Water-resistant low-temperature catalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of catalysis, and relates to a water-resistant low-temperature catalyst and a preparation method and application thereof.The surface of a Mn / Al2O3 catalyst is doped with Cr oxide, and then a certain amount of 2, 4, 6-triisopropyl benzoic acid (Y-CrMn / Al2O3) is grafted to the surface of CrMn / Al2O3. The water-resistant low-temperature catalyst has excellent catalytic activity and water poisoning resistance, 2, 4, 6-triisopropyl benzoic acid is grafted on the surface of the chromium and manganese doped Al2O3 catalyst, the water poisoning resistance of the catalyst in 5% vol water vapor wet flue gas is improved, and the activity of the catalyst is reduced by about 3%. The catalyst is especially suitable for low-temperature catalytic oxidation of VOCs in moisture-containing flue gas, and has a wide application prospect. The catalyst is prepared by adopting conventional dipping, calcining and surface grafting processes, the process is simple, the reproducibility is good, and the catalyst shows good stability and water-resistant stability in long-term use.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of catalysis, and relates to a water-resistant low-temperature catalyst and a preparation method and application thereof. BACKGROUND

[0002] In the low-temperature catalytic removal process of pollutants such as volatile organic compounds (VOCs) and carbon monoxide, water vapor commonly existing in flue gas is easy to compete with active sites on the surface of the catalyst for adsorption, thereby causing a significant decrease in catalytic activity, and even causing irreversible water poisoning and deactivation. Therefore, developing a catalyst material with good low-temperature activity and water poisoning resistance is one of the important technical problems to be solved in the field of atmospheric pollution control.

[0003] Existing researches show that surface modification of inorganic materials by introducing hydrophobic organic molecules on the surface of the materials is an effective means to improve the hydrophobic property of the materials and to control the behavior of water molecules at the interface. However, there are still few related researches on introducing organic molecules into a metal oxide catalyst system to improve the water poisoning resistance of the catalyst, and the main reasons are the following two technical limitations: on the one hand, the organic molecules used for surface modification of the catalyst need to meet multiple requirements, that is, the organic molecules need to have strong hydrophobicity, need to have a functional group that can be stably combined with the surface of the metal oxide, and need to have good thermal stability under the temperature conditions of the catalytic reaction; on the other hand, grafting of the organic molecules on the surface of the metal oxide often occupies or shields part of the metal active sites, thereby weakening the effective contact between the active components and the reactants, and thus causing a decrease in the overall activity of the catalyst, which limits the application of this method in the field of low-temperature catalysis. SUMMARY

[0004] The application aims to overcome the deficiencies of the prior art, and provides a water-resistant low-temperature catalyst and a preparation method and application thereof. Cr oxide is doped on the surface of a Mn / Al2O3 catalyst, and then a certain amount of 2,4,6-triisopropylbenzoic acid (Y-CrMn / Al2O3) is grafted on the surface of the CrMn / Al2O3. Compared with a traditional supported Mn catalyst (Mn / Al2O3), the catalyst has good performance in high-activity removal of VOCs at low temperature and resistance to water vapor poisoning in flue gas.

[0005] The technical solution adopted by the application to solve the technical problems is as follows: The application provides a preparation method of a water-resistant low-temperature catalyst, and the steps are as follows: (1) γ-Al2O3 carrier, manganese salt and chromium salt are dissolved in deionized water, impregnated by stirring, dried in a 70-90 ℃ oven, then ground into fine powder, and calcined in static air at 450-550 ℃ for 2-6 h to obtain a CrMn / Al2O3 catalyst; (2) dispersing the prepared CrMn / Al2O3 catalyst into dichloromethane containing 2-6 mmol / L 2,4,6-triisopropylbenzoic acid by ultrasonic waves to obtain a suspension, stirring the suspension, centrifuging to collect the hydrophobic CrMn / Al2O3 catalyst, washing several times, and drying the hydrophobic CrMn / Al2O3 catalyst at 90-110℃ to obtain the water-resistant low-temperature catalyst (Y-CrMn / Al2O3).

[0006] Preferably, the preparation method of the γ-Al2O3 carrier is as follows: dissolving Al(NO3)3·9H2O, K2SO4 and CO(NH2)2 in a mass ratio of 6-8:3-4:2-3 in 80-120 mL of deionized water to obtain a mixture, then transferring the mixture into a stainless steel high-pressure reaction kettle, placing it in an oven, heating at 170-220℃ for 2-4 h, cooling to room temperature, vacuum filtering, washing the white particles with deionized water until the impurity ions are removed, collecting the white precipitate, drying for 10-14 h, and calcining to obtain the γ-Al2O3 carrier.

[0007] Preferably, the molar ratio of the γ-Al2O3 carrier, the manganese salt and the chromium salt is 8-15:0.5-2:0.5-2, and further preferably 10:1:1.

[0008] Preferably, the manganese salt is one or two or more of MnCl2·4H2O, Mn(CH3COO)2·4H2O and MnSO4·H2O, and the chromium salt is one or two or more of Cr(CH3COO)3, Cr(NO3)3·9H2O, CrCl3·6H2O and Cr2(SO4)3.

[0009] Preferably, the stirring and impregnation time in step (1) is 10-14 h.

[0010] Preferably, the drying in step (1) is carried out in an oven at 70-90℃ for 10-12 h. Further preferably, the drying is carried out in an oven at 80℃ for 12 h.

[0011] Preferably, the suspension is stirred at room temperature for 3-5 h.

[0012] The second aspect of the present application discloses a water-resistant low-temperature catalyst obtained by the above preparation method.

[0013] The third aspect of the present application discloses an application of the water-resistant low-temperature catalyst in VOCs low-temperature catalytic oxidation.

[0014] Preferably, the application method is as follows: placing the water-resistant low-temperature catalyst in a reactor, introducing 40 ppm of toluene, 5 vol.% of O2 and a carrier gas N2, introducing water vapor, monitoring the outlet concentration of toluene, and calculating the removal efficiency.

[0015] Preferably, the catalytic efficiency of VOCs is calculated as follows:

[0016] wherein η represents the catalytic oxidation efficiency, C (in) is the concentration of pollutants (ppm) entering the reactor, C (out) is the concentration of pollutants (ppm) at the outlet of the reactor.

[0017] Preferably, the temperature of catalytic oxidation is 180-220℃.

[0018] The present application proposes a design idea of an organic modification-metal doping synergistically regulated water-resistant low-temperature catalyst, which takes manganese oxide as the main active component and utilizes its excellent low-temperature catalytic activity; takes alumina (Al2O3) as the carrier to improve the dispersity and structural stability of manganese oxide. In order to enhance the stability of the catalyst under the condition of containing water, a kind of organic molecule, 2,4,6-triisopropylbenzoic acid, which has strong hydrophobicity, good thermal stability, contains carboxyl functional groups and can form stable chemical combination with the surface of metal oxide, is introduced as the hydrophobic modifier of the surface of the catalyst.

[0019] In order to avoid the direct combination of the organic modifier with the active sites of manganese oxide and cause the loss of low-temperature activity, the present application introduces chromium oxide to dope the MnOx / Al2O3 catalyst before organic modification, and then grafts 2,4,6-triisopropylbenzoic acid molecules. When manganese oxide and chromium oxide exist on the surface of the catalyst at the same time, the organic carboxylic acid molecules preferentially combine with chromium oxide. The reason is that the surface of chromium oxide has strong Lewis acidity and affinity to carboxyl functional groups, and is more prone to coordinate with 2,4,6-triisopropylbenzoic acid molecules than manganese oxide; at the same time, 2,4,6-triisopropylbenzoic acid molecules have large steric hindrance, and their preferential anchoring on the surface of chromium oxide can form a local hydrophobic layer on the surface of the catalyst, effectively preventing the enrichment of water molecules near the active sites, without significantly shielding the low-temperature active centers of manganese oxide, so as to balance the catalytic activity and water resistance. Therefore, while the organic modifier endows the catalyst surface with hydrophobic properties, it significantly reduces the adverse effects of the organic modifier on the main low-temperature active sites of manganese oxide, thereby achieving the synergistic improvement of catalytic activity and water resistance.

[0020] The advantages and positive effects of the present application are: (1) The water-resistant low-temperature catalyst has excellent catalytic activity and water resistance, and the water resistance of the catalyst in 5%vol water vapor wet flue gas is improved by grafting 2,4,6-triisopropylbenzoic acid on the surface of the chromium and manganese doped Al2O3 catalyst, and the activity of the catalyst is only decreased by about 3%. The catalyst is particularly suitable for low-temperature catalytic oxidation of VOCs in wet flue gas, and has a wide application prospect.

[0021] (2) The catalyst is prepared by conventional impregnation, calcination and surface grafting process, which is simple in process, good in reproducibility, and the catalyst shows good stability and water resistance in long-term use. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 XRD patterns of the catalyst of Example 1 (Y-CrMn / Al2O3) and Comparative Example 1; Figure 2 SEM image of the catalyst of Example 1 (Y-CrMn / Al2O3); Figure 3 Energy dispersive X-ray spectroscopy (EDS) element distribution map of the catalyst of Example 1 (Y-CrMn / Al2O3); Figure 4 Water contact angle test diagram of Example 1 (Y-CrMn / Al2O3), Comparative Example 1 (Mn / Al2O3) and Comparative Example 3 (CrMn / Al2O3); Figure 5 Catalytic conversion efficiency diagram of toluene in dry and wet flue gas of the catalyst modified by different concentrations of 2,4,6-triisopropylbenzoic acid; Figure 6 Conversion efficiency diagram of VOCs in wet flue gas containing 5% water vapor of the catalyst of Example 1 (Y-CrMn / Al2O3) and Comparative Example 1 (Mn / Al2O3); Figure 7 Catalytic activity diagram of toluene in wet flue gas (containing 5% water vapor) of the catalyst prepared in Example 1 and Comparative Examples 4-6. DETAILED DESCRIPTION

[0023] The application will be further described in detail by specific examples, the following examples are only descriptive, not limiting, and cannot limit the protection scope of the application.

[0024] The substances and sources in the following examples are as follows: Al (NO3) 3·9H2O (99.5%, analytical purity AR, Macklin), K2SO4(99.0%, analytical purity AR, Ron), CO(NH2)2(99.0%, analytical purity AR, Ron), MnCl2·4H2O (≥99.0%, analytical purity AR, Comin), chromium acetate (99.9%, analytical purity AR, Ron), zinc chloride (98.0%, GR, Damo), zirconium chloride (98.0%, Aiko Reagent), 2,4,6-triisopropylbenzoic acid (99.9%, analytical purity AR, Ron).

[0025] Example 1 A method for preparing a water-resistant low-temperature catalyst, the steps are as follows: (1) Preparation of γ-Al2O3 carrier: 7.55 g of Al (NO3) 3·9H2O, 3.5 g of K2SO4 and 2.5 g of CO(NH2)2 were dissolved in 80 mL of deionized water to obtain a mixture, and then the obtained mixture was transferred to a 100 mL Teflon-lined stainless steel high-pressure reactor, which was placed in an oven at 180 ℃ for 3 h. After cooling to room temperature, vacuum filtration was carried out, and the white particles were continuously washed with deionized water until the impurity ions were removed. The white precipitate was collected and dried at 80 ℃ for 12 h, and then calcined at 500 ℃ in a muffle furnace for 2 h to obtain a γ-Al2O3 carrier.

[0026] (2) Preparation of Cr oxide doped Mn / Al2O3 catalyst: 0.01 mol of γ-Al2O3 carrier, 0.001 mol of manganese chloride tetrahydrate and 0.001 mol of chromium acetate were placed in 20 mL of deionized water, and impregnated for 12 h under stirring, and then dried in an 80 ℃ oven for 12 h. Then, it was ground into fine powder in a mortar, and calcined at 500 ℃ in static air for 3 h to obtain a CrMn / Al2O3 catalyst.

[0027] (3) Preparation of 2,4,6-triisopropylbenzoic acid modified catalyst: the prepared CrMn / Al2O3 catalyst was dispersed into dichloromethane containing 6 mmol / L of 2,4,6-triisopropylbenzoic acid by ultrasonic wave to obtain a suspension, and the suspension was stirred vigorously at room temperature for 4 h, and then the treated hydrophobic CrMn / Al2O3 catalyst was collected by centrifugation. After washing several times with acetone and ethanol, the hydrophobic CrMn / Al2O3 catalyst was dried at 100 ℃ for 12 h to obtain a water-resistant low-temperature catalyst (Y-CrMn / Al2O3).

[0028] Example 2 The difference from the example is that step (3) uses 2 mmol / L of 2,4,6-triisopropylbenzoic acid in dichloromethane.

[0029] Example 3 The difference from the example is that step (3) uses 4 mmol / L of 2,4,6-triisopropylbenzoic acid in dichloromethane.

[0030] Example 4 The difference from Example 1 is that step (3) uses 8 mmol / L of 2,4,6-triisopropylbenzoic acid in dichloromethane.

[0031] Comparative Example 1 A method for preparing a catalyst, the steps are as follows: (1) The same as Example 1; (2) Put 0.01 mol of γ-Al2O3 carrier and 0.001 mol of manganese chloride tetrahydrate into 20 mL of deionized water together, immerse for 12 h under stirring, dry in an 80 ℃ oven for 12 h, then grind into fine powder in a mortar, and calcine in static air at 500 ℃ for 3 h to obtain a Mn / Al2O3 catalyst.

[0032] Comparative Example 2 A method for preparing a catalyst, the steps are as follows: (1) The same as Example 1; (2) Put 0.01 mol of γ-Al2O3 carrier and 0.001 mol of chromium acetate into 20 mL of deionized water together, immerse for 12 h under stirring, dry in an 80 ℃ oven for 12 h, then grind into fine powder in a mortar, and calcine in static air at 500 ℃ for 3 h to obtain a Cr / Al2O3 catalyst.

[0033] Comparative Example 3 The difference from Example 1 is that step (3) is omitted, and the CrMn / Al2O3 catalyst is used directly.

[0034] Comparative Example 4 A method for preparing a water-resistant low-temperature catalyst, 6 mmol / L of 2,4,6-triisopropylbenzoic acid is directly doped on the surface of Mn / Al2O3 (the preparation method is the same as Comparative Example 1) to obtain Y-Mn / Al2O3.

[0035] Comparative Example 5 A method for preparing a water-resistant low-temperature catalyst, the steps are as follows: (1) The same as Example 1; (2) 0.01 mol γ-Al2O3 carrier was put into 20 mL deionized water together with 0.001 mol manganese chloride tetrahydrate and 0.001 mol zinc chloride, and impregnated under stirring for 12 h, dried in an 80 ℃ oven for 12 h, then ground into fine powder in a mortar, and calcined in static air at 500 ℃ for 3 h to obtain a ZnMn / Al2O3 catalyst.

[0036] (3) The prepared ZnMn / Al2O3 catalyst was dispersed into dichloromethane containing 6 mmol / L of 2,4,6-triisopropylbenzoic acid by ultrasonic wave to obtain a suspension, the suspension was stirred vigorously at room temperature for 4 h, then the treated hydrophobic ZnMn / Al2O3 catalyst was collected by centrifugation, washed with acetone and ethanol for several times, and the hydrophobic ZnMn / Al2O3 catalyst was dried at 100 ℃ for 12 h to obtain a water-resistant low-temperature catalyst (Y-ZnMn / Al2O3 catalyst).

[0037] Comparative Example 6 A method for preparing a water-resistant low-temperature catalyst, comprising the following steps: (1) The same as in Example 1; (2) 0.01 mol γ-Al2O3 carrier was put into 20 mL deionized water together with 0.001 mol manganese chloride tetrahydrate and 0.001 mol zirconium chloride, and impregnated under stirring for 12 h, dried in an 80 ℃ oven for 12 h, then ground into fine powder in a mortar, and calcined in static air at 500 ℃ for 3 h to obtain a ZrMn / Al2O3 catalyst.

[0038] (3) The prepared ZrMn / Al2O3 catalyst was dispersed into dichloromethane containing 6 mmol / L of 2,4,6-triisopropylbenzoic acid by ultrasonic wave to obtain a suspension, the suspension was stirred vigorously at room temperature for 4 h, then the treated hydrophobic ZrMn / Al2O3 catalyst was collected by centrifugation, washed with acetone and ethanol for several times, and the hydrophobic ZrMn / Al2O3 catalyst was dried at 100 ℃ for 12 h to obtain a water-resistant low-temperature catalyst (Y-ZrMn / Al2O3 catalyst).

[0039] Performance test and analysis Example 1 (Y-CrMn / Al2O3), Comparative Example 1 (Mn / Al2O3) and Comparative Example 3 (CrMn / Al2O3) were subjected to XRD analysis, as shown in FIG. 1, and it can be seen from comparison of the XRD spectrum with the standard spectrum of γ-Al2O3 crystal that no characteristic peaks of Mn oxide and Cr oxide are observed in the three catalysts, indicating that the two oxides are highly dispersed. Figure 1

[0040] ​The SEM image of Y-CrMn / Al2O3 of Example 1 is shown in Figure 1. The EDS mapping of Y-CrMn / Al2O3 of Example 1 is shown in Figure 2. It can be seen that Mn oxide and Cr oxide are uniformly distributed on the surface of γ-Al2O3, and C and O elements represent the grafted 2,4,6-triisopropylbenzoic acid. It can be seen from the element distribution that the organic matter is mainly loaded on Cr, which is inconsistent with Mn. Figure 2 Figure 3

[0041] The water contact angle of Example 1 (Y-CrMn / Al2O3), Comparative Example 1 (Mn / Al2O3) and Comparative Example 3 (CrMn / Al2O3) was tested, and the results are shown in Figure 3. It can be seen that the water contact angle of Mn / Al2O3 catalyst is 27.7°, the water contact angle of CrMn / Al2O3 catalyst is 32.8°, and the water contact angle of Y-CrMn / Al2O3 catalyst is 52.3°, which indicates that Cr doping improves the hydrophobicity of the catalyst surface, and surface grafting further improves the hydrophobicity of the catalyst surface. The improvement of hydrophobicity is conducive to reducing the adsorption of water molecules on the catalyst surface, which may be conducive to the catalyst to exhibit good water resistance in the reaction process. Figure 4

[0042] Application of water-resistant low-temperature catalyst in VOCs low-temperature catalytic oxidation: VOCs activity test method: under the condition of 200℃, the catalyst samples of examples and comparative examples were placed in the reactor, 40 ppm toluene, 5vol.% O2 and carrier gas N2 were introduced, the conversion efficiency of toluene on the catalyst in dry flue gas was tested, then 5%vol of water vapor was introduced into the flue gas, and the conversion efficiency of toluene on the catalyst in wet flue gas was tested. The catalytic efficiency formula of VOCs is:

[0043] Wherein, η represents the catalytic oxidation efficiency, C (in) is the concentration (ppm) of pollutants entering the reactor, C (out) is the concentration (ppm) of pollutants at the outlet of the reactor.

[0044] The catalytic activity of toluene in dry flue gas or wet (containing 5% water vapor) flue gas of the catalyst prepared in Examples 1-4 and Comparative Example 3 is shown in Figure 4. Figure 5 ​​​As shown in the table, the catalytic activity of the CrMn / Al2O3 catalyst modified by different concentrations of modifier (2,4,6-triisopropylbenzoic acid) gradually decreases in dry flue gas as the concentration of the modifier increases, but when the concentration of 2,4,6-triisopropylbenzoic acid is 6 mmol / L in wet flue gas containing 5% water vapor, the catalytic activity is the highest, and the conversion rate of toluene on the catalyst in dry flue gas is 87.3% at 200°C, and the water vapor only reduces the activity of the catalyst by about 3%, and the efficiency reaches 86.4%, indicating that the material has water poisoning resistance. The catalytic activity of CrMn / Al2O3 catalyst for toluene in dry flue gas or wet (containing 5% water vapor) flue gas shows that the activity of CrMn / Al2O3 in dry flue gas is about 95% higher, but the water poisoning resistance is poor, and the activity is reduced by about 10% due to the introduction of water vapor. By comparison, it is shown that the addition of 2,4,6-triisopropylbenzoic acid to the catalyst has a significant effect on improving the water poisoning resistance of the catalyst.

[0045] The conversion efficiency of VOCs of the catalysts of Example 1 (Y-CrMn / Al2O3) and Comparative Example 1 (Mn / Al2O3) in wet flue gas containing 5% water vapor is as shown in the table. Figure 6 As shown in the table, the results show that the activity of Mn / Al2O3 is low, and the efficiency is only 58%; the water poisoning resistance is poor, and the activity is reduced by about 17% due to the introduction of water vapor. The conversion rate of toluene on the catalyst Y-CrMn / Al2O3 of Example 1 is 87.3% in dry flue gas, and the water vapor only reduces the activity of the catalyst by about 3%, and the efficiency reaches 84.4%. By comparison, it is shown that the catalyst of the present application has high activity and water poisoning resistance.

[0046] The catalytic activity of the Cr / Al2O3 catalyst prepared in Comparative Example 2 for toluene in dry flue gas or wet (containing 5% water vapor) flue gas is 30% and 20%, respectively.

[0047] The catalytic activity of Example 1 (Y-CrMn / Al2O3), Comparative Example 4 (Y-Mn / Al2O3), Comparative Example 5 (Y-ZnMn / Al2O3 catalyst), and Comparative Example 6 (Y-ZrMn / Al2O3) for toluene in wet (containing 5% water vapor) flue gas is as shown in the table. Figure 7 As shown in the table, it can be seen that 2,4,6-triisopropylbenzoic acid grafted on the surface of Mn / Al2O3 or other doped catalysts (ZnMn / Al2O 3、The modification of 2,4,6-triisopropylbenzoic acid on the surface of ZrMn / Al2O3 leads to a significant decrease in the activity of the catalyst. However, after the grafting of 2,4,6-triisopropylbenzoic acid on the surface of CrMn / Al2O3, the activity of the catalyst is also decreased, but the decrease is smaller. This is because the Cr doping makes 2,4,6-triisopropylbenzoic acid more inclined to be doped on the Cr site, thereby weakening the inhibition of 2,4,6-triisopropylbenzoic acid on the main low-temperature active site Mn, so that the catalyst obtains the water resistance brought by the modification of 2,4,6-triisopropylbenzoic acid, while retaining good reaction activity. Through comparison, it is shown that the Cr doping in the application has a significant effect on the improvement of the activity and water poisoning resistance of the catalyst. The activity of the Zn and Zr doped Mn / Al2O3 catalysts in wet flue gas is not as good as that of the Cr doped catalyst, which may be due to the fact that Zn and Zr are not as effective as Cr in grafting 2,4,6-triisopropylbenzoic acid, resulting in more 2,4,6-triisopropylbenzoic acid being grafted on the Mn site, which deactivates the main active site Mn and reduces the catalytic efficiency.

[0048] The above only describes the preferred embodiments of the application, and it should be noted that those skilled in the art can make several modifications and improvements without departing from the inventive concept, and these all belong to the protection scope of the application.

Claims

1. A method for preparing a water-resistant low-temperature catalyst, characterized in that, The steps are as follows: (1) The γ-Al2O3 support, manganese salt and chromium salt were dissolved together in deionized water, stirred and impregnated, dried and then ground into fine powder and calcined in static air to obtain CrMn / Al2O3 catalyst. (2) The prepared CrMn / Al2O3 catalyst was dispersed in dichloromethane containing 2-6 mmol / L 2,4,6-triisopropylbenzoic acid by ultrasonication to obtain a suspension. The suspension was stirred and centrifuged to collect the hydrophobic CrMn / Al2O3 catalyst. After washing several times, the hydrophobic CrMn / Al2O3 catalyst was dried at 90-110℃ to obtain a water-resistant low-temperature catalyst.

2. The preparation method according to claim 1, characterized in that, The preparation method of the γ-Al2O3 support is as follows: Al(NO3)3·9H2O, K2SO4 and CO(NH2)2 are dissolved in deionized water to obtain a mixture. The mixture is then transferred to a stainless steel high-pressure reactor, heated in an oven, cooled to room temperature, vacuum filtered, washed, dried and calcined to obtain the γ-Al2O3 support.

3. The preparation method according to claim 1, characterized in that, The molar ratio of the γ-Al2O3 support, manganese salt, and chromium salt is 8-15:0.5-2:0.5-2.

4. The preparation method according to claim 1, characterized in that, The manganese salt is one or more of MnCl2·4H2O, Mn(CH3COO)2·4H2O, and MnSO4·H2O, and the chromium salt is one or more of Cr(CH3COO)3, Cr(NO3)3·9H2O, CrCl3·6H2O, and Cr2(SO4)3.

5. The preparation method according to claim 1, characterized in that, The stirring and soaking time in step (1) is 10-14 hours.

6. The preparation method according to claim 1, characterized in that, Step (1) Dry in an oven at 70-90 ℃ for 10-12 h.

7. The preparation method according to claim 1, characterized in that, Step (1) The calcination temperature is 450-550℃ and the calcination time is 2-6h.

8. A water-resistant low-temperature catalyst, characterized in that, It is prepared by the preparation method described in any one of claims 1-7.

9. Application of a water-resistant low-temperature catalyst in the low-temperature catalytic oxidation of VOCs.

10. The application according to claim 9, characterized in that, A water-resistant low-temperature catalyst was placed in a reactor, and 40 ppm toluene, 5 vol.% O2 and carrier gas N2 were introduced, along with 5% vol water vapor. The outlet concentration of toluene was monitored.

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