Aluminum oxide nanoplatelets, methods of making and applications thereof

Abstract

This invention relates to the field of alumina technology, specifically to an alumina nanosheet, its preparation method, and its applications. The alumina nanosheet has a specific surface area ≥150 m² / g. 2 / g; wherein, in the alumina nanosheets, five-coordinated Al 3+ The content of the alumina nanosheets is ≥0.98mmol / g, and the proportion is ≥5%. The alumina nanosheets provided by this invention have a high density of unsaturated coordinated aluminum species and can be widely used in petrochemical and fine chemical industries.

Description

Technical Field

[0001] This invention relates to the field of alumina technology, specifically to an alumina nanosheet, a method for preparing an alumina nanosheet, an application of an alumina nanosheet, a supported catalyst, and an application of a supported catalyst. Background Technology

[0002] Catalysis is involved in over 80% of global chemical process design, and heterogeneous catalysis is a crucial aspect of the entire catalytic process. Catalysts are the core of industrial catalytic processes, and catalyst supports are a key factor influencing catalyst activity. Currently, common supports include metal oxides, metal-organic frameworks (MOFs), molecular sieves, carbon materials, and novel nanomaterials. Nanomaterials are materials with at least one nanoscale dimension. The nanoscale size endows materials with unique properties, such as surface effects and small-size effects. These characteristics allow nanomaterials to shine in optical sensors and displays, solar energy and fuel cells, bioscience, catalysis, and smart materials. Therefore, developing catalyst materials with specific morphologies and structures is a hot research direction for improving the efficiency of industrial processes.

[0003] Alumina is an important ceramic material and plays a crucial role in the field of catalysis. It boasts a specific surface area of ​​hundreds of square meters per gram and a rich pore structure, resulting in excellent adsorption performance. Simultaneously, it exhibits good thermal stability and moderate surface acidity / alkalinity, making it widely used as an adsorbent, catalyst, catalyst support, and automotive exhaust purifier. In catalysis, alumina, as a support, provides catalysts with high thermal and hydrothermal stability, and its varying pore sizes and specific structural exposure surfaces offer favorable sites for the modification and alteration of active metal species.

[0004] Nano-alumina exhibits high hardness, is colorless, wear-resistant, electrically insulating, high-temperature stable, has a high specific surface area, a low coefficient of friction, and is corrosion-resistant. Based on these advantages, nano-alumina can be used in various fields, including catalytic materials, adsorbents, surface coatings, heat-resistant materials, insulating materials, catalyst components, and advanced ceramics.

[0005] Recent studies have found that Al with unsaturated coordination 3+ Defect site structure (i.e., five-coordinate Al) 3+ γ-alumina has a significant impact on the dispersion of metals and can improve the interaction between metals and supports (Nanoscale, 2015, 7, 13313-13344). Based on this, a high specific surface area and high five-coordinate Al2O3 were developed. 3+ The high content of Al2O3 nanosheets is of great significance for the design of efficient industrial catalysts and the development of efficient and energy-saving chemical processes.

[0006] CN107777713A prepared alumina materials with hexagonal nanosheet structures by synergistic use of chemical precipitation and hydrothermal methods under the action of organic amines; CN116459829A prepared alumina nanosheets by using high molecular weight triblock copolymers P123 and / or F127 as template agents and used them to anchor metal Pt species; CN110038547A prepared alumina nanosheet materials by controlling preparation parameters, such as the ratio of aluminum source to precipitant and hydrothermal temperature.

[0007] None of the aforementioned existing technologies address how to simultaneously and effectively improve the specific surface area of ​​alumina nanosheets and the five-coordinated Al. 3+ The content and proportion of [the substance]. Summary of the Invention

[0008] The purpose of this invention is to overcome the above-mentioned technical problems and provide alumina nanosheets, a method for preparing alumina nanosheets, an application of alumina nanosheets, a supported catalyst, and an application of the supported catalyst. These alumina nanosheets possess excellent specific surface area and also have a high content and high proportion of five-coordinated Al. 3+ Meanwhile, this preparation method simplifies the process flow and facilitates industrial production.

[0009] The first aspect of this invention provides alumina nanosheets, wherein the specific surface area of ​​the alumina nanosheets is ≥150 m². 2 / g;

[0010] Among them, the alumina nanosheets contain five-coordinated Al 3+ The content is ≥0.98mmol / g, accounting for ≥5%.

[0011] In this invention, unless otherwise specified, the alumina nanosheets contain Al 3+ The coordination types of species include tetracoordination, pentacoordination, and hexacoordination, namely Al(VI), Al(V), and Al(IV). Among them, Al(VI) and Al(IV) are both coordination-saturated Al... 3+ In other words, Al atoms do not have lone pairs of electrons; however, Al(V) is special in that Al atoms do have lone pairs of electrons. Therefore, Al(V) is an unsaturated, coordinated defect-site species that can adsorb metals and participate in chemical reactions. This is precisely why alumina preparations with high Al(V) content and proportion are required.

[0012] In this invention, unless otherwise specified, five-coordinated Al 3+ A content ≥0.98mmol / g refers to the presence of five-coordinated Al in 1g of alumina nanosheets. 3+ The content is ≥0.98mmol; meanwhile, the proportion is ≥5% in the alumina nanosheets, referring to the five-coordinated Al content.3+ The quantity / molar percentage is ≥5%, that is, n[Al(V)] / {n[Al(VI)]+n[Al(V)]+n[Al(IV)]}≥5%.

[0013] Preferably, in 27 In the solid-state nuclear magnetic resonance spectrum of Al, the alumina nanosheets have characteristic peaks with chemical shifts of 0ppm±10%, 50ppm±10%, and 65ppm±10%.

[0014] A second aspect of this invention provides a method for preparing alumina nanosheets, the method comprising:

[0015] (1) Aluminum source, alkaline compound, surfactant, carbon quantum dots and solvent are mixed and aged to obtain an aged product containing alumina precursor seeds.

[0016] (2) The aging product is subjected to solvent heat treatment, and the resulting solid-liquid mixture is subjected to solid-liquid separation to obtain an alumina precursor; wherein the solvent heat treatment temperature is 80-200℃.

[0017] (3) The alumina precursor is dried and calcined in sequence to obtain alumina nanosheets.

[0018] The third aspect of this invention provides an alumina nanosheet provided in the first aspect, or an alumina nanosheet prepared by the preparation method provided in the second aspect, for use in catalyst supports, gas-liquid adsorption, solid-phase fillers, and wastewater treatment agents.

[0019] A fourth aspect of the present invention provides a supported catalyst comprising: a support and an active component supported on the support, wherein the support is selected from the alumina nanosheets provided in the first aspect, or the alumina nanosheets prepared by the preparation method provided in the second aspect.

[0020] The fifth aspect of this invention provides the application of the supported catalyst provided in the fourth aspect in alkane dehydrogenation and catalytic cracking.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] (1) The alumina nanosheets provided by the present invention effectively enhance the five-coordinated Al content while having a high specific surface area. 3+ The content and proportion of;

[0023] (2) The preparation method provided by the present invention directly uses aging and solvothermal treatment to regulate the density of specific sites on the surface of alumina by means of an aluminum source mixture, specifically by regulating the unsaturated coordinated Al 3+ (five-coordinate Al) 3+The density of unsaturated coordinated aluminum species on the alumina surface is controlled, especially by using alkaline compounds, surfactants and carbon quantum dots to assist in direct aging and solvothermal treatment.

[0024] (3) The preparation method provided by the present invention does not require the addition of additional catalysts and / or emulsifiers, which simplifies the process and facilitates industrial production.

[0025] (4) The alumina nanosheets provided by the present invention have high five-coordinate Al 3+ Its density allows for wide application in petrochemical and fine chemical industries, especially in catalyst supports, gas-liquid adsorption, solid fillers, and wastewater treatment agents. Attached Figure Description

[0026] Figure 1 Here is a SEM image of the alumina nanosheets S1 prepared in Example 1;

[0027] Figure 2 The image shows the XRD pattern of the alumina nanosheets S1 prepared in Example 1.

[0028] Figure 3 The N2 adsorption-desorption curve of the alumina nanosheets S1 prepared in Example 1 is shown.

[0029] Figure 4 The alumina nanosheets S1 prepared in Example 1 27 Al solid-state nuclear magnetic resonance spectrum;

[0030] Figure 5 Here is a SEM image of the alumina nanosheets S2 prepared in Example 2;

[0031] Figure 6 SEM image of alumina DS1 prepared in Comparative Example 1;

[0032] Figure 7 The alumina DS1 prepared in Comparative Example 1 27 Nuclear magnetic resonance spectrum of Al solid. Detailed Implementation

[0033] The endpoints and any values ​​of the ranges disclosed herein 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 the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0034] The first aspect of this invention provides alumina nanosheets, wherein the specific surface area of ​​the alumina nanosheets is ≥150 m². 2 / g; In the alumina nanosheets, five-coordinated Al 3+ The content is ≥0.98mmol / g, accounting for ≥5%.

[0035] The inventors of this invention discovered that the complex structure of alumina surface, particularly its microstructure, enables diverse applications in the fine chemical industry. However, the density of specific structural sites can limit its application in particular fields. Therefore, by controlling the density of specific sites on the alumina surface, especially the unsaturated coordinated aluminum species (five-coordinate Al), this invention can be applied to alumina. 3+ The density of the alumina nanosheets was increased to effectively enhance the five-coordinate Al content while ensuring a high specific surface area. 3+ The density, that is, the five-coordinated Al in the alumina nanosheets. 3+ The content is ≥0.98mmol / g, accounting for ≥5%.

[0036] In this invention, unless otherwise specified, five-coordinated Al 3+ Content based on 27 The calculation is performed using the nuclear magnetic resonance spectrum of Al solid, that is, by analyzing the Al content in the alumina material. 3+ Al is classified into three types, with chemical shifts around 0, 50, and 65 ppm, belonging to Al(VI), Al(V), and Al(IV) respectively. 3+ The structure was determined by integrating the peak areas of the three components and then using the ratio of their peak areas to determine the five-coordinate Al. 3+ The mole fraction of Al(V) is expressed as x[Al(V)] = n[Al(V)] / {n[Al(VI)] + n[Al(V)] + n[Al(IV)]}. Based on this mole fraction, multiplying the mole fraction of Al(V) by twice the number of moles of alumina in 1g of alumina nanosheets yields the molar content of Al(V) = x[Al(V)] × 2 × 0.0098, where 0.0098 represents the number of moles of Al₂O₃ in 1g (1g / (10²g / mol)) = 0.0098 mol; and the number of moles of alumina is the sum of the moles of aluminum species Al(VI), Al(V), and Al(IV).

[0037] In this invention, the alumina nanosheets can be either regular or irregular in shape.

[0038] In some embodiments of the present invention, preferably, the average length of the alumina nanosheets is 200-2000 nm, for example, 200 nm, 500 nm, 600 nm, 800 nm, 1000 nm, 1500 nm, 2000 nm, and any value in the range of any two values, preferably 500-1000 nm.

[0039] In some embodiments of the present invention, preferably, the average width of the alumina nanosheets is 50-500 nm, for example, 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 500 nm, and any value in the range of any two values, preferably 100-300 nm.

[0040] In this invention, the average length and average width parameters of the alumina nanosheets are measured by SEM. Specifically, the length and width of 300 alumina nanosheets are measured and the average value is taken. That is, in the SEM image of an alumina nanosheet sample, the length and width of 300 alumina nanosheets are randomly selected, and the average value is calculated.

[0041] In this invention, the shape of alumina nanosheets is observed using SEM. Note the overall growth direction and possible secondary growth directions of the alumina nanosheets. The length of growth in each direction of the alumina nanosheets is measured using Nanomeasurer, an electron microscopy image analysis software, and the longest length and the shorter directions that are not parallel to the longest growth length are identified. The longest growth length typically represents the main growth direction of the alumina nanosheet, i.e., the principal direction; the directions represented by the shorter growth lengths that are not parallel to the principal direction can be considered secondary directions.

[0042] In this invention, the length of the alumina nanosheet is defined along the primary direction, which is the direction in which the nanosheet extends the furthest. The width of the alumina nanosheet is defined along the secondary direction; the width is typically smaller than the length and may be at an angle to the length direction.

[0043] In this invention, the average length of the alumina nanosheets refers to the arithmetic mean of the lengths of all objects in a set of length statistics. It is calculated by adding up the lengths of all objects in this set and then dividing by the number of objects.

[0044] In this invention, the average width of the alumina nanosheets refers to the arithmetic mean of the widths of all objects in a set of width statistics. It is calculated by adding up the widths of all objects in this set and then dividing by the number of objects.

[0045] In some embodiments of the present invention, preferably, the specific surface area of ​​the alumina nanosheets is 150-500 m². 2 / g, for example, 150m 2 / g、170m 2 / g、180m 2 / g、190m 2 / g、200m 2 / g、220m 2 / g、240m2 / g、250m 2 / g、260m 2 / g、280m 2 / g、300m 2 / g、400m 2 / g、500m 2 / g, and any value within the range of any two values, preferably 200-300m 2 / g.

[0046] In this invention, the specific surface area parameter is measured using a fully automated isothermal adsorption instrument.

[0047] In some embodiments of the present invention, preferably, the alumina nanosheets contain five-coordinated Al. 3+ The content is 0.98-5.88 mmol / g, for example, 0.98 mmol / g, 1 mmol / g, 1.5 mmol / g, 1.96 mmol / g, 2 mmol / g, 2.2 mmol / g, 2.5 mmol / g, 2.8 mmol / g, 3 mmol / g, 3.2 mmol / g, 3.5 mmol / g, 3.8 mmol / g, 3.92 mmol / g, 4 mmol / g, 4.5 mmol / g, 5 mmol / g, 5.5 mmol / g, 5.68 mmol / g, 5.88 mmol / g, and any value within any range of any two values, preferably 1.96-5.68 mmol / g.

[0048] In some embodiments of the present invention, preferably, the alumina nanosheets contain five-coordinated Al. 3+ The percentage is 5-30%, for example, 5%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 26%, 28%, 29%, 30%, and any value within the range of any two values, preferably 10-30%.

[0049] In this invention, alumina nanosheets that meet the above-mentioned range are more conducive to improving the adsorption activity and catalytic activity of unsaturated coordinated aluminum species.

[0050] In this invention, the alumina nanosheets have a mesoporous structure. Preferably, the pore volume of the alumina nanosheets is 0.1-5 cm³. 3 / g, for example, 0.1cm 3 / g, 0.2cm 3 / g, 0.5cm 3 / g, 0.8cm 3 / g, 1cm 3 / g, 1.5cm 3 / g、2cm3 / g, 2.5cm 3 / g, 3cm 3 / g、4cm 3 / g, 5cm 3 / g, and any value within the range of any two values, preferably 0.2-3cm. 3 / g.

[0051] In some embodiments of the present invention, preferably, the average pore size of the alumina nanosheets is 1-20 nm, for example, 1 nm, 2 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 15 nm, 20 nm, and any value within the range of any two values, preferably 5-10 nm.

[0052] In this invention, the average pore size parameter and pore volume parameter are both measured using a fully automatic isothermal adsorption instrument and calculated using the BJH model.

[0053] In some embodiments of the present invention, preferably, the alumina nanosheets have a γ-Al2O3 crystal phase structure.

[0054] In this invention, the crystal phase parameters are obtained by X-ray powder diffraction analysis; the microstructure parameters are measured by scanning electron microscopy.

[0055] In some embodiments of the present invention, preferably, in 27 In the solid-state NMR spectrum of Al, the alumina nanosheets exhibit characteristic peaks with chemical shifts at 0 ppm ± 10%, 50 ppm ± 10%, and 65 ppm ± 10%, which are attributed to Al(VI), Al(V), and Al(IV), respectively. 3+ .

[0056] In this invention, 0ppm±10% means -0.1ppm≤chemical shift≤0.1ppm; 50ppm±10% means 45ppm≤chemical shift≤55ppm; and 65ppm±10% means 58.5ppm≤chemical shift≤71.5ppm.

[0057] A second aspect of this invention provides a method for preparing alumina nanosheets, the method comprising:

[0058] (1) Aluminum source, alkaline compound, surfactant, carbon quantum dots and solvent are mixed and aged to obtain an aged product containing alumina precursor seeds.

[0059] (2) The aging product is subjected to solvent heat treatment, and the resulting solid-liquid mixture is subjected to solid-liquid separation to obtain an alumina precursor; wherein the solvent heat treatment temperature is 80-200℃.

[0060] (3) The alumina precursor is dried and calcined in sequence to obtain alumina nanosheets.

[0061] In the preparation method provided by this invention, an alkaline compound (preferably urea) is used as a precipitant. Through slow hydrolysis during solvothermal treatment, an alkali is formed to promote the formation of alumina. The crystallization rate of the alumina precursor is controlled by combining the conditions of solvothermal treatment and the amount of alkaline compound, thereby achieving the formation of nanosheet alumina. At the same time, surfactants and carbon quantum dots are added. Through specific adsorption during solvothermal treatment (crystallization process), the alumina is guided to form a specific nanosheet morphology, and the pore structure and specific surface area of ​​the alumina are further improved.

[0062] In some embodiments of the present invention, preferably, in step (1), the molar ratio of the aluminum source and the alkaline compound, calculated as Al, is 1:5-150, for example, 1:5, 1:8, 1:10, 1:15, 1:20, 1:30, 1:40, 1:50, 1:60, 1:70, 1:80, 1:90, 1:100, 1:120, 1:150, and any value within the range of any two values, preferably 1:10-150, preferably 1:50-100.

[0063] In this invention, when the molar ratio is greater than 1:3, the amount of alkaline compound is too small, which is not conducive to the precipitation of alumina; when the molar ratio is less than 1:150, the amount of alkaline compound is too large, the precipitation rate during crystallization is too high, which is not conducive to the formation of nano-morphological alumina.

[0064] In some embodiments of the present invention, preferably, in step (1), the mass ratio of the aluminum source to the surfactant is 0.1-10:0.001-5, more preferably 0.5-5:0.1-1.

[0065] In some embodiments of the present invention, preferably, in step (1), the mass ratio of the aluminum source to the carbon quantum dots is 0.1-10:0-1, more preferably 0.5-5:0.001-0.1.

[0066] In this invention, the ratio of the amount of aluminum source, surfactant and carbon quantum dots used to the amount of aluminum source, surfactant and carbon quantum dots can satisfy the above-mentioned limitations.

[0067] In this invention, preferably, carbon quantum dots are added as an inducer during the preparation of alumina nanosheets, which can effectively induce the formation of alumina nanosheets and further increase the specific surface area of ​​alumina nanosheets.

[0068] In this invention, a wide range of types of aluminum source can be selected. Preferably, the aluminum source is a soluble aluminum salt, including but not limited to aluminum nitrate nonahydrate, aluminum nitrate, aluminum chloride, aluminum acetylacetone, aluminum acetate, etc.

[0069] In this invention, solubility means being easily soluble in water, or being easily soluble in water with the help of additives.

[0070] In this invention, a wide range of types of alkaline compounds can be selected. Preferably, the alkaline compound is selected from inorganic bases and / or organic bases, more preferably from at least one of ammonia, urea, sodium hydroxide, and tetrapropylammonium hydroxide, and more preferably from urea.

[0071] In one specific embodiment of the present invention, the concentration of ammonia water is 25 wt%, and the concentration of tetrapropylammonium hydroxide solution is 25 wt%.

[0072] In this invention, a wide range of surfactants can be selected. Preferably, the surfactant is selected from at least one of sodium dodecyl sulfonate, sodium dodecyl sulfate, hexadecyltrimethylammonium bromide, and sodium dodecylbenzene sulfonate.

[0073] In this invention, preferably, the diameter of the carbon quantum dot is 5-20 nm, for example, 5 nm, 8 nm, 10 nm, 15 nm, 20 nm, and any value within the range of any two values.

[0074] In this invention, carbon quantum dots with a diameter of 5-20 nm are used as inducing agents. The purpose is to adsorb carbon quantum dots onto aluminum hydroxide during the aluminum source slurry process, and induce the aluminum source precursor to grow along the plane by taking advantage of its zero-dimensional quantum dot characteristics. At the same time, in step (3), when calcining is carried out, the carbon quantum dots burn and release CO2 in an orderly manner, forming an ideal and orderly pore structure, and ensuring that the subsequent finished catalyst has high catalytic activity.

[0075] In this invention, a wide range of solvents can be selected. Preferably, the solvent is selected from at least one of water, methanol, ethanol, toluene, N,N-dimethylformamide, etc.; more preferably, the solvent is water.

[0076] In this invention, the mixing conditions have a wide range of selection, as long as the above components are mixed. Preferably, the mixing conditions include: a temperature of 0-50°C, for example, 0°C, 10°C, 20°C, 25°C, 30°C, 40°C, 50°C, or any value within the range of any two values, preferably 20-35°C; a rotation speed of 0-1000 rpm, for example, 0 rpm, 100 rpm, 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 800 rpm, 1000 rpm, or any value within the range of any two values, preferably 200-500 rpm; and a time of 0.5-5 h, for example, 0.5 h, 1 h, 1.5 h, 2 h, 5 h, or any value within the range of any two values, preferably 0.5-2 h.

[0077] In this invention, step (1), the aging process, aims to convert aluminum ions in the mixture into alumina precursor seed crystals. Preferably, the aging conditions include: a temperature of 0-100°C, for example, 0°C, 25°C, 30°C, 50°C, 60°C, 80°C, 100°C, or any value within the range of any two values, preferably 30-80°C; and a time of 0.5-24h, for example, 0.5h, 1h, 1.5h, 2h, 5h, 8h, 10h, 12h, 15h, 20h, 24h, or any value within the range of any two values, preferably 0.5-15h.

[0078] In this invention, in step (2), the solvothermal treatment aims to further grow the alumina precursor seed crystals gradually through a dissolution-crystallization process in a hydrothermal environment. By controlling the solvothermal conditions, a product with a specific morphology can be obtained. Without solvothermal treatment, the seed crystals cannot participate in the dissolution-crystallization process and cannot form a specific morphology.

[0079] In some embodiments of the present invention, more preferably, the conditions for the solvothermal treatment include: a temperature of 100-200°C, for example, 100°C, 120°C, 140°C, 150°C, 160°C, 180°C, 200°C, and any value within the range of any two values; and a time of 1-96h, for example, 1h, 4h, 8h, 10h, 15h, 20h, 24h, 36h, 48h, 50h, 60h, 72h, 96h, and any value within the range of any two values, preferably 4-72h.

[0080] In some embodiments of the present invention, the drying is intended to remove residual solvent from the alumina precursor. Preferably, in step (3), the drying conditions include: a temperature of 80-150°C, for example, 80°C, 90°C, 100°C, 110°C, 120°C, 150°C, and any value within the range of any two values, preferably 90-110°C; and a time of 5-72h, for example, 5h, 8h, 12h, 15h, 18h, 20h, 24h, 36h, 50h, 60h, 72h, and any value within the range of any two values, preferably 8-24h.

[0081] In this invention, a wide range of drying methods can be selected. Preferably, the drying methods include, but are not limited to, spray drying, forced-air drying, vacuum drying, etc.

[0082] In some embodiments of the present invention, preferably, in step (3), the calcination conditions include: a temperature of 300-1000℃, for example, 300℃, 400℃, 450℃, 500℃, 550℃, 600℃, 800℃, 1000℃, and any value within the range of any two values, preferably 400-600℃; and a time of 1-15h, for example, 1h, 2h, 3h, 4h, 5h, 6h, 8h, 10h, 12h, 15h, and any value within the range of any two values, preferably 2-8h.

[0083] In this invention, the calcination is carried out in a muffle furnace or a tube furnace, and the calcination atmosphere is a non-reducing gas, preferably at least one of air, nitrogen, and argon.

[0084] In some embodiments of the present invention, preferably, the method further includes: before the drying, sequentially filtering and washing the alumina precursor.

[0085] In this invention, the filtration and washing are intended to remove residual alkaline compounds, carbon quantum dots, unreacted aluminum precursors, etc., from the alumina precursor. Preferably, the filtration apparatus includes, but is not limited to, water pumps, diaphragm pumps, and diffusion pumps.

[0086] In some embodiments of the present invention, preferably, the washing process includes: contacting the filtered product with a washing liquid and washing it. The washing liquid used for washing has a wide range of selections; preferably, the washing liquid is selected from water and / or C1-C5 monohydric alcohols, including but not limited to methanol, ethanol, 1-pentanol, etc.

[0087] The third aspect of the present invention provides an alumina nanosheet provided in the first aspect, or an alumina nanosheet prepared by the method provided in the second aspect, for use in catalyst supports, gas-liquid adsorption, solid-phase fillers, and wastewater treatment agents.

[0088] The alumina nanosheets provided by this invention have high specific surface area and high five-coordinate Al. 3+ The ratio is beneficial for adsorbing more substances in the adsorption reaction; as a catalyst support, it can load more and more metals more stably; as a catalyst, due to the presence of unsaturated coordinated Al, it can provide more reaction sites for the reaction and improve the reaction efficiency.

[0089] A fourth aspect of the present invention provides a supported catalyst comprising: a support and an active component supported on the support, wherein the support is selected from the alumina nanosheets provided in the first aspect, or the alumina nanosheets prepared by the preparation method provided in the second aspect.

[0090] The fifth aspect of this invention provides the application of the supported catalyst provided in the fourth aspect in alkane dehydrogenation and catalytic cracking.

[0091] According to the present invention, when the supported catalyst is used in the above-mentioned applications, the conversion rate of the raw materials and the selectivity of the target product can be effectively improved, thereby increasing the yield of the target product.

[0092] According to a particularly preferred embodiment of the present invention, an alumina nanosheet has a specific surface area of ​​200-300 m². 2 / g, with a length of 500-1000nm and a width of 100-300nm; the pore volume of the alumina nanosheets is 0.2-3cm. 3 / g, with an average pore size of 1-20nm, preferably 5-10nm; the alumina nanosheets contain five-coordinated Al 3+ The content ranges from 0.98 to 5.88 mmol / g, accounting for 10-30%;

[0093] The alumina nanosheets are prepared by the following methods: (1) mixing an aluminum source, an alkaline compound, a surfactant, carbon quantum dots and a solvent, aging the mixture to obtain an aged product containing alumina precursor seeds; (2) subjecting the aged product to solvothermal treatment, separating the solid-liquid mixture to obtain an alumina precursor; wherein the temperature of the solvothermal treatment is 80-200℃; (3) subjecting the alumina precursor to drying and calcining in sequence to obtain alumina nanosheets.

[0094] The molar ratio of the aluminum source and the alkaline compound, calculated as Al, is 1:10-150.

[0095] The present invention will be described in detail below through embodiments.

[0096] The molecular weight of aluminum nitrate nonahydrate is 375 g / mol; the molecular weight of aluminum nitrate is 213 g / mol; the molecular weight of aluminum chloride is 133.35 g / mol; the molecular weight of aluminum acetylacetonate is 324 g / mol; and the molecular weight of aluminum acetate is 204 g / mol.

[0097] The molecular weight of urea is 60 g / mol; the molecular weight of ammonia is 35 g / mol; the molecular weight of sodium hydroxide is 40 g / mol; and the molecular weight of tetrapropylammonium hydroxide is 203 g / mol.

[0098] Preparation method of carbon quantum dots: 5g of citric acid is placed in a crucible and reacted in a muffle furnace at 180℃ for 40h. After the reaction is complete, the sample powder is dissolved in water and the pH is adjusted to 7 with NaOH solution to obtain carbon quantum dot material.

[0099] The physical properties of the products obtained in the examples and comparative examples are listed in Table 1.

[0100] Example 1

[0101] (1) 1.2g aluminum source (aluminum nitrate nonahydrate), 12g alkaline compound (urea), 0.4g surfactant (sodium dodecyl sulfate), 0.01g carbon quantum dots (diameter of 10nm) and 130mL solvent (water) were mixed (temperature of 30℃, rotation speed of 600rpm, time of 1h). The mixture was aged at 30℃ for 6h to obtain an aged product containing alumina precursor seeds.

[0102] The molar ratio of the aluminum source (calculated as Al) to the alkaline compound is 1:63.

[0103] (2) The above-mentioned aging product was transferred to a 200mL hydrothermal reactor and subjected to solvothermal treatment at 100℃ for 20h. The resulting solid-liquid mixture was subjected to solid-liquid separation to obtain an alumina precursor.

[0104] (3) The above alumina precursor was sequentially filtered and washed with deionized water. The washed product was dried in a blower drying oven at 100°C for 10 hours and then calcined in a muffle furnace at 550°C for 4 hours to obtain alumina nanosheets S1.

[0105] The SEM image of the alumina nanosheets S1 is shown below. Figure 1 As shown, the alumina nanosheets S1 exhibit a nanosheet structure with an average length of 290 nm and an average width of 90 nm.

[0106] The XRD pattern of the alumina nanosheets S1 is shown below. Figure 2As shown, the alumina nanosheets S1 exhibit a γ-Al2O3 crystalline phase structure.

[0107] The N2 adsorption-desorption curves of the aforementioned alumina nanosheets S1 are shown in the figure below. Figure 3 As shown, the alumina nanosheets S1 have a mesoporous structure, which is presumably formed by the stacking of alumina nanosheet materials to create mesopores.

[0108] Among them, the above-mentioned alumina nanosheets S1 27 The nuclear magnetic resonance spectrum of Al solid is as follows: Figure 4 As shown, the characteristic peaks with chemical shifts at 7 ppm, 45 ppm, and 60 ppm are attributed to Al(VI), Al(V), and Al(IV) structures, respectively. Calculations indicate that the alumina nanosheet S1 contains five-coordinated Al... 3+ The proportion reached 19%, with a specific content of 3.72 mmol / g.

[0109] Example 2

[0110] (1) 1.2g of aluminum source (aluminum nitrate nonahydrate), 12g of alkaline compound (urea), 0.4g of surfactant (sodium dodecyl sulfate) and 130mL of solvent (water) were mixed (temperature 30℃, rotation speed 600rpm, time 1h). The mixture was aged at 30℃ for 6h to obtain an aged product containing alumina precursor crystals.

[0111] The molar ratio of the aluminum source (calculated as Al) to the alkaline compound is 1:63.

[0112] (2) The above-mentioned aging product was transferred to a 200mL hydrothermal reactor and subjected to solvothermal treatment at 100℃ for 20h to obtain a solid-liquid mixture. Solid-liquid separation was performed to obtain an alumina precursor.

[0113] (3) The above alumina precursor was sequentially filtered and washed with ethanol. The washed product was dried in a blower drying oven at 100°C for 10 hours and then calcined in a muffle furnace at 550°C for 4 hours to obtain alumina nanosheets S2.

[0114] The SEM image of the alumina nanosheets S2 is shown below. Figure 5 As shown, alumina nanosheet S2 has a nanosheet structure with an average length of 540 nm and an average width of 160 nm, and the sheet size is larger than that of the aforementioned alumina nanosheet S1.

[0115] Among them, the XRD pattern of the above-mentioned alumina nanosheets S2 is similar to... Figure 2 Similarly; the N2 adsorption-desorption curves of the above-mentioned alumina nanosheets S2 are similar to... Figure 3 Similarly; the above-mentioned alumina nanosheets S2 27Al solid NMR spectrum and Figure 4 similar.

[0116] Example 3

[0117] (1) Mix 0.5g of aluminum source (aluminum nitrate nonahydrate), 12g of alkaline compound (urea), 0.01g of carbon quantum dots (diameter of 18nm), 0.4g of surfactant (sodium dodecyl sulfonate) and 120mL of solvent (water) (temperature of 20℃, rotation speed of 800rpm, time of 3h), and age the mixture at 30℃ for 6h to obtain an aged product containing alumina precursor seeds;

[0118] The molar ratio of the aluminum source (calculated as Al) to the alkaline compound is 1:150.

[0119] (2) The above-mentioned aging product was transferred to a 200mL hydrothermal reactor and subjected to solvothermal treatment at 100℃ for 48h. The resulting solid-liquid mixture was subjected to solid-liquid separation to obtain an alumina precursor.

[0120] (3) The above alumina precursor was sequentially filtered and washed with 1-pentanol. The washed product was dried in a blower drying oven at 110°C for 10 h and calcined in a muffle furnace at 550°C for 4 h under static air to obtain alumina nanosheets S3.

[0121] Example 4

[0122] (1) 4.5g of aluminum source (aluminum nitrate), 12g of alkaline compound (urea), 0.01g of surfactant (hexadecyltrimethylammonium bromide), 0.03g of carbon quantum dots (5nm in diameter) and 60mL of solvent (water) were mixed (temperature 20℃, rotation speed 1000rpm, time 2h). The mixture was aged at 30℃ for 4h to obtain an aged product containing alumina precursor seeds.

[0123] The molar ratio of the aluminum source (calculated as Al) to the alkaline compound is 1:10.

[0124] (2) The above-mentioned aging product was transferred to a 100 mL hydrothermal reactor and subjected to solvothermal treatment at 100 °C for 48 h. The resulting solid-liquid mixture was subjected to solid-liquid separation to obtain an alumina precursor.

[0125] (3) The above alumina precursor was sequentially filtered and washed with ethanol. The washed product was dried in a blower drying oven at 100°C for 12 hours and calcined in a muffle furnace at 550°C for 6 hours to obtain alumina nanosheets S4.

[0126] Example 5

[0127] (1) 3g of aluminum source (aluminum chloride), 18g of alkaline compound (25wt% ammonia solution), 2g of surfactant (sodium dodecyltrimethylbenzenesulfonate), 0.1g of carbon quantum dots (18nm in diameter) and 35mL of solvent (methanol) were mixed (temperature 25℃, rotation speed 600rpm, time 6h). The resulting mixture was aged at 30℃ for 5h to obtain an aged product containing alumina precursor seeds.

[0128] The molar ratio of the aluminum source (calculated as Al) to the alkaline compound is 1:6.

[0129] (2) The above-mentioned aging product was transferred to a 100 mL hydrothermal reactor and subjected to solvothermal treatment at 100 °C for 20 h. The resulting solid-liquid mixture was subjected to solid-liquid separation to obtain an alumina precursor.

[0130] (3) The above alumina precursor was sequentially filtered and washed with ethanol. The washed product was dried in a blower drying oven at 120°C for 10 hours and then calcined in a muffle furnace at 550°C for 2 hours to obtain alumina nanosheets S5.

[0131] Example 6

[0132] (1) 2g aluminum source (aluminum chloride), 22g alkaline compound (NaOH), 5g surfactant (hexadecyltrimethylammonium bromide), 0.02g carbon quantum dots (diameter of 18nm) and 100mL solvent (toluene) were mixed (temperature of 15℃, rotation speed of 1000rpm, time of 2h). The resulting mixture was aged at 50℃ for 2h to obtain an aged product containing alumina precursor seeds.

[0133] The molar ratio of the aluminum source and the alkaline compound, calculated as Al, is 1:37.

[0134] (2) The above-mentioned aging product was transferred to a 200mL hydrothermal reactor and subjected to solvothermal treatment at 100℃ for 20h. The resulting solid-liquid mixture was subjected to solid-liquid separation to obtain an alumina precursor.

[0135] (3) The above alumina precursor was sequentially filtered and washed with water. The washed product was dried in a blower drying oven at 100°C for 20 hours and then calcined in a muffle furnace at 550°C for 3 hours to obtain alumina nanosheets S6.

[0136] Example 7

[0137] (1) 1g of aluminum source (aluminum chloride), 100g of alkaline compound (25wt% tetrapropylammonium hydroxide solution), 0.05g of carbon quantum dots (18nm in diameter), 0.8g of surfactant (hexadecyltrimethylammonium bromide) and 95mL of solvent (ethanol) were mixed (temperature 0℃, rotation speed 1000rpm, time 10h), and the mixture was aged at 70℃ for 5h to obtain an aged product containing alumina precursor seeds;

[0138] The molar ratio of the aluminum source (calculated as Al) to the alkaline compound is 1:16.

[0139] (2) The above-mentioned aging product was transferred to a 200mL hydrothermal reactor and subjected to solvothermal treatment at 100℃ for 20h. The resulting solid-liquid mixture was subjected to solid-liquid separation to obtain an alumina precursor.

[0140] (3) The above alumina precursor was sequentially filtered and washed with ethanol. The washed product was dried in a blower drying oven at 110°C for 8 hours and then calcined in a muffle furnace at 500°C for 5 hours to obtain alumina nanosheets S7.

[0141] Example 8

[0142] (1) Mix 0.8g of aluminum source (aluminum chloride), 20g of alkaline compound (ammonia water with a concentration of 25wt%), 3g of surfactant (hexadecyltrimethylammonium bromide), 0.1g of carbon quantum dots (diameter of 18nm) and 95mL of solvent (methanol) (temperature of 35℃, rotation speed of 700rpm, time of 2h), and age the mixture at 30℃ for 10h to obtain an aged product containing alumina precursor seeds;

[0143] The molar ratio of the aluminum source (calculated as Al) to the alkaline compound is 1:24.

[0144] (2) The above-mentioned aging product was transferred to a 200mL hydrothermal reactor and subjected to solvothermal treatment at 120℃ for 20h. The resulting solid-liquid mixture was subjected to solid-liquid separation to obtain an alumina precursor.

[0145] (3) The above alumina precursor was sequentially filtered and washed with 1-pentanol. The washed product was dried in a blower drying oven at 120°C for 5 hours and calcined in a muffle furnace at 450°C for 2 hours under static air to obtain alumina nanosheets S8.

[0146] Example 9

[0147] (1) 5g of aluminum source (aluminum acetylacetonate), 32.5g of alkaline compound (ammonia water with a concentration of 25wt%), 1g of surfactant (sodium dodecyl sulfonate), 0.1g of carbon quantum dots (diameter of 5nm) and 90mL of solvent (water) were mixed (temperature of 50℃, rotation speed of 500rpm, time of 6h). The mixture was aged at 30℃ for 5h to obtain an aged product containing alumina precursor seeds.

[0148] The molar ratio of the aluminum source (calculated as Al) to the alkaline compound is 1:15.

[0149] (2) The above-mentioned aging product was transferred to a 200 mL hydrothermal reactor and subjected to solvothermal treatment at 200 °C for 12 h. The resulting solid-liquid mixture was subjected to solid-liquid separation to obtain an alumina precursor.

[0150] (3) The above alumina precursor was sequentially filtered and washed with methanol. The washed product was dried in a blower drying oven at 120°C for 20 hours and then calcined in a muffle furnace at 600°C for 2 hours to obtain alumina nanosheets S9.

[0151] Example 10

[0152] (1) 4g of aluminum source (aluminum acetylacetonate), 30g of alkaline compound (ammonia water with a concentration of 25wt%), 1.1g of surfactant (sodium dodecyl sulfonate), 0.3g of carbon quantum dots (diameter of 5nm) and 120mL of solvent (toluene) were mixed (temperature of 50℃, rotation speed of 500rpm, time of 10h). The resulting mixture was aged at 80℃ for 12h to obtain an aged product containing alumina precursor seeds.

[0153] The molar ratio of the aluminum source and the alkaline compound, calculated as Al, is 1:17.

[0154] (2) The above-mentioned aging product was transferred to a 200mL hydrothermal reactor and subjected to solvothermal treatment at 80℃ for 60h. The resulting solid-liquid mixture was subjected to solid-liquid separation to obtain an alumina precursor.

[0155] (3) The above solid-liquid mixture was subjected to solid-liquid separation. The resulting alumina precursor was sequentially filtered and washed with toluene. The washed product was dried in a blower drying oven at 120°C for 24 hours and then calcined in a muffle furnace at 400°C under static air for 4 hours to obtain alumina nanosheets S10.

[0156] Example 11

[0157] (1) 3g of aluminum source (aluminum acetylacetonate), 15g of alkaline compound (NaOH), 0.1g of surfactant (sodium dodecyl sulfate), 0.5g of carbon quantum dots (5nm in diameter) and 100mL of solvent (methanol) were mixed (temperature 40℃, rotation speed 1000rpm, time 0.5h). The mixture was aged at 70℃ for 10h to obtain an aged product containing alumina precursor seeds.

[0158] The molar ratio of the aluminum source (calculated as Al) to the alkaline compound is 1:41.

[0159] (2) The above-mentioned aging product was transferred to a 200mL hydrothermal reactor and subjected to solvothermal treatment at 150℃ for 72h. The resulting solid-liquid mixture was subjected to solid-liquid separation to obtain an alumina precursor.

[0160] (3) The above alumina precursor was sequentially filtered and washed with 1-pentanol. The washed product was dried in a blower oven at 100°C for 30 h and calcined in a muffle furnace at 550°C for 4 h under static air to obtain alumina nanosheets S11.

[0161] Example 12

[0162] (1) 2g of aluminum source (aluminum acetylacetonate), 40g of alkaline compound (ammonia water with a concentration of 25wt%), 0.02g of surfactant (sodium dodecyl sulfate), 0.7g of carbon quantum dots (diameter of 5nm) and 150mL of solvent (water) were mixed (temperature of 30℃, rotation speed of 800rpm, time of 5h). The mixture was aged at 30℃ for 6h to obtain an aged product containing alumina precursor seeds.

[0163] The molar ratio of the aluminum source (calculated as Al) to the alkaline compound is 1:46.

[0164] (2) The above-mentioned aging product was transferred to a 300 mL hydrothermal reactor and subjected to solvothermal treatment at 120 °C for 20 h. The resulting solid-liquid mixture was subjected to solid-liquid separation to obtain the alumina precursor.

[0165] (3) The above alumina precursor was sequentially filtered and washed with isopropanol. The washed product was dried in a blower drying oven at 120°C for 10 h and calcined in a muffle furnace at 600°C for 6 h under static air to obtain alumina nanosheets S12.

[0166] Example 13

[0167] (1) 1g of aluminum source (aluminum acetate), 45g of alkaline compound (25wt% tetrapropylammonium hydroxide), 0.2g of surfactant (sodium dodecyl sulfate), 0.9g of carbon quantum dots (5nm in diameter) and 150mL of solvent (water) were mixed (temperature 30℃, rotation speed 500rpm, time 3h). The mixture was aged at 50℃ for 12h to obtain an aged product containing alumina precursor seeds.

[0168] The molar ratio of the aluminum source (calculated as Al) to the alkaline compound is 1:11.

[0169] (2) The above-mentioned aging product was transferred to a 300 mL hydrothermal reactor and subjected to solvothermal treatment at 150 °C for 20 h. The resulting solid-liquid mixture was subjected to solid-liquid separation to obtain the alumina precursor.

[0170] (3) The above alumina precursor was sequentially filtered and washed with ethanol. The washed product was dried in a blower drying oven at 120°C for 6 hours and calcined in a muffle furnace at 600°C for 6 hours to obtain alumina nanosheets S13.

[0171] Example 14

[0172] (1) Mix 0.5g of aluminum source (aluminum acetate), 40g of alkaline compound (25wt% tetrapropylammonium hydroxide), 0.02g of surfactant (sodium dodecyl sulfate), 1.1g of carbon quantum dots (10nm in diameter) and 120mL of solvent (methanol) (temperature 0℃, rotation speed 800rpm, time 5h), and age the mixture at 50℃ for 12h to obtain an aged product containing alumina precursor seeds;

[0173] The molar ratio of the aluminum source (calculated as Al) to the alkaline compound is 1:20.

[0174] (2) The above-mentioned aging product was transferred to a 300 mL hydrothermal reactor and subjected to solvothermal treatment at 200 °C for 20 h. The resulting solid-liquid mixture was subjected to solid-liquid separation to obtain an alumina precursor.

[0175] (3) The above alumina precursor was sequentially filtered and washed with isopropanol. The washed product was dried in a blower drying oven at 110°C for 9 hours and calcined in a muffle furnace at 550°C for 4 hours to obtain alumina nanosheets S14.

[0176] Example 15

[0177] (1) 15g of aluminum source (aluminum nitrate nonahydrate), 16g of alkaline compound (NaOH), 0.05g of surfactant (sodium dodecyl sulfate), 1.5g of carbon quantum dots (10nm in diameter) and 130mL of solvent (water) were mixed (temperature 40℃, rotation speed 1000rpm, time 2h). The mixture was aged at 50℃ for 10h to obtain an aged product containing alumina precursor seeds.

[0178] The molar ratio of the aluminum source (calculated as Al) to the alkaline compound is 1:10.

[0179] (2) The above-mentioned aging product was transferred to a 200mL hydrothermal reactor and subjected to solvothermal treatment at 100℃ for 72h. The resulting solid-liquid mixture was subjected to solid-liquid separation to obtain an alumina precursor.

[0180] (3) The above alumina precursor was sequentially filtered and washed with 1-pentanol. The washed product was dried in a blower drying oven at 100°C for 10 hours and calcined in a muffle furnace at 700°C for 6 hours to obtain alumina nanosheets S15.

[0181] Example 16

[0182] (1) Mix 0.5g of aluminum source (aluminum nitrate nonahydrate), 11g of alkaline compound (ammonia water with a concentration of 25wt%), 0.05g of surfactant (sodium dodecyl sulfate), 1.5g of carbon quantum dots (diameter of 10nm) and 200mL of solvent (water) (temperature of 20℃, rotation speed of 800rpm, time of 5h), and age the mixture at 50℃ for 12h to obtain an aged product containing alumina precursor seed crystals;

[0183] The molar ratio of the aluminum source and the alkaline compound, calculated as Al, is 1:59.

[0184] (2) The above-mentioned aging product was transferred to a 300 mL hydrothermal reactor and subjected to solvothermal treatment at 200 °C for 72 h. The resulting solid-liquid mixture was subjected to solid-liquid separation to obtain the alumina precursor.

[0185] (3) The above alumina precursor was sequentially filtered and washed with isopropanol. The washed product was dried in a blower drying oven at 100°C for 10 hours and calcined in a muffle furnace at 800°C for 8 hours to obtain alumina nanosheets S16.

[0186] Example 17

[0187] The method is the same as in Example 1, except that...

[0188] In step (1), the amount of alkaline compound (urea) is replaced with 15.36g, so that the molar ratio of alkaline compound to the above aluminum source calculated as Al is 1:80.

[0189] Under the same conditions, alumina nanosheets S17 were obtained.

[0190] Example 18

[0191] The method is the same as in Example 1, except that...

[0192] In step (2), the temperature of the solvent heat treatment is replaced with 80°C;

[0193] Under the same conditions, alumina nanosheets S18 were obtained.

[0194] Example 19

[0195] The method is the same as in Example 1, except that...

[0196] In step (3), the roasting temperature is replaced with 800℃;

[0197] Under the same conditions, alumina nanosheets S19 were obtained.

[0198] Comparative Example 1

[0199] The method is the same as in Example 1, except that...

[0200] In step (1), the amount of alkaline compound (urea) is replaced with 0g.

[0201] Under the same conditions, alumina DS1 was obtained.

[0202] The SEM image of the aforementioned alumina DS1 is shown below. Figure 6 As shown, alumina DS1 does not have a nanosheet structure, but rather a bulk alumina structure.

[0203] Among them, the above-mentioned alumina DS1 27 The nuclear magnetic resonance spectrum of Al solid is as follows: Figure 7 As shown, the chemical shift has no characteristic peak at 45 ppm, indicating that the above-mentioned alumina DS1 does not have five-coordinated Al. 3+ That is, the Al(V) structure.

[0204] Comparative Example 2

[0205] The method is the same as in Example 2, except that...

[0206] In step (2), the temperature of the solvent heat treatment is replaced with 40°C;

[0207] Under the same conditions, aluminum oxide DS2 was obtained.

[0208] Among them, the SEM image of the above-mentioned alumina DS2 and Figure 6 Similarly; the above-mentioned alumina DS2 27 Al solid NMR spectrum and Figure 7 similar.

[0209] Comparative Example 3

[0210] The method is the same as in Example 1, except that...

[0211] In step (2), the above-mentioned aging product is directly heated at 100°C for 48 hours;

[0212] Under the same conditions, aluminum oxide DS3 was obtained.

[0213] Among them, the SEM image of the above-mentioned alumina DS3 and Figure 6 Similarly; the above-mentioned alumina DS3 27 Al solid NMR spectrum and Figure 7 similar.

[0214] Comparative Example 4

[0215] Commercial alumina (Sinopharm Chemical Reagent Co., Ltd., CAS No.: 1344-28-1, Batch No.: 20170401) was used as alumina DS4.

[0216] Among them, the SEM image of the aforementioned alumina DS4 and Figure 6 Similarly; the above-mentioned alumina DS4 27 Al solid NMR spectrum and Figure 7 similar.

[0217] Table 1

[0218]

[0219] Continued from Table 1

[0220]

[0221]

[0222] As shown in Table 1, compared with Comparative Examples 1-4, the alumina nanosheets prepared by the method provided in this invention in Examples 1-19 have a high specific surface area and a high content and proportion of five-coordinated Al. 3+ .

[0223] Meanwhile, compared to Example 2 (average length of 540 nm and average width of 160 nm), the alumina nanosheets prepared in Example 1, due to the addition of carbon quantum dots, not only have a nanosheet structure, but also have smaller nanosheet sizes (average length of 290 nm and average width of 90 nm).

[0224] Test case

[0225] The alumina nanosheets and alumina prepared in Examples 1-19 and Comparative Examples 1-4 were used as supports for loading cobalt (Co) species. Due to the high specific surface area and abundant five-coordinated Al in the alumina nanosheets… 3+ The structure can effectively anchor Co species.

[0226] The preparation method includes mixing 0.051g of cobalt nitrate hexahydrate, 1g of the above-mentioned support, and 10mL of water, stirring at 25℃ for 4h, and drying at 110℃ for 24h; the dried sample is then calcined in air at 600℃ for 5h to obtain Co-based alumina catalysts with a Co content of 1wt%.

[0227] The catalysts prepared above were used in the oxygen-free dehydrogenation reaction of propane. The specific reaction conditions were: feed ratio C3H8:N2 = 2:3, propane gas velocity 4 mL / min, nitrogen gas velocity 6 mL / min, catalyst dosage 50 mg, heating rate 10 °C / min, and reaction temperature 600 °C. The test results are shown in Table 2.

[0228] Table 2

[0229]

[0230]

[0231] As shown in Table 2, compared with Comparative Examples 1-4, the Co-based catalysts prepared by Examples 1-19 using the alumina nanosheets provided by the present invention as a support exhibit higher propane conversion and propylene selectivity in the oxygen-free dehydrogenation reaction of propane.

[0232] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. An alumina nanosheet, characterized in that, The specific surface area of ​​the alumina nanosheets is ≥150 m². 2 / g; wherein, in the alumina nanosheets, five-coordinated Al 3+ The content is ≥0.98mmol / g, accounting for ≥5%.

2. The alumina nanosheets according to claim 1, wherein, The alumina nanosheets have an average length of 200-2000 nm, preferably 500-1000 nm, and an average width of 50-500 nm, preferably 100-300 nm. And / or, the specific surface area of ​​the alumina nanosheets is 150-500 m². 2 / g, preferably 200-300m 2 / g; And / or, in the alumina nanosheets, five-coordinated Al 3+ The content is 0.98-5.88 mmol / g, preferably 1.96-5.68 mmol / g; And / or, in the alumina nanosheets, five-coordinated Al 3+ The proportion is 5-30%, preferably 10-30%.

3. The alumina nanosheets according to claim 1 or 2, wherein, The alumina nanosheets have a pore volume of 0.1-5 cm³. 3 / g, preferably 0.2-3cm 3 / g; And / or, the average pore size of the alumina nanosheets is 1-20 nm, preferably 5-10 nm.

4. The alumina nanosheets according to any one of claims 1-3, wherein, The alumina nanosheets have a γ-Al2O3 crystal phase structure; And / or, in 27 In the solid-state nuclear magnetic resonance spectrum of Al, the alumina nanosheets have characteristic peaks with chemical shifts of 0ppm±10%, 50ppm±10%, and 65ppm±10%.

5. A method for preparing alumina nanosheets, characterized in that, The preparation method includes: (1) Aluminum source, alkaline compound, surfactant, carbon quantum dots and solvent are mixed and aged to obtain an aged product containing alumina precursor seeds. (2) The aging product is subjected to solvent heat treatment, and the resulting solid-liquid mixture is subjected to solid-liquid separation to obtain an alumina precursor; wherein the solvent heat treatment temperature is 80-200℃. (3) The alumina precursor is dried and calcined in sequence to obtain alumina nanosheets.

6. The preparation method according to claim 5, wherein, In step (1), The molar ratio of the aluminum source and the alkaline compound, calculated as Al, is 1:5-150, preferably 1:10-150; And / or, the mass ratio of the aluminum source to the surfactant is 0.1-10:0.001-5, preferably 0.5-5:0.1-1; And / or, the mass ratio of the aluminum source to the carbon quantum dots is 0.1-10:0-1, preferably 0.5-5:0.001-0.1; And / or, the aging conditions include: a temperature of 0-100°C, preferably 30-80°C; and a time of 0.5-24h, preferably 0.5-15h.

7. The preparation method according to claim 5 or 6, wherein, In step (1), The alkaline compound is selected from inorganic bases and / or organic bases, preferably from at least one of ammonia, urea, sodium hydroxide and tetrapropylammonium hydroxide; And / or, the surfactant is selected from at least one of sodium dodecyl sulfonate, sodium dodecyl sulfate, hexadecyltrimethylammonium bromide and sodium dodecylbenzene sulfonate; And / or, the diameter of the carbon quantum dots is 5-20 nm.

8. The preparation method according to any one of claims 5-7, wherein, In step (2), the conditions for the solvent heat treatment include: a temperature of 100-200℃; and a time of 1-96h, preferably 4-72h. And / or, in step (3), the calcination conditions include: a temperature of 300-1000℃, preferably 400-600℃; and a time of 1-15h, preferably 2-8h.

9. The alumina nanosheets according to any one of claims 1-4, or the alumina nanosheets prepared by the preparation method according to any one of claims 5-8, are used in catalyst supports, gas-liquid adsorption, solid phase fillers, and wastewater treatment agents.

10. A supported catalyst, characterized in that, The supported catalyst comprises: a support and an active component supported on the support, wherein the support is selected from the alumina nanosheets of any one of claims 1-4, or the alumina nanosheets prepared by the preparation method of any one of claims 5-8.

11. The application of the supported catalyst according to claim 10 in alkane dehydrogenation and catalytic cracking.

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