Multi-level structure foamed aluminum and its preparation method and application, catalyst and its preparation method

Abstract

The present invention relates to the field of catalyst carriers, and discloses a multi-level structured aluminum foam, a preparation method and application thereof, a catalyst and a preparation method thereof. The multi-level structured aluminum foam of the present invention comprises aluminum foam and an aluminum oxide structure layer formed by in-situ growth on the surface of the aluminum foam; wherein the aluminum oxide structure layer comprises an aluminum oxide layer and an aluminum oxide nanostructure array layer formed on the surface of the aluminum oxide layer. The preparation method of the present invention has a simple process, and the thickness of the aluminum oxide structure layer and the morphology of the aluminum oxide nanostructure array layer can be regulated. The obtained multi-level structured aluminum foam as a catalyst carrier has the advantages of improving the catalyst reaction activity, preventing the active components from sintering during the reaction, and improving the mass transfer efficiency.

Description

Technical Field

[0001] The present invention relates to the field of catalyst carriers, and in particular to a multi-level structure aluminum foam, a preparation method of the multi-level structure aluminum foam and an application thereof, and a catalyst using the multi-level structure aluminum foam as a carrier and a preparation method thereof. Background Art

[0002] Generally, the catalyst is prepared as a powder, and for ease of use, it often undergoes secondary molding, such as extrusion molding, coating on a support, etc., and finally forms an integral catalyst for application in actual scenarios. Al2O3 is widely used as a catalyst carrier in industry, and its form is generally coated on a support such as cordierite or formed into a block material. However, these catalyst carriers only have the catalyst on the surface to play a catalytic role, and the secondary processing process will have problems such as whether the bonding between the catalyst and the support is firm and whether the specific surface area of ​​the catalyst decreases. This affects the catalytic performance of the catalyst with Al2O3 as a carrier, and increases the difficulty of the preparation process. Foamed aluminum is often used as a catalyst support because of its suitable mechanical strength, good thermal conductivity, and irregular through holes that can enhance gas mass transfer. The composition of foamed aluminum includes an aluminum substrate and a dense aluminum oxide film layer on the surface of the aluminum substrate. Before using foamed aluminum, it is usually necessary to remove the dense aluminum oxide film layer. The commonly used method for removing the dense aluminum oxide film layer in the prior art is to introduce a strong alkaline solution to dissolve the dense aluminum oxide film layer. However, although this treatment method can dissolve the dense aluminum oxide film layer, it is also easy to cause the aluminum foam to melt, and finally destroy the structure and strength of the aluminum foam, making it impossible to use it as a catalyst carrier. In addition, the use of aluminum foam as a support also has problems such as poor adhesion to the catalyst and reduced specific surface area of ​​the catalyst. A preparation method that can directly fix the catalyst on a support is needed.

[0003] "Modification of Al Particle Surfaces by γ-Al2O3and Its Effect on theCorrosion Behavior of Al" (Zhen-Yan Deng, Yu-Fu Liu, Tanaka Y, et al. Journalof the American Ceramic Society, 2010, 88(4):977-979.) discloses a method for mixing aluminum powder and Al(OH)3 powder, ball-milling the mixture, and then calcining the mixture at 600 degrees under vacuum to obtain aluminum powder with a fluffy Al2O3 layer on the surface, which inhibits the formation of a dense aluminum oxide film on the surface of the aluminum powder. When the aluminum powder with the fluffy Al2O3 layer on the surface is in water, the fluffy Al2O3 layer on the surface can promote the oxidation reaction of aluminum in water to generate aluminum hydroxide, and prevent the formation of a dense aluminum oxide film on the surface of the aluminum powder, thereby hindering the reaction. However, the above method can only be implemented for aluminum powder: as a bulk material, aluminum foam cannot be ground to achieve full contact between aluminum hydroxide powder and the aluminum foam interface without destroying its overall structure, and a fluffy Al2O3 layer cannot be grown on the surface of the aluminum foam.

[0004] At present, there is no technology that can in-situ grow an Al2O3 layer on the surface of foamed aluminum and regulate its thickness. Summary of the invention

[0005] The purpose of the present invention is to overcome the problems of the prior art that the secondary coating process of the catalyst with Al2O3 as the carrier is complicated, the carrier is easy to fall off, and the carrier is sintered due to the calcination process after the secondary coating, and to provide a multi-level structure foam aluminum and its preparation method and application, as well as a catalyst with the multi-level structure foam aluminum as the carrier and its preparation method. The preparation method used in the present invention is simple in process, and the thickness of the aluminum oxide structure layer and the microscopic morphology structure of the aluminum oxide nanostructure array layer can be regulated. The obtained multi-level structure foam aluminum as the catalyst carrier has the advantages of improving the catalyst reaction activity, preventing the active components from sintering during the reaction, and improving the mass transfer efficiency.

[0006] In the present invention, the aluminum oxide refers to aluminum oxide, namely Al2O3.

[0007] In order to achieve the above-mentioned object, the present invention provides a multi-level structure foam aluminum in a first aspect, wherein the multi-level structure foam aluminum comprises foam aluminum and an aluminum oxide structure layer formed by in-situ growth on the surface of the foam aluminum;

[0008] Wherein, the aluminum oxide structural layer comprises an aluminum oxide layer and an aluminum oxide nanostructure array layer formed on the surface of the aluminum oxide layer.

[0009] The second aspect of the present invention provides a method for preparing a multi-level structure foam aluminum, wherein the method comprises: (1) removing surface impurities from the foam aluminum to obtain foam aluminum from which impurities have been removed; (2) immersing the foam aluminum from which impurities have been removed in an alkaline solution for oxidation treatment to obtain oxidized foam aluminum; (3) drying and first calcining the oxidized foam aluminum to obtain a multi-level structure foam aluminum; wherein the pH value of the alkaline solution is 9-13.

[0010] The third aspect of the present invention provides the use of the multi-level structure aluminum foam in a catalyst.

[0011] A fourth aspect of the present invention provides an integral foam aluminum catalyst, wherein the catalyst comprises a noble metal as an active component and the above-mentioned multi-level structure foam aluminum as a carrier.

[0012] The fifth aspect of the present invention provides a method for preparing the above-mentioned integral foam aluminum catalyst, wherein the method comprises: (i) immersing the multi-level structure foam aluminum into a precious metal precursor solution, taking it out and drying it with strong wind; (ii) repeating step (i) until the mass of the precious metal precursor loaded on 1L of the multi-level structure foam aluminum is 0.1-10g in terms of precious metal, to obtain an intermediate 1; (iii) subjecting the intermediate 1 to a second calcination to obtain an integral foam aluminum catalyst loaded with precious metals.

[0013] Through the above technical scheme, the present invention performs oxidation treatment on the foamed aluminum and accurately adjusts the pH, temperature and reaction time of the oxidation treatment, and after high-temperature calcination, finally grows an aluminum oxide structure layer including an aluminum oxide layer and an aluminum oxide nanostructure array layer formed on the surface of the aluminum oxide layer on the surface of the foamed aluminum. Among them, the aluminum oxide layer is different from the dense layer formed naturally by aluminum element or by electrochemical methods. This layer is a loose layer grown between the interface of aluminum element and the aluminum oxide nanostructure array layer. The aluminum oxide nanostructure array layer is a nanostructure array layer of aluminum oxide with a specific morphology (a layer formed by an array with a specific morphology and structure on the aluminum oxide layer). The technical scheme of the present invention eliminates the step of removing the dense aluminum oxide film layer, avoids the problem that the foamed aluminum is dissolved during the removal of the dense aluminum oxide film layer, and cannot ensure the structure and strength of the foamed aluminum. It also avoids the problem of weak bonding between the catalyst and the support in the prior art. Compared with the foamed aluminum with irregular aluminum oxide on the surface, it has better gas diffusion characteristics, and the prepared catalyst has better catalytic activity and aging resistance. Specifically, the beneficial effects obtained by the present invention are:

[0014] (1) The multi-level structure aluminum foam of the present invention has both carrier and support functions, thus avoiding the problem of looseness between the support and the catalyst that may occur when using an additional support;

[0015] (2) Compared with the traditional honeycomb ceramics used as carriers, the multi-level structure foam aluminum of the present invention has irregular pores that enhance the turbulent flow of gas and the mass transfer of gas from the gas phase to the catalyst interface; (external diffusion);

[0016] (3) The alumina structure layer on the surface of the multi-level structured aluminum foam of the present invention includes an alumina layer and an alumina nanostructure array layer on the surface of the alumina layer, which enhances the mass transfer and diffusion of gas in the catalyst (internal diffusion) compared to the existing loose porous amorphous alumina layer;

[0017] (4) Foamed aluminum is a good conductor of heat. Compared with the commonly used cordierite support, it can quickly absorb the heat in the atmosphere to quickly heat the catalyst, reducing the catalyst activation time, and can also quickly cool down to avoid high temperatures during the catalytic process;

[0018] (5) The catalyst using the multi-level structure aluminum foam of the present invention as a carrier has an aluminum oxide nanostructure array layer, and its nanostructure arrays are not connected to each other, which not only avoids contact between them and causes carrier sintering during long-term operation at high temperature, but also prevents the active components loaded thereon from agglomerating and reducing the reaction activity;

[0019] (6) The carrier preparation method used in the present invention forms an alumina structural layer by directly growing in situ on the surface of aluminum foam. The alumina structural layer includes an aluminum oxide layer and an aluminum oxide nanostructure array layer on the surface of the aluminum oxide layer, thereby avoiding the problems of carrier shedding and carrier sintering that are prone to occur in the secondary coating process of the traditional method. In addition, the thickness of the aluminum oxide structural layer on the surface of aluminum foam, the micromorphology of the aluminum oxide nanostructure array layer, the exposed crystal surface, etc. can be regulated by adjusting the pH value, time, temperature and other conditions of the alkaline liquid to meet the different requirements of the catalyst for the carrier. For example, the crystal surface structure of the aluminum oxide nanostructure array layer can be designed according to different reactions to improve the reaction activity of the prepared catalyst.

[0020] (7) The preparation method of the multi-level structure aluminum foam used in the present invention is a chemical method, which does not require the investment of corresponding supporting equipment. The alkaline liquid used can be reused and does not produce other harmful substances. The process is simple, saves time cost, and brings high economic benefits.

[0021] (8) The catalyst using the multi-level structure aluminum foam in the present invention can be used without secondary coating, and only a small amount of active component precious metal is required to exert good catalytic activity. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 1 is a SEM image and elemental analysis image of the aluminum foam without any treatment in Preparation Example 1;

[0023] Figure 2 This is the SEM image and element analysis diagram of the multi-level structure aluminum foam A1;

[0024] FIG3 is a SEM image of the aluminum foam without any treatment in Preparation Example 1;

[0025] FIG4 is a SEM image of the multi-level structure aluminum foam A1;

[0026] Figure 5 are photos of the aluminum foam treated in each step in Preparation Example 1 and a photo of the catalyst S1 in Example 1, a is a photo of the aluminum foam without any treatment, b is a photo of the aluminum foam after oxidation treatment and drying, c is a photo of the multi-level structure aluminum foam A1, and d is a photo of the catalyst S1;

[0027] FIG6 is a SEM image of a multi-level structure aluminum foam A2;

[0028] Figure 7 This is the HRTEM image of the multi-level structure aluminum foam A2, showing that the lattice spacing is 0.2nm;

[0029] FIG8 is a SEM image of a multi-level structure aluminum foam A3;

[0030] FIG9 is a SEM image of a multi-level structure aluminum foam A4;

[0031] FIG10 is a SEM image of a multi-level structure aluminum foam A5;

[0032] Fig.11 This is the HRTEM image of the multi-level structure aluminum foam A5, showing that the lattice spacing is 0.28nm;

[0033] FIG12 is a SEM image of a multi-level structure aluminum foam A6;

[0034] FIG13 is a SEM image of a multi-level structure aluminum foam A7;

[0035] FIG14 is a SEM image of a multi-level structure aluminum foam A8;

[0036] FIG15 is a SEM image of a multi-level structure aluminum foam A9;

[0037] FIG16 is a SEM image of a multi-level structure aluminum foam A10;

[0038] FIG17 is a SEM image of a multi-level structure aluminum foam A11;

[0039] FIG18 is a SEM image of a multi-level structure aluminum foam A12;

[0040] Fig.19is the conversion rate of methane and ethylene of catalyst S2 at different reaction temperatures, A is the conversion rate of methane at different reaction temperatures, and B is the conversion rate of ethylene at different reaction temperatures;

[0041] FIG20 is a TEM image of the catalyst S2 before and after aging, A is a TEM image of the fresh catalyst S2 before aging, and B is a TEM image of the catalyst S2 after aging;

[0042] Fig.21 is the conversion rate of methane and ethylene of catalyst S9 at different reaction temperatures, A is the conversion rate of methane at different reaction temperatures, and B is the conversion rate of ethylene at different reaction temperatures;

[0043] FIG22 is a TEM image of the catalyst S9 before and after aging, A is a TEM image of the fresh catalyst S9 before aging, and B is a TEM image of the catalyst S9 after aging;

[0044] Fig.23 is the conversion rate of methane and ethylene of catalyst S11 at different reaction temperatures, A is the conversion rate of methane at different reaction temperatures, and B is the conversion rate of ethylene at different reaction temperatures;

[0045] Fig.24 is the conversion rate of methane and ethylene of catalyst DS1 at different reaction temperatures, A is the conversion rate of methane at different reaction temperatures, and B is the conversion rate of ethylene at different reaction temperatures;

[0046] Fig.25 These are TEM images of the catalyst DS2 before and after aging, A is the TEM image of the fresh catalyst DS2 before aging, and B is the TEM image of the catalyst DS2 after aging. DETAILED DESCRIPTION

[0047] 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.

[0048] A first aspect of the present invention provides a multi-level structural aluminum foam, wherein the multi-level structural aluminum foam comprises aluminum foam and an aluminum oxide structural layer formed by in-situ growth on the surface of the aluminum foam;

[0049] Wherein, the aluminum oxide structural layer comprises an aluminum oxide layer and an aluminum oxide nanostructure array layer formed on the surface of the aluminum oxide layer.

[0050] In some embodiments of the present invention, the thickness of the aluminum oxide structural layer is 1-30 μm, preferably 2-25 μm.

[0051] In some embodiments of the present invention, the thickness of the aluminum oxide nanostructure array layer is 0.1-22 μm.

[0052] In some embodiments of the present invention, the microscopic morphology of the aluminum oxide nanostructure array layer is at least one of a nanowire array, a nanosheet array, a nanocone array, and a nanobelt array, preferably a nanowire array.

[0053] In some embodiments of the present invention, the nanowire array has a nanowire length of 0.1-10 μm and an aspect ratio of 1-50.

[0054] The inventors have found that when the diameter of the nanowire is less than 0.5 μm, the specific surface area of ​​the multi-level structure aluminum foam surface is increased, and the total exposed area of ​​a specific crystal plane per unit volume of aluminum foam is higher, which is more conducive to improving the dispersion of active components on the surface of the multi-level structure aluminum foam when used as a catalyst carrier, and the activity of the prepared catalyst is higher. Therefore, in a preferred case, the diameter of the nanowires of the nanowire array is less than 0.5 μm.

[0055] In some embodiments of the present invention, the nanowires of the nanowire array have a length of 2-10 μm.

[0056] In some embodiments of the present invention, the aspect ratio of the nanowires in the nanowire array is 10-50.

[0057] In some embodiments of the present invention, the nanosheet array has a nanosheet thickness of 0.01-0.06 μm, a nanosheet length of 0.1-0.5 μm, and a nanosheet width of 0.1-0.5 μm.

[0058] In some embodiments of the present invention, the length of the nanocones of the nanocone array is 5-25 μm, and the diameter of the cone base is 3-10 μm.

[0059] In the present invention, the length of the nanocone refers to the length of the vertical line segment from the top of the cone to the bottom of the cone.

[0060] In some embodiments of the present invention, the nanobelts of the nanobelt array have a length of 1-10 μm, a thickness of 0.05-0.5 μm, and a width of 0.1-5 μm.

[0061] The inventors found in their research that when the aluminum oxide nanostructure array layer is a nanowire array, the dispersion of the active component noble metal in the catalyst prepared by using the multi-level structure aluminum foam as a catalyst carrier and the anti-aging ability of the catalyst are enhanced, and the activity of the catalyst is further improved. Therefore, in a preferred case, the microscopic morphology of the aluminum oxide nanostructure array layer is a nanowire array.

[0062] Studies have shown that different crystal faces of alumina often have different reaction characteristics for different reactions, so the ability to prepare alumina that exposes specific crystal faces has more practical application significance. For example, Ja Hun Kwak et al. have shown that the (100) face of gamma alumina is more likely to produce abundant unsaturated coordinated aluminum, which allows the precious metal to be firmly anchored on the carrier in the form of single atoms or atomic clusters, thereby improving the stability of the catalyst. 3+ Centers as Binding Sites for Active Catalyst Phase of Platinum on gamma-Al2O3, science 2009, 325(5948), 1670-1673). In addition, Cai Weimeng et al. reported that the (111) surface of gamma-alumina is conducive to the dehydration of ethanol to prepare vinyl alkyne hydrogenation reaction (Nanotubular Gamma Alumina with High-Energy External Surfaces: Synthesis and High Performance of Catalysis, ACS Catalysis 2017, 7(6), 4083-4092). The inventors found in their research that when the micromorphology of the aluminum oxide nanostructure array layer is a nanowire array and a nanosheet array, the exposed crystal planes of the nanostructures (i.e., nanowires, nanosheets, nanobelts, and nanocones) on the aluminum oxide nanostructure array layer are different; when the micromorphology of the aluminum oxide nanostructure array layer is a nanobelt array, the nanobelts have both the crystal planes exposed by the nanosheets and the crystal planes exposed by the nanowires; when the micromorphology of the aluminum oxide nanostructure array layer is a nanocone array, the crystal planes exposed by the nanocones are the same as those of the nanowire array. In addition, the inventors found in their research that when the micromorphology of the aluminum oxide nanostructure array layer is different arrays, the total area of ​​the crystal planes exposed per unit volume of the aluminum oxide nanostructure array layer is different, the highest total area of ​​the crystal planes exposed is the nanowire array, the lowest is the nanocone array, and the nanobelt array and the nanosheet array are between the nanowire array and the nanocone array.

[0063] A second aspect of the present invention provides a method for preparing a multi-level structured aluminum foam, the method comprising:

[0064] (1) removing impurities from the surface of the aluminum foam to obtain the aluminum foam from which the impurities have been removed;

[0065] (2) immersing the aluminum foam from which impurities have been removed into an alkaline solution for oxidation treatment to obtain oxidized aluminum foam;

[0066] (3) drying and first calcining the oxidized aluminum foam to obtain a multi-level structure aluminum foam;

[0067] Wherein, the pH value of the alkaline solution is 9-13.

[0068] The inventors found in their research that the pH value of the alkaline solution affects the formation of the surface aluminum oxide structure layer of the prepared multi-level structure aluminum foam. When the pH value of the alkaline solution is greater than 13, the aluminum foam and the dense aluminum oxide film layer on its surface will be dissolved, and regular nanostructures such as nanowires, nanosheets, nanocones, etc. cannot be formed, and the aluminum oxide nanostructure array layer cannot be formed, and thus the aluminum oxide structure layer cannot be formed; when the pH value of the alkaline solution is less than 9, the reaction is slow.

[0069] In the present invention, the volume of the multi-level structure aluminum foam refers to the apparent volume. Preferably, the multi-level structure aluminum foam is a rectangular parallelepiped structure with uniform thickness, and the volume of the multi-level structure aluminum foam is obtained by direct measurement (i.e., calculated by multiplying the length, width, and height of the aluminum foam).

[0070] In the present invention, after removing surface impurities from foam aluminum, foam aluminum with impurities removed but retaining a dense aluminum oxide film layer on the surface is obtained. After oxidation treatment, the surface of the obtained oxidized foam aluminum forms a first transition layer mainly transformed from the aluminum oxide film layer and a part of the aluminum matrix, and a second transition array layer on the surface of the first transition layer. After high-temperature calcination, the first transition layer and the second transition array layer form an aluminum oxide layer and an aluminum oxide nanostructure array layer, respectively, and finally a foam aluminum with an aluminum oxide structure layer in situ grown on the surface is obtained, that is, a multi-level structure foam aluminum.

[0071] In the present invention, the AlOOH refers to diaspore, and the Al(OH)3 refers to aluminum hydroxide.

[0072] In some embodiments of the present invention, in step (2), the alkaline solution is a solution of an organic base, an inorganic base, or an alkaline salt.

[0073] In some embodiments of the present invention, the organic base is selected from at least one of methylamine, urea, ethylamine, ethanolamine, ethylenediamine, dimethylamine, trimethylamine, triethylamine, quaternary ammonium base, and guanidine compounds.

[0074] In some embodiments of the present invention, the inorganic base is selected from at least one of sodium hydroxide, potassium hydroxide, calcium hydroxide, barium hydroxide, ammonia water, lithium hydroxide, and cesium hydroxide.

[0075] In some embodiments of the present invention, the alkaline salt is selected from at least one of sodium aluminate, potassium aluminate, sodium carbonate, potassium carbonate, sodium sulfite, potassium sulfite, sodium bicarbonate, potassium bicarbonate, sodium acetate, potassium acetate, sodium sulfate, potassium phosphate, sodium hypochlorite, potassium hypochlorite, calcium hypochlorite, and calcium bicarbonate.

[0076] In the present invention, the quaternary ammonium base may be tetrapropylammonium hydroxide. In the present invention, the guanidine compound may be a guanidine organic base commonly used in the art, for example, metformin.

[0077] In the present invention, in step (2), there is no particular limitation on the amount of the alkaline solution, as long as it can be completely spread on the interface of the foamed aluminum.

[0078] The inventors have found that when the alkaline solution is an alkaline solution of an inorganic base, the alumina structure layer prepared under the same conditions can be more conducive to the diffusion and conduction of the gas interface; when used as a catalyst carrier, it can further improve the dispersion of the active components and the catalytic activity of the catalyst.

[0079] In some embodiments of the present invention, the temperature of the alkaline solution is 20-90°C. When the temperature of the alkaline solution is lower than 20°C, due to the slow oxidation rate of aluminum element, the produced alumina nanostructure array layer is sparse and the single structure generates a relatively sturdy columnar structure, and the active components are easy to agglomerate when used as a catalyst carrier. When the temperature of the alkaline solution is greater than 90°C, the foamed aluminum structure is easily destroyed, and its mechanical strength is easily reduced, making it difficult to use as a catalyst carrier. Preferably, the temperature of the alkaline solution is 25-80°C, and more preferably 40-60°C. When the temperature of the alkaline solution is within the preferred range, the catalyst obtained by using the obtained multi-level structure foamed aluminum as a catalyst carrier has the best activity and the best catalytic performance.

[0080] In some embodiments of the present invention, in step (1), the method for removing surface impurities may be a commonly used method in the art, such as ultrasonic washing with clean water, as long as the surface impurities can be removed without destroying the dense oxide layer on the surface of the foamed aluminum. In the present invention, there is no particular limitation on the conditions for removing surface impurities, as long as the surface dust and stains can be removed and the dense aluminum oxide film layer on the surface can be retained.

[0081] In some embodiments of the present invention, in step (2), the oxidation treatment is carried out for 0.5-24 hours, preferably 2-8 hours. The inventors have found that under the same reaction conditions, within the above oxidation treatment time range, the longer the oxidation treatment time, the greater the thickness of the aluminum oxide structure layer, which is beneficial to improving the catalytic performance.

[0082] The inventors found in their research that the oxidation treatment time has a great influence on the preparation of multi-level structure foam aluminum. When the oxidation treatment time is greater than 24h, the reaction time is too long and a uniform aluminum oxide nanostructure array layer cannot be formed.

[0083] In some embodiments of the present invention, in step (3), the conditions of the first calcination include: a temperature of 500-650°C.

[0084] In the present invention, there is no limitation on the drying method and conditions, as long as the surface liquid can be completely evaporated.

[0085] The third aspect of the present invention provides an application of the above-mentioned multi-level structured aluminum foam in a catalyst.

[0086] In some embodiments of the present invention, the multi-level structured aluminum foam can be used as a carrier in a catalyst.

[0087] A fourth aspect of the present invention provides a catalyst, which includes a noble metal as an active component and the above-mentioned multi-level structure foam aluminum as a carrier.

[0088] In some embodiments of the present invention, the mass of the precious metal is 0.1-10 g relative to 1 L of multi-level structural foam aluminum.

[0089] A fifth aspect of the present invention provides a method for preparing the above-mentioned monolithic foamed aluminum catalyst, the method comprising:

[0090] (i) immersing the hierarchical aluminum foam into a precious metal precursor solution and then drying it with strong wind;

[0091] (ii) repeating step (i) until the mass of the precious metal precursor loaded on 1L of the hierarchical structure aluminum foam is 0.1-10 g, calculated as the precious metal, to obtain an intermediate 1;

[0092] (iii) The intermediate 1 is subjected to a second calcination to obtain a monolithic aluminum foam catalyst loaded with precious metals.

[0093] In some embodiments of the present invention, in step (i), the concentration of the noble metal precursor solution is 0.1-5 wt % based on the noble metal.

[0094] In the present invention, in step (i), the immersion time is not particularly limited, as long as the surface of the multi-level structure aluminum foam is completely covered by the noble metal precursor solution. Preferably, the single immersion time is 10-30 seconds.

[0095] In the present invention, the strong wind drying described in step (i) is a drying method commonly used in the art. Those skilled in the art can adjust the strong wind drying conditions as needed, which will not be described in detail here.

[0096] In the present invention, there is no requirement for the ratio of the multi-level structure aluminum foam and the noble metal precursor solution in step (i), and the surface of the aluminum foam can be completely covered by the noble metal precursor solution.

[0097] In the present invention, the noble metal precursor is a noble metal precursor commonly used as an active component in catalysts in the art, preferably a noble metal salt, such as a salt of gold, silver, ruthenium, rhodium, palladium, osmium, iridium, or platinum, preferably a palladium salt. In a further preferred case, the palladium salt is at least one of palladium nitrate, palladium chloride, and palladium acetate.

[0098] In some embodiments of the present invention, in step (ii), the second calcination conditions include: calcination in an air atmosphere at 300-650°C.

[0099] 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 raw materials used are commercially available, and the methods described are commonly used methods in the art.

[0100] The foamed aluminum was purchased from Shanghai Yinfu Company. The foamed aluminum has a through-hole structure with an opening range of 3-10 mm, a thickness of 9-10 mm, and an apparent density of 0.2-2 g / cm 3 , with an apparent volume of 8.1 cm 3 (30mm×30mm×9mm).

[0101] The SEM images and elemental analysis images were obtained by scanning electron microscope, which was purchased from FEI Company and has the brand Nova NanoSEM 450.

[0102] In the following examples and comparative examples, the determination method of the conversion rate of methane and ethylene by the catalyst is as follows: the gas is monitored and analyzed online using a Fourier transform infrared spectrometer (Multigas 6030 multifunctional gas analyzer produced by Wanji Instrument Co., Ltd., USA), and the reduced concentration of methane and ethylene after passing through the catalyst are calculated. The ratio of the reduced concentration of methane to the initial concentration of methane is the conversion rate of methane, the ratio of the reduced concentration of ethylene to the initial concentration of ethylene is the conversion rate of ethylene, and the ratio of the concentration of methane and ethylene after passing through the catalyst to the initial concentration is the conversion rate of methane and ethylene. The reaction conditions are as follows: the space velocity is 25,000 h -1 Among the raw gas used, the concentration of oxygen was 10 vol%, the initial concentration of ethylene was 0.07 vol.%, the initial concentration of methane was 0.1 vol.%, and the rest was nitrogen.

[0103] The aging method is as follows: the catalyst is placed in a tubular furnace and heated to 600°C at a rate of 10°C / min and maintained for 12 hours, with both ends of the tubular furnace connected to air.

[0104] TEM images of the catalyst before and after aging were obtained by spherical aberration corrected transmission electron microscope, model: JEMARM200F, manufacturer: JEOL.

[0105] The HRTEM image and lattice spacing of the multi-level structured aluminum foam were obtained by spherical aberration-corrected transmission electron microscope (JEM ARM200F, manufactured by JEOL). The lattice spacing was measured and calculated using Gatan Digital Micrograph (version 2.10.1282.0) software.

[0106] Preparation Example 1

[0107] This preparation example is used to illustrate the preparation of multi-level structure foam aluminum

[0108] (1) 30mm×30mm×9mm (volume 8.1cm 3 ) The aluminum foam was ultrasonically washed with clean water to remove surface impurities;

[0109] (2) immersing the aluminum foam obtained in step (1) in a sodium hydroxide solution having a pH value of 12 and a temperature of 60° C. for 4 hours to obtain an oxidized aluminum foam;

[0110] (3) The oxidized aluminum foam obtained in step (2) is dried and calcined at 600° C. for 5 h to obtain the multi-level structure aluminum foam A1.

[0111] The volume of the multi-level structure aluminum foam A1 was not lost and was still 8.1 cm 3 .

[0112] The element analysis of the surface of the cross-section of the foamed aluminum without any treatment is as follows Figure 1 As shown, the element analysis of the cross-section surface of the multi-level structure foam aluminum A1 is as follows Figure 2 As shown. Element analysis shows that the spatial distribution of Al and O elements overlaps on the surface of the cross section, while only Al element is distributed at the cross section, which indicates that aluminum oxide is formed on the surface of aluminum foam.

[0113] The SEM image of the aluminum foam without any treatment is shown in FIG3 , and there is no array layer on its surface.

[0114] The SEM image of the multi-level structure aluminum foam A1 is shown in FIG4 . It can be seen from the SEM image that the surface of the aluminum foam contained in the multi-level structure aluminum foam A1 has an aluminum oxide structure layer with a thickness of 8-12 μm, including an aluminum oxide layer and an aluminum oxide nanostructure array layer on the surface of the aluminum oxide layer, wherein the aluminum oxide layer is a loose layer. The thickness of the aluminum oxide nanostructure array layer is 1-5 μm, and its microscopic morphology is a nanowire array, wherein the nanowire length is 2-5 μm, the diameter is 0.05-0.5 μm, and the aspect ratio is 4-10.

[0115] Sample pictures Figure 5 As shown, Figure 5 a is aluminum foam without any treatment. Figure 5 Figure b shows the aluminum foam after oxidation treatment and drying, and Figure c shows the multi-level structure aluminum foam A1 after calcination at 600℃ for 5h. Figure 5 a and Figure 5 As can be seen from Figure b, the oxidation treatment and drying of the foam aluminum did not affect the internal structure of the foam aluminum, that is, the mechanical strength of the foam aluminum after oxidation treatment did not change significantly. As can be seen from Figure c, the multi-level structure foam aluminum after calcination did not experience the loss of the aluminum oxide structure layer or damage to the foam aluminum structure.

[0116] Preparation Example 2

[0117] This preparation example is used to illustrate the preparation of multi-level structure foam aluminum

[0118] The multi-level structured aluminum foam A2 was prepared according to the method described in Example 1, except that in step (2), the immersion time of the aluminum foam was 8 hours.

[0119] The volume of the multi-level structure aluminum foam A2 was not lost and remained at 8.1 cm 3 .

[0120] The SEM image of the multi-level structure aluminum foam A2 is shown in Figure 6. It can be seen from the SEM image that the surface of the aluminum foam contained in the multi-level structure aluminum foam A2 has an aluminum oxide structure layer with a thickness of 13-25 μm, including an aluminum oxide layer and an aluminum oxide nanostructure array layer on the surface of the aluminum oxide layer, wherein the aluminum oxide layer is a loose layer. The thickness of the aluminum oxide nanostructure array layer is about 3-8 μm, and its microscopic morphology is a nanowire array, wherein the length of the nanowire is 5-8 μm, the diameter is 0.05-0.4 μm, and the aspect ratio is 10-40.

[0121] HRTEM image of multi-level structure aluminum foam A2 Figure 7 As shown, the lattice spacing of the (400) crystal plane of the multi-level structured aluminum foam A2 can be measured and calculated using Gatan DigitalMicrograph software to be 0.2 nm.

[0122] Preparation Example 3

[0123] This preparation example is used to illustrate the preparation of multi-level structure foam aluminum

[0124] The multi-level structured aluminum foam A3 was prepared according to the method described in Example 1, except that in step (2), the immersion time of the aluminum foam was 2 h.

[0125] The volume of the multi-level structure aluminum foam A3 was not lost and was still 8.1 cm 3 .

[0126] The SEM image of the multi-level structure aluminum foam A3 is shown in Figure 8. It can be seen from the SEM image that the surface of the aluminum foam contained in the multi-level structure aluminum foam A3 has an aluminum oxide structure layer with a thickness of 5-8μm, including an aluminum oxide layer and an aluminum oxide nanostructure array layer on the surface of the aluminum oxide layer, wherein the aluminum oxide layer is a loose layer. The thickness of the aluminum oxide nanostructure array layer is 1-3μm, and its microscopic morphology is a nanowire array, wherein the length of the nanowire is 1-3μm, the diameter is 0.05-0.1μm, and the aspect ratio is 20-40.

[0127] Preparation Example 4

[0128] This preparation example is used to illustrate the preparation of multi-level structure foam aluminum

[0129] The multi-level structured aluminum foam A4 was prepared according to the method described in Example 1, except that in step (2), the immersion time of the aluminum foam was 0.5 h.

[0130] The volume of the multi-level structure aluminum foam A4 was not lost and remained at 8.1 cm 3 .

[0131] The SEM image of the multi-level structure aluminum foam A4 is shown in Figure 9. It can be seen from the SEM image that the surface of the aluminum foam contained in the multi-level structure aluminum foam A4 has an aluminum oxide structure layer with a thickness of 1-3 μm, including an aluminum oxide layer and an aluminum oxide nanostructure array layer on the surface of the aluminum oxide layer, wherein the aluminum oxide layer is a loose layer. The thickness of the aluminum oxide nanostructure array layer is 0.1-0.5 μm, and its microscopic morphology is a nanowire array, wherein the length of the nanowire is 0.1-0.5 μm, the diameter is 0.14-0.3 μm, and the aspect ratio is 1-4.

[0132] Preparation Example 5

[0133] This preparation example is used to illustrate the preparation of multi-level structure foam aluminum

[0134] The multi-level structure aluminum foam A5 was prepared according to the method described in Preparation Example 2, except that in step (2), the pH value of the sodium hydroxide solution was 9.

[0135] The volume of the multi-level structure aluminum foam A5 was not lost and remained at 8.1 cm 3 .

[0136] The SEM image of the multi-level structure aluminum foam A5 is shown in Figure 10. Through the SEM analysis of the multi-level structure aluminum foam A5, it can be seen that the surface of the aluminum foam contained in the multi-level structure aluminum foam A5 has an aluminum oxide structure layer with a thickness of 2-3μm, including an aluminum oxide layer and an aluminum oxide nanostructure array layer on the surface of the aluminum oxide layer, wherein the aluminum oxide layer is a loose layer. Among them, the thickness of the aluminum oxide nanostructure array layer is 0.1-0.5μm, and its microscopic morphology is a nanosheet array, the length of the nanosheet is 0.1-0.5μm, the width of the nanosheet is 0.1-0.5μm, and the thickness of the nanosheet is 0.01-0.06μm. The HRTEM image of the multi-level structure aluminum foam A5 is shown in Figure 10. Fig.11 As shown, the lattice spacing of the (220) crystal plane of the multi-level structured aluminum foam A5 can be measured and calculated using Gatan DigitalMicrograph software to be 0.28 nm.

[0137] Preparation Example 6

[0138] This preparation example is used to illustrate the preparation of multi-level structure foam aluminum

[0139] The multi-level structure aluminum foam A6 was prepared according to the method described in Preparation Example 2, except that in step (2), the pH value of the sodium hydroxide solution was 11.

[0140] The volume of the multi-level structure aluminum foam A6 was not lost and remained at 8.1 cm 3 .

[0141] The SEM image of the multi-level structure aluminum foam A6 is shown in Figure 12. Through the SEM analysis of the multi-level structure aluminum foam A6, it can be seen that the surface of the aluminum foam contained in the multi-level structure aluminum foam A6 has an aluminum oxide structure layer with a thickness of 3-5μm, including an aluminum oxide layer and an aluminum oxide nanostructure array layer on the surface of the aluminum oxide layer, wherein the aluminum oxide layer is a loose layer. The thickness of the aluminum oxide nanostructure array layer is 1-3μm, and its microscopic morphology is a nanobelt array, wherein the nanobelt has a thickness of 0.05μm, a width of 0.1-0.5μm, and a length of 1-3μm.

[0142] Preparation Example 7

[0143] This preparation example is used to illustrate the preparation of multi-level structure foam aluminum

[0144] The multi-level structure aluminum foam A7 was prepared according to the method described in Preparation Example 2, except that in step (2), the pH value of the sodium hydroxide solution was 13.

[0145] The volume of the multi-level structured aluminum foam A7 was not lost and remained at 8.1 cm 3 .

[0146] The SEM image of the multi-level structure aluminum foam A7 is shown in Figure 13. It can be seen from the SEM image that the surface of the aluminum foam contained in the multi-level structure aluminum foam A7 has an aluminum oxide structure layer with a thickness of 15-25μm, including an aluminum oxide layer and an aluminum oxide nanostructure array layer on the surface of the aluminum oxide layer, wherein the aluminum oxide layer is a loose layer. The thickness of the aluminum oxide nanostructure array layer is 1-5μm, and its microscopic morphology is a nanowire array, wherein the length of the nanowire is 1-5μm, the diameter is 0.5-1μm, and the aspect ratio is 1-5.

[0147] Preparation Example 8

[0148] This preparation example is used to illustrate the preparation of multi-level structural aluminum foam.

[0149] The multi-level structure aluminum foam A8 was prepared according to the method described in Example 2, except that in step (2), the temperature of the sodium hydroxide solution was 25°C.

[0150] The volume of the multi-level structured aluminum foam A8 was not lost and remained at 8.1 cm 3 .

[0151] The SEM image of the multi-level structure aluminum foam A8 is shown in Figure 14. Through the SEM analysis of the multi-level structure aluminum foam A8, it can be seen that the surface of the aluminum foam contained in the multi-level structure aluminum foam A8 has an aluminum oxide structure layer with a thickness of 15-20μm, including an aluminum oxide layer and an aluminum oxide nanostructure array layer on the surface of the aluminum oxide layer, wherein the aluminum oxide layer is a loose layer. The thickness of the aluminum oxide nanostructure array layer is 3-5μm, and its microscopic morphology is a nanowire array, wherein the length of the nanowire is 3-5μm, the diameter is 1-2μm, and the aspect ratio is 1.5-5.

[0152] Preparation Example 9

[0153] This preparation example is used to illustrate the preparation of multi-level structural aluminum foam.

[0154] The multi-level structure foam aluminum A9 was prepared according to the method described in Preparation Example 2, except that in step (2), the temperature of the sodium hydroxide solution was 40°C.

[0155] The volume of the multi-level structured aluminum foam A9 was not lost and remained at 8.1 cm 3 .

[0156] The SEM image of the multi-level structure aluminum foam A9 is shown in Figure 15. Through the SEM analysis of the multi-level structure aluminum foam A9, it can be seen that the surface of the aluminum foam contained in the multi-level structure aluminum foam A9 has an aluminum oxide structure layer with a thickness of 8-13μm, including an aluminum oxide layer and an aluminum oxide nanostructure array layer on the surface of the aluminum oxide layer, wherein the aluminum oxide layer is a loose layer. The thickness of the aluminum oxide nanostructure array layer is 3-8μm, and its microscopic morphology is a nanowire array, wherein the length of the nanowire is 3-8μm, the diameter is 0.15-0.2μm, and the aspect ratio is 20-40.

[0157] Preparation Example 10

[0158] This preparation example is used to illustrate the preparation of multi-level structure foam aluminum

[0159] The multi-level structure aluminum foam A10 was prepared according to the method described in Preparation Example 2, except that in step (2), the temperature of the sodium hydroxide solution was 80°C.

[0160] The volume of the multi-level structure aluminum foam A10 was not lost and remained at 8.1 cm 3 .

[0161] The SEM image of the multi-level structure aluminum foam A10 is shown in Figure 16. Through the SEM analysis of the multi-level structure aluminum foam A10, it can be seen that the surface of the aluminum foam contained in the multi-level structure aluminum foam A10 has an aluminum oxide structure layer with a thickness of 25-30μm, including an aluminum oxide layer and an aluminum oxide nanostructure array layer on the surface of the aluminum oxide layer, wherein the aluminum oxide layer is a loose layer. The thickness of the aluminum oxide nanostructure array layer is 4-10μm, and its microscopic morphology is a nanobelt array, wherein the length of the nanobelt is 5-10μm, the width is 0.5-3μm, and the thickness is 0.05-0.5μm.

[0162] Preparation Example 11

[0163] This preparation example is used to illustrate the preparation of multi-level structure foam aluminum

[0164] The multi-level structure aluminum foam A11 was prepared according to the method described in Preparation Example 2, except that in step (2), a tetrapropylammonium hydroxide solution with a pH value of 12 and a temperature of 60° C. was used.

[0165] The volume of the multi-level structured aluminum foam A11 was not lost and remained at 8.1 cm 3 .

[0166] The SEM image of the multi-level structure aluminum foam A11 is shown in Figure 17. Through the SEM analysis of the multi-level structure aluminum foam A11, it can be seen that the surface of the aluminum foam contained in the multi-level structure aluminum foam A11 has an aluminum oxide structure layer with a thickness of 20-25μm, including an aluminum oxide layer and an aluminum oxide nanostructure array layer on the surface of the aluminum oxide layer, wherein the aluminum oxide layer is a loose layer. The thickness of the aluminum oxide nanostructure array layer is 10-22μm, and its microscopic morphology is a nanocone array, wherein the length of the nanocone is 18-22μm, and the diameter of the nanocone bottom is 4-6μm.

[0167] Preparation Example 12

[0168] This preparation example is used to illustrate the preparation of multi-level structure foam aluminum

[0169] The multi-level structure aluminum foam A12 was prepared according to the method described in Preparation Example 2, except that in step (2), a sodium aluminate solution with a pH value of 12 and a temperature of 60° C. was used.

[0170] The volume of the multi-level structured aluminum foam A12 was not lost and remained at 8.1 cm 3 .

[0171] The SEM image of the multi-level structure aluminum foam A12 is shown in Figure 18. Through the SEM analysis of the multi-level structure aluminum foam A12, it can be seen that the surface of the aluminum foam contained in the multi-level structure aluminum foam A12 has an aluminum oxide structure layer with a thickness of about 15μm, including an aluminum oxide layer and an aluminum oxide nanostructure array layer on the surface of the aluminum oxide layer, wherein the aluminum oxide layer is a loose layer. The thickness of the aluminum oxide nanostructure array layer is 1-3μm, and its microscopic morphology is a nanobelt array, wherein the nanobelt length is about 3μm, the nanobelt width is 0.1-1μm, and the nanobelt thickness is about 0.1μm.

[0172] Preparation Comparative Example 1

[0173] Foam aluminum DA1 was prepared according to the method of Preparation Example 1, except that in step (2), the foam aluminum was immersed in deionized water with a pH of 7 for 4 hours.

[0174] The SEM analysis and elemental analysis results of DA1 are similar to those of the aluminum foam without any treatment. No aluminum oxide structural layer or aluminum oxide nanostructure array layer is generated on the surface of the aluminum foam.

[0175] Preparation Comparative Example 2

[0176] Foam aluminum DA2 was prepared according to the method of Preparation Example 1, except that in step (2), the foam aluminum was immersed in a sodium hydroxide solution with a pH of 13.5 for 4 hours.

[0177] During the preparation process, the foamed aluminum is directly melted away, causing corrosion of the foamed aluminum pore walls and a sharp decrease in strength, ultimately forming a powdery product.

[0178] Example 1

[0179] This example is used to illustrate the preparation of the catalyst.

[0180] (i) immersing the multi-level structure aluminum foam A1 in 10 g of a palladium nitrate solution having a concentration of 1 wt.% based on palladium metal for 10 seconds, and then drying the solution under strong wind at 120° C.;

[0181] (ii) repeating step (i) until the amount of palladium nitrate supported on the multi-level structure aluminum foam A1 is 4.05 mg, calculated as palladium metal, to obtain intermediate 1;

[0182] (iii) The intermediate 1 was calcined at 550° C. in air atmosphere for 5 h to obtain a monolithic aluminum foam catalyst S1 loaded with 4.05 mg of palladium precious metal. Based on the volume of the multi-level structure aluminum foam, the loading amount of palladium metal was 0.5 g / L.

[0183] Figure 5 d is a physical picture of the integral aluminum foam catalyst S1.

[0184] Example 2-12

[0185] Catalysts S2-S12 were prepared according to the method of Example 12, except that multi-level structured aluminum foams A2-A12 were used respectively.

[0186] Comparative Example 1

[0187] Catalyst DS1 was prepared according to the method of Example 1, except that aluminum foam without any treatment was used.

[0188] Comparative Example 2

[0189] Take 200 mg of palladium nitrate solution (purchased from Shanghai Jiuling Chemical Co., Ltd., with a Pd mass content of 15 w.t.%, and a purity of 99.9%) (about 0.15 mL), dilute it to 5 mL with deionized water and mix it evenly to obtain a dilute palladium nitrate solution. Take 2.97 g of alumina powder (purchased from Shandong Aluminum, with specifications: specific surface area 144.5 m2 / g, median particle size 76.8 μm) and put it into a beaker, add a magnetic bar to start stirring, and add the dilute palladium nitrate solution to the stirred powder to form a viscous slurry. Continue to stir the above viscous slurry and heat it to 60°C, continue to volatilize the water in the slurry until it is close to dry (about 2 hours), and then put it into an oven at 120°C for 12 hours to obtain a dry sample. Grind the above-obtained dry sample into a uniform powder, put it into a muffle furnace, heat it to 550°C at 5°C / min, and keep it for 5 hours before cooling it naturally to obtain the catalyst DS2 (i.e., alumina powder loaded with Pd).

[0190] Test Example 1

[0191] Catalyst S2 was used to catalyze the oxidation of ethylene and methane mixed gas (tail gas from the decarbonization unit in the coal chemical process) to produce carbon dioxide and water, and the conversion rates of methane and ethylene were tested at different reaction temperatures (100°C, 150°C, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, and 500°C). The results are shown in Tables 1, 2, and Fig.19 The reaction conditions are as follows: the space velocity is 25,000 h -1 The raw gas used has an oxygen concentration of 10 vol%, an initial ethylene concentration of 0.07 vol.%, an initial methane concentration of 0.1 vol.%, and the rest is nitrogen. After reaching the reaction temperature, the temperature is maintained for 1 hour, and the concentration of the reactants is detected and analyzed. It can be seen that the methane conversion rate reaches 60.1% at 450°C; the ethylene conversion rate reaches 90% at 350°C.

[0192] Catalyst S2 was aged. The TEM results of catalyst S2 before and after aging are shown in FIG20 . It can be seen that the noble metals on the catalyst support before aging exist in the form of nanoclusters or nanoparticles of 1-2 nm in size ( Fig. 20A ), the particle size of the precious metals did not change significantly after aging ( Fig. 20B ), which indicates that the precious metals did not undergo obvious agglomeration and thermal sintering before and after aging. Therefore, catalyst S2 has good thermal stability.

[0193] Test Example 2

[0194] According to the method of Test Example 1, the catalyst S9 was used to catalyze the oxidation of ethylene and methane mixed gas (tail gas from the decarbonization unit in the coal chemical process) to generate carbon dioxide and water, and the conversion rates of methane and ethylene at different reaction temperatures were tested. The results are shown in Tables 1, 2 and Fig.21 As shown, it can be seen that the methane conversion rate reaches 40% at 350℃ and 68.4% at 450℃; the ethylene conversion rate can reach 87% at 350℃ and 98% at 500℃.

[0195] Catalyst S9 was aged, and the TEM results of catalyst S9 before and after aging are shown in FIG22 . Fig.22A For fresh catalyst S9, Fig. 22B The catalyst S9 after aging. It can be seen that the noble metals on the catalyst carrier before aging exist in the form of nanoclusters or nanoparticles of 1-3 nm ( Fig.22A ), the particle size of precious metals does not increase significantly after aging ( Fig. 22B ), which shows that there is no obvious agglomeration and thermal sintering of precious metals before and after aging.

[0196] Test Example 3

[0197] According to the method of Test Example 1, the catalyst S11 was used to catalyze the oxidation of ethylene and methane mixed gas (tail gas from the decarbonization unit in the coal chemical process) to generate carbon dioxide and water, and the conversion rates of methane and ethylene at different reaction temperatures were tested. The results are shown in Tables 1, 2 and Fig.23 As shown. Fig.23 It can be seen that the methane conversion rate is 17% at 350°C and 53% at 500°C; the ethylene conversion rate is 78% at 350°C and 91% at 500°C.

[0198] Catalyst S11 was aged, and the TEM results of catalyst S11 before and after aging were similar to those obtained in Test Example 2.

[0199] Comparative test example 1

[0200] According to the method of Test Example 1, the catalyst DS1 was used to catalytically oxidize a mixed gas of ethylene and methane (tail gas from a decarbonization unit in a coal chemical process), and the conversion rates of methane and ethylene at different reaction temperatures were tested. The results are shown in Tables 1, 2 and Fig.24 The airspeed is 25,000 h -1 , the ethylene concentration is 700 ppm, and the initial methane concentration is 1000 ppm. It can be seen that the methane conversion rate is still less than 10% at 500℃; the ethylene conversion rate is only 70% at around 350℃.

[0201] Comparative test example 2

[0202] This comparative test example is used to compare the aging resistance of comparative catalysts.

[0203] The catalyst DS2 was aged. Fig.25 As shown, Fig.25 A is fresh catalyst DS2, Fig.25 B is the aged catalyst DS2. It can be seen that the precious metals on the aged Pd-loaded alumina powder are agglomerated, indicating that the catalytic activity of the catalyst DS2 is significantly reduced.

[0204] Table 1

[0205]

[0206] Table 2

[0207]

[0208] It can be known from the above-mentioned preparation examples 1-12 and preparation comparison examples 1-2 that the surface of the foamed aluminum contained in the multi-level structural foam aluminum prepared by the present invention has an aluminum oxide structural layer of 1-30 μm, and the aluminum oxide structural layer includes an aluminum oxide layer and an aluminum oxide nanostructure array layer on the surface of the aluminum oxide layer, and the microscopic morphology of the aluminum oxide nanostructure array layer includes a nanosheet array, a nanobelt array, a nanowire array, and a nanocone array.

[0209] It can be seen from the preparation examples 1-4 that under the same reaction conditions, the longer the oxidation treatment time, the thickness of the aluminum oxide structure layer gradually increases, which is beneficial to improving the catalytic performance. In addition, when the alkaline solution used is a sodium hydroxide solution with a temperature of 60°C and a pH value of 12, the microscopic morphology of the nanoalumina array layer is a nanowire array. As the oxidation treatment time increases, the aspect ratio of the nanowires in the nanowire array increases, which is more conducive to improving the catalytic performance.

[0210] It can be seen from the preparation examples 5-7 that under the same reaction conditions, the greater the pH value of the alkaline solution, the greater the thickness of the aluminum oxide structure layer. Moreover, when the alkaline solution used is a sodium hydroxide solution at a temperature of 60°C, the microscopic morphology of the aluminum oxide nanostructure array layer is nanosheet array, nanobelt array, and nanowire array in order as the pH value of the alkaline solution increases.

[0211] By comparing test examples 1-3 with test example 1 and with test example 2, it can be seen that the activity and stability of the catalyst are better when the multi-level structure foam aluminum prepared by the present invention is used as a carrier and support of the catalyst.

[0212] 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 multi-level structural aluminum foam, characterized in that: The multi-level structured aluminum foam comprises aluminum foam and an aluminum oxide structure layer formed by in-situ growth on the surface of the aluminum foam; Wherein, the aluminum oxide structure layer comprises an aluminum oxide layer and an aluminum oxide nanostructure array layer formed on the surface of the aluminum oxide layer; the aluminum oxide layer is a loose layer grown between the aluminum single substance interface and the aluminum oxide nanostructure array layer; Wherein, the thickness of the aluminum oxide structural layer is 1-30 μm.

2. The multi-level structural aluminum foam according to claim 1, wherein: The thickness of the aluminum oxide structural layer is 2-25 μm.

3. The multi-level structural aluminum foam according to claim 1, wherein: The thickness of the aluminum oxide nanostructure array layer is 0.1-22 μm.

4. The multi-level structural aluminum foam according to claim 1, wherein: The microscopic morphology of the aluminum oxide nanostructure array layer is at least one of a nanowire array, a nanosheet array, a nanocone array and a nanobelt array.

5. The multi-level structural aluminum foam according to claim 4, wherein: The microscopic morphology of the aluminum oxide nanostructure array layer is a nanowire array.

6. The multi-level structural aluminum foam according to claim 4, wherein: The nanowire array has a nanowire length of 0.1-10 μm and an aspect ratio of 1-50.

7. The multi-level structural aluminum foam according to claim 6, wherein: The nanowires of the nanowire array have a length of 2-10 μm; The nanowire array has a nanowire aspect ratio of 10-50.

8. The multi-level structural aluminum foam according to claim 4, wherein: The nanowires have a diameter below 0.5 μm.

9. The multi-level structural aluminum foam according to claim 4, wherein: The nanosheet array has a nanosheet thickness of 0.01-0.06 μm, a nanosheet length of 0.1-0.5 μm, and a nanosheet width of 0.1-0.5 μm.

10. The multi-level structural aluminum foam according to claim 4, wherein: The nanocone length of the nanocone array is 5-25 μm, and the cone bottom diameter is 3-10 μm.

11. The multi-level structural aluminum foam according to claim 4, wherein: The nanobelt array has a nanobelt length of 1-10 μm, a nanobelt width of 0.1-5 μm, and a nanobelt thickness of 0.05-0.5 μm.

12. A method for preparing the multi-level structured aluminum foam according to any one of claims 1 to 11, characterized in that: The method comprises: (1) removing impurities from the surface of the aluminum foam to obtain the aluminum foam from which the impurities have been removed; (2) immersing the aluminum foam from which impurities have been removed into an alkaline solution for oxidation treatment to obtain oxidized aluminum foam; (3) drying and first calcining the oxidized aluminum foam to obtain a multi-level structure aluminum foam; Wherein, the pH value of the alkaline solution is 9-13; Wherein, in step (2), the oxidation treatment condition is: time is 0.5-24h.

13. The preparation method according to claim 12, wherein: In step (2), the alkaline solution is a solution of an organic base, an inorganic base, or an alkaline salt; The organic base is selected from at least one of methylamine, urea, ethylamine, ethanolamine, ethylenediamine, dimethylamine, trimethylamine, triethylamine, quaternary ammonium base, and guanidine compounds; The inorganic base is selected from at least one of sodium hydroxide, potassium hydroxide, calcium hydroxide, barium hydroxide, ammonia water, lithium hydroxide and cesium hydroxide; The alkaline salt is selected from at least one of sodium aluminate, potassium aluminate, sodium carbonate, potassium carbonate, sodium sulfite, potassium sulfite, sodium bicarbonate, potassium bicarbonate, sodium acetate, potassium acetate, sodium sulfate, potassium phosphate, sodium hypochlorite, potassium hypochlorite, calcium hypochlorite, and calcium bicarbonate.

14. The preparation method according to claim 12, wherein: The temperature of the alkaline solution is 20-90°C.

15. The preparation method according to claim 14, wherein: The temperature of the alkaline solution is 25-80°C.

16. The preparation method according to any one of claims 12 to 15, wherein: In step (1), the method for removing surface impurities is ultrasonic washing with clean water.

17. The preparation method according to any one of claims 12 to 15, wherein: In step (2), the oxidation treatment is carried out for 2-8 hours.

18. The preparation method according to any one of claims 12 to 15, wherein: In step (3), the conditions for the first calcination include: a temperature of 500-650°C.

19. Use of the multi-level structured aluminum foam according to any one of claims 1 to 11 in catalysts.

20. An integral foam aluminum catalyst, characterized in that: The catalyst comprises a noble metal as an active component and the multi-level structured foamed aluminum described in any one of claims 1 to 11 as a carrier.

21. The catalyst according to claim 20, wherein Relative to 1L of multi-level structural foamed aluminum, the mass of the precious metal is 0.1-10g.

22. The method for preparing the catalyst according to claim 20 or 21, characterized in that: The method comprises: (i) immersing the hierarchical aluminum foam into a precious metal precursor solution and then drying it with strong wind; (ii) repeating step (i) until the mass of the precious metal loaded on 1L of the multi-level structure aluminum foam is 0.1-10 g, calculated as the precious metal, to obtain an intermediate 1; (iii) The intermediate 1 is subjected to a second calcination to obtain a monolithic aluminum foam catalyst loaded with precious metals.

23. The preparation method according to claim 22, wherein: In step (i), the concentration of the noble metal precursor solution is 0.1-5 wt % based on the noble metal.

24. The preparation method according to claim 22, wherein: In step (iii), the second calcination conditions include: calcination in an air atmosphere at 300-650°C.

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