Water-resistant polycrystalline manganese oxide catalyst as well as preparation method and application thereof

Abstract

The invention discloses a water-resistant polycrystalline manganese oxide catalyst as well as a preparation method and application thereof in catalyzing ozone oxidation to remove dimethyl sulfide. The preparation method comprises the following steps: 1) adopting any one of methods 1-3, wherein the method 1 comprises the following steps: adding potassium hydroxide and divalent manganese salt into an aqueous dispersion of delta-MnO2, and stirring for a period of time at the temperature of 40-60 DEG C; the method II comprises the following steps: adding inorganic acid into the aqueous dispersion of delta-MnO2, and stirring for a period of time at 40-60 DEG C; a third method comprises the following steps: firstly adding potassium hydroxide and divalent manganese salt into the aqueous dispersion of delta-MnO2, stirring for a period of time at 40-60 DEG C, then adding inorganic acid, and continuously stirring for a period of time at 40-60 DEG C; and 2) carrying out solid-liquid separation on the mixed solution obtained in the step 1), washing and drying the solid to obtain the water-resistant polycrystalline manganese oxide catalyst. The catalyst provided by the invention has a polycrystalline manganese oxide in which alpha and delta crystal forms coexist, and an interface structure at the boundary of the alpha crystal form manganese oxide and the delta crystal form manganese oxide.

Description

Technical Field

[0001] The present invention relates to the field of catalytic technology, and particularly relates to a water-resistant polycrystalline manganese oxide (MnO x ) catalyst, a preparation method thereof, and an application for catalytic ozonation to remove dimethyl sulfide. Background Art

[0002] Dimethyl sulfide (DMS) is a common sulfur-containing organic odorant, which widely exists in the exhaust gases discharged from industries such as agriculture and animal husbandry, municipal administration, and chemical industry. It has a very low odor threshold and poses a threat to human health. Ozone molecules have strong electrophilicity and are extremely likely to attack sulfur-containing groups rich in electrons.

[0003] The catalytic ozonation technology can further activate ozone through a catalyst to generate active free radicals, and can achieve efficient removal of sulfur-containing organic odors. Among them, manganese oxide catalysts have received extensive research and attention due to their low cost, rich defects, diverse crystal structures, etc. However, the oxygen vacancies in the MnO x catalyst are easily occupied by H2O as active sites and deactivated. Therefore, developing a water-resistant MnO x catalyst is of great significance for its practical application.

[0004] Existing strategies for improving the water resistance of MnO x mainly include element doping, surface treatment, hydrophobic material composite, etc., in order to reduce the affinity between oxygen vacancies and H2O. For example, patent application CN117504856A discloses a Bi-doped α-MnO2 for catalytic ozonation to remove VOCs, which can improve the water resistance under water vapor conditions. Another example is that patent application CN118161975A discloses a catalyst Mn@ZSM293-I with manganese loaded on confined zeolite, which is used to improve the performance of catalytic ozonation to remove methanethiol under water vapor conditions. However, these improvement strategies have problems such as complex preparation conditions, high cost, and easy deactivation of the catalyst. Summary of the Invention

[0005] The present invention provides a water-resistant polycrystalline manganese oxide catalyst, a preparation method thereof, and an application. Based on the in-situ L-T (layered-tunnel) transformation that easily occurs in layered manganese oxide δ-MnO2 in natural water bodies, the present invention synthesizes polycrystalline MnO x simultaneously having δ and α crystal forms through a simple solution chemistry method. The rich α-δ interface structure therein promotes the adsorption and dissociation of H2O on oxygen vacancies, induces the generation of active hydroxyl sites, which act as the activation sites of O3, thereby improving the catalytic ozonation performance under the condition of the presence of water vapor. The present invention proposes to construct polycrystalline MnO xThe strategy to improve the performance of catalytic ozonation for the removal of methyl mercaptan under humid conditions. The in-situ L-T (layered-tunnel) transformation synthesis method is applicable to the existing δ-MnO2 catalyst, with advantages such as low cost, mild conditions, and convenient popularization and application.

[0006] [1] A preparation method of a water-resistant polycrystalline manganese oxide catalyst, including the steps:

[0007] (1) Use any one of the following methods 1 to 3:

[0008] Method 1: Add potassium hydroxide and divalent manganese salt to the aqueous dispersion of δ-MnO2, and stir at 40-60 °C for a period of time;

[0009] Method 2: Add inorganic acid to the aqueous dispersion of δ-MnO2, and stir at 40-60 °C for a period of time;

[0010] Method 3: First add potassium hydroxide and divalent manganese salt to the aqueous dispersion of δ-MnO2, stir at 40-60 °C for a period of time, then add inorganic acid, and continue to stir at 40-60 °C for a period of time;

[0011] (2) Separate the solid-liquid of the mixed solution obtained in step (1), take the solid, wash and dry it to obtain the water-resistant polycrystalline manganese oxide catalyst;

[0012] The water-resistant polycrystalline manganese oxide catalyst has a polycrystalline manganese oxide with coexisting α-crystalline form and δ-crystalline form, and an interfacial structure at the junction of α-crystalline manganese oxide and δ-crystalline manganese oxide.

[0013] In some embodiments, the δ-MnO2 has a flower-like morphology structure, and the α-crystalline manganese oxide has a rod-like morphology structure.

[0014] In some embodiments, the δ-MnO2 can be prepared by a hydrothermal method. For example, the preparation method of the δ-MnO2 may include: performing a hydrothermal reaction on a mixed solution of potassium permanganate and divalent manganese salt, and after the reaction, taking the solid, washing and drying it to obtain the δ-MnO2.

[0015] In the preparation method of the δ-MnO2, the molar ratio of potassium permanganate to the divalent manganese salt can be 5.5-6:1, such as 5.8:1, etc.

[0016] In the preparation method of the δ-MnO2, the divalent manganese salt may include at least one of manganese sulfate, manganese chloride, manganese nitrate, and manganese acetate.

[0017] In the preparation method of the δ-MnO2, the temperature of the hydrothermal reaction can be 160-200 °C.

[0018] In the preparation method of the δ-MnO2, the hydrothermal reaction time can be 24 to 28 hours.

[0019] In some embodiments, in the preparation methods of the water-resistant polycrystalline manganese oxide catalyst, namely Method 1 and Method 3, the divalent manganese salts can each independently include at least one of manganese sulfate, manganese chloride, manganese nitrate, and manganese acetate.

[0020] In some embodiments, in the preparation methods of the water-resistant polycrystalline manganese oxide catalyst, namely Method 2 and Method 3, the inorganic acids can each independently include at least one of sulfuric acid, hydrochloric acid, and nitric acid, and preferably sulfuric acid, which is beneficial to improving the water resistance and catalytic activity of the catalyst.

[0021] In some embodiments, in the preparation methods of the water-resistant polycrystalline manganese oxide catalyst, namely Method 1 and Method 3, potassium hydroxide can be added respectively and independently according to the molar ratio to the mass ratio of δ-MnO2 of 0.05 - 0.2 mmol:2 g (for example, 0.1 mmol:2 g), and the divalent manganese salt can be added respectively and independently according to the molar ratio to the mass ratio of δ-MnO2 of 0.005 - 0.02 mol:2 g (for example, 0.01 mol:2 g). + 2+

[0022] In some embodiments, in the preparation methods of the water-resistant polycrystalline manganese oxide catalyst, namely Method 2 and Method 3, the inorganic acid can be added respectively and independently according to the mass ratio of inorganic acid to δ-MnO2 of 1 - 5:1, preferably 2 - 5:1.

[0023] In some embodiments, in the preparation methods of the water-resistant polycrystalline manganese oxide catalyst, namely Method 1 and Method 2, the stirring time at 40 - 60 °C can be respectively and independently 4 - 6 hours.

[0024] In some embodiments, in the preparation method of the water-resistant polycrystalline manganese oxide catalyst, namely Method 3, after adding potassium hydroxide and the divalent manganese salt, it can be stirred at 40 - 60 °C for 2 - 4 hours, and after adding the inorganic acid, it can continue to be stirred at 40 - 60 °C for 2 - 4 hours.

[0025] In step (2), the drying temperature can be 80 - 120 °C, and the time can be 12 - 16 hours.

[0026] [2] The water-resistant polycrystalline manganese oxide catalyst prepared by the preparation method according to [1].

[0027] [3] Application of the water-resistant polycrystalline manganese oxide catalyst according to [2] in catalytic ozonation for removing methyl mercaptan.

[0028] [4]A method for catalytic ozonation to remove methyl mercaptan, comprising: using the water-resistant polycrystalline manganese oxide catalyst described in [2] to catalytically ozonize and remove methyl mercaptan.

[0029] In some embodiments, for the method for catalytic ozonation to remove methyl mercaptan, the reaction temperature for catalytic ozonation to remove methyl mercaptan can be 15 - 50 °C (such as 25 °C, etc.), and the space velocity can be 200 - 600 L g cat -1 h -1 (such as 300 L g cat -1 h -1 ), the molar ratio of ozone to methyl mercaptan can be 1.5 - 3:1 (such as 2:1, etc.), and the relative humidity RH can be 0 - 90% (such as 30%, 60%, 80%, etc.). g cat represents the mass of the water-resistant polycrystalline manganese oxide catalyst.

[0030] In some embodiments, for the method for catalytic ozonation to remove methyl mercaptan, a fluid containing methyl mercaptan and ozone can be passed through the water-resistant polycrystalline manganese oxide catalyst.

[0031] In some embodiments, for the method for catalytic ozonation to remove methyl mercaptan, the particle size of the water-resistant polycrystalline manganese oxide catalyst is 20 - 80 mesh, such as 40 - 60 mesh, etc.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] The present invention adopts an in-situ L-T (layered-tunnel) transformation triggered by solution chemical action to synthesize a polycrystalline MnO catalyst with coexisting α and δ crystal forms. This catalyst has both α and δ crystal forms and their interfaces, and can be applied to catalytic ozonation to remove methyl mercaptan. The present invention constructs active hydroxyl sites at the α-δ interface to enhance the catalytic ozonation performance under humid conditions. x The water-resistant polycrystalline manganese oxide catalyst of the present invention can effectively improve the water resistance of the catalyst and the performance of catalytic ozonation to remove methyl mercaptan. At a molar ratio of ozone to methyl mercaptan = 2:1, a relative humidity RH = 60% - 80% (25 °C), and a space velocity of 300 L g

[0034] h cat -1 h -1 condition, a methyl mercaptan removal rate of 96% and an ozone removal rate of 90% are achieved.

[0035] The water-resistant polycrystalline manganese oxide catalyst of the present invention exhibits excellent water resistance and catalytic ozonation activity, and its preparation method has a simple process and is easy to promote and apply. Description of the Drawings

[0036] Figure 1 For the X-ray diffraction (XRD) patterns of δ-MnO2 and three polymorphic MnOs in the specific embodiments x of the catalyst.

[0037] Figure 2 For the scanning electron microscopy (SEM) photos of δ-MnO2 and three polymorphic MnOs in the specific embodiments x of the catalyst.

[0038] Figure 3 For the activity test diagrams of the catalyst under different humidity conditions. Experimental conditions: relative humidity RH = 0 - 80% (25°C), space velocity is 300 L g x h cat -1 h -1 , and the inlet gas is 20 ppm methyl mercaptan and 40 ppm ozone.

[0039] Figure 4 For the removal rate diagrams of methyl mercaptan and ozone by the Mn-SH sample within 20 h when the relative humidity RH = 60% - 80% (25°C). Experimental conditions: relative humidity RH = 60% - 80% (25°C), space velocity is 300 L g cat -1 h -1 , and the inlet gas is 10 ppm methyl mercaptan and 20 ppm ozone. Specific embodiments

[0040] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention.

[0041] For the operating methods without specific conditions noted in the following embodiments, they are generally in accordance with conventional conditions or the conditions recommended by the manufacturer.

[0042] Example 1:

[0043] Preparation of a water-resistant polymorphic manganese oxide catalyst for catalytic ozonation to remove methyl mercaptan. The steps are as follows: Potassium permanganate and manganese sulfate are dissolved in deionized water at a molar ratio of 5.8:1, and hydrothermal reaction is carried out at 200°C for 24 h. The solid product is collected, washed, and dried to obtain a δ-MnO2 sample. 2.0 g of δ-MnO2 is added to 200 mL of deionized water, and 1 mL of KOH solution (0.1 mmol K +) and 1.69 g of manganese sulfate monohydrate were stirred at 60 °C for 4 h. Subsequently, 2.72 mL of 98 wt% H2SO4 was added and stirring was continued at 60 °C for 2 h. After washing and drying the solid product, the catalyst sample Mn-SH of Example 1 was obtained.

[0044] The crystal form and morphology of the catalyst of Example 1 were characterized as Figure 1 and Figure 2 shown. Figure 1 The XRD results in Figure 2 showed that the sample of Example 1 (Mn-SH) had both δ and α crystal forms, proving that it formed a polycrystalline structure through in-situ L-T (lamellar-tunnel) transformation.

[0045] The activity evaluation of the catalyst was as follows: The catalyst powder was pressed into tablets with a tablet press at a pressure of 10 MPa and crushed to 40 - 60 mesh. Exactly 0.3 g of the catalyst was weighed and loaded into the catalytic reaction tube, and the upper and lower layers were fixed with quartz wool. The temperature was controlled at 25 °C by an outer water bath, and the relative humidity was controlled by the water bath temperature and the blowing gas volume of the stripping bottle, with the range controlled at 0% - 80% (25 °C), measured with a Testo 605-H1 temperature and humidity meter, and the space velocity was 300 L g cat -1 h -1 , and the molar ratio of inlet ozone to methyl mercaptan was 2:1. The evaluation results of the catalyst of Example 1 are shown in Table 1, Figure 3 and Figure 4 , and its removal rates of methyl mercaptan at relative humidities RH = 0%, 30%, 60% and 80% were 100%, 100%, 98% and 91% respectively. In Figure 4 , the catalyst of Example 1 was subjected to a 20 h activity test in the range of relative humidity RH = 60% - 80%, and it could maintain a methyl mercaptan removal rate of 96% and an ozone removal rate of 90%.

[0046] Example 2:

[0047] The catalyst preparation was substantially the same as that of Example 1, except that: 2.0 g of δ-MnO2 was added to 200 mL of deionized water, and 1 mL of KOH solution (0.1 mmol K + ) and 1.69 g of manganese sulfate monohydrate were added, and stirred at 60 °C for 6 h. After washing and drying the solid product, the catalyst sample Mn-S of Example 2 was obtained.

[0048] The crystal form and morphology of the catalyst of Example 2 were characterized as Figure 1 and Figure 2 shown. Figure 1The XRD results in Example 2 showed that the diffraction peaks of the sample (Mn-S) were similar to those of δ-MnO2, but the crystallinity decreased. Figure 2 The SEM results in Example 2 showed that the main body of the sample was a flower-like morphology structure of δ-MnO2, but there were a small number of rod-like morphology structures distributed on it, proving that it had a polycrystalline structure.

[0049] The activity evaluation of the catalyst in Example 2 was the same as that in Example 1, and the results are shown in Table 1 and Figure 3 , and it had good performance in removing methyl mercaptan.

[0050] Example 3:

[0051] The catalyst preparation was roughly the same as that in Example 1, except that 2.0 g of δ-MnO2 was added to 200 mL of deionized water, 2.72 mL of 98 wt% H2SO4 was added, and the mixture was stirred at 60 °C for 6 h. After the solid product was washed and dried, the catalyst sample Mn-H in Example 3 was obtained.

[0052] The crystal form and morphology characterization of the catalyst in Example 3 were as Figure 1 and Figure 2 shown. Figure 1 The XRD results in Example 3 showed that the sample (Mn-H) had δ and α crystal forms, and the crystallinity of its α crystal form was lower than that of the sample in Example 1. Figure 2 The SEM results in Example 3 showed that rod-like morphology structures were uniformly distributed in the flower-like morphology structure of the sample, proving that it had a polycrystalline structure.

[0053] The activity evaluation of the catalyst in Example 3 was the same as that in Example 1, and the results are shown in Table 1 and Figure 3 , and it had good performance in removing methyl mercaptan.

[0054] Example 4:

[0055] In the catalyst preparation steps, the amount of sulfuric acid added was 5.44 mL, and the other steps were the same as those in Example 1. The obtained sample was Mn-SH-1.0.

[0056] The activity evaluation of the catalyst in Example 4 was the same as that in Example 1, and the results are shown in Table 1. It had good performance in removing methyl mercaptan.

[0057] Example 5:

[0058] In the catalyst preparation steps, the amount of sulfuric acid added was 1.36 mL, and the other steps were the same as those in Example 1. The obtained sample was Mn-SH-0.25.

[0059] The activity evaluation of the catalyst in Example 5 was the same as that in Example 1, and the results are shown in Table 1. It had good performance in removing methyl mercaptan.

[0060] Example 6:

[0061] In the catalyst preparation step, sulfuric acid is replaced by 6.6 mL of 68 wt% concentrated nitric acid, and the remaining steps are the same as in Example 3. The obtained catalyst sample is Mn-NH.

[0062] The activity evaluation of the catalyst in Example 6 is the same as that in Example 1, and the results are shown in Table 1.

[0063] Example 7 (Comparative Example):

[0064] The catalyst is prepared in the same way as δ-MnO2 in Example 1.

[0065] The crystal form and morphology characterization of the catalyst in Example 7 are as Figure 1 and Figure 2 shown. Figure 1 The XRD results in Figure 2 show that the catalyst sample in Example 7 has a δ crystal form,

[0066] and Figure 3 .

[0067] Example 8 (Comparative Example):

[0068] Catalyst preparation: 0.003 mol of KMnO4 is dissolved in 30 mL of 0.4 M acetic acid solution, stirred for 30 min, then transferred to a 50 mL reaction kettle, hydrothermally treated at 140 °C for 12 h, the solid product is collected, washed and dried to obtain the catalyst sample α-MnO2 of Example 8.

[0069] The activity evaluation of the catalyst in Example 8 is the same as that in Example 1, and the results are shown in Table 1.

[0070] Table 1

[0071]

[0072] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

Claims

1. A preparation method of a water-resistant polycrystalline manganese oxide catalyst, characterized in that, Comprising the steps of: (1) Adopting any one of the following methods 1 to 3: Method 1: Adding potassium hydroxide and a divalent manganese salt to an aqueous dispersion of δ-MnO2, and stirring at 40 - 60 °C for a period of time; Method 2: Adding an inorganic acid to an aqueous dispersion of δ-MnO2, and stirring at 40 - 60 °C for a period of time; Method 3: First adding potassium hydroxide and a divalent manganese salt to an aqueous dispersion of δ-MnO2, stirring at 40 - 60 °C for a period of time, then adding an inorganic acid, and continuing to stir at 40 - 60 °C for a period of time; (2) Separating the solid and liquid of the mixed solution obtained in step (1), washing and drying the solid to obtain the water-resistant polycrystalline manganese oxide catalyst; The water-resistant polycrystalline manganese oxide catalyst has a polycrystalline manganese oxide with coexisting α-crystalline form and δ-crystalline form, and an interfacial structure at the junction of the α-crystalline manganese oxide and the δ-crystalline manganese oxide.

2. The preparation method of the water-resistant polycrystalline manganese oxide catalyst according to claim 1, characterized in that, The preparation method of the δ-MnO2 includes: performing a hydrothermal reaction on a mixed solution of potassium permanganate and a divalent manganese salt, washing and drying the obtained solid after the reaction to obtain the δ-MnO2.

3. The preparation method of the water-resistant polycrystalline manganese oxide catalyst according to claim 2, characterized in that, In the preparation method of the δ-MnO2: The molar ratio of the potassium permanganate to the divalent manganese salt is 5.5 - 6:1; The divalent manganese salt includes at least one of manganese sulfate, manganese chloride, manganese nitrate, and manganese acetate; The temperature of the hydrothermal reaction is 160 - 200 °C, and the time of the hydrothermal reaction is 24 - 28 hours.

4. The preparation method of the water-resistant polycrystalline manganese oxide catalyst according to claim 1, characterized in that, In Method 1 and Method 3, the divalent manganese salt independently includes at least one of manganese sulfate, manganese chloride, manganese nitrate, and manganese acetate; In Method 2 and Method 3, the inorganic acid independently includes at least one of sulfuric acid, hydrochloric acid, and nitric acid.

5. The preparation method of the water-resistant polycrystalline manganese oxide catalyst according to claim 1, characterized in that, In Method 1 and Method 3, independently add potassium hydroxide according to the molar ratio of K to the mass of δ-MnO₂ of 0.05 - 0.2 mmol: 2 g respectively. + Independently add divalent manganese salt according to the molar ratio of Mn to the mass of δ-MnO₂ of 0.005 - 0.02 mol: 2 g respectively. 2+ ​ In Method 2 and Method 3, the inorganic acid is preferably added separately and independently according to the mass ratio of the inorganic acid to δ-MnO2 of 1 - 5:1, more preferably 2 - 5:

1.

6. The preparation method of the water-resistant polycrystalline manganese oxide catalyst according to claim 1, characterized in that, In Method 1 and Method 2, the stirring time at 40 - 60 °C is independently 4 - 6 hours; In Method 3, after adding potassium hydroxide and the divalent manganese salt, stir at 40 - 60 °C for 2 - 4 hours, and after adding the inorganic acid, continue to stir at 40 - 60 °C for 2 - 4 hours.

7. A water-resistant polycrystalline manganese oxide catalyst prepared by the preparation method according to any one of claims 1 - 6.

8. Application of the water-resistant polycrystalline manganese oxide catalyst according to claim 7 in catalytic ozonation for removing methyl mercaptan.

9. A method for catalytic ozonation to remove methyl mercaptan, characterized in that, Comprising: Using the water-resistant polycrystalline manganese oxide catalyst according to claim 7 to catalytically ozonize and remove methyl mercaptan.

10. The method for catalytic ozonation to remove methyl mercaptan according to claim 9, characterized in that, The reaction temperature for catalytic ozonation to remove methyl mercaptan is 15 - 50 °C, the space velocity is 200 - 600 Lg cat -1 h -1 , the molar ratio of ozone to methyl mercaptan is 1.5 - 3:1, and the relative humidity RH is 0 - 90%.

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