A transition metal-doped modified MnO2 catalyst, its preparation method and application

Abstract

The present application discloses a catalyst for transition metal-doped modified MnO2, its preparation method and application, belonging to the field of catalysts. A catalyst for transition metal-doped modified MnO2, the catalyst is cryptomelane octahedron; the catalyst comprises a carrier and an active component; the carrier is diatomite; the active component is Fe / MnO2. The elimination rate of formaldehyde by this catalyst reaches more than 90% at room temperature; it still maintains a relatively high elimination rate of formaldehyde under high humidity conditions.

Description

Technical Field

[0001] The present application relates to a catalyst for transition metal-doped modified MnO2, its preparation method and application, belonging to the field of catalysts. Background Art

[0002] Manganese dioxide (MnO2) is an amphoteric transition metal oxide with a complex structure and incomplete stoichiometry. Therefore, it has unique physical and chemical properties and can be used as a catalyst. Some studies have shown that at normal temperature and pressure, MnO2 has a better catalytic degradation effect than other metal oxides that have a catalytic degradation effect on formaldehyde gas. Therefore, the preparation of MnO2 with different structures, different crystals and different modification methods has become a research hotspot at home and abroad. Summary of the Invention

[0003] According to the first aspect of the present application, a catalyst for transition metal-doped modified MnO2 is provided. The catalyst uses activated diatomite as a carrier. The activation treatment can remove organic substances in the diatomite, making the pore structure and pore size of the diatomite larger and improving the loading effect. Using diatomite as a carrier can enhance the adsorption ability of the active component and prevent the loss of nano-powders. The doping of Fe element can replace potassium ions in the octahedral tunnels of cryptomelane or manganese ions in the framework to adjust the catalytic performance of the original material. In the catalyst, a special Fe-Mn mass ratio can ensure that the catalyst still has a high elimination rate for formaldehyde under high humidity.

[0004] A catalyst for transition metal-doped modified MnO2, the catalyst is an octahedron of cryptomelane;

[0005] The catalyst includes a carrier and an active component;

[0006] The carrier is diatomite;

[0007] The active component is Fe / MnO2.

[0008] Optionally, in the catalyst, the mass ratio of Fe to Mn is 1:4 to 10.

[0009] Optionally, the mass ratio of Fe to Mn is 1:5.5 to 6.5.

[0010] Optionally, in the catalyst, the mass ratio of Fe to Mn independently selects any value or the range value between any two of 1:4, 1:4.5, 1:5, 1:5.5, 1:6, 1:6.5, 1:7, 1:7.5, 1:8, 1:8.5, 1:9, 1:9.5, 1:10.

[0011] Optionally, the mass ratio of the active component to the carrier is 1:1.8 to 2.9.

[0012] Optionally, the mass ratio of the active component to the carrier is independently selected from any value among 1:1.8, 1:2.0, 1:2.2, 1:2.4, 1:2.6, 1:2.8, 1:2.9 or the range value between any two of them.

[0013] The catalyst is negatively charged.

[0014] According to the second aspect of the present application, a preparation method of a transition metal-doped and modified MnO₂ catalyst is provided. In the present application, a transition metal-doped and modified MnO₂ catalyst is obtained by a one-pot hydrothermal method. By reacting divalent Mn ions with potassium permanganate, a transition metal-doped MnO₂ crystal is prepared and then doped. This method is simple to operate, and no other phases or crystals are produced in the hydrothermal product after doping.

[0015] A preparation method of a transition metal-doped and modified MnO₂ catalyst includes the following steps:

[0016] A mixture containing an Fe source, an Mn source, KMnO₄, and diatomite is placed in a closed container and reacted to obtain the catalyst.

[0017] Optionally, the Fe source is selected from at least one of iron nitrate, iron sulfate, and iron chloride.

[0018] Optionally, the Mn source is selected from at least one of manganese acetate, manganese sulfate, manganese nitrate, and manganese chloride.

[0019] Optionally, the Mn source is selected from manganese sulfate.

[0020] Optionally, the diatomite is subjected to an activation treatment.

[0021] Optionally, the activation treatment is calcination;

[0022] The conditions of the calcination are as follows:

[0023] The temperature is 400°C to 600°C;

[0024] The time is 210 min to 270 min.

[0025] Optionally, the temperature is independently selected from any value among 400°C, 420°C, 450°C, 470°C, 500°C, 520°C, 550°C, 570°C, 600°C or the range value between any two of them.

[0026] Optionally, the time is independently selected from any value among 210 min, 220 min, 230 min, 240 min, 250 min, 260 min, 270 min or the range value between any two of them.

[0027] Optionally, the heating rate is 1°C / min.

[0028] Optionally, the mass ratio of the Fe source, the Mn source, the KMnO4, and the diatomaceous earth is 1: 3-5: 2-3: 7-10.

[0029] Optionally, the mass ratio of the Fe source, the Mn source, the KMnO4, and the diatomaceous earth is 1: 3.6: 2.5: 7.5.

[0030] Optionally, the reaction conditions are as follows:

[0031] The temperature is 80 °C to 120 °C;

[0032] The time is 22 h to 26 h.

[0033] Optionally, the temperature is independently selected from any value of 80 °C, 90 °C, 100 °C, 110 °C, 120 °C or the range value between any two of them.

[0034] Optionally, the time is independently selected from any value of 22 h, 23 h, 24 h, 25 h, 26 h or the range value between any two of them.

[0035] Optionally, it includes the following steps:

[0036] S1. Obtain dispersion liquid I containing the Fe source;

[0037] S2. Obtain dispersion liquid II containing the Mn source;

[0038] S3. Obtain dispersion liquid III containing KMnO4;

[0039] S4. Add dispersion liquid I, dispersion liquid II, and activated diatomaceous earth to dispersion liquid III, and obtain the catalyst after hydrothermal reaction.

[0040] According to the third aspect of the present application, an application of a transition metal-doped modified MnO2 catalyst is provided. The elimination rate of formaldehyde by this catalyst reaches more than 90% under room temperature conditions, and it has great market application prospects.

[0041] Application of the above-mentioned catalyst and / or the catalyst obtained by the above-mentioned preparation method in removing formaldehyde.

[0042] The hydrothermal synthesis method was adopted in this experiment. During the preparation of pure manganese dioxide, corresponding masses of nitrates were added to prepare transition metal-doped MnO2 crystals. First, 1 g of KMnO4 was dissolved in 100 ml of deionized water, and then it was placed on a magnetic stirrer and continuously stirred. Then, 1.43 g of MnSO4·H2O and 0.4 g of Fe(NO3)3 were respectively dissolved in 30 ml of deionized water. These two solutions were then slowly dropped into the previously stirred KMnO4 solution drop by drop using a dropper. 3 g of activated diatomaceous earth was added (Activation of diatomaceous earth: The diatomaceous earth was calcined in a muffle furnace. Starting from room temperature of 25°C, the temperature was raised by 1°C per minute. After 500 minutes, the temperature reached 500°C and the heating was stopped and maintained for 240 minutes, then the instrument was turned off. After cooling to room temperature, it was taken out. The purpose was to remove the organic substances in the diatomaceous earth, making the pore structure and pore size of the diatomaceous earth larger and the loading effect better). After stirring evenly, it was ultrasonically treated in an ultrasonic cleaner for 30 minutes. Finally, the above mixed solution was placed in a reaction kettle, sealed and placed in an oven at 100°C for reaction for 24 hours. After the hydrothermal reaction, the sample was filtered by suction, washed until neutral and then dried in the oven. The dried sample was ground and put into a self-sealing bag for standby.

[0043] Different divalent Mn ion precursors can affect the catalytic performance of the finally synthesized catalyst. In this experiment, manganese acetate, manganese sulfate, manganese nitrate and manganese chloride were studied as the precursors of divalent manganese ions, and the catalytic activities of the catalysts prepared with different precursors for formaldehyde were investigated. The results showed that under the same operating conditions, the catalyst using manganese sulfate as the precursor had a higher decomposition rate for formaldehyde.

[0044] Different metal dopings can change the specific surface area, pore volume and thermal stability of the MnO2 catalyst, and can further improve the decomposition rate of the catalyst for formaldehyde on the basis of the above experimental research. In this experiment, MnO2 doped with different transition metals was studied. Co, Fe, and Cu metals were selected for doping, and the catalytic decomposition performances of the catalysts doped with different metals for formaldehyde were investigated. The results showed that the catalyst doped with Fe could maintain a very high formaldehyde decomposition conversion rate at room temperature, far higher than the catalysts doped and modified with Co and Cu.

[0045] It was found in the above experiments that the catalyst doped with Fe element could significantly improve the decomposition conversion rate of formaldehyde. The decomposition conversion rate of formaldehyde at room temperature of Fe / MnO2 catalysts with different Fe-Mn mass ratios (Fe-Mn = 1:4, 1:6, 1:8, and 1:10) was further studied. Catalysts with each ratio showed relatively excellent catalytic activity at a formaldehyde concentration of 40 ppm and room temperature, and the decomposition conversion rates were basically the same. Therefore, the performance differences among different ratios could not be distinguished under this evaluation condition. Considering that water molecules play a certain role in inhibiting the catalytic activity during the decomposition of formaldehyde, the relative humidity in the reaction atmosphere was increased (from the original air humidity of 40% to 90% now). The results showed that when Fe-Mn = 1:6, the prepared catalyst could still maintain a relatively high formaldehyde conversion rate, while the conversion rates of catalysts prepared with other ratios decreased rapidly.

[0046] The beneficial effects that this application can produce include:

[0047] 1) A catalyst for doping and modifying MnO2 with transition metals provided by this application has an elimination rate of formaldehyde reaching more than 90% at room temperature; it still maintains a relatively high elimination rate of formaldehyde under high humidity.

[0048] 2) A preparation method of a catalyst for doping and modifying MnO2 with transition metals provided by this application is simple in operation, and no other phases or crystals are produced in the hydrothermal product after doping. Description of the Drawings

[0049] Figure 1 This is for the formaldehyde removal test using the catalysts prepared with different divalent Mn ion precursors as raw materials in this application.

[0050] Figure 2 This is for the formaldehyde removal test using the catalysts prepared by doping and modifying MnO2 with different transition metals in this application.

[0051] Figure 3 This is for the formaldehyde removal test of the catalysts with different Fe and Mn mass ratios prepared in this application under the condition of 40% relative humidity.

[0052] Figure 4 This is for the formaldehyde removal test of the catalysts with different Fe and Mn mass ratios prepared in this application under the condition of 90% relative humidity. Detailed Embodiments

[0053] The following describes this application in detail with reference to the embodiments, but this application is not limited to these embodiments.

[0054] Unless otherwise specified, the raw materials in the embodiments of this application are all purchased through commercial channels.

[0055] The analysis methods in the embodiments of this application are as follows:

[0056] The formaldehyde concentration was analyzed using a Fourier transform infrared spectrometer (Nicolet is 50FT-IR).

[0057] In the embodiments of this application, the formaldehyde elimination rate was calculated as follows:

[0058] Elimination rate = (inlet formaldehyde concentration - outlet formaldehyde concentration) / inlet formaldehyde concentration * 100%

[0059] Example 1

[0060] (1) Preparation of Fe / MnO2 supported diatomite

[0061] First, 1 g of KMnO4 was weighed and dissolved in 100 ml of deionized water, then placed on a magnetic stirrer and continuously stirred. Then, 1.43 g of MnSO4·H2O and 0.4 g of Fe(NO3)3 were respectively dissolved in 30 ml of deionized water. These two solutions were then slowly dropped into the previously stirred KMnO4 solution drop by drop using a dropper. 3 g of activated diatomite was added (Diatomite activation: The diatomite was calcined in a muffle furnace. Starting from room temperature of 25 °C, the temperature was increased by 1 °C per minute. After 500 minutes, the temperature reached 500 °C, then the heating was stopped and maintained for 240 minutes, and then the instrument was turned off. After cooling to room temperature, it was taken out. The purpose was to remove the organic substances in the diatomite, making the pore structure and pore size of the diatomite larger and the loading effect better). After stirring evenly, it was ultrasonically treated in an ultrasonic cleaner for 30 minutes. Finally, the above mixed solution was placed in a reaction kettle, sealed and reacted in an oven at 100 °C for 24 hours. After the hydrothermal reaction, the sample was filtered by suction, washed until neutral and then dried in an oven. The dried sample was ground and put into a self-sealing bag for standby. After calculation, Fe-Mn = 1:6 could be obtained.

[0062] (2) Degradation of formaldehyde by Fe / MnO2 supported diatomite

[0063] 20 mg of the catalyst from Example 1 was taken, and the corresponding space velocities were 240,000 mL / (g·h). The experimental conditions were as follows: oxygen 21%, nitrogen 79%, the formaldehyde concentration was controlled at 40 ppm, the relative humidity was 40%, and the reaction temperature was 25 °C. Both HCHO and CO2 were measured using an infrared gas cell.

[0064] The catalytic activity of the obtained catalyst was carried out on a fixed reaction bed. When the reaction reached a steady state, the composition of the reaction gas was measured, and the formaldehyde conversion rate of the catalyst was measured to be 93%.

[0065] Example 2

[0066] (1) Preparation of Fe / MnO2 supported diatomite

[0067] Change the addition amount of Fe(NO3)3 to 0.8 g, and other steps are the same as in Example 1. After calculation, Fe-Mn = 1:4 can be obtained.

[0068] (2) Degradation of formaldehyde by Fe / MnO2 supported diatomite

[0069] The steps and test conditions are the same as in Example 1, and the formaldehyde conversion rate is measured to be 89%.

[0070] Example 3

[0071] (1) Preparation of Fe / MnO2 supported diatomite

[0072] Change the addition amount of Fe(NO3)3 to 0.28 g, and other steps are the same as in Example 1. After calculation, Fe-Mn = 1:8 can be obtained.

[0073] (2) Degradation of formaldehyde by Fe / MnO2 supported diatomite

[0074] The steps and test conditions are the same as in Example 1, and the formaldehyde conversion rate is measured to be 91%.

[0075] Example 4

[0076] (1) Preparation of Fe / MnO2 supported diatomite

[0077] Change the addition amount of Fe(NO3)3 to 0.24 g, and other steps are the same as in Example 1. After calculation, Fe-Mn = 1:10 can be obtained.

[0078] (2) Degradation of formaldehyde by Fe / MnO2 supported diatomite

[0079] The steps and test conditions are the same as in Example 1, and the formaldehyde conversion rate is measured to be 90%.

[0080] Example 5

[0081] (1) Preparation of Fe / MnO2 supported diatomite

[0082] Change 1.43 g of manganese sulfate as the reactant raw material to 1.43 g of manganese chloride, and other steps are the same as in Example 1.

[0083] (2) Degradation of formaldehyde by Fe / MnO2 supported diatomite

[0084] The steps and test conditions are the same as in Example 1, and the formaldehyde conversion rate is measured to be 65%.

[0085] Example 6

[0086] (1) Preparation of Fe / MnO2 supported diatomite

[0087] All steps are the same as in Example 1.

[0088] (2) Degradation of formaldehyde by Fe / MnO₂ supported on diatomite

[0089] The relative humidity of the experimental conditions was increased to 90%, and other steps were the same as in Example 1. The measured formaldehyde conversion rate was 90%.

[0090] The specific activity evaluation results of the catalysts prepared in Examples 1-6 are shown in the following table.

[0091] Formaldehyde conversion rate / % Condition change Example 1 93 Initial preferred solution Example 2 89 Only change the Fe-Mn mass ratio to 1:4 Example 3 91 Only change the Fe-Mn mass ratio to 1:8 Example 4 90 Only change the Fe-Mn mass ratio to 1:10 Example 5 65 Only change the reaction manganese source to manganese chloride Example 6 90 Only change the relative humidity to 90%

[0092] It can be seen from this that changing the manganese source of the reaction raw materials has the greatest impact on the formaldehyde conversion rate. The doping modification of the transition metal Fe element is carried out on the basis of selecting a suitable manganese source. When manganese sulfate is preferably used as the reactant raw material, the addition of the doped transition metal can further improve the formaldehyde conversion rate of the catalyst on the original basis. Moreover, after increasing the relative humidity in the test, an appropriate amount of Fe element addition can maintain the performance of the catalyst.

[0093] Verification of the effects of the invention

[0094] The various catalysts prepared in the experiment were used for the catalytic oxidation reaction of formaldehyde:

[0095] Catalysts were prepared using different divalent Mn ion precursors as raw materials for formaldehyde removal tests. The catalyst with manganese sulfate as the raw material was labeled as Catalyst A, the catalyst with manganese acetate as the raw material was labeled as Catalyst B, the catalysts with manganese nitrate and manganese chloride as the raw materials were labeled as Catalyst C and Catalyst D respectively. 20 mg of each catalyst was taken, and the corresponding space velocity was 240,000 mL / (g·h). The experimental conditions were as follows: oxygen 21%, nitrogen 79%, the concentration of formaldehyde was controlled at 40 ppm, the relative humidity was 40%, and the reaction temperature was room temperature.

[0096] The catalytic activities of the obtained catalysts were all carried out on a fixed reaction bed. When the reaction reached a steady state, the composition of the reaction gas was measured. The catalytic activities of the catalysts are as Figure 1 shown.

[0097] From Figure 1 it can be seen that the catalyst using manganese sulfate as the precursor has a relatively high conversion rate of formaldehyde, and the conversion rate reaches 78%. The conversion rate of the catalyst using manganese acetate as the precursor is 70%, while the conversion rate of the catalyst using manganese nitrate as the precursor is 60%, and the conversion rate of the catalyst using manganese chloride as the precursor is less than 60%.

[0098] Catalysts were prepared by doping and modifying MnO₂ with different transition metals and used for formaldehyde removal tests. The Co-metal-doped catalyst is labeled as catalyst A, the Fe-metal-doped catalyst is labeled as catalyst B, and the Cu-metal-doped catalyst is labeled as catalyst C. 20 mg of each catalyst was taken, and the corresponding space velocity was 240,000 mL / (g·h). The experimental conditions were as follows: 21% oxygen, 79% nitrogen, the concentration of formaldehyde was controlled at 40 ppm, the relative humidity was 40%, and the reaction temperature was room temperature.

[0099] The catalytic activities of the obtained catalysts were all carried out on a fixed reaction bed. When the reaction reached a steady state, the composition of the reaction gas was measured. The catalytic activities of the catalysts were as Figure 2 shown.

[0100] It can be Figure 2 seen that the Fe-doped catalyst can maintain a very high formaldehyde decomposition conversion rate at room temperature. The conversion rate reached 94%, which was 16% higher than that of the original catalyst without transition metal doping, and was higher than that of the Co- and Cu-doped modified catalysts. Among them, the conversion rate of the Co-doped catalyst was 85%, and the conversion rate of the Cu-doped catalyst was 79%, with the smallest improvement effect.

[0101] From Figure 2 the tests, it can be found that the catalyst doped with Fe elements can significantly improve the formaldehyde decomposition conversion rate. Continuing to study the efficiency of Fe / MnO₂ catalysts with different Fe-Mn mass ratios for formaldehyde decomposition at room temperature, we prepared various catalysts with Fe and Mn element mass ratios of 1:4, 1:6, 1:8, and 1:10 for testing. Among them, the catalyst with Fe-Mn = 1:4 is labeled as catalyst A, the catalyst with Fe-Mn = 1:6 is labeled as catalyst B, the catalyst with Fe-Mn = 1:8 is labeled as catalyst C, and the catalyst with Fe-Mn = 1:10 is labeled as catalyst D. 20 mg of each catalyst was taken, and the corresponding space velocity was 240,000 mL / (g·h). The experimental conditions were as follows: 21% oxygen, 79% nitrogen, the concentration of formaldehyde was controlled at 40 ppm, the relative humidity was 40%, and the reaction temperature was room temperature.

[0102] The catalytic activities of the obtained catalysts were all carried out on a fixed reaction bed. When the reaction reached a steady state, the composition of the reaction gas was measured. The catalytic activities of the catalysts were as Figure 3 shown.

[0103] It can be Figure 3 seen that under the condition of 40% relative humidity, the four catalysts with different mass ratios all showed relatively excellent reaction activities, and the formaldehyde conversion rates were all above 90%. Therefore, under this condition, it is still impossible to truly distinguish the performance differences of the catalysts with different mass ratios.

[0104] From Figure 3The test results show that in a conventional humidity environment, the performance differences of catalysts with various mass ratios cannot be accurately distinguished. Considering that water molecules play a certain role in inhibiting the activity of the catalyst during the decomposition of formaldehyde, the relative humidity in the reaction atmosphere is increased for further testing. Similar to the above, various catalysts with mass ratios of Fe to Mn of 1:4, 1:6, 1:8, and 1:10 are still used for testing. Among them, the catalyst with Fe-Mn = 1:4 is labeled as catalyst A, the catalyst with Fe-Mn = 1:6 is labeled as catalyst B, the catalyst with Fe-Mn = 1:8 is labeled as catalyst C, and the catalyst with Fe-Mn = 1:10 is labeled as catalyst D. 20 mg of each catalyst is taken, and the corresponding space velocity is 240,000 mL / (g·h). The experimental conditions are as follows: oxygen 21%, nitrogen 79%, the concentration of formaldehyde is controlled at 40 ppm, the relative humidity is 90%, and the reaction temperature is room temperature.

[0105] The catalytic activities of the obtained catalysts are all carried out on a fixed reaction bed. When the reaction reaches a steady state, the composition of the reaction gas is measured. The catalytic activities of the catalysts are as Figure 4 shown.

[0106] It can be seen from Figure 4 this that under the condition of a relative humidity of 90%, when Fe-Mn = 1:6, the prepared catalyst can still maintain a relatively high formaldehyde conversion rate, and the conversion rate reaches 91%. However, the formaldehyde conversion activities of the catalysts prepared with other mass ratios decrease rapidly. When Fe-Mn = 1:4, the conversion rate drops to 80% and then basically remains stable. When Fe-Mn = 1:8 and 1:10, the conversion rates both drop to about 70% and basically remain stable.

[0107] As described above, these are only several embodiments of the present application and do not impose any form of limitation on the present application. Although the present application is disclosed with preferred embodiments as above, it is not intended to limit the present application. Any person skilled in the art, without departing from the scope of the technical solution of the present application, making some changes or modifications using the technical content disclosed above is equivalent to equivalent implementation cases and all fall within the scope of the technical solution.

Claims

1. Application of a transition metal-doped and modified MnO2 catalyst in formaldehyde removal, characterized in that, The catalyst is manganese potassium octahedron; The catalyst comprises a carrier and an active component; The carrier is diatomite; The active component is Fe / MnO2; In the catalyst, the mass ratio of Fe to Mn is 1:5.5 - 6.5; The preparation method of the transition metal doped and modified MnO2 catalyst comprises the following steps: S1. Obtain dispersion liquid I containing an Fe source; S2. Obtain dispersion liquid II containing manganese sulfate; S3. Obtain dispersion liquid III containing KMnO4; S4. Add dispersion liquid I, dispersion liquid II, and activated diatomite to dispersion liquid III, and obtain the catalyst after hydrothermal reaction; The diatomite is subjected to an activation treatment; the activation treatment is roasting; The mass ratio of the Fe source, the manganese sulfate, the KMnO4, and the diatomite is 1:3 - 5:2 - 3:7 - 10.

2. The application according to claim 1, characterized in that, The mass ratio of the active component to the carrier is 1:1.8 - 2.

9.

3. The application according to claim 1, characterized in that, The Fe source is selected from at least one of iron nitrate, iron sulfate, and iron chloride.

4. The application according to claim 1, characterized in that, The conditions of the roasting are as follows: The temperature is 400°C - 600°C; The time is 210 min - 270 min; The heating rate is 1°C / min.

5. The application according to claim 1, characterized in that, The mass ratio of the Fe source, the manganese sulfate, the KMnO4, and the diatomite is 1:3.6:2.5:7.

5.

6. The application according to claim 1, characterized in that, The conditions of the reaction are as follows: The temperature is 80°C - 120°C; The time is 22 h - 26 h.

Images