Basic metal oxide and acidic molecular sieve heterojunction catalyst, and preparation method and application thereof

Abstract

This invention provides a method for preparing and applying a heterojunction catalyst of alkali metal oxide and acidic molecular sieve. The preparation method includes: uniformly mixing alkali metal oxide and acidic molecular sieve at a weight ratio of 0.1-10, followed by granulation; placing the solid obtained from granulation into a reducing atmosphere calcination furnace and calcining at 0.5-1 MPa and 150-350°C for 1-10 h; thus obtaining the heterojunction catalyst of alkali metal oxide and acidic molecular sieve. This heterojunction catalyst is used to produce liquid fuels or aromatic chemicals from CO2 and H2. Utilizing the confinement effect of molecular sieves, cyclic molecules are generated through confined and directional reactions, forcing the Fischer-Tropsch chain growth to terminate within the jet fuel composition range. The resulting products are concentrated in C9 to C11 aromatics; and the selectivity for liquid fuels composed of C6-C12 exceeds 80%, which can be blended with straight-chain alkanes to obtain qualified jet fuel products. By selecting aromatic rings as the final product, the thermodynamic efficiency of the reaction process is improved, resulting in high energy utilization efficiency and significant energy-saving effects.

Description

Technical Field

[0001] This invention relates to the field of direct conversion of syngas to aromatics, specifically to a heterojunction catalyst of basic metal oxide and acidic molecular sieve, its preparation method and 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 CO2 as a carbon source combined with green electricity and green hydrogen generated from wind and solar power to produce high-value-added liquid fuels and green chemicals can be seen as a profitable new industrial process for large-scale carbon dioxide and green hydrogen utilization.

[0003] There are two main routes for producing aromatics from a mixture of carbon dioxide and hydrogen. One is to produce aromatics via a methanol- or other oxygen-containing compound-mediated pathway by mixing a methanol catalyst with a molecular sieve, and the other is to produce aromatics via an olefin-mediated pathway by mixing a modified Fischer-Tropsch catalyst with a molecular sieve.

[0004] However, the catalysts prepared by the above two methods present a contradiction between high conversion rates and high selectivity for the target product during the reaction process. Furthermore, relevant research still lacks catalysts that can be used for efficient CO2 catalysis. x Catalyst for producing liquid fuels with H2. Summary of the Invention

[0005] To address the aforementioned problems in the existing technology, this invention provides a heterojunction catalyst of basic metal oxide and acidic molecular sieve, its preparation method, and its application. The obtained catalyst exhibits both high aromatic hydrocarbon selectivity and high aromatic hydrocarbon yield, and is used for catalyzing CO2. x When producing liquid fuels using H2, the selectivity of C6-C12 liquid fuels in the products is greater than 80%, the selectivity of aromatics is greater than 90%, and the selectivity of methane is less than 3%, showing good prospects for carbon neutralization applications. The specific invention details are as follows:

[0006] In a first aspect, the present invention provides a method for preparing a heterojunction catalyst of an alkaline metal oxide and an acidic molecular sieve, characterized in that the preparation method includes the following preparation steps:

[0007] S1. After uniformly mixing alkaline metal oxides and acidic molecular sieves at a weight ratio of 0.1-10, the mixture is compressed into tablets and granulated.

[0008] S2. The solid obtained by tableting and granulation is placed in a reducing atmosphere calcination furnace and calcined at 0.5-1 MPa and 150-350°C for 1-10 h to obtain the heterojunction catalyst of alkaline metal oxide and acidic molecular sieve.

[0009] Optionally, in step S1, the alkaline metal oxide is a single metal oxide, a bimetallic oxide, or a metal-supported oxide formed by the spontaneous monodispersion of single metal atoms on the single metal oxide or bimetallic oxide.

[0010] The single metal oxide is MnO, CrO, ZrO, GeO, or NiO, and the double metal oxide is ZnCrO. x ZnPdO X or ZnMoO x ;

[0011] The single metal atom is Mo, Fe, Mn, Pd, Ni, or Co;

[0012] In the alkaline metal oxide, the mass percentage of the single metal atom is 0% to 7%;

[0013] The alkaline metal oxides are in the form of spinel, perovskite, solid solution, or mesoporous single crystals.

[0014] Optionally, the acidic molecular sieve is a hydrogen-type silica-alumina molecular sieve with a regular surface and a silica-alumina ratio of 20-200, selected from ZSM-5, ZSM-11 or ZSM-48;

[0015] The hydrogen-form silica-alumina molecular sieve with a regular surface is obtained through the following method:

[0016] The silica-aluminum molecular sieve is added to an acidic solution at 50-90℃ and stirred for 0.5-12 hours. The solid obtained by vacuum filtration is added to an alkaline solution at 50-90℃ and stirred for 0.5-12 hours. Then it is filtered, the filter residue is collected, washed until neutral, dried, and calcined at 300-650℃ for 2-48 hours.

[0017] The acidic solution is selected from at least one of hydrochloric acid, nitric acid, acetic acid, ammonium nitrate, ammonium chloride, and oxalic acid;

[0018] The alkaline solution is selected from at least one of the following: ammonia, n-butylamine, ethylenediamine, tetramethylammonium hydroxide, tetraethylammonium hydroxide, and tetrapropylammonium hydroxide aqueous solution;

[0019] The concentrations of the acidic and alkaline solutions are 0.2–3 mol / L;

[0020] The mass ratio of the silica-alumina molecular sieve to the acidic or alkaline solution is 1:10 to 1:100.

[0021] Optionally, the method for preparing the metal-supported oxide includes:

[0022] S11. The alkaline metal oxide precursor solution and an appropriate amount of 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 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.

[0023] S12. The second mixed solution with a volume ratio of 1:0.01-0.1 is mixed with a carbon source template agent, stirred under negative pressure for 4-26 hours, and then filtered and calcined to obtain an alkaline metal oxide with defect vacancies on the surface.

[0024] S13. Add a metal precursor solution to the alkaline metal oxide with defect vacancies on the surface, mix evenly, and then sonicate for 4-6 hours. Then, perform a second calcination to obtain a metal-supported oxide.

[0025] The alkaline metal oxide precursor solution is a salt containing the metal element of the alkaline metal oxide to be prepared.

[0026] The precipitant is at least one of sodium hydroxide, sodium carbonate, lithium hydroxide, ammonia, sodium carbonate, and ammonium bicarbonate.

[0027] The carbon source template agent is one or more of carbon nanotubes, glucose, cellulose, graphene, and metal-organic framework materials;

[0028] The metal precursor solution is a nitrate, acetate, acetylacetone salt, hydrochloride, acetate, or carbonate containing the single metal atom;

[0029] The volume ratio of the alkaline metal oxide with surface defects to the metal precursor solution is 1:0.5-2.5; the mass of the metal atoms in the metal precursor solution accounts for 0.01-10% of the mass of the alkaline metal oxide with surface defects.

[0030] Optionally, in step S1, the mixing method includes grinding or mechanically ball-milling the alkaline metal oxide and the silica-alumina molecular sieve.

[0031] Optionally, in step S1, the mixing method includes: ultrasonically dispersing in a solvent composed of ethanol and water, stirring until the solvent is completely evaporated, and then drying;

[0032] The volume ratio of ethanol to water is 1:1 to 1:2.

[0033] The mass ratio of the solvent to the mixed powder of the alkaline metal oxide and silica-alumina molecular sieve is 1:30 to 1:300;

[0034] The stirring temperature is 20-80℃;

[0035] The drying temperature is 40-120℃, and the time is 5-24h.

[0036] Optionally, in step S2, the reducing atmosphere roasting furnace is a fluidized bed roasting furnace;

[0037] The reducing gas in the reducing atmosphere roasting furnace is hydrogen or carbon monoxide; the flow rate of the reducing gas is 0.1-1000 ml / min.

[0038] In a second aspect, the present invention provides a heterojunction catalyst of alkaline metal oxide and acidic molecular sieve obtained by the preparation method described in the first aspect above.

[0039] Thirdly, the present invention provides an application of a heterojunction catalyst of alkaline metal oxide and acidic molecular sieve obtained by the preparation method described in the first aspect above, wherein the heterojunction catalyst is used to catalyze the production of aromatic chemicals or liquid fuels from CO2 + H2.

[0040] Optionally, the heterojunction catalyst is used to catalyze CO2. x In the products of producing aromatic chemicals or liquid fuels from H2, H2 and CO are present in a volume ratio of 0.5-3. x The reaction feed gas was used to carry out a catalytic reaction in a fixed-bed reactor at a reaction pressure of 0.5-5 MPa, a reaction temperature of 270℃-450℃, and a reaction space velocity of 300-1000 mL / h·gcat. Among the reaction products obtained, the selectivity of liquid fuel composed of C6-C12 was greater than 80%, the selectivity of aromatics was greater than 90%, and the selectivity of methane was less than 3%.

[0041] Compared with the prior art, the present invention has the following advantages:

[0042] This invention provides a heterojunction catalyst of alkaline metal oxide and acidic molecular sieve, using CO xUsing H2 as a raw material to produce liquid fuel, the molecular sieve confinement effect is utilized to generate cyclic molecules through confined directional reactions, forcing the Fischer-Tropsch chain growth to terminate within the range of aviation kerosene components (aromatic components). The resulting products are concentrated in C9 to C11 aromatics; and the selectivity of liquid fuel composed of C6-C12 exceeds 80%, which can be blended with straight-chain alkanes to obtain qualified aviation kerosene products. Choosing aromatic rings as the final product improves the thermodynamic efficiency of the reaction process, resulting in high energy utilization efficiency and significant energy-saving effect. The acid-base heterojunction catalytic material of metal oxide-molecular sieve is constructed, and the synthesis reaction of aromatics can be carried out under mild conditions of 270-370℃ and 2 MPa, with low overall energy consumption and cost, and has good prospects for carbon neutralization applications. Attached Figure Description

[0043] 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.

[0044] Figure 1 A flowchart illustrating the preparation method of the heterojunction catalyst provided in an embodiment of the present invention is shown;

[0045] Figure 2 A flowchart illustrating the preparation method of metal-supported oxides provided in an embodiment of the present invention is shown;

[0046] Figure 3 The image shown is a scanning electron microscope image of the heterojunction catalyst provided in an embodiment of the present invention;

[0047] Figure 4 The H-TPR data diagram of the heterojunction catalyst provided in the embodiment of the present invention is shown. Detailed Implementation

[0048] 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.

[0049] 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.

[0050] In a first aspect, the present invention provides a method for preparing a heterojunction catalyst of an alkaline metal oxide and an acidic molecular sieve. Figure 1 A flowchart illustrating the preparation method of the heterojunction catalyst provided in an embodiment of the present invention is shown, as follows: Figure 1 As shown, the preparation method includes the following steps:

[0051] S1. After uniformly mixing alkaline metal oxides and acidic molecular sieves at a weight ratio of 0.1-10, the mixture is compressed into tablets and granulated.

[0052] In practical applications, the heterojunction catalyst provided by this invention is used to catalyze CO2. x +H2 is used to produce aromatic chemicals or liquid fuels, during which CO is produced. x First, it is converted into methanol, which is then further converted into aromatic chemicals or liquid fuels under the action of a catalyst. Therefore, in the selection of catalyst, this invention chooses an alkaline metal oxide (used for catalytic CO). x The above conversion is achieved using a combination of methanol conversion (converted to methanol) and silica-alumina molecular sieves (used to catalyze the conversion of methanol into aromatic chemicals or liquid fuels).

[0053] Specifically, the alkaline metal oxide can be selected from single metal oxides, bimetallic oxides, or metal-supported oxides formed by the spontaneous monodispersion of metal atoms on single metal oxides or bimetallic oxides; wherein, the single metal oxide is selected from MnO, CrO, ZrO, GeO, or NiO, and the bimetallic oxide is selected from ZnCrO. x ZnPdO x or ZnMoO x The single metal atoms are selected from Mo, Fe, Mn, Pd, Ni or Co; the mass of the single metal atoms accounts for 0% to 7% of the alkali metal oxide, and the alkali metal oxide is in the form of spinel, perovskite, solid solution or mesoporous single crystal.

[0054] Specifically, Figure 2 A flowchart of the preparation method of the metal-supported oxide provided by the present invention is shown, as follows: Figure 2 As shown, the method includes:

[0055] S11. The alkaline metal oxide precursor solution and an appropriate amount of 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 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.

[0056] S12. Mix the second mixed solution with the carbon source template agent at a volume ratio of 1:0.01-0.1, stir under negative pressure for 4-26 hours, filter and calcine to obtain an alkaline metal oxide with defect vacancies on the surface.

[0057] S13. Add a metal precursor solution to an alkaline metal oxide with defect vacancies on its surface, mix thoroughly, and then sonicate for 4-6 hours. Then, perform a second calcination to obtain a metal-supported oxide (a metal spontaneously fallen-in catalyst with single metal atoms uniformly distributed on the surface of the alkaline metal oxide).

[0058] The alkaline metal oxide precursor solution is a salt containing the metal element of the alkaline metal oxide to be prepared; the precipitant is at least one of sodium hydroxide, sodium carbonate, lithium hydroxide, ammonia, sodium carbonate, and ammonium bicarbonate; the carbon source template agent is one or more of carbon nanotubes, glucose, cellulose, graphene, and metal-organic framework materials; the metal precursor solution is a nitrate, acetate, acetylacetone salt, hydrochloride, acetate, or carbonate containing a single metal atom; the volume ratio of the alkaline metal oxide with surface defect vacancies to the metal precursor solution is 1:0.5-2.5; the mass of the metal atom in the metal precursor solution accounts for 0.01-10% of the mass of the alkaline metal oxide with surface defect vacancies.

[0059] Specifically, the acidic molecular sieve is a hydrogen-type silica-alumina molecular sieve with a regular surface and a silica-alumina ratio of 20-200, selected from ZSM-5, ZSM-11 or ZSM-48. Hydrogen-form silica-alumina molecular sieves with regular surfaces are obtained by the following method: The silica-alumina molecular sieve is added to an acidic solution at 50-90℃ and stirred for 0.5-12 hours. The solid obtained by filtration is then added to an alkaline solution at 50-90℃ and stirred for another 0.5-12 hours. The mixture is then filtered, the filter residue is collected, washed until neutral, dried, and calcined at 300-650℃ for 2-48 hours. The acidic solution is selected from at least one of hydrochloric acid, nitric acid, acetic acid, ammonium nitrate, ammonium chloride, and oxalic acid. The alkaline solution is selected from at least one of aqueous solutions of ammonia, n-butylamine, ethylenediamine, tetramethylammonium hydroxide, tetraethylammonium hydroxide, and tetrapropylammonium hydroxide. The concentrations of the acidic and alkaline solutions are 0.2-3 mol / L. The mass ratio of the silica-alumina molecular sieve to the acidic or alkaline solution is 1:10-1:100.

[0060] Specifically, there are three ways to mix alkali metal oxides and acidic molecular sieves:

[0061] (1) The alkaline metal oxide and acidic molecular sieve powder are mixed and ground, then compressed into tablets and granulated.

[0062] (2) After mixing the alkaline metal oxide and acidic molecular sieve powder solids, mechanical ball milling is performed, followed by tableting and granulation.

[0063] (3) The alkaline metal oxide and acidic molecular sieve powder solids are mixed in an ethanol-water solution and ultrasonically dispersed. The mixture is stirred until the solvent is completely evaporated, dried to obtain solid powder, and then compressed into tablets and granulated. The volume ratio of ethanol in the ethanol-water solution is 1:2 to 1:1, and the mass ratio of the ethanol-water solution to the mixed powder solids of component I and component II is 1:30 to 1:300. The stirring temperature is 20-80℃, the drying temperature is 40-120℃, and the drying time is 5-24h.

[0064] S2. The solid obtained by tableting and granulation is placed in a reducing atmosphere calcination furnace and calcined at 0.5-1 MPa and 150-350℃ for 1-10 h to obtain a heterojunction catalyst of alkaline metal oxide and acidic molecular sieve.

[0065] In the heterojunction catalyst obtained by the preparation method provided by the present invention, the basic metal oxide and the acidic molecular sieve exist in an independent form.

[0066] In some embodiments, under the chemical driving force of high-pressure hydrogen or carbon monoxide reducing gas, the alkaline metal oxide and molecular sieve form a heterojunction by strong contact at the interface. The reducing atmosphere roasting furnace used is a specially designed high-pressure thermal reduction roasting furnace with a roasting system capable of pressure measurement, temperature measurement, temperature control, flow control, and outlet product detection and analysis. The roasting furnace adopts a fluidized bed form and can be used under high or negative pressure. The fluidized bed form ensures uniform heat conduction and efficient heat utilization, resulting in uniform quality of the roasted catalyst. The roasting furnace can be circulated with reducing gas and maintain high pressure or negative pressure and high temperature under a reducing atmosphere. The roasting furnace outlet is equipped with a cyclone separator structure, which can effectively separate the fine powder at the outlet, improve roasting efficiency, and reduce losses. The tail gas recycling system is provided at the rear end of the roasting furnace outlet, which can recover and reuse the reducing gas efficiently.

[0067] In some embodiments, the heterojunction catalyst may specifically be a single metal atom, Fe, uniformly supported on ZnCrO. x Bimetallic oxide surface formation, Fe accounts for ZnCrO x 3% of the quality.

[0068] In some embodiments, the heterojunction catalyst can also be formed by uniformly loading single metal atoms Cr onto the surface of MnO, with Cr accounting for 5% of the mass of MnO.

[0069] In a second aspect, the present invention provides a heterojunction catalyst of alkaline metal oxide and acidic molecular sieve obtained by the preparation method of the first aspect described above.

[0070] Thirdly, the present invention provides an application of a heterojunction catalyst of an alkaline metal oxide and an acidic molecular sieve obtained by the preparation method of the first aspect above, wherein the heterojunction catalyst is used to catalyze CO. x+H2 produces aromatic chemicals or liquid fuels.

[0071] Specifically, heterojunction catalysts are used to catalyze CO2. x In the products of producing aromatic chemicals or liquid fuels from H2, H2 and CO are present in a volume ratio of 0.5-3. x The reaction feed gas was used to carry out a catalytic reaction in a fixed-bed reactor at a reaction pressure of 0.5-5 MPa, a reaction temperature of 270℃-450℃, and a reaction space velocity of 300-1000 mL / h·gcat. Among the reaction products obtained, the selectivity of liquid fuel composed of C6-C12 was greater than 80%, the selectivity of aromatics was greater than 90%, and the selectivity of methane was less than 3%.

[0072] To enable those skilled in the art to better understand this application, the following examples provide a detailed description of the alkali metal oxide and acidic molecular sieve heterojunction catalyst, its preparation method, and its application.

[0073] Example 1

[0074] Step 1: Preparation of ZnCrO x bimetallic oxides

[0075] (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.

[0076] (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.

[0077] (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.

[0078] (4) After mixing, continue stirring and introduce nitrogen gas to allow the mixture to crystallize under a nitrogen atmosphere for 8 hours.

[0079] (5) The obtained metal oxide precursor was subjected to three cycles of vacuum filtration and washing, dried at 110℃, and calcined at 450℃ for 2 hours under air atmosphere with a heating rate of 5℃ / min. 54g of ZnCrO was obtained. x Bimetallic oxide support.

[0080] Step 2: Preparation of surface-regular hydrogen-form ZSM-5 molecular sieves

[0081] (1) Weigh out the ZnCrO obtained in step 1. x The same weight of nano ZSM-5 molecular sieve was stirred with 540g of 2mol / L ammonium nitrate solution at 80℃ for 2h, and then filtered to obtain a solid.

[0082] (2) The obtained solid was mixed and stirred with 800g of 3mol / L tetramethylammonium hydroxide alkaline solution at 50°C for 8h, filtered, and the filter cake was collected and washed until neutral.

[0083] (3) The resulting neutral filter cake was dried at 100℃ for 12 hours;

[0084] (4) The dried sample was calcined in a muffle furnace at 600℃ with a heating rate of 5℃ / min and a calcination time of 10h.

[0085] Step 3: Physically mix the bimetallic oxide obtained in Step 1 and the hydrogen-form ZSM-5 molecular sieve obtained in Step 2.

[0086] ZnCrO x After being mixed and ground with hydrogen-type ZSM-5 in a sand mill for 1 hour, it was then compressed into tablets and granulated.

[0087] Step 4: Preparation of acid-base heterojunction catalyst

[0088] The sample obtained in step 3 was loaded into a specially designed reduction calcination furnace. The temperature of the calcination furnace was raised to 380°C at a rate of 10°C / min, and the pressure inside the calcination furnace was increased to 1 MPa. Carbon monoxide gas was introduced into the calcination furnace at a flow rate of 50 ml / min. After the reducing gas carbon monoxide acted on the furnace for 10 hours, the calcination furnace was automatically depressurized and a negative pressure of 0.1 MPa was formed inside the furnace. After calcination under negative pressure conditions for another hour, an acid-base heterojunction catalyst was formed.

[0089] Figure 3 The image shown is a scanning electron microscope (SEM) image of a heterojunction catalyst provided in an embodiment of the present invention. Figure 3 As shown, the metal oxides are tightly dispersed on the surface of the hydrogen-type nano ZSM-5 molecular sieve.

[0090] Comparative Example 1

[0091] The difference between Comparative Example 1 and Example 1 is that this comparison uses ZnCrO x After being mixed and ground with hydrogen-type ZSM-5 in a sand mill for 1 hour, it was subjected to tableting and granulation. After tableting, it was not roasted in a special reduction roasting furnace.

[0092] Comparative Example 2

[0093] The difference between Comparative Example 2 and Example 1 is that this comparative example uses ZnCrO x It was not directly mixed with hydrogen-type ZSM-5, but rather a layered contact method was used.

[0094] Example 2

[0095] In this embodiment, the preparation step 1 of the acid-base heterojunction catalyst using a single metal oxide and hydrogen-form ZSM-5 is as follows: Single metal oxide MnO x preparation

[0096] (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 80°C;

[0097] (2) Prepare a certain amount of ammonium acetate solution with pH 10, and the mass ratio of the ammonium acetate solution to the manganese nitrate solution is 1:2;

[0098] (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 solution temperature in the three-necked flask at 70-80°C in a water bath, and stir vigorously throughout the process.

[0099] (4) After mixing, continue stirring and introduce nitrogen gas to allow the mixture to crystallize under a nitrogen atmosphere for 24 hours. Then, cool to room temperature, centrifuge and filter, wash three times with deionized water, and dry at 90°C overnight to obtain metal oxide powder.

[0100] The single metal oxide prepared in step 1 and the hydrogen-type ZSM-5 molecular sieve were used to prepare an acid-base heterojunction catalyst according to steps 3 and 4 given in Example 1.

[0101] Example 3

[0102] Step 1: Preparation of mesoporous single-crystal ZnCrO X bimetallic oxides

[0103] (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.

[0104] (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.

[0105] (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.

[0106] (4) After mixing, continue stirring and introduce nitrogen gas to allow the mixture to crystallize under a nitrogen atmosphere for 8 hours.

[0107] (5) The obtained metal oxide precursor was subjected to three cycles of vacuum filtration and washing, dried at 110℃, and calcined at 450℃ for 2 hours under air atmosphere with a heating rate of 5℃ / min. 54g of ZnCrO was obtained. x Bimetallic oxide support.

[0108] (6) The metal oxide powder obtained in step 5 was placed in a specially designed furnace for calcination. The calcination temperature was 450℃, the pressure inside the specially designed furnace was 20 bar, hydrogen gas was introduced at a space velocity of 10 mL / h·gcat, the heating rate of the specially designed furnace was 1℃ / min, and the calcination was carried out for 3 hours to obtain mesoporous single crystal ZnCrO. x Bimetallic oxides.

[0109] The sample obtained in step 1 was used to prepare an acid-base heterojunction catalyst according to steps 3 and 4 given in Example 1.

[0110] Example 4

[0111] Step 1: Prepare a bimetallic oxide support with abundant oxygen vacancies and metal defect landing sites on its surface.

[0112] (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.

[0113] (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.

[0114] (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.

[0115] (4) After mixing, continue stirring and introduce nitrogen gas to allow the mixture to crystallize under a nitrogen atmosphere for 8 hours.

[0116] (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.

[0117] (6) The obtained metal oxide precursor was subjected to three cycles of vacuum filtration and washing, dried at 110℃, and calcined at 450℃ for 2 hours in air at a rate of 5℃ / min. This yielded ZnCrO₂ with abundant oxygen vacancies and metal defect sites on its surface. x Bimetallic oxide support.

[0118] Step 2: Metal falls into place spontaneously

[0119] (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;

[0120] (2) The ZnCrO prepared in step 1 x A bimetallic oxide support was uniformly mixed with a single-atom stock solution. After homogeneity, the mixture was subjected to ultrasonic treatment at a power of 600 W, a frequency of 40 kHz, and a duration of 4 h. Following ultrasonication, the mixture was calcined in air at a rate of 1 °C / min to 350 °C for 2 h. This yielded a spontaneously fallen-in Fe metal catalyst.

[0121] The sample obtained in step 1 was used to prepare an acid-base heterojunction catalyst according to steps 3 and 4 given in Example 1.

[0122] Experiment Example 1: Verification of Various Performance Aspects

[0123] (1) Adsorption capacity test

[0124] The hydrogenation reduction capacity of the acid-base heterojunction catalyst prepared in Example 1 was tested using a chemisorption apparatus. Figure 4 The H2-TPR data of the heterojunction catalyst provided in the embodiments of the present invention are shown in the figure. Figure 4 It can be seen that, compared with Comparative Example 1, the hydrogen consumption in Example 1 is concentrated around 300°C, the catalyst reaction temperature is concentrated, and the reaction is stable. This indicates that the formation of the heterojunction effectively improves the reaction activity of the catalyst.

[0125] (2) Performance testing of fixed-bed micro-carbon dioxide hydrogenation to produce aromatics

[0126] 1) The catalysts prepared in Examples 1, 2, 3, 4, and Comparative Examples 1 and 2 were subjected to carbon dioxide hydrogenation reaction in a fixed bed. Table 1 below shows the performance results of fixed bed micro carbon dioxide hydrogenation to aromatics for each example and comparative example.

[0127] Table 1. Performance results of metal oxide-molecular sieve acid-base heterojunction catalysts for fixed-bed micro-carbon dioxide hydrogenation to aromatics provided in each embodiment and comparative example.

[0128]

[0129] As can be seen from Table 1 above, the reaction conversion rates of Comparative Examples 1 and 2 are significantly lower than those of the other examples. The metal oxide-molecular sieve acid-base heterojunction catalyst prepared in Example 1 can significantly improve catalytic activity and aromatic selectivity.

[0130] Furthermore, the evaluation results of Examples 1 and 2 show that using either single-metal oxides or bimetallic oxides can achieve superior reaction effects during the preparation of the acid-base heterojunction catalyst. In Example 3, the introduction of a reduction calcination step in the metal oxide preparation process further optimizes the microstructure and crystal structure of the metal oxide, improving the catalytic activity after the preparation of the heterojunction catalyst. In Example 4, the introduction of an active metal further enhances the catalyst's reactivity, with only a slight decrease in aromatic selectivity.

[0131] The above provides a detailed description of the heterojunction catalyst of alkaline metal oxide and acidic molecular sieve, its preparation method, and its application. Specific examples have been used to illustrate the principle and implementation of the invention. The above description of the embodiments is only for the purpose of helping to understand the method and core idea of ​​the invention. At the same time, for those skilled in the art, there will be changes in the specific implementation and application scope based on the idea of ​​the invention. Therefore, the content of this specification should not be construed as a limitation of the invention.

Claims

1. A method for preparing a heterojunction catalyst of an alkaline metal oxide and an acidic molecular sieve, characterized in that, The preparation method includes the following preparation steps: S1, after uniformly mixing metal-supported oxide and acidic molecular sieve with a weight ratio of 0.1-10, the mixture is compressed into tablets and granulated. The metal-supported oxide is Fe spontaneously monodispersed in the basic metal oxide ZnCrO. x The acidic molecular sieve is formed on the surface; the acidic molecular sieve is a hydrogen-form ZSM-5 molecular sieve with a regular surface. In step S1, the mixing method includes: Method 1, grinding or mechanically ball milling the alkaline metal oxide and the silica-alumina molecular sieve; Method 2, ultrasonically dispersing in a solvent composed of ethanol and water, stirring until the solvent is completely evaporated, and then drying. The metal-supported oxide is obtained through the following method: S11. The alkaline metal oxide precursor solution and an appropriate amount of 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. S12. The second mixed solution with a volume ratio of 1:0.01-0.1 is mixed with a carbon source template agent, stirred under negative pressure for 4-26 hours, and then filtered and calcined to obtain an alkaline metal oxide with defect vacancies on the surface; the carbon source template agent is one or more of carbon nanotubes, cellulose, graphene, and metal-organic framework materials. S13. Add a metal Fe precursor solution to the alkaline metal oxide with defect vacancies on the surface, mix evenly, and then sonicate for 4-6 hours. Then, perform a second calcination to obtain a metal-supported oxide. The hydrogen-form ZSM-5 molecular sieve with a regular surface is obtained by the following method: ZSM-5 silica-alumina molecular sieve was added to an acidic solution at 50-90 ℃ and stirred for 0.5-12 h. The solid obtained by vacuum filtration was added to an alkaline solution at 50-90 ℃ and stirred for 0.5-12 h. Then it was filtered, the filter residue was collected, washed until neutral, dried, and calcined at 300-650 ℃ for 2-48 h. The concentrations of the acidic and alkaline solutions are 0.2–3 mol / L; The mass ratio of the silica-alumina molecular sieve to the acidic or alkaline solution is 1:10 to 1:

100. The alkaline solution is selected from at least one of the aqueous solutions of ammonia, n-butylamine, ethylenediamine, tetramethylammonium hydroxide, tetraethylammonium hydroxide, and tetrapropylammonium hydroxide; S2. The solid obtained by tableting and granulation is placed in a reducing atmosphere calcination furnace and calcined at 0.5-1 MPa and 150-350℃ for 1-10 h to obtain the heterojunction catalyst of alkaline metal oxide and acidic molecular sieve.

2. The preparation method of the heterojunction catalyst of alkaline metal oxide and acidic molecular sieve according to claim 1, characterized in that, The acidic solution is selected from at least one of hydrochloric acid, nitric acid, acetic acid, ammonium nitrate, ammonium chloride, and oxalic acid.

3. The method for preparing the heterojunction catalyst of alkaline metal oxide and acidic molecular sieve according to claim 1, characterized in that, The alkaline metal oxide precursor solution is a salt containing the metal element of the alkaline metal oxide to be prepared; The precipitant is at least one of sodium hydroxide, sodium carbonate, lithium hydroxide, ammonia, sodium carbonate, and ammonium bicarbonate. The Fe precursor solution is a nitrate, acetate, acetylacetone salt, hydrochloride, acetate, or carbonate containing the Fe metal. The volume ratio of the alkaline metal oxide with surface defects to the Fe precursor solution is 1:0.5-2.5; the mass of Fe atoms in the Fe precursor solution accounts for 0.01-10% of the mass of the alkaline metal oxide with surface defects.

4. The method for preparing the heterojunction catalyst of alkaline metal oxide and acidic molecular sieve according to claim 1, characterized in that, In the second method, the volume ratio of ethanol to water is 1:1 to 1:2; The mass ratio of the solvent to the mixed powder of the alkaline metal oxide and silica-alumina molecular sieve is 1:30 to 1:

300. The stirring temperature is 20-80℃; The drying temperature is 40-120 ℃, and the time is 5-24 h.

5. The method for preparing the heterojunction catalyst of alkaline metal oxide and acidic molecular sieve according to claim 1, characterized in that, In step S2, the reducing atmosphere roasting furnace is a fixed bed or fluidized bed roasting furnace; The reducing gas in the reducing atmosphere roasting furnace is hydrogen or carbon monoxide; the flow rate of the reducing gas is 0.1-1000 ml / min.

6. A heterojunction catalyst of alkaline metal oxide and acidic molecular sieve obtained by any one of the preparation methods of claims 1-5.

7. The application of a heterojunction catalyst of an alkaline metal oxide and an acidic molecular sieve obtained by any one of the preparation methods according to claims 1-5, characterized in that, The heterojunction catalyst is used to catalyze CO. x +H2 to produce liquid fuel.

8. The application according to claim 7, characterized in that, The heterojunction catalyst is used to catalyze CO. x In the products of producing liquid fuels from H2, H2 and CO are present in a volume ratio of 0.5-3. x The reaction feed gas was used to carry out a catalytic reaction in a fixed-bed reactor at a reaction pressure of 0.5-5 MPa, a reaction temperature of 270℃-450℃, and a reaction space velocity of 300-1000 mL / h·gcat. Among the reaction products obtained, the selectivity of liquid fuel composed of C6-C12 was greater than 80%, the selectivity of aromatics was greater than 90%, and the selectivity of methane was less than 3%.

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