Oxygen vacancy cluster regulated manganese dioxide catalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of preparation of VOCs catalytic oxidation catalysts, in particular to an oxygen vacancy cluster regulated manganese dioxide catalyst and a preparation method and application thereof. The MnO2-VO < * > catalyst comprises delta-MnO2 which is used as a basic component and contains oxygen vacancies, and an oxygen vacancy cluster which is formed in the catalyst after being impregnated and calcined in an NH4Cl solution, compared with an existing MnO2 catalyst, the MnO2-VO < * > catalyst has the different structures that the microstructure of the MnO2-VO < * > catalyst prepared by the method is of a spherical nano flower-shaped structure formed by polymerizing nanosheets, so that the MnO2-VO < * > catalyst has a high specific surface area; moreover, by regulating and controlling the number and size of the oxygen vacancy clusters, the catalyst can effectively promote the adsorption and activation of H2O and enhance the electron transfer between H2O molecules and the catalyst, so that water vapor contained in the actually discharged VOCs waste gas can be quickly converted into active hydroxyl and participates in catalytic oxidation reaction, and the catalytic oxidation effect is improved. Therefore, the inhibition effect of H2O molecules in the traditional MnO2 catalyst is converted into the promotion effect.

Description

Technical Field

[0001] The invention relates to the technical field of VOCs catalytic oxidation catalyst preparation, and in particular to a manganese dioxide catalyst regulated by oxygen vacancy clusters, and a preparation method and application thereof. Background Art

[0002] Volatile organic compounds (VOCs) are one of the main sources of air pollution and pose a serious threat to the environment and human health. As an efficient and clean treatment method, the catalytic oxidation technology of VOCs has been widely used in environmental governance. However, in actual industrial treatment processes, the catalytic oxidation process of VOCs is often significantly affected by water vapor. Water vapor not only competes with reactant molecules for adsorption on the catalyst surface, resulting in a significant decrease in catalytic activity, but also causes the accumulation of intermediates on the catalyst surface, causing catalyst deactivation. Solving the problem of water vapor interference is one of the key challenges in the current field of VOCs catalytic oxidation.

[0003] In order to cope with the negative effects of water vapor, researchers have tried to alleviate its inhibitory effect on catalytic activity by improving the physical and chemical properties of catalysts. For example, some studies have focused on the development of hydrophobic catalysts to reduce the adsorption of water vapor. However, although this method can reduce the competitive adsorption of water vapor, it often sacrifices the adsorption capacity and reaction activity of the catalyst for VOCs. Other studies have attempted to improve the ability to resist water vapor interference by increasing the number of oxygen vacancies or surface oxygen activity of the catalyst, but the effects of these improvement methods are still limited, especially in terms of the long-term stability of the catalyst under high humidity conditions, there are still major technical bottlenecks. In addition, the specific surface area of ​​the catalyst is also one of the key factors that determine its catalytic performance. A high specific surface area can not only provide more active sites, effectively improve the adsorption capacity of reactant molecules, but also increase the rate of catalytic oxidation reactions.

[0004] Therefore, how to effectively control the surface properties of the catalyst while increasing its specific surface area, especially how to reasonably utilize water vapor and convert it into an element that helps the catalytic reaction, has become an important research direction for improving the catalytic oxidation performance of VOCs. In response to this problem, the present invention intends to design a method that effectively promotes the adsorption and activation of water vapor on the catalyst surface, and transforms the "hindrance of the catalytic process" of water vapor into "promoting the catalytic process". Summary of the invention

[0005] In order to achieve the above-mentioned purpose, the present invention designs a manganese dioxide catalyst regulated by oxygen vacancy clusters, denoted as MnO2-V O * Catalyst. In this scheme, K + Partially replaced by NH4+ , and promotes NH4 + Ion escape, due to the interlayer K + The ion content is reduced, and in order to maintain the charge balance, a large number of oxygen vacancies are generated in the catalyst. These oxygen vacancies aggregate under the action of thermodynamics to form oxygen vacancy clusters with adjustable number and size. O * Compared with general MnO2 catalysts, the catalyst has the following different technical features:

[0006] The MnO2-V prepared by the present invention O * The microscopic morphology of the catalyst is a spherical nanoflower structure with a diameter of 200 to 600 nm, which is composed of nanosheets with a thickness of 10 to 20 nm. Its specific surface area is 94.0 to 156.3 m 2 / g, pore size is 3.6~7.7nm, pore volume is 0.18~0.27cm 3 / g;

[0007] remember Catalyst The meaning of is oxygen vacancy clusters, where * is the content ratio of oxygen vacancy clusters, and the value range of * is 40-60% (the content ratio of oxygen vacancy clusters in the catalyst refers to the relative number of oxygen vacancy clusters on the catalyst surface or in the crystal lattice, which is a simple quantity ratio), and based on the τ2 value, V O * The size range is 430~460ps.

[0008] As another aspect of the present invention, there is also provided the above-mentioned MnO2-V O * Preparation method of catalyst:

[0009] S1. Preparation of δ-MnO2;

[0010] The MnSO4 solution was added to the KMnO4 solution and stirred thoroughly until the two were evenly mixed, and then reacted at 160°C for 12h to obtain δ-MnO2;

[0011] Let n be the multiplication coefficient and n∈R + , then the content of KMnO4 in KMnO4 solution is 1.25ng, and the volume of the solution is 30nmL; the content of MnSO4·4H2O in MnSO4 solution is 0.28ng, and the volume of the solution is 30n mL;

[0012] S2. Preparation of MnO2-V O * Precursor;

[0013] S2-1, add the δ-MnO2 prepared in S1 to the NH4Cl solution and stir thoroughly until the two are evenly mixed, then react at 25-60°C for 4-8h to obtain MnO2-V O * Precursor 1;

[0014] Let n be the multiplication coefficient and n∈R + , then in the system of S2-1: the amount of NH4Cl added is n[0.01,0.15]g, the volume of the solution is n[20,30]mL, and the amount of δ-MnO2 added is n[0.7,1.0]g;

[0015] Description: δ-MnO2 is a two-dimensional planar structure composed of manganese oxide octahedron (MnO6), with a large amount of K + During the impregnation process using NH4Cl solution, the NH4 contained in the solution + With K + Ion exchange reaction occurs and enters the δ-MnO2 crystal to form MnO2-V O * Precursor 1;

[0016] S2-2, the MnO2-V O * The precursor 1 was centrifuged, washed with deionized water, freeze-dried and ball-milled to obtain powdered MnO2-V O * Precursor II;

[0017] Description: MnO2-V O * Precursor 2 maintains the initial δ-MnO2 crystal form and contains a certain amount of NH4 + , adsorbed water and bound water. Since the temperature window of VOCs catalytic oxidation reaction is 150-300℃, at this temperature, NH4 + , adsorbed water and bound water cannot exist stably. In order to further improve the stability of the catalyst during operation, it is necessary to O * Precursor 2 is calcined to remove adsorbed water and bound water in the catalyst;

[0018] S3. Preparation of MnO2-V O * catalyst;

[0019] The MnO2-V prepared in S2 O *The precursor 2 was heated from room temperature to 300-400°C at a heating rate of 5-10°C / min, kept at this temperature for 2-4h, and then cooled to room temperature to obtain MnO2-V with adjustable oxygen vacancy cluster size and number. O * catalyst.

[0020] Description: MnO2-V O * NH4 contained in Precursor 2 + During the calcination process, it cannot be stably present in the catalyst and escapes. At the same time, due to the K + As the content decreases, a large number of oxygen vacancies are formed in the catalyst based on the charge balance principle, and these oxygen vacancies aggregate into oxygen vacancy clusters under the action of thermodynamics.

[0021] Furthermore, the freeze-drying parameters in S2-2 are: drying temperature of -20 to -10°C, drying time of 10 to 12 hours; the ball milling parameters are: ball milling speed of 200 to 250 r / min, and ball milling time of 20 to 30 minutes.

[0022] As another aspect of the present invention, there is also provided the above-mentioned MnO2-V O * Application of catalyst, the present invention is the MnO2-V O * The catalyst is used for catalytic oxidation of toluene in an environment with a water vapor content of 0 to 5 vol%; at a corresponding temperature T with a toluene conversion rate of 90% 90 As a criterion for evaluating the activity of the catalyst, under the condition of an initial toluene concentration of 1000 ppm, MnO2-V O * T of the catalyst in a dry environment with 0% water vapor content 90 is 231℃; T under humid conditions with a water vapor content of 5 vol% 90 It is 222℃.

[0023] Compared with the existing MnO2 catalyst, the beneficial effects of the present invention are:

[0024] (1) MnO2-V prepared by the present invention O * The catalyst can effectively promote the adsorption and activation of H2O by regulating the number and size of oxygen vacancy clusters, and enhance the electron transfer between H2O molecules and the catalyst, so that the water vapor contained in the VOCs catalytic oxidation intake system can be quickly converted into active hydroxyl groups and participate in the catalytic reaction, thereby converting the H2O molecules that inhibit the progress of the catalytic reaction into components that promote the catalytic reaction of toluene, thereby expanding the application range of the catalyst.

[0025] (2) MnO2-V prepared by the present invention O * Catalyst, specific surface area is 156.3m 2 / g, much higher than the existing MnO2 catalyst (68.3m 2 / g), and the larger specific surface area can effectively promote the contact between the reactant molecules and the catalyst, improve the mass transfer efficiency, and thus accelerate the catalytic reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The MnO2-V prepared by control groups 1-2 in Experimental Example 1 O * Scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the catalyst and the MnO2-M catalyst prepared in the comparative example;

[0027] Figure 2 The MnO2-V prepared by control groups 1-2 in Experimental Example 1 O * X-ray diffraction (XRD) patterns of the MnO2-M catalyst prepared by the catalyst and the comparative example;

[0028] Figure 3 The MnO2-V prepared by control groups 1-2 in Experimental Example 1 O * Electron paramagnetic resonance (EPR) spectra of the catalyst and the MnO2-M catalyst prepared in the comparative example;

[0029] Figure 4 The MnO2-V prepared by control groups 1-2 in Experimental Example 1 O * Comparison curve of the MnO2-M catalyst prepared by the catalyst and the comparative example for catalytic oxidation treatment of toluene under dry and wet conditions. DETAILED DESCRIPTION

[0030] In order to further illustrate the method adopted by the present invention and the effect achieved, the technical solution of the present invention will be clearly and completely described in combination with experiments below.

[0031] Example 1: This example describes a manganese dioxide catalyst regulated by oxygen vacancy clusters.

[0032] The manganese dioxide catalyst regulated by the oxygen vacancy cluster is denoted as MnO2-V O * The catalyst is MnO2-V O *The basic components of the catalyst include: delta-MnO2, oxygen vacancies contained in delta-MnO2, and oxygen vacancy clusters formed in the catalyst after impregnation and calcination with NH4Cl solution; the MnO2-V O * Compared with the MnO2 catalyst with general structure, the catalyst has the following different technical characteristics:

[0033] The MnO2-V prepared by the present invention O * The catalyst is a spherical nanoflower structure with a diameter of 200 to 600 nm, which is formed by the polymerization of nanosheets with a thickness of 10 to 20 nm. Its specific surface area is 94.0 to 156.3 m 2 / g, pore size is 3.6~7.7nm, pore volume is 0.18~0.27cm 3 / g;

[0034] remember Catalyst The meaning of is oxygen vacancy clusters, where * is the content ratio of oxygen vacancy clusters, and the value range of * is 40-60%, and based on the τ2 value, V O * The size range is 430~460ps.

[0035] Example 2: The content of this example is the MnO2-V in Example 1. O * A method for preparing a catalyst.

[0036] S1. Preparation of δ-MnO2;

[0037] Add MnSO4 solution to KMnO4 solution and stir thoroughly until the two are evenly mixed, the stirring rate is 400r / min, and the stirring time is 20min; then react at 160℃ for 12h to obtain δ-MnO2; in the KMnO4 solution, the content of KMnO4 is 1.25g, and the volume of the solution is 30mL; in the MnSO4 solution, the content of MnSO4·4H2O is 0.28g, and the volume of the solution is 30mL;

[0038] S2. Preparation of MnO2-V O * Precursor;

[0039] S2-1, add the δ-MnO2 prepared in S1 to the NH4Cl solution and stir thoroughly until the two are evenly mixed, the stirring rate is 600r / min, and the stirring time is 1h; then react at 25℃ for 4h to obtain MnO2-V O *Precursor 1: In the NH4Cl solution, the amount of NH4Cl added is 0.03 g, the solution volume is 25 mL, and the amount of δ-MnO2 added is 0.8 g;

[0040] S2-2, firstly, MnO2-V O * The precursor was centrifuged until the supernatant was clear, then washed with deionized water until the washing liquid was neutral, then dried at -10 °C for 10 h, and finally ball milled at 200 r / min for 20 min to obtain powdered MnO2-V O * Precursor II;

[0041] S3. Preparation of MnO2-V O * catalyst;

[0042] The MnO2-V prepared in S2 O * The precursor 2 was heated from room temperature to 300°C at a rate of 5°C / min, kept at this temperature for 2h, and then cooled to room temperature to obtain MnO2-V O * catalyst.

[0043] Example 3: The contents of this example are based on Example 2 and are intended to illustrate the effect of MnO2-V on the O * A method for preparing a catalyst.

[0044] S1. Preparation of δ-MnO2;

[0045] Add the MnSO4 solution to the KMnO4 solution and stir thoroughly until the two are evenly mixed, the stirring rate is 500r / min, and the stirring time is 30min; then react at 160℃ for 12h to obtain δ-MnO2; in the KMnO4 solution, the content of KMnO4 is 1.25g, and the volume of the solution is 30mL; in the MnSO4 solution, the content of MnSO4·4H2O is 0.28g, and the volume of the solution is 30mL;

[0046] S2. Preparation of MnO2-V O * Precursor;

[0047] S2-1, add the δ-MnO2 prepared in S1 to the NH4Cl solution and stir thoroughly until the two are evenly mixed, the stirring rate is 700r / min, and the stirring time is 1.5h; then react at 60℃ for 1h to obtain MnO2-V O *Precursor 1: In the NH4Cl solution, the amount of NH4Cl added is 0.10 g, the solution volume is 30 mL, and the amount of δ-MnO2 added is 1.0 g;

[0048] S2-2, firstly, MnO2-V O * The precursor was centrifuged until the supernatant was clear, then washed with deionized water until the washing liquid was neutral, then dried at -20 °C for 12 h, and finally ball milled at 250 r / min for 30 min to obtain powdered MnO2-V O * Precursor II;

[0049] S3. Preparation of MnO2-V O * catalyst;

[0050] The MnO2-V prepared in S2 O * The precursor 2 was heated from room temperature to 400°C at a rate of 5°C / min, kept at this temperature for 4 h, and then cooled to room temperature to obtain MnO2-V O * catalyst.

[0051] Experimental Example 1: The description of this experimental example is based on the content of Example 2, and is intended to illustrate an application of the present invention.

[0052] Experimental design: In order to illustrate the MnO2-V prepared by the present invention O * The catalytic performance of the catalyst for toluene in dry and wet environments, the following experimental groups were designed:

[0053] Blank group: Based on the hydrothermal method, δ-MnO2 was prepared by the in-situ redox reaction of KMnO4 and MnSO4 without using NH4Cl solution for treatment; the obtained product was recorded as MnO2-M;

[0054] Control group 1: The rest of the contents remain unchanged, the content of NH4Cl is 0.045g; the obtained product is recorded as MnO2-V O * 1;

[0055] Control group 2: The rest of the contents remained unchanged, and the content of NH4Cl was 0.134 g; the obtained product was recorded as MnO2-V O * 2;

[0056] The number and size of oxygen vacancy clusters in the catalysts of control group 1, control group 2 and blank group were analyzed by PALS spectroscopy, and the results are shown in Table 1. Among them, τ1 represents isolated oxygen vacancies, τ2 represents oxygen vacancy clusters, and τ3 represents the pore structure between particles in the catalyst. The value of τ2 reflects the size of the oxygen vacancy clusters. The larger the value, the larger the size of the oxygen vacancy clusters; the value of I2 reflects the content of oxygen vacancy clusters. The larger the value, the higher the content of oxygen vacancy clusters. It can be seen that the number and size of oxygen vacancy clusters in the catalyst can be regulated by impregnation with NH4Cl solutions of different concentrations.

[0057] Table 1 Number and size distribution of oxygen vacancy clusters in different catalysts

[0058]

[0059] 0.1 g of catalyst from control group 1, control group 2, and blank group were taken for toluene catalytic oxidation experiment respectively: the catalyst synthesized by the control group and blank group was evaluated by using fixed bed catalyst evaluation device-online gas chromatography, and the specific steps are as follows: 0.1 g of catalyst was accurately weighed and loaded into a quartz tube with an inner diameter of 5 mm, and then placed in a reactor, and the outlet toluene concentration was measured at different temperatures under dry conditions with an initial toluene concentration of 1000 ppm and under humid conditions containing 5 vol% water vapor. The temperature at which the toluene conversion rate is 90% was used as the catalyst activity evaluation standard, and the results are shown in Table 2. In addition, considering the huge difference in the specific surface area of ​​the catalyst in the control group and the blank group, the toluene conversion rate r of the catalyst after normalization of the specific surface area at 230 ° C was calculated. norm .

[0060] Table 2 Catalytic performance of different catalysts for toluene

[0061]

[0062] From Table 1, we can get the T values ​​of control group 1 and control group 2. 90 The MnO2-V prepared in the control group 1 was significantly lower than that in the blank group. O * 1 Catalyst T for toluene under dry and wet conditions 90 231 and 222℃ respectively, and the MnO2-V prepared in control group 2 O * 2 Catalyst T for toluene under dry and wet conditions 90 The T values ​​of the MnO2-M catalyst prepared in the blank group for toluene under dry and wet conditions were 238 and 233 °C, respectively, which were much lower than the T values ​​of the MnO2-M catalyst prepared in the blank group for toluene under dry and wet conditions. 90 (261 and 279 °C). In addition, the toluene conversion rate normalized by specific surface area r normFor comparison, the MnO2-V prepared in control group 1 O * 1 Catalyst r under dry and wet conditions norm 5.14 and 15.04×10 -9 mol·s -1 ·m -2 , which is also higher than that of the MnO2-M catalyst prepared in the blank group, especially the MnO2-V prepared in the control group 1 under humid conditions. O * 1 Catalyst r norm The results further confirm that the oxygen vacancy clusters constructed by the present invention can effectively improve the catalytic oxidation activity of toluene. O * 1 has the largest number of oxygen vacancy clusters (51.84%) and a moderate cluster size (444.5ps), and thus has the best catalytic reaction activity, especially under humid conditions, which can further promote H2O activation and thus promote the catalytic oxidation reaction of toluene.

Claims

1. An oxygen vacancy cluster-regulated manganese dioxide catalyst, denoted as MnO2-V O * Catalyst, the The composition of the catalyst includes delta-MnO2 containing oxygen vacancies as a base component, characterized in that: Said The catalyst composition also includes oxygen vacancy clusters formed after impregnation and calcination in NH4Cl solution; Said The microscopic morphology of the catalyst is a spherical nanoflower structure with a diameter of 200 to 600 nm, which is composed of nanosheets with a thickness of 10 to 20 nm. Its specific surface area is 94.0 to 156.3 m 2 / g, pore size is 3.6~7.7nm, pore volume is 0.18~0.27cm 3 / g; Note Catalyst The meaning of is oxygen vacancy clusters, where * is the content ratio of oxygen vacancy clusters, and the value range of * is 40-60%, and based on the τ2 value of positron annihilation lifetime spectroscopy (PALS) test, V O * The size range is 430~460ps.

2. The method for preparing a manganese dioxide catalyst regulated by oxygen vacancy clusters according to claim 1, characterized in that: The preparation method can convert the interlayer K + Replaced by NH4 + , during the subsequent calcination process, NH4 + The ions escape in the form of NH3. To maintain charge balance, a large number of oxygen vacancies are formed in situ in the catalyst. These oxygen vacancies aggregate under the action of thermodynamics to form oxygen vacancy clusters with adjustable number and size, thereby obtaining MnO2-V O * catalyst.

3. The method for preparing a manganese dioxide catalyst regulated by oxygen vacancy clusters according to claim 2, characterized in that: The following steps are involved: S1, preparation of δ-MnO2; The MnSO4 solution was added to the KMnO4 solution and stirred thoroughly until the two were evenly mixed, and then reacted at 160°C for 12h to obtain δ-MnO2; Let n be the multiplication coefficient and n∈R + , then the content of KMnO4 in KMnO4 solution is 1.25ng, and the volume of the solution is 30nmL; the content of MnSO4·4H2O in MnSO4 solution is 0.28ng, and the volume of the solution is 30n mL; S2. Preparation of MnO2-V O * Precursor; S2-1, add the δ-MnO2 prepared in S1 to the NH4Cl solution and stir thoroughly until the two are evenly mixed, then react at 25-60°C for 4-8h to obtain MnO2-V O * Precursor 1; S2-2, the MnO2-V O * The precursor 1 was centrifuged, washed with deionized water, freeze-dried and ball-milled to obtain powdered MnO2-V O * Precursor II; Let n be the multiplication coefficient and n∈R + , then in S2-1: the amount of NH4Cl added is n[0.01,0.15]g, the volume of the solution is n[20,30]mL, and the amount of δ-MnO2 added is n[0.7,1.0]g; S3. Preparation of MnO2-V O * catalyst; The MnO2-V prepared in S2 O * The precursor 2 was heated from room temperature to 300-400°C at a heating rate of 5-10°C / min, kept at this temperature for 2-4h, and then cooled to room temperature to obtain MnO2-V containing oxygen vacancy clusters. O * catalyst.

4. The manganese dioxide catalyst regulated by oxygen vacancy clusters according to claim 3, characterized in that: In S2-2: The freeze-drying parameters are: drying temperature is -20 to -10°C, and drying time is 10 to 12 hours; The parameters of the ball milling are: a ball milling speed of 200 to 250 r / min, and a ball milling time of 20 to 30 min.

5. The use of a manganese dioxide catalyst regulated by oxygen vacancy clusters as claimed in claim 1, characterized in that: The MnO2-V O * The catalyst is used for catalytic oxidation of toluene in an environment where the water vapor content is 0-5 vol%.

Images