Efficient, stable and water-resistant VOCs catalytic oxidation material as well as preparation method and application thereof

Abstract

The invention belongs to the field of catalyst preparation, and particularly relates to an efficient, stable and water-resistant VOCs catalytic oxidation material as well as a preparation method and application thereof. The preparation method comprises the following steps: firstly, synthesizing a metal organic framework material (MOFs) with a specific morphological structure through screening design of a metal cerium source and an organic ligand, and then deriving under a certain condition by taking the MOFs as a precursor to prepare a cerium dioxide (CeO2) catalytic material with rich morphologies and pore structures. Tests show that the CeO2 catalytic material has activity, stability and water resistance which are obviously superior to those of commercial CeO2 in the catalytic oxidation application of o-xylene which is high in space velocity and difficult to degrade, addition of a regulator, a surfactant and the like is avoided in the preparation process, and finally the cost is far lower than that of a noble metal catalyst adopted in the industry at present.

Description

Technical Field

[0001] The present invention belongs to the field of catalyst preparation, and specifically relates to a highly efficient, stable and water-resistant VOCs catalytic oxidation material and a preparation method and application thereof. Background Art

[0002] Volatile Organic Compounds (VOCs) is a general term for a class of organic compounds with a boiling point between 50 and 260°C under normal temperature and pressure conditions. According to different molecular structures, they can be divided into low-carbon alkanes, aliphatic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, aldehydes, ethers, phenols, alcohols and epoxy compounds. The large-scale emission of VOCs not only directly damages the human respiratory system and induces the "three-cause" effect, but also indirectly causes secondary air pollution such as PM2.5 and ozone.

[0003] The catalytic oxidation method is also called the catalytic combustion method. It uses the action of catalysts to completely oxidize VOCs gas into carbon dioxide and water under sufficient oxygen and low temperature. It has the advantages of high treatment efficiency, no secondary pollution, good safety, wide application range, low investment and energy consumption and operating costs. It has gradually become one of the main technologies for VOCs pollution control, especially suitable for industrial organic waste gas with large emission flow and low concentration, and has broad application prospects.

[0004] The key to VOCs catalytic oxidation is efficient, stable, and low-cost catalytic materials. Currently, the most commonly used precious metal catalysts such as platinum, palladium, and gold have high catalytic activity and low conversion temperature, but their high price and easy poisoning and deactivation limit their large-scale promotion and application in the field of VOCs catalytic oxidation. Metal oxides such as cobalt, manganese, and cerium are cheap and abundant in resources, but they still have relatively low catalytic activity, high conversion temperature, and easy deactivation under humid conditions in VOCs catalytic oxidation reactions.

[0005] Therefore, based on this, the technical solution of the present invention is proposed. Summary of the invention

[0006] In order to solve the problems existing in the prior art, the present invention provides a method for preparing a highly efficient, stable and water-resistant VOCs catalytic oxidation material, the preparation method comprising the following steps:

[0007] (1) adding cerium acetate and an organic ligand to a mixed solution of N,N-dimethylformamide and anhydrous ethanol, and stirring to obtain a mixed solution;

[0008] (2) subjecting the mixed solution to hydrothermal synthesis and centrifugation in sequence to obtain a precipitate; washing and drying the precipitate to obtain a MOFs precursor;

[0009] (3) calcining the MOFs precursor at high temperature in an air atmosphere, and cooling the precursor to obtain the highly efficient, stable, and water-resistant VOCs catalytic oxidation material.

[0010] Preferably, in step (1), the organic ligand comprises 2,5-dihydroxyterephthalic acid or trimesic acid.

[0011] Preferably, in step (1), the molar ratio of cerium acetate to organic ligand is 1:1 to 1:5.

[0012] Preferably, in step (2), the heating temperature is 100 to 200° C., and the heating time is 12 to 48 hours.

[0013] Preferably, in step (2), the drying temperature is 60-100°C.

[0014] Preferably, in step (3), the temperature of the high temperature roasting is 300-500°C, and the roasting time is 3-6 hours. It should be noted that in the prior art, roasting is performed in an inert atmosphere (such as nitrogen), but this technology also has the following disadvantages: (i) the nitrogen roasting temperature is high, which increases energy consumption costs; (ii) the nitrogen high temperature roasting requires high equipment airtightness, and once air infiltrates, thermal nitrogen oxides are easily generated, causing secondary pollution; (iii) after nitrogen roasting, some carbides and nitrides remain, affecting the stability of the catalyst in the catalytic oxidation reaction of VOCs; (iv) if the catalyst stability is to be improved, secondary air roasting is required, and the preparation process is complicated.

[0015] Based on the same technical concept, another scheme of the present invention is to provide a highly efficient, stable and water-resistant VOCs catalytic oxidation material obtained by a preparation method.

[0016] Based on the same technical concept, another solution of the present invention is to provide an efficient, stable and water-resistant VOCs catalytic oxidation material for use in the treatment of o-xylene gaseous pollutants.

[0017] The beneficial effects of the present invention are:

[0018] In order to solve the problems of relatively low catalytic activity, high conversion temperature, and easy deactivation under humid conditions of metal oxides in VOCs catalytic oxidation reactions, the present invention first synthesizes metal organic framework materials (MOFs) with specific morphological structures through the screening design of metal cerium sources and organic ligands, and then uses the MOFs as precursors to derive and prepare cerium dioxide (CeO2) catalytic materials with rich morphologies and pore structures under certain conditions. And it is known from tests that the CeO2 catalytic material of the present invention has significantly better activity, stability and water resistance than commercial CeO2 in the application of high-space-velocity, difficult-to-degrade catalytic oxidation of o-xylene, and avoids the addition of regulators, surfactants, etc. during the preparation process, which ultimately makes the cost much lower than the precious metal catalysts currently used in the industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 It is an X-ray diffraction pattern.

[0021] Figure 2 This is a field emission scanning electron microscope image.

[0022] Figure 3 It is the nitrogen adsorption-desorption isotherm and pore size distribution structure diagram.

[0023] Figure 4 It is a performance diagram of the catalytic oxidation of o-xylene, wherein (a) is a data diagram of the o-xylene conversion rate, and (b) is a data diagram of the carbon dioxide generation rate.

[0024] Figure 5 It is T 50％ and T 20％ Graph showing the water resistance of o-xylene catalytic oxidation under temperature conditions, where (a) is CeO2 catalytic material and (b) is commercial CeO2. DETAILED DESCRIPTION

[0025] To make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0026] Example 1

[0027] This embodiment provides a method for preparing a highly efficient, stable, and water-resistant VOCs catalytic oxidation material, the preparation method comprising the following steps:

[0028] (1) dissolving 1 mmol of cerium acetate and 5 mmol of trimesic acid in a mixed solution of N,N-dimethylformamide and anhydrous ethanol (the volume ratio of N,N-dimethylformamide to anhydrous ethanol is 1:5), and continuously stirring at room temperature until the mixture is uniformly mixed to obtain a mixed solution;

[0029] (2) transferring the mixed solution to a stainless steel reactor lined with polytetrafluoroethylene and reacting at 200° C. for 12 h; after cooling to room temperature, performing solid-liquid separation by centrifugation, washing the obtained precipitate with anhydrous ethanol three times, and drying at 100° C. to obtain a MOFs precursor;

[0030] (3) Preparation of CeO2 by MOFs derivatization: The MOFs precursor (powder) is placed in a crucible and then calcined at 400°C for 5 h in an air atmosphere in a muffle furnace. After cooling to room temperature, CeO2 (i.e., a highly efficient, stable, and water-resistant VOCs catalytic oxidation material) is obtained.

[0031] Example 2

[0032] This embodiment provides a method for preparing a highly efficient, stable, and water-resistant VOCs catalytic oxidation material, the preparation method comprising the following steps:

[0033] (1) dissolving 1 mmol of cerium acetate and 4 mmol of trimesic acid in a mixed solution of N,N-dimethylformamide and anhydrous ethanol (the volume ratio of N,N-dimethylformamide to anhydrous ethanol is 1:3), and continuously stirring at room temperature until the mixture is uniformly mixed to obtain a mixed solution;

[0034] (2) transferring the mixed solution to a stainless steel reactor lined with polytetrafluoroethylene and reacting at 120° C. for 48 hours; after cooling to room temperature, performing solid-liquid separation by centrifugation, washing the obtained precipitate with anhydrous ethanol three times, and drying at 60° C. to obtain a MOFs precursor;

[0035] (3) Preparation of CeO2 by MOFs derivatization: The MOFs precursor (powder) is placed in a crucible and then calcined at 500°C for 3 h in an air atmosphere in a muffle furnace. After cooling to room temperature, CeO2 (i.e., a highly efficient, stable, and water-resistant VOCs catalytic oxidation material) is obtained.

[0036] Example 3

[0037] This embodiment provides a method for preparing a highly efficient, stable, and water-resistant VOCs catalytic oxidation material, the preparation method comprising the following steps:

[0038] (1) dissolving 1 mmol of cerium acetate and 3 mmol of 2,5-dihydroxyterephthalic acid in a mixed solution of N,N-dimethylformamide and anhydrous ethanol (the volume ratio of N,N-dimethylformamide to anhydrous ethanol is 1:4), and continuously stirring at room temperature until the mixture is uniformly mixed to obtain a mixed solution;

[0039] (2) transferring the mixed solution to a stainless steel reactor lined with polytetrafluoroethylene and reacting at 160° C. for 24 hours; after cooling to room temperature, performing solid-liquid separation by centrifugation, washing the obtained precipitate with anhydrous ethanol three times, and drying at 80° C. to obtain a MOFs precursor;

[0040] (3) Preparation of CeO2 by MOFs derivatization: The MOFs precursor (powder) is placed in a crucible and then calcined at 300°C for 6 hours in an air atmosphere in a muffle furnace. After cooling to room temperature, CeO2 (i.e., a highly efficient, stable, and water-resistant VOCs catalytic oxidation material) is obtained.

[0041] Application effect test example

[0042] The present invention provides an application of an efficient, stable and water-resistant VOCs catalytic oxidation material in the treatment of o-xylene gaseous pollutants. Among them, o-xylene has a stable benzene ring structure and is one of the most difficult VOCs to degrade. The test conditions are reaction gas space velocity WHSV = 120,000mL / (g·h), o-xylene reaction concentration C0 = 150ppm, and reaction temperature range of 180-320℃.

[0043] From the results, it can be seen that the CeO2 catalytic material of the present invention has significantly better activity, stability and water resistance than commercial CeO2 in the application of high space velocity, difficult to degrade o-xylene catalytic oxidation, and the cost is much lower than the precious metal catalysts currently used in the industry.

[0044] More specifically: Taking the catalytic oxidation material CeO2 obtained in Example 1 as an object, the CeO2 catalytic material has a cerium ore crystal structure (such as Figure 1 As shown, all its diffraction peaks are consistent with PDF card #43-1002), stacked rod-like morphology (such as Figure 2 As shown in Figure 2, it is a tetrahedral rod with a length of about 10 μm and a diameter of about 200 nm), as well as a large specific surface area and rich pore structure (such as Figure 3 The 90% conversion temperature T of the CeO2 catalytic material of the present invention in the catalytic oxidation of o-xylene is 0.0447 W / m. 90％and 50% conversion temperature T 50％ 300℃ and 220℃ respectively (WHSV=120,000mL / (g·h)), which are 20℃ and 70℃ lower than similar commercial CeO2 (such as Figure 4 In addition, at T 50％ and T 20％ In the catalytic oxidation reaction of o-xylene under temperature conditions, the CeO2 catalytic material of the present invention has good stability; after the introduction of 1 vol.% H2O, its o-xylene conversion rate is improved, showing a certain water resistance, while the o-xylene conversion rate of commercial CeO2 is significantly reduced (such as Figure 5 shown).

[0045] Therefore, the CeO2 catalytic material prepared by the method of the present invention has efficient, stable and water-resistant VOCs catalytic oxidation performance, and can effectively save the cost and energy consumption of VOCs pollution control.

[0046] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for preparing an efficient, stable and water-resistant VOCs catalytic oxidation material, characterized in that: The preparation method comprises the following steps: (1) adding cerium acetate and an organic ligand to a mixed solution of N,N-dimethylformamide and anhydrous ethanol, and stirring to obtain a mixed solution; (2) subjecting the mixed solution to hydrothermal synthesis and centrifugation in sequence to obtain a precipitate; washing and drying the precipitate to obtain a MOFs precursor; (3) calcining the MOFs precursor at high temperature in an air atmosphere, and cooling the precursor to obtain the highly efficient, stable, and water-resistant VOCs catalytic oxidation material.

2. The method for preparing the highly efficient, stable and water-resistant VOCs catalytic oxidation material according to claim 1, characterized in that: In step (1), the organic ligand includes 2,5-dihydroxyterephthalic acid or trimesic acid.

3. The method for preparing the highly efficient, stable and water-resistant VOCs catalytic oxidation material according to claim 1, characterized in that: In step (1), the molar ratio of cerium acetate to organic ligand is 1:1 to 1:

5.

4. The method for preparing the highly efficient, stable and water-resistant VOCs catalytic oxidation material according to claim 1, characterized in that: In step (1), the volume ratio of N,N-dimethylformamide to anhydrous ethanol is 1:2 to 1:

5.

5. The method for preparing the highly efficient, stable and water-resistant VOCs catalytic oxidation material according to claim 1, characterized in that: In step (2), the heating temperature is 100 to 200° C., and the heating time is 12 to 48 hours.

6. The method for preparing the highly efficient, stable and water-resistant VOCs catalytic oxidation material according to claim 1, characterized in that: In step (2), the drying temperature is 60-100°C.

7. The method for preparing the highly efficient, stable and water-resistant VOCs catalytic oxidation material according to claim 1, characterized in that: In step (3), the high temperature calcination temperature is 300-500° C., and the calcination time is 3-6 hours.

8. The efficient, stable and water-resistant VOCs catalytic oxidation material obtained by the preparation method according to any one of claims 1 to 7.

9. Use of the efficient, stable and water-resistant VOCs catalytic oxidation material according to claim 8 in the treatment of o-xylene gaseous pollutants.

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