Preparation and application of a mesoporous titanium dioxide nanofiber supported noble metal catalyst for catalytic wet oxidation

Abstract

This invention discloses the preparation and application of a mesoporous titanium dioxide nanofiber-supported noble metal catalyst for catalytic wet oxidation. The invention first prepares rare earth metal-doped mesoporous TiO2 nanofibers in a one-step electrospinning process. Then, the nanofiber surface is etched with an alkaline solution. Next, a cation exchange strategy is used to uniformly disperse noble metal ions on the surface of the mesoporous TiO2 nanofibers. Finally, the catalyst is obtained through drying, calcination, and reduction treatment. The mesoporous structure and rare earth metal doping effectively enhance the catalytic performance of the TiO2 nanofiber-supported noble metal catalyst. The alkaline etching combined with the cation exchange strategy significantly improves the dispersion of the noble metal, reduces the noble metal loading, and enhances the catalyst's stability. When this catalyst is applied to the batch catalytic wet oxidation treatment of organic wastewater, the COD removal efficiency is greater than 90%. The reaction temperature is 200℃ or below, and the reaction pressure is 2MPa or below, which reduces the requirements for the reaction equipment and significantly lowers equipment investment costs.

Description

Technical Field

[0001] This invention relates to a method for preparing a mesoporous TiO2 nanofiber supported noble metal catalyst for catalytic wet oxidation, which is mainly used for catalytic wet oxidation treatment of high-concentration organic wastewater and belongs to the field of environmental protection catalysts and wastewater treatment technology. Technical Background

[0002] High-concentration organic wastewater mainly originates from production processes in coal chemical, pharmaceutical, papermaking, and printing and dyeing industries. Its significant characteristics include high COD, high color, complex composition, and strong acidity and alkalinity. This wastewater can damage aquatic ecosystems, pollute groundwater and surface water, accelerate eutrophication, and impact human health and environmental stability. Catalytic wet air oxidation (CWAO) technology is currently recognized as an effective technology for treating high-concentration, recalcitrant organic wastewater. It has attracted much attention and shows promising application prospects due to its advantages such as small equipment size, short reaction time, and low secondary pollution. The catalyst is crucial in catalytic wet oxidation, and catalysts are mainly divided into homogeneous catalysts and heterogeneous catalysts. Homogeneous catalysts are relatively simple to prepare and use; generally, aqueous solutions of metal salts such as iron, copper, cobalt, and manganese are directly added to the wastewater being treated, achieving relatively stable wastewater treatment results. However, they suffer from serious problems such as high reagent consumption, high operating costs, metal loss, and secondary pollution. Among heterogeneous catalysts, noble metal catalysts, despite their high cost, possess unparalleled efficiency and are therefore widely used in catalytic wet oxidation reactions. While noble metal catalysts exhibit excellent performance, they can become poisoned in wet oxidation reactions due to carbonaceous deposition and loss of active components, leading to reduced catalyst activity and stability, directly impacting the industrial application of catalytic wet oxidation technology. Therefore, research is of significant importance on how to further reduce the noble metal loading while maintaining high catalytic activity, and simultaneously suppressing carbonaceous deposition and metal leaching during the catalytic wet oxidation process.

[0003] CN108435174A discloses a catalyst for treating high-concentration organic wastewater, its preparation method, and its application. The supported M-Ag catalyst provided by this invention uses APTES as a surface functionalization modifier and Ag as a metal to form alloys with noble metals such as Pd and Au. The addition of the modifier can form adsorption sites for noble metal compounds, while the auxiliary agent alloys the noble metals, reducing their agglomeration during calcination. The catalyst prepared by this method has a low noble metal loading, low production cost, and can achieve a COD removal efficiency of over 95% for high-concentration organic wastewater, exhibiting good catalyst stability. However, the reaction temperature and pressure of this catalyst are relatively high, which places high demands on the safety of the reaction equipment.

[0004] CN111135823A discloses a wet oxidation catalyst, its preparation method, and its application. This catalyst comprises a reducing support and a noble metal active component. The metal elements in both the noble metal active component and the reducing support are stable in low valence states, which is beneficial for oxygen activation and transport, promoting the oxidation of organic matter and thus improving the catalyst's catalytic activity at low temperatures. The catalytic activity can reach 100% at 100 °C. However, the calcination atmosphere during the catalyst preparation process is a flammable gas, posing a significant safety hazard.

[0005] CN109908935A discloses a Pt-Ru bimetallic nanocatalyst for the catalytic wet oxidation of high-concentration organic wastewater and its preparation method. This invention uses CeO2 as the main support, which possesses excellent oxygen storage and release capabilities and higher oxidizing power compared to other supports. TiO2 doping further improves the acid resistance of the support. The invention modifies the support with nitrogen and sulfur, increasing its adsorption capacity for organic matter, effectively improving its electronic structure, and enhancing the interaction between the noble metal nanoalloy and the support, making it less prone to loss of active components and thus improving the catalyst's stability. The active components are Pt and Ru bimetallic compounds, which are formed into a nanoalloy through a preparation process, exhibiting catalytic activity higher than any single-component catalyst with the same content. However, this catalyst requires a reaction temperature of 270 °C and a reaction pressure of 7.0 MPa, which places high demands on the safety of the reaction equipment.

[0006] In summary, support modification and the addition of metal promoters are effective ways to improve the dispersion of precious metals, reduce loading, and lower catalyst production costs. Nitrogen and sulfur-modified supports can enhance catalyst stability, but the temperature and pressure of the activity window remain high, which is not conducive to industrial preparation and application. Loading precious metals onto reducing supports can improve oxygen activation and transfer efficiency and lower reaction temperature; however, the preparation process uses flammable gases, posing significant safety hazards and also hindering industrial preparation and application. None of these three methods can adequately balance catalyst performance, operating conditions, and preparation conditions, thus failing to provide a low-cost, high-activity, and easily prepared synthesis method for precious metal catalysts. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing a mesoporous TiO2 nanofiber supported noble metal catalyst for catalytic wet oxidation. This catalyst is mainly used for catalytic wet oxidation treatment of high-concentration organic wastewater, in order to solve the problems of high loading, poor activity and stability of existing noble metal catalysts for catalytic wet oxidation treatment of high-concentration organic wastewater.

[0008] I. Preparation of Noble Metal Catalysts Supported on Mesoporous TiO2 Nanofibers

[0009] (1) Preparation of rare earth metal-doped mesoporous TiO2 nanofibers

[0010] Rare earth metal salts were added to a mixed solution of ethanol, DMF, and acetic acid and mixed thoroughly. Then, polyvinylpyrrolidone (PVP) and polyether P123 were added sequentially and stirred until homogeneous. Finally, tetrabutyl titanate (TBT) was slowly added dropwise and stirred until the solution became homogeneous and transparent, yielding the precursor spinning solution. Precursor fibers were obtained by electrospinning under a high voltage of 16–20 kV. The precursor fibers were then dried and calcined to obtain rare earth metal-doped mesoporous TiO2 nanofibers.

[0011] The rare earth metal salt is at least one of the nitrates of Ce, La, Sm, Y, Nd, and Pr; in the ethanol-DMF-acetic acid mixed solution, the volume ratio of anhydrous ethanol:DMF:acetic acid is 6:8:1. Ethanol and DMF are used as solvents in the spinning solution to dissolve PVP and P123, while acetic acid acts as a catalyst to accelerate the hydrolysis and condensation process of the titanium source.

[0012] The amount of rare earth metal salt used is 1% to 10% of the molar amount of tetrabutyl titanate. The concentration of PVP in the mixed solution is 0.05 to 0.1 g / ml; the mass ratio of P123 to PVP is 0 to 3:1.

[0013] In electrospinning, the distance between the needle tip and the receiving plate is 12–20 cm; the air humidity is 40–60%. The drying temperature of the precursor fiber is 60–120 °C, and the drying time is 12–24 h; the calcination temperature is 400–600 °C, and the calcination time is 1–5 h. The calcination process completely decomposes the organic matter, forming rare-earth metal-doped TiO2 nanofibers with a mesoporous structure.

[0014] (2) Alkali etching treatment of rare earth metal-doped mesoporous TiO2 nanofibers

[0015] The rare earth metal-doped mesoporous TiO2 nanofibers obtained in step (1) were mixed evenly with an alkaline solution and then heated and stirred in a water bath for alkaline etching. The resulting product was filtered and washed with deionized water until neutral. After filtration and drying, alkaline-etched rare earth metal-doped mesoporous TiO2 nanofibers were obtained.

[0016] The alkaline solution is a NaOH solution with a concentration of 1-5 mol / L; the mass ratio of rare earth metal-doped mesoporous TiO2 nanofibers to the volume of the alkaline solution is 0.05-0.1 g / ml; the alkaline etching treatment temperature is 30-80 ℃, and the time is 6-24 h. The purpose of the reaction between TiO2 nanofibers and the alkaline solution is to promote the formation of sodium titanate from the TiO2 nanoparticles on the surface. Noble metal ions can easily replace sodium ions through cation exchange reactions, thereby achieving uniform distribution on the carrier surface.

[0017] (3) Preparation of rare earth metal-doped mesoporous TiO2 nanofiber supported noble metal catalysts

[0018] The rare earth metal-doped mesoporous TiO2 nanofibers obtained in step (2) were sequentially acid-washed and deionized water-washed, and then added to a noble metal precursor solution. An ion exchange reaction was carried out by stirring at room temperature. After filtration, drying, calcination, and reduction treatment, a noble metal catalyst supported on rare earth metal-doped mesoporous TiO2 nanofibers was finally obtained.

[0019] The acid used for pickling is one of nitric acid, hydrochloric acid, or acetic acid with a concentration of 0.5-1.5 mol / L; the pickling temperature is 50-100 °C, and the pickling time is 1-5 h; the drying temperature is 60-120 °C, and the drying time is 12-24 h. The noble metal precursor is one of the chloride salts of Pt, Rh, Pd, or Ru; the concentration of the noble metal solution is 0.5-1.5 mol / L; and the stirring time is 6-12 h.

[0020] The drying temperature is 60–120 °C, and the drying time is 12–24 h; the calcination temperature is 500–700 °C, and the calcination time is 1–5 h; the reduction is carried out in a hydrogen-nitrogen mixed atmosphere at 300–600 °C for 2–5 h; the volume fraction of hydrogen in the hydrogen-nitrogen mixed atmosphere is 5%–20%. The calcination treatment not only promotes the formation of stable noble metal-O-Ti bonds, enhancing the stability of the noble metal catalyst, but also increases the number of surface oxygen vacancies, thereby improving the performance of the noble metal catalyst.

[0021] II. Application of Mesoporous TiO2 Nanofiber Supported Noble Metal Catalysts in Catalytic Wet Oxidation Treatment of High-Concentration Organic Wastewater

[0022] The COD concentration of the high-concentration organic wastewater was 2000–5000 mg / L. A batch-operated reactor was used for the catalytic wet oxidation reaction. The catalyst-to-wastewater volume ratio was 1–8 g catalyst / L wastewater, the reaction temperature was 120–200 °C, the oxygen partial pressure was 1–5 MPa, the stirring speed was 0–800 r / min, and the reaction time was 1–4 h. Air or oxygen-enriched air was used as the oxidation medium, with the amount of oxygen introduced being 1–3 times the theoretical amount required for complete oxidation of the wastewater. The COD concentration of the solution before and after treatment was measured using a Hach COD analyzer, and the COD removal efficiency of the catalyst was calculated. The results showed that the rare-earth metal-doped mesoporous TiO2 nanofiber-supported noble metal catalyst prepared in this invention can achieve a COD removal efficiency of over 90% for high-concentration organic wastewater.

[0023] In summary, the present invention has the following advantages over the prior art:

[0024] (1) Mesoporous TiO2 nanofibers were prepared in one step using electrospinning technology. As a special type of nanomaterial, mesoporous nanofibers play a key role in the support. First, the mesoporous structure can increase the specific surface area of ​​the support and improve the loading of active components, thereby increasing the number of reactive sites of the catalyst and promoting the reaction. At the same time, the mesoporous structure also has a large porosity, which can improve the adsorption capacity and diffusion performance of the support for the substrate, effectively reduce the diffusion resistance of the substrate in the reaction process, and promote the reaction. In addition, the confinement of mesoporous channels can reduce the size of noble metal particles to the nanoscale, expose more active crystal faces, and limit the migration, agglomeration and loss of noble metal particles in the heat treatment and reaction process, thereby improving the stability of noble metal catalysts.

[0025] (2) Doping rare earth metals into nanofibers can regulate the crystal structure of TiO2, suppress phase transformation, and improve the thermal and structural stability of the catalyst. Rare earth metals can regulate the lattice structure and surface properties of TiO2, increase the number of active centers and the quality of active sites, thereby enhancing the activity of oxidation reactions. In addition, the doping of rare earth metals can also adjust the band structure of TiO2, improve the electron transport performance of the support, increase the efficiency of electron transfer between the active centers of noble metal catalysts and the substrate, and promote the oxidation reaction. Finally, the doping of rare earth metals can introduce strong acid sites, such as Lewis acid sites, improve the selectivity of oxidation reactions, and reduce the formation of by-products.

[0026] (3) Alkali etching of rare earth metal-doped TiO2 nanofibers not only improves the properties and structure of the TiO2 surface, but also increases the dispersion of noble metals on the TiO2 surface and enhances the strong interaction between noble metals and TiO2. During the alkaline etching process, hydroxide ions in the solution react with the Ti-O bonds on the TiO2 surface to form a structure similar to sodium titanate. Then, through a cation exchange strategy, noble metal ions replace Na+. + Uniform distribution on the support surface significantly improves the dispersion of noble metals on the support surface, reduces the noble metal loading rate, and lowers the production cost of the catalyst. Finally, annealing treatment forms stable noble metal-O-Ti bonds, enhancing the stability of the noble metal catalyst. Moreover, the transformation of titanate to TiO2 during annealing creates oxygen vacancies, further increasing the active oxygen content on the support surface, thereby improving the performance of the noble metal catalyst.

[0027] (4) Because rare earth metal doped TiO2 nanofiber supported noble metal catalysts have excellent catalytic performance, the reaction temperature can be reduced to 200℃ and below, and the reaction pressure to 2MPa and below. Therefore, the requirements for reaction equipment are lower, which can greatly reduce equipment investment costs and make it easier to realize industrial application. Detailed Implementation

[0028] The preparation and application performance of the catalyst of the present invention will be further illustrated below through specific embodiments.

[0029] Example 1

[0030] 1. Preparation of noble metal catalysts supported on mesoporous TiO2 nanofibers

[0031] (1) Mix 6 ml of anhydrous ethanol, 8 ml of DMF, 1 ml of glacial acetic acid, 0.2 g of cerium nitrate and 0.1 g of samarium nitrate evenly, then add 1.5 g of PVP and 0.5 g of polyether P123 in sequence and stir evenly. Finally, slowly add 3 g of tetrabutyl titanate and stir until the solution is homogeneous and transparent to obtain the precursor spinning solution. Electrospinning was carried out under the conditions of a spinning voltage of 18 kV, a needle tip distance of 20 cm and an air humidity of 40% to obtain precursor fibers. The precursor fibers were dried at 100 ℃ for 24 h and then calcined at 450 ℃ for 3 h to obtain rare earth metal doped mesoporous TiO2 nanofibers;

[0032] (2) Mix 0.5 g of rare earth metal doped mesoporous TiO2 nanofibers obtained in step (1) with 8 ml of 2 mol / L NaOH solution and place in a water bath at 30 ℃ and stir for 12 h; after filtration, the product is washed with deionized water until neutral and dried at 80 ℃ for 24 h to obtain alkaline etched mesoporous TiO2 nanofibers.

[0033] (3) Mix 0.5 g of rare earth metal-doped mesoporous TiO2 nanofibers obtained in step (2) with 0.8 mol / L nitric acid solution, place in an 80 ℃ water bath and stir for 2 h for acid washing; finally wash again with deionized water until neutral, then add to 0.8 mol / L ruthenium chloride solution and stir at room temperature for 6 h, then wash, filter, dry at 80 ℃ for 24 h, and calcine at 450 ℃ for 2.5 h in air atmosphere. Finally, place in a tube furnace and reduce at 350 ℃ for 3 h in a hydrogen-nitrogen mixed atmosphere (hydrogen gas integral of 10%) to obtain supported noble metal catalyst A-1.

[0034] 2. Application of mesoporous TiO2 nanofiber-supported noble metal catalysts in catalytic wet oxidation treatment of high-concentration organic wastewater

[0035] The performance of the catalyst was evaluated using a batch reaction in a high-pressure reactor. 0.15 g of catalyst was mixed thoroughly with 50 ml of phenol solution (COD concentration: 2900 mg / L) and placed in the reactor. After sealing the reactor, 0.5 MPa of nitrogen gas was introduced, and the gas was then released through the vent. This process was repeated four times to remove all oxygen from the reactor. The reactor was then heated to 200°C, and 2 MPa of oxygen was introduced to initiate catalytic wet oxidation. After 2 hours of reaction, the COD concentration of the solution was measured using a Hach COD analyzer, and the COD removal efficiency of the catalyst was calculated. The results showed that catalyst A-1 achieved a 95% degradation and removal efficiency for high-concentration organic wastewater (Table 1).

[0036] Example 2

[0037] 1. Preparation of noble metal catalysts supported on mesoporous TiO2 nanofibers

[0038] (1) Mix 6 ml of anhydrous ethanol, 8 ml of DMF, 1 ml of glacial acetic acid, 0.19 g of cerium nitrate and 0.02 g of lanthanum nitrate evenly, then add 1.2 g of PVP and 0.8 g of polyether P123 in sequence and stir evenly. Finally, slowly add 3 g of tetrabutyl titanate and stir until the solution is homogeneous and transparent to obtain the precursor spinning solution. Electrospinning was carried out under the conditions of a spinning voltage of 20 kV, a needle tip distance of 20 cm and an air humidity of 50% to obtain precursor fibers. The precursor fibers were dried at 80 °C for 24 h and then calcined at 500 °C for 2.5 h to obtain rare earth metal doped mesoporous TiO2 nanofibers;

[0039] (2) Mix 0.5 g of rare earth metal doped mesoporous TiO2 nanofibers obtained in step (1) with 8 ml of 3 mol / L NaOH solution and place in a water bath at 50 ℃ and stir for 8 h; after filtration, the product is washed with deionized water until neutral and dried at 90 ℃ for 18 h to obtain alkaline etched mesoporous TiO2 nanofibers.

[0040] (3) Mix 0.5 g of rare earth metal-doped mesoporous TiO2 nanofibers obtained in step (2) with 1 mol / L nitric acid solution, place in a 70 ℃ water bath and stir for 1 h for acid washing; finally wash again with deionized water until neutral, then add to 1.2 mol / L ruthenium chloride solution and stir at room temperature for 8 h, then wash, filter, dry at 90 ℃ for 18 h, and calcine at 500 ℃ for 2 h in air atmosphere. Finally, place in a tube furnace and reduce at 400 ℃ for 2.5 h in a hydrogen-nitrogen mixed atmosphere (hydrogen gas integral of 15%) to obtain supported noble metal catalyst A-2.

[0041] 2. Application of mesoporous TiO2 nanofiber-supported noble metal catalysts in catalytic wet oxidation treatment of high-concentration organic wastewater

[0042] The performance of the catalyst was evaluated using a batch reaction in a high-pressure reactor. 0.2 g of catalyst was mixed thoroughly with 50 ml of phenol solution (COD concentration 3300 mg / L) and placed in the reactor. After sealing the reactor, 0.5 MPa of nitrogen gas was introduced, and the gas was then released through the vent. This process was repeated four times to remove all oxygen from the reactor. The reactor was then heated to 180°C, and 1.5 MPa of oxygen was introduced to initiate catalytic wet oxidation. After 2 hours of reaction, the COD concentration of the solution was measured using a Hach COD analyzer, and the COD removal efficiency of the catalyst was calculated. The results showed that catalyst A-2 achieved a 92% degradation and removal efficiency for high-concentration organic wastewater (Table 1).

[0043] Example 3

[0044] 1. Preparation of noble metal catalysts supported on mesoporous TiO2 nanofibers

[0045] (1) Mix 6 ml anhydrous ethanol, 8 ml DMF, 1 ml glacial acetic acid, 0.16 g yttrium nitrate and 0.03 g cerium nitrate evenly, then add 1 g PVP and 1.2 g polyether P123 in sequence and stir evenly. Finally, slowly add 3 g tetrabutyl titanate and stir until the solution is homogeneous and transparent to obtain the precursor spinning solution. Electrospinning was performed under the conditions of a spinning voltage of 19 kV, a needle tip distance of 20 cm and an air humidity of 40% to obtain precursor fibers. The precursor fibers were dried at 100 ℃ for 20 h and then calcined at 550 ℃ for 2 h to obtain rare earth metal doped mesoporous TiO2 nanofibers;

[0046] (2) Mix 0.5 g of rare earth metal doped mesoporous TiO2 nanofibers obtained in step (1) with 10 ml of 2.5 mol / L NaOH solution and place in a water bath at 40 ℃ and stir for 6 h; after filtration, the product is washed with deionized water until neutral and dried at 100 ℃ for 16 h to obtain alkaline etched mesoporous TiO2 nanofibers.

[0047] (3) Mix 0.5 g of rare earth metal-doped mesoporous TiO2 nanofibers obtained in step (2) with 1.2 mol / L nitric acid solution, place in an 80 ℃ water bath and stir for 2.5 h for acid washing; finally, wash again with deionized water until neutral, then add to 1 mol / L platinum chloride solution and stir at room temperature for 10 h, then wash, filter, dry at 100 ℃ for 16 h, and calcine at 450 ℃ for 3 h in air atmosphere. Finally, place in a tube furnace and reduce at 300 ℃ for 3 h in a hydrogen-nitrogen mixed atmosphere (hydrogen gas integral of 10%) to obtain supported noble metal catalyst A-3.

[0048] 2. Application of mesoporous TiO2 nanofiber-supported noble metal catalysts in catalytic wet oxidation treatment of high-concentration organic wastewater

[0049] The performance of the catalyst was evaluated using a batch reaction in a high-pressure reactor. 0.1 g of catalyst was mixed thoroughly with 50 ml of phenol solution (COD concentration: 3500 mg / L) and placed in the reactor. After sealing the reactor, 0.5 MPa of nitrogen gas was introduced, and the gas was then released through the vent. This process was repeated four times to remove all oxygen from the reactor. The reactor was then heated to 180°C, and 2 MPa of oxygen was introduced to initiate catalytic wet oxidation. After 3 hours of reaction, the COD concentration of the solution was measured using a Hach COD analyzer, and the COD removal efficiency of the catalyst was calculated. The results showed that catalyst A-3 achieved a 90% degradation and removal efficiency for high-concentration organic wastewater (Table 1).

[0050] Example 4

[0051] 1. Preparation of noble metal catalysts supported on mesoporous TiO2 nanofibers

[0052] (1) Mix 6 ml anhydrous ethanol, 8 ml DMF, 1 ml glacial acetic acid, 0.19 g lanthanum nitrate and 0.01 g samarium nitrate evenly, then add 0.8 g PVP and 1.5 g polyether P123 in sequence and stir evenly. Finally, slowly add 3 g tetrabutyl titanate and stir until the solution is homogeneous and transparent to obtain the precursor spinning solution. Electrospinning is performed under the conditions of a spinning voltage of 18 kV, a needle tip distance of 18 cm and an air humidity of 50% to obtain precursor fibers. The precursor fibers are dried at 110 °C for 18 h and then calcined at 500 °C for 3 h to obtain rare earth metal doped mesoporous TiO2 nanofibers;

[0053] (2) Mix 0.5 g of rare earth metal doped mesoporous TiO2 nanofibers obtained in step (1) with 7 ml of 3 mol / L NaOH solution and place in a water bath at 30 ℃ and stir for 12 h; after filtration, the product is washed with deionized water until neutral and dried at 110 ℃ for 14 h to obtain alkaline etched mesoporous TiO2 nanofibers.

[0054] (3) Mix 0.5 g of rare earth metal doped mesoporous TiO2 nanofibers obtained in step (2) with 1 mol / L nitric acid solution, place them in an 85 ℃ water bath and stir for 2 h for acid washing; finally wash them again with deionized water until neutral, then add them to 0.8 mol / L palladium chloride solution and stir at room temperature for 8 h, then wash, filter, dry at 110 ℃ for 14 h, calcine at 500 ℃ for 2.5 h in air atmosphere, and finally place them in a tube furnace and reduce them at 350 ℃ for 4 h in a hydrogen-nitrogen mixed atmosphere (hydrogen gas integral of 10%) to obtain the supported noble metal catalyst A-4.

[0055] 2. Application of mesoporous TiO2 nanofiber-supported noble metal catalysts in catalytic wet oxidation treatment of high-concentration organic wastewater

[0056] The performance of the catalyst was evaluated using a batch reaction in a high-pressure reactor. 0.25 g of catalyst was mixed thoroughly with 50 ml of phenol solution (COD concentration: 2300 mg / L) and placed in the reactor. After sealing the reactor, 0.5 MPa of nitrogen gas was introduced, and the gas was then released through the vent. This process was repeated four times to remove all oxygen from the reactor. The reactor was then heated to 200°C, and 1.5 MPa of oxygen was introduced to initiate catalytic wet oxidation. After 3 hours of reaction, the COD concentration of the solution was measured using a Hach COD analyzer, and the COD removal efficiency of the catalyst was calculated. The results showed that catalyst A-4 achieved a 92% degradation and removal efficiency for high-concentration organic wastewater (Table 1).

[0057] Example 5

[0058] 1. Preparation of noble metal catalysts supported on mesoporous TiO2 nanofibers

[0059] (1) Mix 6 ml anhydrous ethanol, 8 ml DMF, 1 ml glacial acetic acid, 0.26 g samarium nitrate and 0.06 g cerium nitrate evenly, then add 0.6 g PVP and 1.8 g polyether P123 in sequence and stir evenly. Finally, slowly add 3 g tetrabutyl titanate and stir until the solution is homogeneous and transparent to obtain the precursor spinning solution. Electrospinning was carried out under the conditions of a spinning voltage of 18 kV, a needle tip distance of 20 cm and an air humidity of 60% to obtain precursor fibers. The precursor fibers were dried at 90 °C for 24 h and then calcined at 450 °C for 4 h to obtain rare earth metal doped mesoporous TiO2 nanofibers;

[0060] (2) Mix 0.5 g of rare earth metal doped mesoporous TiO2 nanofibers obtained in step (1) with 10 ml of 2 mol / L NaOH solution and place in a water bath at 50 ℃ and stir for 24 h; after filtration, the product is washed with deionized water until neutral and dried at 120 ℃ for 12 h to obtain alkaline etched mesoporous TiO2 nanofibers.

[0061] (3) 0.2 g of rare earth metal-doped mesoporous TiO2 nanofibers obtained in step (2) were then mixed with 1.2 mol / L nitric acid solution and placed in a 65 ℃ water bath for 1.5 h of stirring for acid washing. Finally, the mixture was washed again with deionized water until neutral, and then added to a 1.2 mol / L ruthenium chloride solution and stirred at room temperature for 6 h. After washing and filtration, the mixture was dried at 100 ℃ for 12 h and calcined at 450 ℃ for 3 h in air atmosphere. Finally, the mixture was placed in a tube furnace and reduced at 400 ℃ for 3 h in a hydrogen-nitrogen mixed atmosphere (hydrogen gas integral of 15%) to obtain the supported noble metal catalyst A-5.

[0062] 2. Application of mesoporous TiO2 nanofiber-supported noble metal catalysts in catalytic wet oxidation treatment of high-concentration organic wastewater

[0063] The performance of the catalyst was evaluated using a batch reaction in a high-pressure reactor. 0.2 g of catalyst was mixed thoroughly with 50 ml of phenol solution (COD concentration: 2800 mg / L) and placed in the reactor. After sealing the reactor, 0.5 MPa of nitrogen gas was introduced, and the gas was then released through the vent. This process was repeated four times to remove all oxygen from the reactor. The reactor was then heated to 200°C, and 2 MPa of oxygen was introduced to initiate catalytic wet oxidation. After 3 hours of reaction, the COD concentration of the solution was measured using a Hach COD analyzer, and the COD removal efficiency of the catalyst was calculated. The results showed that catalyst A-5 achieved a 94% degradation and removal efficiency for high-concentration organic wastewater (Table 1).

[0064] Comparative Example

[0065] 1. Preparation of noble metal catalysts supported on mesoporous TiO2 nanofibers

[0066] (1) Mix 6 ml of anhydrous ethanol, 8 ml of DMF and 1 ml of glacial acetic acid evenly, then add 0.6 g of PVP and 1.8 g of polyether P123 in sequence and stir evenly. Finally, slowly add 3 g of tetrabutyl titanate and stir until the solution is homogeneous and transparent to obtain the precursor spinning solution. Electrospinning was carried out under the conditions of a spinning voltage of 18 kV, a needle tip distance of 20 cm and an air humidity of 60% to obtain precursor fibers. The precursor fibers were dried at 90 ℃ for 24 h and then calcined at 450 ℃ for 4 h to obtain mesoporous TiO2 nanofibers;

[0067] (2) Mix 0.5 g of the mesoporous TiO2 nanofibers obtained in step (1) with 10 ml of 2 mol / L NaOH solution and place it in a water bath at 50 °C and stir for 24 h. After filtration, the product is washed with deionized water until neutral and dried at 120 °C for 12 h to obtain alkaline-etched mesoporous TiO2 nanofibers.

[0068] (3) 0.2 g of the mesoporous TiO2 nanofibers obtained in step (2) were then mixed with a 1.2 mol / L nitric acid solution and placed in a 65 ℃ water bath for 1.5 h of stirring for acid washing. Finally, the mixture was washed again with deionized water until neutral, and then added to a 1.2 mol / L ruthenium chloride solution and stirred for 6 h. After washing and filtration, the mixture was dried at 100 ℃ for 12 h and calcined at 450 ℃ for 3 h in air. Finally, the mixture was placed in a tube furnace and reduced at 400 ℃ for 3 h in a hydrogen-nitrogen mixed atmosphere (hydrogen gas fraction of 15%) to obtain the supported noble metal catalyst DB.

[0069] 2. Application of mesoporous TiO2 nanofiber-supported noble metal catalysts in catalytic wet oxidation treatment of high-concentration organic wastewater

[0070] The performance of the catalyst was evaluated using a batch reaction in a high-pressure reactor. 0.2 g of catalyst was mixed thoroughly with 50 ml of phenol solution (COD concentration: 3300 mg / L) and placed in the reactor. After sealing the reactor, 0.5 MPa of nitrogen gas was introduced, and the gas was then released through the vent. This process was repeated four times to remove all oxygen from the reactor. The reactor was then heated to 180°C, and oxygen was introduced at 1.5 MPa to begin catalytic wet oxidation. After 2 hours of reaction, the COD concentration of the solution was measured using a Hach COD analyzer, and the COD removal efficiency of the catalyst was calculated. The results showed that catalyst DB achieved a 75% degradation and removal efficiency for high-concentration organic wastewater (Table 1).

[0071]

[0072] As can be seen from Table 1, the COD removal performance of the catalysts prepared in Examples 1-5 is far superior to that of the comparative examples, indicating that rare earth metal oxide doping effectively promotes the degradation of high-concentration organic wastewater.

Claims

1. A method for preparing a mesoporous TiO2 nanofiber-supported noble metal catalyst for catalytic wet oxidation, comprising the following steps: (1) Preparation of rare earth metal-doped mesoporous TiO2 nanofibers by electrospinning: Rare earth metal salts were added to a mixed solution of ethanol-DMF-acetic acid and mixed evenly. Then, polyvinylpyrrolidone and polyether P123 were added in sequence and stirred evenly. Finally, tetrabutyl titanate was slowly added dropwise and stirred until the solution was homogeneous and transparent to obtain the precursor spinning solution. Precursor fibers were obtained by electrospinning under a high voltage of 16~20 kV. The precursor fibers were dried and calcined to obtain rare earth metal-doped mesoporous TiO2 nanofibers. The rare earth metal salt is at least one of the nitrates of Ce, La, Sm, Y, Nd, and Pr, and the amount of rare earth metal salt used is 1% to 10% of the molar amount of tetrabutyl titanate. The roasting temperature is 400~600 ℃, and the roasting time is 1~5 h; (2) Alkali etching treatment of the surface of mesoporous TiO2 nanofibers: The rare earth metal doped mesoporous TiO2 nanofibers obtained in step (1) are mixed evenly with alkaline solution and placed in a water bath for heating and stirring to carry out alkaline etching treatment; the obtained product is filtered and washed with deionized water until neutral; after filtration and drying, alkaline etched rare earth metal doped mesoporous TiO2 nanofibers are obtained. (3) Preparation of noble metal catalyst by cation exchange strategy: The rare earth metal doped mesoporous TiO2 nanofibers obtained in step (2) were successively acid-washed and deionized water-washed, and then added to the noble metal precursor solution. The ion exchange reaction was carried out by stirring at room temperature. After filtration, drying, calcination and reduction treatment, the noble metal catalyst supported on rare earth metal doped mesoporous TiO2 nanofibers was finally obtained. The calcination temperature is 400~700 ℃, and the calcination time is 1~5 h; the reduction is carried out in a hydrogen-nitrogen mixed atmosphere at 300~600 ℃ for 2~5 h, and the volume fraction of hydrogen in the hydrogen-nitrogen mixed atmosphere is 5%~20%.

2. The method for preparing a mesoporous TiO2 nanofiber-supported noble metal catalyst for catalytic wet oxidation as described in claim 1, characterized in that: In the ethanol-DMF-acetic acid mixed solution described in step (1), the volume ratio of anhydrous ethanol:DMF:acetic acid is 6:8:1; the concentration of polyvinylpyrrolidone in the mixed solution is 0.05~0.1g / ml; the mass ratio of polyether P123 to polyvinylpyrrolidone is 0~3:1, and the mass ratio of polyether P123 is not 0.

3. The method for preparing a mesoporous TiO2 nanofiber-supported noble metal catalyst for catalytic wet oxidation as described in claim 1, characterized in that: In step (1), the distance between the needle tip and the receiving plate during electrospinning is 12-20 cm; the air humidity is 40-60%.

4. The method for preparing a mesoporous TiO2 nanofiber-supported noble metal catalyst for catalytic wet oxidation as described in claim 1, characterized in that: In step (1), the drying temperature of the precursor fiber is 60~120℃ and the drying time is 12~24 h.

5. The method for preparing a mesoporous TiO2 nanofiber-supported noble metal catalyst for catalytic wet oxidation as described in claim 1, characterized in that: In step (2), the alkaline solution is a NaOH solution with a concentration of 1~5 mol / L; the mass ratio of rare earth metal doped mesoporous TiO2 nanofibers to the volume ratio of the alkaline solution is 0.05~0.1 g / mL; the alkaline etching treatment temperature is 30~80 ℃ and the time is 6~24 h.

6. The method for preparing a mesoporous TiO2 nanofiber-supported noble metal catalyst for catalytic wet oxidation as described in claim 1, characterized in that: In step (3), the acid used for pickling is one of nitric acid, hydrochloric acid or acetic acid with a concentration of 0.5~1.5 mol / L; the pickling temperature is 50~100℃ and the pickling time is 1~5 h; the drying temperature is 60~120℃ and the drying time is 12~24 h.

7. The method for preparing a mesoporous TiO2 nanofiber-supported noble metal catalyst for catalytic wet oxidation as described in claim 1, characterized in that: In step (3), the noble metal precursor is one of the chloride salts of Pt, Rh, Pd, and Ru; the concentration of the noble metal solution is 0.5~1.5 mol / L; and the ion exchange reaction time is 6~12 h.

8. The method for preparing a mesoporous TiO2 nanofiber-supported noble metal catalyst for catalytic wet oxidation as described in claim 1, characterized in that: In step (3), the drying temperature is 60~120 ℃ and the drying time is 12~24 h.

9. The application of the mesoporous TiO2 nanofiber supported noble metal catalyst prepared by the method described in claim 1 in the catalytic wet oxidation treatment of high-concentration organic wastewater.

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