Metallic self-assembled catalyst, preparation method and application thereof

Abstract

The application provides a metal spontaneous positioning catalyst, a preparation method and application thereof. The metal spontaneous positioning catalyst is composed of a metal oxide with surface defect vacancies and single metal atoms. The single metal atoms are uniformly loaded on the surface of the metal oxide in the form of chemical bonds to form regular surface atomic arrangement. The metal oxide is MnOx, ZnMoO or ZnCr2O x ; the single metal atom is Cu, Cr, Mn, Pd, Zr or Al; and the mass of the single metal atom accounts for 0.01-10% of the mass of the metal oxide. The surface of the metal oxide composing the catalyst has defect vacancies, so that the single metal atoms are stably loaded on the defect sites in the form of chemical bonds, the anchoring of the single metal atoms on the surface of the carrier is enhanced, the agglomeration of the single metal atoms is prevented, the single metal atoms are uniformly dispersed on the carrier to form regular surface atomic arrangement, the utilization rate of the metal atoms is increased, and the overall catalytic activity of the metal oxide catalyst is improved.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, specifically to a metal spontaneous fall-in catalyst, its preparation method, and its application. Background Technology

[0002] As a greenhouse gas, excessive CO2 emissions can cause a series of environmental problems, such as the greenhouse effect and ocean acidification. Therefore, effectively converting CO2 into value-added chemicals can not only control atmospheric CO2 concentrations but also provide a way to replace fossil fuels and achieve sustainable development for human society. Both national renewable energy transitions and the commitment of responsible major powers to dual-carbon goals require the development of renewable liquid fuels and chemicals. Using carbon dioxide as a carbon source combined with green electricity and green hydrogen obtained from wind and solar power to produce high-value-added liquid fuels and green chemicals can be seen as a new and profitable industrial process for large-scale utilization of carbon dioxide and green hydrogen.

[0003] There are two main routes for producing aromatics from a carbon dioxide + hydrogen mixture. One involves mixing a methanol catalyst with a molecular sieve to produce aromatics via a methanol- or other oxygen-containing compound-mediated pathway. The other involves mixing a modified Fischer-Tropsch catalyst with a molecular sieve to produce aromatics via an olefin-mediated pathway. The aromatics produced via the olefin-mediated pathway are primarily light aromatics such as BTX. By controlling reaction conditions and modifying the physicochemical properties of the catalyst, the production of diversified aromatic products can be achieved, allowing for the control of the main product to be C6–C12 liquid fuels.

[0004] However, the technology for preparing aromatics in one step using a mixture of carbon dioxide and hydrogen through oxygen-containing compounds such as methanol has not yet been industrialized. The main technical challenge lies in the limited yield of aromatics due to the reverse water-gas reaction during the reaction process. How to significantly improve the conversion rate and selectivity of the one-step preparation reaction without changing the composition of the aromatic products is a core scientific problem in the production of aromatics using a mixture of carbon dioxide and hydrogen as a reaction feedstock. Summary of the Invention

[0005] To address the aforementioned problems in existing technologies, this invention provides a spontaneous metal fall-in catalyst, its preparation method, and its application. The catalyst utilizes a metal oxide with surface defects and vacancies as a support, where single metal atoms are spontaneously and uniformly dispersed and loaded onto the support surface. During the reaction of carbon dioxide and hydrogen, the single metal atoms can both highly actively promote the reverse water-gas reaction and catalyze the intermediate reaction (carbon monoxide and hydrogen) in conjunction with the metal oxide support. Combining the spontaneous metal fall-in catalyst provided by this invention with a molecular sieve creates a bifunctional metal oxide-molecular sieve catalyst, enabling highly selective one-step conversion of carbon dioxide into liquid fuel, improving aromatic selectivity and reactant conversion rate, and reducing byproduct selectivity in the reaction.

[0006] The specific details of the invention are as follows:

[0007] In a first aspect, the present invention provides a metal spontaneous fall-in catalyst, wherein the metal spontaneous fall-in catalyst is composed of a metal oxide having defect vacancies on its surface and a single metal atom;

[0008] The single metal atoms are uniformly loaded on the surface of the metal oxide in the form of chemical bonds, forming a regular surface atomic arrangement;

[0009] The metal oxide is MnOx, ZrO, MoO, ZnZrOx, ZnMoO, or ZnCr2O. x ;

[0010] The single metal atom is Zn, Cu, Cr, Mn, Pd, Zr, Al, Mo, Ge, In, Ni, Au, Fe, or Y;

[0011] The mass of the single metal atom accounts for 0.01 to 10% of the mass of the metal oxide.

[0012] Optionally, the single metal atom is Cu, Cr, Mn, Pd, Zr, or Al;

[0013] The mass of the single metal atom accounts for 2% to 8% of the mass of the metal oxide.

[0014] Secondly, the present invention provides a method for preparing a spontaneous metal fall-off catalyst, the method comprising the following steps:

[0015] S1. The metal oxide precursor solution and the precipitant with a pH of not less than 8.5 are slowly mixed under continuous stirring to obtain the first mixed solution. During the mixing process, the temperature is maintained at 70℃~100℃ and the pH is maintained at 5.5-8.5. After the mixing is completed, the solution is transferred to a nitrogen atmosphere and continuously stirred for crystallization for 6-48 hours to obtain the second mixed solution.

[0016] S2. The second mixed solution with a volume ratio of 1:0.01-0.1 is mixed with a carbon source template agent, stirred for 4-26 hours, filtered and calcined to obtain a metal oxide with defect vacancies on the surface.

[0017] S3. A metal precursor solution is dropped into the metal oxide with surface defects and vacancies, mixed evenly, and then ultrasonically treated for 4-6 hours, followed by a second calcination to obtain a spontaneously disseminated metal catalyst with single metal atoms uniformly distributed on the surface of the metal oxide; wherein, the volume ratio of the metal oxide with surface defects and vacancies to the metal precursor solution is 1:0.5-2.5; and the mass of the metal atoms in the metal precursor solution accounts for 0.01-10% of the mass of the metal oxide with surface defects and vacancies.

[0018] Optionally, in step S1, the metal oxide precursor solution is a nitrate solution of the metal element in the metal oxide to be prepared.

[0019] Optionally, in step S1, the precipitant is an ammonium carbonate solution, an ammonium acetate solution, or a urea solution.

[0020] Optionally, in step S2, the carbon source template agent is one or more of carbon nanotubes, glucose, cellulose, graphene, and metal-organic framework materials.

[0021] Optionally, in step S2, the calcination is carried out in an air atmosphere, the calcination temperature is 350-750℃, the heating rate is 0.1℃-10℃ / min, and the time is 0.5-48h.

[0022] Optionally, in step S3, the metal precursor solution is obtained by dissolving a salt containing Zn, Cu, Cr, Mn, Pd, Zr, Al, Mo, Ge, In, Ni, Au, Fe or Y elements in deionized water.

[0023] Optionally, in step S3, the power of the ultrasonic treatment is 600W and the frequency is 40kHz.

[0024] Optionally, in step S3, the secondary calcination includes atmospheric calcination and high-pressure calcination; wherein, the atmospheric calcination is carried out in an air atmosphere at a temperature of 300-550°C, a heating rate of 1-10°C / min, and a time of 4-8h.

[0025] The high-pressure calcination is carried out in a reducing atmosphere at a temperature of 350–750°C, a heating rate of 0.1–10°C / min, and a time of 0.5–48 h.

[0026] The reducing gas space velocity is 100-10000 mL / h·g cat .

[0027] Thirdly, the present invention provides an application of a metal spontaneous fall-in catalyst, which combines the metal spontaneous fall-in catalyst with a molecular sieve having two-dimensional or three-dimensional channels to form a bifunctional acid-base heterojunction catalyst, used to catalyze the one-step conversion of a mixture of carbon dioxide and hydrogen into aromatics.

[0028] Optionally, the spontaneous metal fall-in catalyst and H-ZSM-5 molecular sieve form a bifunctional acid-base heterojunction catalyst;

[0029] The mass ratio of the H-ZSM-5 molecular sieve to the spontaneous metal fall-off catalyst is 1:1 to 3.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] This invention provides a spontaneous metal deposition catalyst, which is formed by uniformly loading single metal atoms onto the surface of a metal oxide support. Due to the presence of defect vacancies on the metal oxide surface (created by a carbon source template agent), the single metal atoms are stably loaded at these defect sites through chemical bonds, enhancing the anchoring of the single metal atoms on the support surface. Furthermore, the presence of oxygen vacancies surrounding the metal oxide prevents the aggregation of single metal atoms, resulting in a uniform dispersion of single metal atoms on the support, forming a regular surface atomic arrangement, increasing the utilization rate of metal atoms, and thus improving the overall catalytic activity of the metal oxide catalyst.

[0032] This invention also provides a method for preparing a spontaneous metal fall-in catalyst. The method involves preparing metal oxides from metal salts via precipitation, hydrothermal methods, or hard template methods; then creating oxygen vacancy defects on the surface of the metal oxide support using a specific carbon source template agent; finally, through impregnation and calcination, single metal atoms are spontaneously and uniformly dispersed on the surface of the metal oxide support, thus preparing the spontaneous metal fall-in catalyst. The method is simple and easy to implement, enabling rapid and controllable preparation of spontaneous metal fall-in catalysts, providing an effective preparation route for large-scale development and utilization.

[0033] This invention also provides an application of a metal spontaneous deposition catalyst, which is combined with a molecular sieve having two-dimensional or three-dimensional channels to form an acid-base heterojunction, preparing a metal oxide-molecular sieve bifunctional catalyst for the one-step conversion of a mixture of carbon dioxide and hydrogen into aromatics. Because the metal oxide surface has a uniform and regular arrangement of single metal atoms, the selected single metal atoms have excellent hydrogenation activity. Furthermore, the presence of oxygen vacancies around the metal oxide prevents the aggregation of single metal atoms, achieving uniform dispersion of single metal atoms on the support, forming a regular surface atomic arrangement, increasing the utilization rate of metal atoms, and thus improving the overall catalytic activity of the metal oxide catalyst. This significantly improves the catalytic activity, enabling highly selective one-step conversion of a mixture of carbon dioxide and hydrogen into aromatics. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 The XRD image of the spontaneous metal fall-in catalyst provided in Example 1 of the present invention is shown;

[0036] Figure 2 The HADDF-EDS image of the spontaneous metal fall-in catalyst provided in Example 1 of the present invention is shown.

[0037] Figure 3 The temperature-programmed reduction curves of the metal spontaneous fall-in catalyst provided in Example 1 of the present invention and the catalyst provided in Comparative Example 1 are shown.

[0038] Figure 4 The X-ray diffraction pattern of the spontaneously placed metal catalyst provided in the embodiments of the present invention is shown.

[0039] Figure 5 A flowchart illustrating the preparation method of the metal spontaneous fall-in catalyst provided in an embodiment of the present invention is shown. Detailed Implementation

[0040] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0041] Specific experimental steps or conditions are not specified in the examples; however, they can be performed according to the conventional experimental steps or conditions described in the prior art. Reagents and other instruments used, unless otherwise specified, are all commercially available conventional reagent products.

[0042] The primary objective of this invention is to provide a spontaneously assembled metal catalyst, which is composed of a metal oxide with surface defect vacancies and single metal atoms. The single metal atoms are uniformly loaded onto the surface of the metal oxide via chemical bonds, forming a regular surface atomic arrangement. Specifically, the metal oxide can be a single metal oxide or a bimetallic oxide, and its morphology can be spinel, perovskite, or mesoporous single crystal. The single metal oxide can specifically be MnOx, ZrO, or MoO, and the bimetallic oxide can specifically be ZnCr2O. x ZnZrO x Alternatively, the single metal atoms supported on the surface of the metal oxide by ZnMoO can be Zn, Cu, Cr, Mn, Pd, Zr, Al, Mo, Ge, In, Ni, Au, Fe, or Y; and the mass of the single metal atom accounts for 0.01 to 10% of the mass of the metal oxide.

[0043] In specific implementation, the present invention uniformly loads single metal atoms onto the surface of a metal oxide support with defect vacancies to form a spontaneous metal landing catalyst, thereby giving the catalyst a regular surface atomic arrangement.

[0044] In some embodiments, a further preferred outcome is that the spontaneous metal fall-in catalyst can specifically be composed of Fe atoms uniformly supported on ZnCr2O. x A bimetallic oxide support is formed on the surface. Specifically, the metal oxide is ZnCr2O. x The single metal atom is specifically Fe, and Fe accounts for a significant portion of ZnCr2O. x 3% by mass. Specifically, a spontaneous metal fall-in catalyst can also consist of Cr atoms uniformly supported on a single metal oxide, MnO. X Formation on the carrier surface, specifically, a metal oxide, MnO X The single metal atom is specifically Cr, and Cr accounts for a significant portion of MnO. X 5% of the quality.

[0045] Secondly, the present invention provides a method for preparing the metal spontaneous fall-in catalyst described in the first aspect above. Figure 5 A flowchart illustrating the preparation method of the spontaneous metal fall-in catalyst provided in this embodiment of the invention is shown, as follows: Figure 5 As shown, the preparation method includes the following steps:

[0046] S1. The metal oxide precursor solution and the precipitant with a pH of not less than 8.5 are slowly mixed under continuous stirring to obtain the first mixed solution. During the mixing process, the temperature is maintained at 70℃~100℃ and the pH is maintained at 5.5-8.5. After the mixing is completed, the solution is transferred to a nitrogen atmosphere and continuously stirred for crystallization for 6-48 hours to obtain the second mixed solution.

[0047] In specific implementation, in this preparation step, the metal oxide precursor solution is a salt containing the metal element of the metal oxide to be prepared, specifically a metal nitrate or a metal acetate. The metal element of the metal oxide to be prepared can be MnOx, ZrO, MoO, ZnZrOx, ZnMoO, or ZnCr2O. x When the metal oxide to be prepared is a bimetallic oxide, the metal salt solution contains two metal elements, and the molar ratio of the two metal elements can be 1:1 to 1.5.

[0048] In practice, the precipitant used in this step is selected from ammonium carbonate solution, ammonium acetate solution, or urea solution.

[0049] S2. The second mixed solution with a volume ratio of 1:0.01-0.1 is mixed with a carbon source template agent, stirred for 4-26 hours, filtered and calcined to obtain a metal oxide with defect vacancies on the surface.

[0050] In practice, the carbon source template agent used in this step is selected from one or more of carbon nanotubes, glucose, cellulose, graphene, and metal-organic framework materials. Calcination is carried out in an air atmosphere at a temperature of 350–750℃, a heating rate of 0.1℃–10℃ / min, and a time of 0.5–48 h.

[0051] S3. A metal precursor solution is dropped into the metal oxide with surface defects and vacancies, mixed evenly, and then ultrasonically treated for 4-6 hours, followed by a second calcination to obtain a metal spontaneous deposition catalyst with a single metal element uniformly distributed on the surface of the metal oxide; wherein, the volume ratio of the metal oxide with surface defects and vacancies to the metal precursor solution is 1:0.5-2.5; and the mass of the metal element in the metal precursor solution accounts for 0.01-10% of the mass of the metal oxide with surface defects and vacancies.

[0052] In practice, the metal precursor solution used in this step is obtained by dissolving salts containing Zn, Cu, Cr, Mn, Pd, Zr, Al, Mo, Ge, In, Ni, Au, Fe, or Y in deionized water. Specifically, it can be a carbonate, nitrate, or acetate containing the aforementioned metal elements. The ultrasonic treatment power is 600W, and the frequency is 40kHz.

[0053] In practice, this step employs a combination of atmospheric pressure calcination and high-pressure calcination to obtain a metal spontaneously deposited catalyst with uniformly distributed single metal elements on the surface of the metal oxide. First, calcination is carried out under atmospheric pressure at a temperature of 300–550°C, a heating rate of 1–10°C / min, and a time of 2–8 hours. Then, the product obtained after atmospheric pressure calcination is transferred to a specially designed high-pressure calcination furnace for further calcination in a reducing atmosphere. High-pressure calcination under a reducing atmosphere results in regular microscopic surface pores, abundant oxygen vacancies, and the formation of mesoporous single crystals with a large specific surface area, allowing for more stable monodispersity of single metal atoms on the surface. Specifically, the high pressure can be 10-30 bar, the temperature 350–750°C, the heating rate 0.1–10°C / min, and the time 0.5–48 hours; the reducing gas space velocity is 100–10000 mL / h·g. cat .

[0054] Considering the lack of catalysts with high aromatic selectivity, high reactant conversion rate, and low byproduct selectivity in the process of preparing aromatics from a carbon dioxide + hydrogen mixture via an oxygen-containing compound-mediated pathway such as methanol, the second objective of this invention is to provide an application of the aforementioned spontaneous metal fall-in catalyst. Specifically, this involves combining the spontaneous metal fall-in catalyst provided in the first aspect with a molecular sieve having two-dimensional or three-dimensional channels to form a bifunctional acid-base heterojunction catalyst, used to catalyze the one-step conversion of a carbon dioxide and hydrogen mixture into aromatics.

[0055] In specific implementation, the metal spontaneous placement catalyst provided by the present invention has a regular surface metal atom arrangement, and the regular surface of the metal atoms promotes the formation of acid-base heterojunctions with molecular sieves with two-dimensional or three-dimensional channels at the interface.

[0056] As an example, a spontaneously fallen-in metal catalyst can be combined with H-ZSM-5 molecular sieve to form a bifunctional acid-base heterojunction catalyst; wherein the mass ratio of H-ZSM-5 molecular sieve to the spontaneously fallen-in metal catalyst is 1:1 to 3. When this bifunctional acid-base heterojunction catalyst is used in the process of producing aromatics from a carbon dioxide + hydrogen mixture, it can significantly improve the reactant conversion rate and the selectivity of the aromatic product, while reducing the selectivity of by-products. Specifically, the spontaneously fallen-in metal catalyst provided by this invention is a mesoporous single-crystal metal oxide material with a special surface structure and a large specific surface area. It can be fixed to the molecular sieve by "spot welding" using a special ceramic adhesive, and then spray-granulated to form microsphere catalysts for use in the fluidized bed carbon dioxide hydrogenation to liquid fuel catalytic reaction. The spontaneously fallen metal atoms greatly enhance its catalytic activity.

[0057] In a specific embodiment, when the molecular sieve with two-dimensional or three-dimensional channels is short b-axis ZSM-5, the heterojunction bifunctional catalyst formed by mixing it with the metal spontaneous fall-in catalyst provided by this invention can control the reaction temperature at 270-380℃ and the space velocity at 300-1000 mL / h·g in the catalytic hydrogenation of carbon dioxide and the synthesis of liquid fuels or aromatics from syngas. cat Under conditions where the hydrogen to carbon dioxide volume ratio is 0.5–3, the reactant conversion rate is above 45%, the selectivity for C6-C12 liquid fuels is greater than 80%, the selectivity for aromatics is higher than 90%, and the selectivity for methane is less than 3%. This indicates that the metal spontaneous fall-in catalyst provided by this invention has excellent prospects for carbon neutralization applications as a component of a one-step conversion reaction catalyst.

[0058] This invention creates defects in the oxygen vacancies of a metal oxide support using a carbon source template agent. This results in an abundance of oxygen vacancies and metal defect sites on the surface of the metal oxide support, thereby stabilizing some highly reactive metals at these defect sites. The strong interaction between these metals and the metal oxide support enhances the anchoring of the metals on the support surface. Simultaneously, the oxygen vacancies surrounding the metal oxide prevent the aggregation of single metal atoms, thus improving the dispersion of single metal atoms on the support and further enhancing atom utilization. The highly reactive metals can effectively promote the reverse water-gas reaction during the carbon dioxide hydrogenation process and also catalyze the intermediate reaction (carbon monoxide hydrogenation) in conjunction with the metal oxide support. Combining this with molecular sieves enables a highly selective one-step conversion of carbon dioxide into liquid fuels or aromatics.

[0059] To enable those skilled in the art to better understand this application, the following embodiments are provided to illustrate in detail a metal spontaneous landing catalyst, its preparation method, and its application.

[0060] Example 1

[0061] Step 1: Prepare a bimetallic oxide support with abundant oxygen vacancies and metal defect landing sites on its surface.

[0062] (1) Weigh 13.98g of zinc nitrate hexahydrate and 37.61g of chromium nitrate nonahydrate and dissolve them in beaker A containing 1000g of deionized water. Then place beaker A in a heatable magnetic stirrer. Heat the magnetic stirrer to 60°C and stir continuously for 60 minutes until the solid salts are completely dissolved.

[0063] (2) Prepare a beaker containing 500g of deionized water, labeled beaker B. Add 48.05g of ammonium carbonate to beaker B and place beaker B on a heated magnetic stirrer. Set the temperature to 45℃ and stir thoroughly until the solid is completely dissolved.

[0064] (3) Prepare a three-necked flask, slowly add the solutions in beaker A and beaker B into the three-necked flask, maintain the temperature of the mixed solution at 70-100℃, control the pH of the mixed solution in the three-necked flask to be between 5.5 and 8.5 by adjusting the rate of addition of the solution in beaker A or B, and keep stirring throughout the process.

[0065] (4) After mixing, continue stirring and introduce nitrogen gas to allow the mixture to crystallize under a nitrogen atmosphere for 8 hours.

[0066] (5) After crystallization in step 4, add carbon nanotubes to the mixture at a ratio of 1:0.01. At the same time, turn off the heating and continue stirring, maintaining natural cooling and stirring for 2 to 6 hours until room temperature.

[0067] (6) The prepared metal oxide precursor was subjected to three cycles of vacuum filtration and washing, dried at 110°C, and calcined at 450°C for 2 hours in air at a rate of 5°C / min. A ZnCrOx bimetallic oxide support with abundant oxygen vacancies and metal defect landing sites on the surface was obtained.

[0068] Step 2: Metal falls into place spontaneously

[0069] (1) A certain amount of ferric nitrate nonahydrate was dissolved in deionized water and reacted under microwave power of 300W for 2 min-5 min to prepare a uniformly dissolved single metal atom stock solution, wherein the mass ratio of Fe to metal oxide was 0.03:1;

[0070] (2) The ZnCrOx bimetallic oxide support prepared in step 1 was uniformly mixed with the single-atom stock solution. After uniform mixing, the mixture was subjected to ultrasonic treatment. The ultrasonic treatment power was 600W, the frequency was 40KHZ, and the ultrasonic treatment time was 4h. After ultrasonic treatment, the mixture was calcined at 350℃ for 2h under air atmosphere at a rate of 1℃ / min. Fe metal spontaneous fall-in catalyst was obtained.

[0071] Figure 1 The XRD image of the spontaneous metal fall-in catalyst provided in Example 1 of the present invention is shown; Figure 2 The HADDF-EDS image of the spontaneous metal fall-in catalyst provided in Example 1 of this invention is shown; from Figure 2 It can be clearly seen that Fe atoms are uniformly distributed on the surface of the inert component-doped metal oxide support.

[0072] Figure 3 The following are temperature-programmed reduction comparison curves of the metal spontaneous fall-in catalyst provided in Example 1 of the present invention and the catalyst provided in Comparative Example 1. Figure 3It can be seen that the metal oxide prepared in Example 1 did not show any other reduction peaks, so no extra oxide was introduced. The introduced single-atom metal did not react with the oxide in the solid phase and did not affect the main structure of the oxide. The maximum reduction temperature did not change. Compared with the comparative example, it can be seen that the reduction activity of the metal spontaneously fallen oxide is significantly superior.

[0073] Example 2

[0074] The difference between Example 2 and Example 1 is that in this comparative example, the mass ratio of Fe to metal oxide carrier was 0.0448:1 when preparing the single-atom mixture.

[0075] Example 3

[0076] The difference between Example 3 and Example 1 is that in this comparative example, the mass ratio of Fe to metal oxide carrier was 0.0778:1 when preparing the single-atom mixture.

[0077] Figure 4 The X-ray diffraction pattern of the spontaneously fallen-in metal catalyst provided in the embodiments of the present invention is shown. Figure 4 It can be confirmed that the introduced Fe element and inert components did not change the crystal structure of the metal oxide, and no other impurity components were introduced, indicating that there are basically no other side reactions.

[0078] Example 4

[0079] The difference between Example 4 and Example 1 is that cobalt nitrate was used as the landing metal source in this comparative example, and the mass ratio of cobalt to metal oxide carrier was 0.03:1.

[0080] Example 5

[0081] The difference between this embodiment and Embodiment 1 is that, in the preparation process described in Embodiment 1, the metal oxide support undergoes a calcination step in a specially designed high-pressure reducing atmosphere calcination furnace. After calcination under normal atmospheric pressure, the pressure is increased to 10 bar, and the space velocity is 500 mL / h·g under a carbon monoxide atmosphere. cat The heating rate was 0.5℃ / min, and the calcination was carried out at 350℃ for 3 hours. The remaining steps were the same as in Example 1.

[0082] A spontaneously placed bimetallic mesoporous single-crystal catalyst was prepared. The catalyst prepared in this embodiment was tested using a physical adsorption device, confirming that the sample obtained in this embodiment has a mesoporous structure with a pore size of 4.32 nm.

[0083] Example 6

[0084] Step 1: Prepare a single-metal oxide support MnOx with abundant oxygen vacancies and metal defect landing sites on its surface.

[0085] (1) Dissolve manganese nitrate tetrahydrate in deionized water, with a mass ratio of manganese nitrate tetrahydrate to deionized water of 1:20; stir the prepared manganese nitrate solution continuously on a magnetic stirrer until fully dissolved, and heat to 70-80℃;

[0086] (2) Prepare a certain amount of ammonium acetate solution with pH 9-10, and the mass ratio of the ammonium acetate solution to the manganese nitrate solution is 1:2;

[0087] (3) Add manganese nitrate solution and ammonium acetate solution to the three-necked flask slowly at the same time, control the pH between 6 and 8, maintain the temperature of the solution in the three-necked flask at 70-80°C in a water bath, and stir vigorously throughout the process.

[0088] (4) After mixing, continue stirring and introduce nitrogen gas to allow the mixture to crystallize under a nitrogen atmosphere for 24 seconds.

[0089] (5) After crystallization in step 4, add glucose to the mixture at a ratio of 1:0.1. At the same time, turn off the heating and continue stirring, maintaining natural cooling and stirring for 2 to 6 hours until room temperature.

[0090] (6) The prepared metal oxide precursor was subjected to three cycles of vacuum filtration and washing, dried at 110°C, and calcined at 550°C for 2 hours in air at a rate of 10°C / min. A MnOx single metal oxide support with abundant oxygen vacancies and metal defect landing sites on its surface was obtained.

[0091] Step 2: Metal falls into place spontaneously

[0092] (1) Dissolve a certain amount of cobalt nitrate in deionized water and react it under microwave power of 300W for 2min-5min to prepare a uniformly dissolved single metal atom stock solution, wherein the mass ratio of cobalt to metal oxide is 0.05:1;

[0093] (2) The MnOx bimetallic oxide support prepared in step 1 was uniformly mixed with the single-atom stock solution. After uniform mixing, it was subjected to ultrasonic treatment. The ultrasonic treatment power was 600W, the frequency was 40KHZ, and the ultrasonic treatment time was 4h. After ultrasonic treatment, it was calcined at 350℃ for 2h under air atmosphere at a rate of 1℃ / min.

[0094] (3) The product obtained after calcination in (2) is placed in a specially designed furnace and further calcined in a reducing atmosphere; the calcination temperature is 350℃, the pressure inside the specially designed furnace is 10 bar, and the hydrogen space velocity is 500 mL / h·g. cat A specially designed furnace was used with a heating rate of 0.5℃ / min, and the calcination time was 3 hours. A spontaneously displaced Co metal catalyst was obtained.

[0095] Further XRD and HADDF-EDS images of the spontaneously joined metal catalyst prepared in this embodiment were obtained using scanning transmission electron microscopy. The results were consistent with those obtained in Example 1, and will not be repeated here. X-ray diffraction was also used to test the spontaneously joined metal catalyst prepared in this embodiment, and the results were consistent with those obtained in Example 1. Figure 1 Therefore, this embodiment will not be repeated.

[0096] Comparative Example 1

[0097] Unlike Example 1, no single-atom Fe was introduced in this comparative example after the bimetallic oxide support was prepared.

[0098] Experiment Example 1: Verification of Various Performance Aspects

[0099] (1) Adsorption capacity test

[0100] The adsorption capacity of the spontaneously dispersed Fe catalyst prepared in Example 1 was tested using a chemisorption apparatus. The test results are shown in [Figure 1]. Figure 4 ,from Figure 4 It can be seen that the CO2 adsorption capacity of this embodiment is twice that of Comparative Example 1, indicating that the 16d-site monodisperse Fe can adsorb and activate more CO2.

[0101] (2) Performance test of fixed-bed microreactor synthesis gas to aromatics production

[0102] 1) The H-ZSM-5 molecular sieve was mixed with the catalysts prepared in Examples 1, 2, 3, 4, and Comparative Example 1 at a mass ratio of 1:1 and then mechanically ball-milled to obtain a metal oxide-molecular sieve acid-base heterojunction catalyst. Table 1 below shows the fixed-bed microreactor syngas to aromatics performance results for each example and comparative example.

[0103] Table 1. Performance results of metal oxide-molecular sieve acid-base heterojunction catalysts for fixed-bed microreactor syngas-to-aromatics synthesis provided in each embodiment and comparative example.

[0104]

[0105] As can be seen from Table 1 above, the reaction conversion rate of Comparative Example 1 is significantly lower than that of the other examples. The spontaneously monodisperse Fe catalyst prepared in the examples can significantly improve catalytic activity.

[0106] Furthermore, the evaluation results from Examples 1 and 2 show that the introduction of excessive active metals leads to a decrease in aromatic selectivity, which is attributed to the poisoning effect of excessive Fe on the acidity of the molecular sieve surface.

[0107] The fixed-bed microreactor test results showed that the spontaneous monodisperse Fe catalyst combined with molecular sieve exhibited high aromatization activity and maintained extremely high selectivity.

[0108] 2) The H-ZSM-5 molecular sieve and the Fe metal spontaneously fallen-position metal oxide mesoporous single crystal catalyst prepared in Example 5 were mixed at a mass ratio of 1:1 and then mechanically ball-milled. The ball-milled mixed solid powder was placed in a specially designed high-pressure thermal reduction calcination furnace at a calcination temperature of 350°C, a furnace internal pressure of 1 bar, and a hydrogen space velocity of 500 mL / h·g. cat A specially designed furnace was used with a heating rate of 0.5℃ / min, and the calcination time was 3 hours. A mesoporous single-crystal metal oxide-molecular sieve heterojunction catalyst was obtained.

[0109] The performance of fixed-bed microreactor synthesis of aromatics was tested. The results showed that the aromatics selectivity remained basically unchanged at 80%, the carbon dioxide conversion rate increased to 45%, and the total selectivity of methane and carbon monoxide was less than 18%.

[0110] The present invention provides a detailed description of a spontaneous metal landing catalyst, its preparation method, and its application. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. The application of a metal spontaneous fall-in catalyst, characterized in that, The spontaneous metal fall-in catalyst is combined with H-ZSM-5 molecular sieve to form a bifunctional acid-base heterojunction catalyst, which is used to catalyze the one-step conversion of a mixture of carbon dioxide and hydrogen into aromatics. The spontaneous metal fall-in catalyst is composed of metal oxides with surface defect vacancies and single metal atoms; The single metal atoms are uniformly loaded on the surface of the metal oxide in the form of chemical bonds, forming a regular surface atomic arrangement; The metal oxide is ZnCr2O x The single metal atom is Fe; The mass of the single metal atom accounts for 0.01~10% of the mass of the metal oxide; The preparation method of the spontaneous metal fall-in catalyst includes the following steps: S1. The metal oxide precursor solution and the precipitant with a pH of not less than 8.5 are slowly mixed under continuous stirring to obtain the first mixed solution. During the mixing process, the temperature is maintained at 70℃~100℃ and the pH is maintained at 5.5-8.

5. After the mixing is completed, the solution is transferred to a nitrogen atmosphere and continuously stirred for crystallization for 6-48 hours to obtain the second mixed solution. S2. The second mixed solution with a volume ratio of 1:0.01-0.1 is mixed with a carbon source template agent, stirred for 4-26 hours, filtered and calcined to obtain a metal oxide with defect vacancies on the surface. S3. A single-metal atom precursor solution is dropwise added to the metal oxide with surface defects and vacancies, mixed thoroughly, and then ultrasonically treated for 4-6 hours, followed by a second calcination to obtain a metal spontaneously deposited catalyst with single metal atoms uniformly distributed on the surface of the metal oxide; wherein, the volume ratio of the metal oxide with surface defects and vacancies to the single-metal atom precursor solution is 1:0.5-2.5; the mass of the single metal atoms in the single-metal atom precursor solution accounts for 0.01-10% of the mass of the metal oxide with surface defects and vacancies; The precipitant in step S1 is an ammonium carbonate solution, an ammonium acetate solution, or a urea solution. In step S2, the carbon source template agent is carbon nanotubes; In step S3, the secondary calcination includes atmospheric calcination in an air atmosphere and high-pressure calcination in a reducing atmosphere. The atmospheric calcination temperature is 300~550℃, the heating rate is 1~10℃ / min, and the time is 4~8h. The high-pressure calcination temperature is 350~750℃, the heating rate is 0.1~10℃ / min, and the time is 0.5~48h; The specific steps of the combination are as follows: H-ZSM-5 molecular sieve and the aforementioned spontaneous metal fall-off catalyst were mixed at a mass ratio of 1:1 and then mechanically ball-milled. The ball-milled mixed solid powder was placed in a specially designed high-pressure thermal reduction calcination furnace at a calcination temperature of 350°C, a furnace internal pressure of 1 bar, and a hydrogen space velocity of 500 mL / h·g. cat A specially designed furnace body with a heating rate of 0.5℃ / min was used to calcine the catalyst for 3 hours, thereby obtaining a bifunctional acid-base heterojunction catalyst.

2. The application according to claim 1, characterized in that, In step S1, the metal oxide precursor solution is a nitrate solution containing the metal element in the metal oxide to be prepared.

3. The application according to claim 1, characterized in that, In step S2, the calcination is carried out in an air atmosphere, the calcination temperature is 350~750℃, the heating rate is 0.1℃~10℃ / min, and the time is 0.5~48h.

4. The application according to claim 1, characterized in that, In step S3, the single metal atom precursor solution is obtained by dissolving Fe-containing salts in deionized water.

5. The application according to claim 1, characterized in that, In step S3, the power of the ultrasonic treatment is 600W and the frequency is 40KHZ; The reducing gas space velocity is 100-10000 mL / h·g cat .

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