protection claimed in the present application.

Claims

1. A method for preparing a Ni-based high entropy oxide catalyst, characterized in that: The following steps are involved: (1) mixing a mixture of metal source powders of magnesium, zinc, cobalt and copper with a complexing agent and metal nickel, and then ball milling the mixture at a ball milling frequency of 20-50 Hz and a ball milling time of 30-60 min to obtain a precursor; (2) calcining the precursor obtained in step (1) at high temperature to obtain a Ni-based high entropy oxide catalyst powder; (3) calcining the Ni-based high entropy oxide catalyst powder obtained in step (2) in a reducing gas to form reversible Ni particles; In step (1), the molar ratio of metallic nickel to other metals is 2.6:1-18:1; In step (1), the complexing agent is one or more of sodium citrate, citric acid, diethanolamine, ethylenediaminetetraacetic acid, acetylacetone, dithizone, and sodium triphosphate; In step (2), the high temperature calcination temperature is 850-1200° C., the calcination time is 1-6 hours, and the heating rate during calcination is 1-10° C. / min.

2. The method for preparing a Ni-based high entropy oxide catalyst according to claim 1, characterized in that: In step (1), the metal source is one or more of oxides, chlorides, acetates, nitrates, carbonates, sulfates, sulfates, ammonium oxalates, citrates and gluconates.

3. The method for preparing a Ni-based high entropy oxide catalyst according to claim 1, characterized in that: In step (3), the reducing gas is hydrogen, methane or carbon monoxide, the calcination temperature is 200-850° C., and the calcination time is 20-200 min.

4. A Ni-based high entropy oxide catalyst, characterized in that: The preparation method is described in any one of claims 1 to 3.

5. The use of a Ni-based high entropy oxide catalyst in preparing synthesis gas by reforming carbon dioxide and methane according to claim 4, characterized in that: In the application, the volume ratio of carbon dioxide to methane is 0.8-1.2, the reaction temperature is 650-850°C, the reaction pressure is normal pressure-2MPa, and the reaction raw gas space velocity is 3000-60000mL·g -1 ·h -1 .

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