A doped manganese-molybdenum oxide catalyst, preparation method and method for catalytically removing VOCs

Abstract

The present invention provides a doped manganese-molybdenum oxide catalyst, a preparation method, and a method for catalytically removing VOCs using the same, and relates to the technical field of inorganic materials and air pollution control. The preparation method provided by the present invention uses potassium permanganate, manganese sulfate, and molybdate as raw materials, and distilled water as a solvent, and is prepared by a hydrothermal reaction. The preparation method provided by the present invention is simple and easy to operate, has a large output, and is environmentally friendly. The reaction temperature required for the catalytic removal of VOCs by the prepared catalyst is low, and it can remove more than 90% of benzene at 230°C. It has strong adaptability and still has high catalytic activity in complex atmospheres such as high moisture, particulate matter, and SO2. The catalyst also has strong durability and recyclability, can be used for long-term work in industry, and can work efficiently in industrial environments that require alternating hot and cold temperatures.

Description

Technical Field

[0001] The present invention relates to the technical field of inorganic materials and air pollution control, and in particular to a doped manganese-molybdenum oxide catalyst, a preparation method and a method for catalytically removing VOCs using the catalyst. Background Art

[0002] With the development of modern industrialization, volatile organic compounds (VOCs) have become a key focus of air pollution prevention and control efforts. VOCs are volatile and readily react with atmospheric pollutants such as NOx and SO2 to form photochemical smog, which contributes to the formation of ozone and fine particulate matter. Due to the adverse effects of VOCs on the environment and human health, as well as the continuous increase in VOC emissions, emission standards for VOCs are becoming increasingly stringent. Therefore, an effective method for removing VOCs is needed.

[0003] There are many methods for removing VOCs, among which catalytic oxidation is a very promising control technology, which is characterized by high efficiency and low production of secondary pollutants. The key to this method is to obtain catalysts with high activity, high selectivity and high stability. Existing catalysts can be divided into two categories. One category is precious metal catalysts (Pt, Pd, Ru, etc.). Because they have high catalytic activity for volatile organic compounds under lower temperature conditions, they have become a hot spot in catalyst research because of this advantage. However, due to the high cost and easy poisoning of precious metals, it is not easy to put them into actual production. The other category is non-precious metal catalysts. Due to their high natural abundance, low cost and high thermal stability, people hope to use non-precious metals to replace precious metals.

[0004] Currently, the production process of non-precious metal catalysts is complex and costly. They also have high catalytic temperatures, poor catalytic effects at low temperatures, and are easily poisoned and deactivated in complex atmospheres. Therefore, the development of a low-temperature, high-efficiency, inexpensive, and highly resistant non-precious metal catalyst is urgent. Summary of the Invention

[0005] In view of this, the object of the present invention is to provide a doped manganese-molybdenum oxide catalyst, a preparation method and a method for catalytic oxidation removal of VOCs by the same. The doped manganese-molybdenum oxide catalyst provided by the present invention can catalytically oxidize VOCs in the atmosphere at high efficiency and low temperature, and has a high removal effect on VOCs in complex atmospheres, high moisture atmospheres and particulate matter atmospheres. In addition, the preparation method provided by the present invention is simple to operate and environmentally friendly, and can meet industrial production requirements.

[0006] In order to achieve the above object, the present invention provides the following technical solution: a method for preparing a doped manganese-molybdenum oxide catalyst, which is prepared by a hydrothermal reaction using potassium permanganate, manganese sulfate and molybdate as raw materials and distilled water as solvent.

[0007] Preferably, the molar ratio of potassium permanganate to manganese sulfate is 1:(2.5-3).

[0008] Preferably, in the potassium permanganate, manganese sulfate and molybdate, the mass ratio of manganese element to molybdenum element is 1:(0.05-1).

[0009] The molybdate is selected from one of sodium molybdate, ammonium molybdate, magnesium molybdate and zinc molybdate.

[0010] Preferably, the hydrothermal reaction temperature is 140-180° C., and the reaction time is 10-15 h.

[0011] Preferably, the hydrothermal reaction further includes the steps of filtration, water washing and drying.

[0012] More preferably, the drying temperature is 50-90° C., and the drying time is 20-40 hours.

[0013] Preferably, the specific steps of the reaction are:

[0014] (1) Dissolve potassium permanganate and manganese sulfate in distilled water to obtain solution A and solution B respectively;

[0015] (2) Pour solution A into a reactor and stir, then add solution B dropwise to mix evenly to obtain solution C;

[0016] (3) quickly adding molybdate to solution C and stirring to obtain solution D;

[0017] (4) After solution D is subjected to a hydrothermal reaction, the solid product is filtered, washed with water, and dried.

[0018] The present invention also provides a doped manganese-molybdenum oxide catalyst prepared by the preparation method.

[0019] The present invention also provides a method for catalytically removing VOCs using the doped manganese-molybdenum oxide catalyst, wherein the doped manganese-molybdenum oxide catalyst is placed in exhaust gas at a certain flow rate and a catalytic reaction is carried out at a certain temperature.

[0020] Beneficial technical effects:

[0021] 1. The doped manganese-molybdenum oxide catalyst of the present invention has a low reaction temperature for catalytic removal of VOCs and can remove more than 90% of benzene at 230°C. It has strong adaptability and still has high catalytic activity in complex atmospheres such as high moisture, particulate matter, and SO2.

[0022] 2. The doped manganese-molybdenum oxide catalyst of the present invention has strong durability and cyclability, can work in industry for a long time, and can work efficiently in industrial environments that require alternating hot and cold temperatures.

[0023] 3. The preparation process of the doped manganese-molybdenum oxide catalyst of the present invention is simple and environmentally friendly, and can meet industrial production requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the SEM image of the catalyst obtained in Example 2;

[0025] Figure 2 TEM image of the catalyst obtained in Example 2;

[0026] Figure 3 The performance diagram of the catalysts of Examples 1 to 3 and Comparative Example 1 for catalytic oxidation of benzene in air; Figure 3 a is the conversion rate of benzene catalyzed by the catalyst (in the figure: the horizontal axis represents temperature, unit is ° C; the vertical axis represents the conversion rate of benzene, unit is %), Figure 3 b is the yield of CO2 (in the figure: the horizontal axis represents temperature, unit is °C; the vertical axis represents the yield of CO2, unit is %).

[0027] Figure 4 Graph showing water resistance of the catalysts of Example 2 and Comparative Example 1 (in the graph, the abscissa represents time in h; the ordinate represents benzene conversion in %);

[0028] Figure 5 This is a stability performance diagram of the catalyst in Example 2 for catalytic oxidation of benzene in air; Figure 5 a is the stability test (in the figure: the horizontal axis represents time, unit is h; the vertical axis represents the conversion rate of benzene, unit is %), Figure 5 b is a hot and cold alternating cycle test (in the figure: the horizontal axis represents time, unit is h; the vertical axis represents the conversion rate of benzene, unit is %);

[0029] Figure 6 1 is a performance diagram of the catalyst of Example 2 for catalytic oxidation of benzene in air under different space velocity conditions (in the figure, the abscissa represents temperature, unit: ° C; the ordinate represents benzene conversion, unit: %);

[0030] Figure 7 This is a performance diagram of the effects of the catalyst particles of Example 2 and Comparative Example 1 on the catalytic oxidation of benzene in the air (in the figure: the abscissa represents temperature, unit: ° C; the ordinate represents the conversion rate of benzene, unit: %). DETAILED DESCRIPTION

[0031] The present invention provides a method for preparing a doped manganese-molybdenum oxide catalyst, which comprises the following steps:

[0032] (1) Potassium permanganate and manganese sulfate were dissolved in 50 ml and 10 ml of distilled water, respectively, to obtain solution A and solution B; the molar ratio of potassium permanganate to manganese sulfate was preferably 1:(2.5-3).

[0033] (2) Pour solution A into a reactor and stir, then add solution B dropwise for no more than 3 min to mix evenly, to obtain solution C;

[0034] The mixing mode of the present invention is to control the mixing of solution B by adding it dropwise, so that manganese sulfate and potassium permanganate can be fully mixed and uniformly mixed. The present invention controls the stirring time to not exceed 3 minutes. If the stirring time is too long, the reaction may occur at room temperature, and subsequent addition of reagents will result in uneven stirring, so that the molybdenum element cannot be uniformly doped into the final catalyst.

[0035] (3) quickly adding molybdate to solution C and stirring for 2 to 3 minutes to obtain solution D; the mass ratio of manganese element to molybdenum element in the potassium permanganate, manganese sulfate and molybdate is preferably 1:(0.05 to 1), more preferably 1:(0.1 to 0.9), and most preferably 1:(0.1 to 0.5); the molybdate is selected from one of sodium molybdate, ammonium molybdate, magnesium molybdate and zinc molybdate;

[0036] In the present invention, molybdate is quickly added to solution C to prevent potassium permanganate and manganese sulfate from reacting at room temperature and preventing the molybdenum element from being uniformly doped.

[0037] (4) Solution D is subjected to a hydrothermal reaction to obtain a solid product, which is then repeatedly filtered, washed with water, and dried at 50-90° C. for 20-40 h. The reaction temperature is preferably 140-180° C., more preferably 150-170° C., and most preferably 160° C. The reaction time is preferably 10-15 h, more preferably 12-15 h, and most preferably 12 h.

[0038] After obtaining the solid product, the present invention uses suction filtration to perform solid-liquid separation. The density of the solid product is not much different from that of the liquid, and the effect of centrifugal separation is not good. By using suction filtration, filter paper with a small pore size is selected, and a suction pump is used to reduce the pressure in the suction bottle to achieve solid-liquid separation. This method is easy to operate and has a small loss of solid product.

[0039] The present invention also provides a doped manganese-molybdenum oxide catalyst prepared by the preparation method described in the above technical solution.

[0040] The catalyst prepared by the present invention has a spherical morphology, which is a solid sphere formed by clusters of short rods of varying lengths. Compared with the rod-shaped morphology, this morphology has a larger specific surface area and a smaller average pore size. The large specific surface area and pore volume are beneficial to the mass transfer and adsorption of reactants, while the small pore volume can extend the residence time of the reactants, allowing the reactants to fully contact the catalyst, which is beneficial to catalytic combustion.

[0041] The present invention also provides a method for catalytically removing VOCs using the doped manganese-molybdenum oxide catalyst, wherein the doped manganese-molybdenum oxide catalyst is placed in exhaust gas at a certain flow rate and a catalytic reaction is carried out at a certain temperature.

[0042] The waste gas can be ordinary waste gas or waste gas with high moisture content and complex atmosphere.

[0043] In order to better understand the present invention, the content of the present invention is further illustrated below in conjunction with the examples, but the content of the present invention is not limited to the following examples.

[0044] Example 1

[0045] (1) Dissolve 0.4 g of potassium permanganate in 50 ml of distilled water to obtain solution A. Dissolve 0.171 g of manganese sulfate in 10 ml of distilled water to obtain solution B.

[0046] (2) Solution A was transferred into a 100 ml reactor and magnetically stirred, and solution B was added dropwise for no more than 3 min to ensure uniform mixing, to obtain solution C;

[0047] (3) 0.0075 g of ammonium molybdate was quickly added to solution C and stirred for 3 min to obtain solution D;

[0048] (4) Solution D was placed in an oven and reacted at 160°C for 12 hours to obtain a precipitated oxide, which was then filtered and washed with water three times, and dried in an oven at 60°C for 24 hours to finally obtain a 0.1 manganese molybdenum oxide catalyst (0.1MoMnO2).

[0049] Example 2

[0050] (1) Dissolve 0.4 g of potassium permanganate in 50 ml of distilled water to obtain solution A. Dissolve 0.171 g of manganese sulfate in 10 ml of distilled water to obtain solution B.

[0051] (2) Solution A was transferred into a 100 ml reactor and magnetically stirred, and solution B was added dropwise for no more than 3 min to ensure uniform mixing, to obtain solution C;

[0052] (3) 0.0237 g of ammonium molybdate was quickly added to solution C and stirred for 3 min to obtain solution D;

[0053] (4) Solution D was placed in an oven and reacted at 160°C for 12 hours to obtain a precipitated oxide, which was then filtered and washed with water three times, and dried in an oven at 60°C for 24 hours to finally obtain a 0.3 manganese molybdenum oxide catalyst (0.3MoMnO2).

[0054] Scanning electron microscopy (SEM) was used to characterize the morphology of 0.3MoMnO2. The scanning voltage was 5.kV and the magnification was 100000. Figure 1 As shown in Figure 2, the morphology of the sample is spherical and is assembled from short rods of varying lengths. Transmission electron microscopy (SEM) was used to characterize the morphology and analyze the sample. Figure 2 As shown, the sample is a solid sphere composed of clusters of short rods of varying lengths.

[0055] Example 3

[0056] (1) Dissolve 0.4 g of potassium permanganate in 50 ml of distilled water to obtain solution A. Dissolve 0.171 g of manganese sulfate in 10 ml of distilled water to obtain solution B.

[0057] (2) Solution A was transferred into a 100 ml reactor and magnetically stirred, and solution B was added dropwise for no more than 3 min to ensure uniform mixing, to obtain solution C;

[0058] (3) 0.0478 g of ammonium molybdate was quickly added to solution C and stirred for 3 min to obtain solution D;

[0059] (4) Solution D was placed in an oven and reacted at 160°C for 12 hours to obtain a precipitated oxide, which was then filtered and washed with water three times, and dried in an oven at 60°C for 24 hours to finally obtain a 0.6 manganese molybdenum oxide catalyst (0.6MoMnO2).

[0060] Comparative Example 1

[0061] (1) Dissolve 0.4 g of potassium permanganate in 50 ml of distilled water to obtain solution A. Dissolve 0.171 g of manganese sulfate in 10 ml of distilled water to obtain solution B.

[0062] (2) Solution A was transferred into a 100 ml reactor and magnetically stirred, and solution B was added dropwise and stirred for 5 min to obtain solution C;

[0063] (3) Solution C was placed in an oven and reacted at 160°C for 12 hours to obtain a precipitated oxide, which was then filtered and washed with water three times, and dried in an oven at 60°C for 24 hours to finally obtain a manganese oxide catalyst (MnO2).

[0064] Test example

[0065] 1. The catalysts prepared in Examples 1, 2, 3 and Comparative Example 1 were tested for catalytic oxidation of benzene in the atmosphere:

[0066] 100 mg of each catalyst prepared in Examples 1, 2, 3, and Comparative Example 1 was weighed and placed in a quartz tube fixed-bed flow reactor (inner diameter 6 mm). The reactor was vertically placed in the center of a temperature-programmed tubular furnace. 100 mL / min of synthetic air (20 vol% O2 and 80 vol% N2) containing approximately 460 ppm of benzene was used to achieve a gas hourly space velocity (GHSV) of 60,000 mL / g / h.

[0067] The results of the catalytic removal of benzene performance of Examples 1, 2, 3 and Comparative Example 1 are as follows Figure 3 As shown in a. Figure 3 It can be seen from a that the T of MnO2, 0.1MoMnO2, 0.3MoMnO2 and 0.6MoMnO2 90 The catalytic activities of the four nanostructured manganese dioxide catalysts are as follows: 0.1MoMnO2>0.3MoMnO2>0.6MoMnO2>MnO2. The T 50 The temperatures required for the benzene conversion to reach 50% are 214°C, 182°C, 186°C and 197°C respectively. It is noteworthy that the benzene removal efficiency of the 0.1MoMnO2 sample increases sharply from 50% at 182°C to 90% at 230°C, which means that it has the best catalytic activity among the four catalysts. The yield of carbon dioxide on the catalyst is as follows Figure 3 As shown in Figure 2b, 0.1MoMnO2 can be completely converted into CO2 at 194°C, 0.3MoMnO2 can be completely converted into CO2 at 196°C, and 0.6MoMnO2 can be completely converted into CO2 at 208°C. The temperature at which the modified catalyst is completely converted into CO2 is significantly lower than the temperature required for benzene conversion, indicating that the modified catalyst has excellent CO2 selectivity and can reduce the formation of by-products.

[0068] 2. Investigate the effect of atmospheric moisture on the catalytic activity of catalysts

[0069] Weigh 100 mg of the catalysts prepared in Example 2 and Comparative Example 1, respectively, and heat the catalysts in Example 2 and Comparative Example 1 to 267°C at a rate of 5°C / min. React for 3 hours at a total flow rate of 100 ml / min (20 vol% O2 + 80 vol% N2 + 460 ppm benzene). Then, generate water vapor by blowing synthetic air into a water saturator at ambient temperature. Then, mix the moisture with the benzene flow to achieve a flow rate of 100 ml / min, a water content of about 2.0 vol%, and a benzene content of about 460 ppm. React for 4.5 hours, then change the atmosphere to 100 ml / min (20 vol% O2 + 80 vol% N2 + 460 ppm benzene) and react for 3 hours to investigate the effect of moisture in the atmosphere on the catalytic activity of the catalyst. The results are as follows: Figure 4 shown.

[0070] Under actual working conditions, the reaction gas often contains moisture. Therefore, we conducted a water resistance test on MnO2 and 0.3MoMnO2 at 267℃. The test results are as follows: Figure 4 As shown in the figure, in the absence of water, the benzene conversion rate was nearly 100% within the first 3 hours. However, after the introduction of 2 vol% water vapor into the feed gas, the benzene conversion rate of MnO2 gradually dropped below 90% and continued to decline. After 4.5 hours of reaction, the water vapor was removed, and the benzene conversion rate gradually recovered to nearly 100%. In contrast, the benzene conversion rate of 0.3MoMnO2 remained close to 100%, and remained unchanged after the addition of water. These results indicate that the incorporation of Mo can improve the water resistance of the catalyst.

[0071] 3. Investigate the stability of the catalyst

[0072] 100 mg of the catalyst of Example 2 was weighed and heated to 235°C at a rate of 5°C / min. The reaction was carried out for 48 hours and four cycles in a synthetic air atmosphere (20 vol% O2 and 80 vol% N2) containing about 460 ppm of benzene at a flow rate of 100 mL / min to examine the stability of the catalyst. Figure 5 shown.

[0073] The stability of 0.3MoMnO2 catalyst was tested. Figure 5 As shown in Figure a, the benzene conversion rate of 0.3MoMnO2 catalyst remained above 90% after 48 hours of reaction at 235°C, and there was no significant decline, indicating that 0.3MoMnO2 has good durability and can be used in industry for a long time, reducing costs.

[0074] Four heating-cooling thermal cycling experiments were conducted on the 0.3MoMnO2 catalyst as a method to evaluate the cyclic performance of the inevitable periodic heating-cooling process in practical applications. The results are shown in Figure 2. Figure 5 As shown in Figure 2, after multiple cycles, the 0.3MoMnO2 catalyst was found to still be able to remove more than 90% of benzene at 235°C. The sudden drop in temperature did not significantly affect the catalyst, indicating that the 0.3MoMnO2 catalyst has strong shock resistance and can be used in industrial environments with large temperature fluctuations.

[0075] 4. Investigate the effect of different contact times between reactants and catalytic sites on catalytic activity

[0076] 40 mg, 100 mg, and 250 mg of the catalyst from Example 2 were weighed and tested at different space velocities in 100 mL / min of synthetic air (20 vol% O₂ and 80 vol% N₂) containing approximately 460 ppm benzene. The temperature was programmed to heat at 5°C / min to each measurement temperature. The outlet benzene and CO₂ / CO concentrations were recorded by a GASERA ONE. The experimental results are shown in Figure 1. Figure 6 As shown:

[0077] By changing the mass of the catalyst and the size of the space velocity, the effect of different contact times between the reactants and the catalytic site on the catalytic activity was investigated. The results are as follows: Figure 6 As shown, as the space velocity increases from 60,000 ml / gh to 150,000 ml / gh, the benzene conversion rate decreases due to the reduced contact time between the reactants and the catalytic sites at higher space velocities. However, at a high space velocity of 150,000 ml / gh, 0.3MoMnO2 can still remove 90% of benzene at temperatures below 270°C. The benzene conversion rates at low space velocities of 24,000 ml / gh and 60,000 ml / gh are similar, indicating that increasing contact time does not improve catalytic activity. However, optimal usage levels can be provided for industrial use to avoid waste, reduce losses, and lower costs.

[0078] 5. Test on the effect of particulate matter on catalyst activity

[0079] 100 mg of the catalyst of Example 2 was weighed and soaked in 10 ml of 0.1 M NaSO4 and NaNO3 solution for 10 min, dried, and then subjected to a particulate matter effect test in 100 mL / min synthetic air (20 vol% O2 and 80 vol% N2) containing about 460 ppm of benzene. The experimental results are shown in FIG. Figure 7 As shown:

[0080] Depend on Figure 7The trend in catalyst activity changes clearly shows the changes caused by sulfate and nitrate. Based on the activity of the fresh sample, the degree of deactivation was used to test the catalyst's resistance to deactivation. In the presence of particulate matter, 0.3MoMnO2 performed better than pure MnO2. The catalytic performance of 0.3MoMnO2 was not reduced but instead improved in the presence of particulate matter. This may be due to the presence of sulfate, which increases the acidic sites of the catalyst and thus promotes catalytic performance. This shows that Mo doping can improve the catalyst's resistance to deactivation and is suitable for industrial environments with complex atmospheres such as particulate matter and SO2.

[0081] In summary, the catalyst provided by the present invention is obtained by doping heteroatom Mo into manganese dioxide using a one-step hydrothermal and filtration method, which achieves the effect of the catalyst being able to efficiently catalyze the removal of VOCs under low temperature conditions and effectively catalyze the oxidation of VOCs under low temperature conditions. In addition, the catalyst has a long service life and has the characteristics of water resistance and resistance to particulate matter, and is suitable for large-scale production and use.

[0082] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. Application of a doped manganese-molybdenum oxide catalyst in catalytic removal of VOCs, characterized in that: The preparation method of the doped manganese molybdenum oxide catalyst is: (1) Dissolve potassium permanganate and manganese sulfate in distilled water to obtain solution A and solution B respectively; (2) Pour solution A into a reactor and stir, then add solution B dropwise to mix evenly to obtain solution C; (3) quickly adding molybdate to solution C and stirring to obtain solution D; (4) After solution D is subjected to a hydrothermal reaction, the solid product is filtered, washed with water, and dried; The molar ratio of potassium permanganate to manganese sulfate is 1:(2.5-3); The mass ratio of manganese element to molybdenum element in the potassium permanganate, manganese sulfate and molybdate is 1:(0.05-1); The hydrothermal reaction temperature is 140-180°C and the reaction time is 10-15h; The molybdate is selected from one of sodium molybdate, ammonium molybdate, magnesium molybdate and zinc molybdate; After the hydrothermal reaction, the steps of filtration, water washing and drying are also included; The drying temperature is 50-90°C and the drying time is 20-40h; The morphology of the doped manganese-molybdenum oxide catalyst is a solid sphere formed by clusters of short rods of different lengths.

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