Preparation methods and applications of high specific surface area spiky spherical Mn3O4 catalysts

Abstract

The invention discloses a preparation method of a Mn3O4 catalyst with a high specific surface area in a spiny ball structure and its application in the removal of volatile organic compounds (VOCs), belonging to the field of air pollution control and technology. The catalyst uses potassium permanganate and manganese sulfate as raw materials, deionized water as a solvent, and deionized water and absolute ethanol as detergents. Through steps of preparing a solution, magnetic stirring, suction filtration, washing, and drying, a manganese oxide precursor is prepared; the obtained precursor is calcined in a hydrogen atmosphere at 150-300 °C to obtain a Mn3O4 catalyst with excellent performance. The catalyst prepared by the invention is used in the reaction of thermally catalytically oxidizing and removing toluene in volatile organic compounds VOCs. The results show that the catalyst has a high specific surface area, high catalytic activity, high selectivity, and high hydrothermal stability, and can still maintain high catalytic activity at a high space velocity.

Description

Technical Field

[0001] The present invention relates to a preparation method and application of a catalyst, and in particular to a spiky ball structure Mn with high specific surface area. 3 O 4 The invention relates to a preparation method of a catalyst and application of the catalyst in removing volatile organic compounds (VOCs), belonging to the technical field of air pollution prevention and control. Background Art

[0002] Volatile organic compounds (VOCs) are mainly emitted from household activities and industrial processes. They not only cause various air pollution problems such as photochemical smog, but also seriously threaten human health. At present, many VOCs control technologies have been studied, among which VOCs thermal catalytic oxidation to generate CO 2 and H 2 O, with its high efficiency and few by-products, is regarded as one of the most promising technologies. The key issue of this technology is the development of high-performance catalysts.

[0003] The application of precious metal catalysts is limited by their high cost, easy sintering and easy poisoning. Therefore, it is very important to develop economical and efficient low-temperature catalysts. In recent decades, non-precious metal catalysts including Ce, Co, Fe and Mn-based catalysts have attracted extensive attention from researchers as alternatives to precious metal catalysts. Among them, manganese oxide catalysts have been deeply studied due to their excellent low-temperature redox performance (Sihaib Z, Puleo F, Garcia-Vargas JM, et al. Manganese oxide-based catalysts for toluene oxidation. AppliedCatalysis B: Environmental, 2017,209:689-700.). In the study of manganese oxides of different valence states, low-valent manganese sources (Mn(NO 3 ) 2 ) hydrothermal method and precipitation method, the manganese oxides prepared have small specific surface area and low reaction activity. In recent years, researchers have discovered a variety of synthesis methods for high-performance manganese oxide catalysts, among which high-valent manganese source (KMnO 4 ) The redox method has the advantages of simple synthesis method, large catalyst specific surface area, and high catalytic activity, and has been widely studied (Chen LZ, Liu YJ, Fang X. et al. Journal of Hazardous Materials, 2021,409:125020.). At present, the redox method is mainly used for MnO 2 preparation, but has not been extended to Mn 3 O4 This is because the low-temperature calcination method is used to prepare Mn 3 O 4 It is more difficult to prepare Mn by high temperature calcination. 3 O 4 The pore structure will be severely damaged, which will lead to a significant decrease in its catalytic activity (Piumetti M, Fino D, Russo N, Applied Catalysis B: Environmental, 2015, 163: 277–287.). Therefore, under the redox preparation method, the preparation of Mn 3 O 4 Catalyst, and then improve its catalytic activity, which is of great significance for the preparation of manganese-based catalysts for efficient removal of VOCs. Summary of the invention

[0004] The purpose of the present invention is to prepare a Mn with high specific surface area and high activity by controlling the calcination atmosphere temperature and time on the basis of preparing a manganese oxide precursor by redox method. 3 O 4 Catalyst, and used to efficiently remove VOCs pollutants.

[0005] The present invention selects Mn 3 O 4 As the target catalyst, it has the characteristics of strong oxygen adsorption capacity and abundant active sites among various manganese-based oxide catalysts, but the Mn 3 O 4 The catalyst has a low specific surface area and poor reaction activity. The present invention adopts a redox synthesis method to prepare a precursor with a high specific surface area, rich mesoporous structure and a large number of defect sites, which can be calcined in a hydrogen atmosphere to form a manganese oxide catalyst with excellent catalytic effect. Based on this, the present invention synergistically exerts the Mn 3 O 4 Taking the advantages of catalyst and redox preparation method as the starting point, based on the preparation of manganese oxide precursor by redox method, a Mn with high specific surface area, high activity and high stability was successfully prepared by controlling the calcination atmosphere, temperature and time. 3 O 4 catalyst.

[0006] The present invention provides a high specific surface area thorn ball structure Mn 3 O 4The catalyst preparation method comprises the following steps: using potassium permanganate and manganese sulfate as raw materials, using deionized water as solvent, and using deionized water and anhydrous ethanol as detergents; preparing a solution, magnetic stirring, filtering, washing, and drying to obtain a manganese oxide precursor; and calcining the mixture under a hydrogen atmosphere at 150-300 °C to obtain a spherical Mn with a high specific surface area. 3 O 4 The catalyst was tested for its catalytic oxidation performance for toluene and found to have excellent low-temperature catalytic activity and selectivity (at a toluene concentration of 100 ppm and a weight hourly space velocity of 60,000 h -1 Under normal conditions, the temperature reaches 230 °C and the toluene conversion rate can reach more than 90%), and it has good stability and water resistance, and can maintain high reaction activity at high space velocity.

[0007] The above preparation method specifically comprises the following steps:

[0008] (1) Preparation of salt solution

[0009] Weigh potassium permanganate solid and manganese sulfate solid respectively to prepare 0.1-1 mol·L -1 Potassium permanganate aqueous solution, 0.15-1.5 mol·L -1 of manganese sulfate aqueous solution; measure equal amounts of the two salt solutions and transfer them into dropping funnels one and two respectively for use.

[0010] (2) Preparation of Mn 3 O 4 Precursor

[0011] Place the beaker on a magnetic stirrer and slowly drip the solutions in dropping funnel 1 and dropping funnel 2 into the beaker under magnetic stirring. Control the dropping speed of the two solutions to be equal, 5-15 mL min. -1 Then, stir at 20-60℃ for 2-6 h; after filtration, washing and drying, Mn 3 O 4 Precursor. Among them, MnO 4 - With Mn 2+ The ratio of the amount of substance is 1:1~1:2.

[0012] (3) Preparation of Mn 3 O 4 catalyst

[0013] The Mn 3 O 4 The precursor was placed in a tube furnace and the temperature was programmed to rise at a rate of 2-10 °C min -1 , calcined at 150~300 ℃ in hydrogen atmosphere for 1~3 h to obtain Mn 3 O4 catalyst.

[0014] Preferably, in step (1), the molar concentrations of the potassium permanganate solution and manganese sulfate solution added are 0.1 mol·L -1 and 0.15 mol·L -1 .

[0015] Preferably, in step (2), the volume ratio of the potassium permanganate solution to the manganese sulfate solution is 1:1, and the MnO 4 - With Mn 2+ The molar ratio of the substances was 2:3, and the mixture was stirred at 25 °C for 3 h.

[0016] Preferably, in step (3), the programmed heating rate is 5 °C·min -1 ; The calcination temperature was set to 225 °C in a hydrogen atmosphere, and the calcination time was 2 h.

[0017] The present invention provides a spherical Mn with high specific surface area, high activity and high stability prepared by the above preparation method. 3 O 4 Catalyst, application in the removal of toluene from volatile organic compounds (VOCs).

[0018] In the above applications, high specific surface area, spherical Mn 3 O 4 Toluene removal catalyst is used in toluene removal reaction. The catalyst is first pressed into tablets. The specific operation is as follows: the Mn 3 O 4 The catalyst is placed in a mold and maintained at a pressure of 20 to 30 MPa for 5 to 10 minutes. The pressed sample is slowly taken out and put into a 40 to 60 mesh sieve for grinding and sieving to obtain 40 to 60 mesh particles.

[0019] In the above applications, high specific surface area, spherical Mn 3 O 4 When the toluene removal catalyst is used in the toluene removal reaction, it is carried out in a fixed bed continuous flow quartz reactor; C 7 H 8 The concentration is 1000 ppm, O 2 The content is 20.0 vol.%, H 2 O concentration is 10 vol.%, N 2 As a balance gas, the flue gas space velocity is 30000~90000 h -1 The required catalyst particle mass is 0.1~0.2g, and the reaction temperature is 160~310 ℃.

[0020] Beneficial effects of the present invention:

[0021] (1) The present invention uses hydrogen reduction to reduce the α-MnO prepared by the redox method. 2 Preparation of a Mn with excellent performance by precursor regulation 3 O 4 The catalyst was realized by α-MnO 2 Precursor to Mn 3 O 4 Regulated preparation.

[0022] (2) Mn prepared by the present invention 3 O 4 The catalyst has a large specific surface area and rich mesoporous structure, which improves the performance of manganese-based catalysts in the catalytic oxidation of toluene.

[0023] (3) Mn prepared by the present invention 3 O 4 The catalyst exhibits good low-temperature catalytic activity and high selectivity in the toluene removal reaction.

[0024] (4) Mn prepared by the present invention 3 O 4 The catalyst has good reaction stability and water resistance and can maintain high reaction activity at high space velocity. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The Mn prepared in Example 2 of the present invention 3 O 4 X-ray diffraction intensity spectrum (XRD) and standard cards;

[0026] Figure 2 The Mn prepared in Example 2 of the present invention 3 O 4 Scanning electron microscope (SEM) images of

[0027] Figure 3 The Mn prepared in Example 2 of the present invention 3 O 4 In the toluene removal experiment, the toluene conversion rate and CO 2 Selectivity versus temperature curve;

[0028] Figure 4 The Mn prepared in Example 2 of the present invention 3 O 4 Stability test chart at 230 ℃;

[0029] Figure 5 The Mn prepared in Example 2 of the present invention 3 O4 Water resistance test chart at 230 ℃;

[0030] Figure 6 The Mn prepared in Example 2 of the present invention 3 O 4 At different airspeeds (30000 h -1 、60000 h -1 、90000h -1 ) is a curve of toluene conversion rate changing with temperature. DETAILED DESCRIPTION

[0031] The specific embodiments of the present invention are described in detail below, but are not limited to the following embodiments. Example 1

[0032] (1) Weigh potassium permanganate solid and manganese sulfate solid separately to prepare 0.5 mol·L -1 Potassium permanganate aqueous solution, 0.5 mol·L -1 of manganese sulfate aqueous solution; take equal amounts of two salt solutions (200 mL) and transfer them into dropping funnels one and two respectively for later use.

[0033] (2) Place a beaker on a magnetic stirrer and slowly drip the solutions in dropping funnel 1 and dropping funnel 2 into the beaker under magnetic stirring. The dripping speed of the two solutions should be controlled to be 10 mL min. -1 Then, the mixture was stirred at 25 °C for 4 h. 4 - With Mn 2+ The ratio of the amounts of substances is 1:1.

[0034] (3) The product after the reaction was centrifuged and precipitated, and washed with deionized water and anhydrous ethanol until neutral, and then dried in an oven at 80 °C for 12 h. After sufficient grinding, Mn 3 O 4 Precursor.

[0035] (4) The Mn prepared above 3 O 4 The precursor was placed in a tube furnace, nitrogen was introduced to exclude air, and then hydrogen was introduced at a flow rate of 50 sccm. The temperature was programmed from room temperature to 200 °C for 2.5 h (the program heating rate was 2 °C min -1 ), to obtain Mn 3 O 4 catalyst. Example 2

[0036] (1) Weigh potassium permanganate solid and manganese sulfate solid separately to prepare 0.2 mol·L -1Potassium permanganate aqueous solution, 0.3 mol·L -1 of manganese sulfate aqueous solution; take equal amounts of two salt solutions (400 mL) and transfer them into dropping funnels one and two respectively for later use.

[0037] (2) Place a beaker on a magnetic stirrer and slowly drip the solutions in dropping funnel 1 and dropping funnel 2 into the beaker under magnetic stirring. The dripping speed of the two solutions should be controlled to be 5 mL min. -1 Then, the mixture was stirred at 60 °C for 3 h. 4 - With Mn 2+ The ratio of the amounts of substances is 2:3.

[0038] (3) The product after the reaction was centrifuged and precipitated, and washed with deionized water and anhydrous ethanol until neutral, and then dried in an oven at 80 °C for 12 h. After sufficient grinding, Mn 3 O 4 Precursor.

[0039] (4) The Mn prepared above 3 O 4 The precursor was placed in a tube furnace, nitrogen was introduced to exclude air, and then hydrogen was introduced at a flow rate of 50 sccm. The temperature was programmed from room temperature to 225 °C for 2 h (the program heating rate was 5 °C min-1). -1 ), to obtain Mn 3 O 4 catalyst.

[0040] The present invention uses X-ray diffractometer (XRD) to characterize and analyze the crystal structure of the final product of this embodiment. Figure 1 As shown, it is proved that Mn 3 O 4 Successful synthesis of the catalyst.

[0041] The present invention utilizes scanning electron microscope (such as Figure 2 As shown) for Mn 3 O 4 The catalyst was characterized from Figure 2 It can be seen that Mn 3 O 4 The catalyst has a spherical thorn-like structure with an increased specific surface area, which is beneficial to the exposure of reaction active sites and thus improves its catalytic activity.

[0042] The Mn prepared in this example was measured by a porosity tester. 3 O 4 The catalyst was characterized and the test results of the porosity tester are shown in Table 1.

[0043] Table 1 Preparation of Mn by low temperature hydrogen reduction3 O 4 and hydrothermal method to prepare Mn 3 O 4 Surface area and pore size data

[0044]

[0045] From the data in Table 1, it can be concluded that the catalyst obtained in the present invention has a very high specific surface area and rich mesoporous structure. 3 O 4 (Piumetti M, Fino D, Russo N, Applied Catalysis B: Environmental, 2015, 163: 277–287.), the Mn prepared by the present invention 3 O 4 , with a higher specific surface area, larger pore volume and smaller pore size, which can expose more reaction active sites, is conducive to the adsorption and activation of the reactants and the desorption of the products, thereby improving the performance of the catalyst.

[0046] Embodiment 3:

[0047] (1) Weigh potassium permanganate solid and manganese sulfate solid separately to prepare 0.5 mol·L -1 Potassium permanganate aqueous solution, 1 mol·L -1 of manganese sulfate aqueous solution; take 100 mL of the two salt solutions in equal amounts and transfer them into dropping funnels 1 and 2 for later use. 4 - With Mn 2+ The molar concentration ratio is 1:2.

[0048] (2) Place a beaker on a magnetic stirrer and slowly drip the solutions in dropping funnel 1 and dropping funnel 2 into the beaker under magnetic stirring. The dripping speed of the two solutions should be controlled to be 15 mL min. -1 Then, the mixture was stirred at 40 °C for 6 h. 4 - With Mn 2+ The ratio of the amounts of substances is 1:2.

[0049] (3) The product after the reaction was centrifuged and precipitated, and washed with deionized water and anhydrous ethanol until neutral, and then dried in an oven at 80 °C for 12 h. After sufficient grinding, Mn 3 O 4 Precursor.

[0050] (4) The Mn prepared above 3 O 4The precursor was placed in a tube furnace, nitrogen was introduced to exclude air, and then hydrogen was introduced at a flow rate of 50 sccm. The temperature was programmed from room temperature to 250 °C for 1.5 h (the program heating rate was 10 °C min -1 ), to obtain Mn 3 O 4 catalyst.

[0051] Example 4: Performance evaluation of catalysts for catalytic oxidation of toluene

[0052] The Mn prepared in Example 2 3 O 4 The catalyst is used in the catalytic oxidation reaction of toluene. The specific reaction conditions are as follows:

[0053] The catalytic reaction test was carried out in a fixed bed continuous flow quartz reactor. The catalyst particle size was 40-60 mesh and the dosage was 0.1 g. The reaction gas composition was: 1000 ppm C 7 H 8 , 20 vol% O 2 , N 2 As the balance gas, the reaction gas space velocity is 60000h -1 The catalytic reaction was carried out at 160-310 °C, and the activity data were collected after the reaction reached equilibrium. The products were detected and analyzed by online gas chromatography (GC9790Ⅱ, FULI). 7 H 8 Conversion rate and CO 2 The selectivity is calculated by the following formula:

[0055]

[0056] [C 7 H 8 ] means C 7 H 8 The concentration of [CO 2 ] indicates CO 2 The concentration of in represents the initial concentration before the reaction, and out represents the concentration after the catalyst reaction.

[0057] The above experiments show that the Mn 3 O 4 The catalyst showed good catalytic performance when used for removing toluene (C 7 H 8 Conversion rate, CO 2 Selectivity), the results are shown in the attached Figure 3 (Mn 3 O 4Toluene conversion and CO over catalyst at 230℃ 2 The selectivity can reach 90% and 85% respectively, showing excellent low-temperature catalytic performance.

[0058] Example 5: Catalyst stability performance evaluation

[0059] The Mn prepared in Example 2 3 O 4 The catalyst was subjected to stability performance evaluation. The test apparatus and catalyst dosage were the same as those in Example 4. The reaction gas composition was 20.0 vol.% O 2 , 1000 ppm C 7 H 8 , N 2 As the balance gas, the reaction gas space velocity is 60000 h -1 , reaction temperature is 230 ℃, and reaction time is 100h.

[0060] The present invention uses online gas chromatography (GC9790Ⅱ, FULI) to analyze Mn 3 O 4 The catalyst was tested for its stability in catalytic oxidation of toluene. The results are shown in the attached Figure 4 It can be seen from the figure that the catalyst of the present invention exhibits good stability.

[0061] Example 6: Evaluation of Catalyst Water Resistance

[0062] The Mn prepared in Example 2 3 O 4 The catalyst was evaluated for water resistance. The test apparatus and catalyst dosage were the same as those in Example 4. The reaction gas composition was: 20.0 vol.% O 2 , 1000 ppm C 7 H 8 ,10.0 vol.% H 2 O,N 2 As the balance gas, the reaction gas space velocity is 60000 h -1 , reaction temperature 240 ℃.

[0063] The present invention uses online gas chromatography (GC9790Ⅱ, FULI) to analyze Mn 3 O 4 The water resistance of the catalyst was tested and the results are attached. Figure 5 , it can be seen from the figure that the catalyst of the present invention exhibits good water resistance.

[0064] Example 7: Evaluation of Catalytic Performance of Catalysts for Catalytic Oxidation of Toluene at Different Space Velocities

[0065] The Mn prepared in Example 2 3O 4 The catalyst was applied at different space velocities (30000h -1 、60000h -1 、90000h -1 ) In the catalytic oxidation reaction of toluene, the test device and the amount of catalyst used were the same as those in Example 4. The reaction gas composition was 1000 ppmC 7 H 8 , 20 vol% O 2 , N 2 As balance gas, the reaction gas space velocity is 30000h -1 、60000h -1 、90000h -1 , reaction temperature 160~310 ℃, the results are attached Figure 6 It can be seen from the figure that the catalyst of the present invention can still maintain a relatively high catalytic activity at a high space velocity.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although detailed description is given with reference to the embodiments of the present invention, those skilled in the art should understand that modifications or equivalent substitutions of the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and should all be included in the protection scope of the claims of the present invention.

Claims

1. A method for preparing a high specific surface area thorn ball structure Mn3O4 catalyst, characterized in that: Potassium permanganate and manganese sulfate are used as raw materials, deionized water is used as solvent, deionized water and anhydrous ethanol are used as detergents, and a manganese oxide precursor is prepared through the steps of solution preparation, magnetic stirring, suction filtration, washing and drying, and then calcined in a hydrogen atmosphere at 150-250 ℃ to obtain a Mn3O4 catalyst with excellent performance. The method for preparing the high specific surface area thorn ball structure Mn3O4 catalyst comprises the following steps: (1) Preparation of salt solution Weigh potassium permanganate solid and manganese sulfate solid respectively to prepare 0.1-1 mol·L -1 Potassium permanganate aqueous solution, 0.15-1.5 mol·L -1 of manganese sulfate aqueous solution; take equal amounts of the two salt solutions and transfer them into dropping funnels one and two respectively for later use; (2) Preparation of Mn3O4 precursor Place the beaker on a magnetic stirrer and slowly drip the solutions in dropping funnel 1 and dropping funnel 2 into the beaker under magnetic stirring. Control the dropping speed of the two solutions to be equal, 5-15 mL min -1 , then stirred at 20-60 °C for 2-6 h; after filtration, washing and drying, the Mn3O4 precursor was obtained; (3) Preparation of Mn3O4 catalyst The Mn3O4 precursor prepared above was placed in a tubular furnace and calcined at 150-250°C in a hydrogen atmosphere for 1-3 h to obtain a Mn3O4 catalyst.

2. The method for preparing the high specific surface area thorn ball structure Mn3O4 catalyst according to claim 1, characterized in that: In the step (2), MnO4 in the solution is added dropwise - With Mn 2+ The ratio of the amount of substance is 1:1~1:

2.

3. The method for preparing the high specific surface area thorn ball structure Mn3O4 catalyst according to claim 1, characterized in that: The product after the reaction in step (2) is centrifuged and precipitated, washed with deionized water and anhydrous ethanol until neutral, and then dried in an oven at 80°C for 12 h; and then fully ground to obtain a Mn3O4 precursor.

4. The method for preparing the high specific surface area thorn ball structure Mn3O4 catalyst according to claim 1, characterized in that: In the step (3), before calcination, nitrogen is introduced to exclude air, and then hydrogen is continuously introduced at a flow rate of 50 sccm, and the program heating rate is 2-10 °C·min -1 .

5. Use of a high specific surface area thorn ball structure Mn3O4 catalyst prepared by the preparation method according to any one of claims 1 to 4 in a volatile organic compound removal reaction, characterized in that: When the reaction temperature is 215 ℃, the toluene conversion rate can reach 50%; when the reaction temperature is 230 ℃ ~ 310 ℃, the toluene conversion rate can reach more than 90%.

6. The use according to claim 5, characterized in that: The high specific surface area thorn ball structure Mn3O4 catalyst is used in the volatile organic compound removal reaction. The catalyst is first pressed into tablets. The specific operation is as follows: the calcined Mn3O4 catalyst is placed in a mold, and after maintaining it at a pressure of 20 to 30 MPa for 5 to 10 minutes, the pressed sample is slowly taken out and put into a 40 to 60 mesh sieve for grinding and sieving to obtain 40 to 60 mesh particles.

7. The use according to claim 6, characterized in that: When the catalyst is used in the toluene removal reaction, it is carried out in a fixed bed continuous flow quartz reactor; the C7H8 concentration is 1000 ppm, the O2 content is 20.0 vol.%, the H2O concentration is 10 vol.%, N2 is used as the balance gas, and the flue gas space velocity is 30000~90000 h -1 The required catalyst particle mass is 0.1~0.2 g, and the reaction temperature is 160~310 ℃.

Images