Reticular spherical B-MnO2 catalyst based on B-Ov-Mn active center as well as preparation method and application of reticular spherical B-MnO2 catalyst

Abstract

The invention relates to the technical field of preparation of VOCs catalytic oxidation catalysts, in particular to a reticular spherical B-MnO2 catalyst based on a B-Ov-Mn active center and a preparation method and application of the reticular spherical B-MnO2 catalyst. The B-MnO2 catalyst is prepared from delta-MnO2 serving as a basic component, a B-O-Mn structure formed by doping B into the delta-MnO2, and an asymmetric oxygen vacancy B-Ov-Mn active center formed on the basis of the B-O-Mn structure, compared with the existing MnO2 catalyst, the B-MnO2 catalyst prepared by the preparation method disclosed by the invention is formed by connecting a plurality of nanosheets to form a net-shaped ball, so that the B-MnO2 catalyst has a high specific surface area; moreover, by constructing an asymmetric oxygen vacancy B-Ov-Mn active center, 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 actually discharged VOCs waste gas and water vapor contained in the environment can be quickly converted into active hydroxyl groups and participate in catalytic oxidation reaction, and the catalytic oxidation effect is improved. Therefore, the inhibition effect of H2O molecules in a traditional MnO2 catalyst is converted into the promotion effect, and the MnO2 catalyst has good market competitiveness.

Description

Technical Field

[0001] The invention relates to the technical field of VOCs catalytic oxidation catalyst preparation, and in particular to a net-shaped spherical B-MnO2 catalyst based on a B-Ov-Mn active center, and a preparation method and application thereof. Background Art

[0002] Volatile organic compounds (VOCs) in the air can cause harm to human health, so there is a need to continuously pursue catalysts with higher catalytic efficiency and wider application scenarios.

[0003] Currently, catalysts for VOCs are generally based on heterogeneous catalytic reactions. Their catalytic activity depends not only on the number, distribution and type of their active centers, but also on the specific surface area and pore structure of the catalyst, which also affects the contact efficiency between the active centers of the catalyst and the reactant molecules.

[0004] However, for the above-mentioned catalysts, under high humidity conditions, the water vapor molecules contained in the VOCs catalytic oxidation system are also easily adsorbed on oxygen vacancies, occupying the active centers of the catalyst, hindering the contact between VOCs and the catalyst, thereby causing a decrease in the efficiency of the catalytic oxidation reaction.

[0005] In order to solve the above problems, the present invention intends to design a catalyst that effectively promotes the adsorption and activation of water vapor on the catalyst surface, and transforms "hindering the catalytic process" into "promoting the catalytic process". Summary of the invention

[0006] It is worth noting that the existing articles only reveal the use of metal ions (Co 2+ ,Cu 2+ ,Fe 3+ ,A1 3+ ,Ce 4+ ) There are related technologies for doping δ-MnO2 to change the performance of catalytic oxidation of VOCs under dry conditions (such as the article "Metal ion hydrothermal method for doping δ-MnO2 and its catalytic oxidation performance of chlorobenzene"), but there are no related reports on B-doped δ-MnO2 catalysts and their promotion of VOCs degradation by directional induction of water activation. At the same time, it is considered that actual exhaust gas inevitably contains water vapor, and water vapor usually has an inhibitory effect on δ-MnO2-based catalysts. Based on this, the present invention constructs and utilizes B-Ov-Mn active centers to promote water molecules to adsorb on their surface and dissociate and activate to form active hydroxyl oxygen species and participate in catalytic oxidation reactions, thereby converting the inhibitory effect of H2O molecules in traditional MnO2 catalysts into a promoting effect. At the same time, by directional regulation of the morphology and pore structure of the catalyst, the reactant molecules are promoted to fully contact with the active center, and the catalyst performance is further improved. That is, the present invention is intended to protect a B-MnO2 catalyst based on water activation and morphology engineering and its preparation method and its application in the actual industrial VOCs catalytic oxidation.

[0007] The general structure of the MnO2 catalyst includes δ-MnO2 as a basic component, a metal-O-Mn structure formed by metal doping into δ-MnO2, and an asymmetric oxygen vacancy formed based on the metal-O-Mn structure, i.e., a metal-Ov-Mn active center. The B-MnO2 catalyst prepared by the present invention has the following different technical features compared with the general structure:

[0008] The structure of the minimum catalytic unit of the B-MnO2 catalyst prepared by the present invention includes: δ-MnO2 as a basic component, a BO-Mn structure formed by B ions doped into the δ-MnO2, and an asymmetric oxygen vacancy formed based on the BO-Mn structure, namely, a B-Ov-Mn active center;

[0009] The morphology of the smallest catalytic unit of the B-MnO2 catalyst is a nanosheet with a diameter of 20 to 200 nm, and several nanosheets are connected to form a macroscopic morphology of the B-MnO2 catalyst in the form of a mesh sphere, and the specific surface area of ​​the mesh sphere is 80 to 85 m 2 / g;

[0010] Based on the bonding energy position fitting measurement, the bonding form of the B-Ov-Mn active center in the O1s orbital of the B-MnO2 catalyst accounts for 30% to 60%.

[0011] As another aspect of the present invention, a method for preparing the above-mentioned B-MnO2 catalyst is also provided:

[0012] S1. Preparation of B-MnO2 precursor 1;

[0013] Add (NH4)2B2O7 solution dropwise into KMnO4 solution and continue stirring, then react at 90-120°C for 12-20h to obtain B-MnO2 precursor 1;

[0014] Let n be the multiplication coefficient and n∈R + ,but:

[0015] In the KMnO4 solution, the content of KMnO4 is n[1.26,1.58]g, and the volume of the solution is n[20,30]mL;

[0016] In the (NH4)2B2O7 solution, the content of (NH4)2B2O7·4H2O is n[0.8,1.5]g, and the volume of the solution is n[20,30]mL;

[0017] Description: Using MnO4 in solution - The oxidizing property of NH4 + Due to the reducibility of the solution, MnO2 basic components are generated during the hydrothermal reaction.3+ , the B 3+ During the formation of MnO2, it will enter the MnO2 lattice through the doping effect to form B-MnO2 precursor 1;

[0018] S2, preparing B-MnO2 precursor 2;

[0019] The B-MnO2 precursor prepared in S1 is centrifuged, washed, dried and ground to obtain a powdered B-MnO2 precursor II;

[0020] The operation during centrifugal separation is as follows: centrifuge the B-MnO2 precursor until the liquid and solid phases are separated and the liquid phase is clear;

[0021] The operation during washing is: washing with ultrapure water and anhydrous ethanol alternately until the B-MnO2 precursor 2 is neutral;

[0022] The parameters during drying are: temperature 60-80°C, time 30-40 minutes;

[0023] The operation during the grinding process is as follows: according to the subsequent use requirements, the B-MnO2 precursor 2 after the drying process is ground by a grinder to obtain the B-MnO2 precursor 2 with different particle sizes;

[0024] Description: B-MnO2 precursor II has initially possessed a δ-MnO2 crystal form and contains a large amount of adsorbed water and bound water. Since the temperature window of the VOCs catalytic oxidation reaction is 150-300°C, adsorbed water and bound water cannot exist stably at this temperature. In order to further improve the stability of the catalyst during operation, the B-MnO2 precursor II needs to be calcined to remove the adsorbed water and bound water in the catalyst.

[0025] S3, preparing a mesh spherical B-MnO2 catalyst;

[0026] The B-MnO2 precursor 2 prepared in S2 is heated from room temperature to 300-400°C at a heating rate of 5-10°C / min, kept at this temperature for 2-4 hours, and then cooled to room temperature in the furnace to obtain a mesh spherical B-MnO2 catalyst.

[0027] Note: After calcination, the B-MnO2 catalyst still maintains the δ-MnO2 crystal form, the adsorbed water and bound water have been removed during the heating process, and the stability of the catalyst is enhanced.

[0028] As another aspect of the present invention, the application of the above-mentioned B-MnO2 catalyst is also provided. The present invention uses the B-MnO2 catalyst to catalytically oxidize 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%, 90As a criterion for evaluating the catalyst activity, the T of the B-MnO2 catalyst in a dry environment with a water vapor content of 0 vol% was 90 is 229℃; T under humid conditions with a water vapor content of 5 vol% 90 It is 218℃.

[0029] Compared with the existing MnO2 catalyst for catalyzing toluene, the beneficial effects of the present invention are:

[0030] (1) The mesh spherical B-MnO2 catalyst prepared by the present invention can effectively promote the adsorption and activation of H2O by constructing an asymmetric oxygen vacancy B-Ov-Mn active center, thereby enhancing 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.

[0031] (2) The B-MnO2 catalyst prepared by the present invention has a specific surface area of ​​84.06 m 2 / g, much higher than the existing MnO2 catalyst (43.13m 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

[0032] Figure 1 The electron microscope images of the B-MnO2 catalyst prepared in Example 1, wherein (a) is a scanning electron microscope (SEM) image, and (B) is a transmission electron microscope (TEM) image;

[0033] Figure 2 X-ray diffraction (XRD) patterns of the catalyst prepared in Example 1 and the MnO2 catalyst prepared in the comparative example;

[0034] Figure 3 B1s spectra of X-ray electron spectroscopy (XPS) of the catalyst prepared in Example 1 and the MnO2 catalyst prepared in the comparative example;

[0035] Figure 4 The electron paramagnetic resonance (EPR) spectra of the catalyst prepared in Example 1 and the MnO2 catalyst prepared in the comparative example;

[0036] Figure 5 It is a comparison curve of the catalysts with different B contents prepared in the control groups 1 to 3 in Experimental Example 1 and the MnO2 catalyst prepared in the comparative example for catalytic oxidation of toluene under dry and wet conditions;

[0037] Figure 6 Schematic diagram of the working principle of the B-MnO2 catalyst prepared in Example 1. DETAILED DESCRIPTION

[0038] 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.

[0039] Example 1: This example describes a mesh-shaped spherical B-MnO2 catalyst based on a B-Ov-Mn active center.

[0040] The structure of the smallest catalytic unit of the B-MnO2 catalyst is: δ-MnO2 as the basic component, B doped into δ-MnO2 to form a BO-Mn structure, and an asymmetric oxygen vacancy formed based on the BO-Mn structure, namely, a B-Ov-Mn active center.

[0041] See also Figure 1 In this embodiment, the morphology of the smallest catalytic unit of the B-MnO2 catalyst is a nanosheet with a diameter of 20 to 100 nm, and a number of nanosheets are connected to form a macroscopic morphology of the B-MnO2 catalyst in the form of a mesh ball, and the specific surface area of ​​the mesh ball is 83 to 85 m 2 / g;

[0042] Based on the bonding energy position fitting measurement, the bonding form of the B-Ov-Mn active center in the O1s orbital of the B-MnO2 catalyst accounts for 60%.

[0043] Example 2: This example describes the performance data of another group of mesh spherical B-MnO2 catalysts.

[0044] The structure of the B-MnO2 catalyst is: δ-MnO2 as a basic component, a BO-Mn structure formed by B doping into δ-MnO2, and an asymmetric oxygen vacancy B-Ov-Mn active center formed based on the BO-Mn structure;

[0045] The morphology of the smallest catalytic unit of the B-MnO2 catalyst in this embodiment is a nanosheet with a diameter of 100 to 200 nm, and a number of nanosheets are connected to form a macroscopic morphology of the B-MnO2 catalyst in the form of a mesh ball, and the specific surface area of ​​the mesh ball is 80 to 83 m 2 / g;

[0046] Based on the bonding energy position fitting determination, the bonding form of the B-Ov-Mn active center in the O1s orbital of the B-MnO2 catalyst accounts for 30%;

[0047] Example 3: This example describes the preparation method of the B-MnO2 catalyst in Example 1.

[0048] S1. Preparation of B-MnO2 precursor 1;

[0049] The (NH4)2B2O7 solution was added dropwise into the KMnO4 solution with continuous stirring, and then reacted at 90°C for 12h to obtain B-MnO2 precursor 1;

[0050] In the KMnO4 solution, the content of KMnO4 is 1.26 g and the volume of the solution is 20 mL;

[0051] In the (NH4)2B2O7 solution, the content of (NH4)2B2O7·4H2O is 0.8 g, and the volume of the solution is 20 mL;

[0052] S2, preparing B-MnO2 precursor 2;

[0053] The B-MnO2 precursor prepared in S1 is centrifuged, washed, dried and ground to obtain a powdered B-MnO2 precursor II;

[0054] The operation during centrifugal separation is as follows: centrifuge the B-MnO2 precursor until the liquid and solid phases are separated and the liquid phase is clear;

[0055] The operation during washing is: washing with ultrapure water and anhydrous ethanol alternately until the B-MnO2 precursor 2 is neutral;

[0056] The parameters during drying are: temperature 60°C, time 30 min;

[0057] The operation during the grinding process is as follows: using a grinder to grind the dried B-MnO2 precursor 2 to obtain a B-MnO2 precursor 2 with a particle size of 2 to 3 μm;

[0058] S3, preparing a mesh spherical B-MnO2 catalyst;

[0059] The B-MnO2 precursor 2 prepared in S2 was heated from 25°C to 300°C at a heating rate of 5°C / min, kept warm for 2h, and then cooled to room temperature in the furnace to obtain a mesh spherical B-MnO2 catalyst.

[0060] Example 4: The content of this example is based on Example 3 and is intended to illustrate the preparation method of B-MnO2 catalyst under another parameter.

[0061] S1. Preparation of B-MnO2 precursor 1;

[0062] The (NH4)2B2O7 solution was added dropwise into the KMnO4 solution with continuous stirring, and then reacted at 120°C for 20 h to obtain B-MnO2 precursor 1;

[0063] In the KMnO4 solution, the content of KMnO4 is 1.58 g and the volume of the solution is 20 mL;

[0064] In the (NH4)2B2O7 solution, the content of (NH4)2B2O7·4H2O is 1.5 g, and the volume of the solution is 30 mL;

[0065] S2, preparing B-MnO2 precursor 2;

[0066] The B-MnO2 precursor prepared in S1 is centrifuged, washed, dried and ground to obtain a powdered B-MnO2 precursor II;

[0067] The operation during centrifugal separation is as follows: centrifuge the B-MnO2 precursor until the liquid and solid phases are separated and the liquid phase is clear;

[0068] The operation during washing is: washing with ultrapure water and anhydrous ethanol alternately until the B-MnO2 precursor 2 is neutral;

[0069] The parameters during drying are: temperature 80°C, time 40 min;

[0070] The operation during the grinding process is as follows: using a grinder to grind the dried B-MnO2 precursor 2 to obtain a B-MnO2 precursor 2 with a particle size of 3 to 4 μm;

[0071] S3, preparing a mesh spherical B-MnO2 catalyst;

[0072] The B-MnO2 precursor 2 prepared in S2 was heated from room temperature to 400°C at a heating rate of 10°C / min, kept warm for 4 hours, and then cooled to room temperature in the furnace to obtain a mesh spherical B-MnO2 catalyst.

[0073] Experimental Example 1: The description of this experimental example is based on the content of Example 3, and is intended to illustrate an application of the present invention.

[0074] Experimental design: In order to illustrate the catalytic performance of the B-MnO2 catalyst prepared by the present invention on toluene in a humid environment, the following experimental groups were designed:

[0075] Blank group: MnO2 was prepared by in-situ redox reaction of KMnO4 and MnSO4 based on the hydrothermal method;

[0076] Control group 1: The rest of the contents remain unchanged, and the content of (NH4)2B2O7·4H2O is 0.8g;

[0077] Control group 2: The rest of the contents remain unchanged, and the content of (NH4)2B2O7·4H2O is 1.0g;

[0078] Control group 3: The rest of the contents remain unchanged, and the content of (NH4)2B2O7·4H2O is 1.5g;

[0079] 0.1 g of catalyst from control group 1, control group 2, control group 3 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 1. In addition, considering the huge difference in the specific surface area of ​​the catalysts in control group 1 and the blank group, the toluene conversion rate r of the two catalysts after normalization of the specific surface area at 215 °C was calculated. nor .

[0080] Table 1 Catalytic performance of different catalysts for toluene

[0081]

[0082] From Table 1, we can get the T values ​​of control group 1, control group 2 and control group 3. 90 The T values ​​of the B-MnO2 catalyst prepared in the control group 1 for toluene under dry and wet conditions were significantly lower than those of the blank group. 90 229 and 218℃ respectively, and the B prepared in control group 2 0.8 T of toluene over MnO2 catalyst under dry and wet conditions 90 223 and 220℃, respectively. 1.5 T of toluene over MnO2 catalyst under dry and wet conditions 90 The T values ​​of the MnO2 catalyst prepared in the blank group for toluene under dry and wet conditions were 231 and 218 °C, respectively, which were much lower than the T values ​​of the MnO2 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 nor For comparison, the r of the B-MnO2 catalyst prepared in control group 1 under dry and wet conditions nor 3.27 and 7.64×10 -9 mol·s -1 ·m -2, which is also higher than that of the MnO2 catalyst prepared in the blank group, especially the B-MnO2 catalyst prepared in the control group 1 under humid conditions. nor These results further confirm that the asymmetric oxygen vacancy B-Ov-Mn active center constructed by the present invention can effectively improve the catalytic oxidation activity of toluene, especially under humid conditions, it can further promote H2O activation, thereby promoting the catalytic oxidation reaction of toluene.

Claims

1. A mesh-shaped spherical B-MnO based on B-Ov-Mn active center 2 catalyst, It is characterized in that The B-MnO 2 The structure of the smallest catalytic unit of the catalyst includes: δ-MnO as the basic component 2 , B ions are doped into δ-MnO 2 The BO-Mn structure formed in the reaction chamber, and the asymmetric oxygen vacancies formed based on the BO-Mn structure, namely the B-Ov-Mn active center; The B-MnO 2 The smallest catalytic unit of the catalyst is a nanosheet with a diameter of 20 to 200 nm, and several of the nanosheets are connected to form B-MnO 2 The catalyst has a macroscopic morphology of a mesh ball, and the specific surface area of ​​the mesh ball is 80 to 85 m 2 / g; Based on the bonding energy position fitting determination, the B-MnO 2 The bonding form of the B-Ov-Mn active center in the O1s orbital of the catalyst accounts for 30% to 60%.

2. A mesh ball type B-MnO based on B-Ov-Mn active center as claimed in claim 1 2 catalyst, It is characterized in that The B-MnO 2 The preparation method of the catalyst is: S1. Preparation of B-MnO 2 Precursor 1; (NH 4 ) 2 B 2 O 7 Add KMnO dropwise to the solution 4 The solution was stirred continuously, and then reacted at 90-120°C for 12-20h to obtain B-MnO 2 Precursor 1; Let n be the multiplication coefficient and n∈R + ,but: KMnO 4 In solution, KMnO 4 The content is n[1.26,1.58]g, and the volume of the solution is n[20,30]mL; (NH 4 ) 2 B 2 O 7 In solution, (NH 4 ) 2 B 2 O 7 ·4H 2 The content of O is n[0.8,1.5]g, and the volume of the solution is n[20,30]mL; S2. Preparation of B-MnO 2 Precursor II; The B-MnO prepared in S1 2 The precursor was centrifuged, washed, dried and ground to obtain powdered B-MnO 2 Precursor II; S3. Preparation of mesh spherical B-MnO 2 catalyst; The B-MnO prepared in S2 2 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 2-4 hours, and then cooled to room temperature to obtain a mesh-shaped spherical B-MnO 2 catalyst.

3. A mesh ball type B-MnO based on B-Ov-Mn active center as claimed in claim 1 2 Application of catalysts, It is characterized in that The B-MnO 2 The catalyst is used for catalytic oxidation of toluene in an environment where the water vapor content is 0-5 vol%.

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