CN111185175B

CN111185175B - Metal-based multi-stage structure membrane catalyst and preparation method and application thereof

Info

Publication number: CN111185175B
Application number: CN202010156796.5A
Authority: CN
Inventors: 陈运法; 李双德; 王东东
Original assignee: Institute of Process Engineering of CAS
Current assignee: Institute of Process Engineering of CAS
Priority date: 2020-03-09
Filing date: 2020-03-09
Publication date: 2022-01-04
Anticipated expiration: 2040-03-09
Also published as: CN111185175A

Abstract

The invention relates to a metal-based hierarchical structure membrane catalyst, a preparation method and application thereof. The catalyst comprises an aluminum carrier and M and Al mixed metal oxide sheets grown on the aluminum carrier in situ, wherein M comprises any one or combination of at least two of Co, Ni or Mn; the loading amount of the mixed metal oxide sheet is 0.5-2mg/cm²(ii) a The mixed metal oxide sheets are stacked in a three-dimensional direction and connected into a multilevel structure through surface-surface connection, surface-end connection or end-end connection, and the grain diameter of the multilevel structure is 0.5-5 mu m. The catalyst is a metal-based hierarchical structure membrane catalyst, has high activity and fast heat conduction, and can realize catalytic decomposition of reactants with high efficiency and low energy consumption. According to the method, alcohol and an ammonia releasing agent are introduced, and the properties of the catalytic active component solution are regulated and controlled, so that the active components are stacked in the three-dimensional direction to form a multi-stage structure.

Description

Metal-based multi-stage structure membrane catalyst and preparation method and application thereof

Technical Field

The invention relates to the technical field of environmental protection catalysis, in particular to a metal-based multi-stage structure membrane catalyst and a preparation method and application thereof.

Background

In the industrial activity process, such as benzene, toluene, xylene, styrene, ethyl acetate, n-hexane and other volatile organic substances discharged in the industries of printing, electronics, automobile paint spraying, coating and the like, benzene series and other volatile organic substances discharged in indoor decoration, furniture and the like, and volatile organic substances discharged in catering oil fume are catalytically decomposed into carbon dioxide and water at the temperature of 300-450 ℃ by virtue of a catalyst, and the method is one of the most effective purification technologies.

Currently, the catalysts used are generally prepared by coating a slurry containing a catalytically active component on a honeycomb ceramic substrate. The slurry to be coated needs to be added with a binder, so that the disadvantages of the active component covered by the binder, uneven coating, low catalytic activity and the like are easily caused. In addition, the main components of the honeycomb ceramic are cordierite, mullite and the like, the heat conductivity coefficient of the honeycomb ceramic is about 0.9W/(m.K), the heat conductivity is poor, and the purification energy consumption of volatile organic substances is increased.

CN106732585A discloses a monolithic catalyst for catalytic combustion of volatile organic gas and a preparation method thereof, cordierite is taken as a carrier, and gamma-Al is adopted₂O₃The oxide auxiliary agent and the active ingredient Pd are used as coatings, the cordierite honeycomb ceramic carrier accounts for 82-87 parts by mass, and the gamma-Al₂O₃The catalyst comprises, by mass, 10-14 parts of an oxide auxiliary agent, 0.8-1.5 parts of an oxide auxiliary agent and 0.01-0.05 part of an active ingredient Pd. Pd is dispersed to the special gamma-A by a coating method_l2O₃Drying and roasting the carrier to obtain powder, adding adhesive, lubricant and water to prepare slurry, and loading the slurry on cordierite to obtain the catalyst with toluene decomposition temperature of 300 deg.c and purifying efficiency of 98%. However, the preparation method has the problems that the active sites are easily blocked by the binder, and the cordierite carrier has the defect of slow heat conduction.

Therefore, how to develop a catalyst with fast heat conduction and high catalytic activity, which solves the problems of low catalytic activity and slow heating temperature of the existing catalyst, realizes the catalytic decomposition of volatile organic substances with high efficiency and low energy consumption, and becomes the focus of the current research.

Disclosure of Invention

In view of the problems in the prior art, the invention provides a metal-based multi-stage structure membrane catalyst, and a preparation method and application thereof. The catalyst has the advantages of high catalytic activity and high heat conduction speed, and can catalyze and decompose volatile organic substances with high efficiency and low energy consumption; the preparation method has the advantages of simple process, mild conditions, easy industrialization and high application value.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the present invention provides a catalyst, in particular a metal-based hierarchical structure membrane catalyst, comprising an aluminum support and M and Al mixed metal oxide sheets grown in situ on the aluminum support, wherein the M and Al mixed metal oxide sheets are formed by a method comprising a step of forming a metal oxide layer on the aluminum supportM comprises any one or the combination of at least two of Co, Ni or Mn; the loading amount of the mixed metal oxide sheet is 0.5-2mg/cm²(ii) a The mixed metal oxide sheets are stacked in a three-dimensional direction and connected into a multilevel structure through surface-surface connection, surface-end connection or end-end connection, and the grain diameter of the multilevel structure is 0.5-5 mu m.

In the present invention, the "M and Al mixed metal oxide flake" means: the oxide sheet contains both M oxide and alumina.

In the present invention, the loading amount of the mixed metal oxide flakes may be 0.5mg/cm²、0.7mg/cm²、1mg/cm²、1.5mg/cm²、1.8mg/cm²Or 2mg/cm²Etc., both of which cause a decrease in catalytic activity; the particle size of the multilevel structure may be 0.5 μm, 0.8 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, or the like.

According to the metal-based multi-stage structure membrane catalyst provided by the invention, the aluminum carrier belongs to a high-thermal conductivity carrier, and the thermal conductivity coefficient of metal aluminum is about 237W/(m.K), so that the rapid temperature rise and temperature reduction can be realized; the mixed metal oxide is used as an active component, grows on the carrier in situ, is in a sheet shape, is stacked in the three-dimensional direction, and is in a multistage structure through surface-surface connection, surface-end connection or end-end connection, so that catalytic active sites can be fully exposed, the contact area with reactants is increased, and the reactants can be efficiently catalytically decomposed; the loading amount of the mixed metal oxide tablets in the catalyst is 0.5-2mg/cm²The particle size of the multilevel structure is 0.5-5 μm, so that the multilevel structure has the advantages of high catalytic activity and quick heat conduction, can realize catalytic decomposition of reactants with high efficiency and low energy consumption, and has wide application prospect.

In the present invention, the mixed metal oxide pieces are stacked in a three-dimensional direction into a multilevel structure (e.g., a petal-shaped multilevel structure, see fig. 1) composed of mixed metal oxide pieces by surface-to-surface connection, surface-to-end connection, or end-to-end connection.

In the invention, the multistage structure is beneficial to fully exposing the catalytic active component, is beneficial to quickly carrying out mass transfer and heat transfer on the reactant and the catalytic active component, and realizes high-efficiency catalytic decomposition of the reactant.

Preferably, the aluminium support comprises aluminium flakes and/or foamed aluminium, preferably aluminium flakes.

Preferably, the loading amount of the mixed metal oxide flake is 0.8-1.5mg/cm²For example, it may be 0.8mg/cm²、1mg/cm²、1.2mg/cm²Or 1.5mg/cm²And the like.

In the present invention, the "loading amount" means: mass of mixed metal oxide flakes per unit area of aluminum support.

Preferably, the particle size of the multilevel structure is 0.8-2 μm, and may be, for example, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, or the like.

In a second aspect, the present invention provides a method for preparing a catalyst as described in the first aspect above, the method comprising the steps of:

(1) putting the aluminum carrier into a hydroalcoholic solution of M salt, adding an ammonia releasing agent, controlling the molar ratio of the ammonia releasing agent to the M salt to be (1-6):1, and carrying out hydrothermal reaction to obtain a precursor;

(2) and (2) calcining the precursor obtained in the step (1) to obtain the catalyst.

In the invention, the molar ratio of the ammonia releasing agent to the M salt in the step (1) is (1-6):1, and for example, the molar ratio can be 1:1, 1.5:1, 2:1, 3:1, 4:1, 5:1 or 6:1, and if the molar ratio is less than 1:1, metal salt ions cannot be fully precipitated; the molar ratio is more than 6:1, and metal salt ions are easy to precipitate to generate fine particle agglomeration.

The preparation method of the catalyst provided by the invention comprises the steps of selecting an aluminum carrier, mixing the aluminum carrier with a hydroalcoholic solution of M salt to obtain a catalytic active component solution, introducing alcohol and an ammonia releasing agent to regulate and control the interfacial property of the catalytic active component solution and the precipitation rate of metal salt, so that a precursor of the catalytic active component grows on the aluminum carrier in situ to form a precursor of the catalyst, and calcining to obtain the catalyst; the preparation method has the advantages of simple process, mild conditions, easy industrialization and high application value.

Preferably, before step (1), the aluminum support is pretreated, and the pretreatment method comprises the following steps: and (3) ultrasonically treating the aluminum carrier with water and/or acetone to clean oil stains on the aluminum carrier.

Preferably, the temperature of the ultrasound is 20-40 ℃, for example, 20 ℃, 22 ℃, 25 ℃, 28 ℃, 30 ℃, 35 ℃, 37 ℃ or 40 ℃ and the like.

Preferably, the time of the ultrasound is 0.5-2h, for example, 0.5h, 1h, 1.5h or 2h, etc.

Preferably, the aluminum support of step (1) comprises aluminum flakes and/or foamed aluminum, preferably aluminum flakes.

Preferably, the M salt of step (1) comprises any one of cobalt nitrate, nickel nitrate or manganese nitrate or a combination of at least two thereof, wherein a typical but non-limiting combination is: cobalt nitrate and nickel nitrate, cobalt nitrate and manganese nitrate, nickel nitrate and manganese nitrate, and the like.

Preferably, the M salt concentration in step (1) is 0.05-0.25mol/L, such as 0.05mol/L, 0.08mol/L, 0.1mol/L, 0.15mol/L, 0.2mol/L or 0.25mol/L, etc., preferably 0.1-0.2 mol/L; the concentration can obtain a multi-stage structure such as a petal shape.

Preferably, the alcohol volume ratio in the hydroalcoholic solution in step (1) is 60-100%, for example, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100%, etc., preferably 80-100%; if the volume ratio is less than 60%, it is not easy to form a multi-stage structure.

In the present invention, the "volume ratio of alcohol" refers to the volume fraction of alcohol to the volume of the hydroalcoholic solution.

Preferably, the alcohol in the hydroalcoholic solution of step (1) comprises methanol and/or ethanol.

Preferably, the ammonia releasing agent in step (1) comprises Hexamethylenetetramine (HMT) and/or urea, and the ammonia releasing agent can slowly adjust the alkalinity of the solution, so that the metal salt ions can be controllably precipitated.

Preferably, the molar ratio of the ammonia releasing agent to the M salt in step (1) is (2-4):1, and may be, for example, 2:1, 3:1, or 4:1, etc.

Preferably, the temperature of the hydrothermal reaction in step (1) is 90-170 ℃, such as 90 ℃, 95 ℃, 100 ℃, 110 ℃, 165 ℃ or 170 ℃, preferably 120-; if the temperature is lower than 90 ℃, the ammonia releasing agent cannot be fully hydrolyzed; the temperature is higher than 170 ℃, the ammonia releasing agent is hydrolyzed rapidly, the metal salt ions are precipitated rapidly, and a multi-stage structure is not easy to form.

Preferably, the hydrothermal reaction time in step (1) is 6-20h, such as 6h, 7h, 9h, 10h, 12h, 14h, 17h, 19h or 20h, etc., preferably 6-14 h.

Preferably, the precursor is washed and dried before the calcination in step (2).

Preferably, the cleaning solution used for cleaning comprises water and/or ethanol.

Preferably, the number of washes is 3 or more, for example, 3, 4, 5, 6, 8, 10, etc., preferably 3 to 5.

Preferably, the temperature of the drying is 80-120 ℃, for example, 80 ℃, 85 ℃, 90 ℃, 100 ℃, 110 ℃, 115 ℃ or 120 ℃ and the like.

Preferably, the drying time is 6-24h, such as 6h, 7h, 9h, 10h, 12h, 14h, 17h, 20h, 22h or 24 h.

Preferably, the temperature rise rate of the calcination in the step (2) is 2-10 ℃/min, for example, 2 ℃/min, 3 ℃/min, 5 ℃/min, 8 ℃/min, 10 ℃/min or the like, preferably 2-5 ℃/min; if the temperature rise rate is less than 2 ℃/min, the calcination time is too long, and the crystallinity of the material is improved to cause the reduction of the catalytic activity; the heating rate is more than 10 ℃/min, the interface defects between the composite metal oxides are less, and the catalytic activity is lower.

Preferably, the temperature of the calcination in step (2) is 300-550 ℃, such as 300 ℃, 350 ℃, 400 ℃, 450 ℃, 500 ℃ or 550 ℃, preferably 350-450 ℃; if the temperature is lower than 300 ℃, the precursor can not be converted into the composite metal oxide; the temperature is higher than 550 ℃, the precursor is converted into the composite metal oxide, but the sheet structure is broken.

Preferably, the calcination time in step (2) is 3-6h, such as 3h, 3.5h, 4h, 4.5h, 5h, 5.5h or 6h, etc., preferably 3.5-5 h.

As a further preferred embodiment of the present invention, the method comprises the steps of:

(1) ultrasonically cleaning an aluminum carrier in water for 0.5-2h, taking out, drying by using compressed air, ultrasonically cleaning in acetone for 0.5-2h, taking out, and drying by using compressed air to obtain a pretreated aluminum carrier;

(2) dissolving M salt in a water alcohol solution, controlling the concentration of the M salt to be 0.05-0.25mol/L and the volume ratio of alcohol in the water alcohol solution to be 60-100%, and obtaining the water alcohol solution of the M salt;

(3) putting the pretreated aluminum carrier obtained in the step (1) into a hydroalcoholic solution of M salt, adding an ammonia releasing agent, mixing, controlling the molar ratio of the M salt to the ammonia releasing agent to be (1-6):1, then carrying out hydrothermal reaction at 90-170 ℃ for 6-20h, and cooling to 18-30 ℃ to obtain a precursor;

(4) and (4) respectively cleaning the precursor obtained in the step (3) by using water and ethanol for more than 3 times, drying at 80-120 ℃ for 6-24h, raising the temperature to 300-550 ℃ at the heating rate of 2-10 ℃/min, and maintaining for 3-6h to obtain the catalyst.

In a third aspect, the present invention also provides the use of a catalyst as described in the first aspect above, for the catalytic decomposition of volatile organic materials.

The catalyst is used for catalytically decomposing volatile organic substances, the problems of low catalytic activity and slow heating temperature of the existing catalyst are solved, and the efficient and low-energy-consumption catalytic decomposition of the volatile organic substances is realized.

Compared with the prior art, the invention has the following beneficial effects:

(1) the catalyst provided by the invention is a metal-based hierarchical structure membrane catalyst, and comprises an aluminum carrier and M and Al mixed metal oxide sheets growing on the aluminum carrier in situ, wherein the mixed metal oxide sheets are stacked in a three-dimensional direction to form a multi-level structure (see figure 1) such as a petal shape, which is beneficial to fully exposing catalytic active sites, has the advantages of high catalytic activity and high heat conduction speed, can realize high-efficiency and low-energy-consumption catalytic decomposition of reactants, and can be applied to catalytic decomposition of volatile organic substances;

(2) the preparation method of the catalyst provided by the invention comprises the steps of selecting an aluminum carrier, introducing alcohol and an ammonia releasing agent to regulate the properties of a catalytic active component solution, growing the catalyst on the aluminum carrier in situ to form a precursor of the catalyst, and calcining to obtain the catalyst; the preparation method has the advantages of simple process, mild conditions, easy industrialization and wide application prospect.

Drawings

FIG. 1 is an SEM image of the catalyst prepared in example 4.

Detailed Description

The following further describes the technical means of the present invention to achieve the predetermined technical effects by means of embodiments with reference to the accompanying drawings, and the embodiments of the present invention are described in detail as follows.

Example 1

This example provides a method for preparing a catalyst, comprising the steps of:

(1) ultrasonically cleaning an aluminum sheet in water for 30min, taking out compressed air for drying, ultrasonically cleaning the aluminum sheet in acetone for 10min, and drying the aluminum sheet by the compressed air to obtain a pretreated aluminum sheet;

(2) weighing 5mmol of cobalt nitrate and 30mmol of hexamethylenetetramine, dissolving in a mixed solution of 10mL of water and 90mL of methanol, adding the pretreated aluminum sheet obtained in the step (1), carrying out ultrasonic treatment for 20min, transferring into a reaction kettle, reacting at 140 ℃ for 10h, taking out, cooling to room temperature, washing water and ethanol for 3 times respectively, and drying at 80 ℃ for 6h to obtain a precursor;

(3) and (3) drying the precursor in the step (2), raising the temperature to 400 ℃ at a speed of 2 ℃/min, and maintaining for 4 hours to obtain the catalyst.

Example 2

The only difference compared with example 1 was that 5mmol of cobalt nitrate in step (2) was replaced with 15mmol of cobalt nitrate.

Example 3

The only difference compared with example 1 was that 5mmol of cobalt nitrate in step (2) was replaced with 20mmol of cobalt nitrate.

Example 4

Compared with example 1, the only difference is that 5mmol of cobalt nitrate in step (2) is replaced by 5mmol of cobalt nitrate and 10mmol of manganese nitrate.

The catalyst prepared in this example, whose SEM image is shown in fig. 1, was grown in situ on an aluminum support with mixed metal oxide sheets stacked in three dimensions, in a multi-level structure in the shape of petals by face-to-face connection, face-to-end connection, or end-to-end connection.

Example 5

Compared with example 1, the only difference is that 5mmol of cobalt nitrate in step (2) is replaced by 5mmol of cobalt nitrate and 10mmol of nickel nitrate.

Example 6

Compared with example 1, the difference is only that 5mmol of cobalt nitrate in step (2) is replaced by 15mmol of manganese nitrate.

Example 7

Compared with example 1, the only difference is that 5mmol of cobalt nitrate in step (2) is replaced with 5mmol of cobalt nitrate, 5mmol of nickel nitrate and 5mmol of manganese nitrate.

Example 8

(1) ultrasonically cleaning an aluminum sheet in water for 10min, taking out compressed air for drying, ultrasonically cleaning the aluminum sheet in acetone for 10min, and drying the aluminum sheet by the compressed air to obtain a pretreated aluminum sheet;

(2) weighing 15mmol of cobalt nitrate and 15mmol of hexamethylenetetramine, dissolving in a mixed solution of 10mL of water and 90mL of methanol, putting the pretreated aluminum sheet obtained in the step (1), performing ultrasonic treatment for 20min, transferring into a reaction kettle, reacting at 140 ℃ for 10h, taking out, cooling to room temperature, washing water and ethanol for 3 times respectively, and drying at 80 ℃ for 6h to obtain a precursor;

Example 9

The only difference compared to example 8 is that in step (2) 15mmol of hexamethylenetetramine was replaced by 45mmol of hexamethylenetetramine.

Example 10

The only difference compared to example 8 is that 15mmol of hexamethylenetetramine in step (2) is replaced by 30mmol of urea.

Example 11

The only difference compared to example 8 is that the hydrothermal temperature in step (2) was replaced by 90 ℃.

Example 12

The only difference compared to example 8 is that the hydrothermal temperature in step (2) was replaced by 170 ℃.

Example 13

The only difference compared to example 8 was that the volumes of water and alcohol in step (2) were replaced with 40mL and 60mL, respectively.

Example 14

(1) ultrasonically cleaning foamed aluminum in water for 2 hours, taking out compressed air for drying, placing the foamed aluminum in acetone for ultrasonically cleaning for 0.5 hour, and drying the foamed aluminum by the compressed air to obtain pretreated foamed aluminum;

(2) weighing 25mmol of cobalt nitrate and 150mmol of hexamethylenetetramine, dissolving in a mixed solution of 20mL of water and 80mL of ethanol, adding the pretreated foamed aluminum obtained in the step (1), performing ultrasonic treatment for 30min, transferring into a reaction kettle, reacting at 170 ℃ for 6h, taking out, cooling to 20 ℃, washing water and ethanol for 5 times respectively, and drying at 120 ℃ for 0.5h to obtain a precursor;

(3) and (3) drying the precursor in the step (2), raising the temperature to 550 ℃ at a heating rate of 10 ℃/min, and maintaining for 3 hours to obtain the catalyst.

Example 15

The only difference compared to example 14 is that the calcination temperature in step (3) was replaced with 300 ℃.

Example 16

The only difference compared to example 14 is that the calcination temperature in step (3) was replaced with 350 ℃.

Example 17

The only difference compared to example 14 is that the calcination temperature in step (3) was replaced with 450 ℃.

Comparative example 1

(1) Weighing 5mmol of cobalt nitrate, 10mmol of manganese nitrate and 30mmol of hexamethylenetetramine, dissolving in a mixed solution of 10mL of water and 90mL of methanol, carrying out ultrasonic treatment for 20min, transferring into a reaction kettle, reacting at 140 ℃ for 10h, taking out, cooling to room temperature, carrying out centrifugal cleaning on water and ethanol for 3 times respectively, and drying at 80 ℃ for 6h to obtain a precursor;

(2) and (3) heating the precursor in the step (1) to 400 ℃ at a heating rate of 2 ℃/min, and maintaining for 4h to obtain the catalyst.

(3) And (3) adding the catalyst in the step (2) into an ethanol solution to prepare a suspension of 20mg/mL, curling and soaking an aluminum sheet (width is multiplied by length is multiplied by 1cm and multiplied by 15cm) in the suspension, taking out the aluminum sheet, and drying the aluminum sheet for 6 hours at 80 ℃ to obtain a comparative sample.

Comparative example 2

The only difference compared with example 1 was that the mixed solution of 10mL of water and 90mL of methanol in step (2) was replaced with 100mL of water.

Evaluation of catalyst Performance:

the catalysts prepared in the examples and comparative examples were tested for their catalytic performance by the following method:

rolling the aluminum sheet with the width multiplied by the length of 1cm multiplied by 15cm into a compact roll, wherein a cylinder with the foam aluminum with the width multiplied by 1cm multiplied by 15cm is plugged into a quartz tube reactor with the inner diameter of 10mm, the volume is about 0.785mL, adding quartz sand and quartz cotton into two ends of the catalyst, carrying out temperature programming control on the reaction temperature (100-^-1(space velocity of 20000h^-1) The inlet benzene concentration was 500 ppm. The concentration of VOCs in the gas after the reaction was measured by gas chromatography (Shimadzu GC-2014), and the concentration of VOCs in the gas was measured by an Rt-Stabilwax column (30 m.times.0.53 mm.times.10 μm) and detected by an FID detector.

Evaluation criteria: temperature T required at 90% VOC conversion₉₀As evaluation, T₉₀Lower temperatures indicate higher catalyst activity.

The test results are shown in table 1.

TABLE 1

The following points can be seen from table 1:

(1) it can be seen from the combination of examples 1-17 that examples 1-17 employ hydrothermal reaction in combination with calcination to prepare an aluminum-based multi-stage structured catalyst, T₉₀The catalyst has higher catalytic activity below 352 ℃;

(2) it can be seen from the comprehensive examples 1-3 that the catalyst of example 2 has high activity, and 90% of benzene degradation can be realized at 314 ℃, because the proper active Co element and the proper ratio of Co to HMT, most of the obtained catalysts have multi-stage structures such as petal shapes, and the like, and have many active sites;

(3) it can be seen from the comprehensive examples 4-7 that the catalyst of example 4 has high activity, and 90% of benzene degradation can be realized at 286 ℃, because a composite oxide is formed between Co and Mn elements, and a synergistic effect exists, so that the catalytic activity is improved;

(4) it can be seen from the combination of example 2 and examples 8-10 that the catalyst of example 2 has high activity, and 90% of benzene degradation can be realized at 314 ℃, because the appropriate HMT induces metal ions to synthesize petal-shaped multilevel structures; in addition, when the ammonia releasing agent is urea, the activity of the prepared catalyst is lower than that of the prepared catalyst with the optimal amount of hexamethylene tetramine, because the crystallinity of the catalyst tablet synthesized by urea is better than that of HMT, the active site is reduced, and the activity is reduced;

(5) combining example 8 with examples 11-12, it can be seen that the catalyst of example 8 has a higher activity, and 90% benzene degradation can be achieved at 336 ℃, because the formation of a multi-stage structure is facilitated by the appropriate hydrothermal temperature;

(6) combining example 14 with examples 15-17, it can be seen that the catalyst of example 16 has higher activity and can achieve 90% benzene degradation at 340 ℃, because the calcination temperature affects the specific surface area and pore structure of the catalyst, and the activity is better at a suitable calcination temperature;

(7) it can be seen from the combination of example 4 and comparative example 1 that the raw materials and preparation conditions of comparative example 1 are the same as those of example 4, while the activity of comparative example 1 is significantly reduced because the catalyst prepared in comparative example 1 mostly has a close-packed lamellar structure, while the mixed metal oxide sheets are stacked in three dimensions and the active sites are sufficiently exposed in the catalyst prepared in example 4;

(8) it can be seen from the combination of example 1 and comparative example 2 that the catalyst of comparative example 2 has low activity and 90% benzene degradation can be achieved at 362 c because comparative example 2 uses an aqueous solution, does not easily form a multi-stage structure and the active sites are not sufficiently exposed.

In conclusion, the aluminum carrier of the catalyst provided by the invention belongs to a high-thermal-conductivity carrier, and the thermal conductivity coefficient of the metal aluminum is about 237W/(m.K), so that the rapid temperature rise and temperature reduction can be realized; the mixed metal oxide grows on the carrier in situ, is in a sheet shape, is stacked in the three-dimensional direction, is beneficial to fully exposing catalytic active sites, has the advantages of high catalytic activity and quick heat conduction, and can realize catalytic decomposition of reactants with high efficiency and low energy consumption; according to the method, alcohol and an ammonia releasing agent are introduced to regulate the property of the solution of the catalytic active component, so that the mixed metal oxide sheets are stacked in the three-dimensional direction.

The applicant declares that the present invention illustrates the detailed structural features of the present invention through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must be implemented depending on the above detailed structural features. It should be understood by those skilled in the art that any modifications of the present invention, equivalent substitutions of selected components of the present invention, additions of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.

Claims

1. A catalyst for decomposing volatile organic substances, the catalyst comprising:

an aluminum support and a sheet of mixed metal oxide of M and Al grown in situ on the aluminum support, the M comprising any one or a combination of at least two of Co, Ni or Mn;

the loading amount of the mixed metal oxide sheet is 0.5-2mg/cm²；

The mixed metal oxide sheets are stacked in the three-dimensional direction and are connected into a multilevel structure through surface-surface connection, surface-end connection or end-end connection, and the grain diameter of the multilevel structure is 0.5-5 mu m;

the catalyst is prepared by the following method, and the method comprises the following steps:

(1) putting an aluminum carrier into a hydroalcoholic solution of M salt, adding an ammonia releasing agent, controlling the molar ratio of the ammonia releasing agent to the M salt to be (2-4):1, and carrying out hydrothermal reaction at the temperature of 120-;

(2) calcining the precursor obtained in the step (1) to obtain the catalyst;

wherein, the volume ratio of the alcohol in the water-alcohol solution is 60-100%, and the ammonia releasing agent comprises hexamethylenetetramine and/or urea.

2. The catalyst of claim 1, wherein the aluminum support comprises aluminum flakes and/or foamed aluminum.

3. The catalyst of claim 1, wherein the aluminum support is aluminum flakes.

4. The catalyst of claim 1, wherein the mixed metal oxide tablets are supported at a loading of 0.8-1.5mg/cm²。

5. The catalyst according to claim 1, wherein the particle size of the multilevel structure is 0.8-2 μm.

6. The method for preparing a catalyst according to claim 1, characterized in that it comprises the following steps:

(2) calcining the precursor obtained in the step (1) to obtain the catalyst;

wherein, the volume ratio of alcohol in the water-alcohol solution is 60-100%, and the ammonia releasing agent is hexamethylenetetramine.

7. The method of claim 6, wherein prior to step (1), the aluminum support is pretreated, the method of pretreating comprising: the aluminum support was sonicated with water and/or acetone.

8. The method of claim 7, wherein the ultrasound is at a temperature of 20-40 ℃.

9. The method of claim 7, wherein the sonication time is 0.5-2 hours.

10. The method of claim 6, wherein the aluminum support of step (1) comprises aluminum flakes and/or foamed aluminum.

11. The method of claim 10, wherein the aluminum support of step (1) is aluminum sheet.

12. The method of claim 6, wherein the M salt of step (1) comprises any one of cobalt nitrate, nickel nitrate or manganese nitrate or a combination of at least two thereof.

13. The method of claim 6, wherein the M salt concentration in step (1) is 0.05 to 0.25 mol/L.

14. The method of claim 12, wherein the M salt concentration in step (1) is 0.1 to 0.2 mol/L.

15. The method according to claim 6, wherein the alcohol in the hydroalcoholic solution of step (1) is 80-100% by volume.

16. The method of claim 6, wherein the alcohol in the hydroalcoholic solution of step (1) comprises methanol and/or ethanol.

17. The method according to claim 6, wherein the hydrothermal reaction time in step (1) is 6-20 h.

18. The method according to claim 17, wherein the hydrothermal reaction time in step (1) is 6-14 h.

19. The method of claim 6, wherein the precursor is washed and dried before the calcining in step (2).

20. The method of claim 19, wherein the cleaning fluid used for cleaning comprises water and/or ethanol.

21. The method of claim 19, wherein the number of washes is 3 or more.

22. The method of claim 21, wherein the number of washes is 3-5.

23. The method of claim 19, wherein the temperature of the drying is 80-120 ℃.

24. The method of claim 19, wherein the drying time is 6-24 hours.

25. The method of claim 6, wherein the temperature increase rate of the calcination in step (2) is 2-10 ℃/min.

26. The method of claim 25, wherein the temperature ramp rate of the calcining of step (2) is 2-5 ℃/min.

27. The method as claimed in claim 6, wherein the temperature of the calcination in step (2) is 300-550 ℃.

28. The method as claimed in claim 27, wherein the temperature of the calcination in step (2) is 350-450 ℃.

29. The method of claim 6, wherein the calcination of step (2) is carried out for a period of 3-6 hours.

30. The method of claim 29, wherein the calcining time of step (2) is 3.5-5 hours.

31. The method according to any one of claims 6-30, characterized in that the method comprises the steps of:

(3) putting the pretreated aluminum carrier obtained in the step (1) into a hydroalcoholic solution of M salt, adding an ammonia releasing agent, mixing, controlling the molar ratio of the M salt to the ammonia releasing agent to be (2-4):1, then carrying out hydrothermal reaction at the temperature of 120-150 ℃ for 6-20h, and cooling to 18-30 ℃ to obtain a precursor;

32. Use of a catalyst according to any one of claims 1 to 5 for the catalytic decomposition of volatile organic substances.