Preparation method of manganese-based catalyst, prepared catalyst and application

Abstract

The invention relates to the technical field of catalyst preparation, and discloses a preparation method of a manganese-based catalyst, the prepared catalyst and application, the method comprises the following steps: (1) mixing a mixed solution containing MnO2 and a noble metal precursor hydrolysis auxiliary agent with a noble metal precursor, and separating to obtain a solid product; and (2) washing and calcining the solid product in the step (1) to obtain the manganese-based catalyst, in the step (1), the mass ratio of the noble metal precursor to MnO2 (metered by metal elements) is (0.0005-0.03): 1. According to the method, monatomic dispersion of noble metal is realized on the surface of a MnO2 carrier by regulating and controlling the hydrolysis process of a noble metal precursor, the manganese-based catalyst is obtained through calcination treatment, and the prepared catalyst effectively reduces the CO catalytic oxidation reaction temperature.

Description

Technical Field

[0001] The invention relates to the technical field of catalyst preparation, and in particular to a method for preparing a manganese-based catalyst and the prepared catalyst and application thereof. Background Art

[0002] CO and NO x , SO2, PM, etc. are all basic controlled pollutants listed in the "Ambient Air Quality Standards". CO is flammable and toxic, which seriously endangers the environment and human health. The sources of CO in ambient air are wide-ranging, mainly including waste incineration, fossil fuel combustion, metal smelting, chemical production and automobile exhaust emissions. Industrial source CO emission control is mainly carried out through two technical means: source control and end-of-pipe control. Source control uses clean fuel substitution, improved combustion process, improved combustion form and improved combustion efficiency to reduce the amount of CO generated. However, due to the current combustion technology and the irreplaceability of certain production process fuels, if no further control is imposed, a large amount of CO will still be discharged into the atmosphere. Therefore, the end-of-pipe control technology represented by catalytic oxidation has become the mainstream technology for industrial source CO emission control.

[0003] Precious metal catalysts with Pt, Pd, Au, and Ag as active components are the mainstream CO catalytic oxidation catalysts. Precious metal components usually exist in the form of dispersed nanoparticles, and the commonly used carriers are mostly inert carriers based on Al2O3. This type of catalyst can achieve complete oxidation of CO at a relatively low temperature, but its further promotion and use is still limited by high costs. In traditional precious metal nanoparticles, only the atoms in the outer layer that are in contact with pollutants show catalytic activity, and the precious metal atoms coated inside the particles do not directly participate in the reaction, resulting in low atomic utilization. Improving the atomic utilization of precious metals and reducing the precious metal loading are currently a major difficulty in catalyst research and development. Wan et al. artificially introduced oxygen vacancies on the TiO2 surface to stabilize Au atoms in the oxygen vacancies. The Ti-Au-Ti site can greatly improve the CO oxidation activity (Adv. Mater., 2018, 30(11), 1705369), but the artificial introduction of oxygen vacancies on the TiO2 surface requires a high-temperature reduction step, which is not conducive to large-scale industrial applications. For example, CN112675849A discloses a method for preparing a single-atom catalyst for CO oxidation, in which a single-atom catalyst of single-atom Fe loaded on the surface of CuO is synthesized by an organic ligand-assisted ball milling method. This method is only applicable to the loading process of single transition metal atoms, and the use of organic ligands will cause secondary pollution.

[0004] It has become an urgent need to seek suitable supports and develop simple preparation methods for precious metal catalysts for CO catalytic oxidation. Summary of the invention

[0005] The purpose of the present invention is to overcome the problems of low utilization efficiency of precious metals in precious metal catalysts in the prior art, easy agglomeration of precious metals, and complicated preparation process, and to provide a method for preparing a manganese-based catalyst, a catalyst obtained, and application thereof. The method achieves single-atom dispersion of precious metals on the surface of a MnO2 carrier by regulating the hydrolysis process of a precious metal precursor, and obtains a manganese-based catalyst by calcination and stabilization treatment. The carrier MnO2 has excellent redox performance and can form a strong interaction with a single noble metal atom. The obtained catalyst effectively reduces the temperature of the CO catalytic oxidation reaction.

[0006] In order to achieve the above object, the first aspect of the present invention provides a method for preparing a manganese-based catalyst, the method comprising the following steps:

[0007] (1) mixing a mixed solution containing MnO2 and a noble metal precursor hydrolysis aid with a noble metal precursor, and separating to obtain a solid product;

[0008] (2) washing the solid product of step (1) and calcining to obtain a manganese-based catalyst;

[0009] In step (1), the mass ratio of the noble metal precursor to MnO2, calculated as metal elements, is 0.0005-0.03:1.

[0010] Preferably, the noble metal precursor hydrolysis aid is selected from at least one of (NH4)2CO3, NH4HCO3 and CH3COONH4.

[0011] Preferably, in step (2), deionized water is used to wash the solid product of step (1), and the temperature of the deionized water is 60-90°C, preferably 65-85°C.

[0012] The second aspect of the present invention provides a manganese-based catalyst prepared by the preparation method described in the first aspect.

[0013] The third aspect of the present invention provides a use of the manganese-based catalyst described in the second aspect in a catalytic oxidation reaction.

[0014] Through the above technical solution, the beneficial effects obtained are as follows:

[0015] (1) In the present invention, the hydrolysis process of the noble metal precursor is regulated to achieve single-atom dispersion of the noble metal on the surface of the MnO2 carrier, and coupling of MnO2 and the noble metal is achieved. The non-stoichiometric characteristics of MnO2 are conducive to the stabilization of the noble metal single atoms. The preparation process does not require high-temperature reduction, etching and other treatments, which simplifies the method of loading the noble metal single atoms.

[0016] (2) In the present invention, preferably, the addition of the noble metal precursor hydrolysis aid allows the noble metal to remain in a single-atom dispersed state and adsorbed on the MnO2 surface. The noble metal on the surface of the obtained catalyst is dispersed in the form of a single atom. Compared with the nanoparticle catalyst prepared by the coating method or the adsorption method, its atomic utilization efficiency is greatly improved, which is conducive to the reduction of the noble metal content and thus reduces the catalyst preparation cost;

[0017] (3) In the present invention, preferably, the catalyst carrier MnO2 forms a strong interaction with the noble metal single atom, fully activates the noble metal, enhances the CO activation and oxidation ability of the catalyst, and effectively reduces the CO catalytic oxidation reaction temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is an AC-STEM HAADF photograph of the catalyst prepared in Example 1;

[0019] Figure 2 It is a graph showing the relationship between the catalytic oxidation CO conversion rate and temperature of Examples 1-7 and Comparative Examples 1-3. DETAILED DESCRIPTION

[0020] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0021] A first aspect of the present invention provides a method for preparing a manganese-based catalyst, wherein the method comprises the following steps:

[0022] (1) mixing a mixed solution containing MnO2 and a noble metal precursor hydrolysis aid with a noble metal precursor, and separating to obtain a solid product;

[0023] (2) washing the solid product of step (1) and calcining to obtain a manganese-based catalyst;

[0024] In step (1), the mass ratio of the noble metal precursor to MnO2, calculated as metal elements, is 0.0005-0.03:1.

[0025] In the present invention, by controlling the hydrolysis process of the noble metal precursor, the noble metal is dispersed on the surface of the MnO2 carrier, the interaction between the noble metal and the MnO2 carrier is strengthened, the noble metal is fully activated, the atomic utilization efficiency of the noble metal is effectively improved, and the catalytic activity is excellent.

[0026] According to the present invention, preferably, in step (1), the mass ratio of the noble metal precursor to MnO2 in terms of metal element is 0.0005-0.03:1, such as 0.0005:1, 0.001:1, 0.002:1, 0.003:1, 0.005:1, 0.01:1, 0.02:1, 0.025:1, 0.03:1, or any range between the two, preferably 0.001-0.02:1. If the mass of the noble metal is too low, the catalyst activity is not significantly improved, and if the mass of the noble metal is too high, it is easy to agglomerate on the surface of MnO2, thereby reducing the utilization efficiency of the noble metal.

[0027] In the present invention, preferably, the order of adding the noble metal precursor hydrolysis aid solution and the noble metal precursor is limited, and the noble metal precursor hydrolysis aid solution is added first to generate a solution environment suitable for the slow hydrolysis of the noble metal precursor, so that the noble metal in the prepared catalyst remains in a single atomic dispersed state adsorbed on the carrier surface without aggregation.

[0028] According to the present invention, preferably, based on the mass of MnO2 in the mixed solution as 1g, the molar amount of the noble metal precursor hydrolysis aid in the mixed solution is 0.003-0.27mol, for example, 0.003mol, 0.005mol, 0.01mol, 0.02mol, 0.05mol, 0.07mol, 0.1mol, 0.15mol, 0.2mol, 0.25mol, 0.27mol, or any range between the two, preferably 0.01-0.1mol.

[0029] According to the present invention, preferably, the pH value of the mixed solution is 7-9. The pH of the mixed solution is controlled to be weakly alkaline at 7-9, so that the subsequent precious metal precursor can be slowly hydrolyzed when added. In the present invention, the addition of a precious metal precursor hydrolysis aid helps to adjust the pH value of the mixed solution to 7-9. When the pH value of the mixed solution is not within the range of 7-9, the pH value can be adjusted to 7-9 by adding acid and / or alkali. The type of acid and / or alkali added is not particularly limited, and those skilled in the art can select commonly used acids and / or alkalis as needed, as long as the pH value of the mixed solution is 7-9.

[0030] According to the present invention, the noble metal precursor hydrolysis aid refers to an aid that helps to form an environment suitable for the slow hydrolysis of the noble metal precursor in the mixed solution after being added. Those skilled in the art can choose a conventional NH4 + Preferably, the noble metal precursor hydrolysis aid is selected from at least one of (NH4)2CO3, NH4HCO3 and CH3COONH4.

[0031] In the present invention, preferably, the above-mentioned noble metal precursor hydrolysis aid is used to make the mixed solution weakly alkaline, so that the subsequent noble metal precursor is slowly hydrolyzed when added, and NH4 + Coordinate with the noble metal, so that the noble metal remains in a single atomic dispersion state adsorbed on the surface of MnO2, and does not form aggregated hydroxide. + It can be removed through the subsequent washing process, and will not be difficult to remove due to stable coordination with the precious metal. If a precious metal precursor hydrolysis aid with too strong coordination ability is used to coordinate with the precious metal, it will be difficult to fully hydrolyze the precious metal during the washing process, resulting in partial loss of the precious metal, and the precious metal loading is too low, resulting in insufficient activity.

[0032] According to the present invention, preferably, the crystal form of the MnO2 is not particularly limited, and can be a conventional crystal form of MnO2 in the art, which can be used as a prepared manganese-based catalyst carrier. Preferably, the MnO2 is selected from at least one of α-MnO2, β-MnO2, γ-MnO2, δ-MnO2, R-MnO2, ε-MnO2, λ-MnO2 and amorphous MnO2, preferably α-MnO2 and / or δ-MnO2.

[0033] In the present invention, the source of the MnO2 is not particularly limited, and can be obtained commercially or prepared by existing methods, as long as the crystal form of the MnO2 meets the above conditions. According to a preferred embodiment of the present invention, MnO2 can be prepared by a hydrothermal synthesis method.

[0034] In the present invention, preferably, the single atom dispersion of the noble metal is realized on the surface of the MnO2 carrier, and the coupling of MnO2 and the noble metal is realized. The non-stoichiometric characteristics of MnO2 are conducive to the stabilization of the single noble metal atoms. The non-stoichiometric characteristics of MnO2 refer to the fact that the surface of MnO2 has abundant crystal defects, which can provide sites for the anchoring of the single noble metal atoms, help the noble metal to be dispersed on the carrier surface in the form of single atoms, and improve the CO activation and oxidation ability of the obtained catalyst.

[0035] According to the present invention, preferably, the noble metal of the noble metal precursor is selected from at least one of Au, Ag, Pt and Pd, preferably Au and / or Pt.

[0036] According to the present invention, preferably, the noble metal precursor is selected from at least one of compounds containing Au, Ag, Pt and Pd, and preferably selected from at least one of compounds containing Au and / or Pt.

[0037] In the present invention, the type of the noble metal precursor is not particularly limited, and any compound that can hydrolyze to provide a single noble metal atom is sufficient. Preferably, the noble metal precursor is selected from at least one of HAuCl4, AgNO3, (NH4)2PdCl6, Na2PdCl6, K2PdCl6, (NH4)2PdCl4, Na2PdCl4, K2PdCl4, Pd(NH3)4Cl2, Pd(NO3)2, H2PtCl6, (NH4)2PtCl6, Na2PtCl6, K2PtCl6, (NH4)2PtCl4, Na2PtCl4, K2PtCl4, Pt(NH3)4(NO3)2 and Pt(NO3)2, preferably at least one of HAuCl4, H2PtCl6 and Pt(NO3)2.

[0038] According to the present invention, preferably, step (1) comprises:

[0039] (1-1) mixing a noble metal precursor hydrolysis aid solution with a MnO2 suspension to obtain a mixed solution;

[0040] (1-2) Adding a noble metal precursor solution to the mixed solution to obtain a solid product.

[0041] According to the present invention, there is no particular limitation on the manner in which the noble metal precursor hydrolysis aid solution and the MnO2 suspension are mixed in step (1-1). Preferably, in step (1-1), the noble metal precursor hydrolysis aid solution is slowly added to the MnO2 suspension to obtain a mixed solution.

[0042] In the present invention, the slow addition has a conventional interpretation in the art, which means that it is different from adding all the noble metal precursor hydrolysis aid solutions at one time, and the solution is added within a certain time. There is no particular limitation on the method of slow addition, and those skilled in the art can make adaptive adjustments according to the different amounts of raw material addition. According to a preferred implementation method of the present invention, the slow addition can be dropwise addition and / or slowly poured. The drop rate of the noble metal precursor hydrolysis aid solution added dropwise is not particularly limited, and those skilled in the art can make adaptive adjustments according to the mixing conditions of the mixed solution. Preferably, the drop rate is 20-60 drops / min, such as 20 drops / min, 25 drops / min, 30 drops / min, 35 drops / min, 40 drops / min, 45 drops / min, 50 drops / min, 55 drops / min, 60 drops / min, or any range between the two, preferably 30-40 drops / min. Adding the noble metal precursor hydrolysis aid solution dropwise helps the noble metal to be uniformly dispersed and adsorbed on the MnO2 surface. Adding the noble metal precursor hydrolysis aid solution too quickly can easily cause the noble metal to aggregate. The slow pouring method is suitable for scenarios where a large amount of raw materials are added. Those skilled in the art can adjust the pouring rate adaptively.

[0043] In the present invention, preferably, step (1-1) is mixed under stirring conditions, and the stirring rate and stirring time are not particularly limited, and those skilled in the art can make adaptive adjustments according to the mixing conditions. Preferably, the stirring time is 0.5-1h.

[0044] According to the present invention, preferably, the mass concentration of MnO2 in the MnO2 suspension is 5-40 mg / mL, such as 5 mg / mL, 10 mg / mL, 15 mg / mL, 20 mg / mL, 25 mg / mL, 30 mg / mL, 35 mg / mL, 40 mg / mL, or any range between the two, preferably 10-30 mg / mL. The preparation method of the MnO2 suspension is not particularly limited. According to a preferred embodiment of the present invention, the MnO2 suspension is prepared by dispersing MnO2 powder in deionized water. The MnO2 powder and the dispersion method are not particularly limited. The MnO2 powder is uniformly dispersed in deionized water to form a MnO2 suspension. Preferably, ultrasonic dispersion is adopted, and the ultrasonic time is 30-60 min.

[0045] According to the present invention, preferably, the molar concentration of the noble metal precursor hydrolysis aid in the noble metal precursor hydrolysis aid solution is 0.5-2mol / L, such as 0.5mol / L, 0.6mol / L, 0.7mol / L, 0.8mol / L, 0.9mol / L, 1mol / L, 1.2mol / L, 1.4mol / L, 1.6mol / L, 1.8mol / L, 2mol / L, or any range between the two, preferably 0.8-1.6mol / L. If the concentration of the noble metal precursor hydrolysis aid in the above solution is too low, the noble metal cannot be completely hydrolyzed and adsorbed on the surface of MnO2, thereby causing the loss of the noble metal during the subsequent hot deionized water washing, and if the concentration is too high, it will cause reagent waste.

[0046] According to the present invention, preferably, in the precious metal precursor solution, the molar concentration of the precious metal is 0.5-20mmol / L, for example, 0.5mmol / L, 1mmol / L, 1.5mmol / L, 2mmol / L, 3mmol / L, 4mmol / L, 5mmol / L, 6mmol / L, 7mmol / L, 8mmol / L, 9mmol / L, 10mmol / L, 12mmol / L, 14mmol / L, 16mmol / L, 18mmol / L, 20mmol / L, or any range between the two, preferably 1.5-10mmol / L.

[0047] In the present invention, preferably, in step (1-2), the precious metal precursor solution is slowly added to the mixed solution. According to a preferred implementation method of the present invention, the slow addition can be dropwise addition and / or slowly poured. The dripping rate of the precious metal precursor solution is not particularly limited, and those skilled in the art can adaptably adjust it according to the hydrolysis of the precious metal precursor. Preferably, the dripping rate of the precious metal precursor solution is 20-60 drops / min, such as 20 drops / min, 25 drops / min, 30 drops / min, 35 drops / min, 40 drops / min, 45 drops / min, 50 drops / min, 55 drops / min, 60 drops / min, or any range between the two, preferably 30-40 drops / min. The method of slowly pouring is suitable for scenarios where the amount of raw material addition is large, and those skilled in the art can adaptably adjust the pouring rate.

[0048] In the present invention, preferably, step (1-2) is mixed under stirring conditions, and the stirring rate and stirring time are not particularly limited, and those skilled in the art can make adaptive adjustments according to the mixing conditions. Preferably, the stirring time is 1.5-3h.

[0049] In the present invention, the separation method in step (1) is not particularly limited, and the solid product can be separated from the mixed solution. Those skilled in the art can adjust the separation method according to the separation situation. According to a preferred embodiment of the present invention, the solid product and the mixed solution are separated by suction filtration.

[0050] According to the present invention, preferably, in step (2), deionized water is used to wash the solid product of step (1), and the temperature of the deionized water is 60-90°C, such as 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, or any range therebetween, preferably 65-85°C. In the present invention, hot water washing is used to promote the reaction with NH4 + Pre-coordinated noble metal ions quickly release NH4 + And it is stable on the surface of MnO2. If cold water is used for washing, NH4 + The inability to separate from the precious metals easily causes the precious metals to separate from the surface of MnO2 and enter the filtrate with water, but cannot be deposited on the surface of MnO2.

[0051] According to the present invention, the mass ratio of deionized water to solid product and the number of washing times are not particularly limited. + Preferably, the mass ratio of deionized water to solid product is 100-2000:1, such as 100:1, 250:1, 500:1, 750:1, 1000:1, 1500:1, 2000:1, or any range therebetween, preferably 500-1000:1.

[0052] According to the present invention, preferably, the step (2) further includes a process of drying the solid product before calcination, and the drying conditions are not particularly limited, and the drying conditions include: a drying time of 4-24 hours and a drying temperature of 80-120° C. The drying equipment is not particularly limited, and can be any conventional drying equipment in the art.

[0053] According to the present invention, preferably, the calcination conditions in step (2) include: calcination time of 0.5-4h, preferably 1-3h, calcination temperature of 200-400° C., preferably 250-350° C. Calcination is carried out under the above conditions to avoid calcination at too high a temperature to change the crystal form of the MnO2 carrier, and to avoid agglomeration of the noble metal, thereby reducing the reaction activity of the catalyst.

[0054] In the present invention, the calcination atmosphere and equipment are not particularly limited, and the calcination can be carried out in a conventional atmosphere and in common equipment in the art. According to a preferred embodiment of the present invention, the calcination is carried out in an air atmosphere.

[0055] The second aspect of the present invention provides a manganese-based catalyst prepared by the preparation method described in the first aspect.

[0056] According to the present invention, preferably, the catalyst includes a MnO2 carrier and a noble metal, and preferably the noble metal is dispersed on the carrier surface in a single-atom state. In the present invention, the noble metal dispersed on the carrier surface in a single-atom state can be observed under the high-angle annular dark field image (HAADF) of a spherical aberration-corrected scanning transmission electron microscope (AC-STEM), and the independent bright spots in the field of view are single noble metal atoms. According to the characteristics of the AC-STEM HAADF image, the contrast (brightness) is proportional to the square of the atomic number. It can be inferred from the preparation process that the catalyst contains only Mn, O, and Au, and the O contrast is too low to be observed. Figure 1 The bright spot is Au and the dark spot is Mn.

[0057] In the present invention, dispersing the noble metal in the form of single atoms on the carrier surface to prepare a manganese-based catalyst can effectively improve the utilization rate of the noble metal atoms, and its theoretical atomic utilization rate can reach 100%, and its CO oxidation activity is often higher than that of the noble metal nanoparticle catalyst with the same loading amount.

[0058] According to the present invention, preferably, based on the total mass of the catalyst, the mass percentage of the noble metal in the catalyst is 0.05-3wt%, preferably 0.1-2wt%.

[0059] The third aspect of the present invention provides a use of the manganese-based catalyst described in the second aspect in a catalytic oxidation reaction.

[0060] According to the present invention, preferably, the manganese-based catalyst is used in a CO catalytic oxidation reaction.

[0061] In the present invention, the prepared manganese-based catalyst is used for CO catalytic oxidation reaction, and the carrier MnO2 of the catalyst forms a strong interaction with the noble metal single atom, fully activates the noble metal, improves the CO activation and oxidation ability of the catalyst, and effectively reduces the CO catalytic oxidation reaction temperature.

[0062] In the present invention, the catalytic oxidation reaction device is not particularly limited and can be selected from conventional reaction devices in the art. According to a preferred embodiment of the present invention, the catalytic oxidation reaction is carried out in a fixed bed reaction device.

[0063] In the present invention, the reaction conditions of the catalytic oxidation are not particularly limited, and those skilled in the art can make adaptive adjustments according to the conditions of the catalytic oxidation reaction. The reaction conditions include: the reaction pressure is normal pressure, the reaction temperature is 70-350°C, preferably 90-250°C, and the mass space velocity is 5000-240000 mL·g -1 ·h -1, preferably 20000-120000mL·g -1 ·h -1 .

[0064] In the present invention, the source of CO is not particularly limited, and is preferably CO in flue gas, which is flue gas concentratedly discharged by CO emitting industries such as waste incineration, chemical industry, and metallurgical industry.

[0065] According to a particularly preferred embodiment of the present invention, a method for preparing a manganese-based catalyst comprises the following steps:

[0066] (1) mixing a mixed solution containing MnO2 and a noble metal precursor hydrolysis aid with a noble metal precursor, and separating to obtain a solid product;

[0067] (2) washing the solid product of step (1) and calcining to obtain a manganese-based catalyst;

[0068] The noble metal precursor hydrolysis aid is selected from at least one of (NH4)2CO3, NH4HCO3 and CH3COONH4;

[0069] In step (1), the mass ratio of the noble metal precursor to MnO2, calculated as metal element, is 0.001-0.02:1;

[0070] In step (2), the solid product of step (1) is washed with deionized water, wherein the temperature of the deionized water is 65-85° C.;

[0071] Based on the mass of MnO2 in the mixed solution being 1 g, the molar amount of the noble metal precursor hydrolysis aid in the mixed solution is 0.01-0.1 mol;

[0072] The calcination conditions in step (2) include: calcination time of 1-3h, calcination temperature of 250-350°C.

[0073] The present invention will be described in detail below through examples and comparative examples. In the following examples and comparative examples, unless otherwise specified, the reagents and materials used can be obtained commercially, and the room temperature is 25°C;

[0074] The noble metal content in the manganese-based catalyst was measured by inductively coupled plasma optical emission spectrometry (ICP-OES);

[0075] The surface morphology of the manganese-based catalyst was observed by electron microscopy;

[0076] The activity evaluation of the CO catalytic oxidation reaction was completed on a micro fixed bed reaction device designed and manufactured by Tianjin Pengxiang Technology Co., Ltd., and the composition of the reaction product was measured by a Multigas 2030 infrared detector produced by MKS Company.

[0077] Example 1

[0078] Preparation method of δ-MnO2 powder: weigh 1.5g of KMnO4 and 0.28g of MnSO4·H2O and dissolve them in 80mL of deionized water. After magnetic stirring for 30min, transfer them to a 100mL Teflon reactor and put them in an oven at 160℃ for 12h. After the reaction is completed, wait for the reactor to cool to room temperature. The obtained solid is filtered, washed several times, collected, and dried in an oven at 80℃ for 4h.

[0079] (1-1) Disperse 1.5 g of δ-MnO2 powder into 75 mL of deionized water, ultrasonicate for 30 min to obtain a MnO2 suspension, and continue stirring;

[0080] Prepare 50 mL of a noble metal precursor hydrolysis aid solution with a (NH4)2CO3 concentration of 1 mol / L;

[0081] Take 37.5 mL of the noble metal precursor hydrolysis aid solution, add it dropwise into the MnO2 suspension at a rate of 35 drops / min, keep stirring for 30 minutes, and obtain a mixed solution with a pH value of 8.

[0082] (1-2) Take 7.8 mL of HAuCl4 noble metal precursor solution with a concentration of 1.95 mmol / L, add the noble metal precursor solution dropwise to the mixed solution at a rate of 35 drops / min, keep stirring for 1.5 hours, and separate the solid product by suction filtration.

[0083] (2) The solid product of step (1) is washed with 1L of deionized water at 70°C, dried at 80°C for 8h, and calcined in air atmosphere for 2h at a temperature of 300°C. The mass fraction of precious metal in the obtained single atom catalyst is 0.2wt%.

[0084] Figure 1 AC-STEM HAADF photo of the catalyst obtained in Example 1. Figure 1 As can be seen in the figure, the bright spots are Au atoms, the shadowed sheet matrix is ​​the δ-MnO2 sheet, and the black area on the right is vacuum. Au is dispersed on the surface of the carrier in the form of single atoms, and no cluster structure is formed.

[0085] Example 2

[0086] Preparation method of α-MnO2 powder: weigh 1.25g of KMnO4 and 0.53g of MnSO4·H2O and dissolve them in 80mL of deionized water. After magnetic stirring for 30min, transfer them to a 100mL Teflon reactor and put them in an oven at 160℃ for 12h. After the reaction is completed, wait for the reactor to cool to room temperature. The obtained solid is filtered, washed several times, collected, and dried in an oven at 80℃ for 4h.

[0087] (1-1) Disperse 2 g of α-MnO2 powder into 80 mL of deionized water, ultrasonicate for 30 min to obtain a MnO2 suspension, and continue stirring;

[0088] Prepare 50 mL of precursor hydrolysis solution with NH4HCO3 concentration of 1.5 mol / L;

[0089] Take 40 mL of the precursor hydrolysis solution and add it dropwise into the MnO2 suspension at a rate of 35 drops / min. Keep stirring for 30 minutes to obtain a mixed solution with a pH value of 9.

[0090] (1-2) Take 15 mL of H2PtCl6 noble metal precursor solution with a concentration of 5.47 mmol / L, add the noble metal precursor solution dropwise to the mixed solution at a rate of 35 drops / min, keep stirring for 1.5 hours, and separate the solid product by suction filtration.

[0091] (2) The solid product of step (1) was washed with 1.5 L of deionized water at 70° C., dried at 80° C. for 8 h, and calcined in an air atmosphere for 2 h at a temperature of 300° C. The mass fraction of the precious metal in the obtained single-atom catalyst was 0.8 wt%.

[0092] Example 3

[0093] Preparation method of β-MnO2 powder: Weigh 1.69g of MnSO4·H2O and 2.28g of (NH4)2S2O8 and dissolve them in 80mL of deionized water. After magnetic stirring for 30min, transfer them to a 100mL Teflon reactor and put them in an oven at 140℃ for 12h. After the reaction is completed, wait for the reactor to cool to room temperature. The obtained solid is filtered, washed several times, collected, and dried in an oven at 80℃ for 4h.

[0094] (1-1) Disperse 1.5 g of β-MnO2 powder into 100 mL of deionized water, ultrasonicate for 30 min to obtain a MnO2 suspension, and continue stirring;

[0095] Prepare 50 mL of precursor hydrolysis solution with a CH3COONH4 concentration of 1.2 mol / L;

[0096] Take 50 mL of the precursor hydrolysis solution and add it dropwise into the MnO2 suspension at a rate of 35 drops / min. Keep stirring for 30 minutes to obtain a mixed solution with a pH value of 7.

[0097] (1-2) Take 25 mL of a 6 mmol / L K2PdCl6 noble metal precursor solution, add the noble metal precursor solution dropwise to the mixed solution at a rate of 35 drops / min, keep stirring for 1.5 h, and separate the solid product by suction filtration.

[0098] (2) The solid product of step (1) is washed with 1 L of deionized water at 70° C., dried at 80° C. for 8 h, and calcined in an air atmosphere for 2 h at a temperature of 300° C. The mass fraction of the precious metal in the obtained single-atom catalyst is 1 wt%.

[0099] Example 4

[0100] A manganese-based catalyst was prepared according to the method of Example 1, except that an equal volume of deionized water at room temperature was used for washing in step (2). Other conditions were the same as those of Example 1. The mass fraction of the noble metal in the obtained single atom catalyst was less than 0.2 wt %.

[0101] Example 5

[0102] A manganese-based catalyst was prepared according to the method of Example 1, except that the MnO2 suspension, the noble metal precursor hydrolysis aid solution and the noble metal precursor solution were directly mixed and stirred for 1.5 hours. Other conditions were the same as in Example 1. The mass fraction of the noble metal in the obtained single atom catalyst was 0.2 wt%.

[0103] Example 6

[0104] A manganese-based catalyst was prepared according to the method of Example 1, except that the noble metal precursor hydrolysis aid solution was a 1 mol / L ethylenediamine solution. Other conditions were the same as in Example 1. The mass fraction of the noble metal in the obtained single atom catalyst was less than 0.2 wt %.

[0105] Example 7

[0106] A manganese-based catalyst was prepared according to the method of Example 1, except that the calcination conditions in step (2) were changed to: the dried solid was calcined in an air atmosphere for 2 h at a temperature of 500° C. The mass fraction of the precious metal in the obtained catalyst was 0.2 wt %. Due to the high temperature calcination, some Au single atoms were transformed into nanoparticle agglomerates.

[0107] Comparative Example 1

[0108] A manganese-based catalyst was prepared according to the method of Example 1, except that the noble metal precursor hydrolysis solution and the noble metal precursor solution (no noble metal was loaded) were not added, and other conditions were the same as in Example 1.

[0109] Comparative Example 2

[0110] (1-1) Disperse 1.5 g of δ-MnO2 powder into 75 mL of deionized water and ultrasonicate for 30 min to obtain a MnO2 suspension.

[0111] (1-2) Take 7.8 mL of HAuCl4 noble metal precursor solution with a concentration of 1.95 mmol / L, add the noble metal precursor solution dropwise to the MnO2 suspension at a rate of 35 drops / min, stir for 2 hours, and then let it stand for 2 hours to obtain a solid product.

[0112] (2) As in Example 1, the mass fraction of the precious metal in the obtained catalyst is 0.05 wt%.

[0113] Comparative Example 3

[0114] (1-1) Disperse 1.5 g of δ-MnO2 powder into 75 mL of deionized water and ultrasonicate for 30 min to obtain a MnO2 suspension.

[0115] (1-2) taking 7.8 mL of HAuCl4 noble metal precursor solution with a concentration of 1.95 mmol / L, adding the noble metal precursor solution dropwise to the MnO2 suspension at a rate of 35 drops / min, and performing rotary evaporation at 60° C. to obtain a solid product after the water is completely evaporated;

[0116] (2) The obtained solid was calcined in an air atmosphere for 2 h at a temperature of 300° C. The mass fraction of the precious metal in the obtained catalyst was 0.2 wt %.

[0117] Test Case

[0118] The reaction was carried out under normal pressure, with an initial temperature of 30°C and a temperature increase of 1°C / min to 250°C. The volume composition of the inlet gas was 1% CO + 21% O2 + 78% N2, and the space velocity was 60000 mL·g -1 ·h -1 The reaction results are shown in Table 1.

[0119] CO conversion rate = 1 - (residual CO content / CO raw material content) × 100%.

[0120] Table 1

[0121]

[0122]

[0123] It can be seen from the results in Table 1 that Examples 1-3, 5, and 6 using the preparation method of the present invention have significantly better effects than Comparative Examples 1-3, and catalytic oxidation of CO can be achieved at a lower temperature.

[0124] Figure 2 is a graph showing the relationship between the catalytic oxidation CO conversion rate and temperature of Examples 1-7 and Comparative Examples 1-3, Figure 2 It can be obtained that the CO catalytic oxidation activities of Examples 1-3, 5, and 6 are all better than those of Comparative Examples 1-3 in the range of 30-250°C. The loading of precious metals can significantly improve the catalytic activity of MnO2. The effect of the catalyst prepared by the preparation method of the present invention on the catalytic oxidation of CO is better than that by the adsorption method and the impregnation method. The preparation method of the present invention is simple and easy to implement, has no secondary pollution, is expected to be promoted to industrial applications, and has broad application prospects.

[0125] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for preparing a manganese-based catalyst, characterized in that: The method comprises the following steps: (1) mixing a mixed solution containing MnO2 and a noble metal precursor hydrolysis aid with a noble metal precursor, and separating to obtain a solid product; (2) washing the solid product of step (1) and calcining to obtain a manganese-based catalyst; In step (1), the mass ratio of the noble metal precursor to MnO2, calculated as metal elements, is 0.0005-0.03:

1.

2. The preparation method according to claim 1, wherein In step (1), the mass ratio of the noble metal precursor to MnO2, calculated as metal element, is 0.001-0.02:1; Preferably, based on the mass of MnO2 in the mixed solution as 1g, the molar amount of the noble metal precursor hydrolysis aid in the mixed solution is 0.003-0.27mol, preferably 0.01-0.1mol; Preferably, the pH value of the mixed solution is 7-9.

3. The preparation method according to claim 1 or 2, wherein The noble metal precursor hydrolysis aid is selected from at least one of (NH4)2CO3, NH4HCO3 and CH3COONH4; Preferably, the MnO2 is selected from at least one of α-MnO2, β-MnO2, γ-MnO2, δ-MnO2, R-MnO2, ε-MnO2, λ-MnO2 and amorphous MnO2, preferably α-MnO2 and / or δ-MnO2; Preferably, the noble metal of the noble metal precursor is selected from at least one of Au, Ag, Pt and Pd, preferably Au and / or Pt.

4. The preparation method according to any one of claims 1 to 3, wherein The noble metal precursor is selected from at least one of compounds containing Au, Ag, Pt and Pd, preferably selected from at least one of compounds containing Au and / or Pt; Preferably, the precious metal precursor is selected from at least one of HAuCl4, AgNO3, (NH4)2PdCl6, Na2PdCl6, K2PdCl6, (NH4)2PdCl4, Na2PdCl4, K2PdCl4, Pd(NH3)4Cl2, Pd(NO3)2, H2PtCl6, (NH4)2PtCl6, Na2PtCl6, K2PtCl6, (NH4)2PtCl4, Na2PtCl4, K2PtCl4, Pt(NH3)4(NO3)2 and Pt(NO3)2, preferably selected from at least one of HAuCl4, H2PtCl6 and Pt(NO3)2.

5. The preparation method according to any one of claims 1 to 4, wherein: Step (1) comprises: (1-1) mixing a noble metal precursor hydrolysis aid solution with a MnO2 suspension to obtain a mixed solution; (1-2) Adding a noble metal precursor solution to the mixed solution to obtain a solid product.

6. The preparation method according to claim 5, wherein: The mass concentration of MnO2 in the MnO2 suspension is 5-40 mg / mL, preferably 10-30 mg / mL; Preferably, the molar concentration of the noble metal precursor hydrolysis aid in the noble metal precursor hydrolysis aid solution is 0.5-2 mol / L, preferably 0.8-1.6 mol / L; Preferably, in the noble metal precursor solution, the molar concentration of the noble metal is 0.5-20 mmol / L, preferably 1.5-10 mmol / L.

7. The preparation method according to any one of claims 1 to 6, wherein: In step (2), the solid product of step (1) is washed with deionized water, wherein the temperature of the deionized water is 60-90° C., preferably 65-85° C.; Preferably, the mass ratio of the deionized water to the solid product is 100-2000:1, preferably 500-1000:

1.

8. The preparation method according to any one of claims 1 to 7, wherein: The method further comprises: a process of drying the solid product before the calcination in step (2), wherein the drying conditions include: a drying time of 4-24 hours and a drying temperature of 80-120° C.; Preferably, the calcination conditions in step (2) include: calcination time of 0.5-4h, preferably 1-3h, calcination temperature of 200-400°C, preferably 250-350°C.

9. The manganese-based catalyst prepared by the preparation method according to any one of claims 1 to 8; Preferably, the catalyst comprises a MnO2 carrier and a noble metal, and preferably the noble metal is dispersed on the carrier surface in a single-atom state; Preferably, based on the total mass of the catalyst, the mass percentage of the noble metal in the catalyst is 0.05-3wt%, preferably 0.1-2wt%.

10. Use of the manganese-based catalyst according to claim 9 in catalytic oxidation reactions; Preferably, the manganese-based catalyst is used in a CO catalytic oxidation reaction.

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