Supported cobalt modified phosphorus molybdenum vanadium heteropolyacid catalyst and preparation method thereof

Abstract

The invention belongs to the technical field of volatile organic compound purification, and particularly relates to a supported cobalt modified phosphorus-molybdenum-vanadium heteropolyacid catalyst and a preparation method thereof.The preparation method comprises the following steps that S1, precursor phosphorus-molybdenum-vanadium heteropolyacid is prepared; s2, preparing an active component cobalt modified phosphorus molybdenum vanadium heteropoly acid; s3, preparation of a carrier nitrogen-doped titanium dioxide; s4, preparing nitrogen-doped titanium dioxide loaded cobalt modified phosphorus molybdenum vanadium heteropoly acid; the surface of the supported cobalt-modified phosphorus molybdenum vanadium heteropolyacid catalyst is rich in acid sites and oxygen vacancies, and through substitution of molybdenum atoms in Keggin type phosphomolybdic acid by vanadium atoms, cobalt element modification and nitrogen doping, the oxidation-reduction performance is greatly improved, and the content of adsorbed oxygen is remarkably increased. By synergistically strengthening L-H and MvK reaction mechanisms, a toluene catalytic oxidation process is efficiently driven, and rapid conversion and complete mineralization of toluene and intermediate products thereof are realized.

Description

Technical Field

[0001] This invention belongs to the field of volatile organic compound purification technology, specifically relating to a supported cobalt-modified phosphomolybdenum-vanadium heteropolyacid catalyst and its preparation method. Background Technology

[0002] Volatile organic compounds (VOCs) are compounds with boiling points between 50-260℃ at room temperature, widely originating from industrial manufacturing, transportation, and human activities. VOCs exhibit strong chemical reactivity in the atmosphere, undergoing photochemical reactions with gases such as nitrogen oxides, becoming key precursors to the secondary formation of near-surface ozone and PM2.5, exacerbating air pollution and threatening public health. VOC exposure can cause eye burning, conjunctival congestion, and contact dermatitis; benzene compounds, such as toluene and xylene, can affect the central nervous system and irritate the respiratory tract and skin; benzene, vinyl chloride, formaldehyde, and other VOCs are carcinogenic, and long-term exposure increases the risk of cancer. Furthermore, most VOCs are flammable and explosive, posing a threat to industrial safety in confined spaces. Toluene, as a typical VOC, poses serious harm to human health; simultaneously, its stable aromatic ring structure and resistance to degradation make its control urgent. Currently, various technologies, including catalytic oxidation, condensation, adsorption, membrane separation, photocatalysis, plasma treatment, photothermal catalysis, and biodegradation, are widely used in VOCs treatment. Among them, catalytic oxidation is recognized as an economical and environmentally friendly VOCs control method due to its advantages such as low reaction temperature, high conversion rate, low energy consumption and no secondary pollution, and it is also the mainstream technology for toluene treatment.

[0003] High-performance catalysts are the core material support for toluene catalytic oxidation technology. Noble metal catalysts are currently commonly used materials for toluene catalytic oxidation. Although they exhibit excellent catalytic performance, they are scarce, expensive, prone to sintering at high temperatures, and easily poisoned and deactivated in complex atmospheres containing SO2 and H2O. Among non-noble metal catalysts, cobalt oxides have become effective materials for toluene catalytic oxidation due to their weak Co-O bond, rapid oxygen binding rate, low cost, and environmental friendliness. However, single metal oxides have drawbacks such as poor catalytic activity and poor resistance to sulfur and water. Molybdenum-based heteropolyacids, due to their strong acidity, ease of separation, high reusability, non-toxicity, and ease of processing, as well as their good redox properties, have already been applied in VOCs oxidation reactions. Combining metal oxides and heteropolyacids, utilizing the strong interactions between the components, can not only improve catalyst performance and exert a synergistic effect on toluene catalytic oxidation, but also enhance the catalyst's resistance to sulfur and water.

[0004] For example, Chinese patent CN 116173994B discloses a method for preparing a samarium manganese perovskite@phosphomolybdic acid catalyst for the purification of chlorine-containing VOCs. The SmMnO3 catalyst doped with phosphomolybdic acid exhibits excellent activity and stability under actual working conditions. Chinese patent CN 119114164A discloses a method for preparing a VOCs oxidation catalyst. This method involves dispersing noble metals in heteropolyacids via a self-propagating method to enhance their activity, then impregnating and coating the powdered catalyst onto cordierite. After drying, the coating is modified, effectively reducing the competitive adsorption of reactant gases by water vapor at the active sites.

[0005] However, heteropolyacids have poor thermal stability on catalysts due to their small specific surface area, and how to overcome this defect is an urgent problem to be solved in this field.

[0006] It should be noted that the information disclosed in this background section is only for understanding the background technology of the present application concept, and therefore, the above description is not considered to constitute prior art information. Summary of the Invention

[0007] This disclosure provides at least one supported cobalt-modified phosphomolybdenum vanadium heteropolyacid catalyst and its preparation method.

[0008] In a first aspect, embodiments of this disclosure provide a method for preparing a supported cobalt-modified phosphomolybdenum vanadium heteropolyacid catalyst, comprising the following steps: S1, preparation of the precursor phosphomolybdenum vanadium heteropolyacid: preparing a solution A containing MoO3 and a solution B containing V2O5 respectively, mixing them, heating and filtering, and vacuum drying the filtrate to obtain PMoV powder; S2, preparation of the active component cobalt-modified phosphomolybdenum vanadium heteropolyacid: using cobalt nitrate hexahydrate as the cobalt source, dissolving it in anhydrous ethanol, adding PMoV powder, stirring evenly, evaporating the mixture to dryness, then placing it in a vacuum drying oven for drying, and finally calcining and grinding to obtain the active component Co-PM. oV powder; S3, Preparation of nitrogen-doped titanium dioxide support: Thiourea was used as the nitrogen source and dissolved in deionized water. Then, titanium dioxide with a large specific surface area was added. After magnetic stirring, the mixture was evaporated in a water bath, vacuum dried, calcined in an argon atmosphere, and ground into powder to obtain nitrogen-doped titanium dioxide support, denoted as NTi; S4, Preparation of cobalt-modified phosphomolybdenum vanadium heteropolyacid supported on nitrogen-doped titanium dioxide: Co-PMoV powder and NTi were dispersed in anhydrous ethanol. The mixture was then evaporated in a constant temperature water bath. After that, it was vacuum dried, calcined in an argon atmosphere, and ground to obtain the supported cobalt-modified phosphomolybdenum vanadium heteropolyacid catalyst.

[0009] In one optional embodiment, the method for preparing solution A in step S1 includes uniformly dispersing MoO3 in deionized water, continuously heating and refluxing it in an oil bath, and then adding phosphoric acid to obtain solution A; the concentration of phosphoric acid is 85 wt.%, and the molar ratio of phosphoric acid to MoO3 is 1:8 to 1:11; the reflux temperature is 95 to 105°C, and the reflux time is 6 to 8 hours.

[0010] In one optional embodiment, the method for preparing solution B in step S1 includes dissolving V2O5 in H2O2 solution to obtain solution B; the concentration of H2O2 is 5 wt.%, and the molar ratio of H2O2 to V2O5 is 55:1 to 65:1.

[0011] In one optional embodiment, the vacuum drying temperature in step S1 is 80–105°C, and the drying time is 10–12 h.

[0012] In one optional embodiment, in step S2, the mass ratio of ethanol to cobalt nitrate hexahydrate is 800, the water bath temperature is 60–80°C, the vacuum drying temperature is 80–105°C, the drying time is 10–12 h, the calcination temperature is 300–400°C, and the calcination time is 3–5 h.

[0013] In one optional embodiment, the water bath evaporation temperature in step S3 is 60-80°C, the vacuum drying temperature is 80-105°C, the drying time is 10-12 hours, the calcination temperature is 300-400°C, and the calcination time is 3-5 hours.

[0014] In one optional embodiment, in step S4, the mass ratio of anhydrous ethanol to NTi is 15, the water bath temperature is 60-80°C, the vacuum drying temperature is 80-105°C, the drying time is 10-12 hours, the calcination temperature is 300-400°C, and the calcination time is 3-5 hours.

[0015] Secondly, the present disclosure also provides a supported cobalt-modified phosphomolybdenum vanadium heteropolyacid catalyst, wherein the supported cobalt-modified phosphomolybdenum vanadium heteropolyacid catalyst is prepared by using cobalt-modified phosphomolybdenum vanadium heteropolyacid as the active component and nitrogen-doped titanium dioxide as the support, and the active component accounts for 20 to 40 wt.% of the total weight of the catalyst.

[0016] In one optional embodiment, the molar ratio of V to Mo in the active component is 1:2 to 1:11, and the mass ratio of Co to PMoV is 0.01:1 to 0.06:1.

[0017] In one optional embodiment, the nitrogen-doped titanium dioxide has a specific surface area of ​​not less than 300 m² / g, wherein the molar ratio of N to Ti is 0.005:1 to 0.02:1.

[0018] The beneficial effects of this invention are as follows: the supported cobalt-modified phosphomolybdenum vanadium heteropolyacid catalyst and its preparation method have the following advantages:

[0019] 1. The supported cobalt-modified phosphomolybdic vanadium heteropolyacid catalyst of this invention has a surface rich in acidic sites and oxygen vacancies. Through the substitution of molybdenum atoms in Keggin-type phosphomolybdic acid by vanadium atoms, cobalt modification, and nitrogen doping, the redox performance is significantly improved, and the adsorbed oxygen content is significantly increased. By synergistically enhancing the LH and MvK reaction mechanisms, the catalyst efficiently drives the catalytic oxidation process of toluene, achieving rapid conversion and complete mineralization of toluene and its intermediates.

[0020] 2. The strong acidity of the catalyst itself endows it with excellent SO2 resistance. The strong acidity inhibits SO2 adsorption, promotes the desorption of sulfur species, reduces sulfate formation, and weakens the interference of SO2 on the reaction pathway. At the same time, the large surface area of ​​the catalyst, combined with the increase in Lewis acidity brought about by cobalt modification, can effectively alleviate the competitive adsorption of H2O molecules and enhance the resistance to water vapor, laying a key technical foundation for the engineering application of toluene catalytic oxidation technology.

[0021] 3. The catalyst preparation process of this invention is simple, the raw materials are widely available, the cost is low and the environment is environmentally friendly. By precisely controlling the raw material ratio, the toluene removal activity and sulfur and water resistance of the catalyst can be optimized, providing an efficient and economical solution for the practical application of toluene removal technology in industrial flue gas.

[0022] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention are realized and obtained through the structures particularly pointed out in the description.

[0023] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described in detail below. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] As used herein, the phrases “in one embodiment,” “according to one embodiment,” “in some embodiments,” etc., generally refer to the fact that a particular feature, structure, or characteristic following the phrase can be included in at least one embodiment of this disclosure. Therefore, a particular feature, structure, or characteristic can be included in more than one embodiment of this disclosure, such that these phrases do not necessarily refer to the same embodiment. As used herein, the terms “example,” “exemplary,” etc., are used to “serve as an example, instance, or illustration.” Any implementation, aspect, or design described herein as “example” or “exemplary” is not necessarily to be construed as preferred or superior to other implementations, aspects, or designs. Rather, the use of the terms “example,” “exemplary,” etc., is intended to present concepts in a specific manner.

[0026] In this document, as used herein, expressions such as “at least one of…” modify the entire list of elements when following a list of elements, rather than individual elements in the list. For example, the expression “at least one of a, b, and c” should be understood to include only a, only b, only c, both a and b, both a and c, both b and c, or all of a, b, and c.

[0027] The terminology used herein is for the purpose of describing specific exemplary configurations only and is not intended to be limiting. As used herein, the singular articles “a,” “an,” and “the” may also be intended to include plural forms unless otherwise clearly stated herein. The terms “comprising,” “including,” and “having” are inclusive and thus specify the presence of features, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or combinations thereof. The method steps, processes, and operations described herein should not be construed as requiring them to be performed in the specific order discussed or shown, unless specifically identified as such. Additional or alternative steps may be employed.

[0028] The following describes some embodiments of the present invention in detail. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0029] This disclosure provides a method for preparing a supported cobalt-modified phosphomolybdenum vanadium heteropolyacid catalyst, comprising the following steps: S1, preparation of the precursor phosphomolybdenum vanadium heteropolyacid: preparing a solution A containing MoO3 and a solution B containing V2O5, mixing them, heating and filtering, and vacuum drying the filtrate to obtain PMoV powder; S2, preparation of the active component cobalt-modified phosphomolybdenum vanadium heteropolyacid: using cobalt nitrate hexahydrate as the cobalt source, dissolving it in anhydrous ethanol, adding PMoV powder, stirring evenly, evaporating the mixture to dryness, then placing it in a vacuum drying oven for drying, and finally calcining and grinding to obtain the active component Co-PMoV powder. Finally; S3, Preparation of nitrogen-doped titanium dioxide support: Thiourea was used as the nitrogen source and dissolved in deionized water. Then, titanium dioxide with a large specific surface area was added. After magnetic stirring, the mixture was evaporated in a water bath, vacuum dried, calcined in an argon atmosphere, and ground into powder to obtain nitrogen-doped titanium dioxide support, denoted as NTi; S4, Preparation of cobalt-modified phosphomolybdenum vanadium heteropolyacid supported on nitrogen-doped titanium dioxide: Co-PMoV powder and NTi were dispersed in anhydrous ethanol. The mixture was then evaporated in a constant temperature water bath. After that, it was vacuum dried, calcined in an argon atmosphere, and ground in sequence to obtain the supported cobalt-modified phosphomolybdenum vanadium heteropolyacid catalyst.

[0030] In some embodiments, specifically, the preparation method of solution A in step S1 includes uniformly dispersing MoO3 in deionized water, continuously heating and refluxing it in an oil bath, and then adding phosphoric acid to obtain solution A; the concentration of phosphoric acid is 85 wt.%, and the molar ratio of phosphoric acid to MoO3 is 1:8 to 1:11; the reflux temperature is 95 to 105°C, and the reflux time is 6 to 8 hours.

[0031] In some embodiments, specifically, the method for preparing solution B in step S1 includes dissolving V2O5 in H2O2 solution to obtain solution B; the concentration of H2O2 is 5 wt.%, and the molar ratio of H2O2 to V2O5 is 55:1 to 65:1.

[0032] In some embodiments, specifically, the vacuum drying temperature in step S1 is 80–105°C, and the drying time is 10–12 h.

[0033] In some embodiments, specifically, in step S2, the mass ratio of ethanol to cobalt nitrate hexahydrate is 800, the water bath temperature is 60–80°C, the vacuum drying temperature is 80–105°C, the drying time is 10–12 h, the calcination temperature is 300–400°C, and the calcination time is 3–5 h.

[0034] In some embodiments, specifically, in step S3, the water bath evaporation temperature is 60-80°C, the vacuum drying temperature is 80-105°C, the drying time is 10-12 hours, the calcination temperature is 300-400°C, and the calcination time is 3-5 hours.

[0035] In some embodiments, specifically, in step S4, the mass ratio of anhydrous ethanol to NTi is 15, the water bath temperature is 60–80°C, the vacuum drying temperature is 80–105°C, the drying time is 10–12 h, the calcination temperature is 300–400°C, and the calcination time is 3–5 h.

[0036] This disclosure also provides a supported cobalt-modified phosphomolybdenum vanadium heteropolyacid catalyst, wherein the supported cobalt-modified phosphomolybdenum vanadium heteropolyacid catalyst is prepared using cobalt-modified phosphomolybdenum vanadium heteropolyacid as the active component and nitrogen-doped titanium dioxide as the support, and the active component accounts for 20-40 wt.% of the total weight of the catalyst.

[0037] In some embodiments, specifically, the molar ratio of V to Mo in the active component is 1:2 to 1:11, and the mass ratio of Co to PMoV is 0.01:1 to 0.06:1.

[0038] In some embodiments, specifically, the specific surface area of ​​the nitrogen-doped titanium dioxide is not less than 300 m² / g, wherein the molar ratio of N to Ti is 0.005:1 to 0.02:1.

[0039] This invention develops a nitrogen-doped titanium dioxide-supported cobalt-modified phosphomolybdic-vanadium heteropolyacid catalyst. Leveraging its abundant acidic sites and oxygen vacancies on its surface, it achieves highly efficient adsorption and activation of toluene and oxygen molecules, thereby significantly improving the catalytic oxidation performance of toluene. Firstly, the phosphomolybdic-vanadium heteropolyacid significantly enhances the catalyst's redox performance by substituting molybdenum atoms in Keggin-type phosphomolybdic acid with vanadium atoms, increasing the adsorbed oxygen content and promoting the rapid conversion of toluene and its intermediates until complete mineralization. Secondly, the cobalt modification of the phosphomolybdic-vanadium heteropolyacid and the nitrogen doping of the titanium dioxide support successfully introduce a large number of Lewis acid sites and oxygen vacancies, further improving the adsorbed oxygen content and oxygen migration capacity, and strengthening the adsorption process of toluene and oxygen. This catalyst can synergistically improve the mass transfer and reaction efficiency under the Langmuir-Hinshelwood (LH) mechanism and drive the lattice oxygen cycle under the Mars-van Krevelen (MvK) mechanism, thus efficiently advancing the toluene oxidation reaction.

[0040] Enhancing the acidity of the catalyst is key to improving its resistance to SO2. Firstly, strong acidic sites effectively inhibit the chemical adsorption of SO2 on the catalyst surface through electrostatic repulsion, reducing the risk of deactivation due to sulfate covering of active sites. Secondly, the acidic environment weakens the binding energy between sulfur species and the catalyst, promoting the desorption of adsorbed SO2 and generated sulfates, preventing their deposition on the surface. The supported cobalt-modified phosphomolybdenum-vanadium heteropolyacid catalyst prepared in this invention exhibits a toluene oxidation reaction on its surface following both LH and MvK mechanisms. This catalyst uses Keggin-type heteropolyacid as the main active component. As a typical solid superacid, it exhibits excellent strong acidity due to its unique molecular structure and electronic properties. Modification of the phosphomolybdenum-vanadium heteropolyacid with cobalt, combined with nitrogen doping of titanium dioxide, further enhances the catalyst's acidity. This not only effectively inhibits the adsorption of SO2 in flue gas and reduces sulfate formation but also weakens the interference of SO2 on the LH and MvK reaction pathways, significantly improving the catalyst's ability to resist SO2 poisoning.

[0041] In catalytic reaction systems, H2O molecules readily compete with toluene and oxygen for adsorption sites on the catalyst surface, leading to a decrease in toluene conversion. The supported catalyst developed in this invention possesses a specific surface area as high as approximately 300 m² / g, a characteristic that significantly increases the number of exposed active sites. Even under complex operating conditions containing H2O, this catalyst can retain sufficient usable active sites, effectively mitigating the negative impact of H2O competitive adsorption. Furthermore, cobalt-modified phosphomolybdenum vanadium heteropolyacid can significantly increase the number of Lewis acid sites on the catalyst surface, further enhancing its resistance to H2O inhibition.

[0042] Example 1

[0043] Step 1: Add 3.3835 g of MoO3 to 35 mL of distilled water and heat to 100 °C in an oil bath. Then add a certain amount of H3PO4 (85 wt.%), controlling the molar ratio of P to Mo to be 1:8, to form solution A. Add a certain amount of V2O5 to 48 mL of 5 wt.% H2O2 solution to form solution B, controlling the molar ratio of V to Mo to be 1:2. Subsequently, gradually add solution B to solution A and reflux continuously at 100 °C for 6 hours. After cooling, remove insoluble matter by filtration, collect the filtrate, and vacuum dry at 85 °C. Grind the filtrate to obtain phosphomolybdic-vanadium heteropolyacid PMo8V4.

[0044] Step 2: Weigh 0.2000g of PMo8V4 and a certain amount of Co(NO3)2·6H2O, add them to deionized water and stir for 2 hours, controlling the mass ratio of Co to PMo8V4 to be 0.03. Then, evaporate to dryness in a water bath at 85℃ and vacuum dry at 105℃ for 3 hours. Finally, calcine in a muffle furnace at 350℃ for 3 hours and grind into powder to obtain (0.03)Co-PMo8V4.

[0045] Step 3: Dissolve a certain amount of thiourea (CH4N2S) and 2.0000g of anatase TiO2 with a large specific surface area in deionized water and stir for 2 hours, controlling the molar ratio of N to Ti to be 0.02. Then, evaporate to dryness in a water bath at 85℃ and vacuum dry at 105℃ for 3 hours. Finally, calcine in an argon atmosphere at 350℃ for 3 hours and grind into powder, denoted as (0.02)NTi.

[0046] Step 4: Weigh 0.2000g (0.03)Co-PMo8V4 and 0.8000g (0.02)NTi support, controlling the mass ratio of the active component to the total catalyst weight to be 20%. Dissolve them in deionized water and stir evenly. Stir at room temperature for 1 hour, then evaporate to dryness in an 85℃ water bath, followed by vacuum drying at 105℃ for 3 hours. Finally, calcine in an argon atmosphere at 350℃ for 3 hours. Grind the calcined catalyst to obtain nitrogen-doped titanium dioxide supported cobalt-modified phosphomolybdic vanadate catalyst powder, denoted as 20% (0.03)Co-PMo8V4 / (0.02)NTi.

[0047] Example 2

[0048] The catalyst was prepared using the same steps as in Example 1, except that in step 2, the mass ratio of Co to PMo8V4 was controlled to be 0.015, and the final product was 20% (0.015)Co-PMo8V4 / (0.02)NTi.

[0049] Example 3

[0050] The catalyst was prepared using the same method as in Example 1, except that in step two, the mass ratio of Co to PMo8V4 was controlled to be 0.06, and the final product was 20% (0.06)Co-PMo8V4 / (0.02)NTi.

[0051] Example 4

[0052] The catalyst was prepared using the same method as in Example 1, except that in step one, the molar ratio of V to Mo was controlled at 1:3, and the molar ratio of P to Mo was controlled at 1:9. The final product was 20%.

[0053] (0.03)Co-PMo9V3 / (0.02)NTi.

[0054] Example 5

[0055] The catalyst was prepared using the same method as in Example 1, except that in step one, the molar ratio of V to Mo was controlled at 1:5, and the molar ratio of P to Mo was controlled at 1:10. The final product was 20%.

[0056] (0.03)Co-PMo 10 V2 / (0.02)NTi.

[0057] Example 6

[0058] The catalyst was prepared using the same method as in Example 1, except that in step one, the molar ratio of V to Mo was controlled at 1:11, and the molar ratio of P to Mo was also controlled at 1:11. The final product was 20%.

[0059] (0.03)Co-PMo 11 V1 / (0.02)NTi.

[0060] Example 7

[0061] The catalyst was prepared using the same method as in Example 1, except that in step three, the molar ratio of N to Ti was controlled to be 0.01, and the final product was 20% (0.03)Co-PMo8V4 / (0.01)NTi.

[0062] Example 8

[0063] The catalyst was prepared using the same method as in Example 1, except that in step three, the molar ratio of N to Ti was controlled to be 0.005, and the final product was 20% (0.03)Co-PMo8V4 / (0.005)NTi.

[0064] Example 9

[0065] The catalyst was prepared using the same method as in Example 1, without step two, and the final product was 20% PMo8V4 / (0.02)NTi.

[0066] Example 10

[0067] The catalyst was prepared using the same method as in Example 1, without step three, and the final product was 20%.

[0068] (0.03)Co-PMo8V4 / Ti.

[0069] Example 11

[0070] The catalyst was prepared using the same method as in Example 1, except that in step four, the mass ratio of the active component to the total catalyst weight was controlled to be 10%, and the final product was 10%.

[0071] (0.03)Co-PMo8V4 / (0.02)NTi.

[0072] Example 12

[0073] The catalyst was prepared using the same method as in Example 1, except that in step four, the mass ratio of the active component to the total catalyst weight was controlled to be 40%, and the final product was 40%.

[0074] (0.03)Co-PMo8V4 / (0.02)NTi.

[0075] Catalyst performance testing

[0076] 1. Performance Test 1

[0077] 0.40 g of each catalyst prepared in Examples 1-12 was weighed and placed in a quartz glass fixed-bed reactor with an inner diameter of 8 mm to test its catalytic activity for the oxidation of toluene. The catalyst was supported at the bottom by high-temperature resistant quartz wool. Under the test conditions, the total gas flow rate was set at 100 mL / min and the space velocity was controlled at 15000 mL·h. -1 ·g -1 The inlet gas consisted of toluene (500 ppm), oxygen (10 vol.%) and nitrogen, and the reaction temperature was 150–350 °C. The results are shown in Table 1.

[0078] Table 1. Catalytic activity of the catalysts obtained in Examples 1-12 for the oxidation of toluene.

[0079]

[0080] As shown in Table 1, when H2O and SO2 are absent from the system, the catalysts obtained in Examples 1-12 exhibited excellent catalytic oxidation activity for toluene within the temperature range of 150–350 °C. The catalyst obtained in Example 1 was obtained under optimal conditions, achieving a toluene conversion rate of 97.6% at 300 °C.

[0081] 2. Performance Test Two

[0082] 0.40 g of the catalyst prepared in Example 1 was weighed and placed in a quartz glass fixed-bed reactor with an inner diameter of 8 mm to test its catalytic activity for toluene oxidation. The reaction temperature was set at 300 °C, the SO2 concentration was 0–400 ppm, and the H2O concentration was 0–5 vol.%, and the effects of SO2 and water vapor on the toluene oxidation activity were tested. Other test conditions were the same as those in performance test 1, and the results are shown in Table 2.

[0083] Table 2. Tests on the sulfur and water resistance of the catalyst obtained in Example 1.

[0084] <![CDATA[SO2 concentration (ppm)]]> <![CDATA[H2O concentration (vol.%)]]> Toluene conversion rate (%) 0 0 97.6 0 2 96.5 0 5 93.4 200 0 97.3 400 0 95.2 400 2 92.1 400 5 90.5

[0085] Table 2 shows that 0–5 vol.% water vapor has little effect on the toluene conversion rate of the catalyst obtained in Example 1. After 8 hours of introducing 5% water vapor, the catalytic activity decreased by only about 4.2%. When 0–400 ppm SO2 was introduced into the reaction system for 8 hours, the toluene removal rate of the catalyst obtained in Example 1 was almost unaffected and maintained high activity. The catalyst was more poisoned by the combined action of SO2 and water vapor than by introducing sulfur water alone. Even after 8 hours of introducing both 5 vol.% water vapor and 400 ppm SO2 into the reaction system, the toluene conversion rate remained as high as 90.5%. These results indicate that the nitrogen-doped titanium dioxide-supported cobalt-modified phosphomolybdic acid heteropolyacid catalyst prepared in this invention has strong sulfur and water resistance in the catalytic oxidation of toluene.

[0086] In summary, the supported cobalt-modified phosphomolybdic vanadium heteropolyacid catalyst of this invention has a surface rich in acidic sites and oxygen vacancies. Through vanadium atom substitution of molybdenum atoms in Keggin-type phosphomolybdic acid, cobalt modification, and nitrogen doping, its redox performance is significantly improved, and its adsorbed oxygen content is substantially increased. By synergistically enhancing the LH and MvK reaction mechanisms, it efficiently drives the catalytic oxidation process of toluene, achieving rapid conversion and complete mineralization of toluene and its intermediates.

[0087] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for preparing a supported cobalt-modified phosphomolybdenum-vanadium heteropolyacid catalyst, characterized in that, Includes the following steps: S1, Preparation of precursor phosphomolybdicavanadium heteropolyacid: Solution A containing MoO3 and solution B containing V2O5 were prepared respectively. After mixing, the solution was heated and filtered. The filtrate was dried under vacuum to obtain PMoV powder. S2, Preparation of active component cobalt-modified phosphomolybdenum vanadium heteropolyacid: Cobalt nitrate hexahydrate is used as the cobalt source, dissolved in anhydrous ethanol, and then PMoV powder is added. The mixture is stirred evenly, evaporated to dryness, placed in a vacuum drying oven for drying, and finally calcined and ground to obtain active component Co-PMoV powder. S3, Preparation of nitrogen-doped titanium dioxide support: Thiourea was used as the nitrogen source and dissolved in deionized water. Then, titanium dioxide with a large specific surface area was added. After being magnetically stirred evenly, the mixture was evaporated in a water bath, vacuum dried, calcined in an argon atmosphere, and ground into powder to obtain nitrogen-doped titanium dioxide support, denoted as NTi. S4, Preparation of nitrogen-doped titanium dioxide supported cobalt-modified phosphomolybdenum vanadium heteropolyacid: Co-PMoV powder and NTi were dispersed in anhydrous ethanol, and then the mixture was dried by constant temperature water bath treatment. After that, it was vacuum dried, calcined in argon atmosphere and ground in sequence to obtain the supported cobalt-modified phosphomolybdenum vanadium heteropolyacid catalyst.

2. The preparation method according to claim 1, characterized in that, The method for preparing solution A in step S1 includes uniformly dispersing MoO3 in deionized water, continuously heating it under reflux in an oil bath, and then adding phosphoric acid to obtain solution A. The concentration of phosphoric acid is 85 wt.%, and the molar ratio of phosphoric acid to MoO3 is 1:8 to 1:11; The reflux temperature is 95–105°C, and the reflux time is 6–8 hours.

3. The preparation method according to claim 1, characterized in that, The method for preparing solution B in step S1 includes dissolving V2O5 in H2O2 solution to obtain solution B; The concentration of H2O2 is 5 wt.%, and the molar ratio of H2O2 to V2O5 is 55:1 to 65:

1.

4. The preparation method according to claim 1, characterized in that, In step S1, the vacuum drying temperature is 80–105°C, and the drying time is 10–12 hours.

5. The preparation method according to claim 1, characterized in that, In step S2, the mass ratio of ethanol to cobalt nitrate hexahydrate is 800, the water bath temperature is 60–80°C, the vacuum drying temperature is 80–105°C, the drying time is 10–12 h, the calcination temperature is 300–400°C, and the calcination time is 3–5 h.

6. The preparation method according to claim 1, characterized in that, In step S3, the water bath evaporation temperature is 60–80°C, the vacuum drying temperature is 80–105°C, the drying time is 10–12 h, the calcination temperature is 300–400°C, and the calcination time is 3–5 h.

7. The preparation method according to claim 1, characterized in that, In step S4, the mass ratio of anhydrous ethanol to NTi is 15, the water bath temperature is 60-80℃, the vacuum drying temperature is 80-105℃, the drying time is 10-12h, the calcination temperature is 300-400℃, and the calcination time is 3-5h.

8. A supported cobalt-modified phosphomolybdenum-vanadium heteropolyacid catalyst, characterized in that, The supported cobalt-modified phosphomolybdenum vanadium heteropolyacid catalyst is prepared using cobalt-modified phosphomolybdenum vanadium heteropolyacid as the active component and nitrogen-doped titanium dioxide as the support. The active component accounts for 20-40 wt.% of the total weight of the catalyst.

9. The supported cobalt-modified phosphomolybdenum-vanadium heteropolyacid catalyst as described in claim 8, characterized in that, The molar ratio of V to Mo in the active component is 1:2 to 1:11, and the mass ratio of Co to PMoV is 0.01:1 to 0.06:

1.

10. The supported cobalt-modified phosphomolybdenum-vanadium heteropolyacid catalyst as described in claim 8, characterized in that, The nitrogen-doped titanium dioxide has a specific surface area of ​​not less than 300 m² / g, wherein the molar ratio of N to Ti is 0.005:1 to 0.02:1.

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