A method for preparing a catalyst for a wet hydrogen peroxide oxidation process

Abstract

The application discloses a preparation method of a catalyst for a wet hydrogen peroxide oxidation method, which comprises the following steps: preparing a synthesis liquid, preparing a titanium-silicon molecular sieve carrier, preparing a catalyst precursor, and post-treatment. The catalyst prepared by the method has higher activity, can treat complex organic wastewater with high concentration and high salt, and has the advantages that the removal rate of COD can reach more than 80% at 120-180 DEG C, and the active component loaded on the carrier is not easy to be lost.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation technology, and more specifically to a method for preparing a catalyst by wet peroxide oxidation. Background Technology

[0002] With societal development, the problem of organic wastewater is becoming increasingly prominent. Various large molecules and recalcitrant organic compounds exist in wastewater, making them difficult to remove through physical or biological methods. Advanced oxidation processes are widely used for organic wastewater treatment. Among them, wet catalytic hydrogen peroxide oxidation involves using hydrogen peroxide as an oxidant under high temperature and pressure, utilizing the catalytic action of a catalyst to oxidize the organic matter in the wastewater into carbon dioxide and water, thereby achieving the purpose of pollutant removal. This method has advantages such as wide applicability, high treatment efficiency, and minimal secondary pollution.

[0003] Catalysts used in wet catalytic hydrogen peroxide oxidation can be classified into homogeneous and heterogeneous catalysts. Homogeneous catalysts are simple to prepare, dissolve in water, and have high catalytic efficiency, but they are difficult to separate from water, hard to reuse, and prone to heavy metal pollution. Heterogeneous catalysts involve loading the active component onto a support with a large specific surface area using physical or chemical methods. The support is then placed in the reactor, where the active component performs the catalytic action. Compared to homogeneous catalysts, heterogeneous catalysts can be reused, but they also have certain problems; for example, the catalytic activity of heterogeneous catalysts is not as high as that of homogeneous catalysts, and the active component loaded onto the support is easily lost.

[0004] Therefore, there is an urgent need for a method to prepare catalysts using the wet peroxide oxidation process. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing a catalyst for the wet peroxide oxidation process, so as to solve the problems in the background art.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows.

[0007] A method for preparing a catalyst for wet hydrogen peroxide oxidation includes the following steps:

[0008] S1. Preparation of the synthesis solution: Mix the template agent with deionized water and stir for 10-20 min. Add the titanium source dropwise and stir for 1-2 h. Then add the silicon source, with the Si / Ti molar ratio being 25-35. Stir for 1-2 h to obtain the synthesis solution.

[0009] S2. Preparation of titanium-silicon molecular sieve support: The synthesis solution prepared in step S1 is transferred to a reaction vessel and placed in an oven for crystallization for 1–3 days to obtain a crystallized product; the crystallized product is separated by high-speed centrifugation, washed 3 times, dried in an oven, and then calcined in a muffle furnace to obtain a specific surface area of ​​350–400 m². 2 / g of titanium-silicon molecular sieve carrier;

[0010] S3. Preparation of catalyst precursor: Add the active component salt solution to distilled water in proportion. After complete dissolution, add the titanium-silicon molecular sieve support prepared in step S2 and stir for 1-5 hours. After standing for 12-48 hours, take it out and dry it under vacuum to obtain the catalyst precursor Fe-Ce-Ni-TS-1.

[0011] S4. Post-processing: The catalyst precursor is placed in a muffle furnace for calcination to obtain the supported titanium-silicon molecular sieve catalyst.

[0012] To further optimize the technical solution, the template agent in step S1 is tetrapropylammonium hydroxide with a concentration of 3-10 wt%; the titanium source is tetraethyl titanate, and the silicon source is tetraethyl orthosilicate.

[0013] To further optimize the technical solution, the temperature inside the oven in step S2 is 150-200℃.

[0014] To further optimize the technical solution, the drying temperature in step S2 is 60-100℃ and the time is 12-24h.

[0015] To further optimize the technical solution, the calcination temperature in step S2 is 500–700℃, and the time is 5–10 hours.

[0016] To further optimize the technical solution, the active components of the active component salt solution in step S3 are Fe, Ce, and Ni, and the Fe salt is one or more of FeSO4 and FeCl2; the Ce salt is one or more of Ce(NO3)3 and Ce2(SO4)3; and the Ni salt is one or more of NiSO4 and Ni(NO3)2.

[0017] To further optimize the technical solution, in step S3, the ratio of m(Fe):m(TS-1) in the catalyst precursor Fe-Ce-Ni-TS-1 is 0.05 to 0.15, the ratio of m(Ce):m(TS-1) is 0.01 to 0.03, and the ratio of m(Ni):m(TS-1) is 0.01 to 0.03.

[0018] To further optimize the technical solution, the vacuum drying temperature in step S3 is 100-140℃, and the time is 12-24h.

[0019] To further optimize the technical solution, in step S4, the muffle furnace calcination temperature is 400–600℃ and the time is 3–5 hours.

[0020] Due to the adoption of the above technical solutions, the technical progress achieved by this invention is as follows.

[0021] This invention provides a method for preparing a catalyst for a wet hydrogen peroxide oxidation process, using a titanium-silicon molecular sieve as a support and non-precious metals Fe, Ce, and Ni as active components. The titanium framework in the titanium-silicon molecular sieve can react with hydrogen peroxide to form titanium-hydroperoxide, which more readily generates ·OH. Furthermore, the synergistic effect between the active components not only enhances the decomposition of hydrogen peroxide to generate ·OH but also prevents component loss, extending the catalyst's lifespan. The catalyst prepared by this invention exhibits higher activity and can treat complex organic wastewater with high concentrations and high salinity. At 120–180°C, it can achieve a COD removal rate of over 80%, and the active components loaded on the support are less prone to loss. Detailed Implementation

[0022] A method for preparing a catalyst for wet hydrogen peroxide oxidation includes the following steps:

[0023] S1. Preparation of the synthesis solution: Mix 3-10 wt% tetrapropylammonium hydroxide template agent with deionized water and stir for 10-20 min. Add tetraethyl titanate titanium source dropwise and stir for 1-2 h. Then add tetraethyl orthosilicate silicon source with a Si / Ti molar ratio of 25-35 and stir for 1-2 h to obtain the synthesis solution.

[0024] S2. Preparation of titanium-silicon molecular sieve support: The synthesis solution prepared in step S1 is transferred to a reaction vessel and placed in an oven at 150–200℃ for crystallization for 1–3 days to obtain a crystallized product. The crystallized product is separated by high-speed centrifugation, washed three times, and then dried in an oven at 60–100℃ for 12–24 hours. It is then calcined in a muffle furnace at 500–700℃ for 5–10 hours to obtain the titanium-silicon molecular sieve support.

[0025] The support is a crucial component of a catalyst. It not only provides skeletal support for the active components but also ensures good dispersibility of these components across a large specific surface area, thereby generating more active free radicals. Furthermore, the support possesses good strength and impact resistance, guaranteeing stability during the reaction process. Common supports include activated carbon, titanium-silicon molecular sieves, γ-Al₂O₃, clay, zeolite, and attapulgite. Among these, molecular sieves are supports with unique pore structures. Inserting titanium into the molecular sieve framework can activate hydrogen peroxide under mild conditions, generating ·OH free radicals that catalyze the degradation of organic matter.

[0026] S3. Preparation of catalyst precursor: The active component salt solution is added to distilled water in a certain proportion. The active components of the active component salt solution are Fe, Ce, and Ni, and the Fe salt is one or more of FeSO4 and FeCl2; the Ce salt is one or more of Ce(NO3)3 and Ce2(SO4)3; the Ni salt is one or more of NiSO4 and Ni(NO3)2. After complete dissolution, the titanium-silicon molecular sieve support prepared in step S2 is added and stirred for 1-5 hours. After standing for 12-48 hours, it is taken out and vacuum dried at 100-140℃ for 12-24 hours to obtain the catalyst precursor Fe-Ce-Ni-TS-1. In the catalyst precursor Fe-Ce-Ni-TS-1, m(Fe):m(TS-1) is 0.05-0.15, m(Ce):m(TS-1) is 0.01-0.03, and m(Ni):m(TS-1) is 0.01-0.03.

[0027] S4. Post-processing: The catalyst precursor is placed in a muffle furnace and calcined for 3-5 hours at a temperature of 400-600℃. After calcination, the supported titanium-silicon molecular sieve catalyst is obtained.

[0028] The prepared supported titanium-silicon molecular sieve catalyst, after XRD analysis, still showed that the catalyst had the MFI topology, indicating that the doping of iron, nickel and cerium did not damage the structure of the titanium-silicon molecular sieve.

[0029] In the method of this invention, the titanium-silicon molecular sieve has a large specific surface area, which can adsorb and concentrate organic matter in micropores and on the surface through adsorption, thereby improving the degradation efficiency.

[0030] This invention uses titanium-silicon molecular sieves as a catalyst support, with iron, nickel, and cerium as the active components. These three elements have a synergistic effect, enhancing the generation of hydroxyl radicals. Multi-metal doping further increases reaction sites and improves electron conversion efficiency, resulting in higher catalytic activity. The specific mechanisms are: 1) The addition of Ce reduces Fe dissolution, extending the catalyst's lifespan. 2) Ce enhances Fe... 3+ To Fe 2+ 3) Ce can also react with hydrogen peroxide to produce active oxygen, further increasing catalytic performance. 4) The addition of Ni introduces Ni2O3 into the catalyst system. Ni2O3 is an oxidant with a very high oxidation potential. It can not only react with hydrogen peroxide to produce ·OH, but also generate another nickel oxide, NiO2. NiO2 can react with hydrogen peroxide to produce ·OH and Ni2O3. Ni2O3 is continuously consumed and regenerated, further enhancing the oxidation capacity.

[0031] Ce 4+ +Fe 2+ →Ce 3+ +Fe 3+

[0032] Ce 3+ +O2→Ce 4+ +·O 2-

[0033] ·O 2- +H+→2·OH

[0034] Ce 4+ +H₂O₂→HO₂· / O₂ ·- +H + +Ce 3+

[0035] Ce 4+ +HO2· / O2 ·- →Ce 3+ +H + +O2

[0036] Ni₂O₃ + H₂O₂ → 2NiO₂ + ·OH + OH⁻ -

[0037] 2NiO2 + H2O2 → Ni2O3 + HO2· + H +

[0038] HO2· + H2O2 → O2 + ·OH

[0039] In this invention, the ratio of silicon to titanium sources is adjusted to achieve a Si / Ti molar ratio of 25–35. TS-1 prepared within this range exhibits an MFI topology, with titanium primarily existing as a four-coordinate framework titanium, and a very low content of extra-framework Ti. The Ti within the framework acts as an active site, exhibiting Lewis acidity due to its unsaturated lone pairs of electrons, and possesses the ability to accept electrons, forming unstable titanium-hydroperoxide (Ti-OOH) with hydrogen peroxide. Under acidic conditions, titanium-hydroperoxide decomposes into ·OH radicals more readily than hydrogen peroxide. However, if the Ti content is too high during preparation, it can easily lead to an increase in the extra-framework Ti content in the titanium-silicon molecular sieve, reducing catalytic activity and promoting the self-decomposition of hydrogen peroxide.

[0040] The present invention will now be described in further detail with reference to specific embodiments.

[0041] Example 1:

[0042] S1. Preparation of the synthesis solution: Mix 3 wt% tetrapropylammonium hydroxide template agent with deionized water and stir for 20 min. Add tetraethyl titanate titanium source dropwise and stir for 1.5 h. Then add tetraethyl orthosilicate silicon source with a Si / Ti molar ratio of 30 and stir for 2 h to obtain the synthesis solution.

[0043] S2. Preparation of titanium-silicon molecular sieve support: The synthesis solution prepared in step S1 was transferred to a reaction vessel and crystallized in an oven at 170℃ for 1 day to obtain a crystallized product. The crystallized product was separated by high-speed centrifugation, the supernatant was discarded, and the product was washed with deionized water. After washing, the product was centrifuged again, and the centrifugation and washing were repeated 3 times. The product was then dried in an oven at 90℃ for 12 hours. Finally, it was calcined in a muffle furnace at 550℃ for 6 hours to obtain the titanium-silicon molecular sieve support.

[0044] The prepared catalyst was analyzed by FT-IR at 450 cm⁻¹. -1 550cm -1 800cm -1 1100cm -1 1230cm -1 The presence of a vibrational absorption peak at 310 nm confirms that this catalyst has an MFI topology. Diffuse reflectance spectroscopy analysis revealed only a very small band around 310 nm, indicating that titanium exists primarily as framework titanium, with very low anatase content outside the framework.

[0045] S3. Preparation of catalyst precursor: FeSO4, Ce(NO3)3, and Ni(NO3)2 are added to a salt solution prepared in distilled water in a certain proportion. After complete dissolution, the titanium-silicon molecular sieve support prepared in step S2 is added and stirred for 3 hours. After standing for 24 hours, it is taken out and vacuum dried at 100℃ for 12 hours to obtain catalyst precursor Fe-Ce-Ni-TS-1.

[0046] S4. Post-processing: The catalyst precursor was calcined in a muffle furnace for 5 hours at a temperature of 500℃. After calcination, a supported titanium-silicon molecular sieve catalyst was obtained. The supported Fe:Ce:Ni ratio was 5:1:1.

[0047] By placing the catalyst in a fixed-bed reactor, taking coking concentrate, adjusting the pH of the wastewater to 4, adding 0.8 times the theoretical amount of hydrogen peroxide, mixing thoroughly, and then introducing the mixture into the fixed-bed reactor, with a residence time of 30 minutes, the COD of the wastewater decreased from 1300 mg / L to 300 mg / L, achieving a removal rate of 77%.

[0048] Example 2:

[0049] S1. Preparation of the synthesis solution: Mix 10wt% tetrapropylammonium hydroxide template agent with deionized water and stir for 10 min. Add tetraethyl titanate titanium source dropwise and stir for 1 h. Then add tetraethyl orthosilicate silicon source with a Si / Ti molar ratio of 25 and stir for 1 h to obtain the synthesis solution.

[0050] S2. Preparation of titanium-silicon molecular sieve support: The synthesis solution prepared in step S1 was transferred to a reaction vessel and placed in an oven at 200℃ for crystallization for 3 days to obtain a crystallized product. The crystallized product was separated by high-speed centrifugation, the supernatant was discarded, and the product was washed with deionized water. After washing, the product was centrifuged again, and the centrifugation and washing were repeated 3 times. The product was then dried in an oven at 60℃ for 24 hours. Finally, it was calcined in a muffle furnace at 700℃ for 10 hours to obtain the titanium-silicon molecular sieve support.

[0051] The prepared catalyst was analyzed by FT-IR at 450 cm⁻¹. -1 550cm -1 800cm -1 1100cm -1 1230cm -1 The presence of a vibrational absorption peak at 310 nm confirms that this catalyst has an MFI topology. Diffuse reflectance spectroscopy analysis revealed only a very small band around 310 nm, indicating that titanium exists primarily as framework titanium, with very low anatase content outside the framework.

[0052] S3. Preparation of catalyst precursor: FeSO4, Ce(NO3)3, and Ni(NO3)2 were added to a salt solution prepared in distilled water in a certain proportion. After complete dissolution, the titanium-silicon molecular sieve support prepared in step S2 was added and stirred for 1 hour. After standing for 12 hours, it was taken out and vacuum dried at 140℃ for 24 hours to obtain catalyst precursor Fe-Ce-Ni-TS-1.

[0053] S4. Post-processing: The catalyst precursor was calcined in a muffle furnace for 3 hours at a temperature of 400℃. After calcination, a supported titanium-silicon molecular sieve catalyst was obtained. The supported Fe:Ce:Ni ratio was 7:1:1.

[0054] By placing the catalyst in a fixed-bed reactor, wastewater from a chemical plant with an initial COD as high as 99,000 mg / L was tested. The wastewater pH was adjusted to 3, and 0.5 times the theoretical amount of hydrogen peroxide was added. After thorough mixing, the solution was introduced into the fixed-bed reactor, with a residence time of 20 minutes. The wastewater COD decreased from 99,000 mg / L to 14,850 mg / L, achieving a removal rate of 85%, and the color was significantly reduced.

[0055] Example 3:

[0056] S1. Preparation of the synthesis solution: Mix 7 wt% tetrapropylammonium hydroxide template agent with deionized water and stir for 15 min. Add tetraethyl titanate titanium source dropwise and stir for 2 h. Then add tetraethyl orthosilicate silicon source with a Si / Ti molar ratio of 35 and stir for 1.5 h to obtain the synthesis solution.

[0057] S2. Preparation of titanium-silicon molecular sieve support: The synthesis solution prepared in step S1 was transferred to a reaction vessel and placed in an oven at 150℃ for crystallization for 1.5 days to obtain a crystallized product. The crystallized product was separated by high-speed centrifugation, the supernatant was discarded, and the product was washed with deionized water. After washing, the product was centrifuged again, and the centrifugation and washing were repeated 3 times. The product was then dried in an oven at 100℃ for 18 hours. Finally, it was calcined in a muffle furnace for 5 hours at 500℃ to obtain the titanium-silicon molecular sieve support.

[0058] The prepared catalyst was analyzed by FT-IR at 450 cm⁻¹. -1 550cm -1 800cm -1 1100cm -1 1230cm -1 The presence of a vibrational absorption peak at 310 nm confirms that this catalyst has an MFI topology. Diffuse reflectance spectroscopy analysis revealed only a very small band around 310 nm, indicating that titanium exists primarily as framework titanium, with very low anatase content outside the framework.

[0059] S3. Preparation of catalyst precursor: The titanium-silicon molecular sieve support was placed in a salt solution prepared by adding FeSO4, Ce2(SO4)3 and Ni(NO3)2 to distilled water. After complete dissolution, the titanium-silicon molecular sieve support prepared in step S2 was added and stirred for 5 hours. After standing for 48 hours, it was taken out and vacuum dried at 120℃ for 16 hours to obtain the catalyst precursor Fe-Ce-Ni-TS-1.

[0060] S4. Post-processing: The catalyst precursor was calcined in a muffle furnace for 4 hours at a temperature of 600℃. After calcination, a supported titanium-silicon molecular sieve catalyst was obtained. The supported Fe:Ce:Ni ratio was 6:1:1.

[0061] By placing the catalyst in a fixed-bed reactor, taking coking concentrate, adjusting the pH of the wastewater to 6, adding 1.2 times the theoretical amount of hydrogen peroxide, mixing thoroughly, and then introducing the mixture into the fixed-bed reactor, with a residence time of 30 minutes, the COD of the wastewater decreased from 1400 mg / L to 200 mg / L, achieving a removal rate of 85%.

Claims

1. A method for preparing a catalyst for wet hydrogen peroxide oxidation, characterized in that, Specifically, the following steps are included: S1. Preparation of the synthesis solution: Mix the template agent with deionized water and stir for 10-20 min. Add the titanium source dropwise and stir for 1-2 h. Then add the silicon source, with the Si / Ti molar ratio being 25-35. Stir for 1-2 h to obtain the synthesis solution. S2. Preparation of titanium-silicon molecular sieve support: The synthesis solution prepared in step S1 is transferred to a reaction vessel and placed in an oven at 150~200℃ for crystallization for 1~3 days to obtain the crystallized product; The crystallized product was separated by high-speed centrifugation, washed three times, dried in an oven, and then calcined in a muffle furnace to obtain a specific surface area of ​​350-400 m². 2 / g of titanium-silicon molecular sieve carrier; S3. Preparation of catalyst precursor: Add the active component salt solution to distilled water in proportion, and after it is completely dissolved, add the titanium-silicon molecular sieve support prepared in step S2 and stir for 1-5 hours. After standing for 12-48 hours, take it out and vacuum dry to obtain the catalyst precursor Fe-Ce-Ni-TS-1; the active components of the active component salt solution are Fe, Ce and Ni. In the catalyst precursor Fe-Ce-Ni-TS-1, m(Fe):m(TS-1) is 0.05~0.15, m(Ce):m(TS-1) is 0.01~0.03, and m(Ni):m(TS-1) is 0.01~0.

03. The vacuum drying temperature is 100~140℃, and the time is 12~24h; S4. Post-processing: The catalyst precursor is placed in a muffle furnace for calcination at a temperature of 400-600℃ for 3-5 hours to obtain the supported titanium-silicon molecular sieve catalyst.

2. The method for preparing a wet peroxide-hydrogenation catalyst according to claim 1, characterized in that: The template agent in step S1 is tetrapropylammonium hydroxide with a concentration of 3-10 wt%; the titanium source is tetraethyl titanate and the silicon source is tetraethyl orthosilicate.

3. The method for preparing a wet peroxide-hydrogenation catalyst according to claim 1, characterized in that: In step S2, the drying temperature is 60~100℃ and the time is 12~24h.

4. The method for preparing a wet peroxide-hydrogenation catalyst according to claim 3, characterized in that: In step S2, the calcination temperature is 500~700℃ and the time is 5~10h.

5. The method for preparing a wet peroxide-hydrogenation catalyst according to claim 1, characterized in that: In step S3, the Fe salt is one or more of FeSO4 and FeCl2; the Ce salt is one or more of Ce(NO3)3 and Ce2(SO4)3; and the Ni salt is one or more of NiSO4 and Ni(NO3)2.