Manganese dioxide catalysts regulated by oxygen vacancy clusters, preparation method and application thereof

Abstract

The application relates to the technical field of VOCs catalytic oxidation catalyst preparation, in particular to a manganese dioxide catalyst with oxygen vacancy cluster regulation and a preparation method and application thereof. O * The composition of the catalyst comprises delta-MnO2 with oxygen vacancies as a basic component, and oxygen vacancy clusters formed in the catalyst after calcination by impregnation with an NH4Cl solution; compared with existing MnO2 catalysts, the MnO2-V O * The micro-morphology of the catalyst is a spherical nanoflower structure formed by polymerization of nanosheets, so that the catalyst has a high specific surface area; moreover, by regulating the number and size of the oxygen vacancy clusters, the catalyst can effectively promote the adsorption and activation of H2O, enhance the electron transfer between H2O molecules and the catalyst, make the water vapor contained in the actual emission VOCs waste gas rapidly converted into active hydroxyl and participate in the catalytic oxidation reaction, and thus convert the inhibiting effect of H2O molecules in the traditional MnO2 catalyst into a promoting effect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of VOCs catalytic oxidation catalyst preparation, and particularly relates to a manganese dioxide catalyst based on oxygen vacancy cluster regulation and a preparation method and application thereof. BACKGROUND

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

[0003] In order to cope with the negative effects of water vapor, researchers have tried to improve the physical and chemical properties of the catalyst to reduce its inhibition of catalytic activity. For example, some studies focus on the development of hydrophobic catalysts to reduce the adsorption of water vapor. However, this method can reduce the competitive adsorption of water vapor, but often sacrifices the adsorption capacity and reaction activity of the catalyst for VOCs. Other studies attempt to increase the number of oxygen vacancies or surface oxygen activity of the catalyst to improve its resistance to water vapor interference, but the effect of these improvement methods is still limited, especially in terms of 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 determining its catalytic performance. High specific surface area not only provides more active sites, effectively improving the adsorption capacity of reactant molecules, but also improves the rate of catalytic oxidation reaction.

[0004] Therefore, how to improve the specific surface area of the catalyst while effectively regulating its surface properties, especially how to reasonably utilize water vapor and convert it into an element that is helpful to the catalytic reaction, has become an important research direction for improving the catalytic oxidation performance of VOCs. In view of this problem, the present application aims to design a method for effectively promoting the adsorption and activation of water vapor on the catalyst surface, and to convert the "obstruction of the catalytic process" of water vapor into "promotion of the catalytic process". SUMMARY

[0005] In order to achieve the above purpose, the present application designs a manganese dioxide catalyst with oxygen vacancy cluster regulation, denoted as MnO2-V O * Catalyst. In this scheme, K + part of the interlayer of δ-MnO2 is replaced by NH4+ And promotes NH4 during the subsequent calcination process. + Ion escape, due to interlayer K + As the ion content decreases, a large number of oxygen vacancies are generated in the catalyst to maintain charge balance. These oxygen vacancies aggregate under thermodynamic effects to form oxygen vacancy clusters with adjustable number and size. The MnO2-V prepared in this invention... O * Compared to conventional MnO2 catalysts, this catalyst has the following distinct technical characteristics:

[0006] The MnO2-V prepared in this invention O * The catalyst exhibits a microstructure consisting of spherical nanoflower-like structures with diameters ranging from 200 to 600 nm, formed by the polymerization of nanosheets with a thickness of 10–20 nm, and a specific surface area of ​​94.0–156.3 m². 2 / g, pore size 3.6–7.7 nm, pore volume 0.18–0.27 cm³ 3 / g;

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

[0008] As another aspect of the present invention, the above-mentioned MnO2-V is also provided. O * Catalyst preparation methods:

[0009] S1. Preparation of δ-MnO2;

[0010] MnSO4 solution was added to KMnO4 solution and stirred thoroughly until the two were mixed evenly. Then the mixture was reacted at 160℃ for 12 h to obtain δ-MnO2.

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

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

[0013] S2-1, adding the δ-MnO2 prepared in S1 into NH4Cl solution and stirring thoroughly until the two are mixed uniformly, then reacting at 25-60℃ for 4-8h to obtain MnO2-V O * Precursor one;

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

[0015] Description: δ-MnO2 is a two-dimensional planar structure composed of manganese-oxygen octahedron (MnO6), with a large amount of K + + distributed between the layers. + During the process of impregnation with NH4Cl solution, NH4 + + in the solution undergoes ion exchange reaction with K O + in the crystal of δ-MnO2 and enters the crystal to form MnO2-V * O Precursor one;

[0016] S2-2, adding the MnO2-V * O Precursor one is subjected to centrifugal separation, deionized water washing, freeze-drying and ball milling in sequence to obtain powder-like MnO2-V * O Precursor two;

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

[0018] S3, preparing MnO2-V * O Catalyst;

[0019] S2-2, adding the MnO2-V *The precursor two is heated from room temperature to 300-400℃ at a temperature increasing rate of 5-10℃ / min, and is kept for 2-4h, and then is cooled to room temperature in the furnace to obtain the MnO2-V with adjustable size and quantity of oxygen vacancy clusters O * Catalyst.

[0020] Description: MnO2-V O * NH4 + In the calcination process, the NH4 + contained in the precursor two cannot exist stably in the catalyst and escapes, and due to the decrease of the content of K

[0021] Further, the parameters of freeze-drying in S2-2 are as follows: the drying temperature is-20--10℃, and the drying time is 10-12h; and the parameters of ball milling are as follows: the ball milling speed is 200-250r / min, and the ball milling time is 20-30min.

[0022] As another aspect of the present application, the above-mentioned MnO2-V O * catalyst is also provided. O * The MnO2-V 90 catalyst is used for catalyzing the oxidation of toluene in an environment with a water vapor content of 0-5vol%; the T O * of the catalyst in a dry environment with a water vapor content of 0% is 231℃; and the T 90 of the catalyst in a humid environment with a water vapor content of 5vol% is 222℃. 90

[0023] Compared with the existing MnO2 catalyst, the present application has the following beneficial effects:

[0024] (1) The MnO2-V O * catalyst prepared by the present application can effectively promote the adsorption and activation of H2O by adjusting the quantity and size of oxygen vacancy clusters, and the electronic transfer between H2O molecules and the catalyst is enhanced, so that the water vapor contained in the VOCs catalytic oxidation inlet system can be quickly converted into active hydroxyl and participate in the catalytic reaction, thereby converting the H2O molecules which inhibit the catalytic reaction process into components which promote the catalytic reaction of toluene, and further expanding the application range of the catalyst.

[0025] ​(2) The MnO2-V O * The catalyst has a specific surface area of 156.3 m 2 / g, which is much higher than that of the existing MnO2 catalyst (68.3 m 2 / g). The large 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 DRAWINGS

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

[0027] Figure 2 The MnO2-V O * X-ray diffraction (XRD) spectrum of the MnO2-M catalyst prepared in the comparative example and the MnO2-V

[0028] Figure 3 The MnO2-V O * Electron paramagnetic resonance (EPR) spectrum of the MnO2-M catalyst prepared in the comparative example and the MnO2-V

[0029] Figure 4 The MnO2-V O * Comparison curves of the MnO2-M catalyst prepared in the comparative example and the MnO2-V DETAILED DESCRIPTION

[0030] To further illustrate the manner of carrying out the application and to further substantiate the effects achieved by the application, the technical solutions of the application will be described in detail below with reference to experiments.

[0031] Example 1: The content described in this example is a manganese dioxide catalyst regulated by oxygen vacancy clusters.

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

[0033] The MnO2-V prepared in this invention O * The catalyst is a spherical nanoflower-like structure with a diameter of 200–600 nm, formed by the polymerization of nanosheets with a thickness of 10–20 nm, and has a specific surface area of ​​94.0–156.3 m². 2 / g, pore size 3.6–7.7 nm, pore volume 0.18–0.27 cm³ 3 / g;

[0034] remember In catalyst The meaning is oxygen vacancy clusters, where * represents the content percentage of oxygen vacancy clusters. The value of * ranges from 40% to 60%, and is expressed based on the τ² value. O * The size range is 430 to 460 ps.

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

[0036] S1. Preparation of δ-MnO2;

[0037] MnSO4 solution was added to KMnO4 solution and stirred thoroughly until the two were homogeneous at a stirring rate of 400 r / min for 20 min. The mixture was then reacted at 160 °C for 12 h to obtain δ-MnO2. The KMnO4 solution contained 1.25 g of KMnO4 and had a volume of 30 mL. The MnSO4 solution contained 0.28 g of MnSO4·4H2O and had a volume of 30 mL.

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

[0039] S2-1. Add the δ-MnO2 obtained in S1 to the NH4Cl solution and stir thoroughly until the two are evenly mixed. The stirring rate is 600 r / min and the stirring time is 1 h. Then react at 25 °C for 4 h to obtain MnO2-V. O *The precursor one is centrifuged to clarify the supernatant, then washed with deionized water until the washing liquid is neutral, then dried at -10℃ for 10h, and finally ball-milled at a rotation speed of 200r / min for 20min to obtain the powder-like MnO2-V

[0040] S2-2, first, the MnO2-V O * The precursor one is centrifuged to clarify the supernatant, then washed with deionized water until the washing liquid is neutral, then dried at -10℃ for 10h, and finally ball-milled at a rotation speed of 200r / min for 20min to obtain the powder-like MnO2-V O * The precursor two;

[0041] S3, preparation of MnO2-V O * The catalyst;

[0042] The MnO2-V prepared in S2 is added into the NH4Cl solution and stirred thoroughly until the two are uniformly mixed, the stirring rate is 700r / min, and the stirring time is 1.5h; then reacted at 60℃ for 1h to obtain the MnO2-V O * The precursor two is heated from room temperature to 300℃ at a heating rate of 5℃ / min, and kept for 2h, and then cooled to room temperature in the furnace to obtain the MnO2-V O * The catalyst.

[0043] Example 3: The content described in this example is based on Example 2, and is intended to illustrate the MnO2-V O * The preparation method of the catalyst.

[0044] S1, preparation of δ-MnO2;

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

[0046] S2, preparation of MnO2-V O * The precursor;

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

[0048] S2-2, first, MnO2-V O * The precursor one is centrifuged to clarify the supernatant, then washed with deionized water until the washing liquid is neutral, then dried at-20℃ for 12 h, and finally ball-milled at a rotation speed of 250 r / min for 30 min to obtain the powder-like MnO2-V O * Precursor two;

[0049] S3, preparation of MnO2-V O * Catalyst;

[0050] The MnO2-V prepared in S2 is used as the catalyst O * The precursor two is heated from room temperature to 400℃ at a heating rate of 5℃ / min, and kept for 4 h, and then cooled to room temperature in the furnace to obtain MnO2-V O * Catalyst.

[0051] Experimental example 1, the description of this experimental example is based on the content in example 2, and aims to illustrate an application of the present application.

[0052] Experimental design: in order to illustrate the MnO2-V prepared in the present application O * Catalytic performance of the catalyst in dry and humid environments on toluene, the following experimental groups are designed:

[0053] Blank group: based on the hydrothermal method, δ-MnO2 is prepared through in-situ oxidation-reduction reaction of KMnO4 and MnSO4, and no NH4Cl solution is used for treatment; the prepared product is recorded as MnO2-M;

[0054] Control group 1: the remaining contents are unchanged, and the content of NH4Cl is 0.045 g; the prepared product is recorded as MnO2-V O * 1;

[0055] Control group 2: the remaining contents are unchanged, and the content of NH4Cl is 0.134 g; the prepared product is recorded as MnO2-V O * 2;

[0056] The number and size of oxygen vacancy clusters in the catalysts of the control group 1, the control group 2 and the blank group were analyzed by PALS spectrum, 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 the particles in the catalyst. The value of τ2 reflects the size of the oxygen vacancy cluster, and the larger the value, the larger the size of the oxygen vacancy cluster; the value of I2 reflects the content of the oxygen vacancy cluster, and the larger the value, the higher the content of the oxygen vacancy cluster. It can be seen that the use of different concentrations of NH4Cl solution for impregnation can control the number and size of oxygen vacancy clusters in the catalyst.

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

[0058]

[0059] 0.1 g of the catalysts of the control group 1, the control group 2 and the blank group were respectively taken for toluene catalytic oxidation experiment: the catalysts synthesized by the control group and the blank group were evaluated by using a fixed bed catalyst evaluation device-online gas chromatograph, and the specific steps were 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 reaction furnace, and the outlet toluene concentration at different temperatures was measured under dry conditions with an initial toluene concentration of 1000 ppm and humid conditions with 5 vol% water vapor. The temperature at which the toluene conversion rate was 90% was taken as the standard for evaluating the activity of the catalyst, and the results are shown in Table 2. In addition, considering the great difference in specific surface area between the catalysts of the control group and the blank group, the specific surface area normalized toluene conversion rate r norm .

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

[0061]

[0062] From Table 1, it can be seen that the T 90 of the control group 1 and the control group 2 MnO2-V O * 1 catalysts for toluene under dry and humid conditions 90 were 231 and 222℃ respectively, and the MnO2-V O * 2 catalysts prepared in the control group 2 for toluene under dry and humid conditions 90 were 238 and 233℃ respectively, which were much lower than the T 90 (261 and 279℃) of the MnO2-M catalyst prepared in the blank group for toluene under dry and humid conditions. In addition, by comparing the specific surface area normalized toluene conversion rate r normComparatively, the MnO2-V prepared in the control group 1 O * 1 r of the catalysts under dry and humid conditions norm 5.14 and 15.04 x 10 -9 mol s -1 m -2 , also higher than the MnO2-M catalyst prepared in the blank group, especially under humid conditions, the MnO2-V O * 1 r of the catalysts norm 6.8 times of the MnO2-M catalyst prepared in the blank group. These results further confirm that the oxygen vacancy clusters constructed by the present application can effectively improve the catalytic oxidation activity of toluene. Among them, the catalyst MnO2-V O * 1 has the most number of oxygen vacancy clusters (51.84%) and moderate cluster size (444.5 ps), thus having the best catalytic reaction activity, especially under humid conditions, which can further promote the activation of H2O, thereby promoting the catalytic oxidation reaction of toluene.

Claims

1. An oxygen vacancy cluster regulated manganese dioxide catalyst, denoted as MnO2- δ catalyst, the composition of the MnO2- δ catalyst comprises δ-MnO2 containing oxygen vacancies as a base component, characterized in that: The MnO2- The catalyst composition further comprises oxygen vacancy clusters formed after calcination after impregnation with NH4Cl solution; The MnO2- The micro-morphology of the catalyst is a spherical nanoflower structure with a diameter of 200-600 nm, which is aggregated by nanosheets with a thickness of 10-20 nm, and has a specific surface area of 94.0-156.3 m 2 / g, a pore size of 3.6-7.7 nm, and a pore volume of 0.18-0.27 cm 3 / g. MnO2- in the catalyst means oxygen vacancy clusters, wherein * is the content ratio of the oxygen vacancy clusters, the value of * is 40-60%, and the τ2 value based on positron annihilation lifetime spectroscopy (PALS) test represents, the size range is 430-460 ps.

2. The method for preparing an oxygen vacancy cluster regulated manganese dioxide catalyst according to claim 1, characterized in that, The preparation method can replace K + with NH4 + In the subsequent calcination process, NH4 + ions escape in the form of NH3, and a large number of oxygen vacancies are formed in situ in the catalyst to maintain charge balance. Under the action of thermodynamics, the oxygen vacancies aggregate to form oxygen vacancy clusters with adjustable number and size, and then MnO2- catalyst; the specific steps include: S1, preparing δ-MnO2; The MnSO4 solution is added into the KMnO4 solution and stirred sufficiently until the two are mixed uniformly, and then reacted at 160 ℃ for 12 h to obtain δ-MnO2; Let n be the multiple coefficient and In the KMn04 solution, the content of KMn04 is 1.25n g, and the volume of the solution is 30n mL; in the MnS04 solution, the content of MnS04·4H20 is 0.28n g, and the volume of the solution is 30n mL. S2, preparing Mn02- precursor; S2-1, adding the δ-MnO2 prepared in S1 into the NH4Cl solution and stirring thoroughly until the two are mixed uniformly, and then reacting at 25-60°C for 4-8 h to obtain MnO2- precursor one; S2-2, the MnO2- The precursor one is sequentially subjected to centrifugal separation, deionized water washing, freeze drying and ball milling treatment to obtain the powder-like MnO2- The precursor two; Let n be the magnification coefficient and 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, preparing Mn02 catalyst; The MnO2 prepared in S2 is cooled to room temperature The precursor two is heated from room temperature to 300-400℃ at a temperature increasing rate of 5-10℃ / min, and kept for 2-4 h, and then cooled to room temperature in the furnace to obtain the MnO2 containing oxygen vacancy clusters Catalyst.

3. The method for preparing a manganese dioxide catalyst regulated by oxygen vacancy clusters as described in claim 2, characterized in that, S2-2: The parameters of the freeze-drying are as follows: the drying temperature is -20~ -10 ℃, and the drying time is 10~12 h; The parameters of the ball milling are as follows: the ball milling rotating speed is 200~250 r / min, and the ball milling time is 20~30 min.

4. Use of an oxygen vacancy cluster regulated manganese dioxide catalyst according to claim 1, characterized in that, The MnO2- The catalyst was used for catalytic oxidation of toluene in the presence of water vapor content of 0-5 vol%.

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